JPWO1999034431A1 - Silicon oxide film manufacturing method, semiconductor device manufacturing method, semiconductor device, display device, and infrared light irradiation device - Google Patents

Abstract

(57) [Abstract] A method for manufacturing a silicon oxide film, comprising the steps of forming a silicon oxide film by vapor deposition or the like and irradiating the silicon oxide film with infrared light. Therefore, according to the present invention, a relatively low-quality silicon oxide film formed at a relatively low temperature can be modified into a high-quality silicon oxide film. When the present invention is applied to a thin-film semiconductor device, a high-performance semiconductor device with high operational reliability can be manufactured.

Description

[Detailed Description of the Invention] Silicon Oxide Film Manufacturing Method, Semiconductor Device Manufacturing Method, Semiconductor Device, Display Device, and Infrared Light Irradiation Device Technical Field The present invention relates to a method for manufacturing a high-quality silicon oxide film by vapor deposition. This silicon oxide film is suitable for use as an underlevel protection film, gate insulating film, interlayer insulating film, etc. in semiconductor devices. The present invention also relates to a method for manufacturing high-quality, miniaturized semiconductor devices (e.g., metal-oxide-semiconductor field-effect transistors (MOSFETs)) by oxidizing the semiconductor surface at a relatively low temperature, e.g., about 800°C or less, to form a high-quality, ultrathin silicon oxide film (thickness less than about 10 nm). The present invention also relates to a method for manufacturing high-performance, highly reliable semiconductor devices (e.g., thin-film transistors) at a relatively low temperature, e.g., about 600°C or less. The present invention also relates to high-performance, highly reliable semiconductor devices manufactured using this method and high-performance, highly reliable display devices (e.g., liquid crystal display devices) equipped with the semiconductor devices. The present invention also relates to an infrared light irradiation device capable of manufacturing high-quality silicon oxide films.

BACKGROUND ART Silicon oxide films are widely used as gate insulating films for polycrystalline silicon thin-film transistors (p-Si TFTs) and for ultra-thin oxide films in ultra-small semiconductor devices such as VLSIs. The quality of these silicon oxide films has a significant impact on the electrical characteristics of these semiconductor devices.

When a silicon oxide film is applied to the gate insulating film of a low-temperature p-Si TFT, it must be formed at a relatively low temperature, for example, below about 600°C, at which a general-purpose glass substrate can be used. For this reason, chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods have traditionally been used.

Furthermore, in the manufacture of micro-semiconductor devices such as VLSIs having ultra-thin oxide films, ultra-thin silicon oxide films have traditionally been obtained by thermally oxidizing silicon at relatively low temperatures, for example, below about 800°C, in an atmosphere containing oxygen or hydrochloric acid, or by irradiating a silicon substrate with oxygen plasma.

However, these conventional silicon oxide films have the problem of extremely low film quality due to, for example, the large amount of trapped charge in the oxide film.

Therefore, when a conventional silicon oxide film is used as the gate insulating film of a p-Si TFT, only p-Si TFTs of low quality and low reliability can be obtained. This is because the silicon oxide film has a large amount of oxide film fixed charge, which fluctuates the flat band voltage ( _Vfb ) of the semiconductor device, the high surface trap level increases the threshold voltage ( _Vth ), and the large oxide film trap level makes it easy to inject charges into the oxide film. In other words, semiconductor devices such as conventional p-Si TFTs have many problems due to the low quality of the silicon oxide film.

Similar problems are also seen in ultra-thin silicon oxide (SiO2) films, such as VLSIs. Because these films are typically formed at relatively low temperatures (below 800°C), they suffer from all the problems inherent in low-temperature oxidation. These include extremely high interface states and oxide trapping states, as well as large oxide currents. These problems are the primary causes of limiting the performance and shortening the lifespan of ultra-thin integrated circuits.

The present invention has been made to solve the above-mentioned problems, and its objectives are to provide a method for producing high-quality silicon oxide films by vapor-phase deposition; to provide a method for manufacturing micro-semiconductor devices such as VLSIs having high-quality ultra-thin oxide films using silicon oxide films formed at relatively low temperatures, for example, below about 800°C; to provide a method for manufacturing high-performance, high-reliability semiconductor devices (e.g., thin-film transistors) at relatively low temperatures, for example, below 600°C; to provide such high-performance, high-reliability semiconductor devices and display devices; and to provide a manufacturing apparatus capable of manufacturing high-quality silicon oxide films.

Disclosure of the Invention In the present invention, first, in the silicon oxide film formation process, a silicon oxide film is deposited by a vapor deposition method (e.g., chemical vapor deposition (CVD) or physical vapor deposition (PVD)) on various substrates such as insulating substrates (e.g., quartz glass substrates, general-purpose alkali-free glass substrates, etc.), semiconductor substrates (e.g., single-crystal silicon substrates, compound semiconductor substrates, etc.), and metal substrates. The silicon oxide film is also formed by oxidizing the surface of the semiconductor material by, for example, heat treatment of the surface of the semiconductor material in an oxidizing atmosphere (thermal oxidation), plasma irradiation of the semiconductor material surface with an oxidizing substance (e.g., oxygen or nitrous _oxide ) (plasma oxidation), supply of ozone (O3) (ozone oxidation), or supply of active oxygen generated by a heated metal catalyst (active oxygen oxidation).

These silicon oxide film formation processes may involve forming silicon oxide films directly on semiconductor substrates or glass substrates as field oxide films, gate insulating films, interlayer insulating films, underlevel protection films, etc., or may involve forming a silicon elemental or silicon-based semiconductor film on an insulating material such as an oxide film formed on the surface of a glass substrate or single-crystal silicon substrate, and then forming a silicon oxide film on this semiconductor film.

A silicon-based semiconductor film is a semiconductor film made of a mixture of silicon and other elements such as germanium, with a silicon content of approximately 80% or more. Furthermore, a silicon-based semiconductor film also includes semiconductor films containing impurities such as P, B, Al, and As. Therefore, the term "silicon oxide film" as used in this invention refers not only to pure silicon oxide films (SiO _x films: x is approximately 2), but also to silicon oxide films containing these elements or their oxides. Silicon materials can be in a single crystal state, a polycrystalline state, an amorphous state, or a mixed crystalline state in which polycrystalline and amorphous states are mixed.

The oxide film deposition process using vapor deposition is performed at a relatively low temperature of approximately 600°C or less. PVD methods include sputtering and evaporation. CVD methods include atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), and plasma enhanced chemical vapor deposition (PECVD).

Thermal oxidation processes involve treating semiconductor materials at temperatures ranging from approximately 600°C to approximately 1000°C in an oxidizing atmosphere containing oxygen, water vapor, hydrochloric acid, etc. To form ultrathin oxide films less than 10 nm thick, thermal oxidation is often performed at temperatures below approximately 800°C. Furthermore, in oxide film formation processes such as plasma oxidation, ozone oxidation, and active oxygen oxidation, the semiconductor material is also treated at temperatures below approximately 600°C. (Hereinafter, thermal oxidation, plasma oxidation, ozone oxidation, and active oxygen oxidation at temperatures below approximately 800°C are collectively referred to as low-temperature oxidation methods.) Silicon oxide films obtained by low-temperature oxidation processes are generally of lower quality than thicker thermal oxide films (thicknesses of approximately 50 nm or greater) obtained at temperatures above approximately 1100°C.

Therefore, in the present invention, the film quality of these silicon oxide films is improved by the following infrared light irradiation process. In the infrared light irradiation process, infrared light is irradiated onto the silicon oxide film obtained by the aforementioned vapor phase deposition method or the ultrathin silicon oxide film obtained by the low-temperature oxidation method. The irradiated infrared light is absorbed by the silicon oxide film, raising the temperature of the oxide film. This temperature rise promotes modification of the silicon oxide film itself and its interface. The transmitted light intensity I of infrared light through the silicon oxide film is expressed as I= _I0exp (-kt), where _I0 is the incident light intensity, t (cm) is the thickness of the silicon oxide film, and k (cm ^-1 ) is the absorption coefficient of infrared light by the silicon oxide film. When the substrate is made of a material such as glass that has optical properties similar to those of a silicon oxide film, or a material with a higher absorption coefficient for irradiated infrared light than a silicon oxide film, the irradiated infrared light is absorbed not only by the silicon oxide film but also by the glass substrate. Therefore, if the absorption rate of the silicon oxide film is too low, not only will the temperature of the silicon oxide film not rise effectively, but the infrared light will instead be absorbed primarily by the substrate, resulting in damage to the substrate. Specifically, the substrate may crack or warp. Therefore, it is desirable that the temperature rise due to infrared light be large in the silicon oxide film and small in the glass substrate. The silicon oxide film targeted by the present invention has a thickness of at most 1 μm, while the glass substrate typically has a thickness of several hundred μm or more. Therefore, if the absorption of infrared light by the silicon oxide film exceeds about 10% of the incident light, the absorption by the substrate will be less than about 90%. In this case, because the thickness of the silicon oxide film and the substrate differ by several hundred times, the temperature rise of the substrate will be much lower than that of the silicon oxide film. Since infrared light is irradiated from the surface and passes through the oxide film before entering the substrate, the above formula shows that satisfying k・t>0.1 is sufficient to keep the transmitted light from the silicon oxide film to less than 90%. If the substrate is made of single-crystal silicon, whose absorption coefficient for infrared light is significantly smaller than that of the silicon oxide film, then even if the absorption of infrared light by the silicon oxide film is quite small, the risk of substrate damage is low, so k・t>0.01 can be satisfied.

As described above, to improve the film quality of a silicon oxide film by irradiating it with infrared light, the silicon oxide film must absorb the infrared light. Figure 1 shows the infrared light absorption characteristics of a silicon oxide film deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The left vertical axis represents the absorbance a (absorbance) of the oxide film, and the right vertical axis represents the absorption coefficient k (cm ^-1 ). The relationship between the absorbance a and the absorption coefficient k is k = ln(10) a/t, where t (cm) is the film thickness of the silicon oxide film. The horizontal axis of Figure 1 represents the wave number (cm ^-1 ) of the infrared light and the corresponding wavelength (μm) of the light.

Generally, silicon oxide films have three absorption peaks for infrared light: the asymmetric stretching peak (ABS), the symmetric stretching peak (SBS), and the bond bending peak (BB). As is clear from Figure 1, the asymmetric stretching peak is located at a wavenumber of approximately 1057 cm ^-1 (wavelength 9.46 μm) and has an absorption coefficient of 27,260 cm ^-1 . The symmetric stretching peak is located at a wavenumber of approximately 815 cm ^-1 (wavelength 12.27 μm) and has an absorption coefficient of 2290 cm ^-1 . The bond bending peak is located at a wavenumber of approximately 457 cm ^-1 (wavelength 21.88 μm) and has an absorption coefficient of 8,090 cm ^-1 . The wavelength of the irradiated infrared light can be adjusted to match these three absorption peaks. Therefore, the wavelength of infrared light should be between approximately 8.929 μm (wavenumber 1120 cm ⁻¹ ) and approximately 10 μm (wavenumber 1000 cm ⁻¹ ) for absorption at the asymmetric stretching peak, between approximately 11.364 μm (wavenumber 880 cm ⁻¹ ) and approximately 13.158 μm (wavenumber 760 cm ⁻¹ ) for absorption at the symmetric stretching peak, and between approximately 19.231 μm (wavenumber 520 cm ⁻¹ ) and approximately 25 μm (wavenumber 400 cm ⁻¹ ) for absorption at the bond bending peak.

The asymmetric stretching peak, which has the largest absorption coefficient, absorbs infrared light most effectively. Even the lowest-quality silicon oxide films obtained by vapor-phase deposition have an absorption coefficient of approximately 25,000 ^cm at the asymmetric stretching peak. Therefore, to satisfy the aforementioned relationship between absorption coefficient and oxide film thickness for all silicon oxide films obtained by vapor-phase deposition, a silicon oxide film thickness of approximately 40 nm or greater is sufficient. Similarly, when a single-crystal silicon substrate is oxidized at temperatures below approximately 800°C, the absorption coefficient of the oxide film is ^{approximately} 30,000 cm or greater. Therefore, if the oxide film thickness is at least approximately 3.3 nm, it is possible to improve the film quality of an ultrathin oxide film without damaging the substrate.

That is, in the present invention, the infrared light irradiated onto the silicon oxide film must contain wavelength components that are absorbed by the silicon oxide film. Note that the infrared light may contain wavelength components that are not absorbed by the silicon oxide film, but from the viewpoint of reducing damage to the substrate and semiconductor film, it is preferable that the proportion of such components be as small as possible. In other words, it is preferable that the infrared light irradiated onto the silicon oxide film in the present invention contain, as a main component, wavelength components that are absorbed by the silicon oxide film.

Furthermore, in the present invention, the infrared light irradiated onto the silicon oxide film preferably contains, among the wavelength components absorbed by the silicon oxide film, a wavelength component corresponding to the asymmetric stretching vibration of the silicon oxide film. This is because the large absorption coefficient makes it particularly effective for heating silicon oxide films. While the infrared light may contain wavelength components that do not correspond to the asymmetric stretching vibration of the silicon oxide film, in terms of substrate heating efficiency, it is preferable that this proportion be as small as possible. In other words, it is more preferable that the infrared light irradiated onto the silicon oxide film in the present invention contains, as a major component, a wavelength component corresponding to the asymmetric stretching vibration of the silicon oxide film.

In view of the above, in the present invention, the infrared light irradiated onto the silicon oxide film preferably contains wavelength components of approximately 8.9 μm or more and approximately 10 μm or less, and more preferably contains primarily wavelength components of approximately 8.9 μm or more and approximately 10 μm or less.

To meet this demand, it is sufficient to irradiate the oxide film with infrared laser light having a wavelength near the asymmetric stretching peak. Because laser light oscillates within a narrow wavelength range, it is possible to minimize the risk of light with a wavelength that does not heat the silicon oxide film being irradiated onto the substrate or semiconductor film. The best type of laser light is carbon dioxide ( _CO2 ) laser light, and the most excellent type of light is carbon dioxide laser light with a wavelength of around 9.3 μm. Carbon dioxide laser light with a wavelength of around 9.3 μm will be described later.

Carbon dioxide laser light has many oscillation lines in the wavelength range from 8.9 μm (wavenumber 1124 cm ^{−1 ) to 11 μm (wavenumber 909 cm −1 )} , as typified by a wavelength of 9.3055±0.0005 μm (wavenumber 1074.63±0.05 cm ⁻¹ ), and the wavenumbers of these lights almost coincide with the asymmetric stretching peaks of silicon oxide films obtained by vapor deposition or at relatively low temperatures of around 800°C. Figure 14 shows the oscillation lines of carbon dioxide laser light that can be used in the present invention. The wavelength fluctuation of each oscillation line is about 0.0005 μm, which translates to a wavenumber of about 0.05 cm ⁻¹ . Of these oscillation lines, those that are particularly suitable as irradiated infrared light are those with wavelengths of approximately 9.2605±0.0005 μm (wavenumber 1079.85±0.05 cm ⁻¹ ) to 9.4885±0.0005 μm (wavenumber 1053.91±0.05 cm ⁻¹ ), which are strongly absorbed by almost all silicon oxide films (these carbon dioxide laser lights are referred to as carbon dioxide laser lights with wavelengths of approximately 9.3 μm (wavenumber 1075 cm ⁻¹ )).

The position of the asymmetric stretching peak of a silicon oxide film shifts toward lower wavenumbers as the film quality deteriorates. In fact, the asymmetric stretching peak of a silicon oxide film obtained by vapor deposition is located at an infrared wavenumber of approximately 1055 cm ⁻¹ to 1070 cm ⁻¹ , which roughly corresponds to the wavenumber of carbon dioxide laser light with a wavelength of approximately 9.3 μm (wavenumber 1075 cm ⁻¹ ). In addition, such low-quality films tend to have a large half-width of the asymmetric stretching peak, sometimes reaching 100 cm ⁻¹ . Therefore, even if the asymmetric stretching peak is slightly shifted from the wavenumber of the carbon dioxide laser with a wavelength of approximately 9.3 μm, the silicon oxide film can fully absorb the carbon dioxide laser light. As the oxide film quality improves with carbon dioxide laser irradiation, the half-width decreases, but the asymmetric stretching peak also shifts toward higher wavenumbers, so the oxide film can still efficiently absorb carbon dioxide laser light with a wavelength of approximately 9.3 μm. When a silicon oxide film is obtained by oxidizing a single-crystal silicon substrate, the quality of the oxide film is high at oxidation temperatures of approximately 1100°C or higher, so the asymmetric stretching peak is located at approximately 1081 cm ^-1 . At oxidation temperatures below approximately 1100°C, the position of the asymmetric stretching peak shifts toward lower wavenumbers at a rate of approximately 2 cm ^-1 for every 100°C decrease in oxidation temperature, reaching 1075 cm ^- 1 at oxidation at 800°C. This value coincides with the wavenumber value of a carbon dioxide laser beam with a wavelength of 9.3 μm, indicating that a carbon dioxide laser beam with a wavelength of around 9.3 μm is ideal as irradiated infrared light. The irradiated laser beam may be a single beam having a wavelength around 9.3 μm, such as a wavelength of 9.3055±0.0005 μm, or multiple beams having wavelengths around 9.3 μm may be oscillated simultaneously.

To modify an oxide film by infrared light irradiation, it is generally preferable to perform heat treatment at a high temperature for a long period of time. Experiments have shown that if the infrared irradiation time for a single session is less than about 0.1 seconds, the modification of the oxide film becomes noticeable only after the temperature of the oxide film exceeds about 800°C. Therefore, if the infrared light irradiation is performed so that the temperature of the oxide film reaches about 800°C or higher for a period of about 0.1 seconds, the modification of the oxide film will proceed reliably. The relationship between the temperature and time required for oxide film modification generally holds true: the treatment time shortens by one order of magnitude for every 50°C increase in the oxide film temperature. Therefore, when an oxide film is irradiated with infrared light and the temperature of the oxide film rises to about 800°C or higher, let T _ox (°C) be any oxide film temperature, and let τ (s) be the total time during which that temperature (T _ox ) is reached. If T _ox and τ satisfy the relationship τ>exp(ln(10)(bT _ox +15)) b=-0.02(°C ^-1 ), that is, if infrared light is irradiated under the condition that there is a T _ox that satisfies the relationship τ>exp(-0.04605T _ox +34.539) (1), the oxide film will be modified.

This reduces oxide current, increases dielectric strength, reduces oxide fixed charge, and reduces oxide trap levels.

When a silicon oxide film is formed on elemental silicon or a silicon-based semiconductor material, the infrared light irradiation of the present invention can improve not only the quality of the oxide film but also the interface characteristics between the semiconductor and the insulating film. Whether using vapor-phase deposition or low-temperature oxidation, significant oxidation stress always remains at the interface between the semiconductor and the oxide film immediately after oxide film formation. In low-temperature oxidation of a semiconductor (e.g., Si), oxidation reactants such as oxygen (e.g., _O2 ) diffuse through the oxide film (e.g., _SiO2 ). After the reactants reach the interface between the oxide film and the semiconductor film, they supply oxygen atoms (O) between the semiconductor constituent atoms (e.g., between Si-Si atoms), forming a new oxide layer (e.g., Si-O-Si). Therefore, the distance between adjacent semiconductor atoms in the semiconductor (e.g., Si-Si distance) naturally differs from the distance between semiconductor atoms sandwiching an oxygen atom in the oxide film (e.g., the distance between Si atoms in Si-O-Si). This difference in interatomic distance generates tensile stress in the semiconductor film and compressive stress in the oxide film.

If the oxidation temperature is sufficiently high (generally above 1070°C), viscous flow occurs in the oxide film, and the stress caused by oxidation is relieved. However, if the oxidation temperature is below 1070°C, the stress relief time becomes significantly longer, and the stress caused by oxidation is not relieved and remains in both thin films sandwiching the interface.

A similar problem occurs when an oxide film is formed by vapor-phase deposition. This is because, in the very early stages of oxide film deposition, the oxidation-promoting substances (e.g., _O2 and _O3 ) used in vapor-phase deposition penetrate between the semiconductor constituent atoms, forming an ultrathin oxide film of approximately 0.5 to 2.0 nm. The oxide film then builds up on this ultrathin oxide film. As mentioned above, vapor-phase deposition is performed at temperatures below approximately 600°C, so oxidation stress during ultrathin oxide film formation cannot be alleviated. Regardless of whether the film is single-crystalline or polycrystalline, oxidation stress changes the lattice spacing of the semiconductor constituent atoms, forming trap levels for electrons and holes at the semiconductor-oxide interface and simultaneously reducing the mobility of charge carriers (electrons in the conduction band and holes in the valence band) at the surface. The present invention uses infrared light irradiation to locally raise the temperature of the oxide film, thereby releasing the oxidation stress present at the semiconductor-oxide interface and forming a high-quality interface.

There are optimal conditions for interface modification by infrared light irradiation. Figure 2 shows a calculated relationship between stress relaxation time (vertical axis) and heat treatment temperature (horizontal axis) based on Irene's theory of silicon oxide films (E. A. Irene et al.: J. Electrochem. Soc. 129 (1982) 2594). For example, when the heat treatment temperature is 1230°C, viscous flow of the oxide film occurs within a heat treatment time of approximately 0.1 seconds, and the oxidation stress is released. Therefore, the irradiation conditions for interface modification by infrared light irradiation can be set to satisfy the conditions above the curve in Figure 2 (within the range marked "effective infrared light irradiation region" in Figure 2). Specifically, when infrared light is irradiated onto an oxide film and the temperature of the oxide film rises to 1000°C or higher, let T _ox (°C) be any oxide film temperature, and let τ (s) be the total time during which that temperature (T _ox ) is reached. Tox and τ satisfy the relationship τ>2·(1+ν)·η/E η=η ₀ ·exp(ε/(k·(T _ox +273.15))), that is, infrared light can be irradiated under the condition that there exists a T _ox that satisfies the relationship τ>2·(1+ν)·η ₀ ·exp(ε/(k·(T _ox +273.15)))/E (2) where ν is the Poisson's ratio of the oxide film, E is its Young's modulus, η is its viscosity, η ₀ is the pre-existing potential factor of the viscosity, ε is the activation energy of the viscosity, and k is the Boltzmann constant, and take the following values:

ν=0.18 E=6.6×10¹¹dyn・cm^-2 η₀= 9.549 x 10^-11dyn・s・cm^-2 ε=6.12eV k=8.617×10^-5eV K^-1 To complete infrared heat treatment of an oxide film without damaging the substrate or semiconductor film, it is preferable to heat the same point on the substrate for less than about 0.1 seconds. This is based on experience with rapid thermal processing (RTA), which shows that at temperatures above 800°C, a heating time of about 1 second can cause glass substrates to warp or crack, whereas a short treatment time of less than 0.1 seconds does not cause such problems._oxIf the temperature is above 1230°C, it is possible to set the irradiation time to less than 0.1 seconds. However, if the temperature is below 1230°C, this condition cannot be met with a single irradiation. Therefore, T_oxTo improve interface characteristics under infrared light irradiation conditions below approximately 1230°C, the irradiation time should be less than approximately 0.1 seconds, and the irradiation should be repeated several times so that the total τ satisfies the above inequality. In this sense, it can be said that periodic, discontinuous oscillation of infrared light is preferable to continuous oscillation of infrared light.

The periodic non-continuous oscillation of infrared light occurs as shown in the time-lapse diagram in Figure 3. One cycle of infrared light consists of an oscillation period (t _ON ) and a non-oscillation period (t _OFF ). In order to minimize thermal distortion of materials other than oxide films such as semiconductors, it is desirable to make the oscillation period equal to or shorter than the non-oscillation period (t _ON ≦t _OFF ). This is because having an oscillation period shorter than the non-oscillation period ensures heat dissipation. Furthermore, when productivity is taken into consideration, it is ideal for the oscillation period and non-oscillation period to be approximately equal.

Another important consideration with infrared light irradiation is controlling the maximum temperature of the oxide film. When an oxide film, such as a gate insulating film or an interlayer insulating film, is formed on a semiconductor material and irradiated with infrared light, it is desirable for the maximum temperature of the oxide film to be below the melting point of the semiconductor material. For example, if the semiconductor material is intrinsic silicon or silicon containing a small amount of impurities (impurity concentration less than 1%), the melting point of silicon is approximately 1414°C. Therefore, it is desirable for the maximum temperature of the oxide film to be below 1414°C when irradiated with infrared light. This is because melting the semiconductor material can cause adverse phenomena such as changes in the impurity concentration in the semiconductor, or the interface between the oxide film and the semiconductor becoming disordered and reconstructing, increasing the interface state density. In severe cases, the semiconductor material can evaporate and disperse, destroying the semiconductor device. To avoid such a phenomenon and stably manufacture high-quality semiconductor devices, the maximum temperature that the oxide film reaches should be set below the melting point of the semiconductor material.

When semiconductor materials are in a polycrystalline or amorphous state, dangling bonds exist within the semiconductor, and these dangling bonds are preferably terminated with atoms such as hydrogen (H) or fluorine (F). Dangling bonds create trap levels for electrons and holes deep within the forbidden band (near the center of the bandgap), reducing the number of electrons in the conduction band and the number of holes in the valence band. They also scatter charge carriers, reducing their mobility. Dangling bonds thus degrade semiconductor properties. While the temperature increase of the oxide film due to infrared light irradiation significantly modifies the silicon oxide film itself and the interface, thermal conduction from the oxide film to the semiconductor material may also dissociate the hydrogen or fluorine atoms that terminated the dangling bonds. Therefore, to fabricate superior semiconductor devices such as solar cells with high photoconversion efficiency and thin-film transistors that operate at high speeds at low voltages, it is desirable to include a dangling pair termination process, such as hydrogen plasma irradiation, after infrared light irradiation. This process reduces the number of dangling pair terminations created by infrared light irradiation, thereby increasing the number of charge carriers and simultaneously improving mobility.

In the infrared light irradiation of the present invention, it is desirable that the period during which the same point on the oxide film is heated by a single irradiation be short, on the order of less than 0.1 seconds. Such short irradiation not only prevents thermal damage to the substrate, but also minimizes the diffusion of reactive gases, such as oxygen, from the gas phase through the oxide film, allowing the irradiation atmosphere to be air. Longer irradiation periods could result in oxygen in the air diffusing to the interface, potentially forming a new low-temperature oxide layer during the cooling process of the semiconductor material. This would negate the improved interface properties. For this reason, an inert gas, such as nitrogen, helium, or argon, is preferred. Because infrared light irradiation heats the semiconductor surface to near its melting point, rare gases such as helium or argon are more preferable than nitrogen, which has the potential to nitrify. This eliminates limitations on the infrared light irradiation duration, as long as damage to the substrate or semiconductor material is not inflicted, resulting in a high-quality interface. This control of the irradiation atmosphere is particularly important for ultrathin oxide films, which are prone to diffusion.

In the semiconductor device fabrication method of the present invention, the electrical characteristics of the semiconductor device are significantly improved when the semiconductor film has a thin crystalline film structure with a thickness of less than approximately 200 nm sandwiched between silicon oxide films. A semiconductor device with this structure has both an interface between the semiconductor film and an upper oxide film and an interface between the semiconductor film and a lower oxide film. When the semiconductor film is doped with donor or acceptor impurities and used as an interconnect, these interfaces contribute to electrical conduction. Furthermore, when the semiconductor film is used as the active layer of a silicon-on-insulator (SOI) semiconductor device, the entire thin semiconductor film becomes depleted, and both interfaces also affect the electrical characteristics. Irradiating this structure with infrared light heats the oxide films sandwiching the semiconductor film above and below, thereby improving the quality of both interfaces. Furthermore, when the crystalline semiconductor film is polycrystalline, the semiconductor film is naturally heated by thermal conduction from the upper and lower oxide films, resulting in recrystallization of the polycrystalline semiconductor film. This recrystallization increases the size of the crystal grains that make up the polycrystalline semiconductor film and reduces the number of defects in the semiconductor film, further improving the semiconductor properties.

As described above, the present invention improves conventionally low-quality silicon oxide films (such as silicon oxide films formed by vapor-phase deposition and ultrathin oxide films obtained by low-temperature oxidation) to high quality by adding an infrared light irradiation process, thereby improving the semiconductor-oxide interface. Furthermore, when the semiconductor film is sandwiched between first and second oxide films, both interfaces can be improved. Furthermore, if the semiconductor is a crystalline film, the crystallinity of the semiconductor can also be improved. This provides the excellent benefits of improving the electrical characteristics of semiconductor devices, such as thin-film transistors, while also increasing the operational stability and reliability of the semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing the infrared light absorption characteristics of a silicon oxide film. Figure 2 is a diagram showing the effective region of the present invention. Figure 3 is a time-lapse diagram explaining infrared light oscillation. Figure 4 is a diagram showing the temperature change of an oxide film due to infrared light irradiation. Figure 5 is a diagram explaining a method for manufacturing a semiconductor device of the present invention. Figure 6 is a diagram explaining a display device of the present invention. Figure 7 is a diagram explaining an infrared light irradiation device of the present invention. Figure 8 is a diagram explaining an infrared light irradiation device using a fly's eye lens of the present invention. Figure 9 is a diagram showing the principle of homogenizing the infrared light intensity distribution using a fly's eye lens. Figure 10 is a diagram explaining an infrared light irradiation device using a Fourier transform phase hologram of the present invention. Figure 11 is a diagram showing the principle of homogenizing the infrared light intensity distribution using a Fourier transform phase hologram. Figure 12 is a diagram explaining an infrared light irradiation device using a galvanometer scanner of the present invention. Figure 13 is a diagram explaining an infrared light irradiation device using a polygon mirror of the present invention. Figure 14 is a diagram showing the oscillation line of a carbon dioxide ( _CO2 ) laser.

BEST MODE FOR CARRYING OUT THE INVENTION The semiconductor device of the present invention includes at least a semiconductor film formed on a first silicon oxide film, which is an insulating material, and a second silicon oxide film formed on the semiconductor film. In a top-gate semiconductor device, the first silicon oxide film corresponds to an underlevel protection film, and the silicon oxide film corresponds to a gate insulating film. Conversely, in a bottom-gate semiconductor device, the first silicon oxide film corresponds to a gate insulating film, and the second silicon oxide film corresponds to an interlayer insulating film. Furthermore, a display device of the present invention includes such a semiconductor device.

The first step in fabricating these semiconductor devices and displays is to prepare a substrate. While glass, single-crystal silicon, and other materials are commonly used, other substrates of any type and size are acceptable as long as they can withstand the maximum temperatures encountered during the semiconductor device manufacturing process and contain sufficiently low levels of impurities in the semiconductor film.

First, a first silicon oxide film is formed on a substrate by the aforementioned vapor phase deposition method or low-temperature oxidation method.

If the substrate is made of high-purity quartz glass, the quartz glass substrate can also serve as the first silicon oxide film.

Next, a semiconductor film is formed on the insulating material, at least the surface of which is in contact with the semiconductor film, being a first silicon oxide film. This semiconductor film formation process involves depositing the semiconductor film using a vapor-phase deposition method or the like, and then applying a high-energy source, typically laser light or heat, to the semiconductor film to promote melt crystallization or solid-phase crystallization of the semiconductor film. If the initially deposited thin film is amorphous or a mixed-crystal material consisting of a mixture of amorphous and microcrystalline materials, this process is usually called crystallization. On the other hand, if the initially deposited thin film is polycrystalline, this process is called recrystallization. In this specification, both are simply referred to as crystallization, and no distinction is made between them. The most effective high-energy sources are krypton-fluorine (KrF) excimer lasers and xenon-chlorine (XeCl) excimer lasers. Irradiation with these sources melts and crystallizes at least the surface of the semiconductor thin film. Melt crystallization has the excellent characteristic of having almost no defects within the crystal grains within the molten area. On the other hand, controlling the energy value supplied during melt crystallization is extremely difficult. If the energy density of the excimer laser or other laser applied to the semiconductor thin film is even slightly higher than the optimum value, the diameter of the crystal grains constituting the polycrystalline film suddenly decreases by 1/10 to 1/100, and in severe cases, the semiconductor film may even disappear. Therefore, in the present invention, the laser energy density is set to be approximately 5 mJ cm ^-2 to 50 mJ cm ^-2 lower than the optimum value to perform melt crystallization of the semiconductor film. This allows for stable melt crystallization of the semiconductor film. Of course, the crystallinity of the polycrystalline semiconductor film will not be excellent in this state, but in the present invention, a subsequent process of irradiating the oxide film with infrared light is included.

That is, a second silicon oxide film is formed on the thus obtained crystalline semiconductor film by a vapor phase deposition method or a low-temperature oxidation method, and after the oxide film formation step is completed, a light irradiation step is performed in which the second silicon oxide film is irradiated with infrared light.

When a silicon oxide film is heated by infrared light irradiation, the semiconductor film is also heated to a temperature close to the semiconductor's melting temperature for a relatively long period of time, from a few microseconds to a few milliseconds. In the melt crystallization process described above, the semiconductor film is heated at the melting temperature for a period of tens of nanoseconds. In comparison, the semiconductor temperature during the light irradiation process is slightly lower. However, the heating process lasts for a period of a hundred to a million times longer. Therefore, the crystallinity of the semiconductor film, which was insufficient during melt crystallization, is significantly improved during the light irradiation process. During melt crystallization, high-quality crystal grains are formed only near the surface of the semiconductor film, while numerous micro-defects and amorphous components remain in the lower part of the semiconductor film near the first oxide layer. During the light irradiation process, these residual components are crystallized using the high-quality crystal grains near the surface as seeds, resulting in the formation of a high-quality crystalline film throughout the entire thickness of the semiconductor film. As can be understood from this principle, sandwiching the semiconductor film between the first and second oxide films means that the semiconductor film is heated from both above and below during the light irradiation process, thereby promoting uniform crystallization throughout the semiconductor film. A similar effect observed in melt-crystallized films also occurs when semiconductor films are crystallized in the solid phase. Solid-phase crystallized films contain a large number of intragranular defects, but the light irradiation process of the present invention promotes recrystallization and reduces these intragranular defects.

In systems where a semiconductor film is deposited on a substrate, the semiconductor film always has an upper and lower interface. When the semiconductor film is doped with impurities and used as an electrical conductor, current paths exist near both the upper and lower interfaces. Similarly, when a semiconductor film is used as the active layer (channel formation region) of a field-effect semiconductor device, if the active layer is approximately 150 nm thick, the entire semiconductor film contributes to electrical conduction, and the quality of both interfaces directly affects the electrical characteristics of the semiconductor device. In this invention, the semiconductor film is sandwiched between first and second oxide films, and the irradiated infrared light is selected so that the semiconductor film's absorption coefficient for infrared light is several orders of magnitude smaller than that of the oxide film. This heats both interfaces to approximately the same temperature and modifies them to the same high-quality interface state. This results in a semiconductor device with excellent electrical characteristics.

Example 1. Figure 4 shows the temperature change of an oxide film due to infrared light irradiation. The graph shows a computer-generated estimate of the temperature change experienced by a silicon oxide film constituting a gate insulating film when the silicon oxide film was irradiated with infrared light from a carbon dioxide laser. The vertical axis represents the temperature of the silicon oxide film surface, and the horizontal axis represents the time from the moment irradiation began. A general-purpose alkali-free glass substrate is used. A silicon oxide film serving as an underlevel protection layer is deposited on the substrate by ECR-PECVD to a thickness of 200 nm. A polycrystalline silicon film is deposited on top of this to a thickness of 50 nm, and a silicon oxide film serving as a gate insulating film is deposited on top of this to a thickness of 100 nm by ECR-PECVD. The optical properties of the gate insulating film and underlevel protection layer are identical to those shown in Figure 1. A sample with this film structure is irradiated with a carbon dioxide laser from the front side of the substrate (i.e., the gate insulating film side). The wavelength of the carbon dioxide laser is assumed to be 9.3 μm (wavenumber 1075 cm ⁻¹ ), and the absorption coefficient k of the silicon oxide film formed by ECR-PECVD for this infrared light is 26,200 cm ⁻¹ . Therefore, the product k·t of the absorption coefficient and the thickness of the gate oxide film is 0.262, and the ratio of transmitted light to incident light on the gate insulating film is 77%. The energy density of the carbon dioxide laser light on the gate insulating film surface is assumed to be 200 mJ·cm ⁻² , and the temperature change of the oxide film is calculated under irradiation conditions with an oscillation period (t _ON ) of 10 μs. However, here, a single laser irradiation is assumed, and therefore the non-oscillation period (t _OFF ) is infinite.

According to the calculation results shown in Figure 4, the time _τ1300 required for the oxide film temperature to rise above 1300°C is approximately 4.6 μs, and similarly, the time _τ900 required for the oxide film temperature to rise above 900°C is approximately 13.1 μs. To modify the oxide film at 900°C, according to equation (1), _τ900 must be approximately 1 ms or longer. Therefore, it would seem that this irradiation must be repeated 77 times or more, resulting in a total time above 900°C of 13.1 μs × 77 = 1.0087 ms, which is longer than 1 ms. However, in reality, the time _τ1300 required for the temperature to reach 1300°C or higher is approximately 4.6 μs. According to equation (1), it takes approximately 1 × ^10-11 seconds or more to modify the oxide film at 1300°C, so in fact, this single infrared light irradiation is sufficient to modify the oxide film. As this example clearly shows, in order to improve the film quality of the oxide film and the interface, it is sufficient that conditional expressions (1) and (2) are satisfied at either temperature.

To modify the oxide film-semiconductor film interface under the conditions shown in Figure 4, equation (2) and Figure 2 show that the total time during which the oxide film temperature reaches 1300°C or higher must be approximately 13.8 ms or more. Since _τ1300 for a single discontinuous oscillation irradiation is approximately 4.6 μs, repeating the same irradiation approximately 3000 times results in 4.6 μs × 3000 = 13.8 ms, which means that the total time during which the temperature reaches 1300°C or higher can be approximately 13.8 ms or more. If the oscillation period ( _tON ) and non-oscillation period ( _tOFF ) are both 10 μs, one cycle is 20 μs, and the oscillation frequency is 50 kHz. Therefore, to achieve interface modification, it is sufficient to irradiate the same point with an oscillation frequency of 50 kHz for approximately 60 ms or more, i.e., 20 μs × 3000 = 60 ms.

Some commercially available carbon dioxide lasers have an output of approximately 4 kW. When oscillated at 50 kHz, the energy per irradiation is 80 mJ, and at the aforementioned irradiation condition of an energy density of 200 mJ·cm ⁻² , an area of 0.4 cm ² can be irradiated. An area of 0.4 cm ² corresponds to a rectangular area 0.1 mm wide and 400 mm long. Considering the irradiation of a large glass substrate measuring 400 mm x 500 mm with infrared light, the rectangular irradiation area is scanned along the longitudinal direction of the substrate (the longitudinal direction of the substrate and the width direction of the irradiation area coincide). To irradiate the same point on the substrate 3,000 times, the irradiation area must move 3.33 × 10 ⁻⁵ mm along the width (0.1 mm) of the rectangular irradiation area for each irradiation. Since the oscillation frequency is 50 kHz, this translates to a scanning speed of 1.67 mm/s for the irradiation area. That is, the irradiation time in the longitudinal direction of 500 mm is about 300 seconds, which is sufficiently practical.

(Example 2) Figures 5(a) to 5(d) are cross-sectional views illustrating the manufacturing process for a thin-film semiconductor device that forms a MOS field-effect transistor. In Example 2, a general-purpose alkali-free glass with a strain point of approximately 650°C was used as the substrate 501.

First, a first silicon oxide film was deposited on the substrate 501 by ECR-PECVD to a thickness of approximately 200 nm to serve as the underlevel protection film 502. The deposition conditions for the first silicon oxide film by ECR-PECVD were as follows:

Monosilane ( _SiH4 ) flow rate: 60 sccm; Oxygen ( _O2 ) flow rate: 100 sccm; Pressure: 2.40 mTorr; Microwave (2.45 GHz) output: 2250 W; Applied magnetic field: 875 Gauss; Substrate temperature: 100°C; Deposition time: 40 seconds. An intrinsic amorphous silicon film was deposited on this underlevel protection layer to a thickness of approximately 50 nm using the LPCVD method. The LPCVD reactor was a hot-wall type with a volume of 184.5 l, and the total reaction area after the substrate was inserted was approximately 44,000 ^cm2 . The deposition temperature was 425°C, and the source gas was _disilane ( _Si2H6 ) with a purity of 99.99% or higher, supplied at 200 sccm to the reactor. The deposition pressure was approximately 1.1 Torr, and under these conditions, the silicon film deposition rate was 0.77 nm/min. The amorphous semiconductor film thus obtained was irradiated with a krypton-fluoride (KrF) excimer laser to promote crystallization of the semiconductor film. The irradiated laser energy density was 245 mJ·cm ^-2 , which was 15 mJ·cm ^-2 lower than the optimal value. After forming a crystalline semiconductor film (polycrystalline silicon film), this crystalline semiconductor film was processed into islands to form semiconductor film islands 503 that would later become the active layer of the semiconductor device (Figure 5-a). Next, a second silicon oxide film 504 was formed by ECR-PECVD to cover the patterned semiconductor film islands 503. This second silicon oxide film functions as the gate insulating film of the semiconductor device. The deposition conditions for the second silicon oxide film were the same as those for the first silicon oxide film, except that the deposition time was shortened to 24 seconds. However, just before depositing the second silicon oxide film, the substrate was irradiated with oxygen plasma in the ECR-PECVD reactor to form a low-temperature plasma oxide film on the semiconductor surface. The plasma oxidation conditions were as follows:

Oxygen ( _O2 ) flow rate: 100 sccm; Pressure: 1.85 mTorr; Microwave (2.45 GHz) output: 2000 W; Applied magnetic field: 875 Gauss; Substrate temperature: 100°C; Treatment time: 24 seconds. An oxide film of approximately 3.5 nm was formed on the semiconductor surface by plasma oxidation. After the oxygen plasma irradiation was completed, an oxide film was continuously deposited while maintaining the vacuum. Therefore, the second silicon oxide film consisted of both a plasma oxide film and a vapor-deposited film. The film thickness was 122.5 nm.

After the formation of the second silicon oxide film, these thin films were irradiated with carbon dioxide laser light in air as an infrared light irradiation process. The carbon dioxide laser irradiation area was circular. The laser energy density was maximum at the center of the circle, and the energy density decreased according to a normal distribution function as it moved outward. The diameter of the circle where the energy density was 1/e (e is the natural logarithm: e = 2.71828) of the maximum energy density value at the center was 4.5 mm. Since the maximum energy density at the center was 630 mJ cm ^-2 , the energy density on the circumference of a 4.5 mm diameter circle was 232 mJ cm ^-2 . The carbon dioxide laser's oscillation period (t _ON ) and non-oscillation period (t _OFF ) were each 60 μs, and therefore the oscillation frequency was 8.333 kHz. The circularly symmetric irradiation area was moved by 0.1 mm for each irradiation, and the same point on the silicon oxide film was irradiated with a carbon dioxide gas laser of 232 mJ·cm ⁻² or more 45 times.

After carbon dioxide laser irradiation, the substrate was irradiated with hydrogen plasma to terminate dangling bonds present in the polycrystalline semiconductor film and at the interface with hydrogen. The hydrogen plasma conditions were as follows:

Hydrogen ( _H2 ) flow rate: 1000 sccm; pressure: 500 mTorr; rf wave (13.56 MHz) output: 100 W; electrode distance: 25 mm; substrate temperature: 300°C; processing time: 90 seconds. Thus, gate insulating film deposition and oxide film modification were completed (Figure 5-b). Next, a gate electrode 505 was formed using a thin metal film. In Example 2, a gate electrode was fabricated using α-structure tantalum (Ta) with a film thickness of 750 nm. The sheet resistance of the gate electrode at this time was 0.8 Ω/□.

Next, using the gate electrode as a mask, donor or acceptor impurity ions 506 are implanted to form source/drain regions 507 and channel formation regions 508 in a self-aligned manner with the gate electrode. In Example 2, a CMOS semiconductor device was fabricated. When fabricating an NMOS transistor, the PMOS transistor portion was covered with a thin aluminum (Al) film, and phosphine (PH ₃ ) diluted with 5% hydrogen was selected as the impurity element. The total ions containing hydrogen were implanted into the source/drain regions of the NMOS transistor at a concentration of 7×10 ¹⁵ cm ⁻² at an acceleration voltage of 80 kV. Conversely, when fabricating a PMOS transistor, the NMOS transistor portion was covered with a thin aluminum (Al) film, and diborane (B ₂ H ₆ ) diluted with 5% hydrogen was selected as the impurity element. The total ions containing hydrogen were implanted into the source/drain regions of the PMOS transistor at a concentration of 5×10 ¹⁵ cm ⁻² at an acceleration voltage of 80 kV. (FIG. 5-c) Next, an interlayer insulating film 509 was deposited by PECVD or the like. The interlayer insulating film was made of a silicon dioxide film and had a thickness of approximately 500 nm. After the deposition of the interlayer insulating film, a heat treatment was performed for two hours at 300° C. in a nitrogen atmosphere to sinter the interlayer insulating film and activate the impurity elements added to the source and drain regions.

Finally, contact holes were drilled and wiring 510 was applied using aluminum or other materials to complete the thin-film semiconductor device (Figure 5-d). The transfer characteristics of the thin-film semiconductor device fabricated in this manner were measured. The length and width of the channel formation region of the measured semiconductor device were each 10 μm, and measurements were performed at room temperature. The mobility of the NMOS transistor, determined from the saturation region at Vds = 8 V, was 42.4 ± 1.9 ^cm2 ·V ^-1 ·s ^-1 , and the threshold voltage was 3.87 ± 0.11 V. The mobility of the PMOS transistor, determined from the saturation region at Vds = -8 V, was 21.8 ± 1.2 ^cm2 ·V- ¹ ·s ^-1 , and the threshold voltage was -5.33 ± 0.21 V. Both N-type and P-type semiconductor devices exhibited high mobility and low threshold voltage, and were consistently manufactured without variation.

As this example demonstrates, the present invention allows for the simple and easy fabrication of thin-film semiconductor devices having excellent characteristics and highly reliable oxide films using low-temperature processes that can be carried out on general-purpose glass substrates.

(Comparative Example 1) Comparative Example 1 is an example demonstrating the superiority of the present invention over conventional techniques. In Comparative Example 1, a semiconductor device was fabricated using all the same processes as in Example 2, except that the light irradiation process was omitted. That is, after depositing a second silicon oxide film using the ECR-PECVD method, the hydrogen plasma irradiation described above was immediately performed, and a CMOS semiconductor device was fabricated using the same process as in Example 2.

The mobility and threshold voltage of the semiconductor device obtained in Comparative Example 1 are shown below.

μ(N)=34.4±3.3cm²・V^-1・s^-1 V_tb(N)=5.06±0.16V μ(P)=16.2±1.2cm²・V^-1・s^-1 V_th(P) = -6.30 ± 0.22 V The superiority of Example 2 of the present invention is clear from Comparative Example 1.

(Example 3) The NMOS thin-film semiconductor device obtained in Example 2 was used as the pixel switching element for a color LCD consisting of 200 (rows) x 320 (columns) x 3 (colors) = 192,000 (pixels), and an active matrix substrate was manufactured incorporating a 6-bit digital data driver (column driver) and a scan driver (row driver) using the CMOS thin-film semiconductor device obtained in Example 2.

FIG. 6 shows a circuit diagram of a 6-bit digital data driver. The digital data driver of Example 3 is composed of a clock signal line, a clock generation circuit, a shift register circuit, a NOR gate, a digital video signal line, a latch circuit 1, a latch pulse line, a latch circuit 2, a reset line 1, an AND gate, a reference potential line, a reset line 2, a 6-bit D/A converter using capacitance division, a CMOS analog switch, a common potential line, and a source line reset transistor. The output from the CMOS analog switch is connected to the source line of the pixel section. The capacitance of the D/A converter section satisfies the relationship _C0 = _C1 /2 = _C2 /4 = _C3 /8 = _C4 /16 = _C5 /32. A digital video signal output from a computer's video random access memory (VRAM) can be directly input to the digital video signal line. In the pixel section of the active matrix substrate of Example 3, the source electrode, source wiring, and drain electrode (pixel electrode) are made of aluminum, forming a reflective LCD.

A liquid crystal panel was fabricated using the active matrix substrate thus obtained as one of a pair of substrates. Polymer-dispersed liquid crystal (PDLC) with a black pigment dispersed therein was used as the liquid crystal sandwiched between the pair of substrates, creating a reflective liquid crystal panel in normally black mode (black display when no voltage is applied to the liquid crystal). The resulting liquid crystal panel was connected to external wiring to fabricate a liquid crystal display device.

As a result, the TFTs are high-performance and have uniform characteristics across the entire substrate, allowing both the 6-bit digital data driver and the scan driver to operate normally over a wide operating range. Furthermore, the pixel area has a high aperture ratio, resulting in a liquid crystal display with high display quality even when using black pigment-dispersed PDLC. Furthermore, the excellent interface between the semiconductor film and the oxide film, along with the high quality of the oxide film itself, ensured excellent transistor operational reliability, resulting in significantly improved operational stability for the display.

This LCD display was incorporated into the housing of a full-color portable personal computer (notebook PC). The active matrix substrate incorporates a 6-bit digital data driver, allowing digital video signals from the computer to be input directly to the LCD display, simplifying the circuit configuration and significantly reducing power consumption. Thanks to the high performance of the thin-film semiconductor devices used in the LCD display, this notebook PC is an excellent electronic device with a stunning display screen. Additionally, the LCD display is a reflective type with a high aperture ratio, eliminating the need for a backlight, thereby enabling a compact, lightweight battery and extended battery life. This results in an ultra-compact, lightweight electronic device with long operating times and a beautiful display screen.

(Example 4) In Example 4, an infrared light irradiation device for modifying silicon oxide films, which irradiates a silicon oxide film formed on a substrate with infrared light to improve its quality, is described with reference to Figures 7 through 11. The infrared light irradiation device for modifying silicon oxide films includes at least an infrared light generating means, such as a carbon dioxide laser oscillator 101, an infrared light intensity adjusting means for adjusting the absolute intensity of the generated infrared light, an infrared light homogenizing means for homogenizing the spatial intensity distribution of the intensity-adjusted infrared light, and a scanning mechanism for varying the relative positional relationship between the substrate on which the silicon oxide film is formed and the homogenized infrared light (see Figure 7).

The infrared laser light generated by the carbon dioxide laser oscillator 101 is adjusted to a desired absolute intensity by an optical system 104, which includes an attenuator and other components. In Example 4, this optical system 104 corresponds to the infrared light intensity adjustment means. Specifically, the output intensity is tunable by changing the transmittance of the infrared laser light incident on the optical system 104. The intensity-adjusted infrared light is then guided to an infrared light homogenization means, which includes a homogenizer 103 and other components, where the spatial intensity distribution of the infrared light is homogenized so that no significant spatial variations occur within the infrared light irradiation area on the substrate. The shaped infrared light is introduced into the irradiation chamber 105, where it is irradiated onto the substrate 110 placed in the irradiation chamber.

To create a desired infrared light irradiation atmosphere, such as a vacuum, nitrogen, or argon, the irradiation chamber is equipped with an exhaust means, such as a pump 107, and a gas introduction means, such as a gas system 106. The relative position between the infrared light introduced into the irradiation chamber and the substrate 110 on which the silicon oxide film is formed is variable by moving the stage on which the substrate is placed using a stage controller 108. That is, in Example 4, the scanning mechanism moves the substrate while fixing the infrared light path. As shown in subsequent examples, scanning mechanisms that fix the substrate and move the infrared light path, or scanning mechanisms that move both, are also possible. The computer 109 is a control system that controls the stage controller 108 and the laser controller 102.

To improve the quality of a silicon oxide film formed by vapor deposition or other methods by simultaneously heating the entire film, an infrared laser oscillator with extremely high output power is required.

However, such a high-power laser oscillator does not yet exist. Therefore, in the present invention, infrared light is processed into a strip-shaped irradiation area or a thin line-shaped irradiation area by an infrared light homogenizing means, and this irradiation area is movable by the aforementioned scanning mechanism, thereby enabling uniform light irradiation across the entire substrate. It is desirable that the laser light intensity within the irradiation area be uniform. Therefore, the infrared light homogenizing means according to the present invention will now be described.

Figure 8 shows an example of an infrared light homogenizing means using a fly-eye lens 201. This infrared light homogenizing means has as its basic components a fly-eye lens 201 and a condenser lens 202, with the condenser lens 202 being a cylindrical lens. Reference numeral 203 denotes an incident infrared laser beam. The laser beam 203 incident on the fly-eye lens 201 has its wavefront split by a so-called fly-eye lens, which is composed of multiple rectangular or cylindrical lenses (in Figure 8, five lenses labeled A through E) bundled together in a cross section perpendicular to the optical axis. The split laser beam is focused at the focal position of the fly-eye lens and then enters the condenser lens 202, which is confocal with the fly-eye lens. This condenser lens recombines the split laser beams at the image-side focal point, i.e., on the substrate, to form a uniform laser beam. Figure 9 shows the intensity distribution of the laser beam split into beams A through E on the substrate 110, as well as the intensity distribution of the resulting laser beam after they are superimposed. In this method, the split laser beams that are symmetrical with respect to the optical axis, such as A and E and B and D in Figure 9, have symmetric intensity distributions, and uniformity is ensured by superimposing these beams.

FIG. 10 shows an example of an infrared light homogenizing means using a Fourier transform phase hologram 301. The infrared light homogenizing means here has a lens 300 and a Fourier transform phase hologram 301 (hereinafter referred to as the hologram) as its basic components. The lens 300 and hologram 301 produce a thin laser beam with a uniform laser intensity distribution in the longitudinal direction on a substrate 110, which is the workpiece and has a silicon oxide film formed thereon. Laser light emitted from a laser oscillator 101 passes through a beam shaping optical system 302 consisting of the lens 300 and hologram 301. The laser light is irradiated onto the substrate 110 by the lens 300, but is spatially modulated by the hologram 301, located between the lens 300 and the substrate 110, to produce multiple overlapping irradiation spots aligned in a straight line on the substrate 110. Hologram 301 can arrange each irradiation spot at any position on substrate 110 with any intensity. Figure 11 shows the shape of a laser beam shaped by the laser beam shaping optical system of Figure 10 and irradiated onto a substrate on which a silicon oxide film has been formed. By using hologram 301 in which the irradiation spots are aligned in a straight line as shown in Figure 11 and by setting the overlapping pitch of the irradiation spots to a uniform pitch, it is possible to obtain a laser beam that is uniform in the longitudinal direction on substrate 110.

The hologram 301 divides the laser beam into 400 to 800 irradiation spots, making the intensity distribution of the laser beam uniform.

(Example 5) In Example 5, an infrared light irradiation device for modifying silicon oxide films, which irradiates a silicon oxide film formed on a substrate with infrared light to improve its quality, is described using Figures 12 and 13. This infrared light irradiation device has at least an infrared light generating means, such as a carbon dioxide laser oscillator 101, a light shaping means for shaping the generated infrared light into a spot shape, and a scanning mechanism for varying the relative position between the substrate on which the silicon oxide film is formed and the infrared light shaped into a spot shape.

Infrared laser light generated by the carbon dioxide laser oscillator 101 is guided by mirror 401 to mirror 400 of a galvanometer scanner, a type of scanning mechanism (Figure 12). After being reflected by mirror 400 of the galvanometer scanner, the laser beam is incident on lens 402 and shaped into a spot-shaped beam. In Example 5, this lens 402 serves as a light shaping means for shaping the beam into a spot shape. The shaped infrared light is introduced into irradiation chamber 105, where it is irradiated onto a substrate 110 placed within the irradiation chamber. The configuration and control system of the irradiation chamber are the same as in Example 4. In Example 5, the position of the laser beam irradiated onto the substrate 110 is changed by changing the angle of mirror 400 of the galvanometer scanner using a galvanometer scanner. This irradiation light is scanned linearly or planarly, irradiating the entire surface of the substrate 110 with the infrared laser light. The irradiated laser beam is absorbed by the silicon oxide film deposited on the substrate, heating it and improving the quality of the oxide film.

On the other hand, Figure 13 shows another example of a light irradiation device using a polygon mirror 601 as a scanning mechanism. Laser light emitted from a laser oscillator 101 is reflected by the polygon mirror 601 and enters a lens 402. The infrared light is shaped into a spot-shaped beam by the lens 402 and then guided into an irradiation chamber to irradiate the substrate 110. The scanning mechanism in this example changes the angle of the polygon mirror 601 to change the laser irradiation position on the substrate 110. As in the previous example, the laser light then scans the entire substrate surface, thereby modifying the silicon oxide film.

In these examples, carbon dioxide laser light is used as the infrared light, but IV-VI semiconductor lasers, free electron lasers, etc. may also be used as the infrared light.

INDUSTRIAL APPLICABILITY As described above, the present invention can improve conventionally low-quality silicon oxide films formed at low temperatures by adding a simple infrared light irradiation process. Therefore, when this invention is applied to thin-film semiconductor devices such as TFTs and semiconductor devices such as LSIs, high-performance semiconductor devices with excellent operational reliability can be manufactured stably at low temperatures. Furthermore, when this invention is applied to active-matrix liquid crystal displays, large, beautiful displays can be manufactured easily and stably. Furthermore, when applied to the manufacture of other electronic devices, high-performance electronic devices can be manufactured easily and stably.

Furthermore, the infrared light irradiation device of the present invention is capable of processing large-area substrates at high speed and stably, making it ideal for processing TFT substrates and large silicon substrates with a diameter of 300 mm.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (42)

[Claims] 1. A method for producing a silicon oxide film, comprising the steps of forming a silicon oxide film by a vapor phase deposition method and irradiating the silicon oxide film with infrared light. 2. The method for producing a silicon oxide film according to claim 1, wherein the vapor deposition method is a chemical vapor deposition method. 3. The method for producing a silicon oxide film according to claim 1, wherein the vapor deposition method is a physical vapor deposition method. 4. The method for producing a silicon oxide film according to any one of claims 1 to 3, wherein the infrared light includes a wavelength component that is absorbed by the silicon oxide film. 5. The method for producing a silicon oxide film according to any one of claims 1 to 3, wherein the infrared light includes a wavelength component corresponding to an asymmetric stretching vibration of the silicon oxide film. 6. A method for producing a silicon oxide film according to any one of claims 1 to 3, wherein when the thickness of the silicon oxide film is t (cm) and the absorption coefficient of the infrared light by the silicon oxide film is k (cm ^-1 ), the thickness t and the absorption coefficient k satisfy the relationship k·t>0.1. 7. The method for producing a silicon oxide film according to any one of claims 1 to 3, wherein the infrared light includes wavelength components of approximately 8.9 μm or more and approximately 10 μm or less. 8. The method for producing a silicon oxide film according to any one of claims 1 to 7, wherein the infrared light is laser light. 9. The method for producing a silicon oxide film according to any one of claims 1 to 7, wherein the infrared light is a carbon dioxide (CO ₂ ) laser beam. 10. A method for manufacturing a semiconductor device, comprising the steps of: oxidizing a semiconductor surface to form a silicon oxide film; and irradiating the silicon oxide film with infrared light. 11. The method for manufacturing a semiconductor device according to claim 10, wherein the silicon oxide film formation step is carried out at a temperature of approximately 800°C or less. 12. The method for manufacturing a semiconductor device according to claim 10, wherein the silicon oxide film formation step is carried out by supplying active oxygen to the semiconductor surface. 13. The method for manufacturing a semiconductor device according to claim 10, wherein the silicon oxide film forming step is carried out by plasma oxidizing the semiconductor surface. 14. The method for manufacturing a semiconductor device according to any one of claims 10 to 13, wherein the infrared light includes a wavelength component that is absorbed by the silicon oxide film. 15. The method for manufacturing a semiconductor device according to any one of claims 10 to 13, wherein the infrared light includes a wavelength component corresponding to the asymmetric stretching vibration of the silicon oxide film. 16. The method for manufacturing a semiconductor device according to any one of claims 10 to 13, wherein when the thickness of the silicon oxide film is t (cm) and the absorption coefficient of the infrared light by the silicon oxide film is k (cm ^-1 ), the thickness t and the absorption coefficient k satisfy the relationship k·t>0.01. 17. The method for manufacturing a semiconductor device according to any one of claims 10 to 13, wherein the infrared light includes wavelength components of approximately 8.9 μm or more and approximately 10 μm or less. 18. The method for manufacturing a semiconductor device according to any one of claims 10 to 17, wherein the infrared light is laser light. 19. The method for manufacturing a semiconductor device according to any one of claims 10 to 17, wherein the infrared light is a carbon dioxide (CO ₂ ) laser light. 20. The method for manufacturing a semiconductor device according to any one of claims 10 to 19, wherein the infrared light irradiation step is performed in an inert gas atmosphere. 21. A method for manufacturing a semiconductor device, comprising the steps of forming a semiconductor film on an insulating material, forming a silicon oxide film on the semiconductor film, and irradiating the silicon oxide film with infrared light. 22. The method for manufacturing a semiconductor device according to claim 21, wherein the silicon oxide film forming step is performed by chemical vapor deposition. 23. The method for manufacturing a semiconductor device according to claim 21, wherein the silicon oxide film forming step is performed by physical vapor deposition. 24. The method for manufacturing a semiconductor device according to claim 21, wherein the silicon oxide film formation step is carried out at a temperature of approximately 600°C or less. 25. The method for manufacturing a semiconductor device according to claim 21, wherein the silicon oxide film formation step is carried out by supplying active oxygen to the semiconductor surface. 26. The method for manufacturing a semiconductor device according to claim 21, wherein the silicon oxide film forming step is carried out by plasma oxidizing the semiconductor surface. 27. The method for manufacturing a semiconductor device according to any one of claims 21 to 26, wherein the infrared light includes a wavelength component that is absorbed by the silicon oxide film. 28. The method for manufacturing a semiconductor device according to any one of claims 21 to 26, wherein the infrared light includes a wavelength component corresponding to the asymmetric stretching vibration of the silicon oxide film. 29. A method for manufacturing a semiconductor device according to any one of claims 21 to 26, wherein when the thickness of the silicon oxide film is t (cm) and the absorption coefficient of the infrared light by the silicon oxide film is k (cm ^-1 ), the thickness t and the absorption coefficient k satisfy the relationship k·t>0.1. 30. The method for manufacturing a semiconductor device according to any one of claims 21 to 26, wherein the infrared light includes wavelength components of approximately 8.9 μm or more and approximately 10 μm or less. 31. The method for manufacturing a semiconductor device according to any one of claims 21 to 30, wherein the infrared light is laser light. 32. The method for manufacturing a semiconductor device according to any one of claims 21 to 30, wherein the infrared light is a carbon dioxide (CO ₂ ) laser light. 33. The method for manufacturing a semiconductor device according to any one of claims 21 to 32, wherein the infrared light irradiation step is performed in an inert gas atmosphere. 34. The method for manufacturing a semiconductor device according to any one of claims 21 to 32, further comprising a dangling bond termination step after the infrared light irradiation step. 35. The method for manufacturing a semiconductor device according to any one of claims 21 to 32, wherein the insulating material is a silicon oxide film formed on a glass substrate. 36. A semiconductor device manufactured by the method for manufacturing a semiconductor device according to any one of claims 21 to 35. 37. A display device comprising the semiconductor device according to claim 36. 38. An infrared light irradiation device capable of irradiating a silicon oxide film formed on a substrate with infrared light to modify the silicon oxide film, comprising: an infrared light generating means; an infrared light homogenizing means for homogenizing the spatial intensity distribution of the infrared light; and a scanning mechanism for varying the relative positional relationship between the substrate and the homogenized infrared light. 39. An infrared light irradiation device capable of irradiating a silicon oxide film formed on a substrate with infrared light to modify the silicon oxide film, comprising: an infrared light generating means; a light shaping means for shaping the infrared light into a spot shape; and a scanning mechanism for varying the relative positional relationship between the substrate and the infrared light shaped into the spot shape. 40. The infrared light irradiation device according to claim 38 or 39, wherein the wavelength of the infrared light is between approximately 8.9 μm and approximately 10 μm. 41. The infrared light irradiation device according to claim 38 or 39, wherein the infrared light is laser light. 42. An infrared light irradiation device according to claim 38 or 39, characterized in that the infrared light is carbon dioxide ( _CO2 ) laser light. 43. A method for producing a silicon oxide film, comprising the steps of forming a silicon oxide film on a substrate and irradiating the silicon oxide film with light, wherein, when the temperature of the silicon oxide film rises to 800°C or higher in the light irradiation step, T _ox (°C) is any silicon oxide film temperature, and τ ( _s ) is the total time during which that temperature (T _ox ) is reached, there exists a T _ox such that T ox and τ satisfy the relationship τ > exp(-0.04605 · T _ox + 34.539). 44. A method for producing a silicon oxide film, comprising the steps of forming a silicon oxide film on a semiconductor material and irradiating the silicon oxide film with light, wherein, when the temperature of the oxide film rises to 1000°C or higher in the light irradiation step, T _ox (°C) is any silicon oxide film temperature, and τ (s) is the total time during which that temperature (T _ox ) is reached, the light irradiation step is carried out under conditions such that T _ox exists where T _ox and τ satisfy the relationship τ>2·(1+ν)· _{η 0} ·exp(ε/(k·(T _ox +273.15)))/E (where ν is the Poisson's ratio of the oxide film, E is its Young's modulus, η is its viscosity, η ₀ is the precipitous factor of the viscosity, ε is the activation energy of the viscosity, and k is the Boltzmann constant).