JP3845569B2 - Thin film semiconductor device, method for manufacturing the same, and electronic device including the device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film semiconductor device, a manufacturing method thereof, and an electronic device including the device. Particularly, a thin film semiconductor device such as a thin film semiconductor device (hereinafter referred to as TFT) formed on a substrate having an insulating surface such as glass, a manufacturing method thereof, and an electronic device such as a liquid crystal display device and an organic EL display device provided with the device. About.
[0002]
[Prior art]
In various electronic devices such as an active liquid crystal display device having a plurality of pixels, an organic EL display device, and an image sensor, each pixel is formed on a substrate having an insulating surface such as glass in order to drive each pixel individually. TFT is often used. Also, in recent display elements, a drive circuit for controlling the switching operation of the TFT is often provided on a substrate on which a TFT for driving a pixel is formed. A number of transistors are provided in the drive circuit, and these transistors are also formed of TFTs.
[0003]
A TFT has a thin-film silicon semiconductor (Si) or oxide thereof (silicon oxide (SiO 2) on an insulating surface such as glass. ₂ )) Is deposited, and these processes are repeated while performing an etching process, a heat treatment, an electrode formation process, and other processes. Thin film silicon semiconductors are broadly classified into those having crystallinity and amorphous silicon semiconductors (a-Si).
[0004]
Amorphous silicon semiconductors are the most commonly used thin-film silicon semiconductors used in TFTs because they have a low production temperature, can be produced relatively easily by a vapor phase method, and are also mass-productive. ing. However, an amorphous silicon semiconductor has a defect that physical properties such as conductivity are inferior to a silicon semiconductor having crystallinity. Therefore, in order to increase the operating speed of the TFT in the future, it is very important to establish a TFT using a crystalline silicon semiconductor and a method for manufacturing the TFT.
[0005]
At present, a polycrystalline silicon semiconductor (p-Si) is often used as a crystalline silicon semiconductor because of its ease of manufacture. As a method of forming a thin film-like polycrystalline silicon semiconductor at a low temperature of about 600 ° C. or less that can use a general-purpose glass substrate, an amorphous silicon semiconductor film is formed to a thickness of about 50 nm, and then this amorphous silicon is used. In general, a semiconductor film is irradiated with xenon chlorine (XeCl) excimer laser light (wavelength 308 nm) to melt and crystallize the amorphous silicon semiconductor film to obtain a polycrystalline silicon semiconductor film.
[0006]
However, since the crystal grain boundary of the polycrystalline silicon semiconductor film exists in the channel formation region of the TFT using the above-described polycrystalline silicon semiconductor film, its electrical characteristics are significantly higher than that of the TFT using the single crystal silicon semiconductor. I know it ’s inferior. For this reason, measures such as a method of reducing the influence on the electrical characteristics of the crystal grain boundaries by using a polycrystalline silicon semiconductor having a large grain size have been adopted.
[0007]
[Problems to be solved by the invention]
By the way, in the method of obtaining the polycrystalline silicon semiconductor film by irradiating the above-described conventional excimer laser light, crystal grains of about 1 μm at maximum can be obtained, but the positions of crystal grains and crystal grain boundaries cannot be controlled. For this reason, whether or not the crystal grain boundary is included in the channel formation region is a stochastic event and cannot be controlled at all. The characteristics of the TFT greatly vary depending on whether or not a crystal grain boundary is included in the channel formation region. For example, if the number of crystal grain boundaries present in the channel formation region is large, the electrical characteristics of the TFT are deteriorated. If the number of crystal grain boundaries present in the channel formation region is small, the electrical characteristics of the TFT are relatively good. However, even if the number of crystal grain boundaries existing in the channel formation region can be reduced, the electrical characteristics of the TFT are much inferior to those of a TFT using a single crystal silicon semiconductor.
[0008]
In recent years, electronic devices are required to operate at high speeds. In particular, TFTs provided in electronic devices are required to have excellent electrical characteristics that can be switched at high speed with little variation in the electrical characteristics of each element. ing. For example, taking a liquid crystal display device as an example, when the number of pixels increases due to high definition, the time during which one pixel is in an on state is shortened by the increase. This applies not only to the TFT that drives the pixel, but also to the TFT provided in the drive circuit for driving the TFT. Therefore, in order to improve the characteristics of the electronic device, it is extremely important to improve the electrical characteristics of the basic TFT.
[0009]
The present invention has been made in view of the above circumstances, and is a thin film having a semiconductor film made of large crystal grains with good crystallinity with controlled crystal grain boundary positions and good electrical characteristics and little variation. It is an object of the present invention to provide a semiconductor device, a manufacturing method thereof, and an electronic device including the device.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, a method for manufacturing a thin film semiconductor device according to the present invention is a method for manufacturing a thin film semiconductor device in which a part of a semiconductor film formed on a substrate is used as a channel formation region. A heating mechanism forming step of forming a local heating mechanism on the substrate to locally heat the substrate, a semiconductor film forming step of forming the semiconductor film on the local heating mechanism, performed after the heating mechanism forming step, A crystallization process in which the semiconductor film is melt-crystallized in a state where the semiconductor film is locally heated by a local heating mechanism, an element isolation process in which the semiconductor film is processed into an island shape, and the island shape is processed. With respect to a gate insulating film forming step of forming a gate insulating film on the semiconductor film and a first direction in which crystal growth of the semiconductor film proceeds, the semiconductor film on the vicinity of the center of the local heating mechanism is not An impurity ion implantation step for implanting impurity ions; a gate electrode formation step for forming a gate electrode on the gate insulating film after the impurity ion implantation step; and impurity ions are implanted into the semiconductor film using the gate electrode as a mask. Forming a source region, a drain region, and a channel formation region, wherein the channel formation region is completely included in the local heating mechanism with respect to the first direction and the center of the local heating mechanism It is characterized by being arranged so as to be separated by a predetermined distance on both sides in the vicinity.
In the invention having such a configuration, a local heating mechanism is first formed on a substrate (heating mechanism forming step). As an example, the local heating mechanism includes an island-shaped first semiconductor film formed on a substrate and a lower insulating film covering the first semiconductor film. Therefore, as a specific example of the local heating mechanism forming step, a first semiconductor film deposition step of depositing the first semiconductor film on the substrate, a first semiconductor film processing step of processing the first semiconductor film into a predetermined shape, A step including a lower insulating film forming step of forming a lower insulating film on the first semiconductor film.
Next, a semiconductor film is formed on the local heating mechanism (semiconductor film forming step). The semiconductor film is made of an amorphous semiconductor film or a crystalline semiconductor film. Therefore, a specific example of the semiconductor film forming step is a step of depositing an amorphous semiconductor film on the local heating mechanism, and an amorphous semiconductor film is used as a step of further improving the crystallinity of the amorphous semiconductor film. Examples thereof include a solid phase growth step of crystallizing in a solid phase and a melt crystallization improvement step of improving the crystallinity of an amorphous semiconductor film through a molten state.
Next, the semiconductor film is melted and crystallized in a state where the semiconductor film is locally heated by the local heating mechanism (crystallization step). The crystallization step is a step of irradiating light from the semiconductor film side. When light is irradiated, part of the light is absorbed by the semiconductor film, and part of the light is transmitted through the semiconductor film. A semiconductor film that absorbs a certain amount of light is melted and crystallized. On the other hand, the light transmitted through the semiconductor film is absorbed by the first semiconductor film of the local heating mechanism. The temperature of the first semiconductor film rises by absorbing light, and the semiconductor film on the first semiconductor film is locally heated. Here, the semiconductor film is in the melt crystallization process. In the melt crystallization process, crystal grains grow from the low temperature portion toward the high temperature portion. Since only the portion of the semiconductor film that has a local heating mechanism underneath it becomes hotter than its surroundings, the crystal grains during cooling solidification are from the semiconductor film portion slightly outside the side of the local heating mechanism. It grows toward the semiconductor film part on the center of the local heating mechanism. The temperature difference formed by the local heating mechanism causes crystal lateral growth when the molten semiconductor film is cooled and solidified.
Here, as a specific example of the crystallization process, there is a process of irradiating the semiconductor film with a laser beam that transmits about 20% or more through the semiconductor film. Specific examples of the laser light include harmonics of a solid-state laser having a light wavelength of about 532 nm, and more specifically, a yttrium aluminum garnet (YAG) laser beam doped with neodymium (Nd) that oscillates in a Q switch. Second harmonic (Nd: YAG2ω laser light) and the like can be mentioned.
When the crystallization process is completed, the semiconductor film is processed into an island shape (element isolation process), and impurity ions are implanted into the semiconductor film near the center of the local heating mechanism in the first direction in which the crystal growth of the semiconductor film proceeds. (Impurity ion implantation step). Thereafter, a gate insulating film is formed on the island-processed semiconductor film (gate insulating film forming step), a gate electrode is formed on the gate insulating film (gate electrode forming step), and the gate electrode is used as a mask. Impurity ions are implanted into the semiconductor film to form a source region and a drain region.
In the gate electrode formation step, the gate electrode is formed so as to be completely included in the local heating mechanism in the first direction. The lateral crystal growth in the semiconductor film always starts from a position of about 1 μm outside the local heating mechanism. Therefore, if the local heating mechanism and the gate electrode are set in the above positional relationship, the crystal grain boundary (the crystal grain boundary crossing the current) crossing the first direction (current direction when the semiconductor device operates) in the semiconductor film. ) Can always be one near the center of the local heating mechanism.
In addition, as described above, by implanting impurity ions in the impurity ion implantation step, the resistance near the crystal grain boundary crossing the first direction in the semiconductor film is reduced, and the electrical influence of the crystal grain boundary on the semiconductor device is removed. be able to. This is like forming a channel formation region avoiding a grain boundary crossing the first direction. That is, since a plurality of current paths that do not cross the crystal grain boundary can always be formed in the channel formation region, the thin film semiconductor device includes a plurality of small silicon-on-insulator (SOI) devices using a single crystal silicon thin film. It is equivalent to those connected in parallel, and its performance is drastically improved compared to general thin film semiconductor devices.
Further, since it can be considered that there is no crystal grain boundary crossing the length direction in the channel formation region, there is no variation in characteristics of the thin film semiconductor device due to the presence of the crystal grain boundary. That is, all the thin film semiconductor devices formed on the substrate exhibit almost the same characteristics. Furthermore, as described above, by implanting impurity ions into the channel formation region near the center in the length direction of the local heating mechanism, there is an effect that the off-current of the thin film semiconductor device is reduced. Implanting impurity ions as described above has the same effect as dividing the channel formation region in the length direction. If the channel formation region is divided in the length direction, the source / drain voltage of the thin film semiconductor device is allocated to each channel formation region, and as a result, the electric field in the drain region end depletion region becomes weak. Therefore, the phonon assist tunneling phenomenon accompanied by the Pool-Frenkel effect is suppressed, and the off current of the thin film semiconductor device is reduced.
As described above, according to the above manufacturing method, since the resistance in the vicinity of the grain boundary crossing the length direction in the channel formation region is reduced by impurity ion implantation, the crystal grain crossing the length direction in the channel formation region. It can be considered that there is no boundary at all, and the channel formation region is divided in the length direction, so that a thin film semiconductor device with good electrical characteristics and little variation can be manufactured.
In the method of manufacturing a thin film semiconductor device according to the present invention, the length of the channel formation region in which no impurity is implanted in the first direction is 2 μm or less.
According to this manufacturing method, there is an effect that the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. The size of the lateral growth of the crystal is typically about 2 μm to 2.5 μm, and about 3.5 μm at the maximum. Therefore, if the length of the channel formation region into which the impurity ions are not implanted is 2 μm or less, the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. It is.
In the method for manufacturing a thin film semiconductor device of the present invention, the region into which the impurity ions are implanted is a region of 0.5 μm or more in the first direction from the vicinity of the center of the local heating mechanism in the first direction. It is characterized by.
According to this manufacturing method, there is an effect that the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. Further, the vicinity of the crystal grain boundary that crosses the length direction of the channel formation region protrudes in a mountain shape with the crystal grain boundary part as the top. According to the above manufacturing method, impurity ions can be implanted into a mountain-shaped region having the crystal grain boundary as the top. That is, the channel formation region in which impurity ions are not implanted, which strongly influences the electrical characteristics of the semiconductor device, is formed only in the region where the semiconductor film thickness is thin, so that the electrical characteristics of the semiconductor device are improved. In addition, since the channel formation region where the impurity ions are not implanted is formed in a flat region, the interface state between the channel formation region where the impurity ions are not implanted and the gate insulating film is improved, and the reliability of the semiconductor device is improved. improves.
In order to solve the above problems, a thin film semiconductor device of the present invention is a thin film semiconductor device that uses a part of a semiconductor film formed on a substrate as a channel formation region, and is locally between the substrate and the channel formation region. A heating mechanism is formed, and in the semiconductor film, channel forming regions are formed in two different places, and one crystal grain boundary extending in a second direction crossing the first direction in which the channel forming regions are arranged And impurity ions are implanted in the vicinity of the crystal grain boundary.
According to this configuration, since the resistance in the vicinity of the crystal grain boundary crossing the length direction in the channel formation region is reduced by impurity ion implantation, it can be considered that there is no crystal grain boundary crossing the length direction in the channel formation region. Since the channel formation region is divided in the length direction, the thin film semiconductor device has good electrical characteristics and little variation.
In the thin film semiconductor device of the present invention, the length of each channel formation region in which the impurity ions are not implanted in the first direction is 2 μm or less.
According to the above configuration, there is an effect that the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. The size of the lateral growth of the crystal is typically about 2 μm to 2.5 μm, and about 3.5 μm at the maximum. Therefore, if the length of the channel formation region into which the impurity ions are not implanted is 2 μm or less, the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. It is.
The thin film semiconductor device of the present invention is characterized in that the region into which the impurity ions are implanted is set to a region of 0.5 μm or more in the first direction from the crystal grain boundary.
According to the above configuration, there is an effect that the electrical influence exerted on the semiconductor device by the crystal grain boundary crossing the length direction in the channel formation region can be surely removed. Further, the vicinity of the crystal grain boundary that crosses the length direction of the channel formation region protrudes in a mountain shape with the crystal grain boundary part as the top. According to the above manufacturing method, impurity ions can be implanted into a mountain-shaped region having the crystal grain boundary as the top. That is, the channel formation region in which impurity ions are not implanted, which strongly influences the electrical characteristics of the semiconductor device, is formed only in the region where the semiconductor film thickness is thin, so that the electrical characteristics of the semiconductor device are improved. In addition, since the channel formation region where the impurity ions are not implanted is formed in a flat region, the interface state between the channel formation region where the impurity ions are not implanted and the gate insulating film is improved, and the semiconductor device has high reliability. It becomes.
In order to solve the above problems, an electronic device according to the present invention is a thin film semiconductor device manufactured using the method for manufacturing a thin film semiconductor device described above, or a thin film semiconductor device described above. Is provided as at least one of an electrical switching means and an electro-optical switching means.
According to the present invention, the thin film semiconductor device having good electrical characteristics and little variation is provided as at least one of the electrical switching means and the electro-optical switching means, and the operation speed can be increased. Therefore, it is extremely suitable for use in various electronic devices such as active liquid crystal display devices having a large number of pixels, organic EL display devices, and image sensors.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a thin film semiconductor device according to an embodiment of the present invention, a manufacturing method thereof, and an electronic device including the device will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an example of the overall configuration of an electronic device according to an embodiment of the present invention. The electronic device shown in FIG. 1 is an example of an active matrix type transmissive liquid crystal device using a thin film transistor (hereinafter abbreviated as TFT) as a switching means. FIG. FIG. 1B is a perspective view showing the overall configuration, and FIG. 1B is an enlarged view of one pixel in FIG. In FIG. 1, for easy understanding, the pixel and the TFT provided in the pixel are illustrated in an enlarged manner.
[0012]
In the liquid crystal device 1 as an electronic device according to the present embodiment, as shown in FIG. 1A, the element substrate 2 on the side on which the TFT is formed and the counter substrate 3 are arranged so as to face each other. A liquid crystal layer (not shown) made of liquid crystal having positive dielectric anisotropy is sealed between the substrate 3 and the substrate 3. On the inner surface side of the element substrate 2, a large number of source lines 4 and a large number of gate lines 5 are provided in a lattice shape so as to cross each other. A TFT 6 is formed in the vicinity of the intersection of each source line 4 and each gate line 5, and a pixel electrode 7 is connected to each other through each TFT 6. That is, one TFT 6 and one pixel electrode 7 are provided for each pixel arranged in a matrix. On the other hand, a common electrode 8 is formed on the entire inner surface of the counter substrate 3 over the entire display region in which a large number of pixels are arranged in a matrix.
[0013]
As shown in FIG. 1B, the TFT 6 includes a gate electrode 10 extending from the gate line 5, an insulating film (not shown) covering the gate electrode 10, and a semiconductor made of polycrystalline silicon formed on the insulating film. A layer 11, a source electrode 12 extending from the source line 4 electrically connected to the source region in the semiconductor layer 11, and a drain electrode 13 electrically connected to the drain region in the semiconductor layer 11. Yes. The drain electrode 13 of the TFT 6 is electrically connected to the pixel electrode 7. In the present embodiment, the pixel electrode 7 is formed of a transparent conductive film such as ITO, and the common electrode 8 on the counter substrate 3 side is also formed of a transparent conductive film such as ITO.
[0014]
In FIG. 1, reference numerals 20 and 21 denote drive circuits (source drivers) for driving the TFT 6. The drive circuits 20 and 21 are formed on the inner surface side of the element substrate 2 similarly to the TFT 6, and include a large number of TFTs (not shown). A control signal is supplied to the drive circuits 20 and 21 from a control circuit (not shown), and a drive signal (scanning signal) for driving each TFT 6 is generated based on the control signal. Further, reference numerals 22 and 23 in FIG. 1 denote another drive circuit (gate driver) for driving the TFT 6. The drive circuits 22 and 23 are also configured to include a large number of TFTs, and generate drive signals (data signals) for driving the TFTs 6 from the supplied control signals.
[0015]
The liquid crystal device as an example of the electronic device according to the embodiment of the present invention has been described above. Next, the TFT 6 as the thin film semiconductor device according to the embodiment of the present invention and the TFT (not shown) provided in the drive circuits 20-23. Details of the manufacturing method and the configuration thereof will be described.
[0016]
[Thin Film Semiconductor Device and Manufacturing Method According to First Embodiment]
2 to 6 are process diagrams showing an example of a method of manufacturing a thin film semiconductor device according to the first embodiment of the present invention. 2-6, (a) is sectional drawing of a thin film semiconductor device, (b) is a plane perspective view. In the following description, the XYZ orthogonal coordinate system shown in FIGS. 2 to 6 is set, and the positional relationship of each member will be described with reference to this XYZ orthogonal coordinate system. In the XYZ orthogonal coordinate system shown in FIGS. 2 to 6, an XY plane is set in an interface of a thin film semiconductor device having a stacked structure, and a direction orthogonal to the interface is set as a Z-axis direction.
[0017]
In the thin film semiconductor device of this embodiment, as shown in FIG. 2, first, a quartz substrate 111 having a thickness of 1.1 mm is used as a substrate, and an electron cyclotron resonance plasma chemical vapor phase is formed on the quartz substrate 111 as a base protective film 112. A silicon oxide film (SiO2) is deposited by a deposition method (ECR-PECVD method). ₂ Film) is deposited to a thickness of about 200 nm. Next, an amorphous silicon film (a-Si film) is deposited on the silicon oxide film as the base protective film 112 by a low pressure chemical vapor deposition method (LPCVD method) to a film thickness of about 50 nm, and then by a photolithography method. The amorphous silicon film is patterned to form the first semiconductor film 113.
[0018]
The length (the length in the Y direction) of the first semiconductor film 113 is formed to be about 1 μm longer than the length (the length in the X direction) of an active region (channel formation region) described later. Although details will be described later, the position of the active region in the Y direction is set near the center of the first semiconductor film 113. Here, the length of the first semiconductor film 113 is 5 μm. The width (length in the X direction) of the first semiconductor film is set to about 50 μm, and the active region is set to be completely included in the first semiconductor film 113 in the width direction (X direction).
[0019]
After the first semiconductor film 113 is formed, a silicon oxide film is deposited as a lower insulating film 114 on the first semiconductor film 113 and the base protective film 112 by an ECR-PECVD method to a thickness of about 160 nm. The first semiconductor film 113 and the lower insulating film 114 described above are heat generating members that locally heat a semiconductor film (active semiconductor film) portion that later becomes an active region, and correspond to the local heating mechanism in the present invention. Is. Note that the step of forming the first semiconductor film 113 and the lower insulating film 114 corresponds to the heating mechanism forming step according to the present invention.
[0020]
When the above steps are completed, an amorphous silicon film is deposited as an active semiconductor film 115 on the silicon oxide film as the lower insulating film 114 by an LPCVD method to a thickness of about 50 nm, and then a solid phase growth method is performed in a nitrogen atmosphere 600. The crystallinity of the active semiconductor film 115 is improved by performing a heat treatment at 48 ° C. for 48 hours, and a large grain polycrystalline silicon film as the active semiconductor film 115 is irradiated with a xenon chlorine (XeCl) excimer laser (wavelength 308 nm). This reduces the internal crystal defects in the active silicon film. This step corresponds to the semiconductor film forming step in the present invention.
[0021]
When the above steps are completed, a step of melting and crystallizing the active semiconductor film 115 in a state where the active semiconductor film 115 is locally heated by a heat generating member including the first semiconductor film 113 and the lower insulating film 114 is performed. Specifically, as shown in FIG. 3A, Nd is transferred from the polycrystalline silicon film side as the active semiconductor film 115 to yttrium aluminum garnet. ³⁺ YAG2ω laser light 116 emitted from a laser (YAG2ω laser: wavelength 532 nm) using a second harmonic of a laser (YAG laser: wavelength 1064 nm) whose base crystal is doped with ions is irradiated.
[0022]
The irradiation region of the YAG2ω laser beam 116 has a rectangular shape with a length of 15 mm and a width of 65 μm, and the light intensity distribution in the irradiation region is distributed in a substantially trapezoidal shape in the length direction. It is preferable that the light intensity distribution has a shape or a substantially Gaussian function. The irradiation region of the YAG2ω laser beam 116 is set so that its length direction substantially coincides with the width direction (X direction) of the first semiconductor film 113. Accordingly, the YAG2ω laser beam 116 is sequentially irradiated by moving (advancing) by the width of the irradiation region, and the traveling direction of the irradiation region and the source / drain direction of the thin film semiconductor device are substantially parallel.
[0023]
Here, the irradiation energy density of the YAG2ω laser beam 116 is 450 mJ · cm. ^-2 Thus, an arbitrary point on the active semiconductor film 115 is irradiated with 20 times of pulsed laser light. When the YAG2ω laser light 116 is irradiated, a part of the YAG2ω laser light 116 is absorbed by the polycrystalline silicon film as the active semiconductor film 115, but the remaining YAG2ω laser light 116 is applied to the polycrystalline silicon film as the active semiconductor film 115. Transmits without being absorbed. The YAG 2ω laser light 117 that has passed through the polycrystalline silicon film as the active semiconductor film 115 passes through the silicon oxide film as the lower insulating film 114 and is absorbed by the first semiconductor film 113. A part of the YAG2ω laser light 117 incident on the lower insulating film 114 is absorbed by the first semiconductor film 113 after multiple reflection or interference in the silicon oxide film 11.
[0024]
The first semiconductor film 113 rises in temperature due to the absorption of the YAG2ω laser light 117, and has heat. The heat 118 released from the first semiconductor film 113 affects the active semiconductor film 115, so that the temperature of the active semiconductor film 115 immediately above the first semiconductor film 113 becomes higher than that of the active semiconductor film 115 directly above the first semiconductor film 113. It becomes higher than the temperature. Due to the temperature difference in the active semiconductor film 115 generated in this manner, the crystal growth of the active semiconductor film 115 is a region where the temperature is low (the region where the temperature is higher than the active semiconductor film other than the region directly above the first semiconductor film 113 (the activity directly (Semiconductor film) (Y direction in FIG. 3).
[0025]
Regarding the Y-axis direction, the temperature is highest immediately above the first semiconductor film 113, and the temperature decreases as the temperature proceeds from this position in the Y direction and the -Y direction. Accordingly, the crystal growth proceeds in the Y direction and the −Y direction, but finally, two grown crystals collide immediately above the center of the first semiconductor film 113, and the crystal growth direction (Y direction) there. A crystal grain boundary 119 extending in a direction perpendicular to (X direction) is formed. As shown in FIG. 3B, it should be noted that there is only one crystal grain boundary 119 extending in the X-axis direction, and the other crystal grain boundaries extend in the Y-axis direction. The size of the lateral growth (X direction and Y direction) of the crystal is typically about 2 μm to 2.5 μm, and is about 3.5 μm at the maximum. In addition, the above process is corresponded to the crystallization process said to this invention.
[0026]
After the active semiconductor film 115 is crystallized by irradiating the YAG2ω laser beam 116, the active semiconductor film 115 is processed by the photolithographic method as an element isolation process for forming the active region by processing the active semiconductor film 115 into an island shape. 115 is patterned. Here, as shown in FIG. 4B, the width (length in the X direction) of the active semiconductor film 115 after patterning is shorter than the width (length in the X direction) of the first semiconductor film 113, and Patterning is performed so that the length of the active semiconductor film 115 (length in the Y direction) is longer than the length of the first semiconductor film 113 (length in the Y direction). By patterning in this way, the active region is completely included in the first semiconductor film 113 as a local heating mechanism in the length direction (Y direction).
[0027]
When the above steps are completed, as shown in FIG. 4A, a silicon oxide film is deposited on the active semiconductor film 115 as a gate insulating film by an ECR-PECVD method to a thickness of about 60 nm. This silicon oxide film is used as the gate insulating film 120. Then, an aluminum (Al) film 121 is deposited on the silicon oxide film as the gate insulating film 120 by a sputtering method. Thereafter, Al near the crystal grain boundary 119 in the active semiconductor film 115 is removed by a photolithography method. Here, for example, aluminum is removed from the crystal grain boundary 119 to a distance of 0.5 μm in a direction perpendicular to the crystal grain boundary 119 (Y direction).
[0028]
Next, impurity ions 122 are implanted by ion doping using the aluminum film 121 as a mask. Here, when forming an NMOS transistor, phosphine (PH) diluted in hydrogen at a concentration of 5% as an impurity element. _Three ), And the total ion containing hydrogen at an acceleration voltage of 45 kV is 5 × 10 ¹⁵ cm ^-2 Type in the concentration. On the other hand, when fabricating a PMOS transistor, diborane (B) diluted in hydrogen at a concentration of 5% as an impurity element. ₂ H ₆ ) And select 5 × 10 5 ions with hydrogen at an acceleration voltage of 40 kV. ¹⁵ cm ^-2 Type in the concentration. In the active semiconductor film 115, the region 115a in the vicinity of the crystal grain boundary 119 into which impurity ions are implanted is reduced in resistance by activation annealing performed later. The above process corresponds to the impurity ion implantation process referred to in the present invention.
[0029]
When the above steps are completed, as shown in FIG. 5A, the aluminum film 121 is removed, and a tantalum nitride (TaN) film is deposited on the silicon oxide film as the gate insulating film 120 by sputtering to a thickness of about 50 nm. A tantalum (Ta) film is deposited to about 450 nm. Thereafter, the TaN film and the Ta film are patterned by photolithography to form the gate electrode 123.
[0030]
When patterning the gate electrode 123, the gate is formed so that the active semiconductor film 115 immediately below the gate electrode 123, which becomes a channel formation region of the thin film semiconductor device, is completely included in the first semiconductor film 113 in the length direction (Y direction). An electrode 123 is formed. Here, the length of the gate electrode 123 is set to 4 μm, which is 1 μm shorter than the length of the first semiconductor film 113.
[0031]
The centers of the gate electrode 123 and the first semiconductor film 113 in the length direction (Y direction) are aligned. Therefore, in the active semiconductor film 115 immediately below the gate electrode 123, there is a crystal grain boundary 119 below the center in the length direction (Y direction) of the gate electrode 123, and a position separated from the crystal grain boundary 119 by 0.5 μm in the Y direction. Impurity ions are implanted in the region 115a up to and including the crystal grain boundary that crosses the length direction by lateral growth of the crystal in the channel formation region 115c whose distance from the crystal grain boundary 119 is 0.5 μm to 1.5 μm. Will not exist.
[0032]
Next, impurity ions 124 serving as donors or acceptors are implanted by the ion doping method using the gate electrode 123 as a mask, and as shown in FIGS. 5A and 5B, the source region 115b, the drain region 115d, and the channel The formation region 115c is formed in a self-aligning manner. Here, the implantation conditions for impurity ions are the same as the implantation conditions for the region 115 a in the vicinity of the crystal grain boundary 119. In addition, the source region 115b and the drain region 115d are formed so that carriers move along the lateral growth direction (Y direction) of the crystal of the active semiconductor film 115. Then, in order to activate the impurity element added to the source region 115b, the drain region 115d, and the region 115a near the crystal grain boundary 119, heat treatment is performed at 300 ° C. for 4 hours in a nitrogen atmosphere.
[0033]
Thereafter, as shown in FIG. 6, TEOS (Si (OCH) is formed as an interlayer insulating film 125 by plasma CVD (PECVD). ₂ CH _Three ) _Four ) And oxygen as source gases are deposited to a thickness of about 500 nm. Finally, after forming contact holes by photolithography, aluminum (Al) is deposited by sputtering, and Al is patterned by photolithography to form a source electrode 126 and a drain electrode 127 to form a thin film. A semiconductor device is manufactured.
[0034]
As described above, according to the thin film semiconductor device according to the first embodiment of the present invention, the carrier moves in the active semiconductor film 115 immediately below the gate electrode 123 that becomes the channel formation region 115b of the thin film semiconductor device (Y direction). ), There is one crystal grain boundary 119 in the direction perpendicular to (X direction). Since the resistance near the crystal grain boundary 119 is reduced by impurity implantation, the influence of the crystal grain boundary 119 can be ignored. Therefore, since it can be considered that there is no crystal grain size in the direction (X direction) perpendicular to the direction in which carriers move (Y direction), a high-performance thin film semiconductor device similar to a single crystal semiconductor device is manufactured without variation in characteristics. be able to.
[0035]
[Thin Film Semiconductor Device According to Second Embodiment]
Next, a thin film semiconductor device and a method for manufacturing the same according to a second embodiment of the present invention will be described. In the following description, description of the thin film semiconductor device according to the first embodiment described above and parts common to the manufacturing method thereof will be simplified or omitted. 7A and 7B are views for explaining the thin film semiconductor device according to the second embodiment of the present invention. FIG. 7A is a cross-sectional view of the thin film semiconductor device, and FIG. As in the first embodiment, an XYZ orthogonal coordinate system is set, and the positional relationship of each member will be described with reference to this XYZ orthogonal coordinate system. In the XYZ orthogonal coordinate system shown in FIGS. 2 to 6, an XY plane is set in an interface of a thin film semiconductor device having a stacked structure, and a direction orthogonal to the interface is set as a Z-axis direction.
[0036]
The thin film semiconductor device of this embodiment includes a quartz substrate 211 having a thickness of 1.1 mm as a substrate, and a silicon oxide film is formed on the quartz substrate 211 as a base protective film 212 to a thickness of about 200 nm. Further, a polycrystalline silicon film as an active semiconductor film 213 is formed on the silicon oxide film as the base protective film 212 to a thickness of about 50 nm. Here, similarly to the first embodiment of the present invention, the first semiconductor film and the lower insulating film as a heat generating member between the silicon oxide film as the base protective film 212 and the polycrystalline silicon film as the active semiconductor film 213. And may exist.
[0037]
Further, a silicon oxide film as the gate insulating film 215 is formed on the polycrystalline silicon film as the active semiconductor film 213 described above, and a film thickness as the gate electrode 216 is formed on the silicon oxide film as the gate insulating film 215. A tantalum nitride (TaN) film having a thickness of about 50 nm and a tantalum (Ta) film having a thickness of about 450 nm are formed. Further, a silicon oxide film as an interlayer insulating film 217 and a source electrode 218 and a drain electrode 219 made of aluminum (Al) are formed on the gate electrode 216 and the gate insulating film 215.
[0038]
The polycrystalline silicon film as the active semiconductor film 213 immediately below the gate electrode 216 has a crystal grain boundary 214 below the center in the length direction (Y direction) of the gate electrode 216, and 0 from the crystal grain boundary 214 in the Y direction. Impurity ions are implanted in the region 213a up to a position separated by .5 μm, and the channel region 213c whose distance from the crystal grain boundary 214 is 0.5 μm to 1.5 μm is lengthwise (Y direction) due to lateral growth of the crystal. ) There is no grain boundary crossing. The polycrystalline silicon film as the active semiconductor film 213 just below the gate electrode 216 is implanted with the same impurity ions as the region 213a, and the source region 213b and the drain region 21d are formed. The thin film semiconductor device of this embodiment has the above configuration.
[0039]
As described above, according to the thin film semiconductor device according to the second embodiment of the present invention, the carrier moves in the active semiconductor film 213 immediately below the gate electrode 216 that becomes the channel formation region 213c of the thin film semiconductor device (Y direction). ) There is one crystal grain boundary 214 in the direction perpendicular to the X direction (X direction), but since the resistance of the region 213a in the vicinity of the crystal grain boundary 214 is reduced by impurity implantation, the influence of the crystal grain boundary 214 is ignored. it can. Therefore, since it can be considered that there is no crystal grain size in the direction (X direction) perpendicular to the direction in which carriers move (Y direction), a high-performance thin film semiconductor device similar to a single crystal semiconductor device can be manufactured without characteristic variations. can do.
[0040]
The thin film semiconductor device, the manufacturing method thereof, and the electronic device including the thin film semiconductor device according to the first and second embodiments of the present invention have been described above, but the present invention is not limited to the above embodiment and the scope of the present invention. Can be changed freely. For example, in the above embodiment, the TFT provided for driving the pixel of the liquid crystal display device as the thin film semiconductor device and the TFT provided in the driving device for driving the TFT have been described as examples. However, the present invention can be applied not only to the TFT provided in the liquid crystal display device but also to the TFT provided in the organic EL display device. Of course, the organic EL display device can also be applied to a TFT provided for driving a pixel and a TFT provided in a driving device for driving the TFT. In other words, the present invention can be applied to all cases where crystal grain boundaries are generated in the active region in the process of manufacturing a transistor and electrical characteristics deteriorate.
[0041]
In the above embodiment, a liquid crystal display device is exemplified as an electronic device. However, not only an organic EL display device and an image sensor but also a liquid crystal projector, a multimedia-compatible personal computer (PC), and an engineering workstation (EWS). ), Pagers, mobile phones, word processors, televisions, viewfinder type or monitor direct view type video tape recorders, electronic notebooks, electronic desk calculators, car navigation devices, POS terminals, devices with touch panels, etc. Is possible.
[0042]
【The invention's effect】
As described above, according to the present invention, the semiconductor film is composed of large crystal grains with good crystallinity, the position of the crystal grain boundary in the channel formation region is controlled, the electrical characteristics are good, and the variation is There is an effect that a small number of thin film semiconductor devices can be provided.
In addition, according to the method for manufacturing a thin film semiconductor device of the present invention, there is an effect that a high performance thin film semiconductor device can be easily and stably manufactured using a low temperature process that enables the use of an inexpensive glass substrate. is there.
Therefore, when the thin film semiconductor device of the present invention and the manufacturing method thereof are applied to an active matrix liquid crystal display device, a large and high quality liquid crystal display device can be manufactured easily and stably. Further, even when applied to the manufacture of other electronic circuits, a high-quality electronic circuit can be manufactured easily and stably.
According to the present invention, the thin film semiconductor device having good electrical characteristics and little variation is provided as at least one of the electrical switching means and the electro-optical switching means, and the operation speed can be increased. Therefore, it is extremely suitable for use in various electronic devices such as an active liquid crystal display device having a large number of pixels, an organic EL display device, and an image sensor.
Furthermore, even when applied to the manufacture of other electronic devices, high-quality electronic devices can be manufactured easily and stably.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of the overall configuration of an electronic device according to an embodiment of the present invention.
FIGS. 2A and 2B are process diagrams showing an example of a method for manufacturing a thin film semiconductor device according to the first embodiment of the present invention, wherein FIG. 2A is a cross-sectional view of the thin film semiconductor device, and FIG.
FIGS. 3A and 3B are process diagrams showing an example of a method for manufacturing a thin film semiconductor device according to the first embodiment of the present invention, wherein FIG. 3A is a cross-sectional view of the thin film semiconductor device, and FIG.
FIGS. 4A and 4B are process diagrams showing an example of a method of manufacturing a thin film semiconductor device according to the first embodiment of the present invention, wherein FIG. 4A is a cross-sectional view of the thin film semiconductor device, and FIG.
FIGS. 5A and 5B are process diagrams showing an example of a method for manufacturing a thin film semiconductor device according to the first embodiment of the present invention, wherein FIG. 5A is a cross-sectional view of the thin film semiconductor device, and FIG.
6A to 6C are process diagrams showing an example of a method for manufacturing a thin film semiconductor device according to the first embodiment of the present invention, wherein FIG. 6A is a cross-sectional view of the thin film semiconductor device, and FIG.
7A and 7B are diagrams for explaining a thin film semiconductor device according to a second embodiment of the present invention, FIG. 7A is a cross-sectional view of the thin film semiconductor device, and FIG. 7B is a plan perspective view.
[Explanation of symbols]
20-23 …… Drive circuit
111, 211 ... Quartz substrate
112, 212 ... Base protective film
113 …… First semiconductor film
114 …… Lower insulating film
115, 213 ... Active semiconductor film
115a, 213a ...... area
115b, 213b …… Source region
115d, 213d ...... Drain region
115c, 213c ... channel formation region
116 …… YAG2ω laser light
117... YAG2ω laser light transmitted through active semiconductor film
118 …… The heat of the first semiconductor film
119, 214 ... Grain boundary
120,215 ... Gate insulating film
122 …… Impurity ions
123, 216 ... Gate electrode
124 …… Impurity ions
125,217 …… Interlayer insulating film
126, 218 ... Source electrode
127, 219 ... Drain electrode

Claims (7)

In a method for manufacturing a thin film semiconductor device using a part of a semiconductor film formed on a substrate as a channel formation region,
A heating mechanism forming step of forming a local heating mechanism for locally heating a part of the semiconductor film on the substrate;
A semiconductor film forming step that is performed after the heating mechanism forming step and forms the semiconductor film on the local heating mechanism;
A crystallization step of melt crystallization of the semiconductor film in a state where the semiconductor film is locally heated by the local heating mechanism;
An element isolation step for processing the semiconductor film into an island shape;
Forming a gate insulating film on the semiconductor film processed into the island shape; and
An impurity ion implantation step of implanting impurity ions into the semiconductor film on the vicinity of the center of the local heating mechanism with respect to the first direction in which crystal growth of the semiconductor film proceeds;
A gate electrode forming step of forming a gate electrode on the gate insulating film after the impurity ion implantation step;
Implanting impurity ions into the semiconductor film using the gate electrode as a mask to form a source region, a drain region, and a channel formation region,
The channel forming region is arranged so as to be completely included in the local heating mechanism and spaced apart by a predetermined distance in the vicinity of the center of the local heating mechanism with respect to the first direction. A method for manufacturing a thin film semiconductor device.   2. The method of manufacturing a thin film semiconductor device according to claim 1, wherein a length of the channel formation region into which impurities are not implanted in the first direction is 2 [mu] m or less.   3. The region according to claim 1, wherein the region into which the impurity ions are implanted is a region of 0.5 μm or more in the first direction from the vicinity of the center of the local heating mechanism in the first direction. A method for manufacturing a thin film semiconductor device. In a thin film semiconductor device using a part of a semiconductor film formed over a substrate as a channel formation region,
A local heating mechanism is formed between the substrate and the channel formation region;
In the semiconductor film, channel forming regions are formed at two different locations,
A thin film semiconductor device, wherein one crystal grain boundary extending in a second direction crossing the first direction in which the channel formation region is arranged exists, and impurity ions are implanted in the vicinity of the crystal grain boundary.   5. The thin film semiconductor device according to claim 4, wherein a length of each of the channel formation regions in which the impurity ions are not implanted in the first direction is 2 μm or less.   6. The thin film semiconductor device according to claim 4, wherein the region into which the impurity ions are implanted is set to a region of 0.5 μm or more in the first direction from the crystal grain boundary.   The thin film semiconductor device manufactured using the manufacturing method of the thin film semiconductor device as described in any one of Claims 1-3, or the thin film semiconductor as described in any one of Claims 4-6 An electronic device comprising the apparatus as at least one of electrical switching means and electro-optical switching means.

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