JP2006114614A - Plasma processing apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing apparatus and method which can limit an electron shadow effect and is configured as a wafer process without damage without generating high energy ions or electrons.
A plasma processing apparatus includes a plasma generating unit, a wafer processing unit having a wafer to be processed, a metal grid separating the plasma generating unit and the wafer processing unit, and a plasma generating unit. And an upper electrode 21 having a porous silicon layer 27 for emitting electrons, a gas introduction unit for introducing gas, and a gas introduction port for introducing process gas.
[Selection] Figure 1

Description

  The present invention relates to a plasma processing apparatus and method, and more particularly to a plasma processing apparatus and method with very low electron energy that can be used in dry etching or film forming processes used in the semiconductor industry.

  Plasma assisted wafer processing is an unavoidable step in the semiconductor industry in fabricating integrated circuits on silicon (Si) substrates or other substrates. There are several plasma assisted processes, such as dry etching, physical vapor deposition (PVD), chemical vapor deposition (CVD), surface cleaning and the like. Typically, the plasma attributes required for each process are different, so that one type of plasma is used only for one type of wafer processing. There are several types of plasma. For example, DC plasma, rf plasma, microwave plasma and the like. Each of these plasmas has advantages and disadvantages. In general, plasmas with low electron energy are useful for many types of wafer processing, especially for reducing charge-induced damage for dry etching and CVD applications. However, due to the mechanism of electron heating in most plasma sources, the temperature of the electrons is considerably higher. This is further explained in connection with the dry etching process.

Plasma assisted dry etching is an inevitable step in building an integrated circuit on a silicon wafer. To date, several types of plasma sources exist for this wafer processing, such as inductively coupled plasma, capacitively coupled plasma, and magnetically enhanced capacitively coupled plasma. Dry etching of thin films such as SiO ₂ , metal or polysilicon (poly-Si) is typically performed by high energy ion bombardment. In order to obtain energized ions, the wafer holder is given a negative self-bias voltage by application of rf current. During the etching process, energized ions strike the wafer surface almost continuously. These ions at the wafer surface are neutralized by electron flux. The electron flux enters every rf cycle. However, depending on the plasma generation mechanism and the plasma source hardware, the flux of ions and electrons on the wafer surface can damage the device. In particular, the charge-induced damage to the gate oxide of a metal oxide semiconductor (MOS) in ULSI is a problem that becomes increasingly large. Device damage due to the electron-shading effect becomes dominant, especially when the characteristic size is smaller than 0.2 μm. This is explained in detail with reference to FIGS. 7A and 7B.

  For ease of explanation, a MOS capacitor fabricated on a silicon (Si) wafer is considered. FIG. 7A shows a longitudinal cross-sectional view of a MOS capacitor 150 with a patterned photoresist, which is in a state before plasma assisted etching is performed. FIG. 7B shows a longitudinal sectional view of the MOS capacitor 150 just before the etching is completed. The MOS capacitor 150 includes a photoresist 151, a metal layer 152, and a dielectric layer 153 on the silicon (Si) layer 154. The metal layer 152 is usually called an antenna. For illustration purposes, it is assumed that the photoresist pattern is on a line and the spacing between the photoresist lines is less than 0.20 μm.

  Next, the mechanism of device damage will be described. During plasma assisted etching, the wafer is placed in a plasma environment. A diagram of the plasma processing apparatus is not given. The rf electrode holding the wafer is given an rf current to generate a negative self-bias voltage on its surface. This causes a higher potential difference across the sheath region on the wafer. Ions in the plasma accelerate across the sheath and collide with the wafer. Usually the ions have a low energy, for example an energy lower than 3 eV when they are present in the plasma. The ions will gain large energy after being accelerated through the sheath region on the wafer surface, for example greater than 20 eV. Thus, the energy of ions impinging on the wafer surface is largely dependent on the acceleration voltage. The result is that the trajectories of the ions are almost vertical, thus they reach the bottom surface between the lines.

  The collision of ions on the bottom surface causes the metal antenna 152 to be positively charged. During the next rf period, the electrons will reach the surface of the metal antenna 152 and neutralize the positive charge. When the sheath becomes weak and zero, the electrons impact the wafer surface every rf period. The electrons in the plasma usually have an almost uniform velocity distribution in each direction. Furthermore, the electron energy in the plasma has a Maxwell distribution. That is, there are electrons having high energy, for example, energy of 50 eV. Furthermore, the average electron energy in most plasma sources exists at higher values, for example greater than 3 eV. In particular, in the capacitively coupled plasma, the average electron energy can be approximately equal to 6 eV. Similarly, in these plasmas, the number of high energy electrons increases as well, and the high energy tail in the distribution of electron energy is further extended.

  If the spacing between the photoresist lines (151) is larger, for example 0.4 μm, there will be no problem with the etching. This is because the electron flux reaches the metal antenna 152 and neutralizes the positive charge. However, this condition changes as the spacing between lines (151) becomes smaller. This state is shown in FIG. 7B. Even if the spacing between the lines (151) is smaller, the ions reach the bottom surface and their trajectories are almost vertical. This results in an electric field from the metal antenna 152 to the photoresist 151. The electrons can be accelerated by this electric field and can reach the bottom of the groove. However, if the energy of the electrons is higher, they do not have enough space and time for acceleration by the electric field and will deviate from their own trajectories. Therefore, almost all the electrons 156 collide with the photoresist 151. Only a smaller percentage of electrons (155) reach the bottom 152a of the groove. This phenomenon is called “electronic shadow effect”. This causes the positive charge on the metal antenna 152 to gradually increase. When the positive charge on the metal antenna 152 exceeds the break voltage of the gate dielectric 153a of the dielectric layer 153, current flows through the gate dielectric 153a. A detailed description of the electron shadow effect and the associated plasma induced damage is given by Non-Patent Documents 1 and 2 described below.

  In order to avoid electron shadowing effects, the electron energy in the plasma must be as low as possible. Low energy electrons, such as those with energy less than 2 eV, act in two different ways to reduce the electron shadow effect. The first effect is that due to the low energy of the electrons, their trajectories are changed by a positive electric field generated by excessive ions on the metal antenna. Therefore, these low energy electrons can reach the metal antenna and neutralize its surface. The second effect of low energy electrons is that they have a higher recombination cross section for neutral atoms or molecules. This creates negative ions with very low energy. These negative ions also contribute to neutralizing the surface of the metal antenna.

  However, there are a large number of high energy electrons that are generally unavoidable in conventional plasma sources, which makes it difficult to avoid the aforementioned electron shadowing effect.

Next, in view of the above-mentioned problems related to the conventional plasma source, the applicant filed a patent application on February 12, 2003, and the patent application is executed in the wafer processing unit as shown in Patent Document 1. Disclosed is a radical assisted dry etching apparatus utilizing a Penning ionization process. In addition, as another related prior art, the following Patent Document 2 exists. This patent document discloses a cold electron emission semiconductor element comprising a silicon substrate, a porous silicon layer, an Au thin film electrode, an ohmic electrode, and a collector electrode.
JP 2004-193359 A Japanese Patent No. 3226745 K. Hashimoto, “Charge Damage Caused by Electron Shading Effect”, Japan Society of Applied Physics, 1994, 33, 6013-6018 K. Hashimoto, “New phenomenon of charge damage in plasma etching: High damage only through dense line antenna”, Japan Society of Applied Physics, 1993, 32, 6109-6113

  It is an object of the present invention to provide a plasma processing apparatus and method which can limit the electron shadow effect and is configured as a wafer process without damage without generating high energy ions or electrons.

  The plasma processing apparatus and method according to the present invention are configured as follows to achieve the above-described object.

  The plasma processing apparatus includes a plasma generation unit including a plasma generation mechanism, a wafer processing unit in which a wafer to be processed is disposed on a lower electrode in a wafer holder, and a wafer processing unit by separating the plasma generation unit and the wafer processing unit. A filter for removing undesired ions and electrons arriving at, a top electrode disposed on the plasma generation unit and having a surface for emitting electrons, and a gas introduction unit for introducing gas into the plasma generation unit, And a gas inlet for introducing a process gas into the wafer processing unit.

In the above plasma processing apparatus, preferably, the surface portion of the upper electrode has a porous layer of nanocrystalline polysilicon, a very thin SiO ₂ layer, and a thin metal layer.

  In the above plasma processing apparatus, the thin metal layer on the upper electrode and the filter are preferably given a positive DC voltage to generate and accelerate hot electrons toward the filter.

  In the above plasma processing apparatus, the filter is preferably a metal grid.

  In the above plasma processing apparatus, the porous silicon layer is preferably replaced with another different material, which emits electrons when an electric field is applied.

  The plasma processing apparatus separates the plasma generation unit including the plasma generation mechanism, the wafer processing unit in which the wafer to be processed is disposed on the lower electrode in the wafer holder, and the plasma generation unit and the wafer processing unit. A filter that removes unwanted ions and electrons arriving at the part, a light emitting unit that emits light in the ultraviolet region from the infrared region, and is fixed between the filter and the lower electrode at the location of the wafer processing unit, A gas introduction unit for introducing a gas into the plasma generation unit and a gas introduction port for introducing a process gas into the wafer processing unit.

  In the above plasma processing apparatus, preferably, the light emitted from the light emitting unit interacts with the excited atoms and / or radicals to generate ions, and the wafer disposed on the lower electrode is Processed with the assistance of the ions.

  In the above plasma processing apparatus, the filter preferably includes a gas inlet for introducing a process gas.

  In the plasma processing apparatus, the light emitted from the light emitting unit preferably travels substantially parallel to the surface of the wafer, and the wafer is not directly exposed to light.

  In the plasma processing apparatus, preferably, the light emitting unit emits laser light having a fixed or variable frequency.

  A plasma processing method implemented in a reaction vessel having a plasma generation unit separated from a wafer processing unit by a filter includes a step of generating plasma in the plasma generation unit, and a wafer processing unit through only a radical contained in the plasma through the filter. And the step of generating ions by the interaction of radicals with the light emitted from the light emitting unit in the wafer processing unit, and the step of processing the wafer with the assistance of the ions.

  In the above plasma processing method, the light is preferably laser light parallel to the wafer surface.

  In accordance with the present invention, a plasma processing apparatus is invented in which electrons are accelerated only to obtain sufficient energy for ionized atoms / molecules. As a higher fraction of the energy of the electrons is consumed in creating ions, the result is an excited state of atoms / molecules and radicals where the electrons do not have high energy.

  According to the present invention, a plasma processing apparatus based on porous silicon generates plasma with low energy electrons. Since only two DC power sources are used, the configuration of the plasma processing apparatus is simplified and can be made at a lower cost.

  Furthermore, the plasma processing apparatus or method according to the present invention is invented for wafer processing where ions and low energy electrons are generated by the interaction of light with gaseous radical / excited atoms and are not damaged. Since the energy of light is consumed to make ions from radicals or excited atoms, the generated electrons will inevitably have very low energy. Since this process does not produce high energy ions or electrons, the electron shadow effect and device damage are eliminated.

In the following, preferred embodiments will be described with reference to the drawings. Details of the present invention will be made clear through the description of the embodiments.
[Embodiment 1]

  A first embodiment of the present invention will be described with reference to FIGS. A longitudinal sectional view of the first embodiment is shown in FIG. In FIG. 1, the plasma processing apparatus 1 basically includes a plasma generation unit 100 and a wafer processing unit 200. These two parts 100 and 200 form a reaction vessel or chamber 11 of the plasma processing apparatus 1. In the reaction vessel 11, the plasma generation unit 100 is on the upper side, and the wafer processing unit 200 is on the lower side. Portion 100 creates a plasma generation region (or space), while portion 200 creates a wafer processing region (or space).

  The reaction vessel 11 includes an electrode 21, a metal grid 22, a wafer holder 23, a plurality of gas inlets 24, and a gas outlet 25. The metal grid 22 functions as a filter that separates the reaction vessel 11 into the two parts 100 and 200 described above. The metal grid 22 has a number of openings or holes. The electrode 21 is provided in the plasma generation unit 100, and the wafer holder 23, the gas introduction port 24, and the gas discharge port 25 are provided in the wafer processing unit 200.

  The wafer 15 to be processed is disposed on the lower electrode provided on the wafer holder 23 in the wafer processing unit 200.

  The electrode 21 includes a metal plate 26 and a porous silicon (Si) layer 27. The porous silicon layer 27 is provided on the lower surface of the metal plate 26. The electrode 21 is electrically insulated from other parts of the reaction vessel 11 by being disposed on the dielectric material 12. The thickness of the metal plate 26 is not an important matter, and is selected to be a thickness sufficient to withstand the pressure difference between the inside and the outside of the reaction vessel 11. The type of metal used for the electrode 21 is likewise not important. Usually, aluminum is used as the metal. The metal plate 26 is electrically grounded and may or may not include a cooling device. Normally, the plasma processing apparatus 1 does not require a cooling device for the metal plate 26. The reason is that the electrode 11 does not receive excessive heat. The electrode 11 is heated only by ohmic heating based on the DC current flowing through the metal plate 26 and the porous silicon layer 27.

  The porous silicon layer 27 is formed as follows. First, an undoped nanocrystalline polysilicon layer (nc-poly-Si) is deposited on the metal plate 26. The undoped nanocrystalline polysilicon layer (nc-poly-Si) is then anodized by placing it in a Hf solution diluted with ethanol. For details of the anodizing process, see, for example, the document “T. Komoda, X. Sheng, N.M. Koshida, “Mechanism of Efficient and Stable Surface Emission Cold Cathode Based on Porous Polycrystalline Silicon Film”, Japan Vacuum Science and Technology, B17 (3), 1076 (1999) ”.

  The thickness of the undoped nc-poly-Si layer is not critical. However, this thickness is made as small as possible. The diameter and height of the porous 27a in nc-poly-Si are likewise not important.

  The undoped nc-poly-Si does not necessarily have to be deposited directly on the metal plate 26. Alternatively, doped polysilicon can be deposited first, followed by undoped nc-poly-Si. Furthermore, nc-poly-Si can be deposited on an n-type or p-type silicon substrate, and then the silicon substrate can be fixed on the lower surface of the metal plate 26. Furthermore, the porous silicon layer 27 can be replaced with other different materials. These are, for example, oxides or carbons such as diamond, which behave like porous silicon. That is, when an electric field is applied, these materials also emit hot electrons into the vacuum as well.

A very thin SiO ₂ layer 28 exists on the surface of the porous silicon layer 27. This layer 28 is typically made by rapid thermal annealing under an oxygen atmosphere. A very thin gold electrode 29 is formed on the surface of the thin SiO ₂ layer 28. This gold electrode 29 is usually a transparent gold layer, which is made as thin as possible. The following must be noted: It should be noted that even if the metal plate 26 is electrically grounded, the thin metal layer 29 must not be electrically grounded.

The metal grid 22 is arranged below the electrode 21 at intervals of several mm, usually less than 10 mm. The metal grid 22 is typically a metal mesh made of very thin metal wires. The dimensions of the rectangular openings (or holes) in the metal grid 22 are not critical. Usually, the size of the opening of the metal grid 22 is approximately 1 × 1 mm ² or less.

  The gold electrode 29 and the metal grid 22 are separately connected to the DC power sources 13 and 14, respectively. Both the gold electrode 29 and the metal grid 22 are given a positive voltage. The positive voltage of the metal grid 22 is larger than the positive voltage on the gold electrode 29. The value of the voltage is not critical and can be in the range of tens to hundreds of volts.

  According to the above-described plasma processing apparatus of the first embodiment, first, the wafer processing unit 200, that is, the reaction vessel 11 is evacuated to a low pressure, and an appropriate gas is supplied to achieve a desired low pressure. Maintained. The internal pressure of the wafer processing unit 200 is not an important matter. Usually, pressures below 50 mTorr (6.65 Pa) are desirable for most wafer processing.

Both the gold electrode 29 and the metal grid 22 are given a positive voltage, and the voltage on the metal grid 22 is higher than the voltage of the gold electrode 29. When the gold electrode 29 is given a positive voltage, electrons (hot electrons) are emitted from the porous silicon layer 27 and accelerated toward the gold electrode 29. Due to the positive electric field applied across the thin SiO ₂ layer 28, the hot electrons gain higher energy and pass through the SiO ₂ layer 28 and the gold electrode 29 into the vacuum.

Electrons emitted from the porous silicon layer 27 are accelerated toward the metal grid 22 due to the high positive voltage to obtain energy. The applied voltage applied to the metal grid 22 controls the energy of the electrons. Some of the high energy electrons terminate on the metal grid 22 while the remaining high energy electrons are transmitted through the openings in the metal grid 22 and ionize gaseous atoms / molecules in the wafer processing unit 200. This creates a plasma. The ionization potential differs depending on the gas, for example, argon (Ar), nitrogen (N ₂ ), and oxygen (O ₂ ) have ionization potentials of 15.75 eV, 14.53 eV, and 13.61 eV, respectively. ing. If the energy of the electrons exceeds the ionization energy, the gaseous atoms / molecules are ionized by collision with the electrons. It should be noted that each of the collisions does not contribute to the ionization process; instead, electron-atom collisions result in the separation of excited atoms or molecules into radicals. Thus, during an electron-atom collision, the electron energy is consumed because of the collision, resulting in very low energy electrons. The internal pressure of the wafer processing unit 200 or the distance between the metal grid 22 and the wafer 15 is adjusted so that each electron will experience more than two collisions before reaching the wafer 15. The This technique prevents high energy electrons from reaching the wafer 15.

  The ions, excited atoms / molecules, and radicals can be used to deposit a film on the surface of the wafer 15 disposed on the lower electrode 16 of the wafer holder 23. This film deposition is called chemical vapor deposition. Again, the gaseous species described above can also be used for dry etching of thin layers on the wafer surface. In the case of dry etching, an rf bias is applied to the lower electrode 16 on which the wafer 15 is disposed in order to generate a negative self-bias on the wafer surface. The rf power supply for the bottom electrode 16 and the necessary electrical circuits are not shown in the figure.

For the reasons described above with respect to the first embodiment, there are no high energy electrons in the plasma. Therefore, the electronic shadow effect described in the background section does not exist. This results in an etching process that does not cause damage.
[Embodiment 2]

  Next, a second embodiment of the plasma processing apparatus according to the present invention will be described with reference to FIG. Similarly, the plasma processing apparatus 1 shown in FIG. 3 has a plasma generation unit 100 and a wafer processing unit 200. These two parts 100 and 200 form a reaction vessel 31 of the plasma processing apparatus 1.

  The filter 32 separates the two parts 100 and 200 in the reaction vessel 31. The filter 32 has a plurality of through holes 33. In addition, the reaction vessel 31 of the plasma processing apparatus 1 includes a wafer holder 34, a side wall 35, a top plate 36, a bottom plate 37, and an exhaust port 52. The wafer holder 34 is provided on the bottom plate 37, and the side wall 35 preferably has a cylindrical shape. A light emitting unit 61 is provided on the side wall 35 of the wafer processing unit 200.

  In the plasma generation unit 100, a capacitively coupled plasma (CCP) generation mechanism is provided. The plasma generation unit 100 includes an rf electrode 38, a dielectric material 39 that covers the rf electrode 38 except the lower surface, a cavity 40 defined by the rf electrode 38, a filter 32, and a sidewall 35, which generate plasma. Used to

  The rf electrode 38 is supplied with rf current from the rf generator 41 through the matching circuit 42. The frequency of the rf current is not critical for the intended application of the invention. The frequency of the rf current can be in the range of 10 MHz to 300 MHz.

  The rf electrode 38 is made of metal and is usually made of aluminum (Al). A thin gas reservoir 43 is provided in the rf electrode 38. The plurality of gas inlets 44 are formed to introduce the material gas from the gas reservoir 43 into the cavity 40 as the plasma generation region described above. The material gas is supplied from the outside to the gas reservoir 43 via the gas introduction pipe 56. This gas introduction method is one of many different gas introduction methods. It is therefore possible to use different methods for introducing the gas into the plasma generation region. The gas introduced into the plasma generating region can be any gas or a combination of gases. Usually, an inert gas, typically argon (Ar), is used as the plasma generating gas. The gas pressure outside the plasma generation region or cavity 40 is not critical and can be varied from 1 mTorr to atmospheric pressure. The pressure required for wafer processing in the wafer processing region basically determines the internal pressure of the plasma generation region or cavity 40.

  The side wall and upper surface of the rf electrode 38 are covered with a dielectric material 39 in order to electrically insulate from other parts of the reaction vessel 30. The diameter of the rf electrode 38 is not critical and varies depending on the diameter of the wafer. For example, the diameter of the rf electrode 38 can be as large as 400 mm if the wafer diameter is 300 mm. The diameter of the cylindrical side wall 35 is also dependent on the diameter of the wafer as well. The height of the plasma generation cavity 40 indicated by the symbol “h” in FIG. 3 is preferably selected within the range of 1 cm to 10 cm.

  Even though the second embodiment has been described with respect to the use of capacitively coupled plasma, it may also be used for other techniques for generating plasma, such as inductively coupled plasma, wave heated plasma, or electron cyclotron plasma. it can. The plasma generation mechanism in the plasma generation unit 100 is not important in the present invention.

  The bottom plate of the plasma generation unit 100 is the above-described filter 32 made of a metal member or a dielectric member. Typically, the filter 32 is made of a dielectric material. The thickness of the filter 32 is not an important matter and can be varied in the range of 1 mm to 20 mm. The filter 32 has a plurality of through holes 33. The diameter of the through hole 33 is approximately 1 mm. The number of through holes 33 in the filter 32 is not an important matter and can be changed according to the diameter of the filter. The diameter of the filter 32 is larger than the diameter of the wafer and can be increased to the diameter of the sidewall 35. A detailed description of the plasma generation region can be found in, for example, Japanese Patent Application Laid-Open No. 2000-345349.

  The wafer holder 34 includes an rf electrode 45, a dielectric member 46, an outer ring 47, and a holder side wall 48. The rf electrode 45 is made of metal, typically aluminum (Al). An electrostatic chuck (ESC) is provided on the upper surface of the rf electrode. However, the ESC of the rf electrode 45 is not a requirement for the intended application of this system. The rf electrode 45 is supplied with an rf current from the rf generator 50 via the matching circuit 49. The frequency of the rf current is not critical and exists in the range of 100 kHz to 10 MHz. Typically, a low rf frequency of approximately 2 MHz is provided for the rf electrode 45 to obtain the expected results of the present invention.

  A plurality of gas inlets 53 are formed to introduce a process gas or a mixture of process gases into the wafer processing region 51. In addition, an evacuation port 52 exists for the wafer processing region 51.

  The plasma generation region 54, i.e., the cylindrical sidewall 35 of the cavity 40, may extend to the wafer processing region 51. These two regions 51, 54 can also have cylindrical side walls with different diameters.

  In the light emitting unit 61, the light source 62 may be all around the side wall, or several separate light sources 62 may exist separated from each other around the side wall. Alternatively, the light source 62 is provided only in one-half of the side wall, and the other half of the side wall is formed so as to absorb the collision light in the cavity. As a result, the reflected light in the wafer processing unit 200 is reflected. Can be minimized. The light emitted from the light source 62 may emit light having a wavelength within a wide range or only a selected wavelength. Preferably, the light source emits light in the extreme ultraviolet region.

  The light source 62 is preferably located several centimeters behind the side wall so that direct light coming from the light emitting unit 61 does not strike the wafer surface. It is also possible to use an appropriately configured lens to obtain a parallel light beam. The light beam is parallel to the surface of the wafer. Further, a laser radiation source can be used as the light source 62. The laser light source preferably emits linear light in a continuous mode or a pulsed mode. When a laser light source is used, it is preferably provided only on one-half on the side wall. The basic intent of obtaining a light beam that is focused and parallel to the wafer surface is to avoid direct light hitting the wafer surface. This is to eliminate device damage due to photo support.

  Next, the operation of the above plasma processing apparatus will be described. First, plasma is generated by using an appropriate material gas introduced from the reservoir 43 through the gas inlet 44 in the plasma generation region 54 or cavity 40. There are ions, electrons, gas atoms, and atoms in a neutral excited state in the plasma in the plasma generation region 51. These gas components in the plasma generation region 54 flow to the wafer processing region 51 through the through holes 33 of the filter 32. This is because the entire system is exhausted through the vacuum exhaust port 52 disposed in the wafer processing region 51. As ions and electrons travel through the through hole 33 of the filter 32, they combine on the side wall of the through hole 33. The height of the through-hole 33, that is, the thickness of the filter 32 and the diameter of the through-hole 33 are appropriately selected for complete recombination of ions inside the through-hole 33. That is, there are no ions or atoms arriving at the wafer processing region 51.

  There are quite stable excited states for some gases. For example, Table 1 shows a list of excited states and lifetimes for several gases. Within the plasma generation region 54, a large number of these excited states of gas atoms or radicals are present. Some of these atoms lose their energy while moving through the through-hole 33. However, some of the excited atoms survive and enter the wafer processing region 51.

Excited atoms or radicals are ionized with the help of photons with certain energy. For example, the excited state of Ar4 ³ P ₀ , which has a potential energy of 11.7 eV, which is ionized with a photon with a wavelength of 310 nm or shorter, and the additional 4 eV required for ionization Can be supplied. For example, an ArF laser is used as a photon having this energy, and the wavelength of this laser is 193 nm, but can be easily obtained. This ionization process is conceptually illustrated in FIG. 4 and can be represented by the following equation:

X * + hυ → X ⁺ + e

  Here, “X *” is an excited gas atom or radical, “hυ” is the photon energy, and “e” is an electron. The electrons generated by this process have very low energy. This is because most photon energy is consumed to eject atoms from atoms or radicals.

  In addition to the ionization mechanism described above, neutral gas atoms or radicals are also ionized by accidental photons. However, this ionization process can be ignored. This is because the photon energy for this ionization is quite insufficient. Even if this ionization process occurs, for the same reason as explained above, the emitted electrons have low energy, and most of the photon energy ionizes gas atoms or radicals. Is consumed.

  The plasma generated by the photo-assisted ionization process described above is used for dry etching or film application. In dry etching applications, the rf current is supplied to the lower rf electrode 38 on which the wafer 55 is located. Due to the weak plasma on the wafer surface, a negative self-bias is generated on the wafer surface. If the frequency of the rf current is low, for example 2 MHz, the rf power does not contribute to the generation of plasma on the wafer surface. Instead, the applied rf power is consumed to energize the ions and accelerate these ions to the surface of the wafer 55. Essentially ions have a low energy. Therefore, the energy of ions impinging on the wafer surface is largely determined by the self-bias voltage of the rf electrode 38. This creates a trajectory for vertically moving ions. This is a very important condition in etching holes and grooves with vertical sidewalls that do not bend.

  As described above, the electrons in the wafer processing region 51 have very low energy. Therefore, the electrons do not travel so fast and do not bend toward the bottom of the hole or groove by the electrostatic field at the bottom of the hole or groove. This results in a higher electron flux on the bottom, thereby resulting in complete neutralization of the positive charge. That is, the electronic shadow effect is completely eliminated, and as a result, no charge induced damage is caused to the device.

It should be noted that a higher frequency rf current, for example a 60 MHz rf current, can be applied to the lower electrode 38. It is also possible to provide the bottom electrode 38 with two rf currents that operate at two different frequencies, one at a high frequency and the other at a low frequency. In either case, the etching can be performed sufficiently. However, when a higher frequency rf current is applied to the lower electrode 38, the plasma is generated by capacitive coupling of the rf current. This cannot avoid generating high-energy electrons, which causes device damage due to the electron shadow effect. Therefore, the main condition of this radical (plasma) assisted dry etching apparatus is that the rf current applied to the lower electrode should not contribute to plasma generation in the wafer processing region 51.
[Embodiment 3]

  Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is an extension of the second embodiment. In the third embodiment, the configuration of the filter 32 that separates the plasma generation unit region 54 and the wafer processing region 51 is changed as shown in FIG. Except for the modification of the filter 32, all other hardware is the same as described in the second embodiment.

Filter 32 is made of a metal or dielectric material, preferably a dielectric material. A plurality of through holes 33 are formed in the filter 32. In addition, the gas reservoir 71 is made inside the filter 32. The gas reservoir 71 does not overlap with the through hole 33 made of the filter 32. Process gas is supplied into the gas reservoir 71 via the gas inlet 72. A plurality of gas inlets 73 are created from the gas reservoir 71 to the wafer processing region 51 in order to introduce process gas into the gas processing region 51. Using a process gas introduction technique for region 51 prevents process gas dissociation to a higher degree. The method of operation in the third embodiment is the same as that described in the second embodiment.
[Embodiment 4]

  Further, a fourth embodiment will be described with reference to FIG. Here, the plasma is generated by an inductively coupled mechanism in a plasma generation region 80 formed in a circular shape. The rf coil 81 is slightly higher than the height of the wafer and is disposed in the plasma generation region 80. The rf coil 81 is supplied with an rf current from an rf generator 82 through a matching circuit 83. The operating frequency of this rf current is not critical and can vary from 500 kHz to 100 MHz. In the fourth embodiment, the filter 84 corresponding to the filter 32 described above has a circular shape. A plurality of through holes 85 are formed on the filter 84. The shower head type gas inlet port 86 is disposed in the vicinity of the top plate 36 of the reaction vessel 31, thereby introducing a process gas or a gas mixture. The gas shower head 87 and the top plate 36 are electrically grounded.

  Except for the modification described above, all other hardware is the same as that described in the second embodiment. The method of operation is also the same as that of the embodiment except for the plasma generation mechanism. This system will also give the same results as described in the previous embodiments.

  The present invention is utilized in chemical vapor deposition processes or dry etching with low electron energy that do not cause plasma induced damage in the semiconductor industry.

This figure is a longitudinal sectional view of the first embodiment of the present invention. This figure is an enlarged longitudinal sectional view of the electrode shown in FIG. This figure is a longitudinal sectional view showing a plasma processing apparatus according to a second embodiment of the present invention. This figure shows the transition of energy level and energy state. This figure is a longitudinal sectional view showing a plasma processing apparatus according to a third embodiment of the present invention. This figure is a longitudinal sectional view showing a plasma processing apparatus according to a fourth embodiment of the present invention. This figure is a longitudinal sectional view of the MOS capacitor before etching. This figure is a longitudinal sectional view of the MOS capacitor immediately before the etching is completed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma processing apparatus 15 Wafer 16 Lower electrode 11 Reaction container (chamber)
21 Electrode 22 Metal Grid 23 Wafer Holder 26 Metal Plate 27 Porous Silicon (Si) Layer 28 SiO ₂ Layer 29 Gold Electrode 31 Reaction Vessel 32 Filter 61 Light Radiation Unit 62 Light Source

Claims (12)

A plasma generation unit including a plasma generation mechanism;
A wafer processing unit in which a wafer to be processed is disposed on a lower electrode in a wafer holder;
A filter that separates the plasma generation unit and the wafer processing unit and removes unwanted ions and electrons arriving at the wafer processing unit;
An upper electrode disposed on the plasma generator and having a surface for emitting electrons;
A gas introduction unit for introducing gas into the plasma generation unit;
A gas introduction unit for introducing a process gas into the wafer processing unit;
A plasma processing apparatus comprising: The plasma processing apparatus according to claim 1, wherein the surface portion of the upper electrode includes a polysilicon layer, a nanocrystalline polysilicon porous layer, an extremely thin SiO ₂ layer, and a thin metal layer.   The plasma processing apparatus according to claim 2, wherein the thin metal layer on the upper electrode and the filter are given a positive DC voltage for generating and accelerating hot electrons toward the filter.   The plasma processing apparatus according to claim 1, wherein the filter is a metal grid.   The plasma processing apparatus according to claim 2, wherein the porous silicon layer is replaced with another substance, and the substance emits electrons when an electric field is applied. A plasma generation unit including a plasma generation mechanism;
A wafer processing unit in which a wafer to be processed is disposed on a lower electrode in a wafer holder;
A filter that separates the plasma generation unit and the wafer processing unit and removes unwanted ions and electrons arriving at the wafer processing unit;
A light emitting unit that emits light from the infrared region to the ultraviolet region, and is fixed at a position between the filter and the lower electrode in the wafer processing unit;
A gas introduction unit for introducing gas into the plasma generation unit;
A gas inlet for introducing a process gas into the wafer processing unit;
A plasma processing apparatus comprising:   The light emitted from the light emitting unit reacts with excited atoms and / or radicals to generate ions thereof, and a wafer disposed on the lower electrode is processed with the assistance of the ions. Item 7. The plasma processing apparatus according to Item 6.   The plasma processing apparatus according to claim 6 or 7, wherein the filter includes the gas introduction port for introducing the process gas.   8. The plasma processing apparatus according to claim 6, wherein the light emitted from the light emitting unit travels substantially parallel to the surface of the wafer, and the wafer is not directly exposed to the light.   The plasma processing apparatus according to claim 6 or 7, wherein the light emitting unit emits a laser beam having a fixed or variable frequency. A plasma processing method that is performed in a reaction vessel having a plasma generation unit separated from a wafer processing unit by a filter,
Generating plasma in the plasma generator;
Passing only radicals contained in the plasma through the filter to the plasma processing unit;
Generating ions by interaction of the radicals using light emitted from a light emitting unit in the wafer processing unit;
Processing the wafer with the aid of the ions;
A plasma processing method comprising: The plasma processing method according to claim 11, wherein the light is a laser beam parallel to a surface of the wafer.

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