JP2004311510A - Device and method for microwave plasma treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for microwave plasma treatment by which the uniformity of plasma can be secured on the surface of a substrate by preventing the occurrence of a standing wave near the surface of a dielectric window without performing any complicated processing on the dielectric window. <P>SOLUTION: The dielectric window for transmitting microwave is constituted so that the surface of the window facing the substrate may be positioned at the same position as that of the internal wall surface of the ceiling section of a plasma treatment vessel or in a state where the surface is protruded to the substrate side than the position of the internal wall surface of the ceiling section. In addition, the distance between the outer peripheral section of the dielectric window and the side wall surface of the plasma treatment vessel is adjusted to at least the 1/4 of the wavelength of an introduced microwave or longer. Consequently, the uniformity of the plasma can be secured on the surface of the substrate even when no complicated processing is performed on the dielectric window. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microwave plasma processing apparatus and a processing method using the apparatus.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the miniaturization of semiconductor devices such as LSIs, plasma processing apparatuses have been frequently used in semiconductor device manufacturing processes. The uniformity of the plasma processing in the wafer surface greatly contributes to the stability of the characteristics and the yield of the semiconductor device. This plasma processing uniformity is ensured by uniformly distributing the plasma on the wafer surface. Therefore, for example, it is conceivable that the plasma is diffused by increasing the distance between the plasma generation unit of the plasma processing apparatus and the substrate to make the plasma uniform on the wafer surface.
[0003]
Among plasma processing apparatuses, recently, a microwave plasma processing apparatus that can stably excite plasma even in a high vacuum state having a relatively low pressure has been attracting attention.
[0004]
The plasma processing using this microwave plasma processing apparatus will be specifically described as an example in which a silicon surface is directly oxidized and nitrided to form a high-quality insulating film.
[0005]
When a microwave plasma processing apparatus is used, the insulating film is formed in a metal plasma processing container. An opening is formed in the ceiling of the plasma processing vessel, and a microwave transmitting dielectric window made of quartz or the like is provided in the opening in an airtight manner to introduce microwaves into the apparatus. .
[0006]
In the formation of the insulating film, if the distance between the substrate side surface of the dielectric window and the substrate is about 80 mm or less, the generated plasma is uniform according to the gas type and pressure used in the plasma processing. In some cases, the irradiation intensity of the microwave may be adjusted by an antenna.
[0007]
On the other hand, even when the plasma has a high density in the central portion or a poor uniformity such as formation of a ring-shaped high density portion, the distance between the surface of the dielectric window and the substrate is 80 mm or more. When separated, the plasma is diffused and uniformity is ensured on the substrate surface.
[0008]
By the way, when plasma is excited by the microwave plasma processing apparatus, a microwave wave called a surface wave is formed between the surface of the dielectric window and the generated plasma. This surface wave spreads over the entire surface of the dielectric window, and plasma is formed above the substrate.
[0009]
Usually, since the position of the inner wall surface of the ceiling of the plasma processing vessel projects more toward the substrate than the position of the surface of the dielectric window, the periphery of the dielectric window is formed by an opening formed in the ceiling. Section is surrounded by the section. Therefore, when the surface wave is reflected on the surrounding surface having the cross section of the opening, the surface wave and the reflected wave interfere with each other to form a standing wave near the surface of the dielectric window.
[0010]
This standing wave causes the uniformity of plasma on the substrate surface in the microwave plasma processing to be impaired. That is, there has been a problem that the plasma density at the center of the dielectric window is higher than that at the periphery of the dielectric window.
[0011]
Therefore, conventionally, the outer peripheral portion of the dielectric window and the shape of the device wall on which the dielectric window is installed are made uneven to cancel the reflected wave so that a standing wave is not generated (for example, see Patent Document 1). ).
[0012]
[Patent Document 1]
JP-A-2002-190449 (Claims)
[0013]
[Problems to be solved by the invention]
However, if the microwave irradiation intensity is adjusted by the antenna in accordance with the plasma processing at a specific gas type and pressure, and then the plasma processing is performed at a different gas type or pressure, the uniformity of the plasma is deteriorated. was there.
[0014]
Therefore, when performing plasma processing with a plurality of different gas types or pressures, the microwave irradiation intensity must be adjusted each time, so that a single adjustment cannot perform a plurality of plasma processings with different gas types or pressures. However, there is a problem that the working efficiency is reduced.
[0015]
On the other hand, if the distance between the surface of the dielectric window and the substrate is increased, uniformity on the substrate surface can be ensured, but at the same time, the plasma density on the substrate surface decreases and the amount of reactive species reaching the substrate decreases. However, there has been a problem that it takes time for the plasma processing.
[0016]
Furthermore, in order to prevent the generation of standing waves that hinder the uniformity of plasma on the substrate surface, the outer peripheral portion of the dielectric window and the shape of the side wall surface of the plasma processing vessel in which the dielectric window is installed are modified. Although the above-mentioned inconvenience can be solved by forming the unevenness, the processing technique for forming the unevenness is complicated, and there is a problem that the processing is substantially difficult.
[0017]
The present invention has been made in view of the above-described problems, and does not generate a standing wave near the surface of the dielectric window even without performing complicated processing on the dielectric window, thereby ensuring uniformity of plasma on the substrate surface. It is an object to provide a microwave plasma processing apparatus and a processing method.
[0018]
[Means for Solving the Problems]
In order to solve the above problems, the microwave plasma processing apparatus according to the present invention includes at least a plasma processing container having an open ceiling, and a microwave transmitting dielectric window provided airtightly on the ceiling, In a microwave plasma processing apparatus configured so that a substrate can be set in a plasma processing container facing the dielectric window, the surface of the dielectric window facing the substrate has an inner wall surface of a ceiling portion of the plasma processing container. It is configured to be located at the same position as the position or protruding toward the substrate side from the position of the inner wall surface of the ceiling.
[0019]
According to this configuration, since the outer peripheral portion of the dielectric window has no surrounding surface formed by a cross section of the opening formed in the ceiling portion of the plasma processing container, the surface wave is not reflected, and the standing wave is not formed. Can be suppressed.
[0020]
Therefore, a uniform plasma distribution can be obtained on the substrate surface regardless of the distance between the surface of the dielectric window and the substrate and even when the conditions such as the gas type and the pressure are changed.
[0021]
When the surface of the dielectric window facing the substrate is located closer to the substrate than the inner wall surface of the ceiling of the plasma processing vessel, the distance from the inner wall surface of the ceiling to the surface of the dielectric window is preferably at least 5 mm.
[0022]
When a ring-shaped protrusion is provided on the outer edge of the surface of the dielectric window facing the substrate, the inner surface surrounded by the protrusion is the same as the position of the ceiling inner wall surface of the plasma processing container. It may be configured so as to protrude toward the substrate side from the position or the position of the ceiling inner wall surface.
[0023]
It is preferable that the distance between the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing container is at least ４ of the wavelength of the microwave to be introduced. This provides a space for forming plasma between the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing vessel, so that microwaves are reflected toward the central portion of the dielectric window to form a standing wave. It is to suppress that.
[0024]
Therefore, for example, when the frequency of the microwave to be introduced is 2.45 GHz, the distance between the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing container may be 30 mm or more.
[0025]
Preferably, the diameter of the dielectric window is at least twice the diameter of the substrate. Further, in the case where the above-mentioned protrusion is provided on the outer peripheral portion of the dielectric window, the distance between the inner surface surrounded by the protrusion and the substrate is defined as a radius, and each circle centered on both ends of the substrate. The diameter of the dielectric window may be determined so as not to include the protrusion. The reason why the diameter of the preferable dielectric window differs depending on the presence or absence of the protrusion is to prevent the protrusion from affecting the film thickness of the substrate end.
[0026]
Further, in order to solve the above problem, in the microwave plasma processing method according to the present invention, a raw material gas for exciting plasma is supplied to a plasma processing container by a gas supply unit, and is oscillated and amplified by a microwave generation unit. Microwaves are introduced into the antenna means and irradiated, and the irradiated microwaves are introduced into the above-mentioned plasma processing vessel in a vacuum atmosphere through a microwave transmitting dielectric window, and plasma processing is performed by an electromagnetic field created by the microwaves. In a processing method for generating plasma in a container and performing microwave plasma processing on a substrate provided to face the dielectric window for microwave transmission, the plasma processing may be performed using the microwave plasma apparatus according to any of the above. It is characterized by performing.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a microwave plasma processing apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG.
[0028]
FIG. 1 is a cross-sectional view illustrating a configuration of a microwave plasma processing apparatus for a semiconductor substrate as one embodiment of the present invention. 3 and 4 are cross-sectional views illustrating a conventional general microwave plasma processing apparatus for a semiconductor substrate.
[0029]
In FIG. 1, reference numeral 1 denotes a metal plasma processing container for performing plasma processing. Above the ceiling 101 of the plasma processing vessel 1, a coaxial waveguide converter for adjusting the irradiation intensity of the microwave and the antenna 2 are provided. A slot 3 for irradiating microwaves is provided between the coaxial waveguide converter and antenna 2 and a dielectric window 4 provided airtightly in the opening of the ceiling 101. The raw material of the dielectric window 4 is quartz or the like. The dielectric window 4 transmits the microwave irradiated through the slot 3 and introduces the microwave into the plasma processing container 1.
[0030]
The microwave (2.45 GHz) is oscillated by the magnetron 5 and is introduced into the coaxial waveguide converter and the antenna 2 via the waveguide 8.
[0031]
Inside the plasma processing container 1, an electrode 13 for holding the plasma processing substrate 12 is provided at a position facing the dielectric window 4, and a high frequency power is applied to this electrode 13 from a high frequency power supply 14 as needed. The high-frequency impedance adjustment is performed by the matching unit 15.
[0032]
Next, the operation of the microwave plasma processing apparatus according to the present embodiment will be described. A gas for exciting plasma is supplied from the side of the plasma processing container 1 by gas supply means 9, the inside of the plasma processing container 1 is depressurized by the exhaust system 10, and the process pressure of the plasma processing container 1 is reduced by the pressure regulating valve 11. After the adjustment, the raw material and the reaction by-product gas are exhausted. The microwave oscillated and amplified by the magnetron 5 is introduced into the coaxial waveguide converter and the antenna 2 through the 4E tuner 7 and irradiated from the slot 3. At this time, the reflected wave is returned to the microwave processing vessel 1 by the 4E tuner 7, but the reflected wave that cannot be adjusted is absorbed by the isolator 6 to prevent the reflected wave from returning to the magnetron 5. The microwave radiated from the slot 3 is introduced into the plasma processing vessel 1 in a vacuum atmosphere through the dielectric window 4, and forms a plasma P in the plasma processing vessel 1 by an electromagnetic field generated by the microwave. With the plasma P, etching, a film formation process, and the like can be performed. Note that SWP schematically represents a surface wave of a microwave generated between the surface of the dielectric window 4 and the plasma P.
[0033]
In the case of performing the oxidation treatment using the microwave plasma treatment apparatus, for example, a rare gas such as argon or krypton is mixed with oxygen to introduce a total of 0.17 Pa · m ³ / sec (100 sccm) or more, and 1 to 133 Pa Process in the pressure range of On the other hand, in the case of performing the nitriding treatment, for example, a rare gas such as argon or krypton is mixed with ammonia, nitrogen, and hydrogen, and a total of 0.17 Pa · m ³ / sec (100 sccm) or more is introduced, and a pressure of 1 to 133 Pa is applied. Process in pressure range.
[0034]
In FIG. 1, the position of the surface of the dielectric window 4 on the side facing the substrate 12 protrudes toward the substrate 12 from the position of the inner wall surface of the ceiling 101 of the microwave processing container 1. Therefore, the surface wave SWP does not irradiate the metal surface of the side wall of the plasma processing chamber 1 nor is reflected from the metal surface, and forms antinodes and nodes at the outer peripheral portion of the dielectric window 4. When the surface of the dielectric window 4 is positioned so as to protrude toward the substrate 12 from the position of the inner wall surface of the ceiling 101, the inner wall surface of the ceiling 101 is Is preferably about 5 mm.
[0035]
The diameter of the dielectric window 4 is preferably at least twice as large as the diameter of the substrate 12. However, in the case where a projection is provided on the outer periphery of the dielectric window 4 as shown in FIG. As shown by 2, the distance between the inner surface surrounded by the protrusions and the substrate 12 is defined as a radius r, and the protrusions are not included in the respective circles c centered on both ends of the substrate 12. The diameter of the dielectric window 4 may be determined. The reason why the preferable diameter of the dielectric window 4 differs depending on the presence or absence of the protrusion is to prevent the protrusion from affecting the film thickness at the end of the substrate 4. For example, in FIG. 1, the distance between the inner surface surrounded by the protrusions and the substrate 12 is about 60 mm, and when the substrate 4 is 200 mm, the inner diameter surrounded by the protrusions of the dielectric window 4 is approximately 280 mm. It becomes.
[0036]
At this time, depending on the pressure, a wavy plasma may be formed between the outer peripheral portion of the dielectric window 4 and the side wall surface of the plasma processing container 1 when viewed from the substrate 12 side. The plasma P on the surface of the dielectric window 4 on the substrate 12 becomes uniform because power is consumed in the outer peripheral portion without affecting the processing. In this case, the distance between the outer peripheral portion of the dielectric window 4 and the side wall surface of the plasma processing container 1 may be at least one-quarter of the wavelength of the microwave to be introduced. For example, in the present embodiment, the microwave to be introduced is at 2.45 GHz, so that it is sufficient that the microwave is separated by a distance of about 30 mm or more with respect to the wavelength of 122 mm.
[0037]
In the present embodiment, as means for introducing microwaves into the microwave processing vessel 1, a coaxial waveguide converter that converts microwaves to coaxial and then irradiates through the slots 3 and the antenna 2 are used. However, as the antenna means, one having a slit in the waveguide 8 or the like can be particularly used, and is not particularly limited.
[0038]
The microwave plasma processing apparatus shown in FIGS. 3 and 4 for comparison has the same basic configuration as that of FIG. 1, and the same reference numerals in FIG. 3 denote the same components. The difference between the device shown in FIG. 3 and the device shown in FIG. 4 is that a ring-shaped protrusion is provided on the outer edge of the surface of the dielectric window 4 in FIG. 4, but this protrusion is provided in FIG. That is not done. 3 and 4, in any case, the surface of the dielectric window 4 is located farther from the substrate 12 side than the position of the inner wall surface of the ceiling 101, and therefore, around the dielectric window 4, A metal surrounding surface having a cross section of the opening formed in the ceiling 101 is formed. SWP ′ and SWP ″ are surface waves schematically represented, but both are short-circuited at the metal surrounding surface, and thus generate strong standing waves at the center. As a result, the plasma density also increases at the center of the dielectric window 4 or at a ring-shaped portion surrounding the center of the dielectric window 4, thereby impairing uniformity.
[0039]
【Example】
Hereinafter, an embodiment of the plasma processing performed using the microwave plasma processing apparatus according to the present invention will be described in comparison with the case of the conventional microwave plasma processing apparatus.
[0040]
Using the microwave plasma processing apparatus shown in FIGS. 1 and 3, the substrate 12 from which the natural oxide film was removed was diluted with 0.5% diluted hydrofluoric acid and subjected to plasma oxidation and plasma nitridation, respectively.
[0041]
Plasma oxidation was performed using Kr / O ₂ gas at a pressure of 80 Pa and a processing time of 10 minutes. On the other hand, plasma nitriding was performed using Ar / NH ₃ gas at a pressure of 8 Pa and a processing time of 7 minutes. 1 and 3, the distance between the surface of the dielectric window 4 and the substrate 12 was adjusted to 60 mm in both cases.
[0042]
After the plasma treatment, the film thickness distribution of the oxide film and the nitride film at an arbitrary position on the substrate was measured by a spectral dispersion ellipsometer, and the results were compared. FIG. 5 shows the result of the oxidation treatment, and FIG. 6 shows the result of the nitridation treatment.
[0043]
When plasma processing is performed using the microwave plasma processing apparatus according to the present invention, the film thickness distribution shows good uniformity in all cases. That is, the respective film thicknesses are constant around 71 ° to 72 ° when oxidized (FIG. 5), and constant around 46 ° to 50 ° when nitrided (FIG. 6). Although not shown, the same distribution tendency was observed in the oxidation treatment and the nitridation treatment under conditions different from those described above.
[0044]
On the other hand, when the plasma processing was performed using the microwave plasma processing apparatus of FIG. 3, it was found that the film thickness in the central portion of the substrate was increased in each case. That is, the respective film thicknesses are approximately 80 ° at the peripheral portion of the substrate when oxidized, are approximately 103 ° at the central portion of the substrate (FIG. 5), and are approximately 33 ° at the peripheral portion of the substrate when the nitriding process is performed. However, it is approximately 59 ° at the center of the substrate (FIG. 6). This is because, as indicated by SWP ′ in FIG. 3, the microwave reflected on the metal surrounding surface having the cross section of the opening formed in the ceiling 101 forms a standing wave, and the dielectric window 4 has This is probably because the plasma density at the center of the substrate has increased.
[0045]
Further, when the pressure was relatively high at 80 Pa, a wave-like plasma was formed between the outer peripheral portion of the dielectric window 4 of the microwave plasma processing apparatus of FIG. This is because the distance between the outer peripheral portion of the dielectric window 4 and the side wall surface of the plasma processing vessel 1 is separated by a quarter or more of the wavelength of the microwave to be introduced. In the apparatus, the microwave is reflected to the center of the dielectric window 4, whereas in the apparatus of FIG. 1, the microwave is reflected between the outer periphery of the dielectric window 4 and the side wall surface of the plasma processing vessel 1. This is presumably because plasma was formed to prevent microwaves from being reflected at the center of the dielectric window 4.
[0046]
【The invention's effect】
As is clear from the above description, in the present invention, in the plasma processing using microwaves, the surface of the dielectric window facing the substrate is placed at the same position as the position of the inner wall surface of the ceiling of the plasma processing vessel or the inner wall surface of the ceiling. The distance between the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing container is set to be at least one quarter of the wavelength of the microwave, so that the plasma The standing wave which has caused the uniformity of the laser to be reduced can be suppressed. Therefore, even when the distance between the surface of the dielectric window and the substrate is short, uniformity of the plasma processing can be ensured, and even if the gas type or pressure is changed, the configuration of the apparatus is not adjusted each time. Processing with high plasma uniformity can be performed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a microwave plasma processing apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing how to determine the diameter of a dielectric window when a protrusion is provided. FIG. 3 is a cross-sectional view of a conventional microwave plasma processing apparatus.
FIG. 4 is a cross-sectional view of a conventional microwave plasma processing apparatus (in which a ring-shaped protrusion is provided on the outer edge of the surface of a dielectric window).
FIG. 5 is a view showing a film thickness distribution when a silicon substrate is subjected to plasma oxidation processing using the apparatus of FIGS. 1 and 3; FIG. 6 is a plasma nitridation of a silicon substrate using the apparatus of FIGS. 1 and 3; The figure which shows the film thickness distribution at the time of processing.
DESCRIPTION OF SYMBOLS 1 Plasma processing container 2 Coaxial waveguide converter and antenna 3 Slot 4 Dielectric window 5 Magnetron 6 Isolator 7 4E tuner 8 Waveguide 9 Gas supply means 10 Exhaust pump 11 Pressure regulating valve 12 Substrate 13 Electrode 14 High frequency power supply 15 Matching device P plasma SWP surface wave

Claims (8)

A plasma processing vessel having an open ceiling, and at least a microwave-transmitting dielectric window hermetically provided on the ceiling, so that a substrate can be installed in the plasma processing vessel facing the dielectric window. In the microwave plasma processing apparatus configured as described above, the surface of the dielectric window facing the substrate projects to the substrate side at the same position as the position of the ceiling inner wall surface of the plasma processing vessel or the position of the ceiling inner wall surface. A microwave plasma processing apparatus characterized in that the microwave plasma processing apparatus is configured to be positioned at a right angle. 2. The microwave plasma according to claim 1, wherein the surface of the dielectric window facing the substrate is configured to project at least 5 mm from the position of the inner wall surface of the ceiling of the plasma processing vessel toward the substrate. Processing equipment. When a ring-shaped protrusion is provided on the outer edge of the surface of the dielectric window facing the substrate, the inner surface surrounded by the protrusion is located at the same position as the position of the inner wall surface of the ceiling of the plasma processing vessel. 3. The microwave plasma processing apparatus according to claim 1, wherein the microwave plasma processing apparatus is configured to protrude toward the substrate side from the position of the ceiling inner wall surface. 4. The plasma processing apparatus according to claim 1, wherein a distance between an outer peripheral portion of the dielectric window and a side wall surface of the plasma processing container is at least ４ of a wavelength of the microwave to be introduced. The microwave plasma processing apparatus according to any one of the above. 5. The microwave according to claim 4, wherein, when the frequency of the introduced microwave is 2.45 GHz, the distance between the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing container is 30 mm or more. Plasma processing equipment. 6. The microwave plasma processing apparatus according to claim 1, wherein the diameter of the dielectric window is at least twice the diameter of the substrate. In the case where the dielectric window is provided with the protruding portion according to claim 3, the distance between the inner surface surrounded by the protruding portion and the substrate is defined as a radius, and each of the circles is centered on both ends of the substrate. 6. The microwave plasma processing apparatus according to claim 2, wherein the diameter of the dielectric window is determined so as not to include the protrusion. The source gas for exciting the plasma is supplied to the plasma processing container by the gas supply unit, and the microwave oscillated and amplified by the microwave generation unit is introduced into the antenna unit and irradiated, and the irradiated microwave is applied to the microwave. The microwave is introduced into the plasma processing container in a vacuum atmosphere through a dielectric window for wave transmission, and a plasma is generated in the plasma processing container by an electromagnetic field generated by the microwave. A microwave plasma processing method using a microwave plasma apparatus according to any one of claims 1 to 7, wherein the plasma processing is performed on the provided substrate.

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