JP4261236B2 - Microwave plasma processing apparatus and processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microwave plasma processing apparatus and a processing method using the apparatus.
[0002]
[Prior art]
In recent years, with the miniaturization of semiconductor devices such as LSI, plasma processing apparatuses are frequently used in the manufacturing process of semiconductor devices. The uniformity of the plasma processing in the wafer surface greatly contributes to the stability of the characteristics of the semiconductor device and the yield. The uniformity of this plasma treatment is ensured by uniformly distributing the plasma on the wafer surface. In view of this, for example, it is conceivable to divide the plasma to make it uniform on the wafer surface by increasing the distance between the plasma generation unit of the plasma processing apparatus and the substrate.
[0003]
Among plasma processing apparatuses, recently, a microwave plasma processing apparatus that can stably excite plasma even in a high vacuum state at a relatively low pressure has attracted attention.
[0004]
The plasma processing using this microwave plasma processing apparatus will be specifically described by taking as an example the case where 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 container, and a microwave transmitting dielectric window made of quartz or the like is hermetically provided in the opening to introduce microwaves into the apparatus. .
[0006]
When the insulating film is formed, 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 treatment. In some cases, the intensity of microwave irradiation is adjusted by an antenna.
[0007]
On the other hand, the distance between the surface of the dielectric window and the substrate should be 80 mm or more even when the plasma is dense at the center or when the uniformity is poor, such as when a ring-shaped high-density part is formed. By separating, 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 across the dielectric window, and plasma is formed above the substrate.
[0009]
Usually, since the position of the inner wall surface of the ceiling portion of the plasma processing container protrudes closer to the substrate than the position of the surface of the dielectric window, the periphery of the dielectric window is an opening formed in the ceiling portion. Surrounded by the cross section of the part. Therefore, when the surface wave is reflected on the surrounding surface formed by the opening cross section, 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 is a cause of hindering the uniformity of the plasma on the substrate surface in the microwave plasma processing. 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 shape of the outer peripheral portion of the dielectric window and the wall surface of the device on which the dielectric window is installed is made uneven to cancel the reflected wave so that no standing wave is generated (see, for example, Patent Document 1). ).
[0012]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-190449 (Claims)
[0013]
[Problems to be solved by the invention]
However, if the plasma treatment is performed with a different gas type or pressure after adjusting the microwave irradiation intensity with an antenna corresponding to the plasma treatment with a specific gas type and pressure, the plasma uniformity is deteriorated. was there.
[0014]
Therefore, when plasma processing is performed with a plurality of different gas types or pressures, the microwave irradiation intensity must be adjusted each time. Therefore, a plurality of plasma processing with different gas types or pressures cannot be performed with a single adjustment. There was a problem that work efficiency was lowered.
[0015]
On the other hand, if the distance between the surface of the dielectric window and the substrate is increased, the 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 plasma processing takes time.
[0016]
Furthermore, in order not to generate a standing wave that causes the plasma uniformity on the substrate surface to be disturbed, the shape of the outer peripheral portion of the dielectric window and the side wall surface of the plasma processing vessel in which the dielectric window is installed are changed. Although the above-described inconvenience is solved by making it uneven, there is a problem that the processing technology for making the uneven shape is complicated and the processing is substantially difficult.
[0017]
In view of the above problems, the present invention can prevent the standing wave from being generated in the vicinity of the surface of the dielectric window and ensure the uniformity of the plasma on the substrate surface without performing complicated processing on the dielectric window. It is an object to provide a microwave plasma processing apparatus and a processing method.
[0018]
[Means for Solving the Problems]
To solve the above problem, a microwave plasma processing apparatus according to the present invention comprises a plasma processing chamber ceiling is opened, and a dielectric window for microwave transmission provided hermetically the ceiling, the substrate dielectric to face the window plasma processing chamber is disposed, the surface of the dielectric window, the substrate side of a position of the ceiling portion in the same position or or the ceiling portion inner wall surface and the position of the wall of the plasma processing chamber In the microwave plasma processing apparatus configured to protrude and be positioned on the dielectric window, the dielectric window includes a ring-shaped protrusion on the outer edge of the surface, and an inner surface surrounded by the protrusion, It is located at the same position as the position of the inner wall surface of the ceiling of the plasma processing container or the position of the inner wall surface of the ceiling so as to protrude toward the substrate, and the front surface from the inner surface surrounded by the protrusion. The distance to the substrate and the radius, and characterized in that constructed defines the diameter of the dielectric window so that it does not contain the projecting portions in the respective circle centered on the substrate end portions.
[0019]
According to this configuration, the outer peripheral portion of the dielectric window does not have an enveloping surface formed of a cross section of the opening formed in the ceiling portion of the plasma processing container, so that the surface wave is not reflected and a standing wave is formed. Can be suppressed.
[0020]
Therefore, a uniform plasma distribution can be obtained on the substrate surface regardless of the distance between the dielectric window surface and the substrate, and even if the conditions such as the gas type and pressure are changed.
[0025]
The reason why the preferred dielectric window diameter varies depending on the presence or absence of the protruding portion is to prevent the protruding portion from affecting the film thickness of the end portion of the substrate.
[0026]
In order to solve the above problems, a microwave plasma processing method according to the present invention supplies a source gas for exciting plasma by a gas supply means to a plasma processing vessel, and the microwaves oscillated and amplified by the microwave generation means. Is introduced into the plasma processing container in a vacuum atmosphere through a dielectric window for microwave transmission, and plasma is generated in the plasma processing container by the electromagnetic field generated by the microwave. In the processing method of performing microwave plasma processing on a substrate provided oppositely, the dielectric window is secretly provided on the opening of the plasma processing container, and a ring shape is formed on the outer edge of the surface of the dielectric window. The inner surface surrounded by the protrusion is the same position as the inner wall surface of the ceiling of the plasma processing container or Each of the circles is configured to protrude from the inner wall surface of the well to the substrate side, and the radius from the inner surface surrounded by the protrusion to the substrate is the center of each circle. The diameter of the dielectric window is determined so that the protruding portion is not included therein, and plasma processing is performed by introducing a microwave into the plasma processing container through the dielectric window.
[0028]
FIG. 1 is a cross-sectional view showing a configuration of a microwave plasma processing apparatus for a semiconductor substrate as an embodiment of the present invention. 3 and 4 are sectional views showing a conventional microwave plasma processing apparatus for a general semiconductor substrate.
[0029]
In FIG. 1, reference numeral 1 denotes a metal plasma processing vessel for performing plasma processing. A coaxial waveguide converter and an antenna 2 for adjusting the irradiation intensity of the microwave are provided above the ceiling portion 101 of the plasma processing container 1. A slot 3 for irradiating microwaves is provided between the coaxial waveguide converter / antenna 2 and the dielectric window 4 provided in an airtight manner 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 introduced into the coaxial waveguide converter and the antenna 2 through the waveguide 8.
[0031]
Inside the plasma processing container 1, there is an electrode 13 that holds the plasma processing substrate 12 at a position facing the derivative window 4, and a high frequency is applied to the electrode 13 from a high frequency power source 14 as necessary. The high frequency impedance adjustment is performed by the matching unit 15.
[0032]
Next, the operation of the microwave plasma processing apparatus in this embodiment will be described. A gas for exciting plasma is supplied from the side surface of the plasma processing container 1 by the 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 adjusted by the pressure adjustment valve 11. Adjust and exhaust the feedstock and reaction byproduct gas. The microwaves oscillated and amplified by the magnetron 5 are 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 container 1 by the 4E tuner 7, but the reflected wave that cannot be adjusted is absorbed by the isolator 6 and prevented from returning to the magnetron 5. The microwave irradiated from the slot 3 is introduced into the plasma processing container 1 in a vacuum atmosphere through the dielectric window 4, and plasma P is formed in the plasma processing container 1 by the electromagnetic field generated by the microwave. With this plasma P, etching, film formation process, and the like can be performed. SWP schematically represents a surface wave of a microwave generated between the surface of the derivative window 4 and the plasma P.
[0033]
When the oxidation treatment is performed using the above microwave plasma processing apparatus, for example, a rare gas such as argon or krypton and oxygen are mixed to introduce a total of 0.17 Pa · m ³ / sec (100 sccm) or more to 1 to 133 Pa. In the pressure range. On the other hand, when performing 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 1 to 133 Pa is applied. Process in the pressure range.
[0034]
In FIG. 1, the position of the surface of the dielectric window 4 on the side facing the substrate 12 protrudes closer to the substrate 12 than the position of the inner wall surface of the ceiling portion 101 of the microwave processing container 1. Accordingly, the surface wave SWP does not irradiate the metal surface on the side wall of the plasma processing container 1 or is reflected from the metal surface, and forms an antinode and a node at the outer peripheral portion of the dielectric window 4. Note that when the surface of the dielectric window 4 protrudes toward the substrate 12 rather than the position of the inner wall surface of the ceiling portion 101, the inner wall surface of the ceiling portion 101 extends from the surface of the dielectric window 4. The distance 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, but when the protrusion is provided on the outer periphery of the dielectric window 4 as shown in FIG. 2, the distance between the inner surface surrounded by the protrusions and the substrate 12 is a radius r, and the protrusions are not included in the respective circles c centering on both ends of the substrate 12. The diameter of the dielectric window 4 may be determined. The reason why the diameter of the dielectric window 4 is preferably different 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, when the distance between the inner surface surrounded by the protrusions in FIG. 1 and the substrate 12 is about 60 mm and the substrate 4 is 200 mm, the inner diameter surrounded by the protrusions of the dielectric window 4 is about 280 mm. It becomes.
[0036]
At this time, depending on the pressure, when viewed from the substrate 12 side, 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 vessel 1, which is caused by the plasma on the surface of the substrate 12. The plasma P on the surface of the dielectric window 4 on the substrate 12 becomes uniform because power is consumed at 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 separated by a quarter or more of the wavelength of the microwave to be introduced. For example, in the present embodiment, since the microwave to be introduced is 2.45 GHz, the distance of about 30 mm or more may be separated from the wavelength of 122 mm.
[0037]
In the present embodiment, as a means for introducing the microwave into the microwave processing container 1, the coaxial waveguide converter and the antenna 2 that irradiates through the slot 3 after converting the microwave to the coaxial are used. However, as the antenna means, there can be used in particular those having a slit in the waveguide 8, and the antenna means is not particularly limited.
[0038]
3 and 4 shown for comparison have the same basic configuration as that of FIG. 1, and the same reference numerals as those in FIG. 1 denote the same components. 3 is different from the apparatus of FIG. 4 in that a ring-shaped protrusion is provided on the outer edge of the surface of the dielectric window 4 in FIG. 4, whereas this protrusion is provided in FIG. This is not done. 3 and 4, since the position of the surface of the dielectric window 4 is farther from the substrate 12 side than the position of the inner wall surface of the ceiling portion 101 in both cases, the periphery of the dielectric window 4 is A metal enveloping surface having a cross section of the opening formed in the ceiling portion 101 is formed. SWP ′ and SWP ″ are surface waves schematically represented, but since both are short-circuited by the metal surrounding surface, a strong standing wave is generated in the central portion. As a result, the plasma density also increases at the center of the dielectric window 4 and the ring-shaped portion surrounding the center of the dielectric window 4, and the uniformity is impaired.
[0039]
【Example】
Hereinafter, embodiments of plasma processing performed using the microwave plasma processing apparatus according to the present invention will be described in comparison with the case of a conventional microwave plasma processing apparatus.
[0040]
The substrate 12 from which the natural oxide film was removed was subjected to plasma oxidation treatment and plasma nitridation treatment with 0.5% diluted hydrofluoric acid using the microwave plasma processing apparatus of FIGS. 1 and 3, respectively.
[0041]
Plasma oxidation was performed using Kr / O ₂ gas with a pressure of 80 Pa and a treatment time of 10 minutes. On the other hand, the plasma nitridation was performed using Ar / NH ₃ gas at a pressure of 8 Pa and a treatment time of 7 minutes. 1 and 3, the distance between the surface of the dielectric window 4 and the substrate 12 is adjusted to 60 mm.
[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 with a spectral dispersion ellipsometer, and the results were compared. The result of the oxidation treatment is shown in FIG. 5, and the result of the nitridation treatment is shown in FIG.
[0043]
When plasma processing is performed using the microwave plasma processing apparatus according to the present invention, the film thickness distribution shows good uniformity. That is, the respective film thicknesses are constant in the vicinity of about 71 to 72 mm when oxidized (FIG. 5), and are constant in the vicinity of about 46 to 50 inches when nitrided (FIG. 6). Although not shown, the same distribution tendency was observed in the oxidation treatment and nitridation treatment under conditions different from the above.
[0044]
On the other hand, in the case where the plasma processing is performed using the microwave plasma processing apparatus of FIG. 3, it can be seen that the thickness of the central portion of the substrate is increased. That is, each film thickness is about 80 mm at the periphery of the substrate when oxidized, but is about 103 mm at the center of the substrate (FIG. 5), and is about 33 mm at the periphery of the substrate when nitriding is performed. There are about 59 mm at the center of the substrate (FIG. 6). This is because, as shown by SWP ′ in FIG. 3, the microwave reflected by the metal surrounding surface formed of the cross section of the opening formed in the ceiling 101 forms a standing wave, and the dielectric window 4 This is probably because the plasma density in the center of the substrate has increased.
[0045]
Furthermore, when the pressure was relatively high, 80 Pa, 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 container 1 is more than a quarter of the wavelength of the microwave to be introduced, so that the conventional microwave plasma processing of FIG. In the apparatus, microwaves are reflected on the central portion of the dielectric window 4, whereas in the case of the apparatus of FIG. 1, between the outer periphery of the dielectric window 4 and the side wall surface of the plasma processing chamber 1. This is probably because the plasma is formed and the microwave is prevented from being reflected on the central portion of the dielectric window 4.
[0046]
【The invention's effect】
As is apparent from the above description, in the plasma processing using microwaves, the present invention provides that the surface of the dielectric window facing the substrate is the same position as the position of the inner wall surface of the ceiling of the plasma processing container 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 more than a quarter of the wavelength of the microwave. It was possible to suppress the standing wave that was the cause of lowering the uniformity of. Therefore, even when the distance between the surface of the dielectric window and the substrate is short, the 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. It became possible to perform processing with high plasma uniformity.
[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 (with a ring-shaped protrusion provided on the outer edge of the surface of a dielectric window).
5 is a graph showing a film thickness distribution when a silicon substrate is subjected to plasma oxidation using the apparatus of FIGS. 1 and 3. FIG. 6 is a plasma nitridation of the silicon substrate using the apparatus of FIGS. Diagram showing film thickness distribution when processed 【Explanation of symbols】
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 adjustment valve 12 Substrate 13 Electrode 14 High frequency power supply 15 Matching device P Plasma SWP surface wave

Claims (2)

A plasma processing chamber ceiling is open, this is provided hermetically in a ceiling portion and a dielectric window for microwave transparent, the substrate is placed facing the dielectric window into the plasma processing chamber; In the microwave plasma processing apparatus, wherein the surface of the dielectric window is configured to be located at the same position as the position of the inner wall surface of the ceiling of the plasma processing container or to protrude toward the substrate side from the position of the inner wall surface of the ceiling ,
The dielectric window includes a ring-shaped protrusion on the outer edge of the surface, and the inner surface surrounded by the protrusion is at the same position as the position of the inner wall surface of the ceiling of the plasma processing container or inside the ceiling. The protrusion protrudes toward the substrate from the wall surface, and the distance from the inner surface surrounded by the protrusion to the substrate is a radius. The microwave plasma processing apparatus is characterized in that the diameter of the dielectric window is determined so as not to include a portion . The raw material gas for exciting plasma by a gas supply means is supplied to the plasma processing chamber, oscillated by the microwave generator, the plasma treatment vacuum atmosphere amplified microwave through the dielectric window for microwave transmission In a method of introducing a plasma into a plasma processing container by an electromagnetic field generated by the microwave, and plasma processing a substrate provided facing the dielectric window for microwave transmission,
The dielectric window is secretly provided on the opened ceiling of the plasma processing vessel, and a ring-shaped protrusion is provided on the outer edge of the surface of the dielectric window, and the inner surface surrounded by the protrusion is The plasma processing container is configured to be located at the same position as the position of the inner wall surface of the ceiling portion of the plasma processing container or to protrude toward the substrate side from the position of the inner wall surface of the ceiling portion, and from the inner surface surrounded by the protruding portion, the substrate The diameter of the dielectric window is determined so that the protrusions are not included in the respective circles centered on both ends of the substrate, and the distance to the substrate is set in the plasma processing container through the dielectric window. A microwave plasma processing method comprising performing plasma processing by introducing a microwave.

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