JP2002146542A - Deposited film forming equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a semiconductor thin film for a photovoltaic element or the like having high quality and superior uniformity by transmitting a comparatively large microwave supply power to a discharge space stably for a long time to form a homogeneous plasma, in forming a deposited film on a base body by a plasma CVD process. SOLUTION: The equipment is provided with a vacuum container 102 having an exhaust means, a means 205 for supplying a gaseous starting material for deposited film formation in the vacuum container, and a microwave supply means for feeding a microwave power for the purpose of producing plasma out of the gaseous starting material for deposited film formation. In this equipment for forming a deposited film on a base plate installed in the vacuum container by the microwave plasma CVD process, a groove-shaped dielectric window 104 is arranged on the face that is exposed to the plasma of the microwave supply means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for forming a deposited film on a substrate by a plasma CVD method, and more particularly, to a device such as a solar cell using amorphous silicon, an amorphous alloy, and microcrystalline silicon. The present invention relates to a semiconductor thin film forming apparatus for continuously manufacturing a semiconductor thin film of a photovoltaic element.

[0002]

2. Description of the Related Art Amorphous silicon is a plasma CV.
Since a large-area semiconductor film can be formed by D, it is suitable for manufacturing a large-area semiconductor device as compared with crystalline silicon or polycrystalline silicon. For this reason, the amorphous silicon film is a semiconductor device requiring a large area,
Specifically, it is widely used for a solar cell, a photosensitive drum of a copying machine, an image sensor of a facsimile, a thin film transistor for a liquid crystal display, and the like.

An amorphous silicon film is generally made of SiH
It is produced by a plasma CVD method in which a raw material gas containing Si, such as ₄ or Si ₂ H _6, is decomposed by high-frequency discharge into a plasma state, and a film is formed on a substrate placed in the plasma.

[0004] When an amorphous silicon film is formed by a plasma CVD method, conventionally, an RF frequency (13.5) is used.
High frequency (around 6 MHz) has been generally used. However, in recent years, high-density plasma can be efficiently generated by using a microwave frequency of 2.45 GHz, and there is a possibility that a deposition film formation speed can be improved in a plasma CVD method. Attention has been paid to the plasma CVD method.

[0005] For example, in Japanese Patent No. 2971478, by setting the discharge frequency to a microwave frequency of 13.56 MHz, the deposition rate can be remarkably increased.
It is reported that a good amorphous silicon deposition film can be formed at high speed.

[0006]

However, the plasma CVD method using a microwave requires a relatively high discharge pressure of 133 Pa or more, and if this method is adopted in a microcrystalline silicon deposited film forming apparatus requiring a large power, There were cases where the following problems occurred.

That is, when microwaves are injected into the plasma space through a microwave transmission structure, which is an inlet for microwaves into the plasma space, and a discharge is generated, a high frequency in the conventional RF frequency band is applied to the parallel flat plate. In some cases, considerably higher power was required compared to the method. Furthermore,
If the discharge is continuously maintained for a long time, a deposited film is deposited on the surface of the dielectric window, and the power supplied to the microwave may become unstable or the dielectric window may be cracked.

In view of such circumstances, when forming a deposited film on a substrate by a plasma CVD method, a relatively large microwave input power is stably transmitted to a discharge space for a long time to form a uniform plasma. An object of the present invention is to provide an apparatus for forming a semiconductor thin film such as a photovoltaic element having high quality and excellent uniformity.

[0009]

According to the present invention, there is provided a vacuum vessel provided with an exhaust means, a means for supplying a raw material gas for forming a deposited film to the vacuum vessel, and a method for forming a deposited film. A microwave supply means for supplying microwave power for converting the raw material gas into plasma, and an apparatus for forming a deposited film by a microwave plasma CVD method on a substrate installed in the vacuum vessel; A deposition film forming apparatus is provided, wherein a dielectric window having a groove shape is provided on a surface of the microwave supply means exposed to the plasma.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, since a portion of a dielectric window exposed to a discharge space has a groove structure, film deposition on a dielectric window by high-density plasma is a minimum required at the tip of the groove. Limited to the area. For this reason, the plasma discharge stability for a long time is dramatically improved.

Further, by forming the grooves of the dielectric window in a direction not parallel to the direction of the electric field in the cross section in the traveling direction of the microwave, the influence of the reflection or absorption of the microwave power due to the deposition is greatly reduced. In addition, not only the stability of plasma discharge but also the uniformity of generated plasma is greatly improved.

Further, by forming the dielectric window from a material having a high mechanical strength, a high thermal conductivity, and a low dielectric loss coefficient, not only the microwave loss in the dielectric window itself is reduced but also the dielectric window is reduced. Dielectric heating is reduced, local heating of the dielectric window is reduced even after prolonged exposure to high-power microwave plasma, film-forming components causing microwave transmission loss can be reduced, and atmospheric vacuum tightness is improved. I do.

FIG. 1 illustrates the structure around the dielectric window of the microwave supply means used in the present invention. 101 is a waveguide, 102 is a vacuum vessel partition, 103 is a microwave transmission structure, and 104 is a dielectric window.

In this case, the microwave supply means has a microwave transmission structure and a waveguide, and a dielectric window having a groove shape is disposed on a surface of the microwave transmission structure exposed to plasma. Have been.

FIG. 2 shows a plasma CVD apparatus provided with the microwave supply means shown in FIG. 1 as an example of the deposited film forming apparatus of the present invention. 201 is a microwave power source, 20
2 is a discharge chamber, 203 is a deposition substrate, 204 is a heater, 20
Reference numeral 5 denotes a source gas introduction pipe, and reference numeral 206 denotes an exhaust pipe. In the case of this apparatus, the inside of the vacuum vessel is evacuated from the exhaust pipe 206 by a vacuum pump (not shown). The vacuum is sealed by an O-ring between the microwave transmission structure 103, the vacuum vessel partition wall 102, and the dielectric window 104.

Using the apparatus shown in FIG. 2, for example, a microcrystalline silicon semiconductor can be formed. That is, the microwave power passes from the microwave power supply 201 through the waveguide 101, passes through the dielectric window 104 provided on the end face of the microwave transmission structure 103, and is radiated to the discharge chamber 202. Then, the raw material gas supplied from the gas introduction pipe 205 is decomposed by microwave power and turned into plasma, and a deposited film is formed on the substrate 203 heated to a predetermined temperature by the heater 204.

Hereinafter, the microwave transmission structure and the dielectric window will be described.

(Microwave Transmission Structure) In the microwave transmission structure, the upstream side in the microwave traveling direction is connected to the waveguide, and the downstream side is connected to the dielectric window, and the dielectric window is connected to the deposition film forming substrate. It is arranged to be the optimal position toward
It has the function of transmitting microwaves to the discharge space.

When the dielectric window can be located at the optimum position toward the substrate for forming a deposited film, as shown in FIG. 6, the microwave transmission structure is not provided, and the end face of the waveguide opening is not provided. The dielectric window can be directly disposed on the substrate. In this case, the dielectric window is provided on the inner wall of the vacuum container.

The dimensions and the shape of the microwave transmission structure are arbitrarily set based on the relationship between the frequency of the microwave power supply and the area where the deposited film is formed. In order to minimize microwave loss.

For the cut-off frequency λc defined by the microwave frequency, the major axis a of the waveguide needs to satisfy a> λc / 2, and is often set to a value near a = 0.8λc. .

As long as this relationship is satisfied, it is possible to use a waveguide having an arbitrary size and shape so as to cover a required film forming area. Generally, a rectangular or circular waveguide classified according to a standard is used. Arbitrary dimensions can be selected from the tubes.

Since the waveguide is a high-pass filter in the first place, a microwave in a low frequency band is selected when a large film-forming area is required, and a high-frequency microwave is selected when a small film-forming area is required. It is desirable to do.

(Dielectric Window) The dielectric window has a function of vacuum-sealing the discharge space and the atmosphere and a function of transmitting microwaves transmitted from the microwave transmission structure into the discharge space. As the vacuum vessel is evacuated from the atmosphere to a vacuum, pressure is applied to the dielectric window surface from the atmosphere, and when microwaves are transmitted and a discharge is generated, the microwave is heated by dielectric heating or thermal shock from the plasma. Exposure to harsh environments. Conventionally, as a method for addressing these problems, a plurality of dielectrics have been superposed, and an intermediate pressure region partitioned by a plurality of dielectrics has been provided so that atmospheric pressure does not directly act on the dielectric surface. However, when a plurality of dielectrics are provided, the dielectric loss coefficient increases, so that a relatively large power cannot be supplied or the device structure becomes complicated in some cases.

In the present invention, these inconveniences can be avoided and the stability of discharge can be avoided by installing only one dielectric window made of a dielectric material having a predetermined mechanical strength, thermal conductivity and dielectric loss coefficient. Is secured.

That is, the Young's modulus of the material of the dielectric window is preferably 5.0 × 10 ⁵ kg / cm ² or more, more preferably 1.0 × 10 ⁶ kg / cm ² or more from the viewpoint of mechanical strength. , 1.5 × 10 ⁶ kg / cm ² or more is most preferable.

The thermal conductivity of the material of the dielectric window is preferably 15 W / mK or more, more preferably 30 W / mK or more, and 60 W / mK or more in order to suppress a temperature rise due to heat storage.
Most preferably, it is at least mK.

Further, the dielectric loss coefficient of the material of the dielectric window is preferably 0.01 or less.

The portion of the microwave transmission structure facing the discharge space preferably has a groove structure in a direction parallel to the traveling direction of the microwave and perpendicular to the direction of the electric field of the traveling microwave.

The field direction of the microwave is the fact determined by the waveguide cross section, the groove direction of the dielectric window, for example, in the rectangular waveguide TE ₁₀ mode grooves oriented parallel to the major axis direction of the waveguide section They are arranged side by side (Fig. 3) and have a circular waveguide TM ₀₁
The mode of construction lined groove concentrically from the waveguide the cross-sectional center (Fig. 4), it is circular waveguide TE ₀₁ mode which is a structure lined with grooves radially from the waveguide the cross-sectional center (Fig. 5) Is desirable.

The minimum thickness from the groove bottom to the end face of the dielectric window is desirably 5 mm or more in terms of strength. Further, as the groove dimension of the dielectric window, the width of the concave portion and the convex portion is preferably several mm or less, specifically, 1 mm or less. Further, the depth is 1/4 or less of the microwave wavelength and at least several mm, specifically 5 mm or more, more preferably 10 mm or more. Such a shape is desirable in reducing the effect of energy loss during microwave transmission and the effect of deposition of a deposited film on the surface of the dielectric window.

The material of the dielectric window is not particularly limited, but aluminum nitride, alumina, quartz and the like can be used.
Among them, aluminum nitride is preferable.

By using the dielectric window as described above, the severe thermal shock directly exposed to the plasma is reduced, and the dielectric loss coefficient and the reflection loss in the microwave transmission by the deposition component are reduced. Plasma to be uniform
A stable and uniform deposited film can be formed over a long period of time.

By irradiating the waveguide without changing the cross-sectional shape of the waveguide, the microwave can be efficiently decomposed without changing the transmission mode when the microwave passes through the dielectric window, and a high-quality deposited film can be formed. Generation is possible.

[0035]

EXAMPLES Examples of the deposited film forming apparatus of the present invention will be described below, but the present invention is not limited to these examples.

(Experimental Example 1) In this experimental example, a dielectric window under a predetermined film forming condition was used by using a deposited film forming apparatus having the structure shown in FIG. 2 provided with the microwave supply means shown in FIG. Comparison of stable discharge sustaining power due to the difference in the material of the above.

A dielectric window was manufactured using aluminum nitride (trade name: Shapal), alumina, and quartz as the material of the dielectric window. The dielectric windows all have the same shape and are plate-shaped as shown in FIG. 3, and the dimensions and the like are as shown in Table 1. The minimum thickness from the groove bottom to the end face of the dielectric window is 5m
m. Further, the groove was made parallel to the major axis direction. Further, the arrangement direction of the dielectric window was such that the groove of the dielectric window was not parallel to the electric field direction in the cross section in the microwave traveling direction.

Next, in the apparatus shown in FIG.
A glass substrate (□ 4
7.5 mm × 0.7 t made by Corning 7059) were arranged at equal intervals over the entire surface.

Thereafter, the vacuum vessel was evacuated to 0.1
The air was once evacuated to 33 Pa or less.

The substrate was heated by a substrate heater to a predetermined temperature (250 ° C.) while flowing a constant flow of Ar gas from the gas supply means through a gas introduction pipe.

After the temperature of the substrate reached a constant temperature (250 ° C.), 240 and 720 sccm of SiF ₄ and H ₂ as source gases were introduced instead of Ar, respectively.

In this state, 2.45 from the microwave power supply
Supplying microwave power of GHz, discharge pressure of 133 Pa
The input power at which the glow discharge occurs in the discharge chamber and stabilizes while maintaining the temperature was determined.

As a result, it was found that when aluminum nitride was used as the material of the dielectric window, stable discharge was started at a relatively low applied power.

[0044]

[Table 1]

(Example 2) A dielectric window made of aluminum nitride was manufactured in the same manner as in Example 1 except that the dimensions were set to the values shown in Table 2. Then, the obtained dielectric window was disposed in the deposition film forming apparatus shown in FIG.

Using this apparatus, a long-term discharge experiment was performed. That is, in the same manner as in Example 1, after the substrate was heated to 250 ° C., 240 and 720 sccm of SiF ₄ and H ₂ as source gases were introduced instead of Ar, respectively.

In this state, 2.45 from the microwave power supply
A microwave microwave power was supplied to generate glow discharge inside the discharge chamber, and the raw material gas was plasma-decomposed while maintaining the discharge pressure at 133 Pa, thereby forming a silicon-based amorphous intrinsic semiconductor film on the substrate. . However, here, a dummy substrate (aluminum plate material 375 × 620 mm ² ) was set on the film formation surface to form a film.

As a result, over a continuous 10 hours or more,
It was confirmed that the displayed value of the incident power was within ± 5%, and the displayed value of the reflected power with respect to the incident power was 5% or less. Further, there were no problems such as heat burning of the dielectric itself, unstable abnormal discharge due to conductivity of the deposited film, and discharge interruption.

(Comparative Example 1) As a comparative example, an experiment similar to that in Example 2 was performed using a smooth aluminum nitride dielectric window having the dimensions shown in Table 2 without a groove structure. Discharge could not be maintained.

[0050]

[Table 2]

(Embodiment 3) The dielectric window made of aluminum nitride manufactured in Embodiment 1 was applied to the deposited film forming apparatus shown in FIG.
And an intrinsic semiconductor film of silicon-based microcrystal was formed.

First, of the apparatus shown in FIG.
A glass substrate (□ 4
7.5 mm × 0.7 t made by Corning 7059) were arranged at equal intervals over the entire surface.

Next, the vacuum vessel was evacuated to 0.13
The air was once evacuated to 3 Pa or less.

The substrate was heated by a substrate heater to a predetermined temperature (250 ° C.) while a constant flow rate of Ar gas was passed from the gas supply means through a gas introduction pipe.

After the temperature of the substrate reached 250 ° C., 240 and 720 sccm of SiF ₄ and H ₂ as source gases were introduced instead of Ar.

Under these conditions, 2.45 from the microwave power supply
A microwave power was supplied to generate glow discharge in the discharge chamber, and the raw material gas was plasma-decomposed while maintaining the discharge pressure at 133 Pa to form a silicon-based microcrystalline intrinsic semiconductor film on the substrate.

During the formation of the deposited film, the displayed value of the incident power with respect to the plasma load of the discharge chamber was within ± 5%, and the displayed value of the reflected power with respect to the incident power was stable at 5% or less.

After the film formation for a certain period of time, the discharge power was stopped, the gas supply was stopped, and the heating of the substrate heater was stopped. The inside of the vacuum vessel was sufficiently replaced with an inert gas, and the film formation substrate was taken out and the film formation characteristics were evaluated.

As a result, the film formation area was 375 × 620 mm ²
It was confirmed that in a large area, a high film forming speed and a uniform film forming were achieved with an average film forming speed of 3.5 nm / s and a film forming speed distribution within ± 5%.

When the crystallinity was evaluated, a high-quality microcrystalline silicon semiconductor film having a Raman peak intensity ratio of 5 or more (520 cm ⁻¹ / 480 cm ⁻¹ ) and a crystal grain size of 51.1 nm was obtained.

[0061]

As described above, in the microwave power introduction path provided in the container for depositing a thin film of a semiconductor or the like, the dielectric window having the groove structure is provided at the end face of the waveguide. By doing so, in a large area, at a high deposition rate,
A uniform deposited film can be formed for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining a structural example of a microwave supply means used in the present invention.

FIG. 2 is a schematic sectional view for explaining the structure of a deposited film forming apparatus according to the present invention.

FIG. 3 is a schematic perspective view for explaining a structural example of a dielectric window of the present invention.

FIG. 4 is a schematic perspective view for explaining another structural example of the dielectric window of the present invention.

FIG. 5 is a schematic perspective view for explaining another structural example of the dielectric window of the present invention.

FIG. 6 is a schematic cross-sectional view for explaining another example of the structure of the microwave supply means used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Waveguide 102 Vacuum container partition 103 Microwave transmission structure 104 Dielectric window 201 Microwave power supply 202 Discharge chamber 203 Deposition substrate 204 Heater 205 Source gas introduction pipe 206 Exhaust pipe

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G075 AA24 BC04 CA26 CA47 DA01 EB01 FA05 FC11 FC15 FC20 4K030 AA04 AA06 AA17 BA29 BA30 BB04 CA06 FA01 KA46 5F045 AB04 AC02 AC16 AD06 AE02 AE03 AE05 AE15 E13 AE11 AE11 E13 AE09

Claims (7)

[Claims] 1. A vacuum vessel provided with an exhaust means, a means for supplying a deposition film forming material gas to the vacuum vessel, and a microwave for supplying microwave power for converting the deposition film forming material gas into plasma. Supply means for forming a deposited film on a substrate installed in the vacuum vessel by a microwave plasma CVD method, wherein the surface of the microwave supply means exposed to plasma has a groove shape. An apparatus for forming a deposited film, wherein a dielectric window is provided. 2. The microwave supply means has a microwave transmission structure and a waveguide, and a dielectric window having a groove shape is disposed on a surface of the microwave transmission structure exposed to plasma. 2. The deposited film forming apparatus according to claim 1, wherein said apparatus is provided. 3. The deposited film forming apparatus according to claim 1, wherein said dielectric window is provided on an inner wall of said vacuum vessel. 4. The deposited film formation according to claim 1, wherein the grooves of the dielectric window are arranged in a direction that is not parallel to the direction of the electric field in the cross section in the microwave traveling direction. apparatus. 5. The material of the dielectric window has a Young's modulus of 5.
The deposited film forming apparatus according to any one of claims 1 to 4, wherein the density is 0x10 ⁵ kg / cm ² or more. 6. The thermal conductivity of the material of the dielectric window is 15
The deposition film forming apparatus according to any one of claims 1 to 5, wherein the value is not less than W / mK. 7. The deposited film forming apparatus according to claim 1, wherein a dielectric loss coefficient of a material of said dielectric window is 0.01 or less.