JP2003055773A - Apparatus and method for depositing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for depositing a film in which deposition of a film on a dielectric window is prevented, a homogeneous plasma is formed by transmitting relatively large microwave power into a discharge space of large area consistently for a long time, and a film of high quality and excellent uniformity can be deposited when depositing the film by the plasma CVD method by introducing a microwave via the dielectric window. SOLUTION: In the apparatus and the method for depositing the film on the base material by the microwave plasma CVD method by introducing the microwave into the discharge space via the dielectric window, a plurality of thin plate-like members are disposed on the discharge space side of the dielectric window so as to form a space partitioned across the direction of the electric field by the plurality of thin plate-like members.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Silicon-based non-single crystal is plasma CVD
It can be used for forming a large-area semiconductor film by the method and for forming a large-area semiconductor device relatively easily as compared with crystalline silicon or polycrystalline silicon. Therefore, amorphous silicon films and microcrystalline silicon films are often used in semiconductor devices that require a large area, specifically, solar cells, photosensitive drums of copying machines, image sensors of facsimiles, thin film transistors for liquid crystal displays, and the like. ing.

The amorphous silicon film is generally formed by decomposing a raw material gas containing Si such as SiH ₄ and Si ₂ H ₆ into a plasma state by high frequency discharge, and forming a film on a substrate placed in the plasma. The plasma CVD method is used.

When forming an amorphous silicon film by the plasma CVD method, a conventional RF frequency (13.5) is used.
High frequencies around 6 MHz) have been commonly 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 the deposition film formation rate can be improved in the plasma CVD method. The plasma CVD method that has been used is drawing attention.

For example, Japanese Patent No. 2971478 (registration date August 27, 1999) discloses a discharge frequency of 13.5.
It has been reported that by changing the RF of 6 MHz to the microwave frequency of 2.45 GHz, the film formation rate can be remarkably increased, and a good amorphous silicon deposited film can be formed at a high speed. Here, it is stated that by adopting an appropriate material and dimensions for the microwave transmission window and incorporating a cooling structure, it is possible to eliminate the adverse effects of the high temperature microwave plasma and the adverse effects of the deposited film that crystallizes with the increase in temperature.

[0006]

However, the plasma CVD method using microwaves is relatively high at 6.65.
The following problems have occurred when it is adopted in an apparatus for forming a microcrystalline silicon deposited film which requires a discharge pressure of Pa or more and a large electric power. That is, when microwaves are injected into the plasma space through the microwave transmission structure, which is the inlet of the microwaves into the plasma space, to generate discharge, the microwave plasma is concentrated near the dielectric window and the dielectric window There have been problems that a microcrystalline deposition film is deposited on the surface, the microwave input power becomes unstable, and the dielectric window is cracked.

Therefore, the present invention solves the above problem and prevents the deposition film from adhering to the dielectric window when the deposition film is formed by the plasma CVD method by introducing microwaves through the dielectric window. , A relatively large microwave input power can be stably transmitted to the discharge space for a long time in a large area to form a homogeneous plasma and form a deposited film with high quality and excellent uniformity. It is an object of the present invention to provide a deposited film forming apparatus and a deposited film forming method.

[0008]

In order to achieve the above object, the present invention provides a deposited film forming apparatus and a deposited film forming method configured as in the following (1) to (8). (1) In a deposited film forming apparatus for introducing a microwave into a discharge space through a dielectric window to form a deposited film on a substrate by a microwave plasma CVD method, a plurality of dielectric windows are provided on the discharge space side. A thin film-shaped member, wherein a space partitioned by the plurality of thin plate-shaped members in a direction crossing the electric field direction is formed. (2) The plurality of thin plate-shaped members are arranged in a plurality of groove structures formed on the surface of the dielectric window on the discharge space side so that one ends thereof project toward the discharge space side. The deposited film forming apparatus as described in (1) above. (3) The above-mentioned (2), wherein the length of the plurality of thin plate-shaped members protruding toward the discharge space is equal to or longer than the mean free path of the film deposition component of the material gas. Deposited film forming apparatus. (4) The deposition film formation according to any one of the above (1) to (3), characterized in that the distance between the plurality of thin plate members is equal to or less than the mean free path of electrons of the material gas. apparatus. (5) In a deposited film forming method in which a microwave is introduced into a discharge space through a dielectric window and a deposited film is formed on a substrate by a microwave plasma CVD method, the deposition window is disposed on the discharge space side of the dielectric window. A plurality of thin plate-shaped members form a space partitioned in a direction crossing the direction of the electric field, and a film forming component of the plasma space is formed on the side surface of the thin plate-like member to deposit on the dielectric window. A deposited film forming method, characterized in that a deposited film is formed while preventing the deposition of the film. (6) The plurality of thin plate-shaped members are arranged in a plurality of groove structures formed on the surface of the dielectric window on the discharge space side so that one end thereof projects toward the discharge space side to form a deposited film. The method for forming a deposited film according to the above (5), characterized in that the deposited film is formed. (7) The above-mentioned (6), wherein the length of the plurality of thin plate-shaped members protruding toward the discharge space is equal to or longer than the mean free path of the film deposition component of the material gas. Method for forming deposited film of. (8) The deposition film formation according to any one of the above (5) to (7), wherein the interval between the plurality of thin plate-shaped members is equal to or less than the mean free path of electrons of the material gas. Method.

[0009]

According to the above structure, a plurality of thin plate-shaped members are arranged in the portion of the dielectric window on the discharge space side, so that the film deposition on the dielectric window by the high-density plasma is a thin plate-shaped member. It becomes possible to minimize it at the tip part, and the plasma discharge stability over a long period of time is dramatically improved. Further, since the thin plate member is arranged so as to be fitted into the groove structure of the dielectric window, an abnormal discharge which becomes a problem in the gap between the thin plate member and the dielectric window, or microwave power due to the influence of film deposition is generated. The loss due to reflection or absorption is drastically reduced, and not only the discharge stability of the plasma is obtained, but also the uniformity and directivity of the generated plasma can be greatly contributed.

Further, since the dielectric window has a groove structure in the shape of a heat sink on the discharge space side, the influence of heat from plasma is mitigated, the durability of the dielectric window is improved, and there is no problem in airtightness. Don't give. Moreover, since the thin plate members can be individually removed, the maintainability for film deposition on the thin plate members is also improved.

Next, an embodiment of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic electric field direction sectional view around a dielectric window according to the present embodiment. In FIG. 1, 101 is a waveguide, 102 is a vacuum container partition, 103
Is a microwave transmission structure, 104 is a dielectric window, and 105 is a thin plate member.

FIG. 2 is a schematic view of a plasma CVD apparatus incorporating the apparatus having such a configuration. Next, an example in which a microcrystalline silicon semiconductor is formed using the plasma CVD apparatus shown in FIG. 2 is described. In FIG. 2, 201
Is a microwave power source, 202 is a discharge chamber, 203 is a film formation substrate, 204 is a heater, 205 is a source gas introduction pipe, 206
Is the exhaust pipe. The inside of the vacuum container 102 is evacuated from the exhaust pipe 206 by a vacuum pump (not shown). The vacuum is sealed between the microwave transmission structure 103, the vacuum container partition 102, and the dielectric window 104 by an O-ring.

The microwave power is generated by the microwave power source 201.
Through the waveguide 101 from the microwave transmission structure 10
The light is transmitted through the dielectric window 104 installed at the end face of the No. 3 and radiated to the discharge chamber 202. Then, the source gas supplied from the gas introduction pipe 205 is decomposed into plasma by microwave power, and a deposited film is formed on the substrate 203 heated to a predetermined temperature by the heater 204.

Here, the main part of the above structure is composed of (1) a dielectric window (2) and a thin plate member. Next, details of the main parts (1) and (2) will be described. (1) Dielectric window The dielectric window has both the function of transmitting the microwave transmitted from the waveguide to the discharge space and the function of vacuum-sealing the discharge space and the atmosphere. As the vacuum container is evacuated from the atmosphere to a vacuum, pressure is applied to the dielectric window surface from the direction of the atmosphere, and when microwaves penetrate and discharge occurs, dielectric heating by microwaves and thermal shock from plasma occur. Exposed to harsh environment. Conventionally, as a method to deal with these problems,
It has been dealt with by overlapping a plurality of dielectrics and by having an intermediate pressure region partitioned by a plurality of dielectrics so that atmospheric pressure does not directly act on the dielectric surface. However, there have been problems that the dielectric loss coefficient is increased by equipping a plurality of dielectrics and relatively large electric power cannot be applied and the device structure becomes excessively large.

By applying a dielectric material having a groove shape and provided with a plurality of plate-shaped members, the characteristics required for mechanical strength, thermal conductivity and dielectric loss coefficient are alleviated, and the dielectric window is
It was found that these problems could be avoided and the stability of the discharge could be secured even by installing only one sheet. As the material of the dielectric window, ceramics having excellent mechanical strength, thermal conductivity, and dielectric loss coefficient are preferable. For example, AlN, Al ₂
O ₃ , SiO ₂ , Si ₃ N ₄ , TiO and a composite sintered body thereof are preferable, but no limitation is made as long as the required physical properties are well balanced.

Further, since the vacuum-sealed portion of the dielectric window is easily affected by the dielectric overheating caused by microwaves and the heating from the plasma, the O-ring material is generally made of Viton or silicone. Desirably, the O-ring seal portion of the dielectric window is shielded by conductive metal vapor deposition so that the microwave is not directly exposed to the O-ring.

Since the electric field direction of the microwave is determined by the waveguide cross-sectional shape, the groove direction of the dielectric window is parallel to the major axis direction of the waveguide cross section in the rectangular waveguide TE ₁₀ mode, for example. In the circular waveguide TM ₀₁ mode, the circular waveguide TE _{01 is} arranged concentrically from the center of the waveguide cross section.
In the mode, it is desirable to have a structure in which grooves are arranged radially from the center of the waveguide cross section.

The thickness of the dielectric window is generally set to an odd multiple of 1/4 of the wavelength of the microwave passing through the dielectric in order to reduce the reflection loss of the microwave, but the power required for plasma generation is required. As long as it can be supplied, no limitation is made. There is no problem if the groove depth of the dielectric window is 1 mm or more. Further, it is preferable that the groove width of the dielectric window is slightly larger than the thickness of the thin plate member and includes the thermal expansion of the thin plate member, and the groove interval is 1 mm or less. It is desirable to reduce the energy loss and the influence of the deposited film deposited on the surface of the dielectric window.

As a result, the severe thermal shock directly exposed to the plasma is mitigated, the dielectric loss coefficient and the reflection loss in the microwave transmission due to the film deposition component are reduced, and the generated plasma is made uniform and stable for a long time. It is possible to form a uniform deposited film.

The size and shape of the dielectric window can be arbitrarily set according to the relationship between the microwave power supply frequency and the deposited film formation area, but it is transmitted that the shape of the waveguide to be connected is not changed. It is preferable for minimizing the loss of.
The major axis a of the waveguide needs to be a> λc / 2 with respect to the cutoff frequency λc defined by the microwave frequency, 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 any size and shape so as to cover the required film formation area. Generally, from among rectangular or circular waveguides classified by the standard. Any size can be selected.

The microwave frequency adopted as a reference in the present invention is 2.45 GHz, and the waveguide has a major axis of 109 m.
m is a WRJ-2 type JIS waveguide with a short diameter of 54.5 mm, but since the waveguide is a high-pass filter in the first place, if a larger film formation area is required, microwaves of a lower frequency band are formed. It is desirable to select microwaves in a high frequency band when the area is to be small and concentrated. (2) Thin plate member The thin plate member divides the microwave power transmitted through the dielectric window in the direction crossing the electric field direction, and forms the film deposition component of the plasma space on the side surface of the thin plate member. Also has a role of preventing the deposition of a film on the surface of the dielectric window. Since each space partitioned by the thin plate member in the direction crossing the electric field direction corresponds to a waveguide, it does not affect microwave transmission at all. When the distance between each thin plate member becomes a distance equal to or less than the mean free path of electrons of the introduced material gas, sufficient acceleration energy of electrons cannot be obtained and discharge does not start, but the microwave does not start. When the gas reaches the end surface of the thin plate member on the discharge space side, the material gas is turned into plasma. Therefore, the distance between the thin plate-shaped members is preferably equal to or less than the mean free path of electrons of the material gas, for example, 1 mm or less.

A part of the film-forming particles that have been turned into plasma also move to the transmission window side, but most of them are deposited on the side surface of the thin plate member to prevent the deposition of the film on the surface of the dielectric window. .
Therefore, the longer the protruding length of the thin plate member into the discharge space is, the better, but in reality, there is no problem as long as it is equal to or more than the mean free path of the film forming component of the introduced material gas. Further, the arrangement direction and the arrangement interval of the thin plate-shaped members are determined according to the groove structure of the dielectric window. For example, a rectangular waveguide TE
_{In the 10} mode, the waveguides are arranged in a direction parallel to the major axis direction of the waveguide. The circular waveguide TM ₀₁ mode is concentric with the waveguide cross section center, and the circular waveguide TE ₀₁ mode is a waveguide cross section. It is desirable to have a structure that is arranged radially from the center.

[0023]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. [Embodiment 1] In this embodiment, a device having the structure shown in FIG. 2 incorporating the device of the present invention having the structure shown in FIG. The discharge stability was compared. Table 1 shows the specifications of the present dielectric window structure and the obtained results.

Experiments were carried out in the following procedure using a quartz window in which the distance between the thin plate members and the depth of the groove were changed as the dielectric window in FIG. First, the vacuum container 102 is moved to 0.
It was once evacuated to 133 Pa or less. Then, while the Ar gas at a constant flow rate was circulated from the gas supply means through the gas introduction pipe 205, the substrate heater 204 controlled the heating of the substrate to a predetermined temperature. After the temperature of the substrate 203 reached a constant temperature, SiF ₄ and H ₂ as source gases were introduced instead of Ar at 240 and 720 sccm, respectively.

Then, the microwave power sources 201 to 2.
45 GHz microwave power is supplied and the discharge pressure is 6.6.
While changing the microwave power from 5 Pa to 66.5 Pa from 500 W to 1500 W, glow discharge occurred in the discharge chamber 202 and the discharge state was confirmed. At this time, the condition of stable discharge in all pressure ranges and power ranges was evaluated as ◯, the condition of causing some abnormal discharge was evaluated as Δ, and the condition of not being stable at all was evaluated as x. According to this experiment, it was found that there is no problem if the distance between the thin plate-shaped members is 1 mm and there is no problem if the groove depth is 1 mm or more.

[0026]

[Table 1] [Embodiment 2] In the present embodiment, a thin plate-like material having a different film forming pressure under a predetermined film forming condition is used by using the apparatus having the structure shown in FIG. The lengths of the film-coating portions that entered the member were compared. Table 2 shows the specifications of the present dielectric window structure and the obtained results.

An experiment was conducted in the following procedure using a quartz window in which the height of the thin plate member was changed as the dielectric window of FIG.
First, the vacuum vessel 102 is evacuated to 0.133 Pa.
Exhausted below. Then, while the Ar gas at a constant flow rate was circulated from the gas supply means through the gas introduction pipe 205, the substrate heater 204 controlled the heating of the substrate to a predetermined temperature. After the temperature of the substrate 203 reaches a constant temperature, SiF ₄ and H ₂ which are raw material gases are replaced with 240 instead of Ar, respectively.
720 sccm was introduced.

Then, the microwave power sources 201 to 2.
45 GHz microwave power is supplied and the discharge pressure is 1.3
While changing from 3 Pa to 133 Pa, glow discharge was generated in the discharge chamber 202 for a certain period of time, and the length of the film deposition portion was determined from the upper end of the thin plate member at each pressure. According to this experiment, it was found that if the height of the thin plate member is equal to or longer than the mean free path, the deposited film does not reach the transmission window, and stable discharge can be maintained without any problem.

[0029]

[Table 2] [Embodiment 3] In this embodiment, a device having the structure shown in FIG. 2 incorporating the device of the present invention having the structure shown in FIG. The continuous discharge sustaining time was compared. An experiment was conducted in the following procedure using a grooved quartz window and a thin plate member as the dielectric window in FIG. Table 3 shows the specifications of this dielectric window structure and the obtained results. First, the vacuum container 102 is evacuated to 0.13
It was once evacuated to 3 Pa or less. Then, while the Ar gas at a constant flow rate was circulated from the gas supply means through the gas introduction pipe 205, the substrate heater 204 controlled the heating of the substrate to a predetermined temperature. After the substrate 203 reaches a constant temperature, A
In place of r, the source gases SiF ₄ and H ₂ are each added to 24
0,720 sccm was introduced.

Then, the microwave power sources 201 to 2.
45 GHz microwave power is supplied and the discharge pressure is set to 13.
The input power at which glow discharge occurred and was stabilized in the discharge chamber 202 while maintaining the pressure at 3 Pa was obtained. As a result, consecutive 1
Over 0 hours or more, it was confirmed that the displayed value of the incident power was within ± 5%, and the stable discharge of the reflected power against the incident power was 5% or less. (Table 3) (Comparative Example) As a comparative example, an apparatus having a configuration in which a smooth quartz window without grooves and a thin plate member were used was used. According to the device having the configuration used in this comparative example, as shown in Table 3, the discharge could not be maintained in about 3 hours.

[0031]

[Table 3] [Example 4] In Example 4, in the long-time discharge experiment performed in Example 3, an AlN material having the same groove structure as the quartz material was used instead of the quartz window. Even when the structure of Example 4 is used, as shown in Table 3, stable discharge with a display value of incident power within ± 5% and a display value of reflected power with respect to the incident power of 5% or less was observed for 10 hours or more continuously. It could be confirmed.

[Embodiment 5] In Embodiment 5, the number of abnormal discharges during the long-time discharge experiment in Embodiment 3 was compared. Table 4 shows the specifications of this dielectric window structure and the obtained results. As a result, it was confirmed that when the grooved quartz window was adopted as the dielectric window, the number of abnormal discharges was 5 or less in 10 consecutive hours or more. (Comparative Example) As a comparative example, an apparatus having a structure using a quartz window without grooves and a thin plate member was used. According to the apparatus having the configuration used in this comparative example, as shown in Table 4, abnormal discharge was confirmed 30 times in about 3 hours, and discharge could not be maintained after 3 hours.

[0033]

[Table 4] [Example 6] In Example 6, AlN having the same structure as quartz was used in place of quartz in the long-time discharge experiment performed in Example 3. Even with the configuration of Example 6, as shown in Table 4, it was confirmed that the number of abnormal discharges was 5 or less in 10 consecutive hours or more.

[Embodiment 7] In Embodiment 7, the long-time discharge experiment conducted in Embodiment 3 was conducted by changing the recipe of the raw material gas. Here, the flow rates of SiF ₄ and H ₂ are 240,
960 sccm and 240,1200 sccm were introduced. As a result, in any case of changing the flow rate of the material gas, as shown in Table 5, the display value of the incident power is within ± 5% and the display value of the reflected power with respect to the incident power is 5% for 10 hours or more continuously. The following stable discharges were confirmed.

[0035]

[Table 5]

[0036]

As described above, according to the present invention, the plasma C is generated by introducing the microwave through the dielectric window.
When the deposited film is formed by the VD method, the deposited film is prevented from adhering to the dielectric window, and relatively large microwave input power is stably transmitted to the discharge space in a large area for a long time and is uniform. It is possible to realize a deposited film forming apparatus and a deposited film forming method capable of forming a high quality plasma and forming a deposited film having high quality and excellent uniformity.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a microwave introduction path according to an embodiment and an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a vacuum device for forming an intrinsic semiconductor film, which is provided with a microwave introduction path according to an embodiment and an example of the present invention.

[Explanation of symbols]

101: Waveguide 102: Vacuum container 103: Microwave transmission structure 104: Dielectric window 105: Thin plate member 201: Microwave power source 202: Discharge chamber 203: Film forming substrate 204: heater 205: Gas introduction pipe 206: Exhaust pipe

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H068 DA00 EA25                 4K030 BA30 FA01 KA37 LA16                 5F045 AA09 AB04 AC01 AC02 AC16                       AE17 AE19 BB02 BB15 DP05                       EB02 EE17 EF13 EH03

Claims (8)

[Claims] 1. A deposition film forming apparatus for introducing a microwave into a discharge space through a dielectric window to form a deposited film on a substrate by a microwave plasma CVD method, comprising: 2. A deposition film forming apparatus, comprising: a plurality of thin plate-shaped members, and a space partitioned by the plurality of thin plate-shaped members in a direction crossing an electric field direction. 2. The plurality of thin plate members are arranged in a plurality of groove structures formed on the surface of the dielectric window on the discharge space side so that one ends thereof project toward the discharge space side. The deposited film forming apparatus according to claim 1, wherein: 3. The length of the plurality of thin plate-shaped members protruding toward the discharge space is equal to or longer than the mean free path of the film deposition component of the material gas. The deposited film forming apparatus described. 4. The deposited film according to claim 1, wherein the plurality of thin plate-shaped members have an interval equal to or less than an average free path of electrons of the material gas. Forming equipment. 5. A deposited film forming method for forming a deposited film on a substrate by a microwave plasma CVD method by introducing microwaves into a discharge space through a dielectric window, the dielectric window being closer to the discharge space. A plurality of thin plate-shaped members arranged in a space to form a space partitioned in a direction crossing the electric field direction, and by depositing a film deposition component of the plasma space on the side surface of the thin plate-shaped member, the dielectric window is formed. The method for forming a deposited film, wherein the deposited film is formed while preventing the deposition of the deposited film. 6. The plurality of thin plate-shaped members are deposited in a plurality of groove structures formed on a surface of the dielectric window on the discharge space side so that one end thereof projects toward the discharge space side. The deposited film forming method according to claim 5, wherein a film is formed. 7. The length of the plurality of thin plate members protruding toward the discharge space is equal to or longer than the mean free path of the film deposition component of the material gas. The method for forming a deposited film as described above. 8. The deposited film according to claim 5, wherein an interval between the plurality of thin plate members is equal to or less than an average free path of electrons of the material gas. Forming method.