JP2011086776A - Thin film forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film forming apparatus that forms a semiconductor film uniformly on a meters-scale large-area substrate. <P>SOLUTION: The thin film forming apparatus, wherein a plasma electrode includes: a shower plate 132 provided with many gas blowout holes 134; and a gas buffer chamber 135 a space of which on the opposite side from the gas blowout holes 134 of the shower plate 132 is partitioned into a plurality of nearly concentric small chambers 137, has: an H<SB>2</SB>gas supply pipe 22 for supplying an H<SB>2</SB>gas into each of the small chambers 137; SiH<SB>4</SB>gas supply pipes 26a-26c for supplying an SiH<SB>4</SB>gas into each of the small chambers 137; a mass flow controller for controlling the flow rate of the H<SB>2</SB>gas to the gas buffer chamber 135; a mass flow controller for controlling the flow rate of the SiH<SB>4</SB>gas to each of the small chambers 137; and a control unit that makes a duty control of periodically repeating the supply and cutoff of the SiH<SB>4</SB>gas to each of the small chambers 137 from the SiH<SB>4</SB>gas supply pipes 26a-26c independently for each of the small chambers 137. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film forming apparatus for forming a semiconductor film such as a microcrystalline silicon thin film used in a silicon thin film solar cell.

  Conventionally, microcrystalline silicon thin films having a property of absorbing light in the visible light to infrared light region have been widely used as one of photoelectric conversion layers of silicon thin film solar cells.

As a method for producing a microcrystalline silicon thin film, it is generally deposited on a glass substrate by a plasma CVD (Chemical Vapor Deposition) method using a mixed gas of silane (SiH ₄ ) and hydrogen (H ₂ ). That is, a fixed amount of SiH ₄ gas and H ₂ gas are respectively supplied to the evacuated vacuum vessel, and the gas pressure in the vessel is kept at a predetermined value. In this state, a high-frequency voltage is applied to the cathode side (plasma electrode) of a pair of parallel plate electrodes installed in the container to cause glow discharge between the anode side (ground electrode) and SiH ₄ / H _2. A mixed plasma is generated.

A glass substrate is usually held on a ground electrode heated to about 200 ° C., and a film precursor such as active SiH ₃ or SiH ₂ generated in a SiH ₄ / H ₂ mixed plasma is incident on this surface. By doing so, a thin film of silicon is deposited. In addition, a large amount of H atoms from the plasma are simultaneously incident on the film surface, so that a part of the silicon thin film is crystallized to form a so-called microcrystalline silicon film.

In order to form a microcrystalline silicon thin film by the plasma CVD method, a film forming method generally called “high pressure depletion method” is widely used (see, for example, Patent Document 1). Specifically, under a relatively high gas pressure (for example, 1 to 10 Torr), the SiH ₄ gas flow rate Q (SiH ₄ ) is made sufficiently small (in other words, the H ₂ gas flow rate Q (H ₂ ) is made sufficiently large. ), The flow rate ratio between SiH ₄ and H ₂ is lowered to Q (SiH ₄ ) / [Q (SiH ₄ ) + Q (H ₂ )] = 1-5%, and SiH ₄ in the plasma is depleted. Enables deposition of a microcrystalline silicon thin film (conversely, when the SiH ₄ flow rate ratio Q (SiH ₄ ) / [Q (SiH ₄ ) + Q (H ₂ )] is large, the deposited film becomes amorphous. Become.). It is also known that it is effective for crystallizing a film to narrow the electrode interval between the plasma electrode and the ground electrode (that is, the substrate) to about 5 to 10 mm.

As another method for forming a microcrystalline silicon film, a film formation method called “layer-by-layer method” is also known (see, for example, Patent Document 2 and Non-Patent Document 1). In this layer-by-layer method, generation of SiH ₄ plasma (or SiH ₄ / H ₂ mixed plasma) and generation of H ₂ plasma are alternately repeated many times using the above plasma CVD apparatus. By performing the deposition, even if it is an amorphous thin film at the time of deposition with SiH ₄ plasma, the thin film is crystallized by subsequent exposure to H ₂ plasma. In this method, a SiH ₄ plasma (or _SiH 4 / _{H 2} mixed plasma) important control parameters and generation time _{T H} of generation time _{T Si} and _{H 2} plasma. For example, when fixing the T _Si, by changing the T _H, it has been shown to be able to significantly change the crystallization rate of the silicon film. On the other hand, with respect to the deposition rate of the film (time average value), even when the silicon film by increasing the T _H is changed to a microcrystalline amorphous, the deposition rate is of the order to reduce at most about 30%.

  As a result of applying the microcrystalline silicon thin film obtained by these methods to the photoelectric conversion layer of a solar cell and evaluating a prototype of the solar cell, practical characteristics with a photoelectric conversion efficiency of about 9% at most are obtained.

  In addition, a tandem solar cell in which a power generation layer made of an amorphous silicon thin film and a power generation layer made of a microcrystalline silicon thin film have been proposed has been proposed, and solar cell modules having a total conversion efficiency of about 12% at most are mass-produced. .

  Recently, a substrate with a large area of 1 m × 1 m or more in order to be able to manufacture a solar cell with higher productivity and lower cost for full-scale practical application of a silicon thin film solar cell (For example, 1.4 m × 1.1 m) has come to be used. The formation of the above-mentioned microcrystalline silicon thin film has become more and more important not only for its deposition rate and film quality, but also for large-area and uniform film-forming technology that can uniformly form on such a metric-class large-area substrate. Yes.

In the above plasma CVD apparatus, SiH ₄ gas or H ₂ gas is supplied to the plasma electrode, and after sufficiently mixed in the gas buffer chamber inside the electrode, a shower plate (a number of gas ejection holes are formed on the electrode surface). Gas is introduced into the vacuum vessel from the electrode plate. For this reason, in the reaction space between the plasma electrode and the substrate, SiH ₄ gas and H ₂ gas ejected from the shower plate are decomposed in plasma, adhered to the film surface, recombined, etc. Through the surface reaction, a part is taken into the film, and the remaining unreacted gas is exhausted from the periphery of the electrode and the substrate.

Since SiH ₄ gas mainly decomposes in the plasma and adheres to the surface, consumption increases as it is transported from the center of the electrode or the substrate to the peripheral portion, and the SiH ₄ density decreases. On the other hand, since the H ₂ gas is almost balanced between the decomposition in the plasma and the recombination on the surface, the density is kept almost constant in the plane of the electrode and the substrate. Therefore, when the area of the substrate is large and the distance between the plasma electrode and the substrate is short, the mixing ratio of SiH ₄ gas and H ₂ gas is locally different between the central portion and the peripheral portion of the substrate. It becomes like this.

  In addition, since the non-uniformity of the gas mixture ratio tends to increase as the pressure increases, in the case of a microcrystalline silicon thin film formed under conditions of high gas pressure and narrow electrode spacing, It becomes extremely difficult to form a thin film having a uniform film thickness and film quality on a large-sized substrate of a class.

In order to eliminate the non-uniformity of film formation related to such gas supply, various proposals described below have been made. For example, in the invention described in Patent Document 3, the gas ejection holes of the shower plate are classified into those for SiH ₄ gas and those for H ₂ gas, and the gas ejection holes for SiH ₄ gas have a distribution in the electrode surface. Arranged. Specifically, the density of the ejection holes is reduced at the central part of the electrode, and the density of the ejection holes is increased at the peripheral part. Thereby, the amount of SiH ₄ gas flowing into the plasma from the gas hole can be adjusted to be relatively small at the center portion of the electrode and to increase toward the periphery. As a result, the density of SiH ₄ gas and H ₂ gas can be made uniform in the electrode plane.

  In the invention described in Patent Document 4, the gas buffer chamber inside the plasma electrode is divided into a plurality of small chambers by partition walls, and gas is supplied to each chamber independently from the outside. Furthermore, the gas flow rate supplied to each buffer chamber can be adjusted to a different value in each chamber by a flow rate adjusting means such as a mass flow controller. Thus, the gas flow rate supplied from the shower plate of the plasma electrode to the reaction space can be controlled to a desired in-plane distribution, and uniform film formation is possible even on a large area substrate.

JP 2001-237187 A Japanese National Patent Publication No. 9-508236 JP 2001-223170 A JP 2007-324331 A

N. Layadi, PR Cabarrocas, B. Drevillon, I. Solomon, “Real-time spectroscopic ellipsometry study of the growth of amorphous and microcrystalline silicon thin films prepared by alternating silicon deposition and hydrogen plasma treatment”, Phys. Rev. B, vol .52, pp.5136-5143 (1995)

However, in the production of a silicon thin film solar cell having practical photoelectric conversion efficiency, a process of forming a microcrystalline silicon film having a film thickness of 2 to 3 μm on a large-scale substrate of a metric class is essential. Both the uniformity of the film deposition rate and the uniformity of the crystallinity are required to be about 10% or less. In order to ensure the uniformity of the deposition rate, it is effective to improve the uniformity of the density of the SiH ₄ gas as disclosed in Patent Documents 3 and ₄ . However, the crystallinity of the film is not only the flow rate ratio of SiH ₄ gas to H ₂ gas Q (SiH ₄ ) / [Q (SiH ₄ ) + Q (H ₂ )], but also the distance between the plasma electrode and the substrate, Since it also strongly depends on the substrate temperature, it is difficult to achieve both the deposition rate and the crystallinity uniformity.

  Further, in the invention described in Patent Document 3, in order to improve the uniformity of film formation, the in-plane distribution of the gas ejection holes of the plasma electrode may be optimized, but the gas pressure, high frequency voltage, electrode spacing, etc. Each time the film forming conditions are changed, there is a problem that the optimum gas ejection hole distribution is different. For this reason, it is necessary to prepare a large number of shower plates in advance when setting the film formation conditions, and to change the shower plate by opening the apparatus to the atmosphere for a long time each time the conditions are changed.

In the invention described in Patent Document 4, the gas flow distribution in the electrode surface can be controlled by a plurality of mass flow controllers. However, it is difficult to simultaneously improve the non-uniformity of the film thickness and the non-uniformity of the crystallinity of the film only by adjusting the SiH ₄ gas flow rate. Specifically, when the flow rate of the SiH ₄ gas is locally reduced in a certain region of the plasma electrode, the deposition rate decreases in the vicinity thereof. On the other hand, regarding the crystallinity of the film, when the SiH ₄ gas flow rate is decreased, the gas flow rate ratio Q (SiH ₄ ) / [Q (SiH ₄ ) + Q (H ₂ )] is also decreased, and the crystallinity of the film is improved. .

As described above, in the conventional technique, when the SiH ₄ gas flow rate is changed, both the film thickness uniformity and the crystal uniformity are affected, and these cannot be controlled independently. There was a problem.

  The present invention has been made in view of the above, and an object thereof is to obtain a thin film forming apparatus capable of uniformly forming a semiconductor film on a metric class large-area substrate.

  In order to solve the above-described problems and achieve the object, the present invention includes a substrate holding means for holding a substrate, a plasma electrode provided to face the substrate, and a high-frequency power source for applying a high-frequency voltage to the plasma electrode. A thin film forming apparatus for forming a semiconductor film on a substrate by generating plasma of a mixed gas of a material gas and a hydrogen gas of a thin film to be formed between a substrate holding means and a plasma electrode. A shower plate having a large number of gas ejection holes, and a gas buffer chamber in which a space on the opposite side of the gas ejection holes of the shower plate is defined by a plurality of substantially concentric chambers. The first gas supply means for supplying each of the plurality of chambers, the second gas supply means for supplying the material gas to each of the plurality of chambers, and the supply flow rate of the first gas to the gas buffer chamber are controlled. 1st flow rate Periodic supply means, second flow rate adjusting means for controlling the supply flow rate of the second gas to each of the plurality of chambers, and supply and shutoff of the material gas to the plurality of chambers from the second gas supply means And a control means for independently executing duty control for each room.

  The thin film forming apparatus according to the present invention improves both the deposition rate and the uniformity of crystallinity by controlling the time average value of the flow rate of the material gas supplied to each chamber and the supply / supply stop time, respectively. It is possible to achieve the remarkable effect that the yield is improved.

FIG. 1 is a diagram schematically showing a configuration of an embodiment of a thin film forming apparatus according to the present invention. FIG. 2 is an enlarged view of the plasma electrode of the thin film forming apparatus. FIG. 3 is a diagram illustrating an example of dividing the gas buffer chamber into small chambers by the partition walls. FIG. 4 is a diagram illustrating an example of supply of SiH ₄ gas to each small chamber.

  Embodiments of a thin film forming apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment FIG. 1 is a diagram schematically showing a configuration of an embodiment of a thin film forming apparatus according to the present invention. FIG. 2 is an enlarged view of the plasma electrode of the thin film forming apparatus according to the embodiment. This thin film forming apparatus is based on a conventional plasma CVD apparatus, and includes a substrate stage 12 and a plasma electrode 13 in a vacuum vessel 10 in which an atmosphere for forming a thin film is formed. The substrate stage 12 and the plasma electrode 13 are installed such that the opposing surfaces are parallel to each other. A gas exhaust pipe 11 is provided in the vacuum container 10, and a gas in the vacuum container 10 is exhausted by a vacuum pump (not shown) connected to the gas exhaust pipe 11 so that the inside of the vacuum container 10 has a predetermined degree of vacuum. Is set.

  The substrate stage 12 is electrically grounded in the same manner as the vacuum vessel 10, and a large area substrate 100 (for example, a metric class substrate having a size of 1.4 m × 1.1 m) on which a film forming process is performed is placed. It has a structure. In addition, a heater (not shown) is built in the substrate stage 12, and the substrate temperature is set to a predetermined temperature, for example, a value of about 150 to 250 ° C. during the film forming process. In the present embodiment, the substrate stage 12 is provided on the lower side of the vacuum vessel 10. The substrate stage 12 corresponds to the substrate holding means in the claims.

The plasma electrode 13 includes a cylindrical side surface portion 131 and a bottom surface opposite to the upper surface portion 133 at one end of the cylindrical structure, and a large number of glass ejection holes 134 are uniformly distributed on the bottom surface. The shower plate 132 is provided. Further, a gas buffer chamber 135 for sufficiently mixing and diffusing SiH ₄ gas and H ₂ gas ejected from the gas ejection holes 134 of the shower plate 132 during film formation is provided inside the plasma electrode 13. The buffer chamber 135 is divided into a plurality of small chambers 137 (137a to 137c) by partition walls 136 (136a, 136b). The manner in which the partition walls 136 and the small chambers 137 are arranged varies depending on the shape and dimensions of the substrate on which film formation is performed, but in this embodiment, as shown in FIG. 3, the gas buffer chamber 135 has two ring-shaped partitions. The walls 136a and 136b are divided into three substantially concentric chambers 137a, 137b, and 137c.

  The plasma electrode 13 is disposed at a predetermined distance above the substrate placement surface of the substrate stage 12 so that the shower plate 132 is parallel to the substrate placement surface of the substrate stage 12, and is fixed in the vacuum vessel 10. Here, the cylindrical side surface portion 131 and the upper surface portion 133 of the plasma electrode 13 are electrically insulated from the vacuum vessel 10 by an insulating spacer 14 such as alumina or polytetrafluoroethylene (PTFE). It is fixed to the vacuum vessel 10.

  Furthermore, the cylindrical upper surface portion 133 of the plasma electrode 13 is electrically connected to the high-frequency power source 40 via a shield box 20 installed so as to surround the plasma electrode 13 and an impedance matching device (not shown). Yes. As a result, a high frequency voltage is applied to the plasma electrode 13. The oscillation frequency of the high frequency power supply 40 is generally 13.56 MHz, 27.12 MHz, or the like, but in order to increase the plasma density to increase the film formation speed, a frequency of 30 to 150 MHz, that is, VHF (Very High Frequency) band may be used. As described above, since a high-frequency voltage is applied to the plasma electrode 13, it is necessary to arrange a shield box 20 installed so as to surround the plasma electrode 13 outside the vacuum vessel 10 in order to prevent high-frequency radiation and leakage. is there.

In order to supply H ₂ gas and SiH ₄ gas to each of the plurality of small chambers 137 of the gas buffer chamber 135, a plurality of H ₂ gas supply ports 21 (21 a, 21 b, 21 c) are provided on the upper surface portion 133 of the plasma electrode 13. ) And a plurality of SiH ₄ gas supply ports 25 (25a, 25b, 25c).

In the present embodiment, as shown in FIG. 3, the gas buffer chamber 135 is divided into three small chambers 137a, 137b, 137c, and each of the H ₂ gas supply ports 21 (21a, 21b, 21c) has , H ₂ gas supply pipe 22 is arranged, H ₂ in the upstream portion of the gas supply pipe 22, a mass flow controller 23 for controlling the flow rate of H ₂ gas from the H ₂ gas supply unit (not shown) for supplying the H ₂ gas And a gas valve 24. The mass flow controller 23 and the gas valve 24 are arranged outside the shield box 20.

On the other hand, the method of supplying SiH ₄ gas is different from the above-described case of H ₂ gas, and is performed by individually controlling the flow rates of SiH ₄ gas supplied to the three small chambers 137a to 137c. Therefore, SiH ₄ gas (not shown) for supplying SiH ₄ gas is supplied to the three SiH ₄ gas supply pipes 26 (26a, 26b, 26c) connected to the SiH ₄ gas supply ports 25 (25a, 25b, 25c). Mass flow controllers 27 a, 27 b, 27 c and gas valves 28 a, 28 b, 28 c for controlling the flow rate of SiH ₄ gas from the _four gas supply unit are provided outside the shield box 20.

Thus, the thin film forming apparatus according to the present embodiment can individually control and adjust the flow rate of the SiH ₄ gas supplied to each of the three small chambers 137a to 137c of the gas buffer chamber 135. Since the SiH ₄ gas incident on the plasma from the gas ejection hole 134 of the shower plate 132 is decomposed and consumed as it is transported from the center of the plasma electrode 13 to the peripheral portion, the SiH ₄ density in the plasma is not constant. . When the distance from the center of the plasma electrode 13 is plotted on the horizontal axis and the SiH ₄ concentration is plotted on the vertical axis, the relationship between the two is represented by a graph (the peak at the center of the plasma electrode 13 is the maximum at the center of the plasma electrode 13 and the minimum at the periphery) ). Therefore, the SiH ₄ gas flow rate Q (SiH ₄ ) supplied to the small chamber 137 a located at the center of the plasma electrode 13 is relatively small, and the SiH ₄ gas flow rate Q supplied to the small chamber 137 c located around the plasma electrode 13. By relatively increasing (SiH ₄ ), the SiH ₄ density in the plasma can be adjusted to approach a constant value. As a result, it is possible to improve the uniformity of the thickness of the silicon film formed on the substrate.

Furthermore, in the thin film forming apparatus according to the present embodiment, gas valves 29a, 29b, and 29c that switch the passage / blocking of SiH ₄ gas at high speed are also provided on the SiH ₄ gas supply pipes 26a, 26b, and 26c inside the shield box 20. The supply / stop of supply of SiH ₄ gas into the vacuum vessel 10 can be switched at high speed. In order to switch the supply / stop of supply of SiH ₄ gas as fast as possible, the piping distance between the gas valve 29 and the plasma electrode 13 may be as close as possible. For example, the volume of the SiH ₄ supply pipe 26 between the gas valve 29 and the plasma electrode 13 is smaller when the piping distance between the gas valve 29 and the plasma electrode 13 is 5 cm than when the pipe distance is 10 cm. ₄ gas supply / supply stop switching becomes faster.

  Here, the gas valves 29a, 29b, and 29c are air-driven, and are connected to air supply pipes 30a, 30b, and 30c for sending compressed air. The air supply pipes 30a, 30b, and 30c are provided with electromagnetic gas valves 31a, 31b, and 31c that switch passage / blocking of compressed air outside the shield box 20. As already described, a high-intensity high-frequency electric field exists in the shield box 20, but the gas valves 29a to 29c are air-driven, have no electrical operation, and are opened and closed only by compressed air. In such an environment, it can be used without any problem.

In addition, since a high-frequency voltage or a direct current self-bias voltage is applied to the upper surface portion 133 of the plasma electrode 13, the supply pipes 22 and 26 for H ₂ gas and SiH ₄ gas are made of metal (for example, stainless steel). In order to electrically insulate the plasma electrode 13 and the gas supply pipes 22 and 26 from each other, gas supply ports 21 and 25 for H ₂ gas and SiH ₄ gas are provided inside an insulator block such as alumina or PTFE. The one in which the flow path is formed is used. However, this is not always necessary, and even if the air-driven gas valves 29 a to 29 c are directly attached to the upper surface portion 133 of the plasma electrode 13, there is no problem in the opening / closing operation, so that the SiH ₄ gas is supplied to the vacuum vessel 10. / Convenient for speeding up switching of supply stop. However, in this case, it is necessary to attach an insulating pipe or the like in the middle of the gas pipes 22 and 26 in the shield box 20 and electrically disconnect them.

  In the present embodiment, an air-driven valve has been described as an example of a gas valve that mechanically opens and closes. However, it is needless to say that the present invention is not limited to an air-driven system. Furthermore, even a piezo valve that opens and closes electrically can be applied as long as the electromagnetic shield of the valve is sufficient.

Furthermore, the thin film forming apparatus according to the present embodiment includes a control unit 60 that controls opening and closing of the gas valves 29a to 29c that switch the passage / blocking of the SiH ₄ gas at high speed. The control unit 60 supplies a valve opening / closing signal for switching supply / stop of supply of SiH ₄ gas into the vacuum vessel 10 to the gas valves 31a to 31c at a predetermined cycle.

  Next, a thin film forming method in the thin film forming apparatus having the above configuration will be described. First, after setting the substrate 100 on the substrate stage 12 in the vacuum vessel 10, the inside of the vacuum vessel 10 is evacuated through the gas exhaust pipe 11, and the inside of the vacuum vessel 10 is set to a predetermined degree of vacuum. Further, the substrate 100 is heated by the heater of the substrate stage 12 so that the substrate 100 has a predetermined temperature.

In this state, opening the gas valve 24 provided on the _{H 2} gas supply pipe 21, the _{H 2} gas is _{H 2} gas supply port 22, chamber 137a~137c and continuously to the vacuum vessel 10 via a shower plate 132 Supplied. At this time, the total flow rate of the H ₂ gas supplied to the vacuum vessel 10 is a value set by the mass flow controller 23.

On the other hand, with respect to SiH ₄ gas, opened the gas valve 28a~28c provided upstream of the SiH ₄ gas supply pipes 26 a to 26 c, SiH ₄ gas in the respective flow rates set by the mass flow controller 27a to 27c, SiH ₄ It is supplied to the vacuum vessel 10 through the gas supply port 25, the small chambers 137 a to 137 c and the shower plate 132. Here, the gas valves 28a to 28c are kept open continuously, but the three gas valves 29a to 29c in the shield box 20 are repeatedly opened and closed at a predetermined cycle to supply SiH ₄ gas to the small chambers 137a to 137c. Switch supply stop.

More specifically, in response to the valve opening / closing signal from the control unit 60, first, the gas valves 31a to 31c on the air supply pipes 30a to 30c are opened and closed, respectively, thereby the gas valves 29a to 29a of the SiH ₄ gas supply pipes 26a to 26c. Supply / stop of supply of compressed air to 29c is switched. For example, when the gas valves 29a to 29c for switching between supply / stop of supply of SiH ₄ gas are normally closed, when the valve opening signal is output from the control unit 60 and the gas valves 31a to 31c are opened, the gas valves 29a to 29c are opened. 29c is supplied with compressed air and is in an open state.

Conversely, when a valve closing signal is output from the control unit 60 and the gas valves 31a to 31c on the air supply pipes 30a to 30c are closed, compressed air to the gas valves 29a to 29c that switches supply / stop of supply of SiH ₄ gas. Is stopped, and the gas valves 29a to 29c are closed by the action of air pressure.

In this way, it is possible to switch the supply / stop of supply of SiH ₄ gas to the small chambers 137a to 137c (and further to the vacuum vessel 10 through the shower plate 132) of the gas buffer chamber 135. Here, even when the gas valve 29a~29c by opening and closing switches the supply / supply stop of the SiH ₄ gas, respectively, by the mass flow controller 27a~27c flow rate of SiH ₄ gas supplied to each chamber 137a~137c the corresponding Since it is controlled, the time average value of the gas flow rate is a value set by the mass flow controllers 27a to 27c.

By the way, as described above with respect to the method of forming the microcrystalline silicon film by the “layer-by-layer method”, when the silicon thin film is deposited by alternately generating the SiH ₄ / H ₂ mixed plasma and the H ₂ plasma repeatedly. by adjusting the time _{T H} of generating of _{H 2} plasma to clear the supply time _{T Si} and SiH ₄ gas by turning on the supply of the SiH ₄ gas to generate a _SiH 4 / _{H 2} mixed plasma, silicon The crystallinity of the film can be changed over a wide range from amorphous to microcrystalline. Further, if the time average value of the flow rate of the SiH ₄ gas is kept constant, the deposition rate of the silicon film can be kept substantially constant.

Therefore, by adjusting the opening / closing time of the gas valves 29a to 29c for supplying SiH ₄ gas connected to the small chambers 137a to 137c of the gas buffer chamber 135, the crystallinity is hardly changed. It is possible to improve the in-plane uniformity. For example, when the duty ratio [= T _Si / (T _Si + _TH )] of supplying / stopping supply of SiH ₄ gas is changed and the duty ratio is reduced (T _Si is shortened), the crystallinity of the deposited silicon film is increased. On the contrary, when the duty ratio is increased ( _TSi is increased), the crystallinity is lowered. Thus, the time average value Q of the flow rate of SiH ₄ gas supplied to the chamber 137a~137c (SiH ₄₎ and the supply / supply stop time _(T Si / T _H), by controlling individually for each chamber, It is possible to improve both the deposition rate and the crystallinity uniformity. As described above, SiH ₄ gas is supplied at a relatively small flow rate to the small chamber 137 a located at the center of the plasma electrode 13, and at a relatively large flow rate to the small chamber 137 c located at the periphery of the plasma electrode 13. SiH ₄ gas is supplied (in other words, the small chamber 137a located at the center of the plasma electrode 13 reduces the amount of SiH ₄ gas supplied per unit time, and the small chamber 137c located around the plasma electrode 13 is unit time. By increasing the supply amount of SiH ₄ gas per unit), the density of SiH ₄ in the plasma can be adjusted to approach a certain level, and as a result, the uniformity of the film thickness of the silicon film formed on the substrate is improved. It becomes possible to make it. In this case, the small chamber 137a located at the center of the plasma electrode 13 has a relatively large duty ratio T _Si / (T _Si + _TH ), and the small chamber 137c located at the periphery of the plasma electrode 13 has a duty ratio T _Si / By making (T _Si + _TH ) relatively small, the in-plane uniformity of crystallinity can be improved without impairing the uniformity of the film thickness. An example of the supply of SiH ₄ gas to the small chambers 137a to 137c is shown in FIG.

Note that the silicon film is deposited on the substrate while the SiH ₄ gas is supplied, and the crystallinity of the deposited film changes while the supply of the SiH ₄ gas is stopped. The thinner one is convenient for changing the crystallinity.

After the microcrystalline silicon thin film having a predetermined thickness is formed as described above, the gas valve 24 provided on the H ₂ gas supply pipe 21 and the gas valve 28 provided on the SiH ₄ gas supply pipe 26 are provided. Is closed, the heater of the substrate stage 12 is turned off, and the inside of the vacuum vessel 10 is sufficiently evacuated before returning to atmospheric pressure. Then, the substrate 100 placed on the substrate stage 12 is carried out of the vacuum vessel 10 and the thin film forming process is completed.

The thin film forming apparatus according to this embodiment, the time average value Q of the flow rate of SiH ₄ gas supplied (SiH ₄₎ and the supply / supply stop time _(T Si / T _H), can be controlled respectively for each chamber. For this reason, it is possible to improve both the deposition rate and the uniformity of crystallinity, and the yield is improved. Moreover, since it is not necessary to replace the shower plate 132 when setting the conditions, it is not necessary to open the apparatus to the atmosphere for a long time each time the conditions are changed. For this reason, it is not necessary to depressurize the vacuum vessel 10 associated with the replacement of the shower plate when setting the conditions, and energy consumption can be reduced.

Here, an example will be described in which a microcrystalline silicon thin film was formed on a 1.4 m × 1.1 m large-area glass substrate by the above method and evaluated. Here, the flow rates of SiH ₄ gas supplied to the small chambers 137a, 137b, and 137c are Q (SiH ₄ ) = 1.8 slm (slm: 101.25 hPa, flow rate per minute at 0 ° C.), 2.0 slm, 2 .4 slm, the total flow rate of H ₂ gas is Q (H ₂ ) = 98 slm, the gas pressure in the vacuum vessel 10 is 1500 Pa, the high frequency power (frequency 27.12 MHz) for plasma generation is 15 kW, the plasma electrode 13 and the substrate stage 12 And a distance of 6 mm, and the temperature of the substrate stage 12 was set to 200 ° C. to form a silicon thin film.

SiH ₄ with respect to the supply / stop of gas supply, the range of 10~0.1Hz a repetition frequency, where the supply time of the SiH ₄ gas was formed varied in the range of _{T Si} = _{5ms~5s, T} Si is T It was confirmed that the crystallinity of the film changed within the range of _Si = 10 ms or more and within 1 s. Therefore, the intensity ratio I _c / I _a between the peak I _a (480 cm ⁻¹ ) attributed to amorphous and the peak I _c (520 cm ⁻¹ ) attributed to crystal obtained by Raman scattering spectroscopy of the silicon film is the substrate 100. as in the surface is about 7, and SiH ₄ result of adjusting the gas supply / stop time of the _(T Si / T _H) to each chamber 137A～137c, all supply / stop frequency 5 Hz (period 200 ms), Satisfactory uniform film formation (deposition rate uniformity ± 6%, crystallinity uniformity) when the time for supplying SiH ₄ gas to each chamber 137a, 137b, 137c is set to T _Si = 50 ms, 45 ms, and 30 ms, respectively. ± 9%) was achieved.

In the present embodiment, the gas buffer chamber is formed so that the uniformity of the deposition rate of the silicon film deposited on the substrate 100 is within a desired value (for example, ± 10%) during film formation by the plasma CVD method. The flow rate Q (SiH ₄ ) of the SiH ₄ gas supplied to each of the 135 small chambers 137a to 137c is adjusted by the corresponding mass flow controllers 27a to 27c. In addition, by repeatedly opening and closing the SiH ₄ gas valves 29 a to 29 c connected to the small chambers 137 a to 137 c, the SiH ₄ gas is supplied / stopped at a constant period, and the crystallinity of the silicon film deposited on the substrate 100 is improved. The supply / supply stop time (T _Si / _TH ) of the SiH ₄ gas is adjusted so as to be in a desired range. For example, the intensity ratio I _c / I _a between the peak I _a (480 cm ⁻¹ ) attributed to amorphous and the peak I _c (520 cm ⁻¹ ) attributed to crystal obtained by Raman scattering spectroscopy of the silicon film is 100%. What is necessary is just to set it as 6 or more and 7 or less in a surface. Thereby, compared with the conventional deposition method of a microcrystalline silicon film, the effect that the deposition rate and crystallinity at the time of film-forming can be made more uniform is acquired.

In addition, the said embodiment is an example of suitable implementation of this invention, and this invention is not limited to this. For example, in the above-described embodiment, the method for manufacturing a microcrystalline silicon film using H ₂ gas and SiH ₄ gas has been described as an example. However, an inert gas such as He, Ne, or Ar is used as the H ₂ gas. It may be added. The material gas is not limited to SiH ₄ gas, but may be other gas containing Si (for example, disilane (Si ₂ H ₆ )), diborane (B ₂ H ₆ ), phosphine (PH ₃ ). A dopant gas typified by arsine (AsH ₃ ) may be added. In addition to microcrystalline silicon, the same effect can be obtained in the formation of microcrystalline silicon germanium (Si _x Ge _1-x ) or microcrystalline germanium, and high-speed film formation is possible while maintaining high crystallinity. . In the case of forming a microcrystalline silicon germanium, a mixed gas of SiH ₄ and GeH ₄ may be used as a material gas, and in the case of forming a microcrystalline germanium, a GeH ₄ gas may be used as a source gas. As described above, the present invention can be variously modified.

  As described above, the thin film forming apparatus according to the present invention is useful for manufacturing a solar cell using a microcrystalline silicon thin film using a metric class large-area substrate.

10 the vacuum chamber 11 the gas exhaust pipe 12 substrate stage 13 plasma electrode 14 insulating spacers 20 sealed box 21a, 21b, 21c _{H 2} gas supply port 22 the H ₂ gas supply pipe 23 a mass flow controller (for _{H 2} gas)
24, 28a, 28b, 28c, 29a, 29b, 29c, 31a, 31b, 31c Gas valve 25a, 25b, 25c SiH ₄ gas supply port 26a, 26b, 26c SiH ₄ gas supply pipe 27a, 27b, 27c Mass flow controller (SiH ₄ For gas)
30a, 30b, 30c Air supply pipe 40 High frequency power supply 60 Control unit 100 Substrate 131 Side surface 132 Shower plate 133 Upper surface part 134 Gas ejection hole 135 Gas buffer chamber 136a, 136b Partition wall 137a, 137b, 137c Small chamber

Claims (5)

A substrate holding means for holding a substrate, a plasma electrode provided facing the substrate, and a high frequency power source for applying a high frequency voltage to the plasma electrode, and formed between the substrate holding means and the plasma electrode A thin film forming apparatus for forming a semiconductor film on the substrate by generating plasma of a mixed gas of a material gas and hydrogen gas of a thin film,
The plasma electrode includes a shower plate having a large number of gas ejection holes, and a gas buffer chamber in which a space opposite to the gas ejection holes of the shower plate is defined in a plurality of substantially concentric chambers. And
First gas supply means for supplying the hydrogen gas to each of the plurality of chambers;
Second gas supply means for supplying the material gas to each of the plurality of chambers;
First flow rate adjusting means for controlling a supply flow rate of the hydrogen gas to the gas buffer chamber;
A second flow rate adjusting means for controlling a supply flow rate of the material gas to each of the plurality of chambers;
A thin film forming apparatus comprising: a control unit that independently executes duty control for each of the chambers, which periodically repeats the supply and blocking of the material gas to the plurality of chambers from the second gas supply unit. .   The thin film forming apparatus according to claim 1, wherein the material gas supply flow rate is smaller in a chamber closer to the center of the shower plate.   3. The thin film forming apparatus according to claim 1, wherein the chamber closer to the center of the shower plate has a larger ratio of the supply period in the repetition cycle.   The said control means is provided in the shield box, and is provided with the air valve which opens and closes according to an air pressure, and the opening / closing means which performs the said duty control by opening and closing the said air valve, The Claim 1 to 3 characterized by the above-mentioned. The thin film forming apparatus according to any one of the above. The first and second gas supply means have first and second gas supply pipes connected to each of the plurality of chambers,
The thin film formation according to any one of claims 1 to 4, wherein the first and second flow rate adjusting means are mass flow controllers provided on the first and second gas supply pipes. apparatus.

Images