JP2002270511A - Method for depositing polycrystalline si thin film, polycrystalline si thin film, photovoltaic element and target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polycrystalline silicon thin film with large particle size. SOLUTION: In a polycrystalline Si thin film depositing method, polycrystalline thin film Si is deposited on an oxide substrate. The method includes a process for partially forming a crystalline silicon area on the substrate, and a process for making crystal Si grow in the crystalline silicon area with silicon as a core on a condition that amorphous Si is deposited in an area where crystalline silicon is not formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for depositing a polycrystalline Si thin film having good crystallinity, a polycrystalline Si thin film, and a photovoltaic device.

[0002]

2. Description of the Related Art Conventionally, the following two methods (a) and (b) have been known as methods for depositing a polycrystalline Si thin film.

(A) A thermal CV that blows a gas such as SiH ₄ onto a substrate heated to a high temperature and decomposes the gas to generate deposition seeds and form a polycrystalline Si thin film on the substrate.
D method.

(B) Irradiation of an amorphous Si film or a polycrystalline Si film having a small grain size formed on a substrate by a CVD method or a glow discharge plasma decomposition method with laser light irradiation, infrared light irradiation,
Alternatively, a method combining a CVD method of forming a polycrystalline Si thin film on a substrate by performing a cooling treatment after being heated and melted in an electric furnace or the like, and an annealing treatment.

However, the above methods (a) and (b) require a heat treatment at about 1000 ° C. or higher when producing a polycrystalline Si thin film. For this reason, there has been a problem that ordinary glass or metal cannot be used as a substrate for forming a polycrystalline Si thin film. Therefore, 10
There has been a demand for a method of depositing a polycrystalline Si thin film by a low-temperature process of 00 ° C. or lower.

As a method of realizing the low temperature process, for example, a method (c) of decomposing a gas by using discharge or light instead of heat has been devised.

As a typical gas decomposition method, there are a plasma CVD method and a photo CVD method. The plasma CVD method is superior to the photo CVD method in that the film deposition rate is high. Usually, in these methods, SiH ₄ gas, S
When a source gas such as iF ₄ gas or Si ₂ H ₆ gas is greatly diluted with H ₂ gas to increase discharge power, a polycrystalline Si thin film can be formed even on a substrate at a low temperature of 300 to 450 ° C.

[0008] However, the polycrystalline Si thin film produced by the method (c) contains a large amount of amorphous Si. Therefore, when used as a photoelectric conversion element, there is a problem that the photoelectric conversion characteristics are poor and the crystal grain size is 5 nm or less. It is considered that the reason for this is that the deposited species formed by the non-equilibrium reaction called glow discharge plasma fall on the substrate and are taken into the film, so that the structure of the formed thin film is not sufficiently relaxed. . Accordingly, there has been a demand for a method of depositing a polycrystalline Si thin film that can sufficiently perform the above-mentioned structural relaxation while maintaining a low-temperature process.

As a method for simultaneously realizing the low-temperature process and the structural relaxation, for example, Japanese Patent Application Laid-Open No. 07-5105
No. 7 publication.

[0010] This technique, SiF _{n (n} = 1~3) generated by separate space which is adjacent to the film-forming space by introducing radical, dopant radicals and H radicals into the deposition space, SiF _n radicals And H radicals collide and react in the gas phase to form radicals Si for film formation.
In a deposition method for generating F _l H _m (l + m ≦ 3) and forming a polycrystalline Si thin film on the surface of a substrate in the film formation space, the film formation space is kept flowing with the H radicals. The SiF _n radicals and the dopant radicals are introduced in a time-divided manner, and the time during which the SiF _n radicals and the H radicals flow (t1), and the time during which the dopant radicals and the H radicals flow (t1)
2) and the time during which only the H radical is flowing (t)
The method (d) is characterized in that the film is formed while repeating the three types of times (3).

According to the method (d), the structure of the thin film can be sufficiently relaxed while the low-temperature process is maintained, and a doping gas is mixed into the source gas to form an n-type or p-type polycrystal. It is described that a deposition method capable of obtaining a polycrystalline Si thin film having good crystallinity can also be realized when producing a Si thin film.

However, it is manufactured by the above method (d).
In the polycrystalline Si thin film,_nRadical and H radical
Is a radical that contributes to deposition by a gas phase reaction with
iX _lH_mGenerates radicals. Desirable radio
The proportion of the catalyst depends on the progress of the reaction. Therefore, each la
If the ratio of dicals or the condition of the deposition space is different,
The radicals have different rates of formation. Therefore, the deposition conditions
Once determined, a very high quality polycrystalline film can be obtained,
In order to determine the conditions, an experiment with considerable conditions
Was needed.

[0013] In order to deposit a polycrystalline Si thin film which has little dependency on the state of the film formation space, is excellent in reproducibility, and has good crystallinity, at least two F atoms or Cl atoms are contained per Si atom. Gas in which one or more H atoms are bonded,
Japanese Patent Application Laid-Open No. 08-25575 discloses a method for depositing a polycrystalline Si thin film, in which a film is formed by performing plasma glow discharge using electric power in a plasma excitation power control region.
No. 9 discloses this.

Japanese Patent Application Laid-Open No. 11-26385 discloses that an oxide containing at least one of silicon, aluminum and boron, or a glass containing silicon atoms is used as a substrate, and the temperature of the substrate is 200 ° C. to 200 ° C. 10
The substrate is exposed to hydrogen while being kept at 00 ° C., and oxygen atoms are reduced at various places on the substrate surface by the strong reducing action of hydrogen. At the place where the oxygen atoms are reduced, at least one of silicon, aluminum and boron is formed on the surface. After the element atoms are exposed, the ratio of the source gas to the gas for diluting the source gas to a predetermined concentration and the condition of the high-frequency power applied to convert the gas into plasma are as follows. 0.06 watts / square centimeter and less than 1/29 and 1/5 or less, and the high-frequency power is 0.06 watts / sq.
1/14 if less than watts / square centimeter
A method for obtaining a polycrystalline film by causing a plasma discharge under the condition exceeding 1/5 and not more than 1/5 is described.

The crystal grain size of polycrystalline silicon when used in a solar cell is preferably 5 in order to obtain a short-circuit current and fill factor comparable to that of a bulk polycrystalline silicon solar cell.
It requires μm or more. When a material having a small crystal grain size is mixed with polycrystalline silicon, the fill factor is particularly deteriorated. In addition, since a solar cell is a device in which generated charges flow in a direction perpendicular to a substrate, it is preferable that no grain boundaries exist in the vertical direction. Therefore, it is preferable that the crystal orientation perpendicular to the substrate is uniform.

However, the crystal grain size of the film obtained by this method is about 200 nm, and cannot be used for a solar cell or the like as it is. Then, after that, in order to further grow the crystal grain size of this polycrystalline silicon thin film in order to obtain the desired crystallinity in this thin film, heat treatment is performed on the substrate on which the polycrystalline silicon thin film is deposited, It is an essential condition to perform general annealing such as laser annealing.

Japanese Patent Application Laid-Open No. Hei 7-326575 discloses a method in which metal grains are provided on a tin oxide film, and the metal grains are heat-treated to form a dendritic growth to form a reticulated metal film. A method is described in which an amorphous semiconductor thin film is formed, and the amorphous semiconductor thin film is crystallized by heat treatment to produce a polycrystalline semiconductor thin film. However, this method requires a long heat treatment in order to crystallize the amorphous semiconductor film, which is problematic in terms of productivity.

Japanese Patent No. 3067821 discloses a process of providing a non-nucleation surface and a nucleation surface on a substrate, and generating a single crystal only on the nucleation surface on the substrate by a selective crystal growth method. And forming a polycrystalline continuous film by growing the polycrystalline silicon film. However, in this patent, in the process of providing a non-nucleation surface and a nucleation surface, only a method of performing a photolithography process every time is described.

Japanese Patent Application Laid-Open No. 9-82997 describes a method of forming a crystalline silicon film by forming an amorphous silicon film on a substrate, forming nickel silicide on the surface thereof, and performing heat treatment. ing. In this method, it is described that the heat treatment temperature can be reduced from 600 ° C. to 550 ° C. by forming a silicide. However, although the processing time is slightly improved from the conventional 10 hours to 4 to 8 hours, it is still long. There is a problem in terms of productivity.

However, the crystal grain size of the films produced by these methods is smaller than that of bulk polycrystalline Si. When a polycrystalline Si solar cell is manufactured and its characteristics are evaluated, the short-circuit current is smaller than that of a bulk polycrystalline silicon solar cell, and thus the conversion efficiency is smaller. When the thickness of the sample is increased, the fill factor is reduced because the crystal grain size is small. Therefore, when the conversion efficiency exceeds a certain thickness, it decreases. The inability to increase the thickness of the sample as in a bulk polycrystalline silicon solar cell is the reason that the short-circuit current cannot be increased.

[0021]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polycrystalline silicon film for a thin film polycrystalline silicon solar cell having a short-circuit current and a fill factor comparable to that of a bulk polycrystalline silicon solar cell. To provide a method for manufacturing on an inexpensive oxide substrate.

An object of the present invention is to provide a polycrystalline Si thin film having a crystal grain size comparable to that of bulk polycrystalline Si.

An object of the present invention is to provide a photovoltaic element having characteristics comparable to those using bulk polycrystalline Si (high short-circuit current and high conversion efficiency).

[0024]

In order to achieve the above object, the invention according to the present application provides a polycrystalline thin film on an oxide substrate.
In the method of depositing i, at least a step of partially forming a crystalline silicon region on a substrate and a condition in which amorphous Si is deposited in a region where crystalline silicon is not formed, Growing crystal Si as a nucleus. Further, the step of partially forming the silicon film is characterized in that a needle-shaped silicon target is sputtered.

The step of partially forming the crystalline silicon region is performed by sputtering a silicon target having at least a needle-like sputtering surface.

The target surface is formed of a porous layer.

The porous layer has a thickness of 10 to 300 μm.

The porous layer is characterized in that the surface of a silicon wafer is formed by anodization.

The porous layer is formed by forming the surface of a silicon wafer by using photolithography.

The needle-like portion of the needle-like silicon target has a needle-like portion of 0.1%.
It has a diameter of 1 μm to 5 μm.

The needle-shaped portion of the needle-shaped silicon target is 10
It is characterized by having an interval of １００100 μm.

After the step, the method further comprises a step of growing polycrystalline Si.

The polycrystalline Si thin film of the present invention is characterized by being formed by the above-mentioned deposition method.

The photovoltaic device of the present invention is characterized in that the above polycrystalline Si
It is characterized by using a thin film.

The sputtering target of the present invention comprises:
It is characterized in that the sputtering surface is acicular.

[0036]

[Function] By passing through the above steps, a large-grain type polycrystalline Si thin film can be obtained. That is, by the process of
A crystalline silicon region serving as a nucleus of a silicon crystal is partially formed on a substrate.

In the step (3), a crystal grows using the partially formed crystalline silicon region as a nucleus. The grown crystals also grow horizontally until they meet each other. Therefore, amorphous Si is deposited on a substrate where a silicon film is not partially deposited on which a crystal grain having a large grain size is obtained. Therefore, it does not prevent the crystal grains from growing in the horizontal direction. The portion of amorphous Si decreases as the crystal grains grow.

In the step, crystal grains are grown vertically to a desired thickness.

Accordingly, a crystalline silicon film having a large grain size can be obtained.

[0040]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an example of an apparatus suitable for use in the present invention.

Reference numeral 10 denotes a chamber for performing the above steps. Reference numeral 20 denotes a chamber for performing the above steps. 1 is a load lock chamber for inserting a substrate. Reference numeral 2 denotes a transfer chamber for moving the substrate. The load lock chamber 1 and the transfer chamber 2 are connected via a gate valve 3. The substrate is opened when the substrate is moved from the load lock chamber 1 to the transfer chamber 2, and is moved by the horizontal transfer rod 7. Reference numeral 4 denotes an exhaust device for exhausting the load lock chamber 1. The load lock chamber 1 is connected to an exhaust pipe 5 via a valve 6.

The substrate moved to the front of the chamber 10 of the transfer chamber 2 is transferred from the horizontal transfer rod 7 to the vertical transfer rod 11. The gate valve 13 opens, passes through the chamber connecting pipe 12, and is set at a predetermined location in the chamber 10. The empty vertical transport bar 11 is pulled back into the transport chamber and the gate valve 13 is closed. The chamber 10 is connected to an exhaust device 14 by an exhaust pipe 15.

Reference numeral 16 denotes a valve for controlling the exhaust of the chamber 10. Is completed, the gate valve 13 is opened again, and the vertical transport rod 11 is moved to the chamber 1.
0 and the substrate is transferred to the transport rod 11. Then, the transfer rod 11 is returned to the transfer chamber, and the gate valve 13
Is closed. Next, the substrate moved to the transfer chamber 2 is transferred from the transfer rod 11 in the vertical direction to the transfer rod 7 in the horizontal direction. Thereafter, it is moved to the front of the chamber 20.

The substrate moved to the front of the chamber 20 of the transfer chamber 2 is transferred from the horizontal transfer rod 7 to the vertical transfer rod 21. The gate valve 23 opens, passes through the chamber connecting pipe 22, and is set at a predetermined location in the chamber 20. The empty vertical transport bar 21 is pulled back into the transport chamber and the gate valve 23 is closed. The chamber 20 is connected to an exhaust device 24 by an exhaust pipe 25. 26 is an automatic butterfly valve for adjusting the pressure in the chamber 20.

After completing the steps (1) and (2), the gate valve 23 is opened again, the vertical transport rod 21 is inserted into the chamber 20, and the substrate is transferred to the transport rod 21. Then, the transfer rod 21 is pulled back to the transfer chamber, and the gate valve 23 is closed. Next, the substrate moved to the transfer chamber 2 is transferred from the transfer rod 21 in the vertical direction to the transfer rod 7 in the horizontal direction.

The substrate having undergone the steps (1) and (2) is moved to the load lock chamber 1 by the horizontal transfer rod 7 and taken out.

Hereinafter, each step will be described in detail.

Forming a partially crystalline silicon region. The substrate is inserted into a Si film forming chamber as shown in FIG. A sputter device shown in FIG. 2 is used for the step of partially forming a silicon film. Hereinafter, FIG. 2 will be described. 201 is a vacuum chamber for film formation. 20
2 is a cathode electrode for plasma glow discharge. 20
2 is a vacuum chamber 201 by an insulating ring 203.
And are electrically insulated. The cathode electrode 202 is D
It is connected to the C power supply 205. Reference numeral 206 denotes a shield cylinder which is provided to prevent discharge between the cathode electrode 302 and the inner wall of the vacuum chamber 201. Cathode electrode 2
The distance between 02 and the shield tube 206 is 1 mm. When the pressure is 500 Pa or less, discharge between the cathode electrode 202 and the shield tube 206 does not occur in the gas used according to Paschen's law.

Reference numeral 207 denotes an anode electrode, and the cathode electrode 2
Glow discharge is caused between the light emitting device and the device. Cathode electrode 202
A needle-shaped silicon target 204 is placed on the top. A substrate 208 is provided on the surface of the anode electrode 207. Reference numeral 209 denotes a heater block.
Is embedded, and a thermocouple 211 is attached. The heater 210 and the thermocouple 211 are connected to a temperature controller 212, and the heater block 209 is heated to a desired temperature. As a result, the substrate 208 mounted on the surface of the anode electrode 207 is heated to a desired temperature.

Reference numeral 213 denotes a gas introduction pipe for sputtering. The introduction pipe 213 is connected to the flow controller 214 and the valve 225, and is connected to each gas cylinder and its pressure regulator by the gas pipe 216. The introduction pipe 213 is introduced into the chamber through the outlet 218 via the valve 217.

Reference numeral 219 denotes a vacuum pressure gauge for measuring the pressure in the chamber 201, which sends a signal to the pressure controller 220. The pressure controller 220 controls the opening / closing degree of the automatic butterfly valve 222 attached in the middle of the exhaust pipe 221 by comparing the signal with the set value, and controls the pressure in the chamber 201 to be the set value. I have.

The exhaust pipe 228 is connected to a vacuum exhaust device (not shown).

The chamber connection pipe 12 to the transfer chamber in FIG. 1 is mounted in the vicinity of the substrate 208 in FIG. 2 and in a direction perpendicular to the drawing.

As the substrate, an oxide substrate is suitable.
When a silicon film is formed on an oxide substrate, an amorphous film is easily formed as compared with other substrates. That is, when crystalline silicon is formed in part of a substrate, a condition that a crystalline film is deposited in a region where crystalline silicon is present and an amorphous film is deposited in a region where crystalline silicon is not present is that other substrates It can be set easily compared to. As the oxide substrate, an inexpensive one is preferable, and specific examples thereof include quartz glass, alumina ceramic, a mullite substrate which is a mixture of Al ₂ O ₃ and SiO ₂ , and ZnO, In ₂ O ₃ , SiO ₂ , SnO _2, etc. A film obtained by forming a film of the oxide on a substrate such as stainless steel or a material obtained by oxidizing the surface of a metal silicon substrate is suitable. The temperature of the substrate is generally heated from 450 ° C. to 700 ° C.
The pressure in the chamber is usually kept at 10 ¹ to 10 ³ Pa. As the gas for the sputter, H ₂ or H _{2 and} A
A mixed gas with r is generally used.

Gas is supplied, and power is applied between the cathode electrode 202 on which the target 204 is mounted and the anode electrode 207 while the pressure is stabilized. As a power source, a DC power supply and an RF power supply are generally used, but a DC power supply is preferable in consideration of the cost of the apparatus. The thickness of the Si film is generally selected from 3 nm to 50 nm.

As the needle-shaped silicon target, a porous silicon layer is used. The porous silicon layer is formed by making a silicon single crystal wafer porous by anodization or photolithography. The smaller the tip diameter of the needle-shaped silicon target, the better. However, if it is too small, the workability and durability deteriorate. If the thickness is too large, the crystalline silicon region becomes too wide, and a plurality of crystal grains grow in one crystalline silicon region in the process, so that large crystal grains cannot be obtained. Usually φ0.1μm ~ φ
5 μm is suitable. The distance between the needles of the needle-shaped silicon target determines the grain size of the crystal grown in the step. The crystal grain size increases as the distance between the needles increases, but if it is too long, it takes a long time to deposit adjacent crystal grains in contact with each other. Generally, the interval between the needles is determined in consideration of productivity and the size of a desired crystal grain size. Generally 10μ
m to 100 μm is preferred. Within this range, a polycrystalline film having a large grain size and excellent productivity can be deposited.

In the anodization method for forming the needle-shaped silicon target used in the present invention, a hydrofluoric acid solution is preferably used, and the HF concentration can be increased to 10% or more to make the silicon target porous. The amount of current flowing during anodization is appropriately determined depending on the HF concentration, the desired thickness of the porous layer, the state of the surface of the porous layer, and the like.
^{The range of 2} to several tens mA / cm ² is appropriate.

Further, by adding an alcohol such as ethyl alcohol to the HF solution, the bubbles of the reaction gas generated during the anodization can be removed from the reaction surface without instantaneous stirring, and the porous material can be uniformly and efficiently removed. Silicon can be formed. The amount of alcohol to be added is H
It is appropriately determined depending on the F concentration, the desired thickness of the porous layer, or the surface state of the porous layer, and it is particularly necessary to carefully determine that the HF concentration does not become too low.

FIG. 3 is a cross-sectional view of an apparatus for anodizing a Si wafer with a hydrofluoric acid-based etchant. In the figure, 10
Reference numeral 21 denotes a Si wafer, 1216 denotes a hydrofluoric acid-based etchant, and 1217 and 1218 denote metal electrodes. Since the sputtered silicon region is easily crystallized in the Si wafer 1021 to be anodized, an n-type doped with P at a high concentration is used. It is desirable that the resistivity is 0.1 to 0.001 Ωm.

A voltage is applied between both electrodes by making the left metal electrode 1217 positive and the right metal electrode 1218 negative in FIG. 3 so that the electric field caused by this voltage is applied in a direction perpendicular to the surface of the wafer 1021. When installed, the wafer 1021 is made porous from the negative metal electrode 1218 side. As the hydrofluoric acid-based etchant 1216, concentrated hydrofluoric acid (49% HF)
Is used. During the anodization, bubbles are generated from the wafer 1021, and it is preferable to add alcohol as a surfactant for the purpose of efficiently removing the bubbles. As the alcohol, methanol, ethanol, propanol, isopropanol and the like are desirable.

It is also preferable to use a stirrer instead of the surfactant to perform anodization while stirring. The thickness of the surface to be made porous is preferably 10 to 300 (μm). When the thickness of the porous material is small, the number of times that it can be used as a needle-shaped target is reduced. If it is thick, it will be easily damaged during sputtering. The metal electrodes 1217 and 1218 are made of a material that is not eroded by the hydrofluoric acid solution, for example, gold (A
u), platinum (Pt) or the like is desirably used. The current density for performing anodization is a maximum of several hundred mA / cm 2, and the minimum value need not be 0.

In the anodization step, it is preferable to adjust the current density over time. When the current density of porous Si is large during anodization, the density of the porous Si layer becomes small. For this reason, as the current density increases, the volume of the pores increases, and the porosity (porosity; defined by the ratio of the density of the porous Si to the density of the bulk Si) increases. In order to obtain a polycrystalline silicon film having a large grain size, the porosity is preferably high. Generally 50
The above is preferred.

As another method for producing a needle-shaped silicon target, a photolithography method is used. Apply photoresist on silicon wafer and apply 1μ
A circle having a diameter of the order of magnitude (although the shape is not necessarily limited) is exposed at intervals of about 10 μm to 100 μm so that the resist in the circle is left. The resist other than the circle is removed. Next, an ordinary Si etchant (for example, 5
HNO ₃ : 3HF: 3CH ₃ COOH: 0.2Br)
Etch so as to leave a circle. Finally, the resist in the circle is removed.

A step of depositing a polycrystalline Si film on a substrate in which a crystalline silicon region is partially formed. In this step, a crystal is grown using the crystalline silicon region partially formed on the substrate having covered the surface in the step as a crystal nucleus.

[0065] As the raw material gas used in the process and of the present _{invention, SiH 4, SiF 4, SiCl} 4, Si x F y H z or _{Si x Cl y H z (x} , y, z is an integer of 1 or more) and It is the notation. These gases may be diluted with H ₂ gas as needed. In particular, when using SiH ₄ gas as a raw material, it is difficult to obtain a polycrystalline Si film unless diluted with H ₂ gas at least 10 times. When SiF ₄ or SiCl ₄ is used as a source gas, it is diluted with H ₂ gas, or mixed with a gas containing H in its constituent elements such as a gas such as SiH ₄ or SiCl ₂ H ₂ , or diluted with H ₂ gas and SiH _4, does not flow gas or in one of two ways to the constituent elements as a gas, such as SiCl ₂ H ₂ mixed gas containing H in the film forming space when the membrane No film formation occurs. The substrate is typically heated to a temperature between 150C and 500C.

In the present invention, the plasma excitation power source is V
Frequency ranges such as HF, UHF, and microwave are suitable. Power applied, the matching condition is different by the electrode structure, etc., usually 1W / cm ² ~50W / cm ² about power is applied.

The pressure in the chamber is usually 10 to 50
It is set to about 0 Pa.

After forming an appropriate film thickness, by repeatedly performing the treatment with H radicals on the film formation surface, a high-quality polycrystalline Si film having a larger grain size can be produced. As the main source gas (in this case, Si
Other gas such as H ₄ may be contained at 20% or less. ),
By using a silicon halide gas and mixing H ₂ gas with the silicon halide gas at a ratio of 1:10 to 20: 1, or by using a partially halogenated silicon hydride gas ( A high-quality polycrystalline Si film having a large grain size oriented in 110) can be manufactured.

If a device such as a solar cell that allows current to flow in the vertical direction is intended, a film in which crystal grains are grown in the vertical direction is preferable.

As a deposition apparatus for forming a polycrystalline Si thin film in this step, for example, an apparatus having a structure shown in FIG. 4 is used.

The chamber 20 shown in FIG. 1 has the structure shown in FIG.

Hereinafter, the film forming apparatus will be described in detail with reference to FIG.

Reference numeral 101 denotes a vacuum chamber for film formation.
102 is a cathode electrode for plasma glow discharge.
102 is a vacuum chamber 1 by an insulating ring 103.
01 is electrically insulated. Cathode electrode 102
Is a high frequency power supply 105 via a matching box 104
It is connected to the. Reference numeral 106 denotes a shield cylinder which is provided to prevent discharge between the cathode electrode 102 and the inner wall of the vacuum chamber 101. The distance between the cathode electrode 102 and the shield cylinder 106 is 1 mm. Pressure 50
If the pressure is 0 Pa or less, the discharge between the cathode electrode 102 and the shield cylinder 106 does not occur according to Paschen's law in the used gas.

Reference numeral 107 denotes an anode electrode,
Glow discharge is caused between the light emitting device and the device. Anode electrode 107
A substrate 108 is provided on the surface of the substrate. Reference numeral 109 denotes a heater block in which a heater 110 is embedded, and a thermocouple 111 is attached. The heater 110 and the thermocouple 111 are connected to a temperature controller 112,
Heater block 109 is heated to a desired temperature, and as a result, substrate 108 attached to the surface of anode electrode 107 is heated to a desired temperature.

Reference numerals 113, 114, and 115 are supply pipes for the source gas and the hydrogen gas, respectively. Introductory tubes 113, 11
4 and 115 are flow controllers 116 and 11 respectively.
7, 118 and valves 119, 120, 121, and are connected to respective gas cylinders and their pressure regulators by gas pipes 122, 123, 124, respectively. 113, 114, and 115 are connected in one piece on the way, and are introduced into the chamber through a valve 125 outlet 126.

Reference numeral 127 denotes a vacuum pressure gauge for measuring the pressure in the chamber 101, which sends a signal to the pressure controller 130. The pressure controller 130 controls the opening / closing degree of the automatic butterfly valve 129 attached in the middle of the exhaust pipe 128 by comparing the signal with the set value, and controls the pressure in the chamber 101 to the set value. I have.

The exhaust pipe 128 is connected to a vacuum exhaust device (not shown).

The chamber 101, the exhaust device, the exhaust pipe 128 and the automatic butterfly valve 129 shown in FIG.
5 and the automatic butterfly valve 26.

In order to grow the crystal largely using the region where the crystalline silicon is formed as a nucleus, it is necessary to form amorphous Si in a portion where the crystalline silicon is not formed. If crystalline Si is deposited thereon, its presence will hinder the lateral expansion of polycrystalline Si with the crystalline silicon region as a nucleus. Until the horizontal plane is completely covered by the polycrystal due to the lateral growth of the polycrystal Si, the polycrystal S grown with the crystalline silicon region as a nucleus
Film formation conditions are adopted in which amorphous Si is deposited in a portion where i grows and a crystalline silicon region is not formed. These conditions are not generally defined, the type of the substrate, the device itself, the shapes and intervals of the cathode electrode and the added electrode, the type and flow rate of the source gas, the type and flow rate of the diluent gas, the frequency of the input power and The size, the pressure in the reaction chamber, the substrate temperature and the like are complicatedly related. Therefore, it may be determined in advance by independently performing deposition on the silicon film and the substrate. At this time, confirmation of crystalline and amorphous was carried out by Raman spectroscopy, ellipsometry and RHEE
D. As a result of this step, the manufactured sample is covered with large-sized crystal grains grown with the silicon film as a nucleus. If a device such as a solar cell, which allows current to flow in the vertical direction, is considered, it is preferable to use a grown film in which crystal grains do not form a vertical grain boundary.

Thereafter, while maintaining the growth conditions of the polycrystal in the vertical direction, the conditions are gradually changed to a high film forming rate.

There is no clear demarcation between the end of the step and the start of the step. May be continued in the step, but in general, the conditions are gradually changed to conditions for forming a polycrystal at a high speed. Therefore, the same device as the device is used as it is. Of course, if the crystal structure is not disturbed, the film formation conditions may be changed abruptly, or the film formation may be stopped once, transferred to another apparatus, and continued to grow. In the steps (1) and (2), an apparatus having the same structure as that of FIG. 3 was used.

Evaluation of Crystal The crystal grain size in the present invention was evaluated by observing a cross-sectional TEM image. The state of the growth of the crystal film in the step was evaluated by a spectroscopic ellipsometer (not shown) attached to the chamber 20.

The orientation of the crystal was confirmed by an X-ray diffractometer.

[Example] (Example 1) Step 2 mm thick n-type (100) single crystal silicon wafer (ρ
= 0.01 Ω · cm) in an HF solution, an anodizing solution HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1, current density 1
Anodization was performed under the conditions of 5 mA / cm ² and a formation time of 30 minutes to form a porous silicon layer on the wafer. The anodized thickness was 200 μm. This was set as a needle-shaped silicon target at a position 204 in FIG.

The quartz glass substrate was placed in the load lock chamber 1 shown in FIG.
After fully evacuating, the gate valve 3 is opened and attached to the horizontal transfer rod 7, and the chamber 10 of the transfer chamber 2 is
Moved to the position just before. Gate valve 3 was closed. After the transfer from the horizontal transfer rod 7 to the vertical transfer rod 11, the gate valve 13 was opened and inserted into the chamber 10. After being set on the anode electrode of the chamber 10, the transfer rod 11 was pulled back to the transfer chamber 2, and then the gate valve 13 was closed.

The following steps will be described with reference to FIG.

The substrate 308 is a substrate holder 307 for heating.
Attached to. In this state, 1 ×
It was evacuated to 10 ^-2 Pa or less. The substrate temperature was set at 500 ° C.

The valves 215 and 217 were opened, and H ₂ gas of 30 sccm was introduced into the chamber from the gas introduction pipe 213 under the control of the mass flow controller 214. The pressure in the chamber was adjusted by the pressure controller 220 so as to be 130 Pa. In this state, a DC voltage of 10 kV was applied between the cathode electrode 202 and the anode electrode 207. The current was 1.8 mA. The voltage application time was 2 minutes.

After the discharge was stopped and the introduction of gas was stopped, the temperature of the substrate dropped to near room temperature, and then the gate valve 2 in FIG.
3 was opened, the vertical transport rod 21 was inserted, the substrate was transferred to the transport rod 21, the transport rod 21 was pulled, and then the gate valve 23 was closed. Next, the transfer rod 21 in the vertical direction was transferred to the transfer rod 7 in the horizontal direction, and was moved to a position immediately before the chamber 20.

After the transfer from the horizontal transfer rod 7 to the vertical transfer rod 21,
The gate valve 23 was opened and inserted into the chamber 20. After being set on the substrate holder 207 for heating of the chamber 20, after returning the transfer rod 11 to the transfer chamber 2 by pulling the transfer rod 11,
Gate valve 13 was closed.

The following steps will be described with reference to FIG.

The substrate 108 is attached to the anode 107. In this state, the inside of the chamber is 2 × 10 ^-3 P
a. At the same time, the heater controller 112 was set and heated so that the substrate temperature became 350 ° C.

After a lapse of 30 minutes, the valves 125 and 119,
120, 121 are opened, and SiH ₄
Gas 5 sccm, SiF ₄ gas 5 from the gas introduction pipe 114
5 sccm, H ₂ gas 50 scc from the gas inlet tube 115
m was introduced into the chamber. Next, the pressure in the chamber was set to 65 Pa by the pressure controller 130.

In this state, the VHF power supply was oscillated to generate a discharge between the cathode and the anode. Discharge power is 3.5
The test was performed at W / cm ² . This state was continued for 15 minutes.

Next, without stopping the discharge, the flow rate of the H ₂ gas was gradually reduced to 110 sc.
cm and then continued for 20 minutes. Thereafter, the discharge was stopped, and the introduction of gas was stopped. When ellipsometry was performed in this state, a crystalline signal having a sharp peak was observed. In addition, most of the crystalline phase was used.

After the substrate temperature was cooled to near room temperature, the gate valve 23 of FIG. 1 was opened again, a vertical transport rod 21 was inserted, the substrate was transferred to the transport rod 21, and the transport rod 21 was pulled. Then, the gate valve 23 was closed. Next, the vertical transport rod 21
To the horizontal transport rod 7, the gate valve 3 is opened, the transport rod 7 is inserted into the load lock chamber 1, and the substrate is moved to the substrate mounting place of the load lock chamber, and then the transport rod 7 is pulled. Then, the gate valve 3 was closed. The valve 6 was closed, the load lock chamber was air-breaked, and the obtained sample was taken out. Let it be Sample 1.

Confirmation Experiment 1 In the process of Example 1, a single crystal wafer was used as a target instead of the needle-shaped silicon target.
Other conditions were the same as in Example 1. After the completion of this step, ellipsometry was performed in the chamber 20. As a result, it was confirmed that the Si thin film was entirely crystallized. This is referred to as Reference Sample 1.

Confirmation Experiment 2 In Example 1, the step was omitted, and the steps and were performed to produce a sample. Reference sample 2.

Confirmation Experiment 3 After performing the steps of the steps 1 and 2 in Example 1, the steps 3 and 4 were omitted, and the step 3 was performed under the following conditions, that is, SiH ₄
A sample was formed by forming a film for 30 minutes under the same conditions as in Example 1 except that the flow rate was 5 sccm for the gas, 110 sccm for the SiF ₄ gas, and 50 sccm for the H ₂ gas.
Reference sample 3.

Evaluation of Structure The structures of the obtained sample 1 and reference samples 1, 2, and 3 were evaluated by Raman spectroscopy and RHEED. The measurement results of Raman spectroscopy confirmed that Sample 1 and Reference Samples 1 and 3 were crystalline. On the other hand, in Reference Sample 2, no peak corresponding to crystalline Si was observed. No diffraction pattern was observed in the result of RHEED. From this it can be concluded that it is amorphous.

The results of X-ray diffraction were as follows: sample 1, reference sample 1,
The peak of the (110) orientation was observed in all of the samples of No. 3.

Cross sections of Sample 1 and Reference Samples 1, 2, and 3 were cut out, and cross-sectional TEM images were observed.

FIG. 5-8 is a schematic diagram of the observation results. FIG.
6 is Sample 1, FIG. 6 is Reference Sample 1, FIG. 7 is Reference Sample 2, FIG.
Indicates Reference Sample 3, respectively.

As shown in FIG. 5, in the sample 1, the crystalline silicon region 502 partially formed on the substrate 501 in the step, and the Si layer 503 deposited in the step
It is shown. Crystal grains grew from the partially formed crystalline silicon region 502. As they grew vertically, they grew horizontally until they hit each other. After hitting, there is no growth in the horizontal direction, but growth in the vertical direction like a column. The grown crystal grains were 505.

The amorphous layer 504 was deposited on the region where no crystalline silicon was formed. Crystal grain 509
Decreased with the horizontal growth. The size of the crystal grains grown in a columnar shape was approximately 20 to 30 μm.

As shown in FIG. 6, in Reference Sample 1,
The crystalline silicon layer 602 was uniformly formed on the substrate. A large number of crystal nuclei were generated on the nuclei, which grew while contacting each other in the vertical direction. There was no significant growth in the horizontal direction, and the growth was vertical in a columnar shape. The grown crystal grains were 603. The horizontal size of the grown crystal grains was 250-400 nm.

As shown in FIG. 7, in Reference Sample 2,
On the substrate 701, there is an Si film 703. The Si film 703 was an amorphous film.

As shown in FIG. 8, in the reference sample 3, the structure of the partially formed crystalline silicon region 502 is almost the same as that of the sample 1 of the first embodiment shown in FIG. The size and interval of the region 502 were almost the same. However, the structure of the Si film 803 on the region where the crystalline silicon was not formed was different from that of the sample 1.
That is, the thickness of the amorphous layer 804 in the Si film 803 is 20
When the thickness exceeds about nm, a large number of crystal grains 806 are generated, and growth in the horizontal direction is observed in the vertical direction and until the crystal grains hit the next crystal grains. It seems that its existence is preventing the growth of the crystal grains 805 growing from the silicide region in the horizontal direction. ing.

On the crystal surface, the crystal grains 805 growing from the partially formed crystalline silicon region 502 and the amorphous layer 804 on the region where no crystalline silicon is formed
The crystal grains 806 generated therein were mixed, and the crystal grain size in the horizontal direction was distributed at 0.05 to 3 μm.

Example 2 A substrate was made of stainless steel, and a ZnO film was formed thereon by sputtering.
A polycrystalline Si film was formed under the same steps and under the same conditions. The obtained sample was used as sample 2, and Raman spectroscopy was performed.
The crystal film was found to have a sharp peak at 520 cm ^-1 . As a result of X-ray diffraction, a peak of (110) orientation was observed. When a cross-sectional TEM image of this sample was observed, it had a structure as shown in FIG.
It was about 0 μm.

(Example 3) A polycrystalline Si film was formed under the same steps and under the same conditions as in Example 1 using alumina ceramic for the substrate. The obtained sample was used as Sample 3, and Raman spectroscopy was performed. The crystal film was found to have a sharp peak at 520 cm ^-1 . The result of the X-ray diffraction is (110)
An alignment peak was observed. Observation of a cross-sectional TEM image of this sample revealed that the sample had a structure as shown in FIG. 5 and a crystal grain size of about 20 to 30 μm.

(Example 4) In Example 1, a needle-shaped silicon target was produced by using photolithography in the process of (1). The other conditions were the same as in Example 1. As a result, polycrystalline S having a particle size of 20-30 μm as shown in FIG.
An i thin film was produced.

[0112]

As described above, in the polycrystalline Si thin film deposition method, the step of depositing a polycrystalline Si thin film on a substrate and after the film formation. A step of forming a metal oxide film on the surface of the polycrystalline Si thin film, a step of partially reducing the metal oxide film, and a step in which the polycrystalline Si is exposed on the partially reduced metal oxide film using the nucleus as a core. The portion where the metal oxide film remains is grown, and the portion where the amorphous silicon is deposited is formed under the film-forming conditions for depositing amorphous Si and the process of growing the polycrystalline Si. It has become possible to produce a crystalline Si film having a large grain size on a simple substrate.

The step of partially forming the crystalline silicon region is performed by sputtering a silicon target having at least a sputtered sputtered surface, thereby easily forming a polycrystalline Si thin film having a large grain size. be able to.

When the target surface is formed of a porous layer, the sputtering surface has a needle shape, and a polycrystalline Si thin film having a large grain size can be easily formed.

When the porous layer has a thickness of 10 to 300 μm, it is a highly durable needle-shaped silicon target,
Therefore, a polycrystalline Si thin film having a large grain size can be formed at low cost.

When the porous layer is formed by anodizing the surface of a silicon wafer, an acicular silicon target can be manufactured at low cost.

When the porous layer is formed by photolithography on the surface of a silicon wafer, a needle-shaped silicon target having a desired needle diameter and interval can be manufactured.

The needle-shaped portion of the needle-shaped silicon target has a diameter of 0.1 mm.
When the diameter is 1 μm to 5 μm, a polycrystalline silicon film having a large particle size and excellent durability of the needle-shaped silicon target can be obtained.

The needle-like portion of the needle-like silicon target is 10
When the distance is about 100 μm, a polycrystalline film having a large grain size and excellent in productivity can be deposited.

In the case where a step of growing polycrystalline Si is further provided after the step, a polycrystalline Si thin film having a large grain size can be formed to an arbitrary thickness according to the application.

The polycrystalline Si thin film of the present invention has a crystal grain size of 5 μm or more, has no grain boundaries in the vertical direction, and has characteristics comparable to bulk polycrystalline Si.

The photovoltaic device of the present invention has a large short-circuit current and a high conversion efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an example of an apparatus used in the present invention.

FIG. 2 is an example of an apparatus used in the process of the present invention.

FIG. 3 is a principle diagram of anodization.

FIG. 4 is an example of an apparatus used in and steps of the present invention.

FIG. 5 is a conceptual diagram of a cross-sectional TEM image of Sample 1 manufactured in Example 1.

FIG. 6 is a cross-sectional TEM of Reference Sample 1 produced in Confirmation Experiment 1.
It is a conceptual diagram of an image.

FIG. 7 is a cross-sectional TEM of Reference Sample 2 produced in Confirmation Experiment 2.
It is a conceptual diagram of an image.

FIG. 8 is a conceptual diagram of a TEM image of a cross section of Reference Sample 3 manufactured in Confirmation Experiment 3.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Load lock room 2 Transfer chamber 3 Gate valve 4 Exhaust device 5 Exhaust pipe 6 Valve 7 Horizontal transfer rod 8 Chamber 9 Vertical transfer rod 10 Chamber connecting pipe 11 Gate valve 12 Exhaust device 13 Exhaust pipe 14 Automatic butterfly valve 20 Chamber 21 Vertical transfer rod 22 Chamber connecting pipe 23 Gate valve 24 Exhaust device 25 Exhaust pipe 26 Automatic butterfly valve 101 Vacuum chamber for film formation 102 Cathode electrode for plasma glow discharge 103 Insulation ring 104 Matching box 105 High frequency power supply 106 Shield Cylinder 107 Anode electrode 108 Substrate 109 Heater block 110 Heater 111 Thermocouple 112 Temperature controller 113, 114, 115 Gas inlet tube 116, 117, 118 Flow controller 119, 1 20, 121 valve 122, 123, 124 gas pipe 125 valve 126 outlet 127 vacuum pressure gauge 128 exhaust pipe 129 automatic butterfly valve 130 pressure controller 201 film forming chamber 202 cathode electrode 203 insulating ring 204 needle-shaped silicon target 205 DC high-voltage power supply 206 Shield cylinder 207 Anode electrode 208 Substrate 209 Heater block 210 Heater for substrate heating 211 Thermocouple for temperature measurement 212 Temperature controller 213 Gas introduction pipe 214 Flow rate controller 215 Valve 216 Gas pipe 217 Valve 218 Spout 219 Vacuum pressure gauge 220 Pressure controller 221 Exhaust pipe 222 Automatic butterfly valve 501, 601, 701, 801 Substrate 502, 602, 802 Si film 504, 604, 704, 804 Amorphous Si layer 505, 605, 805 Crystal layer 806 grown using crystalline silicon region as a nucleus Crystal grains generated in the wafer 1021 Si wafer 1216 Etching solution 1217, 1218 Metal electrode

Claims (19)

[Claims] 1. A method for depositing a polycrystalline thin film Si on an oxide substrate, comprising the steps of partially forming at least a crystalline silicon region on the substrate, and forming amorphous silicon on a region other than the crystalline silicon region. Growing the crystalline Si using the crystalline silicon as a nucleus in the crystalline silicon region under the conditions for depositing polycrystalline Si.
Thin film deposition method. 2. The polycrystalline Si according to claim 1, wherein the step of partially forming the crystalline silicon region is performed by sputtering a silicon target having at least a needle-like sputtering surface. Thin film deposition method. 3. The method according to claim 2, wherein the target surface comprises a porous layer. 4. The polycrystal according to claim 3, wherein said porous layer has a thickness of 10 to 300 μm. 5. The polycrystalline Si thin film deposition method according to claim 4, wherein said porous layer is formed by anodizing the surface of a silicon wafer. 6. The polycrystalline Si thin film deposition method according to claim 4, wherein said porous layer is formed by photolithography on the surface of a silicon wafer. 7. The needle-like portion of the needle-like silicon target has a diameter of φ
7. The polycrystalline Si according to claim 2, having a diameter of 0.1 [mu] m to [phi] 5 [mu] m.
Thin film deposition method. 8. The needle-like portion of the needle-like silicon target is 1
The polycrystalline Si thin film deposition method according to any one of claims 2 to 7, wherein an interval between 0 and 100 µm is provided. 9. The method according to claim 1, further comprising the step of growing polycrystalline Si after the step. 10. A polycrystalline Si thin film formed by the method according to claim 1. Description: 11. A photovoltaic device using the polycrystalline Si thin film according to claim 10. 12. A sputtering target, wherein the sputtering surface has a needle shape. 13. The sputtering target according to claim 12, wherein the target is a polycrystalline Si formation target. 14. The sputtering target according to claim 12, wherein the target surface is formed of a porous layer. 15. The sputtering target according to claim 14, wherein the porous layer has a thickness of 10 to 300 μm. 16. The method according to claim 1, wherein the porous layer is formed by anodizing a silicon wafer surface.
5. The sputtering target according to 4. 17. The sputtering target according to claim 14, wherein the porous layer is formed by photolithography on the surface of a silicon wafer. 18. The sputtering target according to claim 12, wherein the needle-shaped portion of the needle-shaped silicon target has a diameter of 0.1 μm to 5 μm. 19. The sputtering target according to claim 12, wherein the needle-like portions of the needle-like silicon target have an interval of 10 to 100 μm.