JPH07153698A - Silicon laminate - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a silicon laminate in which electrical characteristics are improved and a silicon film is not easily peeled off. [Structure] This silicon laminate 20 is a sintered SiC substrate 21.
And an intermediate film 22 of SiCx (0 <x <1) formed on the surface and a polycrystalline silicon film 23 formed on the intermediate film 22. Since the film stress of the polycrystalline silicon film 24 is reduced by the action of the intermediate film 22, and the ratio of carbon atoms is smaller than that of SiC which is a stoichiometric compound, SiCx is applied as the intermediate film, so that the ratio of Si is reduced. Since the lattice mismatch with silicon is alleviated to a high degree, it becomes possible to epitaxially grow the polycrystalline silicon film on the intermediate film. Therefore, when this silicon laminate 20 is applied to a solar cell or the like, its photoelectric conversion efficiency can be improved, and its physical resistance is improved because the silicon film is difficult to peel off, and the silicon layer and the back electrode are It also enables ohmic bonding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a SiC base material and a polycrystalline silicon film formed on the base material, the main part of which is composed of, for example, a silicon layer forming a part of a solar cell. The present invention relates to a silicon laminate that can be integrally applied as a back surface electrode member, and more particularly to an improvement of a silicon laminate that can improve its electrical characteristics.

[0002]

2. Description of the Related Art As this type of silicon laminate, for example, the one described in Japanese Patent Application Laid-Open No. 55-73450 is known.

That is, in this silicon laminate, a carbon fiber woven cloth having a net-like structure having a series of holes is dipped in the melted silicon contained in the melting tank, and the melted silicon is filled in the holes and on the surface. In addition, a structure is known in which the melt is crystallized while being coated, and the melt is crystallized. For example, it is integrally applied as a silicon layer and a back electrode member of the solar cell shown in FIG. There is.

In FIG. 3, a is a p-type silicon layer and b is n.
A type silicon layer, c is an antireflection layer such as ITO, d is a comb-shaped electrode, e is an ohmic contact layer, and f is a backside electrode.

By the way, in this silicon laminated body, a carbon fiber woven cloth having a net-like structure having a series of holes for holding and crystallizing the melt silicon is applied, and this carbon fiber woven cloth is used. Since the electric resistance increases as much as the holes are provided, there is a drawback that it is difficult to improve the photoelectric conversion efficiency of the solar cell incorporating the silicon laminated body.

Therefore, in the past, the thermal CV is usually used.
A polycrystalline silicon film is directly formed on the surface of the sheet-shaped carbon-based base material or heat-resistant metal base material by a film-forming means such as D method or plasma CVD method to manufacture a silicon laminated body, and the silicon laminated body is prepared as described above. The method of incorporating into a solar cell etc. is adopted.

However, the latter silicon laminated body manufactured by applying the above-mentioned film forming means also has the following problems.

First, when a polycrystalline silicon film is formed on a sheet-shaped carbon-based substrate surface by means of a thermal CVD method or the like, due to the difference in thermal expansion coefficient between the carbon-based substrate and silicon. Stress is likely to occur in the formed polycrystalline silicon film, defects and cracks easily occur in the film unless the thickness of the polycrystalline silicon film is set to a certain degree due to this stress, and There is a problem that the polycrystalline silicon film is easily peeled from the base material due to the film stress.

On the other hand, when a polycrystalline silicon film is formed on the surface of the heat resistant metal substrate by means of the thermal CVD method or the like, the metal component of the heat resistant metal substrate diffuses into the formed polycrystalline silicon film. There is a problem in that the electrical characteristics of the polycrystalline silicon film are likely to fluctuate due to the diffusion of the metal component.

Under such a technical background, the present inventor has
A silicon laminated body was devised, the main part of which is composed of a SiC base material and a polycrystalline silicon film formed on the SiC base material. That is, by applying SiC, which has chemical and physical properties similar to silicon, to the base material, it becomes possible to improve the chemical and physical affinity between the base material and the polycrystalline silicon film. Advantages of reducing film stress after forming a polycrystalline silicon film, forming an ohmic contact between the base material and the polycrystalline silicon film, and preventing the diffusion of metal components into the polycrystalline silicon film. have.

[0011]

By the way, the above-mentioned silicon laminated body to which silicon carbide (SiC) is applied as a base material has the advantages as described above, but it is not possible to use silicon carbide (SiC) which constitutes the base material. Since it is difficult to epitaxially grow a polycrystalline silicon film on the above-mentioned substrate due to the lattice mismatch with silicon (Si), the ungrown crystal growth at the interface of the polycrystalline silicon film with the substrate is insufficient. Areas were sometimes formed.

Therefore, there is still room for improvement in improving the electrical characteristics such as electron mobility in the polycrystalline silicon film.

The present invention has been made in view of such a problem, and an object thereof is to provide a silicon laminated body in which electric characteristics such as electron mobility in a polycrystalline silicon film are further improved. Especially.

[0014]

That is, the invention according to claim 1 is such that the silicon laminate is a SiC base material and the Si base material.
It is characterized in that it is composed of an intermediate film made of SiCx (where 0 <x <1) formed on the surface of the C substrate and a polycrystalline silicon film formed on this intermediate film. .

According to this silicon laminate, S
Since an SiCx intermediate film, which has intermediate properties between SiC and silicon, is chemically and physically interposed between the iC base material and the polycrystalline silicon film, the chemical affinity is improved and the polycrystalline silicon film is formed. It is possible to reduce the film stress later. Further, SiCx (where 0 <x <1), which has a smaller ratio of carbon atoms than that of SiC which is a stoichiometric compound, is applied as the intermediate film. ) Is relaxed, and as a result, it becomes possible to epitaxially grow a polycrystalline silicon film on the intermediate film, and it is difficult to form an ungrown region of silicon at the interface with the intermediate film. Therefore, the crystallinity of the polycrystalline silicon film is improved and its electrical characteristics can be improved.

Therefore, when the silicon laminate according to the present invention is applied to a solar cell or the like, the photoelectric conversion efficiency and the like can be improved along with the improvement of the electrical characteristics, and the film can be formed even if the film thickness is set thin. The polycrystalline silicon film has no defects or cracks, and its peeling from the SiC substrate is difficult to occur, so its physical resistance is improved, and ohmic bonding between the silicon layer and the back electrode is also possible. Has the advantage that

Here, the value of x of SiCx forming the intermediate film is set to a large value close to that of SiC on the SiC substrate side within the range of 0 <x <1, while approaching to the polycrystalline silicon film side. It is possible to set the value of x to decrease continuously with the adjustment and adjust the composition in the interlayer to change in the thickness direction, or to set it to a specific value within the range of 0 <x <1. The composition in the intermediate film may be adjusted to be substantially constant in the thickness direction, and can be arbitrarily selected according to the intended electrical characteristics of the polycrystalline silicon film.

Next, the invention according to claim 2 is premised on the silicon laminated body according to the invention according to claim 1, and SiCx
(However, it is characterized in that an n-type or p-type dopant is mixed in the intermediate film of 0 <x <1).

According to the silicon laminated body of the second aspect of the invention, since the n-type or p-type dopant is mixed in the intermediate film made of SiCx, the n-type or p-type dopant acts. It becomes possible to more completely form an ohmic contact between the SiC base material and the polycrystalline silicon film, the electric resistance of the intermediate film is lowered, and an electric field is generated in the polycrystalline silicon film, so that the BSF is formed.
(Back Surface Field) It is also possible to obtain the effect.

Therefore, regarding this silicon laminated body, B
It can be applied as it is to SF type solar cells and the like, and even if the film thickness is set thin, there is no defect or crack in the formed polycrystalline silicon film, and the S
Since peeling from the iC substrate is unlikely to occur, it has an advantage that the physical resistance thereof can be improved.

As the n-type dopant mixed in the intermediate film made of SiCx, there are P (phosphorus), Sb (antimony), As (arsenic) and the like, and as the p-type dopant, B (boron), There are In (indium), Ga (gallium), Al (aluminum), and the like. Further, these dopants include PH ₃ (phosphine) gas, AsH ₃ (arsine) gas, B ₂ H ₆ (diborane) gas, B (CH ₃ ) ₃ (trimethylboron) gas, etc. during the formation of the intermediate film. It can be mixed into the intermediate film by acting a dopant gas.

Further, the application target of the silicon laminated body according to the present invention is not limited to the above solar cell,
For example, an optical sensor may be used.

[0023]

According to the invention of claim 1, a SiC substrate,
SiCx formed on the surface of this SiC substrate (where 0 <
xx <1) and a polycrystalline silicon film formed on the intermediate film to form a silicon laminated body, and SiCx chemically and physically has an intermediate property between SiC and silicon. By the action of the intermediate film, the chemical affinity between the SiC base material and the polycrystalline silicon film can be improved and the film stress after the polycrystalline silicon film formation can be reduced, and between the polycrystalline silicon film and the SiC base material. It is also possible to form the ohmic contact more completely.

Further, SiCx (where 0 <x <1), which has a smaller ratio of carbon atoms than that of SiC which is a stoichiometric compound, is applied as the intermediate film, and this intermediate film has a high Si content. The lattice mismatch with silicon (Si) is relaxed,
Along with this, it becomes possible to epitaxially grow a polycrystalline silicon film on the intermediate film, and it becomes difficult to form an ungrown region of silicon at the interface with the intermediate film. It becomes possible to improve the electrical characteristics.

According to the invention of claim 2, Si
Since the n-type or p-type dopant is mixed in the intermediate film of Cx (where 0 <x <1), the action of the n-type or p-type dopant causes the SiC substrate and the polycrystalline silicon film to be separated from each other. It becomes possible to more completely form the ohmic contact between them, and the electric resistance of the interlayer film is lowered,
Moreover, since an electric field is generated in the polycrystalline silicon film, BS
It is also possible to obtain the F (Back Surface Field) effect.

[0026]

EXAMPLES Examples of the present invention will be described in detail below.

[Example 1] First, as shown in FIG. 1, a silicon laminate 20 according to this example has a sintered SiC substrate 2 as shown in FIG.
1 and an intermediate film 22 made of SiCx (0 <x <1) in which a film is formed on the SiC base material 21 and the value of x is continuously set smaller as the distance from the SiC base material 21 increases.
The polycrystalline silicon film 23 epitaxially grown on the intermediate film 22 constitutes the main part.

The silicon laminate 20 is manufactured by the method described below. That is, FIG.
As shown in FIG. 2, a high temperature plasma generating part 1 capable of forming arc plasma and induction plasma, and a reaction chamber 3 provided adjacent to the high temperature plasma generating part 1 and having a base material holder 7 therein, constitute a main part thereof. The sintered SiC base material 21 is placed in the apparatus, and the inside of the reaction chamber 3 is set to 10 ^-3.
After vacuuming to Torr to exhaust air in the reaction chamber 3, etc., the SiC base material 21 is installed in the base material holder 7 in the horizontal direction prior to ignition to prevent rapid heating and local overheating after plasma ignition. A moving mechanism (not shown) for moving to (1) was operated.

Next, an argon gas and a hydrogen gas were introduced into the plasma generating section 1 and plasma ignition was performed. As the power source, direct current was first applied and then high frequency was applied.
The shape of the high temperature plasma flame varied considerably depending on the flow rates of argon gas and hydrogen gas, but a stable state could be obtained relatively easily. In addition, a pressure control valve is attached to the inlets of argon gas and hydrogen gas and an inlet of silicon raw material, and an exhaust system 4 is provided on the downstream side of the reaction chamber 3 in this apparatus. The pressure in the reaction chamber 3 is maintained at ˜550 Torr.

The SiC base material 21 is heated by the high temperature plasma and the heating means 8 provided in the base material holder 7, and the surface temperature of the SiC base material 21 is monitored to be sufficiently elevated by using a radiation thermometer. Further, when the surface temperature reaches a temperature (1400 ° C.) just below the melting point of silicon, a mixed gas of silane gas and methane gas is introduced from the gas inlet, and the silane gas flow rate is 0.5 liter / mi.
On the other hand, the methane gas flow rate is continuously reduced from 0.5 liter / min and finally set to 0 liter / min while the mixed gas is allowed to undergo a gas phase reaction on the SiC base material 21 to An intermediate film 22 made of SiCx (0 <x <1) in which the value of x was continuously set small was formed.

Next, the temperature of the SiC substrate 21 is set to 1400.
While maintaining the temperature at ℃, while stopping the supply of the mixed gas composed of the silane gas and methane gas, a fixed amount of silicon particles 6 is introduced from the inlet of the silicon raw material to melt the silicon particles 6 in high temperature plasma, and The melt was formed on the intermediate film 22.

Then, this film forming treatment is performed for 2 to 3 minutes,
Further, even after the supply of the silicon particles 6 is stopped, a high frequency is applied to continue the high temperature plasma of argon to control the cooling for about 5 to 10 minutes to form a polycrystalline silicon film 23 with a film thickness of about 1 mm to form the above silicon laminated body. 20 was produced.

The moving mechanism provided on the base material holder 7 is continuously operated before the formation of the intermediate film 22 and during the cooling control of the silicon film, so that the heat input to the surface of the SiC base material 21 is made uniform. I am trying to

(Conditions for Film Formation) Pressure in the reaction chamber to 550 Torr DC plasma input power 5 KW RF plasma input power 30 KW Argon gas flow rate 60 to 80 liters / min Hydrogen gas flow rate 2 to 4 liters / min Silane gas flow rate 0.5 liters / min Methane gas flow rate 0 to 0.5 liter / min Particle size of silicon particles 75 to 150 μm Supply amount of silicon particles 1 g / min Distance between high temperature plasma generating part and base material 10 to 20 cm Polycrystalline silicon film thus obtained As a result of TEM observation of No. 23, it was confirmed that the crystal grain size reached about 100 μm at a film thickness of about 1 mm, and that the film characteristics were also uniform.

[Embodiment 2] When the intermediate film 22 is formed, the flow rate of methane gas is set to 0.3 liter / min under a quantitative condition, and under this condition, the composition in the thickness direction is substantially constant.
A silicon laminate was manufactured under substantially the same conditions as in Example 1 except that the intermediate film 22 made of iCx (x = 0.8) was formed.

The TEM observation of the polycrystalline silicon film 23 of the silicon stack 20 confirmed that the polycrystalline silicon film 23 had substantially the same characteristics as the polycrystalline silicon film of Example 1.

[Embodiment 3] The above-mentioned SiCx (0 <x <1)
5 ml / min when forming the intermediate film 22 of
A silicon stack was manufactured under substantially the same conditions as in Example 1 except that a flow rate of phosphine gas was introduced to form the intermediate film 22 containing n-type dopant phosphorus (P).

As a result of TEM observation, this polycrystalline silicon film also had substantially the same characteristics as the polycrystalline silicon film of Example 1.

[0039]

According to the invention of claim 1, S which chemically and physically has an intermediate property between SiC and silicon.
By the action of the intermediate film of iCx, the chemical affinity between the SiC base material and the polycrystalline silicon film can be improved, and the film stress after the polycrystalline silicon film formation can be reduced, and between the polycrystalline silicon film and the SiC base material. It is also possible to more completely form the ohmic contact. Furthermore, SiCx (however, having a smaller ratio of carbon atoms than SiC which is a stoichiometric compound)
0 <x <1) is applied as the above-mentioned intermediate film, and the lattice mismatch with silicon (Si) is relaxed due to the high Si ratio in this intermediate film. Since it becomes possible to grow the film epitaxially and it becomes difficult to form an ungrown region of silicon at the interface with the intermediate film, the crystallinity of the polycrystalline silicon film is improved and its electrical characteristics are improved. It is possible to plan.

Therefore, there is an effect that it is possible to provide a silicon laminate having good electrical characteristics and in which the polycrystalline silicon film is hard to peel off.

Further, according to the invention of claim 2, Si
By the action of the n-type or p-type dopant mixed in the Cx interlayer film, it becomes possible to more completely form an ohmic contact between the SiC substrate and the polycrystalline silicon film, and the electrical conductivity of the interlayer film is improved. Since the resistance is lowered and an electric field is generated in the polycrystalline silicon film, BSF (Back Surface
It is also possible to obtain the (Field) effect.

Therefore, it has an effect of being able to provide a silicon laminated body which is directly applied to a BSF type solar cell or the like and has good electric characteristics and in which the polycrystalline silicon film is not easily peeled off.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a silicon stack according to an example.

FIG. 2 is a structural conceptual diagram of an apparatus applied to the manufacturing method of the embodiment.

FIG. 3 is a schematic sectional view of a conventional solar cell.

[Explanation of symbols]

 20 Silicon Laminate 21 Sintered SiC Base Material 22 SiCx Intermediate Film 23 Polycrystalline Silicon Film

Claims (2)

[Claims] 1. An SiC base material, and an intermediate film composed of SiCx (where 0 <x <1) formed on the surface of the SiC base material.
A silicon laminated body comprising a polycrystalline silicon film formed on the intermediate film. 2. The silicon laminate according to claim 1, wherein an n-type or p-type dopant is mixed in the intermediate film made of SiCx (where 0 <x <1).