JP3102772B2 - Method for producing silicon-based semiconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a silicon-based semiconductor thin film, and more particularly to a method of manufacturing a silicon-based semiconductor thin film by a thermal CVD method.

[0002]

2. Description of the Related Art Thin-film polycrystalline silicon semiconductors include LSIs,
Active research and development are being carried out in the fields of liquid crystal displays, solar cells and the like.
Attention has been paid to formation on a substrate of iO ₂ , metal, carbon, or the like, that is, a so-called heterogeneous substrate, because of its advantages such as cost reduction of the element.

As a method of forming thin-film polycrystalline silicon, for example, (1) a solid-phase growth method in which amorphous silicon is crystallized by heating and annealing, and (2) an excimer laser is used for amorphous silicon. Excimer laser annealing method for melting and recrystallizing by using (3) thermal CVD method for thermally decomposing and depositing material gas directly on the substrate surface, (4) thermal C
A plasma CVD method in which a raw material gas is decomposed and deposited by a plasma reaction at a substrate temperature slightly lower than the VD method, and the like are mentioned.

[0004] Among these thin film forming methods, the solid phase growth method and the excimer laser annealing method are known as methods for obtaining a polycrystalline silicon film having a relatively large grain size. However, the solid-phase growth method has a problem that the crystal growth layer tends to contain twins and that the annealing time for crystal growth is long. On the other hand, in the excimer laser annealing method, crystallization can be performed in a very short time of the order of ns.
A good polycrystalline layer can be obtained only with a thickness of 00 nm or less. This is a unique problem of this method in which the absorbed laser light (ultraviolet light) is converted into heat and recrystallized.

According to the thermal CVD method or the plasma CVD method,
Since the deposition rate is high, thin-film polycrystalline silicon can be manufactured with high productivity. Therefore, it is an advantageous method for forming a device. Particularly, when a thin polycrystalline silicon film is formed on a silicon substrate, a silicon layer having a quality equal to or higher than that of the substrate can be formed by epitaxial growth according to the thermal CVD method.

[0006]

However, when thin-film polycrystalline silicon is directly deposited on an SiO ₂ substrate such as quartz or glass, or a heterogeneous substrate such as a metal substrate or a carbon substrate by such a thermal CVD method, Only thin-film polycrystalline silicon having a small particle size can be obtained, and thin-film polycrystalline silicon having good film quality cannot be obtained.

As a method for solving such a problem, a polycrystalline silicon film is formed as a base layer on a heterogeneous substrate,
A method of growing a thin-film polycrystalline silicon crystal thereon by a thermal CVD method is considered. However, when such an underlayer is formed by the solid phase growth method, twins are included in the underlayer as described above, and defects based on twins are induced in the crystal growth layer deposited thereon. Therefore, although the film quality is better than the case where the film is formed directly on a heterogeneous substrate, the film quality is insufficient compared with the case where the film is formed on a silicon substrate. Also, when this underlayer is formed by the laser annealing method described above, the crystal grain size is affected by the thermal conductivity of the substrate, and the film thickness that can be crystallized is limited. The above problem has arisen.

It is an object of the present invention to provide a method for producing a silicon-based semiconductor thin film having good quality and few defects with good productivity by a thermal CVD method.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a silicon-based semiconductor thin film by a thermal CVD method, wherein a polycrystalline silicon-based semiconductor layer having a thickness of 1000 to 5000 ° is formed as an underlayer. After melting and recrystallizing at least the surface of the crystal layer by laser annealing, thermal CVD
This is a method in which a silicon-based semiconductor thin film is crystal-grown on this underlayer by a method.

According to the present invention, by irradiating at least the surface of the polycrystalline layer, which is the underlayer, with a laser, and melting and recrystallizing it, defects near the surface of the crystal layer can be reduced. Therefore, a silicon-based semiconductor thin film can be crystal-grown on the surface of the underlayer with few defects, and a silicon-based semiconductor thin film with good film quality can be deposited. Further, since the silicon-based semiconductor thin film is formed by the thermal CVD method, the deposition rate is high and the silicon-based semiconductor thin film can be manufactured with high productivity.

Therefore, according to the present invention, a silicon-based semiconductor thin film with few defects and good film quality can be manufactured with high productivity on a heterogeneous substrate other than the silicon substrate. In the present invention, the polycrystalline layer serving as an underlayer is preferably
This is a polycrystalline layer obtained by solid-phase growing and crystallizing an amorphous silicon-based semiconductor. For example, plasma CVD on a heterogeneous substrate
An amorphous silicon-based semiconductor thin film is formed by a CVD method such as a CVD method, and is heated and annealed, whereby a polycrystalline layer crystallized by solid phase growth is used. As described above, the thin film polycrystalline silicon layer obtained by the solid phase growth method has a relatively large grain size, but contains many twins. Also,
It is known that many defects also exist at grain boundaries and the like. According to the present invention, by subjecting at least the surface of the polycrystalline layer to laser annealing, defects such as twins near the surface of the polycrystalline layer can be reduced. Therefore, a silicon-based semiconductor thin film can be grown on the polycrystalline layer having few defects near the surface as a base layer, and a silicon-based semiconductor thin film having good quality and few defects can be formed.

In the present invention, the polycrystalline layer serving as the underlayer is preferably a polycrystalline layer obtained by solid-phase growth of an amorphous silicon-based semiconductor as described above, but is not limited thereto. A polycrystalline layer may be directly formed as a base layer by a method or the like, and at least the surface of the polycrystalline layer may be subjected to laser annealing.

In the present invention, the thickness of the underlayer is 100
It is in the range of 0-5000 °. If the thickness of the underlayer is too small, it becomes difficult to make the surface of the underlayer into polycrystalline material having good film quality, and it may be impossible to grow a silicon-based semiconductor thin film having good film quality thereon. Also, if the thickness of the underlayer is too large, the time for forming the underlayer is long even though the effect of improving the film quality of the silicon-based semiconductor thin film formed thereon is not improved in proportion to the thickness. As a result, productivity is reduced and economically disadvantageous.

In the case where the polycrystalline layer serving as the underlayer is formed by solid-phase growth of an amorphous silicon-based semiconductor, the annealing temperature for solid-phase growth can be a general temperature for solid-phase growth. For example, the temperature can be in the range of 500 to 600C.

In the present invention, the conditions for laser annealing are not particularly limited as long as at least the surface of the polycrystalline layer can be melted and recrystallized. Generally, the laser power density is 200 to 400 mJ / cm. ² , preferably 250 to 300 mJ / cm ^2, and the number of shots is set to a plurality of times as necessary. Generally, it is about 1 to 128 shots. The laser light source may be any laser light source that can be used for laser annealing.
Excimer laser, KrF excimer laser, ArF
Excimer laser, Ar laser, or the like can be used.

In the present invention, at least the surface of the polycrystalline layer is laser-annealed. The thickness of this surface portion may be any thickness as long as crystal grains having good film quality can be formed, and is generally 20 ° or more.

In the case where the polycrystalline layer as the underlayer is formed by solid phase growth of an amorphous silicon semiconductor, it is preferable to use an amorphous silicon semiconductor doped with impurities. By doping the impurities, crystallization can be promoted, and a polycrystalline layer having a large crystal grain size and good film quality can be obtained. Examples of the impurities include phosphorus and boron, and any of n-type and p-type impurities may be used. The impurity concentration is 10 ¹⁷ to 10 ²⁰ c
It is preferably about m ⁻³ .

In the present invention, the thermal CV
A silicon-based semiconductor thin film is crystal-grown by the D method. The conditions for forming the thermal CVD method in the present invention are not particularly limited, and general conditions can be adopted. For example, as an example of conditions for depositing a crystalline silicon layer, silane gas 10SC such as Si ₂ H ₆ is used.
CM, H ₂ 200~300SCCM, pressure from 0.2 to 0.
5 Torr and a substrate temperature of 700 to 800 ° C.

The present invention can be applied to the formation of a silicon-based semiconductor thin film such as Si, SiC and SiGe. According to the present invention, a silicon-based semiconductor thin film having few defects and good film quality can be formed by a thermal CVD method. Therefore, as compared with the case where a silicon-based semiconductor thin film having a similar thickness is formed by solid-phase growth, the film-forming time can be greatly reduced, and the productivity can be improved.

The production method of the present invention can be applied to the production of silicon-based semiconductor thin films in semiconductor devices such as LSIs, liquid crystal displays, and solar cells. In particular, in a solar cell or the like, it is necessary to form a silicon-based semiconductor thin film having a large thickness. Therefore, the present invention that employs a thermal CVD method having a high deposition rate is useful.

[0021]

1 and 2 are cross-sectional views showing steps of manufacturing a solar cell having a silicon-based semiconductor thin film as a power generation layer formed by the manufacturing method of the present invention.

A glassy carbon substrate was used as the substrate 1 shown in FIG. 1A, and an amorphous silicon layer 2 was formed on the substrate 1 as shown in FIG. 1B. The amorphous silicon layer 2 is formed by a plasma CVD method under the conditions of a source gas flow rate of SiH ₄ : 10 SCCM, PH
₃ (1% / H ₂ ): 10 SCCM, H ₂ : 90 SCC
M, RF power: 25 mW / cm ² , pressure: 0.5 To
rr, substrate temperature: 150 ° C. The thickness 2 of the amorphous silicon layer was 3000 °.

Next, as shown in FIG.
A heat treatment was performed at 600 ° C., and the amorphous silicon layer 2 was crystallized by solid phase growth to form a polycrystalline silicon layer 3.
Next, as shown in FIG. 1D, the surface of the polycrystalline silicon layer 3 was irradiated with a KrF excimer laser to perform surface modification by laser annealing. In this embodiment, the substrate was heated to about 400 ° C. in a vacuum and then irradiated with laser light A to melt and recrystallize the surface of the polycrystalline silicon layer 3.
Conditions for laser irradiation include laser power density 26
0 mJ / cm ² and 128 shots were used.

As shown in FIG. 1E, a high quality polycrystalline silicon layer 3a having fewer defects such as twins was formed on the surface of the polycrystalline silicon layer 3 by laser annealing.

Next, as shown in FIG. 2 (f), a crystal was grown on the surface-modified polycrystalline silicon layer 3a by thermal CVD to form a crystal growth layer 4. Thermal CVD conditions include Si ₂ H ₆ : 10 SCCM, H
₂ : 200 SCCM, pressure: 0.3 Torr, substrate temperature: 800 ° C. The thickness of the crystal growth layer 4 was 4 μm.

Next, as shown in FIG. 2G, an intrinsic amorphous silicon layer 5 (thickness: 50 °) and a p-type amorphous silicon layer 6 (film thickness) are formed on the crystal growth layer 4 as a power generation layer. (Film thickness 50Å)
Was formed by a plasma CVD method to form a heterojunction solar cell structure.

Next, as shown in FIG. 2H, a transparent electrode layer 7 and a comb-shaped electrode 8 were sequentially formed on the p-type amorphous silicon layer 6. FIG. 3 shows the operating characteristics (voltage-current characteristics) of the solar cell obtained as described above. As a comparison, a solar cell according to a comparative example was manufactured in the same manner as in the above example, except that laser annealing was not performed on the surface of the polycrystalline silicon layer 3 serving as an underlayer in the manufacturing process of the solar cell according to the above example. Was prepared. FIG. 3 also shows the operating characteristics of the solar cell of this comparative example.

As is apparent from FIG. 3, a clear difference appears in the operation characteristics between the solar cell of the example according to the present invention and the solar cell of the comparative example. That is, in the solar cell of the example, the open-circuit voltage and the short-circuit current have higher values than those of the solar cell of the comparative example without laser annealing. This is because the film quality near the surface of the underlying layer is improved by subjecting the surface of the underlying polycrystalline silicon layer to laser annealing according to the present invention.
This is considered to be because the silicon layer crystal-grown thereon by the thermal CVD method inherits good information of the underlying layer, and can form a power generation layer with better film quality.

In the above embodiment, an example has been described in which the crystal growth layer is formed as an n-type semiconductor by impurity diffusion from an n-type underlayer. However, the present invention is not limited to this.
Crystal growth may be performed on the base layer of the p-type to form a p-type crystal growth layer. Further, when crystal is grown by thermal CVD, an impurity gas may be introduced for doping.

In the above embodiment, a glassy carbon substrate is used, but another conductive substrate such as a tungsten substrate may be used. In the case of using a substrate material containing an element to deteriorate markedly electrical characteristics for the silicon semiconductor such as iron, on a substrate, forming a film such as SiO _2, SiN _X, prevent impurities from the substrate intrusion be able to. Note that SiO ₂ , SiN _X
In the case of forming such films, the substrate can be used as an electrode by partially forming these films.

Further, an insulating material such as quartz or ceramics can be used as the substrate. When alumina ceramics or the like is used as the substrate material, an impurity intrusion prevention layer may be formed on the substrate as in the case where the iron material is used as the substrate. FIG. 4 is a sectional view showing a substrate on which such an impurity intrusion prevention layer is formed. As shown in FIG. 4, an SiO ₂ layer 12
And a SiN _x layer 13 are sequentially formed.
A comb-shaped metal layer 14 serving as a back side collector of the solar cell is formed. As a material of the metal layer 14, for example, tungsten, titanium nitride, or the like can be used. An amorphous silicon layer serving as an underlayer is formed thereon in the same manner as in the above embodiment, and solid phase growth is performed, followed by laser annealing to form an underlayer, on which a silicon layer is crystal-grown by a thermal CVD method.

[0032]

According to the present invention, at least the surface of the polycrystalline layer is laser-annealed to reduce crystal defects on the surface, and a silicon-based semiconductor thin film is grown on the polycrystalline layer by thermal CVD. Therefore, crystal growth can be performed while inheriting good crystallinity of the underlayer. Therefore, a silicon-based semiconductor thin film having good quality and few defects can be manufactured with high productivity by a thermal CVD method having a high deposition rate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a manufacturing process of a solar cell using the manufacturing method of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a manufacturing process of a solar cell using the manufacturing method of the present invention.

FIG. 3 is a view showing characteristics (voltage-current characteristics) of the solar cell obtained in the example shown in FIGS. 1 and 2.

FIG. 4 is a cross-sectional view illustrating an example of a structure near a substrate when an insulating material is used as the substrate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Amorphous silicon layer 3 ... Polycrystalline silicon layer (underlayer) 3a ... Surface part of polycrystalline silicon layer (surface part of underlayer) 4 ... Silicon crystal growth layer 5 ... Intrinsic amorphous silicon layer 6 p-type amorphous silicon layer 7 transparent electrode layer 8 comb-shaped electrode 11 insulating substrate 12 SiO ₂ layer 13 SiO _X layer 14 metal layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/205 H01L 21/20

Claims (2)

(57) [Claims] 1. A method of manufacturing a silicon-based semiconductor thin film by the thermal CVD method, as a base layer, forming a polycrystalline layer of silicon-based semiconductor having a thickness 1000～5000A, by laser annealing at least the surface of the polycrystalline layer A method for manufacturing a silicon-based semiconductor thin film, comprising: after melting and recrystallization, crystal-growing the silicon-based semiconductor thin film thereon by the thermal CVD method. 2. The method according to claim 1, wherein the polycrystalline layer is a polycrystalline layer obtained by solid-phase growing an amorphous silicon-based semiconductor.