JPS6316616A - Silicon thin film and manufacture of the same - Google Patents

Abstract

PURPOSE:To obtain a small electric resistance and a sufficiently large optical forbidden band width of a silicon thin film which is mostly made of silicon atoms and contains at least one type of element among fluorine, chlorine, bromine, iodine and hydrogen by mingling fine crystal particles in an amorphous layer. CONSTITUTION:The silicon thin film of the present invention is a silicon thin film which is mostly made of silicon atoms and contains at least one type of element selected from among fluorine, chlorine, bromine, iodine and hydrogen and an impurity element and the regularity of its atomic arrangement has a specific feature that fine crystal parts are mingled and dispersed in an amorphous layer. When the thin film is manufactured, a system is operated by a main valve 10 and a predetermined pressure is maintained while the degree of vacuum in a vacuum container 9 is being monitored by a vacuum gauge 11. A radio frequency voltage is applied between electrodes 13 and 13' by a radio frequency oscillator 12 to generate a glow discharge. A substrate 15 is placed on a table heated by a heater 14 and is heated to a predetermined temperature by the heater and a doped silicon hydride thin film is formed on the substrate 15.

Description

[Detailed Description of the Invention] 3. The present invention relates to a silicon thin film and a method for producing the same, and more specifically, a low resistance silicon thin film formed on an arbitrary substrate in a plasma atmosphere and a method for producing the same. Regarding.

A method of manufacturing a silicon thin film on an arbitrary substrate in a plasma atmosphere using a mixture of silane SiH+ and a dopant gas as a raw material gas is well known. The silicon thin film formed by this type of conventional method is completely amorphous. For an amorphous film, its X-ray diffraction pattern shows a halo pattern, and the electrical conductivity of this amorphous silicon thin film semiconductor is.

Maximum of about 1O-2Ω-1Cs-1 for N-type film, 1 for P-type film
0-3Ω-1cm-1, and the activation energy calculated from the temperature dependence of electrical conductivity is also
P+ with a sufficiently degenerate Fermi level that has a fairly large value of about 0.2 eV for both type films and has good atomic properties with metals.
It is difficult to see that it is a type or N+ type film (for example, PHILOSOPHICA
(Refer to L MAGAZINE) 33.935 (1976)), especially in the case of P-type films, the higher the electrical conductivity, the more the optical bandgap (optical forbidden band width) narrows (for example, physical !-(PHYSI
CAL REVIEW ) 19.2041 (1979
), therefore, P-N especially intended for solar cells.
When manufacturing a junction semiconductor device or a P-I-N junction semiconductor device, the optical bandgap of the Pfi film narrows when it comes to two-layer films, so light incident from the two window-side layers is absorbed into the active layer (P/I-N junction semiconductor device) at the junction. Before reaching the N or P/I interface, it is absorbed by the two layers, and the junction becomes a heterojunction, which lowers the potential barrier height and lowers the open circuit voltage.On the other hand, regarding Net ,
The fill factor (fill factor of efficiency) decreases due to poor ohmic contact with the gold layer and high series resistance, which ultimately means that the light energy conversion efficiency decreases.

On the other hand, the CV D (Cheaic
Although the polycrystalline thin film produced by Al Yapor Deposition)i has high electrical conductivity, its optical bandgap (optical forbidden band width) is about 1.2 eV, which is not well suited to the solar spectrum, and the existing crystal The grain interface not only serves as a recombination point for electron-hole pairs, but also
It also causes current leakage.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, have a low electrical resistance, a sufficiently large optical bandgap (optical forbidden band width), and achieve the advantages of an amorphous silicon thin film and a polycrystalline silicon thin film. It is an object of the present invention to provide a silicon thin film having the following properties.

Another object of the present invention is to provide a silicon thin film that has crystal grains in a specific range, has high electrical conductivity, and has a large optical bandgap (optical forbidden band width).

Another object of the present invention is to provide a P-type silicon thin film that has high electrical conductivity, a large optical bandgap (optical forbidden band width), and excellent doping effect, which has been difficult to manufacture in the past. be.

Still another object of the present invention is to provide an N-type silicon thin film with high electrical conductivity and excellent doping effect, which has been difficult to manufacture in the past.

Still another object of the present invention is to provide a method for manufacturing a silicon thin film with low resistance and a large optical bandgap (optical forbidden band width) on any substrate in a plasma atmosphere.

The silicon thin film of the present invention contains fluorine! ! ! A silicon thin film containing at least one element selected from the group consisting of bromine, bromine, iodine and hydrogen and an impurity element and consisting mostly of silicon atoms, the regularity of its atomic arrangement;
In other words, the thin film structure has a significant feature, and a notable feature is that microcrystalline portions are mixed and dispersed in the non-quality layer.

That is, when X-ray diffraction is performed, an amorphous silicon thin film produced in a normal plasma atmosphere exhibits a spectrum with a wide gentle halo pattern and no sharp peaks; A polycrystalline silicon thin film produced by high-temperature annealing etc. shows a spectrum with clear strong peaks originating from the silicon crystal lattice.In comparison, the silicon l1iWA of the present invention has a spectrum originating from the silicon crystal lattice on the halo pattern. Then, the estimated weak peak is expressed as 5i (111) or 5i (
The average grain size of the microcrystals in the silicon thin film of the present invention, shown in the vicinity of 220), is determined by Scherer (
It can be calculated using the formula of
It is about 30 or more and about 500X or less. The microcrystals having a particle size in the range of 2 and 3 are in a range that does not become an optical hindrance in the wavelength range of normal sunlight and can increase electrical conductivity.

In the silicon thin film of the present invention, the presence of fine crystal grains in the amorphous layer as described above is an advantage of the silicon thin film as an amorphous material, which will be explained below, that is, the optical band gap (optical It is presumed that this is closely related to maintaining a sufficiently large forbidden band width and the advantage of a polycrystalline silicon thin film, that is, extremely high electrical conductivity.

In the silicon thin film of the present invention, various impurity elements are used for doping, including phosphorus,
In the case of elements belonging to Group V of the periodic table, such as arsenic, a silicon thin film having the characteristics of an N-type semiconductor is obtained, while in the case of elements belonging to Group M of the periodic table, such as boron and aluminum, the characteristics of a P-type semiconductor are obtained. A silicon thin film having the following properties is obtained. The former silicon thin film has an electrical conductivity of about 10-1 Ω-'am-'
On the other hand, the latter can reach 10°Ω-'cm-'.
Approximately 10-2Ω-'Cm-''''Approx. 10-10-'cm-'
It is characterized by reaching t,=. For similar doping, the activation energy for electrical conductivity is less than about 0.2 eV, and often less than about 0.1 eV.

The doping efficiency is good, the 7-luminium level is sufficiently degenerated,
Another feature is that Nfi and P-type silicon thin films with excellent ohmic contact with metal can be obtained. In addition, the silicon thin film of the present invention maintains a sufficiently large optical band gap (optical forbidden band width) even through doping for both N-type and P-type, and has a polycrystalline quality of about 1.2 eV, which is approximately It has a fairly large value of 1-3 eV to about 1.8 eV, and it also has excellent characteristics of high electrical conductivity and optical bandgap (optical forbidden band width), which were previously unobtainable, especially in P-type thin films. It has at the same time. One of these effects is that the silicon thin film of the present invention is not completely amorphous,
This proves that this is a silicon thin film with a new crystal structure that is not completely polycrystalline.

Next, the method for manufacturing a silicon thin film of the present invention will be described. First, silane SiH or halogenated silane S
i H6-3X4-1 (X: halogen element) or 21! The above mixed gas is diluted with a rare gas such as helium, argon, or hydrogen gas at a high ratio of about 1 = 1, and the dopant gas is mixed at a predetermined ratio, but the order of this mixed dilution is not particularly limited. This mixed gas is heated with a plasma discharge power density of more than about 0.2 W/crn' to bring it into a plasma state, and then the gas is formed on a substrate (glass, plastic, metal, etc.) placed therein. Once formed, the dopant impurity atoms are effectively incorporated into the silicon network in a four-coordinate manner, forming a silicon thin film with high electrical conductivity without narrowing the optical bandgap (optical forbidden band width). . The purpose of diluting silane SiH with a high proportion of hydrogen or rare gas is that normally when a large amount of power is applied during film formation, the decomposition of silane SiH+ will be accelerated and the film formation rate will increase. Impurities are effectively 4-coordinated and difficult to enter the silicon network. Therefore, the silane SiH is diluted with hydrogen or a rare gas so that the film formation rate does not increase (desirably 4 S/S e C or less) even when a large amount of power is applied. In the X-ray diffraction image of the film produced under these conditions, it was observed that microcrystalline grains were mixed in with the amorphous material, and the presence of such microcrystalline grains caused the film to appear as amorphous. It is presumed that the electrical resistance is significantly lowered while imparting the optical properties of the film. The particle diameter of such microcrystalline grains is in the range of about 30 to about 500, according to an X-ray diffraction image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the characteristics of the silicon thin film and the method for manufacturing the silicon thin film according to the present invention will be described below with reference to the drawings.

In FIG. 1, the entire equipment system including the mixing vessel 1 is pumped approximately 10-'to
Vacuum to the vacuum degree of rr, then silane pump 4 and hydrogen pump 5. Further, gas is introduced into the mixing container 1 at a required ratio from the dopant gas pump 6 or 7 and mixed. The mixed gas is introduced into the vacuum vessel 9 through the flow meter 8 at a constant flow rate. The main valve IO is operated to maintain the required pressure while monitoring the degree of vacuum in the vacuum container 9 with a vacuum gauge 11. High frequency oscillator 12 with electrodes 13 and 13
A high-frequency voltage is applied between ′ to generate glow discharge.

The substrate 15 is placed on a base heated by the heater 14 and heated to a required temperature by the heater.
A thin film of doped hydrogenated silicon is deposited over 5.

The if table summarizes examples of the manufacturing method according to the present invention and the characteristics of the produced films in comparison with conventional manufacturing methods.

In this table, No. 1 to No. 3 are P-type silicon thin films manufactured by the conventional method, and the film forming conditions and film characteristics thereof are shown. Examples No. 4 and No. 5 are examples of P-type silicone thin films manufactured according to the present invention. In NO64 and N005, SiH4 is diluted 30 times with hydrogen gas, O, aW and 1.6W.
High power is applied to each. No, 6～No,
9 and No. 11 are N-type silicon thin films manufactured by a conventional method, and No. 10 and No. 12 are examples of N-type silicon thin films manufactured according to the present invention. In No. 10 and No. 12, SiH diluted 10 times with hydrogen gas, O, aW and 1
．． 6W power is applied.

FIG. 2 shows the electrical conductivity of a silicon thin film according to the invention as a function of dopant gas concentration. Second
Curves 16 and 17 in the figure are based on the conventional manufacturing method, and the cathode side plasma discharge power density (input plasma discharge 1! power/cathode side electrode area) is approximately 0. The 0 point 18.19, which indicates the electrical conductivity of P-type and N-type silicon thin films when deposited using IW/c, is the electrical conductivity of the P-type silicon thin film according to the present invention, and the deposition conditions were silane. Dilute SiH 30 times with hydrogen, that is, use a mixed gas of SiH4:H2 = 1:30, and use a mixture of Diporane B and Hb as dopants at 2% (volume basis) with respect to SiH + as a raw material gas, Plasma emission"7ft power density 0 respectively
．． 8W/crn' and l.

6 W/c rrr' 0 points 20.
21 is the electrical conductivity of the N-type silicon thin film according to the present invention.

The film formation conditions were as follows: silane was diluted 10 times with hydrogen, using a mixed gas of SiH+:H2=1:10.
As a dopant, point 20 contains 1% phosphorus pentafluoride PF5 (
For point 21, a mixture of 4500 ppm (volume basis) of phosphine PH3 was used as the raw material gas, and the power density was 0.8 W/crrI' and 1, respectively.
．． 6W/crn'. It can be seen from FIG. 2 that the electrical conductivity of the silicon thin film of the present invention is at least two orders of magnitude higher than that produced by the conventional manufacturing method.

FIG. 3 shows the activation energy of electrical conductivity of a silicon thin film of the present invention as a function of dopant gas concentration. Curves 22.23 in FIG. 3 are based on the conventional manufacturing method, and points 24.25, 26 and 27, which correspond to curves 16.17 in FIG. 2, are based on the present invention. are points 18 and 19.2 in Figure 2, respectively.
Corresponds to 0 and 21. Figure 3 shows 1. The activation energy of the electrical conductivity of the silicon thin film of the present invention is sufficiently small, and the Fermi level with good ohmic properties with metal is degenerated.
This proves that it is a type or N+ type film.

FIG. 4 shows the boron concentration and phosphorus concentration in the silicon thin film according to the present invention measured by the SIMS method and the EDMA method, respectively, as a function of the dopant gas concentration. Curve 2B in Figure 4.

29 is produced by the conventional manufacturing method, and curve 16 in FIG.
．． Six points 30, 31, 32, and 33 corresponding to point 17 are according to the present invention, and the film forming conditions are the same as those of the second method.
Corresponds to points 1B, 19.20 and 21 in the figure. Fourth
The figure shows that the boron concentration and phosphorus concentration in the silicon thin film made by the present invention are lower than those formed by conventional manufacturing methods. It has been proven that the manufacturing method according to the invention is an extremely efficient method for doping.

FIG. 5 shows the optical bandgap (optical forbidden band width) of a P-type silicon thin film according to the present invention as a function of dopant gas concentration. As you can see, the optical bandgap (optical forbidden band width) was determined from 5T7α (hυ −Eo). Here, α is the optical absorption coefficient, hυ is the incident photon energy (ev), and Eo is the optical band gap (optical forbidden band width).Curve 34 in FIG. 5 is due to the conventional manufacturing method. , corresponds to curve 16 in FIG. 2, and the optical bandgap decreases as the boron concentration increases. - Point 35.36 is the measured value for the silicon film of the present invention, The conditions correspond to points 18 and 19 in FIG. 2, respectively. FIG. 5 shows Py! according to the present invention! 1 silicon thin film has high electrical conductivity without narrowing the optical bandgap (optical forbidden band width).

FIG. 6 shows a silicon thin film (film thickness lpm) according to the present invention.
) is an example of an X-ray (CuKα) diffraction image.

Curve 37 in the figure is a representative example of a sample made of the present invention,
Peaks are observed near 5i (ill) and 5t (220). Estimating the crystal grain size from the half width of this peak, it is calculated to be about 100X. On the other hand, curve 38 in FIG. 6 is a silicon thin film manufactured by a conventional method, and no peaks like curve 37 are observed.The halo pattern in FIG. 1 is from glass used as a substrate. The halo pattern from the amorphous silicon thin film is not clearly observed because the film is thin.

As explained above, according to the present invention, a P-type silicon thin film or an N-type silicon thin film having high doping efficiency and high electrical conductivity can be provided, and its application range is extremely wide.In particular, the P-type silicon thin film is suitable for optical It is extremely useful for use in solar cells and the like because it can provide high conductivity without reducing the optical bandgap (optical forbidden band width). Therefore, the present invention can be applied to the electronic industry with great effect.

4. τ Fig. 1 is a schematic diagram showing the silicon thin film of the present invention and an apparatus for carrying out the manufacturing method thereof, Figs. 2 to 5 are graphs showing the characteristics of the silicon thin film of the present invention, and Fig. 6 is a FIG. 2 is a diagram showing an X-ray diffraction image of the silicon thin film of the present invention.

1: Mixing container 2: Oil rotary pump 3: Oil diffusion pump 4 Nijiran cylinder 5: Hydrogen cylinder 6.7: Dopant gas pump 8: Flow meter 9: Vacuum container IO: Main valve 11: Vacuum gauge 12: High frequency oscillator 13.13 ': Electrode 14: Heater 15: Substrate I! IN engraving (no change in content) Fig. 3 B2H4/si H4PF5 or PH3/SiH4 No. 5
Figure 1 σ310-2 BzHs /Si H4 procedural amendment (method)

Claims (1)

[Scope of Claims] 1) A silicon thin film containing at least one element selected from the group of fluorine, chlorine, bromine, iodine and hydrogen, the majority of which is composed of silicon atoms, in an amorphous layer. A silicon thin film characterized by a mixture of microcrystalline grains. 2) The silicon thin film according to claim 1, wherein the silicon thin film has an optical band gap (optical forbidden band width) of about 1.3 eV or more. 3) Claim 1 or 2, wherein the activation energy of the electrical conductivity of the silicon thin film is about 0.2 eV or less.
Silicon thin film described in Section 2. 4) Silane SiH_4 or halogenated silane SiH_
A method for producing a silicon thin film on any substrate in a plasma atmosphere using any one of 0_~_3X_4_~_1 (X: halogen element) or a mixture of two or more of them as a raw material gas, in which the film formation rate is sufficiently increased. For the purpose of controlling and producing a crystalline and amorphous mixed layer, the mixed gas is diluted with a rare gas such as helium, neon, argon, etc. or hydrogen in a ratio greater than about 1:1, and about 0.2 W/ cm^2
A method for producing a silicon thin film, characterized in that the film is formed while applying power with a plasma discharge power density of the above.