JPS589321A - Manufacture of silicon thin-film - Google Patents

Abstract

PURPOSE:To decrease a primitive additive impurity and dope a new impurity, by placing a doped Si thin-film in mixed gas plasma of one of F, Cl and H, primitive additive impurity, and another element gas. CONSTITUTION:A P or N type Si thin-film of single crystal, amorphous or mixture of fine crystal powder in amorphous is placed under plasma discharge, by mixing primitive additive impurity, and the other impure element gas at the rate of 10<-5>-10<-1> to one element of F, Cl and H, adjusting the pressure at 1.5X 10<-2>- 3 Torr, and keeping the flow within a container at a viscosity range, and varying the power density within 0.5-50W/cm<3>. At the same time, the primitive additive impurity decrease depth and new impurity doping depth can be adjusted arbitrarily from the thin-film substrate surface to a depth of 5,000Angstrom at maximum. This method decreases manufacturing processes and brings such devices of excellent characteristics as PN-junction and PIN-junction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon thin film that can be applied to diodes, solar cells, photoconductors for image formation, photoelectric conversion bulkheads for tunneling devices, and the like.

Conventionally, silicon thin films have been used to achieve the intended purpose by
It is used as an n-junction device or a pn* junction device. Such a pin or pn junction element is usually manufactured by forming a thin film of pm [silicon] doped with B (boron) as an impurity in a plasma atmosphere by a glow discharge method,
The active layer is formed on the il silicon thin film without doping il [silicon thin film and P (phosphorous) added nii [silicon thin film] or on the p-doped silicon thin film Kl [*the above nf
jl It is fabricated by two or three deposition steps of growing a silicon thin film. Alternatively, first the Kn layer film is
Next, the manufacturing method of forming a 12-layer film and a p-layer film or a 9-layer film directly on the n-layer film was also carried out in the same manner.

However, when a new upper layer is formed on an already grown lower layer, the impurities in the lower layer (already grown) are extracted in a plasma atmosphere, and the elements fabricated by such a film formation method are damaged. It has the disadvantage of being mixed with As a result, a film grown on a film containing impurities has lower photoelectric conductivity and dark electrical conductivity than a film grown on a substrate that does not contain impurities. For this reason, when manufacturing a p1n junction semiconductor device especially for the purpose of a solar cell, if the device is fabricated using a substrate, a p-layer film, a single-layer film, and an n-layer film, the Kp layer in the middle of the first layer is If the photoelectric conductivity and dark electric conductivity decrease due to the contamination of impurities added to the film, a good bonding surface will not be formed. Regarding the device manufactured by I[K, the impurity added to the n-layer film mixes into the single-layer film and moves the position of the ferrule level, making it impossible to obtain a sufficient open circuit voltage. These things ultimately mean that the energy replacement efficiency of light decreases, which leads to a decrease in performance as a solar cell as well as when used for other purposes.

The present inventors have prepared a pH silicon thin film substrate or a nil silicon thin film substrate doped with an impurity element using a gas containing at least one element selected from the group of fluorine, chlorine, and hydrogen, and a gas of a type different from the impurity in the silicon thin film substrate. When the silicon thin film substrate is subjected to a plasma discharge state of a mixed gas with a gas consisting of impurities, the amount of impurities at a depth of 5 mm from the surface of the silicon thin film substrate decreases, and at the same time, other types of impurities in the mixture gas It has been found that doping can be performed at an arbitrary depth of 1,000 km from the surface of the substrate.

Furthermore, the degree and depth of reduction of impurities from the silicon thin film substrate, the amount of doping of a new different kind of impurity into the silicon thin film substrate, and the doping depth of new impurities are as follows: (1) Gutszu! By adjusting the composition of the mixed gas placed in the discharge state 11, the pressure and time during plasma discharge in the vacuum vessel, and (3) the plasma discharge power density,
Therefore, it was found that various changes can be made.

The present invention has been made based on the above new findings. That is, the method for manufacturing a silicon thin film according to the present invention includes:
A pl [or nil silicon thin film substrate containing an impurity (A) is mixed with a gas containing elements properly translated from the details of fluorine, chlorine and hydrogen, and a gas containing an impurity (B) which is different from the impurity (mu) in the silicon thin film substrate. exposing the silicon thin film substrate to a desired depth from the surface of the silicon thin film substrate by exposing it to a plasma axillary electric current of a mixed gas consisting of;
A distinctive feature is that the impurity (B) is simultaneously doped to an arbitrary depth from the kli surface of the silicon thin film substrate.

Further, it is considered that the dangling bonds formed by removing impurities (mu) bond with fluorine or hydrogen.

For example, if phosphorus atoms are doped from the surface of a pffi silicon thin film containing %t, My atoms as impurities, pnll! When manufacturing an I-combined device according to the present invention, this pm [silicon thin film substrate, phosphine PH,
is exposed to a plasma discharge state of a mixed gas of diluted with hydrogen or a mixed gas of phosphorus pentafluoride diluted with fluorine. By this operation, the amount of dan atoms in the p-type silicon thin film substrate is reduced! ! While the pn! 1
A composite element is produced. In addition, when manufacturing a pn* composite element according to the present invention by doping poron atoms from an n-type amorphous silicon thin film substrate containing phosphorus atoms as an impurity, this n-type silicon thin film substrate may be doped with diborane B, H, The melon trifluoride is exposed to a plasma discharge state of a mixed gas diluted with hydrogen or a mixed gas diluted with fluorine. By this operation, the amount of phosphorus atoms in the nil silicon thin film substrate is reduced to a desired depth from the surface, while the poron atoms in the mixed gas are doped to the desired depth from the surface of the silicon thin film, necessitating a film formation process. A pn junction element is fabricated without doing so.

In any of the above methods, the depth of reduction of impurities from the silicon thin film substrate and the degree of doping of other impurities can be controlled by changing the strength of the mixed gas, that is, the mixing ratio, and thereby the depth of doping of other impurities can be controlled as desired. It is possible to manufacture various pn junction devices with the performance of , and it is also possible to manufacture pin junction devices. To explain in more detail, in the manufacturing method according to the present invention, the composition of the mixed gas is an important parameter when carrying out the manufacturing method according to the present invention, together with the discharge pressure and time and the power density. Regarding the gas composition, when the ratio (impurity (B) gas/fluorine or hydrogen gas) is small, a new The depth from the surface to which the impurity (B) is doped becomes shallow. For this reason, the manufactured atoms become pin junction elements. On the other hand, if the ratio (impurity (B) gas/fluorine or hydrogen gas) is large, the depth at which the impurity (A) in the Crycon thin film substrate is reduced from the surface by fluorine or hydrogen, and the depth at which new impurity (B) is The depth from the surface to be doped is the same. Therefore, the manufactured device becomes a pn junction device. Preferred mixed gas compositions in the practice of the present invention are B, H, BP, /H.

Or, it was found that PH,, PF, /乍 is 10-1 to 1O-1. In addition, the flow rate of the mixed gas into the vacuum container must be set to keep the plasma state stable, and good results were obtained in the range of 0.5 to 10081008 CC.

The discharge pressure, which is one of the important parameters when actually implementing the manufacturing method according to the present invention, is i, s x i o-”T
It is preferable to control the pressure to between orr and 3 Torr. In other words, if the pressure during discharge is 1.5 x 10" Torr or less, the flow inside the vacuum container becomes a diffusion flow, and there is a high possibility that impurities released from the silicon thin film substrate will mix into the silicon thin film substrate again. In order to make the flow inside the vacuum container a viscous flow, the pressure during discharge must be 1.5×10 −” Torr or more. The pressure at the time of discharge of 3 Torr is to prevent discharge between the electrode and the earth shield, and is mainly due to equipment factors. Further, the discharge power density varies depending on the properties of the plasma gas used, but 0.5 to 5 Q W/c- is appropriate. The discharge time under such conditions can be varied between 1 second and 5 hours. In addition, the relationship between discharge power density and discharge time is generally related to the depth of reduction of the originally added impurity element and the doping depth of new impurities, and the discharge time is related to the depth of reduction of the originally added impurity element. It can be said that it is involved in the amount of element reduction and the amount of new impurity doping.

As is clear from the above explanation, the main purpose of the present invention is to
It is an object of the present invention to provide a method for manufacturing a silicon thin film that can manufacture a PNI [or PIN II] silicon thin film with fewer film forming steps than conventional manufacturing methods.

Another object of the present invention is to provide solar cells, image forming photoconductors, photoelectric conversion elements or diodes for reading devices, etc., which have good photoelectric conductivity and dark electric conductivity and have improved light energy conversion efficiency. It is an object of the present invention to provide a method for manufacturing a PNL [or PIN II silicon thin film] that can be used for production INK.

In the manufacturing method according to the present invention, the original silicon thin film substrate to be subjected to the film forming process according to the present invention uses a silicon single crystal semiconductor and a mixture of silane (8iH, ) and a male dopant as the raw material gas and plasma plasma. Although it is possible to use a PL [or n-type silicon thin film such as an amorphous silicon semiconductor film formed on any substrate under a surrounding atmosphere, the present applicant's patent application (% application @55-14
No. 3010) A silicon thin film as described in K.
Silane 8tH, or halogenated silane 8tH, ~, X
Any one of 4 to 1 (X: halogen element), or 2
For the purpose of forming a crystalline or amorphous mixed layer by sufficiently controlling the film formation rate by mixing a dopant gas with a mixed gas of at least one species as a raw material gas, the mixed gas is mixed with helium, neon, argon, etc. When diluted with own gas or hydrogen at a ratio of more than about 1:1, a silicon thin film formed while applying power with a discharge power density of about 0.2 W/cs or more can also be used. It can be conveniently applied.

Next, a method for manufacturing a silicon thin film according to the present invention will be described in Example K.
IA and explain.

Implementation Example 1 In the 1st aiaic, the entire equipment system including the mixing chamber 1 was operated using an oil rotary pump 2 and an oil diffusion pump 3 for about 10 minutes.
A vacuum of @Torr is created, and gases are introduced from the ffKy element tank 4 or hydrogen tank 5, and the dopant gas (ciborane or phosphine) cylinder 6 or 7 at the required ratio of the mixed volume $IK, and mixed.

The mixed gas is introduced into the vacuum chamber 9 through the flow meter 8 at a constant flow rate. The main pulp 10 is operated to maintain the required pressure while monitoring the degree of vacuum in the vacuum container 9 with the vacuum needle 11. The flow conditions within the vacuum vessel are adjusted to the viscous flow regime to prevent re-entrainment of released impurities in the substrate film. This mainly increases the pressure inside the vacuum vessel by 1.5
This can be realized by maintaining KIIl of 10-'' Torr or more.A high-frequency voltage is applied between electrodes 13 and 13' using a high-frequency oscillator or DC power supply 12 to generate gray discharge.

As the substrate 15, a nil or pall silicon thin film substrate is used. The thickness of the substrate thin film is preferably in the range of 0.1 to 1 μm, but in this example, the thickness was set to 0.7 μm. This substrate 15 is placed on a base heated by a heater 14, and heated to a required temperature by the heater. By the above method, the silicon thin film substrate 15 becomes a pn junction element or a pin junction element.

Table 1 shows examples of the manufacturing method according to the present invention.

The performance conditions of the phi silicon thin film substrate used were 81H.
A mixed gas of 4: H, -1: 1 was used, and a mixture of diborane B, H, and SiH4 as dopants was used as the raw material gas [, plasma applied power density Q, I W/Cal', acid film pressure 5 x 10
-”To r r s ji [Material gas flow rate 15 BCC
M, film formation time was 60 minutes, pI [silicon substrate was ■TO transparent electrode, hK was manufactured under the performance conditions described in Example 1 above.

Rectification properties were confirmed from the V-i % properties of Samples M1 and Todoroki 2 elements in Table 1, and from this it was found that pn junction elements were fabricated.

Furthermore, EMXII constant and heating gas release experiments were performed on sample 42, and the results confirmed that 4 m[2] of phosphorus atoms were contained in the p II S' 9 thin film. It was determined that it was doped.

1lll Sample number -1--Carrier gas H, Ha Gas flow rate (8CCM) 5 5
Power density (y/can”) 1.3
0.8 Substrate temperature ("C) 300
300 discharge pressure (Torr)
3X10"-"3X10-"Discharge time (min)
60 30 Substrate conductivity type p pThe second WA shows the electrical conductivity of a thin film produced by the manufacturing method according to the invention as a function of plasma energization time. However, in order to ensure that the bone atomic weight is reduced from the surface of the pmlI film substrate by the manufacturing method of the present invention, the silicon thin film shown in FIG. Manufactured by ~
・That is, the manufacturing method of the sample shown in 2nd WiA & 1, the bombardment binder p silicon thin film, the hydrogen flow rate lo8CCM, the discharge pressure ITorr, the power intensity 0.8
W/aa'' and a substrate temperature of 300° C., it is due to the water bulk plasma discharge. From the 2nd E, it can be seen that the electrical conductivity decreases with the discharge time. This is because
pl [This is because the melon atomic weight decreases from the silicon thin film surface to an arbitrary Keyaki.

Example 2 In the same manner as in Example 1, a boron-doped pH amorphous silicon thin film substrate (thickness 5000λ) was treated in a plasma atmosphere of a mixed gas of gas and hydrogen gas.
An n-type contact element was produced. # Junction element is p from V-1% property
inl! It was confirmed that it was a composite element. Also, the 38th
11 represents the 81 MB result, but from the figure 3, the bones in the substrate film are 35 O0 from the surface.
It will be understood that the phosphorus in the gas mixture is newly doped.

As shown in m1jj above, according to the manufacturing method of the present invention, p
It is possible to reduce the amount of impurities from the surface of the silicon thin film substrate to an arbitrary depth and simultaneously dope new impurities into the silicon thin film. Therefore, the manufacturing method of the present invention It is possible to manufacture pnll* junction devices or pin if junction devices by reducing the It has the effect of creating momentum.

[Brief explanation of drawings]

The i@1 is a schematic diagram showing an apparatus for implementing the silicon thin film manufacturing method according to the present invention. FIG. 2 is a shoe 7 that shows the electrical conductivity of a silicon thin film produced by the manufacturing method according to the present invention as a function of plasma discharge time. FIG. 3 is a graph showing the aIM8f) It determination results of the silicon thin film manufactured by the manufacturing method according to the present invention. l: Mixing container 4.5.6. ? :Gas pump 9:Vacuum container

Claims (1)

[Claims] l) A silicon thin film substrate doped with one impurity element is treated with a gas of at least one element selected from the group of fluorine, chlorine, and hydrogen, and the original added impurity in the silicon thin film substrate is A mixed gas consisting of a gas containing another type of impurity element! The silicon thin film substrate is placed in an atmosphere, thereby reducing the amount of originally added impurities in the silicon thin film substrate to a predetermined depth from the surface of the silicon thin film substrate, and at the same time doping new impurities in plasma to an arbitrary depth. A method for manufacturing a silicon thin film. 2) A manufacturing method according to claim 1, in which the pressure of the mixed gas is adjusted so that the flow inside the container is in a viscous flow region. 3) The pressure during plasma discharge of mixed gas is 1.5 x 10
-'Torr to 3 Torr, the manufacturing method according to claim 1. The composition of the mixed gas can be determined by changing the ratio of impurity element gas to monoelement gas in the range of 10-1 to 1O-1 and the power density in the range of 0.5 to 50 W/3''. The manufacturing method according to claim 3, characterized in that the reduced depth and the doping depth of the new impurity are adjusted. 5) The amount of impurity is determined from the surface of the silicon thin film substrate to
5. The manufacturing method according to claim 4, characterized in that the depth decreases over a depth of oo, 1. 6) The manufacturing method according to claim 1, wherein the silicon thin film substrate is a single crystal silicon semiconductor. +7) The manufacturing method according to claim 1, wherein the silicon thin film substrate is an amorphous silicon semiconductor. 8) The manufacturing method according to claim 8, wherein the silicon thin film substrate is a silicon semiconductor in which microcrystalline grains are mixed in an amorphous layer.