JPS59190209A - Preparation of silicon coating film - Google Patents

Abstract

PURPOSE:To obtain a semiconductor film composed mainly of Si having low oxygen or oxide concentration, by treating silane with HF to remove silicon oxide from the silane in the form of water and SiF4, and using the silane as a raw material of the objective Si coating film. CONSTITUTION:In the filling of a silane, e.g. SiH4, in a bomb, the silane is contaminated with silicon oxide (represented by SiO2) produced by the reaction of SiF4 with residual O2, etc. The above trouble can be prevented as follows: When HF is charged together with SiH4 in the first vessel, SiF4 and water are produced by the reaction of formula II. The produced SiH4 containing impurities is transferred to the second vessel maintained at a cryogenic temperature to effect the trapping of water as a solid and SiF4, etc. as a liquid or solid in the vessel as shown in formula III. The vessel is maintained at a temperature to vaporize only SiH4, and the purified SiH4 obtained by this process is introduced into a reaction furnace at <=1atm and subjected to the photo(plasma)-chemical reaction. A semiconductor film composed mainly of Si and having an oxygen or oxide concentration of <=1X10<18>atom/cc can be formed on the surface of the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves removing silicon oxide contained in silane to produce purified gas-phase applied silane, and using the purified silane to process a gas-phase method (Photo CV method).
The present invention relates to a method of forming a semiconductor film containing silicon as a main component and having an oxygen concentration of 1×10 18 atoms/cc or less by using a photo plasma vapor deposition method (referred to as D) or a photo plasma vapor deposition method (referred to as PPCVD).

This invention uses silane (SiH4 or SinH2n + 2
Hydrogen fluoride (hereinafter referred to as HF) is mixed in a container (generally referred to as a high-pressure cylinder, but herein simply referred to as a container or a first container) filled with hydrogen fluoride (n≧2).

The oxide, typically silicon oxide, then reacts with HP in this container to produce water (H2O) and silicon fluoride (SiF4 general formula H4-xSiFx) as reaction products.

The impurities of this water and silicon fluoride are liquefied and loaded in a container (second container) maintained at 65 to 105°C, or the impurities are trapped and purified using silane.
It is characterized by performing VD or PPCVD.

In general, silane having extremely strong oxidizing power tends to easily contain silicon oxide as an impurity due to its oxidizing power.

However, this silicon oxide is an ultrafine powder (the particle size is estimated to be 100A or less) and a solid.

Because of its ultrafine powder form, it is liberated in the form of a colloid in the silane container, and cannot be filtered through any filter to separate it from silane as a reactive gas for semiconductors. This results in the presence of silicon oxide as an impurity.

Furthermore, since silicon oxide is conventionally a solid, it has been completely undetectable in chemical investigations of its purity as an impurity in silane, and it has been unknown until now to what extent it is mixed in.

That is, chemical impurities in silane have been measured and evaluated using methods such as mass spectrometry, atomic absorption, and gas chromatography.

However, the amount of silicon oxide as an impurity was determined by the present inventor using a charged phase method (Photo CVD [photochemical vapor deposition] method) using this silane or a PPCVD [photo plasma vapor phase method].
This can be achieved by forming a semiconductor film containing silicon as the main component using the por dipos-ion method (collectively called the por dipos-ion method), and detecting and identifying the formed silicon film using SIMS (ion, micro, analyzer). did it.

When such identification was performed, it was found that the conventionally known silicon film contained a concentration of 2×10 19 to 1×10 24 atoms/cc.

In addition, since the silicon concentration was 2×10 19 atoms/cc, it was found that oxygen was contained in a large amount of 0.1 to 5%.

Furthermore, for SiO2, SiO, and SiOH, the representative bonds are determined by the ionic strength (count/se) of the SIMS.
In c), for example, SiO2×104, SiO2×1
02, it was found that SiOH3×103 and Sin2 were contained in extremely large amounts.

The present invention removes such oxides and reduces the oxygen concentration in the formed semiconductor by converting it into amorphous, semi-amorphous (semiconductor having a semi-amorphous structure) or non-single crystal silicon containing a microcrystalline structure. , 1/1018 atom/cc or less, preferably 5×1017 atom/cc or less.

Based on such SIMS data, the present invention has discovered that large amounts of SiO2 cannot be removed even by removing leaks from the reaction system and doping system, and are present in high-pressure containers such as cylinders from the beginning. The present invention is characterized in that hydrogen fluoride, which reacts with silicon oxide to produce water, is filled or mixed into the bomb to react only with impurities.

Purification, film formation, and reaction processes of the present invention will be explained below with reference to the drawings.

Figure 1 shows the reaction formula using monosilane (SiH4) among silanes as an example. When using polysilane, polysilane is prepared from this monosilane by a non-polar discharge method, and the purified polysilane, especially disilane, is It is likewise possible by using

In the drawings, formula (50) represents silicon oxide produced by the reaction between silane and oxygen, particularly residual oxygen when the cylinder is filled or oxygen adsorbed on the inner wall of the introduction pipe.

Silicon oxides include SiOx such as SiO2 and SiO, and some hydroxyl groups may be mixed in to form SiOH bonds, but here SiO is used to represent the reaction formula.

When such silicon oxide is present in a cylinder in the form of a solid ultrafine powder in silane at an amount of 0.1 to 5%, there has been no known method for removing the ultrafine silicon oxide.

In the present invention, silicon fluoride (anhydrous hydrogen fluoride is simply referred to as HF) was filled in the same space in the first container. That is, the first
In addition to sufficiently evacuating the container (to a vacuum of 10 −6 torr or less), the container was heated to a temperature of 150° C. or higher (for example, 250±20° C.) to dehydrate the inside of the container.

Furthermore, HF (purity of 99.8% or more) is filled into this to an extent that the pressure becomes atmospheric. Furthermore, after this, 10 to 30 kg/cm2 of raw silane is added to the first container, for example, 20 kg/cm2.
It was sealed until the pressure reached cm2. As a result, it was possible to incorporate HF into the raw silane at a concentration of 10 to 3%.

In this first container, as shown in equation (51), silicon oxide reacts with HF, and SiF4 (BP-65°C
) and water (BP+100°C, MP0°C) are produced.

Although this container is at room temperature, it is under pressure of 10 to 30 kg/cm2, so the amount remaining as O2 in the container is 1.
PPM or less, all reacted to form silicon oxide, and all reacted with HF to form silicon fluoride, which could be converted from solid to gas.

Further, this impure ring silane was transferred to a second container at a temperature of 112°C or lower, preferably -130 to -150°C. The silane then becomes a liquid, and the impurity water becomes a solid. In addition, hydrogen fluoride etc. become liquid or solid,
Trapped within a second container.

Equation (52) shows that impurities silicon fluoride and water are transformed from gas to liquid or solid.

Next, this second container is heated to -65 to -110°C, preferably -
By maintaining the temperature at 75 to -100°C, the impurities themselves can remain in the second container as a solid, and only the silane can be led out as a gas into the reaction system.

In order to prevent silicon fluoride from being mixed into the silane as a gas during the second purification, the boiling point (BP) of silicon fluoride is -6
The temperature is lower than 5°C, and the BP of the silane (-1
A feature of the present invention is that the temperature is higher than 22°C.

However, considering the partial pressure of each component near this BP, the temperature of the silane to be vaporized is -75 to -100℃.
It was preferable for the purification to be in the range of .

In the method of the present invention, the thus purified silane gas is applied to solid silicon or silicon mixed with hydrogen in a reaction system using the Photo CVD method or P as shown in formula (53).
Metamorphosed using PCVD method. That is, purified silane was used to form a non-single crystal semiconductor mainly composed of silicon or a single crystal silicon semiconductor having an amorphous or crystalline or ordered structure as shown in formula (53).

FIG. 2 shows an outline of an apparatus for carrying out the method of the present invention, in which the reaction system is a CVD method (herein, PPCVD or PhotoCVD are particularly collectively referred to as CVD).

FIG. 2 has a reaction system (10), a doping system (20), and a purification system (30) of the present invention.

The reaction system (10) contains the contents of the reaction container (2) (width 90 cm,
A substrate (1) having a surface to be formed (height: 60 cm, depth: 120 cm) is held by a quartz boulder (19).

This holder is 65 cm long, but has a 20 cm width in the direction of flow of the reactive gas, and holds a 20 cm x 60 cm substrate at 20 cm.
(total area of the surface to be formed: 24,000 cm2) are inserted at the same time.

The substrate is heated by a halogen heater (7), e.g.
heated to 00°C. In addition, 185nm, 253nm
Alternatively, a photochemical reaction lamp (9) emitting light with a wavelength of 10.6 μm is also provided. The reactive gas passes through the nozzle (3) from the inlet (11) and undergoes a reaction '+li (44
), and reaches the exhaust system from (12) through the exhaust port (8).

The exhaust system includes a pressure adjustment valve (13) and a stop valve (
14) Discharge unnecessary materials to the outside from the mechanical booster pump (17) and rotary pump (18).

The substrate is first placed in the preliminary chamber (16) using a holder, and after being evacuated at (23), the board is placed at the gate valve (45).
was opened and moved to the reaction section (44). In the doping system (20), silane is converted into reactive gases (26), P-type reactive gases such as diborane (B2H6), N-type gases (24) such as phosphin (PH3), and nitrogen are added to silicon. A gas (25) such as ammonia or silane for addition or carbon addition, and hydrogen or helium (27) as a carrier gas are respectively added through a flow meter (29) and controlled by a valve (28).

Regarding the silane purification system (30), raw silane in which hydrogen fluoride is mixed with silane is sealed in a first container (31).

In Fig. 2, the second
to the container (40).

The raw silane was purified by the following procedure.

Close the cylinder valve for raw silane (31), open the exhaust system and second container valves (32), (34), (46), and (15); 14), and then close the turbo pump (19) and rotary pump (18).
) at 10-6 torr or less, preferably 10-7 torr
Vacuum r.

Furthermore, the second container (40) is heated to 15
Heat to 0-250°C and degas.

After this, in order to cool the second container (40), the valve (
13), (14), (15), (25), (33), (
34) is closed.

Further, the controller (47) controls the valve (36) from (35) to introduce liquefied nitrogen into the trap (38) through the needle valve (37).

Vaporized unnecessary nitrogen is discharged from (42). This (4
Liquefying 2) again and reducing it to (35) is self-effective as a measure against sparrow energy.

The second container (40) is thus brought to approximately -150°C.

Thereafter, the valves (32) and (46) and the cock of the first container were opened, and the raw silane was transferred to the second container to produce liquefied silane. This is equation (52) in FIG.

After preparing the desired amount of liquefied silane in this container, the valve (
46), (32) and the first container cocks are closed;
The controller (47) controls this second container from -65 to -
The temperature is maintained at 110°C, for example -90°C. After the pressure inside the second container is detected at (41), it is led to (26) at the back of the doping system (20), which has been evacuated in advance, via a valve (33). That is, equation (52) (
53).

This second container is heated to -65 to -110°C, preferably -75°C.
The water and silicon fluoride in the raw silane may be removed in the same way by holding it at ~-100°C, for example, -90°C, and using this container as a cold trap without liquefying the raw silane. .

The semiconductor reactive gas consisting of silane is detected by a flowmeter (29)
The reaction system (10) is reached through the steps. This reaction system has 100~
500°C, preferably 250-350°C, typically 30°C
A surface to be formed is maintained at 0°C, and a reaction area (
44) Pressure of 0.1 to 10 torr, e.g. 2 torr
, the silane flow rate is 1 to 500 cc/min, e.g. 50 c
c/min. The light energy is ultraviolet light 185 nm and 2
Lamp that emits 53 nm (length 680 nm, diameter 10 m)
Light irradiation was performed using a light source (mφ, output: 450 W). Next, the electrical energy is transferred to a high frequency oscillator (frequency 13.56MH).
z) In addition to a pair of (5) and (6) from (4), plasma glow discharge was caused to perform a PPCVD reaction.

The substrate position was arranged parallel to the irradiation light, and the photochemical reaction was carried out on the flying reactive gas rather than on the substrate surface. This allows for mass production of Ph.
I was able to perform otoCVD. Yet another method of the invention added electrical energy in addition to this optical energy. At this time, the substrate was disposed in the positive column region of the generated glow discharge, and a silicon film was formed on the surface to be formed, for example, the glass substrate, by the photoplasma discharge based on equation (53) in Fig. 1. .

This growth rate is from 0.1 to 0.1 in PhotoCVD only.
The 0.3 A/sec analogy was 0.2 A/sec. Also PPC
In VD, it was 6-15 A/sec, for example 12 A/sec.

That is, in the PhotoCVD method, since the substrate surface was not damaged by plasma, a good film quality could be obtained. However, the growth rate of the film is 0.1-0.3A
It has the disadvantage that it is extremely slow (/second) and that the light energy required is extremely powerful.

Photo
We were able to achieve growth 30 times faster than the oCVD method.

In this PPCVD method, it is extremely important that light irradiation is performed in the process and then electrical energy is applied to generate plasma. By doing so, damage to the substrate surface due to plasma shock waves before the start of discharge can be prevented, and electrically, plasma damage can be substantially prevented.

As described above, the method of the present invention shows that the oxygen concentration mainly composed of silicon is 1 x 1018 cm-3 or less, preferably 1 x 10
A non-single crystal semiconductor having a size of 7 cm −3 or less could be formed on the surface to be formed.

Note that the remaining impurities deposited in the second container such as water, silicon fluoride, and other impurities trapped at a temperature below -65°C are removed after the explosion of the semiconductor film is completed.
In Figure 2, the valves (33) and (25) are closed, and the valve (
34) (14) was opened and evacuated using the mechanical booster pump (17) and vacuum pump (18).

Examining the film quality of this silicon film, we found that the oxygen concentration was less than 1 x 1018 atoms/cc (light output 2
．． 0kW discharge output (70W or less).

Furthermore, assuming that the discharge output is 15W, 2×1017ato
m/cc and further reduced to 1/5 of that, and when connected to a conventionally known silane doping system and examining the film, it was found that 3×
1019 atoms/cc, which was found to be about 1/100th of this value.

Tables 2 and 3 show the results of impurities in silicon films produced by the PhotoCVD method or the PPCVD method using the purified silane obtained by the method of the present invention. Furthermore, Table 1 shows the results obtained using the same equipment in the conventional PCVD method using silane.

As shown in Tables 1, 2, and 3, a non-single crystal silicon semiconductor capable of reducing oxygen to 5×10 7 or less could be produced even at 300°C.

This crystallinity progressed further by increasing the substrate temperature to 350°C and 400°C.

The temperature at which this reaction product is produced is also 150°C instead of 300°C.
It was also possible at ~300°C.

A purified silane is used instead of the monosilane described above, and a synthesized low-oxygenated polysilane (for example, SiπH2π+2) can be obtained by modifying this silane by a non-polar discharge method. At least a portion of this polysilane, especially disilane (SiH6/(SiH4+Si2H6)5~
30% (e.g. 15%))
When producing a semiconductor film by the photoCVD method,
The growth rate of the film was 0.6 A/s and 3 for monosilane.
I was able to double it.

Of course, when polysilane was present at a concentration of 90% or more, the growth rate could be further accelerated.

FIG. 3 shows a silicon semiconductor layer having a thickness of 0.5 μm formed on a glass substrate using the apparatus shown in FIG. 2 by the PPCVD method (light output: 1.0 KW, discharge output: 15 W).

Furthermore, a silicon nitride insulator was laminated on this upper surface as a barrier layer for preventing oxidation to a thickness of 500 Å using the same reaction apparatus shown in FIG. Thereafter, a portion of this silicon nitride was removed, and an ohmic contact electrode was provided in this portion as a parallel electrode, and the electrical conductivity characteristics were investigated.

Figure 3 particularly shows the electrical characteristics (57) (64) (65) (6
6) (68), conventional characteristics (57) (63) (58
)(67)(69).

In the drawing, in the conventional example, a region (59) exhibits a dark electrical conductivity (57) of 10-7 to 10-8 (Ωcm)-1.
It has a value of the order of . Here AM1 (100m
When irradiating area (60) with W/cm2), as shown by curve (58) in the conventional method, 1×10(Ωcm)−1
, and the value had deteriorated by about one order of magnitude after 2 hours of continuous irradiation.

In the method of the present invention, the dark conductivity (56) is 5
×1010(Ωcm)−1, and its optical conductivity (64
) has an order of 2×10 (Ωcm) and a photosensitivity of 107, which is about 1 to 2 orders of magnitude larger than that of the conventional example. Almost no deterioration of the electrical conductivity was observed.

Furthermore, in the present invention, the dark conductivity of region (61) after irradiation was also the same within the range of error compared to (66) and (56).

When heating is further performed at 150°C, the curve (67
) becomes (69), and there is an apparent change in property improvement,
After that, when the region (62) was irradiated with light again, the deterioration characteristics were observed again.

That is, in the conventional example, the electrical conductivity is (67)
As shown in Figure 2, it is small and exhibits deterioration characteristics due to light irradiation.

However, in the present invention, the electrical conductivity depends on the presence or absence of light irradiation.
Almost no change or deterioration of properties was observed with or without thermal annealing, and the photoconductivity and photosensitivity (difference between photoconductivity and dark conductivity) were large, and dark conversion conductivity was small.

As described above, it has been found that the method of the present invention has a synergistic effect in that it can provide a highly reliable silicon half-stone phase.

Figure 4 shows the photodegradation characteristics (Photo) of the conventional example in Figure 3.
o Induced Effect, hereinafter referred to as PIE,
This demonstrates the principle of the Stebler-Wronski effect (also known as the Stebler-Wronski effect) and the principle of special improvement according to the present invention.

That is, by light irradiation, the phase (70) changes to the phase (71), and by thermal annealing, the phase (71) changes to the phase (70).

This is shown in equation (73) in the reaction formula, and dangling bonds that act as recombination centers are generated by light irradiation, and hydrogen bonds are formed by thermal annealing and are no longer generated.

Formula (73) shows the reaction formula.

This PIE is important because it determines the amount of oxygen such as SiOH mixed, but the amount of SiOH is as shown in Tables 2 and 3 above.
It has been reduced to 1/140 of the conventional one. Further reducing this concentration is the direction of progress of the present invention.

It is judged that this decrease is due to the reduction in the characteristic deterioration of this PIE.

This PIE promoted a decline in industrial reliability in semiconductor electronics and was extremely harmful.

Such deterioration characteristics have been clarified, and the present invention as a countermeasure against it can be applied to photoelectric conversion devices, optical sensors, electrostatic copying machines, insulated gate field effect semiconductors, and their integrated devices, and is extremely effective industrially. It is judged that

In the present invention, the cylinder was used as the first container as shown in FIG. However, using this cylinder as a third container, the silane is purified at a gas supplier, and the purified silane is filled into the cylinder (high-pressure container) (third container). The present invention is also effective for producing a silicon semiconductor film by directly connecting the reactor to a reaction system for manufacturing semiconductor devices as shown in FIG.

Further, in the present invention, the first container is filled with silane and hydrogen fluoride, but the present invention is equally effective if this container is used as a mixer.

In this specification, a semiconductor film containing silicon as a main component is shown. As shown in FIG. 2 (25), methane or ammonia was simultaneously introduced to form the semiconductor film.
1-x (0<x≦1), Si3N4-x (0<x≦4)
It is effective to make a non-single crystal semiconductor to which carbon or nitrogen is added.

[Brief explanation of drawings]

FIG. 1 is a reaction formula showing the principle of the present invention. FIG. 2 shows a reaction system and a purification system using the method of the present invention. FIG. 3 shows electrical conductivity characteristics obtained by the method of the present invention and the conventional example. FIG. 4 shows the principle of photodegradation characteristics. Patent applicant Shunpei Yamazaki, representative of Semiconductor Energy Research Institute Co., Ltd.

Claims (1)

[Claims] 1. By filling or mixing silane and hydrogen fluoride in a first container, the silicon oxide impurities contained in the solane are transformed into water and silicon fluoride, and the silane is nucleated. a step of removing the water, silicon fluoride, and hydrogen fluoride to produce the silane gas; and injecting the purified silane into a reaction chamber maintained at 1 atm or less. , each time a photochemical reaction or photoplus-7 chemical reaction is performed by supplying light energy, the concentration of oxygen or oxide is increased to 1×10 on the surface to be formed.
A method for producing a silicon film whose motive is to form a semiconductor film whose main component is silicon having a density of 18 atoms/cc or less. 2. A process point in which silicon oxide impurities contained in the silane are transformed into water and silicon fluoride by filling or mixing silane and hydrogen fluoride in a first container; and a step of purifying the silane by removing hydrogen fluoride, a step of generating at least a portion of polysilane from the purified monosilane, and a step of maintaining the silane containing the purified polysilane at a pressure of 1 atmosphere or less. A semiconductor whose main component is silicon, which has an oxygen or oxide concentration of 1 x 1018 atoms/cc or less on the surface to be formed, by introducing it into a reactor and performing a photochemical reaction or a photoplasma chemical reaction by supplying photonic energy. A method for producing a silicon film, characterized by forming a film. 3. In claim 1 or 2, a semiconductor film containing silicon as a main component includes SixC1-x (0<x<1)Si3N4-x to which carbon or nitrogen is added.
A method for producing a silicon film, the method comprising forming a pattern of a non-single crystal semiconductor c (0<x<4).