JPH05226251A - Formation method of high-quality film and manufacture of igfet - Google Patents

Abstract

PURPOSE:To make the concentration of carbon and oxygen in a film extremely low by a method wherein at least one energy out of light, heat and electricity is added to a reactive gas which has been once liquefied and purified and the film is formed. CONSTITUTION:Liquefied nitrogen is introduced into a trap 38 via a needle valve 37 by using a controller 47; a second container 40 is set to about -150 deg.C. After that, valves 32, 46 and a cock for a first container 31 are opened; raw silane is transferred to the second container 40; liquefied silane is produced. After that, the valves 46, 32 and the cock for the first container are closed; the second container is kept at, e.g., -900 deg.C; the liquefied silane is guided to a doping system 26 which has been vacuum-evacuated in advance; high-purity gasified silane which has been obtained is introduced into a reaction system 10 in which a substrate having a face to be formed has been arranged and installed. A beam of light is irradiated; a plasma glow discharge is performed; a PPCVD reaction is performed. Thereby, the concentration of carbon and oxygen in a film can be made extremely low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a photo vapor phase method (Photo Ch
emical Vapor Deposition (hereinafter referred to as Photo CVD) or optical plasma vapor deposition (Photo Plasma Chemical Vapor)
Deposition hereinafter referred to as PPCVD).

[0002]

2. Description of the Related Art Conventionally, in a photo CVD method, a substrate having a surface to be formed is heated from below the substrate, while the surface to be formed, which is the upper surface of the substrate, is irradiated with light vertically upward. Therefore, a method has been known in which a photochemical reaction is caused by photoexcitation of the reactive gas on the surface by light irradiation.

[0003]

This conventional method has a major industrial drawback that it is impossible to form a surface having a size equal to or larger than the area of irradiation light.

Further, for example, when silicon is to be formed using silane, a part of the photoexcited silicon adheres to the window for light irradiation and absorbs the irradiation light, so that it becomes a reactive gas. It had a drawback that the intensity of the irradiation light was weakened.

Therefore, although the photo CVD method has the feature that it does not damage the surface of the substrate, it cannot be applied to mass production at all.

The present invention eliminates these drawbacks and proposes a photo-CVD method which can be industrially mass-produced for the first time.

[0007]

In the high-quality film forming method of the present invention, when at least one of light energy, thermal energy and electric energy is added to a reactive gas to form a film,
A reactive gas that has been liquefied and purified at least once is subjected to film formation to obtain a high-quality film in which the concentrations of carbon and oxygen during film formation are extremely low.

[0008]

In the present invention, the reactive gas causes a photochemical reaction upon irradiation with light. However, the reaction products are limited to materials that do not absorb the irradiation light.

Therefore, in the present invention, in the semiconductor containing silicon as a main component, infrared light having a light energy smaller than the optical gap of 10.6 μ is photoexcited by using a carbon dioxide gas laser or a far infrared light source. .. For insulators such as silicon oxide, silicon nitride, and silicon carbide, ultraviolet light (2537A, 1850A), which is light smaller than the optical band gap (hereinafter referred to as Eg), is used (A: Ohm Strong).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be described below in comparison with a conventional device with reference to the drawings.

FIG. 1 shows an outline of a conventionally known photo CVD apparatus.

In the drawing, a substrate (1) is arranged in a reaction vessel (2), and a heater (53) is used to connect the substrate (2) from the lower side.
It is heated to 00 to 400 ° C. Further ultraviolet light (25
The surface of the substrate (1) is vertically irradiated (51) with a low-pressure mercury lamp (9) through a quartz plate. Oil (54) is applied to the lower side of the quartz plate to reduce the adhesion of reaction products. As the reactive gas, silane (26) from the doping system (20) is supplied from the flow meter (29) through the valve (28) in parallel (50) to the substrate surface. Hydrogen or helium as a carrier gas is supplied from (27), a photochemical reaction is performed, and a semiconductor film is formed on the substrate (1). Unwanted reaction products and carrier gas pass through a valve (13) for pressure adjustment,
It is exhausted to the outside by the vacuum pump (18).

In such a conventional apparatus, when a silicon film is formed of silane, silane is caused to flow from the (50) direction, ultraviolet light is vertically irradiated to the substrate, and the surface reaction on the substrate causes A silicon film is formed.

However, if another substrate is arranged on (1 '), the surface of (1) is not irradiated with ultraviolet light by (1') and is shaded. Therefore, the photochemical reaction cannot be performed on the lower substrate (1).

That is, the conventional method cannot form a large amount on the substrate. In the conventional method, this photochemical reaction has been made based on the fact that the photochemical reaction on the surface of the substrate is rate limiting rather than the photochemical reaction in the reactive gas in flight. Therefore, the configuration other than that shown in FIG. 1 could not be adopted.

However, in this method, since the light source is arranged in the atmosphere, the quartz plate (48) cannot be made large in area in order to prevent damage due to pressure or the like. For this reason, only one 3-inch wafer was used as a substrate, and theoretically, it was impossible to simultaneously insert five 5-inch wafers.

On the other hand, in the present invention, as a result of thorough examination of this photo-CVD method, the photochemical reaction is carried out even for the reactive gas in flight, and the film formation on the film surface is performed by thermal energy rather than irradiation light. We have found that it becomes possible by using.

That is, it was found that it is not always necessary to irradiate the surface of the silicon film with ultraviolet light at a temperature of 250 ° C. or higher, for example, 300 to 350 ° C.

In addition, even at such a temperature, in the photo CVD method, when the mercury excitation method is not used, the growth rate of the film is 0.1 to 0.3 A / sec (6 A / min to 1).
Only 8 A / min) was obtained.

Therefore, in the device of the present invention, electric energy is simultaneously supplied in addition to light energy to promote activation of the reactive gas, and thus the growth rate of the film of the reactive gas is about 10 times or more 6 to 20 A. It is characterized by being able to increase to / second.

In plasma CVD, it has been conventionally said that the substrate surface is sputtered (damaged) by plasma energy, and a photo CVD method has been devised to compensate for such a defect.

However, as a result of a thorough consideration of the plasma generation mechanism, the present inventor found that the reactive gas obtains strong kinetic energy at the start of discharge (glow discharge), which sputters the non-formed surface. It has been found that the activated reactive gas does not have so much kinetic energy once it has started to discharge.

For this reason, the discharge can be started easily and
In order to prevent instability in which this discharge is likely to stop even after it has been discharged, first, light irradiation is performed so that a part of the reactive gas is excited, and then electrical energy reacts with light energy at the same time. It is characterized by facilitating the initiation of the discharge and further facilitating the sustaining of the discharge by adding it to the volatile gas.

The photo CV of the present invention will be described below with reference to the drawings.
Note the D device.

In FIG. 2, the reaction system is CVD (PPCVD or
An outline of an apparatus for carrying out the method of the present invention, which is a Photo CVD method, will be described.

Example 1 FIG. 2 has a reaction system (10), a doping system (20) and a purification system (30) of the present invention.

In the reaction system (10), a quartz holder (19) holds a substrate (1) having a surface to be formed in a reaction container (2) having an internal volume (width 90 cm × height 60 cm × depth 120 cm). ..

This holder has a size of 65 cm × 65 cm, but has a length of 20 cm in the flow direction (50) of the reactive gas, and 20 substrates of 20 cm × 60 cm (total area of the surface to be formed 24000 cm ² ) are simultaneously formed. I have it inserted.

Further, the surface of the substrate (1) on which the reactive gas is formed is introduced vertically from above and discharged downwardly at a constant interval (2 to 10 cm, eg 5c) in the vertical (vertical) direction.
m) are forested separately.

Further, in the device of the present invention, halogen.
The pressure in the space where the heater (7) and the lamp for the photochemical reaction are located is adjusted by opening and closing the valve (49) so that it becomes equal to the pressure in the reaction vessel (2). It is kept at 10 torr.

Therefore, the quartz substrate (48) is not damaged and a large area (80 cm × 80 cm) can be produced. Therefore, it became possible to create a large space of 65 cm × 65 cm × height (20 to 60 cm) as a reaction space.

The substrate is heated to, for example, 200 to 500 ° C. by the halogen heater (7). In addition, 185n
A lamp (9) for photochemical reaction that emits light having a wavelength of m, 253 nm or 10 to 15 μm is provided on the upper light source and the lower light source at the same time. As a result, the flow of the reactive gas (5
0) and irradiation light (51) are arranged in parallel or substantially parallel to the substrate surface, and the irradiation light irradiates the entire reaction space (44). The reactive gas reaches the reaction space (44) from the inlet (11) via the quartz nozzle (3), and reaches the exhaust system from (12) via the quartz outlet (8).

The exhaust system includes a pressure adjusting valve (13), a stop valve (14), a mechanical booster pump (1
7), rotary pump (18), turbo pump (1
9) Dispose of unnecessary substances outside.

The substrate is first placed in a preliminary chamber (1
After arranging in (6) and performing vacuuming at (23), the gate valve (45) was opened and transferred to the reaction section (44). The reactive gas is silane (26) in the doping system (20), other reactive gas for P type such as diborane (B ₂ H ₆ ) or N type gas such as fossine (PH ₃ ) (24). , A gas (25) such as ammonia or methane for adding nitrogen or carbon to silicon, and hydrogen or helium (27) as a carrier gas are controlled by a valve (28) via a flow rate system (29), respectively. ..

In the photo CVD apparatus of the present invention, the reactive gas silane used is further purified.

That is, regarding the silane purification system (30), the original silane is enclosed in the first container (31).

In FIG. 2, the pressure adjusting valve (32)
To the second container (40).

Purification of the original silane was carried out by the following procedure.

First, as a purging step, original silane (31)
The cylinder valve is closed, the exhaust system and the second container are opened with valves (32), (34), (46) and (15), and valves (13), (25), (33) and (14). Closed and the turbo pump (19) and rotary pump (18) for 1
Evacuation is performed at 0 ^-6 torr or less, preferably 10 ^-7 torr. Further, the second container (40) is provided with a heater (39).
At 150 to 250 ° C., degassing purging is performed.

Thereafter, in order to cool the second container (40), the valves (13), (14), (15), (25),
(33) and (34) are closed.

Further, liquefied nitrogen is introduced into the trap (38) through the needle valve (37) by controlling the valve (36) from the controller (47) through the valve (35).

The unnecessary nitrogen vaporized is discharged from (42). It is effective as an energy saving measure to liquefy (42) again and reduce it to (35).

Thus, the second container (40) is filled with about -150.
To ℃.

Then, the valves (32), (46) and the cock of the first container were opened to transfer the original silane to the second container to prepare liquefied silane.

Then, silicon oxide and water contained in the original silane become solid in the second container and adhere to the wall surface.

After producing a desired amount of liquefied silane in this container, the valves (46), (32) and the cock of the first container were closed, and the controller (47) closed this second container at -65. Hold at -110 ° C, for example -90 ° C.
After detecting the pressure in the second container at (41), the pressure is brought to (26) of the doping system (20) which has been evacuated in advance via the valve (33).

Then, among these, impurities such as water, silicon fluoride and hydrogen fluoride remain, and only ultra-high-purity silane vaporizes to reach (26).

This second container is maintained at -65 ° C to -110 ° C, preferably -75 ° C to -100 ° C, for example -90 ° C, and this container is used as a cold trap without liquefying the original silane. Water and silicon fluoride in the silane may be similarly removed by this trap.

The semiconductor reactive gas made of silane reaches the reaction system (10) through the flow meter (29). These reactive gases are exhausted to the rotary pump (18) via the tarvon pump (19). 100 to 500 ° C., preferably 250 to 350 ° C. in the reactor in this reaction system,
Typically, a substrate having a surface to be formed, which is held at 300 ° C., is arranged, and the pressure in the reaction region (44) is 0.1 to 1
The silane flow rate is set to 1 to 0 torr, for example, 2 torr.
The supply was 500 cc / min, for example 50 cc / min. A lamp that emits long-wavelength light with infrared energy of 10.6μ or more (length 680nm, 15mm, maximum output 45)
0w) was used for light irradiation. This was also effective using a carbon dioxide laser. Independently of this light energy, the electrical energy is then fed into a high frequency oscillator (frequency 1
3.56 MHz) (4) pair of electrodes (5), (6)
In addition to the above, a plasma CVD discharge was performed to carry out a PPCVD reaction.

The surface of the substrate is arranged in parallel to the irradiation light for photochemical reaction, and the photochemical reaction is 150-150% by the flying halogen lamp, not by the substrate surface.
It was carried out on a reactive gas heated to 350 ° C., for example 300 ° C.

By doing so, it was possible to prevent the irradiation light from becoming a shadow of the substrate and not to be irradiated to the reactive gas on the opposite side, and it was possible to carry out Photo CVD capable of mass production. Further, in the device of the present invention, the reactive gas is heated to approximately the same temperature as the substrate, and the heated reactive gas is photoexcited, so that the surface of the substrate is sufficiently coated even if the light is not irradiated. It also has the feature that it is possible.

In the device of the present invention, electric energy was applied in addition to the light energy and the heat energy. At this time, the substrate was disposed in the positive column region in the generated glow discharge, and the silicon film was formed on the surface to be formed, for example, the glass substrate by the photo plasma discharge.

The growth rate of this semiconductor film is Photo CV
0.1 to 0.3 A / sec, for example, 0.2 A only in D
/ Sec. In PPCVD, 6 to 15 A
/ Sec, for example, 12 A / sec, a high speed growth of 30 times could be obtained.

That is, in the Photo CVD method, since the substrate surface is not damaged by plasma, good film quality can be obtained. However, the growth rate of the film is 0.1
It has a drawback that it is very slow at .about.0.3 A / sec, and the light energy required therefor is extremely strong.

On the other hand, in the PPCVD of the other inventions, although some damage due to plasma was observed, the film growth rate was 6 to 15 A / sec, which was 30 times faster than that of the Photo CVD method. In this PPCVD method, as a sequence of steps, heat energy is applied to a reactive gas and light irradiation is first performed so that a part of the reactive gas is photoexcited so that it is extremely easily ionized, and then electric energy is added. Generating the plasma reaction is extremely important. By doing so, the plasma shock wave at the start of discharge could be prevented, and the plasma damage on the substrate surface could be substantially prevented.

As described above, a non-single-crystal semiconductor containing silicon as a main component and having an oxygen concentration of 1 × 10 ¹⁸ cm ^-3 or less, which is shown by the method of the present invention, could be formed on the formation surface.

Water, silicon fluoride, and other impurities trapped at a temperature of −65 ° C. or lower as impurities deposited and left in the second container are not shown in FIG. 2, the valves (33) and (25) are closed, the valves (34) and (14) are opened, the second container is heated by the heater (39), and the turbo molecular pump (19) and the rotary pump are added. It was evacuated according to (18).

Examination of the film quality of this silicon film revealed that the oxygen concentration in the SIMS measurement could be 1 × 10 ¹⁸ atom / cc or less (light output 2.0 KW or less, discharge output 70 W or less).

When the discharge output is further set to 15 W, 2 × 1
0 ¹⁷ atom / cc, which is further reduced to 1/5 of that, and the conventionally known silane is connected to the doping system to obtain Photo C.
When the film was formed by the VD method or the PPCVD method and the oxygen content in the film was examined, it was found to be 3 × 10 ¹⁹ atom / cc, which was reduced to about 1/100 of this value.

In the apparatus of the present invention, the substrate temperature is set to 350.
The crystallinity of the coating film formed by controlling the temperature to 400 ° C and 400 ° C further progressed.

The temperature for producing this reaction product was 150 ° C. to 300 ° C. instead of 300 ° C. in the PPCVD method.

In the Photo CVD method, when monosilane is used as the film growth rate reactive gas, it is extremely low and industrial improvement is required.

Purified monosilane is used as the silane instead of the above-mentioned monosilane, and this silane is modified by a nonpolar discharge method to synthesize a lower polysilane (for example, S.
i _n H _{2n + 2)} can be obtained. In the case of producing a semiconductor film by the above-mentioned Photo CVD method using silane containing at least a part (concentration of 5 to 30%) of polysilane, especially disilane, the growth rate of the film is 0.6 A / sec and monosilane is used. I was able to raise it to 3 times.

Further, when the concentration of disilane was 75% or more, the concentration could be further increased to 0.1 to 0.6A.

FIG. 3 shows a case where the device of FIG.
The silicon semiconductor layer of No. 5 was subjected to the PPCVD method (optical output 1.0K
The discharge output is 15 W and the discharge output is (42 mw / cm ² ) is 15 W.

Further, a silicon nitride insulator is used as an anti-oxidation barrier layer on this upper surface by using the same reaction apparatus shown in FIG.
Laminated to a thickness of 0A. After that, this silicon nitride was partially removed, and an ohmic contact electrode was provided as a parallel electrode in this portion, and the electrical conductivity characteristics were investigated.

FIG. 3 particularly shows the electrical characteristics (56), (6) of the silicon semiconductor using the purified silane of the method of the present invention.
4), (65), (66), and (68), and characteristics (57), 63), (58), (67), and (69) of the related art.

In the drawing, the area (5
9) shows dark electric conductivity (57), and is -10 ^-7 (Ωcm)
^It has a value on the order of ^-1 . AM1 (100
When irradiated with mW / cm ² in the area (60), it is 1 × 10 ⁻⁴ (Ωcm) in the conventional method as shown by the curve (58).
^{The value} was ^-1 and the value was degraded by about one digit after continuous irradiation for 2 hours.

On the other hand, the semiconductor film produced by the PPCVD method of the present invention has a dark conductivity (56) of 5 × 10 5.
¹¹ (Ωcm) ^-1 and its photoconductivity (64) is 2 × 1
It has an order of 0 ^-4 (Ωcm) ^-1 and a photosensitivity of 10 ^7, which is about two orders of magnitude larger than the conventional example, and when irradiated with continuous light, it is almost as shown in the curve (65). No deterioration of the electric conductivity was observed.

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

When heating at 150 ° C. is further performed, the curve (67) becomes (69) in the conventional example, and there is an apparent change in characteristics. After that, when light is irradiated again in the region (62),
The deterioration characteristic was seen again.

That is, in the conventional example, the electric conductivity is small as shown by (67), and deterioration characteristics are observed by light irradiation.

In the present invention, however, the electrical conductivity is hardly changed or deteriorated by the presence or absence of light irradiation or the thermal annealing, and the photoconductivity and photosensitivity (photoconductivity and dark conduction are The difference was large and the dark conductivity was small.

Similar high reliability characteristics were obtained even with a semiconductor film formed by Photo CVD.

As described above, it has been found that the method of the present invention has a synergistic effect that a highly reliable silicon semiconductor layer can be provided.

The Photo CVD apparatus of the present invention has substantially no spatter (damage) effect and enables mass production. As a result, the PN or PIN junction can be applied to a photoelectric conversion device, an optical sensor, an electrostatic copying machine, an insulating gate type field effect semiconductor, and an integrated circuit device, which is considered to be extremely effective industrially.

[Embodiment 2] This embodiment shows a case where a silicon nitride insulator is produced.

The device was made using FIG.

185 nm, 2 as a light source for photochemical reaction
UV light at 54 nm was used.

In FIG. 2, NH ₃ / SiH ₄ > from purified silane (26) and ammonia (25).
Supplied as 50.

As a result, in the photo CVD method,
An insulating silicon nitride film of 0.1 A / sec could be produced. Further, the PPCVD method was used to obtain a film growth rate of 3 A / sec at a substrate temperature of 30 with the same electric energy output as in Example 1.
It could be obtained at 0 ° C. and a pressure of 1 torr.

1000 A on a silicon single crystal semiconductor substrate
As a result of forming a film having a thickness of 1 and examining the C-V characteristic, it was possible to obtain an interface charge density of 1 × 10 ¹¹ cm ⁻³ or less. Even if an electric field strength of 2 × 10 ⁶ V / cm is applied, C
No hysteresis phenomenon was found in the −V characteristic, and it was found that the semiconductor surface was scarcely sputtered (damaged).

[Embodiment 3] This embodiment is an example of forming a silicon oxide film by the apparatus of the present invention. The apparatus is the same as in Example 2.

N instead of ammonia as the reactive gas
_It was introduced from (25) using ₂ O. Add silane (2
From 6), it was introduced as N ₂ O / SiH ₄ > 20. The results obtained were similar to those of Example 2. 1 x 10 ⁷
It had a dielectric strength of V / cm.

[0085]

As is clear from the above description, by using the reactive gas which has been liquefied and purified at least once, the impurities in the formed film can be made extremely low. Further, in the present invention, the reactive gas is caused to flow downward from above, and the substrates are vertically (vertically) spaced (3 to 10 cm, for example, 5 cm) so that flakes do not adhere to the formation surface of the substrate.
The features are that the reactive gas is photoexcited during flight by irradiating light parallel to the surface of this substrate so that one substrate does not become a shadow of the other substrate by opening the As a result, as shown in the embodiments of the present invention, 20 substrates of 20 cm × 60 cm or 100 substrates can be inserted similarly to the silicon substrate of 5 inch size, and the maximum size of the conventional method is 5 inch wafers. We believe that it will be possible to produce as many as 20 times as many as five sheets, and the industrial effect will be extremely large.

[Brief description of drawings]

FIG. 1 shows an outline of a conventional photo CVD apparatus.

FIG. 2 shows an outline of a photo CVD apparatus using the method of the present invention.

FIG. 3 shows electric conductivity characteristics obtained by the method of the present invention and a conventional example.

[Explanation of symbols]

 1 Substrate 2 Reaction Container 7 Heater 9 Lamp 10 Reaction System 17 Mechanical Guoster Pump 18 Rotary Pump 19 Turbo Pump

Claims (2)

[Claims] 1. When adding at least one of light energy, heat energy and electric energy to a reactive gas to form a film, the reactive gas that has been liquefied and purified at least once is subjected to the film formation to form carbon and oxygen during the film formation. High-quality film forming method with extremely low concentration. 2. When a silicon film is formed by adding at least one of light energy, heat energy and electric energy to a reactive gas, the reactive gas that has been liquefied and purified at least once is subjected to film formation to remove carbon and oxygen. Concentration is 1 × 1
A method for manufacturing an IGFET having an intrinsic or substantially intrinsic silicon film of 0 ¹⁸ cm ^-3 or less.