JP2654456B2 - Manufacturing method of high quality IGFET - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
o Chemical Vapor Depositi
on, hereinafter referred to as Photo CVD) or photo-plasma vapor phase method (Photo Plasma Chemical).
l Vapor Deposition or below 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, and the surface to be formed, which is the upper surface of the substrate, is irradiated with light from above and below. Thus, there is known a method in which a photochemical reaction is caused by performing photoexcitation by irradiating a reactive gas on the surface with light.

[0003]

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

Further, for example, when silicon is to be formed by using silane, a part of the photoexcited silicon adheres to a window for light irradiation and absorbs the irradiation light, so that the silicon becomes reactive gas. Has the disadvantage that the irradiation light intensity is reduced.

For this reason, the photo CVD method has the feature that it does not damage the substrate surface, but it has never been possible to apply it for mass production.

The present invention proposes, for the first time, a photo CVD method which can be industrially mass-produced by eliminating these disadvantages.

[0007]

SUMMARY OF THE INVENTION The fabrication of the IGFET of the present invention
In the manufacturing method , at least one of light energy, heat energy, and electric energy is added to a reactive gas to form a silicon film.
When forming a reactive gas, a reactive gas that has been liquefied and purified at least once is subjected to film formation, and evacuation is performed with a turbo molecular pump.
By doing so, the concentration of oxygen in SIMS measurement
1 × 10 ¹⁸ cm ^-3 or less intrinsic or substantially authentic
Obtain a silicon film .

[0008]

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

For this reason, in the present invention, in a semiconductor containing silicon as a main component, infrared light having a light energy smaller than the optical gap of 10.6 μ is optically excited using a carbon dioxide laser or a far infrared light source. . What
For insulators such as silicon oxide, silicon nitride, and silicon carbide, ultraviolet light (2537A, 1850A) that is light smaller than the optical band gap (hereinafter referred to as Eg) is used.
Are (A: angstrom).

[0010]

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

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

In the drawing, a substrate (1) is provided in a reaction vessel (2), and a substrate (1) is provided from below by a heater (53).
It is heated to 00 to 400 ° C. In addition, ultraviolet light (25
3 nm) is vertically irradiated (51) on the surface of the substrate (1) through the quartz plate by the low-pressure mercury lamp (9). Oil (54) is applied to the lower side of the quartz plate to reduce the adhesion of reaction products. As for the reactive gas, the silane (26) is supplied from the doping system (20) in parallel (50) to the substrate surface via the valve (28) from the flow meter (29). 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). Unnecessary reaction products and carrier gas pass through a pressure adjusting valve (13),
The air is exhausted from the vacuum pump (18).

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

However, if another substrate is provided in (1 '), the surface of (1) is not irradiated with ultraviolet light and becomes negative due to (1'). Therefore, a photochemical reaction cannot be caused on the lower substrate (1).

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

However, in this method, since the light source is disposed in the atmosphere, the quartz plate (48) cannot be made large in size in order to prevent damage due to pressure or the like. Therefore, the substrate is about one 3-inch wafer, and it is theoretically impossible to even insert five 5-inch wafers simultaneously.

On the other hand, according to the present invention, as a result of a thorough study of the photo-CVD method, the photochemical reaction is performed even on a reactive gas in flight, and the formation of the film on the surface of the film is performed by thermal energy rather than irradiation light. Has been found to be possible by using.

That is, it has been found that it is not 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 A).
8 A / min).

For this reason, in the apparatus of the present invention, electric energy is simultaneously supplied in addition to light energy to promote the activation of the reactive gas and, consequently, the growth rate of the reactive gas film to about 6 to 20 A, which is about 10 times or more. / Sec.

Conventionally, in plasma CVD, the substrate surface has been sputtered (damaged) by plasma energy, and a photo CVD method has been devised to compensate for such a defect.

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

This facilitates the start of discharge,
In order to prevent instability in which this discharge is likely to stop even after having been once discharged, light irradiation is first performed so that a part of the reactive gas is excited, and then the electric energy is reacted simultaneously with the light energy. It is characterized in that the start of the discharge is facilitated and the sustain of the discharge is facilitated by adding to the neutral gas.

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

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 (PPCVD or Photo CVD) method.

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 substrate (1) having a surface to be formed is held in a quartz holder (19) in an inner volume (90 cm in width × 60 cm in height × 120 cm in depth) of the reaction vessel (2). .

This holder is 65 cm × 65 cm, has a length of 20 cm in the direction of flow of the reactive gas (50), and simultaneously holds 20 substrates of 20 cm × 60 cm (total area of the formation surface of 24000 cm ² ). Have been inserted.

Further, the surface of the substrate (1) on which the reactive gas is introduced is introduced at a certain interval (2 to 10 cm, for example, 5 cm) in a vertical (vertical) direction along the flow of introducing the reactive gas from above and discharging the reactive gas downward.
m).

Further, in the apparatus of the present invention,
The pressure of 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 as to be equal to the pressure of 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 formed. Therefore, a large space of 65 cm × 65 cm × height (20 to 60 cm) can be created as a reaction space.

The substrate is heated to, for example, 200 to 500 ° C. by the halogen heater (7). In addition, 185n
m, a lamp (9) for a chemical reaction that emits a wavelength of 253 nm or 10 to 15 μm is provided at the same time for the upper light source and the lower light source. As a result, the flow of the reactive gas (5
0), the irradiation light (51) is disposed 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), and a mechanical booster pump (1).
7), rotary pump (18), turbo pump (1
9) Unnecessary substances are discharged to the outside.

The substrate is first placed in the preliminary chamber (1
After evacuating at (23), the gate valve (45) was opened and transferred to the reaction section (44). The reactive gas is a doping system (20) in which silane is (26), and other P-type reactive gas such as diborane (B ₂ H ₆ ) or N-type gas (24) such as phosphine (PH ₃ ). 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 respectively controlled by a valve (28) through a flow system (29). .

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

That is, with respect to the silane purification system (30), the original silane is sealed in the first container (31).

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

Purification of the raw silane was performed by the following operation.

First, as a purge step, the raw silane (31)
Is closed with the cylinder valve closed, and the exhaust system and the second container are opened with valves (32), (34), (46) and (15), and valves (13), (25), (33) and (14) Is closed and the turbo pump (19) and the rotary pump (18)
0 ^-6 torr or less preferably evacuated to ¹⁰ -7 torr. Further, the second container (40) is heated with the heater (3).
In 9), the mixture is heated to 150 to 250 ° C. and purged by deaeration.

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

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

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

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

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 prepare a liquefied silane.

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

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

Then, water, silicon fluoride and hydrogen fluoride as impurities remain therein, and only the ultra-high-purity silane is vaporized to reach (26).

The second container is kept 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 raw silane. Water and silicon fluoride in the silane may be similarly removed by this trap.

The reactive gas of the semiconductor made of silane reaches the reaction system (10) through the flow meter (29). These reactive gases are exhausted to a rotary pump (18) via a turbon pump (19). 100-500 ° C., preferably 250-350 ° C. in the reactor in this reaction system,
Typically, a substrate having a surface to be formed maintained at 300 ° C. is provided, and the pressure in the reaction region (44) is set to 0.1 to 1
0 torr, for example, 2 torr, and the silane flow rate is 1 to
500 cc / min, for example, 50 cc / min was supplied. A lamp that emits long-wavelength light of infrared light of 10.6 μm or more (length: 680 nm, 15 mm, maximum output: 45)
0w). This was effective even with a carbon dioxide laser. Independent of this light energy, the electrical energy is then converted to a high frequency oscillator (frequency 1
3.56 MHz) From (4), a pair of electrodes (5), (6)
In addition, a plasma glow discharge was performed to perform a PPCVD reaction.

The surface of the substrate is disposed parallel to the irradiation light for the photochemical reaction, and the photochemical reaction is not performed on the surface of the substrate but by a halogen lamp in flight.
The test was performed on a reactive gas heated to 350 ° C., for example, 300 ° C.

Thus, it was possible to prevent the irradiation light from being shaded by the substrate and not being irradiated to the reactive gas on the opposite side, and it was possible to carry out PhotoCVD capable of mass production. Further, in the apparatus of the present invention, the reactive gas is heated to substantially the same temperature as the substrate, and the heated reactive gas is photo-excited, so that the surface of the substrate can be sufficiently coated without being irradiated with light. Is also 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 a positive column region in the generated glow discharge, and a silicon film was formed on a surface to be formed, for example, a glass substrate by photo-plasma discharge.

The growth rate of this semiconductor film is
In the case of only CVD, it was 0.1 to 0.3 A / sec, for example, 0.2 A / sec. In PPCVD, 6
A high-speed growth of 30 to 15 A / sec, for example, 12 A / sec was obtained.

That is, in the PhotoCVD method, the substrate surface was not damaged by plasma, so that a good film quality could be obtained. However, the growth rate of the film
It has the drawback that it is extremely slow at 0.1 to 0.3 A / sec, and the light energy required for it is extremely strong.

On the other hand, in the other PPCVD in the present invention, although damage due to plasma is slightly observed, the growth rate of the film is 6 to 15 A / sec, which is lower than that of the photo CVD method.
It was possible to achieve twice as fast growth. In this PPCVD method, as a sequence of steps, thermal energy is applied to a reactive gas to irradiate light first, and a part of the reactive gas is photoexcited to be extremely easily ionized, and thereafter, electrical energy is applied. It is very important that plasma reactions occur. Thus, the plasma shock wave at the start of the discharge can be prevented, and the plasma damage on the substrate surface can 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 according to the method of the present invention can be formed on the formation surface.

Water, silicon fluoride, and other impurities trapped at a temperature of -65 ° C. or less as remaining impurities deposited in the second container are shown in FIG. In 2, the valves (33) and (25) are closed, the valves (34) and (14) are opened, and the second container is heated by the heater (39). In addition, the turbo-molecular pump (19) and the rotary pump Evacuation was performed by (18).

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

If the discharge output is 15 W, 2 × 1
0 ¹⁷ atom / cc, which is further reduced to 1/5, and by connecting silane to a doping system known in the art,
The film was manufactured by the toCVD method or the PPCVD method, and the oxygen content in the film was determined to be 3 × 10 ¹⁹ atom /
cc, which was found to be about 100 times smaller than this value.

In the apparatus of the present invention, the substrate temperature is set to 350
The crystallinity of the film formed by setting the temperature to 400 ° C. or more was further advanced.

The temperature at which this reaction product is produced is not limited to 300 ° C. in the PPCVD method, but can be 150 ° C. to 300 ° C.

In the case of the Photo CVD method, when monosilane is used as the reactive gas for the film growth rate, the use of monosilane is extremely low, and industrial improvement has been demanded.

Instead of the above-mentioned monosilane, a purified monosilane is used as the silane, and a lower-grade polysilane (for example, S
i _n H _{2n + 2)} can be obtained. In the case where a semiconductor film is formed by the above-mentioned Photo CVD method using the polysilane, particularly the silane containing disilane in at least a part (concentration of 5 to 30%), the growth rate of the film is set to 0.1.
It was 6 A / sec, which was three times higher than that of monosilane.

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

FIG. 3 shows an example in which the apparatus shown in FIG.
No. 5 silicon semiconductor layer was formed by a PPCVD method (light output 1.0K).
W, (42 mw / cm ² ) and a discharge output of 15 W).

Further, a silicon nitride insulator is formed on this upper surface as a barrier layer for preventing oxidation by using the same reactor shown in FIG.
It was laminated to a thickness of 0A. After that, the 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 examined.

FIG. 3 shows, in particular, the electrical characteristics (56) and (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 region (5
9) indicates dark electric conductivity (57) and is 10 ⁻⁷ (Ωc).
m) has a value on the order of ^-1 . AM1 here
When (100 mW / cm ² ) is irradiated in the region (60), as shown in a curve (58), 1 × 10
^-4 (Ωcm) ⁻¹ , and the value was deteriorated by about one digit after continuous irradiation for 2 hours.

On the other hand, the semiconductor film formed by the PPCVD method of the present invention has a dark conductivity (56) of 5 × 10 ^11.
(Ωcm) ⁻¹ and its photoconductivity (64) is 2 × 1
0 ^-4 has 10 ⁷ at ([Omega] ^{cm) -1} orders and photo Sensitivity tape, about 2 orders of magnitude greater than the prior art,
Further, upon irradiation with continuous light, almost no deterioration of the electric conductivity was observed as shown by a curve (65).

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

When heating is further performed at 150 ° C., the curve (67) becomes (69) in the conventional example, and there is an apparent change in the characteristics.
Degradation characteristics were again observed.

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

However, in the present invention, almost no change in the electrical conductivity was observed in the presence or absence of light irradiation and the presence or absence of thermal annealing, and the conductivity and the photosensitivity (photoconductivity and darkness) were not observed. The difference from the conductivity was large, and the dark conductivity was small.

The same high reliability characteristics were obtained 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 of providing a silicon semiconductor layer having high reliability as described above.

With the Photo CVD apparatus of the present invention,
The sputter (damage) effect was practically eliminated, and mass production became possible. As a result, the PN or PIN junction can be applied to a photoelectric conversion device, an optical sensor, an electrostatic copying machine, an insulated gate type field effect semiconductor, and an integrated circuit device, and is determined to be extremely industrially effective.

[0077]

As is apparent from the above description, the use of the reactive gas which has been liquefied and purified at least once has made it possible to extremely reduce impurities in the formed film. In the present invention, the reactive gas is caused to flow downward from above, and the substrate is vertically (vertically) spaced (3 to 10 cm, for example, 5 cm) so that flakes do not adhere to the surface on which the substrate is formed.
Opening and disposing the back sides of each other, and irradiating light parallel to the surface of this substrate to excite the reactive gas during flight so that one substrate does not become the shadow of the other substrate. As a result, as shown in the embodiment of the present invention, 20 or 20 cm × 60 cm substrates can be inserted as well as 20 or 100 inches as well as a 5-inch size silicon substrate. It is possible to produce 20 times as many as 5 sheets, and it is believed that the industrial effect is extremely large.

[Brief description of the 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 electrical conductivity characteristics obtained by the method of the present invention and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Reaction container 7 Heater 9 Lamp 10 Reaction system 17 Mechanical gooster pump 18 Rotary pump 19 Turbo pump

Claims (1)

(57) [Claims] In forming a silicon film by adding at least one of light energy, heat energy, and electric energy to a reactive gas, a reactive gas that has been liquefied and purified at least once is subjected to film formation, and is subjected to a turbo molecular pump. by evacuating the method for manufacturing a IGFET concentration of oxygen is 1 × ¹⁰ 18 ^{cm -3} or less of intrinsic or substantially intrinsic silicon film in the measurement of SIMS.