JP2654466B2 - Reactive gas filling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the filling of reactive gases.

[0002]

2. Description of the Related Art Heretofore, a reactive gas for semiconductors has been filled in an iron cylinder, which has been simply manufactured by a semiconductor device manufacturer and a laboratory by a plasma gas phase process (PCVD) system. Equipment (LP CVD equipment) or epitaxial growth equipment. However, such a reactive gas for semiconductors, typically silane, is chemically produced at the time of producing the raw material, but has a purity of 6N to 7N and an impurity of 1 PPM or less. This is apparent from the fact that the oxygen concentration in the FZ single crystal silicon using the raw material silane is 1 to 9 × 10 ¹⁶ cm ⁻³ or less.

However, when such raw materials are transferred to a transfer tank and further subdivided into 3.4 liter, 10 liter or 47 liter general high-pressure cylinders made of iron, their management is inadequate. Oxygen impurities, especially including oxides, were mixed in as much as 0.1 to 0.01% due to the mixing and the formation of ultrafine silicon oxide powder by air leakage. For this reason, the patent application “Semi-amorphous semiconductor” filed by the present inventor (55-26388 S55.3.3 filed) or a “semiconductor device for photovoltaic generation” having a PN or PIN junction using microcrystals (49-71738) S49.6.22 application), that is, when producing a hydrogenated non-single-crystal semiconductor including an amorphous semiconductor by the PCVD method, the oxygen or carbon is converted into a silicon semiconductor as a silicon oxide insulator or a silicon carbide insulator. Incorporation into the semiconductor deteriorates the characteristics as a semiconductor.

In particular, when this mixed oxygen is mixed into a hydrogenated non-single-crystal semiconductor, if it forms 5 to 50 oxygen clusters, it acts as a recombination center and further has an unpaired bond. In this case, the semiconductor is made into an N-type donor.
It acts as a center, and when coupled, acts as a local insulating current barrier, deteriorating the characteristics of the semiconductor in all aspects.

[0005] In addition, such oxygen is used in the production of a non-single-crystal semiconductor using a glow discharge method utilizing a high frequency discharge of 13.56 MHz at a low temperature of 200 to 300 ° C.
It has been found that the material inhibits ordering in the short-range order of about 200 ° and hinders microcrystallinity.

[0006]

The liquefaction / vaporization step of the reactive gas for semiconductors having a purity of 98% or more of the present invention, typically silane or germane, is carried out at least once to further reduce residual oxygen, By filling a stainless steel container whose water and hydrocarbons are kept at 0.1 PPM or less in a mirror-finished inner surface, a highly purified reactive gas from which high-purity oxygen and carbon impurities have been sufficiently removed is supplied to the container. It is intended to be filled.

[0007] The present invention provides a heavy metal remaining in a reactive gas,
The concentration of oxygen or carbon remaining in the reactive gas after purification by removing water, oxide impurities, particularly ultrafine silicon oxide powder, is preferably 3 × 10 ¹⁷ cm ⁻³ or less, more preferably 1 × 10 ¹⁷
It is intended to make it possible to make it ^{15 to} 3 × 10 ¹⁶ cm ⁻³ .

When these are removed and a silicon thin film as an original semiconductor is to be formed by the PCVD method, it has been found that the purification of silane, which is the starting characteristic of the present invention, is extremely important.

[0009]

According to the present invention, there is provided a semiconductor device having a remarkably low temperature (from room temperature to 40.degree.
The present invention relates to a purification method for producing high-purity silane for forming a semiconductor film at 0 ° C (typically 200 to 300 ° C).

The details will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a purification method using a reactive gas for semiconductors, particularly silane, of the present invention. This can be produced in the same manner as described below in the case of producing germane or diborane or phosphor diluted with hydrogen or the like instead of silane.

[0011] In the drawing, silane cylinder (1) first vessel (2) for liquefaction and vaporization, second vessel (3), third final vessel (4), removal of residual water in purge hydrogen (14) Container (5) Dewar containing liquid nitrogen (6) (7) (8) Degassing heaters (9) (10) (36) for heating the container These temperature controllers (11) ( 12) It has (37). The block diagram in FIG. 1 shows a case of two-stage purification, and the same applies to one-stage or multi-stage purification.

In the drawings, the first, second, and third vessels and the cleaning of a piping system connected to them are abbreviated.

The steps will be described below with reference to the block diagram of FIG.

Purification of Purification Equipment 1. All valves (hereinafter abbreviated as V) must be closed. Installation of silane cylinder. 2. Heater (9) at controller (11) (12) (37)
(10) Heat (36) to 200-350 ° C. 3. Open V (38) from N (13) and exhaust (18) from mixer (17) from flow meter (39). 4. Oil-free exhaust system (16) ON, V (28) V (4
4) V (25) V (24) V (21) V (46) open, container (4)
(3) (2) (5) is evacuated. About 1-5 hours. 5. After purifying hydrogen at V (29) in the container (5) (77 ° K), introduce hydrogen to remove impurities such as water in the container (4). About 1
3 hours. 6. Close V (25), fill containers (2) and (3) with hydrogen and reach 1 atm or more, then open V (22) and heat remove adsorbate in containers (2) and (3). About 1-5 hours. 7. V (22) closed, V (46) closed, V (25) open, container (2)
(3) (4) is evacuated. 8. Replace heaters (9), (10) and (36) with controllers (11) and (1).
2) Turn off at (37).

Further, the adsorbed material having the width of the containers (2), (3) and (4) in the apparatus (40) constituting the refining section was removed as described above. In particular, a container made of stainless steel and having a mirror-finished inner surface with sufficient flatness has a pressure of 150 kg.
/ Cm ² so that the residual fine powder does not stick to the concave portion of the inner wall and cannot be removed.

Further, in order to remove adsorbed oxygen and water in the containers (2), (3) and (4), when the inside of the container heated to 200 to 350 ° C. is evacuated from the outside, hydrocarbons, especially Oil vapor was prevented from flowing back.

That is, in the present invention, since the inside of the cylinder vessel is conventionally evacuated to 10 ^-2 to 10 ^-3 torr by simply using a rotary pump, 0.1% of hydrocarbon is used in the autoclave.
In order to ascertain the fact that the oil has been mixed into the oil, to remove such impurities, a continuous exhaust type turbo pump is used to evacuate to 9 × 10 ^-5 to 10 ^-8 torr, and to back up the oil component. 9 × diffusion (despreading)
10 ^-6 torr or less, preferably 10 ^-7 to 10 ^-9 torr.

Thus, in the containers (2), (3), and (4), water, carbon dioxide, and residual hydrocarbons are stored at 0.1 PPM, preferably 0.1 PPM.
Vacuum was exhausted sufficiently until it became 1-10PPB.

Next, the container (2) was cooled to -150 ° C., and the reactive gas for silane semiconductor was transferred from the cylinder (1).
Further, liquid─vaporization and purification were performed once again from the container (2) and transferred to the second stage container from the container (4). At this time, the vaporization temperature was -100 to -90 ° C, and after a long time of 5 to 50 hours, the silane purified by the liquefaction and vaporization purification was filled in a container (4). The silane liquefaction-vaporization process is described below.

Liquefaction and vaporization and purification of silane gas 1. Confirm that the containers (2), (3) and (4) are evacuated by a compound meter (30) (31) (32). 2. Exhaust system on, V (28) V (44) V (25) V (24) V
(24) V (23) open, V (26) V (27) V (46) V (22)
Confirmation of closing. 3. Fill the dewar (6) of the container (2) with liquid nitrogen. -150 ±
10 ° C. 4. Opening the cock of the silane cylinder (1), opening the V (21), liquefying the silane in the cylinder in the container (2) while supplying liquid nitrogen so as not to overflow while watching the flow meter (41) The pressure gauge (30) is set to 0.5 to 5 atm. 5. After transferring silane from silane cylinder (1), V
(21) Close the cock of the cylinder (1). 6. Close the V (24), fill the dewar (7) with liquid nitrogen, and keep the container (3) at -150 ± 10 ° C. 7. Open V (24), transfer the liquefied silane in the container (2) to the container (3) over time, and perform liquefied vaporization purification. (5 to 50 hours) The flow meter (43) is 10 to 500 cc / min, typically 100 cc / min.
Minutes. The combined gauge is 0.5 to 3 atmospheres, and the container (2) is
It is controlled by a controller at -90 to -100 ° C. 8. When transfer is complete, close V (23), V (27), V (46), V
Confirm that (44) is closed. 9. V (24) V (25) open, Duer (7) at -50 to -70 ° C
Liquefied silane is transferred to the container (4), and the same precautions as in item 7. 10. After filling container 4 (corresponding to the end cylinder) to 12 to 5 atm, purification is completed by closing V (25).

In this purification step, the silane oxide in the cylinder (1) is in the form of fine powder of silicon oxide, so that liquefaction and vaporization alone is not sufficient. Therefore, in order to remove such fine powder, a sintered stainless steel filter is used.
(34) and (35) were provided in two stages in each of the containers (2) and (3), immersed in liquefied silane, and adsorbing and removing the fine powder on the filter. By doing so, the purified silane can have an oxygen concentration of 0.01 PPM (10 ¹⁴ -10 ¹⁵ cm ^-3 ), which is equal to the detection limit of SIMS or activation analyzer, and the carbon content is less than 1 PPM. You can now.

Conventionally, the silane as a starting material is merely a mixture of an oxygen component having a concentration of 10 ¹⁶ to 10 ¹⁷ cm ⁻³ , but when the silane is refilled, the container has irregularities on the inner wall. Since it often looks like the “inner wall of the human intestine”, its impurities are not sufficiently removed. Further, since the evacuation prior to filling was merely performed by a rotary pump, the residual oxygen and carbon components in the container were reduced to 0.1-5 torr by heating the container as in the present invention to 10 ^-5 torr or less. Being below PPM is a huge advance.

In addition, the oxygen concentration can be further reduced to 1/100 or less of 0.01 PPM by subjecting the subsequent silane, which had only been chemically purified, to physical purification.

Finally, the exhaustion of silane remaining in the containers (2) and (3) containing impurities after purification by the purification method of the present invention shown in FIG. 1 will be briefly described below.

Evacuation of residual silane gas impurities 1. Confirm that all valves are closed. 2. N ₂ 13) is opened to V (38) and exhausted from the flow meter (39) via the mixer (17) (18). 3. Convert H ₂ (14) to V (29), V (46), V (24), V (23)
Fill containers (2) and (3) when opened. 4. V (22) is opened, and the flow meter (49) is gradually flown to the mixer (17) from about 5 cc / min so that (H ₂ + SiH ₄ ) / N ₂ > 100.
1-3 hours. 5. Wait until the flow rate difference between the flowmeters (49) and (45) disappears. 6. Heat the heaters (9) and (10) to 100-150 ° C,
Evacuation of impurities in the flow vessels (2) and (3) at a flow rate of 5 to 2 liters / minute 1 to 5 hours. 7. Close the V (22) V (23) V (24) V (46) V (29) and keep the combined gauge (30) (31) in hydrogen at 0.5-3.0 atm.

As described above, the reactive gas purification method and the reactive gas for ultrahigh-purity semiconductors can be filled in the high-pressure vessel.

Using such high-purity silane gas, gross
0.1 torr, 250 ℃, by plasma CVD method using discharge method
A non-single-crystal silicon semiconductor was formed under the conditions using RF output (13.56 MHz), 10 W, and 100% silane.

In the drawing, a curve (53) is prepared by using a conventionally known silane cylinder, and a curve (54) is a stainless steel inner surface finish of the present invention without performing the liquid / gas purification of the present invention. 9 × 10
^-5 torr, preferably 10 ^-5 torr or less. That is, the inner wall of the container was mirror-finished, and a high-pressure and heat-resistant container made of stainless steel was used. In addition, when filling with silane, the container should be kept at 100 ° C. or higher, preferably 250 to
It was heated to 300 ° C and the adsorbate was sufficiently evacuated.
Thus, the oxygen itself and the like mixed therein could be reduced to 1/100 to 1/1000 by devising the container itself as in the present invention and paying sufficient attention to the filling method.

In the drawing, (55) is presumed to be that silicon oxide remaining in the container has gone outside due to almost no residual silane.

When the liquefaction / vaporization purification of the present invention was carried out in two stages, they could be further reduced to 1/10 to 1/1000. In particular, it was found that the measurement point of (57) did not increase as in the measurement point of (55), even when all of the gas remaining in the container was used, where the silicon oxide component did not increase.

When silane is used as the reactive gas for the semiconductor in the method of the present invention, the container shown in FIG.
483 gr, residual amount 10 g, residual pressure 0.5 kg / cm ² , and this silane in the container was made to have an internal volume of 1.5 liters. In container (2), 10 g, and in container (3), 10 g of residual gas and impurities. The container (4) is designed as a 10-liter cylinder and the container (2) can be filled with silane.
After cooling to -150 ± 10 ° C. in the same manner as in (3), the valve (27) was opened to the working system (15) as shown in the figure to obtain the atmospheric concentration, and then used. For this reason, the working pressure of the container (4) should be 15 to
It has a characteristic that it can be 17 kg / cm ² and can be used in exactly the same manner as a conventionally used silane cylinder.

Instead of silane, the reactive gas for the semiconductor may be germane or helium, diborane diluted with hydrogen, phosphine or arsine. These chemical properties are shown in Table 1 below.

[0033]

[Table 1]

That is, when using these reactive gases,
To achieve a 100% concentration, they can be carried out as described above, as with silane. If it is desired to dilute with hydrogen, after filling a necessary reactive gas for semiconductors, hydrogen is charged from (14) through a cold trap (5) through a valve (46) as shown in FIG. Then 50-5000
The PPM may be diluted to a predetermined concentration, for example, 500 to 1000 PPM.

When the gas for dilution is hydrogen or helium, the gas may be similarly introduced from (14).

[0036]

As is evident from the above description, the present invention is applicable to a case where the reactive gas for semiconductor is divided into cylinders so that the mixed amount of oxygen and carbon is 1 PPM or less, preferably 1 to 100 ppb. The characteristic feature is that the amount of mixed oxide gas is reduced to 1/10000 or less by eliminating the contaminating impurities and liquefying the reactive gas in this subdivision and using the vaporization purification and adsorption method together. For the first time, control by plasma CVD and LP CVD was enabled by the purified reactive gas.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a reactive gas purification method of the present invention.

FIG. 2 is a graph comparing the concentration of residual oxygen in silicon measured using a silane obtained by the method of the present invention with that of a conventional method.

Claims (1)

(57) [Claims] Before filling a purified reactive gas used for forming a layer into a high-pressure vessel, a residue such as carbon dioxide and hydrocarbons in the high-pressure vessel is heated to heat the high-pressure vessel.
A method for charging a reactive gas, wherein the reactive gas is filled after evacuating with an oil-free vacuum exhaust device while reducing the residual impurities to 0.1 ppm or less.