JPH0797561B2 - Vapor phase impurity diffusion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a doping (impurity diffusion) process in a gas for manufacturing a semiconductor wafer, a semiconductor device or an intermediate product thereof.

[Prior Art] Recent technological development competition in the electronics field has remarkably advanced and has made rapid progress. Among them, one of the cores of the technology is a semiconductor wafer and a semiconductor device. In these manufacturing processes and in the manufacturing process of these materials, high purity nitrogen, hydrogen, argon,
Balance gas such as nitric oxide, epitaxial gas such as silicon or gallium arsenide used to form a thin film of micron unit on a semiconductor wafer, etching to remove silicon or resist film to form a fine circuit Gas, a doping gas that adds a trace amount of impurities to semiconductor wafers such as silicon and gallium arsenide, and PVD (physical deposition method) as well as CVD (chemical deposition method-pyrolysis method, hydrogen reduction method, sealed tube method, etc.) Deposition method-vacuum evaporation method, sputtering method, ion plating method, etc.) or plasma CV
D, plasma PVD, MOCVD (organic metal CVD) gas, etc.

On the other hand, in the present semiconductor device manufacturing process, high integration (ultra-miniaturization) is rapidly progressing. Therefore, also for the above-mentioned various gases for manufacturing the semiconductor wafer and the semiconductor device, a gas having high purity and no floating dust has come to be required.

With the corrosive doping gas currently on the market, products containing more water can be found with a water content of around 10 ppm.However, due to the water contained in this gas, the quality during the production of semiconductor wafers or semiconductor devices is high. May decrease or the yield may decrease.

At present, an adsorption method using a molecular sieve is partially used for drying gas in the manufacturing process of these semiconductor wafers and semiconductor devices. The molecular sieve is relatively easy to dry general gas, and is widely used as a physical desiccant which does not cause troubles such as deliquescent and swelling.

However, the drawback is that it is 200-400 in the general heating regeneration.
High temperature of ℃ is required for a long time, and floating dust is generated by repeated use for heating and regeneration. Further, the acidic gas such as hydrogen chloride gas causes the molecular sieve to be crushed, which causes suspended dust.

Also, it has nothing to do with dehumidification of these semiconductor-related gases,
Generally, a method of using a polymer thin film as a method of dehumidifying gas is known in JP-A-53-97246 and JP-A-54-152679, but there is no description that these methods are used for dehumidifying gas for semiconductor manufacturing. Not at all.

Further, the films disclosed therein cannot be dehumidified to a high degree of dryness required for a semiconductor-related doping gas.

[Problems to be Solved by the Invention] The disposable molecular sieve adsorption method has a high running cost and may generate dust. In the absence of a desiccant, the quality of the gas that comes out of the gas cylinder may change over time, making it difficult to control the process and eventually adversely affecting the quality of the product semiconductor wafer, semiconductor device and intermediate products. Is. Furthermore, in the conventional manufacturing process without a desiccant, not only the quality and yield, but even if a small amount of water is mixed in the gas, metallic pipes and metallic gas flow rate regulators that guide the gas from the gas cylinder to the reactor. Cause corrosion, and if replaced every six months to at least every two years, become a source of heavy metal and dust scattering due to metal corrosion. At the same time, this cost is also a major factor in cost increase.

Therefore, the method of obtaining a highly dry doping gas which is low in running cost, does not generate dust and impurities, and has a strong need to be developed in the semiconductor market has been a strong technique.

[Means and Actions for Solving Problems] According to the present invention, when a semiconductor wafer, a semiconductor device, or an intermediate product thereof is manufactured by using a doping gas, 70
Dehumidification by contacting a doping gas with one side of a fluoropolymer film having a cation-exchange group heat-treated at ~ 250 ° C and contacting a dry purge gas with the other side or depressurizing the other side. A vapor phase impurity diffusion method is proposed, which is characterized in that impurities are diffused on a semiconductor wafer using the doping gas.

The doping gas that is the gas to be dried of the present invention means B ₂ H ₆ , A
_S H ₃ , PH ₃ , BCl ₃ , SiH ₄ , GeH ₄ , H ₂ Se, PCl ₃ , PF ₂ , A _S Cl ₃ , H ₂ S, SiF
₄ , SF ₆ , POCl ₃ , BF ₃ , BBr ₃ , SeH ₂ , SbH ₃ , A _S F ₃ , (CH ₃ ) ₂ Te, (C
₂ H ₅ ) ₂ Te, (CH ₃ ) ₂ Cd, (C ₂ H ₅ ) ₂ Cd gas or the like, or a mixed gas thereof or the like, but among these, diborane gas, arsine gas, phosphine gas, boron trichloride gas, Alternatively, a mixed gas of these is commonly used. Further, N ₂ gas used before and after the use of these gases, a replacement gas such as He gas, and H ₂ used as a carrier gas.
Gases and the like are also included in the doping gas of the present invention.

The gas to be dried in the method of the present invention is usually a gas filled in a cylinder generally obtained on the market,
The water content is not so high. The gas filled in the cylinder is usually about several tens of ppm, but in some cases, it is 100 ppm or more.

It is possible to obtain the target dehumidification level by changing the membrane area of the water separator or making it in multiple stages according to the concentration of the target gas.

The fluorinated copolymer having a cation exchange group used in the present invention is preferably one having a cation exchange group such as a sulfonic acid group, a carboxylic acid group or a phosphoric acid group. The use of a fluorinated copolymer having a sulfonic acid group is the best in terms of easiness of production, high water content of the membrane, and thermal stability.

There are various structures of the fluorine-based copolymer having a sulfonic acid group, and among them, the general formula (In the formula, _m = 0 or 1, _n = integer of 2 to 5) A fluorine-based copolymer containing a repeating unit is preferable.

Examples of the above-mentioned fluorine-based copolymer include fluorinated olefins such as tetrafluoroethylene, trifluoroethylene, perfluorovinyl ether, vinylidene fluoride, vinyl fluoride and the general formula (II) Those obtained by copolymerizing the perfluorovinyl ether monomer represented by

The sulfonic acid group of the fluorine-based copolymer is preferably introduced as an ion exchange capacity in an amount of 0.5 to 2.5 meq / g H-type dry resin in the copolymer.
By setting the ion exchange capacity of the fluorine-based copolymer within the range of 0.5 to 2.5 meq / g H-type dry resin, the permeation rate of water vapor is not significantly reduced, and the melting point of the copolymer is high. The polymer thin film can be easily manufactured, and the physical strength of the polymer thin film can be maintained without lowering the physical strength. More preferably, the ion exchange capacity is 0.8 to 1.8 meq / g H-type dry resin.

Metal salts as salt of a sulfonic acid group of the fluorine-based copolymer used in the present invention, it is possible to use the ammonia salt form, SO ₃ H type most permeation rate of the water content is high water vapor is large, It has sufficient thermal stability and is preferable.

The shape of the fluorine-based copolymer may be any of a flat membrane, a tubular shape and a hollow fiber membrane, but a hollow fiber membrane having a large membrane area per unit volume and a high treatment capacity is particularly preferable. For example, the airtightness of the device is important for achieving a high degree of dryness with a water content of 10 ppm or less, and particularly a water content of 5 ppm or less, and the hollow fiber membrane is preferable also from that point.

The film of the fluorinated copolymer having a cation exchange group heat-treated at 70 to 250 ° C. used in the present invention,
It is preferable that the fluorine-containing copolymer film containing the repeating unit represented by the general formula (I) is pretreated by heating. The heating pretreatment of this membrane is a fluorine-based copolymer obtained by copolymerizing a monomer represented by the general formula (II) and a fluorinated olefin into a thin film, which is then hydrolyzed with alkali and treated with a strong acid. Thus, after converting the end group SO ₂ F to SO ₃ H,
Heat treatment of the polymer.

The heat treatment can be carried out, if necessary, while purging a trigas, for example, nitrogen gas having a water content of 5 ppm or less, or under reduced pressure. The heat treatment temperature is 70 to 250 ° C.
If the temperature is too high, the ion-exchange group may be eliminated and the performance may be deteriorated. The heat treatment temperature is particularly preferably 70 to 200 ° C.

The heat treatment causes the copolymer to shrink by several tens of percent, and the water absorption rate is also reduced.

A film obtained by heat-treating a film of a fluorocopolymer containing a repeating unit represented by the general formula (I) has a relationship between the water absorption rate W and the ion exchange capacity Q of the formula (III). It has excellent properties, and particularly exhibits excellent performance in highly drying gas.

The heat-treated film having the relationship of the formula (III) enables a high degree of dehumidification with a water content of 1 ppm or less at room temperature. Therefore, it is naturally possible to dehumidify the moisture content to any value such as 10 ppm or less and 5 ppm or less by setting the conditions as necessary. In actual vapor phase impurity diffusion, 10 ppm or less may be sufficient, 5 ppm or less, and further 3 ppm or less or 1 ppm
The present invention is applicable to any of these cases, although it may be useless unless the following.

In the case of a flat membrane among the above-mentioned heat-treated membranes, it can be easily determined by measuring the water absorption whether or not it is produced by the heat treatment.

However, if the membrane is a thin hollow fiber, the water absorption rate is difficult to measure, so that the determination can be made by measuring the heat shrinkage start temperature described below.

Attach a light weight (sufficient to straighten the thread but not enough to stretch it) to the hollow fiber membrane and hang it in the air tank. In that state, the temperature of the air tank is gradually raised, and the change in the yarn length is read and measured with a telescope. An example of the measurement results is shown in FIG. 5 when the temperature is plotted on the horizontal axis and the length is plotted on the vertical axis. L ₂₅ is a length of 25 ° C. and L _t is a length at a temperature of t ° C. In FIG. 5, the temperature indicated by the arrow, that is, the maximum temperature at which there is no dimensional change due to temperature rise is defined as the "maximum temperature at which there is no heat shrinkage." Several hollow fibers having different heat treatment temperatures (t) were prepared, the "maximum temperature (T) without heat shrinkage" was measured, and the results were plotted on a graph, as shown in FIG. That is, T = t (1), and the heat treatment temperature (t) of the hollow fiber membrane can be known by measuring the maximum temperature (T) without heat shrinkage.

The gas to be dried may be supplied to either side of the thin film of the fluorocopolymer. By depressing the membrane and flowing a dry purge gas with a low moisture content to the moisture permeation side, or by reducing the pressure with a vacuum pump, etc., a partial pressure difference, which is the driving force for membrane permeation, is generated, and the purpose of dehumidification can be achieved. .

The film used in the present invention is preferably a thin film having a thickness of several to several hundreds of microns. Regarding the film thickness, the thinner the film, the higher the water vapor permeability and the better the performance, which is preferable, but it is limited by the formability and pressure resistance.

In the case of a hollow fiber membrane, the inner diameter is 400 to 5 depending on the diameter of the hollow fiber.
The film thickness of 00 μm is preferably 40 to 60 μm.

The dry purge gas having a low water content is a gas supplied to dehumidify the water contained in the doping gas by dehumidifying the film, and is preferably an inert gas that is difficult to react even if the temperature rises. . The reduced pressure means a pressure lower than the atmospheric pressure, although it depends on the pressure of the supplied source gas.

Note that the semiconductor device in the present invention also includes a solar cell. A solar cell is a silicon wafer doped with n-type impurities such as P (phosphorus) and A _S (arsenic). A p-type impurity is added to an n-doped wafer B.
Doping of surface layer of (boron) etc. Vapor deposition of metal such as Au, Ni, Sn etc. on p-type region, heat alloying It is manufactured through processes such as vapor deposition of antireflection film such as SiO provided on the light receiving surface. The present invention is applied to the above doping process.

[Examples] The present invention will be described in more detail with reference to production examples, reference examples and examples, but the present invention is not limited to the examples.

In addition, the measurement of the water content of gas in the production examples, reference examples, examples and comparative examples was performed by a dew point meter or a moisture meter, and depending on the gas, the Karl Fischer method.

Production example With tetrafluoroethylene And ion-exchange capacity of 0.94 meq / g H
A mold dry resin was obtained. The resin obtained is molded at a molding temperature of 250 ° C.
A film having a thickness of μm was prepared, and after hydrolyzing this film with an alkaline alcohol solution, ion exchange was performed with a hydrochloric acid aqueous solution to make the end of the side chain a sulfonic acid type (H type) and air-dried. The obtained film was subjected to dry temperature treatment in vacuum, and the equilibrium water absorption was determined at 25 ° C (Fig. 1).

As shown in Fig. 1, the water absorption rate decreased significantly when the dry heat treatment temperature was about 70 ° C or higher. At higher temperatures, the water absorption was almost constant.

Similarly, the monomer species were changed as shown in Table-A to prepare a polymer film having an ion exchange capacity of 0.8 to 1.1 meq / g, and a polymer film having the water absorption rate shown in Table-A was prepared. Table-A
From the results, the relation between the ion exchange capacity and the water absorption rate of the membrane of the present invention is shown by the shaded area in FIG.

Reference example with tetrafluoroethylene Was copolymerized to obtain an H type dry resin having an ion exchange capacity of 0.9 meq / g. The obtained resin was melt-spun at a spinning temperature of 250 ° C. and a spinning speed of 88 mm using a molding machine equipped with a hollow fiber manufacturing die to obtain a hollow fiber membrane having an inner diameter of 500 μm and a film thickness of 60 μm.

After hydrolyzing this hollow fiber with an alkaline alcohol solution, ion exchange was carried out with an aqueous solution of hydrochloric acid, and the side chain was made to have a sulfonic acid type (H type) at the terminal and air dried. 40 cm length of the obtained thread
400 pieces of the dried product were bundled and fixed to the separator made of SUS with epoxy resin at both ends to make a water separator as shown in FIG.
N ₂ gas adjusted to have a water content of 1 ppm (dew point −76 ° C.) or less was pressurized to 5 kg / cm ² G in the water separator, and was hollow at a flow rate of 0.5 / min (flow rate converted to atmospheric pressure; the same applies below). I shed it inside the thread.

Similarly, N ₂ gas adjusted to have a water content rate of 1 ppm (dew point −76 ° C.) or less was flowed at 0.75 / min. This was placed in a constant temperature bath at 70 ° C. and heat-treated for 3 hours, then the water separator was returned to room temperature, and the water content was 31 ppm (dew point −52 ° C.) and the pressure was adjusted to 5 kg / cm ² G N ₂ gas (sample gas ) Is flowed inside the hollow fiber at a rate of 0.5 ppm and a water content of 1 ppm (dew point −
N ₂ gas adjusted to 76 ° C.) or less was flowed at 0.75 / min. When the dew point of the sample gas at the outlet of the water separator was measured, the water content was 1 ppm (dew point −76 ° C.) or less. The continuous operation was continued as it was, and the water content of the sample gas outlet remained 1 ppm (dew point −76 ° C.) or less even after 24 hours.

On the other hand, with respect to the purge gas on the outside of the hollow fiber, the moisture content at the moisture separator outlet dew point was measured for 24 hours, and the moisture content was 4.6 ppm.
It was (dew point -66 ° C). After that, the outlet water content of the sample gas after the continuous operation for about 1000 hours under the same conditions remains 1 ppm (dew point −76 ° C.) or less, and the amount of water reduced by the water separator of the sampling gas and the water separator of the purge gas. The ratio of the amount of water increased in 1.2 was 1.2: 1, which was in agreement within the measurement error.

As for the other films of the present invention, the same results as in the reference example were obtained as shown in Table-A.

Comparative Reference Example When the sample gas and the purge gas were measured under the same conditions as in Example 2 without the heating pretreatment in the same apparatus as the reference example, the moisture content of the sample gas was 10.6 ppm after 44 hours.
It did not reach the (dew point -60 ° C).

Examples 1, 2 and 3 sample gas using the same moisture separator as the reference example, the same conditions for the pressure of the purge gas, the type of sample gas, the moisture content was changed, and the same as the reference example using the decompression method. The water content after treatment was measured with a water separator and the results shown in Table 1 above were obtained. Further, when a semiconductor wafer, a semiconductor device and intermediate products thereof were manufactured by using these gases having a low water content and a doping reaction apparatus as shown in FIG. 4, an improvement of about 5% was realized.

[Effects of the Invention] The effects of the present invention can be summarized as follows.

If there is water in the gas, it decomposes into O ₂ and H _2.
Unexpected generation of oxidative impurities due to O ₂ is prevented.

If moisture in the gas becomes decomposed O ₂ and H _2, the inner O ₂ because strong affinity for carbon, O ₂ and carbon it is often present at the same time, causing deposit formation . This is effective in eliminating this cause.

If water enters during the doping process, it may cause stacking faults, which serve as deposition sites for oxygen atoms, and impurities also attach to these sites. It can serve to prevent this stacking fault.

As the gas exits the gas cylinder, the gas pressure in the cylinder will drop as it is used. This decrease in gas pressure in the cylinder also affects the quality of the gas, and the amount of water that was initially contained in the gas also increases dramatically. However, when the membrane device is used, the moisture content of all the gas supplied is extremely small and constant, and a gas of stable quality can be obtained.

For example, by removing the water content of corrosive gas such as BCl ₃ , the corrosion of the piping through which the corrosive gas passes can be prevented, so that fine heavy metals and dust that cause a decrease in the yield of semiconductor wafers and semiconductor devices can be prevented. And the like are prevented from occurring. At the same time, preventing corrosion of pipes and gas flow rate regulators will extend the life of these incidental devices and contribute to a significant cost reduction.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the dry heat treatment temperature and the equilibrium water absorption of the polymer semipermeable membrane obtained in the production example, and FIG. 2 is the production example.
Ion exchange capacity 0.8 ~ produced by dry heat treatment at 70 ℃ or higher
A graph showing the relationship between the polymer water absorption rate (W) and the ion exchange capacity (Q) of the polymer semipermeable membrane of 1.1, Fig. 3 is a conceptual diagram of a water separator used for carrying out the method of the present invention, FIG. 4 is a conceptual diagram showing the position where the water separator is used in the doping reaction device, and FIG. 5 is a graph for obtaining the maximum temperature without heat shrinkage of the hollow fiber membrane, where the horizontal axis is the temperature,
The vertical axis represents the length (L _t ) of the hollow fiber membrane at t ° C and the temperature of 250.
Ratio with length (L ₂₅ ) in ° C. FIG. 6 is a graph showing the relationship between the heat treatment degree (t) of the hollow fiber membrane and the maximum temperature at which heat shrinkage does not occur, and the heat treatment temperature can be determined from this graph. 1 ... Hollow fiber membrane, 2 ... Sample gas inlet, 3 ... Sample gas outlet, 4 ... Purge gas inlet (closed when decompressing), 5 ... Purge gas outlet (decompressing when decompressing), 6 ... … Cell, 7 …… Separator, 8 …… Moisture separator, 9 …… Doping reactor, 10 …… Various cylinders, 11 …… Cock (valve).

Claims (1)

[Claims] 1. A semiconductor wafer using a doping gas,
When manufacturing semiconductor devices or their intermediate products,
Dehumidification by contacting the doping gas with one side of the film of the fluorinated copolymer having cation exchange groups heat-treated at 250 ° C and the dry purge gas with the other side or depressurizing the other side. A method for diffusing impurities on a semiconductor wafer using the doping gas as described above.