JP2834600B2 - Purified silicon and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to purified polycrystalline or single-crystal silicon (hereinafter collectively referred to simply as "silicon") and a method for purifying the same.

[0002]

2. Description of the Related Art Polycrystalline silicon is widely used as a raw material for single crystal silicon. The shape of the polycrystalline silicon used depends on the method of single crystallization. For example, a lump in the Czochralski method (CZ method) and a rod in the floating zone method (FZ method). Further, the polycrystalline silicon processed into these rod-like or lump-like bodies is generally subjected to etching treatment with a cleaning liquid in advance in order to reduce metal impurities and the like adhering thereto.

However, the polycrystalline silicon which has been subjected to such a normal etching process causes an abnormal growth of an oxide film called a stain during its storage, and the surface of the polycrystalline silicon discolors or loses its luster. In fact, the inside of the abnormal oxide film has a problem that impurities in the atmosphere are taken in with the growth of the oxide film.

It is also known that a single-crystal silicon wafer is stained on its surface during storage after etching, like polycrystalline silicon.

[0005] Therefore, development of an etching technique which does not cause stain on the surface of silicon or a post-treatment technique after etching has been desired.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the surface of silicon, especially immediately after etching, is subjected to a microwave or high-temperature drying treatment. In addition, it was found that the occurrence of spots on the surface was suppressed.

As a result of further study of the reason, purified silicon having a reduced Si—H bond on the surface of the etched silicon and having a SiO 2 film formed thereon,
The present inventors have found that no stain occurs during storage, and have completed the present invention.

That is, the present invention provides purified silicon having an oxide film in which at least 50% of Si-H bonds existing on the silicon surface after the etching treatment are converted into Si-O bonds. Further, according to the present invention, there is provided a typical manufacturing method characterized by irradiating a microwave to a surface of the silicon or subjecting the silicon surface to a high-temperature drying treatment in order to obtain such purified silicon.

The silicon in the present invention is polycrystalline silicon or single-crystal silicon as described above, and is generally a rod-shaped or a lump-shaped lump of polycrystalline silicon.
Wafer-shaped single-crystal silicon. Immediately after the silicon is etched with a processing solution such as hydrofluoric acid or hydrochloric acid, desired purified silicon can be obtained by microwave irradiation or high-temperature drying.

The microwave irradiation or high-temperature drying treatment of the present invention is performed in an atmosphere containing oxygen, such as in the air, to remove Si on the surface of the etched silicon.
-H bonds are generally reduced to 50% or less, preferably to 30% or less, and more desirably the Si-H bonds are made as substantially (substantially) absent as possible to obtain a homogeneous oxide film (SiO2 It is preferable to form a film. The method of processing by such a microwave or high-temperature drying treatment generally uses a microwave region having a frequency of 30 MHz or more, or a heat treatment at a temperature of 100 ° C. or more. The means for performing these treatments only needs to have an ability to give energy enough to form an oxide film only on the surface of silicon.
A conventionally known microwave heating device of 0 MHz, 110
A conventionally known dryer capable of drying at a temperature of ° C. is employed without particular limitation. In addition, the irradiation conditions are appropriately set to a microwave frequency, an irradiation intensity, an irradiation time, or the like according to the mode of the silicon to be irradiated, or the drying conditions are appropriately set to a drying temperature, a drying time, or the like according to the mode of the silicon. Adjustments determine the optimal conditions.

In the present invention, in order to obtain a desired purified silicon, not only the above-mentioned processing means by irradiation with microwaves and high-temperature drying, but also the Si-H bond on the surface of the etched silicon is 50% or less. Any method can be adopted as long as it is a method capable of forming a uniform film of SiO2.

[0012]

As will be understood from the above description, the purified silicon of the present invention has an abnormal oxidation even during storage, because Si-H bonds are reduced on the outermost surface and a uniform natural oxide film is formed. A stable surface free from spots due to film growth is obtained. Therefore, the present invention
A refined silicon having good commercial value without discoloration or loss of luster and having very few impurities is provided.

[0013]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 Immediately after a lump of polycrystalline silicon obtained by crushing rod-shaped polycrystalline silicon was etched with a hydrofluoric-nitric acid-based etchant, it was processed in a microwave heating device. The microwave heating device generates microwaves by the microwave generator inside the device, introduces microwaves from the microwave waveguide, and rotates microwaves by continuous irradiation while rotating the support on which the irradiation target is placed. Is reflected by a shielding plate and can be applied to almost the entire surface of polycrystalline silicon as an irradiation object.

The microwave is applied to 60 massive polycrystalline silicon under the condition that the frequency is fixed at 2450 MHz and the irradiation time and the irradiation intensity are respectively changed.
The occurrence rate (%) of the stain was determined from the number of stains.

The results are shown in FIG. 1 and FIG. In other words, when microwave irradiation was not performed, the incidence of spots was 80% in massive polycrystalline silicon,
Increasing the irradiation time or increasing the irradiation intensity reduced the occurrence rate of spots. No irradiation was observed at 20 seconds at an irradiation intensity of 1400 watts and at 120 seconds at an irradiation intensity of 650 watts.

Example 2 Using the same apparatus as in Example 1, a single crystal silicon wafer etched with a hydrofluoric-nitric acid-based etchant was irradiated with microwaves of 650 watts in air for 30 seconds. The gloss on the surface of the wafer was maintained, and no stain-like clouding occurred. In addition, the surface of the wafer is
According to the results measured by -IR, the irradiation of microwaves reduced the Si-H bonds on the surface to 50% or less,
It was found that the bonding increased to form a SiO2 film. That is, in the spectrum of FT-IR, Si-
The area of the peak at a wave number of 2100 cm ^-1 indicating H bonding was reduced to １ ／ or less of the value immediately after etching by microwave irradiation, and was not observed immediately after etching.
A large peak at a wave number of 1130 cm ^-1 indicating a Si-O bond appeared. When this wafer was treated again with 5% hydrofluoric acid, the peak at a wave number of 1130 cm ^-1 , that is, the surface S
It was confirmed that the i-O bond disappeared and the peak at the wave number of 2100 cm ^-1 , that is, the Si-H bond increased.

Example 3 The same silicon as in Example 1 was etched with a hydrofluoric-nitric acid-based etchant, and immediately thereafter processed with a high-temperature drier. The high-temperature heating dryer was configured to apply high-temperature air to the entire surface of polycrystalline silicon as an object to be heated so as to heat the surface.

Drying was carried out on 60 pieces of bulk polycrystalline silicon under the conditions of different drying time and drying temperature, and the occurrence rate (%) of the stain was determined from the number of stains.

The results are shown in FIG. 3 and FIG. That is, when the high-temperature drying was not performed, the occurrence rate of the stain was 100% in the bulk silicon, but the occurrence rate of the stain was reduced by increasing the drying time or increasing the drying temperature. No spots were observed at all after 30 minutes or more.

Example 4 Using the same apparatus as in Example 3, a single crystal silicon wafer etched with a hydrofluoric-nitric acid-based etchant was treated at 110 ° C. for 30 minutes. As a result, the gloss on the wafer surface was reduced. It was kept and no spot-like clouding occurred.
Further, as a result of measuring the surface of the wafer by FT-IR, it was found that Si-H bonds on the surface were reduced to 50% or less due to high-temperature drying, and Si-O bonds were increased to form a SiO2 film. did. That is, in the FT-IR spectrum, the area of the peak at a wave number of 2100 cm ⁻¹ indicating the Si—H bond is reduced to 以下 or less of the value immediately after etching by microwave irradiation, and is not observed immediately after etching. The wave number 1130c showing the Si—O bond
A large peak at m ^-1 appeared. 5% of this wafer again
The peak at a wave number of 1130 cm ^-1 , that is, the Si—O bond on the surface disappears, and the wave number 2
It was confirmed that the peak at 100 cm ^-1 , that is, the Si-H bond increased.

[Brief description of the drawings]

FIG. 1 is a relationship diagram showing a result of a stain generation rate (%) with respect to an irradiation time (second) obtained in Example 1.

FIG. 2 shows the irradiation intensity (watt) obtained in Example 1.
FIG. 4 is a relationship diagram showing the results of the stain generation rate (%) with respect to.

FIG. 3 is a relationship diagram showing a result of a stain generation rate (%) with respect to a drying time (minute) obtained in Example 3.

FIG. 4 is a relationship diagram showing a result of a stain generation rate (%) with respect to a drying temperature (° C.) obtained in Example 3.

Claims (3)

(57) [Claims] 1. Purified silicon having an oxide film in which 50% or more of Si—H bonds existing on a silicon surface after an etching treatment are converted into Si—O bonds. 2. The method according to claim 1, wherein the surface of the silicon is irradiated with microwaves in an atmosphere containing oxygen.
3. The method for producing purified silicon according to item 1. 3. The method for producing purified silicon according to claim 1, wherein the silicon is dried at a high temperature in an atmosphere containing oxygen.