Patent Application
20110017128
The present invention relates to a vitreous silica crucible used for pulling silicon single crystals, and a method of manufacturing the same. The vitreous silica crucible has a high OH group concentration in a region near the inner surface, and the concentration decreases as a distance from the inner surface increases.
Silicon single crystals used for substrates of semiconductor devices, solar cells, and so on are primarily manufactured by the CZ method. This is a method where highly-pure polycrystalline silicon melt is charged into a vitreous silica crucible, and silicon single crystals are pulled under an inactive gas atmosphere.
Nowadays, in accordance with increase in opening diameter of silicon single crystals, large-size crucibles are used. Because a large amount of polycrystalline silicon is charged in the large-size crucible, crucible temperature during pulling has been increased. This brings about increase in melting loss of the crucible inner surface, and decrease in crucible viscosity. This increase in melting loss and decrease in viscosity inhibits long-time use of the crucible.
In order to prevent deformation of the crucible due to the melting loss of the crucible inner surface and decrease in viscosity, there has been proposed a vitreous silica crucible in which the inner surface is devitrified during pulling (Patent Document-1: Japanese Patent Application Laid-Open Hei 9-110579 etc.). However, when barium (Ba) is applied to the inner surface or alkali metal or alkali earth metal is added in order to devitrify (crystallize) the inner surface during melting polysilicon, contamination of silicon single crystals caused by the impurities can cause problems.
Here, there has been proposed a method to promote crystallization by increasing an OH group concentration in the inner surface layer of the crucible (Patent Document 2: Japanese Patent Application Laid-Open 2005-145732, Patent Document 3: WO-00/06811). In a crucible of Patent Document 2, at least, an OH group concentration in a range of 10 μm and 200 μm from the inner surface is controlled to 250 ppm to 650 ppm. Furthermore, in a crucible of Patent Document 3, an OH group concentration in the inner layer is adjusted to 50 ppm to 250 ppm.
It is known that the crystallization caused by contact between silicon melt and an inner surface of a crucible occur more easily as the OH group concentration of the inner surface increases. However, there is a problem that as the OH group concentration of the inner surface increases, the viscosity of vitreous silica decreases and the vitreous silica deforms more easily. Especially, for a large-size crucible, a larger amount of polycrystalline silicon is charged than that for a small-size crucible, and therefore melting time is lengthened and the crucible temperature is increased. In addition, the inner layer of the crucible having a high OH group concentration is not easily devitrified when there is no silicon melt therein before the polycrystalline silicon is melted to produce silicon melt, and the possibility of deformation is increased because of the high OH group concentration.
The present invention solves the above-mentioned problem which exists in a conventional vitreous silica crucible having a high OH group concentration, and provides a vitreous silica crucible which enables, during pulling, crystallization promotion of the inner surface and retention of the crucible strength. This crucible is formed so as to have an OH group concentration gradient where the OH group concentration increases as a distance from the inner surface decreases, and the OH group concentration rapidly decrease as the distance increases.
The present invention relates to a vitreous silica crucible which has solved the above-mentioned problem by the following configuration, and a method of manufacturing the same.
[1] Provided is a vitreous silica crucible, wherein, in at least a portion of a straight body section of a crucible, a region between 0.3 mm and 3 mm from the crucible inner surface has an OH group concentration and an OH group concentration gradient which increase as a distance from the inner surface decreases, and decrease as a distance from the inner surface increases.
[2] Provided is a vitreous silica crucible as recited in the above [1], wherein a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more and an OH group concentration gradient of 100 ppm/mm or more, and a region between 1.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less.
[3] Provided is a vitreous silica crucible as recited in the above [1], wherein a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration gradient of 100 ppm/mm or more, a region between 0.5 mm and 1.0 mm from the crucible inner surface has an OH group concentration gradient of 50 ppm/mm or more, a region between 1.0 mm and 2.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less, and a region between 2.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 20 ppm/mm or less.
[4] Provided is a vitreous silica crucible as recited in any of the above [1] to [3], wherein a portion or the whole of a region up to 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more, a region between 1.0 mm and 2.0 mm from the crucible inner surface has an OH group concentration of 105 ppm or less, a region between 2.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration of 80 ppm or less, a region between 3.0 mm and 0.8 t (t is the wall thickness of the crucible) from the inner surface has an OH group concentration of 60 ppm or less.
[5] A method of manufacturing a vitreous silica crucible includes the step of heating and melting silica powder deposited on an inner surface of a rotating mold to vitrify the silica powder, wherein vapor-containing air is introduced during or right after the melting to manufacture a vitreous silica crucible where a region between 0.3 mm and 3 mm from the crucible inner surface has an OH group concentration and concentration gradient which increase as a distance from the inner surface decreases and which decrease as a distance from the inner surface increases.
[6] A method of manufacturing a vitreous silica crucible includes the step of heating and melting silica powder deposited on an inner surface of a rotating mold to vitrify the silica powder, wherein the crucible is reheated, after the melting and cooling of the silica powder, under an environment with vapor-containing air to manufacture a vitreous silica crucible where a region between 0.3 mm and 3 mm from the crucible inner surface has an OH group concentration and concentration gradient which increase as a distance from the inner surface decreases and which decrease as a distance from the inner surface increases.
A vitreous silica crucible of the invention has, in at least a portion of a straight body section of a crucible, a region between 0.3 mm and 3 mm from the crucible inner surface having an OH group concentration and an OH group concentration gradient which increase as a distance from the inner surface decreases. Therefore, the inner surface contacting silicon melt becomes easily crystallized. On the other hand, an OH group concentration and an OH group concentration gradient of the region decrease as a distance from the inner surface increases, and therefore the viscosity of the vitreous silica is large and the crucible is hard to be deformed at high temperature.
Specifically, in a vitreous silica crucible of the present invention, a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more, a region between 0.3 mm and 0.5 mm has an OH group concentration gradient of 100 ppm/mm or more, and a region between 1.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less.
As shown in the above OH group concentration distribution and concentration gradient, in a region between 0.3 mm and 0.5 mm from the crucible inner surface, the OH group concentration rapidly increases as a distance from the inner surface decreases, while the OH group concentration gradually decreases as distance from the inner surface increases. Specifically, for example, (a) a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration gradient of 100 ppm/mm or more, and a portion or the whole of a region up to 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more, (b) a region between 0.5 mm and 1.0 mm from the crucible inner surface has an OH group concentration gradient of 50 ppm/mm or more, (c) a region between 1.0 mm and 2.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less and an OH group concentration of 105 ppm or less, and (d) a region between 2.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 20 ppm/mm or less and an OH group concentration of 80 ppm or less.
Thus, because the OH group concentration rapidly increases as a distance from the inner surface decreases, and the OH group concentration is 115 ppm or more, and is preferably 130 ppm or more, a crucible surface is easily crystallized due to contact with silicon melt. On the other hand, in a region of 1.0 mm or more from the crucible inner surface, the OH group concentration is sufficiently law, and therefore the viscosity of the vitreous silica does not rapidly decrease at high temperature, the crucible remains strong, and the deformation is hard to occur.
A manufacturing method of the present invention includes the step of heating and melting silica powder deposited on an inner surface of a rotating mold to vitrify the silica powder, wherein vapor-containing air is introduced during or right after the melting, or the crucible is reheated, after the melting and cooling, under a vapor-containing environment. By this method, a vitreous silica crucible having the above OH group concentration and OH group concentration gradient can be manufactured by introducing vapor-containing air during or right after the melting or during heat treatment after the melting and cooling, and adjusting the amount.
Hereinafter, the present invention will be specifically explained based on an embodiment shown in the drawings.
As shown in
The bottom section 10b is a section constituting a bottom wall orthogonally crossing the central axis of the crucible. The corner section 10C is a curved section positioned between the straight body section 10A and the bottom section 10b. The bottom section 10b may have a shape with a round bottom or a flat bottom. The curvature or the angle of the corner section 10C may be discretionarily set. When the crucible bottom section 10b has a round bottom, the bottom section 10b has a certain curvature, and therefore the difference in curvature between the bottom section 10b and the corner section 10C is much smaller than that when the crucible bottom section 10b has a flat bottom. When the crucible bottom section 10b has a flat bottom, the bottom section 10b has a flat or extremely slightly curved surface, and the curvature of the corner section 10C is very large.
The wall thickness of the crucible is preferably 10 mm or more, because a large-size crucible is required to resist long-time operation, and therefore a certain level of thickness is necessary. Especially, a large-size crucible with a diameter of 32 inches (an opening diameter of about 800 mm) or more is preferred to have a wall thickness of 10 mm or more, and a large-size crucible with a diameter of 40 inches (an opening diameter of about 1000 mm) or more is preferred to have a wall thickness of 13 mm or more.
The vitreous silica crucible 10 is preferred to include an opaque vitreous silica layer 11 provided on the crucible outer surface side and incorporating a large number of microbubbles, and an opaque vitreous silica layer 12 provided on the crucible inner surface side and hardly incorporating bubbles. The opaque vitreous silica layer 11 enables heat from a heater placed on the crucible periphery to be uniformly conducted to silicon melt in the vitreous silica crucible. The transparent vitreous silica layer 12 provided near the crucible inner surface can prevent drop in single crystallization rate which is caused by thermal expansion of the bubbles near the inner surface during heating for pulling a silicon single crystal, the resultant partial peeling off of the crucible inner surface to produce silica pieces, and the resultant mix-in of the silica pieces into the single crystal. The vitreous silica crucible 10 may be formed to include an inner layer made of synthetic silica and an outer layer made of natural quartz, or the whole of the crucible may be formed of natural quartz.
In the vitreous silica crucible 10 of the present invention, the OH group concentration and the OH group concentration gradient increase as a distance from the inner surface decreases, and decrease as a distance from the inner surface increases. At least a portion of the straight body section 10A of the crucible needs to have such OH group concentration and OH group concentration gradient. However, as long as this condition is satisfied, the whole of the straight body section 10A may have such OH group concentration and concentration gradient, or only the main portion of the straight body section 10A may have such OH group concentration and concentration gradient. Furthermore, not only the straight body section 10A, but also the corner section 10C may have such OH group concentration and concentration gradient, and the whole of the crucible including the straight body section 10A, the corner section 10, and the bottom section 10b may have such OH group concentration and concentration gradient.
In general, an OH group concentration in a vitreous silica crucible can be measured by an infrared spectroscopic analysis. Specifically, first, a vitreous silica piece is cut out from the vitreous silica crucible, and used as an original form of a measurement sample. This original form of a measurement sample is processed so as to be a flat plate, and the front and rear surfaces thereof are polished to obtain a measurement sample. Next, Using an infrared spectrophotometer (an optical transmittance measurement device), the front surface of the measurement sample is irradiated with infrared light, the transmitted light out of the rear surface of the measurement sample is received, an infrared light absorption peak associated with OH groups in the measured infrared light absorption spectrum is selected, and the transmittance at the peak is compared with the transmittance at wavelength free of infrared light absorption, to calculate an OH group concentration in the measurement sample.
Therefore, the measurement value plotted at a position of 0.3 mm in the X axis is a value obtained by cutting out a measurement sample of a vitreous silica piece having a thickness of 0.3 mm or more from the crucible inner surface, processing the measurement sample in a way as mentioned above, and performing measurement by the above-mentioned spectroscopic analysis. So, this value indicates the concentration of OH groups contained in a vitreous silica portion of a region from the inner surface (0 mm) to 0.3 mm. Likewise, the measurement value plotted at a position of 0.5 mm indicates the concentration of OH groups contained in a vitreous silica portion of a region from 0.3 mm to 0.5 mm. Furthermore, the measurement value plotted at a position of 1 mm in the X axis indicates the concentration of OH groups contained in a vitreous silica portion of a region from 0.5 mm to 1 mm, the measurement value plotted at a position of 2 mm indicates the concentration of OH groups contained in a vitreous silica portion of a region from 1 mm to 2 mm, and the measurement value plotted at a position of 3 mm indicates the concentration of OH groups contained in a vitreous silica portion of a region from 2 mm to 3 mm. An OH group concentration gradient is indicated by a tilt of a straight line between respective points in
As shown in
Specifically, as shown in the drawing, a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more, a region between 0.3 mm and 0.5 mm has an OH group concentration gradient of 100 ppm/mm or more, and a region between 1.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less.
When a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration of less than 115 ppm, crystallization of the inner surface contacting silicon melt will be insufficient. Furthermore, when the region has an OH group concentration gradient of less than 100 ppm/mm, a region distant from the inner surface will have a high OH group concentration, and therefore the viscosity of the crucible will decrease. Thus, such gradient is not preferred.
Furthermore, when a region between 1.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of more than 25 ppm/mm, it will be difficult to maintain a low OH group concentration in the region.
As shown in the drawing, a vitreous silica crucible of the present invention preferably has the following OH group concentration distribution and OH group concentration gradient.
(a) a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration gradient of 100 ppm/mm or more, and a region between 0.3 mm and 0.5 mm from the crucible inner surface has an OH group concentration of 115 ppm or more.
(b) a region between 0.5 mm and 1.0 mm from the crucible inner surface has an OH group concentration gradient of 50 ppm/mm or more.
(c) a region between 1.0 mm and 2.0 mm from the crucible inner surface has an OH group concentration gradient of 25 ppm/mm or less and an OH group concentration of 105 ppm or less.
(d) a region between 2.0 mm and 3.0 mm from the crucible inner surface has an OH group concentration gradient of 20 ppm/mm or less and an OH group concentration of 80 ppm or less.
Here, in the segment of the above-mentioned region, the temperature gradient is defined from 0.3 mm, not from the crucible inner surface 0 mm. This is because the OH group concentration is measured as a concentration in vitreous silica having a certain thickness, and it is not possible to measure the concentration only on the surface. In addition, the OH group concentration within 0.3 mm from the inner surface needs only to be high, and therefore the concentration can be, for example, constant.
Furthermore, as apparent from
When the conditions about the above-mentioned OH group concentration distribution and OH group concentration gradient are satisfied, the OH group concentration and OH group concentration gradient increase as a distance from the crucible inner surface decreases, and decrease as a distance from the crucible inner surface increases. In addition, difference in OH group concentration increases in proportion to a distance from the crucible inner surface as a distance from the crucible inner surface decreases. Thus, it is possible to maintain a high OH group concentration in a region near the inner surface and decrease an OH group concentration as a distance from the crucible inner surface increases.
Therefore, because a vitreous silica crucible having the above-mentioned OH group concentration distribution and OH group concentration gradient has an OH group concentration which increases as a distance from the crucible inner surface decreases, the inner surface is easily crystallized and the crystallization is promoted when the inner surface is in contact with silicon melt. On the other hand, an OH group concentration rapidly decreases as a distance from the inner surface increases, and a region of 1.0 mm or more from the inner surface has an OH group concentration of 100 ppm or less, and a region of 2.0 mm or more from the inner surface has an OH group concentration of 80 ppm or less, and therefore, the viscosity of the vitreous silica is sufficiently high at high temperature. Therefore, when polycrystalline silicon charged into the crucible is melt, during high-temperature heating to form silicon melt, the crucible remains sufficiently strong.
A method of manufacturing a vitreous silica crucible according to the present invention includes the step of heating and melting silica powder deposited on an inner surface of a rotating mold to vitrify the silica powder, wherein vapor-containing air is introduced during or right after the melting, or the crucible is reheated under a vapor-containing environment.
As shown in
A synthetic fused silica crucible (opening diameter of 32 inches) having an inner layer made of synthetic fused silica and an outer layer made of highly-pure natural fused silica was, right after heating and melting, treated in a heating and melting furnace where air with a relative humidity of 70% and a temperature of 25° C. was introduced for 10 minutes at a flow rate of 120 m3/min. from an inlet provided on a wall of the heating and melting furnace to adjust the OH group concentration of the crucible straight body section (from the upper end of the crucible to a position of 40% of the crucible height) to have distribution shown in Table 1 and
A synthetic fused silica crucible (opening diameter of 32 inches) having an inner layer made of synthetic fused silica and an outer layer made of highly-pure natural fused silica was, after heating and melting, treated in a heating and melting furnace where air with a relative humidity of 70% and a temperature of 25° C. was introduced for 20 minutes at a flow rate of 80 m3/min. from an inlet provided on a wall of the heating and melting furnace to adjust the OH group concentration of the crucible straight body section (from the upper end of the crucible to a position of 40% of the crucible height) to have distribution shown in Table 1 and
A synthetic fused silica crucible (opening diameter of 32 inches) having an inner layer made of synthetic fused silica and an outer layer made of highly-pure natural fused silica was, after heating and melting, treated in a heating and melting furnace where air with a relative humidity of 80% and a temperature of 25° C. was introduced for 20 minutes at a flow rate of 80 m3/min. from an inlet provided on a wall of the heating and melting furnace to adjust the OH group concentration of the crucible straight body section (from the upper end of the crucible to a position of 40% of the crucible height) to have distribution shown in Table 1 and
A synthetic fused silica crucible (opening diameter of 32 inches) having an inner layer made of synthetic fused silica and an outer layer made of highly-pure natural fused silica was, after heating and melting, treated in a heating and melting furnace where air with a relative humidity of 40% and a temperature of 25° C. was introduced for 20 minutes at a flow rate of 120 m3/min. from an inlet provided on a wall of the heating and melting furnace to adjust the OH group concentration of the crucible straight body section (from the upper end of the crucible to a position of 40% of the crucible height) to have distribution shown in Table 1 and
A silicon single crystal with a diameter of about 300 mm was pulled using a crucible of Examples 1 to 2 and Comparative Examples 1 to 2. The resultant deformation amount of the crucible and crystallization state (whether or not devitrification has occurred.) are shown in Table 1. The method of measuring a deformation amount was shown in
As shown in Table 1, in both of Examples 1 and 2, the inner surface was crystallized, the deformation amount was 1.5 mm or less, and therefore it was confirmed that the crucible is hard to be deformed. On the other hand, in Comparative Examples 1 and 2, the inner surface was crystallized, but the deformation amount was 2 mm, and therefore it was confirmed that the deformation amount is large.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-065148 | Mar 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/054521 | 3/10/2009 | WO | 00 | 9/14/2010 |
