Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Reexamination Certificate
2001-02-05
2003-04-29
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
C065S017400, C065S032100, C065S134900, C065S136100, C065S135600, C065S144000, C065S157000, C065S302000, C065SDIG004
Reexamination Certificate
active
06553787
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of producing a silica glass crucible, and especially to a method of producing a silica glass crucible which can improve the yield of semiconductor single crystal when used for pulling of semiconductor single crystal.
BACKGROUND
As a method of producing semiconductor single crystal such as silicon single crystal, “the pulling method” (Czochralski method or CZ method), in which seed crystals as cores are immersed in a liquid surface of molten semiconductor materials such that single crystal is grown from the seed crystal, is known. A silica glass crucible is employed for melting semiconductor materials. In recent years, in order to reduce the production cost in the pulling process of single crystal, Multi-pulling method or large-diameter silicon single crystal pulling method has been attempted. However, in the case of such new methods, a silica glass crucible of a large inside or inner diameter are often required.
When the inner diameter of the silica glass crucible is increased and a large amount of semiconductor materials are melted in the silica glass crucible, the melting time becomes longer and thus a longer time is required for entire pulling process. In order to shorten the time requited for the pulling process, increasing the amount of heat (the amount of inputted heat) which is given to the silica glass crucible by a heater is one possible solution. Further, it is preferable that the amount of inputted heat is relatively large for maintaining the temperature of a large amount of the liquid of the semiconductor materials at a predetermined temperature.
However, when the amount of the inputted heat is large, the following undesirable outcomes may occur. It is known that a considerable amount of gaseous components is mixed into the silica glass crucible from the air during the production process and remains as bubbles therein. These bubbles tend to expand when the silica glass crucible is used at a high temperature, and the bubbles present in the transparent layer as the inner surface layer of the crucible, in particular, tend to explode as a result of increase in volume thereof. Pieces of silica glass resulted from such explosions are mixed into the liquid of silicon, transferred in the melt liquid as cristobalite by convection, and may be deposited to the lower end of single crystal of silicon which are in the midst of the pulling process. The single crystal may then collapse from the portion at which the silica glass piece is deposited, thereby deteriorating the yield of the semiconductor single crystal. This undesirable phenomenon becomes more significant when the amount of inputted heat is increased or the heat load is increased as the time required for the pulling process is prolonged, due to use of the silica glass crucible of a large inside diameter. The larger the number or the size of the bubbles present in the transparent layer is, or the larger the volume increasing rate of the bubbles during the single crystal pulling process is, the more easily the bubbles explode.
As a method of producing silica glass which has a highly transparent glass layer having a relatively small amount of bubbles, there exists a known method in which silica glass is produced by melting silica sand powder in a high-temperature atmosphere. Known examples of such a method include what are called the oxygen-hydrogen Verneuil's method, the arc Verneuil's method, the plasma-Verneuil's method and the like, which are different from each other in types of the heat source which forms the high-temperature atmosphere. Attempts have been made so as to apply these melting methods to the production of the silica glass crucible and make substantially eliminate bubbles in the silica glass crucible. For example, in publication of examined patent application No. Hei 4-22861, a method of producing a silica glass crucible is proposed in which a transparent layer is formed in the inner surface portion of the crucible (by using the arc Verneuil's method, the inner surface portion is made to come into direct contact with the liquid of molten silicon during the pulling process).
In publication of unexamined application No. Hei 8-268727, a method of producing a quartz crucible is disclosed which method includes the steps of: centrifuging silica sand put in a melting pot such that the silica sand has the bowl-like shape; heating the silica sand of bowl-like shape; introducing a rapidly-diffusing gas into the silica sand of bowl-like shape from the outer surface thereof so as to purge remaining gases contained in voids which are formed between every particles of silica sand. In addition, in this method of producing a quartz crucible, vacuum is applied to the bottom of the melting pot of the silica sand such that a flow of the rapidly-diffusing gas is generated, in order to purge the remaining gases from the voids of the silica sand.
In the case of the method of producing a silica glass crucible disclosed in the former of the aforementioned two references, a problem, that the method may not be able to adapt to the current pulling process to a sufficient degree because the heat load is increased or the time required for the pulling process is prolonged due to use of a larger inner diameter of silicon single crystal or introduction of the “multi-pulling” process, may arise. Accordingly, there has been a demand for a silica glass crucible in which bubbles present in the inner surface layer are less likely to explode even when the heat load is relatively large or the time required for the pulling process is relatively long.
According to the method of producing a quartz crucible disclosed in the latter of the aforementioned references, the growth of bubbles in the silica glass crucible during the high-temperature heating process in, for example, manufacturing semiconductor single crystals can be prevented because the gases remaining in the voids of the silica sand are replaced with the rapidly-diffusing gas. However, as the remaining gases (nitrogen gas or oxygen gas) are still not sufficiently replaced with the rapidly-diffusing gas in this production method, bubbles present in the opaque layer tend to increase volume thereof when the crucible is used (i.e., during the pulling process), thereby deteriorating the heat conductivity of the quartz crucible and thus raising the temperature of the quartz crucible. As a result, the bubbles in the transparent layer are also likely to explode.
In general, nitrogen gas and the like trapped in the voids of the silica sand has a larger density than hydrogen gas which is the rapidly-diffusing gas. Accordingly, due to the difference between the density of nitrogen gas and that of hydrogen gas, hydrogen gas simply passes through the voids and thus it takes a long time to complete replacing of nitrogen gas with hydrogen gas. As a result, when the rapidly-diffusing gas is blown into the silica sand for only a short period, the replacement cannot be performed sufficiently and a considerable amount of nitrogen gas and the like are likely to remain in the voids. These remaining gases become the bubbles present in the inner surface layer of the silica glass crucible. In short, according to this method, the number of the bubbles in the crucible remains substantially the same as in the conventional method and cannot be reduced.
In addition, the increase in the amount of inputted heat may also influence the pulling process of semiconductor single crystal. During the pulling process, the silica glass crucible is supported at the outer periphery thereof by a holding member made of graphite, and the holding member is heated by a heater. That is, the semiconductor material in the silica glass crucible is heated by the heater by way of the holding member.
The more transparent the silica glass crucible is, the more effectively the heat from the heater is transferred to the semiconductor materials. However, as a plurality of heater elements are provided with a space between each other, if the silica glass crucible is co
Akiho Kazuhiro
Kusuhara Masaki
Uno Tomoyasu
Watanabe Hiroyuki
Colaianni Michael
Nanwa Quartz, Inc.
LandOfFree
Method for manufacturing quartz glass crucible does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for manufacturing quartz glass crucible, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for manufacturing quartz glass crucible will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3104715