Crystal pulling unit

Details Crystal pulling unit Crystal pulling unit

1999-03-22

2001-05-15

Hiteshew, Felisa (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Apparatus

For crystallization from liquid or supercritical state

C117S018000, C117S213000

Reexamination Certificate

active

06231669

ABSTRACT:

INTRODUCTION AND BACKGROUND
The present invention relates to a crystal pulling unit for the production of a crystal block, which has a crucible for the meltable material which forms the crystal block and which has a recharging tube leading to the crucible to supply the meltable material in granular form.
Crystal pulling units that are generally of the aforementioned type are known for the pulling of crystal blocks of semiconductor material according to the Czochralski method. These units operate mostly continuously, in that during the pulling of the crystal block, the meltable material which ultimately forms the melt is constantly supplied in the form of a granulate. Reference is made to German Patent No. 2,821,481 as an example of the state of the art. Comparable crystal pulling units, however, are also used for semi-continuous Czochralski pulling methods. The recharging tube is made of quartz material, as is the crucible.
In the operation of such crystal pulling units, it is often determined that the recharging tube becomes clogged. This requires a shutdown of the unit, which causes relatively high costs.
It is therefore an object of the invention to design a crystal pulling unit of the type discussed above in such a way that the danger of clogging in the recharging tube is as low as possible.
SUMMARY OF THE INVENTION
The above and other objects of the invention can be achieved by placing a fine-dust separator upstream from the recharging tube, and located outside the container or chamber containing the crucible.
This solution of the problem, in accordance with the invention, is based on the knowledge that the cause of the clogging in the recharging tube is to be found in the finer, dust-like particles in the recharging material. In the formation of a clogging condition, only these fine, dust-like particles of the supplied granulate stick, at first, by melting to the wall of the recharging tube. There, they form an adhesive film, on which later in the course of time, the coarser fractions of the granulate also stick and melt. This danger of the melting of fine fractions is particularly great with a heated recharging tube, as is described in German Patent No. 2,821,481, supra. The fine dust adhering to the granulate can be removed by the fine-dust separation, in accordance with the invention, before the granulate is introduced into the recharging tube, so that the actual cause of clogging is eliminated. At the same time, the danger of a development of dust in the pulling space is reduced by the fine-dust separator, in accordance with the invention.


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