Wafer boat

Details Wafer boat Wafer boat

2000-03-30

2001-09-11

Wilson, Gregory (Department: 3749)

Heating

Accessory means for holding, shielding or supporting work...

Support structure for heat treating ceramics

C432S253000, C211S041180, C118S728000

Reexamination Certificate

active

06287112

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a wafer boat comprising an end member on both extremities connected by at least three axial rods, which rods define a housing surface for receiving of a number of axially spaced wafers. Moreover, for each wafer there are at least three supporting means connected to those columns and provided with accommodations.
2. Background Art
Such wafer boats are usually used vertically, that is, the wafers lie horizontally, one above the other. Any number of wafers can be accepted in such a boat. Such a boat is placed in a reactor where the wafer undergoes a treatment. Many types of treatment are possible, such as heat treatment, oxidation and other chemical and/or physical reactions.
With that, the problem of non-uniformity across the wafer surface occurs. That is, if the treatment gas is supplied radially, this will be depleted towards the center of the wafer. Consequently, the process or reaction in question will be further advanced at the edge of the wafer than in the center of the wafer. Such a non-uniformity is particularly undesirable.
In the American patent U.S. Pat. No. 5,192,371 in the name of ASM Japan K.K., the use of rings is described which are fitted at some distance under the wafer. The internal diameter of the ring corresponds to, or is a little smaller than, the external diameter of the wafer. Consequently, the uniformity of the reaction across the wafer surface is considerably increased, since the edge effect then occurs in the relevant ring.
A further embodiment of such a ring is encountered in the American patent U.S. Pat. No. 5,316,472.
In the first mentioned American patent U.S. Pat. No. 5,192,371, the ring also provides the supporting surface for the wafer.
SUMMARY OF THE INVENTION
Although a considerable improvement in the uniformity of various reactions can be achieved with the use of the above mentioned rings, certain reactions still have the problem that irregularities occur. An example of such a reaction is the so-called HTO process. There, silane and N
2
O are used. Radicals are generated in the gas phase, including sililene. These radicals attach themselves with particular preference onto the surfaces of solid materials such as the material of the axial rods of the boat.
The application of the ring described above gives insufficient uniformity.
The present invention aims to improve this uniformity.
The present invention also aims to provide a suitable support for a wafer.
The present invention also aims to provide centering of the wafer with regard to a shield ring.
According to an aspect of the invention, a wafer boat is provided which comprises an end member on both extremities connected by at least three axial rods, which rods define a housing surface for receiving therein a number of axially spaced wafers.
It has been found that the presence of the rods of the wafer boat has a disrupting effect on the uniformity. That is, an extra surface is created by these rods whereby, at the position of those rods, a depletion of the material taking part in any reaction occurs. This depletion not only occurs in the shield ring but also continues in the adjacent wafer. According to the invention, by locally decreasing the radial distance, less “material” meant for any reaction with the wafer will be removed locally due to the shield ring. This is completely compensated for by the presence of the rods and further fixing constructions of the wafer boat so that, along the circumference of the ring close to the wafer, uniform conditions prevail, whereby the desired uniformity of the process is realized.
Decreasing the distance can either be realized by the external presence of a recess close to the rods or by the internal fitting of such a recess, that is, close to the boundary with the wafer.
These two measures can clearly be combined. For this, any conceivable form can be applied.
According to a further aspect of the invention, the shield ring is provided with projection means on which the wafer rests. Moreover, according to a further variant of the invention, that projection is realized in steps and the wafer should be placed in the lower lying part. The higher lying part is close to the rods along which the wafer must be moved, and is realized with a comparatively small height while, close to the “rear” of the boat, this higher lying part can be higher to enable accurate and easy positioning.
Further aims and advantages of the invention are clear from the following description and several example embodiments.


REFERENCES:
patent: 5192371 (1993-03-01), Shuto et al.
patent: 5310339 (1994-05-01), Ushikawa
patent: 5316472 (1994-05-01), Niino et al.
patent: 5482559 (1996-01-01), Imai et al.
patent: 5820367 (1998-10-01), Osawa
patent: 5897311 (1999-04-01), Nishi
patent: 6099302 (2000-08-01), Hong et al.

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