HIGH STRENGTH CAMFER ON QUARTZWARE

Abstract

A structural member for use in extremely high temperature environments that has substantially flat exterior for resting on a flat surface. The substantially flat exterior of the structural member has a low angle chamfer that is preferably less than 45 degrees and that rises far enough above the flat surface so that when the edge is rolled using conventional processing methods, the resulting high point does not extend a distance far enough to contact with the surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional patent application Ser. No. 61/111,683, filed on Nov. 5, 2008.

TECHNICAL FIELD

This invention relates to a structural member for use in extremely high temperature environments such as those found during the processing and manufacture of silicon wafers and the like.

BACKGROUND OF THE INVENTION

Durable and strong structural members for use in extremely high temperature environments, such as a range between 900 degrees Celsius to 1500 degrees Celsius, are used in a wide variety of applications. For example, in the semi-conductor industry, the manufacture of semi-conductors from silicon frequently requires heating silicon wafers and the like to within this temperature range.

Usually, the wafers are stacked in a rack-type structure, which is referred to in the industry as a “boat”, and the rack containing the plurality of wafers is placed in a furnace. The structural members forming the rack must be sufficiently strong to hold the wafers, even at these extreme temperatures, without weakening due to the extreme heat. Moreover, it is desirable for the rack to be reusable. Accordingly, the members forming the rack, the stand on which the rack is placed, and the even the furnace structures themselves must be sufficiently durable and strong to withstand numerous heating and cooling cycles.

Structural members operating within these extreme temperatures must be formed with materials having melting points well above the range of temperatures in which these structural members are expected to operate. Steel and other alloy-based materials commonly used as structural members in lower temperature environments vaporize and/or melt at these extreme temperatures rendering them useless. Accordingly, known materials for constructing structural members used in such extremely high temperature environments are limited.

Moreover, in cases where a structural member is used in an extremely high temperature to facilitate semi-conductor manufacture, it is important that the structural member limit the amount of impurities released by vaporization during the heating process.

A particularly favorable material used as a structural member in the construction of boats for use in semi-conductor fabrication is fused silica glass, which is also referred to in the industry as fused quartz and collectively refers to materials containing at least one of a group of minerals that are commonly referred to as the “SiO₂” group. This material has a high melting/vaporization point, and can be processed and or selected so as to release few, if any, impurities during the heating process. Moreover, fused silica glass can be formed into structural members, and it can be joined together with other structural members, usually by heat welding, to make a boat or the like.

Despite the benefits of fused silica glass for use as a structural member, it has several drawbacks. For example, component parts made from these hard materials like Quartz glass are often stacked on top of each. In some cases the interface surfaces of these parts are not completely flat and smooth. In many cases the product is fire polished on corner or edge to make them smooth. The corner or edge when fire polished “rolls” due to surface tension. As shown in FIG. 1 (PRIOR ART), this rolled edge tends to produce high points (A) along exterior contact surfaces 48′, which are usually referred to as burms or bumps. Often times, all the weight of the stacked parts in the rack (B) is supported by these high points A as shown. Accordingly, these points (A) serve as substantial points of contact between the boat and the surface the boat rests on during the extreme temperature heating processes the rack is subjected to, and these points of contact tend to develop high stress and are prone to breaking and cracking during static and dynamic loading.

In an attempt to reduce or minimize this characteristic, some extreme high temperature rack manufacturers may chamfer the parts with a 45 deg chamfer from 0.2 mm to 1 mm then fire polish the surface and edge. However, these actions still tend to produce high points (A, FIG. 1 (PRIOR ART)).

SUMMARY OF THE INVENTION

Accordingly, despite the available structural members for use in extremely high temperature environments, there remains a need for an economical thermally resistant, structural member that is more durable than the known structures, particularly during repeated heating and cooling cycles and that does not have bumps or high points at exterior contact surfaces that promote high stress fractures and the like. In addition to other benefits that will become apparent in the following disclosure, the present invention fulfills these needs.

The present invention is structural member for use in high temperature environments that has substantially flat exterior for resting on a flat surface. The substantially flat exterior of the structural member has a low angle chamfer that is preferably less than 45 degrees and that rises far enough above the flat surface so that when the edge is rolled using conventional processing methods, the resulting high point (burm or bump) does not extend a distance far enough to contact with the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (PRIOR ART) is an enlarged, partial front view of prior art structural member for use in extremely high temperatures.

FIG. 2A is a front plan view of a structural member for use in extremely high temperatures in accordance with an embodiment of the present invention.

FIG. 2B is a top plan view of the structural member of FIG. 2A.

FIG. 2C is an enlarged, partial front plan view of the structural member of FIG. 2A taken along arrow 2C of FIG. 2A.

FIG. 3 is an enlarged, partial front plan view of a lower surface of the structural member of FIG. 2A in accordance with an embodiment of the present invention.

FIG. 4 is an enlarged, partial front plan view of a lower surface of the structural member of FIG. 2A in accordance with an alternative embodiment of the present invention.

FIG. 5 is an enlarged, partial front plan view of a lower surface of the structural member of FIG. 2A in accordance with a second alternative embodiment of the present invention.

FIG. 6 is an enlarged, partial front plan view of a lower surface of the structural member of FIG. 2A in accordance with a third alternative embodiment of the present invention.

DETAILED DESCRIPTION

A structural member 30 for use in a high temperature environment is disclosed in FIGS. 2A-6. The structural member 30 is preferably formed of fused silica or the like, which is commonly known in the industry as quartz.

A. Boat Construction

Preferably and referring to FIG. 2A-C, a plurality of structural members 30 are joined together using conventional methods to form a heating boat 36 used to hold silicon wafers 37 (FIG. 2B) and the like during high temperature heating in a furnace. The heating boat 36 can include a plurality of elongate structural members 30 aligned substantially parallel to teach other and joined at their respective ends by an upper member 38 and a lower member 40.

A plurality of spaced-apart notches 42 is preferably provided along each structural member 30. Preferably, the notches 42 in each structural member 30 are aligned substantially horizontally to form substantially horizontal rows 44 of like notches 42 within the structural members 30. Accordingly, a silicon wafer 37 (FIG. 2B) may be secured to the heating boat 36 by being placed within one of the rows 44 of notches 42. More preferably, a plurality of silicon wafers may be secured to the heating boat 36 and spaced-apart from each other by being placed in separate rows 44 of notches 42 on the structural members 30.

As best shown in FIG. 2A, the upper and lower members 38, 40 are preferably planar and have a substantially circular shape. Preferably, three structural members 30 are joined to the upper and lower members 38, 40 and spaced apart from each other as shown so as to allow a silicon wafer 37 (FIG. 2B) to be easily inserted and removed through an open side 46 formed thereby.

B. Surface Engaging Structure

More preferably, the lower exterior side 48 of the lower member 40 has a surface engaging structure 100 configured as shown in one of the embodiments of FIGS. 2A, 2C, and 3-6. Preferably, a low angle chamfer with and angle {acute over (α)} that is less than 45 degrees is provided so that the chamfer will rise far enough above the surface the lower member 40 rests on so that when the edge is rolled the high point 110 (burm or bump) does not extend a distance 142 (FIG. 6) so as to contact the surface. At the intersection 104 of the low angle chamfer and the primary surface 100 there is an intersection point 104. Preferably, a large radius 112 about this intersection point 104 is provided. This radius 112 reduces the effects of any bump or burm 110 arising from the fire polishing process. More preferably, the chamfer extends a distance 140 (FIG. 6) that is 2 to 5 millimeters from the outer edge of the member 40.

The foregoing steps will result in a surface engaging structure 100 with a fire polished surface 48 that has greatly reduced rolled bumps and will result in a less facture prone interface of mating surfaces.

Having here described preferred embodiments of the present invention, it is anticipated that other modifications may be made thereto within the scope of the invention by individuals skilled in the art. Thus, although preferred, more preferred, and alternative embodiments of the present invention have been described, it will be appreciated that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.

Claims

1. A structural member for use in extremely high temperature environments having:

a frame having an upper surface and a lower surface;

said lower surface having a substantially planar exterior engaging surface and an outer edge;

a chamfer extending from said substantially planar exterior engaging surface toward said outer edge by a defined distance away from said exterior engaging surface at said outer edge such that when the lower surface is fire polished resulting burms along said outer edge are shorter than said defined distance.

2. The structural member of claim 1, wherein said structural member is a boat for heating silicon wafers therein.

3. The structural member of claim 1, wherein said structural member is formed of materials selected from SiO2 group.

4. The structural member of claim 3, wherein said structural member is formed of fused silica.

5. The structural member of claim 1, wherein said chamfer extends inwards from said outer edge by a second defined distance.

6. The structural member of claim 5, wherein said second defined distance is between 2 to 5 millimeters.

7. The structural member of claim 1, wherein said defined distance is between 0.25 to 2 millimeters.

8. The structural member of claim 1, further including a radius transitioning from said lower to said chamfer.

9. The structural member of claim 8, wherein said radius is large.

10. The structural member of claim 1, wherein said chamfer angle is less than 45 degrees.