GB2184434A - Method of producing quartz plate - Google Patents

Abstract

A method wherein a cut length of slotted quartz tubing 1 is supported and heated to cause it to unfurl and thereafter is reheated under tension to form a flattened plate. The tubing 1 may be supported by means of a forked framed 5, also of quartz material. It may be stretched and flattened using a similar forked frame 13 by which means a tensioning weight 45 can be suspended. <IMAGE>

Description

SPECIFICATION Method for producing quartz plate Techical Field The present invention concerns improvements in or relating to the production of quartz plate.

High quality, pure fused silica (quartz) material in the form of thin plate has application for example in the manufacture of semiconductor process jigs. There is thus a requirement for a supply of this material, in plate form, at an economically low cost.

Background Art Fused silica material is available in the form of relatively large cross-section ingots. Hitherto, thick plate material has been prepared by sectioning an ingot, using a diamond edged saw, and following this by grinding and polishing sectioned material to the thickness of plate required. Where, however, thin plate, (eg 1.5-2.0 mm) is required, this process is wasteful, labour intensive and most costly. Furthermore, grinding and polishing techniques introduce contamination. Such plates, therefore, need to be etched to remove surface contamination, and then need to be flame glazed for final finish.

Fused silica material is also available in the form of high quality, pure, extruded tubular form. Attempts to produce plate material by unrolling tubes using carbon tabies, roller and paddles, etc, have only produced poor results with unacceptable contamination occurring to the worked surfaces of the quartz. Techniques, similar to those just mentioned, for producing sheet glass from tubing, have been described in the followig texts: Handbook of Glass Manufacture, Ed. Fayv Tooley, Ogden Publishing Co., NY 1960, Vol II pages 226-9; Textbook of Glass Technology, Hodkin & BR< Cousen, Constable 1929, pages 453-457; and Glass in the Modern World, Mahoney, Aldus, 1967 pages 68-9.

Since in the above techniques the glass is supported in contact with a fireclay bed or the like, substantial amounts of contaminants are introduced.

Disclosure of the invention The present invention is intended as a solution to the problem of providing high purity quartz material in thin plate form. The method to be described is straight-forward and provides plate material with good yield and thus at relatively low cost.

In accordance with this invention there is provided a method of producing quartz material in plate form, this method comprising the following steps:- providing a length of high purity quartz tubing; cutting a slot in the quartz tubing, this slot extending axially along the length of the tubing; suspending the slotted tubing and applying heat to unfurl the tubing; and, stretching the unfurled tubing under applied heat and tension to form a flattened plate.

In accordance with a preferred embodiment of the invention there is provided a method of producing quartz material in plate form, this method comprising the following steps:- providing a length of high purity quartz tubing; cutting a slot in the quartz tubing, this slot extending axially and along the entire length of the tubing; attaching an inert support member to the tubing, attachment being made along one edge extremity of the slotted tubing; suspending the tubing by means of the inert support member, the remaining and free edge extremity of the slotted tubing being disposed uppermost; applying heat to the tubing, allowing the tubing to unfurl under its own weight until all but a short tail portion thereof remains unfurled; attaching to the free edge of the unfurled tubing an inert tensioning member; and, reapplying heat to the unfurled tubing until a straightened plate is formed under applied tension.

It is preferable that the support, at least that part attached to the tubing, is of like high purity quartz material. Conveniently it may be of forked form, being attached to the tubing at points of attachment spaced along the axial length of the tubing.

The tensioning member may be of similar form. It is convenient for this member to include a a hooked structure for the suspension of a tensioning weight.

The tubing is preferably heated by a high pressure gas burner using a mixture of combustible gasses.

Brief Introduction of the Drawings In the drawings accompanying this specification: Figure 1 is a perspective view of a cut and slotted section of quartz tubing; Figures 2 and 3 are plan views of a support member and a tensioning member, respectively; Figures 4 and 5 are plan views of two gas burners suited to heat application for this inventive method; Figure 6 is an illustrative perspective view of a gantry arrangement for controiling movement of one of the gas burners, the burner shown in Fig. 5 above, Figure 7 is a cross-section view showing attachment of the support member to quartz tubing; and, Figures 8 and 9 are illustrative views of a suspended quartz tube at two stages of this inventive method.

Description of Preferred Embodiment So that this invention may be better understood, an embodiment thereof will now be described with reference to the accompanying drawings. The description that follows is given by way of example only.

In the method described below, quartz tubing of 100-130 mm internal diameter is opened out and flattened to provide sheet material that can be cut to provide plates typically of 230 mmx310 mm and 230 mmx420 mm finished size. Such tubing is readily available and has been supplied hitherto for the manufacturer of furnace tubes as used in the semiconductor industry.

As shown in Fig. 1 a section 1 of this quartz tubing has been cut to a length of 230 mm and also has been cut lengthways by a diamond edged saw to form a slot 3 extending axially the full length of the section 1.

A three-pronged forked frame structure 5, used here as a support member, is shown in Fig. 2. This forked structure is comprised of high purity quartz material and has a stem portion 7 of length 250 mm formed of 25 mm outer diameter thick wall tubing or rod.

This has at one end a forked extension 9 of 10 mm diameter rod material about 50 mm long and of width suited to the length of cut quartz tubing. Each forked extension has a prong 11 formed of 6 mm diameter rod, each approximately 180 mm long. A three-pronged fork frame structure 13, used here as a tensioning member, is shown in Fig. 3. This forked structure 13 is of like dimensions and material to the forked structure 5 (Fig. 2) just described, but in place of the stem 7, has a hooked member 15.

Two gas torch assemblies are shown in Figs. 4 and 5. The first torch 17 used for initial unfurling, consists of a spaced pair of air cooled nickel or chrome plated 25 mm diameter nozzles 19 and 21 fitted to a 28 mm neck tube 23. Typically, the nozzle orifices are 60 mm apart. The second torch 23 comprises a pair of air cooled 20 mm diameter stainless steel jets 25 and 27 fed by bifurcated tubing 29. The jet nozzles are spaced approximately 45 mm apart. Each torch 17 and 23 uses oxygen gas at 200 p.s.i. (1.4x 106Pa) and propane gas at 80 p.s.i. (5.7 x 105Pa) pressure.

The second torch 23 is mounted by means of a gantry 31 (Fig. 6) and balanced using a counterweight 33 and pulley 35, 37 arragement. This counterbalance is provided to obviate problems of operator fatigue and thus decrease the likelihood of the torch nozzles 25, 27 touching the quartz plate surfaces during the heating process (Fig. 9).

As shown in Fig. 7 the fork support member 5 is arranged tangentially to the quartz tube 1 and the prongs 11 torch welded to form attachment to one edge extremity 39 of the tube 1 on the remote side of the slot 3.

The forked support member 5 is then held vertically in a clamp, the opposite edge extremity 41 of the tube 1 being disposed uppermost as shown in Fig. 8.

Using the first torch 17, heating is commenced. Heat is applied across a band of the quartz tubing 1 about 25 mm or so below the point of attachment to the forked support member 5. Care is taken to avoid overheating the tubing 1 which otherwise would move too rapidly. The tube 1 is allowed to unfurl under its own weight. At this stage slight rippling is inevitable. As the heating is continued, more heat is supplied because of the reducing weight of the remaining 'off centre' bottom portion of the tubing 1. The lower portion 39 of the tubing 1 is then heated using the second torch 23, but no attempt is made to straighten the last 25 to 35 mm without the lower frame, the tensioning member 13, being attached, for otherwise undue distortion would occur.

The forked tensioning member 13 is then attached, by torch welding. Heat is then reapplied using the second torch 23 and the tubing 1 allowed to unfurl further, the hook member 15 being moved into vertical position under the weight of the tensioning member 13.

A tensioning weight 45 is then attached to the hook member 15. A weight of approximately 1.6 kg has been shown to be satisfactory for this final stretch stage of operation.

The first torch 17 is then used to reapply heat, this being carried out by a final cross and down sweep action over the plate to obtain the required finish.

The support and tensioning members 5 and 13 are then removed by diamond saw, 50 mm stubs being left attached to the plate.

This plate is then annealed at circa 1 1000C before being cut to the required plate dimensions.

By adopting the method just described, it has been possible to obtain a sheet flatness of circa +0.75 mm, depending on wall thickness. Best results have been obtained for tubing in the lower wall thickness range of 1.5 to 2.0 mm.

For the production of thickest plate, watercooled gas burners, which have much enhanced hearing capacity, may be used in place of the burners aforementioned.

Claims (7)

1. A method of producing quartz material in plate form, this method comprising the following steps:- providing a length of high purity quartz tubing; cutting a slot in the quartz tubing, this slot extending axially along the entire length of the tubing; suspending the slotted tubing and applying heat to unfurl the tubing; and, stretching the unfurled tubing under applied heat and tension to form a flattened plate.

2. A method, as claimed in claim 1, this method comprising the following steps:- providing a length of high purity quartz tubing; cutting a slot in the quartz tubing, this slot extending axially and along the entire length of the tubing; attaching an inert support member to the tubing, attachment being made along one edge extremity of the slotted tubing; suspending the tubing by means of the inert support member, the remaining and free edge extremity of the slotted tubing being disposed uppermost; applying heat to the tubing, allowing the tubing to unfurl under its own weight until all but a short portion thereof remains unfurled; attaching to the free edge of the unfurled tubing an inert tensioning member; and, reapplying heat to the unfurled tubing until a straightened plate is formed under applied tension.

3. A method, as claimed in claim 2, wherein the support member, the tensioning member, or both, are of high purity quartz material.

4. A method as claimed in claim 3, wherein the support member, the tensioning member, or both are of forked structure.

5. A method, as claimed in any one of the preceding claims, wherein tension is applied by means of suspending a weight from the unfurled tubing.

6. A method, as claimed in any one of the preceding claims wherein heat is applied using high pressure combustible gases.

7. A method of producing quartz material in plate form, performed substantially as hereinbefore described, with reference to and as shown in the accompanying drawings.