GB2126417A

GB2126417A - Support systems for conveying semiconductor devices into hostile environments during manufacture

Info

Publication number: GB2126417A
Application number: GB08303592A
Authority: GB
Inventors: Joseph Louis Lambert
Original assignee: Heraeus Schott Quarzschmelze GmbH
Current assignee: Heraeus Schott Quarzschmelze GmbH
Priority date: 1982-08-26
Filing date: 1983-02-09
Publication date: 1984-03-21
Also published as: GB8303592D0

Abstract

This invention describes a support system for supporting semiconductor wafers to be conveyed into a hostile environment, comprising one or more elongate members 1, 2, 3 of columellate form, wherein the forward portion 6, 7, 8 of the or each such member is made from a material different from the rearward portion 9, 10, 11 thereof. At least this forward portion comprises a material able to withstand the hostile environment, e.g. silicon carbide or polycrystalline silicon for furnace use whereas the rearward portions are of alumina. The members are covered by sheaths 12, 13, 14 of silica. One of the members, 2, lies below the plane of the other two 1,3. <IMAGE>

Description

SPECIFICATION Support systems The present invention relates to support systems as used for supporting semiconductor wafers that have to be introduced into and removed from a furnace for heat treatment, or some other hostile environment for other treatment, by causing the support system to travel into a part of the furnace or other environment and be removed therefrom after the treatment has taken place.

In such circumstances only the forward portion of the support system travels into the most hostile zone of the said environment and the rearward portion remains outside it.

Hitherto, the whole of the support system has been made either from an expensive material or materials that are able to withstand very hostile environments, or from less expensive materials which are not so effective and it is an object of the invention to reduce the cost of such systems.

Accordingly the invention consists in a support system for supporting semiconductor wafers to be conveyed into a hostile environment, comprising one or more elongate members of columellate form, wherein the forward portion of the or each such member is made from a material different from the rearward portion thereof, at least said forward portion comprising a material able to withstand the hostile environment.

Generally only one forward and one rearward portion need be provided but if desired one or more intermediate portions may be provided.

Advantageously the various portions are mounted one within the other from front to rear in interfitting relationship, the degree of insertion being sufficient to preserve linear integrity of the assembly.

The cross-section of the elongate members may take any desired form.

The forward portion of the or each elongate member may be a rod to prevent any access of the hostile environment to the rear of the system but said forward portion may be tubular if desired with a closed forward end for the same purpose.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawing, which shows a plan view of a support system comprising three elongate tubular support members, partly in section.

Referring to the drawing there is shown a plan view of the support system comprising three elongate support members 1, 2 and 3 held cantilever-fashion in spaced relationship in a clamping device schematically illustrated at 4. The clamping device may form part of a transportation system for moving the support system into or out of a hostile environment which is schematically indicated at 5.

As shown, the supporting system is intended for carrying semiconductor wafers loaded into magazines, into and out of the process tube of a furnace. Thus, the forward end of each elongate member is required to withstand a very high temperature e.g.

1 300 C and above, whereas the rearward ends are not subject to such heat. For this particular application where intense heat is involved the choice of material is important to prevent the different parts from reacting with each other or chemically causing mutual degradation or them sticking to each other.

As shown in the drawings, the forward ends of the elongate members comprise rods 6, 7 and 8 and the rearward portions comprise tubes 9, 10 and 11 respectively. If desired the forward portions may be tubes which may be open or closed at their forward ends. The degree of insertion of the rods or tubes 6, 7 and 8 into the tubes 9, 10 and 11 is sufficient to preserve linear integrity of the whole elongate member. For example where the length of each forward portion 6, 7 and 8 is 1 500 mm the amount of insertion may be 500 mm. Owing to the intense heat involved the forward and rearward portions of each respective member must be heat compatible so that there shall be no unsympathetic thermal expansion involved. Preferably, but not necessarily, the forward and rearward portions are provided with an outer sheath 12, 1 3 and 14.The forward ends of the sheaths are closed in the fashion of a test tube to inhibit transfer of the hostile environment from front to back.

It would therefore be desirable to include in the construction a material which has a low thermal conductivity so as to act as a thermal barrier to prevent overheating of the clamping device 4.

For these and other good reasons we have found that suitable materials for the parts are as follows:- Rods or tubes 6, 7 and 8-sili- con carbide (SiC), tubes 9, 10 and 11-sin- tered alumina (Al2O3), sheaths 12, 1 3 and 1 vitreous silica (SiO2). Since vitreous silica does not expand very much, the internal diameter of the sheath is made slightly larger than the outer diameters of the rods and tubes so that when the latter expand under heat the sheath does not crack. Vitreous silica is relatively inert to contamination by dopants used in the semiconductor industry and where the support system is used for introducing semiconductor wafers into a furnace, it protects the wafers and emanations from the materials of the support.

It will be appreciated however that the materials used will depend upon the application and the materials quoted above are only examples. Clearly other materials compatible for the same or different environmental requirements can be selected at will, for example polycrystalline silicon, may be used as one of the materials referred to. Moreover the sintered alumina may be replaced by nonsintered aluminium oxide of any desired form thus including sapphire.

A further advantage accruing from the invention is that the system subdivides the length of each elongate member whereby relatively short and therefore cheaper pieces of material can be used, it being understood that the materials contemplated become more expensive with length.

In the particular construction illustrated, where the elongate members are held cantilever-fashion in a clamping block the telescopic nature of the location clearly signifies the external dimensions of the members increase step-wise from front to rear which stiffens the assembly.

In this embodiment the support members 1 and 3 are arranged in the same plane and actually carry the magazines. The third member shown at 2 is present for stability of the system and is arranged centrally and below the members 1 and 3. It is also of larger diameter. Thus in end view the members are located on the corners of a triangle the apex being member 2 located downwardly and the members 1 and 3 representing the base of the triangle.

However, the wafers in these magazines have not been illustrated in the drawing but it will be understood that the loaded magazines are seated in the upper part of the forward portions 6 and 8 of the elongate members 1 and 3, resting on the sheaths 1 2 and 14.

If desired, the third member 2 may be omitted and the system thus employ only the elongate members. In this event the members 1 and 3 may have relatively larger diameters from those shown, to preserve strength of the assembly.

This invention may also be used in a system wherein the forward part that enters into the hostile environment is borne by a wheel or roller assembly that contacts a wall of the chamber maintaining such environment, e.g.

the process tube of a furnace.

Claims

1. A support system for supporting semiconductor wafers to be conveyed into a hostile environment, comprising one or more elongate members of columellate form, wherein the forward portion of the or each such member is made from a material different from the rearward portion thereof, at least said forward portion comprising a material able to withstand the hostile environment.

2. A support system as claimed in claim 1, wherein the various portions are mounted one within the other from front to rear in interfitting relationship, the degree of insertion being sufficient to preserve linear integrity of the assembly.

3. A support system as claimed in claim 1 or 2, wherein the forward portion of the or each elongate member is a rod.

4. A support system as claimed in claim 1 or 2, wherein the forward portion of the or each elongate member is a tube with a closed forward end.

5. A support system as claimed in any of the preceding claims wherein the forward and rearward portions of the or each elongate member are provided with an outer sheath.

6. A support system as claimed in any of claims 1 to 5, wherein the forward portion of the or each elongate member comprises silicon carbide or polycrystalline silicon.

7. A support system as claimed in any of claims 1 to 5, wherein the forward portion of the or each elongate member comprises silicon carbide and the rearward portion thereof comprises sintered alumina or non-sintered aluminium oxide.

8. A support system as claimed in claim 5, wherein the forward portion of the or each elongate member comprises silicon carbide, the rearward portion thereof comprises sintered alumina or non-sintered aluminium oxide and the sheaths comprise vitreous silica.

9. A support system as claimed in any of claims 1 to 5, wherein the rearward portion of the or each elongate member is silicon carbide or polycrystalline silicon.

10. A support system as claimed in any of the preceding claims wherein the or each elongate member is held cantilever fashion by the rearward end thereof in a clamping device.

11. A support system as claimed in any of the preceding claims 1 to 9, wherein the forward portion of the or each elongate member is borne by a wheel or roller assembly.

1 2. A support system as claimed in any of the preceding claims which comprises three of said elongate support members.

1 3. A support system as claimed in any of the preceding claims which comprises two of said elongate support members.

1 4. An elongate support system substantially as hereinbefore described with reference to the accompanying drawing.