Method of producing optically flat surfaces on processed silicon wafers

• US 5,160,560 A
• Filed: 06/02/1988
• Issued: 11/03/1992
• Est. Priority Date: 06/02/1988
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Goodwin, Norman W., Welkowsky, Murray S., Vasudev, P. K., Reif, Philip G.
• Primary Examiner(s): Ball, Michael W.
• Assistant Examiner(s): YODER, MICHELE
• Application Number:
  US07/201,809
• Time in Patent Office: 1,615 Days
• Field of Search: 156/273.1, 156/273.9, 156/272.2, 156/153, 156/154, 156/155, 156/230, 156/241, 156/299, 437/171, 437/225, 51/216 LP, 51/283 R, 148/DIG. 135, 148/DIG. 12
• US Class Current: 156/154
• CPC Class Codes: H01L 21/2007 Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer H01L21/2011 takes precedence; bonding of semiconductor wafers to semiconductor wafers for junction formation H01L21/187
• CPC Class Codes: H01L 21/302 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
• CPC Class Codes: H01L 21/6833 Details of electrostatic chucks
• CPC Class Codes: Y10S 148/012 Bonding, e.g. electrostatic for strain gauges
• CPC Class Codes: Y10S 148/135 Removal of substrate

Abstract

A method for producing optically flat thin semiconductor wafers (12) bonded to a substrate (16). The wafer (12) is bonded without touching the top surface of the wafer (12). Also, the bond is created without the use of pressure. Electrostatic bonding, or contact bonding or both may be employed. After the wafer (12) is bonded, it is then polished to a desired thickness and flatness. After contact bonding and polishing the wafer (12) may then be removed for further processing. The wafer may then be contact bonded to a final substrate (b 34) or electrostatically bonded to a final substrate (42). The contact bonding technique may also be employed as a means for holding the wafer (12) during precise photolithography. The optical flatness achieved permits improved yields over conventional means for securing wafers during photolithography. The electrostatic bonding technique permits extremely thin optically flat silicon wafers to be produced.

Claims

1. A method of producing a device having an optically flat thin silicon wafer bonded to a glass substrate having a coefficient of thermal expansion which is matched to that of the silicon wafer, said method comprising:

coating the silicon wafer on its bottom surface with SiO₂ ;

bringing the bottom surface of the silicon wafer into intimate contact with the substrate;

heating the silicon wafer and the substrate to a temperature which is near the annealing point of the glass substrate;

applying a direct current voltage of about 1,000 volts across the wafer and the substrate until the current thereby produced lowers and stabilizes, whereby an electrostatic field assisted thermal bond is created between the wafer and the substrate; and

polishing the silicon wafer to achieve optical flatness.

2. The method of claim 1 further including the step of coating the bottom surface of the silicon wafer with a nitride barrier layer before the step of coating with SiO₂.