Method for low temperature bonding of silicon and silicon on sapphire and spinel to nickel and nickel steel and apparatus using such _a bonding technique

摘要

A method for low temperature bonding of silicon and silicon on sapphire and spinel to nickel and nickel steel using a layered structure with an aluminum interface between the nickel or nickel steel and the silicon. The bonding is achieved in a reducing atmosphere using a temperature of 640 to 650 degrees C. with a pressure of 100 to 150 psi on the layered structure for a period of approximately five minutes with a subsequent cooling to avoid strains in the bond. An example of the transducer apparatus utilizing such a bonding technique includes a nickel steel housing and a silicon on spinel transducer wafer having a silicon peripheral pad with an aluminum layer bonding the silicon pad to the nickel steel housing.PPBACKGROUND OF THE INVENTION PP1. Field of the InventionPPThe present invention relates to bonding techniques. More specifically, the present invention is directed to a method for bonding silicon to nickel and a transducer apparatus utilizing such a bonding technique.PP 2. Description of the Prior ArtPPThe development of transducers such as those shown in U.S. Pat. Nos. 3,230,763 and 3,537,319 has led to a composite structure using silicon on sapphire (SOS). The sapphire with a silicon epitaxial layer grown on it may be used for pressure transducers and provides, in effect, strain sensitive resistors. The strain sensitive elements are shaped on the sapphire wafer by a suitable etching process with the resulting wafer being cut into a desired configuration by a diamond saw. A recent development has taken advantage of an improved stress transmission characteristic which is produced by having the composite transducer structure utilize silicon on spinel. Such a structure results in a superior transducer while retaining its electrical insulating characteristics. The production of such silicon on sapphire and silicon on spinel is a well-known technique and is discussed in the Journal of Crystal Growth (1971) in an article by G. W. Cullen on pages 107 to 125 entitled "The preparation and Properties of Chemically Vapor Deposited Silicon on Sapphire and Spinel." In both of these structures the composite end product must be ultimately bonded to a metal support or transducer housing in order to produce a viable transducer. The poor wettability of spinel and sapphire by many metals is well-known and offers a serious problem to the bonding of these materials to metals as well as to ceramics and glasses. One prior art attempt to bond sapphire to metal involved the growing of multiple metallic layers on one or both of the elements and then fusing them together at relatively high temperatures. However, the high temperatures involved can damage the strain elements deposited on the sapphire. On the other hand, the bonding of silicon on spinel to metal remains a problem which has limited the use of the corresponding composite transducer in a useful product.PPSUMMARY OF THE INVENTIONPPAn object of the present invention is to produce a method for bonding silicon to nickel.PP Another of the present invention is to produce an improved transducer apparatus utilizing a novel method of bonding of silicon to nickel.PP In accomplishing these and other objects, there has been provided, in accordance with the present invention, a low temperature bonding method for bonding silicon to nickel by introducing therebetween a layer of aluminum and subjecting the layered structure to a pressure of 100 to 150 psi at a temperature of 640 to 650 degrees C. for a period of approximately five minutes in a reducing atmosphere. An example of a transducer apparatus utilizing such a bonding technique includes a nickel steel housing and a silicon on spinel transducer wafer having silicon peripheral pads with an aluminum layer bonding the silicon pads to the nickel steel housing.