Abstract A wafer of semiconductive material used to form beam lead devices is temporarily bonded face down to a sapphire base member with a low melting temperature wax. A layer of chromium or titanium then is vacuum deposited onto the back of the chip followed by vacuum deposition of a layer of gold. The chromium forms a good low temperature bond to the silicon and the gold in turn forms a good low temperature bond to the chromium so that the gold-chromium layers adhere tightly to the silicon through subsequent etching and separation steps. After the wafer is separated into individual chips or dice, a gold-silicon eutectic bond is formed by heating the chips to the eutectic temperature, with the gold-silicon alloying taking place by a diffusion of the gold through the chromium layer.
The method according to claim 1 including the further step of bonding the chips to a substrate by both thermal compression bonding of the beam leads and eutectic bonding of the silicon chip.
Claim 2
Dependent Claim
21 words
The method according to claim 1 wherein the step of removing said wafer from the base member comprises dissolving the cement.
Claim 3
Dependent Claim
21 words
The method according to claim 1 further including the step of alloying the gold to the silicon through the first layer.
Claim 4
Dependent Claim
22 words
The method according to claim 2 wherein said eutectic bonding step comprises heating said chips to a temperature in excess of 370*C.
Claim 5
Dependent Claim
19 words
The method according to claim 5 wherein the temperature to which said chips are heated is 425* to 450*C.
Claim 6
Dependent Claim
33 words
The method according to claim 1 wherein the step of forming said first layer of metal and the step of forming the layer of gold both comprise steps of vacuum depositing said layers.
Claim 7
Dependent Claim
55 words
The method according to claim 7 wherein the step of vacuum depositing said first layer of metal is used to deposit a layer having a thickness of 100 to 200 angstroms and the step of vacuum depositing the gold layer is used to deposit a layer of gold having a thiCkness of approximately 10,000 angstroms.
Claim 8
Dependent Claim
33 words
The method according to claim 8 further including the step of heating said chips to a temperature in excess of 370*C to form a gold-silicon eutectic alloy through the first layer of metal.
Claim 9
Dependent Claim
19 words
The method according to claim 9 wherein the temperature to which said chips are heated in 425* to 450*C.