Low deflection sputtering target assembly and methods of making same
Described is a design and method for producing a sputtering target assembly with low deflection made from target material solder bonded to composite backing plate with coefficient of thermal expansion (CTE) matching the target material. The composite backing plate is composite configuration composed of at least two different materials with different CTE. The composite backing plate, after plastic deformation, if necessary, has a CTE matching the target material and low and desirable deflection in the bonding process, and therefore, resulting in a low deflection and low stress target material bonded to composite backing plate assembly. The method includes manufacturing composite backing plate with a flat bond surface, heat treating of target blank and composite backing plate to achieve desirable shape of bond surfaces, solder bonding target to a backing plate, and slowly cooling the assembly to room temperature. Matching CTE in both target material and backing plate eliminates the problem of CTE mismatch and prevents the assembly from deflection and internal stress.
1. A method of producing a sputter target assembly, said method comprising the steps of:
a. providing a backing plate composed of a laminated assembly comprising a first layer having a first coefficient of thermal expansion (CTE) and a second layer having a second CTE;
b. providing a sputtering target, said target composed of a third material having a CTE wherein the CTE of said second layer is about 2-5 times greater than the CTE of said first layer and the difference between the CTE of said third material and said first layer is about 7 or less;
c. heating said first and second layers thereby forming a concavity along a top surface of said first layer;
d. providing a liquid bonding medium in said concavity and bonding said target to said first layer along said concavity to provide said sputtering target assembly.
2. The method as recited in claim 1 wherein said first layer has a thickness TA and said second layer has a thickness TB; wherein TA:TB is from about 1:1 to about 100:1.
3. The method as recited in claim 2 wherein said target consists essentially of Si, said first layer consists essentially of Ti and said second layer consists essentially of Al or Al alloys.
4. The method as recited in claim 2 wherein said target consists essentially of W or WSi 2 , said first layer consists essentially of Ti and said second layer consists essentially of Al or Al alloys.
5. The method as recited in claim 2 wherein said target consists essentially of Si, said first layer consists essentially of Mo and said second layer consists essentially of Cu.
6. A method as recited in claim 1 wherein said liquid bonding medium is solder and said step d comprises solder bonding said target to said first layer.