Tungsten Sputtering Target Interlayer Bonding for CTE Mismatch
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Solution Overview
Problem
The challenge is bonding a tungsten containing sputtering target to a copper alloy backing plate without de-bonding or cracking due to the significant difference in their coefficients of thermal expansion, which leads to thermal stress during the cooling phase after bonding.
Innovation Solution
A sputtering target assembly is created with a tungsten containing target and a copper alloy backing plate, where an interlayer comprising an adhesion layer, a first copper layer, and a second copper layer is positioned between them, and diffusion bonding is used, with the second copper layer having a thickness of about 0.1 inches to 0.3 inches, to minimize thermal stress and enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If diffusion bonding is used to join tungsten target to copper alloy backing plate, then bonding strength is improved, but thermal stress causes de-bonding or cracking due to CTE mismatch
Solution Approach 1:
An interlayer comprising an adhesion layer and copper layers is introduced between the tungsten target and copper alloy backing plate. This interlayer acts as a mediator that gradually transitions the CTE from tungsten to copper alloy, reducing thermal stress during cooling while maintaining bonding strength. The adhesion layer provides strong bonding to both tungsten and copper, preventing de-bonding and cracking.
Solution Approach 2:
The bonding interface is transformed from a direct two-material joint to a composite multi-layer structure consisting of tungsten target, adhesion layer, copper layers, and copper alloy backing plate. This composite structure allows each layer to contribute its properties: tungsten provides target functionality, adhesion layer provides bonding, copper layers provide thermal management and CTE transition, and backing plate provides structural support.
2Reliability
If the second copper layer thickness is increased, then thermal stress is reduced and bonding reliability is improved, but device complexity and material usage increase
Solution Approach 1:
The thickness of the second copper layer is optimized to a specific range (0.04 inches to 0.12 inches or 0.1 inches to 0.3 inches) to achieve the desired balance. This parameter optimization ensures sufficient thermal stress reduction and bonding reliability while controlling device complexity and material usage. The adhesion layer thickness is also controlled (1 micrometer to 10 micrometers) to maintain effectiveness without excessive complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration achieves a bond strength of at least 10 ksi (68.9 MPa) and prevents de-bonding or cracking, ensuring the sputtering target assembly remains intact during physical vapor deposition processes, with a bond percentage of at least 98% as determined by C-Scan imaging.
Implementation Method 1
an interlayer positioned between and diffusion bonding the tungsten containing sputtering target and copper alloy backing plate
Data Source
AI summary
A sputtering target assembly comprises a tungsten containing sputtering target, a copper alloy backing plate attached to the tungsten containing sputtering target, and an interlayer positioned between and diffusion bonding the tungsten containing sputtering target and copper alloy backing plate. The tungsten containing sputtering target comprises 0 wt. % to about 50 wt. % of an alloying component and the balance is tungsten. The alloying component is titanium, aluminum or molybdenum. A method of making is also provided.