Diffusion-Bonded Sputter Target Assembly with Interlayer
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Solution Overview
Problem
Conventional diffusion bonded sputtering target assemblies with different thermal expansion coefficients between the target and backing plate materials face issues such as bond cracking, delamination, and stress during high-temperature sputtering, resulting in bond strengths typically less than 45 MPa, especially for brittle targets like tungsten.
Innovation Solution
A method involving encapsulating the target with a second metal or alloy having a lower modulus of elasticity and specific thermal expansion properties, diffusion bonding it with a backing plate, and then exposing the sputtering surface, which includes using materials like aluminum or titanium alloys for the interlayer and backing plate, and applying coatings to enhance bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If diffusion bonding is used to join target and backing plate with different thermal expansion coefficients, then bond strength is improved, but bond cracking and delamination occur during high-temperature sputtering
Solution Approach 1:
An interlayer comprising aluminum or aluminum alloy is introduced between the tungsten target and the titanium backing plate. This interlayer acts as a mediator that accommodates the thermal expansion mismatch between the two materials, preventing bond cracking and delamination during high-temperature sputtering operations while maintaining strong bonding.
Solution Approach 2:
The assembly utilizes a composite structure with three different materials (tungsten target, aluminum interlayer, titanium backing plate) selected for their specific properties. The aluminum interlayer provides a modulus of elasticity between that of tungsten and titanium, creating a graded transition that reduces thermal stress during temperature cycling.
2Adaptability or versatility
If materials with different thermal expansion coefficients are used to meet specific sputtering requirements, then adaptability is improved, but stress and deflection increase during operation
Solution Approach 1:
The invention changes the physical parameters of the bonding interface by selecting materials with specific thermal expansion coefficients and moduli of elasticity. The aluminum interlayer has a thermal expansion coefficient and modulus of elasticity that fall between those of tungsten and titanium, creating a gradual transition that reduces thermal stress while maintaining the ability to meet specific sputtering performance requirements.
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 approach achieves bond strengths exceeding 50 MPa, reducing deflection and stress, and maintaining assembly integrity during high-power sputtering operations.
Implementation Method 1
Diffusion bonds are produced by pressing the surfaces into contact while applying heat to induce metallurgical joining and diffusion to varying extent across the bond interface
Implementation Method 2
This heat is dissipated by use of a cooling fluid typically circulated beneath or around a heat conducting backing plate that is positioned in heat exchange relation with the target
Implementation Method 3
different coefficients of thermal expansion (CTE)
Data Source
AI summary
A method of making a diffusion bonded sputter target assembly is provided. A target blank comprising a first metal or alloy has a first surface defining a sputtering surface and a second surface. A second metal or alloy is placed around the target blank. A backing plate is provided adjacent the second metal or alloy that is positioned alongside of the second target surface. This assembly is then diffusion bonded, and a portion of the second metal overlying the sputtering surface of the target is removed to expose the target sputtering surface. W target or W alloy target/Ti or Ti alloy backing plate assemblies are provided with an Al interlayer positioned intermediate the W or W alloy target and backing plate. The assembly has a bond strength exceeding 50 MPa.