Graded Interlayer for Sputtering Target Bonding
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Solution Overview
Problem
The challenge in bonding sputtering targets to backing plates with dissimilar coefficients of thermal expansion (CTE) is that thermal stresses can lead to de-bonding or cracking, especially at elevated temperatures, due to the large CTE mismatch between materials like tungsten and conventional backing plate materials such as aluminum or copper alloys.
Innovation Solution
A sputtering target assembly is created with an interlayer having a property gradient, formed using additive manufacturing techniques, where the interlayer's composition gradually changes from a higher concentration of one material near the target to a higher concentration of another material near the backing plate, reducing the CTE mismatch and thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-material interlayer is used between target and backing plate, then the bonding process is simple, but thermal stresses cause de-bonding or cracking at elevated temperatures
Solution Approach 1:
The interlayer is designed with spatially varying material composition, where the first portion near the target has higher concentration of first material and the second portion near the backing plate has higher concentration of second material. This local quality variation creates a gradient in coefficient of thermal expansion (CTE) that matches the thermal expansion characteristics of adjacent components, reducing thermal stresses during heating and cooling cycles while maintaining bonding reliability.
Solution Approach 2:
The interlayer is constructed as a composite structure with at least two different materials distributed in a gradient fashion. This composite approach allows the interlayer to simultaneously accommodate the thermal expansion differences between the target and backing plate, preventing de-bonding and cracking while maintaining structural integrity at elevated temperatures.
2Device complexity
If materials with large CTE mismatch are bonded directly, then the assembly is structurally simple, but thermal stresses lead to cracking and de-bonding
Solution Approach 1:
The gradient interlayer acts as an intermediary component between the target and backing plate, with its composition gradually transitioning from first material near the target to second material near the backing plate. This intermediate structure provides a gradual transition in CTE, reducing the thermal shock and stress concentration that would occur with direct bonding of dissimilar materials, thereby preventing cracking and de-bonding.
Solution Approach 2:
The interlayer's material composition parameter is changed gradually across its thickness, creating a continuous or near-continuous gradient in CTE. This parameter variation allows the interlayer to adapt to the thermal expansion characteristics of both adjacent components, reducing thermal stresses and preventing harmful effects like cracking while maintaining a relatively simple overall assembly structure.
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 effectively reduces thermal stresses and prevents cracking, enabling a strong and stable bond between the target and backing plate, even at high temperatures, by smoothing the CTE gradient across the interface.
Implementation Method 1
The challenge in bonding sputtering targets to backing plates with dissimilar coefficients of thermal expansion (CTE) is that thermal stresses can lead to de-bonding or cracking, especially at elevated temperatures, due to the large CTE mismatch between materials like tungsten and conventional backing plate materials such as aluminum or copper alloys
Data Source
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AI summary
A sputtering target assembly includes a sputtering target having a rear surface, a backing plate having a front surface, and an interlayer disposed between the target and the backing plate. The interlayer includes a first interlayer portion disposed proximate the target material rear surface, and a second interlayer portion disposed proximate the backing plate front surface. The first interlayer portion is formed of a first mixture containing a first material and a second material and having a higher concentration of the first material than the second material, and the second interlayer portion is formed of a second mixture containing the first material and the second material and having a higher concentration of the second material than the first material. A method of making is also provided.