High-Strength Molybdenum Sputtering Target Assembly for Thermal Stress
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Solution Overview
Problem
Molybdenum sputtering targets experience thermal stress at the bonding interface with copper alloy backing plates due to differing coefficients of thermal expansion, leading to debonding or cracking during cooling and sputtering duty cycles.
Innovation Solution
Selecting molybdenum powder for sputtering targets based on high transverse rupture strength (TRS) and forming the targets through vacuum hot pressing, followed by diffusion bonding to a copper alloy backing plate with an optional aluminum interlayer, to enhance structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If molybdenum target is diffusion bonded to copper alloy backing plate, then bonding strength is improved, but thermal stress causes debonding or cracking
Solution Approach 1:
The patent introduces an intermediate layer between the molybdenum target and copper alloy backing plate. This intermediate layer acts as a stress buffer that accommodates the thermal expansion mismatch between the two materials, preventing thermal stress from causing debonding or cracking while maintaining bonding strength.
Solution Approach 2:
The patent creates a composite structure consisting of molybdenum target, intermediate layer, and copper alloy backing plate. This composite design allows each layer to contribute its specific properties: molybdenum provides sputtering functionality, the intermediate layer provides thermal stress management, and the copper alloy provides thermal conductivity and structural support.
2Productivity
If high power is applied to sputter molybdenum target, then deposition rate is improved, but thermal stress increases causing cracking
Solution Approach 1:
The intermediate layer serves as a stress buffer that absorbs and distributes thermal stress generated during high-power sputtering operations. This allows the target to operate at high power levels for improved deposition rate while the intermediate layer prevents thermal stress from causing cracking.
Solution Approach 2:
The patent modifies the thermal and mechanical parameters of the target assembly by introducing the intermediate layer with specific thermal expansion properties. This changes the overall thermal stress distribution in the system, allowing high-power operation without compromising structural integrity.
3Quantity of substance
If molybdenum target with high CTE mismatch is used, then material purity is maintained, but thermal stress at bonding interface increases
Solution Approach 1:
The intermediate layer acts as a mediator that decouples the thermal expansion mismatch between pure molybdenum and copper alloy backing plate. This allows the use of high-purity molybdenum material while the intermediate layer absorbs the thermal stress that would otherwise be generated by the CTE difference.
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
The method results in a molybdenum sputtering target assembly with a lower likelihood of cracking, maintaining a strong bond and ensuring durability during high-power sputtering operations.
Implementation Method 1
vacuum hot pressing a sample high purity powder molybdenum from a source to form a specimen
Implementation Method 2
a copper alloy backing plate diffusion bonded to the sputtering target
Implementation Method 3
molybdenum and copper alloys have very different coefficients of thermal expansion (CTE). During cooling down from either the diffusion bonding temperature or the duty cycle of the sputtering, the length change of a molybdenum target blank is much smaller than that of copper alloy backing plate
Implementation Method 4
Physical vapor deposition methodologies are used extensively for forming thin films of material over a variety of substrates
Implementation Method 5
sputtered material 22 is displaced from the sputtering surface 16 of target 14 and used to form a coating (or thin film) 20 over substrate 18
Data Source
AI summary
A molybdenum sputtering target assembly includes molybdenum sputtering target diffusion bonded directly to a molybdenum backing plate. The molybdenum sputtering target consists of molybdenum and the molybdenum backing plate consists of molybdenum or a molybdenum alloy.