Cu-Ga Alloy Sputtering Target Granular Microstructure
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Solution Overview
Problem
The increasing size of thin film solar cells leads to thermal expansion issues in cylindrical sputtering targets, causing cracking during bonding or heat application, which is exacerbated by the anisotropic strength and thermal stress of columnar crystal structures in existing Cu-Ga alloy targets.
Innovation Solution
Employing a centrifugal or continuous casting method to form Cu-Ga alloy cylindrical sputtering targets with a solidified structure composed of granular crystals, which have a uniform coefficient of thermal expansion in all directions, reducing the likelihood of cracking and segregation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a casting method is used to manufacture Cu-Ga alloy sputtering target, then oxygen concentration is reduced and sputter rate is improved, but the target develops columnar crystal structure that causes cracking under thermal stress
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate during casting to be within 1-50°C/s. This specific parameter range transforms the crystal structure from columnar to granular, fundamentally changing the material's thermal expansion behavior and crack resistance properties while maintaining the casting manufacturing method
Solution Approach 2:
The patent creates a composite microstructure by forming granular crystal grains within the Cu-Ga alloy matrix. This granular structure acts as a composite at the microscale, where the uniform grain distribution prevents stress concentration and crack propagation that occur in columnar structures
2Productivity
If the target size is increased to match larger thin film solar cells, then manufacturing efficiency is improved, but thermal expansion causes cracking during bonding
Solution Approach 1:
By changing the cooling rate parameter to 1-50°C/s, the patent creates a granular crystal structure that is insensitive to thermal expansion stresses. This allows the target to be manufactured in large sizes for high productivity while maintaining crack resistance during bonding and operation
3Manufacturing precision
If Ga concentration is increased to 25% or higher to improve film quality, then film performance is enhanced, but brittleness increases and cracking becomes highly likely
Solution Approach 1:
The patent changes the crystallization parameter (cooling rate) to produce granular grains regardless of Ga concentration. This parameter change decouples the relationship between high Ga content and brittleness, allowing 25% or higher Ga concentration for film quality without the associated cracking problems
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 use of granular crystal structures in Cu-Ga alloy targets minimizes cracking during sputtering film formation, decreases manufacturing costs, and enhances productivity by maintaining uniform thermal expansion and preventing Ga segregation.
Implementation Method 1
a solidified structure of the Cu-Ga alloy is made up of granular crystal grains
Implementation Method 2
have a uniform coefficient of thermal expansion in all directions
Data Source
Figure 1~2
Figure 3
Figure 4(A)~4(D)
AI summary
The cylindrical sputtering target is a Cu-Ga alloy cylindrical sputtering target made of a Cu alloy containing 15 atom% to 35 atom% of Ga, in which the Cu alloy has a granular crystal structure.