Cu-Ga Sputtering Target Grain Size Control
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Solution Overview
Problem
Conventional Cu-Ga sputtering targets have high oxygen content and large grain size, leading to abnormal discharges and reduced photoelectric conversion efficiency in CIGS thin-film solar cells.
Innovation Solution
A sputtering target with a Ga content of 20-30 at%, an oxygen content of 100 ppm or lower, and an average grain size of 100 µm or less, exhibiting both γ and ζ phases in X-ray diffraction, produced by sintering a mixture of pure Cu and Cu-Ga alloy powders under atmospheric pressure in a reducing atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Cu-Ga sputtering target is produced by hot pressing, then the oxygen content is reduced to 350-400 ppm, but the average grain size increases to 5-30 μm which causes abnormal discharges
Solution Approach 1:
The patent changes the sintering parameters including temperature (700-900°C), atmosphere (reducing atmosphere with H2 or CO), and time to achieve optimal grain size control. By carefully controlling these parameters, the patent reduces grain size to 100 μm or less while maintaining low oxygen content of 100 ppm or lower, thereby suppressing abnormal discharges during sputtering.
2Reliability
If the Ga content in CuGa target is increased to 1-40 at% to form Cu-Ga alloy layer, then the open circuit voltage increases and peeling-off is prevented, but the phase composition becomes complex with difficulty in controlling grain size and oxygen content
Solution Approach 1:
The patent specifies a local composition range of Ga content at 20-30 at% within the CuGa alloy target. This localized compositional control ensures the formation of desired γ and ζ phases while maintaining grain size and oxygen content within acceptable ranges, thereby achieving high open circuit voltage without excessive complexity in phase composition.
3Reliability
If the average grain size is reduced to 5-30 μm to suppress abnormal discharges, then the sputtering uniformity improves, but the oxygen content increases to 350-400 ppm which reduces photoelectric conversion efficiency
Solution Approach 1:
The patent employs a reducing atmosphere (inert environment) during sintering, using H2 or CO gas to create oxygen-deficient conditions. This allows the formation of fine-grained structure (100 μm or less) while simultaneously maintaining low oxygen content (100 ppm or lower) in the target, thereby achieving both good sputtering uniformity and high photoelectric conversion efficiency.
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
Significantly reduces abnormal discharges and improves photoelectric conversion efficiency by maintaining low oxygen content and small grain size, enhancing the performance of CIGS thin-film solar cells.
Implementation Method 1
a sputtering method has been proposed for forming light-absorbing layers... first an In film is deposited by sputtering using an In target, and then a Cu-Ga binary alloy film is deposited on this In film by sputtering using a Cu-Ga binary alloy target
Implementation Method 2
produced by sintering a mixture of pure Cu and Cu-Ga alloy powders under atmospheric pressure in a reducing atmosphere
Data Source
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AI summary
Provided are a sputtering target composed of a Cu-Ga sintered compact that has a further reduced oxygen content and can suppress abnormal discharges, and a method for producing the same. The sintered compact has a component composition containing a Ga content of 20 at% or higher and less than 30 at% with the balance being Cu and inevitable impurities, and has an oxygen content of 100 ppm or lower and an average grain size of 100 µm or less, and exhibits the diffraction peaks assigned to the γ and ζ phases of CuGa as observed in X-ray diffraction, wherein the main peak intensity of the diffraction peaks assigned to the ζ phase is 10% or higher relative to that of the diffraction peaks assigned to the γ phase.