Non-bonded Semiconducting Target for Sputtering Cathode
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Solution Overview
Problem
The existing sputtering process for cadmium telluride-based thin film photovoltaic devices faces challenges in achieving uniformity due to nodule formation on bonded semiconducting targets, which affects deposition rates and film characteristics, leading to variability in large-scale manufacturing.
Innovation Solution
The use of non-bonded semiconducting targets, such as cadmium sulfide, within a sputtering cathode, where the target is held by a non-bonding attachment mechanism, allowing it to maintain a stable sputtering temperature and reducing nodule formation, resulting in more uniform thin film layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a semiconducting target is bonded to a water cooled backing plate using indium solder or conductive epoxy, then good thermal and electrical contact is achieved, but nodule formation occurs on the target surface during sputtering
Solution Approach 1:
The patent removes the bonding material (indium solder or conductive epoxy) from between the target and backing plate, eliminating the source of nodule formation while maintaining thermal contact through direct mechanical contact and compression
Solution Approach 2:
The patent changes the thermal contact mechanism from bonded contact to compression contact, using spring-loaded arms to apply continuous pressure between the target and backing plate, maintaining thermal contact without bonding materials
2Temperature
If a semiconducting target is bonded to the backing plate, then thermal contact is maintained, but the target requires complex bonding processes and cannot be easily replaced
Solution Approach 1:
The patent divides the target assembly into separable components: the semiconducting target can be independently removed and replaced from the backing plate, eliminating the need to replace the entire bonded assembly
Solution Approach 2:
The patent introduces spring-loaded arms that provide continuous compression force, allowing the target to be held firmly during operation but easily removed when needed, transitioning from static bonded contact to dynamic compression contact
3Productivity
If the semiconducting target erodes during sputtering, then material is deposited on substrates, but nodules form on the target surface that change deposition rate and affect film characteristics
Solution Approach 1:
The patent removes bonding materials that cause nodule formation, eliminating the source of deposition rate variations and film uniformity problems
Solution Approach 2:
The patent changes the target-backing plate interface from bonded to compression contact, preventing nodule formation and maintaining consistent deposition rates throughout the sputtering process
4Reliability
If nodules form on the target surface, then arcs occur in the sputtering chamber, but the bonded target structure cannot be easily modified
Solution Approach 1:
The patent removes bonding materials that create nodule formation sites, eliminating the source of arcs in the sputtering chamber
Solution Approach 2:
The patent changes the interface structure from bonded to compression contact, creating a smoother target surface that prevents arc formation while simplifying the overall target 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 leads to the formation of more uniform cadmium sulfide and cadmium tin oxide layers, with reduced nodule formation and arc occurrence, enhancing the consistency of thin film deposition across substrates and throughout the manufacturing process, while allowing for easier target interchange and potential power savings.
Implementation Method 1
The CdS layer, along with other layers (e.g., a transparent conductive oxide layer of cadmium tin oxide) can be formed via a sputtering process (also know as physical vapor deposition) where the source material is supplied from a semiconducting target
Implementation Method 2
The bond provides good thermal and electrical contact between the semiconducting target and the water cooled backing plate. Thus, the heat created by the plasma on the opposite side of the semiconducting target can be dissipated and carried away from the target by the water cooled backing plate
Data Source
AI summary
A sputtering cathode is generally provided. The sputtering cathode can include a semiconducting target (e.g., a cadmium sulfide target, a cadmium tin oxide target, etc.) defining a sputtering surface and a back surface opposite to the sputtering surface. A backing plate can be positioned facing the back surface of the target and non-bonded to the back surface of the target. A non-bonding attachment mechanism can removably hold the target within the sputtering cathode such that the back surface is facing the backing plate during sputtering.