RF Sputtering Rotary Target for Uniform Solar Cell Deposition
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Solution Overview
Problem
Conventional sputtering systems for solar cell manufacturing face issues with non-uniform target erosion and film deposition due to standing waves and arcing, which affect the quality and efficiency of solar cells, especially when using high-efficiency requirements that DC-pulsed sputtering cannot meet.
Innovation Solution
An RF sputtering system with a rotary target is employed, where RF power is split and fed to both ends of the target, and a capacitance tuner is used to achieve a flat voltage profile, combined with a static magnetic field to ensure uniform target erosion and film deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high DC voltage is applied to the target, then sputtering deposition rate is improved, but charge build-up and arcing occur causing plasma instability
Solution Approach 1:
The patent applies periodic action by using RF (radio frequency) power instead of continuous DC voltage. The RF power source operates at frequencies typically between 13-60 MHz, creating alternating electric fields that prevent charge accumulation on the target surface while maintaining continuous sputtering. This periodic reversal of electric field direction eliminates the arcing problem inherent in DC sputtering while preserving high deposition rates.
Solution Approach 2:
The patent changes the fundamental parameter from DC voltage to RF voltage. By transitioning from direct current to radio frequency alternating current, the system achieves both high deposition rates and plasma stability. The RF parameters (frequency, power level) can be optimized independently to control both productivity and reliability aspects of the sputtering process.
2Manufacturing precision
If conventional sputtering is used, then film deposition is achieved, but non-uniform target erosion and nodule formation occur
Solution Approach 1:
The patent introduces dynamics by rotating the target during sputtering. The rotary target mechanism continuously rotates the target material, ensuring that all regions of the target are exposed uniformly to the plasma. This dynamic rotation prevents localized erosion and nodule formation, maintaining consistent target composition and producing uniform film deposition across the substrate.
Solution Approach 2:
The rotating target ensures continuous and uniform exposure of fresh target material to the plasma throughout the sputtering process. This continuous action prevents the formation of eroded regions and nodules that would occur with stationary targets, maintaining both target composition stability and film uniformity over extended deposition periods.
3Reliability
If DC-pulsed sputtering is used to prevent arcing, then plasma stability is improved, but low-damage requirement for high-efficiency solar cells cannot be met
Solution Approach 1:
The patent changes from DC-pulsed parameters to RF parameters, operating at frequencies typically between 13-60 MHz. This parameter change provides continuous plasma stability without the pulsed interruptions that cause damage to sensitive solar cell structures. The RF regime maintains stable plasma conditions while producing lower-damage films suitable for high-efficiency solar cells.
Solution Approach 2:
Instead of using pulsed DC action, the patent employs continuous RF periodic action. The high-frequency alternating field provides continuous plasma maintenance without the start-stop nature of pulsed DC, resulting in gentler film deposition that meets the low-damage requirements of high-efficiency solar cells while maintaining plasma stability.
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 results in a more uniform film deposition and extended target life, reducing maintenance costs and improving the efficiency of solar cell production by minimizing arcing and nodule formation, while meeting the low-damage requirements for high-efficiency solar cells.
Implementation Method 1
an RF power source coupled to at least one end of the rotary target to enable RF sputtering
Implementation Method 2
a rotary target situated inside the reaction chamber which is capable of rotating about a longitudinal axis
Implementation Method 3
The RF splitter is configured to split output of the RF power source into two portions and feed each of the two portions to one end of the rotary target
Implementation Method 4
a capacitance tuner is used to achieve a flat voltage profile
Implementation Method 5
a plurality of magnets configured to generate a static magnetic field between the rotary target and a carrier that carries a plurality of solar cells
Data Source
AI summary
One embodiment of the present invention provides a sputtering system for large-scale fabrication of solar cells. The sputtering system includes a reaction chamber, a rotary target situated inside the reaction chamber which is capable of rotating about a longitudinal axis, and an RF power source coupled to at least one end of the rotary target to enable RF sputtering. The length of the rotary target is between 0.5 and 5 meters.