Electrostatic Chuck Thermal Loops for Uniform Wafer Cooling
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Solution Overview
Problem
Conventional cooling systems for plasma reactors face challenges in maintaining uniform wafer temperatures under high RF heat loads, leading to temperature non-uniformities and inefficiencies, which affect etch rate distribution and process control.
Innovation Solution
A plasma reactor design incorporating a backside gas pressure source, an evaporator within the electrostatic chuck, and a refrigeration loop with an expansion valve to control coolant flow, allowing for agile temperature control through the latent heat of vaporization, and a thermal model to predict and adjust temperature settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling systems are used to regulate wafer temperature, then the system structure is simple, but temperature uniformity across the wafer deteriorates under high RF heat loads
Solution Approach 1:
The cooling system is segmented into multiple independent thermal zones (first and second cooling zones) with separate coolant flow paths, allowing independent temperature control for different regions of the electrostatic chuck to achieve uniform wafer temperature under high RF heat loads
Solution Approach 2:
Different regions of the electrostatic chuck are provided with different cooling characteristics through the segmented cooling zones, with each zone having optimized coolant flow rates and temperatures tailored to the specific thermal requirements of that region, improving overall temperature uniformity
2Ease of operation
If refrigeration systems with thermal cycles are used, then cooling capability is provided, but temperature control agility and precision deteriorate due to heat propagation delays
Solution Approach 1:
The system performs preliminary temperature adjustments by modifying coolant flow rates and temperatures in advance before RF processing begins, and maintains temperature stability throughout processing by continuously monitoring and adjusting cooling parameters, eliminating temperature drift without requiring rapid changes during processing
Solution Approach 2:
Temperature sensors provide real-time feedback on wafer and electrostatic chuck temperatures to the control system, which continuously adjusts coolant flow rates and temperatures in each cooling zone to maintain desired temperature uniformity, enabling precise and agile temperature control
3Productivity
If high RF power is applied to achieve high etch rates, then productivity increases, but temperature non-uniformities worsen
Solution Approach 1:
The segmented cooling system provides locally optimized cooling to different regions of the electrostatic chuck, with each cooling zone independently adjusted to compensate for non-uniform RF heat generation, allowing high RF power to be applied while maintaining temperature uniformity across the wafer
Solution Approach 2:
The system dynamically adjusts cooling parameters (coolant flow rates, temperatures, and distribution) to match the thermal load generated by high RF power, enabling sustained high etch rates without temperature non-uniformities by continuously optimizing the cooling characteristics
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 design achieves precise and uniform temperature control across the wafer, maintaining etch rate uniformity even under high RF heat loads, enhancing process stability and efficiency.
Implementation Method 1
allowing for agile temperature control through the latent heat of vaporization
Implementation Method 2
a backside gas pressure source coupled to the electrostatic chuck for applying a thermally conductive gas under a selected pressure into a workpiece-surface interface
Data Source
AI summary
A plasma reactor with a reactor chamber and an electrostatic chuck having a surface for holding a workpiece inside the chamber includes a backside gas pressure source coupled to the electrostatic chuck for applying a thermally conductive gas under a selected pressure into a workpiece-surface interface formed whenever a workpiece is held on the surface, and an evaporator inside the electrostatic chuck and a refrigeration loop having an expansion valve for controlling flow of coolant through the evaporator. The reactor further includes a temperature sensor in the electrostatic chuck, a thermal model capable of simulating heat transfer between the evaporator and the surface based upon measurements from the temperature sensor and an agile control processor coupled to the thermal model and governing the backside gas pressure source in response to predictions from the model of changes in the selected pressure that would bring the temperature measured by the sensor closer to a desired temperature.