Multi-Zone Electrostatic Chuck Cooling for Uniform Wafer Temperature
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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 inner and outer zone backside gas pressure sources, evaporators, and a refrigeration loop with zone-specific temperature sensors and processors to simulate and control heat transfer, ensuring agile and uniform temperature management across the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling systems are used with high RF power levels, then cooling capacity is sufficient, but wafer temperature drifts upward significantly before stabilizing
Solution Approach 1:
The system performs preliminary cooling of the electrostatic chuck before wafer introduction to establish a cold thermal reservoir. This preliminary action ensures that when the wafer is introduced and RF power is applied, the chuck is already positioned to rapidly absorb heat, preventing temperature drift rather than reacting to it after it begins.
Solution Approach 2:
The cooling system is segmented into multiple independent coolant flow channels corresponding to different radial zones of the electrostatic chuck. This segmentation allows independent temperature control of different chuck zones, enabling the system to maintain uniform temperature distribution across the wafer surface even under high RF power conditions where heat generation is non-uniform.
2Temperature
If conventional single-phase cooling is used, then system simplicity is maintained, but temperature uniformity across the wafer degrades under high RF heat load
Solution Approach 1:
The electrostatic chuck is divided into multiple radial cooling zones with independent coolant flow control. Each zone has its own flow rate regulation, allowing the system to compensate for non-uniform heat generation across the wafer surface. This segmentation enables precise local temperature control to maintain overall temperature uniformity under high RF power conditions.
Solution Approach 2:
The cooling system implements dynamic flow rate adjustment for each radial zone based on real-time temperature measurements and predicted heat load variations. The system continuously modulates coolant flow rates to maintain optimal temperature uniformity as process conditions change, rather than using fixed flow rates.
3Measurement precision
If temperature probes are introduced near the wafer for accurate sensing, then temperature measurement accuracy improves, but parasitic RF fields are created that distort the uniform environment
Solution Approach 1:
The system uses the backside of the wafer and the electrostatic chuck as an intermediary medium for temperature sensing. Temperature probes are positioned on the chuck backside rather than near the wafer front surface, allowing indirect temperature measurement of the wafer-chuck interface. This intermediary approach enables accurate temperature sensing without introducing probes into the high RF field region near the wafer front surface.
Solution Approach 2:
The electrostatic chuck incorporates a porous structure with embedded coolant channels and temperature sensors on its backside. This porous design allows thermal conduction from the wafer to the chuck for accurate temperature sensing while maintaining electrical isolation and avoiding parasitic RF effects that would occur with direct probe contact near the wafer surface.
4Productivity
If high RF source power is applied to achieve high etch rates, then productivity increases, but temperature control becomes more difficult and etch rate distribution uniformity degrades
Solution Approach 1:
The cooling system is divided into multiple independent radial zones with separate flow rate control, allowing the system to maintain uniform temperature distribution across the wafer even when operating at high RF power levels. Each zone can be independently adjusted to compensate for non-uniform heat generation, preserving etch rate uniformity while enabling high productivity through high power operation.
Solution Approach 2:
The system dynamically adjusts coolant flow rates, temperatures, and pressures as controllable parameters to maintain optimal temperature uniformity across the wafer surface. By actively modulating these thermal parameters in response to measured temperature variations and predicted heat load changes, the system enables operation at high RF power levels while maintaining etch rate distribution uniformity.
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 solution enables precise and uniform temperature control, maintaining etch rate distribution uniformity even under high RF heat loads, enhancing process stability and efficiency by utilizing two-phase cooling and agile temperature feedback control.
Implementation Method 1
The refrigeration loop has inner and outer expansion valves for controlling flow of coolant through the inner and outer evaporators respectively
Implementation Method 2
a thermal model capable of simulating heat transfer through the inner and outer zones, respectively, between the evaporator and the surface
Implementation Method 3
inner and outer zone backside gas pressure sources coupled to the electrostatic chuck for applying a thermally conductive gas under respective pressures to respective inner and outer zones of a workpiece-surface interface
Data Source
AI summary
A plasma reactor having a reactor chamber and an electrostatic chuck having a surface for holding a workpiece inside the chamber includes inner and outer zone backside gas pressure sources coupled to the electrostatic chuck for applying a thermally conductive gas under respective pressures to respective inner and outer zones of a workpiece-surface interface formed whenever a workpiece is held on the surface, and inner and outer zone heat exchangers coupled to respective inner and outer zones of said electrostatic chuck. The reactor further includes inner and outer zone temperature sensors in inner and outer zones of the electrostatic chuck and a thermal model capable of simulating heat transfer through the inner and outer zones, respectively, between the evaporator and the surface based upon measurements from the inner and outer temperature sensors, respectively. Inner and outer zone agile control processors coupled to the thermal model govern the inner and outer zone backside gas pressure sources, respectively, in response to predictions from the model of changes in the respective pressures that would bring the temperatures measured by the inner and outer zone sensors, respectively, closer to a desired temperature.