Multi-Zone Electrostatic Chuck Cooling for Wafer Temperature Uniformity
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Solution Overview
Problem
Conventional plasma reactors face challenges in maintaining uniform wafer temperature and etch rate distribution due to inefficiencies in cooling systems, leading to temperature drift and non-uniformities under high RF heat loads, which affect the precision of plasma etching processes.
Innovation Solution
A plasma reactor design incorporating inner and outer zone temperature sensors, thermal models, and agile control processors to manage backside gas pressure and refrigeration flow, enabling precise temperature control through the use of thermally conductive gases and a two-phase refrigeration loop for efficient heat transfer.
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 drift occurs under high RF heat loads leading to non-uniform wafer temperature
Solution Approach 1:
The electrostatic chuck is divided into multiple independent temperature zones (center zone and peripheral zones) with separate cooling channels. Each zone has its own temperature sensor and control mechanism, allowing independent temperature regulation to achieve uniform temperature distribution across the wafer surface under high RF heat loads.
Solution Approach 2:
The system dynamically adjusts cooling parameters including coolant flow rate, coolant temperature, and zone-specific cooling power based on real-time temperature measurements from multiple sensors. This adaptive parameter adjustment compensates for RF heat load variations and maintains stable temperature control.
2Measurement precision
If temperature probes are introduced near the wafer for accurate temperature sensing, then temperature measurement precision improves, but parasitic RF fields are created that distort the plasma environment
Solution Approach 1:
Temperature sensors are positioned in the electrostatic chuck structure rather than directly in the plasma chamber near the wafer. The chuck acts as an intermediary medium, allowing indirect temperature measurement of the wafer through thermal conduction from the wafer-backside interface, thereby avoiding direct exposure of sensors to parasitic RF fields while maintaining measurement accuracy.
Solution Approach 2:
The system replaces direct electrical temperature probes with optical temperature sensing methods or thermocouples positioned in the chuck structure. This substitution eliminates the creation of parasitic RF fields by conductive probes while maintaining the ability to accurately measure wafer temperature through the chuck interface.
3Productivity
If high RF source power is applied to achieve high etch rates, then productivity increases, but temperature non-uniformities across the wafer increase
Solution Approach 1:
The cooling system is segmented into multiple zones with independent control, allowing differential cooling compensation across the wafer surface. The center zone and peripheral zones can be cooled at different rates to counteract the non-uniform heat generation from high RF power, maintaining temperature uniformity while enabling high etch rates.
Solution Approach 2:
Multiple temperature sensors distributed across the electrostatic chuck provide real-time feedback on temperature distribution. The control system processes this feedback and dynamically adjusts zone-specific cooling parameters to compensate for temperature non-uniformities caused by high RF power, thereby maintaining both high productivity and temperature 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
This solution ensures uniform temperature distribution across the wafer, maintaining high etch rate uniformity even under high RF heat loads, and allows for agile and accurate temperature profiling, addressing the limitations of conventional cooling systems.
Implementation Method 1
a refrigeration loop having respective inner and outer expansion valves for controlling flow of coolant through the inner and outer evaporators respectively
Implementation Method 2
transfers heat between the coolant and the electrostatic chuck through a separate liquid heat transfer medium
Implementation Method 3
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 evaporators inside respective inner and outer zones of the electrostatic chuck and a refrigeration loop having respective inner and cuter expansion valves for controlling flow of coolant through the inner and outer evaporators respectively. 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.