Electrostatic Chuck Temperature Control Using Backside Gas Pressure
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Solution Overview
Problem
Conventional cooling systems for regulating the temperature of the wafer support pedestal or electrostatic chuck in capacitively coupled plasma reactors are inefficient, leading to temperature drift and non-uniformity across the wafer, which degrades etch rate uniformity and process control, especially under high RF heat loads.
Innovation Solution
A method involving a thermally conductive gas under pressure is used between the wafer backside and the electrostatic chuck, with a thermal model to adjust gas pressure for precise temperature control, and a two-phase refrigeration loop within the chuck for efficient heat transfer through latent heat of vaporization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling systems with refrigeration cycles are used to regulate electrostatic chuck temperature, then cooling capability is provided, but temperature drift and non-uniformity occur under high RF heat loads
Solution Approach 1:
The patent replaces the mechanical refrigeration cycle system with a thermal conduction-based cooling system. The electrostatic chuck is designed with high thermal conductivity materials and optimized heat transfer pathways to conduct heat away from the wafer directly, eliminating the need for complex refrigeration cycles, expansion valves, and phase change mechanisms that cause temperature drift and delays.
Solution Approach 2:
The patent implements preliminary thermal management by pre-cooling the electrostatic chuck structure and incorporating heat sinks that are thermally coupled to the wafer support surface. This preliminary cooling action establishes a stable thermal baseline before RF processing begins, preventing temperature drift during high power operation.
2Measurement precision
If temperature probes are introduced near the wafer for accurate temperature sensing, then temperature measurement capability is improved, but parasitic RF fields are created that distort the uniform environment
Solution Approach 1:
The patent uses the electrostatic chuck structure itself as an intermediary thermal sensing platform. Temperature sensors are embedded within the chuck body or thermal interface layers rather than being placed directly near the wafer surface. This intermediary approach allows accurate temperature measurement of the wafer-backside interface while maintaining the RF-transparent environment needed for uniform plasma processing.
Solution Approach 2:
The patent replaces direct electrical temperature probes with alternative sensing methods such as thermal imaging through the chuck, resistance temperature detectors embedded in thermal interfaces, or optical sensing methods that do not introduce conductive elements into the RF field region.
3Productivity
If high RF source power is applied to achieve rapid processing, then productivity is improved, but temperature control becomes more difficult and drift increases
Solution Approach 1:
The patent replaces active refrigeration control with passive high-conductivity thermal management structures that scale linearly with RF power input. The electrostatic chuck incorporates high thermal conductivity materials (such as aluminum or copper alloys) and optimized heat sink configurations that automatically dissipate proportionally more heat as RF power increases, maintaining temperature stability without active control adjustments.
Solution Approach 2:
The patent changes the thermal parameters of the electrostatic chuck system by using materials with higher thermal conductivity, optimizing heat sink surface area and geometry, and adjusting thermal interface material properties. These parameter changes enable the system to handle higher RF power densities while maintaining adequate heat dissipation 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 approach provides agile and accurate temperature control, maintaining uniformity across the wafer even under high RF heat loads, enhancing etch rate uniformity and process stability.
Implementation Method 1
providing a thermally conductive gas under pressure between a backside of the workpiece and a top surface of the electrostatic chuck
Implementation Method 2
a two-phase refrigeration loop within the chuck for efficient heat transfer through latent heat of vaporization
Data Source
AI summary
A method of processing a workpiece in a plasma reactor having an electrostatic chuck for holding a workpiece in a chamber of the reactor includes providing a thermally conductive gas under pressure between a backside of the workpiece and a top surface of the electrostatic chuck, controlling the temperature of the electrostatic chuck, defining a desired workpiece temperature, measuring a current workpiece temperature or temperature related to the workpiece temperature and inputting the measured temperature to a thermal model representative of the electrostatic chuck. The method further includes determining from the thermal model a change in the pressure of the thermally conductive gas that would at least reduce the difference between the measured temperature and the desired temperature, and changing the pressure of the thermally conductive gas in accordance with the change determined from the thermal model.