Electrostatic Chuck Refrigeration Loop for Wafer Temperature Uniformity
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Solution Overview
Problem
Conventional cooling systems for wafer temperature regulation in capacitively coupled plasma reactors suffer from inefficiencies, leading to temperature drift and non-uniformity under high RF power conditions, which compromises etch rate uniformity across the wafer.
Innovation Solution
A refrigeration loop with an evaporator having a meandering passageway beneath the electrostatic chuck, operating in a two-phase constant-temperature process using a refrigerant with a varying liquid-to-vapor ratio to enhance heat transfer through latent heat of vaporization, and an agile temperature control system using backside gas pressure adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling systems with liquid heat transfer medium are used, then the wafer temperature can be regulated, but temperature drift and non-uniformity occur under high RF power conditions
Solution Approach 1:
The patent employs phase change material (PCM) in the thermal management system that undergoes phase transition between solid and liquid states. During the phase transition, the PCM absorbs or releases latent heat at a constant temperature, thereby maintaining uniform wafer temperature even under high RF power conditions. This eliminates the temperature drift problems associated with conventional liquid coolant systems.
Solution Approach 2:
The invention extracts the heat transfer function from the wafer support structure by incorporating a separate thermal management system with PCM. This allows the wafer support to focus on mechanical support and electrostatic chucking functions, while the thermal management system independently handles temperature regulation, improving overall system reliability and temperature uniformity.
2Productivity
If high RF source power is applied to achieve high etch rates, then productivity increases, but temperature non-uniformity across the wafer worsens
Solution Approach 1:
The PCM-based thermal management system absorbs excess RF heat through phase transition, maintaining uniform temperature distribution across the wafer even when high RF source power is applied. This enables high etch rates to be achieved without sacrificing temperature uniformity, thus resolving the contradiction between productivity and temperature distribution.
3Measurement precision
If temperature probes are introduced near the wafer for accurate temperature sensing, then measurement precision improves, but parasitic RF fields are created that distort the uniform environment
Solution Approach 1:
The patent uses the PCM as an intermediary thermal management medium that can be sensed without introducing parasitic RF fields. Temperature sensors can be placed in contact with the PCM or in close proximity without directly interfacing with the high RF field region near the wafer, thus achieving accurate temperature measurement while avoiding the creation of harmful parasitic RF fields.
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 provides stable and uniform wafer temperature distribution even under high RF heat loads, maintaining etch rate uniformity and enabling precise temperature control across the wafer, essential for advanced semiconductor processing.
Implementation Method 1
heat transfer between the electrostatic chuck and the refrigerant within the evaporator is a constant-temperature process
Implementation Method 2
refrigerant within the evaporator is apportioned between a vapor phase and a liquid phase
Implementation Method 3
transfers heat between the coolant and the electrostatic chuck through a separate liquid heat transfer medium
Implementation Method 4
the evaporator includes a meandering passageway distributed in a plane beneath a top surface of the electrostatic chuck
Data Source
AI summary
A plasma reactor for processing a workpiece includes a reactor chamber, an electrostatic chuck within the chamber for supporting a workpiece, an RF plasma bias power generator coupled to apply RF power to the electrostatic chuck and a refrigeration loop having an evaporator inside the electrostatic chuck with a refrigerant inlet and a refrigerant outlet. Preferably, the evaporator includes a meandering passageway distributed in a plane beneath a top surface of the electrostatic chuck. Preferably, refrigerant within the evaporator is apportioned between a vapor phase and a liquid phase. As a result, heat transfer between the electrostatic chuck and the refrigerant within the evaporator is a constant-temperature process. This feature improves uniformity of temperature distribution across a diameter of the electrostatic chuck.