Workpiece Support Pressure Control for Semiconductor Wafer Cooling
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Solution Overview
Problem
High deposition rate PVD processes in the semiconductor industry face challenges in maintaining low wafer temperatures, especially when processing thinned, warped, or insulative wafers, as conventional methods like cold electrostatic chucks struggle to provide sufficient clamping force and thermal conductivity, leading to pressure-induced loss of contact and stress on fragile wafers.
Innovation Solution
A method involving controlled pressure differentials between the chamber and the back region of the workpiece, using a support to maintain contact and enhance cooling, allowing for high deposition rates while minimizing stress on the wafer, with specific pressure ranges and cycles to manage thermal transfer and clamping forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high deposition rate PVD processes are used, then productivity is improved, but wafer temperature increases which affects previously deposited materials
Solution Approach 1:
The patent applies pneumatic pressure differentials to achieve wafer cooling. By controlling the chamber pressure and back pressure to create a pressure differential, gas flow is directed through channels in the workpiece support structure, providing convective cooling to the wafer during high deposition rate processes
Solution Approach 2:
The patent introduces a workpiece support structure with integrated cooling channels as an intermediary between the wafer and the chamber environment. This structure mediates heat transfer from the wafer to the cooling gas flow, enabling temperature control during high power deposition
2Temperature
If cold electrostatic chuck is used for wafer cooling, then wafer temperature control is improved, but clamping force is insufficient for thinned and warped wafers
Solution Approach 1:
The patent segments the wafer support system into distinct functional zones: clamping regions that provide mechanical holding force and cooling regions with gas flow channels. This segmentation allows the workpiece support to simultaneously provide both clamping force and thermal management without compromise
Solution Approach 2:
The workpiece support structure functions as a composite system combining mechanical support properties for clamping with thermal management properties through integrated cooling channels. This composite approach enables both clamping and cooling functions in a single integrated component
3Temperature
If gas back pressure is used to improve thermal conductivity, then cooling efficiency is improved, but pressure differential causes loss of contact for thinned and warped wafers
Solution Approach 1:
The patent dynamically controls the pressure differential between chamber and back pressure to maintain optimal conditions. By adjusting pressures during different process phases, the system maintains wafer contact during deposition while enabling cooling gas flow when needed
Solution Approach 2:
The patent changes pressure parameters dynamically during the deposition process. By controlling chamber pressure and back pressure independently, the system creates pressure differentials that drive cooling gas flow through channels while maintaining sufficient contact force between the wafer and workpiece support
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 enables safe processing of problematic wafers at high deposition rates with improved thermal control and reduced stress, enhancing productivity and maintaining low wafer temperatures, thereby overcoming the limitations of conventional methods.
Implementation Method 1
controlling the differential gas pressure across the thickness of the workpiece
Implementation Method 2
at least P b2 being sufficiently high to enhance cooling of the workpiece
Implementation Method 3
cold electrostatic chuck (ESC)
Data Source
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AI summary
According to the invention there is provided a method of processing a semiconductor workpiece having a front surface and a back surface, including the steps of: i) placing the back surface of the workpiece on a workpiece support in a chamber so that the front surface of the workpiece faces into the chamber for processing, the chamber having an associated chamber gas pressure, and the back surface is in fluid communication with a back region having an associated back gas pressure; ii) performing a workpiece processing step at a first chamber pressure Pc1 and a first back pressure Pb1, wherein Pc1 and Pb1 give rise to a pressure differential, Pb1-Pc1, which is maintained so as to avoid a pressure induced loss of contact between the workpiece and the workpiece support; and iii) performing a workpiece cooling step at a second chamber pressure Pc2 and a second back pressure Pb2, wherein Pc2 and Pb2 are higher than Pc1 and Pb1, respectively, at least Pb2 being sufficiently high to enhance cooling of the workpiece, and wherein Pc2 and Pb2 give rise to a pressure differential, Pb2-Pc2, which is maintained so as to avoid a pressure-induced loss of contact between the workpiece and the workpiece support.