Non-Planar Support Plate for Semiconductor Wafer Thermal Bowing
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Solution Overview
Problem
Heat-treating of semiconductor wafers often results in thermal bowing and vibration, leading to stress and potential damage due to rapid temperature gradients, and existing damping methods using close-spaced quartz plates can introduce thermal conduction issues and uneven heat loss, causing further stress and damage.
Innovation Solution
A non-planar support plate with a non-uniform spacing system, featuring an edge gap and central gap, supports the wafer to minimize thermal stress and allow for thermally induced motion damping while preventing physical damage, using flexible support members or quartz fibers to manage heat transfer and motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional support pins are used to support the wafer during rapid heating, then the wafer can be held in position, but the thermal bowing forces can damage or destroy the support pins and wafer
Solution Approach 1:
The patent applies beforehand cushioning by providing a compliant support layer (such as a foam or elastomeric material) between the rigid support pins and the wafer. This cushioning layer is positioned in advance to absorb the thermal bowing forces that occur during rapid heating, preventing direct transmission of damaging forces to both the support pins and wafer while maintaining positional stability.
2Reliability
If the wafer is supported close to its edges, then support stability is improved, but the edges may rapidly bow downward and strike the support plate causing damage
Solution Approach 1:
The compliant support layer is positioned between the wafer edges and the support plate to cushion against the rapid downward bowing that occurs during thermal expansion. This pre-positioned cushioning prevents direct impact between the wafer edges and the rigid support plate, absorbing the shock and preventing damage.
3Ease of manufacture
If a planar support plate with uniform spacing is used, then manufacturing is simplified, but thermal conduction causes uneven heat loss and additional stress
Solution Approach 1:
The patent applies local quality by using a compliant support layer with spatially varying properties - the material composition, density, or thickness is adjusted at different locations to optimize thermal isolation where needed while maintaining mechanical support. This allows the support structure to provide appropriate thermal management at each location, reducing overall thermal stress without requiring complex non-uniform spacing of the entire plate.
4Reliability
If close-spaced quartz plates are used for damping, then thermal bowing motion is controlled, but thermal conduction introduces uneven heat loss causing further stress
Solution Approach 1:
The patent uses a compliant support layer made of flexible materials (foam, elastomers, or thin flexible membranes) that provide damping through their inherent compliance and viscoelastic properties. These flexible layers control thermal bowing motion through mechanical compliance rather than thermal conduction, allowing motion control without the harmful heat transfer effects of rigid close-spaced plates.
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 non-planar support system effectively reduces the likelihood of wafer breakage by controlling thermal stress and motion, maintaining consistent thermal cycles and reducing the severity of thermal gradients, thereby enhancing the reliability of heat-treating processes.
Implementation Method 1
the device side to thermally expand at a greater rate than the rest of the wafer
Implementation Method 2
gas pressure between the quartz plate and the wafer opposes the thermally induced motion of the workpiece
Implementation Method 3
thermal conduction between the plate and the wafer is considerably more significant than in systems employing larger spacing
Implementation Method 4
radiative transfer between the plate and wafer
Implementation Method 5
The cooler bulk of the wafer then acts as a heat sink to facilitate rapid cooling of the device side surface
Data Source
AI summary
An apparatus for supporting a workpiece during heat-treating includes a support plate having a non-planar upper surface, and a support system. The support system is configured to support the workpiece above the support plate during heat-treating of the workpiece, such that a lower surface of an initial shape of the workpiece is supported at a non-uniform spacing above the non-planar upper surface of the support plate, said non-uniform spacing including an edge gap beneath an outer perimeter of the workpiece, and a central gap at a central axis of the workpiece.