Wafer Thermal Bowing Prevention via Pre-Heating and Support Plate
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Solution Overview
Problem
Heat-treating semiconductor wafers during annealing processes leads to thermal deformation, causing measurement errors and potential damage due to rapid thermal gradients and uneven heating, which can result in thermal runaway and wafer breakage.
Innovation Solution
A method and apparatus that measure deformation of the wafer during heat-treating and adjust the thermal processing accordingly, applying deformation corrections to temperature measurements and modifying the heat-treating process to prevent thermal runaway and optimize the wafer's shape for safer and more uniform heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the device side of the wafer is rapidly heated to a substantially higher temperature than the bulk of the wafer, then the annealing temperature is achieved on the device side, but thermal bowing occurs causing the wafer to deform into a dome or saucer shape
Solution Approach 1:
The wafer is pre-heated to an intermediate temperature before the rapid heating stage. This preliminary thermal conditioning reduces the thermal shock and minimizes thermal bowing during the subsequent rapid heating to annealing temperature, preventing excessive dome or saucer shape deformation
Solution Approach 2:
The heating process uses two distinct temperature stages: an intermediate temperature phase followed by a rapid heating phase to annealing temperature. By controlling and changing temperature parameters in sequence, the system achieves effective annealing while managing thermal stress and minimizing shape deformation
2Force
If the wafer is supported by conventional support pins near its edges, then the wafer is held in place, but the thermal bowing applies large downward forces to the support pins potentially damaging or destroying both the pins and the wafer
Solution Approach 1:
A support plate is introduced as an intermediary between the wafer and the support pins. The support plate distributes the thermal bowing forces across a larger area, preventing concentrated loads on the pins that would cause damage to both the pins and the wafer
3Stress or pressure
If the edges of the wafer rapidly bow downward, then the thermal stress is reduced, but the wafer may strike a support plate above which the wafer is supported, potentially damaging or destroying the wafer
Solution Approach 1:
The wafer is pre-heated to an intermediate temperature before rapid heating, which reduces the magnitude and rapidity of thermal bowing. This preliminary thermal conditioning prevents the edges from rapidly bowing downward and striking the support plate, avoiding mechanical damage while still allowing thermal stress relief
4Force
If conventional support pins are used, then the wafer is supported, but the initial velocities imparted to the various regions of the wafer cause the wafer to overshoot the equilibrium minimum stress shape and rapidly oscillate or vibrate, resulting in additional stress and potentially damaging or destroying the wafer
Solution Approach 1:
Pre-heating the wafer to an intermediate temperature before rapid heating reduces the initial velocities imparted to wafer regions during thermal bowing. This minimizes overshooting of the equilibrium shape and reduces oscillation amplitude, preventing vibration-induced damage and maintaining wafer integrity
Solution Approach 2:
The support plate acts as a cushioning element that absorbs and dampens the oscillations and vibrations caused by thermal bowing. By providing a compliant support surface beforehand, the system prevents vibration-induced damage to the wafer
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 reduces the likelihood of wafer damage, minimizes measurement errors, and maintains thermal uniformity by dynamically adjusting the heat-treating process based on real-time deformation measurements, thereby enhancing the reliability of the annealing process.
Implementation Method 1
The initial pre-heating stage occurs at a rate significantly slower than a thermal conduction time through the wafer
Implementation Method 2
The subsequent surface heating stage occurs much more rapidly than the thermal conduction time through the wafer, so that only the device side surface is heated to the final annealing temperature
Implementation Method 3
The cooler bulk of the wafer then acts as a heat sink to facilitate rapid cooling of the device side surface
Implementation Method 4
Such annealing methods, which involve rapidly heating the device side of the wafer to a substantially higher temperature than the bulk of the wafer, tend to cause the device side to thermally expand at a greater rate than the rest of the wafer
Data Source
AI summary
Methods and apparatus for heat-treating a workpiece are disclosed. An illustrative method includes measuring deformation of a workpiece during heat-treating thereof, and taking an action in relation to the heat-treating of the workpiece, in response to the measuring of the deformation of the workpiece. The workpiece may include a semiconductor wafer. Taking an action may include applying a deformation correction to a temperature or reflectivity measurement of the wafer during thermal processing, or may include modifying the heat-treating of the wafer, for example.