Spindle Thermal Compensation via Unequal Mounting Elements
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Solution Overview
Problem
Thermal expansion and differences in coefficients of thermal expansion between components in mechanical systems, such as wafer inspection systems, lead to errors and accuracy issues due to heat loads, which existing solutions like using low CTE materials like Invar are costly and inefficient to address.
Innovation Solution
A passive thermal compensation apparatus that uses unequal length mounting elements with a temperature gradient to cancel out thermal expansion movements, allowing for precise positioning correction without active software corrections, applicable in various mechanical and inspection systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If materials with very low CTE such as Invar are used to minimize thermal displacement, then thermal expansion errors are reduced, but the system becomes sensitive to environmental temperature changes and the cost increases significantly
Solution Approach 1:
The patent applies thermal expansion by intentionally designing mounting elements with different lengths that expand at different rates when exposed to temperature gradients. The shorter mounting element experiences greater thermal expansion than the longer element, creating a compensatory effect that counteracts the thermal displacement of the spindle. This resolves the contradiction by using controlled thermal expansion of ordinary materials (like aluminum) to achieve the precision previously requiring expensive low-CTE materials like Invar.
2Productivity
If high spindle power is used to increase wafer rotation speed and inspection throughput, then productivity increases, but thermal heat load increases causing position errors and degraded inspection accuracy
Solution Approach 1:
The patent converts the harmful thermal heat load generated by high-power spindle motors into a beneficial effect. By deliberately exposing mounting elements to the temperature gradient created by the motor heat, the patent harnesses thermal expansion to generate compensatory positional shifts. The heat that would normally cause errors is instead used to pre-position the spindle, converting the harmful thermal effect into a beneficial compensation mechanism that maintains accuracy despite high productivity demands.
3Manufacturing precision
If unequal length mounting elements with temperature gradient are used for passive thermal compensation, then defect location accuracy improves from 50 microns to less than 5 microns, but the device complexity increases
Solution Approach 1:
The patent applies asymmetry by using mounting elements of unequal lengths to attach the spindle to the motor housing. This asymmetric configuration is deliberately designed so that the shorter element expands more than the longer element under thermal loading, creating a compensatory moment that counteracts spindle displacement. The asymmetric design is simple in form but achieves sophisticated thermal compensation, improving accuracy without requiring complex active control systems or multiple sensing elements.
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
Reduces defect location errors from up to 50 microns to less than 5 microns, enabling more accurate software corrections and maintaining system accuracy across temperature changes, while allowing the use of cost-effective materials like aluminum.
Implementation Method 1
Any change in temperature affects the position of a component such as the spindle, due in part to the mounting materials' CTE. In an embodiment of the invention, position change of a component is corrected passively by mounting the component on unequal length elements such that the temperature distribution across the mounting elements combines with the physical configuration to cancel out movement due to thermal expansion of the mounting elements.
Data Source
AI summary
Disclosed herein is an apparatus for providing passive correction for thermal effects on a mounted mechanical component. Further disclosed is a wafer inspection system employing the passive thermal effect correction apparatus.