Wafer Shape Measurement Error Compensation via Cavity Tilt
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Solution Overview
Problem
Dual channel reflection-type interferometers face measurement precision degradation due to temperature variations across wafers, leading to errors in optical interferometer measurements, as existing methods require complex sub-modules for temperature control and fail to accurately compensate for shape measurements.
Innovation Solution
The method involves indirect detection and compensation of temperature gradients using cavity tilt measurements, allowing for the calculation of a weighting factor to correct measurement errors without measuring wafer temperature or air refractive index gradients, by performing calibration with a reference wafer and applying this factor to subsequent measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature control sub-modules are added to compensate for thermal effects, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential tilt information from the full temperature field measurement, using cavity tilt as a surrogate parameter to represent thermal effects. This avoids the need for comprehensive temperature control sub-modules while maintaining measurement precision through selective parameter extraction.
Solution Approach 2:
The patent introduces cavity tilt measurements as an intermediary parameter that mediates between temperature variations and measurement errors. Instead of directly controlling temperature or measuring full thermal fields, the cavity tilt serves as a simplified mediator that captures the essential thermal impact on measurements.
2Measurement precision
If comprehensive temperature field measurement is performed, then measurement precision is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent extracts only the cavity tilt parameter from the complete temperature field information, recognizing that full thermal characterization is unnecessary. By taking out only the essential tilt component, the system achieves thermal compensation without complex comprehensive measurement apparatus.
Solution Approach 2:
The patent applies partial action by measuring only cavity tilt rather than the complete temperature field. This partial measurement approach provides sufficient information for thermal compensation while avoiding the complexity and time requirements of comprehensive temperature mapping.
3Measurement precision
If temperature stabilization is implemented, then measurement precision is improved, but productivity decreases due to settling time
Solution Approach 1:
The patent performs preliminary calibration measurements to establish the relationship between cavity tilt and measurement errors before actual production measurements. This preliminary action creates a compensation model that can be applied instantly during production, eliminating the need for stabilization settling time while maintaining precision.
Solution Approach 2:
The patent replaces the mechanical/thermal stabilization approach with an optical measurement and computational compensation approach. Instead of waiting for thermal equilibrium through physical stabilization, the system uses cavity tilt measurements and algorithmic compensation to achieve precision immediately, substituting mechanical waiting time with computational processing.
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 effectively reduces measurement errors caused by thermal effects, improving the accuracy of wafer surface measurements by compensating for thermally induced optical path length differences without the need for separate temperature control modules, thereby enhancing measurement precision.
Implementation Method 1
Each measures the optical interference signal from two beams, a first reflected beam from wafer surface 110, 111 and a second reflected beam reflected from internal reference surface 120, 121
Implementation Method 2
This induces a temperature gradient in air regions 215 and 220, due to natural convection. This temperature gradient in the air adjacent the measurement surfaces of the wafer causes a gradient in the air index of refraction
Implementation Method 3
This induces a temperature gradient in air regions 215 and 220, due to natural convection
Data Source
AI summary
Disclosed herein is a method and apparatus for reducing measurement error resulting from temperature variations across a wafer, without measuring the wafer temperature, the temperature gradient in the surrounding air, or the distribution of the index of refraction of the air.