Multi-Angle Optical Scattering for Fast Roughness and Defect Measurement
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Solution Overview
Problem
Conventional methods for measuring surface roughness and defects on components like burls of electrostatic chucks are time-consuming and limited in spatial resolution, especially for high spatial frequencies, making them impractical for large-scale wafer holding apparatuses.
Innovation Solution
A measuring apparatus with multiple light sources illuminating at different angles and a detector array capturing scattered light images at a fixed viewing angle, allowing simultaneous detection of scattered light images with common spatial frequencies, enabling rapid and precise determination of roughness and defect features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods like AFM are used for roughness measurement, then measurement precision for high spatial frequencies is improved, but measurement time increases excessively and productivity deteriorates
Solution Approach 1:
The patent replaces the mechanical contact method of AFM with an optical scattering measurement system. Multiple light sources illuminate the surface at different angles, and a detector array captures scattered light patterns. This optical substitution enables simultaneous measurement of multiple spatial frequencies without mechanical scanning, resolving the contradiction between precision and speed.
Solution Approach 2:
The patent transitions from one-dimensional sequential scanning (AFM moving across the surface) to two-dimensional parallel detection using a detector array. By capturing scattered light from multiple angles simultaneously across the entire surface, the system achieves both high spatial frequency resolution and rapid measurement, eliminating the time-precision tradeoff.
2Measurement precision
If AFM is used for comprehensive defect detection, then measurement precision is improved, but the measuring field remains very small and time consumption increases
Solution Approach 1:
The patent expands the measuring field from the micrometer-scale AFM tip to a large-area optical measurement field covering the entire wafer holder surface. The detector array captures scattered light patterns across the full field of view, enabling simultaneous detection of defects throughout the entire surface while maintaining precision through multi-angle illumination analysis.
Solution Approach 2:
The optical scattering system performs multiple functions simultaneously: it measures roughness at high spatial frequencies, detects particles, identifies material damage, and characterizes surface topology. This universal measurement capability across the entire surface eliminates the need for multiple separate inspection steps, achieving both comprehensive defect detection and large area coverage.
3Productivity
If white light interferometry is used for surface measurement, then measuring speed is improved compared to AFM, but spatial resolution for high spatial frequencies deteriorates due to low-pass properties
Solution Approach 1:
The patent changes the illumination parameters by using multiple light sources at different angles rather than broad-spectrum white light. This angular diversity in illumination enables the detection of high spatial frequency roughness features while maintaining fast measurement speed, overcoming the low-pass filtering effect that limits white light interferometry.
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 method significantly reduces measurement time to approximately one hour, enhances spatial frequency detection up to 100 μm−1, and improves precision and information content, facilitating reliable detection of burl end faces and other components.
Implementation Method 1
at least two light sources (11A, 11B, 11C, 11D) which are arranged for illuminating a measuring region (3) of the surface with measuring light
Implementation Method 2
a detector device (20) having a detector array (21) with a plurality of detector pixels which are arranged for capturing scattered light scattered at the surface
Data Source
AI summary
A measuring apparatus has at least two radiation sources arranged to illuminate a measuring region of a surface of a sample, the at least two sources configured to illuminate the measuring region along at least two illumination beam paths at different angles of incidence relative to a surface normal of the surface, a detector device configured to detect at least two scattered radiation images of surface sections in the illuminated measuring region at a predetermined viewing angle relative to the surface normal of the surface, portions of the scattered radiation received by the detector device, which portions are formed in each case by the illumination in one of the illumination beam paths, in each case having a common spatial frequency, and an evaluation device configured to determine at least one roughness feature of the surface sections from the at least two scattered radiation images.