Spiral Light Beam Wafer Inspection Depth Determination
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Solution Overview
Problem
Current wafer inspection systems face difficulties in accurately differentiating between defects near the surface and those closer to the focal plane, as the intensity of defects can be influenced by both depth and type, leading to ambiguous depth determination.
Innovation Solution
A computer-based apparatus using a spiral light beam with a phase filter characterized by Gauss-Laguerre Eigen modes, optimized to generate a spiral light beam with a rotational speed greater than 2.0, which enables precise adjustment of the wafer position through an electronic feedback loop to maintain intensity thresholds, allowing for accurate defect depth calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical inspection with non-spiral light is used, then the inspection system is simple and easy to operate, but the depth determination accuracy is poor and cannot differentiate between surface and deeper defects
Solution Approach 1:
The patent changes the fundamental parameter of light by using spiral light beams with orbital angular momentum instead of conventional non-spiral light. This parameter change enables the light to interact differently with defects at various depths, creating distinct intensity patterns that allow accurate depth determination while maintaining system functionality
Solution Approach 2:
The patent introduces a spiral light beam as an intermediary between the light source and the defect detection process. The spiral light beam carries orbital angular momentum that interacts with defects at different depths, serving as a mediator that enables depth discrimination without requiring complex mechanical adjustments or multiple sensors
2Measurement precision
If light intensity is used to estimate defect depth, then the measurement process is simple, but the depth estimation is ambiguous and influenced by defect type rather than just depth
Solution Approach 1:
The patent changes the light parameter to spiral light with orbital angular momentum, which creates a different interaction mechanism with defects. This parameter change transforms the intensity measurement from being ambiguous (influenced by both depth and defect type) to being depth-specific, as the spiral light's rotational characteristics provide additional depth-sensitive information
Solution Approach 2:
Instead of trying to extract depth information from conventional light intensity patterns (which is ambiguous), the patent inverts the approach by using spiral light whose inherent rotational properties naturally encode depth information in the intensity patterns, making depth the primary determinant of intensity rather than a secondary effect
3Measurement precision
If spiral light beam with low rotational speed is used, then the system is easier to implement, but the sensitivity and accuracy of defect depth determination is reduced
Solution Approach 1:
The patent optimizes the rotational speed parameter of the spiral light beam by selecting specific orbital angular momentum values that maximize the sensitivity of intensity variations to depth changes. This parameter optimization ensures that the light rotates fast enough to create distinguishable intensity patterns for different depths while maintaining system implementability
Solution Approach 2:
The patent replaces mechanical adjustment mechanisms with optical parameter control by using electronically controllable spiral light sources with optimized rotational characteristics. This substitution allows precise control of the effective rotational speed through optical design rather than mechanical movement, achieving high sensitivity without mechanical complexity
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 solution enhances the accuracy and sensitivity of defect depth determination, enabling the differentiation between surface and deeper defects, and improves the detection of defects of interest (DOIs) by increasing the rotational speed of the spiral light beam, thus overcoming the limitations of existing methods.
Implementation Method 1
a first light beam rotating in a first spiral about a first central axis
Implementation Method 2
A phase filter generating a spiral light beam with increased rotational speed
Data Source
AI summary
A computer-based apparatus for adjusting an auto-focus in a wafer inspection system, including: a wafer adjustment system; and an electronic feedback loop system configured to compare an intensity of a first light beam rotating in a first spiral about a first central axis, and when the intensity is less than a preselected threshold, adjust, using the wafer adjustment system, a position of the wafer until the intensity reaches the preselected threshold.