Chromatic Confocal Microscope Axial Chromatism Wafer Edge Inspection
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Solution Overview
Problem
Conventional semiconductor wafer inspection systems face challenges with depth of field limitations, making high magnification and large depth of field difficult, especially when inspecting the edges of curved wafers, which are increasingly fragile and sensitive due to larger diameters and finer patterns, requiring precise and slow mechanical movements that can lead to defects and increased production costs.
Innovation Solution
A chromatic confocal microscope with an illumination and analysis path using a polychromatic light source, a slit, and an objective lens with strong axial chromatism, allowing for spatial filtering of unfocused wavelengths and achieving a large depth of field without mechanical focusing adjustments, enabling fast and precise edge inspection with automatic autofocus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If confocal microscopy is used for edge inspection, then measurement precision is improved, but productivity deteriorates due to mechanical readjustments and slow acquisition speed
Solution Approach 1:
The patent replaces the mechanical focus adjustment system with an optical system based on chromatic aberration. Instead of mechanically moving the objective lens to achieve focus, the invention uses a lens with strong axial chromatism where different wavelengths automatically focus at different depths, eliminating mechanical movement and enabling parallel multipoint acquisition across the wafer edge.
Solution Approach 2:
The patent introduces a wavelength dimension to the focus control mechanism. By using polychromatic light and a lens with strong axial chromatism, the system maps different wavelengths to different focal depths, creating a spectral dimension for depth encoding that enables simultaneous multi-depth imaging without mechanical adjustment.
2Measurement precision
If high magnification is used for fine pattern inspection, then measurement precision is improved, but depth of field deteriorates
Solution Approach 1:
The patent changes the optical parameter of the lens by selecting materials with strong axial chromatism (low Abbe number). This parameter change allows the system to achieve both high magnification and extended depth of field simultaneously, as the chromatic aberration creates a natural depth encoding that maintains focus information across different depths.
3Measurement precision
If mechanical focus adjustment is used, then measurement precision is improved, but reliability deteriorates due to friction and contamination risk
Solution Approach 1:
The patent eliminates the mechanical focus adjustment mechanism entirely by using optical chromatic aberration for depth encoding. This substitution removes friction, wear, and contamination risks associated with mechanical moving parts, significantly improving system reliability while maintaining measurement precision through wavelength-based depth discrimination.
4Ease of manufacture
If conventional optical system is used, then ease of manufacture is improved, but measurement precision deteriorates for curved surfaces
Solution Approach 1:
The patent changes the chromatic parameter of the optical lens by selecting materials with strong axial chromatism. This modification enables the conventional optical system to accurately inspect curved wafer edges by encoding depth information in the wavelength domain, maintaining ease of manufacture while dramatically improving measurement precision for curved surfaces.
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 solution provides a high-resolution, fast, and economical edge inspection system capable of mass production, reducing the risk of defects and increasing yield by allowing continuous measurement of the wafer periphery without mechanical movement, suitable for large diameter wafers with varying distances from the optical objective.
Implementation Method 1
an objective with axial chromatism chosen to present chromatic aberration
Implementation Method 2
comprising at least one lens made of a material with an Abbe number less than 50
Implementation Method 3
a chromatic filtering slit configured to spatially filter unfocused wavelengths on the edge of the semiconductor wafer
Implementation Method 4
a light intensity sensor in that order
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A chromatic confocal microscope (7) provided with an illumination channel (10) and an analysis channel (20), the illumination channel (10) comprising a polychromatic light source (11), a slit (12) and an objective (15) with strong axial chromaticism, the analysis channel (20) comprising said objective, a chromatic filtering slit (22) and a light intensity sensor (24) in that order, the slit of the analysis channel providing spatial filtering of wavelengths not focused on the surface of the object (30).