Wafer Inspection with Random Illumination for Periodic Patterns
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Solution Overview
Problem
Existing wafer inspection techniques struggle to acquire high-resolution images when micropatterns on the wafer surface are periodic, as multiple diffraction pattern images become identical, hindering effective imaging.
Innovation Solution
A wafer inspection apparatus utilizing a spatial light modulator to output light in a random pattern, combined with a 4F optical system and a detector, allows for the acquisition of multiple diffraction images by changing the position of a random pattern image without moving the wafer, thereby capturing high-resolution images even with periodic patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diffraction imaging is used with periodic micropatterns, then the imaging process is simple, but all diffraction pattern images become identical and high-resolution imaging fails
Solution Approach 1:
A random pattern generator is introduced as an intermediary component between the light source and the wafer. This generator creates random illumination patterns that modulate the periodic micropatterns, transforming identical diffraction images into diverse patterns that enable high-resolution reconstruction through computational algorithms.
Solution Approach 2:
The illumination parameters are dynamically changed by varying the random pattern across multiple measurements. Instead of using uniform or periodic illumination, the system employs statistically random illumination patterns with controlled parameters (such as spatial frequency content and intensity distribution) to encode different information about the periodic structures.
2Measurement precision
If multiple diffraction images are acquired to improve resolution, then imaging quality improves, but the wafer must be moved or rotated which increases measurement time
Solution Approach 1:
The mechanical system for moving or rotating the wafer is replaced with an optical system that projects different random patterns onto the stationary wafer. The spatial light modulator or acoustic optical modulator dynamically changes the illumination pattern without requiring any mechanical movement of the sample, thereby acquiring multiple diffraction images in rapid succession.
Solution Approach 2:
The system employs periodic modulation of the random illumination patterns at high frequencies. By rapidly switching between different random patterns (effectively creating a time-periodic illumination sequence), the system accumulates multiple diffraction measurements during a single wafer position, enabling high-resolution reconstruction without mechanical movement.
3Measurement precision
If random pattern illumination is used to generate diverse diffraction images, then high-resolution imaging of periodic patterns is achieved, but the optical system complexity increases
Solution Approach 1:
The random pattern generator is designed to serve multiple functions: it illuminates the wafer, modulates the periodic patterns, and encodes spatial frequency information. A single optical component (such as a spatial light modulator) performs what would otherwise require multiple separate systems, reducing overall system complexity while achieving the desired imaging capability.
Solution Approach 2:
Instead of physically moving the wafer to capture different views, the system creates optical copies of the diffraction pattern under different random illuminations. The spatial light modulator generates multiple virtual illumination configurations that mimic the effect of physical repositioning, thereby achieving diverse diffraction images 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
Enables the acquisition of high-resolution images of wafer surfaces with periodic patterns by generating diverse diffraction images through controlled manipulation of the random pattern image, enhancing imaging capabilities.
Implementation Method 1
a spatial light modulator behind an image surface and configured to receive first light from the light source and output second light in a random pattern
Implementation Method 2
an objective lens configured to focus the second light onto an illuminated region of the wafer
Implementation Method 3
detector behind a detection surface and configured to acquire a diffraction image formed on the detection surface based on focused third light reflected from a detection region of the wafer
Implementation Method 4
focused third light reflected from a detection region of the wafer
Data Source
AI summary
A wafer inspection apparatus includes a light source configured to output first light, a spatial light modulator behind an image surface, the spatial light modulator configured to receive the first light and output second light that is in a random pattern, an optical system configured to provide the second light to an illuminated region of a wafer that is behind a sample surface, and a detector behind a detection surface and configured to acquire a diffraction image formed on the detection surface by reflection of the second light from a detection region within the illuminated region of the wafer, where each of the sample surface, the detection surface, and the image surface is a virtual plane that is set in a direction perpendicular to a traveling direction of the second light.