Polishing Apparatus Moire Pattern Pitch Detection

The patent introduces a lattice as an intermediary object with a reference pattern that is superimposed on the wafer pattern. This lattice serves as a mediator that converts the fine, hard-to-detect wafer pattern into a moire pattern with larger, easily detectable features. The moire pattern acts as an intermediary representation that preserves the geometric information of the original pattern while being suitable for optical detection without interference issues.

The patent creates an optical copy of the wafer pattern through the lattice's reference pattern, generating a moire pattern that replicates the essential geometric characteristics (pitch, orientation) of the original pattern. This copied representation allows for accurate measurement of pattern geometry using simple optical means rather than requiring direct observation of the fine original pattern.

The lattice serves as a simple intermediary device that transforms the observation task from direct high-magnification microscopy to low-magnification moire pattern observation. Instead of using a complex microscopic system to directly resolve fine pattern details, the lattice mediates by creating a magnified moire pattern that can be observed with simple optics, thereby achieving the same information gain without the complexity.

The patent transitions from direct spatial observation of fine patterns to observation in a different dimensional representation through moire interference. The moire pattern creates a new dimensional encoding of the original pattern geometry, where pitch and orientation information are represented in the spatial frequency domain of the interference pattern, allowing for easier measurement with simple optics.