Wafer Etching Endpoint Detection via Movable Optical Probe
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Solution Overview
Problem
Current substrate etching systems face challenges in detecting uniformity of film clearing and reducing over-etching and undercutting across wafers, due to non-uniform etching rates and variations in pattern densities and orientations, which leads to false endpoint detection and excessive variations in etched trace characteristics.
Innovation Solution
A substrate etching system with a movable probe and optical monitoring system that scans the wafer to collect measurements at multiple radial positions, determining endpoint status for each zone and adjusting etchant flow or concentration to maintain a target etch rate, reducing within-wafer and wafer-to-wafer non-uniformities and extending etchant bath life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-point endpoint detection method is used, then the system is simple and fast, but it cannot detect within-wafer non-uniformities and leads to false endpoint detection
Solution Approach 1:
The wafer surface is divided into multiple radial zones (e.g., inner, middle, outer zones) and endpoint detection is performed independently for each zone using the movable probe. This segmentation allows the system to detect within-wafer non-uniformities by comparing endpoint timing across different zones, resolving the contradiction between detection accuracy and system simplicity.
2Manufacturing precision
If etching is continued until the slowest region clears, then all zones reach endpoint, but over-etching occurs in faster regions causing undercutting
Solution Approach 1:
The system uses real-time optical reflectance measurements from the movable probe to monitor film clearing status in each zone. When the endpoint is detected in a particular zone, the system provides feedback to adjust etching parameters (such as reducing etchant flow rate or pausing etching for that zone) to prevent over-etching, thereby maintaining trace uniformity without sacrificing overall process efficiency.
3Productivity
If etchant flow rate is increased to speed up etching, then productivity improves, but etching rate variations across the wafer increase
Solution Approach 1:
The system dynamically adjusts the etchant flow rate based on real-time monitoring of film clearing status in different zones. The movable probe detects when specific zones reach endpoint, and the system responds by modulating the etchant flow rate accordingly - reducing flow to zones that have reached endpoint while maintaining or increasing flow to zones that are still etching. This dynamic control enables high productivity while maintaining uniform etching rates across the wafer.
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 real-time detection of individual endpoints across multiple zones, reduces etching non-uniformities, extends etchant bath life, and improves process yield by ensuring accurate endpoint detection and uniform etching rates.
Implementation Method 1
an optical monitoring system may include a light source, a detector, and an optical component to carry light from the light source to the substrate and carry reflected light from the substrate to the detector
Data Source
AI summary
A substrate etching system includes a support to hold a wafer in a face-up orientation, a dispenser arm movable laterally across the wafer on the support, the dispenser arm supporting a delivery port to selectively dispense a liquid etchant onto a portion of a top face of the wafer, and a monitoring system comprising a probe movable laterally across the wafer on the support.