Broad-Area Reflectometry for Plasma Etch End Point Detection
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Solution Overview
Problem
Current methods for determining the end point of a plasma etch process, such as laser-based reflectometry and optical emission spectroscopy, are not well-suited for providing strong signals when the percentage of open area in the mask is low, leading to inaccurate or weak end point signals, especially for high aspect ratio features or features at the bottom of trenches.
Innovation Solution
An apparatus using a white light illumination source with an angle of incidence less than 10° and a camera for successive image capture, with image processing to identify feature locations and measure reflectivity signals, allowing for modification of the plasma etch process based on these signals, thereby providing a strong end point signal across a broad area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser-based reflectometry or interferometry is used to determine end point, then measurement can be performed, but the end point signal is weak or inaccurate when the percentage of open area in the mask is low
Solution Approach 1:
The patent combines multiple measurement approaches by using a broad-area optical measurement system that captures signals from across the entire wafer surface rather than localized spots. This merging of measurement zones compensates for low open area percentages by aggregating signals from all available open areas across the wafer.
Solution Approach 2:
The optical measurement system is designed to universally measure across the entire wafer surface regardless of the specific pattern or percentage of open areas. The system adapts to different mask configurations and feature densities, providing reliable end point detection whether open areas are abundant or scarce.
2Measurement precision
If laser spot size is reduced to measure small features, then measurement precision improves, but alignment difficulty increases and signal representation becomes insufficient
Solution Approach 1:
The patent transitions from one-dimensional localized spot measurements to two-dimensional broad-area measurements. By illuminating and detecting across the entire wafer surface simultaneously, the system eliminates alignment issues while maintaining measurement precision through spatially-resolved detection that can identify specific feature locations within the broad measurement area.
3Area of stationary object
If moving parts are added to scan the laser across the wafer, then measurement coverage improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical scanning systems with a stationary broad-area optical measurement system. Instead of moving the laser or the detector, the system uses wide-angle optics to illuminate and detect across the entire wafer surface simultaneously, eliminating moving parts while achieving complete measurement coverage.
4Reliability
If optical emission spectroscopy is used to detect end point, then plasma property monitoring is achieved, but sensitivity decreases when open area percentage is low
Solution Approach 1:
The patent combines optical emission spectroscopy with broad-area optical reflectometry. While OES monitors plasma properties, the simultaneous broad-area optical measurement aggregates signals from across the entire wafer surface, compensating for low open area percentages and providing reliable end point detection through signal aggregation.
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 approach enables accurate detection of end point signals even with low open areas in the mask, improving the representation of the etch process across a wider area and ensuring precise control of high aspect ratio feature etching.
Implementation Method 1
a white light illumination source for illuminating a region of the substrate during a plasma etch process, wherein the illumination source is mounted to illuminate the region of the substrate with an incident light beam having an angle of incidence of less than about 10° with respect to the normal
Implementation Method 2
a camera arranged to take successive images of the region illuminated by the illumination source
Implementation Method 3
apparatus for plasma etching a substrate... a chamber; a substrate support disposed within the chamber for supporting the substrate to be plasma etched
Data Source
AI summary
A white light illumination source can illuminate a region of a substrate to be plasma etched with an incident light beam. A camera takes successive images of the region being illuminated during a plasma etch process. Image processing techniques can be applied to the images so as to identify a location of at least one feature on the substrate and to measure a reflectivity signal at the location. The plasma etch process can be modified in response to the measured reflectivity signal at the location.