Plasma Mask Etch Uniformity via Backside Optical Monitoring
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Solution Overview
Problem
The mask etch process for ultra large scale integrated (ULSI) circuits faces challenges in achieving uniform etch rate distribution across the mask surface, leading to non-uniform critical dimensions and etch depth, which is exacerbated by RF electrical non-uniformities in the support pedestal and sensitivity to consumable component variations, resulting in high costs and low productivity.
Innovation Solution
The solution involves enhancing RF electrical uniformity across the pedestal by using a continuous titanium ring, nickel plating, and an RF gasket to address RF non-uniformities, and employing backside optical measurement for real-time etch depth monitoring and tunable gas injection orifices to adjust etch rate distribution, allowing for continuous process control and feedback adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If periodic interruption and measurement of etch depth is implemented, then etch depth control precision is improved, but productivity deteriorates
Solution Approach 1:
The patent implements continuous optical monitoring of etch depth through the mask backside during the etch process, eliminating periodic interruptions. The system continuously measures etch depth by detecting light reflection from the etched surface through the transparent mask substrate, allowing the etch process to proceed without interruption while maintaining precise depth control.
Solution Approach 2:
The patent replaces mechanical measurement methods (which require removing the mask from the chamber) with optical measurement. Light is used to probe the etch depth through the mask backside, substituting mechanical intervention with non-contact optical detection, thereby maintaining continuous operation.
2Device complexity
If simple reflectance or OES end point detection is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent uses the transparent mask substrate itself as an optical window or intermediary to allow light to pass through and reflect from the etched surface. This intermediary approach enables precise optical measurement without requiring complex external measurement systems, as the mask backside serves as the transmission medium for the measurement light.
3Ease of manufacture
If mask etch process is performed with typical selectivity, then ease of manufacture is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent implements real-time feedback control by continuously monitoring etch depth through optical measurement and using this information to control the etch process termination. The system provides feedback on the actual etch depth to the process control system, which adjusts the etch process to achieve the target depth with high precision, compensating for variations in etch rate and ensuring uniform critical dimensions.
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 achieves more uniform etch rate distribution, reduces production costs, and enhances productivity by enabling precise control of etch depth and critical dimensions, improving the overall mask etch process.
Implementation Method 1
viewing light reflected from the array of plural locations to the backside of the workpiece
Implementation Method 2
illuminating an array of plural locations on front surface of the workpiece through the backside of the workpiece with light of a wavelength range for which the workpiece is transparent
Data Source
AI summary
A plasma etch method includes simultaneously illuminating an array of plural locations on front surface of the workpiece through the backside of the workpiece with light of a wavelength range for which the workpiece is transparent, while viewing light reflected from the array of plural locations to the backside of the workpiece. The method further includes determining plural etch depths at the array of locations from the light reflected from the array of locations on the front side of the workpiece, and deducing from the plural etch depths a spatial distribution of etch rate across the array of locations. The method also includes changing the etch rate distribution by adjusting a tunable element of the reactor.