Plasma Reactor Cathode Tuning for Etch Uniformity
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Solution Overview
Problem
The mask etch process in photolithographic mask fabrication for ultra large scale integrated semiconductor wafers faces challenges in achieving uniform etch rate distribution and precise etch depth control, leading to non-uniform critical dimensions and high production costs due to RF electrical non-uniformities in the support pedestal and the need for frequent interruptions for depth measurements.
Innovation Solution
The introduction of a plasma reactor with a cathode having a continuous titanium ring and nickel plating to enhance RF electrical uniformity, along with backside endpoint detection using optical sensors to monitor etch depth and rate distribution continuously, allowing for real-time adjustments and reducing the need for process interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional mask etch process is used, then photoresist pattern can be etched into quartz mask, but etch rate distribution is non-uniform across mask surface leading to critical dimension variation
Solution Approach 1:
The patent applies local quality by making the cathode structure non-uniform with a raised central portion and lowered peripheral portions. This creates different local electrical properties across the cathode surface, with the central region having different capacitance and electrical field characteristics compared to the peripheral regions. This local structural variation compensates for the non-uniform plasma distribution, achieving uniform etch rate across the mask surface.
2Measurement precision
If etch depth is precisely controlled by periodic interruptions and measurements, then accurate phase alignment can be achieved, but productivity decreases and contamination risk increases
Solution Approach 1:
The patent implements feedback by incorporating optical sensors that continuously monitor the etch process in real-time. The sensors detect changes in light transmission or reflection through the mask during etching, providing continuous feedback about etch depth and rate. This allows the control system to adjust etch parameters dynamically, achieving precise depth control without periodic interruptions, thereby maintaining high productivity and preventing contamination.
3Manufacturing precision
If inductive source power applicator with inner and outer coils is used, then radial distribution of plasma ion density can be varied, but non-symmetrical non-uniformities cannot be corrected
Solution Approach 1:
The patent applies segmentation by dividing the cathode into distinct functional zones: a raised central portion and lowered peripheral portions. This segmented structure allows independent control of electrical properties in different regions. The central region can be optimized for one plasma density characteristic while the peripheral regions are optimized for another, enabling correction of both symmetrical and asymmetrical non-uniformities that cannot be addressed by simple coil current adjustment.
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 solution achieves more uniform etch rate distribution and precise control of etch depth, reducing production costs and increasing productivity by minimizing non-uniformities and allowing continuous monitoring of the etch process.
Implementation Method 1
The mask etch process... requires a plasma reactor for etching the mask pattern into the quartz mask
Implementation Method 2
backside endpoint detection using optical sensors to monitor etch depth and rate distribution continuously
Data Source
AI summary
A plasma reactor is provided for processing a workpiece such as a transparent mask or a semiconductor wafer. The reactor includes a vacuum chamber having a ceiling and a sidewall. A workpiece support pedestal within the chamber includes a metal cathode having a support surface facing the ceiling and defining a support plane for supporting a workpiece. The cathode has a hollow space formed within its interior. The reactor further includes a movable metal element within the hollow space and a mechanism for controlling a distance between the metal element and the support plane.