Pulsed RF Duty Cycle Optimization for Semiconductor Etching CDU
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Solution Overview
Problem
Semiconductor manufacturing faces challenges in achieving uniformity of critical dimensions during etching processes, particularly in the creation of holes for memory chips, where variations in hole size lead to inconsistent performance across the chip.
Innovation Solution
A method is implemented to optimize Critical Dimension Uniformity (CDU) by performing tests with varying pulsed RF duty cycles in a semiconductor chamber, identifying a range of duty cycles that correspond to minimum CD and CDU values, and selecting a duty cycle that balances etching and deposition to stabilize hole size, using a system with a TCP coil and gas injection for optimal plasma processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous RF is used for etching, then etching speed is improved, but critical dimension uniformity deteriorates
Solution Approach 1:
The patent applies periodic pulsed RF action instead of continuous RF. The RF power is applied in pulses with varying duty cycles (e.g., 10% to 90%) during the etching process. This periodic application allows the plasma chemistry to oscillate between etching-dominated and deposition-dominated states, preventing the formation of microloading effects and improving CDU while maintaining reasonable etch throughput.
2Manufacturing precision
If pulsed RF with low duty cycle is used, then critical dimension uniformity is improved, but etching speed deteriorates
Solution Approach 1:
The patent employs dynamic adjustment of RF duty cycle during the etching process. Rather than using a fixed low duty cycle, the system dynamically varies the duty cycle (e.g., starting at 10% and increasing to 90% or vice versa) to optimize both CDU and etching speed. This dynamic approach allows the process to adapt to changing plasma conditions and feature sizes throughout the etch cycle.
Solution Approach 2:
The periodic pulsed RF with varying duty cycles creates alternating phases of high etching rate and plasma relaxation. During high duty cycle phases, etching speed increases; during low duty cycle phases, plasma chemistry resets and uniformity improves. This periodic variation resolves the trade-off between speed and precision.
3Productivity
If pulsed RF with high duty cycle is used, then etching speed is improved, but critical dimension uniformity deteriorates
Solution Approach 1:
The patent uses periodic pulsed RF where high duty cycle phases (improving speed) are interspersed with low duty cycle phases (maintaining uniformity). This periodic alternation prevents the accumulation of microloading effects that would occur with continuously high duty cycle operation, while still achieving high overall etching throughput through the high-speed phases.
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 ensures consistent and uniform hole sizes across the substrate, improving intra-cell and overall wafer uniformity by selecting a duty cycle that achieves a balance between etching and deposition, resulting in stable and uniform feature sizes.
Implementation Method 1
While processing the wafer, a plasma is created that contains various types of radicals, as well as positive and negative ions. The chemical reactions of the various radicals, positive ions, and negative ions are used to etch features, surfaces and materials of a wafer.
Implementation Method 2
the radio frequency (RF) provided to the coil is pulsed, which generally means the level of RF may be varied
Implementation Method 3
The chemical reactions of the various radicals, positive ions, and negative ions are used to etch features, surfaces and materials of a wafer.
Implementation Method 4
the operation alternates deposition and etching on the hole, where during the operation the hole shrinks until a size of the hole reaches a threshold value that remains substantially stable due to a balancing effect of the etching and the deposition
Data Source
AI summary
Methods, systems, and computer programs are presented for optimizing Critical Dimension Uniformity (CDU) during the processing of a substrate. One method includes identifying an operation of a recipe for processing a substrate within a chamber, the operation being configured to provide a pulsed radio frequency (RF) to the chamber. A plurality of tests are performed in the chamber for the operation utilizing the pulsed RF, each test having a duty cycle for the pulsed RF selected from a plurality of RF duty cycles. The method also includes for each test, measuring the critical dimension (CD) and the CDU for features in the substrate, and selecting a first duty cycle from the plurality of RF duty cycles based on the measured CDs and CDUs for the plurality of tests. The method also includes setting the selected first duty cycle in the operation of the recipe for processing the substrate.