Three-State RF Pulsing for Bow Control and Mask Selectivity
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Solution Overview
Problem
Existing RF generator systems for plasma etching face a trade-off between sidewall polymer passivation and mask selectivity, limiting the achievable pitch and device size.
Innovation Solution
A three-state RF pulsing method is implemented, where a low frequency RF generator and a high frequency RF generator pulse among three states, with synchronized power level adjustments to balance bow control and mask selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF pulsing is used for plasma etching, then sidewall polymer passivation is achieved, but mask selectivity deteriorates
Solution Approach 1:
The RF pulsing cycle is segmented into three distinct states instead of conventional two states. State 1 provides high polymer passivation with low frequency RF dominant, State 2 provides high mask selectivity with high frequency RF dominant, and State 3 provides balanced conditions with both frequencies equal. This segmentation allows independent optimization of passivation and selectivity in different time intervals, resolving the trade-off between these two parameters.
Solution Approach 2:
The system employs periodic pulsing of two RF generators at different frequencies (low frequency and high frequency) with synchronized phase relationships. By periodically alternating between states where low frequency RF dominates (State 1), high frequency RF dominates (State 2), or both are equal (State 3), the process achieves time-averaged optimization of both sidewall passivation and mask selectivity that cannot be achieved with continuous or two-state pulsing.
2Manufacturing precision
If three-state RF pulsing is implemented, then mask selectivity is enhanced, but system complexity increases
Solution Approach 1:
A controller serves as an intermediary device that coordinates the pulsing of both low frequency and high frequency RF generators. The controller generates synchronized pulse signals that switch between three states by controlling the duty cycles and phases of both RF sources. This intermediary management simplifies the overall system control by providing a centralized coordination mechanism rather than requiring complex direct coupling between generators.
Solution Approach 2:
The system dynamically adjusts the duty cycles and power levels of two RF generators during different phases of the pulsing cycle. The low frequency RF generator and high frequency RF generator have their power levels dynamically modulated to achieve three distinct operational states. This dynamic control allows the system to adapt between prioritizing passivation (State 1), prioritizing selectivity (State 2), or maintaining balance (State 3) based on process requirements.
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
The method achieves a significant reduction in bow formation at the sidewall of nitride layers, enhancing mask selectivity by 15% to 20% compared to two-state pulsing, while maintaining optimal etching substrate features with high aspect ratios.
Implementation Method 1
A three-state radiofrequency (RF) pulsing method that breaks a trade-off between sidewall polymer passivation and mask selectivity is described. The trade-off between sidewall polymer passivation and mask selectivity creates a limitation in achieving a pitch to further limit a device size. As an example, the three-state RF pulsing method includes synchronized pulsing of a low frequency RF generator periodically among three states and of a high frequency RF generator periodically among the three states.
Implementation Method 2
A radiofrequency (RF) generator generates an RF signal and supplies the RF signal via a match to a plasma reactor. The plasma reactor has a semiconductor wafer that is etched when the RF signal is supplied and an etchant gas is supplied to the plasma reactor.
Implementation Method 3
During the first state, the primary RF signal has a power level that is greater than a power level of the secondary RF signal. Also, during the second state, the secondary RF signal has a power level that is greater than a power level of the primary RF signal. During the third state, power levels of the primary and secondary RF signals are approximately equal. The method achieves a significant reduction in bow formation at the sidewall of nitride layers
Implementation Method 4
The method achieves a significant reduction in bow formation at the sidewall of nitride layers, enhancing mask selectivity by 15% to 20% compared to two-state pulsing, while maintaining optimal etching substrate features with high aspect ratios.
Data Source
AI summary
A method for multi-state pulsing to achieve a balance between bow control and mask selectivity is described. The method includes generating a primary radio frequency (RF) signal. The primary RF signal pulses among three states including a first state, a second state, and a third state. The method further includes generating a secondary RF signal. The secondary RF signal pulses among the three states. During the first state, the primary RF signal has a power level that is greater than a power level of the secondary RF signal. Also, during the second state, the secondary RF signal has a power level that is greater than a power level of the primary RF signal. During the third state, power levels of the primary and secondary RF signals are approximately equal.