Pulsed RF Bias Plasma Etching of Silicon Nitride Films
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor fabrication methods face challenges in achieving high etch selectivity and straight sidewalls during the plasma etching of deep silicon nitride (SiN) features, leading to potential damage of underlying substrates and incomplete feature formation due to limited mask pattern protection.
Innovation Solution
A plasma etching method using a process gas combination of HBr, O2, and carbon-fluorine-containing gases, along with pulsed radio frequency (RF) biasing power, is employed to etch silicon nitride films, allowing for deep feature formation with straight sidewalls and improved selectivity by controlling RF bias power levels between main and over-etch steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If plasma etching is performed for deep features requiring long exposure times, then the etching depth increases, but the mask pattern is completely removed from the wafer surface leaving the surface unprotected
Solution Approach 1:
The patent applies pulsed RF bias power instead of continuous RF bias power, creating dynamic on/off cycling that modulates the etching rate. During the 'on' phase, etching proceeds at high rate to achieve deep features; during the 'off' phase, etching stops allowing mask protection to be maintained. This dynamic approach resolves the contradiction between achieving deep etching and maintaining mask protection.
Solution Approach 2:
The patent implements periodic pulsed RF bias power application with specific duty cycles (e.g., 10 Hz frequency, 50% duty cycle). This periodic action allows the etching process to proceed in controlled intervals, achieving deep feature etching while providing regular pauses that prevent complete mask removal and maintain protective coverage on the wafer surface.
2Manufacturing precision
If high etch selectivity is required for deep features, then the etching precision improves, but the process complexity increases due to multiple parameters control
Solution Approach 1:
The patent changes multiple process parameters simultaneously: RF bias power level (pulsed vs. continuous), process gas composition (HBr, O2, CF4 ratios), pressure conditions, and temperature control. These parameter changes work together to achieve high etch selectivity for deep SiN features while maintaining straight sidewalls and protecting underlying materials, managing the complexity through coordinated parameter optimization.
Solution Approach 2:
The patent uses a composite process gas mixture containing HBr, O2, and CF4 gases in specific proportions. This composite gas composition provides synergistic effects: HBr contributes to etching SiN, O2 helps maintain mask integrity and reduces lateral etching, and CF4 enhances selectivity and protects underlying layers. The composite approach achieves high precision while managing process complexity through a unified gas mixture strategy.
3Shape
If straight feature sidewalls are required, then the feature geometry improves, but the etching rate decreases due to lateral etching suppression
Solution Approach 1:
The pulsed RF bias power creates periodic etching intervals that allow vertical etching to dominate during the 'on' phase while minimizing lateral etching. During the 'off' phase, lateral etching is suppressed, allowing the mask to maintain its protective function and promoting straight sidewall formation. This periodic action resolves the trade-off between sidewall quality and etching rate.
Solution Approach 2:
The patent optimizes process parameters including RF bias power level, pressure, and gas composition to favor vertical etching over lateral etching. By adjusting these parameters in combination with pulsed RF bias, the process achieves straight sidewalls while maintaining acceptable etching rates through enhanced ion directionality and reduced radical-mediated lateral reactions.
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 method enhances etch selectivity and prevents damage to underlying materials by maintaining sufficient mask pattern protection, achieving high aspect ratios and reducing micro-loading effects in plasma etching processes.
Implementation Method 1
forming a plasma from a process gas containing HBr gas, O2 gas, and a carbon-fluorine-containing gas
Implementation Method 2
transferring the mask pattern to the SiN film by exposing the film stack to the plasma
Implementation Method 3
applying pulsed RF bias power to the substrate
Implementation Method 4
applying pulsed RF bias power to the substrate to provide deep SiN features with straight sidewalls
Data Source
AI summary
A processing method is provided for plasma etching features in a silicon nitride (SiN) film covered by a mask pattern. The method includes preparing a film stack on a substrate, the film stack containing a SiN film on the substrate and a mask pattern on the SiN film, forming a plasma from a process gas containing HBr gas, O2 gas, and a carbon-fluorine-containing gas, applying pulsed RF bias power to the substrate, and transferring the mask pattern to the SiN film by exposing the film stack to the plasma.