Highly selective etching of SiN_xover SiO₂using ClF₃/Cl₂remote plasma

Area of Science:

• Materials Science
• Chemical Engineering
• Semiconductor Manufacturing

Background:

• Highly selective etching of silicon nitride (SiN) over silicon oxide (SiO2) is critical for fabricating advanced vertical semiconductor devices, such as 3D NAND.
• Current etching processes face challenges in achieving sufficient selectivity and etch rates.

Purpose of the Study:

• To investigate the isotropic dry etching characteristics of SiN and SiO2 using ClF3/Cl2 remote plasmas.
• To optimize etching parameters for high SiN over SiO2 selectivity.

Main Methods:

• Utilized ClF3/Cl2 remote plasmas for dry etching of SiN and SiO2.
• Varied the percentage of Cl2 in the ClF3/Cl2 gas mixture.
• Analyzed etch rates and selectivity ratios at room temperature.

Main Results:

• Increasing Cl2 concentration in ClF3/Cl2 enhanced SiN over SiO2 etch selectivity while reducing SiN etch rate.
• Achieved etch selectivity exceeding 500:1 with a SiN etch rate of ~8 nm/min using 15% Cl2.
• Further increased selectivity to over 1000:1 by increasing Cl2 to 20%.
• Identified distinct etching mechanisms: SiN etches via Si-N to Si-F/Si-Cl reactions, while SiO2 etches inefficiently via Si-O to Si-F reactions at room temperature.
• Demonstrated highly selective SiN removal from SiN/SiO2 stacks without significant SiO2 etching or etch loading effects using ClF3/Cl2 (15%).

Conclusions:

• Optimized ClF3/Cl2 remote plasma etching enables ultra-high selectivity for SiN over SiO2.
• The distinct reaction pathways explain the observed selectivity, offering a viable solution for advanced semiconductor fabrication.
• This method provides precise control for etching SiN/SiO2 multilayer structures without compromising underlying layers.