Effect of Mask Geometry Variation on Plasma Etching Profiles.

Area of Science:

• Semiconductor device fabrication
• Plasma etching processes
• Advanced materials science

Background:

• Scaling advanced node transistors, increasing flash memory capacity, and on-chip integration require advanced fabrication techniques.
• Plasma etching, particularly using SF6/O2 chemistry, is a key process for creating 3D features in semiconductor manufacturing.
• A predictive model for SF6/O2 plasma etching is essential for optimizing the semiconductor device design cycle.

Purpose of the Study:

• To implement and validate a physical SF6/O2 plasma etching model.
• To investigate the influence of mask geometry on etched feature profiles.
• To provide guidelines for mask design rules in semiconductor fabrication.

Main Methods:

• Implementation of a physical SF6/O2 plasma etching model based on Langmuir adsorption.
• Calibration and validation of the model using published equipment parameters.
• Utilizing the ViennaPS process simulator with Monte Carlo ray tracing and level set surface description.
• Analysis of etching through circular and rectangular mask openings.

Main Results:

• The mask taper angle significantly impacts etched feature dimensions, including depth and bowing.
• Peak etch depth is observed around a 0.5° mask taper angle, shifting with passivation effects.
• Minimum bowing occurs at peak depth and increases with taper angle; maximum bowing is seen between 15°-20° taper.
• Mask etch rate variations influence vertical etching and bowing, with significant mask erosion leading to increased verticality and reduced bowing.

Conclusions:

• The developed physical model accurately predicts SF6/O2 plasma etching behavior.
• Mask geometry, including taper angle and etch rate, critically affects feature profile control.
• The model serves as a valuable tool for optimizing mask design and establishing design rules for advanced semiconductor devices.