Hard Mask Plasma Etching with Pulsed Bias for Anisotropic Profiles
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Solution Overview
Problem
Existing hard mask etching techniques face challenges in preventing deposition from underlying metal films and achieving an anisotropic shape due to the variety of metal films used in miniaturized semiconductor devices, particularly when high bias ion-assisting properties cause metal deposition on pattern side walls.
Innovation Solution
A plasma processing method involving a two-step etching process using mixed gases (O2, CHF3, NF3, Ar, He) with pulse-modulated RF power in the main etching step and continuous wave (CW) RF power in the over etching step, specifically tailored for etching TEOS and silicon nitride films, to prevent deposition and achieve anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If high bias ion-assisting property is used in over etching step, then anisotropic shape is obtained, but metal deposition occurs on pattern side wall
Solution Approach 1:
The patent applies pulse-modulated radio frequency power in the main etching step, creating periodic cycles of high ion flux (etching) and low ion flux (deposition suppression). This periodic action allows the system to achieve anisotropic etching while periodically reducing ion impact that would otherwise cause metal deposition on side walls.
Solution Approach 2:
The patent changes the radio frequency power parameter from continuous to pulse-modulated, and controls the duty ratio to optimize the balance between ion-assisted anisotropic etching and suppression of metal deposition. By adjusting the pulse width and duty cycle, the system maintains directional etching while limiting cumulative ion damage that causes deposition.
2Object-generated harmful factors
If pulse-modulated radio frequency power is used in main etching step, then metal deposition is suppressed, but etching rate may be reduced
Solution Approach 1:
The pulse-modulated power supply creates periodic high-power intervals that provide intense ion flux for rapid anisotropic etching, followed by low-power intervals that allow deposition suppression. The duty ratio is optimized to ensure that the high-power intervals contribute sufficiently to etching rate while the low-power intervals prevent metal deposition accumulation.
Solution Approach 2:
The system dynamically adjusts the radio frequency power between high and low states, creating time-varying ion flux that adapts to the dual requirements of maintaining high etching rate through periodic intensity spikes while suppressing deposition during low-power phases. This dynamic control allows the system to achieve both productivity and deposition suppression.
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 effectively prevents deposition on metal films and achieves an anisotropic shape with improved selectivity and critical dimension controllability in hard mask etching.
Implementation Method 1
a plasma generated by mixed containing gas oxygen (O2) gas, trifluoromethane (CHF3) gas, nitrogen trifluoride (NF3) gas, argon (Ar) gas, and helium (He) gas
Implementation Method 2
a reaction is prevented by low-flow-rate gas, and the anisotropic shape is obtained using a high bias having a strong ion-assisting property
Implementation Method 3
supplying continuous wave (CW) radio frequency power to the sample stage
Data Source
AI summary
An object of the invention is to provide a plasma processing method for preventing generation of deposition from an underlying metal film and attaining an anisotropic shape in hard mask etching. The plasma processing method for forming a mask using a film to be etched whose underlying layer is a metal film according to the invention includes: a first step of etching, using a plasma generated by mixed gas containing O2 gas, CHF3 gas, NF3 gas, Ar gas, and He gas, while supplying pulse-modulated radio frequency power to a sample stage on which a sample having the film to be etched is placed; and a second step of etching while supplying continuous wave (CW) radio frequency power to the sample stage after the first step. The film to be etched is a TEOS film and a silicon nitride film, and the continuous wave (CW) radio frequency power is smaller than a product of the pulse-modulated radio frequency power and a pulse-modulated duty ratio and is smaller than 50 W.