Silicon Nitride Etching via Oxidized Hard Mask
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Solution Overview
Problem
Conventional etching methods for silicon nitride films on underlying silicon oxide films using a silicon oxide hard mask face challenges in achieving high selectivity without damaging the silicon nitride film, particularly when the underlying silicon oxide film is thin, leading to issues like pitting and surface damage.
Innovation Solution
An etching method that involves etching the hard mask, ashing the resist film, oxidizing the hard mask surface under different conditions, performing main etching with a patterned hard mask, and overetching with a high selectivity to the silicon oxide film, using plasmas generated by oxygen, carbon, fluorine, and hydrogen gases to form a protective oxidation layer on the hard mask.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a gaseous mixture with high selectivity (O2/CH3F ratio 4-9) is used for etching silicon nitride film, then the selectivity of silicon nitride film to silicon oxide film increases, but the silicon oxide hard mask suffers local damage and pitting occurs
Solution Approach 1:
The patent applies preliminary action by performing an oxidation treatment on the silicon oxide hard mask surface before the main etching process. This preliminary oxidation creates a protective layer on the mask surface that prevents damage during subsequent high-selectivity etching, allowing the etching gas to attack the silicon nitride film without causing pitting or local damage to the underlying silicon oxide mask.
Solution Approach 2:
The oxidation layer formed on the silicon oxide hard mask surface acts as a cushioning protective layer before the main etching process. This pre-formed layer absorbs the aggressive action of the high-selectivity etching gas, protecting the underlying silicon oxide mask from direct damage while still allowing the etching to proceed through the silicon nitride film with the desired selectivity.
2Manufacturing precision
If overetching is performed to ensure complete removal of silicon nitride film, then etching completeness improves, but the thin silicon oxide underlying film suffers damage
Solution Approach 1:
The patent uses the oxidized silicon oxide layer as an intermediary protective barrier between the aggressive etching gas and the thin underlying silicon oxide film. This intermediary layer allows the etching process to continue with high selectivity and completeness while mediating the harmful effects on the underlying film, preventing direct damage during overetching.
3Manufacturing precision
If the silicon oxide hard mask is made thinner to achieve finer patterns, then pattern resolution improves, but the mask becomes more susceptible to damage during etching
Solution Approach 1:
The patent applies preliminary oxidation to strengthen the thin silicon oxide hard mask surface before etching. This preliminary treatment creates a robust protective layer that compensates for the reduced thickness of the mask, allowing thin masks to be used for fine pattern resolution while maintaining sufficient durability to withstand the etching process without damage or pitting.
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 effectively prevents damage to the silicon nitride film and reduces pitting by creating a protective layer on the hard mask, allowing for precise etching without impairing the film's surface, especially effective for thin silicon oxide films.
Implementation Method 1
oxidizing the hard mask surface under different conditions, performing main etching with a patterned hard mask, and overetching with a high selectivity to the silicon oxide film, using plasmas generated by oxygen, carbon, fluorine, and hydrogen gases to form a protective oxidation layer on the hard mask
Implementation Method 2
using plasmas generated by oxygen, carbon, fluorine, and hydrogen gases to form a protective oxidation layer on the hard mask
Data Source
AI summary
An etching method, for etching a silicon nitride film on an underlying silicon oxide film by using a hard mask whose principal component is a silicon oxide, includes a step of etching the hard mask by using the resist film as a mask to form a mask pattern therein; a step of ashing the resist film; a step of oxidizing the hard mask; a main etching step of etching the silicon nitride film by using the patterned hard mask as a mask; and a step of overetching the silicon nitride film at a high selectivity of the silicon nitride film to the silicon oxide film. The main etching step is performed after the step of forming the mask pattern in the hard mask and before the overetching step at a selectivity of the silicon nitride film to the silicon oxide film smaller than that in the overetching step.