Sulfur Aromatic Etch Chemistry for HAR Silicon Profile Control
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Solution Overview
Problem
Existing plasma etching processes for high aspect ratio (HAR) structures face challenges such as charge build-up, incomplete etching, bowing, and CD variation due to electron shading, and require new etch gas compositions with low global warming potential (GWP) to maintain selectivity and high aspect ratios across various process conditions.
Innovation Solution
The use of sulfur-containing aromatic etching compounds with a —SH thiol group and an aromatic 6-membered carbon ring, combined with hydrofluorocarbon, fluorocarbon, or nitrogen fluoride gases, to selectively etch silicon-containing films, forming a passivation layer that reduces charge build-up and enhances etch selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If ion energy is increased by increasing effective bias power to overcome charge build-up in HAR holes, then etching capability is improved, but arcing prevention and cooling challenges increase
Solution Approach 1:
The patent introduces sulfur-containing compounds to modify the plasma chemistry parameters, changing the etching mechanism from ion-dominated to chemistry-dominated. This allows effective etching at lower bias powers, reducing the risk of arcing while maintaining etching capability in HAR structures.
Solution Approach 2:
Sulfur-containing compounds act as intermediaries that facilitate the etching process by forming volatile sulfur compounds with silicon. This intermediary chemical mechanism enables etching without requiring high ion energies, thereby preventing arcing issues.
2Productivity
If bias power is increased to improve etching of HAR structures, then etching rate is improved, but charge build-up and electron shading effects worsen
Solution Approach 1:
The patent replaces the mechanical/ion bombardment-based etching mechanism with a chemistry-based etching mechanism using sulfur-containing compounds. This substitution allows high etching rates without the charge build-up and electron shading problems associated with high ion fluxes.
Solution Approach 2:
By changing the chemical composition of the etching plasma through sulfur-containing additives, the patent achieves high etching rates through enhanced chemical reactivity rather than increased ion energy, thereby avoiding charge control issues.
3Reliability
If conventional sulfur-containing gases are used for passivation, then sidewall protection is improved, but global warming potential increases
Solution Approach 1:
The patent uses sulfur-containing compounds that decompose completely during the etching process, leaving no persistent environmental impact. The sulfur compounds serve their passivation function temporarily and then break down into volatile products, unlike conventional gases that may have long atmospheric lifetimes.
Solution Approach 2:
The patent modifies the molecular structure of sulfur-containing gases to achieve complete decomposition during plasma processing, changing the environmental persistence parameter from high (conventional gases) to low (new compounds), thereby reducing global warming potential while maintaining passivation effectiveness.
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 proposed etching method improves etch profile control, reduces sidewall charge, and maintains high aspect ratios while minimizing lateral etching and bowing, with a potential reduction in environmental impact through lower GWP gases.
Implementation Method 1
The sulfur may provide a passivation layer on the amorphous carbon to help protect the surface from oxygen radicals
Implementation Method 2
The sulfur-containing aromatic etching compound contains an aromatic 6 membered carbon ring having a sulfur element attached to the aromatic ring
Implementation Method 3
Plasma etching, especially in HAR structures, is a complex process that has not entirely understood. The chemistry of the plasma is composed of ions and neutrals
Implementation Method 4
The sulfur-containing aromatic etching compound... to selectively remove one or more materials from a substrate
Implementation Method 5
Vertical isotropy of etched features is obtained by ion transport during plasma sheath formation. In principle, positive and negative particles should have the same trajectories inside a hole and equalize the charge at the HAR hole bottom
Implementation Method 6
But due to the electron shading effect, charge build-up at the bottom of HAR mask patterns, which can lead to incomplete etching, bowing, twisting, and CD variation between the top and bottom of the HAR stack
Data Source
AI summary
A method for forming a structure using a patterned mask layer comprises introducing an etching gas containing a sulfur-containing gas into a reaction chamber, converting the etching gas to a plasma, and allowing an etching reaction to proceed between the plasma and the one or more silicon-containing films so that the one or more silicon-containing films are selectively etched versus the patterned mask layer to form the structure, wherein the sulfur-containing gas contains a —SH thiol group and an aromatic 6 membered carbon ring having the formulawherein R1, R2, R3, R4 and R5 are independently selected from F, H, and/or CxFyHz group substituted on the aromatic ring, where x, y and z are integers, and at least one of the R1, R2, R3, R4 and R5 contains at least one fluorine atom, and S represents the —SH thiol group.