Mask Overhang Reduction via Pullback Etch in Semiconductor Fabrication
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor fabrication processes face significant lateral undercut issues during deep etch processes, leading to fill problems such as voids and improper plating, especially when non-sacrificial masking layers are involved, as current methods are costly, complex, or ineffective in eliminating mask overhang.
Innovation Solution
A pullback etch process is employed to reduce or eliminate mask overhang by laterally etching the masking layer, creating a positive step without additional patterning steps, thereby reducing or eliminating lateral substrate undercut, and maintaining at least a portion of the masking layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If deep etch process is used to form deep features, then etch depth is improved, but lateral mask overhang and substrate undercut increase
Solution Approach 1:
The etch process is divided into two distinct segments: a first etch process that forms the deep etched feature with controlled lateral etching, and a second etch process that specifically removes the mask overhang. This segmentation allows each process to be optimized independently - the first for depth and the second for lateral precision.
Solution Approach 2:
The first etch process performs a preliminary action by forming the deep etched feature while intentionally allowing some lateral etching to occur. This preliminary lateral etching creates the mask overhang that will subsequently be removed, rather than trying to prevent it entirely in the first place.
2Manufacturing precision
If sacrificial masking layer is completely removed after etch, then lateral mask overhang is reduced, but this method is not possible when non-sacrificial masking layers are used
Solution Approach 1:
The second etch process applies local quality by selectively removing only the mask overhang region while preserving the main body of the non-sacrificial masking layer. This localized etching approach allows the masking layer to maintain its structural integrity and continue serving its masking function in subsequent processes.
Solution Approach 2:
The second etch process acts as an intermediary step between the deep etch process and subsequent filling operations. It mediates the conflict between maintaining a non-sacrificial masking layer for subsequent processes and removing the problematic mask overhang, by selectively removing only the overhang portion.
3Manufacturing precision
If re-patterning with original masking layer is used, then lateral mask overhang is reduced, but additional photolithography step adds cost and process complexity
Solution Approach 1:
The solution extracts the mask overhang removal function from the complex re-patterning process. Instead of performing a complete re-patterning operation with additional photolithography steps, the invention extracts and applies a targeted second etch process that removes only the problematic overhang portion.
Solution Approach 2:
Instead of adding material (through photolithography re-patterning) to fix the mask overhang, the invention uses the opposite approach by removing material (through a second etch process). This inversion simplifies the process by eliminating the need for additional patterning steps.
4Manufacturing precision
If deep etch process changes are made to reduce lateral mask overhang, then lateral overhang is reduced, but etch rate is significantly lost
Solution Approach 1:
The etching function is segmented into two processes with different optimization goals. The first etch process is optimized for high etch rate and deep feature formation, while the second etch process is optimized for lateral precision and mask overhang removal. This segmentation allows each process to operate at optimal efficiency for its specific purpose.
Solution Approach 2:
The first etch process performs a partial action by intentionally allowing some lateral etching to occur beyond the ideal boundary. This excessive lateral etching creates the mask overhang that will be removed in the second process, but it allows the first process to maintain high etch rate and deep penetration capability.
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 approach effectively reduces or eliminates mask overhang and resulting substrate undercut, leading to improved fill processes with reduced voids and proper plating, maintaining cost-effectiveness and process simplicity.
Implementation Method 1
A pullback etch process exclusive of any additional patterning step following the etching laterally etches the masking layer
Data Source
AI summary
A method of forming IC devices includes providing a substrate and forming a patterned masking layer including at least one masked region having at least one masking layer, and a feature region bounded by the masking layer. Etching forms an etched feature in the substrate, wherein undercutting during the etching forms at least one mask overhang region over a surface portion of the etched feature that is recessed relative to an outer edge of the masking layer. A pullback etch process exclusive of any additional patterning step laterally etches the masking layer. The conditions for the pullback etch retain at least a portion of the masking layer and reduce a length of the mask overhang region by at least 50%, or eliminate the mask overhang region entirely. The etched feature is then filled after the pullback etch process to form a filled etched feature.