Sidewall Spacer Etch Masking for Accurate Critical Dimension Transfer
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Solution Overview
Problem
In semiconductor device manufacturing, sidewall spacers formed on soft photoresist mandrels often have unintended angles due to stress relaxation and non-vertical profiles, leading to inaccuracies in critical dimension transfer during etching processes.
Innovation Solution
The method involves forming a patterned photoresist structure with a predetermined sidewall slope using photolithography, depositing a conformal spacer layer, and directional etching, with techniques such as retrograde focus, underlayer modulated reflectivity, and reactive species to control spacer angles and profiles, ensuring accurate critical dimension transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conformal spacer layer is deposited on a soft photoresist mandrel, then the spacer material conforms to the mandrel profile, but stress relaxation causes the spacer to relax into unintended angles after photoresist removal
Solution Approach 1:
The patent applies preliminary action by forming the spacer on a mandrel with a pre-determined non-vertical profile that anticipates the stress relaxation effect. The mandrel is intentionally designed with a specific angle during photolithography exposure that compensates for the expected relaxation, so that after stress release, the spacer achieves the desired vertical or near-vertical orientation with accurate critical dimensions.
Solution Approach 2:
The patent employs preliminary anti-action by introducing a counterbalancing effect during mandrel formation. The photolithography process uses defocused exposure or underlayer techniques to create a mandrel profile that is intentionally tilted in the opposite direction of the expected stress relaxation, thereby pre-compensating for the distortion and ensuring the final spacer maintains the intended angle and critical dimension.
2Measurement precision
If photolithography is performed at focus to achieve sharp patterns, then the photoresist profile is well-defined, but soft photoresist mandrels still exhibit stress relaxation leading to inaccurate spacer angles
Solution Approach 1:
The patent applies parameter changes by deliberately adjusting the photolithography focus parameter to create a defocused exposure condition. This produces a photoresist mandrel with a specific non-vertical sidewall profile that compensates for stress relaxation. By changing the focus parameter, the mandrel acquires a predetermined angle that ensures accurate spacer critical dimensions after stress release, demonstrating how parameter optimization can overcome material limitations.
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 controls and corrects spacer critical dimensions, maintaining desired angles and profiles, even after photoresist removal, thereby improving the precision of pattern transfer in semiconductor fabrication.
Implementation Method 1
exposing a layer of photoresist to a pattern of actinic radiation using a mask-based photolithography system
Implementation Method 2
depositing a conformal layer of spacer material on the sidewall
Data Source
AI summary
A method for patterning a substrate in which a patterned photoresist structure can be formed on the substrate, the patterned photoresist structure having a sidewall. A conformal layer of spacer material can be deposited on the sidewall. The patterned photoresist structure can then be removed from the substrate, leaving behind the spacer material. Then, the substrate can be directionally etched using the sidewall spacer as an etch mask to form the substrate having a target critical dimension.