Negative Photoresist Undercut Profile via Sub-Resolution Border Pattern
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Solution Overview
Problem
Conventional photolithography methods face challenges in producing three-dimensional structures with sub-resolution features and achieving stable undercut profiles for lift-off processes, as they rely on double resist layers and are sensitive to developing conditions and thermal instability.
Innovation Solution
A method involving a single layer of negative photoresist with a pattern in the border zone, irradiated to create sub-resolution assist features, allowing for cross-linking and controlled solubility, enabling the formation of three-dimensional structures with precise undercut profiles suitable for lift-off processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography methods are used to produce three-dimensional structures, then double resist layers are required, but the process complexity and sensitivity to developing conditions increase
Solution Approach 1:
The patent extracts and removes one of the two resist layers from the conventional dual-layer process, using only a single negative photoresist layer. The border zone pattern acts as a self-contained structure that eliminates the need for the second resist layer, thereby simplifying the overall device structure while maintaining undercut profile control
Solution Approach 2:
The single negative photoresist layer performs multiple functions: it serves as both the primary patterning layer and the undercut formation layer. The border zone pattern within this single layer provides both the structural definition and the undercut profile, making the system more universal and less sensitive to developing conditions
2Reliability
If the developing time is increased to remove photoresist from unilluminated areas, then complete removal is achieved, but the minimal undercut size increases
Solution Approach 1:
The patent applies local quality by creating a border zone pattern with specific dimensional characteristics (smaller than minimal resolution) that is localized at the edges of the resist structure. This local structural feature modifies the developing behavior specifically at the border zones, enabling complete photoresist removal from unilluminated areas while maintaining precise undercut size control through the geometric properties of the border pattern
3Ease of manufacture
If the photoresist layer is not stabilized by flood exposure, then the process is simpler, but thermal instability causes pattern degradation at elevated temperatures
Solution Approach 1:
The patent applies preliminary action by pre-forming the border zone pattern with sub-resolution features before the main developing process. This pre-formed structural feature acts as a stabilizing element that prevents thermal degradation during subsequent processing, eliminating the need for additional flood exposure steps while maintaining pattern integrity at elevated temperatures
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 allows for the production of three-dimensional structures with controlled undercut profiles and improved temperature stability, enabling narrower design rules and reduced thermal degradation, facilitating efficient lift-off processes without the need for double resist layers.
Implementation Method 1
The absorption of incident light by a layer of negative photoresist decreases exponentially with the distance from the layer surface
Implementation Method 2
the remaining portions of the positive photoresist become soluble. They are removed together with the overlying portions of the negative photoresist
Data Source
AI summary
The method comprises the steps of applying a layer of a negative photoresist on a bottom layer, providing the layer of the negative photoresist with a pattern arranged in a border zone of the resist structure to be produced, irradiating a surface area of the layer of the negative photoresist according to the resist structure to be produced, and removing the layer of the negative photoresist outside the irradiated surface area. The pattern is produced in such a manner that it comprises a dimension that is smaller than a minimal resolution of the irradiation. The pattern may especially be designed as a sub-resolution assist feature.