Asymmetric Alt-PSM for Symmetrical Light Intensity
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Solution Overview
Problem
The photolithography process faces challenges in achieving sharply defined transitions between light and dark edges in projected images, particularly for features 150 nm or smaller, leading to reduced contrast and quality of resulting photoresist profiles due to imbalance in transmission intensity between the 0° and 180° phase portions of alternating phase shift masks (Alt-PSMs).
Innovation Solution
An Alt-PSM with a 0° phase portion and a 180° phase portion of different widths, where the 180° phase portion is wider than the 0° phase portion, is used to balance light transmission intensity, resulting in a symmetrical aerial image intensity graph, potentially eliminating the need for double exposure techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional Alt-PSM with equal width phase portions is used, then phase shifting effect is achieved, but light transmission intensity is imbalanced between 0° and 180° portions
Solution Approach 1:
The patent applies asymmetry by making the 180° phase portion wider than the 0° phase portion. This asymmetric width configuration compensates for the inherent intensity imbalance in conventional Alt-PSMs, achieving symmetrical light transmission intensity and improved photoresist profile quality.
2Length of moving object
If phase shifting is applied to sub-150nm features, then feature size reduction is achieved, but edge definition and image contrast deteriorate
Solution Approach 1:
The patent changes the geometric parameter (width) of the phase portions to optimize performance at sub-150nm feature sizes. By adjusting the width ratio between 0° and 180° portions, the system achieves better edge definition and image contrast while maintaining the ability to pattern smaller features.
3Illumination intensity
If double exposure technique is used to balance intensity, then light transmission symmetry is improved, but process complexity and time increase
Solution Approach 1:
The patent incorporates the intensity balancing action directly into the mask structure design itself, rather than requiring subsequent double exposure processing. The asymmetric width configuration is built into the mask during manufacturing, eliminating the need for additional exposure steps and reducing process complexity.
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 configuration enhances the quality of photoresist profiles by achieving symmetrical light intensity curves, reducing CD variation and placement errors, and improving the definition of edges in photoresist patterns, thereby supporting the fabrication of densely packed integrated devices with smaller feature sizes.
Implementation Method 1
alternating phase shifting or alternating phase shift masks (Alt-PSMs) used in those processes. The Alt-PSMs have a physical structure that balances the light transmission intensity through the 0° portion and the 180° portion of the Alt-PSM
Implementation Method 2
During the photolithography process, electromagnetic energy (e.g., light) is transmitted through a photomask or reticle to expose parts of the photoresist layer in the desired pattern
Implementation Method 3
The exposed photoresist can be subjected to a chemical treatment (e.g., 'developing') that removes areas of photoresist that were exposed to the light
Data Source
AI summary
An alternating phase-shifting mask (Alt-PSM) comprising a 0° phase portion having a first width and a 180° phase portion having a second width greater than the first width. Example differences between the width of the 180° phase portion and the 0° phase portion may be 10 nm, 15 nm, or 20 nm. An Alt-PSM having phase portions of different widths can have an aerial image intensity transmission graph that is symmetric, for example, at 0.2-0.3 intensity.