Recessed Photomask Layout for Optical Proximity Correction
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Solution Overview
Problem
In integrated circuit fabrication, the increasing density of transistors leads to smaller dimensions of photomask features, causing optical proximity effects that distort patterns imaged onto photoresist layers, and existing technologies struggle to maintain accurate imaging due to diffraction inaccuracies.
Innovation Solution
A photomask with a recessed region on the translucent substrate is designed to diffract radiation without imaging a pattern, where the recessed region is strategically arranged and dimensioned to match the diffraction pattern of densely arranged features, thereby enhancing the process window and depth of focus by adjusting the pitch between isolated and densely arranged main features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the density of main features on the photomask is increased to meet higher transistor density requirements, then the photomask can support higher integration circuits, but optical proximity effects cause pattern distortion and reduce imaging fidelity
Solution Approach 1:
Assist features (recessed regions, mandrels, or protrusions) are introduced as intermediary elements between the main features and the imaging system. These assist features modify the diffraction pattern of incident radiation to compensate for optical proximity effects, thereby maintaining pattern fidelity while allowing higher feature density on the photomask
Solution Approach 2:
The pitch between assist features and main features is carefully controlled within specific ranges (e.g., 0.7 to 1.3 times the pitch between densely arranged main features) to optimize the diffraction pattern. By adjusting these dimensional parameters, the assist features effectively equalize the imaging performance between isolated and densely arranged main features
2Ease of manufacture
If the pitch between isolated main features is large, then isolated features can be manufactured, but the process window and depth of focus are reduced compared to densely arranged features
Solution Approach 1:
Assist features are positioned near isolated main features to act as optical mediators. These assist features modify the diffraction pattern to simulate the optical environment of densely arranged features, thereby expanding the process window and depth of focus for isolated features without affecting their manufacturability
Solution Approach 2:
The solution extends the problem from two-dimensional feature arrangement to three-dimensional photomask structure by adding vertical depth through recessed regions or protrusions. This dimensional extension allows control over the diffraction pattern in a way that equalizes the imaging performance of isolated and dense features
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 solution effectively increases the sharpness and focus of patterns imaged onto the photoresist layer, ensuring that isolated features perform similarly to densely arranged ones, thereby improving the overall process window and depth of focus of the photomask.
Implementation Method 1
The recessed region is configured to diffract radiation passing through the translucent substrate such that the depth of field of the photomask is increased
Data Source
AI summary
A photomask includes a substrate, an opaque filling formed embedded in the substrate, and an opaque main feature over the substrate. The opaque filling has a first width. The opaque main has a second width greater than the first width of the opaque filling. The opaque filling and the opaque main feature comprise same material.