Photomask Recessed Region for Optical Proximity Correction
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Solution Overview
Problem
In integrated circuit fabrication, the increasing density of transistors requires smaller features on photomasks, leading to optical proximity effects that distort patterns imaged onto photoresist layers, and existing technologies struggle to maintain accurate imaging due to diffraction inaccuracies, especially with isolated features having different process windows than densely arranged ones.
Innovation Solution
A photomask with a recessed region on the translucent substrate is used, configured to diffract radiation without imaging a pattern, which adjusts the diffraction pattern of isolated features to match that of densely arranged features, thereby increasing the process window and depth of focus by reducing the pitch between isolated and dense features through a linear recessed region with specific width and depth calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the dimensions of main features on photomasks are reduced to increase transistor density, then the density of features on photomasks is improved, but optical proximity effects cause distortion in patterns imaged onto photoresist layers
Solution Approach 1:
Assist features are introduced as intermediary elements between the main isolated features and the substrate. These assist features mediate the optical interaction by providing additional diffraction paths that compensate for the optical proximity effects, thereby maintaining pattern accuracy while allowing higher feature density
Solution Approach 2:
The invention changes the physical parameters of the photomask structure by introducing features with specific depth variations (recessed or protruding regions) and tailored dimensions. By adjusting these parameters, the diffraction characteristics are modified to correct optical proximity effects and maintain imaging precision at higher densities
2Manufacturing precision
If assist features are added to correct optical proximity effects, then pattern accuracy is improved, but the complexity of the photomask structure increases
Solution Approach 1:
Instead of uniformly modifying the entire photomask, the invention applies local modifications only in specific regions where optical proximity effects occur. The assist features are strategically placed near isolated features that require correction, leaving other regions unchanged and thereby minimizing overall structural complexity
Solution Approach 2:
The photomask structure is segmented into main features and separate assist features. This segmentation allows the assist features to be independently designed and optimized for their specific corrective function without affecting the main feature design, simplifying the overall system architecture
3Manufacturing precision
If recessed regions are used to diffract radiation without imaging patterns, then depth of focus is increased, but the risk of peeling or collapsing during manufacturing increases
Solution Approach 1:
The recessed regions are designed with predetermined depth limits and structural support considerations before manufacturing begins. By pre-calculating appropriate depths that provide sufficient diffraction correction while maintaining structural integrity, the design prevents peeling or collapsing issues before they occur during manufacturing
Solution Approach 2:
The invention carefully controls the depth parameter of recessed regions within specific ranges that balance optical performance and structural stability. By optimizing this parameter, the recessed regions provide adequate diffraction correction to increase depth of focus while maintaining sufficient mechanical strength to prevent manufacturing defects
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 solution enhances the sharpness and focus of patterns imaged onto photoresist layers, ensuring that isolated features perform similarly to dense features, thereby increasing the overall process window and depth of focus, preventing the recessed region from peeling off or collapsing during manufacturing and application.
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 method includes forming a photoresist layer over a wafer. The photoresist layer is exposed to a pattern of radiation using a photomask. The photoresist layer is developed after the photoresist layer is exposed to the pattern of radiation. The photomask includes a substrate and at least one opaque main feature. The substrate has a recessed region recessed from a first surface of the substrate and has a first width. The at least one opaque main feature protrudes from the first surface of the substrate and has a second width greater than the first width of the recessed region of the substrate. A height of the at least one opaque main feature is greater than a depth of the recess region of the substrate.