Photomask Set Compensation for Orthogonal Corner Rounding
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Solution Overview
Problem
The proximity effect in photolithography causes rounding of orthogonal corners in semiconductor device features due to light scattering, which is not effectively addressed by existing optical proximity correction techniques, especially when orthogonal lines intersect.
Innovation Solution
A photomask set comprising two masks with coordinated opaque and transparent patterns is used to form orthogonal corners, where compensation features like scattering bars are patterned and etched, then removed to improve pattern integrity and reduce rounding effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography with single mask is used, then the process is simple and fast, but orthogonal corners become rounded due to light scattering proximity effect
Solution Approach 1:
The patent divides the single photomask into two separate masks: a first mask containing the primary pattern and a second mask containing compensation features (scattering bars). This segmentation allows each mask to serve a specific function - the first mask defines the basic geometry while the second mask adds scattering bars to compensate for light diffraction effects at orthogonal corners, thereby maintaining corner sharpness without requiring complex single-mask designs
Solution Approach 2:
The compensation features (scattering bars) are pre-patterned on the second mask at specific locations and orientations before the photolithography process. These scattering bars are strategically positioned to intercept and redirect light that would otherwise cause corner rounding, proactively compensating for the proximity effect before it degrades the pattern quality
2Manufacturing precision
If optical proximity correction (OPC) is applied to increase photomask resolution, then pattern definition improves, but it cannot compensate for proximity effect at orthogonal line intersections
Solution Approach 1:
The patent extends the conventional OPC approach by adding a second mask dimension. While traditional OPC modifies a single mask pattern, this invention uses a second mask layer to add scattering bars that address the orthogonal intersection problem from a different dimensional perspective - using vertical scattering bars for horizontal lines and horizontal scattering bars for vertical lines, thereby achieving correction where single-mask OPC fails
3Productivity
If device features are made smaller and closer together to increase integration, then device integration level increases, but proximity effect becomes more prominent
Solution Approach 1:
The patent applies local quality by placing scattering bars only at specific locations where orthogonal lines intersect, rather than uniformly across the entire pattern. The scattering bars are locally positioned at corners and intersections where the proximity effect is most severe, providing targeted compensation that maintains pattern fidelity in critical areas while allowing high device integration elsewhere
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 enables the formation of semiconductor device patterns with sharp, non-rounded orthogonal corners and superior pattern integrity, maintaining the critical dimension accuracy and depth of focus, even at close proximity of device features.
Implementation Method 1
exposing the photosensitive film by projecting light through a photomask that includes transparent areas and an opaque pattern
Implementation Method 2
A light beam that travels along the edge of an opaque feature produces a scattering phenomenon that enlarges the light beam and produces a scattering effect that distorts the pattern being formed
Implementation Method 3
When the light beam passes through the photoresist layer on the substrate, it also reflects off the substructure beneath the photoresist layer and the phenomenon of interference results
Data Source
AI summary
A photomask set includes at least two masks that combine to form a device pattern in a semiconductor device. Orthogonal corners may be produced in a semiconductor device pattern to include one edge defined by a first mask and an orthogonal edge defined by a second mask. The mask set may include a first mask with compensation features and a second mask with void areas overlaying the compensation features when the first and second masks are aligned with one another, such that the compensation features are removed when patterns are successfully formed from the first and second masks. The compensation features alleviate proximity effects during the formation of device features.