Photomask Optical Assist Layout for Mixed-Density Pattern Transfer
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Solution Overview
Problem
The existing photolithography process in semiconductor devices faces challenges in simultaneously satisfying different pattern densities across various regions, leading to pattern transfer distortions and affecting device performance and yield.
Innovation Solution
A photomask design with distinct pattern regions and optical assist members, where the pattern density of one region is greater than another, and the dimensions of assist members are below the exposure limit, ensuring precise pattern transfer by adjusting transmittance and preventing distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single exposure condition is used for the entire photomask, then the exposure process is simple and fast, but pattern transfer distortion occurs at region peripheries due to different pattern densities
Solution Approach 1:
The photomask is divided into multiple pattern regions (first pattern region with high density, second pattern region with low density) that have different local optical properties. Optical assist members are selectively placed in specific regions to adjust local transmittance, allowing each region to be optimized for its specific pattern density requirements while using a single exposure condition.
2Manufacturing precision
If optical assist members with larger dimensions are used, then transmittance adjustment is more effective, but unwanted pattern transfer occurs to the photoresist layer
Solution Approach 1:
The dimensions of optical assist members are precisely controlled to be below the exposure limit of the exposure source. This parameter change allows the assist members to modify transmittance effectively without being large enough to create unwanted patterns that would transfer to the photoresist layer during exposure.
3Ease of manufacture
If pattern density is uniform across the photomask, then exposure conditions are easy to satisfy, but device functionality is compromised due to different region requirements
Solution Approach 1:
Different pattern regions are designed with different pattern densities to match the specific functionality requirements of each region (first device region vs. memory region). Optical assist members are selectively added to specific regions to ensure that each region's exposure conditions are satisfied according to its unique pattern density characteristics.
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
Improves pattern transfer accuracy and device performance by minimizing distortions at region peripheries, enhancing yield and preventing unwanted pattern transfer to adjacent areas.
Implementation Method 1
a dimension of the first optical assist member is less than an exposure limit of the exposure source
Implementation Method 2
The predetermined pattern is disposed in the first pattern region, and the first optical assist member is disposed in the second pattern region
Data Source
AI summary
A photomask configured to corporate with an exposure source to pattern a semiconductor device. The semiconductor device defines a first device region and a memory region disposed adjacent to the first device region, and the semiconductor device includes a memory device disposed in the memory region. The photomask includes a base, a predetermined pattern and a first optical assist member. The base defines a first pattern region and a second pattern region respectively corresponding to the first device region and the memory region. The predetermined pattern is disposed in the first pattern region. The first optical assist member is disposed in the second pattern region. A pattern density of the first pattern region is greater than a pattern density of the second pattern region, and a dimension of the first optical assist member is less than an exposure limit of the exposure source.