Photomask Light Blocking Patterns for Thermal Stress Reduction
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Solution Overview
Problem
In photolithography processes, thermal stress caused by light absorption in photomasks leads to distortion and overlay errors due to heat generation, which affects the accuracy of pattern transfer onto semiconductor wafers.
Innovation Solution
The photomask design incorporates a light transmission substrate with pattern regions and light blocking regions, where the second light blocking patterns have a thinner thickness than the first, reducing light absorption and thermal stress by optimizing the intensity and phase of light transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If light blocking patterns are used to block incident light, then light blocking effectiveness is improved, but heat generation increases causing thermal deformation
Solution Approach 1:
The patent applies different thicknesses to different light blocking patterns: first light blocking patterns (surrounding pattern regions) have a first thickness, while second light blocking patterns (in light blocking regions) have a second thickness that is smaller than the first. This local differentiation allows the first patterns to effectively block light and reduce thermal stress, while the second patterns provide sufficient blocking without excessive heat generation.
Solution Approach 2:
The patent changes the thickness parameter of light blocking patterns based on their location and function. By adjusting the thickness parameter, the patent optimizes the balance between light blocking effectiveness and heat generation, with thicker patterns where thermal stress reduction is critical and thinner patterns where light blocking is sufficient with less material.
2Productivity
If light transmission regions are used to transmit light to the wafer, then exposure effectiveness is improved, but thermal stress on the photomask increases
Solution Approach 1:
The patent segments the light blocking region into two functional zones with different thickness characteristics: first light blocking patterns surrounding each pattern region and second light blocking patterns in the remaining light blocking regions. This segmentation allows differential thermal management, with the first patterns being thicker to reduce thermal stress from the high-intensity light blocking near pattern regions, while the second patterns are thinner where thermal stress is less critical.
3Ease of manufacture
If uniform thickness light blocking patterns are used, then manufacturing simplicity is maintained, but thermal stress distribution becomes uneven causing distortion
Solution Approach 1:
The patent introduces asymmetry in the thickness of light blocking patterns based on their functional requirements. First light blocking patterns have a first thickness optimized for reducing thermal stress, while second light blocking patterns have a second thickness optimized for light blocking. This asymmetric design creates a non-uniform thickness distribution that compensates for varying thermal stress conditions across the photomask, preventing distortion while remaining manufacturable.
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 design reduces the amount of light absorbed by the photomask, minimizing thermal stress and improving the accuracy of pattern transfer onto the wafer, thereby reducing fabrication errors and maintaining the chemical structure of the photoresist layer.
Implementation Method 1
the light blocking patterns may absorb a large amount of energy of the light irradiated onto the photomask, thereby generating heat
Implementation Method 2
The heat may be conducted to the transparent substrate of the photomask, and thus the transparent substrate may expand to cause a thermal deformation due to the heat
Implementation Method 3
the transparent substrate may expand to cause a thermal deformation due to the heat
Data Source
AI summary
A photomask includes a light transmission substrate, a plurality of pattern regions disposed over the light transmission substrate, a shape of the plurality of pattern regions being transferred onto a wafer during an exposure process, and a light blocking region surrounding the plurality of pattern regions. Each of the plurality of pattern regions is a light transmitting region that exposes a portion of the light transmission substrate. The light blocking region includes first light blocking patterns that respectively surround the plurality of pattern regions to have closed loop shapes and second light blocking patterns that are disposed between adjacent first light blocking patterns, adjacent second light blocking patterns being spaced apart from each other by a first distance in a first direction. And the first light blocking patterns have a first thickness and the second light blocking patterns have a second thickness which is smaller than the first thickness.