Photomask Substrate Thickness Compensation for Focus Shift
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Solution Overview
Problem
The increased step height difference between memory cell and peripheral circuit regions on semiconductor wafers complicates focal position correction in exposure apparatuses, leading to pattern transfer failures and yield loss during photolithography processes.
Innovation Solution
A pattern inspection method and photomask design that involves detecting and compensating for residual focus shifts by adjusting the photomask substrate's thickness or optical path length to ensure accurate focal positioning within the focus depth, using either uniform thickness light-shielding bodies or optical path difference adjusting members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the exposure apparatus performs focal position correction using conventional methods, then the focus position can be adjusted for flat wafer surfaces, but accurate pattern transfer fails when significant step height differences exist between memory cell and peripheral circuit regions
Solution Approach 1:
The wafer surface is divided into multiple regions with different step height characteristics (memory cell region and peripheral circuit region). The photomask is correspondingly segmented into multiple regions, with each region having a specific optical path length designed to match the step height of its corresponding wafer region, enabling accurate pattern transfer across uneven surfaces
Solution Approach 2:
The solution transitions from two-dimensional focal plane adjustment to three-dimensional optical path length control. By varying the optical path length in the vertical dimension across different photomask regions, the invention compensates for step height differences and maintains pattern transfer accuracy across the wafer surface
2Ease of manufacture
If the photomask uses uniform thickness light-shielding bodies, then manufacturing is simplified, but residual focus shifts cannot be compensated for regions with step height differences
Solution Approach 1:
Instead of uniform thickness throughout, the photomask employs light-shielding bodies with locally varied thickness. Each region's light-shielding body thickness is specifically designed to compensate for the step height characteristics of its corresponding wafer region, achieving both manufacturing feasibility and focus precision
3Manufacturing precision
If optical path difference adjusting members are used to compensate for step height differences, then pattern transfer accuracy improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the light-shielding function and optical path length control function into a single integrated photomask structure. The light-shielding bodies simultaneously perform pattern definition and focal position compensation, eliminating the need for separate adjusting members and reducing overall device complexity
Data Source
AI summary
According to one embodiment, a pattern inspection method includes detecting a region of a photomask having a pattern that differs from a corresponding design, acquiring an exposure focus shift information including an exposure focus shift amount of a portion of a substrate corresponding to the detected region of the photomask. The exposure focus shift amount for the detected region is acquired from the exposure focus shift information, and then a pass/fail determination for the detected region is performed based on an estimated pattern to be formed on the substrate.