Ghost Pattern Targets for Lithographic Uniformity Control
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Solution Overview
Problem
The challenge in semiconductor manufacturing is achieving uniformity in critical dimensions of integrated circuits on wafers, particularly due to non-uniformity in photolithography processes, which affects yield and performance, and existing methods struggle to accurately measure and correct registration and overlay errors.
Innovation Solution
The method involves using ghost pattern targets on photo masks that do not print under nominal exposure conditions, allowing for the measurement of critical dimension distribution and registration errors, enabling correction of these issues through optical proximity correction and adjustment of exposure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ghost pattern targets are added to the photo mask for measurement purposes, then measurement precision of critical dimension distribution is improved, but device complexity of the photo mask increases
Solution Approach 1:
The photo mask is segmented into two functional sets of patterns: first set of patterns for circuit fabrication and second set of ghost patterns for measurement. This segmentation allows the mask to serve dual purposes while keeping the measurement functions separate and identifiable from the primary fabrication patterns.
Solution Approach 2:
Ghost pattern targets serve as intermediary measurement objects that do not directly contribute to the circuit pattern but enable indirect measurement of critical dimension distribution. These intermediary patterns act as proxies for measuring mask uniformity without interfering with the primary fabrication function.
2Ease of operation
If the second set of patterns is made visible under nominal exposure conditions, then ease of measurement is improved, but manufacturing precision of the circuit pattern is worsened due to registration errors
Solution Approach 1:
The ghost patterns are designed with locally different properties (different dimensions, shapes, or materials) compared to the circuit patterns. This local differentiation ensures that ghost patterns respond differently to exposure conditions, allowing them to be measured under nominal exposure without affecting the critical dimensions of the circuit patterns.
Solution Approach 2:
The dimensions of the second set of patterns are specifically chosen to fall outside the process window for nominal exposure. By changing the dimensional parameters of the ghost patterns, they become visible under nominal exposure conditions while the circuit patterns remain unaffected, enabling measurement without compromising manufacturing precision.
3Measurement precision
If ghost pattern targets are placed in open spaces of the circuit pattern, then measurement precision is improved, but area available for circuit components is reduced
Solution Approach 1:
Only a limited number of ghost pattern targets are placed in the open spaces of the circuit pattern, using just enough measurement points to achieve adequate statistical precision for critical dimension distribution measurement. This partial action approach minimizes the area occupied by measurement targets while still providing sufficient data for accurate measurement.
4Measurement precision
If multiple measurement targets are distributed across the photo mask, then measurement precision of uniformity is improved, but device complexity increases
Solution Approach 1:
Multiple ghost pattern targets are merged into a single second set of patterns on the photo mask, distributed across different locations. This combining of multiple measurement functions into one integrated mask structure allows uniformity measurement across the entire mask area while managing complexity through systematic arrangement and standardized target designs.
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 approach improves critical dimension uniformity, registration accuracy, and overlay precision, enhancing the quality of semiconductor lithography processes by allowing for precise measurement and correction of non-uniformities without interfering with active circuit features.
Implementation Method 1
a first photo mask having a first set of patterns and a second set of patterns... projecting the second set of patterns onto a detector under a second exposure condition
Data Source
AI summary
A photo mask having a first set of patterns and a second set of patterns is provided in which the first set of patterns correspond to a circuit pattern to be fabricated on a wafer, and the second set of patterns have dimensions such that the second set of patterns do not contribute to the circuit pattern that is produced using a lithography process based on the first set of patterns under a first exposure condition. The critical dimension distribution of the photo mask is determined based on the second set of patterns that do not contribute to the circuit pattern produced using the lithography process based on the first set of patterns under the first exposure condition.