Self-Aligned Overlay Mark via Cut Mask Segmentation
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Solution Overview
Problem
In silicon-based memory chip fabrication, it is challenging to form a self-aligned mask that maintains alignment precision with previously formed critical features, especially when using pitch multiplication techniques, as non-critical features can interfere with overlay measurements.
Innovation Solution
A method involving a cut mask layer that covers specific regions on a substrate, exposing the main feature and determining self-alignment with its edges, allowing for precise etching and registration without interference from non-critical features, using pitch-doubling techniques to create a self-aligned overlay mark.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pitch multiplication techniques are used to form array features, then manufacturing capability for dense patterns is improved, but non-critical features interfere with overlay measurements
Solution Approach 1:
The substrate is divided into distinct regions: array regions containing critical pitch-doubled features and peripheral regions containing non-critical features. The mask layer is selectively formed only in peripheral regions, segmenting the measurement area from the critical features. This allows overlay measurements to be performed on array features without interference from non-critical mask patterns.
Solution Approach 2:
The mask layer is applied non-uniformly across the substrate - present in peripheral regions but absent in array regions. This local differentiation ensures that non-critical features exist only where they will not interfere with overlay measurements of critical array features, while still providing necessary protection in peripheral areas.
2Ease of manufacture
If a mask pattern is formed in close proximity to array features, then peripheral regions can be protected, but alignment precision of critical features is compromised
Solution Approach 1:
The mask formation process is segmented by region - peripheral regions receive mask layers for protection, while array regions remain exposed to maintain measurement capability. This spatial segmentation resolves the conflict between needing mask protection and maintaining alignment precision.
Solution Approach 2:
The non-critical mask features are extracted from array regions and placed only in peripheral regions. This removes the harmful interference of mask patterns from the measurement area while preserving the protective function in peripheral areas.
3Ease of manufacture
If non-critical features are present during measurement, then peripheral protection is achieved, but measurement accuracy deteriorates
Solution Approach 1:
The substrate is segmented into measurement regions (array) and protection regions (peripheral). By placing non-critical features only in peripheral regions, the measurement of overlay on array features is isolated from interference, while peripheral protection is simultaneously achieved.
Solution Approach 2:
Different regions of the substrate are given different properties - array regions maintain feature exposure for accurate measurement, while peripheral regions have mask layers for protection. This local quality differentiation resolves the contradiction between measurement accuracy and peripheral protection.
Data Source
AI summary
A method for forming a self-aligned overlay mark is disclosed. First, a first region, a second region and a main feature which is disposed between the first region and the second region all disposed on the substrate are provided. The first region defines a first edge and the second region defines a second edge. Second, a cut mask layer is formed to respectively cover the first region and the second region to expose the main feature. Next, the cut mask layer is determined if it is self-aligned with the second edge or the first edge, and creates a self-aligned overlay mark. Later, a main feature etching step is carried out to transfer the main feature into the substrate when the cut mask layer is determined to be self-aligned with the second edge or the first edge.