Overlay Mark Layout for Dense Electron Beam Overlay Metrology
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Solution Overview
Problem
Current overlay measurement techniques in semiconductor manufacturing are inadequate for complex devices, as they rely on conventional target designs that do not efficiently utilize wafer space and measurement time, leading to suboptimal accuracy and increased production costs.
Innovation Solution
The development of advanced target designs combining electron beam overlay (eOVL) with scatterometry overlay (SCOL) and optical image-based overlay (IBO) targets, which include rotational symmetry and nested polygonal shapes, allowing for denser sampling and increased information content within a smaller area, thereby improving measurement accuracy and reducing measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay measurement targets are used, then the measurement process is simple, but the measurement accuracy and information content are insufficient for complex semiconductor devices
Solution Approach 1:
The patent implements nested polygonal shapes (e.g., inner square within outer square, or concentric polygons) within the overlay target structure. This nesting allows multiple measurement features to be contained within a compact area, increasing the information content and measurement accuracy without proportionally increasing the target area. The nested structures provide multiple reference points and measurement zones that can be analyzed simultaneously.
Solution Approach 2:
The patent transitions from conventional two-dimensional target designs to three-dimensional structured targets with rotational symmetry and nested polygons. This dimensional enhancement creates multiple measurement planes and reference levels, allowing for more comprehensive overlay analysis. The 3D structure provides additional geometric constraints and reference points that improve measurement precision through multi-dimensional data collection.
2Measurement precision
If more overlay targets are placed on the wafer to increase sampling density, then the measurement accuracy improves, but the wafer real estate increases
Solution Approach 1:
By nesting multiple measurement features and polygonal structures within a single compact target area, the patent achieves high information content and effective sampling density without increasing the physical wafer area occupied. The nested design allows multiple measurement functions to coexist in a space-efficient manner.
Solution Approach 2:
The patent combines multiple overlay measurement targets and features into a single integrated target structure with rotational symmetry and nested polygons. This merging consolidates what would traditionally require multiple separate targets into one compact unit, maintaining high measurement capability while reducing the total wafer real estate required.
3Productivity
If conventional single-set scanner corrections are applied to all wafers in a lot, then the process is efficient, but the overlay errors cannot be optimized for individual wafer variations
Solution Approach 1:
The patent segments the overlay measurement and correction process by enabling individual measurement of each wafer through enhanced target designs. The segmented target structures allow for wafer-specific overlay error characterization, which can then feed into customized scanner corrections for each wafer, moving away from blanket single-set corrections applied to entire lots.
Solution Approach 2:
The patent enables dynamic adjustment of overlay correction parameters based on individual wafer measurements. The enhanced target designs provide sufficient measurement data to determine wafer-specific correction parameters, allowing the system to change correction parameters adaptively for each wafer rather than using fixed lot-level corrections.
Data Source
AI summary
The present disclosure provides a target and a method of performing overlay measurements on a target. The target includes an array of cells comprising a first cell, a second cell, a third cell, and a fourth cell. Each cell includes a periodic structure with a pitch. The periodic structure includes a first section and a second section, separated by a first gap. The target further includes an electron beam overlay target, such that electron beam overlay measurements, advanced imaging metrology, and/or scatterometry measurements can be performed on the target.