Split Metrology Targets for Semiconductor Stitching Error Measurement
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Solution Overview
Problem
Semiconductor circuit manufacturing faces challenges in accurately measuring and correcting stitching errors between adjacent exposure fields, which can lead to critical circuit defects due to optical aberrations and scanner motion errors, and existing methods require complex double-exposure processes with overlapping margins.
Innovation Solution
The method involves patterning neighboring semiconductor fields to abut each other without substantial overlap, using non-overlapping 'half-targets' such as linear gratings in the margins for measuring stitching errors, allowing for accurate alignment and correction of misalignment between fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If overlapping margins with double-exposure process are used to measure stitching errors, then measurement capability is provided, but process complexity increases
Solution Approach 1:
The patent divides the measurement target into two separate fields, each containing a portion of the measurement mark. Field 1 contains the first portion and Field 2 contains the second portion, allowing each field to be exposed independently without requiring overlapping margins or double-exposure processes. This segmentation enables stitching error measurement while simplifying the exposure process.
2Measurement precision
If overlapping margins are used for stitching measurement, then misalignment detection is enabled, but manufacturing efficiency decreases
Solution Approach 1:
The measurement mark is segmented into two portions located in separate, non-overlapping fields. This allows the scanner to expose Field 1 and Field 2 independently at different times, eliminating the need for overlapping margins and double-exposure operations, thereby improving manufacturing efficiency while maintaining misalignment detection capability.
Solution Approach 2:
The patent introduces a reference mark positioned away from the measurement mark that serves as an intermediary reference point. This reference mark enables the system to detect misalignment between Field 1 and Field 2 without requiring the fields to overlap, thus improving manufacturing efficiency while maintaining measurement capability.
3Ease of manufacture
If adjacent fields abut without overlap, then exposure process is simplified, but measurement of stitching errors becomes challenging
Solution Approach 1:
The measurement mark is divided into two portions that are respectively positioned in Field 1 and Field 2, which abut without overlap. This segmentation allows the fields to be exposed independently, simplifying the exposure process, while the relative positioning of the two portions enables stitching error measurement through comparison of their positions in the developed photoresist pattern.
Solution Approach 2:
A reference mark is introduced as an intermediary element that is imaged in both Field 1 and Field 2. This reference mark provides a common reference frame that enables the detection of stitching errors between the adjacent, non-overlapping fields, thus solving the measurement challenge while maintaining process simplicity.
Data Source
AI summary
A method of semiconductor metrology includes patterning a film layer on a semiconductor substrate to define a first field on the semiconductor substrate with a first pattern comprising at least a first target feature within a first margin along a first edge of the first field and to define a second field, which abuts the first field, with a second pattern comprising at least a second target feature within a second margin along a second edge of the second field, such that the second edge of the second field adjoins the first edge of the first field. The first target feature in the first margin is adjacent to the second target feature in the second margin without overlapping the second target feature. An image is captured of at least the first and second target features and is processed to detect a misalignment between the first and second fields.