Lithographic Metrology Mark Placement for Stitching Alignment
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Solution Overview
Problem
In lithographic processes, accurately aligning large image sensors or devices requires precise stitching of image portions exceeding the projection beam's cross-sectional area, often undetectable until electrical testing, leading to potential device failure and significant time and resource waste.
Innovation Solution
A method and apparatus that project metrology marks outside the composite image area during the stitching process, allowing real-time alignment measurement of image portions, ensuring accurate positioning and reducing errors by determining the relative positions of metrology marks to assess image portion alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If image portions are projected sequentially onto adjacent target portions to form a composite image, then the area of substrate that can be imaged exceeds the maximum cross sectional area of the projection beam, but alignment accuracy between adjacent image portions deteriorates and becomes undetectable until electrical testing
Solution Approach 1:
The patent introduces metrology marks as intermediary reference objects that are projected alongside image portions onto the substrate. These marks serve as mediators for measuring and verifying the alignment between adjacent image portions, enabling detection and correction of stitching errors without requiring completion of the entire device.
Solution Approach 2:
The patent implements a feedback mechanism by measuring the relative positions of metrology marks after projection and using this measurement information to determine and correct the relative positions of adjacent image portions. This closed-loop feedback enables real-time alignment verification and correction during the lithographic process.
2Measurement precision
If metrology marks are projected inside the composite image area, then alignment measurement is possible, but the area available for active device regions is reduced
Solution Approach 1:
The patent relocates metrology marks from the two-dimensional active image area to the third spatial dimension by projecting them in the scribe lane region outside the composite image boundaries. This dimensional relocation allows alignment measurement functionality to coexist with maximized active device area, as the marks occupy space that would otherwise be unused or used for device separation.
3Measurement precision
If alignment errors are detected only after device completion through electrical testing, then manufacturing precision can be verified, but time and resources are wasted on defective devices
Solution Approach 1:
The patent performs alignment measurement and verification as a preliminary action during the lithographic exposure process itself, by projecting and measuring metrology marks immediately after each image portion is formed. This early detection prevents progression of defective devices through subsequent manufacturing steps, eliminating waste of time and resources that would occur with post-completion testing.
Data Source
AI summary
A lithographic method includes patterning a beam of radiation with a patterning device. The patterning device includes at least two image patterning portions and at least two metrology mark patterning portions. The method also includes projecting at least two image portions of the patterned beam of radiation sequentially onto target portions of a substrate such that the projected image portions are substantially adjacent to each other on the substrate and collectively form a composite image on the substrate. The method also includes projecting a metrology mark onto the substrate outside of the area of the composite image at the same time as projecting each of at least two of the image portions, and measuring the alignment of the metrology marks to determine the relative positions of the at least two image portions.