Photomask Layout Retargeting for Overlay Window Expansion
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Solution Overview
Problem
The increasing feature density in integrated circuits beyond photolithography resolution leads to alignment errors between exposure steps due to pitch constraints, necessitating pattern decomposition, which results in an insufficient overlay window.
Innovation Solution
A method for making a photomask layout that involves decomposing a circuit design layout into overlapping first and second lines and a hole, followed by a retarget step using electronic design automation (EDA) tools to increase the overlay window, and subsequent optical proximity correction (OPC) to enhance pattern alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pattern decomposition is applied to meet pitch constraint requirements, then the photolithography process can handle beyond-resolution pitch sizes, but alignment error between exposure steps increases
Solution Approach 1:
The patent applies preliminary action by performing a retarget step before the exposure process to pre-adjust the positions of pattern endpoints. This preliminary repositioning of pattern elements ensures that when the actual exposure and etching steps are executed, the alignment between decomposed patterns is optimized, thereby reducing alignment error while maintaining the ability to handle beyond-resolution pitch sizes through pattern decomposition
2Adaptability or versatility
If pattern decomposition is applied to meet pitch constraint requirements, then two exposure steps can be used for beyond-resolution pitch sizes, but the overlay window becomes insufficient
Solution Approach 1:
The retarget step performed as a preliminary action repositions pattern endpoints before exposure to maximize the overlay window. By pre-adjusting the pattern layout, the subsequent exposure and etching steps can proceed with sufficient alignment tolerance, thereby improving reliability while maintaining adaptability to pitch constraints through the two-exposure-step decomposition approach
3Ease of manufacture
If the first line and second line are aligned with the hole, then the photomask layout can be formed, but the overlapping area is insufficient leading to short errors
Solution Approach 1:
The retarget step performs a preliminary repositioning of line endpoints away from the hole before the photomask layout is finalized. This preliminary action increases the overlapping area between the first line, second line, and hole, thereby preventing short errors while maintaining ease of manufacture through the systematic retargeting process that adjusts pattern positions before exposure
Data Source
AI summary
A method for making a photomask layout is provided. A first graphic data of a photomask is provided, wherein the first graphic data includes a first line with a first line end target, a second line with a second line end target and a hole, the first line is aligned with the second line, and the first line, the second line and the hole partially overlap with each other. Thereafter, a retarget step is performed to the first graphic data to obtain a second graphic data, wherein the retarget step includes moving the first line end target and the second line end target in opposite directions away from each other.