Overlay Mark Segmentation for Lithography Alignment
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Solution Overview
Problem
Current overlay marks, such as Box-in-Box (BiB) and Advanced Imaging Metrology (AIM), face challenges in maintaining alignment accuracy during IC manufacturing due to erosion from processes like etching, CMP, or ion implant, which can lead to repeated lithography cycles and reduced feature dimension scaling.
Innovation Solution
An improved overlay mark configuration with four rectangular regions, where at least two pattern elements in each region allow for alternative alignment if any element is damaged, enhancing robustness against erosion and ensuring accurate alignment by providing backup alignment options.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional overlay marks (BiB or AIM) are used, then alignment can be performed initially, but erosion from etching, CMP, or ion implant processes damages the pattern elements, leading to loss of alignment accuracy
Solution Approach 1:
The overlay mark is divided into four separate rectangular regions instead of using a single continuous pattern. Each rectangular region contains its own pattern elements that can serve as independent alignment references. This segmentation ensures that erosion in one region does not compromise the entire alignment system, as other regions remain intact and functional.
Solution Approach 2:
Each rectangular region is designed with specific pattern elements tailored to its location and function. The pattern elements within each region are optimized for local alignment requirements, and the varying configurations across regions provide multiple alignment options. This local optimization ensures that at least some regions maintain alignment capability despite process erosion.
2Productivity
If single pattern element alignment is used, then alignment process is simple, but any damage to the pattern element requires repeated lithography cycles
Solution Approach 1:
Multiple pattern elements are pre-configured across four rectangular regions before the lithography process begins. This preliminary preparation of redundant alignment references ensures that if damage occurs during manufacturing, alternative alignment elements are already in place and can be used immediately without requiring repeated lithography cycles.
Solution Approach 2:
The design incorporates redundant pattern elements as a protective measure against potential damage. This beforehand cushioning ensures that even if some pattern elements are damaged by etching, CMP, or ion implant, the alignment function is preserved through the remaining intact elements, preventing the need for costly and time-consuming repeated lithography.
3Reliability
If multiple pattern elements are included in each rectangular region, then alternative alignment options are available, but the overlay mark configuration becomes more complex
Solution Approach 1:
The four rectangular regions are positioned asymmetrically at the corners of the overlay mark, with each region containing pattern elements configured differently from the others. This asymmetric design provides alignment redundancy while maintaining a relatively simple overall structure that is easier to manufacture and detect compared to fully symmetric or densely packed configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures continued alignment accuracy and process reliability by enabling alignment with alternative pattern elements, reducing the need for repeated lithography cycles and improving the precision of photomask alignment, even after erosion from manufacturing processes.
Implementation Method 1
The apparatus used for executing the exposure step is the so-called Stepper, which typically employing charge-coupled diode (CCD) camera for alignment purpose
Implementation Method 2
Through the lens 14, the device patterns on the photomask 12 and the overlay mark 13 are transferred to the surface of the wafer 15. Compared to the actual size, the pattern on the photomask 13 is magnified, and the pattern is shrunk to actual size by lens 14
Implementation Method 3
light source 11 typically may be the Ultra-Violet light emitted by mercury arc lamp
Data Source
AI summary
An overlay mark formed on a photomask, comprising a first rectangular region, a second rectangular region, a third rectangular region, and a fourth rectangular region, each rectangular region having the same pattern configuration, a longer side of the first rectangular region and a longer side of the third rectangular region being parallel to each other, and a longer side of the second rectangular region and a longer side of the fourth rectangular region being parallel to each other, the longer side of the first rectangular region being perpendicular to the longer side of the second rectangular region; wherein each pattern configuration has at least two different pattern elements allowing other pattern elements be chosen to align when any one of the pattern elements on the substrate was damaged during process.