EUV Reflective Mask Alignment Region Design
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Solution Overview
Problem
In EUV lithography, the low contrast of alignment marks due to the presence of conductive layers makes positional alignment between the reflective mask and inspection apparatus challenging, as existing methods either require alterations to the optical system or are not suitable for detecting alignment marks by transmission.
Innovation Solution
A reflective mask design where the absorptive layer is formed directly on the substrate in the alignment region, and the conductive layer is not present, allowing for alignment mark detection by transmission, thereby improving contrast and accuracy in positional arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive layer is formed on the whole surface of the substrate to hold the reflective mask on an electrostatic chuck, then the mask can be securely held, but the contrast of alignment marks is significantly lowered making positional alignment difficult
Solution Approach 1:
The substrate surface is segmented into two distinct regions: a first region with a conductive layer for electrostatic chuck adhesion, and a second region without a conductive layer for high-contrast alignment mark detection. This spatial segmentation allows both functions to coexist without interfering with each other.
Solution Approach 2:
Different regions of the substrate are given different local properties: the first region has conductive properties for electrical adhesion, while the second region has non-conductive properties optimized for optical detection of alignment marks. Each region is optimized for its specific function.
2Manufacturing precision
If the alignment mark is made relatively small to fit the design, then the circuit pattern density is improved, but the contrast is lowered making positional alignment difficult
Solution Approach 1:
The alignment mark region is provided with a specific local quality (absence of conductive layer) that enhances its optical detection properties. This localized modification allows small alignment marks to maintain high contrast for detection while preserving the overall circuit pattern density.
3Device complexity
If existing alignment methods are used with the conductive layer present, then the mask structure is simple, but the positional alignment accuracy is insufficient
Solution Approach 1:
The substrate is divided into functional regions where the second region is specifically designed for alignment operations. This segmentation enables the use of simple transmission-type alignment methods without requiring complex optical system alterations, while achieving high positional alignment accuracy.
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
This design enables accurate and rapid detection of alignment marks by transmission, facilitating precise positional alignment and correction of circuit patterns in EUV lithography.
Implementation Method 1
the other side of the substrate is exposed... allowing for alignment mark detection by transmission
Implementation Method 2
an absorptive layer formed on the intermediate layer... in an alignment region where an alignment mark is provided
Data Source
AI summary
A main object of the invention is to provide a reflective mask for EUV lithography, which may detect an alignment mark by transmission. The invention achieves the object by providing a reflective mask comprising a substrate, a multilayer formed on one side of the substrate, an intermediate layer formed on the multilayer, an absorber formed in pattern on the substrate on which the multilayer and the intermediate layer are formed, and a conductive layer formed on the other side of the substrate, wherein the pattern of the absorber constitutes a circuit pattern and an alignment mark, and in an alignment region where the alignment mark is provided, the other side of the substrate is exposed.