SLM-Based PSM Alignment for Sub-90nm Lithography
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Solution Overview
Problem
Current lithographic techniques face challenges in accurately aligning the second layer pattern on a workpiece with a first layer pattern, particularly in alternating phase shift structures, which requires precise alignment to avoid phase errors and defects, especially as feature sizes shrink to 90-nm and lower technology nodes.
Innovation Solution
The use of a spatial light modulator (SLM) illuminated with a 248 nm DUV laser and a DUV-sensitive CCD camera to create a light stamp image reflected on the first layer alignment marks, allowing for precise measurement and alignment of the second layer pattern without optical alignment differences between measuring and writing, and incorporating a pre-exposure function to maintain signal quality across varying resist thicknesses and AR coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment methods are used for second layer patterning, then the process is simpler, but alignment precision deteriorates leading to phase errors and defects
Solution Approach 1:
The patent introduces an intermediary alignment mark structure consisting of a first alignment mark and a second alignment mark with different orientations. These marks serve as mediators between the writing system and the workpiece, enabling precise alignment through optical reflection and image capture without requiring direct complex mechanical alignment mechanisms.
Solution Approach 2:
The patent replaces mechanical alignment systems with an optical alignment system. Instead of using mechanical positioning devices, the invention uses optical reflection from alignment marks, image capture by a camera, and computational processing to achieve sub-pixel alignment precision, thereby eliminating mechanical complexity while improving measurement precision.
2Productivity
If feature sizes are shrunk to 90-nm and lower technology nodes, then device density increases, but alignment precision requirements become more stringent making alignment more difficult
Solution Approach 1:
The patent segments the alignment system into distinct functional components: alignment marks with specific geometric features, optical illumination system, image capture system, and computational processing. This segmentation allows each component to be optimized independently for the required sub-90nm alignment precision while maintaining overall system productivity.
Solution Approach 2:
The patent changes critical parameters including using 248 nm DUV laser wavelength for illumination, employing alternating phase shift mask structures, and implementing pre-exposure of alignment marks to enhance contrast. These parameter changes enable the system to achieve the required alignment precision for 90-nm and lower technology nodes.
3Measurement precision
If pre-exposure is applied to maintain signal quality across varying resist thicknesses, then measurement precision is maintained, but additional process time is required
Solution Approach 1:
The patent applies preliminary action by pre-exposing the alignment marks before the main measurement process. This pre-exposure enhances the optical contrast and signal quality of the alignment marks, ensuring that subsequent measurements achieve maximum precision. The pre-exposure is performed quickly and locally only on the alignment mark areas, minimizing time loss.
Solution Approach 2:
The patent implements skipping by performing the pre-exposure only on the alignment mark regions rather than the entire wafer, and by using a high-speed DUV laser to rapidly complete the exposure. This selective and accelerated approach maintains signal quality while minimizing the time penalty to under 6 minutes for the complete alignment process.
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 approach achieves sub-pixel accuracy and high precision in second layer alignment, ensuring phase defect avoidance and maintaining measurement precision across different resist thicknesses and AR coating conditions, with alignment times under 6 minutes and a precision of 13-30 nm, effectively addressing the challenges of shrinking feature sizes and phase shift structures.
Implementation Method 1
a spatial light modulator (SLM) illuminated with a 248 nm DUV laser
Implementation Method 2
create a light stamp image reflected on the first layer alignment marks
Implementation Method 3
a DUV-sensitive CCD camera to create a light stamp image
Data Source
AI summary
The present invention relates to alignment of a writing system and a workpiece. In particular, it relates to alignment to write a second layer pattern on a workpiece that has a first layer pattern, using an SLM. It extends to producing a mask or reticle, and to producing a layer of a device using the mask or reticle. Particular aspects of the present invention are described in the claims, specification and drawings.