E-beam Mask Correction for Photolithography CD Uniformity
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Solution Overview
Problem
Existing photolithographic processes face challenges in minimizing undesired intra-field variation in substrate features, such as critical dimension (CD) variations, due to imperfections in masks and projection tools, which can lead to fabrication of inoperable circuitry.
Innovation Solution
A method involving the creation of a difference map between the desired intra-field pattern and the intra-field signature pattern, followed by modifications to E-beam mask features using an E-beam writer to reduce substrate feature variations, by determining relationships among orthogonal dimensions and varying E-beam dose or shape in multiple exposures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithographic processing is used, then substrate features can be formed, but intra-field variation in critical dimension occurs due to mask and projection tool imperfections
Solution Approach 1:
The patent applies preliminary action by pre-compensating for intra-field variation through multiple E-beam exposures with varying doses and shapes. The mask features are deliberately modified before photolithography to counteract anticipated projection tool imperfections, ensuring that the final substrate features achieve the desired critical dimension uniformity across the exposure field.
Solution Approach 2:
The patent implements local quality by applying different E-beam doses and exposure shapes to different regions of the mask corresponding to different areas of the exposure field. Each mask feature receives customized exposure parameters based on the local characteristics of the projection tool, allowing precise compensation for spatially varying imperfections across the field.
2Manufacturing precision
If multiple E-beam exposures with varying doses and shapes are used to compensate for intra-field variation, then substrate feature uniformity improves, but mask formation complexity increases
Solution Approach 1:
The complex multi-parameter E-beam exposure process is performed in advance during mask fabrication. By consolidating the compensation steps into the mask formation phase rather than requiring complex adjustments during substrate processing, the patent achieves high precision substrate features while managing overall process complexity through preliminary preparation.
Solution Approach 2:
The patent replaces complex mechanical adjustments in the projection tool with a programmable E-beam exposure system. Instead of mechanically adjusting the projection tool to compensate for imperfections, the system uses software-controlled variations in E-beam dose and shape parameters, enabling precise compensation through digital control rather than mechanical complexity.
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 effectively reduces substrate feature variations, improving CD uniformity and bias across the exposure field, leading to more accurate and reliable photolithographic processing.
Implementation Method 1
modifications to E-beam mask features using an E-beam writer to reduce substrate feature variations, by determining relationships among orthogonal dimensions and varying E-beam dose or shape in multiple exposures
Implementation Method 2
Photolithographic processing includes forming a patterned image of radiation (i.e., actinic energy) onto a photosensitive material such as photoresist. The radiation alters exposed regions relative to unexposed regions.
Data Source
AI summary
A method of forming a mask includes creating a difference map between a desired intra-field pattern that is to be formed on substrates and an intra-field signature pattern. The intra-field signature pattern represents a pattern formed on an example substrate by an exposure field using an example E-beam-written mask. Modifications are determined to formation of mask features to be made using an E-beam mask writer if forming a modified E-beam-written mask having mask features modified from that of the example E-beam-written mask that will improve substrate feature variation identified in the difference map. The E-beam mask writer is programmed using the determined modifications to improve the substrate feature variation identified in the difference map. It is used to form the modified E-beam-written mask having the modified mask features. One or more substrates are photolithographically processed using the modified E-beam-written mask.