Region-Differentiated Focus Scan Patterns for Lithographic Leveling

Solution Overview

Problem

Variations in focus distance across a wafer coated with a photoresist layer during lithographic exposure lead to degradation of printed images, as small deviations from the optimal focus distance can render patterns unusable, particularly in high-resolution semiconductor device manufacturing.

Innovation Solution

A method is introduced to level the substrate with respect to the optics system of a lithographic exposure tool by generating separate maps of optimal focus distances for different image regions on the semiconductor dies, allowing for precise adjustment along independent horizontal directions to maintain optimal focus across the wafer, ensuring high-quality lithographic patterns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a single focus map is generated for the entire wafer, then the leveling process is simple and fast, but focus variations across different image regions with different patterns cannot be compensated

Engineering Contradiction:

Improvefocus distance uniformityVSAvoidleveling process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The wafer surface is divided into multiple image regions (first image regions and second image regions) with different pattern densities. Separate focus maps are generated for each region type by scanning only the corresponding regions, allowing differentiated focus compensation while reducing the complexity of scanning the entire wafer surface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different focus compensation strategies are applied to different image regions based on their specific pattern characteristics. First focus maps are generated for first image regions with first patterns, and second focus maps are generated for second image regions with second patterns, enabling localized optimization of focus quality for each region type.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the entire wafer surface is scanned to generate a focus map, then comprehensive focus data is obtained, but the measurement time and process complexity increase significantly

Engineering Contradiction:

Improvefocus distance measurement accuracyVSAvoidfocus map generation time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The wafer surface is divided into multiple image regions (first image regions and second image regions) with different pattern densities. Separate focus maps are generated for each region type by scanning only the corresponding regions, allowing differentiated focus compensation while reducing the complexity of scanning the entire wafer surface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of scanning the entire wafer surface, the method scans only specific image regions that are representative of each pattern type. First scan paths scan only first image regions, and second scan paths scan only second image regions, obtaining sufficient focus data for leveling without the time cost of complete surface coverage.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If focus scanning includes all image regions, then complete focus information is captured, but scan paths become complex and processing time increases

Engineering Contradiction:

Improvelithographic exposure qualityVSAvoidexposure tool throughput

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The wafer surface is divided into multiple image regions (first image regions and second image regions) with different pattern densities. Separate focus maps are generated for each region type by scanning only the corresponding regions, allowing differentiated focus compensation while reducing the complexity of scanning the entire wafer surface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of scanning the entire wafer surface, the method scans only specific image regions that are representative of each pattern type. First scan paths scan only first image regions, and second scan paths scan only second image regions, obtaining sufficient focus data for leveling without the time cost of complete surface coverage.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS10209636B1Exposure focus leveling method using region-differentiated focus scan patterns

Publication Date: 2019.02.19 SANDISK TECHNOLOGIES LLC

AI summary

Pattern-dependent random deviations in measurement of optimal focus distances can be minimized by separating scan paths into multiple types of scan paths that scan only a respective predetermined image region in semiconductor dies. A substrate including in-process semiconductor dies is coated with a photoresist layer, and is located onto a stage in a lithographic exposure tool. Maps of optimal focus distances are generated by performing optimal focus distance scans that cover a respective subset of image regions having distinct image patterns. The substrate can be leveled with respect to an optics system of the lithographic exposure tool employing a weighted average of multiple maps of optimal focus distances. Once the substrate is leveled on the stage, a lithographic exposure process can be performed with enhanced uniformity in the focus distances across the in-process semiconductor dies.