IC Test Structure for Electrical Photomask Misalignment Detection

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Solution Overview

Problem

Existing semiconductor fabrication processes face challenges in detecting misalignment of latent images produced by different photomasks, particularly in dopant implantation and diffusion steps, which can lead to defective wafers, as microscopy-based methods are inefficient and may miss misalignments.

Innovation Solution

A test structure and electrical wafer acceptance test (WAT) are developed to detect misalignment of latent images using electrical measurements, which can be performed concurrently with other WAT tests without adding extra workflow steps, providing quantitative measures of misalignment and its direction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If microscopy-based methods are used to detect misalignment, then visual inspection of latent images is possible, but the detection efficiency is low and misalignments may be missed

Engineering Contradiction:

Improvemisalignment detection accuracyVSAvoiddetection efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces microscopy-based visual inspection with electrical measurement methods. Instead of using optical microscopes to visually examine latent images, the invention uses electrical probes to measure electrical characteristics (such as resistance or current) that change in response to misalignment. This substitution of mechanical/optical detection with electrical detection improves both efficiency and reliability of misalignment detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If electrical WAT is performed to detect misalignment, then quantitative measures of misalignment and its direction are provided, but additional test structure complexity is introduced

Engineering Contradiction:

Improvemisalignment quantificationVSAvoidtest structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent divides the test structure into multiple discrete electrical contact regions arranged in specific patterns. By segmenting the measurement into multiple contact points and comparing electrical characteristics between them, the system can determine both the magnitude and direction of misalignment. This segmentation allows quantitative analysis while keeping each individual measurement point relatively simple.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The electrical measurement system serves multiple functions: it detects misalignment, quantifies the degree of misalignment, determines the direction of misalignment, and can be integrated into existing WAT workflows. This multi-functionality reduces the need for separate specialized test structures for different types of measurements.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If microscopy-based detection is used, then latent image alignment can be visually assessed, but the workflow requires extra steps and time

Engineering Contradiction:

Improvemisalignment detection reliabilityVSAvoidworkflow time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent enables misalignment detection to be performed continuously as part of the existing WAT process without interrupting the fabrication workflow. The electrical measurements can be taken automatically during standard testing operations, eliminating the need for separate microscopy inspection steps and maintaining continuous production flow while ensuring reliable detection.

Inventive Principle:

Principle #20Continuity of useful action

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 electrical WAT efficiently detects and quantifies misalignment, enabling diagnostic analysis to identify the source of misalignment, ensuring high fabrication quality and reducing the risk of defective wafers.

Implementation Method 1

measuring a first electrical resistance between a first pair of the active regions of the test structure; measuring a second electrical resistance between a second pair of the active regions of the test structure

Methodology Applied

Scientific EffectElectrical Resistance: Electrical Resistance

Data Source

PatentUS20250323105A1Test structure and integrated circuit test using same

Publication Date: 2025.10.16 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

In a method of fabricating at least one IC, doped regions are formed on a semiconductor wafer using a first photolithography mask, including at least one doped region of a test structure. Active regions are formed on the semiconductor wafer using a second photolithography mask, including active regions of the test structure. Electrical contacts are formed on the active regions of the test structure. Electrical resistances are measured between pairs of active regions of the test structure using the electrical contacts. At least one metric is determined indicating whether the doped regions are spatially aligned with the active regions based on the measured electrical resistances. In response to the at least one metric indicating the doped regions are spatially aligned with the active regions, completing fabrication of the at least one integrated circuit.