Combined Overlay Target for Reticle Grid and Wafer Error

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current alignment marks, such as grating-type (AIM) marks, are not suitable for measuring image placement errors due to their dense nature, which conflicts with the requirement for isolated 'X' and 'Y' edges needed for absolute displacement measurements, especially as semiconductor design rules become smaller, reducing the total error budget for overlay and image placement errors.

Innovation Solution

A combined overlay and image placement error target is introduced, featuring a grating-type mark within a ring-type mark, with both having a common centroid, allowing for separate measurement of overlay and image placement errors without interference, using a first periodic structure on one layer and a second periodic structure on an adjacent layer, enabling robust measurement across smaller design rules.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If grating-type (AIM) marks are used for overlay measurement, then overlay error measurement is improved, but image placement error measurement capability deteriorates

Engineering Contradiction:

Improveoverlay error measurementVSAvoidimage placement error measurement capability

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent combines two previously separate measurement functions into a single hybrid target structure. The target includes both grating-type features (for overlay measurement) and isolated edge features (for image placement error measurement), allowing both measurements to be performed on the same target without requiring separate marks

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The hybrid target structure serves multiple functions simultaneously: it can measure both overlay error and image placement error, making it a universal measurement target that replaces the need for separate grating-type marks and edge-based marks

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Quantity of substance

If smaller design rules are used, then device density is improved, but total error budget for overlay and image placement errors deteriorates

Engineering Contradiction:

Improvedevice densityVSAvoidtotal error budget

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent replaces mechanical measurement methods with optical diffraction-based measurement. By using optical diffraction patterns from the grating structures, the system achieves higher measurement precision without being constrained by mechanical resolution limits, thereby enabling accurate measurement even when the total error budget is reduced due to smaller design rules

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If box-in-box targets are used, then overlay measurement is possible, but measurement accuracy deteriorates due to etched line profile asymmetry and optical aberrations

Engineering Contradiction:

Improveoverlay measurement capabilityVSAvoidoverlay measurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the measurement parameter from direct edge detection (which is sensitive to line profile asymmetry) to diffraction pattern analysis. By measuring the diffraction orders from grating structures, the system achieves measurement accuracy that is independent of etched line profile variations and reduces sensitivity to optical aberrations

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7408642B1Registration target design for managing both reticle grid error and wafer overlay

Publication Date: 2008.08.05 KLA TENCOR TECHNOLOGY CORP

AI summary

A combined overlay target and methods for its use are disclosed. The combined overlay target includes a grating-type overlay target and an image placement error target having substantially perpendicular features with spaced apart edges. The grating-type target and the image placement error target have a common centroid and are sufficiently separated that the grating-type overlay target does not interfere with measurement of image placement error.