Wafer Tilt Correction Mapping for Accurate Semiconductor Metrology

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Solution Overview

Problem

Existing metrology and inspection systems face challenges in achieving accurate measurements due to local wafer tilt, which introduces measurement inaccuracy and tool-to-tool variation, as the positioning stages and chucks do not maintain perfect flatness, leading to variations in illumination angles and focal plane alignment.

Innovation Solution

A method and system for compensating local wafer tilt by generating a wafer orientation correction map based on differences between actual and estimated tilt values from optical and Z-measurements, allowing for accurate tilt correction and improved measurement accuracy across the wafer surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If wafer positioning stage and chuck are used to locate the wafer, then the wafer can be positioned in the optical path, but local wafer tilt occurs due to finite mechanical tolerances and non-perfect flatness

Engineering Contradiction:

Improvewafer positioningVSAvoidmeasurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system performs preliminary measurement of local wafer tilt across the wafer surface using an optical tilt sensor before the actual metrology measurement. This preliminary action generates a tilt map that is used to correct subsequent measurements, thereby eliminating the adverse effect of mechanical tolerances and non-perfect flatness on measurement accuracy

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention replaces reliance on purely mechanical positioning accuracy with an optical measurement and correction system. Instead of depending on the mechanical flatness of the positioning stage and chuck, the system uses optical tilt sensing and computational correction to achieve high measurement precision despite mechanical imperfections

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If local wafer tilt is measured and corrected by adjusting system model calibration values, then some compensation is achieved, but the physical location of incidence of the illumination beam spot is not changed

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidcompensation completeness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The invention introduces an intermediary optical tilt sensor that directly measures the local tilt of the wafer surface at each measurement location. This intermediary measurement provides accurate tilt data that can be used to correct both the illumination angle and focal plane alignment, achieving more complete compensation than direct adjustment of system model values alone

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If wafer orientation correction is performed at each measurement location, then measurement accuracy is improved, but computational effort and time to solution increase

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidtime to solution

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The system divides the wafer surface into multiple measurement locations and performs tilt measurement and correction at each location independently. This segmentation allows for localized correction of wafer tilt, improving measurement accuracy at each spot while enabling parallel processing of multiple locations to reduce overall computational time

Inventive Principle:

Principle #1Segmentation

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 enables precise estimation and correction of wafer tilt, enhancing measurement accuracy and reducing tool-to-tool variation, thereby improving the reliability of metrology and inspection systems in semiconductor manufacturing.

Implementation Method 1

a wafer orientation measurement subsystem is employed to measure an actual orientation of a calibration wafer with respect to a measurement subsystem at each location

Methodology Applied

Scientific EffectOptical tilt measurement:

Implementation Method 2

a normal position sensor subsystem is employed to measure a normal position of the calibration wafer with respect to the measurement subsystem at each location

Methodology Applied

Scientific EffectZ-measurement:

Data Source

PatentUS20240162074A1Methods And Systems For Measurement Of Semiconductor Structures With Active Tilt Correction

Publication Date: 2024.05.16 KLA CORP

AI summary

Wafer tilt is measured and compensated based on corrected measurements of tilt derived from a set of height measurements across a wafer. A set of wafer orientation correction values is generated by a measurement system at a large number of wafer locations. At each location, a wafer orientation correction value is determined based on a difference between the local wafer tilt of a calibration wafer measured by an optical tilt sensor and a corresponding estimated value of the local slope of the calibration wafer derived from Z-measurements. The same measurement system performs Z-measurements of a sample wafer and estimates the local slope at each location. The difference between the corresponding wafer orientation correction value and the local slope at each location accurately estimates the wafer orientation at each measurement location. The wafer orientation is adjusted based on the corrected value of wafer orientation.