Interferometer Wafer Tilt Variation for Flatness Precision

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Solution Overview

Problem

Existing interferometric methods fail to effectively reduce fringe print-through (FPT) error, which is a systematic error affecting precision metrics like SFQR, despite multiple measurements due to correlated interferogram patterns across shared load positions.

Innovation Solution

Introduce random two-dimensional tilts using tilt motors before each measurement to convert systematic error into random error, allowing effective averaging and precision improvement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple measurements are taken and averaged, then random error is reduced, but systematic error (fringe print-through) remains due to correlated interferogram patterns across shared load positions

Engineering Contradiction:

ImproveprecisionVSAvoidsystematic error reduction

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces dynamic random tilts to the workpiece between measurements using tilt motors. This dynamic adjustment changes the load position and interferogram pattern for each measurement, breaking the systematic correlation that prevents error averaging. By making the measurement conditions dynamic rather than static, the systematic error is converted into random error that can be reduced through averaging.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes physical parameters (tilt angles in two dimensions) before each measurement to alter the interferogram pattern. By varying these parameters randomly, the systematic error pattern changes with each measurement, allowing the error to be averaged out. This parameter change approach transforms the persistent systematic error into variable error that diminishes with multiple measurements.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If the workpiece is held fixed during measurements, then measurement stability is maintained, but fringe print-through error persists due to repeated loading at the same position

Engineering Contradiction:

Improvemeasurement stabilityVSAvoidflatness precision

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

Instead of holding the workpiece completely fixed, the patent introduces controlled dynamic tilts using tilt motors. This dynamic approach maintains stability through active control while simultaneously changing the load position to prevent systematic error accumulation. The workpiece is stabilized during each individual measurement but repositioned between measurements to vary the loading pattern.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent converts the harmful systematic error from repeated loading into a beneficial random error pattern. By intentionally introducing random tilts, the consistent systematic error is transformed into variable error that can be averaged out. What was originally a stability issue (repeated loading causing systematic error) becomes a solution mechanism through controlled randomization.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Loss of time

If averaging is performed without breaking correlation, then measurement time is reduced, but error reduction does not approach theoretical limits due to positive covariance between measurements

Engineering Contradiction:

Improvemeasurement timeVSAvoiderror reduction efficiency

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The patent applies preliminary random tilts to the workpiece before each measurement to break the correlation between measurements. This preliminary action ensures that each measurement is statistically independent, allowing the averaging process to achieve theoretical error reduction limits. By preparing the workpiece with random orientation changes before measurement, the system enables efficient error averaging without requiring excessive measurement repetitions.

Inventive Principle:

Principle #10Preliminary 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 method significantly reduces systematic error, bringing precision closer to theoretical limits by randomizing interferogram patterns, enhancing SFQR and thickness map precision.

Implementation Method 1

A random two-dimensional tilt is applied to the workpiece before each of the measurements using at least one tilt motor

Methodology Applied

Scientific EffectRandom tilt variation:

Implementation Method 2

Interferometers are used as metrology tools, where workpiece surface information is encoded in the phase of interferogram

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS20250271251A1Flatness precision improvement with systematic error reduction via induced wafer tilt variation

Publication Date: 2025.08.28 KLA CORP

AI summary

A workpiece is placed on a stage in an interferometer. Measurements of the workpiece are taken using the interferometer. A random two-dimensional tilt is applied to the workpiece before each of the measurements using at least one tilt motor. A stage is configured to hold a workpiece in a path of the beam of light from a beam splitter. The tilt motor is connected with the stage and randomly move the stage in two dimensions before a measurement.