Fourier Filtering Spectral Data for CMP Layer Thickness

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Solution Overview

Problem

Chemical mechanical polishing (CMP) processes face challenges in determining the endpoint of layer planarization on semiconductor substrates due to variations in material removal rates, leading to within-wafer and wafer-to-wafer non-uniformity, which existing optical monitoring techniques fail to adequately address.

Innovation Solution

A method involving in-situ spectrographic monitoring during CMP, using a bandpass filter to isolate and match spectral data corresponding to the layer thickness, allowing for real-time control of the polishing process by correlating filtered spectral data with reference data to achieve precise thickness measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If existing optical monitoring techniques are used during CMP, then real-time thickness monitoring is provided, but measurement precision is insufficient due to interference from patterned features and underlying layers

Engineering Contradiction:

Improvelayer thickness measurement accuracyVSAvoidspectral data processing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes interfering frequency components from the spectral data through Fourier transformation and bandpass filtering. Specifically, the spectral data is transformed to the frequency domain, and frequency ranges corresponding to patterned features and underlying layers are identified and removed, isolating only the frequency components related to the target layer thickness measurement.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces Fourier transformation as an intermediary process between raw spectral data collection and thickness measurement. This mathematical transformation acts as a mediator that converts the complex spectral data into a form where interfering components can be selectively removed through frequency domain filtering, enabling accurate thickness measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If material removal rate variations are not compensated, then CMP process is simpler to operate, but manufacturing precision deteriorates due to within-wafer and wafer-to-wafer non-uniformity

Engineering Contradiction:

Improvewafer uniformityVSAvoidprocess control complexity

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

The patent implements real-time feedback control by continuously monitoring layer thickness during CMP through in-situ optical measurement. The measured thickness data is fed back to the control system, which adjusts polishing parameters to maintain uniform material removal across the wafer and between wafers, compensating for variations in material removal rate.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary Fourier filtering and frequency component removal on the spectral data before thickness measurement. By preprocessing the spectral data to eliminate interfering frequency components related to patterned features and underlying layers, the system prepares clean measurement data in advance, improving measurement accuracy without adding complexity to the physical polishing process.

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

This approach enhances the accuracy of layer thickness measurement by filtering out frequency components associated with patterned features and underlying layers, enabling more precise control of the CMP process and reducing non-uniformity.

Implementation Method 1

monitoring the wafer during the CMP process with an in-situ spectrographic monitoring system to generate spectral data reflected from the wafer

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

applying a bandpass filter operation to the spectral data to generate filtered spectral data, where the bandpass filter may be configured to pass a frequency range corresponding to the layer on the wafer

Methodology Applied

Scientific EffectFourier filtering: Filter (electronic)

Data Source

PatentUS20220371152A1Fourier filtering of spectral data for measuring layer thickness during substrate processing

Publication Date: 2022.11.24 APPLIED MATERIALS INC

AI summary

Determining a thickness of a layer on a wafer during a semiconductor process may include executing the process on the layer on the wafer; monitoring the wafer during the process with an in-situ spectrographic monitoring system to generate spectral data reflected from the wafer; applying a bandpass filter operation to the spectral data to generate filtered spectral data, where the bandpass filter may be configured to pass a frequency range corresponding to the layer on the wafer; and matching the filtered spectral data to a reference filtered spectral data, where the reference filtered spectral data may have been filtered using the bandpass filter operation, and the reference filtered spectral data may be associated with a thickness of the layer.