Optical Pad Vibration Sensing for CMP Endpoint Detection

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Solution Overview

Problem

Existing chemical mechanical polishing (CMP) techniques struggle to accurately determine the polishing endpoint due to variations in slurry distribution, polishing pad condition, relative speed, and load, making it difficult to reliably detect layer transitions and ensure wafer uniformity.

Innovation Solution

An in-situ vibration monitoring system using a light source and sensor to measure polishing pad vibrations, analyzing frequency domain changes to detect the exposure of underlying layers by monitoring displacement at high sampling rates, enabling precise endpoint detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional torque monitoring is used to detect polishing endpoint, then the system complexity is low, but the measurement precision and reliability of endpoint detection deteriorates due to variations in slurry distribution, polishing pad condition, and load

Engineering Contradiction:

Improveendpoint detection precisionVSAvoidmonitoring system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the traditional mechanical torque monitoring system with an optical sensing system. The optical sensor measures vibrations of the polishing pad through non-contact means, eliminating the need for mechanical coupling and torque measurement. This substitution provides more precise endpoint detection while reducing mechanical complexity in the monitoring system.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces the polishing pad itself as an intermediary element. The optical sensor does not directly measure substrate properties but instead measures vibrations of the polishing pad, which indirectly reflect the polishing process state and endpoint conditions. This intermediary approach enables precise measurement without direct contact with the substrate.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If polishing time is used to determine endpoint, then the process is simple to operate, but the manufacturing precision deteriorates due to variations in material removal rate

Engineering Contradiction:

Improveplanarization precisionVSAvoidendpoint determination simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

The patent implements real-time feedback monitoring of polishing pad vibrations during the polishing process. The optical sensor continuously measures vibration characteristics, and the system provides immediate feedback on the polishing state. This enables precise endpoint detection based on actual process conditions rather than predetermined time schedules, maintaining both precision and operational simplicity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary characterization of vibration signatures for different polishing states. By pre-establishing the relationship between vibration patterns and endpoint conditions, the system can quickly and accurately determine endpoint without complex real-time analysis, maintaining ease of operation while achieving high precision.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If high sampling rates are used for vibration monitoring, then the measurement precision and frequency resolution improve, but the use of energy and data processing requirements increase

Engineering Contradiction:

Improvevibration profile resolutionVSAvoidenergy consumption for monitoring

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent applies partial monitoring by focusing measurement efforts only on the critical frequency ranges and time periods most relevant to endpoint detection. Rather than continuously analyzing the entire frequency spectrum at maximum sampling rates, the system selectively monitors specific vibration characteristics, reducing energy consumption while maintaining sufficient measurement precision for accurate endpoint detection.

Inventive Principle:

Principle #16Partial or excessive 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

Enhances the reliability of detecting underlying layer exposure and improves wafer-to-wafer uniformity by providing real-time, accurate polishing endpoint detection.

Implementation Method 1

a light source to emit a light beam and a sensor that receives a reflection of the light beam from a reflective surface of the polishing pad

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentUS12447579B2Chemical mechanical polishing vibration measurement using optical sensor

Publication Date: 2025.10.21 APPLIED MATERIALS INC

AI summary

A chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a substrate against a polishing surface of the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate, an in-situ vibration monitoring system including a light source to emit a light beam and a sensor that receives a reflection of the light beam from a reflective surface of the polishing pad, and a controller configured to detect exposure of an underlying layer due to the polishing of the substrate based on measurements from the sensor of the in-situ pad vibration monitoring system.