Supercooled Droplet Cooling for CMP Pad Temperature Control

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Solution Overview

Problem

Conventional chemical mechanical planarization (CMP) methods face challenges in preventing scratches during the polishing of LSI device surfaces due to insufficient cooling and residue removal, particularly with the miniaturization of devices, where precise temperature control and effective cleaning are crucial to avoid damage and defects.

Innovation Solution

A polishing method and apparatus that utilize a Laval nozzle to jet supercooled droplets onto the polishing pad, providing efficient cooling by controlling the surface temperature and enhancing residue removal through the use of supercooled droplets, which are frozen and can capture and discharge foreign matters from the pad's pores without the need for a diamond dresser.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional air jet cooling is used in CMP, then the pad surface and slurry are cooled, but the cooling capacity is insufficient

Engineering Contradiction:

Improvepad surface temperatureVSAvoidcooling capacity

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent utilizes the phase transition of water from liquid to solid (freezing) when it contacts the supercooled jet stream. This phase change absorbs latent heat of fusion, providing intensive cooling effect that rapidly reduces pad surface temperature and prevents overheating during CMP operations, thereby resolving the insufficient cooling capacity of conventional air jet methods.

Inventive Principle:

Principle #36Phase transitions

Solution Approach 2:

The patent employs a jet stream delivery system that propels supercooled water droplets onto the pad surface using pneumatic pressure. This hydraulic/pneumatic approach delivers cooling medium directly to the heat generation zone with high velocity and precision, achieving superior cooling capacity compared to conventional air jet methods that rely on evaporation alone.

Inventive Principle:

Principle #29Pneumatics and hydraulics

2Reliability

If a diamond dresser is used to clean the polishing pad, then residues and foreign matters are removed, but diamond microparticles may be dropped causing large scratches

Engineering Contradiction:

Improvescratch preventionVSAvoiddiamond particle contamination

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical diamond dresser system with a jet stream cleaning system that uses supercooled water droplets. Instead of mechanically scraping the pad surface with diamond particles, the jet stream freezes and dislodges residues through thermal shock and phase change, eliminating the risk of diamond particle contamination while effectively removing polish residues and foreign matters.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses disposable supercooled water droplets instead of reusable diamond dresser elements. The water freezes upon contact, captures residues, and is then discarded, providing a clean, contamination-free cleaning method that avoids the wear and particle shedding problems associated with reusable diamond dressers.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If polishing is performed without effective cooling, then productivity is maintained, but scratches and defects increase due to temperature rise

Engineering Contradiction:

ImproveCMP processing speedVSAvoidsurface flatness and defect level

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary cooling action by jetting supercooled droplets onto the pad surface before and during the polishing process. This preemptive cooling prevents temperature rise that would otherwise lead to thermal expansion, slurry degradation, and increased scratching, thereby maintaining both high productivity and manufacturing precision throughout the polishing operation.

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 achieves rapid and efficient cooling of the polishing pad and slurry, reducing the risk of scratches and improving productivity by maintaining optimal polishing performance and preventing damage to the LSI device surfaces, while eliminating the risk of diamond particle-induced scratches during the CMP process.

Implementation Method 1

jetting jet stream containing supercooled droplets from a nozzle having a narrow portion toward the polishing pad

Methodology Applied

Scientific EffectSupercooling: Supercooling

Implementation Method 2

the use of supercooled droplets, which are frozen and can capture and discharge foreign matters from the pad's pores

Methodology Applied

Scientific EffectFreezing: Freezing

Implementation Method 3

supercooled droplets, which are frozen and can capture and discharge foreign matters from the pad's pores

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS8740667B2Polishing method and polishing apparatus

Publication Date: 2014.06.03 KIOXIA CORP

AI summary

According to one embodiment, a polishing method comprises pressing a substrate being rotated against a polishing pad being rotated and supplying slurry on the polishing pad, measuring a surface temperature of the polishing pad, and when the surface temperature is not less than a predetermined temperature, jetting jet stream containing supercooled droplets from a nozzle having a narrow portion toward the polishing pad.