One-Coat Encapsulated Graphite Heater for Thermal Stress Reduction

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Solution Overview

Problem

Graphite heaters used in semiconductor processing face issues such as corrosion, particle generation, mechanical fragility, and thermal stress due to coefficient of thermal expansion mismatch, leading to early failure and electrical short circuits.

Innovation Solution

A one-coat encapsulated graphite heater design that incorporates structural inserts made of nitrides, carbides, or oxynitrides to provide support and a coating layer of the same materials to encapsulate the graphite body, reducing thermal and CTE mismatch stresses, and allowing for a single coating operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If graphite heater is machined into serpentine geometry, then heating path is defined, but mechanical integrity deteriorates and heater becomes fragile

Engineering Contradiction:

Improveheating path configurationVSAvoidmechanical integrity

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The heater is divided into discrete heating elements separated by gaps, with structural bridges providing support. This segmentation allows the heating path to be defined while maintaining mechanical strength through the bridge structures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The heater combines graphite heating elements with structural bridges made of graphite or other materials. This composite structure provides both the heating function and the mechanical strength needed to prevent fragility.

Inventive Principle:

Principle #40Composite materials

2Reliability

If graphite heater is coated with protective coating layer, then corrosion resistance is improved, but thermal stress increases due to CTE mismatch

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidthermal stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The heater structure incorporates gaps between heating elements and structural bridges that provide stress relief zones. These local structural modifications allow the protective coating to be applied for corrosion resistance while accommodating thermal expansion differences to reduce overall thermal stress.

Inventive Principle:

Principle #3Local quality

3Strength

If graphite heater is machined to leave graphite bridges, then structural support is provided, but coating process becomes complex requiring multiple steps

Engineering Contradiction:

Improvestructural supportVSAvoidcoating process complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The structural bridges and heating elements are integrated into a single graphite component that can be coated in one operation. The design merges the structural support function with the heating function, allowing both to be present in the same coating process without requiring separate coating steps.

Inventive Principle:

Principle #5Merging (Combining)

4Temperature

If graphite heater operates at high temperature, then heating function is achieved, but dimensional changes occur due to annealing causing bowing

Engineering Contradiction:

Improveoperating temperatureVSAvoiddimensional stability

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

The heater is segmented into heating elements and structural bridges, where the bridges provide dimensional stability during annealing while the heating elements perform the heating function. This segmentation allows differential thermal behavior without compromising overall structural integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The structural bridges are designed with specific geometric parameters and material properties that remain stable during annealing, providing a reference frame that maintains dimensional stability even as other parts of the heater undergo thermal changes.

Inventive Principle:

Principle #35Parameter changes

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 design enhances the mechanical strength and stability of the graphite heater, reducing thermal stress and the risk of electrical short circuits, while simplifying the manufacturing process by eliminating the need for multiple coating steps and graphite bridge removal.

Implementation Method 1

Methodology Applied

Scientific EffectThermal stress reduction through CTE matching: Thermal Expansion

Implementation Method 2

a heating element of pyrolytic graphite (PG) superimposed on a pyrolytic boron nitride base... with two ends connected to a source of external power

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS10687393B2One-coat encapsulated graphite heater and process

Publication Date: 2020.06.16 MOMENTIVE PERFORMANCE MATERIALS QUARTZ INC

AI summary

A coated graphite heater. The heater has a configuration comprising a plurality of heating elements having a major portion disposed parallel to an upper surface of the heater so that the major portion is disposed horizontally. The heater configuration provides a heater that exhibits reduced thermal stress and/or reduced CTE mismatch stress particularly compared to designs having heating elements with a major portion oriented perpendicular to the plane of the upper surface of the heater.