Ceramic Heater With Localized Thickness Control For Wafer Temperature Uniformity

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Solution Overview

Problem

Ceramic heaters used in plasma treatment of wafers face challenges in achieving uniform temperature distribution, with the existing designs being difficult to manufacture and prone to thermal conduction issues, leading to non-uniform heating and potential damage.

Innovation Solution

A ceramic heater with a disk-shaped ceramic plate featuring inner- and outer-peripheral-side heater elements, where the ceramic plate's thickness in a predetermined zone is 3.9% or less of its diameter, allowing for a temperature gradient profile with a flat central zone and gradually increasing or decreasing temperature towards the periphery, achieved by controlling the heater elements to maintain a predetermined temperature difference between the center and periphery.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the ceramic plate thickness is reduced in the predetermined zone to achieve the desired temperature gradient profile, then temperature uniformity in the central zone is improved, but the mechanical strength and structural stability of the ceramic plate deteriorate

Engineering Contradiction:

Improvetemperature uniformity in central zoneVSAvoidmechanical strength of ceramic plate

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The ceramic plate is designed with non-uniform thickness distribution, where the thickness in the predetermined zone (boundary zone between inner and outer peripheral zones) is specifically reduced to 3.9% or less of the ceramic plate diameter. This local thinning creates higher thermal resistance in the boundary zone, preventing excessive heat conduction from the outer peripheral zone to the central zone, thereby maintaining temperature uniformity in the central zone while preserving overall structural integrity through the thicker inner and outer peripheral zones.

Inventive Principle:

Principle #3Local quality

2Stress or pressure

If the ceramic plate thickness is reduced to prevent thermal conduction damage, then thermal stress is reduced, but the structural integrity and damage resistance of the ceramic heater deteriorates

Engineering Contradiction:

Improvethermal stressVSAvoidstructural integrity

Core Design Contradiction:

Stress or pressureVSReliability

Solution Approach 1:

The ceramic plate employs localized thickness reduction only in the predetermined boundary zone, while maintaining adequate thickness in the inner peripheral zone and outer peripheral zone. This selective thinning approach reduces thermal stress concentration at the boundary where temperature gradients are steepest, while the thicker inner and outer zones preserve structural integrity and resistance to mechanical damage.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The ceramic plate is functionally segmented into three zones: inner peripheral zone, predetermined boundary zone, and outer peripheral zone, each with different thickness characteristics. The inner peripheral zone and outer peripheral zone maintain sufficient thickness for structural support, while the boundary zone is thinned to manage thermal stress and control heat flow, effectively dividing the structural and thermal management functions.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If the ceramic plate is made thinner to achieve the temperature gradient profile, then manufacturing complexity is reduced, but the heat resistance and thermal management capability deteriorates

Engineering Contradiction:

Improvemanufacturing complexityVSAvoidheat resistance

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

Rather than uniformly thinning the entire ceramic plate, the invention applies thickness reduction only to the predetermined boundary zone, maintaining adequate thickness in other areas for heat resistance. This localized approach achieves the desired temperature gradient profile and reduces manufacturing complexity compared to designing a completely thin plate, while preserving necessary thermal management capabilities through selective thickness control.

Inventive Principle:

Principle #3Local quality

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 design ensures a nearly flat temperature distribution in the central zone and a gradual temperature rise or fall towards the periphery, reducing thermal stress and preventing damage, while maintaining sufficient strength and heat resistance.

Implementation Method 1

one or more inner-peripheral-side heater elements embedded in an inner peripheral zone of the ceramic plate, and one or more outer-peripheral-side heater elements embedded in an outer peripheral zone of the ceramic plate

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

a difficulty in manufacturing is high and a damage risk accompanies due to thermal conduction occurred inside the ceramic heater

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS10566218B2Ceramic heater

Publication Date: 2020.02.18 NGK INSULATORS LTD

AI summary

A ceramic heater includes a disk-shaped ceramic plate with an upper surface defining a wafer placement surface on which a wafer is to be placed. One or more inner-peripheral-side heater elements are embedded in an inner peripheral zone of the ceramic plate, and one or more outer-peripheral-side heater elements are embedded in an outer peripheral zone of the ceramic plate. A thickness of the ceramic plate in a predetermined zone is 3.9% or less of a diameter of the ceramic plate. The predetermined zone is a zone including a boundary line between the inner peripheral zone and the outer peripheral zone.