Graphite Heater with PBN Coating and Slits for Thermal Stress
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Solution Overview
Problem
Graphite heaters used in semiconductor wafer processing are prone to corrosion, particle generation, mechanical fragility, and irregular heat signatures due to machining, leading to thermal stress and potential electrical short circuits, which affects the uniformity and stability of temperature control.
Innovation Solution
A heater assembly featuring a pyrolytic graphite core coated with pyrolytic boron nitride, designed with a serpentine pattern and exaggerated bends, and incorporating slits or apertures to manage thermal stress and provide a uniform heating profile, along with a lip for enhanced heat transfer and mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If graphite is used as heating element, then temperature resistance and economy are improved, but corrosion resistance and particle generation are worsened
Solution Approach 1:
The patent employs a composite structure consisting of a graphite heating element coated with pyrolytic boron nitride (PBN). The graphite provides excellent temperature resistance and electrical conductivity, while the PBN coating layer protects against corrosion from wafer processing chemicals and prevents particle generation. This composite material approach resolves the contradiction by combining materials with complementary properties.
2Shape
If graphite heater is machined into serpentine geometry, then heating path is improved, but mechanical integrity is worsened
Solution Approach 1:
The patent introduces slits or apertures through the graphite heater body, dividing it into segmented sections. These slits reduce mechanical stress concentrations that would otherwise develop in continuously machined serpentine geometries, thereby improving mechanical integrity while maintaining the serpentine heating path configuration for effective heat distribution.
3Strength
If graphite heater thickness is increased, then mechanical strength is improved, but fragility and handling difficulty are worsened
Solution Approach 1:
By introducing slits that divide the graphite heater into sections, the patent reduces overall fragility while maintaining adequate thickness for strength. The segmented structure allows the heater to flex slightly and reduces stress propagation, making thicker heaters easier to handle and install without sacrificing mechanical strength.
4Temperature
If graphite heater is used, then temperature resistance is improved, but dimensional stability is worsened
Solution Approach 1:
The patent applies pyrolytic boron nitride coating to the graphite heater surface. This coating layer compensates for dimensional changes in the graphite during thermal cycling and annealing processes. The PBN coating maintains a stable dimensional relationship with the graphite substrate, preventing bowing and misalignment that would otherwise occur due to graphite's dimensional instability at elevated temperatures.
5Object-affected harmful factors
If boron nitride coating is applied, then corrosion resistance is improved, but thermal stress is worsened
Solution Approach 1:
The patent carefully selects pyrolytic boron nitride as the coating material because its coefficient of thermal expansion is matched to graphite. This minimizes CTE mismatch stress between the coating and substrate during thermal cycling. The slits introduced in the graphite further help relieve accumulated thermal stress by providing expansion pathways, preventing coating delamination while maintaining corrosion protection.
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 solution provides a robust, thermally stable, and uniformly heated graphite heater assembly that reduces thermal stress, maintains mechanical integrity, and ensures consistent temperature profiles across the heating surface, enhancing the reliability and efficiency of semiconductor wafer processing.
Implementation Method 1
a heating element of pyrolytic graphite ("PG") superimposed on a pyrolytic boron nitride base... two ends connected to a source of external power
Implementation Method 2
graphite is corroded by some of the wafer processing chemical environments... the entire heating assembly is then coated with a pyrolytic boron nitride ("PBN") layer
Implementation Method 3
One or more slits or apertures may be disposed through the body. The slits may cut-off heat transfer between an upper body to a lower body
Data Source
Figure 1A
Figure 1B~1C
Figure 2A
AI summary
A heater assembly (100) is disclosed herein. The heater assembly (100) comprises a tubular body (110). The tubular body includes a graphite core disposed in a heating path (120). The graphite core is coated with an overcoat layer. The tubular body (110) includes slits (5341) that cut-off heat transfer between portions (536, 538) of the tubular body. The heater assembly (100) has a configuration comprising a plurality of heating rungs (140) having a predominant portion (242) disposed substantially perpendicular to an upper surface (102) of the heater so that the predominant portion (242) is disposed vertically. The heater assembly includes a flange (130) at a first end (104) and a lip (212) at a second end (102). The heater assembly configuration provides a heater that exhibits reduced thermal stress and/or reduced CTE mismatch stress particularly compared to other designs.