Case study on high-temperature thermal cycling-induced cracking in SiC-coated graphite components: How can a gradient transition layer extend the service life from 28 cycles to 156 cycles?

Release Date: August 29,2026

Author: Lucy | Head of Process Engineering, SEMICERA

Abstract: From 28 instances to 156 instances – the catastrophic fracture rate decreased from 12% to 2%, and the annual consumables cost was reduced by 35%.

Key takeaway: The client initially perceived the cracking as merely "normal wear and tear of consumables"; however, we ultimately delivered a comprehensive, systematic solution covering everything from the coating architecture to substrate selection and thermal management – the core approach was not simply to replace the components with more durable ones, but to help the client understand the root cause of the cracking and how to address it at its source.                              

A third-generation semiconductor epitaxial equipment manufacturer contacted SEMICERA, reporting that the SiC-coated graphite trays on their production line frequently cracked during high-temperature thermal cycling at 1650°C – with an average service life of just 28 cycles and a catastrophic fracture rate of 12%. The customer's initial request was straightforward: to receive a batch of more durable replacement parts.

Customer Background: Why is an epitaxial equipment manufacturer facing issues with cracking in SiC-coated components?

Key takeaway: The entities seeking our assistance with coating cracking issues are often not end-market wafer fabs, but rather equipment manufacturers or consumables integrators – they are looking for more than just replacement parts; they require a comprehensive technical solution that explains both "why the cracking occurs" and “how to prevent it.”                                                    

The client is a third-generation semiconductor epitaxial equipment R&D and manufacturing enterprise whose core business involves supplying epitaxial growth equipment to SiC power device manufacturers. In this engagement, we collaborated with the Consumables and Process Department, which was addressing a pallet cracking issue on a mass-production SiC epitaxial growth line. These pallets directly support the wafers during the epitaxial growth process, which occurs at temperatures ranging from 1500–1700°C; each processing cycle represents a thermal cycle—from room temperature to high temperature and back to room temperature. Severe pallet cracking can adversely affect the wafer yield, while less severe cases may lead to the scrapping of entire batches or equipment downtime.

According to customer feedback, the supplier previously either provided only “identical-specification replacement parts” – without conducting failure analysis, simply replacing the faulty parts only to find them still malfunctioning; or they simply “accepted all parts as per the drawings and order list” – without evaluating the compatibility between the material system and the process conditions. With the root cause of the problem unresolved, customers were forced to incur recurring downtime-related costs.

Challenge: Why do pallets with a service life of 28 cycles actually crack?

Core conclusion: 28 cycles in a high-temperature thermal cycling test for SiC-coated graphite components already represent a relatively short service life; forcibly thickening the coating or replacing it with a cheaper substrate proves ineffective — the real issue lies in the thermal expansion mismatch between the coating and the substrate, which accumulates into residual stresses during repeated cycling, ultimately exceeding the fracture toughness.                        

We conducted SEM, metallographic cross-sectional, energy-dispersive X-ray spectroscopy, and acoustic scanning analyses on more than 40 failed components, identifying three overlapping root causes: first, the thermal expansion mismatch between the SiC coating (CTE: 4.5×10⁻⁶/K) and the extruded graphite substrate (CTE: 2.8×10⁻⁶/K), leading to the accumulation of residual interfacial stresses under repeated cyclic loading; second, the substrate's bending strength of only 35 MPa made it impossible to arrest crack propagation, ultimately resulting in the failure of the entire wafer; third, the 15°C/min heating/cooling rate on the production line created a temperature difference of approximately 70°C between the center and the edges of the wafer, where the bending stress and mismatch stress superimposed at the edges and grooves, giving rise to stress concentration. The failure followed a four-stage progression: “microcrack initiation → interfacial delamination → coating delamination → catastrophic fracture.”

“Previously, customers and suppliers simply replaced components without conducting any root cause analysis—replacing a faulty part only to find it failed again. For the first time, SEMICERA has clearly identified the root cause of these failures, enabling customers to understand that the issue does not lie in the coating quality, but rather in the proper alignment of the entire material system with the process parameters.” — Lucy, Head of Process Engineering at SEMICERA

Solution: How to implement triple optimization – from coating architecture to substrate selection to thermal management?

Key conclusion: Instead of simply "replacing the coating with a thicker one," we first conducted a failure analysis and clearly explained the three root causes to the client's process team, before developing a solution based on three key dimensions: coating architecture, substrate material, and thermal management.

l Coating Architecture Upgrade: Replaces the traditional single-layer SiC coating with a three-layer structure featuring a gradient transition layer. The intermediate layer (5–10 μm) exhibits a gradient in carbon content, serving as a CTE "bridge" between graphite and SiC; based on finite element stress analysis, the residual stress at the interface is reduced by approximately 40%. The functional layer (80–120 μm) consists of dense β-SiC with grain sizes of 2–5 μm, balancing etch resistance and thermal conductivity; the surface pore-sealing layer (2–5 μm) seals pores and minimizes crack initiation sites.

l Substrate material upgrade: Extruded graphite has been replaced with high-pressurized (HIP) graphite; the CTE increased from 2.8 to 3.5×10⁻⁶/K (reducing the CTE mismatch by 25%), the bending strength increased from 35 MPa to 65 MPa (approximately twofold), the thermal conductivity increased from 100 to 150 W/m·K, and the ash content decreased from <20 ppm to <5 ppm.

l Thermal management optimization: We recommend reducing the heating and cooling rates from 15°C/min to 8°C/min (which reduces transient thermal gradient stress by approximately 35%), increasing the pallet edge chamfer from R1 to R3, and adding fillet transitions on groove walls. None of these changes require any equipment modifications; they can be implemented simply by adjusting the recipe and drawing specifications.

Result: 6-month validation period (28 → 156 events) – catastrophic fracture rate reduced to 2%

Key takeaway: The real outcome of this collaboration isn’t just that service life has been extended fivefold, but more importantly, that the failure mode has shifted from "unpredictable sudden fracture" to "predictable gradual wear" – allowing customers to perform maintenance as scheduled.                                                                  

The first batch of 50 optimized pallets has undergone 6-month production validation on the customer's manufacturing line; the data was sourced from the customer's production line operation records and the test reports issued by the SEMICERA Failure Analysis Laboratory:

 

Upon completion of the verification, 46 units were still in normal service; among the 4 retired units, 3 exhibited only surface microcracks, with no delamination or substrate penetration. The failure mode has shifted from “unpredictable sudden fracture” to "predictable progressive wear." All critical parameters (coating thickness ±5 μm, density> 98% of theoretical density, Ra <0.4 μm) are recorded and traceable by batch; the coefficient of variation (CV) for coating thickness across five consecutive batches is 2.1%.

FAQ

Q1: Why not simply increase the thickness of the coating?

The thicker the coating, the more severe the accumulation of internal stress becomes – and consequently, the higher the risk of cracking. The gradient transition layer addresses the question of "where the stress originates," while the high-strength substrate resolves the issue of "what happens when cracks propagate"; both are essential. Simply thickening the coating is akin to applying an extra layer of paint to a house that already has structural vulnerabilities.

Q2: Will the cost of replacing HIP graphite increase significantly?

While the unit cost has indeed increased, the total cost of ownership has decreased — in this case, the annual total cost of consumables was reduced by 35%, while the service life was extended by a factor of five, downtime was minimized, and the yield improvement generated benefits that far outweighed the incremental cost per unit. We perform cost-performance analyses based on specific manufacturing processes; not all scenarios require the highest-grade materials.

Q3: What should you do if you're unsure which failure mode your cracking belongs to?

SEMICERA provides comprehensive failure analysis services (SEM, metallography, energy dispersive spectroscopy, and acoustic scanning); customers may submit failed components for analysis, and we will issue a detailed analysis report to identify the root cause. The approach to addressing cracking caused by thermal stress, chemical etching, or installation stress is entirely different – only by conducting a thorough analysis before modifying the design can we avoid "guessing and adjusting" the solution.

Conclusion and Next Steps

Core conclusion: High-temperature cracking in SiC-coated components is not an inevitable form of material wear and tear, but rather an engineering challenge that can be identified through failure analysis to pinpoint the root cause and resolved through a systematic approach.                              

High-temperature cracking in SiC-coated graphite components is often treated as “normal wear and tear” —simply replaced when they fail, only to fail again. However, by conducting professional failure analysis to identify the root cause and then implementing systematic optimization across three dimensions—coating structure, substrate selection, and thermal management—the service life can be extended by several times, catastrophic failures can be reduced to single-digit percentages, and the total cost of ownership can actually be lowered.

This article was written by the Process Engineering Team at SEMICERA's Thermal Field Components Division, a team comprising experienced process engineers and a PhD in Materials Science who have long focused on failure analysis of CVD SiC coatings and thermal field components. SEMICERA is ISO 9001:2015 certified for its quality management system, and its products comply with relevant SEMI standards. If your team is also facing high-temperature cracking issues in SiC-coated components or reliability challenges with thermal field components, please feel free to contact us – we will first conduct a professional failure analysis and then provide a practical implementation solution.

Learn more about our SiC-coated graphite components and our SiC coating technology capabilities.