Thermic Edge Ltd is the sole manufacturer of our high purity SiC3 Coating, short for Cubic Silicon Carbide.
Our Revolutionary SiC3 Coating Offers the Following Advantages:
- Cubic structure giving high density coating
This vastly improves corrosion and wear resistance and increases the component’s life.
- Excellent coverage down blind holes
With 30% coating thickness down the bottom of a Ø1x5mm deep hole.
- High Thickness Uniformity
SiC3 coating offers high coating thickness uniformity of +/-10microns on 100micron thick coating. We are working on improving this uniformity further to +/-5 microns, in the near future.
- Very High purity coating (<5ppm impurities)
Is achievable by using high purity gases in the coating process, while also remaining low in N2 absorption to achieve higher than industry standard purity.
- Adjustable surface roughness
The coating process can be tailored to give different surface roughness’s, to suit different applications.
- Fast delivery
Typical coating time is 2 weeks from receipt of the base part.
This very high purity coating is mainly intended for use in the semiconductor and electronics industries, for protecting wafer carriers, susceptors and heating elements from corrosive and reactive environments such as MOCVD and EPI processes, used for wafer processing and device manufacture. The coating is also suitable for vacuum furnaces and sample heating in high vacuum, reactive and Oxygen environments.
Layer thickness can be varied but typically a layer of 80 – 100µm is applied.
Thermic Edge’s state of the art machine shop allows us to offer a complete solution including manufacture of the base graphite, ceramic or refractory metal component, and the SiC3 ceramic coating. We also offer a coating only service for customer supplied parts.
SiC3 High Purity Silicon Carbide Coating overview
SiC3 is our trade name for our high purity cubic Silicon Carbide ceramic coating. It is applied to components to protect them from Oxidation or reaction with other gasses at high temperature. The SiC3 coating is applied using a high temperature, very high purity Chemical Vapour Deposition (CVD) reactor.
SiC3 coating is an electrical insulator, incredibly hard and has good corrosion and oxidation resistance. It can withstand temperatures up to 1600C at atmospheric pressure.
SiC3 Cubic Silicon Carbide ceramic coating can be applied to the following materials:-
- High Purity Isostatic Graphite (low CTE)
- Silicon Carbide (in most forms)
- Silicon Nitride
- Carbon Carbon Composite (CCC)
SiC3 Cubic Silicon Carbide ceramic coating can be used at high temperature in the following environments:-
- Oxygen (O2)
- Hydrogen (H)
- Nitrogen (N2)
- Sulphur (S)
- Ammonia (NH3)
- Hydrogen Chloride (HCL)
- Methane (CH4) and other hydrocarbons
- Carbon-Monoxide (CO) / Carbon-Dioxide (CO2)
- MOCVD Processing
- Epitaxial Processing
- CVD, PECVD & PVD thin film deposition.
- High Vacuum (Max operating temperature is reduced)
- Inert Atmospheres
- RF / DC Plasma processes
Listed below are the typical values for some of the important properties for SIC3 . Some of these (i.e. crystal size, electrical resistivity) can be customised and optimised for specific applications.
|Crystal Structure||3C (cubic; β)|
|Porosity||0% (helium leak tight)|
|Crystal Size||1 – 5 µm|
|Visual Appearance||Grey, satin to dull|
|Thermal Expansion (RT -400oC)||(RT -400oC) 4.2 x 10-6m.K-1|
|Thermal Conductivity (@20oC)||(@20oC) 200 W.m-1.K-1|
|Elastic Modulus||450 GPa|
|Electrical Resistivity (@20oC)||(@20oC) 1MΩ.m|
An XRD Diagram is shown here.
The peaks shown in the diagram perfectly match the 3C crystal structure.
Material High Purity
This table shows the impurities of SiC3 coating Lowest limit of detection with this method. Testing carried out by EAG Laboratories using Glow Discharge Mass Spectroscopy
Our Thermic Edge SiC3 Coating (TEC) is extremely high purity when compared to Silicon Carbide coatings supplied by other companies (C1 and C2)
A typical surface roughness profile is shown here. The typical surface roughness parameters are Ra = 0.8µm, Rz = 5µm and Rt = 8µm
Controlled variation of SiC3 crystal size
At TE we can control the crystal size of our SiC3 coating, as demonstrated in the pictures below. This enables us to control the surface roughness of our SiC3 coating to give a very smooth or very rough coating, or anything in between. From customer feedback we know that the larger crystal size, rough coating, is the better option at high temperature processes such as SiC epi. Our standard coating is a medium roughness.
Thermic Edge Coatings (TEC) deposits a high purity silicon carbide coating on various materials. The cubic, SiC3, coating has excellent corrosion protective properties at low, medium and high temperature. Typically the coating finds application in semiconductor industry, LED and solar production and aerospace. Materials coated are graphite, carbon composites, various ceramics and refractory metals.
The coating can only protect the underlying material effectively when the coating covers all areas visible to the environment, when it adheres well to the material and does not crack after the coating process.
A well adhering coating is therefore essential and the process carried out by TEC accomplishes this on various materials. The process is carried out at high temperature using ultrapure gases amongst which hydrogen which cleans the surface by removing oxides and other contaminants which might hinder good adhesion. During the initial stages of the process there is a trade-off between deposition and etching which further cleans the interface between underlying material and coating.
And of course in many applications graphite is used as the underlying material which has a high porosity. The TEC process penetrates the pores in the graphite very well and gives it a further enhancement for the adhesion. This is very well demonstrated in the figure below.
The adherence is measured regularly by making fracture surfaces from test plates. The method used is very destructive and would immediately show a lack of adhesion due to flaking of the coating from the area where the fracture occurs. Below are some images made by SEM which show the very good coverage of graphite and adherence to graphite.
Penetration depth SiC3
Use of graphite coated parts in high end applications depends on overall coverage of the graphite. This is important for the outside surfaces as well as for small and larger holes (blind, through). The small hole in the satellite disc is a good example and sufficient coating on the inside is important.
At TEC we made a small graphite sample with small holes drilled into the side with a handheld drill. This is for a first assessment only and further testing will commence the coming weeks. The test piece is shown below and after drilling and coating smaller parts were broken of the piece to examine the hole internals.
SEM analysis of a hole shows clearly that the coting penetrates into the small hole dia1.2mm x 5.5mm deep (see below).
SEM analysis of the hole fracture demonstrates the penetration depth in more detail (see below).
At the bottom of the hole (diameter approximately 1.2 mm; depth 5.5 mm) there is still a layer of 10 µm present. Coating of the small satellite disc hole is therefore no problem and at least 60 % of the top layer thickness is expected at the bottom of the hole.
SiC3 coatable materials
Thermic Edge deposits its high purity silicon carbide coating SiC3 on various materials. The cubic, SiC3, coating has excellent corrosion protective properties at low, medium and high temperature. The coating finds application in semiconductor industry, LED and solar production and aerospace.
Materials coated are graphite, carbon composites, various ceramics and some refractory metals. Other materials are not advised as those react with the gas fed into the reactor and/or have incompatible thermal expansion which results in cracking and delamination of the coating. For example, titanium will react with hydrogen at high temperature (above 600C) and steel will react with the silicon compound used to form silicon carbide. To maintain the high standards of purity of the coating, materials should be of the highest purity or purified before coating.
Graphite is used in many high temperature applications for its chemical and mechanical stability and thermal and electrical characteristics. In semiconductor applications these characteristics and compatibility with silicon and other materials are used extensively. However, when graphite is used at high temperature or i.e. in plasma environments it is not chemically stable and can react with the gas environment to form compounds which interact with the process. Graphite is also a very porous material and can store compounds in the pores which can interact with the process.
To avoid interactions between the graphite surface and seal the porosity of the graphite it is coated with SiC3. In this way the characteristics of graphite can be combined with chemical stability of SiC3. Due to the SiC3 process the coating diffuses into the graphite surface and results in a very well adhering layer when the right graphite is selected. For high end applications such as semiconductor industry TEC chooses isostatic graphite qualities from a wide range of suppliers.
As an independent supplier Thermic Edge is able to select from a wide range of suitable graphite types from various suppliers such as GrafTech, Ibiden, Mersen, Morgan, SGL and Tokai Carbon. Our state of the art graphite machining workshops has experience in handling parts for semiconductor applications.
For some applications extruded graphite can be used and coated with SiC3. In most cases the thermal expansion of the graphite is lower than SiC3 coating but the porosity of the extruded graphite is high resulting in well adhering layers and the formation of a smooth transition from graphite to coating.
2. Carbon composites
A large group of materials based on carbon fibres are referred to as carbon composites. It covers a wide range of materials with various characteristics based on the production process. What the materials have in common is the carbon fibre which is moulded (short fibres) or woven (long fibres) into various structures and impregnated to densify the structure. The properties of the fibre vary very much in the length of the fibre and perpendicular to the fibre. Especially the thermal expansion differs and makes it very difficult to coat a composite structure without cracking and/or delamination.
TE has gained some experience with coating carbon composite parts developed for high temperature applications. Due to the large difference in thermal expansion and variations in different directions cracks appear. A good example is given right. The width of the crack in horizontal direction is much larger than in the vertical direction indicating a different orientation of the fibre. Once the material is heated and close to the SiC3 deposition temperature most of the cracks will be closed and could protect the underlying material. .
Another example which is very usable in high temperature furnaces is coating insulation material with SiC3. Even though the penetration depth of the coating is good it will mainly be present near the surface due to the very large surface area. An example of fibre based insulation material coated with SiC3 is shown right.
The most promising ceramics to be coated with SiC3 are the silicon based ceramics such as SiC, SiSiC, Si3N4 etc. The reason being that the thermal expansion of those materials fits very well with the SiC3 coating. The purpose of a top coating on those ceramics is to improve corrosion resistance and to block diffusion of impurities from the base material. In semiconductor industry SiSiC boats and other parts are mostly coated by the ceramics supplier themselves. In that case the coating prevents preferential attack and erosion of silicon from the base material.
So far alumina has proven difficult to coat as well as quartz due to its very low thermal expansion.
4. Refractory metals
Tungsten and molybdenum have been coated successfully with SiC3 coating. Depending on the dimensions and shape up to 250 µm can be applied. The coating adheres very well and the system has a long-term stability at high temperature. The SiC3 coating can prevent oxidation of the underlying base material in oxidising environments.