Silicon Carbide Polishing

Silicon carbide is one of the hardest materials on Earth, second only to diamond and cubic boron nitride. Due to its extreme hardness, silicon carbide makes an ideal material for lapping ceramics, grinding nonferrous metals and deburring materials.

Aluminum oxide blast media can easily cut through painted surfaces and many types of wood, but can wear down faster when used on harder materials like metals.

Abrasive

Silicon carbide is one of the hardest materials next to diamond, so it comes as no surprise that this material makes an excellent abrasive. Silicon carbide can be seen frequently used for grinding and sandblasting applications in industrial sanding applications as well as chemical mechanical polishing (CMP) processes.

Black silicon carbide powder is widely used to polish semiconductors and electronics components, ceramics and hard non-ferrous metals – it even proves useful in metallurgy due to its excellent high temperature resistance and thermal shock resilience.

Due to its hardness, wear resistance, and thermal conductivity properties, diamond is used as a cutting tool in both machining and drilling applications. Available in fine through coarse grit sizes, diamond is often the superior choice when working with low tensile strength materials such as glass, ceramics and stone.

Green silicon carbide is more friable than its black counterpart and resembles aluminum oxide more closely. It is commonly used for wet and dry sanding applications in automotive polishing applications; other uses include wet-dry sanding between finishing coats in woodworking projects; deburring metal and glass; as well as refinishing wood flooring.

Chemical Mechanical Polishing (CMP) is an established technique for creating surfaces with superior global planarization without subsurface damage. CMP requires a balanced interaction between surface oxidation and oxide layer removal – its oxidants determining surface oxidation efficiency while its abrasive particles contributing mechanical force for polishing.

To maximize MRR, it is crucial that the abrasive be evenly spread over all surfaces of a wafer, capable of creating consistent mechanical forces across its entirety. CMP slurry must therefore contain specific pH ranges which have been carefully calibrated against pad asperities and structures for best results.

Ceramic abrasives have proven themselves the most efficient and economical choice for high-speed polishing applications, particularly with aluminium castings, mild steel mill scale, titanium alloys and other hard substrates. We employ our ceramic abrasive on various machines throughout our facilities – particularly effective on aluminium castings, mild steel mill scale and titanium alloys.

Oxidizing Agent

Oxidizing agents play a critical role in CMP by providing chemical driving force that pushes away abrasives and oxide layers from silicon carbide surfaces. For optimal results, an effective oxidant should remain active within certain pH values in order to achieve an atomically flat surface with high MRR ratings; electrostatic interactions between silicon carbide wafers and particles also have an effect on its effectiveness.

Permanganate, potassium hydroxide and nitric acid are ideal for polishing silicon carbide. Permanganate can be added directly to the slurry, while potassium hydroxide works more effectively when added as sodium formate solution. Nitric acid requires special handling; its appropriate concentration must be added into the slurry in order to avoid decomposition of its active oxygen component.

Graphene oxide (GO), an easy and fast way to form OH radicals when reduced, generates more oxidants than its traditional TiO2 counterpart and improves both oxidation efficiency and MRR by about 20%. Just adding some milligrams of GO will bring these advantages.

An essential factor in creating an atomically flat surface is selecting an appropriate slurry composition. According to some researchers, for 4H-SiC some researchers suggest using both SiO2 and Al2O3-based slurries; their combination provides stronger mechanical force which assists in creating an atomically flat surface; additionally using SiO2 reduces electrostatic interactions that could potentially cause damage from using an Al2O3 based abrasive.

As well as choosing an oxidant, selecting an effective abrasive is critical for optimizing MRR. Aluminum oxide is ideal in this regard as it offers both durability and superior slurry permeability – plus, its use is safe in wet or volatile environments.

Tribochemical polishing can also provide an efficient means of producing an ultra-smooth and damage-free surface in silicon nitride. The technique involves rubbing material to be polished against a hard, lubricated surface while friction induces dissolution reactions that produce water molecules, thus dissolving material without needing abrasives. Tribochemical polishing has the ability to achieve Maximum Return Rates of up to 80nm h-1 with this type of polishing.

Chemical Composition

Silicon carbide polishing requires an aqueous polishing slurry consisting of both an abrasive and an oxidizing agent; typically silica sol dispersed into the slurry is typically the source. Meanwhile, an organic or inorganic compound serves to convert its surface into a more reactive state that encourages chemical bonding between substrate and abrasive, enabling faster material removal as well as protection of substrate surface from mechanical abrasion damage.

Silicon carbide is used as an abrasive and grinding powder in processes such as water jet cutting and sandblasting, where coarse grits are frequently employed for these operations. Refractories made from silicon carbide may also serve as replacements for cast iron in industrial furnaces or as ingredients in steel alloys; its melting point, shock/corrosion resistance, strength durability and heat conductivity make it attractive as a material choice.

Produced through smelting silicon monoxide derived from natural gas or coal using the Lely process. A mixture of pure silica sand with ground coke carbon formed around an electric conductor in an electrical resistance furnace is fed electric current in order to trigger chemical reactions that produce silicon carbide.

Silicon carbide may take either single crystal or polycrystalline forms, with two polymorphs of particular interest being alpha silicon carbide (a-SiC), with its Wurtzite crystal structure, and beta silicon carbide having zinc blende crystal structure – both have high reactivity making them valuable materials in producing heterogeneous catalysts.

The present invention presents a preparation method for silicon carbide polishing slurry. The steps include adding dispersing agents, accelerators, pH buffering agents, wetting agents and complexing agents sequentially into deionized water while stirring evenly, then gradually mixing in silica sol abrasives before finally aging the mixture for 30-60 minutes before adding silica sol abrasive.

Method

Silicon carbide is an extremely hard material with many uses in a wide variety of fields. Most commonly produced as powder form and utilized for fine grinding, water-jet cutting, sandblasting shaping and polishing other materials – as well as more coarse applications such as deburring metal and glass and refinishing wood flooring. Furthermore, silicon carbide is frequently included as part of chemical mechanical polishing (CMP) processes for added abrasive polishing (ACP) solutions.

CMP (chemical mechanical polishing) is the process of mechanically abrading surfaces to planarize and undo damage caused by previous steps such as grinding or etching. CMP uses a polishing pad soaked with an abrasive-containing polishing composition or slurry containing both an oxidizing agent and an abrasive, which comes into contact with the substrate surface, creating friction to strip away damaged layers while exposing new material underneath.

Oxidizing agents help reduce the amount of mechanical abrasion needed to achieve desired surface planarization levels, by aiding dissolution of substrate material and decreasing mechanical damage to it. Furthermore, the oxidizing agent also speeds up polishing kinetics by speeding up when abrasive particles interact with substrate surfaces.

For optimal silicon carbide wafer surface finishing with high MRR and minimal defect rates, it is crucial that abrasive particles maintain high elastic interactions with their target surface – this is more challenging when the abrasive is fixed like in diamond CMP processes.

Tribochemical polishing has been used successfully to finish polycrystalline silicon carbide samples. The technique eliminates the need for abrasives and relies on friction-stimulated dissolution in an appropriate reactive fluid, producing defect-free surfaces (Ra =1nm) on SiC slidable surfaces by rubbing against a cast iron tool in 3 weight% CrO3 solution.

CMP involves mixing oxidizing agents into a polishing slurry while the abrasive is supplied as dry material. Ideally, its composition must remain colloidally stable; that means keeping both components suspended for extended periods in the liquid carrier.