Advanced Ceramics in Semiconductor Manufacturing: The Rise of Boron Nitride Solutions

Let’s now drill down into boron nitride: its forms, properties, strengths, and where it shines best in semiconductor environments.

Boron Nitride is not monolithic; one must understand which variant is appropriate:

• Hexagonal Boron Nitride (hBN): The “layered” form, sometimes called white graphite; high temperature stability, good thermal conductivity, excellent electrical insulator, inherently lubricious (low friction). Many machinable ceramics are based on hBN. These range in purity from very high purity to having binders such as calcium borate to control water absorption or boric oxide for legacy semiconductor process.
• Pyrolytic BN / PBN / CVD BN films / coatings: extremely pure BN produced via chemical vapor deposition, often in thin layers for surface passivation, barrier layers, or as interlayer dielectrics.
• Suspensions / pastes / sprays / coatings: BN powders in suspended or sprayable form are used for coating or lubrication layers.

Kennametal’s portfolio includes both pure and composite BN ceramics. Selecting among these depends on whether you need structural parts, insulating supports, wafer carriers, or thin functional films.

Here are some representative numbers and behavior (bearing in mind that properties can depend on orientation, purity, binder, processing, etc.):

• Thermal Conductivity (κ): Depending on grade, direction, and density, BN ceramics can exhibit ~ 30 to 400 W/m·K (especially in high-thermal-conductivity composites)
• Dielectric Strength / Resistivity: BN ceramics often exceed 10¹³ Ω·cm at room temperature; dielectric strength can reach tens of kV/mm.
• Thermal Stability: Many BN grades remain stable up to 1,800–2,000 °C in inert or vacuum environments (less stable in oxidizing atmospheres)
• Coefficient of Thermal Expansion (CTE): BN exhibits relatively low thermal expansion; for some grades, from 20 °C to 1,000 °C, ~0.2–0.3 ×10⁻⁶/K (parallel direction)
• Mechanical Strength / Toughness: Properties can be modified depending on binder, composite formulation and density.
• Moisture Sensitivity: Some BN ceramics using borate binders can absorb moisture, which may degrade properties; improved grades (e.g., calcium borate binders) mitigate this.
• Chemical / Corrosion Resistance: BN is largely inert in many environments (plasmas, halogens, etc.), which is why it's often chosen in semiconductor tool environments.

A caveat: In machinable BN blocks, the microstructure is often anisotropic (due to platelet alignment), so property values can differ “in-plane” vs “out-of-plane” (i.e. parallel vs perpendicular to pressing direction).

From the vantage point of the semiconductor industry, BN stands out for a few synergistic reasons:

• Combination of Thermal Conductivity + Electrical Insulation: This is rare. Many ceramics either conduct heat well but are semi-conducting, or insulate electrically but thermally perform poorly. BN gives a “sweet spot.”
• Low Thermal Expansion / Good Thermal Shock Resistance: Because of BN’s low thermal expansion and high thermal conductivity, it is an excellent choice for rapid thermal cycling.
• Machinability / Near-Net-Shape Fabrication: Unlike many ceramics that require grinding, diamond tools, or slow post-processing, machinable BN can be milled, drilled, lapped to tight tolerances. This allows customization for tool OEMs.
• Purity & Low Contamination Risk: High-purity BN is available (including binder-free or minimal binder composites) and is compatible with ultra-clean semiconductor environments.
• Chemical Inertness: In plasma, vacuum, or reactive gas environments, BN resists attack better than many oxides or nitrides.
• Lubricity / Non-Wetting Behavior: The layered structure gives BN a “solid lubricant” effect, which helps reduce friction or sticking in handling tools.  BN is also not wetted by most molten metals.
• Tailorability via Composite Grades: When “pure BN” lacks mechanical strength, composite grades (e.g. BN + silica, BN + AlN or SiC) can enhance it while preserving core properties.

Taken together, BN is often preferred not because it's perfect in one dimension, but because it is excellent in multiple dimensions essential to semiconductor tools.

While BN is powerful, it is not a panacea. Some of the practical concerns:

• Brittleness & fracture risk: as with all ceramics, BN parts must be designed to avoid sharp stress concentration; care in mounting and handling is essential.
• Binder and moisture sensitivity: some BN grades utilizing borate binders may absorb moisture, impairing dielectric or mechanical behavior. Hence, choice of binder and storage becomes critical.
• Anisotropy of properties: the platelet alignment during pressing means in-plane vs out-of-plane thermal or mechanical properties can differ, so orientation must be considered.
• Limitation in oxidizing atmospheres: At high temperatures in oxygen, BN can oxidize; protective coatings or environments are required.
• Cost and supply considerations: High-purity BN typically comes at a higher price point compared to commodity ceramics, but it offers far broader performance possibilities. Availability and lead times depend on the specialty supplier, making it an area for collaboration and refinement.
• Integration / adhesion challenges in thin film use: as in the case of epitaxial BN, delamination or adhesion challenges can arise during lithographic processing. The recent preprint addresses this.

Nonetheless, these challenges are well recognized, and many BN suppliers (including Kennametal) provide engineering support and customization to help mitigate them.