Diamond Polishing and Grinding Processes: Core Challenges and Industry Hurdles

Diamond is often hailed as the “ultimate material” – ranking 10 on the Mohs hardness scale, boasting an ultra‑high thermal conductivity (~2,200 W/(m·K)), excellent chemical stability, and broad optical transparency. These properties make it irreplaceable in cutting‑edge applications such as semiconductor heat dissipation, high‑end optics, and quantum chips. Yet the paradox of “good materials are hard to process” is nowhere more evident than in diamond. From rough grinding for planarization to atomic‑level finishing, every step in the polishing and grinding workflow demands a delicate balance between precision, efficiency, and damage control.

1. Intrinsic Material Barriers

The difficulty of machining diamond stems from three fundamental characteristics:

1.1 Extreme Hardness – Tooling Struggles to Keep Up

Diamond is the hardest known natural material. Conventional abrasives are ineffective; machining relies almost exclusively on super‑hard grits (diamond particles) or energy‑beam techniques. This leads to rapid tool wear and escalating costs. Even when using diamond‑grit‑loaded polishing plates, high rotational speeds and heavy loads are required – not only causing uneven plate wear but also generating frictional heat that can induce a phase transformation from sp³ (diamond) to sp² (graphite) on the surface, softening the material and degrading surface quality.

1.2 Anisotropy – Different Crystal Faces, Different Hardness

Single‑crystal diamond exhibits significant hardness variations across different crystallographic orientations. Mechanical polishing often results in uneven removal rates, leading to deviations in total thickness variation (TTV). Polycrystalline diamond adds another layer of complexity: grain boundaries have mismatched coefficients of thermal expansion, making them prone to height differences and micro‑cracking.

1.3 Chemical Inertness – Conventional Etching Fails

Diamond’s extreme chemical stability renders it resistant to most standard wet or dry chemical etching methods. Material removal typically demands high temperatures, high‑energy environments, or specialised oxidising systems, further complicating process control and increasing operational difficulty

.

2. The “Triangular Trade‑off” Between Precision, Efficiency, and Damage

The overarching goal of diamond polishing is to achieve nanometre‑ or even atomic‑scale surface quality, while maintaining acceptable throughput and minimising subsurface damage. However, these objectives are inherently conflicting. For high‑end applications like semiconductor substrates and optical windows, requirements often call for surface roughness Ra ≤ 0.1 μm, TTV ≤ 5 μm, and subsurface damage depth limited to a few micrometres.

Conventional Mechanical Polishing (MP) – Fast, but Damaging

Mechanical polishing can rapidly reduce the surface roughness of polycrystalline diamond from an initial \5,000 nm down to \150 nm – a clear efficiency advantage. However, the high frictional heat generated during the process triggers diamond‑to‑graphite transformation, creating an amorphous layer and subsurface cracks. Increasing the rotational speed from 12 m/s to 60 m/s can extend the damage layer to nearly 10 μm. In one reliability test, a diamond heat spreader polished by conventional MP showed a 35% increase in thermal interface resistance after high‑temperature ageing – resulting in an 18 °C rebound in chip junction temperature. The surface may look smooth, but the subsurface is riddled with hidden defects.

Atomic‑Scale Finishing – High Quality, Low Throughput

Chemical mechanical polishing (CMP) is currently the most widely used finishing approach, combining chemical oxidation with mechanical abrasion to achieve Ra ≤ 0.05 μm. However, traditional CMP removal rates are often below 1 μm/hour – making the polishing of large‑area diamond wafers extremely time‑consuming. Non‑contact techniques such as ion‑beam polishing and plasma‑assisted polishing can reduce damage, but they suffer from high equipment costs and complex process control, limiting their industrial scalability.

3. Advanced Challenges: Composite Structures and Larger Sizes

Composite Substrates – Multiple Layers, Multiple Risks

As diamond gains traction in semiconductor thermal management, CVD‑based composite substrates (with a diamond layer, transition layer, and base material) have become increasingly common. However, the significant mismatch in coefficients of thermal expansion between diamond and the metal/ceramic base induces severe stress concentrations under polishing forces and temperature variations – often leading to micro‑crack propagation and even delamination. Industry data show that without optimised processes, the yield for such composite substrates can be as low as 50‑60% – almost one reject for every two parts produced.

Large Diameters – Uniformity Control Grows Exponentially Harder

As the industry moves toward 4‑inch and larger diamond wafers, maintaining uniformity in surface roughness, TTV, and subsurface damage across the entire area becomes exponentially more challenging. Laser polishing can achieve global planarisation, but localised heating may generate cracks in the diamond film. Mechanical polishing faces issues with pad flatness and pressure distribution, leading to edge chipping and thickness variations on large wafers. Processing time per piece also increases substantially, driving up production costs.

4. Outlook

Advancing diamond polishing and grinding processes is, at its core, a pursuit of the material’s ultimate performance limits. For next‑generation chips with sub‑3‑nm nodes, the required defect density on diamond surfaces is < 0.1 defects/μm² – a quantum leap in process stability. The only sustainable path forward lies in deep synergy among materials, process engineering, and equipment development – reducing cost while pushing the frontiers of atomic‑scale surface integrity control.

As demand for high‑performance materials continues to surge in the semiconductor, aerospace, and quantum technology sectors, diamond polishing technology is evolving steadily toward intelligent, high‑precision, and environmentally friendly solutions. In overcoming these formidable challenges, it is reshaping the future of advanced manufacturing.