Atomic Layer Polishing for Quantum Technologies: Addressing Surface Challenges

Executive Summary

This whitepaper examines how Atomic Layer Polishing (ALP) technology addresses critical surface quality challenges in quantum computing hardware. We explore the fundamental limitations imposed by surface imperfections on quantum device performance and demonstrate how ALP's atomic-scale precision offers breakthrough improvements in coherence times, optical quality, and overall quantum system reliability.

1. Introduction

Quantum technologies -- spanning quantum computing, quantum sensing, and quantum communication -- demand exceptionally high-performance hardware. Whether in superconducting qubits on a chip, spin-based defects in a crystal, or photonic waveguides on an optical circuit, a common limiting factor is the quality of surfaces and interfaces. Nanoscale surface roughness, contamination, and amorphous "dead" layers can introduce stray electromagnetic modes, two-level system (TLS) defects, and scattering sites that degrade qubit coherence times, reduce gate fidelities, and increase losses.

For example, in superconducting devices, microscopic dielectric defects at metal and substrate surfaces absorb energy and shorten qubit relaxation times. In photonic devices, sidewall roughness causes optical scattering that lowers the quality factor of resonators and increases waveguide attenuation. And in spin-based sensors like NV centers in diamond, polishing-induced damage creates surface states that rapidly decohere near-surface spins. Mitigating these surface-induced problems is critical for improving quantum hardware performance.

Atomic Layer Polishing (ALP), a recently developed technique by NanoClear Technologies, offers an innovative solution to these challenges. ALP is an ultra-precise, "atomic-level" polishing process capable of smoothing material surfaces to the angstrom scale (sub-nanometer roughness) with minimal induced damage. Unlike conventional chemical-mechanical polishing (CMP) that can leave scratches or stress, ALP is a touchless process that relies on controlled chemical reactions (and possibly atomic layer etching) to remove surface asperities monolayer by monolayer, without mechanically gouging the surface.

The technique has been demonstrated on a wide range of substrate materials (over 25 types, including Si, GaN, and metals) and complex 3D topographies, achieving root-mean-square (RMS) surface roughness below 0.2 nm uniformly across wafers. By virtually eliminating surface defects, debris, and atomic-scale peaks/valleys, ALP creates ultra-smooth, defect-free interfaces that are ideal for quantum applications.

2. Atomic Layer Polishing (ALP): Fundamentals and Advantages

ALP is a novel atomic-scale surface refinement process distinguished by its precision and non-mechanical nature. Instead of physically abrading the surface with slurries or pads (as in CMP), ALP employs finely tuned chemical reactions (in gas or solution phase) to selectively remove atomic layers from a substrate.

The process typically involves cycles of surface chemical modification and etching, analogous in spirit to atomic layer etching (ALE) used in semiconductor fabrication. Each cycle might chemisorb reactive species onto high points or defect sites and then gently strip away a few angstroms of material, resulting in an overall smoothing effect.

Because removal occurs uniformly and terminates at the scale of single atomic layers, ALP can polish surfaces to extremely low roughness (<1 nm) while avoiding the micro-scratches, slurry residues, and subsurface damage that conventional polishing can introduce. NanoClear's ALP, for instance, has demonstrated RMS roughness ~0.1–0.2 nm on GaN, Si, and other semiconductor surfaces, essentially rendering them atomically flat.

2.1 Key Advantages for Quantum Applications

Several key advantages make ALP particularly attractive for next-generation quantum device fabrication:

2.1.1 Angstrom-Level Smoothness

ALP routinely achieves <0.2 nm RMS surface roughness on a variety of materials. This ultralow roughness approaches the ideal of an atomically perfect surface, minimizing extrinsic loss channels. Such smooth surfaces reduce electron scattering and electric field non-uniformities at interfaces, directly addressing sources of noise and decoherence.

2.1.2 No Mechanical Damage or Stress

Because it is a non-contact polishing method, ALP avoids mechanically induced defects like micro-cracks, strain, or beveled edges. Traditional polishing of brittle materials (for example, diamond or GaN) often creates a damaged surface layer that must be removed or annealed out. In diamond NV-center applications, for instance, hard polishing can introduce subsurface damage that drastically shortens spin coherence times.

2.1.3 Material Versatility

ALP has been demonstrated on over 25 substrate types, including metals (like copper, niobium), compound semiconductors (GaAs, GaN), elemental semiconductors (silicon), and dielectrics. The process is chemically "tunable" -- specific precursor gases and etch chemistries are chosen to optimally polish a given material system.

This versatility is crucial for quantum technologies, which use diverse material stacks (superconducting metals, metal oxides, III–V semiconductors, diamond, etc.). ALP can, in principle, smooth a superconducting metal film, an oxide layer, and a semiconductor chip all with the same tool by simply changing the chemistry recipe.

2.1.4 3D and Complex Surface Compatibility

Unlike CMP, which typically requires a planar surface and can struggle with high-aspect-ratio topography, ALP's conformal, chemical nature allows it to polish non-planar and structured surfaces. According to NanoClear, ALP has 3D polishing capability for surfaces of "all sizes, shapes and configurations".

It can smooth the trenches of a waveguide sidewall or the side of a through-silicon via just as easily as a wafer face. This is especially useful in heterogeneous quantum devices where different components may not lie on the same plane -- for example, smoothing the facets of an optical chip that will be bonded to a quantum chip, or polishing the vertical via sidewalls in a 3D-integrated qubit module.

3. Conclusion

In summary, ALP provides a near-ideal polishing solution for modern quantum device fabrication: it achieves extreme smoothness and cleanliness across a broad range of materials and structures, all while minimizing damage and integrating with existing workflows. The following sections discuss in detail how these capabilities can be leveraged to tackle surface-related issues in various quantum hardware platforms, from superconducting qubits to photonic circuits and beyond.

References

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