Deposition

Summary

The parameters that decide outcomes are not exotic. Rate and temperature budget set what substrates survive. Conformality decides whether high-aspect-ratio features can be lined at all. Residual stress and microstructure, set by process pressure in sputtering, propagate into function: dense, smooth (111)-textured platinum films grown at low sputter pressure gave the highest hydrogen evolution activity despite less surface area than the porous, rougher films grown at high pressure. Phase selection is the other lever: reactive sputtering tends to favour metastable rocksalt-derived nitrides, so layered FeWN2 and FeMoN2 required post-deposition ammonia annealing, and FeMoN2 was only phase-pure at Fe-poor compositions.

The most useful single result in the set is a controlled comparison of routes at fixed chemistry. Amorphous Al2O3 films of similar stoichiometry were grown by PLD, ALD and sputter deposition; all PLD microcantilevers accommodated total strains above 10% without fracture, while half the ALD cantilevers fractured in an elastic-brittle manner and half showed bending plasticity. Composition did not determine mechanical behaviour; the growth route did. The same logic appears in the growth-axis elastic anisotropy of ion-beam-sputtered silica, a 6% compressive anisotropy along the film normal that the standard 500 C, 10 h detector anneal does not remove.

Deposition’s economic ceiling is not set by deposition alone. Walker’s 3D NAND cost model shows that stacking more deposited device layers does not reduce die cost monotonically: because any deep etch has a non-zero taper angle, the top-of-stack cell pitch grows linearly in layer count, so array footprint eventually grows faster than the layer count saves, producing a minimum in die cost Walker 2013 Rigorous 3D Nand Flash Cost Analysis. Films are cheap to add; the patterning of a thick stack is what bites.

Evidence base

• November 2013: a rigorous 3D NAND cost model shows die cost per bit has a minimum in device layer count, because deep-etch taper makes top-of-stack cell pitch grow linearly with layers, and a layered approach using three critical masks per device layer can undercut vertical-channel NAND on total cost Walker 2013 Rigorous 3D Nand Flash Cost Analysis.
• 4 May 2026: an in-situ sputtered sub-nanometre (0.5 nm) silicide template formed by rapid thermal annealing, demonstrated across 25 metallic species, gives low-vertical-resistance ohmic GaN epitaxy on Si(111) and serves as a platform for MOCVD overgrowth.
• 4 May 2026: atomic layer deposition and gas condensation tuned hBN resonators with quality factors ~4300 (1D photonic crystal cavities) and ~8300 (microdisks), shifting resonances by ~9 nm and ~16 nm respectively.
• 5 May 2026: amorphous Al2O3 films of similar stoichiometry grown by PLD, ALD and sputtering behaved differently in microcantilever bending; all PLD cantilevers exceeded 10% total strain without fracture while half the ALD cantilevers fractured in elastic-brittle mode.
• 8 May 2026: Brillouin light scattering showed ion-beam-sputtered SiO2 has cylindrical elastic symmetry with 6% compressive anisotropy along the film normal, unchanged by the 500 C, 10 h anneal currently used in ground-based gravitational-wave detectors but nearly eliminated at 900 C.
• 8 May 2026: magnetron-sputtered Pt films deposited at low sputter pressure were dense, smooth and (111)-textured and gave the highest hydrogen evolution activity, while higher sputter pressures produced porous, rougher films with reduced activity despite greater surface area.

Open questions

• Does the PLD advantage in amorphous alumina ductility survive scaling from microcantilevers to wafer-scale coatings, and what structural difference between PLD, ALD and sputtered films of identical stoichiometry causes it?
• Does the 0.5 nm sputtered silicide template for GaN on Si(111) reproduce on production-diameter wafers and across the full set of 25 metallic species, and what vertical resistance is achieved in a finished device rather than a test structure?
• Is the 6% growth-axis elastic anisotropy in ion-beam-sputtered silica a general property of ion-beam-sputtered oxides, and does removing it at 900 C degrade other coating properties?
• Can kinetically driven dopant patterning during CVD, demonstrated in vanadium-doped WS2, be controlled deliberately rather than observed after the fact?

Assessment drafted 2026-08-31 from up to 18 KB sources using the technology-scorecard framework; scores are a draft read pending review.