Specific Process Knowledge/Thin film deposition/Deposition of Aluminium Nitride

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All text by DTU Nanolab staff

Aluminium Nitride (AlN)

Aluminum nitride (AlN) is a wide‑bandgap (~6.2 eV) ceramic that pairs very high thermal conductivity (> 200 W m^-1K^-1 ), strong piezoelectric and acoustic properties, and a high dielectric breakdown field in a chemically inert, CMOS‑compatible matrix. It is deposited by reactive magnetron sputtering for dense, c-axis-oriented films widely used in RF devices, and by atomic layer deposition (ALD) when conformal, thickness-precise coatings are required on high-aspect-ratio or temperature-sensitive structures. In semiconductor technology, AlN acts as a nucleation or buffer layer for GaN power/high‑frequency devices, a robust passivation and diffusion barrier, and—when alloyed with Sc—to form ferroelectric AlScN for next‑generation non‑volatile FeFETs and piezoelectric MEMS actuators. Optically, its transparency from deep-UV to the IR and modest refractive index (~2.1) enable low-loss waveguides, UV LEDs/lasers, and protective or anti-reflective coatings that withstand high optical power and harsh environments. AlN’s strong piezoelectricity and high acoustic velocity underpin surface‑ and bulk‑acoustic‑wave filters, film bulk‑acoustic‑resonators, energy harvesters, and high‑Q MEMS resonators used in 5G RF front‑ends and timing devices. Beyond electronics and photonics, AlN substrates and thin films offer excellent thermal management for power modules, high-temperature, biocompatible passivation layers for sensors and implants, and mechanically robust coatings for corrosion and wear resistance, thereby cementing its role as a versatile thin-film material across semiconductor, optical, and engineering applications.

Deposition of Aluminium Nitride

AlN films can be deposited by reactive sputtering or by atomic layer deposition (ALD).

In sputter systems, AlN can be deposited either by direct sputtering of an AlN target or by reactive sputtering with an Al target in a mixture of argon and nitrogen.

Atomic Layer Deposition of Aluminium Nitride (AlN)

Aluminium Nitride (AlN) can be deposited using the plasma-enhanced atomic layer deposition method from TMA and NH3 precursors. The process is well known, and the following link describes all the details:

• AlN deposition using ALD2

Reactive p-DC Sputtering of Aluminium Nitride (AlN)

Cluster Lesker is the best option for deposition of AlN, especially the Sputter-System Metal-Nitride(PC3) chamber, which has no history of oxygen. The process requires elevated temperatures and uses an Al substrate as a source. The films are highly textured. To improve quality, it is also possible to dope the AlN with scandium. At DTU Nanolab, there is an option to perform co-sputtering of both Sc and Al at different powers to get ScAlN thin films.

Comparison of the methods for deposition of AlN

	Sputter-System (Lesker)	Sputter-System Metal-Nitride(PC3)	ALD2
Generel description	Reactive Sputtering (2" Al target)	Pulsed reactive DC sputtering (PDC, 4" Al target) Reactive HIPIMS (high-power impulse magnetron sputtering)	Plasma Enhanced Atomic Layer Deposition
Stoichiometry	Oxygen contamination issue (in 2016 a user got ~ 30 % O in the AlN, measured by XPS in the bulk of the layer).	Al:N:O ~ 53 : 46 : 1.5 in the bulk (see acceptance test results here). It should be possible to tune the Al:N ratio somewhat.	AlN
Film Thickness	few nm - 200 nm	few nm - ~ 1 μm	0nm - 50 nm
Deposition rate	0.055 nm/s (Power: 300W, pressure:1 mTorr, temp.: 400C, N2 ratio: 50%)	at least 0.5 nm/s (see conditions)	0.0625 nm/cycle on a flat sample 0.0558 nm/cycle on a high aspect ratio structures
Step coverage	Good	Not known, most likely medium-good	Very good
Process Temperature	Up to 400 °C	Up to 600 °C	350 °C
Substrate size	chips 1x 100 mm wafer 1x 150 mm wafer	chips 10 x 100 mm wafer or 10 x 150 mm wafer	Several small samples 1 50 mm wafers 1 100 mm wafers 1 150 mm wafer
Allowed materials	Silicon Silicon oxide, silicon nitride Quartz/fused silica Photoresist PMMA Mylar SU-8 Any metals	Similar to the Sputter-System (Lesker), see cross-contamination sheet	Silicon Silicon oxide, silicon nitride Quartz/fused silica Al, Al2O3 Ti, TiO2 Other metals (use dedicated carrier wafer) III-V materials (use dedicated carrier wafer) Polymers (depending on the melting point/deposition temperature, use carrier wafer)

• For further information on AlN deposition using the sputter systems, please contact the Thin Film Group (thinfilm@nanolab.dtu.dk). The Sputter-System Metal-Nitride(PC3) was acquired partly to make it possible to deposit high-quality of AlN films.