Harm Knoops^1,2, Dmytro Besprozvannyy¹, Louise Bailey¹, Michael Powell¹, Silke Peeters², Lisa Nelissen², Erwin Kessels², Russ Renzas^1
1Oxford Instruments Plasma Technology, Bristol, United Kingdom
²Eindhoven University of Technology, Eindhoven, Netherlands
Due to the potential of excellent film control, uniformity, and conformality, atomic layer deposition (ALD) is seen as very promising for quantum devices where interface and material quality and their uniformities are a big challenge. Furthermore, for superconducting circuits, the deposition rate of ALD can be an issue since sufficient film thickness (> 50 nm) is needed to minimize kinetic inductance effects on resonator frequency and the shielding effectiveness of superconducting vias for crosstalk mitigation depends on film thickness and film conformality in the 3D structures. The challenge here is to deliver a sufficiently fast processes while maintaining the desired film properties and benefits of ALD.
Here, we will share our recent development of a new remote plasma ALD system providing high-quality superconducting NbN and TiN for quantum applications at rates > 25 nm/hour, which is approximately 3x faster than previously reported. The RF-driven remote plasma source design and chamber of our ALD system are optimized to enable this high deposition rate.
The quality of the deposited films was demonstrated to be excellent, as measured by four-point probe electrical resistivity, conformality (100% on 8:1 trench for NbN, verified by SEM), and superconducting transition temperature (Tc). Good superconducting properties of the film were demonstrated by SQUID measurements. A thickness non-uniformity of < ±5% across a 150 mm Si wafer was achieved with good repeatability. Both NbN and TiN films show cubic crystalline structure as confirmed by XRD measurements. We will also show how stress can be tuned as a function of process parameters, such as the RF source power and discuss film composition, stoichiometry and purity levels such as carbon and oxygen. We will also touch upon how ALD is well-suited to combine processes and provided ternary films such as NbTiN.
Emerging quantum technologies based on superconducting nitride materials are showing great promise and will benefit not only from the uniformity of the deposition, conformality and film quality, but also from the speed and control provided by ALD processes on this system.