(Invited) Thin Film Technologies for Micro/Nano Systems; A Review
Authors: van Zeijl Henk W. 
Published: February 2020

Thin film technology is employed since ages in the field of art, household appliances, optics, metallurgy etc. But the invention of solid state electronic devices, more specifically integrated circuits, really boosted thin film technology to a level of atomic precision in a high volume manufacturing environment. Today the mass production of nano electronic devices principally relies on the deposition and patterning on thin films. Consequently the performance of these devices and systems is determined by the relevant properties of patterned thin films.

For conventional applications in the microelectronic domain, the function of a thin film is either an insulator or a conductor; the electrical properties of such films are of overriding importance in the application. And because silicon is the preferred substrate material for current and future CMOS technologies, the thin film deposition technologies must be silicon compatible. However, the continuous scaling of CMOS brings conventional thin films beyond physical limitations. Therefore novel materials like high K gate dielectrics and low K intermetallic dielectrics where introduced in the CMOS process flow. Moreover in combination with the electrical parameters also other domains like mechanical stress needs to be controlled to enhance the charge carrier mobility, often complicating the formation of the film stack and subsequent processing. In addition the increasing aspect ratio of downscaled and novel device structures like fin-fet also put constraints on the deposition techniques. Consequently, over time a broad portfolio of thin film deposition technologies and thin films properties has been developed.

But the application of thin films is not limited to IC technology only, also the fabrication microelectronic mechanical systems (MEMS), biomedical devices, solid state lighting technology, and novel approaches to micro and nano system integration, all rely (partly) on thin film technologies. This class of non-CMOS technologies will be further referred to as micro/nano systems technology. The device scaling in micro/nano system technology follows different rules compared with CMOS and spans multi domains and multi scales, even more than in CMOS.

The broad portfolio of thin film technologies originally developed for CMOS now employed in micro/nano system technology today churns out a large number of different process sequences to yield a broad spectrum of device structures process flows. Novel discoveries in the domain of nano science, biology, the technology push in solid state lighting and the further industrialisation of MEMS and NEMS will broaden this technology portfolio even more. And contrary to a CMOS transistor, the structure and manufacturing process of micro/nano devices is strongly dictated by its application. Hence a micro/nano system does not have a generic structure, and in some cases very specific thin films and corresponding deposition technologies are required.

CMOS scaling as we know may end in the not too distant future, while the exploration of micro and specifically nano systems rise from the ranks. Novel 3D devices, heterogeneous integration schemes and micro/nano system will emerge to provide increasing functionality. The expanding application domain of newly developed micro/nano systems will result in new thin film deposition technologies, tools and new requirements. In addition, the diversity in device structures, the multi scale and multi domain applications are a challenging task for the numerical simulation of such systems.

In this paper, the major applications of thin film technologies, applied in micro/nano system technology today will be reviewed, the diversity will be addressed and novel structures will be discussed with an outlook into the future.