We're all familiar with conventional deposition techniques, the most popular being CVD, but what are the other methods/ways currently under research?

HiTUS Deposition

HiTUS ("high-target-utilization sputtering") is classified under sputter deposition, where plasma is used - making the ion current independent of the applied voltage. This PVD process differs from CVD as it uses a liquid or solid source (in this case plasma) to eject material from a "target" (typically a metal alloy for thin film applications such as TFTs) towards the substrate.

The HiTUS system produces a high-density magnetized plasma in the order of 10^13 ions per cubic centimeter. Control is achieved by manipulating the following variables: RF power, DC power, and process pressure. Major benefits of such a process include the ability to coat with a fast deposition rate, high density films onto temp. sensitive polymeric materials. 


PECVD ("plasma-enhanced chemical vapor deposition") is a CVD that, just like HiTUS, uses plasma (deposit of thin films in the form of sufficiently ionized gas to the substrate). It yields the fastest deposition rates at the expense of uniformity (does this mean more planarization cycles? I don't know) and is in popular use in the industry. One study aimed to use Ge-on-Si PECVD for lowering the cost of Ge-on-Si devices. Using an Oxford Instruments System 100 PECVD tool, germanium was grown on a 6 in. silicon wafer.

n-Si wafer, showing non-selective growth and removal of stress relieving hillocks using a 2-step growth method.

Figure 1. Ge-on-Si SEM images of various Ge-on-Si PECVD growth recipes. (a) Cross-section of sample A, showing voids in layer due to high growth rate. (b) Cross-section of sample B, showing removal of voids by reducing the growth rate. (c) Plan view of sample D, showing a high number of stress relieving pyramidal hillocks. (d) Angled cross-section of recipe E, grown on a patterned 
The study successfully proved the effectiveness of Ge-on-Si PECVD. The study is open-source and can be viewed by following the link below:



[1] Tsakonas C., Wakeham S., et. al.(2015). Transparent and thin film electroluminescent devices using HiTUS deposition and LASER processing fabrication. IEEE Journal of the Electron Devices Society, Vol. 4, Issue 1, pp. 22-29

[2] Youfu G., Zhen Y., et. al.(2016). Femtosecond LASER ablated polymer SERS fiber probe with photoreduced deposition of silver nanoparticles. IEEE Photonics Journal, Vol. 8, Issue 5

[3] Littlejohns C.G., Kokhar A.Z., et.al.(2015). Germanium-on-Silicon plasma-enhanced chemical vapor deposition for low-cost photodectors. IEEE Photonics Journal, Vol.7, Issue 4