| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Monday Sessions |
| Session TF-MoA |
| Session: | Emerging ALD Applications |
| Presenter: | Paul Poodt, TNO, Netherlands |
| Authors: | P. Poodt, TNO, Netherlands A. Illiberi, TNO, Netherlands M. Smets, TNO, Netherlands R. Knaapen, TNO, Netherlands F. Roozeboom, TNO & Eindhoven University of Technology, Netherlands A. van Asten, TNO, Netherlands |
| Correspondent: | Click to Email |
Atomic Layer Deposition is a deposition technique capable of producing ultrathin conformal films with control of the thickness and composition of the films at the atomic level. The major drawback of ALD is its low deposition rate (~ 1 nm/min). Recently, fast ALD concepts were developed based on the spatial separation of the half-reactions, instead of temporal, combined with gas-bearing technology1. With this technique, deposition rates for Al2O3 of more than 1 nm/s have been reported2. This has led to the development of the high-throughput, industrial scale ALD tools for surface passivation of crystalline silicon solar cells2, 3.
A new field of applications for fast ALD are flexible electronics4, including system-in-foil, flexible displays, OLEDs and solar cells. Flexible electronics are slowly but surely evolving from lab-scale to industrial production. This opens up new possibilities for fast ALD as high-throughput production tool for functional layers such as transparent oxide (semi)conductors (e.g. ZnO) and moisture barriers (e.g. Al2O3). One important prerequisite is that these applications require low temperature processes (below 100oC), as they are often temperature sensitive. We present two approaches for low temperature Fast ALD; low temperature thermal fast ALD and atmospheric plasma enhanced fast ALD.
A low temperature thermal fast ALD process for alumina from tri-methyl aluminum and water has been developed. It was observed that the kinetics of the water half-reaction is significantly different than at high temperatures (>200oC). Multilayer adsorption of water molecules at low temperatures seems to hinder the self-limiting nature of the ALD process at temperatures below 75oC. Nevertheless, if very low temperatures are not required, low temperature thermal fast ALD is a very suitable technique. Potentially lower deposition temperatures could be achieved by atmospheric plasma enhanced fast ALD. We have integrated an atmospheric plasma source in our reactor in which an He/O2 plasma is created to act as the oxidant half reaction. However, the chemistry of atmospheric plasmas is different than that of conventionally used low pressure plasmas and has a lower reactivity that can limit the throughput.
Another important aspect of fast ALD for flexible electronics is the processing of flexible substrates, either sheet-to-sheet or roll-to-roll. Approaches for roll-to-roll fast ALD, their challenges and possible solutions will be briefly discussed.
1 P. Poodt et al., Adv. Mater. 22 (2010) 3564.
2 www.solaytec.com .
3 I. Cesar, et al, , Proc. 35th IEEE PVSC, Honolulu, Hawaii (2010), in press
4 J. van den Brand et al., Microelect. Rel. 48 (2008) 1123