Several techniques are available to deposit films of many different materials including polymers, metals, metal oxides, semiconductors and ceramics. Polymers are often soluble in a liquid phase solvent and are usually deposited via spin-coating. Other materials are not soluble in the same sense, but can often be sublimed or "sputtered" from a solid target in vacuum and the film condensed onto a sample which is present in the chamber. The main point is that the material needs to be "extracted" from a target in order to be deposited on the sample. How this is done depends on the properties of the material. The simplest method is to simply heat the material sufficiently that it starts to sublime at the low pressure in the vacuum chamber. If this isn't possible, the material can be "sputtered" with high energy argon ions, which physically expel target atoms into the low pressure medium.
spin coating
SU-8 photoresist applied to a wafer
Spin coating is a simple technique where a sample piece or wafer is held on a spinning chuck, and a defined volume of polymer solution is put on the surface. The sample is then spun using an optimized speed, time and ramp rate. The conditions used for spin coating should be optimized for each resist in order to obtain a film of the desired thickness.
An electron beam is generated in the same way as in a light bulb, and focused onto the desired target to heat it up sufficiently for it to sublime. This method is very flexible and capable of depositing a wide variety of materials. It is normally performed under high vacuum. The better the vacuum, the less impurities will be present in the deposited film. In the Nanolab, it can be done on the Eurovac, Edwards and Sputnik systems.
sputtering
How sputtering works (image: University of Kentucky)
Bombarding a piece of target material with high energy argon ions generated in a magnetron plasma source allows extraction of surface atoms which can then be condensed onto the substrate. The target doesn't need to be heated, which is an advantage for some materials, for example for alloys and other mixtures. It also produces films with high quality. Two Aja Orion systems are available for sputter deposition in the Nanolab.
Find details on the deposition systems in the Nanolab
here
, and spin coating
here
