Principles of Operation

Patterning of Electron Sensitive Resists

Electron beam lithography is carried out on electron-sensitive resist materials such as the polymer, PMMA. Solutions of the resist are spin-coated onto a sample and baked to leave a hardened thin-film on the surface of sample. The EBL system is then used to move a focused electron beam across the sample to selectively expose a pattern in the resist previously designed with the system´s in-built CAD tools.

Exposure of a positive tone resist such as PMMA to electrons causes fragmentation of the polymer chain into smaller molecular units in a process known as chain-scission. A suitable developer solution can then be used to selectively dissolve the fragmented polymer chains in the exposed areas of resist, whereas as the unexposed resist remains insoluble in the developer solution. The process therefore leaves a patterned resist mask on the sample that can be used for further processing on the sample.

Pattern Transfer Techniques

The resulting pattern in the resist can be transferred into the sample using either metal lift-off or etching. Reactive ion etching (RIE) or inductively coupled plasma (ICP) etching is generally preferred over wet chemical etching for e-beam lithography applications since it maintains the small feature sizes produced in the resist.