Proton Beam Writing
Proton beam writing (p-beam writing) is a promising new direct-write lithographic technique for three-dimensional micro- and nanofabrication. In p-beam writing a megaelectronvolt proton beam is focused to a small spot size (in MTA Atomki we can achieve a 1 micron spot, the present world record is below 100 nm), and scanned over a suitable resist material.
Unlike electrons, when a proton beam interacts with resist it follows an almost straight path resulting in high aspect ratio structures with vertical, smooth sidewalls. The secondary electrons induced by the primary proton beam have low energy and therefore limited range, resulting in minimal proximity effects.
The most common positive resist material is PMMA (Poly(methyl methacrylate)). SU-8 (MicroChem Corp. (MCC)) is a well established negative resist. Apart from these two, there are many other materials that have been investigated, and shown good results (HSQ, Foturan glass, Silicon, CR-39, TADEP, etc.).
Currently, applications of this technology are under development in many fields, e.g. medical applications, micro-fluidics (lab-on-a-chip technology), micro-photonics, etc.
P-beam writing in Silicon results in a patterned damage profile that can be used in a variety of ways. It has been used for producing micropatterned Si surfaces, controlled photoluminescence from patterned porous Si, and controlled reflectivity from patterned porous Si Bragg reflectors.
As an example an SEM photo is shown below. This is a micro-turbine made in Silicon by using two different proton energies for the irradiation. 2 MeV was used to implant the house of the turbine, and 1.6 MeV was used for the wheel. The difference in penetration depth is sufficient enough to under-etch the wheel, but not the house. This work is submitted to Nucl. Instr. and Meth.
Publications related to PBW are listed here.
Contact person: IstvŠn RAJTA
rajta at atomki dot hu