Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Fabrication of cantilevers on CMOS substrates by NIL

A cantilever can be used as a universal platform for sensing applications, especially as a mass detector. An added mass to the cantilever will be registered as a change in deflection or a shift in resonance frequency. By decreasing the dimensions of the cantilever the sensitivity, of the Nano Electro Mechanical System (NEMS), can be increased to the point where it is possible to perform single molecule detection. Using nanocantilevers, however, will make optical read-out impossible. A viable alternative is capacitive read-out, and a prerequisite for this is to integrate electronics and the cantilever in order to minimize parasitic capacitances. This is the goal of the NANOMASS project.

In the Nanomass project the electronic chips are manufactured by standard CMOS technology and in the last step the cantilever is made in a pre-defined nanoarea. It is electrostatically excited and oscillates laterally, the width of the cantilever is about 500nm as well as the distance to the driver. The structures need to be made from conducting material, this can be either metal or silicon, and in both cases an etching process follows a metal deposition. The structures can be made by a variety of methods, here we suggest nanoimprint lithography (NIL) as a fast and parallel approach. This is a challenge since both alignment and imprint over topography is required.

We use an external optical alignment process. This means that a transparent stamp is needed, the material we choose was fused silica. To accommodate the topography we use a mesa on the stamp. This is done by EBL patterning in a negative resist followed a buffered HF etch. Then an etch mask for the cantilever structure is created, again using EBL. RIE is used for etching out the final structure after which an anti-sticking layer is deposited before printing

For the lift-off process a bi-layer resist scheme is used, with PMMA on LOR (lift off resist from Shipley). Alignment is done in a Karl Suss contact mask UV lithography machine. The stamp/substrate package is moved into the NIL machines and printed. Imprint parameters are; temperature 200°C, pressure 50bar and hold time 3min. Oxygen ashing is used to remove the remaining residual PMMA layer. The LOR is selectively removed with MF 319. After metal evaportation lift-off is done in Remover S-1165.

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