Fabrication of cantilever based mass sensors integrated with CMOS using direct write laser lithography on resist

Abstract

A CMOS compatible direct write laser lithography technique has been developed for cantilever fabrication on pre-fabricated standard CMOS. We have developed cantilever based sensors for mass measurements in vacuum and air. The cantilever is actuated into lateral vibration by electrostatic excitation and the resonant frequency is detected by capacitive readout. The device is integrated on standard CMOS circuitry. In the work a new direct write laser lithography (DWL) technique is introduced. This laser lithography technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of poly(methyl methacrylate) (PMMA) on lift-off resist (LOR). Laser writing evaporates the PMMA, exposing the LOR. A resist solvent is used to transfer the pattern down to the substrate. Metal lift-off followed by reactive ion etching is used for patterning the structural poly-Si layer in the CMOS. The developed laser lithography technique is compatible with resist exposure techniques such as electron beam lithography. We demonstrate the fabrication of sub-micrometre wide suspended cantilevers as well as metal lift-off with feature line widths down to approximately 500 nm.

Swelling signals of polymer films measured by a combination of micromechanical cantilever sensor and surface plasmon resonance spectroscopy

“…Recently, thin polymer films [7][8][9] and polymer brushes [10] have been used as responsive coatings on MCSs. The swelling of a thin polymer film results in a static bending of the MCS (static mode), which can be measured by various optical techniques [11,12] or microelectronic principles [9,13,14]. The bending depends on the concentration of the solvent in which the MCS is situated [15].…”

Microcantilever Sensors

“…Some recent developments are reviewed in [53][54][55][56][57][58]. Major topics published include the following studies: the fabrication of silicon piezoresistive [59,60] or polymer [61] cantilevers, detection of vapors and volatile compounds, e.g., mercury vapor [62], HF vapor [63,64], chemical vapors [65], as well as the development of gas sensors based on the piezoresistive concept [66]. Pdbased sensors for hydrogen [67], deuterium and tritium [68] are reported, as well as sensors taking advantage of the sensing properties of hydrogels [69] or zeolites [70].…”

Fabrication of metal suspending nanostructures by nanoimprint lithography (NIL) and isotropic reactive ion etching (RIE)

“…A reduction of the dimensions of the mechanical sensor leads to a new generation of systems called nano-electromechanical systems (NEMS) [2,3] , which represents an improvement on sensitivity, spatial resolution, integration, energy efficiency and time of response. So far, applications of nanocantilever sensors are mainly focused on dynamic mode silica based nano-sensors (nano-resonator) used as mass sensors.…”

“…Previous attempts at fabricating submicron scale suspending structures include electron beam lithography (EBL), Atomic Force Microscopy lithography, and directing writing laser lithography (DWL), combined with wet etching [3,6,8] . However, the throughput of the aforementioned lithography techniques is very low and these techniques are not very suitable for a mass fabrication of nano-cantilever sensors.…”