A study of the surface chemistry, morphology and wear of silicon based MEMS

Abstract

Polysilicon microelectromechanical systems (MEMS) are the subject of intense research activity. This paper reports on the surface chemistry, topography and nanowear properties of a MEMS test structure fabricated at Sandia National Laboratories, studied using XPS and atomic force microscopy (AFM). XPS C 1s and Si 2p spectra from the polysilicon components, silicon nitride substrate and a reference Si wafer are compared. The results confirm the presence of a self-assembled monolayer (SAM) on the MEMS surface. An island-like morphology is found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 µm in diameter and 20 nm in height. It is concluded that a dual columnar and equiaxed microstructure develops during growth of these low pressure chemical vapour deposition (LPCVD) layers and the islands are caps to the columnar structures. A 35 µN load applied to the AFM diamond tip leads to a wear depth of 1.4 ± 0.13 nm and 2.1 ± 0.06 nm on the polysilicon and silicon nitride MEMS equiaxed surfaces, respectively. Under the same load, greater wear of the columnar caps on both surfaces is observed. The results suggest that the morphology present on the polysilicon surface will be worn flat during operation and will not adversely affect the wear properties of the polysilicon components.

The influence of an OTS self‐assembled monolayer on the wear‐resistant properties of polysilicon based MEMS

“…These results provide strong evidence for the presence of the OTS monolayer on the MEMS surface. The XPS Si 2p and C 1s spectra have been presented previously [7] and the results are also supportive of OTS being present on the MEMS surface.…”

Vapour phase formation of amino functionalised Si3N4 surfaces

“…However, ellipsometric data indicates that the equivalent of two or three layers of APTMS have formed rather than a monolayer. Therefore, this vapour deposition methodology provides a facile means of chemically-modifying the surface of MEMS devices so that they provide amino functionality as opposed to hydrophobic surfaces previously formed on Si 3 N 4 via vapour deposition techniques [19][20][21] 9. AFM images of Si/Si 3 N 4 substrates exposed to APTMS vapour for 60 min at various deposition pressures (P dep ).…”

“…Vapour phase techniques for the formation of SAMs have been performed under elevated temperature [12,21,[26][27][28], or by injecting a surfactant into the system using a carrier gas [3]. Low pressure chemical vapour deposition methods have previously been used to form SAMs of hydrophobic OTS on Si 3 N 4 as anti-stiction coating for MEMS devices [19,20].…”

“…In this way, for example, resonant MEMS devices may be functionalized to detect specific molecules at the attogram level [18]. SAMs have been studied as coatings for MEMS devices for both their anti-stiction [15,[19][20][21] and chemical immobilization properties [5].…”

Benzyl Nicotinate as an Efficient Corrosion Inhibitor for Cold Rolled Steel in a 1 M HCl Solution

“…The free energy ΔGads of BN comes around 37-39 kJ/mol, indicating that the comprehensive adsorption is accompanied by both physisorption and chemisorption. The negative values of ΔH indicate that adsorption is an exothermic process [36], hence, the inhibition efficiency decreases with an increase in temperature. Generally, the exothermic process is attributed to either physisorption or chemisorption, while the endothermic process indicates pure chemisorption.…”