Chemical vapor deposition of fluoroalkylsilane monolayer films for adhesion control in microelectromechanical systems

Abstract

We have developed a new process for applying a hydrophobic, low adhesion energy coating to microelectromechanical (MEMS) devices. Monolayer films are synthesized from tridecafluoro-1 ,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor in a low-pressure chemical vapor deposition process at room temperature. Film thickness is self-limiting by virtue of the inability of precursors to stick to h e fluorocarbon surface of the film once it has formed. We have measured film densities of -3 molecules nm2 and film thickness of -I nm. Films are hydrophobic. lvirh n water contact angle >llOo. We have also incorporated an in-situ downstream microwave plasma cleaning process, which provides a clean. reproducible oxide surface prior to film deposition. Adhesion tests on coated and uncoated lMEMS test structures demonstrate superior performance of the FOTS coatings. Cleaned, uncoated cantilever beam structures exhibit high adhesion energies in a high humidity environment. -Ln adhesion energy of 100 mJ m-' is observed after exposure to >90% relative humidity.Fluoroalkylsilane coated beams exhibit negligible adhesion at low humidity and 5 20 pJ m-2 adhesion energy at >90% relative humidity. No'obvious film degradation was observed for films exposed to >90% relative humidity at room temperature for >24 lir.

LDRD Project 52523 final report :Atomic layer deposition of highly conformal tribological coatings.

“…Indeed, multiple research groups have observed nano g ang et al [3]; Chu and Barnett [4]; Misra et al [5]). There have been several attempts to model hard ns; however, the models tend to diverge from experimental results at very small length scales idm d ncreasing resistance at smaller thickness (Ruff and Lashmore [8]). Additionally, in-TEM ponent blanket films (Kramer and Foecke [9]).…”

“…(Beuth [2]; Beuth and Klingbell [3]; Hu et al [4]; Hutchinson and Suo [5]; Nakamura and Kamath [6]; Thouless, Cao, and Mataga [7]; Thouless [8]; Thouless, Olsson, and Gupta [9]; Vlassak [10]; Xia and Hutchinson [11]; Ye et al [12];) These analyses are based on the assumptions that the film and substrate are elastic isotropic solids with dissimilar elastic moduli, the film is subject to a uniform, equib axial in-plane tensile lease the film. For a through-thickness single channel crack forming in a residually stressed film, the mode I steady state strain energy release rate at fracture, Iss , is given by, (Hu et al [4]); Thouless [8]; Beuth [2]; Hutchinson and Suo [5]), (1) In this equation, is the stress in the film, h is the film thickness, E f is the elastic modulus of the film, f Poissons ratio for the film, and g( , ) is nondimensionalized integral of the crack opening displacement. (Beuth [2]) The analysis was extended to multiple crack systems to account for crack interaction effects on strain energy release rates and is a function of crack spacing and film thickness.…”

Development of highly integrated magetically and electrostatically actuated micropumps : LDRD 64709 final report.

“…Typically fluoroalkylsilane (FOTS) monolayer films are deposited [18]. This coating provides additional resistance to stiction, reduces wear on any rubbing surfaces and changes the released surfaces from hydrophilic to hydrophobic (contact angle of approximately 110%).…”

Directional shear force microscopy

“…For this reason, all of the data were acquired with a hydrophobic glass tip that was coated with a monolayer of CF 3 ͑CF 2 ͒ 5 ͑CH 2 ) 2 -SiCl 2 via vapor phase deposition. 16 Water layers are expected to be present under the ambient conditions of ϳ20% relative humidity. However, there was no evidence of capillary condensation between the tip and the PDA films.…”