Atomic layer deposition of TiN for the fabrication of nanomechanical resonators

Abstract

Films of titanium nitride were grown by atomic layer deposition (ALD) over a range of temperatures from 120 °C to 300 °C, and their deposition rates were characterized by ellipsometry and reflectometry. The stress state of the films was evaluated by interferometry using a wafer bowing technique and varied from compressive (−18 MPa) to tensile (650 MPa). The crystal structure of the films was assessed by x-ray diffraction. The grain size varied with temperature in the range of 2–9 nm. The chemical composition of the films was ascertained by high-resolution x-ray photoelectron spectroscopy and showed the presence of O, Cl, and C contaminants. A mildly tensile (250 MPa) stressed film was employed for the fabrication (by electron beam lithography and reactive ion etching) of doubly clamped nanoresonator beams. The resonance frequency of resonators was assayed using an interferometric resonance testing apparatus. The devices exhibited sharp mechanical resonance peaks in the 17–25 MHz range. The uniformity and controllable deposition rate of ALD films make them ideal candidate materials for the fabrication of ultranarrow (<50 nm) nanobeam structures.

Precursor-surface interactions revealed during plasma-enhanced atomic layer deposition of metal oxide thin films by in-situ spectroscopic ellipsometry

“…During the ALD process, the subsequent exposure of the surface to precursors, separated by purging agents leads to cyclic surface modifications, and the control of which may play a critical role in the resulting thin film quality. To the best of our knowledge, unraveling such complex processes have not been attempted previously by in-situ spectroscopic ellipsometry in ALD or PEALD growth of ultra-thin films 41,46,[64][65][66][67][68][69][70][71][72][73][74][75][76][77] . The analysis of the evolution of the optical properties of ultra-thin films during growth cycles in ALD using in-situ SE as reported here in our work using the dynamic dual box model may gain further insight into the kinetics of the surface modifications within individual cycles.…”

“…www.nature.com/scientificreports www.nature.com/scientificreports/ Klaus et al suggested the application of in-situ SE during ALD growth processes 64 , and accurate thickness monitoring was reported for metal nitride thin films 41,65,66 and metal oxide thin films 46,[67][68][69][70][71][72][73][74][75][76][77] , for example. In these previous reports, in-situ SE data was measured once for every ALD cycle in order to determine the thickness GPC.…”

Is Poly(methyl methacrylate) (PMMA) a Suitable Substrate for ALD?: A Review

“…The PMMA removal step is an important feature in device fabrication and different strategies are ranging from wet to dry procedures. In this context, the PMMA layer can be eliminated by immersing in organic solvents (dichloromethane [ 84 ], acetone [ 85 , 86 , 87 , 88 , 89 ], isopropanol [ 87 ], or a mixture of acetone and isopropanol [ 87 , 89 , 90 ]), rinsing solvents like methanol [ 86 , 91 ] and finally washed with de-ionized water [ 25 , 84 , 91 ]. Sometimes, the PMMA residues are removed by annealing [ 86 ], Tan et al and Cho et al removed the layer with UV-ozone treatment [ 82 , 92 ].…”

“…The PMMA mask can also be processed as a patterned layer, the first step consisting in spin-coating the polymer over the substrate [ 73 , 79 , 91 , 93 , 95 , 96 , 97 , 98 , 100 , 101 , 102 , 103 ] and, sometimes, heat treating at 180 °C [ 51 , 93 , 97 , 99 ] or soft heat treating [ 51 , 79 , 91 , 96 ] for a short time, followed by an etching process to reveal the desired pattern. The techniques employed to etch the PMMA substrate and create the pattern are: (1) lithography (optical lithography [ 96 ], photolithography [ 93 , 97 ], deep-UV lithography [ 79 ], electron beam lithography [ 51 , 85 , 89 , 100 , 103 ]); (2) heated cantilever probe tip (thermal writing) [ 95 ]; (3) chemical writing with isopropanol: methyl isobutyl ketone: methyl ethyl ketone in 75:24:1 ratios [ 99 ]; (4) nanoimprint and etching [ 98 , 101 ].…”

“…After the patterning, it is necessary to create a smooth surface and clean the excess of PMMA to regularize the template shapes; some authors suggest the O 2 plasma descum etch [ 85 , 95 , 101 ] while others advise vacuum annealing [ 79 , 91 ]. Färm et al and Sinha et al used a similar approach exposing the resultant pattern to a solution of isopropyl alcohol/methyl isopropyl ketone [ 81 ] or isopropyl alcohol/methyl isobutyl ketone [ 79 ].…”