Control of stress in tantalum thin films for the fabrication of 3D MEMS structures

Abstract

Effect of oxygen on the thermomechanical behavior of tantalum thin films during the β -α phase transformation Accuracy of thin film stress measurements with c -Si microbeams fabricated by dry etching Sputtered tantalum (Ta) thin-films subjected to high compressive stress have been used for fabricating out-of-plane microelectromechanical systems (MEMS) clamped-clamped beams. The as-deposited film stress has been investigated as a function of sputtering conditions (pressure and power) in order to determine the optimal deposition parameters for achieving a compressive state. A variation of the as-deposited film stress has been observed as a function of time at atmospheric conditions and reduced by $85% using annealing in oxygen atmosphere at 100 C. By surface-micromachining Ta thin-films deposited in compressive state (beyond the critical buckling load), buckled out-of-plane beams have been fabricated with lengths in the range of 500 lmÀ5.8 mm and central out-of-plane deflection up to $60 lm. A final stress of $À850 MPa has been calculated from the measured beams' deflection. The modal behavior of the buckled out-of-plane beams has been investigated with optical measurements and finite element simulations. The large curvature and high residual stress experienced by the beams have shown to affect the usual order of consecutive bending mode shapes. The devices presented can be utilized for implementing cutting-edge three-dimensional MEMS.

Compression and decompression of structural tantalum films exposed to buffered hydrofluoric acid

“…Of particular interest in this work, a large shift, not precisely quantified but on the order of hundreds of MPa, in Ta fixed-fixed beams towards more compressive stress was measured by Al-masha'al et al after two different release processes [6,11]. In the first process, the sacrificial layer was a photoresist, and the release process was an oxygen plasma ash.…”

“…The understanding gained in this work represents a useful step potentially leading to the more widespread use of Ta as a MEMS structural material in applications such as those mentioned in the Introduction [1,2,5,6]. acknowledge the Kavcic-Moura Endowment Fund for support and use of the Materials Characterization Facility at Carnegie Mellon University under Grant No.…”

“…For instance, a low average stress and stress gradient are desirable for RF switches [2]. Residual stress also affects the dynamic response of Ta clamped-clamped beam structures [6]. But stress control is a complex issue in metal thin films, where residual stresses are strongly dependent on deposition conditions and on subsequent thermal treatments [7][8][9][10].…”

The effect of vacuum annealing on the microstructure, mechanical and electrical properties of tantalum films

“…Tantalum (Ta) is one of the refractory metals which in thin film form is of interest for applications in microelectronic devices such as resistors, heaters and capacitors [1][2][3][4]. Due to high melting temperature (~3050°C), high strength, and good corrosion and wear resistance, such electronic devices can work in harsh environment and/or at high temperatures [5].…”

MEMS design and modelling based on resonant gate transistor for cochlear biomimetical application

“…Concurrently, the electrical signals within the hair cells of the cochlea can be reproduced by the channel region between the source and drain of RGT. The fabrication process, measurement analysis and interface circuit design for RGT can be found in (Koickal et al 2011;Latif et al 2010;Latif et al 2011;Mastropaolo et al 2013;…”