Effect of particle bombardment on the orientation and the residual stress of sputtered AlN films for SAW devices

Abstract

We present a study of the effect of particle bombardment on the preferred orientation and the residual stress of polycrystalline aluminum nitride (AlN) thin films for surface acoustic wave (SAW) applications. Films were deposited on silicon (100) substrates by radio frequency (RF) sputtering of an aluminum target in an argon and nitrogen gas mixture. The main deposition parameters were changed as follows: the total pressure from 4 mTorr to 11 mTorr, the N2 content in the gas mixture from 20% to 80%, and the substrate self-bias voltage from ;10 V to ;30 V. If a sufficiently high negative substrate self-bias voltage is induced, (00.2)-oriented films are obtained over the full ranges of pressure and N2 content. Such films have values of residual stress ranging from ;3 GPa to +1 GPa, depending on the deposition conditions. Our results suggest that the energy of the Ar ions colliding with the substrate controls the preferred orientation of the films, whereas the directionality of the ions (for the same energy) is the main factor determining the residual stress. To demonstrate the suitability of our material for the intended application, SAW filters with good electroacoustic response have been fabricated using AlN thin films with optimized (00.2) orientation and controlled residual stress.

The sputtering of AlN films on top of on- and off-axis 3C-SiC (111)/Si (111) substrates at various substrate temperatures

“…However, several applications could make use of AlN films with such tensile stress. For example, Iborra et al [36] reported similar range of residual stress for their sputtered AlN films and successfully developed the SAW filters.…”

Influence of AlN quality on the transverse and longitudinal coupling coefficients of acoustic devices

“…However, it is common to find grains exhibiting other orientations, in particular the (10·1), (10·2) and (10·3). The deposition conditions [7], the nature and roughness of the substrate [8], and the residual gases present in the deposition chamber [6,9] are the determining factors of crystal quality of the films, which includes the amount of misaligned grains. The dominant polarization direction finally determines the piezoelectric response of the films.…”

Advanced determination of piezoelectric properties of AlN thin films on silicon substrates

“…Among the different piezoelectric materials, AlN is an interesting candidate for this integration process. Its good mechanical, chemical and dielectric properties, as well as the compatibility with CMOS technology, have determined its choice [4,5]. A number of complex techniques have been used to determine AlN piezoelectric properties, such as the piezoelectric coefficients d 33 and d 31 [6][7][8][9][10][11].…”