Thin Solid Films 422 (2002) 87–91 0040-6090/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0040-6090 Ž 02 . 00978-1 Degradation during sputter deposition of solid electrolyte thin films for microsystems J.-L. Seguin, C. Lambert-Mauriat, K. Aguir, M. Bendahan, C. Jacolin, P. Lauque* Laboratoire Materiaux et Microelectronique de Provence (L2MP, UMR 6137 CNRS), Faculte des Sciences de St. Jerome, Case 152, ´ ´ ´ ´ˆ 13397 Marseille Cedex 20, France Received 10 May 2002; received in revised form 2 October 2002; accepted 4 October 2002 Abstract Copper dendrites formation in copper(I) bromide (CuBr) thin films was observed during sputter deposition. The phenomenon has been reproduced at atmospheric pressure using a CuyCuBryAu cell polarized under d.c. voltage. We show that this results from the electrolysis of CuBr film submitted to the potential drop, between the floating potential above the film and the grounded metallic substrate. This type of in situ electrolytic decomposition may explain failure in thin film preparation of advanced materials with noticeable ionic mobility. A solution is proposed to avoid this degradation, which is detrimental for thin film applications. Moreover, a similar phenomenon was observed on the CuBr target used in magnetron sputtering.  2002 Elsevier Science B.V. All rights reserved. Keywords: Electromigration; Plasma processing and deposition; Solid electrolyte interface; Halides 1. Introduction Solid ionic conductors have many applications in the fields of solid state batteries, electrochromic devices and electrochemical sensors w1x. A decisive advantage, com- pared to liquid electrolytes, is the possibility of minia- turisation of devices enabling their integration in new microsystems. Solid state microbatteries w2x and inte- grated gas sensors w3x have been developed using solid electrolytes thin films. A well-adapted deposition tech- nique for these devices, radio-frequency (r.f.) sputtering, allows both controlled composition and microstructure of compound materials. In solid ionic or mixed conduc- tors, the ions move at ambient temperature over a certain number of vacant lattice sites, due to the presence of doping impurities in the crystal. Such a mechanism is, for instance, assumed in the mixed Cu ion yelectron q hole conductor copper(I) bromide (CuBr) w4x. We are currently studying sputtered CuBr films, which have remarkable sensing properties for ammonia gas detection at room temperature w5,6x. *Corresponding author. Tel.: q33-491-288-975; fax: q33-491- 288-970. E-mail address: pascal.lauque@l2mp.fr (P. Lauque). Tree-like patterns are observed on CuBr films depos- ited on insulating substrates with metallic electrodes, using r.f. sputtering (Fig. 1). These patterns were obvi- ously created during film deposition. Equivalent struc- tures were also observed between conductive tracks on printed circuit boards (PCB) in a high humidity envi- ronment. The formation of these dendrites promotes leakage across the PCB and finally can cause short- circuit w7x. Assuming such patterns could be the result of an electrochemical migration in the solid electrolyte film, experiments were performed with the aim of interpreting and avoiding this phenomenon, which is detrimental for most of applications. 2. Experimental The experimental set-up used for the deposition of the CuBr thin films was a conventional r.f. sputtering device, built in the laboratory. The pumping system was composed of a turbomolecular pump backed up with a mechanical pump. The sputtering gas (argon) was intro- duced through a mass flow controller into the vacuum chamber and the operating pressure was measured using a capacitive manometer. The substrate-holder was sus-