N ELSEVIER Applied Surface Science 86 (1995) 475-483 applied surface science Laser processing of tungsten from WF6 and Sill 4 Michel Meunier *, Patrick Desjardins, Maleck Tabbal, Nada Elyaagoubi, Ricardo Izquierdo, Arthur Yelon Groupe des CouchesMinces and D@artment de G&ie Physique, Ecole Polytechnique de Montr&l, P.O. Box 6079, Station "Centre-Ville" 2900, Edouard-Montpetit, Montr&l, Qu&ec, Canada H3C 3A7 Received 27 May 1994; accepted for publication 20 September 1994 Abstract Low temperature laser processing of W using WF 6 and Sill 4 is discussed. This process can be applied with limited thermal budget to various substrates, giving the possibility of depositing thin films on fragile substrates like polyimide or GaAs. In a direct writing mode, an Ar + laser and a diode laser have been used to produce WSi x with various controlled line profiles on polyimide and TiN. Best resistivities are between 40 and 80/.cO. cm and the composition W/Si vary from 1.4 to 1.8. Excimer laser induced deposition of W on GaAs for making Schottky contacts has also been investigated. This process yields pure c,-W deposits with resistivities of 20 / , ~ . cm. 1. Introduction Laser beams directed onto a surface can be used to induce thin film deposition by either pyrolytic or photolytic chemical reactions in the gas phase or on the substrate [1]. In a pyrolytic laser chemical vapor deposition (LCVD) process, lasers are used as the heat source to induce a localized thermal reaction where the beam is focused on the substrate. The displacement of the beam on the surface leads to the direct 'writing' of patterns. However, UV photons may induce both pyrolytic and photolytic chemical reactions, either in the gas phase or on the surface. Projecting the UV photons from an excimer laser through a mask can lead to thin film deposition with high resolution patterns. * Corresponding author. E-mail: meunier@phys.polymtI.ca. Fax: + 1 514 340 3218. Tungsten is particularly interesting in microelec- tronics because it is a low resistivity refractory metal ( Pbutk = 5.6 /*1"1• cm). It can be used as a thermally stable interconnect material and it forms good Schot- tky contacts on GaAs. Laser processing using W(CO) 6 has been extensively studied [2-8], but growth rates are relatively low and the resistivity of the deposits is usually high (~ 200 /9bulk) , owing to C and O incorporation in the films. In contrast, the use of WF6 as the precursor usually leads to high purity thin films with low resistivity (~ 2 Pbulk) at relatively high growth rates. Tungsten has been de- posited from WF6 using excimer [9-13], CO 2 [14,15] and ion (Ar ÷ and Kr +) [16-28] lasers. Most of these studies relied on the reduction of WF6 by hydrogen or by silicon substrates. However, hydrogen reduc- tion of WF6 occurs at relatively high temperature (> 400°C), and Si reduction, which takes place at lower temperatures, is self-limited to very thin films [22]. 0169-4332/95/$09.50 @ 1995 Elsevier Science B.V. All rights reserved SSD] 0169-4332(94)00383-1