Laser Cvd of Tungsten on Silicon Oxynitride
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LASER CVD OF TUNGSTEN ON SILICON OXYNITRIDE
R. IZQUIERDO, A.LECOURS AND M. MEUNIER Groupe des Couches Minces and D6partement de G6nie Physique, Ecole Polytechnique de Montr6al, Qu6bec, Canada, H3C 3A7. ABSTRACT
Laser direct writing of tungsten from WF6 onto 0.6 lim thick films of silicon oxynitride on silicon using an argon-ion laser beam is investigated. XPS studies show that WF6 is chemisorbed on the oxynitride surface and that nitrogen plays a role in this adsorption. Deposits have good adhesion, columnar growth structure and resistivities ranging from 13 to 25 gQ-cm. The deposition conditions significantly affect the deposit morphology and profile. In particular, increasing the hydrogen pressure increases the linewidth but reduces the thickness. Mass transport phenomena are invoked to explain these effects. INTRODUCTION
As the complexity of microelectronic circuits increases, the time and cost of prototype production and test also increase. The ability to modify existing prototypes can be economically significant. Laser deposition of metal lines for circuit modification has been widely studied in recent years [1,2,3]. It is possible to deposit tungsten, through the reduction reaction of tungsten hexafluoride (WF6 ) by hydrogen. Most studies of tungsten deposition have been performed using Si or Si covered by a native oxide layer of a few A [4,5]. However, circuit repair or modification requires metallic lines to be deposited over a much thicker passivating layer (> 0.5 lam). Since the use of silicon oxynitride (SiOxNy) as a passivating layer is becoming more frequent, we investigated the deposition of W on this dielectric, with emphasis on the problem of process control. X-Ray Photoelectron Spectroscopy (XPS) studies of the adsorption of the WF6 on the SiOxNy surface are presented. The influence of various parameters, such as laser power, gas composition, and writing speed, on line morphology and profile has been studied. LASER CVD SYSTEM
The laser direct writing deposition system is based on an Ar+ laser operated at 488 nm with a maximum power of 1.4 W. The beam is focused on the substrate using either a 0.15 or 0.31 NA objective. Because these objectives are not designed to work with an infinite conjugated ratio, we use a diverging lens at the entrance of the microscope. The spot size, at e- 2 in intensity, measured by the scanning knife-edge technique, is 3.7 lam for the 0.15 NA objective and estimated to be about 2 Igm for the 0.31 NA objective. The position which yields a focus on the substrate is controlled by measuring the intensity of the reflected beam passing through a pin-hole. The substrate is placed in a stainless steel reaction chamber, mechanically pumped to a base pressure of 10-3 Torr. The writing is done by moving the chamber with computer controlled X-Y stages which have a resolution of 0.1 lam and a maximum speed of 100 tim/s. Deposits may be made either in an isolated reaction cell, filled to the operation pressures with WF6 and H2, or by flowing the two gases at a determined flow ratio
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