Rapid Thermal Annealing Of Sputtered Niobium Silicide Thin Films

Abstract

Rapid thermal annealing of sputtered niobium silicide thin films T.P. Chow+, D. Hodul* and R.A. Powell*+General Electric CompanyCorporate Research and DevelopmentSchenectady, New York 12301*Varian Central Research and Development611 Hansen Way Palo Alto, California 94303.AbstractThin film properties of niobium silicide (Si/Nb ~ 2.1) on SiOo/Si substrates after rapid thermal annealing in two different systems were investigated^ The structural and compositional properties were examined with X-ray diffraction and Rutherford backscatter- ing spectrometry. X-ray diffraction revealed that NbSi2 was the predominant silicidephase present, as the grain size increased from 10 to 160& before and after annealing at 1100°C for 10 sec. Isochronal and isothermal annealing at 800-1200°C for 10-120 sec showed that over 50% decrease in resistivity occurred in the first 10 sec and the lowest resistivity value of 85£uQ-cm was obtained after annealing at 1200°C for 120 sec. Also, a corresponding increase in film reflectance was observed with the decrease in sheet resis­ tivity. Furthermore, annealing at 1300°C led to precipitate formation on the silicide surface.IntroductionRefractory metal silicides are being incorporated into silicon VLSI integrated circuits as MOS gates and interconnects due to their low resistivity, oxidation resistance and com­ patibility with MOS processes1' 2. Among the silicides, the most widely used ones are MoSi2, TaSior WSi2 and TiSio. Recently, NbSio was also reported3 5 to have similar pro­ perties as the other refractory silicides. These films were deposited by either sputter­ ing from alloy targets3' 4 or by coevaporation from individual metal and silicon sources5. After deposition, a high-temperature (typically 1000°C) annealing is needed to recrystal- lize the silicide and hence lower its resistivity. Since conventional furnace annealing at 1000°C or above also results in excessive dopant diffusion and hence junction depth, rapid thermal annealing (RTA) for dopant activation has been successfully performed . Application of RTA for silicide recrystallization has also been demonstrated for several silicides710. In this paper, the RTA characteristics of niobium silicide films sputtered from a cold-pressed target on SiO^/si substrates were studied and compared with those of films annealed in a conventional furnace.Niobium silicide films, 2400-26008 thick, were deposited at room temperature from a cold-pressed composite silicide target (nominally, 99.6% pure and Si/Nb ratio of 2.3) in a batch dc magnetron sputtering system (Varian 3140) onto thermally oxidized silicon, sub­ strates. The background pressure before argon refill was always less than 6x10 Torr.Rutherford Backscattering Spectrometry (RBS) was done with a 2 MeV He* beam from a linear accelerator. X-ray diffraction using the Cu Kc( line was performed with a Siemens D-500 automated diff ractometer. The two rapid thermal annealing systems used were an AG Heat- pulse,- system (Model 210) under argon flow and a Varian IA-200 system under vacuum (~10~ Torr). The film sheet resistance was measured with a four-point probe and the film reflectivity was monitored with a commercial reflectance spectrometer (Optronics Lab., Model 740A) in the range of 350-llOOnm.BesultsThe as-deposited niobium silicide films were essentially amorphous but after RTA at elevated temperatures even for a few seconds, they quickly recrystallized into a predom­ inantly NbSi~ structure. Figures l(a) and (b) show X-ray diffraction patterns for a sili­ cide film beTore and after RTA at 1100 C for 10 sec. A majority of the diffraction peaks are attributed to NbSi0 . The most intense peaks of NbSi~ are at 28 of 21.4, 25.4, 40.1, 41.2 and 47.0°, corresponding to the (100), (101), (111), (003) and (112) planes respec-