Formation of Suicides by Rapid Thermal Annealing over Polycrystalline Silicon
- PDF / 2,705,917 Bytes
- 7 Pages / 417.6 x 639 pts Page_size
- 39 Downloads / 229 Views
ABSTRACT The formation of titanium silicide over polycrystalline silicon has been investigated after rapid thermal annealing treatment in nitrogen and argon ambients. After rapid thermal annealing 300 A thick titanium overlayer at 9000 C for 10 seconds, the sheet resistance of about 3 0/0 was achieved, which decreased to 2 0/0 after I i 000 C / 1Os treatment. The T15i 2 phase was found to be stable after RTA treatments up to 1IOOC /lOs with no or negligible migration of titanium along the grain boundaries in polycrystalline silicon. In the nitrogen ambient, an external layer (titanium rich, mixture of titanium oxide and nitride) was observed to form after the RTA treatment, but the surface was found clean in the argon ambient. INTRODUCTION In MOS technology, polycrystalline silicon is commonly used as a gate electrode and interconnection-line material. As the size of devices gets smaller, additional requirements are placed on the stability and improved conductivity of metallization systems. As a part of the self-aligned (Sa licide) process, the formation of metallic silicide over polysilicon has been proposed because of the following advantages: (a) the silicide layer reduces sheet resistance, and (b) it maintains well-characterized polysilicon-SiO 2 interface [1-4]. Titanium silicide TiSi 2 has many advantages for VLSI applications because of easy formability, low resistivity, and high-temperature stability [5]. It has been also reported that native oxide on silicon substrate is broken up by the titanium sillcide reaction resulting in a relatively clean sllicide-silIcon interface. Since the metal overlayer reacts with the polycrystalline silicon substrate during silicidation, rapid diffusion of metal along the grain boundaries can occur resulting in degradation of gate insulators. Previous studies reported rapid diffusion of titanium along the grain boundaries during conventional thermal annealing at 850 to 900 0 C for 30
Mat. Res. Soc. Symp. Proc. Vol. 54. ý 1986 Materials Research Society
754 minutes [6]. In this paper, we show that rapid thermal annealing up to 1l00°C for 10 seconds results in the formation of low-resistivity TiSi 2 with virtually no penetration of titanium along the grain boundaries. Furthermore, the silicides remained stable in this temperature regime. A thermal budget of 11000 Cfor 10 seconds represents an upper limit for annealing ion implantation damage and electrical activition of dopants. It should be pointed out that the thermal budget associated with ion implantation damage and annealing is usually the largest of all the semiconductor processing steps. EXPERIMENTAL Silicon single crystals ( orientation, 5 Q-cm) were thermally oxidized to form 250A thick S502. These specimens were used to deposit polycrystalline silicon by LPCVD (Low-pressure chemical vapor deposition) method to a thickness of 2500 to 4000A. The polycrystalline silicon contained columner grains - 400 A across with boundaries aligned along the deposition direction. A 300 A thick titanium film was deposited on these sp
Data Loading...
