278 Nuclear Instruments and Methods in Physics Research B7/8 (1985) 278-286 North-Holland, Amsterdam RBS STUDY OF THE EFFECT OF ARSENIC AND PHOSPHORUS INTERFACIAL SEGREGATION UPON THE SINTERING OF CONTACI-S BETWEEN IMPLANTED POLYCRYSTALLINE SILICON AND ALUMINUM : SILICON( 1%) Nicole HERBOTS *, Maurice LOBET and Femand Van de WIELE Microekxtronics Lab, Uniwrsite Catholique de Lmamin, 3, place du Levant. B - 1348 Lauvain -la - Neuve, Belgium The sintering behavior of the interface between Al : Si(l%) alloy and polycrystalline Si (poly-Si) was studied as a function of the poly-Si implantation dose by combining RBS, SEM, TEM and X-ray microanalysis. Two different N-dopants were used: arsenic and phosphorus. The dopants were implanted in the poly-Si layer and thermal annealing was used to obtain dopant segregation towards the poly-Si interfacea. After sir&ring, two main effects were detected: (1) Al-Si eutectic phase precipitates and Si crystallites are formed at the interface. (2) The density of precipitates is a function of the implantation dose. For doses above 1 x lOI5 at./cm2. segregated arsenic and phosphorus are found to completely inhibit this precipitation process, provided that the segregation peak of the dopant profile is preserved before metallization. Several conclusions can be drawn: for surface concentrations higher than 8~10’~ at./cm3, arsenic and phosphorus inhibit the precipitation of the Al-Si eutectic phase, and thus inhibit interactions between the films at the interface. Moreover, argon gas, used for sputtering deposition of aluminum, segregated at the poly-Si/Al : Si(l%) interface and may also inhibit the metal-semiconductor interdiffusion. 1. Introduction Aluminum is widely used as interconnection material, and the stability of the Al/Si interface is a key factor in IC manufacturing. The extensive interdiffusion between Al/Si upon sir&ring [1,2] has prompted much research effort during the last decade [3,4]. In the case of polycrystalline Si (poly-Si), interdiffu- sion is enhanced because of the preferential migration of aluminum along grain boundaries (GB), as shown by Nakamura [5,6]. Classical solutions aiming at inhibiting Al/Si inte i-mixing such as the use of the Al : Si(1 W) alloy [7] do not work with Al/poly-Si contacts [8]. Similar problems of interdiffusion also arise at inter- faces between poly-Si and silicides as well as at inter- faces between poly-Si and diffusion barriers (9). The nresent work proposes a new solution to the poly-Si/metal interdiffuston problem, based on the un- derstanding of the microscopic mechanisms and kinetics of the interaction rather than on the thermodynamic properties of the materials. We started from the obvious fact that interdiffusion can occur only if transport of material is possible through the interface. Therefore, we focused our attention on the preparation of the inter- faces present in a poly-Si film, that is the grain * IRSIA Doctoral Fellow. Present address: Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. boundaries (GB) and top surface. In a previous work [lo], we reported that the pres- ence of an arsenic segregation peak at the Al/poly-Si interface stabilizes this interface very efficiently, as compared to plain “GB stuffing” [4], or to the use of a tungsten diffusion barrier [4]. Al/poly-Si/SiO, struc- tures with a segregated arsenic peak withstand severe sintering tests and show a dramatic decrease of interdif- fusion. We also reported that there is a threshold con- centration of about 1.0 x 1019 at/cm) (fig. 1, from ref. [lo]) for the arsenic peak to act as an effective inhibitor of intermixing. This threshold also appears in other diffusion phenomena in poly-Si [11,12]. 2. Theoretical background We proposed a model to explain how the arsenic segregation inhibits interdiffusion both by an electronic and a steric effect. Fig. 2 shows the microscopic mecha- nism we deduced from our work in ref. [lo], in the case of undoped Si. Fig. 2a shows an atomically clean Si surface, disordered or not, before aluminum deposition (note that if a native SiO, is present on the surface, it is reduced during the sintering process). Fig. 2b shows the same surface with one monolayer of Al, and the cova- lent bonding occurring between silicon and aluminum atoms, as reported by Kobayashi in ref. [14]. Fig. 2c shows the occurrence of interdiffusion when the 0168-583X/85/$03.30 0 Elsevier Science Publishers B.V (North-Holland Physics Publishing Division)