Arsenic Dopant Influence upon the Sintering Behavior of the Aluminum‐Polysilicon Interface

Abstract

Interdiffusion between thin films of aluminum (A1) and polycrystalline silicon (poly-Si) has been studied with the purpose of obtaining a stable interface upon sintering for IC metallization. The solid-phase crystal regrowth of Si due to this low temperature interdiffusion has also been investigated. Dopant segregration towards the interfaces and the grain boundaries of arsenic~implanted poly-Si was used successfully to control the kinetics of Al-poly-Si interactions. The correlation between the arsenic depth profiles, the Si-layer microstructure, and the sintering behavior of the Al-poly-Si interface was measured by RBS, (scanning) AES, SEM, TEM, and grazing incidence x~rays. Quantitative results and discussion of the diffusion mechanisms at work are presented. It is shown that the presence of an arsenic segregation peak on top of the poly-Si layer stabilizes AYpoly-Si interface. A concentration of 10 '9 atom/cm ~ appears to be a minimum threshold for sintering at 465~The aluminum-silicon (ANSi) contact, which is eXtensively used in semiconductor technology, is a limiting factor in scaling down integrated circuit components. The sintering of the A1-Si interface, necessary to obtain good ohmic contacts, introduces reliability problems due to interdiffusion between A1 and Si and crystal regrowth of the dissolved material. These interactions may appear for any structural morphology of the Si substrate: single-crystal Si (1, 2), polycrystalline Si (poly-Si) (3), or amorphous Si (4, 5). The low temperature enhancement of Si crystal regrowth, due to the diffusion of A1 atoms, presents interesting prospects for solid-phase epitaxy (6, 7).Because of the extensive use of LPCVD poly-Si in integrated circuits, poly-Si-A1 interfaces command particular attention. Forming contacts by means of Al-poly-Si structures has been shown to reduce diode reverse current by a factor of 10 and enhances bipolar transistor gain (8). In addition, MOS circuit density might be increased if the Al-contact were made directly on the poly-Si gate.Such /kl-poly-Si structures require well-defined, stable interfaces. This requirement is not fulfilled by classical Al-metallization, justifying the use of sophisticated technologies to create diffusion barriers between A1 and Si. In the present work, a good stability of the Al-poly-Si contact has been brought about by taking advantage of the presence of arsenic, which segregates to the grain boundaries (GB's) and to the interfaces of the poly-Si film. Indeed, A1 diffuses mainly along the GB's in the poly-Si layer (9, 11), while Si atoms are mainly extracted from the poly-Si GB's (10, 11), and solute atoms within the GB's of polycrystalline films are known to decrease the diffusivities within the layers involved (12) both for selfdiffusion and impurity diffusion.This paper shows that Al-poly-Si interdiffusion strongly depends upon the dose of dopant in Al-polySi and the location of this dopant within the microstructure; it gives evidence that dopant segregation can reduce A1 diffusivity in poly-Si, and t...

Surface Characterization of Arsenic Implanted Silicon (100): A New Insight into the Inhibition of Aluminum/Silicon Interdiffusion

“…In previous studies, [1,2] it was shown that the presence of segregated impurities at the interface between two thin films could inhibit the interdiffusion between the layers.…”