In-Situ Study of Ti/TiN Stability under Nitrogen Anneal
- PDF / 612,325 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 67 Downloads / 188 Views
ABSTRACT The effectiveness of a TiN capping layer to prevent the conversion of ca-titantium to titanium nitride when annealed in a nitrogen ambient has been studied over the temperature range 300-700'C using in-situ high temperature diffraction and transmission electron microscopy. Over the time range of interest (four hours), no evidence of Ti reaction was observed at 300'C. At 450°C. nitrogen was found to diffuse into the Ti to form a Ti(N) solid solution. Above 500'C the titanium is transformed to a second phase; however this reaction follows two different kinetic paths, depending on the annealing temperature. Below 600'C. the reaction proceeds in two stages, with the first stage consisting of Ti(N) formation, and the second stage consisting of the conversion of the Ti(N) with a transformation mechanism characteristic of short range diffusion (grain edge nucleation). Above 600'C, a simple linear transformation rate is observed. INTRODUCTION Ti/TiN is a commonly used liner for Al interconnect metallization in ULSI devices. The importance of texture to Al electromigration performance [I] as well as the principle of texture inheritance in Ti/TiN/A1 structures 12] are well established. Hence, in designing a manufacturing process for optimum texture. maintaining the phase integrity of the Ti liner can be of critical importance. Annealing of the Ti/TiN can occur before and after aluminum deposition, and these anneals are often done in a nitrogen ambient. A number of studies have been done to examine the stability of the Ti/TiN layer. Gignac, et. al.[31 showed that PVD Ti/CVD TiN/CVD Al films reacted to form Ti,N and TiAI1 in the temperature range of 500 to 600'C. Wang and Allen [4] annealed TiN/Ti/TiN films in vacuum; they observed that nitrogen dissolved from the TiN into the Ti between 405 and 474°C. and that Ti and TiN reacted to form s-TiN in the temperature range of 505 to 548°C. Hamamura, et. al. [5] annealed SiO,/Ti/TiN films in nitrogen; they reported a conversion of the Ti to TiN at temperatures above 450*C. This paper summarizes a systematic study of the reaction kinetics of the Ti/TiN film when annealed in nitrogen using high temperature x-ray diffraction. The purpose of the study was to determine if there was a threshold temperature below which the titanium layer was stable, as well as examine the reaction rate of the titanium at various temperatures. EXPERIMENTAL For this study a blanket film of 30nm PVD Ti / l0nm PVD T'iN / 60nm CVD Al / I lPm AI-0.5 wt% Cu deposited on silicon with a thermally grown SiO, layer was used. The aluminum was removed by selective chemical etch. Previous XRD studies had been carried out on this film [3] and showed the titanium to have a strong texture in both the and planes. The 465 Mat. Res. Soc. Symp. Proc. Vol. 564 0 1999 Materials Research Society
titanium nitride phase was found to be that of TiN (osbornite) with a preferred orientation along the planes. Samples were cut to a size (5mm x 7mm) suitable to fit into the furnace of a Rigaku Theta-Theta diffractometer with 2
Data Loading...
