LPCVD Titanium Nitride for ULSIs

Abstract

Characteristics of TiN films formed by low-pressure chemical vapor deposition (LPCVD) are investigated for application to the barrier layers in ultra-large-scale integration (ULSI) which have fine, high-aspect-ratio contact holes. The evaluation focuses on the characteristics crucial for barrier layer usage, such as step coverage, N/Ti atomic concentration ratio, x, in TiNs, and C1 content. Film resistivities are also measured. Excellent step coverage is confirmed. A high-aspect-ratio hole, such as one with a diameter of 0.5 i~m and a depth of 0.8 ~m, is completely filled by TiN film. The atomic concentration ratio x for films formed at 500~176 is nearly equal to 1. Reduction in the C1 content coming from the source material, TIC14, is a matter of concern. High-temperature deposition is very effective in reducing C1 content. A film deposited at 700~ contains < 1 atom percent (a/o) of C1, much less than films formed at lower temperatures contain. High-temperature annealing after deposition can also reduce C1 content. The C1 content in a film formed at 500~ is reduced from 5.7 a/o to 2.7 a/o by H2 annealing at 1000~ for 30 min. The resistivity of a film formed at 700~ is 80 I~" cm, which is lower than that of a film formed at lower temperatures. This reduction may be due to the decrease in C1 content.As the feature size of ULSIs is minimized, it becomes more difficult to achieve reliable interconnection. For 16-Mbit DRAMs, the narrowest width of the A1 alloy lines and the smallest diameter of the contact holes will be about half a micron. Many problems'concerning metallization will have to be faced in such advanced ULSIs.First, increased resistivity of A1 alloy lines, due to Si precipitation coming from Si-containing A1 alloy, will severely restrict device performance. Refractory metal silicide barrier layers such as MoSix (x > 2) between A1 alloy lines and Si substrate have been applied to disperse Si precipitation all under lines, not to concentrate it at the contacts. However, silicide barriers do not prevent precipitation itself, so they cannot be a solution to resistivity increase of A1 alloy lines. Moreover, silicide barriers cannot restrain interaction between A1 alloy lines and silicon substrate at rather low temperatures, such as 500~ Interaction brings about high contact resistivity. For fine lines with a width of less than one micron, it will be necessary to restrain Si precipitation and interaction between A1 alloy and substrate. A new diffusion barrier layer, in place of silicide barriers, will become essential for reliable interconnection in highly packed ULSIs.Refractory metals and their alloys such as W and TiW can be applied to prevent this problem. Unfortunately, these materials do not always show sufficient heat resistance. Interdiffusion between the A1 and the barriers occurs at relatively low temperatures. A barrier layer such as TiN is thus desired to effectively prevent this interdiffusion even at temperatures higher than 400~The second problem is migration immunity degradation of A1 alloy li...

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