Diffusion barrier materials, TiN and WN, were deposited by atomic layer deposition (ALD). The chlorine concentration of the TiN film was as low as 1.2 at.-%, and resistivity was below 200 lX cm. Ultra high aspect ratio (AR = 85) trenches were used to assess step coverage. Tungsten nitride film, deposited from WF 6 and ammonia, was found to have high resistivity, although the residue content was low. The barrier deposition compatibility was studied using the copper surface exposed on the bottom of vias in the copper dual-damascene structure. The deposition on copper of both TiN and WN was found to be very challenging.
The sources of non-uniformity in thin films produced using atomic layer deposition (ALD) have been investigated by reviewing the mechanical hardware of ALD reactors, precursors, and the by-products of surface reactions. The most common causes of non-uniformity are overlapping pulses, thermal self-decomposition of precursors, and non-uniform gas distribution. Less studied, however, are the consequences of downstream surface reactions of gaseous by-products. In particular, titanium nitride films have been found to be significantly less uniform than those of transition metal oxides deposited from metal halides. The influence of reaction by-products on the TiN film growth has been studied by comparing the deposition in the cross-flow and showerhead style reactors. Finally, the sources of non-uniformity in plasma enhanced (PE) ALD are illustrated by studying the TiN deposition process.
This study explores TiN film deposition using the plasma enhanced atomic layer deposition (PEALD) technique, comparing the results of PEALD-TiN with the previous results of ALD-TiN and ALD-TiN with in situ reduction. Each of the studies used
TiCl4
precursor as the titanium source. The ALD-TiN study used ammonia as the reducing agent. Nitrogen and hydrogen gases are not reactive in the ALD-TiN deposition, but they were successfully used in PEALD-TiN. This study shows that the concept of self-saturating reaction in ALD differs from PEALD. Although the growth rate saturates as a function of pulse lengths, the number of active surface sites and the film composition can be changed by the plasma pulsing parameters. In all deposition techniques the TiN films exhibit excellent film properties including low resistivity, low impurity concentration, and high-density films. PEALD provides significant advantages if the deposition temperature is lower than 350°C.
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