Atomic Layer Deposition of Metal and Transition Metal Nitride Thin Films and In Situ Mass Spectrometry Studies

Marika Juppo
Abstract & Cover

The shrinking feature sizes of basic electronic components, like transistors, memory cells and  metal wires, in integrated circuits sets high demands on both materials and thin film deposition  methods.One of themajor changes in thematerials has been the adoption of copper interconnects.  Due to the tendency of copper to react with silicon and insulators, use of a diffusion barrier is  necessary.With the currently used depositionmethods the future requirements for thin films, for  example, strict conformality and lowdeposition temperature, can not be fulfilled at the same time.  One of the most promising methods to be exploited in the near future is atomic layer deposition  (ALD). In the presentwork theALDmethod was used to deposit copper andmolybdenum films,  and some transition metal nitride films focusing on TiN.  Copper andmolybdenum films were deposited from the corresponding chlorides using zinc as a  reducing agent.The dissolution and outdiffusion of zinc caused problemswith the controllability  of the film growth.The deposition of copperwas also studied from various copper precursors and  reducing agents of different chemical nature. Altogether, the ALD of metals seemed quite  complicated, and although metals could be deposited their properties were only modest.  The main problem with the existing TiN ALD processes is that usually the films have to be  deposited at too high temperatures to obtain films with reasonably good properties. Fairly good  properties can be achieved by using zinc as an additional reducing agent, but it is known to  dissolve into silicon. In most of the previous ALD processes NH3 has been used as a nitrogen  source and but it is not very effective at low temperatures. In order to be able to grow TiN films  at temperatures tolerable in the future (below 400 °C), the deposition of TiN films was studied  from titanium halides by using twodifferent approaches. Nitrogen sourcesmore reactive thanNH3,  namely dimethylhydrazine, tert-butylamine and allylamine,were used.Another approach was to  deposit TiN films by using trimethylaluminium (TMA) as an additional reducing agent withNH3.  Each of the studied approaches produced filmswith better properties than those obtainedwith bare  NH3at lowtemperatures. The lowest resistivity (around 150:Scm)was obtained by usingTMA  as an additional reducing agent, but the carbon contamination was quite high (above 6 at.%).  Somewhat higher resistivities were obtainedwith dimethylhydrazine and amines (200 - 500 :S  cm), but with tert-butylamine the carbon contents were only minor (below 1 at.%).  In order to understand the reactionmechanisms involved inALD, the growth of Al2O3 andTi(Al)N  were studied bymeans of in situmass spectrometry. The results obtained gave information about  the possible surface reactions, and it seems that through the in situ mass spectrometry the ALD  reaction mechanisms can be identified.  

Source of Information
FinALD40 exhibition material,
University of Helsinki, Department of Chemistry, Laboratory of Inorganic Chemistry
(Helsinki, Finland)
Other notes
Oksana: In this thesis terms ALD, ALD cycle, temperature window are used
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