Tin oxide thin films were grown by atomic layer deposition (ALD) from bis[bis(trimethylsilyl) amino]tin(II) with ozone and water. The ALD growth rate of tin oxide films was examined with respect to substrate temperature, precursor doses, and number of ALD cycles. With ozone two ALD windows were observed, between 80 and 100 C and between 125 and 200 C. The films grown on soda lime glass and silicon substrates were uniform across the substrates. With the water process the growth rate at 100-250 C was 0.05-0.18 Å /cycle, and with the ozone process, the growth rate at 80-200 C was 0.05-0.11 Å /cycle. The films were further studied for composition and morphology. The films deposited with water showed crystallinity with the tetragonal SnO phase, and annealing in air increased the conductivity of the films while the SnO 2 phase appeared. All the films deposited with ozone contained silicon as an impurity and were amorphous and nonconductive both as-deposited and after annealing. The films were further deposited in TiO 2 nanotubes aiming to create a pn-junction which was studied by I-V measurements. The TiO 2 nanostructure functioned also as a test structure for conformality of the processes. V

Thin films of rare-earth (RE) oxides (Y2O3, PrO x , Gd2O3, and Dy2O3) were deposited by atomic layer deposition from liquid heteroleptic RE­( i PrCp)2( i Pr-amd) precursors with either water or ozone as the oxygen source. Film thickness, crystallinity, morphology, and composition were studied. Saturation was achieved with Gd2O3 when O3 was used as the oxygen source at 225 °C and with Y2O3 with both oxygen sources at as high temperature as 350 °C. The growth rates were 0.90–1.3 Å/cycle for these processes. PrO x was challenging to deposit with both oxygen sources but with long, 20 s purges after the water pulses uniform films could be deposited. However, saturation was not achieved. With Dy2O3, uniform films could be deposited and the Dy­( i PrCp)2( i Pr-amd)/O3 process was close to saturation at 300 °C. The different oxygen sources had an effect on the crystallinity and impurity contents of the films in all the studied processes. Whether ozone or water was better choice for oxygen source depended on the metal oxide material that was deposited.

No abstract

As the atomic layer deposition (ALD) method is based on sequential, self-limiting surface reactions the precursor chemistry is the key to a successful processing of conformal high quality thin films. ALD precursor chemistry has traditionally been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides and alkoxides. However, these precursors sometimes have drawbacks such as possible halide contamination and low thermal stabilities. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes. Here, examples of heteroleptic precursors for ALD processes of transition metals and their oxides are given. Special focus is given to oxides of the rare earths and groups 4 and 5. Trends in the properties of heteroleptic precursors are discussed. Several examples of our recent results are shown, including introduction of novel processes based on amidinate-cyclopentadienyl complexes for ALD of rare earth oxides.

Three heteroleptic Zr precursors were studied for atomic layer deposition of ZrO2. Films were deposited from Zr(Cp)(t BuDAD)(O i Pr), Zr(MeCp)(TMEA) and Zr(Me5Cp)(TEA) with either water or ozone as the oxygen source (t BuDAD = N,N-bis(tertbutyl)ethene-1,2