ERBIUM CYCLOPENTADIENYLS, ALKYLCYCLOPENTADIENYLS
Erbium tris (cyclopentadienyl) Er(C5H5)3
Erbium tris (cyclopentadienyl) Er(C5H5)3 is polymeric in the solid state with subunits connected via bridging cyclopentadienyl ligands. Er(C5H5)3 achieves vapor pressure sufficient for the MOCVD applications at evaporation temperatures over 200°C. [4]
According to literature data, the vapor pressure of ErCp3 is quite low: only 0.01 torr /200° C, and the melting point is 285° C.
ErCp3 for Er2O3 thin films by ALD (ab initio calculations)
The ALD growth mechanism of Er2O3 using ErCp3 as precursor was studied using first principles periodic density functional theory (DFT) computations.
According to DFT calculations, Er2O3 ALD growth on the hydroxylated (001) surface of the hexagonal erbia phase proceeds in following steps: (i) hydrogen transfers spontaneously from the surface to the adsorbing precursor, (ii) reactive adsorption is thermodynamically
favoured over desorption, and (iii) the final adsorbate is predicted to be Er(Cp). (unlike La2O3 ALD deposition LaCp3 where the final adsorption fragment is predicted to be La(Cp)2.). Ligand elimination is significantly
more favourable on surfaces of Er2O3, compared to La2O3, predicting that Er2O3 ALD is a more favourable process for preparation of pure oxide films. It was explained by stronger
Er—O bonding, as well as restoration of a less distorted surface. [[i]]
[i] M. Nolan, S. D. Elliott, Chem. Mater., 2010, 22 (1), pp 117–129, DOI: 10.1021/cm902469c, “Competing Mechanisms in Atomic Layer Deposition of Er2O3 versus La2O3 from Cyclopentadienyl Precursors”
ErCp3 for C-contaminated Er thin films (or ErCx) by MOCVD
Fig . RBS spectrum of C-contaminated Er films (grown on Si using ErCp3 at 600°C)
ErCp3
(in comparison with Er(N(SiMe3)2)3 )was tested as precursor for MOCVD of metallic Er thin films. ErCp3 was evaporated at temperature 200° C, and carried by 200sccm Ar carrier gas diluted by 4.8 slm of
H2. A layer of 400 nm thick elemental erbium was deposited in 2 hours at a substrate temperature of 600° C, however the layer was severely contaminated by C impurity: carbon content of this layer exceeded 90% by atomic ratio.[i]
[i] William S. Rees, Jr., US 5583205, 10 Dec 1996, http://www.google.de/patents/US5583205
ErCp3 for Er-doped GeCx films by MOCVD
ErCp3 (combined with GeMe4 as liquid Ge source) was tested as precursor for the MOCVD growth of erbium-doped germanium film Ge:Er. The deposition conditions were following: growth temperature 825'C, ErCp3 carrier flow rate 100 sccm, GeMe4 flow rate 20 sccm (GeM4 source bubbler temperature -5°C), process pressure 75 torr, total flow 5 slm H2. (the conditions were chosen targeting to reduce carbon contamination in the films).
However, actually nearly stoichiometric germanium-carbide GeC doped with few percent Er was deposited
(according to Auger spectroscopy). This result showed that ErCp3 is a poor source to the growth of Er-doped Ge layers by MOCVD (but good for Er-doped GeCx layers). [i]
[i]A.C. Greenwald, W.S. Rees, Jr.", U.W. Lay, Mat. Res. Soc. Symp. Proc. Vol. 301. 1993 , p.21-26, « MOCVD ERBIUM SOURCES », http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA277517#page=18
Er(MeCp)3 for ErAs by MOCVD
Erbium tris(cyclopentadienyl) ErCp3 (and for comparison Er(MeCp)3 and Er[(N(SiMe3)]3 , see below)) was applied (combined with
tBuAsH2 and AsH3 as As sources) for the epitaxial growth of ErAs layers on <100> GaAs substrates by MOCVD. ErCp3 source was evaporated at 200°C (at ca.75mbar pressure
– close to the reactor pressure). ErAs films with excellent crystal quality were obtained; the diffusion rates of Er exceeded diffusion rates for common dopants (like Si) at preferred GaAs growth temperatures of 650°C. [[i]]
[i] Dr. Greenwald, Final rept. 1 Jul-31 Dec 93, SPIRE CORP BEDFORD MA, Url: ADA292490,
« ErAs/GaAs Superlattice Infrared Detector by Chemical Vapor Deposition. », http://www.dtic.mil/dtic/tr/fulltext/u2/a292490.pdf
Erbium tris(methylcyclopentadienyl) Er(C5H4Me)3 (or Er(MeCp)3)
Er(MeCp)3 for Er2O3 by ALD
Er(MeCp)3, with water H2O as co-reactant, has been applied for the preparation of cubic (preferentially (111) oriented ) Er2O3 thin films by ALD at deposition temperatures 175°C-450°C on Si(100) and soda-lime glass substrates. ALD-type growth was obtained at relatively low deposition temperatures of 250 °C and 300 °C, with high growth rate (1.5 Å per cycle). Low impurities.concentration (C and H) smooth and uniform Er2O3 films were deposited; the effective permittivity ca. 10 was obtained for the Er2O3/native SiO2 insulator stack. [i]
[i] J. Päiväsaari, J. Niinistö, K. Arstila, K. Kukli, M. Putkonen, L. Niinistö, Chemical Vapor Deposition, 2005, Vol. 11, Iss. 10, pages 415–419, « High Growth Rate of Erbium Oxide Thin Films in Atomic Layer Deposition from (CpMe)3Er and Water Precursors »
Er(MeCp)3 for ErxGa2-xO3 by ALD
Erbium tris(methylcyclopentadienyl) Er(C5H4Me)3 (and for comparison) Er(thd)3 ) was applied for ALD growth of ErxGa2-xO3 (0 ≤ x ≤ 2) thin films in the two precursor systems: Er(C5H4Me)3/Ga2(NMe2)6/H2O and Er(thd)3/Ga(acac)3/O3. Erbium cyclopentadienyl/gallium alkylamide system allowed to grow films at lower substrate temperature (250°C) and at much higher growth rate (1.0 -1.5 Å/cycle) than Er β-diketonate-containing system (350°C and 0.25-0.28Å/cycle). However, Er-β-diketonate containing system produced purer films except fluorine impurity (C, H, N <0.2-0.3at.%, F 0.6-2.2at.%) than Er cyclopentadienyl –containing system.(C 2.0–6.1%, H 5.0–10.3%, N 0.3–0.7%, and 0.1at% F) according to RBS and TOF-ERDA. Both precursor systems produced uniform films, surface-limited ALD growth was observed. The value of x in ErxGa2-xO3 was easily varied by selecting a pulse sequence in an appropriate Er/Ga precursor ratio. The effective permittivity of representative samples was similar for both systems: 10 - 11.3 for diketonates/O3 system and 9.2 - 10.4 for the amide/cyclopentadienyl/H2O. As deposited films were amorphous, their crystallisation behaviour upon annealing and smoothness (rms roughness <1.0 nm by AFM) was independent on the precursor system [469]
Er(MeCp)3 for ErAs by MOCVD
Erbium tris(methylcyclopentadienyl) Er(MeCp)3 (and for comparison ErCp3 and Er[(N(SiMe3)]3) , and tBuAsH2 (TBA) and AsH3 as As sources) was used for the MOCVD growth of epitaxial ErAs layers on <100> GaAs substrates. Er(MeCp)3 source was evaporated at 180°C (lower than 200°C for ErCp3, but higher than 170°C for Er[(N(SiMe3)]3)
(at bubbler pressure close to the reactor pressure (50-200mbar)). Excellent crystal quality ErAs films were grown; at preferred GaAs growth temperatures of 650°C the diffusion rates of Er exceeded common dopants
(like Si) diffusion rates. The use of ErCp3 combined with tBuAsH2 resulted in reduced C contamination.[i]
[i] Dr. Greenwald, Final rept. 1 Jul-31 Dec 93, SPIRE CORP BEDFORD MA, Url: ADA292490,
« ErAs/GaAs Superlattice Infrared Detector by Chemical Vapor Deposition. », http://www.dtic.mil/dtic/tr/fulltext/u2/a292490.pdf
Erbium tris(isopropylcyclopentadienyl) Er(C5H4iPr)3
Tris(isopropylcyclopentadienyl)erbium precursor Er(iPrCp)3, combined with O2 as oxygen source, was applied as precursor for the growth of thin
films of Er2O3 by low-pressure MOCVD on p-type Si(100), Si(111), c-axis-oriented α-Al2O3(0001) and Corning glass. The deposited Er2O3 layers were extensively studied for their application as high-k gate dielectrics as well as antireflective and protective
coatings. The dependence of the structural, morphological, optical, and electrical properties of Er2O3 thin films on the used substrate and nucleation kinetics was investigated. The growth of (111)-oriented Er2O3 was observed by fast nucleation governed by
surface energy minimization on Si(100), glass, and α-Al2O3 substrates. In opposite, nonhomogeneous nucleation obtained on Si(111) substrates lead to the deposition
of polycrystalline Er2O3 films. Er2O3 films grown on Si(100) possessed superior properties. The deposited Er2O3 films have high
refractive index of 2.1 at 589.3 nm, high transparency in the near UV-vis range, optical bandgap of 6.5 eV, in view of antireflective and protective coating
applications. Er2O3 is also potentially useful as high-k dielectric material in complementary metal oxide semiconductor (CMOS) devices due to a static dielectric constant of 12–13 and very low density of interface traps ( 4.2 × 1010 cm2 eV–1
for 5–10 nm thick Er2O3 layers grown on Si(100) ).[i]
[i] M. Losurdo, M. M. Giangregorio, P. Capezzuto, G. Bruno, R. G. Toro, G. Malandrino, I. L. Fragalà, L. Armelao, D. Barreca, E. Tondello, A.A. Suvorova, D. Yang, E. A. Irene, Advanced Functional Materials, 2007, Vol.17, Iss. 17, p. 3607–3612, “Multifunctional Nanocrystalline Thin Films of Er2O3: Interplay between Nucleation Kinetics and Film Characteristics »
Erbium cyclopentadienyl bis(isopropylcyclopentadienyl) Er(C5H4iPr)2(C5H5)
Erbium tris(tert-butylcyclopentadienyl) Er(C5H4tBu)3
Alkyl substituted erbium cyclopentadienyls are monomeric complexes having higher vapor pressures compared to Er(C5H5)3. Thus, Er(iPrCp)2(Cp) and Er(tBuCp)3 are more volatile than unsubstituted erbium tris(cyclopentadienyl), they have been applied as erbium dopant precursors in the MOVPE growth of erbium-doped GaAs epitaxial films. ErCp(iPrCp)2 resulted in an order of magnitude higher erbium levels compared to those achievable with Er(tBuCp)3.[4]
Erbium tris(n-butylcyclopentadienyl) Er(C5H4nBu)3
Tris(n-butylcyclopentadienyl)- erbium [Er(C4H9C5H4)3] was applied as liquid source precursor for incorporation of Erbium into GaAs; epitaxial layers Er-doped
GaAs layers were grown on (100)-oriented Si-doped or undoped GaAs substrates, at substrate temperatures 620°C to 680°C. The dependence of incorporation of Er trivalent ion on growth parameters (growth temperature,
V/III ratio, and growth rate) was qualitatively monitored by photoluminescence measurements. The epitaxial layer thickness (and thus growth rate) was determined by staining a cleaved segment of the wafer; the typical growth rates were ~1-2 pm/h. The Er concentration
in the layers was controlled by the Er(nBuCp)3 bubbler temperature (175°C to 225°C) and the H2 source flow through the bubbler (50 - 210 sccm). Always good morphology was obtained for growth of GaAs at 680°C, however the addition of Er(nBuCp)3
vapor caused a degradation of the morphology. However at a substrate temperature reduced to 620°C (with similar other deposition conditions), a mirror-like featureless surface of Er-doped GaAs was obtained (luminescence showed the incorporation of.Er(3+)
). It was speculated that Er is segregating at the front surface at the higher growth temperature due to its larger atomic size, and thus degrades the crystalline quality. [[i]]
[i] V.T. Coon, Final rept. 1 Jul-31 Dec 1992, MICROTRONICS ASSOCIATES PITTSBURGH PA;
“Rare Earth Doped III-V Semiconductors for Optoelectronics »
http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA268279
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