ERBIUM ALKYLSILYLAMIDES

Erbium tris[bis(trimethylsilyl)amide] Er[N(SiMe3)2]3

Fig. Structure of Er[N(SiMe3)2]3

    Erbium tris[bis(trimethylsilyl)]amide Er[N(SiMe3)2]3 (M= 648.42) is pink powder with meting point 162° C), subliming at 130°-140° C/ lxl0-4 torr.

    Er[N(SiMe3)2]3 is a homoleptic F-series metal amide which can be prepared by the metathesis reaction between erbium trichloride (ErCl3) and bis-trimethylsilyl lithium amide Li[N(SiMe3)2], employing reverse addition techniques (under dry N2 or Ar atmosphere using standard Schlenk or inert gas-filled glove box techniques). The lithium trimethylsilylamide solution was cooled to 0° C, and anhydrous ErCl3 was added in several portions over a period of 2 hours; whereby ErCl3 dissolved and the solution developed a pink color; after warming to RT and stirring for 24 hours, white precipitate (LiCl) formed. All volatiles were removed in vacuo, the residue was extracted by Et2O and the extracts were evaporated to dryness at RT/ lx10-2 Torr  yielding pink colored powder, which was recrystallized from Et2O/hexanes (1/1) at -30° C. The white lithium amide voliatile impurity was sublimed at 80°C/ 5xl0-2 torr to a cold finger (-78° C).

     The pink residue of Er[N(SiMe3)2]3 was then sublimed at 130°-140° C/ lxl0-4 torr, producing pink amorphous powder of pure Er[N(SiMe3)2]3 (20% yield based on ErCl3). [[i]]

 [i] William S. Rees, Jr., US 5583205, 10 Dec 1996, http://www.google.de/patents/US5583205

NMR analysis of Er[N(SiMe3)2]3

Fig. NMR spectrum of Er[N(SiMe3)2]3

The purity of the Er[N(SiMe3)2]3 was checked by the NMR (Fig. ), the spectra showed single very sharp peak proving high material purity (total contaminant concentration <0.1 ppm).

TGA analysis and volatility of Er{N[SiMe3]2}3

Fig. TGA analysis of Er[N(SiMe3)2]3

      Decomposition kinetics of Er{N[Si(CH3)3]2}3 was studied by TGA (Fig.): the melting point is 162°C, rapid sublimation occurs at 175°C, and the decomposition temperature is 257°C. Vapor pressure of Er{N[Si(CH3)3]2}3 is 0.1 Torr/ 120°C (for comparison, the vapor pressure of ErCp3 is only 0.01 Torr /200° C, and the melting point is 285° C).[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(N(SiMe3)2)3 for metallic Er films by MOCVD

     The synthesized Er[N(SiMe3)2]3  (and for comparison ErCp3) was applied as the erbium MOCVD precursor for the growth of epitaxial Er metal thin films on silica substrates under H2 atmosphere and Ar as carrier gas, at reactor pressure 10-75 torr and inductively heated susceptor (650° - 850° C).

    For the MOCVD growth using Er[N(SiMe3)2]3  , bubbler temperature 175° C was used  (lower source temperature of 150° C failed to produce any visible erbium deposits). 4 nm metal Er layer was formed on a silica coated substrate. As per AES data, metal Er layer deposited using Er{N[Si(CH3)3]2}3 exhibited substantially decreased carbon contamination (essentially zero excluding atmospheric contamination) as compared to the erbium layer deposited using Er(C5H5)3, and only little trace of silicon, nitrogen. Er[N(SiMe3)2]3   is therefore preferred as an erbium source compound for the growth of metallic Er films by MOCVD. [[i]]

 [i] William S. Rees, Jr., US 5583205, 10 Dec 1996, http://www.google.de/patents/US5583205

Er(N(SiMe3)2)3 for Er-doped Si and GaAs by MOCVD

Erbium tris(trimethylsilylamide) Er(N(SiMe3)2)3 was applied as precursor for the preparation of erbium-doped Si and GaAs by MOCVD. Low carbon and oxygen levels were achieved in the GaAs films growth using this precursor, however Si incorporated from precursor acted as n-type dopant for GaAs. [4]

Er[N(SiMe3)2]3 for ErAs by MOCVD

   Erbium tris-trimethyldisilylamide Er[N(SiMe3)2]3 (and for comparison ErCp3 and Er(MeCp)3, with two arsenic sources – AsH3 and tBuAsH2), was applied as precursor for growth of ErAs on <100> GaAs substrates by MOCVD. Erbium tris-trimethyldisilylamide was evaporated at 170°C, with pressure ca. 75 Torr (close to reactor pressure), carrier flow 50 to 200 was used. Er[N(SiMe3)2]3 combined with arsine AsH3 appeared to be the best precursor combination (all other combinations resulted in excessive C incorporation into the ErAs film). The obtained ErAs layers had excellent crystal structure. The diffusion rate of Er at preferred GaAs growth temperature ~650°C exceeded common dopants (such as Si) diffusion rates.[i]

[i] A.C. Greenweld, Final rept. 1 Jul-31 Dec 1993, SPIRE CORP BEDFORD MA, PDF Url : ADA292490, Report Date: 31 DEC 1993, « ErAs/GaAs Superlattice Infrared Detector by Chemical Vapor Deposition »,http://www.dtic.mil/dtic/tr/fulltext/u2/a292490.pdf 

Er(N(SiMe3)2)3 for Er metal adn Er-doped Ge by MOCVD

     Erbium tris[bis(trimethylsilyl)amide] was tested as erbium precursor (combined with tetramethylgermane GeMe4 as Ge source) for the deposition of Er metal  and Er-doped Ge films by MOCVD. Growth conditions were as follows: growth temperature 825°C, carrier flow rate 100 sccm for Er source, 20 sccm (@-5°C) for Ge source, pressure 75 torr , total flow 5 slm H2. Initial tests at deposition temperatures 400-600°C with Er(N(SiMe3)2)3 bubbler at 150°C source temperature produced no visible deposits at substrate. However, when source temperature was raised to 175°C, an ultrathin (4 nm) film was formed on a silica coated wafer. Analysis of the as-grown surface by Auger electron spectroscopy (AES) is shown in Fig. (no sputter cleaning was performed, as it would have removed the film). According to AES, much less carbon was incorporated with silylamide precursor (as compared to ErCp3). The amount of carbon and  oxygen  found on the surface, according to the authors is typical for uncleaned samples (however, the elemental ratios are close to the erbium silicate Er2(SiO4)3. The silica on the surface indicated that the deposition is of an island growth nature, and complete coverage had not been reached. [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

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