Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/04—Hydrides of silicon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
  • C01B6/06—Hydrides of aluminium, gallium, indium, thallium, germanium, tin, lead, arsenic, antimony, bismuth or polonium; Monoborane; Diborane; Addition complexes thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/058—Ge germanium

Definitions

• trisilane relative to traditional Si hydrides is its higher reactivity, allowing low temperature growth conditions compatible with development of strained Si channels.
• Previously reported methods for synthesizing trisilane have significant drawbacks. They are based on electric silent discharge of lower Si-hydrides, which typically produce mixtures of materials at low yields. To isolate the trisilane product in pure form, complicated separation and purification procedures need to be employed. [0005] Previous reports discuss the potential synthesis of tetragermylsilane,
• It an object of the present invention to provide compounds that display the necessary physical and chemical properties to be viable precursors for chemical vapor deposition (CVD) of Si-Ge semiconductors and related group IV alloys.
• the method includes combining a silane triflate with a compound comprising a GeH 3 ligand under conditions whereby the silicon-germanium hydride is formed.
• the compound comprising the GeH 3 ligand is selected from the group consisting Of KGeH 3 , NaGeH 3 and MR 3 GeH 3 , wherein M is a Group IV element and R is an organic ligand.
• the silane triflate can comprise H x Si (OSO 2 CF 3 ) 4-X or H x Si (OSO 2 C 4 Fp) 4-X .
• an alternative method for synthesizing (H 3 Ge) 2 SiH 2 .
• the method comprises combining H 3 GeSiH 2 (OSO 2 CF 3 ) with KGeH 3 under conditions whereby (H 3 Ge) 2 SiH 2 is formed.
• trisilane in practical yields by a straightforward approach that is convenient and potentially less expensive than previously known methods, and we have thereby demonstrated that trisilane can be used as a low temperature single- source alternative to the commercially available derivatives such as disilane (SiH 3 ) 2 and digermane (GeH 3 ) 2 for industrial and research applications. Potentially, this method affords iso-tetrasilane (H 3 Si) 3 SiH in high yields. The more reactive iso-tetrasilane (H 3 Si) 3 SiH is expected to be a better candidate for low temperature CVD of strained Si layers. Our approach provides a rational and systematic step-by-step mechanism leading to the isolation of the desired materials as the primary product at high yield and purity excluding formation of hazardous byproducts and mixtures.
• the synthetic routes of the aforementioned molecules utilize high-yield single-step substitution reactions involving commercially available starting materials.
• a complete characterization was conducted via a range of spectroscopic and analytical methods such as multinuclear NMR, gas source IR, mass spectrometry and elemental analysis for Si and Ge.
• the data collectively confirm the assigned molecular structures and correlate well with other related silyl and germyl silanes and methanes.
• the experimental results compare extremely well with first principles calculations of the spectroscopic and bonding properties of the molecules.
• a detailed investigation of the physical and chemical properties has shown that the compounds can be purified to yield semiconductor grade materials that are highly suitable for industrial application in Si-based technologies and manufacturing processes.
• the synthesis method according to our invention presents a new and straightforward approach that can afford a low temperature CVD route to Ge rich Sii -x Ge x (x>50at.%) alloys, which currently have crucial application in the areas of optoelectronic IR devices as well as buffer layers and virtual substrates with tunable morphology composition, structure and strain. These buffer layers are used as templates for growth of strained Si and Ge films (channels) that have applications in high mobility electronic devices.
• FIG. 1 shows the molecular structure of the most common configuration of SiH 3 GeH 3 obtained according to the method of the present invention.
• FIG. 2 shows the molecular structure / of the most common configurations of SiGe 2 H 8 .
• the symmetric, ( ⁇ ) SiH 2 (GeH 3 ) 2 has been obtained according to the method of the present invention. ;
• FIG. 3 shows the molecular structure of the most common configuration of SiGe 3 Hi 0 .
• the symmetric, ( ⁇ ) SiH(GeHs) 3 has been obtained according to the method of the present invention.
• FIG. 4 shows the molecular structure of the most common configuration of Si(GeH 3 ) 4 obtained according to the method of the present invention.
• FIG. 5 shows the normalized theoretical and experimental infrared spectra for SiH 2 (GeH 3 ) 2 for (a) the low frequency portion of the spectrum and (b) the high frequency hydrogen bands.
• FIG. 6 shows the normalized theoretical and experimental infrared spectra for SiH(GeH 3 ) 3 for (a) the low frequency portion of the spectrum and (b) the high frequency hydrogen bands.
• FIG. 7 shows the normalized theoretical and experimental infrared spectra for Si(GeH 3 ) 4 for (a) the low frequency portion of the spectrum and (b) the high frequency hydrogen bands.
• Reaction (1) is carried out in a high boiling point solvent, such as n- decane, at O 0 C.
• a high boiling point solvent such as n- decane
• the low vapor pressure of decane allows for a convenient and effective separation and purification of the compound from the solvent.
• the product is obtained in 20%-25% yield as a colorless, air-sensitive and volatile liquid with a vapor pressure of 30 torr at 22° C and 17 torr at 0° C.
• H 3 Ge-SiH 2 -GeH 3 is thermally stable at 22° C, and it less reactive with air and much safer than the H 3 GeGeH 3 analog.
• H 3 Ge-SiH 2 -GeH 3 The substantial vapor pressure and sufficient thermal stability of H 3 Ge-SiH 2 -GeH 3 suggest that the molecule could be a highly suitable single-source CVD precursor to silicon-germanium semiconductor alloys. Notably, this compound appears to possess higher stability than the well known homonuclear analogs such as trisilane (H 3 Si) 2 SiH 2 , and digermane H 3 GeGeH 3 which are currently commercially available and are considered the gas sources of choice for low temperature deposition of Si- based devices including high mobility strained Si channels.
• H 3 Ge-SiH 2 -GeH 3 offers the possibility of becoming a safer and more efficient alternative to these compounds in the preparation of Si-Ge alloys with high Ge-rich concentrations. These alloys are much more difficult to grow in device quality form and are highly sought for important application in modern optical devices including IR photodetectors and sensors fully integrated with silicon technologies.
• the (H 3 Ge) 2 SiH 2 compound is readily identified and characterized by its infrared (IR), NMR, and mass spectra. Its IR spectrum in vapor form is relatively simple and shows two sharp absorptions at 2152 cm “1 and 2074 cm “1 which are assigned to the Si-H and Ge-H stretching modes, respectively. These assignments are consistent with the literature values of the H 3 SiGeH 3 compound as described by J. Urban, P.R. Schreiner, G. Vacek, P.v.R. Schleyer, J.Q. Huang, J. Leszczynski, Chem. Phys. Lett. 1997, 264, 441-448.
• the intensity of the Ge-H peak in the H 3 Ge-SiH 2 -GeH 3 spectrum is significantly stronger than the Si-H peak which is consistent with the greater number of Ge-H bonds versus Si-H bonds in the molecule.
• Other prominent absorptions at 805 cm “1 and 702 cm “1 are attributed to Si-H and Ge-H bending modes, respectively.
• a weak band at 324 cm “1 can be attributed to the skeletal Si-Ge stretching mode.
• the mass spectrum of the compound displays well-defined isotopic envelopes for (M + -HH) and (M + - GeH 3 + ), suggesting a (H 3 Ge) 2 SiH 2 structure in which a central SiH 2 group is bonded with two terminal GeH 3 ligands.
• the 1 H NMR spectra are consistent with the proposed structure. The spectra show the expected triplet centered at 3.106 ppm ( ⁇ Ge-H) due to the GeH 3 moieties and a septet at 3.396 ppm ( ⁇ Si-H) due to SiH 2 .
• the integrated Ge-H/Si-H proton ratio in the NMR spectrum is 3:1, as expected.
• the NMR frequencies also correlate well with the corresponding chemical shifts of SiH 3 GeH 3 , which are reported to be at 3.520 ppm and 3.180 ppm as Si-H and Ge-H quartets, respectively.
• reaction (2) The synthesis of (H 3 Ge) 2 SiH 2 , as described by reaction (2), gives a highly pure product in which the overall yield is slightly higher than obtained via the previous method. Nevertheless, the method shown in reaction (2) has afforded the formation of the new and highly reactive species, (H 3 Ge)SiH 2 (OSO 2 CF 3 ), which might be a suitable starting material for the synthesis of other useful semiconductor specialty gases that incorporate the direct Si-Ge bonds.
• H 3 Ge-SiH 2 -GeH 3 we conducted extensive electronic structure calculations which are based on hybrid density function theory (DFT) using the B3LYP functional as implemented in the GaussianO3 and GAMESS codes.
• DFT hybrid density function theory
• a variety of basis sets were employed to study the structural and vibrational trends of H 3 Ge-SiH 2 -GeH 3 as well as the GeH 3 -GeH 2 -SiH 3 isomer.
• the properties of the classical SiH 3 GeH 3 analog were calculated for comparison (see Table 1).
• Earlier studies of SiH 3 GeH 3 have established the importance of augmenting the basis sets by the inclusion of extra d-type polarization functions on heavy atoms (Si,Ge) and extra p-type polarization functions on the hydrogens.
• FIG. 2 shows the structure of H 3 Ge-SiH 2 -GeH 3 obtained using the 6-
• FIGs. 1, 3 and 4 show concomitant data for the SiH 3 GeH 3 , SiH(GeH 3 ) 3 and Si(GeH 3 ) 4 analogs, respectively, as well as those of plausible isomers.
• hydrogen atoms are represented by white spheres
• silicon atoms are represented by small dark gray spheres
• germanium atoms are represented by light gray spheres.
• Table 1 shows structural and energetic parameters of SiGeH 6 and the symmetric, ( ⁇ ), and asymmetric, ( ⁇ ), SiGe 2 H 8 and SiGe 3 H 10 molecules.
• E 0 and Ea 1 refer to the static and thermally corrected (300 0 K) electronic molecular energies, respectively. Lengths are given in Angstroms, zero-point energies in kcal/mol, dipole moments in Debye and total energies in Hartree.
• Ge 1 refers to central Ge atom in the structures of FIGs. 1-4.
• the ⁇ Ge-Si-Ge bond angle (112.1°) is slightly larger than the tetrahedral value, but this is compensated by a slightly reduced value for the ⁇ H-Si-H angle (108°).
• Our calculations also show that the asymmetric isomer is more stable by ⁇ 18 kcal/mol than its symmetric counterpart (see Table 1), which is consistent with the formation of the former almost exclusively in the silent discharge experiments.
• FIG. 5 compares the calculated and experimental IR spectra and Table 2 summarizes the frequencies of key vibrational bands and their corresponding assignments and compares the observed and calculated values. Gratifying agreement between experiment and theory is obtained using a uniform frequency scale factor of 0.989 for the low frequency bands ( ⁇ ⁇ 1000 cm-1). For the high frequency Si-H and Ge-H vibrations a scale factor of 0.98 is found to yield optimal correspondence with experiment. The latter value was also obtained by Urban et al. in their treatment of Si 2 H 6 , Ge 2 H 6 and SiH 3 GeH 3 .
• SiH 3 isomer (not shown) and found that it is in excellent agreement with the data reported previously by K.M. Mackay, S.T. Hosfield and S.R. Stobart, J. Chem Soc. (A), 1969, 2938.
• a comparison between the IR spectra of the GeH 3 -SiH 2 -GeH 3 (FIG. 5) and GeH 3 -GeH 2 -SiH 3 corroborates the NMR findings that in our experiments we produced almost exclusively the symmetric (GeH 3 ) 2 SiH 2 analog.
• H 3 Ge-SiH 2 -GeH 3 A liquid sample of H 2 Si(OTf) 2 (4.38 g, 13.3 mmol) was added dropwise via an addition funnel to a slurry of solid KGeH 3 (4.0 g, 34.9 mmol) in 40 mL of dry decane. The slurry was prepared in a 250 mL, two-neck flask using a 33% excess of KGeH 3 . The addition funnel was attached to the flask and the reaction assembly was evacuated to 0.200 torr. The H 2 Si(OTf) 2 was added at 0°C.
• Vapor pressure 30 Torr (22° C), 17 Torr (0° C).
• the identity and purity of the H 3 GeSiH 2 was further established by mass spectrometry and NMR spectroscopy.
• the Si-H and Ge-H stretching modes were observed at 2155 cm “1 and 2071 cm “1 , respectively, indicating the presence of the SiH 2 GeH 3 moiety.
• a series of bands between 1450 cm “1 and 1100 cm “1 revealed the presence of the triflate (OSO 2 CF 3 ) group.
• the 1 H NMR resonance revealed a quartet at 5.430 ppm and a triplet at 3.514 ppm corresponding to silyl and germyl proton resonances consistent with the SiH 2 GeH 3 group.
• Vapor pressure 8.0 Torr at 22° C, 3 Torr at 0° C.
• EIMS isotopic envelopes centered at 179 (M + -GeH 3 ), 149 (CF 3 SO 3 + ),
• the product was obtained in ⁇ 30 % yields as a colorless, air-sensitive and volatile liquid with a vapor pressure (of 6-7 Torr at 22° C) and is stable at 22° C.
• the 1 H NMR spectra showed a deciplet at 3.429 ppm and a doublet at 3.317 ppm for the Si-H and Ge-H proton signals, respectively.
• the splitting patterns of the Si-H and Ge-H protons and their corresponding integrated peak ratio of 1:9 is consistent with the isobutane-like (H 3 Ge) 3 SiH structure. Furthermore, a 29 Si-HMQC spectrum revealed a chemical shift of -112.73 ppm and that the 1 H-NMR signal at 3.429 ppm is coupled with the silicon in trigermylsilane. A 1 H-COSY experiment confirmed that the Si-H and and Ge-H chemical shifts are coupled with one another as expected. The mass spectra show an isotopic envelop at 255-238 amu as the highest mass peak corresponding SiGe 3 H x .
• the IR spectrum of the compound shows the characteristic Si-H and Ge-H stretching modes at 2071 cm “1 and 2132 cm “1 , respectively, and a set of absorptions at 881 cm “1 788 cm “1 , and 680 cm “1 correspond to prominent bending modes of the molecule.
• the IR spectrum for (H 3 Ge) 3 SiH was also calculated using the B3LYP functional and the 6-311++G(2d,2p) basis set.
• FIG. 6 compares the calculated and experimental IR spectra and Table 3 summarizes the frequencies of key vibrational bands and their corresponding assignments and compares the observed and calculated values. A close agreement between experiment and theory is obtained.
• Table 3 Vibrational mode assignments for the symmetric SiH(GeH 3 ) 3 molecule.
• the resulting mixture was stirred at -35°C for 30 minutes after which it was slowly warmed to ambient temperature over the course of 90 minutes. A colorless solid was observed and the mixture was stirred at ambient temperature for 5 hrs.
• the volatiles were distilled into a U-trap held at -196°C under dynamic vacuum for 2 1/2 hours. The contents of the trap were redistilled through a series of traps held at -40° C (H 3 Ge) 3 SiH and trace ether), -78°C (ether and traces Of H 3 Ge) 2 SiH 2 ) and 196° C (ether and traces Of GeH 4 ).
• the product (- 40°C trap) was obtained by repeated distillation through -25°C and -78°C traps with no pumping. Gas phase IR revealed that the -25°C trap contained trigermylsilane and the -78°C trap contained a small amount Of (H 3 Ge) 2 SiH 2 .
• trigermylsilane (H 3 Ge) 3 SiH was obtained in a yield of 25-30 % further characterized as follows: Vapor p: essure: 6 torr (22° C).
• the (H 3 Ge) 4 Si compound is a colorless liquid with ⁇ 1-2 Torr vapor pressure at 22 0 C and was characterized by FTIR, NMR and GCMS.
• the high symmetry of the molecule leads to an extremely simple IR spectrum, which shows absorptions at 2072 cm “1 and 2062 cm “1 corresponding to the symmetric and asymmetric Ge-H stretches respectively.
• the peak positions and relative intensities in the FTIR closely match closely the calculated spectrum (see FIG. 7 and Table 4 for theoretical and experimental IR spectra and corresponding peak assignments). No Si-H vibrational modes are detected by FTIR.
• the 1 H NMR spectrum shows a singlet at 3.40 ppm, which confirms the presence of single-environment GeH 3 ligands in the molecule.
• the highest mass peak in the GCMS spectrum is observed in the range of 328-318 amu.
• the peak position and the isotopic distribution indicate SiGe 4 H x type species consistent with the Si(GeH 3 ) 4 tetrahedral structure of the molecule.
• the spectroscopic data collectively provide strong evidence for the successful synthesis and isolation of Si(GeH 3 ) 4 .
• a vapor pressure of ⁇ l-2 Torr for the compound is within the expected value and is similar to that reported for C(GeH 3 ) 4 (1-2 torr).
• a 3-neck, 10OmL round bottom flask was charged with 2.98 g (26 mmol) of KGeH 3 and 50 mL of dry diethyl ether to form a solution.
• a liquid sample of Si(OTf) 4 (2.40 g, 6 mmol) was subsequently added to KGeH 3 /ether over the course of 30 minutes at -50 0 C.
• the pressure in the reaction assembly was reduced to 300 torr prior to the addition of Si(OTf) 4 .
• the flask was slowly warmed to ambient temperature over the course of 2-3 hours.
• Vapor pressure , 1-2 Torr (22° C).
• Trisilane is currently the preferred gas source for commercial CVD growth of strained Si channel devices with highly enhanced electronic properties such as high electron and hole mobilities.
• the strained films are formed on Si substrates via graded buffer layers of Si-Ge using low temperature growth conditions to prevent strain relaxation and formation of defects.
• a major advantage of trisilane in strained Si applications relative to traditional Si hydrides such as SiH 4 and Si 2 H 6 is its higher reactivity, leading to facile dehydrogenations at the required low-temperature range.
• Si-based devices although it is expected to be more suitable for low-temperature growth applications because of its higher reactivity and hence lower decomposition temperature relative to trisilane.
• the branched structure suggests that this compound is likely to be stable and possess significant volatility at room-temperature comparable to trisilane. It is thus expected to be a viable CVD source for commercial, large-scale applications and its full development warrants immediate consideration. There are several accounts for the possible existence of this compound but no definitive synthesis route and characterization of its properties have been reported to date.

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