Si2H6 Exposure Research Articles

Electron-enhanced SiO2 atomic layer deposition at 35 °C using disilane and ozone or water as reactants

Electrons can enhance SiO2 atomic layer deposition (ALD) at low temperatures using disilane (Si2H6) and either ozone (O3/O2) or water (H2O) as reactants. SiO2 electron-enhanced ALD (EE-ALD) was demonstrated at 35 °C by exposing the sample to sequential electron, oxygen reactant, and Si2H6 exposures. The reaction sequence was electron beam exposure for 3 s, purge for 5 s, O3/O2 or H2O exposure at 0.5–1.0 Torr for 3 s, purge for 10 s, Si2H6 exposure at 100 mTorr for 1 s, and purge for 15 s. The electron exposure was an electron current of ∼150 mA for 3 s. The electrons were produced by a hollow cathode plasma electron source typically operating with a grid bias of ≈−300 V. These electrons could irradiate a sample area of ∼2 × 2 cm2. In situ spectroscopic ellipsometry measurements determined that SiO2 EE-ALD films nucleated rapidly and deposited linearly versus number of EE-ALD cycles. The SiO2 EE-ALD growth rate was 0.89 Å/cycle using O3/O2 and 0.88 Å/cycle using H2O. The SiO2 growth rate was also self-limiting at higher electron and Si2H6 exposures. In addition, SiO2 EE-ALD films were grown by changing the reaction sequence or codosing the electrons with the oxygen reactant. The SiO2 EE-ALD films could be grown on conducting silicon wafers or insulating SiO2 films. SiO2 EE-ALD is believed to be possible on insulating SiO2 films because the secondary electron yield for SiO2 at electron energies of ∼100–300 eV is greater than unity. Under these conditions, the SiO2 film charges positive during electron exposure and then pulls back secondary electrons to maintain charge neutrality. The SiO2 EE-ALD films had properties that were comparable with thermal SiO2 oxides. The refractive indices of the SiO2 EE-ALD films were similar at n = 1.44 ± 0.02 for various process conditions and equivalent to the refractive index of a wet thermal SiO2 oxide film. In addition, all the SiO2 EE-ALD films yielded etch rates in dilute buffered oxide etch solution that were only slightly higher than the etch rate of a thermal SiO2 oxide film. SiO2 EE-ALD should be useful to deposit high-quality SiO2 films for various applications at low temperatures.

Selective atomic layer deposition of MoSix on Si (0 0 1) in preference to silicon nitride and silicon oxide

Highly selective deposition of MoSix on Si in preference to SiO2 and SiNx was achieved via atomic layer deposition (ALD) using MoF6 and Si2H6 at 120 °C. The selectivity was enabled by the lack of chemical reactivity between the reactants and the SiO2 and SiNx substrates. In contrast, MoF6 nucleated in a self-limiting manner on H-terminated Si, and a following Si2H6 exposure reduced MoFx to Mo0 which is consistent with Mo-Si bond formation. X-Ray photoelectron spectroscopy (XPS) revealed that the 5 ALD cycles of MoF6 and Si2H6 selectively deposited a substoichiometric MoSi2 film on the Si substrate in contrast to previous results showing a nearly pure Mo deposition. Extra Si2H6 doses on the substoichiometric MoSi2 film incorporated more Si into the film without disturbing the inherent selectivity over SiO2 and SiNx. A depth-profiling study showed that the bulk of the film has Si/Mo = 1.7–1.9 with <10% F and O impurities. The data is consistent with higher pressure Si2H6 doses inducing silicide formation instead of metal deposition. To verify selectivity on the nanoscale, the selective deposition of MoSix was investigated on a patterned Si wafer containing three-dimensional (3D) nanoscale SiO2 and SiNx features. Cross-sectional transmission electron microscopy (TEM) showed that selective MoSix deposition was achieved on nanoscale 3D structures. AFM documented that there were less than 10 nuclei/µm2 on SiO2.; since SiO2 has ∼106/µm2 OH groups, this corresponds to an intrinsic selectivity of about 106:1 between the OH groups on SiO2 and Si-H groups on Si. This inherent substrate-dependent selectivity for silicide deposition allows the elimination of pre-positioning of passivants.

Molybdenum Atomic Layer Deposition Using MoF6 and Si2H6 as the Reactants

Mo ALD has been demonstrated by fluorosilane elimination chemistry using MoF6 and Si2H6 as the reactants. The nucleation and growth characteristics of Mo ALD were investigated using a variety of in situ and ex situ techniques in both high vacuum and viscous flow reactors. Quartz crystal microbalance (QCM) and X-ray reflectivity (XRR) investigations showed that Mo ALD has significant growth rate of 500−600 ng/cm2 per cycle or 6−7 Å per cycle for temperatures between 90 and 150 °C. The large growth rates could result from extra Mo deposition by MoF6 → Mo + 3F2 that may be facilitated by the very exothermic reaction of MoF6 with silicon-containing surface species. The QCM studies revealed that the Mo ALD surface chemistry is self-limiting. The QCM and Auger electron spectroscopy (AES) studies indicated that Mo ALD nucleates very rapidly on Al2O3 ALD surfaces and reaches the linear growth regime after only 4−5 ALD cycles. Oscillatory behavior for the total mass gain and individual mass gains was observed versus ALD cycle number during the nucleation region. The AES studies revealed that Mo films grown in a high vacuum reactor do not contain silicon impurities. In contrast to the AES results, Rutherford backscattering spectroscopy (RBS) analysis showed that Mo ALD films grown in a viscous flow reactor contain ∼16 at % Si impurities. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of silicon and showed that varying temperature, precursor dose and purge parameters did not lower the Si impurities significantly. Glancing incidence X-ray diffraction (GIXRD) studies indicated that Mo ALD films were nanocrystalline. The Si impurities may exist at grain boundaries or amorphous Mo silicides as a result of Si2H6 decomposition during the highly exothermic fluorosilane elimination reaction. Fourier transform infrared (FTIR) analysis revealed that MoFx surface species are reduced to metallic Mo during the Si2H6 exposure. Because of its rapid nucleation rate, Mo ALD films could serve as ultrathin continuous conducting films or as adhesion layers for other metal ALD systems on oxide surfaces.

Nucleation period, surface roughness, and oscillations in mass gain per cycle during W atomic layer deposition on Al2O3

Nucleation phenomena are critical for the fabrication of W/Al2O3 nanolaminates using atomic layer deposition (ALD) techniques. The nucleation and growth of W ALD on hydroxylated Al2O3 ALD surfaces and Al2O3 ALD on fluorinated W ALD surfaces was studied using in situ quartz crystal microbalance (QCM) and ex situ atomic force microscope (AFM) techniques. The QCM investigations revealed that Al2O3 ALD readily nucleated on the fluorinated W surface and displayed “substrate-enhanced growth.” In contrast, W ALD required 4–10 ALD cycles to nucleate on the hydroxylated Al2O3 surface and displayed “substrate-inhibited growth.” The W ALD nucleation period was shorter for higher Si2H6 and WF6 reactant exposures. The most rapid nucleation of W ALD on the Al2O3 surface occurred with much larger Si2H6 and WF6 exposures on the initial ALD cycle with the WF6 exposure prior to the Si2H6 exposure. By analyzing the individual Si2H6 and WF6 mass gain per cycle (MGPC), three main regions were identified in the W ALD nucleation and growth: initial deposition on Al2O3, W island growth and coalescence, and steady state growth. The root mean square (rms) roughness of the resulting W ALD film was dependent on the Si2H6 exposures and the number of ALD cycles required to nucleate the W ALD. A linear dependence was observed between the rms roughness and the number of ALD cycles required to reach one-half the maximum W MGPC. The W ALD also displayed very periodic oscillations in the W MGPC that were consistent with island nucleation and growth. Four local minima and three local maxima were observed in the W MGPC versus the number of ALD cycles. Comparing the results for W ALD on Al2O3 surfaces with recent simulations of ALD nucleation helps to establish the relationship between the nucleation period and surface roughness with island growth during nucleation.

Optimization and Structural Characterization of W/Al2O3 Nanolaminates Grown Using Atomic Layer Deposition Techniques

W/Al2O3 nanolaminates were fabricated using atomic layer deposition (ALD) techniques. ALD of tungsten was performed using alternating exposures of WF6 and Si2H6. ALD of Al2O3 was performed using alternating exposures of Al(CH3)3 and H2O. The fabrication of optimum nanolaminates was very dependent on nucleation during the ALD of each layer. The nucleation of Al2O3 ALD on W surfaces and W ALD on Al2O3 surfaces was examined using quartz crystal microbalance investigations. Al2O3 ALD on W nucleated easily during the first Al(CH3)3/H2O reaction cycle. In contrast, W ALD nucleation on Al2O3 required multiple WF6/Si2H6 reaction cycles and was very sensitive to the Si2H6 exposure. The W ALD nucleation required at least six or seven WF6/Si2H6 reaction cycles. The optimum reaction parameters for nucleation were utilized to fabricate W/Al2O3 nanolaminates with a total targeted thickness of ∼1000 Å that were composed of various numbers of bilayers. Transmission electron microscopy (TEM) images revealed very well defined two-bilayer and four-bilayer W/Al2O3 nanolaminates grown at 177 °C. Depth-profile secondary ion mass spectrometry (SIMS) measurements confirmed the composition of the W/Al2O3 nanolaminates. Both the TEM and SIMS results showed that sharper interfaces were observed when W ALD nucleates on Al2O3, and rougher interfaces were observed when Al2O3 ALD nucleates on W. X-ray reflectivity (XRR) investigations indicated that the W/Al2O3 nanolaminates were much thicker than the ∼1000 Å target for the total thickness when the W/Al2O3 nanolaminates were composed of a larger number of bilayers. These results were consistent with much lower than expected film densities for the thin Al2O3 ALD nanolayers. Atomic force microscope studies revealed that the surface roughness of W/Al2O3 nanolaminates was lower at lower growth temperatures and lower at higher interfacial densities. XRR investigations also revealed a pronounced Bragg peak with a high X-ray reflectivity from 64-bilayer W/Al2O3 nanolaminates grown at 177 °C. The X-ray reflectivity of the 64-bilayer W/Al2O3 nanolaminates grown at 177 °C was constant versus annealing up to 500 °C. The reflectivity then dropped rapidly for annealing at ≥600 °C. This thermal instability will place some limits on the application of W/Al2O3 nanolaminates as thermal barrier coatings and X-ray mirrors.

Gas phase reaction products during tungsten atomic layer deposition using WF6 and Si2H6

The gas phase reaction products during tungsten (W) atomic layer deposition (ALD) using WF6 and Si2H6 were studied using quadrupole mass spectrometry. The gas phase reactions products were different for the WF6 and Si2H6 reactions. No surface reactions were observed for WF6 exposures at room temperature. The WF6 reaction produced H2, HF and SiF4 at a reaction temperature of 473 K. Mass spectrometer cracking patterns established that SiF4 is the silicon reaction product instead of SiHF3. Auger electron spectroscopy (AES) measurements confirmed that the H2, HF and SiF4 gas phase reaction products during WF6 exposure coincided with the loss of silicon surface species. The Si2H6 reaction showed two separate reaction channels depending on reaction temperature. At room temperature, a temperature insensitive reaction produced SiHF3 and H2 reaction products. A second reaction produced H2 as the reaction product at 473 K. AES measurements confirmed that the SiHF3 and H2 reaction products during Si2H6 exposure were concurrent with the gain of silicon surface species. Together with previous FTIR spectroscopy and AES studies, these mass spectrometer results help to identify the stoichiometry of the surface reactions during the sequential WF6 and Si2H6 exposures that define W ALD.

In situ resistivity measurements during the atomic layer deposition of ZnO and W thin films

In situ monitoring of the electrical resistivity of ZnO and W thin films during atomic layer deposition (ALD) was performed using a four-point probe. Large oscillations were observed during the ZnO ALD resistivity measurements. The resistivity dramatically increased during each diethyl zinc exposure and decreased during each H2O exposure. In contrast, the W ALD resistivity measurements exhibited a steplike pattern where the resistivity decreased during the Si2H6 exposures and remained constant during the WF6 exposures. In situ resistivity measurements will be useful to monitor ALD processing and also may help to optimize and understand the properties of gas sensors.

Self-limiting atomic-layer deposition of Si on SiO2 by alternate supply of Si2H6 and SiCl4

Atomic-layer deposition of Si on SiO2 with a self-limiting growth mode was achieved at substrate temperatures between 355 and 385 °C by means of alternate supply of Si2H6 and SiCl4 gas sources. The growth rate was saturated at 2 ML per cycle at these temperatures and for Si2H6 exposure time over 120 s. The smooth surface (∼0.26 nm in arithmetic average roughness) was obtained under the self-limiting condition irrespective of a film thickness up to 6.5 nm.

Nucleation and Growth During Tungsten Atomic Layer Deposition on Oxide Surfaces

ABSTRACTNucleation and growth has been studied during tungsten (W) atomic layer deposition (ALD) on oxide surfaces. Auger electron spectroscopy (AES) was utilized to examine the deposition of W during the sequential (A) WF6 and (B) Si2H6 reaction cycles that define W ALD. The AES results displayed an initial nucleation period of ∼10 AB cycles to deposit one tungsten monolayer on SiO2. Subsequently, the W and Si AES signals grew and oscillated dramatically versus WF6 and Si2H6 exposures. The increase in the W AES signal in the growth region was consistent with a W ALD growth rate of 3.5 Å per AB cycle. An examination of the oxygen and tungsten AES signals versus AB cycles indicated that W ALD displayed nearly ideal “layer-by-layer”, Frank- van der Merwe growth after the nucleation period. On Al2O3, the AES results displayed a much shorter nucleation period for W ALD. Only 3 AB cycles were required to deposit one tungsten monolayer. Subsequently, the tungsten film grew at a rate of 3.6 Å per AB cycle. The initial nucleation period and growth mechanism during ALD are important because they will affect the roughness of the resulting ALD film.

Mechanisms and kinetics of Si atomic-layer epitaxy on Si(001)2×1 from Si2H6

Single-crystal Si films have been grown on Si(001)2×1 substrates by ultraviolet (UV) photostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML), 1 ML=6.8×1014 cm−2, over a wide range of deposition parameters: growth temperature (Ts=180 –400 °C), Si2H6 exposure (peak pressure during gas pulse=0.1–5 mTorr), UV laser energy density (ℰ=250–450 mJ cm−2 where ℰmax is determined by Ts ), and number of UV laser pulses per cycle. A film growth model, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, is used to describe the reaction pathway for the process. Si2H6 is dissociatively adsorbed on Si surface dimers as two SiH3 radicals which subsequently dissociate to SiH2 and H. Site blocking during the adsorption and surface dissociation steps limits the surface coverage to 2.9×1014 SiH2 cm−2 (hence, R=0.43 ML per cycle). The H terminated silylene-saturated surface is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≊20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts&amp;lt;180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≊0.5 eV. At Ts&amp;gt;400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Plan-view and cross-sectional transmission electron micrographs together with selected-area and convergent-beam electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.

UV Photostimulated Si Atomic-Layer Epitaxy

ABSTRACTSingle-crystal Si films have been grown on Si(001)2×1 substrates by UVphotostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML) over a wide range of deposition parameters: growth temperature (Ts= 180–400 °C), Si2H6 exposure (peak pressure during gas pulse = 0.1−5 mTorr), laser energy density ( = 250–450 mJ cm−2 where is determined by Ts), and number of UV laser pulses per cycle. A film growth mocrel, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, Is used to describe the reaction pathway for the process. The Hterminated silylene-saturated surface formed by adsorption and desorption of disilene is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≅20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts &lt; 180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≅0.5 eV. At Ts &gt; 400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Transmission electron micrographs together with selected-area electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.

The friction and wear of ion-implanted ceramics: the role of adhesion: S J Bull and T F Page,Nucl Instrum Meth Phys Res,B32, 1988, 91–95

Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and reflection high-energy electron diffraction (RHEED) were used to investigate the adsorption, surface dissociation, and thermal desorption of Si2H6 on Ge(001)2 × 1. At room temperature, EELS results show that Si2H6 is dissociatively adsorbed onto Ge dangling bonds and further decomposes to yield a disordered overlayer consisting of SiH2, GeH, and undissociated SiH3. A saturated coverage of approximately 0.5 monolayers is obtained with Si2H6 exposures greater than or equal to 1 × 1015 cm-2. RHEED results indicate that, in contrast to Si2H6-saturated Si(001), the saturated Ge(001) surface still exhibits a significant fraction of dimerized bonds. H2 desorption from the silicon dihydride phase occurs during 1 min anneals at Ta > 150°C while hydrogen desorption from the silicon monohydride phase and Ge surface segregation both occur at significant rates at Ta ⩾ 350 °C. All hydrogen is desorbed by 450°C, compared with ⋍ 550°C for the saturated Si(001) surface.