电子束辐照下的石墨烯上的原子层沉积Al2O3介质层

为了研究石墨烯与高k介质的结合,使用原子层沉积氧化铝在石墨衬底上。沉积前使用电子束辐照,观测到了氧化铝明显改善的形貌。归因于电子束辐照过程中的石墨层的无定形变化过程。     

原子层沉积低温生长α-MoO3薄膜

以六羰基钼和氧气为前驱体,通过等离子增强原子层沉积技术（PE-ALD）在硅基片上实现了α-MoO₃薄膜的低温制备。利用X射线衍射仪、扫描电子显微镜、原子力显微镜、X射线光电子能谱仪等手段对薄膜的晶体结构、表面形貌及薄膜成分进行表征和分析。研究发现衬底温度和氧源脉冲时间对MoO₃薄膜的晶体结构和表面形貌变化起关键作用。当衬底温度为170℃及以上时所制备的薄膜为α-MoO₃;适当延长ALD单循环中的氧源脉冲时间有利于低温沉积沿（0k0）高度择优取向的MoO₃薄膜。根据对不同厚度MoO₃薄膜表面的原子力显微图片分析,MoO₃薄膜为岛状生长模式。     

Silica deposition by excimer-laser-induced chemical vapour deposition in perpendicular configuration

Silicon oxide films have been deposited on silicon wafers at low temperature by irradiation of the substrates with an ArF (λ = 193 nm) excimer laser beam in a SiH₄ and N₂O atmosphere. A systematic study of the growth rate and properties of the films as a function of the processing parameters (gas composition, substrate temperature, laser pulse energy, pulse repetition rate, total pressure and gas flow rate) has been performed. The process is photolytically activated in the gas phase and the diffusion of photodecomposed precursor species towards the surface plays an important limiting role. The N₂O/SiH₄ ratio mainly controls the film composition; for ratios above 40, stoichiometric silica may be obtained, as confirmed by Rutherford backscattering (RBS) measurements. The role of the surface temperature in the growth kinetics is not critical, so that deposition of films is possible down to substrate temperatures as low as 70°C. Nevertheless, the density of the films varies greatly with the substrate temperature. The fact that no Si(SINGLE BOND)H vibration was detected with Fourier transform infrared (FTIR) spectrophotometry is surprising, since hydrogen incorporation is a very typical phenomenon encountered in most silane systems. This effect is probably associated with the ultraviolet photon irradiation of the adsorbed species and the film as it grows, thus breaking bonds and affecting the bond structure of the film.     

Carbon and hydrogen incorporation in ZnTe layers grown by metalorganic chemical vapor deposition

The metalorganic chemical vapor deposition growth of ZnTe has been performed at atmospheric pressure under helium and hydrogen carrier gases. Epitaxial growth was achieved on GaAs (100) substrates with the combination of diethylzinc and diethyltellurium as precursors. We have studied the incorporation of carbon and hydrogen in as-grown layers of ZnTe by secondary ion mass spectroscopy analysis and out-diffusion experiments with different carrier gases and growth temperatures. The amount of carbon and hydrogen incorporated in the ZnTe layers greatly depends on the nature of the gas considered. Under helium atmosphere, the amount of carbon and hydrogen incorporated are greater than under H₂ with an origin from organometallic precursors.     

基于MIS电容器的Al2O3与In0.74Al0.26As的界面特性

采用In_0.74Al_0.26As/In_0.74Ga_0.26As/In_xAl_1-xAs异质结构多层半导体作为半导体层,制备了金属-绝缘体-半导体（MIS）电容器。其中,SiN_x和SiN_x/Al₂O₃分别作为MIS电容器的绝缘层。高分辨率透射电子显微镜和X射线光电子能谱的测试结果表明,与通过电感耦合等离子体化学气相沉积生长的SiN_x相比,通过原子层沉积生长的Al2_O3可以有效地抑制Al₂O₃和In_0.74Al_0.26As界面的In₂O₃的含量。根据MIS电容器的电容-电压测量结果,计算得到SiN_x/Al₂O₃/In...     

ALD-grown seed layers for electrochemical copper deposition integrated with different diffusion barrier systems

The deposition of Cu seed layers for electrochemical Cu deposition (ECD) via atomic layer deposition (ALD) of copper oxide and subsequent thermal reduction at temperatures between 110 and 120 °C was studied on different diffusion barrier systems. While optimization of the process is required on TaN with respect to reduction and plating, promising results were obtained on blanket PVD Ru. The plating results on layers of ALD Cu with underlying Ru even outperformed the ones achieved on PVD Cu seed layers with respect to morphology and resistivity. Applying the processes to via and line patterns gave similar results, suggesting that a combination of ALD Cu with PVD or ALD-grown Ru could significantly improve the ECD Cu growth.     

Selective deposition of TiSi2 on oxide patterned wafers using low pressure chemical vapor deposition

The selective deposition of titanium disilicide was investigated using a cold-wall, low pressure chemical vapor deposition (LPCVD) technique with silane and titanium tetrachloride as the silicon and titanium sources, respectively. In-situ hydrogen plasma effectively cleaned the silicon wafer surface for deposition of C54 TiSi₂ at 760‡ C with full selectivity. A new method using a plasma only at the beginning of the deposition of the silicide further decreased the temperature to 680‡ C without losing selectivity. The result was a fine grained film probably due to the enhanced nucleation rate of the silicide. Cross-sectional TEM studies showed that the silicide grew into the silicon substrate, suggesting significant silicon consumption. The silicon substrate, consequently, seems to play a major role in the silicide formation. Silane, on the other hand, plays a minor role as a silicon source but does act as a scavenger of HC1 in the gas or on the silicide surface.     

Atomic layer deposition of Zn1−xMgxO buffer layers for Cu(In,Ga)Se2 solar cells

Fabrication of Zn_1−xMg_xO films by atomic layer deposition (ALD) has been studied for use as buffer layers in Cu(In,Ga)Se₂ (CIGS)‐based solar cell devices. The Zn_1−xMg_xO films were grown using diethyl zinc, bis‐cyclopentadienyl magnesium and water as precursors in the temperature range from 105 to 180°C. Single‐phase ZnO‐like films were obtained for x < 0·2, followed by a two phase region of ZnO‐ and MgO‐like structures for higher Mg concentrations. Increasing optical band gaps of up to above 3·8 eV were obtained for Zn_1−xMg_xO with increasing x. It was found that the composition of the Zn_1−xMg_xO films varied as an effect of deposition temperature as well as by increasing the relative amount of magnesium precursor pulses during film growth. Completely Cd‐free CIGS‐based solar cells devices with ALD‐Zn_1−xMg_xO buffer layers were fabricated and showed efficiencies of up to 14·1%, which was higher than that of the CdS references. Copyright © 2006 John Wiley & Sons, Ltd.     

Metal–Organic chemical vapour deposition (mocvd) growth utilising cu(acac)2 (acac  pentane-3, 5-dionato) as a source for copper-containing materials: Influence of carrier gas on surface morphology

The unsubstituted bis-β-diketonato complex of copper, Cu(acac)₂ (acac ? pentane-3, 5-dionato), has been used to deposit both elemental copper and copper oxide thin films by metal–organic chemical vapour deposition (MOCVD). For all Cu(II) bis-β-diketonates, growth of oxygen-free layers requires the breakage of four copper–oxygen bonds present in the precursor. The influence of carrier gas composition on deposit morphology has been examined for six parameter sets: both hydrous and anhydrous streams, each for reducing (H₂), inert (Ar) and oxidising (O₂) environments.     

Atomic layer deposition of titanium nitride from TDMAT precursor

TiN was grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (TDMAT). Both thermal and plasma enhanced processes were studied, with N₂ and NH₃ as reactive gases. Using an optimized thermal ammonia based process, a growth rate of 0.06 nm/cycle and a resistivity of 53 × 10³ μΩ cm were achieved. With an optimized plasma enhanced NH₃ process, a growth rate of 0.08 nm/cycle and a resistivity of 180 μΩ cm could be obtained. X-ray photo electron spectroscopy (XPS) showed that the difference in resistivity correlates with the purity of the deposited films. The high resistivity of thermal ALD films is caused by oxygen (37%) and carbon (9%) contamination. For the film deposited with optimized plasma conditions, impurity levels below 6% could be achieved. The copper diffusion barrier properties of the TiN films were determined by in-situ X-ray diffraction (XRD) and were found to be as good as or better than those of films deposited with physical vapor deposition (PVD).     

Thin films of ZrO2 metal organic chemical vapor deposition

ZrO₂ layers were deposited for the purpose of obtaining high dielectric constant insulating layers for capacitance applications. Trifluoroacety lacetonate of zirconium was used as the source material in our open MOCVD system. Layer thickness was in the range 300–1500 Å, the substrate being degenerate n-type silicon wafers. Under optimum conditions layers with good adhesion and uniformity were obtained. The layers were polycrystalline with characteristic linear dimensions of 400 Å. Electrical measurements were used for characterization and the relative dielectric constants obtained were 30 ± 1.     

Revealing the nucleation and growth mechanism of a novel solder developed from Sn-3.5Ag-0.5Cu nanoparticles by a chemical reduction method

Sn-3.5Ag-0.5Cu nanoparticles were synthesized by chemical precipitation with NaBH₄. By using x-ray diffraction and transmission and scanning electron microscopy, the microstructural characteristics of particle growth were evaluated. The results indicated that the primary particles after precipitation were (Ag,Cu)₄Sn, with a size of 4.9 nm. (Ag,Cu)₄Sn was transformed into (Ag,Cu)₃Sn, when the total amount of Sn contributed from both (Ag,Cu)₄Sn and Sn covering the (Ag,Cu)₄Sn overtook that of (Ag,Cu)₃Sn. The final particle size of polycrystalline particles was 42.1 nm owing to the depletion of Sn atoms in the solution. Nucleation and growth mechanisms of Sn-3.5Ag-0.5Cu nanoparticles are also discussed and proposed.     

An electro-enhanced metalorganic chemical vapor deposition technique for producing thin copper films with (hfac)Cu(COD) as a precursor

A novel electro-enhanced metalorganic chemical vapor deposition (EEMOCVD) technique for producing copper (Cu) thin films on TaN/Si substrates with hexafluoroacetylacetonate-copper(I)-1,5-cyclo-octadine, (hfac)Cu^I(COD), as a precursor was investigated in this paper. This novel technique features supplying a direct current (DC) to TaN/Si substrates while the deposition of Cu thin films is in progress. Experiments on EEMOCVD yielded fortuitously positive results: (1) the deposited Cu films were superior in quality and (2) the growth rate of Cu film deposition increased. The above results are more desirable than those achieved through the conventional MOCVD (CMOCVD) technique. The proposed EEMOCVD technique hence proves to be more effective in forming smooth and continuous thin copper films.     

Drain current enhancement and negligible current collapse in GaN MOSFETs with atomic-layer-deposited HfO2 as a gate dielectric

Accumulation-type GaN metal-oxide-semiconductor field-effect-transistors (MOSFET’s) with atomic-layer-deposited HfO₂ gate dielectrics have been fabricated; a 4 μm gate-length device with a gate dielectric of 14.8 nm in thickness (an equivalent SiO₂ thickness of 3.8 nm) gave a drain current of 230 mA/mm and a broad maximum transconductance of 31 mS/mm. Owing to a low interfacial density of states (D_it) at the HfO₂/GaN interface, more than two third of the drain currents come from accumulation, in contrast to those of Schottky-gate GaN devices. The device also showed negligible current collapse in a wide range of bias voltages, again due to the low D_it, which effectively passivate the surface states located in the gate-drain access region. Moreover, the device demonstrated a larger forward gate bias of +6 V with a much lower gate leakage current.     

Atomic-layer-deposited Al2O3 and HfO2 on GaN: A comparative study on interfaces and electrical characteristics

Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO₂ and GaN, whereas the absence of an interfacial layer at Al₂O₃/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ calculated from the C-V measurement are 9, 16.5, and 13.8, respectively. The Al₂O₃ employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO₂ and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO₂/Al₂O₃ film is lower than that of HfO₂, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.     

Preparation and characterization of thin films of MgO,Al2O3 and MgAl2O4 by atomic layer deposition

MgO, Al₂O₃ and MgAl₂O₄ thin films were deposited on silicon substrates at various temperatures by the atomic layer deposition (ALD) method using bis(cyclopentadienyl)magnesium, triethylaluminum, and H₂O and were characterized systematically. High-quality polycrystalline MgO films were deposited for a substrate temperature above 500°C, and amorphous thin films were deposited around 400°C. The deposited Al₂O₃ and MgAl₂O₄ thin films were characterized as amorphous in structure. Applicability of ALD to complex oxides is discussed.     

Low pressure metalorganic chemical vapor deposition of InP and related compounds

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga_0.47In_0.53 As and Ga_xIn_1-xAs_yP_1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm² V⁻¹S⁻¹ at 300 K and 58 900 cm² V⁻¹ S⁻¹ at 77₂K, and for GaInAs was 11900 cm² V⁻¹ S⁻¹ at 300 K, 54 600 cm² V⁻¹ S⁻¹ at 77 K and 90 000 cm V⁻¹S⁻¹ at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.     

原子层沉积氧化铝薄膜对多晶太阳能电池表面钝化的影响

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.     

低温退火对具有HfO2/TiN栅结构的MOS电容电学性能的影响

The effects of low temperature annealing,such as post high-k dielectric deposition annealing(PDA),post metal annealing(PMA)and forming gas annealing(FGA)on the electrical characteristics of a metal–oxide–semiconductor(MOS)capacitor with a TiN metal gate and a HfO2dielectric are systematically investigated.It can be found that the low temperature annealing can improve the capacitance–voltage hysteresis performance significantly at the cost of increasing gate leakage current.Moreover,FGA could effectively decrease the interfacial state density and oxygen vacancy density,and PDA could make the flat band positively shift which is suitable for P-type MOSs.     

Silicide formation in co-deposited TiSix layers: The effect of deposition temperature and Mo

The silicide reaction in co-deposited TiSi_x layers on single crystal and pre-amorphized Si has been studied in detail. Both the co-deposition ratio and the co-deposition temperature were found to have a strong effect on the formation of the C54-TiSi₂ phase in these films. An unusual dependence of the sheet resistance on the co-deposition ratio was observed for films deposited at room temperature and those deposited at 400°C: the C54-TiSi₂ phase forms more easily for layers deposited at 400°C in the co-deposition ranges x∼0 and x>1.5, while it forms more easily for layers deposited at room temperature in the co-deposition ratio range of x∼0.2–1.5. These dependencies are explained by the formation of crystalline silicide phase(s) with composition close to the co-deposition ratio. With a Si rich ratio, the C49-TiSi₂ phase forms at 400°C with very small grain size, which facilitates the C54-TiSi₂ phase formation. The initial reaction of Ti-rich layer deposited at 400°C involves the formation of metal rich silicide, which impedes the formation of the C54-TiSi₂ phase. An ultra-thin MoSi_2.0 layer (<0.5 nm) was found to promote the formation of the C54-TiSi₂ phase in layers co-deposited at room temperature, but it showed little effect on layers co-deposited on pre-amorphized substrates at elevated temperature.