The use of langmuir probe measurements to investigate the reaction mechanisms of remote plasma-enhanced chemical vapor deposition

Langmuir probe measurements of plasma density and electron temperature have been used to investigate the reaction kinetics in remote plasma-enhanced chemical vapor deposition (RPCVD) of Si on Si (100) substrates. The increased growth rate for negative substrate bias indicates that positively charged ions are involved in the deposition reaction. A comparison of growth rate and plasma density data indicates that the growth rate is proportional to the ion flux. It is concluded that the rate limiting reaction in RPCVD is H desorption from the hydrogenated Si surface by ion bombardment.     

The effects of substrate bias,substrate temperature,and pulse frequency on the microstructures of chromium nitride coatings deposited by pulsed direct current reactive magnetron sputtering

Recently, great attention has been devoted to the pulsed direct current (DC) reactive magnetron sputtering technique, due to its ability to reduce arcing and target poisoning, and its capability of producing insulating thin films. In this study, chromium nitride (CrN) coatings were deposited by the bipolar symmetric pulsed DC magnetron reactive sputtering process at different pulse frequency, substrate bias voltage, and the substrate temperature. It was observed that the texture of CrN changed from (111) to (200) as substrate temperature increased to 300°C as deposited at 2 kHz without substrate bias. With increasing pulsing bias and pulse frequency of target, predominated (200) orientation of CrN film was shown due to the ion bombardment/channeling effect to preferentially sputter those unaligned planes. For the CrN coatings deposited with pulsed biasing, the grain size decreased with increasing pulse frequency and substrate bias, whereas the surface roughness showed a reverse trend. The deposition rate of the CrN films decreased with increasing pulse frequency. It was concluded that the pulse frequency, substrate bias, and substrate temperature played important role in the texture, microstructure, and surface roughness of the CrN coatings deposited by the pulsed DC magnetron sputtering process.     

Independent control of ion density and ion bombardment energy in adual RF excitation plasma

A dual RF excited discharge is described. The dual RF excitation system provides a method to control the substrate self-bias without affecting the state of the discharge. The substrate can be RF-biased utilizing an appropriate excitation frequency and power significantly less than the plasma generating RF power. The substrate self-bias dependence on various system parameters, including substrate excitation frequency, pressure, plasma generating upper electrode RF power, substrate material, and process gas compositions, is described. For a simplified model, a linear relationship between self-bias and RF power is derived using the space-charge limited assumption. The effect of substrate bias on the thermal-oxide etch rate has been studied. The results show good correlation between the ion bombardment energy, i.e., the potential difference across the substrate dark space, and the SiO ₂ etch rate. The SiO₂ etch rate in a CF₄ plasma increases linearly with the ion bombardment energy, having a threshold etch energy of ~19 V     

Microwave and hot filament chemical vapour deposition of diamond multilayers on Si and WC-Co substrates

A serious problem in the use of chemical-vapour-deposited polycrystalline diamond coatings in electronics, optics as well as in cutting tools is the high surface roughness. In our work, microcrystalline and nanocrystalline diamond films with a thickness of 0.5-5 μm were deposited using microwave chemical vapour deposition (MW CVD), and with a thickness of 1-4 μm by hot filament chemical vapour deposition (HF CVD). For both deposition technologies, we investigated the effect of a negative bias upon the formation of microcrystalline and nanocrystalline diamond multilayers. In the cases of smooth Si and relief WC-Co substrate surfaces, the multilayers were found to have a “cauliflower” look. The structure and composition of deposited layers were checked by scanning electron microscopy and Raman spectroscopy.     

金刚石薄膜的人工合成及其结合力的评估

在硬质合金ＷＣ—Ｃｏ基体上，用热丝ＣＶＤ法，人工合成出金刚石薄膜。利用Ｘ衍射、激光拉曼光谱和扫描电镜对金刚石薄膜的结构进行了测定，结果是令人满意的。精确测量金刚石薄膜与基体间的结合力是很困难的。本文报导了金刚石薄膜涂层刀具的实际切削结果，并以此来评估该涂层与基体间的结合力。     

Auger recombination-enhanced hot carrier degradation in nMOSFETs with a forward substrate bias

Enhanced hot carrier degradation in nMOSFETs with a forward substrate bias is observed. The degradation cannot be explained by conventional channel hot electron effects. Instead, an Auger recombination-assisted hot electron process is proposed. In the process, holes are injected from the forward-biased substrate and provide for Auger recombination with electrons in the channel, thus substantially increasing channel hot electron energy. Measured hot electron gate current and the light emission spectrum provide evidence that the high-energy tail of channel electrons is increased with a positive substrate bias. The drain current degradation is about ten times more serious in forward-biased substrate mode than in standard mode. The Auger-enhanced degradation exhibits positive temperature dependence and may appear to be a severe reliability issue in high temperature operation condition.     

HFCVD金刚石薄膜的热场模拟及实验

基体温度是影响金刚石薄膜生长质量的重要因素之一.基于有限元分析法,通过AN-SYS CFX软件对基体温度场进行模拟仿真,得到基体表面温度场的分布,并分别讨论了热丝-基体距离、热丝间距、水冷系数等参数对系统温度场均匀性和一致性的影响.经仿真优化后得到的参数值分别为热丝-基体距离10 mm、热丝间距15 mm、水冷系数1 000 W/(m2·K).在此优化工艺的基础上进行热丝化学气相沉积(HFCVD)金刚石薄膜的实验,并采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对金刚石薄膜表面特征进行检测.结果表明:利用仿真优化后的薄膜生长参数,可以在金刚石薄膜生长区域得到比较均匀的多晶金刚石薄膜.     

EA-HFCVD 沉积纳米金刚石膜的光致发光分析

采用电子辅助-热丝化学气相沉积法(EA-HFCVD)在硅片上沉积出晶粒尺寸为30nm的均匀金刚石膜。生长过程中,预先加6A偏流生长1h,然后在0.8kPa条件下,无偏流生长3h。光致发光谱中存在4个发光中心分别位于1.682eV,1,564eV,1,518eV和1.512eV的发光峰。1.682eV处发光峰源于衬底硅原子掺杂于膜中引起的缺陷;其他发光峰源于金刚石晶格振动声子。光致发光强度越大对应的缺陷密度越大,从而降低了场发射域值电场强度,其关键可能源于金刚石膜电导型晶界。     

Diamond icosahedron on a TiN-coated steel substrate

Diamond layers have been deposited by hot filament chemical vapour deposition (HF CVD) on TiN-coated steel substrates. After deposition, we could observe separate, well-developed diamond icosahedrons and decahedrons on the surface. We have found that a lower content of methane in hydrogen supports their growth, this being a result of multifold twinning. The quality of diamond layers has been evaluated by Raman spectroscopy and scanning electron microscopy.     

TEM investigation of silicon carbide wafers with reduced micropipe density

A technique to reduce the micropipe density in SiC substrates by first filling in the defects and then growing an LPE layer on the filled material has been developed by TDI. LPE growth in SiC is known to result in poor surface morphology, namely step-bunching due to the off-axis substrate orientation. Chemical vapor deposition (CVD) growth experiments on SiC substrates with reduced micropipe density using a cold-wall CVD reactor resulted in a significant improvement in the surface morphology. Although preliminary device results are encouraging, the exact nature of the filled micropipes nor the impact of growing CVD epitaxial layers on LPE SiC had not been fully characterized. We have preformed transmission electron microscopy (TEM) measurements to evaluate the crystallographic properties of the CVD/LPE and LPE/substrate interface. It was observed that no new dislocations were nucleated at the LPE/CVD interface. Although a micropipe was not located in the samples characterized, a tilt of 1.5° was observed between the LPE layer and the substrate. In addition, dislocations were observed to propagate through the LPE layer from the substrate which are most likely the 1C close-core screw dislocations common to SiC hexagonal substrates.     

The effect of substrate bias on hot-carrier damage in NMOS devices

Hot-carrier stressing carried out as a function of substrate voltage on 2-μm NMOS devices under bias conditions V_d =8 V and V_g=5.5 V is discussed. The time power-law dependence of stressing changes as a function of substrate bias (V_b), having a power-law gradient of 0.5 for V_b=0 V and 0.3 for V_b=-9 V. Investigation of the type of damage resulting from stressing shows that at V_b=0 V, interface state generation results, while at V_b=-9 V, the damage is mostly by charge trapping. Measurements of the gate current under these two substrate bias conditions show that the gate electron current increases by over two orders of magnitude upon application of a strong back bias. It is suggested that the electron trapping arises from this enhanced gate electron current under large substrate voltage conditions     

Effect of Electron Drag on Performances of Carbon Nanotubes as Flow Sensors

Experimentally, the electron drag effect on carbon nanotube surface in flowing liquids was investigated. It was found that electric current could be generated in metallic carbon nanotubes immersed in the liquids. Carbon nanotubes were synthesized on Si substrate by hot filament chemical vapor deposition. The experimental results showed that the flow--induced current on the surface of carbon nanotube films was closely depended on the flow rate, concentration, properties and temperature of liquids. The flow--induced current was increased with the increasing of flow rate, concentration and temperature of liquids. The obtained results were discussed in detail.     

Controlling the formation of nanoparticles for definite growth of carbon nanotubes for interconnect applications

Our interest is the integration of carbon nanotubes (CNT) in electronic devices (IC, NEMS). In the scope of this work, we present a study on the preparation of the catalyst Ni particles from ultrathin films and the synthesis of carbon nanotubes by the chemical vapour deposition method. For the preparation, we use a cold-wall CVD reactor especially designed for handling samples up to a size of a 4” wafer. We show the influence of different process conditions like temperature, initial layer thickness of catalyst and substrate on particle formation characterized by scanning electron microscopy (SEM). We show that the optimization of process conditions in the catalyst preparation phase is constitutive for dense CNT films. Regarding the application of CNTs as electrical interconnects, we studied the arrangement of nanoparticles on Al and TiN supporting layer. Furthermore, we fabricated the first test structures for the selective growth of CNTs out of contact holes on a Cu/TiN metallization layer system.The growth of multi-walled nanotubes (MWNTs) was performed with thermal CVD with ethylene as a precursor gas and hydrogen as supporting gas mixed in a nitrogen gas flow. The effects of growth condition on the quality and morphology of the CNTs were characterized by scanning electron microscopy, transmission electron microscopy (TEM) and Raman spectroscopy. The influence of temperature, gas composition and substrate on CNT growth will be presented. We managed to grow dense CNTs even at temperatures as low as 500 °C.     

Improvement of the crystallinity of 3C-SiC films by lowering the electron temperatures in the afterglow plasma region using triode plasma CVD

Crystalline SiC films were grown at low temperatures by triode plasma chemical vapor deposition (CVD) using dimethylchlorosilane diluted with hydrogen as the source gas. Influences of the grid bias on the electron temperature in the discharge region and in the afterglow region, and on the properties of the SiC films such as crystallinity, chemical bonding structure, and composition were investigated. Under negative grid bias conditions, the electron temperature in the discharge region increased and that in the afterglow region became about one-tenth of that under positive bias conditions. The crystallinity of the SiC films grown under low electron temperatures in the afterglow plasma region was remarkably improved and the composition of the films became stoichiometric. Under the negative grid bias, a high density of active hydrogen radicals was generated in the discharge region, diffused toward the substrate surface, and extracted the weak bonds or excessive methyl groups from the growing film surface under low electron temperature. As a result of these processes, SiC films with good crystallinity were grown.     

Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.     

Improvement of the Crystallinity of Silicon Films Deposited by Hot-Wire Chemical Vapor Deposition with Negative Substrate Bias

We have investigated the effect of negative substrate bias on microcrystalline silicon films deposited on glass and stainless steel by hot-wire chemical vapor deposition (HWCVD) to gain insight into the effect of negative substrate bias on crystallization. Structural characterization of the silicon films was performed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. It was found that the crystallinity of the films is obviously improved by applying the substrate bias, especially for films on stainless steel. At hot-wire temperature of 1800°C and negative substrate bias of ?800 V, grain size as large as 200 nm was obtained on stainless-steel substrate with crystalline fraction 9% higher than that of films deposited on glass and 15% higher than that of films deposited without substrate bias. It is deduced that the improvement of the crystallinity is mainly related to the accelerated electrons emitted from the hot wires. The differences in this improvement between different substrates are caused by the different electrical potential of the substrates. A solar cell fabricated by HWCVD with ?800 V substrate bias is demonstrated, showing an obviously higher conversion efficiency than that without substrate bias.     

Bipolar transistor fabrication in low-temperature (745°C) ultra-low-pressure chemical-vapor-deposited epitaxial silicon

In this letter we report for the first time the successful fabrication of bipolar transistors in low-temperature (Tdep= 745°C) epitaxial silicon deposited by a chemical-vapor-deposition (CVD) technology. The epitaxial layers were deposited by an ultra-low-pressure CVD (U-LPCVD) technique utilizing an optimized in-situ predeposition argon sputter clean. The critical parameter during the sputter clean has been identified as the substrate bias. Bias voltages of -200 or -300 V create dislocations that form emitter-collector shunts during the bipolar transistor fabrication process; a bias voltage of -100 V, however, permits the deposition of essentially defect-free (<10 dislocations cm^-2by defect etching) epitaxial films suitable for bipolar transistor fabrication.     

The 3D nanostructure growth evaluations by the real-time current monitoring on focused-ion-beam chemical vapor deposition

In this study, we examined the potential of real-time monitoring for the detection of structural defects such as deposits on substrates formed during the three-dimensional (3D) nano- and micro-structure fabrication by focused-ion-beam chemical vapor deposition (FIB-CVD). We evaluated the changes in the real-time current in the substrate during the 3D nanostructure growth. The results indicated that the substrate current does not depend on the vertical growth height. We evaluated the changes in the secondary electron (SE) current during vertical and lateral growth of nanostructures also evaluated. The dynamic profile of the substrate current agreed with that of the SE current. In addition, we found that an increase in the substrate current was caused by the formation of structural defects such as deposits on the substrate. This result implied that the increase in the substrate current was caused by a change in the positional relationship between the growth edge of nanostructures and the Ga⁺ FIB. These results indicate that detection and prevention of structural defects in the 3D nanostructure fabrication can be achieved by integrating a current-feedback function into the 3D computer-pattern generator.     

碳化硅衬底外延石墨烯

通过高温热解法和化学气相沉积(CVD)法在SiC(0001)衬底外延石墨烯。采用光学显微镜、原子力显微镜、扫描电子显微镜、喇曼光谱、X射线光电子能谱和霍尔测试系统对样品进行表征,并对比了两种不同生长方法对石墨烯材料的影响以及不同的成核机理。结果表明,高温热解法制备的石墨烯材料有明显的台阶形貌,台阶区域平坦均匀,褶皱少,晶体质量取决于SiC衬底表面原子层,电学特性受衬底影响大,迁移率较低。CVD法制备的石墨烯材料整体均匀,褶皱较多,晶体质量更好。该方法制备的石墨烯薄膜悬浮在SiC衬底表面,与衬底之间为范德华力连接,电学特性受衬底影响小,迁移率较高。