Continuous-Wave Electrically Pumped 1.55-$mu$m Edge-Emitting Platelet Ridge Laser Diodes on Silicon

We report the successful integration on silicon of small footprint, low-threshold electrically pumped edge-emitting lasers by a new approach incorporating microcleaving technology to produce 6-$mu$ m-thick platelet lasers with cleaved facets, microscale pick. and place assembly to position them on the substrate, and diaphragm pressure solder bonding to attach/connect them permanently in place. InP-based ridge-waveguide platelet lasers integrated on silicon lase at 1550-nm continuous-wave to 55 $^{circ}$C (pulsed to 80 $^{circ}$C) with output powers as high as 26.8 mW, external differential quantum efficiencies as high as 81%, and threshold currents as low as 18 mA.      

Fabrication and application of metallic nano-cantilevers

A new approach was developed in this work to fabricate metallic nano-cantilevers using a one-mask process and a deep reactive ion etch (DRIE) technique. 40-nm-thick Al and 70-nm-thick Au cantilevers of lengths from 5 μm and widths in the range of 200-300 nm were fabricated on a silicon substrate. The silicon underneath the suspended beams was completely etched. Short Al nano-cantilevers were used to find local residual stress induced in rapid thermal oxidation and the oxidized spots according to the deflection profiles of the nano-cantilevers. The deflection profiles were determined with the aid of a scanning electron microscope (SEM). Compared with a single feedback in the existing cantilever-based static methods, i.e., the deflection of the open end of a cantilever, the whole deflection profile provides more information regarding the effect of surface stresses on a cantilever.     

Young's Modulus Measurements in Standard IC CMOS Processes Using MEMS Test Structures

This letter¹ presents a method to measure the Young's moduli of individual thin-film layers in a commercial integrated circuit (IC) foundry process. The method is based on measuring the resonance frequency of an array of micromachined cantilevers and using the presented optimization analysis to determine the elastic modulus of each layer. Arrays of cantilever test structures were fabricated in a commercial CMOS IC process and were released using XeF₂ as a postprocessing etch. A piezoelectric transducer placed under the test chip was used to excite the cantilevers to resonance, and the resonance frequency was measured using a laser Doppler vibrometer. It is reported that excellent agreement for values of Young's modulus is observed for cantilevers between 200 and 400 mum in length, with average standard deviation being 4.07 GPa.     

The dry etching of TEOS oxide for poly-Si cantilevers in supercritical CO2

Dry etching of p-tetraethylorthosilicate (TEOS) with HF/H₂O in supercritical carbon dioxide (scCO₂) was studied. The etch rate of TEOS increased with HF concentration and reaction temperature, while the concentration of H₂O and processing pressure were found to have little effect on the etch rate. Finally, poly-Si cantilevers with high aspect ratios (1:150) were released using this technique without stiction and residue on the surface.     

Chemical beam etching of InP in GSMBE

Etching of InP using a beam of PC1₃ is demonstrated in a standard gas source molecular beam epitaxy machine. The principle of an atomic layer accurate end-point detection technique usingin-situ reflection high energy electron diffrac-tion is described and used to study the kinetics of PCl₃ etching. The etch rate is found proportional to the PCI₃ fluence and weakly dependent on the substrate temperature. The morphology of etched surfaces and the etch rate uniformity is compatible with the regrowth of high quality InGaAsP active structures and with the realization of etch and regrowth sequences controlled at the nm scale. Etch profiles at mask edges are defined by nearly perfect crystallographic facets with a very limited mask undercut (≈100 nm) due to the beam nature of the etching technique.     

Process characterisation of hot-carrier-induced β degradation in bipolar transistors for BiCMOS

This paper investigates the effect of various process parameters on the variation in forward current gain lifetime caused by hot carrier generation of BiCMOS bipolar transistors. Statistical process control and statistical designed experiments were used in this evaluation. The device lifetime in reverse bias operation was calculated from the forward current gain. Various process parameters were examined in this work, i.e., the intrinsic base implant dose and energy, selective collector implant dose, collector plug dose, spacer etch ratio, overetch thickness of nitride spacer and emitter poly etch time. It was deduced that high current gain lifetime can be obtained with high base implant doses, high base implant energies, long bulk nitride etch times and short emitter poly etch times.     

沉积、退火条件以及刻蚀液对PECVD氮化硅薄膜湿法刻蚀速率的影响

The influence of deposition, annealing conditions, and etchants on the wet etch rate of plasma enhanced chemical vapor deposition （PECVD） silicon nitride thin film is studied. The deposition source gas flow rate and annealing temperature were varied to decrease the etch rate of SiNx：H by HF solution. A low etch rate was achieved by increasing the SiH4 gas flow rate or annealing temperature, or decreasing the NH3 and N2 gas flow rate. Concentrated, buffered, and dilute hydrofluoric acid were utilized as etchants for Sit2 and SiNx：H. A high etching selectivity of Sit2 over SiNx：H was obtained using highly concentrated buffered HE     

Electron-cyclotron resonance etching of mirrors for ridge-guidedlasers

Etched laser mirrors are important for the monolithic integration of lasers in optical circuits without cleaved facets. Electron cyclotron resonance (ECR) etching is ideal for opto-electronic fabrication since the etching parameters are independently adjustable and a variety of masking materials are available for creating multiple etch depths, e.g., for etched ridge lasers with etched mirror facets. We report on the fabrication and characterization of ECR etched laser mirrors and waveguides. The quality of the ECR etch is ascertained by measuring the reflection coefficients of 90° turning mirrors in GaAs-AlGaAs multiple-quantum-well (MQW) lasers incorporating multiple numbers of 90° bends. The average reflection coefficient is found to be approximately 80%     

氮化硅的ECCP刻蚀特性研究

本文对氮化硅的增强电容耦合等离子刻蚀进行研究,为氮化硅刻蚀工艺的优化提供参考。针对SF_6+O_2气体体系,通过设计实验考察了功率、压强、气体比、氦气等对刻蚀速率和均一性的影响,并对结果进行机理分析和讨论。实验结果表明:功率越大,刻蚀速率越大,与源极射频电力相比,偏置射频电力对刻蚀速率的影响更为显著;压强增大,刻蚀速率增大,但压强增大到一定程度后,刻蚀速率基本不变,刻蚀均匀性随着压强增大而变差;在保证SF_6/O_2总流量保持不变下,O_2的比例增大,刻蚀速率先增大后减小,刻蚀均匀性逐步变好;He的添加可以改善刻蚀均匀性,但He的添加量过多时,会造成刻蚀速率降低。     

Mechanical properties and applications of custom-built gold AFM cantilevers

Silicon and silicon nitride metal-coated cantilevers have been in use for a long time in several scanning probe microscopy applications that require electrically conductive probes. However, conventional metalized cantilevers present several drawbacks such as limited life-time of the metal layer due to wear, and increased tip radius. This work focuses on monolithic metallic cantilevers developed in order to overcome the limitations of conventional metalized atomic force microscopy (AFM) probes. These custom-made cantilevers are designed for several applications such as in current-sensing AFM (CSAFM), Kelvin probe force microscopy (KPFM), and tip-enhanced Raman spectroscopy (TERS). Determination of the dynamic and static mechanical properties of these cantilevers in a non-destructive way is reported here. Key parameters under investigation are the cantilever spring constant and the frequency response using finite element method (FEM). Gold cantilevers are selected for this study, which allow optimizing the design and the process of developing these metallic cantilevers with parameters engineered for the applications mentioned above. This work contributes to the establishment and applicability of custom-made probes in advanced scanning probe microscopy methods and their performance understanding using computer simulations.     

GaAs/GaAlAs asymmetric Mach-Zehnder demultiplexer with reduced polarization dependence

A two-channel GaAs/AlGaAs asymmetric Mach-Zehnder wavelength demultiplexer with reduced polarization dependence was demonstrated. The device was fabricated on a single heterostructure comprising a 1.45- mu m-thick layer of GaAs on a 6.0- mu m-thick Ga/sub 0.85/Al/sub 0.15/As buffer layer. The epitaxial layers were grown by MOCVD (metalorganic chemical vapor deposition) on an n/sup +/ GaAs substrate. The single-mode rib waveguides, 3 mu m wide and 0.29 mu m high, were fabricated using standard photolithographic techniques followed by chemical etch and removal of the resist mask. Extinction ratios of 24.1 dB for transverse electric (TE) and 22.5 dB for transverse magnetic (TM) polarized light were measured on a device with an anti-reflection coating on its input and output facets. The active length of the device is approximately 6.5 mm and total loss of 1.1 dB was obtained in a 16-mm-long chip.<>     

Optimization of sidewall masked isolation process

This paper presents modifications of the Sidewall Masked Isolation (SWAMI) process for VLSI device isolation which improve process reproducibility, eliminate stress induced defects, and permit flexibility in channel stop implant optimization. A novel "undercut-and-backfill" technique is introduced to eliminate a localized failure mechanism of the oxidation mask by increasing the strength of the nitride-to-nitride joint. The primary variable influencing stress-induced defect generation is the vertical length of the sidewall nitride mask as determined by the amount of recessed silicon etch prior to sidewall nitride formation. In general, a maximum length can be found below which defect-free structures can be fabricated. An optional second recessed silicon etch, following the formation of the sidewall nitride, has been developed which increases the flexibility in optimizing the channel stop implantation. Defect-free low-leakage devices with near-zero electrical channel width reduction have been obtained.     

Optimization of Sidewall Masked Isolation Process

This paper presents modifications of the Sidewall Masked Isolation (SWAMI) process for VLSI device isolation which improve process reproducibility, eliminate stress induced defects, and permit flexibility in channel stop implant optimization. A novel "undercut-and-backfill" technique is introduced to eliminate a localized failure mechanism of the oxidation mask by increasing the strength of the nitride-to-nitride joint. The primary variable influencing stress-induced defect generation is the vertical length of the sidewall nitride mask as determined by the amount of recessed silicon etch prior to sidewall nitride formation. In general, a maximum length can be found below which defect-free structures can be fabricated. An optional second recessed silicon etch, following the formation of the sidewall nitride, has been developed which increases the flexibility in optimizing the channel stop implantation. Defect-free low-Ieakage devices with near-zero electrical channel width reduction have been obtained.     

Process design for plasma etching of polysilicon/silicon nitride/polysilicon sandwich structures for sensor applications

An in situ two-step process has been developed for plasma etching of poly-Si/silicon nitride/poly-Si sandwich structures for a surface micromachined tactile sensor. The first step of the process uses a CF₄-based gas mixture to etch the upper poly-Si layer and the second uses a CHF₃-based gas mixture to etch the silicon nitride with an etching selectivity of three over the lower poly-Si layer. Both the upper poly-Si and the silicon nitride of the sandwich structure can be etched with the same photoresist mask, while the lower poly-Si layer remains relatively un-etched. Compared with a one-step process which uses the same chemistry as in step one of the two-step process, the two-step process provides the desired etch selectivity, better uniformity and process tolerance.     

Chemically assisted ion beam etching of gallium nitride

Chemically assisted ion beam etching of gallium nitride (GaN) grown by metalorganic chemical vapor deposition has been characterized using an Ar ion beam and Cl₂gas. The etch rate of GaN was found to increase linearly with Ar ion beam current density, increase linearly then saturate with Ar ion beam energy, vary slightly with Cl₂ flow rate, and lastly, increase moderately with substrate temperature. Etch rates as high as 330 nm/min were obtained at high beam energies and 210 nm/min at a more nominal level of 500 eV. The anisotropy of etched profiles improved in the presence of Cl₂ in comparison to those etched by Ar ion milling only. Elevated substrate temperatures further enhanced the anisotropy to obtain near-vertical profiles for fairly deep-etched structures. Auger electron spectroscopy was used to investigate etch-induced surface changes. Oxygen contamination was observed on the as-etched surface but a dilute HC1 treatment restored the stoichiometry of the material to its unetched state.     

Very Low Pressure Magnetron Reactive Ion Etching of GaN and Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N Using Dichlorofluoromethane (Halocarbon 12)

In this work we report on the magnetron reactive ion etch (MRIE) technology for gallium nitride (GaN) and aluminum gallium nitride (Al _x Ga_1−x N) using dichlorodifluoromethane (CCl₂F₂), commonly known as halocarbon 12, with etch rates greater than 1,000 and 840 ?/min, respectively. Magnetic confinement of a very low pressure (10⁻⁴ Torr range) radio frequency (RF) discharge generates high-density plasmas, with low sheath voltages at the bounding surfaces, and very high dissociation of the source gas. Furthermore, the very low pressure of the etch process is characterized by long mean free paths so that sputtering contamination is reduced. MRIE chemistry has been monitored in situ by means of mass spectroscopy. Finally, we report on the successful fabrication of an indium gallium nitride (In _x Ga_1−x N) blue light emitting diode (LED), whose fabrication sequence included the MRIE etching of GaN in CCl₂F₂.     

Digital etching of III-N materials using a two-step Ar/KOH technique

A two-step digital etch technique, based on an argon plasma exposure followed by a 0.2 M boiling KOH surface treatment, is shown to be effective for etching III-N materials. Etching takes place as a result of the fact that damaged nitride material, whose depth can be controlled by the argon reactive ion etching (RIE) plasma, is susceptible to removal in heated solutions of KOH, which has been demonstrated for GaN, AlGaN, and InGaN. The process is shown to be highly linear across a number of digital etch cycles and capable of producing smooth surface morphologies.     

Comparison of plasma etch techniques for III–V nitrides

Fabrication of group-III nitride devices relies on the ability to pattern features to depths ranging from 1000 Å to >5 μm with anisotropic profiles, smooth morphologies, selective etching of one material over another and a low degree of plasma-induced damage. In this study, GaN etch rates and etch profiles are compared using reactive ion etch (RIE), reactive ion beam etching (RIBE), electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) etch systems. RIE yielded the slowest etch rates and sloped etch profiles despite dc-biases >−900 V. ECR and ICP etching yielded the highest rates with anisotropic profiles due to their high plasma flux and the ability to control ion energies independently of plasma density. RIBE etch results also showed anisotropic profiles but with slower etch rates than either ECR or ICP possibly due to lower ion flux. InN and AlN etch characteristics are also compared using ICP and RIBE.     

Silicon Nitride Films Deposited by RF Sputtering for Microstructure Fabrication in MEMS

In the present work, we report silicon nitride films deposited by a radio- frequency (RF) sputtering process at relatively low temperatures (<260°C) for microelectromechanical system (MEMS) applications. The films were prepared by RF diode sputtering using a 3-inch-diameter Si₃N₄ target in an argon ambient at 5 mTorr to 20 mTorr pressure and an RF power of 100 W to 300 W. The influence of the film deposition parameters, such as RF power and sputtering pressure, on deposition rate, Si-N bonding, surface roughness, etch rate, and stress in the films was investigated. The films were deposited on single/double-side polished silicon wafers and transparent fused-quartz substrates. To explore the RF-sputtered silicon nitride film as a structural material in MEMS, microcantilever beams of silicon nitride were fabricated by bulk, surface, and surface-bulk micromachining technology. An RF-sputtered phosphosilicate glass film was used as a sacrificial layer with RF-sputtered silicon nitride. Other applications of sputtered silicon nitride films, such as in the local oxidation of silicon (LOCOS) process, were also investigated.     

Short-cavity GaAlAs laser by wet chemical etching

A short-cavity (GaAl)As stripe geometry laser with a threshold current of 30 mA has been fabricated by a new chemical etch process which uses a multilayer metal mask. The laser is 23 ?m long and 12 ?m wide, and does not have reflective coatings on the etched facets. Quasi-single-mode operation is obtained in pulsed conditions.