A self-aligned fabrication process is presented for making surface-emitting high-power AlGaAs/GaAs GRIN-SCH-SQW semiconductor laser sources designed to produce > 1 W optical output at the nominal GaAs wavelength of 830 nm. The process uses double-layer masking with photoresist masks used as repeatedly changed selector masks on top of a semimetallic amorphous carbon (SMAC) mask which is an unchanging master mask on top of the AlGaAs/GaAs. The SMAC master mask, defined in one photolithography step, thus assuring the self-alignment, contains all the edges to be etched at all the different angle/depth specifications. Four separate Cl2+/Cl2 chemically assisted ion beam etches of AlGaAs/GaAs at three different angle/depth specifications create the three-dimensional microstructures of vertical ridges, back-to-back external 45-degrees reflectors, and vertical laser facets with current deflection trenches, in large arrays. Final encapsulation is by plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon-rich nitro-oxide hydrogenated (a-Si(w)N(y)O(z):H), thin film having triple use as chemical passivation, optical antireflection coating, and electrical insulation. We propose that PECVD amorphous silicon-rich carbo-nitro-oxide hydrogenated (a-Si(w)C(x)N(y)O(z):H), thin film might be an improved triple-use encapsulation thin film.

Smoothness of etched facets at all angles is a critical requirement for photonic devices in such materials as AlGaAs/GaAs which are etched at variable angles by directed ion beam/reactive gas etching systems such as chemically assisted ion beam etching (CAIBE). Semimetallic amorphous carbon thin films have been found to produce excellent etched facets that are smoother than those etched with other mask materials. This material also exhibits very low CAIBE etch rates and very low chemical reactivity with substrate materials such as AlGaAs/GaAs or silicon. The semimetallic amorphous carbon was deposited up to 400 nm thick by electron beam sublimation of graphitic carbon onto substrates such as polished wafers of GaAs, Si, Ge, and onto glass. The electron-beam sublimation deposited (EBSD) semimetallic amorphous carbon, EBSD semimetallic a-C, can be patterned directly by SF6 reactive ion etcher via a standard photoresist mask, it can be used as an etch mask in CAIBE systems, and it can be stripped clean in hydrogen or oxygen plasmas. Etch rate selectivities of approximately 30:1 of (AlGaAs):(EBSD semimetallic a-C) were observed in CAIBE experiments. The EBSD semimetallic a-C is being used as the etch mask in a self-aligned four-CAIBE steps process to microfabricate surface-emitting high-power single-mode AlGaAs/GaAs laser arrays.

High quality etch masks for nanometer plasma processing can be formed from thin films of semimetallic amorphous carbon that are deposited by electron beam sublimation of graphitic carbon. These films are amorphous, hard, semimetallic, and mirror-reflective. These electron beam sublimation deposited (EBSD) semimetallic amorphous carbon (semimetallic a-C) thin films can be routinely deposited up to at least 400 nm thick and patterned by SF6 plasma reactive ion etching (RIE) via standard photoresist masks. They are demonstrated to be excellent etch masks on gallium arsenide, silicon, and germanium substrates using chemically assisted ion beam etching (CAIBE), also known as ion beam assisted etching (IBAE), reactive ion beam etching (RIBE), and RIE. The carbon etch masks have fine grain, low chemical reactivity, low sputter rates, and high thermal stability. Finally, the EBSD semimetallic a-C can be readily stripped by SF6 or O2 or H2 plasmas.

We report the fabrication and characterization of facetless Bragg reflector surface-emitting AlGaAs/GaAs lasers. Both first-order (120-nm period) and second-order (240-nm period) gratings were fabricated by electron-beam lithography and chemically assisted ion-beam etching (CAIBE). These grating pairs provide the optical feedback of the laser, eliminating the need for cleaved or etched mirror facets. Specifically, this work includes: the fabrication and testing of a variable pitch grating-laser array which demonstrates optical emission peaks with 5-Å separation for adjacent lasers; demonstration of facetless Bragg reflector lasers with 120/240-nm grating pairs that show lower threshold currents, higher quantum efficiencies, and improved beam width compared to conventional facetless second-order grating lasers; and a demonstration of grating surface-emitting diode lasers with hybrid first-order and nonresonant, 120/307-nm, grating pairs that produced a directed beam at 45° with respect to the substrate. The fabrication technology and optical performance of these devices are presented.

GaAs optoelectronic integrated circuits (OEICs) require the combination of several types of devices that place widely differing demands upon the layer structure and processing technologies. We report on the development of MESFETs, bipolar transistors, detectors, and a unique class of beam-steered facetless grating surface-emitting lasers and the integration of up to 300 devices of multiple types.

Molecular-dynamics methods are used to model diffusion in a \ensuremath{\Sigma}=5 [100] Al tilt boundary and in bulk. The diffusion coefficient D and activation energy Q for atoms in the boundary and in bulk are calculated for several different Al empirical interatomic pair potentials. These include a Morse potential, spline potentials fitted to bulk experimental data (elastic constants, phonon spectra, etc.), and a pseudopotential. Reasonable agreement is obtained with experimental diffusion values for Al, although activation energies are low. There is also a wide variation in results from one potential to another because the atomic motion is sensitive to the shape of the primary well or minimum of the interatomic potential. Rescaling the data with rough estimates of the different bulk melting temperatures that each potential predicts reduces the discrepancy between potentials. This is shown to be true for virtually any pair potential by calculating diffusion rates for Morse potentials with changing potential-well depth, position, and width. The variations between potentials are also explained in a quantitative sense by a simple calculation of potential-energy barrier height for vacancy migration in a bulk model. A method is given for using a linear relation between barrier height and melting temperature to predict diffusion coefficients and general transport properties in grain boundaries and bulk for any pair potential in any fcc metal.

We report on the spatially dependent enhanced etch rate of SiO2 in a CF4 planar reactive ion etcher due to the presence of the compounds GaAs or InP, or the single elements Ti, V, Nb, Ta, Cr, Mo, W, Ni, Pd, Pt, Cu, Ag, Au, Al, Ga, In, or Ge. The etch rate enhancement is maximum immediately adjacent to the source of the material and decreases nonlinearly with increasing distance away from the source of the material. Of the materials studied, the largest local etch rate increase was due to the element Ni (65% increase), followed closely by the elements In (57%) and Ga (43%) and the compounds InP (55%) and GaAs (40%). The lateral range of the effect extends 5 to 30 mm away from the material depending on the element or compound. Material interaction, possibly a catalized reaction, with the CF4 plasma reactants and lateral transport to provide an increased local concentration of fluorine at the SiO2 surface is a preliminary suggestion for the observed etch rate increase.

We present a simple analysis of the chemically assisted ion beam etching (CAIBE) yield of a solid under exposure to an ion beam and flux of molecular chlorine, using a mass-balance approach. In this model, dichloride species formed by the dissociative chemisorption of physisorbed chlorine are removed by collisional cascade mechanisms. We show that the energy and ion flux dependences of the yield deviate from expected forms depending primarily on the surface chemisorption rate and the surface flux ratio, but even in this simple model there are reasons why the latter might not be a good parameter for the comparison of experimental data. The model describes the important features of the etch rates of GaAs in chlorine and low-energy (500–1250 eV, 0.05–0.35 mA/cm2) Ar+, including a changing energy dependence of the yield with chlorine partial pressure.

We report on the fabrication and characterization of broad-area, grating-coupled, distributed Bragg reflector, surface-emitting, AlGaAs/GaAs laser diodes. Electron-beam lithography and chemically assisted ion-beam etching (CAIBE) were used to fabricate both first-order (120-nm period) and second-order (240-nm period) gratings. Gratings were patterned by exposing PMMA resist using 50-keV electrons in a JEOL 5DIIU direct write electron-beam lithography system. The resist image was transferred into the AlGaAs layer by CAIBE. CAIBE was performed using chlorine gas in conjunction with a 500-eV argon-ion beam in a modified Technics Plasma GmbH RIB 160 etcher. Surface-emitting lasers using second-order gratings were fabricated on AlGaAs/GaAs asymmetric separate confinement double heterostructure layers grown by liquid-phase epitaxy. Wet chemical etching was used to remove the upper cladding layer, exposing the waveguide in selected areas. Gratings were then etched into the waveguide to produce surface emitting window regions. The far-field light intensity pattern shows a lateral angular spread of 2.4° for a 50-μm-wide stripe. This lateral angular distribution is the lowest reported for a broad-area (not array) grating surface-emitter.

This paper will discuss direct-write electron beam lithography and multilayer resist processing for the fabrication of T-shaped gates. Gates whose length at the bottom of the T are less than 100 nm have been fabricated by this method using a multilayer of polynethylnethacrylate and lift-off. Because of the large cross-section of the T-gate, the resistance is reduced. The end-to-end resistance of the 100 nm T-shaped lines was less than 25) Ohninin as compered to 2000 Ohm/nin for a 100 nm conventional gate, i.e., an eight-fold decrease. In order to facilitate the fabrication of these gates a series of computer programs were written to simulate the development process in a multilayer of electron resists. These programs are based on a string development model of resist development. They allowed rapid prediction of the resist profiles. As a demonstration of the increased device performance made possible by this prociss, modulation-doped field effect transistors (HOLEY) have been fabricated using these T-gate structures . The extrapolated unity current gain frequency (ft) of these transistors is 113 Gilz.

Electromigration failure of a series-parallel configuration of aluminum interconnects overlayed on tungsten contacts was measured using a novel multiple lognormal analysis. The analysis examined early failure mechanisms and allowed rapid determination of electromigration parameters on a statistically large number of junctions. The primary failure mode of these stuctures was complete migration of Al off of the W pads. This work suggested that Al/W metallizations, with a large number of series contacts, are prone to short mean time to failures.

AlGa/GaAs modulation-doped field-effect transistors (MODFETs) have been fabricated with 'T' cross-section 0.1 mu m gates using electron-beam lithography. A unity current gain cutoff frequency f/sub T/ of 113 GHz has been measured for a spike-doped MODFET with a GaAs buffer. This is the highest measured f/sub T/ reported to date for FETs of any kind.<>

We have fabricated GaAs metal–semiconductor field-effect transistors (MESFET’s) and GaAs/AlGaAs modulation-doped field-effect transistors (MODFET’s) with gate lengths of 50 and 100 nm. A JEOL 5DIIU electron-beam lithography system was used in the fabrication of these nanometer transistors. This system has demonstrated a 30-nm overlay accuracy and liftoff metal lines as narrow as 25 nm. The electrical measurement results showed a room temperature extrinsic transconductance (gm) of 540 mS/mm for the 100-nm MESFET’s and over 600 mS/mm for the 100-nm MODFET’s. The MESFET also exhibited a small signal gain of 16 dB at 18 GHz at the low-noise bias point which is the highest ever reported for a MESFET. A significant short channel effect, however, has also been observed in these very short gate transistors. In this paper, transistor fabrication will be discussed and electrical results will be presented.

Bilayers of Fe/Al have been used to contrast two types of irradiations, pulsed-beam and conventional implantation. The Fe/Al bilayers were reacted with ∼ 70 ns, 280 keV light ion pulsed-beam irradiation and 550 keV Xe ion implantation. Rutherford backscattering spectrometry and electron and X-ray diffraction data reveal that pulsed beam irradiation results in substantially larger interface reactions compared to Xe implantation. Monte Carlo simulations indicate that the reactions observed in the pulsed-beam irradiated Fe/Al do not stem from nuclear cascade mixing and heating. These reactions are the result of lattice heating which occurs when the energy deposited into the electronic system of the Fe/Al is coupled to the lattice. Heat flow calculations have indicated that the irradiation induced lattice heating causes rises in the surface temperature and the melting of Al.

Factors affecting the ultimate resolution of ion beam lithography are discussed. These factors are primary ion scattering, recoil atom scattering, range of secondary electrons, and resist properties (i.e., resist sensitivity and molecule size in the resist). From a consideration of these factors, it is estimated that minimum linewidths of ≲10 nm can be achieved in polymethyl methacrylate (PMMA) using light ions. For heavy ions such as gallium, the resolution limit is estimated to be ∼30 nm with the limitation being due to recoil atom scattering. Fabrication of high resolution silicon nitride stencil masks is described and replication of the masks with protons in PMMA is demonstrated with features as small as 20 nm.

Using a custom designed beam analyzer system, the ionic species from a broad beam ion source have been measured under various etching conditions. In broad beam ion-beam-assisted etching (IBAE), it was observed that up to 25% of the ionic species are from the reactive neutral component backdiffusing into the ion source through the extraction grids depending on the ambient conditions. With the use of the constructed beam analyzer, known ionic species were also used for reactive sputtering and IBAE. The ionic species from Ar, Kr, Xe, Cl2, and CCl4 gases were directed at a Si substrate at 1 keV both with and without the presence of a chemically reactive neutral component of Cl2. In reactive sputtering, the etch yields were primarily dependent on the reactivity of the ionic species. However, in IBAE the etching mechanisms are more dramatically affected by the reactive neutral component on the surface than by the ion beam. That is, the etching component of the ion beam in IBAE is dominated more by its mass and acceleration voltage than by the reactivity of the species.

Some applications of focussed ion beams are discussed with special emphasis on the lithography aspects. Experimental data on the ranges of H+, Be+ and Si++ in polymethylmethacrylate (PMMA) are presented. The sensitivity of PMMA to Si++ ions is measured to be 0.35 µC/cm2. It is shown by replication through a transmission mask that Si++ ions with low to moderate incident energies, such as found in focussed ion beam systems, can be used for submicrometer lithography in single and multi-layer resist systems.