In recent years interest in dry-etch processing of laser struc-tures has grown dramatically. Reactive-ion-etching (RIE) has developed from a high resolution pattern transfer technique for silicon in-tegrated circuit processing into a successful method for fabricating the smooth, vertical facets required by double heterostructure (DH) lasers. However, in addition to RIE several other new plasma processes have been developed and applied to the developement of dry etched laser structures. This paper reviews the motivations behind this work, provides some examples of recent developements in the field of dry-etching as applied to DH laser structures and attempts to point out some of the problems associated with dry etching of optoelectronic devices.

A number of advanced processing tools and techniques have been used to demonstrate a multilevel metal interconnect module for VLSI circuits with <1µm design rules. A Perkin Elmer AEBLE 150 e-beam lithography tool has been used to print features with a range of dimensions as small as 0.5μm. These results are compared to those obtained on an ULTRATECH model 1000 1X stepper. Multilevel masking techniques plus dry etching have been used to ensure vertical feature walls and to reduce the loss of critical dimensions during the pattern transfer process. In order to completely fill contacts and vias, chemical vapor deposited tungsten (CVD W) was used in conjunction with a TiW barrier between the W and the silicon/silicide in the contact openings. To lower the interconnect resistance, aluminum alloy films (AlTi(0.2%) or AlCu(1.5%)) have been sputter deposited on top of the W film. In some cases where first metal resistance is not a critical issue, 0.45μm of CVD W without Al on top has been used as a metal film. Low temperature deposited oxides (both doped and undoped) have been used in conjunction with spin-on-glass (SOG) and etchback techniques to form partially planar ILD structures. Test structures fabricated using these processes have been examined with electrical testing and physical analysis.

A novel wafer processing technology to fabricate ridge-waveguide laser diode has been developed, using a low thermal expansion polyimide and an etch-back process. A low threshold current of 15mA, a high To value of 145K, and a maximum power output higher than 30mW/facet under cw operation have been achieved in a GRIN-SCH single quantum well PBR(Polyimide Buried Ridge) laser emitting at 780nm. High temperature oscillation at 1900C and To of 165K have been also obtained in a GRIN-SCH multiple quantum well PBR laser. A planar configuration in the present PBR laser is suitable for opto-electronic integration.

The species dependence of ion induced superlattice mixing has been examined in AlAs-GaAs superlattice samples grown by molecular beam epitaxy. The interdiffusion of the superlattices induced by ion implantation with comparable ranges, doses and subsequent thermal anneals were measured with secondary ion mass spectrometry. The effects of elements of comparable mass (Ga, As, and Ge) and comparable valence (Si and Ge, Be and Zn) were compared. The experimental results show that Ga and As implantation cause only collision-induced mixing, while Ge implantation results in collision-induced mixing with additional impurity-induced mixing beyond the implant range. In comparison with Ge, Si induced mixing is similar in nature though there is a significant difference in the depth and extent of the mixing. The extent of the mixing is found to depend on the local Ge or Si concentration. The mixing effect of Be and Zn is predominately an impurity effect.

GaAs layers grown on silicon by molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (OMCVD) have been characterized using transmission electron microscopy (cross-section and plan view) and high-resolution electron microscopy. The nature of defects in the GaAs layers has been analyzed as a function of growth technique. The type, density and distribution of dislocations was virtually the same in both samples, however the MBE sample also had a high density of planar defects (twins and microtwins). The effect of rapid thermal annealing (RTA) on the defect density and nature has also been studied for both growth techniques. RTA leads to a decrease in the dislocation density in the near surface region and eliminates virtually all the twins and microtwins in the MBE sample.

A study of carrier activation and mobility was performed in pulsed laser annealed samples of GaAs implanted with doses of Si and Se from 2.2x1012 to 6.0x1014 cm-2. The samples were annealed using a pulsed XeCl excimer laser ( λ=308 nm) and a pulsed dye laser ( λ=728 nm) with energy densities from 0.1 to 0.9 J/cm2 and a 10 nsec pulse. Very high carrier concentrations of 3x1019 and 1.5x1019 cm-3 were obtained for best n-type GaAs samples annealed with the dye laser and excimer laser, respectively. Dye laser consistently produced higher activation than excimer laser annealing. A transient reflectivity experiment was performed to identify the GaAs melt threshold and the melt phase dynamics of the GaAs,under the nitride cap. The threshold energies for cap damage were 0.34 and 0.12 J/cm2 for excimer and dye lasers, respectively. High carrier activation, as measured by Van der Pauw method, was achieved even for lightly doped samples although the room temperature Hall mobility was low. Raman spectroscopy was used to identify the threshold energies for the GaAs implant layer recrystallization and for optimum carrier activation.

Atomic layer epitaxy is a new growth which proceeds by the alternate deposition of column III and column V species. The deposition is self-limiting, and only one monolayer is deposited per growth cycle independent of the column III or V fluxes. This technique is thus able to achieve better control of layer thickness and uniformity, abrupt interfaces, ordered structure, planer doping, low temperature growth and others. The potential application of atomic layer epitaxy will be reviewed.

We report for the first time the use of ion beam assisted etching in the lOad-lock of a molecular beam epitaxy (MBE) chamber for in-situ patterning and regrowth of GaAs/AlGaAs microstructures. Microstructural analysis with electron microscopy indicates that the quality of the overgrowth improves dramatically as the substrate temperature for regrowth is raised from 580 C to 680 C. Using ion beam assisted etching in conjunction with fluoride masks compatible both with the electron beam lithography process and the need for low reactivity with GaAs at elevated growth temperatures, epitaxical single-crystal AlGaAs layers have been regrown on sub-micron structures.

Photochemical vapor deposition (PCVD) of GaAs on fused silica, silicon and GaAs substrates is reported here. A 1000 watt Hg-Xe arc lamp is utilized as the light source with arsine and triethylgallium serving as the reactants. Epitaxial film growth is shown to occur for deposition on both GaAs and silicon substrates. These thin films are characterized using Auger electron spectroscopy, energy dispersive spectrometry, scanning electron microscopy and x-ray diffraction. The results of this study demonstrate the effectiveness in utilizing both photolysis and pyrolysis to achieve deposition.

We have studied surface plasma modes in type I and type II semiconductor superlattices, with and without an in-plane electric field. We demonstrate feasibility of the current driven mode-amplification in both systems, and determine the threshold drift velocities for this effect.

A compeletely new technique of growing (Na,K)3Sb multialkali photocathodes in the high vacuum facilities of the molecular beam epitaxy (MBE) is developed. The main principle of semiconductor technology is used: all sources are operated simultaneously and the vapour concentration of Na and K is well above of the stoichiometric one. The intensity flux control is provided with the help of a specia.11y designed quadrupole masspectrometer as well as with the original procedure of atomic beams tomography. Fast baked effusion cells having low heat intertia have been designed. The photocathodes synthesis is provided onto monocrystalline sapphire substrates, on which the contact tungsten ring is eveporated. The choice of tungsten is determined by its small vapourization during the course of the substrate high temperature (1300°K) processing. It is important to note that the total cycle of the photocathode growing process does not exceed 15-20 minutes for the photocathode thickness of about 1000 Å. We have studied the influence of the substrate temperature on photoemission parameters. Quantum efficiency of the MBE grown photocathodes approaches to ten-forty percents at blue sensitivity edge. A qualitative emission theory of the MBE grown photocathodes is suggested.

Rapid isothermal processing (RIP) based on incoherent sources of light has emerged as a major semiconductor processing technique. In this paper, a review of our own and other works on the RIP of dielectrics is presented.

Experimental studies of the low temperature (800° C) processing and characterization of thermally grown films of SiO2 on Si in the thickness range of 1 to 20 nm is reported here. Breakdown voltage, High Resolution Transmission Electron Microscopy (HRTEM), Electrolyte Electro Reflectance (EER), single wavelength and Spectroscopic Ellipsometry (SE) techniques have been employed to characterize these films. Nearly Free Electron (NFE) model such as that of Penn is then employed to interpret the energies corresponding to the peak in the EER SE spectra.

Laser processing of semiconductors offers the promise of fast turn around of custom chips. Already lasers are used for mask repair and as a heat source for some thermal processes at the wafer level. This paper describes the development of a machine for the purpose of customizing gate arrays by using a laser as a point source of heat to cause various thermal reactions at the semiconductor surface.

A five-component glass has been reactive ion etched with CF4- 02 plasma over a range of pressure, power and gas composition. There are two kinds of components in glass: those chemically etchable and those chemically non-etchable. For the former both chemical reaction and physical bombardment contribute to the etch. For the latter physical bombardment dominates the etch. A feeding stream concentration change was used to illustrate chemical reaction effects. The cathode self-bias voltage was used to evaluate the bombardment mechanism. The addition of argon into the plasma not only increased the glass etch rate but also smoothed the surface topography. SEM and Auger results proved the existence of differential etching mechanisms for glass components.

Growth of epitaxial dielectrics of II-A fluorides on Si and compound semiconductors has generated considerable research interest in recent years. In general, MBE and vacuum deposition techniques are being employed for the epitaxial growth of II-A fluorides on semiconductor substrate maintained between about 400 and 900°C during the deposition of dielectric material. With the typical deposition rate of about 1-2 Å/s, 8-10 minutes are required to deposit 1000 Å of dielectric material. This type of prolonged heating may not be suitable for future submicron and three-dimensional Si integrated circuits, as well as for compound semiconductor devices. We have developed a new reduced thermal budget (product of processing temperature and time) processing technique for the deposition of epitaxial dielectric films on Si and compound semiconductors. In this process, epitaxial dielectric is deposited in the e-beam system at room temperature and subsequently subjected to in-situ rapid isothermal processing by using incoherent light sources incorporated in the e-beam system. In this paper, electrical and structural characteristics of thin epitaxial dielectric films on Si are described.

We report on the novel application of Langmuir-Blodgett film deposition of cadmium di-stearate to form a high barrier height Schottky barrier on n-In0.53Ga0.47As. The method is simple and can be applied to integrated optoelectronics where conflicting device requirements impose astringent constraints on the material and processing technology. Using this technique to form the gate electrode, we fabricated a 1μm gate length inverted InP-InGaAs modulation doped field effect transistor (MODFET) with an extrinsic transconductance of 170 mS/mm and a current gain cut-off frequency fT of 19 GHz.

An advanced technique of Isolated Silicon Epitaxy (ISE) has been used to produce silicon-on-insulator (SOI) material of high quality. AUGER spectroscopy of ISE shows a chemically clean film with no heavy metal contamination. Structural studies by transmission electron microscopy and Nomarski optical microscopy on ISE SOI show only isolated threading dislocations yielding defect densities of (~3 X 105/cm2). Double crystal x-ray diffraction shows a FWHM of 44 arcsec in the isolated Si film. Material quality is discussed in detail.

The chemical and electrical characteristics of ~10 nm MOS gate dielectrics formed by the rapid thermal postoxidation of rapid thermally nitrided oxides (RTO/RTN oxides) are described. TEM micrographs show that the interface smoothed by the RTN (1000°C,60s) of SiO2 is roughened by the subsequent heavy RTO (1100°C,60s). The fixed charge and interface state densities of the produced films are strongly dependent on the degree of reoxidation of Si at the interface. MOS capacitor results indicate that, as compared to pure oxide films, the RTO/RTN oxide samples exhibit reduced bulk trap and interface state generation rates under high electrical field stress. Optimized RTN and RTO processes can produce thin dielectrics with enhanced charge to breakdown (QBD strength and flat band voltage (VFB) stability. This multiple rapid thermal processing (RTP) procedure is found to be compatible with MOSFET fabrication technology and to reduce weak spots in thermal oxides. The electrical characteristics of n-channel transistors fabricated with RTO/RTN dielectrics are comparable to those of transistors fabricated with pure oxides.

A new generation of integrated circuits is foreseen in which quantum dots with discrete electronic states are used to construct logic and memory elements. Successful implementation of this technology will require significant improvements in semiconductor processing technology.

We have studied defects and interfaces in ZMR silicon using transmission electron microscopy. Both plan view and cross sectional samples were examined and the silicon/oxide interfaces were studied at high magnification. The substrate/oxide interface exhibited a roughness of the order of a monolayer while the oxide/overlayer interface was slightly rougher with a roughness of the order of two to three monolayers. Subboundaries were not observed in the silicon overlayer. Dislocations were the dominant type of defects in the overlayer and dislocation reactions of the type a/2[101] (111) + a/2[011] (111) = a/2[110] (001) were frequently observed. The mechanism of formation of these nodes during the ZMR process is discussed.

A new type of defect occurring in n++p+-junctions prepared by the diffusion of high concentrations of phosphorus and gallium into neutron transmutation doped (111)-silicon is reported. The defect is identified as a complex of a metal precipitate interacting with a Shockley-Read type of generation centre and has a strong influence on the recombination and generation properties of emitter structures. Instabilities in the generation current, occurring at well defined temperatures and influenced by the electric field, are interpreted as structural or phase changes among the defects. The concentration of the defects is dependent on the concentration of gallium.

We report high peak power low threshold AlGaAs/GaAs double heterostructure stripe geometry laser diodes on Si substrates grown for the first time by hybrid migration-enhanced MBE (MEMBE) and MOCVD. The lasers with 6 pm silicon oxide stripes were tested unmounted under pulsed conditions (i.e., 50 ns pulse width and 10 KHz pulse repetition rate) at room temperature. These lasers show a peak output power as high as 184 mW per facet and a threshold current as low as 150 mA at 300 K for a cavity length of 350 μm. The differential quantum efficiency of 30 % was obtained without mirror facet coating. A threshold current density of 7 kA/cm2 was obtained based on the nominal stripe dimensions without considering current spreading and lateral diffusion; we estimate about 2 kA/cm2 when taking these effects into account. For comparison, the pulsed threshold current density of the broad area DH lasers on GaAs substrates was 1.1 kA/cm2 at room temperature. This would be further reduced for lasers with a quantum well (e.g., GRIN-SCH SQW) active region. These results show the highest output peak power reported so far with a low threshold current for conventional double heterostructure stripe laser diodes grown on Si substrates.