Energy effect of the laser-induced vertical metallic link

In this paper, the energy effect of the laser vertical metallic link is investigated from a microscopic point of view through experimental observations and simulations. Sample structures that were irradiated under different laser energies were cross-sectioned and observed using a FIB/SEM dual-beam system. Failure criterion at the high energy level was defined by excessive material loss in the lower metal (metal 1) and passivation cracking. Micro-images also suggest that, for an optimal link metal (metal 2) opening should be larger than the lower metal linewidth considering the dielectric-step-induced lens effect. Taking into account both measured electrical resistance and observed voids in the lower metal, the normalized energy process window is defined to be the absolute energy range divided by the average energy. For the structures with 1-, 2-, 3-, and 4-μm lower metal linewidths, the relative process windows are 0.83, 0.87, 0.9, and 0.96, respectively. Simulations also revealed consistent results with the experimental observations, which is a monotonically decreasing trend of relative energy process windows for more scaled links. A simple equation to evaluate the spot size of the laser beam for various link structures is presented. These results demonstrate the application of commercially viable vertical linking technology to VLSI applications     

Vertically integrated silicon-on-insulator waveguides

A SiO₂-Si-SiO₂-Si-SiO₂-Si structure produced by the separation by implantation of oxygen (SIMOX) process used for dual vertically integrated waveguiding in silicon at λ=1.3 μm is discussed. Independent waveguiding is observed when 2-μm-thick Si cores are separated by 0.36-μm-thick SiO₂ . Coupled waveguiding is found for an 0.12-μm intercore oxide thickness     

A new method of forming a thin single-crystal silicon diaphragmusing merged epitaxial lateral overgrowth for sensor applications

Merged epitaxial lateral overgrowth (MELO) of silicon was combined with an SiO₂ etch stop to form a 9-μm-thick and 250-μm×1000-μm single-crystal Si membrane for micromechanical sensors. When epitaxial lateral overgrowth (ELO) silicon merges on SiO₂ islands, it forms a local silicon-on-insulator (SOI) film of moderate doping concentration. The SiO₂ island then acts as a near-perfect etch top in a KOH- or ethylenediamine-based solution. The silicon diaphragm thickness over a 3-in wafer has a standard deviation of 0.5 μm and is precisely controlled by the epitaxial silicon growth rate (≈0.1 μm/min) rather than by conventional etching techniques. Diodes fabricated in the substrate and over MELO regions have nearly identical reverse-bias currents, indicating good quality silicon in the membrane     

InGaAsP (λ=1.3 μm) strip buried heterostructure lasersgrown by MOCVD

The authors describe InGaAsP-InP index guides strip buried heterostructure lasers (SBH) operating at 1.3 μm with a 1.1-μm guiding layer grown by a two-step atmospheric pressure metalorganic chemical vapor deposition (MOCVD) growth procedure. These lasers are compared with buried heterostructure lasers having similar guiding layers under the active layer but terminated at the edge of the active layer. SBH lasers with 0.15-μm-thick active layer strips, 5-μm wide, and guide layers varying from 0 to 0.7 μm have threshold currents increasing from 34 to 59 mA, and nearly constant differential external quantum efficiencies of 0.2 mW/mA. The threshold current increases more rapidly with temperature with increasing guide layer thickness, with T₀ decreasing from 70°C for lasers without a guide layer to 54.3°C for lasers without a guide layer to 54.3°C for lasers with 0.7-μm-thick guide layers. Output powers of up to 30 mW/facet have been obtained from 254-μm-long lasers and were found to be insensitive to guide layer thickness     

Compact free-electron laser resonators utilizingelectron-transparent mirrors

The potential advantages and the physical properties of several electron-transparent mirrors (e.g., metal meshes, thin foils, pierced mirrors, and Bragg reflectors) to be used in infrared free-electron laser resonators are reviewed. The conditions under which the effect on the electron beam quality can be kept small are discussed, and experimental results on the angular spread produced by a 2.5-μm-thick metal mesh on a 5 MeV electron beam are presented. The experimental test of a resonator with two different electron transparent output couplers is reported     

Comparison of high-temperature-superconductor and metal-basedresonators

A 50-Ω coplanar waveguide (CPW) resonator designed for a fundamental frequency of about 4.75 GHz was fabricated on LaAlO₃ . Two versions were fabricated: the first using 1.9-μm-thick gold and the second using 0.6-μm-thick YBa₂Cu₃O ₇. The devices were identically packaged and tested at 77 K. It was found that the high-temperature superconductor (HTS) resonator had a surface resistance, R_s, about six to nine times lower than the Au one. At 45 K, the R_s of the HTS resonator decreases by another factor of 4 compared with its 77 K value. Device characteristics for the HTS resonator are presented     

The effect of cladding layer thickness on large optical cavity650-nm lasers

The reduction in penetration of the optical mode into the cladding layers in large optical cavity (LOC) laser structures offers the possibility of reducing the cladding-layer thickness. This could be particularly beneficial in GaInP-AlGaInP high-power devices by reducing the thermal impedance and the electrical series resistance. We have designed and characterized 650-nm LOC lasers by modeling the optical loss due to incomplete confinement of the optical mode by the cladding layers and calculating the thermally activated leakage current. This indicated that the cladding thickness could be reduced to 0.5 μm without adversely affecting performance. We investigated devices with 0.3-, 0.5-, and 1-μm-wide cladding layers. The measured optical mode loss of the 0.3-μm-wide cladding device was 36.2 cm^-1 compared with 12.4 and 11.3 cm^-1 for the 0.5- and 1-μm-wide cladding samples, respectively. The threshold current densities of the 0.5- and 1.0-μm devices were similar over the temperature range investigated (120-320 K), whereas the 0.3-μm devices had significantly higher threshold current density. We show that this can be attributed to the higher optical loss and increased leakage current through the thin cladding layer. The intrinsic gain characteristics were the same in all the devices, irrespective of the cladding-layer thickness. The measured thermal impedance of 2-mm-long devices was reduced from 30.7 to 22.3 K/W by reducing the cladding thickness from 1 to 0.5 μm. Our results show that this can be achieved without detriment to the threshold characteristics     

Room temperature pulsed operation of 1.5 μm GaInAsP/InPvertical-cavity surface-emitting laser

Room-temperature pulsed operation of a GaInAsP/InP vertical-cavity surface-emitting laser diode (VCSELD) with an emission wavelength near 1.55 μm is reported. A double heterostructure with a 34-pair GaInAsP (λ_g=1.4 μm)/InP distributed Bragg reflector (DBR) was grown by metalorganic chemical vapor deposition (MOCVD). The measured reflectivity of the semiconductor DBR is over 97% and threshold current is 260 mA for a 40-μmφ device with a 0.88-μm-thick active layer. Threshold current density is as low as 21 kA/cm² at room temperature     

Cryogenic processed metal-semiconductor-metal (MSM) photodetectorson MBE grown ZnSe

Molecular beam epitaxy grown 0.5-μm and 2.0-μm thick undoped ZnSe on semi-insulating (100) GaAs substrates were prepared for metal-semiconductor-metal (MSM) photodetector devices. The MSM photodetectors consisted of interdigitated metal fingers with 2, 3, and 4 μm width/spacing on a wafer. A multilayer resist process was employed using polyimide and SiO₂ thin films before the pattern generation to aid in a special low temperature (LT) lift-off process. Dark current-voltage (I-V), DC photo I-V, high frequency I-V, spectral response, and frequency response techniques were employed for testing the device performance. The cryogenic processed metallization provided an improved interface between metal and semiconductor interface. The breakdown voltage in these devices is dependent on the electrode width/spacing and not on film thickness. Dark current remained at around 1 pA for a bias of ±10 V. The devices exhibited a high spectral responsivity of 0.6 (A/W) at a wavelength of 460 nm at 5 V applied bias. A maximum spectral responsivity of 1 (A/W) at an applied bias of 5 V was obtained in these devices indicating an internal gain mechanism. This internal gain mechanism is attributed to hole accumulation in ZnSe epilayers     

1.55-μm InGaAsP-InP spot-size-converted (SSC) laser with simpletechnological process

In this letter, we report the realization of a 1.55-μm spot-size-converted (SSC) laser using conventional SCH-MQW active layers and conventional photolithography. The laser consists of a 300-μm-long rectangular gain section, with compensated multiple-quantum-well (MQW) structure, and a 300-μm-long tapered passive waveguide, fabricated on lower SCH layer. The device exhibits a beam divergence of 13°×18° and 3.5-dB coupling loss with a cleaved single-mode fiber (SMF). The 1-dB alignment tolerance is ±2.3 μm in the vertical direction and ±1.9 μm in the lateral direction, respectively     

Optical waveguides in SIMOX structures

Propagation characteristics determined experimentally and theoretically for planar optical waveguides formed in separation by implantation of oxygen (SIMOX) structures are discussed. All samples were found to support both TE and TM modes at both 1.15 μm and 1.523 μm with a lowest propagation loss of 8 dB/cm. This loss was measured at a wavelength of 1.15 μm for the TE₀ mode of a planar waveguide with a 2.0-μm-thick Si guiding layer     

Efficient Nd:YAG slab longitudinally pumped by diode lasers

An efficient scalable 1.06-μm continuous-wave (CW) Nd:YAG slab laser longitudinally pumped by diode lasers is discussed. The 809-nm diode radiation is focused into every laser channel emerging from the reflection points of the 1.06-μm beam on the coated slab surfaces. A maximum CW TEM₀₀ output power of 675 mW has been obtained at a diode pump power of 2 W resulting in a slope efficiency of 40%     

Coherent laser radar at 2 μm using solid-state lasers

The development of a coherent laser radar system using 2-μm Tm and Tm, Ho-doped solid-state lasers, which is useful for the remote range-resolved measurement of atmospheric winds, aerosol backscatter, and differential absorption lidar (DIAL) measurements of atmospheric water vapor and CO₂ concentrations, is described. Measurements made with the 2-μm coherent laser radar system, advances in the laser technology, and atmospheric propagation effects on 2-μm coherent lidar performance are discussed. Results include horizontal atmospheric wind measurements to >20 km. vertical wind measurements to >5 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km     

A BiCMOS process utilizing selective epitaxy for analog/digitalapplications

A 2-μm BiCMOS process that has been designed for 10-V analog/digital applications is described. This process utilizes selective epitaxial growth to integrate a vertical n-p-n bipolar with an f_T of 3.0 GHz, and a nonoptimized vertical p-n-p structure into a 2-μm CMOS process with poly-to-n⁺ capacitors. The insertion of the bipolar structures is accomplished with only two added masking steps, and with no changes to the critical process parameters that determine the performance of the MOS transistors. The circuit worthiness of the process is demonstrated by fabricating CMOS, vertical n-p-n RTL, and vertical p-n-p RTL ring oscillators, and demonstrating high yields for these circuits     

LD optical switch with polarization insensitivity over a widewavelength range

A double-heterostructure (DH) laser with TM mode lasing has been achieved with a narrow active-layer width, and a laser-diode optical switch (LDSW) module with less than a 0.35-dB gain difference between the TE and TM modes over a wide wavelength range has been constructed by introducing a square bulk active layer formed by dry etching and regrowth. The polarization-insensitive width of a 0.3-μm-thick DH laser is clarified to be between 0.30 and 0.35 μm, since the 0.30- and 0.35-μm-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-μm-thick LDSW is estimated to be about 0.32 μm for the fabricated LDSW with a trapezoidal active layer by measuring the single-pass gain and the gain difference between the TE and TM modes. This must be to within 0.01 μm. A 0.35-μm-wide, 300-μm-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 μm at 20 mA. The gain difference between the TE and TM modes is as low as 0.35 dB, The rise and fall times are 1.0 and 0.55 ns, respectively. The bulk active-layer LDSW module is promising for use as a polarization-insensitive optical-gate switch in optical information systems     

A 64-Mb DRAM with meshed power line

A 64-Mb dynamic RAM (DRAM) has been developed with a meshed power line (MPL) and a quasi-distributed sense-amplifier driver (qDSAD) scheme. It realizes high speed, t_RAS=50 ns (typical) at V_cc=3.3 V, and 16-b input/output (I/O). This MPL+qDSAD scheme can reduce sensing delay caused by the metal layer resistance. Furthermore, to suppress crosstalk noise, a V_SS shield peripheral layout scheme has been introduced, which also widens power line widths. This 64-Mb DRAM was fabricated with 0.4-μm CMOS technology using KrF excimer laser lithography. A newly developed memory cell structure, the tunnel-shaped stacked-capacitor cell (TSSC), was adapted to this 64-Mb DRAM     

The sublinear relationship between index change and carrier densityin 1.5 and 1.3 μm semiconductor lasers

The carrier-induced index change was measured using a novel injection-reflection technique in combination with differential carrier lifetime data. The observed relation between index change and injected carrier density at bandgap wavelength is nonlinear and is approximately given by δn_act=-6.1×10^-14 ( N)^0.66 for a 1.5-μm laser and δn _act=-1.3×10^-14 (N)^0.68 for a 1.3-μm laser. The carrier-induced index change for a 1.3-μm laser at 1.53-μm wavelength is smaller and is given by δn _act=-9.2×10^-16 (N)^0.72      

A kilohertz repetition rate 1.9 μm H2 Ramanoscillator

Raman conversion of a high-repetition-rate Q-switched Nd:YAG laser using a gaseous H₂ Raman medium is reported. With a H₂ cell placed in a focusing intracavity Raman oscillator, 3 W of average power at 1.9 μm was obtained from a 15-W 1.06-μm laser operating at 2 kHz. Although the pump beam was multimode, the Stokes output was diffraction limited. At kilohertz repetition rates, conversion efficiencies were improved with a flowing gas cell which substantially reduced the thermal lensing effect in the Raman medium. A rate equation approach was used to model the intracavity conversion process     

Polarization Effect in Laser Processing of Fine Pitch Link Structures for Advanced Memory Designs

Metal fuses for laser redundant links have been widely used for years in laser repair application to enhance yield. Shrinking design rules in IC fabrication have necessitated decreased fuse pitches in the redundancy circuitry. Current infrared lasers are facing the 2 $mu{hbox{m}}$ pitch barrier due to the diffraction limited spot size and depth of focus capabilities. In this paper, we present experimental results showing how we have achieved successful laser cut processes of future metal fuse structures down to 1.0 $mu{hbox{m}}$ pitch using a combination of the small spot of short wavelength laser and the polarization effect to tightly pitched neighbor structures. Inline polarization with link length minimizes the adjacent link damages and thus improves the energy process window for robust cutting. Electrical measurement data of metal link structures with various pitches, metal width and top passivation thicknesses shows the importance of controlling of top oxide thickness on the fine pitch structure. This enabling technology provides a viable production solution for laser fuse processing down to 45-nm node technology and below.      

Molecular beam epitaxy-grown PbSnTe-PbEuSeTe buried heterostructurediode lasers

Buried heterostructure (BH) PbSnTe-PbEuSeTe lasers with a PbSnTe active layer were fabricated for the first time using a two-stage molecular beam epitaxy (MBE) growth procedure. Lasers with 4-μm-wide and 0.65-μm-thick buried Pb_0.961Sn_Sn0.039Te active layer and Pb_0.985Eu_0.015Se_0.02Te _0.98 cladding layers were grown. Continuous wave (CW) operating temperature of 175 K was measured with CW threshold currents of 1.6 mA (20 K), 13.6 mA (80 K), and 195 mA (160 K). Single-mode operation with 3.0-cm^-1-mode tuning was measured at 1639.8 cm ^-1 emission