1,565 research outputs found

    Investigation of low dielectric constant (k) films for deep sub-micron CMOS application.

    Get PDF
    Silica (Si02) thin film on Si with low dielectric constant (k) properties has been systematically prepared and investigated. Two types of this low-k material have been deposited on Si via sol-gel spin-on coating. Filem nipis silika (Si02) yang berpemalar dieletrik rendah endap di atas Si tlah disediakan dan dikaji dengan sistematik. Dua jenis film nipis telah disediakan menggunkan pemutaran sol-gel

    MEMS suljenta kuparin lÀmpöpuristusliitÀnnÀllÀ

    Get PDF
    Copper thermocompression is a promising wafer-level packaging technique, as it allows the bonding of electric contacts simultaneously to hermetic encapsulation. In thermocompression bonding the bond is formed by diffusion of atoms from one bond interface to another. The diffusion is inhibited by barrier forming surface oxide, high surface roughness and low temperature. Aim of this study was to establish a wafer-level packaging process for MEMS (Mi-croElectroMechanical System) mirror and MEMS gyroscope. The cap wafer of the MEMS mirror has an antireflective coating that limits the thermal budget of the bonding process to 250°C. This temperature is below the eutectic temperature of most common eutectic bonding materials, such as Au-Sn (278°C), Au-Ge (361°C) and Au-Si (370°C). Thus a thermocompression bonding method needed to be developed. Copper was used as a bonding material due to its low cost, high self-diffusivity and resistance to oxidation in ambient air. The bond structures were fabricated using three different methods and the bonding was further enhanced by annealing. The bonded structures were characterized with scanning acoustic microscopy, scanning electron microscope and the bond strength was determined by shear testing. Exposing the bond structures to etchant during Cu seed layer removal was found to drastically increase the surface roughness of bond structures. This increase proved detrimental to bond strength and dicing yield and thus covering the bond surface during wet etching is recommended. The native oxidation on copper surfaces was completely removed with combination of ex situ acetic acid wet etch and in situ forming gas anneal. Successful thermocompression bonding process using sputtered copper films was established at a low temperature of 200°C, well below the thermal limitation set by the antireflective coating. The established wafer bonding process had high yield of 97% after dicing. The bond strength was evaluated by maximum shear strength and recorded at 75 MPa, which is well above the MIL-STD-883E standard (METHOD 2019.5) rejection limit of 6.08 MPa.Kuparin lÀmpöpuristusliitÀntÀ on lupaava kiekkotason pakkausmenetelmÀ, sillÀ se mahdollistaa sekÀ sÀhköisten liitÀntöjen, ettÀ hermeettisen suljennan toteuttamisen samanaikaisesti. LÀmpöpuristusliitÀnnÀssÀ sidos muodostuu atomien diffuusiosta liitospinnalta toiselle. Diffuusiota rajoittavat estokerroksen muodostava pinta oksidi, korkea pinnan karheus ja matala lÀmpötila. Diplomityön tavoitteena oli luoda kiekkotason pakkausmenetelmÀ mikroelektromekaaniselle (MEMS, MicroElectroMechanical System) peilille ja MEMS gyroskoopille. Peilin lasisen kansikiekon pinnalla oleva antiheijastava kalvo rajoitti liitÀnnÀssÀ kÀytettÀvÀn lÀmpötilan korkeintaan 250°C:een, mikÀ on alempi lÀmpötila kuin useimpien kiekkoliitÀnnÀssÀ kÀytettyjen materiaaliparien eutektinen piste. EsimerkkinÀ mainittakoon mm. Au-Sn (278°C), Au-Ge (361°C) ja Au-Si (370°C). Kuparin alhainen hinta, korkea ominaisdiffuusio ja hidas hapettuminen ilmakehÀssÀ puoltavat sen valintaa liitÀntÀmateriaaliksi. LiitÀntÀrakenteet valmistettiin kolmella menetelmÀllÀ ja liitÀnnÀn vahvuutta parannettiin lÀmpökÀsittelyllÀ. Liitetyt rakenteet karakterisoitiin pyyhkÀisy elektronimikroskoopin, akustisen mikroskoopin ja liitoslujuus-mittauksen avulla. Liitospintojen altistamisen hapolle havaittiin lisÀÀvÀn pinnankarkeutta ja olevan siten haitallista liitokselle ja laskevan saantoa. Liitospintojen suojaaminen siemenkerroksen syövytyksen aikana on suotavaa. Pintaoksidi pystytÀÀn poistamaan tÀysin suorittamalla oksidin mÀrkÀetsaus jÀÀetikalla sekÀ lÀmpökÀsittely N2/H2 atmosfÀÀrissÀ. Sputteroidut kuparikalvot pystyttiin liittÀmÀÀn onnistuneesti yhteen 200°C lÀmpötilassa, mikÀ on alle anti-heijastavan pinnan asettaman lÀmpötilarajan. TÀllÀ liitÀntÀ menetelmÀllÀ saavutettiin kiekkoliitoksella yhteen liitettyjen sirujen sahauksessa korkea 97% saanto. Liitoslujuus mÀÀritettiin maksimi-leikkausvoiman avulla ja sen suuruudeksi mitattiin 75 MPa. Lujuus oli yli kymmenkertainen MIL-STD-883E standardin (METHOD 2019.5) asettamaan hylkÀysrajaan 6.08 MPa nÀhden

    Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

    Full text link
    Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials. Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits. But, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, alpha-Ta, during thin film deposition. It has long been known that a thin Nb layer permits the room-temperature nucleation of alpha-Ta, although neither an epitaxial process nor few-photon microwave loss measurements have been reported for Nb-nucleated Ta films prior to this study. We compare resonators patterned from Ta films grown at high temperature (500 {\deg}C) and films nucleated at room temperature, in order to understand the impact of crystalline order on quantum coherence. In both cases, films grew with Al2O3 (001) || Ta (110) indicating that the epitaxial orientation is independent of temperature and is preserved across the Nb/Ta interface. We use conventional low-power spectroscopy to measure two level system (TLS) loss, as well as an electric-field bias technique to measure the effective dipole moments of TLS in the surfaces of resonators. In our measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 +/- 0.1 x 10^-5) than non-nucleated (5 +/- 1 x 10^-6) in approximate proportion to defect densities as characterized by X-ray diffraction (0.27 {\deg} vs 0.18 {\deg} [110] reflection width) and electron microscopy (30 nm vs 70 nm domain size). The dependence of the loss tangent on domain size indicates that the development of more ordered Ta films is likely to lead to improvements in qubit coherence times. Moreover, low-temperature alpha-Ta epitaxy may enable the growth of new, microstate-free heterostructures which would not withstand high temperature processing

    Mechanisms of layer-transfer related to silicon-on-insulator structures

    Get PDF
    The objective of this dissertation was to study the mechanisms that affect an efficient hydrogenation process in silicon and to validate a hypothesis concerning the hydrogenation mechanism of pre-implanted silicon wafers under hydrogen-plasma processing. These studies are related to a general process. A trapping layer for hydrogen was introduced by ion beam implantation into the silicon wafer. Next, this wafer was hydrogenated using a hydrogen plasma. It was hypothesized that the trapping layer acts as a getterer for the hydrogen diffusing into the silicon wafer. It was found that a large amount of hydrogen could be absorbed in the trapping layer by hydrogen plasma processing. The depth of layer transfer and surface blistering could be controlled by the trapping layer after annealing. This research focused on the mechanism of hydrogen plasma reacting with the buried, heavily disordered silicon layer, deep level defects in the wafer, and nano-/microcrack growth enhanced by the effect of inertial gas bubbles and hydrogen plasma processing. This dissertation also studied suitable wafer bonding methods for a novel method to produce nanoscale silicon-on-insulator materials. Silicon wafers were implanted by different elements (He, N, Ne, Ar) at appropriate energy. A hydrogen trapping layer formed in the depth of ~100 nm based on calculations. Two different types of trapping layers were formed, one composed of a vacancy cluster, and the other was a gas bubble formation. In the trap layer, there were many vacancies, interstitials and micro-voids. Due to the presence in the plasma of molecular and atomic hydrogen and extremely strong acids H3+ and H2+ the surface of Si wafer could be modified by H+, H2+, H3+ in H-plasma. The surface strained Si-Si bonds were damaged. H2 readily dissociated, bound to the surface and diffused into the Si bulk at low temperatures (150 - 200 °C). At higher temperatures (300- 350°C), the trapped in silane-like species was detrapped, and hydrogen atoms diffused deeper into the Si bulk. When these atoms met the buried disorder layer and bubbles, they formed another Si-H structure and molecular hydrogen accumulated in the interstitial voids. In plasma-ion-immersion-implantation processing, compared with non-implantation samples, less hydrogen was trapped in the disordered structure and many hydrogen was trapped in the internal surface of the voids. Many small defects could be generated in normal H Pill processing. Inertial gas pre-implantation may help remove these small defects and produce good quality transferred layer in the later layer exfoliation. It is found that many voids could be generated in bonding wafers by using only RCA clean activation, annealed at temperature above 200 °C. These voids could not disappear until annealed to above 1050 °C. These voids were induced from dissociated H2 from water and evaporated CHX. Plasma activation and hot nitric acid activation for direct wafer bonding may be a good choice for SOT fabrication

    Characterization of Nano-Porous Si-Cu Composites to Enhance Lubricant Retention Impacting the Tribological Properties of Sliding Surfaces

    Get PDF
    As the expectations for modern machinery\u27s tribological and thermal performances continue to rise, the retention of lubricant on the contact surfaces of their sliding components becomes an increasingly important issue. Friction and wear cause heat-related failures which lead to catastrophic damage to machinery. Evaporation of a lubricant\u27s volatile constituents as well as lubricant migration leads not only to a reduction in lubricant quantity but also in its quality, thus facilitating component failures. In order to enhance component reliability, the surface should incorporate features that actively retain lubricants. The unique properties of nano-porous topographies such as their high surface area-to-volume ratio indicate they hold great potential to address these lubrication issues. Thermodynamics-based numerical models of smooth and nano-porous Si-Cu composite topographies were developed to predict the trends of lubricant retention. Photolithographic processes as well as physical etching and thin film deposition tools were utilized to fabricate smooth and patterned Si-Cu composite sample types. The nano-porous topographies incorporated various nano-pore geometries for determination of the optimum conditions for lubricant retention. Amorphous Si film was deposited on the samples using chemical vapor deposition which served as a surface chemistry modification to examine the film\u27s potential to enhance lubricant retention. Lubricant retention tests were performed using a custom-fabricated apparatus for evaporating lubricant from the sample types. Finally, the model\u27s predictions of lubricant retention trends were compared to actual testing results to examine the validity of those predictions. The predictions of the models were supported by the evaporation testing data obtained from the samples. It was found that surface nano-pores having the proper geometry, in combination with the dehydrogenated amorphous Si surface chemistry, could significantly enhance retention above the one micrometer fluid film thickness typically formed between interacting surfaces of machine components undergoing relative motion. The surface features show potential to prevent many types of mechanical failures, reduce maintenance costs, and achieve higher energy efficiency
    • 

    corecore