Showing papers on "Substrate (electronics) published in 1991"

Stress‐related problems in silicon technology

Abstract: The silicon integrated‐circuits chip is built by contiguously embedding, butting, and overlaying structural elements of a large variety of materials of different elastic and thermal properties. Stress develops in the thermal cycling of the chip. Furthermore, many structural elements such as CVD (chemical vapor deposition) silicon nitride, silicon dioxide, polycrystalline silicon, etc., by virtue of their formation processes, exhibit intrinsic stresses. Large localized stresses are induced in the silicon substrate near the edges and corners of such structural elements. Oxidation of nonplanar silicon surfaces produces another kind of stress that can be very damaging, especially at low oxidation temperatures. Mismatch of atomic sizes between dopants and the silicon, and heteroepitaxy produce another class of strain that can lead to the formation of misfit dislocations. Here we review the achievements to date in understanding and modeling these diverse stress problems.

Deposition of device quality, low H content amorphous silicon

Abstract: Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

Process for forming silicon oxide film

Abstract: A process for forming a silicon oxide film comprising the step of depositing a thin film of a silanol, a polymer thereof or a siloxane polymer, each containing an organic group, on a substrate by exciting a gas containing an organosilane or organosiloxane gas and a gas containing H and OH on a substrate in a reaction chamber to cause a reaction in a gas phase or on the substrate and the step of removing the organic group from the thin film by plasma treatment. Preferably the thin film is formed by repeating the depositing step and the removing step in the same chamber and is heat treated at a temperature of 450 °C or below. This process provides a good insulation film having a flatness comparable to that of an SOG film.

III-V nitrides for electronic and optoelectronic applications

Abstract: Recent developments in III-V nitride thin-film materials for electronic and optoelectronic applications are reviewed. The problems that are limiting the development of these materials and devices made from them are discussed. The properties of cubic boron nitride, aluminum nitride, gallium nitride, AlN/GaN solid solutions and heterostructures, and indium nitride are discussed. It is pointed out that the lack of a suitable substrate, with the possible exception of SiC for AlN, is a problem of considerable magnitude. This is compounded by the presence of shallow donor bands in GaN and InN which are apparently caused by N vacancies. The question of whether these vacancies occur (if they do) as a result of intrinsic or extrinsic (as a result of deposition) nonstoichiometry has not been answered. However, the recent advances in the fabrication of p-type GaN and a p-n junction light emitting diode via the electron beam stimulation of the Mg dopant are very encouraging and may considerably advance the technology of this material. This would indicate that self-compensation effects, similar to those observed in ZnO and ZnSe, may not be present in the III-V nitrides, since cubic BN (cBN) AlN and now GaN have been reportedly doped both n- and p-type. >

Novel metalorganic chemical vapor deposition system for GaN growth

Abstract: A novel metalorganic chemical vapor deposition (MOCVD) system, which has two different flows, has been developed. One flow carries a reactant gas parallel to the substrate, and the other an inactive gas perpendicular to the substrate for the purpose of changing the direction of the reactant gas flow. The growth of a GaN film was attempted using this system, and a high quality, uniform film was obtained over a 2 in. sapphire substrate. The carrier concentration and Hall mobility are 1×1018/cm3 and 200 cm2/V s, respectively, which are the highest for GaN films grown directly on a sapphire substrate by the MOCVD method.

Method for forming a thin layer on a semiconductor substrate and apparatus therefor

Abstract: A method and apparatus for manufacturing a semiconductor device having a thin layer of material formed on a semiconductor substrate with a much improved interface between them are disclosed. A silicon substrate is heated up to a temperature around 300° C. in the presence of ozone gas under exposure to UV light. Through this process, organic contaminants that might be present on the surface of the silicon substrate are dissipated by oxidation, and a thin oxide film is formed on the substrate surface on the other. The silicon substrate with the thin oxide film coated thereon is then heated up to temperatures of 200°-700° C. in the presence of HCl gas under illumination to UV light to strip the oxide film off the substrate surface, thereby exposing the cleaned substrate surface. Finally, HCl cleaned surface of the silicon substrate is coated with a thin layer of material such as monocrystalline silicon without exposing the cleaned substrate surface. The method provides a semiconductor with the thin layer of material formed thereon having a well-controlled, well organized interface between them.

A fully automated hot-wall multiplasma-monochamber reactor for thin film deposition

Abstract: We present a study on the development and the evaluation of a fully automated radio‐frequency glow discharge system devoted to the deposition of amorphous thin film semiconductors and insulators. The following aspects were carefully addressed in the design of the reactor: (1) cross contamination by dopants and unstable gases, (2) capability of a fully automated operation, (3) precise control of the discharge parameters, particularly the substrate temperature, and (4) high chemical purity. The new reactor, named ARCAM, is a multiplasma‐monochamber system consisting of three separated plasma chambers located inside the same isothermal vacuum vessel. Thus, the system benefits from the advantages of multichamber systems but keeps the simplicity and low cost of monochamber systems. The evaluation of the reactor performances showed that the oven‐like structure combined with a differential dynamic pumping provides a high chemical purity in the deposition chamber. Moreover, the studies of the effects associated with the plasma recycling of material from the walls and of the thermal decomposition of diborane showed that the multiplasma‐monochamber design is efficient for the production of abrupt interfaces in hydrogenated amorphous silicon (a‐Si:H) based devices. Also, special attention was paid to the optimization of plasma conditions for the deposition of low density of states a‐Si:H. Hence, we also present the results concerning the effects of the geometry, the substrate temperature, the radio frequency power and the silane pressure on the properties of the a‐Si:H films. In particular, we found that a low density of states a‐Si:H can be deposited at a wide range of substrate temperatures (100 °C≤Ts≤300 °C).

Low temperature thin films formed from nanocrystal precursors

Abstract: Nanocrystals of semiconductor compounds are produced. When they are applied as a contiguous layer onto a substrate and heated they fuse into a continuous layer at temperatures as much as 250, 500, 750 or even 1000° K below their bulk melting point. This allows continuous semiconductor films in the 0.25 to 25 nm thickness range to be formed with minimal thermal exposure.

Low hydrogen content stoichiometric silicon nitride films deposited by plasma‐enhanced chemical vapor deposition

Abstract: We have deposited silicon nitride films by plasma‐enhanced chemical vapor deposition (PECVD) at 250 °C with properties similar to films prepared at 700 °C by low‐pressure chemical vapor deposition (LPCVD). Films are prepared using silane and nitrogen source gases with helium dilution. The film properties, including N/Si ratio, hydrogen content and electrical quality are most sensitive to changes in the silane flow rate during deposition. For films deposited under optimized conditions at a substrate temperature of 250 °C, current versus voltage measurements in metal‐insulator‐semiconductor structures show the onset of carrier injection at 3–4 MV/cm, slightly lower than LPCVD films. When bias‐stressed to 2 MV/cm, capacitance versus voltage measurements show some hysteretic behavior and evidence for positive fixed charge, similar to LPCVD films. For the optimized films: N/Si=1.33±.02; refractive index (λ=6328 A)=1.980±0.01; dielectric constant (1 MHz) ∼7.5; density=2.7±0.1; and the etch rate in 10% buffered ...

Molecular-resolution images of Langmuir–Blodgett films using atomic force microscopy

Abstract: THE ability to prepare thin films of amphiphilic molecules (Langmuir–Blodgett (LB) films) is valuable to many areas of research. In biology they provide models for ideal membranes; the two-dimensional behaviour and structural phase transitions are of fundamental interest in surface physics; and their tribological characteristics suggest potential engineering applications. For determining the structure of these films, the common techniques such as X-ray and neutron scattering are limited to thick ( ≳200 A) multilayers. Thinner films can be studied by transmission electron microscopy and low-energy electron diffraction1,2, but these electron-beam techniques tend to damage thin films. More recently, the scanning tunnelling microscope3 has provided a non-destructive means of investigating the structures of LB films4–6, but as the films are insulating, the interpretation of such images has been controversial. The atomic force microscope7 is not plagued with these ambiguities, as it does not require a conductive sample. Here we present images, with molecular resolution, of LB films of cadmium arachidate deposited on an amorphous silicate substrate. Despite the disorder in the substrate, the films display a periodic structure over large distances (several hundreds of angstroms). This suggests that the adsorbed molecules near the interface are driven to self-assemble primarily, if not solely, by intermolecular forces rather than by dependence on substrate periodicity.

Zeta potential measurements of Ta2O5 and SiO2 thin films

Abstract: Flat-plate streaming potential measurements were carried out on samples of tantalum pentoxide and silicon dioxide. The Ta2O5 samples were 150 nm films on silicon substrates, fabricated by the deposition of tantalum followed by oxidation in pure oxygen at 550°C. The SiO2 samples were 1 μm thick films prepared by steam oxidation of a silicon substrate. The electrolyte used in the measurements was NaCl, at concentrations of 10−1, 10−2, and 10−3 M. The point of zero zeta potential (pHiep) was between 2.7 and 3.0 for the Ta2O5 samples and between 2.6 and 3.2 for SiO2. In both cases, this agrees well with previous literature determinations, and indicates the reliability of the flat-plate method. We observed that the zeta potential of thin films of Ta2O5 was more stable and had less hysteresis than the zeta potential of thin SiO2 films.

Switchable vanadium oxide films by a sol‐gel process

Abstract: Thin polycrystalline films of VO2 and V2O3 were deposited on a variety of substrates using a sol‐gel process. The orientation, microstructure, optical constants, and optical and electrical switching behavior are presented. These films exhibited sharp optical switching behavior even on an amorphous substrate such as fused silica. The method yields reproducible results and is amenable to the coating of large substrates and curved surfaces such as mirrors and lenses.

In situ deposition of epitaxial PbZrxTi(1−x)O3 thin films by pulsed laser deposition

Abstract: Epitaxial thin films of PbZrxTi(1−x)O3 (PZT) with 0≤x≤0.6 have been deposited in situ by pulsed laser deposition from stoichiometric targets onto 〈100〉 oriented single crystals of MgO and SrTiO3. Film composition was extremely sensitive to the substrate temperature and the oxygen deposition pressure. In a high (200–300 mTorr) oxygen ambient, phase‐pure 〈100〉 oriented PZT films (x=0.54) were formed at a substrate temperature of 550 °C on SrTiO3. On MgO, competition between formation of the ferroelectric phase and a nonferroelectric (pyrochlore) phase was observed for compositions near the morphotropic phase boundary (x∼0.54). Polycrystalline PZT films which were 70%–90% PZT were also deposited on Pt coated Si and GaAs under similar conditions.

Surface micromachined pressure transducers

Abstract: Typical IC processing is fundamentally two dimensional; sensors are three-dimensional structures. In surface micromachining, two-dimensional IC processing is extended to sensor structures by the addition of one or more sacrificial layers which are removed by lateral etching. The resulting sensor structures involve the substrate and one or more deposited films which form the intended micromechanical component. The concepts of this type of sensor manufacturing are readily demonstrated by considering absolute pressure transducers in some detail. Absolute pressure transducers involve a vacuum-sealed cavity and a deformation sensing technique. The cavity is formed from the substrate and a low-pressure chemical vapor deposited polycrystalline silicon film. The mechanical properties of this film must be controlled well enough to allow the device to be designed. This implies morphological control during processing. Optimized films which do exhibit controlled compressive or tensile strains exclude oxygen or nitrogen and are therefore not modified by extended hydrofluoric acid etches. Their mechanical behavior is monitored by micromechanical test structures which measure Euler buckling and thereby determine the value of the built-in strain. The cavity vacuum is established by reactive sealing. Long-term vacuum integrity is achieved by a low-stress silicon nitride barrier which also acts as a dielectric isolation barrier. Sensing is accomplished via deposited polysilicon resistors. These devices behave like metal resistors in terms of their temperature coefficient of resistance and noise figure. Their piezoresistive behavior is larger than that of typical metal film structures and smaller than that of single-crystal resistors. Pressure sensors with four diaphragms, two active and two inactive, have been constructed and optimized towards manufacturability. The measured performance is excellent and agrees with the predictions of the design algorithm.

Anisotropic Nd–Fe–B thin‐film magnets for milli‐size motor

Abstract: Efforts were made to obtain anisotropic thin‐film magnets at low substrate temperature. This is an important criterion for practical applications such as to build motors. The influence of substrate materials as well as film thickness on the c‐axis orientation were studied. It has been shown that thin‐film magnets with the easy axis of magnetization normal to the film plane could be deposited at a substrate temperature of around 450 °C by choosing the composition near the line from Nd13Fe76B11 to Nd13Fe70B17 in the ternary phase diagram. It was found that the anisotropic film magnets could be also deposited on the metallic substrate. The c‐axis orientation tended to be isotropic with an increase in film thickness. The obtained results were used to fabricate a milli‐size motor by depositing 20‐μm‐thick Nd–Fe–B films on a silicon steel disk substrate of 5‐mm diam. The milli‐size motor exhibited a torque of 0.8 g mm at a rotational speed of 3000 rpm.

Process for preparing a polycrystalline semiconductor thin film transistor

Abstract: A process for preparing a polycrystalline semiconductor thin film transistor wherein a non-singlecrystalline semiconductor formed on a transparent insulating substrate is annealed by laser beams, such process comprising forming a gate insulation layer and a gate electrode on the non-singlecrystalline semiconductor; implanting impurity ions into a source-drain region of the semiconductor wherein the gate electrode is used as a mask, and irradiating laser beams from the rear surface side of the transparent insulating substrate to thereby polycrystallize the non-singlecrystalline semiconductor under the gate electrode or improve the crystallinity of the semiconductor without causing the non-singlecrystalline semiconductor in a completely molten state.

Alignable epitaxial liftoff of GaAs materials with selective deposition using polyimide diaphragms

Abstract: The authors report the selective and alignable deposition of patterned thin-film epitaxial GaAs/GaAlAs devices onto a host substrate such as silicon for low cost, manufacturable hybrid integrated optoelectronic circuits. The authors use a thin polyimide diaphragm as the transparent transfer medium for these patterned epitaxial devices. Each of these devices or a group of these devices on the polyimide is then optically aligned and selectively deposited onto the host substrate. The use of the polyimide transfer diaphragm also allows both the bottom and the top of the device to be processed while under substrate support. Using this technique, a light emitting diode 50*50 mu m in area and 2 mu m thick was grown on a GaAs substrate, lifted off, aligned and selectively deposited onto a silicon host substrate, and electrically contacted and tested. >

SrTiO3 thin film preparation by ion beam sputtering and its dielectric properties

Abstract: SrTiO3 thin films have been prepared on Pd-coated sapphire substrates by ion beam sputtering of a SrTiO3 target, and their dielectric properties have been studied. Oxygen flow introduction was necessary to obtain good insulating films. Dielectric constant er values were 190 and 240 for 430°C and 540°C substrate temperatures, respectively. These er values were not dependent on film thickness in the range from 200 nm down to 50 nm. A 53 nm-thick film indicated leakage current density of less than 10-8 A/cm2 at up to 2 V, along with a 230 er value.

Silicon diaphragm piezoresistive pressure sensor and fabrication method of the same

Abstract: A silicon diaphragm piezoresistive pressure sensor having a diaphragm formed by a single-sided fabrication method. The pressure sensor is made up of a substrate on which there is a diaphragm at or near the surface of the substrate with a chamber under the diaphragm. The pressure sensor is fabricated by undercutting a silicon substrate to form a diaphragm and a cavity within the bulk of the substrate under the diaphragm. The fabricating steps including a) forming a buried low resistive layer under a predetermined diaphragm region; b) converting the low resistance layer into porous silicon by anodization of silicon in a concentrated hydrofluoric acid solution; c) removing the porous silicon by selective etching; d) filling the openings formed in the etching of porous silicon with a deposited material to form a sealed reference chamber. Adding appropriate means to the exterior of the diaphragm and substrate to detect changes in pressure between the reference chamber and the surface of the substrate.

A new bonding technology using gold and tin multilayer composite structures

Abstract: A bonding technology which utilizes chromium, gold, and tin and gold deposited directly on the backside of a device die to form a multilayer composite is reported. The substrate accepting the die is coated with chromium and gold layers. The die and the substrate are brought into contact and heated to 310-320 degrees C. Due to the unique feature of the gold-tin alloy system, the tin layer melts first and dissolves the gold layers of the composite to produce a solution mixed with solid, which in turn would dissolve a portion of the gold layer on the substrate to develop a near eutectic bonding. In the composite, since the tin layer is protected by an outer gold layer in the same vacuum cycle, tin oxidation, which is a major cause of difficulty in achieving quality bondings, is reduced. This technology thus eliminates the requirement of preforms, prevents tin oxidation, and provides precise control of the bonding thickness. Results of bonding 4-mm by 4-mm GaAs dice on alumina substrates show that high-quality bondings are obtained as determined by a scanning acoustic microscope (SAM). >

Effects of Ge concentration on SiGe oxidation behavior

Abstract: The oxidation of SiGe layers grown by molecular beam epitaxy was studied. Auger depth profile showed that after oxidation, Ge was completely rejected from the oxide and Ge‐rich layers were formed. However, the Ge concentration in the SiGe layer was found to play an important role in the formation of these Ge‐Rich layers. For SiGe with Ge concentration below 50%, Si was preferentially oxidized and only one Ge‐rich layer was formed at the oxide/substrate interface. On the other hand, for SiGe with Ge concentration above 50%, two Ge‐rich layers were formed after oxidation with one at the oxide/substrate interface and the other at the oxide surface. X‐ray photoelectron spectroscopy studies showed that Ge at the oxide/substrate interface is in elemental form, while Ge at the oxide surface is in an intermediate oxidized state. A classical binary alloy oxidation theory is employed to explain the overall oxidation behavior qualitatively.

Substrate temperature dependence of electrical properties of ZnO:Al epitaxial films on sapphire (12̄10)

Abstract: ZnO:Al films were deposited on (1210) oriented sapphire substrates heated up to 400 °C by rf magnetron sputtering from a ZnO target mixed with Al2O3 of 2 wt%. Films deposited on a substrate heated to a temperature in the range 50–350 °C were (0001) oriented single crystals but those grown at 400 °C consisted of crystallites with the (0001) and (1101) orientation. The former films had relatively smooth surfaces whereas the latter exhibited very rough surfaces. Electrical properties such as resistivity, carrier concentration, and the Hall mobility were measured as a function of substrate temperature. The carrier concentration decreased as the substrate temperature was increased up to 300 °C, although the Al content remained unchanged in this temperature range. From these measurements, it was found that the native donors were important as a source of carriers, even in ZnO:Al films. However, it was found that the Hall mobilities for films with a thickness of more than 200 nm experienced minor changes over a...

Low emissivity film

Abstract: A low emissivity film which comprises: a substrate; and a coating of oxide and metallic films alternately formed on the substrate in a total of (2n+1) layers where n is an integer being equal to or more than 1, with the innermost layer being an oxide film, wherein the oxide film (B) formed on the outer side of the metallic film (A) being most apart from the substrate, has an internal stress which is equal to, or less than 1.1×10 10 dyne/cm 2 .

Novel metal ion surface modification technique

Abstract: We describe a method for applying metal ions to the near‐surface region of solid materials. The added species can be energetically implanted below the surface or built up as a surface film with an atomically mixed interface with the substrate; the metal ion species can be the same as the substrate species or different from it, and more than one kind of metal species can be applied, either simultaneously or sequentially. Surface structures can be fabricated, including coatings and thin films of single metals, tailored alloys, or metallic multilayers, and they can be implanted or added onto the surface and ion beam mixed. We report two simple demonstrations of the method: implantation of yttrium into a silicon substrate at a mean energy of 70 keV and a dose of 1×1016 atoms/cm2, and the formation of a titanium‐yttrium multilayer structure with ion beam mixing to the substrate.

Organic thin-film element

Abstract: An organic thin film element has a structure in which an organic thin film layer, an insulating layer, and a back electrode are sequentially formed on a substrate obtained by forming an electrode, an insulating layer and a layer consisting of polycyclic aromatic group molecules or a derivative thereof or a carbon layer having a graphite structure on the surface of a substrate main body. An effect of controlling the orientation of the organic thin film layer can be enhanced by the surface layer of the substrate similar in chemical structure to molecules constituting the organic thin film layer. A neutral-ionic transition of a complex can be effectively caused by an electric field applied from the electrodes.

Semiconductor film bolometer thermal infrared detector

Abstract: A thermal infrared detector comprising a dielectric pellicle (5) suspended over a cavity in a substrate (6), the pellicle supporting a detector element (1) comprising a heat sensitive semiconductor layer (3) between a pair of thin film metallic contacts (2, 4), these being deposited on the pellicle, the cavity being formed by etching and removal of the substrate material through holes or slots (8) in the surface of the substrate.