Oriented Silicon Wafers Research Articles

Fabrication of very smooth walls and bottoms of silicon microchannels for heat dissipation of semiconductor devices

In microchannel fabrication, smooth walls and bottom formation has been an uphill task during micromachining of (110) silicon due to its orientation-dependent chemical etching. A new method to fabricate deep microchannels on (110)-oriented silicon wafers for cooling excessive-heat dissipating semiconductor devices has been developed. Potassium hydroxide, water and isopropanol-based etchants have been used to etch silicon anisotropically for fabricating deep, narrow and smooth-walled microchannels. For etching U-grooved microchannels, (110)-oriented and 500–550μm-thick monitor grade silicon wafers are used. Proper orientation of the pattern to be etched is aligned with reference to the standard flat provided in the wafer. A new method replacing conventional additional plane-finding etching procedure has been developed, where proper orientation is experimentally determined on the given wafer for pattern delineation. Very smooth walls and bottom of about 400μm deep silicon microchannels have been obtained after controlling the etchant composition, temperature and orientation of the masking pattern. In this paper process details are presented along with experimental results. This process has further been used for separating the silicon microchannel chips.

Reproducible Large‐Area Microfabrication of Sub‐100 nm Apertures on Hollow Tips

We report on a silicon‐based microfabrication process to generate apertures with dimensions of less than 100 nm at the apex of hollow silicon dioxide tips. The fabrication process is self‐adjusting and leads to highly reproducible aperture dimensions. It relies substantially on the inhomogeneous thickness distribution and modified etch rate of a silicon dioxide layer thermally grown on structured (001) oriented silicon wafers at relatively low temperatures of about 900–950°C. Process parameters are presented to obtain single or double aperture tips. Once the apertures are fabricated, a further reduction of aperture size below 80 nm is achieved by thin film deposition of, e.g., metal layers or other materials. The possibility of fabricating apertures reliably and reproducibly on large areas, e.g., complete silicon wafers, is emphasized. © 2000 The Electrochemical Society. All rights reserved.

Structural and electrical characterization of epitaxial, large area ferroelectric films of Ba2Bi4Ti5O18 grown by pulsed excimer laser ablation

Excimer laser ablation was used to deposit epitaxial thin films of Ba2Bi4Ti5O18 having mostly c-axis oriented grains. The ferroelectric layer was deposited on an epitaxial conducting oxide electrode layer of LaNiO3, the electrode layer in turn being grown on an epitaxial buffer layer stack on single crystalline (100)-oriented silicon wafers of 3 in. diameter. X-ray diffraction measurements indicate a strong c-axis orientation of the ferroelectric layer. Scanning electron microscopy and atomic force microscopy were used to observe the microstructure of the films and these revealed the homogenous quality of the film with good uniformity over the wafers. Well-defined, saturated ferroelectric hysteresis loops were observed in the compound with values of 1.3 and 0.6 μC/cm2 as saturation and remnant polarization values, respectively, and a coercive field of 47 kV/cm. The results of I–V measurements and complex impedance spectroscopy measurements are presented and a defect formula is proposed for the compound.

Formation of (Nd,Y)-silicides by sequential channeled implantation of Y and Nd ions

A buried hexagonal Nd0.32Y0.68Si1.7 layer is formed by a sequential implantation of Y and Nd ions into (111)-oriented silicon wafers. The orientation relationship between the epitaxial Nd0.32Y0.68Si1.7 and the silicon is (0001)Nd0.32Y0.68Si1.7//(111)Si with 〈112̄0〉Nd0.32Y0.68Si1.7//〈11̄0〉Si. High temperature annealing (1000°C) results in a gradual transition into an orthorhombic ternary (Nd,Y)-silicide. Between the orthorhombic (Nd,Y)-silicide and the Si a preferential orientation relationship exists: (110)orth//(11̄0)Si with 〈001〉orth//〈111〉Si. However, as not all orthorhombic silicide grains follow this epitaxial relationship, the minimum yield in the Rutherford backscattering spectrometry (RBS) spectrum increases compared to the results after a low temperature annealing.

Study of low-temperature direct bonding of (111) and (100) silicon wafers under various ambient and surface conditions

Wafer bonding of commercially available (100) and (111) silicon wafers was performed in the range of temperatures from 80°C to 400°C in nitrogen, oxygen and low-vacuum atmosphere. Surface preparation with modified RCA cleaning method and hot nitric acid provided extremely clean and hydrophilic surfaces that were later brought into intimate contact. Various combinations of surface terminations such as thin chemical native silicon dioxide and thick thermal silicon dioxide on (111)- and (100)-oriented silicon wafers were prepared and investigated. Bonding quality evaluated by the tensile strength measurements showed the highest values obtained for strengthening in nitrogen atmosphere, reaching 12 MPa. Correlation between prebonding treatment, initial surface roughness and microroughness was made revealing the influence on the bonding energy. Interface imperfections of bonded samples were investigated by infrared transmission imaging revealing bubbles at the bonded interface only in case when bonding was performed in oxygen ambient. Thickness of the chemical native oxide after surface preparation step necessary for good bonding was found to be at least 0.8 nm. Wafers in the (111) orientation exhibited higher bonding abilities compared to (100) in case of bonding wafers with native oxides. This is believed to be due to higher density of available bonding sites as a consequence of enhanced chemical oxide growth rate and its homogeneity on (111) surface. Moreover, it is believed that due to higher positive charge of oxides grown on (111)-oriented silicon compared to (100), desorption of interfacial water is accelerated thus increasing the bonding energy at lower temperature. In conclusion, the best bonding results were obtained by bonding wafers with thick thermal oxide to (111) wafers with native oxide and annealed in nitrogen ambient.

Epitaxial growth of alloy Cr(Ni)Si 2 by metal vapour vacuum arc ion source implantation and post-annealing

〈1 1 1〉 oriented silicon wafers were implanted with 50 keV Cr ions using a metal vapour vacuum arc (MEVVA) ion source implanter, the randomly grown disilicide has been formed in the as-implanted samples. Sequential Ni implantation was performed on the samples. Apparently, the second implantation greatly reduces the Cr concentration due to stronger sputtering effect. However, the total areal density of metals is larger. When annealing was performed at moderate temperature, it was found that the Cr+Ni implanted rather than the singly Cr implanted samples develop into a textured phase (Cr(Ni)Si 2). This shows that the introduction of the Ni causes a well-oriented alloy silicide to form on Si(1 1 1).

Comparison between ATLAS forward microstrip detectors made on 6″ (100) and 4″ (111) crystal oriented silicon wafers

The noise seen by the front-end readout electronics of silicon microstrip detectors depends on the capacitive load on each channel and the shot noise due to the reverse current in the detector. Because ofthe short integration time ofthe LHC electronics (25 ns), the shot noise contribution is negligible as long as the current is kept to an acceptable level. However, any inter-strip capacitance increase after irradiation will degrade the noise performances of the detectors. A dependence of the capacitance on the crystal orientation ofthe silicon crystal used as a substrate for silicon detectors has been recently reported (Feld L.et al.,Radiation induced changes in the Interstrip Capacitance of Silicon Microstrip Detectors, 4thROSE Workshop on Radiation Hardening of Silicon Detectors, CERN 2-4 December 1998, Published in CERN/LEB 98-11 (697)). We present here the results ofirradiation ofsilicon microstrip detectors made on 6″ (100) and 4″ (111) crystal oriented silicon wafers in term of inter-strip capacitance and noise, measured using LHC speed binary electronics (LBIC, Spencer E.et al.,IEEE Trans. Nucl. Sci. NS-42 (1995) 796), as a function of bias. A strong dependence ofthe inter-strip capacitance on the bias applied to the detector has been found for the irradiated detectors made on (111) silicon, but this dependence decreases with the frequency of the measurement. At high frequencies, which are the only ones relevant for the noise behaviour ofthe detectors, we found no differences at high bias voltages between the values before and after irradiation for detectors made on silicon with different crystal orientations. The effect on the noise has been checked and at the nominal operation bias we found no measurable differences between detectors made on silicon with different crystal orientations.

The surface/bulk micromachining (SBM) process: a new method for fabricating released MEMS in single crystal silicon

This paper presents the surface/bulk micromachining (SBM) process to allow fabricating released microelectromechanical systems using bulk silicon. The process starts with a [111]-oriented silicon wafer. The structural patterns are defined using the reactive ion etching technique used in surface micromachining. Then the patterns, as well as sidewalls, are passivated with an oxide film, and bare silicon is exposed at desired areas. The exposed bare silicon is further reactive ion etched, which defines sacrificial gap dimensions. The final release is accomplished by undercutting the exposed bulk silicon sidewalls in aqueous alkaline etchants. Because {111} planes are used as etch stops, very clean structural surfaces can be obtained. Using the SBM process, 5-, 10-, and 100-/spl mu/m-thick arbitrarily-shaped single crystal silicon structures, including comb-drive resonators, at 5-, 30-, and 100-/spl mu/m sacrificial gaps, respectively, are fabricated. An electrostatic actuation method using p-n junction isolation is also developed in this paper, and it is applied to actuate comb-drive resonators. The leakage current and junction capacitance of the reversed-biased p-n junction diodes are also found to be sufficiently small for sensor applications. The developed SBM process is a plausible alternative to the existing micromachining methods in fabricating microsensors and microactuators, with the advantage of using single crystal silicon.

Transmission Electron Microscopy Observation of CMOS Devices of Titanium Self-Aligned Silicide Technology with Nitrogen (N+) Implantation Process

TiSi2 is widely used as contact, gate and interconnect material in high-performance metal-oxide-semiconductor (MOS) devices because of its low resistivity (15±20 iU-cm) [1], high-temperature stability and ` self-aligned'' properties [2, 3]. The rapid scaling in device dimensions necessitates the use of low resistivity materials for interconnects and also for back-end metallization. The implementation of the Ti self-aligned silicide (SALICIDE) process becomes increasingly dif®cult, however, especially at the deep sub-micron regime as a result of the well-known ` ®neline effect'' [4, 5]. Hiroshi [6] reported that lowleakage and low-resistance sub-micron silicided complimentary metal oxide semiconductor (CMOS) devices are achievable through Ti SALICIDE technology with recoil nitrogen ions, which were introduced through a contamination-restrained, oxygen-free, lowpressure, chemical-vapor-deposited nitride layer. In this work, we directly implanted nitrogen ion (N‡) to understand the bulk effects of deeply implanted nitrogen. Cross-sectional transmission electron microscopy (XTEM) analysis was performed to investigate the changes associated with N‡ implantation in the Ti SALICIDE process and to relate these changes to the electrical properties observed. In this experiment, a p-type (1 0 0)-oriented silicon wafer was used as the substrate for device fabrication. Nitrogen ions (N‡) with 5 3 10 ions cmy2 dosage and 80 keV energy were introduced through ion implantation. The projected range (Rp) of the N‡ implantation was about 0.2 im based on transport of ions in matter (TRIM) 90 simulations. Subsequently, a single layer of 70 nm Ti was deposited by physical vapor deposition (PVD) followed by a ®rst rapid thermal anneal (RTA) at 690 8C and second RTA at 850 8C to form the ®nal C-54 phase TiSi2 ®lm. Fig. 1 is a XTEM image of the control specimen, i.e., without N‡ ion implantation. The thickness of the C-54 TiSi2 ®lm is about 91 nm. No signi®cant defects were observed in this specimen. For the N‡implanted specimen, we observed (1) a thicker C-54 phase TiSi2 ®lm on the narrow poly-Si gate, (2) defects near the spacer and ®eld oxide and (3) two layers of end-of-range (EOR) defect in the underlying Si substrate. All these observed abnormalities are likely to in uence the device performance.

Growth of high-quality buried Y- and (Y, Nd)-silicide layers prepared by channelled ion implantation

A buried hexagonal YSi 1.7 layer is formed by channelled implantation of Y ions into (1 1 1) oriented silicon wafers. The orientation relationship between the epitaxial YSi 1.7 and the silicon is (0 0 0 1) YSi 1.7 ‖(1 1 1) Si with 〈1 1 2 ̄ 0〉 YSi 1.7 ‖〈1 1 ̄ 0〉 Si . Annealing at 600°C for 1 h and subsequently at 1000°C for 0.5 h improves the crystalline quality of the buried YSi 1.7 layer. On the other hand, Nd-disilicide cannot be grown epitaxially on a Si(1 1 1) substrate. However, by using a sequential implantation of Y and Nd ions, a buried hexagonal Nd 0.32Y 0.68Si 1.7 layer with good crystalline quality is formed in the Si(1 1 1) substrate.

Ion beam synthesis of Ni–Fe–Si layer by TEM

Nickel and iron ions were selected to be implanted sequentially into (100) orientation silicon wafers to synthesize Ni–Fe–Si ternary silicide film. By using the metal-vapour vacuum-arc ion-implantation system MEVVA 80-10, a ternary silicide layer of γ-Fe 0.6Ni 0.4Si 2 with CaF 2 structure has been formed at implantation conditions of 7×10 16 Ni ions cm −2 and 1.4×10 17 Fe ions cm −2. With increase in annealing temperature, the grain size in the layer grows and the γ phase is decomposed into nickel-rich and iron-rich phases. In the temperature range from 500 to 600 °C, a valuable structure of β-Fe 0.6Ni 0.4Si 2/CaF 2-Fe 0.35Ni 0.65Si 2/Si can be obtained. At proper annealing conditions, the γ phase is decomposed into NiSi 2 and FeSi 2 phases. The morphology evolution of Ni–Fe–Si ternary silicide with increasing annealing temperature ranges from the layer thickness increasing to the film shrinking into isolated islands at 850 °C.

A micromachined vibration isolation system for reducing the vibration sensitivity of surface transverse wave resonators

A micromachined system has been developed for reducing the vibration sensitivity of surface transverse wave (STW) resonators. The isolation system consists of a support platform for mounting the STW resonator, four support arms, and a support rim. The entire isolation system measures 8 mm by 9 mm by 0.4 mm without the resonator mounted on the platform. The system acts as a passive vibration isolation system, decreasing the magnitude of high frequency (>1.2 kHz) vibrations. Finite element analysis is used to analyze the acceleration sensitivity of the mounted resonator. The isolation system is then modeled as a damped mass-spring system and the transmissibility of vibration from the support rim to the support platform is calculated. Multiplying the acceleration sensitivity of the resonator by the transmissibility results in the expected system vibration sensitivity. The isolation systems are fabricated using two sided bulk etching of (110) oriented silicon wafers. STW resonators were mounted on the isolation systems, and the isolated units were mounted on commercial hybrid oscillator substrates. Vibration sensitivity measurements were taken for vibrations with frequencies ranging from 100 Hz to 5 kHz. The measured data show that the system performs as expected with a low frequency (<500 Hz) vibration sensitivity of 1.8x10(-8)/g and a high frequency roll off of 12 dB/octave.

Optical reflectivity of micromachined {111}-oriented silicon mirrors for optical input - output couplers

In this work, bulk-micromachined -oriented silicon mirrors at have been fabricated in 20 wt% KOH solution at various temperatures and characterized with single-mode fibers (10/125 and 5/125). In fabricating the mirrors, the etch rate of the (100) silicon surface was widely varied from 5.3 to as the processing temperatures were varied from 40 to C. In spite of the tremendous variation of etch rate, the measured reflectivities of the mirrors showed fairly stable values of 63.7 - 58% at 1330 nm and 55.4 - 57.7% at 1550 nm. This paper describes the silicon mirror processing conditions, measured reflectivities, reflected beam profiles, and a prototype integrated optical I - O coupler with the realized mirrors. The results obtained from this work show that optical I - O couplers with mirrors on conventional (100)-oriented silicon wafers are feasible, enabling us to envisage a synchronized optical clock distribution system as well as a distributed remote optical sensing system with low manufacturing cost.

RF plasma treatment of porous silicon

The effect of oxygen and hydrogen rf plasmas on the photoluminescence (PL) spectra of porous silicon (PS) was studied. PS samples were prepared from p-type, (100) oriented silicon wafers with a resistivity of 0.03 Ω cm by electrochemical anodization in an ethanol-containing solution. The plasma treatments were carried out in a planar reactor for 150 min, whereas the samples were placed on the ground electrode and heated to 250°C. The PL was excited by the 548 nm line of Hg lamp and measured using a monochromator and lock-in amplifier. Both hydrogen and oxygen plasma treatments led to a decrease in PL intensity. The decrease was with a factor of 5 after hydrogen and 2.5 after oxygen plasma treatment. It was established by means of Auger electron spectroscopy (AES) that both plasma treatments led to an increase in the oxygen content and to a decrease in the carbon content on the PS surface. However, no direct correlation between the AES data and the PL intensity could be established. We suggest that the appearance of plasma-induced electronic defects, rather than the change in the surface chemistry, accounts for the PL quenching.

An SEM on a Chip

A silicon microfabrication technique has been applied toward the development of a Miniature Scanning Electron Microscope (MSEM). The fabrication technology is not only precise but is inexpensive compared to conventional methods of electron microscope construction and is easily extended to the construction of arrays of MSEMs for applications in high throughput e-beam lithography and wafer inspection.An electrostatic electron lens consists of a series of planar electrodes with central apertures that are precisely aligned to and electrically isolated from one another. This structure is fabricated using silicon as the electrode material and Pyrex optical fibers as the insulators. The electrodes are fabricated on four inch (100) orientation silicon wafers that are patterned on both sides and anisotropically etched to form four orthogonal v-grooves and an open diaphragm with a circular aperture in the center. The apertures are formed by reactive ion etching. The wafers are then diced to create approximately 100 7 mm by 9 mm electrodes.

Microstructural studies of Fe-silicide films produced by metal vapor vacuum arc ion implantation of Fe into Si substrates

Iron-silicide films have been formed by metal vapor vacuum arc (Mevva) ion implantation of iron into (111) and (100) oriented silicon wafers. In the as-implanted samples with a dose of 1 × 10 17 ions/cm 2, metastable γ-FeSi 2 is the dominant phase accompanied by a small fraction of the CsCl-derived defect phase Fe 1 − x Si. The silicide grains form a surface layer on (111) silicon, whereas they are embedded in (100) silicon substrate at a depth of 30 nm. In the samples with a higher dose of 4 × 10 17 ions/cm 2, a primitive orthorhombic FeSi 2 phase is formed. Some grains with this new structure contain stacking faults which are lying on (100) planes.

Preparation of highly c-axis-oriented Bi 4Ti 3O 12 thin films and their crystallographic, dielectric and optical properties

Bismuth titanate (Bi 4Ti 3O 12) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi 2TiO 5 ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi 4Ti 3O 12 film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm −2 and 20 kV cm −1, respectively.

Preparation and characterization of highly c-axis-oriented Bi 4Ti 3O 12 thin films

Highly c-axis-oriented bismuth litanale (Bi 4Ti 3O 12) thin films were prepared on (100)-oriented silicon wafers by rf planar magnetron sputtering using a target of Bi 2TiO 5 ceramic at a low substrate temperature of 600 °C. The films with a c-axis orientation up to 99%. were obtained under high deposition rate approximately 1.1 μm h 1. Dielectric constant of these films were dependence of film thickness. This behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the dielectric constant of Bi 4Ti 3O 12 film was estimated to be approximately 140. This value is similar to that along the c-axis in a bulk form. A D E hysteresis characteristic has been observed at room temperature. The remanent polarisation and the coercive field are 0.8 μC cm 2 and 20 kV cm 1. respectively. From analysis of refractive index, interface layer was confirmed an oxidixed silicon, which was formed before and or during film deposition.

Preparation and Characterization of Ferroelectric Bi 4Ti 3O 12 Thin Films Grown on (100)-Oriented Silicon Wafers

Ferroelectric bismuth titanate (Bi4Ti3O12) thin films were prepared directly on (100) silicon substrate by rf planar magnetron sputtering using a Bi2TiO5 ceramic target. Highly c-axis-oriented films were obtained at a high deposition rate of about 17 nm/min. The deposited thin films, consisting of plate-like grains about 2 µm in diameter, were grown uniformly parallel to the substrate surface. The remanent polarization (P r) and the coercive field (E c) of this film at 50 Hz were estimated to be 0.8 µC/cm2 and 20 kV/cm, respectively.

Properties of Ferroelectric BaMgF4 on Si(100), (110) and (111) Substrates Obtained by Post-Deposition Rapid Thermal Annealing

Substrate orientation dependence of metal-ferroelectric BaMgF4-silicon capacitors obtained by post-deposition rapid thermal annealing was investigated. Fluoride films were deposited on Si(100)-, (110)- and (111)-oriented wafers in an ultrahigh-vacuum system at a substrate temperature of 300°C. Post-deposition annealing was conducted for 10 s at 600°C. The resistivity of the ferroelectric BaMgF4 film increased from a typical value of 1–2×1011 Ω\\cdotpcm before annealing to about 5×1013 Ω\\cdotpcm at 1 MV/cm, and the interface state density of the BaMgF4/Si interface decreased to 5–8×010/cm2·eV. Apparent remanent polarizations of BaMgF4 films on (100)- and (111)-oriented silicon wafers were about 0.5–0.6 µC/cm2 and that of film on the (110) wafer was about 1.2 µC/cm2.