Bare Silicon Wafers Research Articles

Dielectric constant measurement of thin films using goniometric terahertz time-domain spectroscopy

Goniometric time-domain spectroscopy (GTDS), employing an ultrashort electromagnetic (EM) pulse technique, has been developed for measuring the dielectric constant of thin films in a broad band of gigahertz to terahertz. An ultrafast optoelectronic system, including an emitter and a detector unit, is constructed with a /spl theta/-2/spl theta/ goniometer. A silicon wafer was analyzed as the reference substrate material. A sharp /spl pi/ phase-shift of the reflected EM wave was observed at the Brewster angle of 73.5/spl deg/ for a bare silicon wafer. The phase shift for a film on the Si substrate is relatively smooth due to its two surfaces' providing a complex reflectance. The dielectric constant of the film on Si, related with angular dependency of the phase shift, can be extracted by means of fitting the curve or measuring slope of the curve near the Brewster angle. The measured dielectric constants of FLARE, TiO/sub x/, and PZT film are reported.

Polymer crystallization in quasi-two dimensions. I. Experimental results

We have used atomic force microscopy to investigate the patterns obtained by isothermal crystallization of quasi-2-D monolayers of poly(ethylene oxide) adsorbed onto bare silicon wafers. These monolayers were prepared by a pseudo-dewetting process. Fingerlike branched structures were observed with a characteristic width which increased rapidly with crystallization temperature. The patterns are explained by a simple model considering the interplay of transport on the surface and the probability of attachment to the crystal. The influence of molecular weight was also studied. The average stem length increases with increasing temperature for the longer polymer. The shorter one crystallized in the (almost) fully extended form for all temperatures investigated. Temperature jumps during crystallization resulted in patterns with two different length scales.

Quantitative study of chemical mechanical planarization process affected by bare silicon wafer front surface topography

Chemical mechanical planarization (CMP) is an enabling technology in the fabrication of advanced semiconductor devices. The surface topography of the starting bare silicon substrate before CMP can have a significant impact on the results of the CMP process, specifically on the uniformity of the oxide film final thickness. The quantitative studies of this phenomenon are just beginning. In this article, a laser based optical scanning measurement was used to determine the front surface topography of the bare silicon substrates prior to thermal oxide growth. Fast two-dimensional mapping of the surface height variation is obtained with very high spatial and height resolution. The one-dimensional cross-section profile extracted from the measurement is demonstrated to have good correlation with the stylus based profiler measurement. A thermal oxide layer was grown and then polished in a high efficiency planarization process on a group of substrates, which had different levels of surface topography variations on the starting surface. A signature match between the oxide thickness variation and the silicon substrate front surface topography was identified. The resultant correlation reveals the potential impact on CMP process window from the starting material due to the degradation of within-die and die-to-die uniformity. Consequently, the product yield could be threatened. The optical topographical measurement using this laser scanning measurement is demonstrated here to be capable of providing fast, vital and unique information critical to achieving satisfactory results in the oxide CMP process.

Study on photon sensitivity of silicon diodes related to materials used for shielding

Abstract Large area silicon diodes used in electronic neutron dosemeters have a significant over-response to X- and gamma-rays, highly non-linear at photon energies below 200 keV. This over-response to photons is proportional to the diode's active area and strongly affects the neutron sensitivity of such dosemeters. Since silicon diodes are sensitive to light and electromagnetic fields, most diode detector assemblies are provided with a shielding, sometimes also used as radiation filter. In this paper, the influence of materials covering the diode's active area is investigated using the MCNP-4A code by estimating the photon induced pulses in a typical silicon wafer (300 μm thickness and 1 cm diameter) when provided with a front case cover. There have been simulated small-size diode front covers made of several materials with low neutron interaction cross-sections like aluminium, TEFLON, iron and lead. The estimated number of induced pulses in the silicon wafer is calculated for each type of shielding at normal photon incidence for several photon energies from 9.8 keV up to 1.15 MeV and compared with that in a bare silicon wafer. The simulated pulse height spectra show the origin of the photon-induced pulses in silicon for each material used as protective cover: the photoelectric effect for low Z front case materials at low-energy incident photons (up to about 65 keV) and the Compton and build-up effects for high Z case materials at higher photon energies. A simple means to lower and flatten the photon response of silicon diodes over an extended X- and gamma rays energy range is proposed by designing a composed photon filter.

Design of Photoresists with Reduced Environmental Impact. 1. Water-Soluble Resists Based on Photo-Cross-Linking of Poly(vinyl alcohol)

The feasibility of a chemically amplified fully water-soluble negative-tone resist based upon the cross-linking of a poly(vinyl alcohol) (PVA) matrix resin has been demonstrated. Two-component resists incorporating PVA and (2,4-dihydroxyphenyl)dimethylsulfonium triflate as a water-soluble photoacid generator were formulated in deionized water and spin-coated onto bare silicon wafers. Negative-tone images were obtained upon irradiation at 254 nm, postbaking, and subsequent development in pure water. The two-component resist suffered from swelling during development, but improved performance was obtained through the addition of a cross-linking agent, hexamethoxymethylmelamine (HMMM). The resulting three-component, water-soluble resist was able to resolve micron-sized images using a 248 nm stepper, at a dose of ca. 200 mJ/cm2. Model studies conducted using 13C NMR monitoring with 2,4-pentanediol as a model for PVA showed that under acidic catalysis HMMM reacts to form active electrophilic species that add to the diol, affording ether linkages with concomitant liberation of methanol.

Low Thermal Budget In Situ Surface Cleaning for Selective Silicon Epitaxy

In this paper, we present a process which provides low thermal budget removal of carbon, oxygen, and chlorine from the silicon surface by annealing the substrate in a vacuum ambient with water and oxygen partial pressures less than 10−9 Torr. Following the in situ clean, silicon was deposited epitaxially, and carbon, oxygen, and chlorine levels at the epitaxy/substrate interface were quantified using secondary ion mass spectroscopy. It was demonstrated that these contaminants were removed from the silicon surface with a 10 s anneal at temperatures as low as 750°C. Both patterned and bare silicon wafers were employed, and the patterns on the surface did not show any effect on the in situ clean efficiency. The impact of chlorine as a contaminant was also studied, and no effect on the in situ cleaning efficiency was observed. Surface roughness was quantified by atomic force microscopy, which revealed that surface roughness on Si〈;100〉 did not increase after in situ cleaning in vacuum. A defect analysis was performed using optical and scanning electron microscopy. A correlation was obtained between the defect density and the carbon levels at the epitaxy/substrate interface. However, electrical device characterization did not show any correlation between different in situ clean temperatures and the n‐channel metal‐oxidation‐silicon field effect transistor leakage current or transconductance.

Noncontact Measurement of Doping Profile for Bare Silicon

In this study, we evaluate the doping concentrations of bare silicon wafers by noncontact capacitance–voltage (C–V) measurements. The metal-air-insulator-semiconductor (MAIS) method enables the measurement of C–V characteristics of silicon wafers without oxidation and electrode preparation. This method has the advantage that a doping profile close to the wafer surface can be obtained. In our experiment, epitaxial silicon wafers were used to compare the MAIS method with the conventional MIS method. The experimental results obtained from the two methods showed good agreement. Then, doping profiles of boron-doped Czochralski (CZ) wafers were measured by the MAIS method. The result indicated a significant reduction of the doping concentration near the wafer surface. This observation is attributed to the well-known deactivation of boron with atomic hydrogen which permeated the silicon bulk during the polishing process. This deactivation was recovered by annealing in air at 180°C for 120 min.

Atomic Force Microscopy and X-ray Reflectivity Studies of Albumin Adsorbed onto Self-Assembled Monolayers of Hexadecyltrichlorosilane

Atomic force microscopy (AFM) and X-ray reflectivity (XR) have been used together to provide a detailed and direct look at the structure of human serum albumin protein adsorbed onto well-characterized self-assembled monolayer (SAM) surfaces at several protein concentrations. The duration of SAM deposition was also varied to investigate the influence of the density of hydrocarbon chains in the SAM on protein binding tenacity. Concurrent study of adsorption to bare silicon wafers with native oxide surfaces provided a comparison with a hydrophilic surface similar to widely studied glass and quartz surfaces. Both AFM and XR measurements showed that after adsorption, rinsing, and drying, the surfaces of all substrates were covered with no more than a single layer of adsorbed protein. Thin dense protein layers were seen for the substrates exposed to protein concentrations of 0.1 and 0.5 mg/mL. Partial surface coverage by protein aggregates having larger thicknesses was seen for substrates exposed to lower conce...

End Group Effects on Adhesion of Perfluoropolyether Lubricants to Solid Substrates

Interfacial interactions of several commercial perfluoropolyether (PFPE) and aromaticmodified lubricants with silicon oxide or carbon substrates were investigated through contact angle measurement, dipping tests, fluorescence spectroscopy and contact-start-stop testing. All commercial lubricants that have not been thermally treated are displaced from the solid substrate by contact with water. Contact angles of water on ZDOL, a PFPE doubly-terminated with hydroxyl groups, spun on silicon and carboncoated wafers were measured as a function of thermal annealing treatment. The adhesion of commercial lubricants to such previously thermally-bonded layers is stronger than to the bare silicon wafers. The thermal reaction of ZDOL on silica gel and carbon was investigated by thermogravimetric analysis and FTIR. The thermal reaction takes place when the baking temperature exceeds 70°C; at least part of this surface-bonding involves condensation of terminal hydroxyl groups with isolated surface silanols. Finally, stiction values for aromatic-modified lubricants are substantially lower than for the unmodified commercial PFPE lubricants, but there are still significant humidity effects.

Crystallization of Adsorbed Polymer Monolayers

We present atomic force microscopy results and corresponding computer simulations on crystallization of quasi-2D monolayers of polyetheleneoxid adsorbed onto bare silicon wafers. Fingerlike branched patterns with a characteristic width $w$ resulted from crystallization at temperatures ${T}_{c}$ below the melting point ${T}_{m}$. $w$ decreased exponentially as $({T}_{m}{\ensuremath{-}T}_{c})$ increased. The patterns are explained by a simple model considering the interplay of transport on the surface and the probability of attachment to the crystal.

Integration of Silicon and Diamond, Aluminum Nitride or Aluminum Oxide for Electronic Materials

AbstractMaterial integration for the formation of advanced silicon-on-insulator materials by wafer bonding and etch-back will be discussed. Wafer bonding allows combining materials that may not be possible to grow on top of each other by any other technique. In our experiments, polycrystalline diamond, aluminum nitride or aluminum oxide films with thickness of 0.1-5 µm were deposited on silicon wafers. Bonding experiments were made with these films to bare silicon wafers with the goal of forming silicon-on-insulator structures with buried films of polycrystalline diamond, aluminum nitride or aluminum oxide. These silicon-on-insulator structures were aimed to address self-heating effects in conventional silicon-on-insulator materials with buried layers of silicon dioxide. The surfaces of the deposited diamond films were, by order of magnitude, too rough to allow direct bonding to a silicon wafer. In contrast the deposited aluminum nitride and aluminum oxide films did allow direct bonding to silicon. Bonding of the diamond surface to silicon was instead made through a deposited and polished layer of polycrystalline silicon on top of the diamond. In the case of the aluminum nitride electrostatic bonding was also demonstrated. Further, the compatibility of these insulators to silicon process technology was investigated.

Improvement of Sensor for Noncontact Capacitance/Voltage Measurement and Lifetime Measurement of Bare Silicon(100)

In order to develop a new field of application and to improve the measurement accuracy, a new sensor for the noncontact capacitance/voltage system [metal-air-insulator-semiconducter method (MAIS method)] was successfully developed. The new sensor fulfilled the guard ring function and eliminated the stray capacitance which influenced the measurement accuracy. The bare silicon wafer just after buffered HF cleaning was measured as an application example and the accumulation and quasi inversion were verified. The apacitance/voltage ( C–V) and capacitance/time ( C–t) curve beheviors of the bare silicon wafer were closely related to the high-density interface states localized in the vicinty of the midgap within the energy gap. Moreover, it was confirmed that the generation lifetime of the bare p-type silicon wafer could be measured by the MAIS method using the new sensor.

Spatially resolved, excited state densities and neutral and ion temperatures in inductively coupled argon plasmas

Spatially resolved, line integrated, excited state densities, and neutral and ion temperatures have been measured in inductively coupled argon plasmas. Absorption spectroscopy was used to measure the line integrated density and temperature of the argon 1s5, 1s4, 1s3, and 1s2 energy levels. Laser-induced fluorescence was used to confirm the neutral temperatures and to measure argon metastable ion temperatures. For rf powers between 50 and 300 W and pressures of 4–50 mTorr, the line integrated density of the 1s5 energy level varied between 1×1016 and 2×1016 m−2. The densities of the 1s4, 1s3, and 1s2 levels were approximately 4–10 times smaller. In the center of the plasma, the ion and neutral temperatures were identical, between 550 and 1000 K for plasma powers between 30 and 240 W and pressures between 4 and 50 mTorr. The neutral temperature had a maximum in the center of the discharge and decreased towards the edge of the discharge. However, the ion temperature increased to between 3000 and 4000 K at the edge of the discharge. Ion drift velocity in the radial direction was between 1×105 and 2×105 cm/s at the edge of the plasma. No significant changes in the spatial density distribution or temperature were observed when either a rf bias was applied to the lower electrode or when the stainless-steel lower electrode was covered with a bare silicon wafer. The addition of nitrogen to the argon discharge resulted in the density of the 1s5 state decreasing by a factor of 2 and the density of the 1s4 state decreasing by a factor of 10. Implications of these measurements on the radial electric fields, radiation trapping, and the energy transport in the plasma are discussed.

Recent Developments in Heteroepitaxial Nucleation and Growth of Diamond on Silicon

After the successful controlled heteroepitaxial nucleation of diamond on 3C-SiC epitaxial films and on bare silicon wafers, respectively, obtained by research groups in the USA and Germany in 1992, considerable technical progress and scientifical understanding in the area of heteroepitaxy of CVD diamond have been achieved. The decisive role of ion bombardment for the bias-enhanced epitaxial diamond nucleation is clearly demonstrated. Cross-sectional high resolution electron microscopic (XREM) investigations show the direct epitaxy of diamond on silicon with a periodic 3-to-2 registry of {111} atom planes of the epitaxial diamond—silicon interface. Although the epitaxial growth is of Volmer-Weber type with slight misorientation, i.e., polycrystalline with epitaxial orientation of individual crystallites, the crystallographical and physical properties of these films represent a significant improvement over the usual randomly oriented films, owing to the reduction of the grain boundary angle distribution width to a few degrees. This paper summarizes results obtained recently in our group in the area of heteroepitaxy of diamond on silicon and discusses problems still to be resolved.

Outdiffusion of impurity atoms from silicon crystals and its dependence upon the annealing atmosphere

The outdiffusion of boron, antimony, and phosphorus from the bare silicon wafer at 1200 °C, especially its dependence upon the annealing atmosphere, has been studied with spreading resistance and secondary ion mass spectroscopy (SIMS). It is found that the boron outdiffusion proceeds when the crystal is annealed in hydrogen, but is completely suppressed in argon even if the doping concentration is as high as 3×1018 cm−3 and the annealing time is as long as 2 h. The dramatic dependence upon the atmosphere has not been observed for the other impurities and is temporarily related with the desorption process of boron atoms from the surface.

Tisi2 Characterization of CVD-Titanium and RTP on a Cluster Platform–an Initial Investigation

AbstractThe silicidation of chemical vapor deposited (CVD) titanium has been investigated utilizing the Materials Research Corporation (MRC) PHOENIX™ cluster-tool platform which incorporated an AST elektronik GmbH cluster RTP chamber. This initial investigation focuses on C49 and C54 TiSi2 phase formation on bare silicon wafers. Equipment description, process results, comparison to classical PVD Ti silicide processing and future investigations will be presented.

Effect of SC-1 Process Parameters on Particle Removal and Surface Metallic Contamination

ABSTRACTThe effect of bath temperature, megasonic power, and NH4-OH:H2O ratio are studied for particle removal efficiency, surface roughness, and surface Fe concentration in SC-1 cleaning solutions. Experimental results are presented which show removal efficiencies better than 97% on bare silicon wafers for optimized process conditions. These results are related to the etch rate of thermal oxides and a model is developed for reducing surface roughness and minimizing Fe contamination levels while maximizing particle removal efficiency.

Flow cell for real time observation of single particle adhesion and detachment

A flow cell was built for observing particle removal from test surfaces in real time. The removal force is the hydrodynamic force exerted on the particle by liquid flowing parallel to the test surface. Particle removal was detected visually either through a microscope or on a video monitor. All experimental results reported here are based on the removal of deposited 10 μm polystyrene (PSL) spheres from one of 3 surfaces: polished aluminum; polished bare silicon wafers (native oxide only); or thertnally oxidized silicon wafers. One of 3 cleaning liquids was used: dilute SC-1, dilute SC-2, or de-ionized water containing 0.01% Micro®. The hydrodynamic removal force was controlled primarily by controlling the liquid flow rate. In all experiments, as the flow rate increased, single polystyrene latex (PSL) spheres detached first, then doublets, then triplets and finally larger agglomerates; that is, the adhesion force increased more rapidly with agglomeration than the hydrodynamic removal force. By applying the...

Sizing Accuracy, Counting Efficiency, Lower Detection Limit and Repeatability of a Wafer Surface Scanner for Ideal and Real‐World Particles

The performance characteristics of a Tencor Surfscan 4000 wafer surface scanner have been evaluated using ideal polystyrene latex (PSL) spheres and irregularly shaped real‐world particles of Si and . The particles were uniform in size and were deposited on bare silicon wafers and used as standard calibration wafers to study the scanner response. Particles in the 0.1 to 1.0 μm diam range were used. The sizing accuracy, counting efficiency, lower detection limit, and count repeatability of the scanner were studied systematically. The full Maxwell's electromagnetic equations also have been solved numerically on a supercomputer to obtain the light‐scattering cross section of the particles on bare silicon wafers. The calculation compares favorably with the experimental results. Because of the high refractive index of silicon, the wafer surface scanner detects Si particles to a considerably smaller size than PSL. The data suggest that Si particles as small as 0.1 μm have been detected by the Surfscan 4000 with 90% counting efficiency even though the nominal lower limit of the instrument is 0.3 μm based on PSL calibration.

Bioactive Silk-Like Protein Polymer Films on Silicon Devices

ABSTRACTCoatings of genetically engineered protein polymers based on the crystalline segment of B. Mori silk fibroinand cell binding domains from extracellular matrix proteins (ProNectin™ by Protein Polymer Technologies, Inc.) were applied to bare silicon wafers used to mimic microcircuit devices. These silicon devices have applications in the stimulation and monitoring of central nervous system activity but need bioactive coatings for integration into nervous tissue. Gel point coating technology was developed by preparing solutions at the onset of phase separation in protein polymer/formic acid/ ethanol systems. Dipping silicon wafer substrates into such solutions produced homogeneous thin protein polymer coatings. Quench coating techniques that create rough surfaces in a controlled manner were explored by driving protein polymer solutions through different regions of the protein polymer/formic acid/methanol system before drying. Atomic force microscopy was used to characterize the protein films.