Deterioration of insulating films on silicon wafer due to surface charging during ion implantation

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1 μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35 keV As⁺ at the beam currents of 1 mA to 10 mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide were influenced by the beam distribution.     

Nondestructive evaluation of the semiconductor interface states' density using the transverse acoustoelectric voltage

Nondestructive determination of the interface states' density (D_it) is presented. The measurement technique, utilizing the surface acoustic waves, is applied to silicon/thermal oxide structure. The detected signal is the transverse acoustoelectric voltage amplitude (TAV) which is monitored as a function of the applied bias voltage (TAV-V). D_it is measured by comparing the theoretical and experimental TAV-V curves. The calculation procedure of the D_it and the experimental example are presented.     

The effect of cleaning procedures on surface charging of varioussubstrates

Contact electrification occurs when two dissimilar materials are brought into contact, Each surface is left positively or negatively charged depending on the relative difference between surface state electron density in each material. A technique is described which measures the current generated when two solid surfaces are abruptly brought into contact and the current that results when they are subsequently separated. The theory of metal-insulator contacts forms the basis for this unique measurement. The technique allows measurement of surface charging of a variety of substrates after immersion in solvents used in routine semiconductor wafer cleaning and deionized water (DI) rinsing. Quantitative results are used to describe the effect of cleaning on generation of surface charge. Advantages of this technique are its simplicity and the fact that the measurement requires much less time than conventional charge measurement techniques, All the substrates in this study were significantly charged by immersion in deionized water. Charging due to immersion in isopropyl alcohol (IPA) was significantly lower than charging due to immersion in deionized water. Surface charging after immersion in other solvents could be reduced or eliminated by making isopropyl alcohol the final rinsing agent     

Initial stages of gold adsorption on silicon stepped surface at elevated temperatures

Experimental study performed by ultrahigh vacuum reflection electron microscopy and atomic force microscopy reveals step instability on Si(111) surface during gold deposition at elevated temperatures (higher than 900°C). Our results show that transformations of regular atomic steps into the system of step bunches and vice versa depend on the gold coverage and direction of the electrical current heating the sample. The mechanism and conditions of the surface morphology transformations are discussed. The text was submitted by the authors in English.     

Effect of adsorption of the donor and acceptor molecules at the surface of porous silicon on the recombination properties of silicon nanocrystals

The effect of adsorption of the donor and acceptor molecules on the spectra of photoluminescence and electron spin resonance (ESR) of microporous silicon is studied. It is found that photoluminescence of microporous silicon is quenched, the photoluminescence peak shifts to shorter wavelengths, and the intensity of the ESR signal increases after adsorption of molecules of nitrogen dioxide and pyridine. The results obtained are interpreted using a model of radiative excitonic recombination in porous silicon that takes into account the formation of both the charged (NO₂)^? and (C₅H₅N)⁺ complexes and defects (e.g., dangling bonds at the silicon surface) at the surface of silicon nanocrystals.     

The effect of surface species on the photoluminescence of porous silicon

The photoluminescence of porous Si immersed in alcohol exhibits a blue shift and a marked decrease in intensity relatively to dry, as-anodized wafers. However, when the immersed samples are treated with ultraviolet (UV) light for a few minutes, the photoluminescence (PL) peak shifts to longer wavelength. Fourier transform infrared spectroscopy reveals that alkoxy surface species and silicon hydride species backbonded to oxygen atoms appear on the UV-treated samples. Furthermore, the PL characteristics and surface species of the UV-treated samples can be recovered to those of as-anodized wafers by dipping in hydrofluoric acid. These results point out the importance of surface chemistry in the luminescence process of porous Si.     

牛血清蛋白在亲水硅片表面吸附的原子力显微成像

本文用原子力显微术（AFM）研究了牛血清白蛋白（BSA）在亲水硅片表面的吸附，硅片表面经亲水处理后，将牛血清蛋白（BSA）吸附在表面，采用轻敲模式，可获得清晰的AFM图像，牛血清蛋白（BSA）的AFM图像表明：BSA在亲水硅片表面是单分子，水平吸附在硅片表面，且吸颗粒状；1mg/ml的BSA在吸附30min后为饱和吸附。BSA到达硅表面后，蛋白中可移动的带正电荷的基团可以趋向亲水表面，使BSA与硅表面的静电相互作用由斥力变为吸引力，BSA可以稳定地吸附在亲水硅片表面。     

The effect of the dynamic adsorption mode on impedance of composite structures with porous silicon

Impedance and optical properties of pressed composites based on microcrystalline and nanoporous silicon powders were studied. Porous silicon crystallites were obtained by stain etching of initial microcrystalline silicon powder. Oxygen passivation of the surface during porous-powder formation provided stability of composite characteristics. An analysis of experimental dependences of the impedance in a frequency range of 1–10⁶ Hz allowed separation of contributions of grain bulk and crystallite interfaces to the total composite conductivity. The results of the study of the time dependences of the impedance were used to determine the variation rates of electrical parameters of composite structures under dynamic adsorption-desorption influence of external reactants (H₂O and C₂H₅OH).     

The effect of surface roughness on the radiative properties ofpatterned silicon wafers

The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications     

The effect of adsorption on the electrical properties of structures based on oxidized porous silicon

The effect of adsorption of hydrogen-sulfide and acetone polar molecules on current-voltage characteristics and time dependences of the current was studied for the 〈Pd-por-Si(O)-p⁺-Si-Al〉 structures based on oxidized porous silicon. Structures of two types were obtained—those with a Schottky barrier and those with space-charge-limited currents. The presence of a positive space charge was found near the palladium electrode; this charge defined the current-voltage characteristics in the region of V<0.2 V and varied appreciably depending on the gas used. The parameters of the layer of oxidized porous Si and the range of operating voltages corresponding to the most marked effect of a gas were determined. A maximum current variation up to 10³ times under the action of hydrogen sulfide with a concentration of ～10 ppm was obtained for the structures with the Schottky barrier with a reverse voltage close to that of reversible breakdown. The results obtained are explained by the charge exchange of traps, which is corroborated by a Fermi level shift and a Schottky barrier lowering caused by the adsorption of polar molecules.     

Redistribution of deep selenium and sulfur impurities in silicon upon surface doping with phosphorus

The study is concerned with the effect of short-term high-temperature heating on Si:Se and Si:S samples, whose surface layers are doped with phosphorus to high concentrations. It is found that the resistivity of the wafers substantially increases deep in the bulk within up to ～10 μm. The experimental data suggest that this effect is due to enhanced diffusion of chalcogen in the presence of the phosphorus-doped surface region. The mechanism of the effect is the injection of nonequilibrium interstitial silicon atoms from the layer heavily doped with phosphorus to the bulk of the sample. This results in a shift of the equilibrium between the concentrations of substitutional and interstitial impurity atoms towards higher concentrations of interstitials and, as a consequence, towards the increase in the relative content of the fast-diffusing interstitial component of the impurity.     

The effect of narrowing of the band gap on surface recombination in silicon

The effect of narrowing of the band gap on the effective surface recombination rates in silicon is studied. It is shown that the effect results in an increase in the effective surface recombination rate if the concentration of charge carriers at the surface is higher that in the bulk; otherwise, the effect causes the rate to decrease. The changes induced by narrowing of the band gap in the open-circuit voltage of solar cells are calculated taking into account the contribution of surface recombination.     

硅氢键对波导表面光滑化影响的理论仿真

低损耗高Q值硅基纳米光波导谐振腔,是高灵敏探测器、生物传感器、光通讯器件等发展的关键。而波导表面粗糙度会造成较大的光传输损耗,是制约硅基纳米光波导谐振腔Q值提高的一个重要因素。降低硅基纳米光波导表面粗糙度已成为光波导器件发展的一个关键问题,氢退火工艺是当前改善波导表面粗糙度的一种关键技术。基于表面硅氢键流密度理论,利用Materials Studio软件模拟氢退火光滑化处理过程中硅与氢之间的反应,搜索反应过渡态,探究硅氢键、温度等因素对反应的影响。结果表明:在高温氢退火氛围下,波导表面硅原子与氢原子之间能够形成硅氢键,且温度越高,在硅氢键作用下表面硅原子迁移速率越快,表面由高能态向低能态过渡,表面光滑化效果越明显。     

Formation of nanoparticles on the silicon surface under the effect of femtosecond laser pulses

Nanoparticles were formed on the surface of single-crystal silicon as a result of irradiation of this surface with femtosecond laser pulses. According to the data of the atomic-force microscopy, the height of these nanoparticles ranges from 2 to 30 nm and their transverse size varies from 70 to 200 nm.     

Variations in the electrical properties of silicon MOS structures with a nanodimensional silicon oxide under the effect of water vapors

The dependences of surface potential and the density of surface states of silicon MOS structures with nanoscale silicon oxide on the humidity of the surrounding gaseous medium were investigated. Based on the model of moisture sensitivity of such structures being in depletion modes and weak inversion, an analytical dependence of the surface potential on the humidity was received and the criteria of its linearity were determined. The validity of the analytical dependence was confirmed experimentally.     

The influence of microwave plasma microtreatment at low adsorption on the nanomorphology of the surface of silicon (100) crystals

The regularities of the effect of highly ionized plasma electron cyclotron resonance (ECR) microwave low-pressure gas discharge on the nanomorphology of the surface of monocrystal silicon with crystallographic orientation (100) and natural oxide coating is investigated. The main characteristic parameters of the nanomorphology of surface and modeling mechanisms of processes providing its modification by low-energy microwave plasma treatment under low adsorption using fluorine reactive gas is considered.     

Observation of surface charging at the edge of a Schottky contact

Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential changes near the Schottky contact of a GaN Schottky diode. After application of a reverse bias, the surface potential near the Schottky contact gradually decreased with time, indicating an increase of band bending. Surface potential traces recorded after turning off the reverse bias indeed revealed increased band bending near the Schottky contact. A higher reverse bias caused a larger increase of band bending. The authors suggest that a reverse bias facilitates electron tunneling at the edge of the Schottky contact by decreasing the potential barrier width. Capture of these tunneled electrons by surface states causes the observed increase of band bending.     

Application of the 1-D silicon limit to varactors

Solid-state varactor performance is evaluated in light of fundamental tradeoffs imposed by semiconductor material. This leads to the important conclusion that the product of Q factor, frequency, tuning range, and breakdown voltage has an upper limit (between 5 and 40 THz/spl middot/V for silicon) that is dictated primarily by semiconductor material parameters, and to a lesser degree on doping level and temperature. This limit is then approached by experimental hyperabrupt profiles with a product of 17 THz/spl middot/V that were fabricated in a SiGe BiCMOS process. Two complementary analysis techniques based on LCR and high-frequency measurements are presented.     

The stability of glazed silicon surfaces to water attack

IBM has developed a glassing technology for the passivation of transistors and diodes. For effective surface protection, the glass should have long-term stability to ambient attack, particularly moisture attack. Since it is difficult to evaluate all glasses under moderate moisture conditions for extended periods, several accelerated tests for determining the stability of glasses to water and humidity were compared. Although the results obtained from exposure of a glassed silicon wafer to boiling water for times ranging from a few minutes to an hour were more severe than those obtained by conventional long-term humidity tests, the results could be correlated. The films were evaluated by infrared spectroscopy and by changes in weight, thickness, and microscopic appearance. It was found that glazed silicon surfaces can best be evaluated for water stability by comparison of the infrared spectra of the films before and after boiling in water. Changes in film thickness or weight was found to be insufficient for a complete evaluation.     

Contamination of silicon surface due to contact with solid polymers

The present research investigates material transfer associated with the contact between polymers and silicon surfaces. Material transfer from a variety of solid polymers (UHMWPE, Teflon, KEL-F, PMMA, Nylon 66, and PEEK) was studied and characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, and by computer image analysis. Experimental results suggest that material transfer is affected by the Hertz contact area. The number of particles and the total particle area increase with an increase in load and a decrease in the Young's modulus. Also, material transfer increases when the contacting surfaces are rougher. Friction appears to be a weak parameter in the material transfer phenomenon. Additionally, hardness is significant only when normal loading is great enough to initiate plastic deformation in the polymer