bluuebunny/crossref_metadata_2025 huggingface dataset:
Focused ion beam machining of Si, GaAs, and InP
Authors: Pellerin J. G. , Griffis D. P. , Russell P. E.
Published: July 2002

The focused ion beam (FIB) has been demonstrated as a precision fabrication tool for a wide variety of applications, primarily for semiconductor related processing. In order to facilitate the practical utilization of this tool, the Ga+ FIB micromachining characteristics of Si (100), Si(111), GaAs (100), and InP (100) were investigated. Rectangular wells having dimensions of 4×10×1 μm were sputtered into the above materials at 15 and 25 keV and dwell times ranging from 25 μs to 100 ms per point for a fixed total machining time. Planview and cross section scanning electron microscope examination was used to quantify sputter yield and characterize feature shapes. Sputter yield and material redeposition variations dependent on beam dwell times were observed as evidenced by changes in side wall slope, crater bottom flatness, and material redeposition.
Imaging surface atomic structure by means of Auger electrons
Authors: Hubbard Arthur T. , Frank Douglas G. , Chyan Oliver M. R. , Golden Teresa
Published: July 2002

It has recently been demonstrated that the surface atomic structure of single crystals, monolayers, and thin films can be imaged by means of Auger electrons. Angular distribution Auger microscopy (ADAM) produces subatomic resolution images of atomic structure by measuring and displaying the complete angular distribution of low-energy Auger electrons emitted from atoms near the surface of a substrate or thin film. Auger angular distributions contain the silhouettes of surface atoms backlit by emission from atoms located deeper in the solid, revealing the relative positions of atoms near the surface. High-energy Auger electrons have a larger escape depth and are therefore less surface sensitive but contain crystallographic information, particularly the locations of channels in the crystal. Consequently, ADAM is a powerful new technique for the characterization of semiconductor surfaces and epitaxial thin films, and also for fundamental studies of electron physics provided that certain important experimental criteria are met. Described here are recent applications of ADAM to probing the structures of single-crystal surfaces and thin films.
Electron-stimulated desorption of chlorine from GaAs(100) surfaces
Authors: Mokler S. M. , Watson P. R. , Ungier L. , Arthur J. R.
Published: July 2002

We have characterized the removal of chlorine adsorbed on GaAs (100) surfaces by electron-stimulated desorption (ESD). Such processes may form the basis for the use of electron beams as a focused energy source for high-definition assisted etching. We find that chlorine adsorbed on a GaAs(100) surface is sensitive to ESD and that loss of chlorine proceeds via two processes on different time scales. Furthermore, chlorine adsorbed on areas of the surface that have not been under the influence of the electron beam does not diffuse at a detectable rate into areas stripped of chlorine by ESD. We have determined mass spectrometrically that, under low chlorine coverage conditions, ESD products consist solely of chlorine atoms, although it is possible that under a high chlorine flux etching may occur.
Intersubband absorption in Si1−xGex/Si superlattices for long wavelength infrared detectors
Authors: Rajakarunanayake Y. , McGill T. C.
Published: July 2002

We have calculated the absorption strengths for intersubband transitions in n-type Si1−xGex/Si superlattices. These transitions can be used for the detection of long-wavelength infrared radiation. A significant advantage in Si1−xGex/Si superlattice detectors is the ability to detect normally incident light; in Ga1−xAlxAs/GaAs superlattices intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. We present detailed calculations of absorption coefficients, and peak absorption wavelengths for [100], [111], and [110] Si1−xGex/Si superlattices. Peak absorption strengths of about 2000–6000 cm−1 were obtained for typical sheet doping concentrations (≊1012 cm−2). Absorption comparable to that in Ga1−xAlxAs/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.
The effects of broadband 250 nm illumination on process latitude
Authors: Kuyel Birol , Sewell Harry
Published: July 2002

The effects on lithography of the spectral bandwidth of the illumination used in an optical step-and-scan projection aligner have been studied J. Buckley and C. Karatzas, SPIE 1088, 424 (1989). An illumination bandwidth of 240–255 nm is compared with a single wavelength of 248 nm representing mercury–xenon lamp and excimer-laser spectra, respectively. Linewidth control for resist-thickness variations, resist-profile effects, and linewidth stability on topography are reported. The experimental results on critical-dimension variations were obtained from tests run on a deep-UV 0.35 numerical aperture (NA) 4× step-and-scan system using the Shipley XP89-142 negative resist system, and on a 0.35 NA 5× excimer stepper using both SNR248 and XP89-142 (SNR248-3×) resist. An HP 8450 photospectrometer was used to study resist reflectivity variations with wavelength and thickness. Both SEM and electrical-probe measurements are reported. It is demonstrated that resist thickness variations cause larger critical-dimension variations in monochromatic exposures than in broadband exposures. It is shown that the critical-dimension variation due to resist-thickness variation over topography reduces the process window, particularly in the case of monochromatic illumination. It is also demonstrated that the full benefit of the spectral width of the broadband illumination is only achieved when the illumination source spectrum, the deep-UV filter-transmission characteristics, and the resist transmission are all matched.
Commissioning of aurora: The smallest synchrotron light source
Authors: Yamada H.
Published: July 2002

The first synchrotron light from the smallest storage ring Aurora was observed on November 2, 1989. We have established a half-integer-resonance injection method. The electron energy is successfully boosted up to 650 MeV without exciting the prepared resonance jumper. The stored current is presently limited by performance of the injector microtron which produces 10 μA on average, but we could accumulate 45 mA because of very large acceptance of the ring. The measured lifetime is 20 h when the vacuum pressure is better than 1×10−9 Torr. The observed beam size is 1.2(0.14) mm in radial (vertical) direction. Remodeling of the injector is in progress.
Design of a high-current-density focused-ion-beam optical system with the aid of a chromatic aberration formula
Authors: Kawanami Yoshimi , Ohnishi Tsuyoshi , Ishitani Tohru
Published: July 2002

A 30-kV high-current-density focused-ion-beam optical system using a liquid metal ion source, has been designed for micromachining under the following restrictions: (1) all inter-electrode voltages are less than the acceleration voltage; (2) the sample and deflectors are not biased; (3) working distance is longer than 20 mm; and (4) the beam has an intermediate crossover. The design guidelines were obtained from an analysis of the chromatic aberration formula. The system has a tetrode condenser lens (zoom lens) and an einzel objective lens, each of which is made up of thin Butler-type lens electrodes. Both of the lenses are used in the deceleration mode. Calculated beam current density of the system is 1–10 A/cm2 in a wide range of beam diameters of 0.04−2 μm.
Experimental performance of a large-diameter multipolar microwave plasma disk reactor
Authors: Sze F. C. , Reinhard D. K. , Musson B. , Asmussen J. , Dahimene M.
Published: July 2002

Microwave electron-cyclotron-resonance (ECR) discharges have demonstrated excellent potential for single-wafer etching and thin-film deposition. An important technical challenge is concerned with controlling uniformity of processing over large surfaces with high processing rates and minimal damage. The ability to scale microwave plasma disk reactor (MPDR) ECR discharges to large diameters is reviewed and the design and experimental performance of two plasma sources with discharge diameters of 20–25 cm is described. These ECR plasma sources make use of a 12- or 14-pole multipolar static magnetic field geometry enclosed in a 36- or 45-cm cylindrical MPDR. Microwave excitation of 200–1000 W is applied either as a single-mode applicator at 915 MHz or with a controlled multimode excitation at 2.45 GHz. The ECR discharge diffuses into a multipolar, magnetically confined processing chamber producing a uniform, low-energy plasma for processing. The processing chamber plasma density is characterized by double-probe measurements. These measurements indicate that plasma densities in excess of 1011 /cm3 are easily achieved with as little as 1000 W and large-diameter excitation produces uniform densities with less than 3% standard deviation over 15–20 cm diam. Experiments with three wafers placed on an 18-cm-diam wafer holder also indicate uniform etching. Using a SF6 /Ar plasma to etch silicon resulted in a standard deviation of 2.9% in etch depth over a 15-cm-diam region on the wafer holder.
The effect of resist contrast on linewidth error induced by e-beam proximity exposure
Authors: Liu Hua-Yu , Owen Geraint
Published: July 2002

In electron beam lithography, resolution is limited by two important factors: proximity effect and resist contrast. The relation between these two factors is investigated in a chemically amplified negative resist system. It has been discovered that proximity effect induced critical dimensions variation is not monotonically dependent on resist contrast; the worst proximity effects are apparent at medium contrast values. At higher contrast values, increasing the contrast can reduce the proximity effect; at lower values, increasing the contrast worsens the proximity effect. It has also been found that a parabola-shaped curve is obtained when interproximity effect is plotted as a function of exposure dose. Dissolution rate ratio and overdevelopment effect were used to explore the impact of resist contrast on e-beam proximity effect.
A high accuracy and high throughput electron beam reticle writing system for 16M dynamic random access memory class and beyond devices
Authors: Takigawa T. , Ogawa Y. , Yoshikawa R. , Koyama K. , Tamamushi S. , Ikenaga O. , Abe T. , Hattori K. , Nishimura E. , Kusakabe H. , Wada H. , Nishino H. , Anze H. , Goto M. , Shigemitsu F. , Munakata M. , Shimazaki K. , Watanabe S. , Saito T. , Ilo T.
Published: July 2002

A new electron beam reticle writing system has been developed for a 16-256M dynamic random access memory (DRAM) class reticle pattern making. A continuously moving stage, variable-shaped beam and vector-scanning method has been adopted. The acceleration voltage was varied from 20 to 12.5 kV. An acceleration voltage of 15 kV provided proximity effect correction free exposure for reticle patterns larger than 2 μm corresponding to the minimum feature size of 16M DRAM class devices. A single reticle processing autoloader has also been developed for quick turn around time. Parallel processing of data conversion has enabled the system to convert Gaussian beam system data to the new variable shaped beam system data of 10 MB volume in about 20 min.
An error measure for dose correction in e-beam nanolithography
Authors: Pati Y. C. , Teolis A. , Park D. , Bass R. , Rhee K. , Bradie B. , Peckerar M. C.
Published: July 2002

In this paper we address the problem of dose correction in ultrahigh resolution electron beam lithography. Here, the emphasis is on providing precise resist development profiles. This contrasts with the case of standard near-micron e-beam lithography in which computational efficiency and an ability to handle large data files are the major goals. The approach employed here is one of non-linear optimization. Rather than using the conventional quadratic cost function for dose optimization, the specifics of the resist development curve (i.e., saturation behavior, minimum critical dose, and gamma) are incorporated as inequalities. Results (both experimental and theoretical) are given for half-micron lines. Preliminary results on subhalf-micron lines are also given.
Charging effects on trilevel resist with an e-beam lithography system
Authors: Itoh Hiroyuki , Nakamura Kazumitsu , Hayakawa Hajime
Published: July 2002

The charging effect on a trilevel resist system was investigated with a variable-shaped electron beam (e-beam) lithography system. A test pattern which consists of two-dimensionally arrayed marks was exposed on the trilevel resist and measured by the e-beam. A method evaluating the correlation of repetitive measurement errors due to charging has been developed. This evaluation method was characterized such that the repetitive measurement and charging process occurred simultaneously without a conductive coating on the resist. The evaluation method of the charging process at 20 and 30 kV is demonstrated in this article. The resist result is different from that of silicon dioxide, and these phenomena are discussed together with the associated discharging processes.
Study of tip magnetization behavior in magnetic force microscope
Authors: Sueoka K. , Okuda K. , Matsubara N. , Sai F.
Published: July 2002

The behavior of the magnetic moment at the tip end of the magnetic force microscope (MFM) was investigated by using two types of tip: iron wire and iron coated. MFM images of a magnetic head obtained by these two tips show quite different features. These differences were explained by assuming that the magnetic moment of the iron wire tip is almost fixed along the tip axis, while that of the iron coated tip follows the external field. In addition, it was found that the moment of the iron coated tip can respond to an ac excited head field of up to 50 MHz.
Tip-surface forces during imaging by scanning tunneling microscopy
Authors: Salmeron M. , Ogletree D. F. , Ocal C. , Wang H.-C. , Neubauer G. , Kolbe W. , Meyers G.
Published: July 2002

The effect of compressive and shear forces between tip and surface during the operation of the scanning tunneling microscope (STM) is illustrated with examples obtained both in air and vacuum environments. We show that at typical gap resistances used in STM (≤20 GΩ) these forces can have significant effects. Compressive or repulsive forces give rise to anomalous topographic corrugations (elastic deformations) as well as to permanent damage (inelastic or plastic deformation). These forces also cause the anomalously low values obtained in measurements of the tunneling barrier height. The effects of shear forces when imaging weakly bound material will also be demonstrated.
Imaging of cell membrane proteins with a scanning tunneling microscope
Authors: Hörber J. K. H. , Schuler F. M. , Witzemann V. , Schröter K. H. , Müller H. , Ruppersberg J. P.
Published: July 2002

We demonstrate that a scanning tunneling microscope can be used to obtain structural information on membrane proteins in their natural environment and of isolated protein molecules deposited on graphite. We focused on ion channel forming proteins, i.e., gramicidin and the nicotinic acetylcholine receptor. The latter is a well described membrane channel in the neuromuscular synapse. To get more than topological information we developed a fast and stable method to characterize the changes of the current/voltage curvature while scanning over a sample. This results in a material-dependent image color which is also sensitive to variations of chemical structure inside the molecule. The method was first tested with liquid crystals on graphite clearly showing their atomic structure in the STM image. In a second step the method was applied to obtain structural information about gramicidin adsorbed on graphite.
A pulse-deposition method for scanning tunneling microscopy of deoxyribonucleic acid on graphite
Authors: Allen Michael J. , Tench Robert J. , Mazrimas Joe A. , Balooch Mehdi , Siekhaus Wigbert J. , Balhorn Rod
Published: July 2002

Images of three different synthetic DNAs have been obtained by scanning tunneling microscopy (STM) following their deposition on graphite using a voltaic pulse. DNA applied to the STM tip is desorbed during a 4 V/10 μs pulse and deposited intact onto the surface of highly oriented pyrolytic graphite. Images of 22, 47, and 100 base-pair molecules show that deposition occurs in close proximity to the tunneling tip and that the molecules appear to deposit singly or in highly oriented groups.
Imaging of single-stranded DNA with the scanning tunneling microscope
Authors: Cricenti A. , Selci S. , Chiarotti G. , Amaldi F.
Published: July 2002

Uncoated single-strand DNA mixed with BAC (benzyldimethylalkylammonium chloride) were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images showed both double- and single-stranded DNA. Along the single DNA backbone we have, tentatively, assigned small structures to phosphate and sugar group components; bumps aside single filaments, that correspond, presumably, to the bases of DNA, have sometimes been observed.
Scanning tunneling microscopy of actin filament
Authors: Masai Junji , Shibata Teiko , Kondo Shunzo , Ishiwata Shin’ichi
Published: July 2002

We present a scanning tunneling microscopy (STM) image of a supramolecular structure of biological importance, fibrous actin (F-actin) polymers from muscle. F-actin is one of the major components in biological contractile machinery such as muscle. A drop of a solution containing F-actin was put on a highly oriented pyrolytic graphite (HOPG) surface and dried in air at room temperature. F-actin deposited on an HOPG surface was imaged by using a commercially available STM operated in air without metal coating. A sheet type of F-actin paracrystal from sample preparation in the presence of 12 mM MgCl2 has been observed. The STM images showed corrugations consistent with the geometry expected from the known configuration of the sheet type paracrystal. We discuss the STM image and compare it with a conventional transmission electron microscope image.
Scanning tunneling microscopy of bacterial flagella
Authors: Nakagiri Nobuyuki , Fujisaki Hisao , Aizawa Shinichi
Published: July 2002

Scanning tunneling microscopy (STM) images have been obtained for three different types of uncoated helical flagella of bacteria, salmonella typhimurium SJW1103: intact flagella, sonicated flagella, and disassembled flagella (i.e., flagellin). Glycerol has been added to the desalinated sample solutions to prevent the aggregation of the sample in the solution, and to adhere to the samples onto the graphite surface. Freeze drying has been used to prevent the aggregation of the sample in the drying process. The molecular arrangement observed by STM is similar to that of the reported structure for straight flagella determined by x-ray diffraction.
Studies of the electrical properties of large molecular adsorbates
Authors: Lindsay S. M. , Li Y. , Pan J. , Thundat T. , Nagahara L. A. , Oden P. , DeRose J. A. , Knipping U. , White J. W.
Published: July 2002

The scanning tunneling microscope (STM) was used to investigate the conductivity of organic aggregates on gold electrodes. DNA fragments can form very stable aggregates in the presence of tris(hydroxymethyl)aminomethane buffer salt. With a submonolayer coverage, the tip can be moved back and forth between ‘‘clean’’ gold (in contact with the electrolyte) and an organic adsorbate patch. In these conditions, a systematic variation of the current voltage (I–V) characteristics indicates that the electrical characteristics are not dominated by a contaminant particle on the STM tip. The dependence of image contrast on tip bias was also studied over the range +0.3 to −0.3 V. It is found that: (a) the image contrast does not depend strongly on tip bias; (b) the I–V curves over what appears to be ‘‘clean’’ gold under the electrolyte are similar to those observed over clean gold maintained in an inert atmosphere; (c) the I–V curves over an adsorbate patch are diode-like; (d) the I–V curves show no sign of a large voltage offset of the sort that is characteristic of an electrochemical interface; (e) the conductance over the organic adsorbate can be much larger than that over ‘‘clean’’ gold. It is concluded from (a) and (d) that current is most likely carried by electrons, not ions. Here (c) is inconsistent with (a) unless the closing of the STM servoloop causes significant modification of the electronic properties of the adsorbate (by adjusting ‘‘pressure’’ in the tunnel gap). The I–V curves over the organic adsorbate have an unusual dependence on initial set-point voltage, consistent with such an effect.
Observation and control of adsorbed molecules
Authors: Mizutani W. , Shigeno M. , Ohmi M. , Suginoya M. , Kajimura K. , Ono M.
Published: July 2002

Molecular movement induced by an electric field was observed by scanning tunneling microscopy. The observed feature of the molecular lines of liquid crystal 4-hexyl-4′-cyanobiphenyl on graphite appeared to change drastically in 2 min after the polarity inversion of the bias voltage, together with small shifts in the lateral arrangement of individual molecules. The rearrangements took place at the bias voltage at around 2 V and the process was found to be reversible. When a bias voltage less than −2.8 V was applied to the tip, an irreversible process, the deposition of molecules, occurred. The minimum deposition size was about 20 nm and was found to be determined by the tip shape.
Fabrication of tenth of micron stress minimized electroplated gold patterns for x-ray lithography masks
Authors: Kebabi B. , Malek C. Khan
Published: July 2002

An optimized gold direct current (dc) electroplating process from a cyanide bath was developed for the fabrication of x-ray lithography masks. The stress behavior of 0.4–2 μm thick gold thin films dc electrodeposited from a neutral cyanide bath was studied as a function of their deposition parameters. Temperatures in the 40–70 °C range and current densities varying from 1 to 10 mA/cm2 were used. Deposits with low total tensile stress (down to 10 MPa) were obtained. The influence of the plating base was addressed. A structuring process was developed, which enabled the fabrication of 0.65 μm thick gold patterns for x-ray lithography masks. The minimum linewidth obtained was 70 nm in a single layer process and 0.2 or 0.3 μm period gratings in a single layer or trilayer stencil, respectively. The problem of thickness uniformity in the deposits was also studied.
Filamentless neutralization of broad ion beams
Authors: Korzec D. , Kessler T. , Keller H. M. , Engemann J.
Published: July 2002

A new, effective technique of broad ion beam neutralization, based on alternating ion and electron extraction via the same optic is presented and discussed. The screen and accelerator grids of a two-grid extraction system are biased with bipolar and unipolar pulses of varying amplitude and frequency, respectively. Pulse frequencies of 500 Hz–20 kHz have been tested. In each period ions are extracted with screen pulse amplitudes of 200–800 V and accelerator voltages kept at 10%–20% of the respective screen grid potential. Similarly, electrons are extracted with screen pulse amplitudes of −50–−200 V and a grounded or slightly negatively biased accelerator grid. An electrically nonconductive target bombarded subsequently by ions and electrons will charge and discharge periodically, possibly resulting in a zero target bias. The neutralization effect has been studied in two ways: (i) measurement of a metallic target bias being electrically insulated from ground by a 220 nF capacitor; (ii) etching experiments of 1.2 μm thick polyimide layers (HPR 204) deposited on a Si3N4/Si substrate. A high positive target bias resulting from insufficient beam neutralization correlates with low etch rate and poor quality of the etched substrate surface. A negative target bias (overneutralization) increases the energy of impinging positively charged ions resulting in increased etch rates. Although unwanted in general this effect may be used intentionally in some cases. Zero target bias in all cases assures good surface quality and high etch rates. The neutralization principle presented is of prime importance in reactive ion beam processes when filamentless ion sources are used. This holds especially when interactions of chemically reactive ions with electrically insulating surfaces are considered.
Optimizing electron beam lithography writing strategy subject to electron optical, pattern, and resist constraints
Authors: Veneklasen Lee H.
Published: July 2002

A new model for the exposure rate of electron beam lithography is developed, accounting for electron optical, electronic, resist, and pattern statistics/quality constraints. Resist heating and beam interaction effects, as well as current density, flash size and edge resolution are included as measurable parameters that couple in rather complicated ways to determine performance for a specific task. Gaussian beam raster scan, small fixed shaped beam, and variable shaped beam vector scan machine strategies are compared using hypothetical but realistic assumptions. Address grid, minimum feature dimension, and the maximum flash area influence coverage in different ways, and pattern fracture techniques profoundly influence coverage, particularly in variable shaped beam systems. Remarkably small shapes, high current density, and high flash rates are usually favored. A constant flash area fracture is desirable because it maximizes the average beam current. The controlling resist parameter is sensitivity divided by the maximum beam current useable to achieve a given level of pattern quality. This parameter is frequently limited by heating effects. Examples of lithography guided by this model are given.
A new scanning tunneling microscope with large field of view and atomic resolution
Authors: Shang G. Y. , Yao J. E. , He J.
Published: July 2002

A new STM which features atomic resolution, large field of view, and an x/y specimen stage has been developed. A dual scanner consisting of a piezomechanical coarse scanner and a piezotube fine scanner has been constructed. It covers a wide scan range from 0.4 nm to 0.2 mm. Searching the specimen area of interest was accomplished by the x/y specimen stage with a range of 4×4 mm2 movement and a resolution of several microns. In order to achieve atomic resolution, rather rigid structure and vibration isolator were adopted. This kind of the instrument would be used in wide variety of projects such as studies of biological specimen, microfabrication, and nonhomogeneous surfaces.
Controls and software for tunneling spectroscopy
Authors: Schummers A. , Halling H. , Besocke K. H. , Cox G.
Published: July 2002

A versatile software based on common computer hardware has been developed for scanning tunneling microscope (STM) operation. The application of an accelerating signal processor board renders online data acquisition and fast signal and image processing. A newly developed method for tunneling spectroscopy has been implemented. Utilizing block matching algorithms, various types of local spectroscopic characteristics can be measured under consideration of thermal drifts and erratic tip changes. Additional features are: flexible system control, various data processing and display functions, and mapping of atomic surface models onto the measured spectroscopic data. The system is applied to the STM generation of the BEETLE type. A demonstration of performance, flexibility, and features are discussed on actual experiments.
Scanning tunneling microscopy and spectroscopy of the Si(111)5×5 surface
Authors: Feenstra R. M. , Lutz M. A.
Published: July 2002

The scanning tunneling microscope is used to study the structural and electronic properties of the 5×5 reconstruction on the Si(111) surface. The 5×5 structure is formed by annealing 2×1 cleaved surfaces. Results are described for temperature-dependent imaging, voltage-dependent imaging, and spectroscopy. The structure of the 5×5 surface is found to be consistent with the dimer–adatom–stacking-fault model. From a comparison of neighboring regions of 2×1 and 5×5 structures, the π-bonded chain structure for the 2×1 surface is also confirmed.
Ordering transition on the K/Si(001) surface
Authors: Kubby J. A. , Greene W. J. , Soukiassian P.
Published: July 2002

We have used the tunneling microscope to characterize the adsorption of potassium on the Si(001)-2×1 surface. At submonolayer coverages, we have observed the formation of alkali metal chains that run perpendicular to the substrate dimer rows. At this coverage, the potassium atoms have been observed to adsorb onto a variety of different sites. At the saturation coverage of one monolayer, the alkali metal atoms become ordered, with the one-dimensional chains running parallel to the substrate dimer row direction.
Axial radio frequency electric field intensity and ion density during low to high mode transition in argon electron cyclotron resonance discharges
Authors: Carl D. A. , Williamson M. C. , Lieberman M. A. , Lichtenberg A. J.
Published: July 2002

To investigate the transition from the low density mode to the high density mode in an electron cyclotron resonance (ECR) discharge, a Langmuir probe and an E field probe were used to measure ion density and E field intensity as functions of axial position and power. The experiments were performed in argon at 0.13 Pa in a 7.9 cm diam cyclindrical source chamber propagating TE11 mode 2.45 GHz microwave power. Low mode was characterized by a standing wave throughout the plasma chamber and minimal power absorption. High mode exhibited nearly complete power absorption and no standing wave past the ECR zone. A sliding short (ss) was used to determine if the position of an E field null in the source chamber affected the transition between these two modes for various magnetic field configurations. The ss position had little effect on mode transition, relative power absorption or ion density when positioned downstream from a broad, large volume resonance zone (resonance near the mirror midplane). However, the plasma could not be ignited if the short was placed at or upstream from the large volume resonance zone.

If the magnetic field was adjusted to yield a sharp, small volume resonance zone (resonance midway between the midplane and the throat), then positioning the ss to force an E field null at the resonance zone would prevent plasma ignition, even at 800 W forward power. The ion density exhibited a hysteresis (i.e., a direct jump from no plasma to a plasma density observed at other sliding short positions for that same forward power, thereafter following the ion density versus forward power dependence observed at nearby ss positions) on power cycling when the sliding short was within ∼1 cm of the broad resonance zone or within ∼1 cm of forcing a null in the sharp resonance zone caes. The ion density versus power curve for the broad volume case exhibited a change in slope over the transition region (Pforward ≊40 W) when the ion density at the resonance zone was ≊1×1011 cm−3. For the narrow zone cases, a region of bistability (i.e., rapid plasma density fluctuations between low and high mode with little or no change in external input power) was observed for which the ion density fluctuated between a value near 5×1010 cm−3 in low mode and 5×1011 cm−3 in high mode. Similar transitions were observed in a 14.6 cm diam ECR source with a TM01 mode, indicating that the effect is not solely dependent on the microwave field structure in the ECR chamber.
Magnetron etching of polysilicon: Electrical damage
Authors: Greene W. M. , Kruger J. B. , Kooi G.
Published: July 2002

We report comparison of etch damage between reactive ion and magnetron plasma etch environments and propose a qualitative model. Gate oxide damage is controlled by both plasma current and voltage and under some conditions can be worse for magnetron etching, especially in the case of very thin gate oxide. Moderate magnetron voltages (<50 V) may still be high enough (given the increased plasma density) to charge polysilicon gates causing degradation. Further reduction of voltage (and hence current) through modification of geometry and chemistry can reduce this damage to gate oxide and the gate edge diode for magnetron etching, producing results superior to reactive ion etching.
Gate oxide damage from polysilicon etching
Authors: Gabriel Calvin T.
Published: July 2002

Damage to thin gate oxides from etching of polysilicon gates was studied using gate oxide breakdown histograms and time-dependent dielectric breakdown measurements. The effect of various polysilicon etch parameters was investigated in a radio frequency (rf) triode etcher. Increasing rf power caused a substantial increase in damage. Reducing bias at constant power also resulted in an increase in damage, indicating that ion energy is not the only cause of damage. Area, isolation edge, and source/drain edge contributions to gate oxide defect densities were calculated as a function of rf power during polysilicon etch. As rf power was increased, the area contribution increased the most, indicating that gate oxide damage from polysilicon etching is not an edge phenomenon but a surface phenomenon. The effect of gate oxide thickness was investigated. Damage increased significantly as gate oxide thickness was reduced. Finally, the rf triode etcher was compared with a microwave electron cyclotron resonance (ECR) etcher. The ECR etcher caused fewer damaged capacitors, but some modifications to the triode etch process (such as lower rf power or pure chlorine chemistry) produced fewer damaged capacitors than the ECR.
A new supermagnetron plasma etcher remarkably suited for high performance etching
Authors: Kinoshita Haruhisa , Matsumoto Osamu
Published: July 2002

A new type of plasma etcher named a supermagnetron plasma etcher equipped with two parallel cathodes and an annular permanent magnet was developed. Using the supermagnetron plasma etcher, two kinds of experiments for the high rate etching of SiO2 and the highly uniform etching of photoresist and SiO2 under a stationary magnetic field were investigated. In the etchings of 6-in.-diam bare and patterned SiO2 wafers, high etch rates of 570 and 710 nm/min were obtained, respectively, using C2F6 gas of 7.5 mTorr. The etch selectivities of SiO2 to Si became as high as 6–15 using CHF3 gas at 3–6 mTorr. In a stationary magnetic field, the highly uniform etching of photoresist and SiO2 were also obtained using two types of supermagnetron plasma etchers. The etch uniformities depend on rf powers supplied to the upper and lower cathodes, gas pressure, and the position of a magnet, etc. High etch uniformities of ±5% were obtained without the rotation of a magnetic field in the etching of 3-in.-diam photoresist film and 6-in.-diam SiO2 at phase differences of rf voltages of about 180 and 250 degrees, respectively. Applying the CHF3 and O2 supermagnetron plasmas to submicron pattern etchings, SiO2 contact holes with tapered side walls and photoresist lines with vertical side walls were obtained, respectively.
Remarkable effects in wet-etched GaAs/GaAlAs rings
Authors: Lee K. Y. , Kern D. P. , Ismail K. , Washburn S.
Published: July 2002

Coupled GaAs/GaAlAs rings have been fabricated using electron-beam lithography and wet chemical etching. We report the first observation of conductance steps associated with e2/h in etched structures, and clear Aharonov–Bohm oscillations in multiple rings connected in parallel. The amplitude of the oscillations is found to be dependent on the number of rings indicating the possibility of phase coupling between electrons traversing different rings.
Growth interfaces of Si1−xGex/Si heterostructures studied by i
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u laser light scattering
Authors: Robbins D. J. , Cullis A. G. , Pidduck A. J.
Published: July 2002

Elastic scattering of laser light has been used to monitor surface topography in real time during growth of Si1−xGex heterostructures. Large increases in scattered intensity were caused by surface height fluctuations in the alloy layers which, after growth, could be imaged in cross section by transmission electron microscopy and in plan view by scanning optical microscopy. For pseudomorphic alloy layers (x=0.19±0.01) grown at 750 °C the surface height fluctuations were periodic, the wavelength of approximately 270 nm giving strong laser scattering. Plan view transmission electron micrographs on such a layer showed periodic strain fluctuations with the same wavelength, whereas an equivalent layer grown at 610 °C showed strain fluctuations which were irregular in shape and spatial distribution. The intensity of light scattered from the surface of this layer was much lower. Thick alloy layers grown beyond the critical thickness for appearance of misfit dislocations showed strong scatter which increased more quickly in intensity at higher growth temperature.
Scanning tunneling microscopy and spectroscopy of thin film superconductor Pb
Authors: Chen T. , Tessmer S. , Tucker J. R. , Lyding J. W. , Van Harlingen D. J.
Published: July 2002

A variable-temperature scanning tunneling microscope system, which operates in the temperature range of 4<T<400 K, was employed to perform topographic and spectroscopic studies of conventional superconductors at low temperatures. Images of Pb thin films were obtained and local tunneling spectroscopy was performed. The N–I–S tunneling characteristic revealing superconducting gap structure was observed. In mapping the electronic density of states over the Pb surface, abrupt changes in the measured N–I–S tunneling characteristics were found, showing the existence of apparent normal surface regions. The implications of the tunneling spectroscopy results are discussed.
Silicon-containing resist for phase-shifting masks
Authors: Watanabe Hisashi , Todokoro Yoshihiro , Inoue Morio
Published: July 2002

A novel silicon-containing chemical amplified resist has been developed for a shifter layer of phase-shifting masks. The resist is composed of an alkaline-soluble silicone polymer and onium salt as an acid generator. The base polymer has a ladder structure and contains a methyl group as a side group and ethoxy and hydroxy groups as an end group. Shifter patterns were directly fabricated on mask substrates by electron-beam exposure and development of the new resist. Improved resolution using an i-line stepper can be achieved with the phase-shifting mask having the new silicon-containing resist shifter.
Simulation of profile evolution in silicon reactive ion etching with re-emission and surface diffusion
Authors: Singh Vivek K. , Shaqfeh Eric S. G. , McVittie James P.
Published: July 2002

This article describes a model that simulates etching profiles in reactive ion etching. In particular, models are developed to explain the significant lateral etch rate that is observed in many etch profiles. The total etch rate is considered to consist of two superimposed components: an ion-assisted rate and a purely ‘‘chemical’’ etch rate, the latter rate being due to etching by radicals in the absence of ion bombardment. The transport of radicals to the evolving interface is studied for two different transport mechanisms: re-emission from the surface and diffusion along the surface. For the case of transport by surface re-emission, a reactive sticking coefficient is defined for the radicals, and a formulation is developed to simulate etching for any value (between zero and unity) that this sticking coefficient may assume. When the sticking coefficient approaches either zero or unity, the method of characteristics is shown to be useful for profile simulation. Transport of radicals by surface diffusion is also investigated, and it is shown that the important dimensionless parameter governing profile evolution is the Damkohler number. The two models are compared to experiments performed on the etching of silicon in a SF6 plasma, and the surface re-emission model is shown to accurately predict the development of etching profiles.
Characterization of Si1−xGex/Si (100) heterostructures by photoluminescence and admittance spectroscopy
Authors: Souifi A. , Brémond G. , Benyattou T. , Guillot G. , Dutartre D. , Berbezier I.
Published: July 2002

The authors report a complete and systematic study based on photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements performed on fully strained or relaxed SiGe/Si single heterostructures (SH) and fully strained double heterostructures (DH) grown by rapid thermal chemical vapor deposition (RTCVD). First of all, the well-resolved free excitonic PL transition, clearly observed in high-quality pseudomorphic SiGe single layers grown by RTCVD, is used to acceed to the structural and interfacial characteristics of thin strained SiGe layers in the DH. The main results show the striking efficiency of a Si epitaxial capping layer in reducing drastically the SiGe surface recombination and the influence of the alloy disorder. In fact, this disorder must be taken into account to explain the broadening of the excitonic line. Moreover, the measurement of the no-phonon line full width at half-maximum is reported to be useful to control and analyze when the layer starts to relax or when some interfacial roughness occurs due to growth conditions. In a second hand, strong deep level behavior have been detected and analyzed in the relaxed layers by PL and DLTS. Sharp lines similar to the dislocation related D lines in Si, are attributed to the influence of the misfit dislocations at the SiGe/Si heterointerface and are associated with an Ev+0.51 eV interface state trap observed by DLTS. PL broad bands are assigned to originate from the 60° dislocations located in the SiGe layer and are connected with a Ev+0.38 eV deep level trap. Finally, this study has been conducted to characterize SiGe/Si heterostructures in order to acceed to the quality of the heterointerface, a crucial parameter for the future development of Si-advanced devices.
The role of oxygen excitation and loss in plasma-enhanced deposition of silicon dioxide from tetraethylorthosilicate
Authors: Raupp Gregory B. , Cale Timothy S. , Hey H. Peter W.
Published: July 2002

The deposition rate of silicon dioxide from tetraethylorthosilicate/O2 capacitively coupled plasmas increases with increasing applied rf power, increasing total pressure and decreasing wafer temperature. These measured deposition rate dependences can be explained by a simple plasma deposition model in which deposition occurs through both an ion-assisted and an oxygen atom initiated pathway. The relative contributions of these pathways were roughly isolated using limiting step coverage measurements on low aspect ratio trenches. Limiting step coverages decreased, and hence directionality increased, with increasing rf power density, decreasing total pressure, and increasing wafer temperature. A simple bulk plasma chemistry model combined with an analytical sheath model was developed to qualitatively explain our experimental findings. The model suggests that the ion-enhanced deposition rate is directly proportional to oxygen ion flux, with a reactive sticking coefficient approaching unity. Using literature values for reaction rate parameters and rate forms for oxygen plasma reactions, the rate of the neutral-induced deposition reaction was found to be nearly independent of temperature and tetraethylorthosilicate concentration and directly proportional to oxygen atom concentration. The model reveals that the influence of an activated atomic oxygen surface recombination reaction on oxygen atom concentration is responsible for the apparent negative activation energy for deposition of −2 kcal/mol. The model further shows that under the conditions of the experiments, oxygen atom loss was controlled by surface reaction processes and convective flow; volume recombination reactions were found to be relatively unimportant.
Spreading resistance analysis with carrier spilling correction
Authors: Leong M. S. , Choo S. C. , Lee Y. T. , Ong H. L. , Ng K. P.
Published: July 2002

This paper presents results obtained in extracting dopant profiles from spreading resistance (SR) data, with carrier spilling effects taken into account. The inversion process involves a one-dimensional solution of Poisson’s equation, followed by the application of a multilayer analysis to calculate the spreading resistance for a planar structure whose surface is defined by the probe position on the beveled SR sample. The dopant profiles of n/n+ epitaxial and p-well structures were recovered using the method of regularization. A detailed description is provided of the procedure employed in applying the method of regularization.
A Poisson solver for spreading resistance analysis
Authors: Dickey D. H.
Published: July 2002

It has become evident in recent years that carrier concentration profiles measured on beveled surfaces with a spreading resistance probe might not accurately reflect the associated vertical dopant profiles. Carrier spilling, even in the absence of surface states, can move an on-bevel junction 1/2 micron or more from its metallurgical depth. This article describes a Poisson solver which we have developed for use in spreading resistance data reduction. It allows the calculation of dopant profiles from measured on-bevel profiles. Examples from a variety of structures are given.
Semiconductor damage from inert and molecular gas plasmas
Authors: Seaward K. L. , Moll N. J.
Published: July 2002

The change in sheet conductance of a thin, highly doped layer of GaAs is measured after exposure to inert gas plasmas (He, Ar, and Xe) and to molecular gas plasmas (CCl2F2, CF4, SF6, and O2) in a parallel-plate rf discharge. In order to compare these data, the change in sheet conductance is converted to a damage depth scale. A different linear relationship is found for the damage dependence on the rf-induced dc bias for each plasma. An inverse-mass relationship is derived from the data for He, Ar, and Xe plasma exposures. Using this, two models are tested for their ability to predict the damage from the molecular gas plasmas. For one model, the assumption is that damage is caused by molecular ions that remain intact upon impact. For the other model, which is quite successful at predicting the measured damage, the assumption is that molecular ions fragment completely upon impact. This interpretation indicates that Cl+ and/or F from CF+ in CCl2F2 plasma, F from CF+ in CF4 plasma, and S from SF+ in SF6 plasma are responsible for the measured damage effect. Neither model adequately predicts the low level of damage from O2 plasma. Helium ions caused the greatest amount of damage; when mixed with CCl2F2, the measured damage was a factor of three lower. Using optical emission spectroscopy, quenching of He ions was observed when molecular gases were introduced into a He plasma. Quenching was also observed in other mixed gas plasmas and this indicates that ions with ionization potentials substantially higher than those of other ions in the plasma will not be formed in typical rf glow discharges.