bluuebunny/crossref_metadata_2025 huggingface dataset:
Si/SiGe field-effect transistors*
Authors: König U. , Glück M. , Höck G.
Published: July 2002

Over the last few years, SiGe heterodevices with outstanding rf performance have been introduced to meet the needs of modern consumer electronics, which require novel silicon-based low cost–high speed components with improved current gain, low noise, and reduced power consumption operating in the GHz range. This article reviews device and the first circuit results of lateral modulation doped SiGe modulation doped hetero-field-effect transistors (MODFETs) with Schottky gates as well as lateral and vertical SiGe metalorganic field effect transistors (MOSFETs) focusing on dc characteristics, rf performance comprising cutoff frequencies, delays, and on layer design. With an fmax, of up to 92 GHz, the highest maximum frequency of oscillation reported so far for any Si-based FET, and transconductances gme up to 470 mS/mm, the n-SiGe MODFET is presently improving in speed with combining the advantages of heterodevices with well-established Si technology. For p-SiGe MODFETs cutoff frequencies ft of 70 GHz and fmax of 84 GHz have been measured. A reduced gate leakage and an improved voltage swing is achieved using MOS-gated heterodevices. For p-channel SiGe hetero-MOSFETs room temperature transconductances up to 210 mS/mm for 0.25 μm gate-length devices have been measured. Vertical MOSFETs allow further device scaling into the deep sub-100 nm range and thus enable us to overcome performance limits due to minimum feature sizes using state-of-the-art lithography techniques.
Magnetron ion etching of through-wafer via holes for GaAs monolithic microwave integrated circuits using SiCl4
Authors: Mitra A. , Nordquist C. D. , Jackson T. N. , Mayer T. S.
Published: July 2002

A dry etching process is described for the fabrication of through-wafer via holes in GaAs-based monolithic microwave integrated circuits by magnetron ion etching using SiCl4. The process has been used to etch via holes through 80 μm GaAs substrates with good anisotropy and etch rates exceeding 1 μm/min for via holes as small as 18×20 μm2. Etch anisotropy appears to be due to an etch-inhibiting layer, which forms on the sidewalls but can be removed readily using a brief SF6/O2 etch. The process also exhibits good selectivity to Au and Ni frontside metal.
Positive sample bias effect in scanning tunneling microscope imaging of low coverage alkali metal atoms on Si(111)7×7 surface
Authors: Eitle J. , Gorelik D. , Aloni S. , Margalit T. , Meyler D. , Haase G.
Published: July 2002

Already at coverages as low as 0.005 monolayer of potassium on room temperature Si(111)7×7 surfaces, atomic resolution is gradually lost when imaging the surface with scanning tunneling microscope at positive sample bias, giving rise to bright triangles over the faulted halves of the 7×7 unit cells and dark triangles above the unfaulted halves. We suggest that this is due to potassium atoms that are picked up by the tip from K islands at the surface, as is evident by the observed lowering of the tunneling energy barrier. This phenomenon vanishes upon thermal desorption of K islands or upon exposure to 0.1 L oxygen.
Assessment of thermal loading-induced distortions in optical photomasks due to e-beam multipass patterning
Authors: Shamoun Bassam , Engelstad Roxann , Trost David
Published: July 2002

Thermal loading-induced distortion in the photomask during e-beam patterning has recently received special attention due to its significant contribution to overlay errors. Multipass e-beam writing, a strategy proposed to reduce the heating effects and associated distortions, was simulated using three-dimensional finite element models. Thermal responses of the photomask during multipass patterning were determined and global in-plane distortions were calculated. For the given system exposure conditions of 40 μC/cm2 at 50 keV, the average value of the 3σ pattern placement error due to the bulk heating of the photomask obtained from multipass writing was found to be ≈3.5 nm which is 28% lower than that of single pass writing. Parametric studies showed that thermal radiation has a large influence on the mask cooling.
Aerial image slope and proximity effects on critical dimensions in mask lithography
Authors: Sagle Allan , Gesley M. , Kao H. , Innes R.
Published: July 2002

Critical dimension (CD) control for isolated lines has been experimentally studied as a function of aerial image slope and proximity effects on a photomask. The aerial image slope was controlled by defocusing a 50 kV shaped beam. Isolated crosses of 0.2, 0.3, 0.5, and 1.0 μm were written on a chrome on glass mask. When all of the features are written at the same dose a nonlinearity of 100 nm and a uniformity of 3σ=65 nm were observed for an aerial image slope of 120 nm. These were reduced to a nonlinearity of 20 nm and a uniformity of 3σ=18 nm when a dose correction was performed for each feature size. This suggests that proximity correction and not small aerial image slope is the most critical improvement needed to achieve good CD control.
Commercialization of SCALPEL masks
Authors: Farrow R. C. , Novembre A. E. , Peabody M. , Kasica R. , Blakey M. , Liddle J. A. , Werder K. , DeMarco R. , Ocola L. , Rutberg L. , Saunders T. , Unruh J. , Qian F. , Smith M.
Published: July 2002

To investigate the viability of large scale manufacture of SCALPEL masks, key components of the SCALPEL mask process have been performed by commercial suppliers. SCALPEL mask blanks have been fabricated by MCNC to specifications supplied by Lucent and have been delivered, patterned, and utilized. Patterning, inspection, and metrology have been performed by DuPont Photomask and Photronics using the standard set of tools used for photomasks. A wet chemical pattern transfer process has been developed that is compatible with the processing tools in the mask shops and is extensible to the 0.1 μm generation of integrated circuits. SCALPEL masks that have been fabricated using these processes and tools exhibit excellent pattern fidelity and feature edge quality.
Characteristics of plasma enhanced chemical vapor deposition-grown SiNx films prepared for deep ultraviolet attenuated phase-shifting masks
Authors: Chen H. L. , Wang L. A. , Hsu C. W.
Published: July 2002

Suitable SiNx films for constructing attenuated phase-shifting masks (APSMs) to be operated in the deep ultraviolet (DUV) regime are obtained by varying the gas flow ratios in a plasma enhanced chemical vapor deposition process. Characteristics of the films such as optical constants, optical band gaps, material compositions, irradiation stability, etching selectivity, and adhesion strength are experimentally analyzed in detail. Subquarter micron patterns on SiNx films are obtained by utilizing DUV lithography and silylation technique for the proof of feasibility. These results indicate that the SiNx films thus fabricated can meet all the requirements for building such APSMs working at wavelengths of 248 and 193 nm.
Performance of adaptive alignment method on asymmetric signals
Authors: Chen X. , Ghazanfarian A. A. , McCord M. A. , Pease R. F. W.
Published: July 2002

Common problems in alignment include signal asymmetry from a nominally symmetric mark and variation across the wafer, from wafer to wafer and from mask level to mask level. Signal asymmetry arises from many sources, including uneven coating of overlayers, smearing effects of chemical mechanical polishing, or aberration and uneven illumination in the optical alignment systems. All reported alignment algorithms assume symmetric alignment signals. These alignment algorithms perform poorly when the signal is asymmetric. In previous publications [X. Chen, A. A. Ghazanfarian, M. A. McCord, and R. F. W. Pease, J. Vac. Sci. Technol. B 15, 2185 (1997); A. A. Ghazanfarian, X. Chen, M. A. McCord, and R. F. W. Pease, Proc. IEEE 4, 1913 (1998)], we proposed a new alignment method that incorporates prior knowledge by building a model for the asymmetry and process variations using alignment signals and overlay data from prior wafers. In this article, we present experimental results that convincingly demonstrate the viability of the adaptive alignment method. The experiments are carried out using deliberately distorted alignment marks placed alongside undistorted marks. It is shown that even under conditions when conventional alignment systems fail altogether, the mean-plus-three-sigma value of the alignment errors is less than 50 nm when the proposed algorithm is used.
Exploiting structure of wafer distortion in global alignment
Authors: Ghazanfarian Amir A. , Chen Xun , McCord Mark A. , Fabian R. , Pease W. , Nguyen Khanh , Levinson Harry
Published: July 2002

One of the most critical emerging challenges in lithography is achieving rapid and accurate alignment. The problem is exacerbated by wafer and stage distortions. Thus, an effective learning process is needed to rapidly acquire the best possible positional information from an array of marks across the wafer. An algorithm based on a neural network model of global alignment was presented [A. A. Ghazanfarian et al., Proc. SPIE 3051, 629 (1997); J. Vac. Sci. Technol. B 15, 2146 (1997)], which incorporated both wafer and stage distortion. Yet in almost all cases, the stepper machines are precalibrated and the stage distortion is well controlled. Therefore, the aforementioned methods need to be revisited to specifically address the wafer distortion problem. In this article, we propose a new global alignment algorithm based on array processing techniques [J. Rissanen et al., Automatica 14, 465 (1978); M. Wax et al., IEEE Trans. Acoust., Speech, Signal Process], which exploits the structure of the overlay data from prior wafers to characterize the wafer distortion for a new wafer. The algorithm has been applied to overlay data from Advanced Micro Devices, Inc., Overlay error has been measured on 9(3×3) sites, with five measurements per site. We have used data for two pairs of lots, each pair belonging to the same process. The model obtained from the first lot of each pair is used in global alignment of the wafers in the second lot. Results indicate more than 70% improvement in alignment accuracy compared to the current global alignment algorithm, with the average error reduced by about 30 nm. It is also faster than the site-by-site alignment algorithm; simulation results from a bowing distortion example show that the proposed algorithm requires measurement from only six sites.
Properties of sputtered Cr–O and reactively sputtered Cr–N–O as passivation layers against copper oxidation
Authors: Chuang Jui-Chang , Chen Mao-Chieh
Published: July 2002

Passivation layers of 200 Å sputtered Cr–O as well as reactive sputtered Cr–N–O were studied with respect to the passivation capability against thermal oxidation of Cu in flowing nitrogen and flowing oxygen ambients. In a flowing N2 ambient, both Cr–O and Cr–N–O passivation layers were able to prohibit oxidation of Cu at temperatures up to 700 °C. In an O2 ambient, the passivation capability of Cr–N–O layer was found to be 500 °C, which is 150 °C higher than that of Cr–O layer. The superiority of the passivation capability of the Cr–N–O layer is presumably due to decoration of the surface defects and grain boundaries with nitrogen, which provide fast paths for oxygen and copper diffusion.
Nonerratic behavior of overerased bits in flash EEPROM
Authors: Nkansah F. D. , Prinz E. , Hatalis M.
Published: July 2002

We report the effects of flash “channel” programming, or severe gate disturb, on the threshold voltage of fast or overerased bits. Experiments have been performed to establish that this class of fast bits are nonerratic and remain fast after 250 °C bake. These fast bits exhibit identical subthreshold characteristics similar to that of a normal bit after ultraviolet erase, thus establishing that the initial charge stored on the floating gate is the same for both normal and fast bits. Polysilicon grain boundary enhanced electric fields which result in impact ionization by tunneling electrons, thus generating trapped positive charges in the grain boundary oxide ridges are believed to play an important role in the generation of fast bits.
Fabrication of electron beam generated, chirped, phase mask (1070.11–1070.66 nm) for fiber Bragg grating dispersion compensator
Authors: Tiberio R. C. , Carr D. W. , Rooks M. J. , Mihailov S. J. , Bilodeau F. , Albert J. , Stryckman D. , Johnson D. C. , Hill K. O. , McClelland A. W. , Hughes B. J.
Published: July 2002

We report on the fabrication of a chirped, phase mask that was used to create a fiber Bragg grating (FBG) device for the compensation of chromatic dispersion in longhaul optical transmission networks. Electron beam lithography was used to expose the grating onto a resist-coated quartz plate. After etching, this phase mask was used to holographically expose an index grating into the fiber core [K. O. Hill, F. Bilodeau, D. C. Johnson, and J. Albert, Appl. Phys. Lett. 62, 1035 (1993)]. The linear increase in the grating period, “chirp,” is only 0.55 nm over the 10 cm grating. This is too small to be defined by computer aided design and a digital deflection system. Instead, the chirp was incorporated by repeatedly rescaling the analog electronics used for field size calibration. Special attention must be paid to minimize any field stitching and exposure artifacts. This was done by using overlapping fields in a “voting” method. As a result, each grating line is exposed by the accumulation of three overlapping exposures at 1/3 dose. This translates any abrupt stitching error into a small but uniform change in the line-to-space ratio of the grating. The phase mask was used with the double-exposure photoprinting technique [K. O. Hill, F. Bilodeau, B. Malo, T. Kitagawa, S. Thériault, D. C. Johnson, J. Albert, and K. Takiguchi, Opt. Lett. 19, 1314 (1994)]: a KrF excimer laser holographically imprints an apodized chirped Bragg grating in a hydrogen loaded SMF-28 optical fiber. Our experiments have demonstrated a spectral delay of −1311 ps/nm with a linearity of +/−10 ps over the 3 dB bandwidth of the resonant wavelength of the FBG. The reflectance, centered on 1550 nm, shows a side-lobe suppression of −25 dB. Fabrication processes and optical characterization will be discussed.
Parallel and hierarchical postprocessing for variable spot electron beam lithography
Authors: Dick Gregory J. , Ganong Abigail S. , Lai Chising , Merillat Mary L. , Pavick John W.
Published: July 2002

Chip designs, for both logic and memory, are becoming increasingly large and complex. It is not unusual for the postprocessing of these designs to be one of the biggest bottlenecks in the mask order processing pipeline. To address this bottleneck a parallel postprocessing system was developed. It was named P5 for practically perfect parallel postprocessor. This system is in use for production processing of designs to be written on IBM’s EL4+ electron beam lithography tool located in the Advanced Mask Facility in Essex Junction, VT. In addition the system is being enhanced with the addition of hierarchical data handling capability. Early results of this enhancement work are presented in this article.
Mask bias requirement for 0.13 μm e-beam block exposure lithography
Authors: Takahashi Kimitoshi , Kanata Hiroyuki , Nara Yasuo
Published: July 2002

Coulomb interactions have been discussed as an obstacle for 0.13 μm line and space (L/S) resolutions in the block exposure or the cell projection lithography. In this article, effects of the Coulomb interactions are experimentally analyzed in the 50 kV block exposure lithography system. Blurs of the e-beam profiles, which characterize the Coulomb interactions, were obtained by knife-edge experiments. From the results, the following theoretically predicted facts have been clarified. The blur increases with the increasing current monotonously. We have obtained linear relationships, δ=0.03×Ib+0.05 (μm) between the blurs and an e-beam current. The dynamic refocusing technique can suppress the Coulomb interactions only partially. In order to resolve 0.13 μm L/S, practical methods to reduce the Coulomb interactions by reducing the current are needed. It is clarified that mask biasing, where widths of the mask openings are narrowed, is more effective to achieve high contrast than current density reduction or shot size reduction. It is also clarified that the mask biasing is effective to resolve 0.13 and 0.10 μm L/S patterns. We have applied the current reduction techniques and have successfully obtained fine 0.13, 0.12 and 0.10 μm L/S patterns.
Electrical transport and far-infrared transmission in a quantum wire array
Authors: Lefebvre J. , Beerens J. , Feng Y. , Wasilewski Z. , Beauvais J. , Lavallée E.
Published: July 2002

A wide set of data obtained on a two-dimensional electron gas submitted to a tunable lateral modulation, induced using a split-gate technique, is presented. Owing to a unique design of the sample, it has been possible to combine in a single experimental run, far-infrared transmission measurements and electrical transport measurements in both directions parallel and perpendicular to the lateral modulation. The discussion of the results emphasizes the correspondence between various features observed in both types of measurements. Based on these features, three regimes of modulation are clearly identified, namely the weak, intermediate and strong modulation regimes. Far-infrared transmission data show that each of these regimes is characterized by plasmon modes with a distinctive behavior. These behaviors are analyzed further with the use of transport data, which allow to determine the electron concentration in the structure for every condition of gate voltage. In the weak modulation regime, a quantitative analysis shows that the collective mode energy is consistent with that of a classical 2D plasmon at q=2π/a (where a is the period of the split gate), using the average electron concentration under the gate as the relevant parameter. In the intermediate regime, the collective modes are confined plasmons. The observation of “confined Bernstein modes” indicates that the bare confinement potential is nonparabolic in this regime. In the strong modulation regime, the observation of a far-infrared resonance energy which does not depend on the modulation amplitude, while the effective 2D electron concentration (within each wire) varies with gate voltage, shows that the collective mode is a Kohn mode.
BCl
3
/
Ar
reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors
Authors: Kuo C. W. , Su Y. K. , Lin H. H. , Chin C. Y.
Published: July 2002

BCl 3 reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) is found improved by the addition of an appropriate amount of Ar to the gas flow. The influence of the BCl3/Ar gas flow ratio on GaAs to GaInP etch selectivity, surface roughness, and surface damage was studied. The results indicate that the conditions for minimum plasma damage, as determined by photoreflectance (PR) spectroscopy, corresponded with the conditions for minimum surface roughness, as determined by atomic force microscopy (AFM). The optimal BCl3/Ar gas flow ratio for minimum surface damage and roughness was found to be 6:4. Two BCl3:Ar flow rate ratios, 6:4 (optimal ratio) and 10:0 (pure BCl3) were used for gate recess etching in the fabrication of GaInP/InGaAs/GaAs PHEMTs. From drain–source current to gate–source voltage (Ids–Vgs) measurements, it was found that the plasma-induced damage for the sample Sc dry etched with 6:4 BCl3/Ar is less than that of the sample Se dry etched with pure BCl3. The dc and small signal rf characteristics of PHEMT Sc were superior to those of the wet-etched PHEMT S0 and PHEMT Se dry etched with pure BCl3. The improvement is attributed to the lower parasitic source resistance associated with the tighter recess geometry of the BCl3 plasma recess device. These results show that photoreflectance spectroscopy is a powerful tool for investigating surface damage and can be used to improve the performance of PHEMTs.
Quantitation of latent resist images using photon tunneling microscopy
Authors: Liddle J. A. , Johnson J. A. , Cirelli R. , Mkrtchyan M. M. , Novembre A. E. , Peabody M. L.
Published: July 2002

Photon tunneling microscopy (PTM) is an optical microscopy technique that can, by using frustrated total internal reflection, be sensitive to changes in surface topography as small as 1 nm. We have developed a simple calibration technique that generates plots of sample reflectivity as a function of topography. This empirical data is then used to convert a gray-scale image of a specimen into an accurate topographic image. Errors, such as accurate magnification calibration and detector nonlinearity, lead to only small differences between the empirical data and our theoretical prediction. We have used PTM to study the evolution of latent images in a chemically amplified resist, ARCH2, as a function of dose, both after exposure and after postexposure bake, and have obtained good agreement between the topography measured in the PTM with thickness changes determined by ellipsometry from large exposed areas. Comparison of the results of the PTM with those obtained by near-field scanning optical microscopy demonstrate that changes in topography on the order of 3–5 nm are visible in the PTM. The topography that appears to develop in a latent image is a function of feature size. This effect occurs before the lateral resolution limit of the microscope is reached, and is a result of the mechanical constraint arising from unexposed resist material around the exposed features. Techniques such as adjusting the polarization and wavelength of the illumination can improve the sensitivity of the technique to small changes in topography, while in the case of materials that undergo changes in refractive index, contrast can be seen even in the absence of topography.
Fabrication of silicon stencil masks with vitreous carbon ion-absorbing coatings
Authors: Ruchhoeft P. , Wolfe J. C. , Wasson J. , Torres J. , Wu H. , Nounu H. , Liu N. , Herbordt M. , Morgan M. D. , Tiberio R. C.
Published: July 2002

We show how to integrate a vitreous carbon ion-absorbing coating with current silicon stencil mask technology to create a mask for ion beam lithography with dramatically improved radiation resistance. The masks were formed by first sputtering a graphitic carbon film onto the nonplanar side of a patterned silicon stencil mask. The carbon film was subsequently vitrified by He+ ion implantation and patterned by O2 reactive ion etching using the silicon mask itself as an etching template. In the example reported herein, the thicknesses of the silicon mask and carbon film were 0.7 and 1.0 μm, respectively. Silicon mask openings as small as 80 nm were faithfully replicated in the carbon, making a 20:1 aspect ratio in the bilayer mask. The mean stress of these multilayer masks is extremely stable when lithography ions are stopped within the carbon layer: stress change is less than experimental error (0.5 MPa) for at least 500 000 proximity exposures. Compared to silicon stencil masks, which wrinkle after only 100 exposures, these masks represent a breakthrough in nanostructure manufacturing.
Economical sampling algorithm using Fourier analysis for mapping wafer critical dimension variations
Authors: Ouyang Xu , Berglund C. N. , McCord Mark A. , Pease R. F. W. , Spence Chris , Liu Hua-Yu
Published: July 2002

Characterizations of critical dimension (CD) errors on wafers are usually based on the assumption that the errors are random and normally distributed, and that they therefore can be fully described by a mean and 3σ value. However many sources of CD errors are known to be primarily systematic and are often spatially correlated. In order to establish an efficient measurement sampling scheme and data analysis algorithm that accounts for such nonrandom errors, we collected 900 CD data points using electrical test structures on each of nine wafers that were fabricated in two different fabrication facilities. Wafers using both phase-shifting mask and conventional mask lithography were measured. Fourier analysis was then used to study the errors in the spatial frequency domain. It was found that in all cases systematic and spatially correlated errors, in particular a set of errors that were largely repetitive with stepper field periodicity, dominated over random CD errors. By taking advantage of the correlated nature of these errors, an economical two-step sampling algorithm is defined that significantly reduces the amount of sampling needed (by approximately fourfold). By combining the results of the two-step sampling in the spatial frequency domain, an accurate map of actual error spatial distribution can be extracted. The accuracy of the scheme is verified by using subsets of the 900 data point measurements, and comparing the results to those from the full set of data.
Evaluation of total uncertainty in the dimension measurements using critical-dimension measurement scanning electron microscopes
Authors: Mizuno Fumio , Shimizu Minoru , Sasada Katsuhiro , Mizuno Takeshi , Yamada Satoru
Published: July 2002

Total uncertainty can be discussed in terms of bias and reproducibility. We have studied bias and reproducibility in the critical dimension measurement scanning electron microscope and measurements have derived expressions of them, and discussed the parameters which determine them by making a comparison with measurement data.
Whole film inspection using an extended source
Authors: Aiyer Arun , Chau Henry
Published: July 2002

Currently, one measures dielectric thin film thickness on a wafer surface by sampling a predetermined number of points across the wafer. Point measurements do not provide accurate information on the trend in thickness variation across the wafer surface. Such information could be quite useful while developing new coating, deposition, etching, or polishing processes. Hence, a system that can map single layer film thickness across the whole wafer or a large area of the wafer will be very useful to process developers. In this article, we will discuss a technique that can map film thickness across a large area in a relatively short amount of time. It takes about 4 s to determine about 23 000 thickness values across the wafer. The approach has been breadboarded and demonstrated. Using a single wavelength, this technique makes it possible to characterize single layer film thickness without having to know optical constants of the substrate material.
Pattern collapse in the top surface imaging process after dry development
Authors: Mori Shigeyasu , Morisawa Taku , Matsuzawa Nobuyuki , Kaimoto Yuko , Endo Masayuki , Matsuo Takahiro , Kuhara Koichi , Sasago Masaru
Published: July 2002

In this article the pattern collapse in a 193 nm top surface imaging process after dry development is described. We dry developed the resist with O2 and SO2 plasmas at low temperature in order to replicate a fine pattern profile. Pattern collapse occurred because of stress from neighboring patterns when SO2 was added at low substrate temperatures and the line/space binary pattern was below 0.15 μm. We found, using Auger electron spectroscopy analysis, that a sulfuric compound covered the side walls of the pattern when SO2 was used. We propose a pattern collapsing mechanism caused by the reaction of H2O with the evaporation of water adsorbed by the sulfuric compound on the resist pattern. It is therefore effective to decrease the sulfuric compound on the patterns before the wafer is removed from the etching chamber. Finally, we successfully replicated a sub-0.10 μm line and space pattern without pattern collapse.
Fabrication and characterization of buried subchannel implant n-metal–oxide–semiconductor transistors
Authors: Wang W. , McCarthy D. , Park D. , Ma D. , Marrian C. , Peckerar M. , Goldsman N. , Melngailis J. , Berry I. L.
Published: July 2002

The shrinking of the gate length is not only a challenge for lithography but also for device performance. Subthreshold current increases, so short channel transistors are hard to turn off. In order to reduce the subthreshold current, transistors with buried subchannel implants were modeled and then fabricated by a self-aligned process. This article describes the buried implant metal–oxide–semiconductor field effect transistor (MOSFET) model, fabrication, and measured performance. The simple analytic model developed predicts less short channel effects in the buried implant MOSFETs. A novel self-aligned process has been applied to fabricate the subchannel implants directly under the gate. Identical devices of various gate lengths down to 0.25 μm were fabricated with and without the buried p+ implant. The devices with the p+ implant exhibited a slower threshold voltage roll-off and less subthreshold swing.
Artificial dielectric optical structures: A challenge for nanofabrication
Authors: Giaconia C. , Torrini R. , Murad S. K. , Wilkinson C. D. W.
Published: July 2002

Diffractive optical components can be made using multiple level kinoforms or single level artificial dielectric structures. The latter require the fabrication of pillars of equal depth but differing width and spacing. As a demonstration device, the diffractive optic equivalent of a wedge has been made in GaAs for use at 1.15 μm. The need for all pillars to have the same height was met by using a selective etch and a very thin etch-stop layer on AlGaAs. The experimental diffraction efficiency was 87.8%, among the best ever obtained and close to the theoretical maximum of 97.6%.
Atom technology project: Recent activities
Authors: Tanaka Kazunobu
Published: July 2002

The “Atom Technology” project started in fiscal 1992 as one of MITI’s 10 year projects, aims at systematically establishing technology for handling individual atoms and molecules on a solid surface or in a three-dimensional space, as a generic technology for various fields of industry. This project, closely adjacent to science, emphasizes the following three key focuses: atom manipulation, nanoscale self-organization, and critical-state phase control, with two basic approaches of in situ dynamical observation (experimental) as well as ab initio calculation (theoretical). In this article, several topics were picked up from recent activities at the Joint Research Center for Atom Technology (JRCAT) for Phase I of the initial 6 years (1992–1997) and some technical details were described: (1) ultrathin SiO2 on Si(001) surfaces; layer-by-layer oxidation, its kinetics, scanning reflection electron microscopy observation, and scanning tunneling microscopy observation of leakage sites; (2) growth and transport of structure-controlled SinHx+ clusters for deposition using a novel ion trap; and (3) colossal magnetoresistance and related phenomena in perovskite-type manganese oxides. Research plans for phase II (1998–2001) of the project will be also touched upon.
Plasma source for ion and electron beam lithography
Authors: Lee Y. , Gough R. A. , Leung K. N. , Vujic J. , Williams M. D. , Zahir N. , Fallman W. , Tockler M. , Bruenger W.
Published: July 2002

A new plasma source configuration, coaxial source, has been developed at the Lawrence Berkeley National Laboratory suitable for ion and electron beam lithography applications. The axial ion energy spread and electron temperature of the multicusp ion source have been reduced considerably from 2 and 0.3 eV to a record low of 0.6 eV by employing a coaxial source arrangement. Results of ion projection lithographic exposure at the Fraunhofer Institute demonstrate that feature size less than 65 nm can be achieved by using a filter-equipped multicusp ion source. Langmuir probe measurements also show that very low energy spread electron beams can be obtained with the multicusp plasma generator.
Imaging interferometric lithography: A wavelength division multiplex approach to extending optical lithography
Authors: Chen Xiaolan , Brueck S. R. J.
Published: July 2002

The critical dimension (CD) limits of conventional optical lithography follow directly from the low-pass filter characteristics of the imaging optical system (|k|≲2πNA/λ where λ is the optical wavelength and NA the numerical aperture). In contrast, the linear systems limits of optics extend to spatial frequencies of 4π/λ (interference between counterpropagating beams at grazing incidence). Imaging interferometric lithography is introduced as a technique to approach this linear systems limit while retaining the arbitrary pattern capability of an imaging optical system. Multiple, wavelength-division-multiplexed exposures are used, each exposure recording a different portion of frequency space. A conventional, coherent illumination exposure provides the low frequency information, within the lens passband. Offset exposures provide the high spatial frequency information. Off-axis illumination shifts a portion of the high spatial frequency diffraction from the mask into the lens passband and interference with a reference beam resets the frequencies once they are transmitted through the optical system. For a typical x-y geometry pattern, offset exposures in the x and y directions provide a sufficient coverage of frequency space. Model calculations illustrate that the imaging capabilities of imaging interferometric lithography (IIL) for dense features extend to ∼λ/3 (130 nm at I line; 65 nm at an ArF exposure wavelength). Initial experiments are reported at I line with a modest (NA=0.04) optical system. The results are in good agreement with the model calculations. A resolution enhancement of ∼3× from dense 6 μm CDs for a conventional, coherent illumination exposure to ∼dense 2 μm CDs for an IIL exposure sequence is demonstrated.
Influences of off-axis illumination on optical lens aberration
Authors: Smith Bruce W. , Petersen John S.
Published: July 2002

Through modification of the illumination system of optical lithography tools, resolution and focal depth improvements can allow for near diffraction limited imaging. Most often, lens aberrations are evaluated assuming full use of a lens pupil. With off-axis illumination (OAI), diffraction information is distributed selectively over the lens pupil, influencing the impact of aberrations on imaging. This article describes these effects through a modified set of aberration coefficients and their variance over a pupil illuminated using OAI. Results in general show that astigmatic effects can worsen while spherical aberration and defocus effects can be improved. Coma induced image placement can be further aggravated with OAI unless rebalanced with tilt. The analysis presented here can also be extended to phase-shift masking approaches.
Evaluation of a two-mask resolution enhancement technique
Authors: White D. L. , Wood O. R.
Published: July 2002

We have evaluated the performance of an optical projection lithography camera employing a two-mask resolution enhancement technique proposed by Matsumoto et al. [K. Matsumoto et al., Proc. SPIE 2197, 844 (1994)] and Kamon et al. [K. Kamon et al., Jpn. J. Appl. Phys., Part 1 33, 6848 (1994)] in 1994 that automatically provides a different illumination for every feature on the reticle. Our simulations show that such a system can provide better imaging performance than a system that employs ordinary quadrupole illumination and can enhance the depth of focus by more than 50% in specific cases.
Characteristics of Ta-based amorphous alloy film for x-ray mask absorbers
Authors: Iba Yoshihisa , Kumasaka Fumiaki , Iizuka Takashi , Aoyama Hajime , Yamabe Masaki
Published: July 2002

We examined Ta-based amorphous alloy films and studied their characteristics for application in an x-ray mask with dimensions of the 0.1 μm design rule. From the viewpoint of x-ray absorption, Ge is a suitable element for a compound with Ta. We found that a Ge inclusion atomic ratio of 20%–30% in a Ta–Ge compound film was suitable with respect to stress control and stress stability. It was possible to adjust the stress of the Ta–Ge film after deposition by annealing it at high temperature while maintaining control as good as 0.56 MPa/ °C. During pattern fabrication by dry etching, it was possible to successfully etch the Ta–Ge film with a single-layer resist using a chroline based plasma, and scale patterns of 0.1 μm were obtained.
Enhanced pattern area density proximity effect correction
Authors: Ea C. S. , Brown A. D.
Published: July 2002

In this article, we describe and analyze the sources of correction error in the pattern area density proximity effect correction (PADPEC) method of Murai et al. [F. Murai, H. Yoda, S. Okazaki, N. Saitou, and Y. Sakitani, J. Vac. Sci. Technol. B 10, 3072 (1992)]. By focusing on the dominant contribution to the overall error, we are able to enhance the technique further, developing the enhanced PADPEC, or EPADPEC method. EPADPEC further reduces linewidth errors by factors ranging from 4 to 11, while increasing the computation time by a factor of only 1.23. [Migrating EPADPEC to a dedicated (parallel) environment will enable the data throughput rate to be dramatically increased.]
Low-voltage operation from the tower structure metal–oxide–semiconductor field-effect transistor Si field emitter
Authors: Koga Keisuke , Kanemaru Seigo , Matsukawa Takashi , Itoh Junji
Published: July 2002

To improve emission stability and realize low turn-on voltage, a silicon field emitter controlled by a metal–oxide–semiconductor field effect transistor (MOSFET) was fabricated and demonstrated. The emitter cathode was fabricated in the n-well drain of the MOSFET on a p-type silicon substrate. In addition to the extraction gate, another electrode was introduced as the MOSFET’s control gate. This gate’s oxide thickness was designed to be thinner than that of the extraction gate for low turn-on voltage. Furthermore, two types of drain structure were adopted to compare device reliability with regard to impact ionization effect. Experimental results showed that emission current was effectively controlled by the MOSFET at a gate voltage of less than 5 V. It was found that impact ionization was caused near the drain edge, where a high electric field was concentrated, in the conventional drain structure. Consequently, MOSFET characteristics were significantly influenced.
Effects of nitrogen addition on the structure and field emission properties of amorphous carbon
Authors: Chi Eung Joon , Shim Jae Yeob , Baik Hong Koo
Published: July 2002

The films of amorphous carbon with different amounts of incorporated nitrogen are deposited by helical resonator plasma enhanced chemical vapor deposition using CH4, Ar, and N2 gas mixtures. As the nitrogen content in the films increases, the optical band gap and sp3 bond fraction decreased. The higher field emission current and the lower turn-on voltage are obtained from the sample of the higher nitrogen content. The calculated emission barrier heights for a-C:N (5/5) and (10/0) are 0.76 and 0.70 times that for a-C, respectively. The increase of the conducting part of the films and the role of nitrogen as an electrical donor are responsible for the enhanced field emission.
Distributed amplifier based on a field emitter array and a low-loss transmission line
Authors: Galdetskiy A.
Published: July 2002

A new design of distributed amplifier is considered that consists of a coplanar transmission line using open-circuit field emitter arrays (FEAs). This structure has very low “cold” losses (one to two orders less than a FEA) and renews the opportunity to develop a high frequency, wide-band distributed amplifier. As an example, an amplifier design having an output power of 37 W and a gain of 13 dB at frequencies up to 45 GHz is considered.
Strained InGaAs/AlGaAs tilted T-shaped quantum wires fabricated by glancing-angle molecular beam epitaxy
Authors: Shimomura S. , Ohta K. , Tatsuoka Y. , Hiyamizu S. , Fujita K. , Egami N.
Published: July 2002

A pseudomorphic InGaAs/AlGaAs tilted T-shaped quantum wire (T-QWR) structure was fabricated on a (100) GaAs substrate with reverse mesa stripes by glancing angle molecular beam epitaxy (GA-MBE) for the first time. The tilted T-QWRs consist of a (GaAs)10(InAs)1(GaAs)10/Al0.3Ga0.7As (6.3 nm/25 nm) multiquantum well (MQW) on a (100) face and a 6.1-nm-thick In0.175Ga0.825As single quantum well (SQW) on a (111)B facet which has a cross section of the (100) MQW and was formed at the stripe edges during GA-MBE growth. Suitable growth condition was obtained by investigating substrate temperature dependence of growth mode and lateral indium content profile of an InGaAs layer on the (111)B facet and the adjacent (100) face by scanning electron microscopy observation and energy dispersive x-ray spectroscopy measurements. Cathodoluminescence (CL) from the tilted T-QWRs was measured at 78 K. A CL peak due to irradiation from excitons confined in the T-QWR region was clearly observed at 1.438 eV, which was 38 meV lower than the CL peak energy for the (111)B SQW, and 79 meV lower than that for the (100) MQW. The confinement energy value (38 meV) is 2.1 times higher than that of GaAs/AlGaAs tilted T-QWRs (18.3 meV) with almost the same wire widths.
A comparative study of carbon incorporation in heavily doped GaAs and Al0.3Ga0.7As grown by solid-source molecular beam epitaxy using carbon tetrabromide
Authors: Lubyshev D. , Micovic M. , Gratteau N. , Cai W.-Z. , Miller D. L. , Ray O. , Streater R. W. , SpringThorpe A. J.
Published: July 2002

The electrical properties of carbon doped GaAs and AlGaAs were studied as a function of substrate temperature and CBr4 flux for the doping range ∼1018–1020 cm−3. Hall measurements indicate a strong reduction in the free carrier concentration of GaAs films grown with the same CBr4 flux at substrate temperatures above 620 °C. Secondary ion mass spectroscopy measurements, however, show no reduction of chemical carbon concentration. The electrical properties of GaAs:C epilayers grown on (n11)A and B surfaces, where n=2–5, show strong dependence on crystallographic orientation. Based on these measurements, the model of free carrier concentration reduction in GaAs:C based on formation of electrically inactive C–C pairs has been proposed. In contrast, no anomalous carbon incorporation in AlGaAs has been detected for the doping range ∼1018–1020 cm−3 and the substrate temperature range 550–700 °C. The resulting material exhibits excellent transport and optical properties.
Molecular beam epitaxial growth of normal and inverted two-dimensional electron gases in AlGaN/GaN based heterostructures
Authors: Murphy M. J. , Chu K. , Wu H. , Yeo W. , Schaff W. J. , Ambacher O. , Smart J. , Shealy J. R. , Eastman L. F. , Eustis T. J.
Published: July 2002

Two-dimensional electron gases in AlGaN/GaN heterostructures grown by plasma induced molecular beam epitaxy have been formed by polarization induced interface charge effects. Growth of the “normal” structure (AlGaN on GaN) has formed a two-dimensional electron gas confined in the GaN when grown on sapphire with an AlN nucleation layer, SiC (Si face), or on GaN nucleated by organometallic vapor phase epitaxy on sapphire. Hall mobilities in GaN for normal interfaces are as high as 1238 cm2/V s at 300 K and 3182 cm2/V s at 77 K. Direct current results from field effect transistors fabricated from this material yield a maximum transconductance of 210 mS/mm and a current density of 710 mA/mm. Microwave measurements gave a ft of 27 GHz and a fmax of 37 GHz. When nucleating GaN directly on sapphire, an “inverted” structure (GaN on AlGaN) was used to create a two-dimensional electron gas. The difference in the normal and inverted structures is the polarity of the (Al)GaN layers. The flipping of the (Al)GaN polarity on sapphire is achieved through the use of the AlN nucleation layer.
Growth of 1.3 μm InGaAsN laser material on GaAs by molecular beam epitaxy
Authors: Mars D. E. , Babic D. I. , Kaneko Y. , Chang Ying-Lan , Subramanya Sudhir , Kruger Joachim , Perlin Piotr , Weber Eicke R.
Published: July 2002

We have grown bulk GaAsN and InGaAsN quantum well laser structures using molecular beam epitaxy and an electron cyclotron resonance plasma source with N2 gas. X-ray diffraction measurements in GaAsN grown on GaAs were used to determine the concentration of N in the range of 0% to ∼2%. Room temperature photoluminescence (PL) measurements were done on quantum well test structures and half lasers. The PL intensity decreases and the PL full width at half maximum (FWHM) increases as the wavelength increases. Rapid thermal annealing (RTA) at 850 °C for 10 s improves the PL intensity by a factor of 8 and increases the PL peak emission energy by 80 meV. The longest wavelength measured to date in laser structures with single quantum wells of InGaAsN is 1480 nm with a FWHM of 60 meV. Samples with and without RTA were fabricated into broad-area lasers with dimensions of 50×500 μm2. Laser devices with RTA operated in the pulsed mode at 1.3 μm with a threshold current density of 9.5 kA/cm2.
Growth and characterization of epitaxial FexAl1−x/(In,Al)As/InP and III–V/FexAl1−x/(In,Al)As/InP structures
Authors: Sacks R. N. , Qin L. , Jazwiecki M. , Ringel S. A. , Clevenger Marvin B. , Wilt David , Goorsky M. S.
Published: July 2002

We report on the growth of high quality epitaxial FexAl1−x on (In,Al)As/InP with x=0.45–0.80 and thicknesses up to 1000 Å, and on overgrowth of III–V semiconductor on the metal. Buffer layers of (In,Al)As were grown on InP substrates in a III–V growth chamber, then transferred to an attached ultrahigh vacuum chamber with dual e-beam evaporators, where FexAl1−x layers were grown by co-evaporation. Despite a large lattice mismatch of ∼1%–2% between the metal and the semiconductor, high quality layers of FexAl1−x with thicknesses of up to 1000 Å were grown. The metal layers showed bright, streaky reflection high-energy electron diffraction patterns, were specular under Nomarski microscopy, and had roughnesses of ∼1–2 monolayers as measured by atomic force microscopy. High resolution x-ray diffraction showed that even at 1000 Å, the layers were fully strained, and Pendellosung oscillations were observed, indicating high crystalline quality. Metal layers over ∼200 Å thick had resistivities in the range of those expected of bulk layers (50–100 μΩ cm). Reflectivities greater than 90% for λ=4–20 μm were observed for metal layers 1000 Å thick. Overgrowth of (In,Ga)As and (In,Al)As on the metal layers shows a marked sensitivity to As overpressure, possibly due to an In surface-riding layer on top of the metal.
In situ monitoring of AlGaAs compositions and GaAs growth at high temperature by spectroscopic ellipsometry and desorption mass spectroscopy
Authors: Taferner W. T. , Mahalingam K. , Dorsey D. L. , Eyink K. G.
Published: July 2002

In situ spectroscopic ellipsometry has been used in conjunction with desorption mass spectrometry to determine both the composition of Al and growth rate of AlxGa1−xAs and GaAs at high temperatures (600–720 °C). Ex situ cross sectional transmission electron microscopy verified the AlGaAs/GaAs layer thicknesses grown by molecular beam epitaxy at these elevated temperatures. The substrate temperature dependence on Ga desorption rates, given the As, Ga, and Al fluxes and V/III flux ratios, was examined by Monte Carlo simulation. These simulations showed good agreement with the experimental results.