bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoscale topography control for the fabrication of advanced diffractive optics
Authors: Liddle J. Alexander , Salmassi Farhad , Naulleau Patrick P. , Gullikson Eric M.
Published: December 2003

Gray-scale electron beam lithography has been used to create high-efficiency (63%, output normalized) blazed gratings suitable for use at extreme ultraviolet (EUV) wavelengths (i.e., 13.4 nm). The total blaze height at these wavelengths is ≈7 nm. The surface topography was generated in a single processing step in hydrogen silsesquioxane (HSQ). This material converts to SiO2 upon exposure and forms a robust substrate for subsequent operations, unlike conventional organic resists. The HSQ is overcoated with a Mo/Si multilayer to provide reflectivity at EUV wavelengths. The grating efficiency is determined by the fidelity of the profile to the ideal and by the surface roughness of the HSQ. A region of the resist response curve was identified that enabled sufficient topography to be generated while maintaining the surface roughness of the resist below 2.5 nm root mean square. Large area (0.5×2.0 mm2) gratings were fabricated, and the resulting dose profile was adjusted during the course of the exposure to compensate for observed delay-time/reciprocity effects in HSQ.
Dynamic model for predicting in-plane displacement of extreme ultraviolet mask due to chucking
Authors: Chiba Akira , Sugawara Minoru , Nishiyama Iwao
Published: December 2003

A simulation model was devised to predict the in-plane displacement (IPD) of an extreme ultraviolet mask during a chucking operation with friction. The model is based on the theory of two-dimensional plane stress, and employs time evolution to predict the dynamic response of IPD. The IPD for a stepwise chucking force was found to reach a stationary state in 100 μs, after the vibrations attenuated. With regard to glass ceramic materials for the substrate, the effect of the coefficient of friction on IPD during a chucking operation was investigated. The IPD was found to decrease as the pattern density decreased. In order to reduce the IPD due to chucking, it is necessary to reduce the stress of the multilayer and absorber films, and to employ a substrate material with a high Young’s modulus.
Effects of chrome pattern characteristics on image placement due to thermomechanical distortion of optical reticles during exposure
Authors: Abdo A. , Capodieci L. , Lalovic I. , Engelstad R.
Published: December 2003

As optical lithography is extended to the sub-90 nm nodes, more stringent requirements are placed on the mask critical dimension and registration budget. Errors in image placement (IP) due to exposure-induced thermal loading of the optical reticle can be a significant contribution to the overlay error budget. Thermal loading on the mask is primarily caused by the chrome pattern that absorbs a large fraction of exposure light. The effects of the chrome pattern density, local pattern distribution, and chrome reflectivity were studied using three-dimensional finite-element models for both 193 and 157 nm technologies. It was found that the chrome pattern density has a stronger influence on the thermomechanical response than the pattern distribution. Also, it was found that as the chrome reflectivity increases, the reticle maximum temperature rise decreases, thus it follows a linear relationship. In addition, various reticle/chuck mounting designs were investigated to identify what type of configuration is necessary to reduce IP errors. The effects of different exposure tool parameters and resist sensitivities on IP errors were also evaluated.
Metallic tunable photonic crystal filter for terahertz frequencies
Authors: Drysdale Timothy D. , Mills Gordon , Ferguson Susan M. , Blaikie Richard J. , Cumming David R. S.
Published: December 2003

A tunable metallic photonic crystal filter has been fabricated by deep reactive ion etching of a silicon substrate followed by metallization. The filter plate’s two-layer orthogonal grid structure and integrated mounting lugs were fabricated from a single silicon wafer in two etching steps. A three-step metallization process (evaporation, sputtering, and electroplating) ensured all surfaces were coated with gold to greater than 4.6 times the skin depth at the frequencies of interest. The filter employs a mechanical tuning mechanism, the performance of which was predicted with rigorous full-vector electromagnetic simulations (finite-difference time domain). The prototype has been characterized at frequencies of 70–150 GHz using free-space measurement techniques. Its measured center frequency shifts from 144 to 137 GHz for 300 μm lateral shift of one of the plates, and it has an insertion loss of less than 1 dB.
Patterning of circular structure arrays with interference lithography
Authors: Solak Harun H. , David Christian
Published: December 2003

We have developed an interference lithography method that enables the production of circular periodic patterns. The range of accessible patterns includes concentric circular rings, spiral- and spoke-like patterns, and dots positioned periodically on concentric circular tracks. The method is based on the use of transmission diffraction gratings to create circular beams with wave fronts that are not accessible with reflective or refractive optics. Diffraction gratings with equally spaced concentric circles are used to obtain diverging or converging conical waves with radial phase variation and spiral-like gratings are used to obtain waves with the phase varying in both radial and azimuthal directions. We have experimentally demonstrated the method with electron-beam written diffraction gratings, which we illuminated with a coherent laser beam to form the interference patterns. Many different designs are possible that bring two, three, or more beams together to form a desired interference pattern. The technique should in general be useful in applications requiring circular periodic patterns, which may include production of patterned magnetic media, spoke patterns for angular encoders, and photonic crystals with circular symmetry.
Nanometer-level stitching in raster-scanning electron-beam lithography using spatial-phase locking
Authors: Hastings J. T. , Zhang Feng , Smith Henry I.
Published: December 2003

Pattern-placement inaccuracy is a persistent problem in scanning-electron-beam lithography (SEBL) despite the high-resolution obtained in SEBL systems. Pattern-placement errors stem from a variety of environmental and system variations; however, the fundamental issue is the open-loop nature of the system, i.e., the beam location on the substrate is not monitored during exposure. In contrast, spatial-phase-locked electron-beam lithography (SPLEBL) provides closed-loop control of the beam position by monitoring the signal from a fiducial grid on the substrate. By detecting the spatial phase of the grid signal one can estimate the beam position within a small fraction of the grid period. We have implemented SPLEBL by adding real-time signal processing, feedback control, and raster-scan exposure capability to an inexpensive SEBL system. Using a 246 nm period, electron-transparent fiducial grid that covers the entire substrate, we have exposed patterns that exhibit global placement accuracy with respect to the grid and field-stitching precision better than 1.3 nm (one standard deviation).
Measurement of semi-isolated polysilicon gate structure with the optical critical dimension technique
Authors: Shivaprasad Deepak , Hu Jiangtao , Tabet Milad , Hoobler Ray , Mui David , Liu Wei
Published: December 2003

The semiconductor road map predicts the production of sub-100 nm transistor gates that push further the limits of the size and speed posed by 180 nm gates that are currently in use. With this decrease in gate size, it has become extremely critical to measure these lines accurately using nondestructive techniques. The optical critical dimension (OCD) technique is emerging as one of the most promising CD measurement techniques for sub-0.1 μm device fabrication. Compared to CD scanning electron microscopy and X-SEM, OCD has several distinct advantages. It is nondestructive, has a fast turnaround time, is sensitive to sidewall profiles, and has sensitivity to sub-100 nm linewidths. It has been successfully used in important structures such as photoresist, shallow trench isolation, and polysilicon and tungsten silicide gates. In the OCD technique, a broadband polarized light beam is focused onto a grating at angle normal to the grating surface, and the spectrum of zeroth order reflection is measured. The spectrum contains the signature of the grating profile that is analyzed in real time using rigorous coupled wave analysis. Real time curve fitting algorithms, which do not require library generation, make the analysis simple and easy to extend to a variety of grating structures. Since the OCD technique is based on specular diffraction, a primary requirement for the OCD measurement target is to have periodical grating structures with a line to space ratio typically larger than 1:1. In this article, we report use of the OCD technique to measure polysilicon gate gratings with line to space ratios as large as 1:20. Polysilicon gate grating structures with critical dimensions of 30–40 nm were measured for line to space ratios of 1:10 and 1:20. In both cases, the measurement showed extreme sensitivity to the linewidth and detailed profile, without deterioration of the repeatability. This study has significantly extended the measurement range of the OCD technique and its application to isolated line measurements.
Effects of temperature and HCl flow on the SiGe growth kinetics in reduced pressure–chemical vapor deposition
Authors: Hartmann J. M. , Loup V. , Rolland G. , Séméria M. N.
Published: December 2003

Using a reduced pressure chemical vapor deposition cluster tool, we have studied at 20 Torr the growth kinetics of SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl leads at 700 °C to a significant increase in the germanium content x of SiGe layers. Adopting a x2/(1−x)=n(F(GeH4)/F(SiH2Cl2)) dependence of x on the F(GeH4)/F(SiH2Cl2) mass flow ratio, this translates into an n value linearly increasing with the HCl mass flow from n=0.66 (no HCl) up to n=2.24 (F(HCl)/F(H2)=0.00625). The SiGe growth rate increases strongly with an increasing GeH4 flow. This is attributed to an increased hydrogen desorption caused by the presence of Ge atoms on the growing surface that frees nucleation sites for the incoming Ge and Si atoms. Meanwhile, adding HCl leads to a strong, linear reduction of the SiGe growth rate with the HCl mass flow. As expected, the Ge concentration decreases significantly as the growth temperature increases from 650 to 750 °C. The associated n parameter depends exponentially on the reverse absolute temperature, with an “activation energy” of the order of −15 kcal mol−1. At the same time, the SiGe growth rate increases strongly as the growth temperature increases, with an activation energy dropping from 47 down to 12 kcal mol−1 as the Ge content in the film goes up (from 0% up to 27% at 700 °C).
Technique for preventing stiction and notching effect on silicon-on-insulator microstructure
Authors: Li J. , Zhang Q. X. , Liu A. Q. , Goh W. L. , Ahn J.
Published: December 2003

The notching (undercutting or footing) and stiction problem, which widely exists in silicon-on-insulator microstructure were resolved in this study regardless of the feature sizes, by the introduction of a spacer oxide thin film. In this modified process, the deep reactive ion etching was divided into several steps, where conformal plasma enhanced chemical vapor deposition oxide coating, and anisotropic oxide etch were employed to prevent the notching effect. Dry chemical release was also realized in this approach but the deep etching did not etch through the device layer. The notching or footing effect was exploited for attaining the lateral etching following the deployment of the anisotropic plasma etching of the inductively coupled plasma. This method was proven useful for both the uniform and nonuniform feature designs. To validate the proposed etching method, an optical switch was fabricated. The details and benefits of the proposed process and its extensions to more valuable and flexible design were all discussed in this article.
Positive charge effect in atomic force microscope anodization lithography using self-assembled monolayers of metal phosphate as resists
Authors: Kim Sang Min , Lee Haiwon
Published: December 2003

Various metal phosphate monolayers prepared as resists on silicon substrates were prepared for atomic force microscope (AFM) anodization lithography. The metal phosphate monolayers were prepared by binding tetravalent (Zr4+, Hf4+) or divalent (Ca2+, Mg2+) metal ions on a phosphorylated Si substrate. The presence of the metal ions on a phosphorylated Si substrate was confirmed using Auger electron spectroscopy. Since the divalent and tetravalent metal ions are changed to be neutral and divalent, respectively, after binding on phosphorylated substrates, the role of a positive ion in the monolayer structure in AFM anodization lithography was systematically investigated. The presence of positively charged metal ions in case of Zr4+ and Hf4+ enhances the electron transfer from a tip to a substrate under a tip negative bias. In addition to the effect of lowering a bias for anodization process, the lithographic scan speed was also enhanced by the order of magnitude in the presence of the positive ions. After patterning of protruding lines on Zr2+ phosphate monolayer, the etching process was also accomplished.
Study of beveled angle effect on morphology of dual damascene via filling using ionized physical vapor deposition
Authors: Hwang Chi-Chuan , Chang Jee-Gong , Weng Ming-Hang , Lin Hong-Chang
Published: December 2003

This article employs a molecular dynamics (MD) simulation approach to investigate the influence of beveled angles on the filling mechanisms of a dual damascene process. The objective of the present study is to propose a method that overcomes the problem of incomplete via filling associated with the traditional dual damascene process. The simulation incorporates three separate MD models, namely the dual via model, the deposition model, and the potential model. Furthermore, the simulation adopts the thermal control layer marching algorithm to increase the accuracy of the solution and to reduce the computational time. The present results indicate that the introduction of beveled angles at the upper via corners has a detrimental impact upon the filling of the lower via at moderately low via-radius ratios (1.75, 2.0). At a via-radius ratio of 1.75, the filling morphology changes from one of complete filling to one with trapped voids within the via when beveled angles are introduced, while at the slightly larger via-radius ratios of 2.0 and 2.5, the voids in the lower via are observed to grow in size. It is noted that the influence of beveled angles at the upper via corners on the lower via filling becomes less significant as the via-radius ratio increases (2.5, 3.0). In general, it is found that the introduction of beveled angles at the lower via corners is beneficial to the filling coverage of the lower via, but has no impact upon the filling of the upper via.
Electron beam lithography process using radiation sensitive carboxylate metalorganic precursors
Authors: Jeyakumar Augustin , Henderson Clifford L. , Roman Paul , Suh Seigi
Published: December 2003

A bilayer process has been developed for electron beam lithography using radiation sensitive metalorganic precursors as imaging layers in conjunction with organic planarizing layers. Upon electron beam irradiation, the precursor is converted to a metal oxide which serves as an etch mask for subsequent pattern transfer through the planarizing layer. In this article, a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor was investigated that exhibits sensitivity and contrast of 495 μC/cm2 and 2.75, respectively, 10 keV accelerating potential. The sensitivity was further enhanced to 72 μC/cm2 using a pre-exposure thermal bake to partially convert the precursor to metal oxide prior to electron beam imaging. Additionally, it was found that combining the titanium(n-butoxide)2(2-ethylhexanoate)2 precursor with a similar precursor containing a higher atomic number metal center, barium(2-ethylhexanoate)2 in this work, also enhanced the sensitivity to 157 μC/cm2 for a 1:1 molar mixture of the precursors. After imaging and development, the patterns were completely converted to metal oxide by thermal baking to improve the etch resistance of the hard mask. This postdevelopment thermal conversion step was found to result in vertical shrinkage of the features and minimal lateral shrinkage. For bilayer processing, the titanium precursor was imaged on top of hard baked novolac and the pattern was transferred through the novolac using an O2 reactive ion etch. Sub-100 nm patterning is demonstrated using both single layer and bilayer processes with these materials, with aspect ratios greater than five achieved with the bilayer process.
Ultrathin TiO2 amorphous films for high transmittance APSM blanks at 157 and 193 nm wavelength simultaneously
Authors: Lai F. D. , Chang C. M. , Wang L. A. , Yih T. S.
Published: December 2003

Ultrathin TiO2 amorphous films are deposited on ultraviolet grade fused silica substrates and CaF2 by using rf reactive unbalanced magnetron sputtering from a Ti metal target in atmosphere of Ar and O2. For an O2/Ar flow rate ratio of more than 1.5, the deposited TiO2 thin films are stoichiometric. TiO2 thin films that meet the optical requirements of a high transmittance attenuated phase-shifting mask (HTAPSM) at 157 and 193 nm wavelengths can also be properly inspected since the transmittance at 257 nm wavelength is less than 28%. The simulated thickness range of such a TiO2 thin film is found to be between 16 and 20 nm. A TiO2 amorphous thin film with thickness of 23.5 nm, transmittance of 24.9% and reflectance of 15.0% at wavelength of 193 nm, transmittance of 16.3% at 157 nm wavelength and transmittance of 23.0% at 257 nm wavelength is shown to be able to serve as an absorber layer for HTAPSM blanks at 157 and 193 nm wavelength.
Near edge x-ray absorption fine structure measurements of surface segregation in 157 nm photoresist blends
Authors: Jablonski Erin L. , Prabhu Vivek M. , Sambasivan Sharadha , Lin Eric K. , Fischer Daniel A. , Goldfarb Dario L. , Angelopoulos Marie , Ito Hiroshi
Published: December 2003

The surface and bulk chemistry of photoresist blends for use at the 157 nm node were analyzed using near edge x-ray absorption fine structure spectroscopy to quantify component segregation and identify surface phenomena that may impact pattern formation. Spectral combinations of the constituent polymers are used to fit the spectra of the blend films. Significant segregation of one component to the surface of the photoresist film was found, in excess of the composition of that component in the blend. The bulk data were consistent with initial blend compositions. As expected, the more hydrophobic or lower surface tension component wets the film surface even under typical photoresist processing conditions.
Extending optics to 50 nm and beyond with immersion lithography
Authors: Switkes M. , Kunz R. R. , Rothschild M. , Sinta R. F. , Yeung M. , Baek S.-Y.
Published: December 2003

Numerical imaging simulations demonstrate the capability of immersion lithography to print features smaller than 45 nm (35 nm) with good depth of focus at a vacuum wavelength of 193 nm (157 nm). The optical impact of index variation of the immersion liquid is simulated and found to be a shift of focus of 1 nm for each 1 ppm change in the bulk index of the liquid. For an index which varies through the thickness of the liquid (e.g., due to nonuniform temperature), the focus shift is found to be proportional to the total change in optical path length (OPL), with a 1 nm change in OPL leading to a ∼1.5 nm focus shift at 1.3 numerical aperture. A focus offset of 1–3 nm can be expected due to heating during scanning exposure. The possible formation of nanobubbles at resist surfaces is also discussed. While simulations show that even 10 nm thick bubbles at the surface of the resist cause 30% modulation in the aerial image intensity, no evidence of bubbles is seen in open frame immersion exposures. Imaging of 100 nm features is shown using an immersion contact phase-edge technique, with no evidence of bubbles or adverse liquid–resist interactions. Finally, we describe progress in the search for low absorbance liquids for use at 157 nm. Liquid purity, including dissolved O2 and H2O, is found to be critical. The current absorbance record, 0.64±0.07 cm−1, held by perfluorotriglyme (CF3[OCF2CF2]3OCF3), is enough for a 350 μm working distance at 95% transmission.
Imprinting polymer film on patterned substrates
Authors: Tan L. , Kong Y. P. , Bao L.-R. , Huang X. D. , Guo L. J. , Pang S. W. , Yee A. F.
Published: December 2003

We have developed a technique to create polymer film patterns on substrates with microstructures using an elastomeric polydimethylsiloxane (PDMS) pad, wherein either a continuous or a patterned film on flat PDMS was used for pattern creation. During patterning of the continuous film, a polymer film is first spin coated onto the elastomer pad, and the pad is then brought into contact with the patterned substrate of interest. Since the PDMS can deform elastically around features on the substrate and its surface has low interfacial energy, films on PDMS can be successfully transferred onto the substrate. The resulting profile of the transferred film would depend on the pattern dimensions of the substrate, polymer properties, and conditions for imprinting. Three distinctive film patterns can be achieved, which we designate as continuous film transfer over microstructures, film transfer on both trenches and protrusions, and film transfer on protrusions. Interestingly, a negative replica of patterns on substrates can be simultaneously created on the PDMS pad in the last patterning process and the pattern can be further utilized in subsequent patterning steps. This affords the capability of transferring a patterned film from the PDMS to the sidewalls of the topographic features. Because of the great versatility of this patterning technique, it can be used to rapidly form channels, conformal coating on a patterned substrate, and micro- or nanometer sized patterns inside trenches of a patterned substrate.
Carbon nanopillar laterally grown with electron beam-induced chemical vapor deposition
Authors: Fujita J. , Ishida M. , Ichihashi T. , Ochiai Y. , Kaito T. , Matsui S.
Published: December 2003

We found that the lateral growth of a carbon nanopillar with electron beam-induced chemical vapor deposition (EB-CVD) was mainly dominated by forward scattering of the electron beam. The minimum diameter of the carbon nanopillar was reduced to 5 nm. In contrast, vertical growth with EB-CVD produced thicker pillars ∼50 nm in diameter, with a shape that reflected forward scattering of the primary electrons. Graphitization of the amorphous carbon nanopillars was also demonstrated by annealing, in which nanoiron particle traces were graphitized.
Transistor structures for the study of scaling in carbon nanotubes
Authors: Wind S. J. , Radosavljević M. , Appenzeller J. , Avouris Ph.
Published: December 2003

We report on the fabrication and electrical characterization of two uniquely structured carbon nanotube field-effect transistors (CNFETs). These devices have been designed to emphasize different aspects of their electrical switching behavior, so that we may learn more about their transport properties. In one structure, back-gate CNFETs were built to study the effects of vertical scaling by varying the thickness of an underlying high-quality gate dielectric. An unexpected dependence of the subthreshold slope and transconductance on the gate dielectric thickness was observed, and was attributed to Schottky barrier switching at the metal/nanotube contacts. A second structure incorporates a top gate electrode with multiple, individually addressable segments of different width. This design decouples the interior of the device from the contacts, thereby enabling the study of lateral scaling within the same physical device structure. Clear indications of bulk switching were observed in this device, with strong evidence of ballistic transport, suggesting that CNFETs do not follow conventional gate length scaling rules.
Observations and measurements of photomasks using an electron beam with energy of 50 keV or higher
Authors: Mizuno Fumio , Ohfuji Takeshi , Amano Tsuyoshi
Published: December 2003

Applying a high-energy electron beam during photomask observations has been studied for improving resolution and reducing measurement uncertainty. Photomasks can be observed and measured by using an electron beam of 50 keV or higher in combination with a conductive coating over the photomask surfaces. Though image brightness and contrast vary with electron-beam exposure time, the effects of brightness and contrast on images are not significant and not essentially different from the effects with conventional low-energy electron beams. Therefore, a high-energy electron beam has the possibility of providing a higher measurement certainty than a conventional low-energy electron beam.
Benchmarking stencil reticles for electron projection lithography
Authors: Wood O. R. , Trybula W. J. , Lercel M. J. , Thiel C. W. , Lawliss M. J. , Edinger K. , Stanishevsky A. , Shimizu S. , Kawata S.
Published: December 2003

Electron projection lithography (EPL) is one of the leading candidates for next-generation lithography at the 65 nm lithography node, particularly for contact levels. This article describes the results of an experimental effort to benchmark the current state of EPL stencil mask making. In this article, we report on the current status of the data handling software needed to pattern an EPL stencil reticle, EPL stencil reticle repair techniques, and EPL stencil mask stability following prolonged electron-beam irradiation.
Effect of incident angle of off-axis illumination on pattern printability in extreme ultraviolet lithography
Authors: Sugawara Minoru , Chiba Akira , Nishiyama Iwao
Published: December 2003

The effect of the incident angle of off-axis illumination on the printability of 22-nm-wide line patterns was investigated for three absorber stack configurations. Shadowing due to off-axis illumination and the absorber wall degrades printability, especially for a dense pattern layout. It was found that the influence of shadowing on resolution and pattern fidelity could be suppressed by employing a small incident angle and thin buffer and absorber films. An incident angle below 6.0° and an absorber stack with an optical density of 2.0 provide a practical level of pattern fidelity. Furthermore, a small incident angle below 5.0° and a thin absorber stack eliminate differences in fidelity for patterns with different orientations with respect to the direction of the off-axis light incident on a mask.
Effect of oxygen adsorption on the efficiency of magnesium photocathodes
Authors: Yuan Quan , Baum Aaron W. , Pease R. Fabian W. , Pianetta Piero
Published: December 2003

The quantum efficiency (QE) of photocathodes is key to their being used as electron sources in electron beam lithography and inspection. We have built and are using equipment for measuring quantum efficiency, weight gain, and residual gas pressure. During exposure to oxygen at 10−10–10−8 Torr, we observed an initial rise of between five- and eightfold in quantum efficiency to 0.2% followed by a decrease in QE and saturation of the oxygen uptake (weight gain). At lower oxygen pressures, the cathode exhibits a higher peak QE and larger total weight gain. The peak quantum efficiency can be kept stable to within 1% over 24 h if the ambient pressure is 2×10−10 Torr. The drop in quantum efficiency upon further exposure to oxygen at pressures >10−9 Torr suggests the growth of an oxide layer that reduces emission and the presence of a loosely bound adlayer of molecular oxygen during oxygen exposure.
Ab initio calculations of field emission from ultrathin Si(100) films
Authors: Gohda Y. , Watanabe S.
Published: December 2003

We have analyzed field emission from ultrathin Si(100) films on a metal substrate by using ab initio density functional calculations incorporating scattering states. We have shown that the clean Si(100) film can screen an external electric field sufficiently due to metallic states of surface dangling bonds, and thus field emission from the clean silicon film is attributed to that from surface states. We have also analyzed effects of metal adsorption on field emission from Si(100) films. We have obtained a much larger emission current from the Si(100)2×2-Al surface at 0.5 monolayer coverage than that from clean silicon and aluminum surfaces. The minimum local barrier height clearly explains the difference between the Si(100)2×2-Al surface and the clean Al(100) surface, which cannot be explained from the small difference in the work function between the two surfaces. We have also found that the emission current further increases with a change in the atomic position of adsorbed aluminum addimers which causes both a decrease in the minimum local barrier height and an increase in the local density of states at a surface around the Fermi level.
Structure, hardness, and elastic modulus of Pd/Ti nanostructured multilayer films
Authors: Xu Junhua , Kamiko Masao , Sawada Hidetaka , Zhou Yaomin , Yamamoto Ryoichi , Yu Lihua , Kojima Isao
Published: December 2003

The structure, hardness, and elastic modulus of Pd/Ti multilayers deposited by radio-frequency magnetron sputtering were investigated by x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. Both the Ti and Pd layers were face-centered-cubic structures in all modulation periods from 2.8 nm to 90.0 nm in Pd/Ti multilayers. There are stacking faults in Ti layers at large modulation periods, where the crystal structure is hexagonal close packed. An anomalous hardness enhancement was observed. The hardness values of Pd/Ti multilayers are three times and two times the values measured in Pd films and as calculated by the rule of mixture for Pd and Ti films, respectively. The modulus values of Pd/Ti multilayers are between those of constituent single layer films at a larger modulation period, and increase slightly at a smaller modulation period. The elastic modulus difference model cannot explain this hardness enhancement, since the elastic modulus is almost the same for the constituent materials in the Pd/Ti multilayers. The hardening mechanisms in the multilayers have been discussed.
Water-in-carbon dioxide microemulsions for removing post-etch residues from patterned porous low-k dielectrics
Authors: Zhang Xiaogang , Pham Joseph Q. , Martinez Hunter J. , Wolf P. Josh , Green Peter F. , Johnston Keith P.
Published: December 2003

A hierarchy of CO2-based solvents is used to remove post-etch residues from vias and trenches in low-k patterned porous methylsilsesquioxane (pMSQ) interlayer dielectrics. Spectroscopic ellipsometry measurements indicate that, upon pressurization and depressurization with CO2, the thickness and refractive index return to values near the original values indicating that collapse or voiding of the pores did not occur. Post-etch residue could not be removed by pure water, CO2, with or without cosolvent, or dry CO2 with a surfactant. These results suggest that the particles could not be removed by a dissolution mechanism alone. The via and the bottom trench were cleaned with a solvent containing water, CO2, and a hydrocarbon surfactant. In this mild detergent system, particles may be removed both as a suspension and in the dissolved state in microemulsions and macroemulsions. The low interfacial tension prevents collapse of the pMSQ during water removal. This mild detergent system does not produce voids in the pMSQ. Thus, this detergent cleaning technique appears to be selective for post-ash residues on pMSQ dielectrics and is of significant practical interest.
Formation of metastable c-AlN and its effect on the mechanical properties of AlN/(Ti,Al)N nanoscale multilayers
Authors: Hu Xiaoping , Yu Xiaojiang , Lao Jijun , Li Geyang , Gu Mingyuan
Published: December 2003

The formation of metastable phases has a great influence on the mechanical properties of multilayers. A series of AlN/(Ti,Al)N nanoscale multilayers with various modulation periods were synthesized by reactive magnetron sputtering. X-ray diffraction analysis, high resolution transmission microscopy and the microindentation technique were employed to characterize the microstructure and mechanical properties of the multilayers. The results show that metastable c-AlN forms due to the “template” effect of (Ti,Al)N in AlN/(Ti,Al)N multilayers with small modulation periods, and forms columnar crystals with (Ti,Al)N through epitaxial growth and results in lattice distortion due to the lattice mismatch between c-AlN and (Ti,Al)N. Correspondingly, the hardness and the elastic modulus of the multilayers increase with a decrease of modulation period monotonically and reach the maximal hardness (29 GPa) and elastic modulus (377.8 GPa) at a modulation period of 1.3 nm.
Improved productivity on diamond-like carbon coating optical disk stamper
Authors: Ueng H. Y. , Guo C. T.
Published: December 2003

We report on a proposed process for depositing a diamond-like carbon (DLC) film on the back surface of a submaster stamper after a nickel electroforming process. This process could keep friction low and improve the productivity of an optical disk. Hydrogenated amorphous carbon films were deposited from a mixture of argon and acetylene by electron cyclotron resonance-chemical vapor deposition at pressures of about 5–9×10−3 mbar. In order to improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN supporting mutilayers were deposited on the stampers. The structural characteristics of DLC films were investigated by Raman spectroscopy. The properties of a DLC film coating on a stamper are summarized as follows: microhardness (five times improved), roughness less than 4 nm, excellent adhesion of 65 N, and coefficients of friction less than 0.1. The characteristics of the back surface coated by DLC film were improved, and the productivity of an optical disk per stamper is estimated at about 1.7 times more than obtained. Finally, the DLC submaster stamper could be used to overcome the barrier and dramatically improve the economics and yield of increased productivity of polymer compact disks.
Smooth surface glass etching by deep reactive ion etching with SF6 and Xe gases
Authors: Li Li , Abe Takashi , Esashi Masayoshi
Published: December 2003

This article reports on a smooth surface glass etching using deep reactive ion etching with a mixture of sulfur hexafluoride (SF6) and xenon (Xe) gases. A surface roughness of 23 Å was achieved with SF6/Xe(=1/1) and 18 Å with SF6/Ar(=1/4) under a condition of −390 V self-bias voltage and 0.2 Pa pressure. The surface roughness in the order of several angstroms (5.9 Å) was obtained at a pressure of 0.1 Pa (SF6/Xe=1/1). The average surface roughness (Ra) after the etching by SF6/Xe gas was smaller than those after the etching with SF6 only or SF6/Ar at a same mole fraction of the inert gas to SF6+inert gas. Since heavy inert gas increases the physical sputtering effect, the addition of the heavy inert gas helps to remove contaminant residues remaining on the etched surface. The optimum condition of smooth glass etching with high etch selectivity (21) is a pressure of 0.2 Pa and a mole fraction of Xe to SF6 gas is 8 to 7. We also make an analysis of the relationship between the surface average roughness on the bottom and the etched depth. The average roughness of the etched surface was smooth not only for the bottom but also for the sidewalls. The average surface roughness of the sidewalls was about 16 nm for 50-μm-deep etching under the same optimum condition. This technology was applied to a deep etching of quartz crystal used for a mass sensor.
Diffusion barrier properties of very thin TaN with high nitrogen concentration
Authors: Rossnagel S. M. , Kim H.
Published: December 2003

TaN deposited by magnetron sputtering has application in semiconductor interconnect structures as a diffusion barrier and adhesion layer. TaN used in these applications has a hexagonal or cubic structure consistent with roughly 1:1 Ta:N levels, with a bulk resistivity of 300–500 μΩ cm and a diffusion barrier failure temperature for 5 nm films of around 650 °C (Ref. 1). The diffusion barrier failure temperature (for Si/TaN-barrier/Cu samples) is a strong function of nitrogen concentration in the TaN; at the highest N levels (equivalent to nearly Ta3N5), the failure temperature exceeded 900 °C. At intermediate compositions, the failure temperature was found to exceed 700 °C even for films as thin as 0.4 nm. This suggests an interfacial contribution to diffusion barrier effectiveness, in addition to conventional grain boundary or bulk interdiffusion resistance, which may dominate conventional grain boundary diffusion.
Investigation of InGaP/GaAs heterojunction bipolar transistor with doping graded base
Authors: Chen Yen-Wei , Hsu Wei-Chou , Hsu Rong-Tay , Wu Yue-Huei , Chen Yeong-Jia , Lin Yu-Shyan
Published: December 2003

An n-p-n InGaP/GaAs heterojunction bipolar transistor (HBT) using a graded base doping profile has been fabricated by low pressure metalorganic chemical vapor deposition. A current gain of 77 and a base sheet resistance of 251 Ω/sq are achieved in the graded-base HBT. Compared to the graded-base structure, the nongraded-base structure has a lower current gain (68) and a higher base sheet resistance (294 Ω/sq). Furthermore, the studied graded-base HBT device also shows better microwave characteristics. The measured unity current-gain cutoff frequency (fT) can be improved from 18 to 22 GHz. The functional dependences of current gain, base sheet resistance, and microwave characteristics on the base doping profile are attributed to the graded-doping enhanced built-in field across the base and higher base doping at the emitter edge.
Characterization of sidewall roughness of InP/InGaAsP etched using inductively coupled plasma for low loss optical waveguide applications
Authors: Bae J. W. , Zhao W. , Jang J. H. , Adesida I. , Lepore A. , Kwakernaak M. , Abeles J. H.
Published: December 2003

The effects of etch depth on the sidewall roughness (SWR) of InGaAsP/InP waveguides fabricated utilizing two types of masks, NiCr/SiO2 and SiO2/NiCr/SiO2, were investigated with an atomic force microscopy. All the waveguides were etched in an inductively coupled plasma–reactive ion etching to depths ranging from 4 to 8 μm. The root-mean-square (rms) sidewall roughness values of the waveguides etched to depths of 4, 6, and 8 μm with SiO2 remasking layer were measured to be 2.97, 3.45, and 3.64 nm, respectively. Also the rms SWR values of the waveguides etched without the remasking layer were 3.2, 3.65, and 3.89 nm, respectively. The SiO2 thin remasking layer deposited on NiCr/SiO2 mask structure reduced the SWR of the waveguides. Measurements indicated that SWR increased with etch time, which is ascribed to an increase in mask erosion during etching.
Single electron memory devices: Toward background charge insensitive operation
Authors: Yadavalli Kameshwar K. , Orlov Alexei O. , Snider Gregory L. , Korotkov Alexander N.
Published: December 2003

We present an experimental study of charging mechanisms in aluminum single electron memory cells where the SiO2 surface between the floating gate and the control gate is used as a barrier dielectric and the single electron transistor is used as a readout device. We study several regimes of charging for different barriers separating the floating gate and the control gate. For thinner barriers, the floating gate acts as a single electron trap, while for thicker barriers a few tens of electrons could be stored on the floating gate to represent a bit. This allows us to realize a background charge insensitive operation of the memory cell. In devices with a barrier thickness in the range 30–100 nm we observe no charge transfer to the floating gate, but rather charging of the surface traps present in the barrier. Our results are in good agreement with theoretical calculations where specific details of device geometry are included in the model.
Phase masks working in 157 nm wavelength fabricated by immersion interference photolithography
Authors: Cheng W. C. , Wang L. A.
Published: December 2003

We demonstrate that phase masks can be made from modified fused silica with a period of 180 nm and ∼8 mm long by using immersion interference photolithography. The fabrication process of the phase mask is optimized to generate the largest intensity ratio of diffracted ±1 to 0 order. The phase mask is demonstrated to produce a photoresist pattern with halved period (90 nm) when illuminated with a laser of 157 nm wavelength. The phase masks are also capable of generating two-dimensional patterns of holes and dots and serving as molds for imprint applications.
Adaptive membrane masks
Authors: Zhuang X. , Conkerton D. , Lal A. , Jiang L. , Feldman M. , O’Reilly T. , Smith H.
Published: December 2003

As overlay requirements for integrated circuits have tightened, the control of mask distortions has become critically important. Rather than make the mask as rigid as possible, a feedback approach has been suggested in which overlay is measured and corrective displacements are thermally generated in a membrane mask. The principle corresponds to that used in adaptive optics, where an active feedback system is used to maintain perfect wave-fronts by distorting the optical surfaces. An important advantage of adaptive masks is that the feedback may be used either to obtain absolute accuracy, or to incorporate desired displacements, for example, to compensate for distortions in previous levels patterned on the wafer. Previous work focused on modeling the temperature distributions required for arbitrary mask displacement distributions. This modeling has now been verified in two very dissimilar experimental arrangements.
Wafer heating analysis for electron-beam projection lithography
Authors: Chang J. , Nellis G. F. , Engelstad R. L. , Lovell E. G. , Sogard M. R.
Published: December 2003

Electron projection lithography (EPL) is one of the principal next-generation lithography technologies for the sub-65 nm regime. To satisfy the stringent resolution requirements, all image placement errors must be characterized and minimized. These include the distortions of the device wafer during exposure. The wafer absorbs beam energy which produces temperature increases and thermomechanical strains that directly contribute to pattern-placement errors, stitching errors between adjacent subfields, and image blur. Thus, CD control and pattern overlay will be directly affected. In this article, the thermomechanical distortions caused by wafer heating in the EPL system have been simulated using finite element models that include the effects of the interaction between the wafer and chuck.
Metal nanogap devices fabricated by conventional photolithography and their application to deoxyribose nucleic acid analysis
Authors: Hashioka Shingi , Saito Masato , Tamiya Eiichi , Matsumura Hideki
Published: December 2003

A low-cost and simple fabrication technique is proposed to prepare the metal nanogap devices (MNGDs) of sub-50 nm size. Only currently available mass-production technologies such as photolithography and anodic oxidation of patterned metal films are utilized in the technique. The gap width of MNGD can be easily and accurately controlled by the applied voltage of the anodic oxidation process. For example, the gap width formed between titanium electrodes by anodic voltage 15 V is about 10 nm, and the standard deviation (σ) of the width fluctuation is about only 2 nm (20% of the fabrication size). Thus, the accuracy of the fabrication technique is on the almost same level with the electron beam (EB) lithography. Multigap MNGD containing several different gap widths were fabricated for the use of deoxyribose nucleic acid (DNA) analysis. As an application of MNGD, pure water containing DNA was dropped on MNGD, dried in air and the current–voltage characteristics of DNA were measured. From these results, it is expected that low-cost DNA analyzer can be provided by the present technique to fabricate MNGD.
Extreme ultraviolet mask fabrication with high inspection contrast TaSiNx absorber stack
Authors: Wasson J. R. , Weisbrod E. J. , Lu B. , Mangat P. J. S. , Dauksher W. J. , Resnick D. J. , Sohn J. , Engelstad R. , Pettibone D.
Published: December 2003

Extreme ultraviolet lithography (EUVL) is a leading candidate for next generation lithography with the potential for extendibility beyond the 45 nm node. The three-layer absorber stack for EUVL reticles consists of an absorber, repair buffer and etch stop layers, while a two-layer absorber stack eliminates the etch stop layer. Improving inspection contrast is critically important to finding defects. In previous work, using TaSiN as the EUV absorber, the inspection contrast was less than 10%, which did not allow for effective defect detection to occur. However, other TaSiN properties such as thin film stress control and critical dimension etch bias were clearly superior to the Cr absorber. An improved process using a Ta-based absorber stack that maintains the beneficial characteristics of the film, on SEMI Standard P1-92 6025 format substrates, is discussed.
High-performance proximity effect correction for sub-70 nm design rule system on chip devices in 100 kV electron projection lithography
Authors: Ogino Kozo , Hoshino Hiromi , Machida Yasuhide , Osawa Morimi , Arimoto Hiroshi , Takahashi Kimitoshi , Yamashita Hiroshi
Published: December 2003

The proximity effect correction (PEC) system to achieve the practical processing time and data volume for sub-65 nm design-rule system on chip (SoC) devices is improved. The lump method, which is the technique to process several subfields at a time, is used to reduce the processing time for PEC. The hierarchical data processing for PEC is also proposed to reduce the data volume. A PC cluster system has been used to reduce the processing time for PEC. For an actual 70 nm design-rule SoC device data, the processing time has been reduced from 7.8 h to 10.3 min and the data volume has been reduced from 12.4 to 2.6 GB by using the lump method, the hierarchical data processing, and a ten PC cluster system. And, we have confirmed that the required critical dimension accuracy of ±5% is achieved for the device data in the simulation. We have successfully fabricated a full-size 8 in. Si stencil mask using the data with our PEC system for an actual 70 nm design-rule SoC device.
Fabrication of an integrated nanofluidic chip using interferometric lithography
Authors: O’Brien M. J. , Bisong P. , Ista L. K. , Rabinovich E. M. , Garcia A. L. , Sibbett S. S. , Lopez G. P. , Brueck S. R. J.
Published: December 2003

The fabrication of nanoscale structures with dimensions approaching the scale of biological molecules offers approaches to the study of fluid dynamics and biomolecular transport. Ultimately, a parallel lithographic approach will be necessary if devices based on these nanofluidics are to achieve widespread availability and acceptance. We report on a flexible, all-optical lithography alternative that is amenable to large-scale production. We use interferometric lithography (IL) and anisotropic etching to produce large areas of parallel, nanofluidic channels with widths of ∼100 nm and depths of up to 500 nm. We also use standard optical lithography to create interfacing microchannels, such that the range of spatial scales on one chip varies by 104 (from mm scale reservoirs to 100 nm nanochannels). We provide initial demonstrations of capillary action and electrophoretic motion of fluorescent dye solutions.