Volume 17, Issue 6, November 1999
- review article
- regular articles
- brief reports and comments
- rapid communications
- papers from the 43rd international conference on electron, ion, and photon beam technology and nanofabrication
- etching and deposition
- electron and ion beam sources and optics
- electron beam lithography
- emerging technologies
- euv lithography
- focused ion beam technology
- ion beam lithography
- nanotechnology: devices and fabrication
- optical lithography
- resist technology
- x-ray lithography
Index of content:
- REVIEW ARTICLE
17(1999); http://dx.doi.org/10.1116/1.591102View Description Hide Description
The need to substitute with low dielectric constant (κ) materials increases with each complementary metal–oxide–semiconductor process generation as interconnect RC delay, crosstalk, and power dissipation play an ever larger role in high-performance integrated circuits. Fluorinated amorphouscarbonfilms (a-C:F,H) with low-κ properties (κ∼2.0–2.4) deposited by plasma-assisted chemical vapor deposition(CVD) techniques provide several advantages including low temperature processing, good gap fill capabilities, minimal moisture absorption, and simple implementation. Several deposition techniques have been examined, including high-density plasma and parallel-plate plasma-assisted CVD. In each case, it is possible to deposita-C:F,H films with widely varying properties, such as κ and thermal stability. This has led to a good deal of confusion as to what is required to produce useful material. Results from many different sources are examined to develop a coherent picture of the relationships between deposition techniques, microstructural features, and macroscopic properties, and to summarize the scientific and technical challenges that remain for a-C:F,H implementation. The relationships between filmdeposition parameters such as applied substrate bias and filmproperties are presented in the discussion. In addition, x-ray photoelectron spectroscopy and network constraint theory are used to develop connections between microstructural and macroscopic properties, as well as to show how deposition parameters can be used to create a predictive model. This will demonstrate what process parameters are important in film formation. Finally, efforts to incorporate this material into integrated circuits, as well as measurements of the reliability and performance will be reviewed.
- REGULAR ARTICLES
17(1999); http://dx.doi.org/10.1116/1.591103View Description Hide Description
The surface mobility of alkanethiol-passivated Aunanocrystals on inert surfaces makes them challenging to image by scanning tunneling microscopy(STM). However, the potential for obtaining information on the density of states of these nanocrystals from tunneling spectroscopy measurements justifies the effort to find sample preparations that effectively immobilize them. We have explored the use of dithiol molecules as a means of strengthening the interaction between the substrate and the nanocrystal, with the goal of imaging isolated nanocrystals on a conducting substrate. Modifying the nanocrystals by substituting dithiol molecules into the passivation layer allowed the nanocrystals to bind strongly to the Au(111) surface. The formation of a self-assembledmonolayer of xylenedithiol on the Au substrate allowed unmodified nanocrystals to more strongly adsorb to this modified surface. In both cases, isolated 1.7 nm nanocrystals were easily imaged by STM on Au(111), even at room temperature. These are significant steps toward the goal of obtaining high quality tunneling spectra from this class of materials.
Field induced local oxidation of Ti and Ti/Au structures by an atomic force microscope with diamond coated tips17(1999); http://dx.doi.org/10.1116/1.591104View Description Hide Description
We have investigated field induced local oxidation of thin Ti films with the tip of an atomic force microscope. Tips, which have been coated with a diamond layer to improve their wear resistance, are shown to have a much longer lifetime than conventional uncoated Si tips. We have studied the oxidation characteristics as a function of the applied tip-sample voltage and scanning speed for both diamond coated and uncoated tips. We find that the diamond coated tips result in a thinner oxide layer for the same voltage and scanning speed. The dependence of the oxidation process on the film thickness was studied for diamond coated tips. Thin films can be completely transformed into an oxide layer for a thickness up to 15 nm. Moreover, for these sufficiently thin films the measured ratio between the oxide height and the Ti film thickness is a constant. It is also possible to completely oxidize Ti films which cover Au islands, opening the way to fabricate more complicated structures.
In situ electrochemical atomic force microscopy study on Au(100)/Cd interface in sulfuric acid solution17(1999); http://dx.doi.org/10.1116/1.591105View Description Hide Description
The Cd electrodeposition on Au(100) in sulfuric acid solution was investigated by means of in situelectrochemicalatomic force microscopy (EC-AFM) and long time polarization experiments. Initially, the Cd adlayer was formed at underpotentials V/NHE) in a structure, which changed to a structure at V/NHE. Within the potential range from −0.3 to −0.45 V/NHE, a quick-alloying process was observed at the interface. The dynamic of the surfacealloying was found to depend on polarization conditions. EC-AFM observation of the stripping process showed that the removing of the Cd bulk phase and the surface alloyed phase roughened the electrode surface. The mechanism that was proposed for surfacealloying took into consideration the turnover process between Au and Cd atoms and the interdiffusion process of either Au or Cd atoms through the vacancy-rich surface alloy within the top layers. During bulk deposition at V, Cd film was formed by a Stranski–Krastanov mechanism, with the Cd(0001) plane parallel to Au(100).
Vapor-deposited gold film formation on highly oriented pyrolitic graphite. A transition from pseudo-two-dimensional branched island growth to continuous film formation17(1999); http://dx.doi.org/10.1116/1.591106View Description Hide Description
Growth of vapor-deposited gold islands on highly oriented pyrolitic graphite (HOPG) using evaporation rates in the range 0.01–0.1 nm/s has been investigated with ex situscanning tunneling microscopy. Equivalent mean gold thickness and substrate temperature were varied from 1 to 20 ML and 333 to 358 K, respectively. Gold ad-islands several layers high grow both atop large HOPG terraces and along HOPG steps. Images show split and stable tip branched islands, depending on individual ad-island height and equivalent mean gold thickness. Initially, the diffusion of gold atoms towards island edges occurs via the HOPG surface, whereas soon thereafter it includes diffusion via gold terraces and steps. These two very dissimilar possibilities are due to both misfit strain variation with local gold-deposit thickness, and large differences in sticking probabilities of gold on HOPG and gold. Addition of gold to islands more than 20 layers high produces island-top flattening, branch coarsening with pronounced facetting, and tip stabilization, as a result of diffusion of gold from island tops to valleys and interbranch spaces. Extended flat areas present monoatomic-high triangular gold terraces. The transition from split to stable-tip branched islands is associated with a surface diffusion barrier which decreases with island height as a result of reduced lattice mismatch. Seemingly, early stages of branched gold island formation can be assimilated to a deposition, diffusion, and aggregation-type model that nucleates surface atom at island or terrace edges. Once flat gold terraces set in, the growth process can be described by an Edwards–Wilkinson-type model. Coalescence of gold ad-islands more than 20 layers high explains the well-known continuous films obtained in metal coaters under comparable growth conditions.
17(1999); http://dx.doi.org/10.1116/1.591107View Description Hide Description
The recrystallization process of highly oriented pyrolytic graphite (HOPG) surface bombarded by argon ions with an ion energy of 2.0–2.5 keV at doses of was examined by scanning tunneling microscopy. The hillocks formed by the ion bombardment of HOPG coalesced to form larger grains with increasing annealing temperature. Three types of ringlike superstructures of of graphite were found on the curved surface of the grains after annealing in the temperature range of 1823–2673 K. The specimen surface became flat above 2773 K, where the ringlike superstructure disappeared and the triangular structure of graphite appeared in its place. The effect of the curved surface of the grains on the formation of the ringlike superstructure during graphitization is discussed.
17(1999); http://dx.doi.org/10.1116/1.591108View Description Hide Description
The newly developed method of siliconsurfacestructuring by local desorption of passivating hydrogen with a 30 keV focused ion beam has been investigated with respect to the damage induced by the irradiation. The substrate damage was analyzed by atomic force microscopy and thermal wave analysis. The measurements show that damage can be minimized if the substrate is heated to 200 during irradiation and dwell times below 20 are used for the exposure, even at a dose of which exceeds the minimum dose required to define a feature by a factor of 10. The irradiated surfaces remain flat after KOH etching, the surface roughness being smaller than 0.3 nm for all samples.
17(1999); http://dx.doi.org/10.1116/1.591109View Description Hide Description
The formation of regular nanostructures by photopolymerization of three diolefin derivative crystals, P2VB, DSP, and p-CPAEt, is investigated using atomic force microscopy (AFM) and known crystal packing data. AFM reveals that the crystal face (100) and (010) of P2VB exhibit volcanoes, whereas (100) and (010) of DSP give floelike structures. The main face and long side face of p-CPAEt give rise to volcanoes. All of those are guided by the crystal structure. Molecular interpretations of the AFM features of P2VB and DSP are given.
17(1999); http://dx.doi.org/10.1116/1.591110View Description Hide Description
Polystyrene (PS)thin film modified with a novel ultrasonic scratching method has been studied using an atomic force microscope(AFM).Ultrasonic scratching can be realized by a combination of an AFM and a quartz crystal resonator (QCR). The PSthin film was deposited on the surface of an AT-cut QCR which oscillates with mechanical shear deformation at its resonant frequency (6.5 MHz) with amplitude of a few nm. The oscillating surface is scratched with the AFM’s diamond tip to generate an effective cutting force. Scratching without a QCR oscillation forms bumps on the PS surface, which is known well to be a unique phenomenon of scratched polymer surfaces. However, ultrasonic scratching can result in the carving of PSthin films without the formation of bumps. The depressed bottom carved by ultrasonic scratching is flat in comparison with that scratched without surface oscillations. Furthermore, on the previously modified area of ultrasonic scratching, bumps are not formed, even after overlapping of the scratching without surface oscillations.
Near-field polarization states and optical images in transmission mode through different surface structures17(1999); http://dx.doi.org/10.1116/1.591111View Description Hide Description
We provide a theoretical study of the near-field optical image of a homogeneous dielectricsurface with deterministic sub-wavelength structures. Numerical simulations for different shapes of the sample are performed at constant-height mode with normal incidence. Near-field polarization states have been calculated by analyzing the difference of the transmitted intensities of p- and s-polarized light. We show that the near-field intensity depends more stronger on the feature form than the feature size. However, the polarization property is more sensitive to the shape of the sample rather than the distance of detection.
Nanometric aperture arrays fabricated by wet and dry etching of silicon for near-field optical storage application17(1999); http://dx.doi.org/10.1116/1.591112View Description Hide Description
We fabricated nanometric aperture arrays in order to apply to an optical probe in high-density near-field optical storage for increase of data-transmission rate. The aperture arrays were fabricated by forming concave pyramidal grooves on a silicon-on-insulator wafer with electron beamlithography and wet anisotropicetching. Modification of the apex shape of the grooves by re-oxidation and subsequent reactive ion dry etching was able to increase the uniformity of the aperture size remarkably. The light transmission efficiency of the fabricatedapertures was measured to be when the aperture size was 100 nm, which was higher than that of a conventional optical fiber probe by several orders of magnitude.
17(1999); http://dx.doi.org/10.1116/1.591113View Description Hide Description
A nanometer-scale recording technique was demonstrated on N-(3-nitrobenzylidene)–p-phenylenediamine (NBPDA) organic thin films with a scanning tunneling microscope(STM). NBPDA thin films were fabricated by vacuum thermal deposition. The results of ultraviolet-visible absorption and infrared transmission spectra showed that the structure of the NBPDA film was the same as that of NBPDA crystal. An atomic force microscope was utilized to characterize the surface morphology of the NBPDA film. Data were recorded by applying voltage pulses between the tip and the substrate. The current–voltage characteristics measured by the STM indicated that the local electrical property changed from an insulating property into a metallic property after the data were written. Data marks, 1.4 nm in diameter, corresponded to a data storage density of A preliminary calculation was presented to explain the recording mechanism.
17(1999); http://dx.doi.org/10.1116/1.591114View Description Hide Description
Submicron spin valves and Co/Cu pseudo spin valves with widths ranging from 200 to 0.5 μm have been realized by direct deposition and liftoff. The resulting configurations were structurally characterized by atomic force microscope and cross-sectional transmission electron microscopy.Transport and magnetic properties of arrays of these spin-valve structures were studied using superconducting quantum interference device magnetometry. Magnetic measurements carried out on several spin-valve structures showed that both coercivity and field at which maximum magnetoresistance(MR) occurs increase with decrease in widths of the spin valves. Comparison of the results obtained from the magnetometry and transport measurements indicated the existence of an offset between the coercive field and field of maximum MR. Resistance versus temperature measurements for varying linewidth show a minimal shift in peak temperature, indicating that processing effects are minimal.
Nanoscale elemental imaging of semiconductor materials using focused ion beam secondary ion mass spectrometry17(1999); http://dx.doi.org/10.1116/1.591115View Description Hide Description
The semiconductor industry demands elemental information from ever smaller regions. The sensitivity of secondary ion mass spectrometry, coupled with the lateral resolution of a focused ion beam, can provide nanoscale elemental data that are competitive with that from other analytical techniques. Ion images of the sidewalls in repetitive semiconductor features tilted to present a large surface area have shown boron contamination after an etch process. The boron is removed by a specific cleaning step. Spot defect analysis was enhanced by the use of mass spectra that provide information on a range of elements before the defect is removed by sputtering. Ion implanted samples were analyzed in cross section and the implant shape detected. Summation of the secondary ion counts in the implant cross section over a few micrometers resulted in detection limits below 0.1 at. %. Implantation profiles have been detected for Al, Cr, Na, Li, and K without the aid of secondary ion enhancing species, such as oxygen or cesium.
17(1999); http://dx.doi.org/10.1116/1.591116View Description Hide Description
Galliumliquid metalion sources (LMISs) have been exposed to common gas and liquid phase laboratory and vacuum system contaminants. Minor changes in the direct current and pulsed operation of the LMISs were observed after contaminant exposure. Time-of-flight mass analysis of the ion emission revealed that contaminant species are primarily field evaporated with the gallium substrate. Low vapor pressurecontaminants have been observed to constitute a significant portion of the total emitted ion current.
17(1999); http://dx.doi.org/10.1116/1.591117View Description Hide Description
Comparisons are made of two atomic force microscopes in different modes of operation, and two scanning electron microscopes, one high and one lower resolution for quantifying the edge roughness of patterned features in resist and silicon. Definitions of the edge roughness magnitude and spatial frequency are given. For each metrology method, the parameters that limit the edge roughness measurement and how they compare to the parameters that limit the critical dimension measurement are addressed. An attempt to quantify the edge roughness spatial frequency is also discussed. For the two best metrology methods the repeatability of the measurements was determined, and measurements were made to understand the correlation between them.
Focus drilling and attenuated phase shift mask for subwavelength contact window printing using positive and negative resists17(1999); http://dx.doi.org/10.1116/1.591118View Description Hide Description
We have investigated the process latitude and resolution limit of printing contact windows using a high numerical aperture KrF stepper and attenuated phase shift mask (APSM). We show that both positive and negative resists can be used depending on the size of the window on the mask. The advantages and disadvantages of using the positive and negative resists are presented. A combination of APSM and focus drilling are shown to extend the focus latitude of subwavelength window printing.
Electron beam lithography process for T- and -shaped gate fabrication using chemically amplified DUV resists and PMMA17(1999); http://dx.doi.org/10.1116/1.591119View Description Hide Description
A new process has been developed to fabricate T-shaped gates and -shaped gates for high performance metal–semiconductor field effect transistors and high electron mobility transistors using a bilayer of Shipley UVIII DUV resist and poly(methylmethacrylate). The two resists are separated by a 20–30 nm thick layer of aluminum and after patterning by electron beam lithography a two-stage development technique is used to remove the aluminum and to produce well-defined resist profiles. The process can be used to fabricate T-shaped and -shaped gates with footwidth sizes as small as 50 nm and headwidth to footwidth ratios in excess of 40:1 for T gates and 35:1 for gates. The ability to fabricate gates with these dimensions arises from the fact that the UVIII resist is considerably more sensitive to electron beam exposure than PMMA. Further benefits derived from using a UVIII: PMMA bilayer are better control of footwidth dimensions and shorter electron beam patterning times compared to bilayers of PMMA with copolymers of PMMA. This article describes process optimization and the relationship between feature size and exposure dose.
17(1999); http://dx.doi.org/10.1116/1.591134View Description Hide Description
The effects of low-energy electron irradiation (10–50 eV, up to on thin films of poly(methyl methacrylate) (PMMA), deposited on air-exposed Al, have been studied in situ as a function of temperature (∼200–300 K) using polarization-modulated infrared reflection absorption spectroscopy. Near 300 K damage is seen in the form of a loss of material, as shown by a decrease in the intensity of the entire PMMA spectrum. At low temperature, in addition to damage, evidence is seen for a radiation-induced change in chain configuration leading to an increased interaction between ester groups and the Al surface. This configuration is unstable and is removed by annealing to ∼300 K.
17(1999); http://dx.doi.org/10.1116/1.591120View Description Hide Description
A practical bilayer bottom antireflective coating (BARC) process, consisting of an upper conventional organic film and a lower amorphous-Si blackout film, is introduced to realize highly antireflective performance and efficient pattern-transfer performance simultaneously. The application of a thin-resist process for KrF imaging to 130 nm device fabrication is also investigated including a practical pattern-transfer process, especially in the gate layer and the metal-wiring layer. It is demonstrated that no standing-wave effects in the resist are observed due to the effective bilayer BARC structure; furthermore, the resist patterns, which are 215 nm thick, are successfully transferred to the substrates in the gate layer and the metal-wiring layer. Finally, experimental and simulation results suggest that the thin-resist process, in combination with the practical bilayer BARC process using KrF imaging featuring a numerical aperture of 0.68 and a partial coherency of 0.75 with a 2/3 annular aperture, could guarantee the early stage of 1 Gb dynamic random access memory device fabrication.