AVS1996 Session NS-MoP: NST Instrumentation and Fabrication Poster Session

Monday, October 14, 1996 5:30 PM in Ballroom A
Monday Afternoon

Time Period MoP Sessions | Topic NS Sessions | Time Periods | Topics | AVS1996 Schedule

NS-MoP-1 A Variable Temperature Cryogenic Scanning Tunneling Microscope
M. Rose, S. Behler, F. Ogletree, M. Salmeron (Lawrence Berkeley National Laboratory)
We have constructed a Scanning Tunneling Microscope (STM) that operates at variable sample temperature (20 - 300 K). The design consists of a sample holder mounted on a continous-flow cryostat. By rotation and linear motion of the cryostat the sample can be positioned in front of various surface preparation and analysis instruments contained in a single UHV chamber. A lightweight beetle-type STM head is lowered from the top onto the sample by a linear manipulator. To avoid helium convection in the cryostat, the entire UHV system including a liquid helium storage dewar can be tilted by a few degrees (perpendicular to the cryostat axis) which drastically improves the operation. The liquid helium sample cooling is designed to cause minimal vibrations and strong thermal contact. At a sample temperature of 25 K, a vertical resolution of 0.1 Å can be achieved. We analyzed the origin of the resolution-limiting vibrations and found that they are related to horizontal translation reson! ances of the STM head. The performance of the instrument is demonstrated by atomically-resolved images of a Pd(111) surface.
NS-MoP-2 A 77 K STM Designed for Imaging Molecular Adsorbates
V. Hallmark (San Jose, California); B. Melior (IBM Almaden Research Center); C. Pearson, G. Anderson, S. Chiang (University of California, Davis)
We report on the testing of a novel low temperature scanning tunneling microscope (STM). Using this STM, we routinely cool samples to 77 K from room temperature and image. Surrounding the STM stage is a thick aluminum tube which provides both radiation shielding and heat sinking capabilities. The top of the tube attaches to a liquid nitrogen cryostat while the bottom of the tube is capped and contains a clamping mechanism. When activated, the clamping mechanism provides a thermal path between the STM stage and the heat sink. A room temperature sample introduced into the cold STM reaches 77 K in 15 minutes. During imaging, the clamping mechanism is deactivated and the stage is released from the heat sink. In this state, the temperature rise at the sample is less than 1 K per hour. Vibration isolation is achieved through a triple stage system consisting of dual spring stages incorporating eddy current damping, together with a bellows isolated liquid nitrogen cryostat. Samples are initially prepared in a separate adjoining chamber which includes both low energy electron diffraction (LEED) optics and a cylindrical mirror analyzer for Auger electron spectroscopy (AES) and then transferred to the STM. The complete surface analysis system will be used in the investigation of molecular adsorbed species on Pd(111). The low temperature imaging ability will elucidate molecular orientation and binding sites on the surface as well as molecular tilt out of the surface plane.
NS-MoP-4 Formation of Single Tips of Atomically Sharp Silicon
Y. Zhang, Y Zhang, R. Marcus (New Jersey Institute of Technology)
Atomically sharp silicon tips for AFM probes and field emitters are typically fabricated by wet or dry etching followed by oxidation sharpening. However, multiple tips instead of the desired single tips often form after the oxidation sharpening step. We analyzed the mechanisms likely to be responsible for forming multiple tips and found that the likely mechanism involves the presence of sharp corners before oxidation sharpening. This analysis led to the development of a processing scheme that eliminates the sharp corners and produces only single tips of silicon with typical atomic sharpness. This analysis and processing scheme for forming single tips will be described.
NS-MoP-5 Nanoscale Characterisation of Solid Surfaces by Conducting Scanning Force Microscopy (CSFM)
P. Zhdan, C. Burt, J. Castle (University of Surrey, United Kingdom)
The potential of Conducting Scanning Force Microscopy (CSFM) for the examination of solid surfaces at the nanoscale has been investigated. A special constant current unit was designed to perform CSFM studies using a Nanoscope III SPM system: highly doped conducting high-aspect ratio Si-tips have been employed in all experiments. CSFM has been applied to examine surfaces of carbon fibre based composites; CuNi alloys after oxidation and sulphidation; and duplex steels after corrosion treatment. The fresh surfaces of graphite (conducting) and PTFE (insulating) were used as a reference materials. Experiments have been performed in air and under liquids (including electrolytes). Questions, concerning with reproducibility of the CSFM data in different environments are reviewed and discussed. A comparison is made between the CSFM results and the coresponding Height, Deflection and Friction SFM data acquired simultaneously. In particular, the relationship between Friction and CSFM data is considered and additional details of the surface composition provided by CSFM have been addressed. The conclusion is made that CSFM is not limited to flat specimens and can be used sucessfully for mapping rough surfaces. It is shown that the sensitivity to detection of the local conducting (and/or resistive) phases on solid surrfaces is greatly improved by CSFM which allows mapping with a nanometric resolution. CSFM provided a valuable insight into the mechanisms of chemical and electrochemical corrosion of Cu-containing alloys and duplex steels and the formation of carbon fibre-matrix interfaces in composite materials.
NS-MoP-6 A High Scan Speed Atomic Force Microscope Compatible with Ordinary Optical Microscopes
K. Nakano (Nikon Co., Japan)
Most atomic force microscopes (AFM) are not compatible for use with both upright and inverted optical microscopes. Since the space either above or beneath AFM sample is occupied by the tube scanner, an AFM can only be used together with either an upright or an inverted optical microscope, but not both. Furthermore, the low resonance frequency of the scanner limits the scan speed. In order to overcome these problems, we have developed a novel scanner employing three stacked PZT actuators. One is a short stacked PZT which moves the AFM probe vertically (z-PZT), and the other two are long stacked PZTs which move the probe horizontally. Mechanical levers were added in order to enlarge the scan area and to improve the mechanical accuracy of the scanning. By employing the short stacked z-PZT, the AFM became compact enough to be combined with both upright and inverted optical microscopes. It was also our purpose to obtain a high mechanical resonance frequency in z direction. In our design the cantilever is scanned over the sample, which remains stationary. The cantilever's deflection was observed by employing an optical balance method using a laser beam. Mirrors attached to the actuators enabled the laser beam to track the movement of the cantilever. The scanner has a total height of 13 mm, and can be inserted between a sample and a 50x objective lens. Its scan range is 50 x 50 x 4 microns. A vertical resonance frequency of 10 kHz was obtained. This AFM can be operated up to a maximum sampling rate of 20 kHz, i. e, 3 sec per one 256-line image. Its vertical resolution was 3 nm for a 3 sec image and less than 0.1 nm for a 30 sec image.
NS-MoP-7 Room Temperature Molecular Manipulation with a Scanning Tunneling Microscope
W. Pai, Z. Zhang, J. Zhang, J. Wendelken (Oak Ridge National Laboratory)
The manipulation of atomic scale objects by the scanning tunneling microscope (STM) has shown great potential for the fabrication of nanoscale structures and for studying novel physics in the quantum regime [1]. While single atoms can be manipulated, the size limit for molecular manipulation remains to be probed, and new manipulation modes are yet to be found. We demonstrate that the fragmented molecular ligands cyclopentadienyl, C\sub 5\H\sub 5\ (abbreviated as Cp) having a width of only ~6=C5, are observed on the Ag(100) substrate following the dissociative adsorption of ferrocene [Fe(C\sub 5\H\sub 5\)] and can be manipulated in various ways by a STM at room temperature. The Cp ligands are identified by the fivefold symmetry in atomically resolved STM images and by electron energy loss spectroscopy. Even with a gap resistance as large as 2 Gohms, Cp can be manipulated. In contrast to a "serial" mode of manipulation in which one adsorbate is involved at a time, a novel "parallel" mode of manipulation is observed in which all Cp can be displaced. The paths of Cp motion can be imaged during manipulation, and they appear as streaky tracks. These tracks reveal that the Cp motion is preferentially along the high symmetry [110] directions regardless of the scanning angle, and thus indicate a combined effect of extrinsic STM-assisted motion and intrinsic self-diffusion process. =46urthermore, individual Cp can be selectively desorbed with a sample bias less than -1.8 V, allowing the repair of nanoscale molecular structures. [1] M. F. Crommie, et. al., Nature 363, 524-527 (1993). ORNL, managed by Lockheed Martin Energy Research Corp. for the U.S. DOE under contract no. DE-AC05-96OR22464.
NS-MoP-8 STM Nanolithography in Resists
E. Dobisz (Naval Research Laboratory); H. Koops (Deutschen Telekom, Germany); F. Perkins, S. Brandow (Naval Research Laboratory)
Proximal probe lithography is important because it has been shown to eliminate the proximity effects found in high voltage e-beam lithography. Atomic resolution lithography has been successfully demonstrated on specialized atomically smooth surfaces. However, to be useful as a lithographic tool, the patterns must be written in a viable imaging layer. STM lithography has been performed in vacuum in the commercial resist, SAL-601, of thickness 25-50 nm and a phenylethylenediamine organosilane self assembling monolayer. Exposure voltages of 8 V to 80 V have produced linewidths from 15-1000 nm. Probe tips were dc etched tungsten, with measured radii of 50 nm. EO-3D simulations from Munro's Electron Beam Software have been performed to model the STM lithography with a dielectric resist layer. Simulations were performed for tip radii of 10 and 50 nm and resist thicknesses of 1-50 nm and tip-resist separations of 1-20 nm. For a fixed tip-sample voltage, the electric field at the tip and voltage of electrons incident on the resist surface relative to the tip-substrate voltage decreased continuously with increasing fraction of the tip-substrate filled with resist. The results are consistent with our experimental observation that the STM entered a 30 nm thick layer of resist at tip-sample voltages less than 15 V. The calculations were performed for a spherical tip with mean energy spread of emission 0.29 eV width, as expected for cold emission, and angular spread of +/- 45 degrees. The assumption of a single work function emission centered on the axis predicted spot sizes smaller than observed. The results can be explained by a larger angular emission area from the tip.
NS-MoP-9 High Selectivity Pattern Transfer Processes for Self-Assembled Monolayer Electron Beam Resists
D. Carr, C. Whelan, M. Lercel, H. Craighead (Cornell University); K. Seshadri, D. Allara (Pennsylvania State University)
Novel processes have been developed for transfering patterns using self-assembled monolayer (SAM) electron beam resists. Because the SAMs are very thin, high-selectivity processes are required. Several separate techniques have been studied for patterning intermediate layers for use as reactive ion etch (RIE) masks. The thin intermediate layers allow for high-resolution patterning with the high-selectivity anisotropic RIE. A bilayer process using the native oxide as an intermediate etch mask has been used to etch into both crystalline and poly-crystalline silicon. The native oxide (~2 nm thick) is patterned with the SAM resist after a UV/ozone development step and the oxide is then used as a mask in an electron cyclotron resonance (ECR) RIE. This process has been used to produce ~25 nm etched features in silicon. We are exploring an extension of this technique to trilayer resist systems involving a thick polymer planarizing layer. A SAM resist is used to pattern a very thin inorganic layer which is subsequently used for patterning the polymer layer with an oxygen plasma. Instead of its selective removal, an alternative technique for forming the intermediate etch mask layer is the selective deposition of the layer. Thin nickel layers have been formed with an electroless (EL) plating technique on silicon. This non-catalyst electroless deposition is highly selective for producing nickel plating on bare silicon as opposed to the silicon oxide. The catalyst size is often the limiting factor in resolution of EL plating. These novel high-selectivity techniques demonstrate the ability for ultra-thin SAM resist layers to pattern silicon and other materials.
NS-MoP-10 Nanometer-scale Lithography on H-passivated Si(100) with an Atomic Force Microscope in Air
S. Park, H. Lee, J. Oh (Kwangju Institute of Science and Technology, Korea); J. Ha, K. Park (Electronics and Telecommunications Research Institute, Korea); J. Ku (Korea Research Institute of Standards and Science)
We demonstrate a new use of the atomic force microscope(AFM) for nanometer-scale lithography on a hydrogen-passivated silicon. Nanoscale patterning of the hydrogen terminated Si(100) surface has been achieved with AFM in a contact mode in air. The Si(100) samples were passivated in dilute hydrofluoric acid after an RCA clean. Patterning occurred when a silicon nitride tip removes hydrogen using an atomic force of 300 nN, converting the surface into clean silicon. Mechanical scratch on the silicon surface by AFM tip was not observed under this atomic force. Local chemistry was also demonstrated by the selective oxidation and etching of the patterned areas. Linewidths of 20 nm for oxide films were achieved by this technique. The created oxide mask was used as a positive resist to pattern a line on the silicon substrate. Wet chemical etching of this pattern in KOH solution for 10 sec could produce a line with tens of micro-meter length, 40 nm FWHM, and 10 nm height, indicating the potential use of this technique in multistep lithography process. Results will also be presented correlating the atomic force and etching time to AFM images of resulting nanometer-scale silicon structures. This work was supported under the contract from ETRI.
NS-MoP-12 Selective Metal Patterning and Etching using an AFM-Tip
J. Tegenfeldt, P. Hallberg (Lund University, Sweden); B. Heidari (Optical Disc Technologies AB, Sweden); L. Montelius (Lund University, Sweden)
A combined selective lithography and etching method for metal surfaces using the atomic force microscope (AFM) has been created. We have used a simple electrochemical cell consisting of only two electrodes, the sample and the tip. Non-contact tips have been metallized and in order to minimize the extension of the current field, the tips were then partly insulated. The conducting nature of these tips has been proven and these tips have been used to etch metal surfaces of chrome, creating sub 100 nm lines, smallest obtained line width was 35 nm. The samples used where Au on silicon with 25x25 m large squares of chrome on top of the gold surface. We can see a clear difference between the lines created in the gold compared to the lines in the chrome. For pure scratching, as is the case for gold, the lines are irregular and lots of debris can be observed at the edges. However, for chrome where material is etched away, the lines are nice and clean.
NS-MoP-13 Metal Pattern Fabrication using the Local Electric Field of a Conducting Atomic Force Microscope
S. Brandow, E. Snow, P. Campbell, J. Calvert (Naval Research Laboratory)
Two approaches have been developed which use the conducting tip of an ambient AFM to lithographically pattern metal on silicon oxide surfaces which have been either acid cleaned or modified by the attachment of self- assembling monolayer. The difference in surface chemical reactivity between the patterned and unpatterned regions on the surface was used to selectively bind a colloidal Pd(II) catalyst capable of initiating the deposition of electroless Ni. The patterned Ni film was used as a mask for transfer of features into the underlying substrate by reactive ion etching. In one case, catalyst is bound directly to the AFM oxide/contamination pattern resulting in negative tone images following metallization and etching. In the second case, the AFM was used to selectively destroy the ligating ability of a deposited self-assembled monolayer. Catalyst was then bound in the unexposed regions resulting in positive tone images following metallization and etching.
NS-MoP-14 Local Modification of Ag Thin Films on Si(100) Substrates by STM
U. Memmert, U. Hodel, U. Hartmann (KFA J\um u\lich, ISI, Germany)
We present an investigation on the modification of Ag thin films on Si(100) surfaces by UHV-STM. The samples were prepared in-situ in UHV with varying thicknesses below 50 nm by deposition of Ag from an evaporation cell. When using the STM with a junction voltage above +3V - +4V and at the same time oscillating the tip in a feed back oscillation mode, the Ag film is locally molten and material is drawn towards the tip, leaving on the surface about 100 nm high cones with a base diameter of 150 - 300 nm. The film is modified over its entire thickness and even the Si-substrate is partially affected. Upon moving the tip over the surface solid lines consisting of Ag or Ag-Si alloy can be written into the film. The total width of the structures varies in the range from 50 nm up to 500 nm, depending on experimental parameters. The formation of an eutectic Ag/Si solution can result in significant rearrangements of the Si substrate, leaving after Ag evaporation notches of up to 30 nm depth and down to 50 nm width in the substrate. The process is investigated as a function of experimental parameters like voltage, current, writing speed, film morphology and film thickness. The use of this method to modify contact lines on devices will be discussed.
NS-MoP-15 Sculptured Thin Solid Films with Nano-engineered Microstructure for Optical, Chemical, and Biological Application
K. Robbie, M. Brett (University of Alberta, Canada); A. Lakhtakia (Pennsylvania State University); A. Elezzabi (University of Alberta, Canada)
Thin films with three dimensional microstructure controlled on the 10 nm scale have been fabricated with an evaporation technique. Oblique angle deposition and substrate motion were employed to "sculpt" columnar microstructure into desired forms. As one example, the technique was used to produce thin films consisting of helical shaped columns oriented perpendicular to the substrate as shown in the figure. This thin film was found to rotate the plane of polarization of light 340o /mm in a manner analogous to cholesteric liquid crystals. A second example application arises from the tailorable porosity attainable (measured densities as low as 6% of bulk) with these films. The low density of the films makes their effective index of refraction very small (measured with a prism coupler to as low as 1.04 in agreement with predictions form density measurements and Biot-Arago mixing rule) and the nanometer scale of the structure allows them to behave as homogeneous media for suitably long wavelength radiation. Applications of these films as chemical reaction surfaces, biological filters, and optical devices will be discussed.
NS-MoP-16 Fabrication of a Nanothermal Probe
S. Choi, M. Jung, D. Kim (Sun Moon University, Korea); Y. Kuk (Seoul National University, Korea)
Scanning force microscope (SFM) is a force imaging technique with a nanosize resolution unlike a current-imaging scanning tunneling microscope (STM). In this report, the non-contact optical deflection techniques are exploited in order to measure the deflection of the cantilever. The micron-size cantilevers are fabricated of Si or Si\sub 3\ N \sub 4\ using microfabrication techniques. The dimension of the lever is found to be about 500 micrometers long, 1 micrometer thick and 40 micrometers wide. The Pt thin film layer releases the heat due to catalytic process of H\sub 2\ and O\sub 2\ upon introduction of the gases on the Pt layer. The induced temperature gradient along the Pt/Al/Si results in angular bending of the lever from the bimetallic effect. The deflection of the lever will be examined by the position sensitive detector with a nanosize resolution. The measurement of a SFM deflection techniques are known to provide capability of measuring 1 pJ.
Time Period MoP Sessions | Topic NS Sessions | Time Periods | Topics | AVS1996 Schedule