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We have developed a novel AFM (atomic force microscope) measurement technique which can examine side-walls of fine patterns etched into wafers. This technique uses a sharpen tip tilted at an angle in combination with a "step-in" mode operation, and is thus referred as "tilt-step-in" mode. This method allows one to measure side wall shape including under cut and line edge roughness (LER).

Small AFM cantilever with a resonant frequency of about 6.6 MHz was developed using a Si micro process with SOI wafer. The cantilever was triangular in shape with a length of [email protected] and a thickness of

The possibility of SPM-based data storage is described regarding both its recording density and readout speed for ultrahigh density data storage. We consider their gap control to achieve high-speed readout. Suitable SPM-based storages are selected and their details are studied. As a result, scanning near-field optical microscope (SNOM)- and atomic force microscope (AFM)-based storages are expected to be candidates for future storage. SNOM-based storage is for . AFM-based storage is for . Using new force modulation AFM pit recording, an ultrahigh recording density of and a readout speed of are demonstrated.

To clarify the possibility of ultrahigh-density recording with an areal density of more than 1 Tb/in2, we investigated ultrahigh-density writing and high-speed reading using an atomic force microscope (AFM). Nanometer-sized pits were formed through plastic deformation of the surface of the polycarbonate (PC) disk, which was pressed by an AFM tip; in addition, nanobit writing with a bit interval of 20 nm and a track interval of 40 nm was demonstrated. In high-speed reading, the motion of the tip following the PC surface with nanostructures was detected in the prototype of a disk AFM recording system with a high resonant frequency cantilever, and reading with a period of 1.2 μs was conducted. These results indicate that AFM-based recording may be used to attain a recording density of 1.2 Tb/in2 and a readout speed of 1.25 Mb/s in a rate 1/2 (2, 7) code.

In this study, we investigated the limitations of optical reading of very fine pits using conventional optics, immersion lens optics and near-field optics. Using very fine pits 160 nm in size using a lens with a numerical aperture (NA) of 0.95 (17 Gb/in2). In addition, an oil immersion lens optics with a NA of 1.4 read fine pits only 100 nm in size (45 Gb/in2). Advanced near-field optics is a promising tool for achieving ultrahigh-density optical reading of trillion bits/in2.

A method for achieving high repeatability in edge detection considering a three-dimensional (3D) feature of a pattern sidewall was developed. An edge-detection condition is regarded as the metric representing the z-coordinate (height) of the edge position. The dependences of line-edge or linewidth roughness (LER/LWR) and LER/LWR bias on the edgedetection condition were calculated. The calculated dependence is interpreted as the qualitative z-dependence of the roughness metrics. The 3D feature of the sidewall can therefore be roughly estimated from the dependence. The condition that minimizes the LER/LWR bias to achieve high repeatability for local measurements was determined. First, to check the validity of this method, the feasibility of 3D information extraction was examined. Unbiased LER and LER bias of resist and silicon pattern samples were plotted against the edge-detection condition, and it was found that the characteristics of the graphs of the unbiased LER and bias are related to the 3D feature observed by atomic force microscopy. Next, the robustness of the method against a change in the pattern shape caused by exposure defocus was demonstrated. Finally, it was shown that the method actually improves local measurement repeatability. In the case of the linewidth of a 9-nm-long line, repeatability was improved by 40% compared with that under the conventional edgedetection condition.

A magnetic force microscope (MFM) using frequency modulation detection was combined with a scanning electron microscope (SEM). The first goal was to facilitate the selection of the MFM imaging field by positioning the magnetic tip using the SEM. The second goal was to improve the performance of the MFM by operating it in a vacuum. The efficiency of the combined SEM was proved by imaging the particular region (about 3 μm in length) on the sample. The improved features of a MFM operated in a vacuum were demonstrated by comparing images taken in air and in a vacuum. The lateral resolution was improved to 50 nm in a vacuum while it was 100 nm in air, although that resolution could possibly be due to atomic force. The dependence of the MFM image on the tip to sample spacing is discussed also.

In this work, for the purpose of contact-hole process control, new metrics for contact-hole edge roughness (CER) are being proposed. The metrics are correlated to lithographic process variation which result in increased electric fields; a primary driver of time-dependent dielectric breakdown (TDDB). Electric field strength at the tip of spoke-shaped CER has been simulated; and new hole-feature metrics have been introduced. An algorithm for defining critical features like spoke angle, spoke length, etc has been defined. In addition, a method for identifying at-risk holes has been demonstrated. The number of spike holes can determine slight defocus conditions that are not detected though the conventional CER metrics. The newly proposed metrics can identify contact holes with a propensity for increased electric field concentration and are expected to improve contact-hole reliability in the sub-40-nm contact-hole process.

Natural oxide growth on silicon facets is observed through an atomic force microscope (AFM) with current measurement. The sample is prepared by means of cleaning and heating a silicon (111) surface with direct electric heating in an ultrahigh vacuum, which creates various facets formed by step bunching. The silicon facets and steps can be observed with the AFM in air. The silicon surface structure and the current distribution can simultaneously be obtained. The results clarify that natural oxide growth on a few special high‐index‐orientation silicon facets is smaller than that on the other silicon facets ({111}, {110}, {100}, etc.).

We have developed a new measurement techniques employing digital probing with AFM (Atomic Force Microscope) that can examine sidewalls of fine patterns. This new technique employs digital probing operations, such sample-tilt step-in operation, tilt-step-in operation with a sharpened tilted tip, and multi-angle step-in operation with a flared tip. First, we examined the validity of digital probing operation using a carbon nanotube (CNT) tip, showing the measurement repeatability of approximately 1 nm (3σ) on a fine trench pattern with 50 nm width and 300 nm depth. After the slip calculation between the tilted-tip and the sidewall for the new sidewall measurement technique, we measured a perpendicular reference sidewall with two types of operations, namely, tilt-step-in and multi-angle step-in operations. We then obtained 3D images of ArF resist patterns that involved measurement of sidewall surface roughness. Finally, we demonstrated a possibility of extending the technique for measuring denser trench patterns by using sample-tilt method and a tilted CNT tip.

A critical-dimension atomic force microscope system equipped with an ultra-high resolution, three-axis laser interferometer was constructed and tested. The MIRAI (Millennium Research for Advanced Information Technology) project has been improving the precision of critical dimension measurements with atomic force microscopy (AFM) by implementing modularized laser interferometers, to meet requirements for dimensional measurement in 45 nm technology node. The stability of the cross-sectional profile of an AFM image for a rectangular cross-section was greatly improved by optimizing interferometer linearity and resolution with DSP signal processing and reducing the angular motion and mechanical vibration of the monolithic three-dimensional probe scanner with a unique parallel spring mechanism. The repeatability of linewidth measurement of a nominal 100 nm linewidth along the same scanned line showed a standard deviation of 0.5-1.0 nm (3-sigma). This shows AFM to be one of the most promising metrological tools for next-generation nanodevice fabrication processes. Instrumentation, measurement results, and precision will be discussed.

A design of a high-resolution homodyne interferometer is presented, modularized, and installed in a prototype, critical-dimension atomic force microscope (CD-AFM). A newly designed symmetrical layout of the optical path of the homodyne interferometers enabled highly stable measurements of the mechanical displacements of a wafer-positioning stage and an AFM scanner. In the performance measurement of the wafer-positioning stage, the mechanical drift after long-stroke travel and unlocking of the servo control was reduced to less than ten nanometers per minute by optimizing the preceding motion before stopping. An AFM scanner with a three-dimensional (3D) parallel spring structure has been implemented for the interferometer modules. Using a DSP-based electronic interpolation technique, displacement of the scanner was resolved and calibrated at better than 50 pm and 200 pm, respectively.

To investigate whether field evaporation of gold atoms is responsible for dot formation in an atomic force microscope (AFM) gold‐coated tip/vacuum/SiO2 film/p‐type Si substrate configuration, we have performed elemental analysis of the dots and measured the dependence of the threshold voltage on SiO2 thickness with both polarities for the dot formation. The experiments demonstrate that it is feasible to form gold dots on SiO2 films 17–107 A thick by adjusting the pulsed voltages applied to the gold‐coated AFM tip. Energy dispersive x‐ray spectroscopy (EDX) shows that the dots include gold. The threshold voltages increase almost linearly with the SiO2 thickness. Furthermore, the voltage with negative polarity is lower than that with positive polarity. These results provide evidence that the dot formation on the SiO2 film using AFM occurs by field evaporation.

A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 μm in diameter are observed using a polarized optical microscope.

Prototyped XY-stages driving electron beam (EB) writing system is developed to research the possibility to write fine patterns. High density optical recording pattern with 25 Gbit/in/sup 2/ is demonstrated. It is also clear that EB writing (drawing) system has a potential to achieve a required fine pattern for 100 Gbit/in/sup 2/.

Feasibility of ultrahigh density information data storage has been newly demonstrated by using an atomic force microscope (AFM) and a scanning near-field optical microscope (SNOM). Ultrasmall gold dots about 20 to 80 nm in diameter could be stably formed on Si substrate in air by adjusting an applied pulsed voltage of AFM probe coated with gold thin film. Magnetic domains about 60 to 80 nm in diameter also could be successfully recorded on magneto optical disk material (Pt/Co multilayer) by controlling a writing pulsed laser power of sharp fiber probe with SNOM. These indicate that this technique has a potential to realize a storage density of more than 100 Gb/in2 and even 1 Tb/in2.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed a high-precision atomic force microscope (AFM) for measuring fine pattern structures for semiconductor process evaluation. Three-axis ultrahigh-resolution displacement sensors using modularized laser interferometers were built into an AFM scanner combined with piezoactuators, elastic parallel-plate structures and an on-axis optical microscope. A newly designed symmetrical layout of the optical path of homodyne interferometers and a digital signal processor (DSP) enabled highly stable measurements of the mechanical displacements of the tip of an AFM scanner. As a result of their ultrafine positioning capabilities, a resolution of the displacement sensors of 0.05 nm was achieved. The periodic error of laser waves was compensated by employing DSP-based processing. Thus, a wide linearity range from 0.1 to 1000 nm was demonstrated and a one-sigma repeatability of 0.25 nm was obtained by measuring reference samples of 50 and 1000 nm step heights. Finally, micro-roughness with a 0.1 nm height, a GaAs atomic step with a 0.3 nm height, patterns with high aspect ratios, and resist patterns were clearly observed using an interferometer displacement signal.

We have developed a new critical dimension (CD) measurement technique using atomic force microscope (AFM) which can measure width-dimensions and examine sidewall-shapes of fine patterns on a wafer. The technique employs a flared-type tip in combination with digital probing and multi-angle scanning mechanism that allows the tip to trace the sidewalls on both sides of a feature (or trench) by making physical contacts with the sidewall surface. First, by using finite element method (FEM) we analyzed deformation of the tip and cantilever to compensate errors caused by the deformation. To verify our compensation method we measured quartz reference patterns either with perpendicular sidewalls or undercuts. In this paper we will describe the applications and usefulness of this multi-angle operation and show some measurement results of ArF resist patterns with 200 nm width and 400 nm depth that were obtained with a flared tip of 120 nm diameter.

A new atomic force microscope (AFM) imaging has been used to study the bending of a sharpened and slim probe in the digital probing method (step-in mode) for the critical dimension (CD)-AFM technique. The bending of the AFM probe indicates a serious problem in measuring very fine patterns with a high aspect ratio with an error of less than 1 nm when we use the sharpened and slim probe. In our estimation, position errors Δr (in plane) and Δz (in perpendicular) rapidly increase with the slope angle and a controlled force. In experiments, we measured a degradation of the pattern profile as the controlled force increased in the AFM system. We have to control the probe at a force of 5 accurately.

Cantilevers as small as 10 µm in length are required in order to achieve a practical data transfer rate in a read-only memory system using cantilevers as head. Thus, a new optical lever design concept that can detect the motion of such small cantilevers is necessary. The new optical lever concept that we propose makes it possible to use an objective lens with a high numerical aperture and to reduce the expansion rate of the projected light source image on the cantilever surface. As a result, we were able to reduce the incident laser spot diameter to 5 µm. It was also possible to expand the operation bandwidth to 10 MHz while achieving a displacement sensitivity of 0.48 Å (when a 10-µm long cantilever was used) by using a small spot position sensor, because the laser spot diameter on the detector could to be reduced to an arbitrary size.

The authors designed a photo-polymer objective lens which can be used for both red and blue lasers. The following two conditions were set to facilitate this lens production process. 1) We chose photo-polymer resin as one of the doublet lens materials. 2) One surface of the photo-polymer lens was designed to be flat. We installed this lens in pickup heads and played back some disks. Its performance was almost as good as that of a noncompatible glass lens.

We prototyped a next-generation digital-versatile-disc (DVD) dual-layer disc system using a blue laser diode. Numerous technologies were investigated for our proposal, such as new signal-processing techniques, a disc mastering process using photobleachable dye and silver alloy as a semireflective material. The dual-layer disc for the blue laser system has a 27.4 Gbyte capacity on a 12 cm disc. Where the threshold level of the jitter value was provided at 15%, the radial tilt margin was within ±0.66 degrees on layer 0 and ±0.64 degrees on layer 1, while the tangential tilt margin was within ±0.73 degrees on layer 0 and ±0.70 degrees on layer 1. These values are sufficiently large for the playback system when compared with the DVD system.

A novel, to our knowledge, optics pickup for semiconfocal optical disk is proposed. Five tracks are imaged simultaneously by use of one linear-shaped beam that extends over the tracks in the radial direction with the focusing and the tracking position controlled. We also show how the cross talk between tracks is eliminated automatically. The approximately diffraction-limited width of the beam and the small-signal detector elements make semiconfocal detection possible in the tangential direction.

In this paper we describe a narrow pitch tracking method for data storage using an atomic force microscope (AFM) probe head. A track position of the AFM head on a recording disk was controlled by an optical tracking method. Narrowing of the track pitch was achieved by locating eight recording tracks in one groove of the disk. These track positions were controlled by eight phase tracking-error signals which were created from one groove of the disk. In writing, we used the force modulation recording method which forms written pits by applying force pulses between the AFM tip and the polycarbonate recording disk. Using the recording system, we achieved 200 nm pitch tracking control and readout from written pits as small as 40 nm in diameter. A scanning electron micrograph of the written pits showed that the tracking accuracy was about 20 nm.

We propose force modulation atomic force microscopy (FM)-(AFM) pit recording and demonstrate the possibility of achieving ultrahigh density recording with high speed readout. A minimum pit size of around 10 nm in diameter is formed by cold plastic deformation of the polycarbonate disk surface at a force of over 40 nN. Using a prototype of the rotation type FM-AFM pit recording system, an ultrahigh recording density of 1.2 Tb/in.2 and a readout speed of 1.25 Mb/s are demonstrated in 1/2(2,7) code recording.

The feasibility of field-evaporating metal atoms onto an insulator/conducting substrate has been investigated. Theoretical and experimental studies clarify that field evaporation is possible in an atomic force microscope (AFM) metal probe/vacuum/thin insulator/conductor configuration. Theoretically, field evaporation is easily achieved on thin SiO2 insulators of less than 100 Å, though image potential and electric field weaken in the presence of an insulating layer. Experiments confirm that ultrasmall gold dots can be formed on a natural SiO2/Si substrate with a threshold voltage of around 10 V. Small dots of 15 nm diameter can be obtained.

Nanometer‐sized Au (gold) dots on a Si substrate were formed by field evaporation using an atomic force microscope (AFM) in air. Theoretical and experimental studies show that field evaporation is possible in the AFM metal probe/vacuum/thin insulator/conductor configuration. Theoretically, the field evaporation is generated by further application of an additional bias voltage less than 30–40 V in a thin insulator. Experiments demonstrated that ultrasmall gold dots were formed on a natural SiO2/Si substrate by the applied voltage less than 10 V, and ultrasmall gold dots of 15 nm in diameter were made on the insulator.

Nanometer recording has been demonstrated with tens nanometer diameter pits and gold mounds formed on graphite and Si substrate using an atomic force microscope at atmospheric pressure. The probe is prepared by means of coating thin gold film on an SiO2 birdbeak-type cantilever probe, fabricated by a Si microprocess. Applications of voltage pulses between the probe and the graphite make about 10-nm diameter pits and Au mounds. Furthermore, about 50-nm to 30-nm diameter Au mound formations on Si wafer covered with natural silicon oxide are also demonstrated. The results indicate that the technique has potentials to achieve Tera-bit/in2 highly packed storage in air, and directly to write nanometer sized patterns on an insulating thin film.

A 3-dimensional (3-D) magnetic stray field and the surface structure have been observed using an atomic and magnetic force microscope (A/MFM) with an optical-beam-deflection force detector. Measurement is carried out by operating the microscope as a surface structure observer in constant repulsive force AFM mode. The 3-D magnetic stray field measurement is done in force gradient MFM mode with probe position control above the surface. Initial results have demonstrated that the 3-D magnetic stray field and surface structure of magneto-optical disk can be imaged simultaneously.

The MIRAI project has been improving the precision of critical dimension measurements with atomic force microscopy (AFM) by implementing modularized laser interferometers to meet requirements for dimensional measurement at the 45 nm technology node. Recent advances in semiconductor process technologies require a breakthrough in nanometer‐pattern dimensional measurement on large wafers such as linewidth, hole diameter, and depth. AFM is promising method to meet this need because of its spatial atomic‐level resolution along three axes. The higher the resolution is, the better we can know geometrical shape of a target pattern. We discuss the design of a high‐resolution homodyne interferometer modularized and installed in a critical‐dimension AFM (CD‐AFM) prototype. The symmetrical optical path layout of the homodyne interferometer makes measurement of the mechanical displacements of an AFM scanner highly stable. The stability of the cross‐sectional AFM profile for a pattern with a rectangular cross‐section was greatly improved by optimizing interferometer linearity and resolution with DSP signal processing and reducing the angular motion and mechanical vibration of the monolithic three‐dimensional probe scanner with a unique parallel spring mechanism. Repeated measurement of a nominal 100 nm linewidth along the same scanned line showed a standard deviation of 0.5–1.0 nm (3 sigma). This shows AFM to be one of the most promising metrological tools for next‐generation nanodevice fabrication processes. We detail instrumentation, performance, and measurement results.