Bradley N. Damazo

Atomic-resolution measurements with a new tunable diode laser-based interferometer

We develop a new implementation of a Michelson interferometer designed to make measurements with an uncertainty of less than 20 pm. This new method uses a tunable diode laser as the light source, with the diode laser wavelength continuously tuned to fix the number of fringes in the measured optical path. The diode laser frequency is measured by beating against a reference laser. High-speed, accurate frequency measurements of the beat frequency signal enables the diode laser wavelength to be measured with nominally 20-pm accuracy for the measurements described. The new interferometer design is lightweight and is mounted directly on an ultra-high vacuum scanning tunneling microscope capable of atomic resolution. We report the simultaneous acquisition of an atomic resolution image, while the relative lateral displacement of the tip along the sample distance is measured with the new tunable diode laser Michelson interferometer.

A macro-micro motion system for a scanning tunneling microscope

As nano-lithography technology improves, more companies and research groups have the capability to create nano-scale structures. Scanning tunneling microscopes (STMs) are commonly used to create these structures and evaluate them afterward. One difficulty is that these nanostructures are difficult to find on a one centimeter-size die cut from a silicon wafer without very specialized hardware and post-processing and analysis. The National Institute of Standards and Technology (NIST) is conducting research into developing a macro-micro motion system that would allow these nano-structures to be more effectively located and identified on the die. An XY stage system using linear piezo-actuators can perform the macro motion by moving the sample to where the STM tip can scan a particular region of the die to make an analysis. The STM tip would then perform the micro motion by scanning the region for the nano-structure. A vibration isolation system has been designed for this macro-micro motion system using springs and eddy current dampers. This vibration isolation system will isolate the entire system from the outside world and the individual components from each other. A high-precision interferometer system is also installed to independently monitor a flexure driven stage for the STM tip. A graphical programming system was developed for controlling the motion of the STM tip. All of these systems combine to form the initial steps toward coordinated closed-loop control of the STM.

Development of a metrology frame to improve the positioning accuracy of micro/meso-scale machine tools

The small work volumes of Micro/Meso-scale Machine Tools (MMMTs) often present problems for calibration and error compensation, but also allow solutions not practical on the traditional scale. Measuring tool position with a separate metrology frame and compensating for error motions is one such solution. The metrology frame design follows principles of precision design and allows measurement of the position of the tool tip with respect to the workpiece while minimising Abbe errors. Kinematic analysis provides the relationship between metrology frame measurements and machine tool coordinates. Error analysis reveals that sensor error has the only first order influence on measurement accuracy.

SEM sentinel-SEM performance measurement system

This paper describes the design and implementation of a system for monitoring the performance of several major subsystems of a critical dimension measurement scanning electron microscope (CD-SEM). Experiments were performed for tests involving diagnosis of the vacuum system and column stability by monitoring of the following subsystems and associated functional parameters. These include: 1) Vacuum system with pressure as a function of time being recorded for the electron-optical column (gun chamber), the specimen chamber, and the sample-loading unit. 2) The action of several components of the wafer handling system can be timed. 3) The electron gun emission currents and other signals to monitor the characteristics of the condenser and objective lenses may be used to correlate with image quality. 4) Image sharpness, electron beam current, signal-to-noise ratio, etc. can be evaluated.

Nanoparticle size and shape evaluation using the TSOM method

A novel through-focus scanning optical microscopy (TSOM) method that yields nanoscale information from optical images obtained at multiple focal planes will be used here for nanoparticle dimensional analysis. The TSOM method can distinguish not only size differences but also shape differences among nanoparticles. Size evaluation based on simulations will be presented along with experimental data for nanoparticles and nanodots with sizes below 100 nm. Size determination using an experimentally created library will also be presented.

Accurate nanometer-scale imaging and measurements with SEM

Scanning electron microscopes (SEMs) are incredibly versatile instruments for millimeter to nanometer scale imaging and measurements of size and shape. New methods to improve repeatability and accuracy have been implemented on the so-called Reference SEMs at the National Institute of Standards and Technology (NIST). These methods include: 1) very fast digital imaging and real-time corrective composition of SEM images, showing superiority over both traditional fast or slow image collection methods; 2) high-precision sample stage with laser interferometry, providing traceability and compensation for stage drift and vibration with sub-nanometer performance; and 3) contamination and charging mitigation through hydrogen and oxygen plasma cleaning. These new methods can be applied in other SEMS as well to realize quantitative scanning electron microscopy.

Introduction to special session on microscopy for Science, Technology, Engineering and Math (STEM) educators

The future of our nation hinges on our ability to prepare our next generation to be innovators in science, technology, engineering and math (STEM). Excitement for STEM must begin at the earliest stages of our education process. Yet, today far too few of our students are prepared for the challenges ahead. Several initiatives are trying to change this situation. “Microscopy for STEM Educators” was an initiative that demonstrated the value of incorporating microscopy into STEM education. Several notable invited speakers discussed their successful programs implementing microscopy in STEM education in order to foster student interest and excitement. A hands-on session with table-top scanning electron microscopes was held at the end of the presentations and the attendees were encouraged to bring samples of interest and operate the instruments. This paper outlines some of the accomplishments and goals of this session.

Laser sample stage-based image resolution enhancement method for SEMs

The development of a very fast, very accurate laser stage measurement system facilitates a new method to enhance the image and line scan resolution of scanning electron microscopes (SEMs). This method, allows for fast signal intensity and displacement measurements, and can report hundreds of thousands of measurement points in just a few seconds. It is possible then, to account for the stage position in almost real time with a resolution of 0.2 nm. The extent and direction of the stage motion reveal important characteristics of the stage vibration and drift, and helps to minimize them. The high accuracy and speed also allows for a convenient and effective technique for diminishing these problems by correlating instantaneous position and imaging intensity. The new measurement technique gives a possibility for significantly improving SEM-based dimensional measurement quality.

New method for the measurement of SEM stage vibrations

The National Institute of Standards and Technology (NIST) has implemented a high bandwidth laser interferometer measurement system in a specialized metrology microscope. The purpose of the system is the certification of SEM magnification calibration samples by moving the sample under a finely focused stationary electron beam in the metrology electron microscope. Using a laser interferometer with displacement measurements traceable to basic wavelength standards, the motion is measured while recording the secondary or backscattered electron output signal. The recent upgrade to the laser measurement system enables a measurement bandwidth of 300 kHz to be achieved in the sampling of the X-Y position of a test sample, along with measuring the intensity of the secondary electron beam output signal. This high bandwidth stage position measurement capability becomes a tool to measure the effects of environmental vibrations on SEM measurements. This paper outlines this ongoing research and presents the current results along with details of the measurement possibilities based on this new technique.

An Overview of Nano-Micro-Meso Scale Manufacturing at the National Institute of Standards and Technology (NIST)

The future of nano-, micro- and meso-scale manufacturing operations will be strongly influenced by a new breed of assembly and manufacturing tools that will be intelligent, flexible, more precise, include in-process production technologies and make use of advanced part design, assembly and process data. To prioritized NIST efforts in nano, micro and meso manufacturing, several visits to industrial and government research laboratories and two workshops were organized. The identified needs at the meso and micro Scale include: dimensional and mechanical metrology, assembly and packaging technology and standards, and providing a science base for materials and processes emphasizing materials testing methods and properties data. Nanocharacterization, nanomanipulation, nanodevices and magnetics industry support have been identified at the nanoscale. Nanometrology and nanomanipulation have a substantial base from which to expand within the Manufacturing Engineering Laboratory (MEL). Therefore, MEL is initiating a new long-term Strategic Program in nano-manufacturing to conduct research and development, to provide the measurements and standards needed by industry to measure, manipulate and manufacture nanoscale discrete part products. The program will address the measurement and standards issues associated with the manufacture of both nanoscale products themselves, as well as with the development of the production systems required for their manufacture.