The project focuses on the development of the “ruler” (NanoScale) which can be applied to the technologies to control, process and measure the nano structure with super-fine precision. The NanoScale is intended to offer the calibration traceable to the national measurement standards for both lateral and depth directions, and to serve as the certification reference material to which the certification value and uncertainty are assigned.

The National Metrology Institute of Japan (NMIJ) is presently providing the calibration standard for 1-D grating sample (0.2-8µm) and GaAl/AlAs superlattice reference material as the relevant measurement standard (Figure 1). The SEM (scanning electron microscope), which is integrated with the calibrated standard microscale (240nm pitch), is marketed as the CD-SEM for semiconductors. It is one of the major measurement tools developed in Japan that contributes to the field of semiconductors.

In this project, the aim is to develop a NanoScale of 25nm pitch for the lateral direction, and that of 3-10nm pitch for the depth direction. Figure 2 represents the outline of the project.

By developing the calibration technology of a minute scale of nanometers that is traceable to the length standard, the lateral NanoScale of 1-D grating structure is calibrated and supplied as the certification reference material. Each of the created lateral NanoScales involves minute deviance and fluctuation from the nominal value that is caused by the incomplete fabrication process. Therefore, it is indispensable to measure (calibrate) such minute discrepancies by means of the accurate "ruler".

For this purpose, the project focuses on the development of an atomic force microscopy (Traceable-AFM) which is equipped with a laser interferometer with a resolution of about one fifth of the atomic size. Utilizing the iodine stabilized laser which is currently used as a length standard, direct traceablity to the length standard is achieved by feedback control using the laser interferometer.

Reference materials for calibration for the depth direction is to be developed for each semiconductor system with a view to applying the standards to the structure evaluation of both compound and silicon semiconductors. In the study of the NanoScale for the depth direction, it is necessary to control not only the uniformity of the layer thickness but also other factors, unlike in the case of lateral NanoScale. These factors include the uniformity of density and composition of the substances that comprise the layer in the depth direction, roughness of both surface and interface, and a peculiar interface structure of the transition layer. For this purpose, at Ultra-Fine Profiling Technology Laboratory, it is sought to establish the method to reduce a structural transition layer to the minimum, by forming silicon-dioxide films utilizing ozone oxidization in the low temperature environment.

There is a requirement to accurately evaluate nano particles as a building block of nano structure, as well as fine particles, for the purpose of quality management of semiconductors, environmental control for exhaust gasses and so on. One of the key technologies to attain this objective is to supply the accurate reference material for the particle diameter. AIST has been supplying the world's best precision standards for particle diameter of 100 nm and is currently striving to develop the nanoparticle reference material in the range of even smaller diameters.

In this project, the practical application of the new technique of measuring mass of fine particles is pursued by using the equilibrium between the centrifugal force and the electrostatic force both working on the particles (Figure 3). In the field of polymer materials, the diffusion coefficient of polymers and nanoparticles in the solution is measured with precision using dynamic light scattering and nuclear magnetic resonance, and the average particle diameter is determined. Furthermore, the scattering pattern measurement is implemented on the samples separated by size exclusion, by using the multi angle laser light scattering (MALLS), that leads to the establishment of the technique to accurately measure the particle distribution.

The porous materials with nanopores of a few nanometer diameter are attracting attention as low-k dielectrics for the wiring system of the next generation semiconductor device. In order to measure this nanopore, the development of the positron annihilation method is to be implemented. Utilizing this method, it is possible to obtain the information regarding both the average size and size distribution of nanopores, by calculating positron lifetime based on the energy distribution of gamma rays generated by positron annihilated in the samples, which is found in the nanopores of sub-nm to 10 nm scale of the material. There is also a need to measure the period of gamma ray emission. In this collaboration project with Photonics Research Institute, it is attempted to develop a popular-type compact-size positron lifetime spectrometer (Figure 4) which utilizes the positron beam obtainable from radioisotope.

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are widely used as the means of characterization of surface composition, electronic state etc. of the materials that have functional surfaces, such as thin films, catalysts, sensing devices and so on. The target of the project is placed at the development of tunable photoelectron spectroscopy technology with synchrotron orbit radiation as an excitation source. Also, the objective is the establishment of quantitative reliability of conventional XPS and AES excitated by Kα-ray of Mg and Al.

In addition, a database for surface analysis is to be constructed based on the collection of the standard spectrum of the samples whose physical and chemical change is kept to the minimum. The technique to eliminate background distortion of spectrum caused by inelastic scattering of photoelectron is also a subject of study.

Thermophysical values of thin films such as thermal diffusion ratio, specific heat capacity, coefficient of thermal conductivity and coefficient of thermal expansion are indispensable in terms of the thermal and structural designing.

In this project, the thermal change on the reverse side of the thin film is observed referring to the change of reflectance to the laser beam, by heating the film surface using pico-second laser (pico-second thermo reflectance technique). Thereby the measurement technology is to be created for thermal diffusion ratio of thin films and the coating material, interface thermal resistance between thin films, and interface thermal resistance between the coating and the base material. By means of the laser interferometer, the technology to accurately measure the coefficient of thermal expansion of solid materials is to be established.

The above is a brief introduction of a variety of projects aiming for the establishment of nano metrology standards. The NanoScale is to be developed in the 3D Nano Project as a certified reference material which will be supplied in the final year of the project. As part of the Nanotechnology Material Metrology Project, the standards are to be supplied for a calibration service as well as for the certified reference materials.