Ichiko Misumi

Uncertainty in pitch measurements of one-dimensional grating standards using a nanometrological atomic force microscope

Precision measurements of 240 nm-pitch one-dimensional grating standards were carried out using an atomic force microscope (AFM) with a high-resolution three-axis laser interferometer (nanometrological AFM). Laser sources of the three-axis laser interferometer in the nanometrological AFM were calibrated with an I2-stabilized He–Ne laser at a wavelength of 633 nm. The results of the precision measurements using the nanometrological AFM have direct traceability to the length standard. The uncertainty in the pitch measurements was estimated in accordance with the Guide to the Expression of Uncertainty in Measurement. The primary source of uncertainty in the measurements was derived from interferometer nonlinearity, and its value was approximately 0.115 nm. Expanded uncertainty (k = 2) of less than 0.31 nm was obtained. It is suggested that the nanometrological AFM is a useful instrument for the nanometrological standard calibration.

Simple, real-time method for removing the cyclic error of a homodyne interferometer with a quadrature detector system

The cyclic error of a homodyne interferometer is caused mainly by phase mixing due to the imperfection of polarizing optical components such as polarizing beam splitters. In Appl. Opt. 43, 2443 (2004), we concentrated on the relationship between these imperfect optical characteristics and the cyclic error and found the preamplifier-gains condition for removing the cyclic error. Here we demonstrate the cyclic error correction method experimentally and show that the method can be applied in real time. We obtained 0.04-nm cyclic errors, with a standard deviation above 5 microm.

Removing nonlinearity of a homodyne interferometer by adjusting the gains of its quadrature detector systems

Most homodyne interferometers have a quadrature detector system that includes two polarizing beam splitters that cause nonlinearity of the order of a few nanometers by phase mixing. Detectors should have the same gains to reduce nonlinearity under the assumption that there is no loss in optical components. However, optical components exhibit some loss. We show that nonlinearity can be reduced to an order of 0.01 nm when the detector gains are adjusted by simulation to include the optical characteristics. The compensated nonlinearity is 18 times smaller than that when the four detector gains are set to be equal.

Submicrometre-pitch intercomparison between optical diffraction, scanning electron microscope and atomic force microscope

Intercomparison of pitch measurements for one-dimensional-grating standards (240 nm pitch), one of the widely used reference standards for nanometric lateral scales, was performed by three different methods, optical diffraction, critical dimension scanning electron microscopy and nanometrological atomic force microscopy. Average pitch values obtained by the three methods deviated by a maximum of only 0.67 nm with expanded uncertainties (k = 2) of less than 1.2 nm. The calculated En number, the index of measurement quality, of less than 1 indicates consistency of the measured pitch values and subsequent uncertainty analyses performed by three methods.

Nanometric lateral scale development using an atomic force microscope with directly traceable laser interferometers

One-dimensional grating standards with sub-hundred nanometre pitches are required for calibration of nanometrological instruments. Nanometric lateral scales (design pitches: 100, 60 and 50 nm) for the calibration of nanometrological instruments were designed and fabricated by electron beam cell projection lithography. An offset-locked laser system consisting of an I2-stabilized He–Ne laser and a slave laser was installed in an atomic force microscope with differential laser interferometers (DLI-AFM) for the realization of a continuously, directly length-standard-traceable system and the pitches of the lateral scales were calibrated using the new DLI-AFM. The average pitches were quite close to the design pitches and the expanded uncertainties (k = 2) were less than 0.6% of the design pitches. The developed nanometric lateral scales are of sufficiently high quality and are candidates for certified reference materials (CRMs).

Bilateral comparison of 25 nm pitch nanometric lateral scales for metrological scanning probe microscopes

One-dimensional (1D) and two-dimensional (2D) gratings are some of the most important transfer standards for the calibration of nanometrological instruments. National Metrology Institutes (NMIs) demonstrate their calibration capability through international comparisons among themselves and provide pitch calibration services for their customers. In the past, international comparisons were performed three times for gratings with large pitches such as 4000 nm, 1000 nm, 700 nm and 300 nm. Additionally, a bilateral comparison was conducted for 100 nm and 50 nm between the Japanese National Metrology Institute (NMIJ) and the German National Metrology Institute (PTB). The industry, however, requires calibration services for increasingly smaller pitches. In a previous study, NMIJ developed a nanometric lateral scale, a special 1D grating with 25 nm pitch consisting of Si/SiO2 multilayer thin-film structures, and calibrated the pitch of this scale by using the NMIJs atomic force microscope equipped with differential laser interferometers (DLI-AFM). In this paper, we will report results of an informal bilateral comparison for the nanometric lateral scale between NMIJ and PTB.

Nanometric lateral scale development with Si/SiO2 multilayer thin-film structures and improvement of uncertainty evaluation using analysis of variance

A nanometric lateral scale (design pitch: 25 nm) with Si/SiO2 multilayer thin-film structures was developed. The pitch of the developed nanometric lateral scale was calibrated using an atomic force microscope with a differential laser interferometer, and the uncertainty in pitch measurement was evaluated. In the uncertainty evaluation, two evaluation methods were revised to avoid overestimation. The analysis of variance was applied to the evaluation of uncertainties caused by the nonuniformity of the scale and the repeatability of the measurements in the same location. The expanded uncertainties (k = 2) were 29?154 pm in this study and became smaller than 0.43 nm, which is the expanded uncertainty evaluated in our previous study.

Application of a GaAs/InGaP superlattice in nanometric lateral scales

The National Institute of Advanced Industrial Science and Technology (AIST), National Metrology Institute of Japan (NMIJ) developed nanometric lateral scales (design pitch: 25 nm) consisting of a GaAs/InGaP superlattice (multilayer) for atomic force microscope (AFM) and scanning electron microscope (SEM) calibration. The pitch of the fabricated nanometric lateral scales was measured using our AFM with a differential laser interferometer (DLI-AFM) and the uncertainty in the pitch measurements was evaluated. The average pitch and its expanded uncertainty (k = 2) were 25.39 nm and 0.43 nm, respectively. The quality of the developed scales was high enough to make them a suitable candidate for CRMs. On the basis of the obtained results in this technical study, the fabrication procedure and layout of the nanometric lateral scales will be optimized for the future distribution of these scales.

Round-robin measurements of 100- and 60-nm scales among a deep-ultraviolet laser diffractometer, a scanning electron microscope and various atomic force microscopes

An intercomparison of nanometric lateral scales, which are special one-dimensional (1D) grating standards with sub-hundred-nanometre pitches, among a deep-ultraviolet (DUV) laser diffractometer, a critical dimension scanning electron microscope (CD-SEM) and different types of atomic force microscope (AFM) was performed. The reference value and its expanded uncertainty were provided by the National Metrology Institute of Japan (NMIJ) using an atomic force microscope with differential laser interferometers (DLI-AFM). The consistency of the measurement results obtained using the DUV laser diffractometer, CD-SEM and some AFMs was satisfactory; however, that in the measurement results obtained using other AFMs was unsatisfactory. An improvement in AFM calibration technology using nanometrological standards is required for both AFM manufacturers and AFM users, including metrology institutes.

25 nm pitch comparison between a traceable x-ray diffractometer and a metrological atomic force microscope

A one-dimensional grating (1D grating) is one of the most important reference standards to calibrate nanometrological instruments, such as a critical dimension scanning electron microscope. Recently, the resolutions of nanometrological instruments have become higher, and 1D grating standards with smaller pitches are required. Based on this demand, 1D gratings with 25 nm pitch consisting of Si/SiO2 multilayer thin-film structures have been developed. Furthermore, pitch calibrations using metrological atomic force microscopes (metrological AFMs) and an x-ray diffractometer have been applied. In this study, the results of a 25 nm pitch comparison between a length-and-angle-standards-traceable x-ray diffractometer and a metrological AFM are reported.