Method for linear measurements in the nanometre range

At the IX Session of the Commission of Length in September 1997, the values of the frequency and wavelength of He–Ne laser emission, stabilized by a saturated absorption line in molecular iodine, ν = 473 612 214 705 kHz, λ = 632.991 398 22 nm, were recommended. The emission of such lasers is used all over the world as a material bearer of a length unit. In Russia, reproduction and transmission of its size is realized with the help of a reference interferometric device, an atomic force microscope of original design, where displacement along the X, Y and Z axes is controlled by a laser interferometric nanodisplacement measuring device. By this means, scanning in all three coordinates is measured in fractions of laser emission wavelength, which in its turn serves as a material unit length bearer. In practice, linear measurements in the nanometre range are carried out with scanning electron (SEM) and scanning probe (SPM) microscopes. A standard of the width of the line and of the pitch, called 'MShPS-2.0K', is used in Russia. This standard enables us to determine the SEM magnification, as well as the effective diameter of its electron probe. Moreover, one can determine the SPM scale factor for the three scanning axes, the Z-scanner nonorthogonality and the effective radius of the SPM cantilever tip by means of the standard MShPS-2.0K (Russian abbreviation). The authors describe in the present paper the methods for the linear measurements in the nanometre range with the use of the SEM and SPM. These methods were proposed by Russian specialists, and have been employed at Russian research institutes as well as at Russian manufacturing enterprises.