A. V. Rakov

Linear Standard for SEM–AFM Microelectronics Dimensional Metrology in the Range 0.01–100 μm

Linear standards for the calibration of SEMs and AFMs are reviewed. Requirements to a surface pattern designed to serve as a universal standard for the above purpose are defined. A trapezoidal pitch structure is proposed, in which the sidewalls of basic units essentially make a large angle with the normal to the surface. Its uses in SEM–AFM dimensional metrology are considered. A new, universal standard implementing the structure is described. Its certification is briefly reported. SEM and AFM experiments with the standard are presented.

Silicon test object of the linewidth of the nanometer range for SEM and AFM

The results of the study of a test object on scanning electron microscopes and atomic force microscopes are presented. The test object presents a relief on a monosilicon surface, and it is fabricated by the anisotropic etching of monosilicon. The relief elements have a trapezoidal profile with large angles of inclination of the sidewalls. The sides of the relief elements coincide with the crystallographic planes {100} and {111} of silicon. The test object is intended for calibration of scanning electron microscopes and atomic force microscopes.

SEM linewidth measurements of anisotropically etched silicon structures smaller than 0.1 µm

Scanning electron microscopy (SEM) is a standard method for linewidth (CD) metrology. For structure sizes smaller than 0.1 µm the information volume of the scanning electron probe is of the same order of magnitude as the structure size and the resulting SEM signal profile is a superposition of structural information from the whole structure. Evaluation of top and bottom linewidths needs to take into account the electron diffusion in the solid state. SEM linewidth measurements at anisotropically etched silicon structures with an exact edge slope angle of 54.7° and a top linewidth smaller than 0.1 µm were performed by a low-voltage SEM metrology system. Different algorithms were applied for linewidth evaluation which were especially adapted for measurements at small structures. The results of SEM linewidth evaluation were compared among each other and to AFM measurements performed by a large-range scanning probe microscope.

Measurement of the parameters of the electron beam of a scanning electron microscope

Results of investigations in the field of measurements of geometrical characteristics of the electron beam of a scanning electron microscope (SEM) are presented. Methods for determining the electron beam diameter are developed and tested on various microscopes. Besides, methods for obtaining the dependence of the electron beam diameter on the beam current, the energy of the primary electrons, and the focusing of the beam are also developed. Finally, method for determining the electron density distribution in the electron beam is proposed.

Measurement of dimensions of resist mask elements below 100 nm with help of a scanning electron microscope

We studied the effect of focusing of the electron probe of a scanning electron microscope (SEM), operating in the mode of collection of slow secondary electrons, on the form of a signal obtained when scanning elements of nanorelief of two kinds of objects with electron probe: (a) resist masks, and (b) protrusions and trenches on silicon. The shift of the positions of the points of reference, the distance between which is usually used to determine the size of the relief elements, was observed. The linear dependence of such distance on the size of the electron probe was found. We propose a method to measure the width of the nanorelief element, based on the extrapolation of this linear dependence to the zeroth size of the electron probe. With the help of this method, we measured the widths of nanorelief elements of resist masks, as well as of protrusions and trenches on silicon.

Test objects with right-angled and trapezoidal profiles of the relief elements

Comparison is made for parameters and properties of test objects based on the relief structures with right-angled and trapezoidal profiles, which are used for calibration of scanning electron microscopes (SEMs) and atomic force microscopes (AFMs). Methods of calibration of SEMs and AFMs with help of this test objects are presented. Comparative analysis has shown that trapezoidal structures with large angles of sidewall inclination, created by anisotropic etching of silicon with the (100) orientation of its surface, possess the most universal characteristics. Such structures could be used for development of internationally recognized measures of length in the nanometer range for calibration of SEMs and AFMs.

First Russian standards in nanotechnology

The problem of ensuring uniformity of measurements in nanotechnology is discussed. A functional block diagram is developed for length unit size transfer from the primary length standard (meter) to the nanometric range. The first six Russian national standards are presented, which ensure this transfer using scanning electron and atomic force microscopes.

Defining the parameters of a cantilever tip AFM by reference structure.

A method of measurement and control of atomic force microscope (AFM) probe parameters is offered. The AFM real cantilever parameters are defined.

Metrology of vlsi critical element sizes

Methods are surveyed for measuring the critical dimensions of VLSI components. The General Physics Institute of the Russian Academy of Sciences has developed a method that meets the requirements for metrological support up to the year 2010 as set out in the National Technology Roadmap for Semiconductors of the USA.

Russian standards for dimensional measurements for nanotechnologies

In order to provide the uniformity of measurements at the nanoscale, seven national standards have been developed in the Russian Federation. Of these seven standards, three standards specify the procedures of fabrication and certification of linear measures with the linewidth lying in the nanometer range. The other four standards specify the procedures of verification and calibration of customers atomic force microscopes and scanning electron microscopes, intended to perform measurements of linear dimensions of relief nanostructures. For an atomic force microscope, the following four parameters can be deduced: scale factor for the video signal, effective radius of the cantilever tip, scale factor for the vertical axis of the microscope, relative deflection of the microscopes Z-scanner from the orthogonality to the plane of a sample surface. For a scanning electron microscope, the following two parameters can be deduced: scale factor for the video signal and the effective diameter of the electron beam. The standards came into force in 2008.