High Precision Dimensional Metrology of Periodic Nanostructures using Laser Scatterometry

At PTB different laser scatterometers with partly novel and outstanding metrological capabilities have been developed and are available for high-resolution dimensional metrology of periodic nanostructures. Two different systems are described and their metrological potential discussed: a laser diffractometer for pitch calibration and a versatile goniometric scatterometer for multi-parameter characterisation of nanostructures. Introduction Many current and future technologies require a highly accurate and reproducible metrology of microand nanostructures. Especially the semiconductor industry greatly pushes the metrological requirements. Although sophisticated ultra-high resolution microscopic techniques like SEM and AFM are available, optical methods are of interest and are important because they are non-destructive, fast and have a good in-line capability. Scatterometry is a promising candidate to solve future challenges in dimensional nanometrology. At PTB, recently two different laser scatterometers with partly novel and outstanding metrological capabilities have been developed, a diffractometer for pitch calibration and a versatile goniometric scatterometer. These systems are now available for high-resolution metrology and their features and capabilities are described in the following. Diffractometer for pitch calibration For the accurate measurement of the period (or mean pitch) of oneand two-dimensional gratings, an optical diffractometer has been developed at PTB which offers the possibility of period calibrations with an uncertainty down to a few pm [1]. The period of a grating is determined by means of diffraction of laser radiation using a Littrow configuration, see Fig.1. The sample is mounted on a precision turntable connected with a rotary encoder which is used to measure the angle of the incident laser beam relative to the sample. The detector, a CMOS linear image sensor, is mounted slightly below the incident laser beam (approximate Littrow configuration). Different lasers emitting at different wavelengths can be used: a 10th IMEKO TC14 Symposium on Laser Metrology for Precision Measurement and Inspection in Industry Braunschweig, GERMANY, 2011, September 12-14