Optical metrology of micro- and nanostructures at PTB: status and future developments

Abstract

Today, various types of high resolution dimensional metrology instrumentation are in use for a quantitative characterisation of micro-and nanostructures. Although sophisticated ultra high resolution microscopic techniques like SEM and AFM are available, optical methods like microscopy and scatterometry are still of interest and are important because they are non-destructive, fast and have a good in-line capability.At PTB different optical tools are used for high-resolution metrology. Our standard instrument for CD metrology is a special UV transmission microscope. A new 193nm microscope is currently under development which will meet future requirements at least for the 32nm node as specified in the ITRS roadmap. A special alternating grazing incidence dark field microscope is used to measure the width of single features down to 100nm. For grating structures, we developed an optical diffractometer for pitch calibrations with an uncertainty down to 10 pm. Recently we realised a DUV scatterometer and ellipsometer capable to measure accurately CD, edge profile, layer thickness, and optical parameters. A versatile EUV scatterometer can be used to characterise absorber structures e. g. on EUV photomasks. For accurate measurements a thorough modelling on the basis of rigorous diffraction calculation is essential, which accounts for both polarisation effects and the 3D geometry of the structures. We use the rigorous coupled wave analysis (RCWA) method and the finite elements (FEM) method.We present an overview of PTB's current and future activities in optical high-resolution metrology and how these systems compare to ultra-high resolution microscopy like SEM or AFM.

Development of a sinusoidal phase-shifting self-mixing interferometer for real-time displacement measurement with nanometer accuracy

“…This assumption forms the basis for our subsequent research. Equation (2) shows that the SMI has the same form as a two-beam interferometer so that phase-shifting methods can be applied to SMI to solve for the phase ϕ(t). Let the EOM be driven by a sinusoidal wave ψ(t) = a cos(2π f m t + φ).…”

“…In recent decades, with the rapid development of semiconductor technology, nanotechnology, biotechnology and other scientific researches, the precision measurement of displacement or position becomes more and more important. There is increasing demand for measuring long-range displacement of mechanical components with nanometric resolution [1][2][3]. As for the micro-electromechanical systems (MEMs), a cooperative target like the triple mirror retro-reflector necessitated in the commercial heterodyne interferometer may not be available due to 1 Author to whom any correspondence should be addressed.…”

Micro-displace sensor based on self-mixing interference of the fiber laser with phase modulation

“…The optical measurement techniques including the Michelson interferometer, Fabry-Perot (F-P) interferometer, and heterodyne interferometer, etc. are of great interest and importance because they are fast, contamination free, non-destructive and have a good in-line capability [5]. Self-mixing interference (SMI) occurs when a portion of light emitted from the laser is reflected or backscattered by an external object and is allowed to re-enter the laser cavity, causing the variation of both the output power and spectra of the laser [6].…”

Challenges in nanometrology: high precision measurement of position and size

“…At PTB, different microscope systems are used for feature width metrology. Figure 9 shows a UV transmission microscopy system, which has been described in detail in [15]. The achievable measurement uncertainty of this UV microscope system for CD on lithographic features of high quality on photomasks has been determined to be U 95% = 19 nm.…”