The characteristics of the Si–vacuum interface were compared with the characteristics of the oxide–air interface formed following room temperature oxidation for a variety of samples. Scanning tunneling microscopy was used to measure the surface structure following vacuum preparation, and atomic force microscopy was used to measure the oxide surface on the same samples following exposure to air. Samples investigated included nominally flat Si(111) with equilibrated and quenched surface configurations, Si(111) miscut by 1.25° toward the [2̄11] and equilibrated to yield the faceted structure, and nominally flat Si(001) wafers. In all cases, the step morphology of the clean surfaces was duplicated on the surface of the oxide.

The 2019 revision of the International System of Units (SI) linked the seven base units to fundamental constants; only a minor rewording was necessary for the metre whose definition was already linked to the speed of light. However, the largest change in the metre realisation since 1983 occurred with the adoption of the lattice parameter of silicon as a secondary realisation of the metre to support dimensional nanometrology. The traceability of the silicon lattice spacing has been established through combined optical and x-ray interferometry with a relative uncertainty of and three routes to traceability via the silicon lattice spacing have been formally recognised in the Mise en Pratique for the metre. These are length measurement using x-ray interferometry (relying on the known value for the lattice spacing rather than using x-ray interferometry to measure the lattice spacing) counting atoms on linewidth structures using transmission electron microscopy and using monoatomic steps to calibrate scanning probe microscopes. This paper describes these routes and highlights the opportunities this new secondary realisation presents.

Resist slimming under electron beam exposure introduces significant measurement uncertainty in the metrology of 193 nm resists. Total critical dimension (CD) uncertainty of up to 10 nm can arise from line slimming through a combination of the line slimming during the initial measurement pass and the variation of line slimming across the wafer. For a 100 nm process, the entire CD error budget, can be consumed by line slimming. This research examines the uncertainty that results from the use of offset techniques to account for resist slimming in the process control of 193 nm resist CDs. The uncertainty associated with such offset techniques can be as great as 10 nm, depending upon the 193 nm resist and landing energy evaluated. Data are presented to demonstrate that 193 nm resist CD features experience line slimming greater than 5 nm at 500 eV landing energy during the initial measurement pass. Further, subsequent measurements demonstrate greatly reduced slimming and as a result are not indicative of the true magnitude of line slimming. Experiments conducted using CD-AFM pre-and post-analysis, demonstrate that ultra low landing energies significantly decrease the line slimming, reducing it to 1 nm or less.

The implementation of a new test structure for HRTEM (High-Resolution Transmission Electron Microscopy) imaging, and the use of CD AFM (CD Atomic Force Microscopy) to serve as the transfer metrology, have resulted in reductions in the uncertainties attributed to critical dimension (CD) reference-material features, having calibrated CDs less than 100 nm. The previous generation of reference materials, which was field-tested in 2001, used electrical CD as the transfer metrology. Calibrated CD values were in the range 80 nm to 150 nm and expanded uncertainties were approximately ± 14 nm. The second-generation units, which have now been distributed to selected industry users for evaluation, have uncertainties as low as ±1.5 nm and calibrated CDs as low as 43 nm.

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