Reference metrology using a next-generation CD-AFM

Abstract

International SEMATECH (ISMT) and the National Institute of Standards and Technology (NIST) are working together to improve the traceability of AFM dimensional metrology in semiconductor manufacturing. Due to the unique metrology requirements and the rapid change in the semiconductor industry, relevant standards are often not available. Consequently, there is often no traceable linkage between the realization of the SI (Systeme International d'Unites, or International System of Units) unit of length -the meter -and measurements in the fab line. To improve this situation, we have implemented a Reference Measurement System (RMS) using a next-generation critical-dimension atomic force microscope (CD-AFM). We performed measurements needed to establish a traceability chain and developed uncertainty budgets for pitch, height, and critical dimension (CD) measurements. At present, the standard uncertainties are estimated to be approximately 0.2 % for pitch measurements, 0.4 % for step height measurements, and 5 nm for CD measurements in the sub-micrometer range. Further improvement in these uncertainties is expected with the use of newer samples for scale and tip calibration. We will describe our methodology for RMS implementation and the major applications for which it has been used. These include measurements on new NIST/ISMT linewidth standards, a reference tool for CD-scanning electron microscopes (SEMs), metrology on photo-masks, CD-SEM benchmarking, and 193 nm resist shrinkage measurements. As part of the NIST/ISMT linewidth standards project, we are performing an extensive comparison experiment of AFM and TEM (transmission electron microscopy) measurements of linewidth.

SI-Traceable Spring Constant Calibration of Microfabricated Cantilevers for Small Force Measurement

“…Since the spring constant of a cantilever scales with length j3 [cf. equation (1)], this allowed for a wide range of spring constants to be tested.…”

“…The tip of the beam deflects in direct proportion to an applied force following Hooke_s law: F = kz, where F is applied force, z is the resulting displacement, and k is the spring constant of the system. The use of AFM for dimensional metrology has been established [1]. AFM is primarily used as a tool for imaging surfaces, and is increasingly used for small force measurement.…”

Progress on implementation of a reference measurement system based on a critical-dimension atomic force microscope

“…4 Because the RMS is expected to function at a higher level of performance than inline tools, much effort has been taken to reduce the uncertainty budget by using calibration samples directly measured at NIST, and to refine the treatment of some of the uncertainty components. This ensures that the measurements the instrument supports have low uncertainties.…”

“…1,2 Details of the RMS implementation and initial uncertainty budgets are well documented. [3][4][5] A major goal of the RMS project is to continue to reduce the uncertainty of measurements made with the system by using suitable samples with close traceability to the SI meter, and by carefully examining all possible error sources. In this work, we outline steps we have taken to reduce the uncertainty of our height and pitch measurements, and the way the RMS is used to support other metrology equipment.…”

Helium ion beam induced growth of hammerhead AFM probes

“…2,3 The first demonstration of such a probe was reported by Martin and Wickramasinghe 2 for CD measurements, where a 3D-AFM with a hammerhead or boot tip shape is scanned in CD mode and in deep-trench mode. Later, these 3D probes have been applied for the critical dimension metrology by Dixson et al 3,4 and Foucher et al 5,6 However, still lacking is a one-step fabrication method to grow such probes with high reproducibility. Various attempts have been made to grow or to shrink the size of these probes by electron beam induced deposition (EBID) followed by plasma etching.…”