Advanced CD-AFM probe tip shape characterization for metrology accuracy and throughput

Abstract

As semiconductor and data storage industries apply Critical Dimension Atomic Force Microscopy (CD-AFM) for their metrology needs in research and production, (1) measurement accuracy/repeatability and (2) measurement throughput are the major criteria for acceptance. However, these two requirements are usually contradictory for a metrology instrument. For example, a scatterometer can take a snapshot of a wafer in seconds, but such indirect CD measurements are biased by the availability of library models and uncertainty of computer simulations. Transmission Electron Microscopy (TEM) provides an atomic-scale resolution that is traceable back to the lattice structure of atoms, yet the cross-section data is highly localized and can take days or weeks to acquire.In the case of CD-AFM, since the scanning probe physically interacts with the structure of interest at a close proximity, the determination of sample morphology comes from direct measurements. Therefore, the measurement uncertainty can be attributed to: (1) AFM probe tip shapes and (2) system control and scan algorithms. For the former, past efforts have been mainly focused on improving metrology accuracy and repeatability by reducing the dimensional uncertainty of a tip shape. This approach includes characterizing the probe tip shape periodically. Inevitably, such tip shape calibration procedure takes time (approximately 5 min) and burdens production throughput.In this paper, we introduce several new methods for AFM probe tip shape characterization with different designs of tip shape characterizers. The new tip shape characterizers were designed to address the limitation of current structures. First, a single silicon overhang structure with wear-resistant coatings was used as the characterizer for both tip width and tip shape profile. Tip-to-tip scan repeatability data (0.7 nm 3 Sigma) and measurement statistics suggest an improvement over present state-of-the-art practice. Tip shape profiles of several high aspect ratio (20:1 to 25:1), low lateral stiffness probes were successfully characterized with this method. Furthermore, the use of single characterizer provides an opportunity to shorten tool calibration time, and consequently, increase measurement throughput.In addition, a carbon nanotube characterizer prototype is proposed for CD-AFM. When scanning probe geometry shrinks with semiconductor technology nodes, it has become a challenge to characterize a probe with a few tens of nanometer of width with a micrometer-size characterizer. Using a comparable or smaller size of characterizer for a small (20 to 50 nm) AFM probe not only reduces the dimensional uncertainty, but also expands the 2-D profiling capability of current tip shape characterization.We will discuss limitations of current tip shape profiling techniques, proof-of-concept experiments for new characterizers, implementation of new tip shape characterization methods, and approaches to increasing measurement throughput. BACKGROUNDCD AFM is a direct metrology instrument that uses a probe tip to acqui...

Traceable calibration of a critical dimension atomic force microscope

“…11,12,[21][22][23] However, for many purposes a simplified, two-dimensional model is useful. 11,12,[21][22][23] However, for many purposes a simplified, two-dimensional model is useful.…”

“…11,12,[21][22][23] However, for many purposes a simplified, two-dimensional model is useful. 11,12,22,23 Because these effects have a strong dependence on the specific geometry of each tip and feature, it is difficult to make general statements about the resulting uncertainties, and it is necessary to make a specific assessment for every measurement. This offset is referred to as the tip width or zeroth order tip correction.…”

“…[21][22][23] Figure 4 shows a comparison of calibrated linewidth measurements using both our new CD-AFM and a prior generation instrument. However, as the uncertainty of the tip width correction improved, the characterization of tip shape effects has become increasingly important, and the advent of software to correct for tip shape using mathematical morphology now allows such effects to be treated quantitatively.…”

Atomic force microscopy tip characteriser based on the fabrication of nanorod array structures

“…It can reduce the influence of AFM image noise and sample‐dimensional uncertainty of tip blind estimation results while only the local information of the AFM tip can be obtained. Other special structures, such as a single silicon overhang structure with wear‐resistant coatings [11] and wedge‐shaped knife‐edge structures [12] have been used as tip testers. The tip shape cannot be determined accurately because the small radius of the curvature of the surface features is not guaranteed.…”

The analysis of morphological distortion during AFM study of cells

“…AFM probe is a key component of microscopic system; the resolution of images and the information obtained by AFM depend strongly on the probe or tip used, whose artifacts mainly include asymmetric cantilever tips (Kaupp et al 1995) and surface topography of scanning probe (Kitching et al 1999). Therefore, with AFM's popularization, more and more scientists have begun to characterize the quality of AFM probes (Liu et al 2007) and analyze their effects on image quality (Chen et al 2004). In addition, in our previous study, the effects of double-probe cantilever, double-tip, or multipletip probes on morphology have been evaluated in detail (Chen et al.…”