Critical dimension metrology: perspectives and future trends

Abstract

3D-metrology is becoming mandatory for nanofabrication in the production environment.Every flowchart in micro-and nanofabrication includes several critical dimension (CD) metrology steps to guarantee device performance. To measure pattern density in highly-controlled processes such as lithography, plasma etching, and materials deposition, engineers traditionally employ electron-or photonbased techniques. Most common in semiconductor manufacture are scatterometry, an optical diffraction-based method, and scanning electron microscopy (CD-SEM), a secondary electron emission-based technology. Although both are eminently repeatable, fast, and useful in terms of cost per measurement, will they remain state-of-the-art with the advent of ever smaller nanodevices?Indeed, as dimensions and architectures move towards sub32nm node, CD metrology, both for production process monitoring and process development, must cope with challenges presented by the latest materials, the new process flowcharts like the double patterning approach for lithography, and novel architectures such as 3D-multiwires field-effect transistor (FET) devices (see Figure 1). [1][2][3] Therefore, accuracy of measurement at the nanometer scale in all axes (x, y, and z) represents the advent of a non-negligible factor in the race to downsize device dimensions, as illustrated in Figure 2. For the conventional complementary metal-oxide semiconductor (CMOS) device with vertical gate and channel underneath, the single most important parameter is the bottom CD value (CD1 as indicated in Figure 2a). However, for nanowire FET devices, a full set of parameters must be tightly controlled as described in Figure 2b, with in-line metrology including alignment, thickness, critical dimensions, and length.In addition to a multiple set of morphological outputs for future nanodevices, feature edge roughness will play a key role in the quality of device performance and in the ramp-up time for pilot lines. Indeed, as illustrated in Figure 3, as we are Continued on next page

A CD probe with a tailored cantilever for 3D-AFM measurement

“…The larger the LWR is, the more signal is reflected back to its origin, which minimizes the transfer efficiency. Therefore, great attention should be paid to the critical dimension measurement during the manufacturing process to guarantee the product's quality [2,3].…”

9nm node wafer defect inspection using three-dimensional scanning, a 405nm diode laser, and a broadband source

“…At the same time, new architectures such as three-dimensional (3D) and monolayer based transistors are also being implemented into devices. Thus, detection of killer defects in a patterned silicon wafer has become a grand challenge [1,2].…”

“…Currently, the most widely used wafer CD metrology tools are based on optical microscopy, scanning electron microscopy (SEM), and atomic force microcopy (AFM). A discussion on wafer critical dimension metrology is presented in reference [2]. Optical metrology methods are advantageous over other methods due to their nondestructive and high throughput nature.…”