Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Process Optimization for Lattice-Selective Wet Etching of Crystalline Silicon Structures



Ronald G. Dixson, William F. Guthrie, Richard A. Allen, Ndubuisi G. Orji, Michael W. Cresswell, Christine E. Murabito


Lattice-selective etching of silicon is used in a number of applications, but it is particularly valuable in those for which the lattice-defined sidewall angle can be beneficial to the functional goals. A relatively small but important niche application is the fabrication of tip characterization standards for critical dimension atomic force microscopes (CD-AFMs). CD-AFMs are commonly used as reference tools for linewidth metrology in semiconductor manufacturing. Accurate linewidth metrology using CD-AFM, however, is critically dependent upon calibration of the tip width. Two national metrology institutes (NMIs) and at least two commercial vendors have explored the development of tip calibration standards using lattice-selective etching of crystalline silicon. The NIST standard of this type is called the single crystal critical dimension reference material (SCCDRM). These specimens, which are fabricated using a lattice-plane-selective etch on (110) silicon, exhibit near vertical sidewalls and high uniformity and can be used to calibrate CD AFM tip width to a standard uncertainty of less than 1 nm. During the different generations of this project, we experimented with different variations on the starting material and process conditions. Some of our starting materials required a large etch bias to achieve the desired linewidths. During the optimization experiment described in this paper, we found that for KOH etching of the silicon features, it was possible to independently tune the target linewidth and minimize the linewidth non-uniformity. Consequently, this process is particularly well-suited for small-batch fabrication of CD-AFM linewidth standards.
Journal of Micro/Nanolithography, MEMS, and MOEMS


lattice-selective etching, crystalline silicon etching, CD-AFM, metrology, CD, linewidth, SCCDRM, standards, calibration


Dixson, R. , Guthrie, W. , Allen, R. , Orji, N. , Cresswell, M. and Murabito, C. (2016), Process Optimization for Lattice-Selective Wet Etching of Crystalline Silicon Structures, Journal of Micro/Nanolithography, MEMS, and MOEMS, [online], (Accessed June 20, 2021)
Created March 9, 2016, Updated February 19, 2017