Nano Lithography

Chapter 6

Metrology for Lithography ¹

6.1. Introduction

This chapter is intended to present the implications, problems and existing or potential solutions relating to the critical dimension (CD) measurement stage of lithography, for either R&D or industrial processes.

During the fabrication of electronic devices, CD measurement occurs after each technological step that may induce a topological change to the surface. As the dimensions of electronic devices get smaller, the metrological steps get more critical and accuracy of measurement is all the more necessary. Consequently, the intrinsic limits of each metrological technique, likely to provide dimensional information for manufactured patterns, must be known.

First, the needs of lithography (in terms of dimensional characterization and what is at stake with these needs in the short/long term future) are defined. Secondly, each of the traditional measurement techniques commonly used after lithography, to measure fabricated patterns and guarantee the dimensions initially desired, will be presented. Hence three categories of characterization techniques are presented: scanning electron microscopy (SEM), 3D atomic force microscopy (AFM 3D) and scatterometry.

6.2. The concept of CD in metrology

6.2.1. CD measurement after a lithography stage: definitions

CD is the Critical Dimension of an object made on a given substrate (a silicon wafer, for example). As shown in Figure 6.1, theoretical CD corresponds to the dimensions of a pattern ...