33.1 INTRODUCTION

One of the key drivers of the semiconductor industry is constant improvement, which is based on the ability to measure what is done. In the submicron world, this is not a trivial thing to do.

Critical dimension (CD) metrology is a basic concept in manufacturing that helps keep a process stable. The measured critical dimension is used for statistical process control (SPC) in which a process is kept within the specification limits of the design and within control limits to maintain stability.

The CD-SEM monitors a range of features (1) lines/space/pitch [one dimensional (1D)] and also to a lesser extent minimum distances between features that are becoming more common and important, (2) round features (2D), and (3) depth/sidewall angle information (3D). The layers that are measured can be any layers with topography, such as all patterned photoresists after develop inspection (ADI) and all etched wafers after etch inspection (AEI). Usually the monitored layers are:

• Shallow trench insulator (STI) ADI/AEI

• Gate ADI/AEI

• Contact ADI/AEI

• Metal 1, 2 ADI/AEI for copper (trench 1, 2 ADI/AEI)

• Via 1, 2 ADI/AEI

The CD measurements are used both for engineering and production in the fab where engineering tasks require relatively more data than they did in the past due to optical proximity correction (OPC) characterization.