Translation of lithography variability into after-etch performance: monitoring of golden hotspot

Abstract

In the early phases of technology development, designers and process engineers have to converge toward efficient design rules. Their calculations are based on process assumptions and result in a design rule based on known process variability capabilities while taking into account enough margin to be safe not only for yield but especially for reliability. Unfortunately, even if designs tend to be regular, efficient design densities are still requiring aggressive configurations from which it is difficult to estimate dimension variabilities. Indeed, for a process engineer it is rather straightforward to estimate or even measure simple one-dimensional features (arrays of Lines & Spaces at various CD and pitches), but it starts to be less obvious for complex multidimensional features. After a context description related to the process assumptions, we will outline the work flow which is under evaluation to enable robust metrology of 2 dimensional complex features. Enabling new metrology possibilities reveals that process hotspots are showing complex behavior from lithography to etch pattern transfer. In this work we studied the interaction of lithography variability and etching for a mature 28 nm CMOS process. To study this interaction we used a test feature that has been found very sensitive to lithography process variations. This so-called “golden” hotspot shows edge-to-edge geometries from 88nm to 150nm, thus comprising all the through pitch physics in the lithography pattern transfer [1, 2]. It consists of three trenches. From previous work it was known that through trench there is a systematic variation in best focus due to the Mask 3D effects. At a given chosen focus, there is a distinct difference in profiles for the three trenches that will lead to pattern displacement effects during the etch transfer.