NPGS : Dose Matrix (with ~14 nm lines/spaces)
These pictures show SEM images of a dose testing matrix where the lines
were designed with different widths along the rows and each column used a
different dose. Each group of lines was designed with an ideal line/space
ratio of 1:1. The numbers on the right indicate the designed linewidths that
range from 14 to 26 nm, while the labels along the bottom are index numbers
to denote the different doses (26 through 40 are shown in the main image
Careful measurements of the linewidths show that the groups in the bottom row range from 14.1 nm (group #26) to 16.2 nm (group #36). The top row ranges from 24.7 nm (group #26) to 26.7 nm (group #36). The groups with doses above #36 are increasingly over exposed.
The smaller image shows an enlarged view of the doses near #30 which produced lines in the bottom row that are ~15 nm wide with ~13 nm spaces.
The imaging was done after development without any metallization. The resist is a proprietary resist on a silicon substrate.
This work was done by Inpria Corporation using NPGS at the University of Oregon.
This image shows the lower doses of a similar dose matrix which has the same
range of designed linewidths from 14 nm to 26 nm arranged in rows with columns
of different doses. (Note that the `10' and `15' in the image refer to the
dose index numbers, not to the intended linewidths.) In this case, nearly
every group of lines is under exposed and they show the typical random defects
seen in under exposed features defined by e-beam lithography.
Tips: When initially exposing a dose matrix, the goal is to obtain features that clearly range from `too low' to `too high' as shown in the images above. Subsequent exposures may be performed that target a smaller range that includes the ideal dose. Also, when the test features are all aligned in one direction, as in the case of these vertical lines, including the diagnostic wheel structure is very useful in order to confirm that the astigmatism in the beam was well optimized during the exposure.
Images Copyright © 2011, Inpria Corporation. Used by permission.