Adding Grayscale Layer to Chrome Photomasks - Professor Glenn ...

Figure 11. Test square structures with sizes of 1, 2, 3, 5, 10 and 50 µm 2 . The entire area of the test square
structures was laser scanned by the argon laser at 0.1W (maximum) power. Laser scanning makes the
Bi/In layer transparent, thus revealing the original binary structures on the chrome layer.
5.4 Grayscale Test Patterns
Directly above the line test structures at the bottom of the cleared chrome area are the grayscale test structures of
different shapes. The bitmap image used for these test structures is shown in Figure 12. An important setting that
affects how the bitmap is written on to the photomask is the pixel size. The pixel size describes the photomask
dimensions for each pixel in the bitmap. In this example, Figure 12 is a bitmap image with 300 by 3500 pixels. Using a
1 um/pixel pixel size, the resulting pattern written on the mask is 300 µm by 3500 µm. Using a 2 µm/pixel pixel size,
the resulting pattern is 600 µm by 7000 µm. In our experiment, we used a total of three different pixel sizes: 1, 2, and
4 µm/pixel. Figure 13 - Figure 18 show the resulting grayscale structures on the bimetallic-chrome photomask with two
different laser spot size (1 µm/pixel and 2 µm/pixel) and three different minimum to maximum argon laser power ranges
(0.01W to 0.065W, 0.01W to 0.06W and 0.01W to 0.045W). Examining the grayscale bar at the top of each figure, the
effect the voltage can be seen changing the position of where the grayscale shifts from white to black.
Figure 12. Bitmap image for the grayscale test structures.
Figure 13. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to 0.065W
and a 1 µm laser spot size. The size of the entire pattern is
300 µm wide by 3500 µm tall.
Figure 14. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to
0.065W and a 2 µm laser spot size. The size of the entire
pattern is 300 µm wide by 3500 µm tall.
Figure 15. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to 0.06W
and a 1 µm laser spot size. The size of the entire pattern
is 300 µm wide by 3500 µm tall.
Figure 16. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to 0.06W
and a 2 µm laser spot size. The size of the entire pattern is
300 µm wide by 3500 µm tall.
Figure 17. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to
0.045W and a 1 µm laser spot size. The size of the entire
pattern is 300 µm wide by 3500 µm tall.
Figure 18. Grayscale pattern using a minimum to
maximum argon laser power range from 0.01W to 0.045W
and a 2 µm laser spot size. The size of the entire pattern is
300 µm wide by 3500 µm tall.
5.5 Grayscale Test Squares
Table 2 summarizes the argon laser power used to scan the ten squares at the top of the chrome mask and their
measured optical densities.