Add solutions to first three homework assignments.

HW1.tex

@@ -58,7 +58,10 @@ Not quite sure what this question means, but I have a few thoughts:
         193nm light, and focused on refining the technique.
     \item We started to perform multiple lithography (and maybe etch)
         steps for a single layer, which made it possible to
-        halve (or further reduce) the minimum pitch.
+        halve (or further reduce) the minimum pitch. Exposing
+        photoresist more than once also made it possible (from what I can tell) to use all the special
+        techniques (off-axis illumination, immersion, RET), which otherwise constrain masks to being only
+        horizontal or only vertical.
     \item Self-aligned mutli-patterning techniques cannot really lay down
         ``holes'' in lines; these holes have to be added later.
         As a result, layouts of modern CPUs are very regular,
@@ -71,7 +74,14 @@ Not quite sure what this question means, but I have a few thoughts:
 From the ``Rosetta Stone of Lithography'' it looks like with true double patterning,
 the smallest we can get is the 10nm node (50nm pitch).
 
+However, the Breakfast Bytes article, right after saying 50nm is the smallest
+pitch we can get with double patterning, brings up SADP, which is also
+double patterning, but can go as low as 40nm. In the Rosetta Stone,
+however, 40nm seems to correspond to `Higher-order pitch division', and not
+double patterning, so I still think 50nm pitch / 10nm node is the answer here.
+
 \section*{Q7}
 We use tin plasma! Apparently, tin is ``fairly efficient'' at converting laser
 light into EUV.
+
 \end{document}