How realistic is the famous "Bill sux" picture of a chip internals artwork?
It is a hoax, you can read more at Snopes and here. 

But to add a bit of info, the story became popular in 1998, so the scale they would be working in was at best 250 nano-meters, so the picture would have been taken with an electron scope. 

Here is the original picture:




  The image is a clever digital manipulation of an image that appears on
  the cover of Darrell Duffie's book


...


  It's a clever prank playing off the idea that a couple of Apple
  aficionados could surreptitiously sneak an anti-Bill Gates message
  onto the world's most popular CPU, where it could be seen only through
  a powerful microscope, but it's a hoax.


Here's another link with more information.

Semiconductor manufacturing improvements by year:

10 µm — 1971

3 µm — 1975

1.5 µm — 1982

1 µm — 1985

800 nm (.80 µm) — 1989

600 nm (.60 µm) — 1994

350 nm (.35 µm) — 1995

250 nm (.25 µm) — 1998

180 nm (.18 µm) — 1999

130 nm (.13 µm) — 2000

90 nm — 2002

65 nm — 2006

45 nm — 2008

32 nm — 2010

22 nm — 2012