Warning! This is the archived 1999 Fabweb site! Here is the latest site
11. PR2 (second photoresist step): A different mask pattern is then etched into the oxide using the same photoresist steps
described above. This time, however, a careful alignment is needed between
the pattern already on the wafer and the new "layer".
12. Phosphorous Predeposition: In a furnace at 1,000 degrees Celcius with phosphorus pentoxide present,
phosphorous diffuses into the silicon in the openings in the oxide.
The phosphorus concentration surpasses that of the boron in those areas,
converting them back to N-type. In some places, the phosphorous is diffused into
the N-type substrate to make them even more N-type allowing for better electrical
contact later.
During the diffusion, a thin layer of silicon dioxide with phosphorous in it (Phosphosilicate
Glass) is formed on the surface, and must be etched away, just as the
borosilicate glass was removed after the boron predeposition.
This screen is maintained by
Kevin Beernink - U of Illinois ECE Dept. - beernink@uiuc.edu
E-mail comments and suggestions to ece344@uiuc.edu or use the
FEEDBACK FORM.
overview5.html
Warning! This is the archived 1999 Fabweb site! Here is the latest site