Chemical shrink and SAFIER are two resist shrinking processes that have been proved effective to reduce the trench
and contact hole CD with enhanced resolution and process windows. Patterning sub-20 nm trenches, however, is found
to be challenging using a single shrink process. To shrink resist trenches from 40-60 nm to sub-20 nm, a double shrink
process seems more promising and we have studied the double chemical shrink, double SAFIER, and other possibilities.
It is found that SAFIER process is capable of shrinking trenches by more than 30 nm with improved LER, but it suffers
from severe CD non-uniformity (e.g., much smaller trenches at wafer center) induced by high SAFIER bake
temperature applied to resists to obtain large shrinkage. Chemical shrink can also result in a fairly large shrinkage at
high bake temperature, but LER is poor with no improvement in CDU. A novel hybrid process to combine chemical
shrink (first) and SAFIER (last) together is proposed and developed. We find that this hybrid approach avoids the
disadvantages of two mentioned shrinking processes and has the capability of patterning sub-20 nm trenches in resists
with manufacturable process window, CDU and LER. Oxide and nitride etching process with APF (Advanced
Patterning Film) as a hard mask is developed and sub-20 nm oxide/nitride trench patterning with excellent LER and
acceptable CDU is achieved. APF hard mask is found to significantly improve CDU and LER of small trenches. Relations between CD/shrinkage and process temperature, pitch, and mask trench CD are investigated and the experimental results will be presented in this paper.