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There are strong demands for techniques which are able to extend application of ArF immersion lithography.
Especially, the leading edge techniques are required to make very small hole patterns below 50nm. Several
techniques such as double patterning technique, free-form illumination and resist shrinkage technology are
considered as viable candidates. Most of all, NTD (Negative Tone Development) is being regarded as the most
promising technology for the realization of small hole patterns
When NTD process is applied, hole patterns are defined by island type features on the reticle and consequently its
optical performance shows better result compared with PTD (Positive Tone Development) process. However it is
still difficult to define extremely small hole patterns below 40nm, new combination process of NTD with RELACS
is being introduced to overcome resolution limitation. NTD combined with RELACS, which is the most advanced
lithography technology, definitely enable us to generate smaller size hole patterns on the wafer.
A chemical shrinkage technology, RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink),
utilizes the cross linking reaction catalyzed by the acid component existing in a predefined resist pattern. In case of
PTD combined with RELACS process, we already know that CD change after the shrinkage process is not
influenced by duty ratio. So we could easily reflect the RELACS bias to meet the CD target during OPC (Optical
Proximity Correction) procedure.
But NTD combined with RELACS process was not understood clearly, nor verified. It requires more investigation
of physical behavior during combined process in order to define exact hole patterns. The newly introduced process
might require additive OPC modeling procedure to satisfy target CD when NTD RELACS bias has different values
according to pitch and shape.
This study is going to include the investigation on two types of resist shrinkage process, PTD and NTD. The
optimized OPC methodology will be discussed through the evaluation on simple array hole patterns and random
hole patterns.
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