Immersion based 20nm technology node and below becoming very challenging to chip designers, process and integration due to multiple patterning to integrate one design layer . Negative tone development (NTD) processes have been well accepted by industry experts for enabling technologies 20 nm and below. 193i double patterning is the technology solution for pitch down to 80 nm. This imposes tight control in critical dimension(CD) variation in double patterning where design patterns are decomposed in two different masks such as in litho-etch-litho etch (LELE). CD bimodality has been widely studied in LELE double patterning. A portion of CD tolerance budget is significantly consumed by variations in CD in double patterning.
The objective of this work is to study the process variation challenges and resolution in the Negative Tone Develop Process for 20 nm and Below Technology Node. This paper describes the effect of dose slope on CD variation in negative tone develop LELE process. This effect becomes even more challenging with standalone NTD developer process due to q-time driven CD variation. We studied impact of different stacks with combination of binary and attenuated phase shift mask and estimated dose slope contribution individually from stack and mask type. Mask 3D simulation was carried out to understand theoretical aspect. In order to meet the minimum insulator requirement for the worst case on wafer the overlay and critical dimension uniformity (CDU) budget margins have slimmed. Besides the litho process and tool control using enhanced metrology feedback, the variation control has other dependencies too. Color balancing between the two masks in LELE is helpful in countering effects such as iso-dense bias, and pattern shifting. Dummy insertion and the improved decomposition techniques  using multiple lower priority constraints can help to a great extent. Innovative color aware routing techniques  can also help with achieving more uniform density and color balanced layouts.
Two aspects of NTD resists, deprotection-induced shrinkage, and retrograde sidewalls, are investigated through experimentation and simulation.
Simulation predicts that NTD resist profiles should often have retrograde sidewall angles due to the attenuation of light as it propagates down through the resist. Resist shrinkage induced from both the de-protection during PEB and from exposure to electrons during SEM can cause CD and sidewall changes. The interplay between the shrinkage and the retrograde sidewalls is discussed.
Deprotection-induced shrinkage is measured by AFM while SEM induced shrinkage is estimated from repeated SEM measurements. SEM images for various features are analyzed and compared to simulation.