Current flash memory technology is facing more and more challenges for 45nm and 32nm node technology. To get good
CD and yield control, optimized RET, OPC modeling and DFM techniques have to be applied . To enhance process
window (PW) and better CD control for main features, assist features (SB) have to be used. Simulation and wafer
evaluation show that the SB CD performance is very critical. Based on OPC simulation, we can get a very good
prediction about the CD size and placement of assist features. However, we can not always get what we want from mask
suppliers. For 45nm node technology and beyond, The SB CD size (~ 20nm at 1X) has almost pushed to the current
mask process limit. Wafer fabs have a very big concern about the stability of linearity signatures from different
suppliers and different products in order to keep high accuracy of OPC models. Actually the CD linearity signature
varies from one mask supplier to another and also varies from product to product. To improve the SB CD control, the
ideal goal is to make "flat" linearity for all mask suppliers. By working closely with TPI mask supplier, we come up
solutions to improve SB CD control to get "flat" linearity. Also technology development is causing more severe SB
printability, we proposed a methodology to use AIMS for predicting SB printability. Wafer results proved the feasibility
for these methodologies.
EUV lithography is to date the most promising NGL technology for the sub-50nm technology node. In this work, we have designed and synthesized several types of organoelement resists with minimum oxygen content for high transparency. Either silicon or boron was incorporated in the resist structures to improve both etch resistance and transparency. In the exposure studies, it was possible to image the silicon-containing polymers to 22.5 nm line/space patterns using EUV interferometry. A second type of EUV transparent resist platform was studied involving boron-containing polymers. Carborane carboxylic acid was attached to a copolymer backbone to introduce boron atoms with controlled structure attachment level. In a preliminary study, these polymers could be imaged by 248nm exposure. Effect of structure on line edge roughness is also to be included in the discussion.
EUV lithography is perhaps the most promising of the NGL technologies for sub-100nm resolution. To address needs in this area, we have designed and synthesized several types of organoelement resists using only low absorbing elements, including H, C, Si and B. One category is based on silicon-containing block and random polymers. They show high transparency according to theoretical simulations and have high oxygen reactive ion etch resistances compared to Novolac resins. In a preliminary study, we were able to image these polymers to 180 nm line/space patterns using EUV exposure. A second type of EUV transparent resist platform involves boron-containing polymers. Carborane carboxylic acid was attached to a copolymer backbone to introduce boron atoms with controlled attachment level. It was found that incorporation of a small amount of B provides remarkably high oxygen etch resistance.