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 [1]. 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.
For the latest photomask fabrication, critical dimension (CD) control is required more for ArF lithography. To satisfy the requirement, Alternating Phase-Shifting Mask (Alt.PSM) is expected to be the most effective approach for resolution enhancement. We investigated the optimization of shifter structure and evaluated phase defect detectability for 130 to 100nm node ArF Alt.PSM. Considering the process and defect control, shifter trench type is the most popular approach. However, in order to achieve smaller CD on reticle, dual trench type becomes also necessary. Therefore, we investigated the performance of the two types of shifter structure, and we compared the optical characteristics. On the other hand, Using test reticles contained programmed phase defects of various shape and size, phase defect printability was analyzed with the Aerial Image Measurement System, MSM193, and phase defect detectability was evaluated with some inspection tools. As a result, the manufacturing technology of ArF Alt.PSM for 100nm node was established.
Be accompanied with gate length will tend to be smaller in LSI manufacturing, assist bar type OPC masks are vigorously investigated to take into mass production. In this research, we examined problems about manufacturing and guarantee of assist bar type OPC masks. We applied 50KeV-accelerated Vector-type E-beam system to mask manufacturing that is going to be a major equipment from now on. Firstly, we remarked the CD error that occurred in mask manufacturing, and the error was valuated. Secondly, we estimated the influence of mask accuracy to false defect occurrence. Lastly, we made the masks for defect check. The defects of the masks were measured using SEM, and wafer printability of the defects was checked by simulation. And we estimated the sensitivity of inspection. As results, it is proved to be possible that manufacturing and inspecting the assist bar type OPC masks in 100 nm node.
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