Byeong-Ok Cho

Thermally Robust Multi-layer Non-Volatile Polymer Resistive Memory

The feasibility of the charge-transfer based polymer resistive memory as a future data storage device was tested using a thermally robust polyimide and PCBM composite film, available by low-cost solution processing. The prototype device with a simple 4F cross-point cell structure demonstrated basic non-volatile memory functions (> 1000 write/erase cycles and 1-week data retention in an ambient without encapsulation). Not only bi-polar but also uni-polar operation scheme with multi-level programming worked for the device. The cells on both the top and the bottom layers of a stacked device with additional heat budget of > 300 degC for 1 hour exhibited no degradation on the performance

Analysis of overlay errors induced by exposure energy in negative tone development process for photolithography

Negative tone development (NTD) process with positive resist and organic solvent-based developer enhances image contrast and uses a light-field mask to make same feature in opposition to positive tone development (PTD). Due to extremely high transmission rate of a light-field mask, absorption of exposure energy on a mask becomes imperceptible. However, the exposure energy transmitted through the mask influences not only lens heating but also wafer heating. Overlay budget by wafer heating becomes a considerable amount in NTD process. In this paper, to clarify overlay change induced by wafer heating in NTD process, four different levels of exposure energy are applied and the overlay errors are deteriorated by increasing energy. Due to wafer heating, the remarkable correlation between Y-overlay errors and scanning direction are observed. Especially, Ty, RK8, and RK12 have mostly considerable correlation with scanning direction. In NTD process, to avoid this phenomenon, exposure energy has to be minimized. In case scanning direction dependency in overlay is not prevented by minimization of exposure energy, fingerprint correction in wafer field is able to reduce this overlay error.