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The Most chip makers want KrF lithography is extended below sub 90nm lithography due to cost and process stability, even though ArF lithography has been growing and its performance is enough to apply to 90nm node. But process control of KrF lithography will become difficult at sub 90nm node because of patterning limitation of KrF lithography. Specially, mask error factor (MEF) is growing to be important for patterning. Generally, chromeless phase shifting mask (PSM) has known widely as a good solution for better patterning than any other PSM, but there are a few companies to apply this mask to their process due to some fatal weakness which are design complexity, difficulties of mask making, control of mask defect, and so on. This paper shows the new modified chromeless HTPSM has solution for some special pattern by using KrF lithography and compares with strong aperture result at 90nm node. The most of island pattern has different MEF with width and length. And patterning control of length axis has been very difficult from mask making to wafer printing. In addition, its control is seriously depended on width axis in the low k1 level. Patterning of storage node contact which is 1:2 duty with width and length axis is very difficult in general DRAM pattern, its MEF is over 5 at width axis and over 15 at length axis in 90nm node. Both axis controls are too hard to achieve good patterning simultaneously. Generally, chromeless PSM has a good MEF performance so we apply and create new modified chromeless HTPSM to overcome our storage node contact pattern. This PSM consist of three layers which are 0° Qz, 180° Qz, and 360° half-tone pattern. 180° Qz pattern play important role in this PSM as a assist pattern to achieve good patterning. First of all, we should make a choice of optimum layout and then we decide on how to make a mask because it is very important factor to control overlay accuracy between 0° Qz and 180° Qz pattern. This overlay accuracy affect to patterning result seriously. Modified chromeless HTPSM has strong patterning performance but overlay accuracy between major and assist pattern will be controlled tightly. This reason is what we hesitate to apply modified chromeless HTPSM to real device development.
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