Alternating Aperture Phase Shifting Mask (Alt-APSM) has been expected as one of the practical techniques for 45nm node ArF lithography. We have already discussed and proposed the Single trench with undercut (UC) and bias structure is the primary candidate for 65nm node Alt-APSM structure. In fact, we have selected this structure as a standard in production for 65nm node Alt-PSM. For the 45nm node, according to the design shrinkage, mask rule such as MRC which specify minimum chrome CD between 0 and pi degree apertures and etc. is getting tighter. So, we need to consider about single trench with no undercut and bias structure. Such two types of structure are the candidates for 45nm node Alt-APSM. Exposure conditions will be considered as 0.9 or higher NA and the immersion technology as well. In this work, we will discuss about 45nm node Alt-PSM structure in terms of lithographic performance by using 3D rigorous optical simulation software. Two types of structure, single trench with UC and bias, and single trench with No UC and bias are compared. We examined the following items to find optimum Alt-PSM structure, 0/pi space bias to minimize CD difference at the wafer, quartz depth to optimize effective phase and optical proximity correction (OPC) to adjust printed line CD in through pitch condition. Wafer printing performance will be evaluated by the stability of line CD and 0-pi CD difference, contrast, NILS, phase angles, MEEF, ED-window and gate position shift.