cell instances 2311 3165

Case 1 Case 2 Case 3 Case 4 Case 5 # dirs: 1 # dirs: 2 # dirs: 4

Case 1 Cases 2 and 3 Cases 4 and 5

Circuit 1 Circuit 2

In this section, we proposed an ILP-based cell library development methodology to reduce the number of EB shots. All optimization processes finished within a second. More than 3.85% reduction of EB shots was achieved only by distinguishing between the differently mirrored cells whose functions are identical.

We examined the influence of cell directions on both area and delay time of the circuit. It was experimentally confirmed that both of the horizontal and vertical flipping of cells had little influence on delay time of chips. The horizontal flipping had little influence on area while the vertical flipping had some influence on area. This examination helps which cell direction should be implemented on CP aperture masks.

The forbiddance of horizontal flipping caused little deterioration of area while 25.6% reduction of EB shots. It was found that the forbiddance of horizontal flipping was effective to reduce the number of EB shots while it deteriorated little area and delay time of chips. The forbiddance of vertical flipping caused 13.9% increase of area while it caused less than 1% increase of delay time. The forbiddance of vertical flipping should be determined with taking a tradeoff between area and EB shots into account. For many chips of the state of the art, cells are placed so "loosely" that the deterioration of area caused by forbiddance of multi directions of cells might have less impact on area. The relation between cell directions and EB shots in design of such chips should be further examined as future work.
