Proximity effect correction using multilevel area density maps for character projection based electron beam direct writing toward 14 nm node and beyond

We propose an advanced proximity effect correction method, in which all patterns of various sizes are written by character projection (CP) method, and the dose modulation and the auxiliary shot generation are performed using multiple area density maps with different mesh sizes according to the range of electron scatterings. We investigated the possibility that all patterns of various sizes could be written by using small number of CP characters of a single line with fixed width, which is called the "master-CP". We then estimated the range of the designed line width that can be supported by a master-CP and the number of master-CPs which are needed in order to support all patterns of various sizes. We found that only 5-7 master-CPs are required in terms of the dose margin, the rate of increase in the correction dose caused by using the master-CP of different width from the design pattern and the shot positioning error, and they have a low impact on the CP mask. Moreover, we estimated the effect of auxiliary shots on the throughput for 14 nm node technology. The percentage of auxiliary shots in the exposure time was less than 12.1%, even though a test pattern data was made by shrinking a 65 nm node logic LSI where the layout did not repeat very regularly. Therefore, as the layout becomes regularly-repeated to 14 nm node, the effect of the auxiliary shots would not be a dominant factor for the throughput.