We will present a complete example that demonstrates daily CD monitor for good CDSEM control, including sampling plan, monitoring procedure, and monitoring and matching data for multiple CDSEM. In addition, we also investigate two methods to address the carbon contamination problem. In the first method, carryover trends on three different film stacks, poly, metal, and multi-layer metal, before and after plasma clean are compared in search of ways to minimize carryover. The second method applies statistical treatment to remove the effect of carryover while maintaining sensitivity over small fluctuations in line CD monitor results. Both linear regression and exponentially weighed moving average calculated from daily monitor data are used to model the baseline carryover trend for the purpose of isolating tru tool variability. Using this method, we can easily quantify the long-term stability of each CDSEM, and with that, we are able to calculate the true long-term process variation Cp by subtracting the CDSEM variation component from the observed total Cp.