To use a Monte Carlo analysis in Spectre you also need to add statistics blocks, which are used to describe the random variations in your parameters to the simulator. You can find information on how to do this by typing spectre -h montecarlo into your shell.

It is hard to imagine individual users having enough information to describe the statistical variations in the process, so the process blocks should come from the foundries. However, few actually do provide this information. I am aware of at least one large company having statistical information, and the corresponding Monte Carlo process blocks, for the TSMC processes, but I do not know how they acquired them.

Hello Wael,

Sometimes a file with mismatch measurement results is included in the design kit, and it is up to the customer to translate this into simulation parameters. In case you cannot get statistical parameters from your foundry, you can still add some "generic" statistical parameters to give you a feel of the sensitivity of your circuit to device mismatch. Anyway, from my personal perspective, if you rely on the exact values of mismatch parameters to make your circuit work, I guess it won't. In modern technologies, you have phenomena like NBTI, hot carriers and so on which modify the threshold voltage over time and which are usually not included in the mismatch parameters.

You can get an order of magnitude for mismatch parameters from the following papers (ieeexplore is your friend  ;) ):

An easy-to-use mismatch model for the MOS transistor
Croon, J.A.; Rosmeulen, M.; Decoutere, S.; Sansen, W.; Maes, H.E.;
IEEE Journal of Solid-State Circuits, Volume 37

Physical modeling and prediction of the matching properties of MOSFETs
Croon, J.A.; Decoutere, S.; Sansen, W.; Maes, H.E.;
ESSDERC 2004

Paul