Is Low Accelerating Voltage Always the Best for Semiconductor Inspection and Metrology
Michael T. Postek, Andras Vladar
An alternative technique for semiconductor metrology and inspection that minimizes, if not eliminates the sample charging is environmental or high pressure scanning electron microscopy. It offers the advantage and possible application of higher landing energies or accelerating voltages, different contrast mechanisms and charge neutralization. Higher landing energies means that higher resolution imaging is possible than at the lower accelerating voltages. But of course, beam penetration is increased. This method employs a gaseous environment to help neutralize the charge build-up that occurs under irradiation with the electron beam. Although very desirable for the charge neutralization, for varioustechnical reasons, this methodology has not been in use in semiconductor inspection or metrology until just recently. This is a relatively new application of this technology to this area and much still needs to be learned. But, as illustrated in Figure lb, this technology shows great promise in the inspection, imaging and metrology of optical photomasks in a charge-free operational mode. In addition, this methodology affords a path that minimizes, if not eliminates, the need for charge modeling which is needed for higher accuracy measurements. The modeling of charging is exceptionally difficult since each sample,methodology shows great potential if the optimal balance can be achieved in a reproduciblemanner. Further research is currently underway to understand the ways to optimize these operating conditions. This paper presents some new results in high pressure SEM metrology of photomasks.
environmental, ESEM, high pressure, low accelerating voltage, SEM