Patent Number: 
Section: claims

1. Method of protecting a radiation detector in a charged particle beam apparatus, the apparatus including a source for producing a beam of charged particles, a condenser system including lenses for illuminating a sample, a projection system including lenses for forming a magnified image of the sample on a detector system, the detector system including a radiation detector, the method comprising:exposing the detector to radiation using a first set of parameters, the set of parameters including condenser lens settings, projection lens settings, charged particle beam energy and beam current,predicting the flux density to which the detector will be exposed at a changed parameters before implementing said change in parameters, the prediction based on an optical model and/or a look-up table with one or more input variables from the group of condenser lens settings, projection lens settings, charged particle beam energy, beam current as input, andcomparing the predicted flux density with a predetermined value, and, depending on the comparison, eitherImplement said change of parameters when the predicted flux density is below the predetermined value, orAvoid exposure of the detector to the flux density associated with the requested change in parameters when the predicted flux density is above the predetermined value. 2. The method of claim 1 in which comparing the predicted flux density with a predetermined value includes generating a warning or an error message when the predicted flux density exceeds said predetermined value. 3. The method of claim 1 in which the detector is a direct electron detector, the radiation comprises electrons and the flux density is a current density. 4. The method of claim 3 in which the detector is equipped to detect electrons transmitted through a sample. 5. The method of claim 2 in which, when an error message or a warning is generated, the excitation of the lenses and the beam energy are not changed. 6. The method of claim 2 in which, when an error message or a warning is generated, the beam is blanked by a beam blanker. 7. The method of claim 1 in which the beam is blanked by a beam blanker when changing the parameters. 8. The method of claim 1 in which exposure of the detector to a dose exceeding the predetermined value results in permanent damage to the detector. 9. The method of claim 1 in which the detector is equipped with a CMOS chip or a CCD chip for direct detection of electrons. 10. The method of claim 1, the method further comprising, prior to exposing the detector to radiation using a first set of parameters, calibrating the optical model and/or Look-Up Table by measuring the beam current for different sets of parameters. 11. Software carrier carrying program code for programming a charged particle beam apparatus comprising a programmable controller to perform the method of claim 1. 12. A method of protecting a radiation detector in a charged particle beam apparatus, comprising:exposing the detector to radiation using a first set of parameters, the set of parameters including condenser lens settings, projection lens settings, charged particle beam energy and beam current,predicting the flux density to which the detector will be exposed at a changed parameters before implementing said change in parameters, the prediction based on an optical model and/or a look-up table with one or more input variables from the group of condenser lens settings, projection lens settings, charged particle beam energy, beam current as input, andcomparing the predicted flux density with a predetermined value,when the predicted flux density is below the predetermined value, implementing said change of parameters, andwhen the predicted flux density is above the predetermined value, avoiding exposure of the detector to the flux density associated with the requested change in parameters. 13. The method of claim 12 in which avoiding exposure of the detector to the flux density associated with the requested change in parameters includes blanking the beam. 14. The method of claim 12 further comprising generating a warning or an error message when the predicted flux density exceeds said predetermined value. 15. The method of claim 12 in which the detector is equipped with a CMOS chip or a CCD chip for direct detection of electrons. 16. The method of claim 12 in which the detector is equipped to detect electrons transmitted through a sample. 17. The method of claim 12 in which the detector is a direct electron detector, the radiation comprises electrons and the flux density is a current density.