Abstract: In a secondary ion mass spectrometer an aperture mask (3), which is not part of the secondary ion optics (5) of the spectrometer, is arranged very near to the surface of a specimen (1) to be analyzed, for example a semiconductor. The primary and secondary ions pass through the aperture (3A) in the aperture mask (3). The position of the specimen relative to the aperture mask dictates the location on the specimen (1) to be analyzed. The outer dimension of the mask is larger than the field of view of the secondary ion optics (5). Due to the masked region the fringe areas of the specimen are shielded ionoptically so that they cannot result in any falsification of the electric field. An electrical dc or ac potential can be applied to the mask (3) so that the electric field between the aperture (3A) and the specimen (1) can be additionally influenced. A contact device (3B) can be applied between the mask (3) and the specimen (1) for preventing electrical charging of the specimen (1).

Abstract: In a secondary ion mass spectrometry (SIMS) method for analysis of a sample, in a first process step, the kinetic energy of the emitted primary ions emitted by a primary ion source (2) is set to a relatively low value, so that the surface of the sample (1) is enriched with primary ions, and erosion of the surface of the sample (1) essentially does not take place, and in a second process step, the kinetic energy of the primary ions emitted by one and the same primary ion source (2) is set to a relatively high value, so that the surface of the sample (1) can be eroded by the primary ion beam, where the formation of secondary ions in the second process step is promoted by the primary ions implanted during the first process step. Over and above this, targeted, locally differentiated enrichment of the sample surface ("chemical gating") can be carried out.