Utilization of electron impact ionization of gaseous and sputtered species in the secondary ion acceleration region of a magnetic sector SIMS instrument

Negative secondary ion insulator analysis using a normal incidence electron gun (NEG) on CAMECA magnetic sector SIMS instruments can be difficult due to an inability to adequately determine the electron beam impact region during NEG alignment. The electron impact energy is too low to utilize phosphor cathodoluminescent materials that can be used for NEG alignment for positive secondary ion analyses. Detection of electron beam desorbed H is often used for NEG alignment, but the presence of H on the surface is not always uniform and it is transient, making it difficult to determine whether variations in the H secondary ion intensity are due to non-uniformity of the electron beam or of the H on the sample. To overcome this difficulty, a new technique has been developed that takes advantage of sputtering of the sample surface by positive ions created by electron impact ionization in the spectrometer secondary ion acceleration region between the sample and the immersion lens of the mass spectrometer. The formation of the ions occurs by interaction of residual gas species in the spectrometer secondary ion acceleration region with the NEG electron beam. This method is used to align the NEG for negative secondary ion charge neutralization. # 2004 Elsevier B.V. All rights reserved.