(Received March 11, 1977)
Analytical conditions for sensitive detection of molecular ions are examined using thin oxide films grown naturally in air on silicon single crystal surfaces. This is carried out to clarify the behavior of these ions in SIMS. It is found that molecular ions can be detected more sensitively under the condition of the low energy primary ion beam incident at large angles. Secondary molecular ions have energies several electron volts lower than elemental secondary ions.
SiO2-, and SiO3-, ions are hardly detected in 1500 Å thick CVD oxide layers, but are sensitively detected at the SiO2-Si interface and also in naturally oxidized layers. This result suggests that the chemical composition of the CVD oxide interface is similar to that of the natural oxide on silicon single crystals.