PHOTOION DETECTION WITH A WIDE DYNAMIC-RANGE USING A QUADRUPOLE MASS-SPECTROMETER FOR NONRESONANT MULTIPHOTON IONIZATION OF SPUTTERED NEUTRALS

A sputtered neutral mass spectrometer using nonresonant multiphoton ionization by an excimer laser has been developed. The composition of this instrument is similar to the dynamic secondary ion mass spectrometer. Depth profiling with a wide dynamic range can easily be performed by the combination of a quadrupole mass spectrometer and pulse-counting ion detection. The mass spectrum of photoionized neutrals of GaAs shows that the dynamic range of detection is more than six orders of magnitude and that the product of ionization efficiency and mass spectrometer transmission is about 2.1 X 10(-3). The detection limit for Zn impurity in GaAs is under 1 ppm at a laser repetition rate of 50 Hz.