The authors developed a new remote laser particle detection system of laser beam scanning type in order to cover weak points of commonly used optical particle counters and to make direct measurements of particle concentration without field disturbance. The new system introduces a photomultiplier and a pulse height analyzer. This paper presents the outline of the new system with measuring principle and characteristics, and its application to measurements of particle concentration near wafers. The measuring space volume of the system is estimated as a function of laser beam diameter, scanning frequency, slit size, photo detection angle and optical magnification ratio. Chracteristics of the system are evaluated through comparison with a currently used optical particle counter. Relations are observed between concentration values obtained by the two systems as functions of scanning frequencies and slit heights. Correlations are also established between concentration values obtained by the two systems. Particle concentration near wafers is measured by using the system under changes of particle generation position, airflow velocity and particle diameter. The results can be summarized as follows : (1) Good agreement is observed between concentration values obtained by the remote laser particle detection system and an optical particle counter as functions of scanning frequencies and slit heights. (2) Good correlation is found between concentration values obtained by the remote laser particle detection system and a currently used optical particle counter. (3) Particle concentration near wafers can be measured directly by the remote laser particle detection system without field distur- bance.

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