The particle counting efficiency of an optical particle counter on photoresist coated wafers was determined. Although absolute quantitative results and accurate size evaluation are not possible, quantitative comparisons are feasable. Based on this knowledge, we studied the influence of several photoresist spin coating parameters on the light point defect (LPD) density on coated wafers. The results show that the surface particle density before coating, the particle concentration in photoresist, the dispense mode, and the dispense system have a big impact on the LPD density after coating. In contrast the spin rate, the number of dispense before coating and the "environment" of the spinner did not have any influence. The size distribution and the distribution over the wafers show two different types of LPDs on coated wafers : (i) nonuniform photoresist coating defects which can be attributed to a bad dispense system, a large "defect" on the surface before coating, or a bad dispense mode; (ii) particles deposited on wafers before and during coating.