Defects in x-ray masks: Detection and printability

Abstract

X-ray mask defects occur mainly as particles on the mask and as random defects in the absorber. However, some of these mask defects do not generate disturbing resist defects. The theoretical investigation of the transfer mechanism shows two essential results. The x-rays penetrate completely organic particles of thicknesses up to 4 μ. The Fresnel diffraction limits the transfer of absorber defects at 0.17 μ size with a 50 μ proximity gap. Good agreement is found between the measured and the calculated size distribution of absorber pinspots, confirming the considerations concerning the defect printability. Only disturbing defects are detectable by inspecting the lithographical resist copy of the mask. The inspection itself can be performed by optical means. It has been shown by experiment with a specially designed test pattern that 0.2 μ defects in 0.5 μ structures can be detected reliably by using a white-light microscope.