Properties Of Fused Silica For 157Nm Photomasks

Modified fused silica is the primary candidate material for 157-nm photomask substrates. Standard UV excimer grade silica, such as Corning HPFS, does not transmit below about 175nm because of its high OH content. In contrast, fused silicas with low OH contents and low levels of fluorine with measured transmissions up to 73.8%/6.4mm and internal transmittance up to 87.9%/cm at 157nm, have been prepared.