UV detection for excimer lamps using CVD diamond in various gaseous atmospheres

Abstract

The recently emerged high-power vacuum ultraviolet excimer lamps operating at 222, 172 and 126 nm will require robust photodetectors to ensure efficient operation for the photo-processing of materials which is often carried out in various ambient atmospheres. Conventional silicon detectors could not meet the stringent requirements, particularly for the 172 and 126 nm lamps. In this paper, we report an initial study on the use of the thin film CVD diamond device for the excimer VUV detection in air, oxygen or nitrogen. The device in the 3 atmospheres exhibits a low similar dark current around 0.3 nA. Working in air leads to significantly prolonged “turn-off” time due to the increased surface conductivity of the device, caused mainly by moisture penetrating into the surface layer. The moisture penetration is enhanced by the increased surface porosity of diamond due to the strongly oxidizing ozone and active oxygen species formed during 172 nm illumination reacting with non-diamond carbon and amorphous materials within the film. However, the UV detection in different environments can still give similar outputs from the same lamp source, probably due to several counteracting effects. Preliminary results on the UV detection for more energetic 126 nm excimer photons using this diamond device have also been reported.