Stable high brightness radio frequency driven micro-discharge lamps at 193 (ArF^*) and 157 nm ( )

Abstract

A stable discharge between two pin electrodes separated by several hundred micrometres in a high pressure rare gas (∼900 mbar) halogen (∼1 mbar) mixture is shown to yield continuous wave (CW) ultra violet (UV) and vacuum UV light sources. Lamps operating at 193 (ArF*) and 157 nm ( ) have been demonstrated. Total CW output power in the UV was measured to be 30 for ArF* and 20 mW for . The brightness of the light sources is estimated to be of the order of several W cm−2 sr−1. With direct current excitation, electrode lifetimes are limited to a few minutes due to fluorine salt deposits. However, using a radio frequency (RF) field to drive the discharge, the lifetime of the lamps increased to hundreds of hours. A one-dimensional model of the RF micro-discharge explaining the increase in electrode lifetime is presented. The technology described can be adapted to many other wavelengths and promises even higher powers in future.

Electron-beam–ignited, high-frequency–driven vacuum ultraviolet excimer light source

“…It is interesting to note that the high frequency discharge causes no damage to the thin ceramic entrance foil for the electron beam. This is similar to the advantages of RF discharges with respect to electrode sputtering as for example discussed in reference [12]. 6.…”

Optical Emission Spectroscopy of Argon–Fluorocarbon–Oxygen Fed Atmospheric Pressure Dielectric Barrier Discharges

“…The triatomic Ar 2 F excimer emits a structureless broadband continuum centred at 290 nm, due to the transitions from an electronically bound ionic excited state (2 2 B 2 ), characterized by an isosceles triangular geometry, to repulsive covalent lower states (1 2 A 1 and 1 2 B 2 ) which rapidly dissociates into ground state atoms 35, 40, 41, 46, 48, 49. This emission, observed in electron‐beam excited high pressure ArF 2 and ArNF 3 mixtures as well as in high pressure ArF 2 excimer lasers,40, 41, 43–48 was always associated to the ArF signal. Both experimental evidence and theoretical calculations indicate the third‐body reaction of ArF with two Ar atoms as the dominant Ar 2 F formation process,40, 48 which therefore can be considered a possible pathway for nonradiative quenching of ArF excimer.…”

“…The presence of the new continuum centred at 290 nm and definitely evident at an O 2 concentration of 90% could explain the slight variation of the CF emission (220–360 nm) observed at 30% O 2 , reasonably due to the overlap of the two continua. A careful investigation of published data allows to ascribe the narrow emission at 193 nm and the broad continuum peaked at 290 nm to ArF,34, 35, 37–44 and Ar 2 F 35, 40, 41, 44–49 excimers, respectively. Excimer emission is a topic not sufficiently investigated in fluorocarbon fed DBDs even though it is well known that DBDs are suitable for efficient production of high intensity VUV (vacuum ultra violet) and UV radiation from excimers, namely excited dimers or trimers, which make them widely utilized in excimer lamps 50–54…”

“…Rare gas‐halide excimers radiate in a narrow VUV or UV band by undergoing a transition (B 2 Σ + 1/2 –X 2 Σ + 1/2 ) from a bound ion‐pair electronically excited state to an unbound covalent ground state that dissociates into neutral atoms 34, 37–39. For ArF this transition is responsible for the intense signal peaked at 193 nm 35, 37, 39–44…”

“…In electron‐beam excited ArF 2 mixtures and laser media, two main reaction pathways leading to the formation of ArF excimer, have been reported:37, 40, 43, 44 An ionic channel, i.e. a three‐body reaction in which Ar + and F − recombines in the presence of an argon atom; a neutral channel, namely a harpoon reaction between an excited argon atom and F 2 . …”