Development and Evaluation of Microwave
Discharge Lamp for VUV Point Light Source
K. Ohta*, H. Yajima*, N. Kanai*, I. Serizawa*, and A. Hatta**, **** ORC Manufacturing, Co., Ltd., 4896 Tamagawa, Chino, Nagano, 391-0011, Japan,** Dept. Ele. & Photo. Eng., *** Center for Nanotechnology, Research Institute, Kochi University of Technology, 185 Miyanokuchi,
Tosayamada, Kami, Kochi, 782-8502, Japan
Abstract-- We have been developing a vacuum ultraviolet (VUV) point light source. A small short arc lamp filled with xenon gas
was prepared for microwave discharge. An intense peak at 172 nm from xenon excimer was confirmed by emission spectroscopy.
The VUV emission was localized only on the electrode surface in the observation of luminance distribution image while the UVvisible emission widely distributed between the electrodes. It was expected that the characteristic of point light source could be
improved by decreasing the electrode gap.

I. INTRODUCTION

III. RESULTS AND DISCUSSIONVUV light below 200 nm in wavelength has highphoton energy sufficient to induce the interaction ofvarious organic bonds. VUV light has been used forsemiconductor manufacturing processes, UV cleaning,sterilization, ozone generation, and so on. As
commercially available VUV source, the excimer lamps
have been widely used. The conventional excimer lamps
are long length tubes or wide area type designed foruniform and high-speed processing to large area targets.
There are few examples of high intensity VUV point lightsource necessary for application to imaging opticalsystems such as photolithography.
While a short arc lamp is promising for a point lightsource, the DC arc discharge thermally damages theelectrodes with resulting in short lamp life. It is expected
that, by using microwave discharge, the thermal load canbe reduced and lamp life can be extended. In themicrowave discharge, the electrode temperature isactually lower than that of DC arc discharge.
In this study, a novel short arc lamp using microwave
discharge is developed for VUV point light source. For
characterization of the lamp, VUV spectroscopy andobservation of luminance distribution are carried out.

The emission spectrum of the lamp is shown in Fig. 2.
An intense VUV emission from the xenon excimer wasconfirmed at the wavelength of 172 nm and xenon atomicemission peaks were found in the visible region. The
luminance distribution images of the lamp are shown inFig.3 for the VUV region and the UV-visible region. It
was found that the VUV emission was localized only on
the electrode surfaces while the UV-visible emission waswidely distributed in the space between the electrodes.
The rapid potential gradient near the electrode surface
caused electron amplification, which shrank the ion
sheath region and rapidly increased the electron and ion
densities with resulting in promoting production of xenon
excimer (Xe2*). From the results of localized VUVemission on the surfaces of electrodes, it was expected
that, by bringing the electrodes closer to each other, thelight spot could become smaller and the lamp could
perform better as the point light source.

II. MATERIAL AND METHODS
A prototype short-arc lamp made of synthetic quartz(SUPRASIL-310, Shin-Etsu Quartz) with a light-emitting
tube diameter of 11 mm and an effective antenna lengthof 31 mm was fabricated (Fig.1). The tungsten electrodes
were sealed with a gap length of 1 mm; the filled gas wasxenon at 1–5 atm in pressure. A 2.45 GHz microwave
power source (Collabora Technica) was used to excite
discharge. A vacuum ultraviolet spectrometer (JASCOCorporation) and an ultraviolet-visible spectrometer(Otsuka Electronics Co., Ltd.) were used for emission
spectroscopy. An ICCD camera (Teledyne Technologies)
was used to capture the luminance distribution in thelamp with separation of wavelength between the VUVand the UV-visible regions using a bandpass filter(Fujitoku) with a wavelength of 172 nm.

Fig.1 Appearance of the lamp

Fig.2 Emission spectrum

Fig.3 Brightness image(Left: VUV region, Right: ultraviolet to visible light region)

IV. CONCLUSIONS
We developed a microwave discharge VUV point lightsource. The emission of xenon excimer at 172 nm inwavelength was localized on the electrode surfaces. By
reducing the electrodes gap, the characteristic of point
light source could be improved.
REFERENCES[1] A. Oda, Y. Sakai, H. Akashi and H. Sugawara, J. Phys. D:Appl. Phys., 32 (1999) 2726–2736.