An EUV light source is disclosed which may comprise at least one optical
element having a surface, such as a multi-layer collector mirror; a laser
source generating a laser beam; and a source material irradiated by the
laser beam to form a plasma and emit EUV light. In one aspect, the source
material may consist essentially of a tin compound and may generate tin
debris by plasma formation which deposits on the optical element and, in
addition, the tin compound may include an element that is effective in
etching deposited tin from the optical element surface. Tin compounds may
include SnBr.sub.4, SnBr.sub.2 and SnH.sub.4. In another aspect, an EUV
light source may comprise a molten source material irradiated by a laser
beam to form a plasma and emit EUV light, the source material comprising
tin and at least one other metal, for example tin with Gallium and/or
Indium.