Patent ID: 7745079

Claim:
A particle deposition reduction apparatus for an object comprising: an object with a surface to be protected from particle deposition in a first plane, wherein the surface to be protected is at a first temperature, Tr; a stage that scans a reticle; and a chamber containing the object and maintained at a pressure, Pc, wherein the chamber comprises: a shielding plate disposed in a second plane substantially parallel to the first plane, the shielding plate having an aperture opposite the surface to be protected, the shielding plate comprising: a plurality of gas ports disposed on the face of the shielding plate opposite the first plane, wherein two or more of the plurality of gas ports are adapted to emit gas substantially parallel between the first and second planes and away from the aperture, wherein at least one of the gas ports has a substantially slit-shape opening, which is substantially perpendicular to the scanning direction of the stage; and at least one projection forming a low conductance seal with the surface to be protected and preventing significant volumetric rates of gas from flowing out of the chamber through the aperture; a gas supply at a pressure, Ps, in a range from about 2.5 to about 4 times Pc, connected to two or more of the plurality of gas ports, wherein the higher pressure gas accelerates away from the aperture and, after expanding and cooling to a temperature Tg<Tr, cools the space between the object and the shielding plate.