Method and apparatus for EUV mask inspection

A method for producing a protective buffer flow in an EUV light source, comprising:

• directing light along a light path from the EUV light source toward a collector;
• injecting a first buffer gas from a buffer gas injector through a plurality of through holes in the collector, wherein the first buffer gas is directed away from a surface of the collector;
• and
• injecting a second buffer gas from a manifold buffer gas injector in a ring manifold arranged peripherally to the collector such that there is a gap between the ring manifold and the collector and arranged a first distance toward the light path in relation to the collector, wherein the manifold buffer gas injector faces away from the surface of the collector, wherein the second buffer gas is directed away from the surface of the collector and is directed farther from the surface of the collector than the first distance, wherein there is a first wall on the collector extending away from the light path and a second wall on the ring manifold extending away from the light path, and wherein the first wall and the second wall are separated by the gap;
• wherein the first distance corresponds to a distance from the collector where the first buffer gas merges into a single flow.