Gas flow configurations for semiconductor inspections

A non-transitory computer-readable medium, storing program instructions executable on a computer system for performing a computer-implemented method for inspecting a specimen, wherein the computer-implemented method comprises:

• directing light to an area on a specimen and generating output responsive to light from the area on the specimen with an inspection subsystem, wherein all optical hardware of the inspection subsystem is not located within a vacuum;
• replacing a gas in a first local volume surrounding the area on the specimen with a first medium during said directing and said generating, wherein the first medium scatters less of the light than the gas, and wherein the first medium is the vacuum;
• replacing the gas in a second local volume located proximate to the first local volume with a second medium during said directing and said generating, wherein the second medium is different than the first medium;
• and
• detecting abnormalities on the specimen based on the output.

A method for inspecting a specimen, comprising:

• directing light to an area on a specimen and generating output responsive to light from the area on the specimen with an inspection subsystem, wherein all optical hardware of the inspection subsystem is not located within a vacuum;
• replacing a gas in a first local volume surrounding the area on the specimen with a first medium during said directing and said generating, wherein the first medium scatters less of the light than the gas, and wherein the first medium is the vacuum;
• replacing the gas in a second local volume located proximate to the first local volume with a second medium during said directing and said generating, wherein the second medium is different than the first medium;
• and
• detecting abnormalities on the specimen based on the output, wherein said detecting is performed by a computer system.