Wavelength combining of multiple source

A metrology system, comprising:

• a radiation source configured to generate light;
• a projection grating configured to receive the light and project an image towards a substrate;
• a detection grating configured to receive the image reflected off a surface of the substrate;
• and
• a detector configured to receive the image from the detection grating and measure a height of the surface of the substrate based on the received image,
• wherein the radiation source comprises:
• a plurality of light sources,
• a first filter configured to reflect over 50% of the light generated from a first source of the plurality of light sources, and to transmit over 50% of the light generated from a second source of the plurality of light sources, and
• a second filter configured to reflect over 50% of the light generated from the first source and the second source of the plurality of light sources, and to transmit over 50% of the light generated from a third source of the plurality of light sources,
• wherein an angle of incidence of the light generated from the first source on a surface of the first filter is less than 30 degrees.

A lithographic apparatus, comprising:

• an illumination system configured to illuminate a pattern of a patterning device;
• a projection system configured to project an image of the pattern onto a target portion of a substrate;
• and
• a metrology system configured to determine a height of a surface of the substrate,
• wherein a radiation source of the metrology system comprises:
• a plurality of light sources,
• a first filter configured to reflect over 50% of the light generated from a first source of the plurality of light sources, and to transmit over 50% of the light generated from a second source of the plurality of light sources, and
• a second filter configured to reflect over 50% of the light generated from the first source and the second source of the plurality of light sources, and to transmit over 50% of the light generated from a third source of the plurality of light sources,
• wherein an angle of incidence of the light generated from the first source on a surface of the first filter is less than 30 degrees.