Diffraction-based illumination sampling
An illumination system may include an optical homogenizer to homogenize a beam of light and a grating positioned in a path for the homogenized beam of light, to diffract light from the homogenized beam. The illumination system also includes a detector to receive light diffracted by the grating and to measure a power of the received light. The grating is disposed, for example, on an inner surface of the optical homogenizer or on a surface of a focusing mirror. Alternatively, the grating is disposed on the surface of the focusing mirror and the optical homogenizer is omitted from the illumination system.
1 . An illumination system, comprising:
an optical homogenizer to homogenize a beam of light;
a grating positioned in a path for the homogenized beam of light, to diffract light from the homogenized beam; and
a detector to receive light diffracted by the grating and to measure a power of the received light.
2 . The illumination system of claim 1 , wherein:
the optical homogenizer comprises inner surfaces forming a tunnel through the optical homogenizer, the inner surfaces being reflective to reflect the light in the beam;
the beam of light is to enter a first end of the tunnel, propagate through the tunnel, and exit a second end of the tunnel; and
the grating is disposed on an inner surface of the tunnel at the second end of the tunnel.
3 . The illumination system of claim 2 , wherein:
the tunnel is a rectangular tunnel having four inner surfaces;
the grating is a first grating disposed on a first inner surface of the tunnel at the second end of the tunnel;
the detector is a first detector to receive light diffracted by the first grating and to measure a power of the received light diffracted by the first grating; and
the illumination system further comprises:
a second grating disposed on a second inner surface of the tunnel at the second end of the tunnel, to diffract light from the beam; and
a second detector to receive light diffracted by the second grating and to measure a power of the received light diffracted by the second grating.
4 . The illumination system of claim 2 , wherein:
the beam of light comprises in-band (IB) extreme ultraviolet (EUV) light; and
the inner surfaces of the optical homogenizer are reflective of the IB EUV light.
5 . The illumination system of claim 4 , wherein:
the light diffracted by the grating comprises a diffraction order of the IB EUV light;
the detector is positioned to receive the diffraction order of the IB EUV light; and
the detector is to measure a power of the received diffraction order of the IB EUV light.
6 . The illumination system of claim 5 , wherein:
the detector is a first detector;
the beam of light further comprises out-of-band (OOB) light having longer wavelengths than the IB EUV light;
the light diffracted by the grating further comprises a diffraction order of a particular wavelength of the OOB light; and
the illumination system further comprises a second detector positioned to receive the diffraction order of the particular wavelength of the OOB light, wherein the second detector is to measure a power of the received diffraction order of the particular wavelength of the OOB light.
7 . The illumination system of claim 6 , wherein:
the particular wavelength of the OOB light is ultraviolet;
the light diffracted by the grating further comprises a diffraction order of a visual wavelength of the OOB light; and
the illumination system further comprises a third detector positioned to receive the diffraction order of the visual wavelength of the OOB light, wherein the third detector is to measure a power of the received diffraction order of the visual wavelength of the OOB light.
8 . The illumination system of claim 1 , further comprising a focusing mirror to focus the beam of light, as homogenized by the optical homogenizer,
wherein the grating is disposed on a surface of the focusing mirror.
9 . The illumination system of claim 8 , wherein:
the optical homogenizer comprises inner surfaces forming a tunnel through the homogenizer, the inner surfaces being reflective to reflect the light in the beam; and
the beam of light is to enter a first end of the tunnel, propagate through the tunnel, and exit a second end of the tunnel.
10 . The illumination system of claim 9 , wherein:
the beam of light comprises in-band (IB) extreme ultraviolet (EUV) light; and
the inner surfaces of the optical homogenizer are reflective of the IB EUV light.
11 . The illumination system of claim 10 , wherein:
the light diffracted by the grating comprises a diffraction order of the IB EUV light;
the detector is positioned to receive the diffraction order of the IB EUV light; and
the detector is to measure a power of the received diffraction order of the IB EUV light.
12 . The illumination system of claim 8 , wherein:
the beam of light comprises in-band (IB) extreme ultraviolet (EUV) light;
the light diffracted by the grating comprises a diffraction order of the IB EUV light;
the detector is positioned to receive the diffraction order of the IB EUV light; and
the detector is to measure a power of the received diffraction order of the IB EUV light.
13 . A method, comprising:
homogenizing a beam of light;
diffracting light from the homogenized beam, using a grating positioned in a path for the homogenized beam; and
measuring a power of the diffracted light.
14 . The method of claim 13 , wherein:
homogenizing the beam comprises providing the beam to an optical homogenizer comprising inner surfaces forming a tunnel through the optical homogenizer;
providing the beam to the optical homogenizer comprises transmitting the beam into a first end of the tunnel, wherein the beam propagates through the tunnel while being reflected by the inner surfaces of the tunnel and exits the tunnel at a second end of the tunnel; and
the grating is disposed on an inner surface of the tunnel at the second end of the tunnel.
15 . The method of claim 14 , wherein:
the beam of light comprises in-band (IB) extreme ultraviolet (EUV) light;
the inner surfaces of the optical homogenizer reflect the IB EUV light;
the diffracting comprises producing a diffraction order of the IB EUV light; and
the measuring comprises measuring a power of the diffraction order of the IB EUV light.
16 . The method of claim 15 , wherein:
the beam of light further comprises out-of-band (OOB) light having longer wavelengths than the IB EUV light;
the diffracting further comprises producing a diffraction order of a particular wavelength of the OOB light; and
the measuring further comprises measuring a power of the diffraction order of the particular wavelength of the OOB light.
17 . The method of claim 13 , further comprising focusing the homogenized beam of light, using a focusing mirror,
wherein the grating is disposed on a surface of the focusing mirror.
18 . The method of claim 17 , wherein:
homogenizing the beam comprises providing the beam to an optical homogenizer comprising inner surfaces forming a tunnel through the optical homogenizer;
providing the beam to the optical homogenizer comprises transmitting the beam into a first end of the tunnel, wherein the beam propagates through the tunnel while being reflected by the inner surfaces of the tunnel and exits the tunnel at a second end of the tunnel;
the beam comprises in-band (IB) extreme ultraviolet (EUV) light;
the inner surfaces of the optical homogenizer reflect the IB EUV light;
the diffracting comprises producing a diffraction order of the IB EUV light; and
the measuring comprises measuring a power of the diffraction order of the IB EUV light.
19 . An illumination system, comprising:
a focusing mirror to focus an unhomogenized beam of light;
a grating, disposed on a surface of the focusing mirror, to diffract light from the beam; and
a detector to receive light diffracted by the grating and to measure a power of the received light.
20 . The illumination system of claim 19 , wherein:
the beam of light comprises in-band (IB) extreme ultraviolet (EUV) light; and
the focusing mirror is reflective of the IB EUV light.