Optical isolator, ultraviolet laser apparatus, and electronic device manufacturing method

An ultraviolet laser apparatus comprising:

• an oscillation-stage laser configured to output a pulse laser beam of linearly polarized light having an ultraviolet wavelength;
• an amplifier configured to amplify and output the pulse laser beam;
• and
• an optical isolator disposed on an optical path between the oscillation-stage laser and the amplifier,
• the optical isolator including
• a first polarizer disposed to have a transmission axis with a normalized transmittance of 0.9 or higher for incident light, the incident light being linearly polarized light having an ultraviolet wavelength;
• a Faraday rotator containing a Faraday material that rotates a polarization direction of light having transmitted through the first polarizer by a magnetic field;
• and
• a second polarizer disposed to have a transmission axis with a normalized transmittance of 0.9 or higher for the incident light having transmitted through the Faraday rotator,
• the Faraday material being calcium fluoride crystal,
• when a, b, and c axes are defined to be [001], [100], and [010] crystallographic axes of the calcium fluoride crystal, respectively, and x, y, and z axes are defined to be respective axes obtained by rotating the three axes of the a, b, and c axes by a first angle about the c axis and by a second angle about the b axis rotated by the first angle,
• the first angle being 40° to 50° inclusive,
• the second angle being 45° to 75° inclusive,
• the z axis being parallel to a propagation direction of light incident on the calcium fluoride crystal from the first polarizer,
• the calcium fluoride crystal being disposed such that the transmission axis of the first polarizer and the x axis have an angle difference of 0° to 45° inclusive.

An electronic device manufacturing method comprising:

• generating a laser beam amplified by an amplifier by using an ultraviolet laser apparatus, the ultraviolet laser apparatus including
• an oscillation-stage laser configured to output a pulse laser beam of linearly polarized light having an ultraviolet wavelength,
• the amplifier configured to amplify and output the pulse laser beam, and
• an optical isolator disposed on an optical path between the oscillation-stage laser and the amplifier,
• the optical isolator including
• a first polarizer disposed to have a transmission axis with a normalized transmittance of 0.9 or higher for incident light, the incident light being linearly polarized light having an ultraviolet wavelength,
• a Faraday rotator containing a Faraday material that rotates a polarization direction of light having transmitted through the first polarizer by a magnetic field, and
• a second polarizer disposed to have a transmission axis with a normalized transmittance of 0.9 or higher for the incident light having transmitted through the Faraday rotator,
• the Faraday material being calcium fluoride crystal,
• when a, b, and c axes are defined to be [001], [100], and [010] crystallographic axes of the calcium fluoride crystal, respectively, and x, y, and z axes are defined to be respective axes obtained by rotating the three axes of the a, b, and c axes by a first angle about the c axis and by a second angle about the b axis rotated by the first angle,
• the first angle being 40° to 50° inclusive,
• the second angle being 45° to 75° inclusive,
• the z axis being parallel to a propagation direction of light incident on the calcium fluoride crystal from the first polarizer,
• the calcium fluoride crystal being disposed such that the transmission axis of the first polarizer and the x axis have an angle difference of 0° to 45° inclusive;
• outputting the amplified laser beam to an exposure apparatus;
• and
• exposing a photosensitive substrate to the laser beam in the exposure apparatus to manufacture an electronic device.