Low-contamination optical arrangement

A method of using a projection objective, the method comprising:

• illuminating an object in an object field;
• and
• using the projection objective to project an image of the object into an image field,
• wherein the projection objective comprises an optical arrangement which comprises:
• a plurality of optical elements including a first optical element, each of the plurality of optical elements comprising a body and a reflective surface supported by the body, the plurality of optical elements configured to transmit a beam along a beam path;
• and
• a first partial housing extending from the reflective surface of the first optical element into a direction of a first portion of the beam which is incident on and/or reflected from the reflective surface of the first optical element;
• and
• a measurement structure which does not support the plurality of optical elements, the measurement structure comprising a sensor configured to determine a position and/or an orientation of the first optical element relative to the measurement structure, and
• wherein:
• the first partial housing surrounds the first portion of the beam;
• the first partial housing surrounds the reflective surface of the first optical element such that there is a gap between the first partial housing and the body of the first optical element;
• the first partial housing is constructed to fully support the first optical element by a first mounting;
• the first optical element has a reference surface;
• a distance between the reference surface of the first optical element and the sensor is at most 50 millimeters;
• and
• the measurement structure at least partly surrounds the first partial housing.

A method of using a projection exposure system which comprises an illumination system and a projection objective, the method comprising:

• using the illumination system to illuminate an object in an object field;
• and
• using the projection objective to project an image of the object into an image field,
• wherein the projection objective comprises an optical arrangement which comprises:
• a plurality of optical elements including a first optical element, each of the plurality of optical elements comprising a body and a reflective surface supported by the body, the plurality of optical elements configured to transmit a beam along a beam path;
• and
• a first partial housing extending from the reflective surface of the first optical element into a direction of a first portion of the beam which is incident on and/or reflected from the reflective surface of the first optical element;
• and
• a measurement structure which does not support the plurality of optical elements, the measurement structure comprising a sensor configured to determine a position and/or an orientation of the first optical element relative to the measurement structure, and
• wherein:
• the first partial housing surrounds the first portion of the beam;
• the first partial housing surrounds the reflective surface of the first optical element such that there is a gap between the first partial housing and the body of the first optical element;
• the first partial housing is constructed to fully support the first optical element by a first mounting;
• the first optical element has a reference surface;
• a distance between the reference surface of the first optical element and the sensor is at most 50 millimeters;
• and
• the measurement structure at least partly surrounds the first partial housing.

A system, comprising:

• an optical arrangement, comprising:
• a plurality of optical elements including a first optical element, each of the plurality of optical elements having a body including a reflective surface, the plurality of optical elements configured to transmit a beam along a beam path;
• and
• a first partial housing extending from the reflective surface of the first optical element into a direction of a first portion of the beam which is incident on and/or reflected from the reflective surface of the first optical element;
• and
• a measurement structure which does not mechanically support the plurality of optical elements,
• wherein:
• the first partial housing surrounds the first portion of the beam;
• the first partial housing surrounds the reflective surface of the first optical element such that there is a gap between the first partial housing and the body of the first optical element;
• the first partial housing is constructed to fully support the first optical element by a first mounting;
• the measurement structure at least partly surrounds the first partial housing;
• at least 25% of a surface of the body of the first optical element is outside a volume defined by the first partial housing, the reflective surface of the first optical element and the gap between the first partial housing and the body of the first optical element;
• the first optical element has a reference surface;
• the measurement structure comprises a sensor configured to determine a position and/or an orientation of the first optical element relative to the measurement structure;
• a distance between the reference surface of the first optical element and the sensor is at most 50 millimeters;
• and
• the system is an EUV projection exposure system.