Auto focus system with a mask

Abstract

An autofocusing system comprising: an illumination path configured to illuminate a sample using an illumination beam forming a plurality of spot arrays on the sample, the spot arrays including a first set of spot arrays formed on a first side of an imaging region and a downstream set of spot arrays formed on another side of the imaging region; a controller; a collection path configured to receive a first and a second remotely collected beam from the sample; wherein the collection path includes: a mask located at an entrance pupil, the mask including a pair of off-axis slits for truncating each remotely collected beam to provide a pair of light rays for each remotely collected beam; a beam splitter configured to (i) direct a first light ray associated with the first remotely collected beam to a first branch, and (ii) direct a light ray associated with the second remotely collected beam to a second branch; and a sensor connected after the first and second branches and configured to receive a pair of spots for each of the plurality of spot arrays.

Claims

1. An autofocus system, the autofocus system comprising: An irradiation path is configured to irradiate a sample using irradiation beams, the irradiation beams forming a plurality of spot arrays on the sample, the spot arrays including a first set of spot arrays formed on a first side of an imaging region and a downstream set of spot arrays formed on the other side of the imaging region. A collection path, configured to receive a first and a second collection bundle from the sample; The collection path includes: a shield located at an entrance pupil, the shield including a pair of off-axis slits for truncating each collection beam to provide a pair of light rays for each collection beam; and a beam splitter configured to (i) direct a first light ray associated with the first collection beam to a first branch, and (ii) direct a light ray associated with the second collection beam to a second branch. and a sensor connected after the first branch and the second branch, and configured to receive a pair of spots for each of the plurality of spot arrays, wherein a distance between each pair of spots indicates a focus state associated with a corresponding spot array; wherein an optical axis of the first branch is oriented toward an optical axis of the second branch.

2. The autofocus system as claimed in claim 1, wherein the first branch includes a first spherical telescope, a first field curvature compensator, and a first collimation repeater; and wherein the second branch includes a second spherical telescope, a second field curvature compensator, and a second collimation repeater.

3. The autofocus system as described in claim 2, wherein the first field curvature compensator is substantially composed of an optical element in a first segment.

4. The autofocusing system as claimed in claim 3, wherein the first rays comprise a pair of central rays and two pairs of peripheral rays, wherein the optical element of the first segment is substantially composed of: a first segment having a first refractive index through which the pair of central rays propagate, and a second segment having a second refractive index through which the two pairs of peripheral rays propagate, wherein the first refractive index is different from the second refractive index.

5. The autofocusing system of any one of claims 2-4, wherein the first spherical telescope is configured to provide a reduced image of the entrance pupil at a focal plane of a first spherical telescope output lens.

6. The autofocusing system as claimed in claim 5, further comprising a pair of first prisms located at the focal plane of the output lens of the first spherical telescope.

7. The autofocus system of any one of claims 2-4, wherein the first collimation repeater comprises a repeater input spherical lens and a repeater output spherical lens.

8. The autofocus system as claimed in claim 7, further comprising applying a first collimator repeater moving mechanism configured to change a distance between the repeater input spherical lens and the repeater output spherical lens.

9. The autofocus system as claimed in claim 8, wherein different distances between the relay input spherical lens and the relay output spherical lens are associated with different trade-offs between a dynamic range of the autofocus system and a sensitivity of the autofocus system.

10. The autofocus system as claimed in claim 8, wherein different distances between the relay input spherical lens and the relay output spherical lens are associated with different effective focal lengths of the first collimating repeater.

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