Minimizing filed size to reduce unwanted stray light
Stray and air scattered light can be reduced by configuring a size of the collection area of a sensor, which reduces a source of sensitivity-limiting noise in the system. By adjusting a size of the collection area, stray deep ultraviolet light and air-scattered deep ultraviolet light can be reduced. A servo can control a position of an illumination spot that is collected by the time delay and integration sensor.
1. A system comprising:
a time delay and integration sensor having a collection area, wherein the collection area includes a plurality of zones, wherein only a fraction of the zones are activated, and wherein a waveform is not applied to a remainder of the zones;
a servo that controls a position of an illumination spot, wherein light in the illumination spot is collected by the time delay and integration sensor; and
wherein the time delay and integration sensor is configured to adjust the collection area using an optical mask comprising a metal deposition on a glass plate disposed on the time delay and integration sensor such that the waveform is not applied to the remainder of the zones, selective collection of photocharge, or a clock circuit, whereby the adjusting reduces stray and air-scattered deep ultraviolet light.
2. The system of claim 1 , wherein the time delay and integration sensor is a charge-coupled device.
3. The system of claim 1 , wherein the servo is a beam steering and shaping module servo.
4. The system of claim 1 , further comprising a calibration system in electronic communication with the servo, wherein the calibration system provides automatic calibration of a position of the servo.
5. The system of claim 1 , further comprising a dark field light source that provides the illumination spot.
6. The system of claim 1 , wherein the collection area is 83 microns or less in width.
7. The system of claim 6 , wherein the collection area is from 64 pixels to 128 pixels.
8. The system of claim 6 , wherein the collection area is from 40 pixels to 128 pixels.
9. The system of claim 1 , wherein the air-scattered deep ultraviolet light is reduced to below 1.1 ppb.
10. The system of claim 1 , wherein the time delay and integration sensor and the servo are part of an inspection system.
11. The system of claim 10 , wherein the inspection system includes a chuck configured to hold a wafer.
12. A method comprising:
imaging a wafer using a time delay and integration sensor having a collection area, wherein the collection area includes a plurality of zones, wherein only a fraction of the zones are activated, and wherein a waveform is not applied to a remainder of the zones; and
adjusting the collection area using an optical mask comprising a metal deposition on a glass plate disposed on the time delay and integration sensor such that the waveform is not applied to the remainder of the zones, selective collection of photocharge, or a clock circuit, whereby the adjusting reduces stray and air-scattered deep ultraviolet light.
13. The method of claim 12 , further comprising positioning an illumination spot collected by the time delay and integration sensor using a servo.
14. The method of claim 12 , wherein the collection area is 83 microns or less in width.
15. The method of claim 14 , wherein the collection area is from 64 pixels to 128 pixels.
16. The method of claim 14 , wherein the collection area is from 40 pixels to 128 pixels.
17. The method of claim 12 , wherein the air-scattered deep ultraviolet light is reduced to below 1.1 ppb.
18. The method of claim 12 , wherein the imaging includes dark field illumination.
19. A system comprising:
a time delay and integration sensor having a collection area with a plurality of zones, wherein at least a part of the time delay and integration sensor is obscured such that only a first fraction of the zones receive light; and
a servo that controls a position of an illumination spot, wherein light in the illumination spot is collected by the time delay and integration sensor; and
wherein the time delay and integration sensor is configured to adjust the collection area using an optical mask comprising a metal deposition on a glass plate disposed on the time delay and integration sensor such that the waveform is not applied to the remainder of the zones, selective collection of photocharge, or a clock circuit, whereby the adjusting reduces stray and air-scattered light.
20. The system of claim 19 , wherein the servo is a beam steering and shaping module servo.