Particle control near reticle and optics using showerhead
A method and an apparatus to protect a reticle against particles and chemicals in an actinic EUV reticle inspection tool are presented. The method and apparatus utilizes a pair of porous metal diffusers in the form of showerheads to provide a continual flow of clean gas. The main showerhead bathes the reticle surface to be inspected in smoothly flowing, low pressure gas, isolating it from particles coming from surrounding volumes. The secondary showerhead faces away from the reticle and toward the EUV illumination and projection optics, supplying them with purge gas while at the same time creating a buffer zone that is kept free of any particle contamination originating from those optics.
1. A particle control arrangement for an EUV illumination inspection system comprising:
a thermal shroud;
a first diffuser plate, said first diffuser plate having an area and an upper surface and a lower surface;
a second diffuser plate, said second diffuser plate having an area a first surface and a second surface, wherein said first surface faces said lower surface;
a reticle having an area;
a movable holder, said movable holder having a holder area and supporting said reticle;
a gas source, said gas source delivering a flow of gas in a channel defined by said lower surface and said first surface;
a post optics box attached to said shroud and extending away from said channel and said second surface;
a light tunnel having walls, said walls extending between said first diffuser plate and said second diffuser plate; and,
an EUV illumination port defined by said thermal shroud;
wherein said post optics box contains an inspection lens system; and
wherein said holder moves at least part of the area of said reticle over said inspection hole.
2. The particle control system as recited in claim 1 wherein said first diffuser plate and said second diffuser plate are fabricated from porous metal.
3. The particle control system as recited in claim 1 wherein said attachment to said shroud is a supporting rib.
4. The particle control system as recited in claim 1 further comprising a metrology subsystem.
5. The particle control system as recited in claim 4 wherein said metrology subsystem includes said movable reticle/mask holder.
6. The particle control system as recited in claim 4 wherein said metrology subsystem includes a Littrow mirror.
7. The particle control system as recited in claim 1 wherein the gas from said gas source is hydrogen.
8. The particle control system as recited in claim 1 wherein the gas from said gas source is a noble gas.
9. The particle control system as recited in claim 1 wherein a pressure of said gas flow is <5 Pa.
10. The particle control system as recited in claim 1 wherein said particle control system is contained within a vacuum.
11. The particle control system as recited in claim 1 wherein said shroud is water cooled.
12. The particle control system as recited in claim 1 wherein said holder is square, said square having a side length three times longer than a side length of said reticle.
13. The particle control system as recited in claim 1 wherein said first diffuser is larger than said second diffuser.
14. The particle control system as recited in claim 1 wherein said first diffuser is square and has twice the side length of said reticle.
15. The particle control system as recited in claim 14 wherein during movement of said movable holder, said area of said first diffuser remains within said holder area.
16. The particle control system as recited in claim 1 wherein said gas flow is a laminar gas flow.