Apparatus and method for indirect surface cleaning
View Patent ↗Methods for cleaning a surface of a photomask and for increasing the useable lifetime of the photomask are disclosed. One method includes, a first wafer print processing using a photomask and a pellicle disposed across the photomask, and cleaning the photomask. The cleaning the photomask includes directing a laser beam through the pellicle toward the photomask, the laser beam having a wavelength that is substantially equal to a local maximum of an absorption spectrum of the photomask, heating the photomask with the laser beam, and transferring heat from the photomask to a contaminant disposed on the photomask, thereby thermally decomposing the contaminant.
1. A wafer fabrication process, comprising:
a first wafer print processing using a photomask and a pellicle disposed across the photomask; and
cleaning the photomask, including
directing a laser beam through the pellicle toward the photomask, the laser beam having a wavelength that is substantially equal to a local maximum of an absorption spectrum of the photomask,
heating the photomask with the laser beam, and
transferring heat from the photomask to a contaminant disposed on the photomask, thereby thermally decomposing the contaminant.
2. The method of claim 1 , further comprising directing a gas flow onto the pellicle to control a temperature of the pellicle.
3. The method of claim 1 , wherein the photomask includes a thin film layer disposed thereon.
4. The method of claim 3 , wherein the thin film layer is patterned and includes void areas under which respective portions of the photomask are exposed.
5. The method of claim 1 , further comprising maintaining a temperature of the photomask below a threshold temperature to prevent damage thereto.
6. The method of claim 1 , wherein the contaminant is a contaminant layer.
7. The method of claim 6 , wherein the contaminant layer is a haze layer.
8. The method of claim 7 , wherein the haze layer includes ammonium sulfate.
9. The method of claim 6 , wherein the contaminant layer is inorganic.
10. The method of claim 1 , wherein the wavelength of the laser beam is selected to effect absorption of an energy of the laser beam by the photomask.
11. The method of claim 1 , wherein the contaminant is a particle.
12. The method of claim 11 , wherein the particle contains ammonium sulfate.
13. The method of claim 1 , further comprising a second wafer print processing using the photomask, the second wafer print processing occurring after the cleaning the photomask.
14. The method of claim 13 , further comprising post-print wafer processing after the second wafer print processing.
15. The method of claim 14 , further comprising pre-print wafer processing before the first wafer print processing.