초록 ▼

An improved method for laser processing that prevents material redeposition during laser ablation but allows material to be removed at a high rate. In a preferred embodiment, laser ablation is performed in a chamber filled with high pressure precursor (etchant) gas so that sample particles ejected d

An improved method for laser processing that prevents material redeposition during laser ablation but allows material to be removed at a high rate. In a preferred embodiment, laser ablation is performed in a chamber filled with high pressure precursor (etchant) gas so that sample particles ejected during laser ablation will react with the precursor gas in the gas atmosphere of the sample chamber. When the ejected particles collide with precursor gas particles, the precursor is dissociated, forming a reactive component that binds the ablated material. In turn, the reaction between the reactive dissociation by-product and the ablated material forms a new, volatile compound that can be pumped away in a gaseous state rather than redepositing onto the sample.

대표청구항 ▼

1. A method of removing material from a sample by laser ablation while reducing redeposition, the method comprising: providing an apparatus for laser micromachining having an airtight evacuable chamber for holding a sample, a source of a precursor gas, and a laser system for operating on the sample

1. A method of removing material from a sample by laser ablation while reducing redeposition, the method comprising: providing an apparatus for laser micromachining having an airtight evacuable chamber for holding a sample, a source of a precursor gas, and a laser system for operating on the sample in the vacuum chamber, the laser system generating a pulsed laser beam having an energy great enough to ablate the sample;loading a sample into the vacuum chamber;filling the vacuum chamber with a desired concentration of precursor gas to form an atmosphere of precursor gas particles in the vacuum chamber around the sample, the precursor gas being a gas that will react with the sample material, when sufficient energy is provided to initiate said reaction, to form a volatile compound that will not redeposit onto the sample surface; anddirecting the laser at the sample to ablate the surface, the laser operated at a fluence greater than the ablation threshold of the sample material so that sample particles are ejected into the precursor gas atmosphere in the vacuum chamber; the laser providing sufficient energy to the ejected sample particles to initiate the reaction with the precursor gas particles; wherein directing the laser at the sample comprises directing the laser at the sample using a photonic fiber having negative group-velocity dispersion:wherein the desired concentration of precursor gas is high enough that that the volume of ejected particles that collide with and react with gas particles and are thereby volatilized is high enough to significantly reduce redeposition onto the sample. 2. The method of claim 1 further comprising providing a pump for removing gas from the vacuum chamber, and after ejected particles have reacted with the precursor gas to form a volatile compound, pumping that volatile compound out of the vacuum chamber in gaseous form. 3. The method of claim 1 in which at least 50% of the sample material ejected from the sample surface via laser ablation is volatilized in the vacuum chamber atmosphere so that it does not redeposit. 4. The method of claim 1 where the majority of material removed from the surface is ejected from the sample surface via laser ablation and volatilized in the vacuum chamber atmosphere so that it does not redeposit. 5. The method of claim 1 in which less than 10% of the material removed reacts with the precursor gas on the sample surface without being ejected into the vacuum chamber atmosphere by the laser ablation. 6. The method of claim 1 in which the desired pressure of precursor gas is from 13 Pa to 6666 Pa. 7. The method of claim 1 in which the precursor gas is XeF2, Cl2, I2, SiF4, CF4, NF3, N2O, NH3+O2, WF6, or NO2. 8. The method of claim 1 in which the laser system comprises a pulsed laser beam. 9. The method of claim 1 in which the laser system comprises a nanosecond to femtosecond pulsed laser beam. 10. The method of claim 1 in which the laser system comprises a Ti: Sapphire laser, a fiber-based laser, or a ytterbium or chromium doped thin disk laser. 11. The method of claim 1 in which the laser system comprises a laser having an energy of 10 nJ to 1 mJ. 12. The method of claim 1 in which the laser system comprises a laser having fluence of 0.1 J/cm2 to 100 J/cm2. 13. The method of claim 1 in which the precursor gas is XeF2. 14. The method of claim 1 wherein the laser providing sufficient energy to the ejected sample particles to initiate the reaction with the precursor gas particles comprises the laser providing sufficient energy to ablate the sample surface so that the gas precursor is dissociated by some combination of hot ablated material ejected from the sample by the laser, photoelectrons ejected from the sample by the laser, high energy photons (X-rays) ejected from the sample by the laser, or the field generated by the laser beam. 15. The method of claim 14 in which the precursor gas dissociates into at least a reactive dissociation byproduct which binds to the ablated material, forming a volatile compound which can be pumped away in gaseous form rather than redeposited on the sample. 16. The method of claim 1 wherein loading a sample into the vacuum chamber and filling the vacuum chamber with a desired concentration of precursor gas comprises loading the sample into a smaller sample cell within the main sample chamber and filling the sample cell with a desired concentration of precursor gas. 17. The method of claim 16 wherein directing the laser at the sample comprises directing the laser at the sample through a window in the sample cell that is transparent to the laser wavelength. 18. The method of claim 1 in which the laser system includes a lens. 19. The method of claim 1 further comprising evacuating the vacuum chamber to a pressure of less that 1.33×10−1 Pa before filling the vacuum chamber with a desired concentration of precursor gas. 20. The method of claim 1 further comprising evacuating the vacuum chamber and employing a charged particle beam to process the target. 21. A method of removing material from a sample by laser ablation while reducing redeposition, the method comprising: providing an apparatus for laser micromachining having a vacuum chamber for holding a sample, a source of a precursor gas, and a laser system for operating on the sample in the vacuum chamber, the laser system generating a pulsed laser beam having an energy great enough to ablate the sample;loading a sample into the vacuum chamber;filling the vacuum chamber with a desired concentration of precursor gas to form an atmosphere of precursor gas particles in the vacuum chamber around the sample, the precursor gas being a gas that will react with the sample material, when sufficient energy is provided to initiate said reaction, to form a volatile compound that will not redeposit onto the sample surface; anddirecting the laser at the sample to ablate the surface, the laser operated at a fluence greater than the ablation threshold of the sample material so that sample particles are ejected into the precursor gas atmosphere in the vacuum chamber; the laser providing sufficient energy to the ejected sample particles to initiate the reaction with the precursor gas particles:wherein the desired concentration of precursor gas is high enough that that the volume of ejected particles that collide with and react with gas particles and are thereby volatilized is high enough to significantly reduce redeposition onto the sample; andwherein directing the laser at the sample comprises directing the laser at the sample using a photonic fiber having negative group-velocity dispersion.