Gas-assisted laser ablation

Abstract

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.

We claim as follows: 
     
         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 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; and   directing 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   and wherein at least 80% 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.   
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The method of  claim 1  in which at least 90% 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. 
     
     
         6 . 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. 
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . The method of  claim 1  in which the desired concentration of precursor gas is between 133 Pa and 1333 Pa. 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . The method of  claim 1  in which the sample comprises SiO 2 . 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . (canceled) 
     
     
         24 . (canceled) 
     
     
         25 . (canceled) 
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . (canceled) 
     
     
         30 . An apparatus for laser micromachining adapted to minimize redeposition of material removed from a sample by laser ablation, the apparatus comprising:
 a vacuum chamber for holding a sample;   a source of a precursor gas for filling the vacuum chamber with said precursor gas to a desired pressure;   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 so that material removed from the surface is ejected into the gas atmosphere where at least a portion of the ejected material reacts with gas particles to form a volatile compound that will not redeposit onto the sample surface; and   the desired gas pressure providing an adequate concentration of gas particles in the vacuum chamber so that substantially all of the ejected material is volatilized in the atmosphere of the vacuum chamber before redeposition.   
     
     
         31 . The method of  claim 30  further comprising a charged particle beam column. 
     
     
         32 . The method of  claim 30  in which the laser system includes a lens. 
     
     
         33 . The method of  claim 1  in which the laser system includes a lens.