System to reduce heat-induced distortion of photomasks during lithography

Abstract

The present invention relates generally to methods, apparatus and materials to reduce or minimize the heating of a substrate (and associated distortions of the photomask) caused by electron-beam energy deposited in the substrate during patterning. Heating of the substrate is exacerbated by radiative transfer of infrared energy from the substrate to other nearby components of the e-beam apparatus followed by reflection or re-radiation of a portion of the energy back to the substrate. The present invention provides useful materials and methods for reducing such reflection or re-radiation effects, leading to temperature stability of the substrate, reduced thermal distortion and the possibility of increased patterning accuracy. The infrared absorbing materials of the present invention also possess sufficient electrical conductivity to dissipate scattered electrons residing on the material, and sufficient thermal conductivity to dissipate heat rapidly and not result in local heating or significant temperature rise of the absorber. The semiconducting material silicon carbide (SiC) is satisfactory for the practice of the present invention. Doped SiC having altered electrical conductivity may also be used. It is shown that emission and re-absorption from the uncoated face of the substrate dominates the substrate's temperature rise.

We claim:  
     
         1 . A method of reducing thermal distortion of a photomask and substrate during patterning comprising placing infrared absorbing material adjacent to the substrate, said absorbing material having a location so as to absorb substantial amounts of infrared radiation emitted from said substrate, and wherein said absorbing material has sufficient electrical conductivity to dissipate electric charge accumulating thereon, and wherein said absorbing material has sufficient thermal conductivity to dissipate heat radiatively deposited therein from said substrate without significant temperature rise.  
     
     
         2 . A method as in  claim 1  wherein said absorbing material is silicon carbide.  
     
     
         3 . A method as in  claim 1  wherein said absorbing material is doped silicon carbide.  
     
     
         4 . A method as in  claim 1  wherein said absorbing material is located adjacent to the uncoated face of said substrate.  
     
     
         5 . A method as in  claim 4  wherein said absorbing material is coated on the pallet adjacent to said substrate.  
     
     
         6 . A method as in  claim 4  wherein said absorbing material is adhesively attached to the pallet adjacent to said substrate.  
     
     
         7 . A method as in  claim 4  wherein the pallet adjacent to said substrate comprises said absorbing material.  
     
     
         8 . A method as in  claim 4  wherein the pallet adjacent to said substrate is larger than said substrate.  
     
     
         9 . An electron beam lithography apparatus comprising a beam of electrons directed upon a target, wherein said target comprises a photomask on a substrate, further comprising infrared absorbing material located so as to absorb substantial amounts of infrared radiation emitted from said substrate, and wherein said absorbing material has sufficient electrical conductivity to dissipate electric charge accumulating thereon, and wherein said absorbing material has sufficient thermal conductivity to dissipate heat radiatively deposited therein from said substrate without significant temperature rise.  
     
     
         10 . An apparatus as in  claim 9  wherein said absorbing material is silicon carbide.  
     
     
         11 . An apparatus as in  claim 9  wherein said absorbing material is doped silicon carbide.  
     
     
         12 . An apparatus as in  claim 9  wherein said absorbing material is located adjacent to the uncoated face of said substrate.  
     
     
         13 . An apparatus as in  claim 12  wherein said absorbing material is coated on the pallet adjacent to said substrate.  
     
     
         14 . An apparatus as in  claim 12  wherein said absorbing material is adhesively attached to the pallet adjacent to said substrate.  
     
     
         15 . An apparatus as in  claim 12  wherein the pallet adjacent to said substrate comprises said absorbing material.  
     
     
         16 . A method as in  claim 12  wherein the pallet adjacent to said substrate is larger than said substrate.