Apparatus for uniformly baking substrates such as photomasks

Abstract

An apparatus for baking a film onto a substrate. A film, such as a layer of photoresist, is disposed on a first surface of a substrate while a second surface is exposed to a liquid bath. The liquid bath is maintained at a pre-selected temperature. Exposure of the substrate to the liquid bath allows the film on the opposite surface to bake. The liquid bath is re-circulated to maintain a constant and uniform temperature gradient across the substrate.

1 . An apparatus for baking a film on a substrate comprising: 
 a primary tank adapted to contain a liquid bath, wherein the liquid bath heats the substrate;    a retaining device adapted to hold a first surface of a substrate in contact with the liquid bath in the primary tank, wherein the film disposed on a second surface of the substrate is baked; and    a secondary tank in fluid communication with the primary tank and disposed to receive an excess of the liquid bath overflowing from the primary tank.    
   
   
       2 . The apparatus of  claim 1 , wherein the primary tank is configured as a weir within the secondary tank.  
   
   
       3 . The apparatus of  claim 1 , comprising a pump in fluid communication with the primary tank, wherein the liquid bath is circulated by the pump to facilitate control of the temperature of the liquid bath.  
   
   
       4 . The apparatus of  claim 3 , wherein the pump is disposed to receive a volume of the liquid bath from the secondary tank and to supply the volume of the liquid bath to the primary tank.  
   
   
       5 . The apparatus of  claim 4 , comprising at least one baffle positioned in the primary tank to facilitate dispersion of the volume of liquid bath entering the primary tank from the pump.  
   
   
       6 . The apparatus of  claim 1 , comprising a heat exchanger operatively coupled to the primary tank to facilitate control of the temperature of the liquid bath.  
   
   
       7 . The apparatus of  claim 6 , wherein the heat exchanger is configured to heat the liquid bath above 100° C.  
   
   
       8 . The apparatus of  claim 6 , wherein the heat exchanger is disposed along a supply conduit configured to facilitate transport of the liquid bath from a pump to the primary tank.  
   
   
       9 . A system for baking a film on a substrate comprising: 
 a tank adapted to contain a liquid bath substantially inert to the film, wherein the liquid bath heats the substrate;    a retaining device configured to hold a first surface of the substrate in contact with the liquid bath in the tank, wherein the film is disposed on a second surface of the substrate;    a pump in fluid communication with the primary tank, wherein the liquid bath is circulated by the pump; and    a distribution device configured to disperse within the tank in a plurality of directions the liquid bath circulating through the tank to facilitate temperature control of the liquid bath.    
   
   
       10 . The system of  claim 9 , wherein the distribution device comprises a baffle configuration at least a portion of which is disposed within the tank near an inlet to the tank.  
   
   
       11 . The system of  claim 9 , comprising a heat exchanger disposed inside the tank and configured to facilitate control of the temperature of the liquid bath.  
   
   
       12 . The system of  claim 9 , comprising a heat exchanger disposed outside of the tank and configured to heat the liquid bath circulating external to the tank.  
   
   
       13 . A system for baking a film on a substrate comprising: 
 a primary tank adapted to contain a liquid bath;    a retaining device configured to hold a first surface of the substrate in contact with the liquid bath in the primary tank;    a heat exchanger operatively coupled to the primary tank to heat the liquid bath, the heat exchanger disposed external to the primary tank; and    a pump in fluid communication with the primary tank, wherein the liquid bath is circulated by the pump to maintain a substantially constant temperature gradient through the substrate.    
   
   
       14 . The system of  claim 13 , wherein the heat exchanger is configured to facilitate control of the temperature of the liquid bath.  
   
   
       15 . The system of  claim 13 , wherein the heat exchanger comprises an electrical heater.  
   
   
       16 . The system of  claim 13 , wherein the pump is disposed to receive a volume of the liquid bath from the primary tank and to supply the volume of the liquid bath past the heat exchanger to the primary tank.  
   
   
       17 . The system of  claim 13  comprising a secondary tank in fluid communication with the primary tank and disposed to receive an excess of the liquid bath flowing from the primary tank.  
   
   
       18 . The system of  claim 17 , wherein the pump is disposed to receive a volume of the liquid bath from the secondary tank and to supply the volume of the liquid bath past the heat exchanger to the primary tank.  
   
   
       19 . The system of  claim 13 , comprising a distribution device disposed within the primary tank and configured to facilitate dispersion of a volume of liquid bath entering the primary tank from the pump.  
   
   
       20 . An apparatus for baking film on a substrate comprising: 
 means for containing a liquid bath to heat the substrate;    means for holding the substrate such that a first side of the substrate is exposed to the liquid bath;    means for maintaining the temperature of the liquid bath at a pre-selected temperature to bake the film disposed on a second side of the substrate;    means for maintaining a liquid level of the liquid bath in the containing means; and    means for secondarily containing an excess of the liquid bath overflowing from the containing means.    
   
   
       21 . The apparatus of  claim 20 , comprising means for re-circulating the liquid bath in the containing means adjacent to the substrate.  
   
   
       22 . The apparatus of  claim 20 , comprising means for dispersing the liquid bath re-circulated into the containing means.  
   
   
       23 . An apparatus for baking a film on a substrate comprising: 
 a tank adapted to hold a liquid bath that heats the substrate, wherein the tank is not configured for pumped recirculation of the liquid bath through the tank;    a retaining device configured to hold a first surface of a substrate in contact with the liquid bath in the tank; and    a heat exchanger positioned to facilitate natural-convection agitation and temperature control of the liquid bath in the tank.