Precursor preparation for controlled deposition coatings

Abstract

We have devised an apparatus useful for and a method of removing impurities from vaporous precursor compositions used to generate reactive precursor vapors from which thin films/layers are formed under sub-atmospheric conditions. The method is particularly useful when the layer deposition apparatus provides for precise addition of quantities of different combinations of reactants during a single step or when there are a number of different individual steps in the layer formation process, where the presence of impurities has a significant affect on both the quantity of reactants being charged and the overall composition of the reactant mixture from which the layer is deposited. The method is particularly useful when the vapor pressure of a liquid reactive precursor is less than about 250 Torr at atmospheric pressure.

1 . An apparatus useful in removing impurities from a liquid precursor composition which is used to generate reactive precursor vapors for deposition of a thin film, layer, or coating at sub-atmospheric pressure, wherein said apparatus includes at least one precursor composition containment vessel; at least one limited volume container which is, at least initially, at a lower pressure than a vapor pressure in said composition containment vessel; a device which senses pressure, which device is in communication with said limited volume container; a control system which compares a pressure in said limited volume container with an indicated, nominal pressure or change in pressure; and an exhaust opening from said limited volume container, where vapor is exhausted from said opening in response to output from said control system.  
   
   
       2 . An apparatus in accordance with  claim 1 , wherein said apparatus for removing impurities is in-line with other apparatus which is used for deposition of a thin film, layer, or coating at sub-atmospheric pressure.  
   
   
       3 . An apparatus in accordance with  claim 1  or  claim 2 , wherein said precursor containment vessel includes at least one device providing heating capability.  
   
   
       4 . An apparatus in accordance with  claim 1  or  claim 2 , wherein said precursor containment vessel includes at least one device providing cooling capability.  
   
   
       5 . An apparatus in accordance with  claim 1  or  claim 2 , wherein said exhaust opening is in periodic communication with a vessel which is at sub-atmospheric pressure.  
   
   
       6 . A method of removing impurities from a liquid precursor composition which is used to generate reactive precursor vapors for deposition of a thin film, layer, or coating at sub-atmospheric pressure, said method comprising the steps of: 
 a) passing a vapor from a vapor space of said liquid precursor composition through at least one aperture in a manner such that said precursor composition vapor expands into a lower pressure, confining environment;    b) collecting said precursor composition vapor in said confining environment;    c) sensing a pressure of said precursor composition vapor in said confining environment;    d) comparing said sensed pressure with an indicated nominal pressure or with a change in pressure; and    e) exhausting said precursor composition vapor from said confining environment when said precursor composition vapor does not meet requirements with respect to said indicated nominal pressure or said change in pressure.    
   
   
       7 . A method in accordance with  claim 6 , wherein said aperture is a conduit or a path through a valve.  
   
   
       8 . A method in accordance with  claim 7 , wherein said valve is selected from the group consisting of a solid wedge gate valve, a flexible wedge gate valve, a globe valve, a diaphragm valve, a ball valve, a butterfly valve, a needle valve, and a restricting orifice.  
   
   
       9 . A method in accordance with  claim 8 , wherein a control valve is used and an actuator is used in combination with a valve selected from the group.  
   
   
       10 . A method in accordance with  claim 6 , including an additional step: 
 f) repeating steps a) through e) until said sensed pressure corresponds sufficiently with said indicated nominal pressure or with said change in pressure to meet requirements related to a reactive precursor vapor for deposition of a thin film, layer, or coating at sub-atmospheric pressure.    
   
   
       11 . A method in accordance with  claim 10 , wherein a temperature of the liquid precursor composition at which said reactive precursor vapor is generated is at least within about 10° C. of the boiling point of the liquid precursor composition at the pressure which is initially present in the lower pressure confining environment.  
   
   
       12 . A method in accordance with  claim 10 , wherein temperature of the liquid precursor composition is such that the precursor composition is capable of producing sufficient vapor to achieve a rate of increase in pressure in the lower pressure confining environment which ranges between about 0.5 Torr/second to about 4.0 Torr/second.  
   
   
       13 . A method in accordance with  claim 11  or  claim 12 , wherein said temperature ranges from about 20° C. to about 150° C.  
   
   
       14 . A method in accordance with  claim 6 , or  claim 10 , or  claim 11 , or  claim 12 , wherein said liquid precursor composition has a vapor pressure of about 250 Torr or less at 25° C.  
   
   
       15 . A method in accordance with  claim 13  wherein said liquid precursor composition is at a temperature ranging from about 20° C. to about 120° C. when said vapor in said vapor space is generated.  
   
   
       16 . A method of removing impurities from a liquid precursor composition which is used to generate reactive precursor vapors for deposition of a thin film, layer, or coating at sub-atmospheric pressure, said method comprising the steps of: 
 a) cooling said liquid precursor composition until at least an exposed surface of said liquid precursor composition becomes a solid;    b) drawing vapor present in a space above said solid exposed surface away from said solid exposed surface;    c) applying heat so that said solid exposed surface returns to a liquid form, whereby new vapor is released into said space above said solid exposed surface; and    d) repeating steps a) through c) at least once, whereby impurities present in said vapor space are removed from said liquid precursor composition, enabling the use of said liquid precursor composition to generate reactive precursor vapors at a temperature of room temperature or higher.    
   
   
       17 . A method in accordance with  claim 16 , wherein the vapor pressure of said liquid precursor composition prior to carrying out the method of  claim 15  is higher than 1 Torr at 25° C.