High Strength Carbon Fiber Composite Wafers For Microfabrication

Abstract

A method of making a high strength carbon fiber composite (CFC) wafer with low surface roughness comprising at least one sheet of CFC including carbon fibers embedded in a matrix. A stack of at least one sheet of CFC is provided with the stack having a first surface and a second surface. The stack is pressed between first and second pressure plates with a porous breather layer disposed between the first surface of the stack and the first pressure plate. The stack is cured by heating the stack to a temperature of at least 50° C.

What is claimed is: 
     
         1 . A method of making a wafer, the method comprising:
 a. providing a stack of at least one sheet of carbon fiber composite (CFC) including carbon fibers embedded in a matrix, the stack having a first surface and a second surface;   b. pressing the stack between first and second pressure plates with a porous breather layer disposed between the first surface of the stack and the first pressure plate; and   c. curing by heating the stack to a temperature of at least 50° C., defining a first curing process.   
     
     
         2 . The method of  claim 1 , further comprising disposing a solid, polished layer between the second surface of the stack and the second pressure plate during the first curing process with the polished layer having a root mean square surface roughness Rq of less than 300 nm in an area of 100 micrometers by 100 micrometers, on a side facing the stack. 
     
     
         3 . The method of  claim 1 , further comprising:
 a. releasing pressure from the stack;   b. removing the porous layer from the stack;   c. disposing a polished layer on each side of the stack, the polished layers having a root mean square surface roughness Rq of less than 300 nm in an area of 100 micrometers by 100 micrometers, on a side facing the stack; and   d. pressing the stack and polished layers between first and second pressure plates;   e. curing by heating the stack to a temperature of at least 50° C., defining a second curing process.   
     
     
         4 . The method of  claim 1 , wherein the porous breather layer comprises a porous polymer layer facing the stack and a nylon mesh facing the first pressure plate. 
     
     
         5 . The method of  claim 1 , wherein providing the stack includes a sheet of polyimide disposed adjacent to the second surface of the stack. 
     
     
         6 . The method of  claim 1 , wherein curing by heating the stack includes creating a vacuum of less than 50 torr between the pressure plates, and maintaining the vacuum through at least 50% of the curing process. 
     
     
         7 . The method of  claim 1 , wherein each sheet in the stack has a thickness of between 20 to 350 micrometers. 
     
     
         8 . The method of  claim 1 , further comprising micropatterning the wafer by laser ablation, water jet, or combinations thereof to form an x-ray window support structure comprising:
 a. a support frame defining a perimeter and an aperture;   b. a plurality of ribs extending across the aperture of the support frame and carried by the support frame;   c. openings between the plurality of ribs; and   d. the support frame and the plurality of ribs comprising a support structure.   
     
     
         9 . The method of  claim 1 , wherein at least 90% of the carbon fibers have a diameter of between 2 and 10 micrometers. 
     
     
         10 . The method of  claim 1 , wherein the matrix comprises a material selected from the group consisting of polyimide, bismaleimide, epoxy, or combinations thereof. 
     
     
         11 . The method of  claim 1 , wherein the matrix comprises a material selected from the group consisting of amorphous carbon, hydrogenated amorphous carbon, nanocrystalline carbon, microcrystalline carbon, hydrogenated nanocrystalline carbon, hydrogenated microcrystalline carbon, or combinations thereof. 
     
     
         12 . The method of  claim 1 , wherein the matrix comprises a ceramic material selected from the group consisting of silicon nitride, boron nitride, boron carbide, aluminum nitride, or combinations thereof. 
     
     
         13 . The method of  claim 1 , further comprising a polyimide sheet cured together with and abutting the at least one sheet of carbon fiber composite. 
     
     
         14 . The method of  claim 13 , wherein the polyimide sheet has a thickness of between 0.1-100 micrometers. 
     
     
         15 . The method of  claim 1 , wherein the matrix comprises polyimide. 
     
     
         16 . The method of  claim 1 , wherein the matrix comprises bismaleimide. 
     
     
         17 . A wafer formed by the method of  claim 1 , wherein the wafer comprises:
 a. a wafer thickness of between 10-500 micrometers;   b. at least one side of the wafer having a root mean square surface roughness Rq of less than 300 nm in an area of 100 micrometers by 100 micrometers and less than 500 nm along a line of 2 millimeter length;   c. a yield strength at fracture of greater than 0.5 gigapascals (GPa), wherein yield strength is defined as a force, in a direction parallel with a plane of a side of the wafer, per unit area, to cause the wafer to fracture; and   d. a strain at fracture of more than 0.01, wherein strain is defined as the change in length caused by a force in a direction parallel with a plane of the wafer divided by original length.   
     
     
         18 . The wafer of  claim 17 , wherein the yield strength is between 2 GPa and 3.6 GPa. 
     
     
         19 . The wafer of  claim 17 , wherein the root mean square surface roughness is less than 200 nanometers in an area of 100 micrometers by 100 micrometers. 
     
     
         20 . The wafer of  claim 17  micropatterned by laser ablation, water jet, or combinations thereof to form an x-ray window support structure comprising:
 a. a support frame defining a perimeter and an aperture; 
 b. a plurality of ribs extending across the aperture of the support frame and carried by the support frame; 
 c. openings between the plurality of ribs; and 
 d. the support frame and the plurality of ribs comprising a support structure.