Metal liftoff tools and methods

Abstract

In certain embodiments the metal liftoff tool comprises an immersion tank for receiving a wafer cassette with wafers therein, the immersion tank including an inner weir, a lifting and lowering mechanism capable of raising and lowering the wafer cassette while submerged in fluid in the immersion tank, low pressure high velocity primary spray jets for stripping the metal, the primary spray jets positioned at opposing sides of the immersion tank parallel to the wafer surfaces planes, and secondary spray jets for pressure equalization force, positioned at the bottom of the immersion tank. A wafer lift insert is positioned at the bottom of the immersion tank to receive and periodically lift the wafers within the cassette.

1 . A metal liftoff apparatus comprising:
 a. an immersion tank having a first and second opposing sidewalls and a bottom, the immersion tank dimensioned to receive a cassette of wafers and a working fluid;   b. primary spray jets positioned on the first and second opposing side walls of the immersion tank;   c. secondary spray jets positioned on the bottom of the immersion tank; and   d. a lifting and lowering mechanism connectable to a cassette of wafers configured to raise and lower the cassette of wafers while in the cassette of wafers remains submerged in the immersion tank.   
     
     
         2 . The metal liftoff apparatus of  claim 1  further comprising an inner weir in the immersion tank over which the secondary spray jets are configured to spray working fluid stream to force stripped metal pieces from the immersion tank inner weir. 
     
     
         3 . The metal liftoff apparatus of  claim 1  further comprising a recessed area formed in the bottom of the immersion tank in which recessed area stripped metal pieces not forced over the inner weir are collected. 
     
     
         4 . The metal liftoff apparatus of  claim 3  further comprising a lifting assembly configured to lift the wafers a distance from a bottom portion of the cassette such that all portions of the wafer surfaces are exposed to spray jets while submerged in the immersion tank. 
     
     
         5 . The apparatus of  claim 1  further comprising an outer weir configured to collect working fluid and stripped metal pieces that flow over the inner weir of the immersion tank. 
     
     
         6 . The apparatus of  claim 2  further comprising a screen configured to capture stripped metal pieces from the working fluid flowed from the outer weir. 
     
     
         7 . The apparatus of  claim 2  further comprising a filtration loop configured to remove stripped metal particles from the working fluid stream. 
     
     
         8 . The apparatus of  claim 1  further comprising a heater configured to heat the fluid stream and/or working fluid in the immersion tank and/or prior to entering the immersion tank. 
     
     
         9 . The apparatus of  claim 5  further comprising a pump configured to pressurize the fluid stream. 
     
     
         10 . The apparatus of  claim 5  further comprising a valve configured to independently control the fluid jets. 
     
     
         11 . The apparatus of  claim 5  further comprising a removable filter-trap. 
     
     
         12 . The apparatus of  claim 5  further comprising a computer controller and computer software configured to operate the pumps, valves, jets and/or heater. 
     
     
         13 . A metal liftoff apparatus comprising:
 a. an immersion tank configured to receive a cassette of wafers and a working fluid;   b. primary spray jets positioned on opposing side walls of the immersion tank, the primary jets configured to flow streams of working fluid in a direction parallel with planes defined by wafer surfaces in the cassette, while the wafers are immersed in the working fluid;   c. secondary spray jets positioned on the bottom of the immersion tank configured to direct working fluid flow directly in an upward direction relative to the bottom of the immersion tank; and   d. a lifting assembly configured to lift the wafers a distance from a bottom portion of the cassette such that no portion of the cassette covers a wafer surface but the wafers remain submerged in the immersion tank when in a lifted position.   
     
     
         14 . A method comprising: removing metal from a wafer surface by
 a. immersing a cassette of wafers in a working fluid in an immersion tank;   b. directing working fluid streams from primary fluid spray jets positioned along at least one sidewall of the immersion tank directly toward the surfaces of the wafers, such that the working fluid stream flows over surfaces of the wafers in the cassette while immersed in the working fluid;   c. simultaneously to directing working fluid streams from the primary fluid spray jets, raising and lowering the cassette of wafers within the immersion tank through the primary fluid spray jets; and   d. directing working fluid streams from secondary fluid spray jets positioned at the bottom of the immersion tank such that working fluid streams flow directly upward relative to the bottom of the immersion tank.