Sputtered Spring Films With Low Stress Anisotropy

Abstract

Methods are disclosed for fabricating spring structures that minimize helical twisting by reducing or eliminating stress anisotropy in the thin films from which the springs are formed through manipulation of the fabrication process parameters and/or spring material compositions. In one embodiment, isotropic internal stress is achieved by manipulating the fabrication parameters (i.e., temperature, pressure, and electrical bias) during spring material film formation to generate the tensile or compressive stress at the saturation point of the spring material. Methods are also disclosed for tuning the saturation point through the use of high temperature or the incorporation of softening metals. In other embodiments, isotropic internal stress is generated through randomized deposition (e.g., pressure homogenization) or directed deposition techniques (e.g., biased sputtering, pulse sputtering, or long throw sputtering). Cluster tools are used to separate the deposition of release and spring materials.

1 . An integrated processing tool comprising: 
 a central transfer chamber including a robot for transferring wafers into and out of said central transfer chamber;    a first physical vapor deposition chamber directly accessible via a valve with said central transfer chamber, having a target comprising a selected release material; and    a second physical vapor deposition chamber directly accessible via a valve with said central transfer chamber, having a target comprising a selected spring material.    
   
   
       2 . The integrated processing tool according to  claim 1 , wherein the release material is Ti, and wherein the spring material is MoCr alloy.  
   
   
       3 . The integrated processing tool according to  claim 1 , further comprising a third physical vapor deposition chamber directly accessible via a valve with said central transfer chamber, having a target comprising the selected spring material.  
   
   
       4 . The integrated processing tool according to  claim 3 , wherein the release material is Ti, and wherein the spring material is MoCr alloy.  
   
   
       5 . The integrated processing tool according to  claim 1 , further comprising a third physical vapor deposition chamber directly accessible via a valve with said central transfer chamber and configured for precleaning the wafers.  
   
   
       6 . The integrated processing tool according to  claim 1 , further comprising a third physical vapor deposition chamber directly accessible via a valve with said central transfer chamber and configured for dehydration baking of the wafers.  
   
   
       7 . A method for producing a spring structure on a wafer utilizing an integrated multi-chamber tool having a central transfer chamber including a robot for transferring the wafer into and out of the central transfer chamber, a first physical vapor deposition chamber directly accessible via a valve with said central transfer chamber and having a first target comprising a selected release material, and a second physical vapor deposition chamber directly accessible via a valve with said central transfer chamber and having a second target comprising a selected spring material, the method comprising: 
 causing the robot to position the wafer in the first physical vapor deposition chamber;    controlling the first physical vapor deposition chamber to deposit a release material layer on the wafer from the first target;    causing the robot to remove the wafer from the first physical vapor deposition chamber and to position the wafer in the second physical vapor deposition chamber; and    controlling the second physical vapor deposition chamber to deposit a spring material layer on the release material layer from the second target such that the spring material film has a stress variation in the growth direction and including at least one layer having an isotropic internal stress.    
   
   
       8 . The method according to  claim 7 , further comprising removing the wafer from the integrated multi-chamber tool and removing a portion of the spring material film and a portion of the release material layer, thereby forming a spring finger having an anchor portion attached to the substrate and a free portion bending away from the substrate due to the internal stress gradient.