Study of Chromium Hard Mask Formation and Wall Angle Control for Deep Etching Application

Abstract

Burnish head is widely used for burnishing process which is one of the critical ways to remove such asperities from the disk surface prior to assembly into hard disk drive. To achieve glide performance for ultra-low flying height, disk media with asperities that exceed the flying height of the magnetic head must be eliminated. One of critical parameter of burnish head is the rail dimension which required very deep etching at > 30 microns. To produce such etching depth, a Cr hard mask is needed. Wet etching process for Cr film was selected to form the Cr hard mask. In this study, the interactions of wet etching condition with the Cr hard mask were investigated in terms of the process impact to the mask wall angle. The chemical reaction was studied and discussed here in term of mass transportation condition. XPS revealed that the etch byproduct was Cr nitrate (Cr(NO3)3) and Cr oxide (Cr2O3). These byproducts passivated the metal surface and limited the fresh etchant arrival onto unetched surface. From the etched topography study, the process is said to be under mass transport control, and the reaction rate was determined to be influenced by the rate of mass transfer of reactants and products to and from the surface.