Structure and process to fabricate lead overlay (LOL) on the bottom spin valve

#1. Field of the Invention

#This invention relates generally to the fabrication of a giant magnetoresistive (GMR) magnetic field sensor of the bottom spin-valve (BSV) type and more specifically to methods for eliminating undesirable oxidations and diffusions during annealing and patterning when forming lead overlay (LOL) type lead layers.

#2. Description of the Related Art

#The objects, features and advantages of the present invention are understood within the context of the Description of the Preferred Embodiment, as set forth below. The Description of the Preferred Embodiment is understood within the context of the accompanying figures, wherein:

#FIG. 1 is a schematic drawing of a prior art LOL BSV sensor configuration.

#FIG. 2 is a schematic drawing of a prior art BSV sensor stack configuration.

#Referring first to FIG. 3a there is shown a schematic cross-sectional view through an ABS plane of a bottom spin valve (BSV) GMR sensor stack subsequent to a first annealing process but before the formation of a contiguous longitudinal hard bias layer and blanket LOL layer. The stack is formed in accord with the preferred embodiment of the present invention.

#Moving vertically upward in the stack structure, on the substrate (10) there is first seen a seed layer (20), which is typically a structure enhancing layer of NiCr and which is typically formed to a thickness of between approximately 50 and 65 angstroms, with approximately 60 angstroms being preferred. On the seed layer there is then formed a pinning layer (30) of antiferromagnetic material, typically MnPt, formed to a thickness of between approximately 100 and 150 angstroms, with approximately 120 angstroms being preferred. On the pinning layer there is then formed a pinned layer (40), which, in this embodiment, is a synthetic antiferromagnetic tri-layer comprising a lower ferromagnetic layer (designated AP2) (42) of CoFe, formed to a thickness of between approximately 15 and 20 angstroms, with approximately 15 angstroms being preferred, a coupling layer (44) of Ru formed on AP2 to a thickness of between approximately 7 and 8 angstroms, with approximately 7.5 angstroms being preferred, and an upper ferromagnetic layer (designated AP1) (46) formed on the coupling layer, which upper layer is also a layer of CoFe, formed to a thickness of between approximately 20 and 25 angstroms with approximately 20 angstroms being preferred. On the pinned layer is then formed a non-magnetic spacer layer (50), which is typically a layer of Cu formed to a thickness of between approximately 16 and 25 angstroms with approximately 18 angstroms being preferred. On the spacer layer is then formed a ferromagnetic free layer (60), which is here a bilayer of CoFe (62) and NiFe (64), wherein the CoFe layer is between approximately 5 and 15 angstroms with approximately 10 angstroms being preferred and the NiFe layer is between approximately 15 and 30 angstroms with approximately 20 angstroms being preferred. On the free layer is then formed a barrier layer (69), which is a layer of Ru formed to a thickness of between approximately 5 and 15 angstroms, with approximately 10 angstroms being preferred. On the Ru barrier layer is then formed a capping bilayer, the lower layer of which is a Ta capping and adhesion layer (70), said layer being formed in a low resistance phase and to a thickness of between approximately 10 and 40 angstroms, with approximately 30 angstroms being preferred. On this Ta capping and adhesion layer is then formed an upper capping layer, which is an Au capping layer (75), said layer being formed to a thickness of between approximately 75 and 150 angstroms, with approximately 100 angstroms being preferred and said layer completing the GMR stack. The entire GMR stack thus formed is formed in the GMR sputtering system in a single pump-down. The Au capping layer (75) protects the Ta capping and adhesion (70) layer from oxidation during the subsequent pinned layer (40) annealing process to magnetize the pinned layer (said magnetization shown in FIG. 3b as (80) and (81)).

#Referring next to FIG. 3b, there is shown, schematically, the stack of FIG. 3a subsequent to a pinned layer annealing in a transverse 10 kOe field at 280° C. for 5 hours to set the pinned layer magnetization. A circle (81) and a circle and cross (80) indicate the transverse magnetizations of the pinned layer (40). A contiguous longitudinal hard bias layer (110) is now formed contacting the stack edges, said layer being a layer of CoPtCr formed to a thickness of between approximately 200 and 400 angstroms, with 300 angstroms being preferred. The CoPtCr layer is then capped with a second capping layer, which is a bilayer comprising a lower layer of Ta (114) on which is formed an upper layer of Au (116), said Ta layer being formed to a thickness of approximately 20 angstroms and said Au layer being formed to a thickness of approximately 100 angstroms. It is to be noted that two novel protective layers have thus far been formed. The barrier layer ((69) in FIG. 3a), to protect the free layer from oxidation and diffusion during annealing and subsequent etching (discussed below) and the first Au capping layer (75) to protect the first Ta capping layer from oxidation during annealing. For example, GMR annealing in a transverse 10 kOe field at 280° C. for 5 hours to set the pinned layer magnetization has been shown to produce a severe degradation of a free layer capped only with Cu, indicating diffusion of Au through the Ta/Cu layer into the free layer. The presence of a Ru barrier layer, such as layer (69) in FIG. 3a, of at least 5 angstroms in thickness eliminates this degradation.