Method for making a tunneling magnetoresistive (TMR) sensor
View Patent ↗A tunneling magnetoresistive sensor has an extended pinned layer wherein both the MgO spacer layer and the underlying ferromagnetic pinned layer extend beyond the back edge of the ferromagnetic free layer in the stripe height direction and optionally also beyond the side edges of the free layer in the trackwidth direction. A patterned photoresist layer with a back edge is formed on the sensor stack and a methanol (CH 3 OH)-based reactive ion etching (RIE) removes the unprotected free layer, defining the free layer back edge. The methanol-based RIE terminates at the MgO spacer layer without damaging the underlying reference layer. A second patterned photoresist layer may be deposited and a second methanol-based RIE may be performed if it is desired to have the reference layer also extend beyond the side edges of the free layer in the trackwidth direction.
1. A method for making a tunneling magnetoresistive sensor comprising:
providing a substrate;
depositing a first ferromagnetic layer on the substrate, a MgO spacer layer on the first ferromagnetic layer, a second ferromagnetic layer on the MgO spacer layer and a nonmagnetic capping layer on the second ferromagnetic layer;
patterning a layer of photoresist on the capping layer, the patterned photoresist having a back edge;
reactive ion etching (RIE) the second ferromagnetic layer in methanol to define a back edge for the second ferromagnetic layer; and
terminating said RIE at the MgO spacer layer, leaving the MgO spacer layer and underlying first ferromagnetic layer extending beyond the back edge of the second ferromagnetic layer.
2. The method of claim 1 wherein the photoresist layer is a first photoresist layer and the RIE is a first RIE, and further comprising, after terminating said first RIE:
removing the first photoresist layer from the capping layer;
depositing a first electrically insulating layer on the MgO layer in the region beyond the back edge of the second ferromagnetic layer;
patterning a second layer of photoresist on the capping layer and said first insulating layer, the patterned second layer of photoresist having two spaced-apart side edges generally orthogonal to the back edge of the second ferromagnetic layer;
performing a second RIE in methanol of the second ferromagnetic layer to define two spaced-apart side edges for the second ferromagnetic layer;
terminating said second RIE at the MgO spacer layer, leaving the MgO spacer layer and underlying first ferromagnetic layer extending beyond the two side edges of the second ferromagnetic layer;
depositing a second electrically insulating layer on the MgO layer in the regions beyond the side edges of the second ferromagnetic layer;
depositing a ferromagnetic said second insulating layer;
depositing a capping layer on said ferromagnetic biasing layer; and
removing the second layer of photoresist.
3. The method of claim 1 wherein depositing the capping layer comprises depositing the capping layer selected from Ru, Rh, Ta and TaN, and further comprising, prior to the RIE, ion milling the capping layer, using the patterned photoresist as an etch mask, to expose the underlying second ferromagnetic layer.
4. The method of claim 1 further comprising, after terminating the RIE, depositing an electrically insulating backfill layer on the MgO spacer layer and in contact with the back edge of the second ferromagnetic layer.
5. The method of claim 1 further comprising depositing an antiferromagnetic layer on the substrate, and wherein depositing the first ferromagnetic layer comprises depositing the first ferromagnetic layer on the antiferromagnetic layer.
6. The method of claim 1 further comprising depositing a hardmask layer on the capping layer prior to said patterning, and wherein patterning the layer of photoresist comprises patterning the layer of photoresist on the hardmask layer, transferring the photoresist pattern to the hardmask layer; and removing the patterned photoresist prior to said RIE.