Method to form tapered magnetic shield for perpendicular recording head

The inadvertent introduction of stray fields at the media surface by the shields that form part of a magnetic read-write head has been eliminated by using a combination of masking and ion milling to remove small amounts of material close to the shields' outer edges. As a consequence, instead of presenting a sharp edge to the ABS, a shield's lower surface slopes gently away from it.

FIELD OF THE INVENTION

The invention relates to the general field of perpendicular magnetic recording (PMR) with particular reference to shaping the associated magnetic shields

BACKGROUND OF THE INVENTION

As magnetic recording is pushed to higher areal densities, perpendicular recording offers advantages in thermal stability over longitudinal recording, thus delaying arrival at the super-paramagnetic limit. Another advantage of perpendicular recording with single pole (SP) head and perpendicular media, with a soft underlayer (SUL), is the ability to produce a larger write field than that of a ring head to record on relatively thick media with high anisotropy constant.

A typical read-write unit is illustrated inFIG. 1which provides an ABS (air bearing surface) view of the assembly i.e. the unit as seen when looking directly up from the surface of the recording media. Shown inFIG. 1are perpendicular magnetic write pole11and GMR (giant magneto-resistance) read head12. Also shown, and of particular interest for the present invention, are three magnetic shields. Read head12is seen to be symmetrically disposed between shields13and14while write pole11is centrally located between shields14and15.

Shields13,14, and15can serve as magnetic flux conductors for external fields which causes them to direct a certain amount of flux into the recording medium. When such a flux density is large enough, unwanted writing or erasing can occur. In particular, because of the magnetic softness of the shield materials, a small amount of external field can induce relatively large fields in the media and cause unintended erasure of information on the media.

In most current PMR designs the shields have a strictly rectangular shape as seen inFIG. 2. Due to the finite thickness and moment of the soft magnetic underlayer, flux distribution is not uniform over the surfaces of the shields. At sharp corners and edges, the flux density can be much higher than that at the shield center. In general, data under a shield corner will usually be erased first.

In application Ser. No. 11/117,672 filed Apr. 28, 2005, we disclosed a method and structure which greatly reduces a PMR head's sensitivity to stray field erasure, especially from shield corner field concentration. The basic principle disclosed there is to recess the corner from the ABS with an angle, shown as angle31inFIG. 3. This approach is pursued further In the present invention and a novel process is disclosed which allows excellent control of shield wall edge angle by post-lapping the ABS by means of ion milling.

InFIG. 4we show the calculated dependence of maximum field in the media on the shield recess angle (inFIG. 3). The dimension of the shield in the calculation are 60 μm (W), 20 μm (L), and 4 μm (T). An external field of 200 Oe is assumed. As can be seen, the erasing field monotonically drops with reducing shield wall angle, the reduction being more pronounced when the wall angle is less 10 deg. However, creating such a small wall angle at wafer level poses great difficulties for current wafer processes. In the present invention we disclose a novel method to control the shield wall angle

A routine search of the prior art was performed with the following references of interest being found:

In U.S. Pat. No. 6,198,597, Tateyama et al. disclose corner portions of the rear part of the magnetic pole recessed from the ABS by 0.05 microns or more by ion milling. An angle of 45 degrees is mentioned. In U.S. Pat. No. 6,742,241, Sasak, describes a light shield mask having an acute angle at the corner but this is not the same type of shield as that with which the present invention is concerned.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the present invention to eliminate stray fields at the edges of magnetic shields used in conjunction with magnetic read-write heads.

Another object of at least one embodiment of the present invention has been to provide a process for tapering shield edges.

Still another object of at least one embodiment of the present invention has been that said process require little or no modification to the processes currently in use for the manufacture of such magnetic shields.

These objects have been achieved by using a combination of masking and ion milling to remove small amounts of material close to the shields' outer edges. Thus, instead of presenting a sharp edge to the ABS, the shield's lower surface slopes gently away from the ABS so that the inadvertent of stray fields at the media surface is eliminated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We now present details concerning our method to control the shield wall angle by post-lapping the ABS using an ion milling process.FIG. 5shows an ion milling mask51, generally of photoresist though a hard mask could be used if preferred. The width W of mask is less than that of shields. The length L can be chosen by either greater than the spacing of bottom shield to top shield (FIG. 5) or less than that (mask52inFIG. 6).

In conventional practice the mask width W is usually much larger than the shield width. During ion milling, the entire shield structure is protected by the mask, always resulting in sharp corners. In the present invention the mask width W is carefully chosen so that an outside portion of the shield will be trimmed by the ion beam to form a gentle slope at the shield's edge.

When ion milling is performed, the portion of the shield area that is without mask protection will recess away from the ABS at a shallow angle. In the case ofFIG. 5, the recess of the shield will be one directional (cross-track). In the caseFIG. 6, shield recess is two dimensional (cross-track and down-track), leading to further reductions in the erasing field.FIG. 7shows the front view of shield75(originally shield15) after ion-milling. The angle is between about 1 and 10 and the maximum recess depth h is between about 100 nm and 200 nm, which is sufficient to ensure that the outside corner after ion milling would not cause erasure. This ion milling can be integrated with the current slider building process.

Returning briefly toFIG. 1, the process of the present invention begins with the provision of an assembly that includes magnetic read head12, centrally disposed between magnetic shields13and14, and perpendicular magnetic write pole11disposed between magnetic shields14and15. This assembly is then polished so that the read and write heads and all three shields have coplanar lower surfaces that constitute an ABS (surface25inFIG. 2being one of these surfaces).

Referring next toFIG. 5, mask51is formed on this ABS. The mask covers the read and write heads, as well as the magnetic shields, except for opposing unprotected areas53,54, and55that extend inwards, between about 1 and 30 microns, from the shields' vertical edges.

At the conclusion of the ion beam treatment, as seen inFIG. 7, the lower surfaces of the shields, including shield15, take on the form of a centrally located lower surface72, that is coplanar with the ABS, together with two opposing lower surfaces73that are parallel to, and located a short distance, of between about 500 and 5,000 Angstroms, above, the ABS. Surfaces72and73are connected to one another through sloping surfaces74.

If mask51was used, the process of the invention would be terminated at this point with the removal of mask51. Alternatively, in a second embodiment of the invention, mask61(FIG. 6) may be used. In such a case, in addition to the areas53,54, and55, areas66(each of which extends inwards from the outer horizontal edges of shields13or15a distance that is between about 0.1 and 1 microns) are also left uncovered. As in the previous embodiment, ion milling is now used to modify the form of the assembly's lower surface.

FIG. 8is an isometric ABS view of the lower surface of shield15. Seen there is centrally located lowest surface81that is coplanar with the ABS. Located a short distance above the ABS is surface82which surrounds lowest surface81on three sides. Opposing sloping surfaces83connect surfaces81and82along a horizontal direction while single sloping surface84performs the same function along a vertical direction. As before, the process concludes with the removal of mask61.

For both of the above-described embodiments, we have determined that erasing magnetic fields at the shields' sloping edges are reduced by at least 30% relative to erasing fields potentially present in prior art designs wherein the shields edges are orthogonal to the ABS.