Ion Beam Trimming of Write Pole of Thin Film Recording Heads

The fabrication of a hard disk drive write/read head is a complex production process involving several hundred in­di­vid­ual steps. Each of those steps  requires highest precision for a maximum yield of devices with identical properties within narrow specification ranges.

The width of the write pole needs to be adjusted precisely since it directly de­ter­mines the strength of the write field within the hard disk drive. Too small of a pole width will result in a magnetic field too weak to switch the data bits, whereas too large of a write pole may lead to write fields strong enough to overwrite adjacent data bits, both resulting in total loss of data.

Furthermore, the layer thickness must be very uniform. The read-/write head flies over the hard disk with a relative speed of several tens of meters per second. In­ho­mo­gen­eities may lead to turbulence that can cause head crashes and thus permanent damage to the hard disk.

Current production devices are thus pushed towards their limits necessitating further pro­cess­ing steps.

The pole width of the write pole is adjusted by a defined removal of material (Fig. 1, left). Conventionally, this is done by chemical mechanical polishing (CMP), where the wafer surface is ground by an abrasive and corrosive slurry. However, at the polishing stops the desired surface quality cannot be reached and may lead to an undesired step structure with extremely negative influence on the further processing steps, device handling and thus device yield.

The scia Trim 200 uses localized ion beam etching for precise adjustment of film  thickness and thus the lateral width of the write pole (Fig. 1, right). The ion beam is scanned over the wafer surface varying the velocity and thus the dwell time for removal of precisely the desired amount of material at each location.

Since the removal rate is dependent on both the material and the angle of incidence of the ion beam with respect to the wafer surface, it is possible to tune the ratio of removal rates of the materials present in the wafer to the desired value. For instance, the write pole of NiFe alloy and its surrounding Al2O3 matrix can be trimmed with exactly the same rate at an ion beam incidence angle of about 55° – the width of the write pole can be set without formation of steps at the bound­aries between materials on the wafer surface (Fig. 2).

Related product: scia Trim 200 for Ion Beam Trimming

  • Pole width adjustment
  • Step height reduction
  • Improvement of thickness homogeneity
  • Increase of device yield
  • High volume production system
  • Equipped with handling robot for standard semiconductor cassettes

Fig.1: Write pole cross section

Schematic drawing of NiFe alloy embedded in an Al2O3 matrix. Left: Wafer exhibits significant variations in the surface profile. Right: Defined removal of excess material leads to smoothened surface and adjusted target pole width.

Fig. 2: Removal rates

Removal rates of NiFe alloy and Aluminium Oxide as a function of the ion beam incidence angle. At an angle of about 55° both materials are removed with an equal rate.