Bit patterned device

The invention relates to bit patterned recording media having a stop layer for chemical mechanical polishing. One embodiment of the present invention is a method of manufacturing a magnetic recording medium comprising the step of planarizing by chemical mechanical polishing until the stop layer is reached. The present invention also provides a magnetic recording medium having a stop layer.

BACKGROUND

Magnetic recording media are widely used in various applications, e.g., in hard disk form, particularly in the computer industry, for storage and retrieval of large amounts of data/information. These recording media are conventionally fabricated in thin film form and are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation (i.e., parallel or perpendicular) of the magnetic domains of the grains of the magnetic material constituting the active magnetic recording layer, relative to the surface of the layer.

In the operation of magnetic media, the magnetic layer is locally magnetized by a write transducer or write head to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field applied by the write transducer is greater than the coercivity of the recording medium layer, then the grains of the polycrystalline magnetic layer at that location are magnetized. The grains retain their magnetization after the magnetic field applied by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.

In conventional hard disk drives, data is stored in terms of bits along the data tracks. In operation, the disk is rotated at a relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which radially positions the head on the disk surface. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks.

Lithographically patterned media, also known as bit-patterned media, are being pursued to increase areal recording density as compared to conventional recording media. Bit-patterning combines several hundred media grains into one single magnetic island, which does not require large coercivities. The manufacturing of lithographically patterned media typically involves using photolithography techniques to form a pattern of discrete and separated magnetic regions. This may include a nanoimprint process, i.e., the stamping of soft resist materials with hard stampers to mold a pattern within the resist.

As the size and spacing of magnetic device features have decreased to increase recording density, the height of the steps of these features have increased. Also, as the number of layers deposited during the manufacture of magnetic devices increases, irregularities in the surface of the layers increases. As a result, chemical mechanical polishing (CMP) may be used to planarize feature surfaces during processing.

CMP is used to remove surface topography in order to achieve planar surfaces suitable for photolithographic patterning of complex patterns. Material is removed during a CMP process by a combination of chemical etching and mechanical abrasion. CMP processes typically have a material removal rate of 300 to 500 nanometers (nm) per minute under normal process conditions. Removal continues until an endpoint is reached, which is theoretically the point where all of the excess material is removed, and a smooth planar surface remains.

The CMP endpoint may be determined by a variety of techniques. For example, prior CMP processes have incorporated instruments to measure changes in the surface optical reflectivity, changes in the surface temperature, and changes in eddy currents induced through the layers. Other CMP processes alternatively use prior test runs to estimate polish time to the endpoint. However, these prior CMP endpoint detection techniques are subject to variations as to when the endpoints are detected. Thus, there is a need in the industry for a process capable of accurately detecting CMP endpoints for fabricating consistent and accurate features in bit-patterned media.

SUMMARY

The present invention relates to bit patterned recording media having a stop layer for chemical mechanical polishing.

One embodiment of the invention is magnetic recording medium having a substrate; a magnetic layer supported by the substrate, where the magnetic layer has an array of discrete magnetic bits separated by a non-magnetic filler material; and a stop layer for chemical mechanical polishing. In another variation, the magnetic recording medium further includes one or more cap layers and/or lubricant layers.

According to another variation, the stop layer is disposed between the discrete magnetic bits. In another variation, the stop layer has a thickness of about 2 to about 200 nm, preferably about 2 to about 10 nm.

According to yet another variation, the filler material is selected from Al2O3, SiO2, SiOxNy, and combinations thereof, preferably Al2O3. In another variation, the stop layer is selected from carbon, platinum, gold, chromium, ruthenium, diamond, tungsten, SiC, SiOxNy, NiCu, and combinations thereof, preferably carbon. In one preferred embodiment, the filler material is Al2O3and the stop layer is carbon.

Another embodiment of the present invention is a method of manufacturing a magnetic recording medium including the steps of (a) forming a magnetic layer upon a substrate, the magnetic layer having an array of discrete magnetic bits separated by a non-magnetic filler material; (b) depositing a stop layer upon the magnetic layer; (c) depositing an excess layer upon the stop layer; and (d) planarizing by chemical mechanical polishing until the stop layer is reached.

According to one variation, the excess layer comprises Al2O3.

According to another variation, the step of planarizing by chemical mechanical polishing includes measuring an increase in induced polishing friction to determine the stop layer has been reached.

In another variation, the step of planarizing by chemical mechanical polishing comprises measuring changes in surface optical reflectivities to determine the stop layer has been reached.

In yet another variation, the step of planarizing by chemical mechanical polishing comprises measuring changes in electrical currents to determine the stop layer has been reached.

Additional advantages of this invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION

As used herein “substrate” refers to one or more layers that provide a surface suitable for the formation of a bit-patterned magnetic layer thereupon in the manufacture of a magnetic recording medium. The substrate may comprise one or more different materials.

FIG. 1is a sectional view depicting a portion7of a magnetic recording medium according to one embodiment of the present invention, which includes substrate8, optional overlying layer(s)9, and magnetic layer10. Underlying substrate8is the portion of the magnetic recording medium that is formed prior to magnetic layer10, and includes top surface8a, upon which magnetic layer10is formed. Optional overlying layer(s)9is the portion of the magnetic recording medium that is disposed on top of magnetic layer10, after magnetic layer10is formed and planarized. Underlying substrate8and overlying layer(s)9may provide a variety of characteristics for the magnetic recording medium, such as additional magnetic properties, magnetic isolation, or protection.

Magnetic layer10includes an array of discrete magnetic bits12(represented singularly inFIG. 1), non-magnetic filler material14, and stop layer16, where stop layer16is used to detect a chemical mechanical polishing (CMP) endpoint. Through the use of stop layer16, target thickness of magnetic layer10is accurately controlled, and within wafer non-uniformity (WIWNU) is improved.

Magnetic bit12is the portion of magnetic layer10that provides magnetic properties, and exists in a region dimensionally defined by surfaces12a-12d. Surfaces12b,12dare disposed adjacent to filler material14. While surfaces12a-12ddepict magnetic portion12as rectangular, magnetic bit12may alternatively be other shapes, such as trapezoidal. Magnetic bit12is derived of one or more high-magnetic-moment materials, such as a magnetic alloy. Examples of suitable magnetic alloys include iron, cobalt, nickel, and combinations thereof. Examples of suitable combinations include nickel-iron, cobalt-iron, and nickel-cobalt-iron materials.

Filler material14is a non-magnetic layer and includes top surface14a. Filler material14isolates magnetic portion12in the lateral directions of surfaces12b,12d. Filler material14is derived from non-magnetic materials, such as oxide materials. Examples of suitable oxide materials include aluminum oxide (Al2O3), silica dioxide (SiO2), SiOxNy, and combinations thereof. An example of a particularly suitable material includes aluminum oxide.

Filler material14may have a thickness as individual needs may require, for example, where the thickness of filler material14is the distance between top surface14aand top surface8aof underlying substrate8. Preferably, filler material14has a thickness less than the thickness of magnetic bit12to account for the thickness of stop layer16(i.e., the thickness of magnetic bit12equals the combined thicknesses of filler material14and stop layer16).

Stop layer16is disposed on top surface14aof filler material14adjacent to surfaces12b,12dof magnetic portion12. Stop layer16includes top surface16aand provides a means for detecting the CMP endpoint for planarizing magnetic layer10. This provides an accurate control of the target thickness of magnetic feature10. Preferably stop layer16has a thickness between about 2-100 nm, and more preferably between about 2-10 nm, where the thickness is the distance between top layers16aof stop layer16and top layer14aof filler material14.

Stop layer16is non-magnetic, corrosion resistant, and has high removal rate selectivity versus the magnetic alloys of magnetic bit12and magnetic isolation materials of filler material14(i.e., relatively high abrasion resistance). By being non-magnetic, stop layer16assists filler material14in magnetically isolating magnetic portion12in the lateral directions of surfaces12b,12d. Corrosion resistance is also desired so that stop layer16withstands chemical attacks by CMP slurries.

Preferably, the selectivities of the materials for stop layer16versus the magnetic alloys of magnetic bit12and magnetic isolation materials of filler material14are at least about eighty-to-one. Examples of suitable materials for stop layer16include platinum, gold, chromium, ruthenium, diamond, tungsten, SiC, SiOxNy, NiCu, and combinations thereof. An example of a particularly suitable material for stop layer16is carbon. Carbon is non-magnetic, corrosion resistant, and provides a high selectivity versus materials for magnetic bit12and filler material14.

Stop layer16provides a means for accurately detecting the endpoint of a CMP process, which may be accomplished in several manners. First, the CMP endpoint may be detected based upon measurable fluctuations in the motor current of a CMP apparatus (not shown). These fluctuations are induced by changes in polishing friction during a polishing process (i.e., changes in removal rates), and correlate to the differences in removal rate selectivities between the layers. Additionally, the CMP endpoint may also be detected by changes in surface optical reflectivity and changes in eddy currents induced through the layers. The detection of the CMP endpoint through these techniques allows top surface16aand surface12ato be evenly planarized for providing a smooth surface for magnetic layer10.

FIGS. 2A-2Gare sectional views illustrating one embodiment of a method of forming a magnetic recording medium according to the present invention.FIG. 2Adepicts portion107of a magnetic recording medium, which is analogous to portion7, prior to the formation of magnetic layer10. As illustrated, portion107includes underlying substrate108and magnetic layer110at an initial stage of formation prior to the formation of discrete magnetic bits and the additional of filler material by conventional photolithography processes. Alternatively, bit-patterning processes as described above may be used.

Whether by conventional photolithographic processes or bit-patterning, discrete magnetic bits112are formed on substrate108, as depicted inFIG. 2B. As shown, magnetic bit112has dimensions defined by surfaces112a-112d. Magnetic bit112has a width defined by the distance between surfaces112b,112d.

As depicted inFIG. 2C, after magnetic bit112is formed, non-magnetic material is deposited on top surface108aof underlying substrate108and magnetic bit112to form filler material114. After deposition, filler material114has a thickness defined by the distance between top surface114aof filler material114and top surface108aof underlying substrate108. Filler material114also includes a step portion, noted by step surface113b, formed over magnetic bit112.

After filler material114is deposited, stop layer116is formed by depositing material on top of filler material114. This is depicted inFIG. 2D. After deposition, stop layer116has a thickness defined by the distance between top surface116aof stop layer116and top surface114aof filler material114. Stop layer116also includes a step portion, noted by step surface116b, formed over magnetic bit112.

As previously mentioned, it is preferable that the combined thicknesses of filler material114and stop layer116are generally equal to the thickness of magnetic bit112. Alternatively, the combined thicknesses of filler material114and stop layer116may be less than the thickness of magnetic bit112. In this case, the additional amount of magnetic bit112will be removed by the CMP process. Moreover, it is noted that the combined thicknesses of filler material114and stop layer116should not be greater than the thickness of magnetic bit112. This would prevent the CMP process from planarizing magnetic layer110when stop layer116is reached.

After stop layer116is formed, an additional layer of non-magnetic material is deposited on top of stop layer116, as depicted inFIG. 2Eto form excess layer118. The thickness of excess layer118is the distance between top surface118aof excess layer118aand top surface116aof stop layer116. Excess layer118is incorporated to provide an adequate polishing time to remove the step portions above magnetic bit112, noted by step surfaces114b,116b.

Suitable materials for excess layer118include the suitable materials described inFIG. 1for filler material14. Moreover, it is desirable that the materials used for stop layer116have higher removal rate selectivities versus the materials used for excess layer118. This allows the CMP process to remove excess layer118at a greater rate than stop layer116. Generally, preferred thicknesses of excess layer118provide an adequate polish time to remove the step portions above magnetic bit112.

After magnetic layer110as depicted inFIG. 2Eis formed, magnetic layer110is polished via a CMP process to planarize magnetic layer110and expose magnetic bit112. During the CMP process, material is removed from excess layer118by a combination of chemical etching and abrasion by the polishing pad of the CMP apparatus (not shown). While the polishing pad removes the material from excess layer118, polishing friction is induced on the polishing pad. This polishing friction corresponds to the material removal rate and is measurable by the motor current of the CMP apparatus.

Additionally, the CMP endpoint may further be detected by changes in the surface optical reflectivities when excess layer118is removed and top surface116aof stop layer116is exposed. The surface optical reflectivity is measured for an entire wafer, by laser or by normal light enhanced by optical fibers. The light is directed to the surface being polished (i.e., excess layer118), reflects the light at a given angle based upon the material used for excess layer118. As excess layer118is removed by the CMP apparatus, the reflectivity remains substantially unchanged. However, when stop layer116is reached, the reflectivity changes because of the differences in reflectivities between the materials of stop layer116and excess layer118. The CMP endpoint may additionally be triggered when this change in surface optical reflectivity is detected. Those skilled in the art will appreciate and understand suitable systems for measuring the surface optical reflectivity.

The CMP endpoint may also be detected by measuring changes in electrical currents (i.e., eddy currents) induced through the layers. The electrical currents are induced from the CMP slurry through the layers of magnetic feature110, and are detected by a sensor (not shown) located below the wafer. As material is being removed by polishing, the electrical currents correspondingly change due to the drop in electrical resistance. As such, the rate of change in the electrical currents detected correlate to the rate of material removal. Therefore, when the rate of material removal is substantially reduced (e.g., when stop layer116is reached), the rate of change in the electrical current is also substantially reduced. The CMP endpoint may additionally be triggered when the rate of change in the electrical current are substantially reduced. Those skilled in the art will appreciate and understand suitable systems for inducing and measuring eddy currents.

Moreover, detecting the CMP endpoint by combinations of these techniques further decreases the variations in detecting the CMP endpoint. This provides greater accuracy in controlling the thickness of magnetic layer110.

FIG. 2Fdepicts magnetic layer110after a portion of excess layer118has been removed such that step surface116bof stop layer116is exposed. At this point, because of the higher removal rate selectivity of stop layer116versus excess layer118, friction induced on the polishing pad increases (i.e., removal rate decreases). Nonetheless, the increased friction due to the encounter of step surface116bof step layer116does not trigger the CMP endpoint detection. The step portion over magnetic bit112is relatively small compared to the overall size of magnetic layer110. As such, the increase in the friction induced on the polishing pad at this point is not great enough to trigger the CMP endpoint detection.

Moreover, the surface optical reflectivity remains substantially unchanged because excess layer118still remains in the regions over top surface116aof stop layer116. The rates of change in the electrical current are also not substantially reduced by the reduction in the material removal rate imposed by top surface116bof stop layer116. Removal of material by the CMP process continues until top surface116aof stop layer116is reached. At this point, due to the high removal rate selectivity of stop layer116versus excess layer118, the increase in friction induced on the polishing pad is high enough to trigger the CMP endpoint detection.

Additionally, the surface optical reflectivity changes because excess layer118is removed to expose stop layer116. Moreover, because the material removal rate is substantially reduced at stop layer116, the rate of change in the induced electrical current is correspondingly reduced. These additional techniques also provide signals for triggering the CMP endpoint detection.

Through the use of stop layer116, the CMP endpoint is accurately detected, which minimizes thickness variations induced by under-polishing and over-polishing.FIG. 2Gdepicts portion107with magnetic layer110after the CMP endpoint has been detected and polishing has been stopped. The result is a smooth planar surface defined by surface112aof magnetic bit112and top surface116aof stop layer116. The thickness of magnetic layer110is also accurately determined and may be consistently replicated through this method. Subsequently, optional overlying layer(s)9may be formed to provide desired electrical and mechanical properties. In some embodiments, the stop layer116is external or outside the interface or common/shared boundary of the magnetic bits112and the nonmagnetic filler114.

By detecting the CMP endpoint through a stop layer, the target thickness of bit patterned features is accurately controlled and WIWNU is improved. This allows magnetic recording media to be fabricated accurately and consistently.