US20060168794A1 - Method to control mask profile for read sensor definition - Google Patents

Abstract

A method for constructing a magnetoresistive sensor that avoids shadowing effects of a mask structure during sensor definition. The method includes the use of an antireflective coating (ARC) and a photosensitive mask deposited there over. The photosensitive mask is formed to cover a desired sensor area, leaving non-sensor areas exposed. A reactive ion etch is performed to transfer the pattern of the photosensitive mask onto the underlying ARC layer. The reactive ion etch (RIE) is performed with a relatively high amount of platen power. The higher platen power increases ion bombardment of the wafer, thereby increasing the physical (ie mechanical) component of material removal relative to the chemical component. This increase in the physical component of material removal result in an increased rate of removal of the photosensitive mask material relative to the ion mill resistant mask. This avoids the formation of a bulbous or mushroom shaped photoresist mask and therefore, avoids shadowing effects during subsequent manufacturing processes.

Description

FIELD OF THE INVENTION
• The present invention relates to the manufacture of magnetoresitive sensors and more particularly to a method for accurately defining the side walls and track width of a magnetoresistive sensor.
BACKGROUND OF THE INVENTION
• The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, a thin layer of air develops between the slider and the rotating disk. When the slider rides on this air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
• The write head includes a coil layer embedded in insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
• In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
• The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
• When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer).
• The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
• Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
• Traditionally, GMR sensors have been constructed as current in plane (CIP) GMR sensors, wherein current flows through the sensor from one side to the other in a direction parallel with the planes of the layers making up the sensor. More recently, increased attention has been focused on current perpendicular to plane (CPP) GMR sensors. As its name suggests, in a CPP sensor, current flows through the sensor from top to bottom in a direction perpendicular to the planes of the layers making up the sensor.
• Another type of magenetoresistive sensor is a tunnel junction sensor (TMR) or tunnel valve. A tunnel valve includes a pinned layer and a free layer, similar to a GMR sensor. However, instead of having a non-magnetic electrically conductive spacer layer between the free and pinned layers, a tunnel valve has a thin dielectric, non-magnetic barrier layer, which can be constructed of for example alumina Al₂O₃. A tunnel valve operates based on the spin dependent scattering of electrons through the thin barrier layer. When the magnetic moments of the free and the pinned layer are aligned parallel with one another, electrons much more readily pass through the barrier layer than when they are the moments are antiparallel. Therefore, current travels through a tunnel valve in a direction perpendicular to the plane of the layers making up the sensor, similar to a current perpendicular to plane (CPP) GMR.
• With reference toFIG. 1A, magnetoresitive sensors have traditionally been constructed by a method that includes first depositing thesensor layers102 as full film layers, on asubstrate104, which can be for example an alumina gap layer, or in the case of a CPP GMR or tunnel valve could be an electrically conductive magnetic material such as NiFe. Then, a full film layer of material that is resistant to chemical mechanical polishing (CMP stop)106 is deposited. Alayer108 of antireflective coating (ARC) material, such as Duramide, that is resistant to removal by ion milling is then deposited over the CMPresistant material106. Amask110 that includes one or more layers of a photoreactive material such as photoresist is then formed to cover the area where the sensor is desired and exposing other portions. A reactive etching process is then used to remove the ARC and CMP resistant materials.
• With reference now toFIG. 1B, areactive ion etch112 is then performed to remove portions of the ion millresistant layer108 andCMP stop106 that are not covered by thephotoresist mask110. This process is known in the industry as transferring the image of thephotoresist mask110 onto theunderlying mask layers106,108. The RIE process used to transfer the image of the photoresist mask onto theunderlying layers106,108 is chosen to be a RIE process that can readily remove the materials making up theunderlying layers106,108.
• With reference toFIG. 1B, it can be seen that, since the RIE process used to perform the image transfer preferentially removes thelayer108 at a faster rate than it removes thephotoresist layer110, a bulbous or mushroom shape forms on themask layers106,108,110. Sensor performance depends, to large extent on the clean and precise definition of the sensor by the ion mill process. For example, the trackwidth of the sensor is determined by this ion milling procedure, so accurate location of the side walls is critical. In addition, accurate definition of the trackwidth depends upon having a sharp sensor edge that is as close to vertical as possible. A sloping sensor side wall results in a poorly defined trackwidth. Furthermore, a clean vertical side wall is necessary for efficient free layer biasing, since the hard bias layers will abut this side wall.
• Unfortunately, the bulbous mask structure prevents clean, accurate sensor definition. For example, the bulbous mask structure results in shadowing during the image transfer process and during the sensor defining ion mill process. In addition, the bulbous mask shape result in non-uniform deposition of layers such as hard bias layers and lead layers.
• Therefore, there is a strong felt need for a method for defining the track width and stripe height of a magnetoresistive sensor that overcomes the shadowing problems resulting from the bulbous mask structure described above. Such a method would preferably not result in significant added expense or process time and would preferably
SUMMARY OF THE INVENTION
• The present invention provides a method for manufacturing a sensor in which the precision of the sensor definition is not diminished by shadowing effects. The method involves depositing a series of sensor layers as full film layers onto a substrate. A CMP stop layer can then be deposited over the sensor layers, followed by an antireflective coating layer (ARC). Then a photosensitive mask is formed over the ion mill resistant mask layer. A reactive ion etch is then performed to remove exposed portions of the underlying ion mill resistant mask and the CMP stop. The reactive ion etch is performed while applying a platen power greater than a 70 Watts (W), and preferably of at least 100 Watts (W). More preferably, the reactive ion etch is performed while applying a platen power of around 300 W. The application of this higher platen power increases the physical component of material removal, increasing the rate at which the photoresist mask material is removed, thereby eliminating the formation a bulbous or mushroom shaped mask layer and eliminating any shadowing effects resulting therefrom.
• After the reactive ion etch RIE has been performed an ion mill may be performed to define the sensor. Then a layer of hard magnetic material such as CoPtCr and a layer of electrically conductive material such as Ta or Rh or some other material can be deposited to form the hard bias layers and seeds. A CMP process may then be performed to remove the mill resistant mask.
• The platen power applied during the reactive ion etch REI can be 70 W to 500 W. More preferably, the power applied during the reactive ion etch is between 250 W and 350 W or about 300 W.
• The inventive method of constructing a sensor advantageously avoids the formation of a bulbous or mushroom shaped mask layer, thereby preventing the shadowing effects ordinarily associated with the use of a photoresisist mask formed over an ion mill resistant mask.
• These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale.
• FIGS. 1A and 1B are cross sectional views illustrating a prior art method of manufacturing a magnetoresistive sensor;
• FIG. 2 is a schematic illustration of a disk drive system in which the present invention might be embodied;
• FIG. 3 is an ABS view of a slider illustrating the location of a magnetic head thereon;
• FIG. 4 is an ABS view of a magnetic sensor according to an embodiment of the present invention taken fromcircle4 ofFIG. 3, shown enlarged and rotated 90 degrees counterclockwise;
• FIGS. 5-9 are ABS views of a magnetoresitive sensor in various intermediate stages of manufacture; and
• FIG. 10 is flowchart summarizing a method of manufacturing a magnetoresistive sensor according to an embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
• The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.
• Referring now toFIG. 2, there is shown adisk drive200 embodying this invention. As shown inFIG. 2, at least one rotatablemagnetic disk212 is supported on aspindle214 and rotated by adisk drive motor218. The magnetic recording on each disk is in the form of annular patterns of concentric data tracks (not shown) on themagnetic disk212.
• At least oneslider213 is positioned near themagnetic disk212, eachslider213 supporting one or moremagnetic head assemblies221. As the magnetic disk rotates,slider213 moves radially in and out over thedisk surface222 so that themagnetic head assembly221 may access different tracks of the magnetic disk where desired data are written. Eachslider213 is attached to anactuator arm219 by way of asuspension215. Thesuspension215 provides a slight spring force whichbiases slider213 against thedisk surface222. Eachactuator arm219 is attached to an actuator means227. The actuator means227 as shown inFIG. 2 may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied bycontroller229.
• During operation of the disk storage system, the rotation of themagnetic disk212 generates an air bearing between theslider213 and thedisk surface222 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force ofsuspension215 and supportsslider213 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
• The various components of the disk storage system are controlled in operation by control signals generated bycontrol unit229, such as access control signals and internal clock signals. Typically, thecontrol unit229 comprises logic control circuits, storage means and a microprocessor. Thecontrol unit229 generates control signals to control various system operations such as drive motor control signals online223 and head position and seek control signals online228. The control signals online228 provide the desired current profiles to optimally move andposition slider213 to the desired data track ondisk212. Write and read signals are communicated to and from write and readheads221 by way ofrecording channel225.
• With reference toFIG. 3, the orientation of themagnetic head221 in aslider213 can be seen in more detail.FIG. 3 is an ABS view of theslider213, and as can be seen the magnetic head including an inductive write head and a read sensor, is located at a trailing edge of the slider. The above description of a typical magnetic disk storage system, and the accompanying illustration ofFIG. 2 are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders.
• With reference now toFIG. 4, amagnetoresistive sensor400 according to an embodiment of the invention includes asensor stack402. The sensor stack includes a magnetically pinnedlayer404, a magneticallyfree layer406 and a non-magnetic, electricallyconductive spacer layer408 sandwiched there between. It should be pointed out that although the sensor is being described in terms of a GMR sensor, it could also be a tunnel valve (TMR) sensor, in which case thespacer layer408 would be a non-magnetic, electrically insulating material such as alumina (Al₂O₃).
• The pinnedlayer404, may be one of several types of pinned layers, such as a simple pinned, AP pinned, self pinned or AFM pinned sensor. For purposes of simplicity, the sensor will be described herein as an AP pinned, AFM pinned sensor having anAP1 layer410,AP2 layer414, and a non-magnetic, AP coupling layer, such asRu412 sandwiched there between. The AP1 andAP2 layers410,414 can be constructed of several magnetic materials such as, for example NiFe or CoFe, and havemagnetic moments416,418 that are pinned by exchange coupling of theAP1 layer410 with a layer of antiferromagnetic material (AFM layer)420 such as PtMn.
• Thesensor stack402 is sandwiched between first and second non-magnetic, electrically insulating gap layers422,424, and may include acap layer426, such as Ta, to protect thesensor stack402 from damage during manufacturing. First and second hard bias layers428,430 extend laterally from the sides of the sensor and magnetostatically couple with thefree layer406 to bias themagnetic moment432 of the free layer in a desired direction parallel with the ABS. First and second electrically conductive leads434,436 are provided above the hard bias layers to provide a sense current to thesensor400.
• With reference now toFIGS. 5-7, a method for manufacturing thesensor400 will be described. More particularly, the method is for defining the width and stripe height of the sensor and defines the sensor with desired clean, vertical, well defined side walls. With particular reference toFIG. 5, a series ofsensor layers502 are deposited on asubstrate504, such as a non-magnetic, electrically insulating gap layer. The sensor layers502 include full film layers of material that will make up theAFM420, pinnedlayer404space408,free layer406 andcap layer426, previously described with reference toFIG. 4. Other layers may be includes as well.
• With reference toFIG. 5, a layer of material that is resistant to chemical mechanical polishing (CMP stop layer)506 may be deposited on the sensor layers. TheCMP stop layer506 may be, for example, diamond like carbon (DLC) or some other material. Then, a layer of antireflective coating material (ARC)508 is deposited. Preferably thelayer508 is a material such as Duramide, which is resistant to removal by ion milling. Thelayer508 can also be for example, hard baked photoresist. Then, a layer of photoreactive material or TIS such asphotoresist510 is spun onto thelayer510 and is photlithographically patterned to form asensor mask510. Themask510 covers an area that will become the sensor stack502 (FIG. 4), and leaves other areas uncovered.
• With reference now toFIG. 6 a reactive ion etch (RIE)600 is performed to transfer pattern of the mask onto theunderlying layers508,506. REI processes include both a chemical component and a mechanical or physical component to their total material removal performance. A RIE process is performed in a plasma chamber in an atmosphere that may contain a gas such as O₂or CO₂preferably O₂. Power is applied to the gas to strike a plasma in the chamber and a bias voltage is applied to a chuck holding the workpiece, in order to bias ions toward the workpiece. Bombardment of ions against the workpiece results in the removal of material from the workpiece. The strength of this ion bombardment determines the physical component of the material removal. A chemical reaction of the plasma or other gasses in the chamber causes a chemical component of the material removal.
• For purposes of the present invention, theRIE600 is performed in a chamber with an O₂gas plasma. As discussed in the Background of the Invention, prior art RIE processes have removed the millresistant layer508 at a faster rate than thephotoresist mask510. We have found that this is because the chemical component of the material removal preferentially attacks the millresistant layer508 more readily than thephotoresist layer510. According to the present invention, theRIE600 is performed with an increased physical component to increase the ratio ofphotoresist510 relative to the removal of millresistant material508.
• An increase in the physical component of material removal can be achieved by increasing the bias voltage applied to the chuck on which the workpiece is held within the plasma chamber. This increased bias voltage causes the ions within the plasma to strike the workpiece with increased speed and, therefore, increased power. This bias voltage is determined by the platen power. The platen power is preferably at least 70 W and may be about from 70 W to 500 W. The platen power is more preferably 250 W to 350 W, or about 300 W.
• The image transfer using the RIE process at the power settings described above results in thephotoresist mask510 having a conical shape as shown inFIG. 6, without any overhang or mushroom shape to thephotoresist layer510. This advantageously prevents shadowing during an ion mill process described below. Because thephotoresist layer510 does not have any overhang, the sensor can be accurately defined by the ion milling.
• With reference now toFIG. 7, to define the sensor amaterial removal process700, which is preferably an ion milling process is used to remove portions of thesensor layer502. Thision milling process700 can be performed sufficiently to remove all of the exposed portions of thesensor layer502 such that the ion mill extends down into thegap layer504. Preferably, however, the ion mill process terminates at some point within the level of the sensor layers502, such as within the AFM layer420 (FIG. 4). Such termination of the ion milling operation with the sensor layers502 can be called a partial mill process. The ion milling operation removes most or all of thephotoresist mask510, leaving the ionmill resitant mask508 andCMP stop layer506 relatively intact.
• With reference toFIG. 8, a layer of hardmagnetic material802 may be deposited full film to provide the hard bias layers428,430 (FIG. 4) in thefinished sensor400. One or more seed layers (not shown) may be deposited before depositing the hard magnetic material. Such seed layers may include Cr, CrMo, Si, NiTa The hardmagnetic material802, may be, for example, CoPtCr, or some other magnetic material having a high coercivity (Hc).
• After the hardmagnetic material802 has been deposited, a layer of electricallyconductive material804, such as Cu, Au, Rh or Ta is deposited to provide material for theleads434,436 (FIG. 4). An additionalCMP protection layer806 such as DLC is deposited over the electrically conductive material. Thereafter, with reference toFIG. 9, a chemical mechanical polishing process (CMP) may be performed, to remove themask508 and to planarize the leads804. TheCMP stop layer806 prevents the CMP process from damaging the leads804. The first CMPprotective layer506 protects the sensor from damage during the CMP process. After the CMP process all remaining CMPprotective material806 and506 are moved by a RIE process. Thereafter, a layer of non-magnetic, electrically insulating material, such as alumina may be deposited to form the second gap layer424 (FIG. 4).
• With reference toFIG. 10, a method for manufacturing a magnetoresistive sensor as described above will be summarized. In a step1002 a substrate is provided. This substrate may be for example analumina gap layer504. Then, in a step,1004, a series ofsensor layers502 are deposited full film. Thereafter, in a step1006 aCMP stop layer506 is deposited and in astep1008 anARC layer508 is deposited. Then, in a step,1010 a layer of photoresist material is spun on and is then photolithographically patterned to form aphotoresist mask510 covering a sensor area and leaving non-sensor areas uncovered. Thereafter, in astep1012, a material removal process is performed, such as reactive ion etch (RIE). TheRIE process600 is performed with a relatively high platen power, or at least 70 W. The platen power may be from 70 W to 500 W and is preferably 250 W to 350 W or about 300 W. TheRIE600 results in a photoresist mask having a cone or domed shape, without any mushroom overhang.
• With continued reference toFIG. 10, in astep1014 anion milling process700 is performed to remove a desired amount of sensor material that is not covered by themask508 and CMP stop506. Then, in a step1016 a layer of hardmagnetic material802 is deposited, and in a step1018 a layer of electrically conductivelead material804 is deposited. In a step1019 a layer of CMP resistant material such as diamond like Carbon DLC is deposited. Then, in a step1020 a chemical mechanical polishing process (CMP) is performed to remove the remaining millresistant mask508, and to planarize the lead material layers804. An optional second reactive ion etch process (RIE) may be performed to remove theCMP stop mask506. Then, in a step1022 a layer of non-magnetic, electrically insulating material such as alumina may be deposited to form thegap layer424.
• While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims (20)

1. A method for manufacturing a magnetoresistive sensor, comprising:

providing a substrate;

depositing a plurality of sensor layers;

depositing an antireflective coating (ARC) layer;

forming a photoresist mask on the (ARC) layer;

performing a reactive ion etch (RIE) to remove portions of the ARC layer that are not covered by the photoresist mask, the RIE being performed in a plasma chamber having a platen, the performing the RIE further comprising applying a platen power of at least 70 W.

2. A method as inclaim 1, where the platen power is between 70 W and 500 W.

3. A method as inclaim 1, wherein the platen power is between 250 W and 350 W.

4. A method as inclaim 1, wherein the platen power is about 300 W.

5. A method for manufacturing a magnetoresistive sensor, comprising:

providing a substrate;

depositing a plurality of sensor layers;

depositing a layer of material that is resistant to removal by chemical mechanical polishing (CMP stop layer);

depositing an ion mill resistant mask layer;

forming a photoresist mask on the ion mill resistant layer;

performing a reactive ion etch (RIE) to remove portions of the ion mill resistant mask that are not covered by the photoresist mask, the RIE being performed in a plasma chamber having a platen, the performing the RIE further comprising applying a platen power of at least 70 W.

6. A method as inclaim 5, wherein the CMP stop layer comprises diamond like carbon.

7. A method as inclaim 5, wherein the ion mill resistant material comprises Duramide.

8. A method as inclaim 5, wherein the platen power applied to the platen is between 70 W and 500 W.

9. A method as inclaim 5 wherein the platen power applied to the platen is between 250 W and 350 W.

10. A method as inclaim 5 wherein the platen power applied to the platen is about 300 W.

11. A method as inclaim 5 wherein the RIE is performed in a plasma chamber containing an O₂atmosphere.

12. A method as inclaim 5 further comprising, after performing the ion mill, depositing a layer of magnetically hard material.

13. A method as inclaim 12, further comprising after depositing the magnetically hard material, depositing an electrically conductive lead material.

14. A method as inclaim 5 further comprising, after performing the ion mill:

despositing a layer of magnetically hard material;

depositing an electrically conductive lead material; and

performing a chemical mechanical polish (CMP).

15. A method as inclaim 14 further comprising after performing the CMP, depositing a layer of non-magnetic, electrically insulating material.

16. A method as inclaim 5 wherein the photoresist mask is TIS.

17. A method as inclaim 5 further comprising, after performing the ion mill:

depositing a seed layer;

depositing a layer of hard magnetic material;

depositing a layer of non-magnetic, electrically conductive lead material;

performing a chemical mechanical polish; and

depositing a layer of non-magnetic, electrically insulating gap material.

18. A method as inclaim 17, wherein the non-magnetic, electrically conductive lead material comprises Rh.

19. A method as inclaim 17, wherein the non-magnetic, electrically conductive lead material comprises Ta.

20. A method as inclaim 17, wherein the non-magnetic, electrically conductive lead material comprises Au.

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