Method of manufacturing a plasmon generator

A plasmon generator including a wide portion and a narrow portion is manufactured by etching an initial plasmon generator using an etching mask. The etching mask includes a first mask layer for defining the shape of one of the narrow portion and the wide portion, and a second mask layer for defining the shape of the other of the narrow portion and the wide portion. The etching mask is formed by forming a first hard mask, a second initial mask layer and a second hard mask in this order on a first initial mask layer, and etching the first and second initial mask layers by using the first and second hard masks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a plasmon generator for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by applying near-field light thereto.

2. Description of the Related Art

With recent increases in recording density of magnetic recording devices such as magnetic disk drives, there has been demand for improved performance of thin-film magnetic heads and recording media. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).

Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.

To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, disadvantageously lowers the thermal stability of magnetization of the magnetic fine particles. To overcome this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, thereby making it difficult to perform data writing with existing magnetic heads.

As a solution to the problems described above, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are applied almost simultaneously to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.

In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator provided near the medium facing surface of the slider.

U.S. Patent Application Publication No. 2011/0170381 A1 discloses a thermally-assisted magnetic recording head including a main pole, a waveguide and a plasmon generator. The main pole has an end face located in the medium facing surface, and produces a write magnetic field from the end face. The plasmon generator has a near-field light generating surface located in the medium facing surface. The waveguide includes a core and a cladding. In this head, the surface of the core and the surface of the plasmon generator face each other with a gap interposed therebetween. This head is configured to excite surface plasmons on the plasmon generator by using evanescent light which is generated at the surface of the core from the light propagating through the core, and to generate near-field light from the excited surface plasmons at the near-field light generating surface.

A thermally-assisted magnetic recording head suffers from the problem that heat generated by the plasmon generator causes the plasmon generator to shrink and become distant from the medium facing surface, and also causes the main pole to be corroded, thereby shortening the life of the thermally-assisted magnetic recording head.

In order to achieve higher recording density, it is essential to make the track width smaller. Making the track width smaller increases the track density. In the case of a thermally-assisted magnetic recording head including a plasmon generator, the plasmon generator produces a spot of near-field light on a recording medium. The size of the spot of near-field light will hereinafter be referred to as light spot size. It has conventionally been considered that a smaller light spot size is effective for achieving higher recording density. In order to make the light spot size smaller, it is effective to reduce the width of the near-field light generating surface of the plasmon generator.

U.S. Patent Application Publication No. 2011/0170381 A1 discloses a plasmon generator including a narrow portion and a wide portion. The narrow portion includes the near-field light generating surface located in the medium facing surface. The wide portion is located farther from the medium facing surface than is the narrow portion. Here, the length of the narrow portion in a direction perpendicular to the medium facing surface will be referred to as neck height. In the plasmon generator disclosed in U.S. Patent Application Publication No. 2011/0170381 A1, heat generated at the narrow portion, particularly at the near-field light generating surface, may cause the narrow portion to shrink and become distant from the medium facing surface, and consequently cause the plasmon generator to become unable to form a sport of near-field light on the recording medium. A conceivable countermeasure to prevent this is to reduce the neck height. More specifically, reducing the neck height can enhance the heat sink effect of the wide portion to dissipate the heat generated at the narrow portion. Reducing the neck height can also increase the efficiency of generation of near-field light.

The neck height has an influence on the performance and reliability of a thermally-assisted magnetic recording head including a plasmon generator. The neck height is determined by the position of boundary between the narrow portion and the wide portion. Thus, it is of importance to control the position of boundary between the narrow portion and the wide portion. According to the conventional manufacturing method for a plasmon generator, however, it is difficult to accurately control the position of boundary between the narrow portion and the wide portion.

U.S. Pat. No. 9,472,230 B1 discloses a plasmon generator including a main body and a front protrusion protruding from the main body, and a manufacturing method for the plasmon generator. In the plasmon generator, the main body has first and second inclined surfaces located on opposite sides of the front protrusion in the track width direction. The manufacturing method for the plasmon generator includes the steps of: forming an initial plasmon generator; forming a first mask on the initial plasmon generator, the first mask being intended for defining the width of the front protrusion; forming a second mask on the initial plasmon generator and the first mask, the second mask being intended for defining the location of the first and second inclined surfaces; and etching the initial plasmon generator using the first and second masks.

The manufacturing method for the plasmon generator disclosed in U.S. Pat. No. 9,472,230 B1 uses a photoresist mask as the second mask. The photoresist mask is formed to cover part of the top surface of the initial plasmon generator and part of the first mask protruding upward from the top surface of the initial plasmon generator. The photoresist mask is thus formed on a non-flat surface. This manufacturing method thus has a disadvantage in that the shape of the photoresist mask tends to become deformed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a manufacturing method for a plasmon generator including a narrow portion and a wide portion, the manufacturing method enabling accurate control of the position of boundary between the narrow portion and the wide portion.

A plasmon generator manufactured by a manufacturing method of the present invention includes a wide portion, and a narrow portion protruding from the wide portion. The narrow portion has a proximal end which is a boundary with the wide portion, and a near-field light generating surface which is a protruding end. The proximal end is located at a distance from an imaginary plane including the near-field light generating surface. The wide portion is greater than the narrow portion in maximum width in a first direction parallel to the imaginary plane. The plasmon generator is configured to excite a surface plasmon from light on the wide portion, and to generate near-field light from the surface plasmon at the near-field light generating surface.

The manufacturing method for the plasmon generator of the present invention includes the steps of: forming an initial plasmon generator; forming an etching mask on the initial plasmon generator, the etching mask including a first mask layer for defining the shape of one of the narrow portion and the wide portion and a second mask layer for defining the shape of the other of the narrow portion and the wide portion; and etching the initial plasmon generator into the plasmon generator by using the etching mask.

The step of forming the etching mask includes the steps of: forming a first initial mask layer; forming a first initial hard mask on the first initial mask layer; forming a first resist mask on the first initial hard mask by photolithography, the first resist mask being intended for defining the shape of the first mask layer; etching the first initial hard mask into a first hard mask by using the first resist mask; forming a second initial mask layer on the first initial mask layer and the first hard mask; forming a second initial hard mask on the second initial mask layer; forming a second resist mask on the second initial hard mask by photolithography, the second resist mask being intended for defining the shape of the second mask layer; etching the second initial hard mask into a second hard mask by using the second resist mask; and etching the first and second initial mask layers into the first and second mask layers, respectively, by using the first and second hard masks.

In the manufacturing method of the present invention, the first initial mask layer may include a first carbon layer. The second initial mask layer may be a second carbon layer. The first initial mask layer may include an etching stopper layer, and a layer to be etched which is formed on the etching stopper layer. In such a case, the step of etching the first and second initial mask layers may etch the layer to be etched and the second initial mask layer until the etching stopper layer is exposed.

In the manufacturing method of the present invention, the step of etching the first initial hard mask may be performed by employing reactive ion etching or ion beam etching.

In the manufacturing method of the present invention, the step of etching the second initial hard mask may be performed by employing reactive ion etching or ion beam etching.

In the manufacturing method of the present invention, the step of etching the first and second initial mask layers may be performed by employing reactive ion etching.

In the manufacturing method of the present invention, the step of etching the initial plasmon generator may be performed by employing ion beam etching.

In the manufacturing method of the present invention, the wide portion may have a first end face portion and a second end face portion located with the proximal end of the narrow portion therebetween. The first and second end face portions are parallel to the imaginary plane.

In the manufacturing method of the present invention, the narrow portion may have a first side surface and a second side surface which are perpendicular to the first direction.

The manufacturing method for the plasmon generator of the present invention enables accurate formation of each of the first mask layer and the second mask layer of the etching mask. The present invention thus enables accurate control of the position of boundary between the narrow portion and the wide portion of the plasmon generator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Preferred embodiments of the present invention will now be described in detail with reference to the drawings. First, reference is made toFIG. 3andFIG. 4to describe the configuration of a thermally-assisted magnetic recording head of a first embodiment of the invention.FIG. 3is a cross-sectional view showing the configuration of the thermally-assisted magnetic recording head.FIG. 4is a front view showing the medium facing surface of the thermally-assisted magnetic recording head.

The thermally-assisted magnetic recording head of the present embodiment is intended for perpendicular magnetic recording, and is incorporated in a slider configured to fly over the surface of a rotating recording medium90. The slider has a medium facing surface80configured to face a recording medium90. When the recording medium90rotates, an airflow passing between the recording medium90and the slider causes a lift to be exerted on the slider. The lift causes the slider to fly over the surface of the recording medium90.

As shown inFIG. 3, the thermally-assisted magnetic recording head has the medium facing surface80. Here, we define X direction, Y direction, and Z direction as follows. The X direction is the direction across the tracks of the recording medium90, i.e., the track width direction. The Y direction is a direction perpendicular to the medium facing surface80. The Z direction is the direction of travel of the recording medium90as viewed from the slider. The X, Y, and Z directions are orthogonal to one another.

As shown inFIG. 3andFIG. 4, the thermally-assisted magnetic recording head includes: a substrate1formed of a ceramic material such as aluminum oxide-titanium carbide (Al2O3—TiC) and having a top surface1a; an insulating layer2formed of an insulating material and lying on the top surface1aof the substrate1; a bottom shield layer3formed of a magnetic material and lying on the insulating layer2; and an insulating layer4lying on the insulating layer2and surrounding the bottom shield layer3. The insulating layers2and4are formed of alumina (Al2O3), for example. The Z direction is also a direction perpendicular to the top surface1aof the substrate1.

The thermally-assisted magnetic recording head further includes: a bottom shield gap film5which is an insulating film lying on the top surfaces of the bottom shield layer3and the insulating layer4; a magnetoresistive (MR) element6serving as a read element lying on the bottom shield gap film5; two leads (not illustrated) connected to the MR element6; and a top shield gap film7which is an insulating film disposed on the MR element6.

An end of the MR element6is located in the medium facing surface80. The MR element6may be an element formed of a magneto-sensitive film that exhibits a magnetoresistive effect, such as an anisotropic magnetoresistive (AMR) element, a giant magnetoresistive (GMR) element, or a tunneling magnetoresistive (TMR) element. The GMR element may be of either the current-in-plane (CIP) type in which a current used for detecting magnetic signals is fed in a direction generally parallel to the planes of layers constituting the GMR element or the current-perpendicular-to-plane (CPP) type in which the current used for detecting magnetic signals is fed in a direction generally perpendicular to the planes of layers constituting the GMR element.

The thermally-assisted magnetic recording head further includes a top shield layer8formed of a magnetic material and lying on the top shield gap film7, and an insulating layer9lying on the top shield gap film7and surrounding the top shield layer8. The insulating layer9is formed of alumina, for example. The parts from the bottom shield layer3to the top shield layer8constitute a read head unit.

The thermally-assisted magnetic recording head further includes a nonmagnetic layer10formed of a nonmagnetic material and lying on the top shield layer8and the insulating layer9, and a write head unit lying on the nonmagnetic layer10. The nonmagnetic layer10is formed of alumina, for example.

The write head unit includes a return pole layer11formed of a magnetic material and lying on the nonmagnetic layer10, and an insulating layer12lying on the nonmagnetic layer10and surrounding the return pole layer11. The insulating layer12is formed of alumina, for example.

The write head unit further includes two coupling sections13A and13B located away from the medium facing surface80and lying on a part of the return pole layer11, an insulating layer14lying on another part of the return pole layer11and on the insulating layer12, and a coil15lying on the insulating layer14. The coupling sections13A and13B are formed of a magnetic material. Each of the coupling sections13A and13B includes a first layer lying on the return pole layer11, and a second, a third, and a fourth layer stacked in this order on the first layer. The first layer of the coupling section13A and the first layer of the coupling section13B are arranged to be adjacent in the track width direction (the X direction). The coil15is wound around the first layers of the coupling sections13A and13B. The coil15is formed of a conductive material such as copper. The insulating layer14is formed of alumina, for example.

The write head unit further includes: an insulating layer16located in the space between every adjacent turns of the coil15; an insulating layer17around the coil15; and an insulating layer18on the coil15and the insulating layers16and17. The insulating layer16is formed of photoresist, for example. The insulating layers17and18are formed of alumina, for example. The first layers of the coupling sections13A and13B are embedded in the insulating layers14and17.

The write head unit further includes a waveguide including a core20and a cladding, the core20allowing light to propagate therethrough, the cladding being provided around the core20. As shown inFIG. 3in particular, the core20has a front end face20afacing toward the medium facing surface80, an evanescent light generating surface20bwhich is a top surface, a bottom surface20c, and two side surfaces.

The cladding includes cladding layers19,21and22. The cladding layer19lies on the insulating layer18. The core20lies on the cladding layer19. The cladding layer21lies on the cladding layer19and surrounds the core20. The cladding layer22is disposed over the evanescent light generating surface20bof the core20and the top surface of the cladding layer21.

The core20is formed of a dielectric material that transmits laser light to be used for generating near-field light. The laser light emitted from a non-illustrated laser diode enters the core20and propagates through the core20. The cladding layers19,21and22are each formed of a dielectric material that has a refractive index lower than that of the core20. For example, the core20may be formed of tantalum oxide such as Ta2O5or silicon oxynitride (SiON), whereas the cladding layers19,21and22may be formed of silicon oxide (SiO2) or alumina.

The second layers of the coupling sections13A and13B are embedded in the insulating layer18and the cladding layer19. The third layers of the coupling sections13A and13B are embedded in the cladding layer21. The third layer of the coupling section13A and the third layer of the coupling section13B are located on opposite sides of the core20in the track width direction (the X direction), each being at a distance from the core20.

The write head unit further includes a plasmon generator40according to the present embodiment. The plasmon generator40lies on the cladding layer22in the vicinity of the medium facing surface80. The plasmon generator40is configured to excite surface plasmons on the principle to be described later. The plasmon generator40is formed of, for example, one of Au, Ag, Al, Cu, Pd, Pt, Rh and Ir, or an alloy composed of two or more of these elements. The shape of the plasmon generator40will be described in detail later.

The write head unit further includes a dielectric layer23lying on the cladding layer22and surrounding the plasmon generator40, a dielectric layer24disposed to cover the dielectric layer23and part of the plasmon generator40, and a dielectric layer25lying on the plasmon generator40and the dielectric layer24. The dielectric layer24has a top surface and an end face closest to the medium facing surface80. The distance from the medium facing surface80to any point on the aforementioned end face of the dielectric layer24decreases with decreasing distance from the point to the top surface1aof the substrate1. The dielectric layers23to25are formed of alumina, for example.

The write head unit further includes a main pole26formed of a magnetic material. The main pole26is disposed on the dielectric layer25in such a manner as to ride over the aforementioned end face and part of the top surface of the dielectric layer24. The plasmon generator40lies between the core20and the main pole26. The main pole26has an end face located in the medium facing surface80.

The write head unit further includes a dielectric layer27disposed around the main pole26. The fourth layers of the coupling sections13A and13B are embedded in the cladding layer22and the dielectric layers23to25and27. The top surfaces of the main pole26, the dielectric layer27and the fourth layers of the coupling sections13A and13B are even with each other. The dielectric layer27is formed of silicon oxide, for example.

The write head unit further includes a coil28lying on the dielectric layer27, an insulating layer29disposed to cover the coil28, and a yoke layer30formed of a magnetic material and lying on the main pole26, the coupling sections13A and13B, the dielectric layer27and the insulating layer29. The yoke layer30magnetically couples the main pole26to the coupling sections13A and13B. The coil28is wound around portions of the yoke layer30that are located on the coupling sections13A and13B. The coil28is formed of a conductive material such as copper. The insulating layer29is formed of photoresist, for example.

The thermally-assisted magnetic recording head further includes a protective layer31disposed to cover the write head unit. The protective layer31is formed of alumina, for example.

As has been described, the thermally-assisted magnetic recording head of the present embodiment includes the medium facing surface80, the read head unit, and the write head unit. The read head unit and the write head unit are stacked on the substrate1. The write head unit is located on the trailing side, i.e., the front side in the direction of travel of the recording medium90(the Z direction), relative to the read head unit.

The write head unit includes the coils15and28, the main pole26, the waveguide, and the plasmon generator40. The waveguide includes the core20and the cladding. The cladding includes the cladding layers19,21and22.

The write head unit further includes the return pole layer11, the coupling sections13A and13B, and the yoke layer30. The coils15and28produce magnetic fields corresponding to data to be written on the recording medium90. The return pole layer11, the coupling sections13A and13B, the yoke layer30and the main pole26form a magnetic path for passing magnetic fluxes corresponding to the magnetic fields produced by the coils15and28. The coils15and28are connected in series or in parallel so that the magnetic flux corresponding to the magnetic field produced by the coil15and the magnetic flux corresponding to the magnetic field produced by the coil28flow in the same direction through the main pole26. The main pole26passes the magnetic flux corresponding to the magnetic field produced by the coil15and the magnetic flux corresponding to the magnetic field produced by the coil28, and produces a write magnetic field for use to write data on the recording medium90by means of a perpendicular magnetic recording system.

The plasmon generator40according to the present embodiment will now be described in detail with reference toFIGS. 1 and 2.FIG. 1is a perspective view showing the plasmon generator40.FIG. 2is a plan view showing the plasmon generator40.FIGS. 1 and 2also show the X, Y and Z directions mentioned previously.

As shown inFIGS. 1 and 2, the plasmon generator40includes a wide portion42, and a narrow portion41protruding from the wide portion42. The narrow portion41has a proximal end41bwhich is the boundary with the wide portion42, and a near-field light generating surface41awhich is a protruding end. The near-field light generating surface41ais located in the medium facing surface80. The near-field light generating surface41agenerates near-field light on the principle to be described later.

As shown inFIGS. 1 and 2, let us assume an imaginary plane P including the near-field light generating surface41a. The imaginary plane P is also the XZ plane including the near-field light generating surface41a. The medium facing surface80is included in the imaginary plane P. For example, the plasmon generator40is rectangular in cross section parallel to the imaginary plane P. The thickness (the dimension in the Z direction) of the plasmon generator40is generally constant regardless of distance from the imaginary plane P.

The proximal end41bof the narrow portion41is located at a distance from the imaginary plane P. In the present embodiment, the narrow portion41further has a first side surface41cand a second side surface41dlocated at opposite ends of the narrow portion41in the track width direction (the X direction). The first and second side surfaces41cand41dmay be perpendicular to the X direction. In such a case, the width of the narrow portion41in the X direction is constant regardless of distance from the medium facing surface80. The X direction is parallel to the imaginary plane P, and corresponds to the first direction in the present invention.

The width (the dimension in the X direction or the track width direction) of the near-field light generating surface41ais defined by the width of the narrow portion41in the medium facing surface80. The width of the near-field light generating surface41afalls within the range of 5 to 70 nm, for example. The height (the dimension in the Z direction) of the near-field light generating surface41ais defined by the height of the narrow portion41in the medium facing surface80. The height of the near-field light generating surface41afalls within the range of 5 to 40 nm, for example.

As shown inFIGS. 1 and 2, the wide portion42is greater than the narrow portion41in maximum width in the X direction. In the present embodiment, the wide portion42has a first end face portion42a, a second end face portion42band a bottom surface42c, the first and second end face portions42aand42bbeing located with the proximal end41bof the narrow portion41therebetween. The first and second end face portions42aand42bare parallel to the imaginary plane P. When the first and second side surfaces41cand41dof the narrow portion41are perpendicular to the X direction, the angle that the first end face portion42aforms with the first side surface41cand the angle that the second end face portion42bforms with the second side surface41dare both 90°.

Now, the principle of generation of near-field light in the present embodiment and the principle of thermally-assisted magnetic recording using near-field light will be described in detail. Laser light emitted from a laser diode (not illustrated) enters the core20. As shown inFIG. 3, the laser light50propagates through the core20toward the medium facing surface80, and reaches the vicinity of the plasmon generator40. The evanescent light generating surface20bof the core20generates evanescent light from the laser light50propagating through the core20. More specifically, the laser light50is totally reflected at the evanescent light generating surface20b, and this causes the evanescent light generating surface20bto generate evanescent light permeating into the cladding layer22. In the plasmon generator40, surface plasmons are excited on the bottom surface42cof the wide portion42through coupling with the aforementioned evanescent light. The excited surface plasmons propagate to the near-field light generating surface41aof the narrow portion41, and the near-field light generating surface41aof the narrow portion41generates near-field light from those surface plasmons.

The near-field light generated at the near-field light generating surface41ais projected toward the recording medium90, reaches the surface of the recording medium90and heats a portion of the magnetic recording layer of the recording medium90. This lowers the coercivity of the portion of the magnetic recording layer. In thermally-assisted magnetic recording, the portion of the magnetic recording layer with the lowered coercivity is subjected to a write magnetic field produced by the main pole26for data writing.

A manufacturing method for the thermally-assisted magnetic recording head of the present embodiment will now be described with reference toFIGS. 3 and 4. The manufacturing method for the thermally-assisted magnetic recording head includes the steps of: forming components of a plurality of thermally-assisted magnetic recording heads, except the substrates1, on a wafer that includes portions to become the substrates1of the thermally-assisted magnetic recording heads, thereby fabricating a substructure including a plurality of pre-head portions arranged in rows, the plurality of pre-head portions becoming individual thermally-assisted magnetic recording heads later; and cutting the substructure to separate the plurality of pre-head portions from each other and forming the medium facing surface80for each of the plurality of pre-head portions (this step will be referred to as the step of forming the medium facing surface80). A plurality of thermally-assisted magnetic recording heads are produced in this manner.

The manufacturing method for the thermally-assisted magnetic recording head of the present embodiment will be described in more detail below with attention focused on a single thermally-assisted magnetic recording head. In the manufacturing method for the thermally-assisted magnetic recording head, first, the insulating layer2is formed on the substrate1. The bottom shield layer3is then formed on the insulating layer2. Then, the insulating layer4is formed to cover the bottom shield layer3. The insulating layer4is then polished by, for example, chemical mechanical polishing (hereinafter referred to as CMP), until the bottom shield layer3is exposed.

Then, the bottom shield gap film5is formed over the bottom shield layer3and the insulating layer4. On the bottom shield gap film5, the MR element6and two leads (not illustrated) connected to the MR element6are then formed. Then, the top shield gap film7is formed to cover the MR element6and the leads. The top shield layer8is then formed on the top shield gap film7. Then, the insulating layer9is formed to cover the top shield layer8. The insulating layer9is then polished by, for example, CMP, until the top shield layer8is exposed.

Then, the nonmagnetic layer10is formed over the top shield layer8and the insulating layer9. The return pole layer11is then formed on the nonmagnetic layer10. Then, the insulating layer12is formed to cover the return pole layer11. The insulating layer12is then polished by, for example, CMP, until the return pole layer11is exposed. Then, the insulating layer14is formed over the return pole layer11and the insulating layer12.

The insulating layer14is then selectively etched to form therein two openings for exposing the top surface of the return pole layer11. Then, the first layers of the coupling sections13A and13B are formed on the return pole layer11at the positions of the two openings. The coil15is then formed on the insulating layer14. The insulating layer16is then formed in the space between every adjacent turns of the coil15. Then, the insulating layer17is formed over the entire top surface of the stack. The insulating layer17is then polished by, for example, CMP, until the first layers of the coupling sections13A and13B, the coil15, and the insulating layer16are exposed. The insulating layer18is then formed over the first layers of the coupling sections13A and13B, the coil15, and the insulating layers16and17.

The insulating layer18is then selectively etched to form therein two openings for exposing the top surfaces of the first layers of the coupling sections13A and13B. The second layers of the coupling sections13A and13B are then formed on the first layers of the coupling sections13A and13B. Then, the cladding layer19is formed to cover the second layers of the coupling sections13A and13B. The cladding layer19is then polished by, for example, CMP, until the second layers of the coupling sections13A and13B are exposed. The third layers of the coupling sections13A and13B are then formed on the second layers of the coupling sections13A and13B.

Then, the core20is formed on the cladding layer19. The cladding layer21is then formed over the entire top surface of the stack. The cladding layer21is then polished by, for example, CMP, until the core20and the third layers of the coupling sections13A and13B are exposed. Then, the cladding layer22is formed over the entire top surface of the stack. The plasmon generator40is then formed on the cladding layer22. The step of forming the plasmon generator40will be described in detail later.

Next, the dielectric layer23is formed to cover the plasmon generator40. The dielectric layer23is then polished by, for example, CMP, until the plasmon generator40is exposed. Then, the dielectric layer24is formed on the dielectric layer23and part of the plasmon generator40. The dielectric layer25is then formed on the plasmon generator40and the dielectric layer24. The cladding layer22and the dielectric layers23to25are then selectively etched to form therein openings for exposing the top surfaces of the third layers of the coupling sections13A and13B. Then, the main pole26is formed on the dielectric layer25, and the fourth layers of the coupling sections13A and13B are formed on the third layers of the coupling sections13A and13B. The dielectric layer27is then formed to cover the main pole26and the fourth layers of the coupling sections13A and13B. The dielectric layer27is then polished by, for example, CMP, until the main pole26and the fourth layers of the coupling sections13A and13B are exposed.

Next, the coil28is formed on the dielectric layer27. Then, the insulating layer29is formed to cover the coil28. The yoke layer30is then formed over the main pole26, the fourth layers of the coupling sections13A and13B, the dielectric layer27and the insulating layer29. The protective layer31is then formed to cover the yoke layer30. Wiring, terminals, and other components are then formed on the top surface of the protective layer31. When the substructure is completed thus, the step of forming the medium facing surface80is performed. A protective film for covering the medium facing surface80may be formed thereafter. Being provided with the medium facing surface80, each pre-head portion becomes a thermally-assisted magnetic recording head.

The step of forming the medium facing surface80includes the step of polishing the surface of each pre-head portion that has resulted from cutting the substructure, and the step of forming a rail on the polished surface for allowing the slider to fly.

The step of forming the plasmon generator40will now be described. The following descriptions include descriptions of the manufacturing method for the plasmon generator40according to the present embodiment. The step of forming the plasmon generator40includes the steps of: forming an initial plasmon generator; forming an etching mask on the initial plasmon generator; and etching the initial plasmon generator into the plasmon generator40by using the etching mask. The etching mask includes a first mask layer for defining the shape of one of the narrow portion41and the wide portion42, and a second mask layer for defining the shape of the other of the narrow portion41and the wide portion42. For the present embodiment, descriptions will be given of the case where the first mask layer defines the shape of the narrow portion41and the second mask layer defines the shape of the wide portion42.

Reference is now made toFIGS. 5A to 12Cto describe the step of forming the plasmon generator40in detail.FIGS. 5A to 12Ceach show a stack of layers formed in the process of manufacturing the thermally-assisted magnetic recording head. Fig. nA (n is an integer between 5 and 12 inclusive) shows a cross section of the stack taken at the location at which the medium facing surface80is to be formed. Fig. nB shows a cross section that intersects the end face of the main pole26and that is perpendicular to the medium facing surface80and to the top surface1aof the substrate1. Fig. nC shows the top surface of part of the stack. Figs. nA and nB, excludingFIGS. 12A and 12B, omit the illustration of portions that are located on the substrate-1side relative to the initial plasmon generator.FIGS. 12A and 12Bomit the illustration of portions that are located on the substrate-1side relative to the cladding layer22.FIG. 11Dis a perspective view of part of the stack.

FIGS. 5A to 5Cshow a step following the formation of the cladding layer22. In this step, first, the initial plasmon generator40P is formed on the cladding layer22. Then, a first initial mask layer61P is formed on the initial plasmon generator40P. Then, a first initial hard mask62P is formed on the first initial mask layer61P.

The first initial mask layer61P may include an etching stopper layer61A, and a layer to be etched61B formed on the etching stopper layer61A. Now, a description will be given of requirements pertaining to the materials of the etching stopper layer61A, the layer to be etched61B and the first initial hard mask62P and etching conditions for each of the step of completing the etching mask and the step of etching the first initial hard mask62P to be described later.

The step of completing the etching mask is performed by employing reactive ion etching (hereinafter referred to as RIE). What is required for this step is to select a combination of materials of the etching stopper layer61A, the layer to be etched61B and the first initial hard mask62P and etching conditions so as to achieve a sufficiently higher etching rate for the layer to be etched61B than for the etching stopper layer61B and the first initial hard mask62P. Such a requirement will be referred to as the first requirement.

The step of etching the first initial hard mask62P is performed by employing RIE or ion beam etching (hereinafter referred to as IBE). What is required in the case of employing RIE for the step of etching the first initial hard mask62P is to select a combination of materials of the layer to be etched61B and the first initial hard mask62P and etching conditions so as to achieve a sufficiently higher etching rate for the first initial hard mask62P than for the layer to be etched61B. Such a requirement will be referred to as the second requirement.

The first and second requirements must be met where the step of etching the first initial hard mask62P is performed by employing RIE. Depending on the etching conditions for each of the step of completing the etching mask and the step of etching the first initial hard mask62P, examples of combinations of materials meeting the first and second requirements include a combination of carbon as the material of the layer to be etched61B and Ta, alumina or silicon oxide as the material of the etching stopper layer61A and the first initial hard mask62P. The etching conditions for each of the step of completing the etching mask and the step of etching the first initial hard mask62P will be described later.

Where the step of etching the first initial hard mask62P is performed by employing IBE, only the first requirement needs to be met. Depending on the etching conditions for the step of completing the etching mask, examples of combinations of materials meeting the first requirement include a combination of carbon, silicon oxide, alumina, tantalum oxide or aluminum alloy as the material of the layer to be etched61B and Ru, NiFe or NiCr as the material of the etching stopper layer61A and the first initial hard mask62P.

Carbon is particularly preferable as the material of the layer to be etched61B. Hereinafter, the layer to be etched61B as it is formed of carbon will be referred to as the first carbon layer.

FIGS. 6A to 6Cshow the next step. In this step, a first resist mask63for defining the shape of the first mask layer, i.e., the shape of the narrow portion41, is formed on the first initial hard mask62P by photolithography. The planar shape of the first resist mask63corresponds to that of the narrow portion41. The planar shape refers to the shape viewed from above. The first resist mask63has a wall face63afor defining the position of the first side surface41cof the narrow portion41and a wall face63bfor defining the position of the second side surface41dof the narrow portion41. The first resist mask63does not have any undercut that a resist mask used in a lift-off process would have. The first resist mask63is preferably composed of a single layer of photoresist.

FIGS. 7A to 7Cshow the next step. In this step, first, the first initial hard mask62P is etched into a first hard mask62by using the first resist mask63. The first hard mask62is provided with an end62awhose position is defined by the wall face63aof the first resist mask63, and an end62bwhose position is defined by the wall face63bof the first resist mask63. The first resist mask63is then removed.

As mentioned above, the step of etching the first initial hard mask62P is performed by employing RIE or IBE. In the case of employing the aforementioned example of combinations of materials meeting the first and second requirements, an example of etching conditions for the step of etching the first initial hard mask62P is the use of a gas containing Cl2and BCl3or a gas containing CF4as the etching gas.

FIGS. 8A to 8Cshow the next step. In this step, first, a second initial mask layer64P is formed on the first initial mask layer61P and the first hard mask62. Then, a second initial hard mask65P is formed on the second initial mask layer64P.

Now, a description will be given of requirements pertaining to the materials of the second initial mask layer64P and the second initial hard mask65P and etching conditions for each of the step of completing the etching mask and the step of etching the second initial hard mask65P to be described later.

What is required for the step of completing the etching mask is to select a combination of materials of the second initial mask layer64P and the second initial hard mask65P and etching conditions so as to achieve a sufficiently higher etching rate for the second initial mask layer64P than for the second initial hard mask65P. Such a requirement will be referred to as the third requirement.

The step of etching the second initial hard mask65P is performed by employing RIE or IBE, as is the step of etching the first initial hard mask62P. What is required in the case of employing RIE for the step of etching the second initial hard mask65P is to select a combination of materials of the second initial mask layer64P and the second initial hard mask65P and etching conditions so as to achieve a sufficiently higher etching rate for the second initial hard mask65P than for the second initial mask layer64P. Such a requirement will be referred to as the fourth requirement.

The third and fourth requirements must be met where the step of etching the second initial hard mask65P is performed by employing RIE. Depending on the etching conditions for each of the step of completing the etching mask and the step of etching the second initial hard mask65P, examples of combinations of materials meeting the third and fourth requirements include a combination of carbon as the material of the second initial mask layer64P and Ta, alumina or silicon oxide as the material of the second initial hard mask65P. The etching conditions for each of the step of completing the etching mask and the step of etching the second initial hard mask65P will be described later.

Where the step of etching the second initial hard mask65P is performed by employing IBE, only the third requirement needs to be met. Depending on the etching conditions for the step of completing the etching mask, examples of combinations of materials meeting the third requirement include a combination of carbon, silicon oxide, alumina, tantalum oxide or aluminum alloy as the material of the second initial mask layer64P and Ru, NiFe or NiCr as the material of the second initial hard mask65P.

Carbon is particularly preferable as the material of the second initial mask layer64P. Hereinafter, the second initial mask layer64P as it is formed of carbon will be referred to as the second carbon layer.

FIGS. 9A to 9Cshow the next step. In this step, a second resist mask66for defining the shape of the second mask layer, i.e., the shape of the wide portion42, is formed on the second initial hard mask65P by photolithography. The planar shape of the second resist mask66corresponds to that of the wide portion42. The second resist mask66has a wall face66afor defining the position of the first and second end face portions42aand42bof the wide portion42. The second resist mask66does not have any undercut that a resist mask used in a lift-off process would have. The second resist mask66is preferably composed of a single layer of photoresist.

The shape of the second resist mask66is depicted in a simplified manner inFIGS. 9B and 9C. In other figures illustrating steps subsequent to this step, the shape of any portion defined by the second resist mask66is also depicted in a simplified manner.

FIGS. 10A to 10Cshow the next step. In this step, first, the second initial hard mask65P is etched into a second hard mask65by using the second resist mask66. The second hard mask65is provided with an end65awhose position is defined by the wall face66aof the second resist mask66. The end65ais located to intersect the ends62aand62bof the first hard mask62as viewed from above. The second resist mask66is then removed.

As previously mentioned, the step of etching the second initial hard mask65P is performed by employing RIE or IBE. In the case of employing the aforementioned example of combinations of materials meeting the third and fourth requirements, an example of the etching conditions for the step of etching the second initial hard mask65P is the use of a gas containing Cl2and BCl3or a gas containing CF4as the etching gas.

FIGS. 11A to 11Dshow the next step. This step is to complete the etching mask. In this step, the first and second initial mask layers61P and64P are etched into the first and second mask layers61and64, respectively, by using the first and second hard masks62and65. The etching mask60is thereby completed.FIG. 11Comits the illustration of the first and second hard masks62and65. The step of forming the etching mask60in the present embodiment includes a series of steps illustrated inFIG. 5AthroughFIG. 11D.

In the case where the first initial mask layer61P includes the etching stopper layer61A and the layer to be etched61B, the step of etching the first and second initial mask layers61P and64P etches the second initial mask layer64P and the layer to be etched61B until the etching stopper layer61A is exposed. In such a case, the first mask layer61is composed of the etching stopper layer61A and the layer61B etched.

The etching mask60is provided with a wall face60awhose position is defined by the end62aof the first hard mask62, a wall face60bwhose position is defined by the end62bof the first hard mask62, and a wall face60cwhose position is defined by the end65aof the second hard mask65. The wall faces60aand60bbelong to the first mask layer61. The wall face60cextends across the first mask layer61and the second mask layer64. The wall face60adefines the position of the first side surface41cof the narrow portion41to be formed later. The wall face60bdefines the position of the second side surface41dof the narrow portion41to be formed later. The wall face60cincludes a first portion60c1defining the position of the first end face portion42aof the wide portion42to be formed later, and a second portion60c2defining the position of the second end face portion42bof the wide portion42to be formed later.

As previously mentioned, this step is performed by employing RIE. Where the first initial mask layer61P includes the first carbon layer and the second initial mask layer64P is the second carbon layer, an example of the etching conditions for this step is the use of a gas containing O2as the etching gas.

FIGS. 12A to 12Cshow the next step. In this step, first, the initial plasmon generator40P is etched into the plasmon generator40by using the etching mask60. In the case where the first mask layer61(the first initial mask layer61P) includes the etching stopper layer61A, the etching stopper layer61A is also etched when the initial plasmon generator40P is etched. The etching mask60is then removed.

The step of etching the initial plasmon generator40P is performed by employing IBE. In this case, the etching mask60and the first and second hard masks62and65are also etched when the initial plasmon generator40P is etched.FIGS. 12A to 12Cillustrate an example in which the second mask layer64, the first hard mask62and the second hard mask65have been completely removed by etching.

As described above, in the manufacturing method for the plasmon generator40according to the present embodiment, the initial plasmon generator40P is etched into the plasmon generator40by using the etching mask60. According to the present embodiment, it is possible to accurately form the first mask layer61and the second mask layer64of the etching mask60through the use of the first and second hard masks62and65. The present embodiment thus enables accurate control of the shape of the narrow portion41and the wide portion42of the plasmon generator40, and consequently, enables accurate control of the position of boundary between the narrow portion41and the wide portion42.

In the present embodiment, in particular, the wide portion42has the first end face portion42aand the second end face portion42blocated with the proximal end41bof the narrow portion41therebetween. The position of boundary between the narrow portion41and the wide portion42is defined by the position of the first and second end face portions42aand42b. According to the present embodiment, the second mask layer64serves to accurately control the position of the first and second end face portions42aand42b. The present embodiment thus enables accurate control of the position of boundary between the narrow portion41and the wide portion42.

A mask formed of carbon is advantageous over a mask formed of a material other than carbon in that it has high resistance to dry etching such as IBE and that it is easily removable by ashing. The present embodiment provides these advantages when the first initial mask layer61P includes the first carbon layer and the second initial mask layer64P is the second carbon layer.

In the present embodiment, the second resist mask66is formed on a flat surface. This enables accurate formation of the second resist mask66. According to the present embodiment, this also contributes to accurate control of the position of boundary between the narrow portion41and the wide portion42.

Now, the effect of the manufacturing method for the plasmon generator40according to the present embodiment will be described in more detail in comparison with a manufacturing method for a plasmon generator of a comparative example. First, the manufacturing method for the plasmon generator of the comparative example will be described with reference toFIGS. 13A to 16C.FIGS. 13A to 16Ceach show a stack of layers formed in the process of manufacturing a thermally-assisted magnetic recording head. Fig. nA (n is an integer between 13 and 16 inclusive) shows a cross section of the stack taken at the location at which the medium facing surface80is to be formed. Fig. nB shows a cross section that intersects the end face of the main pole26and that is perpendicular to the medium facing surface80and to the top surface1aof the substrate1. Fig. nC shows the top surface of part of the stack. Figs. nA and nB, excludingFIGS. 16A and 16B, omit the illustration of portions that are located on the substrate-1side relative to the initial plasmon generator.FIGS. 16A and 16Bomit the illustration of portions below the cladding layer22.

The manufacturing method for the plasmon generator of the comparative example proceeds through the same steps as those of the manufacturing method for the plasmon generator40according to the present embodiment up to the step of forming the first hard mask. The first initial mask layer, the etching stopper layer, the layer to be etched and the first hard mask of the comparative example will be denoted by the symbols71P,71A,71B and72, respectively. Like the first hard mask62of the present embodiment, the first hard mask72of the comparative example is provided with an end72awhose position is defined by the wall face63aof the first resist mask63and an end72bwhose position is defined by the wall face63bof the first resist mask63.

FIGS. 13A to 13Cshow a step following the formation of the first hard mask72. In this step, a resist mask73for defining the shape of the wide portion42is formed on the first initial mask layer71P and the first hard mask72by photolithography. The resist mask73is a resist mask to be used in a lift-off process, and has an undercut. As shown inFIGS. 13A and 13B, the resist mask73includes a lower layer73A and an upper layer73B. The lower layer73A has an opening73Aa shaped to correspond to the planar shape of the wide portion42. The upper layer73B has an opening73Ba shaped to correspond to the planar shape of the wide portion42. The opening73Aa is larger than the opening73Ba in planar shape.

FIGS. 14A to 14Cshow the next step. In this step, first, a second initial hard mask is formed over the entire top surface of the stack. The second initial hard mask is formed of the same material as the first hard mask72. Then, the resist mask73is lifted off. As a result, the remaining second initial hard mask makes a second hard mask74. The second hard mask74has an end74afor defining the position of the first and second end face portions42aand42bof the wide portion42.

FIGS. 15A to 15Cshow the next step. In this step, the first initial mask layer71P is etched by using the first and second hard masks72and74. This makes the first initial mask layer71P into an etching mask70. The etching conditions for the first initial mask layer71P are the same as those for the first and second initial mask layers61P and64P of the present embodiment. The etching mask70is composed of the etching stopper layer71A and the layer71B etched.

The etching mask70is provided with a wall face70awhose position is defined by the end72aof the first hard mask72, a wall face70bwhose position is defined by the end72bof the first hard mask72, and a wall face70cwhose position is defined by the end74aof the second hard mask74. The wall face70adefines the position of the first side surface41cof the narrow portion41to be formed later. The wall face70bdefines the position of the second side surface41dof the narrow portion41to be formed later. The wall face70cincludes a first portion70c1defining the position of the first end face portion42aof the wide portion42to be formed later, and a second portion70c2defining the position of the second end face portion42bof the wide portion42to be formed later.

FIGS. 16A to 16Cshow the next step. In this step, first, the initial plasmon generator40P is etched into the plasmon generator40by using the etching mask70. The step of etching the initial plasmon generator40P is performed by employing IBE. The etching stopper layer71A is also etched when the initial plasmon generator40P is etched. The etching mask70is then removed.

The comparative example cannot accurately control the position of boundary between the narrow portion41and the wide portion42. This problem will be discussed with reference toFIG. 17.FIG. 17is a cross-sectional view showing a stack after the formation of the second initial hard mask.FIG. 17shows the second hard mask74in place of the second initial hard mask. According to the comparative example, the position of boundary between the narrow portion41and the wide portion42is defined by the position of the first and second end face portions42aand42bof the wide portion42. The position of the first and second end face portions42aand42bis defined by the end74aof the second hard mask74. As shown inFIG. 17, since the resist mask73has an undercut, the second hard mask74is formed such that a portion thereof extends into the space resulting from the undercut of the resist mask73. For this reason, the comparative example cannot accurately control the position of the end74aof the second hard mask74, and consequently cannot accurately control the position of boundary between the narrow portion41and the wide portion42.

In contrast, according to the present embodiment, the second resist mask66has no undercut. This makes it possible to accurately control the position of the end65aof the second hard mask65, and consequently allows accurate control of the position of the wall face60cof the etching mask60. By virtue of this, the present embodiment allows controlling the position of boundary between the narrow portion41and the wide portion42with higher accuracy as compared with the comparative example.

Second Embodiment

A manufacturing method for a plasmon generator according to a second embodiment of the invention will now be described. As has been described in relation to the first embodiment, the etching mask used in the step of etching the initial plasmon generator40P includes the first mask layer for defining the shape of one of the narrow portion41and the wide portion42and the second mask layer for defining the shape of the other of the narrow portion41and the wide portion42. For the present embodiment, descriptions will be given of the case where the first mask layer defines the shape of the wide portion42of the plasmon generator40and the second mask layer defines the shape of the narrow portion41of the plasmon generator40.

Reference is now made toFIGS. 18A to 24Cto describe the manufacturing method for the plasmon generator40according to the present embodiment.FIGS. 18A to 24Ceach show a stack of layers formed in the process of manufacturing the thermally-assisted magnetic recording head. Fig. nA (n is an integer between 18 and 24 inclusive) shows a cross section of the stack taken at the location at which the medium facing surface80is to be formed. Fig. nB shows a cross section that intersects the end face of the main pole26and that is perpendicular to the medium facing surface80and to the top surface1aof the substrate1. Fig. nC shows the top surface of part of the stack. Figs. nA and nB, excludingFIGS. 24A and 24B, omit the illustration of portions that are located on the substrate-1side relative to the initial plasmon generator.FIGS. 24A and 24Bomit the illustration of portions below the cladding layer22.FIG. 23Dis a perspective view of part of the stack.

FIGS. 18A to 18Cshow a step following the formation of the cladding layer22(seeFIGS. 3 and 4). In this step, first, the initial plasmon generator40P is formed on the cladding layer22. Then, a first initial mask layer161P is formed on the initial plasmon generator40P. Then, a first initial hard mask162P is formed on the first initial mask layer161P.

The first initial mask layer161P may include an etching stopper layer161A, and a layer to be etched161B formed on the etching stopper layer161A.

In the step shown inFIGS. 18A to 18C, a first resist mask163for defining the shape of the first mask layer, i.e., the shape of the wide portion42, is then formed on the first initial hard mask162P by photolithography. The planar shape of the first resist mask163corresponds to that of the wide portion42. The first resist mask163has a wall face163afor defining the position of the first and second end face portions42aand42b(seeFIGS. 1 and 2) of the wide portion42. The first resist mask163does not have any undercut that a resist mask used in a lift-off process would have. The first resist mask163is preferably composed of a single layer of photoresist.

The shape of the first resist mask163is depicted in a simplified manner inFIGS. 18B and 18C. In other figures illustrating steps subsequent to this step, the shape of any portion defined by the first resist mask163is also depicted in a simplified manner.

FIGS. 19A to 19Cshow the next step. In this step, first, the first initial hard mask162P is etched into a first hard mask162by using the first resist mask163. The first hard mask162is provided with an end162awhose position is defined by the wall face163aof the first resist mask163. The first resist mask163is then removed. The step of etching the first initial hard mask162P is performed by employing RIE or IBE.

FIGS. 20A to 20Cshow the next step. In this step, first, a second initial mask layer164P is formed on the first initial mask layer161P and the first hard mask162. Then, a second initial hard mask165P is formed on the second initial mask layer164P.

FIGS. 21A to 21Cshow the next step. In this step, a second resist mask166for defining the shape of the second mask layer, i.e., the shape of the narrow portion41, is formed on the second initial hard mask165P by photolithography. The planar shape of the second resist mask166corresponds to that of the narrow portion41. The second resist mask166has a wall face166afor defining the position of the first side surface41c(seeFIGS. 1 and 2) of the narrow portion41and a wall face166bfor defining the position of the second side surface41d(seeFIGS. 1 and 2) of the narrow portion41. The second resist mask166does not have any undercut that a resist mask used in a lift-off process would have. The second resist mask166is preferably composed of a single layer of photoresist.

FIGS. 22A to 22Cshow the next step. In this step, first, the second initial hard mask165P is etched into a second hard mask165by using the second resist mask166. The second hard mask165is provided with an end165awhose position is defined by the wall face166aof the second resist mask166, and an end165bwhose position is defined by the wall face166bof the second resist mask166. The ends165aand165bare located to intersect the end162aof the first hard mask162as viewed from above. The second resist mask166is then removed. The step of etching the second initial hard mask165P is performed by employing RIE or IBE.

FIGS. 23A to 23Dshow the next step. This step is to complete the etching mask. In this step, the first and second initial mask layers161P and164P are etched into the first and second mask layers161and164, respectively, by using the first and second hard masks162and165. The etching mask160is thereby completed.FIG. 23Comits the illustration of the first and second hard masks162and165. The step of forming the etching mask160in the present embodiment includes a series of steps illustrated inFIG. 18AthroughFIG. 23D.

In the case where the first initial mask layer161P includes the etching stopper layer161A and the layer to be etched161B, the step of etching the first and second initial mask layers161P and164P etches the second initial mask layer164P and the layer to be etched161B until the etching stopper layer161A is exposed. In such a case, the first mask layer161is composed of the etching stopper layer161A and the layer161B etched.

The etching mask160is provided with a wall face160awhose position is defined by the end165aof the second hard mask165, a wall face160bwhose position is defined by the end165bof the second hard mask165, and wall faces160c1and160c2whose positions are defined by the end162aof the first hard mask162. The wall faces160aand160bextend across the first mask layer161and the second mask layer164. The wall faces160c1and160c2belong to the first mask layer161. The wall face160adefines the position of the first side surface41cof the narrow portion41to be formed later. The wall face160bdefines the position of the second side surface41dof the narrow portion41to be formed later. The wall face160c1defines the position of the first end face portion42aof the wide portion42to be formed later. The wall face160c2defines the position of the second end face portion42bof the wide portion42to be formed later. The step of etching the first and second initial mask layers161P and164P is performed by employing RIE.

Requirements pertaining to materials and etching conditions for the step of forming the etching mask160are the same as the requirements pertaining to materials and etching conditions for the step of forming the etching mask60in the first embodiment.

FIGS. 24A to 24Cshow the next step. In this step, first, the initial plasmon generator40P is etched into the plasmon generator40by using the etching mask160. In the case where the first mask layer161(the first initial mask layer161P) includes the etching stopper layer161A, the etching stopper layer161A is also etched when the initial plasmon generator40P is etched. The step of etching the initial plasmon generator40P is performed by employing IBE. The etching mask160is then removed.

According to the present embodiment, the first mask layer161serves to accurately control the position of the first and second end face portions42aand42b. The present embodiment thus enables accurate control of the position of boundary between the narrow portion41and the wide portion42.

The present invention is not limited to the foregoing embodiments, and various modifications may be made thereto. As far as the requirements of the appended claims are met, the shape and configuration of the etching mask can be freely chosen without being limited to the examples illustrated in the foregoing embodiments. For example, the etching mask may include three or more mask layers of different shapes.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims and equivalents thereof, the invention may be practiced in other embodiments than the foregoing most preferable embodiments.