US20110094888A1

US20110094888A1 - Rejuvenation method for ruthenium plating seed

Info

Publication number: US20110094888A1
Application number: US12/589,599
Authority: US
Inventors: Chao-Peng Chen; Chien-Li Lin; Jas Chudasama; Situan Lam
Original assignee: Headway Technologies Inc
Current assignee: Headway Technologies Inc
Priority date: 2009-10-26
Filing date: 2009-10-26
Publication date: 2011-04-28
Also published as: JP2011090770A

Abstract

A method of rejuvenating a Ru plating seed layer during write pole fabrication in a PMR head is disclosed that involves forming an opening in a mold forming layer. A Ru seed layer is deposited by CVD within the opening and on a top surface of the mold forming layer. The substrate with the Ru seed layer is immersed in an acidic solution and an electric potential is applied for 1 to 2 minutes such that hydrogen is generated to reduce ruthenium oxides to Ru metal on the seed layer surface in an activation step. One or more surfactants are used to improve wettability of the Ru layer. The substrate is transferred directly to an electroplating solution without drying following the activation step to minimize exposure to oxygen that could regenerate oxides on the surface of the Ru layer. As a result, write pole voids and delamination are significantly reduced.

Description

RELATED PATENT APPLICATION

This application is related to Docket # HT09-005, Ser. No. 12/460,432, filing date Jul. 17, 2009; assigned to the same assignee as the current invention and which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to a method of forming a main pole layer in a PMR writer that involves improving wettability of a seed layer by converting ruthenium oxides to Ru thereby substantially reducing void and delamination defects and enhancing write pole performance.

BACKGROUND OF THE INVENTION

Perpendicular magnetic recording (PMR) has become the mainstream technology for disk drive applications beyond 200 Gbit/in², replacing longitudinal magnetic recording (LMR) devices. Due to the continuing reduction of transducer size, high moment soft magnetic thin films with a Bs above 22 kG are required for write head applications. PMR uses a magnetic yoke surrounded by field coils that terminates in a single pole that is used for the write head. The write pole must be wide enough at one end to attach to the yoke and narrow enough at the other end to confine the write flux to a very small area typically about 0.1×0.1 microns.
A conventional PMR write head as depicted in FIG. 1 typically has a main pole layer 10 or write pole with a pole tip 10 t at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip 10 t at the ABS is high enough to switch magnetizations in the recording media 4. A trailing shield is added to improve the field gradient in the down-track direction.
Referring to FIG. 2, a top view is shown of a typical main pole layer 10 that has a large, wide portion called a yoke 10 m and a narrow rectangular portion 10 p called a write pole that extends a neck height (NH) distance y from the ABS plane 5-5 to a plane 3-3 parallel to the ABS where the pole intersects the yoke at the neck 12. The main pole layer 10 flares outward at an angle θ from a dashed line 11 that is an extension of one of the long rectangular sides of the pole 10 p. PMR technologies require the write pole 10 p at the ABS to have a beveled shape (as viewed from the ABS) so that the skew related writing errors can be suppressed. In other words, the top edge 10 a of the main pole layer 10 usually overhangs the lower edge 10 b by a certain amount.
Although a PMR head which combines the features of a single pole writer and a soft magnetic underlayer has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density, PMR still faces some challenges. One major issue is related to trapezoidal write pole plating or the so-called through via plating in the semiconductor industry. In particular, there is a tendency to form void defects on the bottom and sidewalls of the write poles. Void defects are undesirable since they can lead to corrosion in the downstream slider process and adversely affect writer performance and wafer yields.
One cause of void defects is considered to be air bubbles trapped on the seed layer surface inside narrow openings when the wafer is submerged into a solution prior to plating. Poor wettability or hydrophobic characteristics of the seed layer make it difficult for small air bubbles to escape from a high aspect ratio cavity layer. In a conventional plating process, seed layer wettability is improved by the addition of excess surfactant such as sodium lauryl sulfate or sodium dodecyl sulfate to the plating solution. Unfortunately, surfactant may decompose during plating and can be co-deposited into the plated film. Higher surfactant loadings can easily raise the impurity level in the plated write pole and thereby lower its corrosion resistance and writability. Surfactant can also interact with other additives in the plating solution to form unwanted nodules in the plated film.
H. Gu et al. in U.S. Patent Application Publication 2007/0080067 provide a method for reducing the formation of void defects on the surface of a substrate during Cu plating by oxidation of the plating seed layer prior to substrate immersion. However, this method cannot be applied to high magnetic moment write pole plating where a Ru seed is generally used as a plating seed, write gap as well as a CMP stop layer. Oxidation of a Ru seed layer forms ruthenium oxides on the plating seed surface which improves the seed wettability in plating solution. Unfortunately, the plated high magnetic moment materials such as CoFe adhere poorly to ruthenium oxides, resulting in plated film delamination. Furthermore, ruthenium oxides cannot be removed by immersion in an acidic plating solution typically used for write pole formation.
Ruthenium is typically deposited by an ion beam deposition (IBD) process. However, this method produces poor Ru thickness uniformity and is being replaced in the industry by a Ru chemical vapor deposition (CVD) process. A Ru CVD method has been described by Xia in U.S. Patent Application Pub. No US 2008/0214003. Referring to FIG. 3, each of the four steps (1)-(4) in a Ru CVD process has a timeline on the left side of the drawing and a pictorial representation of the associated chemical event on the right side. In step (1), a Ru precursor such as Ru ₄ 51 is pumped into the reaction chamber where RuO₄is decomposed into RuO₂ 52 and O₂ 53, and RuO₂is deposited on substrate 50. During the second step (2), an inert gas such as Ar 54 is fed into the reaction chamber to purge unreacted RuO ₄ 51 and reaction by-product O ₂ 53. In step (3), a reducing agent such as H₂ 55 is injected into the reaction chamber to convert RuO₂ 52 into Ru metal 56 on substrate 50 and yields water 57 as a by-product. Finally, step (4) involves pumping an inert gas (Ar) 54 into the reaction chamber to remove unreacted H₂ 55 and water vapor 57. The sequence of steps (1) to (4) is called a cycle and multiple cycles are required to provide the desired thickness of Ru seed 56.
One potential issue with Ru CVD is incomplete conversion of RuO₄and RuO₂into Ru metal. Incomplete conversion can arise from changes in reaction rate due to variations in Ru precursor concentration, reaction temperature, and/or reaction time and results in Ru plating seed layer containing undesired ruthenium oxide components which will adversely affect surface wettability, electrical conductivity as well as the subsequent plated film integrity. Thus, one or both of voids and delamination defects may be observed after plating. In addition to incomplete Ru CVD cycles, RuO₂can also form on a Ru surface during a period of idling or in a descum process where an oxygen plasma is applied to remove organic residues from the substrate. Therefore, a method for Ru rejuvenation prior to plating a main pole layer is necessary to generate Ru plating seed films free of oxides and thereby enable electroplating to proceed without voids and delamination issues.
U.S. Pat. No. 7,442,267 describes a method of annealing a Ru seed layer in an oxygen free atmosphere to reduce oxides and thereby reducing Ru resistivity before immersing the substrate in a plating solution. Related patent application Ser. No. 10/915,865 teaches a multi-step immersion process during plating to minimize bubble formation on electroplated surfaces.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a method for rejuvenating a Ru plating seed layer that converts RuO₄and RuO₂to Ru metal and thereby minimizes void formation in recessed cavities during a plating operation to form a write pole in a perpendicular magnetic recording device.
Another objective of the present invention is to provide a method for rejuvenating a Ru plating seed layer that can be readily incorporated into a process flow for fabricating a main pole layer in a write head.
According to one embodiment of the present invention, these objectives are realized by first providing a substrate upon which a mold forming layer has been formed. For example, the substrate may be an etch stop layer. The mold forming layer may be a composite including an insulation layer such as alumina formed on the substrate and an upper Ta layer that serves as a hard mask and chemical mechanical polish (CMP) stop layer. A mold or opening for the main pole layer is formed in the mold forming layer by a sequence of photoresist imaging and etching steps. In one aspect, a photoresist layer is coated on the mold forming layer and patternwise exposed to form an opening in the shape of a main pole layer with yoke and pole sections that uncovers a portion of mold forming layer. Thereafter, the opening is transferred through the mold forming layer by a reactive ion etch (RIE) process that stops on the etch stop layer. Optionally, the mold formation sequence may include a first photoresist patterning and etching sequence followed by a second photoresist patterning and etching sequence to define different portions of the opening that correspond to different sections of the main pole layer. For example, the yoke opening may be formed in one patterning and etch sequence and the opening for the write pole section may be formed in a second patterning and etch sequence. The opening for the write pole section typically has a trapezoidal shape determined by sloped sidewalls that extend from the top surface of the mold forming layer to the substrate, a top opening within the top surface of the mold forming layer, and a bottom surface at the substrate. Preferably, the top opening has a greater width along the ABS than the bottom surface in the write pole opening.
After the photoresist layer is removed above the mold opening, a conformal alumina layer may be deposited on the surface of the mold forming layer, on the sloped sidewalls within the opening, and on exposed regions of the substrate. In one aspect, the alumina layer may be formed by atomic layer deposition (ALD) with a thickness that may be varied to adjust the track width. Then a Ru seed layer may be deposited on the conformal alumina layer by a sputter deposition method, chemical vapor deposition (CVD), physical vapor deposition (PVD), or ALD method, for example. A key feature of the present invention is the conversion of undesirable ruthenium oxides on the surface of the seed layer to Ru metal. The Ru rejuvenation or “activation” process is performed by immersing the substrate with the Ru seed layer in an acidic solution with a surfactant to improve wettability of the Ru seed layer surface. The electrical potential of the Ru layer is then lowered below the hydrogen evolution reaction (HER) potential by applying a voltage below a certain value that is dependent on pH of the acidic solution but preferably just below the potential that generates H₂gas as indicated in a Pourbaix ruthenium diagram. The Ru substrate serves as a cathode while a metal such as Ni serves as the anode. The electrical potential is maintained below the HER potential for a period of 1 to 2 minutes at a temperature between 10° C. and 25° C. to ensure a continuous generation of H₂that will reduce all of the ruthenium oxides on the surface of the seed layer to Ru metal. Then the Ru substrate is transferred to an electroplating bath where the magnetic write pole material is plated on the rejuvenated Ru metal layer. Subsequent steps follow in a conventional process flow such as annealing, and performing a CMP step to planarize the main pole layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional PMR writer showing the main write pole, flux return pole, magnetic recording media, and coils that generate magnetic flux.

FIG. 2 is a top view showing a main write pole layer of a conventional PMR write head that has a narrow write pole section adjacent to the ABS and a larger yoke section with sides that flare outward at an angle θ from the sides of the narrow write pole.

FIG. 3 is a drawing showing a timeline on the left side for each of the four Ru CVD steps and a pictorial representation on the right side for the chemical event in each of the four Ru CVD steps.

FIGS. 4-7 are cross-sectional views representing a process flow sequence according to a prior art method where electroplating of a write pole layer is performed directly on a Ru seed layer in a recessed opening.

FIG. 8 is a Pourbaix diagram that shows electrochemical equilibria for Ru and ruthenium oxides in aqueous solutions.

FIG. 9 is a process flow diagram that illustrates a sequence of steps starting from seed layer formation in a write pole opening and continuing through the electroplating of a write pole according to a method of the present invention.

FIG. 10 is a sectional view illustrating a Ru substrate immersed in an activation solution within a tank according to an embodiment of the present invention.

FIG. 11 is a cross-sectional view that shows the formation of a conformal Ru seed layer in a recessed opening according to an intermediate step of the present invention.

FIG. 12 is a cross-sectional view showing a rejuvenated Ru seed layer formed in a recessed opening according to an intermediate step of the present invention.

FIG. 13 is a cross-sectional view of the structure in FIG. 12 after a magnetic layer is electroplated in the recessed cavity according to a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method of forming a write pole in a PMR write head that minimizes or eliminates common defects such as voids and impurities in the write pole layer by rejuvenating a Ru plating seed layer. Note that the words mold and opening are used interchangeably when referring to the cavity in which the write pole is formed. The write head described in the exemplary embodiment may be part of a merged read-write head configuration. Although a write pole is described as the magnetic layer deposited on a rejuvenated Ru plating seed layer in the preferred embodiments, the present invention also anticipates that other magnetic layers such as shield layers may be formed on a rejuvenated Ru seed layer for the purpose of reducing delamination and minimizing voids in the electroplated magnetic layer.
FIGS. 4-7 are cross-sectional views from an ABS that relate to a process sequence previously practiced by the inventors illustrating a method for forming a write pole. It should be understood that a write pole is typically formed simultaneously with a yoke portion of a main pole layer. Referring to FIG. 4, a first step involved in forming an opening for a write pole is depicted. There is a substrate 18 such as AlTiC on which an etch stop layer 19 otherwise known as a RIE resistant layer is deposited. The RIE resistant layer 19 with a thickness of 200 to 1000 Angstroms may formed on the substrate 18 by a sputter deposition or PVD process, for example, and preferably includes a material such as Ru or NiCr that has a high etch selectivity relative to an insulating layer made of alumina or the like during a subsequent RIE etch that uses BCl₃, chlorine, and fluorocarbon gases. An insulation layer 20 is formed on the RIE resistant layer 19 and may be comprised of Al₂O₃or silicon oxide that is deposited by a PVD process, a sputtering technique, or the like in the same deposition tool as the RIE resistant layer. The insulation layer 20 may also be made of other dielectric materials known in the art.
Thereafter, a hard mask 21 made of Ta, for example, is formed on the insulation layer 20. The hard mask is advantageously employed in a subsequent RIE step where an opening is transferred into the insulation layer. Together, hard mask 21 and insulation layer 20 may be considered a composite mold forming layer and have a combined thickness essentially equivalent to the desired thickness of the write pole and main pole layer to be deposited in a later step. A photoresist layer 22 is coated on hard mask 21 and a well known lithography technique is used to form a pattern including an opening 23 that preferably comprises the shape of the write pole to be formed in subsequent steps. In one aspect, opening 23 extends beyond a neck height distance from the ABS and also comprises a cavity (not shown) for the yoke portion of the main pole layer.
Alternatively, two photoresist patterning and etching sequences may be used to form different sections of opening 23. For example, in Headway patent application Ser. No. 11/820,962, a two mask process is disclosed that provides an advantage of improving dimensional control of the pole by minimizing the effect of ABS positioning errors. In this example, a first photoresist layer is patterned and etched to form a rectangular shape that corresponds to the write pole section of the main pole layer. The rectangular shape is transferred through the insulation layer by a RIE process comprising BCl₃, Cl₂, and a fluorocarbon gas to generate a trench with beveled sidewalls. Thereafter, the first photoresist layer is removed and a second photoresist layer is coated on the insulation layer and patterned to form a yoke shape opening that is partially superimposed over the rectangular trench. A second etch process involving BCl₃and Cl₂may be employed to transfer the yoke shape opening through the insulation layer and form essentially vertical sidewalls in the yoke section of the mold for the main pole layer.
Referring to FIG. 5, the pattern including opening 23 in photoresist layer 22 is transferred through hard mask 21 by a first etching step that is preferably a RIE process to accurately reproduce the opening in the hard mask. The first etch step stops on the insulation layer 20. Following the first etch step, the photoresist is stripped by a conventional method. Then, a second etch step is performed to transfer the opening 23 through the insulation layer 20 and stops on RIE resistant layer 19. Note the lower portion of opening 23 within insulation layer 20 has sloped sidewalls 24 that extend from a bottom surface of the hard mask 21 to the RIE resistant layer 19. The slope of the sidewalls may be adjusted by changing RIE conditions such as gas chemistry, pressure, and RF power. As a result, the width w₁at the top of opening 23 is greater than the width w₂along the bottom surface 24 b of the opening, and the lower portion of the opening within the insulation layer 20 has a trapezoidal shape.
Referring to FIG. 6, a dielectric layer 25 such as alumina may be deposited by an ALD method to form a conformal film on the top surface 21 s, on bottom surface 24 b, and along sidewalls 24 in opening 23. The primary purpose of the conformal dielectric layer 25 is to adjust the width of opening 23 prior to seed layer deposition. For instance, if the patterning and etch sequence described previously generates an opening 23 having a width w₁larger than a target value, then the thickness of dielectric layer 25 may be increased to compensate for a larger than desired size for width w₁. Thereafter, a seed layer 26 which is preferably Ru is formed as an essentially conformal layer on dielectric layer 25 by a CVD method. However, the seed layer 26 may also be deposited by an ALD method, sputter deposition process, or another technique. As a result, opening 23 a has a width along the top surface 26 s of less than w₁and is bounded on the sides by sidewalls 24 a that are sloped at an angle α of about 5 to 20 degrees with respect to a plane formed perpendicular to the RIE resistant layer 19. The write pole which will be deposited in a later step will have a beveled shape with an angle α with respect to a plane formed perpendicular to the ABS so that the skew related writing errors can be suppressed.
Referring to FIG. 7, the wafer comprising substrate 18 is immersed in a plating solution and an electroplating process is performed to deposit a magnetic layer 27 that fills opening 23 a (FIG. 6) and also covers the top surface 26 s of the seed layer 26. As mentioned earlier, a Ru seed layer 26 after CVD deposition or deposited by other techniques typically contains RuO₂or RuO₄that has not been converted to a metal form. Rutherium oxides lead to poor wettability characteristics that enables air bubbles (not shown) to be trapped along sidewalls 24 a when submerged in a plating solution. During plating of magnetic layer 27, the bubbles may be cause voids 32 to form along sidewalls 24 a or at the bottom of opening 23 a as the opening is filled with plated material. Adding excess surfactant to the plating solution may decrease void formation somewhat but in turn increases the likelihood of surfactant or other additives being included in the plated magnetic layer 27.
As shown in FIG. 7, voids 32 remain in the write pole 27 p after the plated magnetic layer is planarized by a CMP process to form a top surface 27 s that is essentially coplanar with top surface 26 s of the seed layer. Even if voids are reduced by employing additional surfactant in the plating solution, write pole performance is degraded because of extra impurities included in the magnetic material.
We have discovered a new process sequence for forming a write pole that significantly reduces voids without the need for elevated surfactant levels and takes advantage of improved film uniformity provided by a Ru CVD deposition process. The process sequence can be readily implemented in existing fabrication lines at minimal cost since existing equipment and materials may be utilized without significantly affecting throughput. There is a cost associated with a Ru rejuvenation step requiring a dedicated tank according to the present invention. However, the savings realized by dramatically reducing void formation and the number of rejected parts caused by degraded write pole performance more than offsets any expense of including an additional process step.
As depicted in Pourbaix's ruthenium diagram taken from Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, National Association of Corrosion Engineers, Houston, Tex. (1974), ruthenium oxide can be converted to Ru metal by lowering the electrical potential of the oxide in solution below the hydrogen evolution reaction (HER) potential. For example, starting at point A along dashed line 40, RuO₄may be converted to RuO₂in a hydrated form (point B) by applying a potential of 1 volt in an aqueous solution at pH=3. If the potential is lowered to 0.7 volts (point C), RuO₂becomes Ru(OH)₃in the acidic solution. Further reduction of electrical potential to below −0.2 volts such as −0.3 volts at point D (below dashed line a) will convert Ru(OH)₃to Ru metal.
Referring to FIG. 9, the process flow of the present invention begins at a stage where an opening has been formed in a mold forming layer as represented by FIG. 4. In step 100, a plating seed layer that is preferably Ru with a thickness from 400 to 700 Angstroms is deposited in a conformal manner in opening 23 and on the top surface of a mold forming layer preferably by a CVD process such as the one described in FIG. 3. However, the present invention also anticipates that the Ru seed layer may be deposited by an alternative technique such as ALD, sputter deposition, or the like.
The following step 101 is a key feature of the present invention wherein the Ru seed layer 26 along the sidewalls and bottom of the opening 23 and on a top surface 26 s that is parallel to the plane of the substrate is rejuvenated or “activated” by applying an electrical potential to the substrate 18 under a hydrogen evolution reaction (HER) condition in an acidic solution hereafter referred to as the activation solution. In one embodiment, the HER condition includes immersing the Ru substrate in the activation solution with a pH from 0 to 7 and comprised of a surfactant such as sodium dodecyl sulfate (SDS) or sodium lauryl sulfate at a temperature between 10° C. and 25° C. The surfactant additive has a concentration from 0 to 1 gm/liter and improves wettability of the exposed Ru layer 26 to the acidic solution. The present invention also encompasses an embodiment where more than one surfactant is included in the activation solution. Preferably, the pH is maintained between 2 to 3 in order to match the optimum pH range in an electroplating solution that will be employed in the following step. In one embodiment, substrate 18 is immersed in an electroplating solution (not shown) directly after being removed from the activation solution in order to minimize exposure to oxygen that could oxidize the Ru seed layer. Optionally, the substrate 18 may be rinsed with water but not dried after being removed from the activation solution. Then the substrate is placed in an electroplating solution to form the write pole layer 30 (FIG. 13).
The acid in the activation solution may be HCl or H₂SO₄but is not limited to the aforementioned materials. Furthermore, a buffer agent such as boric acid may be added to maintain the pH within a desired pH range. During the immersion, an electrical potential from about 0 to −0.8 Volts depending on the pH value is applied in a direct current mode for a period of 1 to 2 minutes to generate hydrogen at the surface of substrate 18, and specifically at the surface of Ru seed layer 26. Note that on the Pourbaix plot where line 40 represents the different chemical states of Ru at pH=3, the electrical potential needed to rejuvenate Ru according to the present invention should be below the bottom dashed line a or below −0.1 Volts. However, one skilled in the art will appreciate that the optimum HER condition at pH=3 is just below the dashed line a in the range of about −0.2 to −0.5 Volts and not at larger negative voltage values in order to minimize the amount of H₂produced for safety reasons. For pH values above or below 3, the optimum applied voltage to generate a HER condition necessary for Ru rejuvenation varies from about 0 to −0.3 V at pH=0 to −0.5 to −0.8 V at pH=7. Thus, the electrical potential required to establish the HER condition becomes a more negative value as the pH becomes a larger positive number.
It should be understood that the Ru seed layer serves as the cathode and metal such as Ni serves as an anode in the electrochemical reaction to produce H₂which in turn is responsible for the reduction of ruthenium oxide to Ru metal. Preferably, a single substrate is immersed in the activation solution which may be stirred to promote better uniformity of additives. As a result, a Ru seed layer 26 having a certain amount of ruthenium oxide content is converted to a rejuvenated Ru seed layer 26 r that has a surface essentially free of ruthenium oxides.
In one embodiment as depicted in FIG. 10, the activation step 101 may be performed in a tank 60 that is typically employed for an electroplating reaction except the electroplating solution is removed and replaced with the previously described activation solution 61 having a top surface 61 a. The substrate 18 with overlying layers including the Ru seed layer (not shown) is attached to a cathode 62 during the Ru rejuvenation process such that the Ru layer faces away from the cathode. Cathode 62 is attached to a power source 67 by a lead 64 a while anode 63 is attached to the power source by a lead 64 b. Furthermore, there is a H₂reference electrode 66 immersed in the activation solution 61 and connected to the power source 67 by a lead 64 c. It should be understood that the applied voltage between the cathode and anode during the activation step is measured against the H₂reference electrode 66.
In step 102, the rejuvenated Ru layer 26 r and substrate 18 are immersed in an electroplating bath and a current or voltage is applied to fill the opening 23 a with magnetic material such as CoFe or alloys thereof. A CMP process may be used to planarize the electroplated material so that the write pole 30 has a top surface 30 s which is coplanar with a top surface 29 of the rejuvenated Ru seed layer 26 r.
Each of the steps 100-102 is described in more detail with regard to FIGS. 11-13. In FIG. 11, a dielectric layer 25 and seed layer 26 are sequentially formed on the top surface of a hardmask and along the sidewalls and bottom of an opening according to a previously described procedure practiced by the inventors. As a result, there is an exposed top surface 26 s of the seed layer, and an opening 23 a having sidewalls 24 a formed in the composite mold forming layer that includes insulation layer 20 and hard mask 21. In a preferred embodiment, the dielectric layer 25 is made of alumina and has a thickness in the range of 10 to 1000 Angstroms and the seed layer 26 is comprised of Ru and may have a thickness between 400 and 700 Angstroms, for example. The Ru seed layer 26 may be deposited by a CVD, ALD, sputter deposition, or ion beam deposition (IBD) method.
Referring to FIG. 12, the Ru rejuvenation or activation process is performed under HER conditions to convert ruthenium oxides (not shown) on the surface of seed layer 26 into Ru metal and thereby form a rejuvenated Ru seed layer 26 r. The thickness of Ru seed layer 26 r is essentially unchanged from that of the seed layer 26 prior to the activation process.
Referring to FIG. 13, a write pole 30 is electroplated by a conventional method to fill opening 24 a and cover the top surface 29. Subsequently, the write pole 30 is planarized by a CMP process, for example, such that a top surface 30 s is coplanar with the top surface 29 of the rejuvenated Ru seed layer 26 r. Because of the improved wettability of the rejuvenated Ru seed layer 26 r, the occurrence of voids in the plated film is substantially reduced and in some cases essentially eliminated to give a uniform write pole 30 with improved magnetic properties. Total thickness of the resulting write pole is typically about 1 micron but may be adjusted higher or lower to modify the performance of the PMR writer as appreciated by those skilled in the art.
In addition to the reduction or elimination of void defects in a write pole formed according to an embodiment of the present invention, improved write pole performance is achieved and enhanced wafer yields are realized. In particular, an improved surface of the Ru plating seed layer which is free of oxides is achieved which improves wettability during a subsequent electroplating reaction and substantially lowers the frequency of delamination of the write pole layer. The Ru rejuvenation is compatible with current manufacturing process flows and is versatile in that it may be applied to a Ru layer initially deposited by a CVD, ALD, sputter deposition, or by other methods.
While this invention has been particularly shown and described with reference to, the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of this invention.

Claims

1. A method of forming a write pole in a perpendicular magnetic recording head, comprising:

(a) forming an opening in a mold forming layer having a top surface, said opening has a bottom that exposes a portion of a substrate and has sidewalls that extend from the top surface to said substrate;

(b) forming a Ru seed layer along the top surface and sidewalls, and on the bottom of the opening;

(c) immersing said substrate including said Ru seed layer in an acidic solution comprising at least one surfactant, said substrate is attached to a cathode that is electrically connected to an anode wherein both of said cathode and anode are immersed in said acidic solution;

(d) applying an electrical potential that is below a hydrogen evolution reaction condition for the Ru seed layer in said acidic solution to convert any ruthenium oxides on a surface of the Ru seed layer to Ru metal;

(e) removing said substrate from the acidic solution; and

(f) immersing said substrate in an electroplating solution and performing an electroplating process that deposits a magnetic material which fills said opening.

2. The method of claim 1 wherein the mold forming layer is a composite layer comprised of a lower alumina layer and an upper Ta layer.

3. The method of claim 1 wherein the Ru seed layer has a thickness between about 400 Angstroms and 700 Angstroms.

4. The method of claim 1 wherein the Ru seed layer is formed by a CVD deposition, ALD deposition, sputter deposition, or ion beam deposition technique.

5. The method of claim 1 wherein the acidic solution has a pH between about 0 and 7, a temperature between about 10° C. and 25° C., and is comprised of HCl or H₂SO₄.

6. The method of claim 1 wherein the at least one surfactant is sodium dodecyl sulfate or sodium lauryl sulfate and has a concentration in the acidic solution from 0 to about 1 gm/liter.

7. The method of claim 1 wherein the electrical potential is between about 0 and −0.8 volts and is applied for a period of about 1 to 2 minutes, said electrical potential depends on the pH and has a larger negative value as the pH becomes a higher positive number.

8. The method of claim 1 wherein the substrate is immersed in the electroplating solution without drying the substrate after step (d) is completed.

9. The method of claim 5 wherein the electroplating solution has a pH that matches the pH of the acidic solution employed in steps (c) and (d).

10. The method of claim 1 wherein the anode is comprised of Ni.

11. The method of claim 1 wherein the electrical potential is measured against a hydrogen reference electrode that is immersed in said acidic solution.

12. A method of rejuvenating a Ru plating seed layer, comprising:

(a) providing a substrate with a mold forming layer having a top surface thereon and an opening having sidewalls and a bottom surface in the mold forming layer in which a magnetic layer will be deposited in a subsequent step;

(b) forming a Ru plating seed layer along the top surface of the mold forming layer and on the sidewalls and bottom of the opening;

(c) immersing said substrate including said Ru seed layer in an acidic solution comprising at least one surfactant, said substrate is attached to a cathode that is electrically connected to an anode wherein both of said cathode and anode are immersed in said acidic solution; and

(d) applying an electrical potential that is below a hydrogen evolution reaction condition for the Ru seed layer in said acidic solution to convert any ruthenium oxides on a surface of the Ru seed layer to Ru metal.

13. The method of claim 12 wherein the mold forming layer is a composite layer comprised of a lower alumina layer and an upper Ta layer.

14. The method of claim 12 wherein the Ru seed layer has a thickness between about 400 Angstroms and 700 Angstroms.

15. The method of claim 12 wherein the Ru seed layer is formed by a CVD deposition, ALD deposition, sputter deposition, or ion beam deposition technique.

16. The method of claim 12 wherein the acidic solution has a pH between about 0 and 7, a temperature between about 10° C. and 25° C., and is comprised of HCl or H₂SO₄.

17. The method of claim 12 wherein electrical potential is between about 0 and −0.8 volts and is applied for a period of about 1 to 2 minutes, said electrical potential depends on the pH and has a larger negative value as the pH becomes a higher positive number.

18. The method of claim 12 wherein the at least one surfactant is sodium dodecyl sulfate or sodium lauryl sulfate and has a concentration in the acidic solution from 0 to about 1 gm/liter.

19. The method of claim 12 wherein the acidic solution is further comprised of a buffer agent to maintain the pH in a certain range.

20. The method of claim 12 wherein the electrical potential is measured against a hydrogen reference electrode that is immersed in said acidic solution.