Abstract:
A fabrication method using a bottom anti-reflective coating (BARC) eliminating deleterious effects of unwanted reflected light during the photo exposure step of a photolithographic process. The BARC coating comprises a carbon coating having a thickness of 300 angstroms, deposited by a carbon ion beam deposition tool, and an initial silicon BARC coating layer having thickness of 20 angstroms deposited before the carbon coating. Where the BARC layer is utilized in a photolithographic NiFe pole tip fabrication process, a NiFe seed layer is first deposited upon a substrate. The BARC layer is then formed on the NiFe seed layer and the pole tip trench is then photolithographically created. Thereafter, the BARC layer is removed from the bottom of the trench, utilizing a reactive ion etch process, exposing the NiFe seed layer. The NiFe pole tip is then fabricated into the trench, and any remaining photoresist and BARC layer are removed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods for fabricating thin film magnetic heads, and more particularly to the use of anti-reflective coatings in photolithographic process steps for fabricating narrow components such as pole tips of magnetic heads. 
     2. Description of the Prior Art 
     The magnetic pole pieces of thin film magnetic heads are generally fabricated utilizing photolithographic techniques that are well known to those skilled in the art. The ongoing efforts to increase the areal data storage density on magnetic media has led to a need to fabricate magnetic pole pieces with a smaller width, because the width of the pole pieces, particularly the P 2  pole tip width, generally determines the track width of the data track written by the magnetic head. A problem that occurs in the use of photolithographic techniques in fabricating components with such small dimensions is the unwanted reflection of the exposing light energy from the surface of the substrate upon which the photolithographic resist is formed. The reflected light can expose the photoresist in unintended areas, thus degrading the accuracy of the photolithographic process. The present invention solves this problem through the use of a bottom antireflection coating (BARC) in the photolithographic process. 
     The use of BARC coating in the semiconductor process industry for making integrated circuits and the like is well known. However the use of such BARC coatings in the magnetic head fabrication industry, as well as the particular BARC coating process parameters described herein has not heretofore been accomplished. 
     SUMMARY OF THE INVENTION 
     The fabrication method of the present invention involves the utilization of a bottom antireflective coating (BARC) to eliminate the deleterious effects of unwanted reflected light during the photo exposure step of a photolithographic process. The BARC coating is particularly effective where small components, such as a pole tip of a magnetic head, are photolithographically fabricated. The BARC coating of the present invention is comprised of a carbon coating having a thickness of approximately 300 angstroms, and to obtain good adherence of the carbon coating to a substrate layer, an initial coating layer of silicon is deposited before the carbon coating. The silicon coating layer is formed with a thickness of approximately 20 angstroms. A carbon ion beam deposition tool is preferably utilized to deposit the carbon layer. Where the BARC layer is utilized in a photolithographic process to fabricate a NiFe pole tip, a NiFe seed layer is first deposited upon a substrate, such as the write gap layer of a magnetic head. An adhesion layer may be deposited prior to the NiFe seed layer if necessary. The BARC layer of the present invention is then formed on the NiFe seed layer and the pole tip trench is then photolithographically created. The BARC layer eliminates reflected light during the photoexposure step, resulting in more faithfully reproduced trench walls. Thereafter, the BARC layer is removed from the bottom of the trench, utilizing a reactive ion etch process, such that the surface of the NiFe seed layer is exposed. The NiFe pole tip is then fabricated into the trench, and thereafter the remaining photoresist and the remaining BARC layer are removed. The use of the BARC layer therefore is not apparent in the finally fabricated magnetic head; however, the dimensional characteristics of the pole tip are improved. 
     It is an advantage of the fabrication method of the present invention that increased accuracy is obtained in the photolithographic fabrication of small components of magnetic heads. 
     It is another advantage of the fabrication method of the present invention that a carbon BARC antireflective coating has been developed for use in the photolithographic fabrication of magnetic head components. 
     It is a further advantage of the fabrication method of the present invention that it utilizes a BARC coating comprised of carbon. 
     It is yet another advantage of the fabrication method of the present invention that it utilizes carbon and carbon deposition tools that are generally already utilized in the fabrication of magnetic heads, such that new fabrication tools and chemistries are not introduced into the magnetic head manufacturing process. 
     These and other features and advantages of the present invention will no doubt become well understood by those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of a standard prior art magnetic head; 
     FIG. 2 is an end elevational view of the prior art magnetic head depicted in FIG. 1; 
     FIG. 3 is a side cross-sectional view depicting the photoexposure step of a photolithographic process for fabricating a pole tip of a magnetic head; 
     FIG. 4 is an end elevational view of the photoexposure step depicted in FIG. 3; 
     FIGS. 5-10 depict a series of fabrication steps of the present invention for photolithographically forming a narrow structure such as the P 2  pole tip of a magnetic head, wherein a carbon BARC coating is advantageously utilized; 
     FIG. 11 is a perspective view depicting a T-head design, wherein the antireflective coating process of the present invention is advantageously utilized; and 
     FIG. 12 is a perspective view depicting an alternative T-head design, including a recessed P 3  layer, wherein the antireflective coating of the present invention is advantageously utilized. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The written track width of a magnetic head is generally determined by the width of the P 2  pole tip, as is well known to those skilled in the art. Such pole tips are photolithographically fabricated, and where it is attempted to fabricate pole tips with narrow widths, reflected light in the photoexposure step can prevent the accurate formation of such narrow pole tips. The present invention teaches the utilization of a bottom antireflective coating (BARC) in the photolithographic process to eliminate light reflection in the photoexposure step, as is described in detail herebelow. 
     A cross-sectional view of a standard prior art magnetic head is presented in FIG. 1 to provide a contextural understanding of the present invention, and an end elevational view of the magnetic head is presented in FIG.  2 . As depicted in FIGS. 1 and 2 the magnetic head  10  includes a slider substrate  14  upon which are formed a first shield layer  18 , a read head element  22  (formed within insulation layers  26 ), a second read head shield layer  30  which also functions as a first write head magnetic pole (P 1 ) layer  30 , a write gap layer  34  and a second P 2  pole layer  38  which includes a P 2  pole tip portion  42  and a yoke portion  46 . Induction coils  50  are disposed between the P 1  pole layer  30  and the yoke  46  of the P 2  pole layer  38 , such that the P 2  pole  38  is formed upon an insulator layer  56  having a topology which includes a relatively flat yoke surface  60 , a relatively flat P 2  pole tip surface  64 , and a sloped surface  68  that is formed between the yoke  46  and the P 2  pole tip  42 . An encapsulation layer  72  encloses the magnetic head components. As is best seen in FIG. 2, the P 2  pole tip  42  is quite narrow, because it is the width w of the P 2  pole tip  42  that determines the width of the data track that is written onto magnetic media. It is in the ongoing efforts to reduce the width w of the P 2  pole tip  42  that the reflection of light energy in the photolithographic fabrication process becomes problematic, as is best seen with the aid of FIGS. 3 &amp; 4 and next discussed. 
     FIGS. 3 and 4 depict a stage in the standard prior art photolithographic process for fabricating the P 2  pole of the magnetic head depicted in FIGS. 1 and 2, and common structures are numbered identically. As is seen FIGS. 3 and 4, a photoresist layer  74  has been deposited upon the insulation layer  56  in preparation for forming the P 2  pole tip  42 . In the light exposure step of the photolithographic process, light energy  84  is projected through a photomask  80  (depicted in phantom). The light energy  84  is incident upon the photoresist above the yoke portion  60 , the sloped portion  68  and the P 2  pole tip portion  64  of the device. Reflected light  88  from yoke portion  60  passes generally upwardly whereas light  92  reflected from the sloped portion  68  passes downwardly toward the P 2  pole tip  42 , and light  96  reflected in the flat P 2  pole tip region  64  passes generally upwardly although some light  100  reflects off-normal (see FIG.  4 ). The unwanted reflected light  92  and  100  therefore illuminates the photoresist in unintended areas of the P 2  pole tip region  64 , and causes an uncontrollable degradation in the narrow dimensions that are sought to be achieved at the P 2  pole tip region  64 . This degradation occurs both in the flat P 2  pole tip areas  64  due to the off-normal reflected light  100 , as well as the sloped areas  68  where light  92  is angularly reflected. Thereafter, when the photoresist  74  is developed the hoped for narrow dimensions and vertical trench walls of the P 2  pole tip region  64  are degraded due to the reflected light  92  and  100 . While light reflection during the photoresist process has been known whenever photolithographic process have been used in manufacturing magnetic heads, such light reflection has not been particularly problematic until the fabrication of magnetic heads with exceedingly narrow P 2  pole tip widths have been attempted. The use of the bottom antireflective coating of the present invention solves this problem and is next described with the aid of FIGS. 5 through 10. 
     FIGS. 5 through 10 depict the fabrication steps for photolithographically forming a narrow structure such as the P 2  pole tip of a magnetic head. As depicted in FIG. 5, a generalized substrate layer  120  having an upper surface  124  for the deposition of a structure such as the P 2  pole tip is presented upon a supporting layer  126 . The layer  120  may therefore be the write gap layer  34  and/or the insulator layer  56  of a magnetic head, and may be composed of a material such as alumina. It is therefore desired to photolithographically form a P 2  pole tip structure upon the top surface  124  of the alumina layer  120  that is composed of a magnetic material such as NiFe 45/55. A first step in the pole tip formation is the deposition of a seed layer  140  upon the alumina surface  124 . Because a NiFe layer will generally not adhere well to an alumina surface, an initial adherence layer  144  of tantalum having a thickness of approximately 20-80 angstroms is initially deposited; titanium and perhaps other metals may alternatively serve as an adherence layer  144 . Thereafter, the NiFe seed layer portion  148  having a thickness of approximately 800 angstroms is deposited. 
     In prior art photolithographic pole tip fabrication processes, the next step would generally be the formation of the photoresist layer on top of the seed layer  140 ; however, the next step in the present invention is the deposition of the bottom antireflective coating (BARC) upon the seed layer  140 . A suitable material for the BARC coating of the present invention is carbon. Carbon is advantageously utilized as a BARC coating in the manufacturing of magnetic heads because the use of carbon, as well as fabrication tools for applying thin film layers of carbon, is well known and already generally in place in magnetic head fabricating facilities to create anti-wear surface coatings for magnetic heads and hard disks. Therefore, the deposition of a carbon BARC coating does not generally involve the introduction of new chemistries and/or new fabrication tools into the manufacturing process of magnetic heads. This is a significant advantage of the present invention in savings of cost and the avoidance of unpredictable manufacturing problems where new chemistries and new tools are introduced into a fabrication process. 
     As depicted in FIG. 6 a carbon BARC coating  160  is next deposited upon the NiFe seed layer. The direct deposition of carbon onto the NiFe typically results in serious adhesion problems, in that the carbon layer will generally fail to adhere to the NiFe surface. A carbon layer is typically very compressive, and stresses within the carbon layer can cause it to detach from the seed layer and to pull up portions of the seed layer. To solve this problem, an initial layer of silicon  164 , having a thickness of approximately 20 angstroms is therefore first deposited upon the NiFe layer  148 . The silicon layer  164  adequately adheres to the NiFe, and thereafter a carbon coating layer  168  having a thickness of approximately 300 angstroms is deposited upon the silicon layer; the carbon will adequately adhere to the silicon layer. 
     Various carbon layer thicknesses from 200 angstroms to 1,000 angstroms were investigated in developing the present invention. It was determined that carbon layers of approximately 300 angstroms and approximately 800 angstroms unexpectedly performed approximately equally and somewhat better than thinner or thicker layers. The preferred embodiment of the present invention therefore utilizes a carbon layer of approximately 300 angstroms, because the layer is more rapidly and easily deposited and because it is more rapidly and easily removed than an 800 angstrom layer. 
     The carbon BARC coating of the present invention is preferably deposited utilizing a carbon ion beam deposition tool Such tools are currently utilized to apply the carbon wear resistant coatings in magnetic head and magnetic hard disk fabrication processes as mentioned above. Other carbon deposition processes, such as sputter deposited carbon and PECVD processes can alternatively be utilized, however the carbon ion beam deposition process results in a smooth, uniform coating that is preferred. Another reason for preferring the 300 angstrom carbon BARC coating thickness is because the carbon ion beam deposition tools are typically utilized to deposit thin films on the order of 100 angstroms. The deposition of a 300 angstrom carbon film is therefore generally within the performance characteristics of such tools, whereas the deposition of an 800 angstrom coating is somewhat more difficult with such tools. 
     With regard to process parameters of the carbon ion beam deposition tool, it was found that the use of commonly utilized and well known process parameters for depositing the wear resistance coating were entirely suitable for the deposition of the 300 angstrom carbon BARC coating of the present invention. Therefore, the use of a carbon ion beam deposition tool manufactured by Veeco Instruments, Inc., and operating with the following general process parameters is suitable for the deposition of the carbon BARC of the present invention. It has been found that the carbon ion beam deposition tool, operating with a beam voltage of 250-300 volts, with a beam current of 240-360 mA, and a suppressor voltage of 400 volts, together with a CH 4  flow rate of 50-90 sccm provides a carbon film with suitable antireflective properties. 
     Following the deposition of the carbon BARC coating  168 , standard photolithographic techniques are utilized to form the trench for the following component fabrication. FIG. 7 depicts a photolithographic exposure step in which a photoresist layer  180  deposited upon the carbon BARC coating  168  is exposed to light  184 . The phantom trench wall lines  190  depict the edge of light exposure, and it is significant that no light is reflected from the carbon BARC coating  168 . Following the light exposure step the photoresist layer is developed and the exposed photoresist  194  is removed. FIG. 8 depicts the fabrication stage in which the trench  198  is formed by the photoresist removal. The trench walls  204  are more vertical and smoother than the prior art fabrication process walls due to the BARC layer  160  of the present invention. 
     At this point, the BARC layer  160  has performed its purpose of eliminating light reflection during the photoexposure step. Now, prior to the fabrication of the component within the trench, the BARC layer  160  must be removed from the bottom of the trench, such that a good electomagnetic connection can be made between the NiFe seed layer  148  and the component that is formed within the trench  198 . To remove the BARC layer an RIE process is next performed. In the preferred embodiment, an oxygen RIE process step is utilized to remove the carbon layer portion  168  of the BARC  160 , although other oxidizing gases such as carbon dioxide are suitable. The silicon layer portion  164  of the BARC  160  is generally somewhat resistant to oxygen RIE, and a fluorine gas RIE may be preferentially utilized to remove it, such that the surface  208  of the NiFe seed layer is exposed. Where the surface of the NiFe seed layer is significantly oxidized, it may be necessary to utilize a hydrogen gas reducing RIE upon that surface to promote good electromagnetic conduction. 
     As is next depicted in FIG. 9, following the removal of the BARC layer from the bottom of the photolithographic trench  198 , the pole tip component  220  is plated up into the trench utilizing standard process techniques and parameters, as are well known to those skilled in the art. Thereafter, as depicted in FIG. 10, the photoresist layer is removed, such that the remaining BARC layer and seed layer therebelow remain and are exposed. The BARC carbon and silicon layers are removed utilizing a similar RIE process to that which was utilized to remove the BARC layers from the bottom of the trench; that is, utilizing and oxidizing RIE such as with oxygen, followed by fluorine if necessary to remove the silicon layer. Thereafter, the remaining NiFe seed layer and tantalum adhesion layer are removed utilizing standard process techniques, such as by sputter etching, as is well known to those skilled in the art. 
     As can be understood from the device as depicted in FIG. 10, the BARC process of the present invention is transparent in the final product. That is, while the BARC process of the present invention adds new process steps, there is no indication in the final device that an antireflective coating was used in the fabrication process, and the final device is substantially identical to the devices resulting from the pre-existing fabrication processes. A significant difference however in the final device produced utilizing the process of the present invention is that the narrow structural components, such as a 0.25 micron width P 2  pole tip  220  are more accurately and more reliably fabricated. 
     The antireflective coating of the present invention can be advantageously utilized in the fabrication of a T-head design for a magnetic head, and a perspective view of such a T-head design  250  is provided in FIG. 11. A basic feature of the T-head design  250  is that a P 2  pole tip  254  is separately fabricated in a photolithographic process, followed by the photolithographic fabrication of the yoke portion  258  of the P 2  pole. In this T-head design, the yoke portion  258  is commonly referred to as the P 3  pole. The T-head design  250  is attractive because the P 2  pole tip is separately fabricated with a lower aspect ratio (trench wall height to width) than the device depicted in FIGS. 5-10, such that a narrow P 2  pole tip can be more accurately fabricated. The P 3  pole  258  includes a pole tip portion  262  that is fabricated in magnetic connection with the P 2  pole tip  254 , such that magnetic flux can flow between the P 3  pole and the P 2  pole tip. Because the P 3  pole is fabricated on top of the inductive coils  50  and insulative layer  56 , the P 3  pole  258  includes a sloped portion  268 , and such a sloped portion  268  can lead to the reflected light problems described hereabove. Therefore, the use of an antireflective coating, as is next described, in the fabrication of the P 3  pole of a T-head design is advantageous, as is next described. 
     Initially, the P 2  pole tip  254  is fabricated upon a write gap layer  34 , and an insulative layer  274  is fabricated to the thickness of the P 2  pole tip. Thereafter, induction coil traces are fabricated, and an insulative layer  56  is deposited upon the induction coil traces  50 , such that the insulative layer  56  slopes downwardly  268  to an exposed top surface of the P 2  pole tip. To fabricate the P 3  pole  258 , a NiFe seed layer (which may require an initial adhesion layer) is first deposited. An antireflective coating of the present invention is next deposited upon the top surface of the NiFe layer. As described in detail hereabove, the antireflective layer preferably includes a first adhesion layer composed of silicon and a subsequent antireflective layer composed of carbon. The thicknesses and fabrication parameters provided hereabove are suitable for this anti-reflective coating. Thereafter, utilizing photolithographic techniques, as have been described hereabove, a patterned photoresist is fabricated upon the antireflective layer such that a P 3  pole trench is formed above the insulative layer  56 , the sloped portion  268  and the top surface of the P 2  pole tip  254 . Thereafter, utilizing RIE techniques described hereabove, the carbon and silicon antireflective coating layers are removed from the bottom of the P 3  pole trench. Thereafter, the P 3  pole is fabricated utilizing electroplating techniques into the P 3  pole trench. Following the fabrication of the P 3  pole, the remaining photoresist material is removed, and the remaining antireflective layer is subsequently removed utilizing RIE processing as discussed hereabove. Thereafter, the NiFe seed layer is likewise removed in areas that were under the photoresist, as has been described hereabove. 
     The T-head design, as depicted in FIG. 11, includes no indication in the final device that the antireflective coating of the present invention was used in the fabrication process. However, the P 3  pole  258 , and particularly the P 3  pole tip  262  is more accurately and more reliably fabricated due to the use of the antireflective coating of the present invention. 
     FIG. 12 depicts a perspective view of an alternative T-head design  300  of the present invention. A comparison of FIG. 12 with FIG. 11 reveals that the significant difference between the T-head design of FIGS. 11 and 12 is that the P 3  pole tip  304  of the P 3  pole  306  of the T-head design  300  of FIG. 12 is recessed from the subsequently formed ABS surface  308 , as compared to the P 3  pole tip  262  of the T-head design  250  depicted in FIG.  11 . However, the significant similarity between the T-heads  300  and  250  is that they each contain a P 3  pole  306  and  258  having a sloped portion  312  and  268  respectively. The utilization of the antireflective coating of the present invention in fabricating the recessed P 3  pole tip T-head design  300  depicted in FIG. 12 provides similar advantages to the use of the anti-reflective coating in fabricating the T-head design  250  depicted in FIG.  11 . That is, the use of the antireflective coating results in a more accurate and reliably fabricated P 3  pole tip  304 . The process steps in the fabrication and utilization of the anti-reflective coating of the present invention in fabricating the T-head design  300  depicted in FIG. 12 will be well understood by those skilled in the art having read and understood the use of the antireflective coating in fabricating the T-head  250  depicted in FIG. 11, and a detailed description thereof is therefore deemed unnecessary. 
     While the present invention has been shown and described with reference to certain preferred embodiments, it is to be understood that those skilled in the art will develop various alterations and modifications in form and detail hereto. It is therefore intended that the following claims include all such alterations and modifications that nevertheless include the true spirit and scope of the present invention.