The present invention relates to perpendicular magnetic recording and more particularly to a method for manufacturing a magnetic write pole using a novel multi-gas chemistry during reactive ion etching of a write pole defining polymer mask under-layer.
The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension amr to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head can include a magnetic write pole and a magnetic return pole, the write pole having a much smaller cross section at the ABS than the return pole. The magnetic write pole and return pole are magnetically connected with one another at a region removed from the ABS. An electrically conductive write coil induces a magnetic flux through the write coil. This results in a magnetic write field being emitted toward the adjacent magnetic medium, the write field being substantially perpendicular to the surface of the medium (although it can be canted somewhat, such as by a trailing shield located near the write pole). The magnetic write field locally magnetizes the medium and then travels through the medium and returns to the write head at the location of the return pole where it is sufficiently spread out and weak that it does not erase previously recorded bits of data.
A magnetoresistive sensor such as a GMR or TMR sensor can be employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, or barrier layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. First and second leads are connected to the sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos Θ, where Θ is the angle between the magnetizations of the pinned and free layers. In a read mode, the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
At very small bit sizes it is very important to define the write pole very accurately. For example, processes used to manufacture the write pole defining mask structure can result in the mask structure being poorly defined, with rough sidewalls, irregular undercuts and other deformities. This makes an accurate definition of the write pole difficult to achieve.
The present invention provides a method for manufacturing a magnetic write head that includes, depositing a magnetic write pole material, and after depositing the magnetic write pole material, depositing a polymer mask under-layer. A dielectric hard mask is deposited over the polymer mask under-layer, and a photoresist mask is formed. The image of the photoresist mask is transferred onto the dielectric hard mask, and a reactive ion etching is performed to transfer the image of the dielectric hard mask onto the under-layer polymer mask layer, the reactive ion etching (RIE) being performed in a chemistry that includes an oxygen containing gas and a nitrogen containing gas.
The presence of both the oxygen containing gas and the nitrogen containing gas advantageously allows the polymer mask under-layer to be formed with smooth, straight well defined side walls, without footing, with little to no undercutting or other defects. This allows the write pole to be more accurately defined by a subsequent ion milling process that transfers the pattern of the polymer mask under-layer onto the magnetic write pole material.
The invention presents an alternate process method to fabricate magnetic laminate write heads. This new method uses a novel RIE plasma chemistry to etch the under-layer pole mask by introducing a certain amount of non-oxygen containing gas into an oxygen containing atmosphere, such as a carbon dioxide (CO2) dominated plasma. The results of this two-gas chemistry showed dramatically different performance from the CO2 only etching. The geometry of the polymer mask under-layer is more controllable, the defects such as irregular undercuts are minimized and bottom footing is completely removed. More importantly, the side walls of the polymer mask under-layer are much smoother, the cross-sectional profile of the under-layer is much better controlled toward the desired shape required by the subsequent mill process. In addition, it gives wider process margin for the subsequent ion milling.
These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.
For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale.
The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.
Referring now to
At least one slider 113 is positioned near the magnetic disk 112, each slider 113 supporting one or more magnetic head assemblies 121. As the magnetic disk rotates, slider 113 moves radially in and out over the disk surface 122 so that the magnetic head assembly 121 may access different tracks of the magnetic disk where desired data are written. Each slider 113 is attached to an actuator arm 119 by way of a suspension 115. The suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122. Each actuator arm 119 is attached to an actuator means 127. The actuator means 127 as shown in
During operation of the disk storage system, the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension 115 and supports slider 113 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by control unit 129, such as access control signals and internal clock signals. Typically, the control unit 129 comprises logic control circuits, storage means and a microprocessor. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112. Write and read signals are communicated to and from write and read heads 121 by way of recording channel 125.
With reference to
The write head 300 may also include a trailing magnetic shield 318, located at the air bearing surface (ABS) and separated from the write pole 302 by a non-magnetic trailing gap layer 320. The trailing magnetic shield 318 can be connected with the other magnetic structures at the back of the write head 300 by a trailing magnetic pole 322.
This under-layer 608 (which also can be referred to as an image transfer layer) provides masking during an ion milling process that will be described herein below. The thickness of the under-layer 608 depends upon the duration and strength of the ion milling that will be performed to define the write pole, however the layer 608 can be from a few hundred nanometers to more than two thousand nanometers.
The dielectric hard mask layer 610 can be constructed of a dielectric material and is preferably constructed of a Si containing hard mask material such as silicon oxide, silicon nitride, silicon oxynitride or a silicon containing organic material such as SIHM® (Shin-Etsu Chemical Co., Ltd.), UVAS (Floneywell International Inc.) and etc. The thickness of the dielectric hard mask 610 depends on the thickness of the underlayer 608. Generally, the thicker the under-layer 608, the thicker the dielectric hard mask 610 will have to be. An optional Bottom Anti-Reflective Coating (BARC) 612 may be applied over the dielectric hard mask 610. The determination of whether a BARC layer 612 is needed depends on the requirements of the photolithograph and on the material used for the dielectric hard mask 610. For example, if the dielectric hard mask 610 itself is a material that acts as a BARC, then no BARC layer 612 is needed. Such materials include silicon oxynitride, SIHM (Shin-Etsu Chemical Co., Ltd.), UVAS (Honeywell International Inc.). Also, no BARC 612 is needed if the dielectric hard mask 610 is sufficiently thin and the critical dimensions of the magnetic pole are large enough that the under-layer 608 can function as a BARC. However, some form of BARC is desirable to control photolithography parameters such as reflective swing and photo critical dimensions.
After deposition of the layers 604, 606, 608, 610 and option layer 612, a layer of photoresist 614 is deposited. The thickness of the photoresist must be thick enough to effectively mask the BARC 612 and/or dielectric hard mask 610 when transferring the image of the photoresist mask onto the dielectric hard mask 610 (as will be described below). The photoresist layer 614 is photolithographically patterned to define a write pole defining mask, leaving a structure as shown in
As shown in
A second RIE process is then performed to transfer the image of the dielectric hard mask 610 onto the under-layer 608 by removing portions of the layer 608 that are not protected by the dielectric hard mask 610, leaving a structure as shown in
After under-layer 608 has been patterned as described above, an ion milling is performed to transfer the image of the patterned under-layer 608 onto the under-lying ion milling mask 606 and magnetic laminate material 604, leaving a structure as shown in
As can be seen, the patterned under-layer 608 defines the shape of the final, formed write pole 604. Therefore, it is important that the shape of the under-layer 608 be very well defined, and especially that the sides 902, 904 are well defined.
As mentioned above, the present invention utilizes a novel reactive ion etching process that overcomes these challenges described above with reference to
One plasma tool especially suitable for the RIE process to etch the Si containing hard mask material and polymer mask under-layer is Plasma-Therm's Versalock™ etcher, which is an inductively coupled plasma (ICP) etch system in which the plasma is generated by means of inductively coupling 2 MHz RF power (the source power) while independently controlling the ion energy directed toward the substrate via 13.56 MHz bias power. This separate power control allows for the conduction of wider RIE processes ranging from highly chemical processes to highly physical processes. The Versalock etcher is equipped with Optical Emission Spectrometry (OES) endpoint system that the over-etch amount can be precisely controlled via the determination of etch endpoint.
Many Other ICP etchers equipped with both source and bias power suppliers, such as TCP® 9400DFM from Lam Research Inc., or DPS® from Applied Materials Inc., can also be used for the RIE process of the Si containing hard mask material and polymer mask under-layer. We expect that the RE process presented in this art can be transferable transparently in different ICP etchers. If fact, our test in TCP® 9400DFM from Lam Research Inc. confirmed that it could give the same results as we have obtained in Plasma-Therm's Versalock™ etcher by doing minor tuning of the RIE parameters.
As discussed above, an ideal under-layer 608 should have such features that the cross section of the pole is a slightly tapered trapezoid with little bit smaller bottom CD than top CD and the edge profile must be straight and smooth, also there should be no top/bottom undercut and no bottom footing as shown in
The features of the under-layer 608 formed by this new plasma chemistry are dramatically different from the conventional ones in several respects:
1) The roughness on the side walls 902, 904 of the under-layer 608 is dramatically reduced and the edge profile is much smoother. Therefore, it is expected that there will be much less re-deposition on the side wall of the under-layer 608 during ion milling process.
2) The shape of the under-layer 608 is basically tapered with a slightly larger top CD and smaller bottom CD, as described with reference to
3) There is very little or no top undercut, thus eliminating the metal re-deposition at top of the under-layer 608 during ion milling.
4) There is no footing found at the bottom of the under-layer 608, which gives better control on both CD and shape of the laminate poles 604 during the subsequent ion milling process.
Unlike the conventional RIE processes in which only oxygen containing gases (carbon dioxide (CO2) or oxygen (O2) are used to produce the plasma to etch the under-layer, in the newly developed RIE process, a certain amount of nitrogen (Ne) gas is added to oxygen containing plasma. The addition of nitrogen (Nz) provides a different plasma chemistry in etching the under-layer 608 and provides an opportunity to re-tune the RIE process to reach desired parameters. Development was focused on carbon dioxide (CO2) and nitrogen (N2) plasma. The process tuning of this two-gas plasma chemistry can be optimized by adjusting the following parameters, the relative ratio of carbon dioxide (CO2) gas flow to nitrogen gas (N2) flow, the total amount of carbon dioxide and nitrogen gas flow, the gas pressure of the plasma chamber, the input amount of the bias power, and the input amount of source power, the relative ratio of bias power to source power, the over-etch amount, the temperature of the wafer (or the temperature of the chuck on which the wafer is held) and back side helium cooling pressure. However, the last two parameters have relatively less sensitive effect on process tuning as other RIE parameters and are also not so convenient to adjust due to the restriction of tool sharing with many other production processes and thus usually remain as constant throughout entire testing.
While the total gas flow is limited by the hardware of the reactive ion etching tool (such as gas flow meter and chamber pressure controlling), the gas ratio between carbon dioxide and nitrogen can be adjusted in a certain range which could give desired effects. The range of the gas ratio (gas flow of carbon dioxide to gas flow of nitrogen) can vary from 15 to 1.5. If the gas ratio is beyond the high limit, then there is so little nitrogen in the mixed gas that the effect of nitrogen may not be effective, the plasma chemistry is more close to that of the pure carbon dioxide, the profile of the etched under-layer pole is toward that of pure carbon dioxide and thus cause undesired footing at tihe bottom of the under-layer pole and roughness on the side wall of the under-layer pole. If the gas ratio is below the low end limit, then there is too much nitrogen which causes three undesired results: more curved side wall profile on the upper part of the under-layer 608, a broader CD at near the top of the pole, and faster shoulder erosion of the dielectric hard mask.
Besides the adjustment of the gas ratio, other parameters such as the chamber pressure can also be changed to assist process tuning. In test, the chamber pressure was kept in the range of 2 to 10 mT. A pressure lower than this range may cause pressure control issue due to the hardware limitations, and higher pressure may cause profile issues such as excessive bottom undercut and CD shrinkage and also may produce more roughness on side wall of the under-layer 608 due to the excessive isotropic etch to the side wall. In addition, the power ratio (bias-power to source power) also plays important role in the process tuning, the desirable range of the power ratio (bias power/source power) is from 0.5 to 1.5. Generally, the higher the power ratio is the less the top under-cut and CD shrinkage will be. For even lower power ratios, too much isotropic etching from source power causes more side-wall etching which may give rise too much top and bottom undercut, plus the profile of the under-layer 608 will be more tapered, and the side wall will get rougher. For higher power ratio, too high of a bias-power means more physical etching such that the dielectric hard mask get eroded much faster, especially at the shoulder of the mask which may cause quick rounding of the dielectric hard mask 610 and causing loss of mask function.
The mechanism by which the addition of nitrogen to carbon dioxide reduces the roughness of the side wall of the polymer mask under layer 608 during plasma etching is not clear yet. Further research and study are necessary to figure out the mechanism. One possible mechanism is that the nitrogen radicals or nitrogen ions may clean the surface of the side wall of the under layer 608 which may have re-deposition containing carbon/nitrogen complexes and make the side wall smooth. With existence of nitrogen in plasma during etching of the under-layer 608, the re-deposition of the carbon/nitrogen containing materials created during RIE etching of the under-layer can be instantaneously removed when it is formed, therefore, the side wails 902, 904 of the under-layer 608 are always re-deposition free, thus keeping the side walls 902, 904 smooth. Another possible mechanism is that nitrogen radicals or nitrogen ions are a much gentler etchant than oxygen or oxygen containing radicals/ions, so that the plasma attacking of the side walls 902, 904 of the under-layer 608 is reduced with the addition of nitrogen, this may relate with the phenomena that with more addition of nitrogen that the top CD of the under-layer 608 gets larger. That is, the nitrogen is more effective at removing the re-deposition on the wall surface of the under-layer 608 but has less etching ability on the materials of the pole, where the chemical compositions of the re-deposition may be different from those of the under-layer material 608.
The importance of this newly developed etching process for patterning of the under-layer mask 608 is that it produces much smoother side walls 902, 904 than the conventional process, that it will not allow the re-deposition exist during ion milling process, and that it produces the right main pole shape and profile. In addition, since there is no top undercut, that also eliminates the re-deposition under the dielectric mask which often causes problem with regard to ion milled ABS poles. Moreover, it gives a better control to both of the top and bottom CD which are critical to the final CD control of the main pole. Overall, the new process to fabricate under-layer mask 608 gives better performance over conventional processes and is being used in fabrication of the new generations of the magnetic writer heads and is also expected to be applied to fabricating the more advanced generations of the magnetic writer heads.
While various embodiments have been described, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.