Patent Publication Number: US-6658922-B2

Title: Optical equipment assemblies and techniques indexed to a common spindle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of United States provisional patent application, application Ser. No. 60/270,415, filed Feb. 20, 2001, and U.S. provisional patent application, application Ser. No. 60/312,923, filed Aug. 16, 2001, each of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to optical equipment assemblies and techniques, and more particularly to disc media metrology. 
     2. Description of the Related Art 
     A form of an information storage and retrieval device is a hard disc drive (“disc drive”). A disc drive is conventionally used for information storage and retrieval with computers, data recorders, redundant arrays of independent discs (RAIDs), multi-media recorders and the like. A disc drive comprises one or more disc media. 
     Each disc media comprises a substrate upon which materials are deposited to provide a magnetically sensitive surface. In forming the magnetically sensitive surface, a servo pattern or more particularly servo pattern media, may be formed on such substrate. A servo pattern media conventionally is a pattern of raised features, such as posts or columns. In a servo pattern, position error signal (PES) marks may be formed. Such PES marks conventionally are a pair of contiguous or inter connected posts. In addition to such servo pattern media, another form of pattern media that may be formed on a substrate is bit pattern media. A bit pattern or bit pattern media is an arrangement of posts or columns for storing bits of information. 
     As disc media storage requirements increase, namely, density is enhanced, topographic features whether for servo pattern media, bit pattern media or other media become smaller. For example, PES marks in bit patterns may be formed below 500 nanometers in lateral dimension. Moreover, as such posts become smaller in lateral dimension, spacing between posts also decreases. Thus, viewing such posts, as well as regions between posts, by conventional means is not practical. For example, a conventional interference based microscope uses a monochromatic light source of approximately 550 nanometers. Because the wavelength of the light source is larger than lateral dimension of the bit pattern elements themselves, a conventional interference based microscope is not sufficient for detailed resolution of topographic information associated with such pattern media. 
     Accordingly, an atomic force microscope (AFM) may be used to scan a disc media surface. An AFM scans not optically, but by physical touch using a contact probe. However, a difficulty arises in locating patterns for identifying a correct contact starting position for an AFM scan. Conventionally, a technician uses an interference-based microscope to locate a pattern; however, as mentioned above owing to resolution limitations of such conventional interference-based microscopes placement of probe tip is problematic. It should be appreciated that an AFM probe tip may be as narrow as 1 nanometer. 
     Not all servo pattern media uses topographic features. Some servo patterns are completely magnetically written. Conventional magnetically written servo patterns do not have topographic features, and thus rather than relying on spacing loss to generate a differential signal as in topographically patterned surfaces, magnetically written patterns rely on magnetic domain switching. Such magnetically written patterns are not detectable with topography. However, some servo patterns are a combination of topographic features and detectable magnetic information. 
     Accordingly, it would be desirable to provide for detection of servo or other patterns or features whether produced topographically or magnetically or both. More particularly, it would be desirable to provide for detection of servo patterns for determining a starting position for an AFM scan in order to obtain nano-scale image or other information. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides method and apparatus for detecting a scanning a media. More particularly, an aspect of the present invention comprises a stage, a spindle configured to support the media, a first linear actuator connected to the stage, a second linear actuator connected to the stage, a polarization detector connected to the first linear actuator and positionable to scan the media, and an atomic force microscope connected to the second linear actuator and positionable to scan the media. The polarization detector is configured to provide optical energy incident on the media and to detect change in polarization of the optical energy reflected from the media to provide magnetic imagery of the media. The polarization detector and the atomic force microscope indexed to the spindle. 
     Another aspect of the present invention is a method for scanning a media. A polarization detector, an atomic force microscope, a platform, a first linear actuator, a second linear, and a spindle are provided. The spindle is centrally located with respect to the platform. The first linear actuator is coupled to the platform and the polarization detector, and the second linear actuator is coupled to the platform and the atomic force microscope. A servo pattern magnetically written to the media is detected with the polarization detector. The atomic force microscope is positioned in response to the servo pattern for the scanning of the media with the atomic force microscope. 
     Another aspect of the present invention is an apparatus for scanning a media comprising means for supporting and rotating the media; means for detecting polarization for providing a magnetic image of the media indexed to the means for supporting and rotating the media; means for probing the media for providing a topographic image indexed to the means for supporting and rotating the media; and means for providing a common rotatable platform for the means for detecting polarization and the means for probing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     FIG. 1 is a block diagram of an exemplary portion of an embodiment of a metrology system in accordance with one or more aspects of the present invention. 
     FIG. 2 is a block diagram of an exemplary portion of a topographically formed pattern of a disc media in accordance with the prior art. 
     FIG. 3 is a block diagram of an exemplary embodiment of an AFM objective lens/optical detector/AFM probe tip in accordance with one or more aspects of the present invention. 
     FIG. 4 is a block diagram of an elevated view of an exemplary embodiment of a disc media having multiple optical detectors in accordance with one or more aspects of the present invention. 
     FIG. 5 is an exemplary embodiment of a metrology system in accordance with one or more aspects of the present invention. 
     FIGS. 6A,  6 B,  6 C and  6 D are polarization diagrams of a portion of a linearly polarized energy source reflecting off of a magnetically charged portion of disc media surface in accordance with the magnetic Kerr effect. 
     FIG. 7 is a flow diagram of an exemplary embodiment of a metrology process in accordance with one or more aspects of the present invention. 
     FIG. 8 is a block diagram of an exemplary embodiment of an information processing system configured in accordance with one or more aspects of the present invention. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a block diagram of an exemplary portion of an embodiment of a metrology system  10  in accordance with one or more aspects of the present invention. Metrology system  10  comprises linear actuator  13 , AFM  12 , optical detector  11  which may be configured to detect scattered optical energy or polarization of optical energy or both, information processing system  17 , spindle  16  and stage/platform  15 . Spindle  16  is configured to be rotated. Conventionally, spindle  16  is rotated at approximately 10,000 revolutions per minute (RPM). Platform  15  may be, but need not be, configured to rotate. Located on spindle  16  is disc media  14 . Accordingly, it should be appreciated that linear actuator assembly  13  may be used to position scatter detector  11  inwardly or outwardly with respect to disc media  14 . Moreover, rotation of either or both stage  15  or spindle  16  may be used to position scatter detector  11  with respect to disc media  14 , to initially align an AFM probe for AFM scanning of disc media  14 . Optionally, a precision conveyor  19  having a plurality of spindles  16  attached to it may be used under control of information processing system  17 . 
     Optical detector  11  may be optically coupled or in communication with an objective lens of AFM  12 . Optical detector  11  is used to resolve servo spokes on disc media  14  with sufficient positional accuracy for moving AFM  12  to a starting position for topographic scanning, or magnetic force microscopy scanning as described below in more detail. Information collected by optical detector  11  and AFM  12  is provided to information processing system as one or more signals  81 . Additionally, control signals as one or more of signals  81  may be provided from information processing system  17  to either or both optical detector  11  and AFM  12 . Control of rotation of spindle  16  and platform  15  may be provided by signals  84  and  83 , respectively, from information processing system  17 . Control of linear movement by linear actuator  82  may be provided by information processing system  17  via signal  82 . As optical detector  11 , AFM  12 , linear actuator assembly  13 , spindle  16 , rotatable platform  15 , and information processing system  17  are known, unnecessary details regarding their configuration are not included herein in order to avoid obscuring one or more aspects of the present invention. 
     System or arrangement  10  may be used for automatically locating a topographically detectable pattern on disc media  14  using optical detector  11 , for example to locate servo spokes. A differential optical signal is used. In other words, for light scatter, light reflected off of disc media  14  is affected by topography, and thus there is a difference in reflected light as detected by optical detector  11 . The optical energy source for the light may be a laser or other high intensity light source. Though a separate optical energy source may be used, AFM  12  comprises an optical energy source for providing light incident to a surface of disc media  14 . Similarly, a region of disc media  14  comprising magnetic transitions, for example in servo spokes, produces an altered light polarized state which is measurable by optical detector  11  when configured to detect polarization, namely, polarization detector  11 . 
     Accordingly, optical detector  11  may be used to locate servo spokes or another pattern on disc media  14  as indicated from detected reflected light. If a disc substrate is optically transparent, then light scattering techniques need to be adapted. Notably, back side reflection or scatter from spokes causing ghosts peaks may be substantially removed or eliminated by narrowing or otherwise adjusting scatter channel  18 , as is illustratively shown with a double-arrow line in FIG. 3, to limit or avoid detecting dispersed-reflected light at unwanted angles. Thus, forward scattered or reflected light, namely optical on axis light, is more likely to be detected than off axis, especially wide angle off axis, light by more narrowly limiting detector scatter channel  18 . Once a pattern is located by either or both light scatter or polarization, an AFM probe or piezo, conventionally mounted to an objective lens of such an AFM, may be positioned to such pattern, and disc media  14  is rotated at a controlled speed on spindle  16 . 
     Referring to FIG. 2, there is shown a block diagram of an exemplary portion of a topographically formed pattern  20  of a disc media  14  in accordance with the prior art. Topographically formed pattern  20  may be a portion of a servo spoke pattern having PES marks  22  and posts  21  separated by spaces  29 . Lateral resolution of metrology system  10  is approximately two to three microns, which is sufficient to position its field of view to PES marks  22  embedded in servo spoke pattern  20 . Notably, as indicated in cut-away three-dimensional view  23 , PES marks  22  are dimensionally formed above a surface of a substrate assembly  25  of disc media  14 . The same applies to posts  21 . Accordingly, it should be appreciated that posts  21  and PES marks  22 , formed with contiguous posts  21 , which may or may not be overlapped, may be used to obtain topographic information. 
     Referring to FIG. 3, there is shown a block diagram of an exemplary embodiment of an AFM objective lens/optical detector/AFM probe tip in accordance with one or more aspects of the present invention. With continuing reference to FIG.  3  and renewed reference to FIG. 1, after resolving a pattern, such as servo spokes, AFM probe tip  28  coupled to objective lens  27  may be automatically positioned using at least one of linear actuator  13 , rotatable spindle  16  and rotatable platform  15 . For example, AFM objective lens  27  may be focally aligned to an edge of a servo spoke pattern as a starting reference for scanning. Scanning size may be five microns by five microns; however, other scan sizes may be used. Position tolerance of AFM objective lens  27  is approximately plus or minus seven microns. Notably, this is approximately two to three times the resolution of optical detector  11 , which is approximately two to three microns. Thus, positioning is still dependent upon moving AFM objective lens  27  to a correct location, and accordingly by having AFM  12  and optical detector  11  physically connected and indexed to a single spindle  16 , accurate positioning is enhanced. Moreover, information processing system  17  may be in communication with one or more of linear actuator  13 , rotatable stage  15  and rotatable spindle  16  for controlled movement thereof. 
     Because scattered channel detection is coupled with an AFM scanning capability, the above-mentioned tolerances are dependent upon individual capabilities of instrumentation employed. An embodiment of metrology system  10  was built using a reflectometer from Candela OSA and AFM from JMAR. Furthermore, information processing system  17  may be programmed with peak detection software to determine spoke location for an automated approach to scanning servo patterns. Accordingly, information processing system may be a programmed computer. 
     Referring to FIG. 4, there is shown a block diagram of an elevational view of an exemplary embodiment of a disc media  14  having multiple optical detectors  11  in accordance with one or more aspects of the present invention. Disc media  14  comprises spokes  26 . Two exemplary positions  24 A and  24 B for multiple detectors  11  are shown. Though four detectors  11  are shown in a square pattern alignment, fewer or more detectors  11  may be used and arranged as a square or other geometric pattern, such as a circle, a triangle, and the like depending on the number of detectors employed. Multiple detectors  11  gather additional data as compared to a single detector during a scatter detector scanning stage. Notably, multiple detectors  11  may be used without lengthening acquisition time as compared to just having one detector. Though detectors  11  are for detecting scattered light, they may be configured to detect polarization orientation of reflected light, as described in more detail below. 
     Scattered channel  18  may be used to generate topography-based map capable of resolving an area of as little as approximately three-square microns. By having multiple detectors arranged in a pattern, position of detectors  11  with respect to disc media  14  may be determined by identifying which detectors  11  detect a spoke pattern. Moreover, with respect to position  24 B, if no detectors detect a spoke pattern, it may be determined that detectors  11  are positioned in an area of tracks of disc media  14 . Thus, by using multiple detectors  11 , spokes  26  may be identified more quickly than having a single detector  11 . Additionally, by having multiple detectors  11 , determining one or more defects, apparent size of a detected defect, and rapidity of scanning a surface area of disc media  14  are enhanced. 
     Referring to FIG. 5, there is shown an exemplary embodiment of a metrology system  50  in accordance with one or more aspects of the present invention. Metrology system  50  of FIG. 5 is similar to metrology system  10  of FIG.  1 . Differences include the addition of an optical energy source, such as a laser,  34  coupled to one or more polarization detectors  39 , collectively optical polarization detector  30 , and optionally optical microscope  31 . Polarization detectors  39  are use for determining orientation of polarization. Moreover, polarization detectors  39  may be configured to detect scattered light. A plurality of detectors  39  may be arranged as described above with respect to use of multiple detectors  11 . Optical polarization detector  30  and optical microscope  31  are mounted on respective linear actuator assemblies  13 . Scatterometer linear actuator assembly  13  may be in communication with information processing system  17  for controlled movement of optical polarization detector  30 , and optionally optical microscope linear actuator assembly  13  may be in communication with information processing system  17  for controlled movement of optical microscope  31 . Addition of optical microscope  31 , which may employ white light or ultraviolet energy source, allows user intervention in deciding whether a given defect or feature should be scanned by AFM  12 . 
     In an embodiment, optical polarization detector  30  may be used to identify one or more defects, if any, on a surface of disc media  14 . Once any defect is identified, optical microscope  31  may be used to identify defect size. Alternatively to or in combination with optical viewing through microscope  31 , optical polarization detector  30  may be used to detect apparent defect size. AFM probe  28  is used to measure actual defect topography based on lateral scan dimensions taken from optical microscope  31  or optical polarization detector  30 . In order to observe the same defect on multiple systems, defect location must be mapped out precisely with optical polarization detector  30 . Because multiple pieces of equipment are integrated so that they are on a same platform  15  and indexed to a same spindle  16 , defect relocation may be achieved with greater rapidity and quickness as compared to equipment not integrated on a same platform and not indexed to a single spindle. 
     In another embodiment, optical polarization detector  30  may be configured to incorporate at least one of Kerr effect microscopy, ellipsometry and reflectometry, which may be in addition to scatterometry capability. AFM  12  may be configured with at least one of module  55  of magnetic force microscopy, conductance/capacitance microscopy, and face measurement in addition to conventional topography mapping functions. These additions to optical polarization detector  30  and AFM  12  enhance functionality. 
     As mentioned above, polarization states of light reflected from disc media  14  may be detected. More particularly, with respect to polarization detector  30 , magnetization states of magnetic media of disc  14  are detected optically using the magnetic Kerr effect. A linearly polarized light, such as a laser beam, is provided to be incident on the surface of disc media  14 . Polarization of reflected light from such laser beam undergoes a slight rotation with respect to that of incident light. The amount and sense of such rotation angle depends on magnetization state of the media spot from which such light is reflected. 
     Referring to FIGS. 6A,  6 B,  6 C and  6 D, there are shown polarization diagrams of a portion of a linearly polarized energy source  42 , such as a laser beam, reflecting off of a magnetically charged portion  41  of disc media surface  49  in accordance with the magnetic Kerr effect. Energy beam  42  comprises polarized components as indicated by arrows  43 . Incident light is linearly polarized, and the plane of such polarization is perpendicular to one defined by magnetization vectors  44  of disc media portion  41 . Moreover, plane of polarization of beam  42  is perpendicular to the propagation vector of beam  42 . Reflected beam  45  has electric field vectors as indicated by arrows  46  wherein there is a degree of rotation of such vectors. Note that for two opposite magnetization states of disc media portion  41 , corresponding rotations of electric field vectors have opposite rotation directions. For example, in FIG. 6B, direction of magnetization as indicated by arrows  48  is opposite that of FIG. 6A, and consequently rotation direction of polarization as indicated by arrows  47  is opposite that as indicated by arrows  46 . Accordingly depending on direction of magnetization of disc media portion  41  with respect to that media&#39;s surface upon which a light source is incident, reflected light from such surface has a polarization that takes on an orientation associated with direction of such magnetization. This is true for perpendicularly magnetized media, such as in FIGS. 6A and 6B, as well as longitudinally magnetized media, as illustratively shown in FIGS. 6C and 6D. Thus, whether polar Kerr effect or longitudinal Kerr effect is applied, magnetization state may be detected independent of topography. In other words, upper surface  49  may be completely flat, and yet a pattern such as a servo spoke pattern can be detected. As mentioned above, once a servo spoke pattern is determined by polarization detector  30 , a probe of AFM  12  may be initially positioned for purposes of scanning. 
     There are many possible uses for metrology system  50 . Examples of such uses include carbon film thickness mapping, carbon filled thickness where in correlation with localized corrosion sights, loop thickness mapping, contact force measurements in localized sights, large-scale scratch detection, high-resolution topography in magnetic force interaction with scratches, magnetically mapping of transitions—especially in servo patterns or in a data zone, and inspecting discrete bits or individual servo patterns. 
     In another embodiment, instead of polarization detector  30  and/or optical microscope  31 , a laser-based interferometer system that images large fields of view and captures images on a high resolution CCD may be used. 
     Referring to FIG. 7, there is shown a flow diagram of an exemplary embodiment of a metrology process  60  in accordance with one or more aspects of the present invention. With continuing reference to FIG.  7  and renewed reference to FIG. 5, at step  61  defects are identified. This is done by use of an optical microscope  31  or optical polarization detector assembly  30 . At step  62 , such defects are measured. This is done by use of an optical microscope  31  or optical polarization detector assembly  30 , the latter of which may comprise one or more detectors to measure both optical scatter and polarization. At step  63 , magnetic or topographic orientation is measured. Magnetic orientation is measured by use of polarization detector  30 , for example using a Kerr effect. This will produce a magnetic image, which may be used to disclose a pattern, such as a servo pattern. Topographic orientation may be measured as described above. At step  64 , AFM  12 , which may be configured with a magnetic force microscopy module  55 , is aligned, for example to such servo pattern, using such magnetic image, or a topographic image as described above. At step  65 , disc media surface is scanned by AFM  12 . 
     Accordingly, defects may be identified, as well as generation of topographic and magnetic images of a disc media surface. 
     Referring to FIG. 8, there is shown a block diagram of an exemplary embodiment of an information processing system  17  configured in accordance with one or more aspects of the present invention. Information processing system  17  comprises processor, such as a microprocessor,  71 , memory  72 , such as random access memory, read only memory, magnetic memory, optical storage memory, and the like, and input output (I/O) interface  73 . Additionally, information processing system  17  may comprise one or more input and/or output devices  75 , such as a display, a keyboard, a curser positioning device, a printer, and the like. Information processing system may be coupled to a network  74 . Memory  72  may comprise all or a portion of process  60  for automatically identifying defects in accordance therewith. 
     With renewed reference to FIGS. 1 and 5 and continuing reference to FIG. 8, one or more of signals  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87  and  88  are provided to I/O interface  73 . Alternatively, one or more of signals  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87  and  88  may be provided to information processing system  17  via a network  74  coupled to I/O interface  73 . Signals  86  and  87  are similar to above described signal  82 , but are for linear movement of optical microscope  31  and optical polarization detector  30 , respectively, instead of AFM  12 . Signal  85  is similar to above described signal  81 , except detector  11  is not coupled to AFM  12  in the embodiment shown in FIG. 5; rather, optical polarization detector  30  provides and is provided with information to and from information processing system  17  via signal  88 . 
     While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.