Abstract:
Techniques for performing metrology on magnetic media disk formations that are arranged in curvilinear patterns are disclosed. Small integrated test patterns having rectangular periodicity are integrated among the concentric circles of patterned media formations. The test patterns cover only very small areas of the disk so as to not significantly affect disk capacity. The periodicity of the test patterns allows their formations to be more readily measured by metrology technology than those having a curvilinear periodicity.

Description:
This application is a continuation of U.S. patent application Ser. No. 11/857,074, filed Oct. 22, 2007, and is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to media disks and, in particular, to an improved system, method, and apparatus for performing metrology on the patterned magnetic media disks used in hard disk drives with integrated test pattern areas. 
     2. Description of the Related Art 
     Magnetic media such as the disks used in hard disk drives are typically constructed with concentric circular patterns of formations (e.g., lines, dots, etc.) that are on the order of nanometers in their dimensions. These formations on the patterned media must be qualified during manufacturing to ensure the quality and reliability of the product. 
     Patterned media may be evaluated with metrology technologies that utilize optical instruments based on spectroscopic ellipsometry or reflectometry. An alignment procedure typically is used for metrology and includes an additional pattern of one or more alignment marks. Alignment is required for pattern search and accurate measurement. These technologies precisely measure critical dimensions, sidewall angles, and multiple layer film thicknesses. The measurements are made on two-dimensional line and space structures, as well as three-dimensional hole and island structures. This technology produces accurate and precise models for production use of scatterometry results for both stand-alone and integrated metrology applications. 
     However, conventional metrology technologies only work in measuring formations that are arranged in rectilinear (e.g., rectangular, parallelogram-like, or hexagonal) patterns, rather than formations that have curvilinear periodicity such as those on magnetic media disks. In addition, the sizes of patterns, dots, and lines are too small to identify with the inspection techniques used by ellipsometry and x-ray refractivity. These techniques can only provide average dimensions for a periodic collection of islands. Moreover, SEM inspection techniques are slow, expensive and destructive to the sample being measured (i.e., because it requires the sample to be broken into smaller pieces, or because it contaminates the sample). This issue is becoming more significant as the data density (e.g., bits/nm 2 ) in disk drives continues to increase. 
     As shown in  FIG. 1 , the regularity of features on magnetic media disks varies according to the radial position of the sample being analyzed on the surface of the disk due to the concentric circular patterns. For example, at sample  11 , which is a laser spot having a diameter of 50 μm located at a radial distance of 0.3 inches from the disk center  13 , the radius of curvature of the pattern of formations is far more pronounced than at sample  15 , which is located at a radial distance of 1.25 inches from the disk center  13 . Although current measurement technologies provide adequate metrology for some rectilinear formation patterns, they are not as well suited for curved formation patterns such as those in samples  11  and  15 . Thus, an improved solution for measuring features that are arranged in curvilinear patterns would be desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of a system, method, and apparatus for improving the metrology of formations and features on patterned media disks for disk drives are disclosed. The disks are provided with a measurement assistance tool comprising small, integrated test pattern areas. In one embodiment, the test patterns are formed with and interspersed among the concentric circles of patterned media used for data storage on the surface of the disks. Unlike the curvilinear patterns of formations, the test pattern areas may be arranged in rectangular, parallelogram or hexagonal patterns. Since some embodiments of the test pattern areas are not usable for data storage, the test pattern areas cover only very small areas of the disk so as to not significantly affect disk capacity. The formations in the test pattern areas are more readily measured by metrology technology than those formations having curvilinear periodicity, which makes the qualification of media disks in manufacturing non-distractive, easier and faster. 
     In one embodiment, the test pattern areas may be formed as blanket film patterns or featureless pads, which are well suited for film characterizations of thickness, density, and composition. Latticed dot patterns address metrology parameters of pattern size characterizations, including critical dimensions, height, angle, roughness, and rounding of those features. The trimming of latticed dot patterns, or the introduction of empty rows or spaces, addresses on the more high resolution patterns. This has the effect of lowering the density of features and enabling better measurements for some applications. In addition, solid lines and spaces assist in characterizing track patterns, discrete track, and pre-patterned servo patterns, including critical dimensions, height, angle, roughness, and rounding of those features. The addition of these kinds of patterns in selected small areas of the disks enables good measurements to be taken for better process control. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic diagram of a patterned disk surface illustrating the variance in periodicity of formations formed thereon; 
         FIG. 2  is a schematic diagram of one embodiment of a magnetic media disk having test patterns constructed in accordance with the invention; 
         FIGS. 3A-F  are illustrations of various embodiments of formations and patterns of the test patterns of  FIG. 2  and are constructed in accordance with the invention; and 
         FIG. 4  is a schematic diagram of one embodiment of a disk drive constructed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 2 and 3 , embodiments of a system, method, and apparatus for improving the metrology of formations and features on patterned media disks for disk drives are disclosed. As schematically diagramed in  FIG. 2 , a data storage disk  21  comprises a substrate having a large plurality of data storage formations  23  (e.g., lines, dots, etc.) of magnetic media configured with a curvilinear periodicity. In addition, the disk may be provided with measurement areas that are featureless (i.e., no lines or dots), which are useful for measuring film thickness. Featureless areas also are useful for manufacturing process control since the film thickness relates to the height of the formations. 
     The data structures  23  may comprise circular tracks of magnetic islands, each of which typically comprises a small pillar of material. In some fabrication methods, a pillar is formed on the substrate by printing, lithography and etching, imprint lithography, electron beam lithography, etc., and magnetic material is blanket-deposited over the pillars, leaving some on top of the pillars and some in the trenches surrounding them. The magnetic material on the tops of the pillars serves as the isolated magnetic islands that are used for data storage on patterned media. 
     In other fabrication methods, a full film of magnetic material is deposited on the disks. The film is then lithographically patterned and etched to remove material between islands, leaving islands of magnetic film with no magnetic material between the islands. Regardless of which method is used, it is important during manufacturing to have good process control so that the target dimensions can be maintained consistently. This requires quick measurement of representative critical dimensions, and then making adjustments to manufacturing equipment based on the information gathered. 
     Some of the dimensions that are measured include: (1) island diameter (or length, width, etc., if not exactly circular); (2) island height; (3) island sidewall slop; (4) any rounding of the edges of the island (which is an undesirable result that can happen in etching). 
     For manufacturing process control, there is no need to measure every island. Representative measurements are sufficient to provide an average of performance information. There may be variations over different regions of the disk since the equipment does not always etch uniformly over the entire surface. Thus, it is important to measure a disk in several representative areas of the disk. Advanced optical scatterometry, optical ellipsometry, and various x-ray techniques can be used for this purpose. None of these techniques can measure the dimensions of a single island. However, if a periodic array of islands is provided, they can provide average dimension information about the collection of islands within the spot size of the measurement, which will typically be at least a few μm in diameter up to approximately one mm, depending on the technique used. 
     Again referring to  FIG. 2 , the disk  21  also is configured with one or more very small test areas  25  of test formations  27  (shown greatly exaggerated in size). In one embodiment, the test areas  25  are formed with and integrated into the curvilinear periodicity of the data storage formations  23  as shown. However, unlike the data storage formations  23 , some embodiments of the test formations  27  are configured with a rectilinear periodicity for facilitating metrology of the test formations  27  and the data storage formations  23 . For example, the rectilinear periodicity may comprise rectangular, parallelogram-like, or hexagonal patterns. Thus, the test formations are uniquely patterned magnetic media that is mixed in with the regular magnetic media that is used for data storage. The test areas may or may not be used for data storage depending on the application. 
     In one embodiment, the substrate has a radial center  31 , the curvilinear periodicity of the data storage formations  23  comprises a plurality of concentric circular patterns that are arrayed about the radial center  31 . The test areas  25  are symmetrically interspersed in the curvilinear periodicity. The test areas  25  may be arrayed in a plurality of spokes (e.g., three shown in  FIG. 2 ) that extend radially from the radial center  31 , and each test area may be configured with a rectangular perimeter. 
     In other embodiments, the test areas of test formations may comprise other types of physical structures on the disk. The physical structures may comprise topographic features in a dielectric film. Alternatively, they may be a magnetic layer etched into islands, which will then also look like topographic patterns. In another embodiment, the physical structures comprise a patterned magnetic layer with a conformal overcoat that allows the topography to “show through” to the surface of the overcoat. These various embodiments enable measurements to be taken at various points in the fabrication process of the disks, depending on the fabrication process chosen. 
     The test areas also may comprise many different types and combinations of features and formations. For example, as shown in  FIG. 2 , the test areas may comprise featureless pads in blanket film patterns for film characterizations of thickness, density, and composition. As shown in  FIGS. 3A-E , the test areas also may comprise latticed dot patterns for pattern size characterizations of critical dimensions, height, angle, roughness, and rounding. The latticed dot patterns may be trimmed to form empty rows and spaces for measuring high resolution patterns, or the test areas may be configured with other types of empty rows and spaces. 
     In  FIG. 3E , the “linked” dots are not linked intentionally. This is an example of a process control problem that can be measured and then corrected by using the present invention. Measurements of the average dimensions of the islands in the test pattern can reveal that linking is occurring, and the process can be altered to correct this problem on subsequent disks being manufactured. 
     In addition to the dense, regular lattice pattern shown in  FIG. 3A , which is representative of the arrangement and density of features in the data areas, numerous other simplified or less dense patterns also may be used. The reason for this is that optical scatterometry has some difficulty with dense patterns because of the very small island sizes being examined, which are at the fringes of what scatterometry can properly measure. In addition, more sparsely populated patterns give additional information that facilitates the measurement process. For example, the patterns shown in  FIGS. 3B through 3E  have lower densities and provide additional information that assists in characterization of average island dimensions. 
       FIG. 3F  depicts a pattern that also can be used in this manner. It is suitable for the purposes described above, and for characterizing the line features (which are also included in sector header regions of the data area of the disk) for average dimensions and line edge roughness, which also are of interest. For example, these test areas may comprise solid lines and spaces that also may be used for characterizing track patterns, discrete track, and pre-patterned servo patterns of critical dimensions, height, angle, roughness, and rounding. 
     Referring now to  FIG. 4 , a schematic drawing of one embodiment of an information storage system comprising a magnetic hard disk file or drive  111  for a computer system in accordance with the invention is shown. Drive  111  has an outer housing or base  113  containing at least one magnetic disk  115 . Disk  115  is rotated by a spindle motor assembly having a central drive hub  117 . An actuator  121  comprises one or more parallel actuator arms  125  in the form of a comb that is pivotally mounted to base  113  about a pivot assembly  123 . A controller  119  is also mounted to base  113  for selectively moving the comb of arms  125  relative to disk  115 . 
     In the embodiment shown, each arm  125  has extending from it at least one cantilevered load beam and suspension  127 . A magnetic read/write transducer or head is mounted on a slider  129  and secured to a flexure that is flexibly mounted to each suspension  127 . The read/write heads magnetically read data from and/or magnetically write data to disk  115 . The level of integration called the head gimbal assembly is the head and the slider  129 , which are mounted on suspension  127 . The slider  129  is usually bonded to the end of suspension  127 . The head is typically formed from ceramic or intermetallic materials and is pre-loaded against the surface of disk  115  by suspension  127 . 
     Suspensions  127  have a spring-like quality, which biases or urges the air bearing surface of the slider  129  against the disk  115  to enable the creation of the air bearing film between the slider  129  and disk surface. A voice coil  133  housed within a voice coil motor magnet assembly  134  is also mounted to arms  125  opposite the head gimbal assemblies. Movement of the actuator  121  (indicated by arrow  135 ) by controller  119  moves the head gimbal assemblies radially across tracks on the disk  115  until the heads settle on their respective target tracks. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.