This disclosure relates in general to a magnetic storage systems, and more particularly to a method and apparatus for manufacturing silicon sliders with reduced susceptibility to fracture of the substrate from which they are manufactured.
Hard disk drives utilizing magnetic data storage disks are used extensively in the computer industry. A head/disk assembly typically includes one or more commonly driven magnetic data storage disks rotatable about a common spindle. At least one head actuator moves one or more magnetic read/write heads radially relative to the disks to provide for reading and/or writing of data on selected circular concentric tracks of the disks. Each magnetic head is suspended in close proximity to one of the recording disks and supported by an air bearing slider mounted to the flexible suspension. The suspension, in turn, is attached to a positioning actuator.
During normal operation, relative motion between the head and the recording medium is provided by the disk rotation as the actuator dynamically positions the head over a desired track.
The relative motion provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a known suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head normally resides toward the trailing end, which tends to fly closer to the recording surface than the leading edge.
Conventional magnetic recording head sliders are typically made from wafers of a two-phase ceramic, TiC/Al2O3, also called Al—TiC. After the thin film processing to prepare the recording heads is performed on the Al—TiC wafers, also called Al—TiC substrates, the sliders are then formed. The sliders are fabricated by cutting, grinding and lapping the wafer made of the above material. This involves a series of shaping and polishing operations, and also the formation of an air bearing, usually using dry etching, on the polished surface.
Silicon is being considered as a replacement for Al—TiC as a substrate material for recording heads of the future. Silicon sliders boast clear advantages including material cost, higher yield of sliders per substrate, several potential HDD advantages, and strategic advantages that may include active electronic devices within the slider.
Today, 125 mm diameter monocrystalline silicon substrates are most commonly oriented in the {100} crystallographic plane, although other orientations are available commercially. Compatibility of silicon substrates with existing magnetic recording head thin film manufacturing lines dictates that many of the mechanical dimensions be adopted from the specification for 125 mm diameter Al—TiC substrates. In addition, when working with silicon suppliers, it is most efficient to adopt a number of the conventions of the monocrystalline silicon specification, SEMI M1-0600 and the related specification SEMI M1.15-1000.
Also of importance, in both specifications, are the dimensions of the notch in the substrate that is used for orienting the substrate in manufacturing tools. For example, notch depth, radius and angle are specified for the pattern recognition systems on stepper lithography tools that use them for coarse alignment of the stepper. Indeed, the notch dimensions are identical in both specifications. However, in addition, SEMI M1-0600 specifies that the notch for {100} substrates be oriented in the <110> crystallographic direction, which is contained in the {110} and {111} primary cleavage planes of silicon. The notch is specified in this way so as to facilitate dicing of wafers by sawing after thin film processing. However, this specification contributes to increased fragility of the substrate in the manufacturing line, due to the tendency of notches to be the initiation site for fracture failure in brittle materials. Many operations use the notch for wafer positioning, in which case the mechanical interaction with a pin or guidepost can lead to chipping locally at the notch. A compounding factor is that the easiest fracture path for a circular wafer under point-load induced bending stress is along the diameter, which in the case of the <110> oriented notch, is in the <110> direction. Both primary cleavage fracture planes in a silicon wafer can be activated in this direction, making this diameter particularly vulnerable, when coupled with a potential fracture initiation point.
Magnetic recording head thin film manufacturing lines have been configured to work with the more robust Al—TiC substrates. As a result, in the aforementioned manufacturing lines, silicon substrates that use the SEMI M1-0600 standard specification for the notch have shown a wafer yield that is lower than desired. These substrates are susceptible to fracture, which is initiated at the notch, breaking the substrates into at least two pieces, thereby rendering the substrate worthless.
Thus, although many tools in thin film manufacturing lines can readily process silicon substrates without wafer breakage or chipping at the notch, other tools impart stresses to the notch that result in fracture of silicon wafers (as opposed to Al—TiC wafers) and thus yield loss. Costly retooling of the manufacturing line may circumvent this problem. However, a costless yield-improving change in the specification of the silicon substrate is needed.
It can be seen that there is a need for a method and apparatus for manufacturing silicon substrates with reduced susceptibility to fractures.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for manufacturing silicon substrates with reduced susceptibility to fracture.
The present invention solves the above-described problems by providing improved wafer robustness and projecting a substantial yield improvement in future manufacturing using a silicon wafer notch in the <100> direction for {100} oriented silicon substrates.
A silicon wafer in accordance with the principles of the present invention includes a {100}-oriented monocrystalline substrate and a notch oriented substantially in the <100> crystallographic direction for positioning the wafer.
In another embodiment of the present invention, a wafer is provided from which a plurality of silicon sliders may be cut, wherein the silicon wafer is oriented in the {100} crystallographic plane and includes a notch oriented substantially in the <100> direction.
In another embodiment of the present invention, a magnetic storage system is provided. The magnetic storage system includes at least one magnetic storage medium, a motor for moving the at least one magnetic storage medium, at least one slider for flying over the data surface of the at least one magnetic storage medium and an actuator, coupled to the slider, for positioning the slider relative to the at least one magnetic storage medium, wherein the slider is manufactured from a silicon wafer oriented in the {100} crystallographic plane having a notch oriented substantially in the <100> direction.
In another embodiment of the present invention, a method of forming a silicon wafer having a crystallographic orientation in the {100} crystallographic plane is provided. The method includes growing a single crystal silicon ingot having a {100} oriented monocrystalline structure, determining the crystallographic orientation of the ingot, forming a notch having an orientation substantially in the <100> direction in the single crystal silicon ingot and slicing the silicon ingot into individual wafers.
In another embodiment of the present invention, another method of forming a silicon wafer having a crystallographic orientation in the {100} crystallographic plane is provided. This method includes forming a {100} oriented monocrystalline silicon wafer of silicon, determining the crystallographic orientation of the wafer, and forming a notch having an orientation substantially in the <100> direction in the side of the {100} oriented monocrystalline silicon wafer.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
a shows lattice planes and directions of the silicon lattice, as described by the mathematical description known as the Miller Indices and relates them to the {100} oriented monocrystalline wafer (or substrate) having a notch oriented in a <110> direction according to the specification SEMI M1-0600 and the related specification SEMI M1.15-1000;
b shows lattice planes and directions of the silicon lattice, and relates them to the {100} oriented monocrystalline wafer (or substrate) having a notch orientation in the <100> direction according to an embodiment of the present invention; and
In the following description of the embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration the specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized because structural changes may be made without departing from the scope of the present invention.
The present invention provides a method and apparatus for manufacturing silicon sliders with reduced susceptibility to fracture of the substrates from which they are made. Improved wafer robustness and a substantial yield improvement in future manufacturing is provided using a silicon wafer notch substantially in the <100> direction for {100} oriented silicon substrates.
More specifically, actuator assembly 118 pivots about axis 121 to rotate head gimbal assemblies 116 generally along an arc 119, which causes each head gimbal assembly 116 to be positioned over a desired one of the tracks on the surfaces of disks in disk pack 112. HGAs 116 can be moved from tracks lying on the innermost radius, to tracks lying on the outermost radius of the disks. Each head gimbal assembly 116 has a gimbal that resiliently supports a slider relative to a load beam so that the slider can follow the topography of the disk. The slider, in turn, includes a transducer that is utilized for encoding flux reversals on, and reading flux reversals from, the surface of the disk over which it is flying.
a-b show the modifications to the orientation of the silicon wafer notch according to an embodiment of the present invention.
However, as described earlier, orientation of the notch in the <110> direction increases the fragility of the substrate due to the tendency of notches to be the initiation site for fracture failure in brittle materials. It turns out that the easiest fracture path for a circular silicon wafer under point-load induced bending stress is along the diameter, which in the case of the <110> oriented notch 720, is in the <110> direction 712. Both primary cleavage fracture planes in a silicon wafer can be activated in this direction, making this diameter particularly vulnerable, when coupled with a potential fracture initiation point. Accordingly, silicon substrates that use the SEMI M1-0600 standard specification for the notch 720 in the <110> direction 712 exhibit a wafer yield that is lower than desired. These substrates are susceptible to fracture which is initiated at the notch 720 in the <110> direction 712, breaking the substrates into at least two pieces, thereby rendering them worthless.
b illustrates a notch orientation in the <100> direction according to an embodiment of the present invention.
The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.