Patent Application
20140174655
The present invention relates to wafer fabrication and more particularly to a tool for polishing a wafer that provides uniform polishing across a wafer such as an AlTiC wafer used for fabrication of magnetic recording sliders.
Chemical mechanical polishing, commonly referred to as CMP, is a method of planarizing or polishing substrates. CMP may be used as the final preparation step in the fabrication of substrates from semiconductor slices to provide substantially planar front and back sides thereon. CMP is also used to remove high elevation features, or other discontinuities, which are created on the outermost surface of the substrate during the fabrication of microelectronic circuitry on the substrate.
In a typical CMP process, a large rotating polishing pad, which receives a chemically reactive slurry thereon, is used to polish the outermost surface of the substrate. To position the substrate on the polishing pad, the substrate is located in a carrier. The carrier is received on, or directly above, the polishing pad, and it maintains a bias force between the surface of the substrate and the rotating polishing pad. The carrier may also oscillate, or rotate the substrate on the polishing pad. The movement of the slurry whetted polishing pad across the planar face of the substrate causes material to be chemically and mechanically polished from that face of the substrate.
In addition to use in manufacturing and processing Si disks for semiconductor circuits, CMP is also used in the processing of wafers that are used as substrates for the manufacture of sliders for magnetic data recording. A slider is a structure that is configured to fly over a magnetic media in a magnetic data recording system in order to record or read data from the magnetic media. A slider is generally formed as a rectangular prism having an air bearing surface and a magnetic head formed on its trailing edge. Such sliders are formed from wafers constructed of a hard material such as AlTiC. Many thousands of read/write heads are formed on such a wafer. The wafer is then sliced into rows of sliders and processed to form a desired topography on the air bearing surface in order to promote a desired flight profile over the magnetic disk.
CMP is used in the manufacturing of such wafers, not only to produce a smooth flat surface on the wafer before forming magnetic heads thereon, but also in the actual manufacture of the heads thereon. For example, CMP can be used to remove certain topography and mask structures in the formation of a read sensor of the magnetic head or in the manufacture of a magnetic writer of the magnetic head. One challenge of using CMP in the processing of such wafers arises as a result of the increased hardness of such wafers as compared to relatively softer Si/Ge wafers. The increased Young's module of such AlTiC wafers makes it more difficult for them to respond to carrier applied forces. This for example has caused CMP processes to be non-uniform across a wafer, such as with slower material removal at the center of the wafer and increased material removal at the outer periphery of the wafer. In the magnetic slider industry, engineers have been struggling for many years to find a way to solve this problem in order to provide better CMP uniformity across the wafer. Approaches such as in-situ pad conditioning can alleviate the problem, but cannot fundamentally solve the problem. In addition, in-situ pad conditioning results in increased cost of ownership and increased process defects such as scratches. Therefore, there remains a need for providing uniform CMP process control across a wafer, especially in the processing of hard wafers such as AlTiC wafers used in the manufacture of magnetic data recording sliders.
The present invention provides a wafer carrier that includes a bladder having an inner portion and an outer portion, and a pneumatic supply configured for pressurizing the inner portion of the bladder without pressurizing an outer portion of the bladder.
The water carrier can further include a bladder holder; and an inner zone plate located between the bladder and the bladder holder, the inner zone plate being configured to engage the bladder so as to form an air space at the inner portion of the bladder. The bladder can be configured with a raised ring that is configured to engage the inner zone plate, and which defines a boundary between the inner portion and outer portion.
The wafer carrier advantageously applies increased polishing pressure to an inner portion of a wafer held thereon so as to increase the polishing rate at the inner portion of the wafer. The amount of this increase in polishing rate can be controlled by controlling the amount of pneumatic pressure applied.
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.
The inner zone plate 304 affixes to the dual zone bladder holder 306 by attachment screws 310, through holes 312 in the dual zone bladder holder 306 and holes 314 in the inner zone plate 394. Pneumatic elbows 308 are connected the inner zone bladder 302 through holes 316 and extend through openings 320 in the dual zone bladder holder. The bladder 302 has a raised ring 322 which, when engaged with the inner zone plate 304 when assembled seals an inner air space between the bladder 302 and the inner zone plate 304 at an inner region 324 of the bladder 302. The pneumatic elbows 308 can be connected with pneumatic lines (not shown) that can either supply air pressure to or apply a vacuum to the air space 324.
The air or vacuum provided by the pneumatic elbows 308 provides a twofold function. The bladder has holes 326. In order to determine if a wafer is in place on the carrier, a vacuum can be applied through one or more of the elbows 308. If the wafer is in place on the opposite side of the bladder 302 (as shown in
The elbows also provide another function with regard to ensuring uniform polishing across the wafer surface. As discussed above, during lapping of very hard wafers such as the AlTiC wafers used for the manufacture of sliders, the center of the wafer can be polished at a slower rate than the outer portions of the wafer. If a wafer is in place in the tool, the holes 326 will be blocked due to the presence of the wafer thereon. During lapping, air pressure is supplied through the pneumatic elbows 308 to the air space 324 between the bladder 302 and the inner zone plate 304. As can be seen, this will cause only the inner portion of the bladder 302 to balloon outward, leaving the outer portions of the bladder 302 unpressurized. This outward ballooning of only the inner portion of the bladder will cause only the inner portion of the wafer to be pushed outward, thereby providing increased pad pressure and thereby increasing the polishing rate at the inner, center portions of the wafer.
This can be better understood with reference to
While various embodiments have been described above, 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.
