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  Wafer-retaining carrier, double-side grinding device using the same, and double-side grinding method for waferUSPTO Application #: 20060178089Title: Wafer-retaining carrier, double-side grinding device using the same, and double-side grinding method for wafer Abstract: The present invention is a wafer-holding carrier 1 wherein the carrier has polishing agent-passing holes 3, 4 for passing the polishing agent through as well as wafer-holding holes 2 for containing and holding wafers, and the total area of the polishing agent-passing holes occupies 15% or more of a main surface of the carrier. Preferably, the total area of the polishing agent-passing holes occupies 30% or less of the main surface of the carrier, and each of the polishing agent-passing holes has a circular shape of a diameter of 5 mm-30 mm, and the holes are arranged in the form of concentric circle or lattice on the carrier entirely. Thereby, there can be provided an art that even when performing polishing by using a hard polishing pad in a double-side polishing apparatus, particularly, a double-side polishing apparatus having a carrier moving circularly without rotation, it is not necessary to reform the apparatus largely, and the wafer of high flatness can be finished without a tapered shape, peripheral sag, and such. (end of abstract)
Agent: Oliff & Berridge, PLC - Alexandria, VA, US Inventor: Junichi Ueno USPTO Applicaton #: 20060178089 - Class: 451041000 (USPTO) Related Patent Categories: Abrading, Abrading Process, Glass Or Stone Abrading The Patent Description & Claims data below is from USPTO Patent Application 20060178089. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention mainly relates to a wafer-holding carrier that is used when polishing both sides of a wafer such as a silicon wafer, and also further relates to a double-side polishing apparatus and a double-side polishing method. BACKGROUND ART [0002] Conventionally, an apparatus 20 where a planetary gear mechanism as shown in FIG. 4 is used has been known as a polishing apparatus that polishes both sides of a silicon wafer at the same time. The polishing apparatus 20 has an upper turn table 16 and a lower turn table 17 to which polishing pads 18, 19 are attached respectively, a turn table-moving mechanism (rotation axes 12, 13) for moving the upper turn table 16 and the lower turn table 17 relatively, a wafer-holding carrier 11 for holding a wafer W between the upper turn table 16 and the lower turn table 17, a carrier-moving mechanism (an external gear 14, an internal gear 15) for moving the carrier 11 between the upper turn table 16 and the lower turn table 17, and so on. [0003] The upper turn table 16 and the lower turn table 17 are rotated in a prescribed direction by rotation axes 12, 13 respectively. And, the upper turn table 16 is provided with holes passing through in the vertical direction (polishing agent-supplying hole) 22 so as to supply a polishing agent from above through the polishing agent-supplying holes 22 by pumping power and gravity (natural drop). [0004] As shown in FIG. 5, plurality of the carrier 11 are set between the internal gear 15 and the external gear (sun gear) 14, and these carriers 11 intermesh with the internal gear 15 and the external gear 14 to rotate between the upper and lower turn tables 16, 17 (polishing pads 18, 19). The double-side polishing apparatus 20 as above has been called four-way (driving) system because the upper turn table 16 and the lower turn table 17 are rotated and the carriers 11 revolve with rotating. [0005] When polishing a wafer W by using the double-side polishing apparatus 20, after containing a wafer W in each of the wafer-holding holes 2 of the carrier 11, the wafer W is sandwiched between the upper and lower turn tables 16, 17, and the carrier 11 is rotated while supplying a liquid polishing agent (also called slurry) containing abrasive grains and such. Slurry made by dispersing abrasive grains such as colloidal silica in an alkaline solution is generally used as a polishing agent when polishing a silicon wafer. The polishing agent supplied from the upper turn table side is also supplied to the lower side of the wafer W (the lower turn table side) from between the carriers 11, and both front and back surfaces of the wafer W are polished to be mirror-surface. [0006] If a wafer W is polished by the double-side polishing apparatus 20, because both surfaces of the wafer W are polished at the same time, polishing efficiency can be improved compared to polishing by using a so-called single-side apparatus. [0007] However, with respect to the double-side polishing apparatus 20 where a planetary gear mechanism is used as described above, there is a problem that it is difficult to correspond to recent enlargement of a silicon wafer. Namely, because the carrier 11 has a structure of moving between the internal gear 15 and the external gear 14, the diameter of the carrier 11 is smaller than the radius of the turn tables 16, 17. Therefore, particularly, in a case that a wafer with a large diameter (for example, 300 mm) is polished, it is necessary to enlarge the apparatus. However it is difficult to enlarge the apparatus because a complex gear mechanism is necessary. And also, a large internal gear becomes necessary. Problems of cost rise, efficiency lowering, setting space, and so on are caused when the apparatus is enlarged. [0008] On the other hand, a downsized double-side polishing apparatus 30 has been developed as shown in FIG. 6 and FIG. 7. Because the polishing apparatus 30 performs polishing by moving the carrier 11 so as to draw a small circle without rotation in a plane through a carrier holder 26, it is not necessary to rotate the carrier around an external gear as the four-way system, and therefore it is possible to downsize the apparatus even when a wafer having a large diameter is polished (See, Japanese Patent Laid-open (Kokai) Publication No. 10-202511). [0009] However, because the carrier 11 becomes a form so as to cover the lower turn table 17 wholly in the polishing apparatus 30, there is a problem that when slurry is supplied from the upper turn table side, the slurry stays on the upper side of the carrier 11 not to be supplied to the polishing pad 19 in the lower side sufficiently. If a polishing agent is not sufficiently supplied to the lower turn table side, rotation of the wafer in a holding hole is prevented. Therefore, a wafer shape becomes a tapered shape, or so-called peripheral sag is generated by accumulation of heat due to friction between the polishing pad 19 and the carrier 11 or the wafer W. Therefore, the wafer cannot be finished to have high flatness. [0010] Accordingly, in order to promote supply of a polishing agent to the lower turn table side, it has been suggested that a carrier 11 is provided with several holes for passing a polishing agent therethrough, and also an apparatus has a hole in the center of a lower turn table 17 so as to force a polishing agent to discharge therefrom (See, Japanese Patent Laid-open (Kokai) Publication No. 2000-42912). However, there are problems that even if the carrier is provided with several holes, the wafer cannot be finished to have high flatness, and in the apparatus provided with the hole in the lower turn table, it is necessary to reconstruct a turn table largely which is generally used conventionally, and therefore cost rise, complicating of apparatus, and so on, are caused. [0011] On the other hand, with respect to polishing pad, a hard polishing pad that rubber or such is a main component has been used in the recent years so as to polish a wafer to higher flatness. If the hard polishing pad is used in a single-side polishing apparatus, it is possible to polish the wafer to high flatness. However, there is a problem that if the hard polishing pad is used in a double-side polishing apparatus, because slurry is difficult to penetrate to the polishing pad and slurry-holding force is weak, the wafer shape becomes a tapered shape, or the wafer periphery is excessively polished to generate peripheral sag, and therefore sufficient flatness cannot be achieved. [0012] Therefore, particularly, in a downsized polishing apparatus as shown in FIG. 6 and FIG. 7, it was extremely difficult to easily put double-side polishing by using a hard polishing pad into practical use. DISCLOSURE OF THE INVENTION [0013] Accordingly, the present invention was conceived in view of the above problems. An object of the present invention is to provide an art that even when performing polishing by using a hard polishing pad in a double-side polishing apparatus, particularly, a double-side polishing apparatus having a carrier moving circularly without rotation, it is not necessary to reform the apparatus largely, and the wafer of high flatness can be finished without a tapered shape, peripheral sag, and such. [0014] In order to accomplish the above object, according to the present invention, there is provided a wafer-holding carrier which is used when holding wafers between an upper turn table and a lower turn table to which polishing pads are attached, and polishing both sides of the wafers by a polishing agent, wherein the carrier has polishing agent-passing holes for passing the polishing agent through as well as wafer-holding holes for containing and holding the wafers, and the total area of the polishing agent-passing holes occupies 15% or more of a main surface of the carrier. [0015] If the total area of the polishing agent-passing holes occupied in a main surface of the carrier (hereinafter, also simply called, "occupied area") is 15% or more as described above, even when the carrier is used in what type of a double-side polishing apparatus, sufficient slurry comes to the lower turn table side through the polishing agent-passing holes from the upper turn table side to suppress generation of heat in the process. Further, movement of the wafer in the holding hole becomes smooth, and therefore the wafer can be finished to high flatness without generating a tapered shape of the wafer, peripheral sag, and such. [0016] Moreover, because, by using the above-described carrier, it is not necessary to reconstruct parts except carrier of the apparatus, the carrier can be easily applied to a double-side polishing apparatus used conventionally. [0017] In this case, it is preferable that the total area of the polishing agent-passing holes occupies 30% or less of the main surface of the carrier. [0018] If the occupied area of the polishing agent-passing holes is 30% or less, formation of the wafer-holding hole may not be affected and strength as a carrier can be assured sufficiently. [0019] Each of the polishing agent-passing holes preferably has a circular shape of a diameter of 5 mm-30 mm. [0020] If each of the polishing agent-passing holes has the above-described size, because many polishing agent-passing holes come to be formed so as to disperse in the carrier entirely, the carrier can suppress lowering of the carrier strength and pass the polishing agent all over the carrier through many polishing agent-passing holes. [0021] It is preferable that the polishing agent-passing holes are arranged in the form of concentric circle or lattice on the carrier entirely. Continue reading... Full patent description for Wafer-retaining carrier, double-side grinding device using the same, and double-side grinding method for wafer Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Wafer-retaining carrier, double-side grinding device using the same, and double-side grinding method for wafer patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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