JP2006108125A - Double-sided polishing method of semiconductor wafer, and polishing equipment for use therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method in which the polishing end point of a bare wafer can be detected, without causing variation in the polishing conditions during polishing operation, the profile of polishing cloth will not deteriorate, and the planarity of the wafer being polished will also not degrade. <P>SOLUTION: In the double-sided polishing method of a wafer 50, where a carrier plate 30 having a hole inserted with the wafer is held between polishing cloths stuck to the opposing surfaces of upper and lower rotatable polishing plates and the wafer 50 is polished by rotating the polishing plates and the carrier plate 30 relatively, while pressing the polishing clothes of the upper and lower polishing plates relatively, a ring 34 for polish adjusting the member of a material having a wear rate higher than that of the wafer 50 is arranged around the hole of the carrier plate 30 for inserting the wafer 50, at a height corresponding to the target polishing thickness of the wafer 50. The wafer 50 is polished to a predetermined target thickness during polishing operation, and the polishing end point of the wafer 50 is detected, by detecting the moment when the frictional resistance is varied by polishing the material 34 of high wear rate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor wafer polishing method and a polishing apparatus used therefor.

  When finishing the surface of a semiconductor wafer to a mirror surface, CMP (Chemical Mechanical Polishing) is generally used. This is because a semiconductor wafer is fixed to the surface of a rotatable surface plate, an abrasive cloth is attached to the surface of the rotatable surface plate provided opposite to the surface, and the surface of the surface facing the surface is supplied while supplying an abrasive. This is a method of polishing a semiconductor wafer by relatively rotating a disc.

  Such polishing of a semiconductor wafer has been generally performed for polishing a wafer having a surface on which patterning for forming a device, unevenness and the like are formed, and various proposals have been made. However, in the polishing of a bare wafer whose device structure is not formed on the surface, management of the polishing amount has not been particularly emphasized so far. For this reason, the bare wafer is polished by a uniform method in which the polishing time is constant and the number of times the polishing cloth is used is managed.

  However, in such conventional polishing of bare wafers, the polishing rate decreases due to the decrease in polishing temperature due to clogging of the polishing cloth, resulting in a large error in the amount of polishing, resulting in variations in the finish. It had a great influence on the product yield.

As a prior art for determining the polishing end point of a semiconductor wafer, there is one in which the polishing friction force is detected to change with a preset change amount h within a preset unit time t (for example, Patent Document 1). ). In addition, there is one that is determined based on the difference between the frictional force when polishing the unevenness and the frictional force when polishing the flat surface, and the polishing end point is after a predetermined time from that point (patent) Literature 2.). Further, there is one that detects a polishing end point by detecting a temperature change point when polishing (Patent Document 3). Further, there is a technique for detecting a polishing end point by irradiating a wafer being polished with white light from a light source unit through an observation window formed on a polishing pad and performing spectroscopic analysis of the reflected light (Patent Document 4). ). Furthermore, in double-sided polishing of the wafer, a core that is hard and hard to wear is inserted into the carrier plate that holds the wafer, and the polishing end point is detected when the thickness of the core is reached after the wafer is polished. There is something like that (Patent Document 5).
JP 2002-353179 A (Claim 1) JP-A-9-131663 (Claim 1) JP-A-8-330261 (Claim 1) JP 2003-168667 A (Claim 1) JP-A-5-169365 (Claims 1, 3, page 3, column 3, step 0012)

  Patent Documents 1 to 4 of the above prior art are all techniques for single-side polishing of a wafer, and those in which an oxide film, irregularities, and other device structures are formed on the wafer surface of the workpiece to be polished are applied. Is related to CMP. However, when the above oxide film, device structure, etc. are formed on the wafer surface, the layers stacked while the wafer surface is being polished change, so the polishing temperature, head rotation current, etc. Polishing conditions change greatly. Each of the above prior arts is a technique using such a change in polishing conditions that occurs during polishing, and there is no oxide film, device structure, etc. on the wafer surface, and for bare wafers in which the polishing conditions do not change during polishing. There is no disclosure of technology.

  Further, although Patent Document 5 is a technique for double-side polishing of a wafer, there is no description about the polishing of a bare wafer in this prior art as well. Furthermore, in this technique, a plurality of holes are provided in the carrier plate, and a plurality of hard cores such as an alumina sintered body are inserted into the holes, so that the thickness of the object to be polished approaches the height of the core during polishing of the wafer. Since the core acts to reduce the degree of friction, this point is detected and a wafer polished with good flatness is obtained as a polishing end point. However, since this technique uses a hard core such as an alumina sintered body, if the core comes into contact with the polishing cloth during polishing, the polishing resistance decreases in this portion, and until the polishing end point is detected, the polishing cloth However, the shape of the polishing cloth is deteriorated due to being pressed by the core, and therefore the flatness of the polishing wafer may be deteriorated.

  The invention of the present application is a bare wafer polishing apparatus in which polishing conditions do not change during polishing, and a ring of a thickness adjusting member having high wearability is embedded around a wafer insertion hole of a carrier plate into which a wafer is inserted. Thus, a double-sided polishing apparatus for a wafer is obtained in which the frictional resistance is changed without deteriorating the shape of the polishing cloth during polishing so that the end point of polishing can be easily determined.

  In this invention, a carrier plate in which a wafer is inserted in a hole is sandwiched between polishing cloths affixed to opposite surfaces of a rotatable upper surface plate and a lower surface plate, so that the polishing cloth of the upper surface plate and the lower surface plate are This is a method of polishing both sides of the wafer by rotating the surface plate and the carrier plate relatively while pressing the polishing cloth against the wafer. The carrier plate is more wearable than the wafer around the hole for inserting the wafer. The ring of the material polishing adjustment member is placed at a height corresponding to the target polishing thickness dimension of the wafer, and the wafer is polished to a predetermined target thickness dimension during polishing, resulting in high wear resistance. A double-side polishing method for a semiconductor wafer characterized in that a polishing end point of a wafer is detected by detecting a time point when a frictional resistance value is changed by polishing of a material to be rotated. Possible An upper surface plate and a lower surface plate each having a polishing cloth affixed to the two opposing surfaces, a carrier plate provided with a hole for inserting a wafer between the upper and lower surface plates, and provided around the carrier plate A wafer double-side polishing apparatus comprising a sun gear that meshes with a gear and rotates a carrier plate, and an internal gear that surrounds the carrier plate and revolves the carrier plate. A ring of a polishing adjustment member made of a material that is more wearable than the wafer is placed at a height position corresponding to the target thickness of the wafer, and friction is caused by polishing the material that is more wearable. A double-side polishing apparatus for a semiconductor wafer (Claim 2) and the polishing adjusting member, wherein the resistance value is changed, A double-sided polishing apparatus for semiconductor wafers according to claim 2, wherein the silicon member in which polysilicon is coated (claim 3).

  According to the semiconductor wafer double-side polishing method of the present invention, since the oxide film and other device structures are not formed on the wafer surface, the polishing of the wafer is performed even in the polishing of the bare wafer where the polishing conditions do not change at all during polishing. It is possible to easily determine the end point.

  Also, the ring of the polishing adjusting member that detects the difference in frictional resistance during polishing and functions as a thickness adjusting member is coated with a soft material that is more abrasive than the wafer. Even if the polishing adjusting member is pressed against the polishing cloth at the time of detection, the polishing process can be completed without changing the shape of the polishing cloth.

  FIG. 1 is a side sectional view of a polishing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic view conceptually showing the relationship between a carrier plate into which a wafer is inserted and a sun gear and an internal gear meshing with the carrier plate. The wafer double-side polishing apparatus of the present invention is characterized by the structure of the carrier plate, and the other structures are the same as those of the conventional apparatus.

  As shown in FIG. 1, the polishing apparatus is installed so that an upper surface plate 11 and a lower surface plate 12 face each other about a rotating shaft 10 that is rotated by a driving source (not shown). On the upper surface plate 11 and the lower surface plate 12, polishing cloths 13 and 14 are attached to the upper surface plate 11 and the lower surface plate 12, respectively, facing the inside so as to polish both surfaces of the wafer.

  The upper surface plate 11 and the lower surface plate 12 have holes 15 and 16, respectively, and probes 17 and 18 are inserted into the holes 15 and 16, respectively. Polishing cloths 19 and 20 are attached to the tips of the probes 17 and 18, respectively, and the tips are the same as the polishing cloths 13 and 14 attached to the opposing surfaces of the upper surface plate 11 and the lower surface plate 12, respectively. It has a surface. A temperature change during polishing of the probes 17 and 18 is detected by temperature detection (not shown). 21 is a polishing liquid supply pipe for supplying the polishing liquid to the polishing surface of the carrier plate.

  Further, a plurality of carrier plates 30 are provided between the polishing cloths 13 and 14 provided on the opposing surfaces of the upper surface plate 11 and the lower surface plate 12 so as to be sandwiched and pressed between the upper and lower surface plates. . The gear 31 provided on the outer periphery of the carrier plate 30 is meshed with a sun gear 32 provided around the rotating shaft 10 as shown in FIG. 2 and meshes with an internal gear 40 on the outside. It has become. The internal gear 40 is rotated by a drive source (not shown), so that the carrier plate 30 revolves while the polishing pads 13 and 14 rotate. Although only one carrier plate 30 is shown in FIG. 2, the positional relationship with the rotary shaft 10 is actually set to be rotated around the rotary shaft 10 in the same manner as shown in FIG. is there.

  A plurality of holes 33, 33... Are formed in the carrier plate 30, and the wafers 50, 50,. The carrier plate 30 is made of a synthetic resin such as an epoxy resin, and the thickness thereof is set to be thinner (for example, 500 μm) than the target thickness (for example, 725 μm) of the polishing finish of the wafer 50 inserted therein. ).

  Further, as shown in FIGS. 3 and 4, a ring 34 of a polishing adjusting member is fixed to the carrier plate 30 around the insertion holes 33, 33... Of the wafers 50, 50 on the front side and the back side. . As shown in FIG. 4, the ring 34 is positioned so as to correspond to the target polishing thickness of the wafer 50, and has a detachable step on the upper and lower outer periphery of the wafer insertion hole 33 of the carrier plate 30. Are arranged. The surface of the ring 34 is made to be flush with the carrier plate surface. In FIG. 4, the upper and lower broken lines of the wafer 50 indicate the target polishing thickness of the wafer.

  As the material of the ring 34 used here, it is preferable to process and use a material (for example, high-purity polysilicon) having a higher wear property than the wafer as the material to be polished. More preferably, the material is a ring made of silicon, and the surface thereof is preferably coated with polysilicon. The thickness of the ring 34 is not particularly limited, but is preferably about 250 to 400 μm for obtaining workability, strength, and the like. 4 shows a form in which the ring 34 is detachably disposed on the upper and lower outer periphery of the wafer insertion hole 33 of the carrier plate 30, but as shown in FIG. 5, the entire outer periphery of the wafer insertion hole 33 is the ring. It may be 34.

  In any case, as shown in FIG. 4 and FIG. 5, the arrangement or thickness of the ring 34 is made larger than the thickness of the carrier plate 30, so that the flatness of the carrier plate itself is not improved. It is sufficient to process the thickness uniformly.

  Next, the operation of this polishing apparatus will be described. As shown in FIGS. 1 and 2, while supplying the polishing liquid from the polishing liquid supply pipe 21, while pressing the carrier plate 30 between them with the polishing surface plates 11 and 12 with a predetermined pressure, the sun gear 32 and the internal gear 40 are used. The wafer 50 is polished while being held by the carrier plate 30 and rotated relatively.

  That is, while rotating the rotating shaft 10, the internal gear 40 is rotated around the rotating shaft 10 in the same direction as the rotating shaft by a driving device (not shown), and the carrier plate 30 rotates while the rotating shaft 10 is centered. To revolve. In this state, the upper and lower surface plate polishing cloths 13 and 14 rotating around the rotation shaft 10 are inserted into the carrier plate 30 revolving around the rotation shaft 10 while rotating. To polish. Until the polishing is started, the wafer 50 is thicker than the thickness of the carrier plate 30 (see FIG. 4). As a result of this polishing process, polishing proceeds from the thick wafer 50 and further wear of the wafer 50 progresses. The thickness of all the wafers 50 becomes uniform at the target thickness. As the polishing further proceeds, the upper surface of the wafer 50 coincides with the position of the surface height of the ring 34 of the polishing adjusting member disposed on the outer periphery of the carrier insertion hole 33 of the carrier plate 30. Further, the wafer is polished to the same position on the lower surface of the carrier plate, and the same state is obtained.

  When the polishing of the wafer proceeds up to this stage, the frictional resistance between the polishing cloth and the wafer up to that point is changed by the addition of the frictional resistance between the polishing cloth and the ring 34 arranged on the surface of the carrier plate. This change in frictional resistance is detected by a temperature change at the tip of the probe incorporated in the surface plate, and is taken as the polishing end point of the wafer, and polishing is automatically terminated at that point. As a result, the wafer is always the same thickness as the processed carrier plate and there is no variation in the finish, and a uniform polished wafer can be obtained. Further, since the ring 34 is a soft material, the shape of the polishing cloth at the polishing end point is not deteriorated, so that the shape of the outer peripheral portion of the wafer becomes flat and the flatness is improved. Further, when polysilicon is used for the polishing adjusting member, there is an effect of gettering metal contamination during polishing by the gettering force of the polysilicon.

In order to confirm the effect of the present invention, 20 8-inch wafers were polished by the polishing apparatus shown in FIG. 1, and the flatness (TTV) of the obtained wafers was evaluated. A comparative example of polishing by a conventional method not using a ring of a polishing adjusting member is shown.

Explanatory drawing which showed notionally the cross section of the apparatus used for the wafer grinding | polishing endpoint detection method which becomes this invention. FIG. 2 is an explanatory view schematically showing a positional relationship among a carrier plate, a central axis and an internal gear of the wafer polishing apparatus shown in FIG. 1. FIG. 3 is a front view of the carrier plate and a carrier plate in which a ring of a polishing adjusting material is fixed to the outer periphery of the wafer insertion hole. The schematic diagram which showed typically the height positional relationship of the ring of the grinding | polishing adjustment material arrange | positioned in the upper and lower outer periphery of the wafer insertion hole of a carrier plate, and a wafer. The schematic diagram which showed typically the height positional relationship of the ring of the grinding | polishing adjustment material arrange | positioned to the whole outer periphery of the wafer insertion hole of a carrier plate, and a wafer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Rotary shaft, 11 ... Upper surface plate, 12 ... Lower surface plate, 13, 14 ... Polishing cloth, 15, 16 ... Hole, 17, 18 ... Prog, 21 ... Polishing liquid supply pipe, 30 ... Carrier plate, 32 ... Sun gear 40 ... Internal gear, 50 ... Wafer, 34 ... Ring adjusting member ring.

Claims (3)

  Hold the carrier plate in which the wafer is inserted in the hole between the polishing cloth affixed to the opposite surface of the upper and lower surface plates, and place the polishing cloth on the upper surface plate and the lower surface plate on the wafer. The wafer is double-side polished by rotating the surface plate and the carrier plate relatively while pressing the wafer, and the polishing adjustment of the material with higher wear resistance than the wafer around the hole for inserting the wafer in the carrier plate The ring of the member is placed at a height corresponding to the target thickness dimension of the wafer to be polished, and the wafer is polished to a predetermined target thickness dimension during polishing to polish a material with high wear characteristics. A double-side polishing method for a semiconductor wafer, characterized in that a polishing end point of a wafer is detected by detecting a point in time when a frictional resistance value changes.   An upper surface plate and a lower surface plate, each of which is fixed to a rotating shaft and is rotatable and has an abrasive cloth affixed to the opposite surface, and a carrier plate provided with a hole for inserting a wafer between the upper and lower surface plates A wafer double-side polishing apparatus comprising: a sun gear that meshes with a gear provided around the carrier plate to rotate the carrier plate; and an internal gear that surrounds the carrier plate and revolves the carrier plate. A ring of a polishing adjustment member made of a material that is more wearable than the wafer is placed around the hole for inserting the wafer in the carrier plate at a height corresponding to the target thickness of the wafer to be worn. A double-side polishing apparatus for a semiconductor wafer, characterized in that the frictional resistance value is changed by polishing a material having high properties.   3. The double-side polishing apparatus for a semiconductor wafer according to claim 2, wherein the polishing adjusting member is a silicon member coated with polysilicon.

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