JP2006231464A - Polishing pad - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad capable of performing a uniform polishing in polishing characteristic even it is a large diameter wafer. <P>SOLUTION: The polishing rate can be made to be uniform in a whole surface of the workpiece to be polished by using the polishing pad 1 which is brought into contact with the workpiece to be polished, has a polishing layer 21 polishing the workpiece to be polished, and has a different hardness of the polishing layer 21 at each area. Though the polishing rate at the central part of the workpiece is largely different from the other part, the polishing rate can be made to be uniform in the whole surface of the workpiece by increasing the hardness of a second area 24 contacting the workpiece and decreasing the hardness of a first area 23 and a third area 25 not contacting the central part of the workpiece. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention provides chemical mechanical polishing (Chemical polishing) in the manufacturing process of semiconductor devices and the like.
The present invention relates to a polishing pad used for planarizing an object to be polished such as a silicon wafer by mechanical polishing (CMP).

  In general, in the CMP method, as shown in FIG. 1, a polishing pad 1 is held on a surface plate 11, an object 13 such as a silicon wafer is held on a polishing head 14, and slurry is supplied from a slurry supply unit 15. However, polishing is performed by sliding the polishing pad 1 and the object 13 to be polished relatively in a pressurized state.

  In such a CMP method, the polishing pad 1 has a uniform polishing pad surface and cross-sectional structure such as hardness in order to uniformize polishing characteristics such as a polishing amount per unit time (hereinafter referred to as “polishing rate”) ( For example, see Patent Document 1). Moreover, as a polishing pad, the polishing pad which is comprised by three layers, a surface layer, an intermediate | middle layer, and an innermost layer, and at least an intermediate | middle layer is divided | segmented into the segment form is mentioned (for example, refer patent document 2).

JP 2004-123975 A JP-A-11-48131

  However, in the polishing pad of Patent Document 1, when the object to be polished 13 is enlarged, a phenomenon that the center part is hard to be cut (center throw) occurs, and conversely, a phenomenon that the center part of the silicon wafer is cut faster (center). First) may occur. As a result, a phenomenon that the surface of the polished article 13 is polished non-uniformly occurs.

  Further, in the polishing pad of Patent Document 2, the surface layer can be changed following the warpage of the workpiece 13, but it does not reduce the center throw and the center first.

  Accordingly, an object of the present invention is to provide a polishing pad that can uniformly polish a workpiece even when the workpiece is enlarged.

The present invention has a polishing layer for contacting the object to be polished and polishing the object to be polished,
The polishing layer is a polishing pad in which the hardness in the same layer varies from region to region.

Further, the present invention has a polishing layer for contacting the object to be polished and polishing the object to be polished,
The polishing layer is a polishing pad having different hardness for each concentric region.

Further, the present invention has a polishing layer for contacting the object to be polished and polishing the object to be polished,
The polishing layer is a polishing pad in which the hardness in the same layer is different for each concentric region.

  In the invention, it is preferable that the polishing layer has different hardness depending on a central part contact region that contacts the central part of the object to be polished and a central part non-contact region other than the central part contact region.

  According to the present invention, the polishing layer has a portion whose hardness is different in the surface direction of the polishing surface in the same layer, so that the object to be polished can be made uniform even when the object to be polished is enlarged. Can be polished.

  Further, according to the present invention, the polishing object can be uniformly polished even when the object to be polished is enlarged by having a portion having a different hardness for each concentric region in the polishing layer. .

  In addition, according to the present invention, even if the object to be polished is enlarged by having a portion having a different hardness for each concentric region in the same layer in the same layer, the object to be polished is uniformly polished. can do.

  Further, according to the present invention, when the object to be polished is enlarged due to the difference in hardness between the center part contact area that contacts the center part of the object to be polished and the center part non-contact area other than the center part contact area. Even so, the object to be polished can be polished more uniformly.

  The polishing pad according to the present invention is a polishing pad having a polishing layer for polishing the object to be polished while being in contact with the object to be polished, and the hardness of the polishing layer varies from region to region. When a polishing pad 1 according to the present invention is provided in a CMP apparatus as shown in FIG. 1 and a silicon wafer 13 as an object to be polished is polished, the polishing rate can be made uniform over the entire surface of the object 13 to be polished. That is, the region where the polishing object is difficult to polish is brought into contact with the region where the polishing layer is easily polished, and conversely, the region where the polishing object is easily polished is brought into contact with the region where the polishing object is difficult to polish. Therefore, the polishing rate can be made uniform over the entire surface of the object to be polished.

  FIG. 2 is a plan view of the polishing pad 1 according to the first embodiment of the present invention, and FIG. 3 is a cross-sectional view of the polishing pad 1 of FIG. As described above, the polishing pad 1 is used in a CMP apparatus. At the time of polishing, the polishing pad 1 comes into contact with a silicon wafer 13 that is an object to be processed and is held by a carrier unit 14 of the CMP apparatus, and the polishing pad 1 and the silicon wafer 13 are relative to each other. The surface of the silicon wafer 13 is polished by the movement. As shown in the cross-sectional view of FIG. 3, the polishing pad 1 includes a polishing layer 21 that performs polishing in contact with the silicon wafer 13 held by the carrier portion 14, and an underlayer 22 that fixes the polishing layer 21 to the surface plate 11. And comprising. As shown in FIGS. 2 and 3, the polishing layer 21 includes a first region 23 that is a central portion of the polishing layer 21, which is a concentric region centered on the center of the polishing layer 21, and a central portion of the silicon wafer 13. It is composed of three regions, a second region 24 that contacts and a third region 25 that is the periphery of the polishing layer 21. The second region 24 is a polishing layer harder than the first region 23 and the third region 25, and the polishing layer 21 has regions of different hardness in the surface direction of the polishing surface in the same layer.

  The hardness of the second region 24, which is a hard region, is preferably greater than the hardness of the first region 23 and the third region 25, which are soft regions, by 1% or more and 20% or less in Shore D hardness described later. If it is less than 1%, it is not possible to sufficiently reduce the difference in polishing rate that occurs when the object to be polished is polished using a polishing pad having a uniform hardness over the entire polishing layer. In addition, if it is 1% or more, a region that is difficult to be polished can be easily polished, and the difference in polishing rate can be reduced. If it is more than 20%, a region that is difficult to be polished is easily polished. The difference in the polishing rate becomes large.

  The polishing layer 21 is not particularly limited, and any polishing layer can be used as long as it can be used as a polishing layer of a polishing pad. In other words, the polishing layer 21 can be a foamed polishing layer or a non-foamed polishing layer. Even if it is a single polishing layer, a plurality of layers of two or more layers can be used. Even a polishing layer can be used. Further, when the polishing layer 21 is formed in a plurality of layers, the outermost outermost layer, which is a surface layer in contact with the object to be polished, has a hardness for each region as shown in FIGS. It only has to be different. Examples of the polishing layer having a foam structure include a closed foam and a continuous foam. An independent foam is a foam obtained by mixing additives, such as a micro hollow body, and gas, such as air, for example. The continuous foam is, for example, one obtained by foaming and curing a resin with an additive, a foaming agent, or the like, or one obtained by impregnating a resin during fiber entanglement using a nonwoven fabric or the like as a base material. Examples of the non-foamed polishing layer include those in which fine hollow fibers are contained in a resin. The resin used for the polishing layer is not particularly limited, and any resin can be used as long as the desired properties as the polishing layer can be obtained. Examples thereof include, but are not limited to, polyurethane and polyester.

  Since the hardness of the polishing layer varies depending on the material and structure, a polishing layer having a desired hardness can be easily obtained by various methods. Although not limited to the following methods, for example, when forming a polishing layer, the degree of crosslinking, molecular weight, and the like are changed by changing the type and amount of the monomer and the crosslinking agent, and the desired hardness is obtained. A polishing layer can be obtained. In addition, by changing the irradiation conditions of ultraviolet rays and the heating conditions that are irradiated when the polishing layer is formed, the degree of crosslinking and the molecular weight can be changed to obtain a polishing layer having a desired hardness. Furthermore, the polishing layer can be changed to a desired hardness by adding a crosslinking agent to the already formed polishing layer, and performing a heat treatment, an ultraviolet irradiation treatment, etc., and a polishing layer having the desired hardness can be obtained. Obtainable.

  The underlayer 22 is not particularly limited, and may be any material as long as the polishing layer 21 can be fixed to the surface plate 11. For example, an adhesive tape, a foam tape, a nonwoven fabric, and other elastic bodies can be used.

  Further, the polishing layer 21 may have a groove formed on the surface that contacts the object to be polished 13. By doing so, it becomes easy to hold slurry in the polishing layer. The shape of the groove is not particularly limited, and may be any shape such as a concentric shape, a lattice shape, a radial shape, and a spiral shape. Further, the cross-sectional shape of the groove is not particularly limited, and may be any shape such as an arc shape or an inverted triangular shape.

  A method for determining the hardness of each region of the polishing layer will be described. First, the object to be polished is polished using a polishing pad for determining hardness whose hardness of the polishing layer is uniform over the entire surface. By doing so, the relationship between the hardness of the polishing layer and the polishing rate is obtained, and the difference in the polishing rate depending on the region, for example, the difference in the polishing rate between the central portion and the peripheral portion of the workpiece is obtained.

For example, a case where a silicon wafer having a diameter of 8 inches (about 20 cm) is used as an object to be processed and a SiO ₂ insulating layer formed on the surface of the silicon wafer is polished will be described.

FIG. 4 is a graph showing the influence on the polishing rate of the silicon wafer when the hardness of the polishing layer is changed in the polishing pad for hardness determination. The vertical axis represents the polishing rate of the silicon wafer, and the horizontal axis represents the hardness of the polishing layer. Here, the polishing rate is the thickness of the silicon wafer removed by polishing per unit time, and is obtained by measuring the weight before and after polishing. The hardness of the polishing layer is determined by ASTM (American Society for Testing and
Materials) Measured with an Asker D-type rubber hardness tester (manufactured by Kobunshi Keiki Co., Ltd.) according to a measuring method based on Standard D 2240, JIS K 7215 and JIS K 6253.

  As shown in FIG. 4, it can be seen that the harder the polishing layer (the larger the Shore D hardness value of the polishing layer), the higher the polishing rate of the silicon wafer and the easier the polishing. Furthermore, if it is the range of the hardness normally used as a polishing pad, if a polishing layer is hardened, a polishing rate will increase linearly as shown in FIG.

  When an object to be polished is polished using a polishing pad having a uniform hardness such as a polishing pad for determining hardness, the polishing rate at the center of the silicon wafer may be smaller than the polishing rate at the periphery. Therefore, the polishing layer is hardened so that the difference between the polishing rate at the central part of the silicon wafer and the polishing rate at the peripheral part is reduced, and the other area is softened. Design the hardness. By doing so, a polishing pad that can make the polishing rate uniform over the entire surface of the object to be polished is obtained.

  The polishing pad 1 can be easily formed by cutting a polishing layer 21 having a predetermined hardness into a predetermined size and bonding it to a base layer 22 such as an adhesive tape.

  For example, as the polishing layer in the second region 24, a polishing layer having a hardness determined to be preferable for a region in contact with the center of the silicon wafer by the method for determining the hardness of the polishing layer described above is used. As the polishing layer in the region 23 and the third region 25, a polishing layer having a hardness determined to be preferable for a region in contact with the peripheral portion of the silicon wafer is used. The first region 23 cuts the above-described polishing layer into a cylindrical shape. The second region 24 is cut into a cylindrical shape whose inner diameter is the diameter of the first region 23 and whose width is smaller than the diameter of the silicon wafer. The third region 25 is cut into a cylindrical shape whose inner diameter is the outer diameter of the second region 24. The polishing pad 1 is formed by pasting each of the cut out polishing layers on the base layer 22.

  Moreover, the polishing pad 1 may be other than the above manufacturing methods, for example, it is manufactured by the following method. In the ultraviolet irradiation treatment when forming the polishing layer, irradiation conditions such as irradiation time are changed for each region of the polishing layer. The more the ultraviolet ray is applied to the polishing layer, the more the crosslinking reaction proceeds, the degree of crosslinking increases, and the polishing layer becomes harder. Therefore, the polishing pad 1 having different hardness for each region can be produced. The polishing pad 1 may be a heat treatment as well as the ultraviolet irradiation treatment, and the polishing pad 1 having different hardness for each region is produced by changing the heating conditions such as the heating time and the heating temperature for each region. be able to.

  Furthermore, even if a crosslinking agent is added to the entire surface of the polishing layer having a uniform hardness, and the degree of crosslinking is changed by changing irradiation conditions and heating conditions for each region of the polishing layer, the hardness varies from region to region. The polishing pad 1 can be produced.

  When the polishing pad is formed by these methods, it is possible to form the polishing pad 1 having a uniform density and different hardness for each region. Depending on the type of the object to be polished, such a polishing pad may make the polishing rate more uniform.

  The second embodiment of the present invention is the same as the first embodiment except that the polishing layer 21 is a polishing pad in which the second region 24 is a softer polishing layer than the first region 23 and the third region 25. It is the same.

  By doing so, if the object to be polished is polished using a polishing pad having a uniform hardness over the entire surface of the polishing layer, and the center of the object to be polished is easily scraped, the center of the object to be polished is polished. Since a soft polishing layer that is difficult to polish an object can be brought into contact and polished, the polishing rate can be made uniform over the entire surface of the object to be polished.

  FIG. 5 is a plan view of the polishing pad 2 according to the third embodiment of the present invention. The polishing pad 2 has the polishing layer 31 of the first embodiment and the second embodiment except that the polishing layer 31 is divided into four regions of a first region 32, a second region 33, a third region 34, and a fourth region 35. The same as the pad 1.

  Since the polishing layer is divided into four regions, the hardness of the polishing pad can be changed more according to the ease of polishing for each region of the object to be polished, so that the polishing rate is more uniform over the entire surface of the object to be polished Can be.

  In addition, the area | region which contacts the center part of to-be-polished object is the 2nd area | region 24 shown in FIG. 2 and FIG. 3, or the 2nd area | region 33 and the 3rd area | region 34 shown in FIG. Further, the areas other than the area in contact with the center of the object to be polished are the first area 23 and the third area 25 shown in FIGS. 2 and 3, or the first area 32 and the fourth area 35 shown in FIG.

Below, the Example using the polishing pad 1 which is the 1st Embodiment of this invention is shown.
First, a hardness determining polishing pad is prepared. A hard polyurethane having a Shore D hardness of 55 is used as the polishing layer, a foam tape (manufactured by Toyo Ink) is used as the underlayer, and the polishing layer is attached on the underlayer, and polishing for hardness determination Make a pad.

The hardness-determining polishing pad is attached to a surface plate of a polishing machine (SH-24, manufactured by Speedfam) with a double-sided tape. Thereafter, the silicon wafer is polished under the conditions of a pressing pressure of 7 psi (about 4.83 × 4 ¹⁰ Pa), a platen rotation speed of 60 rpm, and a head rotation speed of 60 rpm. The polishing rate (RR) is measured using Nanospec (Nanometrics, film thickness measurement system). The silicon wafer used here is a silicon wafer having a diameter of 8 inches (about 20 cm), and the object to be polished by the polishing pad is an SiO ₂ insulating layer formed on the surface.

  As a result, the polishing rate when the polishing pad for hardness determination was used was 3100 ｍｉｎ / min at the center of the silicon wafer, whereas it was 3700 Å / min at the outer periphery of the silicon wafer. That is, when polishing is performed using a polishing pad having a polishing layer having a uniform hardness, the center portion of the silicon wafer is difficult to be scraped and the outer peripheral portion of the silicon wafer is easily scraped.

  Therefore, from the relationship between the hardness of the polishing layer and the polishing rate in FIG. 4, the hardness of the region in contact with the center portion of the silicon wafer is set to 57 in Shore D hardness, and the hardness of the region not in contact with the center portion of the silicon wafer is determined. The Shore D hardness was 53. That is, a polishing layer in which the hardness of the second region 24 shown in FIG. 2 is 57 Shore D hardness and the hardness of the first region 23 and the third region is 53 Shore D hardness is used.

  A polishing pad having a polishing layer in which the hardness of the second region 24 is Shore D hardness 57 and the hardness of the first region 23 and the third region is 53 Shore D hardness is a Shore D hardness. Are cut into a cylindrical shape having an outer diameter of 24 inches (about 61 cm) and an inner diameter of 21 inches (about 53 cm) and a diameter of 18 inches (about 46 cm). A rigid polyurethane having a Shore D hardness of 57 is cut into a cylindrical shape having an outer diameter of 21 inch (about 53 cm) and an inner diameter of 18 inch. As shown in FIGS. 2 and 3, the hard polyurethane cut out is attached to the underlayer to produce a polishing pad.

  Using this polishing pad, the silicon wafer is polished by the same method as the above polishing method. As a result, the polishing rate is 4000 Å / min at the center of the silicon wafer and 3500 Å / min at the outer periphery of the silicon wafer.

  FIG. 6 is a graph showing the evaluation results of nonuniformity. FIG. 6 shows the non-uniformity in Examples 1 to 3 and Comparative Examples 1 to 3. Examples 1 to 3 are results for three times when a silicon wafer is polished using a polishing pad 1 having different hardness for each region, and Comparative Examples 1 to 3 are for determining hardness with uniform hardness. It is a result for 3 times when a silicon wafer is polished using a polishing pad. The non-uniformity is a value obtained by measuring the thickness at a plurality of locations of the polished silicon wafer, for example, 49 locations, and expressing the difference between the maximum value and the minimum value with respect to the average value of the thickness of the silicon wafer as a percentage. The smaller the thickness, the better the thickness uniformity of the workpiece.

  As can be seen from FIG. 6, the non-uniformity of Examples 1 to 3 is smaller than the non-uniformity of Comparative Examples 1 to 3. That is, when the silicon wafer is polished using the polishing pad 1 having different hardness for each region as in Examples 1 to 3, the difference in polishing rate between the center portion and the outer peripheral portion of the silicon wafer is greatly improved. It was found that the thickness uniformity was satisfied.

It is a general-view figure which simplifies and shows the structure of a chemical mechanical polishing (CMP) apparatus. 1 is a plan view of a polishing pad 1 according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the polishing pad 1 of FIG. 2 as viewed from a cutting plane line A-A ′. It is a graph which shows the influence with respect to the polishing rate of a silicon wafer when changing the hardness of a polishing layer. It is a top view of the polishing pad 2 which is the 3rd Embodiment of this invention. It is a graph which shows the evaluation result of nonuniformity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Polishing pad 11 Surface plate 13 Silicon wafer 14 Carrier part 15 Slurry supply part 21 Polishing layer 22 Underlayer 23,32 1st area 24,33 2nd area 25,34 3rd area 35 4th area

Claims (4)

A polishing layer for polishing the object to be polished in contact with the object to be polished;
The polishing pad, wherein the polishing layer has different hardness in each layer. A polishing layer for polishing the object to be polished in contact with the object to be polished;
The polishing pad, wherein the polishing layer has different hardness for each concentric region. A polishing layer for polishing the object to be polished in contact with the object to be polished;
The polishing pad, wherein the polishing layer has different hardness in each concentric region.   The hardness of the polishing layer is different depending on a central contact area that is in contact with a central portion of the object to be polished and a central non-contact area other than the central contact area. The polishing pad as described in any one.

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