JP4904027B2 - Polishing pad - Google Patents

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 planarization of an object to be polished such as a silicon wafer by Mechanical Planarization (CMP).

  In the field of semiconductor manufacturing, with the high integration by miniaturization and multilayering of semiconductor elements, the planarization technology of semiconductor layers and metal layers has become an important elemental technology. When forming an integrated circuit on a wafer, if the layers are stacked without flattening the unevenness due to electrode wiring or the like, the step becomes large and the flatness becomes extremely poor. Further, when the step becomes large, it becomes difficult to focus on both the concave portion and the convex portion in photolithography, and miniaturization cannot be realized. Therefore, it is necessary to perform a planarization process for removing irregularities on the wafer surface at an appropriate stage during the lamination. For the flattening process, an etching back method for removing uneven portions by etching, a film forming method for forming a flat film by plasma CVD (Chemical Vapor Deposition), a fluidizing method for flattening by heat treatment, a concave portion by selective CVD, etc. There is a selective growth method for embedding.

  The above method has problems that it is appropriate depending on the type of film such as an insulating film and a metal film, and that the region that can be flattened is extremely narrow. As a planarization technique that can overcome such problems, there is planarization by CMP.

  In the flattening process by CMP, while the polishing composition in which fine silica particles (abrasive grains) are suspended is supplied to the surface of the polishing pad, the pressed polishing pad and the silicon wafer as the object to be polished are relatively moved. By polishing the surface, the wafer surface over a wide range can be flattened with high accuracy.

  In the CMP processing step, a test wafer is processed periodically in order to perform an appropriate polishing process, and the processing result is confirmed, and then the product wafer is processed. However, the cost for using the test wafer is low. There is a problem that processing time is required. Therefore, in order to solve this problem, a method of measuring the progress of polishing in real time from the film thickness of the layer to be polished and feeding back the result is mainly employed. As a result, the detection accuracy of the processing end point is improved and polishing is performed efficiently.

  End point detection methods include torque measurement method, optical measurement method, capacitance measurement method, vibration analysis method, temperature measurement method, differential transformer method, ultrasonic thickness measurement method, electrical resistance measurement method, slurry analysis method, etc. Is in practical use.

  Among these methods, the optical measurement method is a method in which the film thickness of the layer to be polished is directly measured during the polishing process by spectral reflectance measurement. For example, the wafer being polished is irradiated with laser light, and the film thickness is measured by the reflectance.

  In this measuring method, it is necessary to secure an optical path of laser light from the measuring device to the wafer in the polishing pad in order to irradiate the wafer with laser light and receive reflected light during the polishing process. For example, a configuration in which a through hole is provided in a part of the polishing pad and a window member having translucency is provided in the through hole is used.

  As the polishing pad, a multi-layer pad in which a polishing layer for polishing a wafer is laminated on a base layer having a material and structure such as hardness and compressibility different from the polishing layer is used in order to improve the flatness of the wafer. May be. In the case of such a multi-layer pad, light is transmitted in the thickness direction by providing a cavity under the window member (see Patent Document 1).

JP 2004-6663 A

  In the polishing pad described in Patent Document 1, since the bottom of the window member is hollow, the window member is easily distorted and becomes a window member having unevenness on the surface in contact with the object to be processed. If the surface of the window member is uneven, when polishing the workpiece, slurry accumulates in the recess, or the recess changes color due to the accumulated slurry, and when detecting the end point of the polishing process, a detection error occurs. Will occur.

Such a polishing pad has various problems because the material and characteristics of the window member are different from those of other portions of the polishing pad. For example, if the window member is softer than the other part, the window member is more easily worn than the other part. Therefore, if the number of polishing increases, the window member will be depressed, and slurry and polishing debris will stay there and scratch will be generated. Will occur. Also, if the window member is harder than the other part, if the number of polishing increases, the window member that is hard to be worn will protrude from the other part, and scratches may occur or the wafer may be caught by a step and fall off. . Further, in such a case, the window member is not easily worn uniformly, and the irregularities on the surface of the window portion remain, so that the processing end point detection failure is not eliminated.
An object of the present invention is to provide a polishing pad with high detection accuracy of a processing end point.

The present invention has a polishing layer for polishing an object to be polished, and an underlayer for supporting the polishing layer,
The polishing layer is provided with a first window member that transmits light in the thickness direction so that both surfaces of the polishing layer are flush with each other.
The base layer is provided with a second window member that transmits light in the thickness direction at a position corresponding to the first window member so that both surfaces of the base layer are flush with each other.
The amount of deformation, which is the difference in thickness when a predetermined different force is applied, is uniform in the window region in which the first window member and the second window member are formed and in the pad region other than the window region. It is comprised so that it may become. It is a polishing pad characterized by the above-mentioned.

The present invention is characterized in that the second window member comprises a plurality of transparent members.

  According to the present invention, the polishing pad has a polishing layer for polishing an object to be polished and a base layer for supporting the polishing layer. A first window member that transmits light in the thickness direction is formed in the polishing layer, and a second window member that transmits light in the thickness direction is formed in the base layer at a position corresponding to the first window member. Has been.

  Here, the first window member and the second window member are provided for detecting the end point of the polishing process and serve as an optical path of the laser light. By providing the second window member at a position corresponding to the first window member, the first window member is less likely to be distorted, and the surface of the first window member on the side to be polished is not uneven, so the surface of the first window member Thus, no slurry is accumulated, and the discoloration of the first window member due to the slurry is eliminated. Therefore, the end point of the polishing process can be detected without causing a detection error.

  Further, according to the present invention, the deformation amount is configured to be uniform between the window region where the first window member is formed and the pad region other than the window region. Even if all of the other portions of the polishing layer are evenly worn and the first window member has irregularities, the irregularities are eliminated by using the polishing pad. Therefore, the end point of the polishing process can be detected without causing a detection error.

  According to the invention, the second window member may include a plurality of transparent members. By doing so, the deformation amount of the window region and the pad region can be easily made uniform, and the first window member can be prevented from being further distorted.

  FIG. 1 is a cross-sectional view of a polishing pad 1 according to a first embodiment of the present invention. The polishing pad 1 is used in a CMP apparatus and is placed on a rotating surface plate. At the time of polishing, the surface of the silicon wafer is polished by relative movement of the polishing pad 1 and the silicon wafer by being pressed against an object to be polished such as a silicon wafer held on the carrier portion of the CMP apparatus.

  As shown in FIG. 1, the polishing pad 1 includes a polishing layer 2 that performs polishing in contact with a silicon wafer that is an object to be polished, and a base layer 3 that fixes the polishing layer 2 to a surface plate of a CMP apparatus. Composed. The polishing layer 2 is provided with a first window member 4 that transmits light in the thickness direction in a region in contact with the silicon wafer in order to detect a processing end point. Further, the base layer 3 is provided with a second window member 5 that transmits light in the thickness direction at a position corresponding to the first window member 4. For example, as shown in FIG. 1, the position corresponding to the first window member 4 is a position in contact with the surface of the first window member 4 on the base layer 3 side, and the first window member 4 and the second window member 5. Is an optical path of the laser beam for detecting the end point of the polishing process. As the laser beam for detecting the end point of the polishing process, a laser beam having a wavelength of 150 nm to 4000 nm is used.

  As shown in FIG. 1, by providing the second window member 5 at a position corresponding to the first window member 4, the first window member 4 is supported from below by the second window member 5. 4 becomes difficult to distort, and the surface of the first window member 4 on the workpiece side cannot be uneven. Therefore, when the silicon wafer is polished using the polishing pad 1, the slurry does not accumulate in the first window member 4, and the polishing layer 2 is not discolored by the slurry. Therefore, the end point of the polishing process can be detected without causing a detection error.

Next, a method for producing the polishing pad 1 will be described.
The resin that forms the first window member 4 is placed in the mold, the resin that forms the polishing layer 2 is poured into the mold together with additives such as a curing agent, and cured at a predetermined temperature to obtain a molded body. Then, the polishing layer 2 provided with the first window member 4 is obtained by slicing the molded body. Then, the obtained polishing layer 2 is laminated on the base layer 3 in which an opening is formed at a position corresponding to the first window member 4. Furthermore, the polishing pad 1 is obtained by sticking the second window member 5 so as to fill the opening.

  In addition, the polishing pad 1 may be other than the above manufacturing method, and for example, is manufactured by the following method.

  A resin for forming the polishing layer 2 is poured into a mold together with an additive such as a curing agent, cured at a predetermined temperature to obtain a molded body, and then the molded body is sliced to obtain the polishing layer 2. . Thereafter, an opening is formed in the polishing layer 2, and the obtained polishing layer 2 is laminated on the base layer 3 in which the opening is formed at a position corresponding to the first window member 4. Further, the first window member 4 is attached so as to fill the opening formed in the polishing layer 2, and the second window member 5 is attached so as to fill the opening of the base layer 3, thereby polishing pad. 1 is obtained.

  Any polishing layer 2 can be used as long as it can be used as a polishing layer of a polishing pad. For example, the polishing layer 2 can be used as a polishing layer having a foamed structure or a polishing layer having a non-foamed structure. 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. 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.

  Further, the polishing layer 2 may have a groove formed on the surface that contacts the silicon wafer. 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.

  The underlayer 3 may be made of any material as long as the polishing layer 2 can be fixed to the surface plate. For example, an adhesive tape, a foam tape, a nonwoven fabric, and other elastic bodies can be used. As a nonwoven fabric, nonwoven fabrics, such as nylon, polyester, an acryl, a polypropylene, are mentioned, for example.

  The first window member 4 is made of a transparent resin that can transmit a laser beam for detecting the end point of the polishing process. As the transparent resin, known resins can be used. For example, polyurethane, acrylic resin, polycarbonate, polyamide, polyester, polyvinyl chloride, polyvinylidene fluoride, polyethersulfone, polystyrene, polyethylene, polytetrafluoroethylene, etc. These resins are mentioned.

  The cross-sectional shape of the first window member 4 in the polishing surface direction is preferably a closed curve including a curved portion, for example, an elliptical shape. Further, when the cross-sectional shape is an ellipse, it is preferable to form the first window member 4 so that the longitudinal direction is perpendicular to the radial direction of the polishing pad 1. By doing so, it is possible to prevent degradation of polishing characteristics such as generation of scratches and dropping of the silicon wafer due to the silicon wafer being caught by the first window member 4.

  The second window member 5 can be made of any material as long as it can transmit a laser beam for detecting the end point of the polishing process having a wavelength of 150 nm or more and 4000 nm or less. For example, the same resin as that of the first window member 4 can be used. Besides, a silicone sheet, a silicone rubber, a silicone bag filled with silicone oil, an air bag filled with a transparent gas such as air, or the like can be used. it can. The second window member 5 is preferably selected so that the deformation amount is uniform between the window region where the first window member 4 is formed and the pad region other than the window region. For example, when the first window member 4 uses a material having a higher compressibility than the polishing layer 2, the second window member 5 uses a material having a lower compressibility than the base layer 3. Further, when the first window member 4 uses a material having a compression rate lower than that of the polishing layer 2, the second window member 5 uses a material having a compression rate higher than that of the base layer 3. By doing so, the amount of deformation becomes uniform between the window region and the pad region, so that all of the polishing layer 2 and the first window member 4 are evenly worn. Further, even if the first window member 4 is provided, the polishing characteristics such as the polishing rate and flatness are not deteriorated. Furthermore, even if the polishing layer is worn and the surface of the first window member is not uneven, even if the surface of the first window member is uneven, the unevenness is eliminated by using the polishing pad. Therefore, the end point of the polishing process can be accurately detected without degrading the polishing characteristics such as the polishing rate and flatness. The compression ratio is a percentage of the difference between the original thickness of the polishing pad when a predetermined load is applied to the polishing pad and the thickness when applied with respect to the original thickness. The deformation amount is a difference between the original thickness of the polishing pad when a predetermined load is applied to the polishing pad and the thickness at the time of weighting, and is a value calculated by a calculation method described later.

  The size of the second window member 5 is preferably slightly smaller than the size of the first window member 4. By doing so, when the first window member 4 is attached to the opening of the polishing layer 2 to produce the polishing pad 1, not only the first window member 4 is attached to the second window member 5, but also the underlying layer. 3, the first window member 4 is difficult to peel off from the polishing pad 1.

  FIG. 2 is a cross-sectional view of the polishing pad 11 according to the second embodiment. As shown in FIG. 2, the polishing pad 11 includes a polishing layer 12 and a base layer 13. The polishing layer 12 is provided with a first window member 14, and the base layer 13 is provided with a second window member 15 that transmits light in the thickness direction at a position corresponding to the first window member 14.

  The second window member 15 is composed of a plurality of transparent members. As shown in FIG. 2, for example, a sheet 15b made of a material having a low compressibility such as an acrylic resin may be laminated so as to be sandwiched between sheets 15a made of a material having a high compressibility such as a silicone resin.

  As a method of adjusting the deformation amount to be uniform between the window region in which the first window member 14 is formed and the pad region other than the window region, a method of changing the material of the first window member 14; There are a method of changing the material of the second window member 15 and a method of changing the material of the first window member 14 and the second window member 15.

  Since the change of the material of the first window member 14 that is in direct contact with the object to be polished has a large influence on the polishing characteristics, the material of the first window member 14 cannot be changed so much. Therefore, in the method of changing the first window member 14 and the method of changing the material of the first window member 14 and the second window member 15, it is difficult to adjust the deformation amount to be uniform. A method of changing the material of the window member 15 is preferable.

  If only the material of the second window member 15 is changed, the amount of deformation may not be uniform. In such a case, the amount of deformation is adjusted to be uniform by forming the second window member 5 with a plurality of transparent members. For example, by changing the second window member 15 to the configuration shown in FIG. 2, it is possible to easily adjust the deformation amount to be uniform between the window region and the pad region without deteriorating the polishing characteristics. it can.

  Furthermore, since the second window member 15 that is in direct contact with the first window member 14 is a member 15a made of a material having a low compression rate, there is no reduction in transparency due to damage to each other.

In the above description, the polishing pad in which the first window member and the second window member are in contact with each other has been described. However, the configuration of the polishing pad is not limited to this configuration, and a space is provided between the first window member and the second window member. There may be a polishing pad in which the first window member and the second window member are in contact with each other during polishing.
Below, the Example about the polishing pad 1 which is the 1st Embodiment of this invention is shown.

(Example)
As the material of the polishing pad 1 having the structure shown in FIG.
Polishing layer 2: Nitta Haas, IC1000, thickness 1.27 mm
Underlayer 3: Polyurethane foam, thickness 1.27 mm
1st window member 4: Transparent polyurethane, thickness 1.27mm
Second window member 5: silicone rubber sheet MQ (according to ASTM D1418), thickness 1.27 mm

(Comparative example)
Example 2 is the same as Example 1 except that the second window member 5 is not used and there is a cavity below the first window member 4.

  About an Example and a comparative example, deformation amount was computed as follows, and also detection accuracy evaluation was performed. Table 1 shows the calculated change amount and the evaluation result of the detection accuracy evaluation. Regarding the symbols in the table, ◯ indicates that the detection accuracy is good and the practicality is high, and x indicates that a detection error may occur and the practicality is low.

(Deformation amount)
The deformation amount of the polishing pad was calculated from the following equation based on the measured value of the thickness of the polishing pad measured by a method based on JIS L1096.
Deformation amount (μm) = T1-T2

Here, T1 is the thickness of the polishing pad when a stress of 641 g / cm ² is applied to the polishing pad from an unloaded condition for 60 seconds and T2 is 5161 g / cm from the state of T1 to the polishing pad. It is the thickness of the polishing pad when a stress of cm ² is applied and held for 60 seconds.

  As can be seen from Table 1, in the case of the polishing pad (Example) having the second window member 5 and having no cavity under the first window member 4, the deformation amount of the window region is 80 μm to 100 μm, and the average The value is 90 microns, the deformation amount of the pad region is 65 μm to 110 μm, and the average value is 87.5 microns. Therefore, the deformation amount of the window region and the deformation amount of the pad region are uniform and the detection accuracy is high.

  On the other hand, in the case of a polishing pad (comparative example) that does not have the second window member 5 and has a cavity under the first window member 4, the deformation amount of the window region is 250 μm to 450 μm, and the average value is 350 microns, the deformation of the pad region is 65 μm to 110 μm, and the average value is 87.5 microns. Therefore, the deformation amount of the window region and the deformation amount of the pad region are greatly different, and the detection accuracy is low as compared with the embodiment.

  From the above, by providing the second window member 5 at a position corresponding to the first window member 4, the end point of the polishing process can be detected without causing a detection error.

It is sectional drawing of the polishing pad 1 which is the 1st Embodiment of this invention. It is sectional drawing of the polishing pad 11 which is 2nd Embodiment.

Explanation of symbols

1,11 Polishing pad 2,12 Polishing layer 3,13 Underlayer 4,14 First window member 5,15 Second window member

Claims (2)

A polishing layer for polishing an object to be polished, and an underlayer for supporting the polishing layer,
The polishing layer is provided with a first window member that transmits light in the thickness direction so that both surfaces of the polishing layer are flush with each other.
The base layer is provided with a second window member that transmits light in the thickness direction at a position corresponding to the first window member so that both surfaces of the base layer are flush with each other.
The amount of deformation, which is the difference in thickness when a predetermined different force is applied, is uniform in the window region in which the first window member and the second window member are formed and in the pad region other than the window region. It is comprised so that it may become. The polishing pad characterized by the above-mentioned.   The polishing pad according to claim 1, wherein the second window member includes a plurality of transparent members.

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