JP2008263120A - Wafer polishing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wafer polishing device in which change in surface temperature of a polishing pad in a wafer polishing process can be reduced. <P>SOLUTION: In the wafer polishing device 100, a wafer W is pressed against a polishing pad 14 and polished while an abrasive agent is supplied onto the polishing pad 14. The wafer polishing device 100 includes: a polishing head 18 which pushes the wafer W onto the polishing pad 14; a retainer ring 22 of which the bottom surface is located closer to the polishing pad 18 than to the polishing surface of the wafer W and which can be attached to and removed from the polishing head 18 in such a manner as to surround the outer circumference of the wafer W, the retainer ring 22 including a groove 22a for flowing a cooling liquid as a temperature adjusting medium; and a second cooling mechanism 24 which supplies the cooling liquid to a flow path 23 formed by the groove 22a when the retainer ring 22 is attached to the polishing head 18. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wafer polishing apparatus used for polishing a surface of a semiconductor wafer in a semiconductor device manufacturing process.

  Recently, in order to realize high integration and high speed of semiconductor devices, multilayered metal wiring is progressing in the manufacturing process of semiconductor elements, and low resistance copper is used as the wiring material. ing.

  As a method for forming the copper wiring, there is a so-called damascene method. In this damascene method, a trench to be a wiring pattern is formed in an interlayer insulating film by dry etching, a copper thin film is formed on the entire wafer surface by sputtering or the like, and then copper is deposited on the copper thin film by electroplating or the like. Then, chemical mechanical polishing (CMP) is performed on the wafer surface to remove excess copper while leaving the copper embedded in the groove, and at the same time, planarize the wafer surface.

  The CMP process used here refers to a polishing pad that is made by rotating both a polishing head that holds a wafer and a turntable to which a polishing pad is attached, and that contains abrasive grains such as alumina and colloidal silica. While pressing the wafer polishing surface against the polishing pad with a constant force, the mechanical action by the abrasive grains contained in the slurry and the chemical action such as etching or modifying the copper film into a copper complex layer Thus, copper is removed.

  In this CMP process, since the wafer and the polishing pad are slidably brought into contact with each other, the surface temperature of the polishing pad rises due to frictional heat generated by friction between the wafer and the polishing pad. This increase in the surface temperature of the polishing pad fluctuates the polishing rate of the wafer. In particular, in a copper CMP process, the polishing rate varies greatly depending on the temperature because copper is polished using a chemical action. Therefore, for example, by flowing cooling water to the turntable on which the polishing pad is affixed or cooling the polishing head holding the wafer, fluctuations in the surface temperature of the polishing pad are suppressed (for example, Patent Documents 1 and 2).

  However, in the case of the method for cooling the turntable, since the polishing pad is made of a material that does not have high thermal conductivity, such as a polyurethane foam material, rapid and sufficient cooling cannot be performed. Also, in the case of the method of cooling the polishing head, the polishing pad is cooled via the wafer, so that sufficient cooling performance cannot be obtained.

  Further, recently, during the CMP process, the polishing pad is conventionally attached to the polishing head so as to surround the outer periphery of the wafer so as to prevent the wafer from popping out so that the polishing pad contacts the entire polishing surface of the wafer with a uniform force. A method of positively pressing the retainer ring against the polishing pad has been used.

In this case, since frictional heat due to the sliding contact between the retainer ring and the polishing pad is further applied, even if the conventional method of cooling the polishing head and the turntable is used in combination, the cooling is not sufficient and the fluctuation of the polishing rate is suppressed. It has become difficult.
JP 2002-231672 A (paragraphs [0018], [0019], FIG. 1 etc.) JP 2004-237373 A (paragraphs [0021], [0022], FIG. 1 etc.)

  An object of the present invention is to provide a wafer polishing apparatus that makes it possible to suppress a change in the surface temperature of a polishing pad in a wafer polishing process.

  The present invention is a wafer polishing apparatus for polishing by pressing a wafer to be polished against the polishing pad with a predetermined force while supplying an abrasive to the polishing pad, and a polishing head for pressing the wafer to be polished against the polishing pad, A retainer ring that has a bottom surface positioned closer to the polishing pad than the polishing surface of the wafer to be polished and is detachably attached to the polishing head so as to surround an outer periphery of the wafer to be polished, and for adjusting the temperature of the retainer ring And a temperature polishing mechanism for the wafer.

  According to the present invention, it is possible to suppress a change in the surface temperature of the polishing pad in the wafer polishing process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a sectional view showing a schematic configuration of a wafer polishing apparatus. The wafer polishing apparatus 100 includes a turntable 10, a polishing pad 14 attached to the upper surface of the turntable 10, a first cooling mechanism 16 for cooling the turntable 10, and a polishing head 18 that holds a wafer W. And a pressing mechanism 20 for pressing the wafer W held by the polishing head 18 against the polishing pad 14 with a constant force, a retainer ring 22 configured to be detachable from the polishing head 18, and the retainer ring 22 are cooled. A second cooling mechanism 24 is provided.

  The turntable 10 is rotatable by a rotary drive mechanism (not shown) such as a motor, and a flow path 12 is provided inside the turntable 10 for flowing a coolant as a temperature control medium for adjusting the temperature of the turntable 10. Is formed. As the first cooling mechanism 16, for example, a cooling water preparation and circulation device (so-called chiller) is used, and a coolant having a constant temperature is supplied from the first cooling mechanism 16 to the flow path 12 and flows through the flow path 12. The coolant whose temperature has changed is returned to the first cooling mechanism 16 again.

  As the polishing pad 14, a conventionally used porous polyurethane resin sheet, artificial suede sheet, or a composite sheet of these and other resin sheets is used, and is adhered to the upper surface of the turntable 10 with an adhesive or the like. ing.

  Here, it is assumed that the polishing head 18 holds the wafer W by vacuum suction. In FIG. 1, the detailed structure of the polishing head 18 for vacuum suction and the illustration of the vacuum suction mechanism are omitted. The pressing mechanism 20 presses the polishing head 18 against the polishing pad 14 by hydraulic pressure, air pressure, or the like. The polishing head 18 is configured to be rotatable by a drive shaft 21 by a rotation drive mechanism such as a motor (not shown).

  In order to mount the retainer ring 22 on the outer peripheral portion of the polishing head 18, the lower diameter of the polishing head 18 is smaller than the upper diameter, and the retainer ring 22 is fixed to this portion with screws or a buckle. It is attached by means (not shown). That is, the retainer ring 22 is detachable from the polishing head 18.

  In a state where the retainer ring 22 is attached to the polishing head 18, the bottom surface of the retainer ring 22 is more polishing pad than the polishing surface of the wafer W (that is, the lower surface of the wafer W when the wafer W is held by the polishing head 18). It is located on the 14th side. Therefore, when the wafer W is polished, the bottom surface of the retainer ring 22 is polished while being in sliding contact with the polishing pad 14. For this reason, it is necessary to periodically replace the retainer ring 22 with a new one. By making the retainer ring 22 detachable from the polishing head 18, this replacement can be easily performed.

  The retainer ring 22 is preferably made of ceramics having excellent thermal conductivity and wear resistance.

  FIG. 2 shows a plan view of the retainer ring 22. On the upper surface of the retainer ring 22, a groove 22 a for flowing a coolant as a temperature control medium is formed. Here, a structure is shown in which the groove 22a is provided with partition walls 22b and 22c that partition the groove 22a into a semicircular arc shape. In a state where the retainer ring 22 is attached to the polishing head 18, the upper surface of the retainer ring 22 comes into close contact with the horizontal contact surface 18 a formed on the outer peripheral portion of the polishing head 18, so that the groove 22 a allows the cooling water to flow. It becomes the flow path 23.

  In order to prevent leakage of the coolant from the flow path 23, the inner side and the outer side of the groove 22 a between the horizontal contact surface 18 a of the polishing head 18 and the upper surface of the retainer ring 22, respectively, as necessary. A rubber or copper seal ring may be arranged. The inner peripheral surface of the retainer ring 22 is not necessarily in contact with the polishing head 18.

  In order to allow cooling water to flow through the flow path 23, communication holes 19 a and 19 b communicating with the flow path 23 are formed in the polishing head 18. The cooling water is substantially divided into two by the partition wall 22b when flowing into the flow path 23 from the communication hole 19a. After flowing through the flow path 23, the coolant merges with the communication hole 19b.

  The second cooling mechanism 24 returns to the temperature adjustment unit 28 from the first temperature sensor 26 that measures the surface temperature of the polishing pad 14, a temperature adjustment unit 28 that prepares cooling water to be supplied to the flow path 23, and the flow path 23. A second temperature sensor 30 for measuring the temperature of the cooling water, a cooling water supply unit 32 for adjusting the temperature of the cooling water returning from the flow path 23 to the temperature control unit 28 before returning to the temperature control unit 28, and first and second A control unit 34 is provided for controlling the temperature and circulating flow rate of the cooling water prepared by the temperature control unit 28 based on the temperature detection signals of the temperature sensors 26 and 30.

  As the cooling water, water added with a rust inhibitor is generally used. In order to make it easy to recognize the leakage of the cooling water, a pigment or the like may be added thereto. An organic solvent can also be used as a refrigerant. In this case, the non-volatile solvent is preferable from the viewpoint of the working environment and the liquid amount management in the temperature control unit.

  As the first temperature sensor 26, a non-contact type radiation thermometer is used, and the surface temperature of the polishing pad 14 is measured in real time. As the second temperature sensor 30, for example, a thermocouple can be used. The temperature data from the first and second temperature sensors 26 and 30 are sent to the control unit 34.

  Both the temperature control unit 28 and the cooling water supply unit 32 are cooling water preparation and circulation devices (chillers). The cooling water supply unit 32 lowers the cooling water returned from the flow path 23 to a constant temperature and supplies the cooling water to the temperature adjustment unit 28. Thereby, preparation of the cooling water in the temperature control unit 28 by the control unit 34 becomes easy.

  As described above, the temperature of the coolant supplied from the coolant supply unit 32 to the temperature control unit 28 is constant in the normal operation state, but the cooling returns to the coolant supply unit 32 from the flow path 12 due to some abnormality. When the temperature of the water rises, the temperature of the coolant supplied from the cooling water supply unit 32 to the temperature adjustment unit 28 may change.

  Therefore, the control unit 34 constantly monitors the temperature information measured by the second temperature sensor 30 to facilitate the preparation of the cooling water in the temperature adjustment unit 28. In addition, according to such a viewpoint, the 2nd temperature sensor 30 may be the structure which measures the temperature of the cooling fluid supplied to the temperature control unit 28 from the cooling water supply unit 32. FIG. Further, when the temperature adjustment unit 28 has sufficient cooling water temperature adjustment capability, the cooling water supply unit 32 is not necessarily required.

  The temperature of the cooling water is set in a range in which a desired surface temperature of the polishing pad 14 can be obtained, but is preferably in the range of 5 ° C to 20 ° C. If the cooling water is excessively cooled, condensation occurs in the piping through which the cooling water flows, including the retainer ring 22, which flows to the polishing pad 14 and thins the slurry, or the chemical components contained in the slurry are altered and polished. Performance may be reduced. On the other hand, if the temperature is raised too much, it becomes difficult to quickly lower the surface temperature of the polishing pad 14.

  The control unit 34 controls the temperature and flow rate of the cooling water to be prepared by the temperature adjustment unit 28 by PID control mainly from the change in the surface temperature of the polishing pad 14 measured by the first temperature sensor 26.

  The details of the cooling water flow structure between the second cooling mechanism 24 and the communication holes 19a and 19 are omitted in FIG. 1, but this is described in, for example, Japanese Patent Laid-Open No. 2002-231672 mentioned above. A known structure such as the structure disclosed in FIG. 1 or the like can be used. The circulation of the cooling water between the first cooling mechanism 16 and the flow path 12 provided in the turntable 10 also follows this.

  The wafer polishing apparatus 100 includes a slurry supply nozzle 36 that supplies a slurry 38 as an abrasive to the polishing pad 14. The temperature of the slurry 38 is adjusted to 20 ° C. to 25 ° C., for example. In the metal film CMP for removing the metal film formed on the surface of the wafer W, the slurry 38 includes chemical components having an action of oxidizing the metal film and abrasive grains for physically polishing the film surface. In order to stabilize the chemical reaction with the metal film, the one whose pH is adjusted is generally used. As the abrasive grains contained in the slurry 38, known materials such as colloidal silica and alumina are used.

  In the wafer polishing apparatus 100, according to the above configuration, the polishing pad 14 and the polishing head 18 are rotated while supplying the slurry 38 to the polishing pad 14, and the polishing head 18 holds the wafer W and presses it against the polishing pad 14. Thus, the wafer W is polished. Friction heat due to friction between the wafer W and the polishing pad 14 and friction heat due to friction between the retainer ring 22 and the polishing pad 14 are generated. By cooling the retainer ring 22 by flowing cooling water through the flow path 23, Since the surface of the polishing pad 14 slidably contacted by the retainer ring 22 is directly cooled, an excellent cooling effect is obtained. At this time, by further cooling the turntable 10, a higher cooling effect can be obtained. In this way, fluctuations in the surface temperature of the polishing pad 14 can be kept small.

  This effect is particularly useful for the metal film CMP that actively uses chemical reaction during wafer polishing, whereby the polishing rate can be kept constant. This effect will be described in detail with reference to FIG.

  FIG. 3 shows the relationship between the wafer polishing time, the temperature of the polishing pad, and the polishing rate. In FIG. 3, the solid line A indicates the change in the surface temperature of the polishing pad 14 when the first cooling mechanism 16 cools the polishing pad 14 but the second cooling mechanism 24 does not cool the polishing pad 14, and the solid line B indicates A change in the surface temperature of the polishing pad 14 when the polishing pad 14 is cooled by the first and second cooling mechanisms 16 and 24 is shown.

  As shown by the solid line A in FIG. 3, even if only the turntable 10 is cooled, the temperature rise suppression effect of the polishing pad 14 is not sufficient, and the surface temperature of the polishing pad 14 increases with the lapse of the polishing time. . On the other hand, as shown by the solid line B in FIG. 3, the surface temperature of the polishing pad 14 is kept substantially constant by cooling the retainer ring 22 as well.

  A broken line C shown in FIG. 3 indicates a polishing rate according to a temperature change of a solid line A when an acidic slurry is mainly used. In this case, when the surface temperature of the polishing pad 14 exceeds a certain temperature, the chemical reaction is rapidly accelerated excessively, and the polishing rate is increased. As a result, problems such as pattern dishing on the wafer surface occur.

  A broken line D shown in FIG. 3 indicates a polishing rate according to the temperature change of the solid line A when an alkaline slurry is mainly used. In this case, when the surface temperature of the polishing pad 14 exceeds a certain temperature, the amount of by-product due to excessive reaction between the metal film to be polished and a predetermined component contained in the slurry increases, and this by-product is caused to become abrasive. The polishing rate is drastically reduced by significantly reducing the physical polishing performance of the abrasive grains by adhering to the grains. As a result, the throughput is reduced.

  A two-dot chain line E shown in FIG. 3 indicates a polishing rate according to the temperature change of the solid line B. When the surface temperature of the polishing pad 14 is constant, the polishing rate can be kept constant regardless of whether the slurry is acidic or alkaline.

  Next, another embodiment of the polishing head 18 and the retainer ring 22 constituting the wafer polishing apparatus 100 will be described. FIG. 4 is a schematic sectional view of the polishing head 50 and the retainer ring 56.

  This polishing head 50 has a structure in which a ring-shaped outer wall portion 52b is integrally provided on the outer periphery of a disc-shaped horizontal plate portion 52a. A pipe 54 is provided on the outer wall 52b so as to protrude from the bottom surface in order to allow the coolant to flow.

  In order to attach the retainer ring 56 to the bottom surface of the outer wall portion 52 b, a groove 56 a that fits the pipe 54 is formed on the upper surface of the retainer ring 56. Even in such a structure, the retainer ring 56 can be cooled by flowing the coolant through the pipe 54. In addition, since the coolant does not flow through the retainer ring 56 itself, there is no possibility that the coolant leaks from the attaching / detaching surfaces of the polishing head 50 (outer peripheral wall 52b) and the retainer ring 56.

  The retainer ring 56 is detachably attached to the outer wall portion 52b by using fixing means (not shown) such as screwing or a buckle. A narrow gap may be formed between the pipe 54 and the groove 56a formed in the retainer ring 56 due to processing accuracy. For example, such a gap may be made of more thermally conductive grease or the like. By filling, heat conduction between the coolant and the retainer ring 56 can be performed efficiently.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to such a form. For example, the wafer polishing apparatus 100 is configured to supply / recover cooling water to the flow path 23 formed in the retainer ring 22 using the communication holes 19 a and 19 provided in the polishing head 18. A hole for supplying / recovering the cooling water directly to the retainer ring 22 may be provided without providing the communication holes 19a and 19b.

  In the wafer polishing apparatus 100, the temperature of the cooling liquid flowing through the flow path 12 of the turntable 10 is constant. However, in order to keep the polishing processing temperature constant, the temperature of the cooling liquid supplied to the flow path 12 is also changed. It may be adjustable. In this case, for example, without providing the first cooling mechanism 16, the second cooling mechanism 24 supplies the same cooling liquid as the cooling liquid supplied to the flow path 23 of the retainer ring 22 to the flow path 12 of the turntable 10. It can also be configured.

  Further, in the wafer polishing apparatus 100, a flow path for flowing a coolant to the polishing head 18 itself is provided so as to communicate with the communication holes 19a and 19b, whereby the held wafer W is cooled and further polished via the wafer W. The pad 14 may be cooled.

  In the above embodiment, the temperature of the retainer rings 22 and 56 is adjusted using the cooling liquid. However, as shown in FIG. 3, even if the surface temperature of the polishing pad rises to a certain temperature, The polishing rate is almost constant. Therefore, at the start of wafer polishing, a temperature control medium that intentionally raises the surface temperature of the polishing pad can be used, and after reaching a predetermined temperature, a cooling liquid can be flowed to maintain the temperature. The temperature control medium is not limited to a liquid, and a gas can also be used.

Sectional drawing which shows schematic structure of a 1st wafer grinding | polishing apparatus. The top view of a retainer ring. The graph which shows the relationship between polishing time, the surface temperature of a polishing pad, and a polishing rate. FIG. 4 is a schematic cross-sectional view of another polishing head and a retainer ring.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Turntable, 12 ... Flow path, 14 ... Polishing pad, 16 ... 1st cooling mechanism, 18 ... Polishing head, 18a ... Horizontal contact surface, 19a, 19b ... Communication hole, 20 ... Pressing mechanism, 21 ... Drive shaft 22 ... Retainer ring, 22a ... Groove, 22b, 22c ... Partition wall, 23 ... Flow path, 24 ... Second cooling mechanism, 26 ... First temperature sensor, 28 ... Temperature control unit, 30 ... Second temperature sensor, 32 ... Cooling water supply unit, 34 ... Control unit, 36 ... Slurry supply nozzle, 38 ... Slurry, 50 ... Polishing head, 52a ... Horizontal plate part, 52b ... Outer wall part, 54 ... Pipe, 56 ... Retainer ring, 56a ... Groove, 100: Wafer polishing apparatus.

Claims (5)

A wafer polishing apparatus for polishing by pressing a wafer to be polished against a polishing pad with a predetermined force while supplying an abrasive,
A polishing head for pressing a wafer to be polished against a polishing pad;
A retainer ring that has a bottom surface positioned closer to the polishing pad than the polishing surface of the wafer to be polished and is detachable from the polishing head so as to surround an outer periphery of the wafer to be polished;
And a temperature adjusting mechanism for adjusting the temperature of the retainer ring. The retainer ring includes a groove portion that forms a medium flow path between the retainer ring and a mounting surface to the polishing head in a state of being mounted on the polishing head,
The polishing head includes a hole communicating with the groove,
The wafer polishing apparatus according to claim 1, wherein the temperature adjustment mechanism supplies a temperature adjustment medium to the medium flow path through the hole. The polishing head includes a pipe provided so as to protrude on a mounting surface with the retainer ring as a medium flow path for flowing a temperature control medium,
The retainer ring includes a groove that fits with the pipe,
The wafer polishing apparatus according to claim 1, wherein the temperature adjustment mechanism supplies a temperature adjustment medium to the medium flow path. The temperature adjustment mechanism and the medium flow path form a circulation system in which the temperature adjustment medium supplied from the temperature adjustment mechanism to the medium flow path returns to the temperature adjustment mechanism again.
The temperature adjustment mechanism is
A first temperature sensor for measuring a surface temperature of the polishing pad;
A temperature control unit for adjusting and preparing a temperature control medium to be supplied to the medium flow path;
A second temperature sensor for measuring the temperature of the temperature control medium returning from the medium flow path to the temperature control unit;
The control unit for controlling the temperature of the temperature control medium and the circulation flow rate in the temperature control unit based on the temperature detection signals of the first and second temperature sensors. Item 4. The wafer polishing apparatus according to Item 3.   The said polishing pad is affixed on the turntable, The another medium flow path for flowing a predetermined | prescribed temperature control medium is also provided in the said turntable. The wafer polishing apparatus according to claim 1.

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