JP2008108940A - Device and method for polishing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method capable of absolutely detecting the polishing completion. <P>SOLUTION: The polishing method of this invention polishes the object (111) to be polished by pressing and rotating while swinging a polishing head (101) with a polishing member (201) provided to the object (111) to be polished held on a rotating chuck (109). An amplitude of a swing caused by the swing of a torque applied to the polishing head is obtained, and the completion point of the polishing is detected by the variation of the amplitude generated by the swing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polishing apparatus and a polishing method, and more particularly to a polishing apparatus or a polishing method used for planarization polishing of a semiconductor device performed in a process of manufacturing a semiconductor such as ULSI (Ultralarge-scale integrated).

  As the semiconductor integrated circuit is highly integrated and miniaturized, the number of steps of the semiconductor manufacturing process is increasing and complicated. Along with this, it has become difficult to ensure the flatness of the surface of the semiconductor device. The presence of a step on the surface leads to disconnection of wiring, an increase in local resistance, etc., leading to disconnection and a decrease in electric capacity. Insulating films also lead to breakdown voltage degradation and leakage.

  On the other hand, as the semiconductor integrated circuit is highly integrated and miniaturized, the light source wavelength of photolithography is shortened, and the numerical aperture, so-called NA, is increasing, so that the depth of focus of the semiconductor exposure apparatus is substantially reduced. It is coming. In order to cope with a decrease in the depth of focus, the device surface needs to be flattened more than ever. As a method for planarizing such a semiconductor surface, a chemical mechanical polishing (Chemical Mechanical Polishing or Chemical Mechanical Planarization, hereinafter referred to as CMP) technique is considered a promising method.

  A polishing apparatus using CMP includes a platen having a polishing member attached to the upper surface and a polishing head having a polishing object such as a wafer attached thereto. The platen and the polishing head each rotate at a predetermined number of rotations in a state where the polishing head presses the object to be polished against the polishing member. Further, the polishing head performs a reciprocating motion (hereinafter referred to as swinging) on the polishing member. In this way, the surface of the object to be polished is polished to a flat and mirror surface by the polishing member.

  In such a polishing apparatus, a method for detecting a change in polishing friction force during polishing is known as a method for detecting the end point of polishing. A wafer that is an object to be polished has a laminated structure made of different materials such as semiconductors, conductors, and insulators. Since different materials have different friction coefficients due to polishing, by detecting a change in polishing frictional force, it is possible to detect that the material to be polished has changed, and to detect the end point of polishing.

  On the other hand, the polishing frictional force is changed by the oscillation of the polishing head. When detecting the polishing end point by detecting the change in the polishing friction force, it is convenient to remove the change in the polishing friction force due to the oscillation of the polishing head. When the change due to the oscillation of the polishing head is removed by the analog low-pass filter, it is necessary to adjust the cutoff frequency, the gain, and the like, and a delay of several tens of seconds occurs. Therefore, it has been proposed to detect the end of polishing by obtaining an average value of the polishing friction force for each oscillation cycle (for example, Patent Document 1).

  However, since the average value of the polishing friction force for each oscillation cycle varies depending on other factors such as the state of the oscillation mechanism, the polishing end can be ensured only by the average value of the polishing friction force for each oscillation cycle. It may not be detected.

Japanese Patent Laid-Open No. 10-202513

  Therefore, there is a need for a polishing apparatus and a polishing method that can reliably detect the end of polishing.

  The polishing method according to the present invention is a polishing method in which the polishing object is polished by pressing and rotating a polishing head provided with a polishing member against a polishing object held on a rotating holding means. Then, the amplitude generated by the oscillation of the torque applied to the polishing head is obtained, and the polishing end point is detected by the change in the amplitude generated by the oscillation.

  The width of the amplitude of the torque applied to the polishing head due to the oscillation is closely related to the flatness of the material to be polished, that is, the end of the polishing. Can be detected.

  A polishing method according to an embodiment of the present invention is characterized in that an amplitude generated by the swing is obtained from a difference between a maximum value and a minimum value of a torque applied to the polishing head within one cycle of the swing.

  According to the present embodiment, it is possible to reliably determine the amplitude caused by the swing from the difference between the maximum value and the minimum value within one cycle of the swing.

  In a polishing method according to another embodiment of the present invention, a value of the torque applied to the polishing head is determined by removing the influence of the fluctuation, and the polishing end point is determined by further considering the value from which the influence of the fluctuation is removed. It is characterized by detecting.

  The value of the torque applied to the polishing head, which eliminates the influence of oscillation, depends on the difference in the material of the material to be polished and is closely related to the end of polishing. It is possible to reliably detect the end of polishing.

  In a polishing method according to another embodiment of the present invention, a difference between the torque applied to the polishing head and the torque applied to the holding unit is obtained by removing the influence of the fluctuation, and the value obtained by removing the influence of the fluctuation is obtained. Further, it is characterized in that the polishing end point is detected.

  The value of the difference between the torque applied to the polishing head and the torque applied to the holding means, which eliminates the influence of oscillation, depends on the material difference of the material to be polished and is closely related to the end of polishing. By observing with the amplitude width, it is possible to reliably detect the end of polishing.

  A polishing method according to another embodiment of the present invention is characterized in that a window of a polishing end detection target period is defined and polishing end detection is performed within a time range of the window.

  According to the present embodiment, it is possible to prevent useless detection processing by determining the window of the detection target period. In addition, erroneous detection of the end of polishing can be prevented.

  A polishing apparatus according to the present invention includes a holding unit that holds an object to be polished on an upper surface, a mechanism that rotates the holding unit, a polishing head that includes a polishing member, a mechanism that rotates the polishing head, and a holding unit. And a device for detecting the torque applied to the polishing head, and a device for detecting a polishing end point, wherein the device for detecting the polishing end point comprises the polishing An amplitude of the torque applied to the head caused by the oscillation is obtained, and a polishing end point is detected by a change in the amplitude caused by the oscillation.

  The width of the amplitude of the torque applied to the polishing head due to the oscillation is closely related to the flatness of the material to be polished, that is, the end of the polishing. Can be detected.

  ADVANTAGE OF THE INVENTION According to this invention, the grinding | polishing apparatus and the grinding | polishing method which can detect completion | finish of grinding | polishing reliably are obtained.

  FIG. 1 is a diagram showing a configuration of a polishing apparatus according to an embodiment of the present invention. The polishing apparatus according to the present embodiment includes a polishing head 101 to which a polishing member 201 is attached, and a chuck (holding means) 109 that holds a polishing object 111 such as a wafer on its upper surface.

  The polishing head 101 is configured to be rotated by a polishing head rotating motor 103. Further, the polishing head 101 is configured to swing on the polishing object 111 by a swing mechanism 107. The chuck 109 is configured to be rotated by a chuck rotating motor 113. During polishing, the polishing member 201 is pressed against a polishing object 111 such as a wafer on the chuck 109, the polishing head 101 and the chuck 109 rotate, and the polishing head 101 swings. The polishing object 111 is polished by the polishing member 201.

  The polishing apparatus according to the present embodiment further includes a load torque detection device 105 for the polishing head, a load torque detection device 115 for the chuck, and a polishing end determination device 121. When the motor current of the polishing head rotation motor 103 is used as the load torque data of the polishing head, the load torque detection device 105 of the polishing head collects the motor current data from the polishing head rotation motor 103. To the polishing end determination device 121. Alternatively, load torque data may be collected by attaching a torque meter to the rotating shaft of the polishing head 101 as the load torque detection device 105 of the polishing head. When the motor current of the chuck rotation motor 113 is used as the chuck load torque, the chuck load torque detection device 115 collects motor current data from the chuck rotation motor 113 and determines the end of polishing. 121. Alternatively, as the load torque detecting device 115 for the chuck, a torque meter may be attached to the rotation shaft of the chuck 109 to collect load torque data. As the polishing end determination device 121, various types of processors can be used. The polishing end determination process executed by the polishing end determination device 121 will be described below.

  FIG. 2 is a flowchart showing a polishing end determination process executed by the polishing end determination device 121 according to an embodiment of the present invention.

  Prior to the polishing end determination process, one period of oscillation of the polishing head 101 and a window for a detection target period are determined. One period of oscillation of the polishing head 101 may be determined by actually oscillating the polishing head 101 and measuring the time of one period. As an example, one cycle of oscillation is 2 seconds. The window of the detection target period is a period estimated to include the polishing end point, and is therefore a period that is a target of polishing end detection. The window of the detection target period may be determined as follows. First, a polishing amount for a predetermined time is obtained using a test wafer, and a polishing rate is obtained from the polishing amount for the predetermined time. Next, a polishing end point estimated from the target polishing amount and the polishing rate is obtained, and a predetermined range including the estimated polishing end point is defined as a window of a detection target period. By defining the detection period window, useless detection processing can be prevented. In addition, erroneous detection of the end of polishing can be prevented.

  In step S205 of FIG. 2, the polishing end determination device 121 determines whether the time has reached the lower limit value of the window of the detection target period. If the time has not reached the lower limit value of the detection target period window, the process proceeds to step S245, and after a predetermined time has elapsed, the process returns to step S205. The predetermined time corresponds to a data sampling interval, and is 5 to 10 milliseconds as an example. When the time has reached the lower limit value of the detection target period window, the process proceeds to step S210.

  In step S210 of FIG. 2, the polishing end determination device 121 determines whether the time exceeds the upper limit value of the window of the detection target period. If the time exceeds the upper limit value of the detection target period window, the process proceeds to step S215, and if not, the process proceeds to step S220.

  In step S215 of FIG. 2, an abnormality process is performed. Specifically, a display indicating an abnormality and an audio output are performed. In this case, the abnormality means that the end of polishing could not be detected within the detection target period window.

  In step S <b> 220 of FIG. 2, the polishing end determination device 121 acquires the motor current of the polishing head rotation motor 103 from the load torque detection device 105 of the polishing head.

  FIG. 3 is a diagram showing the motor current value of the polishing head rotating motor 103. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The detection period window is denoted by W.

  In step S225 of FIG. 2, the maximum value and the minimum value of the motor current of the polishing head rotating motor 103 are obtained at predetermined time intervals for one cycle of the oscillation before that time. As an example, the predetermined time is 10 milliseconds. In addition, if one cycle of oscillation is 2 seconds and the sampling interval is 10 milliseconds, the maximum value and the minimum value of 200 data of the motor current value are obtained.

  In step S230 of FIG. 2, the amplitude of the motor current of the polishing head rotating motor 103 is obtained at each predetermined time. The difference between the maximum value and the minimum value of the motor current of the polishing head rotating motor 103 obtained in step S225 is the motor current amplitude.

  FIG. 4 is a diagram showing a periodic change of the motor current due to the oscillation of the polishing head 101. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The value of the motor current is represented by 401. The period of oscillation is P, and the amplitude of the motor current is A.

  FIG. 5 is a diagram illustrating a change in the value of the amplitude of the motor current obtained in step S230. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The detection period window is denoted by W.

  In step S235 of FIG. 2, the amplitude value obtained in step S230 is smoothed. As an example, an average value for two oscillation periods is taken at each time point.

  FIG. 6 is a diagram showing a change in the amplitude value of the motor current smoothed in step S235. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The detection period window is denoted by W.

  In step S240 of FIG. 2, it is determined whether the amplitude value smoothed in step S235 satisfies a predetermined relationship. For example, the end of polishing may be determined when the smoothed amplitude value becomes smaller than a predetermined value (for example, 0.2). Further, a change in the value of the smoothed amplitude is detected by obtaining a first derivative of time, or detected as an inflection point by obtaining a second derivative of time, and the end of polishing is determined. Also good. A change in the smoothed amplitude value may be detected by any method.

  The width of the amplitude of the torque applied to the polishing head due to the oscillation is closely related to the flatness of the material to be polished, that is, the end of the polishing. Can be detected.

  If the smoothed amplitude value satisfies the predetermined relationship, the process proceeds to step S250. If the smoothed amplitude value does not satisfy the predetermined relationship, the process proceeds to step S245, and after a predetermined time has elapsed, the process returns to step S205.

  In step S250 of FIG. 2, a polishing end process is performed. Specifically, a display indicating the end of polishing and an audio output are performed.

  FIG. 7 is a flowchart showing a polishing end determination process executed by the polishing end determination device 121 according to another embodiment of the present invention.

  Prior to the polishing end determination process, as in the embodiment described with reference to FIG. 2, one period of oscillation of the polishing head 101 and a window of a detection target period are determined.

  In step S705 in FIG. 7, the polishing end determination device 121 determines whether the time has reached the lower limit value of the window of the detection target period. If the time has not reached the lower limit value of the detection target period window, the process proceeds to step S755, and after a predetermined time has elapsed, the process returns to step S705. The predetermined time corresponds to a data sampling interval, and is 5 to 10 milliseconds as an example. When the time has reached the lower limit value of the detection period window, the process proceeds to step S710.

  In step S710 of FIG. 7, the polishing end determination device 121 determines whether the time exceeds the upper limit value of the window of the detection target period. If the time exceeds the upper limit value of the detection target period window, the process proceeds to step S715, and if not, the process proceeds to step S720.

  In step S715 of FIG. 7, an abnormality process is performed. Specifically, a display indicating an abnormality and an audio output are performed. In this case, the abnormality means that the end of polishing could not be detected within the detection target period window.

  In step S720 of FIG. 7, the polishing end determination device 121 acquires the motor current of the polishing head rotation motor 103 from the load torque detection device 105 of the polishing head, and the chuck rotation motor from the load torque detection device 115 of the chuck. The motor current of 113 is acquired.

  In step S725 in FIG. 7, the maximum value and the minimum value of the motor current of the polishing head rotating motor 103 are obtained at predetermined time intervals for one cycle of oscillation before that time. As an example, if one cycle of oscillation is 2 seconds and the sampling interval is 10 milliseconds, the maximum value and the minimum value of 200 data of motor current values are obtained.

  In step S730 in FIG. 7, the amplitude of the motor current of the polishing head rotating motor 103 is obtained at each predetermined time. The difference between the maximum value and the minimum value of the motor current of the polishing head rotating motor 103 obtained in step S725 is the amplitude of the motor current. The change in the value of the amplitude of the motor current is shown in FIG.

  In step S735 of FIG. 7, the amplitude value obtained in step S730 is smoothed. As an example, an average value for two oscillation periods is taken at each time point. The change in the value of the amplitude of the smoothed motor current is shown in FIG.

  In step S740 of FIG. 7, the difference between the motor current of the polishing head rotating motor 103 and the motor current of the chuck rotating motor 113 is obtained for each sampling period, and the average of one period of oscillation of the polishing head 101 is obtained for the difference. Find the value. As a result, an average value of one oscillation period is obtained for each sampling period. The average value thus obtained is referred to as a moving average value.

  The reason for obtaining the difference between the motor current of the polishing head rotating motor 103 and the motor current of the chuck rotating motor 113 is that the difference corresponds to the torque applied to the object to be polished. Actually, since the value of the motor current of the chuck rotation motor 113 is small, the value of the motor current of the polishing head rotation motor 103 may be used instead of the difference.

  FIG. 8 is a diagram showing changes in the moving average values of the motor currents of the polishing head rotating motor 103 and the chuck rotating motor 113. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The scale on the left vertical axis is a scale for the motor current moving average value 801 of the polishing head rotating motor 103, and the scale on the right vertical axis is the scale for the motor current moving average value 803 of the chuck rotating motor 113. It is. The change in the moving average value 803 is smaller than the change in the moving average value 801.

  FIG. 4 is a diagram showing a periodic change of the motor current due to the oscillation of the polishing head 101. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The value at that time is 401, and the moving average value is 403. The oscillation cycle is P, and the amplitude of the motor current is A. When the moving average value is taken, the swing component is canceled out, and the motor current value without the swing component is obtained.

  In step S745 in FIG. 7, a time differential value of the moving average value obtained in step S740 is obtained.

  FIG. 9 is a diagram showing changes in the moving average value 901 and its time differential value 903. The horizontal axis is time, and the unit is 10 milliseconds. The vertical axis represents the relative value of current. The detection period window is denoted by W.

  In step 750 of FIG. 7, a time point at which the smoothed amplitude value shown in FIG. 6 satisfies a predetermined relationship and a time point at which the time differential value shown in FIG. 9 satisfies the predetermined relationship are obtained.

  As an example, a time point at which the smoothed amplitude value becomes smaller than a predetermined value (for example, 0.2) is obtained. Further, a change in the value of the smoothed amplitude is detected by obtaining a first derivative of time, or detected as an inflection point by obtaining a second derivative of time, and the end of polishing is determined. Also good. A change in the smoothed amplitude value may be detected by any method.

  On the other hand, as an example, a time point at which the time differential value becomes larger than a predetermined value is obtained. In FIG. 9, the time differential value is larger at a plurality of time points (A and B in FIG. 9) than at other time points. Therefore, the end of polishing may be determined at a time point (A in FIG. 9) closest to a time point at which the smoothed amplitude value becomes smaller than a predetermined value among the plurality of time points.

  The width of the amplitude of the torque applied to the polishing head and the moving average value of the torque applied to the material to be polished are closely related to the end of polishing. Therefore, the end of polishing can be reliably detected by taking into account the change in amplitude due to the oscillation and the change in the moving average value.

  If the time differential value and the smoothed amplitude value satisfy a predetermined relationship, the process proceeds to step S760. If the time differential value and the smoothed amplitude value do not satisfy the predetermined relationship, the process proceeds to step S755, and after the predetermined time has elapsed, the process returns to step S705.

  In step S760 of FIG. 7, a polishing end process is performed. Specifically, a display indicating the end of polishing and an audio output are performed.

  According to the present invention, the end of polishing can be reliably detected by detecting the change in the amplitude caused by the fluctuation of the torque applied to the polishing head.

It is a figure which shows the structure of the grinding | polishing apparatus by one Embodiment of this invention. It is a flowchart which shows the completion | finish determination process of grinding | polishing by one Embodiment of this invention. It is a figure which shows the value of the motor current of the motor for polishing head rotation. It is a figure which shows the periodic change of the motor electric current by rocking | fluctuation of a polishing head. It is a figure which shows the change of the value of the amplitude of a motor current. It is a figure which shows the change of the value of the amplitude of the smoothed motor current. It is a flowchart which shows the completion | finish determination process of grinding | polishing by other embodiment of this invention. It is a figure which shows the change of the moving average value of the motor current of a polishing head rotation motor and a chuck rotation motor. It is a figure which shows the change of the moving average value of the difference of the electric current value of the polishing head rotation motor, and the electric current value of the chuck rotation motor, and its time differential value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Polishing head, 109 ... Chuck, 111 ... Polishing object, 121 ... Polishing completion judgment apparatus, 201 ... Polishing member

Claims (11)

  A polishing method for polishing an object to be polished by pressing and rotating a polishing head provided with a polishing member against a polishing object held on a rotating holding means to polish the object to be polished. A polishing method characterized by obtaining an amplitude of torque caused by oscillation and detecting an end point of polishing by a change in amplitude caused by oscillation.   The polishing method according to claim 1, wherein an amplitude generated by the swing is obtained from a maximum value and a minimum value of a torque applied to the polishing head within one cycle of the swing.   The polishing method according to claim 1, wherein an amplitude generated by the oscillation of a torque applied to the polishing head is obtained from a current value of a motor for rotating the polishing head.   4. The polishing end point is detected by further obtaining a value of the torque applied to the polishing head from which the influence of the fluctuation is removed and further considering the value from which the influence of the fluctuation is removed. The polishing method according to any one of the above.   5. The polishing method according to claim 4, wherein a value obtained by removing the influence of the oscillation is obtained by averaging values of one cycle of oscillation of the torque applied to the polishing head.   6. The polishing method according to claim 4, wherein a value obtained by removing the influence of the oscillation is obtained from a current value of a motor for rotating the polishing head.   A value obtained by removing the influence of the fluctuation of the difference between the torque applied to the polishing head and the torque applied to the holding means is obtained, and the polishing end point is detected further considering the value from which the influence of the fluctuation is removed. The polishing method according to claim 1, wherein:   The polishing method according to claim 7, wherein a value obtained by removing the influence of the fluctuation is obtained by averaging values of the difference for one period of the fluctuation.   9. The polishing method according to claim 7, wherein a value obtained by removing the influence of the oscillation is obtained from current values of a rotation motor of the polishing head and a rotation motor of the holding unit.   The polishing method according to claim 1, wherein a window of a polishing end detection target period is defined, and polishing end detection is performed within a time range of the window. Holding means for holding the polishing object on the upper surface;
A mechanism for rotating the holding means;
A polishing head comprising a polishing member;
A mechanism for rotating the polishing head;
A mechanism for swinging the polishing head on the holding means;
A device for detecting torque applied to the polishing head;
A device for detecting an end point of polishing,
The apparatus for detecting an end point of polishing obtains an amplitude caused by fluctuation of torque applied to the polishing head, and detects an end point of polishing based on a change in amplitude caused by the fluctuation. apparatus.

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