POLISHING APPARATUS, POLISHING METHOD AND POLISHING CONTROL PROGRAM

Abstract

A polishing unit polishes a semiconductor wafer. An eddy current sensor measures an eddy current variable according to variation of the film thickness of the semiconductor wafer at plural measurement times. A sensor processor calculates the film thickness of the semiconductor wafer at the measurement times based on the eddy current measured by the eddy current sensor. A film thickness estimating unit estimates film thicknesses after lapse of a processing delay time from the measurement times by using the calculated film thickness.

Claims

1. A polishing apparatus for polishing a polishing target, comprising: a polishing unit for polishing the polishing target; a measuring unit for measuring a physical quantity variable according to variation of a film thickness of the polishing target at a plurality of measurement times; a film thickness calculator for calculating data corresponding to the film thicknesses of the polishing target at the measurement times based on the physical quantity measured by the measuring unit; and a film thickness estimating unit for estimating the data with respect to at least some measurement times of the plurality of measurement times after lapse of a processing delay time from the at least some measurement times by using the calculated data.

2. The polishing apparatus according to claim 1, wherein the film thickness estimating unit estimates a variation amount of the data with respect to the at least some measurement times of the plurality of measurement times after lapse of the processing delay time from the at least some measurement times by using the calculated data, and estimates the data after lapse of the processing delay time from the at least some measurement times by using the estimated variation amount.

3. The polishing apparatus according to claim 2, wherein the film thickness estimating unit calculates a polishing rate by using the calculated data, and estimates the variation amount by using the calculated polishing rate.

4. The polishing apparatus according to claim 1, wherein the wording of after lapse of the processing delay time from the at least some measurement times indicates times at which after the measuring unit measures the physical quantity at the at least some measurement times, it is possible for the film thickness calculator to finish calculation of the data of the polishing target based on the physical quantity.

5. The polishing apparatus according to claim 1, wherein the wording of after lapse of the processing delay time from the at least some measurement times indicates times at which after the measuring unit measures the physical quantity at the at least some measurement times, it is possible for the film thickness estimating unit to finish estimation of the data by using the calculated data.

6. A polishing method for polishing a polishing target, comprising: a polishing step of polishing the polishing target; a measuring step of measuring a physical quantity variable according to variation of a film thickness of the polishing target at a plurality of measurement times; a film thickness calculating step of calculating data corresponding to the film thicknesses of the polishing target at the measurement times based on the physical quantity measured in the measuring step; and a film thickness estimating step of estimating the data with respect to at least some measurement times of the plurality of measurement times after lapse of a processing delay time from the at least some measurement times by using the calculated data.

7. The polishing method according to claim 6, wherein the film thickness estimating step estimates a variation amount of the data with respect to the at least some measurement times of the plurality of measurement times after lapse of the processing delay time from the at least some measurement times by using the calculated data, and estimates the data after lapse of the processing delay time from the at least some measurement times by using the estimated variation amount.

8. A polishing control program used to control a polishing apparatus for polishing a polishing target, the polishing apparatus having a measuring unit for measuring a physical quantity variable according to variation of a film thickness of the polishing target at a plurality of measurement times, the program causing a computer to function as a film thickness calculator for calculating data corresponding to the film thicknesses of the polishing target at the measurement times based on the physical quantity measured by the measuring unit, and a film thickness estimating unit for estimating the data with respect to at least some measurement times of the plurality of measurement times after lapse of a processing delay time from the at least some measurement times by using the calculated data.

9. The polishing control program according to claim 8, wherein the film thickness estimating unit estimates a variation amount of the data with respect to the at least some measurement times of the plurality of measurement times after lapse of the processing delay time from the at least some measurement times by using the calculated data, and estimates the data after lapse of the processing delay time from the at least some measurement times by using the estimated variation amount.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a diagram showing the basic configuration of a polishing apparatus according to an embodiment;

[0028] FIGS. 2A and 2B are diagrams showing the configuration of an eddy current sensor, wherein FIG. 2A is a block diagram showing the configuration of the eddy current sensor, and FIG. 2B is an equivalent circuit diagram of the eddy current sensor;

[0029] FIG. 3 is a schematic diagram showing an example of the configuration of a sensor coil in the eddy current sensor of the embodiment;

[0030] FIG. 4A is a graph showing an actual film thickness of a semiconductor wafer 18, FIG. 4B is a graph showing a film thickness of the semiconductor wafer 18 which is output from a sensor processor 28, and FIG. 4C is a graph showing an estimated film thickness of the semiconductor wafer 18 which is output from a film thickness estimating unit 32; and

[0031] FIG. 5 is a flowchart showing a case where polishing is performed until a predetermined film thickness, and the polishing is finished at the time when the film thickness reaches a predetermined film thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] A polishing apparatus according to an embodiment of the present invention will be described hereunder with reference to the drawings. First, the basic configuration of a polishing apparatus will be described, and then detection of a polishing endpoint of a polishing target will be described.

[0033] FIG. 1 is a diagram showing the basic configuration of a polishing apparatus 100 according to an embodiment. The polishing apparatus 100 for polishing a semiconductor wafer (polishing target) 18 includes a polishing unit 30 for polishing the semiconductor wafer 18, an eddy current sensor (measurement unit) 50, and a sensor processor (film thickness calculator) 28. The eddy current sensor 50 measures a physical quantity variable according to variation of the film thickness of the semiconductor wafer 18 at plural measurement times. The sensor processor 28 calculates data corresponding to the film thickness of the semiconductor wafer 18 at each measurement time based on the eddy current measured by the eddy current sensor 50.

[0034] The measurement times in this embodiment are set to times having a time interval of 0.5 second. The physical quantity in this embodiment is an eddy current in the semiconductor wafer 18. Variation of the film thickness of the semiconductor wafer 18 increases or decreases the eddy current. In the present invention, the physical quantity which is variable according to the variation of the film thickness is not limited to the eddy current. The physical quantity may be polishing frictional force under polishing or reflectivity of the surface of the polishing target.

[0035] The polishing apparatus 100 further has a controller 29. The controller 29 contains a film thickness estimating unit 32. By using the data corresponding to the film thickness calculated by the sensor processor 28, the film thickness estimating unit 32 estimates data corresponding to a film thickness after lapse of a processing delay time from a measurement time for each measurement time. The data corresponding to the film thickness in this embodiment is a film thickness obtained from the magnitude (absolute value) of an impedance Z described later.

[0036] The film thickness estimating unit 32 estimates the variation amount of the film thickness after lapse of the processing delay time for each measurement time by using a calculated film thickness, and estimates the film thickness after lapse of the processing delay time from the measurement time by using the estimated variation amount. The present invention is not limited to the method of estimating the film-thickness variation amount and then estimating the film thickness by using the estimated variation amount. For example, the film thickness may be directly estimated without estimating any film-thickness variation amount. As the method of directly estimating the film thickness, the film thickness after lapse of a processing delay time from a measurement time may be estimated by spline interpolation using a calculated film thickness.

[0037] The film thickness estimating unit 32 calculates a polishing rate by using the calculated film thickness, and estimates the variation amount by using the calculated polishing rate. The details of a method of calculating the polishing rate will be described later.

[0038] “After lapse of a processing delay time from a measurement time” in this embodiment corresponds to a time at which after the eddy current sensor 50 measures an eddy current at the measurement time, the sensor processor 28 has finished the calculation of the film thickness of the semiconductor wafer 18 based on the eddy current. “After lapse of the processing delay time” corresponds to, for example, the time after 0.2 second elapses from the measurement of an eddy current by the eddy current sensor 50. In the present invention, the time after lapse of the processing delay time is not limited to the time when the sensor processor 28 has finished the calculation of the film thickness of the semiconductor wafer 18 based on the eddy current. For example, the time after lapse of the processing delay time from the measurement time may be set to the time when after the eddy current sensor 50 measures the eddy current at the measurement time, it is possible for the film thickness estimating unit 32 to finish the estimation of the film thickness using the calculated film thickness.

[0039] The details of the polishing unit 30 will be described with reference to FIG. 1. The polishing unit 30 includes a polishing table 12 having an upper surface onto which a polishing pad 10 can be fitted, a first electric motor 14 for rotating the polishing table 12, a top ring 20 capable of holding a semiconductor wafer 18, and a second electric motor 22 for rotating the top ring 20. The rotor of the first electric motor 14 is connected to a motor shaft 15, and the polishing table 12 is rotated by the motor shaft 15.

[0040] The top ring 20 is caused to approach to and get away from the polishing table 12 by a holding device (not shown). When the semiconductor wafer 18 is polished, the top ring 20 is approached to the polishing table 12 so that the semiconductor wafer 18 held on the top ring 20 is brought into contact with the polishing pad 10 fitted to the polishing table 12.

[0041] When the semiconductor wafer 18 is polished, the semiconductor wafer 18 held on the top ring 20 is pressed against the polishing pad 10 while the polishing table 12 is rotated. Furthermore, the top ring 20 is rotated by the second electric motor 22 around an axial line 21 which is eccentrically displaced from the rotational axis 13 of the polishing table 12. When the semiconductor wafer 18 is polished, polishing abrasive liquid containing polishing agent is supplied from a polishing agent supply device (not shown) onto the upper surface of the polishing pad 10. The semiconductor wafer 18 set on the top ring 20 is pressed against the polishing pad 10 supplied with the polishing abrasive liquid while the top ring 20 is rotated by the second electric motor 22.

[0042] The eddy current sensor 50 is embedded in the polishing table 12. A connection cable of the eddy current sensor 50 passes inside the motor shaft 15 of the polishing table 12 via a rotary joint (not shown) provided to the shaft end of the motor shaft 15 to the sensor processor 28.

[0043] Next, the eddy current sensor 50 equipped to the polishing apparatus according to the embodiment will be described with reference to FIGS. 2 and 3.

[0044] FIGS. 2A and 2B are diagrams showing the configuration of the eddy current sensor 50, wherein FIG. 2A is a block diagram showing the configuration of the eddy current sensor 50, and FIG. 2B is an equivalent circuit diagram of the eddy current sensor 50.

[0045] As shown in FIG. 2A, the eddy current sensor 50 is configured so that a sensor coil 51 is arranged in the neighborhood of a metal film (or conductive film) mf as a detection target, and an AC signal source 52 is connected to the coil. Here, the metal film (or conductive film) mf as the detection target is a thin film of Cu, Al, Au, W or the like formed on the semiconductor wafer 18, for example. The sensor coil 51 is a coil for detection, and arranged in the neighborhood of, for example, at a distance of about 1.0 to 4.0 mm from the metal film (or conductive film) as the detection target.

[0046] There are two types of eddy current sensors. One type of eddy current sensors is a frequency type in which occurrence of an eddy current in the metal film (or conductive film) mf varies the oscillation frequency, and the metal film (or conductive film) is detected from this variation of the oscillation frequency, and the other type is an impedance type in which occurrence of an eddy current in the metal film (conductive film) mf varies the impedance, and the metal film (conductive film) is detected from this variation of the impedance. That is, in the frequency type, when an eddy current I.sub.2 varies in an equivalent circuit shown in FIG. 2B, the impedance Z varies. When the impedance Z varies, the oscillation frequency of the signal source (frequency-variable oscillator) 52 varies. When the oscillation frequency varies, the variation of the oscillation frequency is detected by a detection circuit 54, whereby variation of the metal film (or conductive film) can be detected. The sensor processor 28 is configured by the AC signal source 52 and the detection circuit 54.

[0047] In the impedance type, when an eddy current I.sub.2 varies in the equivalent circuit shown in FIG. 2B, the impedance Z varies. When the impedance Z varies, the impedance Z when viewed from the signal source (fixed frequency oscillator) 52 varies. This variation of the impedance Z is detected by the detection circuit 54, and thus the variation of the metal film (or conductive film) can be detected. The data corresponding to the film thickness in this embodiment are obtained from the magnitude (absolute value) of the impedance Z by the sensor processor 28. Specifically, for example, the detection circuit 54 multiplies the impedance Z by a predetermined number, and outputs a value coincident with an actual film thickness to the film thickness estimating unit 32. Accordingly, in this embodiment, the output of the detection circuit 54, that is, the output of the sensor processor 28 is the value coincident with the actual film thickness.

[0048] The impedance type eddy current sensor is capable of taking out signal outputs X, Y, the phase, the impedance Z, etc. The signal outputs X, Y represent the real-number component and imaginary-number component of the impedance Z, respectively. Measurement information of the film thickness of the metal film (or conductive film) Cu, Al, Au or W is obtained from the frequency F, the impedance Z or the like. The eddy current sensor 50 can be incorporated at an inner position of the polishing table 12 which is in the vicinity of the surface. The eddy current sensor 50 is arranged so as to face the semiconductor wafer as the polishing target through the polishing pad. The eddy current sensor 50 can detect variation of the film thickness of the metal film (or conductive film) from an eddy current flowing in the metal film (or conductive film) on the semiconductor wafer.

[0049] FIG. 3 schematically shows an example of the configuration of the sensor coil of the eddy current sensor 50 according to the embodiment. As shown in FIG. 3, the sensor coil 51 is configured so that a coil for forming an eddy current in the metal film (or conductive film) and a coil for detecting the eddy current in the metal film (or conductive film) are arranged to be separated from each other. The sensor coil 51 includes three layers of coils 72, 73 and 74 wound around a bobbin 71. Here, the center coil 72 is an oscillation coil connected to the AC signal source 52. The oscillation coil 72 forms an eddy current in the metal film (or conductive film) mf on the semiconductor wafer 18 arranged in the neighborhood of the oscillation coil 72 by magnetic field which is generated by a voltage supplied from the AC signal source 52. The detection coil 73 is arranged at the upper side (the metal film (or conductive film) side) of the bobbin 71, and detects magnetic field generated by the eddy current formed in the metal film (or conductive film). The balance coil 74 is arranged on the opposite side to the detection coil 73 with respect to the oscillation coil 72. The balance coil 74 is used to perform balance adjustment in a resistance bridge circuit used for measurements. Adjustment of a zero point can be performed by the balance coil 74. Accordingly, it is possible to detect the eddy current flowing in the metal film (or conductive film) from a state where the eddy current is equal to zero, and thus the detection sensitivity of the eddy current in the metal film (or conductive film) is enhanced.

[0050] Next, the processing of the film thickness estimating unit 32 in the controller 29 will be specifically described with reference to FIGS. 4A to 4C. FIG. 4A is a graph showing an actual film thickness of the semiconductor wafer 18 which varies with lapse of the polishing time, FIG. 4B is a graph showing a film thickness of the semiconductor wafer 18 which is output from the sensor processor 28 with lapse of the polishing time, and FIG. 4C is a graph showing an estimated film thickness of the semiconductor wafer 18 which is output by the film thickness estimating unit 32. The abscissa axes of these graphs are common to one another, and represent the time. The unit of the time is “second”. The ordinate axes of these graphs represent the film thickness, and have the same scale. The unit of the film thickness is “μm”. A curve 34 shown in FIG. 4A represents that polishing progresses and the film thickness decreases with lapse of the time.

[0051] The times t1 to t4, t6 to t10 represent times at which the measurement is performed by the eddy current sensor 50 and the output thereof is transmitted to the sensor processor 28. In this embodiment, the outputs of the sensor processor 28 shown in FIG. 4B are values coincident with the actual film thicknesses. However, some deviation occurs between the graph of FIG. 4A and the graph of FIG. 4B because there is a time delay from the time when an input from the eddy current sensor 50 is received until the sensor processor 28 outputs a processing result.

[0052] In FIGS. 4A to 4C, the measurement and the processing are performed until the time t4. The film thicknesses s1 to s4 are outputs of the sensor processor 28, and correspond to results obtained by processing inputs from the eddy current sensor 50 at the times t1 to t4, respectively. There is a time lag 36 between each of the times t1 to t4 and the corresponding one of times at which the film thicknesses s1 to s4 are output. Film thicknesses r1 to r4 are film thicknesses output from the film thickness estimating unit 32, and has been subjected to time-lag correction. The film thicknesses r1 to r4 are the values obtained by actually performing the measurement at the times t1 to t4, respectively. Therefore, the film thicknesses r1 to r4 are obtained by performing an operation of turning back the film thicknesses s1 to s4 by only the time lag 36. The film thicknesses s1 to s4 and the film thicknesses r1 to r4 have the same values. The time lag 36 corresponds to a time which is required for the sensor processor 28 to perform the processing. A curve 40 is a curve representing the actual film thickness, and a curve 42 is a curve representing the estimated film thickness.

[0053] The time “after lapse of a processing delay time from a measurement time” in this embodiment corresponds to a time at which after the eddy current sensor 50 measures an eddy current at the measurement time, the sensor processor 28 has finished the calculation of the film thickness of the semiconductor wafer 18 based on the eddy current. The processing delay time corresponds to the time lag 36. “After lapse of the processing delay time” corresponds to the time t5. The time lag 36 is, for example, the time after 0.2 second from the time t4 when the eddy current sensor 50 measures an eddy current. In this embodiment, the time required for the processing in the film thickness estimating unit 32 is negligible. In FIGS. 4A to 4C, the film thicknesses r1 to r4 are past data 44, and the film thickness r5 is the latest estimation data.

[0054] Actual measurement values can be obtained at the times t1 to t4, t6 to t10. However, the actual film thickness is unclear at an intermediate time between the times t1 to t4, t6 to t10, for example, at a time t5 at which the sensor processor 28 outputs the film thickness s4. The film thickness estimating unit 32 estimates the film thickness at the time t5. The film thickness estimating unit 32 calculates a polishing rate before the measurement time t4 by using the film thicknesses s1 to s4 which have been already calculated, and estimates the film thickness r5 at the time t5 by using the calculated polishing rate. The polishing rate R (t4) at the time t4 is calculated from the film thickness s3 at the time t3 and the film thickness s4 at the time t4 by the following expression (1):

R(t4)=(s4−s3)/(t4−t3)  (1)

The film thickness r5 at the time t5 is calculated by the following expression (2):

r5=r4+R(t4)*(t5−t3)  (2)

[0055] The variation amount 38 shown in FIG. 4C is the difference between the film thickness r4 and the film thickness r5, and is equal to R(t4)*(t5−t3) of the expression (2).

[0056] A method of calculating the polishing rate is not limited to only the expression (1). That is, the calculation method is not limited to the method using only the polishing rate R(t4) as the polishing rate. As another calculation method, for the times t1 to t3, the polishing rates R(t1) to R(t3) may be likewise calculated as in the case of the expression (1), and the average value of these four polishing rates R(t1) to R(t4) may be used in place of the R(t4) of the expression (2). The film thickness r5 may be directly calculated from the film thicknesses r1 to r4 by spline interpolation without calculating the variation amount.

[0057] The controller 29 containing the film thickness estimating unit 32 executes a polishing control program used to control the entire polishing apparatus 100. The controller 29 has a storage device such as a magnetic hard disc device or a semiconductor storage device (not shown), and stores film thickness data generated by the sensor processor 28 as a database. The storage device stores the film thickness data along a time sequence while associating each time with each film thickness at the time. The controller 29 has an operation unit (not shown), and it estimates the polishing rate based on the data stored in the storage device and estimates the film thickness. The controller 29 has CPU (Central Processing Unit), a memory and an auxiliary storage device which are connected to one another through a bus. The operation unit functions as the sensor processor 28 and the film thickness estimating unit by executing programs.

[0058] A polishing method of polishing the semiconductor wafer 18 in the polishing apparatus 100 configured described above will be described with reference to FIG. 5. FIG. 5 is a flowchart showing a case where polishing is performed until a predetermined film thickness and the polishing is finished at the time when the film thickness reaches a predetermined film thickness. For example, a case where the film thickness at the time t5 is estimated will be described. The same processing is performed for the other times.

[0059] When the polishing of the semiconductor wafer 18 is started (polishing step S10), an eddy current (specifically, an impedance Z) of the semiconductor wafer 18 is measured at each time (measuring step S12). When the impedance Z is measured at the time t4, the data corresponding to the film thickness of the semiconductor wafer 18 at the time t4 is calculated based on the measured impedance Z (film thickness calculating step S14, S16). For the time t4, data after only the time lag 36 elapses from the time t4 are estimated by using the calculated data as described above (film thickness estimating step S18, S20). In the film thickness estimating step S18, the polishing rate R(t4) is calculated based on the time-sequential data of the film thickness. In the film thickness estimating step S20, the film thickness r5 at the current time is calculated based on an estimated value of the polishing rate. Subsequently, it is determined whether the polishing has been executed until a predetermined film thickness based on the film thickness r5 (step S22). When the polishing has been executed until the predetermined film thickness (YES), the polishing is finished. When the polishing has not yet been performed until the predetermined film thickness (NO), the polishing is continued.

[0060] The examples of the embodiments of the present invention have been described above. The foregoing embodiments of the present invention are provided to make the understanding of the present invention easy, and do not limit the present invention. The present invention can be modified and improved without departing from the subject matter of the present invention, and contains equivalents thereto. In a range where at least a part of the foregoing problem can be solved or in a range where at least a part of the effect can be achieved, it is possible to make any combination or eliminate the respective constituent elements described in the claims and the specification.

[0061] This application claims priority under the Paris Convention to Japanese Patent Application No. 2016-127611 filed on Jun. 28, 2016. The entire disclosure of Japanese Patent Laid-Open No. 2012-135865 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.

REFERENCE SIGNS LIST

[0062] 12 . . . polishing table [0063] 18 . . . semiconductor wafer [0064] 28 . . . sensor processor [0065] 29 . . . controller [0066] 30 . . . polishing unit [0067] 32 . . . film thickness estimating unit [0068] 50 . . . eddy current sensor [0069] 51 . . . sensor coil [0070] 52 . . . AC signal source [0071] 54 . . . detection circuit [0072] 100 . . . polishing apparatus