JP2009026850A - Cmp device, and wafer polishing method by cmp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a film to be polished on a wafer have a constant film thickness during high-speed polishing even if a polishing pad has variance in thickness. <P>SOLUTION: A novel polishing pad 13 is set on a rotary platen 14 of a CMP device. Then the thickness of the new polishing pad 13 is measured. The measurement result is input to a polishing control unit 19. Then the polishing control unit 19 determines a threshold corresponding to the thickness of the novel polishing pad 13 by reference to a data table 19b. Further, the threshold which is thus found is registered. Then the wafer 11 to be polished is polished using the threshold. Specifically, the wafer 11 is polished fast until the output of an eddy current sensor reaches the threshold, the high-speed polishing is switched to low-speed polishing once the threshold is reached, and the polishing is ended once a polishing end point is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a CMP (Chemical Mechanical Polishing) apparatus and a method for polishing a semiconductor wafer by CMP, and more particularly, to a method for detecting timing for switching a polishing rate.

  CMP plays an important role in the manufacture of semiconductor devices. In a semiconductor integrated circuit chip, a conductive layer, an insulating layer or other thin film layer is formed on a wafer in a predetermined order, and a pattern layer is formed by performing photolithography and etching for each layer as necessary. It is manufactured by cutting and separating individual chips on the wafer after forming the layer. Here, if there are irregularities or steps on the ground surface during film formation, the film thickness of the material film formed on the ground is partially reduced, resulting in poor step coverage and reduced yield. Problems arise. In addition, since the upper layer is affected by the lower pattern layer and has unevenness, there is a problem that the focal point at the time of exposure is not determined and a precise pattern cannot be transferred. Therefore, it is necessary to planarize the surface of the material film, and CMP is used for this purpose.

  In CMP, the throughput (the number of wafers that can be polished within a unit time) is improved by polishing the wafer as fast as possible. However, there is a problem that erosion increases when a metal film such as tungsten (W), copper (Cu), titanium nitride (TiN), etc. is polished at high speed. Therefore, in metal-based CMP, high-speed polishing is first performed, and erosion is suppressed by switching from high-speed polishing to low-speed polishing when the thickness of the metal film reaches about several tens of nm.

As one method for measuring the film thickness of a metal film during high-speed polishing, a method using an eddy current sensor is known (see Patent Document 1). An eddy current sensor measures the film thickness of a metal film using a high-frequency magnetic field. The eddy current sensor outputs a predetermined threshold value by polishing the metal film at high speed while measuring the film thickness with the eddy current sensor. At this point, the high-speed polishing ends and the low-speed polishing is switched.
JP-T-2004-525521

  However, if there is a variation in the thickness of the polishing pad, the remaining film of the metal film also has a thickness corresponding to the variation in thickness. When the polishing pad is thick, the distance to the metal film to be polished increases, so even if high-speed polishing is finished when the eddy current sensor reaches a predetermined output value, the metal film thickness is more than the target film thickness. Also thicken. In addition, when the polishing pad is thin, the distance to the metal film to be polished is shortened, so even if polishing is terminated when the eddy current sensor reaches a predetermined output value, the film thickness of the metal film is the target film thickness. Thinner. This variation in the remaining film becomes a variation in polishing time in the subsequent low-speed polishing (barrier clear polishing), and when the polishing pad is thick, the remaining film becomes thick, which causes a problem that the throughput of CMP is lowered. Further, when the polishing pad is thin, the remaining film is also thinned, which may cause quality deterioration due to erosion or the like.

  Therefore, an object of the present invention is to provide a CMP apparatus capable of making a film to be polished on a wafer at a constant film thickness during high-speed polishing even if the thickness of the polishing pad varies, and polishing a wafer by CMP. It is to provide a method.

  The above object of the present invention is to respond to an exchangeable polishing pad, a film thickness sensor for measuring the film thickness of a film to be polished on a wafer through the polishing pad, and an output value of the film thickness sensor exceeding a threshold value. And a polishing control unit that switches polishing conditions, and the polishing control unit includes a storage unit that stores a threshold value corresponding to the thickness of the new polishing pad when the polishing pad is replaced. Achieved by:

  In the present invention, the storage unit further stores conversion information indicating the relationship between the thickness of the polishing pad and the output value of the film thickness sensor when the film thickness of the polishing target film is constant, and the polishing control unit is It is preferable to obtain the output value of the film thickness sensor corresponding to the thickness of the new polishing pad with reference to the conversion information and register the output value as a threshold value.

  In the present invention, the polishing control unit sets a reference wafer on which a film to be polished having a predetermined film thickness is set, then measures the film thickness of the film to be polished using a film thickness sensor, and outputs the film thickness sensor. It is preferable to register the value as a threshold value.

  In the present invention, the film thickness sensor is preferably an eddy current sensor. Further, the film to be polished is preferably a metal film or a metal compound film.

  The above object of the present invention also includes a polishing pad setting step for setting a new polishing pad, a threshold value registration step for registering a predetermined threshold value corrected based on the thickness of the new polishing pad, and setting a wafer to be polished. A high-speed polishing step that performs high-speed polishing while monitoring the film thickness of the film to be polished by the film thickness sensor, a polishing condition switching step that switches from high-speed polishing to low-speed polishing when the output of the film thickness sensor reaches a threshold value, and a wafer to the polishing end point The present invention can also be achieved by a CMP wafer polishing method comprising a low-speed polishing step for performing low-speed polishing.

  In the present invention, the threshold registration step refers to conversion information indicating the relationship between the thickness of the polishing pad and the output value of the film thickness sensor when the film thickness of the film to be polished is constant, and the new polishing pad thickness It is preferable to include a step of obtaining an output value of the film thickness sensor corresponding to the above and a step of registering the output value as a threshold.

  In the present invention, the threshold value registration step includes a step of setting a reference wafer on which a polishing target film having a predetermined film thickness is formed on a polishing head, a step of measuring a film thickness of the polishing target film using a film thickness sensor, and Preferably, the method includes a step of registering the output value of the film thickness sensor as a threshold value.

  As described above, according to the present invention, the threshold value of the eddy current sensor is corrected in accordance with the thickness of the polishing pad. Therefore, it is possible to accurately measure the switching timing of the polishing mode in the metal-based CMP, thereby improving throughput and erosion. Can be prevented.

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

  FIG. 1 is a schematic diagram showing a configuration of a CMP apparatus according to a preferred embodiment of the present invention.

As shown in FIG. 1, a CMP apparatus 100 includes a polishing head 12 that holds a wafer 11, a rotating surface plate 14 to which a polishing pad 13 is attached, and a polishing liquid that contains an abrasive such as silica (SiO ₂ ) fine particles. A slurry supply unit 15 for supplying (slurry), a dresser 17 for sharpening the polishing pad 13, an eddy current sensor 18 for measuring the film thickness of a tungsten film that is a metal film to be polished on the wafer 11, and polishing A pad probe 16 for measuring the state of the pad 13 and a polishing control unit 19 for controlling these parts are provided.

  The polishing head 12 includes a spindle mechanism for rotating the wafer 11 and a pressurizing mechanism for pressing the wafer 11 against the polishing pad 13 with an optimum pressing force. A guide ring 12 a is provided on the outer periphery of the wafer 11 set on the polishing head 12, whereby the wafer 11 can be reliably held. The rotating surface plate 14 also includes a spindle mechanism that rotates the polishing pad 13. Thus, the wafer 11 and the polishing pad 13 can be moved relative to each other, and efficient and uniform polishing is possible.

  The polishing pad 13 is affixed to the main surface of the rotating surface plate 14. The polishing pad 13 has a two-layer structure of a polishing sheet having a fine porous structure and a cushion sheet, and a rigid polyurethane foam is used as the polishing sheet. The polishing pad 13 is a consumable item, and the polishing surface is regenerated by periodically dressing it with the dresser 17, but the completely worn polishing pad 13 is removed from the rotating surface plate 14 and replaced with a new polishing pad. Is done.

  The pad probe 16 detects the life of the polishing pad 13, the dressing end point, and the process abnormality by monitoring the coefficient of friction of the surface of the polishing pad 13. When the surface of the polishing pad 13 is measured with the pad probe 16 and the friction coefficient is lower than the reference value, the polishing pad 13 is sharpened.

  A dresser (also referred to as a pad conditioner) 17 is used for dressing the polishing pad 13 having a reduced friction coefficient due to clogging or the like. Diamond abrasive grains are embedded in the contact surface with the polishing pad 13, and the surface of the polishing pad 13 is cut by the diamond abrasive grains.

  The eddy current sensor 18 measures the thickness of the metal film using a high-frequency magnetic field, and is provided in the vicinity of the main surface of the rotating surface plate 14. The output signal of the eddy current sensor 18 is supplied to the polishing controller 19 and is used to determine the timing for switching the polishing conditions.

  The polishing control unit 19 is for controlling the polishing head 12, the rotating surface plate 14, and the slurry supply unit 15. Specifically, the position and rotation speed of the polishing head 12, the rotation speed of the rotary platen 14, the amount of slurry supplied from the slurry supply unit 15, and the like are controlled.

  The memory 19a in the polishing control unit 19 records a data table 19b indicating the relationship between the thickness of the polishing pad 13 and the output value of the eddy current sensor 18 when the film thickness of the tungsten film is constant (for example, 20 nm). ing. The eddy current sensor 18 faces the wafer 11 via the polishing pad 13, and the distance from the eddy current sensor 18 to the polishing surface of the wafer 11 also changes according to the thickness of the polishing pad 13. The output also varies depending on the thickness of the polishing pad 13. For example, when the standard thickness variation of the polishing pad 13 is ± 0.25 mm, the tungsten film thickness also varies ± 15 nm. Normally, the film thickness of the tungsten remaining film used for the determination of the switching timing is set to 10 to 30 nm. When the film thickness of the tungsten remaining film is set to 20 nm, the film thickness of the tungsten remaining film due to the thickness variation of the polishing pad 13. Is 20 ± 15 nm, that is, the maximum film thickness is 35 nm and the minimum film thickness is 5 nm.

  Thus, in the case where the polishing pad 13 is relatively thick and thin, even if the polishing is stopped when the output of the eddy current sensor 18 reaches a predetermined value, the film thickness of the tungsten film after the polishing is stopped. Will be different from each other. However, by referring to the data table 19b and correcting the film thickness threshold, the film thickness of the tungsten film can be accurately measured without being affected by the variation in the thickness of the polishing pad 13. The timing for switching from polishing to low-speed polishing can be determined with high accuracy. The threshold value 19c of the tungsten film thickness thus obtained is also recorded in the memory 19a.

  FIG. 2 is a flowchart showing a method for polishing the wafer 11 using the CMP apparatus 100.

  As shown in FIG. 2, in the polishing of the wafer 11 according to the present embodiment, the wafer 11 is first set on the polishing head 12 with the processing surface of the wafer 11 facing downward, and the wafer 11 is pressed against the polishing pad 13 while flowing the slurry. High-speed polishing of the wafer 11 is performed by rotating the polishing pad 13 at high speed (S11). Thereafter, when the film thickness of the tungsten film reaches about several tens of nm, the high-speed polishing is finished (S12Y), and the low-speed polishing is switched (S13). Then, when the polishing end point is detected, the polishing of the wafer 11 is completed (S14Y).

  As described above, the film thickness measurement of the tungsten film is performed using the eddy current sensor 18, but the film thickness of the tungsten film at the time when the high-speed polishing is completed varies with the thickness variation of the polishing pad 13. Therefore, when the polishing pad 13 is replaced, the threshold value used for determining the polishing condition switching timing is reset.

  FIG. 3 is a flowchart illustrating an example of a threshold resetting procedure.

  As shown in FIG. 3, in resetting the threshold, first, a new polishing pad 13 is set on the rotating surface plate 14 (S21). The novel polishing pad 13 here refers to a polishing pad 13 having a standard thickness variation. Therefore, it is not necessary that the polishing pad 13 is unused, and all polishing pads 13 having thickness variations are targets for threshold setting.

  Next, the thickness of the new polishing pad 13 is measured (S22). The thickness of the polishing pad 13 is measured, for example, by calculating an output voltage value when the wafer 11 using a prescribed tungsten film thickness is water-polished, and subtracting the output voltage value for the wafer 11 therefrom. The measurement result is input to the polishing control unit 19.

  Next, the polishing control unit 19 determines a threshold value corresponding to the thickness of the new polishing pad 13 with reference to the data table 19b (S23). As described above, the data table 19b records the relationship between the thickness of the polishing pad 13 and the output value of the eddy current sensor 18 when the film thickness of the tungsten film is set as the threshold for the polishing condition switching timing.

  Next, the threshold value thus obtained is registered (S24). Thereafter, the wafer 11 to be polished is polished using this threshold value. That is, the wafer 11 is polished at a high speed until the output of the eddy current sensor reaches a threshold value. When the threshold value is reached, the high speed polishing is switched to the low speed polishing, and the polishing is terminated when the polishing end point is detected. Such polishing of the wafer 11 is repeated until the polishing pad 13 is consumed, and dressing of the polishing pad 13 by the dresser 17 is performed as necessary.

  As described above, according to the present embodiment, the threshold value for determining the polishing condition switching timing is changed according to the thickness of the polishing pad 13, so that the film thickness of the remaining tungsten film can be measured more accurately. The polishing condition switching timing can be determined with high accuracy. Therefore, even if the thickness of the polishing pad 13 varies, the film thickness of the remaining tungsten film can be made constant, and the quality of the CMP process, such as throughput and erosion, can be made constant.

  Next, a second embodiment of the present invention will be described. A feature of this embodiment is that a reference wafer having a predetermined thickness is prepared, the reference wafer is measured using an eddy current sensor when setting the polishing pad 13, and the measurement result at this time is registered as a threshold value. is there. The CMP apparatus used in this embodiment is substantially the same as the CMP apparatus 100 shown in the first embodiment except that a data table is not required.

  FIG. 4 is a flowchart illustrating another example of the threshold resetting procedure.

  As shown in FIG. 4, in resetting the threshold, first, a new polishing pad 13 is set on the rotating surface plate 14 (S31). Further, a reference wafer on which a tungsten film having a predetermined thickness is formed is set (S32).

  FIG. 5 is a schematic partial sectional view showing the structure of the reference wafer.

As shown in FIG. 5, the reference wafer 50 and the tungsten film 51 is deposited, the tungsten film 51 is already polished, is adjusted from the high-speed polishing target film thickness t ₀ is the timing of switching to the low-speed polishing ing.

  Next, the film thickness of the tungsten film 51 of the reference wafer 50 is measured by the eddy current sensor 18 (S33). Since the tungsten film 51 of the reference wafer 50 has already become an ideal film thickness, the output of the eddy current sensor 18 obtained when this film thickness is measured is a correct output value indicating the polishing condition switching timing. In addition, the thickness takes into account the thickness variation of the polishing pad 13.

  Next, the output value of the eddy current sensor 18 obtained in this way is registered as a threshold value used in actual wafer polishing (S34). Thereafter, the wafer to be polished is polished using this threshold value. That is, the wafer is polished at a high speed until the output of the eddy current sensor reaches a threshold value. When the threshold value is reached, the high speed polishing is switched to the low speed polishing, and the polishing is terminated when the polishing end point is detected. Polishing of the polishing target wafer is repeated until the polishing pad 13 is consumed, and dressing of the polishing pad 13 by the dresser 17 is performed as necessary.

  As described above, according to the present embodiment, the threshold for determining the polishing condition switching timing is changed according to the thickness of the polishing pad 13, so that the film thickness of the tungsten film to be polished is measured more accurately. It is possible to determine the timing for switching the polishing conditions with high accuracy. Therefore, even if there is variation in the thickness of the polishing pad 13, the film thickness of the tungsten remaining film can be made constant, and the quality of the CMP process, such as throughput and erosion, can be made constant.

  Although the present invention has been described based on the preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, these are also included in the scope of the present invention.

  For example, in the above embodiment, an eddy current sensor is used as a film thickness sensor for measuring the film thickness of the film to be polished on the wafer, but the present invention is not limited to the eddy current sensor, and various The sensor can be used.

  Further, the polishing target film is not limited to tungsten, and various metals or metal compounds such as copper (Cu) and titanium nitride (TiN) can be targeted.

  In the above embodiment, the data table is used as the conversion information for obtaining the thickness of the polishing pad 13 from the output value of the eddy current sensor 18, but the present invention is not limited to the data table. The thickness of the polishing pad 13 may be obtained from the output value of the eddy current sensor 18 using an arithmetic expression.

FIG. 1 is a schematic diagram showing the configuration of a CMP apparatus according to a preferred embodiment of the present invention. FIG. 2 is a flowchart showing a method for polishing the wafer 11 using the CMP apparatus 100. FIG. 3 is a flowchart illustrating an example of a threshold resetting procedure. FIG. 4 is a flowchart illustrating another example of the threshold resetting procedure. FIG. 5 is a schematic partial sectional view showing the structure of the reference wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Wafer 12 Polishing head 12a Guide ring 13 Polishing pad 14 Rotary surface plate 15 Slurry supply part 16 Pad probe 17 Dresser 18 Eddy current sensor 19 Polishing control part 19a Memory 19b Data table 19c Threshold data 50 Reference wafer 51 Metal film (tungsten film)
100 CMP equipment

Claims (8)

A replaceable polishing pad;
A film thickness sensor that measures the film thickness of the film to be polished on the wafer via the polishing pad;
A polishing control unit that switches polishing conditions in response to an output value of the film thickness sensor exceeding a threshold value,
The CMP apparatus according to claim 1, wherein the polishing control unit includes a storage unit that stores the threshold value corresponding to a thickness of a new polishing pad when the polishing pad is replaced. The storage unit further stores conversion information indicating the relationship between the thickness of the polishing pad and the output value of the film thickness sensor when the film thickness of the polishing target film is constant,
The polishing control unit obtains an output value of a film thickness sensor according to the thickness of the new polishing pad with reference to the conversion information, and registers the output value as the threshold value. The CMP apparatus described in 1.   The polishing control unit sets a reference wafer on which a film to be polished having a predetermined film thickness is set, then measures the film thickness of the film to be polished using the film thickness sensor, and outputs the film thickness sensor. The CMP apparatus according to claim 1, wherein a value is registered as the threshold value.   The CMP apparatus according to claim 1, wherein the film thickness sensor is an eddy current sensor.   The CMP apparatus according to claim 1, wherein the polishing target film is a metal film or a metal compound film. Polishing pad setting step to set a new polishing pad,
A threshold registration step of registering a predetermined threshold corrected based on the thickness of the new polishing pad;
A high-speed polishing step that sets a wafer to be polished and performs high-speed polishing while monitoring the film thickness of the film to be polished with a film thickness sensor.
A CMP wafer comprising: a polishing condition switching step for switching from high-speed polishing to low-speed polishing when the output of the film thickness sensor reaches the threshold; and a low-speed polishing step for performing low-speed polishing of the wafer to a polishing end point. Polishing method. The threshold registration step includes:
The film thickness sensor corresponding to the thickness of the new polishing pad with reference to conversion information indicating the relationship between the thickness of the polishing pad and the output value of the film thickness sensor when the film thickness of the polishing target film is constant The wafer polishing method according to claim 6, further comprising: obtaining an output value of: and registering the output value as the threshold value. The threshold registration step includes:
Setting a reference wafer on which a film to be polished having a predetermined film thickness is formed on the polishing head;
The wafer polishing method according to claim 6, comprising: measuring a film thickness of the film to be polished using the film thickness sensor; and registering an output value of the film thickness sensor as the threshold value. .

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