JP3634060B2 - Polishing method and polishing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polishing process for a surface of a workpiece, and more particularly, to a polishing method and a polishing apparatus suitable for planarizing a Si wafer surface in a semiconductor manufacturing process.
[0002]
[Prior art]
Fine irregularities on the surface of the Si wafer generated in each process of the wafer manufacturing process tend to cause insufficient resolution during pattern transfer by lithography and loss of the metal wiring film. It has come to be regarded as a main factor that brings about a decrease in the reliability of LSI as a product. Therefore, in the wafer manufacturing process, a mirror polishing process of the Si wafer surface by CMP (chemical mechanical polishing) or the like is introduced as a final process. Note that CMP here refers to a polishing process that removes a minute reaction portion generated at a processing contact point by abrasive grains that are rich in solid-phase reactivity with a workpiece and are softer than the workpiece. In general, a polishing apparatus of the same type as that of normal lapping or polishing is used. That is, while supplying a slurry containing the abrasive grains between the Si wafer to be polished and the polishing pad, the polishing plate with the polishing pad is rotated to rotate the Si wafer under a constant polishing pressure. The polishing pad is slid. Note that fine irregularities, pits, and the like are formed on the work surface of the polishing pad so that the slurry can be appropriately held.
[0003]
Now, in the mirror polishing process of the Si wafer by CMP or the like, the dummy substrate is usually removed every time a predetermined number of Si wafers are polished in order to grasp the polishing performance of the polishing pad that changes with the progress of the polishing process. Polishing is being performed on a trial basis. That is, the polishing efficiency (polishing amount per unit time of the polishing pad) of the polishing pad is periodically measured as an index representing the polishing performance of the polishing pad. Specifically, the ratio (t / T) of the difference t between the thicknesses of the Si oxide films on the surface of the dummy substrate before and after the polishing with respect to the polishing time T is calculated as the polishing efficiency of the polishing pad. Yes. An example of an apparatus for measuring the thickness of the Si oxide film on the surface of the dummy substrate is a thin film thickness gauge Nanospec 4100 manufactured by Nanometrix (USA). As a result, for example, in a polishing process under the following polishing conditions, the main component is a foamed polyurethane having a compression elastic modulus of 100 Mpa, which polishes a Si wafer (diameter 150 mm) on which a Si oxide film having a thickness of about 2 μm is formed. It is confirmed that the polishing efficiency of the polishing pad (thickness 1 mm) to be changed as shown in FIG. 9 with the progress of polishing.
[0004]
(1) Slurry: aqueous solution with 3% SiO ₂ abrasive content (2) Slurry feed rate: 100 ml / min
(3) Polishing pressure: 500 g / cm ²
(4) Rotating speed of polishing surface plate: 250 mm / s
(5) Rotational angular velocity of Si wafer: 12 rad / min
Then, based on the result, the timing (for example, the polishing efficiency is a predetermined value m) of applying a dosing process (a process of correcting the polishing pad smoothed by abrasion or the like using a diamond grindstone or the like) to the work surface of the polishing pad. And the polishing time set at the beginning is corrected as appropriate.
[0005]
As a result, the polishing efficiency of the polishing pad does not vary greatly during polishing, and the polishing amount is controlled on the order of submicrons, so that a flatness of about 2 μm can be achieved for all Si wafers. That is, the quality of the Si wafer can be maintained at a certain level by introducing a mirror polishing step of the Si wafer surface by CMP or the like into one step of the wafer manufacturing process.
[0006]
Hereinafter, the polishing process described here is referred to as a conventional polishing process.
[0007]
[Problems to be solved by the invention]
However, the conventional method for measuring the polishing efficiency employed during the polishing process has a drawback that the polishing efficiency of the polishing pad that changes with the progress of the polishing process cannot be measured in real time. Therefore, there is a possibility that the optimal timing for executing the polishing pad correction process and the polishing time correction process may be missed. In addition, since a measurement process using a dummy substrate has to be performed, there is a drawback that the production efficiency of the Si wafer is reduced.
[0008]
Therefore, the present invention provides a polishing apparatus equipped with a measurement system capable of automatically measuring the polishing performance of a polishing pad in use in real time in a polishing process, and aims to improve the efficiency of the polishing process. Objective. Another object is to optimize polishing conditions based on the polishing performance of the polishing pad measured by such a measurement system.
[0009]
[Means for Solving the Problems]
The present invention is a polishing method for polishing the surface of a workpiece,
A polishing step of polishing the surface of the workpiece with an abrasive;
Measuring the reflectivity of the abrasive, and quantifying the polishing efficiency of the workpiece when polished with the abrasive based on the measured reflectivity of the abrasive Repeated measurement steps;
A polishing amount calculation step of calculating a total polishing amount of the surface of the workpiece using the polishing efficiency quantified in the quantification step repeatedly executed in the measurement step;
Ending the polishing step when the total polishing amount calculated in the polishing amount calculating step reaches a desired value;
There is provided a polishing method characterized by comprising:
[0011]
The present invention also provides:
A polishing apparatus that polishes the surface of the workpiece by imparting relative motion to the abrasive and the workpiece,
Drive means for holding the abrasive and the workpiece, respectively, and applying the relative motion to the abrasive and the workpiece;
Measuring means for measuring the reflectance of the abrasive held by the driving means;
Storage means for storing information associating the reflectance of the abrasive with the polishing efficiency of the workpiece when polished by the abrasive having the reflectance;
Quantifying means for determining the polishing efficiency associated with the reflectance of the abrasive measured by the measuring means from the information stored by the storage means;
Using the polishing efficiency obtained by the quantifying means, calculating means for calculating the total polishing amount of the workpiece;
Stopping means for stopping the driving means when the total polishing amount calculated by the calculating means reaches a desired value;
A polishing apparatus is provided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment according to the present invention will be described with reference to the accompanying drawings.
[0013]
First, the basic configuration of the polishing apparatus according to the present embodiment will be roughly described with reference to FIG. In the present embodiment, a polishing apparatus of the same type as the polishing apparatus that performs CMP or the like described in the section of the prior art (that is, the polishing platen 7 to which the polishing pad 6 is attached is rotated by a motor 8 so that an arbitrary A polishing apparatus that slides the workpiece and the polishing pad 6 with a polishing pressure of 1) is used, and here, the configuration that characterizes this polishing apparatus will be mainly described.
[0014]
In addition to the well-known basic configuration as a polishing apparatus, the polishing apparatus further includes a sensor 9 for measuring the amount of light reflected by the surface 6a of the polishing pad 6 affixed to the polishing surface plate 7, and a polishing pad described later. 6, an information processing apparatus 11 that executes the polishing performance evaluation process 6 and the control of the entire apparatus, a correction unit A that recovers the polishing performance of the polishing pad 6 attached to the polishing surface plate 7, and the polishing surface plate 7. A controller 13 that controls the motor 8 to be rotated and a display device 12 that displays the evaluation result of the polishing performance of the polishing pad 6 and the like are provided. In addition, a nozzle (not shown) for injecting air toward the surface 6a of the polishing pad 6 is attached and adheres to the surface 6a of the polishing pad 6 which prevents reflection of light emitted from the sensor 9. It is possible to eliminate foreign substances such as slurry.
[0015]
Hereafter, each structure with which this polishing apparatus shown in FIG. 1 is provided is each demonstrated in detail.
[0016]
First, the optical system of the sensor 11 will be described with reference to FIG.
[0017]
The optical system of the sensor 11 includes a light source 21 that irradiates illumination light e at an arbitrary incident angle θ (about 15 ° in the present embodiment) with respect to the surface 6a of the polishing pad 6, two photodiodes 24a, 24b. Specifically, the illumination light e emitted from the light source 21 passes through the collimator lens 22 and is divided into two directions by the beam splitter 25, and then one of the lights e ₁ is reflected by the condenser lens 26. The light e ₂ is guided to the photodiode 24 a and reflected by the surface 6 a of the polishing pad 6, and then guided to the other photodiode 24 b by the condenser lens 23.
[0018]
The outputs of the two photodiodes 24a and 24b are each digitally converted by the A / D converter 10 and then input to the information processing apparatus 11 (see FIG. 1).
[0019]
Next, a functional configuration of the information processing apparatus 11 will be described.
[0020]
The information processing apparatus 11 includes a performance evaluation unit 11 a that evaluates the polishing performance of the polishing pad, a polishing amount calculation unit 11 b that calculates the polishing amount, a control unit 11 c that controls the correction unit A and the controller 13. The performance evaluation unit 11a, the polishing amount calculation unit 11b, and the control unit 11c referred to here are actually processes realized by a CPU (not shown) and data stored in the memory 11c. . Hereinafter, the process performed by each part 11b and 11c is demonstrated.
[0021]
The performance evaluation unit 11a uses the output of the sensor 11 (that is, the light amount m ₁ of the light e ₁ detected by the photodiode 24a and the light amount m ₂ of the light e ₂ detected by the photodiode 24b) to polish the polishing pad. The reflectance (m ₂ / m ₁ ) of 6 is calculated.
[0022]
Thereafter, the polishing efficiency of the polishing pad 6 is calculated by using the reflectance (m ₂ / m ₁ ) of the polishing pad 6 calculated from the output of the sensor 11 and the function f relating the reflectance of the polishing pad and the polishing efficiency. calculate. As a result, for example, the reflectance (m ₂ / m ₁ ) of the polishing pad 6 used under the same polishing conditions as those described in the section of the prior art is shown in FIG. 5 as the polishing process proceeds. It is confirmed that This is because, in the surface 6a of the polishing pad 6 immediately after polishing before or dressing process, as shown in FIG. 2 (a), the light e ₂ tends to diffuse with fine unevenness, smoothing with the progress of polishing This is because the light e ₂ is likely to be regularly reflected on the surface 6 a of the polished polishing pad 6 as shown in FIG.
[0023]
Here, the function f relating the reflectance of the polishing pad and the polishing efficiency here is a function prepared in advance based on experimental data. That is, as the polishing progresses, the polishing efficiency k (t) of the polishing pad is sequentially measured by the same measuring method as in the prior art, and this is displayed in association with the reflectance (m ₂ / m ₁ ) of the polishing pad 6. Then, as shown in FIG. 6, it can be seen that there is a function (k (t) = f (m ₂ / m ₁ )) that can generally associate both values uniquely. This function (k (t) = f (m ₂ / m ₁ )) is a function f relating the reflectance and polishing efficiency of the polishing pad here.
[0024]
Then, based on the polishing efficiency k (t) of the polishing pad calculated sequentially, the superiority or inferiority of the polishing performance of the polishing pad during the polishing process is evaluated. In this embodiment, it is determined that the polishing performance of the polishing pad has deteriorated when the polishing efficiency k of the polishing pad falls below a predetermined value. In addition, when the polishing efficiency k of the polishing pad exceeds a predetermined value, it is determined that the polishing performance of the polishing pad has been recovered.
[0025]
Furthermore, the polishing amount (Σｔk (t) dt) of the Si wafer from the start of the polishing process to the present time is calculated using the polishing efficiency k (t) of the polishing pad calculated sequentially. The polishing efficiency of the polishing pad and the polishing amount of the Si wafer are displayed on the display device 12, respectively.
[0026]
On the other hand, when the performance evaluation unit 11a determines that the polishing performance of the polishing pad is deteriorated, the control unit 11b gives an operation command to the valve 3 of the correction unit A described later, and the performance evaluation unit 11a When it is determined that the polishing performance has been recovered, a stop command is given to a valve 3 and a controller 13 of the correction unit A described later. Further, when the polishing amount of the Si wafer calculated by the performance evaluation unit 11a reaches the target polishing amount, a stop command is given to the controller 13 described later.
[0027]
Next, the correction unit A and the controller 13 will be described.
[0028]
When a stop command is given from the control unit 11b of the information processing apparatus 11, the controller 13 stops the motor 8 that rotates the polishing surface plate 7 to which the polishing pad 6 is attached, and polishes the Si wafer currently being polished. Terminate.
[0029]
On the other hand, when an operation command is given from the control unit 11b of the information processing apparatus 11, the valve 3 of the correction unit A causes the flow path 14a between the air compressor 4 and 1a of the air cylinder 1, the 1b of the cylinder 1 and the outside world. The flow path 14b in between is opened. As a result, the surface 6a of the polishing pad 6 is subjected to a dressing process by the diamond grindstone 5 rotated by a motor (not shown). The polishing pressure at this time is controlled by the pressure regulator 2.
[0030]
Further, during the dressing process, when a stop command is given from the control unit 11b of the information processing apparatus 11, the valve 3 of the correction unit A closes the flow paths 14a and 14b that are currently open, The flow path 15a between the air cylinder 1a and the outside and the flow path 15b between the air compressor 4 and the air cylinder 1b are opened. As a result, the diamond grindstone 5 is pulled up, and the dressing process for the surface 6a of the polishing pad 6 is completed.
[0031]
This is the end of the description of each component included in the polishing apparatus.
[0032]
In the present embodiment, the information processing apparatus 11 controls the controller 8 and the valve 3 of the correction unit A. However, this is not always necessary, and the operation of monitoring the display on the display device 12 is not necessary. The operator may determine the timing of the dressing process and the timing of completion of the polishing process, and manually operate the controller 8 and the valve 3 of the correction unit A as necessary.
[0033]
In addition, after the rotation of the polishing platen 7 is stopped once, the prism 26 is disposed at a position on the surface 6 a of the polishing pad 6 to which the light e ₂ from the sensor 11 is irradiated, and the boundary between the prism 26 and the polishing pad 6. You may make it measure the reflectance of a surface. In this way, although there is some time loss, the slurry and the like adhering to the surface 6a of the polishing pad 6 can be removed, and foreign matter floating in the atmosphere is applied to the surface 6a of the polishing pad 6. Since it does not adhere, more accurate reflectance of the polishing pad 6 can be obtained. The prism 26 preferably has a shape having side surfaces 26a and 26b perpendicular to the incident light and the emitted light. If the influence of light absorption by the prism 26 is taken into consideration, a correction term may be added to the function f relating the reflectance of the polishing pad and the polishing efficiency.
[0034]
Here, the effects obtained by adopting the present polishing apparatus in the mirror polishing step in the wafer manufacturing process will be summarized.
[0035]
The polishing efficiency of the polishing pad that changes with the progress of the polishing process can be automatically measured in real time, so you can accurately grasp the polishing performance of the polishing pad that changes with the progress of the polishing process without taking time and effort. be able to. Such an effect derives the following effect and further improves the reliability of the LSI as the final product.
[0036]
(1) Since the optimum timing of the dressing process of the polishing pad is not missed, the polishing performance of the polishing pad can always be maintained at a certain level.
[0037]
(2) Since a more accurate polishing amount can be estimated, more appropriate polishing can be performed on the Si wafer.
[0038]
In addition, since the polishing efficiency of the polishing pad can be measured without stopping the polishing process line, there is also a second effect that the production efficiency of the Si wafer does not decrease.
[0039]
In the present embodiment, the Si wafer is targeted for polishing, but the same effect can be achieved even if other workpieces are targeted for polishing.
[0040]
【Example】
Hereinafter, an example of polishing using the polishing apparatus shown in FIG. 1 will be described in comparison with an example of conventional polishing. In this embodiment, polishing conditions similar to the polishing conditions described in the prior art column are set. The target polishing amount of the Si wafer to be polished is 1 μm.
[0041]
First, the effect of the above (2) is confirmed.
[0042]
After polishing each of 25 Si wafers continuously by both polishing processes, the polishing amount of each Si wafer is measured. Here, in both polishing processes, the dressing process is not performed on the polishing pad 6 during the polishing process. Further, in the conventional polishing process, every time 10 Si wafers are polished, the polishing efficiency is measured again to correct the polishing time.
[0043]
As a result, according to the conventional polishing process, a variation of about ± 0.2 μm occurs in the polishing amount of the Si wafer, whereas according to the polishing process using the present polishing apparatus, the variation in the polishing amount of the Si wafer. Was suppressed to about ± 0.05 μm (see FIG. 7).
[0044]
From the above results, it was confirmed that the effect (2) was achieved.
[0045]
Next, the effect of the above (1) is confirmed.
[0046]
By polishing both 100 wafers continuously by both polishing processes, the polishing amount of each Si wafer is measured. At this time, in both polishing processes, when the polishing efficiency of the polishing pad 6 falls below a predetermined value, the polishing pad 6 is subjected to a dressing process.
[0047]
As a result, according to the conventional polishing process, a variation of about ± 0.1 μm occurs in the polishing amount of the Si wafer, whereas according to the polishing process using this polishing apparatus, the variation in the polishing amount of the Si wafer. Was suppressed to about ± 0.03 μm (see FIG. 8).
[0048]
From the above results, it was confirmed that the effect (1) was achieved.
[0049]
The time required for polishing 100 Si wafers was about 1700 minutes in the polishing process using the conventional method, but about half of that in the polishing process using the present polishing apparatus was about 900 minutes. It was. That is, it was confirmed that the second effect was achieved.
[0050]
【The invention's effect】
According to the polishing method and the polishing apparatus of the present invention, the polishing performance of the polishing pad in use can be automatically measured in real time in the polishing process. Therefore, it is possible to reduce the time and labor that are conventionally spent measuring the polishing performance of the polishing pad. In addition, since the polishing performance of the polishing pad that changes with the progress of the polishing process can be accurately grasped, a more optimal polishing process can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a polishing apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing how light is reflected on the surface of a polishing pad;
FIG. 3 is a diagram for explaining the principle of measuring the reflectance of a polishing pad.
FIG. 4 is a diagram for explaining the principle of measuring the reflectance of a polishing pad.
FIG. 5 is a view showing the reflectivity of a polishing pad in association with the total number of polished Si wafers.
FIG. 6 is a diagram showing the relationship between the reflectance of a polishing pad and the polishing efficiency.
FIG. 7 is a diagram for explaining an effect obtained by using the polishing apparatus according to the embodiment of the present invention.
FIG. 8 is a diagram for explaining an effect obtained by using the polishing apparatus according to the embodiment of the present invention.
FIG. 9 is a diagram showing the polishing efficiency of a polishing pad measured by a conventional method in association with the total number of polished Si wafers.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air cylinder 2 ... Pressure regulator 3 ... Valve 4 ... Air compressor 5 ... Diamond grindstone 6 ... Polishing pad 7 ... Polishing surface plate 8 ... Motor 9 ... Sensor 10 ... A / D converter 11 ... Information processing apparatus 12 ... Display apparatus 13 ... Controller

Claims (8)

A polishing method for polishing a surface of a workpiece,
A polishing step of polishing the surface of the workpiece with an abrasive;
Measuring the reflectivity of the abrasive, and quantifying the polishing efficiency of the workpiece when polished with the abrasive based on the measured reflectivity of the abrasive Repeated measurement steps;
A polishing amount calculation step of calculating a total polishing amount of the surface of the workpiece using the polishing efficiency quantified in the quantification step repeatedly executed in the measurement step;
Ending the polishing step when the total polishing amount calculated in the polishing amount calculating step reaches a desired value;
A polishing method characterized by comprising: The polishing method according to claim 1,
The polishing method, wherein the measuring step is also executed during the polishing step. The polishing method according to claim 1,
The measurement step further includes:
A determination step of determining whether or not the polishing efficiency quantified in the quantification step is lower than a predetermined reference;
The polishing method is
A polishing method comprising: a dressing step of performing a dressing process on the abrasive when it is determined in the measuring step that the polishing efficiency is lower than the predetermined reference. The polishing method according to claim 3 , wherein
Performing the measuring step in the dressing step;
A polishing method, wherein the polishing material is subjected to the dressing treatment until the polishing efficiency is not determined to be lower than the predetermined reference in the measurement step. A polishing apparatus that polishes the surface of the workpiece by imparting relative motion to the abrasive and the workpiece,
Drive means for holding the abrasive and the workpiece, respectively, and applying the relative motion to the abrasive and the workpiece;
Measuring means for measuring the reflectance of the abrasive held by the driving means;
Storage means for storing information associating the reflectance of the abrasive with the polishing efficiency of the workpiece when polished by the abrasive having the reflectance;
Quantification means for determining the polishing efficiency associated with the reflectance of the abrasive measured by the measurement means from the information stored by the storage means;
Using the polishing efficiency obtained by the quantifying means, calculating means for calculating the total polishing amount of the workpiece;
Stopping means for stopping the driving means when the total polishing amount calculated by the calculating means reaches a desired value;
A polishing apparatus comprising: The polishing apparatus according to claim 5 , wherein
A polishing apparatus comprising: output means for outputting the polishing efficiency obtained by the quantification means or the total polishing amount of the workpiece calculated by the calculation means. The polishing apparatus according to claim 5 , wherein
Determining means for determining whether or not the polishing efficiency obtained by the quantifying means is lower than the predetermined reference;
When the determination means determines that the polishing efficiency is lower than the predetermined reference, polishing means for performing a dressing treatment on the abrasive;
A polishing apparatus comprising: The polishing apparatus according to claim 7 , wherein
The polishing apparatus, wherein the polishing means performs the dressing process on the abrasive according to a program that defines the dressing process.

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