JP2012064835A - Polishing method of semiconductor wafer, and semiconductor wafer polishing device - Google Patents

Abstract

Semiconductor wafer polishing method and semiconductor wafer polishing capable of accurately estimating the progress of polishing when polishing both surfaces of a semiconductor wafer held on a carrier by upper and lower rotating surface plates without increasing the work load Providing the device.
Polishing for simultaneously polishing both surfaces of a wafer W by sandwiching a wafer W held on a carrier 6a by upper and lower rotating surface plates 2, 3 and rotating the upper and lower rotating surface plates 2, 3. A wafer polishing method using the apparatus 1, wherein the surface plate load current value of the polishing apparatus 1 when both surfaces of the wafer W are simultaneously polished is monitored, and is constant using the monitored surface plate load current value. The standard deviation of the platen load current value within the time is calculated for each reference time, and when the change pattern of the standard deviation per time satisfies a predetermined relationship, it is estimated that the polishing is finished.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor wafer polishing method and a semiconductor wafer polishing apparatus, for example, a semiconductor wafer polishing method and a semiconductor wafer polishing apparatus for simultaneously polishing both surfaces of a semiconductor wafer using a carrier between upper and lower surface plates.

In recent years, as semiconductor devices have been highly integrated, the flatness required for the semiconductor wafer (hereinafter also referred to as “wafer”), which is the material, has become stricter. Further, from the viewpoint of reducing the manufacturing cost, the wafer diameter has been increased, and it has become more difficult to improve the flatness.
In the wafer processing process, a process is proposed in which a grinding process is introduced after etching. In the mirror polishing process following the grinding, a double-side polishing method having processing accuracy superior to that of the conventional single-side polishing has been attracting attention. .

  Patent Document 1 discloses a planetary gear type polishing apparatus that performs double-side polishing of a wafer. Here, the configuration of the conventional planetary gear type polishing apparatus described in Patent Document 1 will be described with reference to FIG.

As shown in FIG. 9, the polishing apparatus 100 includes a horizontally supported disk-shaped lower surface plate 101, a disk-shaped upper surface plate 102 facing the lower surface plate 101, and a disk-shaped lower surface plate 101. And a sun gear 103 disposed on the inside of the.
The lower surface plate 101 is driven to rotate by a motor. The upper surface plate 102 is suspended from a cylinder through a joint, and is rotated in the reverse direction by a motor different from the motor that drives the lower surface plate 101.

In addition, the upper surface plate 102 is equipped with a polishing liquid supply system including a tank for supplying the polishing liquid to the lower surface plate 101.
A polishing cloth made of a nonwoven fabric impregnated with urethane resin or a foamed urethane or the like is affixed to the opposing surfaces of the lower surface plate 101 and the upper surface plate 102.
A carrier 104 is set on the lower surface plate 101 so as to surround the sun gear 103, and a ring-shaped internal gear (not shown) is arranged outside the set carrier 104. The internal gear is driven to rotate independently by a motor different from the motor that drives the surface plates (the lower surface plate 101 and the upper surface plate 102).

The wafer polishing operation is performed according to the following procedure.
First, the upper surface plate 102 is raised and separated from the lower surface plate 101, and in this state, a plurality of carriers 104 are set on the lower surface plate 101 so as to surround the sun gear 103.
Each set carrier 104 meshes with the inner sun gear 103 and an internal gear (not shown).

Next, a predetermined number of carriers 104 are set on the lower surface plate 101, and when the wafer 105 is set in each carrier 104, the upper surface plate 102 is lowered and a predetermined pressure is applied to each wafer 105.
Next, while the polishing liquid is supplied between the lower surface plate 101 and the upper surface plate 102 with the above-mentioned applied pressure applied, the lower surface plate 101, the upper surface plate 102, and the internal gear (not shown) are moved to a predetermined level. Rotate in a direction at a predetermined speed.
By the above rotating operation, a so-called planetary motion is performed in which a plurality of carriers 104 revolve around the sun gear 103 while rotating between the lower surface plate 101 and the upper surface plate 102. The wafer 105 held by each carrier 104 is in sliding contact with the upper and lower polishing cloths in the polishing liquid, and both upper and lower surfaces are polished simultaneously.

By the way, in the wafer double-side polishing process described above, not only the flatness of the wafer is improved, but also processing distortion generated up to the previous process of the double-side polishing process and correction of the surface roughness are performed. Management is an important management item.
The amount of polishing in the wafer double-side polishing step is generally managed by managing the polishing time based on experience.

Specifically, in the management of the polishing time based on the above experience, polishing was performed for a predetermined time based on an empirical rule, and then the finished thickness of the wafer was measured, and the polishing time was adjusted based on the measurement result (if necessary) In this case, further polishing was performed).
Moreover, in the management of the polishing time based on the above experience, a method (fixed polishing time method) in which a fixed polishing time is set and polishing is performed for the determined polishing time is often employed.
Patent Document 1 also proposes estimating the polishing end point from the change in the surface plate vibration frequency in the double-side polishing process of the wafer, without managing the polishing time based on the above experience.

JP 2005-252000 A

However, the management of the polishing time based on the above-described experience adjusts the polishing time based on the measurement result (because it is necessary to perform further polishing if necessary). The wafer has a technical problem that the wafer cannot be processed until the measurement result is determined.
Further, in the above-described fixed polishing time method, after a work such as dressing of the polishing cloth or a water jet for clogging is eliminated, a phenomenon occurs in which the polishing rate after the work is lowered. There is a technical problem that the thickness may not be finished.
Specifically, if the work such as dressing (dressing) of the polishing cloth with a diamond dresser or a water jet for eliminating clogging is performed during the processing, the surface temperature of the polishing cloth is lowered and the polishing rate is lowered. As a result, the finished thickness of the wafer was thicker than the target value.
In the method of estimating the polishing end point from the change in the surface plate vibration frequency of Patent Document 1, it is difficult to select the optimum surface plate vibration frequency, and the initial setting operation of the apparatus is troublesome. Further, when changing the machining conditions, the surface plate vibration frequency changes, and it is necessary to change the setting each time the change is made.

  The present invention has been made to solve the above technical problem, and an object of the present invention is to polish when polishing both surfaces of a semiconductor wafer with upper and lower rotating surface plates without increasing the work load. It is an object of the present invention to provide a semiconductor wafer polishing method and a semiconductor wafer polishing apparatus capable of accurately estimating the progress of the process.

  The method for polishing a semiconductor wafer according to the present invention, which has been made to solve the above problems, sandwiches a semiconductor wafer held by a carrier with an upper and lower rotary platen, and rotates the upper and lower rotary platen, A method of polishing a semiconductor wafer using a polishing apparatus for simultaneously polishing both surfaces of the semiconductor wafer, the step of monitoring a platen load current value of the polishing apparatus when simultaneously polishing both surfaces of the semiconductor wafer; Using the monitored surface plate load current value, the standard deviation of the surface plate load current value within a predetermined time is calculated for a predetermined period for each reference time, and the change pattern of the standard deviation per time satisfies a predetermined relationship. And a step of estimating that it is the end point of polishing.

The above configuration was adopted because the inventor of the present application investigated the change over time of the polishing apparatus with the progress of double-side polishing of the semiconductor wafer, and as a result, changed due to the frictional resistance accompanying the polishing of the wafer and carrier. This is because the platen load current value, which is the device detection value, changes to reflect the degree of progress of polishing (the variation becomes smaller). That is, it was found that the progress of polishing of the semiconductor wafer can be accurately estimated by examining the standard deviation of the platen load current value.
Therefore, according to the present invention, the finish of the semiconductor wafer can be achieved without burdening the work (because there is no need to adjust the polishing time based on the measurement results) as compared with the conventional method based on “management of polishing time based on experience”. The thickness can be brought close to the “target thickness”.

In particular, the present invention is characterized in that when the change pattern of the standard deviation per time satisfies a predetermined relationship, it is estimated that the polishing is finished.
As described above, the platen load current value changes to reflect the progress of polishing (the variation becomes small), so the polishing end point can be accurately determined by the standard deviation value and change pattern of the platen load current value. Can be estimated.

  Here, the step of estimating the end point of polishing calculates a standard deviation of the platen load current value within a predetermined time for a predetermined period for each reference time, and with respect to the standard deviation calculated in the predetermined period , Y = mX + b (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept), the slope m is calculated, and a change pattern of the slope m is obtained. It is desirable to estimate that it is the end point of polishing when the inclination m satisfies the condition of “a predetermined threshold or more”.

  Further, in the step of estimating that the polishing is finished, the standard deviation of the platen load current value within a predetermined time is calculated every reference time, and the calculated nearest standard deviation and the predetermined time before are calculated. It is desirable to calculate a difference from the standard deviation, obtain a change pattern of the difference, and estimate that the polishing is finished when the difference satisfies a condition that “a predetermined threshold or more”.

In addition, a semiconductor wafer polishing apparatus according to the present invention, which has been made to solve the above-described problems, sandwiches a semiconductor wafer held by a carrier with upper and lower rotating surface plates and rotates the upper and lower rotating surface plates. A semiconductor wafer polishing apparatus for simultaneously polishing both surfaces of the semiconductor wafer, a drive control unit for controlling the rotation operation of the upper and lower rotating surface plates, and a surface plate for simultaneously polishing both surfaces of the semiconductor wafer A standard deviation of a platen load current value within a fixed time using a detection unit that monitors the load current value and the monitored platen load current value is calculated for each reference time, and the change in the calculated standard deviation A polishing progress status estimation unit that estimates the degree of progress of polishing, and the polishing progress status estimation unit satisfies a predetermined relationship with a change pattern per hour of the standard deviation calculated for each reference time And when, to the drive controller, and the signal transmission end of the polishing, a rotational movement of the rotary plate is stopped, it is characterized in that to terminate the polishing.
According to such a semiconductor wafer polishing apparatus of the present invention, the platen load current value that changes (the variation becomes small) reflecting the progress of the polishing is monitored, and the standard deviation of the monitored platen load current value is monitored. Since the progress of polishing can be estimated, the progress of polishing of the semiconductor wafer can be accurately estimated, and the finished thickness of the semiconductor wafer can be determined without burdening the work (no need to adjust the polishing time based on the measurement results). It can be close to the “target thickness”.

  Here, the polishing progress state estimating unit calculates a standard deviation of the platen load current value within a predetermined time for a predetermined period for each reference time, and Y = mX + b with respect to the standard deviation calculated for the predetermined period. The slope m is calculated from a linear approximation represented by the following formula (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept), the change pattern of the slope m is obtained, and the slope It is desirable to estimate that the polishing end point is reached when m satisfies the condition of “a predetermined threshold or more”.

  In addition, the polishing progress estimation unit calculates a standard deviation of the platen load current value within a predetermined time for each reference time, and calculates the nearest standard deviation calculated and a standard deviation calculated before a predetermined time. It is desirable to calculate a difference, obtain a change pattern of the difference, and estimate that the polishing is finished when the difference satisfies a condition of “a predetermined threshold or more”.

  According to the present invention, there are provided a semiconductor wafer polishing method and a semiconductor wafer polishing apparatus capable of accurately estimating the progress of polishing when both surfaces of a semiconductor wafer are polished by upper and lower rotating surface plates without increasing the work load. can do.

It is a block diagram showing typically the composition of the polish device of the embodiment of the present invention. It is the graph which matched the upper surface plate load current value at the time of the grinding | polishing apparatus which grind | polishes both surfaces of a semiconductor wafer simultaneously grinding | polishing a wafer in correlation with grinding | polishing time. The standard deviation of the upper platen load current value during the fixed time when the polishing apparatus for simultaneously polishing both surfaces of the wafer is polishing the wafer is shown in correspondence with the polishing time of the wafer. It is a graph. The standard deviation of the upper platen load current value within a predetermined time when the polishing apparatus for simultaneously polishing both surfaces of the wafer is polishing the wafer is calculated for a predetermined period for each reference time, and the standard calculated within the predetermined period is calculated. For the deviation, the slope m is calculated for each reference time from a linear approximation expressed by the equation Y = mX + b (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept). 5 is a graph showing a change pattern of the inclination m in association with a polishing time of a wafer. The standard deviation of the upper platen load current value during the fixed time when the polishing apparatus that polishes both sides of the wafer is polishing the wafer is calculated for each reference time. 7 is a graph showing a difference between the calculated standard deviation and the change pattern of the difference in association with the polishing time of the wafer. FIG. 5 is a schematic diagram showing a correlation between a finished thickness of a wafer and a standard deviation of an upper surface plate load current value immediately before completion of polishing for specifying the finished thickness. It is the flowchart which showed the procedure of the process which estimates the progress state of the wafer grinding | polishing process which the grinding | polishing apparatus of this embodiment performs from the inclination of the standard deviation of an upper surface plate load current value. It is the flowchart which showed the procedure of the process which estimates the progress condition of the wafer grinding | polishing process which the grinding | polishing apparatus of this embodiment performs from the difference of the standard deviation of an upper surface plate load current value. It is the schematic diagram which showed the structure of the grinding | polishing apparatus of the planetary gear system of a prior art.

Hereinafter, a semiconductor wafer polishing method and a semiconductor wafer polishing apparatus (hereinafter referred to as “polishing apparatus”) according to an embodiment of the present invention will be described with reference to the drawings.
First, the structure of the polishing apparatus of this embodiment will be described with reference to FIG.
FIG. 1 is a block diagram schematically showing the configuration of the polishing apparatus according to the embodiment of the present invention.

As shown in the figure, the polishing apparatus 1 is an apparatus for simultaneously mirror-polishing both surfaces of a semiconductor wafer W (hereinafter referred to as “wafer W”) that is a substrate to be processed, and simultaneously processes a plurality of semiconductor wafers W (batch processing). It is set as the apparatus structure to do.
Further, the polishing apparatus 1 includes a surface plate load current detection unit 12 and a control unit 20, and an apparatus detection value (a state of the polishing apparatus 1) at the time of polishing the wafer W by the surface plate load current detection unit 12 and the control unit 20. The standard deviation σ of the device detection value monitored within a certain time (for example, 60 seconds) is calculated from the monitored device detection value for each reference time (for example, every second), and the calculation is performed. The progress of the polishing process of the wafer W is estimated from the transition of the standard deviation σ.
Note that the configuration of the polishing apparatus 1 of the present embodiment is the same as the known technology except for the configuration (the platen load current detection unit 12 and the control unit 20) that estimates the progress of the polishing process of the wafer W.
Therefore, hereinafter, the configuration of the polishing apparatus 1 other than “the platen load current detection unit 12 and the control unit 20” will be described in a simplified manner.

Specifically, the polishing apparatus 1 includes an upper surface plate (upper rotation surface plate) 2 and a lower surface plate (lower rotation surface plate) 3, and the opposite surfaces thereof are for polishing both surfaces of the wafer W. Abrasive cloths 4 and 5 are respectively attached.
A plurality of carriers 6 a for holding a plurality of wafers W are arranged between the upper surface plate 2 and the lower surface plate 3. Further, the upper and lower surfaces of the wafer W held by each carrier 6 a are in a state of facing the polishing cloths 4 and 5.

Further, the upper surface plate 2 is provided so as to be movable up and down by the elevating drive unit 7, and during the polishing process, the elevating drive unit 7 moves the upper surface plate 2 downward, and each carrier 6a is moved up and down. It is sandwiched between boards and pressed with a predetermined pressure. On the other hand, the upper surface plate 2 is moved up and down with respect to the lower surface plate 3 by the elevating drive unit 7 during loading / unloading of the wafer W, maintenance, and the like.
Note that the drive of the lift drive unit 7 is controlled based on a command signal from the control unit 20.

Further, the upper surface plate 2 is provided with a rotating shaft 2a that is rotated around an axis by the upper rotation driving unit 8a. And the upper surface plate 2 rotates with the rotating shaft 2a driven (rotated) by the upper rotation drive part 8a.
Further, the lower surface plate 3 is provided with a rotating shaft 3a that rotates about the axis by the lower rotation driving unit 8b. The lower surface plate 3 rotates (rotates in the direction opposite to the upper surface plate 2) together with the rotation shaft 3a driven (rotated) by the lower rotation driving unit 8b.
The operations of the upper rotation drive unit 8a and the lower rotation drive unit 8b are controlled based on a command signal from the control unit 20.

Further, the plurality of carriers 6a are arranged on a circumference around a rotation shaft (not shown) arranged coaxially with the rotation shaft 2a and the rotation shaft 3a described above, and each side portion is rotated in the rotation direction. It meshes with a sun gear (not shown) provided around a shaft (not shown).
Further, an annular internal gear 6c is provided on the outer side of the plurality of carriers 6a around the rotating shaft (not shown) so as to surround the entire carrier 6a, and meshes with the side portion of each carrier 6a. Has been made. The internal gear 6c is driven to rotate independently from a mechanism (upper rotational drive unit 8a, lower rotational drive unit 8b) that drives the surface plates (upper surface plate 2, lower surface plate 3) and a separate motor. Yes.

Further, the upper surface plate 2 is provided with a polishing liquid supply pipe 10 for supplying a polishing liquid to the polishing surface of the carrier 6a, and this polishing liquid supply pipe 10 is supplied with a polishing liquid consisting of a polishing liquid storage tank, a pump and the like. The polishing liquid is supplied by the part 11.
The operation of the polishing liquid supply unit 11 is controlled based on a command signal from the control unit 20.

In addition, the polishing apparatus 1 of the present embodiment is provided with a surface plate load current detection unit 12 connected (electrically connected) to an upper rotation driving unit 8a that rotates the upper surface plate 2.
The surface plate load current detection unit 12 monitors (detects) the “upper surface plate load current value” while the upper rotation driving unit 8 a rotates the upper surface plate 2, and the surface plate load of the control unit 20. The current acquisition unit 22 is configured to transmit the monitored “upper surface plate load current value”.

Further, the polishing apparatus 1 of the present embodiment includes a control unit 20 that controls the operation of the entire apparatus and estimates the progress of the polishing process of the wafer W.
The control unit 20 includes a drive control unit 21 that controls the operation of the entire apparatus, a platen load current acquisition unit 22 that receives an “upper platen load current value” transmitted by the platen load current detection unit 12, A polishing progress estimation unit 23 that estimates the progress (degree of progress) of polishing of the wafer W using the “upper surface plate load current value” received by the panel load current acquisition unit 22.

Moreover, the hardware configuration of the control unit 20 is not particularly limited. For example, the control unit 20 can be configured by a computer having a CPU and a memory. In this case, the memory stores a program for realizing the functions of the “drive control unit 21, the surface plate load current acquisition unit 22, and the polishing progress estimation unit 23”.
The functions of “the drive control unit 21, the surface plate load current acquisition unit 22, and the polishing progress estimation unit 23” are realized by the CPU executing the program stored in the memory.

Hereinafter, functions of each unit of the control unit 20 will be described in detail.
The drive control unit 21 transmits various command signals (control signals) to each part of the polishing apparatus 1 (elevation drive unit 7, upper rotation drive unit 8a, lower rotation drive unit 8b, polishing liquid supply unit 11, etc.), Control the operation of each part.
Further, the surface plate load current acquisition unit 22 receives the “upper surface plate load current value” transmitted from the surface plate load current detection unit 12 and stores it in a predetermined area of the memory of the control unit 20.

Further, the polishing progress state estimation unit 23 uses the upper platen load current value stored in the memory as a reference for the standard deviation σ of the upper platen load current value monitored within a predetermined time (for example, 60 seconds). It is calculated every time (for example, every 1 second), and the progress of the polishing process of the wafer W is estimated from the transition of the calculated standard deviation σ. When the thickness of the semiconductor wafer being polished is estimated to be the “target thickness”, a polishing end signal is transmitted to the drive control unit 21 to stop the rotation operation of the rotating platen, It is comprised so that grinding | polishing may be complete | finished.
In the present embodiment, the thickness (thickness dimension) of the carrier 6a of the polishing apparatus 1 is set so that the final thickness of the wafer W (wafer W) can be estimated so that the progress of the polishing process of the wafer W can be estimated with high accuracy. The thickness of the wafer W is preferably the same as or a thickness within the range of a slight difference (preferably a thickness within the range of ± 6 μm from the center value of the finished thickness of the wafer W).

  Further, in order to be able to estimate the progress of the polishing process of the wafer W with high accuracy, it is desirable that the carrier 6 a be formed of a material whose surface friction coefficient is smaller than that of the wafer W surface. . For example, the carrier 6a may be formed by coating a DLC (diamond-like carbon) film having a low friction coefficient on the surface of the base material made of stainless steel, titanium, resin, or the like.

The reason for adopting the configuration in which the progress of the polishing process of the wafer W is estimated using the monitored upper surface plate load current value is as follows.
The inventor of the present application has investigated in detail the change over time of the polishing apparatus 1 as the wafer W is being polished, and as a result, apparatus detection values that change due to the frictional resistance accompanying the polishing of the wafer W and the carrier 6a (for example, This is because the upper platen load current value) is reflected in the progress of polishing.
In addition, when the inventor performs polishing of the wafer W by making the thickness of the carrier 6a of the polishing apparatus 1 equal to or slightly thinner (or slightly thicker) than the target finish thickness of the wafer W, the polishing progresses. This is because the variation in the detected value (such as the upper platen load current value) of the polishing apparatus 1 is reduced by the reduction in the thickness dimension of the wafer W.

  Specifically, the inventor of the present application monitored the upper platen load current value at the time of polishing the wafer W every second by performing double-side polishing processing once (1 batch) in a general double-side polishing apparatus. Then, create a two-dimensional coordinate with the “elapsed polishing time” on the X-axis and the “upper surface plate load current value” on the Y-axis, and plot the monitored value on the two-dimensional coordinate. The result shown in FIG. 2 was obtained. Referring to FIG. 2, it can be seen that the variation in the upper platen load current decreases with the lapse of the polishing time.

Further, using the monitored upper surface plate load current value, the standard deviation σ of the upper surface plate load current value for 60 seconds is calculated every second, and the “elapsed polishing time” is taken on the X axis. When a two-dimensional coordinate taking the “standard deviation σ of the upper platen load current value for 60 seconds” on the axis is created and the calculated value is plotted on the two-dimensional coordinate, the result shown in FIG. 3 is obtained. .
Referring to FIG. 3, the standard deviation σ of the upper platen load current value becomes smaller as the polishing time elapses and becomes the minimum value (when the X axis in the figure is 1330 seconds), and then starts to rise. I understand that.

This is considered to be a phenomenon that occurs when the main subject to be polished changes as the polishing progresses (the polishing target shifts from “wafer W” → “wafer W and carrier 6a” → “carrier 6a”).
That is, as described above, when the thickness of the wafer W is thicker than that of the carrier 6a, the wafer W is subjected to polishing by the polishing cloths 4 and 5, and then the thickness of the wafer W and the thickness of the carrier 6a. Are added to both the wafer W and the carrier 6a, and when the thickness of the wafer W becomes thinner than the thickness of the carrier 6a, the addition is transferred to the carrier 6a. It is considered a thing.
Therefore, the minimum value of the standard deviation σ shown in FIG. 3 is considered to be a point in time when the thickness dimension of the wafer W and the thickness dimension of the carrier 6a become the same.

Therefore, in the present embodiment, the phenomenon shown in FIG. 3 is used, and the standard deviation σ of the upper platen load current value monitored within a predetermined elapsed time (standard deviation σ of the platen load current value within a fixed time) is used as a reference. A predetermined period is calculated every time (every second), and when the change pattern of the standard deviation σ per time satisfies a predetermined relationship, it is estimated that the polishing is finished.
This change pattern refers to an indicator of a change in standard deviation within a predetermined time or a difference between a calculated standard deviation and a standard deviation calculated before a predetermined time.

For example, with respect to the result of the standard deviation of the upper platen load current value for 60 seconds calculated every second shown in FIG. 3, the slope of the standard deviation for 150 seconds is calculated every second, and “polishing” is applied to the X axis. Is taken, and the Y-axis is taken to create a two-dimensional coordinate taking the “slope of the standard deviation of the upper platen load current value for 60 seconds for 150 seconds”, and the calculated value is represented on the two-dimensional coordinate. When plotted, the results shown in FIG. 4 are obtained.
Also, with respect to the result of the standard deviation of the upper platen load current value for 60 seconds calculated every second shown in FIG. 3, the difference from the standard deviation of 150 seconds before is calculated every second, A two-dimensional coordinate was created by taking the “elapsed polishing time” and taking the “difference from the standard deviation of the upper platen load current of 60 seconds for 150 seconds” on the Y axis, and the above calculation was made on the two-dimensional coordinate. When the values are plotted, the results shown in FIG. 5 are obtained.

  Referring to FIGS. 4 and 5, it can be seen that both the slope or the difference changes rapidly around 1400 seconds. That is, the polishing end time can be estimated by providing a threshold value for the value representing the change in the standard deviation.

Further, the inventor of the present application verified the relationship between the value of the standard deviation σ immediately before the end of processing and the thickness of the finished wafer W.
Specifically, the standard deviation σ of the upper platen load current value for 60 seconds during polishing of the wafer W is calculated every second, the processing time is changed to 11 conditions, and the wafer thickness before polishing is substantially equal. The wafer W was polished, and the relationship between the “thickness of the finished wafer W” and the “standard deviation σ of the upper platen load current value for 60 seconds immediately before the completion of polishing of the wafer W” was verified. FIG. 6 shows the correlation between the standard deviation σ and the finished wafer thickness.

From the results shown in FIG. 6, it can be seen that the transition of the standard deviation σ reflects the thickness of the finished wafer W. The above transition is processed as an index of the change pattern, and polishing is performed when a predetermined relationship is satisfied. It has been found that the thickness of the finished wafer W can be brought close to a desired target value by estimating the end time.
Further, when it is desired to make the finished target thickness of the wafer W smaller than the thickness dimension of the carrier 6a, the polishing end time is defined as the time when the index of the change pattern satisfies the predetermined relationship for the predetermined time. You can also.

Next, the operation of the polishing apparatus 1 will be described.
In the polishing apparatus 1 configured as described above, when the unpolished wafer W is placed on each carrier 6a, the upper surface plate 2 is moved downward under the control of the control unit 20. Then, the wafer W held by the carrier 6a is sandwiched between the upper surface plate 2 and the lower surface plate 3, and is pressed with a predetermined load.
Next, the rotary shafts 2a and 3a are rotationally driven, and each carrier 6a rotates around a rotary shaft (not shown) while rotating while the polishing liquid is supplied from the polishing liquid supply pipe 10. Thereby, both surfaces of the wafer W are simultaneously polished by the polishing cloths 4 and 5.

  When the polishing process of the wafer W is started, the control unit 20 monitors the upper platen additional current value via the platen additional current detection unit 12 and executes the processing steps of FIG. The polishing end time is estimated, and the polishing process of the wafer W by the polishing apparatus 1 is ended.

Next, processing for estimating the progress of the polishing process of the wafer W performed by the polishing apparatus 1 of the present embodiment will be described with reference to FIG.
Here, FIG. 7 is a flowchart showing the procedure of the process for estimating the progress of the wafer polishing process performed by the polishing apparatus of the present embodiment, and the process performed by the polishing progress estimating unit 23 constituting the control unit 20. Is shown.
In parallel with the processing steps of FIG. 7, the platen load current detection unit 12 and the platen load current acquisition unit 22 monitor the “upper platen load current value” and store it in a predetermined area of the memory of the control unit 20. Processing is in progress.

  Specifically, when the polishing process of the wafer W is started, the polishing progress estimation unit 23 waits until the elapsed time T from the start of polishing becomes “A seconds (for example, 60 seconds)”. When T becomes “A second”, the process proceeds to S2 (S1).

Next, the polishing progress status estimation unit 23 uses the “upper platen load current value” stored in the memory to “A seconds before” based on the “elapsed time T from the start of polishing”. The standard deviation σ of the “upper surface plate load current value” monitored at (a fixed time) is calculated (S2).
In parallel with the processing steps of FIG. 7, the standard deviation σ calculated in S <b> 2 is stored in a predetermined area of the memory of the control unit 20.

Next, if the elapsed time T from the start of polishing is “B (for example, 150 seconds) seconds or longer”, the polishing progress status estimating unit 23 proceeds to the process of S5, and the elapsed time T is “less than B seconds”. If there is, the process proceeds to S4 (S3).
Next, if the elapsed time T from the start of polishing is “C (for example, 900 seconds) seconds or longer”, the polishing progress estimation unit 23 proceeds to the process of S6, and the elapsed time T is “less than C seconds”. If there is, the process proceeds to S4 (S5). In S5, while ensuring the minimum polishing time, it is possible to suppress the erroneous detection of the end of polishing due to the fluctuation of the inclination due to the variation of the standard deviation in the first half of the polishing (the inclination up to 900 seconds in FIG. 4). Because it does not detect any variation.)
In S6, the polishing progress estimation unit 23 calculates Y = mX + b with respect to the standard deviation σ calculated until “B seconds ago” (predetermined period) with reference to “elapsed time T from the start of polishing”. The slope m is calculated from a linear approximation represented by the following formula (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept).
Next, if the slope m is “threshold (for example, 0) or more”, the polishing progress state estimation unit 23 proceeds to S8, and if the slope m is “less than the threshold”, proceeds to the process of S4 (S7). .

Specifically, in this step (S7), when the inclination m is equal to or greater than a threshold value (that is, the variation of the “upper surface plate load current value” is equal to or greater than a predetermined level), the polishing progress state estimating unit 23 determines that the wafer W Is estimated to have been polished to the finished target thickness, and the process proceeds to S8.
That is, the inclination m changes from a negative inclination to a positive inclination as shown in FIG. 4, for example. Therefore, by setting the slope m to “threshold (for example, 0) or more”, the thickness dimension of the wafer W being polished becomes substantially the same as the thickness (thickness dimension) of the carrier 6a of the polishing apparatus 1. This can be estimated, and it can be estimated that the wafer W has been polished to the finished target thickness.
On the other hand, in this step (S7), if the inclination m is equal to or smaller than the threshold value (that is, the variation in the variation of the “upper surface plate load current value” is equal to or smaller than a predetermined level), the polishing progress state estimating unit 23 finishes the wafer W. It is estimated that the target thickness has not been polished, and the process proceeds to S4.

In S <b> 8, the polishing progress state estimation unit 23 estimates that the polishing is finished, and ends the polishing process of the wafer W via the drive control unit 21.
Specifically, the polishing progress state estimation unit 23 notifies the drive control unit 21 at the end of polishing when the slope m is equal to or greater than a threshold value, that is, when the variation in the variation of the “upper surface plate load current value” exceeds a predetermined level. Send a signal indicating that there is.
Further, when the drive control unit 21 receives a signal indicating that the polishing is finished, each unit of the polishing apparatus 1 (elevating drive unit 7, upper rotary drive unit 8a, lower rotary drive unit 8b, polishing liquid supply unit 11, etc.). ), Various command signals (control signals) are transmitted to finish the polishing process.

On the other hand, in S3, the polishing progress situation estimation unit 23 increments “a” to “T” until “T ≧ B” in S3 (T ← T + a), and then proceeds to S2 described above. The processes of S3 and S4 are repeated.
On the other hand, in S5, the polishing progress situation estimation unit 23 increments “a” to “T” until “T ≧ C” in S5 (T ← T + a), and then proceeds to S2 described above, and S2 , S3, S4, and S5 are repeated.
On the other hand, when progressing from S5 to S6, the polishing progress status 23 increments “a” to “T” until “inclination m ≧ threshold” in S7 (T ← T + a), and then S2 described above. The process of S2, S3, S4, S5, S6, and S7 is repeated until “slope m ≧ threshold” is satisfied in S7.

  In this way, by repeating the processing of “S2, S3, S4, S5, S6, S7”, B seconds of the standard deviation of the “upper platen load current value” monitored in the latest A seconds (fixed time A) The inclination in (predetermined period B) can be calculated for each reference time (a second).

  As described above, in this embodiment, the standard deviation σ of the “upper platen load current value” monitored within the latest predetermined elapsed time (a fixed time A second) is calculated every reference time (every second), Since the progress of polishing of the wafer W is determined based on the slope of the linear approximation of the standard deviation σ within the elapsed time (predetermined period B seconds), the progress of polishing near the carrier thickness can be estimated in real time.

As described above, according to the wafer polishing method (see FIGS. 7 and 8) and the polishing apparatus 1 of the present embodiment, compared with the conventional method based on “management of polishing time based on experience”, Without increasing labor, the finished thickness of the wafer W can be brought close to the “target thickness”, and deterioration of the flatness of the wafer W due to excessive or insufficient polishing can be suppressed.
In addition, this invention is not limited to embodiment mentioned above, A various change is possible within the range of the summary.

For example, in the above-described embodiment, the “upper platen load current value” is monitored in order to estimate the progress of the polishing process of the wafer W, but the present invention is not limited to this.
The “upper surface plate load current value” is merely an example of a signal that changes due to frictional resistance accompanying polishing of the wafer W or the carrier 6a. If the detected value of the apparatus changes due to the frictional resistance, the progress of the polishing process of the wafer W can be used for estimation.
Specifically, not the “upper surface plate load current value” but the “lower surface plate load current value” is monitored, and the standard deviation σ of the monitored “lower surface plate load current value” is calculated for each reference time, The progress of the polishing process of the wafer W may be estimated from the change pattern of the calculated standard deviation σ.

In the above-described embodiment, the standard deviation of the “upper surface plate load current value” monitored within a predetermined elapsed time (a fixed time A second) is calculated for each reference time (a second), and within the predetermined elapsed time ( The inclination by linear approximation of the predetermined period B seconds is calculated, and the size of the target wafer W is within the predetermined elapsed time (a fixed time A second, the predetermined period B seconds) and the reference time (a second). It shall be appropriately set according to the above.
For example, the predetermined elapsed time (fixed time A second) is set to “10 to 300 seconds”, the reference time (a second) is set to “0.1 seconds to 10 seconds”, and the predetermined elapsed time (predetermined period B seconds) is set. ) Is preferably "10 to 300 seconds".

Further, in the above-described embodiment, the progress of the polishing process is estimated by the linear approximation of the standard deviation of the monitored device detection value (upper surface plate load current value, etc.), but this is particularly limited to this. is not. Even if it is other than the slope by linear approximation, any index that represents the change pattern of the standard deviation (for example, the difference between the standard deviation calculated in real time and the standard deviation before a predetermined time) can be applied to the present invention. .
Specifically, as shown in FIG. 8, “calculate the slope m by linear approximation of σ up to B seconds before T based on T” in S 6 in FIG. By substituting “d (difference) ≧ threshold?” In “S (7) for“ difference d from σ before second ”” and “d (difference) ≧ threshold?” In S7, the change pattern of the standard deviation is represented by the difference and polished. It is possible to make a flowchart showing the procedure of the process of estimating the progress status of. The flow of the flowchart is the same as the flowchart (FIG. 7) when the change pattern of the standard deviation is represented by an inclination.

  Next, the polishing method (and the polishing apparatus) according to the present invention will be further described based on examples. In this example, the double-side polishing process of the wafer W was performed according to the above embodiment, and the effect of the present invention was verified.

[Example 1]
In Example 1, double-side polishing of a φ300 mm silicon wafer W was performed for 20 cycles under the following conditions using the above-described polishing apparatus 1 (flowchart in FIG. 7).
In Example 1, the target value of the finished wafer W thickness was set to “775 μm”. The carrier 6a is made of stainless steel as a base material and the base material surface is coated with a DLC film and has a thickness of “775 μm”.

Further, as the apparatus detection value for estimating the polishing end point, the “top platen load current value” is used as in the above-described embodiment (the flowchart of FIG. 7), and the standard deviation of 60 seconds every second is used. The slope by linear approximation was calculated from the standard deviation up to 150 seconds before, and the time when the slope calculated in the polishing time of 900 seconds or more became “0 (threshold)” or more was estimated as the polishing end time.
The polishing apparatus 1 is of a type that simultaneously polishes five wafers W (one wafer W for one carrier 6a) between the upper surface plate 2 and the lower surface plate 3. The polishing cloths 4 and 5 were made of hard polyurethane. Moreover, the abrasive | polishing agent used colloidal silica aqueous solution, and performed supply amount management, supply temperature management, and pH management. The processing pressure was “150 g / cm ² ”.

  For each of the “center thickness”, “GBIR”, and “SFQR maximum value” of 100 wafers W polished according to the above-described conditions, “average value”, “standard deviation”, “maximum value”, When the “minimum value” was measured, the results shown in Table 1 were obtained.

[Example 2]
In Example 2, the polishing apparatus 1 described above (the flowchart in FIG. 8) was used to perform double-side polishing of a φ300 mm silicon wafer W under the following conditions for 20 cycles.
Specifically, similarly to Example 1 described above, the finished wafer W thickness target value was set to “775 μm”. The carrier 6a is made of stainless steel as a base material and the base material surface is coated with a DLC film and has a thickness of “775 μm”.
Further, as the apparatus detection value for estimating the polishing end point, the “top platen load current value” is used as in the above-described embodiment (the flowchart in FIG. 8), and the standard deviation of 60 seconds every second is used. And the difference from the standard deviation before 150 seconds was calculated, and the point in time when the difference calculated after the polishing time of 900 seconds or more became “0 (threshold)” or more was estimated as the polishing end point.
The polishing apparatus 1 simultaneously polishes five wafers W (one wafer W for one carrier 6a) between the upper surface plate 2 and the lower surface plate 3 as in the first embodiment. The type was used. The polishing cloths 4 and 5 were made of hard polyurethane. Moreover, the abrasive | polishing agent used colloidal silica aqueous solution, and performed supply amount management, supply temperature management, and pH management. The processing pressure was “150 g / cm ² ”.
For each of the “center thickness”, “GBIR”, and “SFQR maximum value” of 100 wafers W polished according to the above-described conditions, “average value”, “standard deviation”, “maximum value”, When the “minimum value” was measured, the results shown in Table 1 were obtained.

[Comparative Example]
In this comparative example, double-side polishing of a silicon wafer W having a diameter of 300 mm was performed 20 cycles under the following conditions by double-side polishing with a constant polishing time as in the above-described example.
Specifically, the finished wafer W thickness target value was set to “775 μm” as in the above-described example. The carrier 6a is made of stainless steel as a base material and the base material surface is coated with a DLC film and has a thickness of “775 μm”.

The polishing apparatus is of the type that simultaneously polishes five wafers W (one wafer W for one carrier 6a) between the upper surface plate 2 and the lower surface plate 3 as in the above embodiment. Things were used.
The polishing cloths 4 and 5 were made of hard polyurethane as in the above example. Moreover, the abrasive | polishing agent used colloidal silica aqueous solution similarly to the said Example, and performed supply amount management, supply temperature management, and pH management. The processing pressure was “150 g / cm ² ”.
The polishing time was “1500 seconds”.

  For each of the “center thickness”, “GBIR”, and “SFQR maximum value” of 100 wafers W polished according to the above-described conditions, “average value”, “standard deviation”, “maximum value”, The “minimum value” was measured and the results shown in Table 1 were obtained.

  From the above examples and comparative examples, it was confirmed that the variation in the finished wafer thickness and flatness can be reduced according to the polishing method according to the present invention, compared to the method of double-side polishing with a constant polishing time.

W Semiconductor wafer (wafer)
DESCRIPTION OF SYMBOLS 1 Polishing apparatus 2 Upper surface plate 2a Rotating shaft 3 Lower surface plate 3a Rotating shaft 4 Polishing cloth 5 Polishing cloth 6a Carrier plate (carrier)
6c Internal gear 7 Lifting drive unit 8a Upper rotation drive unit 8b Lower rotation drive unit 10 Polishing liquid supply pipe 11 Polishing liquid supply unit 12 Surface plate load current detection unit 20 Control unit 21 Drive control unit 22 Surface plate load current acquisition unit 23 Polishing Progress estimation section

Claims (6)

A semiconductor wafer polishing method using a polishing apparatus that simultaneously polishes both surfaces of a semiconductor wafer by sandwiching a semiconductor wafer held by a carrier with upper and lower rotary surface plates and rotating the upper and lower rotational surface plates. There,
Monitoring the platen load current value of the polishing apparatus when simultaneously polishing both surfaces of the semiconductor wafer;
When using the monitored surface plate load current value, a standard deviation of the surface plate load current value within a predetermined time is calculated for a predetermined period for each reference time, and a change pattern per time of the standard deviation satisfies a predetermined relationship And estimating the end of polishing;
A method for polishing a semiconductor wafer, comprising: The step of estimating the end of polishing is as follows:
Calculate the standard deviation of the platen load current value within a certain period of time for each reference time,
From the linear approximation represented by the equation of Y = mX + b (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept) with respect to the standard deviation calculated in the predetermined period, The inclination m is calculated, the change pattern of the inclination m is obtained,
2. The method for polishing a semiconductor wafer according to claim 1, wherein when the inclination m satisfies a condition of "greater than or equal to a predetermined threshold value", it is estimated that the polishing end point is reached. The step of estimating that it is the end point of polishing calculates the standard deviation of the platen load current value within a certain time every reference time,
Calculate the difference between the calculated most recent standard deviation and the standard deviation calculated a predetermined time ago, and obtain a change pattern of the difference,
2. The method for polishing a semiconductor wafer according to claim 1, wherein when the difference satisfies a condition of "a predetermined threshold value or more", it is estimated that the polishing end point is reached. A semiconductor wafer polishing apparatus for simultaneously polishing both surfaces of a semiconductor wafer by sandwiching a semiconductor wafer held by a carrier with upper and lower rotating surface plates and rotating the upper and lower rotating surface plates,
A drive control unit for controlling the rotation operation of the upper and lower rotating surface plates;
A detector for monitoring a platen load current value when simultaneously polishing both surfaces of the semiconductor wafer;
Using the monitored surface plate load current value, the standard deviation of the surface plate load current value within a predetermined time is calculated for each reference time, and the polishing progress status is estimated from the change of the calculated standard deviation An estimation unit,
When the change pattern of the standard deviation per time calculated for each reference time satisfies a predetermined relationship, the polishing progress state estimation unit transmits a polishing end signal to the drive control unit, and the rotation constant A semiconductor wafer polishing apparatus, wherein the rotation operation of the board is stopped and polishing is terminated. The polishing progress estimation unit calculates a standard deviation of a surface plate load current value within a predetermined time for a predetermined period for each reference time,
For the standard deviation calculated in the predetermined period,
The slope m is calculated from a linear approximation represented by the equation Y = mX + b (where X: elapsed time, Y: standard deviation σ, m: slope, b: intercept), and a change pattern of the slope m is obtained. ,
5. The semiconductor wafer polishing apparatus according to claim 4, wherein when the inclination m satisfies a condition of “predetermined threshold value or more”, it is estimated that the polishing end point is reached. The polishing progress estimation unit calculates the standard deviation of the platen load current value within a fixed time for each reference time,
Calculate the difference between the calculated standard deviation and the standard deviation calculated a predetermined time ago, and find the change pattern of the difference.
5. The semiconductor wafer polishing apparatus according to claim 4, wherein when the difference satisfies a condition that “a predetermined threshold value or more” is satisfied, it is estimated that the polishing end point is reached.

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