JP6253382B2 - Polishing method - Google Patents

Description

  The present invention relates to a polishing method for polishing a plate-like workpiece.

  A plate-like workpiece typified by a semiconductor wafer includes, for example, a polishing surface plate provided with a polishing member such as a nonwoven fabric on the upper surface, and a holding mechanism for sucking and holding the workpiece above the polishing surface plate. Polishing is performed with a polishing apparatus (see, for example, Patent Document 1).

  In this polishing apparatus, the polishing surface plate and the holding mechanism are configured to be rotatable relative to each other. By rotating the holding mechanism that holds the workpiece and the polishing surface plate, the workpiece is pressed against the polishing member with a predetermined pressure while supplying slurry containing the abrasive to the polishing member. The workpiece can be polished.

  The pressure (pressing pressure) for pressing the workpiece against the polishing member is adjusted based on, for example, the experience of the operator. In this way, by adjusting the pressing pressure to an optimum value, it is possible to realize good polishing by interposing the slurry between the workpiece and the polishing member.

JP-A-3-248532

  However, as described above, it is not always easy to adjust the pressing pressure to an optimum value based on the experience of the operator. If the pressing pressure is set larger than the optimum value, the slurry does not enter between the workpiece and the polishing member, and the polishing cannot proceed well. On the other hand, when the pressing pressure is set smaller than the optimum value, the gap between the polishing member and the workpiece becomes excessively large, and the polishing progress speed is significantly reduced.

  It is also possible to select an optimum value by repeating processing while changing the pressing pressure. However, this method of selecting the pressing pressure by trial and error requires a great deal of labor.

  In addition, if the conditions such as the type of workpiece or slurry and the required processing quality change, the optimum pressing pressure also changes. In this case, the optimum value must be selected again. There is also.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a polishing method capable of more easily realizing good polishing.

According to the present invention, there is provided a polishing method for polishing a workpiece, wherein the workpiece is pressed by the polishing means while pressing the workpiece surface of the polishing means against the processing surface of the polishing means via a slurry containing an abrasive. A distance between the processing surface of the polishing means facing the processing surface of the workpiece and the processing surface of the workpiece before or during the polishing step. A distance detecting step detected by a detecting means; and the processing surface of the polishing means and the processing surface of the workpiece based on the distance detected in the distance detecting step before or during the polishing step. A moving step for relatively moving the distance away from each other , and when the value of the distance detected in the distance detecting step is smaller than the average abrasive grain size of the abrasive, the moving step includes the polishing means. The processing surface of the workpiece and the processing surface of the workpiece are relatively separated from each other. Polishing method characterized by causing is provided.

In the present invention, in the moving step, the polishing means is maintained so that the distance value detected in the distance detecting step is g and the reference values are g ₁ and g ₂ and is kept in a range of g ₁ ≦ g ≦ g _2. It is preferable to move the processed surface of the workpiece and the processed surface of the workpiece relatively close to and away from each other.

  The polishing method of the present invention includes a distance detection step for detecting a distance between a processing surface of the polishing means and a processing surface of the workpiece by the detection means, and polishing based on the distance detected by the distance detection step. A moving step for moving the processing surface of the means and the processing surface of the workpiece relatively close to and away from each other, so that the distance between the processing surface of the polishing means and the processing surface of the workpiece is determined. The workpiece can be polished with arbitrary control.

  That is, in the polishing method of the present invention, not the pressing pressure that presses the workpiece against the polishing means, but the distance between the processing surface of the polishing means and the processing surface of the workpiece, The workpiece can be polished satisfactorily by using the distance at which the abrasive contained in the slurry can appropriately enter as a reference for control. Thus, according to the polishing method of the present invention, it is possible to more easily realize good polishing as compared with the case of controlling the pressing pressure for pressing the workpiece.

It is a figure which shows typically the structural example and grinding | polishing step of a grinding | polishing apparatus used with the grinding | polishing method which concerns on this Embodiment. It is a figure which shows a distance detection step and a movement step typically.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The polishing method according to the present embodiment includes a distance detecting step (see FIG. 2), a moving step (see FIG. 2), and a polishing step (see FIG. 1).

  In the distance detection step, the sensor unit (detection means) detects the distance (interval) between the processing surface of the polishing member (polishing means) provided in the polishing apparatus and the processing surface of the workpiece. In the moving step, the processing surface of the polishing member and the processing surface of the workpiece are moved relatively close to or away from each other based on the detection result of the distance detection step.

  In the polishing step, the workpiece is pressed against the polishing member and polished while supplying the slurry containing the abrasive to the processing surface of the polishing member. Here, the distance between the processing surface of the polishing member and the processing surface of the workpiece is controlled by a distance detection step and a movement step. Hereinafter, the polishing method according to the present embodiment will be described in detail.

  First, the configuration of a polishing apparatus used in the polishing method according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram schematically illustrating a configuration example and a polishing step of a polishing apparatus used in the polishing method according to the present embodiment, and FIG. 2 is a diagram schematically illustrating a distance detection step and a movement step. is there. As shown in FIG. 1, the polishing apparatus 2 includes a disk-shaped polishing surface plate 4 having a flat upper surface.

  The polishing surface plate 4 is connected to a rotation mechanism (not shown) such as a motor and rotates around a rotation axis extending in the vertical direction. A polishing member (polishing means) 6 for polishing the workpiece 11 is disposed on the upper surface of the polishing surface plate 4. As the polishing member 6, for example, a nonwoven fabric or the like can be used.

  A holding mechanism (holding means) 8 that sucks and holds the workpiece 11 is disposed above the polishing member 6. The holding mechanism 8 is connected to a rotation mechanism (not shown) such as a motor, and rotates around a rotation axis extending in the vertical direction. The holding mechanism 8 is moved up and down (moved up and down) by an elevating mechanism (moving mechanism) 10.

  The lower surface 8 a of the holding mechanism 8 is a holding surface that sucks and holds the upper surface 11 a side of the workpiece 11. A negative pressure of a suction source acts on the holding surface through a channel formed inside the holding mechanism 8, and a suction force for sucking the workpiece 11 is generated. When the holding mechanism 8 sucks and holds the upper surface 11 a side of the workpiece 11, the upper surface 6 a of the polishing member 6 faces the lower surface 11 b of the workpiece 11.

  At a position adjacent to the holding mechanism 8, a nozzle 12 for supplying a slurry 15 in which an abrasive (abrasive grain) 13 (FIG. 2) is dispersed is disposed on the upper surface 6 a of the polishing member 6. The nozzle 12 is positioned at a position where it does not interfere with the holding mechanism 8 or the like.

  The workpiece 11 is typically a disk-shaped semiconductor wafer. The holding mechanism 8 holding the workpiece 11 and the polishing surface plate 4 are rotated with each other, and then the holding mechanism 8 is moved down by the elevating mechanism 10 to supply the slurry 15 and the upper surface 6a of the polishing member 6. By pressing against, the lower surface 11b side of the workpiece 11 can be polished.

  That is, in the present embodiment, the lower surface 11b of the workpiece 11 exposed downward while being held by the holding mechanism 8 serves as the workpiece surface, and the upper surface 6a of the polishing member 6 exposed upwards the workpiece 11. It becomes the processing surface to process.

  A sensor unit (detecting means) 14 for detecting the distance between the lower surface 11b of the workpiece 11 serving as the processing surface and the upper surface 6a of the polishing member 6 serving as the processing surface is provided on the side portion of the holding mechanism 8. Is provided. The sensor unit 14 is controlled by a control device 16 connected via wiring or the like.

  As shown in FIG. 2, an ultrasonic sensor 18 that transmits ultrasonic waves toward the polishing member 6 to be detected and receives the reflected waves is disposed at the lower part of the housing of the sensor unit 14. The ultrasonic sensor 18 includes a piezoelectric element (ultrasonic transducer) 18a that mutually converts electric power (voltage) and vibration (ultrasonic wave).

The piezoelectric element 18a is made of a material such as lead zirconate titanate (PB (Zi, Ti) O ₃ ), barium titanate (BaTiO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), for example. It is formed. In addition, lead zirconate titanate is sometimes called PZT or the like.

  When a predetermined pulse voltage (alternating voltage) is applied to the piezoelectric element 18a, an ultrasonic wave having a frequency corresponding to the frequency of the applied pulse voltage is generated. Further, when an ultrasonic wave as described above is applied to the piezoelectric element 18a, a pulse voltage having a frequency corresponding to the frequency of the applied ultrasonic wave is generated at the terminal of the piezoelectric element 18a.

  An ultrasonic transmission member 18b that transmits ultrasonic waves is provided at the lower end of the piezoelectric element 18a. The ultrasonic transmission member 18b is made of, for example, a material such as crystal or acrylic resin, and propagates ultrasonic waves generated by the piezoelectric element 18a satisfactorily. The lower surface of the ultrasonic transmission member 18 b is exposed from the lower part of the housing of the sensor unit 14 and is in contact with the slurry 15 supplied to the upper surface 6 a of the polishing member 6.

  A pulse voltage generator 20 that generates a pulse voltage is connected to a terminal of the piezoelectric element 18a. The pulse voltage generator 20 generates a pulse voltage having a voltage of about 250 V and a frequency of about 1 kHz based on an instruction from the control device 16 and applies the pulse voltage to the piezoelectric element 18 a of the ultrasonic sensor 18.

  In addition, a converter (converter) 22 that converts a pulse voltage output from the piezoelectric element 18 a into an electric signal that can be identified by the control device 16 is connected to a terminal of the piezoelectric element 18 a. The converter 22 converts the pulse voltage generated in the piezoelectric element 18 a by receiving the ultrasonic wave (reflected wave) into an electrical signal that can be identified by the control device 16 and outputs the electrical signal to the control device 16.

  The sensor unit 14 configured in this manner applies the pulse voltage generated by the pulse voltage generator 20 to the piezoelectric element 18 a based on an instruction from the control device 16. As a result, an ultrasonic wave is generated from the piezoelectric element 18a and propagates through the ultrasonic transmission member 18b.

  As described above, the slurry 15 supplied to the upper surface 6a of the polishing member 6 is in contact with the lower surface of the ultrasonic transmission member 18b. Therefore, the ultrasonic wave propagated through the ultrasonic transmission member 18 b is applied to the slurry 15 and reflected on the upper surface 6 a of the polishing member 6.

  The ultrasonic wave (reflected wave) reflected by the upper surface 6a of the polishing member 6 propagates through the slurry 15 and the ultrasonic transmission member 18b and is applied to the piezoelectric element 18a. The piezoelectric element 18 a converts the applied ultrasonic wave into a pulse voltage and outputs the pulse voltage to the converter 22. When a pulse voltage is input from the piezoelectric element 18 a, the converter 22 converts the pulse voltage and outputs it to the control device 16.

  The control device 16 includes a time measuring unit 16 a that measures time t until the ultrasonic wave transmitted from the ultrasonic sensor 18 is reflected by the upper surface 6 a of the polishing member 6 and received by the ultrasonic sensor 18. .

  For example, the time measurement unit 16a compares the difference between a time t1 when the ultrasonic sensor 18 is instructed to transmit an ultrasonic wave and a time t2 when the ultrasonic sensor 18 receives the ultrasonic wave reflected on the upper surface 6a of the polishing member 6. (T2-t1 (= t)) is measured.

  The time t measured by the time measuring unit 16a is notified to the distance calculating unit 16b of the control device 16. The distance calculation unit 16b calculates a distance (interval) g between the lower surface 11b of the workpiece 11 to be processed and the upper surface 6a of the polishing member 6 to be processed based on the notified time t. calculate.

The distance calculation unit 16b calculates the distance g based on the following formula (1), for example. In Equation (1), v represents the speed of sound in the slurry 15, w ₀ represents the thickness of the workpiece 11, and d represents the distance from the lower surface of the ultrasonic transmission member 18b to the lower surface 8a of the holding mechanism 8. ing.
(1) ... g = v (t / 2)-(d + w ₀ )

The control device 16 compares the value of the distance g calculated by the distance calculation unit 16b with, for example, arbitrary reference values (reference distances) g ₁ and g ₂ (g ₁ ≦ g ₂ ), The lower surface 11b of the object 11 and the upper surface 6a of the polishing member 6 are kept at an appropriate distance.

Specifically, when the value of the distance g is smaller than the reference value g ₁ , the control device 16 raises the holding mechanism 8 with the lifting mechanism 10, and the lower surface 11 b of the workpiece 11 and the upper surface 6 a of the polishing member 6. To separate.

On the other hand, when the value of the distance g is larger than the reference value g ₂ , the control device 16 lowers the holding mechanism 8 with the elevating mechanism 10 to bring the lower surface 11 b of the workpiece 11 and the upper surface 6 a of the polishing member 6 close to each other. . Thereby, the distance g between the lower surface 11b of the workpiece 11 and the upper surface 6a of the polishing member 6 can be maintained in the range of g ₁ ≦ g ≦ g ₂ .

  Next, a polishing method performed using the polishing apparatus will be described. In the polishing method according to the present embodiment, first, as a preparation step, the workpiece 11 is held by the holding mechanism and the slurry 15 in which the abrasive 13 is dispersed is supplied to the upper surface 6 a of the polishing member 6. Then, the holding mechanism 8 is lowered to bring the slurry 15 into contact with the lower surface of the ultrasonic transmission member 18b (FIGS. 1 and 2).

  After performing the preparation step, a distance detection step of detecting a distance (interval) g between the upper surface 6a of the polishing member 6 and the lower surface 11b of the workpiece 11 is performed. In this distance detection step, first, an ultrasonic wave USa is transmitted from the sensor unit 14 toward the polishing member 6, and the ultrasonic wave USb reflected by the upper surface 6a of the polishing member 6 is received by the sensor unit 14 (FIG. 2).

  When the ultrasonic wave USb is received, the time measuring unit 16a calculates the time t required from the transmission of the ultrasonic wave USa to the reception of the ultrasonic wave USb, and notifies the distance calculation unit 16b. The distance calculation unit 16b calculates a distance g between the lower surface 11b of the workpiece 11 and the upper surface 6a of the polishing member 6 based on the notified time t.

After carrying out the distance detection step, the holding mechanism 8 is moved up and down based on the value of the distance g to carry out a moving step for keeping the lower surface 11b of the workpiece 11 and the upper surface 6a of the polishing member 6 at an appropriate distance. . In this movement step, first, the value of the distance g calculated by the distance calculation unit 16b is compared with arbitrary reference values g ₁ and g ₂ (g ₁ ≦ g ₂ ).

If the value of the distance g is the reference value g ₁ is smaller than, the controller 16 raises the holding mechanism 8 in the lifting mechanism 10, thereby separating the lower surface 11b of the workpiece 11, the upper surface 6a of the polishing member 6 (FIG. 2). On the other hand, when the value of the distance g is larger than the reference value g ₂ , the control device 16 lowers the holding mechanism 8 with the elevating mechanism 10 to bring the lower surface 11 b of the workpiece 11 and the upper surface 6 a of the polishing member 6 close to each other. .

The amount of movement of the holding mechanism 8 (the distance between separation and proximity) is arbitrary. For example, the moving amount of the holding mechanism 8 can be determined according to the difference between the reference value g ₁ or the reference value g ₂ and the distance g. In this case, since the moving amount of the holding mechanism 8 changes according to the value of the distance g, it is easy to keep the lower surface 11b of the workpiece 11 and the upper surface 6a of the polishing member 6 at an appropriate distance. However, the movement amount of the holding mechanism 8 is not limited to this and may be constant.

As the reference value g _1, it is preferable to use the value of the average abrasive grain size of the abrasive material 13 contained in the slurry 15. For example, when the value of the distance g is smaller than the value of the average abrasive grain size of the abrasive 13, sufficient abrasive 13 is interposed between the lower surface 11 b of the workpiece 11 and the upper surface 6 a of the polishing member 6. It becomes difficult and good polishing cannot be realized.

Therefore, using the values of the average abrasive grain size of the abrasive material 13 contained in the slurry 15 as a reference value g _1, the value of the distance g is controlled so as not to fall below the value of the average abrasive grain size of the abrasive material 13. Thereby, sufficient polishing material 13 is interposed between the lower surface 11 b of the workpiece 11 and the upper surface 6 a of the polishing member 6, thereby realizing good polishing.

The reference value g _2, for example, may be used a value average abrasive grain size on the order of approximately equal abrasive material 13. The reference value g ₂ which is the upper limit of the distance g By setting in this way, requires the moving speed of the polishing without greatly reduced, can maintain productivity. The reference value _{g 2} may be the same as the reference value _{g 1.}

  After performing the moving step, a polishing step for polishing the workpiece 11 is performed. In this polishing step, the holding mechanism 8 holding the workpiece 11 and the polishing surface plate 4 are rotated with each other while supplying the slurry 15 containing the abrasive 13 to the polishing member 6.

  The distance between the lower surface 11b of the workpiece 11 and the upper surface 6a of the polishing member 6 is appropriately controlled in advance by the distance detection step and the movement step described above. Therefore, the workpiece 11 can be polished satisfactorily.

  Since the workpiece 11 becomes thinner as the polishing progresses, it is necessary to repeat the distance detection step and the movement step even during the polishing step. During the polishing step, the distance detection step and the movement step may be repeated continuously or may be repeated after a predetermined time interval. The timing for performing the distance detection step and the movement step is arbitrarily set according to the progressing speed of the polishing.

  As described above, in the polishing method according to the present embodiment, the distance g between the upper surface 6a serving as the processing surface in the polishing member (polishing means) 6 and the lower surface 11b serving as the processing surface in the workpiece 11 is set. The distance detection step detected by the sensor unit (detection means) 14 and the upper surface 6a of the polishing member 6 and the lower surface 11b of the workpiece 11 are relatively close to or separated from each other based on the distance g detected in the distance detection step. Therefore, the workpiece 11 can be polished while the distance g between the upper surface 6a of the polishing member 6 and the lower surface 11b of the workpiece 11 is arbitrarily controlled.

  That is, in the polishing method according to the present embodiment, the distance g between the upper surface 6a of the polishing member 6 and the lower surface 11b of the workpiece 11 is not the pressing pressure that presses the workpiece 11 against the polishing member 6. Therefore, for example, the workpiece 11 can be satisfactorily polished by using the distance at which the abrasive 13 contained in the slurry 15 can appropriately enter as a reference for control. Thus, according to the polishing method according to the present embodiment, it is possible to more easily realize good polishing as compared with the case where the pressing pressure for pressing the workpiece 11 is controlled.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the above embodiment, the distance g is calculated based on the formula (1), but the method for calculating the distance g is not limited to this.

  Formula (1) assumes that the ultrasonic transmission member 18b is sufficiently thin (when the distance from the lower surface of the piezoelectric element 18a to the lower surface of the ultrasonic transmission member 18b is short). When the ultrasonic transmission member 18b is thick, it is desirable to calculate the distance g in consideration of the thickness of the ultrasonic transmission member 18b, the speed of sound of ultrasonic waves propagating through the ultrasonic transmission member 18b, and the like.

  In the above-described embodiment, the holding mechanism 8 is moved up and down to bring the upper surface 6 a serving as the processing surface in the polishing member (polishing means) 6 and the lower surface 11 b serving as the processing surface in the workpiece 11 close to or away from each other. However, the upper surface 6a and the lower surface 11b may be relatively close to or separated from each other. For example, the polishing surface plate 4 may be moved up and down, or both the polishing surface plate 4 and the holding mechanism 8 may be moved up and down.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be changed as appropriate without departing from the scope of the object of the present invention.

2 Polishing device 4 Polishing surface plate 6 Polishing member (polishing means)
6a Upper surface 8 Holding mechanism (holding means)
8a Lower surface 10 Lifting mechanism 12 Nozzle 14 Sensor unit (detection means)
DESCRIPTION OF SYMBOLS 16 Control apparatus 16a Time measurement part 16b Distance calculation part 18 Ultrasonic sensor 18a Piezoelectric element (ultrasonic transducer)
18b Ultrasonic transmission member 20 Pulse voltage generator 22 Converter (converter)
11 Workpiece 11a Upper surface 11b Lower surface 13 Abrasive material 15 Slurry USa ultrasonic wave USb ultrasonic wave (reflected wave)

Claims (2)

A polishing method for polishing a workpiece,
A polishing step of polishing the workpiece with the polishing means while pressing the processing surface of the workpiece against the processing surface of the polishing means through the slurry containing the abrasive;
Before or during the polishing step, a distance detection in which a distance between the processing surface of the polishing means facing the processing surface of the workpiece and the processing surface of the workpiece is detected by a detection means Steps,
Before or during the polishing step, the moving step of moving the processing surface of the polishing means and the processing surface of the workpiece relatively close to and away from each other based on the distance detected in the distance detection step. and, with a,
When the value of the distance detected in the distance detection step is smaller than the average abrasive grain size of the abrasive material, in the moving step, the processing surface of the polishing means and the processing surface of the workpiece are A polishing method characterized by relatively moving apart. In the moving step, the processed surface of the polishing means is maintained so that g ₁ ≦ g ≦ g ₂ , where g is the distance value detected in the distance detecting step, and g ₁ and g ₂ are reference values. The polishing method according to claim 1, wherein the workpiece and the workpiece surface of the workpiece are moved relatively close to and away from each other.