JP2006043857A - Polishing pad and observing device of polishing pad - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad and an observing device of polishing pad, quantitatively determining the service life to the number of wafers depending on the state of the polishing pad, accurately determining the end of life of the polishing pad, and automatically determining the use start time of the polishing pad. <P>SOLUTION: A projecting part 50 having continuously variable sectional area is formed in the direction of thickness of the polishing pad 14 in a groove of the polishing pad 14. The observing device having an image sensor 52 for imaging the projecting part 50 and a determination part 56 for calculating the diameter and area of the top face 64 of the projecting part 50 to decide the life end of the polishing pad 14 is installed in a polishing apparatus. The projecting part 50 is imaged by the image sensor 52 every time one wafer W is polished or two or more wafers are polished, the diameter and the sectional area are calculated by a CPU 60 of the determination part 56, and a warning is given from a speaker 68 when the calculated diameter of the top face 64 of the projecting part 50 reaches an area determined to be the end of life. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polishing pad and a polishing pad observation device, and more particularly to a polishing pad of a polishing device and a polishing pad observation device for polishing a workpiece such as a semiconductor wafer by chemical mechanical polishing (CMP).

  In recent years, with the development of semiconductor technology, the miniaturization of design rules and the formation of multilayer wiring have progressed. For this reason, when it is attempted to form the pattern of the next layer as it is on the layer on which the pattern has been formed as in the prior art, it is difficult to form a good pattern in the next layer due to the unevenness of the previous layer. there were. Therefore, the surface of the layer on which the pattern is formed is flattened, and then the pattern of the next layer is formed. As a planarization apparatus in this case, a polishing apparatus using a CMP method is used.

  Conventionally, this type of polishing apparatus is composed of a polishing surface plate and a polishing head each rotated by an independent rotation mechanism, and a polishing wafer adhered to the polishing surface plate with the semiconductor wafer held by the polishing head. By pressing against the pad and supplying a slurry mixed with an abrasive, the surface of the semiconductor wafer is mechanically polished while being chemically corroded.

  In order to supply slurry uniformly to the polishing surface, the polishing pad is usually used in which a plurality of grooves are formed on the polishing surface, and when polishing scraps adhere to these grooves and the polishing rate decreases. The polishing surface is periodically dressed by a dressing device.

  Further, the polishing pad is judged to have reached the end of its life when the groove depth becomes shallow due to wear of the polishing surface. For this reason, the groove depth of the polishing pad is measured after dressing, and the durable number is determined empirically based on the groove depth at that time and the number of processed sheets so far, and the life of the polishing pad is reached when the durable number is reached. Judging that it came, it was replaced with a new polishing pad.

  There has also been proposed an apparatus that detects the end of the life of the polishing pad based on fluctuations in the rotational torque of the polishing head without measuring the groove depth (for example, Patent Document 1).

By the way, the dressing of the polishing pad stabilizes the polishing rate of the polishing pad when it is replaced with a new polishing pad in addition to the normal dressing process performed during the polishing operation for sharpening the polishing surface. It is also carried out during the start-up process in which the polishing pad is conspicuous up to the state, that is, the use start state. The determination of the use start state was made empirically by the operator observing the polishing pad after dressing with a microscope or the like and viewing the state.
JP 2001-9700 A

  However, in the conventional method of predicting the number of service life and the arrival of the life of the polishing pad based on the depth of the groove formed in the polishing pad, there is no way to efficiently measure the amount of wear of the polishing pad. However, there is a problem that the reliability of the sheet is low and the durable sheet number cannot be obtained quantitatively.

  Further, the method of Patent Document 1 that detects the arrival of the life of the polishing pad based on the fluctuation of the rotational torque of the polishing head has a drawback that the reliability is low because factors other than the polishing pad greatly affect the determination of the arrival of the life. there were. This is because, for example, the abrasive mixed with the slurry, and depending on the type of the abrasive, there is an effect on the fluctuation of the rotational torque. As another factor, there is a difference in the type of whether or not a pattern is formed on the wafer. In the case of a wafer on which a pattern is formed, the torque is high at the beginning of polishing to polish the pattern, and then the torque is reduced when the pattern is polished and flattened thereafter.

  On the other hand, in the conventional dressing technique in which the polishing pad is conspicuous to the use start state, since the start state is determined empirically by the operator, there is a demand for automating the determination.

  The present invention has been made in view of such circumstances, and the number of serviceable sheets can be quantitatively determined according to the state of the polishing pad, and the arrival of the life of the polishing pad can be accurately determined. An object of the present invention is to provide a polishing pad and a polishing pad observation device that can automatically determine when to start using the polishing pad.

  In order to achieve the above object, the invention according to claim 1 is a polishing pad in which a workpiece is polished and a groove is formed on a polishing surface thereof, and in the groove of the polishing pad, in the thickness direction of the polishing pad, A protrusion having a shape whose cross-sectional area continuously changes is formed.

  In order to quantitatively determine the number of usable sheets depending on the state of the polishing pad and accurately determine the arrival of the life of the polishing pad, it is necessary to devise the polishing pad as well. Therefore, according to the invention of the polishing pad of the first aspect, the protrusion having a shape in which the cross-sectional area continuously changes in the thickness direction of the polishing pad is formed in the groove of the polishing pad. Further, the upper surface of the protrusion is preferably flush with the polishing surface.

  In the polishing apparatus using the polishing pad according to claim 1, as described in claim 2, the imaging device is installed at an opposing position of the polishing pad and images the protrusion, and the imaging unit captures an image. A polishing pad observation device comprising: a determination unit that calculates an area of an upper surface of the protrusion based on the projected image of the protrusion and determines a state of the polishing pad based on the area. It is said.

  According to the observation device of claim 2, the projection is imaged each time one workpiece is polished by the imaging means or each time a plurality of workpieces are polished, and the area of the upper surface is calculated by the determination unit. The state of the polishing pad is determined based on the area.

  The invention according to claim 3 is the invention according to claim 2, wherein the determination unit calculates the reference area of the upper surface of the protrusion that is determined as the life of the polishing pad and the calculation of the protrusion. A comparison unit for comparing the area and / or a notice unit for notifying the remaining number of the work pieces that can be polished, the use ratio up to the present time of the life, and the number of use based on the calculated area of the protrusion. It is characterized by that.

  According to the observation apparatus of claim 3, the comparison unit compares the reference area of the protrusion that indicates the life of the polishing pad stored in advance and the area of the current protrusion, and the area is the reference area. When they match, it is determined that the life of the polishing pad has come. Therefore, according to the present invention, the projection is formed on the polishing pad capable of efficiently measuring the abrasion amount of the polishing pad, and the observation device for judging the life of the polishing pad based on the area of the projection is provided. The arrival of the life of the polishing pad can be automatically and accurately determined. In addition, by acquiring the number of workpieces to be processed corresponding to the area of the upper surface of the protrusion in advance and storing this information in the storage unit of the notice unit, the remaining number of workpieces that can be polished from the area calculated at that time Can be easily estimated, and the usage rate relative to the life of the polishing pad can be obtained quantitatively.

  Furthermore, in the invention according to claim 4, in the invention according to claim 3, the determination unit detects that the calculated area of the protrusion has reached the reference area by the comparison unit. It is characterized in that alarm means is provided for issuing an alarm when it is issued.

  Thus, according to the observation device of the fourth aspect, the operator can confirm that the polishing pad is in the replacement period due to the life by the alarm issued from the alarm means. The polishing apparatus is controlled so as to automatically stop at the timing when an alarm is issued from the alarm means or at the end of polishing of the workpiece.

  On the other hand, in order to automatically determine when to start using the polishing pad, it is necessary to devise the polishing pad. Therefore, according to the invention of the polishing pad of claim 5, the polishing surface of the polishing pad is colored with a predetermined color. This color may be a color different from the color of the polishing pad, and the coloring position may be a part of the polishing pad or the whole. Considering that the paint is peeled off, it is preferable to color a part of the polishing pad.

  Further, in the polishing apparatus using the polishing pad according to claim 5, as described in claim 6, the imaging device is installed at an opposed position of the polishing pad and images the polishing surface, and the imaging device captures an image. A polishing pad observation device comprising: a determination unit that calculates a colored area of the polished surface based on the image of the polished surface and determines a polishing start time of the workpiece based on the colored area; It is characterized by that.

  According to the observation apparatus of claim 6, the polished surface is dressed by the dressing device, and the colored polished surface is imaged at predetermined time intervals by the imaging means between the dressings. The colored part is gradually peeled off by dressing. The area of the colored portion that gradually decreases is always calculated by the determination unit, and the use start time of the polishing pad is determined based on the area of the colored portion. Therefore, the use start time of the polishing pad can be automatically determined.

  According to the observation apparatus of claim 7, the determination unit is provided with an alarm unit that issues an alarm when the calculated colored area reaches a reference area corresponding to a work polishing start time. It is a feature.

  According to the polishing pad observation device of the present invention, the projection is imaged by the imaging means, the area of the upper surface of the projection is calculated by the determination unit, and the state of the polishing pad is determined based on the area. Thus, it is possible to automatically and accurately determine the life of the polishing pad.

  Further, according to the polishing pad observation device of the present invention, the colored polishing surface is imaged by the imaging means, the colored area is calculated by the determination unit, and the polishing start time of the polishing pad is calculated based on the colored area. Therefore, the use start time of the polishing pad can be automatically determined.

  Preferred embodiments of a polishing pad and a polishing pad observation device according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a perspective view of a main part of a wafer polishing apparatus 10 to which the polishing pad and the polishing pad observation apparatus of the embodiment are applied. A wafer polishing apparatus 10 shown in the figure is a polishing apparatus for polishing a semiconductor wafer by a CMP method, and a polishing pad 14 made of polyurethane is attached to the upper surface of a rotating polishing surface plate 12. The polishing pad 14 is a grooved pad in which a large number of grooves 18, 18... A polishing head 20 is disposed above the polishing pad 14. The polishing head 20 is rotated by the rotational force transmitted from the motor 21 of FIG. 1 via the rotary shaft 22 while holding the wafer W as shown in FIG. 16 is arranged so as to be in contact with 16.

  The polishing head 20 includes a head body 24, a back plate 26, a retainer ring 28, a protective sheet 30, a back plate airbag 32, a retainer ring airbag 34, and the like.

  The back plate airbag 32 is a space formed by the rubber sheet 36 and the head body 24, and air is supplied from the air line 38 to press the back plate 26 toward the polishing pad 14. The retainer ring airbag 34 is a space formed by the rubber sheet 36 and the head body 24 and is provided on the outer peripheral side of the back plate airbag 32. Air is supplied from the air line 40 to the retainer ring airbag 34, and presses the retainer ring 28 toward the polishing pad 14.

  Further, air jet holes 42, 42,... Are formed on the outer periphery of the back plate 26, and air jet ports 44, 44,. The air outlets 42, 42... Are connected to the main air injection path 46, while the air outlets 44, 44... Are connected to the positive pressure line and the negative pressure line via the sub air injection path 48 and a switching valve (not shown). ing.

  The protective sheet 30 has a peripheral edge held by the retainer ring 28, prevents the wafer W from coming into direct contact with the hard back plate 26, contacts the wafer W, and air pressure from the back plate 26 is applied to the wafer W. introduce. The air injected from the back plate 26 is exhausted to the outside through a gap between the back plate 26 and the retainer ring 28. The polishing shape of the wafer W is controlled by adjusting the air pressure through the main air injection path 46 and the air pressure through the sub air injection path 48, respectively.

  A suction port (not shown) for sucking a wafer is formed in the protective sheet 30 and is used for sucking and holding the wafer W when the wafer W is transported. That is, at the time of suction of the wafer W, the sub air injection path 48 is switched to the negative pressure line by the switching valve, and the suction force is transmitted to the wafer W through the plurality of suction ports.

  The polishing head 20 is configured as described above. While the wafer W held by the polishing head 20 is pressed against the grooved polishing surface 16 of the polishing pad 14, the polishing surface plate 12 and the polishing head 20 are rotated, respectively. By supplying the slurry onto the polishing pad 14, the wafer W is polished.

  Incidentally, the polishing pad 14 according to the embodiment has a protrusion 50 formed in a part of the groove 18 as shown in the enlarged view of the main part shown in FIG. The protrusion 50 is for determining the wear state of the polishing pad 14 and is formed in a shape whose cross-sectional area continuously changes in the thickness direction of the polishing pad 14. Further, the upper surface of the protrusion 50 is formed flush with the polishing surface 16 of the polishing pad 14. In addition, although the projection part 50 of embodiment is formed in the truncated cone shape as shown in FIG. 4, a triangular frustum shape and a square frustum shape may be sufficient.

  In FIG. 1, an image sensor (imaging means) 52 constituting the polishing pad observation apparatus of the embodiment is installed above the polishing pad 14. The image sensor 52 is a CCD camera, and is placed with the photographing lens 54 facing the polishing pad 14 and is positioned at a position where the projection 50 shown in FIG. 3 can be imaged from above. That is, when the projection 50 is imaged by the image sensor 52, the polishing surface plate 12 is rotated so that the projection 50 is positioned below the image sensor 52 as shown in FIG. The position at which the protrusion 50 is formed is not particularly limited. However, when the wafer W is polished, it is preferable to dispose the protrusion 50 at a location where the amount of wear is particularly large in terms of life evaluation. Further, the number of the protrusions 50 is not limited to one, but may be plural. In that case, a different color is colored for each protrusion, and the protrusion and the amount of wear are associated with each other. It is preferable to keep it.

  As shown in FIG. 5, the image signal of the protrusion 50 output from the image sensor 52 is output to the image processing unit 58 constituting the determination unit 56 of the observation apparatus of the embodiment, and is subjected to image processing. Then, the CPU 60 incorporated in the determination unit 56 outputs to the monitor 62 a video signal indicating the protrusion 50 subjected to image processing by the image processing unit 58. As a result, an image showing the upper surface 64 of the protrusion 50 shown in FIG. 3 is displayed on the monitor 62 as shown in FIG.

  Further, the CPU 60 shown in FIG. 5 extracts the edge portion of the upper surface 64 of the protrusion 50 by, for example, performing black and white binarization processing on the video signal image-processed by the image processing unit 58, and coordinates of the edge portion It has the function of calculating the diameter of the upper surface 64 based on the position, and also has the function of calculating the area from this diameter. The calculated diameter and area are numerically displayed on the monitor 62 together with the image of the protrusion 50 (see FIG. 6).

  Furthermore, a ROM (storage unit) 66 is incorporated in the determination unit 56 shown in FIG. The ROM 66 stores information indicating the life area (reference area) of the upper surface 64 of the protrusion 50 determined to have reached the end of the life of the polishing pad 14 and information indicating the diameter of the upper surface 64 of the protrusion 50. Information indicating the remaining number of wafers W that can be polished based on the area of the upper surface 64 or the diameter of the upper surface 64 of the protrusion 50 is stored.

  The CPU 60 has a comparison function (comparison unit) that compares the lifetime area stored in the ROM 66 with the actually calculated area of the upper surface 64, and based on the actually calculated area of the upper surface 64, It also has a notice function (notice part) for notifying the remaining number. The content compared by the comparison function, for example, the content of the percentage of the current area with respect to the lifetime area, is numerically displayed on the monitor 62, and the remaining number notified by the notification function is also numerically displayed on the monitor 62. . As a result, the operator can quantitatively confirm the usage rate with respect to the life of the polishing pad 14. Further, when the CPU 60 confirms that the actually calculated area of the upper surface 64 has reached the lifetime area, it controls the speaker (alarm means) 68 to generate an alarm. Thereby, the operator can confirm that the polishing pad 14 is in the replacement period due to its life by the alarm issued from the speaker 68.

  Next, the operation of the polishing pad observation apparatus configured as described above will be described.

  First, before starting the polishing of the wafer W, the projection 50 before wear is imaged as shown in FIG. 3, and the image of the projection 50 is displayed on the monitor 64 as shown in FIG. 6, and the diameter and area of the upper surface 64 at this time are displayed. Is displayed.

  Since the protrusion 50 of the embodiment has a truncated cone shape, a change in the diameter of the protrusion 50 due to wear of the polishing pad 14 will be described. Of course, it may be explained by a change in the cross-sectional area of the upper surface of the protrusion 50, but it is easier to understand that the frustoconical protrusion 50 is described by a change in diameter than a change in cross-sectional area. On the other hand, in the case of the triangular frustum shape and the quadrangular frustum shape, it is easier to understand the explanation given by the change in the cross-sectional area.

For example, the state of FIGS. 7 to 9 in which the diameter of the upper surface of the protrusion 50 before starting polishing is 2 mm (3.14 mm ^{2 in} the case of a cross-sectional area) and the protrusion 50 is worn by 0.5 mm. It is assumed that the diameter of the upper surface 64 of the protrusion 50 is 3 mm (7.07 mm ^{2 in} the case of a cross-sectional area). Information of 3 mm (7.07 mm ^{2 in} the case of a cross-sectional area) is stored in the ROM 66.

  The protrusion 50 is picked up by the image sensor 52 every time one or more wafers W are polished, and the diameter and cross-sectional area thereof are determined by the CPU 60 of the determination unit 56 shown in FIG. The calculated diameter and cross-sectional area are numerically displayed on the monitor 62. Further, the number of remaining wafers that can be polished is numerically displayed on the monitor 62 together with the diameter and the cross-sectional area. For example, when the diameter of the upper surface 64 of the protrusion 50 calculated by the CPU 60 is 2.2 mm, the polishing pad 14 is worn by about 0.1 mm from the ratio of the diameter to the height, and reaches 20% of the total life. It will be done. The CPU 60 numerically displays on the monitor 62 the content that has reached 20% of the total lifetime, reads out the remaining number of wafers W that can be polished based on the diameter from the ROM 66, and displays the remaining number on the monitor 62 as a numerical value.

  Then, the CPU 60 determines that the life of the polishing pad 14 has arrived when the calculated diameter of the upper surface 64 of the protrusion 50 reaches 3 mm, and issues an alarm from the speaker 68. Thus, the operator can easily confirm that the polishing pad 14 is in the replacement period due to its life.

  As described above, according to the observation apparatus for the polishing pad 14 of the embodiment, the protrusion 50 capable of efficiently measuring the amount of wear of the polishing pad 13 is formed in the groove 18 of the polishing pad 14. Since the life of the polishing pad 14 is determined on the basis of the cross-sectional area or diameter of the upper surface 64, the life of the polishing pad 14 can be automatically and accurately determined.

  Further, the number of processed wafers W corresponding to the cross-sectional area of the protrusion 50 is acquired in advance and stored in the ROM 66 of the determination unit 56 as information, so that polishing can be performed from the cross-sectional area or diameter calculated at that time. The remaining number of wafers W can be easily estimated, and the usage ratio with respect to the life of the polishing pad 14 can be obtained quantitatively.

  By the way, when the polishing pad 14 is replaced with a new polishing pad 14, the polishing pad 14 is noticed by the dressing apparatus until the polishing rate is stabilized, that is, until the use is started, and then the polishing of the wafer W is started. .

  Next, a method for automatically determining when to start using the polishing pad 14 will be described.

  First, for this purpose, a portion 15 of the polishing surface of the polishing pad 14 is colored with a predetermined color as shown in FIG. This color may be a color different from the color of the polishing pad 14, and the coloring position may be a part of the polishing pad or the whole. Considering that the paint is peeled off, it is preferable to color a part of the polishing pad. In the embodiment, the entire surface of the rectangular die portion (part) 15 formed by being sandwiched between the two vertical grooves 18 and the two horizontal grooves 18 is colored.

  The colored dice unit 15 is picked up by the image sensor 52 shown in FIG. 1, and the image signal is subjected to image processing by the image processing unit 58 of the determination unit 56 shown in FIG. The CPU 60 outputs a video signal indicating the dice unit 15 subjected to the image processing by the image processing unit 58 to the monitor 62. As a result, an image showing the dice unit 15 is displayed on the monitor 62.

  Further, the CPU 60 performs, for example, black and white binarization processing on the video signal image-processed by the image processing unit 58, thereby extracting the edge portion 70A of the coloring portion 70 in FIG. Based on this, it has a function of calculating the area of the colored portion 70. The calculated area is numerically displayed on the monitor 62.

  Further, the ROM 66 of the determination unit 56 stores information indicating the area of the coloring unit 70 that is determined as the use start time of the polishing pad 14.

  The CPU 60 has a comparison function (comparison unit) that compares the area stored in the ROM 66 with the actually calculated area of the coloring unit 70. The content compared by the comparison function, for example, the content of what percentage the current area is relative to the area at the start of use is displayed numerically on the monitor 62. Further, when the CPU 60 confirms that the actually calculated area of the coloring portion 70 has reached the area at the start of use, the CPU 60 controls the speaker 68 to generate an alarm. Thus, the operator can confirm that the polishing pad 14 has been dressed in the use start state by an alarm issued from the speaker 68.

  When the polished surface of the replaced polishing pad 14 is dressed by a dressing apparatus, the four edges 15A of the die portion 15 are worn more than the surface as shown in FIG. The part 70 is shaved from the outer peripheral part toward the center part. This situation is picked up by the image sensor 52 and the area is calculated by the CPU 60.

Since the area at the start of use of the coloring portion 70 is empirically 10% of the surface area of the die portion 15, the ROM 66 stores the area of 10%. For example, in the case of the die portion 15 having an area of 15 mm × 15 mm (2.25 mm ² ), 10% of the area (0.225 mm ² ) is stored. Therefore, when the actually calculated area of the colored portion 70 reaches 0.225 mm ² , the CPU 60 determines that the polishing pad 14 has reached the use start state, and controls the speaker 68 to generate an alarm. Thereby, the use start time of the polishing pad 14 can be determined automatically.

A perspective view of a wafer polisher to which a polishing pad observation device of an embodiment is applied 1 is a longitudinal sectional view of the main part of the wafer polishing apparatus shown in FIG. Explanatory drawing which showed the state by which the projection part was imaged by the image sensor Enlarged perspective view of the protrusion shown in FIG. Block diagram showing the control system of the polishing pad observation device Explanatory drawing which showed the image of the projection part imaged with the image sensor An enlarged cross-sectional view of the main part of a worn polishing pad Enlarged perspective view of the main part of a worn projection Explanatory drawing which showed the image of the projection part of FIG. 8 imaged with the image sensor. The perspective view which expanded and showed a part of colored polishing pad The perspective view which showed that a part of polishing pad shown in FIG. 10 was dressed to a use start state

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Wafer polisher, 12 ... Polishing surface plate, 14 ... Polishing pad, 16 ... Polishing surface, 18 ... Groove, 20 ... Polishing head, 50 ... Projection part, 52 ... Image sensor, 54 ... Shooting lens, 56 ... Judgment part 58 ... Image processing unit, 60 ... CPU, 62 ... Monitor, 64 ... Upper surface of projection 50, 66 ... ROM, 68 ... Speaker, 70 ... Coloring unit

Claims (7)

In a polishing pad with a groove formed on the polishing surface while polishing the workpiece,
A polishing pad, wherein a protrusion having a shape in which a cross-sectional area continuously changes in a thickness direction of the polishing pad is formed in a groove of the polishing pad. Provided in a polishing apparatus for pressing and polishing the workpiece against the polishing surface of the polishing pad according to claim 1;
An imaging unit that is installed at a position facing the polishing pad and that images the projection;
A determination unit that calculates the area of the upper surface of the protrusion based on the image of the protrusion captured by the imaging unit, and determines the state of the polishing pad based on the area;
An apparatus for observing a polishing pad, comprising:   The determination unit is a comparison unit that compares a reference area of the upper surface of the protrusion determined to be the life of the polishing pad with the calculated area of the protrusion, and / or the calculated area of the protrusion. The polishing pad observation apparatus according to claim 2, further comprising a notifying unit for notifying the remaining number of work pieces that can be polished or the ratio of use up to the present time and the number of used work pieces.   The determination unit is provided with alarm means for issuing an alarm when the comparison unit detects that the calculated area of the protrusion has reached the reference area. Item 4. The polishing pad observation apparatus according to Item 3. In a polishing pad for polishing a workpiece by its polishing surface,
A polishing pad, wherein the polishing surface is colored with a predetermined color. It is provided in a polishing apparatus for polishing by pressing the workpiece against the polishing surface of the polishing pad according to claim 5,
An imaging unit that is installed at a position facing the polishing pad and images the polishing surface;
Calculating a colored area of the polished surface based on the image of the polished surface imaged by the imaging means, and a determination unit for determining the polishing start time of the workpiece based on the colored area;
An apparatus for observing a polishing pad comprising:   7. The polishing pad according to claim 6, wherein the determination unit is provided with alarm means for issuing an alarm when the calculated colored area reaches a reference area corresponding to a workpiece polishing start time. Observation device.

Images