JP2010069517A - Working apparatus and working method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform uniform working by surely and accurately detecting variance in height of a workpiece surface, particularly in a workpiece such as a sapphire substrate. <P>SOLUTION: A working apparatus is provided with a mechanism 30 for detecting variance in height of the surface of the workpiece, which includes: an interferometer 1 which uses a light source 2 for emitting light that does not go through the workpiece W to be worked and that has a wavelength equal to or more than twice as long as the size (e.g., 2 μm) of the variance in height of the surface of the workpiece, for example, a wavelength of ≥10 μm, and which makes use of interference of reference light and detection light; and a height measuring means 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a processing apparatus and a processing method for detecting the height position of a workpiece surface and performing processing such as cutting and drilling on the workpiece based on the detected height position.

  In the semiconductor device manufacturing process, multiple areas are defined by streets (cutting lines) arranged in a grid on the surface of a substantially disk-shaped semiconductor workpiece, and circuits such as IC and LSI are formed in the partitioned areas. To do. The semiconductor work is cut along the streets to divide the work into circuits to manufacture individual semiconductor chips. Cutting along the street of a semiconductor work is usually performed by a cutting device called a dicer, and a processing method of cutting by irradiating a laser beam has also been attempted (for example, see Patent Document 1).

  Also, an optical device work in which a plurality of regions are defined by streets formed in a lattice pattern on the surface of the sapphire substrate, and an optical device such as a gallium nitride compound semiconductor is stacked on the partitioned regions is also along the streets. By cutting, it is divided into optical devices such as individual light emitting diodes and laser diodes, which are widely used in electronic equipment.

JP-A-10-305420

  However, plate-like workpieces such as semiconductor wafers and sapphire substrates have undulation, and if the thickness varies, uniform processing cannot be performed on the surfaces of the semiconductor wafers and sapphire substrates. Therefore, it is necessary to detect the unevenness of the region to be irradiated with the laser beam in advance and perform processing by causing the laser beam irradiation means to follow the unevenness.

  The present invention has been made in view of the above, and is capable of performing uniform processing by reliably detecting the height variation of the workpiece surface in a workpiece, particularly a workpiece such as a sapphire substrate, with high accuracy. An object is to provide an apparatus and a processing method.

  In order to solve the above-described problems and achieve the object, a machining apparatus according to the present invention detects a height position of a workpiece surface and performs machining on the workpiece based on the detected height position. A light source that does not transmit the workpiece to be processed and emits light having a wavelength that is twice or more the height variation of the workpiece surface, and the light emitted from the light source is a reference An optical system that splits light into detection light and detection light and guides the detection light to the work; and receives light that interferes with the reference light and the detection light reflected from the work surface; A light receiving element for detecting the intensity of reflected interference light at the light source, an optical path length adjusting means for adjusting a difference in optical path length from the light source to the light receiving element between the reference light and the detection light, and a work at a predetermined location in the work Height measurement to measure surface height A workpiece surface variation detection mechanism comprising a step, a machining mechanism for machining the workpiece, and a control means for controlling the machining mechanism based on the workpiece surface height variation detected by the workpiece surface variation detection mechanism; It is characterized by providing.

  Further, the machining method according to the present invention is a machining method for detecting the height position of the workpiece surface and machining the workpiece based on the detected height position, and transmits the workpiece to be machined. And the light having a wavelength more than twice the height variation of the workpiece surface is split into the reference light and the detection light to guide the detection light to the workpiece, and the reference A reflected interference light intensity detecting step for detecting reflected interference light intensity on the workpiece surface by receiving light interfered with the detection light reflected on the workpiece surface and the detection light reflected on the workpiece surface, and detecting in the reflected interference light intensity detecting step An optical path length adjusting step for adjusting a difference in optical path length from the light source to the light receiving element between the reference light and the detection light so that the reflected interference light intensity is larger than a minimum value and smaller than a maximum value; Predetermined location on the workpiece Calculated based on a reference height measurement step for measuring the workpiece surface height as a reference height, a reflected interference light intensity detected in the reflected interference light intensity detection step, and a reference height measured in the reference height measurement step. And a machining step of machining the workpiece while controlling a machining mechanism based on the workpiece surface height variation.

  The processing method according to the present invention is characterized in that, in the above invention, the processing step is performed using the processing mechanism that irradiates the workpiece with a laser beam.

  In the processing method according to the present invention, in the above invention, the light used in the reflected interference light intensity detection step is light having a wavelength of three times or more the height variation of the workpiece surface. And

  In the processing method according to the present invention, in the above invention, the workpiece to be processed is a sapphire substrate, and the light used in the reflected interference light intensity detection step is light having a wavelength of 10 μm or more. Features.

  According to the present invention, interference between the reference light and the detection light is used by using light having a wavelength that does not pass through the workpiece to be processed and is twice or more the height variation of the workpiece surface. Since it has a workpiece surface height variation detection mechanism consisting of an interferometer and a height measuring means, it is possible to reliably detect the workpiece surface height variation in a workpiece, particularly a workpiece such as a sapphire substrate, with high accuracy. By controlling the machining mechanism based on this detection result, there is an effect that uniform machining can be performed on a workpiece having irregularities on the surface.

  Hereinafter, a processing apparatus and a processing method which are the best mode for carrying out the present invention will be described with reference to the drawings. As an example, the present embodiment is applied to a case where a workpiece to be processed is a sapphire substrate and the workpiece surface has a height variation of about 1 to 2 μm.

(Outline of the principle of the present invention)
First, as a typical non-contact type sensor that detects the unevenness of the surface of a measurement object using light, there are a confocal type and an interference type such as a Michelson interferometer. Here, when targeting a sapphire substrate, in the case of a confocal sensor, it is a problem how to separate the reflected light noise from the back of the sapphire substrate when the confocal optical system is assembled from the signal light. It has become.

  On the other hand, in the case of a general sensor using a visible light source, an interference type sensor (interferometer) is intended to detect a height variation of 1 μm or less, and a measurement range (1) required for a sapphire substrate. It is smaller than about 2 μm), and the surface irregularity state in the case of the sapphire substrate cannot be accurately detected. In addition, since the sapphire substrate is transparent to visible light having a wavelength of 635 nm, reflection on the back surface of the sapphire substrate occurs.

  Therefore, in the present invention, in order to detect the surface irregularity state of the sapphire substrate, an interferometer that uses interference between the reference light and the detection light is first used. Optimize the measurement range.

  First, consider the wavelength of light used in the interferometer. FIG. 1 is a characteristic diagram showing the wavelength dependence of the light transmittance of a sapphire substrate. In the case of a sapphire substrate, light having a wavelength of about 0.15 to 6 μm has a high light transmittance. Therefore, basically, by using a light source for the interferometer that emits light with a wavelength of 0.15 μm or less or a wavelength of 6 μm or more that does not pass through the sapphire substrate, the influence of back surface reflected light is avoided by reducing the transmittance. Is possible.

  Next, consider the target measurement range. FIG. 2 is a schematic diagram illustrating an interference signal of reflected interference light intensity in an interferometer that uses interference between reference light and detection light. In the interference signal shown as a sine wave, the maximum point and the minimum point of the reflected interference light intensity exist at positions where the optical path length difference between the reference light and the detection light is an integral multiple of the wavelength used. In order to measure the height of the concavo-convex state using such an interference signal, it is basically necessary that the wavelength of the used light is twice or more the maximum height of the concavo-convex state. Conversely, the measurement range is ½ or less of the wavelength of the used light. Within one wavelength, a region where the light intensity decreases from the maximum point to the minimum point and a region where the light intensity increases from the minimum point to the maximum point exist symmetrically, and the wavelength of the light used is uneven. This is because when the height is less than twice the maximum height, two light intensities are generated for different optical path lengths. If the wavelength of the light used is at least twice the maximum height of the uneven state, the light intensity decreases from the maximum point to the minimum point, and the light intensity increases from the minimum point to the maximum point. Only one of and can be used.

Here, when the interference signal shown in FIG. 2 is further considered, the reflected interference light intensity increases linearly with respect to the optical path length difference between the reference light and the detection light between the minimum point and the maximum point. There are about 1/3 wavelength areas. By using this area as a proportional area for measurement, it is possible to detect with high accuracy the uneven height corresponding to the optical path length difference between the reference light and the detection light from the reflected interference light intensity. Therefore, by using a light source that emits light having a wavelength of 10 μm or more, for example, a CO ₂ laser light source, an interferometer that can cover the target 1-2 μm in the sapphire substrate is obtained. FIG. 3 is a characteristic diagram showing the relationship between the height position of the surface of the sapphire substrate and the intensity of reflected interference light detected by the interferometer when a CO ₂ laser light source that emits light having a wavelength of 10 μm or more, for example, is used. Note that the reflectance is constant. Thus, it can be seen that the target measurement range of 1 to 2 μm in the sapphire substrate can be linearly covered.

  That is, as the light emitted from the light source, it is preferable to use light having a wavelength that is at least three times the surface height variation (1-2 μm) of the sapphire substrate, but the longer the wavelength, the more dynamic the measurement range. Since the resolution is lowered and the resolution is lowered, and the wavelength of the actual laser light source is limited, it is desirable to keep it slightly larger than three times.

  In addition, as an area of about 1/3 wavelength used as a measurement proportional area, the reflected interference light intensity between the maximum point and the minimum point is different from the optical path length difference between the reference light and the detection light. It may be a linearly decreasing area (left side in FIG. 2).

  In this case, there are two states in which the interference intensity falls within the measurement range: a linear decrease region and a linear increase region, and uneven height information corresponding to the optical path length difference between the reference light and the detection light and the interference The intensity is reversed. Therefore, when an incorrect measurement range is used, for example, +2 μm is misread as −2 μm. Therefore, it is sufficient to confirm in advance that the interference intensity is entirely increased when the sapphire substrate is raised by Δμm from the measurement range, and the interference intensity is entirely reduced when the sapphire substrate is lowered by Δμm. In practice, it is only necessary to confirm that the moving direction of the Z axis coincides with the increase / decrease direction of the interference intensity in order to move the Z axis in one direction to be within the measurement range. .

  Therefore, according to the present invention, an interferometer as shown in FIG. 4 can be proposed as a Michelson interferometer type interferometer having a measurement range of 1 to 2 μm with respect to the sapphire substrate. FIG. 4 is a schematic diagram showing the configuration of the interferometer 1. The interferometer 1 includes a light source 2, a spectroscopic optical system 3, a reference mirror 4, and a two-dimensional light receiving element 5.

As the light source 2, a CO ₂ laser light source having an output of 40 mW collimated to a wavelength of 10.8 μm and a beam diameter of 50 mm is used. The light emitted from the light source 2 is split into reference light and detection light by an optical system 3 including a beam splitter (for example, a half mirror can be used). The detection light passes through the optical system 3 and is guided to the surface of the sapphire substrate 6 which is a workpiece to be measured, and is irradiated on the entire surface of the sapphire substrate 6. Then, the light is regularly reflected on the surface of the sapphire substrate 6, reaches the optical system 3 again, and is reflected on the light receiving element 5 side. On the other hand, the reference light reflected by the optical system 3 is specularly reflected by the reference mirror 4, then reaches the optical system 3 again, passes therethrough, and enters the light receiving element 5. The light receiving element 5 is composed of a two-dimensional CCD, for example. The reference light and the detection light reflected by the surface of the sapphire substrate 6 form an interference fringe on the surface of the light receiving element 5, which is read as a signal of reflected interference light intensity to obtain height information. Convert.

  Here, the distribution of the reflected interference light intensity on the entire surface of the sapphire substrate 6 detected by the light receiving element 5 is larger than the minimum value and smaller than the maximum value, so that it is within the measurement range shown in FIG. The optical path length difference between the light source 2 and the light for detection from the light source 2 to the light receiving element 5 is adjusted.

  After the optical path length difference is adjusted so as to be within the measurement range as described above, the light receiving element 5 obtains a detection result indicating the relationship between the light intensity and the detection ratio, for example, as shown in FIG. FIG. 5 shows a detection result on one vertical plane in the sapphire substrate 6. For such a detection result, by using a height conversion table in which the relationship between height and light intensity as shown in FIG. 3 is used, detection of the relative uneven height state on the surface of the sapphire substrate 6 is performed. Is possible.

  Here, since the detection of the concavo-convex height state of the surface of the sapphire substrate 6 by the interferometer 1 is relative, an actual measurement of one predetermined point on the sapphire substrate 6 using a separate height measurement means. Measure the surface height. FIG. 6 is a schematic view showing a state in which the surface height of one point of the sapphire substrate 6 is measured using the non-contact type height measuring means 7. Thus, when the surface height of the point A, which is one point on the sapphire substrate 6, is measured to be 124.195 mm, for example, by applying it to the detection result as shown in FIG. All the actual surface heights of the entire surface of the sapphire substrate 6 are found. FIG. 7 shows an example of application results. For example, the surface height of each point can be determined such that point B is 124.193 mm, point C is 124.194 mm, and point D is 124.196 mm.

(Embodiment)
Next, an embodiment of the present invention based on the outline of the principle of the present invention as described above will be described. FIG. 8 is an external perspective view showing the overall configuration of the processing apparatus according to the embodiment of the present invention as viewed from the front side, and FIG. 9 is an external perspective view showing the overall configuration of the processing apparatus as viewed from the back side. FIG. 10 is a perspective view showing the configuration of the processing mechanism.

  The processing apparatus 10 according to the present embodiment is for performing a cutting process by irradiating a workpiece W made of a sapphire substrate or the like with a laser beam. A variation detection mechanism 30 is provided.

  Here, as shown in an enlarged view in FIG. 8, the workpiece W may be of a large size type in which only one piece is attached on the protective tape T attached to the annular frame F, or the annular frame. It may be a small-sized type affixed on the protective tape T affixed to F (in the case of the sapphire substrate 6, there are many small-sized types).

  Further, the processing mechanism 20 is of a laser processing type. As schematically shown in FIG. 10, a chuck table 21, a laser beam irradiation unit 22, a first feed mechanism 23, and a second feed are provided. A mechanism 24 and an imaging means 25 are provided. The chuck table 21 sucks and holds the workpiece W to be processed by a suction unit (not shown), and can be rotated in a horizontal plane by a motor (not shown), so that the posture of the workpiece W with respect to the laser beam irradiation unit 22 can be changed. Yes.

  The laser beam irradiation unit 22 is arranged such that a condenser 22a attached to the tip is opposed to the chuck table 21 from above, and from the condenser 22a to the workpiece W on the chuck table 21. Irradiate with a laser beam. The imaging means 25 is disposed in a part of the laser beam irradiation unit 22 in a state where the positional relationship with the condenser 22a is fixed, faces the chuck table 21, and is held on the chuck table 21. By imaging W, it is used for street alignment processing or the like.

  The first feed mechanism 23 moves the chuck table 21 in the X-axis direction (front-rear direction) with respect to the laser beam irradiation unit 22, and includes a known mechanism using a ball screw 23a, a motor 23b, and the like. The second feed mechanism 24 moves the chuck table 21 in the Y-axis direction (left and right direction) with respect to the laser beam irradiation unit 22, and is a known mechanism using a ball screw 24a, a motor 24b, and the like. Become. By providing such first and second feeding mechanisms 23 and 24, the laser beam irradiation unit 22 can scan the entire surface of the workpiece W on the chuck table 21.

  The workpiece surface variation detection mechanism 30 is provided so as to be movable up and down above the chuck table 11 disposed on the front side of the chuck table 21. FIG. 11 is a schematic diagram showing a configuration around the workpiece surface variation detection mechanism 30 of the present embodiment mounted on the machining apparatus 10, and FIG. 12 shows a state around the workpiece surface variation detection mechanism 30 during height measurement. FIG. The workpiece surface variation detection mechanism 30 includes the interferometer 1 having the above-described principle configuration, an optical path length adjusting unit 31, and a height measuring unit 7.

  That is, the interferometer 1 includes a light source 2, a spectroscopic optical system 3, a reference mirror 4, and a light receiving element 5. The optical path length adjusting means 31 is set so that the distribution of reflected interference light intensity from the entire surface of the workpiece W detected by the light receiving element 5 is larger than the minimum value (0) and smaller than the maximum value (maximum interference intensity). The optical path length difference from the light source 2 to the light receiving element 5 between the reference light and the detection light is adjusted so as to be within a predetermined measurement range. For this reason, the optical path length adjusting means 31 is composed of, for example, a Z-axis feed mechanism that moves the position of the entire interferometer 1 relative to the workpiece W up and down.

  Further, the height measuring means 7 is provided in a part of the interferometer 1 and measures the workpiece surface height at a predetermined point on the workpiece W as a reference height. In the principle explanation, the optical non-contact type was explained, but FIG. 11 shows a stylus type. At the time of measuring the workpiece surface height at one predetermined location of the workpiece W, as shown in FIG. 12, the chuck table 11 is moved by a predetermined amount, so that the height measuring means 7 has a desired XY coordinate value. For example, it is positioned at point A. This point A touched by the height measuring means 7 is set to be a non-device region. And the actual workpiece | work surface height in A point is measured by making the height measurement means 7 descend | fall and making it contact with A point.

  Further, the processing apparatus 10 of the present embodiment includes a control means 40. The control means 40 calculates the surface height variation for the entire surface of the workpiece W based on the outputs from the light receiving element 5 and the height measuring means 7, and controls the machining mechanism 20 based on the calculated surface height variation. However, the workpiece W is subjected to laser processing.

Therefore, in the processing apparatus 10 of the present embodiment, the processing process is executed according to the processing procedure shown in FIG. FIG. 13 is a schematic flowchart showing the processing method of the present embodiment. First, the workpiece W is taken out from a cassette (not shown) (step S1), and the taken workpiece W is held on the chuck table 11 (step S2). Next, height correlation information on the entire surface of the workpiece W is acquired by detecting the reflected interference light intensity by the interferometer 1 using the reference light and the detection light (step S3: reflected interference light intensity detection step). That is, light having a wavelength of 10.8 μm is emitted from a light source 2 using a CO ₂ laser, and is split into reference light and detection light by the optical system 3 to guide the detection light to the work W and irradiate the entire surface of the work W. At the same time, the light that has interfered with the reference light and the detection light reflected on the surface of the workpiece W is received by the light receiving element 5, and the distribution of the reflected interference light intensity on the entire surface of the workpiece W is detected.

  Here, it is determined whether or not the distribution of the reflected interference light intensity detected by the light receiving element 5 is in an appropriate state that falls within a desired measurement range as shown in FIG. 2 (step S4). If not appropriate (step S4: No), the optical path length is adjusted (step S5: optical path length adjustment step). That is, the optical path length adjustment means 31 moves the interferometer 1 up and down in the Z-axis direction to finely adjust the distance between the workpiece W and the optical path from the light source 2 to the light receiving element 5 for the reference light and the detection light. Adjust the length difference to be appropriate (so that all detected reflected interference light intensities fall within the measurement range).

  If it is appropriate (step S4: Yes), the surface height of one point at a predetermined location of the workpiece W is measured by the height measuring means 7 (step S6: reference height measuring step). And the surface height variation of the whole workpiece | work W is calculated by the control means 40 (step S7). That is, by comparing the actual height information of one point measured by the height measuring means 7 with the entire intensity distribution of interference light detected from the surface of the workpiece W, the focus of the laser beam for processing is obtained. The surface height variation of the entire surface of the workpiece W is acquired.

  Thereafter, the workpiece W is moved to the machining mechanism 20 side, and the machining mechanism 20 is controlled so that the focal position of the laser beam irradiated on the workpiece W is raised or lowered based on the calculated surface height variation information of the entire workpiece W. Then, the workpiece W is processed (step S8: processing step). That is, the unevenness information of the street irradiated with the laser beam is detected in advance, and the cutting is performed according to the unevenness state on the surface of the workpiece W by processing the focal position of the laser beam according to the unevenness information. Processing can be performed. This process is performed for all the streets of the work W.

  When the processing is completed (step S9: Yes), the workpiece W is taken out from the processing mechanism 20, washed by a cleaning machine (not shown) (step S10), and the processing is completed by transporting and storing the workpiece W in a collection cassette. (Step S11).

  As described above, according to the present embodiment, it is possible to reliably detect the workpiece surface height variation in the workpiece W, particularly the workpiece such as the sapphire substrate 6, with high accuracy. Therefore, based on the detection result, the machining mechanism 20. By controlling the sapphire, uniform processing can be performed on the sapphire substrate 6 having irregularities on the surface.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, although the present embodiment has been described as an application example in the case of the sapphire substrate 6 as the workpiece W, it is applicable not only to the sapphire substrate 6 but also to various workpieces. For example, semiconductor wafers such as silicon wafers, adhesive members such as DAF (Die Attach Film) provided on the back surface of the wafer for chip mounting, semiconductor product packages, ceramic, glass or silicon substrates, Processing accuracy of several μm order may be required.

  Further, in the present embodiment, the example in which the workpiece W is cut by irradiating the laser beam along the street of the workpiece W has been described. However, the present invention is not limited thereto, and for example, Japanese Patent Application Laid-Open No. 2003-163323. As shown in the gazette, it may be a drilling process or the like for forming a fine hole (via hole) at a desired position of the workpiece. Further, the processing mechanism 20 is not limited to laser processing using the laser beam irradiation unit 22, and can be similarly applied to a case where a chopper cut is performed at a desired processing position of a workpiece using a disk-shaped blade, for example. It is.

It is a characteristic view which shows the wavelength dependence of the light transmittance of a sapphire substrate. It is a schematic diagram which shows the interference signal of the reflected interference light intensity | strength in the interferometer using the interference of the light for a reference | standard, and the light for a detection. It is a characteristic view which shows the relationship between the height position of the surface of a sapphire substrate, and the reflected interference light intensity detected with an interferometer. It is a schematic diagram which shows the structure of an interferometer. It is a characteristic view of the detection result which shows the relationship between light intensity-detection ratio. It is a schematic diagram which shows a mode that the surface height of one point of a sapphire substrate is measured using a non-contact-type height measuring means. It is a characteristic view which shows the application result of the surface height of A point with respect to interference intensity distribution. It is an external appearance perspective view which shows the structure of the whole processing apparatus of embodiment seen from the front side. It is an external appearance perspective view which shows the structure of the whole processing apparatus seen from the back side. It is a perspective view which shows the structure of a processing mechanism. It is the schematic which shows the structure around a workpiece surface variation detection mechanism. It is the schematic which shows the state around the workpiece surface variation detection mechanism at the time of height measurement. It is a schematic flowchart which shows the processing method of this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Interferometer 2 Light source 3 Optical system 5 Light receiving element 6 Sapphire substrate 7 Height measuring means 20 Processing mechanism 30 Work surface height variation detection mechanism 40 Control means W Workpiece

Claims (5)

A processing device that detects the height position of the workpiece surface and performs processing on the workpiece based on the detected height position,
A light source that does not pass through the workpiece to be processed and emits light having a wavelength of at least twice the height variation of the workpiece surface, and detects the light emitted from the light source as reference light And an optical system that splits the light into the work light and guides the detection light to the workpiece, and receives the light that interferes with the reference light and the detection light reflected from the work surface, and reflects the interference light on the work surface. A light receiving element for detecting intensity, an optical path length adjusting means for adjusting a difference in optical path length from the light source to the light receiving element between the reference light and the detection light, and a workpiece surface height at a predetermined position in the workpiece. A workpiece surface variation detection mechanism comprising: a height measuring means for measuring;
A machining mechanism for machining the workpiece;
Control means for controlling the machining mechanism based on the workpiece surface height variation detected by the workpiece surface variation detection mechanism;
A processing apparatus comprising: A processing method for detecting the height position of the workpiece surface and performing processing on the workpiece based on the detected height position,
Spect the light that does not pass through the workpiece to be processed and that has a wavelength of at least twice the height variation of the workpiece surface into reference light and detection light. A reflected interference light intensity detecting step for detecting the reflected interference light intensity on the work surface by receiving the light interfered with the reference light and the detection light reflected on the work surface while guiding to the work;
Difference in optical path length from the light source to the light receiving element between the reference light and the detection light so that the reflected interference light intensity detected in the reflected interference light intensity detection step is larger than a minimum value and smaller than a maximum value. An optical path length adjustment process for adjusting
A reference height measurement step of measuring the workpiece surface height at a predetermined location in the workpiece as a reference height;
The workpiece is controlled while controlling a machining mechanism based on the workpiece surface height variation calculated based on the reflected interference light intensity detected in the reflected interference light intensity detection step and the reference height measured in the reference height measurement step. A processing step for performing
The processing method characterized by including.   The processing method according to claim 2, wherein the processing step is performed using the processing mechanism that irradiates the workpiece with a laser beam.   The processing method according to claim 2, wherein the light used in the reflected interference light intensity detection step is light having a wavelength of three times or more the height variation of the workpiece surface. The workpiece to be processed is a sapphire substrate,
The processing method according to claim 2, wherein the light used in the reflected interference light intensity detection step is light having a wavelength of 10 μm or more.

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