Substrate thickness measurement device and substrate thickness measurement method

Abstract

To provide a substrate thickness measurement device and substrate thickness measurement method that can stably and accurately measure the thickness of a substrate regardless of the type of substrate being the measurement object.SOLUTION: A substrate thickness measurement device that is installed in a substrate polishing apparatus in which a substrate is brought into slide contact with a polishing cloth attached to a surface plate to polish the surface of the substrate, and that emits wavelength-variable laser light to the substrate during polishing to measure the thickness of the substrate on the basis of the interference between reflected light from the surface of the substrate and reflected light from the rear surface, includes: a wavelength-variable laser light source; an observation window through which the wavelength-variable laser light irradiated to the substrate and the reflected light from the substrate pass; a photodetector; and an analysis unit. The surface of the observation window is the surface vertically tilted relative to the optical axis of the wavelength-variable laser light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a substrate thickness measuring device and a substrate thickness measuring method. [Background technology]

[0002] As an example of a method for manufacturing a semiconductor wafer, a method for manufacturing a silicon wafer will be described. For example, first, a silicon single crystal ingot is grown by the Czochralski method (CZ method) or the like, and the obtained silicon single crystal ingot is sliced ​​to produce a silicon wafer. After that, the silicon wafer is subjected to each process such as chamfering, lapping, etching, etc., in order, and then a polishing process is performed to turn at least one main surface of the wafer into a mirror finish.

[0003] In the wafer polishing process, for example, when polishing both sides of silicon wafers, a double-sided polishing machine may be used. Such a double-sided polishing machine is usually a so-called four-way type double-sided polishing machine having a planetary gear structure in which a carrier for holding the wafer is disposed between a sun gear in the center and an internal gear on the periphery.

[0004] This four-way double-sided polishing machine inserts and holds silicon wafers in multiple carriers formed with wafer holding holes, and while supplying polishing slurry from above the held silicon wafers, presses upper and lower surface plates, with polishing cloths affixed to opposing surfaces, against the front and back surfaces of each wafer and rotates them in relative directions, while at the same time rotating and revolving the carriers around their axes using the sun gear and internal gear in the center, thereby polishing both sides of the silicon wafers simultaneously.

[0005] However, even if polishing is performed using the above-mentioned double-sided polishing machine, the polishing speed of the wafer varies with each polishing due to deterioration of the polishing cloth, processing tools such as the carrier, and materials. Therefore, if polishing is performed with a fixed polishing time, there is a problem that the thickness of the wafer after polishing varies due to the difference in the polishing speed. As a device for solving such a problem, a double-sided polishing machine that uses a laser light to measure the thickness of the wafer during polishing while polishing is known (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-034462 A [Patent Document 2] JP 2017-011099 A Summary of the Invention [Problem to be solved by the invention]

[0007] When a substrate is polished while measuring the thickness using a conventional substrate thickness measuring device, the signal to be measured may be hidden by noise, making accurate measurement impossible, depending on the substrate being polished. This phenomenon is prominent in silicon wafers, for example, with a large amount of doping impurities (low resistivity), and it is thought that the high absorption rate of laser light in the wafer causes the signal to be measured to be hidden by noise, reducing the accuracy of the measurement or making it impossible to measure at all.

[0008] The present invention has been made to solve the above problems, and aims to provide a substrate thickness measuring device and a substrate thickness measuring method that are capable of stably and accurately measuring the thickness of a substrate regardless of the type of substrate being measured. [Means for solving the problem]

[0009] The present invention has been made to achieve the above-mentioned object, and provides a substrate thickness measuring device that is installed in a substrate polishing apparatus that polishes a surface of a substrate by sliding the substrate against a polishing cloth attached to a surface plate, and that irradiates a tunable laser light onto the substrate during polishing to measure the thickness of the substrate based on the interference between the reflected light from the surface and the reflected light from the back surface of the substrate, the substrate thickness measuring device comprising a tunable laser light source, an observation window through which the tunable laser light irradiated onto the substrate and the reflected light from the substrate pass, a photodetector, and an analysis unit, and the surface of the observation window is a surface that is inclined from perpendicular to the optical axis of the tunable laser light.

[0010] Such a substrate thickness measuring device makes it possible to stably measure the thickness of a substrate with high accuracy, regardless of the type of substrate being measured.

[0011] In this case, when the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) 2 ×sinθ / n>R / 2 The substrate thickness measuring device can satisfy the above.

[0012] This suppresses interference that causes noise due to reflected light from the surface of the observation window facing the object to be measured, making it possible to measure the thickness of the substrate more stably and with higher accuracy.

[0013] In this case, the tunable laser light may have a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more.

[0014] This makes it possible to measure the thickness of the substrate more stably and with higher accuracy.

[0015] In this case, the observation window may be made of either sapphire or diamond.

[0016] These materials are stable and are less susceptible to damage from slurries and the like used in substrate polishing equipment, making it possible to measure the thickness of a substrate more stably and with high accuracy.

[0017] In this case, the substrate polishing apparatus may be a substrate polishing apparatus in which the substrate thickness measuring device is installed.

[0018] Such a substrate polishing apparatus is capable of polishing a substrate while stably and highly accurately measuring the thickness of the substrate, regardless of the type of substrate being measured, and is a substrate polishing apparatus that can increase the uniformity of the thickness of the substrates being polished from substrate to substrate.

[0019] The present invention also provides a substrate thickness measurement method that is installed in a substrate polishing apparatus that polishes the surface of a substrate by sliding the substrate against a polishing cloth attached to a surface plate, and irradiates a tunable laser beam onto the substrate during polishing to measure the thickness of the substrate based on the interference between reflected light from the surface and reflected light from the back surface of the substrate, in which an observation window having a surface inclined from a plane perpendicular to the optical axis of the tunable laser beam is installed in the optical path of the tunable laser beam, and the tunable laser beam is irradiated onto the substrate.

[0020] According to this substrate thickness measuring method, the thickness of the substrate can be measured stably and with high accuracy regardless of the type of substrate to be measured.

[0021] In this case, when the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) 2 ×sinθ / n>R / 2 The substrate thickness measuring method can be configured so that the inclination angle θ satisfies the above.

[0022] This makes it possible to suppress interference that causes noise due to reflected light from the surface of the observation window facing the object to be measured, thereby enabling the thickness of the substrate to be measured more stably and with higher accuracy.

[0023] In this case, the method for measuring the thickness of a substrate may use, as the variable wavelength laser light, a laser light having a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more.

[0024] This makes it possible to measure the thickness of the substrate more stably and with higher accuracy.

[0025] In this case, the method for measuring the thickness of the substrate may use an observation window made of either sapphire or diamond.

[0026] These materials are stable and are less susceptible to damage from slurries and the like used in substrate polishing equipment, and therefore the thickness of the substrate can be measured more stably and with high accuracy.

[0027] In this case, the method may be such that the substrate has a resistivity of 10 mΩ·cm or less, or the substrate is any one of Si, SiC, and GaN.

[0028] The substrate thickness measuring method according to the present invention is particularly effective for such substrates having low resistivity.

[0029] At this time, the method for producing a polished substrate can be characterized in that the substrate is polished while the thickness of the substrate is measured using the above-mentioned substrate thickness measuring method, thereby producing a polished substrate.

[0030] According to this method for manufacturing a polished substrate, it is possible to polish a substrate while measuring the thickness of the substrate stably and with high precision, regardless of the type of substrate being measured, and it is possible to improve the uniformity of the thickness of the substrate being polished from substrate to substrate. Effect of the Invention

[0031] As described above, the substrate thickness measuring device of the present invention makes it possible to measure the thickness of a substrate stably and with high accuracy, regardless of the type of substrate to be measured. The substrate polishing device of the present invention makes it possible to polish a substrate while measuring the thickness of the substrate stably and with high accuracy, regardless of the type of substrate to be measured, and makes it possible to increase the uniformity of the thickness of the substrate to be polished between substrates. The substrate thickness measuring method of the present invention makes it possible to measure the thickness of a substrate stably and with high accuracy, regardless of the type of substrate to be measured. The polished substrate manufacturing method of the present invention makes it possible to polish a substrate while measuring the thickness of the substrate stably and with high accuracy, regardless of the type of substrate to be measured, and makes it possible to increase the uniformity of the thickness of the substrate to be polished between substrates. [Brief description of the drawings]

[0032] [Figure 1] 1 shows a substrate thickness measurement device according to the present invention; [Diagram 2] A more specific configuration of the substrate thickness measuring device is shown. [Diagram 3] 3 shows the vicinity of an observation window in the substrate thickness measuring device according to the present invention. [Figure 4] 5A and 5B are diagrams illustrating the relationship between the inclination of an observation window and the optical path of laser light according to the present invention. [Diagram 5] 4 shows the measurement signal when using a substrate thickness measuring device according to the present invention (with an observation window surface tilt of 1.6°). [Figure 6] 4 shows the measurement signal when a substrate thickness measuring device according to a conventional example (with the observation window surface inclined at 0°). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention will be described in detail below, but the present invention is not limited thereto.

[0034] As described above, there has been a demand for a substrate thickness measuring device and a substrate thickness measuring method that are capable of stably and accurately measuring the thickness of a substrate regardless of the type of substrate being measured.

[0035] As a result of intensive research into the above-mentioned problems, the inventors have discovered that a substrate thickness measuring device is installed in a substrate polishing apparatus which polishes the surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, and which irradiates a tunable laser light onto the substrate during polishing to measure the thickness of the substrate based on the interference between the reflected light from the front surface and the reflected light from the back surface of the substrate, the substrate thickness measuring device comprising a tunable laser light source, an observation window through which the tunable laser light irradiated onto the substrate and the reflected light from the substrate pass, a photodetector, and an analysis unit, and the surface of the observation window is a surface that is inclined from perpendicular to the optical axis of the tunable laser light, thereby making it possible to stably measure the thickness of a substrate with high accuracy regardless of the type of substrate to be measured, and have completed the present invention.

[0036] The inventors have also discovered that a substrate thickness measurement method in which a substrate is installed in a substrate polishing apparatus that polishes the surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, and a tunable laser light is irradiated onto the substrate during polishing to measure the thickness of the substrate based on the interference between the light reflected from the surface and the light reflected from the back surface of the substrate, in which an observation window having a surface inclined from a plane perpendicular to the optical axis of the tunable laser light is installed in the optical path of the tunable laser light and the tunable laser light is irradiated onto the substrate, makes it possible to stably measure the thickness of a substrate with high accuracy regardless of the type of substrate to be measured, and completed the present invention.

[0037] The following description will be given with reference to the drawings.

[0038] [Substrate polishing equipment] First, a substrate polishing apparatus according to the present invention will be described. The substrate polishing apparatus will be described below using a double-sided polishing apparatus as an example, but the substrate polishing apparatus according to the present invention is not limited to a double-sided polishing apparatus. Any other type of substrate polishing apparatus may be used as long as it polishes the surface of the substrate by bringing the substrate into sliding contact with an abrasive cloth attached to a surface plate.

[0039] As shown in Fig. 1, a substrate polishing apparatus (double-sided polishing apparatus) 100 is equipped with a substrate thickness measuring device 10 (described in detail later) according to the present invention for measuring the thickness of a substrate W during polishing. The substrate polishing apparatus (double-sided polishing apparatus) 100 may be equipped with a lower surface plate 12 having a flat polishing upper surface that rotates to hold the substrate W, an upper surface plate 11 that is disposed opposite the lower surface plate 12 and has a flat polishing lower surface that rotates, and a carrier 13 having a substrate holding hole for holding the substrate W. In addition, a hole 14 for installing an observation window for measuring the substrate thickness during polishing by the substrate thickness measuring device 10, a polishing slurry supply port 15, etc. are provided on the side of the upper surface plate 11.

[0040] By providing a plurality of holes 14 in the upper surface plate 11 or the lower surface plate 12, which are used to install observation windows for measuring the thickness of the substrate, the frequency of thickness measurement can be increased. This is particularly suitable when a plurality of substrates are polished simultaneously in a batch manner, and this can improve the measurement accuracy. The holes 14 can be provided at equal intervals around the periphery of the upper surface plate 12. In this way, if the upper surface plate has a plurality of holes provided at equal intervals, it is possible to prevent the polishing slurry from leaking from each of the plurality of measurement holes. This makes it easy to perform maintenance of the surface plate. It is also possible to prevent the possibility of a problem occurring in measuring the thickness of the substrate. It is also convenient to measure the thickness of all substrates in, for example, a four-way double-sided polishing apparatus.

[0041] Furthermore, when at least one of the polishing load, the rotation speed of the upper platen 11, and the rotation speed of the lower platen 12 is changed during polishing, the upper platen 11 and the lower platen 12 can be controlled by providing a polishing machine control unit 17 as shown in the figure to the double-sided polishing apparatus 10. This makes it possible to change at least one of the polishing load, the rotation speed of the upper platen 11, and the rotation speed of the lower platen 12.

[0042] This makes it possible to appropriately respond to changes in polishing conditions due to deterioration of the polishing cloth, processing jigs such as carriers, and materials, which are determined from the measured substrate thickness, during polishing of the substrate W. Therefore, substrates with extremely high surface flatness after polishing can be stably obtained while reducing variations between substrates.

[0043] [Substrate thickness measuring device] The substrate thickness measuring device 10 includes a tunable laser light source 16c, an observation window 20 through which the tunable laser light L irradiated to the substrate W and the reflected light from the substrate W pass, a photodetector 16b, and an analysis unit 16d that calculates the wafer thickness from the detected laser light. The observation window is necessary to prevent slurry, water, and water vapor from rising from the hole 14 (observation hole), and seals the hole 14. As shown in a more specific configuration in FIG. 2, the substrate thickness measuring device 10 can include an optical unit 16a including an optical system such as an attenuator, an optical circulator, and a focusing system in addition to the tunable laser light source, the observation window, the photodetector, and the analysis unit. The substrate thickness measuring device 10 uses a tunable laser light source 16c with a wavelength optically transmitted through the substrate, and can analyze the interference between the reflected light from the substrate surface reflected by the substrate surface and the reflected light from the substrate back surface reflected by the laser light incident on the substrate W. For example, the thickness of the substrate during polishing can be evaluated with an accuracy of the order of several nm to several tens of μm.

[0044] Fig. 3 shows the vicinity of the observation window in the substrate thickness measuring device 10 according to the present invention. As shown in Fig. 3, the surface of the observation window 20 in the substrate thickness measuring device 10 according to the present invention is a surface that is inclined from the perpendicular to the optical axis of the wavelength-tunable laser light L. By configuring the observation window 20 in this manner, it is possible to reduce interference that causes noise due to reflected light L1 and L2 from the two surfaces of the observation window 20 (the wavelength-tunable laser light source 16c side and the substrate W side), thereby reducing noise and increasing the SNR (signal to noise ratio).

[0045] The tunable laser light L that passes through the observation window 20 passes through the slurry, rinse, etc. (slurry, etc. 30) and is reflected by the front and back surfaces of the substrate W, and the reflected light returns along the path of the tunable laser light L. This reflected light is detected by the photodetector 16b and spectrally analyzed by the analysis unit 16d. As a result, the substrate thickness measuring device 10 according to the present invention can strengthen only the target signal from among weak signals, making it possible to stably measure the thickness of a substrate with high accuracy regardless of the type of substrate being measured.

[0046] The shape of the observation window is not particularly limited, and may be a cylinder, an elliptical cylinder, a square cylinder, or the like, with the upper and lower surfaces beveled, but a cylinder is preferred. Also, a cylinder or the like may be installed by tilting it without tilting the upper and lower surfaces. The means and method for installing the observation window 20 in the hole 14 are not particularly limited, but as shown in FIG. 3, a cylinder 21 can be used to hold the observation window 20 inside, and the cylinder 21 can be installed in the hole 14.

[0047] By using a variable wavelength laser device (light source), even if the thickness of the substrate to be polished changes significantly, the wavelength of the incident laser light can be changed to accommodate the change, and there is no need to change the light source itself. This simplifies the setup process and reduces costs.

[0048] The tunable laser light L is not particularly limited, but may have a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more. If the tunable laser light has a central wavelength of 1100-1400 nm, it is possible to suppress a decrease in the intensity of the reflected laser light caused by partial absorption of the measurement laser light by the substrate or polishing slurry, and it is possible to measure the thickness of the substrate with high accuracy.

[0049] The surface of the observation window 20 may be a surface inclined from the perpendicular to the optical axis of the wavelength-tunable laser light, and there is no particular limitation on the angle at which the surface of the observation window 20 is inclined from the perpendicular to the optical axis of the wavelength-tunable laser light. The lower limit of the inclination angle is given by: d×(cosθ) 2 ×sinθ / n>R / 2 It is preferable that the above formula is satisfied.

[0050] The relationship between the inclination of the observation window and the optical path of the laser light according to the present invention will be described with reference to Fig. 4. If the inclination angle of the observation window surface from the plane perpendicular to the optical axis of the tunable laser light L is θ (°), the incidence angle of the tunable laser light relative to the perpendicular direction of the surface of the observation window 20 is also θ (°). To avoid complicating the illustration, in Fig. 4, θ (°) is added to the incidence angle of the tunable laser light relative to the perpendicular direction of the surface of the observation window 20. Hereinafter, these may be simply referred to as "inclination angle θ".

[0051] As shown in Figure 4, if the length of the observation window in the direction of incidence of the tunable laser light is d (mm), the inclination angle of the observation window surface from the plane perpendicular to the optical axis of the tunable laser light L is θ (°), the refractive index of the observation window is n, the spot diameter of the tunable laser light is R (mm), and the angle (refractive angle) of the laser light in the observation window with respect to the axis perpendicular to the observation window surface is α (°), reflected light L2 reflected by the surface of the observation window facing the object to be measured will be reflected and returned to a position shifted by X (mm). In this case, X>R / 2 That is, d×(cosθ) 2 ×sinθ / n>R / 2 In this case, the reflected light L2 reflected from the surface of the observation window facing the object to be measured does not return to the photodetector, so that interference that causes noise due to the reflected light from the surface of the observation window facing the object to be measured can be suppressed, making it possible to measure the thickness of the substrate more stably and with high accuracy. The spot diameter of the laser light is preferably a diameter that includes 95% or more of the laser light energy. The deviation Y (mm) of the optical path of the tunable laser light L itself after passing through the observation window 20 is Y = d × cosθ × sin(θ-α) / cosα It is.

[0052] Although the upper limit of the inclination angle θ (°) of the surface of the observation window 20 is not particularly limited and can be set according to the size of the observation window and the hole in which the observation window is installed, as the inclination angle θ (°) is increased, the reflected light L2 reflected by the surface of the observation window facing the object to be measured may strike the wall surface of the holding means for the observation window (cylinder 21), which may cause noise. Therefore, it is preferable to set the upper limit to an inclination angle at which the reflected light L2 from the observation window does not strike the wall surface of the holding means for the observation window (cylinder 21), and this can be set taking into consideration the size of the observation window, etc.

[0053] Specifically, referring to FIG. 4, when the observation window is cylindrical and its diameter is φ, d×cosθ×sin(θ-α) / cosα + R / 2 < φ / 2 It is possible to make the observation window satisfy the following relationship. If the observation window is not cylindrical, the minimum value of the size of the observation window surface (the minor axis if the surface is elliptical, or the length of the shortest side if the surface is rectangular) can be used instead of the above diameter φ. The angle can be selected from the range that satisfies this relationship, and stable measurement can be expected when the observation window has a θ≦10°.

[0054] The material of the observation window 20 is not particularly limited, but it is preferable that the observation window 20 is made of either sapphire or diamond. These materials are stable and are less susceptible to damage from slurries used in substrate polishing devices, and therefore the substrate thickness measuring device can measure the thickness of the substrate more stably and with high accuracy.

[0055] A substrate polishing apparatus equipped with the substrate thickness measuring device according to the present invention described above is capable of polishing a substrate while stably measuring the thickness of the substrate with high accuracy, regardless of the type of substrate being measured, and is a substrate polishing apparatus that can increase the uniformity of the thickness of the substrates being polished from substrate to substrate.

[0056] Next, a method for measuring a substrate thickness and a method for producing a polished substrate according to the present invention will be described below.

[0057] [Board thickness measurement method] The substrate thickness measuring method according to the present invention is a method for measuring the thickness of a substrate by irradiating a tunable laser beam onto a substrate polishing apparatus that polishes the substrate surface by sliding the substrate against an abrasive cloth attached to a surface plate, and measuring the thickness of the substrate based on the interference between the reflected light from the substrate surface and the reflected light from the substrate back surface. An observation window having a surface inclined from a plane perpendicular to the optical axis of the tunable laser beam is provided in the optical path of the tunable laser beam, and the tunable laser beam is irradiated onto the substrate to measure the substrate thickness. Specifically, the substrate thickness measuring apparatus 10 according to the present invention as described with reference to Figs. 1 and 3 can be used to stably and accurately measure the substrate thickness regardless of the type of substrate.

[0058] When an observation window 20 having a surface inclined from a plane perpendicular to the optical axis of the tunable laser light L is provided and the tunable laser light L is irradiated onto the substrate W, the reflected light L1 from the tunable laser light source 16c side at the observation window 20 and the reflected light L2 from the substrate W side do not return to the path of the tunable laser light L, so that it is possible to reduce interference that causes noise. The tunable laser light L that has passed through the observation window 20 passes through the slurry or the like 30, is reflected by the front and back surfaces of the substrate W, and returns along the path of the tunable laser light L. By analyzing these lights, it is possible to stably measure the thickness of the substrate W to be measured with high accuracy, regardless of the type of the substrate W.

[0059] When the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) 2 ×sinθ / n>R / 2 It is more preferable to install the observation window so that the inclination angle θ satisfies the above. Since it is possible to suppress interference that causes noise due to reflected light L2 from the surface of the observation window facing the object to be measured, it is possible to measure the thickness of the substrate more stably and with high accuracy. It is preferable that the spot diameter of the laser light is a diameter that includes 95% or more of the laser light energy.

[0060] It is preferable to use, as the variable wavelength laser light L, one having a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more, since this allows the thickness of the substrate to be measured more stably and with higher accuracy.

[0061] The observation window is preferably made of either sapphire or diamond, which are stable materials that are less damaged by slurries used in substrate polishing equipment, and therefore the thickness of the substrate can be measured more stably and with higher accuracy.

[0062] The substrate to be measured (polished) may have a resistivity of 10 mΩ·cm or less. The substrate thickness measuring method according to the present invention is capable of stably and accurately measuring the thickness of a substrate having a low resistivity, particularly one with a high laser light absorption rate. However, it goes without saying that more accurate measurements can be made for substrates having a high resistivity, which does not have a high laser light absorption rate. The substrate to be measured (polished) may be any of Si, SiC, and GaN. The substrate thickness measuring method according to the present invention is particularly effective for such substrates.

[0063] [Method of manufacturing polished substrate] A polished substrate can be manufactured by polishing a substrate while measuring the thickness of the substrate using the substrate thickness measuring method according to the present invention.

[0064] For example, first, the substrate W to be polished is set in the substrate holding hole of the carrier 13. At this time, multiple substrates W can be set. Then, the substrate W is sandwiched between the lower polishing surface of the upper surface plate 11, the upper polishing surface of the lower surface plate 12, and the carrier 13, and polishing slurry is supplied from the polishing slurry supply port 15. Polishing is started while rotating the upper surface plate 11 and the lower surface plate 12 in a horizontal plane.

[0065] At this time, polishing is performed while measuring the thickness of the substrate W using a substrate thickness measuring device 10 through an observation window 20 provided in a hole 14 provided in the upper surface plate 11 or the lower surface plate 12 .

[0066] By polishing the substrate in this manner, the state of the polished surface of the substrate can be known without interrupting the polishing, and for example, the thickness of the substrate during polishing can be known at any time, so that it is possible to determine whether the target thickness of the substrate has been reached while polishing. Therefore, it is possible to determine whether the target thickness has been reached without interrupting the polishing, and the time required for polishing can be shortened. In addition, since the substrate can be brought to the target thickness without fixing the polishing time, there is no risk of over-polishing or under-polishing, and it is possible to suppress deterioration of flatness.

[0067] Furthermore, in the method for manufacturing a polished substrate of the present invention, it is possible to polish a substrate while measuring the thickness of the substrate stably and with high precision, regardless of the type of substrate being measured, and it is possible to increase the uniformity of the thickness of the substrate being polished from substrate to substrate. EXAMPLES

[0068] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0069] (Example) Using the polishing apparatus shown in Figure 1, the surface of the observation window was inclined 1.6° from perpendicular to the optical axis of the wavelength-tunable laser light (tilt angle 1.6°) as shown in Figure 3 and placed in the hole in the upper surface plate. A silicon wafer (diameter 300 mm, resistivity 8.45 mΩ·cm) was polished on both sides while measuring its thickness, and a signal during thickness measurement was obtained. The central wavelength of the tunable laser was 1305 nm, and the tunable wavelength range was 60 nm. In this example, the spot diameter R of the laser light was set under the following conditions: d×(cosθ) 2 ×sinθ / n>R / 2 However, for a substrate with an even lower resistivity, such as 5 mΩ·cm or less, it is preferable that the spot diameter R of the laser light is set to a diameter that includes 97.5% or more of the laser energy.

[0070] (Comparative Example) A signal during thickness measurement was obtained in the same manner as in the Example, except that the surface of the observation window was placed in the hole in the upper platen without being inclined from perpendicular to the optical axis of the wavelength-variable laser light (tilt angle 0°).

[0071] FIG. 5 shows the signals obtained in the Example, and FIG. 6 shows the signals obtained in the Comparative Example. In both FIG. 5 and FIG. 6, the region of 700 to 800 μm in wafer thickness corresponds to the thickness of the polished silicon wafer. In the Example, since the noise was suppressed, a peak appeared in the portion corresponding to the thickness of the silicon wafer as shown in FIG. 5. On the other hand, in the Comparative Example, the peak in the portion corresponding to the thickness of the silicon wafer was hidden by the noise as shown in FIG. 6. According to the Example, the noise was reduced (SNR was improved), and the substrate thickness could be measured with high accuracy.

[0072] The present specification includes the following aspects. [1]: A substrate thickness measuring device that is installed in a substrate polishing apparatus that polishes a surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, and that irradiates a variable wavelength laser light onto the substrate during polishing to measure the thickness of the substrate based on interference between reflected light from the surface and reflected light from the back surface of the substrate, a tunable laser light source, an observation window through which the tunable laser light to be irradiated onto the substrate and the reflected light from the substrate pass, a photodetector, and an analysis unit; a surface of the observation window that is inclined from the perpendicular to the optical axis of the tunable laser light; [2]: the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) 2 ×sinθ / n>R / 2 The substrate thickness measuring device according to the above item [1] satisfies the above requirements. [3]: The substrate thickness measuring device according to [1] or [2] above, wherein the tunable laser light has a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more. [4]: The substrate thickness measuring device according to [1], [2] or [3] above, wherein the observation window is made of either sapphire or diamond. [5]: A substrate polishing apparatus equipped with the substrate thickness measuring device according to [1], [2], [3] or [4] above. [6]: A substrate thickness measurement method that is installed in a substrate polishing apparatus that polishes the surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, irradiates a tunable laser beam onto the substrate during polishing, and measures the thickness of the substrate based on the interference between the reflected light from the surface and the reflected light from the back surface of the substrate, in which an observation window having a surface inclined from a plane perpendicular to the optical axis of the tunable laser beam is installed in the optical path of the tunable laser beam, and the tunable laser beam is irradiated onto the substrate. [7]: The length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) 2 ×sinθ / n>R / 2 The substrate thickness measurement method described above in [6], in which the inclination angle θ satisfies the following. [8]: The method for measuring a substrate thickness according to [6] or [7] above, wherein the variable wavelength laser light has a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more. [9]: The method for measuring a substrate thickness according to [6], [7] or [8] above, wherein the observation window is made of either sapphire or diamond.

[10] : The method for measuring a substrate thickness according to [6], [7], [8] or [9] above, wherein the substrate has a resistivity of 10 mΩ·cm or less.

[11] : The method for measuring a substrate thickness according to [6], [7], [8], [9] or

[10] , wherein the substrate is any one of Si, SiC, and GaN.

[12] : A method for producing a polished substrate, comprising polishing a substrate while measuring the thickness of the substrate using the substrate thickness measurement method described above in [6], [7], [8], [9],

[10] or

[11] to produce a polished substrate.

[0073] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0074] 10...substrate thickness measuring device, 11...upper surface plate, 12...lower surface plate, 13...carrier, 14: hole; 15: polishing slurry supply port; 16a: optical unit; 16b...photodetector; 16c...tunable laser light source; 16d...analysis unit; 17: Polishing machine control unit; 20: Observation window; 21: Cylinder; 30: Slurry, etc.; 100...Substrate polishing apparatus (double-sided polishing apparatus). L: tunable laser light; L1, L2: reflected light from the observation window; W: substrate.

Claims

1. 1. A substrate thickness measuring device that is installed in a substrate polishing apparatus that polishes a front surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, and that irradiates a wavelength-variable laser light onto the substrate during polishing to measure a thickness of the substrate based on interference between reflected light from the front surface and reflected light from the back surface of the substrate, a tunable laser light source, an observation window through which the tunable laser light to be irradiated onto the substrate and the reflected light from the substrate pass, a photodetector, and an analysis unit; a surface of the observation window that is inclined from the perpendicular to the optical axis of the wavelength-variable laser light;

2. When the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) ２ ×sinθ / n>R / 2 2. The substrate thickness measuring device according to claim 1, wherein the following is satisfied:

3. 2. The substrate thickness measuring device according to claim 1, wherein the tunable laser light has a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more.

4. 2. The substrate thickness measuring device according to claim 1, wherein said observation window is made of either sapphire or diamond.

5. 5. A substrate polishing apparatus comprising the substrate thickness measuring device according to claim 1.

6. A substrate thickness measurement method for measuring a thickness of a substrate, the method being installed in a substrate polishing apparatus that polishes a surface of a substrate by sliding the substrate against an abrasive cloth attached to a surface plate, the method irradiating a wavelength-variable laser light onto the substrate during polishing, and measuring a thickness of the substrate based on interference between reflected light from the surface and reflected light from the back surface of the substrate, the method comprising: A method for measuring a substrate thickness, comprising: providing an observation window having a surface inclined from a plane perpendicular to the optical axis of the tunable laser light in an optical path of the tunable laser light; and irradiating the tunable laser light onto the substrate.

7. When the length of the observation window in the incident direction of the wavelength-tunable laser light is d (mm), the inclination angle of the surface of the observation window from a plane perpendicular to the optical axis of the wavelength-tunable laser light is θ (°), the refractive index of the observation window is n, and the spot diameter of the wavelength-tunable laser light is R (mm), d×(cosθ) ２ ×sinθ / n>R / 2 7. The method for measuring a thickness of a substrate according to claim 6, wherein the inclination angle θ satisfies the following:

8. 7. The method for measuring a substrate thickness according to claim 6, wherein the variable wavelength laser light has a central wavelength of 1100-1400 nm and a variable wavelength width of 50 nm or more.

9. 7. The method for measuring a thickness of a substrate according to claim 6, wherein the observation window is made of either sapphire or diamond.

10. 7. The method for measuring a thickness of a substrate according to claim 6, wherein the resistivity of the substrate is 10 mΩ·cm or less.

11. 7. The method of measuring a thickness of a substrate according to claim 6, wherein the substrate is made of any one of Si, SiC, and GaN.

12. 12. A method for producing a polished substrate, comprising polishing a substrate while measuring the thickness of the substrate using the method for measuring substrate thickness according to claim 6, thereby producing a polished substrate.

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