Measurement method and measurement system

Abstract

Provided is a measurement method using a quantum optical system configured to cause quantum interference between a plurality of physical processes in which quantum entangled photon pairs of signal photons and idler photons are generated, the method comprising executing object part quantum measurement for acquiring a quantum interference signal for a measurement object part included in a sample and having unknown reflectance at the wavelength of the idler photons, and calculating the reflectance of the measurement object part from the quantum interference signal acquired by the object part quantum measurement, the object part quantum measurement including sweeping the optical path length difference between the optical path length of the signal photons and the optical path length of the idler photons by adjusting the optical path length of the signal photons, or the optical path length of the idler photons when the idler photons are reflected by the measurement object part.

Description

Measurement Method and Measurement System

[0001] The present disclosure relates to a measurement method and a measurement system.

[0002] Patent Document 1 discloses a method for measuring quantum interference of signal light by absorbing a part of idler light passing through a sample as infrared quantum absorption spectroscopy.

[0003] Japanese Patent Application Laid-Open No. 2024-013431

[0004] The technology according to the present disclosure appropriately measures the reflection characteristics of a sample.

[0005] One aspect of the present disclosure is a measurement method using a quantum optical system configured to cause quantum interference among a plurality of physical processes in which entangled photon pairs of signal photons and idler photons are generated. The method includes performing target part quantum measurement to obtain a quantum interference signal for a measurement target part included in a sample, the reflectance of which at the wavelength of the idler photons is unknown, and calculating the reflectance of the measurement target part from the quantum interference signal obtained in the target part quantum measurement. The target part quantum measurement includes sweeping an optical path length difference between the optical path length of the signal photons and the optical path length of the idler photons by adjusting the optical path length of the signal photons or the optical path length of the idler photons when the idler photons are reflected by the measurement target part.

[0006] According to the present disclosure, the reflection characteristics of a sample can be appropriately measured.

[0007] It is a plan view showing an outline of a configuration example of a measurement system. It is a cross-sectional schematic view showing an outline of a configuration example of a wafer as a sample. It is a flowchart showing an outline of a configuration example of a measurement method. It is a flowchart showing an outline of a configuration example of reference part quantum measurement. It is a flowchart showing an outline of a configuration example of target part quantum measurement. It is an explanatory diagram showing an example of a state of a quantum optical system related to reference part quantum measurement. It is an explanatory diagram showing an example of a state of a quantum optical system related to target part quantum measurement. It is a cross-sectional schematic view showing an outline of a configuration example of a polymer wafer as a sample according to a modification. It is an explanatory diagram showing an example of a state of a quantum optical system of reference part quantum measurement according to a modification. It is an explanatory diagram showing an example of a state of a quantum optical system of target part quantum measurement according to a modification.

[0008] The configuration of the measurement system according to this embodiment will be described below with reference to the drawings. In this specification and the drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant explanations will be omitted.

[0009] <Measurement System> Figure 1 is a schematic diagram showing the configuration of the measurement system 1 according to this embodiment. The measurement system 1 is configured to calculate the reflectance of a wafer W, which is an example of a sample, at a measurement target Wt, which will be described later. The measurement system 1 comprises a quantum optical system 10, a photodetector 11, and a control unit 20.

[0010] The quantum optical system 10 is configured to generate quantum interference between multiple physical processes that produce entangled photon pairs from pump light to signal light and idler light. In the figure, the pump light is denoted by P. The optical path of the signal light (light consisting of signal photons) is denoted by S, and the optical path of the idler light (light consisting of idler photons) is denoted by I. The wavelength of the pump light is denoted by λp, the optical path length and wavelength of the signal photons are denoted by Ls and λs, and the optical path length and wavelength of the idler photons are denoted by Li and λi. Note that in Figure 1, the pump light, signal light, and idler light are shown separately as white outlines or shaded with different densities, and the widths of each optical path are also shown differently. These are for illustrative purposes only and do not represent their characteristics.

[0011] The quantum optical system 10 includes an excitation light source 101, a fixed mirror 103, a first lens 104, a first dichroic mirror 105, a nonlinear optical crystal 110, a rotating stage 111, a second dichroic mirror 121, a second lens 122, a movable mirror 123, a mirror stage 124, a third lens 131, a wafer stage 132, a fourth lens 141, a power meter 151, a pinhole 152, and a polarizing beam splitter 153.

[0012] The excitation light source 101 emits pump light to excite the nonlinear optical crystal 110. The pump light is a continuous wave (CW) laser light contained in the visible range. In one embodiment, the excitation light source 101 is a semiconductor laser that emits green laser light with a wavelength of 532 nm.

[0013] The power meter 151, the pinhole 152, and the polarizing beam splitter 153 are used in the angle alignment described later. The position of the pinhole 152 is adjusted so that the light intensity is maximized when the pump light (dotted line in Figure 1) reflected by the movable mirror 123 is measured by the optical power meter 151. During the angle alignment of the wafer W described later, the light intensity of the pump light reflected from the wafer W and transmitted through the pinhole 152 is detected by the optical power meter 151, and the angle is aligned so that this intensity is maximized. The detection result of the reflected light detected by the optical power meter 151 is output to the control unit 20. Based on the detection result, the control unit 20 determines whether the angle alignment of the wafer W is appropriate. Details of the determination of the angle alignment of the wafer W will be described later. Note that these configurations used for angle alignment are merely examples and are not limited to such examples.

[0014] The fixed mirror 103 is positioned between the excitation light source 101 and the first lens 104. The angle and other parameters of the fixed mirror 103 are adjusted so that it reflects the pump light from the excitation light source 101 and guides it to the first lens 104.

[0015] The first lens 104 is positioned between the fixed mirror 103 and the first dichroic mirror 105. The first lens 104 focuses the pump light from the excitation light source 101 and is adjusted so that the focused pump light is focused on the nonlinear optical crystal 110.

[0016] The first dichroic mirror 105 is positioned between the first lens 104 and the nonlinear optical crystal 110. The first dichroic mirror 105 transmits signal light while reflecting pump light. Pump light from the excitation light source 101 is reflected by the first dichroic mirror 105 and irradiates the nonlinear optical crystal 110.

[0017] The nonlinear optical crystal 110 generates signal light and idler light from pump light focused by the first lens 104. More specifically, the nonlinear optical crystal 110 generates photon pairs of signal photons and idler photons by spontaneous parametric down-conversion (SPDC) of the pump light. In one embodiment, the nonlinear optical crystal 110 is a type I lithium niobate (MgO:LiNbO3) crystal with a thickness of 0.5 mm. In this case, the signal light is visible light and the idler light is infrared light (near-infrared or mid-infrared light). Furthermore, the nonlinear optical crystal 110 is not limited to LiNbO3; for example, lithium tantalate (LiTaO3), silver thiogallate (AgGaS2), gallium phosphide (GaP), gallium arsenide (GaAs), zinc selenide (ZnSe), etc., can also be used.

[0018] The nonlinear optical crystal 110 is an example of a "nonlinear optical element" according to this disclosure. The "nonlinear optical element" according to this disclosure is not limited to a nonlinear optical crystal, and may be, for example, a ring resonator, or an optical waveguide formed of silicon (Si) and / or silicon nitride (SiN). Furthermore, spontaneous four-wave mixing (SFWM) may be used instead of SPDC of pump light to generate entangled photon pairs. When a ring resonator, optical waveguide, etc. are used as a "nonlinear optical element", SFWM can be suitably used.

[0019] The rotating stage 111 is configured to rotate the nonlinear optical crystal 110 with respect to the pump light in accordance with a control command from the control unit 20. The rotating stage 111 is an example of a "wavelength sweep unit" according to this disclosure. The rotation angle of the nonlinear optical crystal 110 with respect to the perpendicular incidence direction of the pump light is referred to as the "crystal rotation angle θ". The crystal rotation angle θ is an example of a "control parameter" according to this disclosure. The rotating stage 111 is configured to change the phase matching condition of the SPDC (see equation (1) below) by gradually changing the crystal rotation angle θ within a predetermined range (hereinafter referred to as "sweeping" the crystal rotation angle θ).

[0020] The second dichroic mirror 121 is positioned between the nonlinear optical crystal 110 and the movable mirror 123, and between the nonlinear optical crystal 110 and the wafer stage 132. In this embodiment, the second dichroic mirror 121 transmits visible light and reflects infrared light. Signal light in the visible range passes through the second dichroic mirror 121 along with the pump light and proceeds to the movable mirror 123. On the other hand, idler light in the infrared range is reflected by the second dichroic mirror 121 and proceeds to the wafer stage 132. Depending on the arrangement of the movable mirror 123 and the wafer stage 132, the second dichroic mirror 121 may transmit infrared light and reflect visible light.

[0021] The second lens 122 is positioned between the second dichroic mirror 121 and the movable mirror 123. The second lens 122 makes the pump light and signal light parallel.

[0022] The movable mirror 123 is, for example, a plane mirror, and reflects the pump light and signal light that have passed through the second dichroic mirror 121. The reflected pump light and signal light are focused by the second lens 122, pass through the second dichroic mirror 121, and return to the nonlinear optical crystal 110. The pump light passes through the nonlinear optical crystal 110 and is reflected by the first dichroic mirror 105. On the other hand, the signal light passes through the nonlinear optical crystal 110 and also passes through the first dichroic mirror 105.

[0023] The mirror stage 124 is configured to move the movable mirror 123 along the direction of propagation of the pump light and signal light according to control commands from the control unit 20. The mirror stage 124 according to this embodiment includes a motor drive mechanism 124a that is mechanically displaced according to control commands from the control unit 20, for example. The mirror stage 124 according to one embodiment includes a piezoelectric element (piezo element) that is displaced according to an applied voltage as a control command from the control unit 20, for example.

[0024] Hereinafter, the optical path length difference between the signal optical path length Ls and the idler optical path length Li is represented by ΔL. The mirror stage 124 is configured to change the optical path length difference ΔL by sweeping the position of the movable mirror 123 in the direction of propagation of the pump light and the signal light. The movable mirror 123 and the mirror stage 124 according to this embodiment constitute the "optical path length difference sweeping unit" according to this disclosure. The sweeping of the position of the movable mirror 123 is performed within a predetermined range that includes the position where the signal optical path length Ls and the idler optical path length Li coincide, i.e., ΔL.

[0025] The third lens 131 is positioned between the second dichroic mirror 121 and the wafer stage 132. The third lens 131 converts the idler light reflected by the second dichroic mirror 121 into parallel light.

[0026] The wafer stage 132 includes a mounting surface 132a on which a wafer W is placed. The wafer stage 132 also includes an angle adjustment mechanism 132b configured to adjust the angle (hereinafter referred to as "mounting surface angle φ") that the mounting surface 132a makes with respect to the direction of travel of idler light. The angle adjustment mechanism 132b includes a motor drive mechanism that is mechanically displaced according to a control command from the control unit 20, for example. In one embodiment, the wafer stage 132 also includes a horizontal position adjustment mechanism (not shown) configured to move the relative horizontal position of the mounting surface 132a with respect to the incident position of idler light. The horizontal position adjustment mechanism includes a motor drive mechanism that is mechanically displaced according to a control command from the control unit 20, for example.

[0027] In the measurement method described later, a wafer W is placed on the wafer stage 132. At least a portion of the idler light that travels from the third lens 131 to the mounting surface 132a of the wafer stage 132 is reflected by the wafer W on the mounting surface 132a. The idler light reflected by the wafer W is focused by the third lens 131, reflected by the second dichroic mirror 121, and returns to the nonlinear optical crystal 110.

[0028] The fourth lens 141 is positioned between the first dichroic mirror 105 and the photodetector 11. The fourth lens 141 collects the signal light that has passed through the first dichroic mirror 105 and guides the collected signal light to the photodetector 11.

[0029] In one embodiment, the quantum optical system 10 includes a long-pass filter, an iris, and a band-pass filter (not shown) between the fourth lens 141 and the photodetector 11. The long-pass filter, iris, and band-pass filter remove pump light (and background light) that is not reflected by the first dichroic mirror 105 and instead travels toward the photodetector 11. The band-pass filter may be positioned on a translational stage (not shown) for adjusting the position of the band-pass filter.

[0030] In the quantum optical system 10 shown in Figure 1, a quantum interferometer similar to a Michelson interferometer is employed. However, the quantum optical system according to this disclosure may have a configuration similar to a Mach-Zehnder interferometer, which includes a plurality of nonlinear optical elements.

[0031] One embodiment of the photodetector 11 is, for example, a silicon-based photodetector that has high sensitivity in the visible range (and a part of the near-infrared range). One embodiment of the photodetector 11 includes a single-pixel type photodetector (not shown). Specifically, the photodetector 11 includes a photodiode such as a PIN photodiode or an APD (avalanche photodiode). The photodetector 11 may also include a phototube, a photomultiplier tube (PMT), or a superconducting single photon detector (SSPD). However, a configuration in which the photodetector 11 includes a multi-pixel type photodetector is not excluded. The photodetector 11 may be optically coupled to an optical fiber (multimode fiber) for guiding signal light. The photodetector 11 detects signal light and outputs the detection signal to the control unit 20. The intensity of the signal light detection signal is directly proportional to the number of signal photons detected by the photodetector 11.

[0032] The control unit 20 processes computer-executable instructions that cause the measurement system 1 to perform the various processes described herein. The control unit 20 may be configured to control each element of the measurement system 1 to perform the various processes described herein. Control of each element of the measurement system 1 includes, for example, control of control parameters in the excitation light source 101, the rotating stage 111, the mirror stage 124, and the wafer stage 132. The control unit 20 also performs calculation processing to calculate the reflectance in the measurement target Wt based on the detection signal of signal light from the photodetector 11 (a quantum interference signal described later). In one embodiment, part or all of the control unit 20 may be included in the measurement system 1. The control unit 20 may include a processing unit, a storage unit, and a communication interface. The control unit 20 is implemented, for example, by a computer. The control unit 20 may be one or more circuits, and may be provided as a single unit or in parts. The control unit 20 may include a processing unit, a storage unit, and a communication interface. The functions realized by the processing units described in this disclosure may be implemented in circuits or processing circuits, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to realize the functions described. A processor is considered to be a circuit or processing circuit, including transistors and other circuits. A processor may be a programmed processor that executes a program stored in memory. This program (computer program product) may be stored in memory beforehand or may be retrieved via a medium when needed.The medium may be various computer-readable storage media, such as memory cards, optical discs, HDDs (Hard Disk Drives), or other removable storage media, and the program may be provided in a form stored on such storage media. Alternatively, the medium may be a communication line connected to a communication interface, and the program may be distributed by a remote server device or the like. The acquired program is stored in the storage unit and read from the storage unit and executed by the processing unit. The memory unit may include storage media such as RAM (Random Access Memory), ROM (Read Only Memory), EEPROM (Electronically Erasable Programmable Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), or combinations thereof. The communication interface may communicate with the measurement system 1 via a communication line such as a LAN (Local Area Network). In this disclosure, circuits, units, and means are hardware programmed to perform or execute the functions described. Such hardware may be any hardware described in this disclosure, or any hardware known to be programmed to perform or execute the functions described. If the hardware is a processor that is considered to be a type of circuit, then the circuit, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0033] <Sample> Next, an example of the configuration of a wafer W, which is placed on the wafer stage 132 of the measurement system 1, will be described. Figure 2 is a schematic cross-sectional view and a partially enlarged view thereof showing an example of the configuration of a wafer W according to one embodiment.

[0034] In one embodiment, wafer W is a semiconductor wafer such as a silicon substrate. As shown in Figure 2, in wafer W, the side on which idler light is incident is described as the surface Wa, and the side opposite to surface Wa is described as the back surface Wb. Hereinafter, the thickness direction of wafer W from surface Wa to back surface Wb will be described as "depth". In one embodiment, wafer W has a structure in which a laminated film Wl containing a device pattern Wd is formed on a substrate layer Ws.

[0035] In wafer W, the measurement target Wt shown in Figure 7 is a portion whose reflectance to idler light is unknown and whose reflectance is to be determined by the measurement method described later. The reflectance to be determined for the measurement target Wt is referred to as the "target reflectance Rt". In this embodiment, the measurement target Wt includes the device pattern Wd. The measurement target Wt is not limited to a region at a specific depth of wafer W, but may be a region at each of several different depths. Furthermore, the measurement target Wt is not limited to a specific region in the plane of wafer W at a certain depth, but may be multiple regions in the plane of wafer W at that depth.

[0036] Furthermore, in the wafer W, the reference portion Wr shown in Figure 6 is a portion whose reflectivity to idler light is known. The known reflectivity of the reference portion Wr is referred to as the "reference portion reflectivity Rr". In one embodiment, the reference portion reflectivity Rr is measured or theoretically calculated in advance prior to the measurement method described later and stored in the control unit 20. In one embodiment, at least a portion of the substrate layer Ws constitutes the reference portion Wr. In another embodiment, a reflective layer (not shown) with a known reflectivity to idler light is formed on the back surface Wb, and in this case, at least a portion of the reflective layer constitutes the reference portion Wr.

[0037] In one embodiment, the reference section Wr is provided at the same horizontal position as the measurement target section Wt, but at a different depth, inside the wafer W on the optical path of the idler light.

[0038] In one embodiment of the wafer W, the reference portion Wr may be a region of the substrate layer Ws near the interface between the back surface Wb of the wafer W and the mounting surface 132a. "Near the interface" refers, for example, to a range within 20 μm in the depth direction from the interface. In another embodiment of the wafer W, if a reflective layer is provided on the back surface Wb side of the wafer W, the reference portion Wr may be a region of the substrate layer Ws or the reflective layer near the interface between the substrate layer Ws and the reflective layer, or a region of the reflective layer near the interface between the reflective layer and the mounting surface 132a.

[0039] Furthermore, in the measurement method described later according to one embodiment, a silver mirror as a standard sample, whose reflectivity to idler light is known, may be placed on the mounting surface 132a of the wafer stage 132. The silver mirror may be placed on the mounting surface 132a only during initial calibration, or it may always be placed near the area on the mounting surface 132a where the wafer W is placed.

[0040] The sample measured by the measurement system 1 is not limited to wafer W. A sample can be any structure that includes a desired measurement target Wt and a reference section Wr whose reflectivity to idler light is known. In one embodiment, the reference section Wr may be located within the structure at the same horizontal position as the measurement target Wt but at a different depth along the optical path of the idler light.

[0041] <Measurement Method> Next, as an example of the measurement method of this disclosure, a method for determining the reflectance Rt of the target portion Wt of the wafer W in the measurement system 1 will be described. Figure 3 is a schematic flowchart of an example configuration of the measurement method according to this embodiment.

[0042] First, the wafer W is placed on the mounting surface 132a of the wafer stage 132 (step St101 in Figure 3). At this time, global alignment of the wafer W may be performed so that the horizontal position or azimuth angle of the center or periphery of the wafer W with respect to the mounting surface 132a is in a predetermined position.

[0043] Next, the angular alignment of the wafer W is performed (step St102 in FIG. 3). In the angular alignment, the mounting surface angle φ is adjusted so that the condensing range in the non-linear optical crystal 110 of the signal light overlaps with the condensing range in the non-linear optical crystal 110 of the idler light.

[0044] The angular alignment according to one embodiment can be performed as follows, for example. First, the excitation light source 101 is controlled to emit pump light. The pump light passes through the non-linear optical crystal 110, is reflected by the second dichroic mirror 121, passes through the third lens 131, enters the surface Wa of the wafer W, and a part thereof is reflected. The reflected pump light returns to the non-linear optical crystal 110, passes through the non-linear optical crystal 110, and is reflected by the first dichroic mirror 105. The pump light reflected by the first dichroic mirror 105 is reflected by the polarization beam splitter 153. The pump light reflected by the polarization beam splitter 153 is condensed by the lens 154 onto the pinhole 152 and enters the optical power meter 151. At this time, when the angle of the wafer W is correct, the optical path of the pump light reflected by the movable mirror 123 and the optical path of the reflected light of the idler light reflected by the wafer W should overlap. In this case, the intensity of the light incident on the optical power meter 151 through the pinhole 152 becomes maximum. On the other hand, when the angle of the wafer W is incorrect, the optical paths of the two reflected lights do not overlap, and part of the light incident on the optical power meter 151 cannot pass through the pinhole 152, and the intensity of the pump light becomes smaller. In the angular alignment, using this fact, the angle adjustment mechanism 132b of the wafer stage 132 is controlled to sweep the mounting surface angle φ while monitoring the intensity of the pump light incident on the optical power meter 151. Then, the position where the intensity is maximum is determined as the position where the angle of the wafer W is correct, and the angle is stored in the control unit 20. The pinhole 152 is adjusted in advance to a position where the optical power of the optical power meter 151 of the pump light reflected by the movable mirror 123 becomes maximum.

[0045] In the above embodiment, an alignment method of adjusting to a position where the optical power of the optical power meter 151 becomes maximum is shown, but it is not limited thereto, and it may be adjusted based on clarity.

[0046] Next, following the angular alignment, the crystal rotation angle θ(n) of the nonlinear optical crystal 110 is set to an initial angle θ(1) within a sweep range (n is a natural number, n = 1 to N) (step St103 in FIG. 3). The sweep range of the crystal rotation angle θ(n) is determined in advance corresponding to the range of the reflectance (reflection spectrum) for each wavelength λi of the idler light to be acquired in the measurement target portion Wt.

[0047] Next, quantum measurement of the reference portion of the wafer W is performed (step St104 in FIG. 3). There are a method of using a silver mirror or the like with a known reflectance Rsys for the reference portion and a method of using the back surface of the wafer W with a known reflectance Rr. In the former case, it is necessary to separately perform steps St101 and St102 in FIG. 3 with the wafer W replaced by a silver mirror. In the quantum measurement of the reference portion, quantum measurement for measuring the clarity of the reference portion is performed. Specifically, the quantum measurement of the reference portion in step St104 can be executed by a sub-process as shown in FIG. 4.

[0048] In the quantum measurement of the reference portion, first, the excitation light source 101 is controlled to emit pump light. Then, measurement of the quantum interference signal detected by the photodetector 11 is started (step St1041 in FIG. 4).

[0049] Next, the position of the movable mirror 123 is adjusted so that the optical path length Li of the idler light from the nonlinear optical crystal 110 to the reference portion Wr (dashed-dotted arrow in FIG. 6) and the optical path length Ls of the signal light from the nonlinear optical crystal 110 to the movable mirror 123 (arrow in FIG. 6) coincide with each other (step St1042 in FIG. 4). Here, quantum interference appears only when the optical path length Li of the idler light and the optical path length Ls of the signal light are close, and the position where the clarity of the quantum interference becomes maximum can be regarded as the position where the optical path lengths Li and Ls coincide with each other.

[0050] Although the detailed measurement principle is omitted, in step St1041, the quantum interference signal between the signal light generated when the pump light emitted from the excitation light source 101 passes through the nonlinear optical crystal 110 for the first time and the signal light generated when the pump light reflected by the movable mirror 123 passes through the nonlinear optical crystal 110 for the second time is detected by the photodetector 11. In the present embodiment, the quantum interference signal is detected as the number of photons per unit time (photon count).

[0051] Next, the mirror stage 124 is controlled to repeatedly sweep the position of the movable mirror 123 and measure the number of photons (step St1043 in Figure 4). In step St1043 according to one embodiment, the movable mirror 123 is swept to include a position where the optical path length difference ΔL is 0.

[0052] As described above, the reference region Wr may be a region having a desired width in the depth direction of the wafer W. Therefore, in step St 1043, the movable mirror 123 may be swept over that width. In this case, the quantum interference signal of the reference region Wr at a depth position corresponding to the optical path length Li of the idler light, which is equal to the optical path length Ls of the signal light, is detected at any time. After the sweep of the movable mirror 123 is completed in step St 1043, the excitation light source 101 may be controlled to stop the pump light and stop the measurement of the quantum interference signal.

[0053] Next, the visibility Vr of the reference section Wr or the visibility Vsys of the silver mirror is calculated from the photon count measurement results in the sweep range of the movable mirror 123 (step St1044 in Figure 4). The visibility Vr or Vsys is calculated as (a-b) / (a+b) using the maximum value a and minimum value b of the photon count in the sweep range.

[0054] Following the reference portion quantum measurement in step St104 described above, a target portion quantum measurement of wafer W is performed (step St105 in Figure 3). In the target portion quantum measurement, a quantum measurement is performed to measure the reflectance of the measurement target portion Wt. In the target portion quantum measurement, the actual measured reflectance Rt of the target portion in the measurement environment is determined. Specifically, the target portion quantum measurement in step St105 may be performed as a subprocess as shown in Figure 5.

[0055] In the target quantum measurement, first the wafer W is placed, and the excitation light source 101 is controlled to emit pump light. Then, the measurement of the quantum interference signal detected by the photodetector 11 is started (step St1051 in Figure 5).

[0056] Next, the position of the movable mirror 123 is adjusted so that the optical path length Li of the idler light from the nonlinear optical crystal 110 to the measurement target Wt matches the optical path length Ls of the signal light from the nonlinear optical crystal 110 to the movable mirror 123 (line arrow in Figure 6) (step St1052 in Figure 5, dashed line arrow in Figure 7). In step St1052, similar to step St1042 of the reference unit quantum measurement, the optical path length Li of the idler light can be predicted from the information of the depth position of the measurement target Wt inside the wafer W. In step St1052, the position of the movable mirror 123 may be adjusted by reading out the optical path length Li that has been predicted as described above and stored in the control unit 20 beforehand.

[0057] Next, the mirror stage 124 is controlled to repeatedly sweep the position of the movable mirror 123 and measure the number of photons (step St1053 in Figure 5).

[0058] Steps St1052 and St1053 are the same as steps St1042 and St1043 in the reference section quantum measurement, and as shown in Figure 7, the position sweep of the movable mirror 123 is performed so that the optical path length Ls of the signal light (solid arrow in Figure 7) is equal to the optical path length Li of the idler light acquired in step St1052.

[0059] Next, the clarity of the target area Vt in the measurement target area Wt is calculated from the measurement results of the photon count in the sweep range of the movable mirror 123 (step St1054 in Figure 4). The clarity of the target area Vt is calculated as (c-d) / (c+d) using the maximum value c and minimum value d of the photon count in the sweep range. In the method using a silver mirror, the reflectance Rt of the target area is obtained from the clarity of the target area Vt, the standard clarity Vsys of the silver mirror, and the known reflectance Rsys of the silver mirror using the following formula (2). (step St106)

[0060] Next, a method for calculating the reflectance Rt of the target area by referring to the reference area Wr will be described (step St106). Specifically, the reflectance Rt of the target area can be calculated as follows, for example, from the known reference area reflectance Rr, reference area clarity Vr, and target area clarity Vt calculated by target area quantum measurement, without using the standard clarity Vsys. First, the measured reflectance Rmr of the reference area Wr is expressed by equation (3) because the idler light passes through the wafer surface Wa twice.

[0061] By multiplying (Equation (3)) by (Equation (2)), we obtain the following equation (4).

[0062] Here, if we define α by equation (5) below, equation (4) can be transformed into equation (6) below.

[0063] Solving equation (6) for Rt, the reflectance Rt of the target area can be determined without using the standard clarity Vsys by equation (7) below.

[0064] In the above embodiment, a method was described in the case of no absorption or scattering, but equations (3) to (7) above may be formulated to take absorption and scattering into consideration.

[0065] Next, it is determined whether to terminate the sweep of the crystal rotation angle θ(n) of the nonlinear optical crystal 110 (step St107 in Figure 3). In step St107, if the predetermined sweep range n of the crystal rotation angle θ(n) is less than N, the process returns to step St104, and quantum measurements in steps St104 and St105 are performed for the next crystal rotation angle θ(n+1). This sequentially determines the reflectance Rt of the target part at each crystal rotation angle θ within the sweep range. If the sweep range of the crystal rotation angle θ(n) is n = N, the process terminates.

[0066] In one embodiment of the measurement method, after the completion of step St107, quantum measurements may be performed on the measurement target Wt at different depths of the wafer W. Specifically, after determining that step St107 is finished, the process returns to step St105. Then, in step St1051, when acquiring the optical path length Li of the idler light, the optical path length Li of the idler light up to a different depth position of the measurement target Wt inside the wafer W may be obtained by referring to the information of that depth position. This makes it possible to sequentially perform quantum measurements on measurement target Wt at different depths at the same horizontal position on the wafer W surface. In this case, the measured reference reflectance Rmr calculated in a single reference quantum measurement (step St104) may be used to calculate the target reflectance Rt for the measurement target Wt at multiple different depths.

[0067] In one embodiment of the measurement method, after the completion of step St107, quantum measurement may be performed on the measurement target Wt at different horizontal positions on the wafer W. Specifically, after determining that the process has ended in step St107, the horizontal position adjustment mechanism of the wafer stage 132 is used to move the position of the wafer stage 132 horizontally, thereby moving the horizontal position of the wafer W on which the idler light is incident. Then, the process returns to step St101, and steps St101 to St107 are executed sequentially. This makes it possible to sequentially perform quantum measurement on the measurement target Wt at different horizontal positions on the wafer W surface. In this case, the measured reference part reflectance Rmr calculated in the reference part quantum measurement (step St104) for the measurement target Wt at a certain horizontal position that is measured first may be used to calculate the target part reflectance Rt for the measurement target Wt at other horizontal positions. In that case, the reference part quantum measurement (step St104) can be omitted in the measurement method for the measurement target Wt at the other horizontal position.

[0068] In the above embodiment, the reflected coefficient Rmr of the reference section and the reflected coefficient Rmt of the target section are calculated sequentially by quantum measurement in steps St104 and St105. However, these calculation steps may be performed together separately from steps St104 and St105.

[0069] Furthermore, in the above embodiment, the order of steps St104 and St105 is not limited to this, and step St105 may be performed first, followed by step St104.

[0070] Furthermore, although the above embodiment describes a method for determining reflectance using clarity, the method for determining reflectance is not limited to this. For example, reflectance may be determined based on the amplitude of the Fourier spectrum obtained by the Fourier transform of the quantum interference signal obtained in the quantum measurement of steps St104 and St105. More specifically, reflectance may be determined by Q-FTIR (Quantum Fourier-Transform Infrared Spectroscopy) as described in Patent Document 1.

[0071] The significance of the measurement system 1 and measurement method configured as described above is not limited to this, but can be explained as follows.

[0072] While SEM imaging and X-ray inspection are used to evaluate the device patterns on wafers W, these methods are costly. Therefore, simpler measurements using optical non-destructive testing are desirable.

[0073] For example, optical measurement using infrared reflected light is conceivable, but in typical infrared reflected light measurements, the reflection spectrum includes not only the surface light of the wafer W but also the light reflected from the back surface and other sources. Therefore, it is difficult to measure the reflection spectrum of only the surface light of the wafer W using infrared reflected light measurements.

[0074] Patent Document 1 discloses a method for measuring the quantum interference of signal light using infrared quantum absorption spectroscopy, which utilizes the fact that a portion of the idler light passing through a sample is absorbed by the sample. In such quantum measurement, an absorption spectrum is obtained that sums up all structures in the depth direction of the wafer W through which the idler light passes. Therefore, it is not possible to evaluate the surface, interior, and back surface of the wafer W separately, and it is difficult to obtain optical properties of only the surface of the wafer W, for example.

[0075] In view of the above problems, the inventors of the present invention have conceived of using the principle of quantum interference to obtain the reflectance of idler light reflected at a desired depth position in the wafer W.

[0076] When using the reflection of idler light, in principle, information can only be obtained for the surface where the optical path length Ls of the signal light and the optical path length Li of the idler light coincide. Therefore, when it is desired to obtain the reflectance of the measurement target Wt as in this embodiment, the optical path length Ls of the signal light is adjusted to be equal to the optical path length Li of the idler light up to the measurement target Wt. This allows the reflectance of only the measurement target Wt to ​​be obtained. In this case, reflections from the wafer W structure existing in the depth direction other than the measurement target Wt do not affect the quantum measurement.

[0077] In determining the reflectance using this method, the inventors first investigated a method in which they first determined the measured standard clarity Vsys using a silver mirror as a standard sample, and then directly determined the reflectance Rt of the target area. This method makes it possible to determine the reflectance Rt of only the target area Wt at a desired depth position of the wafer W, thereby solving the above problem.

[0078] On the other hand, when using a standard sample, the standard sample is placed on the wafer stage 132 and quantum measurement is performed, and then the wafer W used as the sample is replaced and quantum measurement is performed. Further investigation by the inventors revealed that if there is a difference in the alignment (e.g., angular alignment) between the standard sample and the sample on the wafer stage 132, measurement errors may occur. It was also found that if there is a time gap between the measurement of the standard sample and the measurement of the sample, measurement errors may occur due to instability of the quantum optical system 10, etc.

[0079] The inventors further investigated the above-mentioned problems when using standard samples. As a result, they conceived of a method to calculate the reflectance Rr of a reference portion Wr of a wafer W whose reflectance to idler light is known, as illustrated in step St104 above, and then calculate the reflectance Rt of the target portion based on this. In this case, if the horizontal positions of the reference portion Wr and the measurement target portion Wt are the same within the wafer W plane, no alignment changes occur due to the replacement of the standard sample with the sample or horizontal movement of the sample. The method including step St104 of this embodiment makes it possible to calculate the reflectance Rt of the target portion without using standard clarity Vsys, thus solving the above-mentioned problems when using standard samples.

[0080] (Modifications) According to the technology of this disclosure, a measurement method relating to modified samples can be constructed for modified samples as described below.

[0081] Figure 8 is a schematic cross-sectional view and a partially enlarged view thereof showing an example of the configuration of a polymerized wafer T as an example of a sample according to this modified example. As shown in Figure 8, the polymerized wafer T according to this modified example is formed by joining a first wafer W1, which is a support substrate, and a second wafer W2, which is a device substrate. In the polymerized wafer T, the side on which idler light is incident is referred to as the surface Ta, and the side opposite to the surface Ta is referred to as the back surface Tb. Hereinafter, the thickness direction of the polymerized wafer T from the surface Ta to the back surface Tb will be referred to as "depth". The polymerized wafer T has a structure in which a laminated film Tl is formed between the first wafer W1 and the second wafer W2.

[0082] The first wafer W1 and the second wafer W2 are semiconductor wafers, such as silicon substrates, similar to the wafer W in the above embodiment. On the first wafer W1, the side that is joined to the second wafer W2 is called the front surface W1a, and the side opposite to the front surface W1a is called the back surface W1b. Similarly, on the second wafer W2, the side that is joined to the first wafer W1 is called the front surface W2a, and the side opposite to the front surface W2a is called the back surface W2b. That is, the first wafer W1 and the second wafer W2 are joined to each other at their front surfaces (front surfaces W1a and front surfaces W2a). In the example of Figure 8, the back surface W1b of the first wafer W1 constitutes the front surface Ta of the polymerized wafer T, and the back surface W2b of the second wafer W2 constitutes the back surface Tb of the polymerized wafer T.

[0083] The first wafer W1 includes a laser absorption layer P and a surface film F1 as a laminated film Tl on a substrate layer W1s. The first wafer W1 is bonded to the second wafer W2 via the surface film F1. In this modified example, the first wafer W1 serves as a support substrate, supporting the second wafer W2 while desired processing such as device formation is performed on the second wafer W2.

[0084] The surface film F1 is composed of, for example, an oxide film (SiO2 film, TEOS film), a SiC film, a SiCN film, or an adhesive.

[0085] The separation layer P is composed of a material that can absorb laser light (e.g., CO2 laser, MIR laser, FIR laser), such as an oxide film (SiO2, TEOS, ThOx, etc.), a polysilicon film doped with a desired dopant (n-type or p-type), an Epi-Si film, a Poly-SiGe film, an Epi-SiGe film, or a film in which an oxide film and a nitride film are laminated. In one embodiment, the laminated film Tl does not have a separation layer P.

[0086] The second wafer W2 includes a device layer D and a surface film F2 as a laminated film Tl on a substrate layer W2s. The second wafer W2 is bonded to the first wafer W1 via the surface film F2. The surface film F2 is configured in the same way as the surface film F1. The device layer D is the same as the laminated film Wl in the wafer W according to the above embodiment and includes a device pattern Wd.

[0087] In one embodiment, part or all of the first wafer W1 may be separated from the second wafer W2 by a process involving irradiation of the laminated film Tl with laser light. In this case, the separation between which layers of the laminated film Tl occurs can be predetermined by the composition of the laminated film Tl, the laser light irradiation conditions, etc. As an example, the separation can be configured to occur between desired layers, such as the interface IF1 between the surface film F1 and the surface film F2, which are the bonding interface between the first wafer W1 and the second wafer W2, the interface IF2 between the separation layer P and the surface film F1, and the interface IF1 between the substrate layer W1s of the first wafer and the separation layer P.

[0088] In one embodiment, both the first wafer W1 and the second wafer W2 may be configured as device substrates. In this case, the laminated film Tl may have a device layer (not shown) between the isolation layer P and the surface film F1, for example, containing a device pattern Wd.

[0089] At least a portion of the laminated film Tl described above as being formed on the first wafer W1 may be formed in advance on the second wafer W2. Conversely, at least a portion of the laminated film Tl described above as being formed on the second wafer W2 may be formed in advance on the first wafer W1. The configuration of the laminated film Tl is not limited to the above example and may include other desired layers.

[0090] Hereinafter, as an example of a measurement method relating to a modification of the present disclosure, a method for determining the reflectance Rt of the target portion Wt of the polymerized wafer T in the measurement system 1 will be described. The measurement method relating to this modification, using the polymerized wafer T as a sample, is generally the same as the measurement method according to the above embodiment described with reference to Figure 3, so the parts that overlap with the measurement method according to the above embodiment will be omitted from the explanation.

[0091] Regarding the placement of the polymerized wafer T (see St101 in Figure 3), the polymerized wafer T is placed so that its back surface Tb is in contact with the mounting surface 132a of the wafer stage 132.

[0092] For quantum measurement of the reference portion of the polymerized wafer T (see step St104 in Figure 3 and Figure 4), as shown in Figure 9, the surface Ta of the polymerized wafer T is used as the reference portion Wr. The back surface W1b of the first wafer W1 that constitutes the surface Ta of the polymerized wafer T has a known reflectance Rr. In the measurement of the polymerized wafer T, the surface Ta of the polymerized wafer T with a known reflectance Rr can be used as the reference portion Wr. If the reflectance Rr is known, a component of the desired laminated film Tl, such as the separation layer P or surface films F1, F2, can also be used as the reference portion Wr.

[0093] The specific calculation method is described below. First, the reference reflectance Rr is obtained from the clarity Vr of the back surface W1b of the first wafer, the standard clarity Vsys of the silver mirror, and the known reflectance Rsys of the silver mirror using the following formula (8).

[0094] Next, since the reflected light from the measurement target Wt passes through the back surface W1b of the wafer twice, the measured reflectance Rmt is obtained using the reflectance Rt of the measurement target Wt and the reflectance Rr of the reference part from the following equation (9). Alternatively, the measured reflectance Rmt can also be obtained from equation (9) using the clarity Vt of the measurement target Wt.

[0095] By multiplying (Equation (9)) by (Equation (8)), we obtain the following equation (10).

[0096] Since the reference reflectance Rr is known, the target reflectance Rt can be determined from the clarity of the wafer back surface W1b and the measurement target Wt without using the standard clarity Vsys.

[0097] For quantum measurement of the target area of ​​the polymerized wafer T (see step St105 in Figure 3 and Figure 5), as shown in Figure 10, the target area Wt is defined as the interface IF1 between surface films F1 and F2, which is the bonding interface between the first wafer W1 and the second wafer W2. In this case, the reflectance at the interface IF1 is calculated. This allows the degree of bonding between the first wafer W1 and the second wafer W2 to be measured.

[0098] In one embodiment, the target portion Wt is not limited to the interface IF1, but any of the interfaces IF1, IF2, and IF3 (see Figure 8) after irradiation with laser light for separating the first wafer W1 and the second wafer W2 may be used as the target portion Wt. In this case, the reflectance of the interfaces IF1, IF2, and IF3 is calculated. This makes it possible to measure the thickness of the space layer between the first wafer W1 and the second wafer W2 or the degree of separation (the degree of formation of delamination points).

[0099] The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the appended claims. For example, the constituent elements of the embodiments described above can be combined in any way. Such any combination will naturally yield the functions and effects of each constituent element in the combination, as well as other functions and effects that will be apparent to those skilled in the art from the description herein.

[0100] Furthermore, the effects described herein are merely descriptive or illustrative and not limiting. In other words, the technology relating to this disclosure may produce other effects that will be apparent to those skilled in the art from the description herein, in addition to or in lieu of the effects described herein.

[0101] 1 Measurement system 10 Quantum optical system 11 Photodetector 20 Control unit W Wafer

Claims

1. A measurement method using a quantum optical system configured to cause quantum interference between multiple physical processes in which quantum entangled photon pairs of signal photons and idler photons are generated, comprising: performing a target quantum measurement to acquire a quantum interference signal for a part of a sample, the reflectance of the idler photon at the wavelength of the idler photon is unknown; and calculating the reflectance of the target from the quantum interference signal acquired by the target quantum measurement, wherein the target quantum measurement includes sweeping the difference in optical path lengths between the optical path length of the signal photon and the optical path length of the idler photon when the idler photon is reflected at the target.

2. The measurement method according to claim 1, wherein the quantum optical system includes an optical path length difference sweep unit configured to sweep the optical path length difference, the optical path length difference sweep unit includes a movable mirror that reflects the signal photon, and a mirror stage that moves the movable mirror along the direction of propagation of the signal photon, and the sweep of the optical path length difference includes adjusting the optical path length of the signal photon by moving the movable mirror along the direction of propagation of the signal photon using the mirror stage.

3. The measurement method according to claim 1, further comprising performing a reference quantum measurement to acquire a quantum interference signal for a reference portion contained in the sample, wherein the reflectivity at the wavelength of the idler photon is known, the reference quantum measurement comprising adjusting the optical path length of the signal photon to sweep the difference in optical path length between the optical path length of the signal photon and the optical path length of the idler photon when it is reflected by the reference portion.

4. The measurement method according to claim 3, characterized in that the reference portion is the front or back surface of the sample.

5. The measurement method according to claim 3, comprising: calculating the reflectance of the part to be measured from the quantum interference signal obtained by quantum measurement of the part to be measured; calculating the clarity and measured reflectance of the reference part from the quantum interference signal obtained by quantum measurement of the reference part; and calculating the reflectance of the part to be measured based on the clarity and measured reflectance of the part to be measured and the clarity, known reflectance and measured reflectance of the reference part.

6. The measurement method according to claim 3, further comprising performing angular alignment of the sample, wherein the angular alignment includes adjusting the angle of the sample such that the optical path of the incident light of the idler photons incident on the measurement target portion or the reference portion of the sample overlaps with the optical path of the reflected light of the idler photons reflected by the measurement target portion or the reference portion.

7. A measurement system comprising a quantum optical system configured to cause quantum interference between a plurality of physical processes that generate quantum entangled photon pairs of signal photons and idler photons, wherein the quantum optical system includes a nonlinear optical element that generates the quantum entangled photon pairs by irradiation with pump light; a wavelength sweep unit configured to sweep the wavelength of the quantum entangled photon pairs; and a path length difference sweep unit configured to sweep the path length difference between the optical path length of the signal photons and the optical path length of the idler photons by adjusting the optical path length of the signal photons.

8. The measurement system according to claim 7, wherein the optical path length difference sweep unit includes a movable mirror that reflects the signal photon and a mirror stage that moves the movable mirror along the direction of propagation of the signal photon, and the sweep of the optical path length difference includes adjusting the optical path length of the signal photon by moving the movable mirror along the direction of propagation of the signal photon using the mirror stage.

9. The measurement system according to claim 7, further comprising a control unit, the control unit being configured to perform control including: performing a target quantum measurement to acquire a quantum interference signal for a target unit contained in a sample whose reflectance at the wavelength of the idler photon is unknown; and calculating the reflectance of the target unit from the quantum interference signal acquired by the target quantum measurement, wherein the target quantum measurement includes adjusting the optical path length of the signal photon to sweep the difference in optical path length between the optical path length of the signal photon and the optical path length of the idler photon when the idler photon is reflected at the target unit.

10. The measurement system according to claim 9, wherein the control unit is configured to perform control that further includes performing a reference quantum measurement to acquire a quantum interference signal for a reference unit contained in the sample, the reflectance of the idler photon at the wavelength known, the reference quantum measurement includes adjusting the optical path length of the signal photon to sweep the difference in optical path length between the optical path length of the signal photon and the optical path length of the idler photon when the idler photon is reflected by the reference unit.

11. The measurement system according to claim 10, wherein the control unit is configured to perform control including: calculating the reflectance of the part to be measured from the quantum interference signal acquired by the quantum measurement of the part to be measured; calculating the clarity and measured reflectance of the reference unit from the quantum interference signal acquired by the quantum measurement of the reference unit; and calculating the reflectance of the part to be measured based on the clarity and measured reflectance of the part to be measured and the clarity, known reflectance and measured reflectance of the reference unit.

12. The measurement system according to claim 10, wherein the quantum optical system further includes a stage having a mounting surface on which the sample is placed, the stage comprises an angle adjustment mechanism configured to adjust the angle made by the mounting surface with respect to the direction of travel of the idler photons, the control unit is configured to perform control that further includes angular alignment of the sample, the angular alignment includes adjusting the angle of the sample such that the optical path of the incident light of the idler photons incident on the measurement target portion or the reference portion of the sample overlaps with the optical path of the reflected light of the idler photons reflected by the measurement target portion or the reference portion.

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