Optical probe, optical probe array, and probe system

Abstract

To provide an optical probe, optical probe array, and probe system that can suppress a time required for alignment with an optical device and suppress increase in a connection loss.SOLUTION: An optical probe 10 transmits / receives optical signals to / from an optical device. The optical probe 10 comprises: a tip end surface 101 which is a curved surface having a convex shape facing the optical device 20; a refractive index distribution-type optical waveguide 100 having a first end connected to the tip end surface 101; and a base end surface 102 to which a second end of the optical waveguide 100 is connected.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical probe, an optical probe array, and a probe system used for measuring optical devices. [Background technology]

[0002] Silicon photonics technology is used to form silicon devices (hereinafter also referred to as "optical devices") on semiconductor wafers, through which optical signals propagate. Optical probes and electrical probes are used to measure the characteristics of the optical devices formed on the semiconductor wafers. In measurements using optical probes, the optical device and the optical probe are aligned to reduce loss of the optical signal (hereinafter also referred to as "propagating optical signal") propagating through the optical waveguide of the optical probe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-550547 Summary of the Invention [Problem to be solved by the invention]

[0004] When the optical transmission path of an optical probe through which a propagating optical signal passes is single-mode, the numerical aperture of the optical transmission path is small. Furthermore, because the size of the optical signal terminal through which the optical signal of an optical device enters and exits is small (approximately a few micrometers), the tolerance for error in aligning the optical signal terminal of the optical device with the tip of the optical probe is low. This makes it difficult to accurately align the optical device and the optical probe. For example, after coarse positioning adjustment to position the optical device and the optical probe facing each other, precise positioning is performed using an actuator capable of six-axis adjustment, including X, Y, and Z positioning and rotational movement. As a result, when measuring optical devices, the time required for alignment increases, resulting in longer measurement times, and inaccurate alignment can lead to increased and variable connection loss.

[0005] In view of the above problems, an object of the present invention is to provide an optical probe, an optical probe array, and a probe system that can reduce the time required for alignment with an optical device and can also reduce increases and fluctuations in connection loss. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an optical probe having a tip surface that is a convex curved surface facing an optical device, a refractive index distribution type optical waveguide having a first end connected to the tip surface, and a base end surface to which a second end of the optical waveguide is connected. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an optical probe, an optical probe array, and a probe system that can reduce the time required for alignment with an optical device and also prevent an increase in connection loss. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an optical probe according to an embodiment. [Figure 2] FIG. 2 is a graph showing the shape of the mode field pattern of the optical probe according to the embodiment. [Figure 3] FIG. 3 is a schematic diagram showing another example of use of the optical probe according to the embodiment. [Figure 4A] FIG. 4A is a graph showing the relationship between the numerical aperture and the beam diameter of a propagating optical signal. [Figure 4B] FIG. 4B is a graph showing the relationship between the numerical aperture and the refractive index distribution coefficient. [Figure 5] FIG. 5 is a graph showing the relationship between the ratio of the mode field diameter of the optical signal to the mode field diameter of the optical probe according to the embodiment and loss. [Figure 6] FIG. 6 is a table showing conditions for reducing the amplitude of an optical signal propagating through an optical probe according to the embodiment. [Figure 7A]FIG. 7A is a graph (part 1) showing ray tracing of an optical signal propagating through an optical waveguide of an optical probe according to an embodiment. [Figure 7B] FIG. 7B is a graph (part 2) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 7C] FIG. 7C is a graph (part 3) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 7D] FIG. 7D is a graph (part 4) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 8A] FIG. 8A is a graph (part 5) showing ray tracing of an optical signal propagating through an optical waveguide of an optical probe according to an embodiment. [Figure 8B] FIG. 8B is a graph (part 6) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 8C] FIG. 8C is a graph (part 7) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 8D] FIG. 8D is a graph (part 8) showing ray tracing of an optical signal propagating through an optical waveguide of the optical probe according to the embodiment. [Figure 9] FIG. 9 is a schematic diagram showing the configuration of an optical probe according to a first modified example of the embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the configuration of an optical probe according to a second modified example of the embodiment. [Figure 11A] 1 is a schematic diagram illustrating a configuration of a probe system using an optical probe according to an embodiment. [Figure 11B] FIG. 1 is a schematic plan view showing the configuration of a probe system using an optical probe according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic. Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical ideas of the present invention, and the structures and arrangements of the components of the embodiments of the present invention are not limited to those described below. Various modifications can be made to the embodiments of the present invention within the scope of the claims.

[0010] An optical probe 10 according to the embodiment shown in Fig. 1 transmits and receives optical signals to and from an optical device 20 formed on a semiconductor wafer 200. Fig. 1 shows a case in which an optical signal L emitted from the optical device 20 and incident on the optical probe 10 propagates through an optical waveguide 100 of the optical probe 10. The optical probe 10 has a tip surface 101 that is a convex curved surface facing the optical device 20, a graded-index optical waveguide 100 having a first end connected to the tip surface 101, and a base end surface 102 to which a second end of the optical waveguide 100 is connected.

[0011] As shown in Fig. 1, the central axis C10 of the optical waveguide 100 of the optical probe 10 is defined as the Z-axis direction, and the plane perpendicular to the Z-axis direction is defined as the XY plane. The central axis C10 is the optical axis of the optical probe 10. The left-right direction of the paper surface of Fig. 1 is defined as the X-axis direction, and the direction perpendicular to the paper surface is defined as the Y-axis direction. Hereinafter, the X-axis direction, Y-axis direction, and Z-axis direction will also be collectively referred to as the "XYZ-axis direction."

[0012] The optical probe 10 can be an optical fiber or a combination of an optical fiber and a lens. The optical waveguide 100 is composed of a core 11 and a cladding 12 arranged on the outer periphery of the core 11. The optical waveguide 100 is designed so that the refractive index of the core 11 gradually decreases from the optical axis, which is the central axis of the optical waveguide 100, toward the outside. In other words, the refractive index of the core 11 gradually decreases from the optical axis of the optical probe 10 toward the region adjacent to the cladding 12. The shape of a cross section of the optical probe 10 along the XY plane (hereinafter referred to as the "cross-sectional shape") may be circular or rectangular.

[0013] Hereinafter, the length from the distal end surface 101 to the proximal end surface 102 of the optical waveguide 100 of the optical probe 10 will also be referred to as the “optical path length.” The optical path length of the optical probe 10 shown in FIG.

[0014] As shown in FIG. 1 , the inner diameter of the core portion 11 of the optical probe 10 is 2×Cr, and the inner diameter of the optical probe 10 including the cladding portion 12 is 2×Cd. When the cross-sectional shape of the core portion 11 is circular, the radius of the core portion 11 is Cr, and the radius of the optical probe 10 is Cd. When the cross-sectional shape of the core portion 11 is rectangular, the size of the cross-sectional shape of the core portion 11 in the X and Y directions is 2×Cr, and the size of the cross-sectional shape of the optical probe 10 in the X and Y directions is 2×Cd. Hereinafter, half the inner diameter of the core portion 11 is referred to as the core diameter Cr, and half the inner diameter of the cladding portion 12 is referred to as the cladding diameter Cd. The core diameter Cr is the length from the central axis C10 of the optical waveguide 100 to the boundary between the core portion 11 and the cladding portion 12. The cladding diameter Cd is the length from the central axis C10 to the outer edge of the optical probe 10.

[0015] 1, the optical probe 10 is held by the support 50 so that the central axis C10 is linear. In other words, the optical waveguide 100 is linear from the distal end surface 101 to the proximal end surface 102. Because the optical waveguide 100 is linear, no optical path difference occurs in the propagating optical signal propagating through the optical waveguide 100, and the occurrence of multimode can be suppressed.

[0016] For example, if the optical probe 10 is an optical fiber, the optical fiber is held by the support 50 so as not to bend. For example, the optical probe 10 may be supported by the support 50 having a through hole formed in a substrate of a dielectric material such as ceramic or plastic, with the optical probe 10 passing through the through hole. Alternatively, the support 50 may have a structure in which thin plates of a dielectric material, each having a circular or rectangular through hole through which the optical probe 10 passes, are laminated. Furthermore, the optical probe 10 may be fixed by the support 50 having a structure in which a V-groove or U-groove is formed in a substrate. In this way, various methods can be used to support the optical probe 10.

[0017] The optical probe 10 is held so that the tip surface 101 faces the optical device 20 formed on a semiconductor wafer 200 placed on a stage 60. The semiconductor wafer 200 is held on the stage 60 by, for example, vacuum suction.

[0018] The optical device 20 is a silicon photonics device that combines optical and electronic circuits. The integration of these circuits increases the circuit's operating speed, improves functionality, and reduces power consumption due to the optical circuit's insensitivity to electromagnetically induced noise. Silicon photonics devices can be fabricated in large numbers on composite laminate substrates, such as silicon-on-insulator (SOI) substrates, using semiconductor microfabrication techniques, such as CMOS integrated circuits. For optical measurements of the optical device 20 formed on a semiconductor wafer 200, an optical signal terminal including a diffraction grating at the end of the silicon waveguide of the optical device 20 may be placed on the top surface of the semiconductor wafer 200 and used as the measurement input / output terminal. By placing a diffraction grating on the optical signal terminal of the optical device 20, the optical signal L emitted from the optical signal terminal of the optical device 20 propagates in the Z-axis direction, as shown in FIG. 1 .

[0019] The tip surface 101 of the optical probe 10 is optically connected to an optical signal terminal of the optical device 20, which emits an optical signal L with a radiation angle α. The tip surface 101 is a convex curved surface with a radius of curvature Ra. Details of the radius of curvature Ra will be described later. The optical signal L emitted from the optical device 20 is incident on the tip surface 101 of the optical probe 10.

[0020] The optical probe 10 is disposed at a working distance WD along the Z-axis direction from the optical device 20. The working distance WD is set within a range in which the optical probe 10 can receive the optical signal L emitted by the optical device 20. In other words, the working distance WD is set so that the incident range of the optical signal L on the distal end surface 101 is inside the core portion 11.

[0021] The base end face 102 of the optical probe 10 is optically connected to the light receiving element 310. That is, the optical signal L emitted from the optical device 20 propagates through the optical waveguide 100 of the optical probe 10, and then is emitted from the base end face 102 and enters the light receiving element 310, where it is photoelectrically converted. The light receiving element 310 is electrically connected to a measuring device (not shown), and the characteristics of the optical signal L are measured by the measuring device.

[0022] As described above, the core 11 has a refractive index distribution type structure. That is, the refractive index of the core 11 gradually decreases from the refractive index at the optical axis, which is the central axis C10 (hereinafter referred to as the "optical axis refractive index"), in the radial direction toward the cladding 12. In other words, the refractive index in the region of the core 11 adjacent to the cladding 12 (hereinafter referred to as the "edge refractive index") is the smallest. Using the optical axis refractive index n0 and the edge refractive index n1, the refractive index distribution N(x) of the core 11 at a position at a distance x from the optical axis in the X direction is expressed by the following parabolic equation (1): N(x)=n0×{1-(A 1 / 2 ×x) 2 / twenty one) In equation (1), A 1 / 2 is the refractive index profile coefficient, which is given by equation (2): A 1 / 2 ={(n0 2 -n1 2 ) / (n0×Cr) 2} 1 / 2 ···(2)

[0023] The larger the difference between the optical axis refractive index n0 and the outer edge refractive index n1 (n0-n1), the greater the refractive index distribution coefficient A 1 / 2 is large, and the confinement of the propagating optical signal in the optical waveguide 100 is strong. "Confinement" means that the propagating optical signal propagates inside the core portion 11 and is not radiated to the cladding portion 12. Note that the refractive index profile coefficient A 1 / 2 The larger the amplitude of the optical signal propagating through the optical waveguide 100, the smaller the amplitude of the optical signal propagating through the optical waveguide 100.

[0024] On the other hand, the optical axis refractive index n0, the outer edge refractive index n1, and the refractive index distribution coefficient A 1 / 2Once this is set, the core diameter Cr of the optical waveguide 100 can be set as shown in equation (3): Cr={(n0 2 -n1 2 ) / (A 1 / 2 ×n0 2} 1 / 2 ···(3)

[0025] By strengthening the confinement, even if a fluctuation such as a positional deviation in the XY direction or a positional deviation in the beam diameter with respect to the optical axis occurs between the optical probe 10 and the optical device 20 (hereinafter also referred to as "positional deviation"), the optical connection between the optical probe 10 and the optical device 20 is stable. For example, according to the study by the inventors, when the refractive index distribution coefficient A 1 / 2 is preferably 0.004 or more.

[0026] The optical path length T of the optical waveguide 100 is expressed by the following equation (4): T=2π×P / A 1 / 2 ···(4) In equation (4), P is called the pitch length, which corresponds to one period (2π) of the propagating optical signal, and is an arbitrary value greater than zero.

[0027] If P=1, T=2π / A 1 / 2 and is the waveform length of one period of the propagating optical signal. In the optical probe 10, the radius of curvature Ra of the tip facet 101 may be set so as to satisfy the relationship Cr≧Ra. The smaller the radius of curvature Ra of the tip facet 101 is set, the smaller the amplitude of the propagating optical signal in the optical waveguide 100 can be made.

[0028] Because the distal end surface 101 is a convex curved surface, the optical signal L incident on the distal end surface 101 is refracted with respect to the optical axis. This reduces the amplitude of the propagating optical signal inside the optical waveguide 100. This provides a spatial margin of the size (2 × Cr) of the XY plane of the core 11 with respect to the propagation path of the propagating optical signal. As a result, even if the position of the optical device 20 is misaligned in the XY directions with respect to the optical axis of the optical probe 10, the propagating optical signal propagates through the core 11 without being radiated to the cladding 12. The propagating optical signal propagated through the core 11 is then stably incident on the light-receiving element 310 via the proximal end surface 102 of the optical probe 10.

[0029] The radiation angle α of the optical signal L emitted from the optical signal terminal of the optical device 20 is determined by the beam diameter ωg of the optical signal L. The relationship between the beam diameter ωg and the radiation angle α is approximately expressed by equation (5): α / 2=tan -1 {λ / (π ωg)} (5) In equation (5), λ is the wavelength of the optical signal L. The numerical aperture NA of the optical probe 10 is NA=sin(α / 2).

[0030] From Figure 1, we can approximately obtain the following equation (6): Sin(α / 2)=tan -1 (Cr / WD) (6) The numerical aperture NA and the beam diameter ω have a relationship such that the larger the numerical aperture NA, the smaller the beam diameter ω. The range of the effective working distance WD at which the optical probe 10 can receive the optical signal L is expressed by equation (7): Cr / tan{sin -1 (NA)}≧WD>0 (7) If the working distance WD satisfies the condition of formula (7), it is possible for all of the optical signals L from the optical device 20 to be incident on the optical waveguide 100 from the tip facet 101 .

[0031] When the beam diameter formed by the tip surface 101 having the radius of curvature Ra is ωa and the beam diameter of the optical signal L is ωg, the radius of curvature Ra is set so that the relationship of equation (8) holds: ωa>ωg (8) For example, when the wavelength λ of the optical signal L is 1.55 μm and the beam diameter ωg is 4 μm, the numerical aperture NA of the optical device is 0.24. In this case, the distal end surface 101 of the optical probe 10 is spherically machined to have a radius of curvature Ra so that the numerical aperture NA of the distal end surface 101 is smaller than 0.24. Furthermore, when the core diameter Cr is 32.5 μm, the working distance WD is 130 μm or less.

[0032] Figure 2 shows the relationship between the mode field pattern Pa of the light incident on the optical probe 10 and the mode field pattern Pg of the optical signal L when the above conditions are met. By making the tip surface 101 curved, a mode field pattern is formed that exhibits a broad beam intensity PW distribution with a flat peak. As shown in Figure 2, the mode field pattern Pa has a larger mode field diameter and a wider beam diameter than the mode field pattern Pg. Therefore, even if the optical probe 10 and the optical device 20 are misaligned due to a positional shift, the overlapping portion of the mode field patterns does not change. This prevents fluctuations in the connection strength between the optical device 20 and the optical probe 10. In other words, even if there is a positional shift, loss of the propagating optical signal is suppressed. The mode field pattern Pa depends on the numerical aperture NA (= sin α), which is related to the radius of curvature R of the tip surface 101 of the optical probe 10.

[0033] In the above description, the optical signal L emitted from the optical device 20 travels in the normal direction to the top surface of the semiconductor wafer 200, and the central axis C10 of the optical probe 10 is in the normal direction to the semiconductor wafer 200. However, the traveling direction of the optical signal L may intersect with the normal direction. For example, if the angle between the traveling direction of the optical signal L and the normal direction to the semiconductor wafer 200 is angle θ, the central axis C10 of the optical probe 10 may be installed so as to be tilted by the angle θ in the same direction as the traveling direction of the optical signal L.

[0034] FIG. 3 shows a case where an optical signal L emitted from a light-emitting element 320 is incident on an optical signal terminal of an optical device 20 via an optical probe 10. The light-emitting element 320 is, for example, a semiconductor laser element. The optical signal L emitted from a semiconductor laser element having a numerical aperture NAr is incident on the base end face 102 of the optical probe 10, propagates through the optical waveguide 100, and is emitted from the tip end face 101. In FIG. 3, an optical probe 10 having a tip end face 101 with a radius of curvature Rb is used, and an optical signal L with a radiation angle α is emitted from the tip end face 101.

[0035] In this case, the relationship between the beam diameter ωb formed by the tip end face 101 with a radius of curvature Rb and the beam diameter ωg of the optical device 20 is set such that NAr < NAg under the same conditions as in the case of FIG. 1, and the radius of curvature Rb is set so that the relationship of Equation (9) holds: ωb > ωg ···(9) In Equation (9), the beam diameter of the optical signal L received by the optical device 20 is ωg, and the numerical aperture for realizing it is NAg.

[0036] By satisfying Equation (9), the relationship between the beam diameter ωg and the beam diameter ωb becomes the same as the relationship between the beam diameter ωg and the beam diameter ωa shown in FIG. 2. Therefore, even if a positional deviation in the XY direction occurs with respect to the optical axis of the optical probe 10, fluctuations in the intensity of the light incident on the optical device 20 are suppressed.

[0037] In the above description, the radius of curvature of the front end face 101 when the optical signal L output from the optical device 20 is incident thereon is defined as Ra, and the radius of curvature of the front end face 101 when the optical signal L output from the front end face 101 is incident on the optical device 20 is defined as Rb. The values ​​of the radii of curvature Ra and Rb may be the same or different. For example, the radius of curvature Rb may be smaller than the radius of curvature Ra. This allows the optical signal L to be reliably incident on a small-sized diffraction grating. Hereinafter, the radii of curvature Ra and Rb will also be collectively referred to as the "radius of curvature R." Similarly, the beam diameter ωa formed by the front end face 101 with the radius of curvature Ra and the beam diameter ωb formed by the front end face 101 with the radius of curvature Rb may be the same or different. Hereinafter, the beam diameters ωa and ωb will also be collectively referred to as the "beam diameter ω."

[0038] 4A and 4B are graphs showing the basic characteristics of the optical waveguide 100 of the optical probe 10. FIG. 4A is a graph showing the relationship between the numerical aperture NA and the beam diameter ω of the propagating optical signal. The larger the numerical aperture NA, the narrower the beam diameter ω. For example, if the wavelength λ of the propagating optical signal is 1.55 μm and the numerical aperture NA is 0.24, the beam diameter ω is 4 μm. When the beam diameter of the optical signal L of the optical device 20 is ωg and the numerical aperture that realizes this is NAg, the beam diameter of the propagating optical signal of the optical probe 10 is ωa and the numerical aperture is NAa, and the radius of curvature R is set so that NAg > NAa.

[0039] Depending on the shape of the optical device 20, the beam diameter ωg of the optical signal L may be asymmetric in a first direction (e.g., the X direction) and a second direction (e.g., the Y direction) perpendicular to the first direction in an XY plane perpendicular to the normal direction of the vertex of the distal end face 101. For example, if the beam diameters in the first and second directions are defined as a first beam diameter ωg1 and a second beam diameter ωg2, respectively, the first beam diameter ωg1 and the second beam diameter ωg2 have different values. In this case, by making the mode field diameter of the optical probe 10 asymmetric in the first and second directions, the connection efficiency between the optical device 20 and the optical probe 10 is improved and the measured characteristics are stabilized. For example, if the radius of curvature of the distal end face 101 of the optical probe 10 in the first direction is defined as a first radius of curvature R1 and the radius of curvature in the second direction is defined as a second radius of curvature R2, the first radius of curvature R1 and the second radius of curvature R2 are set to different values. In this case, the difference between the first radius of curvature R1 and the second radius of curvature R2 corresponds to the difference between the first beam diameter ωg1 and the second beam diameter ωg2. As described above, the first radius of curvature R1 in the first direction (e.g., X direction) and the second radius of curvature R2 in the second direction (e.g., Y direction) perpendicular to the first direction may be different.

[0040] FIG. 4B shows the numerical aperture NA and refractive index distribution coefficient A of the optical waveguide 100 of the optical probe 10. 1 / 2 The value of the optical axis refractive index n0 is changed in the range of 1.44 to 1.55. By increasing the optical axis refractive index n0, the refractive index distribution coefficient A 1 / 2 For example, when the numerical aperture NA is near 0.28, the refractive index distribution coefficient A 1 / 2 is 0.006. Using the optical waveguide 100 having the above parameters, the numerical aperture NAg of the optical device 20 satisfies the condition NAg≧NA.

[0041] Fig. 5 is a graph showing the relationship between the ratio of the mode field diameter of the optical signal L to the mode field diameter of the optical probe 10 (MFD ratio MR) and loss. In Fig. 5, the horizontal axis represents MR = ωa / ωg, and the loss Pd is plotted using the deviation d = B / ωa, which is a parameter using the amount of misalignment B in the X and Y directions. As shown in Fig. 5, when the MFD ratio MR is greater than 1, the loss relative to the amount of misalignment B in the X and Y directions is small. For example, when MR = 1.5 and d = 0.2, the loss is small, about 0.1 dB, and the impact of differences in mode field diameter is small.

[0042] FIG. 6 is a table showing conditions for reducing the amplitude of the propagating optical signal propagating through the optical probe 10. The propagating optical signal propagates sinusoidally through the refractive index distribution optical waveguide 100. Therefore, a smaller amplitude of the propagating optical signal can prevent the propagating optical signal from being radiated to the cladding portion 12 due to fluctuations in amplitude caused by the positional misalignment B and angular misalignment Δ of the optical signal L. The angular misalignment Δ is the angle between the optical axis of the optical signal L and the optical axis of the optical probe 10. The condition for reducing the amplitude of the propagating optical signal is the refractive index distribution coefficient A of the optical waveguide 100. 1 / 2 is preferably larger, and the radius of curvature R of the tip surface 101 of the optical probe 10 is made smaller. Furthermore, the amplitude of the propagating light signal can be made smaller as the working distance WD is larger. By making the amplitude of the propagating light signal smaller, the optical connection between the optical probe 10 and the optical device 20 can be stabilized even if a positional misalignment B in the X and Y directions and an angular misalignment Δ occur with respect to the optical axis, and measurements can be made with stable intensity characteristics even if positional fluctuations occur.

[0043] 7A to 7D show ray tracing of 1P (one period) of a propagating optical signal propagating through the optical waveguide 100 of the optical probe 10. The conditions of the optical waveguide 100 are: A 1 / 2 =0.006, Cr=32.5 μm, and the numerical aperture NA of the optical signal L from the optical device 20 is 0.24. The horizontal axis in Figures 7A to 7D is the position M from the distal end face 101 toward the proximal end face 102, and the vertical axis is the distance D in the inner diameter direction from the central axis C10.

[0044] 7A to 7D compare the state of the propagating light signal when the radius of curvature Ra of the tip surface 101 of the optical probe 10 is 15 μm or 20 μm and the working distance WD is 10 μm or 15 μm. Note that this is the case when the positional misalignment B=0 μm and there is no angular misalignment. As shown in FIGS. 7A to 7D, the smaller the radius of curvature Ra of the tip surface 101 of the optical probe 10, the smaller the amplitude of the propagating light signal, and the longer the working distance WD, the smaller the amplitude of the propagating light signal.

[0045] 8A to 8D show ray tracing of 1P (one period) of a propagating optical signal propagating through the optical waveguide 100. The horizontal axis of FIGS. 8A to 8D represents the position M from the distal end face 101 toward the proximal end face 102, and the vertical axis represents the distance D in the inner diameter direction from the central axis C10. FIGS. 8A and 8B show the state of 1P (one period) of a propagating optical signal when the radius of curvature Ra of the distal end face 101 is 15 μm or 20 μm, the working distance WD is 5 μm, and the positional misalignment B is 2 μm. In both FIGS. 8A and 8B, even when the positional misalignment B=2 μm occurs, the propagating optical signal is contained within the core diameter Cr and there is almost no leakage from the optical waveguide 100. It is also estimated that a smaller radiation angle α of the incident and exit light provides more tolerance to positional misalignment even if the amplitude of the propagating optical signal fluctuates. Figures 8C and 8D show ray tracing of the propagating optical signal when an angular misalignment Δ of 2.4 degrees occurs in addition to the positional misalignment B relative to the optical axis under the above conditions. In both Figures 8C and 8D, amplitude fluctuations are observed, but the propagating optical signal is able to propagate within the optical waveguide 100. From the above, it can be seen that reducing the radiation angle α of the incident and exiting light is effective in providing a margin for fluctuations in the propagating optical signal. Furthermore, by increasing the working distance WD, it is possible to provide a margin for amplitude fluctuations in the propagating optical signal when a positional misalignment B and an angular misalignment Δ occur relative to the optical axis. This makes it less likely for intensity fluctuations to occur, resulting in stable measurements.

[0046] <Modification> In the optical probe 10 according to a first modification of the embodiment shown in FIG. 9, the extension direction of the optical waveguide 100 reaching the base end surface 102 intersects the base end surface 102 at an angle. As a result, the direction of propagation of the propagating optical signal changes at the boundary between the optical waveguide 100 and the base end surface 102. For example, the extension direction of the optical waveguide 100 intersects the base end surface 102 at an angle of 45 degrees, and the direction of propagation of the propagating optical signal changes by 90 degrees. By arranging the light-receiving element 310 in the changed direction of propagation of the propagating optical signal, the light-receiving element 310 receives the optical signal L emitted from the optical device 20. For example, the base end surface 102 may be inclined with respect to the central axis C10 by mirror polishing (plus a reflective coating made of a dielectric multilayer film may be applied). An air layer is present outside the base end surface 102.

[0047] 10 shows an optical probe 10 according to a second modification of the embodiment, in which an optical element 70 for changing the direction of propagation of a propagating optical signal is disposed on the proximal end surface 102. The optical element 70 is, for example, a minute prism. The optical element 70 changes the direction of propagation of the propagating optical signal by, for example, 90 degrees. As in FIG. 9, by disposing a light receiving element 310 in the changed direction of propagation of the propagating optical signal, the light receiving element 310 receives the optical signal L emitted from the optical device 20.

[0048] 9 and 10, the light receiving element 310 can be installed in a direction intersecting the optical axis of the optical probe 10 (for example, at 90 degrees). Alternatively, the light emitting element 320 can be installed in a direction intersecting the optical axis of the optical probe 10. This allows, for example, the light receiving element 310 or the light emitting element 320 to be arranged perpendicular to the optical axis of the optical probe 10. This allows for flexibility in the mounting of the probe card that holds the optical probe 10.

[0049] As described above, the optical probe 10 according to the embodiment has a curved tip surface 101 and a refractive index distribution type optical waveguide 100, and therefore is less likely to experience intensity fluctuations even when there is a positional misalignment B in the X-axis direction and a Y-axis direction and an angular misalignment Δ. Therefore, two-stage alignment, consisting of coarse position adjustment and precise position adjustment using an actuator capable of six-axis degree-of-freedom adjustment, is not required. For example, the optical probe 10 and the optical device 20 can be aligned simply by position adjustment in the X, Y, and Z axes and rotational adjustment in the Z axis.

[0050] On the other hand, precise alignment is required to measure an optical device 20 with an input / output mode field diameter of the optical signal terminal of approximately several micrometers using a single-mode fiber with a small numerical aperture (NA) of approximately 0.11 to 0.13 as an optical probe. Furthermore, minute vibrations and fluctuations are prone to radiation loss of light propagating within the fiber, making the measurement results sensitive and unstable, and making it difficult to ensure connection stability. For this reason, it is difficult to stably measure an optical device 20 using a single-mode fiber.

[0051] In contrast, with the optical probe 10 according to the embodiment, the intensity fluctuation is small with respect to the positional misalignment amount B and the angular misalignment amount Δ, so that the time required to align the optical probe 10 and the optical device 20 can be shortened and the increase and fluctuation of the connection loss can be suppressed.

[0052] The radius of curvature R of the tip surface 101 of the optical probe 10 may be, for example, about 5 to 20 μm. By making the tip surface 101 a curved surface, the refractive index distribution type optical waveguide 100 has a wide mode field pattern with a flat peak in the beam intensity distribution. Therefore, even if a positional fluctuation such as the occurrence of a positional misalignment amount B occurs, the overlapping portion of the mode field of the optical waveguide 100 and the optical signal L does not change. As a result, a stable connection without intensity fluctuations can be achieved.

[0053] Furthermore, compared to optical probes with single-mode optical waveguides, the optical probe 10 has more leeway in confining optical signals in the Z-axis direction, and the core inner diameter 2Cr can be made approximately 10 times larger, allowing for a wider working distance WD.

[0054] Furthermore, the numerical aperture of the refractive index distribution type optical waveguide 100 of the optical probe 10 is approximately 0.25 to 0.30, which is larger than the numerical aperture of a single-mode fiber, which is 0.11 to 0.13. Therefore, even when an angle misalignment Δ occurs, the confinement is strong, and by reducing the amplitude of the propagating optical signal propagating through the optical waveguide 100, radiation loss is suppressed and fluctuations in the intensity of the propagating optical signal are unlikely to occur.

[0055] As described above, the optical probe 10 enables stable propagation of the propagating optical signal despite misalignment in the X, Y, and Z axes and angular misalignment of the optical axis, resulting in stable connection characteristics. Therefore, stable measurements are possible even when a multi-core optical probe 10 is configured and used for measurement. Furthermore, by using a probe set that integrates the optical probe 10 with an electric probe that transmits and receives electric signals to and from the optical device 20, and by providing the electric probe with several tens of micrometers of elasticity when connected to the optical device 20, it is possible to align the electric probe and the optical probe 10 in a single step. This simplifies the mechanical components of the measurement system, facilitates control, and significantly reduces measurement and inspection time.

[0056] An optical probe array may be formed by arranging a plurality of optical probes 10. By using the optical probe array to measure the optical device 20, it is possible to simultaneously align multiple optical signal terminals with the optical probes 10. Therefore, by using the optical probe array, it is possible to measure the characteristics of the optical device 20 in a short time. In other words, by using an optical probe array to connect the optical probes 10 and the optical signal terminals with multiple cores, the time required for alignment can be significantly reduced compared to a measurement method in which the optical probes 10 are aligned with the optical signal terminals one by one.

[0057] When an optical probe array is formed by arranging multiple optical probes 10, there is a possibility that an error of ±several μm may occur in the position of the optical probes 10 arranged in the optical probe array. However, the optical probe 10 has a high tolerance for positional misalignment B in the X, Y, and Z axes and angular misalignment Δ. Therefore, an optical probe array formed with the optical probes 10 can reduce intensity fluctuations even if the relative positions of the optical probe 10 and the optical device 20 fluctuate or if angular misalignment occurs in the angular direction of the optical axis. Therefore, using an optical probe array formed with the optical probes 10, it is possible to easily align the optical probes 10 with each of the optical signal terminals of the optical devices 20, many of which are formed on the semiconductor wafer 200, while reducing intensity fluctuations.

[0058] That is, measurement using an optical probe array composed of optical probes 10 can shorten the measurement time and reduce the connection loss fluctuation by simultaneously aligning and measuring multiple optical devices 20. As a result, measurement and evaluation of the optical devices 20 can be performed stably and easily, improving yield and productivity.

[0059] 11A and 11B show configuration examples of a probe system 1 using an optical probe 10. As shown in Fig. 11A, the probe system 1 includes a probe head 40 as a support for supporting the optical probe 10. The probe head 40 holds an optical probe array 15 in which a plurality of optical probes 10 are arranged in a multicore array. For example, although not shown, the optical probes 10 are arranged at equal intervals on the optical probe array 15 along the Y-axis as well as the X-axis.

[0060] 11B, in the probe system 1, the optical probe 10 is supported using a probe head 40 made of a dielectric material in which a V-shaped groove 400 is formed in a plan view seen from the Z-axis direction. The optical probe 10 is fitted and fixed in the V-shaped groove 400 formed in the probe head 40. As an alternative method, a number of through-holes may be formed in the probe head 40, and the optical probe 10 may be inserted into the through-holes and fixed.

[0061] The optical probe 10 held by the probe head 40 is positioned so that the tip surface 101 faces the positions of the optical signal terminals of the plurality of optical devices 20 formed in an array on the semiconductor wafer 200. If the positional intervals of the optical signal terminals of the optical devices 20 are uniform, measurement of the optical devices 20 using the optical probe 10 becomes smooth and easy.

[0062] The probe system 1 includes a moving device 45 capable of precisely adjusting the position of the probe head 40 to align the tip surface 101 of the optical probe 10 with the optical device 20. The probe head 40 may be moved in the X-axis, Y-axis, and Z-axis directions by controlling the moving device 45. Furthermore, the probe head 40 may be moved in a rotational direction about the Z-axis by controlling the moving device 45. Note that if such a position adjustment mechanism is provided on the prober on which the semiconductor wafer 200 to be measured is mounted, the moving device 45 is not necessary. In this manner, the optical probe 10 and the optical device 20 can be aligned in the probe system 1. Note that a method is also possible in which the position of the probe head 40 is fixed and the stage 60 is moved in the X-axis, Y-axis, and Z-axis rotational directions. Alternatively, the probe head 40 may be moved in the X-axis and Y-axis directions, and the stage 60 may be moved in the Z-axis direction. In this manner, various adjustment methods can be used to align the optical probe 10 with the optical device 20.

[0063] The probe system 1 may also include an electric probe for applying a current or voltage to drive the optical device 20. In this case, the alignment of the optical probe 10 with the optical device 20 and the alignment of the electric probe with the optical device 20 may be performed independently, or the optical probe 10 and the electric probe may be configured and aligned as an integrated unit. The optical probe 10 has a high tolerance for the positional misalignment B and the angular misalignment Δ, so connection loss can be reduced even when the alignment of the electric probe with the optical device 20 is on the order of microns, which does not require high precision on the order of submicrons.

[0064] After aligning the optical probe 10 and the optical device 20, an optical signal is propagated through the probe system 1 shown in Fig. 11A to measure the optical device 20. For example, the optical probe 10 receives the optical signal L emitted by the optical device 20. Alternatively, an optical signal emitted from a light-emitting element disposed opposite the base end face 102 propagates through the optical probe 10 and is incident on the optical device 20 on the semiconductor wafer 200.

[0065] 11 shows a configuration in which the optical probes 10 are aligned in an array, the optical probe array 15 may have other configurations. For example, the optical probe array 15 may have a configuration in which the optical probes 10 are arranged at any positions in the X-axis direction or the Y-axis direction.

[0066] (Other embodiments) Although the present invention has been described above by way of certain embodiments, the descriptions and drawings that form part of this disclosure should not be understood as limiting the present invention. From this disclosure, various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art. It goes without saying that the present invention also includes various embodiments not described above. [Explanation of symbols]

[0067] 1 Probe System 10 Optical Probes 11 Core 12 Cladding section 15 Optical probe array 20 Optical Devices 40 probe head 45 Mobile Device 50 Support 60 stages 70 Optical Elements 100 optical waveguide 101 Tip surface 102 Proximal surface 200 semiconductor wafers 310 Photodetector 320 Light-emitting element 400 grooves

Claims

1. An optical probe for transmitting and receiving optical signals to and from an optical device, a tip end surface that is a convex curved surface facing the optical device; a refractive index distribution type optical waveguide having a first end connected to the tip surface; a base end surface to which a second end of the optical waveguide is connected; An optical probe comprising:

2. The optical probe according to claim 1 , wherein the optical waveguide is linear from the distal end surface to the proximal end surface.

3. the optical waveguide is composed of a core portion and a clad portion disposed on the outer periphery of the core portion, the radius of curvature R of the tip surface and the inner diameter 2×Cr of the core portion satisfy the relationship R≦Cr; The optical probe according to claim 1 .

4. the optical waveguide is composed of a core portion and a clad portion disposed on the outer periphery of the core portion, The refractive index distribution coefficient A of the optical waveguide 1 / 2 , an inner diameter 2×Cr of the core portion, an optical axis refractive index n0 in the optical axis of the core portion, and an outer edge refractive index n1 in the region of the core portion adjacent to the cladding portion, Cr={(n0 2 -n1 2 ) / (A 1 / 2 ×n0 2 } 1 / 2 The optical probe according to claim 1 , which satisfies the relationship:

5. In a plane perpendicular to the normal direction of the vertex of the tip surface, The optical probe according to claim 1 , wherein a first radius of curvature R1 in a first direction is different from a second radius of curvature R2 in a second direction perpendicular to the first direction.

6. an extending direction of the optical waveguide that reaches the base end surface and the base end surface intersect obliquely; a propagation direction of the optical signal changes at a boundary between the optical waveguide and the base end surface; The optical probe according to claim 1 .

7. The extension direction and the base end surface intersect at 45 degrees, The traveling direction of the optical signal changes by 90 degrees. The optical probe according to claim 6 .

8. The optical probe according to claim 1 , wherein an optical element for changing the traveling direction of the optical signal is disposed on the base end surface.

9. The optical probe according to claim 8 , wherein the optical element changes the propagation direction of the optical signal by 90 degrees.

10. An optical probe array comprising a plurality of optical probes according to any one of claims 1 to 9 arranged in an array.

11. The optical probe according to any one of claims 1 to 9; a probe head that holds the optical probe; a moving device that moves the probe head to align the tip surface of the optical probe with the optical device; A measurement system comprising:

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