Optical probe, optical probe array, and probe system

Abstract

The invention provides an optical probe, an optical probe array and a probe system. This optical probe transmits and receives an optical signal to and from an optical device, and is provided with: a tip surface which 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; and a base end surface to which the second end portion of the optical waveguide is connected.

Description

Technical Field

[0001] This invention relates to an optical probe, an optical probe array, and a probe system used in the measurement of optical devices. Background Technology

[0002] Silicon-based photonics technology is used to form silicon devices (hereinafter referred to as "optical devices") for the propagation of optical signals on semiconductor wafers. To measure the characteristics of optical devices formed on semiconductor wafers, optical probes and electron probes are used. In measurements using optical probes, the optical devices and optical probes are aligned to reduce the loss of the optical signal (hereinafter referred to as "propagating optical signal") propagating in the optical waveguide of the optical probe.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2022-550547 Summary of the Invention

[0006] When the optical transmission path of the optical probe through which the propagating optical signal passes is single-mode, the numerical aperture of the optical transmission path is small. Furthermore, the size of the optical signal terminals of the optical device, which handle the incident and emitted optical signals, is relatively small, around several μm. Therefore, the tolerance for error when aligning the optical signal terminals of the optical device with the front end face of the optical probe is low. Consequently, it is difficult to accurately align the optical device and the optical probe. For example, after coarse positioning adjustment to bring the optical device and the optical probe together, a six-axis actuator capable of adjusting the XYZ axes and rotating along each axis is used for precision positioning adjustment. As a result, in the measurement of the optical device, there is an increase in measurement time due to the time required for positioning alignment, and an increase in connection loss due to inaccurate positioning, leading to variations in measurement.

[0007] In view of the above-mentioned problems, the object of the present invention is to provide an optical probe, an optical probe array, and a probe system that can suppress the time required for alignment with optical devices and suppress the increase and variation of connection loss.

[0008] The optical probe involved in the embodiment includes: a front end face, which is a convex curved surface facing the optical device; a refractive index distribution type optical waveguide, the first end of which is connected to the front end face; and a base end face, the second end of which is connected to the base end face.

[0009] According to the embodiments, an optical probe, an optical probe array, and a probe system can be provided that can suppress the time required for alignment with the position of an optical device and suppress the increase in connection loss. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating the structure of the optical probe involved in the embodiment.

[0011] Figure 2 It is a graph showing the shape of the mode field pattern of the optical probe involved in the embodiment.

[0012] Figure 3 This is a schematic diagram illustrating another example of the use of the optical probe involved in the embodiment.

[0013] Figure 4A It is a graph showing the relationship between numerical aperture and the diameter of the beam carrying the optical signal.

[0014] Figure 4B It is a graph showing the relationship between numerical aperture and refractive index distribution coefficient.

[0015] Figure 5 It 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 and the loss in the embodiment.

[0016] Figure 6 This is a table showing the conditions under which the amplitude of the optical signal propagating in the optical probe is reduced according to the embodiments.

[0017] Figure 7A This is a graph (one) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0018] Figure 7B This is a graph (second one) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0019] Figure 7C This is a graph (third one) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0020] Figure 7D This is a graph (fourth one) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0021] Figure 8A This is a graph (fifth) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0022] Figure 8B This is a graph (sixth) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0023] Figure 8C This is a graph (seventh) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0024] Figure 8D This is a graph (eighth one) showing the ray tracing of the optical signal propagating in the optical waveguide of the optical probe involved in the embodiment.

[0025] Figure 9 This is a schematic diagram illustrating the structure of the optical probe involved in the first variation of the embodiment.

[0026] Figure 10 This is a schematic diagram illustrating the structure of the optical probe involved in the second variation of the embodiment.

[0027] Figure 11A This is a schematic diagram showing the structure of a probe system using the optical probe involved in the embodiment.

[0028] Figure 11B This is a schematic top view showing the structure of a probe system using the optical probe involved in the embodiment. Detailed Implementation

[0029] Next, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the drawings, the same or similar parts are labeled with the same or similar reference numerals. However, it should be noted that the drawings are schematic. Furthermore, the embodiments shown below illustrate apparatus and methods for embodying the technical concept of the present invention, and the embodiments of the present invention do not specifically specify the construction, arrangement, etc., of structural components as described below. Various modifications can be made to the embodiments of the present invention within the scope of the claims.

[0030] Figure 1 The optical probe 10 involved in the illustrated embodiment transmits and receives optical signals with the optical device 20 formed on the semiconductor wafer 200. Figure 1 The diagram illustrates the propagation of an optical signal L emitted from optical device 20 and incident on optical probe 10 within the optical waveguide 100 of optical probe 10. Optical probe 10 has: a front end face 101, which is a convex curved surface facing optical device 20; a refractive index-distributed optical waveguide 100, the first end of which is connected to the front end face 101; and a base end face 102, to which the second end of the optical waveguide 100 is connected.

[0031] like Figure 1 As shown, 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. Figure 1The left-right direction of the paper is defined as the X-axis, and the direction perpendicular to the paper is defined as the Y-axis. Hereinafter, the X-axis, Y-axis, and Z-axis will be collectively referred to as the "XYZ-axis directions".

[0032] The optical probe 10 can employ optical fiber, or a structure combining optical fiber and a lens. The optical waveguide 100 comprises a core 11 and a cladding portion 12 disposed around the outer periphery of the core 11. The optical waveguide 100 is designed such that the refractive index of the core 11 gradually decreases outward from the optical axis, which is the central axis of the optical waveguide 100. In other words, the refractive index of the core 11 gradually decreases from the optical axis of the optical probe 10 towards the region adjacent to the cladding portion 12. The shape of the cross-section of the optical probe 10 along the XY plane (hereinafter referred to as "cross-sectional shape") can be circular or rectangular.

[0033] Hereinafter, the length of the optical waveguide 100 of the optical probe 10 from the front end face 101 to the base end face 102 will also be referred to as the "optical path length". Figure 1 The optical path length of the optical probe 10 shown is T.

[0034] like Figure 1 As shown, the inner diameter of the core 11 of the optical probe 10 is set to 2×Cr, and the inner diameter of the optical probe 10, including the cladding portion 12, is set to 2×Cd. When the cross-sectional shape of the core 11 is circular, the radius of the core 11 is Cr, and the radius of the optical probe 10 is Cd. When the cross-sectional shape of the core 11 is rectangular, the dimensions of the cross-sectional shape of the core 11 in the X and Y directions are 2×Cr, and the dimensions of the cross-sectional shape of the optical probe 10 in the X and Y directions are 2×Cd. Hereinafter, half the inner diameter of the core 11 is called the core radius Cr, and half the inner diameter of the cladding portion 12 is called the cladding radius Cd. The core radius Cr is the length from the central axis C10 of the optical waveguide 100 to the boundary between the core 11 and the cladding portion 12. The cladding radius Cd is the length from the central axis C10 to the outer edge of the optical probe 10.

[0035] For example, such as Figure 1 As shown, the optical probe 10 is held by the support body 50 with its central axis C10 in a straight line. In other words, the optical waveguide 100 is straight from the front end face 101 to the base end face 102. Because the optical waveguide 100 is straight, the propagating optical signal in the optical waveguide 100 will not produce optical path difference, and the occurrence of multimode can be suppressed.

[0036] For example, when the optical probe 10 is an optical fiber, the fiber is held in place by the support 50 to prevent bending. For instance, the optical probe 10, passing through a through-hole, can be supported by the support 50, which is formed by creating a through-hole in a substrate of a dielectric material such as ceramic or plastic. Alternatively, the support 50 can be constructed by stacking thin sheets of dielectric material having circular or rectangular through-holes through which the optical probe 10 passes. Furthermore, the optical probe 10 can be fixed by the support 50, which has a V-groove or U-groove formed in the substrate. Various methods can be employed to support the optical probe 10 in this way.

[0037] The optical probe 10 is held with its front end 101 facing the optical device 20 formed on the semiconductor wafer 200 placed on the stage 60. The semiconductor wafer 200 is held on the stage 60, for example, by vacuum adsorption.

[0038] Optical device 20 is a silicon-based photonic device that integrates optical and electronic circuits, thereby achieving high-speed operation, improved functionality, and reduced power consumption due to the insensitivity of optical circuits to electromagnetic noise. A large number of silicon-based photonic devices can be formed on composite substrates such as SOI (Silicon on Insulator) substrates using silicon and quartz through semiconductor microfabrication techniques such as CMOS integrated circuits. In optical measurement of optical device 20 formed on semiconductor wafer 200, the optical signal terminal of optical device 20, including a diffraction grating at the silicon waveguide end, can be disposed on the upper surface of semiconductor wafer 200 as the incident and exit ends for measurement. By arranging a diffraction grating at the optical signal terminal of optical device 20, such as... Figure 1 As shown, the optical signal L emitted from the optical signal terminal of the optical device 20 travels along the Z-axis.

[0039] The front end face 101 of the optical probe 10 is optically connected to the optical signal terminal of the optical device 20 for emitting a light signal L with a radiation angle α. The front end face 101 is a convex surface with a radius of curvature Ra. Details about the radius of curvature Ra will be described later. The light signal L emitted from the optical device 20 is incident on the front end face 101 of the optical probe 10.

[0040] The optical probe 10 is configured to be separated from the optical device 20 by a working distance WD along the Z-axis. The working distance WD is set within the range where the optical probe 10 can receive the light signal L emitted by the optical device 20. In other words, the working distance WD is set such that the incident range of the light signal L at the front end face 101 is inside the core 11.

[0041] The base surface 102 of the optical probe 10 is optically connected to the light-receiving element 310. That is, the light signal L emitted from the optical device 20 propagates in the optical waveguide 100 of the optical probe 10, then exits from the base surface 102 and is incident on the light-receiving element 310 for photoelectric conversion. The light-receiving element 310 is electrically connected to a measuring device (not shown), which measures the characteristics of the light signal L.

[0042] As described above, the core 11 has a refractive index distribution structure. That is, regarding the refractive index of the core 11, the refractive index 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"), along the radial direction toward the cladding portion 12. In other words, the refractive index (hereinafter referred to as the "peripheral refractive index") of the core 11 in the region adjacent to the cladding portion 12 is the smallest. Using the optical axis refractive index n0 and the peripheral refractive index n1, the refractive index distribution N(x) of the core 11 at a distance x in the X direction from the optical axis is expressed by the following parabolic equation (1):

[0043] N(x) = n0 × {1 - (A 1 / 2 ×x) 2 / twenty one)

[0044] In equation (1), A 1 / 2 It is the refractive index distribution coefficient, expressed by equation (2):

[0045] A 1 / 2 ={(n0) 2 -n1 2 ) / (n0×Cr) 2} 1 / 2 …(2)

[0046] The larger the difference (n0-n1) between the axial refractive index n0 and the outer edge refractive index n1, the larger the refractive index distribution coefficient A. 1 / 2 The larger the value, the stronger the confinement of the propagating optical signal in the optical waveguide 100. "Confinement" means that the propagating optical signal propagates within the core 11 without radiating into the cladding 12. Furthermore, the refractive index distribution coefficient A... 1 / 2 The larger the amplitude, the smaller the amplitude of the propagating optical signal in the optical waveguide 100.

[0047] On the other hand, when the axial refractive index n0, the peripheral refractive index n1, and the refractive index distribution coefficient A are set... 1 / 2 At that time, the core radius Cr of the optical waveguide 100 can be set as shown in equation (3):

[0048] Cr={(n0 2 -n1 2 ) / (A 1 / 2 ×n0) 2} 1 / 2 …(3)

[0049] By enhancing the constraint, the optical connection between the optical probe 10 and the optical device 20 remains stable even if there are positional shifts in the XY direction relative to the optical axis or positional shifts in the beam diameter (hereinafter also referred to as "positional shifts"). For example, according to the research of the inventors, the refractive index distribution coefficient A of the optical waveguide 100 is... 1 / 2 The preferred value is 0.004 or higher.

[0050] The optical path length T of the optical waveguide 100 is expressed by the following equation (4):

[0051] T = 2π × P / A / 1 / 2 …(4)

[0052] In equation (4), P is called the spacing length, which is equivalent to one period (2π) of the propagating optical signal and is any value greater than zero.

[0053] When P = 1, T = 2π / A 1 / 2 , is the length of one cycle of the propagating optical signal. In the optical probe 10, the radius of curvature Ra of the front end face 101 can be set to satisfy the relationship Cr≥Ra. The smaller the radius of curvature Ra of the front end face 101 is set, the smaller the amplitude of the propagating optical signal in the optical waveguide 100 can be.

[0054] Because the front end face 101 is a convex curved surface, the light signal L incident on the front end face 101 is refracted relative to the optical axis. Therefore, the amplitude of the propagating light signal is reduced inside the optical waveguide 100. As a result, the dimensions (2×Cr) of the core 11 in the XY plane can provide spatial margin relative to the propagation path of the propagating light signal. Consequently, even if the position of the optical device 20 is offset in the XY direction relative to the optical axis of the optical probe 10, the propagating light signal does not radiate towards the cladding portion 12 but propagates in the core 11. Then, the propagating light signal, after propagating in the core 11, is stably incident on the light-receiving element 310 via the base end face 102 of the optical probe 10.

[0055] The radiation angle α of the optical signal L emitted from the optical signal terminal of optical device 20 is defined 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):

[0056] α / 2=tan -1 {λ / (π·ωg)} …(5)

[0057] 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).

[0058] according to Figure 1 We can approximate the following equation (6):

[0059] α / 2=tan -1 (Cr / WD) …(6)

[0060] The numerical aperture NA and the beam diameter ω are related as follows: the larger the numerical aperture NA, the smaller the beam diameter ω. The effective working distance WD of the optical probe 10 that can receive the optical signal L is expressed by equation (7):

[0061] Cr / tan{sin -1 (NA)}≥WD>0 …(7)

[0062] If the working distance WD satisfies the condition of equation (7), then all the optical signal L from the optical device 20 can be incident from the front end face 101 onto the optical waveguide 100.

[0063] When the beam diameter formed by the front face 101 of the radius of curvature Ra is set as ωa and the beam diameter of the optical signal L is set as ωg, the radius of curvature Ra is set in such a way that the relationship of equation (8) holds:

[0064] ωa>ωg …(8)

[0065] For example, when the wavelength λ of the optical signal L is 1.55 μm and the beam diameter ωg is 2 μm, the numerical aperture NA of the optical device 20 is 0.24. In this case, regarding the radius of curvature Ra, the front end face 101 can be spherically machined so that the numerical aperture NA of the front end face 101 of the optical probe 10 is less than 0.24. Furthermore, when the core radius Cr is set to 32.5 μm, the working distance WD is 130 μm or less.

[0066] exist Figure 2 The diagram illustrates the relationship between the mode field pattern Pa of the incident light from the optical probe 10 and the mode field pattern Pg of the optical signal L, under the aforementioned conditions. A mode field pattern representing the distribution of the beam intensity PW, with a flat peak and wide amplitude, is formed by making the front end face 101 curved. Figure 2 As shown, compared to the mode field pattern Pg, the mode field pattern Pa has a larger mode field diameter and a wider beam diameter. Therefore, even if there is a positional change between the optical probe 10 and the optical device 20, the overlapping portion of the mode field pattern will not change. Consequently, there is no change in the connection strength between the optical device 20 and the optical probe 10. In other words, even with positional changes, the loss of the propagating optical signal can be suppressed. Furthermore, the mode field pattern Pa depends on the numerical aperture NA (=sin(α / 2)) related to the radius of curvature R of the front end face 101 of the optical probe 10.

[0067] The above describes the case where the light signal L emitted from the optical device 20 travels along the normal direction of the upper surface of the semiconductor wafer 200, and the central axis C10 of the optical probe 10 is in the normal direction of the semiconductor wafer 200. However, the direction of travel of the light signal L can also intersect the normal direction. For example, when the angle between the direction of travel of the light signal L and the normal direction of the semiconductor wafer 200 is angle θ, the central axis C10 of the optical probe 10 can be set to be tilted at an angle θ in the same direction as the direction of travel of the light signal L.

[0068] Figure 3 This illustrates the case where an optical signal L emitted from a light-emitting element 320 is incident via an optical probe 10 onto the optical signal terminal of an optical device 20. The light-emitting element 320 is, for example, a semiconductor laser element. The optical signal L emitted from the numerical aperture NAr semiconductor laser element is incident on the base end face 102 of the optical probe 10, propagates in the optical waveguide 100, and exits from the front end face 101. Figure 3 In this process, an optical probe 10 with a front end face 101 having a radius of curvature Rb is used, and a light signal L with a radiation angle α is emitted from the front end face 101.

[0069] In this case, the relationship between the beam diameter ωb formed by the front face 101 with radius of curvature Rb and the beam diameter ωg of the optical device 20 is related to... Figure 1 Under the same conditions, let NAr < NAG, and set the radius of curvature Rb in a way that makes the relationship in equation (9) hold:

[0070] ωb>ωg …(9)

[0071] In equation (9), the beam diameter of the optical signal L received by the optical device 20 is set as ωg, and the numerical aperture that realizes the beam diameter is set as NAg.

[0072] By satisfying equation (9), the relationship between beam diameter ωg and beam diameter ωb is the same as... Figure 2 The relationship between the beam diameter ωg and the beam diameter ωa is the same. Therefore, even if there is a positional shift in the XY direction relative to the optical axis of the optical probe 10, the intensity variation of the light incident on the optical device 20 can be suppressed.

[0073] In the above description, the radius of curvature of the front end face 101 when the light signal L emitted from the optical device 20 is incident is denoted as Ra, and the radius of curvature of the front end face 101 when the light signal L emitted from the front end face 101 is incident on the optical device 20 is denoted as Rb. The values ​​of the radius of curvature Ra and the radius of curvature Rb can be the same or different. For example, the radius of curvature Rb can be smaller than the radius of curvature Ra. Thus, the light signal L can be reliably incident on a small diffraction grating. Hereinafter, the radius of curvature Ra and the radius of curvature Rb will also be collectively referred to as "radius of curvature R". Similarly, the beam diameter ωa formed by the front end face 101 with radius of curvature Ra and the beam diameter ωb formed by the front end face 101 with radius of curvature Rb can be the same or different. Hereinafter, the beam diameter ωa and the beam diameter ωb will also be collectively referred to as "beam diameter ω".

[0074] Figure 4A and Figure 4B This is a graph showing the basic characteristics of the optical waveguide 100 of the optical probe 10. Figure 4A This 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 smaller 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, then the beam diameter ω is 2 μm. When the beam diameter of the optical signal L of the optical device 20 is ωg and the numerical aperture to achieve this beam diameter is NAg, the beam diameter of the propagating optical signal of the optical probe 10 is set to ωa, and the numerical aperture is set to NAa, so that the radius of curvature R is set in such a way that NAg > NAa.

[0075] Furthermore, the beam diameter ωg of the optical signal L can be asymmetrically shaped in a first direction (e.g., the X direction) and a second direction (e.g., the Y direction) perpendicular to the normal direction of the vertex of the front end face 101, depending on the shape of the optical device 20. For example, when the beam diameters in the first and second directions are respectively set as the first beam diameter ωg1 and the second beam diameter ωg2, the values ​​of the first beam diameter ωg1 and the second beam diameter ωg2 are different. In this case, by also setting the mode field diameter of the optical probe 10 to an asymmetrical shape 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 stable. For example, when the radius of curvature in the first direction of the front end face 101 of the optical probe 10 is set as the first radius of curvature R1, and the radius of curvature in the second direction is set as the second radius of curvature R2, the first radius of curvature R1 and the second radius of curvature R2 are set to different values. At this time, 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., the X direction) and the second radius of curvature R2 in the second direction perpendicular to the first direction (e.g., the Y direction) can also be different.

[0076] Figure 4B This shows the numerical aperture NA and refractive index distribution coefficient A of the optical waveguide 100 of the optical probe 10. 1 / 2 The graph shows the relationship between the two. The value of the axial refractive index n0 varies in the range of 1.44 to 1.55. By increasing the axial refractive index n0, the refractive index distribution coefficient A... 1 / 2 Increase. For example, when the numerical aperture NA is around 0.28, the refractive index distribution coefficient A... 1 / 2 The value is 0.006. Using an optical waveguide 100 with the above parameters, the numerical aperture NAg of the optical device 20 satisfies the condition NAg≥NA.

[0077] Figure 5 This 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 to MR) and the loss. Figure 5 In the diagram, MR = ωa / ωg is used as the horizontal axis, and the deviation d = B / ωa of the position offset B in the XY direction is used as the parameter to illustrate the loss Pd. For example... Figure 5 As shown, when the MFD is greater than MR by 1, the loss relative to the position offset B in the XY direction is small. For example, when MR = 1.5 and d = 0.2, the loss is small, around 0.1 dB, and the effect of the difference in the mode field diameter is small.

[0078] Figure 6This table illustrates the conditions for reducing the amplitude of the propagating optical signal in the optical probe 10. The propagating optical signal propagates sinusoidally in the refractive index distribution type optical waveguide 100. Therefore, the smaller the amplitude of the propagating optical signal, the better it can suppress the situation where the amplitude of the propagating optical signal changes due to the positional offset B and angular offset Δ of the optical signal L, thus preventing the propagating optical signal from radiating to the cladding portion 12. The angular offset Δ is the angle between the optical axis of the optical signal L and the optical axis of the optical probe 10. As a condition for reducing the amplitude of the propagating optical signal, the refractive index distribution coefficient A of the optical waveguide 100... 1 / 2 Ideally, the radius of curvature R of the front end face 101 of the optical probe 10 should be relatively large, and the radius of curvature R of the front end face 101 of the optical probe 10 should be reduced. In addition, the larger the working distance WD, the more the amplitude of the propagating optical signal can be reduced. By reducing the amplitude of the propagating optical signal, even if there is a positional offset B and an angular offset Δ in the XY direction relative to the optical axis, the optical connection between the optical probe 10 and the optical device 20 can be stabilized, and the measurement can be performed with stable intensity characteristics even when positional changes occur.

[0079] Figure 7A to 7D This illustrates 1P (one cycle) ray tracing of a propagating optical signal propagating in the optical waveguide 100 of the optical probe 10. The conditions of the optical waveguide 100 are: A 1 / 2 =0.006, Cr =32.5μm, and the numerical aperture NA of the optical signal L from optical device 20 is 0.24. Figure 7A to 7D The horizontal axis is the position M from the front end face 101 to the base end face 102, and the vertical axis is the distance D in the inner diameter direction from the central axis C10.

[0080] Figure 7A to 7D The propagation of the optical signal is shown comparatively when the radius of curvature Ra of the front end face 101 of the optical probe 10 is set to 15 μm or 20 μm, and the working distance WD is set to 10 μm or 15 μm. Furthermore, this is the case where the position offset B = 0 μm and there is no angular offset. Figure 7A to 7D As shown, the smaller the radius of curvature Ra of the front end face 101 of the optical probe 10, the smaller the amplitude of the propagated optical signal; the longer the working distance WD, the smaller the amplitude of the propagated optical signal.

[0081] Figure 8A to 8D The ray tracing of a propagating optical signal for 1P (one cycle) propagating in optical waveguide 100 is shown. Figure 8A to 8D The horizontal axis is the position M from the front end face 101 to the base end face 102, and the vertical axis is the distance D in the inner diameter direction from the central axis C10. Figure 8A and Figure 8BThe diagram illustrates the state of 1P (one cycle) of the propagating optical signal when the radius of curvature Ra of the front face 101 is 15 μm or 20 μm, the working distance WD is 5 μm, and the position offset B is 2 μm. Figure 8A and Figure 8B Even with a positional offset B = 2 μm, the propagating optical signal remains within the core radius Cr with almost no leakage from the optical waveguide 100. Furthermore, it is estimated that the smaller the radiation angle α of the incident and emitted light, the more margin there is relative to the positional offset, even if the amplitude of the propagating optical signal changes. Figure 8C and Figure 8D This illustrates ray tracing of a propagating optical signal under conditions where, in addition to the positional offset B relative to the optical axis described above, an angular offset Δ = 2.4 degrees is also generated. Figure 8C and Figure 8D In both cases, amplitude variations can be observed, but the propagating optical signal can still propagate within the optical waveguide 100. Based on the above, reducing the radiation angle α of the incident and emitted light is effective in providing a margin for variation in the propagating optical signal. Furthermore, by increasing the working distance WD, a margin for amplitude variation in the propagating optical signal can be maintained even with positional offset B and angular offset Δ relative to the optical axis. Therefore, intensity variations are less likely to occur, resulting in stable measurements.

[0082] <Variation Example>

[0083] exist Figure 9 In the optical probe 10 of the first variation of the illustrated embodiment, the extending direction of the optical waveguide 100 reaching the base end face 102 intersects the base end face 102 at an angle. As a result, the direction of propagation of the optical signal changes at the boundary between the optical waveguide 100 and the base end face 102. For example, if the extending direction of the optical waveguide 100 intersects the base end face 102 at a 45-degree angle, the direction of propagation of the optical signal changes by 90 degrees. A light-receiving element 310 is positioned in the changed direction of propagation of the optical signal, and the light-receiving element 310 receives the optical signal L emitted from the optical device 20. For example, the base end face 102 can be machined at an angle relative to the central axis C10 by mirror polishing (or by applying a reflective coating utilizing a positive dielectric multilayer film). An air layer is located on the outer side of the base end face 102.

[0084] exist Figure 10 In the second variation of the illustrated embodiment, the optical probe 10 includes an optical element 70 disposed on its base end face 102 to change the direction of propagation of the light signal. The optical element 70 is, for example, a tiny prism. Through the optical element 70, the direction of propagation of the light signal is changed by, for example, 90 degrees. Figure 9 Similarly, by arranging the light-receiving element 310 in the direction of travel after the change of the propagation of the light signal, the light-receiving element 310 receives the light signal L emitted from the optical device 20.

[0085] according to Figure 9 and Figure 10 The optical probe 10 of the modified example shown can have a light-receiving element 310 disposed in a direction intersecting the optical axis of the optical probe 10 (e.g., 90 degrees). Alternatively, a light-emitting element 320 can be disposed in a direction intersecting the optical axis of the optical probe 10. Thus, for example, the light-receiving element 310 or the light-emitting element 320 can be arranged perpendicular to the optical axis of the optical probe 10. Therefore, the mounting of the probe card holding the optical probe 10 can be made more flexible.

[0086] As explained above, the optical probe 10 according to the embodiment has a curved front end surface 101 and a refractive index-distributed optical waveguide 100, thus, even if positional offsets B and angular offsets Δ occur in the X-axis and Y-axis directions, intensity variations are less likely to occur. Therefore, position alignment does not require two stages: coarse position adjustment and precise position adjustment using actuators capable of six-axis degree of freedom adjustment. For example, the optical probe 10 and the optical device 20 can be aligned using only XYZ-axis position adjustment and Z-axis rotation adjustment.

[0087] On the other hand, in order to use a single-model fiber with a numerical aperture (NA) of approximately 0.11 to 0.13 as an optical probe to measure optical devices 20 with incident and exit mode field diameters of several μm at optical signal terminals, precise alignment is required. Furthermore, due to the radiative loss of light propagating within the fiber caused by minute vibrations and variations, the measurement results are sensitive and unstable, making it difficult to ensure connection stability. Therefore, it is difficult to stably measure optical devices 20 using single-model fibers.

[0088] In contrast, the optical probe 10 according to the embodiment has small intensity variation relative to the position offset B and the angle offset Δ, thus shortening the time required for the optical probe 10 to be aligned with the optical device 20 and suppressing the increase and variation of connection loss.

[0089] The radius of curvature R of the front end face 101 of the optical probe 10 can be, for example, about 5 μm to 20 μm. By making the front end face 101 curved, the refractive index distribution type optical waveguide 100 has a mode field pattern with a flat peak and a wide range of beam intensity distribution. Therefore, even if positional changes such as positional offset B occur, the overlap between the mode field of the optical waveguide 100 and the optical signal L will not change. As a result, a stable connection without intensity fluctuations can be achieved.

[0090] Furthermore, compared to optical probes with single-mode optical waveguides, optical probe 10 has more margin in restricting the optical signal in the Z-axis direction, allowing the core inner diameter 2Cr to be increased by approximately 10 times. Therefore, a wider working distance WD can be set.

[0091] Furthermore, the numerical aperture of the refractive index-distributed optical waveguide 100 of the optical probe 10 is approximately 0.25–0.30, which is significantly larger than the numerical aperture of a single-model fiber (0.11–0.13). Therefore, even with an angular offset Δ, the confinement is strong, and by reducing the amplitude of the propagating optical signal in the optical waveguide 100, radiation loss is suppressed, and variations in the intensity of the propagating optical signal are less likely to occur.

[0092] As described above, the optical probe 10 enables stable propagation of optical signals relative to positional offsets in the XY and Z axes and angular offsets in the optical axis, resulting in stable connection characteristics. Therefore, stable measurements can be performed even when the measurement is performed using a multi-core optical probe 10. Furthermore, by using a probe assembly that integrates the electronic probe (which transmits and receives electrical signals with the optical device 20) and the optical probe 10, and by providing the electronic probe side with tens of μm of elasticity when connected to the optical device 20, the positions of the electronic probe and the optical probe 10 can be aligned through a step-by-step adjustment. This simplifies the mechanism of the measurement system, facilitates control, and significantly reduces measurement and inspection time.

[0093] Multiple optical probes 10 can also be arranged to form an optical probe array. By using the optical probe array for the measurement of the optical device 20, multiple optical signal terminals can be simultaneously aligned with the optical probes 10. Therefore, by using the optical probe array, the characteristics of the optical device 20 can be measured in a short time. In other words, by using the optical probe array to connect the optical probes 10 to the optical signal terminals in a multi-core manner, the time required for alignment can be significantly reduced compared to the measurement method of aligning the optical probes 10 one by one with the optical signal terminals.

[0094] When multiple optical probes 10 are arranged to form an optical probe array, the position of the optical probes 10 arranged in the optical probe array may have an error of about ± a few μm. However, the tolerance for the positional offset B and angular offset Δ of the optical probes 10 relative to the XYZ axes is large. Therefore, with the optical probe array composed of optical probes 10, even if the relative position of the optical probes 10 and the optical device 20 changes, or if an angular offset occurs in the angular direction of the optical axis, the intensity variation can be reduced. Therefore, by using the optical probe array composed of optical probes 10, the positional alignment of each optical signal terminal of the numerous optical devices 20 formed on the semiconductor wafer 200 with the optical probes 10 can be easily achieved with reduced intensity variation.

[0095] In other words, by using an optical probe array composed of optical probes 10 for measurement, and by simultaneously aligning and measuring multiple optical devices 20, the measurement time can be shortened and the variation in connection loss can be reduced. As a result, the measurement and evaluation of optical devices 20 can be performed stably and easily, thereby improving yield and productivity.

[0096] exist Figure 11A and Figure 11B The diagram shows a structural example of a probe system 1 using an optical probe 10. For example... Figure 11A As shown, the probe system 1 includes a probe head 40 as a support for the optical probes 10. The probe head 40 holds an optical probe array 15 in which a plurality of optical probes 10 are arranged in a multi-core array. For example, although not shown in the figure, the optical probes 10 are also arranged at equal intervals in the optical probe array 15 along the Y-axis direction, just as in the X-axis direction.

[0097] In probe system 1, such as Figure 11B As shown, an optical probe 10 is supported by a probe head 40 made of dielectric material with a V-shaped groove 400 formed in a top view viewed from the Z-axis direction. The optical probe 10 is embedded and fixed in the V-shaped groove 400 formed in the probe head 40. Alternatively, 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 for fixation.

[0098] The optical probe 10, held by the probe head 40, is configured such that its front end face 101 faces the positions of the optical signal terminals of a plurality of optical devices 20 formed in an array on the semiconductor wafer 200. If the positions of the optical signal terminals of the optical devices 20 are uniformly spaced, the measurement of the optical devices 20 using the optical probe 10 will be smooth and easy.

[0099] The probe system 1 includes a moving device 45, which is capable of precisely adjusting the position of the probe head 40 to align the front end face 101 of the optical probe 10 with the optical device 20. The probe head 40 can also be moved along the X-axis, Y-axis, and Z-axis directions under the control of the moving device 45. Furthermore, the probe head 40 can also be moved in the rotational direction of the Z-axis under the control of the moving device 45. Furthermore, if such a position adjustment mechanism is provided on the detector side of the semiconductor wafer 200 to be measured, the moving device 45 is not required. In this way, the position alignment of the optical probe 10 and the optical device 20 can be performed in the probe system 1. Alternatively, the position of the probe head 40 can be fixed while the stage 60 moves in the XYZ-axis directions and the rotational direction of the Z-axis. Alternatively, the probe head 40 can be moved along the X-axis and Y-axis directions, and the stage 60 can be moved along the Z-axis direction. Thus, various adjustment methods can be used for the position alignment of the optical probe 10 and the optical device 20.

[0100] Furthermore, the probe system 1 may also include an electronic probe for applying current or voltage to drive the optical device 20. In this case, the optical probe 10 and the optical device 20 can be aligned independently, as can the electronic probe and the optical device 20, or the optical probe 10 and the electronic probe can be integrally formed and aligned. Since the optical probe 10 has a large tolerance for positional offset B and angular offset Δ, even micrometer-level alignment between the electronic probe and the optical device 20, which does not require submicrometer-level precision, can reduce connection losses.

[0101] After the optical probe 10 and the optical device 20 are aligned, via Figure 11A The probe system 1 shown propagates an optical signal to measure the optical device 20. For example, the optical probe 10 receives the optical signal L emitted by the optical device 20. Alternatively, the optical signal emitted from the light-emitting element disposed opposite to the base end face 102 propagates in the optical probe 10 and is incident on the optical device 20 on the semiconductor wafer 200.

[0102] In addition, Figure 11A and Figure 11B The diagram shows a structure in which the optical probes 10 are arranged in an array, but the optical probe array 15 can also be other structures. For example, the optical probe array 15 can also be a structure in which the optical probes 10 are arranged at any position in the X-axis direction or the Y-axis direction.

[0103] (Other implementation methods)

[0104] As described above through one embodiment of the invention, the discussion and drawings that form part of this disclosure should not be construed as limiting the invention. Various alternative embodiments, examples, and techniques will be apparent to those skilled in the art based on this disclosure. The invention naturally includes various embodiments not described above.

Claims

1. An optical probe for transmitting and receiving optical signals with an optical device, the optical probe comprising: The front end face is a convex curved surface facing the optical device; A refractive index-distributed optical waveguide, the first end of which is connected to the front end face; and The second end of the optical waveguide is connected to the base end face.

2. The optical probe according to claim 1, wherein, The optical waveguide is linear from the front end face to the base end face.

3. The optical probe according to claim 1, wherein, The optical waveguide is composed of a core and a cladding portion disposed on the outer periphery of the core. The radius of curvature R of the front end face and the inner diameter 2×Cr of the core satisfy the relationship R≤Cr.

4. The optical probe according to claim 1, wherein, The optical waveguide is composed of a core and a cladding portion disposed on the outer periphery of the core. The refractive index distribution coefficient A of the optical waveguide 1 / 2 The inner diameter of the core (2×Cr), the refractive index n0 of the optical axis at the optical axis of the core, and the refractive index n1 of the outer edge of the core in the region adjacent to the cladding portion satisfy the following relationship: Cr={(nO 2 -n1 2 ) / (A 1 / 2 ×nO) 2 } 1 / 2 。 5. The optical probe according to claim 1, wherein, The first radius of curvature R1 of the front face in a first direction in a plane perpendicular to the normal direction of the vertex of the front face is different from the second radius of curvature R2 in a second direction perpendicular to the first direction.

6. The optical probe according to claim 1, wherein, The direction of the optical waveguide extending to the base end face intersects the base end face at an angle. The direction of travel of the optical signal changes at the boundary between the optical waveguide and the base end face.

7. The optical probe according to claim 6, wherein, The extension direction intersects the base end face at approximately 45 degrees. The direction of travel of the optical signal changes by approximately 90 degrees.

8. The optical probe according to claim 1, wherein, An optical element is disposed on the base end face to change the direction of travel of the optical signal.

9. The optical probe according to claim 8, wherein, The optical element causes the direction of travel of the light signal to change by approximately 90 degrees.

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

11. A probe system comprising: The optical probe according to any one of claims 1 to 9; The probe head, which is used to hold the optical probe; and A moving device that moves the probe head to align the front end face of the optical probe with the position of the optical device.

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