Optical probe, optical probe array, and probe system

Abstract

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

Description

[Technical Field]

[0001] This invention relates to an optical probe, an optical probe array, and a probe system for measuring optical devices. [Previous Technology]

[0002] The silicon element (hereinafter also referred to as "optical element") for transmitting optical signals is formed on a semiconductor wafer using silicon photonics technology. Optical probes and electrical probes are used to measure the characteristics of the optical element already formed on the semiconductor wafer. At this time, in order to reduce the loss of the optical signal (hereinafter also referred to as "transmitted optical signal") transmitted through the optical waveguide of the optical probe, alignment of the optical element and the optical probe must be performed during the measurement using the optical probe. [Previous Art Documents] [Patent Documents]

[0003] Patent Document 1: Japanese Patent Publication No. 2022-550547 [Summary of the Invention]

[0004] [Problem to be Solved by the Invention] When the optical transmission path of the optical probe through which the optical signal is transmitted is single-mode, the numerical aperture of the optical transmission path is small. Furthermore, since the size of the optical signal terminals of the optical element, which supply and emit optical signals, is as small as a few μm, the tolerance for error during alignment between the optical signal terminals of the optical element and the front end face of the optical probe is low. Therefore, it is difficult to correctly align the optical element and the optical probe. For example, after coarse adjustment of the relative positions of the optical element and the optical probe, a six-degree-of-freedom actuator capable of adjusting the XYZ axis position and the rotational movement of each axis is used for precise position adjustment. As a result, in the measurement of the optical element, the measurement time increases due to the time spent on alignment, and / or the connection loss increases or varies due to incorrect alignment.

[0005] 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 capable of suppressing the time spent aligning with optical elements and suppressing the increase and variation of connection losses. [Means for solving the problems]

[0006] The optical probe system of the embodiment includes: a front end face, which is a convex curved surface facing the optical element; a refractive index distribution type optical waveguide, the first end of which is connected to the front end face; and a base end face, which is connected to the second end of the optical waveguide. [Invention Benefits]

[0007] Depending on the embodiment, an optical probe, an optical probe array, and a probe system may be provided that can suppress the time spent aligning with optical elements and suppress the increase in connection loss.

Implementation Method

[0009] Next, embodiments of the present invention will be described with reference to the accompanying drawings. In the following drawings, the same or similar parts are labeled with the same or similar symbols. However, it should be noted that the drawings are schematic. Furthermore, the embodiments shown below are illustrative of apparatuses and methods used to embody the technical concept of the present invention; the embodiments of the present invention do not specifically specify the structure, arrangement, etc., of the constituent elements as described below. Various modifications can be made to the embodiments of the present invention within the scope of the patent application.

[0010] The optical probe 10 shown in FIG1 transmits and receives optical signals between itself and the optical element 20 formed on the semiconductor wafer 200. FIG1 shows the transmission of the optical signal L emitted from the optical element 20 and injected into the optical probe 10 in the optical waveguide 100 of the optical probe 10. The optical probe 10 has: a front end face 101, which is a convex curved surface facing the optical element 20; a refractive index distribution type optical waveguide 100, the first end of which is connected to the front end face; and a base end face 102, which is connected to the second end of the optical waveguide 100.

[0011] As shown in Figure 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 in Figure 1 is defined as the X-axis direction, and the direction perpendicular to the paper is defined as the Y-axis direction. Hereinafter, the X-axis direction, Y-axis direction, and Z-axis direction will be collectively referred to as the "XYZ-axis direction".

[0012] The optical probe 10 may be constructed using optical fiber, or a combination of optical fiber and lens. The optical waveguide 100 is composed of a core 11 and a coating 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 from the central axis, i.e., the optical 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 coating 12. The shape of the cross-section of the optical probe 10 along the XY plane (hereinafter referred to as "cross-section shape") can be circular or rectangular.

[0013] Hereinafter, the length from the front end face 101 to the base end face 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 FIG1 is T.

[0014] As shown in Figure 1, 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 cover 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 of the inner diameter of the core 11 is called the core radius Cr, and half of the inner diameter of the cover portion 12 is called the cover diameter Cd. The core radius Cr is the length from the central axis C10 of the optical waveguide 100 to the junction of the core 11 and the cover portion 12, and the cover diameter Cd is the length from the central axis C10 to the outer edge of the optical probe 10.

[0015] For example, as shown in FIG1, the central axis C10 of the optical probe 10 is held in a straight line by the support 50. In other words, the optical waveguide 100 is straight from the front end face 101 to the base end face 102. The optical waveguide 100 is straight, thereby preventing optical path difference in the transmitted optical signal transmitted through the optical waveguide 100 and suppressing the generation of multimode.

[0016] For example, when the optical probe 10 is an optical fiber, the optical fiber is held in place by the support 50 to prevent bending. For example, the optical probe 10 can be supported by the support 50 having a through hole formed in a substrate of a dielectric material such as ceramic or plastic. Alternatively, the support 50 can be a structure formed by laminating thin plates 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 having a structure formed by forming V-grooves or U-grooves in the substrate. In this way, various methods can be used to support the optical probe 10.

[0017] The front end face 101 of the optical probe 10 is held facing the optical element 20, which is formed on a semiconductor wafer 200 placed on the probe stage 60. The semiconductor wafer 200 is held on the probe stage 60, for example, by vacuum adsorption.

[0018] The optical element 20 is a silicon photonics device, which integrates optical and electronic circuits. By integrating the optical and electronic circuits, the optical circuit becomes less sensitive to electromagnetic noise, thus achieving higher circuit operating speed, enhanced functionality, and reduced power consumption. Multiple silicon photonics devices can be formed on composite multilayer substrates such as SOI (Silicon On Insulator) substrates containing silicon and quartz using semiconductor microfabrication techniques such as CMOS integrated circuits. In measuring the optical properties of the optical element 20 formed on the semiconductor wafer 200, an optical signal terminal containing a diffraction grating can be disposed on the upper surface of the semiconductor wafer 200 as an input / output terminal for measurement. A diffraction grating is configured at the optical signal terminal of the optical element 20, so that, as shown in FIG1, the optical signal L emitted from the optical signal terminal of the optical element 20 will travel along the Z-axis direction.

[0019] The front end face 101 of the optical probe 10 is optically connected to the optical signal terminal of the optical element 20 that emits an optical 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 optical signal L emitted from the optical element 20 will enter the front end face 101 of the optical probe 10.

[0020] The optical probe 10 is configured to separate from the optical element 20 along the Z-axis by an operating distance WD. The operating distance WD is set to the range within which the optical probe 10 can receive the optical signal L emitted by the optical element 20. In other words, the operating distance WD is set such that the incident range of the optical signal L in the front end face 101 is located inside the core 11.

[0021] The base surface 102 of the optical probe 10 is optically connected to the light-receiving element 310. That is, after the optical signal L emitted from the optical element 20 is transmitted through the optical waveguide 100 of the optical probe 10, it is emitted from the base surface 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 in the figure), and the characteristics of the optical signal L are measured by the measuring device.

[0022] As explained above, the core 11 has a refractive index distribution structure. That is, the refractive index of the core 11 is such that the refractive index gradually decreases from the refractive index of the optical axis (hereinafter referred to as the "optical axis refractive index") which is the central axis C10 along the radial direction toward the cover portion 12. That is, the refractive index (hereinafter referred to as the "peripheral refractive index") in the region of the core 11 adjacent to the cover portion 12 is the minimum. The refractive index distribution N(x) of the core 11 at a distance x from the optical axis in the X direction is expressed using the optical axis refractive index n0, the peripheral refractive index n1, and the following parabolic equation (1). N(x)=n0×{1-(A1 / 2×x)2 / 2}･･･(1) In equation (1), A1 / 2 is the refractive index distribution coefficient, and is expressed by equation (2): A1 / 2={(n02-n12) / (n0×Cr)2}1 / 2･･･(2)

[0023] The greater the difference (n0-n1) between the optical axis refractive index n0 and the outer edge refractive index n1, the greater the refractive index distribution coefficient A1 / 2, and the stronger the restriction on the transmission of optical signals in the optical waveguide 100. The so-called "restriction" refers to the situation where the transmitted optical signal is transmitted inside the core 11 and does not radiate to the coating 12. Incidentally, the greater the refractive index distribution coefficient A1 / 2, the smaller the amplitude of the transmitted optical signal transmitted in the optical waveguide 100.

[0024] On the other hand, when the optical axis refractive index n0, the outer edge refractive index n1, and the refractive index distribution coefficient A1 / 2 are set, the core radius Cr of the optical waveguide 100 can be set as shown in equation (3). Cr={(n02-n12) / (A1 / 2×n0)2}1 / 2･･･(3)

[0025] The restrictions are strengthened so that even if there are changes such as positional offset in the XY direction or beam diameter offset between the optical probe 10 and the optical element 20 relative to the optical axis (hereinafter also referred to as "positional variation"), the optical connection between the optical probe 10 and the optical element 20 will remain stable. For example, according to the inventors' review, the refractive index distribution coefficient A1 / 2 of the optical waveguide 100 is preferably 0.004 or higher.

[0026] The optical path length T of the optical waveguide 100 is represented by the following formula (4): T=2π×P / A1 / 2･･･(4) In formula (4), P is called the spacing length and is equivalent to one period (2π) of the transmitted optical signal, and is any value greater than zero.

[0027] When P=1, then T=2π / A1 / 2, which is the length of the waveform of one periodic component of the transmitted 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 more the amplitude of the transmitted optical signal in the optical waveguide 100 can be reduced.

[0028] The front end face 101 is a convex curved surface, so the optical signal L incident on the front end face 101 will be refracted relative to the optical axis. Therefore, the amplitude of the optical signal transmitted inside the optical waveguide 100 will be reduced. In this way, there is a spatial margin of 2×Cr in the size of the XY plane of the core 11 relative to the transmission path of the transmitted optical signal. As a result, even if there is an XY direction offset at the position of the optical element 20 relative to the optical axis of the optical probe 10, the transmitted optical signal is transmitted in the core 11 in a way that does not radiate to the covered part 12. Furthermore, the transmitted optical signal transmitted in the core 11 is stably incident on the light receiving element 310 via the base end face 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 element 20 is limited by the beam diameter ωg of the optical signal L. The relationship between the beam diameter ωg and the radiation angle α is roughly 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, the following formula (6) can be roughly obtained: α / 2 = tan-1 (Cr / WD) ･･･ (6) There is a relationship between numerical aperture NA and beam diameter ω. The larger the numerical aperture NA is, the smaller the beam diameter ω is. The effective operating distance WD of the optical probe 10 that can receive the optical signal L can be represented by formula (7): Cr / tan{sin-1(NA)WD>0･･･ (7) If the operating distance WD satisfies the condition of formula (7), then the optical signal L from the optical element 20 can be completely injected from the front end face 101 into the optical waveguide 100.

[0031] When the beam diameter formed by the front end face 101 with curvature radius Ra is set as ωa, and the beam diameter of the optical signal L is set as ωg, the curvature radius Ra is set in such a way that the relationship of the arithmetic expression (8) holds. ωa>ωg･･･(8) For example, when the wavelength λ of the optical signal L is 1.55μm and the beam diameter ωg is 2μm, the numerical aperture NA of the optical element 20 is 0.24. In this case, as long as the front end face 101 is spherically processed for the curvature radius Ra, 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 32.5μm, the condition for the operating distance WD is 130μm or less.

[0032] Figure 2 shows the relationship between the modal field distribution Pa of the incident light of the optical probe 10 and the modal field distribution Pg of the optical signal L when the above conditions are met. By setting the front end face 101 as a curved surface, a modal field distribution with a flat peak and a wide peak intensity PW distribution can be formed. As shown in Figure 2, compared with the modal field distribution Pg, the modal field diameter of the modal field distribution Pa is larger and the peak diameter is wider. Therefore, even if the position of the optical probe 10 and the optical element 20 is shifted, the overlapping part of the modal field distribution will not change. Thus, there will be no change in the connection strength between the optical element 20 and the optical probe 10. That is, even if there is a positional shift, the loss of transmitted optical signal can be suppressed. In addition, the modal field distribution Pa depends on the numerical aperture NA (=sin(α / 2)) which is related to the radius of curvature R of the front end face 101 of the optical probe 10.

[0033] The above description indicates that the light signal L emitted from the optical element 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 travel direction of the light signal L may also intersect the normal direction. For example, when the angle formed by the travel direction of the light signal L and the normal direction of the semiconductor wafer 200 is angle θ, it is sufficient to set the central axis C10 of the optical probe 10 to be tilted in the same direction as the travel direction of the light signal L by angle θ.

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

[0035] In this case, the relationship between the beam diameter ωb formed by the front end face 101 of the radius of curvature Rb and the beam diameter ωg of the optical element 20 is set to NAr < NAG under the same conditions as in Figure 1, and the radius of curvature Rb is set in such a way that the relationship of the formula (9) holds: ωb > ωg･･･(9) In the formula (9), the beam diameter of the optical signal L received by the optical element 20 is set to ωg, and the numerical aperture that realizes this formula is set to NAG.

[0036] Make the relationship between beam diameter ωg and beam diameter ωb satisfy equation (9), so that it will be the same as the relationship between beam diameter ωg and beam diameter ωb shown in Figure 2. 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 element 20 will be suppressed.

[0037] The above explanation defines the radius of curvature of the front end face 101 when the optical signal L emitted from the optical element 20 is incident upon it as Ra, and the radius of curvature of the front end face 101 when the optical signal L emitted from the front end face 101 is incident upon the optical element 20 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 set to be smaller than the radius of curvature Ra. In this way, the optical signal L can be reliably incident upon a small diffraction grating. Hereinafter, the radius of curvature Ra and the radius of curvature Rb will be collectively referred to and labeled 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 be collectively referred to and labeled as "beam diameter ω".

[0038] Figures 4A and 4B are graphs showing the basic characteristics of the optical waveguide 100 of the optical probe 10. Figure 4A is a graph showing the relationship between the numerical aperture NA and the beam diameter ω of the transmitted optical signal. The larger the numerical aperture NA, the narrower the beam diameter ω becomes. For example, if the wavelength λ of the transmitted 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 element 20 is ωg, and the numerical aperture realized is NAg, the beam diameter of the transmitted optical signal of the optical probe 10 is set to ωa, and the numerical aperture is set to NAa, so that NAg > NAa, and the radius of curvature R is set in this way.

[0039] Incidentally, the beam diameter ωg of the optical signal L is determined based on the shape of the optical element 20. In the XY plane perpendicular to the normal direction at the vertex of the front end face 101, an asymmetrical shape is achieved using a first direction (e.g., the X direction) and a second direction perpendicular to the first direction (e.g., the Y direction). For example, when the beam diameters of 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 will be different. In this case, the modal field diameter of the optical probe 10 is also set to an asymmetrical shape along the first and second directions, thereby improving the connection efficiency between the optical element 20 and the optical probe 10 and stabilizing the measured characteristics. For example, when the radius of curvature of the front end face 101 of the optical probe 10 in the first direction 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 will be set to different values. At this point, 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 be different.

[0040] Figure 4B is a graph showing the relationship between the numerical aperture NA and the refractive index distribution coefficient A1 / 2 of the optical waveguide 100 of the optical probe 10. The value of the optical axis refractive index n0 varies in the range of 1.44 to 1.55. Increasing the optical axis refractive index n0 increases the refractive index distribution coefficient A1 / 2. For example, when the numerical aperture NA is around 0.28, the refractive index distribution coefficient A1 / 2 is 0.006. Using the optical waveguide 100 with the above parameters, the numerical aperture NAg of the optical element 20 will satisfy the condition NAg≧NA.

[0041] Figure 5 is a graph showing the relationship between the ratio of the modal field diameter of the optical signal L to the modal field diameter of the optical probe 10 (MFD to MR) and the loss. In Figure 5, MR = ωa / ωg is set as the horizontal axis, and the deviation d = B / ωa obtained by using the position offset B in the XY direction is set as the parameter to show the loss Pd. As shown in Figure 5, when the MFD to MR is greater than 1, the loss relative to the position offset B in the XY direction is less. For example, when MR = 1.5 and d = 0.2, the loss is as small as 0.1 dB, because the influence caused by the difference in modal field diameter is less.

[0042] Figure 6 is a table showing the conditions for reducing the amplitude of the transmitted optical signal to be transmitted by the optical probe 10. The transmitted optical signal is transmitted in a sinusoidal shape in a refractive index distribution type optical waveguide 100. Therefore, a smaller amplitude of the transmitted optical signal can suppress the situation where the amplitude of the transmitted optical signal changes due to the position offset B and angular offset Δ of the optical signal L, resulting in the transmitted optical signal radiating to the covered portion 12. The angular offset Δ is the angle formed by the optical axis of the optical signal L and the optical axis of the optical probe 10. As for the condition for reducing the amplitude of the transmitted optical signal, it is preferable to have a larger refractive index distribution coefficient A1 / 2 of the optical waveguide 100, which will reduce the radius of curvature R of the front end face 101 of the optical probe 10. Furthermore, a larger operating distance WD can reduce the amplitude of the transmitted optical signal. By reducing the amplitude of the transmitted 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 element 20 can be stabilized, and the intensity characteristics can be measured even when there is a positional change.

[0043] Figures 7A to 7D show the ray tracing of the 1P (one cycle) component of the transmitted optical signal transmitted through the optical waveguide 100 of the optical probe 10. The conditions of the optical waveguide 100 are A1 / 2 = 0.006, Cr = 32.5 μm, and the numerical aperture NA of the optical signal L from the optical element 20 is 0.24. The horizontal axis of Figures 7A to 7D is the position M from the front end face 101 toward the base end face 102, and the vertical axis is the distance D from the inner diameter direction of the central axis C10.

[0044] Figures 7A to 7D show a comparison of the transmitted optical signal states 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 operating distance WD is set to 10 μm or 15 μm. Incidentally, this is the case where the position offset B = 0 μm and there is no angular offset. As shown in Figures 7A to 7D, the amplitude of the transmitted optical signal is smaller when the radius of curvature Ra of the front end face 101 of the optical probe 10 is smaller, and the amplitude of the transmitted optical signal is smaller when the operating distance WD is longer.

[0045] Figures 8A to 8D show the ray tracing of the 1P (one cycle) component of the transmitted optical signal transmitted in the optical waveguide 100. The horizontal axis of Figures 8A to 8D represents the position M from the front end face 101 toward the base end face 102, and the vertical axis represents the distance D from the inner diameter direction of the central axis C10. Figures 8A and 8B show the state of the 1P (one cycle) component of the transmitted optical signal when the radius of curvature Ra of the front end face 101 is 15 μm or 20 μm, the operating distance WD is 5 μm, and the position offset B is 2 μm. In both Figures 8A and 8B, even if a position offset B = 2 μm occurs, the transmitted optical signal will converge within the core radius Cr and will not leak from the optical waveguide 100. Furthermore, it can be estimated that the smaller incident / outgoing radiation angle α still provides a margin for position offset even if the amplitude of the transmitted optical signal changes. Figures 8C and 8D show the ray tracing of the transmitted optical signal when, in addition to the positional offset B relative to the optical axis under the conditions described above, an angular offset Δ = 2.4 degrees also occurs. Although amplitude variations can be observed in both Figures 8C and 8D, the transmitted optical signal can still be transmitted within the optical waveguide 100. Based on the above, to ensure a margin for variation in the transmitted optical signal, it is beneficial to reduce the radiation angle α of the incident / emitted light. Furthermore, increasing the operating distance WD allows for a margin for amplitude variation in the transmitted optical signal even when positional offset B and angular offset Δ relative to the optical axis occur. Therefore, since intensity variations are less likely to occur, the measurement will be stable.

[0046] <Modification> In the first modification of the embodiment shown in FIG9, the optical probe 10 extends to the base end face 102 of the optical waveguide 100 at an angle. In this manner, the direction of travel of the transmitted optical signal changes at the interface between the optical waveguide 100 and the base end face 102. For example, if the extension direction of the optical waveguide 100 intersects the base end face 102 at a 45-degree angle, the direction of travel of the transmitted optical signal changes by 90 degrees. A light-receiving element 310 is arranged along the changed direction of travel of the transmitted optical signal, thereby receiving the optical signal L emitted from the optical element 20. For example, the base end face 102 can be tilted relative to the central axis C10 by mirror polishing (applying a reflective coating composed of a multilayer positive dielectric film). An air layer is located on the outer side of the base end face 102.

[0047] The optical probe 10 of the second variant of the embodiment shown in FIG10 has an optical element 70 disposed on its base end face 102, which changes the direction of travel of the transmitted optical signal. The optical element 70 is, for example, a tiny triangular mirror. By means of the optical element 70, the direction of travel of the transmitted optical signal is changed by, for example, 90 degrees. Similar to FIG9, a light-receiving element 310 is disposed along the changed direction of travel of the transmitted optical signal, so that the light-receiving element 310 receives the optical signal L emitted from the optical element 20.

[0048] According to the modified optical probe 10 shown in Figures 9 and 10, the light-receiving element 310 can be positioned along a direction intersecting the optical axis of the optical probe 10 (e.g., 90 degrees). Alternatively, the light-emitting element 320 can be positioned along a direction intersecting the optical axis of the optical probe 10. In this way, 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 109. Therefore, the mounting of the probe card holding the optical probe 10 can be flexible.

[0049] 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, so that even if positional offsets B and angular offsets Δ occur in the X-axis and Y-axis directions, intensity variations are not easily generated. Therefore, it is not necessary to use actuators capable of coarse position adjustment and six-axis degree of freedom adjustment for two-stage alignment to achieve precise position adjustment. For example, alignment of the optical probe 10 and the optical element 20 can be achieved by adjusting the position along the XYZ axes and the rotation along the Z-axis alone.

[0050] On the other hand, in order to use a relatively small single-mode fiber with a numerical aperture (NA) of 0.11 to 0.13 as an optical probe to measure the optical element 20 with an incident / emission mode field diameter of several μm at the optical signal terminal, precise alignment is required. Moreover, minute vibrations and variations can easily cause radiation loss of the light transmitted within the fiber, making the measurement results sensitive and unstable, thus making it difficult to ensure connection stability. Therefore, it is difficult to use single-mode fiber to stably measure the optical element 20.

[0051] Compared with the above situation, according to the embodiment of the optical probe 10, since the intensity change is smaller than the position offset B and the angle offset Δ, the time required for the optical probe 10 and the optical element 20 to be aligned can be shortened, and the increase and change of connection loss can be suppressed.

[0052] The radius of curvature R of the front end face 101 of the optical probe 10 can be, for example, about 5 to 20 μm. By making the front end face 101 curved, the refractive index-distributed optical waveguide 100 has a broad modal field distribution with a flat peak value in the beam intensity distribution. Therefore, even if positional changes occur, such as the generation of a positional offset B, the overlap between the modal fields 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.

[0053] Furthermore, compared with optical probes having single-mode optical waveguides, optical probe 10 has leeway in limiting the optical signal even in the Z-axis direction, allowing the core inner diameter 2Cr to be increased by about 10 times. Therefore, the operating distance WD can be set significantly.

[0054] Furthermore, the numerical aperture of the refractive index-distributed optical waveguide 100 of the optical probe 10 is in the range of 0.25 to 0.30, which is larger than the numerical aperture of a single-mode optical fiber, which is 0.11 to 0.13. Therefore, even in the case of an angular offset Δ, the amplitude of the transmitted optical signal transmitted through the optical waveguide 100 is reduced due to strong confinement, thereby suppressing radiation loss and making it less likely for the intensity of the transmitted optical signal to change.

[0055] As described above, based on the optical probe 10, stable transmission of optical signals can be achieved by adjusting the positional offset relative to the XY and Z axes and the angular offset relative to the optical axis, and the connection characteristics are stable. Therefore, stable measurement can be performed even when the optical probe 10 is configured as a multi-core type. Furthermore, by integrating the optical element 20 and the electrical probe for transmitting and receiving electrical signals with the optical probe 10 to form a probe assembly, the optical element 20 has a flexibility of tens of μm when connected to the electrical probe side, and the alignment of the electrical probe and the optical probe 10 can be performed in stages. This simplifies the mechanism of the measurement system, makes control easier, and significantly shortens the measurement and inspection time.

[0056] Alternatively, the optical probes 10 can be arranged in multiples to form an optical probe array. Using the optical probe array for the measurement of the optical element 20 allows multiple optical signal terminals to be simultaneously aligned with each of the optical probes 10. Therefore, by using an optical probe array, the characteristics of the optical element 20 can be measured in a short time. That is, by connecting the optical probes 10 to the optical signal terminals in a multi-core manner using an optical probe array, the alignment time can be significantly reduced compared to the measurement method of aligning the optical probes 10 one by one with the optical signal terminals.

[0057] When a plurality of optical probes 10 are arranged to form an optical probe array, there is a possibility of an error of ± a few μm in the position of the optical probes 10 arranged in the optical probe array. However, the tolerance for the positional offset B and angular offset Δ of the optical probes 10 relative to the XYZ axis is relatively large. Therefore, based on the optical probe array formed by the optical probes 10, even if the relative position of the optical probes 10 and the optical element 20 changes or an angular offset occurs in the angular direction of the optical axis, the intensity variation can be reduced. Therefore, using the optical probe array formed by the optical probes 10, it is easy to align each of the optical signal terminals of the plurality of optical elements 20 formed on the semiconductor wafer 200 with the optical probes 10 in a state of reduced intensity variation.

[0058] That is, by using an array of optical probes composed of optical probes 10 for measurement, multiple optical elements 20 can be simultaneously aligned and measured, thereby shortening the measurement time and reducing the variation in connection loss. As a result, the measurement and evaluation of optical elements 20 can be performed stably and easily, and the yield and productivity can be improved.

[0059] Figures 11A and 11B show an example of the configuration of the probe system 1 using the optical probe 10. As shown in Figure 11A, the probe system 1 includes a probe head 40 that serves as a support for the optical probe 10. The probe head 40 holds the optical probe array 15, which is a plurality of optical probes 10 arranged in a multi-center array. Although not shown in the figure, for example, even if the optical probes 10 are aligned with the Y-axis in the same direction as the X-axis, they are arranged in the optical probe array 15 at equal intervals.

[0060] As shown in FIG11B, in the top view viewed from the Z-axis direction, the probe system 1 uses a probe head 40 of dielectric material with V-shaped grooves 400 to support the optical probe 10. The optical probe 10 is fixed by embedding it into the V-shaped grooves 400 formed in the probe head 40. Alternatively, a plurality of through holes may be formed in the probe head 40, and the optical probe 10 may be fixed by inserting it into the interior of the through holes.

[0061] The front end face 101 of the optical probe 10 held in the probe head 40 is configured to face the positions of the optical signal terminals of a plurality of optical elements 20 formed in an array on the semiconductor wafer 200. If the positional spacing of the optical signal terminals of the optical elements 20 is uniform, the measurement of the optical elements 20 using the optical probe 10 can be performed smoothly and easily.

[0062] The probe system 1 includes a moving device 45, which can precisely adjust the position of the probe head 40 to align the front end face 101 of the optical probe 10 with the optical element 20. The probe head 40 can also be moved along the X-axis, Y-axis, and Z-axis directions by controlling the moving device 45. Furthermore, the probe head 40 can also be moved along the Z-axis rotation direction by controlling the moving device 45. Incidentally, when the probe card on which the semiconductor wafer 200 to be measured is mounted has the position adjustment mechanism described above, the moving device 45 is not required. In this way, the alignment of the optical probe 10 and the optical element 20 can be performed in the probe system 1. Alternatively, the position of the probe head 40 can be fixed while the probe stage 60 is moved along the XYZ-axis and the Z-axis rotation direction. Or, the probe head 40 can be moved along the X-axis and Y-axis directions while the probe stage 60 is moved along the Z-axis direction. In this way, various adjustment methods can be used to align the optical probe 10 and the optical element 20.

[0063] Furthermore, the probe system 1 may include an electrical probe used to apply a current or voltage to drive the optical element 20. In this case, the alignment of the optical probe 10 with the optical element 20 and the alignment of the electrical probe with the optical element 20 can be performed independently; or the optical probe 10 and the electrical probe can be integrally formed and aligned. The optical probe 10 has a large tolerance for positional offset B and angular offset Δ, so even if the electrical probe and the optical element 20 do not require high-precision micron-level alignment at the sub-micron level, connection loss can be reduced.

[0064] After the optical probe 10 is aligned with the optical element 20, an optical signal is transmitted via the probe system 1 shown in FIG11A to measure the optical element 20. For example, the optical probe 10 receives the optical signal L emitted by the optical element 20. Alternatively, the optical signal emitted from the light-emitting element arranged opposite to the base end face 102 is transmitted through the optical probe 10 and injected into the optical element 20 on the semiconductor wafer 200.

[0065] Furthermore, Figure 11 shows a configuration in which the optical probes 10 are neatly arranged in an array; however, the optical probe array 15 may also be configured in other ways. For example, the optical probe array 15 may also be configured to arrange the optical probes 10 at any position in the X-axis or Y-axis direction.

[0066] (Other Embodiments) The present invention has been described above with reference to embodiments. However, it should be understood that the discussions and drawings that form part of this disclosure are not intended to limit the invention. Those skilled in the art to which this invention pertains can conceive of various alternative embodiments, examples, and applications based on this disclosure. It goes without saying that the present invention includes various embodiments not described in this description. [Simplified Explanation of the Diagram]

[0008] Figure 1 is a schematic diagram showing the configuration of the optical probe in the embodiment. Figure 2 is a graph showing the mode field distribution shape of the optical probe in the embodiment. Figure 3 is a schematic diagram showing another usage example of the optical probe in the embodiment. Figure 4A is a graph showing the relationship between numerical aperture and the beam diameter of the transmitted optical signal. Figure 4B is a graph showing the relationship between numerical aperture and refractive index distribution coefficient. Figure 5 is a graph showing the relationship between the ratio of the mode field diameter of the optical signal in the embodiment to the mode field diameter of the optical probe and the loss. Figure 6 is a table showing the conditions for reducing the amplitude of the optical signal transmitted by the optical probe in the embodiment. Figure 7A is a ray tracing graph (one) showing the optical signal transmitted by the optical waveguide of the optical probe in the embodiment. Figure 7B is a ray tracing graph (two) showing the optical signal transmitted by the optical waveguide of the optical probe in the embodiment. Figure 7C is a ray tracing graph (three) showing the optical signal transmitted by the optical waveguide of the optical probe in the embodiment. Figure 7D shows a ray tracing diagram (fourth) of the optical signal transmitted through the optical waveguide of the optical probe in the embodiment. Figure 8A shows a ray tracing diagram (fifth) of the optical signal transmitted through the optical waveguide of the optical probe in the embodiment. Figure 8B shows a ray tracing diagram (sixth) of the optical signal transmitted through the optical waveguide of the optical probe in the embodiment. Figure 8C shows a ray tracing diagram (seventh) of the optical signal transmitted through the optical waveguide of the optical probe in the embodiment. Figure 8D shows a ray tracing diagram (eighth) of the optical signal transmitted through the optical waveguide of the optical probe in the embodiment. Figure 9 is a schematic diagram showing the configuration of the optical probe of the first modified embodiment. Figure 10 is a schematic diagram showing the configuration of the optical probe of the second modified embodiment. Figure 11A is a schematic diagram showing the configuration of the probe system using the optical probe of the embodiment. Figure 11B is a schematic top view showing the configuration of the probe system using the optical probe of the embodiment.

Claims

1. An optical probe for transmitting and receiving optical signals between itself and an optical element, the optical probe comprising: a front end face, which is a convex curved surface facing the optical element; a refractive index distribution type optical waveguide, the first end of which is connected to the front end face; and a base end face, which is connected to the second end of the optical waveguide.

2. The optical probe as described in claim 1, wherein, The aforementioned optical waveguide is linear from the aforementioned front end face to the aforementioned base end face.

3. The optical probe as described in claim 1, wherein, The aforementioned optical waveguide system is composed of a core and a coating portion disposed on the outer periphery of the aforementioned core; the radius of curvature R of the aforementioned front end face and the inner diameter 2×Cr of the aforementioned core satisfy the relationship R≦Cr.

4. The optical probe as described in claim 1, wherein, The aforementioned optical waveguide is constructed by a core and a coating disposed on the outer periphery of the aforementioned core. The refractive index distribution coefficient A1 / 2 of the aforementioned optical waveguide, the inner diameter 2×Cr of the aforementioned core, the optical axis refractive index n0 of the aforementioned core, and the outer edge refractive index n1 of the aforementioned core in the region adjacent to the aforementioned coating satisfy the following relationship: Cr={(n02-n12) / (A1 / 2×n0)2}1 / 2.

5. The optical probe as described in claim 1, wherein, In a plane perpendicular to the normal direction of the vertex of the aforementioned front face, the first radius of curvature R1 in the first direction and the second radius of curvature R2 in the second direction perpendicular to the aforementioned first direction are different.

6. The optical probe as described in claim 1, wherein, The extension direction of the aforementioned base end face of the aforementioned optical waveguide intersects the aforementioned base end face at an angle; the direction of travel of the aforementioned optical signal changes at the junction of the aforementioned optical waveguide and the aforementioned base end face.

7. The optical probe as described in claim 6, wherein, The aforementioned extension direction intersects the aforementioned base surface at a 45-degree angle; the aforementioned direction of travel of the optical signal is changed by 90 degrees.

8. The optical probe as described in claim 1, wherein, The aforementioned base end face is provided with an optical element that changes the direction of travel of the aforementioned optical signal.

9. The optical probe as described in claim 8, wherein, The aforementioned optical element changes the direction of travel of the aforementioned optical signal by 90 degrees.

10. An array of optical probes, comprising a plurality of optical probes as described in any one of claims 1 to 9.

11. A measurement system comprising: an optical probe as described in any one of claims 1 to 9; a probe head for holding the optical probe; and a moving device for moving the probe head to align the aforementioned front end face of the optical probe with the aforementioned optical element.

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