Optical probe, inspection optical module and measurement system

Abstract

The optical probe of the present invention comprises: a medium for propagating optical signals; a plano-convex first lens disposed on a first surface of the medium with its bottom surface facing the medium; and a plano-convex second lens, which is aligned with the optical axis of the first lens and forms a composite lens with its bottom surfaces connected to the first lens. The second lens is embedded in the medium, and the radius of curvature of its convex surface is larger than that of the first lens. The refractive index of the medium is larger than that of the composite lens.

Description

[Technical Field]

[0001] The present invention relates to an optical probe, an optical module for inspection, and a measurement system for measuring optical devices. [Previous Technology]

[0002] Silicon devices (hereinafter also referred to as "optical devices") that transmit optical signals are formed on semiconductor wafers using silicon photonics technology. Optical probes and electrical probes are used to measure the characteristics of the optical devices formed on the semiconductor wafer. In measurements using optical probes, alignment between the optical device and the optical probe is performed to reduce the loss of the optical signal transmitted through the probe.

[0003] In optical measurement and inspection of optical devices, single-core or multi-core array-shaped optical probes are used. For example, multiple diffraction grating-shaped light incident and exit ends are arranged on the upper surface of a semiconductor wafer at the silicon waveguide end of the optical device, and the light incident and exit ends are aligned with the optical probes. This alignment involves precise multi-degree-of-freedom position adjustment of the optical probes to match the position and direction of the optical axes and the mode field diameter of the optical probes and light incident and exit ends, thereby achieving a non-contact optical connection between the optical device and the optical probes. (Prior Art Documents) (Patent Documents)

[0004] Patent Document 1: Japanese Patent Publication No. 2022-550547 [Summary of the Invention]

[0005] When the optical transmission path of the optical probe through which the optical signal passes is single-mode, the numerical aperture of the optical transmission path is small. Furthermore, the size of the input / output ends of the optical signal from the optical device is small, around several μm, resulting in low tolerance for alignment errors between the input / output ends of the optical device and the front end face of the optical probe. For example, the numerical aperture (NA) of the single-mode fiber used as the optical probe is small, around 0.1 to 0.13, making it difficult to correctly align the optical device and the optical probe. Moreover, when the optical axis of the optical signal from the optical device is not aligned with the optical axis of the optical probe, the optical signal will radiate, and the connection efficiency between the optical device and the optical probe will drastically decrease. Therefore, when adjusting the optical axis direction and position, for example, an actuator capable of adjusting the XYZ axis position and rotating along each axis is used. After coarse position adjustment to orient the optical device and the optical probe relative to each other, precise position adjustment is performed using the receiving intensity of the optical system. As a result, in the measurement of optical devices, the measurement time is extended due to the time-consuming alignment, and the connection loss increases and varies due to incorrect alignment.

[0006] In view of the above-mentioned problems, the object of the present invention is to provide an optical probe, an optical module for inspection, and a measurement system that can suppress the time required for the alignment of the optical device and the optical probe and suppress the increase and variation of connection loss.

[0007] The optical probe system of an embodiment of the present invention comprises: a medium for propagating optical signals; a first lens in a plano-convex shape, disposed on a first surface of the medium with its bottom surface facing the medium; and a second lens in a plano-convex shape, wherein the radius of curvature of its convex surface is larger than that of the first lens. The first lens and the second lens are aligned with optical axes and form a composite lens whose bottom surfaces are connected to each other. The second lens is embedded in the medium, and the refractive index of the medium is larger than that of the composite lens.

[0008] According to an embodiment of the present invention, an optical probe, an inspection optical module, and a measurement system are provided that can suppress the time required for alignment of the optical device and the optical probe and can suppress the increase in connection loss.

Implementation Method

[0010] Next, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or similar parts are given the same or similar element symbols. However, it should be noted that the drawings are illustrative. Furthermore, the embodiments shown below are examples of the apparatus and methods necessary to embody the technical concept of the present invention, and the embodiments of the present invention do not define the structure, arrangement, etc., of the constituent parts as described below. Various modifications can be made to the embodiments of the present invention within the scope of the patent application.

[0011] The optical probe 10 shown in FIG1 transmits and receives optical signals L between itself and the optical device 2 formed on the semiconductor wafer 200. FIG1 shows the situation when the optical signal L emitted by the optical device 2 enters the optical probe 10.

[0012] The optical probe 10 includes: a medium 12 for propagating optical signal L; a first lens 111 in a plano-convex shape; and a second lens 112 in a plano-convex shape, wherein the radius of curvature of the convex surface is larger than that of the first lens 111. The first lens 111 is disposed on the first surface 121 of the medium 12 with its bottom surface facing the medium 12. The second lens 112 is aligned with the optical axis of the first lens 111 and forms a compound lens 11 with its bottom surfaces connected to each other. The second lens 112 is embedded in the medium 12. The refractive index of the medium 12 (hereinafter referred to as "second refractive index n2") is larger than the refractive index of the compound lens 11 (hereinafter referred to as "first refractive index n1"). That is, n1 < n2.

[0013] As described above, the compound lens 11 is configured to align the optical axes of the first lens 111 and the second lens 112 and to have the bottom surfaces of the first lens 111 and the second lens 112 facing each other. The optical axis C10 of the light probe 10 is the optical axis of the first lens 111 and the second lens 112.

[0014] As shown in Figure 1, the direction in which the optical axis C10 of the optical probe 10 extends (hereinafter also referred to as the "optical axis direction") is set as the Z-axis direction, and the plane perpendicular to the Z-axis direction is set as the XY plane. The left-right direction of the paper in Figure 1 is set as the X-axis direction, and the direction perpendicular to the paper is set as the Y-axis direction. In the following, the X-axis direction, Y-axis direction, and Z-axis direction are collectively referred to as the "XYZ-axis direction".

[0015] In the following, the radius of curvature of the first lens 111 is denoted as the first radius of curvature R1, and the radius of curvature of the second lens 112 is denoted as the second radius of curvature R2. That is, R1 < R2. The area of ​​the bottom surface of the second lens 112 is larger than the area of ​​the bottom surface of the first lens 111. In other words, when viewed from the optical axis, the outer edge of the second lens 112 is located further outward than the outer edge of the first lens 111. As described above, the compound lens 11 is an asymmetric lens.

[0016] For example, the first lens 111 has a first radius of curvature R1 of about 5 μm to 20 μm and an outer diameter of the bottom surface of about 10 μm to 30 μm. For example, the second lens 112 has a second radius of curvature R2 of about 10 μm to 40 μm and an outer diameter of the bottom surface of about 10 μm to 50 μm.

[0017] The optical signal L is propagated through the composite lens 11 and the medium 12 of the optical probe 10. The medium 12 is, for example, a silicon-based material. In the following, the path through which the optical signal L is propagated by the optical probe 10 is referred to as the "propagation path" of the optical probe 10.

[0018] As shown in FIG. 1, the optical probe 10 is supported by the support 20 such that the first lens 111 faces the light incident and emitting end (not shown) of the optical device 2 formed on the semiconductor wafer 200. The dimensions of the support 20 in the XY direction can be, for example, about 100 μm to 200 μm. The support 20 is miniaturized and requires precision machining. The material of the support 20 is preferably a dielectric material with excellent insulating properties, such as ceramic or resin.

[0019] The semiconductor wafer 200 is mounted on a stage 300. The semiconductor wafer 200 is, for example, fixed on the stage 300 of a probe scanner by vacuum adsorption.

[0020] Optical device 2 is a silicon photonic device that integrates optical circuits and electronic circuits. In silicon photonic devices that integrate optical circuits and electronic circuits, the insensitivity of optical circuits to electromagnetic noise allows for faster circuit operation, improved performance, and reduced power consumption. For example, multiple silicon photonic devices can be formed using semiconductor microfabrication techniques employed in the fabrication of CMOS (Complementary Metal Oxide Semiconductor) integrated circuits on composite multilayer substrates such as silicon and quartz SOI (Silicon On Insulator) substrates. In optical measurements of optical device 2 formed on semiconductor wafer 200, terminals containing diffraction gratings can be disposed on the upper surface of semiconductor wafer 200 at the silicon waveguide end of optical device 2 as light input / output terminals for measurement. By configuring a diffraction grating at the light incident and emission end of the optical device 2, as shown in Figure 1, the light signal L emitted from the light incident and emission end of the optical device 2 travels along the Z-axis direction.

[0021] The optical probe 10 shown in FIG1 is combined with optical elements optically connected to the optical probe 10 to form an inspection optical module 100. The optical element of the inspection optical module 100 shown in FIG1 is a light-receiving element 31 arranged opposite to the second surface 122 of one end face of the propagation path of the medium 12. A compound lens 11 is arranged on the first surface 121 of the other end face of the propagation path of the medium 12, and the spherical surface of the first lens 111 is opposite to the light incident and exit end of the optical device 2. The first lens 111 is optically connected to the light incident and exit end of the optical device 2 that emits a light signal L with an emission angle of 2ε. Hereinafter, the first surface 121 opposite to the optical device 2 is also referred to as the "front end surface". Hereinafter, the second surface 122 opposite to the optical element is also referred to as the "base end surface". There is a fine space between the base end surface and the light-receiving element 31, which may be filled with a light-transmitting resin or the like.

[0022] The first lens 111 of the optical probe 10 is configured to be separated from the optical device 2 along the Z-axis by an operating distance WD. The operating distance WD is set within a range that allows the optical probe 10 to receive the optical signal L emitted by the optical device 2. The optical signal L emitted from the optical device 2 propagates through the medium 12 after passing through the composite lens 11.

[0023] The base end face of the propagation path of the optical probe 10 is optically connected to the light-receiving element 31 through the space between the medium 12 and the light-receiving element 31. In order to prevent resonance and stray light caused by end-face reflection between the base end face of the medium 12 and the light-receiving element 31, it is preferable to apply a non-reflective coating to the base end face, or to adopt a design that slightly tilts the base end face, or to apply an anti-reflection coating to the inner side of the support 20. As described above, the light signal L emitted from the optical device 2 enters the composite lens 11, propagates through the propagation path of the optical probe 10, and then exits from the base end face and enters the light-receiving element 31. For example, the light-receiving element 31 performs photoelectric conversion on the light signal L. The light-receiving element 31 is electrically connected to the electrode pad 50 disposed on the outer surface of the support 20 via the connection terminal 40 connected to the light-receiving element 31. The electrical signal output from the light-receiving element 31 is transmitted via the electrode pad 50 to a measuring device (not shown in the diagram), which measures the characteristics of the light signal L. The light-receiving element 31 can be an ultra-miniature silicon-based or indium gallium arsenide (InGaAs)-based photodiode, depending on the application and usage conditions.

[0024] Next, referring to Figure 2, the light path of the light signal L incident on the light probe 10 will be explained. Figure 2 is an enlarged diagram of the area including the compound lens 11 and the medium 12. To make the explanation clearer, the shading lines representing cross-sections are omitted in Figure 2. Figure 2 shows the XZ plane with the optical axis C10 as the Z-axis and the first surface 121 of the medium 12 as the X-axis. The same light path as the XZ plane also exists in the YZ plane, and due to the spherical symmetry of the optical axis, it has the same relationship as the XZ plane. Therefore, the following explanation is limited to the XZ plane for simplicity.

[0025] In Figure 2, the center of the spherical surface of the first lens 111 on the optical axis C10 is taken as the first center point A, and the center of the spherical surface of the second lens 112 is taken as the second center point B. The first center point A is taken as the origin of the X-axis and Z-axis. The position where the light signal L passes through the spherical surface of the first lens 111 is set as the first passing point P1. The first passing point P1 shown in Figure 2 is the position where the light signal L enters the first lens 111. The coordinates of the first passing point P1 are (Xi, Yi, Zi), and it is represented by (Xi, Zi) because it is on the XZ plane. The first passing point P1 is the position offset by ΔX from the optical axis C10 along the X-axis direction. The position where the light signal L passes through the spherical surface of the second lens 112 is taken as the second passing point P2. The second passing point P2 is the point where the light signal L passes through the interface between the second lens 112 and the medium 12. In Figure 2, the second passing point P2 is the position where the light signal L exits from the second lens 112. The coordinates of the second passing point P2 are (Xφ, Yφ, Zφ), and it is represented by (Xφ, Zφ) because it is in the XZ plane.

[0026] The following description takes the case where the first point P1 of the light signal L passes through the light probe 10 and is offset from the optical axis C10 along the X-axis as an example. The case where the first point P1 is offset from the optical axis C10 along the Y-axis is the same.

[0027] To illustrate the ray path of the optical signal L, as shown in Figure 2, the straight line passing through the first center point A and the first passing point P1 is defined as the first straight line H1. Furthermore, the straight line passing through the first passing point P1 and parallel to the first surface 121 is defined as the second straight line H2. The straight line passing through the first passing point P1 and parallel to the optical axis C10 is defined as the third straight line H3.

[0028] As shown in Figure 2, the angle between the direction of travel of the light signal L before entering the compound lens 11 and the first straight line H1 is set as α, and the angle between the direction of travel of the light signal L and the second straight line H2 is set as θ. The offset angle (hereinafter also referred to as "angular deviation") of the optical axis of the light signal L relative to the optical axis C10 is set as ω. Then the light signal L enters the compound lens 11 at an incident angle of α±ω.

[0029] After the optical signal L enters the compound lens 11 at the first point P1, the optical axis of the optical signal L changes accordingly to the difference between the refractive index of the space between the optical probe 10 and the optical device 2 and the refractive index of the compound lens 11. Specifically, the direction of travel of the optical signal L changes in such a way that the angle between the optical axis of the optical signal L and the optical axis C10 is reduced inside the compound lens 11.

[0030] As shown in Figure 2, the refraction angle between the direction of travel of the light signal L inside the compound lens 11 and the first straight line H1 is set as β, and the angle between the direction of travel of the light signal L and the first surface 121 is set as γ. The refraction angle β is expressed by the following formula (1): β=sin-1(sin(α±ω) / n1) … (1)

[0031] After the optical signal L travels from the compound lens 11 to the medium 12 at the second point of passage P2, the optical axis of the optical signal L changes accordingly to the difference between the refractive index of the compound lens 11 and the refractive index of the medium 12. Specifically, inside the medium 12, the optical axis of the optical signal L is approximately parallel to the optical axis C10. At this time, as long as the optical axis of the optical signal L incident into the medium 12 is parallel to the optical axis C10 and the distance from the optical axis C10 to the optical axis of the optical signal L (hereinafter also referred to as "position deviation") is smaller than ΔX, it means that the optical axis of the optical signal L has been corrected. In other words, if the position of the optical axis of the optical signal L propagating through the medium 12 is closer to the Z-axis, i.e., the optical axis C10 of the optical probe 10, than the X coordinate of the first point of passage P1, the optical axis of the optical signal L has been corrected.

[0032] Viewed from the Z-axis direction, the coordinates of the first passing point P1 in the XY plane are (Xi, Yi), and the coordinates of the second passing point P2 are (Xφ, Yφ). The linear equation for the direction of travel of the optical signal L is represented by Y = a × X + b. The slope a of this line is (Yi - Yφ) / (Xi - Xφ), and the intercept b is Yi - aXi. Furthermore, if we assume the distance between the first passing point P1 and the optical axis C10 is the first position deviation DLi, then DLi = (Xi² + Yi²)¹ / ². When the optical axis belonging to the Z-axis moves to the position of the intercept b, the relationship shown in Figure 2 is obtained.

[0033] In the inspection light module 100, even with arbitrary angular deviation ω and first position deviation DLi, the light path relationship shown in FIG2 can still be formed by moving the Z-axis position to the intercept b in the Y-axis direction. Therefore, the optical axis system of the light signal L can be corrected. For example, while monitoring the received intensity, the inspection light module 100 can be finely adjusted in the Y-axis direction to optimize the positional relationship between the light probe 10 and the light signal L, thereby correcting the angular deviation ω and the first position deviation DLi system. The same applies to the X-axis direction; the inspection light module 100 can also be finely adjusted in the X-axis direction. It is possible to arbitrarily choose whether to finely adjust in the Y-axis direction or the X-axis direction.

[0034] Next, referring to FIG3, the light path of the light signal L propagating from the second lens 112 to the medium 12 will be explained. FIG3 is an enlarged diagram of the connection area between the second lens 112 and the medium 12. To make the explanation clearer, the shaded lines representing cross-sections are omitted in FIG3. FIG3 shows the XZ plane with the optical axis C10 as the Z-axis and the first surface 121 of the medium 12 as the X-axis.

[0035] To illustrate the ray path of the optical signal L, as shown in Figure 3, the straight line passing through the second center point B and the second passing point P2 is defined as the fourth straight line H4. Furthermore, the straight line passing through the second passing point P2 and parallel to the first surface 121 is defined as the fifth straight line H5. The tangent to the spherical surface of the second lens 112 at the second passing point P2 is defined as the sixth straight line H6.

[0036] As shown in Figure 3, the angle between the optical axis C10 and the fourth straight line H4 is set as φ. In addition, the angle between the direction of travel of the optical signal L traveling inside the medium 12 and the fourth straight line H4, that is, the refraction angle of the optical signal L entering the medium 12, is set as ζ.

[0037] The incident angle of the sphere entering the second lens 112 is φ + (π / 2 - γ). Using the angle of refraction ζ, the following equation (2) holds: n1 × sin(π / 2 - γ + φ) = n2 × sin(ζ) … (2)

[0038] When the refraction angle ζ is set to ζ=φ, the optical axis of the light signal L incident on the medium 12 is parallel to the optical axis C10. That is, for the function F(φ) shown in the following equation (3) derived from equation (2), find the value of φ that satisfies the equation F(φ)=0, thereby obtaining the condition for correcting the optical axis of the light signal L to be parallel to the optical axis C10: F(φ)=(π / 2-γ+φ)-sin-1{n2 / n1×sin(φ)} … (3) φ is the angle formed by the second center point B of the sphere passing through the center of the second lens 112, the fourth straight line H4 passing through the second point P2, and the optical axis C10.

[0039] Let γ be the angle between the direction of travel of the light signal L in the compound lens 11 and the first surface 121, let n1 be the refractive index of the compound lens, and let n2 be the refractive index of the medium 12. Then, by setting φ in a way that satisfies the equation F(φ)=0, the optical axis of the light signal L can be corrected. That is, the optical axis of the light signal L in the medium 12 becomes parallel to the optical axis C10.

[0040] Based on the value of φ satisfying the equation F(φ)=0, the exit coordinates (Xφ, Zφ) of the light signal L from the second lens 112 to the second point P2 of the medium 12 are set. The spherical system of the second lens 112 is represented by X2+(ZB)2=R2. Thus, let the Z coordinate of the second center point B be Bz, and the following equations (4) and (5) hold: Xφ=R×sin(φ) … (4) Zφ=R×cos(φ)-Bz … (5)

[0041] As long as Xφ < Xi, the position of the optical axis of the optical signal L at the second passing point P2 is closer to the optical axis C10 of the optical probe 10 than at the first passing point P1. That is, the position and angle of the optical axis of the optical signal L are corrected to be close to the optical axis C10.

[0042] Under the same conditions as described above, the exit coordinates (Xφ, Yφ) of the light signal L exiting the compound lens 11 in the XY plane can be obtained from the incident coordinates (Yi, Zi) of the light signal L entering the compound lens 11 in the YZ plane. When the distance from the optical axis C10 to the second passing point P2 in the XY plane is set as the second position deviation DLφ, then DLφ = (Xφ2 + Yφ2)1 / 2. Since the optical axis of the light signal L has been corrected, DLφ < DLφ.

[0043] Figures 4 and 5 show the relationship between the angular deviation ω and the positional deviation X of the medium 12. The graphs in Figures 4 and 5 show the offset (hereinafter also referred to as "optical axis deviation") ΔX between the optical axis of the light signal L emitted from the optical device 2 and the optical axis C10 of the optical probe 10 when it is 0.5 μm, 1 μm, and 2 μm. The graphs in Figures 4 and 5 are obtained by calculating F(φ) = 0 using Newton's method, where the first refractive index n1 is 1.44 and the second refractive index n2 is 3.48. Figure 4 shows the relationship between the angular deviation ω and the positional deviation X when the first radius of curvature R1 is 10 μm and the second radius of curvature R2 is 15 μm. Figure 5 shows the relationship between the angular deviation ω and the positional deviation X when the first radius of curvature R1 is 5 μm and the second radius of curvature R2 is 7 μm.

[0044] As shown in Figures 4 and 5, even with an incident angle deviation of ω = ±2.5 degrees, the positional deviation X under all conditions is still smaller than the optical axis deviation ΔX. That is, it can be seen that the optical probe 10 corrects the position of the optical axis of the optical signal L to be close to the optical axis C10. Furthermore, even if an angular deviation of ±ω occurs, it is converted into a positional deviation. The positional deviation and optical axis deviation in the Y-axis direction are the same as those in the X-axis direction.

[0045] Figure 6 shows the relationship between the mode field distribution Pa of the incident and emitted light of the composite lens 11 and the mode field distribution Pg of the incident and emitted light of the optical device 2. The mode field diameter of the mode field distribution Pa is set to be slightly larger than that of the mode field distribution Pg, resulting in a wider beam diameter. Therefore, even if the optical axis positions of the beam diameter Wa of the composite lens 11 and the beam diameter Wg of the optical signal L shift due to optical axis offset in the XY direction, the overlapping area of ​​their beam diameters remains unchanged. Thus, even if the connection efficiency decreases slightly, the connection strength between the optical device 2 and the optical probe 10 remains unchanged. The intensity distribution of the mode field of the composite lens 11 depends on the numerical aperture NA associated with the first radius of curvature R1 and the first refractive index n1 of the first lens 111 into which the optical signal L is incident.

[0046] Figure 7 is a graph showing the relationship between numerical aperture NA and beam diameter W. The larger the numerical aperture NA, the narrower the beam diameter W. The numerical aperture NA depends on the emission angle 2ε of the optical signal L, and is represented by NA=sin(ε). In terms of the wavelength λ of the optical signal L and the beam diameter W, the relationship is ε=tan⁻¹{λ / (π･W)}.

[0047] For example, in the case of λ=1.55μm and W=4μm, NA=0.24, then the emission angle 2ε=28 degrees. As mentioned above, to obtain the required beam diameter W, a numerical aperture NA equivalent to the beam diameter W must be set.

[0048] Figure 8 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. In Figure 8, MR=Wa / Wg is used as the horizontal axis, and the optical axis offset deviation d=Wg1 / Wg, calculated using the position offset of the optical axis using the beam diameter, is used as the parameter to display the loss Pd. As shown in Figure 8, when MFD to MR is greater than 1, the loss for the optical axis offset deviation d in the XY direction is less. For example, when MR=1.5 and d=0.1 to 0.5, the loss is small, about 0.1dB to 0.7dB, suppressing the loss variation caused by the difference in mode field diameter.

[0049] Figures 9A to 9C are graphs showing the relationship between the numerical aperture NA and the actuation distance WD when the first radius of curvature R1 is 5 μm, 10 μm, and 15 μm. Figure 9A shows the case when the first refractive index n1 (the refractive index of the compound lens 11) is 1.4, Figure 9B shows the case when the first refractive index n1 is 1.5, and Figure 9C shows the case when the first refractive index n1 is 1.6.

[0050] As shown in Figures 9A to 9C, the larger the first radius of curvature R1, the greater the actuation distance WD can be when the numerical aperture NA is the same. Furthermore, the smaller the first refractive index n1, the greater the actuation distance WD can be when the numerical aperture NA is the same. In other words, the larger the refractive index and the smaller the radius of curvature of the first lens 111, the wider and more stable the range of usable numerical aperture NA can be when the actuation distance WD is the same. For example, in a composite lens 11 with a refractive index of 1.4, when the first radius of curvature R1 is 10 μm, the second radius of curvature R2 is 15 μm, and the wavelength λ is 1.55 μm, if NA=0.2, WD=15 μm, Wa=5 μm, Wg=4 μm, and MR=1.25, the loss characteristics can be set to approximately 0.2 dB.

[0051] The above description describes the case where the inspection optical module 100 contains a light-receiving element 31, but it can also be as shown in FIG10, where the inspection optical module 100 contains a light-emitting element 32 as an optical element. In the inspection optical module 100 shown in FIG10, a compound lens 11 is disposed at the base end face (second face 122) of the propagation path. The light signal L enters the first lens 111 from the light-emitting element 32, and the light signal L propagated through the light probe 10 is emitted from the front end face (first face 121) to the optical device 2.

[0052] Alternatively, as shown in FIG10, a third lens 113 may be disposed on the front end face of the optical probe 10. For example, the spherical surface of the plano-convex third lens 113 disposed on the first surface 121 of the medium 12 is optically connected to the optical device 2. The optical signal L propagating through the medium 12 is focused by the third lens 113, and the focused optical signal L is emitted to the optical device 2.

[0053] In the inspection optical module 100 shown in FIG. 10, the optical axis of the light signal L emitted from the light-emitting element 32 is brought close to the optical axis C10 and corrected to be parallel to the optical axis C10 by means of the compound lens 11 and the medium 12. Then, the light signal L, which propagates parallel to the optical axis C10 through the medium 12, passes through the third lens 113 disposed on the front end face and enters the optical device 2. The numerical aperture NA of the optical device 2 is designed to be larger than the numerical aperture NA of the third lens 113. In this way, the mode field diameter of the optical probe 10 is made slightly larger than the mode field diameter of the optical device, which can stabilize the connection characteristics between the optical probe 10 and the optical device 2.

[0054] As explained above, the optical probe 10 in this embodiment includes a composite lens 11 formed by connecting a first lens 111 with a first radius of curvature R1 and a second lens 112 with a second radius of curvature R2. The second lens 112 is embedded in a medium 12. By designing the second radius of curvature R2 to be larger than the first radius of curvature R1, and embedding the second lens 112 in a medium 12 with a refractive index greater than that of the composite lens 11, the optical axis of the optical signal L can be corrected in the medium 12 in a manner that is parallel to and close to the optical axis C10 of the optical probe 10.

[0055] Furthermore, the mode field distribution of the incident and emitted light of the composite lens 11 is designed such that its mode field diameter is slightly larger than that of the mode field distribution of the incident and emitted light of the optical device 2. Therefore, even if the optical axis position shifts between the optical device 2 and the optical probe 10, the overlapping area of ​​their beam diameters remains unchanged, and the connection strength between the optical device 2 and the optical probe 10 does not change.

[0056] As described above, based on the optical probe 10, the optical axis of the optical signal L within the optical probe 10 can be corrected to be parallel to the optical axis C10. Furthermore, even if an angular deviation occurs, it is converted into a positional deviation, and the position of the optical axis of the optical signal L within the optical probe 10 can be made closer to the optical axis C10 than the first passing point P1. Moreover, even if the optical axis position shifts between the optical device 2 and the optical probe 10, the connection strength between the optical device 2 and the optical probe 10 remains unchanged. Therefore, the alignment of the optical probe 10 and the optical device 2 does not require a two-stage alignment process involving coarse position adjustment using an actuator capable of 6-axis adjustment and precise position adjustment at the sub-micron level. For example, the alignment of the optical probe 10 and the optical device 2 can be performed with only 3 to 4 degrees of freedom adjustments, including XYZ axis position adjustment and Z-axis rotation adjustment. Therefore, based on the optical probe 10 and the inspection optical module 100, the time required for alignment with the optical device 2 can be suppressed, and the increase and variation in connection loss can be suppressed.

[0057] The following is an example of the manufacturing method of the optical probe 10.

[0058] The dielectric 12 can be, for example, a silicon substrate with a refractive index of about 3.4. To form the spherical recess required for embedding the second lens 112 in the dielectric 12, photolithography can be used as follows. For example, a mask with micro-holes is disposed on the surface of the silicon substrate, and the spherical recess is formed in the dielectric 12 by anisotropic etching using an alkaline solution. The alkaline solution used is potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH), etc.

[0059] Then, in order to form the second lens 112, a light-transmitting resin material such as a silicone resin or a transparent polymer with a refractive index of 1.4 to 1.6 is filled into the recess formed on the silicon substrate. Next, the first lens 111 is formed. The first lens 111 can be manufactured by various methods, one example of which is shown below. A sheet of transparent polymer or the like is formed using an array of hemispherical precision molds, and then the material is dropped by inkjet printing and processed into a spherical shape by meniscus. Next, the first lens 111 is precisely positioned onto the sheet on the surface of the silicon substrate on which the second lens 112 is formed. Alternatively, after the recess is formed on the silicon substrate, resin material is dropped by inkjet printing, and then the composite lens 11 is formed by precision molds.

[0060] In addition, the photoprobe 10 can also be manufactured using a micro-optics method employing an ultra-fine 3D printer. Furthermore, a silicon oxide (SiO2) substrate can also be used to manufacture the photoprobe 10. As described above, there are various options for the process used to form the photoprobe 10.

[0061] In the manufacture of the optical probe 10, the substrate on which a plurality of composite lenses 11 are formed can be cut into a single piece according to the required configuration using a dicing saw or the like. In addition, regarding countermeasures against reflected light and stray light that cause problems in the measurement of the optical device 2, it is preferable to apply an AR (Anti-Reflection) coating composed of a dielectric multilayer film on the substrate.

[0062] Furthermore, the direction of the optical axis C10 can be changed inside the optical probe 10. For example, as shown in FIG11, the optical probe 10 may have an optical path alteration structure that changes the optical axis of the optical signal L by 90 degrees inside the medium 12. The inspection optical module 100 shown in FIG11 has a mirror-shaped reflective surface 123 formed at a 45-degree angle to the extending direction of the optical axis C10 in the micro-prism-shaped medium 12 in order to change the optical axis of the optical signal L by 90 degrees. The other side of the reflective surface 123 is an air layer. The operation of the inspection optical module 100 shown in FIG11 is the same as that described with reference to FIGS. 1 to 3.

[0063] According to the inspection light module 100 shown in FIG11, the light-receiving element 31 or the light-emitting element 32 can be arranged in a direction (e.g., 90 degrees) intersecting the optical axis of the incident and emitted light of the light device 2. Therefore, the installation of the inspection light module 100 can be flexible. For example, the space in the height direction can be reduced. In addition, since the main surface of the electrode pad 50 faces the horizontal direction, it is also easy to make electrical connections such as wiring patterns on the circuit board by wire bonding, soldering, etc. of the electrode pad 50.

[0064] FIG. 12 shows a configuration example of a measurement system 1 having a plurality of inspection optical modules 100. In the measurement system 1 shown in FIG. 12, a single medium 12 is used to construct a plurality of inspection optical modules 100. In other words, a plurality of compound lenses 11 are disposed on a single medium 12. Alternatively, individual mediums 12 may be used to individually construct a plurality of inspection optical modules 100.

[0065] Figure 12 shows an example of the configuration of a measurement system 1 containing two inspection optical modules 100 each containing a light-receiving element 31 and two inspection optical modules 100 each containing a light-emitting element 32. However, the types of optical elements contained in the measurement system 1 can be arbitrarily set. For example, all inspection optical modules 100 of the measurement system 1 may contain a light-receiving element 31, or all inspection optical modules 100 may contain a light-emitting element 32.

[0066] The spacing D1 to D3 of the inspection optical modules 100 configured in the measurement system 1 can be set to, for example, 100 μm to 500 μm. Furthermore, the number and configuration of the inspection optical modules 100 included in the measurement system 1 can be arbitrarily set. For example, the inspection optical modules 100 can be configured in an array along the X-axis and Y-axis directions.

[0067] The measurement system 1 includes a moving device 400 capable of precisely adjusting the position of the support 20 for aligning the front end face of the optical probe 10 with the optical device 2. The support 20 can be moved along the X-axis, Y-axis, and Z-axis directions under the control of the moving device 400. For example, the moving device 400 moves the support 20 along a plane parallel to the first surface 121, thereby aligning the optical axis of the optical probe 10 with the optical axis of the optical signal L. Furthermore, the moving device 400 can also control the support 20 to rotate along the Z-axis. Alternatively, when the stage 300 on which the semiconductor wafer 200 is mounted has a position adjustment mechanism, the moving device 400 may not be necessary. For example, a method can be used to fix the position of the support 20 by moving the stage 300 along the XYZ-axis and the Z-axis rotation direction. As described above, the alignment of the optical probe 10 and the optical device 2 can be performed in the measurement system 1. Alternatively, the support 20 can be moved along the X and Y axes, while the stage 300 can be moved along the Z axis. Various adjustment methods can be used to align the optical probe 10 and the optical device 2.

[0068] The measuring system 1 includes a driving circuit 500 that drives the light-receiving element 31 and the light-emitting element 32. The driving circuit 500 includes, for example, an amplifier circuit 501 and a driver circuit 502. The amplifier circuit 501 amplifies the electrical signal obtained by photoelectric conversion of the light-receiving element 31 and sends it to the measuring device (not shown). The driver circuit 502 supplies power to the light-emitting element 32 under the control of the measuring device, thereby driving the light-emitting element 32.

[0069] Alternatively, the support 20 and the driving circuit 500 can be integrally mounted onto a multilayer substrate-shaped module such as a probe card and then mounted onto a probe tester. This enables the measurement of the optical device 2 using the probe tester.

[0070] In addition, the measurement system 1 may also include an electrical probe for applying current or voltage to drive the optical device 2. In this case, the alignment of the optical probe 10 with the optical device 2 and the alignment of the electrical probe with the optical device 2 can be performed independently, or the optical probe 10 and the electrical probe can be integrated for alignment. Since the optical probe 10 has a large tolerance for positional and angular offsets, the alignment of the electrical probe with the optical device 2 does not require sub-micron level high precision, and even micron level alignment can reduce connection losses.

[0071] After the optical probe 10 and the optical device 2 are aligned, the optical signal is transmitted through the measurement system 1 shown in FIG. 12 to measure the optical device 2. For example, the optical signal L emitted by the optical device 2 is received by the light receiving element 31 via the optical probe 10. Alternatively, the optical signal L emitted from the light emitting element 32 is transmitted through the optical probe 10 and enters the optical device 2 on the semiconductor wafer 200.

[0072] According to the measurement system 1 shown in FIG12, the optical axis of the incident and emitted light of the optical signal L is corrected by the optical probe 10, and the deviation in the XY plane is maintained by setting the mode field diameter of the optical probe 10 to be slightly larger than the mode field diameter of the optical signal L. Therefore, the optical connection between the optical signal L and the inspection optical module 100 is easy, and the measurement of the optical device 2 by the incident and emitted light of the optical signal L can be performed stably. In addition, the measurement operation does not require precise adjustment of the position and angle of the optical probe 10 by an actuator capable of 6-axis degree of freedom adjustment. Thus, for example, the inspection optical module 100 can be directly mounted and fixed to the probe card mounted on the probe probe machine, and the measurement of the optical device 2 can be performed by simply adjusting the position of the probe probe in the XYZ axis direction and the Z-axis rotation.

[0073] (Other Embodiments) As described above, the present invention has been illustrated by way of embodiments, but it should not be construed that the discussion and drawings that form part of this specification limit the present invention. Various alternative embodiments, examples, and applications will become apparent to those skilled in the art from this specification.

[0074] For example, the above describes the case where the normal direction of the main surface of the semiconductor wafer 200 is parallel to the optical axis C10 of the optical probe 10. In contrast, when the optical signal L is emitted at an angle relative to the normal direction of the main surface of the semiconductor wafer 200, the optical axis direction of the optical probe 10 can also be tilted to match the travel direction of the optical signal L.

[0075] As described above, it is self-evident that the present invention includes various embodiments not described in this specification. [Simplified Explanation of the Diagram]

[0009] Figure 1 is a schematic diagram showing the structure of the inspection optical module in the embodiment. Figure 2 is a schematic diagram illustrating the light path of the optical probe in the embodiment. Figure 3 is a schematic diagram illustrating the light path of the optical probe in the embodiment. Figure 4 is a graph showing the relationship between the angular deviation and the distance between the optical signal and the optical axis when the first radius of curvature is 10 μm and the second radius of curvature is 15 μm. Figure 5 is a graph showing the relationship between the angular deviation and the distance between the optical signal and the optical axis when the first radius of curvature is 5 μm and the second radius of curvature is 7 μm. Figure 6 is a graph showing the shape of the mode field distribution (pattern) of the optical probe in the embodiment. Figure 7 is a graph showing the relationship between the numerical aperture and the beam diameter. Figure 8 is a graph showing the relationship between the ratio of the mode field diameter and the loss. Figure 9A is a graph showing the relationship between the numerical aperture and the actuation distance when the first radius of curvature is 5 μm. Figure 9B is a graph showing the relationship between the numerical aperture and the actuation distance when the first radius of curvature is 10 μm. Figure 9C is a graph showing the relationship between numerical aperture and actuation distance when the first radius of curvature is 15 μm. Figure 10 is a schematic diagram showing other components of the inspection optical module in the embodiment. Figure 11 is a schematic diagram showing the configuration of the inspection optical module in a modified example of the embodiment. Figure 12 is a schematic diagram showing the configuration of the measurement system using the optical probe of the embodiment.

Claims

1. An optical probe for transmitting and receiving optical signals between itself and an optical device; the optical probe comprising: a medium for transmitting the optical signals; a plano-convex first lens disposed on a first surface of the medium with its bottom surface facing the medium; and a plano-convex second lens aligned with the optical axis of the first lens and forming a composite lens with its bottom surfaces connected to the first lens, and embedded in the medium, wherein the radius of curvature of the convex surface is larger than that of the first lens; and the refractive index of the medium is larger than that of the composite lens.

2. The optical probe as described in claim 1, wherein, Let γ be the angle between the direction of the aforementioned optical signal traveling in the aforementioned composite lens and the aforementioned first surface; let γ be the angle between the straight line passing through the point where the aforementioned optical signal passes through the interface between the aforementioned second lens and the aforementioned medium and the center of the spherical surface of the aforementioned second lens, and the optical axis of the aforementioned composite lens; let n1 be the refractive index of the aforementioned composite lens; let n2 be the refractive index of the aforementioned medium; at this time, the following relationship is satisfied.

3. The optical probe as described in claim 1, wherein, The aforementioned medium is a silicon-based material.

4. The optical probe as claimed in claim 1, having an optical path alteration structure that causes the optical axis of the aforementioned optical signal to change by 90 degrees within the aforementioned medium.

5. An inspection optical module comprising: an optical probe as described in any one of claims 1 to 4; and an optical element optically connected to the optical probe; wherein the front end face of the propagation path of the optical signal in the optical probe faces the optical device; and the optical element is configured to face the base end face of the propagation path.

6. The inspection optical module as described in claim 5, wherein, The aforementioned composite lens is disposed on the aforementioned front end face, and the aforementioned first lens is opposite to the aforementioned optical device; the aforementioned optical element is a light receiving element, which receives the aforementioned light signal emitted from the aforementioned optical device and transmitted through the aforementioned medium after entering the aforementioned composite lens.

7. The inspection optical module as described in claim 5, wherein, The aforementioned composite lens is disposed on the aforementioned base end face, and the aforementioned first lens is opposite to the aforementioned optical element; the aforementioned optical element is a light-emitting element, which causes the aforementioned light signal to be injected into the aforementioned light probe; and the aforementioned light signal propagated through the aforementioned light probe is emitted to the aforementioned optical device.

8. The inspection optical module as described in claim 7 further includes a third lens disposed on the aforementioned front end face; the aforementioned third lens focuses the aforementioned optical signal propagating through the aforementioned medium and emits it to the aforementioned optical device.

9. A measurement system comprising: an inspection optical module as described in claim 5; a support for supporting the aforementioned optical probe; and a moving device for moving the aforementioned support for alignment of the aforementioned optical probe with the aforementioned optical device.

10. The measurement system as described in claim 9, wherein, The aforementioned moving device aligns the optical axis of the aforementioned optical probe with the optical axis of the aforementioned optical signal by moving the aforementioned support body parallel to the aforementioned first surface.

11. The measurement system as described in claim 9, which includes a plurality of the aforementioned inspection optical modules.

12. The measurement system as described in claim 11, wherein, A plurality of the aforementioned composite lenses are configured in a single aforementioned medium.

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