Optical device for observation and observation device

Abstract

To provide an optical device for observation using the principal of a confocal method and an observation device including the same, in which, although of a simple structure, focus scanning at high speed is made possible.SOLUTION: An optical device for observation according to the present invention comprises: a light source; a light reception unit; an illumination optical system for condensing light emitted from the light source and entering it to the surface of an observation object; an observation optical system for guiding light emitted from the observation object to the light reception unit and forming an image of the observation object on the light reception surface of the light reception unit; and a spatial light phase modulator capable of changing the relationship between the incidence direction and the outgoing direction of light by electrical control. The illumination optical system converges light from the light source and enters it to the observation object, the light reception surface is located at a position confocal with the surface of the observation object regarding the observation optical system, and the spatial light phase modulator is located on an optical path leading from the light source to the light reception unit, modulating light heading toward the light reception unit and changing with the passage of time the distance between the light reception surface and the convergence position of a light beam reflected by the observation object and entering the light reception unit via the observation optical system.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an optical observation device used for the purpose of optically observing an object, for example, for the purpose of observing for the inspection of semiconductor products, and to an observation device using the same. [Background technology]

[0002] Three-dimensional packaging technology, which stacks semiconductor chips perpendicular to their main surfaces, is attracting attention as a method for increasing the density and performance of semiconductor products. With this technology, numerous tiny protrusions called bumps are formed on the surface of the semiconductor chip to establish electrical connections with other layers. Currently, the typical size of bumps is about 30 μm in diameter and height, and at an arrangement pitch of about 60 μm, but further reductions in diameter and pitch are required.

[0003] To ensure reliable electrical connections via bumps, each bump must be formed to the specified dimensions. In particular, to ensure proper conduction for each of multiple bumps, it is necessary for the height of each bump to be uniform. For this reason, a technology is needed to inspect manufactured semiconductor chips and measure the dimensions of the formed bumps in three dimensions.

[0004] As a method for measuring such bumps, light section method, white light interference method, confocal method, etc. are being considered, but due to the trend toward miniaturization of bumps mentioned above, it is expected that the confocal method, which has high resolution in the height direction and is suitable for such applications, will become mainstream. An observation device using the confocal method is described in Patent Document 1, for example.

[0005] Observation devices using confocal optical systems can selectively receive only focused light from the observation object, thereby obtaining high-contrast observation images and achieving high resolution, particularly in the height direction (depth direction). For this reason, as exemplified in Patent Document 1, they are often used for the purpose of observing and measuring the three-dimensional structure of biological samples such as living tissues and cells. In the conventional technology described in Patent Document 1, the confocal optical system is scanned horizontally and vertically relative to the observation object to obtain three-dimensional data of the observation object. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2023-541449 Summary of the Invention [Problem to be solved by the invention]

[0007] When attempting to apply such measurements based on the principles of the confocal method to semiconductor chip inspection, which is based on in-line 100% inspection, the following problems arise. In a typical confocal observation device, the operation of acquiring images at each height while changing the focus position in the vertical direction (focus scanning) is achieved by moving the optical system relative to the observation object. However, scanning involving such mechanical movement makes it difficult to perform measurements at high speeds. Furthermore, the above-mentioned conventional technology replaces mechanical scanning by simultaneously irradiating the observation object with multiple illumination lights with different focus positions in the vertical direction, but this results in extremely complex structures for the illumination and observation optical systems. For these reasons, there is a need for practical observation optical devices that are capable of high-speed scanning with a simpler structure.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology that enables high-speed focus scanning to be achieved with a simple structure in an observation optical device that uses the principle of the confocal method and an observation device that includes the same. [Means for solving the problem]

[0009] The observation optical device according to the present invention includes a light source, a light receiving unit, an illumination optical system that focuses light emitted from the light source and causes it to be incident on the surface of an observation object, an observation optical system that guides light emitted from the observation object to the light receiving unit and forms an image of the observation object on the light receiving surface of the light receiving unit, and a spatial light phase modulator that can change the relationship between the incident direction and the outgoing direction of light by electrical control. Here, the illumination optical system causes a light beam obtained by converging light emitted from the light source to be incident on the observation object, and the light receiving surface is located at a position conjugate with the surface of the observation object with respect to the observation optical system. The spatial light phase modulator is located on an optical path from the light source to the light receiving unit and modulates the light directed toward the light receiving unit to change over time the distance between the convergence position of the light beam that is reflected by the observation object and incident on the light receiving unit via the observation optical system and the light receiving surface.

[0010] In the invention configured as described above, in addition to the high resolution in the height direction based on the principle of confocal imaging, high-speed scanning in the height direction can be achieved for the following reasons. First, when a spatial light phase modulator is not provided on the optical path, due to the conjugate positional relationship, the light beam reflected by the object of observation and emitted from the observation optical system converges on the light-receiving surface of the light-receiving unit. This situation can be changed by providing an electrically controllable spatial light phase modulator on this optical path to modulate the light.

[0011] Specifically, by modulating light to converge or diverge using a spatial light phase modulator, the convergence position of the sightseeing beam can be changed in the optical axis direction, thereby changing the distance from the light receiving surface. This achieves the same effect as moving the focus position relative to the object of observation in its height direction. In other words, focus scanning is achieved by moving the focus position in the height direction and acquiring an image of the object of observation at each height. By using an electrically controllable spatial light phase modulator, the focus position can be moved much faster than when mechanical movement is involved, enabling high-speed scanning. This effect can be achieved simply by adding a spatial light phase modulator to the confocal optical system configuration, thereby avoiding the complex configuration required in the prior art described above.

[0012] Furthermore, an observation apparatus according to the present invention includes an observation optical device having the above-described configuration, a support unit that supports an observation object, a movement mechanism that moves the support unit and the observation optical device relatively, and a control unit that controls the spatial light phase modulator. In the invention configured in this manner, by including an observation optical device that has a simple configuration as described above and is capable of high-speed focus scanning, it is possible to quickly observe the three-dimensional shape of the surface of an observation object. [Effects of the Invention]

[0013] As described above, according to the present invention, the focus scanning in the height direction in the confocal optical system is realized by electrically controlling the spatial light phase modulator, which allows for much faster measurement than mechanical scanning and avoids the need for a complicated device configuration. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a schematic configuration of an embodiment of an observation device according to the present invention. [Figure 2] 1A and 1B are diagrams illustrating the structure of a semiconductor chip; [Figure 3] FIG. 2 is a diagram showing a schematic configuration of an observation optical device provided in the observation device. [Figure 4] FIG. 1 is a diagram schematically illustrating the structure of a MEMS phased array. [Figure 5] FIG. 1 is a diagram illustrating the operation of a MEMS phased array. [Figure 6] 10A and 10B are diagrams illustrating the operation of the optical modulator in this embodiment. [Figure 7] FIG. 2 is a ray diagram in an observation optical device. [Figure 8] 1A and 1B are diagrams illustrating the principle of focus scanning in this embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of focus scanning. [Figure 10] FIG. 10 is a diagram showing another example of the configuration of the observation optical device. DETAILED DESCRIPTION OF THE INVENTION

[0015] Fig. 1 is a block diagram showing a schematic configuration of one embodiment of an observation apparatus according to the present invention. This observation apparatus 1 is an apparatus for observing the surface of a semiconductor chip C for the purpose of inspecting the chip. Specifically, as will be described in detail later, a large number of bumps Bc are formed on one main surface of the semiconductor chip C, which is the object to be observed. The observation apparatus 1 optically measures the surface shape of these bumps Bc, specifically at least one of their position, size, and height, to obtain a surface profile, and then inspects the semiconductor chip C based on the results.

[0016] The observation device 1 includes a stage unit 2 that holds the object to be observed, an irradiation unit 4 that irradiates a laser light beam onto the object to be observed, a light receiving unit 6 that detects reflected light from the object to be observed, and a control unit 9 that controls the operation of each of these units.

[0017] To consistently indicate positions and directions in the following figures, an XYZ Cartesian coordinate system is set as shown in Figure 1. Here, the X and Y axes are set horizontally, and therefore the XY plane represents the horizontal plane. The Z axis is set vertically, and more specifically, the (-Z) direction represents the vertical downward direction.

[0018] The stage unit 2 includes a stage 21, the upper surface of which serves as a holding surface on which an object to be observed can be placed, guide rails 22 that are fixed to a base (not shown) and support the stage 21 so that it can move freely in the X direction, and a drive mechanism 23 that moves the stage 21 along the guide rails 22. The drive mechanism 23 can be appropriately selected from known linear motion mechanisms such as a ball screw mechanism, a linear motor mechanism, a linear motion guide mechanism, a belt or chain drive mechanism, etc. The drive mechanism 23 operates in response to control commands from the control unit 9. It is more preferable that the position of the stage 21 at each time can be grasped by the control unit 9. Furthermore, the stage 21 is appropriately provided with a mechanism for fixing and supporting the object to be observed on its upper surface, such as a vacuum suction mechanism.

[0019] The irradiation unit 4 irradiates a laser light beam that converges in the X direction and has a light intensity distribution that spreads in the Y direction as illumination light L1 toward an observation object on the stage 21. The light receiving unit 6 receives reflected light L2 from the observation object and outputs data corresponding to the amount of light to the control unit 9.

[0020] The control unit 9 controls each part of the device and obtains the inspection results of the object being observed. Specifically, the control unit 9 includes a CPU (Central Processing Unit) 91, a memory 92, a storage 93, and an interface (IF) 94. The CPU 91 executes a control program pre-stored in the storage 93, thereby realizing the following functional blocks in software. Note that these functional blocks may be combined with appropriate hardware resources.

[0021] The stage control unit 912 controls the stage unit 2 to move the stage 21. The irradiation control unit 914 controls the irradiation unit 4 to emit a light beam having a predetermined spot shape toward the stage 21. The irradiation unit 4, which irradiates the observation object with light in the Y direction all at once, and the stage unit 2, which moves the observation object in the X direction, work together to achieve two-dimensional optical scanning of the observation object. The light-receiving control unit 916 controls the light-receiving unit 6 and acquires data corresponding to the light reflected from the observation object from the light-receiving unit 6. The data processing unit 918 performs appropriate processing on the received data to calculate the surface shape of the observation object.

[0022] The interface 94 is connected to appropriate input and output devices, and is responsible for receiving operation inputs from a user via the input devices and for notifying the user via the output devices. For example, the interface 94 can be configured to notify the user of the test results of the semiconductor chips C.

[0023] Fig. 2 is a diagram illustrating the structure of a semiconductor chip. More specifically, Fig. 2(a) and Fig. 2(b) are partially enlarged views showing the structure of a semiconductor chip C as an example of an observation object of the observation device 1, with Fig. 2(a) being a perspective view and Fig. 2(b) being a side view. Fig. 2(c) is a diagram illustrating another example of an observation object.

[0024] As shown in Figure 1, a large number of bumps Bc are formed on one main surface of a semiconductor chip C. As shown in Figures 2(a) and 2(b), each of the bumps Bc is a hemispherical protrusion made of a conductive material, such as metal solder or solder paste. The dimensions and arrangement pitch of the bumps Bc vary, but typically, the diameter and height are about 30 to 50 μm, and the arrangement pitch is about 60 to 150 μm.

[0025] The semiconductor chip C is attached to a carrier such as a printed wiring board. Specifically, the semiconductor chip C is attached to the carrier with the surface on which the bumps Bc are formed (hereinafter referred to as the "bump surface Fb") facing the carrier. This electrically connects the conductive pads on the carrier to the bumps Bc, ensuring electrical continuity between the semiconductor chip C and the carrier.

[0026] The semiconductor chip C may be attached directly to the carrier, or may be attached to the carrier via an intermediate layer. For example, as shown in Figure 2(c), the semiconductor chip C may be attached to an intermediate substrate I, made of, for example, ceramic, and the intermediate substrate I may be further attached to a printed wiring board P, which serves as a carrier. In this case, the bumps Bc on one side of the semiconductor chip C come into contact with the conductive pads Pi on one side of the intermediate substrate I, and the bumps Bi on the other side of the intermediate substrate I come into contact with the conductive pads Pp on one side of the printed wiring board P, thereby establishing electrical continuity between the semiconductor chip C and the printed wiring board P.

[0027] In general, the bumps Bc provided on the semiconductor chip C are smaller and have a narrower pitch than the bumps Bi provided on the intermediate substrate I. For this reason, the bumps Bc provided on the semiconductor chip C are sometimes specifically referred to as "microbumps."

[0028] To ensure reliable electrical connection via the bumps, the dimensions of each bump, such as size, position, and arrangement pitch, must be formed according to specifications. The observation device 1 of this embodiment can be suitably applied to optically observe bumps and measure their dimensions. Both the bumps (microbumps) Bc formed on the semiconductor chip C and the bumps Bi formed on the intermediate substrate I can be measured by this observation device 1. This observation device 1 can also be used to observe and measure other structures, such as conductive pads and via holes formed on the intermediate substrate I and the printed wiring board P. However, the following explanation of the operation will be focused on the case where the bumps Bc formed on the semiconductor chip C are measured as a representative example.

[0029] FIG. 3 is a diagram showing the schematic configuration of an observation optical device installed in an observation apparatus. In this observation apparatus 1, an irradiation unit 4 and a light-receiving unit 6 function together as one embodiment of the "observation optical device" according to the present invention. In FIGS. 3(a) and 3(b), the dashed dotted line indicates the center line of the optical path. This center line also coincides with the optical axes of the optical elements (described below) provided in the irradiation unit 4 and the light-receiving unit 6. The operation and functions of these will be described in detail later, but first an overview of the configuration of the observation optical device will be described.

[0030] As shown in FIG. 3(a), the illumination unit 4 of the observation optical device includes a light source 41, a collimating lens 42, an optical modulator 43, and a focusing lens 44. The light source 41 is a laser light-emitting element that outputs visible light or infrared light. The laser light has a spread within a predetermined range, and within that range it can be considered to be essentially a point light source. The collimating lens 42 converts the light emitted from the light source 41 into parallel light.

[0031] The collimated light enters the optical modulator 43. The optical modulator 43 is a MEMS (Micro Electro Mechanical Systems) phased array that functions as a spatial light phase modulator. The optical modulator 43 reflects the incident collimated light and spatially modulates the emitted light by changing the reflection direction in response to a control command from the irradiation control unit 914. The modulated light is converged by the focus lens 44, and the convergent light beam is irradiated as illumination light L1 onto the bump surface Fb of the semiconductor chip C, which is the observation object.

[0032] Reflected light L2 from the bump surface Fb enters the light receiving unit 6. That is, the light receiving unit 6 includes an objective lens 61, an imaging lens 62, a light receiving element 63 which is a one-dimensional image sensor, and an aperture 64, which are arranged on the optical path of the specularly reflected light from the bump surface Fb. An image of the bump surface Fb is formed on the light receiving surface of the light receiving element 63 via the objective lens and the imaging lens 62. The light receiving element 63 outputs image data corresponding to the image of the bump surface Fb to the light receiving control unit 916. The aperture 64 functions as a light blocking member that removes blurred light that would otherwise enter the light receiving element 63.

[0033] The functions and operations of the observation optical device configured in this way will be explained in detail later. However, in the following explanation, for ease of understanding, the center line of the optical path, which is actually folded back by reflection as shown in Figure 3(a), will be expanded into a straight line as shown in Figure 3(b).

[0034] Next, the configuration of the optical modulator 43 will be described. The optical modulator 43 is, for example, a movable ribbon-type MEMS (Micro Electro Mechanical Systems) phased array. In this embodiment, the MEMS phased array is used as a programmable one-dimensional diffraction grating optical element that diffracts incident light and outputs it, and changes the output direction over time. Hereinafter, the MEMS phased array may be referred to as a "diffractive optical element." As a diffractive optical element (DOE), for example, a GLV (Grating Light Valve; "GLV" is a registered trademark of Silicon Light Machines) element can be suitably applied.

[0035] FIG. 4 is a diagram schematically illustrating the structure of a MEMS phased array. FIG. 5 is a diagram illustrating the operation of the MEMS phased array. More specifically, FIG. 4(a) is a diagram schematically illustrating the general configuration of a diffractive optical element 40, which is one form of a MEMS phased array. FIG. 4(b) is a diagram illustrating possible states of the diffractive optical element 40. FIG. 5(a) and FIG. 5(b) are diagrams illustrating the operation of the MEMS phased array.

[0036] As shown in Figure 4(a), diffractive optical element 40 has a general configuration in which multiple movable ribbons 402 are arranged on substrate 401 at regular intervals in a direction parallel to the surface, facing the surface of flat bottom electrode 403. The upper surfaces of movable ribbons 402 are reflective surfaces that reflect light, for example, by metal coating. Each movable ribbon 402 is fixed at a regular interval relative to bottom electrode 403. In other words, the distance between movable ribbon 402 and bottom electrode 403 is determined by a pair of post anchors 404 that are erected on substrate 401 so as to sandwich bottom electrode 403 between them.

[0037] In the following description, Cartesian coordinates are set as shown in FIG. 4(a) to uniformly indicate directions in diffractive optical element 40 while distinguishing from the spatial coordinates shown in FIG. 1. Of the directions along the surface of substrate 401, the arrangement direction of multiple movable ribbons 402 is defined as the Dx direction, and the longitudinal direction of each movable ribbon 402 is defined as the Dy direction. The direction perpendicular to the surface of substrate 401 is defined as the Dz direction. The arrangement pitch of movable ribbons 402 in the Dx direction is represented by the symbol D.

[0038] In the diffractive optical element 40, a large number of movable ribbons 402, each with its longitudinal direction being the Dy direction, are arranged in the Dy direction, and the length of the entire diffractive optical element 40, which is an assembly of these ribbons, is greater in the Dx direction than in the Dy direction. Therefore, when viewed as a whole, the Dx direction can be considered to be the longitudinal direction of the diffractive optical element 40.

[0039] The movable ribbons 402 are displaceable relative to the bottom electrode 403. Specifically, as shown in FIG. 4(b), when a control voltage V is applied between the movable ribbons 402 and the bottom electrode 403, the movable ribbons 402 are deformed by electrostatic force and displaced in the direction toward or away from the bottom electrode 403, i.e., the Dz direction, as indicated by the solid and dotted lines. The amount of displacement of the movable electrode 402 depends on the magnitude of the control voltage V. A drive circuit (CMOS driver) (not shown) is provided in the irradiation control section 914 of the control unit 9, and the control voltage V is applied to the movable ribbons 402 from this drive circuit.

[0040] The control voltage V applied from the drive circuit can be set individually for each movable ribbon 402. Therefore, the height of each movable ribbon 402 in the Dz direction can be individually controlled by the magnitude of the control voltage V. Therefore, when the surfaces of the multiple movable ribbons 402 are viewed macroscopically, various uneven patterns are realized depending on the differences in the height of each movable ribbon 402.

[0041] 5(a), when the surface height of all the movable ribbons 402 is the same, the surfaces of those movable ribbons 402 collectively form a plane mirror. That is, when light (solid arrow) is incident on the surface of the movable ribbon 402, the specularly reflected light (dashed arrow) is emitted from the surface of the movable ribbon 402. In other words, the surface of the diffractive optical element 40, which is an assembly of the movable ribbons 402, acts as a plane mirror.

[0042] 5(b), when the surface height of adjacent movable ribbons 402 is made slightly different to form a stepped uneven pattern, light reflected with a phase difference between the individual movable ribbons 402 interferes with each other, causing a diffraction phenomenon. As a result, only diffracted light in a specific direction (indicated by the dashed arrow) is emitted from diffractive optical element 40.

[0043] The diffraction angle θ is determined by the wavelength of light (hereinafter represented by the symbol λ), the pitch P of the concave-convex pattern, and the height difference H. In the example on the left side of FIG. 5(b), a stepped pattern is formed with five movable ribbons 402 as one unit, and the pitch P of this pattern is 5D. In the example on the right side of FIG. 5(b), a stepped pattern is formed with four movable ribbons 402 as one unit, and the pitch P of this pattern is 4D.

[0044] These concave and convex patterns can be varied by electrical control. By controlling the control voltage V applied to each movable ribbon 402 to form a blazed pattern with a height difference H=(λ / 2), the diffraction angle θ can be arbitrarily changed. The diffraction angle θ at this time can be calculated using the wavelength and the repetition pitch P as follows: θ=λ / P=λ / (n·D) … (Equation 1) where n is the number of movable ribbons 42 that make up one unit of the stepped pattern, and Figure 5(b) shows n = 5 (example on the left) and n = 4 (example on the right), with the resulting diffraction angles θ being θ1 and θ2 (≠θ1), respectively. Therefore, in addition to the function of a flat mirror that outputs incident parallel light as parallel light, it is possible to realize the function of a curved mirror that converges or diverges light.

[0045] In reality, the desired optical scanning can be achieved by specifying the value of n corresponding to the desired direction of light emission and controlling each movable ribbon 402 to form a corresponding blazed pattern. Note that the value of n is not limited to an integer and can take on a continuous real value. A blazed pattern corresponding to a value of n other than an integer can be achieved by using a discrete number of ribbons forming the stepped pattern or by setting the displacement of the movable ribbons 402 at the end of each stepped pattern to a value greater than 0 and less than (λ / 2).

[0046] In this way, the diffractive optical element 40 realized by the MEMS phased array is a spatial light phase modulation element that has the function of emitting (diffracting) incident light in different directions using interference due to phase difference, and the light emission direction can be changed by electrical control. In other words, the relationship between the incident direction and emission direction of light can be electrically controlled. Furthermore, by changing the concave-convex pattern created by the movable ribbons 402 over time, the light emission direction can be changed from moment to moment. This can be used to modulate the emitted light.

[0047] In this embodiment, a diffractive optical element (spatial light phase modulation element) 40 having the structure and characteristics described above is used as the optical modulator 43 of the irradiation unit 4. In the actual observation device 1, the optical modulator 43 is arranged so that the longitudinal direction Dx of the optical modulator 43 coincides with the Y direction of the observation device 1, and so that the Dy direction and Dz direction have a predetermined inclination with respect to the direction of the center line of the incident light.

[0048] Figure 6 shows the operation of the optical modulator in this embodiment. Figure 6(a) shows the optical path of light that enters and is reflected by the optical modulator 43, and Figure 6(b) shows the expanded view of the folded optical path. In the longitudinal direction Dx of the optical modulator 43, in which a large number of movable ribbons 402 are arranged, the output direction of the light is adjusted independently for each position.

[0049] More specifically, at the center of the longitudinal direction Dx of the optical modulator 43, light that enters without a Dx-direction component is emitted without a Dx-direction component. On the other hand, at other parts, the light emission direction is changed as necessary so that the emitted light has a Dx-direction component. In this embodiment, the emission directions on the (+Dx) side and the (-Dx) side are set to be symmetrical about the center in the Dx direction. In particular, when the concave-convex pattern is a repeated sawtooth pattern symmetrical about the center, the optical modulator 43 functions as if it were a "diffractive Fresnel lens with a focal length that can be changed in multiple stages."

[0050] As a result, for example, when parallel light is incident on the optical modulator 43, it is possible to realize a mode in which the output light is output as parallel light as is, as shown by the solid arrows in Figures 6(a) and 6(b), a mode in which the output light is output as diverging non-parallel light, as shown by the dashed arrows, and a mode in which the output light is output as converging non-parallel light, as shown by the dotted arrows.

[0051] The operation of the observation optical device (illumination unit 4, light receiving unit 6) including such an optical modulator 43 will be described with reference to Figures 7 to 9. Note that, since spatial directions such as horizontal and vertical directions do not have any special meaning in the optical path diagram, directions will be indicated by appropriately adding directions Dx, Dy, and Dz shown in Figure 4(a).

[0052] 7A and 7B are ray diagrams for the observation optical device. More specifically, Fig. 7A shows a ray diagram in the DyDz plane, and Fig. 7B shows a ray diagram in the DxDz plane. Note that the optical modulator 43 in this case functions as a plane mirror.

[0053] 7(a), laser light emitted from a light source 41, which can be regarded as a point light source, while diverging, is converged on the surface of an optical modulator 43 by a collimating lens 42. In other words, the optical modulator 43 is disposed at a position where the output light from the collimating lens 42 converges. At this time, with respect to the illumination optical system including the collimating lens 42 and the focus lens 44, the light source 41 and the bump surface Fb are in a positional relationship that is conjugate with each other.

[0054] 7(b), the light emitted from the light source 41 is output as parallel light in the Dx direction. That is, the collimator lens 42 has greater power in the Dy direction than in the Dx direction. As a result, a so-called line light beam, whose light intensity distribution is wide in the Dx direction and narrow in the Dy direction, is incident on the optical modulator 43.

[0055] Regarding how the light travels from this point on, the path of the light on the DyDz plane will first be explained with reference to Figure 7(a). At this time, the optical modulator 43 functions as a plane mirror, so the light is emitted without being modulated. The convergent light that passes through the optical modulator 43 diverges again and enters the focus lens 44, where it is emitted as parallel light and enters the surface of the semiconductor chip C, which is the object of observation, i.e., the bump surface Fb. The light reflected by the bump surface Fb enters the light-receiving element 63 via the objective lens 61 and imaging lens 62 of the light-receiving unit 6.

[0056] 7(b), on the DxDz plane, the light that enters the optical modulator 43 as parallel light enters the focus lens 44 as parallel light. The focus lens 44 converges the light onto the surface (bump surface Fb) of the semiconductor chip C, which is the observation object. The light reflected by the bump surface Fb enters the light receiving element 63 via the objective lens 61 and the imaging lens 62 of the light receiving unit 6.

[0057] Considering the path of light on the DyDz plane shown in Fig. 7(a) and the path of light on the DxDz plane shown in Fig. 7(b), a line light beam whose light intensity distribution is wide in the Dy direction and narrow in the Dx direction is incident on the bump surface Fb. Since the Dx direction coincides with the Y direction (Fig. 1) in the observation device 1, a line light beam whose light intensity distribution is narrow in the X direction and wide in the Y direction is irradiated onto the bump surface Fb as illumination light L1.

[0058] 1, the entire area of ​​the bump surface Fb in the Y direction is illuminated from one end to the other. The stage movement moves the semiconductor chip C in the X direction, thereby achieving two-dimensional optical scanning of the bump surface Fb. Light reflected from each part of the area of ​​the bump surface Fb irradiated with the illumination light L1 (irradiated area) enters the light receiving unit 6 as reflected light L2.

[0059] 1, 7(a), and 7(b), at a certain time, an image of the irradiated area of ​​the bump surface Fb is formed on the light-receiving surface of the light-receiving element 63. The light-receiving element 63 is a one-dimensional image sensor (linear image sensor) with position resolution in the Dy direction. That is, on the optical path obtained by linearly expanding the light folded by reflection, the longitudinal direction (Dx direction) of the optical modulator 43 and the longitudinal direction of the one-dimensional image sensor are perpendicular to each other.

[0060] Therefore, the light receiving element 63 can separately detect the amount of reflected light at each portion of the irradiated area in the Y direction. In other words, the light receiving element 63 can acquire an image of the irradiated area of ​​the bump surface Fb. When combined with movement in the X direction by the stage unit 2, it is possible to acquire a two-dimensional image of the entire bump surface Fb.

[0061] Here, if we focus on the optical path in the DxDz plane, the light-receiving surface of the light-receiving element 63 and the bump surface Fb are arranged in an optically conjugate position with respect to the observation optical system including the objective lens 61 and the imaging lens 62. This makes it possible to eliminate blurred light using the principle of confocal imaging. To make this possible, an aperture 64 is arranged just before the light-receiving element 63. More specifically, as shown in FIG. 7(a), the aperture of the aperture 64 is set to be large in the Dy direction, and small in the Dx direction, as shown in FIG. 7(b). In other words, the aperture of the aperture 64 is a slit with the Dy direction as its longitudinal direction.

[0062] Therefore, the diaphragm 64 functions as a pinhole in the Dx direction, blocking stray light that is not focused on the bump surface Fb and allowing only focused light to enter the light receiving element 63. On the other hand, in the Dy direction, the diaphragm 64 does not function as a light blocking member, allowing all light to enter the light receiving element 63. This allows the light receiving element 63 to receive an image of the bump surface Fb in a focused state at each position in the Y direction. As a result, the light receiving element 63 can capture an image of the bump surface Fb with high contrast.

[0063] In order to accurately measure the shape, such as the height, of the bump Bc formed on the bump surface Fb, it is necessary to perform a so-called focus scan, in which multiple images are taken near the bump surface Fb while changing the focal position in the height direction.

[0064] Such component inspections are generally performed as in-line 100% inspections. For this purpose, high-speed focus scanning is required, and scanning by mechanical movement of the optical system or the object being observed, for example, cannot meet such speed requirements. While it is possible to prepare multiple optical systems with different focus positions in advance, this would result in a complex device configuration. Therefore, in this embodiment, focus scanning is performed using an optical modulator 43 capable of high-speed optical modulation.

[0065] 8 is a diagram illustrating the principle of focus scanning in this embodiment. As described above, in this embodiment, the optical modulator 43 changes the path of the incident parallel light in the Dx direction so that it diverges or converges. Note that the optical modulator 43 does not affect the direction of light in the Dy direction, and the ray diagram is the same as that shown in FIG. 7(a), so only the ray diagram in the DxDz plane is shown here.

[0066] 8(a), the solid line indicates the path of light when the optical modulator 43 acts to diverge the light, and the dotted line indicates, for comparison, a portion of the path of light when the optical modulator 43 emits light as parallel light. The light emitted from the optical modulator 43 is slightly divergent, so that the illumination light L1 incident on the bump surface Fb from the focus lens 44 converges behind the bump surface Fb. Therefore, the light emitted from the imaging lens 62 also converges behind the light-receiving surface of the light-receiving element 63.

[0067] 8(b), the solid lines indicate the path of light when the optical modulator 43 acts to converge the light, and the dotted lines indicate part of the path of light when the optical modulator 43 emits the light as parallel light. In this case, the illumination light L1 converges in front of the bump surface Fb, and the light emitted from the imaging lens 62 also converges in front of the light-receiving surface.

[0068] In this way, the optical modulation performed by the optical modulator 43 causes the convergence position of the illumination light L1 to move back and forth, and the position of the image plane formed by the observation optical system (objective lens 61, imaging lens 62) also fluctuates accordingly. In other words, the effective focus position moves in the Dz direction. This phenomenon can be used as focus scanning in place of mechanical movement.

[0069] For example, in focus scanning when a confocal optical system is used to capture multifocal images, it is necessary to move the light-receiving surface in accordance with the movement of the imaging plane. On the other hand, in focus scanning for measuring height, etc., it is not necessary to move the light-receiving surface in accordance with the movement of the imaging plane. The reason for this is as follows: The objective of acquiring the surface profile of the bump surface Fb can be achieved by obtaining, for each position in the XY plane, information representing the focus height (Z-direction position) when the focus state is achieved at that position. In other words, it is sufficient to detect the difference in contrast between the focused and unfocused states. In particular, if an aperture 64 is provided, the difference in contrast becomes even more apparent due to its light-blocking effect. Therefore, it is not necessary to acquire an image in focus at each focus position.

[0070] The calculation of the surface profile based on the output of the light receiving element 63 is performed by the data processing unit 918 of the control unit 9. A known method as a measurement technique based on the principle of the confocal method can be applied to calculate such a profile. Therefore, a description of the profile calculation method will be omitted here.

[0071] FIG. 9 shows an example of focus scanning. More specifically, FIG. 9(a) is a timing chart showing how the focus height changes as achieved by the optical modulator 43, and FIG. 9(b) is a diagram showing a schematic diagram of the change in focus position at that time. As described above, in this embodiment, the optical modulator 43 functions as a Fresnel lens with a variable focal length. That is, the illumination control unit 914 changes the uneven pattern achieved by the optical modulator 43 at a constant period, thereby making it possible to periodically change the focus position of the illumination light L1 in multiple stages, as shown in FIG. 9(a). Here, an example is shown in which the focus position changes in 10 stages.

[0072] As shown by the dotted line in Fig. 9(b), the target surface profile can be obtained by setting the focus position change range so that it includes the range in which the profile is to be acquired. The number of steps in which the focus position is changed and the amount of displacement between each step can be determined appropriately depending on the required height resolution and measurement range.

[0073] In the time axis direction, when a GLV is used as the optical modulator 43, it is possible to switch the concave and convex patterns with a control clock of several hundred kHz. For example, when a clock of 350 kHz is used as the control frequency, the switching period T1 and repetition period T2 shown in Figure 9(a) are approximately 2.86 μsec and approximately 28.6 μsec, respectively. In this way, it is possible to achieve focus scanning at an extremely high speed.

[0074] In combination with the movement in the X direction due to stage movement, the movement speed of the stage 21 and the control frequency of the optical modulator 43 may be determined so that the relationship between the movement speed of the stage 21 and the repetition period T1 or T2 satisfies the required position resolution in the X direction. When the control frequency is sufficiently small relative to the stage movement speed, it is possible to consider that there is essentially no change in the position of the observation object during focus scanning. It is also preferable that the frame rate of the light receiving element 63, which is a one-dimensional image sensor, is set so that the focus scanning period and the imaging period are synchronized.

[0075] Fig. 10 is a diagram showing another example of the configuration of the observation optical device. In the example configuration shown in Fig. 3(a), an optical modulator 43 is provided on the optical path from the light source 41 to the bump surface Fb, which is the observation object, and the light incident on the bump surface Fb is modulated. However, the location of the optical modulator is not limited to this position. For example, as shown in Fig. 10(a), an irradiation unit 4a without an optical modulator and a light receiving unit 6a with an optical modulator 65 may be combined. In Fig. 10, the same components as those in Fig. 7 are designated by the same reference numerals, and their description will be omitted.

[0076] The optical modulator 65 is disposed on the optical path between the objective lens 61 and the imaging lens 62, and is preferably disposed at a position on the DyDz plane where the output light from the objective lens 61 converges, as shown in Fig. 10(a). As in the above embodiment, the modulation effect of the optical modulator 65 does not affect the path of light within the DyDz plane.

[0077] 10(b) and 10(c), within the DxDz plane, the modulation action of the optical modulator 65 causes the focus position when the bump surface Fb is viewed from the observation optical system side to fluctuate, and accordingly, the convergence position on the light receiving element 63 side also fluctuates. This provides the same effect as the above embodiment. That is, by periodically controlling the optical modulator 65, high-speed focus scanning becomes possible.

[0078] As described above, the observation optical device of this embodiment and the observation apparatus 1 equipped with it irradiate a light beam onto the bump surface Fb of the semiconductor chip C having a plurality of bumps Bc formed on its surface, which is the object to be observed and inspected, and receive the reflected light. Based on the light reception results, a surface profile representing the unevenness of the bump surface Fb is obtained.

[0079] The light beam irradiated onto the bump surface Fb is a linear light beam that has a relatively large spread in one axial direction along the bump surface Fb and is narrowed in the other axial direction perpendicular to the first axial direction. This allows light to be irradiated all at once to a narrow area of ​​the bump surface Fb that extends along the one axial direction. Then, by moving the semiconductor chip C along the other axial direction using the stage 21, the irradiated area moves sequentially in that direction, resulting in two-dimensional optical scanning.

[0080] Light reflected from the irradiated area is converged onto the light-receiving surface of the light-receiving element 63 via the observation optical system (objective lens 61, imaging lens 62), and an image of the irradiated area is formed on the light-receiving surface. The light-receiving element 63 is a one-dimensional image sensor that can convert the image of the irradiated area into image data and output it. This allows imaging of the irradiated area. From the imaging results, it is possible to determine the surface profile of the object being observed based on the principles of confocal measurement.

[0081] The optical modulator 43 (65) provided on the optical path periodically modulates the light to diverge and converge, thereby varying the distance between the light receiving surface of the light receiving element 63 and the convergence point of the light beam incident thereon over time. This allows focus scanning in the height direction of the object to be observed. This type of focus scanning using an optical modulator can be performed much faster than focus scanning using conventional techniques that rely on mechanical movement.

[0082] This makes it possible to apply this observation device 1 to applications that require high-speed inspection, such as in-line 100% inspection. Furthermore, because the focus position is changed by electrically controlling the optical modulator, a simpler device configuration can be used compared to conventional technology that uses multiple optical systems with different focus positions.

[0083] As explained above, in this embodiment, the semiconductor chip C, and in particular its bump surface Fb, corresponds to the "object to be observed" of the present invention. Furthermore, in the observation device 1 of this embodiment, the irradiation units 4, 4a and the light-receiving units 6, 6a function together as the "optical observation device" of the present invention. Furthermore, the stage 21 and the movement mechanism 23 function as the "support unit" and the "movement mechanism" of the present invention, respectively. Furthermore, the control unit 9 functions as the "control unit" of the present invention.

[0084] In the irradiation unit 4, 4a, the light source 41 functions as the "light source" of the present invention, and the collimator lens 42 and the focus lens 44 together constitute the "illumination optical system" of the present invention. On the other hand, in the light-receiving unit 6, 6a, the objective lens 61 and the imaging lens 62 together constitute the "observation optical system" of the present invention, and the light-receiving element 63 and the diaphragm 64 respectively function as the "light-receiving section" and the "light-blocking member" of the present invention. The light-receiving element 63 also corresponds to the "one-dimensional image sensor" of the present invention.

[0085] In the above embodiments, the optical modulators 43 and 65 correspond to the "spatial optical phase modulator," "one-dimensional diffraction grating," and "movable ribbon-type one-dimensional diffraction grating" of the present invention. The movable ribbon 402 functions as the "movable ribbon" of the present invention. In the optical modulator 43, the Dx direction corresponds to the "first direction" of the present invention, and the Dy direction corresponds to the "second direction."

[0086] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, the surface profile of the object to be observed is determined based on the image of the surface. However, for example, the observation device 1 can also be applied to more simply determine the height of protrusions formed on the flat surface of an object to be observed.

[0087] Furthermore, in the above embodiment, the optical modulator is disposed at a position where the light beam converges in the DyDz plane. This is effective in efficiently directing light into the optical modulator, which has a small dimension in the Dy direction. On the other hand, from the viewpoint of modulation in the Dx direction, the effect is the same regardless of the position on the optical path of the parallel light. In this sense, it can be said that there is a higher degree of freedom in the position where the optical modulator is disposed. In other words, the position where the optical modulator is disposed on the optical path is not limited to that in the above embodiment.

[0088] In the above embodiment, a GLV, which is a one-dimensional spatial light phase modulation element, is used as the optical modulator. However, other devices capable of realizing similar spatial light modulation at high speed may be used as the optical modulator. Furthermore, the optical modulator and the light receiving element are not limited to being one-dimensional, and may be, for example, one having position resolution in two dimensions.

[0089] Furthermore, the observation device 1 of the above embodiment is used for the purpose of inspecting semiconductor chips C having bumps Bc formed on their surfaces and / or electronic products including such semiconductor chips. However, the observation target of the observation device according to the present invention is not limited to these, and can be any object. In particular, this observation device 1 can be suitably applied to the visual inspection of various industrial products that require high-speed observation and inspection.

[0090] As described above with reference to specific embodiments, in the observation optical device according to the present invention, a light-shielding member for removing blurring light may be disposed between the observation optical system and the light-receiving surface, for example. With such a configuration, it becomes possible to obtain high contrast by eliminating blurring light reflected from the surface of the observation object in an unfocused state based on the principle of the confocal method.

[0091] Furthermore, for example, the light source may be a point light source located at a position conjugate with the surface of the object of observation relative to the illumination optical system. With this configuration, the light source, the surface of the object of observation, and the light-receiving surface are in a conjugate positional relationship with each other, thereby achieving a high contrast improvement effect using the confocal method. This can improve measurement accuracy, for example, when measuring the surface shape of the object of observation.

[0092] For example, the illumination optical system may be configured to have a light intensity distribution that spreads in a first direction perpendicular to the optical axis, while causing a light beam that is converged in a second direction perpendicular to the optical axis and the first direction to be incident on the observation object. This configuration makes it possible to irradiate light collectively onto an area of ​​the surface of the observation object that has a predetermined length along the first direction. This shortens the time required to optically scan the surface of the observation object.

[0093] In this case, for example, the spatial light phase modulator may be a one-dimensional diffraction grating whose arrangement direction is the second direction, or may be a movable ribbon type one-dimensional diffraction grating in which a plurality of movable ribbons whose longitudinal direction is the first direction are arranged along the second direction. These configurations are suitably applicable to the above-mentioned application of spatial light modulation in the second direction.

[0094] Furthermore, for example, the light receiving unit may be a one-dimensional image sensor whose longitudinal direction is the first direction. With this configuration, it is possible to collectively receive reflected light from each part within an area of ​​the surface of the object to be observed that extends along the first direction, thereby further shortening the time required for optical scanning.

[0095] In addition, in the observation device according to the present invention, for example, the control unit can control the spatial light phase modulator so as to change the distance between the convergence position of the light beam and the light receiving surface in multiple stages and periodically. With this configuration, focus scanning can be performed at high speed, changing the focus position relative to the observation object in multiple stages and periodically.

[0096] Furthermore, for example, the control unit may be configured to acquire a surface profile of the observation object based on the light reception result of the light receiving unit. From the light reception result, it is possible to detect the position, size, height (depth), etc. of protrusions and depressions on the surface of the observation object, and by combining these, it is possible to acquire the surface profile of the observation object. [Industrial Applicability]

[0097] The present invention is suitably applicable to the inspection of various industrial products such as semiconductor chips, and is particularly suitable for applications requiring high speed, such as in-line 100% inspection. [Explanation of symbols]

[0098] 1. Observation equipment 4, 4a Irradiation unit (optical device for observation) 6, 6a Light receiving unit (optical device for observation) 9 Control unit (control section) 21 Stage (support part) 23 Moving mechanism 40 Diffractive optical element 41 Light source 42 Collimating lens (illumination optical system) 43,65 Optical modulators (spatial light phase modulators, one-dimensional diffraction gratings, movable ribbon type one-dimensional diffraction gratings) 44 Focus lens (illumination optical system) 61 Objective lens (observation optical system) 62 Imaging lens (observation optical system) 63 Photodetector (photodetector, one-dimensional image sensor) 64 Aperture (light blocking member) 402 Movable Ribbon C. Semiconductor chip (object of observation) Dx 1st direction Dy 2nd direction Fb Bump surface (object of observation)

Claims

1. A light source and A light receiving unit; an illumination optical system that condenses the light emitted from the light source and makes the light incident on the surface of an observation object; an observation optical system that guides light emitted from the observation object to the light receiving unit and forms an image of the observation object on a light receiving surface of the light receiving unit; A spatial light phase modulator that can change the relationship between the incident direction and the outgoing direction of light by electrical control. Equipped with the illumination optical system causes a light beam obtained by converging light emitted from the light source to be incident on the observation object; the light receiving surface is disposed at a position conjugate with the surface of the observation object with respect to the observation optical system, the spatial light phase modulator is disposed on an optical path from the light source to the light receiving unit, and modulates light directed toward the light receiving unit to change, over time, the distance between the light receiving surface and a convergence position of the light beam reflected by the observation object and incident on the light receiving unit via the observation optical system.

2. 2. The observation optical device according to claim 1, further comprising a light blocking member for removing blurred light, disposed between the observation optical system and the light receiving surface.

3. 2. The observation optical device according to claim 1, wherein the light source is a point light source arranged at a position conjugate with the surface of the observation object with respect to the illumination optical system.

4. 2. The observation optical device according to claim 1, wherein the illumination optical system has a light intensity distribution that spreads in a first direction perpendicular to an optical axis, while causing the light beam that is converged in a second direction perpendicular to the optical axis and the first direction to be incident on the observation object.

5. 5. The observation optical device according to claim 4, wherein the spatial light phase modulator is a one-dimensional diffraction grating whose arrangement direction is the second direction.

6. 6. The observation optical device according to claim 5, wherein the spatial light phase modulator is a movable ribbon type one-dimensional diffraction grating in which a plurality of movable ribbons, each having a longitudinal direction in the first direction, are arranged along the second direction.

7. 6. The observation optical device according to claim 5, wherein the light receiving section is a one-dimensional image sensor whose longitudinal direction is in the first direction.

8. An observation optical device according to any one of claims 1 to 7; a support portion that supports the observation object; a moving mechanism that moves the support unit and the observation optical device relative to each other; a control unit for controlling the spatial light phase modulator; An observation device comprising:

9. 9. The observation device according to claim 8, wherein the control unit controls the spatial light phase modulator to periodically change the distance between the convergence position of the light beam and the light receiving surface in multiple stages.

10. The observation device according to claim 8 , wherein the control unit acquires a surface profile of the observation object based on a light reception result of the light receiving unit.

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