JP2004006504A - Bump inspection method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bump inspection method and apparatus for rapidly and accurately detecting the height and shape of a bump. <P>SOLUTION: When the bump formed on the surface of a work is inspected, light irradiates a bump position in terms of design on the surface of the work from a normal line direction of the surface of the work concerned, an actual bump position is detected from optical information where regular reflection components or irregular reflection components in the reflection light are obtained through a mask, and slit light irradiates the surface of the work from an oblique direction to the actual bump position, thus detecting the height or shape of the bump from the optical information obtained from the reflection light. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for inspecting bumps (projections) formed on a surface of a work.
[0002]
[Prior art]
In mounting semiconductor chips, bumps are used instead of wire bonding for the purpose of improving the mounting density and connecting multiple pins. In the case of bump connection, the mounting time can be reduced compared to the connection of the lead wire, the mounting area can be reduced compared to the connection of the lead wire, and the signal arrival time can be reduced compared to the connection of the lead wire. This is because it has advantages.
By the way, in mounting using these bumps, since a large number of bumps are collectively bonded to corresponding portions of a mounting substrate such as a lead frame, it is required that the surface shape, formation position, width, and height of the bumps be appropriate. You. In today's world, where the degree of integration and miniaturization of semiconductor integrated circuits has advanced, this is even more so.
Therefore, various bump inspection systems or bump inspection apparatuses for inspecting bumps on semiconductor substrates such as semiconductor wafers and semiconductor chips have been proposed today.
[0003]
[Problems to be solved by the invention]
However, types of bumps formed on a semiconductor substrate include ball bumps and straight bumps, and there is no bump inspection method and apparatus that can quickly and accurately detect the height and shape of a bump regardless of the type of bump. Was.
[0004]
The present invention has been made in view of the above problems, and has as its object to provide a bump inspection method and apparatus capable of quickly and accurately detecting the height and shape of a bump.
[0005]
[Means for Solving the Problems]
In the bump inspection method according to claim 1, in inspecting a bump formed on the surface of the work, light is applied to a designed bump position on the surface of the work from a direction normal to the surface of the work, The actual bump position is detected from the optical information obtained through the mask with the regular reflection component or the irregular reflection component of the reflected light, and the actual bump position on the surface of the work is irradiated with slit light obliquely from the reflected light. It is characterized in that the bump height or shape is detected from the obtained optical information.
In this case, it is preferable that the “mask” is located at or near the focal plane position of the observation optical system that observes the reflected light. In addition, for example, to obtain optical information of the specular reflection component, a mask in which a portion near the optical axis of the observation optical system is a light transmitting portion and a peripheral portion is a light shielding portion is used. In order to obtain (1), a mask having a light-shielding portion near the optical axis of the observation optical system and a light-transmitting portion around the portion is used. Further, in order to detect the bump height or the shape by irradiating the slit light, for example, a known light cutting method is used. In this case, each bump may be irradiated with one slit light, or two or more parallel slit lights may be irradiated. Furthermore, all the bumps may be irradiated with slit light at a time.
The “bump position in the design” refers to a bump position determined in the design when forming a bump on a work.
Further, it is preferable to use a digital mirror device or a transparent liquid crystal for forming an irradiation pattern for detecting a bump position or detecting a bump height or a shape.
[0006]
According to such a bump inspection method, an actual bump position is detected from the regular reflection component or irregular reflection component of the light reflected on the work surface, and slit light is irradiated based on the bump position. Therefore, the bump height or shape can be accurately detected. In addition, when the deviation between the actual bump position and the designed bump position is not within the allowable range, a bump failure can be determined. On the other hand, when the deviation between the actual bump position and the designed bump position is within the allowable range, or when the actual bump position and the designed bump position are not within the allowable range, the bump formation is not performed. If necessary for the analysis of the process, the bump height and shape can be detected at the actual bump position.
[0007]
The bump inspection method according to claim 2 is the bump inspection method according to claim 1, wherein when the bump is a spherical bump, the beam size of the light irradiated from the normal direction is larger than the size of the bump. It is characterized in that the actual bump position is detected from optical information that is a regular reflection component. The term "a bump having a spherical top" is not particularly limited, but refers to a ball bump, a mushroom bump, or the like.
[0008]
According to this bump inspection method, when light is applied to the surface of the work from the normal direction, if the upper part is a spherical bump, the regular reflection component of the reflected light is the one reflected at the top of the bump. Therefore, the actual bump position can be accurately detected by mainly obtaining the optical information of the specular reflection component.
If the beam size of the light is larger than the size of the bump when the upper portion is a spherical bump, not only the optical information of the specular reflection component from the top of the bump but also the optical information of the specular reflection component from the surface of the work. , The image processing becomes complicated.
[0009]
The bump inspection method according to claim 3 is the bump inspection method according to claim 1, wherein, when the bump is a straight bump, a beam dimension of light irradiated from the normal direction is larger than a dimension of the straight bump. It is characterized in that the actual bump position is detected from optical information which is a diffuse reflection component. The “straight bump” refers to a bump having a flat surface such as a gold bump, but having a rougher surface than the work surface. In this case, it is preferable that the “light beam size” is determined in consideration of the allowable range of the bump displacement. For example, when the deviation of the bump position exceeds the allowable range, if the beam size is set so that the specular reflection component from the top of the bump cannot be detected, it is possible to easily determine whether or not the bump is defective.
[0010]
According to this bump inspection method, when light is applied to the surface of the work from its normal direction, in the case of a straight bump, the irregularly reflected component of the reflected light is reflected on the upper surface of the bump. The actual bump position can be accurately detected by obtaining the optical information of the irregular reflection component. Incidentally, the light reflected on the surface of the work becomes a regular reflection component when the work is a semiconductor wafer.
[0011]
5. A bump inspection apparatus for inspecting a bump formed on a surface of a work, wherein the bump position on the surface of the work in design is irradiated with light from a normal direction of the surface of the work. Then, the actual bump position is detected from the optical information obtained through the mask, the specular reflection component or the irregular reflection component of the reflected light, and the actual bump position on the surface of the work is irradiated with slit light from an oblique direction. The bump height or shape is detected from optical information obtained from the reflected light. In this case, one bump light may be applied to each bump, or two or more parallel slit lights may be applied to each bump. Further, the slit light may be applied to all the bumps (or all the bumps excluding the bump failure) at once.
[0012]
According to such a bump inspection apparatus, the actual bump position is detected from the regular reflection component or the irregular reflection component of the light reflected on the surface of the work, and the slit light is irradiated based on the bump position. Therefore, the bump height or shape can be accurately detected.
[0013]
According to a fifth aspect of the present invention, in the bump inspecting apparatus according to the fourth aspect, the irradiation pattern is formed by a spatial light modulator. Here, as the “spatial light modulator”, for example, a digital mirror device or a transparent liquid crystal can be considered.
[0014]
By using this spatial light modulator, it is possible to easily change the irradiation pattern.
[0015]
According to a sixth aspect of the invention, in the bump inspection apparatus of the fifth aspect, the optical system for irradiating the slit light constitutes a Scheimpflug optical system.
[0016]
When the optical system is a Scheimpflug optical system, it is possible to focus on the entire surface of the work, and it is possible to more accurately detect the bump height and the shape.
[0017]
In irradiating the slit light in the bump inspection method or apparatus, it is also possible to selectively irradiate a wide or narrow slit light from an oblique direction to the surface of the work. In this case, it is preferable that the width of the wide slit light is set to be larger than the width or diameter of the bump, and the width of the narrow slit light is set to be smaller than the width or diameter of the bump. Further, in the case of narrow slit light, it is preferable to apply a plurality of parallel slit lights to the same bump. By doing so, a plurality of portions of the same bump can be inspected at the same time, so that the inspection time can be reduced and the accuracy can be improved.
[0018]
In such a configuration, a wide or narrow slit light is applied to the surface of the work according to the type of the bump. In this case, when a wide slit light is applied, a shadow of the bump is formed. By measuring the length of the shadow and the like, the bump height can be measured. The wide slit light is not particularly limited, but is particularly effective when inspecting a ball bump.
On the other hand, when the narrow slit light is applied to the bump arrangement portion, the positions of the bright portion corresponding to the bump upper surface and the bright portion corresponding to the base surface are shifted. This amount of displacement reflects the bump height. The narrow slit light is not particularly limited, but is particularly effective when inspecting a straight bump.
[0019]
Further, in the bump inspection method or apparatus, it is preferable to irradiate slit light extending along the bump arrangement direction of the work. In this way, a plurality of arranged bumps can be inspected simultaneously.
[0020]
Further, in the bump inspection method or apparatus, it is preferable that the observation optical system that observes the reflected light of the slit light includes a line sensor as a light receiving unit. In this case, the extending direction of the line sensor is a direction orthogonal to the extending direction of the slit light, and it is preferable to inspect the bump by moving the line sensor in the extending direction of the slit light. According to this bump inspection apparatus, since light is received by the line sensor (one-dimensional sensor), the inspection can be performed more quickly than when a two-dimensional sensor is used.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
1. Configuration of Bump Measuring Apparatus As shown in FIGS. 1 to 3, a bump measuring apparatus according to the present invention includes a DMD (digital mirror device) 100 capable of holding an arbitrary projection pattern, and a DMD illumination optical system 200 for illuminating the DMD 100. And a bump position measuring optical system 300 for measuring the bump position on the test surface 500 and a bump height measuring optical system 400 for measuring the bump height. In this case, the DMD 100 and the DMD illumination optical system 200 can be used as both a bump position detecting device for obtaining a bump position and a device for obtaining a bump height. In this case, for example, when the angle of the entire DMD 100 is changed, the bump position is obtained, and the bump height is obtained, the bump position measuring optical system 300 and the bump height optical system 400 What is necessary is just to set it as the structure which can be switched.
[0022]
2. The DMD 100 shown in FIGS. 1 to 3 is configured such that each pixel arranged two-dimensionally is constituted by a minute mirror, and the inclination of the minute mirror can be controlled by an electrostatic field effect of a memory element for each pixel. This is a reflection-type display element that turns on and off by changing the angle of reflection of light from a mirror, and can hold an arbitrary projection pattern.
[0023]
3. 1. Configuration of DMD Illumination Optical System 200 The DMD illumination optical system 200 shown in FIG. 1 includes a lamp 201, a reflecting mirror 202, a condenser lens 203, an integrator rod 204, and a condenser lens 205.
As the lamp 201, a halogen lamp, a metal halide lamp, a xenon lamp, or the like is used. An elliptical reflecting mirror is used as the reflecting mirror 202, and a lamp 201 is provided at one focal point of the elliptical reflecting mirror. Light from the lamp 201 is reflected by the reflecting mirror 202 and becomes parallel light. The condenser lens 203 collects light from the reflecting mirror 202 and guides the light to the integrator rod 204. The integrator rod 204 averages the light flux. The condenser lens 205 converts the light from the integrator rod 204 into parallel light. The DMD 100 is illuminated by the parallel light.
[0024]
4. Configuration of Bump Position Measurement Optical System 300 The bump position measurement optical system 300 shown in FIG. 4 includes a projection lens 301, an imaging lens 302, an objective lens 303, a half mirror 304, an imaging lens 305, a total reflection mirror 306, An image lens 307, a mask 308, an imaging lens 309, and a CCD 310 are provided.
The projection lens 301 projects the DMD 100 into parallel light and projects the light. The imaging lens 302 is for imaging the light from the projection lens 301. The objective lens 303 converts the light from the imaging lens 302 into parallel light and irradiates the light onto the surface 500 to be inspected, and forms an image of the light reflected by the surface 500 to be inspected. From the irradiating light. Further, the imaging lens 305 receives the light from the half mirror 304, and the total reflection mirror 306 deflects the direction of the light from the imaging lens 305. An image forming lens 307 is for forming an image of light from the total reflection mirror 306, and a mask 308 is for blocking a part of the light from the image forming lens 307, and focuses on the image forming lens 307. Position (aperture surface). Further, the imaging lens 309 is for converting the light from the mask 308 into parallel light, and the CCD 310 is for receiving the light from the imaging lens 309 and converting it into an electric signal. The CCD 310 is preferably configured as a two-dimensional sensor.
[0025]
5. As the constituent mask 308 of the mask 308, as shown in FIG. 4, a ball bump mask 308a and a straight bump mask 308b are used. The ball bump mask 308a has a light-transmitting portion at the center and a light-shielding portion at the periphery, and blocks the irregular reflection component on the surface 500 to be measured. On the other hand, the straight bump mask 308b has a light-shielding portion at the center and a light-transmitting portion at the periphery, and blocks a specular reflection component on the surface 500 to be measured. In this case, two types of masks, a ball bump mask 308a and a straight bump mask 308b, may be prepared, and these may be switched and used as required. The bump mask 308a and the straight bump mask 308b may be configured.
In the case of a mushroom bump mask, the same configuration as the ball bump mask may be used.
[0026]
6. Principle of Measuring Bump Position (1) In the Case of Ball Bump As shown in FIG. When light is applied from the normal direction, light that hits the top is specularly reflected, and light that hits other places is irregularly reflected. Therefore, by observing only the specular reflection component out of the light radiated to the ball bump 600 and reflected therefrom, the top position of the ball bump 600 and thus the bump position can be detected. In this case, it is preferable to apply a light beam (spot light) smaller than the size (diameter or size) of the ball bump 600 to the ball bump 600. The surface of the test surface 500 on which the ball bumps 600 are formed is a flat surface and is relatively smooth, so that light hitting the flat surface is prevented from being simultaneously detected as a regular reflection component.
The same applies to mushroom bumps.
[0027]
(2) In the case of a straight bump As shown in FIG. 5B, the upper surface of the straight bump 700 is substantially flat, but the upper surface is rough (high roughness), so that light hitting the upper surface is irregularly reflected. Ingredients. On the other hand, the light reflected from the surface of the test surface 500 is a regular reflection component, so that the bump position can be detected by detecting the boundary. In this case, it is preferable to apply a light flux (area light) larger than the size (dimension) of the straight bump 700 to the straight bump 700.
[0028]
7. Configuration of Bump Height Measurement Optical System 400 The bump height measurement optical system 400 shown in FIG. 3 includes a projection lens 401, an objective lens 402, an imaging lens 403, and a CCD 404.
The projection lens 401 converts the light from the DMD 100 into parallel light and irradiates the light onto the surface 500 to be measured. The DMD 100, the projection lens 401, and the test surface 500 constitute a Scheimpflug optical system. The Scheimpflug optical system is used in order to match the optical path length from each part of the DMD 100 to the corresponding position of the test surface 500. The objective lens 402 forms an image of light from the surface 500 to be measured, and the imaging lens 403 receives light from the objective lens 402. The CCD 404 receives light from the imaging lens 403 and converts the light into an electric signal. In this case, the CCD 404 is preferably configured as a line sensor. A diaphragm 405 is provided at a diaphragm position between the objective lens 402 and the imaging lens 403, and these constitute a double-sided telecentric optical system. In this telecentric optical system, the aperture angle is narrowed, thereby increasing the depth of focus.
[0029]
8. An example of the principle of measuring the height of the bumps The arrangement pitch of the bumps formed on the test surface 500 is obtained by image processing using a computer based on the bump position data obtained by the optical system 300 for measuring bump positions.
[0030]
Next, depending on the type of the bump, it is selected whether to use a wide slit light or a narrow slit light. Specifically, when the type of bump is a ball bump or a mushroom bump, a wide slit light is selected. In other cases, that is, when the type of a bump is a straight bump, a narrow slit light is selected. In addition, since the arrangement pitch of the bumps has already been determined, the computer calculates the scanning speed of the one-dimensional sensor (configured by the line sensor: CCD 404) from the arrangement pitch.
[0031]
In this case, when a wide slit light is selected, a wide slit light having a width of about twice the diameter of the bump is detected at an incident angle θ (for example, 45 °) as shown in FIG. The light is irradiated onto the surface 500, and the bump height measuring optical system 400 captures an optical image of the surface 500 to be measured at a reflection angle θ (for example, 45 °). At this time, the one-dimensional sensor is moved in the direction in which the slit light extends.
[0032]
The situation at this time is shown in FIG. 6 and FIG. However, FIGS. 6 and 7 show straight bumps as an example for convenience of explanation. At this time, the shadow of the bump 600 is formed by the light hitting the bump 600. The height of the bump is determined by the computer from the length of the shadow. In the case where the bump is a ball bump 700, the light that hits the bump 700 creates a shadow of the bump 700, while the vertex of the bump 700 becomes a bright point. The height of the bump can be determined by the above.
[0033]
FIG. 7A is a cross-sectional view of the bump taken along the line AA in FIG. 7B, where the peaks indicate the bumps and the valleys indicate the base surface of the test surface 500.
[0034]
On the other hand, when the narrow slit light is selected, the light having a narrow width of about の of the diameter of the bump 600 is covered with the incident angle θ (for example, 45 °) as shown in FIG. Irradiation is performed on the inspection surface 500, and an optical image of the inspection surface 500 is captured by the bump height measuring optical system 400 at a reflection angle θ (for example, 45 °). At this time, the one-dimensional sensor 32 is moved in the direction in which the slit light extends.
[0035]
The situation at this time is shown in FIGS. 8 and 9 show the straight bump 600 as an example for convenience of explanation. At this time, as shown in FIG. 8 and FIG. 9B, the position of the slit light that has hit the bump 600 and the position of the slit light that hit the surface (base) of the test surface 500 are misaligned in the light image (bright portion). This displacement amount reflects the bump height. Therefore, the bump height can be obtained by measuring the amount of displacement of the optical image.
[0036]
9A shows a cross-sectional view of the bump along the line AA in FIG. 9B, and the valleys show the surface of the test surface 500.
[0037]
9. Example of Bump Inspection Process (1) In the case of a ball bump First, bump position data on design is read into a computer (S1). Based on the bump position data, a spot light is applied to the designed bump position of the test surface 500 (S2). In this case, the irradiation pattern of the spot light is formed by controlling the mirror of the DMD 100 by the processing device of the computer. Then, the actual bump position is obtained by the processing unit of the computer from the optical information of the specular reflection component in the reflected light from the test surface 500. Next, the deviation amount between the designed bump position and the actual bump position is calculated by a processing device of a computer to determine whether the bump is good or bad. If a bump failure is found, the entire work may be determined to be defective and the detection of the bump height may be stopped for the work, or the height of only good bumps may be measured. In this case, the slit light is applied to the good bumps of the test surface 500 based on the bump position data of the good bumps. In this case, the irradiation pattern of the spot light is formed by controlling the mirror of the DMD 100 by the processing device of the computer. Then, a bump height is calculated by a processing device of a computer from optical information which is reflected light from the surface 500 to be measured.
On the other hand, when the bump height of the defective bump is also detected, the defective bump on the test surface 500 is irradiated with slit light based on the actual bump position data of the defective bump. In this case, the irradiation pattern of the spot light is formed by controlling the mirror of the DMD 100 by the processing device of the computer. Then, a bump height is calculated by a processing device of a computer from optical information which is reflected light from the surface 500 to be measured.
It should be noted that the bump inspection is performed in the same manner also for a mushroom bump instead of a ball bump.
[0038]
(2) In the case of a straight bump Also in the case of a straight bump, a bump inspection is performed by a substantially similar process except that an area light is irradiated instead of a spot light.
[0039]
9. Configuration of an Example of a Bump Inspection System FIG. 10 shows a bump inspection system in which the bump measuring device is incorporated.
This bump inspection system includes a bump position measuring device 800 and a bump height measuring device 900. In this bump inspection system, the DMD 100 of the bump position measuring device 800 and the bump height measuring optical system 900 is controlled by the host computer 1000 via the DMD controllers 2100 and 2200. The CCDs 310 and 404 are connected to an image processing unit 1300 via CCD controllers 1100 and 1200, and the image processing unit 1300 is connected to a host computer 1000. In the figure, reference numeral 1400 denotes an XYθ stage, which is connected to the host computer 1000 via an XYθ stage controller 1500. Reference numeral 1600 denotes an XZ stage, which is connected to the host computer 1000 via an XZ stage controller 1700. Reference numeral 1800 denotes a monitor, and reference numeral 1900 denotes a CRT.
[0040]
Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and it goes without saying that various modifications can be made without departing from the scope of the invention.
[0041]
【The invention's effect】
Explaining the effect of the typical embodiment of the present invention, since the bump position is obtained and then the bump height is obtained, the bump height can be accurately detected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a DMD illumination optical system according to an embodiment.
FIG. 2 is a configuration diagram of a bump position measuring optical system according to the embodiment.
FIG. 3 is a configuration diagram of a bump height measuring optical system according to the embodiment.
FIG. 4 is a configuration diagram of a mask according to the embodiment.
FIG. 5 is a diagram showing a principle of measuring a bump position according to the embodiment.
FIG. 6 is a diagram illustrating an operation when a wide slit light is applied.
FIG. 7 is a diagram for explaining how shadows of bumps appear when a wide slit light is applied.
FIG. 8 is a diagram showing an operation when a narrow slit light is applied.
FIG. 9 is a diagram for explaining an optical image when narrow slit light is applied.
FIG. 10 is a configuration diagram of a bump inspection system.
100 DMD
200 Optical system for DMD illumination 300 Optical system for bump position measurement 400 Optical system for bump height measurement 500 Test surface 600 Ball bump 700 Straight bump

Claims (6)

In inspecting the bumps formed on the surface of the work, light is irradiated from the normal direction of the surface of the work to the designed bump position on the surface of the work, and the specular reflection component or the irregular reflection of the reflected light. The actual bump position is detected from the optical information obtained through the mask of the component, the actual bump position on the surface of the work is irradiated with slit light from an oblique direction, and the bump height or shape is obtained from the optical information obtained from the reflected light. A bump inspection method characterized by detecting the following. When the bump is a spherical bump at the top, the beam size of the light irradiated from the normal direction is made smaller than the size of the bump, and the actual bump position is detected from optical information that is a regular reflection component. The method for inspecting a bump according to claim 1, wherein: When the bump is a straight bump, the beam size of light irradiated from the normal direction is made larger than the size of the straight bump, and an actual bump position is detected from optical information that is a diffuse reflection component. Item 2. The bump inspection method according to Item 1. In a bump inspection apparatus for inspecting a bump formed on a surface of a work, light is irradiated from a normal direction of the surface of the work to a bump position in design on the surface of the work, and specular reflection of the reflected light is performed. The actual bump position is detected from the optical information obtained through the mask of the component or the irregular reflection component, the actual bump position on the surface of the work is irradiated with slit light from an oblique direction, and the bump height is obtained from the optical information obtained from the reflected light. A bump inspection apparatus for detecting a height or a shape. 5. The bump inspection apparatus according to claim 4, wherein the irradiation pattern is formed by a spatial light modulator. 6. The bump inspection apparatus according to claim 5, wherein the optical system that irradiates the slit light constitutes a Scheimpflug optical system.

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