JP2971658B2 - Method and apparatus for inspecting bonding state of bump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for inspecting the bonding state of bumps, and more particularly to a method for inspecting the bonding state of bumps in a silicon semiconductor chip mounted on a substrate by bonding bumps. And an apparatus.

In recent years, with the rapid development of semiconductor technology, technology for mounting a semiconductor chip on a printed circuit board has been actively developed. The performance required for mounting technology is that the electrical path is short, that many terminals can be connected,
And high reliability. Techniques that satisfy these requirements include techniques such as bump bonding and TAB, and the bump bonding technique has received particular attention in terms of high-speed signal transmission and multi-pin coupling.

In this bump bonding technique, small metal protrusions are formed on the surface of a semiconductor chip, and these are bonded to terminals on a substrate to perform electrical conduction and mechanical fixation of the semiconductor chip. According to this method, it is possible to reduce the length of the electrical connection portion and to form as many as 1000 junctions in one semiconductor chip, as compared with a method in which leads are drawn out of the semiconductor chip.

[0004] However, the joint is located between the semiconductor chip and the substrate, and the joint cannot be visually observed, and it is difficult to inspect for defects.

[0005] Therefore, there is a demand for the development of a method that can easily inspect the state of the bump and the joint thereof while the bump is joined.

[0006]

2. Description of the Related Art FIG. 7 shows an enlarged view of a bump joint. Metal bumps 2 are formed on the surface of a semiconductor chip 1 made of silicon, and are joined to terminals 4 formed on a substrate 3.

FIG. 8 shows a defect of the bump. In the left side of the figure, the terminal 4 on the substrate 1 and the bump 2 are not completely welded, and the right side bump 2 is cracked. I have.

[0008] Such a defect of the bump 2 is difficult to find by an appearance inspection, and a large defect can be found by an electrical continuity test, but a small defect cannot be found.

Therefore, as a conventional method of inspecting a bump, there is a method of irradiating an X-ray to a bump portion, obtaining an image of the bump by the transmitted light, and observing the image.

[0010]

However, the above-mentioned method using X-rays requires a large-sized X-ray generator,
There was a problem that a large shielding device was required due to the problem of exposure.

The present invention has been made in view of the above problems, and has as its object to provide a bump bonding state inspection method and apparatus which can inspect a bump bonding state without requiring a large-scale apparatus.

[0012]

According to a first aspect of the present invention, an infrared laser beam is applied to a semiconductor chip made of silicon in a state where the semiconductor chip is joined by bumps. After obtaining image information of the first speckle pattern formed by the reflected light from the bonding surface between the surface of the semiconductor chip and the bump, the bump is selectively heated, and the infrared laser light is again irradiated to irradiate the surface of the semiconductor chip. And after obtaining the image information of the second speckle pattern formed by the reflected light from the bonded surface of the heated bump, the image information of the first speckle pattern and the second speckle pattern is digitized The difference is calculated, and the difference is compared with a predetermined threshold value to determine whether the bonding state of the bump is good or bad.

According to a second aspect of the present invention, there is provided an inspection apparatus for inspecting a state in which a semiconductor chip made of silicon is joined by a bump, wherein low-power infrared laser light is emitted from a side opposite to a joining surface side of the semiconductor chip. A laser irradiating means for irradiating, a means for receiving infrared laser light irradiated from the laser irradiating means and reflected by the semiconductor chip to obtain image information, and selectively selecting only bumps irradiated with the infrared laser light And heating means for heating, and comparing the image information before and after the heating to determine the quality of the bonding state of the bumps.

[0014]

According to the first aspect of the present invention, after obtaining the image information of the speckle pattern by the bonding surface of the bump, the bump is heated and expanded to deform the bonding surface between the bump and silicon, and then the bonding of the bump is performed again. In the method of obtaining the image information of the speckle pattern by the surface, the image information of the speckle pattern before and after heating can be compared, whereby the degree of deformation of the bonding surface between the semiconductor chip and the bump can be expressed by a numerical value.

According to the second aspect of the present invention, the infrared laser beam is irradiated and the reflected light is received to obtain image information. The infrared laser beam is transmitted through the silicon layer of the semiconductor chip. Reflected light is obtained from both surfaces of the surface and the bonding surface of the bump. Then, the reflected lights from both surfaces interfere with each other to form a speckle pattern, and this image information can be obtained. Further, the configuration having the heating means for selectively heating the bumps causes only specific bumps to thermally expand and deform the bonding surface between the silicon and the bumps.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For convenience of explanation, the principle of obtaining image information of a speckle pattern by a bonding surface between a semiconductor chip and a bump will be described first.

FIG. 2 is a graph showing the relationship between the change in light wavelength and the transmittance of polycrystalline n-type or p-type 2 mm thick silicon. The horizontal axis indicates the wavelength of light to be transmitted, and the vertical axis indicates the transmittance.

As can be seen from the line I in FIG.
From around m, the transmittance sharply increases, and the wavelength becomes approximately 1.4μ.
In the infrared region around m, the transmittance exceeds 0.5.
Therefore, it can be seen that silicon transmits infrared laser light having a wavelength of around 1.5 μm.

Here, a case will be described where the silicon semiconductor chip 1 to which the bumps 2 are bonded is irradiated with infrared laser light inclined with respect to the silicon surface. FIG. 3 shows the state at this time. For convenience, the bump 2 is shown enlarged on the semiconductor chip 1.

The infrared laser light 5 irradiated with the optical axis inclined to the surface 1a of the semiconductor chip 1 is partially reflected by the surface 1a, but partially incident into the semiconductor chip 1. Reaches the bonding surface 1b between the semiconductor chip 1 and the metal bump 2 formed on the opposite side. The infrared laser beam 5 that has reached the bonding surface 1b is reflected by the bonding surface 1b, passes through the inside of the semiconductor chip 1 again, and is emitted from the surface 1a to the outside.

The surface 1a of the semiconductor chip 1 has a certain surface roughness as compared with the wavelength of the infrared laser light 5, and the infrared laser light 5 reflected by the surface 1a of the semiconductor chip 1 has a phase Misalignment occurs. In a portion where the infrared laser light 5 reflected on the surface 1a of the semiconductor chip 1 and the infrared laser light 5 reflected on the bonding surface 1b overlap, the two infrared laser lights 5 interfere with each other, A so-called speckle pattern is formed. The image of the speckle pattern appears as the intensity of infrared laser light, and can be extracted as electrical image information by an image sensor or the like.

The above is the principle of obtaining the image information of the speckle pattern of the bump joint.

Next, an embodiment of the present invention will be described.

FIG. 1 shows the configuration of an embodiment of the present invention. The substrate 3 on which the semiconductor chip 1 to be inspected is mounted by bump bonding is mounted on the upper surface 11 a of the XY table 11. Above the XY table 11, a low-output infrared laser oscillator 12 (for example, a helium-neon laser) having a wavelength of 1.5 μm, a reflecting mirror 13 for changing the angle of the emitted laser light, and a collector An optical lens 14 is provided. The laser light emitted from the infrared laser oscillator 12 is reflected by the semiconductor chip 1, and an imaging lens 15 is disposed in a direction in which the laser light travels. A camera 16 is arranged.

The infrared camera 16 is connected to a frame memory 20, and the frame memory 20 is further connected to a high-speed computer 21.
It is connected to the. The high-speed computer 21 is connected to the controller 22 and controls operations for storing and processing image information from the infrared camera 16. The controller 22 is further connected with a pass / fail judgment display device 23 and a driver 26 for driving the moving motors 24 and 25 of the XY table 11.

The XY table 11 is located at a position where the infrared laser light emitted from the infrared laser oscillator 12 is irradiated.
A condensing lens 17 is located vertically above the upper surface 11a of the device, and a reflecting mirror 18 is located further above. Also YAG
(Yttrium Aluminum Garnet) Laser 1
Reference numeral 9 is provided at a position where the emitted laser light enters the condenser lens 17 by the reflecting mirror 18. Therefore, YA
The laser light emitted from the G laser 19 irradiates the position where the infrared laser light from the infrared laser oscillator 12 is reflected from above vertically.

Here, the laser beam from the YAG laser 19 is for selectively heating only one bump to be inspected, and this operation will be described below with reference to FIG.

When the laser beam 27 from the YAG laser 19 is irradiated from above the bump 2 vertically, the laser beam 27 passes through the silicon layer of the semiconductor chip 1 and is absorbed by the bump 2. The YAG laser is a laser having a relatively large power, and the metal bump 2 is heated and expands (shown by a bump on the right side in FIG. 4). However, since the bumps other than the heated bump remain as they are, the distance between the semiconductor chip 1 and the substrate 3 does not change, so that the heated and expanded bump 2 presses the bonding surface 1b with the semiconductor chip 1 and the bonding surface 1b Transforms. For example, when a bump having a thickness of 100 μm is heated at 10 ° C., the amount of expansion and deformation in the thickness direction becomes 0.03 μm.

On the other hand, as shown by the bump 2 on the left side of FIG. 4, in the bump 2 having a defect such as a crack or insufficient adhesion of the joint surface, the expansion force causes a crack or a gap between the crack and the joint surface. It will be absorbed. Therefore, the amount of deformation of the bonding surface 1b between the semiconductor chip 1 and the bump 2 is smaller than that of the normal bump 2.

When the above-mentioned heated bump 2 is irradiated with an infrared laser beam as shown in FIG. 5 and a speckle pattern is formed by the joint surface 1b, the speckle pattern differs from the speckle pattern before being heated. I have. This is because the bonding surface 1b between the semiconductor chip 1 and the bump 2 is deformed, and the phase of the infrared laser light 5 reflected on this surface is shifted. However, in the case of the bump 2 having a defect, the deformation of the bonding surface 1b is small, and the change of the speckle pattern is also small.

In this embodiment, the presence or absence of a bump defect is inspected by paying attention to the change in the speckle pattern. Therefore, according to the inspection apparatus according to the present embodiment, it is possible to determine the quality of the bonding state of the bumps without using an X-ray inspection apparatus requiring a large-scale apparatus, and the inspector is exposed to the X-ray. Danger can be avoided.

Next, a method of judging the quality of a bump based on image information of a speckle pattern before and after heating will be described.

In the image information of the speckle pattern obtained by the infrared camera 16 and stored in the frame memory 20, the image intensity distribution before heating is defined as f ₁ (x _n, y _n ), and the image intensity distribution after heating is calculated. distribution _{f 2 (x n, y n} ) as,

[0034]

(Equation 1)

When the image is taken over the entire screen, the output F = 0 when the light and dark intensity distributions of the two speckle pattern images match. Then, as the difference between the light and dark intensity distributions of the two images increases, the value of the output F also increases.

Therefore, a predetermined threshold value is provided for the value of F,
If the value of F is smaller than the predetermined threshold, it is determined that there is no change in the image, and it is determined that there is some defect in the bump. If the value of F is equal to or larger than the predetermined threshold, it is regarded as normal. In other words, if the image before and after heating shows a certain degree of change, it means that the bonding surface between the bump and the semiconductor chip is deformed, and the bump is considered to be bonded in a normal state. is there.

Since the calculation of the equation (1) is performed by dividing the image into a very large number of very small parts, the amount of calculation is enormous. However, it is necessary to use a high-speed computer such as a device for calculating a correlation function. Can be processed quickly.

Next, a method for inspecting the bonding state of bumps using the present embodiment will be described.

FIG. 6 is a flowchart showing the procedure of the inspection. First, the substrate 3 to be inspected is placed on the upper surface 11a of the XY table 11 with the semiconductor chip 1 facing upward. Then, the XY table 11 is moved, and the bump 2 to be inspected is moved to a range irradiated with the infrared laser light 5 (step S1).

Next, the infrared laser light 5 is emitted from the infrared laser oscillator 12 to irradiate the bump 2 and the first speckle pattern by the reflected light is detected by the infrared camera 16 and converted into image information. (Step S2). Then, the image information obtained in step 2 is stored in the frame memory 20 (step S3).

Next, the laser beam 27 from the YAG laser 19 is
And irradiates the bump 2 to selectively heat the bump 2 (step S4).

Then, the heated bump is again irradiated with the infrared laser beam 5, and the second speckle pattern by the reflected light is detected by the infrared camera 16 and converted into image information (step S5).

The image information of step S2 and the image information of step S5 thus obtained are sent to the high-speed computer 21 and the difference between them is calculated (step S6). Then, the difference is compared with a predetermined threshold (step S7). If the difference is smaller than the threshold, it is determined as a defect, and if the difference is greater than or equal to the threshold, it is displayed as normal on the pass / fail determination display device 23 (step S8).

Thus, the inspection of one bump 2 is completed.

Then, returning to step S1, step S1
To step S8 are repeated, and the next bump 2 is sequentially inspected.

As described above, according to the inspection method using this embodiment, it is possible to determine the quality of the bonding state of the bumps without the need for operation of a complicated apparatus such as an X-ray inspection apparatus. Further, a high-speed computer can be used to process the image information by converting it into a numerical value, and the quality can be determined quickly.

[0047]

As described above, according to the first aspect of the present invention,
By digitizing the speckle pattern by the bonding surface of the bump before and after heating and comparing the difference with a threshold value, the quality of the bonding state of the bump can be quickly known, and the inspection can be speeded up.

According to the second aspect of the present invention, it is possible to obtain an apparatus for inspecting the bonding state of bumps by using an infrared laser beam. The inspection apparatus can be reduced in size and simplified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing transmittance of silicon with respect to the wavelength of light.

FIG. 3 is a diagram illustrating a speckle pattern by infrared laser light.

FIG. 4 is a diagram illustrating heating of a bump by a YAG laser.

FIG. 5 is a diagram illustrating a speckle pattern by a heated bump.

FIG. 6 is a flowchart showing an inspection procedure of the embodiment of FIG.

FIG. 7 is a diagram illustrating a bump.

FIG. 8 is a diagram illustrating a defect of a bump.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor chip 1a Surface 1b Joining surface 2 Bump 3 Substrate 4 Terminal 5 Infrared laser beam 11 XY table 12 Infrared laser oscillator 13,18 Reflector 14,17 Condenser lens 15 Imaging lens 16 Infrared camera 19 YAG laser 20 Frame Memory 21 High-speed computer 22 Controller 23 Pass / fail judgment display device 24, 25 Motor 26 Driver 27 Laser beam

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoji Nishiyama 1015 Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-4-370945 (JP, A) JP-A-63-148650 (JP, a) JP Akira 60-59743 (JP, a) JP Akira 64-10636 (JP, a) JP flat 2-174261 (JP, a) (58 ) investigated the field (Int.Cl. ⁶ H01L 21/66 H01L 21/60 321

Claims (2)

(57) [Claims] An infrared laser beam is irradiated to a semiconductor chip (1) in a state where the semiconductor chip (1) made of silicon is bonded by a bump (2), and the surface (1a) of the semiconductor chip (1) is The bonding surface (1) of the bump (2)
The image information of the first speckle pattern formed by the reflected light from b) is obtained, the bumps (2) are selectively heated, and the bumps (2) are again irradiated with the infrared laser light to thereby obtain the surface (1) of the semiconductor chip.
a) and image information of a second speckle pattern formed by reflected light from the bonding surface (1b) of the bump (2) heated, and the first speckle pattern and the second spec A method for inspecting the bonding state of the bumps (2), wherein the difference is calculated by numerically converting the image information of the pattern, and the difference is compared with a predetermined threshold value to determine whether the bonding state of the bump (2) is good. 2. An inspection apparatus for inspecting a state in which a semiconductor chip (1) made of silicon is joined by a bump (2), wherein a low-output infrared laser beam is applied to a side opposite to a joining surface side of the semiconductor chip. Irradiating means for irradiating from outside (12,13,14)
Irradiating from the laser irradiating means (12, 13, 14),
Means (15, 16) for receiving the infrared laser light reflected by the semiconductor chip (1) to obtain image information; and selectively heating only the bumps (2) irradiated with the infrared laser light. Heating means (17, 18, 19) for comparing the image information before and after heating to determine whether the bonding state of the bump (2) is good or not. Bonding condition inspection device.