JPH06201332A - Inspection device for appearance of bump - Google Patents

Abstract

PURPOSE:To accurately inspect whether a bump is good or defective by using a bump appearance inspection device for inspecting the height of the bump by radiating the scanning light from a semiconductor laser to the bump on a semiconductor chip. CONSTITUTION:The level of a driving signal LD is modulated by a laser modulation circuit 46 so that a first laser beam of first energy intensity corresponding to first reflectance, and a second laser beam of second energy intensity corresponding to second reflectance are alternately emitted from a semiconductor laser 14. Output currents Ia, Ib of a PSD(Position Sensitive Detector) 12 are sampled by a sample hold circuit 47 at an emission timing of the laser beam of the first energy intensity based on the driving signal LD, and by a sample hold circuit 48 at an emission timing of the laser beam of the second energy intensity. The height of the bump 1 from the surface of a chip 2 is calculated by a bump height calculation means consisting of each calculation circuit 49, 50 and a height detection/correction circuit 51, based on the sampling results of the sample hold circuits 47, 48.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump visual inspection apparatus, and more particularly to a bump visual inspection apparatus for irradiating a bump on a semiconductor chip with scanning light from a semiconductor laser to inspect the bump height.

In recent years, with the demand for miniaturization of electronic devices and the like, the integration and density of semiconductor devices have increased, and the number of leads has increased. Therefore, a technique for forming a large number of bumps on a semiconductor chip having a limited size has been developed. For example, an area bump is known in which thousands of bumps are formed on the entire surface of the semiconductor chip by a flip chip (FC) method. ing.

Therefore, it is required to precisely inspect the shape and dimensions of the bumps so that these bumps can be bonded to the substrate reliably.

[0004]

2. Description of the Related Art FIG. 5 is a diagram showing an example of a conventional semiconductor chip having area bumps formed therein, wherein 1 is an LSI chip and 2 is a plurality of bumps formed on the entire surface of an LSI chip 1. The LSI chip 1 has a side of 10 mm or more, and L
The aluminum electrode on the SI chip 1 is Pb by FC system.
The bump 2 made of -Sn or the like is formed into a dome shape, for example, through a thin metal film such as chromium.

FIG. 6 is a view showing an example of a conventional semiconductor substrate, showing a plurality of LSI chips 1 formed as shown in FIG. 5 on a substrate 3.

The bumps 2 of the respective LSI chips 1 are aligned with the aluminum electrodes on the substrate 3, and the LSI chips 1 are joined to the substrate 3 by reflow soldering. A method of mounting a plurality of LSI chips 1 on one substrate in this manner is called a multi-chip module (MCM) method, and is widely used in semiconductor devices for high-performance computers.

In order to surely bond all the area bumps to the aluminum electrodes on the substrate 3, it is necessary to form the bumps 2 as uniform as possible in size and shape, and in particular, their heights must be uniform.

FIG. 7 is a diagram showing a typical bump defect example of a conventional semiconductor chip having area bumps formed thereon.
In the same figure (A), the bump 2a is abnormally large and the bump 2b
Is unusually small. Further, FIG. 2B shows an example in which a bridge 2c is generated by connecting (electrically short-circuiting) adjacent bumps in a wet-back process when forming bumps. In the case of these shape defects, the heights of the bumps are not uniform, which causes a bonding failure.

Therefore, it has been conventionally practiced to inspect the dimension and shape of the bumps by an inspection apparatus as described below and remove defective products to prevent defective bonding with the substrate.

8 to 9 are views showing an example of a conventional bump appearance inspection apparatus. FIG. 8 shows a scanning mechanism section thereof, and FIG. 9 shows a circuit section thereof.

In FIG. 8, the laser light L output from the semiconductor laser 14 at a constant energy is a collimator lens 1
The light is collimated through 5 and enters the side surface of the octagonal prism-shaped polygon mirror 16. The polygon mirror 16 is provided with a reflecting mirror on each side surface thereof and is rotationally driven at a high speed in the counterclockwise direction in the drawing. Therefore, the reflected light from the polygon mirror 16 becomes high-frequency scanning light S _{1 in the} X direction and is reflected by the optical path changing mirror 19 via the f · θ lens 18.

On the other hand, the LSI chip 1 is placed on the uniaxial stage 22 in the lower part of the figure, and the scanning light S ₂ from the optical path changing mirror 19 scans the LSI chip 1. ing. In addition, the uniaxial stage 22 is Y
And the LSI chip 1 is scanned in both XY directions.

Then, the scanning light S ₃ reflected by the LSI chip 1 has a PSD (Po
It is irradiated onto the sition sensitive detector 21 via the imaging lens 20. The PSD 21 is scanned in the x direction, and the irradiation position of the scanning light S ₄ is displaced in the direction perpendicular to the x direction according to the shape of the bump 2.

The PSD 21 is a well-known photodetector that outputs currents Ia and Ib corresponding to the incident position of light from the terminals 21a and 21b, and the magnification of the imaging lens 20 is M and the optical scanning width is W. , And the electrode length L is L ≧ M · W (1).

By subjecting the currents Ia and Ib to a predetermined process in the circuit section shown in FIG. 9, the dimension and shape of the surface of the LSI chip 1, that is, the height of the bump 2 is obtained.

In FIG. 8, reference numeral 17 denotes a PIN photodiode, which is arranged at a position where the reflected light from the polygon mirror 16 enters each time the polygon mirror 16 rotates and the laser light L enters the different side surface thereof. Has been done. Therefore, the PIN photodiode 17 detects the scanning cycle of the polygon mirror 16 and outputs the current Ix at the same cycle as the scanning cycle.

The clock generation circuit 24 in FIG.
Based on the above, the line clock CL synchronized with the scanning cycle is generated, and the dot clock CD having a predetermined frequency sufficiently higher than the line clock CL is generated and sent to the height correction circuit 25.

On the other hand, the height calculation circuit 23 has the above-mentioned PS.
Voltage Va based on currents Ia and Ib from D21 and
After Vb is generated, d = (Va-Vb) / (Va + Vb) (2) is calculated and sent to the height correction circuit 25. This value d is P
Scanning light S on SD21 _FourRepresents the irradiation position of and corrects the height
In the circuit 25, the height of the bump 2 is calculated based on the value of d.
Will be issued.

FIG. 10 is a view for explaining the principle of bump height calculation. In the figure, the y-axis indicates the surface of the LSI chip (1) in the scanning direction of the uniaxial stage 22. Further, the bump 2 has a spherical shape for explanation, the diameter (actual height perpendicular to the chip surface) is h, and the correction distance is y ₀ . The uniaxial stage 22 moves one pitch for each main scanning line by the polygon mirror 16 to perform sub scanning.

The distance between the irradiation position on PSD of the scanning light S ₂ is the scanning light S ₃ that is reflected at the apex of the bump 2 (21), and has been irradiated position reflected against the surface of the LSI chip (1) is M・ D, and the incident angle of the scanning light S ₂ with respect to the y-axis (=
Let θ be the reflection angle) and y ₁ be the coordinates of the virtual incident position on the y-axis, the actual height h of the bump 2 and the correction distance y ₀ are h = d · sin θ / sin α (3) y ₀ = D · cos θ / sin α (4) (where α = 180 ° −2θ) in the height correction circuit 25 of FIG. These values are temporarily stored in the height data memory 26.

The bump height inspection circuit 27 has an internal memory in which standard values such as the size, shape, and position of the bump are stored in advance, and the bump height inspection circuit 27 actually stores the bump 2 stored in the height data memory 26. The calculated values of the height h and the correction distance y ₀ are compared with the standard values to inspect whether they are good or defective.

In the conventional bump appearance inspection apparatus, the bump height is obtained as described above, and the inspection for good or defective is performed.

[0023]

However, in the conventional bump appearance inspection apparatus which scans the LSI chip with the energy intensity of the laser light being constant as described above, when the reflectance between the chip surface and the bump is remarkably different from each other. There was a problem that a precise inspection could not be performed.

FIG. 11 is a diagram for explaining the above problem.
In the figure, the horizontal axis represents the scanning time, that is, the scanning position on the chip, and the bumps are formed at the positions corresponding to approximately the time Tb. The vertical axis represents the calculated bump height h.

FIG. 1A shows a case where the energy intensity of the laser beam L is inspected so that the reflected light from the chip surface has an appropriate size, and the inspection is performed. Since the reflectance of is much higher than the reflectance of the bump, even if the value of the denominator (Va + Vb) representing the amount of light received by the PSD in equation (2) is set small,
For times other than Tb, the height h is calculated according to the shape of the chip surface. However, since the amount of light received by the PSD is small, the amount of light reflected from the bumps is small, and due to shot noise and thermal noise in the PSD and the circuit, at time Tb, the S / N ratio decreases and the noise is reduced. I will be affected.

On the other hand, FIG. 3B shows a case where the energy intensity of the laser beam L is intensified more than the above so as to make the reflected light from the bumps have an appropriate size, and the inspection is performed. The height h is calculated according to the shape of the bump without being affected by. However, at times other than Tb, P
The amount of light received at SD becomes too large and the output currents Ia and Ib
Was saturated and the calculated value h was blunted as shown in the figure.

The present invention provides a bump appearance inspection device capable of calculating the height of the scanning surface according to the shapes of both the chip surface and the bumps having different reflectances, and accurately inspecting whether the bumps are good or bad. The purpose is to do.

[0028]

In order to solve the above-mentioned problems, the present invention has the following constitution.

That is, the semiconductor laser, the excitation means for exciting the semiconductor laser with the laser light having the energy intensity corresponding to the level of the drive signal when the drive signal is input, and the second reflection on the chip surface having the first reflectance. Scanning means for scanning a semiconductor chip on which bumps having a certain ratio are formed with laser light from a semiconductor laser, light detection means for generating a light detection signal according to the incident position of incident light, and reflected light from the semiconductor chip In the bump appearance inspection apparatus, which comprises an image forming means for forming an image on the light detecting means as the incident light and inspects the appearance of the bump based on a light detection signal from the light detecting means, the semiconductor laser has a first reflectance. The level of the drive signal to the excitation means so as to alternately emit the laser beam having the first energy intensity corresponding to the above and the laser beam having the second energy intensity corresponding to the second reflectance. Modulation means for adjusting, a first sampling means for sampling a light detection signal from the light detection means on the basis of the drive signal at a timing at which laser light having a first energy intensity is emitted, and a light detection on the basis of the drive signal. Second sampling means for sampling the light detection signal from the means at the timing when the laser light having the second energy intensity is emitted; and the chip surface of the bump based on the sampling results of the first and second sampling means. The bump height calculating means for calculating the height is provided.

[0030]

According to the above-mentioned structure, the semiconductor laser emits the laser beam having the first energy intensity corresponding to the first reflectance and the laser beam having the second energy intensity corresponding to the second reflectance by the modulating means. Timing at which the level of the drive signal to the excitation means is modulated so as to emit alternately, and the first sampling means emits the light detection signal from the light detection means based on the drive signal to the laser light of the first energy intensity. Sampled at the second
Sampling means samples the photodetection signal from the photodetection means on the basis of the drive signal at the timing when the laser light having the second energy intensity is emitted, and the bump height calculation means of the first and second sampling means. It acts to calculate the height of the bump from the chip surface based on the sampling result.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing a scanning mechanism portion of an embodiment of the present invention together with a control processing circuit, both of which are the same as FIG. The same reference numerals are given to the components, and the description thereof will be omitted.

In FIG. 1, the bump height calculation circuit 49, the chip surface height calculation circuit 50, and the height detection / correction circuit 51 constitute bump height calculation means means. The sample and hold circuits 47 and 48 are the first and second sampling means, the imaging lens 20 is the imaging means, and the PSD.
The (Position Sensitive Detector) 21 is a light detecting means, and the laser modulation circuit 46 is an exciting means and a modulating means.

The scanning mechanism section which is the scanning means in FIG. 2 comprises the scanning optical system 13 and the conveying section 41 in FIG. 1, and the scanning optical system 13 has the collimator lens 15 and the polygon as described in FIG. It is composed of a mirror 16, an f · θ lens 18, and an optical path changing mirror 19.

Further, in FIG. 1, the carrying section 41 is a semiconductor chip.
1 is placed and controlled by the control processing circuit 52.
As shown, bumps are actually formed on the wafer.
Transported before being diced into semiconductor chips 1
To do. That is, as shown in FIG.
Wafers 40 stored in a carrier 39 (not shown) ₁
Is conveyed to the pre-alignment stage 38 by
The rotation of the realignment stage 38 causes the orientation flat.
Matching is done.

[0035] When the orientation flat is a predetermined position, the wafer 40 is conveyed onto the uniaxial stage 22 by the carrier 39 _2, after being scanned in the scanning optical system (13) with a predetermined visual inspection is completed, the carrier 39 ₃ It is configured to be transported and stored in another cartridge (not shown).

Returning to FIG. 1, the laser modulation circuit 46 uses the line clock C from the clock generation circuit 24.
The drive signal LD is generated based on L, and the semiconductor laser 14
The internal drive circuit (excitation means) drives the energy intensity of the output of the drive circuit so as to change it at a timing according to the drive signal LD.

Here, FIG. 3 is a diagram showing the signal waveforms of the main parts in FIG. 1, and FIG. 3A shows the drive signal LD. The drive signal LD is a rectangular wave with a predetermined period t that is sufficiently shorter than the bump size. As described above, since the solder bump has a remarkably lower reflectance than the chip surface, the levels Lmax and Lmin of the drive signal LD are determined by the output current Ia,
Ib is set to have an appropriate value for both the solder bump and the chip surface.

Output currents Ia and Ib from the PSD 21 are sent to the sample and hold circuits 47 and 48 of FIG. 1, respectively, and the sample and hold circuits 47 and 48 of FIG.
Sampling pulse SP ₁ or SP shown in (B) and (C)
_The output currents Ia and Ib are sampled and held at a timing corresponding to ₂ .

The sampling pulses SP ₁ and SP
₂ is generated in the laser modulation circuit 46 together with the drive signal LD, and for example, detects each edge of the drive signal LD and generates a high level pulse for a certain period (shorter than Lmax, Lmin) after a predetermined time. Can be obtained at.

As a result of the above sampling process, the bump height calculation circuit 49 receives only the output current from the PSD 21 by the scanning light S ₃ having the energy intensity corresponding to the reflectance of the solder bump, and the chip surface height. Only the output current from the PSD 21 by the scanning light S ₃ having the energy intensity corresponding to the reflectance of the chip surface is sent to the arithmetic circuit 50. Then, in each of the arithmetic circuits 49 and 50, the value db or dc corresponding to the bump height or the chip surface height is calculated, respectively, as described above, and the calculated value is sent to the height detection / correction circuit 51.

FIG. 4 is a diagram for explaining the operation of the embodiment of the present invention shown in FIG. 1, in which the horizontal axis represents the scanning time, that is, the scanning position on the chip, and the position corresponding to approximately time Tb. Solder bumps are formed on. The vertical axis indicates each arithmetic circuit 4
9 and 50, the value db corresponds to the bump height in the period Tb, and the value dc corresponds to the chip surface height in the periods other than Tb.

Each calculated value is set to a value corresponding to each shape in this way, and is not affected by noise or blunted by the saturation of the output current.

On the other hand, the height detection correction circuit 51 is supplied with the line clock CL and the dot clock CD from the clock generation circuit 24, and the height detection correction circuit 51 calculates the value db based on the timing of each clock. , Dc are sampled and the actual height of the bump apex and the actual height of the chip surface are calculated in the same manner as described above, and the difference between these is calculated to detect the bump height hb from the chip surface.

Further, a correction distance y ₀ for address correction
Is also calculated in the same manner as described above, and is temporarily stored in the height data memory 26 together with the bump height hb.

The bump height inspection circuit 27 has an internal memory in which standard values such as dimensions, shapes and positions of solder bumps are stored in advance, and the bump height hb and the bump height hb stored in the height data memory 26 are stored. The calculated value of the correction distance y ₀ is compared with the standard value to inspect whether it is a good product or a defective product, and the inspection result is sent to the control processing circuit 52.

The control processing circuit 52 controls the L in the wafer 40.
From the heights of all (thousands) solder bumps on the SI chip 1, their average value, standard deviation, and the like are calculated, and, for example, the process capability index and the quality / failure of the LSI chip 1 are inspected.

As described above, according to the present embodiment, even if the bumps formed on the semiconductor chip and the chip surface have significantly different reflectances, the output energy intensity of the semiconductor laser can be varied according to the respective reflectances. As a result, the height of the scanning surface can be accurately calculated, so that it is possible to provide a bump appearance inspection device capable of accurately inspecting whether the bump is good or defective.

[0048]

As described above, according to the present invention, a laser beam having a first energy intensity corresponding to a first reflectance and a laser beam having a second energy intensity corresponding to a second reflectance are emitted from a semiconductor laser. Are alternately emitted based on the drive signal to scan the semiconductor chip, and the photodetection signal from the photodetection means is the first
And the second sampling means performs sampling at the timing when the laser light having the first energy intensity is emitted and the timing when the laser light having the second energy intensity is emitted, and the bump height calculating means is based on the sampling result. Since the height of the bump from the chip surface is calculated,
Even if the reflectance distribution of the semiconductor chip is not uniform and shows the first reflectance and the second reflectance, it is possible to accurately calculate the height of the scanning surface and accurately determine whether the bump is good or bad. There is a feature that can be inspected.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a scanning mechanism unit according to an embodiment of the present invention.

FIG. 3 is a diagram showing signal waveforms of main parts in FIG.

FIG. 4 is a diagram for explaining the operation of the embodiment of the present invention.

FIG. 5 is a diagram showing an example of a conventional semiconductor chip.

FIG. 6 is a diagram showing an example of a conventional semiconductor substrate.

FIG. 7 is a diagram showing a typical bump defect example.

FIG. 8 is a diagram showing an example of a conventional bump appearance inspection apparatus (scanning mechanism section).

FIG. 9 is a diagram showing an example of a conventional bump appearance inspection device (circuit portion).

FIG. 10 is a diagram illustrating the principle of bump height calculation.

FIG. 11 is a diagram illustrating a problem of a conventional bump appearance inspection device.

[Explanation of symbols]

 1 Semiconductor Chip 2 Bump 13 Scanning Optical System 14 Semiconductor Laser 20 Imaging Lens 21 PSD (Position Sensitive Detector) 41 Conveying Section 46 Laser Modulation Circuit 47, 48 Sample Hold Circuit 49 Bump Height Calculation Circuit 50 Chip Surface Height Calculation Circuit 51 Height detection correction circuit

Continuation of the front page (72) Inventor Gotoshi Ando 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (1)

[Claims] 1. A semiconductor laser (14), and a pumping means () for inputting a drive signal (LD) and for exciting the semiconductor laser (14) with laser light having an energy intensity corresponding to the level of the drive signal (LD). 46) and scanning for scanning the semiconductor chip (1) having the bumps (2) having the second reflectance formed on the surface of the chip having the first reflectance with the laser light from the semiconductor laser (14). Means (13, 41), light detecting means (21) for generating light detection signals (Ia, Ib) according to the incident position of the incident light, and reflected light from the semiconductor chip (1) as the incident light. An image forming means (20) for forming an image on the light detecting means (21), and based on the light detection signals (Ia, Ib) from the light detecting means (21), the appearance of the bump (2) is determined. In the bump appearance inspection device for inspecting, the semiconductor laser (14) is The excitation means (46) is configured to alternately emit laser light having a first energy intensity corresponding to a first reflectance and laser light having a second energy intensity corresponding to the second reflectance. A modulation means (46) for modulating the level of the drive signal (LD), and the light detection means (2) based on the drive signal (LD).
1) sampling means (47) for sampling the light detection signals (Ia, Ib) from 1) at the timing when the laser light of the first energy intensity is emitted; and based on the drive signal (LD), The light detecting means (2
Second sampling means (48) for sampling the light detection signals (Ia, Ib) from 1) at the timing when the laser light of the second energy intensity is emitted; and the first and second sampling means (48). Bump height calculation means (4) for calculating the height of the bump (2) from the chip surface based on the sampling result of (47, 48).
9, 50, 51), and a bump appearance inspection device.