JP3140591B2 - Bump appearance inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

In recent years, with the demand for miniaturization of electronic devices and the like, the integration and density of semiconductor devices have been advanced, and the number of leads has been increasing. 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 for forming thousands of bumps on the entire surface of a semiconductor chip by a flip chip (FC) method is known. ing.

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

[0004]

2. Description of the Related Art FIG. 5 is a view showing an example of a conventional semiconductor chip on which area bumps are formed. Reference numeral 1 denotes an LSI chip, and reference numeral 2 denotes a plurality of bumps formed on the entire surface of the LSI chip 1. The length of one side of the LSI chip 1 is 10 mm or more.
Pb is applied to the aluminum electrode on SI chip 1 by FC method.
A bump 2 made of -Sn or the like is formed, for example, in a dome shape via a metal thin film such as chrome.

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

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

In order to securely bond all of the area bumps to the aluminum electrodes on the substrate 3, the dimensions and shapes of the bumps 2 need to be formed as uniformly as possible, and their heights must be particularly uniform.

FIG. 7 is a view showing a typical example of a bump failure of a conventional semiconductor chip having an area bump formed thereon.
In FIG. 3A, the bump 2a is abnormally large and the bump 2b
Are abnormally small. FIG. 2B shows an example in which the adjacent bumps are connected to each other (electrically short-circuited) to generate a bridge 2c in a wet-back step in forming the bumps. In the case of these defective shapes, the heights of the bumps are not uniform, which causes defective bonding.

Therefore, it has been conventionally performed to inspect the dimensions and shapes of the bumps by using an inspection apparatus as described below, and to remove defective products to prevent defective bonding with the substrate.

FIGS. 8 and 9 show an example of a conventional bump appearance inspection apparatus. FIG. 8 shows a scanning mechanism section and FIG. 9 shows a circuit section.

In FIG. 8, a laser beam L output at a constant energy from a semiconductor laser 14 is a collimator lens 1.
The light is converted into parallel light via the light source 5 and enters the side surface of the polygon mirror 16 having an octagonal prism shape. The polygon mirror 16 is provided with a reflection mirror on each side thereof, and is driven to rotate at high speed in a counterclockwise direction in the figure. Therefore, the reflected light from the polygon mirror 16 is turned into 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, an LSI chip 1 mounted on a uniaxial stage 22 is disposed below the figure, and the scanning light S ₂ from the optical path changing mirror 19 scans the LSI chip 1. ing. The uniaxial stage 22 is Y
And the LSI chip 1 is scanned in both X and Y directions.

Then, the scanning light S ₃ reflected by the LSI chip 1 is applied to a PSD (Pod) disposed at a predetermined imaging position.
The light is radiated onto a sition sensitive detector 21 via an 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 according to the incident position of light from the terminals 21a and 21b. If the magnification of the imaging lens 20 is M and the light scanning width is W, The electrode length L is set to L ≧ MW (1).

By performing predetermined processing on the currents Ia and Ib in the circuit section shown in FIG. 9, the dimensions and shape of the surface of the LSI chip 1, that is, the height of the bumps 2 are obtained.

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

The clock generation circuit 24 in FIG.
, A line clock CL synchronized with the scanning cycle is generated, and a 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 calculating circuit 23 is provided with the aforementioned PS
A voltage Va based on currents Ia and Ib from D21 and
After generating Vb, 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 _FourHeight correction
The circuit 25 calculates the height of the bump 2 based on the value of d.
Will be issued.

FIG. 10 illustrates the principle of calculating the bump height. In the figure, the y-axis shows the surface of the LSI chip (1) in the scanning direction of the uniaxial stage 22. The bump 2 is spherical for explanation, a diameter (actual height perpendicular from the chip surface) h, the correction distance is y _0. The one-axis stage 22 moves by one pitch for each main scanning line by the polygon mirror 16 and performs 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 angle of incidence y-axis of the scanning light S ₂ (=
If the reflection angle) is θ, and the coordinate of the virtual incident position on the y-axis is y ₁ , 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) is obtained 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 actual data of the bump 2 stored in the height data memory 26 is stored. the height h and the calculated value of the correction distance y ₀ as compared with the standard value to check whether good or defective.

In the conventional bump appearance inspection apparatus, the bump height is determined as described above, and a good / defective inspection is performed.

[0023]

However, as described above, in the conventional bump appearance inspection apparatus which scans an LSI chip while keeping the energy intensity of the laser beam constant, if the reflectance between the chip surface and the bump is significantly different, There was a problem that 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 bumps are formed at positions substantially corresponding to the time Tb. The vertical axis represents the calculated height h of the bump.

FIG. 3A shows a case where the inspection is performed with the energy intensity of the laser beam L constant so that the reflected light from the chip surface becomes an appropriate size. Is much higher than the reflectivity of the bumps. Therefore, 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 reduced, and due to shot noise and thermal noise in the PSD and the circuit, the S / N ratio decreases at time Tb as shown in FIG. Affected.

On the other hand, FIG. 6B shows a case where the energy intensity of the laser beam L is made higher than that described above so that the reflected light from the bumps becomes an appropriate size, and the inspection is performed at a constant level. The height h is calculated according to the shape of the bump without being affected by the above. However, at times other than Tb, P
The amount of light received by the SD becomes too large and the output currents Ia and Ib
Is saturated, and the calculated value h is distorted as shown in the figure.

The present invention provides a bump appearance inspection apparatus capable of calculating the height of a scanning surface in accordance with the shapes of both a chip surface and a bump having different reflectivities and accurately inspecting the quality of bumps. The purpose is to do.

[0028]

According to the present invention, in order to solve the above-mentioned problem, the following constitution is provided.

That is, a semiconductor laser, an exciting means for receiving a drive signal and exciting a laser beam having an energy intensity corresponding to the level of the drive signal to the semiconductor laser, and a second reflection means for applying a second reflection to a chip surface having a first reflectance. Scanning means for scanning a semiconductor chip on which a bump having a ratio is formed with laser light from a semiconductor laser, light detection means for generating a light detection signal corresponding to the incident position of incident light, and light reflected from the semiconductor chip. An image forming means for forming an image on the light detecting means as the incident light, wherein the semiconductor laser is provided with a first reflectance based on a light detection signal from the light detecting means. The level of the drive signal to the exciting means is changed so as to alternately emit laser light of the first energy intensity corresponding to the second energy intensity and laser light of the second energy intensity according to the second reflectance. Modulation means for modulating the light, first sampling means for sampling a light detection signal from the light detection means based on the drive signal at a timing at which a laser beam having a first energy intensity is emitted, and light detection based on the drive signal. A second sampling means for sampling a light detection signal from the means at a timing at which a laser beam of a second energy intensity is emitted; and a method for detecting a bump from a chip surface based on a sampling result of the first and second sampling means. And a bump height calculating means for calculating the height.

[0030]

According to the above arrangement, the modulating means causes the semiconductor laser to emit a laser beam having a first energy intensity according to the first reflectance and a laser beam having a second energy intensity according to the second reflectance. The timing of modulating the level of the drive signal to the excitation means so as to emit the light alternately, and the first sampling means changing the light detection signal from the light detection means based on the drive signal when the laser light of the first energy intensity is emitted Sampled at the second
Sampling means samples the light detection signal from the light detection means based on the drive signal at the timing when the laser light of the second energy intensity is emitted, and the bump height calculation means performs the sampling of the first and second sampling means. It works to calculate the height of the bump from the chip surface based on the sampling result.

[0031]

1 is an overall block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing a scanning mechanism section of an embodiment of the present invention together with a control processing circuit. The same components are denoted by the same reference numerals, and description thereof will be omitted.

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

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

In FIG. 1, the transport unit 41 is a semiconductor chip.
1 is mounted and controlled by the control processing circuit 52.
As shown, bumps are actually formed in the wafer state.
Transported before being diced into semiconductor chip 1
I do. That is, as shown in FIG.
The wafer 40 accommodated in the carrier 39 (not shown) ₁
Is transferred onto the pre-alignment stage 38 by the
When the realignment stage 38 rotates, the orientation flat
Matching is performed.

[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 conveyed and stored in another cartridge (not shown).

Returning to FIG. 1, the laser modulation circuit 46 controls the line clock C from the clock generation circuit 24.
The drive signal LD is generated on the basis of the
Is driven by an internal drive circuit (excitation means) so as to vary the energy intensity of the output at a timing according to the drive signal LD.

FIG. 3 is a diagram showing signal waveforms of main parts in FIG. 1, and FIG. 3A shows a drive signal LD. The drive signal LD is a rectangular wave having a predetermined period t that is sufficiently short with respect to the bump size. As described above, since the reflectivity of the solder bump is significantly lower than that of the chip surface, each level Lmax, Lmin of the drive signal LD depends on the output current Ia,
Ib is set to be an appropriate value for both the solder bump and the chip surface.

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

Note that the sampling pulses SP ₁ and SP
Reference numeral ₂ denotes a pulse generated in the laser modulation circuit 46 together with the drive signal LD. For example, a pulse which is at a high level for a predetermined period (however, shorter than the period of Lmax and Lmin) after a predetermined time after detecting each edge of the drive signal LD Is obtained.

As a result of performing the above-mentioned sampling processing, 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 is output to the bump height calculating circuit 49. the arithmetic circuit 50, only the output current from PSD21 by scanning light S ₃ of the energy intensity corresponding to the reflectivity of the chip surface is respectively transmitted. Each of the arithmetic circuits 49 and 50 calculates a value db or dc corresponding to the bump height or the chip surface height in the same manner as described above, and sends the calculated value 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 FIG. 4, the horizontal axis represents the scanning time, that is, the scanning position on the chip, and the position substantially corresponding to the time Tb. Are formed with solder bumps. The vertical axis is each arithmetic circuit 4
9 and 50, a value db corresponding to the bump height during the period Tb, and a value dc corresponding to the chip surface height during periods other than Tb.

Each of the calculated values is a value corresponding to each shape as described above, and is not affected by noise and does not become round due to saturation of the output current.

On the other hand, the line clock CL and the dot clock CD from the clock generation circuit 24 are supplied to the height detection and correction circuit 51, and the height detection and correction circuit 51 calculates the calculated value db based on the timing of each clock. , Dc, 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 them is obtained to detect the bump height hb from the chip surface.

Further, a correction distance y ₀ for address correction.
Is 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 the size, shape, and position of the solder bump 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 a standard value to check whether it is a non-defective product or a defective product, and sends the inspection result to the control processing circuit 52.

The control processing circuit 52 controls the L
From the heights of all (thousands) solder bumps on the SI chip 1, an average value, a standard deviation and the like are calculated, and, for example, a process capability index and a pass / fail of the LSI chip 1 are inspected.

As described above, according to the present embodiment, even if the reflectivity of the bump formed on the semiconductor chip and that of the chip surface are significantly different, the output energy intensity of the semiconductor laser can be varied according to each reflectivity. Thus, the height of the scanning surface can be accurately calculated, so that it is possible to provide a bump appearance inspection apparatus capable of precisely inspecting the quality of a bump.

[0048]

As described above, according to the present invention, a laser beam having a first energy intensity according to a first reflectance and a laser beam having a second energy intensity according to a second reflectance are provided from a semiconductor laser. Are emitted alternately based on the drive signal to scan the semiconductor chip, and the light detection signal from the light detection means
And sampling is performed by the second sampling means at a timing at which the laser light having the first energy intensity is emitted and at a timing at which the laser light having the second energy intensity is emitted, and the bump height calculating means is provided based on the sampling result. Since the height of the bump from the chip surface is calculated,
Even if the reflectivity distribution of the semiconductor chip is not uniform and shows the first reflectivity and the second reflectivity, the height of the scanning surface can be calculated accurately, and the quality of bumps can be accurately determined. There is a feature that can be inspected.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating 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 illustrating the operation of one embodiment of the present invention.

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

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

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

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

FIG. 9 is a diagram illustrating an example of a conventional bump appearance inspection apparatus (circuit section).

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2 Bump 13 Scanning optical system 14 Semiconductor laser 20 Imaging lens 21 PSD (Position Sensitive Detecter) 41 Carrier 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 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-64-21581 (JP, A) JP-A-58- 171611 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01N 21/84-21/958 H01L 21/64-21/66

Claims (1)

(57) [Claims] An excitation means for receiving a semiconductor laser (14) and a drive signal (LD) and exciting the semiconductor laser (14) with laser light having an energy intensity according to the level of the drive signal (LD); 46) scanning the semiconductor chip (1) in which the bump (2) having the second reflectivity is formed on the chip surface having the first reflectivity by laser light from the semiconductor laser (14). Means (13, 41); light detection means (21) for generating light detection signals (Ia, Ib) corresponding 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 the appearance of the bump (2) is determined based on a light detection signal (Ia, Ib) from the light detecting means (21). In the bump appearance inspection device to be inspected, the semiconductor laser (14) is in front. The pumping means (46) sends the laser light of the first energy intensity corresponding to the first reflectance and the laser light of the second energy intensity corresponding to the second reflectance alternately to the excitation means (46). A modulating means (46) for modulating the level of the driving signal (LD); and the light detecting means (2) based on the driving signal (LD).
A first sampling means (47) for sampling the light detection signals (Ia, Ib) from 1) at a timing when the laser light of the first energy intensity is emitted; and The light detecting means (2
A 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 ( A bump height calculating means (4) for calculating the height of the bump (2) from the chip surface based on the sampling results of (47, 48).
9. An appearance inspection apparatus for bumps, comprising: 9, 50, 51).