JP4382315B2 - Wafer bump appearance inspection method and wafer bump appearance inspection apparatus - Google Patents

Description

[0001]
The present invention relates to a method and an apparatus for inspecting the appearance of bumps on the surface of a semiconductor wafer, and in particular, the appearance inspection of wafer bumps suitable for inspecting the appearance of bumps on the surface of a wafer having warpage or thickness change. The present invention relates to a method and a wafer bump appearance inspection apparatus.
[0002]
[Prior art]
A large number of bumps are formed on the surface of the IC chip formed on the semiconductor wafer in order to connect wiring such as an IC package. The wafer bump inspection apparatus is an apparatus for inspecting whether or not the appearance of such a bump is defective. The wafer bump inspection device has a projection optical system and a detection optical system, and irradiates the inspection wafer such as a light beam from the projection optical system to the inspection wafer, and the intensity of the reflected light reflected from the surface of the inspection wafer. Is detected by the detection optical system, and the shape of the bump on the surface of the wafer to be inspected is measured. Then, by comparing the shape of the measured bump for each chip, it is inspected whether the appearance of the bump is free of defects.
[0003]
[Problems to be solved by the invention]
Usually, a plurality of IC chips are formed on a wafer to be inspected, and a large number of bumps are formed on each IC chip. If there is a warp or thickness change on the wafer to be inspected, the distance from the projection optical system to the surface of the wafer to be inspected and the surface of the wafer to be inspected to the detection optical system will not be constant. It cannot be measured with high accuracy.
[0004]
An object of the present invention is to accurately measure the shape of a bump even if the wafer to be inspected is warped or has a change in thickness.
[0005]
[Means for Solving the Problems]
In the wafer bump inspection method according to the present invention, a wafer to be inspected on which a plurality of chips having bumps are formed is mounted on a wafer mounting table, and inspection light is transmitted from the projection optical system to the wafer to be inspected mounted on the wafer mounting table. The detection optical system detects the intensity of the reflected inspection light reflected from the surface of the wafer to be inspected, detects the displacement of the height of the upper surface of the bump from the intensity of the reflected light of the inspection light, and A difference in height displacement for each chip is detected, and the height of the wafer mounting table is adjusted based on the difference in height displacement for each chip on the upper surface of the bump.
[0006]
A wafer bump inspection apparatus according to the present invention includes a wafer mounting table on which a wafer to be inspected on which a plurality of chips having bumps are formed, and a projection optical for irradiating the inspection wafer mounted on the wafer mounting table with inspection light. System, a detection optical system that detects the intensity of the reflected light of the inspection light reflected on the surface of the wafer to be inspected, and a displacement of the height of the upper surface of the bump from the intensity of the reflected light of the inspection light detected by the detection optical system A displacement detecting means for detecting, a difference detecting means for detecting a difference in height of the upper surface of the bump detected by the displacement detecting means for each chip, and a displacement of the height of the upper surface of the bump detected by the difference detecting means for each chip. And an adjusting means for adjusting the height of the wafer mounting table based on the difference.
[0007]
In the wafer bump inspection method and the wafer bump inspection apparatus according to the present invention, the difference in height of the upper surface of the bump is detected for each chip, and the height of the wafer mounting base is adjusted based on this difference. The distance from the light projecting optical system to the surface of the wafer to be inspected and the distance from the surface of the wafer to be inspected to the detection optical system are kept within a certain range. Generally, a circuit pattern and a protective film are formed on the surface of the wafer to be inspected, so it is difficult to accurately measure the height of the surface of the wafer to be inspected, but there is no protective film on the upper surface of the bump. Accurate height adjustment can be performed by using the displacement of the height of the upper surface.
[0008]
In addition, detecting the difference in the top surface height displacement of each bump from the average value of the top surface height of the bumps for each chip improves the detection accuracy and increases the height of the wafer mounting table. Can be adjusted with high accuracy.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a wafer bump inspection apparatus according to an embodiment of the present invention. The wafer bump inspection apparatus according to the present embodiment includes an inspection stage unit, an inspection optical system, and a signal processing unit.
[0010]
The inspection stage unit includes a stage moving mechanism 300, a stage driving circuit 305, and a wafer mounting table 306. As shown in FIG. 2, the stage moving mechanism 300 includes an X stage moving mechanism 301, a Y stage moving mechanism 302, a Z stage moving mechanism 303, and a θ stage moving mechanism 304, and the wafer 100 that is an object to be inspected. Is moved in the XYZ direction and the θ direction. The stage driving circuit 305 is controlled by the image processing / control apparatus 600 and drives and controls the stage moving mechanism 300 so that the beam spot relatively scans the wafer 100 on the wafer mounting table 306 in the X direction and the Y direction. The height of the wafer mounting table 306 in the Z direction is adjusted as will be described later.
[0011]
The inspection optical system basically includes a projection optical system that irradiates the wafer 100 with laser light of inspection light, and a detection optical system that guides the laser light reflected by the wafer 100 to an optical sensor. The projecting optical system includes a semiconductor laser light source 400, an S polarizing plate 401, a collimating lens 402, an acousto-optic deflector (AOD) 404, a deflector driving circuit 405, an fθ lens 406, a lens 408, and a polarizing beam splitter. 410 includes a quarter-wave plate 412 and an objective lens 414.
[0012]
The semiconductor laser light source 400 generates laser light having a predetermined frequency. The S polarizing plate 401 transmits only the S polarization component of the laser light generated from the semiconductor laser light source 400. The collimating lens 402 converts the S-polarized component laser light transmitted through the S-polarizing plate 401 into a parallel light beam. The acousto-optic deflector 404 converts the parallel light flux of the S-polarized component transmitted through the collimator lens 402 into deflected light that reciprocates in the Y direction in the detection region 308 of the wafer 100. The deflector drive circuit 405 is controlled by the image processing / control device 600 and supplies a drive signal having a predetermined frequency (about 4 MHz) to the acousto-optic deflector 404. The fθ lens 406 and the lens 408 operate so as to optimally focus the laser beam at each scanning position of the detection region 308 of the wafer 100. The polarization beam splitter 410 reflects S-polarized component laser light and transmits P-polarized component laser light. Accordingly, the polarization beam splitter 410 reflects the S-polarized component laser light transmitted through the fθ lens 406 and the lens 408 to the wafer 100 side. The laser beam reflected by the polarization beam splitter 410 is converted into a circularly polarized component laser beam by the quarter-wave plate 412 and is condensed on the wafer 100 via the objective lens 414.
[0013]
The detection optical system includes an objective lens 414, a quarter-wave plate 412, a polarizing beam splitter 410, a half mirror 416, and a bump defect detection optical system. The reflected laser beam of the circularly polarized component reflected by the surface of the wafer 100 passes through the objective lens 414 and the quarter wavelength plate 412. At this time, the reflected laser beam of the circularly polarized component is converted into the reflected laser beam of the P-polarized component by being transmitted through the quarter-wave plate 412 and introduced into the polarization beam splitter 410. The polarizing beam splitter 410 transmits the reflected laser light of the P-polarized component from the quarter-wave plate 412 to the subsequent half mirror 416 side, which is reflected laser light from the wafer 100. The half mirror 416 is disposed at an angle of 45 degrees with respect to the optical axis of the P-polarized component reflected laser light from the polarizing beam splitter 410, and about half of the reflected laser light is disposed on the side surface of the optical axis. The reflected light is reflected to the bump defect detection optical system side, and approximately half of the reflected laser light is transmitted to the wafer surface defect detection optical system side (not shown).
[0014]
The bump defect detection optical system includes a half mirror 418, shielding plates 420 and 422, imaging lenses 424 and 426, and two-divided optical sensors 428 and 430. The half mirror 418 is disposed at an angle of 45 degrees with respect to the optical axis of the reflected laser light from the half mirror 416, and approximately half of the reflected laser light is disposed on the side surface of the optical axis. The light is reflected on the 428 side, and approximately half of the reflected laser light from the half mirror 416 is transmitted to the two-split optical sensor 430 side. The shielding plates 420 and 422 are arranged between the half mirror 418 and the two-divided optical sensors 428 and 430, and shield one half area of each of the different cross sections of the reflected laser light reflected by the half mirror 416. In the case of FIG. 1, the shielding plate 422 shields the lower half region of the laser light transmitted through the half mirror 418, that is, the lower half region of the laser light reflected by the half mirror 416. The right half region of the laser beam reflected by the mirror 418, that is, the upper half region of the laser beam reflected by the half mirror 416 is shielded. The shielding plates 420 and 422 may be disposed between the imaging lenses 424 and 426 and the two-split optical sensors 428 and 430.
[0015]
The imaging lenses 424 and 426 form images corresponding to the laser beams not shielded by the shielding plates 420 and 422 on the two-divided optical sensors 428 and 430, respectively. The two-split optical sensors 428 and 430 receive the reflected laser light from the half mirror 416 and output detection signals A to D corresponding thereto. The two-divided optical sensors 428 and 430 are photosensors in which the light receiving area is divided into two along the same Y direction (deflection direction) as the detection area 308 of the wafer 100. Therefore, the two-divided optical sensors 428 and 430 output independent detection signals A to D, respectively.
[0016]
A wafer surface defect detection optical system (not shown) receives reflected laser light transmitted through the half mirror 416, detects a defect on the surface of the wafer 100 based on its intensity, and outputs a defect detection signal.
[0017]
The signal processing unit includes an image processing / control device 600, amplifiers 502A to 502D, and analog-digital (A / D) converters 504 and 505. The amplifiers 502A to 502D amplify the detection signals A to D output from the respective terminals of the two-divided optical sensors 430 and 428, and supply them to the A / D converters 504 and 505. The A / D converters 504 and 505 convert the analog detection signals A to D output from the amplifiers 502 A to 502 D into digital signals and supply them to the image processing / control apparatus 600.
[0018]
FIG. 2 is a block diagram illustrating a schematic configuration of the image processing / control apparatus. The image processing / control apparatus 600 according to the present embodiment includes a displacement detection circuit 601, a comparison circuit 602, an averaging circuit 603, a storage circuit 604, a difference detection circuit 605, and a Z stage control circuit 606. Further, the image processing / control apparatus 600 includes a microcomputer system (not shown) including a microprocessor unit (CPU), a program memory (ROM), a working memory (RAM), a hard disk device (HDD), an external interface, and the like. It is configured to execute various processes. Although not shown, the image processing / control apparatus 600 is connected to a keyboard, a monitor screen, and the like, and a graphical user interface (GUI) is constructed with the operator. The memory (ROM, RAM, HDD) in the image processing / control apparatus 600 stores various programs such as a bump height shape detection program, a wafer scanning program, a defect detection program, and a focusing program.
[0019]
The bump height shape detection program is executed in response to an operation of a predetermined inspection start key on the keyboard. By executing the bump height shape detection program, the image processing / control apparatus 600 executes each program in the order of the focusing program, the wafer scanning program, and the defect detection program.
[0020]
The focusing program adjusts the fθ lens 406, the lens 408, and the objective lens 414 based on the detection signals A to D output from the A / D converters 504 and 505 so that the focus of the laser light is on the surface of the wafer 100. Focus so that it is positioned. The wafer scanning program supplies control signals to the stage driving circuit 305 and the deflector driving circuit 405, repeatedly executes main scanning and sub-scanning, and detects detection signals A to D output from the A / D converters 504 and 505. A defect detection signal output from a wafer surface defect detection optical system (not shown) is temporarily stored in the memory area. The defect detection program detects bump height information based on the detection signals A to D output from the A / D converters 504 and 505, detects bump defects and the like based on the bump height information, and wafer surface defects (not shown) Based on a defect detection signal output from the detection optical system, a defect position such as foreign matter, dirt, scratches, or chips on the wafer 100 is specified on the wafer 100.
[0021]
The displacement detection circuit 601 detects the height displacement of the surface of the wafer 100 based on the detection signals A to D output from the A / D converters 504 and 505. The wafer bump inspection apparatus according to the present embodiment employs a knife edge method as a method for measuring the height displacement based on the reflected light corresponding to the unevenness of the surface of the wafer to be inspected. The knife edge method is conventionally known, and the basic principle thereof is that the reflected light from the wafer 100 is received by the two-divided optical sensors 428 and 430 through the shielding plates 420 and 422 which are knife edges, The height of the unevenness on the surface of the wafer 100 is detected based on the detection signals A to D. The height information ε is calculated by applying the values of the detection signals A to D to the arithmetic expression {(A−B) + (C−D)} / (A + B + C + D).
[0022]
When the wafer 100 has neither convex portions (protrusions) nor concave portions (dents), the values of the detection signals A to D output from the two-split optical sensors 428 and 430 are substantially equal. 0 ". When a convex portion (protrusion) exists on the wafer 100, the convex portion (protrusion) is formed on the upper side (detection signal A side) of the two-split optical sensor 430 and on the left side (detection signal C side) of the two-split optical sensor 428. ) Is irradiated with a beam spot of a semicircular reflection laser beam having a diameter corresponding to the size (height). Accordingly, the height information ε = {(A−B) + (C−D)} / (A + B + C + D) in this case is a positive value (ε> 0). When the wafer 100 has a recess (depression), the recess (depression) is provided on the lower side (detection signal B side) of the two-divided optical sensor 430 and on the right side (detection signal D side) of the two-segment optical sensor 428. The beam spot of the semicircular reflected laser beam having a diameter corresponding to the size (depth) of the laser beam is irradiated. Therefore, the height information ε = {(A−B) + (C−D)} / (A + B + C + D) in this case is a negative value (ε <0).
[0023]
As described above, when the height information ε is obtained based on the detection signals A to D from the two systems of the two-divided optical sensors 428 and 430, the detection accuracy is improved. Furthermore, even if spot scanning deviation occurs due to thermal fluctuations of the optical elements of the projection optical system, the numerator of the arithmetic expression {(AB) + (CD)} / (A + B + C + D) for obtaining the height information ε Since the value {(A−B) + (C−D)} on the side is a substantially constant value without fluctuation, there is an effect that high-precision height measurement can be performed without being influenced by the value. . Note that the spot scanning deviation refers to a case where the laser light is incident on the wafer 100 from the objective lens 414 and is incident on the wafer 100 with a certain angle.
[0024]
The comparison circuit 602 determines whether the displacement of the height of the surface of the wafer 100 detected by the displacement detection circuit 601 is on the upper surface of the bump, and the height of the surface of the wafer 100 detected by the displacement detection circuit 601 is determined. The displacement of the height is compared with a threshold value, and if it is equal to or greater than the threshold value, it is output as a displacement of the height of the upper surface of the bump.
[0025]
The average circuit 603 calculates the average value of the height displacement of the upper surfaces of the plurality of bumps for each chip from the displacement of the height of the upper surface of the bumps output from the comparison circuit 602. The storage circuit 604 stores the average value calculated by the average circuit 603. The difference detection circuit 605 detects a difference between the average value calculated by the average circuit 603 and the average value of the chip measured before stored in the storage circuit 604.
[0026]
The Z stage control circuit 606 controls the stage drive circuit 305 based on the difference between the average values detected by the difference detection circuit 605. The stage drive circuit 305 drives the Z stage moving mechanism 303 under the control of the Z stage control circuit 606 to adjust the height of the wafer mounting table 306 in the Z direction.
[0027]
FIG. 3 is a diagram for explaining the operation of the wafer bump inspection apparatus according to the embodiment of the present invention. FIG. 3A shows an example in which a certain inclination occurs due to warpage or the like on the wafer 100, and the first chip bump 61, the second chip bump 62, and the third chip on the wafer 100. A chip bump 63, a fourth chip bump 64, a fifth chip bump 65, and a sixth chip bump 66 are shown side by side. Although not shown, it is assumed that a plurality of bumps are arranged on each chip on the wafer 100 in the drawing depth direction behind the bumps 61 to 66. The broken line 61H indicates the average value of the height displacement of the upper surfaces of the plurality of bumps for the first chip having the bumps 61.
[0028]
FIG. 3B shows an example in which the present invention is applied, and after adjusting the heights in the Z direction of the bumps 61 and 62 of the first and second chips and the wafer mounting table 306, respectively. The bumps 63 to 66 of the third to sixth chips are shown side by side. The broken line 61H indicates the average value of the height displacement of the upper surfaces of the plurality of bumps for the first chip having the bumps 61. The average value 61H is calculated by the average circuit 603 and stored in the storage circuit 604 after the measurement of the first chip is completed. A broken line 62H indicates the average value of the height displacement of the upper surfaces of the plurality of bumps for the second chip having the bumps 62. The average value 62H is calculated by the average circuit 603 after the measurement of the second chip is completed. Now, assuming that the difference between the average value 61H of the first chip and the average value 62H of the second chip is d, the difference d is detected by the difference detection circuit 605 after the measurement of the second chip is completed. The Z stage control circuit 606 controls the stage drive circuit 305 based on the detected difference d, and adjusts the height of the wafer mounting table 306 in the Z direction. As a result, the bottom surface of the bump 63 of the third chip moves as indicated by a broken line arrow Z2.
[0029]
Next, after the measurement of the third chip, the average value of the third chip is calculated by the average circuit 603, and the difference from the average value 61H of the first chip is detected by the difference detection circuit 605. The Z stage control circuit 606 controls the stage drive circuit 305 based on the detected difference, and adjusts the height of the wafer mounting table 306 in the Z direction. As a result, the bottom surface of the bump 64 of the fourth chip moves as indicated by the dashed arrow Z3. Similarly, the height of the wafer mounting table 306 in the Z direction is adjusted after the measurement of the fourth and fifth chips, respectively, and the bottom surfaces of the bumps 65 and 66 of the fifth and sixth chips are respectively indicated by broken line arrows Z4. , Z5.
[0030]
In this way, the distance from the light projecting optical system to the surface of the wafer to be inspected and the distance from the surface of the wafer to be inspected to the detection optical system when measuring each chip is kept within a certain range. In the example of FIG. 3, since the inclination of the wafer 100 is constant, the movement amounts of the bottom surfaces of the bumps 63 to 66 of the third to sixth chips are the same, but if the inclination of the wafer 100 is not constant, The movement amounts of the bottom surfaces of the bumps 63 to 66 of the third to sixth chips are different.
[0031]
In this embodiment, since the second chip and thereafter, after the measurement of one chip is completed, the height of the wafer mounting table in the Z direction is adjusted before the measurement of the next chip based on the measurement result. The height of the wafer mounting table can be adjusted with high accuracy in accordance with the sled, thickness change, and the like. However, the present invention is not limited to this. For example, the height of the wafer mounting table in the Z direction may be adjusted before starting the measurement of the fourth or fifth chip based on the measurement result of the second chip. .
[0032]
In the present embodiment, the average value of the first chip is used as a reference, and the difference from the average value of the first chip is always detected after the second chip. You may make it detect the difference with the average value of a chip | tip.
[0033]
In the embodiment described above, the semiconductor laser light source is described as an example of the light source, but other light sources such as white light may be used. In the above-described embodiment, the acousto-optic deflector has been described as an example of deflecting the light beam so as to reciprocately scan at a predetermined cycle. However, a polygon mirror, a galvanometer mirror, a digital micromirror device (DMD) Other deflectors such as) may be used. Furthermore, in the embodiment described above, the optical sensor is divided into two as the number of divisions of the optical sensor. However, the number of divisions may be larger than this, or a two-dimensional CCD light receiving element may be used. Good.
[0034]
【The invention's effect】
According to the wafer bump inspection method and the wafer bump inspection apparatus of the present invention, the distance from the light projecting optical system to the surface of the wafer to be inspected and the surface of the wafer to be inspected to the detection optical system is within a certain range when measuring each chip. Can be kept in. Therefore, even if the wafer to be inspected is warped or has a change in thickness, the shape of the bump can be accurately measured. Generally, a circuit pattern and a protective film are formed on the surface of the wafer to be inspected, so it is difficult to accurately measure the height of the surface of the wafer to be inspected, but there is no protective film on the upper surface of the bump. Accurate height adjustment can be performed by using the displacement of the height of the upper surface.
[0035]
Further, according to the wafer bump inspection method and the wafer bump inspection apparatus of the present invention, the difference of the upper surface height displacement of each bump from the average value of the upper surface displacement of the plurality of bumps for each chip is calculated for each chip. Since the detection accuracy can be improved by detection, the height of the wafer mounting table can be adjusted with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a wafer bump inspection apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of an image processing / control apparatus.
FIG. 3 is a diagram for explaining the operation of a wafer bump inspection apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Wafer, 300 ... Stage moving mechanism, 303 ... Z stage moving mechanism, 305 ... Stage drive circuit, 600 ... Image processing / control device, 601 ... Displacement detection circuit, 602 ... Comparison circuit, 603 ... Average circuit, 604 ... Memory Circuit, 605... Difference detection circuit, 605... Z stage control circuit

Claims (4)

In the wafer bump appearance inspection method of irradiating the inspection wafer on which a plurality of chips having bumps are formed with inspection light and inspecting the appearance of the bump for defects from the intensity of the inspection light,
The wafer to be inspected is mounted on a wafer mounting table,
Irradiate inspection light on the wafer mounted on the wafer mounting table from the projection optical system,
The reflected light of the inspection light reflected on the surface of the wafer to be inspected is detected by the detection optical system by dividing into the intensity of the half area of the reflected light and the intensity of the other half area using the knife edge method ,
Detecting the displacement of the height of the upper surface of the bump from the difference in intensity of the reflected light respectively detected by the detection optical system ;
Detect the difference in the height displacement of the upper surface of the bump for each chip,
Based on the difference in the displacement of the height of the upper surface of the bump for each chip , the distance from the projection optical system to the surface of the wafer to be inspected and from the surface of the wafer to be inspected to the detection optical system is kept within a certain range. A method for inspecting the appearance of a wafer bump , wherein the height of the wafer mounting table is adjusted so that it can be bent . 2. The wafer bump appearance inspection according to claim 1, wherein a difference in the height displacement of the upper surface of the bump for each chip is detected from an average value of height displacement of the upper surface of the plurality of bumps for each chip. 3. Method. In the wafer bump appearance inspection device that irradiates the inspection wafer on which a plurality of chips having bumps are formed with inspection light and inspects whether or not there is a defect in the appearance of the bump from the intensity of the inspection light.
A wafer mounting table for mounting the wafer to be inspected ;
A light projecting optical system for irradiating inspection light onto the wafer to be inspected mounted on the wafer mounting table;
A detection optical system including a half mirror for detecting the reflected light of the inspection light reflected on the surface of the wafer to be inspected and dividing it into the intensity of the half area and the intensity of the other half area and a shielding plate which is a knife edge ; ,
A displacement detecting means for detecting a displacement of the height of the upper surface of the bump from a difference in intensity of the reflected light detected by the detection optical system ;
A difference detection means for detecting a difference in the displacement of the height of the upper surface of the bump detected by the displacement detection means for each chip;
Based on the difference of the height displacement of the upper surface of the bump detected by the difference detection unit for each chip , from the projection optical system to the surface of the wafer to be inspected and from the surface of the wafer to be inspected to the detection optical system. An apparatus for inspecting the appearance of wafer bumps , comprising: adjusting means for adjusting the height of the wafer mounting table so that the distance is maintained within a certain range . The difference detecting means includes an averaging means for calculating an average value of the height displacement of the upper surfaces of the plurality of bumps for each chip, a storage means for storing the average value calculated by the averaging means, and the averaging means. 4. The wafer bump appearance inspection apparatus according to claim 3, further comprising means for detecting a difference between the calculated average value of a certain chip and an average value of another chip stored in the storage means. .

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