KR20060133208A - Wafer back grinding apparatus using ultrasonic cleaning - Google Patents

Abstract

A wafer back grinding apparatus using an ultrasonic cleaning method is provided to oscillate a cleaning solution and enhance cleaning efficiency by using an injection nozzle having an ultrasonic cleaner. A front surface of a wafer is loaded and fixed on a chuck table. The chuck table is used to rotate the wafer. A polishing unit is positioned and rotated at an upper side of the chuck table and comes in contact with a rear surface of the wafer. A cleaning solution injection nozzle(35) is used for injecting a cleaning solution(38) onto the rear surface of the wafer. The cleaning solution injection nozzle includes an ultrasonic cleaner(39) for oscillating the cleaning solution by generating ultrasonic waves.

Description

Wafer back grinding apparatus using ultrasonic cleaning

1 is a perspective view schematically showing a part of a wafer backside polishing apparatus according to the prior art.

FIG. 2 is a partially enlarged cross-sectional view of the lower portion of the polishing wheel of the wafer backside polishing apparatus shown in FIG.

3 is a perspective view schematically showing a wafer backside polishing apparatus according to an embodiment of the present invention.

4 is a partially enlarged cross-sectional view of the cleaning liquid jet nozzle of the wafer backside polishing apparatus illustrated in FIG. 3.

<Description of Reference Number Used in Drawing>

10: wafer back polishing apparatus 12: chuck table

13: polishing wheel 14: polishing wheel lower part

14a: abrasive particles 14b: binder

14c: pocket 14d: foreign object

15: cleaning liquid jet nozzle 20: wafer

21: protective tape 30: wafer backside polishing apparatus

31: turntable 32a, 32b, 32c, 32d: chuck table

33a, 33b: polishing wheel 33c: polishing pad

35, 35a, 35b, 35c, 35d: cleaning liquid spray nozzle

36: washing table 38: washing liquid

39: ultrasonic cleaner 39a: oscillator

39b: oscillator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer backside polishing technique, and more particularly, to a wafer backside polishing apparatus using an ultrasonic cleaning method in order to increase cleaning efficiency in a wafer backside polishing process and to prevent wafer damage due to a polishing operation.

Semiconductor wafers, which have completed a series of wafer fabrication processes, are subjected to back grinding before being separated into individual chips. The backside polishing process is a process for making the thickness of the wafer thin by mechanically polishing the backside of the wafer. Wafers generally have a thickness of 730-750 μm for 8 inches and 790-800 μm for 12 inches. Wafer backside polishing processes such wafer thicknesses as thin as 50-450 μm. In this case, the final thickness of the target wafer may vary depending on the type of semiconductor product or the needs of the customer.

Wafer backside grinding processes typically include wafer loading, wafer aligning, rough grinding, fine grinding, polishing, cleaning, wafer unloading, etc. Proceeds in the order of. In this regard, a conventional wafer back polishing apparatus is disclosed, for example, in Korean Patent Publication No. 10-0425471.

The wafer backside polishing process will be briefly described. First, the wafer is introduced into the backside polishing apparatus, and then an alignment step is performed to orient the wafer in order to put the wafer in the correct position. Subsequently, a roughing step is performed using a rough grinding wheel to roughly grind the back surface of the wafer to be 20 to 30 µm thicker than the final target thickness. Subsequently, a fine grinding wheel is used to perform the finishing step of precisely grinding the back side of the wafer to the final target thickness. A polishing step is then performed to mirror the surface of the wafer using a slurry and a grinding pad to reduce warpage of the wafer and increase chip strength. After the wafer is finally cleaned, the wafer is ejected from the apparatus.

In the above-described wafer backside polishing process, the roughing and finishing steps basically use a mechanical grinding action. That is, the wafer surface is mechanically removed by friction between the polishing wheel and the wafer. Therefore, silicon debris is generated on the wafer during the mechanical grinding process, and the cleaning liquid is sprayed through the nozzle at each step to clean the wafer. In the polishing step, the cleaning solution is sprayed to remove the slurry, and after the whole process, a separate cleaning process is performed.

However, despite these efforts, it is virtually difficult to completely remove foreign substances such as silicon debris and slurry remaining on the wafer surface. However, as the thickness of the wafer becomes thinner and thinner, even a very fine foreign matter may remain on the surface of the wafer, causing damage or defects in the wafer, which may lower the process yield. Therefore, there is a need for a method to further increase the cleaning efficiency in the wafer backside polishing process.

On the other hand, in the roughing and finishing step of the wafer backside polishing process, a wafer burning phenomenon occurs in which the wafer is burned black due to excessive pressure of the polishing wheel and the grinding action is not properly performed. This will be described in more detail with reference to FIGS. 1 and 2.

1 is a perspective view schematically showing a part of a wafer backside polishing apparatus 10 according to the prior art. The configuration and manner of operation of the device 10 shown in FIG. 1 applies basically to the roughing and finishing steps. However, only the particle size of the abrasive grains formed in the lower end 14 of the polishing wheel 13 is different.

Referring to FIG. 1, the wafer 20 is mounted on a chuck table 12 so that the rear surface thereof faces upward while the front surface is covered with the protective tape 21. The abrasive wheel 13 is located above the chuck table 12, and abrasive particles are formed at the lower end 14 thereof. In the state where the chuck table 12 on which the wafer 20 is mounted rotates, the polishing wheel 13 is lowered so that the lower end portion 14 contacts the rear surface of the wafer 20. At the same time, the polishing wheel 13 rotates in the opposite direction or in the same direction as the chuck table 12. Therefore, the back surface of the wafer 20 is ground by the abrasive particles of the lower end of the polishing wheel 14. On the other hand, the cleaning liquid spray nozzle 15 is located near the contact surface of the wafer 20 and the lower end portion 14 of the polishing wheel to spray the cleaning liquid.

2 is a partially enlarged cross-sectional view of the polishing wheel lower end 14 shown in FIG. 1. Referring to FIG. 2, the lower end portion 14 of the abrasive wheel has a fixed structure in which a plurality of abrasive particles 14a such as diamond are evenly distributed in the binder 14b. The binder 14b wears out little by little during the grinding process. Therefore, as the abrasive particles 14a of the lower layer are separated, pockets 14c are formed in place, and the process of exposing the abrasive particles 14a of the upper layer is repeated. Since the binder 14b is usually formed by foaming, the pocket 14c may be formed while the pores formed inside the binder 14b are exposed.

By the way, in the pocket 14c, the foreign material 14d, such as the silicon debris which generate | occur | produced during grinding processing, or the adhesive agent of the wafer protection tape (21 of FIG. 1), may be stuck. If the foreign material 14d is stuck and the pocket 14c is clogged, the surface of the lower end portion 14 of the polishing wheel is blunted, so that the grinding operation is not performed properly. In addition, the cleaning liquid is not smoothly discharged between the polishing wheel lower end 14 and the wafer, thereby reducing the cooling function of the cleaning liquid for removing frictional heat. As described above, the foreign material 14d in the pocket 14c acts as one of the main causes of the wafer burning phenomenon, and thus, there is a need for a method of reducing the wafer burning phenomenon by removing it.

An object of the present invention is to provide a wafer back polishing apparatus capable of increasing the cleaning efficiency of the wafer back polishing process.

Another object of the present invention is to provide a wafer backside polishing apparatus capable of preventing wafer burning in the wafer backside polishing process.

In order to achieve these objects, the present invention provides a wafer backside polishing apparatus using ultrasonic cleaning.

The wafer backside polishing apparatus according to the present invention comprises a chuck table, a polishing machine and a cleaning liquid spray nozzle. On the chuck table, a wafer is mounted and fixed so that the rear side faces upward, and the chuck table rotates the mounted wafer. The grinder is located above the chuck table, rotates and mechanically ground in contact with the backside of the wafer. The cleaning liquid injection nozzle is for injecting the cleaning liquid to the back of the wafer and is located near the polishing machine. In particular, the cleaning liquid injection nozzle is characterized by including an ultrasonic cleaner for generating ultrasonic waves to oscillate the cleaning liquid.

In the wafer backside polishing apparatus according to the present invention, the chuck table includes a standby table on which the wafer waits, a roughing table on which the roughing step is performed on the wafer, a finishing table on which the finishing step on the wafer is performed, and a polishing step on the wafer. It is desirable to have a polishing table. In addition, the polishing machine preferably includes a coarse polishing wheel located above the roughing table, a fine polishing wheel located above the finishing table, and a polishing pad located above the polishing table, wherein the cleaning liquid spray nozzles have a coarse polishing wheel. It is preferred to have a first spray nozzle located near the second spray nozzle, a second spray nozzle located near the fine polishing wheel, and a third spray nozzle located near the polishing pad.

The wafer backside polishing apparatus according to the present invention may further include a turn table on which a waiting table, a roughing table, a finishing table, and a polishing table are radially installed. The turn table can rotate the chuck tables in a batch.

The wafer backside polishing apparatus according to the present invention may further include a cleaning table and a fourth spray nozzle. The cleaning table is positioned adjacent to the turn table, and the wafer is mounted and fixed to the cleaning table so that the rear side of the wafer faces upward. The fourth spray nozzle is located above the cleaning table, and sprays the cleaning liquid on the rear surface of the wafer. The fourth spray nozzle also includes an ultrasonic cleaner for generating ultrasonic waves to oscillate the cleaning liquid.

In the wafer polishing apparatus according to the present invention, the ultrasonic cleaner may include an oscillator for generating a high frequency electric signal and a vibrator for causing vibration in the cleaning liquid by the high frequency electric signal of the oscillator.

Example

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

In describing the embodiments, descriptions of technical contents which are well known in the technical field to which the present invention belongs and are not directly related to the present invention will be omitted. This is to more clearly communicate without obscure the subject matter of the present invention by omitting unnecessary description. For the same reason, some components in the accompanying drawings are exaggerated, omitted, or schematically illustrated, and the size of each component does not entirely reflect the actual size. The same or corresponding components in each drawing are given the same reference numerals.

3 is a perspective view schematically showing a wafer backside polishing apparatus 30 according to an embodiment of the present invention.

Referring to FIG. 3, the wafer backside polishing apparatus 30 of this embodiment includes one turn table 31, four chuck tables 32a, 32b, 32c, and 32d and one cleaning table 36. As shown in FIG. It includes. Four chuck tables 32a-32d are mounted radially (eg at 90 degree intervals) on the turn table 31, and the cleaning table 36 is separately installed next to the turn table 31. The wafer 20 is mounted on each of the chuck tables 32a to 32d and the cleaning table 36 with the rear surface facing upward. Each of the chuck tables 32a to 32d and the cleaning table 36 fixes the wafer 20 by a vacuum suction method and is capable of rotating itself.

The chuck tables 32a to 32d provided on the turn table 31 are waiting tables 32a, roughing tables 32b, finishing tables 32c, and polishing tables 32d, respectively. The waiting table 32a is a place where a wafer put into the apparatus or a wafer on which a backside polishing process is completed is waiting and a wafer alignment step is performed. The roughing table 32b, the finishing table 32c, and the polishing table 32d are places where the roughing step, the finishing step, and the polishing step for the wafer are performed, respectively.

Among the chuck tables, polishing machines 33a, 33b, 33c are positioned above the roughing table 32b, the finishing table 32c, and the polishing table 32d. The polishing machine located on the roughing table 32b and the finishing table 32c is a coarse polishing wheel 33a and a fine polishing wheel 33b, respectively, and the polishing machine located on the polishing table 32d is a polishing pad 33c. Each of the grinders 33a, 33b, 33c can be moved up and down by a spindle and rotates, and mechanically contacts the back surface of the wafer 20.

The abrasive wheels 33a and 33b have a conventional configuration in which abrasive particles (14a in FIG. 2), such as diamond, are formed at the lower end. The coarse abrasive wheel 33a has a particle size of 300-350 mesh, for example 325 mesh, and the fine abrasive wheel 33b has a particle size of 1500-2500 mesh, for example 2000 mesh. The polishing pad 33c has a conventional structure in which a bottom surface is covered with a material such as cloth and a slurry supply part is formed therein. The slurry is obtained by suspending abrasive particles such as silica in an alkaline solution.

The turn table 31 may rotate the chuck tables 32a to 32d collectively. Therefore, the names of the chuck tables 32a to 32d are merely referred to for convenience on the basis of the process steps in progress. In other words, when the waiting table 32a moves to the position of the roughing table 32b by the 90 degree rotation of the turn table 31, and the roughing table 32b moves to the position of the finishing table 32c, the waiting table 32a ) Becomes a new roughing table 32b, and the roughing table 32b becomes a new finishing table 32c. As described above, each of the four chuck tables 32a to 32d installed on the turn table 31 rotates by 90 degrees at the end of each process step, and the next process step proceeds continuously.

The wafer backside polishing apparatus 30 further includes cleaning liquid jet nozzles 35a, 35b, 35c, and 35d. The cleaning liquid spray nozzles 35a to 35d spray the cleaning liquid on the rear surface of the wafer 20 to remove foreign substances such as silicon debris or slurry remaining on the surface of the wafer 20. Among the cleaning liquid spray nozzles 35a to 35d, the first spray nozzle 35a is adjacent to the coarse polishing wheel 33a, and the second spray nozzle 35b is adjacent to the fine polishing wheel 33b, and the third spray nozzle 35c are respectively located adjacent to the polishing pad 33c. In addition, the fourth spray nozzle 35d is located above the cleaning table 36.

Each of the cleaning liquid injection nozzles 35a to 35d is characterized by having an ultrasonic cleaner. Hereinafter, the cleaning liquid jet nozzle including the ultrasonic cleaner will be described in detail with reference to FIG. 4. 4 is a partially enlarged cross-sectional view of the cleaning liquid injection nozzle 35.

Referring to FIG. 4, the ultrasonic cleaner 39 installed in the cleaning liquid injection nozzle 35 is for generating an ultrasonic wave to oscillate the cleaning liquid 38. The ultrasonic cleaner 39 includes an oscillator 39a and a vibrator 39b. The oscillator 39a generates a high frequency electric signal and sends it to the vibrator 39b. The vibrator 39b causes fine vibration to the cleaning liquid 38 by the electric signal of the oscillator 39a. The oscillation frequency of the ultrasonic cleaner 39 is, for example, 400 KHz, 1 MHz, 1.5 MHz, 3 MHz, or the like. Ultrapure water (DI water) is mainly used for the cleaning solution 38, and chemical solutions, such as hydrogen peroxide, hydrofluoric acid, etc., which play a similar role as necessary, may be used.

The ultrasonic waves applied to the cleaning liquid 38 by the vibrator 39b become a small wave, and the compressive force and the expansion force repeatedly appear. Bubbles are generated inside the cleaning liquid 38 during the expansion cycle, and these bubbles disappear during the next compression cycle. These bubbles grow in size as they generate and disappear tens of thousands of times a second. Above a certain aperture, the bubble contracts and bursts all at once, producing a very large shock wave. This shock wave can easily remove foreign substances such as silicon debris or slurry remaining on the surface of the wafer (20 in FIG. 3), and foreign matters stuck in the pocket (14c in FIG. 2) at the bottom of the polishing wheel (14d in FIG. 2). ) Can be removed. Therefore, the cleaning efficiency of the wafer backside polishing process can be increased, and the wafer burning phenomenon can be prevented.

In order to increase the cleaning efficiency by ultrasonic waves, the end portion of the cleaning liquid injection nozzle 35 is preferably at a distance as close as possible to the cleaning area (for example, about 20 mm). This is to proceed with the cleaning operation in a state in which the oscillation effect remains sufficiently in the cleaning liquid 38 oscillated by ultrasonic waves.

In the above-described embodiment, the wafer backside polishing apparatus 30 includes a roughing table 32b, a finishing table 32c, a polishing table 32d, and a washing table 36 separately provided on the turn table 31. However, the wafer backside polishing apparatus of the present invention is not necessarily limited to this configuration. For example, the polishing table may not be installed or there may be no separate cleaning table. The wafer backside polishing apparatus of the present invention may have any configuration as long as it includes a chuck table and a polishing machine and an ultrasonic cleaner is provided in the cleaning liquid jet nozzle. On the other hand, the vibrator 39b of the ultrasonic cleaner 35 may have a form in which a plurality of vibrators are coupled to the vibrating plate.

As described through the examples so far, the wafer backside polishing apparatus according to the present invention includes a cleaning liquid jet nozzle provided with an ultrasonic cleaner. The ultrasonic cleaner generates ultrasonic waves to generate fine vibrations in the cleaning liquid, thereby increasing the wafer cleaning efficiency by the cleaning liquid and preventing wafer damage such as wafer burning.

In the present specification and drawings, preferred embodiments of the present invention have been disclosed, and although specific terms have been used, these are merely used in a general sense to easily explain the technical contents of the present invention and to help the understanding of the present invention. It is not intended to limit the scope. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

Claims (5)

A chuck table on which the wafer is mounted and fixed so that a rear surface of the wafer faces upward, and rotates the wafer; A grinding machine located above the chuck table, rotating and mechanically grinding in contact with a rear surface of the wafer; Located near the polisher, and includes a cleaning liquid spray nozzle for spraying a cleaning liquid on the back of the wafer, The cleaning liquid jet nozzle comprises an ultrasonic cleaner for generating ultrasonic waves to oscillate the cleaning liquid. The method of claim 1, The chuck table includes a waiting table on which the wafer waits, a roughing table on which the roughing step is performed on the wafer, a finishing table on which the finishing step on the wafer is performed, and a polishing table on the polishing step on the wafer. , The polishing machine includes a coarse polishing wheel located above the roughing table, a fine polishing wheel located above the finishing table, and a polishing pad located above the polishing table, The cleaning liquid spray nozzle includes a first spray nozzle located near the coarse polishing wheel, a second spray nozzle located near the fine polishing wheel, and a third spray nozzle located near the polishing pad. Wafer backside polishing apparatus. The method of claim 2, And the turn table for radially installing the waiting table, the roughing table, the finishing table, and the polishing table to rotate the chuck tables in a batch. The method of claim 3, A cleaning table positioned adjacent to the turn table, and fixed to the wafer so that a rear surface of the wafer faces upward; Located above the cleaning table, further comprising a fourth spray nozzle for spraying a cleaning liquid on the back of the wafer, And the fourth spray nozzle comprises an ultrasonic cleaner for generating ultrasonic waves to oscillate the cleaning liquid. The method according to any one of claims 1 to 4, And the ultrasonic cleaner comprises an oscillator for generating a high frequency electric signal and a vibrator for generating vibration in the cleaning liquid by the high frequency electric signal of the oscillator.

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