JP2000164543A - Method for polishing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for polishing wafers which flattens surfaces of the wafers. SOLUTION: In this method, a wafer accommodated in a cassette is transported under a chuck mechanism by a conveying mechanism, and the wafer is attracted to the chuck mechanism, and is pressed on the surface of a polishing cloth of a polishing board 3, and the wafer polishing board 3 is rotated to polish the wafer. At this time, before the wafer is chucked to the chuck mechanism, a wafer surface which is chucked to the chuck mechanism is cleaned by the use of a detergent being irradiated with ultrasonic waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bare wafer, a device wafer obtained by slicing an ingot and grinding the sliced ingot.
The present invention relates to a method for polishing a surface of a wafer such as an SOI wafer, a magnetic head wafer, and the like.

[0002]

2. Description of the Related Art As a method of polishing a semiconductor wafer, for example, a polishing apparatus 1 shown in FIG. 6 is used. That is, on the surface of a polishing platen (also referred to as a platen) 3 in which a polishing cloth (polishing pad) 3 a is attached to a surface supported by the rotating shaft 2,
A small hole 6a shown in FIG. 2 or FIG.
Are fixed by bolts, and a flange 6c of a glass fiber reinforced epoxy resin is provided on the outer peripheral edge of the mounting plate surface shown in FIG. 8, and a hole 6d is formed in accordance with the small hole. Transfer pad (JP-A-2-193815, JP-A-4-193815) on the lower surface of a chuck mechanism (JP-A-4-14848) in which the resin buffer sheet 6b is attached with an adhesive.
No.-23750) or a robot arm transfer mechanism grips or sucks a wafer w stored in a cassette (not shown), inverts and transports the wafer, and suctions the wafer to a chuck mechanism by depressurizing the tube 9. Let it.

Then, the wafer fixed to the chuck mechanism is pressed against the polishing cloth of the polishing machine, the pressure in the pipe 9 is stopped, and the wafer is pressurized by supplying pressurized air from the pipe 10.
Are rotated in the forward and reverse directions or in the same direction to polish the wafer. During polishing, an abrasive is supplied from tube 17. The inside of the hollow shaft 4 of the polishing apparatus 1 is connected to a vacuum pump (not shown) via a rotary valve 7 and a valve 8, and a pipe 9, a trap 9 'for adsorbing the wafer w to the adsorption plate 6, a trap 9' The pressurized gas introduction tube 10 and the cleaning liquid supply tube 14 are connected. 8, 11, and 13 are valves (see FIG. 6).

The polished wafer stops the valve 11,
Next, a cleaning liquid (pure water) is supplied from the nozzle 17 'to the surface of the polishing cloth to dissolve and remove abrasives and polishing debris adhering to the polishing cloth and the wafer. After the cleaning, the valve 8 is opened, the wafer is sucked, the shaft 4 is raised by the air cylinder 15, and the polished wafer is transferred to the spin cleaning mechanism by a transfer mechanism such as a robot arm, and the wafer is cleaned. And stored in another cassette by a transport mechanism (Japanese Unexamined Patent Application Publication No.
193815, Japanese Patent Application No. 10-208540, 10
-234870).

[0005] Before the wafer is mounted on the chuck mechanism, the wafer is transferred to a temporary mounting table, and the chuck mechanism of the polishing apparatus may suck the wafer on the temporary mounting table. In some cases, a temporary mounting table is provided with a pure water supply mechanism to clean the back surface of the wafer. Further, as a wafer chuck mechanism, a backing mat chuck, a vacuum chuck,
A hydro chuck may also be used ("Journal of Precision Engineering", Vol. 62, No. 4, 1996, 491-4).
95).

[0006] Polishing of a bare wafer is usually performed in a clean room. However, invisible particles and polished debris may adhere to the cassette, the transport mechanism, the wafer mounting plate of the polishing apparatus, and the like in the clean room, and these may cause the polishing of the polished wafer. Flatness may be impaired. Therefore, the cassette containing 25 wafers is immersed in the cleaning tank, the wafer is taken out from the cassette taken out of the cleaning tank by the transfer mechanism, the wafer mounting surface of the chuck mechanism is brush-scrubbed, and the mounting plate is ultrasonically cleaned. Washing (JP-A-4-213826, 9-234665)
No. 9-283486).

However, even if these cleaning processes are performed, one polished 200 mm-diameter wafer contains 1 wafer.
Defective products (see Fig. 5 or "Monthly Semi
conductor World February 1997, 103-107
Page). In particular, the wafer diameter is 200 mm, 3
As the thickness increases to 00 mm and 450 mm, and as the thickness of the wafer decreases, the rate of occurrence of dents increases.

[0008]

As a cause of the occurrence of dimples on the chuck surface of the polished wafer, abrasive slurry enters the gap between the wafer and the mounting surface of the chuck mechanism, causing the abrasive to be indented. Abrasive slurry in which the abrasive grains are sandwiched, or the suspended particles or abrasive debris are taken in
This may be caused by the penetration of the solid particles into the gap between the wafer and the mounting surface of the chuck mechanism. An object of the present invention is to provide a method for polishing a wafer, in which the defective rate of a polished wafer in which these dents occur is 1% or less.

[0009]

According to one aspect of the present invention, a wafer housed in a cassette is transferred under a chuck mechanism by a transfer mechanism, the wafer is attracted to the chuck mechanism, and the wafer is placed on a polishing pad of a polishing machine. In a method of polishing a wafer by pressing against a surface and rotating a wafer polishing board, a wafer surface to be attracted to the chuck mechanism is cleaned using a cleaning liquid irradiated with ultrasonic waves before the wafer is attracted to the chuck mechanism. And a method for polishing a wafer.

According to a second aspect of the present invention, the frequency of the ultrasonic wave is
The polishing method according to claim 1, wherein the polishing frequency is 20 KHz to 3 MHz. According to a third aspect of the present invention, there is provided the polishing method according to the first aspect, wherein the ultrasonic irradiation alternately performs ultrasonic waves having frequencies different by at least 20 KHz.

[0011]

[Function] Before the wafer is mounted on the chuck mechanism, the suspended particles attached to the wafer surface are removed from the wafer suction surface by ultrasonic cleaning, so that the probability that the polished wafer is dented on the chuck surface side is reduced. did. This probability is further reduced by using two or more ultrasonic waves having different frequencies.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a top view of a polishing apparatus 1 used for carrying out the present invention. FIG. 2 is a plan view showing a cleaning apparatus for ultrasonically cleaning a wafer on a temporary mounting table loaded with the wafer in FIG. FIG. 4 is a perspective view of an index head, and FIG. 4 is a surface thickness distribution diagram of a wafer surface on a chuck surface side of a polished acceptable wafer obtained by carrying out the present invention.

1, 2 and 3, 1 is a polishing apparatus, A is an index head, A 'is a rotation drive shaft of the index head, w is a wafer, 3 is a platen for rough polishing, and 3' is a finish. Polishing platens, 4a, 4b, 4c,
4d is a chuck mechanism, 5, 5, 5, and 5 are heads, 18 is a temporary mounting table for wafer loading supported on a rotating shaft (not shown), and 19 is a wafer unloader mounted on a rotating shaft (not shown). , A cassette for storing wafers before polishing, 20 'a cassette for storing wafers after polishing, 21 and 21' for robots,
Reference numerals 1a and 21a 'denote an arm; 22, 22 a conditioner of a plate polishing cloth; 23, an ultrasonic generator;
a is an ultrasonic oscillator, 23b is a cleaning liquid supply pipe, 23c, 2
3d is a moving arm, 23e is a drive control unit, and 23f is a pure water supply amount control unit. The transfer of the wafer from the cassette to the temporary mounting table and the transfer from the temporary receiving table to the cassette are performed by using a belt-type transfer mechanism and a suction pad disclosed in Japanese Patent Application Laid-Open No. 5-77148 instead of the robot transfer mechanism shown in FIG. May be used.

The step of polishing a bare wafer using this polishing apparatus will be described below. (1) The wafer w1 stored in the cassette 20 is sucked by the suction pad of the arm 21a of the robot arm 21,
After the arm is retracted and turned over, the wafer is rotated and expanded and contracted, and the wafer is placed on the temporary loading table 18. (2) While rotating the temporary table 18, pure water subjected to ultrasonic vibration is caused to flow on the surface of the wafer on the temporary table to ultrasonically clean the wafer surface. Then, the supply of pure water is stopped.

(3) Then, pure water is supplied to the back surface 18a of the temporary mounting table to float the wafer, the wafer w1 is sucked by the chuck mechanism 5a, and the chuck mechanism 5a is raised. (4) After rotating the index head 90 degrees in the forward direction, the wafer w1 is pressed against the first platen 3 to supply the abrasive slurry and rotate both the shafts 2 and 4 to remove the wafer. The wafer w2 is polished and placed on the loading temporary mounting table 18 from the cassette in the same manner as in the above step (1), the surface of the wafer w2 is ultrasonically cleaned, and then the wafer w2 is sucked by the chuck mechanism 5d. Chuck mechanism 5d
To rise.

(5) Move the index head 90 in the forward direction.
After rotating the wafer w1, the wafer w1 is pressed against the second platen 3 ', and both shafts 2 and 4 are rotated to finish polish.
The wafer w2 is pressed against the first platen 3, and the two shafts 2,
Rotate 4 to polish. At the same time, the wafer w3 is placed on the temporary mounting table for loading, and the wafer w3 is sucked by the ultrasonic cleaning and chuck mechanism c, and the chuck mechanism 5c is raised. (6) After rotating the index head 90 degrees in the forward direction, the wafer w1 is transferred to the unloading temporary receiving table 19, and further stored in the cassette 20 ', and the wafer w2 is transferred to the second platen. Then, both shafts 2 and 4 are rotated to finish polishing, and wafer w3 is pressed to the first platen to rotate both shafts 2 and 4 for polishing and wafer w4.
Is placed on the loading temporary mounting table 18, and after ultrasonic cleaning, it is adsorbed to the chuck mechanism 5b to raise the chuck mechanism 5c.

(7) After rotating the index head A 90 degrees in the reverse forward direction, the wafer w2 is moved to a temporary loading table for unloading and further stored in the cassette 20 ', and the wafer w3 is stored in the second cassette. Pressing against the platen 3 'and rotating both shafts 2 and 4 for finish polishing, the wafer w4 is placed on the first platen.
The wafer w5 is pressed on the tenn, and the two shafts 2 and 4 are rotated and polished, and the wafer w5 is placed on the temporary loading table 18;
After the ultrasonic cleaning, the chuck mechanism 5a is sucked, and the chuck mechanism 5a is raised. (8) Hereinafter, the new wafer w6, w7, w8, w
9 is repeated to supply to the loading temporary mounting table, ultrasonic cleaning, transfer of the first polished, second polished and finish polished wafers to the unloading temporary cradle, and storage in the cassette. . The number of rotations of the rotating shafts 2 and 4 is 20 to 200
rpm, the pressure at which the wafer is pressed against the polishers 3, 3 'is 0.1 to 1 kg / cm < ² >. The rotation directions of the rotation shaft 2 of the polisher and the rotation shaft 4 of the chuck mechanism may both be forward directions or forward and reverse directions.

The supply amount of the cleaning liquid to be irradiated with the ultrasonic wave is 0.1.
8 to 45 l / min are preferred. The ultrasonic frequency is 2
It is good to alternately irradiate two or more kinds of ultrasonic waves having different frequencies from 0 KHz to 3 MHz, preferably 20 KHz or more. Abrasive slurry is a dispersion of abrasive particles such as aluminum oxide, cerium oxide, single crystal diamond, polycrystalline diamond, silicon oxide, silicon carbide, chromium oxide and glass powder in an aqueous medium. Salt, dispersing aid, chelating agent, polishing oil,
Contains rust inhibitor, defoamer, pH adjuster, fungicide, etc.

[0019]

EXAMPLE 1 Using the polishing apparatus shown in FIG. 1 and FIG.
A silicon bare wafer having a thickness of 220 μm was polished by 20 μm. The polishing conditions were as follows: the rotation speeds of the first and second platens were 80 rpm, the rotation speed of the chuck mechanism was 80 rpm, and a slurry containing colloidal silica as an abrasive slurry.
, And rough polishing and finish polishing were performed for 5 minutes each. Ultrasonic cleaning of the wafer on the loading temporary mounting table was performed by irradiating pure water (supply rate 100 cc / min) with ultrasonic waves having a frequency of 400 KHz for 30 seconds to apply vibration. The pressure of the hollow shaft of the chuck mechanism during polishing was reduced, and the wafer was sucked. Of 100 polished wafers,
One defective product had a dent of 0.02 μm or more (confirmed by scattered light due to oblique incidence of laser light). ADE Capacitance Type Thickness Meter “Ultra G”
FIG. 4 shows a distribution diagram of the thickness of the chuck surface of an acceptable wafer having no dents (recesses) drawn using Age 9500 "(trade name).

Comparative Example 1 A wafer was polished in the same manner as in Example 1 except that the ultrasonic cleaning of the wafer before the chuck was not performed. 17 out of 100 sheets were defective. FIG. 5 shows a distribution diagram of the thickness of the chuck surface of the rejected wafer. Example 2 In Example 1, ultrasonic cleaning of the wafer before chucking was performed by adding ultrasonic waves having a frequency of 20 KHz to pure water and 100 KHz.
The ultrasonic wave of the frequency of 400 KHz
The irradiation was performed for 30 seconds while alternately irradiating every second. 1 defective
0 out of 00 sheets.

[0021]

According to the method of polishing a wafer of the present invention, a polished wafer having a flat surface can be obtained without being affected by suspended substances and polishing debris even if the diameter of the wafer is large or the thickness is small.

[Brief description of the drawings]

FIG. 1 is a top view of a polishing apparatus according to the present invention.

FIG. 2 is a plan view showing a state where a wafer is subjected to ultrasonic cleaning.

FIG. 3 is a partial perspective view of an index head.

FIG. 4 is a thickness distribution diagram of a polished wafer (acceptable product).

FIG. 5 is a thickness distribution diagram of a polished wafer (failed product).

FIG. 6 is a sectional view of another polishing apparatus.

FIG. 7 is a top view of a surface adjustment mounting plate of the chuck mechanism.

FIG. 8 is a top view of a perforated resin packing sheet of the chuck mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polishing apparatus A Index head w Wafer 3 Polishing board (platen) 4 Rotation axis of a chuck mechanism 5 Head 6 Mounting plate 14 Pure water supply pipe 18 Temporary table 20 Cassette 21 Robot 23 Ultrasonic cleaning equipment

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takahiko Mitsui 3009 Kamiyori, Atsugi-shi, Kanagawa F-term in Okamoto Machine Tool Works, Ltd. Semiconductor Division 3C058 AA07 AB03 AB04 AC05 CB01 CB02 CB10 DA17

Claims (3)

[Claims] 1. A wafer stored in a cassette is transported under a chuck mechanism by a transfer mechanism, the wafer is attracted to the chuck mechanism, and the wafer is pressed against a polishing cloth surface of a polishing disk, and the wafer polishing disk is rotated. A method of polishing a wafer by adhering a wafer to a chuck mechanism with a cleaning liquid irradiated with ultrasonic waves before adsorbing the wafer to the chuck mechanism. Method. 2. The frequency of an ultrasonic wave is 20 KHz to 3 MH.
The polishing method according to claim 1, wherein z is z. 3. The method of claim 1, wherein the ultrasonic irradiation has a frequency of at least 20.
The polishing method according to claim 1, wherein ultrasonic waves having different frequencies of KHz are alternately performed.