JP2002252189A - Polishing liquid for semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the polishing efficiency of a silicon wafer, using polishing liquid which does not contain free abrasive grains, and to prevent the metallic pollution of the wafer at polishing. SOLUTION: The polishing liquid is made by adding an inorganic alkaline agent to pure water and adjusting the pH value of this solution to 11.0-12.5. Each quantity of KOH (or NaOH) and K2 CO3 (or Na2 Co3 ) to be added is 0.05-0.2 wt.%. A polishing tool (polishing roller, a polishing tape, etc.), where polishing abrasive grains are fixed to the polish working face, and a silicon wafer are set in a polisher. The polish working face of the polishing tool is brought into pressure contact with the surface of the silicon wafer so as to polish it, while supplying the surface of the silicon wafer with the above polishing liquid at a prescribed flow rate. As a result, a mirror face silicon wafer free of metallic pollution can be obtained at 0.5-0.7 μm/min. As compared with the conventional polishing liquid consisting of pure water, this polishing liquid accelerates polishing of the semiconductor wafer by the molded item of the fixed abrasive grains. The polishing liquid is superior in stability, and forms a complex with metallic elements, so it can prevent pollution caused by the metallic element at the surface of the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing liquid for semiconductor wafers, and more particularly to a polishing liquid for semiconductor wafers used in a mirror polishing process for semiconductor wafers using a polishing tape or a polishing roller having abrasive grains fixed thereto or a CMP process for semiconductor devices. Related to polishing liquid.

[0002]

2. Description of the Related Art A silicon wafer is manufactured from a silicon single crystal ingot through slicing, lapping, chamfering, etching, donor killer heat treatment, mirror polishing, cleaning, and the like, which are shipped to a device maker. A device maker produces a device on the surface of the silicon wafer. In the device process, CMP for planarizing the surface of the oxide film covering the device is performed. In the mirror polishing step, the surface is mirror-polished by pressing the wafer while supplying an abrasive to a polishing cloth such as a urethane pad. That is, an abrasive in which colloidal silica is dispersed in water or an alkaline solution is supplied, and the surface of the silicon wafer is pressed against the polishing surface of the rotating polishing cloth, whereby colloidal silica as fine particles (free abrasive particles) is pressed. The surface of the wafer is polished by the grinding action of ()). In addition, planarization polishing (CM) performed in the device process
As for P), a polishing treatment was performed using a polishing cloth and an abrasive in the same manner as described above.

[0003]

As described above, in the conventional wafer polishing, the wafer surface is polished by free abrasive grains in an abrasive. For this reason, clogging of the polishing cloth occurs due to long-term use. Therefore, it is necessary to dress or exchange the polishing cloth at regular intervals. Further, there is a problem that a polishing waste liquid containing a large amount of abrasive grains is generated. As a countermeasure against this, Japanese Patent Application Laid-Open No. 11-21667
In Japanese Patent Application Publication No. 6 (JP-A-6), a polishing compact made of silica, alumina, and ceria is proposed. When this molded article for polishing is used for a polishing platen, a wafer is polished using a polishing liquid or a polishing liquid containing a small amount of polishing abrasive grains.

[0004] However, in a polishing apparatus comprising the above-mentioned polishing molded body, a predetermined polishing efficiency cannot be obtained because water is used as a polishing liquid. Then, as a result of researching to improve the polishing efficiency, the inventor has completed a polishing liquid having the following properties.

[0005]

According to the first aspect of the present invention, there is provided a polishing liquid for a semiconductor wafer used for polishing a semiconductor wafer using a polishing tool to which abrasive grains are fixed, the polishing liquid comprising pure water and And a polishing liquid for semiconductor wafers comprising an inorganic alkali agent. Here, the polishing tool to which the abrasive grains are fixed includes a polishing tape in which the abrasive grains are fixed to the polishing surface, a polishing roller in which the abrasive grains are integrally formed with resin, and the like.

According to a second aspect of the present invention, the inorganic alkaline agent is prepared by adding K ₂ CO ₃ or N ₂ to KOH or NaOH.
a polishing liquid for semiconductor wafer according to claim 1 obtained by mixing a ₂ CO _3.

[0007] According to a third aspect of the invention, in addition amount of the KOH or NaOH is from 0.05 to 0.2 wt%, amount of the _K 2 CO ₃ or _Na 2 CO ₃ is 0.05
The polishing liquid for a semiconductor wafer according to claim 2, which is 0.2% by weight. If the addition amount of each chemical is less than 0.05% by weight, the polishing rate will be low, and the polished surface of the semiconductor wafer will be damaged. If each addition amount exceeds 0.2% by weight, the etching action in polishing becomes excessive and surface roughness occurs.

According to a fourth aspect of the present invention, in the polishing method for a semiconductor wafer according to any one of the first to third aspects, the pH value of the polishing liquid for a semiconductor wafer is 11.0 to 12.5. Liquid. The pH value of the mixed solution is adjusted to 11.0 to 12.5 with the above alkaline agent. When the pH value is less than 11.0, the polishing rate becomes slow. When the pH value exceeds 12.5, the etching action becomes larger, and the precision of the polished surface deteriorates.

[0009]

The polishing using the polishing liquid for semiconductor wafer according to the present invention is as follows. First, an inorganic alkali agent is added to pure water, and the pH value of this solution is adjusted to 11.0 to 12.5.
To prepare a polishing liquid. KOH (or NaOH) to be added and K ₂ CO ₃ (or Na ₂ C
The added amount of O ₃ ) is 0.05 to 0.2% by weight. Then, a polishing tool (polishing roller, polishing pad, polishing tape, etc.) and a silicon wafer having polishing abrasive grains fixed on the polishing surface are set in the polishing apparatus. Here, while the polishing liquid is supplied to the surface of the silicon wafer at a predetermined flow rate, the polishing surface of the polishing tool is pressed against the surface of the silicon wafer to polish the surface under predetermined conditions. As a result, there is no metal contamination (Cu on the surface is 1 × 10 ^{9 at.}
(ms / cm ² or less) A mirror-polished silicon wafer can be obtained at a predetermined polishing rate (for example, 0.5 to 0.7 μm / min).

[0010]

FIG. 1 shows an embodiment of a polishing apparatus using a polishing liquid according to the present invention. This polishing apparatus is used for polishing (PCR) of a chamfered surface of a silicon wafer. The polishing apparatus is provided with a rotatable holding member 2 for sucking and holding the silicon wafer 1 on its flat upper surface.
A grinding wheel 3 having a central portion narrowed and narrowed in a drum shape and having abrasive grains fixed on its outer surface; a driving unit for rotating the grinding wheel 3; A nozzle for supplying the polishing liquid to the concave outer surface having a curvature. This grinding wheel 3
Is obtained by mixing 15 parts by weight of spherical silica abrasive grains having an average particle size of 3 μm with respect to 100 parts by weight of a binder made of epoxy resin, and forming the above-mentioned drum shape. The holding member 2 is configured to be driven to rotate about an axis perpendicular to the surface of the silicon wafer by a driving device 4 (motor).
Therefore, polishing of the chamfered surface of the silicon wafer 1
The silicon wafer 1 is sucked on the holding member 2 by the suction device, the silicon wafer is rotated by the driving device 4, and the polishing liquid according to the present invention is supplied to the polishing surface (chamfered surface) of the silicon nozzle 1 from the supply nozzle at, for example, 20 ml / min. While rotating the polishing wheel 3 at a predetermined speed, the polishing wheel 3 is pressed against the chamfered surface of the wafer. As a result, the chamfered surface of the silicon wafer 1 is mirror-finished. After the polishing, the silicon wafer is washed with pure water, for example, to remove waste abrasive grains and the like on the silicon wafer surface (the entire surface including the chamfered surface).

The polishing liquid supplied from the nozzle is a mixed liquid obtained by adding KOH and K ₂ CO ₃ to pure water.
The pH value of the solution was adjusted to 11.0 to 12.5. The amount of each of KOH and K ₂ CO ₃ added is 0.
Between 0.5 and 0.2% by weight.

FIG. 2 shows another example of the polishing apparatus. This polishing apparatus is an apparatus for polishing the surface (main surface) of a silicon wafer. The molded body 13 for polishing was prepared by mixing 15 parts by weight of spherical silica abrasive grains having a particle diameter of 3 μm with respect to 100 parts by weight of a binder made of epoxy resin, and having a diameter of 300 m.
It is manufactured in a disk shape with a thickness of 10 mm and a thickness of 10 mm. The molded body 13 is rotatably supported by a driving device 14 via a shaft 15. First, polishing of the silicon wafer 11 is performed.
The back surface of the wafer is sucked onto the holding plate 12. In this state,
While the silicon wafer 11 is rotated by the driving device 16, the lower surface of the rotating polishing formed body 13 is pressed against the surface thereof at a predetermined polishing pressure. Thereby, the surface of the silicon wafer 11 is mirror-polished. At this time, the polishing liquid according to the present invention is supplied to the polished portion (entire surface) of the silicon wafer 11 at a rate of 5 ml / min.

[0013]

[Example 1] A silicon wafer cut from the same CZ ingot, chamfered, wrapped and etched in the same lot, was sampled. The test specimen was mounted on the apparatus shown in FIG. 2 (a disk-shaped molded article having a diameter of 300 mm and a thickness of 10 mm in which 15 parts by weight of colloidal silica having a particle size of 3 μm was mixed with 100 parts by weight of an epoxy resin binder). Mirror polishing was performed under predetermined conditions (supply amount of polishing liquid: 5 ml / min, processing pressure: 300 g / cm ² , platen rotation speed: 20 rpm). The polishing liquid used at this time is as follows. KO against pure water
H and K ₂ CO ₃ were mixed to prepare a polishing liquid. Then, with the supply amount of the polishing liquid (pure water / KOH / K ₂ CO ₃ ) kept constant, the state of change in the polishing rate when the addition amount of KOH / K ₂ CO ₃ was changed was measured in accordance with a standard method. The result is shown in FIG. In this case, metal contamination was measured on the silicon wafer surface after mirror polishing using ICP-MS, and all were good (1 × 10 ^{9 with} Cu).
atoms / cm ² or less).

[Embodiment 2] The polishing apparatus (FIG. 2) used in Embodiment 1 was used, and a polishing liquid (pure water / NaOH) was used.
/ Na ₂ CO ₃ ), a polishing liquid having the same composition as in Example 1 was prepared (pH = 11.5), and the stability and polishing amount of the polishing liquid were measured. As a result, the stability was good, and the polishing rate was 0.6 μm / min, which was almost the same as in Example 1. All were measured by a known method.

Comparative Example Using the polishing apparatus used in Example 1, pure water was used as a polishing liquid, and the pH value was adjusted to 11.0 ± 0.5 with potassium hydroxide. When this polishing liquid was used and polished under the same polishing conditions, the polishing rate was 0.4 μm / min, and the state of contamination (Cu
Contamination) was about 1 × 10 ¹¹ atoms / cm ² .

[0016]

It has been confirmed that the polishing liquid according to the present invention promotes the polishing of a semiconductor wafer by a molded product of fixed abrasive grains as compared with the conventional polishing liquid consisting of pure water alone. Therefore, the processing time of the polishing process is shortened, and it is possible to improve the manufacturing capacity and reduce the manufacturing cost. The polishing liquid according to the present invention not only has excellent stability but also forms a complex with a metal element. Therefore, contamination of the wafer surface with the metal element can be prevented. Further, the waste abrasive can be removed from the wafer surface and reused. Therefore, the amount of waste discharged can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing a polishing apparatus for polishing a chamfered surface using a polishing liquid according to the present invention.

FIG. 2 is a longitudinal sectional view schematically showing an apparatus for performing mirror polishing of a wafer using a polishing liquid according to the present invention.

FIG. 3 is a graph showing the relationship between the amount of amine added to a polishing liquid and the polishing rate according to an example of the present invention.

Claims (4)

[Claims] 1. A polishing liquid for a semiconductor wafer, which is used when polishing a semiconductor wafer using a polishing tool with fixed abrasive grains, the polishing liquid comprising pure water and an inorganic alkali agent. 2. The inorganic alkaline agent is KOH or N
aOH, K₂CO ₃Or Na₂CO₃Mixed
The polishing liquid for a semiconductor wafer according to claim 1. 3. The addition amount of KOH or NaOH is as follows:
0.05 to 0.2 percent by weight, the _K 2 CO ₃ or a polishing liquid for semiconductor wafer according to claim 2 amount of _Na 2 CO ₃ is 0.05 to 0.2 wt%. 4. The polishing liquid for a semiconductor wafer according to claim 1, wherein the pH value of the polishing liquid for a semiconductor wafer is 11.0 to 12.5.