A polishing liquid, a method for producing the polishing liquid, and a polishing method

Abstract

To recovery metal ions more easily than in a case of evaporating waste liquid by solving a problem in which the operation of recovering the metal ions becomes very complicated when an operation such as evaporating the entire waste liquid is required in order to recover metal ions.SOLUTION: A polishing liquid supplied to a polishing pad when polishing at least one surface of a workpiece using the polishing pad includes abrasive grains, and a functional group capable of coordinating with metal ions to form metal complexes is provided on the surface of the abrasive grain.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a polishing liquid supplied to a polishing pad when polishing a workpiece using the polishing pad, a method for manufacturing the polishing liquid, and a method for polishing a workpiece using the polishing liquid.

Background Art

[0002] Electronic devices such as mobile phones and personal computers are equipped with device chips. The device chips are manufactured, for example, by forming devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) on the surface side of a silicon wafer and then dividing the wafer into individual devices.

[0003] Before dividing the wafer, in order to thin the wafer to a predetermined thickness, usually, rough grinding and finish grinding are sequentially performed on the back side of the wafer (see, for example, Patent Document 1). However, with grinding, grinding marks (saw marks) are formed on the back side of the wafer.

[0004] Since the flexural strength of a device chip singulated with grinding marks remaining is lower than that of a device chip with the grinding marks removed, usually, the grinding marks are removed by chemical mechanical polishing (CMP) (see, for example, Patent Document 2). For example, as described in Patent Document 2, a polishing liquid (slurry) containing free abrasive grains is supplied to a polishing pad without abrasive grains, and the wafer is polished.

[0005] By the way, the polishing liquid may contain metal ions such as copper ions. Such metal ions contaminate the wafer, so usually, a polishing liquid added with a chelating agent such as ethylenediamine (EDA) is used to prevent metal contamination.

[0006] By ligands such as EDA coordinating with metal ions to form a chelate complex, metal contamination of the wafer is prevented. However, it is relatively difficult to recover metal ions in the used polishing liquid (i.e., waste liquid).

[0007] For example, since the metal ions that have become chelate complexes cannot be recovered even by using an ion exchange resin, operations such as evaporating the entire waste liquid are required. Therefore, the operation of recovering metal ions in the waste liquid becomes very complicated.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of such problems, and an object thereof is to recover metal ions more easily than in the case of evaporating the waste liquid.

Means for Solving the Problems

[0012] According to an aspect of the present invention, there is provided a polishing method for polishing at least one surface of a workpiece using a polishing pad, the method including: a holding step of holding the workpiece on a holding surface of a chuck table; and a polishing step of supplying a polishing liquid containing abrasive grains having a functional group capable of coordinating with metal ions to form a metal complex to the polishing pad and polishing the one surface side with the polishing pad, wherein the abrasive grains are made of silicon oxide, cerium oxide, green silicon carbide, or white alumina 1. and a polishing method is provided. The workpiece is a bare wafer formed of silicon or a compound semiconductor.

Effects of the Invention

[0013] ​On the surface of the abrasive grains contained in the polishing liquid according to one aspect of the present invention, functional groups capable of coordinating with metal ions are provided. Therefore, if the abrasive grains in the waste liquid are recovered, the metal ions contained in the waste liquid can be recovered, so that the metal ions can be recovered more easily than in the case of evaporating the waste liquid.

Brief Description of Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] With reference to the accompanying drawings, embodiments according to one aspect of the present invention will be described. First, the polishing liquid 1 of the present embodiment will be described. FIG. 1 is a schematic diagram of the polishing liquid 1. The polishing liquid 1 is supplied to the polishing pad 20 when polishing the workpiece 11 with the polishing pad 20 that does not have abrasive grains (see FIG. 4).

[0016] The polishing liquid 1 usually contains a large number of abrasive grains 3 (that is, free abrasive grains). The abrasive grains 3 are formed of one kind of material selected from silica (silicon oxide. For example, SiO2), ceria (cerium oxide. For example, CeO2), GC (green silicon carbide), WA (white alumina), and the like.

[0017] The size of the abrasive grains 3 is usually expressed by the particle diameter. There are known methods such as the geometric diameter, the equivalent diameter, etc. for expressing the particle diameter. The geometric diameters include the Feret diameter, the maximum diameter in a fixed direction (Krummbein diameter), the Martin diameter, the sieve diameter, etc., and the equivalent diameters include the projected area circle equivalent diameter (Heywood diameter), the equal surface area sphere equivalent diameter, the equal volume sphere equivalent diameter, the Stokes diameter, the light scattering diameter, etc.

[0018] In order to specify the particle size of the particle group of the abrasive grains 3, the most frequent particle size (i.e., the mode diameter), the particle size when the cumulative frequency reaches 50% of the whole (i.e., the median diameter. D 50 is sometimes expressed as such.), the arithmetic mean diameter in terms of weight, area, volume, etc. is used.

[0019] On the surface 3a of the abrasive grains 3 of the present embodiment, a predetermined functional group capable of coordinating with metal ions to form a chelate complex (metal complex) 9 (see FIG. 2) is provided. For example, by immersing the powdery abrasive grains 3 in a liquid coupling agent and performing a surface treatment on the abrasive grains 3, the surface 3a is modified with a predetermined functional group.

[0020] In the present embodiment, a silane coupling agent is used as the coupling agent. As the silane coupling agent, for example, a benzotriazole group-containing silane coupling agent is used.

[0021] Examples of the benzotriazole group-containing silane coupling agent are shown in Chemical Formula 1 or Chemical Formula 2. In Chemical Formula 1 and Chemical Formula 2, R means an alkyl group having a predetermined number of carbon atoms. In Chemical Formula 1, Me means a methyl group, and in Chemical Formula 2, Et means an ethyl group.

[0022]

Chemical Formula

[0023]

Chemical Formula

[0024] On the surface 3a of the abrasive grains 3 formed of silica, ceria, GC, WA, etc., a hydroxyl group (OH group) exists. By reacting this hydroxyl group with the coupling agent (such as hydrogen bonding, dehydration condensation, etc.), as shown in FIG. 1, a benzotriazole (benzotriazole, hereinafter abbreviated as Bt) group 5 can be provided on the surface 3a.

[0025] For example, when abrasive grains 3 are immersed in a liquid Bt group-containing silane coupling agent containing Bt groups 5, alkoxy groups such as MeO and EtO become silanol groups by hydrolysis and form hydrogen bonds with the hydroxyl groups on the surface 3a.

[0026] Furthermore, dehydration condensation may occur, and the oxygen of the silanol group may bind to the surface 3a of the abrasive grains 3. In FIG. 1, a state where the oxygen of the silanol group is bound to the surface 3a of the abrasive grains 3 is shown, but the Bt groups 5 may be bound to the surface 3a by hydrogen bonds.

[0027] In FIG. 1, for the sake of convenience, a case where three Bt groups 5 are provided on the surface 3a of the abrasive grains 3 is shown, but in reality, a large number of Bt groups 5 are provided substantially uniformly on the surface 3a. The Bt groups 5 can coordinate with metal ions (for example, monovalent or divalent copper ions).

[0028] FIG. 2 is a schematic diagram of a chelate complex 9 formed by the coordination of two abrasive grains 3 with copper ions. At least two Bt groups 5 coordinate with metal ions to form a chelate complex 9. In this way, the polishing liquid 1 having a plurality of abrasive grains 3 has a chelating action on metal ions.

[0029] Therefore, after polishing using the polishing liquid 1, if the abrasive grains 3 in the used polishing liquid 1 (that is, the waste liquid) are recovered, the metal ions contained in the waste liquid can be recovered, so that the metal ions can be recovered more easily than in the case of evaporating the waste liquid.

[0030] By the way, in addition to the abrasive grains 3, the polishing liquid 1 further contains a liquid 7 such as pure water and an alkaline component that contributes to the chemical reaction with the workpiece 11. As the alkaline component, for example, organic alkalis such as ammonia and amines are used. Further, the polishing liquid 1 may further have additives such as a pH adjuster, a viscosity adjuster, a rust inhibitor, and a preservative.

[0031] (Experimental Example 1) Next, an experiment to confirm whether the abrasive grains 3 and metal ions form the chelate complex 9 will be described. As the abrasive grains 3, silica abrasive grains (D 50 = 10 nm) with the product name ST-30 sold by Nissan Chemical Industries, Ltd. were used, and as the silane coupling agent, the product name X-12-1214A sold by Shin-Etsu Chemical Co., Ltd. was used.

[0032] After a stirring step of mixing 30 g of the abrasive grains 3, 1 wt% of the silane coupling agent for the abrasive grains 3, and pure water and stirring with a glass stirring rod for 1 minute, it was left standing for about 8 hours.

[0033] To this polishing liquid 1, 0.5 g of an aqueous copper sulfate solution containing 0.5 wt% of Cu 2+ (divalent copper ions) was dropped and stirred, and then left standing for 1 hour.

[0034] Figure 3 is a diagram showing the experimental results confirming that a plurality of abrasive grains 3 form the chelate complex 9 with copper ions. The median diameter (D 50 ) of the abrasive grains 3 was measured by the laser diffraction / scattering method using a particle size distribution measuring device of Microtrac Bell Co., Ltd.

[0035] The broken-line graph in Figure 3 shows the particle size distribution of the abrasive grains 3 before adding the aqueous copper sulfate solution to the polishing liquid 1. Before adding the aqueous copper sulfate solution, the median diameter (D 50 ) of the abrasive grains 3 was 14 nm. This is considered to indicate that the abrasive grains 3 are mainly free alone in the polishing liquid 1 (i.e., in the state of primary particles).

[0036] The solid-line graph in Figure 3 shows the particle size distribution of the abrasive grains 3 after adding the aqueous copper sulfate solution to the polishing liquid 1 and leaving it standing for 1 hour. After adding the aqueous copper sulfate solution, the D 50 of the abrasive grains 3 became 26 nm. This is considered to indicate that, as shown in Figure 2, mainly two abrasive grains 3 and copper ions formed the chelate complex 9 and became secondary particles.

[0037] (Experimental Example 2) As the abrasive grains 3, silica abrasive grains (D 50 = 100 nm) with the product name ST-30 sold by Nissan Chemical Industries, Ltd. were used. Similarly, an experiment was conducted to determine whether the abrasive grains 3 form the chelate complex 9 using the above-mentioned X-12-1214A as the silane coupling agent.

[0038] In Experimental Example 2, 30 g of the abrasive grains 3, 1 wt% of the silane coupling agent for the abrasive grains 3, and pure water were mixed, and after a stirring step of stirring for 1 minute, the mixture was left standing for about 8 hours. Then, 0.5 g of an aqueous copper sulfate solution was dropped in and stirred, and the mixture was left standing for 1 hour.

[0039] In Experimental Example 2, a transparent supernatant was formed, and the bluish abrasive grains 3 precipitated. This is considered to suggest that the abrasive grains 3 formed a chelate complex 9 with copper ions and became secondary particles.

[0040] By the way, in the above-described embodiments and experimental examples, a Bt group-containing silane coupling agent was used. However, instead of this, a polyamine-containing silane coupling agent capable of coordinating with copper ions can also be used.

[0041] As the polyamine-containing silane coupling agent, for example, N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane with the product name KBM-602 sold by Shin-Etsu Chemical Co., Ltd. can be used.

[0042] Also, for example, N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane with the product name KBM-603 sold by the same company can be used. In either case, the predetermined functional group capable of forming the chelate complex 9 (see Figure 2) is a polyamine.

[0043] Incidentally, the above-mentioned Bt group-containing silane coupling agent and polyamine-containing silane coupling agent can also coordinate with monovalent copper ions to form a metal complex. Further, the Bt group 5 is not limited to the above structure, and it is considered that similar results can be obtained with its tautomers. As for the coupling agent, it is considered that the larger the number of NH groups, the easier it is to form a metal complex.

[0044] Next, a polishing method for polishing the workpiece 11 using the polishing liquid 1 and the polishing apparatus 2 will be described. FIG. 4 is a cross-sectional view showing an outline of the polishing apparatus 2. Note that the Z-axis direction in FIG. 4 is substantially parallel to the vertical direction. The polishing apparatus 2 has a disk-shaped chuck table 4.

[0045] The output shaft of a rotary drive source (not shown) such as a motor is connected to the lower part of the chuck table 4. The output shaft is arranged substantially parallel to the Z-axis direction, and when the rotary drive source is operated, the chuck table 4 rotates in a predetermined direction around the rotation axis.

[0046] The chuck table 4 has a disk-shaped frame 6 made of a metal such as stainless steel. A disk-shaped recess is formed in the upper part of the frame 6, and a disk-shaped porous plate 8 made of porous ceramics or the like is fixed in this recess.

[0047] The upper surface of the porous plate 8 and the upper surface of the frame 6 are flush with each other, forming a substantially flat holding surface 4a. The porous plate 8 is connected to a suction source (not shown) such as an ejector via flow paths 6a and 6b formed in the frame 6. When the suction source is operated, a negative pressure is transmitted to the upper surface of the porous plate 8.

[0048] The workpiece 11 is placed on the holding surface 4a. The workpiece 11 shown in FIG. 4 is a disk-shaped bare wafer made of silicon, but the workpiece 11 may be made of a compound semiconductor such as silicon carbide (SiC) or gallium nitride (GaN).

[0049] On the surface 11a side of the workpiece 11, a circular protective member 13 made of resin is attached to prevent contamination, impact, etc. The workpiece 11 is placed on the holding surface 4a so that the back surface 11b located on the side opposite to the surface 11a faces upward.

[0050] The workpiece 11 is sucked and held by the negative pressure generated on the holding surface 4a via the protective member 13. Above the holding surface 4a, a polishing unit 10 is arranged. The polishing unit 10 has a cylindrical spindle housing (not shown).

[0051] A Z-axis direction moving unit (not shown) for moving the polishing unit 10 up and down along the Z-axis direction is connected to the spindle housing. Inside the spindle housing, a cylindrical spindle 12 is rotatably accommodated.

[0052] The longitudinal direction of the spindle 12 is arranged substantially parallel to the Z-axis direction. At the upper end of the spindle 12, a rotation drive source (not shown) such as a servo motor for rotating the spindle 12 is provided.

[0053] At the lower end of the spindle 12, the center of the upper surface of a disc-shaped mount 14 is connected. The mount 14 has a diameter larger than that of the workpiece 11. A disc-shaped polishing tool 16 having substantially the same diameter as the mount 14 is attached to the lower surface of the mount 14.

[0054] The polishing tool 16 has a disc-shaped base 18 connected to the lower surface of the mount 14. The base 18 is formed of a metal such as stainless steel. A polishing pad 20 having substantially the same diameter as the base 18 and not containing abrasive grains 3 is fixed to the lower surface of the base 18.

[0055] The polishing pad 20 is composed of, for example, a rigid foam resin such as urethane resin or epoxy resin, or a non-woven fabric. The radial center positions of the polishing pad 20, the base 18, the mount 14, and the spindle 12 substantially coincide, and a cylindrical through hole 22 is formed so as to pass through these center positions.

[0056] At the upper end of the through hole 22, a pipe (not shown) of the polishing liquid supply source 26 is connected. The polishing liquid supply source 26 includes a liquid feed pump (not shown), a storage tank (not shown) of the polishing liquid 1, and the like. The polishing liquid supply source 26 supplies the polishing liquid 1 to the polishing pad 20 through the through hole 22.

[0057] FIG. 5 is a flowchart of a polishing method for polishing at least the back surface (one surface) 11b of the workpiece 11 using the polishing liquid 1 and the polishing apparatus 2. When polishing the back surface 11b, first, the surface 11a side of the workpiece 11 is sucked and held by the holding surface 4a (holding step S10).

[0058] After the holding step S10, a polishing step S20 is performed. In the polishing step S20, the chuck table 4 is rotated in a predetermined direction, and the spindle 12 is rotated in a predetermined direction. While supplying the polishing liquid 1 from the polishing liquid supply source 26 to the polishing pad 20 and pressing the polishing pad 20 downward with a predetermined pressure, the back surface 11b side is polished by chemical and mechanical actions.

[0059] In addition to the back surface 11b side, the front surface 11a side may be polished. In this case, the protective member 13 is peeled off from the front surface 11a side, the protective member 13 is attached to the back surface 11b side, and similarly, through the holding step S10 and the polishing step S20, the front surface 11a side is polished. However, when devices such as ICs and LSIs are formed on the front surface 11a side, only the back surface 11b side is polished.

[0060] After the polishing step S20, the used polishing liquid 1 is recovered by a waste liquid recovery mechanism (not shown). The waste liquid recovery mechanism has a waste liquid receiving portion. The waste liquid receiving portion is connected to a storage tank through a predetermined pipe. When a flocculant is added to this storage tank, the abrasive grains 3 in the waste liquid settle. Next, the abrasive grains 3 are recovered through a filter paper or the like.

[0061] As described above, functional groups capable of coordinating with metal ions are provided on the surface 3a of the abrasive grains 3. Therefore, if the abrasive grains 3 in the waste liquid are recovered, the metal ions contained in the waste liquid can be recovered, so that the metal ions can be recovered more easily than in the case of evaporating the waste liquid.

[0062] In addition, the structures, methods, etc. according to the above embodiments can be appropriately modified and implemented without departing from the scope of the object of the present invention. Note that it is not limited to copper ions, and metal cations such as iron ions (Fe 3+ ), zinc ions (Zn 2+ ) are also considered to be recoverable by the above-described abrasive grains 3.

Explanation of Reference Numerals

[0063] 1: Polishing liquid, 3: Abrasive grains, 3a: Surface, 5: Bt group (functional group), 7: Liquid 9: Chelate complex, 11: Workpiece, 11a: Surface, 11b: Back surface, 13: Protective member 2: Polishing apparatus, 4: Chuck table, 4a: Holding surface, 6: Frame body, 6a, 6b: Flow paths 8: Porous plate, 10: Polishing unit, 12: Spindle, 14: Mount, 16: Polishing tool, 18: Base, 20: Polishing pad, 22: Through hole, 26: Polishing liquid supply source

Claims

【Claim 1】 A polishing method for polishing at least one surface of a workpiece using a polishing pad, comprising: a holding step of holding the workpiece on a holding surface of a chuck table; a polishing step of polishing the one surface side with the polishing pad while supplying a polishing liquid containing abrasive grains having a functional group capable of coordinating with metal ions to form a metal complex to the polishing pad; the abrasive grains are made of silicon oxide, cerium oxide, green silicon carbide, or white alumina; the workpiece is a bare wafer formed of silicon or a compound semiconductor. The polishing method is characterized by this.

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