JP2002141311A - Wafer polishing method and wafer washing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer polishing method which prevents contamination caused by polishing agent and reduces nanotopography, and a wafer washing method which removes a protection film from a polished wafer readily. SOLUTION: In a method for polishing a wafer by holding one surface of a wafer by evacuation to a holding table while adding polishing agent with the other surface of a wafer held to a polishing cloth, the other surface of a wafer is polished with a wafer. A protection film of a plurality of layer is formed in one surface and held by a holding table. A first protection film which absorbs irregularities of one surface of a wafer is formed in a side in contact with a wafer in a protection film of a plurality of layers, and a second protection film with etching resistance to polishing agent is formed in a side held by a holding table. A wafer polished by the wafer polishing method is immersed in alkaline solution, isopropyl alcohol and alkaline solution in this order and a protection film of a plurality of layers formed in a wafer is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor wafer,
The present invention relates to a method for polishing a wafer or the like made of quartz or ceramic material (hereinafter simply referred to as a wafer) and a method for cleaning a wafer.

[0002]

2. Description of the Related Art In a polishing process of a wafer as a workpiece to be polished, rigid materials such as glass, metal,
A plate made of ceramics or the like is used as a holding board, and a wafer is attached to the surface of the holding board with an adhesive such as wax, or a vacuum-absorbing material is used on the surface of a holding board having a porous material or a large number of through holes on the surface. A method of holding and polishing a wafer has been used. The wafer holding surface of this holding plate is polished to make the surface flat.

[0003] When the wafer is held on such a holding plate, the applicant of the present invention does not stain or etch the surface (back surface) of the wafer held by the holding plate during polishing. Forming and polishing,
This is proposed in a prior patent application filed by the present applicant (Japanese Patent Application No. 11-123653). As this protective film, polyvinyl butyral (PVB) resin is used as a protective film which has etching resistance to a polishing agent, has good adhesiveness to a wafer, and is easy to peel off after polishing.
When the PVB resin is used, the wafer is not contaminated or excessively etched.

[0004]

By the way, there is a undulation of about 0.1 μm on the back surface of the wafer. The wafer holding surface of the holding plate is flattened by polishing, but has a undulation of about 0.2 μm. When the wafer is held and polished on the holding plate, the undulations of the wafer holding surface and the back surface of the wafer are transferred to the polished surface of the wafer.

In recent years, in a semiconductor device manufacturing process, a metal wiring is formed on a wafer, an insulating film is formed thereon, and the insulating film is chemically and mechanically polished (Chemical Mechanical Polishing).
When a metal oxide film and a second metal wiring are further formed thereon by flattening by lishing (CMP), undulations (irregularities) in a minute area called nanotopography existing on the polished surface of the wafer described above. Has become a problem.
Nanotopography (also referred to as nanotopology) refers to a wavelength of about 0.1 mm to 20 mm and an amplitude of several nm to 1 nm.
It means irregularities of about 00 nm. The evaluation method is a square of 0.1 mm to 10 mm on a side or 0.1 mm in diameter.
mm to 10 mm circular block range (Window Si
In a region called ze or the like), a height difference (PV value: Peak to Valley) of unevenness on the wafer surface is evaluated. PV
The value is also called Nanotopography Height or the like. In particular,
It is desired that the maximum value of the unevenness existing in the evaluated wafer surface is small.

When a wafer is polished while protecting the wafer with PVB resin, the thickness of the PVB protective film is usually thinner and harder than the undulation on the back surface of the wafer and the undulation on the surface of the holding plate. Can not. on the other hand,
When the wafer is affixed to the holding plate via wax and polished, the thickness of the applied wax is usually about 1 μm and is softer than PVB resin, so that the undulation on the back surface of the wafer and the undulation on the holding plate surface can be absorbed. . However, when the wafer is held by vacuum suction, the wax has a low etching resistance to the abrasive, so that the wax melts during polishing and the abrasive is easily sucked between the wafer and the holding plate and easily broken. There is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of polishing a wafer which prevents contamination by an abrasive and reduces nanotopography. Another object of the present invention is to provide a wafer cleaning method for easily removing a protective film from a polished wafer.

[0008]

In order to solve the above-mentioned problems, a polishing method according to the present invention comprises holding one surface of a wafer on a holding plate by vacuum suction, and pressing the other surface of the wafer against a polishing cloth. In a polishing method of polishing while adding a polishing agent, a polishing step of holding a wafer having a plurality of protective films formed on one surface of the wafer by a holding plate and polishing the other surface of the wafer. A first protective film that absorbs irregularities on one surface of the wafer is formed on a side of the plurality of protective films that comes into contact with the wafer; A second protective film having a property is formed.

According to this polishing method, the first protective film for absorbing the unevenness on one surface (back surface) of the wafer is formed, so that the transfer of the unevenness on the back surface of the wafer can be prevented, and the nanotopography of the polished surface of the wafer can be improved. Reduce. Further, since the second protective film having etching resistance to the abrasive is formed on the side held by the holding plate, the first protective film is protected from the abrasive, and the first protective film during polishing is prevented from peeling off. Can be suppressed,
The wafer backside is protected. Further, since the second protective film is not eroded by the abrasive, the back surface of the wafer becomes dirty,
The wafer can be polished without being etched.

The first protective film is typically a wax used for attaching a wafer, for example, a rosin-based liquid adhesive, but is not limited thereto. Any other material can be used as long as it can absorb the size of. Furthermore, as long as it can absorb the size of foreign matter or the like mixed between the holding plate and the wafer in the polishing step, dents and distortion of the polished surface can be reduced. Also, the second
As the protective film, polyvinyl acetal resin PVB
Examples include, but are not limited to, resins. For example, an acrylic resin or the like that has etching resistance to the abrasive and can protect the first protective film from the abrasive may be used.

It is preferable that the first protective film is soft, and the second protective film is harder than the first protective film. In particular, it is preferable that the first protective film is soft enough to absorb the size of irregularities on the surface of the holding plate, through holes, the back surface of the wafer, foreign matter, and the like.

Further, it is preferable that the first protective film has good adhesiveness to the wafer, and the second protective film has good adhesiveness to the first protective film. In this case, it is possible to prevent the abrasive from entering the gap between the protective films and between the protective film and the wafer and to prevent the protective film from being broken, thereby preventing the back surface of the wafer from being stained and polishing the wafer. Therefore, contamination of the wafer can be reduced. Further, it is preferable that the first protective film be easily peeled off after polishing.

The first protective film has a thickness of 0.1 μm or more and 10 μm or more.
It is preferably not more than μm. If the thickness is less than 0.1 μm, the irregularities on the back of the wafer cannot be absorbed and
If it is thicker, the flatness of the polished wafer will deteriorate,
This is because cleaning takes time.

On the other hand, when the second protective film is formed of a polyvinyl butyral resin, the thickness is preferably 0.01 μm or more and 1 μm or less. This is 0.01μ
If the thickness is smaller than m, the film may be peeled off during polishing. If the thickness is larger than 1 μm, cleaning after polishing requires a long time.

A method for cleaning a wafer according to the present invention is a method for cleaning a wafer polished by the above-described method for polishing a wafer, wherein the first method comprises immersing the wafer in an alkaline solution.
A second step of immersing the wafer in isopropyl alcohol and a third step of immersing the wafer in an alkaline solution
And removing a plurality of protective films formed on the wafer. According to this cleaning method, a plurality of protective films can be easily removed from the wafer simply by immersing the wafer in the cleaning liquid. A typical example of the alkaline solution is a mixture of aqueous ammonia and aqueous hydrogen peroxide.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a wafer polishing method and a wafer cleaning method according to the present invention will be described with reference to the drawings, but various modifications are possible without departing from the technical idea of the present invention. Needless to say. FIG. 1 is a schematic configuration diagram of a wafer polishing apparatus for carrying out a polishing method according to the present invention. FIGS. 2 and 3 show steps of a wafer processing method according to the present invention. FIG. FIG. 3 is a process block diagram. The polishing apparatus 10 holds one surface (back surface) of the wafer W on a holding plate 11 by vacuum suction, and presses the other surface of the wafer W against a polishing cloth 13 stuck on a rotary platen 12 to perform polishing. Polishing is performed while an abrasive 15 is added from the agent supply device 14. A large number of through holes 16 (FIG. 2) for holding the wafer W under vacuum in the holding plate 11
Is formed, and the wafer holding surface is polished in advance.

As shown in FIG. 2, on the back surface of the wafer W,
A first protection film 21 is formed, and a second protection film 22 is formed so as to cover the first protection film 21. First protective film 2
As 1, the alkali resistance may be weak, and a wax for bonding a wafer is used. The thickness of the first protective film 21 is 0.1 μm or more and 10 μm or less. The reason why the thickness is set to 0.1 μm or more is to absorb irregularities of about 0.1 μm on the back surface of the wafer W, and the thickness is set to 10 μm or less to prevent deterioration of the flatness of the polished surface of the wafer W and to clean the wafer W. This is to reduce the time. In addition, the surface of the holding plate 11 has a 0.
Preferably, the thickness of the first protective film 21 is 0.3 μm or more and 2 μm or less in order to absorb irregularities of about 2 μm, to prevent deterioration of the flatness of the polished surface of the wafer W, and to shorten the cleaning time.

As the second protective film 22, the first protective film 21
A material having a higher hardness and a higher alkali resistance is used. This is because the polishing agent 15 usually has a pH of 10 to 11. As the second protective film 22, PVB resin is used. The polymerization degree of the PVB resin is preferably about 300 to 1,000. The second protective film 22 has a thickness of 0.01
The thickness is set to not less than 1 μm and preferably not less than 0.1 μm and not more than 0.3 μm. If the thickness is too thin, the peeling of the second protective film 22 during polishing cannot be prevented. If the thickness is too thick, the cleaning time after polishing becomes long. In order to prevent the first protective film 21 from being destroyed during polishing, it is preferable to completely cover the first protective film 21 with the second protective film 22.

In a state where the second protective film 22 side is vacuum-sucked to the holding plate 11 and the wafer W is held on the holding plate 11,
The other surface of the wafer W is polished on one side using the polishing apparatus 10 shown in FIG.

By interposing the soft first protective film 21 between the wafer holding surface of the holding plate 11 and the wafer W, the surface of the holding plate 11, the through holes 16, the back surface of the wafer W, transfer of irregularities such as foreign matter, etc. And the nanotopography and dents on the polished surface of the wafer W are reduced. Also, only the soft first protective film 21 made of wax or the like is easily peeled off by the abrasive 15, but it has alkali resistance and hard PVB.
By protecting the wafer W so as to cover the first protective film 21 with the resin, the first protective film 21 and the second protective film 22 are not peeled off, and the back surface of the wafer W is not stained or etched. Can be polished.

Next, a method of processing the wafer W will be described.
First, in the protective film forming step (a), a soft first protective film 21 is formed on the back surface of the wafer W (a-1). The first protective film 21 is formed by applying a liquid wax 23 by a spin coating means 24, rotating the wafer W, applying the wax to the entire back surface of the wafer, and performing a heat treatment at a temperature of 50 ° C. to 200 ° C. for 30 seconds to 720 seconds. Is formed. Then, a second protective film 22 of PVB resin, which is a hard synthetic resin, is formed on the first protective film 21 so as to cover the first protective film 21 (a-2). This second protective film 22 is made of P
The VB resin was converted to IPA (PVB resin concentration 0.2% by mass to 5.
0 mass%), and spin-coating means 2
6, the solution is dropped on the first protective film 21, the wafer W is rotated and applied, and the temperature is 50 ° C. to 200 ° C. for 30 seconds to
It is formed by performing a heat treatment for 720 seconds.

The wafer W on which the two protective films 21 and 22 are formed on the back surface is polished by the polishing apparatus 10 in the wafer polishing step (b). At this time, a vacuum is generated by a vacuum device (not shown) connected from the through hole 16 through the vacuum path 19, and the back surface of the wafer W is held on the holding plate 1
The wafer W is held on the wafer holding surface 1 by vacuum suction, and the wafer W is pressed against the polishing pad 13 with a predetermined load. Rotating shaft 17
, And the holding plate 11 rotates about a rotation shaft 18. Then, the abrasive supply device 14
The wafer W is polished by rotating the wafer W while supplying the polishing agent 15 between the wafer W and the polishing pad 13.

Thereafter, the first protective film 21 and the second protective film 22 are removed from the wafer W in a wafer cleaning step (c). First, the wafer W is placed in a cleaning tank 30 of ammonia water + hydrogen peroxide at a temperature of 50 ° C. to 90 ° C. for 30 seconds.
Immerse for 600 seconds (c-1). Next, the wafer W is placed in a cleaning tank 31 of isopropyl alcohol (IPA) at 20 ° C.
Dipping at a temperature of 〜50 ° C. for 30 seconds to 600 seconds (c-
2). And a washing tank 3 of ammonia water + hydrogen peroxide water
2 is immersed at a temperature of 50C to 90C for 30 seconds to 600 seconds (c-3). At this time, the first protective film 21 is removed from the wafer W.
And the second protective film 22 is removed. Thereafter, the wafer W is immersed in the pure water rinsing bath 34 (c-4). Finally, the wafer W is dried (c-5).

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first protective film 21 made of a soft material is composed of a wax (a rosin-based liquid adhesive) and a second protective film 2 made of a hard material.
For 2, PVB resin (polymerization degree: 1000, butyralization degree: 71 mol%) was used. In the protective film forming step (a), the liquid W is dripped onto the back surface of the wafer W by the spin coating means 24 without rotating the wafer W at a room temperature of 24 ° C.
The wax 23 was spread over the entire back surface of the wafer W while being rotated at rpm. Then, the rotation of the wafer W is stopped and 1
After heat treatment at 00 ° C., it is cooled at 24 ° C.
A first protective film 21 having a thickness of μm was formed.

Next, while rotating the wafer W at 500 rpm at a room temperature of 24 ° C., the PVB resin
(25% PVB resin concentration)
Is dropped by the spin coating means 26, and the first solution is added to the solution 25 while rotating the wafer W at 1800 rpm.
The protective film 21 was spread so as to be covered. And wafer W
After stopping the rotation and performing a heat treatment at 150 ° C. for 60 seconds,
After cooling at 24 ° C., a second protective film 22 having a thickness of 0.2 μm was formed.

After protecting the wafer W in this manner, in the wafer polishing step (b), the single-side polishing apparatus shown in FIG.
Uba600, polishing pressure 300 g / cm ² , p
Polishing cloth 1 with colloidal silica abrasive 15 of H = 10.5
The wafer W was polished for 15 minutes while being supplied onto the wafer No. 3.

After the polishing, in the wafer cleaning step (c), the wafer W is first immersed in a rinsing bath at 24 ° C. for 5 minutes.
Ammonia water + hydrogen peroxide water (28 mass% ammonia water: 30 mass% hydrogen peroxide water: water = 0.1: 1: 10)
Was immersed in the washing tank 30 at 80 ° C. for 5 minutes. Next, after immersing the wafer W in a rinsing bath at 24 ° C. for 5 minutes, the IPA (9
(9.9% by mass) in the washing tank 31 at 24 ° C. for 5 minutes. Thereafter, the wafer W is immersed in a rinsing bath at 24 ° C. for 5 minutes, and then ammonia water + hydrogen peroxide solution (28% by mass ammonia water: 30% by mass hydrogen peroxide solution: water = 1: 1: 1)
It was immersed in the washing tank 32 of 0) at 80 ° C. for 5 minutes. And
After being immersed in a pure water rinsing tank 33 at 24 ° C. for 5 minutes, it was dried. The nanotopography of the wafer polished and washed in this manner is measured using a nanotopography measuring device (ADE, manufactured by W
(IS-CR83-SQM), and etching and contamination with an abrasive were evaluated.

Also, as Comparative Example 1, except that the wafer was protected by a single-layer PVB resin protective film having a thickness of 0.2 μm.
The wafer polished under the same conditions as in the example and from which the protective film was removed was evaluated in the same manner as in the example. Further, as Comparative Example 2,
The wafer was polished under the same conditions as in the example except that the wafer was protected with a single-layer wax protective film having a thickness of 1 μm, and the wafer from which the protective film was removed was evaluated in the same manner as the example.

Table 1 shows the measurement results of the nanotopography of each wafer of Example, Comparative Example 1 and Comparative Example 2. The measurement of the nanotopography is made by measuring the side of the wafer by 0.5
The area was divided into square block areas (Window Size) of mm, 2.0 mm, and 10.0 mm, and the PV value (Nanotopography Height) was evaluated in each area. Then, the maximum value of Nanotopography Height existing in the evaluated wafer surface was obtained.

[0030]

[Table 1]

From Table 1, it can be seen that for any Window Size,
It can be seen that, compared to Comparative Examples 1 and 2, the nanotopography of the example protected by the two protective films was reduced. Neither the etching nor the contamination by the abrasive was confirmed in either the embodiment or the comparative example 1. However, in the comparative example 2 protected by the single-layer protective film made of only wax, the protective film was almost completely dissolved during polishing. The defective rate of back surface stain was almost 100%. In the case of Comparative Example 2, since the wax protective film was melted, the irregularities on the back surface of the wafer and the irregularities on the surface of the holding plate were transferred to the polished surface, and the nanotopography deteriorated as well as Comparative Example 1 protected by the PVB resin protective film. .

As described above, even if a single layer of protective film is made of an optimum material, especially an optimum hardness, it is possible to protect the layer as it is. However, the transfer of the shape of the holding plate and the etching with an abrasive are possible. In order to prevent simultaneously, by forming a protective film of two or more layers and changing its hardness and etching resistance, it is possible to more easily and almost completely eliminate stains and etching due to transfer and abrasives, It is possible to reduce the nanotopography, the dent defect, and the contamination defect of the wafer.

[0033]

According to the method for polishing a wafer according to the present invention, the first protective film for absorbing the unevenness on the back surface of the wafer is formed, so that the transfer of the unevenness on the back surface of the wafer can be prevented, and the nanotopography of the polished surface of the wafer can be prevented. Is reduced. Further, since the second protective film having etching resistance to the abrasive is formed on the side held by the holding plate, the second protective film is not eroded by the abrasive, and the first protective film is protected from the abrasive. Thus, peeling of the first protective film during polishing can be suppressed, and the back surface of the wafer is protected. Therefore, contamination defects on the back surface of the wafer are reduced.

According to the wafer cleaning method of the present invention, a plurality of protective films can be easily removed from a wafer simply by immersing the wafer in a cleaning solution.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a wafer polishing apparatus for performing a polishing method according to the present invention.

FIG. 2 is a schematic diagram illustrating the steps of a wafer processing method according to the present invention.

FIG. 3 is a process block diagram of a wafer processing method according to the present invention.

[Explanation of symbols]

 W wafer 10 single-side polishing apparatus 11 holding plate 13 polishing cloth 15 abrasive 16 through hole 21 first protective film 22 second protective film 23 wax 24, 26 spin coating means 25 solution 30 ammonia + hydrogen peroxide cleaning tank 31 IPA cleaning Tank 32 Ammonia + hydrogen peroxide water washing tank 33 Pure water rinse tank

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B24B 37/04 B24B 37/04 H H01L 21/306 H01L 21/306 M

Claims (6)

[Claims] In a polishing method, one surface of a wafer is held on a holding plate by vacuum suction, and the other surface of the wafer is pressed against a polishing cloth and polished while adding an abrasive. Holding a wafer having a plurality of protective films formed on a surface thereof by a holding plate, and having a polishing step of polishing the other surface of the wafer, of the plurality of protective films, A first protective film for absorbing irregularities on one surface of the wafer is formed, and a second protective film having etching resistance to the abrasive is formed on the side held by the holding plate; Polishing method. 2. The method according to claim 1, wherein the first protective film is soft and the second protective film is soft.
The method according to claim 1, wherein the protective film is harder than the first protective film. 3. The first protective film has good adhesion to a wafer, is easy to peel off after polishing, and
The wafer polishing method according to claim 1, wherein the protective film has good adhesion to the first protective film. 4. The method according to claim 1, wherein the first protective film has a thickness of 0.1 μm or more and 10 μm or less.
The method for polishing a wafer according to any one of the above. 5. The second protective film is formed of a polyvinyl butyral resin, and has a thickness of 0.01 μm or more and 1 μm or more.
The method for polishing a wafer according to claim 1, wherein: 6. A method for cleaning a wafer polished by the method for polishing a wafer according to claim 5, comprising: a first step of immersing the wafer in an alkaline solution; and a second step of immersing the wafer in isopropyl alcohol. A third step of immersing the wafer in an alkaline solution, and removing a plurality of protective films formed on the wafer.