JP2004075859A - Method for cleaning polishing slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a cleaning method for cleaning polishing slurry such as CMP (Chemical Mechanical Polishing) slurry by efficiently removing a metal ion from the polishing slurry, preventing metal contamination of semiconductor wafers, etc., as much as possible or further capable of recycling the polishing slurry without hindrance. <P>SOLUTION: The method for cleaning the polishing slurry comprises efficiently capturing an ion of a metal such as iron, aluminum, copper, nickel, zinc, chromium, molybdenum or tungsten existing in the polishing slurry and removing the metal ion by using a chelate-forming fiber obtained by introducing a functional group having a metal chelate-forming ability into a fiber molecule and adding the fiber to the polishing slurry. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention uses a chelate-forming fiber having a chelate-forming functional group introduced into a fiber molecule, and uses, for example, a trace amount of metal ions, for example, iron contained in a CMP (Chemical Mechanical Polishing) slurry for polishing a semiconductor wafer. The present invention relates to a method for efficiently capturing and removing aluminum, copper, nickel, zinc, chromium, molybdenum, tungsten, and the like for cleaning.
[0002]
According to this cleaning method, the polishing slurry can be easily and efficiently cleaned. Therefore, the cleaned polishing slurry can be used without hindrance to polishing of, for example, highly integrated semiconductor wafers which remarkably dislike metal ion adhesion. In addition, the used polishing slurry can be cleaned and recycled.
[0003]
[Prior art]
2. Description of the Related Art In recent years, as the speeding up of computers has rapidly progressed, semiconductor integrated circuits (ICs) used have been further highly integrated. In order to adapt to such high integration of ICs, it is necessary to miniaturize wiring patterns and adopt a multilayer laminated structure. Chemical mechanical polishing (CMP) is widely used as a technique for further flattening each layer in order to realize multi-layering.
[0004]
CMP is generally performed by polishing the surface of a semiconductor wafer mounted on a carrier while supplying polishing slurry to a rotating polishing pad. The polishing slurry used here is obtained by dispersing an abrasive in a solution, and an acidic or alkaline solution is used for chemically etching a metal layer or an oxide film layer.
[0005]
Examples of the abrasive used include colloidal silica, fumed silica, fumed alumina, precipitated alumina, and the like. The abrasive slurry contains trace amounts of Fe, Al, Cu, and Ni derived from these abrasives. May be contained. When a silicon wafer or the like is polished using a polishing slurry containing these impure metal ions, for example, the metal ions are easily diffused into silicon, so that the polished wafer is contaminated with the impure metal ions.
[0006]
On the other hand, used polishing slurries have heretofore been thrown away because of the higher impurity metal ion content. However, recently, there has been an attempt to recycle used polishing slurries in response to demands for reduction of polishing agent cost and reduction of drainage.
[0007]
However, when the polishing slurry is recycled, ions eluted from the metal to be polished (such as tungsten) or metal ions such as Zn, Cr, and Mo mixed as contamination from the polishing apparatus are mixed into the polishing slurry. Therefore, these metal ions contaminate the semiconductor wafer. Therefore, a method of removing trace metal ions in the polishing slurry, cleaning the slurry, and reusing the polishing slurry has been studied.
[0008]
As one of such cleaning methods, there is a method of capturing and removing metal ions using an ion exchange resin or a chelate resin. This method has an advantage that metal ions can be relatively easily removed, but on the other hand, those resins are porous bead-like resins based on a polymer containing, for example, polyvinylstyrene as a monomer component. Therefore, the diffusion rate of metal ions into the resin is low, and it is difficult to obtain a satisfactory processing efficiency. In addition, since the abrasive in the polishing slurry is taken in the form of being physically adsorbed in the porous substrate, the effective surface area for capturing metal ions decreases rapidly with the progress of the cleaning treatment, and the processing efficiency is reduced within a short time. Lost.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to efficiently clean a polishing slurry such as a CMP slurry by a simple method and to reduce metal contamination of a semiconductor wafer as much as possible. It is another object of the present invention to provide a cleaning method which can prevent the polishing slurry from being recycled and can use the polishing slurry without any trouble.
[0010]
[Means for Solving the Problems]
The method for cleaning a polishing slurry according to the present invention, which can solve the above-described problems, uses a chelating fiber in which a functional group having a metal chelate forming ability is introduced into a fiber molecule, and is present in the polishing slurry. It has a gist in capturing and removing metal ions.
[0011]
As the functional group having a metal chelate forming ability in the present invention, an aminopolycarboxylic acid group or a phosphoric acid group, or at least a part of an acid type functional group composed of an aminopolycarboxylic acid group or a phosphoric acid group is an alkali metal salt. Alternatively, an ammonium salt is preferable, and an aminopolyol group is also one of the preferable chelate-forming functional groups.
[0012]
More specific examples of the functional group capable of forming a metal chelate include iminodiacetic acid group, nitrilotriacetic acid group, ethylenediaminetriacetic acid group, ethylenediaminetetraacetic acid group, diethylenetriaminepentaacetic acid group, ethylenediamine disuccinic acid group, and glutamic acid. Examples thereof include a diacetate group, an N-methyl-D-glucamine group, and a D-glucamine group, each of which may be only one type introduced into a fiber molecule serving as a base material, or two or more types. A plurality of types may be introduced.
[0013]
Particularly preferable as the fiber as the base material is a fiber having a hydroxyl group in a molecule, and specifically, a vegetable fiber, a regenerated fiber, and a semi-synthetic fiber mainly composed of cellulose. Further, as the polishing slurry to be cleaned in the present invention, as described above, a polishing slurry for a semiconductor wafer or the like in which the attachment and mixing of metal ions has a significant effect on the quality of the object to be polished is exemplified and removed. Typical examples of the metal ion include iron, aluminum, copper, nickel, zinc, chromium, molybdenum, and tungsten.
[0014]
As a specific method for carrying out the cleaning method of the present invention, the chelate-forming fiber is added to and brought into contact with a polishing slurry, and the metal ions contained in the slurry are added to the chelate-forming fiber molecules. A method in which chelate is captured by the introduced chelate-forming functional group, or a method in which a polishing slurry is passed through a container filled with the chelate-forming fibers to capture and remove metal ions in the slurry is also preferable. Recommended as a cleaning method.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The chelate-forming fiber used in the present invention is a fiber in which a functional group having a chelate-forming ability is introduced into fiber molecules such as animal or vegetable natural fibers, regenerated fibers, and synthetic fibers. Examples of the chelating fiber include those disclosed by the present applicant in JP-A-10-183470, JP-A-2000-169828, and JP-A-2000-248467.
[0016]
That is, as an effective method for obtaining a chelate-forming fiber, a crosslinking reactive compound having both a reactive double bond and a glycidyl group in a molecule (specifically, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, etc.) ) Is used to introduce a chelate-forming functional group into the fiber substrate molecule.
[0017]
More specifically, when a fiber substrate such as a natural fiber or a synthetic fiber is contact-reacted with the crosslinking reactive compound in the presence of, for example, a redox catalyst, a reactive double bond in the compound reacts with a fiber molecule. It reacts and a group having a glycidyl group as a reactive functional group is pendant-grafted into the fiber molecule. A chelate-forming compound having a functional group reactive with a glycidyl group (for example, iminodiacetic acid group, nitrilotriacetic acid group, ethylenediaminetriacetic acid group, ethylenediaminetetraacetic acid group, diethylenetriaminepentaacetic acid group, ethylenediaminetriacetic acid group, Succinic acid group, glutamic acid diacetate group, N-methyl-D-glucamine group, D-glucamine group, phosphoric acid, etc.), the reactive functional group is grafted to the glycidyl of the crosslinking reactive compound. Reacts with the group to introduce a chelating functional group into the fiber molecule.
[0018]
As a result, a chelate-forming functional group is introduced to the surface of the fiber molecule, and the chelate-forming functional group is combined with an interaction with a nitrogen atom, a sulfur atom, or the like present in the vicinity thereof, so that a heavy metal ion or a noble metal ion is formed. And exhibit excellent chelate capturing ability.
[0019]
When the chelate-forming functional group is in the acid form, it is of course possible to use the acid form as described above, but depending on the type of metal ion to be captured and removed, It is also effective to change a part or the whole to an alkali metal salt or an ammonium salt.
[0020]
By the way, when the chelate-forming fiber having the acid-type chelate-forming functional group introduced therein is brought into contact with the polishing slurry as it is, depending on the type of the polishing slurry, the pH of the slurry decreases due to the presence of the acid-type functional group, The trapping efficiency for heavy metal ions and the like may decrease. Therefore, in such a case, after the introduction of the acid-type chelate-forming functional group, a part or all of the functional group is changed to an alkali metal salt or an ammonium salt before it is used as a cleaning material for a polishing slurry. It is desirable to keep. Then, particularly, Cu, Ni, Cr, Co, Fe, Pb, Cd and the like contained in the polishing slurry can be efficiently trapped and removed.
[0021]
The method of changing the acid-type chelate-forming functional group to an alkali metal salt or an ammonium salt does not require special conditions, and a normal neutralization method may be employed. Specifically, the fiber into which the acid-type chelate-forming functional group has been introduced is neutralized by batch immersion in, for example, 0.01 to 1 mol / L of an alkali metal aqueous solution or aqueous ammonia, or through a column. The method is adopted. When a cellulosic fiber is used as the fiber base material, if a slightly excessive amount of alkali is used in the neutralization treatment step, the acid-type chelate-forming functional group is converted into an alkali metal salt or an ammonium salt, and It is preferable because the fiber itself becomes an alkali cellulose and exhibits a more excellent metal ion trapping action by improving the auxiliary chelating action as a base material.
[0022]
The type of fiber serving as the base material of the chelate-forming fiber used in the present invention is not particularly limited, and natural fibers including plant fibers and animal fibers, regenerated fibers, and synthetic fibers such as polyamide fibers and polyester fibers are all used. Although it is possible to take into consideration the ease and amount of the chelate-forming functional group introduced into the fiber molecule as described above, the handling amount as a fiber material, the cost, and the like, it is particularly preferable to use cotton or hemp. And various vegetable fibers including wood, etc .; regenerated fibers such as cupra, rayon and polynosic; semi-synthetic fibers such as acetate; and animal fibers including silk and wool.
[0023]
Among these fibers, particularly preferred are vegetable fibers, regenerated fibers, and semi-synthetic fibers mainly composed of cellulose. That is, vegetable-based vegetable fibers have numerous methylol groups and hydroxyl groups in the molecule, and the chelating functional groups can be easily and efficiently introduced by using the crosslinking reactive compound as described above. In addition to the above, when the acid-type functional group is converted into an alkali salt or an ammonium salt, the base fiber itself becomes an alkali-cellulose type, and the metal ion capturing action is further enhanced.
[0024]
There is no particular limitation on the shape of the base fiber, long filament monofilament, multifilament, short fiber spun yarn or a woven or knitted woven or knitted fabric, or even a nonwoven fabric. In addition, a fiber or a woven or knitted fabric obtained by compounding or blending two or more fibers can be used. It is also possible to use wood pulp and paper, as well as wood chips, wood chips and thin plates.
[0025]
Furthermore, in order to increase the contact efficiency with the polishing slurry to be treated, it is also effective to use short fiber powder or a fiber material processed into a filter as the base fiber.
[0026]
The preferred shape of the short fiber powder used here has a length of 0.01 to 5 mm, preferably 0.03 to 3 mm, a single fiber diameter of about 1 to 50 μm, and preferably 5 to 30 μm. It is about 1 to 600, preferably about 1 to 100.
[0027]
If such a short fiber powder material is used, the short fiber powder chelate-forming fiber is added to the polishing slurry containing metal ions, stirred, and separated through a screen of an appropriate size. With a simple method, metal ions contained in the polishing slurry can be efficiently captured and removed. In some cases, the same metal ion trapping effect can be obtained by filling the column or the like with the short fiber powder-like chelate-forming fibers and passing the polishing slurry.
[0028]
When the chelate-forming fiber is used as a filter medium, after a cross-linking reactive compound as described above is grafted on a fiber material constituting the filter medium, chelation is performed on a glycidyl group of the cross-linking reactive compound graft-bonded to fiber molecules. The chelate-forming functional group may be introduced by an addition reaction of a reactive compound and processed into the above-mentioned filter material shape for use. In addition, the above-mentioned fiber material is processed into an appropriate filter material shape for purification. Incorporation into an apparatus, a grafting reaction is performed by contacting a treatment liquid containing a cross-linking reactive compound with the fiber base incorporated in the apparatus, and further contacting with a chelate-forming compound, whereby the fiber base is post-processed. It is also possible to introduce a chelate-forming functional group into the polymer.
[0029]
When the polishing slurry is treated using the fiber material having the chelate-forming functional group introduced as described above, the fiber material may be batch-processed as it is or in alkaline water or ammonia water. The polishing slurry may be treated after the acid type is changed to an alkali salt or an ammonium salt by dipping or passing through a column.
[0030]
As described above, by introducing a chelate-forming functional group into a fiber material having a function as a filter medium, it is possible to combine a chelate-capturing ability and a coarse-contaminant-capturing ability, and coarse particles that may be mixed into the polishing slurry. Contaminants can also be removed and cleaned at the same time.
[0031]
As a method for introducing a chelate-forming functional group into a molecule of a fiber base material, a method of reacting a chelate-forming compound via a cross-linking reactive compound as described above is industrially effective. The method is not limited to the method described above. In short, any method capable of introducing a chelate-forming functional group into a fiber molecule can be used, for example, as described in JP-A-10-183470, JP-A-2000-169828 and JP-A-2000-169828. It is of course possible to employ a method as disclosed in, for example, 248467.
[0032]
In the above, an aminopolycarboxylic acid group most effective as a chelate-forming functional group, more specifically, an iminodiacetic acid group, a nitrilotriacetic acid group, an ethylenediaminetriacetic acid group, an ethylenediaminetetraacetic acid group, a diethylenetriaminepentaacetic acid group; and Although a phosphoric acid group was shown, in addition to those of the present invention, a chelate-forming functional group such as an ethylenediamine disuccinic acid group, a glutamic acid diacetate group, an N-methyl-D-glucamine group, or a D-glucamine group was introduced. Within the technical scope of
[0033]
A method for introducing a chelate-forming functional group into a molecule by using a cellulosic fiber as a fiber base material and using a cross-linking reactive compound in the molecule is not particularly limited, but preferred methods are as follows.
[0034]
That is, the cellulosic fiber is immersed in an aqueous solution of a ferrous salt in advance for about 1 to 30 minutes at room temperature, washed, and then washed with a hydrogen peroxide solution, thiourea dioxide and a crosslinking reactive compound (if necessary, a homogeneous reaction such as an emulsifier, etc.) (Accelerator), and reacted at 40 to 100 ° C. for about 10 minutes to 5 hours.
[0035]
According to this method, the cross-linking reactive compound efficiently graft-reacts to the hydroxyl group or amino group in the cellulosic fiber molecule, and the glycidyl group which easily reacts with the chelate-forming compound can be efficiently introduced into the fiber molecule.
[0036]
Next, the fiber having the glycidyl group introduced therein by the above reaction and the chelate-forming compound are mixed with water or a polar solvent such as N, N'-dimethylformamide or dimethylsulfoxide at 50 to 100 ° C for 10 minutes to several tens as needed. When the reaction is performed by heating for about an hour, an amino group or an acid group in the chelate-forming compound reacts with the glycidyl group, and a chelate-forming functional group is introduced into the fiber molecule.
[0037]
The amount of the chelate-forming compound introduced into the fiber substrate is determined by considering the amount of the reactive functional group in the fiber molecule, and the amount of the cross-linking reactive compound used in the introduction reaction, or the amount of the chelate-forming compound and the reaction conditions. Can be arbitrarily adjusted, but in order to impart sufficient metal ion capturing ability to the fiber, the substitution rate calculated by the following formula is adjusted to be about 10% by mass or more, more preferably about 20% by mass or more. It is desirable to do.
Substitution ratio (% by mass) = [(fiber mass after substituent introduction−fiber mass before substituent introduction) / fiber mass before substituent introduction] × 100
(However, the substituent means all the substituents derived from the crosslinking reactive compound and the chelating compound).
[0038]
In order to enhance the metal ion-capturing ability and improve the cleaning effect, the higher the substitution rate is, the more preferable it is.Therefore, the upper limit of the substitution rate is not particularly defined.However, when the substitution rate is too high, the crystallinity of the substituent-introduced fiber is increased. Since the fibers tend to become brittle and tend to be brittle, the substitution rate is reduced to about 200% by mass or less, more preferably about 100% by mass or less, when comprehensively considering the practicality and economy as a metal ion scavenger. It is desirable to suppress. However, depending on the type and shape of the base fiber, the type of the chelate-forming compound, or the application, etc., it is also possible to increase the metal ion trapping ability by setting the substitution rate to a high level of 150 to 200% by mass. .
[0039]
The chelate-forming fibers obtained as described above may be monofilament, multifilament, spun yarn, non-woven, fiber woven / knitted, powder, filter, etc., depending on the properties of the fiber base used as described above. Although it can be obtained in any form, in any case, substantially all of the chelating functional groups introduced on the surface of the fine fiber molecule effectively act to trap metal ions, and thus, for example, granules Exhibits excellent metal ion trapping ability as compared to trapping materials in the shape of a film or film.
[0040]
Therefore, the fiber is brought into contact with a slurry containing metal ions, specifically, the fiber is mixed with a polishing slurry to trap metal ions in the slurry, or the fiber is woven or knitted into a non-woven fabric of any mesh. When processed into a shape and the polishing slurry is passed, metal ions contained in the polishing slurry can be efficiently captured and removed.
[0041]
Thus, according to the present invention, metal ions contained in various polishing slurries, such as CMP slurries for polishing highly integrated semiconductor wafers, which remarkably dislike the adhesion of metal ions, such as iron, aluminum, copper, By efficiently capturing and removing nickel, zinc, chromium, molybdenum, tungsten, and the like and cleaning them, metal contamination can be prevented as much as possible. Alternatively, it is possible to efficiently remove and clean metal ions even from used polishing slurries mixed with various metal ions, and to carry out recycling and reuse of polishing slurries without hindrance. You can enjoy the benefits.
[0042]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately modified within a range that can conform to the purpose of the preceding and following descriptions. All of them are included in the technical scope of the present invention.
[0043]
Example 1
Chelating fibers (iminodiacetate immobilized via glycidyl methacrylate) on rayon yarn of about 3 dtex cut to a length of about 0.5 mm (introduction amount of chelating functional groups: 0.798 mmol / g) ) 0.5 g was added to 100 ml of an acidic polishing slurry containing colloidal silica (pH 2.5) containing 1.2 ppm of Cu and 0.9 ppm of Ni as impurity metals, and stirred at 20 ° C. for 2 hours. Thereafter, when the concentrations of Cu and Ni in the polishing slurry were measured, both were 20 ppb or less.
[0044]
Next, for comparison, the same operation as above was repeated except that a commercially available iminodiacetic acid type chelate resin was used instead of the chelate-forming fiber, and the concentrations of Cu and Ni in the polishing slurry were examined. , Cu; 0.2 ppm, Ni; 0.3 ppm.
[0045]
As is clear from the comparison of these results, it is clear that the cleaning method of the present invention can capture and remove metal ions in the polishing slurry with much higher efficiency than the conventional method and can clean the slurry.
[0046]
Example 2
Chelating fiber (iminodiacetate immobilized via glycidyl methacrylate) on rayon yarn of about 3 dtex, cut to an average length of 0.5 mm (introduction amount of chelating functional group: 0.808 mmol / g) 300 g was filled in a polypropylene container having an inner diameter of 7 cm and a length of 25 cm, and the container was attached to the housing. Then, a 0.5 mol / L aqueous sodium hydroxide solution was added at a flow rate of 200 ml / min. After passing through 1 liter, 10 liters of ion-exchanged water was passed through and washed to obtain a sodium-type chelating fiber.
[0047]
5 L of a colloidal silica-containing alkaline polishing slurry (pH 11.0) containing 0.5 ppm of Cu and 0.4 ppm of Fe as an impure metal was passed through at a flow rate of 200 ml / min. When the concentrations were measured, it was confirmed that the concentrations were all reduced to 20 ppb or less.
[0048]
Example 3
Chelate-forming fibers obtained by immobilizing N-methyl-D-glucamine via glycidyl methacrylate on rayon yarn of about 15 decitex cut to a length of about 1 mm (introduction amount of chelate-forming functional group: 0.750 mmol) / G) 300 g was filled in a polypropylene container having an inner diameter of 7 cm and a length of 25 cm, and the container was mounted on a housing, and then colloidal silica containing Cr: 0.3 ppm, Fe; 0.2 ppm as an impurity metal. Five liters of the contained acidic polishing slurry (pH 2.6) was passed through at a flow rate of 200 ml / min, and the concentrations of Cr and Fe in the effluent were measured. As a result, it was confirmed that both were reduced to 20 ppb or less.
[0049]
【The invention's effect】
The present invention is configured as described above and can efficiently capture and remove trace impurities contained in a polishing slurry such as a CMP slurry, so that the polishing slurry can be recycled and used, and a highly integrated semiconductor wafer or the like can be obtained. , Metal contamination can be prevented as much as possible.

Claims (11)

A method for cleaning a polishing slurry, comprising using a chelating fiber in which a functional group capable of forming a metal chelate is introduced into a fiber molecule and removing metal ions present in the polishing slurry. The cleaning method according to claim 1, wherein the functional group capable of forming a metal chelate is an aminopolycarboxylic acid group or a phosphoric acid group. 2. The cleaning method according to claim 1, wherein the functional group capable of forming a metal chelate is obtained by converting at least a part of an acid type functional group comprising an aminopolycarboxylic acid group or a phosphoric acid group into an alkali metal salt or an ammonium salt. . The cleaning method according to claim 1, wherein the functional group capable of forming a metal chelate is an amino polyol group. Functional groups having metal chelate forming ability are iminodiacetic acid group, nitrilotriacetic acid group, ethylenediaminetriacetic acid group, ethylenediaminetetraacetic acid group, diethylenetriaminepentaacetic acid group, ethylenediaminedisuccinic acid group, glutamic acid diacetate group, N-methyl- The cleaning method according to any one of claims 1 to 4, wherein the cleaning method is at least one selected from the group consisting of a D-glucamine group and a D-glucamine group. The cleaning method according to any one of claims 1 to 5, wherein a fiber having a hydroxyl group in a molecule is used as the fiber. The cleaning method according to claim 6, wherein a cellulosic fiber is used as the fiber. The cleaning method according to claim 1, wherein the polishing slurry to be cleaned is a polishing slurry for a semiconductor wafer. The cleaning method according to any one of claims 1 to 8, wherein the metal ions to be removed are at least one selected from the group consisting of iron, aluminum, copper, nickel, zinc, chromium, molybdenum, and tungsten. The cleaning method according to claim 1, wherein the chelate-forming fibers are added to a polishing slurry to capture and remove metal ions contained in the polishing slurry. The cleaning method according to any one of claims 1 to 9, wherein the chelate-forming fibers are filled in a container, and a polishing slurry is passed through the container to capture and remove metal ions contained in the polishing slurry. .