JP2007109767A - Cmp conditioner and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CMP conditioner which can suppress the occurrence of scratches by certainly preventing the dropout of abrasive grains of even a very corrosive slurry used for CMP equipment, and to provide a manufacturing method of a CMP conditioner which can manufacture such a CMP conditioner without requiring complicated manufacturing processes. <P>SOLUTION: In the CMP conditioner and its manufacturing method; an abrasive grain layer 3 wherein abrasive grains 6 are adhered to each other by a metal bonding phase 7 is formed on the surface of a substrate 1, and a protection film 9 fabricated by sol-gel method is formed on the surface of the abrasive grain layer 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a CMP conditioner used for conditioning (dressing or dressing) a polishing pad of a CMP (Chemical Mechanical Polishing) apparatus for polishing a semiconductor wafer or the like, and a method for manufacturing the same.

As this type of CMP conditioner, for example, Patent Document 1 discloses that a plurality of substantially cylindrical protrusions are formed on the upper surface of a disk-shaped base body (base metal) at intervals, and a plurality of protrusions are formed on the surfaces of these protrusions. In the proposed method, diamond grains and other abrasive grains are fixed by a metal plating binder phase. Further, Patent Document 2 proposes that a ceramic coating such as SiC is coated on the surface of the metal binder phase to which the abrasive grains are fixed in this way by a vapor phase coating technique such as CVD or ion plating.
JP 2001-71269 A JP 2001-210613 A

  By the way, in such a CMP apparatus in which the polishing pad is conditioned by the CMP conditioner, a highly acidic or alkaline corrosive slurry is used when polishing a semiconductor wafer or the like, so that a metal binder phase holding abrasive grains is present. There is a problem that the slurry is corroded (eluted) by the slurry and the abrasive grains fall off, and the semiconductor grains are damaged by the dropped abrasive grains to cause scratches. In particular, when the abrasive grains are diamond and the binder phase is a metal plating phase such as Ni, the wettability of the metal plating to the abrasive grains is poor, so there is a very small gap at the boundary (cavity) between the two. As a result, the slurry enters from the gap and corrodes the metal plating phase, and as a result, the removal of the abrasive grains is further promoted.

  In this regard, in the CMP conditioner in which the surface of the metal binder phase is coated with a ceramic film as described in Patent Document 2, the corrosion of the metal bond phase is prevented by protecting the metal bond phase with the ceramic film. Can also be suppressed. However, on the other hand, when the ceramic film is coated by the gas phase coating technique as described in Patent Document 2, the film is also coated on the surface of abrasive grains such as diamond protruding from the metal binder phase. As a result, the sharpness of the abrasive grains is impaired, and the pad polishing rate is significantly reduced. Therefore, in order to obtain a pad polishing rate that can be used as a CMP conditioner, a process of removing the coating film coated on the surface of the abrasive grains as described in Patent Document 2 is required, and the manufacturing process is required. Complicated is inevitable.

  The present invention has been made under such a background, and it is possible to reliably prevent the abrasive grains from falling off and prevent the generation of scratches even in a highly corrosive slurry used in a CMP apparatus. It is an object of the present invention to provide a conditioner and to provide a CMP conditioner manufacturing method capable of manufacturing such a CMP conditioner without requiring a complicated manufacturing process.

  In order to solve the above problems and achieve such an object, a CMP conditioner according to the present invention is a CMP conditioner in which an abrasive grain layer is formed on a substrate surface by abrading grains fixed by a metal binder phase. The surface of the abrasive layer is characterized in that a protective coating produced by a sol-gel method is formed, and the method for producing a CMP conditioner of the present invention comprises: An abrasive grain is fixed by a metal binder phase to form an abrasive grain layer, and a protective film is then formed on the surface of the abrasive grain layer by a sol-gel method.

In the present invention, a coating technique by a sol-gel method used when forming a protective film on the surface of the abrasive layer is, for example, “Ceramic Coating Technology” (May 25, 1984, General Technology Center Co., Ltd.) supervised by Rihei Tomino. Issued April 1, 1985, 2nd edition, p. 105-p. 113), and a sol-gel solution containing silica sol, metal alkoxide, etc. is applied and gelled by hydrolysis and polycondensation reaction. This is heat-treated to produce a protective coating, SiO ₂ , TiO ₂ , Al ₂ O ₃ , SnO ₂ , ZnO, VO ₂ , V ₂ O ₅ , MO ₃ , WO ₃ , TaO ₅ , ZnO _2. A metal oxide film having corrosion resistance such as can be obtained. Then, when such a sol-gel liquid is applied to the surface of the abrasive grain layer to which the abrasive grains are fixed by the metal binder phase, the sol-gel liquid becomes abrasive because the surface tension of the sol-gel liquid is small. A protective film is formed so as to enter the above-mentioned extremely small gap by the capillary phenomenon from the boundary between the metal and the metal binder phase and seal the gap at this boundary, while the abrasive protruding from the metal binder phase The sol-gel solution is repelled on the surface of the grains, and a film is not substantially formed.

  Therefore, according to the thus produced CMP conditioner of the present invention, the protective coating is formed at the boundary between the abrasive grains and the metal binder phase particularly on the surface of the abrasive grain layer. It is possible to prevent intrusion of the slurry from the part and prevent the abrasive grains from falling off due to corrosion of the metal binder phase, and it is possible to polish a high-quality semiconductor wafer or the like while suppressing the generation of scratches. On the other hand, since the protective coating is not formed on the surface of the abrasive grains as described above, there is no need for a step of removing the coating after the formation of the coating, and the sol-gel solution The coating can be performed by a relatively simple method such as dip coating, and the temperature during the heat treatment is also relatively low. Therefore, according to the manufacturing method of the present invention, a complicated manufacturing process, an expensive apparatus, etc. are required. Therefore, it is possible to provide the excellent CMP conditioner as described above.

  Here, in the CMP conditioner, when using a (strong acid) slurry having a strong corrosiveness to the metal, in order to prevent metal contamination of the wafer due to the corrosion dissolution of the metal binder phase, It is desirable to coat a film made of a tetrafluoride organic compound. Such a tetrafluoride organic compound is chemically stable and highly corrosion-resistant, and can be reliably coated on a protective film such as the above metal oxide film by electrodeposition coating or the like. It becomes possible to prevent metal contamination of the wafer due to corrosion dissolution of the binder phase.

  1 and 2 show a first embodiment of a CMP conditioner of the present invention. In this embodiment, the base body (base metal) 1 is formed in a substantially disc shape centering on the axis O with a metal material such as stainless steel, and one circular surface perpendicular to the axis O is used for the CMP apparatus during conditioning. The conditioning surface 2 is in contact with the polishing pad so as to face the polishing pad, and the abrasive layer 3 is formed on the conditioning surface 2. In such a CMP conditioner, the conditioning surface 2 is brought into contact with and parallel to the polishing pad surface of the CMP apparatus, and is rotated around the axis O at a position away from the rotation axis of the polishing pad. 1 itself is also swung to the inner and outer circumferences of the pad surface and used for conditioning (dressing or dressing) of the polishing pad.

  In the present embodiment, an annular end surface 4f parallel to the conditioning surface 2 and a tapered surface 4t gradually retreating from the end surface 4f toward the outer periphery are provided on the outer periphery side of the conditioning surface 2. A ring portion 4 that protrudes in an annular shape with a constant width around the axis O is formed, and on the inner peripheral side of the ring portion 4, it is also parallel to the conditioning surface 2 and has a protrusion height equal to the ring portion 4. A plurality of substantially cylindrical projections 5 having a circular end surface 5f and having the same shape and the same size are formed at intervals. However, among these, as shown in FIG. 1, the protrusion 5 forms a plurality of (three in FIG. 1) concentric circles with the axis O as the center only in the outer peripheral portion of the inner periphery of the ring portion 4. The circles are arranged at equal intervals for each circle, and adjacent circles are arranged in a staggered pattern.

  In the present embodiment, the abrasive grain layer 3 is formed on the conditioning surface 2, that is, the surface of the base 1, on the end surface 4 f and the tapered surface 4 t of the ring portion 4 and the end surface 5 f of the protrusion 5. Note that the bottom surface (the portion between the protrusions 5) 2f of the conditioning surface 2 on the inner peripheral side of the ring portion 4 is a flat surface perpendicular to the axis O, and the abrasive grain layer 5 is not formed, and the end surface 4f, Strictly speaking, 5f is parallel to the bottom surface 2f and is positioned so as to protrude from each other in the direction of the axis O.

  Here, as shown in FIG. 2, the abrasive grain layer 3 includes a ring portion 4 and a diamond abrasive grain 6 as an abrasive grain 6 and a metal bonding phase 7 formed by electrodeposition with a metal plating phase such as Ni. A plurality (large number) of each protrusion 5 is dispersed and fixed in a single layer, and the abrasive grains 6 protrude from the surface of the metal binder phase 7 at a portion of about 30% of the average particle diameter. This portion is buried and held in the metal bonded phase 7. However, the diamond abrasive grains 6 fixed with the metal plating phase by electrodeposition as the metal bonding phase 7 in this way have a very small wettability with the metal plating, and thus are extremely small at the boundary portion 8 with the metal bonding phase 7. A gap is formed, and particularly on the surface of the abrasive grain layer 3, the boundary portion 8 is formed in a concave shape that is microscopically depressed as shown in FIG.

  Thus, in the present embodiment, the protective film 9 generated by the sol-gel method is formed on the surface of the abrasive grain layer 3, particularly at the boundary 8 between the abrasive grains 6 and the metal binder phase 7. That is, in one embodiment of the CMP conditioner manufacturing method of the present invention for manufacturing such a CMP conditioner, the base 1 on which the abrasive layer 3 as described above is formed on the conditioning surface 2 is made of silica sol, metal alkoxide or the like. For example, the sol-gel solution is immersed in the sol-gel solution, and the sol-gel solution is applied to the surface of the abrasive grain layer 3. Gelling by polycondensation reaction, followed by heat treatment at a higher temperature for a longer time, thereby forming the protective coating 9 made of a metal oxide coating contained in the sol-gel solution.

  Thus, the protective film 9 produced by the sol-gel method has a small (weak) surface tension when the sol-gel liquid is applied to the surface of the abrasive grain layer 3, so that the sol-gel liquid is ground. It enters into the gap by capillary action from the boundary portion 8 between the grain 6 and the metal binder phase 7 and accumulates in the concave portion formed on the surface side of the abrasive grain layer 3 of the boundary portion 8, and is gelled and heat-treated as it is. Thus, the boundary portion 8 is formed to be sealed on the surface side of the abrasive grain layer 3. For this reason, even when the CMP conditioner is used for dressing the polishing pad of the CMP apparatus under a highly corrosive slurry, it is possible to prevent the slurry from entering the gap of the boundary portion 8 and corroding the metal bonded phase 7. Thus, the abrasive grains 6 can be securely held without falling off, and the generation of scratches can be suppressed, so that a high-quality semiconductor wafer or the like can be polished.

  On the other hand, the sol-gel liquid having such a small surface tension is repelled by the surface of the abrasive grain 6 on the tip end side of the abrasive grain 6 protruding from the metal binder phase 7 in a state of being applied to the surface of the abrasive grain layer 3. Therefore, the gel is rarely gelled while adhering to the tips of the abrasive grains 6. That is, even if the protective coating 9 is formed at the boundary 8 between the abrasive grains 6 and the metal binder phase 7 on the surface of the abrasive grain layer 3, it is not formed at the tip of the abrasive grains 6. There is no need for a step of removing the protective coating 9 on the abrasive grains 6 after the formation of the protective coating 9, and it is possible to maintain a high pad polishing rate by sufficiently securing the sharpness due to the abrasive grains 6. Become. Moreover, in the sol-gel method, the sol-gel liquid can be easily applied to the surface of the abrasive layer 3 by the above-described immersion, that is, dip coating, and drying and heat treatment do not require a very high temperature. In the manufacturing method of the present embodiment, it is possible to manufacture a CMP conditioner having excellent corrosion resistance with simple equipment as compared with the case where a film is formed by a vapor phase coating technique such as CVD or ion plating.

In addition, as the protective film 9 thus produced by the sol-gel method, SiO ₂ , TiO ₂ , Al ₂ O ₃ , SnO ₂ , ZnO, VO ₂ , V ₂ O ₅ , MO ₃ , WO ₃ , TaO ₅ , A metal oxide film having corrosion resistance, such as ZnO _2, is preferably mentioned. In particular, when a silicon wafer is polished in a CMP apparatus, a SiO ₂ film is desirable from the viewpoint of preventing contamination. In addition, in order to apply the sol-gel liquid to the surface of the abrasive grain layer 3, it is possible to apply it by spray coating or spin coating with the conditioning surface 2 facing upward in addition to the dip coating described above.

  By the way, as described above, the sol-gel liquid applied to the surface of the abrasive grain layer 3 in this way is difficult to adhere to the tip of the abrasive grain 6 protruding from the metal binder phase 7 due to its surface tension. On the other hand, if the surface of the metal bonded phase 7 between the plurality of abrasive grains 6 is flat, it is also difficult to adhere in the sol state because of its high fluidity. As shown in FIG. 2, the protective film 9 is not formed on the surface 7 or even if it is formed, it becomes extremely thin. That is, the protective coating 9 is formed substantially only on the boundary portion 8 between the abrasive grains 6 and the metal binder phase 7 on the surface of the abrasive grain layer 3. Metal elution may occur from the metal bonding phase 7 between the abrasive grains 6, which may cause metal contamination of the wafer.

  Therefore, in order to surely prevent the abrasive grains 6 from falling off due to the corrosion of the metal binder phase 7 between the abrasive grains 6, as in the second embodiment of the CMP conditioner of the present invention shown in FIG. On the surface of the abrasive layer 3, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA) It is desirable to coat the coating 10 made of a tetrafluorinated organic compound such as tetrafluoroethylene / ethylene copolymer resin (ETFE). In the second embodiment shown in FIG. 3, the same reference numerals are assigned to the same parts as those in the first embodiment shown in FIG. In the second embodiment of the CMP conditioner manufacturing method of the present invention for manufacturing the CMP conditioner of the second embodiment, the CMP manufactured by the manufacturing method of the first embodiment is performed. The coating 10 is formed by immersing the substrate 1 of the conditioner in a liquid in which the above-described tetrafluoride organic compound is dispersed and performing electrodeposition coating.

  In such a CMP conditioner of the second embodiment, since the tetrafluoride organic compound forming the coating film 10 hardly reacts with a highly corrosive slurry, high corrosion resistance is obtained. Moreover, on the protective coating 9 formed on the metal bonded phase 7 portion between the abrasive grains 6 on the surface of the abrasive grain layer 3 or the boundary portion 8 between the abrasive grains 6 and the metal bonded phase 7 by the above-described electrodeposition coating or the like. Also, the coating 10 can be reliably coated. Therefore, according to the second embodiment, it is possible to suppress the metal elution by the metal bonding phase 7 between the abrasive grains 6 as described above, and to prevent the metal contamination of the wafer.

  In addition, by coating the coating film 10 made of the tetrafluoride organic compound in this way, in the second embodiment, a so-called ceria-based slurry in which fine particles of, for example, cerium oxide are dispersed is used as the grinding liquid. Even in such a case, it is possible to prevent such fine particles from aggregating and adhering to the end faces 4f and 5f of the conditioning surface 2 of the substrate 1 which are in contact with the polishing pad. Accordingly, the fine particles that have adhered in this manner prevent the abrasive grains 6 from biting the polishing pad, thereby deteriorating the polishing rate, and the particles that have been condensed and adhered are peeled off, resulting in scratches on the semiconductor wafer. Therefore, the above-described scratch reduction effect can be achieved more reliably, and the pad polishing rate can be stabilized.

  Next, an example of the present invention based on the above embodiment will be given to demonstrate the effect. In this example, a CMP conditioner (Example 1) in which only the protective film 9 generated by the sol-gel method based on the first embodiment is formed, and this Example 1 based on the second embodiment. A CMP conditioner (Example 2) was produced in which the surface of the abrasive grain layer 3 was coated with a coating 10 made of a tetrafluoroorganic compound. Further, as a comparative example for Examples 1 and 2, this comparison was made with a CMP conditioner (Comparative Example 1) in which an abrasive grain layer 3 in which abrasive grains 6 were fixed by a metal bonding phase (metal plating phase) 7 was formed. A CMP conditioner (Comparative Example 2) in which the surface of the abrasive layer 3 of Example 1 was coated with a SiC coating was also produced. In other words, in Examples 1, 2 and Comparative Example 2, the protective coating 9, the coating 10, and the SiC coating were formed on the CMP conditioner of Comparative Example 1 in which the abrasive grain layer 3 was formed on the substrate 1 by a well-known method. Is.

In Examples 1 and 2 and Comparative Examples 1 and 2, the base body 1 has an outer diameter of the conditioning surface 2 (the outer diameter of the base body 1) of 101.6 mm, the inner diameter of the ring portion 4 is 90 mm, and the outer surface of the end face 4f. The diameter is 94 mm, the outer diameter of the ring portion 4 including the tapered surface 4 t is 97 mm, the outer diameter of the protrusion 5 is 2 mm, and the protruding height of the ring portion 4 and the protrusion 5 from the bottom surface 2 f of the conditioning surface 2 (above-mentioned The height of the end faces 4f and 5f) is 0.3 mm. In addition, the protrusions 5 are arranged as shown in FIG. 1 on concentric circles with the axis line O as the center and at substantially equal intervals in a range of an annular surface centering on the axis line O having an inner diameter of 67 mm and an outer diameter of 85 mm. Yes. Further, the abrasive grains 6 are diamond abrasive grains having an average particle diameter of 160 μm, the concentration is 40 / mm ^2, and the metal binding phase 7 is a Ni plating phase.

Of these, when the protective coating 9 is formed in Examples 1 and 2, the substrate 1 having the abrasive layer 3 formed on the conditioning surface 2 is first immersed in an alkaline degreasing solution to increase the cleanliness of the surface. Then, after electrolytic degreasing, it was immersed in an acidic (hydrochloric acid) bath and washed with water. The substrate 1 is immersed in a SiO ₂ sol-gel solution (SiO ₂ concentration 5 wt%, solvent propanol) for 1 minute, and then dried at 200 ° C. for 2 hours to cause a hydrolysis / polycondensation reaction, thereby causing a sol-gel solution. Was further heat-treated by heating at 500 ° C. for 8 hours to produce a protective coating 9 made of SiO ₂ . As shown in FIG. 2, the protective coating 9 thus formed is substantially concentrated only at the boundary 8 between the abrasive grains 6 of the abrasive grain layer 3 and the metal binder phase 7, and has a maximum thickness t. ₁ (see FIG. 2) was about 10 μm.

Further, in Example 2, the substrate 1 of the CMP conditioner of Example 1 thus formed with the protective coating 9 was immersed in a liquid in which polytetrafluoroethylene (PTFE) was dispersed as a tetrafluorinated organic compound. The coating film 10 was formed by applying electrodeposition. The film 10 of the organic tetrafluoride compound thus formed had a thickness t ₂ (see FIG. 3) on the metal binder phase 7 between the abrasive grains 6 of about 5 μm. On the other hand, in Comparative Example 2, the SiC film was formed by a well-known CVD method, and the film thickness was about 1 to 2 μm.

In this embodiment, the CMP conditioners of Examples 1 and 2 and Comparative Examples 1 and 2 are used to polish a silicon wafer with the polishing pad while conditioning the polishing pad in a CMP apparatus under the same conditions. The number of scratches generated on the wafer and the pad polishing rate were measured for each predetermined conditioning time. The results are shown in Table 1 for the number of scratches and Table 2 for the pad polishing rate. The polishing pad is a foamed polyurethane pad (trade name: IC1000) manufactured by Rohm and Haas, the outer diameter is 360 mm, and the pad rotation speed is 80 rpm. p. m, conditioner rotation speed is also 80 r. p. m, the conditioner rocking speed is 3000 mm / min, and while applying a load of 49 N to the base 1 of the conditioner, 100 ml / w of highly corrosive W film polishing slurry (W2000 + H ₂ O ₂ ) is used as the slurry. Conditioning was performed while feeding at min.

  From the results shown in Tables 1 and 2, in the CMP conditioner of Comparative Example 1 in which the abrasive layer 3 was first formed and no film was formed, scratching was observed 3 hours after the start of conditioning. During the lapse of -7 hours, the number exceeded 12 and reached 12, and the subsequent pad polishing had to be stopped. In addition, the pad polishing rate is also a high polishing rate at the beginning of conditioning, but the polishing rate is remarkably lowered with the lapse of the conditioning time, which is not preferable from the viewpoint of maintaining a stable polishing rate. Further, in the CMP conditioner of Comparative Example 2 in which the SiC film was coated on Comparative Example 1, it was confirmed that there was no generation of scratches until 17 hours after the start of conditioning, and the falling of the abrasive grains 6 was suppressed. On the other hand, the pad polishing rate is low from the beginning of conditioning, and it is not possible to condition the polishing pad efficiently, that is, to recover its flatness and prevent clogging.

  On the other hand, in the CMP conditioners of Examples 1 and 2 according to the present invention, even in Example 1 in which the protective film 9 is only formed, scratchless wafer polishing can be performed until 9 hours after the start of conditioning. After that, the number of generated scratches was almost zero. On the other hand, with respect to the pad polishing rate, while maintaining a high rate from the beginning of conditioning, the decrease in polishing rate over time is suppressed to a small level, that is, stable conditioning is performed over a long period of time. I understand. Further, in Example 2 in which the coating film 10 of the tetrafluoride organic compound is coated on Example 1, although the pad polishing rate itself is smaller than that of Example 1, the decrease in the polishing rate over time is still sufficiently suppressed. The occurrence of scratches was zero until 21 hours (completion of wafer polishing), which exceeded that of Comparative Example 2.

Further, the CMP conditioners of Examples 1 and 2 and Comparative Examples 1 and ₂ were immersed in the highly corrosive slurry for W film polishing process (W2000 + H ₂ O ₂ ) as they were and left at 50 ° C. for 48 hours. The amount of Ni elution from the conditioner to the slurry was measured by ICP. The results are shown in Table 3 below.

  From the results shown in Table 3, although the CMP conditioner of Comparative Example 2 in which the surface of the abrasive grain layer 3 was coated with a SiC coating had the least amount of Ni elution, the sol- The CMP conditioner of Example 2 in which the surface of the abrasive grain layer 3 having the protective coating 9 produced by the gel method was coated with a coating 10 made of a tetrafluoride organic compound had an elution prevention effect similar to that of Comparative Example 2 above. I understand that Moreover, in Example 1 which only produced | generated the protective film 9 by the sol-gel method, although it is inferior to these Example 2 and Comparative Example 2, the abrasive grain 6 is simply made into the metal binder phase (metal plating phase) 7. It can be seen that a sufficient Ni elution prevention effect is obtained for the CMP conditioner of Comparative Example 1 having the abrasive layer 3 that is only fixed, and from the number of scratches generated and the pad polishing rate in Tables 1 and 2. Considering comprehensively, it was confirmed that the CMP conditioner of Example 1 was desirable and the CMP conditioner of Example 2 was more desirable.

It is a top view of the conditioning surface 2 which shows the 1st Embodiment of this invention. It is an expanded sectional view of the abrasive grain layer 3 in embodiment shown in FIG. It is an expanded sectional view of the abrasive grain layer 3 which shows the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base | substrate 2 Conditioning surface 3 Abrasive grain layer 6 Abrasive grain 7 Metal bonding phase 8 Boundary part of abrasive grain 6 and metallic bonding phase 7 Protective film produced | generated by the sol-gel method 10 Film which consists of tetrafluoro organic compounds

Claims (4)

  A CMP conditioner in which an abrasive grain layer formed by abrading grains fixed by a metal binder phase is formed on a surface of a substrate, and a protective film generated by a sol-gel method is formed on the surface of the abrasive grain layer. A CMP conditioner that is formed.   2. The CMP conditioner according to claim 1, wherein the protective film is formed at a boundary portion between the abrasive grains and a metal binder phase on a surface of the abrasive layer.   3. The CMP conditioner according to claim 1, wherein the surface of the abrasive grain layer is further coated with a film made of a tetrafluoroorganic compound. 4. A CMP condition characterized in that an abrasive grain is fixed on a surface of a substrate by a metal binder phase to form an abrasive grain layer, and then a protective film is formed on the surface of the abrasive grain layer by a sol-gel method. Na production method.

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