KR20090059443A - Method for preparing slurry of cerium oxide for chemical mechanical planarization - Google Patents

Abstract

A method for preparing slurry of cerium oxide is provided to minimize the coherence of abrasives by uniformizing sizes of ceria particles within slurry and improving dispersion stability, and to improve polishing capacity, reliability and productivity of a semiconductor process. A method for preparing slurry of cerium oxide comprises the steps of: (a) calcining cerium carbonate to prepare cerium carbonate; (b) primarily pulverizing the cerium carbonate; (c) mixing the primarily pulverized cerium carbonate with solvent and a dispersing agent to prepare slurry; and (d) milling the mixed cerium carbonate slurry at a milling speed of 20~120 rpm by using bead with particle size of 0.5~2.0 mm.

Description

Method for producing cerium oxide slurry for CPM {METHOD FOR PREPARING SLURRY OF CERIUM OXIDE FOR CHEMICAL MECHANICAL PLANARIZATION}

The present invention relates to a method for producing a cerium oxide slurry for chemical mechanical polishing (CMP) during the manufacturing process of a semiconductor device, to reduce the macroparticles that cause scratches during wafer polishing, and to improve the dispersion stability of the slurry ultrafine pattern It relates to a method for producing a cerium oxide slurry that can be applied to the manufacture of semiconductor devices that require.

As the degree of integration of microminiature semiconductor devices continues to increase, the planarization process used to manufacture such devices becomes even more important. As a method of manufacturing a highly integrated semiconductor device, processes of stacking multiple interconnections and other layers on a semiconductor wafer are generally performed, but the inelasticity of the wafer surface generated after such a process causes many problems. Doing. Accordingly, planarization techniques have been employed in various manufacturing process steps to minimize non-uniformity on the wafer surface.

One such planarization technique is chemical mechanical polishing (CMP). In the CMP process, the wafer surface is pressed against a relatively rotating polishing pad, and during polishing, chemical reaction solutions known as abrasives and CMP slurries flow into the polishing pad. Flatten.

One example of applying the CMP process is shallow trench isolation (STI). In the STI technique, relatively shallow device isolation trenches are formed, which are used to form field regions that separate active regions on the wafer.

A typical STI process is shown in FIG. Specifically, after the pad silicon oxide films (SiO ₂ , 101) and the silicon nitride film (Si ₃ N ₄ ) etch finish layer 102 are sequentially stacked on the semiconductor substrate, the photosensitive resin pattern is formed on the Si ₃ N ₄ etch finish layer. Is formed. Next, using the photoresist pattern as a mask, the Si ₃ N ₄ etch stop layer 102, the pad silicon oxide film 101, and the semiconductor substrate 100 are partially etched to form a plurality of trenches 103. Form.

After that, the trenches 103 are filled to form a field region, and the insulating silicon oxide film 104 is covered with a low pressure chemical vapor deposition (LPCVD) method and a plasma plasma deposition (PECVD) method to cover the surface of the Si ₃ N ₄ etch termination layer 102. It is deposited by an enhanced chemical vapor doposition method or a high density plasma chemical vapor deposition (HDP VCD) method. Thereafter, the insulating silicon oxide film 104 is polished until the Si ₃ N ₄ etch stop layer 102 is exposed, and the Si ₃ N ₄ etch stop layer 102 and the pad silicon oxide film 101 between the active regions are exposed. ) Is removed through an etching process, and finally a gate silicon oxide film 105 is formed on the surface of the semiconductor substrate.

In the same process as STI, cerium oxide (CeO ₂ ) fine particles used as a chemical mechanical polishing (CMP) abrasive is generally manufactured by calcining cerium carbonate and solid-phase reaction. Since it is included in the polishing may generate a micro scratch (micro scratch) on the substrate, which has a problem that is one of the causes of the yield reduction of the semiconductor manufacturing process.

The present inventors have studied to minimize alleles having a particle diameter of 3 μm or more, which causes micro scratches during chemical mechanical polishing, and found that the fraction of alleles can be reduced when dispersed with low energy during milling of the cerium oxide slurry. In particular, it was found that the milling speed and the size of the beads affect the elimination of alleles, especially when milling using beads as milling media.

The present invention is based on this.

The present invention comprises the steps of: a) calcining cerium carbonate as a raw material to produce cerium oxide; b) grinding the cerium oxide firstly; c) mixing the primary pulverized cerium oxide with a solvent and a dispersant to prepare a slurry; And d) milling the mixed cerium oxide slurry using a bead in a range of 0.5 mm to 2 mm in diameter at a milling speed in the range of 20 to 120 rpm. Provide a way to.

The present invention also provides a cerium oxide slurry produced by the method described above, wherein the number of particles of 3 µm or more per ml of slurry is 20000 or less.

In addition, the present invention provides a shallow trench isolation method (STI) method characterized by using the cerium oxide slurry described above.

The present invention provides a method for producing a cerium oxide slurry, by applying a low energy to the cerium oxide particles by adjusting the milling speed and the size of the beads during milling, it is possible to reduce the large particles that cause micro scratches during wafer polishing In addition, the agglomeration of the abrasive can be minimized by making the particle size of the cerium oxide fine particles in the slurry uniform and improving the dispersion stability. Therefore, the polishing performance can be improved in the polishing process applied to the manufacture of semiconductor devices requiring ultrafine patterns, thereby improving the reliability and productivity of the semiconductor manufacturing process.

The present invention is a method for producing a cerium oxide slurry for chemical mechanical polishing (CMP) using a cerium oxide powder synthesized by a solid-phase reaction, applying a low energy during milling, and the beads of the appropriate size to the milling media (milling media) It is characterized by minimizing alleles with an average particle diameter of 3㎛ or more, the low energy can be achieved by adjusting the milling speed in the range of 20 ~ 120 rpm, the bead of the appropriate size is 0.5 mm ~ 2 mm diameter This can be achieved by using a bead of.

In the conventional manufacturing process of abrasive particles, it is common to apply high energy to increase the grinding efficiency to make smaller particles, and various methods and types of milling have been proposed to apply higher energy. However, high energy milling not only crushes alleles of several tens of micrometers in size, but also makes nanoparticles of several tens of hundreds of nm in size smaller. This is why such high energy milling is used to produce ultrafine nanopowders on the order of a few nm.

However, in the case of the cerium oxide powder used as the abrasive for CMP, when the average particle diameter is too small, there is a problem that the polishing rate is lowered, so that the diameter of 3 µm or more that causes micro scratches is maintained while maintaining the average particle diameter of an appropriate size. It is important to reduce the allele fraction.

Therefore, the present invention used a two-step particle size control process to match the cerium oxide powder synthesized by the solid phase reaction to the desired particle size, the first grinding of the two-step particle size control process is a cerium oxide powder synthesized by the solid phase reaction As a process for crushing to a suitable level, any of those known to those skilled in the art as a dry or wet grinding process can be used, and the secondary milling is slurryed by mixing the primary milled cerium oxide with water and a dispersant, A process of milling using beads as a milling media, by applying low energy to the cerium oxide powder during milling, nanoparticles having an appropriate particle size for CMP polishing are not pulverized, but are mainly pulverized with all particles larger than 3 μm. It is to. Therefore, in order to apply such low energy to the cerium oxide particles, the milling speed during the second milling of the cerium oxide slurry of the present invention is preferably adjusted in the range of 20 to 120 rpm.

On the other hand, as illustrated in Figure 3, it can be seen that the larger the size of the beads as milling media is advantageous for the grinding of large particles, the smaller the size of the beads is advantageous for the grinding of small particles.

However, since the size of the beads may be advantageous for crushing the particles of any size, the size of the beads may vary depending on the nature of the particles to be crushed. Therefore, it is preferable to empirically check the system. It is preferable not to use beads having a diameter of less than 0.5 mm, and to use beads having a diameter of 0.5 mm to 2 mm in order to pulverize alleles having a particle size of 3 μm or more in the slurry dispersed in the slurry.

In the conventional manufacturing process of cerium oxide slurry for CMP, high-speed high-energy milling is often used, and in the case of using a bead of 0.5 mm or more, problems of impurities may be caused by wear of beads and wear of the inner wall of the chamber. As such, milling with beads of less than 0.5 mm is common in the art.

However, in the low-speed low-energy milling as in the present invention, even if the size of the beads increases, there is almost no wear of the beads, and there is no problem in using beads having a size of 0.5 mm or more. In order to achieve this, it is preferable to use beads having a diameter of 0.5 mm to 2 mm.

The cerium oxide slurry production method of the present invention is as follows.

a) calcining cerium carbonate as a raw material to produce cerium oxide;

b) grinding the cerium oxide firstly;

c) mixing the primary pulverized cerium oxide with a solvent and a dispersant to prepare a slurry; And

d) milling the mixed cerium oxide slurry using beads having a diameter of 0.5 mm to 2 mm at a milling speed ranging from 20 to 120 rpm.

It includes.

The step a) is a step of forming cerium oxide by calcining cerium carbonate at a predetermined temperature to solidify the reaction. Cerium carbonate, which is a raw material, may be known to those skilled in the art, and the manufacturing method is not particularly limited. Cerium carbonate of hexagonal crystal structure prepared by precipitating ammonium carbonate and hydrothermal reaction under normal pressure or hydrothermal reaction may be used.

The method of calcining cerium carbonate to form cerium oxide includes a method of heat treatment in a single step at a specific temperature, a method of heat treatment at a higher temperature after the first heat treatment at a lower temperature, and the like, and is not limited to a specific method in the present invention. Does not.

In the case of single-step heat treatment, a method of heat treatment for 30 minutes to 6 hours at a temperature of 600 to 1200 ° C. may be used, and in the case of two-step heat treatment, after the first heat treatment for 6 to 100 hours at a temperature of 200 to 400 ° C. Alternatively, the grinding process may be optionally performed, and then, a method of heat treatment at a temperature of 600 to 1200 ° C. for 30 minutes to 6 hours may be used.

The above heat treatment can be carried out using a conventional heating apparatus such as a box heating furnace, an automatic transfer continuous furnace, or a rotary continuous furnace in an air or an oxidizing atmosphere.

Step b) is a step of pulverizing the particles by primarily pulverizing the calcined cerium oxide, as described above, the grinding method is not particularly limited as long as it is known to those skilled in the art as a dry or wet ceramic powder grinding method, It may or may not use milling media such as balls or beads, and non-limiting examples include jet mills, ball mills, disc mills, bead mills and the like. However, the dry grinding method is preferable because it can reduce additional process steps, such as separate drying and classification, more preferably may use a jet mill (Jet mill).

In the case of using a jet mill, which is a dry pulverization method, since the pulverization is caused by the mutual collision between the aggregated particles, impurity contamination may be reduced than in the case of high-speed milling using beads.

In the manufacturing method of the present invention, the average particle diameter of the cerium oxide powder after the primary grinding may be in the range of 500 nm to 1.5 ㎛, the cerium oxide powder primary grinding in the above range is chemical by the subsequent low energy secondary milling It can be milled to a particle size suitable for mechanical polishing (CMP). On the other hand, when slurrying cerium oxide powder having an average particle diameter of 1 μm or more, precipitation is likely to occur, and therefore, the average particle diameter of the cerium oxide powder after the first grinding may be more preferably in the range of 500 nm to 1 μm.

Since the primary pulverization is intended to pulverize and agglomerate particles that have been agglomerated or overgrown by heating at a high temperature during firing, it is possible to use a milling method having a high energy, and the cerium oxide particles pulverized by such a method Although it may be pulverized to a suitable size as an abrasive, there is a possibility that the average particle size may be further reduced by subsequent secondary milling, so that the average particle size range in the primary grinding is sufficient.

Step c) is to prepare a slurry of the first pulverized cerium oxide powder, using water as a solvent, for example, and a dispersant for facilitating the dispersion of cerium oxide.

The amount of cerium oxide powder in the slurry is preferably 0.1 to 50 wt%. When the cerium oxide powder in the slurry is less than 0.1 wt%, the polishing rate of the silicon oxide film may be significantly lowered, and when it exceeds 50 wt%, There is a problem in that it is impossible to supply a stable slurry during the dispersion and polishing of high viscosity.

The dispersant used in the slurry of the present invention may use a nonionic polymer or an anionic polymer, and non-limiting examples thereof include poly vinyl alcohol (PVA), ethylene glycol (EG), glycerin, polyethylene Nonionic polymers such as polyethylene glycol (PEG), polypropylene glycol (PPG), or polyvinyl pyrrolidone (PVP), or polyacrylic acid, polyammonium acrylate, or polyacrylic acid Anionic polymers can be used.

The dispersant may be included in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of cerium oxide, and when the content is less than 0.5 parts by weight, the dispersing force of the abrasive particles in the slurry is lowered, so that the precipitation proceeds quickly and precipitates even when the abrasive is transported. (Separation of solid and liquid) may occur. In addition, when the amount exceeds 10 parts by weight, a sufficient selection ratio may not be realized during polishing.

The content of water in the slurry of the present invention may be included as much as the remaining amount after the content of the abrasive particles, dispersant, other additives, etc. is determined.

Step d) is a step of dispersing by milling in order to make a stable and uniform slurry after mixing the cerium oxide, dispersant and water.

Dispersion by milling is preferably carried out by a wet grinding method so as to control the particle size finely and accurately, a method using a milling media such as balls or beads can be used, and the non-limiting Examples include ball mills, bead mills, and attention mills.

As described above, the milling step d) is for removing alleles having an average particle diameter of 3 μm or more, so that milling speed is adjusted in a range of 20 to 120 rpm to apply low energy to the cerium oxide particles during milling, and a diameter of 0.5 mm to It is preferable to use beads in the 2 mm range.

At this time, it is preferable to mill using only one bead of the above-mentioned diameter range, but it is also possible to mix and use 2 or more types of beads within the said diameter range. In general, high-speed, high-energy milling has been known to have a problem of abrasion of beads when mixed with beads of different sizes, but bead wear is not a problem in low-energy milling such as the present invention. It is also possible to use a mixture of.

After the milling, the cerium oxide powder dispersed in the final slurry is preferably such that the average particle diameter is in the range of 50 nm to 1㎛. If the average particle diameter is smaller than 50 nm, there is a problem that the polishing rate is lowered. If the average particle diameter is smaller than 1 μm, problems may occur such as an increase in the polishing rate of the silicon nitride film (a decrease in selectivity), generation of fine scratches on the polished surface, and a decrease in storage stability. More preferably, the average particle diameter of the cerium oxide powder dispersed in the final slurry may range from 70 nm to 300 nm. The particle size was measured using a particle size distribution measuring device (Horiba LA-910).

On the other hand, the cerium oxide slurry production method of the present invention may further comprise a step of dispersing by applying ultrasonic (sonication) to the milled cerium oxide slurry as described above.

The ultrasonic dispersion may be one known to those skilled in the art as a dispersion method by ultrasonic waves commonly used for particle dispersion, and is not particularly limited in the present invention, but a non-limiting example is a bath type, a tip ( tip type, continuous type, and the like, and the output of the ultrasonic dispersion device may range from 200 to 1500 W, preferably 700 to 1200 W.

The method of manufacturing the cerium oxide slurry of the present invention may further include filtration of the milled cerium oxide slurry to remove alleles.

The filtration may be known to those skilled in the art as a filtration method commonly used for fine particle classification, and is not particularly limited in the present invention, but non-limiting examples of the filtration method include a circulation method and a pass. ) And the like. In the circulation method, the pump and filter are connected to the slurry tank to continuously circulate the slurry, and the pass method is a method in which a pump and a filter are installed between the two slurry tanks to be repeatedly transported.

On the other hand, the cerium oxide slurry prepared by the method of milling using beads in the range of 0.5 mm to 2 mm in diameter at a milling speed in the range of 20 to 120 rpm as described above is characterized by minimizing alleles of 3 μm or more. And, the number of particles 3㎛ or more per ml of slurry may be 20000 or less.

The number of large particles may vary depending on the measuring method, measuring equipment and measuring conditions (slurry concentration, slurry dilution ratio, data collection time, etc.).

For example, a cerium oxide slurry having a concentration of 5 wt% may be measured five times using a fixed sample dilution value of 800, and then the average value obtained by averaging the remaining three values and discarding the two large deviations may be used. .

On the other hand, the CMP slurry of the present invention is an additive for improving polishing performance, for example, a weight average molecular weight of 500 or less, and a monomer material containing any one or both of hydroxy group (OH) and carboxyl group (COOH) In addition, the polymer may further include a linear polymer material having a weight average molecular weight of 2,000 to 50,000, or a graft type polymer acid having a weight average molecular weight of 1,000 to 20,000, but is not limited thereto.

On the other hand, the present invention provides a shallow trench isolation (STI) method of the semiconductor device to which the CMP slurry as described above is applied, the shallow trench isolation method according to the STI method commonly used in the art Of course, it can be carried out.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited thereto.

Example 1

1 kg of cerium carbonate powder was charged into an alumina crucible, and the pulverized powder was calcined at 750 ° C. for 2 hours to prepare a very light yellow cerium oxide powder. The calcined cerium oxide powder was ground with a jet mill to prepare a powder having an average particle diameter of 1 μm.

500 g of the cerium oxide powder prepared above, 10 g of a polyacrylic acid dispersant (Aldrich), and 5 L of pure water were mixed and then adjusted to pH 7.5 by adding ammonia water to prepare a dispersion of cerium oxide.

The cerium oxide dispersion was placed in a 1 L bottle made of polypropylene, 1.4 kg of zirconia beads having a diameter of 1 mm was put as milling media, and then milled at 75 rpm to obtain a dispersed slurry. The obtained dispersion slurry was filtered with a 0.3 μm filter and distilled water was added to adjust the cerium oxide powder content to 5 wt% based on the total weight of the slurry.

In addition, the slurry was sonicated for 1 hour at an output of 1000 W using a sonicator.

The average particle diameter of the cerium oxide powder dispersed in the slurry was measured by a particle size distribution analyzer (Horiba LA-910), it was confirmed that the average particle diameter is 217nm.

Meanwhile, after preparing a 1wt% aqueous solution of gluconic acid, the solution was adjusted to pH 7.2 by adding ammonium hydroxide (NH ₄ OH) to the aqueous solution. The aqueous solution was mixed to 2 wt% to prepare a CMP slurry.

㎛ 이상 거대입자의 개수는 5077개임을 확인하였다. The number of large particles was measured by Accusizer FX (NICOMP), diameter 3

It was confirmed that the number of the larger particles was 5077 or more.

 Example 2

A cerium oxide slurry for CMP was prepared in the same manner as in Example 1 except that no sonication treatment was performed on the dispersion slurry.

㎛ 이상 거대입자의 개수는 14068개였다. The average particle size was 221 nm and the diameter was 3

The number of the microparticles | fine-particles or more was 14068 pieces.

Comparative Example 1

After milling to an average particle size of 500 nm using zirconia beads of 1 mm in diameter, milling again to a target particle size of 220 nm using zirconia beads of 0.3 mm in diameter, the milling speed was 150 rpm, and the sonication treatment for the dispersion slurry was performed. A cerium oxide slurry for CMP was prepared in the same manner as in Example 1, except for not performing the same.

The average particle size was 220 nm and the number of large particles having a diameter of 3 μm or more was 35851.

Comparative Example 2

Zirconia beads with a diameter of 0.1 mm were used only, and the milling speed was 3000 rpm using an Ultra APEX mill (Kotobuki, Japan), and the same method as in Example 1 except that no sonication treatment was performed on the dispersion slurry. A cerium oxide slurry for CMP was prepared.

㎛ 이상 거대입자의 개수는 30000개였다. Average particle size was 220 nm, diameter 3

The number of microparticles | fine-particles or more were 30000 pieces.

Comparative Example 3

Oxidation for CMP was carried out in the same manner as in Example 1 except that the zirconia beads with a diameter of 3 mm were milled to an average particle diameter of 500 nm, followed by milling again to a target particle size (220 nm) using zirconia beads with a diameter of 1 mm. Cerium slurry was prepared.

The average particle size was 223 nm and the number of large particles having a diameter of 3 μm or more was 21032.

Particularly, in the case of Comparative Example 3, the number of macroparticles in the slurry was tested in the same conditions as in Example 1 except that 3 mm beads outside the scope of the present invention were used in one step and 1 mm beads were used in two steps. In the present invention, it can be seen that the bead size range and the milling speed described in the present invention are effective for removing macroparticles. It was found that one-step milling within the bead size and milling speed range of the present invention is more effective than two-stage milling.

TABLE 1

Bead size (mm) Milling speed (rpm) Average particle size (nm) Sony Number of large particles over 3㎛ (EA / ml) Example 1 One 75 217 O 5077 Example 2 One 75 221 X 14068 Comparative Example 1 1 / 0.3 150 220 X 35851 Comparative Example 2 0.1 3000 220 X 30000 Comparative Example 3 3/1 75 223 O 21032

 Experimental Example 1

The polishing performance of the CMP slurry prepared in Examples and Comparative Examples was evaluated on wafers on which silicon oxide films were deposited at a thickness of 7000 kPa by plasma enhanced chemical vapor deposition (PECVD). 100 mL of CMP slurries were added dropwise to the polishing plate with a polyurethane polishing pad, respectively, for 1 minute. At this time, the substrate holder was pressed to the surface plate at a pressure of 280 g / cm 2, and the substrate holder and the surface plate were ground while rotating at 90 rpm, respectively, and the downforce was 4 psi. After the polishing, the substrate was cleaned and the film thickness change before and after polishing was measured using a film thickness measuring apparatus (Nanospec 6100, Nanometrics, USA).

In the surface scratch analysis, the nitride film was etched and stripped after pattern wafer polishing, and the scratch number of the wafer surface was counted with KLA-TENCOR Puma 9000.

TABLE 2

Oxide polishing speed (Å / min) Final WIWNU (%) Scratch number less than 20㎛ (EA) Example 1 3257 1.95 310 Example 2 3026 2.12 344 Comparative Example 1 3120 3.36 5994 Comparative Example 2 3200 3.2 3500 Comparative Example 3 3212 2.98 1451

As can be seen in Table 2, when the cerium oxide slurries prepared in Examples 1 and 2 were polished, scratches were less generated on the wafer than in the cerium oxide slurries prepared in Comparative Examples 1 to 3. Figure (WIWNU, Within Wafer Non-Uniformity) (%) also showed an excellent value.

1 is a schematic diagram of a method of separating a typical shallow trench device.

<Description of the symbols for the main parts of the drawings>

100: semiconductor substrate 101: pad silicon oxide film (SiO ₂ )

102: silicon nitride film (Si ₃ N ₄ ) etching termination layer

103: trench 104: silicon oxide film for insulation

105: gate silicon oxide film

Figure 2 is a flow chart for the manufacturing process of the cerium oxide slurry according to an embodiment of the present invention.

3 is a schematic diagram illustrating the removal of macroparticles by comparing the sizes of beads and cerium oxide particles in one embodiment of the present invention.

4 is a view showing a micro scratch measurement result of the surface after polishing the wafer according to an embodiment of the present invention.

Claims (11)

a) calcining cerium carbonate as a raw material to produce cerium oxide; b) grinding the cerium oxide firstly; c) mixing the primary pulverized cerium oxide with a solvent and a dispersant to prepare a slurry; And d) milling the mixed cerium oxide slurry using beads having a diameter of 0.5 mm to 2.0 mm at a milling speed ranging from 20 to 120 rpm. Method for producing a cerium oxide slurry including. The method according to claim 1, wherein the milling is performed using beads having a diameter of 0.7 mm to 1.2 mm at a milling speed in a range of 50 to 100 rpm. The method of claim 1, wherein the average particle diameter of the cerium oxide particles after the first grinding is in the range of 500 to 1.5㎛. The method according to claim 1, wherein the average particle diameter of the cerium oxide particles in the cerium oxide slurry after milling is in the range of 50 nm to 1 µm. The method of claim 1, wherein the primary grinding is characterized by a jet mill method. The method of claim 1, further comprising dispersing by sonication in the milled cerium oxide slurry. The method of claim 1, further comprising filtration of the milled cerium oxide slurry to remove alleles. The method of claim 1, wherein the dispersant is selected from the group consisting of polyvinyl alcohol, ethylene glycol, glycerin, polyethylene glycol, polypropylene glycol, polyvinyl pinolidon, polyacrylic acid, poly ammonium salt of polyacrylic acid and polyacrylic maleic acid Manufacturing method. The method of claim 1, wherein the content of the dispersant is 0.5 to 10 parts by weight based on 100 parts by weight of cerium oxide. A cerium oxide slurry produced by the method according to any one of claims 1 to 9, wherein the number of particles having a thickness of 3 µm or more per ml of the slurry is 20,000 or less. Shallow Trench Isolation (STI) method characterized by using the cerium oxide slurry according to claim 10.

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