JP5077752B2 - Magnetron sputtering equipment - Google Patents

Description

  The present invention relates to a magnetron sputtering apparatus that forms a thin film on a substrate surface using magnetron discharge in which a magnetic field and an electric field are orthogonal to each other.

  In the manufacturing process of electronic components such as semiconductor ICs, liquid crystal displays, and plasma displays, a thin film is formed on the surface of the substrate, so that the deposition rate of the thin film is high and electrons do not collide with the substrate. Magnetron sputtering devices have been used that have the advantage of being possible. According to the magnetron sputtering apparatus, a target disposed in a vacuum chamber so as to face the substrate on the anode side is connected to a predetermined power source, for example, as a cathode, and an inert gas of 13.33 to 0.13 Pa (for example, Ar gas) ), A voltage is applied between the electrodes to cause glow discharge to ionize the inert gas, capture secondary electrons emitted from the target in a plane perpendicular to the magnetic field, and perform cycloid motion on the target surface. The ionization is promoted by colliding with gas molecules, and the target material is condensed and deposited on the substrate as neutral atoms, thereby forming a thin film.

  That is, in the magnetron sputtering apparatus, the inert gas excited to the plasma state exists in a form confined to the target surface due to the influence of the magnetic flux lines generated by the magnetic circuit arranged on the back surface of the target. Glow discharge is performed on the surface, and sputtering is performed by knocking out molecules on the target surface.

  In particular, in the manufacture of liquid crystal displays, plasma displays, and the like, single-wafer sputtering apparatuses that process substrates one by one are used. In addition, as the size of the substrate increases (large area) due to the demand for larger screens and lower display manufacturing costs, manufacturing apparatuses including sputtering apparatuses are also increasing in size. However, since the manufacturing cost increases when the manufacturing apparatus is increased in size, the cost merit due to the increased substrate size is lost. Also, in terms of the performance of the sputtering apparatus, it is necessary to improve the uniformity of the thin film in proportion to the substrate size.

  In order to create a closed space (tunnel-shaped space) for confining an inert gas in a plasma state, a horizontal component (10 mT or more) usually contributes greatly as the direction component of the leakage magnetic field. Therefore, in a normal magnetic circuit in a magnetron sputtering apparatus, in order to create this region (to generate a racetrack-like leakage magnetic field as seen from the plane), a central magnet consisting of a block magnet magnetized in the height direction parallel to the target surface And a magnet unit having a structure in which a block magnet magnetized in the opposite direction so as to surround the central magnet and an outer peripheral magnet made of an arc magnet are fixed on the surface of the yoke.

  That is, in the normal magnetic circuit, the direction of the main magnetic flux generated by the central magnet is parallel to the magnetization direction and is perpendicular to the target. This creates a horizontal magnetic flux flow on the target surface. However, since a permanent magnet having a magnetization direction perpendicular to the direction of the leakage magnetic field necessary for film formation is used, the magnetic resistance increases and the efficiency of the permanent magnet is reduced. For this reason, the magnetic circuit must be enlarged.

  In the magnetron sputtering apparatus, erosion inevitably occurs on the surface of the target during film formation, and in particular, according to the above magnetic circuit structure, the horizontal component (magnetic flux density) of the magnetic field formed above the central magnet. ) Is low (0.1 T or less), the progress of erosion in the region facing the central magnet on the target surface is slow (locally sputtered), and the film thickness of the thin film formed on the substrate becomes uneven. There is a drawback. Therefore, a magnetic circuit structure has been proposed in which the corner shape of the outer peripheral magnet is a horseshoe shape so that the magnetic flux density of the magnetic field lines on the target is uniform at each location (see Patent Document 1).

  In addition, in order to obtain a uniform film quality distribution by a magnet moving type magnetron sputtering apparatus that generates a racetrack plasma, the maximum value of the vertical magnetic field at the end of the magnet long side in the target surface magnetic field is It has been proposed that the maximum value of the vertical magnetic field be 0.8 times or less (see Patent Document 2).

  Further, in the magnetron sputtering apparatus, in order to improve the productivity, for example, the second and second magnetic poles are made to have the same magnetic pole direction on both sides of the first rectangular permanent magnet magnetized in the length direction. The three permanent magnets are juxtaposed, the magnetic pole end faces of these permanent magnets are aligned, and the yoke for magnetically short-circuiting the magnetic pole end faces of the second and third permanent magnets while surrounding the magnetic pole end faces of the first permanent magnet is provided. It has been proposed to form a film on both sides of a magnetic circuit device attached to the magnetic pole ends of the second and third permanent magnets (see Patent Document 3).

Japanese Patent Laid-Open No. 7-34244 (page 3, FIG. 1) Japanese Patent Laid-Open No. 9-310176 (pages 3 to 4, FIGS. 1 and 2) Japanese Examined Patent Publication No. 2-52842 (pages 1 and 2, FIG. 3)

  Even in the conventional magnetic circuit structure as described in Patent Documents 1 and 2, the magnetic field uniformity is improved by arranging a ferromagnetic body (pole piece) on the magnetic pole surface of the permanent magnet on the leakage magnetic field generation side. However, there is a problem that it cannot be put to practical use because the installation space for the pole piece cannot be taken. Therefore, in order to ensure the uniformity of the magnetic field, it is conceivable to reduce the variation in the magnetic characteristics of the single permanent magnet. However, in the magnetic circuit used in the large magnetron sputtering apparatus, all the permanent magnets are formed as a single product. This is difficult, and a large number of pieces divided into appropriate sizes are used in combination. However, in order to ensure a predetermined magnetic field strength, a permanent magnet having a large magnetic property such as a Nd—Fe—B rare earth sintered magnet is used in industrial production. However, since this rare earth sintered magnet tends to cause variations in magnetic properties due to subtle differences in manufacturing conditions in the manufacturing process, all the magnetic properties of a large number of permanent magnets are measured, and appropriate permanent magnets are selected. The production yield of the permanent magnet is lowered, and the production cost of the magnetic circuit is increased.

  Moreover, although the uniformity of film thickness distribution improves by the structure described in patent document 1 and 2, the permanent magnet which has a magnetic pole of a reverse polarity with the magnetic pole of the permanent magnet of the center part is arrange | positioned on the outer side, These The direction of magnetization of the permanent magnet is perpendicular to the component direction of the magnetic flux density necessary to form a magnetic field for creating a space for confining the inert gas in the plasma state. Therefore, a large amount of permanent magnets are required to generate a magnetic field necessary for confinement. In addition, since the yoke (ferromagnetic material) serving as a magnetic path is disposed only on one of the magnetic pole surfaces of the permanent magnet, a substantial portion of the magnetic flux generated from the permanent magnet leaks to the outside of the magnetic circuit, and the generated magnetic flux The utilization efficiency of is reduced. Therefore, in order to increase the utilization efficiency of the generated magnetic flux, it is necessary to install a large amount of permanent magnets on the surface of the yoke. Therefore, since the ratio of the permanent magnet to the total weight of the magnetic circuit is high, there is a problem that the weight of the magnetic circuit is increased and the manufacturing cost thereof is increased.

  The magnetic circuit structure described in Patent Document 3 is a complicated structure in which three types of permanent magnets and a pair of yokes are combined, increasing manufacturing costs and forming a film only in a narrow range, and thus cannot be put to practical use. There is a problem.

  Therefore, an object of the present invention is to more uniformly create a magnetic field for making a region where an inert gas is confined more efficiently than in the past, and to improve the productivity of a thin film, and to manufacture a device. It is an object of the present invention to provide a magnetron sputtering apparatus that prevents an increase in cost.

  In order to achieve the above object, a magnetron sputtering apparatus of the present invention includes a vacuum vessel, a pair of targets installed in the interior thereof at a predetermined interval, and a tunnel-like leakage magnetic field along the surface of each target. A magnet unit for generating, an electric field generating means for generating an electric field in a direction perpendicular to the magnetic field, and a pair of substrates on which a thin film is formed by the magnetic field and a racetrack-like plasma generated by the electric field, The unit includes a straight portion and corner portions at both ends thereof, and at least the straight portion includes a central yoke made of a ferromagnetic material, an outer yoke surrounding the central yoke, and between the central yoke and the outer yoke. It has a permanent magnet installed and magnetized so that the magnetic pole of the same polarity faces the central yoke.

  In the magnetron sputtering apparatus of the present invention, it is preferable that a chamber isolated from the vacuum container is installed and the magnet unit is accommodated in the chamber.

  In the magnetron sputtering apparatus of the present invention, it is preferable that the magnet unit has a protective cover made of a non-magnetic material facing the surface on the side where a leakage magnetic field is generated.

  In the magnetron sputtering apparatus of the present invention, the electric field generating means applies a high frequency voltage to each target, a cathode electrode that supports each target, an anode electrode that faces the cathode electrode through each substrate, and 1 It is preferable to have one or two power supplies.

  According to the magnetron sputtering apparatus of the present invention, it becomes possible to reduce the amount of permanent magnets used, and the ratio of permanent magnets to the manufacturing cost of the magnetron sputtering apparatus can be greatly reduced. The increase in the manufacturing cost due to can be suppressed.

In the present invention, the amount of permanent magnet used can be reduced for the following reasons.
(1) Permanent magnets with magnetization directions parallel to the necessary leakage magnetic field are arranged symmetrically to form a magnetic circuit, so that the magnetic resistance of the magnetic circuit is greatly reduced and the magnetic flux of the permanent magnet is effectively used. Can be used (to generate a magnetic field necessary for efficient confinement).
(2) Since a permanent magnet having a magnetization direction in a direction parallel to the magnetic flux density component necessary to make the region confining the inert gas into a closed space is used, a magnetic field necessary for efficient confinement is generated. Can do.
(3) Since the yoke is in contact with each magnetic pole face of the permanent magnet that generates a racetrack-like magnetic field, and the leakage magnetic flux from the permanent magnet is reduced, the predetermined magnetic field strength is reduced with a smaller amount of permanent magnets than in the past. Can be obtained.

  Also, in terms of the performance of the magnetron sputtering apparatus, the ferromagnetic yoke absorbs variations in the magnetic properties of the permanent magnet alone by arranging the ferromagnetic yoke on the magnetic pole surface of the permanent magnet that contacts the central portion and the outer peripheral portion. Therefore, the effect that the magnetic flux generated from the ferromagnetic yoke can be made more uniform can be obtained.

  In particular, by providing a yoke made of a ferromagnetic material on the magnetic pole surface of the permanent magnet in contact with the central portion and the outer peripheral portion, it is possible to obtain an effect that maintenance of the magnetron sputtering apparatus (target replacement operation, etc.) can be performed smoothly.

  Since the permanent magnets are arranged vertically symmetrically with respect to the target surface, it is usually possible to place the target placed on one side of the magnetic circuit on both sides of the magnetic circuit, and magnetron sputtering on the upper and lower sides of the magnetic circuit. Thus, productivity can be greatly improved.

  Details of the present invention will be described below with reference to the accompanying drawings. 1 is a sectional view of a magnetron sputtering apparatus according to the first embodiment of the present invention, FIG. 2 is a sectional view of a magnetron sputtering apparatus according to the second embodiment of the present invention, and FIG. 3 is a third section of the present invention. FIG. 4 is a cross-sectional view of a magnetron sputtering apparatus according to a fourth embodiment of the present invention, and FIG. 5 is an arrow view of the magnet unit viewed from the direction A in FIG. 6 and 6 are cross-sectional views taken along the line B-B of FIG. 5, and FIG. 7 is a cross-sectional view showing another example of the magnet unit. In FIGS. This is indicated by a symbol.

(First embodiment)
A magnetron sputtering apparatus (hereinafter simply referred to as a sputtering apparatus) shown in FIG. 1 has an inside (center) of a vacuum vessel 2 having a vacuum exhaust port communicating with a vacuum pump and a gas introduction pipe (both not shown) for introducing an inert gas. Part), the magnet unit 3 is installed, a pair of targets 4a and 4b are arranged on both sides of the magnet unit 3, and an electric field generating means 5a (5b) for generating an electric field on the surface of each target is installed. . Further, at the time of film formation, the substrates 6 a and 6 b are arranged inside the vacuum container 2 so as to face the surface of each target. The electric field generating means 5a (5b) includes a cathode electrode 51a (51b) arranged on the back surface of the target 4a (4b) and an anode electrode 52a (on the opposite side of the substrate 4a (6b) from the target 4a (4b)). 52b) and a high frequency power supply 53a (53b) for applying a voltage to both electrodes. As will be described later, the magnet unit 3 has a magnetic circuit structure in which a central yoke, an outer peripheral yoke, and a permanent magnet are combined, and is configured to generate a racetrack-like tunnel magnetic field on the surface of each target 4a (4b). Has been.

According to this sputtering apparatus, an inert gas (for example, 10 to 10 ⁻⁶ Pa Ar gas) is introduced into the vacuum chamber 2 and a high frequency voltage (for example, 0.2 to 10 kV) is applied to the target to continuously The high-density plasma is generated near the surface of the target 4a (4b) by the electric field [for example, power density: (3-30) × 10 ⁻⁶ W / m ² ] perpendicular to the tunnel-like magnetic field, and thus the substrate 6a A thin film is formed on the surface of (6b).

  In FIG. 1, by using two high-frequency power sources 53a and 53b, film forming conditions can be changed between the target 4a and the target 4b. Further, instead of using the two high-frequency power sources 54a and 54b, a single high-frequency power source 53 (shown by a one-dot chain line) is used, and the cathode electrode 51a (51b) and the anode electrode 52a (52b) are connected to this power source. be able to. Thereby, since one power supply can be omitted, the cost of the sputtering apparatus can be reduced.

(Second Embodiment)
The sputtering apparatus shown in FIG. 2 divides the inside of the vacuum vessel 2 with a pair of shielding plates 21a and 21b in FIG. 1, and forms a chamber 20 isolated from the vacuum part between them, and the magnet unit 3 is placed there. It has an arranged structure. According to this structure, since the magnet unit 3 is isolated from the vacuum chamber, the durability of the magnet unit 3 can be improved.

(Third embodiment)
The sputtering apparatus shown in FIG. 3 supports the magnet unit 3 in the vacuum vessel 1 through the slide mechanisms 7a and 7b in FIG. 1 and uses a single high-frequency power source 53. The cathode electrode 51a ( 51b) and an anode electrode 52a (52b) are connected. The slide mechanism 7a (7b) has a slide bearing 73 interposed between a linear guide 71 fixed to both ends (upper end surface and lower end surface) of the magnet unit 3 and a slide base 72 fixed to the inner surface of the vacuum vessel 2. Is. By providing the slide mechanism 7a (7b), the magnet unit 3 can be moved along the surface of the target, so that the magnet unit can be easily installed inside the vacuum vessel 1.

(Fourth embodiment)
The sputtering apparatus shown in FIG. 4 divides the inside of the vacuum vessel 2 with a pair of shielding plates 21a and 21b in FIG. 3, and forms a chamber 20 isolated from the vacuum part therebetween, and the magnet unit 3 is placed there. It is an arranged structure. According to this structure, by providing the slide mechanism 7a (7b), the magnet unit 3 can be moved along the surface of the target, so that the magnet unit can be easily installed inside the vacuum vessel 1. Since the magnet unit 3 is isolated from the vacuum vessel, the magnet unit 3 is prevented from being damaged.

(Magnet unit)
In the sputtering apparatus of the present invention, for example, a magnet unit 3 shown in FIG. 5 can be used. The magnet unit 3 is arranged on the back side of the target at a predetermined interval, is made of a ferromagnetic material (steel material or the like), and has a flat central yoke 31 having both ends formed in an arc shape, It has an elliptical outer peripheral yoke 32 made of a ferromagnetic material (steel material or the like) and installed so as to surround the yoke. Referring also to FIG. 6, the linear portion (length La) has a rectangular space formed between the central yoke 31 and the outer peripheral yoke 32 in a horizontal direction {a plurality of magnetized magnets parallel to the target surface. A block-shaped (rectangular parallelepiped) linear portion permanent magnet 33 is provided. Each of the linear portion permanent magnets 33 is installed such that a magnetic pole having the same polarity, for example, an N pole faces the central yoke 2.

  The corner portion (length Lb) is magnetized in an arcuate space formed between the central yoke 31 and the outer peripheral yoke 32 and on both ends of the central yoke 31 in the horizontal direction (parallel to the target surface). A plurality of block-shaped (cuboid) corner permanent magnets 34 are provided. The permanent magnets 34 for the corner portions are arranged radially so that the same polarity magnetic poles, for example, the N poles, face the central yoke 31, as with the linear portion permanent magnets 33.

  According to the above magnet unit, most of the magnetic flux lines flowing out from the N pole of each permanent magnet flow into the outer yoke 32 from the upper surface after passing through the central yoke 31, and flow into the S pole of each permanent magnet. Magnetic flux concentrates above each permanent magnet, and a magnetic field (perpendicular to the electric field in the vicinity of the electrode) distributed in a racetrack as viewed from the plane is formed. That is, the region where the magnetic field strength (magnetic flux density horizontal component) necessary for confining the inert gas excited in the plasma state (to generate plasma with high electron density) is 10 mT or more is expanded compared to the conventional case. Since the erosion region is expanded, the life of the target is extended, and a film having a uniform thickness can be realized on the substrate. When the width W is 150 mm or less, the magnet unit can realize film formation having a more uniform thickness on the substrate. The width W is preferably 100 mm or less for practical use. The dimension in the length direction may be set according to the substrate size.

  Further, since the amount of use (weight) of the permanent magnet can be reduced by about 20 to 30% compared to the conventional magnet unit (magnetic circuit), the manufacturing cost of the magnet unit can be greatly reduced. Moreover, since the amount of permanent magnets used can be reduced, a single magnetic circuit can be reduced in weight by 10 to 20%. Weight reduction is possible.

  Along with the increase in the size of the sputtering apparatus, the magnet unit also becomes larger (length of 1 m or more), and the target is exchanged under the leakage magnetic field. Therefore, in the conventional magnet unit, the tool is a permanent magnet of the magnet unit. It was inevitable that the permanent magnet was damaged by contact with the magnet. On the other hand, according to the above magnet unit, since the magnetic pole surface of the permanent magnet is covered with the ferromagnetic material, even when the tool comes into contact with the magnet unit, it is prevented from coming into direct contact with the permanent magnet, so that maintenance can be performed. There is an advantage that it can be carried out smoothly (improvement of work efficiency and reduction of burden on workers).

  In the magnet unit, the thickness t1 of the central yoke 31 and the outer yoke 32 is formed to be equal to or greater than the thickness t2 of the linear permanent magnet 33, and the linear permanent magnet 33 is the central yoke 31 and the outer yoke 32. It is installed not to protrude from. Satisfying such a positional relationship greatly reduces the chance that the permanent magnet will come into direct contact with a tool or the like, thereby preventing the permanent magnet from falling over or breaking when the magnet unit 3 is installed in the magnetron sputtering apparatus. Can do. Even when there is no step between the central yoke 31 and the outer yoke 32 and the linear permanent magnet 33, the chance that the permanent magnet comes into contact with a tool or the like is greatly reduced.

  In the sputtering apparatus provided with the above-described magnet unit, in order to further extend the life of the target, it is necessary to perform more uniform sputtering at the corner portion. Therefore, the corner portion permanent magnet 34 is the linear portion permanent magnet 33. It is preferable to form it thinner. However, if the step difference between the corner permanent magnet 34 and the straight portion permanent magnet 33 is too large, the uniformity of the magnetic field of the entire magnetic circuit is impaired, so this step is preferably 10 mm or less.

  The magnet unit is not limited to the structure shown in FIG. 6, but may have a structure in which protective covers 36a and 36b made of a non-magnetic material are provided on both surfaces (surfaces facing the target) as shown in FIG. This is possible, and damage to the magnet unit 3 can be prevented.

  In the present invention, only the linear portion of the magnet unit can have the structure shown in FIG. 6 or FIG. 7, and the corner portion can have another structure. In other words, since the corner portion has a curvature, the plasma becomes unstable and it may be difficult to obtain uniform thin film characteristics. Therefore, the corner portion is installed on both sides of a flat yoke made of a ferromagnetic material, for example. A structure having a first magnet magnetized in the vertical direction and a second magnet provided around the first magnet and magnetized in the opposite direction to the first magnet and having the same height as the first magnet can be provided. Even in this structure, since most of the magnet unit (straight line portion) has the magnetic circuit structure shown in FIG. 6 (FIG. 7), the cost of the sputtering apparatus can be reduced.

  In the present invention, each permanent magnet can be formed of a known permanent magnet material, but it is preferable to use a rare earth magnet in order to obtain a high magnetic flux density, and in particular, R (R is a rare earth element such as Nd). R-T-B system anisotropic sintered magnets containing T (T is Fe or Fe and Co) and B as essential components (various in terms of corrosion resistance). It is more preferable to use those having been subjected to the surface treatment. In this R-T-B system anisotropic sintered magnet, the magnetic flux density on the target surface is improved, the erosion region of the target is expanded, the life of the target is extended, and a uniform thickness is formed on the substrate. In order to realize the film formation having a thickness, it is more preferable to have a magnetic characteristic having a maximum energy product of 40 MGOe or more.

  The present invention is not limited to the above structure, and various modifications can be made. For example, the shape of the corner portion (as viewed from the plane) is not limited to an arc shape, but may be a polygonal shape (eg, a trapezoidal shape).

  In addition, when forming a film on a large substrate (for example, the fourth generation or later) using an integrated target, a plurality of magnetic circuits are installed in parallel at predetermined intervals, and each magnetic circuit is used as a support member. Fix and move (swing) each magnetic circuit to the same extent as the above-mentioned interval (a mechanism for adjusting the distance between the upper surface of each magnetic circuit and the target surface may be provided), and a large area (whole area of the target) Sputtering may be performed.

1 is a cross-sectional view of a magnetron sputtering apparatus according to a first embodiment of the present invention. It is sectional drawing of the magnetron sputtering apparatus concerning the 2nd Embodiment of this invention. It is sectional drawing of the magnetron sputtering apparatus concerning the 3rd Embodiment of this invention. It is sectional drawing of the magnetron sputtering apparatus concerning the 4th Embodiment of this invention. It is the arrow view which looked at the magnet unit in FIG. 1 from the A direction. FIG. 6 is a sectional view taken along line B-B in FIG. 5. It is sectional drawing which shows the other example of a magnet unit.

Explanation of symbols

1: magnetron sputtering device, 2: vacuum vessel, 3: magnet unit, 31: central yoke, 32: outer yoke, 33: permanent magnet for straight portion, 34: permanent magnet for corner portion, 35: protective plate, 4a, 4b : Target, 5, 5a, 5b: Electric field generating means, 51a, 51b: Cathode electrode, 52a, 52b: Anode electrode, 53, 53a, 53b: Power supply, 6a, 6b: Substrate, 7a, 7b: Slide mechanism part, 71 : Base, 72: Bearing, 73: Linear guide

Claims (4)

A vacuum vessel, a pair of targets installed at a predetermined interval therein, a magnet unit installed between the pair of targets and generating a tunnel-like leakage magnetic field along the surface of each target; comprising an electric field generating means for generating an electric field in a direction perpendicular to the leakage magnetic field, a pair of substrates on which the thin film is formed by the leakage magnetic field and racetrack-shaped plasma generated by said electric field, said magnet unit is strong A flat central yoke made of a magnetic material, an oval outer yoke made of a ferromagnetic material so as to surround the central yoke, and a rectangular shape formed between the central yoke and the outer yoke a permanent magnet for a plurality of linear portions disposed in the space, the arc which is and formed on both ends of the central yoke between said center yoke and said outer circumferential yoke A plurality of permanent magnets for the corner portion disposed in the space, the permanent magnets for the permanent magnet the straight portion corner portion has the same polarity magnetic poles of the central yoke while being parallel to the magnetization on the surface of said target A magnetic circuit installed so as to face , the leakage magnetic field is generated on both surfaces of the magnetic circuit facing the surface of each target, and the central yoke, the outer yoke, the linear portion permanent magnet, Each thickness of the corner permanent magnet in a direction perpendicular to the surface of the target is such that the central yoke and the outer yoke are thicker than the linear permanent magnet and the corner permanent magnet, and the corner permanent. The magnet is thinner than the linear part permanent magnet, and the linear part permanent magnet and the corner part magnet are separated from the central yoke and the outer yoke. Magnetron sputtering apparatus characterized by being installed so as not to appear.   2. The magnetron sputtering apparatus according to claim 1, wherein a chamber isolated from the inside of the vacuum vessel is installed, and the magnet unit is accommodated in the chamber. The magnetron sputtering apparatus according to claim 1, wherein the magnet unit is provided with a protective cover made of a non-magnetic material on a surface facing each target .   The electric field generating means includes a cathode electrode that supports each target, an anode electrode that faces the cathode electrode via each substrate, and one or two power sources that apply a high-frequency voltage to each target. The magnetron sputtering apparatus according to any one of claims 1 to 3.

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