JP7326036B2 - Cathode unit for magnetron sputtering equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode unit for a magnetron sputtering apparatus, and more particularly to a cathode unit suitable for forming a predetermined thin film such as an oxide film or a nitride film by reactive sputtering by also introducing a reaction gas.

For example, by sputtering a target made of a metal such as aluminum or copper or an alloy containing these, the metal is deposited on the surface of a substrate such as a silicon wafer with a good in-plane uniformity of film thickness of ±3% or less, more preferably about ±1%. A cathode unit for a magnetron sputtering apparatus used for depositing films and alloy films is known, for example, from US Pat. This device is provided with a magnet unit which is arranged on the side opposite to the sputtering surface of a target having a circular outline matched to the substrate and which is rotationally driven about the center of the target. The magnet unit is a first magnet in which a plurality of magnet pieces are arranged without gaps on the main surface (target-side surface) of a plate-shaped yoke along the outline of, for example, a circular shape, an elliptical shape obtained by deforming a circular shape, or a heart shape. and a second magnet in which a plurality of magnet pieces having the same magnetization are arranged in a line without gaps, surrounding the first magnet with a predetermined interval, with the polarities on the target side being changed. A leakage magnetic field, which is offset in one radial direction with respect to the center of the target and has an endless position where the vertical component of the magnetic field is zero, acts in front of the sputtering surface.

The above cathode unit is attached to a vacuum chamber of a sputtering apparatus, a rare gas (sputtering gas) such as argon gas is introduced at a predetermined flow rate into the vacuum chamber in a vacuum atmosphere in which the substrate is present, and direct current power having a negative potential is applied to the target. or AC power of a specified frequency. An endless plasma is then generated in front of the sputtering surface between the substrate and the sputtering surface of the target. Then, the target is sputtered by ions of the sputtering gas ionized by the plasma, and sputtered particles that scatter from the sputtering surface according to a predetermined cosine law adhere and accumulate on the substrate surface to form a predetermined thin film. At this time, the sputtering surface of the target is eroded so that the shape of the plasma is transferred. While forming a film on the substrate surface, the target can be eroded over substantially the entire surface.

Here, for example, an ITO target is used as a target, and when an ITO film is formed on the substrate surface by reactive sputtering by introducing a rare gas as a sputtering gas and an oxygen gas as a reaction gas at a predetermined flow rate during film formation, metal In-plane uniformity of film thickness equivalent to that in the case of forming a film or the like can be obtained. However, when the film quality of the deposited thin film is evaluated by, for example, a specific resistance value, an annular region having a relatively high specific resistance value is generated in the substrate surface and includes the center of the target inside, resulting in a surface with good film quality. It was found that internal uniformity could not be obtained. Therefore, the present inventors conducted extensive research and found that a region with a high specific resistance value corresponds to a region inside the first magnet where the constant leakage magnetic field does not act. It has been found that the reactivity is locally decreased.

JP 2010-245296 A

The present invention has been made based on the above knowledge, and when a predetermined thin film is formed on a substrate surface by reactive sputtering, while obtaining a good uniformity of the film thickness distribution, a good in-plane film quality can be obtained. It is an object of the present invention to provide a cathode unit for a magnetron sputtering apparatus in which uniformity can also be obtained.

In order to solve the above problems, a cathode unit for a magnetron sputtering apparatus of the present invention is arranged on the side opposite to the sputtering surface of a target installed in a vacuum chamber, and is driven to rotate around the center of the target. A magnet unit is provided, and the magnet unit has a first magnet arranged in an annular shape and a second magnet surrounding the first magnet with a first spacing, with the polarities on the target side being changed, so that the The offset first leakage magnetic field, in which the position where the vertical component of the magnetic field is zero is closed endlessly, is applied in front of the sputtering surface, and the second magnetic field is annularly arranged inside the first magnet with a second interval. It is characterized in that three magnets are provided by changing the polarities of the first magnet and the target side so that an endless second leakage magnetic field acts on the inside of the first leakage magnetic field and in front of the sputtering surface.

According to the above, the cathode unit is attached to a vacuum chamber of a sputtering apparatus, a sputtering gas is introduced at a predetermined flow rate into the vacuum chamber in a vacuum atmosphere in which the substrate exists, and DC power having a negative potential or a predetermined frequency is applied to the target. Turn on AC power. As a result, an endless plasma (hereinafter referred to as "first plasma") is generated in front of the sputtering surface, and another endless plasma (hereinafter referred to as "first plasma") is generated inside the first plasma. , referred to as “second plasma”) are generated substantially concentrically. When a film is formed on the substrate surface by reactive sputtering by introducing a reactive gas such as oxygen gas at a predetermined flow rate during film formation, the reactivity between the sputtered particles and the reactive gas is improved by the second plasma. Good in-plane uniformity of film quality can be obtained.

In addition, the existence of the second plasma expands the eroded region of the sputtering surface toward the center of the target, thereby improving the target utilization efficiency. However, since electrons and secondary electrons are trapped even in the second leakage magnetic field, thermal damage to the substrate can be reduced. Moreover, since the electrons in the first plasma and the electrons in the second plasma move in opposite directions to each other according to the polarities of the first, second and third magnets on the target side, the first plasma and the stability of the second plasma is improved. When the second plasma is generated substantially concentrically inside the first plasma as described above, the scattering distribution of the sputtered particles scattered from the sputtering surface of the target changes. sexuality may be compromised. In such a case, for example, if the sputtering conditions such as the distance between the sputtering surface of the target and the substrate surface (for example, shortening the so-called inter-TS distance) and the partial pressure of the sputtering gas during sputtering are set appropriately, In-plane uniformity of film thickness can be adjusted.

By the way, when the first magnet, the second magnet, and the third magnet are configured by arranging, for example, a plurality of magnet pieces with the same magnetization in a line without gaps along a predetermined contour, the first leakage magnetic field is stronger than the first leakage magnetic field. 2 The leakage magnetic field of the leakage magnetic field is weakened. When the target is sputtered in this state, the portion of the target facing the region where the plasma density is relatively high due to the action of the first leakage magnetic field is preferentially eroded. As the target erodes, the distance between the target and the first magnet, the second magnet, or the third magnet (the distance between the TMs) increases, causing the second leakage magnetic field to act and the plasma density to become relatively low. There is a risk that the second plasma (in other words, the plasma impedance is relatively high) will become unstable (that is, the plasma will extinguish). Therefore, in the present invention, it is preferable to employ a configuration further comprising a first moving means for moving at least the third magnet relative to the first magnet in a direction toward or away from the sputtering surface of the target. According to this, as the target erodes, for example, the third magnet is brought closer to the sputtering surface of the target (that is, the inter-TM distance between the target and the third magnet is locally shortened). By increasing the magnetic field intensity of the second leakage magnetic field, it is possible to prevent the second plasma from becoming unstable.

Further, the present invention further comprises second moving means for reciprocating the first magnet, the second magnet and the third magnet integrally and parallel to the sputtering surface along the direction in which the first leakage magnetic field is offset. is preferred. According to this method, the entire sputtering surface is eroded by moving the first magnet, the second magnet, and the third magnet at a predetermined cycle, or by reciprocating them with a constant stroke during film formation. This is advantageous because it can be used as a region and the efficiency of using the target can be further improved.

1 is a schematic cross-sectional view of a sputtering apparatus provided with a cathode unit according to an embodiment of the invention; FIG. FIG. 3 is a schematic plan view of the cathode unit viewed from the target side.

Hereinafter, with reference to the drawings, the target is an ITO target, and is applied to a magnetron type sputtering apparatus capable of forming an ITO film on the surface of a substrate Sw having a circular contour such as a silicon wafer by reactive sputtering in which oxygen gas is also introduced. The cathode unit CU according to the embodiment of the present invention will be described by taking as an example the case where In the following, directions such as up and down are based on the installation posture of the sputtering apparatus shown in FIG.

Referring to FIG. 1, Sm is a magnetron type sputtering apparatus provided with the cathode unit of this embodiment. A sputtering apparatus Sm comprises a vacuum chamber 1 . The vacuum chamber 1 is provided with an exhaust port 11 to which one end of an exhaust pipe 21 is connected. The other end of the exhaust pipe 21 is connected to a vacuum pump 2 composed of a rotary pump, a cryopump, a turbomolecular pump, or the like, so that the inside of the vacuum chamber 1 can be evacuated to a predetermined pressure. The vacuum chamber 1 is also provided with a gas introduction port 12 to which one end of a gas introduction pipe 31 is connected. The other end of the gas introduction pipe 31 communicates with a gas source (not shown) through flow rate control valves 32a and 32b configured by a mass flow controller or the like, and argon gas (rare gas) and oxygen as sputtering gases whose flow rates are controlled. A gas (reactive gas) can be introduced into the vacuum chamber 1 .

A stage 4 is arranged below the vacuum chamber 1 with an insulator 41 interposed therebetween, and the substrate Sw is placed on the stage 4 . The stage 4, although not shown and described, is composed of, for example, a metal base having a cylindrical outline and a chuck plate adhered to the upper surface of the base. It can be adsorbed and held. As for the structure of the electrostatic chuck, since a known one such as a monopolar type or a bipolar type can be used, further detailed description will be omitted. Further, the base may incorporate a coolant circulation passage and a heater so that the substrate Sw can be controlled at a predetermined temperature during film formation. A cathode unit CU of this embodiment is detachably attached to the upper portion of the vacuum chamber 1 so as to face the substrate Sw placed on the stage 4 .

Also referring to FIG. 2, the cathode unit CU is composed of a target 5 made of ITO and a magnet unit 6 arranged above the target 5 . The target 5 is made circular in plan view according to the contour of the substrate Sw by a known method. The target 5 is attached to the top of the vacuum chamber 1 via an insulator 53 with the sputtering surface 52 facing downward while being mounted on a backing plate 51 . A sputtering power supply Ps having a known structure is connected to the target 5 so that DC power having a negative potential, pulse DC power, or high-frequency power can be applied during film formation by sputtering. The magnet unit 6 arranged above the target 5 has a first magnet 61a which is arranged radially in one direction with respect to the target center Tc and which is arranged in an annular shape having a substantially heart-shaped outline, and a first space D1. A second magnet 61b surrounding the first magnet 61a and a third magnet 61c annularly arranged with a second gap D2 inside the first magnet 61a are arranged on the target 5 side (the lower surface side thereof). The polarities are exchanged with each other. As for the arrangement of the first magnets 61a and the second magnets 61b, which can obtain good uniformity of the film thickness distribution, a known arrangement can be used, so further explanation is omitted.

The first magnet 61a and the second magnet 61b are arranged on the lower surface of a heart-shaped plate-like first yoke 62a that substantially matches the outline of the second magnet 61b. That is, the first magnet 61a and the second magnet 61b are arranged on the lower surface (main surface) of the first yoke 62a along the outline of a heart shape with a plurality of cylindrical magnet pieces 63 having the same magnetization. and are configured. At a predetermined position of the first yoke 62a, an accommodation space 64 is formed penetrating in the plate thickness direction (see FIG. 1). 2 yokes 62b are arranged. In this case, as will be described later, the second yoke 62b can be connected to the second rotating shaft and has a substantially Z-shaped vertical cross section so as not to interfere with the first yoke 62a when vertically moved. there is A third magnet 61c is formed by arranging a plurality of columnar magnet pieces 63 having the same magnetization as described above along the outline of a heart shape without gaps on the lower surface (principal surface) of the second yoke 62b. ing. As a result, a first leakage magnetic field Mf1 that is offset in one radial direction with respect to the target center Tc and the position where the vertical component of the magnetic field is zero closes endlessly, and a vertical component of the magnetic field inside the first leakage magnetic field Mf1. A second leakage magnetic field Mf2 that endlessly closes the position where is zero acts below the sputtering surface 52 . In this case, the number of magnet pieces 63 constituting the first magnet 61a, the second magnet 61b and the third magnet 61c is gradually reduced, so that the first magnet 61a and the second magnet 61b are arranged in the same plane parallel to the sputtering surface 52. And when the lower surface of the third magnet 61c is positioned, the magnetic field strength of the second leakage magnetic field Mf2 is weaker than that of the first leakage magnetic field Mf1.

The first yoke 62a is attached to the lower surface of the rotating plate 71 made of the same material. A hollow first rotating shaft 72 is connected to the rotating plate 71 so as to be aligned with an imaginary axis extending vertically through the target center Tc. A first gear 72a is fitted around the first rotating shaft 72, and a second gear 72b is in mesh with the first gear 72a. By rotating the second gear 72b by the motor M1, the rotating plate 71 is rotated at a predetermined speed via the first rotating shaft 72. As shown in FIG. Further, the rotating plate 71 is formed with a central opening (not shown) penetrating in the plate thickness direction having a hole axis coinciding with the imaginary axis line. The lower end of the solid second rotating shaft 73 arranged in the upper end of the second yoke 62b is inserted therethrough and connected to the upper surface of the second yoke 62b.

The portion of the second rotating shaft 73 located within the first rotating shaft 72 is formed as a spline shaft portion (not shown) and engages a ball spline nut 74 provided at a predetermined position within the first rotating shaft 72. there is As a result, the second rotating shaft 73 is rotated in synchronization with the rotation of the first rotating shaft 72, and the motor M1 rotates the first magnet 61a, the second magnet 61b, and the third magnet 61c around the target center Tc. driven. A portion of the second rotating shaft 73 projecting upward from the first rotating shaft 72 is formed as a threaded portion (not shown), and a ball screw nut 75 is screwed thereon. By rotationally driving the ball screw nut 75 by the motor M2, the second rotating shaft 73 moves up and down with a predetermined stroke, thereby moving the third magnet 61c up and down with respect to the first magnet 61a (target direction). In this embodiment, parts such as the motor M2 and the ball screw nut 75 constitute the first moving means. The vertical movement stroke of the third magnet 61c is appropriately set according to the thickness of the target 5 when not in use. The deposition of the ITO film using the sputtering apparatus Sm including the cathode unit CU of this embodiment will be described below.

After placing the substrate Sw on the stage 4 , the vacuum pump 2 evacuates the inside of the vacuum chamber 1 to a predetermined pressure. When the inside of the vacuum chamber 1 reaches a predetermined pressure, argon gas and oxygen gas are introduced at a predetermined flow rate, and DC power having a negative potential, pulsed DC power, or high-frequency power is applied to the target 5 by the sputtering power source Ps. . Then, an endless first plasma (not shown) is generated below the sputtering surface 52 by the first leakage magnetic field Mf1, and an endless second plasma (not shown) is substantially generated inside the first plasma. occur concentrically. At the same time, the motor M1 rotates the first magnet 61a, the second magnet 61b, and the third magnet 61c around the center of the target at a predetermined speed. As a result, the target 5 is sputtered by the ions of the sputtering gas ionized by both the first and second plasmas, and the sputtered particles that scatter from the sputtering surface 52 according to a predetermined cosine law react with the oxygen gas and reach the upper surface of the substrate Sw. An ITO film is formed by adhesion and deposition. At this time, the reactivity between the sputtered particles scattered from the sputtering surface 52 and the reactive gas is improved by the second plasma, so that excellent in-plane uniformity of film quality can be obtained. When the second plasma is generated substantially concentrically inside the first plasma as described above, the scattering distribution of the sputtered particles scattered from the sputtering surface 52 changes. may be impaired. In such a case, for example, by appropriately setting the sputtering conditions such as the distance between the TSs between the sputtering surface 52 of the target 5 and the upper surface of the substrate Sw and the partial pressure of the sputtering gas during sputtering, the in-plane thickness of the film can be reduced. Uniformity can be adjusted.

By the way, in the magnet unit 6, the leakage magnetic field of the second leakage magnetic field Mf2 is weaker than the first leakage magnetic field Mf1. A portion of face 52 will be preferentially eroded. As the erosion of the target 5 increases the distance between the TMs between the sputtering surface 52 and the first magnet 61a, the second magnet 61b, or the third magnet 61c, the second leakage magnetic field Mf2 acts to generate plasma. There is a risk that the second plasma, which has a relatively low density (in other words, a relatively high plasma impedance), becomes unstable (that is, the plasma arc extinguishes). In this case, the ball screw nut 75 is rotationally driven by the motor M2 to move the third magnet 61c relative to the first magnet 61a in the direction of approaching the sputtering surface 52 via the second rotating shaft 73 ( That is, by shortening the distance between the TMs of the third magnet 61c and increasing the magnetic field intensity of the second leakage magnetic field Mf2, it is possible to prevent the second plasma from becoming unstable.

According to the above, if the ITO film is formed by the sputtering apparatus Sm including the cathode unit CU of the present embodiment, it is possible to obtain excellent in-plane uniformity of film quality while obtaining excellent uniformity of film thickness distribution. becomes possible. In addition, the use efficiency of the target 5 can be improved by expanding the eroded region of the sputtering surface 52 toward the target center Tc due to the presence of the second plasma. In this case, the rotating plate 71 is provided with a direct-acting motor M3 as a second moving means, and the first magnet 61a is moved in the radial direction (horizontal direction in FIG. 2) as the direction in which the first leakage magnetic field Mf1 is offset. , the entire cathode unit CU including the second magnet 61b and the third magnet 61c may be moved parallel to the sputtering surface 52 at a predetermined cycle, or may be reciprocated with a constant stroke during film formation. As a result, the erosion area can be expanded to the outer peripheral side of the target 5, and the usage efficiency of the target 52 can be further improved. Further, in the conventional example, electrons and secondary electrons act on the substrate Sw in the region where the leakage magnetic field does not act. Thermal damage of Sw can be reduced. Moreover, since the electrons in the first plasma and the electrons in the second plasma move in opposite directions to each other according to the polarities of the first magnet 61a, the second magnet 61b and the third magnet 61c on the target side, Stability of the first plasma and the second plasma is improved.

In order to confirm the above effect, the following experiment was conducted. That is, the target 5 of the cathode unit CU is made of ITO with a diameter of 400 mm, and the first magnet 61a and the second magnet 61b as the magnet unit 6 are concentrically arranged in a heart shape with a first spacing D1, and are made of aluminum, copper, or the like. When a metal film or an alloy film is formed by sputtering a target made of a metal or an alloy containing these, existing ULVAC products that can form a film with a good in-plane uniformity of ± 3% or less ( The third magnet 61c is further concentrically arranged in a heart shape inside the first magnet 61a of the cathode unit CU of the conventional product with a second spacing D2, and the TM distance of the third magnet 61c can be changed. (inventive product) were prepared and attached to the sputtering apparatus Sm, respectively, and an ITO film was formed on the surface of a silicon wafer Sw of Φ300 mm. As the sputtering conditions, the distance between the target 5 and the silicon wafer Sw was set to 95 mm, the power supplied by the sputtering power source Ps was set to 4.0 kW, the sputtering time was set to 25 sec, and the rotational speed of the magnet unit 6 was set to 30 rpm. Also, argon gas and oxygen gas were used as the sputtering gas, and argon gas was introduced into the vacuum chamber 1 at a flow rate of 200 sccm and oxygen gas at a flow rate of 1 sccm.

According to the above experiments, in the conventional product, the film thickness distribution of the ITO film after film formation is 100 nm ± 1.9%, which is equivalent to the film thickness distribution when a metal film or alloy film is formed. is obtained. On the other hand, looking at the distribution of the specific resistance value, it is 220 μΩm±10%. (that is, a region with low reactivity) is formed. On the other hand, in the inventive product, when the first magnet 61a, the second magnet 61b, and the third magnet 61c are positioned in the same plane parallel to the sputtering surface 52, the distribution of the specific resistance value of the ITO film after film formation is was 190 μΩm±5%, and it was confirmed that the in-plane uniformity of the resistivity value could be improved. At this time, the film thickness distribution of the ITO film after film formation was 100 nm±1.4%. In addition, in the inventive product, when film formation was continuously performed on a plurality of substrates Sw, as the integrated power to the target 5 increased (that is, the erosion of the sputtering surface 52 of the target 5 progressed). ), the film thickness distribution and the resistivity distribution tended to deteriorate. Therefore, when the third magnet 61c was moved downward relative to the first magnet 61a by a predetermined stroke (the distance between the TMs was shortened), the film thickness distribution of the ITO film after film formation was 100 nm±1. 4%, and the resistivity distribution was 190 μΩm±5%, confirming that the film thickness distribution and the resistivity distribution as well as the in-plane uniformity were not impaired.

Although the embodiments of the present invention have been described above, various modifications are possible without departing from the scope of the technical idea of the present invention. In the above embodiment, the third magnet 61c is vertically moved relative to the first magnet 61a. , or the first magnet 61a or the second magnet 61b alone may be configured to relatively move in the vertical direction.

In the above-described embodiment, the first magnet 61a, the second magnet 61b and the third magnet 61c are formed by arranging the magnet pieces 63 having the same magnetization along the outline of the heart shape without gaps. , as long as a predetermined in-plane uniformity of film thickness can be obtained when forming a metal film or an alloy film, the first magnet 61a, the second magnet 61b, and the third magnet 61b are not limited to these. The magnet 61c can be composed of an integrated magnet, and its outline may be circular or elliptical, which is a modified circular shape. Further, considering the uniformity of the film quality distribution and the uniformity of the film thickness distribution, the outline of the third magnet 61c can be made different from those of the first magnet 61a and the second magnet 61b. Furthermore, although the magnet piece 63 having the same magnetization is used for the first magnet 61a, the second magnet 61b, and the third magnet 61c, it is described as an example. As the magnet piece 63, magnet pieces different in magnetization from those of the first magnet 61a and the second magnet 61b may be used to appropriately adjust the leakage magnetic field of the second leakage magnetic field Mf2.

Further, in the above embodiment, the case where the target 5 is ITO and the ITO film is formed on the surface of the substrate Sw by reactive sputtering in which oxygen gas is introduced has been described as an example. The present invention can be widely applied to deposition of other oxide films such as films and nitride films such as TiN and SiN by reactive sputtering.

CU... cathode unit, D1... first interval, D2... second interval, M2... motor (first moving means), M3... direct-acting motor (second moving means), Mf1... first leakage magnetic field, Mf2... second Leakage magnetic field Sm Sputtering apparatus Tc Target center 1 Vacuum chamber 5 Target 52 Sputtering surface 6 Magnet unit 61a First magnet 61b Second magnet 61c Third magnet 75... Ball screw nut (first moving means).

Claims (2)

Equipped with a magnet unit arranged on the side opposite to the sputtering surface of the target installed in the vacuum chamber and driven to rotate about the center of the target,
The magnet unit has first magnets annularly arranged on the target-side surface of the first yoke, and second magnets surrounding the first magnets with a first spacing therebetween, with opposite polarities on the target side. , a cathode unit for a magnetron sputtering apparatus that acts in front of a sputtering surface of a first leakage magnetic field that is offset from the target center and closed endlessly at a position where the vertical component of the magnetic field is zero,
A magnet unit includes a second yoke disposed in a housing space formed in a first yoke portion located inwardly of the first magnet, and a second yoke surrounded by the first magnet with a second space therebetween. A third magnet arranged in a ring on the target-side surface of is further provided by changing the polarity of the first magnet and the target side , and an endless magnetic field inside the first leakage magnetic field and weaker than the first leakage magnetic field. When power is applied to the target while the second leakage magnetic field is applied in front of the sputtering surface and the sputtering gas is introduced into the vacuum chamber having a vacuum atmosphere, endless first plasma and second plasma are concentrically generated. configured to
The apparatus further comprises a first moving means for moving the second yoke relative to the first yoke magnet in a direction toward and away from the sputtering surface of the target, and moves the second yoke in the direction toward the target as the target erodes. A cathode unit for a magnetron sputtering apparatus, characterized in that it is configured to stabilize the second plasma . 3. The apparatus further comprises a second moving means for reciprocating the first magnet, the second magnet and the third magnet integrally and parallel to the sputtering surface along the direction in which the first leakage magnetic field is offset. 2. A cathode unit for a magnetron sputtering apparatus according to 1 .

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