JP2010245296A - Film deposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film deposition method of depositing a film at a high bottom coverage rate for fine holes of high aspect ratio with good in-plane uniformity in film thickness distribution. <P>SOLUTION: A substrate W is held in a vacuum chamber 1, and a sputter gas is introduced so that a high-pressure region of 10 to 30 Pa is held in the chamber. A DC voltage is applied to a target 2 disposed opposite in proximity to a substrate and a high-frequency bias voltage is applied to the substrate to generate a convolution plasma, composed of target-side DC plasma and substrate-side high-frequency bias plasma, between the target and substrate, thereby sputtering the target to deposit a film. A magnet unit 6 for generating a magnetic field locally below the target is arranged while offset outward from the target center in a radius direction, and rotated and moved during film depositing so that an outer periphery of the target except at least its center portion is eaten away. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a film forming method using a sputtering method, and more particularly to a film forming method capable of forming a film with a high bottom coverage ratio with respect to a fine hole with a high aspect ratio and with a good uniformity of film thickness distribution.

  In a semiconductor device manufacturing process, for example, a sputtering (hereinafter referred to as “sputtering”) apparatus is used to form various wiring films and a barrier film that prevents mutual diffusion of different layers. This type of sputtering equipment has a high bottom coverage ratio for high-aspect-ratio fine holes due to the recent miniaturization of wiring patterns (deposition rate on the bottom surface of the hole relative to the deposition rate on the surface surrounding the hole). It is strongly demanded that the ratio can be achieved.

  As a sputtering apparatus that can improve the bottom coverage rate, a so-called ionized sputtering apparatus that ionizes sputtered particles made of a metal material such as Cu, Ta, or Ti and uses it for film formation is known from Patent Document 1, for example.

  In the above-mentioned Patent Document 1, a high-frequency power source having a frequency of 13.56 MHz and an output of 8 to 10 kW (a power source for performing high-frequency sputtering) having a frequency of 13.56 MHz is used as a sputtering power source for supplying power to the target. Sputter discharge is generated in a sputtering gas such as Ar to generate plasma in the space between the target and the substrate. Then, the sputtered particles emitted from the target are ionized in the plasma, and a high frequency bias power is applied to a stage that holds the substrate so that the ionized sputtered particles are drawn into the substrate to be incident thereon.

  Here, it is generally known that in a sputtering apparatus using a high frequency power source, if the output frequency (for example, 60 MHz) is increased from the high frequency power source, the plasma density increases accordingly. For this reason, increasing the frequency is applied to the one described in Patent Document 1 to increase the amount of sputtered particles (ionization rate) ionized by the plasma with higher density, and further improve the bottom coverage rate. It is possible to plan. However, such a high-output, high-frequency high-frequency power supply requires a high-performance impedance matching device that matches the input impedance and load impedance in order to efficiently supply the output to the plasma load, and the device configuration is complicated. In addition, there is a problem in that the cost of the device itself is increased.

  Therefore, the present inventors have a first sputtering power source for supplying DC power to the target and a second sputtering power source for supplying high-frequency power to a substrate disposed opposite to the target, and power is supplied from both sputtering power sources. Then, while proposing a sputtering apparatus in which the target and the substrate are arranged in close proximity so that a plasma in which the DC plasma on the target side and the high-frequency bias plasma on the substrate side are generated is generated between the target and the substrate, this sputtering apparatus is proposed. The pressure in the vacuum chamber is 10 to 30 Pa (hereinafter, in the present invention, this pressure range is referred to as a “high pressure region”, and a pressure in the range of 0.1 to 10 Pa lower than this is used. It is proposed to introduce a sputtering gas composed of a rare gas such as Ar so as to be maintained in a “low pressure region” (Japanese Patent Application No. 200). See JP -283,679).

  In the sputtering apparatus, the magnet unit is disposed above the target, with the direction from the target toward the substrate as the lower side and the direction from the substrate toward the target as the upper side. This magnet unit generates a magnetic field in the space below the target, captures electrons etc. ionized below the sputtering surface during sputtering, and efficiently ionizes sputtered particles scattered from the target while increasing the plasma density. . As the magnet unit, when the target has a circular shape in plan view, for example, a unit in which a plurality of magnets are alternately changed in the lower polarity along a circularly deformed ellipse or a heart-shaped outline is used.

  By the way, according to the experiments by the present inventors, when film formation is performed in the high pressure region with the above sputtering apparatus, target erosion is performed as compared with the case where film formation is performed in the low pressure region using the same magnet unit. It was found that the area was narrowed (about 1/5). In this case, if the center portion of the target is eroded by sputtering, the plasma is likely to concentrate at the center of the target, and the film cannot be formed with good in-plane uniformity of film thickness distribution. On the other hand, it has also been found that when the magnet unit is configured so that the central portion of the target is not eroded, the sputtered particles easily adhere to the central portion during film formation. In this case, if a flake-like film is formed in the center of the target due to redeposition, it will cause the generation of particles and adversely affect the film formation on the substrate surface, so the target needs to be frequently replaced, Productivity deteriorates.

JP 2007-197840 A

  Therefore, in view of the above, the present invention provides a highly productive film forming method capable of forming a film with a high bottom coverage ratio and a good in-plane uniformity of film thickness distribution for a high aspect ratio fine hole. The task is to do.

  In order to solve the above problems, the present invention holds a substrate to be processed in a vacuum evacuable chamber so that the pressure in the chamber is maintained in a high pressure region in a pressure range of 10 to 30 Pa. A sputtering gas is introduced, and a DC voltage is applied to a circular target in plan view arranged opposite to the substrate, and a high-frequency bias voltage is applied to the substrate so that the target-side DC plasma and the substrate-side high-frequency bias plasma are superimposed. Film formation method for generating a plasma between the target and the substrate and sputtering the target to form a film on the substrate, wherein the direction from the target to the substrate is downward and the direction from the substrate to the target is upward The magnet unit that locally forms a magnetic field above the target and below the target is turned off radially from the target center. Tsu reports open place, during film formation, and wherein the rotating movement of the magnet unit so that its outer peripheral region excluding the central portion of at least the target is eroded.

  According to the present invention, when the film is formed by sputtering in the high pressure region, the target erosion region becomes narrower as compared with the case where the film is formed in the low pressure region regardless of the form of the magnet unit. If the magnet unit is configured so that it is sputtered to the center, the plasma is more likely to concentrate, but the magnet unit is placed offset radially outward from the center of the target, and this magnet unit is placed on the target during film formation. By rotating and moving as if tracing on the same peripheral surface, it becomes possible to form a film with a high bottom coverage ratio and a film thickness distribution with good in-plane uniformity for a fine hole with a high aspect ratio.

  By the way, in the film forming method, since the central portion of the target is not eroded, sputtered particles are reattached to the central portion during film formation, and a flake-shaped film is formed. Therefore, in the present invention, for example, when the substrate is sequentially transferred to a position facing the target to form a single-wafer type film, the number of film-forming processes on the substrate reaches a predetermined number. It is desirable to periodically perform a dummy process for sputtering the target by controlling the introduction of the sputtering gas so that the inside becomes a low pressure region. As a result, the target erosion area becomes wider compared to the case where film formation is performed in the high pressure region using the same magnet unit, so that the target is sputtered up to the center of the target, and reattaches and flakes. It can be removed up to the film. As a result, the cause of the generation of particles is eliminated, the target need not be frequently replaced, and productivity can be improved. The dummy processing in the present invention refers to a case where a dummy substrate other than the substrate to be deposited is transported to a position facing the target and sputtered, and a shielding means such as a shutter is disposed between the target and the substrate. And the case of sputtering.

  In the present invention, it is optimal that the target is composed of a single metal of Cu, Ti, Co, Ni, Al, W or Ta, or two or more alloys selected from these.

The schematic diagram explaining the structure of the sputtering device which can implement the film-forming method of this invention. The top view explaining the magnet unit shown in FIG. The graph which shows the experimental result which measured the in-plane distribution of the film thickness. The figure which shows the relationship between the chamber internal pressure at the time of film-forming, and the erosion width | variety of a target.

  Hereinafter, referring to the drawings, as a substrate W to be processed, an insulating film formed on a substrate such as a silicon wafer is used in which a fine hole with a high aspect ratio is formed. A film forming method of the present invention that can form a film at a high rate and with good in-plane uniformity of the film thickness distribution will be described.

As shown in FIG. 1, a sputtering apparatus M that can carry out the film forming method of the present invention includes a vacuum chamber 1 having a predetermined volume. A vacuum pump is connected to the side wall in the vicinity of the bottom of the vacuum chamber 1 through an exhaust pipe (not shown) so that it can be evacuated to a predetermined pressure (for example, 10 ⁻⁵ Pa).

  A cathode unit is provided in the upper part of the vacuum chamber 1. The cathode unit is disposed so as to face the sputtering chamber 1a and has a circular target 2 in plan view with an outer shape that is slightly larger than the outer shape of the substrate W. In the present embodiment, a direction from the target 2 toward the substrate W described later is defined as a downward direction, and a direction from the substrate W toward the target 2 is defined as an upward direction.

  The target 2 is made of a simple metal such as Cu, Ti, Co, Ni, Al, W or Ta, or two or more alloys selected from these, and is a thin film to be formed on the surface of the substrate W. Each is prepared by a known method depending on the composition. The target 2 is bonded to a backing plate 3 that cools the target 2 during sputtering through a bonding material such as indium or tin, and the target 2 is bonded to the backing plate 3 to the vacuum chamber 1 via the insulating plate 4. Installed. After the target 2 is mounted, a shield S1 (not shown) serving as an anode grounded to the ground is attached around the target 2. Further, the target 2 is connected to an output from a DC power source 5 that is a first sputtering power source disposed outside the vacuum chamber 1 so that a negative DC voltage (input power is in a range of 1 to 30 kW) can be applied. It has become.

  A magnet unit 6 is provided above the target 2 (on the side opposite to the sputtering surface in FIG. 1), and a balanced closed-loop tunnel-like magnetic field is formed below the target 2, and ionization is performed below the target 2. By capturing the generated electrons and secondary electrons generated by sputtering, the electron density below the target 2 is increased to increase the plasma density, and the sputtered particles scattered from the target 2 are efficiently ionized.

  As shown in FIG. 2, the magnet unit 6 includes a plurality of magnets 62 s and 62 n alternately arranged in a lower polarity along a heart-shaped contour on a circular yoke member 61 in plan view. A known structure is used. The magnet unit 6 is connected to a rotation shaft 63 of a motor (not shown) arranged so as to be positioned on the center line of the target 2, and is rotated about the rotation shaft 63. In this case, the rotation speed is set in the range of 20 to 100 rpm.

  On the bottom of the vacuum chamber 1, a stage 7 for holding the substrate W at a position facing the target 2 is provided via an insulating material 7a. An electrostatic chuck (not shown) is provided on the upper surface of the stage 7 as a substrate mounting surface. After the substrate W is positioned by the electrostatic chuck, it is attracted and held. Further, the stage 7 is connected to an output from a high-frequency power source 8 as a second sputtering power source, and a high-frequency bias voltage can be applied to the substrate W. As the high-frequency power source 8, an existing one having a frequency of 13.56 MHz and an output of 0.1 to 2.0 kW is used.

  The target 2 and the stage 7 (and consequently the substrate W) are superposed with the DC plasma on the target 2 side and the high-frequency bias plasma on the substrate W side when power is applied from both sputtering power sources 5 and 8 in the sputtering gas atmosphere. So as to face each other. In order to generate such superimposed plasma between the target 2 and the substrate W, in the present embodiment, the distance D between them is set in the range of 40 to 70 mm. In order to make the distance D freely changeable, the stage 7 may be provided with lifting means (not shown) with a linear motor.

  According to the sputtering apparatus M of the present embodiment, it is possible to increase the density of plasma generated between the target 2 and the substrate W with a simple configuration using an existing sputtering power source. In the sputtering apparatus M, if the interval is smaller than 40 mm, it is difficult to ensure in-plane uniformity of the film thickness, and if it exceeds 70 mm, the plasma cannot be densified. As a result, it is possible to obtain a high sputter rate in combination with shortening the distance D between the target 2 and the substrate W and applying DC power to the target side, thereby improving productivity. Become.

  On the side wall of the vacuum chamber 1, an earth-grounded adhesion-preventing plate S <b> 2 is provided so as to be movable up and down. Prevents adhesion. Further, a gas pipe 11 connected to a gas source 9 and having a mass flow controller 10 interposed therein is connected to the side wall of the vacuum chamber 1, and a sputtering gas composed of a rare gas such as Ar (in some cases, reactive sputtering). The sputter chamber 1a can be introduced at a constant flow rate through the gap between the deposition preventing plate S2 and the shield S1.

  Next, a method of forming a film on the substrate W using the sputtering apparatus M will be described by taking an example in which a target made of Ti is used as a target. First, in a state where the target 2 is mounted as described above, the substrate W is transported by a transport robot (not shown) and is sucked and held on the stage 7. Then, the vacuum chamber 1 is sealed and evacuated to a predetermined degree of vacuum by a vacuum pump.

  When the pressure in the vacuum chamber 1 reaches a predetermined value, Ar gas (sputtering gas) is introduced from the gas pipe 11 at a predetermined flow rate (2 to 200 sccm), and the target is supplied by the first and second sputtering power supplies 5 and 8. A negative set DC voltage is applied to 2 and a high-frequency bias voltage is applied to the substrate W. At this time, the mass flow controller 10 is controlled to keep the pressure in the vacuum chamber 1 in a high pressure region in the range of 10 to 30 Pa.

  Thereby, high-density plasma superimposed between the target 2 and the substrate W is generated, and the ion sheath region is present in the vicinity of the substrate W. The sputtered particles emitted from the target 2 are efficiently ionized by high-density plasma, and the ionized sputtered particles (Ti) are extracted from the ion sheath region by the high frequency bias voltage applied to the stage 7. At this time, since the extracted sputtered particles have a short interval between the ion sheath region and the substrate W, the sputtered particles are attracted to and incident on the substrate W substantially vertically. As a result, a Ti film is formed with a high bottom coverage rate even for fine holes with a high aspect ratio.

  Here, the inventors conducted the following experiment. That is, in the sputtering apparatus M of FIG. 1, a target unit 2 made of Ti having a diameter of 440 mm (purity 99.99%) is used, and a plurality of magnets 62s and 62n are arranged along a substantially heart-shaped outline. 6 is the position indicated by the alternate long and short dash line in FIG. 2 (in this case, the position of the vertical component 0 of the magnetic field is substantially located at the center of the target 2).

  As sputtering conditions, the interval between the target 2 and the substrate W was set to 45 mm, the input power from the first sputtering power source 5 was set to 14 kW, and the input power from the second sputtering power source 8 was set to 100 W. Further, while controlling the amount of sputtering gas introduced so that the pressure in the vacuum chamber 1 during sputtering is maintained at 30 Pa (high pressure region), the magnet unit 6 is rotated at a rotational speed of 60 rpm for 15 minutes. A film was formed on the substrate W. Then, when the film thickness distribution of a plurality of substrates is measured, it can be seen that the film thickness distribution at the center of the substrate is locally high as shown by-♦-in FIG.

  Next, the position of the magnet unit 6 indicated by the solid line in FIG. 2 (in this case, the position of the vertical component 0 of the magnetic field is offset 10 mm radially outward from the center of the target 2 so that the center of the target 2 is not sputtered. ). Then, each substrate W is controlled while controlling the introduction amount of the sputtering gas so that the pressure in the vacuum chamber 1 during sputtering is maintained at 0.5 Pa (low pressure region) and 20 Pa (high pressure region), respectively. The film was formed under the same sputtering conditions as described above. In both the low pressure region and the high pressure region, the magnet unit 6 was rotated at a rotational speed of 60 rpm.

  FIG. 4 shows the results of measuring the target erosion area (erosion width) when sputtering is performed as described above. According to this, when the film is formed in the high pressure region by the sputtering apparatus M, the erosion width of the target is about 20 mm, which is significantly narrower than the erosion width (about 70 mm) when the film is formed in the low pressure region. I understand that. When the film is formed in the high pressure region, the magnet unit 6 is rotated at a rotational speed of 60 rpm, and after film formation on the plurality of substrates W for 15 minutes, the chamber 1 is opened to the atmosphere and the target 2 is opened. When the surface was visually confirmed, it was confirmed that a flaky redeposition film was formed.

  Therefore, in the film forming method of the present invention, the magnet unit 6 is offset from the center of the target 2 to the outside in the radial direction by utilizing the difference in erosion width when the film is formed in the high pressure region and the low pressure region. The film was formed by rotating the magnet unit 6 so that the outer peripheral area except the central part of the target 2 was eroded during film formation. That is, when sputtering is performed in the low pressure region, the region including the central portion of the target 2 is sputtered. However, when sputtering is performed in the high pressure region, the magnet unit 6 is offset so that the central portion of the target 2 is not sputtered. . Note that the amount of offset to the outside in the radial direction is appropriately changed depending on the form of the magnet unit to be used and the magnetic force of each magnet (that is, the size of the central portion of the present invention is the shape of the magnet unit 6 to be used). And the type of magnet used).

  According to the film forming method of the present embodiment, when the film is formed by sputtering in the high pressure region with the sputtering apparatus M, the magnet unit 6 is arranged offset from the center of the target 2 radially outward, and the film is formed. Inside, this magnet unit 6 is rotated and moved as if it were traced on the same peripheral surface of the target 2, so that the bottom coverage ratio is high with respect to fine holes with a high aspect ratio and the film thickness distribution is in-plane. The film can be formed with good uniformity.

  However, since the central portion of the target 2 is not eroded, sputtered particles are reattached to the central portion during film formation, and a flake-like film is formed. Therefore, in the film forming method of the present embodiment, when the substrate W is sequentially transferred to a position facing the target 2 to form a film, the number of film forming processes on the substrate W reaches a predetermined number (for example, 25). Then, a dummy substrate other than the product is transported and held on the stage 7, the introduction of the sputtering gas is controlled so that the inside of the chamber 1 becomes a low pressure region, and the dummy processing by sputtering is performed. As a result, the erosion area of the target 2 becomes wide, so that the target 2 is sputtered up to the center, and is reattached and removed to the flake-like film. As a result, the cause of the generation of particles is removed, and there is no need to frequently replace the target 2 and the productivity can be improved.

  In order to confirm the above effects, a silicon oxide film is formed over the entire surface of a silicon wafer having a diameter of 300 mm as a substrate W to be processed using a Ti target in the sputtering apparatus M of FIG. A barrier layer made of Ti was formed on a material film in which fine holes having an aspect ratio of 2 were patterned by a known method.

  The target 2 was made of Ti having a diameter of φ440 mm (purity 99.99%), and the distance between the target 2 and the substrate W was set to 45 mm. In addition, as sputtering conditions, the input power from the first sputtering power source 5 was set to 14 kW, and the input power from the second sputtering power source 8 was set to 100 W. And it formed into a film, hold | maintaining the pressure in the vacuum chamber 1 during sputtering at 20 Pa.

  In FIG. 3, − ▲ − is a graph showing the film thickness distribution in the surface of the substrate W when the film is formed under the above conditions. According to this, it was confirmed that the uniformity of the film thickness in the surface of the substrate W was about ± 5%, and a high bottom coverage rate of 70% or more was obtained.

  The film forming method of the present embodiment has been described above, but the present invention is not limited to the above. In the above embodiment, a dummy substrate different from the product is transported as a dummy process and a film is formed in a low pressure region. However, a shielding means such as a shutter is disposed between the target and the substrate to perform sputtering. It may be.

  Moreover, although the experimental example using Ti as a target was demonstrated, it will not restrict | limit especially if it draws in the sputtered particle ionized with plasma, and it will not restrict | limit, Cu, Co, Ni, Al, W or Ta single-piece | unit The above effect can also be obtained in the case of a target made of two or more alloys selected from metals or Ti-containing materials.

  M ... Sputtering device, 1 ... Vacuum chamber (chamber), 2 ... Target, 5 ... DC power supply (first sputtering power supply), 6 ... Magnet unit, 7 ... Stage, 8 ... High frequency power supply (second sputtering power supply), 9 ... Gas source (sputtering gas), 10 ... Mass flow controller, 11 ... Gas pipe, W ... Substrate to be processed

Claims (3)

Hold the substrate to be processed in a evacuated chamber,
A sputtering gas is introduced so that the pressure in the chamber is maintained in a high pressure region that is a pressure range of 10 to 30 Pa,
A DC voltage is applied to a circular target in plan view disposed in close proximity to the substrate, a high frequency bias voltage is applied to the substrate, and a plasma in which the DC plasma on the target side and the high frequency bias plasma on the substrate side are superimposed A film forming method for forming a film on a substrate by sputtering between targets generated between the substrates,
A magnet unit that locally forms a magnetic field below the target and offset from the center of the target in a radial outward direction, with the direction from the target toward the substrate as the bottom and the direction from the substrate to the target as the top. Then, during the film formation, the magnet unit is rotated so that at least the outer periphery excluding the central portion of the target is eroded.   2. The film forming method according to claim 1, wherein a dummy process for sputtering the target is performed periodically by controlling the introduction of the sputtering gas so that the inside of the chamber becomes a low pressure region. The said target is comprised from the single metal of Cu, Ti, Co, Ni, Al, W, or Ta, or 2 or more types of alloys selected from these, The Claim 1 or Claim 2 characterized by the above-mentioned. The film forming method.

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