JP5693175B2 - Sputtering method - Google Patents

Description

  For example, in the manufacturing process of a semiconductor device, the present invention covers the entire surface of a processing object including holes and the like on a processing object in which fine holes or trenches having a predetermined aspect ratio are formed by patterning. The present invention relates to a sputtering method for forming a metal film, and particularly relates to an optimum method for forming a seed layer made of a Cu film for a fine hole having a high aspect ratio.

  Conventionally, it is generally known to use a PVD method such as a sputtering method as a method of forming a seed layer made of a Cu film with a good coverage in a fine hole or trench having a predetermined aspect ratio in a semiconductor device manufacturing process. (See Patent Document 1).

  In the above, Ar ions in the plasma collide with the target surface made of Cu, Cu atoms and Cu ions are released from the target surface, and toward the substrate on which bias power (for example, 50 W) is input. In addition, the seed layer made of a Cu film is formed by being drawn and adhered and deposited with straightness.

  By the way, with recent high integration and miniaturization of semiconductor devices, there is a further demand for miniaturization of wiring dimensions. However, the thickness of wiring films and interlayer insulating films reduces capacitance, parasitic capacitance, and the like. Therefore, it is necessary to maintain a predetermined thickness. In order to satisfy such requirements, some holes (via holes, contact holes, etc.) having a predetermined opening diameter have an aspect ratio of 3 or more. When forming a sheet layer made of Cu, for example, in such a hole, it is difficult to form a layer with a good coverage rate (especially, the coverage rate at the bottom of the ball (bottom coverage rate) by the above-described sputtering method). As a result, it was a problem in forming a highly reliable wiring structure. Here, as one of the methods for improving the bottom coverage rate, it can be considered to lengthen the film formation time. However, this causes a problem that the film formation time is remarkably increased and the productivity is lowered.

JP 2002-80962 A

  In view of the above points, it is an object of the present invention to provide a sputtering method capable of forming a predetermined metal film at a high film formation rate with good coverage with respect to a high aspect ratio hole or trench. .

In order to solve the above-mentioned problems, the present invention assumes that a processing object is formed by patterning fine holes or trenches having an aspect ratio of 3 or more, and a metal is formed over the entire surface of the processing object including these holes. A sputtering method for forming a film, in which a processing object and a target prepared according to a metal film to be formed on the processing object are arranged opposite to each other in a vacuum chamber, and the processing object is processed from the target. down direction toward the, the top direction from the processing object to the target, the wall surface of the vacuum chamber along the vertical direction, a first coil and a second coil formed by turning each winding at intervals in the vertical direction Current in the range of 15A to 30A to generate a vertical magnetic field so that a vertical magnetic field acts on the entire surface of the object to be processed, and a magnet unit provided above the target. A magnetic field is applied to the lower part of the target by means of a target, a sputtering gas is introduced into the vacuum chamber, a predetermined direct current power is applied to the target, plasma is formed in the vacuum chamber, the target is sputtered, and the sputtering gas is used as argon. During sputtering, the film is formed while maintaining the partial pressure of argon in the vacuum chamber in the range of 5 to 30 Pa.

  According to the present invention, the argon partial pressure in the range of 5 to 30 Pa is higher than the film forming conditions (partial pressure lower than 5 Pa) in the conventional sputtering method for forming a seed layer made of a predetermined metal during sputtering. By holding, the ionization of metal ions is further promoted and the ratio of metal ions in the plasma is increased. Then, by applying a vertical magnetic field toward the object to be processed, the metal ions in the plasma reach the bottom of the hole or the like with higher directivity and strong straightness toward the object to be processed. It becomes like this. As a result, the film formation rate at the bottom of holes and the like is improved, and the bottom coverage rate is greatly improved. In addition, the metal film once adhered and deposited on the bottom of the hole or the like is reverse sputtered by Ar ions (metal ions) or the like drawn at the same time, and the reverse sputtered metal atom includes the side wall including the lower portion of the side wall of the fine hole. It adheres and accumulates throughout. As a result, the inside of the hole or the like can be formed in a short time with a predetermined film thickness over the entire surface with good coverage. In the present invention, when the argon partial pressure is lower than 5 Pa, the bottom coverage rate cannot be effectively improved. On the other hand, when the argon partial pressure exceeds 50 Pa, metal ions are remarkably reduced by scattering with argon. , The problem that the coverage is reduced occurs.

  In the present invention, a film forming rate may be further improved by applying a predetermined bias power to the object to be processed during sputtering and drawing the sputtered particles from the target or the ions of the sputtered particles electronized in the plasma. . In this case, the bias power applied to the object to be processed is preferably 50 to 200 W. When the bias power is lower than 50 W, the film formation rate at the bottom of the hole cannot be effectively improved. When the bias power exceeds 200 W, the reverse sputtering amount increases so that the film formation rate at the bottom of the fine hole is reversed. Become slow.

  The present invention uses Cu as the target, and is optimal for forming a seed layer made of Cu with high coverage at a high film formation rate for holes having a predetermined aspect ratio, particularly an aspect ratio of 3 or more. It is.

1 is a schematic cross-sectional view of a sputtering apparatus according to an embodiment of the present invention. The figure which illustrates typically a state when it forms into a film using a sputtering device. The graph which shows the experimental result according to this invention. The graph which shows the other experimental result according to this invention.

  Hereinafter, with reference to the drawings, a processing object W is formed by forming a silicon oxide layer with a predetermined thickness on the surface of a substrate such as a silicon wafer, and the silicon oxide layer has a fine hole with an aspect ratio of 3 or more. The sputtering method of the embodiment of the present invention will be described by taking as an example the case where a Cu film is formed in this hole (see FIG. 2).

  With reference to FIG. 1, SM is a sputtering apparatus capable of forming a film by the sputtering method of the present embodiment. The sputtering apparatus SM includes a vacuum chamber 1 capable of forming a vacuum atmosphere, and a cathode unit C is attached to a ceiling portion of the vacuum chamber 1. In the following description, in FIG. 1, the direction facing the ceiling portion side of the vacuum chamber 1 is referred to as “up” and the direction facing the bottom portion side is described as “down”.

  The cathode unit C includes a target 2 and a magnet unit 3 disposed above the target 2. The target 2 is made of Cu, and is formed in a circular shape or a rectangular shape in plan view by a known method according to the contour of the processing object W. The target 2 can be appropriately selected according to the metal film to be formed on the object to be processed. For example, the target 2 can be made of Ti, Al, Ta, Co, Ni, W, or Mo. The target 2 is attached to the upper portion of the vacuum chamber 1 via the insulator I with its sputtering surface facing downward while mounted on a backing plate (not shown). The target 2 is connected to a sputtering power source E1 such as a DC power source or a high frequency power source, and power having a negative potential is applied to the target 2 during sputtering.

  The magnet unit 3 disposed above the target 2 generates a magnetic field in a space below the sputtering surface 21 of the target 2, captures electrons and the like ionized below the sputtering surface 2 a during sputtering, and scatters from the target 2. It has a known closed magnetic field or cusp magnetic field structure for efficiently ionizing particles, and detailed description thereof is omitted here.

  A conductive anode shield 4 is disposed in the vacuum chamber 1. The anode shield 4 is a cylindrical member that covers the periphery of the target 2 and extends downward. The anode shield 4 is normally connected to the ground, but may be connected to another DC power source E2 to apply a positive potential. In this case, the anode shield 4 reflects the ions of the ionized sputtered particles and assists in being released to the substrate W with strong straightness.

  A stage 5 is disposed at the bottom of the vacuum chamber 1 so as to face the cathode unit C, and the processing object W is positioned and held. The stage 5 is connected to a high-frequency power source E3, and during sputtering, a bias potential is applied to the stage 5 and eventually the substrate W, and in particular plays a role of actively attracting ions of sputtered particles to the substrate W. A gas pipe 6 for introducing argon gas as a sputtering gas is connected to the side wall of the vacuum chamber 1, and the gas pipe 6 communicates with a gas source (not shown) via a mass flow controller 6a. These components constitute gas introduction means, and a sputter gas whose flow rate is controlled can be introduced into the vacuum chamber 1.

  On the side wall of the vacuum chamber, an upper coil 7u and a lower coil 7d formed by winding a conducting wire 72 around a ring-shaped yoke 71 are provided at predetermined intervals in the vertical direction. 7d can be energized. The sputtered particles generated by sputtering of the target 2 reach the entire surface of the substrate efficiently without being deactivated by the influence of the vertical magnetic field, and extend over the entire sputtering surface 21 of the target 2 and the entire surface of the workpiece W. A downward vertical magnetic field is generated so that the vertical magnetic field lines MF pass at predetermined intervals. The number of coils is not limited to the above, and the distance between the upper coil 7u and the lower coil 7d, the diameter of the conductive wire 72, and the number of turns are, for example, the area of the sputtering surface 21 of the target 2 and the target 3 Is appropriately set according to the distance between the substrate W and the substrate W, the rated current value of the power supply device E4, and the magnetic field strength (Gauss) to be generated.

  Connected to the bottom of the vacuum chamber 1 is an exhaust pipe 8 leading to a vacuum exhaust apparatus (not shown) such as a turbo molecular pump or a rotary pump. The sputtering apparatus SM has a known control means 9 having a microcomputer, a sequencer, etc., and the control means 9 controls the operations of the power sources E1 to E4, the operation of the mass flow controller 6a, the operation of the vacuum exhaust device, and the like. It comes to manage.

Next, a sputtering method for the processing object W using the sputtering apparatus 1 will be described. First, the evacuation unit is operated to evacuate the vacuum chamber 1 to a predetermined degree of vacuum (for example, 10 ⁻⁵ Pa). After the processing object W is set on the stage 5, the upper coil 7u and the lower coil 7d are energized by the power source E4 so that the downward vertical magnetic field lines MF pass through the entire surface of the target 2 and the processing object W at a predetermined interval. Generate a vertical magnetic field. Then, the mass flow controller 6a is controlled in the vacuum chamber 1 to introduce argon gas (sputtering gas) at a predetermined flow rate, and a predetermined electric power having a negative potential is applied to the target 2 from the sputtering power source E1 to discharge it. A plasma atmosphere is formed in the chamber 1.

  Here, in the prior art, when forming a Cu film, the argon partial pressure during sputtering is set to a range of 0 to 5 Pa, such as stopping the introduction of argon gas by the mass flow controller 6a after the formation of the plasma atmosphere, For example, it is known to form a film by forming a self-discharge plasma. However, in a fine hole with an aspect ratio exceeding 3, even if the current value and bias power applied to the upper coil 7u and the lower coil 7d are appropriately adjusted, the coverage rate at the bottom of the hole is effectively improved. Cannot improve.

  In the present embodiment, the partial pressure of argon in the vacuum chamber 1 is kept in the range of 5 to 30 Pa in the sputtering gas. Thereby, Ar ions (or Cu ions) collide with the sputtering surface 21 of the target 2 and are sputtered, and Cu atoms are scattered from the target 2. At this time, by increasing the argon partial pressure, the amount of Cu atoms scattered from the target 2 increases, and the ionization of Cu is promoted to increase the Cu ion ratio in the plasma.

  Then, the Cu atoms generated by sputtering of the target 2 and the ionized Cu ions are generated by vertically generating the entire surface of the processing target W and applying a predetermined bias power to the processing target W by the high frequency power source E3. The processing object W is drawn to the bottom of the hole with higher directivity and strong straightness. As a result, as shown in FIG. 2, the film formation rate at the bottom Hb of the hole H is improved, and in particular, the bottom coverage rate is greatly improved. In addition, the Cu film once adhered and deposited on the bottom Hb of the hole H is reverse sputtered by Ar ions drawn at the same time, and this reverse sputtered Cu includes the lower portion of the side wall Hs of the hole H. It adheres and accumulates over the entire surface (that is, the coverage rate of the side wall Hs of the hole H is also improved). As a result, the inside of the hole H can be formed in a short time with a predetermined film thickness over the whole (see FIG. 2).

  Note that when the argon partial pressure is lower than 5 Pa, the bottom coverage rate cannot be effectively improved. On the other hand, when the argon partial pressure exceeds 50 Pa, metal ions are remarkably reduced due to scattering with argon, and coverage is reduced. The problem of a drop occurs. The bias power is set to a range value of 50 to 200W. If it is lower than 50 W, the film formation rate at the bottom of the hole cannot be effectively improved. On the other hand, if it exceeds 200 W, the amount of reverse sputtering increases so that the film formation rate at the bottom of the fine hole is slowed down. A malfunction occurs. Furthermore, the energization current value to the upper coil 7u and the lower coil 7d is set in the range of 15 to 30A. If it is lower than 15 A, the film formation rate at the bottom of the hole cannot be improved effectively, while if it exceeds 30 A, there is a problem that the plasma becomes uneasy.

  Next, in order to confirm the above effects, the following experiments were performed using the sputtering apparatus SM shown in FIG. In Experiment 1, a processing object W prepared by patterning holes having an opening diameter of 0.06 μm and an aspect ratio of 5 in a silicon oxide film was prepared. Then, the Cu film was formed using a high purity Cu target as the target 2. As sputtering conditions, the distance between the target 2 and the object W to be processed is 400 mm, the input power from the sputtering power source E1 to the target 2 is 20 kW, the input voltage from the power source E2 to the earth shield is 30 V, and the bias is input from the power source E3. The power was set to 200 W and the sputtering time was set to 10 seconds. In addition, a downward vertical magnetic field is generated by setting the current supplied to the upper coil 7u and the lower coil 7d to 30A. In Experiment 1, during sputtering, the partial pressure of the sputtering gas was changed in the range of 0 to 50 Pa to form a film on the object to be processed.

  FIG. 3 is a graph obtained by measuring the coverage rate of the bottom Hb of the hole H with respect to the partial pressure of argon when a film is formed on the object to be processed under the above conditions. The coverage rate was calculated by the formula of a / b × 100. Here, a is the film thickness of the Cu film on the surface of the object to be processed, and b is the film thickness of Cu at the bottom of the hole H (see FIG. 2). According to this, it can be seen that when the argon partial pressure is 5 Pa or more, the coverage rate at the bottom Hb of the hole H can be made substantially 100%. It was also confirmed that the coverage rate at the side wall of the hole H could be improved as compared with that of the prior art.

  Next, in Experiment 2, a film was formed under the same conditions as in Experiment 1 except that the energization current to the coils 7u and 7d and the argon partial pressure were changed. FIG. 4 shows the deposition rate (nm / sec) when the energizing currents to the coil coils 7u and 7d are set to 0A, 15A, and 30A, respectively, and the partial pressure of the argon gas is changed at each energizing current. It is a graph. According to this, in the range of 5 Pa or more where the coverage rate at the bottom Hb of the hole H can be improved, the energizing current to the coils 7u and 7d is 0A, that is, the etching rate is extremely high when a vertical magnetic field is not applied to the object to be processed. It can be seen that it has dropped. On the other hand, when a vertical magnetic field is applied, the amount of decrease in the etching rate can be reduced. In the case of 30A, it can be suppressed to about half the amount of decrease, and it can be seen that the productivity is not significantly impaired.

  As mentioned above, although embodiment of this invention was described, this invention is not limited above. In the above embodiment, a vertical magnetic field is generated using a coil, but a magnetic field can be generated using a permanent magnet or the like. As the sputtering gas, a rare gas other than argon can be used. If the magnetic field strength is appropriately adjusted according to the rare gas used as the sputtering gas, the same effect as described above can be obtained. Further, the object to be processed is not limited to the above, and the present invention can be widely applied as long as fine holes and trenches are formed with a predetermined aspect ratio.

  SM ... Sputtering device, 1 ... Vacuum chamber, 2 ... Target, 6 ... Gas pipe, 7u, 7d ... Coil (vertical magnetic field generation), C ... Cathode unit, E1-E4 ... Power supply, MF ... Magnetic flux, W ... Process object , H ... Hall.

Claims (3)

It is a sputtering method for forming a metal film over the entire surface of a processing target including a hole on which the processing target is formed by patterning fine holes or trenches having an aspect ratio of 3 or more. ,
In a vacuum chamber, a processing object and a target prepared according to the metal film to be formed on the processing object are arranged to face each other.
Down in a direction toward the processing target from the target, the direction from the processing object to the target as above, the wall surface of the vacuum chamber along the vertical direction, a first coil formed by turning each winding at intervals in the vertical direction The second coil is energized in a range of 15A to 30A to generate a vertical magnetic field so that a vertical magnetic field acts on the entire surface of the object to be processed, and a magnet unit provided above the target is used to lower the target. A magnetic field is applied to
Sputter gas is introduced into the vacuum chamber, a predetermined direct current power is supplied to the target, plasma is formed in the vacuum chamber, and the target is sputtered.
A sputtering method, wherein sputtering is performed using argon as a sputtering gas, and the sputtering is performed while the partial pressure of argon in the vacuum chamber is maintained in the range of 5 to 30 Pa during sputtering. 2. The sputtering method according to claim 1, wherein during the sputtering, a predetermined bias power is supplied to the object to be processed, and the sputtered particles from the target or the ions of the sputtered particles ionized in the plasma are drawn. The sputtering method according to claim 1, wherein Cu is used as the target.

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