JPH0361365A - Ion assisted sputtering method and device - Google Patents

Abstract

PURPOSE:To arbitrarily regulate the structure and internal stress of a film by setting a solenoid coil 7 near a peripheral magnetic pole having larger saturation magnetic flux than a central magnetic pole, controlling the amt. of ions in accordance with electric current supplied to the coil and carrying out film formation. CONSTITUTION:A central magnetic pole 1 and a peripheral magnetic pole 2 are formed with permanent magnets so that saturation magnetic flux 12 from the pole 2 is made larger than that 11 from the pole 1. A solenoid coil 7 is set near the pole 2. The amt. of ions is controlled in accordance with exciting electric current supplied to the coil 7, potential difference is produced between plasma 14 and a substrate 8 and film formation is carried out while controlling kinetic energy applied to the ions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion-assisted sputtering method and apparatus for producing thin films with various functions, and the structure and internal stress of the thin films are suitable for the purpose of use. The present invention relates to an ion-assisted sputtering method and apparatus that can be arbitrarily controlled to suit the needs of the user.

[Prior Art] For example, in the process of depositing desired material atoms onto a substrate using a device that combines a vapor deposition device and an ion gun, the deposited atoms are bombarded with ions by an ion generator provided separately such as an ion gun (ion gun). (It is referred to as bombardment, ion peening, or ion assist.Hereafter, it will be referred to as ion assist.) When a thin film is formed, the adhesion force with the substrate and the deposited thin film's weight increase compared to those without ion assist. , the density is improved and, as a result, the surface hardness.

It is known that various functional improvements such as surface roughness, optical reflectance, and electrical resistance can be achieved. This is because ions with kinetic energy collide with the deposited atoms, causing the deposited atoms to move horizontally with respect to the film surface (referred to as migration) and remain in the most stable location, resulting in the atoms being densely packed. It is thought that this is because it becomes an array.

However, even if you aim to achieve the same effect by combining a sputtering device with an ion gun, with current technology, the gas pressure level used in the sputtering device and the gas pressure level used in the ion gun are different, and they operate simultaneously in the same vacuum chamber. That is difficult. Furthermore, the combination of an ion gun and conventional vapor deposition equipment or sputtering equipment has the drawback of being complicated in structure and expensive.

In addition, a method called bias battering has been proposed in which a bias voltage is applied to the substrate to improve the properties of the film, but this method only controls the energy available to the ions. The increase or decrease in the amount of ions cannot be controlled. In particular, the amount of ions in magnetron sputtering is extremely small, and even if ion energy is applied, no effect can be expected.

Therefore, instead of using a separate ion source as described above, a negative bias voltage is applied to the substrate by guiding the working gas ions in the plasma that are inevitably generated during sputtering to the vicinity of the substrate by adjusting the magnetic field. An attempt was made to change the organizational structure of a thin film by imparting kinetic energy to ions near the substrate during film formation and hitting the atoms deposited on the substrate with the ions (ion assist).
and N.

J, Vac, S avvides et al.
ci, Technol.

A4 (2), Mar, /Apr, 1986,
Proposed on p 196 et seq.

This method, such as B and Window, sputters target atoms using an annular plasma confined in a tunnel-shaped magnetic field formed by magnetron sputtering, and at the same time adjusts the magnetic field near the plasma to guide ions to the substrate. A bias potential is applied to impart kinetic energy to ions, and film formation is attempted while hitting sputtered atoms deposited on the substrate surface, that is, while ion assisting.

However, the disadvantage of this method is that the position of the plasma expands and contracts in the radial direction from the center of the target due to the influence of the magnetic field that is adjusted to guide ions from the annular plasma position confined in the tunnel magnetic field for sputtering. It is in the point of doing. The kinetic energy given to the ions can be adjusted by adjusting the voltage applied to the substrate (hereinafter referred to as the bias voltage), but the amount of ions can be adjusted by changing the excitation current of the nrenoid coil and changing the magnetic field by using a tunnel that confines the plasma. This affects the magnetic field distribution, and as a result, the position of the annular plasma formed on the target surface moves so as to expand and contract in the radial direction from the target center.

In the magnetron sputtering method, there is a close relationship between the plasma ring position and the film thickness distribution deposited on the substrate, and the film thickness distribution corresponds to the plasma position. In conventional magnetron sputtering that does not use ion assist, the position of the plasma ring does not move, and the distance between the substrate and target is generally adjusted in order to increase the area where the film thickness distribution is uniform. However, if the plasma position changes in the radial direction each time the ion amount is adjusted, as in the case of J2, the distance between the substrate and the target must be adjusted each time the ion amount is set. In the case of an apparatus in which the distance between the substrate and the target is fixed, the area where the film thickness distribution is uniform depending on the amount of ions is limited. Furthermore, if it is desired to adjust the amount of ions at the beginning and during the film-forming operation and to obtain a large area of uniform film thickness, it is necessary to temporarily stop the film-forming operation and adjust the distance between the substrate and the target.

If the distance between the substrate and target is adjusted during film deposition operation, the gas pressure within the vacuum chamber will fluctuate, making steady operation virtually impossible.

The amount of ions that reach the substrate is J+, the number of particles deposited on the substrate is J+i, and the number of ions that arrive per second per unit area (1 cm') of the substrate is j◆, which is called ion flux, and the unit area of the substrate is The number of sputtered particles that arrive at (1 cm') M per second is referred to as a sputtered particle flux as Jll. Also, the ratio of ion flux to sputtered particle flux j +
/ j rrr is the ion flux ratio (ion flux
ratio ). The energy for accelerating these ions is defined as acceleration energy E.

The process of bombarding the substrate with ions by combining the ion flux ratio j +/j II and the acceleration energy E will be referred to as ion assist.

When controlling the tissue structure of membranes by ion assist,
The ratio of the amount of ions reaching the substrate per unit area time, that is, the ion flux j+, and the number of target particles deposited on the substrate, that is, the sputtered particle flux jI11, that is, the value of the ion flux ratio j+/jm. Two important controlling factors are the kinetic energy E imparted to the ions. However, when the distance between the substrate and the target or the gas pressure is changed in order to enlarge the area of uniform film thickness distribution as described above, the ion flux j+ of the substrate E also changes.

Generally, the larger the distance between the substrate and the target and the higher the gas pressure, the smaller the ion flux j♦.

Furthermore, the movement of the plasma changes the target particles, ie, the sputtered particle flux jm, directed toward the substrate. This is because, in addition to the difference in film thickness distribution, the intensity of the discharge plasma also changes.

The change in the discharge plasma is also clear from the difference in discharge voltage in Table 5.6.7 of Table I of the paper by B, Wind et al.

In other words, in order to control the increase/decrease in the amount of ions, changing the excitation current of the solenoid coil causes a change in discharge.
By changing the energy that impacts the target, the sputtering rate (1
This changes the number of target atoms ejected by each ion, and also changes the rate at which target atoms are deposited on the substrate.

Therefore, due to the movement of the plasma, the sputtered particle flux j+
o changes, and it becomes complicated and difficult to control the ion flux ratio j + / j ra to finely control the membrane structure. Therefore, in magnetron sputtering, which forms a film while performing ion assist, the position of the plasma ring must be fixed so that it does not move in the radial direction.However, in conventional magnetron sputtering, in which the plasma position does not move, Since the ions are completely confined by a strong tunnel-like magnetic field and magnetically balanced between the magnetic poles, there are few lines of magnetic force directed toward the vicinity of the substrate, and almost no ions exist near the substrate. Therefore, no ion assist effect can be expected even if /
When trying to control +, the sputtered particle flux j+ changes,
As a result, there is a drawback that the ion flux ratio j+/jIl cannot be set to a desired value.

[Problem to be Solved by the Invention] Next, the problem to be solved by the present invention will be explained while specifically showing a conventional example using the drawings.

Figure 4 shows a typical example of the electrode configuration of conventional magnetron sputtering. 1 is a central magnetic pole made of a permanent magnet or a magnetic material, 2 is an outer magnetic pole made of a magnetic material or a permanent magnet, and 4 is a central magnetic pole IJ-outer. A magnetic yoke magnetically couples the captive pole 2, 6 a target, 8 a substrate, 11
14 shows a schematic cross-sectional view of a tunnel-shaped magnetic field formed between the central magnetic pole 1 and the outer magnetic pole 2, and 14 shows a schematic cross-sectional view of annular plasma confined by the tunnel magnetic field 11.

In FIG. 4, either the central magnetic pole 1 or the outer magnetic pole 2 is a permanent magnet and is magnetically balanced. That is, it is designed so that the number of magnetic flux lines emitted from the central magnetic pole l (magnetic flux density x cross-sectional area) and the number of magnetic flux lines entering the outer magnetic pole 2 are equal, making it a complete magnetron. Therefore, the magnetic field lines form a tunnel-like magnetic field 11 on the upper surface of the target 6, the plasma 14 is completely confined, and the number of ions near the substrate 8 is extremely small.Therefore, in the type shown in FIG. 4, a bias voltage is applied to the substrate. Even if given, the amount of ions is small, so an ion assist effect cannot be expected.

Figure 5 shows B, F in the paper by Window et al.
ig.

This is one of the ones shown in 2. In Figure 5, 12
is a schematic diagram of lines of magnetic force directed in a direction approximately perpendicular to the substrate 8, and other symbols are the same as in FIG. It is made magnetically unbalanced.

Note that the saturation magnetic flux (saturation magnetic flux density x cross-sectional area) used in this specification refers to the maximum number of magnetic flux lines that can pass through (permeate) one magnetic pole. Indicates the maximum possible number of magnetic flux lines (magnetic permeability x cross-sectional area), and in the case of permanent magnets, indicates the magnetic flux line a (magnetic flux density x cross-sectional area) generated from itself. Also, 1 m magnetic saturation means the above saturation. This shows that the magnetic flux is filled up to the magnetic flux.

In FIG. 5, the central magnetic pole 1 is magnetically saturated;
Even if all the magnetic flux lines emitted from the central magnetic pole 1 enter the outer magnetic pole 2, the outer magnetic pole pi2 will not be magnetically balanced. The lines of magnetic force 12 that are substantially perpendicular to the substrate 8 bypass the magnetic field 12 and head toward the outer magnetic pole 2, and as a result, ions can be guided to the vicinity of the substrate 8. However, in the case shown in Fig. 5, the magnetic pole is composed only of a permanent magnet and a magnetic material, so the amount of ions is constant and the main plasma does not move.
It is not possible to control the increase or decrease of the ion amount j+.

FIG. 6 is another example shown in FIG. 2 of the above-mentioned paper P197 by Wil'1dolf et al.

In Fig. 6, 1 is a central magnetic pole made of a soft magnetic material, 2 is an outer magnetic pole made of a soft magnetic material, 4 is a magnetic yoke that magnetically couples the central magnetic pole 1 and the outer magnetic pole 2, 6 is a target, and 7 is an outer magnetic pole. Solenoid coil placed nearby, 8 is the board, 17
11 is a cross-sectional schematic diagram of a tunnel-shaped magnetic field formed between the central magnetic pole l and the outer magnetic pole 2; 12 is a schematic diagram of lines of magnetic force directed in a direction substantially perpendicular to the substrate; 13 is a schematic diagram showing the excitation direction of the solenoid coil 7, 14 is a schematic cross-sectional diagram of an annular plasma confined in the tunnel magnetic field 11, and 18 is a schematic diagram showing the excitation direction of the solenoid coil 17. When designed so that the saturation magnetic flux of the outer magnetic pole 2 is larger than the saturation magnetic flux of the magnetic pole 1, and when the central magnetic pole l is excited by the solenoid coil 17 until the central magnetic pole 1 is magnetically saturated, the magnetic flux is emitted from the central magnetic pole 1. All of the magnetic lines of force enter the outer magnetic pole 2 to form a tunnel-like magnetic field 11, confining the annular plasma 14. In this state, the outer magnetic pole 2 has a large saturation magnetic flux, is not magnetically saturated, and is in magnetron mode. Next, when the solenoid coil 7 is excited in the direction indicated by reference numeral 13, the lines of magnetic force 12 in a direction substantially perpendicular to the substrate 8 are directed toward the outer magnetic pole 2, so that the magnetic field near the outer magnetic pole 2 is not confined. Ions in the plasma are guided to the vicinity of the substrate 8.

Therefore, by adjusting the excitation flow of the solenoid coil 7, the amount of ions can be adjusted, and by applying a bias voltage to the substrate 8, it is possible to give kinetic energy to the ions and perform ion assist. However, since each magnetic pole is made of a magnetic material, if the excitation current of the solenoid coil 7 is changed when changing the amount of ions, the leakage magnetic field mode of the central magnetic pole 1 tends to change, and the position of the plasma changes to the target 6. Move radially from the center. 6th
Regarding the type shown in the figure, the excitation current of the solenoid coil 17 is kept constant at -1OA, and the ion distribution state when the excitation current of the solenoid coil 7 is changed is 7.
FIG. 8 shows the film thickness distribution and plasma position.

The main conditions in this case are that the target 6 is oxygen-free copper, the distance between the substrate 8 and the target 6 is 60 mm, the outer diameter of the outer magnetic pole 2 is φ160 mm, the outer diameter of the substrate 8 is φ120 mm, and the gas pressure is 2 mTorr (At ), the discharge current is DCo
, 5AXlain, the current of the solenoid coil 17 is constant at -1OA, and the excitation current of the solenoid coil 7 is +8A, +6A.

Figure 7 shows the ion current distribution when changing to the three types of +3 + + 2 A, and Figure 8 shows the film thickness distribution and plasma position.
As shown in FIG. 7, it is possible to increase or decrease the number of ions by adjusting the solenoid fill 7. However, as shown in FIG. 8, the amount of movement of the plasma position in the radial direction is large, and it can be seen that this effect causes a large difference in the film thickness distribution.

In other words, the conventional magnetron sputtering method that can perform ion assist as shown in FIG. Each time, the amount that the main plasma position moves is large, and as a result,
Conditions must be adjusted to ensure uniform film thickness distribution.
Conversely, it is not possible to control the increase or decrease in the amount of ions while keeping the conditions for uniform film thickness distribution, such as the distance between the substrate 8 and the target 6, the gas pressure, etc., constant.

When hitting the substrate 8 with ions, the ion assist effect is determined by the ratio of the number of sputtered particles jm per unit area per unit time and the number of ions j+, that is, the ion flux ratio j + / j m and the way the acceleration energy E is applied. It will be different. For example, the properties of the resulting film are It will be different.

In particular, with regard to the internal stress of the thin film, when the ion energy E is increased, the internal stress of the film shifts significantly toward the compressive stress side.

That is, in order to be compatible with a wide variety of functional fi membranes, the ion flux ratio j+/jm must be controlled within a wide range. A common drawback of the conventional technology is that when adjusting the ion aj◆, the plasma position changes, resulting in a change in the film thickness distribution.In addition, the number of sputtered particles also changes, and as a result, the ion flux ratio j+
/jm cannot be controlled to increase or decrease.

The reason for this is that in the case shown in FIG. 6, the magnetic pole forming the plasma 14 is directly adjusted by a solenoid coil.

Therefore, in the present invention, the position of the main plasma i4 is made difficult to move, and the ion amount j0 is made large,
Suppressing changes in film thickness distribution and reducing ion flux ratio
◆/jta can now be controlled.

[Means and Effects for Solving the Problems] The present invention relates to an ion-assisted magnetron sputtering method and apparatus that have improved the above-mentioned drawbacks, and which suppress the movement of the position of the plasma ring formed by magnetron sputtering as much as possible, and It is designed to guide ions to.

Therefore, it is possible to independently control the ion flux ratio j + / j rm and its kinetic energy E according to the purpose without affecting the film thickness distribution, and it is possible to adjust the tissue structure and internal stress of the thin film. This is what I did.

For this purpose, in the present invention, the central magnetic pole and the outer magnetic pole are permanent magnets whose saturation magnetic flux satisfies the outer magnetic pole≧the central magnetic pole,
A solenoid coil is placed near the outer magnetic pole, and the ion feeding is controlled by the excitation current applied to the solenoid coil.
We adopted an ion-assisted sputtering method that controls the kinetic energy given to the ions to form a film by applying a potential difference between the plasma and the substrate. The center magnetic pole and the outer circumferential magnetic pole are permanent magnets whose saturation magnetic flux is greater than or equal to the outer circumferential magnetic pole. A solenoid coil is arranged near the outer circumferential magnetic pole, and a current that can control the value of the excitation current given to the solenoid coil is provided. A device was adopted in which the control means was connected to a solenoid coil.

That is, one feature of the present invention is that both the annular central magnetic pole and the outer circumferential magnetic pole arranged on the outer periphery thereof are permanent magnets, and
The saturation magnetic flux of the outer magnetic pole is made larger than that of the central magnetic pole,
All lines of magnetic force from the central magnetic pole to the outer magnetic pole are directed toward the outer magnetic pole, and a solenoid coil placed near the outer magnetic pole is energized in a direction that strengthens the polarity of the outer magnetic pole. Ions are guided near the substrate in a direction substantially perpendicular to the substrate, and by applying a bias voltage to the substrate, the ions are accelerated and hit the substrate, thereby enabling ion assist. The central magnetic pole may be solid as long as the saturation magnetic flux of the outer magnetic pole is small.

When a soft magnetic material is used for one of the central magnetic pole and the outer magnetic pole, when the solenoid coil is excited, the magnetic lines of force corresponding to the unbalanced saturation magnetic flux leak from the soft magnetic material, the mode of the magnetic force lines changes, and as a result, the position of the plasma changes. Unsteady and easy to move,
On the other hand, in the present invention, both the central magnetic pole and the outer magnetic pole are made of permanent magnets, so even if the solenoid coil is excited, the leakage magnetic field mode remains constant. Since the movement of the film is small, the influence on the mode change of the film thickness distribution can be reduced.

[Embodiments] Different embodiments of the present invention are shown in FIGS. 1 to 3.

In FIGS. 1 to 3, l is a central magnetic pole made of a permanent magnet, 2 is an outer circumferential magnetic pole made of a permanent magnet, 4 is a yoke made of a soft magnetic material that magnetically couples the central magnetic pole l and the outer circumferential magnetic pole 2, and 7 is a solenoid coil placed on the outer periphery of the outer magnetic pole to adjust the amount of ions by adjusting the magnetic balance; 6 is the target; 8 is the substrate; 11 is the central magnetic pole l and the outer magnetic pole 2.
12 is a schematic diagram of magnetic lines of force running in a direction substantially perpendicular to the substrate 8; 13 is a schematic diagram showing the excitation direction of the solenoid coil 7; 14 is a diagram of tunnel-shaped magnetic lines of force formed by a magnetic circuit between 1 is a schematic cross-sectional view of an annular plasma confined by magnetic lines of force 11. Each magnetic pole 1
．． When the saturation magnetic flux of 2 is set such that the outer magnetic flux>the central magnetic pole, the central magnetic pole 1 becomes magnetically saturated by the lines of magnetic force 11 from the outer magnetic pole 2, forms a tunnel magnetic field, and confines the plasma 14. At this time, when the solenoid coil 7 is excited in the direction of the arrow 13 in FIGS. 1 to 3, the extra magnetic force line 12 from the outer magnetic pole 2 goes in a direction substantially perpendicular to the substrate 8, the vertical component increases, and When excited in the opposite direction, the vertical component decreases, and eventually the magnetic fluxes from the central magnetic pole 1 to the outer magnetic pole 2 become equal, forming a perfect magnetron. That is, by adjusting the magnitude and direction of the excitation current of the solenoid coil 7, the amount of ions guided to the substrate 8 can be controlled. By applying an electric field such as a bias voltage to ions near the substrate 8, these ions are accelerated and collide with the substrate 8. By adjusting the magnitude of the electric field, the kinetic energy impinging on the substrate 8 can be controlled.

In the embodiments shown in FIGS. 1 and 2, only the permanent magnet 2 is used as the central magnetic pole l. However, if the magnetic capacity of the central magnetic pole 1 is small, as shown in FIG.
An auxiliary solenoid coil 9 may be provided on the outer periphery of the auxiliary solenoid coil 9. In the embodiments shown in FIGS. However, the same effect can be achieved even if these polarities are completely reversed. In the embodiments of FIGS. 1 and 2, each magnetic pole 1.
The case where the magnetic field is applied by the solenoid coil 7 is shown in which the saturation magnetic flux (magnetic capacity) of No. 2 is set in advance as the outer magnetic pole > the center magnetic pole, but the excitation current of the solenoid coil 7 is increased by setting the saturation magnetic flux as the outer magnetic pole = the center magnetic pole in advance. The same effect can be obtained as ion assist, but when performing ion assist,
There is a drawback that the current to be applied by the solenoid coil 7 is large.

FIG. 9 shows the ion distribution on the substrate 8 when the excitation current of the solenoid coil 7 is changed for the one shown in FIG. 1, and FIG. 10 shows the results of examining the plasma position and the corresponding film thickness distribution. The main conditions are that oxygen-free copper is used as the target 6, the distance between the substrate 8 and the target 6 is 60 mm,
The outer diameter of the outer magnetic pole 2 is φ160 mm, and the diameter of the substrate 8 is φf2.
0mm, gas pressure 2mTorr, discharge current DCo,
5AX 1 win, and the case where the current of the solenoid coil 7 is changed to three types: -4A, -OA, and -4A is shown.

Comparing the results in FIGS. 9 and 10 with the conventional results in FIGS. 7 and 8, it can be seen that the movement of the plasma 14 from the target center in the radial direction is small, and the ion amount can be adjusted over a wide range. I understand.

[Effects of the Invention] In the present invention, the central magnetic pole and the outer magnetic pole are made of strong permanent magnets, and the saturation magnetic flux is designed so that the outer magnetic pole≧the central magnetic pole, and a solenoid coil is provided near the outer magnetic pole. The amount of ions guided to the substrate is controlled by the magnitude and direction of the excitation current applied to the substrate, a power source is provided to accelerate the ions to the substrate, and the kinetic energy of the ions is controlled by adjusting the voltage. The bottom film can be formed by bombarding the substrate with ions in the plasma generated by magnetron sputtering itself, without using an ion source. This ion-assisted sputtering method allows the structure and internal stress of the film to be adjusted.

[Brief explanation of drawings]

1 to 3 are electrode configuration diagrams for explaining different embodiments of the present invention, FIGS. 4 to 6 are electrode configuration diagrams for explaining different conventional examples similar to the present invention,
FIG. 7 is a diagram showing the ion current distribution state in the case shown in FIG. 6, FIG. 8 is a diagram showing the film thickness distribution state and plasma position in the case shown in FIG. Diagram showing the ion current distribution state in the case shown in Fig. 10.
The figure is a diagram showing the film thickness distribution state and plasma position in what is shown in FIG. 1. 1... Central magnetic pole, 2... Outer magnetic pole, 4... Magnetic yoke, 6... Target, 7.17... Solenoid coil, 8 ...Substrate, 11.12...Schematic lines of magnetic force, 13...Excitation direction, 14...Plasma.

Claims (2)

[Claims] (1) The central magnetic pole and the outer magnetic pole are permanent magnets whose saturation magnetic flux is greater than or equal to the central magnetic pole, a solenoid coil is placed near the outer magnetic pole, and the amount of ions is controlled by the excitation current applied to the solenoid coil. , an ion-assisted sputtering method that controls the kinetic energy given to ions to form a film by applying a potential difference between the plasma and the substrate. (2) An outer magnetic pole is provided on the outer periphery of the central magnetic pole, the central magnetic pole and the outer magnetic pole are permanent magnets whose saturation magnetic flux is greater than or equal to the outer magnetic pole, and a solenoid coil is placed near the outer magnetic pole. An ion assisted sputtering device in which a solenoid coil is connected to a current control means capable of controlling the value of excitation current applied to the ion assisted sputtering device.