JP5461264B2 - Magnetron sputtering apparatus and sputtering method - Google Patents

Description

  The present invention relates to a magnetron sputtering apparatus and a magnetron sputtering method.

Sputtering is a method for forming a thin film on a solar cell substrate or a semiconductor wafer.
In particular, a magnetron sputtering apparatus in which a magnet is disposed on the back side of a cathode to which a target is attached is excellent in stability of film formation and is easy to increase in size of the target and is widely used.
In order to improve productivity, attempts have been made to increase the number of substrates that can be produced with one target by making the erosion depth of the target as uniform as possible.
Further, in order to improve the film thickness distribution uniformity on the substrate, the erosion depth shape is also controlled to a desired shape.

As described above, controlling the erosion depth shape of the target is almost the same as controlling the plasma density distribution in the discharge space on the target surface side.
The plasma density distribution is determined mainly by an electric field and a magnetic field in the discharge space. In particular, the magnet arranged on the back side of the target is greatly influenced by the magnetic field shape created in the discharge space on the target surface side. Therefore, in many cases, the shape of the magnet is devised to control the erosion depth shape, or the magnet is rotated or reciprocated.

In magnetron sputtering, as shown in FIG. 8, as a normal magnet structure, a permanent magnet (hereinafter referred to as an inner magnet) is arranged in a certain area in the direction facing the surface of the south pole, for example, so as to surround it. Permanent magnets (hereinafter referred to as outer magnets) are arranged in such a direction that the N poles of opposite polarities face the surface.
These are arranged on a normal ferromagnetic yoke. Hereinafter, the inner magnet, the outer magnet, and the yoke are collectively referred to as a magnet unit.

The inner magnet and the outer magnet are often fixed to the yoke with an adhesive.
Therefore, a flat plate-like yoke is used so that the work is easy. Since the inner magnet and the outer magnet generate a force in the adsorbing direction, a certain degree of strength is required for the yoke in order to firmly fix them.

The yoke has a function of improving the magnetic field strength as a magnet as compared with the case without the yoke. Therefore, a yoke having a certain degree of thickness and a high magnetic permeability is usually used so as not to cause magnetic saturation.
In a large sputtering apparatus, a rectangular target is often used, and in that case, a rectangular unit as shown in FIG. 8 is used as a magnet unit. One or a plurality of such magnet units are arranged for one target and magnetron sputtering is performed. One example of a large-scale sputtering apparatus using such a magnet unit is disclosed in Patent Document 1.

Japanese Patent Laid-Open No. 2001-140069

However, the conventional magnet unit has the following problems.
That is, as a method of easily changing the magnetic field shape and magnetic field strength on the target surface side, a method of attaching a thin ferromagnetic plate (hereinafter referred to as a magnetic material plate) to the target side surfaces of the inner magnet and outer magnet of the magnet unit There is. The magnetic plate can reduce the magnetic field strength generated from the N and S poles in the region where the magnetic plate is attached by short-circuiting the N and S poles of the inner and outer magnets in a magnetic circuit manner. .
The magnetic plate is thin enough to be magnetically saturated and forms a magnetic field on the target surface side to some extent through the magnetic plate. Therefore, the magnetic field strength of the entire magnet unit can be controlled by changing the position and thickness of the magnetic plate to be attached.

However, the magnet unit is usually installed close to the target-side structure.
Specifically, a target back plate and a chamber wall may exist between the target and the magnet unit. In order to increase the magnetic field strength on the target surface side as much as possible, the distance between the magnet unit and the target needs to be small, and the magnet unit may be installed with a gap of about several millimeters against the target back plate or chamber wall. Many.

For this reason, in order to attach the above-described magnetic plate to the surface of the magnet unit, the magnet unit must be moved largely to the opposite side of the target to create a space on the surface of the magnet unit.
Recently, for example, in a large-scale sputtering apparatus in which the size of the substrate exceeds 1 m, since the magnet unit is large and heavy, the means for moving the magnet unit greatly from the target side becomes large and complicated. There was a problem that the manufacturing cost of the apparatus was high.

In order to solve the above problems, a magnetron sputtering apparatus is a magnetron sputtering apparatus in which a magnet unit capable of reciprocating movement is disposed along the back side of a cathode to which a target is attached, and the magnet unit has one polarity. An inner magnet composed of a permanent magnet with the magnetic pole surface facing the cathode, and an outer magnet arranged in a rectangular shape so as to surround the inner magnet, with the magnetic pole surface having the opposite polarity to the inner magnet facing the cathode A non-magnetic material that fixes the inner magnet and the outer magnet, a ferromagnetic material, and located on the opposite side of the inner magnet and the cathode of the outer magnet, and the inner magnet and the outer magnet. A plate-like yoke for connecting the magnetic poles, and the distance between the substrate side surface of the magnet unit and the back surface of the cathode is one. The yoke has a plate shape and is divided into a plurality of pieces in the long side direction of the outer magnets arranged in the rectangular shape, and each of the divided yokes has a different thickness. It can be exchanged.

Specifically, in the magnetron sputtering apparatus described above, when the divided yokes are arranged so that the thickness of the yoke at the front end is thinner than the center in the long side direction of the magnet unit. Further preferred.

  According to the present invention, by changing the yoke thickness from the back side of the magnet unit without largely moving the magnet unit from the target side, the magnetic field shape and magnetic field strength on the target surface side can be easily changed, and the manufacturing cost of the apparatus can be reduced. Can be reduced.

1 shows a schematic diagram of a magnetron sputtering apparatus according to an embodiment of the present invention. FIG. It is the magnet unit which concerns on this invention, (a) is a front view, (b) is AA sectional drawing of (a), (c) is BB sectional drawing of (a), (d) is (a) ) Shows a state without a yoke. It is a figure for demonstrating the magnetic field analysis in the magnet unit which concerns on this invention. It is a figure which shows the result of the magnetic field analysis of the magnet unit which concerns on this invention. It is a figure explaining the method for making the front-end | tip part magnetic field intensity weaker than a center part in the magnet unit which concerns on this invention. It is a figure explaining the method for making the front-end | tip part magnetic field intensity stronger than the center part in the magnet unit which concerns on this invention. It is the schematic at the time of using a magnetic body with the magnet unit which concerns on one Embodiment of this invention. It is a figure explaining the conventional magnet unit, (a) is a front view, (b) is AA sectional drawing of (a), (c) shows BB sectional drawing of (a), respectively.

Hereinafter, a magnetron sputtering apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a magnetron sputtering apparatus according to the first embodiment of the present invention.
A substrate 2 is placed on a substrate holder 5 in the chamber 1. The chamber 1 is evacuated to vacuum by an unillustrated exhaust pump, and a process gas such as Ar gas is supplied from a not-illustrated gas pipe so as to have a predetermined pressure.

  A target 3 is disposed above and facing the substrate 2. The target 3 is bonded to the target back plate 4, and the target back plate 4 is installed in the chamber 1 through an insulator 6.

In this embodiment, an example is shown in which the back side opposite to the substrate 2 of the target back plate 4 is exposed to the atmosphere. The target back plate 4 is connected to a DC power source (not shown).
A magnet unit 10 is installed on the back side of the target back plate 4 with a gap of several millimeters. The magnet unit 10 can reciprocate without changing the distance from the target back plate 4 during film formation by a moving mechanism (not shown).

Next, the magnet unit 10 of the present invention will be described with reference to FIG.
FIG. 2A is a front view of the magnet unit 10 and shows a state seen from the target 3 side.
There is an elongated permanent magnet inner magnet 11 magnetized to show the south pole on the front surface, and an outer permanent magnet 12 magnetized to show the north pole on the front surface so as to surround it.

As shown in FIG. 2B, which is an AA sectional view of FIG. 2A, and FIG. 2C, which is a BB sectional view of FIG. 2A, an inner magnet 11 and an outer magnet 12 are provided. The connection between them is fixed by a non-magnetic material 13.
As the nonmagnetic material 13, for example, aluminum or nonmagnetic stainless steel is used, and the inner magnet 11 and the outer magnet 12 are fixed by an adhesive.
FIG. 2D shows a cross section without the yoke 14, but the inner magnet 11 and the outer magnet 12 are fixed only by the non-magnetic material 13 and need not be fixed by the yoke 14.

The yoke 14 is made of a ferromagnetic material such as iron or SUS430.
As shown in FIG. 2C, the yoke 14 connects the magnetic pole surfaces of the inner magnet 11 and the outer magnet 12 opposite to the target 3 so as to short-circuit the magnetic circuit. The yoke 14 here is only attached by the magnet's attracting force (magnetic force), and the magnet and the yoke 14 are not fixed by bonding.

  As shown in FIG. 2B, the yoke 14 is divided into eight in the long side direction of the magnet unit 10 here, and the thicknesses thereof are different. In the region where the yoke 14 is thick, the magnetic field strength on the target surface is strong, and in the region where the yoke 14 is thin, the magnetic field strength on the target surface is weak. The relationship between the magnetic field strength and the yoke thickness will be described in detail later.

  The yoke 14 can be easily removed by being attracted by the magnetic force of the magnet and by being divided. Accordingly, the yoke 14 having a different thickness can be easily replaced, and this facilitates the control of the magnetic field strength on the target surface.

  Although not shown, the divided yokes 14 have the same effects even when thin ferromagnetic plates are used. In this case, the magnetic force acting on the thin ferromagnetic yoke 14 is reduced, and the thin ferromagnetic yokes 14 can be easily detached from the magnet unit 10 one by one.

Usually, in the magnetron sputtering apparatus, it is not necessary to bring a structure close to the yoke side, which is the back side of the magnet unit, so that a space can be secured. Therefore, the yoke can be easily exchanged by a human hand, and thereby the magnetic field strength on the target surface can be changed.
Therefore, it is not necessary to move the magnet unit largely in the direction opposite to the target as in the prior art.

Next, the relationship between the yoke thickness and the magnetic field strength on the target surface will be described.
The magnetic field strength on the target surface of the magnet unit 10 as shown in FIG. 3 was calculated by the magnetic field analysis software ELF / MAGIC.

  The thickness of the yoke 14 of the magnet unit 10 was set to 10 mm in the vicinity of the center portion, and the yoke thickness a in the region of the tip portion 100 mm was changed from 0 mm to 10 mm. The target surface (not shown) is at a position 40 mm from the surface of the magnet unit 10, and the magnetic flux density at a position 30 mm inside from the tip of the magnet unit where the magnetic flux density vector is substantially parallel to the surface of the target (not shown). A parallel component (symbol 20) was calculated. The inner magnet 11 and the outer magnet 12 are, for example, neodymium magnets, and the yoke 14 is SUS430.

The calculation results are shown in FIG.
As the tip yoke thickness a increases, the magnetic flux density on the target surface increases. When the tip yoke thickness a is 6 mm or more, the magnetic flux density on the target surface hardly changes. This is because the tip yoke is not magnetically saturated when the tip yoke is 6 mm or more.

For the control of the magnetic field strength on the target surface, the yoke thickness can be in the range of 0 mm to 6 mm.
The tip yoke thickness “a” of 0 mm means that the yoke 14 is not installed in that region as shown in FIG.

  In the example of FIG. 5, the magnetic field strength at the tip of the magnet unit is made weaker than that at the center. Conversely, in order to make the magnetic field strength at the center weaker than that at the tip, as shown in FIG. The yoke 14 at the center may be thickened and the yoke 14 at the center may be thinned.

In general, the erosion depth becomes deep in a region where the magnetic flux density in the direction parallel to the target surface is large on the target surface, and becomes shallow in a region where the magnetic flux density is small.
In the magnet unit of the present invention, the erosion in the region where the yoke thickness is increased becomes deep, and the erosion in the region where the yoke thickness is reduced becomes shallow.
Thus, a desired erosion depth shape can be easily obtained by partially changing the yoke thickness.

Next, a film forming method using the magnetron sputtering apparatus according to the present invention will be described.
The yoke of the magnet unit has a non-uniform thickness, for example, a uniform thickness at the center and a thinner tip.
After the substrate is placed on the substrate holder of the chamber evacuated to vacuum, a process gas such as Ar gas is introduced into the chamber so that a predetermined pressure is obtained.

  The DC power supply is turned on while the magnet unit is reciprocated by a moving mechanism, and DC power is applied to the target to perform sputter deposition. After a certain time, the DC power is turned off to complete the film formation.

The thickness of the film deposited on the substrate is measured to confirm whether a desired film thickness distribution has been obtained.
When the film thickness distribution is poor and it is desired to reduce the film thickness in a certain region on the substrate, the magnetic field strength is reduced by replacing the corresponding magnet unit yoke from a thicker one to a thinner one.

On the other hand, when it is desired to increase the film thickness in a certain region on the substrate, the magnetic field strength is increased by replacing the corresponding yoke of the magnet unit from a thin one to a thick one. In this state, the same film formation is performed again to confirm the film thickness distribution.
By repeating such an operation several times, a desired film thickness distribution can be obtained.

Next, a second embodiment according to the present invention will be described.
As shown in FIG. 7A, the inner magnet 11 and the outer magnet 12 are respectively connected to the magnetic poles 15 made of a ferromagnetic material such as iron or SUS430 with the magnetic poles on the opposite side of the target 3 with an adhesive or the like. Yes.
The magnetic body 15 connected to the inner magnet 11 and the outer magnet 12 is connected via a yoke 14 in a magnetic circuit manner.

  The yoke 14 is not fixed with an adhesive or the like, and can be removed simply by sticking with the attraction force (magnetic force) of the magnet. There is a non-magnetic body 13 between the inner magnet 11 and the outer magnet 12, and the magnetic body 15 and the non-magnetic body 13 are fixed with an adhesive or a bolt.

  FIG. 7B shows the present embodiment when there is no yoke 14. Since the magnetic body 15 and the non-magnetic body 13 are fixed, they can be held in this shape even when the yoke 14 is not provided. In this case, the inner magnet 11 and the outer magnet 12 are not short-circuited as a magnetic circuit, and have the same magnetic field strength as the case where the yoke 14 of the first embodiment is not provided.

  In this way, the magnetic plate and the non-magnetic material are first connected and assembled, and then the inner magnet and the outer magnet are assembled thereon. Therefore, the process is the same as the conventional process of assembling the magnet on the integral yoke. Easy assembly.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

1 chamber 2 substrate 3 target 4 target back plate 5 substrate holder 6 insulator 10 magnet unit 11 inner magnet 12 outer magnet 13 nonmagnetic material 14 yoke 15 magnetic material
20 Parallel component of magnetic flux density

Claims (2)

A magnetron sputtering apparatus in which a magnet unit capable of reciprocating movement is arranged along the back side of a cathode to which a target is attached,
The magnet unit is
An inner magnet composed of a permanent magnet with a magnetic pole face of one polarity facing the cathode side;
An outer magnet that is arranged in a rectangular shape so as to surround the inner magnet, and that has a magnetic pole surface with a polarity opposite to that of the inner magnet facing the cathode side;
A nonmagnetic material for fixing the inner magnet and the outer magnet;
A plate-shaped yoke that is made of a ferromagnetic material and is located on the opposite side of the inner magnet and the outer magnet with respect to the cathode, and connects the inner magnet and the magnetic pole of the outer magnet;
The distance between the substrate side surface of the magnet unit and the back surface of the cathode is constant,
The yoke has a plate shape and is divided into a plurality of pieces in the long side direction of the outer magnets arranged in a rectangular shape, and each of the divided yokes can be replaced with a different thickness. There is a magnetron sputtering apparatus. The magnetron sputtering apparatus , wherein the divided yokes are arranged so that the thickness of the yoke at the tip portion is thinner than the center portion in the long side direction of the magnet unit .