JPH03170665A - Method and device for sputtering - Google Patents

Abstract

PURPOSE:To expand the region of a substrate which is not significantly affected by a negative ion emitted from a target by converging plasma in the vicinity of the peripheral part of the target opposed to the substrate. CONSTITUTION:An annular magnet 211 is arranged around the target 31 in the sputtering device, for example for forming an oxide superconductor thin film. Plasma is maintained by the ionization of the sputtered gas due to the bombardment of the secondary electron emitted from the target. The ionization of the sputtered gas is accelerated as the electron makes a cycloidal movement and the radius of the movement decreases. Consequently, the sputtered gas is ionized most violently in the vicinity of a magnet where a strong magnetic field is generated, namely in the vicinity of the peripheral part of the target. Accordingly, even if the direction of the line of magnetic force differs between the regions A and B, the plasma is converged close to the inner wall of the region 102, and the erosion region 402 can be positioned at the peripheral part of the target.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sputtering method and apparatus characterized by a plasma convergence region.

[Prior Art] Various methods are known for producing thin films of oxides such as ITO and ZnO in the field of oxide superconductors and transparent conductive films, but these methods are excellent in mass production and have a large area. The sputtering method is mainly used because it is easy to use.

FIG. 5 shows a schematic diagram of a conventional high frequency simple sputtering apparatus. The vacuum container 1 is evacuated by an exhaust system 2. Sputtering gases are supplied from an inert gas (eg, Ar) cylinder 12 and an oxygen gas cylinder 13, and the flow rates of these gases are kept constant by a valve 14 (eg, a variable leak valve, a flow controller, etc.). An inert gas alone or a mixed gas of an inert gas and oxygen gas is introduced into the vacuum container 1, and high frequency power is transmitted from the high frequency electric power 1iQ7 through the impedance matching circuit 8 to a target containing an oxide superconductor element (hereinafter referred to as ) 31 to generate plasma. The target holder 9 is insulated from the vacuum vessel 1 by an insulator 10, and the target 31 is insulated with cooling water 41.
cooled by

The substrate 4 is attached to the substrate holder 5, and the target 3
It is facing 1.

Here, when the anode is grounded, the electric current in the discharge space generally has a distribution as shown in FIG. 7. In the sputtering apparatus, the target is a cathode, and positive ions in the plasma are accelerated toward the cathode by the potential difference in the cathode sheath shown in FIG. sputtering atoms. Atoms of the sputtered target are deposited as a film on the surface 7 of the substrate 4 on the substrate holder 5 which is at ground potential or floating potential.

FIG. 6 is a schematic front sectional view of a conventional high frequency magnetron sputtering apparatus. Components corresponding to the apparatus shown in FIG. 5 are designated by the same reference numerals, and explanation 4 will be omitted. In this device, an inner magnet 201 and an outer magnet 202 are connected to a target 3.
1, the plasma is focused on a region 101 in the figure near the surface of the target 31 (magnetron region), thereby improving sputtering efficiency and increasing the film forming rate. (The potential in the discharge space in this case also has the distribution shown in Figure 7.) Figures 5 and 6 show devices that generate high-frequency discharges, but they also apply to devices with conductive targets. A DC discharge type sputtering apparatus using a DC power source instead of the high frequency power source 7 and impedance matching circuit 8 shown in the figure is also often used.

[Problems that Hatsushi is trying to solve] All oxide superconductors, such as the Y-Ba-Cu-0 system, have a complex structure consisting of multiple elements.
When producing a thin film of such an oxide superconductor,
Controlling the composition of films to obtain effective superconducting properties has become an important issue.

When such a thin film of an oxide superconductor is fabricated using the simple sputtering equipment shown in Fig. 5, the composition ratio distribution of the raw film within the substrate surface becomes relatively uniform, but the film The assembly ratio will deviate significantly from the target assembly ratio.

Furthermore, when fabricating using the magnetron sputtering apparatus shown in Figure 6, the film composition near the center of the substrate is almost the same as the target composition compared to a simple type apparatus, but the composition ratio distribution within the substrate surface of the raw film is becomes non-uniform. Particularly above the plasma convergence region, the composition ratio of the film deviates significantly from the composition ratio of the target.

The rationale behind this is explained below. When sputtering an oxide superconductor target with positive ions, there is a very high probability that the oxygen contained in the target will be released as negative ions (mostly O-, but there is also a small amount of 02'''). Therefore, a large amount of negative oxygen ions are emitted from the target along with neutral (non-ionic) sputtered particles.As mentioned above, the potential in the discharge space has a distribution as shown in Figure 7, so from this target The released negative oxygen ions are accelerated in a direction away from the target due to the potential difference in the cathode sheath portion shown in FIG. 7, impact the film on the substrate facing the target (cathode), and re-sputter the film.

During this re-sputtering, selective sputtering occurs because the sputtering rate differs for each element in the film, and the structure of the film deviates from the structure of the target. Y-Ba
In the case of the -Cu-0 system, more Cu and Ba are re-sputtered than Y. In particular, it has been confirmed that the re-sputtering of Ba is remarkable and the composition of Ba is lowered.

In the conventional simple sputtering apparatus as shown in FIG. 5, since the entire surface of the target is sputtered, negative oxygen ions are also emitted from the entire surface of the target. Therefore, the impact of oxygen negative ions on the film on the substrate occurs over the entire surface of the film, and the composition of the film deviates significantly from the composition of the target over the entire surface of the substrate. For this reason, countermeasures such as adjusting the composition of the target may be taken in anticipation of the deviation in composition in advance.

In the conventional magnetron sputtering apparatus shown in FIG. 6, the magnetic fields of magnets 201 and 202 trap electrons in the region 101 in the figure and converge the plasma, so the region where the target is sputtered (hereinafter referred to as "erosion") It is called.

) is only the area indicated by the depression 401 in the figure.

Therefore, negative oxygen ions are also generated from this erosion portion.

By the way, the emission angle distribution of neutral sputtered particles emitted from a target generally follows the cosine law, but oxygen emitted as negative ions is absorbed by the electric field at the part of the cathode sheath that generates an electric field perpendicular to the target surface. receive force in the direction. Therefore, the bombardment of the film by oxygen negative ions is greatest above the erosion part, and the substrate region above the center of the target is not so much bombarded. As a result, a film having a composition approximately equal to that of the target can be obtained on the center of the target. However, this region is extremely narrow compared to the total area of the target, and there is a problem that the area of the film equal to the target composition relative to the target area, that is, the utilization efficiency of the target is also extremely low. In a magnetron sputtering device, in order to increase the area of a film equal to the target composition, the inner diameter of the erosion must be increased. However, in conventional magnetron sputtering equipment, the magnet is placed on the back of the target, so if the magnet is made larger in an attempt to increase the inner diameter of the erosion, the target itself must also have a large area. There was a problem that the usage efficiency of the system did not improve.

The following explanation describes the production of thin films of oxide superconductors, and cites the difference between the film composition and the target composition as an effect of negative oxygen ions, but there are also other effects such as destroying the crystals of the film. In extreme cases, there is also the problem that it becomes impossible to attach the film to the substrate. In addition, IT in the field of oxides other than oxide superconductors, such as permeable conductive films,
Even in oxides such as O and ZnO, the influence of oxygen negative ions cannot be ignored, and problems similar to those of oxide superconductors occur.

The purpose of this bombardment is to provide a sputtering method and apparatus that can widen the substrate area and not be affected by negative ions flying out from the target.

[Means and effects for solving the problem] In order to achieve the above object, the sputtering method of the present invention is characterized by arranging a substrate to face the target and converging plasma near the peripheral edge of the target. It is said that Target!・If the plasma is focused near the periphery of the target, even if negative ions fly out toward the substrate from the erosion region, the substrate region facing the center of the target will hardly be affected by the negative ions, and the It is possible to increase the area of the substrate where the film on the substrate is not adversely affected by ions.

When using this sputtering method to form a thin film with the same composition as the target on a substrate using an oxide target, negative oxygen ions flying out from the target bombard the central region of the substrate. The film composition matches the target composition over a wide area at the center of the substrate. Examples of oxide targets include oxide superconductor targets and targets for permeable conductive films such as ITO and ZnO.

In particular, when forming an oxide superconductor thin film by the sputtering method described above using a target with the same composition as the oxide superconductor, the composition of the film will not deviate from the target 1 composition, which is important for controlling the composition. It is effective for producing superconductor thin films. Examples of oxide superconductor targets include Y-Ba-Cu-0 system, La-Ba-Cu-0 system,
BiS r-Ca-Cu-0 system, TI-Ca-BaCu
There are various inserts such as -0 series.

This starting point is not limited to the oxide target I, but it is also possible to sputter the target by introducing oxygen gas and sputtering the target.
It can also be applied to reactive spasotering such as forming an AV film of oxide on the base 11iL. In this reactive sputtering, the oxygen of the reaction gas is attached to the target I, and when the target is sputter-linked, the oxygen 11 ions are also ejected, so that the oxide target I,
Similarly, the adverse effects of oxygen-11 ions can be prevented by a large area at the center of the substrate.

This inventive sputtering device is a device for realizing the sputtering method described above, and is characterized by having an annular magnet arranged around the target. This annular magnet consists of a plurality of magnet pieces, which are arranged so that the magnetization directions of adjacent magnet pieces are opposite to each other. When the magnetization directions of adjacent magnet pieces are reversed, the magnetic field generated by the annular magnet becomes stronger only in the vicinity of the annular magnet, and rapidly attenuates as it moves away from the magnet. Therefore, it is possible to converge the plasma near the periphery of the target. The overall shape of the annular magnet depends on the shape of the target. If the target is circular, the magnet will be an annular magnet, and if the target 1 is in the shape of a square, it will be an annular magnet. That is, the annular magnet means a magnet surrounding the target in a loop shape. The number of magnet pieces constituting the annular magnet is preferably about 8 to 20 pieces, because if it is too small, it will be impossible to generate a strong magnetic field only in the vicinity of the magnet. It does not matter if the number of magnet pieces is greater than this.

The magnetization direction of the magnet piece can be, for example, the circumferential direction of the annular magnet. In this case, the magnetic pole of each magnet piece is
Opposite magnetic poles of adjacent magnet pieces face each other. That is, the N pole of each magnet piece faces the S pole of the adjacent magnet piece,
The south pole of each magnet piece faces the NtIiI of the adjacent magnet piece. Therefore, the annular magnet is Nt+! The parts where the north poles face each other and the parts where the south poles face each other will be arranged alternately in the circumferential direction, and the lines of magnetic force coming from the parts where the north poles are the same or facing each other will have the south poles facing each other. Get into the part. This creates a region with a strong magnetic field only near the annular magnet.

Another magnetization direction of the magnet pieces can be in the radial direction of the annular magnet. In this case, the magnetic pole of each magnet piece is separated by 1 km from the opposite magnetic pole of the adjacent magnet piece with a gap in between. The lines of magnetic force coming out from the N pole of each magnet piece enter St+m of the adjacent magnet piece.

This creates a region with a strong magnetic field only near the annular magnet.

[Example] Embodiments of the present invention will be explained below with reference to the drawings.

FIG. 1 is a front sectional view schematically showing an embodiment in which the present invention is applied to a sputtering apparatus for producing an oxide superconductor thin film. This arrangement corresponds to the conventional device shown in FIG. 5 or 6, and corresponding parts and months are given the same reference numerals and explanations are omitted.

An annular magnet 211- is arranged around the target 31. The magnet 211 is housed in the water-cooled container 21 and is water-cooled. Container 21 is grounded. Cooling water enters through the inlet 42 and exits through the outlet 43. Figure 1 shows the case of high-frequency discharge, and the high-frequency power supply 7 in the figure
A DC power supply may be used instead of the impedance matching circuit 8.

A specific structure of the annular magnet 211 shown in FIG. 1 is shown in FIG. FIG. 2 is a plan view of the magnet 211.

The magnet 211 consists of 16 magnet pieces 221 to 236, each of which is magnetized in the circumferential direction, and arranged so that the same magnetic poles of adjacent magnet pieces face each other. In FIG. 2, adjacent magnet pieces are placed in close contact with each other, but they may be arranged with some spacing between them. The magnetic lines of force 501 generated inside the magnet 211 have a shape as shown in FIG.

Here, the shape of plasma when this magnet 211 is used will be explained.

The plasma is maintained by ionization of the sputtering gas by the bombardment of secondary electrons emitted from the target. The potential in the discharge space has a distribution as shown in FIG. 7, and an electric field is generated in the cathode sheath portion that is perpendicular to the target 1 plane, that is, an electric field that goes from the substrate to the target. Secondary electrons emitted from the target undergo cycloidal motion within this cathode sheath due to interaction between the magnetic field and the electric field.

In region A in Figure 2, that is, in the region where the magnetic field lines are oriented counterclockwise around the target center when the target is viewed from above, the secondary electrons ejected from the target are moved by the magnetic field lines to the inner wall of the magnet. It moves in a cycloidal direction and moves in a cycloidal direction. That is, the drift direction of the cycloid motion is toward the inner wall of the magnet, and the plasma is also focused near the inner wall of the magnet. On the other hand, B where the direction of the magnetic field lines is clockwise around the target center
In this region, the drift direction of the cycloidal motion of the secondary electrons is toward the center of the target. Since the strength of the magnetic field decreases as it approaches the center of the target, the radius of the cycloidal motion gradually increases as it approaches the center of the target. Eventually, it leaves the cathode sheath where the electric field exists and ceases to move cycloidally.

The ionization of the slatter gas is more intense where the electrons are in cycloidal motion and the radius of the cycloidal motion is smaller. Therefore, near the inner wall of the magnet where the magnetic field is strong,
That is, the ionization of the sputtering gas is most intense near the peripheral edge of the target, and plasma is inevitably generated. Therefore, even if the directions of the magnetic lines of force in the A region and the B region are different, the plasma converges in the region indicated by 102 in FIG. 1, that is, near the inner wall of the magnet. In this way, the erosion area 402
can be located at the periphery of the target 1.

By arranging the annular magnet around the target 1 in this way, it is possible to bring the erosion region, which causes a change in the composition ratio of the produced film, to the periphery of the target.
A wide film region having approximately the same composition as the target composition can be secured on the substrate without increasing the size of the target itself. This makes it possible to improve target utilization efficiency compared to conventional devices.

Although the target 31 in FIG. 1 is disk-shaped, it may also be a ring-shaped target with a hollow portion that is not sputtered (the portion indicated by D in the figure).

By doing so, it becomes possible to further improve the utilization efficiency of the target.

FIG. 3 is a plan view of another example of an annular magnet. In this example, a magnet piece 241 magnetized in the radial direction of the annular magnet
A magnet is constructed by combining 16 pieces of ~256. In this case, unlike the example shown in FIG. 2, a gap 257 must be provided between adjacent magnet pieces. It is preferable that the interval is smaller than the length of the magnet piece in the magnetization direction. In the magnet shown in FIG. 3, the magnetic field strength increases at the gap between adjacent magnet pieces inside the magnet, and the plasma converges there.

FIG. 4 is a plan view of yet another example of an annular magnet. This magnet is similar to the magnet pieces 241 to 2 of the magnet shown in FIG.
A yoke 300 is provided around the outer periphery of the magnet 56 to prevent lines of magnetic force from leaking.

The sputtering apparatus shown in FIG. 1 obtains a dense plasma by the cycloidal movement of electrons due to the five-phase action of the magnetic field and the electric field, but this cycloidal movement does not last, so it does not result in so-called magnetron sputtering. Therefore, the apparatus shown in FIG. 1 cannot achieve a sputtering rate as high as that of the magnetron sputtering apparatus.

However, the sputtering speed is higher than that of a simple sputtering device.

In addition, although the above-mentioned embodiment showed a disk-shaped target, the shape of the target may be square or rectangular, and the annular magnet for converging the plasma may be arranged according to the shape of the target used. .

[Effects of the Invention] In the sputtering method of the present invention, since the plasma is focused near the periphery of the target, the influence of negative ions flying out from the erosion region is almost eliminated over a wide area at the center of the substrate.

In this sputtering method, if an oxide target is used to form a thin film with the same composition as targets I and 2 on substrate 1, negative oxygen ions ejected from the target will not bombard the central region of the substrate. The film composition matches the target composition over a large area. In particular, if an oxide superconductor thin film is formed using a target with the same composition as the oxide superconductor, the composition of the film will not deviate from the target composition, and composition control is important for the production of oxide superconductor thin films. Effective.

Even when this invention is applied to reactive sputtering in which oxygen gas is introduced to form a target oxide thin film on a substrate, the negative effects of oxygen negative ions can be applied to the substrate as in the case of an oxide target. This can be prevented with a large area in the center.

Hatsukawa's sputtering equipment has an annular magnet placed around the target, so the plasma can be focused near the periphery of the target, making it possible to use this equipment to perform the sputtering method described above. .

[Brief explanation of the drawing]

FIG. 1 is a front cross-sectional view of a sputtering apparatus according to an embodiment of the present invention, FIGS. 2, 3, and 4 are plan views showing various examples of annular magnets, and FIG. 5 is a conventional high-frequency FIG. 6 is a front sectional view of a simple sputtering device, FIG. 6 is a front sectional view of a conventional high-frequency magnetron sputtering device, and FIG. 7 is a graph showing the potential distribution in the discharge space. 4... Substrate 31... Target 102... Plasma convergence region 211... Annular magnets 221 to 236... Magnet piece 402... Erosion area 501... Magnetic wire

Claims (6)

[Claims] (1) A sputtering method characterized by placing a substrate facing a target and converging plasma near the peripheral edge of the target. (2) The sputtering method according to claim 1, wherein an oxide target is used to form a thin film having the same composition as the target on the substrate. (3) The sputtering method according to claim 2, wherein a target having the same composition as the oxide superconductor is used. (4) A thin film of the target oxide is formed on the substrate by supplying oxygen to the plasma space.
Sputtering method described. (5) A sputtering apparatus characterized in that a ring-shaped magnet made up of a plurality of magnet pieces in which adjacent magnet pieces have opposite magnetization directions is arranged around a target. (6) The sputtering apparatus according to claim 5, wherein the magnetization direction of each magnet piece is in the circumferential direction of the annular magnet, and the magnetic pole of each magnet piece faces the opposite magnetic pole of an adjacent magnet piece. (7) The magnetization direction of each magnet piece is the radial direction of the annular magnet, and the magnetic pole of each magnet piece is aligned with the opposite magnetic pole of an adjacent magnet piece with a gap in between. sputtering equipment.