JPH0480357A - Sputtering system and its target electrode - Google Patents

Abstract

PURPOSE:To minimize the impact of negative ion on a substrate and to prevent a lowering of efficiency in utilizing the target by forming a region not to be impressed with a target potential at the center of a target electrode. CONSTITUTION:The target electrode consists of an electrode main body 20 and a backplate 19, the backplate 19 is fixed to the upper end of the main body 20, and a circular hole 19a is provided at the center of the backplate 19. The target electrode is used in magnetron sputtering, a magnet assembly provided with an outer circular magnet 22a and an inner circular magnet 22b is placed in the target electrode, both magnets are fixed to a yoke 21, and the assembly is easily placed in and removed from the main body 20. Consequently, the secondary electron or negative ion is not generated from the center of the target electrode. Meanwhile, even if the secondary electron and negative ion stray into the region, the electron and ion are not accelerated toward the substrate since there is no potential gradient called the cathode sheath.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a target electrode for a sputtering device, which has a characteristic electrode shape, and also relates to a sputtering device equipped with this target electrode.

[Background Art] In recent years, the creation of thin films using sputtering phenomena and the creation of devices by processing the films have been actively carried out both in terms of research and practical application. This sputtering phenomenon is a phenomenon in which sputter particles (neutral particles) are generated from the target by injecting ions with high energy into the target, and the sputter particles are deposited on a substrate. Oxide superconductor thin films and ITO thin films (transparent conductive films), which have recently been in the spotlight, are also produced using this sputtering phenomenon.

[Problems to be Solved by the Invention] In order to create oxide-based materials such as oxide superconductor thin films and ITOWi films by sputtering, it is necessary to use a target made of these materials or a target containing compositional components of these materials. However, in such an oxide target, negative ions (mainly oxygen negative ions) are also generated in addition to sputtered particles during the sputtering phenomenon. These negative ions are accelerated toward the substrate by the electric field of the cathode sheath near the target surface and become high-energy negative ions. These high-energy negative ions impinge on the substrate and cause the problem of re-sputtering the sputtered particles (film) deposited on the substrate. When this re-sputtering phenomenon occurs, the composition of the oxide superconductor thin film deviates from the stoichiometric composition. As a result, superconducting properties deteriorate. In addition, due to the same re-sputtering phenomenon,
The conductivity of the ITO thin film also deteriorates.

By the way, in the McNetron sputtering method currently in practical use, electrons are trapped by a closing magnetic field and gas is ionized at high density, thereby forming an erosion region locally on the target. In this erosion region, many negative ions are generated together with sputtered particles. As a result, the portion of the substrate facing the erosion region is most susceptible to negative ion bombardment.

Therefore, if the substrate is placed in a position that does not face the erosion region, the negative ion impact can be alleviated.

However, since the target potential (which is more negative than the plasma) exists on the target surface other than the erosion area, the electric field due to this target potential is caused by secondary electrons generated in the target and flying from the erosion area. This will accelerate the negative ions. As a result, there is a problem in that these secondary electrons and negative ions collide with the substrate to some extent even in parts of the substrate opposite to the target surface other than the erosion region.

For example, using a single target with a diameter of 4 inches (approximately 100 mm), Y, Ba2 Cu30. When producing an oxide superconductor thin film of
m, and outside this region, the composition varies greatly, the crystallinity is poor, and the superconducting properties are greatly deteriorated.

As described above, conventional target electrodes cannot completely solve the problem of negative ions generated from the target colliding with the substrate.

By the way, in magnetron sputtering, it is possible to set the erosion region at a position away from the center of the target or to narrow the width of the erosion region to increase the substrate area as much as possible so that negative ions do not collide with it. can. Thereby, the thin film in the substrate region located directly 1- in the center of the target can be made to have a uniform composition over a relatively large area. However, in this case, the area ratio of the erosion region to the target surface area becomes considerably small, resulting in poor target utilization efficiency.

This invention was developed to eliminate the above-mentioned drawbacks, and its purpose is to provide a target electrode that minimizes negative ion bombardment onto the substrate and does not reduce target utilization efficiency. Another object of the present invention is to provide a sputtering apparatus equipped with this target electrode.

[Means for Solving the Problems] The first invention is characterized in that a region to which no target potential is applied is formed in the center of the target electrode.

The second invention is a more specific version of the first invention, in which the target electrode is formed into an annular shape, and a space is provided in the center of the target electrode.

In addition to the configuration of the second invention, the third invention includes a target shield covering the inner peripheral edge of the annular target electrode.

The fourth invention is a more specific version of the first invention, in which the target electrode is formed into an annular shape, a conductor is placed in the center of the target electrode, and a target shield covers the conductor and the outer periphery of the target electrode. are electrically connected.

A fifth invention is an invention of a sputtering apparatus equipped with the above-mentioned target electrode, and is characterized in that a substrate is disposed facing a region of the target electrode to which no target potential is applied.

[Effect] When a region where no target potential is applied is formed in the center of the target electrode, there is no potential gradient called a cathode sheath in this region, so even if secondary electrons or negative ions generated in the target stray into this region, There's no way it's going to be accelerated. Of course, since there is no target in this region, this region does not become a source of secondary electrons or negative ions.

One method for creating a region to which no target potential is applied is to form a target electrode in a ring shape and provide a void in the center. In this case, by covering the inner peripheral edge of the annular target electrode with a target shield, it is possible to block secondary electrons and negative ions that would travel toward the substrate from around the inner peripheral edge.

Another way to create a region where no target potential is applied is to
A conductor is placed in the center of the annular target electrode, and the conductor and the target shield are electrically connected and grounded. In this way, a potential gradient like that near the target surface does not occur near the surface of the conductor.

When using a target electrode as described in (2) above, if the substrate is placed so as to face the region of the target electrode to which no target potential is applied, the substrate will not be subjected to negative ion bombardment.

[Example] Next, the present invention will be described in detail with reference to the drawings.

FIG. 11 is a front sectional view showing an example of a sputtering apparatus for forming an oxide thin film.

The pressure in the vacuum container 1 can be maintained at a vacuum of 10-7 Torr or less by a main exhaust system installed in the direction of arrow 13. A gas introduction system 29 for supplying gas necessary for producing a thin film is provided in the vacuum container 1, and a valve 10a is provided.
, 10. Gas is introduced into the vacuum vessel 1 via b.

For example, by supplying Ar gas from the direction of arrow 11,
02 gas is supplied from the direction, mixed and introduced into the vacuum container 1. The pressure inside the vacuum vessel 1 can be set to an appropriate value by adjusting the mass flow meter (not shown) of the gas introduction system 29 and the main exhaust system installed in the direction of the arrow 13. A substrate holder 5 that can hold the substrate 4 and heat it up to 800° C. is installed inside the vacuum container 1. The heating method is a method in which the lamp heater 7 is controlled using a temperature adjustment device 8, a thyristor transformer 9, and a thermocouple 6 attached to the surface of the substrate holder 5. A target electrode 3 is arranged at a position facing the substrate holder 5. A target shield 2 is installed on the outer periphery of the target electrode 3, and an electrically insulating ring 14 (made of fluororesin) is provided between the target shield 2 and the target electrode 3.

This target electrode 3 is provided with cooling water (arrows 15a, 15b).
) is running. A high frequency power source 17 is connected to the target electrode 3 via an impedance matching device 16.

FIG. 1 is a perspective view showing an example of a target electrode that can be used in the sputtering apparatus shown in FIG. 11. The target electrode consists of an electrode body 20 and a back plate 19. A back plate 19 is attached to the upper end of the electrode body 20. At the center of the back plate 19 is a circular hole 19a. This target electrode is used for magnetron sputtering, and a magnet assembly shown in FIG. 2 is placed inside the target electrode. This magnet assembly includes an outer circular magnet 22a and an inner circular magnet 22.
b, both of which are fixed to the yoke 21. This magnet assembly can be easily installed and removed inside the electrode body 20.

3 is a front sectional view of a target mechanism incorporating the target electrode of FIG. 1, and FIG. 4 is a plan view thereof. In FIG. 3, a target back plate 19 is attached to the upper end of the electrode body 20, and a target 18 is attached to this back plate 19.
are bonded. Back plate 19 and target 1
8 is a disk with a hole in the center. The electrode body 20 is fixed on a hollow circular electrical insulating plate 23 (made of fluororesin). Inner peripheral surface 20a of electrode body 20
The outer peripheral surface 20b is surrounded by a shield plate 24. The outer peripheral edges of the back plate 19 and the target 18 are also covered with a shield plate 24. A water cooling pipe is connected to the electrode body 20, and the cooling water flows from the direction of arrow 15a to the direction of arrow 15b. There are O-rings 30 and 31 on the lower surface of the back plate 19 to seal the cooling water. The electrode body 20 includes
A high frequency power source 17 is connected via an impedance matching device 16, so that a predetermined power can be applied.

In this target electrode, the inner peripheral surface 20a of the electrode body 20
A space 60 is formed by the circular hole 19a of the back plate 19.

FIG. 3 also shows a substrate 4 facing the target mechanism.
It shows the position of. The substrate 4 is arranged to face the cavity 60, and the diameter D1 of the substrate 4 is smaller than the inner diameter D2 of the cavity 60.

Next, the function of this target electrode mechanism will be explained.

A magnetic field 33 is formed on the surface of the target 18 by the magnets 22a and 22b. When a high frequency voltage is applied to the electrode body 20, a discharge occurs, and plasma is concentrated, particularly in the portion where the magnetic field 33 is parallel to the target surface. Then, the positive ions during the discharge sputter the target 18 and deposit sputtered particles on the substrate 4.

By the way, since the space 60 at the center of the target electrode is directly below the substrate 4, the sputtered particles that will adhere to the substrate 4 are those that have come obliquely from the target 18. On the other hand, the secondary electrons and negative ions 32 generated by the target 18 are accelerated by the potential gradient of the cathode sheath on the surface of the target 18 and fly almost perpendicularly to the target surface. Therefore, secondary electrons and negative ions do not fly to the substrate 4. Secondary electrons and negative ions are vacant spaces 60
Even if they enter above the substrate 4, the secondary electrons and negative ions will not be accelerated toward the substrate 4 because there is no cathode sheath in this part.

Since the target 18 of this embodiment has a hole in the center, the ratio of the erosion area to the target surface area is larger than that of a conventional target, and the target usage efficiency is improved.

Next, an example of producing an oxide superconductor thin film using this target mechanism will be described. As the target 18, a Y, Ba2Cu 30° sintered target with a diameter of 4 inches was used. The valve 10a, by the gas introduction system 29 in FIG.
10b and a mass flow meter (not shown), arrow 1
Ar gas was introduced from one direction, and 02 gas was introduced from the direction of arrow 12, and these were mixed and introduced into the vacuum body 1. At this time, the flow rate ratio of Ar gas and 02 gas was set to 1:1.

Further, the pressure inside the vacuum body 1 was set to 25 mTorr. A high frequency power of 150 W was applied to the electrode body 20 from a high frequency power source 17, and the reflected wave was adjusted by an impedance matching device 16 so that the reflected wave became OW (zero watt). Also,
In order to obtain superconducting properties in an as-grown state, the substrate 4
The thin film was deposited while heating the sample to 600-700°C. Note that the substrate 4 is made of MgO(100), S rTi
Since 03(100) was used, the obtained film was a C-axis oriented film.

The oxide superconductor thin film produced in this manner will be compared with a conventional thin film produced using a magnetron target without voids.

(a) Superconductor thin film film composition produced in this example: YI
Ba2Cu3 oy (Center) Uniform region of film composition (within ±2%): Superconducting critical temperature within a diameter of 45 mm: Tce=90K (b) Conventional thin film composition: YlB a 1. sCu2. a Oy
(Central area) Uniform region of film composition (within ±2%): Superconducting critical temperature within a diameter of 20 mm: Comparing the above two results at Tce = 72, the film composition is improved in the case of the example. In particular, the area of uniform film composition is more than twice that of the conventional one.

FIG. 5 is a front sectional view of the target mechanism of the second embodiment, and FIG. 6 is a plan view thereof. This targeting mechanism is
A characteristic feature of this embodiment is that a shield plate 25 is disposed in a space at the center of the target electrode, and other points are the same as the embodiment shown in FIG.

The shield plate 25 is made of a conductor, and in this embodiment is formed integrally with the shield plate 24. When the central void is covered with the shield plate 25, the potential of this part becomes the ground potential, so the potential gradient directly under the substrate 4 is completely eliminated, and damage to the substrate 4 due to negative ions etc. can be prevented by implementing the method shown in FIG. It will be less than in the example case.

FIG. 7 is a front sectional view of the target mechanism of the third embodiment, and FIG. 8 is a plan view thereof. This targeting mechanism is
It is characteristic that the upper end portion 26 of the shield plate that covers the inner circumferential surface 20a of the electrode body 20 covers the inner circumferential edge of the target 18. Other points are similar to the embodiment shown in FIG. Providing the upper end portion 26 in this manner has the effect of blocking negative ions that would fly toward the substrate 4 from the inner peripheral edge of the target 18.

FIG. 9 is a front sectional view of the target mechanism of the fourth embodiment, and FIG. 8 is a plan view thereof. This targeting mechanism is
The characteristic feature is that the target electrode has a rectangular shape. Other points are basically the same as the embodiment shown in FIG. In FIG. 9, the shape of the electrode body 40 is a rectangular parallelepiped with a hollow part in the center. The shapes of the magnets 42a, 42b and yoke 41 installed therein are also hollow rectangular parallelepipeds. Target 58, target back plate 59
The shape is a square plate with a square hole in the center. The inner peripheral surface and outer peripheral surface of the electrode body 40 are surrounded by a shield plate 44. The length of one side of the square board 4 is
It is smaller than the length of one side of the square void 60.

Note that the present invention is applicable not only to Y and Ba2Cu3o but also to other oxide superconductors as described below.

(1) MBa2Cu30° Here, M = element of the silantane series La, Ce, Pr, Nd, Pm.

Sm, Eu, Gd, Tb, Dy.

Ho, Er, Tm, Yb, Lu (2) B 12 S r2 Can-I Cun O
y where n=1.2. 3.4 (3) T12Ba2Can, Cun o.

Here, n=1.2. 3.4 (4) T I 1B a2Can-1Cu, , Oy where n=1. 2. 3.4. 5. 6 (5) A compound having the same elemental composition (other elements may be included) as the above compound and a different stoichiometry [Effects of the Invention] In the target electrode of the first invention, the central part of the target electrode Since a region is formed in which no target potential is applied, this region will not become a source of secondary electrons or negative ions, and even if secondary electrons or negative ions stray into this region, they will not be connected to the cathode sheath. Since there is no so-called potential gradient, no secondary electrons or negative ions are accelerated toward the substrate. Furthermore, since the central portion of the target is unnecessary, especially in magnetron sputtering, the ratio of the erosion region to the target surface area is large (thus, the target usage efficiency is improved).

In the second invention, a void is formed as a region to which no target potential is applied, and the structure is the simplest.

In the third invention, since the inner peripheral edge of the annular target electrode is covered with a target shield, it is possible to block secondary electrons and negative ions that would travel toward the substrate from around the inner peripheral edge.

In the fourth invention, a conductor is placed in the empty space, and this conductor and a normal target shield are electrically connected and grounded. The potential gradient is completely eliminated.

In the sputtering apparatus of the fifth aspect of the invention, the substrate is disposed so as to face the region of the target electrode to which no target potential is applied, so that the substrate is not subjected to negative ion bombardment. As a result, it is possible to form a thin film with good properties, especially when producing an oxide thin film that tends to generate negative ions.

[Brief explanation of drawings]

1 is a perspective view of a target electrode according to a first embodiment of the present invention, FIG. 2 is a perspective view of a magnet assembly used in the target electrode of FIG. 1, and FIG. 3 is a perspective view of a target mechanism according to a first embodiment of the present invention. 4 is a plan view of the target mechanism of FIG. 3, FIG. 5 is a front sectional view of the target mechanism of the second embodiment, and FIG. 6 is the target #! of FIG. 5. Measures (1 dead face, 7th
8 is a plan view of the target mechanism of FIG. 7, FIG. 9 is a front sectional view of the target mechanism of the fourth embodiment, and FIG. 10 is a front sectional view of the target mechanism of the fourth embodiment. FIG. 11 is a plan view of the target mechanism shown in the figure, and FIG. 11 is a front sectional view of a sputtering apparatus to which the present invention can be applied. 4... Substrate 18... Target 19... Back plate 20 of target electrode... Electrode body 24, 25, 26... Shield plate 60... Blank space of target electrode

Claims (5)

[Claims] (1) A target electrode for a sputtering apparatus, characterized in that a region to which no target potential is applied is formed in the center of the target electrode. (2) The target electrode according to claim 1, characterized in that the target electrode is formed into an annular shape and has a space provided in the center thereof. (3) The target electrode according to claim 2, wherein the inner peripheral edge of the annular target electrode is covered with a target shield. (4) Claim 1 characterized in that the target electrode is formed into an annular shape, a conductor is placed in the center of the target electrode, and the conductor is electrically connected to a target shield that covers the outer periphery of the target electrode. Target electrode as described. (5) A sputtering apparatus comprising the target electrode according to any one of claims 1 to 4, wherein a substrate is disposed facing a region of the target electrode to which no target potential is applied.