JP2975649B2 - Sputtering equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sputtering apparatus provided with a target electrode having a distinctive electrode shape.

[Prior art] In recent years, a thin film has been created using a sputtering phenomenon,
Fabrication of a device or the like by processing the film is actively performed in both research and practical use.
This sputtering phenomenon is a phenomenon in which high-energy ions are incident on a target to generate sputter particles (neutral particles) from the target and deposit sputter particles on a substrate. Oxide superconductor thin films and ITO thin films (transparent conductive films), which have recently been in the limelight, are also being manufactured using this sputtering phenomenon.

[Problems to be Solved by the Invention] In order to prepare an oxide-based substance such as an oxide superconductor thin film or an ITO thin film by sputtering, a target composed of these substances or a target containing a composition component of these substances is used. However, such an oxide-based target also generates negative ions (mainly oxygen negative ions) in addition to sputtered particles during a sputtering phenomenon. The negative ions are accelerated in the direction of 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 collide with the substrate and cause a problem of resputtering sputtered particles (films) 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, the superconducting characteristics deteriorate. In addition, similar re-sputtering phenomenon causes ITO
The conductivity of the thin film also deteriorates.

By the way, in the magnetron sputtering method which is currently put into practical use, an erosion region is locally formed on a target by trapping electrons by a closing magnetic field and ionizing a gas at a high density.
In this erosion region, many negative ions are generated together with sputtered particles. As a result, the substrate portion facing the erosion region is most susceptible to negative ion bombardment. Therefore, if the substrate is arranged at a position not facing the erosion region, the negative ion bombardment is reduced. However, since a target potential (which is more negative than plasma) exists on the target surface other than the erosion region, an electric field due to the target potential scatters from secondary electrons generated in the target or from the erosion region. This accelerates the negative ions. As a result, there is a problem that these secondary electrons and negative ions collide with the substrate to some extent even in the substrate portion facing the target surface other than the erosion region.

For example, when a single target having a diameter of 4 inches (approximately 100 mm) is used to produce an oxide superconductor thin film of Y ₁ Ba ₂ Cu ₃ O _y , the composition variation of the film on the substrate (from the stoichiometric ratio) Gap)
Is within 2% only in the region within the range of 20 mm in diameter. Outside this region, the composition fluctuates greatly, the crystallinity is poor, and the superconducting properties are greatly deteriorated.

As described above, in the conventional target electrode,
The problem that negative ions generated from the target collide with the substrate has not been completely solved.

By the way, in magnetron sputtering,
By providing the erosion region at a position away from the center of the target, or by reducing the width of the erosion region, it is possible to increase the substrate area so that negative ions do not collide. Thus, the thin film in the substrate region located immediately above the center of the target can have a uniform composition with a relatively large area. However, in this case, the area ratio of the erosion region to the target surface area is considerably reduced, and the use efficiency of the target deteriorates.

The present invention has been developed in order to solve the above-mentioned drawbacks, and an object of the present invention is to provide a target electrode that minimizes negative ion bombardment on a substrate and that does not reduce the use efficiency of the target. It is to provide a sputtering device.

[Means for Solving the Problems] According to a first aspect of the present invention, a sputtering apparatus is provided with a target electrode in which a region to which a target potential is not applied is formed in a central portion, and the substrate is opposed to a region where the target potential of the target electrode is not applied. It is characterized by being arranged.

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

According to a third aspect, in addition to the configuration of the second aspect, the inner peripheral edge of the annular target electrode is covered with a target shield.

The fourth invention is a more specific example of the first invention,
The target electrode is formed in an annular shape, and a conductor is disposed at the center of the target electrode. The conductor is electrically connected to a target shield covering the outer peripheral edge of the target electrode.

[Operation] If a region to which the target potential is not applied is formed in the center of the target electrode, a potential gradient called a cathode sheath does not exist in this region. Therefore, even if secondary electrons or negative ions generated in the target are lost in this region. There is no such thing as acceleration. Of course, since no target exists in this region, this region does not become a source of secondary electrons or negative ions.

One method of forming a region to which a target potential is not applied is to form a target electrode in a ring shape and provide a space in the center thereof. In this case, if the inner peripheral edge of the annular target electrode is covered with the target shield, it is possible to block secondary electrons and negative ions that would go to the substrate from near the inner peripheral edge.

Another way to create a region where no target potential is applied is to place a conductor in the center of the annular target electrode and electrically connect this conductor and the target shield to ground. In this case, a potential gradient near the surface of the conductor as in the vicinity of the target surface does not occur.

When the above-described target electrode is used, if the substrate is arranged so as to face a region of the target electrode to which the target potential is not applied, the substrate is not subjected to negative ion impact.

Embodiment Next, an embodiment of the present invention will be described 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 of the vacuum vessel 1 is increased by 10 ^-7 by the main exhaust system installed in the direction of arrow 13.
It can be kept at a vacuum below Torr. A gas introduction system 29 for supplying a gas necessary for producing a thin film is provided in the vacuum vessel 1, and the gas is introduced into the vacuum vessel 1 via the valves 10a and 10b. For example, Ar gas is supplied from the direction of arrow 11 and O ₂ gas is supplied from the direction of arrow 12, and these are mixed and introduced into the vacuum vessel 1. The pressure in the vacuum vessel 1 can be set to an appropriate value by adjusting a mass flow meter (not shown) of the gas introduction system 29 and a main exhaust system installed in the direction of arrow 13. A substrate holder 5 that can hold the substrate 4 and heat it to 800 ° C. is installed in the vacuum vessel 1. The heating method is a method of controlling the lamp heater 7 using the temperature control device 8, the thyristor transformer 9, and the thermocouple 6 attached to the surface of the substrate holder 5. The target electrode 3 is arranged at a position facing the substrate holder 5. A target shield 2 is arranged on the outer peripheral edge of the target electrode 3, and an electrode insulating ring 14 is provided between the target shield 2 and the target electrode 3.
(Made of fluororesin).

Cooling water (arrows 15a and 15b) flows through the target electrode 3. A high frequency power supply 17 is connected to the target electrode 3 via an impedance matching unit 16.

FIG. 1 is a perspective view showing an example of a target electrode usable in the sputtering apparatus of FIG. The target electrode includes an electrode body 20 and a back plate 19. The 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 contains a magnet assembly shown in FIG. 2 inside. The magnet assembly includes an outer circular magnet 22a and an inner circular magnet 22b, both of which are fixed to the yoke 21. This magnet assembly can be easily attached and detached inside the electrode body 20.

FIG. 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 the target 18 is bonded to the back plate 19. Each of the back plate 19 and the target 18 is a circular plate having a hole in the center. Electrode body 20
Is fixed on a hollow circular electric insulating plate 23 (made of fluororesin). The inner peripheral surface 20a and the outer peripheral surface 20b of the electrode body 20 are surrounded by a shield plate 24. The outer peripheral edges of the back plate 19 and the target 18 are also covered with the shield plate 24. Electrode body
A water cooling pipe is connected to 20, and the water cooling water flows from the direction of arrow 15a to the direction of arrow 15b. O-rings 30 and 31 are provided on the lower surface of the back plate 19 to seal the cooling water. Electrode body
20 includes a high-frequency power supply 17 via an impedance matching unit 16.
Are connected so that predetermined power can be applied.

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

FIG. 3 also shows the position of the substrate 4 facing the target mechanism. The substrate 4 is disposed so as 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 operation of the target electrode mechanism will be described.

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

By the way, immediately below the substrate 4 is a space 60 at the center of the target electrode, so that sputtered particles that will adhere to the substrate 4 have come obliquely from the target 18. On the other hand, the secondary electrons and negative ions 32 generated in the target 18 are accelerated by the potential gradient of the cathode sheath on the surface of the target 18 and fly almost perpendicular to the target surface. Therefore, secondary electrons and negative ions do not come to the substrate 4. Even if secondary electrons and negative ions enter above the space 60, the cathode sheath does not exist in this portion, so that the secondary electrons and negative ions are not accelerated toward the substrate 4.

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

Next, an example in which an oxide superconductor thin film is manufactured using this target mechanism will be described. As the target 18, a 4 inch diameter Y ₁ Ba ₂ Cu ₃ O _y sintered body target was used. Eleventh
An Ar gas and an O ₂ gas are introduced from the direction of arrow 11 and O ₂ gas from the direction of arrow 12 through the valves 10a and 10b and a mass flow meter (not shown) by the gas introduction system 29 shown in FIG. Introduced inside. At this time, the flow ratio of the Ar gas to the O ₂ gas was 1: 1. The pressure inside the vacuum body 1 is 25 mTor.
r. High-frequency power of 150 W was applied to the electrode body 20 from the high-frequency power supply 17, and the impedance matching unit 16 adjusted the reflected wave to be 0 W (zero watt). Also,
In order to obtain superconductivity in the as-grown state,
The thin film was deposited while being heated to 700 ° C. Since MgO (100) and SrTiO ₃ (100) were used for the substrate 4, the obtained film was a C-axis oriented film.

The following is a comparison between the oxide superconductor thin film thus manufactured and a conventional thin film formed using a magnetron target having no void.

(A) Superconductor thin film produced in this example Film composition: Y ₁ Ba ₂ Cu ₃ O _y (center) Uniform region of film composition (within ± 2%): Within 45 mm diameter Superconducting critical temperature: Tce = 90K (b) Conventional thin film Film composition: Y ₁ Ba _1.8 Cu _2.8 O _y (center) Uniform region of film composition (within ± 2%): within 20mm diameter Superconducting critical temperature: Tce = 72K Comparing the results, in the case of the example, the film composition was improved, and in particular, the uniform region of the film composition was twice as large as 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 target mechanism is characterized in that a shield plate 25 is arranged in a central space of a target electrode, and the other points are the same as those of the embodiment of FIG. The shield plate 25 is formed of a conductor, and is formed integrally with the shield plate 24 in this embodiment. When the central space is covered with the shield plate 25, the potential at this portion becomes the ground potential, so that the potential gradient immediately below the substrate 4 completely disappears, and damage to the substrate 4 due to negative ions or the like is prevented. Less than in the example.

FIG. 7 is a front sectional view of the target mechanism of the third embodiment, and FIG. 8 is a plan view thereof. This target mechanism is characterized in that the upper end portion 26 of the shield plate that covers the inner peripheral surface 20a of the electrode body 20 covers the inner peripheral edge of the target 18. The other points are the same as in the embodiment of FIG.
By providing the upper end portion 26 in this manner, the target
This has the effect of blocking negative ions that would fly toward the substrate 4 from the inner peripheral edge of 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 target mechanism is characterized in that the shape of the target electrode is rectangular. Other points are basically the same as those of the embodiment of FIG. In FIG. 9, the shape of the electrode body 40 is a rectangular parallelepiped having a hollow portion at the center. Similarly, the shapes of the magnets 42a and 42b and the yoke 41 installed therein are also hollow rectangular parallelepipeds. The shape of the target 58 and the target back plate 59
It is a square plate with a square hole in the center. The inner and outer peripheral surfaces of the electrode body 40 are surrounded by a shield plate 44. The length of one side of the square substrate 4 is the square space 60
Is smaller than the length of one side.

The present invention is applicable not only to Y ₁ Ba ₂ Cu ₃ O _y but also to other oxide superconductors described below.

(1) MBa ₂ Cu ₃ O _y where M = lanthanum series element La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu (2) Bi ₂ Sr ₂ C _n-1 C _n O _y where n = 1,2,3,4 (3) Tl ₂ Ba ₂ C _n-1 C _n O _y where n = 1,2,3, _{4 (4) Tl 1 Ba 2} Ca n-1 Cu n O y , where, n = 1,2,3,4,5,6 (5) or more compounds with the same elemental composition (also contain other elements Good) and a compound having another stoichiometry [Effect of the Invention] In the sputtering apparatus of the first invention, a region where the target potential is not applied is formed in the center of the target electrode. It does not become a source of secondary electrons or negative ions, and even if secondary electrons or negative ions get into this area, there is no potential gradient called a cathode sheath. There is no acceleration. In addition, since the central portion of the target is unnecessary, particularly in magnetron sputtering, the ratio of the erosion region to the target surface area is increased, and the target use efficiency is improved. Since the substrate is disposed so as to face the region of the target electrode to which the target potential is not applied, the substrate is not subjected to negative ion bombardment. As a result, a thin film having good characteristics can be formed particularly when an oxide thin film that easily generates negative ions is manufactured.

According to the second aspect, a void is formed as a region to which the target potential is not applied, and the configuration is the simplest.

According to the third aspect of the present invention, since the inner periphery of the ring and the target electrode is covered with the target shield, it is possible to block secondary electrons and negative ions that would go to the substrate from near the inner periphery.

According to the fourth aspect of the present invention, since a conductor is arranged in a space portion and this conductor is electrically connected to a normal target shield and grounded, the vicinity of the surface of the conductor is similar to the vicinity of the target surface. Potential gradient completely disappears.

[Brief description of the drawings]

FIG. 1 is a perspective view of a target electrode used in the 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 first embodiment. FIG. 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, FIG. 6 is a plan view of the target mechanism of FIG. FIG. 7, FIG. 7 is a front sectional view of the target mechanism of the third embodiment, FIG. 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, FIG. FIG. 9 is a plan view of the target mechanism of FIG. 9, 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 ... target electrode back plate 20 ... target electrode electrode body 24, 25, 26 ... shield plate 60 ... empty space

Claims (4)

(57) [Claims] 1. A sputtering apparatus comprising: a target electrode provided with a region to which a target potential is not applied in a central portion; and a substrate arranged to face a region of the target electrode to which a target potential is not applied. 2. The sputtering apparatus according to claim 1, wherein the target electrode is formed in an annular shape, and a space is provided in the center of the target electrode. 3. An inner peripheral edge of an annular target electrode is covered with a target shield.
The sputtering apparatus as described in the above. 4. The target electrode is formed in a ring shape, a conductor is disposed in the center of the target electrode, and the conductor is electrically connected to a target shield covering an outer peripheral edge of the target electrode. Item 2. The sputtering apparatus according to Item 1.