GB1569117A - Sputtering device - Google Patents

Description

(54) SPUTTERING DEVICE (71) We, KABUSHIKI KAISHA TOKUDA SEISAKUSHO, a Japanese company of 371 Futago, Takatsu-Ke, Kawasaki-Shi, Kanagawa-Ken, Japan do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to sputtering devices, that is, to devices which deposit a metallic film on the surface of a workpiece by the utilization of a cathode sputtering phenomenon which occurs with glow discharge.

In general, in sputtering devices, a cathode sputtering phenomenon accompanying glow discharge, that is, in response to bombardment by gas ions of the discharge, the material of a cathode is gasified into metallic atoms or a mass of metallic atoms by the bombardment of gas ions thereto, a part of the atoms being scattered, is utilized.

The metallic atoms thus scattered are adhered to the surface of a workpiece positioned in the vicinity of the anode thereby to form a metallic film thereon.

The feature of this sputtering is that the lower the pressure of the gas atmosphere, in which the sputtering is effected, the smaller is the probability that the metallic atoms emitted from the cathode will collide with the residual gas molecules present between the electrodes is, and at the same time the finer is the finish of a metallic film obtained by deposition of the metallic atoms arriving directly upon the workpiece is.

That is, the pressure of the gas atmosphere should be as low as possible to improve the quality of the metallic film deposited on the workpiece.

In known sputtering devices of this type, the conditions for effectively conducting the sputtering with glow discharge are experimentally determined by the nature and state of the gas and those of the cathode material employed therein, and especially the pressure of the gas must be maintained at a certain value (of the order of 1-2 X 10-2 Torr in direct current glow discharge, in general) for the occurrence of glow discharge, Thus, the amount by which the pressure of the gas can be lowered is limited.

Furthermore, in the known sputtering devices, electrons emitted from the target during the sputtering collide with the anode thereby increasing the temperature of the latter, and the temperature of a workpiece placed near the anode is also increased by the radiant heat from the anode. Therefore, the heat stability of the workpiece must be taken into consideration.

It is an object of the invention to provide an improved sputtering device in which one or more of the above-mentioned disadvantages is overcome or reduced.

The invention provides a sputtering device for forming a metallic film on the surface of a workpiece placed in the vicinity of an anode in a low-pressure gas atmosphere by utilizing cathode sputtering, said device comprising, within an evacuable enclosure, anode means and a cathode arranged to define cylindrical surfaces coaxial about an axis and permanent magnet means, comprising at least one body symmetrical about said axis and polarised therealong, disposed in relation to said cathode in such a manner that the direction of the magnetic field produced thereby crosses orthogonally the direction of an electric field produced when an electric potential is applied between said anode means and said cathode, and magnetic lines of force in the inter-electrode space start from and return to said cathode to enclose electrons emitted from said cathode in said inter-electrode space, whereby sputtering may be effected in a low pressure gas atmosphere.

An advantage of the invention is that it may be used to provide a sputtering device in which a target is uniformly sputtered, and therefore the distribution in thickness of a metallic film deposited on a workpiece is uniform.

Another advantage of the invention is that it provides a sputtering device which has cxcdlent cooling and so may be used to carry out sputtering at low temperature.

In an embodiment of the invention a sputtering device is provided in which a permanent magnet of simple construction is used and which is also simple to handle during sputtering.

As will become evident hereinafter, in the sputtering device according to this invention having cylindrical cathode and anode electrodes defining coaxially disposed cylindrical surfaces, a magnetic field is generated orthogonal with the electric field between the electrodes thereby causing a drift motion of electrons so that the electrons do not reach the anode unless they lose their energy upon colliding with gas molecules. In order to cause the drift motion of the electrons to occur in a particular region, a single magnet or a plurality of magnets having a radial magnetic field are disposed parallel to the target or cathode (perpendicularly to the electric field).

The sputtering device thus organized has the following merits: (1) Forming a metallic film on a workpiece can be achieved in a high vacuum (less than 2-3 X 10-4 Torr in direct current discharge).

(2) The temperature rise of a workpiece is less than in known sputtering devices. It is said that a main cause of the temperature rise of the workpiece is the flow of electrons into the anode (which sometimes serves as a base plate).

(3) Deposition rate is high. Since the temperature rise of the workpiece is less as was described above, a large electric power can be applied to the sputtering device, and therefore a high deposition rate can be obtained.

(4) The structure of a target is simple.

(a) Since the electric discharge is effec ted in a high vacuum, insulation for the target can be simple. Thus, it is unneces sary to provide a dark space shield, and the like.

(b) The discharge is effected only at a place where the electric and magnetic fields are orthogonal. Therefore, the cathode covered with a material to be deposited only at a position where the discharge is effected.

(5) Cooling an electrode can be readily achieved.

(a) The cathode can be cooled with water in a conventional water-cooling method if a permanent magnet is em ployed.

(b) One or several rods disposed parallel to the cathode and perpendicu larly to the direction of the drift motion of the electrons can be used as anodes.

If these anodes are replaced by pipe shaped anodes, they can be readily cooled with water. Furthermore, since the energy of the electrons is small when they have reached the anodes, the amount of water necessary for cooling the anode can be relatively small.

The invention will become more apparent from the following detailed description of embodiments thereof, given by way of example, and the appended claims when read in conjunction with the accompanying drawings in which like parts are designated by like reference characters: wherein: Figures 1(a) and 1(b) are respectively a vertical sectional view and a horizontal sectional view illustrating a first example of a sputtering device according to this invention:: Figures 2 (a) and 2 (b) are respectively a vertical sectional view and a horizontal sectional view illustrating a second example of a sputtering device according to the invention; Figure 3 is a vertical sectional view showing a third example of a sputtering device according to the invention; Figure 4 is a graphical representation indicating the distribution in thickness of a metallic film deposited on a workpiece by the sputtering device shown in Figures 1 (a) and 1(b); Figure 5 is a graphical representation indicating the distribution in thickness of a metallic film deposited on a workpiece by the sputtering device shown in Figure 3; Figure 6 is a vertical sectional view illustrating a fourth example of a sputtering device according to the invention; and Figure 7 is a vertical sectional enlarged view showing a decaying condition of a target incorporating a magnet shown in Figures 1 (a} and 1(b).

A first example of a sputtering device, as shown in Figures 1 (a) and 1(b), comprises a base plate 1 and a cylindrical cover 2 which is hermetically and detachably mounted on the base plate 1 by the use of a packing 101, to provide a vacuum container 3. In this container 3 there are coaxially provided a target (or a cathode) 4, anodes 5, and workpieces 6.

The target 4 is obtained by plating or spraying target material 41, such as chromium Cr, on to the outer surface of a cylinder 8 of non-magnetic material which is mounted through an insulator 7 on the central portion of the base plate 1, or by winding a wire or strip of target material 41 such as molybdenum Mo or tungsten W around the cylinder 8. If the cylinder 8 is made of material such as aluminium Al, copper Cu, or stainless steel, no treatment such as those described above is necessary, and it can be used without such coating as the target 4.

In this example, the anodes 5 are rodshaped electrodes provided on the base plate 1. The rod-shaped electrodes 5 are disposed in such a manner that they surround the target 4. Furthermore, the workpieces 6 are placed in such a manner that they surround the electrodes 5.

In the cylinder 8, there is provided a cylindrical magnet 9 having a through-hole along its axis in such a manner that the direction of the magnetic field of the magnet 9 crosses orthogonally the direction of the electric field produced by the application of an electric potential between the electrodes 4 and 5.

Packing 10 are provided between the base plate 1 and the insulator 7, and between the insulator 7 and the bottom of the cylinder 8 so that the inside of the cylinder is maintained airtight. A cooling-water inlet pipe 12 for introducing cooling water W into the cylinder 8 and a cooling water outlet pipe 11 for discharging the cooling water W out of the cylinder 8, as shown in Figure 1 (a), penetrate into the cylinder 8 through the base plate 1, the outlet pipe 11 extending through the through-hole of the magnet 9 so that the cooling water is circulated in the cylinder 8 so as to cool the target 4 the temperature of which is increased by bombardment of gas ions.

Furthermore, in the base plate 1 there are provided an air suction port 14 to which a vacuum pump 13 is connected, and a gas injection port 17 to which a gas cylinder 15 is connected through a control valve 16.

The operation of the sputtering device thus organized will now be described.

First, the vacuum pump 13 is operated to create a vacuum in the vacuum container 3. The vacuum container 3 is then filled with gas from the gas cylinder 15; however, the gas in the vacuum container 3 is maintained at a predetermined pressure at all times by adjustment of the control valve 16 of the gas cylinder 15.

If, now, a suitable exciting voltage V is applied across the target 4 and the anodes 5 to produce a glow discharge therebetween, the cathode sputtering phenomenon described before takes place, that is, the target atoms sputtered adhere to and are deposited on the surfaces of the workpieces 6, thus forming a film on the workpiece which is strongly adhered thereto.

In this operation, the magnetic field H of the magnet 9 causes a force F along the electrodes 4 and 5, which define coaxial cylindrical surfaces, to act on the electrons which have been emitted from the target 4 by the bombardment of the gas ions, as a result of which the electrons are enclosed in a space defined by the electric field formed by the electrodes 4 and 5 and the magnetic field of the magnet 9 (hereinafter referred to as "an electrode space" when applicable), and are caused to move in the axial direction with respect to the electrodes. Accordingly, the density of the electrons in the electrode space is increased, and therefore the glow discharge becomes vigorous and the sputtering is effected more actively.

Thus, even if in the sputtering device as described the pressure in the vacuum container 3 is reduced from 1 X 10-2 Torr to a value of the order of 1 X 10-4, the sputtering can be carried out with high efficiency.

Furthermore, in the said sputtering device the proportion of electrons emitted by the cathode which collide with the workpieces is considerably reduced, and the temperature rise of the workpieces is also considerably reduced.

A second example of a sputtering device according to this invention is shown in Figures 2 (a) and 2 (b). Its operating principle is the same as that of the first example described above with respect to Figures 1 (a) and 1(b).

In the second example, a workpiece holder 18 is provided at the central portion of a vacuum container 3 made of nonmagnetic insulating material, and a target 42 and a hollow cylindrical magnet 91 (both being cylindrical) surround the workpiece holder 18. More specifically, the target 42 has outer and inner walls forming a cylindrical chamber 19 in which the magnet 91 is disposed and cooling water W is circulated through inlet and outlet pipes 12 and 11.

A workpiece 6 is put on the workpiece holder 18 as is shown in Figures 2 (a) and 2 (b). Since in this case the surface of the target 42 is larger in area than that of the workpiece, the rate in growth of a metallic film on the workpiece is quicker. This is one of the advantages of the second example.

Thus, the sputtering devices according to this invention are advantageous in that sputtering can be achieved with high efficiency even in a gas atmosphere of extremely low pressure, and a fine metallic film is therefore deposited on a workpiece.

In addition, a sputtering device according to this invention may readily be cooled, so that it is possible to form a metallic film even on materials, such as paper and synthetic resin, which have a low thermal stability.

In the examples described above, the direct current sputtering method is employed; however, it should be noted that the invention is not limited thereto or thereby. That is, a RF sputtering method using a high-frequency electric source can be employed in the examples.

A third example of a sputtering device according to this invention, as shown in Figure 3 is similar to the first example except that a plurality of small magnets 92 are disposed in the target 4 so that the distribution in thickness of a metallic film deposited on a workpiece 6 is substantially uniform.

In the sputtering device having a cylindrical magnet such as that shown in Figures 1 (a) and 1(b), the field of the magnet 9 defines a single sputtering source, and therefore, the thickness of the metallic film formed is uneven as is shown in Figure 4.

This has been established through several experiments.

In order to overcome this difficulty, associated with the first example, the single cylindrical magnet 9 shown in Figures 1 (a) and 1 (b) is divided into a plurality of cylindrical magnets 92 (Fig. 3) that is, a plurality of sputtering sources are formed so that the distribution of metallic atoms emitted by sputtering is uniform throughout the target material.

The third example is otherwise similar in construction and operation to the first example shown in Figures 1(a) and 1 (b).

However, the magnets 92 are spaced at suitable intervals along the target material 41. More specifically, the magnets 92 provided at the top and the bottom portion of the target material are spaced at relatively short intervals and at the same time the magnets provided at the middle portion thereof are spaced at relatively long intervals so that the distribution of metallic atoms emitted by sputtering is uniform throughout the target material as shown in Figure 5, that is, the density of the metallic atoms emitted in the electrode space is uniform. Accordingly, the distribution in thickness of a metallic film deposited on a workpiece 6 becomes uniform, too.Therefore, the size (especially the height) of a workpiece 6 to be treated by the third example can be greater than that of a workpiece which can be treated by known sputtering devices or by the first and second examples described before.

Similarly as in the first and second examples, the sputtering device shown in Figure 3 is also advantageous in that the sputtering can be achieved with high efficiency even in a gas atmosphere of extremely low pressure, and a fine metallic film is deposited on a workpiece.

A fourth example of a sputtering device according to this invention, as shown in Figure 6, is similar in construction to that shown in Figure 1 (a) except that a magnet 93 provided in the target 4 is moved along the axis of the target 4 so as to obtain uniformity in thickness of a metallic film deposited on a workpiece 6 and also uniformity in consumption of the target 4 (or 41) in the electrode space.

In the sputtering device shown in Figures 1 (at and 1(b), the portion of the target 4 where the magnet is provided forms the sputtering source. If it is assumed that the electric power applied to the sputtering device is constant, the rate of sputtering the target 4 is proportional to the strength of the magnetic field H and is also affected by the closeness of approximation to perpendicularity of the magnetic field H with the electric field E at on the surface of the target. Therefore, the consumption of the target 4 due to the sputtering, as shown in Figure 7, is concentrated at the central portion of the target decays. The more the sputtering advances, the more the consume tion is increased. Thus, the central portion of the target 4 is consumed sooner than the other portion.Therefore, it is necessary to replace the target 4 when the central portion of the target material has been consumed. Otherwise, the sputtering rate is decreased, which leads to a lowering of the efficiency of the sputtering device.

Accordingly, the service life of the target 4 is short in this sputtering device, and the arrangement is uneconomical.

Furthermore, the thickness of a metallic film formed on a workpiece 6 is greater at its portion opposite to the central portion of the target which has been most deeply decayed by sputtering than the other portion, and it is therefore impossible to deposit a metallic film uniform in thickness on the workpiece by the use of the sputtering device shown in Figure 1(a).

The sputtering device shown in Figure 6 seeks to overcome the above-described difficulty accompanying the sputtering device of Figure 1(a).

In the sputtering device shown in Figure 6, the length of the magnet 93 is shorter than the length L of the target 4, and this magnet 93 is moved vertically, or along the target 4, by means such as a manual operation, a motor-operated mechanism, or a hydraulic mechanism.

In the sputtering device thus organized, during one sputtering operation the magnet 93 is moved along the target 4 during the progress of the sputtering. Accordingly, as the magnet 93 is moved in this way, the portion of the target 4 where most sputtering is effected is also moved. As a result, the surface of the target 4 is uniformly consumed, and therefore a metallic film of uniform thickness is deposited on a workpiece 6.

In the sputtering device shown in Figure 6, the phenomenon that the target surface is non-uniformly consumed, as is the case in known sputtering devices, and in the first and second examples of the invention is not observed. Instead, the target is uniformly consumed, and accordingly, the target can be effectively and economically used.

Moreover, the thickness of a metallic film deposited on a workpiece is uniform.

Thus, with the sputtering device shown in Figure 6, the deposition of metal film can be achieved economically with satisfactory results. This sputtering device is suitable for depositing a metallic film on a relatively long workpiece.

Furthermore, since the magnet 93 is movable as described above, that is, the distribution of the magnetic field in the electrode space is controlled, the sputtering can be effected at a desired portion of the target, that is, the distribution in thickness of a metallic film on a workpiece can be controlled as desired.

It will be seen that a sputtering device disclosed herein is based on the fact that the lower the pressure of a gas atmosphere, in which glow discharge is effected, the smaller is the probability that metallic atoms emitted from a target or cathode by sputtering will collide with residual molecules between the electrodes, and the finer is the finish of a metallic film formed by depositing the metallic atoms arriving directly to a workpiece, and that if the energy of electrons emitted from the target is weakened upon arrival at the anode, the temperature rise of the inside of the device and especially that of the workpiece can be minimized.

The target and the anode are arranged to define coaxial cylindrical surfaces, and a magnet is disposed in the target in such a manner that the direction of the magnetic field orthogonally crosses that of the electric field, so that the electro-magnetic force encloses the electrons in the inter-electrode space to increase the density of electrons therein, whereby sputtering is effectively carried out even in a gas atmosphere of extremely low pressure and electrons are prevented from colliding directly with the anode, thus minimizing the temperature rise of the workpiece.

WHAT WE CLAIM IS: - 1. A sputtering device for forming a metallic film on the surface of a workpiece placed in thevicinity of an anode in a lowpressure gas atmosphere by utilizing cathode sputtering, said device comprising, within an evacuable enclosure, anode means and a cathode arranged to define cylindrical surfaces coaxial about an axis and permanent magnet means, comprising at least one body symmetrical about said axis and polarised therealong, disposed in relation to said cathode in such a manner that the direction of the magnetic field produced thereby crosses orthogonally the direction of an electric field produced when an electric potential is applied between said anode means and said cathode, and magnetic lines of force in the inter-electrode space start from and return to said cathode to enclose electrons emitted from said cathode ;;n said inter-electrode space, whereby sputtering may be effected in a low pressure gas atmosphere.

2. A sputtering device as claimed in Claim 1, in which said cathode is made as a hollow cylindrical cathode which is cooled with water, said magnet is disposed within said hollow cylindrical cathode, and said anode means comprises a plurality of rodshaped anodes are arranged equidistantly from said cathode to surround the latter, and said workpiece is positioned radially outside said plurality of rod-shaped anodes.

3. A sputtering device as claimed in Claim 1, in which said cathode is a hollow cylindrical cathode with a water-cooling chamber, said hollow cylindrical cathode being positioned on the periphery of said device, said magnet is disposed in said chamber, said anode means comprises a plurality of rod-shaped anodes disposed equidistantly from said cathode in such a manner that said anodes are surrounded by said cathode, and said workpiece is placed at the centre of said plurality of rod-shaped anodes.

4. A sputtering device as claimed in Claim 2, in which a plurality of said magnetic bodies are arranged spaced apart along the length of said cathode so that the distribution in thickness of a metallic film is substantially uniform.

5. A sputtering device as claimed in Claim 2, in which during sputtering said magnet means is moved along said cathode so that the cathode is consumed uniformly throughout in the electrode space.

6. A sputtering device substantially as herein described with reference to Figures 1 (a) and 1 lob), Figures 2 (a) and 2 (b), Figure 3 or Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. known sputtering devices, and in the first and second examples of the invention is not observed. Instead, the target is uniformly consumed, and accordingly, the target can be effectively and economically used. Moreover, the thickness of a metallic film deposited on a workpiece is uniform. Thus, with the sputtering device shown in Figure 6, the deposition of metal film can be achieved economically with satisfactory results. This sputtering device is suitable for depositing a metallic film on a relatively long workpiece. Furthermore, since the magnet 93 is movable as described above, that is, the distribution of the magnetic field in the electrode space is controlled, the sputtering can be effected at a desired portion of the target, that is, the distribution in thickness of a metallic film on a workpiece can be controlled as desired. It will be seen that a sputtering device disclosed herein is based on the fact that the lower the pressure of a gas atmosphere, in which glow discharge is effected, the smaller is the probability that metallic atoms emitted from a target or cathode by sputtering will collide with residual molecules between the electrodes, and the finer is the finish of a metallic film formed by depositing the metallic atoms arriving directly to a workpiece, and that if the energy of electrons emitted from the target is weakened upon arrival at the anode, the temperature rise of the inside of the device and especially that of the workpiece can be minimized. The target and the anode are arranged to define coaxial cylindrical surfaces, and a magnet is disposed in the target in such a manner that the direction of the magnetic field orthogonally crosses that of the electric field, so that the electro-magnetic force encloses the electrons in the inter-electrode space to increase the density of electrons therein, whereby sputtering is effectively carried out even in a gas atmosphere of extremely low pressure and electrons are prevented from colliding directly with the anode, thus minimizing the temperature rise of the workpiece. WHAT WE CLAIM IS: -

1. A sputtering device for forming a metallic film on the surface of a workpiece placed in thevicinity of an anode in a lowpressure gas atmosphere by utilizing cathode sputtering, said device comprising, within an evacuable enclosure, anode means and a cathode arranged to define cylindrical surfaces coaxial about an axis and permanent magnet means, comprising at least one body symmetrical about said axis and polarised therealong, disposed in relation to said cathode in such a manner that the direction of the magnetic field produced thereby crosses orthogonally the direction of an electric field produced when an electric potential is applied between said anode means and said cathode, and magnetic lines of force in the inter-electrode space start from and return to said cathode to enclose electrons emitted from said cathode ;;n said inter-electrode space, whereby sputtering may be effected in a low pressure gas atmosphere.

2. A sputtering device as claimed in Claim 1, in which said cathode is made as a hollow cylindrical cathode which is cooled with water, said magnet is disposed within said hollow cylindrical cathode, and said anode means comprises a plurality of rodshaped anodes are arranged equidistantly from said cathode to surround the latter, and said workpiece is positioned radially outside said plurality of rod-shaped anodes.

3. A sputtering device as claimed in Claim 1, in which said cathode is a hollow cylindrical cathode with a water-cooling chamber, said hollow cylindrical cathode being positioned on the periphery of said device, said magnet is disposed in said chamber, said anode means comprises a plurality of rod-shaped anodes disposed equidistantly from said cathode in such a manner that said anodes are surrounded by said cathode, and said workpiece is placed at the centre of said plurality of rod-shaped anodes.

4. A sputtering device as claimed in Claim 2, in which a plurality of said magnetic bodies are arranged spaced apart along the length of said cathode so that the distribution in thickness of a metallic film is substantially uniform.

5. A sputtering device as claimed in Claim 2, in which during sputtering said magnet means is moved along said cathode so that the cathode is consumed uniformly throughout in the electrode space.

6. A sputtering device substantially as herein described with reference to Figures 1 (a) and 1 lob), Figures 2 (a) and 2 (b), Figure 3 or Figure 4 of the accompanying drawings.