Reactive sputtering apparatus

A reactive sputtering apparatus includes a vacuum chamber, a cathode fixed to an inner surface of the chamber, a power source for applying a voltage to the cathode, a magnetic circuit, installed in the cathode and having magnets for generating a magnetic field, a target, installed adjacent the magnets, having an opening at a portion corresponding to a region between the magnets of the magnetic circuit, a vacuum device for evacuating air inside the chamber to obtain vacuum, a first gasintroducing device, disposed at a wall of the chamber, for supplying reactive gas into the chamber, a second gas-introducing device for supplying discharge gas from the opening of the target into the chamber, a first gas flow rate control device for controlling the supply of the reactive gas, a second gas flow rate control device for controlling the supply of the discharge gas, and a substrate holder, disposed in opposition to the target inside the chamber, for securing a substrate thereto.

BACKGROUND OF THE INVENTION 
The present invention relates to a reactive sputtering apparatus to be used 
in the process of manufacturing an object such as a semiconductor or an 
electronic component. 
In a reactive sputtering apparatus, reactive gas such as nitrogen gas is 
added to a discharge gas such as argon gas used in a normal sputtering 
apparatus so as to deposit a compound, formed by the reaction of the 
reactive gas with particles sputtered from the material of a target, in 
the form of a thin film on a substrate. 
Since a reactive sputtering apparatus is capable of easily forming various 
kinds of thin films merely by introducing reactive gas into a normal 
sputtering apparatus, the reactive sputtering apparatus is preferably used 
in the process of manufacturing a semiconductor or an electronic 
component. 
An example of a conventional reactive sputtering apparatus is described 
below with reference to FIG. 6. 
The reactive sputtering apparatus comprises a vacuum chamber 1; a vacuum 
discharge opening 2 for evacuating air from the chamber 1; a 
gas-introducing pipe 3 for supplying discharge gas 5 and reactive gas 6 
into the chamber 1; a gas flow rate controller 4 for controlling the flow 
rate of the discharge gas 5 and the reactive gas 6; a target 7 mounted on 
a cathode 8; a power source 9 for applying a voltage to the cathode 8 
fixed to the inner surface of the chamber 1; a magnetic circuit 10, 
mounted in the cathode 8 and having a center circular magnet 10a and an 
annular magnet 10b, for generating a magnetic field; a substrate holder 11 
to which a substrate 12 is secured; and an erosion region 13, of the 
target 7, in which plasma density is highest during magnetron discharge. 
The erosion region 13 is located between the magnets 10a and 10b. The 
target 7 is located below the magnets 10a and 10b in the cathode 8. 
The operation of the reactive sputtering apparatus of the above-described 
construction will now be described below with reference to FIG. 6. First, 
air is evacuated from the chamber 1 by a vacuum pump (P) through the 
vacuum opening 2 to a degree of vacuum as high as approximately 10.sup.-7 
Torr. The discharge gas 5 and the reactive gas 6 are introduced into the 
chamber 1 through the gas-introducing pipe 3 connected with the chamber 1, 
with the quantity of the discharge gas 5 and the reactive gas 6 being 
controlled by the gas flow rate controller 4. 
The pressure inside the chamber 1 is kept at 10.sup.-3 to 10.sup.-2 Torr. A 
negative voltage is applied by the power source 9 to the magnetron cathode 
8. Plasma is generated by magnetron discharge in the vicinity of the 
surface of the target 7 under the action of a magnetic field generated by 
the magnetic circuit 10 disposed inside the cathode 8 and that of an 
electric field generated by the power source 9. A compound formed as a 
result of the reaction of particles sputtered from the target 7 with the 
reactive gas 6 is deposited in the form of a thin film on the substrate 12 
fixed to the substrate holder 11. 
It is known that sputtered particles and the reactive gas 6 react with each 
other mainly on the substrate 12. 
According to the conventional reactive sputtering apparatus, the discharge 
gas and the reactive gas are supplied into the chamber through the same 
gas-introducing pipe. As a result, the reactive gas exists not only in the 
vicinity of the substrate 12 but also in the erosion region of the target 
in which plasma density is highest in magnetron discharge. Consequently, a 
compound formed as a result of the reaction of the material of the target 
with the reactive gas deposits on the surface of the target. The compound 
greatly prevents particles from being sputtered from the target. 
Therefore, the thin film is formed on the substrate at a speed of 1/3 to 
1/5 the speed at which a thin film is formed by a normal sputtering 
apparatus. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a reactive sputtering 
apparatus which forms a thin film on a substrate without lowering the 
formation speed of the thin film. 
In accomplishing these and other objects, according to one aspect of the 
present invention, there is provided a reactive sputtering apparatus 
comprising: 
a chamber; 
a cathode fixed to an inner surface of the chamber; 
a power source for applying a voltage to the cathode; 
a magnetic circuit, installed in the cathode and having magnets, for 
generating a magnetic field; 
a target, installed adjacent the magnets, having at least one opening at a 
portion corresponding to a region between the magnets of the magnetic 
circuit; 
a vacuum means for evacuating air inside the chamber to obtain vacuum; 
a first gas-introducing means, disposed at a wall of the chamber, for 
supplying reactive gas into the chamber; 
a second gas-introducing means for supplying discharge gas from the opening 
of the target into the chamber; 
a first gas flow rate control means for controlling the supply of the 
reactive gas; 
a second gas flow rate control means for controlling the supply of the 
discharge gas; and 
a substrate holder, disposed in opposition to the target inside the 
chamber, for securing a substrate thereto. 
According to the above-described construction, since the discharge gas is 
supplied to the chamber through the second gas-introducing means and the 
reactive gas is supplied thereto through the first gas-introducing means, 
the gas which contributes to plasma formed in the vicinity of the surface 
of the target by magnetron discharge consists mostly of the discharge gas. 
As a result, the reaction of the reactive gas with the material of the 
target occurs at a decreased rate and thus a resulting compound is formed 
on the surface of the target in a reduced rate. Accordingly, a compound 
formed by the reaction of particles sputtered from the target with the 
reactive gas can be deposited on the substrate as a thin film without 
lowering the film-forming speed, unlike the conventional art.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout the 
accompanying drawings. 
A reactive sputtering apparatus according to a first embodiment of the 
present invention is described below with reference to FIGS. 1 through 3. 
FIG. 1 is a sectional view showing the reactive sputtering apparatus 
according to the first embodiment. Parts having the same functions as the 
parts of the conventional reactive sputtering apparatus are each denoted 
by the same reference numeral and the descriptions thereof are omitted. 
The construction of the reactive sputtering apparatus according to the 
first embodiment is different from that of the conventional one in that a 
plurality of small openings 19 is formed through the target 7 made of 
metal such as titanium. The openings 19 are circularly arranged and a 
gas-introducing pipe 14 for introducing the discharge gas into the chamber 
1 is provided and connected with the small openings 19 of the target 7. 
FIG. 2 is a partial sectional view showing the cathode portion of the 
reactive sputtering apparatus of FIG. 1. FIGS. 3A through 3C are sectional 
views taken along lines a--a', b--b', and c--c', of FIG. 2, respectively. 
Referring to FIGS. 2 and 3A-3C, the main body 15 of the cathode 8 
accommodates the magnetic circuit 10 for generating magnetron discharge. 
The magnetic circuit 10 includes the center circular magnet 10a and the 
annular magnet 10b surrounding the magnet 10a through an annular space 
thereon. Those magnets 10a and 10b are coaxially arranged. A backing plate 
16 on which the target 7 is disposed has therein an annular slit, namely, 
an annular groove 17 formed coaxially therewith. A small gasintroducing 
opening 18 is formed into a certain depth from the surface of the backing 
plate 16 opposite to the surface to which the target 7 is fixed. The small 
gas-introducing opening 18 communicates with the annular groove 17 and 
connects the annular groove 17 18 with the gasintroducing pipe 14. 
The plurality of small gas blowoff openings 19 is formed in the erosion 
region 13 of the target 7 by soldering the target 7 onto the backing plate 
16 by means of indium. The erosion region 13 is located between the 
magnets 10a and 10b. 
More specifically, as shown in FIGS. 1 and 2, the openings 19 are formed in 
the target 7 at the center of the erosion region 13. Since the center of 
the erosion region 13 naturally is aligned with the portion of the 
magnetic field having a maximum component parallel to the target (and thus 
no component normal to the target), it follows that the openings 19 are 
aligned with the portion of the magnetic field having a maximum component 
parallel with the target 7. 
The operation of the reactive sputtering apparatus of the above-described 
construction is described below. 
First, air is discharged from the chamber 1 through the vacuum opening 2 by 
the vacuum pump (P) to a degree of vacuum as high as approximately 
10.sup.31 7 Torr. 
Then, discharge gas 5, such as argon gas at 100 ccm is supplied to the 
chamber 1 through the gasintroducing pipe 14, the small gas-introducing 
opening 18, the annular groove 17 of the backing plate 16, the small gas 
blowoff openings 19 of the target 7 and the erosion region 13 of the 
target 7. 
Reactive gas 6, such as nitrogen gas of 50 ccm, is supplied to the chamber 
1 through the gas-introducing pipe 3. 
The pressure inside the chamber 1 is kept at 10.sup.-3 to 10.sup.-2 Torr. 
The flow rate of each gas is controlled by each gas flow rate controller 
4. 
A negative voltage is applied by the power source 9 to the magnetron 
cathode 8. Plasma is generated by magnetron discharge in the vicinity of 
the surface of the target 7 under the action of a magnetic field generated 
by the magnetic circuit 10 disposed inside the cathode 8 and that of an 
electric field generated by the power source 9. Since the discharge gas 5 
is supplied into the chamber 1 via the erosion region 13 of the target 7 
in this embodiment, the discharge gas 5 mainly exists in the vicinity of 
the surface of the target 7. That is, the gas which contributes to plasma 
formed in the vicinity of the surface of the target 7 by magnetron 
discharge consists mostly of the discharge gas 5. 
Since the reactive gas 6 exists not in the vicinity of the target 7 but in 
other regions, it is difficult for the reaction of the reactive gas 6 with 
the material of the target 7 to occur and thus a resulting compound is 
formed on the surface of the target 7 at a reduced rate. Accordingly, 
particles can be easily sputtered from the material of the target 7. 
Therefore, a compound formed by the reaction of sputtered particles with 
the reactive gas 6 can be deposited on the substrate 12 as a thin film 
without lowering the formation speed of the thin film. 
In the first embodiment, the number of openings 19 may be more than or 
equal to one. For example, the target 7 may have two small substantially 
semi-annular gas blowoff openings 19a and 19b as shown in FIG. 3D; or may 
have a plurality of openings arranged in an annular pattern as shown in 
FIGS. 3A and 3C; or may have a single annular opening as shown in FIG. 3B. 
A second embodiment of the present invention is described below. In the 
second embodiment, the gasintroducing pipe 14 communicates with a circular 
pipe 14b disposed outside the cathode 8 through pipes 14a as shown in 
FIGS. 4 and 5. The circular pipe 14b is disposed at the periphery of the 
circular target 7 and has a plurality of openings 14c to supply the 
discharge gas 5 from the periphery of the target 7 in the chamber 1. The 
second embodiment also can obtain the same advantages as the first 
embodiment. 
Although the present invention has been fully described in connection with 
the preferred embodiments thereof with reference to the accompanying 
drawings, it is to be noted that various changes and modifications are 
apparent to those skilled in the art. Such changes and modifications are 
to be understood as included within the scope of the present invention as 
defined by the appended claims unless they depart therefrom.