Magnetron sputtering apparatus

There is disclosed a magnetron sputtering apparatus including a sputtering chamber, a substrate and target disposed within the sputtering chamber to form a desired space therebetween, device for applying a voltage between the substrate and target, and device for producing a magnetic field; and the apparatus comprises the magnetic field-producing device adapted to excite a magnetic field so that the direction of the magnetic field may be inverted on the magnetic symmetry axis within the space. The magnetron sputtering apparatus of the present invention can form metal films having no crack without heating of the substrate and also form a magnetic recording film layer having an increased coercive force perpendicular to the surface of the film.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetron sputtering apparatus, more 
particularly, to a magnetron sputtering apparatus capable of improving the 
magnetic field on the surface of a target to form a metal film without any 
deffect such as crack or the like. 
As a method for forming a useful metal film on the surface of various 
substrates, there have been broadly employed methods such as vacuum 
depositing, plating, sputtering or others. 
Among these, the vacuum depositing has the disadvantage that it is 
difficult to control the composition of a film made of a multi-component 
alloy which contains elements different from one another in vapor 
pressure. Plating causes a problem with respect to environmental pollution 
which may take place in treating the waste liquor. Therefore, attention 
has been directed to sputtering. For example, for the preparation of 
vertical type magnetic recording media having magnetic recording films of 
cobalt (Co)-chromium (Cr) alloy, there have been manufactured currently on 
the sputtering rather than the vacuum depositing since there is a large 
difference in vapor pressure between Co and Cr. 
In the prior art film forming apparatus which utilizes the sputtering 
process, there is normally used a planar diode sputtering apparatus of 
such a type that two electrodes are used one for each of the target and 
substrate to form an electric field. However, the prior art apparatus 
provides a formation of film at a reduced speed. In addition, the 
temperature of the substrate increases up to several hundreds of degrees 
centigrade. It becomes, therefore, difficult to form a sputter film on a 
substrate made of a polymer since the substrate itself is deformed by 
heat. 
In order to overcome such a disadvantage in the prior art sputtering 
apparatus, a magnetron sputtering apparatus has been developed in which 
films can be formed more rapidly without any rise of temperature in 
substrates. The developed apparatus comprises electrodes and magnetic 
poles which are arranged such that the electric field intersects the 
magnetic field in a sputter chamber in so that they are perpendicular to 
each other, as shown in FIG. 1. In this figure, A is a magnet system while 
B is an exhaust system. In this magnetron sputtering apparatus, for 
instance, as shown in FIG. 13, the magnetic field on an imaginary 
perpendicular line passing to a target through or by the magnetic symmetry 
axis is entirely directed to either the target or substrate. 
However, according to said apparatus, defects with respect to structure 
such as micro-crack, crack and others often happens on the surface of the 
formed films. Among these defects, the crack is serious in that it 
increases as films are increased in thickness and that cracks remarkably 
appear on films where substrates are made of a polymer subject to 
heat-deformation, such as acrylonitrile-butadiene-styrene resin. Cracks 
are undesirable, particularly, if films are formed for various purposes 
such as magnetic recording, decoration, resist, surface hardening and 
others. Cracks, for example, generated on the magnetic recording layer of 
a magnetic recording medium lead to troubles, that is, (1) reduction of 
recording signals; (2) frictional wear of the magnetic head according to 
sliding at a time of recording or playback; and (3) the reduced durability 
of the magnetic recording medium itself. In addition, where a vertical 
type magnetic recording medium is formed with a magnetic recording layer 
of ferromagnetic Co-Cr alloy film, etc. by the use of the prior art 
magnetron sputtering apparatus, a new and important problem is caused in 
that the coercive force perpendicular to the surface of the magnetic 
recording film is reduced to decrease the output on reproducing. 
In order to overcome such a disadvantage, it is effective to increase the 
substrate in temperature even in a magnetron sputtering apparatus. Such a 
procedure, however, cannot be applied to polymers subject to 
heat-deformation as in the planar diode sputtering apparatus, and also 
does not provide a desired means for preventing any crack since the 
magnetron sputtering apparatus constructed according to this principle 
becomes more complicated. 
SUMMARY OF THE INVENTION 
The present invention overcomes the above-mentioned disadvantages in the 
prior art magnetron sputtering apparatus. An object of the present 
invention is to provide a magnetron sputtering apparatus which can form a 
metal film having no crack without heating of a substrate used therein and 
which can form a magnetic recording layer having an increased coercive 
force perpendicular to the surface of the film when it is used for 
formation of the film made of Co-Cr alloy. 
The present invention provides a magnetron sputtering apparatus comprising 
a sputtering chamber; a substrate and target disposed within said 
sputtering chamber to form a desired space therebetween; means for 
applying a voltage between said substrate and target; and means for 
producing a magnetic field; said apparatus being characterised in that 
said magnetic field-producing means is adapted to excite a magnetic field 
so that the direction of the magnetic field may be inverted on the 
magnetic symmetry axis within said space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The magnetron sputtering apparatus according to the present invention 
comprises main components of a sputtering chamber, a target and substrate 
disposed within said chamber, a source of electric power for providing an 
electric field between the target and substrate, and means for producing a 
magnetic field. More particularly, an electric field is formed by a 
voltage which is applied between the target and the substrate, for 
example, by energizing a target electrode disposed on the back of the 
target and an electrode (substrate holder) disposed on the back of the 
substrate. Further, a magnetic field is formed between the target and 
substrate, for example, by a magnetic field-producing means located on the 
back of the target such that part of the magnetic field will intersect the 
above electric field at a right angle. 
The magnetic field-producing means used in the present invention includes a 
permanent magnet, solenoid coil and the like which may be disposed to form 
the above-mentioned magnetic field. Alternatively, the magnetic 
field-producing means may include various combinations, that is, a 
combination of permanent magnets with a solenoid coil, a combination of 
permanent magnets with a yoke made of a ferromagnetic material being 
relatively soft in its magnetic property such as iron, etc., and a 
combination of permanent magnets with the yoke and solenoid coil. In these 
means, the combination of the permanent magnets with the yoke and the 
combination of the permanent magnets with the yoke and solenoid coil are 
preferred. 
Some embodiments of magnetic field-producing means according to the present 
invention will now be described. 
If it is desired to form the above-mentioned magnetic field only by the use 
of permanent magnets, one of the permanent magnets (A sectional area 
parallel to the target surface is referred to S.sub.1. The permanent 
magnet will be abbreviated to magnet I for convenience sake.) is located 
on the central area of the back of a target with the south pole of the 
magnet facing the target. A plurality of additional magnets (The total 
sectional area parallel to the surface of the target is referred to 
S.sub.2. The additional magnets will be abbreviated to magnets II for 
convenience sake.) having substantially the same function as the above 
magnet I are disposed on the back of the target along the peripheral edge 
thereof symmetrically about the magnet I with the north poles thereof 
facing the target. At this time, the sectional area S.sub.2 should be 
larger than the sectional area S.sub.1. Preferably, the ratio of S.sub.2 
to S.sub.1 is three or more. Thus, the magnet I is magnetically saturated 
while the magnetic flux from the north poles of the magnets II penetrates 
in part into the south pole of the magnet I and directly returns in part 
to the south poles of the magnets II themselves. Accordingly, the magnetic 
field produced by the magnets I and II will be inverted in direction on 
the magnetic symmetry axis. 
Further, the magnetic poles in the magnets I and II may be reversed in 
direction. In such a case, the direction of the produced magnetic field 
will be oriented along an imaginary perpendicular line from the substrate 
to the target. However, the advantage of the present invention will not be 
adversely affected by such an orientation in the magnetic field only for 
such a reason why the electrons are reversed in the direction of magnetron 
motion. 
Where permanent magnets and solenoid coils are together utilized, for 
instance, as shown in FIG. 2, permanent magnets are disposed on the back 
of the target 1 as in the arrangement in which only permanent magnets are 
used described hereinbefore in addition to an arrangement in which a 
target 1 and solenoid coil 12 are located. By using the solenoid coils, 
the distribution of the magnetic field can be controlled simply by 
changing the current passing through the solenoid coils. 
Where permanent magnets are used in combination with a yoke, the permanent 
magnets are arranged in a manner similar to that in the aforementioned 
structure in which only the permanent magnets are used, except that the 
yoke is made of a ferromagnetic material being relatively soft in its 
magnetic property and located on the central area of the back of the 
target (see FIGS. 3 and 4). In consideration with the differential 
saturated magnetic flux between the yoke and permanent magnets and the 
magnetic property of the yoke, such a structure provides the desired 
magnetic field on the basis of the similar saturation magnetization 
phenomenon and the flow of flux created by the magnetic resistance in the 
yoke. 
Further, even in such an arrangement that the magnet-yoke system shown in 
FIGS. 3 and 4 is combined with solenoid coils arranged as shown in FIG. 2, 
magnetic field-producing means capable of controlling the magnetic field 
can be provided. 
The magnetron sputtering apparatus of the present invention may be used to 
form a plurality of magnetic fields with respect to the present invention 
in the same target. 
The magnetron sputtering apparatus including the aforementioned magnetic 
field-producing means can continuously operate sputtering by moving the 
substrate without interruption (FIG. 9). 
If such an apparatus as shown in FIG. 10 is used, the substrate can be 
sputtered at its opposite faces. In practice, the magnetron sputtering 
apparatus of FIG. 10 is preferably used to manufacture, for example, a 
floppy disc having magnetic recording media which are formed on its 
opposite faces. 
By using the magnetron sputtering apparatus provided as described 
hereinbefore, a magnetic field may be improved in comparison with the 
prior art sputtering apparatuses. As a result, charged particles (for 
example, electrons) may properly be incident upon the substrate to 
increase only the surface of the substrate in temperature without any 
crack. 
In accordance with the present invention, the magnetron sputtering 
apparatus can form metal films having no crack without heating of the 
substrate and also form a magnetic recording layer having an increased 
coercive force perpendicular to the surface of the film when applied it to 
the formation of the film made of Co-Cr alloy. 
Some examples and comparative examples will be described hereinbelow. 
EXAMPLE 1 
As shown in FIGS. 3 and 4, a target 1 of 60 mm.times.120 mm was located on 
the upper face of a copper electrode 2. Samarium-cobalt magnets 3 of 15.2 
mm diameter and 20 mm height were disposed as shown by broken lines in 
FIG. 3 with the north poles thereof facing the underside of the target 1. 
Substantially E-shaped yoke 4 was disposed below the undersides of the 
magnets and also at the central area of the underside of the target 
electrode 2. The direction of the magnetic field produced in the space 
above the target 1 and the intensity of the vertical component in this 
magnetic field (oersted: Oe) are shown in FIGS. 5 and 6, respectively. 
FIG. 5 is a diagrammatic view in which the direction of the magnetic field 
between the target 1 and the substrate 5 is shown by arrows. FIG. 6 
illustrates the intensity of vertical components in the magnetic field on 
an imaginary perpendicular line passing through or by the center of the 
magnetic circuit in the space above the target 1 toward the target 1. In 
FIG. 6, the vertical line represents the intensity as plus in the 
direction of the target while the horizontal line represents the height 
from the target surface (mm). 
In the above-mentioned magnetron sputtering apparatus, the spacing between 
the target 1 and the substrate 5 was 100 mm, and the substrate was made of 
acrylonitrile-butadiene-styrene resin. The sputtering chamber 6 was filled 
with argon gas of 5.times.10.sup.-3 Torr. Thereafter, films were formed at 
sputtering speeds of 600 .ANG./min. and 1000 .ANG./min. without heating. 
The target 1 was made of three different materials, that is, chromium (Cr) 
with 1.0 mm thickness, cobalt (Co)- chromium (Cr) alloy with 2.0 mm 
thickness and its saturation magnetization of 450 gausses, and iron (Fe)- 
nickel (Ni) alloy with 2.0 mm thickness and its saturation magnetization 
of 620 gausses. By using the respective targets made of these materials, 
films of 1000 .ANG., 5000 .ANG. and 5000 .ANG. thickness were obtained, 
respectively. 
With visual and microscopic observations, no crack could be found on all 
the films obtained. In any event, the Co-Cr alloy film was 1080 oersteds 
in its coercive forces perpendicular to the surface thereof. 
EXAMPLE 2 
As shown in FIG. 7, a target 1 of 60 mm diameter was used while a magnet 3' 
of 23.6 mm diameter slightly larger than that of the magnet in Example 1 
was located with the south pole thereof facing the central area of the 
underside of a target electrode 2. Further, the same magnets 3 as in 
Example 1 were disposed about the target magnet 2 along the peripheral 
edge of the underside of the target electrode with the north poles thereof 
facing the underside of the target electrode. Films were made through the 
same procedure as in Example 1. Ratio of S.sub.2 /S.sub.1 was 
approximately 5. The direction of magnetic field was substantially 
identical with that of FIG. 5. FIG. 8 shows a curve with respect to the 
relationship between the height from the surface of the target 1 and the 
intensity of vertical components in the magnetic field. 
Three different targets 1 were made respectively of chromium with 1.0 mm 
thickness, Co-Cr alloy with 3.5 mm thickness and its saturation 
magnetization of 350 gauss, and Fe-Ni alloy with 2.5 mm thickness and its 
saturation magnetization of 620 gausses. Films obtained by using these 
targets had no crack. Co-Cr alloy film was 1120 oersteds in its coercive 
force perpendicular to the surface thereof. 
EXAMPLE 3 
The apparatus used in Example 1 was combined with a film carrying system 
shown in FIG. 9 in which the substrate 5 was moved in the direction shown 
by an arrow. Thus, there was provided a magnetron sputtering apparatus for 
continuously forming films. 
The film carrying system included a supply roll 7 around which an elongated 
film-shaped substrate 5 is wound; guide rollers 8 for guiding the 
substrate 5 continuously fed to a sputtering station; a substrate holder 9 
spaced from and opposed to a target 1 by a distance of 100 mm with the 
underside thereof slidably engaging with the moving substrate 5; a take-up 
roll 10 around which the treated substrate 5 is rolled; and a mask 11 
spaced away from the substrate 5 by 0.5 mm to provide a sputtering region 
having its longitudinal dimension of 70 mm for the substrate 5. 
In the above apparatus, the substrate 5 was Kapton film (trade name, 
available from DuPont de Nemours & Co. Inc.) of 25 .mu.m thickness and 1/2 
inches width while the target 1 was made of Co-Cr alloy with the 
dimensions of 60 mm.times.120 mm.times.2.0 mm and its saturation 
magnetization of 450 gausses. Films of 2400 .ANG. thickness were formed as 
the substrate was moved at speeds of 0.93 cm/min. and 1.9 cm/min. 
The resulting films had no crack. The coercive force perpendicular to the 
surface of film was 930 oersteds at the substrate moving speed of 0.93 
cm/min. and 1050 oersteds at the subtrate moving speed of 1.9 cm/min. 
EXAMPLE 4 
A magnetron sputtering apparatus was composed of the apparatus used in 
Example 2 and the film carrying system used in Example 3. 
The sputtering region had its dimension of 30 mm. The target 1 was made of 
Co-Cr alloy with a diameter of 60 mm and a thickness of 3.7 mm and with 
its saturation magnetization of 350 gausses. The substrate was moved at 
two speeds of 0.3 cm/min. and 0.4 cm/min. Films having a thickness of 2400 
.ANG. were formed through the same pocedure as in Example 3. 
The resulting films had no crack. The coercive force perpendicular to the 
surface of film was 1350 oersteds at the substrate moving speed of 0.3 
cm/min. and 1400 oersteds at 0.4 cm/min. 
COMATIVE EXAMPLE 1 
As shown in FIGS. 11 and 12, samarium-cobalt magnet 3 having dimensions of 
18 mm.times.78 mm.times.15.5 mm (height) was located below the central 
area of a copper target electrode 2 with the south pole of the magnet 3 
facing the underside of the electrode 2. A yoke 4 of iron was disposed 
below the magnet with the peripheral upstanding portion of the yoke 
opposed to the peripheral undeside portion of the target electrode 2. 
Films were formed through the same procedure as in Example 1 without 
heating of the substrate. FIG. 13 shows the direction of the magnetic 
field produced in this example while FIG. 14 shows a curve representing 
the relationship between the height from the surface of the target 1 and 
the intensity of vertical components in the magnetic field. 
The magnetic field was identical with that of the prior art sputtering 
appartus. The direction of magnetic field on an imaginary perpendicular 
line passing through or by the center of the magnetic circuit toward the 
target 1 was fully oriented to the target. 
All the resulting films had remarkable cracks. The same results were 
obtained even if the spacing between the target and the substrate was 
selected both to be 50 mm and 150 mm. The coercive force perpendicular to 
the surface of the Co-Cr alloy film was 380 oersteds. 
COMATIVE EXAMPLE 2 
As shown in FIG. 15, a samarium-cobalt magnet 3 having a diameter of 20 mm 
and a height of 20 mm was located below a traget electrode 2 at the 
central underside thereof. A plurality of similar samarium-cobalt magnets 
3 of 10 mm.times.20 mm.times.2.5 mm were disposed below the target 
electrode 2 along the peripheral underside thereof. Films were formed 
through the same procedure as in Example 2. A curve representing the 
relationship between the height from the surface of the target 1 and the 
intensity of vertical components in the magnetic field in this example is 
shown in FIG. 16. The direction of magnetic field in the space above the 
target 1 is omitted because it is substantially identical with that of 
Comparative example 1. 
All the resulting films had remarklable cracks. The same results were 
obtained even if the spacing between the target and substrate was changed 
to 50 mm; the speed at whcih the films were formed to 300 .ANG./min.; the 
pressure of argon gas to 2.8.times.10.sup.-3 Torr and 7.times.10.sup.-3 
Torr, respectively. The coercive force perpendicular to the surface of the 
Co-Cr alloy film was 400 oersteds. 
COMATIVE EXAMPLE 3 
By using a magnetron sputtering apparatus constituted of the apparatus used 
in Comparative example 1 and the film carrying system of Example 3 
incorporated into the above apparatus, films were formed through the same 
procedure as in Example 3. 
All the resulting films had remarkable cracks. The same results were 
obtained even though the spacing between the target and substrate was 
changed to 50 mm and 120 mm; and the pressure of argon gas to 
3.times.10.sup.-3 Torr and 6.5.times.10.sup.-3 Torr, respectively. The 
coercive force perpendicular to the surface of the film was 420 oersteds 
at the substrate moving speed of 0.93 cm/min. and 380 oersteds at 1.9 
cm/min. 
COMATIVE EXAMPLE 4 
A magnetron sputtering apparatus was obtained by incorporating the film 
carrying system of Example 3 into the apparatus of Comparative example 2. 
By using such an apparatus, films were obtained through the same procedure 
as in Example 4. 
All the resulting films had remarkable cracks. The coercive force 
perpendicular to the film surface was 400 oersteds at both the substrate 
moving speeds of 0.3 cm/min. and 0.4 cm/min.