Magnetron sputtering apparatus and mask

A magnetron sputtering apparatus for forming a thin metal film on one of the major surfaces of a light-transmitting disc-shaped substrate as a disc substrate for an optical disc as mutually intersecting magnetic fields are applied by a magnetic field application unit provided at back of a target. The apparatus includes a center mask tightly contacted with the outer peripheral portion of one major surface of the disc substrate on which the thin film is formed for masking the center portion of the substrate and an outer peripheral mask tightly contacted with the outer peripheral portion of the one major surface of the disc substrate on which the thin film is formed for masking the outer peripheral portion. The outer peripheral mask is separated from and independent of the center mask.

BACKGROUND 
1. Field of the Invention 
The present invention relates to a magnetron sputtering apparatus. More 
particularly, the present invention relates to a magnetron sputtering 
apparatus employing a mask intimately affixed to a film-forming surface. 
2. Background of the Invention 
Optical discs, such as so-called Compact Discs (CDs), have come into 
widespread use for recording digital audio informations or video 
informations. Such optical disc has a substrate of a transparent synthetic 
resin, such as polycarbonate, on the surface of which a thin film layer of 
aluminum (Al) of high reflectivity is formed by vapor deposition or 
sputtering. On the surface of the substrate carrying the Al thin film 
layer is formed a pattern of micro-sized lands and recesses, termed pits, 
corresponding to the digital information of "1" or "0". The light beam is 
radiated on these pits through the substrate and the information recorded 
on the optical disc is read on the basis of the reflected light beam from 
the thin film layer. 
Since a thin film can be formed on an optical disc substrate within a 
shorter time, an apparatus shown in FIG. 1 is employed for continuously 
sputtering plural discs one by one. 
FIG. 1 shows only the essential mechanism of such magnetron sputtering 
apparatus. In FIG. 1, substrates 102, 102, . . . of optical discs, such as 
CDs, are transported in succession by an external transporting mechanism 
101, such as a belt conveyor. The substrates 102, 102 thus transported are 
sucked by a suction pad 104 of a disk-shaped transporting device 103, 
rotatable about its axis and movable between an upward direction and a 
downward direction, and are transported in this state into a sputtering 
chamber 105. 
The substrate 102, transported by the suction pad 104, is set in the 
sputtering chamber 105 on a transporting table 106 which is similarly 
rotatable about its axis and movable in the upward direction and the down 
ward direction. The substrate 102, set on the transporting table 106, is 
transported to a position facing a sputtering source 107 by the rotation 
and vertical movement of the transporting table 106. Film spatter is 
carried out by the sputtering source 107 on the substrate 102 mounted 
opposing the sputtering source 107. Following the film sputter, the 
substrate 102 is again set on the transporting table 106 and taken out to 
outside by the transporting device 103. 
The substrate 102, transported into the sputtering chamber 105, is moved in 
the upward direction by the transporting table 106 into intimate contact 
with the lower end face of a mask 108 provided within the sputtering 
source 107, as shown to an enlarged scale in FIG. 2. A film-forming 
chamber 109, in which the film sputter is carried out by sputtering, 
includes anti-sputter shields 112a, 112b and the mask 108 mounted on the 
inner wall surface of an outer enclosure 110. If there is no substrate 102 
in the film-forming chamber 109, the inside of the film-forming chamber 
109 is evacuated via a space 111 in the mask 108 by a vacuum pump, not 
shown. 
The substrate 102, transported by the transporting table 106, is supported 
by the mask 108, and yet has its non-film-forming portion shielded by the 
mask 108. The mask 108 is fabricated to high precision and intimately 
bonded and secured to the outer enclosure 110 by utilizing its force of 
thermal expansion. An Al target 113 is secured to a target cooling plate 
114 for constituting a cathode electrode and supplies a magnetic field in 
the film-forming chamber 109 in cooperation with a magnet 115. The magnet 
115 is mounted for being rotated at a position offset from the center of 
the film-forming chamber 109 and is adapted for supplying a more uniform 
magnetic field for improving the exploitation efficiency of the target 
113. 
The cathode electrode induces a discharge electrical field on the order of 
75 (W/cm.sup.2) on the target surface. In order to suppress the 
temperature on the target 113 during film formation to not higher than 200 
to 300 (.degree. C.), a ring-shaped hollow space is formed within the 
inside of the target cooling plate 114 so as to be supplied with the 
cooling water via a water supply pipe 116. The inside of the film-forming 
chamber 109 is supplied an argon gas required fir film sputter through a 
gas inlet tube 117. The pressure during film formation is in a range of 
0.2 to 5.0 (Pa). Since the magnetron sputtering apparatus is used under 
different operating conditions from one user to another, the internal 
pressure is known to be varied over an extensive range as described above. 
With the above-described magnetron sputtering apparatus, the Al target 113 
is struck by argon gas atoms to produce a sputtering action to form an Al 
film on the surface of the substrate 102. After the film sputter, ejection 
of argon gas atoms ceases, and the substrate 102 is again placed on the 
transporting table 106 so as to be taken out by the transporting device 
103. 
With the above-described magnetron sputtering apparatus, a film sputtered 
on the substrates 102, 102 . . . transported thereto in succession occurs 
at a short cycle of about 6 seconds per substrate. Consequently, the time 
necessary for actual film formation is an extremely short period on the 
order of two seconds during which the electrical field is supplied to the 
Al target 113. 
It is however not possible with the mask 108 now in use to form a film on 
all surface of the substrate 102, as shown in FIGS. 3 and 4. The reason is 
that four pillars 120 are provided for interconnecting a central mask 
portion 118 for masking the central portion of the substrate 102 and an 
outer peripheral mask portion 119 for masking the outer peripheral portion 
of the substrate, as shown in FIGS. 3 and 4. That is, since these pillars 
120 are provided on the surface of the substrate 102 to be sputtered, 
atoms or molecules struck out of the target 113 are screened by these 
pillars 120, as a result of which the thin film is not formed on the all 
surface of the substrate. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a magnetron 
sputtering apparatus which resolves the above-mentioned problems. 
It is another object of the present invention to provide a magnetron 
sputtering apparatus which resolves the above-mentioned problems. 
According to the present invention, there is provided a magnetron 
sputtering apparatus for forming a thin metal film on one of the major 
surfaces of a light-transmitting disc-shaped substrate as a disc substrate 
for an optical disc as mutually intersecting magnetic fields are applied 
by a magnetic field application unit provided at back of a target. The 
apparatus includes a center mask and an outer mask. The center mask is 
tightly contacted with the central portion of one major surface on which 
the thin film is formed for masking the center portion of the substrate. 
The outer peripheral mask is tightly contacted with the outer peripheral 
portion of the one major surface on which the thin film is formed for 
masking the outer peripheral portion of the substrate. The outer 
peripheral mask is separated from and independent of the center mask. 
According to the present invention, there is provided a magnetron 
sputtering apparatus including a target, a target cooling unit, a magnetic 
field application unit, a center mask, an outer peripheral mask, and a 
substrate holding unit. The target forms a thin film on one of the major 
surfaces of a disc-shaped substrate. The target cooling unit is mounted on 
the opposite side of the target for cooling the target. The magnetic field 
application means is arranged at back of the target for applying mutually 
intersecting magnetic fields. The center mask is mounted in an insulated 
state on the target cooling unit and tightly contacted with the central 
region of the major surface of the substrate on which the thin film is 
formed and masks the central region. The outer peripheral mask is mounted 
at a stationary portion of the film forming chamber and tightly contacted 
with the outer peripheral region of the major surface of the substrate on 
which the thin film is formed and masks the outer peripheral region. The 
outer peripheral mask is provided independently of the center mask. The 
substrate holding unit causes the substrate to be moved vertically in a 
direction toward and away from the center mask and the outer peripheral 
mask. 
According to the present invention, there is provided a mask employed for 
forming a film by sputtering on a disc-shaped substrate. The mask includes 
a center mask, an outer peripheral mask and a separating portion. The 
center mask is tightly contacted with the central portion of one of the 
major surfaces of the substrate on which the thin film is formed and masks 
the central portion. The outer peripheral mask is tightly contacted with 
the outer peripheral portion of one of the major surfaces of the substrate 
on which the thin film is formed and masks the outer peripheral portion. 
The central portion of the outer peripheral mask is formed with a circular 
opening within which the center mask is arranged. The separating portion 
is formed between the center mask and the inner rim of the opening in the 
outer peripheral mask over the entire inner rim of the opening for 
extending along the entire thickness of the mask. The center mask and the 
outer peripheral mask are independent of each other via the separating 
portion. 
According to the present invention, since the outer peripheral mask is 
provided independently of the center mask, and hence there is no 
impediments in the mask possibly obstructing atoms ejected form the 
target, it becomes possible to form a film on all surface of the substrate 
.

DESCRIPTION OF THE INVENTION 
Referring to the drawings, preferred embodiments of the present invention 
will be explained in detail. 
The magnetron sputtering apparatus according to the present invention is 
mainly composed of a target 1, a center mask 3 and an outer peripheral 
mask 4 for masking pre-set portions of a disc-shaped substrate 2, and a 
magnet 5 for applying mutually intersection electric and magnetic fields, 
as shown in FIG. 5. The disc substrate 2, used herein, is formed of a 
light transmitting material, and has micro-sized recesses and lands, that 
is pits, corresponding to the information signals. 
The target 1, functioning as the cathode electrode, is used for forming a 
thin film on the surface of the disc substrate 2 carrying the pits, that 
is the surface of the disc substrate to be sputtered. For fabricating an 
optical disc, the target 1 formed of aluminum is employed. The target 1 is 
formed as a disc larger in diameter than the disc substrate 2 and has a 
reduced thickness only at its outer peripheral portion. That is, the 
target is formed as a disc having a protruded central portion facing the 
disc substrate 2. 
On the surface of the target 1 opposite to its target surface 1a struck by 
atoms, such as argon atoms, there is provided a target cooling device 6 
for cooling the target 1. The target cooling device 6 is in the form of a 
disc having an outer diameter substantially equal to the outer diameter of 
the target 1. 
The target cooling device 6 has a hollow duct, at a mid portion of the 
plate thickness thereof for circulation of the cooling water therein. To 
an inlet and an outlet of the hollow duct for circulation of cooling water 
are connected a cooling water supply pipe 7 for supplying fresh cooling 
water and a cooling water discharge pipe 8 for discharging the water 
circulated through the duct, respectively. 
Thus the cold water introduced via the cooling water supply pipe 7 is 
circulated through the cooling water circulating duct of the target 
cooling device 6 and, after cooling the target 1 mounted in contact with 
the target cooling device 6, is discharged via the cooling water discharge 
pipe 8. This prevents the temperature from being increased during 
sputtering. 
The magnet 5 applies mutually intersecting electrical and magnetic fields 
on atoms striking the target 1 under the argon gas atmosphere. The magnet 
5 is mounted at a rearward offset portion with respect to the distal end 
of a rotary shaft 9 on the opposite side of the target 1 with the target 
cooing device 6 in-between. Thus the applied magnetic field is rendered 
uniform as the magnet performs offset rotation, thereby improving the 
exploitation efficiency of the target 1. 
The center mask 3 is used for masking the central portion of the disc 
substrate 2, and is adapted for holding the substrate 2 by being 
intimately contacted with its central portion. Such center mask 3 has the 
shape of a flared cylinder having a larger diameter on the side thereof 
contacted with the disc substrate 2. 
Along the center axis of the center mask 3 is formed a through-hole 11 
adapted to be passed through by a bolt 10 insulatingly processed or formed 
of an insulating material for securing the center mask 3 to the target 
cooling device 6. On the opening end of the through-hole 11 is formed a 
fitting portion 17 adapted to be contacted with a disc centering member as 
later described and with the center mask 3. The fitting portion 17 is 
formed as a recess in which the disc centering member has a fit. 
If the bolt 10 is formed of an insulating material, it may be ceramics, 
plastics or polytetrafluoroethylene (PTFE). 
The portion of the center mask 3 introduced into the target 1 is of a 
slightly reduced diameter to form a step surface. Between the step surface 
and the target surface 1a is interposed a annular spacer 12 which is 
insulatingly processed or made of an insulating material for insulation 
between the target 1 and the center mask 3. If such spacer 12 is formed of 
an insulating material, the same insulating material as that of the bolt 
10 may be employed. 
On the outer perimeter of the smaller diameter portion of the center mask 3 
is fitted a holder 13 which is insulatingly processed or formed of an 
insulating material for insulating the center mask 3 with respect to the 
target 1 and the target cooling device 6. The holder 13, which is formed 
of a bottomed cylinder fitted on the smaller-diameter portion of the 
center mask 3 and opened on one end, is fitted into a holder mounting hole 
15 bored at the center of the target 1. If such holder 13 is formed of an 
insulating material, the same insulating material as that of the spacer 12 
may be employed. 
In the bottom surface of the holder 13 is formed a circular bolt-inserting 
opening 14 passed through by the distal end of the bolt 10 passed through 
the through-hole 11 of the center mask 3. The bottom side of the center 
mask 3 is formed with a flange 16 for preventing the holder 13 from being 
detached from the mounting hole 15 when the holder 13 is fitted in the 
mounting hole 15. 
The outer peripheral mask 4 plays the role of masking the outer peripheral 
portion of the disc substrate 2 by being intimately contacted with such 
outer peripheral portion and is mounted on an outer enclosure constituting 
the film-forming chamber, not shown herein and shown in FIG. 2, 
independently of the center mask 3. The outer peripheral mask 4 is formed 
as a disc having a blind hole 18 of the same size as the outer diameter of 
the protruding portion of the target 1 and a center hole 19 which is a 
circular through-hole having a diameter slightly smaller than the outside 
diameter of the disc substrate 2. 
Between the inner wall surface of the center hole 19 of the outer 
peripheral mask 4 and the outer periphery of the free end of the center 
mask 3 formed with a contact surface 3a is formed a void 25 in the 
direction of the thickness of the masks 3 and 4 over the entire periphery 
of the inner wall surface of the center hole 19, as shown in FIG. 5. The 
outer peripheral mask 4 and the center mask 3 are completely separated and 
isolated from each other by the void 25. It is via this void 25 that atoms 
from the target 1 are sputtered on the substrate 2. A contact surface 4a 
of the outer peripheral mask 4, adapted to be intimately contacted with 
the outer peripheral portion of the disc substrate 2, is flush with the 
contact surface 3a of the center mask 3 for maintaining the disc substrate 
2 in a horizontal position and for forming a uniform film by sputtering. 
The disc substrate 2 is tightly contacted with the contact surfaces 3a of 
the center mask 3 and with the contact surface 4a of the outer peripheral 
mask 4 by a substrate holding unit 20. The substrate holding unit 20 is 
mounted at the distal end of a shaft 22 of a cylinder 21 adapted for 
setting the disc substrate 2 thereon and for vertically moving the disc 
substrate 2 in directions towards and away from the center mask 3 and the 
outer peripheral mask 4 as indicated by arrows X. The substrate holding 
unit 20 is maintained at an anodic potential by means of a shaft 22. 
The substrate holding unit 20 has a disc centering member 23 adapted for 
being fitted in the circular through-hole formed at the center of the disc 
substrate 2 and a disc setting table 24 for supporting the centered disc 
substrate 2. 
The disc centering member 23 is positioned for facing a through-hole formed 
at the center of the disc substrate 2 for centering the disc substrate 2, 
and is frusto-conically-shaped so as to be projected from the disc setting 
table 24 and so as to be gradually tapered towards its distal end. A 
disk-shaped disc setting table 24 for stably supporting the disc substrate 
2 is provided on the proximal side of the disc centering member 23. 
During sputtering, the disc substrate 2 is uplifted by the cylinder 21 in a 
state in which it is set on the disc setting table 24. The disc substrate 
2, thus moved in an upward direction, has its central portion and outer 
peripheral portion tightly contacted by the center mask 3 and the outer 
peripheral mask 4, respectively. Thus the surface 2a of the disc substrate 
2 to be sputtered is exposed in its entirety without being shielded by the 
masks 3 and 4, as a result of which the film formed on the surface to be 
sputtered 2a is of a uniform thickness. 
At this time, the disc centering member 23 of the substrate holding unit 20 
is fitted and contacted with the fitting portion 17 in the center mask 3, 
so that the center mask 3 is maintained at an anodic potential. The center 
mask 3 is positively isolated by the bolt 10, spacer 12 and the holder 13 
with respect to the target 1 and the target cooling device 6 and hence is 
positively maintained at the anodic potential. 
During sputtering, the center mask 3 is subjected to an elevated 
temperature. However, it is cooled by the target cooling device 6 via the 
bolt 10 and the holder 13 provided in contact with the target cooling 
device 6. 
While the present invention has been described with reference to preferred 
embodiments, it is not limited to the details set forth therein and is 
intended to cover any modifications that come within the scope of the 
invention set forth in the following claims.