Gas distribution system for sputtering cathodes

A gas distribution system for use with a sputtering cathode mounted in a vacuum chamber and provided with a planar target formed of the material to be sputtered upon planar substrates passing therebeneath, in which two divergent streams of gas are introduced into the vacuum chamber, one of the gases being an inert gas directed into the upper portion of the chamber adjacent the target and the other gas being a reactive gas directed into the lower portion of the chamber adjacent the substrate.

FIELD OF THE INVENTION 
The present invention is concerned with the art of sputtering and in 
particular with the reactive cathodic sputtering of metals or metal alloys 
on the surface of substrates in an evacuable coating chamber. 
BACKGROUND OF THE INVENTION 
One method of sputter-coating involves ion bombarding a target of the 
coating material in an ionized gas atmosphere in a chamber in which a 
controlled vacuum is maintained to cause atomic particles of the coating 
material to be dislodged and deposited by condensation on the substrates 
to be coated. The gas employed is a non-reactive or inert gas, such as 
argon. 
However, many processes in vacuum deposition utilize a method known as 
reactive deposition where a pure metal or alloy target material is 
liberated from it's bulk and directed toward a substrate which is intended 
to collect the material as or after it has reacted with a gas which is 
present in the path of the liberated target material or at the substrate 
surface. 
The reactive sputtering is often difficult to control, rates of deposition 
are erratic, arcing of the target occurs due to resistive film build up on 
the target face, and yields are often unpredictable. 
OUTLINE OF THE INVENTION 
It is a primary purpose of this invention to provide a reactive sputtering 
method which embodies a novel gas distribution system designed to shield 
the target material from the reactive gases employed when an attempt is 
made to create a reaction between the target material and a reactive gas, 
such as nitrogen or oxygen. 
In essence, the gas distribution system of this invention consists in 
simultaneously introducing into the coating chamber after it has been 
pumped down a non-reactive gas, such as argon, and a reactive gas, such as 
nitrogen or oxygen, and maintaining them substantially separate from one 
another, the non-reactive gas being directed toward and upon the target 
surface and serving to protect said surface from the reactive gas which is 
directed toward and upon the substrate surface. 
Such a gas distribution system has assisted in eliminating many of the 
problems associated with reactive deposition. It provides for increased 
target rate of deposition; decreases power levels required; eliminates 
spiking or arcing; eliminates need to "pulse" gases to keep the target 
clean, and efficiency of conversion is high per unit gas volume, i.e. more 
efficient usage of reactive gas.

DETAILED DESCRIPTION 
Referring to the drawings and particularly to that form of the invention 
illustrated in FIGS. 1 to 4, the sputtering apparatus includes an 
evacuable coating chamber 10 in which is mounted a planar sputtering 
cathode 11. The coating chamber is usually part of a continuous sputtering 
apparatus through which planar substrates 12, such as glass sheets or the 
like, are supported horizontally upon and carried by conveyor rolls 13 
beneath cathode 12 to receive the coating material sputtered therefrom. 
The cathode 11 comprises a housing of substantially rectangular boxlike 
form composed of a bottom wall or base plate 14, side walls 15 and 16, end 
walls 17 and 18 and a top or cover plate 19 which defined a chamber 20. 
Applied to the outer surface of the base plate 14 is a sheet or layer 21 
of the material to be sputtered onto the substrates and which is generally 
referred to as the target. 
The base plate 14 of the cathode housing is secured to the side and end 
walls 15-16 and 17-18 respectively by screws 22 which pass upwardly 
therethrough and are threaded into elongated metal strips 23 welded or 
otherwise suitably secured to the said side and end walls. Pressure tight 
seals 24 are provided between the base plate and the side and end walls, 
while arranged outwardly of said side and end walls are the insulating 
shields 25. 
The side walls 15-16 and end walls 17-18 of the cathode housing terminate 
at their upper ends in outwardly directed flanges 26 and 27 respectively 
which form a continuous rim surrounding the housing for supporting the 
cathode in operative position. More particularly, the top wall 29 of 
coating chamber 10 is provided with a transverse opening 30 through which 
the cathode is lowered into said chamber where it is supported by the 
continuous rim which overlaps the adjacent portions of the top wall 29. 
Strips of insulating material 31 are positioned between the top wall 29 of 
the coating chamber and the supporting rim, while pressure tight seals 32 
and 33 are located at opposite sides of the insulating strips 31. Similar 
seals 34 are provided between the supporting rim and the cover plate 19 of 
the cathode. 
The cathode 11 herein disclosed by way of illustration is a planar 
magnetron cathode and to this end magnetic means 35 are mounted in the 
cathode chamber 20 and supported on the base plate 14. The magnetic means 
35 consists of two parallel rows of substantially U-shaped permanent 
magnets 36 and 37, with the magnets in the two rows being alternately 
arranged in overlapping relation. 
The outer legs 38 of the magnets 36 are secured to a magnetic strip 39 by 
screws 40, while the outer legs of the magnets 37 are secured to a similar 
magnetic strip 42 by screws 43. The inner legs 44 and 45 of the magnets 36 
and 37 are secured to a central magnetic strip 46, extending parallel with 
the strips 39 and 42, by screws 47 and 48 respectively. 
The means for cooling the target are not shown as any desired means may be 
provided for this purpose. Likewise, the electrical means for operating 
the cathode are not shown since the operation of magnetron cathodes is 
well known. 
In the operation of a cathode of the above character, an inert gas, such as 
argon, is usually admitted to the vacuum chamber 10 to provide a 
non-reactive gas atmosphere after the chamber has been pumped down to the 
desired pressure. This pressure is usually in the neighborhood of 5 to 10 
microns. The argon is ionized to establish a plasma and the argon ions 
dislodge molecules of the material from which the target is made, these 
molecules then impinge upon the substrates that are moved slowly 
therebeneath to coat the same. 
Such cathodes may also be employed to reactively sputter a metal oxide 
coating in a reactive gas atmosphere containing, for example, oxygen or 
nitrogen. However, the use of a reactive gas coming in contact with the 
target material is not without objections for the reasons stated above. 
Hence, the purpose of this invention is to provide a reactive sputtering 
apparatus which can be operated with greater efficiency and improved 
results than heretofore. 
According to the present invention, there is provided a novel gas 
distribution system in which an inert gas, such as argon, is directed 
toward and into contact with the target, while a reactive gas, such as 
oxygen or nitrogen, is simultaneously directed toward and into contact 
with the substrate to be coated and in which the two gases are maintained 
substantially separated from one another. This allows the target to 
function as it would in a totally non-reactive environment, while the 
material liberated from the target and directed toward the substrate will 
be acted upon by the reactive gas in its path of movement or at the 
surface of the substrate as it would in a reactive environment. 
To accomplish the objects of the invention, there is provided a gas 
distribution system including metallic support members 49 and 50 in the 
form of elongated substantially rectangular beams horizontally mounted in 
the coating chamber 10 at opposite sides of the cathode 11. Each support 
member is made up of three parallel sections 51, 52 and 53 positioned in 
contacting relation one above the other and secured together by screws 54. 
The meeting faces of the sections 51 and 52 of each support member 49 and 
50 are provided with semi-circular grooves 60 and 61 respectively which 
together form an annular opening extending longitudinally of said support 
member and in which is mounted a pipe 62 formed of a suitable porous 
material. The meeting faces of the support sections 52 and 53 are provided 
with similar semi-circular grooves 63 and 64 in which is mounted a pipe 65 
also of porous material. As shown in FIG. 3, the porous pipes 62 at 
opposite sides of the cathode are closed at one end as at 162 while, at 
their opposite ends, they are joined to pipes 163 that extend inwardly and 
are connected to a gas inlet pipe 67. The porous pipes 65 at opposite 
sides of the cathode are closed at one end as at 165 and connected at 
their opposite ends to a gas inlet pipe 68. The porous pipe 62 is adapted 
to receive a non-reactive gas, such as argon, while the porous pipe 65 
receives a reactive gas, such as oxygen or nitrogen. 
The meeting faces of the sections 51 and 52 of each support member 49 and 
50, inwardly of the porous pipe 62, are slanted upwardly and inwardly as 
at 69 and 70 and spaced slightly from one another to provide a slit 71 
(FIG. 4) through which the non-reactive or inert gas escaping through the 
porous pipe 62 will be directed toward and upon the target 21. Similarly, 
the meeting faces of the sections 52 and 53 of each support member 
inwardly of the porous pipe 65 slant inwardly and downwardly as at 72 and 
73 and are spaced slightly from one another to provide a slit 74 through 
which the reactive gas escaping through the porous pipe 65 will be 
directed toward and upon the substrate 12. In this way, the target face 
will be shielded from the reactive gas by the layer of non-reactive gas 
which is next to the target. Thus, the sputtering from the target face 
takes place in a non-reactive gas atmosphere, while the reaction desired 
takes place in a reactive gas atmosphere at or adjacent to the substrate. 
In practice, the coating chamber is first pumped down to the desired 
pressure and an inert gas, such as argon, introduced into the upper 
portion thereof through the porous pipes 62. The reactive gas, such as 
oxygen or nitrogen, is then introduced through the porous pipe 65 into the 
lower portion of the chamber. The gas introduced into the upper portion of 
the chamber is usually 100% inert gas, such as argon, while the gas 
introduced into the lower portion of the chamber is not necessarily 100% 
reactive gas. This gas may be a mixture of argon and oxygen or nitrogen; 
for example 80% oxygen or nitrogen and 20% argon. The presence of the 
argon gas above the reactive gas will prevent the reactive gas from 
passing upwardly into contact with the target face. 
The target may be formed of a pure metal such as titanium or tantalum. When 
the reactive gas used is oxygen and the molecules of titanium or tantalum 
are sputtered from the target they will be convered into titanium oxide or 
tantalum oxide respectively when they hit the oxygen. Likewise, when 
nitrogen gas is used the titanium and tantalum molecules will be converted 
into titanium nitride and tantalum nitride. 
To control the amount of gas introduced into the vacuum chamber 10, set 
screws 75 and 76 are threaded through the top and bottom sections 51 and 
53 of each support member 49 and 50 and are received within openings 77 
and 78 in the central section 52. Upon rotation of the set screws, the 
meeting faces 69-70 and 72-73 can be sprung slightly toward or away from 
one another to increase or decrease the width of the slits and thus 
regulate the amount of gas passing therethrough. 
In FIGS. 5 to 7 is illustrated an alternate form of gas distribution system 
embodying the basic features of the invention as described above. The 
cathode illustrated in FIG. 5 is the same as in FIGS. 1 to 3 so that like 
numerals have been used to designate like parts. 
The gas distribution system herein disclosed comprises a rectangular frame 
77 which encircles the lower portion of the cathode 11 within vacuum 
chamber 10 and is secured to the underside of the top wall 29 of said 
chamber by brackets 78. The frame is composed of upper and lower 
horizontal tubular side members 79 and 80 integral with the tubular end 
members 81 and 82. The upper and lower side and end members are joined 
together by the side and end metal plate members 83 and 84 respectively. 
The gases are introduced into the upper and lower tubular side members 79 
and 80 through feed pipes 85 and 86 and exit therefrom and from the end 
members 81 and 82 through aperatures 87 and 88 respectively. The openings 
87 in the upper tubular members are positioned to direct an inert gas 
upwardly and inwardly toward the target 21, while the openings 88 in the 
lower tubular members are positioned to direct a re-active gas, or a 
mixture of inert and reactive gases, downwardly and inwardly toward the 
substrate 12 as explained above. 
The operation and advantages of this form of the invention are the same as 
those above described with relation to that form of the invention 
illustrated in FIGS. 1 to 4. 
Modifications may be made without departing from the spirit or scope of the 
invention as defined in the appended claims.