Cathode targets of silicon and transition metal

Silicon-chromium cathode targets comprising 5 to 80 weight percent chromium are disclosed for sputtering absorbing coatings of silicon-chromium alloy in atmospheres comprising inert gas, reactive gases such as nitrogen, oxygen, and mixtures thereof which may further comprise inert gas, such as argon, to form nitrides, oxides, and oxynitrides as well as metallic films. The presence of chromium in the cathode target in the range of 5 to 80 weight percent provides target stability and enhanced sputtering rates over targets of silicon alone, comparable to the target stability and sputtering rates of silicon-nickel, not only when sputtering in oxygen to produce an oxide coating, but also when sputtering in inert gas, nitrogen or a mixture of nitrogen and oxygen to produce coatings of silicon-chromium, silicon-chromium nitride or silicon-chromium oxynitride respectively. The chromium in the target may be replaced in part with nickel, preferably in the range of 5 to 15 weight percent, to produce coatings of silicon-chromium-nickel and the oxides, nitrides and oxynitrides thereof.

BACKGROUND 
1. Field of the Invention 
The present invention relates generally to the art of sputtering 
silicon-containing target materials and to the art of fabricating cathode 
targets of silicon alloys comprising transition metal. 
2. Description of the Related Art 
U.S. Pat. Nos. 4,990,234 and 5,170,291 to Szczyrbowski et al. disclose 
sputtering silica and silicides, such as nickel silicide (NiSi.sub.2), in 
an oxidizing atmosphere to deposit dielectric oxide films. 
U.S. Pat. No. 5,320,729 to Narizuka et al. discloses a sputtering target 
with which a high resistivity thin film consisting of chromium, silicon 
and oxygen can be produced. The target is formed by selecting the grain 
size of chromium powder and silicon dioxide powder drying the powders by 
heating and mixing the dried powders to obtain a mixed powder containing 
from 20 to 80 percent by weight of chromium, preferably 50 to 80 percent, 
the remainder being silicon dioxide, packing the mixed powder in a die, 
and sintering the packed powder by hot pressing to produce a target which 
has a two phase mixed structure. The sputtering target is used to 
manufacture thin film resistors and electrical circuits.

SUMMARY OF THE INVENTION 
The present invention involves cathode targets of silicon alloys containing 
a transition metal such as chromium, chromium-nickel, or iron. Targets of 
silicon alloys containing chromium, chromium-nickel or iron may be 
sputtered in an atmosphere comprising inert gas, nitrogen, oxygen and 
mixtures thereof to produce silicon-metal containing coatings including 
oxides, nitrides and oxynitrides, as well as metallic films. The 
silicon-metal cathode target compositions of the present invention 
comprise sufficient metal to provide target stability and a desirable 
sputtering rate. 
Adding chromium, which as an oxide or nitride is very hard and chemically 
resistant, to the silicon provides a mechanically and chemically durable 
silicon alloy compound coating. When the alloy is sputtered in pure argon, 
the resultant silicon alloy coating is harder than silicon. 
The purpose of these silicon-chromium, silicon-chromium-nickel and 
silicon-iron alloys is to provide target materials which sputter readily, 
in inert gas, reactive gas or gas mixtures, to produce extremely durable 
coatings with variable optical properties. Each target material 
combination produces coatings with different optical constants, i.e. 
refractive index and absorption coefficient. These optical constants 
generally increase as the percentage of chromium, chromium-nickel or iron 
in the silicon alloy increases. When sputtered reactively, each target 
material combination also produces coatings with a range of optical 
constants, which generally increase as the reactive gas mixture, with or 
without inert gas such as argon, is varied from oxygen, to combinations of 
oxygen and nitrogen with increasing proportions of nitrogen, to nitrogen. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention, oxides, nitrides and oxynitrides 
of silicon-chromium, silicon-chromium-nickel and silicon-iron are 
sputtered using dc magnetron sputtering. For this purpose, 
silicon-chromium, silicon-chromium-nickel and silicon-iron cathode targets 
of the present invention are used for the sputtering targets. Coating 
transmission is measured as an indicator of the optical properties of 
refractive index and absorption coefficient as shown in FIGS. 1 and 2. 
The silicon-chromium, silicon-chromium-nickel, and silicon-iron cathode 
targets of the invention are found to sputter with arcing and rates 
comparable to silicon-nickel alloys. Since it is desirable in a production 
process to use the same target material for many coating applications and 
vary the reactive gas to sputter different compositions, the chromium, 
chromium-nickel or iron content in accordance with the present invention 
is kept high enough to give the desirable sputtering rate and target 
stability. 
Silicon-chromium alloy cathode targets ranging between 5 and 80 weight 
percent, preferably 10 to 60 weight percent, most preferably 10 to 50 
weight percent, chromium are sputtered in argon, nitrogen, and/or oxygen; 
preferably in an argon-oxygen gas mixture with up to 50 percent oxygen, or 
in a nitrogen-oxygen gas mixture containing up to 40 percent oxygen. When 
the coating includes silicon and chromium, the weight percent chromium in 
the coating based on the combined weight of silicon and chromium is from 5 
to 80%. When the coating includes silicon and chromium and is sputtered in 
an inert atmosphere, the weight percent chromium in the coating based on 
the combined weight of silicon and chromium is 5 to 50%. Silicon-chromium 
alloy cathode targets may have some of the chromium substituted with 
nickel. The amount of nickel is preferably below 15 percent by weight 
based on the combined weight of silicon, chromium and nickel. The amount 
of nickel is preferably below 15 percent, preferably in the range of 5 to 
15 percent, with at least 5 percent chromium based on the total weight of 
silicon, chromium and nickel. 
Silicon-chromium-nickel alloy cathode targets with 5 to 15 weight percent 
nickel and 5 to 65 weight percent chromium, preferable 5 to 10 weight 
percent nickel and 5 to 40 weight percent chromium, are preferably 
sputtered in inert gas such as argon, in argon-oxygen gas mixtures with up 
to 50 percent oxygen, and in nitrogen-oxygen gas mixtures containing up to 
40 percent oxygen. Silicon-iron alloy cathode targets preferably contain 
up to 20 weight percent iron based on the combined weight of silicon, but 
may contain more iron or other transition metal subject to the limitation 
that the alloy remain nonmagnetic for magnetron sputtering. 
The silicon-chromium, silicon-chromium-nickel and silicon-iron cathode 
target compositions of the present invention are determined by the DC 
Plasma Emission method from pieces of target material to determine weight 
percent of chromium, nickel or iron. The coating compositions are measured 
using X-ray fluorescence to determine the weight percent chromium, nickel 
or iron. 
In particularly preferred embodiments of the present invention, as 
illustrated in FIGS. 1 and 2, silicon-chromium alloys having compositions 
with 58, 25 and 10 percent weight chromium are reactively sputtered. The 
alloy containing 58 percent chromium deposits a coating with strong 
absorption both as an oxide and nitride, as indicated by the decrease in 
transmission with increasing number of passes. The alloy containing 25 
percent chromium deposits a coating which shows some absorption as an 
oxide. The alloy containing 10 percent chromium deposits a coating which, 
as an oxide, shows insignificant absorption, and a refractive index which 
is less than the refractive index of the glass substrate. This is evident 
because the transmission increases above that of the substrate (6.0 mm 
float glass) as the coating is deposited. The nitride coatings of all the 
alloys containing chromium show strong absorption. FIGS. 1 and 2 
illustrate these properties of the oxide and nitride respectively. As 
shown in FIG. 1, the coating transmission as a function of coating 
thickness, shown as number of passes, indicates that the absorption and 
the refractive index of the coatings generally increase as the chromium 
content increases. 
In a preferred embodiment of the present invention, coatings are produced 
on a large-scale magnetron sputtering device capable of coating glass up 
to 100.times.144 inches (2.54.times.3.66 meters). In the following 
examples, the coatings are deposited on a smaller scale, using planar 
magnetron cathodes having 5.times.17 inch (12.7.times.43.2 centimeters) 
silicon-chromium targets. Base pressure is in the 10.sup.-6 Torr range. 
The coatings are made by first admitting the sputtering gas to a pressure 
of 4 millitorr and then setting the cathode at constant power of 3 
kilowatts (kw). In each example, 6 millimeter thick glass substrates pass 
under the target on a conveyor roll at a speed of 120 inches (3.05 meters) 
per minute. The transmittance is monitored every other pass during the 
sputtering process at a wavelength of 550 nanometers using a Dyn-Optics 
580D optical monitor. 
EXAMPLE 1 
A sample is prepared using a silicon-chromium cathode target containing 58 
weight percent chromium in an oxygen-argon gas mixture with an oxygen flow 
of 106 standard cubic centimeters per minute (sccm) and an argon flow of 
108 sccm. The cathode voltage is 548 volts. The sputtered film deposited 
in this oxygen-argon gas mixture is 58 weight percent chromium based on 
the total weight of silicon and chromium in the film. The transmittance of 
the coating, monitored at 550 nanometers, is 81.2 percent after 29 passes. 
The coating thickness is 1593 Angstroms. 
EXAMPLE 2 
A sample is prepared using a silicon-chromium cathode target containing 25 
weight percent chromium in an oxygen-argon gas mixture with an oxygen flow 
of 46 sccm and an argon flow of 46 sccm. The cathode voltage is 381 volts. 
The sputtered film deposited in this oxygen-argon gas mixture is 23 weight 
percent chromium based on the total weight of silicon and chromium in the 
film. The transmittance of the coating, monitored at 550 nanometers, is 
89.8 percent after 39 passes. The coating thickness is 2123 Angstroms. 
EXAMPLE 3 
A sample is prepared using a silicon-chromium cathode target containing 10 
weight percent chromium in an oxygen-argon gas mixture with an oxygen flow 
of 46 sccm and an argon flow of 46 sccm. The cathode voltage is 348 volts. 
The sputtered film deposited in this oxygen-argon gas mixture is 8.2 
weight percent chromium based on the total weight of silicon and chromium 
in the film. The transmittance of the coating, monitored at 550 
nanometers, is 92.8 percent after 16 passes. The coating thickness is 1044 
Angstroms. 
EXAMPLE 4 
A sample is prepared using a silicon-chromium cathode target containing 58 
weight percent chromium in pure nitrogen gas atmosphere with a flow of 158 
standard cubic centimeters per minute (sccm). The cathode voltage is 564 
volts. The transmittance of the coating, monitored at 550 nanometers, is 
9.8 percent after 35 passes. 
EXAMPLE 5 
A sample is prepared using a silicon-chromium cathode target containing 10 
weight percent chromium in pure nitrogen gas atmosphere with a flow of 100 
standard cubic centimeters per minute (sccm). The cathode voltage is 495 
volts. The sputtered film deposited in this nitrogen gas is 10.3 weight 
percent chromium based on the total weight of silicon and chromium in the 
film. The transmittance of the coating, monitored at 550 nanometers, is 
80.0 percent after 16 passes. The coating thickness is 1053 Angstroms. 
EXAMPLE 6 
A sample is prepared using a silicon-chromium-nickel cathode target 
containing 5 weight percent chromium and 15 weight percent nickel in pure 
nitrogen gas atmosphere with a flow of 160 standard cubic centimeters per 
minute (sccm). The cathode voltage is 517 volts. The sputtered film 
deposited in this nitrogen gas is 4.8 weight percent chromium and 15.5 
weight percent nickel based on the total weight of silicon, chromium, and 
nickel in the film. The transmittance of the coating, monitored at 550 
nanometers, is 66.7 percent after 12 passes. The coating thickness is 782 
Angstroms. 
EXAMPLE 7 
A sample is prepared using a silicon-chromium-nickel cathode target 
containing 10 weight percent chromium and 10 weight percent nickel in pure 
nitrogen gas atmosphere with a flow of 102 standard cubic centimeters per 
minute (sccm). The cathode voltage is 506 volts. The sputtered film 
deposited in this nitrogen gas is 9.6 weight percent chromium and 10.4 
weight percent nickel based on the total weight of silicon, chromium, and 
nickel in the film. The transmittance of the coating, monitored at 550 
nanometers, is 68.0 percent after 12 passes. The coating thickness is 750 
Angstroms. 
EXAMPLE 8 
A sample is prepared using a silicon-chromium-nickel cathode target 
containing 5 weight percent chromium and 15 weight percent nickel in an 
oxygen-argon gas mixture with an oxygen flow of 75 sccm and an argon flow 
of 75 sccm. The cathode voltage is 373 volts. The sputtered film deposited 
in this oxygen-argon gas mixture is 4.1 weight percent chromium and 11.3 
weight percent nickel based on the total weight of silicon, chromium, and 
nickel in the film. The transmittance of the coating, monitored at 550 
nanometers, is 89.0 percent after 12 passes. The coating thickness is 781 
Angstroms. 
EXAMPLE 9 
A sample is prepared using a silicon-chromium-nickel cathode target 
containing 10 weight percent chromium and 10 weight percent nickel in an 
oxygen-argon gas mixture with an oxygen flow of 44 sccm and an argon flow 
of 44 sccm. The cathode voltage is 377 volts. The sputtered film deposited 
in this oxygen-argon gas mixture is 9.3 weight percent chromium and 7.3 
weight percent nickel based on the total weight of silicon, chromium, and 
nickel in the film. The transmittance of the coating, monitored at 550 
nanometers, is 91.9 percent after 12 passes. The coating thickness is 704 
Angstroms. 
EXAMPLE 10 
A sample is prepared using a silicon-iron cathode target containing 8 
weight percent iron in pure nitrogen gas atmosphere with a flow of 92 
sccm. The cathode voltage is 475 volts. The transmittance of the coating, 
monitored at 550 nanometers, is 80.3 percent after 14 passes. The coating 
thickness is 698 Angstroms. 
EXAMPLE 11 
A sample is prepared using a silicon-chromium-nickel cathode target 
containing 5 weight percent chromium and 14 weight percent nickel in pure 
argon gas atmosphere with a flow of 136 sccm. The cathode voltage is 932 
volts. The transmittance of the coating, monitored at 550 nanometers, is 
3.2 percent after 6 passes. The coating thickness is 732 Angstroms. 
The above examples illustrate the present invention which relates to using 
silicon-chromium, silicon-chromium-nickel and silicon-iron cathode targets 
sputtered in pure nitrogen, in nitrogen-oxygen mixtures ranging up to 40 
percent oxygen, and in argon-oxygen mixtures comprising up to 50 percent 
oxygen. Based on the data illustrated in the figures, a single 
silicon-alloy cathode target containing a given weight percentage of 
chromium, chromium-nickel or iron can be used for stable sputtering of a 
range of film compositions including oxides, nitrides and oxynitrides with 
varying absorption at high sputtering rates. The above examples illustrate 
the concept of the present invention, the scope of which is defined by the 
following claims.