U.S. patent number 3,766,634 [Application Number 05/245,889] was granted by the patent office on 1973-10-23 for method of direct bonding metals to non-metallic substrates.
This patent grant is currently assigned to General Electric Company. Invention is credited to Guy L. Babcock, Walter M. Bryant, James F. Burgess, Constantine A. Neugebauer.
United States Patent |
3,766,634 |
Babcock , et al. |
October 23, 1973 |
METHOD OF DIRECT BONDING METALS TO NON-METALLIC SUBSTRATES
Abstract
A method is described for direct bonding of metallic members to
non-metallic members at elevated temperatures in a controlled
reactive atmosphere without resorting to the use of electroless
plating, vacuum deposition or intermediate metals. The method
comprises placing a metal member such as copper, for example, in
contact with a non-metallic substrate, such as alumina, heating the
metal member and the substrate to a temperature slightly below the
melting of the metal, e.g., between approximately 1,065.degree.C.
and 1,080.degree.C. for copper, the heating being performed in a
reactive atmosphere, such as an oxidizing atmosphere, for a
sufficient time to create a copper-copper oxide eutectic melt
which, upon cooling, bonds the copper to the substrate. Various
metals, non-metals and reactive gases are described for direct
bonding.
Inventors: |
Babcock; Guy L. (North
Syracuse, NY), Bryant; Walter M. (Liverpool, NY),
Neugebauer; Constantine A. (Schenectady, NY), Burgess; James
F. (Schenectady, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
22928519 |
Appl.
No.: |
05/245,889 |
Filed: |
April 20, 1972 |
Current U.S.
Class: |
228/188; 174/259;
361/779; 174/252 |
Current CPC
Class: |
H05K
3/38 (20130101); C04B 37/021 (20130101); C04B
2235/6584 (20130101); C04B 2237/74 (20130101); C04B
2237/06 (20130101); C04B 2237/341 (20130101); C04B
2237/40 (20130101); C04B 2237/60 (20130101); C04B
2237/406 (20130101); C04B 2237/403 (20130101); C04B
2237/346 (20130101); C04B 2237/706 (20130101); C04B
2237/08 (20130101); C04B 2237/34 (20130101); C04B
2237/407 (20130101); C04B 2235/6567 (20130101); C04B
2235/6586 (20130101); C04B 2237/408 (20130101); C04B
2237/54 (20130101); C04B 2237/708 (20130101); C04B
2237/343 (20130101); C04B 2237/405 (20130101); C04B
2235/658 (20130101) |
Current International
Class: |
C04B
37/02 (20060101); H05K 3/38 (20060101); B23k
031/02 () |
Field of
Search: |
;29/471.9,472.9,473.1
;287/189.365 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
761,045 |
|
Nov 1956 |
|
GB |
|
784,931 |
|
Oct 1957 |
|
GB |
|
Primary Examiner: Baldwin; Robert D.
Assistant Examiner: Shore; Ronald J.
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. A method of direct bonding a metallic member to a non-metallic
refractory material substrate, said method comprising the steps
of:
placing said metallic member in contact with said non-metallic
material substrate;
providing a reactive gas atmosphere which at an elevated
temperature will react with the metal surface to form a
eutectic;
heating the member and substrate to a temperature below the melting
point of the metallic member in said reactive atmosphere to form
said eutectic with said metallic member which wets the member and
the substrate; and
cooling the member and the substrate with the member bonded
thereto.
2. The method of claim 1 wherein said metallic member is selected
from the group consisting of copper, nickel, cobalt, iron and
chromium and the step of heating in a reactive atmosphere forms
said eutectic with the selected metallic member.
3. The method of claim 2 wherein said reactive gas is oxygen.
4. The method of claim 2 wherein said reactive gas is a
sulfur-bearing gas.
5. The method of claim 2 wherein said reactive gas is a
phosphorus-bearing gas.
6. The method of claim 1 wherein said substrate is alumina or
beryllia and the metallic member is copper.
7. The method of claim 6 wherein said copper member is in the form
of a sheet having a thickness of between approximately 1 and 250
milli-inches and said reactive atmosphere is argon, helium or
nitrogen with approximately 0.01 to 0.5 per cent by volume of
oxygen.
8. The method of claim 7 wherein said eutectic is copper-copper
oxide which forms at a temperature of approximately
1,065.degree.C.
9. The method of claim 2 wherein said metallic member has a
thickness of between approximately 1 and 250 mils.
10. The method of claim 2 wherein said non-metallic material is
selected from the group of alumina, beryllia and fused silica,
titanates and spinnels.
11. The method of claim 1 further comprising placing a second
non-metallic material in contact with said metallic member to bond
said non-metallic materials together.
12. The method of claim 1 further comprising placing a second
metallic member in contact with said non-metallic material to form
bonds on opposite surfaces of said non-metallic material.
13. The method of claim 1 wherein the step of cooling is followed
by selective masking and etching of the metallic member.
14. The method of claim 1 wherein said reactive atmosphere includes
a partial pressure of a reactive gas in excess of the equilibrium
partial pressure of the reactive gas in the metal at or above the
eutectic temperature.
15. The method of claim 1 wherein said metallic member is selected
from the group of alloys consisting of copper-nickel,
nickel-cobalt, copper-chromium, copper-cobalt, iron-nickel,
silver-gold and beryllium-copper.
16. A method of bonding a metallic member to a non-metallic member
comprising:
placing a metallic member selected from the group consisting of
copper, nickel, cobalt, iron and chromium in contact with a
non-metallic member;
providing a reactive gas atmosphere which at an elevated
temperature will react with the metal surface to form a
eutectic;
forming said eutectic with said metallic member in said reactive
atmosphere at a temperature below the melting point of the members,
said eutectic wetting said metallic and non-metallic members;
and
cooling said members to form a bond therebetween.
17. The method of claim 16 wherein the step of cooling is followed
by bonding a semiconductor device to said metallic member.
18. The method of claim 16 wherein the step of cooling is followed
by patterning said metallic member.
19. The method of claim 16 wherein the step of forming a eutectic
comprises:
flowing a mixture of a substantially inert gas with approximately
0.01 and 0.5 per cent by volume of a reactive gas over said
metallic and non-metallic members.
20. The method of claim 19 wherein said reactive gas is oxygen in a
percentage of between approximately 0.03 and 0.1 by volume of the
reactive atmosphere.
Description
The present invention relates to improved bonds and methods of
bonding together non-metallic members to metal members and
non-metallic members to other non-metallic members. This
application relates to concurrently filed application Ser. No.
245,890 of common assignee, the entire disclosure of which is
incorporated herein by reference thereto.
Various methods of bonding non-metallic members together or to
metallic members have been employed in an attempt to satisfactorily
wet both members. One such method includes a mixture of titanium
hydride and a solder metal, such as copper, silver or gold, applied
to the member to be metallized or bonded and the hydride is
disassociated by the application of heat in the presence of the
solder metal. In this process, the heating is preferably done in a
non-oxidizing atmosphere, such as pure dry hydrogen. The
description found in U.S. Pat. No. 2,570,248 is typical of such a
process.
Another method of bonding metals to ceramics is described by J.T.
Klomp of Philips Research Laboratories. This method is described as
employing low-oxygen affinity metals applied to a ceramic under
high pressures, e.g., 1 Kg/cm.sup.2. Where oxygen-affinity metals
are employed, sufficiently high pressures are required "to destroy
the oxide film so that metal-ceramic contact can be made." Hence,
this method employs extremely high pressures to effect bonding.
While these methods may produce desirable bonds for many
applications, obviously the most desirable bond would be a direct
bond between the copper and the ceramic substrate which did not
require high pressures.
Another process for forming metallic bonds is described in U.S.
Pat. No. 2,857,663 by James E. Beggs. Basically, this method
employs an alloying metal, such as a metal from the titanium group,
IVb, of the Periodic Table, and an alloying metal, such as copper,
nickel, molybdenum, platinum, cobalt, chromium or iron. When the
alloying metal and a member of the titanium group are placed
between non-metallic refractory materials or a non-refractory
metallic material and a metallic material and are heated to a
temperature at which a eutectic liquidus is formed, a strong bond
forms between the adjacent members. While this process has been
satisfactory for many applications, the desire to improve the
integrity of the bond, increase the thermal conductivity between a
metal member and a non-metallic refractory member as well as
providing a high current carrying conductor on the non-metallic
refractory member has prompted researchers to seek still other
methods of bonding.
It is therefore an object of this invention to provide a bond and a
method of bonding non-metallic materials together, and metal
members to non-metallic members without the use of intermediary
bonding layers.
Another object of this invention is to provide a bond and a method
of bonding non-metallic refractory materials together or to metal
members in a simple heating step without the need for intermediate
wetting agents.
Yet another object of this invention is to provide a tenacious bond
and a method of forming this bond between a non-metallic refractory
material and a metal which is useful in the formation of integrated
circuit modules, and to provide high current carrying electrical
conductors on insulating members with high thermal conductivity
paths to a heat sink and to provide hermetic seals between two
non-metallic refractory materials.
It is also an object of this invention to provide a bond for
joining together a metallic and a non-metallic member, which bond
forms at a temperature below the melting point of the metal, but at
a temperature which produces a eutectic with the metal.
Briefly, our invention relates to bonds and methods of bonding
together non-metallic members to metallic members. By way of
example, a bond between metallic and non-metallic members is formed
by placing a metallic member in contact with a non-metallic member
preferably exhibiting refractory characteristics and elevating the
temperatures of the members in a reactive atmosphere of selected
gases and at controlled partial pressures for a sufficient time to
produce a eutectic composition which exhibits a eutectic melt. This
eutectic melt forms at a temperature below the melting point of the
metallic member and wets the metallic member and the non-metallic
refractory member so that upon cooling, a tenacious bond is formed
between the metallic and non-metallic members. Useful metallic
materials include copper, nickel, cobalt and iron, for example.
Useful reactive gases include oxygen, phosphorus-bearing compounds
and sulfur-bearing compounds, for example. In general, the amount
of reactive gas necessary to produce tenacious bonds is dependent,
in part, upon the thickness of the metallic and non-metallic
members and the times and temperatures required to form the
eutectic melt.
Other objects and advantages of our invention will become more
apparent to those skilled in the art from the following detailed
description taken in connection with the accompanying drawings in
which:
FIG. 1 illustrates a typical bond between non-metallic and metallic
materials in accord with our invention;
FIG. 2 is a series of schematic illustrations in the process of
making a metal to non-metal bond in accord with one embodiment of
our invention;
FIG. 3 is a flow diagram illustrating the process steps in accord
with the embodiment of FIG. 2;
FIGS. 4 and 5 illustrate still other bonds made in accord with our
invention;
FIG. 6 schematically illustrates a horizontal furnace useful in
practising our invention; and
FIG. 7 schematically illustrates a vertical furnace useful in
practising our invention.
FIG. 1 illustrates, by way of example, a typical bond 11 between a
non-metallic refractory member 12 and a metallic member 13. The
bond 11 comprises a eutectic composition formed with the metallic
member and a reactive gas in accord with the novel aspects of our
invention.
As used herein, the term non-metallic material is intended to
include refractory materials such as alumina (Al.sub.2 O.sub.3),
beryllia (BeO), fused silica or other useful materials, such as
titanates and spinnels, for example. Alumina and beryllia are
particularly useful in the practice of our invention since they
exhibit a high thermal conductivity which makes them particularly
useful for semi-conductor integrated circuit applications or in
high power electrical circuits. However, other non-metallic
refractory materials may also be employed, if desired, and our
invention is not limited solely to these materials.
The metallic member 13 may include such materials as copper, iron,
nickel, cobalt, chromium and silver, for example. Also, alloys of
these materials, such as copper-nickel, nickel-cobalt,
copper-chromium, copper-cobalt, iron-nickel, silver-gold, and
ternary compositions of iron, nickel and cobalt, are useful in
practising our invention. As will become more apparent from the
following description, still other metallic materials, such as
beryllium-copper, for example, may also be advantageously employed,
if desired.
The novel process for making a tenacious bond between the metallic
member 13 and a substrate 12 such as a non-metallic refractory
material 12 is illustrated schematically in FIG. 2 and in the flow
chart of FIG. 3. More specifically, FIG. 2 illustrates a
non-metallic refractory material 12, such as alumina or beryllia,
for example, with a metallic member 13 overlying the non-metallic
refractory substrate 12. The substrate 12 and the metallic member
13 are placed in a suitable oven or furnace including a reactive
atmosphere which at an elevated temperature forms a eutectic
composition 11 on the surfaces of the metallic member 13. The term
eutectic or eutectic composition means a mixture of atoms of the
metallic member and the reactive gas or compound formed between the
metal and the reactive gas. For example, where the metallic member
is copper and the reactive gas is oxygen, the eutectic is a mixture
of copper and copper oxide. Where the metal is nickel and the
reactive gas is phosphorus, the eutectic is a mixture of nickel and
nickel phosphide. Still further, where the metallic member is
cobalt and the reactive gas is a sulfur-bearing gas, the eutectic
is formed between cobalt and cobalt sulfide.
Table I is a representative listing of still other eutectics which
are useful in practising our invention. These eutectics are formed
by reacting the metallic member to be bonded with a reactive gas
controllably introduced into the oven or furnace.
TABLE I
Per Cent by Weight Metal-Gas Eutectic of Reactive Gas Eutectic
Temp. .degree.C. at Eutectic Temperature Iron-oxygen 1532.degree.
0.16 O.sub.2 Copper-oxygen 1065.degree. 0.39 O.sub.2
Chromium-oxygen 1800.degree. 0.6 O.sub.2 Chromium-sulfur
1550.degree. 2.2 S Copper-phosphorus 714.degree. 8.4 P
Nickel-oxygen 1438.degree. 0.24 O.sub.2 Nickel-phosphorus
880.degree. 11.0 P Molybdenum-silicon 2070.degree. 5.5 Si
Silver-sulfur 906.degree. 1.8 S Silver-phosphorus 878.degree. 1.0 P
Copper-sulfur 1067.degree. 0.77 S Cobalt-oxygen 1451.degree. 0.23
O.sub.2 Aluminum-silicon 577.degree. 11.7 Si
Tenacious bonds are formed in accord with our invention by
increasing the temperature of the metallic and non-metallic members
until the eutectic composition forms. This eutectic composition
wets the adjoining non-metallic and metallic members so that upon
cooling, the metallic and non-metallic members become tenaciously
bonded together. Where alloys are employed as the metallic member,
the eutectic composition is believed to form with one of the
elemental metals, generally the one with the lower melting
point.
One factor which appears to affect the tenacity and uniformity of
the bond is the relationship between the melting point of the
metallic member and the eutectic temperature. Where the eutectic
temperature is within approximately 30.degree. to 50.degree.C. of
the melting point of the metallic member, for example, the metallic
member tends to plastically conform to the shape of the substrate
member and thereby produce better bonds than those eutectics which
become liquidus at temperatures greater than approximately
50.degree.C. below the melting point of the metallic member. The
uniformity of the bond therefore appears to be related to the
"creep" of the metal which becomes considerable only near the
melting point. From Table I, for example, it can be seen that the
following eutectic compounds meet this requirement: copper-copper
oxide, nickel-nickel oxide, cobalt-cobalt oxide, iron-iron oxide
and copper-copper sulfide.
FIG. 4 illustrates an alternative embodiment of our invention
wherein a non-metallic refractory material 12 has two metallic
members 13 bonded to opposite surfaces thereof by bonds 11.
FIG. 5 illustrates still another embodiment of our invention
wherein two non-metallic members 12, such as alumina or beryllia,
for example, are bonded together by a metallic member 15. In this
embodiment of our invention the eutectic forms in substantially the
same manner as described above but for the fact that bonding occurs
on both surfaces of the metallic member 15. This embodiment of our
invention is particularly useful in forming hermetic seals between
non-metallic refractory materials, for example, such as those
employed in the fabrication of vacuum tubes, such as high frequency
type tubes.
Having thus described some useful embodiments of our invention and
the overall method of forming metal-to-non-metal and
non-metal-to-non-metal bonds, apparatus useful in practising our
invention along with more specific details of the process will now
be described with reference to FIG. 6. More specifically, FIG. 6
illustrates a horizontal furnace comprising an elongated quartz
tube 22, for example, having a gas inlet 23 at one end thereof and
a gas outlet 24 at the other end. The quartz tube 22 also includes
an opening or port 25 through which materials are placed into and
removed from the furnace. The materials are placed on a holder 26
having a push rod 27 extending through one end of the furnace so
that the holder and materials placed thereon may be introduced and
removed from the furnace.
The furnace 21 is also provided with suitable heating elements,
illustrated in FIG. 6 as electrical wires 28 which surround the
quartz tube 22 in the region to be heated. The electrical wires 28
may, for example, be connected to a suitable current source, such
as a 220-volt alternating current source. The electrical wires 28
may then be surrounded by suitable insulating material 29 to
confine the heat generated by the electrical wires to the region
within the quartz tube. Obviously, those skilled in the art can
readily appreciate that other heating means may also be employed,
if desired, and that FIG. 6 is merely illustrative of one such
heating means. The temperature of the furnace is detected by a
suitable thermocouple 29 which extends through an opening in the
quartz tube so that electrical connections can be made thereto.
FIG. 6 also illustrates a substrate 12 such as a non-metallic
refractory material positioned on the holder 26 and a metallic
material 13 overlying the substrate 12. These materials are
introduced into the quartz tube through the opening 25 which is
then sealed by suitable stopper means.
The quartz tube 22 is then purged with a reactive gas flow of
approximately 4 cubic feet per hour, for example. As used herein
reactive gas flow or atmosphere means a mixture of an inert gas
such as argon, helium or nitrogen, for example, with a controlled
minor amount of a reactive gas, such as oxygen, a
phosphorus-containing gas such as phosphine, for example, or a
sulfur-containing gas such as hydrogen sulfide, for example. The
amount of reactive gas in the total gas flow is dependent, in part,
on the materials to be bonded and the thickness of the materials,
in a manner more fully described below. In general, however, the
partial pressure of the reactive gas must exceed the equilibrium
partial pressure of the reactive gas in the metal at or above the
eutectic temperature. For example, when bonding copper members to
refractory members in a reactive atmosphere including oxygen, the
partial pressure of oxygen must be above 1.5 .times. 10.sup.-.sup.6
atmosphere at the eutectic temperature of 1,065.degree.C.
After purging the quartz tube, the furnace is then brought to a
temperature sufficient to form a eutectic liquidus or melt at the
metal-substrate interface. For example, for a copper-alumina bond
with oxygen as the reactive gas, the temperature of the furnace is
brought to between approximately 1,065.degree.C. and
1,075.degree.C. Within this range of temperatures, a copper-copper
oxide eutectic forms on the copper member 13. This eutectic melt
then wets the copper and the alumina to form a tenacious bond
therebetween.
In general, the times necessary to form this eutectic melt range
between approximately 10 minutes for 1-mil-thick copper members and
approximately 60 minutes for 250-mil-thick copper members. A more
detailed relationship between copper thickness and time at an
elevated temperature of between 1,065.degree. and 1,075.degree.C.
is presented below in Table II for a reactive atmosphere including
oxygen.
TABLE II
Copper Substrate Time at elevated Thickness, Thickness,
temperature, mils mils minutes 1 25 Mil, 96% 10 Alumina 2 25 Mil,
96% 15 Alumina 5 25 Mil, 99% 15 Alumina 5 25 Mil, 99% 15 Beryllia
10 25 Mil, 96% 30 Alumina 20 25 Mil, 96% 45 Alumina 5 150 Mil, 99%
30 Alumina 250 25 Mil, 96% 60 Alumina
Table II illustrates the relationship between copper thickness,
non-metallic refractory material thickness and firing time in the
furnace, i.e., the time at which the metal-non-metal materials
remain in the furnace. From this table it is readily apparent that
the firing time increases with the metal thickness, although there
does not appear to be a linear relationship between the two.
By way of further example, the formation of metallic bonds to
non-metallic refractory materials in accord with our invention may
also be achieved by employing a vertical-type furnace, such as that
illustrated in FIG. 7. More specifically, FIG. 7 illustrates a
vertical furnace 31 including a vertically positioned quartz tube
32, for example, with a carbon susceptor 33 positioned on a fused
silica pedestal 34. The quartz tube 32 is surrounded with R.F.
heating coils 35 which are powered by an external R.F. generator,
not shown.
FIG. 7 also illustrates a substrate 36 such as a non-metallic
refractory material resting on the susceptor 33 with a metal member
37 placed thereover. Inert and oxidizing gases are introduced
through inlets 38 and 39, respectively. The combined gas flows pass
through conduit 40 onto the metallic and non-metallic members and
exhaust through an exhaust outlet 41. Flow meters 42 and 43 on each
inlet monitor and control the rate of flow of the gases into the
furnace.
By way of example, the operation of the vertical furnace will be
described with reference to the formation of a bond between a
5-mil-thick copper member and an approximately 70-mil-thick
beryllia member. The flow meters 42 and 43 are adjusted so that
pure argon is introduced at inlet 38 and argon containing 2 per
cent oxygen is introduced at inlet 39. The quartz tube is then
flushed or purged for approximately 10 minutes with a flow rate of
approximately 2 cubic feet per hour of argon and approximately 1
cubic foot per hour of the argon-containing oxygen gas produces a
total oxygen content in the combined gases of approximately 0.04
molar per cent.
During the purging time, the temperature of the susceptor, beryllia
and copper members is maintained at room temperature. After the
purging period, the R.F. power is applied until the temperature of
the copper member exceeds 1,065.degree.C., but is below
1,083.degree.C. Typically, 2 to 5 minutes are required to produce
this temperature which may, for example, be monitored optically.
Optical monitoring of temperature is well known in the art and as
the copper member heats up from room temperature, a red-brown
oxidation color typical of copper oxide appears on the surface.
Above 600.degree.C., the copper surface emits light strongly. At a
temperature of 1,065.degree.C., a liquid layer is observed around
the copper member. The liquid layer wets both the beryllia and
copper members as evidenced by a drastic color change. Wetting
first occurs at the outer edges of the copper member where a black
color appears which then moves toward the center of the copper,
until the entire copper member appears black to the eye. Under
these conditions, the copper member retains its structural
integrity and does not break up into separate liquid droplets. When
the wetting process is completed over the entire surface area, the
R.F. power is removed and the members permitted to cool. Upon
removal of the copper and beryllia from the furnace, the copper is
strongly bonded to the beryllia and bond strengths in excess of
20,000 pounds per square inch have been observed.
The shape of the bonded copper member is substantially the same as
that of the original unbonded copper. However, there is some
evidence of oxidation and precipitation of copper oxide in the
bonded member. Also, some recrystallization of the grain structure
within the copper member is discernible.
Without limiting our invention to any particular theory of
operation, it is believed that the tenacious bonds formed in accord
with our invention result from the reaction of the metal with the
reacting gas during the heating period prior to the formation of
the eutectic melt. During this period, a small amount of the
reacting gas dissolves into the metal, but most of it reacts with
the metal to form a eutectic with the metal over its exposed
surfaces. At the eutectic temperature, 1,065.degree.C. for
copper-oxide, for example, a liquid phase of or near the eutectic
composition forms a "skin" around the metal. The thickness of this
molten "skin" depends upon the partial pressure of the reacting gas
and the length of time at the elevated temperature. For example,
for copper-oxygen systems, a partial pressure of oxygen less than
1.5 .times. 10.sup.-.sup.6 atmosphere (the equilibrium partial
pressure over Cu.sub.2 O at 1,065.degree.C.), the copper-oxygen
eutectic will not form. Hence, partial pressures in excess of this
value are required to produce the desired eutectic.
Under conditions permitting the formation of the eutectic, the
eutectic appears to wet the metal and the non-metallic refractory
material in such a way that upon cooling, a strong bond forms
between the two materials. A strong bond has also been observed
between pure copper at its melting point of 1,083.degree.C., in the
absence of a reacting gas (or even in a reducing atmosphere),
however, the copper member loses its structural integrity and forms
liquid droplets which are bonded to the non-metallic refractory
material.
If the partial pressure of the reacting gas is too high, all the
metal reacts with the reactive gas and forms, for example, an
oxide, sulfide, phosphide, etc., which prevents the formation of
the eutectic melt. Thus, an intermediate reacting gas partial
pressure is required so that both the eutectic melt phase and the
metallic phase are present simultaneously. Tests have illustrated
that extremely strong bonds are achieved when both phases are
present. Accordingly, in practising our invention the partial
pressure of the reacting gas must be sufficiently great to permit
the formation of a eutectic with the metal but not so great as to
completely convert the metal to the oxide, sulfide, phosphide, etc.
during the bonding time.
More specifically, we have found that consistently good bonds are
achieved between metals and non-metallic materials, such as copper
and alumina or beryllia, for example, in the presence of oxygen, so
long as the percentage of oxygen in the inert gas ranges between
approximately 0.03 and 0.1 per cent by volume. No bonding occurred
where the percentage of oxygen was less than approximately 0.01 per
cent by volume because there was insufficient oxide formation.
Also, no bonding occurred where the percentage of oxygen was above
0.5 per cent of the total gas flow because of complete oxidation of
the metal. In the intermediate regions, i.e., 0.01 to 0.03 and 0.1
to 0.5, marginal bonding occurs. Accordingly, to produce
consistently good bonds between copper and alumina or beryllia,
operation is preferable within the range of approximately 0.03 and
0.1 per cent by volume.
Table III illustrates ranges for partial pressures of the reactive
gases at which good bonding occurs for other metals and gases. Only
those eutectics which exhibit a eutectic temperature within
50.degree.C. of the melting point of the metal are listed.
TABLE III
Eutectic % Reactive Gas Compound by volume Cu-CuO 0.01-0.5 Cu-CuS
0.01-0.5 Ni-NiO 0.01-0.3 Co-CoO 0.01-0.4 Fe-FeO 0.01-0.3
it is to be understood that these selected metals, non-metals and
reactive gases are given merely by way of illustration and not
limitation. Further examples of suitable materials and reactive
gases will occur to those skilled in the art.
For example, useful bonds are formed with the aforementioned binary
metallic composition such as copper-nickel, nickel-cobalt,
copper-chromium, copper-cobalt, iron-nickel and beryllium-copper in
a reactive atmosphere including oxygen. Ternary compositions of
iron, nickel and cobalt also form useful bonds in a reactive
atmosphere of oxygen. Also, silver-gold compositions bond to
non-metallic refractory members in a reactive atmosphere including
a sulfur-bearing gas such as hydrogen sulfide, for example.
Those skilled in the art can also readily appreciate that metallic
members bonded to a non-metallic refractory material may be
patterned by photolithographic masking and etching techniques to
produce a desired pattern in the metallic member after forming the
desired bond. This method of forming patterned conductors is
preferable in the fabrication of semiconductor integrated circuits,
for example, where the size of the conductor if preformed before
bonding would pose serious handling problems.
Microwave tests performed on electrical circuits formed by
patterning copper bonded to alumina exhibit Q's comparable to those
formed by thin film techniques. For example, Q's in excess of 450
have been observed.
While particular embodiments of the invention have been described,
it will be obvious to those skilled in the art that various changes
and modifications may be made thereto without departing from the
invention in its broader aspects. For example, the total gas flow
rate may be varied over wide limits without materially affecting
the bond and economic considerations will generally control the
acceptable gas flow rate. Further, the partial pressure of the
reactive gas in the inert gas also can be varied depending in part
on the relative sizes of the materials to be bonded, the gas flow
rate, the presence of reactive elements in the flow system, such as
carbon susceptors in the case of an oxygen system, the warm-up rate
prior to bonding and the presence of residual oxygen or water in
the bonding system and bonding time. Therefore, it is intended that
the appended claims cover all such changes and modifications as
fall within the true spirit and scope of our invention.
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