Abstrict A desiccant for semiconductor packaging which may be applied in
liquid form consists essentially of approximately 60% by weight
absolute ethyl alcohol, 25% by weight ethyl acetate, 5% by weight
water, 5% by weight a source of boron, aluminum or phosphorus and
5% by weight of an organic silane having the structural formula:
##STR1## where R.sub.1 is a radical selected from the group consisting
of H.sup.-, CH.sub.2 .dbd.CH.sup.-, CH.sub.3 O.sup.-, C.sub.2 H.sub.5
O.sup.-, CH.sub.3 CO.sub.2 .sup.-, C.sub.2 H.sub.5 CO.sup.-, and
C.sub.3 H.sub.7 O.sup.-, and R is a radical selected from the group
consisting of CH.sub.3 O.sup.-, C.sub.2 H.sub.5 O.sup.-, C.sub.3
H.sub.7 O.sup.-, CH.sub.3 CO.sub.2.sup.-, C.sub.2 H.sub.5 CO.sub.2.sup.-,
Si.sup.+, OH.sup.-, and O.sup.-. The sources of boron, aluminum,
and phosphorus may be halides, oxides or nitrates. Also a process
for incorporating the foregoing into semiconductor package and process
for formulating the above solution.
Claims What is claimed is:
1. A method of packaging a semiconductor chip in a hermetic enclosure
formed by assembly of a first enclosure portion bearing said semiconductor
chip to a second enclosure portion, said enclosure including a desiccant,
the improvement comprising placing a coating of a liquid material
consisting essentially of ethyl alcohol, water, ethyl acetate, tetraethylorthosilicate,
and 0.1% to 10% by weight of a metallic ion selected from the group
consisting of boron, aluminum, and phosphorus, on part of said second
enclosure portion prior to said assembly, and drying said coating
in the range 80.degree.-500.degree. C. to provide a desiccant adherent
to said second enclosure portion.
2. The method of claim 1 where said metallic ion is aluminum.
3. The method of claim 1 where the source of said metallic ion
comprises the halides, oxides, and nitrates of said group.
4. The method of claim 1 where the weight percentage of tetraethylorthosilicate
in said liquid material is greater than the percentage of said metallic
ion and less the percentage of ethyl alcohol and the percentage
of ethyl acetate.
5. A method of packaging a semiconductor device as recited in claim
1 and further including the steps of drying said coating at 80.degree.-200.degree.
C. to form a porous complex silicate adhering to said second enclosure
portion.
6. The method of claim 5 where said silicate has a density of
1.4-1.8.
7. A method of packaging a semiconductor device as recited in claim
1 5 or 6 and further including the step of exposing said coating
to a temperature of 200.degree.-500.degree. C. for 10-30 minutes
during the assembly of said enclosure portions.
8. A method of packaging a semiconductor chip in a hermetic enclosure
formed by assembly of a first enclosure portion bearing said semiconductor
chip to a second enclosure portion, said enclosure including a desiccant,
the improvement comprising placing a coating of a liquid material
consisting essentially of ethyl alcohol, water, ethyl acetate, 0.1%
to 10% by weight of a metallic ion selected from the group consisting
of boron, aluminum, and phosphorus, and an organic silane having
the structural formula ##STR6## where R.sub.1 is a radical selected
from the group consisting of H.sup.-, CH.sub.2 .dbd.CH.sup.-, CH.sub.3
0.sup.-, C.sub.2 H.sub.5 O.sup.-, CH.sub.3 CO.sub.2.sup.-, C.sub.3
H.sub.7 O.sup.-, and R is selected from the group consisting of
CH.sub.3 O.sup.-, C.sub.2 H.sub.5 O.sup.-, C.sub.3 H.sub.7 O.sup.-,
CH.sub.3 CO.sub.2.sup.-, and C.sub.2 H.sub.5 CO.sub.2.sup.- on part
of said second enclosure portion prior to said assembly, and drying
said coating in the range 80.degree.-500.degree. C. to provide a
desiccant adherent to said second enclosure portion.
Description BACKGROUND OF THE INVENTION
This invention relates to semiconductor devices and more particularly
to the composition and process for eliminating corrosion within
semiconductor packages.
Semiconductor devices, particularly semiconductor integrated circuits,
are formed in a semiconductor chip or die, for example, of silicon,
by standard photolithographic and diffusion techniques and then
provided with suitable metallized bonding pads. The completed chip
is placed in the suitable packaging structure having electric leads
therethrough for providing electrical connection between interiors
of the package and the circuit or system into which it is to be
connected. The circuit between the chip and the package leads is
completed by bonding wires. Typically, the bonding pads on the chip
and the bonding wires are of aluminum. One prevalent problem with
this type of package is that corrosion takes place between the aluminum
bonding wire and the aluminum bonding pad thus resulting in early
failure of otherwise operative semiconductor integrated circuit
chips. This problem has been especially found in CMOS (complementary
metal oxides semiconductor) integrated circuits packaged in dual-in-line
ceramic packages. Although these packages are considered and intended
to be hermetically sealed, it has been found that a certain amount
of carbon dioxide and water is present in the packaged device. Hence,
a mechanism for eliminating or gettering of this carbon dioxide
and water vapor has been found to be necessary.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to provide an improved
desiccant or gettering agent for a semiconductor integrated circuit.
A further object of the invention is to provide a desiccant or
getter for water vapor and carbon dioxide in semiconductor packages.
Still more particularly, it is an object of this invention to provide
a desiccant or gettering material for semiconductor integrated circuits
in ceramic packages.
A still further object of the invention is to provide a method
of manufacturing semiconductor integrated circuits which includes
the steps of placing and retaining desiccant into the package.
A further object of the invention is to provide a method of manufacture
of a desiccant or gettering material for semiconductor devices.
SUMMARY OF THE INVENTION
In accordance with the foregoing object there is provided a desiccant
for semiconductor packaging consisting essentially of approximately
60% by weight absolute ethyl alcohol, 25% by weight ethyl acetate,
5% by weight water, 5% by weight of a source of boron, aluminum,
or phosphorous and 5% by weight of an organic silane having the
structural formula: ##STR2## where R.sub.1 is a radical selected
from the group consisting of H.sup.-, CH.sub.2 .dbd.CH.sup.-, CH.sub.3
O.sup.-, C.sub.2 H.sub.5 O.sup.-, CH.sub.3 CO.sub.2.sup.-, C.sub.2
H.sub.5 CO.sup.-, and C.sub.3 H.sub.7 O.sup.-, and R is a radical
selected from the group consisting of CH.sub.3 O.sup.-, C.sub.2
H.sub.5 O.sup.-, C.sub.3 H.sub.7 O.sup.-, CH.sub.3 CO.sub.2.sup.-,
C.sub.2 H.sub.5 CO.sub.2.sup.-, Si.sup.+, OH.sup.-, and O.sup.-.
There is also provided a method of utilizing the foregoing desiccant
material which includes the steps of (a) providing the ingredients
17% to 23% ethyl alcohol, 3% to 9% water and 0.1% to 10% of a metallic
ion selected from the group consisting of boron, aluminum, and phosphorous,
and the halides, oxides and nitrates thereof; (b) refluxing said
ingredients of alcohol, water and metallic ion source until reaction
thereof is essentially complete; (c) adding to said refluxed ingredients
36% to 42% by weight ethyl alcohol, 17% to 23% by weight ethyl acetate
and 9% to 15% by weight of tetraethylorthosilicate; and (d) coating
the resulting solution on at least a portion of a semiconductor
package.
There is also provided a method of packaging semiconductor devices
which includes the step of coating a portion of the semiconductor
package with a liquid material consisting essentially of approximately
60% by weight ethyl alcohol, 25% by weight of a source of boron,
aluminum or phosphorous and 5% by weight of an organic silane and
having the structural formula: ##STR3## where R.sub.1 is a radical
selected from the group consisting of H.sup.-, CH.sub.2 .dbd.CH.sup.-,
CH.sub.3 O.sup.-, C.sub.2 H.sub.5 O.sup.-, CH.sub.3 CO.sub.2.sup.-,
C.sub.2 H.sub.5 CO.sup.-, and C.sub.3 H.sub.7 O.sup.- and R is a
radical selected from the group consisting of CH.sub.3 O.sup.-,
C.sub.2 H.sub.5 O.sup.-, C.sub.3 H.sub.7 O.sup.-, CH.sub.3 CO.sub.2.sup.-,
C.sub.2 H.sub.5 CO.sub.2.sup.-, Si.sup.+, OH.sup.-, O.sup.-.
THE DRAWINGS
Further objects and advantages of the invention will be understood
from the following complete description thereof and from the drawings
wherein:
FIG. 1 is an expanded view of a semiconductor package embodying
the invention; and
FIG. 2 is a cross-section thereof.
COMPLETE DESCRIPTION
The sealing of semiconductor devices in packages may be accomplished
in a low dew point atmosphere of air, an inert gas atmosphere, or
a vacuum. During such processing every effort has been made to prevent
materials, such as water vapor and carbon dioxide from being contained
in the package. However, as integrated circuits have gotten smaller
and more complex, smaller amounts of carbon dioxide and water vapor
can lead to corrosion of the device internal of the package. Since
a certain amount of water vapor and carbon dioxide is probably placed
in the package, merely from the material being used to seal the
package, it is necessary to provide a desiccant or gettering agent
within the package which does not produce deleterious results. Normal
gettering material such as might be used for receiving tubes or
electronic devices of other types is not suitable since most of
these desiccants rely upon chemical combination utilizing materials
which themselves would present chemical damage to the semiconductor
chip.
In accordance with the preferred embodiment of the invention, a
suitable desiccant is provided by mixing absolute ethyl alcohol
of about 20% by weight and distilled deionized water of about 3%
by weight with a metal ion source of aluminum, boron or phosphorous
of about 3% by weight. Such source of aluminum, boron or phosphorous
ion may be a halide, oxide or nitrate. These three ingredients are
refluxed until the reaction thereof is essentially complete. Generally,
this takes place in the order of about one-half hour. Following
filtering of the refluxed ingredients another 39% by weight of absolute
ethyl alcohol, 3% by weight of glycerol and approximately 25% by
weight of ethyl acetate and approximately 12% by weight of an organic
silane having the structural formula: ##STR4## wherein R.sub.1 is
a radical selected from the group consisting of H.sup.-, CH.sub.2
.dbd.CH.sup.-, CH.sub.3 O.sup.-, C.sub.2 H.sub.5 O.sup.-, CH.sub.3
CO.sub.2.sup.-, C.sub.2 H.sub.5 CO.sup.-, and C.sub.3 H.sub.7 O.sup.-,
and R is a radical selected from the group consisting of CH.sub.3
O.sup.-, C.sub.2 H.sub.5 O.sup.-, C.sub.3 H.sub.7 O.sup.-, CH.sub.3
CO.sub.2.sup.-, and C.sub.2 H.sub.5 CO.sub.2.sup.-. Preferably this
material is tetraethylorthosilicate.
The above results in a liquid desiccant coating comprising and
combination by weight 59% absolute ethyl alcohol, 20% ethyl acetate,
12% tetraethylorthosilicate and 3% each of water, gylcerol and a
metal ion source such as phosphorous, boron or aluminum. A coating
of this material is placed on at least some parts of the semiconductor
package and dried at 80.degree.-200.degree. C. for 10-30 minutes.
This produces a porous silicon coating having a density of 1.4 to
1.8 as contrasted with ordinary SiO.sub.2 which has a density of
2.3.
As shown in FIG. 1 a semiconductor package for a semiconductor
integrated circuit chip 10 is enclosed in a package comprising four
basic structures:
(a) a box-like ceramic mounting base 11 with castellations 12 to
act as a jig for the external leads 13; (b) and a top cover 14;
(c) a bottom cover 15; and (d) leads 13 which are normally provided
in a single sheet of metal with surrounding frame (not shown) which
is later trimmed off.
The frame holding the leads serves to hold the leads in the castellated
base 11 while the leads 13 are sealed thereto with a solder glass.
Following securing of the leads 13 in the base member 11 the bottom
lid 15 is secured thereto. Typically, a solder glass coating 16
is provided about the periphery of the cover 15 and the cover is
then juxtaposed with the base 11 which has sealed-in leads 13. If
desired the leads 13 the base member 11 and the bottom cover 15
may be assembled in a single operation by heating these three major
member together at a high enough temperature to cause the solder
glass to flow.
The semiconductor chip 10 having a plurality of bonding pads 17
is then placed in this assembly and bonding wire 18 (FIG. 2) connect
the bonding pads 17 to the respective lead members 13. A top cover
14 is then prepared by placing a solder glass coating about its
periphery and the coating of the above-referred-to desiccant in
the central area thereof. The top cover 14 is then dried at 80.degree.-200.degree.
C. for 10-30 minutes resulting in a porous coating 19 on the interior
surface of the top cover 14. The top cover 14 is then placed on
the semiconductor package and heated at 200.degree.-500.degree.
C. for about 10-30 minutes to effect the sealing. of the glass solder
to the base member 11 completing the package.
The foregoing treatment results in a coating which adheres well
to the package cover 14 and has a large affinity for water. It is
theorized that the following structure and reaction takes place:
Structure: ##STR5## Where X, Y & Z could be Si, O, OH in various
stoichimetries containing certain percentages of Al, B, P. The small
amounts of Al, B, or P increases adhesion to similar materials,
i.e., introduction of Al promotes better adhesion to Al.sub.2 O.sub.3
based ceramics.
Thus the foregoing results in a complex silicate having several
dangling bonds which mechanically and/or chemically absorb the carbon
dioxide and water remaining in the package. Comparative data has
demonstrated that a package made by prior technique without the
desiccant coating contains about 0.6 volume % water and approximately
5 volume % carbon dioxide. With use of the desiccant it is found
that the water content is reduced below 0.2% and carbon dioxide
below 3%. It is thus deemed that the desiccant in accordance with
the invention removes 66% of the water and approximately one-half
of the CO.sub.2 leading to devices which have increased life.
While the invention has been disclosed by way of the preferred
embodiment thereof it will be appreciated that suitable modifications
may be made therein without departing from the spirit and scope
of the invention. |