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Патент USA US3086902

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April 23, 1963
R. L. HUNTINGTON
3,085,892
SEMICONDUCTOR DEVICES AND METHOD OF MAKING SAME
Filed Sept. 2'7, 1960
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Richard L. Huntington
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BY
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United States Patent
1
3,086,892
a
lag
3,086,892
Patented Apr. 23» 1963.
2
plished in the following manner: before the electrode pel
let is alloyed to the semiconductor wafer so as to form a
rectifying barrier, at least one member of the pellet-wafer
pair is coated with a solution of a silicon compound se
OF MAKING SAME
lected from the group consisting of siloxanes and silicones
Richard L. Huntington, Van Buren, Ohio, assignor to
Radio Corporation of America, a corporation of Del
dissolved in an organic solvent. The exact concentration
of the solution is not critical, but preferably the solution
aware
Filed Sept. 27, 1960, Ser. No. 58,781
utilized contains at least one-half (0.5) weight percent of
7 Claims. (Cl. 148-15)
the compound. The solution is permitted to dry, thus
forming a thin ?lm of the silicon compound on the pellet
This invention relates to semiconductor devices, and 10 or on the wafer, or on both. The pellet is then alloyed
SEMICONDUCTQR DEVEQES AND METHOD
more particularly to improved methods of making junc
tion type semiconductor devices With uniform electrical
characteristics.
A typical junction device of this class is the transistor,
into the wafer to form a rectifying barrier.
The invention will be described in greater detail with
reference to the accompanying drawing, in which FIG
URES 1 through FIGURE 3 are cross-sectional, sche
which comprises a semiconductive wafer with at least two 15
matic views of successive steps in the fabrication of a
PN junctions as rectifying barriers, and at least three elec
semiconductor device according to the invention.
trodes, usually denoted emitter, collector, and base.
Referring to FIGURE 1 of the drawing, a wafer 19 of
Semiconductor devices of this class may be fabricated by
semiconductive
crystalline material is prepared with two
the surface alloy or fusion method, in which a pellet of a
opposing major faces. The wafer 10 may consist of ger
material which produces conductivity of one type in a 20
manium, silicon, germanium-silicon alloys, or the like,
semiconductor material is positioned on a surface of a
and may be of either conductivity type. For purposes of
semiconductor water of the opposite conductivity type.
The assemblage of wafer and pellet is then heated so as
illustration, it will be assumed that wafer 10 consist of
N-conductivity type germanium. Advantageously, the
to melt the pellet material and alloy it into the surface of
surface of Wafer 10 is cleaned by treating the wafer with
the semiconductor wafer, thus forming a PN junction at 25 a mild etchant, and washing the wafer in distilled water.
the interface of the different conductivity regions. A
The electrode pellets utilized in the fabrication of sur
serious production problem in this method is the excessive
face alloy junctions in N-conductivity type wafers contain
and irregular lateral spreading of the pellet material over
material which is an acceptor in the particular semi
the surface of the semiconductor wafer during the alloying 30 aconductor
utilized for the wafer. Suitable acceptors for
step. The spreading of the pellet material produces un
the
germanium
wafer of this example include boron, alu-v
satisfactory devices for three reasons: ?rst, the excessive
minum,
gallium,
indium, and their alloys. The electrode
spreading of the pellet material may cause a short circuit
pellets, also known as dots, may be of any convenient
to the base electrode; second, the spreading of the pellet
shape, such as spherules, discs, or rings. in this exam
material causes excessive collector capacitance; third, ir
ple,
electrode pellets 11 and 12 consist of indium spherules.
regular spreading causes junctions of variable size and
For transistor fabrication, it is advantageous to utilize,
shape, which results in devices having variable electrical
electrode pellets of two different sizes, and make the
characteristics from one unit to another, Whereas junctions
larger pellet (11 in this example) the collector electrode
with uniform electrical characteristics are desired in order
of the completed device. Electrode pellets 11 and 12
to provide devices with uniform performance. The exces 40 are immersed in a beaker containing a solution of a
sive lateral spreading of the pellet material is particularly
compound selected from the siloxanes and silicones in an
marked when puri?ed semiconductor material having a
organic solvent. In this example, the solution consists of
low edge dislocation density is utilized.
one ml. Dimethyl-diethoxysilane and one hundred ml.
There have been many attempts to solve this problem.
xylene. The electrode pellets are rinsed in the solution,
One method has been to con?ne the spreading of the 45 so that the surfaces of pellets 11 and 12 are uniformly
pellet to the desired area on the semiconductor wafer by
coated with a thin ?lm 21 and 22 respectively. The
coating the remaining surface of the wafer with a thin
solution is then decanted and the pellets are dried on a
inert ?lm, which prevents the pellet material from wetting
sheet of ?lter paper. Alternatively, the solution is applied
that portion of the semiconductor water which is pro
as a spray to the assemblage of Wafer and pellets. Any
tected by the ?lm and thereby con?nes the lateral spread 50 convenient method of applying the solution may be uti
ing of the pellet material to the ?lm~free portion of the
lized. The coated pellets 11 and 12 are then coaxially
wafer. Films previously used for this purpose include
positioned on the opposing major faces of wafer 19 as
germanium oxide, silicon monoxide, silicon dioxide, and
shown ‘in FIGURE 2.
magnesium fluoride. Although these methods have been
Referring now to FIGURE 3, the electrode pellets 11
successfully utilized to fabricate satisfactory devices, fur 55 and 12 are ‘alloyed to wafer 10 by heating the assemblage
ther improvement is desirable as to ease of application in
of wafer and pellets in a non-oxidizing atmosphere for
order to reduce handling cost.
about 10 to 20 minutes at a temperature of about 550°
An object of the present invention is to provide im
C. During this step the electrode pellets 11 and 12 melt
proved methods of making improved semiconductor de
and dissolve a portion of the semiconductor wafer mate
60 rial. When the assemblage is cooled, the dissolved Wafer
vices.
Another object of the invention is to provide improved
material precipitates and is recrystalized immediately be
methods of making semiconductor devices with one or
neath the pellets in the original crystal lattice of the Wafer.
more rectifying barriers.
The recrystallized regions 13 and 14 beneath the alloyed
Still another object of the invention is to provide im
electrodes 11 ‘and 12 respectively contain suf?cient indium
proved methods of making semiconductor devices of the 65 to
be of P-conductivity type. Rectifying barriers or PN
alloy junction type having desirable electrical character
junctions 15 and 16 are thus formed at the interfaces be
istics.
tween
the P-type recrystalized regions 13‘ and 14 respec
Another object of the invention is to provide improved
tively and the N-type bulk of wafer 10.
methods of making semiconductor devices of the alloy
During the alloying step the electrode pellets 11 and
junction type so as to prevent excessive lateral spreading 70
of electrode pellets during alloying.
These and other objects of the invention are accom
12 tend to assume a hemispherical shape, as shown in
FIGURE 3, due to the surface tension of the molten pel
3
3,086,892.
lets. It is believed that during the heating step the silox
ane compound is decomposed so as to leave a residue of
silicon oxides adhering to the pellet and Wafer surface.
The adherent residue of silicon oxides acts as a sort of
container around the electrode pellet and prevents ex
cessive spreading of the pellets over the wafer surface
during the alloying.
4
lar surface alloyed devices were fabricated as described
above, utilizing a solution comprising 3.5 grams XL—52l
in 100 ml. xylene. It was found that surface alloyed de
vices such as transistors made according to the prior art
had a scrap rate of about 20 percent due to unsatisfactory
alloying and spreading of the electrode pellets. In con—
trast, when the electrode pellets or the semiconductor
The device is completed by ohmically bonding a base
wafers were coated in accordance with the invention with
tab 13 to wafer 10‘, and attaching terminal leads 17 and
a compound selected from the siloxanes and silicones,
19 to collector electrode 11 and emitter electrode 12 re 10 the percentage of units scrapped due to unsatisfactory
spectively. While the device illustrated is a triode tran
alloying and spreading of electrode pellets dropped to
sistor, various other types of devices such ‘as rectifying
less than one percent.
diodes, tetrodes, and hook transistor-s may be fabricated
What is claimed is:
in a similar manner.
1. The method of fabricating a rectifying barrier in
In the above example, the electrode pellets only were 15 a semiconductor wafer of a given conductivity type com
coated with the silicone compound, but it will be under
prising the steps of preparing a pellet of electrode mate
stood that alternatively the advantages of the invention
rial capable of imparting to said wafer conductivity of
may be obtained 'by coating the wafer instead of the elec
the opposite type, coating said Wafer and said pellet with
rode pellets. If desired, ‘both the ‘Wafer and electrode
a thin ?lm of a substance selected from the group con
pellets may be coated. The silicone compound may be 20 sisting of siloxanes and silicones, and alloying said pel-_
applied by any convenient technique, for example, by
spraying a solution of the compound over the pellets or
the Wafers separately, or over the assemblages of pellets
let into said wafer at a temperature sut?cient to decom
pose said ?lm.
2. The method of fabricating a rectifying barrier in
and wafers.
semiconductor wafer of given conductivity type com
It Will be understood that although the method of this 25 aprising
the steps of preparing a pellet of electrode mate
invention has been described in terms of alloying P-type
rial capable of imparting to said wafer conductivity of.
electrode pellets to an N-type wafer, the method is equally
the opposite type, coating said wafer and said pellet with
applicable to the alloying of N-type electrodes on P-type
a thin ?lm of a substance selected from the group con
Wafers. With germanium and silicon wafers, the N-type
electrode pellets include such donors as phosphorus, ar 30 sisting of siloxanes and silicones, drying said coated mem
ber, and alloying said pellet into said wafer at a tem
senic, and antimony. When compound semiconductors
perature su?icient to decompose said ?lm.
such ‘as indium phosphide, gallium aresenide, and the like
3. The method of fabricating a rectifying barrier in
are utilized, appropriate donors are selenium and tel
a semiconductor Wafer of given conductivity type com
lurium, while appropriate acceptors are zinc and cad
prising the steps of preparing a pellet of electrode ma
mium.
35 terial capable of imparting to said wafer conductivity of
In the above example, the organic solvent was xylene
the opposite type, spraying a solution of a compound
but it will be appreciated that other organic solvents
selected from the group consisting of. siloxanes and sili
including aryl compounds such as benzene, toluene,
cones dissolved in an organic solvent over both said
and the like, and alkyl solvents such as acetone, pro
panol, and the like may be utilized instead of xylene. 40 Wafer and said pellet, drying said pellet and said. wafer,
and alloying said pellet into said wafer at a temperature
Other siloxanes such as tetraethoxysiilane, amyl trieth
su?icient to decompose said ?lm.
oxysillane, et-hyl triethoxysilane, phenyl triethoxy silane,
vinyl triethoxysilane, and the like, may be utilized in place
of dimethyl diethoxysilane, since the siloxanes all decom
4. The method as in claim 3, in which said solution
contains at least one-half Weight percent of said com
:silicone oils; while the polymers of relatively high mo
rial capable of imparting to said Wafer conductivity of
the opposite type, coating said pellet and said wafer with
pose and leave a residue of silicon oxides, when heated. 45 pound.
5. The method as in claim 4, in which said organic
Other siloxane compounds having the general formula
solvent consists of xylene.
H3Si(OSiH2)nOSiH3, Where n is an integer, may also be
6. The method of fabricating a rectifying barrier in a
utilized. The exact nature of the silicon oxide residue
semiconductor wafer of given conductivity type, com
is not de?nitely ascertained but it is probably not a single
substance such as silicon dioxide, "but rather a mixture of 50 prising the steps of preparing a pellet of electrode mate
rial capable of imparting to said wafer conductivity of
silicon oxides.
the opposite type, coating said pellet with a thin ?lm of
The class of compounds known 'as silicones also de
a substance selected from the group consisting of silox
compose on heating so as to leave a residue of silicon
anes and silicones, and- alloying said pellet into said
oxides, and hence may also be utilized in the practice of
the invention. The silicones are generally complex pol 55 Wafer at a temperature su?‘icient to decompose said ?lm
and leave a silicon oxide residue on said pellet.
ymers of monomers having the general formula RIRQSiO,
7. The method of fabricating a rectifying barrier in a
where R1 and R2 may be either aryl or alkyl groups.
semiconductor wafer of given conductivity type, com
The silicones which are polymers of relatively low mo
prising the steps of preparing a pellet of electrode mate
lecular weight end to remain liquids and are known as
lecular Weight tend to ‘be solids, and are known as silicone
vresins. An example of a suitable silicone for the practice
a thin ?lm of a substance selected from the group con
sisting of siloxanes .and silicones, and alloying said pellet
of the invention is that commercially available from Dow
into said Wafer at a temperature sufficient to decompose
“Corning as DC-‘200, which may be obtained with vis
cosity ranging from 100 cp. to 200,000 cp. The low vis 65 said ?lm and leaving a silicon oxide residue on said pel
let.
cosity materials are oils, while the high viscosity mate
References Cited in the ?le of this patent
rials approach the properties of a Wax. An example of
a silicone resin suitable for the practice of the invention
UNITED STATES PATENTS
is that commercially available from Union Carbide as
2,796,562
Ellis et al _____________ __ June 18, 1957
XL-52l. Surface alloy devices were fabricated as de 70 2,807,561
Nelson ______________ __ Sept. 24, 1957
scribed above utilizing a solution comprising 1 ml. DC
2,832,702
Schwartz ____________ __ Apr. 29, 1958
200 in 100 ml. xylene to coat the electrode pellets. It
2,913,538
Harrington et a1 _______ __ Nov. 17, 1959
was found that dot spreading was greatly reduced. Simi
2,932,594
Mueller ______________ __ Apr. 12, 1960
It
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