Note: Descriptions are shown in the official language in which they were submitted.
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2901-619D
This is a divisional application of copending
Canadian patent application Serial No. 414,043 filed October 22,
1982, assigned to Raytheon Company.
This invention relates yenerally to semiconductor
de~ices and more particularly to semiconductor devices adapted
to operate with high levels of microwave power.
As is known in the art, it is frequently desirable to
use microwave diodes in a variety of high power applications.
When used in such applications the diode may be mounted to a
pedestal shaped heat sink used to extract heat from the diode.
Further, in the fabrication of individually mesa shaped diodes,
prior to dicing the wafer into individual diodes a wafer used
to form such diodes has disposed on the entire back surface
thereof a thick plated heat sink. After separating the diodes
thls thick plated heat sink is mounted to the pedestal shaped
heat sink. When the material of the pedestal heat sink has a
higher thermal conductivity than the material of the thick
plated heat sink forming part of the mesa shaped diode, it is
desirable to minimize the thickness of the thick plated
heat sink in order to minimize the thermal resistance of the
diode. However, a thick plated heat sink generally is required
to provide structural integrity to the wafer after the diodes
have been formed into mesas. This is because after mesa
definition, the wafer of mesa shaped diodes is supported only
by the gold plated heat sink structure and further photo-
lithographic steps and processing steps are still generally
required after the mesa definition. Therefore, if the heat
sink is too thin the structure supporting the mesa shaped
diodes may flex, bend, or crease making it difficult to
handle during the additional photolithographic and processing
12~3~
steps, thus resulting in lower device yields.
As also known in the art, a critical step in the
assembly of microwave power diodes is the step of mounting the
diode in a microwave package and the subsequent interconnection
of the diode to the package terminals. Generally, the inter-
connection is accomplished by soldering the plated heat sink
into the package to form a first contact and using a wire pre-
form attached to the top of -the mesa shape diode as a second
contact. The wire preform is typically ultrasonically bonded
to the top of the mesa shaped diode. This packaging technique
has several short comings, however, particularly when applied
to millimeter wave diodes. The mesas shaped millimeter wave
diodes are comparatively small and fragile compared to X-band
diodes, for example. This imposes several constraints on the
bondiny operations and the preform lead wires: bonding forces
and ultrasonic power must be kept to a minimum, often producing
a bond of questionable strength, bonding tool diameters must
be small in order to avoid excessive force on the mesas tops
and damage by off center bonds, and lead preforms are difficult
to precisely shape leading to unpredictable package parasitics,
resulting in degraded device performance~ Moreover, lead
bonding is a costly and time consuming process requiring a
high degree of bonding operator skill.
As is also known in the art, it is frequently desir-
able to use a plurality of individual mesa-shaped diodes with
the mesa shaped diodes having a total area equal to an equival-
ent single mesa shaped diode. A plurality of individual diodes
adapted to operate at X-band may be individually mounted in
a package. However when the diodes are designed to operate
at multimeter wavelengths, for example, their size is so small
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that mounting them individually to provide a plurality of diodes
in such a package is difficult.
In accordance with one aspect of the invention a wafer
including a plurality of mesa shaped diodes, each having a thin
plated heat sink attached to one surface thereof, is supported,
for metallization processing by a thicker support structure
having a plurality of apertures, such apertures defining the
areas of the thin plated heat sink. After metallization and
subsequent dicing each diode device has a relatively thin plated
heat sink. The diode device thus will have a lower thermal
resistance than diode devices having thicker plated heat sinks,
a feature particularly desirable when the diode device is
mounted on a material having a higher thermal conductivity
than that of the plated heat sink. The support structure pro-
vides the necessary structural integrity to the plurality of
mesa diodes for the metallization processing. In addition, the
apertures provided in the thick support may be used to align
a dicing mask used for dicing the wafer into individual mesa
shaped diode devices.
In accordance with another aspect of the invention a
multi-mesa shaped diode device is provided having an upper elec-
trode formed by depositing a layer of photoresist over top sur-
faces of the diodes forming a plurality of apertures in the
photoresist layer aligned with the top surfaces of the mesa shap-
ed diodes, substantially levelling the photoresist layer to the
top surfaces of the mesa shaped diodes, providing a layer of an
adherent material on the photoresist layer, and providing
a layer of a conductive material on the adherent layer. A
plurality of apertures having a diameter smaller than the
corresponding diameter of the top surfaces of the mesa shaped
~LZ~ r~oi~3
diodes is formed through the adherent layer and layer of con-
ductive material. A second layer of photoresist is then
provided which defines an upper electrode pattern such as over-
lay or beam lead pattern. The electrode pattern is then plated
directly to the top surfaces of the diodes thus forming the
upper electrode pattern for the device. With such a structure
a multi-mesa diode device having a top electrode pattern on a
top surface thereof interconnecting each of the individual
mesa shaped diodes is realized. The top electrode pattern
provides support for the multi-mesa diode structure after
dicing. During packaging, the top electrode pattern provies a
lead pattern which can be made thicker, wider and heavier than
that used with ultrasonically bonded preform leads thereby
reducing the series, resistance and inductance of the diode.
Further a multi-diode device adapted to operate at multimeter
wavelengths may be easily packaged since the plurality of diodes
are integrally formed as a single device.
In accordance with one aspect of the invention a
multimesa diode device having a thin heat sink attached to one
surface of each mesa shaped diode and an upper electrode attach-
ed to a second surface thereof is provided by: plating a heat
sink layer on a surface of a wafer of semiconductor material;
masking selected portions of the plated heat sink layer; and
plating the unmasked portions of the layer to increase the thick-
ness thereof to provide a support layer. A plurality of multi-
mesa diodes are formed in regions of the semiconductor material
disposed on the masked portions of the plated heat sink layer
Upper electrodes used to support the multimesa diode of the
device after dicing of the wafer are provided by: depositing a
layer of photoresist on the heat sink layer and the mesa shaped
diodes; providing apertures in the photoresist layer; levelling
~Zl;3Çi ~'9
the photoresist layer to the mesa tops; providing a metaliza-
tion layer on the photoresist layer; and providing a plurality
of undersized apertures in the metalization layer aligned with
the mesa tops. A second layer of photoresist is then provided
on the metalization layer and is patterned to expose portions
of the metalization layerO The upper electrodes are then
plated directly onto por~ions of the metalization layer ex-
posed by the photoresist layer. The photoresist layers and
metalization layer are removed and the multimesa diode devices
are diced apart. With such an arrangement a multimesa diode
device is provided with a thin heat sink on one surface and a
top electrode on the second surface. The thermal transfer
advantages of the multimesa diode device are thus realized
without the packaging and handling difficulties generally asso-
ciated with individual diodes.
Broadly, according to one broad aspect, the invention
of this divisional application provides a semiconductor
device comprising: a mesa-shaped diode having upper and lower
mesa portions; a first electrode contact disposed on a first
one of upper and lower mesa portions of said mesa~shaped diode;
and a second electrode contact comprising a thermally conduc-
tive material having a thickness in the range of one micron
to two microns disposed on a second, different one of upper
and lower mesa portions of the mesa-shaped diode, with said
second electrode contact providing a heat sink portion of said
mesa-shaped diode.
According to another broad aspect, the invention pro-
vides a semiconductor device comprising: a plurality of mesa-
shaped diodes, each mesa having upper and lower mesa portions
and each interconnected by a first electrode contact disposed
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on a corresponding first one of upper and lower mesa portions
of said plurality of mesa-shaped diodes; and a plurality of
second electrode contacts comprising a thermally conductive
material having a thickness in the range of one micron to two
microns disposed on a corresponding second, different one of
upper and lower mesa portions of each of said mesa-shaped
diodes, with said second electrode contacts each providing a
heat sink portion of the corresponding mesa-shaped diode.
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Brief Description of the Drawings
For a better understanding of the invention, reference
is made in the following detailed description to the drawings
wherein:
FIGS. 1-4 are a series of fragmentary isometric cross-
sectional views showing steps in the construction of single
mesa shaped diode device having a thin heat sink layer in
accordance within the invention;
FIG. 5A is a cross-sectional view useful in under-
standing a dicing operation of a wafer of diodes having the
thin heat sink layer provided in accordance with Figs. 1-4;
FIG. 5B is a top view of the cross-sectional view of
Fig. SA showing the photoresist pattern used in the dicing
step;
FIG. 5C is a cross-sectional view of a mesa shaped diode
having a heat sink in accordance with the invention;
FIGS. 6-8 are a series of fragmentary isometric partially
broken away views showing steps in the construction of a
multimesa diode device having a thin heat sink layer and beam
leads;
FIG. 9 is a isometric view of a multimesa diode device
constructed in accordance with Figs. 6-~ having thin heat
sink layer and beam leads;
FIG. 10 is a fragmentary isometric partially broken away
view showing the diode cluster of Fig. 7 with a first layer of
photoresist used in fabricating interconnect patterns in
accordance with the invention;
FIGS. 11-13 are a series of cross-sectional views showing
steps in the construction of the interconnect patterns;
FIGS. 14-15 are a series of fragmentary isometric partially
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bro~en away views showing the steps in the construction of an
overlay in accordance with the invention on a wafer at the
stage of processing shown in Fi~. 13;
FIG. l~A is a isometric view of a plurality of diodes
interconnected by a overlay in accordance with the
invention.
FIGS. 16-17 are a series of fragmentary isometric
partially broken away views showing the steps in the con-
struction of beam leads, for a single mesa diode device in
accordance with the invention;
FIG. 17~ is an isometric view of a diode device having
a beam lead pattern in accordance with the invention;
FIG. 18 is a top view of an interdigitated beam lead
pa~tern;
FIG. 19 is a cross sectional view of a single mesa diode
device having a thin heat sink layer and beam leads, mounted
in a ceramic ring package in accordance with the invention;
and
FIG. 20 is a cross-sectional view of a multimesa diode
device having a thin heatsink and overlays mounted in a ceramic
ring package in accordance with the invention.
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Description of the Preferred Embodiments
-
Construction of semiconductor devices having thin heat
sink layers in accordance with the teachings of the present
invention will be described in conjunction with the isometric
cross-sectional views of Figs. 1 through 4. Referring first
to Fig. 1, a substrate 25, here conductive gallium arsenide
(GaAs~, is shown to include an active layer 24 of epitaxially
grown semiconductor GaAs. Active layer 24 may have one of
many different doping density profiles depending upon the
particular application for the diode. here, for example, a
doping density profile described in my U. S. Patent 4,160,992
issued July 10, 1979 and assigned to the assignee oL this
invention is used. A first metal layer 26, here of platinum
(Pt), is sputtered upon the active layer 24 to a thickness in
the range of 10~ Angstroms to 200 Angstoms ~A). A second metal
layer 28, here of titanium (Ti), is then sputtered over the
platinum layer 26 to a thickness of 1000 A to 2000 A. Titanium
is the preferred material although tungsten, hafninum, or
other refractory metals may be used for layer 28. Upon the
layer 28 a 1000 A to 2000 A thick layer 29 of highly conductive
gold is evaporated, forming the lower contact for the diode
device. Next, a thermally and electrically conductive heat
sink layer 30, here of gold one to two microns thick, is plated
over evaporated gold layer 29. A layer 31 of photoresist is
then deposited on the plated gold layer 30, as shown.
Referring now to Fig. 2, the photoresist layer 31 is
masked, developed, and chemically etched away in selective areas
using well known photoresist techniques, to leave portions 32,
thereof, remaining over selected regions of the plated gold
3n heat sink layer 30, as shown.
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Now referring to Figure 3, a support layer 36 is
formed by plating the unmasked portions of the thin heat sink
layer 30 with gold, here to a thickness of ten microns. The
regions 32 (Figure 2) of photoresist layer 31 are removed
leaving an apertured support layer 36. It is noted that the
heat sink layer 30 remains at the original thickness but the
support layer 36 is made sufficiently thick to provide struc-
tural integrity for -the diodes to be formed in wafer 21 in a
manner to be described hereinafter. Suffice it to say here,
however, that the support layer 36 has formed therein a plur-
ality of apertures 34 corresponding to areas where the photo-
resist pattern 32 (Figure 2) was provided. The plurality of
apertures 34 define the areas of the thin plated heat sink
layer 30.
Referring now also to Figure 4, the substrate 25, is
thinned to a predetermined thickness, a plurality of top con-
tacts 22 are provided on the top of the thinned substrate 25
and a plurality of mesa shaped diodes 20 are formed from the
thinned substrate 25 and active layer 24 between the top
contact 22 and platinum layer 26, as shown. Where the doping
profile of the active layer 24 is as described in above-
mentioned U.S. Patent 4,160,992, the mesa-shaped diodes are
IMPATT (impact avalanche transit time) diodes. The plurality
of top contacts 22 are formed by first depositing a photo-
resist layer (not shown) on the thinned substrate 25. The
photoresist layer is masked, developed, and chemically etched
away in predetermined locations using well-~nown photoresist
techniques leaving a plurality of here circular apertures on
the photoresist layer (not shown). Each circular aperture
(not shown) is precisely aligned with a corresponding one of
121~ 9
the plurality of apertures 34 in the thick gold plated support
36. The circular apertures (not shown) are then plated with
gold forming the previously mentioned top contacts 22. The
alignment for the top contacts 22 to the apertures 34 is
realized by a front to back alignment
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step of the top contact mas~ (not shown) used to provide the
photoresist pattern for the circular gold contacts 22. A
general front to back alignment procedure is described in U. S.
Patent No. 4,169,992, previously~mentioned. The plurality of
mesas diodes 20 are formed between the top contacts 22 and the
platinum layer 26. The mesa diodes 20 are formed by providing
a pattern in photoresist on the thinned su~strAte 25, using
well known photoresist techniques. The alignment of the mesa
forming mas~ (not shown~ used in forming the pattern for the
mesa diodes 20 is realized by the front to back alignment
technique as described in U. S. Patent No. 4,169,992, referred
to above. After mask alignment, the mesa diodes 20 are formed
~y chemically etching away portions of the thinned substrate
25 and active layer 24 between the the top contact layer 22
and the platinum layer 26, as shown. Thus mesa diodes 20
formed from the thinned substrate 25 and active layer 24 are
supported by the support layer 36.
Referring now to Figs. SA and SB, the wafer 21 having a
plurality of mesa diodes 20 is mounted on a wafer support 40
with a non-reactive wax 44 filling the space between and around
mesa diodes 20 and gold contacts 22, as shown. The wafer 21
with the wax protected mesa diodes 20 is pressed against the
upper surface of support 40. A photoresist layer is deposited
on the plated support layer 36 of the wafer 21. A dicing mask
(not shown) is provided on the plated support layer 36 of the
wafer 21, and using well known photoresist techniques, a dicing
pattern 38 of photoresist is produced. The apertures 34 in
the thick plated support layer 36 are here used to align the
dicing mask. The diodes 20 are diced from the wafer 21 within
regions 39 provided in the dicing pattern 38 of photoresist.
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The wafer 21 is here placed in a spray etching system of a
type described in U. S. Patent 4,160,9~2 mentioned previously.
The spray etch system (not shown) provides an etchant (not
shown) which completely etches through the exposed portions 3g
of layers 30, 29, 28 and 26 to separate the diode devices from
the thick support layer 36. After dlcing, the individual diode
devices 46 an exemplary one thereof being shown in Fig. SC, may
be collected and cleaned using any well known technique.
Referring now to Fig. 6, a wafer 121, includes a plurality
of clusters, or sets, of mesa shaped diodes 42 (each cluster of
mesa diodes 42 having a total area equal to a single mesa diode
equivalent) formed over a corresponding plurality of apertures
34 provided by the thick plated support 36, as shown. The
wa~er 121 is formed in a similar manner as wafer 21 shown in
Fig. 4 except during mesa definition a cluster mask (not shown)
is provided to produce a pattern in a layer of photoresist
corresponding to a plurality of clusters of mesa diodes. This
cluster mask (not shown) is front to back aligned as explained
in U. S. Patent 4,160,992, previously mentioned. The plurality
of the clusters of mesas diodes 42 are formed by chemically
etching away portions of the substrate 25 between the top
contact layer 22 and the platinum layer 26, as previously
explained.
Now referring to Fig. 7, the wafer 121 is placed in a
sputter etching system (not shown) and portions of the layer
26 of platinum unmasked by the di~des 20 are removed. A chemical
etch here a two percent solution of hydrofloric acid (2~ HF:H2O)
is then used to remove portions of layer 28 unmasked by diodes
20. The wafer 121 at this point has the layer 26 of platinum
and the layer 28 of titanium removed in all areas except for
6 ~'~
those areas forming part of the individual mesa diodes 20 of
each cluster of mesa diodes 42, leaving gold layer 29 exposed
on the mesa diode side of the wafer 121. Exposing gold on the
mesa diode side of wafer 121 is used to particular advantage
in a dicing op~ration to be described in conjunction with Fig.
8 and Fig. 9.
Now referring to Fig. 8 and Fig. 9, beam leads 48 are
here shown attached to the cluster of mesa diodes 42 for
reasons to be described in cor.nection with Figs. 16-17. Suffice
it to say here, however, that the thick plated support layer 36
is used to support the individual mesa diodes 20 at this stage
in the processing while the attached gold plated beam leads 48
provide support for the individual mesa diodes 20 during and
after the dicing operation. As shown in Fig. 8, gold is exposed
on the upper s~rfaces of the wafer 121. A layer of wax 45 is
here provided on the bottom side of the wafer 121, completely
filling in the apertures 34 of the gold plated support layer 36.
The wafer 121 and wax layer 45 are supported by a wafer support
41. Since gold is exposed on both sides of the wafer 121 a
gold etching solution is here used to etch from the mesa diode
side of the wafer with the plated heat sink side mounted down.
Here, the wafer 121 is placed in a conventional emersion bath
of etchant (not shown). The etchant flows on the mesa side of
the wafer 121, but substantially below the tops of the mult-
mesa diode device 120, and thus the etchant does not attack
the beam leads 48. This technique,uses the mesa shaped diodes
20 themselves as a mask during the dicing procedure. Since
the gold layers 29, 30 exposed on the mesa diode side within
the aperture 34 of the thick gold plated support layer 36 are
substantially thinner than other exposed gold areas, the
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portions of the gold in layers 29, 30 disposed over the aperture
34 will etch âway beore other gold areâs of the diode cluster
42 âre significantly disturbed thus forming clusters, or sets,
of here four diodes in each device 120 as shown in Fig. 9.
Referring now to Fig. 10, a wafer 121' will be processed
in âccordance with an âlternative embodiment of the invention.
Thus, wâfer 121' is shown in Fig. 10 at an equivalent stage of
processing âS the wafer 121 shown in Fig. 7, however here
wafer 121' is provided with a first thick layer of photores~st
60, as shown. A plurality of apertures 66 aligned with the
mesa top contacts 22 are formed in the photoresist 60 to
exposure the top contacts 22 using well known photoresist
techniques. The photoresist layer 60 is then levelled with
the top contacts 22 by conventional techniques such as
controlled light exposure or mechanical lapping.
Referring now to Fig. 11, zn adherent layer 62 here of
titanium, approximately 200 A thick is sputtered over the to?
of the wafer section 121'. Other metals such as molybedenum,
nickel, nickel-chrome and similar metals or metallic systems
may be used for the adherent layer 62. A conductive layer
64 here a 200 A thick layer of gold is sputtered over the
adherent layer 62 of titanium. Other conductive metals such
as platinum, silver and copper may be used for conductive
layer 64. The preferred combination, however, is titanium-
gold, because this combination provides a contact system
virtuâlly alloyless and is not subject to loss of adhesion.
The adherent layer 62 is sputtered within the apertures 66
(Fig. 10) formed in the photoresist 60. The adherent layer 62
provides a contact layer interconnecting the individual diodes
20 (Fig~ 10) in each cluster of diode 42 (Fig. 2).
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Now to referring to Fig . 12, the wafer 121' is provided
with a second layer 68 of photoresist. The layer 68 of
photoresist is masked, developed, and etched away in selective
areas using well known photoresist techniques to provide a
pattern in the photoresist layer 68 of a plurality undersized
circular aperatures 67 aligned to the diode top contacts 22.
Referring now to Fig. 13 the first layer 62 and the second
layer 64 are selectively removed from the mesa tops 22, within
each of the apertures 67 formed in the photoresist layer 68.
A plurality of apertures 69 are thus formed in layers 62 and
64. A thin layer of the first layer 62 and the second layer
64, thus remain attached to the eZges of the mesa tops 22,
because the apertures 69 are smaller than the mesa diode top
contacts 22. The wafer 121' at this stage of processing
may be provided with either a plurality of top electrode
contacts su~h as the overlays shown in Fig. 15 or the beam
leads shown in Fi~. 17. Selection between the gold overlay
pattern (Fig. 15) or the beam lead pattern (Fig. 17) is here
primarily determined by the physical size of the mesa diodes.
For example, for X band quadramesa diodes where the mesas are
relatively large in comparison to millimeter wave mesas, the
use of a beam lead interconnect is here impractical. This is
because on a given wafer of semi-insulating material such as
GaAs as used here, relatively few beam lead devices can be
manufactured for X-band diodès due to the relatively long
lengths of the beam leads in relation to the size o the mesa
diodes. Here, the gold overlay structure is provided to inter-
connect the quadramesas X-band diodes to provide a more
eficient interconnection scheme and thus a more efficient
utilization of the area of the wafer 121'. However, for
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millimeter wave quadramesa diodes having relatively small
mesas compared to X-band mesa diodes, a dense pattern of beam
leads is plated to the mesa diodes to provide the interconnect
portion for the mesa diodes. Fabrication of beam leads diodes
are described in conjunction with Figs. 16 and 17.
Referring now to Figs. 14 and 15 fabrication of an overlay
70 (Fig. 15) for interconnecting each mesa diode 20 of the
cluster of mesa diode 42 in accordance with the invention will
now be described. Referring first to Fig. 14, a wafer 121'
in the same stage of fabrication as that shown in Fig. 13, is
provided with a layer of photoresist 71. The photoresist layer
71 is deposited on the second layer 54 and is masked, developed
and etched away in selective locations using well known photo-
resist techniques to form a plurality of apertures 72.
Referring now to Fig. 15, the gold overlay 70 is plated
to a thickness of here four microns within the areas exposed
by the apertures 72. These overlays 70 interconnect each of
the diodes 20 within each of the plurality of clusters of diodes
42. Further the overlay provides the support for each diode 20
of the cluster of diodes 42, after dicing. The overlay pattern
70 may be plated to any desired thickness, typically however,
the thickness is in the range of four microns to ten microns.
After plating the titanium layer 62, the gold layer 64, the
thick photoresist layer 60, and the photoresist pattern 72 are
removed from the wafer by conventional means leaving the ~afer,
as shown. Since gold is exposed on both sides of the wafer
121', a gold etching solution is here used to etch from the
mesa diode side of the wafer 121'. The emersion etching
technique described in conjunction with Fig. 8 is here used
to dice the wafer 121'. Thus, the quadramesa diodes
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interconnected by the gold overlay 70 are used as a mask during
the dicing operation. Since gold exposed in the region of the
aperture 34 of the thick plated support 36 is substantially
thinner than other exposed gold areas the gold in the region
of the aperture 34 will etch through before other gold areas
of the cluster of mesa diodes 42 or the gold overlay 70 are
significantly disturbed thereby ~orming four diode devices, an
exemplary one thereof~ here device 50, as shown in Fig. 15A.
Fabrication of mesa diodes having plated beam leads 80
is next described in conjunction with Fig. 16 and Fig. 17.
Re~erring first to Fig. 16 a wafer section 21', in the same
stage of construction as that shown in Fig. 13, includes a
plurality of individual diode elements 20, as shown. The
wafer 21' now is provided with a second layer 82 of photoresist.
This photoresist layer 82 is disposed on the second layer
64, and is masked, developed and etched away in selective
locations using well known photoresist techniques to form a
pattern 84 for the beam leads.
Referring now also to Fig. 17 the ~eam lead pattern 84 is
plated to the diodes 20 in the areas exposed within the photo-
resist layer 82. The beam lead pattern may be plated to any
desired thickness, typically however, the thickness is in the
range of four microns to ten microns. The photoresist layer 82,
titanium layer 62, the gold layer 64 and the thick photoresist
layer 60 are then removed using well known techniques leaving
the mesa diodes 20 with plated beam leads 48, as shown. Since
gold is exposed on both sides of the wafer 21 a gold etching
solution is here used to etched from the mesa diode side of
the wafer 21 as previously explained in conjunction with
Fig. 8 to separate the diodes into individual devices 52, and
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exemplary one thereof, here device 52, as shown in Fig. 17A.
Alternatively, the overlays 70 or the beam leads 48 may
be formed on the diodes after the wafer has been diced, as
explained in conjunction wlth Fig. 8. In this case, the wafer
having been diced is still supported by a wafer support 41
and a wax layer 45 filling in the apertures 34 o the support
36, as shown in Fig. lS and Fig. 17. The beam lead or overlay
interconnect patterns are then formed as explained above, and
the diodes with the plated interconnects are then dismounted
from the wax 45. This provides a method whereby the inter-
connect structure is not exposed to the etchant used in the
dicing operation, since the interconnect pattern is no~ present
during the wafer dicing step.
Now referring to Fig. 18, a portion of a tightly packed
beam lead pattern 84 which may be plated directly to an entire
wafer provides a plurality of mesa diodes, as shown. This
pattern is provided for interconnecting single mesa or multi-
mesa diodes.
Referring again to Figs. 8-9, the beam lead quadramesa
diode 120 having the plated beam leads is for~ed in the same
manner as the single mesa diode device 52 having plated beam
leads, except for the use of a multimesa mask, for defining the
diode mesas. The beam lead pattern as shown in Fig. 18 is here
also used to provide the pattern of beam leads in photoreslst
for the multi-mesa diode.
Referring now ~o Fig. 15, the single mesa diode device 52
having plated beam leads is here mounted in a package 10, as
shown. The package 10 includes a conventional stub support 18
here of copper having a screw slot 19, for package mounting.
The stub support 18 here supports a pedestal 16 which is h~re of
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gold plated diamond. The thicXness of the gold plating on the
diàmond pedestal 16 is here 2 microns thick. Alternatively the
pedestal 16 may be embedded in the stub support 18 or may be
formed from the stub support 18.- A conductive ring 17 here
gold plated copper is spaced from the stub 18 by a insulating
ring spacer 14. The insulating ring spacer 14 is here ceramic
but may be quartz or any other suitable insulating material.
The plated heat sink side of the diode 20 is here mounted to
the pedestal 16 by a thermal compression bond. Mounting the
diode 88 to the pedestal 16 causes the beam leads 48 to bend
upward and extend up toward the edge of the con2uctlve ring
17. Thermal compression bonds are here used to bond each of
the beam leads to the conductive ring 17. A conductive lid
19 is then provided to add further support to the package 10.
The lid 19, here gold plated copper is thermal compression
bonded to the conductive ring 17 and may form a hermetic seal
between ring 17 and lead 19. This structure provides a package
10 wherein a diode 20 having extended beam leads 48 as top
electrodes, which are bonded to the conductive ring 17 using a
thermal compression bond on the plated leads, without having to
bond a lead to the diode mesa itself. Diode package 10 should
have lower parasitic capacitance and inductance than other
diode packages, thus enhancing the diode's electrical charac-
teristics.
Referring now to FIG. 20, a multi-mesa diode device 50
interconnected by an overlay pattern is pac~age in a diode
package 90 as shown. The package 90 includes a conventional
stub support 18 here of copper having a screw slot 19, for
package mounting. The stub support 18 here supports a pedestal
16 which is here of gold plated diamond. Alternatively, the
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pedestal 16 may be embedded in the stub support 18 or may be
formed from the stub support 18. A conductive flange 13 here
gold plated copper is spaced from the stub 18 by an insulating
ceramic ring spacer 14. The insulating ring spacer is here
ceramic buy may be quartz or any other suitable insulating
material. The plated heatsin~ side of the multimesa diode
device 50 is here mounted to the pedestal 16 by a thermal
compression bond. A gold ribbon strip 15 is then thermally
compression bonded to the conductive flange 13 and the overlay
70. A conductive lid 19 is then provided to add further support
to the package 10. The lid 19, here gold plated copper is
thermal compression bonded to the conductive flange 13 and may
form a hermetic seal between flange 13 and lid 19.
From the foregoing, it will be apparent that all of the
objectives of this invention have been achieved by the
structures shown and described herein. It also will be
apparent, however, that various changes may be made by those
skilled in the art without departing from the spirit of the
invention as expressed in the appended claims. It is to be
understood, therefore, that all matter shown and described
herein is to be interpreted as illustrative and not in a
limiting sense.
DGM:jp
Case No. 32784
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