Note: Descriptions are shown in the official language in which they were submitted.
1043466
~ he pre~ent invention relate~ to thyristors of the type
compri~ing a semiconductor body which possesses an emitter
: zone on a ~urface of the body at least partially covered by an
. emitter electrode, a basé zone which lies beneath the emitter
i 5 zone, but appears at the surface of the body and is th~re.con-
ne.cted to a control electrode, a contact electrode supported
on the emitter electrode and having a flat face towards the
. semiconductor body, and an auxiliary emitter zone which i~
.~ arranged between the control electrode and the emitter electrode
i 10 and i~ provided with an auY`iliary emitter electrode.
In combination with the other zones of the ~emiconductor
body, the auxiliary emitter zone has the function of amplifying
: a control current fed into the.de~ice through the control
electrode. ~he control current flow3 from the control electrode
into the base zone and thence to the auxiliary emitter zone. ~he
. latter in~ects charge carriers into the ba~e zone, a~ a result of
. which the control current i~ amplified through the known feedback
mechanism in a four-layer structure and flows through the base
zone as an amplified control current to the emitter zone o~ the
. 20 thyristor.
~ hyristors are generally traversed by high currents and
are therefore contacted by means of a contact electrode having
a large area arranged on the emitter electrode and projecting
. beybnd this electrode. In order that the function of the current-
ampliiying auxiliary emitter zone should be retained, the latter
must not come into electrical contact with the contact electrode.
It has therefore been proposed to displace both the auxiliary : -
emitter zone and the auxiliary emitter electrode into the ba~e of
a pit provided in the ~emiconductor body so that the face of the .~ :
co~tact electrode facing towards the semico~auctor element can be
flat. ~his solut1on i8 however extremely complicated ~ince it i8
~irst nece~sary to produce ~uch a pit and the base of thi~ pit
; 2 ~ .
,
, .
:, , , , - . : , ,
. .,. ~ , . . .
1()43466
must t~en be metallised.
It is an object of the present invention to provide a
thyristor of the type referred to above with which these
problems do not occur.
According to the invention, there is provided a thyristor
comprising a semiconductor body having an emitter zone in a
sur~ace thereof, said emitter zone being at least partially
¢o~ered by an emitter electrode, a base zone extending to said
surface and ~rovided with a control electrode, an auxiliary
emitter 30ne in said surface between said emitter ~on`e and said
~ontrol ele~rode~ said auxiliary emitter zone being provided
with an auxiliary emitter electrode, and a contact electrode
supported on said emitter electrode and pro~ecting over ~aid
auxiliary emitter electrode, said contact electrode having a
15 flat surface facing said semiconductor body, ~herein, in order --
to avoid electrical contact between said auxiliary emitter
electrode and said contact electrode, the thicknes~ of said
auxiliary emitter electrode i9 less than that of said emitter
- electrode 90 that the ~ree surface of said auxiliary emitter is
spaced from the surface of said contact electrode facing said
¦ eemiconductor body.
~ he auxiliary emitter electrode can be produced in a
relatively simple manner by covering the surface of the semi-
Conductor body containing the emitter zone with a metal layer
25 which has a thickness equal to the required thickness of the ~- --
emitter electrode, then using a first photo-mask and a fir~t
etching process producing the de~ired outllne~ of the emitter
electrode and of the auxiliary emitter electrode by etching
away unwanted portions of the metal layer, and ~inally using a
3 second photo-mask and a second etching procéss etching away the
auxiliary emitter electrode to the required thickness.
-- 3
. " ' . ' .' ' -
. ~ , . . . .
~43466
Alternatively, after thc application of the metal layer,
using a first photo-mas~, a first photosensitive lacquer is
applied to the metal surface in a pattern corresponding to and
covering only the areas of the emitter electrode and of the
control electrode, thereafter using a second photo-mask a
second pattern photosensitive lacquer is applied to the suxface .
of the metal layer to cover the area of the auxiliary emitter
electrode, the second photosen~itive lacquer being removable by
a ~olvent which does.not dissolve the first photosensitive
la¢quer, thereafter using a first etching process the unmasked
regions of the metal layer are etched away, the second photo-
sensitive lacquer is removed, and the auxiliary emitter electrode
18 then etched to the required thickness by a second etching
process.
In a further simple alternative, the semiconductor body
i8 covered with a metal layer of the required thickness of the
emitter electrode, then using a fixst photo-mask and a first
etching process a pit whose area corre~ponds to that of the
ausiliaxy emitter electrode is etched into this metal layer, to
a depth such that the residual metal layer below the pit has the
required thickness of the auxiliary emitter electrode, and that
then the portiong o~ the metal layer lying betwee~ the emitter
electrode and the pit are etched away using a second photo-mask :~
and a second etching process. - : -
- ,
The lnvention will now be fuxther described with reference
to the dxanings, in which ~
~igure 1 is a schematic side-sectional view of a thyristor
accordlng to the invention;
~igures 2 to 5 are similar schemat$c side-sectional views
of one half o~ a semiconductox body to il1ustrate
~uccessive ~tages in a first method of producing
the tra~si~tor of ~igure 1
- 4 -
,~ 'si
, ,
- `
1~)43466
.~igures 6 to 10 are similar views to those o~ ~igure~
2 to 5 to illustrate successive stage3 in a
second method of producing the thyristor of
Figure 1; and
Figures 11 to 14 are similar views to those of Figures
2 to 10 to illustrate successive stage~ in a
thixd method of producing the thyristor of
~igure 1.
~he semiconductor element shown in Figure 1 comprises a
9emiconductor body of circular plan with ~our zones of alter-
nating conductivity types, namely an emitter zone 1, a ba~e
zone 2 and two further zones 3 and 4, and also an aù~iliary
emitter zone 5, which is of the same conductivity type as the
emitter zone 1 and lies in the same surface of the semiconductor
body a~ the emitter zone. ~he emitter zone, which is annular in
shape is covered by an emitter electrode 6 whilst the auxiliary
emitter zone 5, which i9 also annular in shape, is electrically ~ ~ -
connected to an annular auxiliary emitter electrode 7, whilst ~
. the base zone 2 is electrically connected to a central control .; `
electrode 8.. ~he auxiliary emitter electrode 7;is also
electrically connected to the base zone 2 at its outer periphery
facing the emitter electrode 6. A large-area contact electrode ~ ~
9 which contacts the emitter electrode 6 is supported on this : ~-
electrode but pro~ects inwardly over the auxiliary emitter . ;.~.-.
electrode 7. Contact with the auxiliary emitter electrode 7
is avoided by making the latter thinner than the emitter ~ .-~
electrode 6 90 that its upper sur~ace lies at a lower level
than the upper surface of the emitter electrode 6. ~he lower .
~urfaces of the two electrodes lie at the same 1evel. ~he .~ :
30 auxiliary emitter electrode 7 may, for example, ~e 15 ~ thick, .. ~ -
whilst the emitter electrode 6 has a thickness o~, ~or example,
30 ~.
.
''''
., . - .
1~43466
~he thicknes~ of the auxiliary emitter electrode 7
which i~ less than that of the emitter electrode 6 can advan-
tageously be achieved by etching making use of the known photo-
masking technique3.
~hree particularly simple processes for the production of
the electrodes of the thyristor of Figure 1 will now be described
with reference to Figures 2 to 5, Figures 6 to 10, and Figure3 11
to 14 respecti~ely. In Figures 2 to 4, the semiconductor body
of Figure 1 provided with ~ones 1 to 5 is shown in a simplified
form at 10. ~o the semiconductor body 10 there is first applied
a metal layer 11 which may consi~t, for example, of aluminium or
~ilver-plated aluminium. ~he metal layer may be, for example,
30 ~ thick. Using the known photo-mask technique, a photo-
lacquer pattern having layers 12, 13 and 14 is produced on the
metal layer. ~he lacquer layer 12 corresponds in shape and area
to the emitter electrode 6, whilst the shape and area of the
lacquer layer 13 correspond to tho~e of the auxiliary emitter
electrode 7 and the shape and area of the lacquer layer 14
correspond to those of the control electrode 8. ~he metal layer -~
11 is now etched away at the areas not covered with lacquer down
to the surface of the semiconductor body 10, as shown in Figure 3.-
~acquer layer~ 15 and 16 are then applied to the electrodes 6 and
8 by mean~ of a ~econd photolacquering step. Finally, (~igure 4)
the auxiliary emitter electrode 7 is etched away to the desired
thickness, for example, 15 ~ t~igure 5). After the removal of
the lacquer layers 15 and 16 the semiconductor element is con-
tacted with the contact electrode 9 in known manner.
The alternative electrode production process illustrated
in Figures 6 to 10 basically differs from that illustrated in
Figure~ 2 to 5 only in that the area of the auxiliary emitter
electrode 7 i~ covered with a lacguer layer 18 which consists of
a different photo-lacquer v~hich can be dissolved by a ~olvent
- 6 -
~)434~;6
which does not dissolve the lacquer layers 12 and 14. ~he
lacquer layer~ ~2 and 14 can, for example, be made of the
known negative lacquer R~R manufactured by Kodak which is
soluble in ~he known lacquer solvents, whilst the lacquer layer
18 can be made of a kno~n positive lacquer, e.g. that known a~
v ~ 1350H made by Shipley, which is soluble, for example, in
acetone. After the application of the lacquer layers 12 and 14
(~igure 6) and the lacquer layer 18 (Figure 7), the metal layer
11 is etched away at its exposed areas down to the semiconductor
body 10 (Figure 8). ~he lacquer layer 18 is then removed without
affecting the layers 12 and 14, an~ the auxiliary emitter
electrode 7 is etched to the required height of, for e~ample,
t5 ~ (Figure 9). After the removal of the lacquer layers 12 and
14 the semiconductor element is contacted in known manner with
the contact electrode 9.
In a further proce~ illu~trated in Figures 11 to 14, the
metal layer 11 is covered with lacquer layers 20 and 21 which
leave exposed between them an area whose shape corresponds to the
shape of the auxiliary emitter electrode. ~hen, using, for
example, a phosphoric acid - acetic acid mixture, a pit 22 is
etched into the metal layer 11 to such a depth that the remaining ~ -
metal layer below the pit corresponds to the required thickness
of the auxiliary emitter electrode. ~he layers 20 and 21 are
then removed and photo-lacqùer layers 24 and 25 whose 3hape and
area correspond to those of the emitter electrode and the
control electrode respectively are applied to the me-tal surface.
At the same time, the base of the pit 22 i~ covered with a --
lacquer layer 23. ~he metal layer between the pit and the lacquer
layers 24 and 25 is then etched away down to the semiconductor
body 10. After the removal of the layer~ 23, 24 and 25, the ~-
semiconductor element i8 contacted in known manner with the
contact electrode 9,
~ t~ 7
,. . , .. ' '' '"' ..
