Note: Descriptions are shown in the official language in which they were submitted.
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The present lnvention relates t~ semiconductor component-
~having a se~iconductor element which consists of sillcon.
A basic pro~lem with semiconductor components is Xeeping
the current-voltage characteristlc stable. In the case of
rectifiers and transistors, the important characteristic ~
that in the blocking d~rection, whereas in the case o~ thyris-
- tors, the attention must be given to the stabil~ ty of the
characteristics in bo~h the block~ng and the tri~ger~ng direct-
lons. It is already known to passivate the surfaces of the
semiconductor elements of such semiconductor component~ by
applying various organic or inorganic surface layers thereto.
Lacquers, rubbers and glass ha~e, for example, already been
: proposed for this purposeO Generally speaking, it is possible
;~ to achieYe an adequate stability of the char cteristic by the
use of such surface layers. However, on occas~on instabilitles
have been found to occur, the causes of whlch may be found in
unrecognised changes 1n the properties of the surface layers
and~or of the surface of the semicond~ctor element. In the
past, this has frequently led to heavy fluctuations in the
2Q yield of serviceable semiconductor components.
It has ~ ready been proposed to passivate a semiconductor
element by thermally ~rowing a s~licon layer thereon. Howev~r
this passivation process is extremely t~me-consu~ing and compl~-
cated and, ~n additlon, necessitates the use of temperatures of
between 600 and 700 C., which rules out its use for components
which have ~ready been contacted, and possibly soldered. It ls
also necessary to etch away the sllicon layer at those areas at
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which it is not required.
It is an object of the present invention to provide a
semiconductor component having a semiconductor element provided
with a passivating silicon surface layer with which a substanti-
ally stable current-voltage characteristic can be achieved at a
basically low cost.
According to the invention, there is provided a semi-
conductor component comprising a semiconductor element made of
silicon having at least one pn-junction, that extends up to the
surface of the semiconductor element, and a passivating protect-
ive layer of silicon, that is deposited on the semiconductor
- element by evaporation of silicon at least at that point where
the pn-junction comes to the surface of the semiconductor ele-
ment, wherein the vapour-deposited silicon contains at least one
reactive gas.
The vapour-deposited silicon layer may also contain
one or more dopants and/or metals. Preferably, the thickness of
the vapour-deposited silicon layer is at least O.l~um. In order
to increase the dielectric spar~-over resistance, the vapour-
deposited silicon layer may be provided with a further pro-
tective layer.
The invention will now be further described with
reference to the drawing, in which:
Figure 1 is a schematic side-sectiona' view of a thy-
ristor in accordance with the invention; and
Figure 2 is a schematic side-sectional view of part of
a thyristor similar to that shown in Figure 1 to illustrate
operation of the component.
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Referring to Figure 1, a thyristor has a semiconductor
- element having four zones, a cathode-side emitter zone 1, a
cathode-side base zone 2, an inner base zone 3, and an anode-
side emitter zone 40 P-n junctions 5, 6 and 7 are located be-
tween the zones 1 and 2, 2 and 3, and 3 and 4 respectively.
The semiconductor element consists of silicon, and the zones 1,
2, 3 and 4 are doped in the usual manner in accordance with the
purpose for which the semiconductor component is to be used.
A protective layer 8 which consists of vapour-deposited
silicon is arranged on the peripheral surface of the semiconductor
element. This protective layer has a thickness of 0.1 /um. It
may, however, be thicker, for example, it may have a thickness of
1 /um. In order to increase the dielectric spark-over resistance~
a further protective layer 9, which may consist, for example, of
standard rubber or of a protective lacquer, is arranged on the
vapour-deposited silicon layer 8.
The silicon layer 8 may contain one or more dopan~s,
such as, for example, boron or phosphorus. One or more reactive
gases, such as, for example, o~ygen, can also be incorporated in
the silicon layer. The layer 8 may also contain one or more
metals, such as, for example, aluminium. These additives serve
to influence the specific resistance and conductivity type of the
layer 8. By changing ~he specific resistance, it is possible to
adjust the potential co~ditions at the peripheral surface of the
semiconductor element. The layer 8 may be doped, for example~ ~ith
phospho~us, and may have a specific resistance, of, for example, ;
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106 Ohm cm.
As already mentioned, the thickness o~ the layer 8 may
be between 0.1 and 1 ~m. This layer has been vapour-deposited
using a conventional vacuum-vapour-deposition system at a
pressure of 5 x 10 6 ~orr. ~ silicon block may for example be
used as the s~licon source. The energy source used to vaporise
the silicon ~ay, for example, be an electron beam. Us~ng an
electron beam at an acceleration voltage of 8 kV and a current
o~ about 0.5 amps, a vapour-deposi~ion rate of 0.2S ~mfmin can
be achievet. The vapour-deposition rate can be increased, for
example, to 0.5 ~m/min by increaslng the electron current andf
or by ~ncreasing its ener~y. It is also possible to construct
the layer 8 of a plura~ity of su~-layers haYing di~ferent
granule sizes. In thi~ way, it ls possible to achieve a change
in ~he specific resi~tance within the thic~ness of the layer 8
and th~s to influence the potential cond~tions at the per~pher~
surface of the semiconductor element. Sub-layers of different
granule size can be produced, for example, by using different
growth rates for the deposited sil~con~
An essential ad~antage of using a vapour-deposited
silicon layer is that the substrate, i.e. the semiconductor
element? can remain cold during the vapo~r-depos~tion. EYen
with other methods of vaporisat~on, for example, using radiat-
ion heat, the semiconductor element can be ma~ntained at room
temperature, for example~
Semiconductor elements which have ~een provided with a
passivation layer made of vapour-deposited silicon~ exhibit a
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surprisingly good current-voltage characteristic stability.
This applies both to the characteristi~ in the blocXing
directlon in the case of diodes and transistors, and also to
the characteristics in both the blocXing and triggering
directions, ~n the case of thyristors. Thls may be estab-
lished, for example, by using known photoelectric methods to
investigate the space-charge zones at the periphery of a semi-
conductor element.
Figure 2 illustrates the form of the space-charge zone
10 in a conventional thyr~s~or without a layer ~ when the p-n
~unction 7 i5 ~iased ~n the blocking direction. At the start
~f the blocking biasing, the boundaries 11, 12 of the space-
charge zone 10 run approximately parallel to t-he p-n ~un~tions.
If the bloc~ing b~as persists for a long period, the space-
rharge zone expands in that the boundary 12 of the space-
char~e zone 10 at the periphery of the semiconductor element
shifts towards the p-n ~unction 6. At the same time, the
boundary 11 of the space-charge zone 10 moves in a direction
away from the p-n ~unction 7, although only to a considerably
lesser extent since the zone 4 is doped more strongly than is
the zone 3. The expansion of the space-charge zone is indi
cated ~n broken lines in Figure 2. With an increasing expan-
sion of the space-charge zone, the blocking current increases
until, when the p-n ~unction 6 is reached at the periphery, so-
called punch through occurs, whereupon the p-n junction 6
loses its capacity for blocking. The expansion also takes
place correspondingly at the p-n ~unctions 5 and 7, when the
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semiconductor element is biased with a voltage in the reverse
direction, i.e. in the triggering direction.
It has been established that, when a vapour-deposited
s~licon layer is present, no expansion of the space-charge
zone 10 takes place at the periphery of the element. This
means that there is no increase in the bloc~ing currents, that
ls to say, the char~cteristics remain stable. ~hls also applies
to b~ as~ng of the semiconductor element at the operating t~7p-
erature~
Although the invention has been descri~ed wlth particular
reference to a thyristor, it can equally be used for diodes and
transistors, and for other semiconductor components.
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