Device with a P-N junction and a means of reducing the risk of breakdown of the junction

The arrangement with a pn-junction and the measure for reducing the risk of a breakdown of the junction is composed of a combination of a field plate (4) and a stop electrode respectively having a multi-step edge section (40 or, respectively, 50) with a JTE technique, as a result whereof blocking voltages clearly above 2500 Volts can be achieved given slight space requirement.

BACKGROUND OF THE INVENTION 
The invention is directed to an arrangement with a junction from a p-doped 
zone to an n-doped zone according to the preamble of claim 1. 
An arrangement of said species is known from Intern. Electron Devices 
Meeting, Techn. Digest, San Francisco, Calif., 13-15 December 1982, pages 
72 through 75 and is suitable for blocking voltages of 1040 Volts. 
In semiconductor components with a pn-junction for medium and high blocking 
voltages, it is necessary to undertake measures where the blocking 
pn-junction comes to the surface of the body of semiconductor material 
that reduce or entirely eliminate the risk of an electrical arc-over or of 
a breakdown of the pn-junction. 
Given diodes, particularly power diodes, and bipolar transistors with 
isolated gate (IGBTs, IGBT standing for Isolated Gate Bipolar Transistor) 
for a blocking voltage of 1000 Volts, a measure according to IEEE 
Transactions on Electron Devices, Vol. 40, No. 10, pp. 1845 through 1854 
(1993) for reducing the risk of an electrical arc-over or breakdown of the 
pn-junction formed in a body of semiconductor material, this pn-junction 
being a junction between a p-doped zone fashioned in this body at the 
surface thereof and an n-doped zone of the body adjoining this zone, is 
that 
on the surface of the body, 
an electrode is arranged in the region of the p-doped zone, said electrode 
having a multi-step edge section offset from the surface over a contour of 
this p-doped zone that limits the p-doped zone at the surface, and 
an electrode having a multi-step edge section is arranged outside the 
p-doped zone in the region of the n-doped zone, said multi-step edge 
section lying opposite and spaced from the edge section of the electrode 
arranged in the region of the p-doped zone and being offset from the 
surface. 
The body of semiconductor material is composed, for example, of silicon and 
the electrodes are composed, for example, of aluminum or polysilicon. 
The space required for this measure in the direction of the spacing between 
the edge regions of the electrodes amounts to approximately 350 .mu.m. 
The step heights in the multi-step edge regions are determined by the 
thickness of electrically insulating material, for example oxide layers, 
lying under the multi-step edge sections and between these sections and is 
limited to an overall thickness of about 10 .mu.m for process-oriented 
reasons. 
Each step of the multi-step edge section of the electrode arranged in the 
region of the p-doped zone generates an electrical field peak in the 
semiconductor material that is in turn blunted by the respectively 
following part of this electrode, so that this electrode can be 
interpreted as a field plate which is intended to effect that optimally no 
electrical field peaks occur in the body of semiconductor material. 
The electrode arranged outside the p-doped zone in the region of the 
n-doped zone can be interpreted as a stop electrode that is intended to 
effect that a space charge zone does not spread farther in the body of 
semiconductor material. 
The reduction of the blocking capability by the field peaks generated by 
the steps of the edge section field plate [sic] should be as slight as 
possible, which requires a good matching of the step height of every step 
measured perpendicular to the surface of the body and step length of every 
step measured parallel to this surface in the direction away from the 
p-doped zone. The field peak at a free end of the edge section of this 
electrode can no longer be reduced, as described, and therefore limits the 
maximally possible blocking capability of the body given a prescribed 
thickness of the layer of electrically insulating material, i.e. given a 
prescribed spacing of this free end from the surface. 
Two field plate-protected field rings are therefore additionally introduced 
for components having a pn-junction for 1600 Volts blocking voltage, but 
these require much space, for example 650 .mu.m. Such an arrangement 
becomes more and more unfavorable for even high blocking voltages. 
Another proposed possibility of a measure for reducing the risk of an 
electrical arc-over or breakdown of a pn-junction is comprised of a 
junction extension technique (=JTE technique, JTE standing for Junction 
Termination Extension), whereby a p-doped zone more lightly doped compared 
to the p-doped zone is formed in the body at the surface thereof at the 
pn-junction formed in the body of semiconductor material, this pn-junction 
here also being a junction between a p-doped zone formed in the body at 
the surface thereof and an n-doped zone of the body adjoining this zone, 
said more lightly doped p-doped zone adjoining both the p-doped zone as 
well as the n-doped zone of the body. 
When a blocking voltage is applied, the more lightly p-doped zone is partly 
but not entirely cleared of free charge carriers, whereby no greater field 
strength peaks occur. 
The problem given this other measure is that a specific dose of the lighter 
p-doping must be very exactly observed in order to obtain a high blocking 
capability. Accordingly, the structure is very sensitive to surface 
charges and is technologically difficult to govern. 
SUMMARY OF THE INVENTION 
The invention recited is advantageously suited for blocking voltages of 
1600 V and more given a low space requirement. 
The inventive arrangement is advantageously suited for a voltage range from 
1600 V to 2500 V, and blocking voltages of clearly above 2500 V can even 
be achieved given a slight space requirement of, for example, only 550 
.mu.m. 
In a certain sense, the invention is composed of a novel combination of the 
two above-described, proposed measures and avoids their disadvantages. 
The effect of the inventive combination is based on the following: 
On the one hand, the more lightly p-doped zone reduces the field strength 
peaks, so that a higher blocking voltage can be achieved than without this 
more lightly p-doped zone given the same maximum spacing from the surface 
of the free end of the edge section of every electrode offset from the 
surface of the body of semiconductor material. 
On the other hand, the exact dose of the lighter p-doping is less critical 
since charge lacking in the more lightly p-doped zone is made available to 
a certain extent by the electrode arranged in the region of the p-doped 
zone. 
In general terms the present invention is an arrangement having a junction 
fashioned in a body of semiconductor material between a first p-doped zone 
formed in the body at the surface thereof and an n-doped zone of the body 
adjoining said zone. 
A first electrode is arranged on the surface of the body in the region of 
the p-doped zone. The electrode has a multi-step edge section offset from 
the surface over a contour of the first p-doped zone that limits the first 
p-doped zone at the surface of the body. A second electrode has an at 
least single-step edge section outside the first p-doped zone in the 
region of the n-doped zone. The at least single-step edge section lying 
opposite and spaced from the edge section of the first electrode is 
arranged in the region of the p-doped zone and is offset from the surface. 
At least one more lightly p-doped zone, as compared to the first p-doped 
zone, is formed in the body at the surface thereof between the edge 
section of the first electrode arranged in the region of the first p-doped 
zone and the edge section of the second electrode arranged outside the 
first p-doped zone in the region of the n-doped zone. The junction is a 
pn-junction, whereby the n-doped zone adjoins the first p-doped zone. The 
more lightly p-doped zone adjoins the n-doped zone. 
Advantageous developments of the present invention are as follows. 
The more lightly p-doped zone is adjacent to the first p-doped zone under 
the edge section of the first electrode arranged in the region of the 
p-doped zone. 
The more lightly p-doped zone extends continuously from the first p-doped 
zone in the direction toward the second electrode arranged outside the 
first p-doped zone in the region of the n-doped zone up to a point under 
the edge section of the second electrode. 
The more lightly p-doped zone extends continuously from the first p-doped 
zone in the direction toward the second electrode arranged outside the 
first p-doped zone in the region of the n-doped zone up to a point under 
the edge section of the second electrode. The lightly p-doped zone has at 
least one interruption. 
The more lightly p-doped zone has an interruption under the edge section of 
the first electrode arranged in the region of the first p-doped zone. 
An interruption of the more lightly p-doped zone is located in the 
proximity of that end of the edge section of the first electrode arranged 
in the region of the first p-doped zone that faces away from the first 
electrode. 
The second electrode arranged outside the first p-doped zone in the region 
of the n-doped zone is arranged in the region of a more highly n-doped 
zone as compared to the n-doped zone in the body at the surface thereof. 
In particular, the arrangement having the interruption of the move lighty 
p-doped zone has the advantage that the region of the lighter p-dose in 
which the highest voltage is reached spreads.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the exemplary embodiment according to FIG. 1 of the inventive 
arrangement, the body 1 of semiconductor material, for example silicon, 
comprises a pn-junction (referenced 23 and indicated by a broken line) 
that is a junction between a p-doped zone 2 fashioned in the body 1 at the 
surface 10 thereof and an n-doped zone 3 of the body 1 that is adjacent to 
this zone 2 and likewise at the surface 10. 
The p-doped zone 2 preferably comprises a high doping concentration of 
10.sup.17 through 10.sup.18 cm-.sup.-3 and is referred to below as p.sup.+ 
-doped zone for this reason. By contrast, the n-doped zone 3 preferably 
comprises a low doping concentration of 10.sup.13 through 10.sup.14 
cm.sup.-3 and is referred to below as n.sup.- -doped zone for this reason. 
At the surface 10 of the body 1, the p.sup.+ -doped zone 2 comprises a 
contour 20 that limits this zone 2 and simultaneously marks the 
pn-junction from the p.sup.+ -doped zone 2 to the n.sup.- -doped zone 3 at 
the surface 10 of the body 1. 
An electrode 4 is arranged on the surface 10 of the body 1 in the region of 
the p.sup.+ -doped zone 2, this electrode 4 comprises a multi-step edge 
section 40 over the contour 20 of the p.sup.+ -doped zone 2 offset from 
the surface 10 whose boundary with the electrode 4 is indicated by the 
broken line 45 perpendicular to the surface 10 of the body 1. 
At its side facing toward the surface 10 of the body 1, the multi-step edge 
section 40 comprises several, for example three adjoining steps that are 
referenced 40.sub.1, 40.sub.2 and 40.sub.3 in sequence from left to right 
in FIG. 1, whereby the last step 40.sub.3 adjoins an end 41 of this edge 
section 40 that faces away from the electrode 4. 
An electrode 5 is likewise arranged on the surface 10 of the body 1 but 
outside the p.sup.+ -doped zone 2 in the region of the n.sup.- -doped zone 
3, this electrode 5 comprising an at least one-step edge section 50 lying 
opposite the edge section 40 of the electrode 4 arranged in the region of 
the p.sup.+ -doped zone 2 at the distance d and being offset from the 
surface 10, the boundary of this edge section 50 with the electrode 5 
being indicated by the broken line 55 perpendicular to the surface 10 of 
the body 1. 
The edge section 50 can be structured simpler than the edge section 40; for 
manufacture-conditioned reasons, however, it is often expedient to 
likewise structure it multi-stepped, particularly essentially identical to 
the edge section 40. 
In the example of FIG. 1, the edge section 50 is fashioned essentially the 
same as the edge section 40 and comprises three adjoining steps at its 
side allocated to the surface 10 of the body 1 that are referenced 
50.sub.1, 50.sub.2 and 50.sub.3 in sequence from right to left in FIG. 1, 
whereby the last step 50.sub.3 is adjacent at an end 51 of this edge 
section 50 facing away from the electrode 5 and facing toward the end 41 
of the edge section 40, this lying opposite the end 41 of the edge section 
40 at the distance d. 
Inventively, at least one more lightly p-doped zone 6 compared to the 
p.sup.+ -doped zone 2 is formed in the body 1 at the surface 10 thereof 
between the edge section 40 of the electrode 4 and the edge section 50 of 
the electrode 5, this zone 6 adjoining the n.sup.- -doped zone 3, which is 
indicated by a dot-dash line 63. 
The more lightly p-doped zone 6 preferably comprises a relatively low 
doping concentration of 10.sup.15 cm.sup.-3 through 10.sup.16 cm.sup.-3 
and is referred to below as p.sup.- -doped zone for this reason. 
The p.sup.- -doped zone 6 under the edge section 40 of the electrode 4 is 
preferably adjacent to the p.sup.+ -doped zone 2 and, in the example of 
FIG. 1, extends continuously from the p.sup.+ -doped zone 2 in the 
direction toward the electrode 5 up to a point under the edge section 50 
of this electrode 5. 
The steps 40.sub.1 through 40.sub.3 have the effect of respectively 
generating a field peak in the semiconductor material of the body 1, 
whereby each field peak generated by a step is in turn blunted by the part 
of the edge section 40 of the electrode 4 adjoining this step at the right 
in FIG. 1. The part of the edge section 40 adjoining the step 40.sub.1 at 
the left has the job of blunting the field peaks occurring at the 
right-hand edge of the p.sup.+ -doped zone 2. 
The electrode 5 has the job of stopping the spread of a space charge zone 
in the body 1 toward the right in FIG. 1 and can therefore also be 
referred to as stop electrode. For this job, it is beneficial when 
electrode 5 is arranged in the region of a more highly doped zone 7 in the 
body 1 compared to the n.sup.- -doped zone 3, this zone 7 adjoining the 
surface 10 thereof and its boundary with the n.sup.- -doped zone 3 being 
indicated by a dotted line 73 in FIG. 1. The doping concentration of the 
more highly n-doped zone 7 is preferably higher than 10.sup.18 cm.sup.-3 
and can therefore be referred to as n.sup.+ -doped zone. 
The electrodes 4 and 5 and their steps 40.sub.1 through 40.sub.3 or, 
respectively, 50.sub.1 through 50.sub.3 are expediently generated with the 
assistance of a stepped coating of an electrically insulating material, 
for example oxide, that is generated partially on the surface 10 of the 
body 1 and defines the steps of the electrodes 4 and 5, whereby the 
electrodes 4 and 5 are produced by application of one or more layers of 
electrically conductive material onto the surface 10 of the body 1 and 
onto the stepped coating. Such a stepped coating fills up the space 8 
between the electrodes 4 and 5. 
That surface 42 or, respectively, 52 of the electrodes 4 and 5 facing away 
from the surface 10 of the body 1 is not flat given the indicated 
manufacture, as shown in FIG. 1, but likewise comprises steps that 
approximately follow the illustrated steps. 
It is expedient--and not only given this manufacture--when the step height 
of the steps of the two electrodes 4 and 5 lying at the same level 
relative to the surface 10 are [sic] the same measured perpendicular to 
the surface 10 of the body 1. According to FIG. 1, for example, the steps 
40.sub.1 and 50.sub.1 have the same step height a1, the steps 40.sub.2 and 
50.sub.2 have the same step height a2 and the steps 40.sub.3 and 50.sub.3 
have the same step height a3. The horizontally measured lengths of the 
individual steps in FIG. 1 can differ from one another, particularly 
comparing the two electrodes 4 and 5 to one another. 
The critical p.sup.- -doped zone 6 extending beyond the end 41 of the 
electrode 4 in the direction to the electrode 5 advantageously reduces the 
field strength peaks, so that, given the same maximum spacing of the end 
41 of the edge section 40 of the electrode 4 from the surface 10 of the 
body 1, a higher blocking voltage can be achieved than without this 
p.sup.- -doped zone 6; on the other hand, the exact doping concentration 
of the p.sup.- -doping is advantageously less critical since lacking 
charge in the p.sup.- -doped zone 6 is made available up to a certain 
extent by the electrode 4 arranged in the region of the p.sup.+ -doped 
zone 2. 
The breakdown voltages of the pn-junction 23 for various doping 
concentrations of the n.sup.- -doping of the body 1 of semiconductor 
material dependent on various doping concentrations of the n.sup.- -doped 
zone 3 can be derived from the diagram shown in FIG. 2. It is thereby 
assumed that the body 1 is composed of silicon, the doping concentration 
of the p.sup.+ -doped zone 2 is equal to 10.sup.17 cm.sup.-3 through 
10.sup.18 cm.sup.-3 and the vertical thickness b1 thereof in FIG. 1 
typically amounts to about 6 .mu.m, the doping concentration of the 
n.sup.- -doped zone 3 lies in the range from 3.multidot.10.sup.13 through 
7.multidot.10.sup.13 cm.sup.-3, the doping concentration of the p.sup.- 
-doped zone 6 at the surface 10 of the body 1 lies in the range from 
10.sup.15 cm.sup.-3 through 7.multidot.10.sup.15 cm.sup.-3 and the 
vertical thickness b2 thereof in FIG. 1 typically amounts to about 6 
.mu.m, the two electrodes 4 and 5 are composed of polysilicon and/or metal 
with a typical thickness of 15 .mu.m, the step height a1 is equal to 2 
.mu.m, the step height a2 is equal to 1.5 .mu.m and the step height a3 is 
equal to 4.8 .mu.m, and the horizontal dimension of the overall 
arrangement in FIG. 1 is approximately equal to 550 .mu.m. 
In sequence, the curves I through IV in FIG. 2 respectively indicate the 
curve of the breakdown voltage of the pn-junction 23 dependent on the 
doping concentration of the p.sup.- -doped zone 6 at the surface 10 of the 
body 1 for the specific doping concentrations 6.4.multidot.10.sup.13 
cm.sup.-3, 4.8.multidot.10.sup.13 cm.sup.-3, 3.6.multidot.10.sup.13 
cm.sup.-3 or, respectively, 3.2.multidot.10.sup.13 cm.sup.-3 of the 
n.sup.- -doped zone 3. The curves respectively exhibit a relatively broad 
maximum, which sees to it that the range of the doping concentration at 
the surface 10 of the p-doped zone 6 in which the highest breakdown 
voltage is achieved is relatively broad and it is thus not a matter of an 
exact doping concentration of this zone 6. The maximum of the curve IV 
also shows that a maximum breakdown voltage of approximately 3.25 kV can 
be achieved given the horizontal dimension of 550 .mu.m for the overall 
arrangement. 
The exemplary embodiment of FIG. 3 differs from the exemplary embodiment of 
FIG. 1 only in that the p.sup.- -doped zone 6 extending from the p.sup.+ 
-doped zone 2 in the direction toward the electrode 5 up to a point under 
the edge section 50 of this electrode 5 comprises at least one 
interruption. Otherwise, this exemplary embodiment is identical to the 
example of FIG. 1. 
In the example of FIG. 3, the p.sup.- -doped zone 6 preferably comprises an 
interruption 60 under the edge section 40 of the electrode 4 and/or in the 
proximity of the end 41 of the edge region 40 of this electrode 4. An 
interruption 60 under the end 41 advantageously leads thereto that the 
range of the doping concentration of the p.sup.- -doped zone 6 at the 
surface 10 in which the highest breakdown voltage is achieved becomes 
broader compared to the comparison example of FIG. 1. 
The latter can be seen from the diagram of FIG. 4, in which the curve of 
the breakdown voltages of the pn-junction 23 for the doping concentrations 
4.8.multidot.10.sup.13 cm.sup.-3, 3.6.multidot.10.sup.13 cm.sup.-3 and 
3.2.multidot.10.sup.13 cm.sup.-3 of the n.sup.- -doped zone 3 are entered 
in curves II, III or, respectively, IV dependent on various doping 
concentrations of the n.sup.- -doped zone 3, whereby the same conditions 
as in FIG. 2 otherwise form the basis. Compared to the corresponding 
curves II, III or, respectively, IV in FIG. 2, these curves show a clearly 
broader maximum. The maximum of the curve IV in FIG. 4 likewise shows that 
a maximum breakdown voltage of approximately 3.25 kV can be achieved given 
the horizontal dimension of 550 .mu.m for the overall arrangement. 
By way of example, FIG. 5 shows a traditional arrangement with two 
electrodes 4 and 5 that only differs from the inventive arrangement of 
FIG. 1 or 3 in that it lacks the p.sup.- -doped zone 6 but is otherwise 
the same. 
By way of example, FIG. 6 shows a traditional arrangement in JTE technique 
with a p.sup.- -doped zone 6 that differs from the inventive arrangement 
of FIGS. 1 or 3 only in that it lacks the electrodes 4 and 5 but is 
otherwise the same. 
In the curve IV, the diagram of FIG. 7 shows the curve of the breakdown 
voltage of the pn-junction 23 of the traditional arrangement according to 
FIG. 6 for the doping concentration 3.2.multidot.10.sup.13 cm.sup.-3 of 
the n.sup.- -doped zone 3 dependent on the doping concentration of the 
p.sup.- -doped zone 6 at the surface 10 of the body 1, whereby the 
horizontal dimension of the overall traditional arrangement again amounts 
to 550 .mu.m. The maximum of this curve lying above 3 kV can be clearly 
seen, but this is very pointed and narrow compared to the corresponding 
curves IV in FIG. 2 and FIG. 4, so that the range of the doping 
concentration of the p.sup.- -doped zone 6 at the surface 10 in which the 
highest breakdown voltage is achieved is unbeneficially very narrow. 
The invention is not limited to the particular details of the apparatus 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described apparatus without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrative and not in a limiting sense.