Power semiconductor component, IGBT and field-effect transistor

Details Power semiconductor component, IGBT and field-effect transistor Power semiconductor component, IGBT and field-effect transistor

2003-01-28

2004-11-09

Lee, Eddie (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S331000

Reexamination Certificate

active

06815769

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a power semiconductor component. The power semiconductor component has a semiconductor body. Into one surface of the semiconductor body, a trench is introduced. An electrode device is provided in the trench. A first semiconductor zone of a first conductivity type that adjoins the trench is provided with a first metallization. The first metallization is provided on the surface of the semi-conductor body and is separated from a second semiconductor zone of the first conductivity type by a third semiconductor zone of the second conductivity type, opposite to the first conductivity type, which adjoins the trench. The second semiconductor zone adjoins the lower region of the trench. A power semiconductor component of this type may, for example, be an IGBT (insulated gate bipolar transistor), a special variant of an IGBT, namely an IEGT (injection enhanced gate transistor) or a field-effect transistor. The present invention also relates to a method for fabricating a power semiconductor component of this type.
In IGBTs, the reverse transfer capacitance, i.e. the gate-collector capacitance, which is also known as Miller capacitance, has a significant influence on the on and off switching performance of the component and on its stability in the event of a short circuit. Specifically, a high reverse transfer capacitance leads to longer switching operations and therefore increased switching losses. Moreover, in the event of a short circuit, a capacitance having a negative effect may be produced; this can result in unstable component behavior. An unstable behavior of this type manifests itself, for example, in an increased tendency to oscillate and an uncontrolled rising gate voltage and current (cf. also in this respect I. Omura et al.: IGBT Negative Gate Capacitance and Related Instability Effects, IEEE Electron device Letters, Vol. 18, No. 12, 1997, pages 622-624, and I. Omura et al.: Oscillation Effects in IGBT's Related to Negative Capacitance Phenomena, IEEE Transactions on Electron Devices, Vol. 46, No. 1, 1999, pages 237-244). It has been found that this undesirable effect of a negative capacitance can in principle be avoided by having a low ratio of the reverse transfer capacitance to the gate-source capacitance.
In a trench IGBT with an n-conducting source zone (or emitter zone), also known as n-source (or n-emitter) for short, a p-body zone, an n-base zone and a p-drain zone (or p-collector zone), especially in the case of a wide n-base zone which is constructed for relatively high voltages of above approximately 1200 V, the gate surface area that adjoins this n-base zone is large, so that there is inevitably also a very high reverse transfer capacitance with the drawbacks that have been outlined above. It should be noted at this point that for a field-effect or MOS transistor it is normal to speak of source, gate and drain, while in the case of an IGBT the corresponding connections are also known as the emitter, gate and collector.
In the following text, first of all the prior art relating to trench IGBTS with reduced reverse transfer capacitance is to be explained with reference to
FIGS. 8
to
12
.
FIG. 8
shows the basic structure of a trench IGBT (cf. also in this respect, by way of example,
FIG. 1
of European Patent No. EP 0 847 090 A2, which corresponds to U.S. Pat. No. 6,072,214, and DE 19 651 108 A1, which corresponds to U.S. patent application Ser. No. 6,218,217B1, and U.S. Pat. Nos. 6,111,290A and 5,894,149A, or U.S. Pat. No. 5,894,149 or U.S. Pat. No. 6,111,290), having a semiconductor body
1
, in which an n-base zone
7
, a p-base or body zone
8
, an n-source or emitter zone
5
and trenches
3
with a gate electrode
4
, made, for example, from polycrystalline silicon and a gate insulation layer
30
surrounding this in the trench
3
, as well as a p-drain or collector zone
22
are provided.
The conductivity types indicated may, of course, in each case be reversed. This applies in the same way to the following examples relating to the prior art and to the subsequent exemplary embodiments of the invention.
The semiconductor body
1
preferably is made from silicon. However, other semiconductor materials, such as for example SiC A
III
B
v
, etc. are also conceivable. Examples of dopants for n-type conductivity or p-type conductivity are phosphorus or boron. In this case, it is also possible to use other dopants. This applies in the same way to the following examples and to the exemplary embodiments of the invention.
On a first surface
2
of the semiconductor body
1
, there is a source or emitter metallization
6
, while on a second, opposite surface
12
of the semiconductor body
1
there is a drain or collector metallization
9
. By way of example, aluminum or another suitable contact metal can be used for the metallizations
6
,
9
. It is also conceivable to use polycrystalline silicon.
The gate electrode
4
is electrically isolated from the metallization
6
by an insulation layer
35
. By way of example, silicon dioxide and/or silicon nitride can be used for this insulation layer
35
.
For relatively high reverse voltages, the variant of the IGBT that is known as an IEGT, has proven more favorable, because of its reduced forward voltage. IEGTs are described, for example, in U.S. Pat. Nos. 5,329,142, 5,448,083, and 5,585,651.
In these IEGTS, the basic principle involves making a relatively narrow current path available to the holes flowing via the body zones (cf.
8
in
FIG. 8
) to the front-surface contact (cf.
6
in FIG.
8
), so that a high hole current density and therefore a high charge carrier gradient is established below the body zones. This high charge carrier gradient then leads to a high charge carrier flooding in the low-doped n-base zone (cf.
7
in FIG.
8
). Since, in particular in the case of a thick n-base zone, i.e. with relatively highly blocking IGBTs, for voltages above approximately 1200 V the voltage drop in the n-base zone dominates the entire forward voltage, it is in this way possible to reduce the forward voltage of the IGBT despite the resistance which opposes the holes in the narrow current path. The narrow current path is generally produced by the fact that the trench IGBT cells are not disposed directly adjacent, but rather have a space between them (c.f. also in this respect British Patent No. GB 2 314 206 or European Patent No. EP 0 813 250 A2, EP 0 847 090 A2 (which corresponds to U.S. Pat. No. 6,072,214) and DE 19 651 108 A1 (which corresponds to U.S. patent application Ser. No. 6,218,217B1, and U.S. Pat. Nos. 6,111,290 and 5,894,149). Specifically, in this respect,
FIG. 9
shows an IEGT in which only every third strip of the strip-like trenches
3
contains source or emitter zones
5
, while there are no source or emitter zones in the other strips, and the body zones
8
are not connected to the source metallization
6
.
FIG. 10
shows an IEGT in which the region between the active strips or cells provided with source or emitter zones
5
is filled by a floating p-region
16
that has defused deep into the n-base
7
.
FIG. 11
shows an IEGT which is similar to the IEGT shown in
FIG. 10
but in which an intercell region
14
has been covered by polycrystalline silicon of the gate electrode
4
, and
FIG. 12
shows an IEGT that is similar to the IEGT shown in
FIG. 11
, but in this case the polycrystalline silicon of the gate electrode
4
in the intercell region
14
has a stepped profile, that contributes to a reduction in the reverse transfer capacitance.
Nevertheless, all the IEGTs shown in
FIGS. 9
to
12
still have a high reverse transfer capacitance. The high reverse transfer capacitance is ultimately attributable to the large surface area of the gate insulation layer
30
, which is not required for the MOS channel in the body zone
8
.
The reverse transfer capacitance can be reduced in planar IGBTs (i.e. not in trench IGBTs) if the thickness of the gate insulation layer outside the actual channel region, i.e. outsi

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