JPS60260151A - Mos gate bipolar transistor - Google Patents

Abstract

PURPOSE:To form a MOS gate bipolar transistor enabled to perform high speed motion having short turn-off time without depending upon usual heavy metal doping, projection of a neutron beam or an electron beam by a method wherein impurity concentration of a region to constant P-N junction is lowered. CONSTITUTION:Concentration of P-N junction constructed usually of a concentration layer of 10<19> and a concentration layer of 10<14> respectively is made to P-N junction of concentration of the degree of 10<16> and 10<14>. To put it concretely, a P<-> type epitaxial layer 1'of concentration of the degree of 10<16> is grown, and after then an N<-> type epitaxial layer 2 is grown. According to this construction, holes implanted at the order of 10<19> from a P<+> type layer 1 up to now are reduced to the order of 10<16> according to existence of the layer 1'. When the process is performed in such a way, turn-off time is reduced. Moreover, a MOS gate bipolar transistor of the same performance can be obtained without containing a process, which may be said even harmful for a MOS process such as Au diffusion, neutraon beam projection, electron beam projection, etc.

Description

TECHNICAL FIELD The present invention relates to a power transistor (MO8) whose source and drain are arranged in the vertical direction of a semiconductor body.

(Conventional technology #) The well-known power MO8IT has a high switching speed, does not cause secondary breakdown, and can be easily connected in parallel.
It has excellent features such as a simplified gate control circuit. However, because it is a unipolar device, especially in high-voltage devices, there is a large voltage drop in the low-concentration layer that is needed to soften the electric field, which also has the drawbacks of increased loss when it is on and a small current capacity that it can handle. .

As a method to balance these advantages and disadvantages, a MOS gate bipolar transistor whose structure is slightly modified to perform bipolar operation has been proposed. The MOS gate bipolar transistor has the structure shown in FIG. 1 in the case of an N channel MOS gate. That is, the conventional power M
In the O8FET, layers 1 and 3 in Figure 1 were each an N+ substrate and an N-)-1 layer, but these were changed to a P sufflate layer and a p++ layer, and between them and the N- electric field relaxation layer of layer 2. A pn junction is formed. This structure is
N- electric field relaxation calendar 2 by performing so-called epitaxial growth
can be easily obtained by simply changing the N substrate to the P substrate 1 and slightly changing the diffusion process. Furthermore, the most average impurity concentration profile when formed in this manner is shown in FIG. 1(b). 1, a and b are sources, 7 is a gate, 8F
! It is a drain.

Now, in the MOS gate bipolar transistor having the structure shown in Fig. 1, holes are mainly injected from the layer 1 to the layer 2 by diffusion from the P+N+ junction composed of layers 1 and 2, and the amount of injection is When is large, conductivity modulation occurs in the N layer 2, causing a large current to flow, and since the resistance of the N layer 2 is effectively reduced, the on-state loss is also reduced. However, as a matter of course, holes, which are minority carriers in this N layer, have a long life, so the turn-off time of this transistor becomes long.
The high switching speed, which was the greatest feature of the power MO8FET, is lost. For this reason, the turn-off time is shortened by lowering the N-layer 2 hole lifetime by doping with heavy metals or irradiating with neutron beams or electron beams.

As a result, the switching speed is slower than the power MO81T, but faster than a normal bipolar transistor, the gate control is as simple as the power MO8FET, and secondary breakdown is less likely to occur because the collector current is not controlled by base injection of minority carriers. With such characteristics, still
The current that can be handled can be increased to the extent that secondary breakdown does not occur.

However, heavy metal doping is not compatible with normal power MOSFET processes, and neutron beam or electron beam irradiation damages the gate oxide film of the MOS, which is not preferable.

(Objects and Structure of the Invention) An object of the present invention is to provide a MOS gate bipolar transistor that has a short turn-off time and can operate at high speed without using conventional heavy metal doping, neutron beam, or electron beam irradiation, and has its characteristics. The reason is that the concentration of 46.4 impurities constituting the PN junction has been lowered.

(Example) The present invention will be explained according to the drawings. In the present invention, the conventional PN junction is made up of a layer with a concentration of 1019 and a layer with a concentration of 1014, but is changed to a pn junction with a concentration of about 101@ and 1014, respectively. Specifically, conventional P
As shown in FIG. 2, the N layer 2 (FIG. 1) is epitaxially grown on the substrate 1 as it is, and the above 10 layers are grown as shown in FIG.
According to the structure of the present invention, a P-type epitaxial layer 1' of about 16 layers is grown, and then an N''-W epitaxial layer 2 is grown. is reduced to the order of 101 due to the presence of layer 1'.If this is the case, for example, if the current flowing through the pn junction of layers 1'-2 is assumed to be only holes (
1) In order to express it as shown in the formula, I3 changes from 1011 to 10
By dropping to 16, the Is decreases by about 10-3.

qv/niding ■-Is (e -1) ...(1) On the other hand, the same I
Since the Pn junction layer required to obtain the equation (1) is an exponential function, it is only 0.2■ at most. As can be seen from the figure, in the case of the present invention, the amount of minority carriers in the N layer 1' is about 10<-3> compared to the conventional case, and the turn-off time is reduced by this order. Further, the voltage required for the pn junction increases by about 0.2 .mu. compared to the conventional method, but this increase will continue due to the decrease in lifetime even if diffusion, neutron beam irradiation, and electron beam irradiation are performed. As described above, according to the present invention, Au diffusion, neutron irradiation, electron beam irradiation
An MO8 gate high hole transistor with equivalent performance can be obtained without including a process that can be said to be harmful to the process. It goes without saying that a reverse polarity type, in which the polarities of P and n in the above explanation are reversed, has exactly the same effect.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic cross-sectional view of a conventional MOS gate bipolar transistor, FIG. 1(b) is an impurity distribution diagram along line 9 in FIG. 2(a), and FIG. 2(a) is a diagram according to an embodiment of the present invention. M
Schematic cross-sectional diagram of an OS gate bipolar transistor, 2nd
Figure (b) is an impurity distribution diagram along line 9 in (a). 1...P Substrate, 1',...
P-epitaxial layer, 2...N-epitaxial layer, 3...P+i, 4...P layer,
5...1 layer, 6...source electrode (emitter electrode), 7...gate electrode, 8...
・Drain electrode (collector electrode). 2nd ward ((2) 2nd ward (b)

Claims (1)

[Claims] Comparatively, the conductivity of the cylinder impurity is the same conductivity on the mold substrate! a first semiconductor layer of a low concentration type and a low concentration, a second semiconductor layer of a low concentration and opposite conductivity type on the first semiconductor layer, and a gate electrode, a source and a source on the surface of the second semiconductor layer. 1. A MOS gate bipolar transistor having one electrode of a drain, and having the other electrode of a source and a drain on the substrate.