JPS6046829B2 - semiconductor equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and particularly to a field effect switching thyristor.

Recently developed field effect switching thyristors are
Thyristors are attracting attention as devices that can control large currents using electric fields and have faster switching speeds than conventional thyristors.

In other words, in the conventional normal thyristor, the turn-off time is at most Al-
For I, SOE, and NOG thyristors, it is easy to reduce the time to 1 μs or less. Both FIG. 1 and FIG. 2 are cross-sectional views showing the structure of a conventional example of this field effect switching thyristor. In the figures, 1 is an N-type base region, 2 is a P* color anode region, and 3 is an N* A colored cathode region, 4 a P* colored gate region, 5 an anode electrode, 6 a cathode electrode, 7 a gate electrode, and 8 an insulating film.

The P*color gate region 4 is formed in a mesh or striped shape within the N-type base region 1, and in the example shown in FIG. Electrodes 7 are not shown here, but are provided at appropriate locations on the device. When a gate voltage is applied between the gate electrode 7 and the cathode electrode 6 to reverse bias the PN junction formed by the gate region 4 and the base region 1, a depletion layer is formed around the gate region 4 (Fig. The gate region 4 is formed in such a way that the area (range indicated by a broken line) can block the anode current flowing between the anode electrode 5 and the cathode electrode 6.

Figure 3 is a diagram showing the anode-cathode voltage VAK vs. anode current IA characteristic at various gate voltages. Characteristic curve a is the characteristic when the gate voltage is zero, and PfN-N'''
Corresponds to the forward characteristics of a diode.

As the gate voltage is gradually increased, characteristic curves B, c,
The forward blocking state as shown in d is shown. If the gate has a resistance, it has a characteristic that when the anode voltage AK exceeds the respective breakover voltages V8Ob, BOc, BOd, the gate becomes conductive through a negative resistance characteristic region. In this way, this field effect switching thyristor can be made to change from a current blocking state to a conducting state (turn on), or in the opposite direction (turn off) by changing the gate voltage or gate resistance. You can do it by leaning. As described above, in this field effect switching thyristor, (1) the turn-off voltage changes depending on the gate voltage;

In addition, (2) the gate control ability is not lost even in a conductive state;

(3) Conventional normal thyristors cannot reduce the gate series resistance, but this thyristor can significantly reduce the gate series resistance, and since the gate is formed in a mesh or striped shape, the electric capacitance can also be reduced. can be made smaller, thus reducing the gate input time constant.

It has advantages such as

Since the structure shown in FIG. 2 has a surface wiring type in which a metal gate electrode made of aluminum, titanium, nickel, chromium, etc. is formed on the surface, the gate resistance can be sufficiently reduced.

Now, the operating mechanism of this field-effect switching thyristor shows the forward characteristics of a P+N-N+ diode when conducting, and when cut off, shows the characteristics when the base current of a PNP transistor consisting of a gate, base, and anode is zero. .

By the way, in order to reduce the switching loss of this thyristor, it is necessary to pay particular attention to the anode current during turn-off.

Figure 4 shows a typical waveform showing the change in the anode current at turn-off.In order to reduce the above-mentioned switching loss, it is necessary to shorten the drop period of the anode current and to change the anode current waveform as shown in Figure 4. It is necessary to reduce the current value during the tail period. For this purpose, it is necessary to increase the turn-off gain so that the anode current disappears easily, that is, it is necessary to decrease the current amplification factor α of the PNP transistor. In order to reduce this current amplification factor α, it is sufficient to dope an impurity such as gold, which is a center of carrier capture, from the anode side. FIG. 5 is a sectional view of a field effect switching thyristor manufactured in this manner, in which the dashed hatched area is the carrier trapping center impurity doped region. In this structure, when a reverse voltage is applied to the gate to turn it off from a conductive state when a forward voltage is applied, holes of majority carriers in the P+ type anode region 2 are transferred to the N type substrate (base region) 1. The injected holes and holes of minority carriers existing in the N-type base region 1 are drawn out to the P+-type gate region 4.

As these excess carriers dissipate, the current begins to decrease and a gate reverse voltage is established, which is then dissipated by recombination in the N-type substrate (base region) 1. This rate of recombination is increased by carrier trapping centers due to impurities such as doped gold.

However, impurities such as gold doped to reduce the current amplification factor α increase the resistivity of the N-type substrate, increasing the forward voltage drop of the thyristor, increasing power loss, and causing thermal breakdown of the device. There is a risk that this may occur. This invention was made in view of these points, and by selectively doping impurities that form carrier trapping centers,
It is an object of the present invention to provide a field effect switching thyristor with low switching loss and low forward voltage drop.

FIG. 6 is a sectional view showing the structure of an embodiment of the present invention, in which the gate region 4 of the N-type base layer 1 is
The impurity, such as gold, which acts as a carrier trapping center is selectively doped near the .

In this figure as well, this impurity doped region is indicated by diagonal lines. The thickness of this doped region in the N-type base region 1 may be approximately the same as the diffusion length of minority carriers (holes in this case). For example, the concentration of gold is 2×1015c! n(, then
The lifetime τ2 of minority carriers (holes) is approximately 0.01
μs, the diffusion length Lp is Lp・=JDpTp(D
p is the hole diffusion coefficient) and is approximately 4 μm. A field effect switching thyristor having such a structure can be formed using conventional gold diffusion techniques.

It is sufficient to selectively deposit gold only on the surface of the gate region 4 and then thermally diffuse it, but if gold is deposited on the entire surface of the gate region, lateral diffusion will occur during thermal diffusion, and the gold diffusion force will be low in the sorting region 3. This may even hinder the reduction of the forward voltage drop of the thyristor. Therefore, gold is selectively deposited only on a part of the surface of the gate region 4 and thermally diffused thereon to obtain a desired impurity-doped region. Since the field-effect switching thyristor constructed in this manner has an impurity-doped region around the gate region 4, the anode current disappears quickly during the above-mentioned cutoff, and therefore the switching loss is small. 100kHz to reduce the temperature of about 1% to about 0.1% with the operation of
With this operation, it is possible to reduce the voltage from about 10% to about 1%, and since the current path between the anode and cathode is not doped with impurities, the forward voltage drop is low, for example, about 1.2V. be able to.

As detailed above, the present invention includes a gate region of a field effect switching thyristor, which extends from the gate region into the base region by at least the -diffusion length of carriers, and closes the current path between the anode region and the cathode region. Since the impurity, which is the center of carrier trapping, is diffused in the region where the thyristor is not present, the anode current disappears quickly when the thyristor is turned off, and therefore the switching loss is small, and the forward voltage drop during operation is also small. The performance of the switching thyristor can be greatly improved.

[Brief explanation of the drawing]

Figures 1 and 2 are both cross-sectional views showing the structure of a conventional field-effect switching thyristor, and Figure 3 shows the anode-cathode voltage AK vs. anode current h characteristics at various gate voltages of this thyristor. 4 is a waveform diagram showing the anode current when the thyristor is turned off, FIG. 5 is a sectional view showing an improved conventional example, and FIG. 6 is a sectional view showing an embodiment of the present invention. In the figure, 1 is an N-type base region, 2 is a P+-type anode region, 3 is an N+-type cathode region, and 4 is a tomoe-shaped gate region.

Claims (1)

[Claims] 1. An anode region having a first conductivity type, a base region having a second conductivity type forming a junction with the anode region, and a base region having a first conductivity type embedded within the base region. A current flows between the gate region formed in a predetermined pattern on the surface thereof and the anode region having a second conductivity type with a high impurity concentration on the surface of the base region without being hindered by the gate region itself. and a cathode region provided so as to be able to pass through the anode region, the cathode region including the gate region and extending from the gate region into the base region by at least a carrier diffusion length, and providing a current path between the anode region and the cathode region. A semiconductor device characterized in that impurities that serve as carrier capture centers are diffused into an unclosed region.