JPS6019149B2 - thyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thyristor, and particularly to a high voltage and large current thyristor suitable for power control.

In general, a thyristor consists of a semiconductor substrate having a four-layer structure of consecutive pnpn layers of alternating conductivity types so as to form a pn junction between adjacent layers, and a single layer in ohmic contact with the p-layer and n-layer on both outer sides of the semiconductor substrate. A pair of main electrodes and an electrical connection for converting the non-conducting state to the conducting state between the main electrodes.
The structure includes an optical trigger means.

A typical example will be explained with reference to the drawings.

It is assumed that a p-type layer is formed by diffusion using an n-type semiconductor wafer as a starting material according to a general manufacturing method. In FIG. 1, a semiconductor substrate 10 includes a p-type emitter layer 1 exposed on one main surface 101 of the semiconductor substrate 10, an n-type base layer 2 adjacent to the p-type emitter layer 1, and an n-type base layer 2 adjacent to the n-type base layer 2. It consists of a p-type base layer 3 and an n-type emitter layer 4 adjacent to the p-type base layer 3 and exposed on the other main surface 102 of the semiconductor substrate 10 together with the p-type base layer 3. Between the p-type emitter layer 1 and the n-type base layer 2, n
Between the type base layer 2 and the p-type base layer 3 and between the p-type base layer 3 and the n-type emitter layer 4, pn junctions J,
, J2 and J3 are formed.

At least the exposed portion of the n-type emitter layer 4 on one main surface 101 and the other main surface 102 of the semiconductor substrate 10 and the exposed portion of the p-type base layer 3 on the other main surface 102 include: A pair of main electrodes and trigger signal applying means, ie, an anode electrode 5, a cathode electrode 6, and a gate electrode 7, are formed respectively. The n-type emitter layer 4 and the p-type base layer 3 are partially short-circuited by the cathode electrode 6 in the region 8, forming a so-called short-circuit emitter structure. Figure 2 shows the pn
An example of impurity concentration distribution in the pn portion is shown.

The impurity concentration near the semiconductor substrate surface 101 of the p-type emitter layer 1 is high in order to make good ohmic contact with the anode electrode 5 and to inject a large amount of holes into the n-type base layer 2 in a conductive state. There is. This kind of thyristor is
When a forward voltage below the limit voltage, usually called forward breakdown voltage, is applied between the main electrodes 5 and 6, with the anode side positive and the cathode side negative, the blocking state is maintained and the trigger is triggered by a trigger means such as a gate electrode. When a signal is applied, it shifts to the conductive state.

The thyristor is thus turned on (conducting state) and off (
Since it has a switching function (blocking state), it has high withstand voltage and low leakage current in blocking state, low voltage drop (ON voltage) in conductive state, and has high switching speed and good mechanical performance. I can say that.

As is well known, the leakage current n in the blocking state is
'Ma112MIg/{11M(Q, 10Q2)}

Here, 1g is the current due to carriers generated in the depletion layer of the reverse biased J2 junction, M is the avalanche multiplication coefficient, Q, is the current amplification factor of the pnp transistor part, and Q2 is the npn
This is the current amplification factor of the transistor part. Forward breakdown voltage VB
O is the voltage applied between the anode and cathode when M(Q, +Q2) becomes 1. From this, in order to reduce the leakage current and increase the withstand voltage, M and (Q, 10Q2)
It turns out that you can make it smaller. Power thyristors usually have a short-circuit emitter structure as shown in Figure 1.
Since electron injection from the n-type emitter layer 4 is suppressed at a small current level, Q2 is generally Q,
Q is smaller than Q, and Q is dominant as a current amplification factor.

Therefore, in order to improve the blocking characteristics, the resistivity of the n-type base layer 2 is increased, the electric field at the pn junction J2 is weakened, and the coefficient M is decreased, and the current amplification factor Q of the pnp transistor portion is decreased. It is important to do so. The current amplification factor Q, is the product of the hole injection efficiency y from the p-type emitter layer 1 to the n-type base layer 2 and the hole transport efficiency 8 in the n-type base layer 2, 8,y. Given.

8 represents the percentage of holes injected from the p-type emitter layer 1 that reach the depletion layer of the pn junction J2.

In other words, it represents how many holes pass through the non-depleted region of the n-type base layer 2 and reach the depletion layer without being annihilated by recombination. Therefore, the thicker the n-type base layer 2, the smaller 3 becomes. From this point of view, conventional measures have been taken to increase the breakdown voltage of thyristors by making the n-type base layer sufficiently thick.

However, when the n-type base layer is made thicker, the resistance of the '1' n-type base layer increases and the on-state voltage increases.

'2} Since it takes time for the resistance of the n-type base layer to be modulated by the injected carriers, the turn-on time becomes longer, and [3} The turn-off time increases because the amount of carriers accumulated in the n-type base layer increases. becomes longer.

This causes serious drawbacks in terms of characteristics.

For this reason, it has conventionally been difficult to increase the withstand voltage of a thyristor while maintaining good on-characteristics and switching characteristics. An object of the present invention is to provide a new high-voltage silister which eliminates the above-mentioned drawbacks, and its characteristics are that the injection efficiency is reduced by defining the structure of the emitter layer, and current amplification is achieved. The objective is to reduce the ratio and thereby achieve high breakdown voltage without increasing the thickness of the base layer.

More specifically, the thyristor according to the present invention is characterized by impurities in the emitter layer adjacent to the base layer having a low impurity concentration among the two intermediate base layers and exposed on one main surface of the semiconductor substrate. When the semiconductor is alloyed with a part where the concentration distribution is deep and low from the one main surface, and a metal etc. that gives the same conductive turtle type as the emitter when it enters the semiconductor as an impurity. It is formed by a recrystallized layer formed by a recrystallized layer, and consists of a high concentration portion having a small depth from the one surface, and the maximum concentration of the low concentration portion is 1.
The depth from the boundary between the low-concentration portion and the high-concentration portion to the pn junction is set to be less than 5 × 1 × 6 am ms/and more than 60 mm. The fact that the thyristor can be made to have a high breakdown voltage with the above configuration will be explained with reference to the drawings based on the experimental results of the present inventors.

Since the conductivity type of the emitter layer in question is the same whether it is p-type or n-type, the p-type emitter will be explained. FIG. 3 is an example of a schematic diagram of the impurity concentration distribution of the p-type emitter layer of the thyristor according to the present invention.

When the high concentration layer on the surface of the emitter layer is formed by an alloy method as in the present invention, the boundary between the high concentration portion and the low concentration portion generally becomes stepwise as shown in the figure. Here, as shown in the figure, the maximum concentration of the low concentration part is N, the thickness of the high concentration part is Z, and the distance from the boundary between the high concentration part and the low concentration part to the pn junction J is W.
shall be. FIG. 4 shows the relationship between forward breakdown voltage VB and W.

The forward breakdown voltage here is the voltage when the leakage current density at high temperature (125 qo) is limited to 3 mA/block, and is the voltage V at which the thyristor described above transitions from the non-conducting state to the conducting state.
Lower than Bo. The VB is determined from the viewpoint of device reliability.
This provides a substantial forward breakdown voltage of the device. As can be seen from the figure, when W is reduced by 4.0, the withstand voltage VB also becomes lower.

This is because when the high concentration part of the emitter PE is close to the pn junction, in addition to holes being injected from the low concentration part into the n type base layer, holes are also injected into the n type base layer from the high concentration part which has a large number of holes. This is because the injection of holes from the pn junction J, into the n-type base layer increases, and the current amplification factor Q, increases. As W becomes larger and the high concentration part becomes farther from the pn junction J, the influence of the high concentration part becomes weaker, and when W exceeds 60 m, the influence of the high concentration part disappears and VB is kept at a constant high level. dripping That is, by setting W to 60 fm or more, the withstand voltage is high;
And even if W varies slightly due to etching variations,
It is possible to obtain a thyristor with little variation in breakdown voltage.

However, unnecessarily increasing W increases the on-state voltage, which is not preferable. The upper limit of W is preferably 200 to 250 m. When the high-concentration part on the surface of the emitter layer is formed by a recrystallized layer made of alloy as in the present invention, the carrier lifetime near the boundary between the high-concentration part and the low-concentration part becomes short. Hole injection from

Therefore, the lower limit of the thickness W of the low concentration portion can be made smaller than in the case where the high concentration portion is formed by diffusion or the like, and there is an effect that the degree of freedom in the process of forming the low concentration portion is increased. FIG. 5 is a diagram showing the relationship between the forward breakdown voltage VB and the maximum concentration N of the low concentration portion of the emitter layer.

When W was 60 m or more, the relationship shown in FIG. 5 did not depend on W. When the maximum concentration N of the low concentration portion becomes smaller, the hole injection efficiency y from the emitter layer becomes smaller, and the breakdown voltage VB increases as shown in the figure. This effect appears when N is less than 1.5 × 1 and 6 atoms/atoms, and N is 1 × 1 and 6
It is clear from the figure that the effect becomes more pronounced when atoms/ is less than or equal to . This tendency hardly changes if W is 60 m or more. Therefore, the impurity concentration N is set to 1.
5 x 1 and 6 atoms/ is less than or equal to, preferably 1 x 1 and 6 atoms/
If it is less than atoms/copy, the effect of the present invention of reducing the injection efficiency of the emitter layer and increasing the withstand voltage can be obtained. At this time, the minimum value of the impurity concentration N is inevitably higher than the concentration of the adjacent base layer when the low concentration portion of the emitter layer is formed by diffusion, and when formed by other methods such as epitaxial growth. In such cases, it is determined by the limitations of manufacturing technology. In addition, in order to provide a reverse breakdown voltage in the pn junction between the emitter layer and the adjacent base, which is the current problem, it is possible to suppress the lower limit of N to such an extent that the depletion layer on the emitter layer side does not extend to the high concentration area. , is desirable in order to weaken the electric field strength on the element surface and suppress breakdown on the surface. An embodiment of the present invention will be described below. n with a resistivity of 200 to 3000 arc and a thickness of about 900 mm
Using a type silicon single crystal wafer as a starting material, aluminum was diffused from both sides of the wafer at 1250 qo for about 4 hours to form a low concentration p-type diffusion layer with a depth of about 120 m.

Next, both sides of the wafer were etched away by approximately 20 m, and phosphorus was selectively diffused from one side of the wafer at 1100 pm to form an n-type emitter layer with a thickness of 7 to 10 um. Furthermore, aluminum was vapor-deposited to a thickness of about 20 mm on the surface of the wafer opposite to the n-type emitter layer, and the anode electrode of the tungsten plate was heated at 730°C for about 20 cm through the aluminum film.
The alloy was bonded to the wafer by heat treatment for 0 minutes.

As a result, a highly concentrated p-type layer with an impurity concentration of about 1×1 toms/m and a thickness of about 3 m was formed on the surface of the wafer on the side to which the alloy was bonded. Next, aluminum was vapor-deposited in a predetermined shape on the surface of the wafer on the side where the n-type emitter layer was located to form a cathode electrode and a gate electrode. Furthermore, the end face of the wafer was formed into a predetermined shape, and the device was completed. The n-type base thickness of this device was about 650 mm, and the impurity concentration distribution of the p-type emitter layer was as shown in FIG.

The characteristics of the thyristor of this example are that the high temperature withstand voltage in the forward direction is 4.
．． 2kV, on-voltage is 2.0V, turn-on time is about 4
The turn-off time was less than 200 seconds.

For comparison, in a conventional thyristor in which the maximum concentration of the low concentration portion of the p-type emitter layer is 3 x 17 atoms/ground, it is necessary to obtain the same high temperature withstand voltage of 4.2 kV as in this example. The thickness of the n-type base layer was about 800 mm, the on-voltage was about 2.3 V, the turn-on time was about 7 seconds, and the turn-off time was about 300 seconds.

Thus, in the thyristor of this example, an element with good conduction characteristics and switching characteristics and high breakdown voltage was obtained. In the above embodiments, an example was described in which an anode electrode metal plate was bonded to a wafer, but the present invention is not limited to such a case. For example, a metal plate may be bonded to a wafer on which an aluminum film has been attached by vapor deposition Alternatively, heat treatment may be applied to alloy aluminum and the wafer surface, and the resulting recrystallized layer may be used as a high concentration portion on the emitter surface. Furthermore, instead of attaching the film to be alloyed to the wafer by vapor deposition or the like, the metal thin film and the wafer may be brought into contact and heat treated to form an alloy.

In short, any method can be applied to the present invention as long as it produces a recrystallized layer through alloying. Also,
The film to be alloyed is not limited to aluminum; for example, N
-Any material may be used as long as it gives the same conductivity type as the emitter layer when alloyed into a semiconductor wafer such as -Si eutectic. The present invention, as shown in FIGS. 3 and 6,
The position of the maximum concentration in the low concentration part of the emitter layer is not limited to the boundary between the high concentration part and the low concentration part, and as shown in FIG. 7, there is a position of maximum concentration within the low concentration part. It can also be applied to things.

Such a concentration distribution occurs, for example, when the concentration near the wafer surface decreases due to out diffusion during diffusion. Although the present invention has been described below using an example using an n-type silicon wafer, the effects of the present invention remain the same even if a p-type silicon substrate is used and the p-type region and n-type region in the above embodiments are reversed.

Further, since the effect of the present invention is not affected by the trigger means, other means than the electric trigger described in the embodiments, such as an optical trigger, may be used as the trigger means, and the present invention is also applicable to thyristors other than short emitters. can. As described above, according to the present invention, by reducing the injection efficiency of the emitter, the thyristor can be made to have a high breakdown voltage without increasing the base width. It has the effect of being able to be converted into

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a typical thyristor, Fig. 2 is a general impurity concentration distribution diagram of a thyristor, Fig. 3 is a definition diagram of the concentration and dimensions of the emitter layer of the thyristor in the present invention, Figs. Figure 5 is an explanatory diagram for explaining the effects of the present invention,
FIG. 6 is a diagram showing the impurity concentration distribution of the p emitter layer in the embodiment of the present invention, and FIG. 7 is a diagram showing a modified example of the impurity concentration distribution of the p emitter layer in the embodiment of the present invention. 1...p-type emitter layer, 2...n-type base layer, 3...p
Type base layer, 4... n-type emitter layer, 5... anode electrode, 6... cathode electrode, 7...
...Soot electrode. Hoko 1 Figure 2 Husband 3 Figures 4 Spear 5 Figure 6 Spear 7 Figure

Claims (1)

[Scope of Claims] 1. A semiconductor substrate having a pair of main surfaces located on opposite sides and four consecutive pnpn layers having different conductivities alternately so as to form a pn junction between adjacent layers between the main surfaces. , a pair of main electrodes each in ohmic contact with the outer layer on both main surfaces, and means for applying a trigger signal for transitioning between the main electrodes from a non-conducting state to a conducting state, Among them, the impurity concentration distribution of one of the outer layers adjacent to one of the intermediate layers having a low impurity concentration and exposed on one of the main surfaces is such that the impurity concentration distribution is a part that has a large depth from the one of the main surfaces and has a low concentration. , the high concentration portion is formed by a recrystallized layer of the alloy, and the maximum concentration of the low concentration portion is 1.5×10 ^1
^6atoms/cm^3 or less, and the depth from the boundary between the low concentration part and the high concentration part to the pn junction formed between one intermediate layer and one outer layer is 60 μm or more. A thyristor featuring: 2. The thyristor according to claim 1, wherein the conductivity type of the one outer layer is p-type. 3. The thyristor according to claim 1, wherein the conductive field of the one outer layer is n-type.