JP2688521B2 - Self-protected thyristor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power thyristor, and more particularly to a safety device that does not destroy an element even when a forward voltage is applied during a turn-off period of the element. The present invention relates to a self-protection type thyristor having a device structure capable of being turned on, that is, having a so-called forward recovery protection function.

[Prior Art] As a conventional technology relating to a self-protection type thyristor, for example, the technology described in JP-A-53-80981 is known. Hereinafter, this kind of prior art will be described with reference to the drawings.

FIG. 2 is a cross-sectional view showing the structure of a self-protection type thyristor according to this type of prior art, and FIG. 3 is a view for explaining its operation. In FIG. 2, 1 is a semiconductor substrate, 2 is an anode electrode, 3 is a cathode electrode, 5 is a p-emitter layer, 6 is an n-base layer, 7 is a p-base layer, and 8 is an n-emitter layer.

In this conventional thyristor, the semiconductor layer in the vicinity of the gate region is partially removed and thinned, and then the p base layer 7 is formed to locally form the thin n base layer 6. . Since this locally thin n-base layer 6 has a lower breakover voltage than the breakover voltage of the other regions, this prior art thyristor first ignites from this region when a forward overvoltage is applied. To do.

As described above, in the above-described conventional technique, when the overvoltage is applied, the turn-on is always started in the vicinity of the gate region,
Accordingly, the turn-on area is spread over the entire area, so that the device can be protected safely.

However, this protection function works only when the overvoltage is applied quasi-statically, and does not work in the transient state described below.

That is, in FIG. 3, the thyristor shown in FIG. 2 is in a conducting state during a period τ ₁ in which a forward voltage is applied, and maintains a conducting state in a period τ ₂ when a reverse voltage is applied. Cannot be performed, and shifts to the blocking state. Period τ
_{When the} forward voltage is applied again after the elapse of ₂ , the thyristor maintains the blocking state or re-ignites depending on the magnitude of the period τ ₂ . This restriking phenomenon does not always start from the gate region of the device, and it is completely uncertain from which region it starts. This re-ignition phenomenon is usually
It is called turn-off failure.

This phenomenon of turn-off failure, which is caused by accumulated carrier remaining in the internal element during the period tau _2, because the accumulated carrier Yuku gradually disappear with time tau ₂ is long, does not occur. The minimum value of the period τ ₂ required to prevent the turn-off failure is called the turn-off time.

When the device fails to turn off, current concentrates on the region of the device that is re-calling, and the device is destroyed. As a conventional technique for preventing such element destruction, a method of providing a protection circuit in a thyristor is known.

FIG. 4 is a diagram showing an example of a protection circuit for a light ignition thyristor.

This protection circuit detects a forward voltage applied during the turn-off period of the device, a light emitting diode LED connected in parallel to the device, an opto-electric conversion circuit, an electro-photo conversion circuit, It is composed of a light guide.

In FIG. 4, it is assumed that the thyristor is in the turn-off period and a forward voltage is applied to the thyristor during this period. In this case, the light emitting diode LED detects this forward voltage and emits light. This optical signal is guided to the light guide, converted into an electrical signal by the optical-electrical conversion circuit and sufficiently amplified, and then converted again into an optical signal by the electrical-optical conversion circuit, and used as a trigger signal for the optical thyristor. To be done. That is, this protection circuit protects the optical thyristor by forcibly firing the optical thyristor when a forward voltage is applied during the turn-off period of the optical thyristor.

Such a protection circuit may not be able to protect the element due to a time delay between the application of the forward voltage and the generation of the optical signal for detecting the forward voltage and turning on the element. , The number of parts has increased,
Reliable.

Therefore, there is a strong demand for the element itself to have a protective function, and this requirement is particularly strong in an optical gate thyristor capable of dramatically simplifying a gate circuit as compared with a conventional electric gate thyristor.

5 (a) and 5 (b) are a top view and a cross-sectional view showing a structure of a conventional light ignition thyristor for electric power having no self-protection function. In FIGS. 5 (a) and 5 (b),
Reference numeral 4 is an auxiliary cathode electrode, 9 is an auxiliary n emitter layer, 12 is a light guide, and other symbols are the same as those in FIG.

This optical thyristor has a first conductivity type that is different from each other.
Of the conductivity type emitter layer (p emitter layer) 5, the second conductivity type base layer (n base layer) 6, the first conductivity type base layer (p base layer) 7, and the second conductivity type emitter layer (n emitter layer) 8. The four layers form _three junctions J ₁ , J ₂ , J ₃ and are laminated in the semiconductor body 1 between the two main electrodes, namely the anode electrode 2 and the cathode electrode 3. There is. A light receiving portion for receiving an optical signal from the light guide 12 is provided in the central portion of the element, and the light receiving portion is provided with the auxiliary n emitter layer 9 and the auxiliary cathode electrode 4, and
An auxiliary thyristor is formed together with the base layer 7, the n base layer 6 and the p emitter layer 5. Around the auxiliary thyristor, the cathode electrode 3, the n emitter layer 8, the p base layer 7, the n base layer 6, the p emitter layer 5 and the anode electrode 2 are surrounded.
Is composed of the main thyristor. In addition, the region where the main thyristor is formed partially penetrates the n emitter layer 8 and is joined by the p base layer 7 and the cathode electrode 3.
It has a so-called shorted emitter structure that short-circuits J ₃ .

When the light ignition thyristor having such a structure is turned on, first, the auxiliary thyristor unit is first turned on by the optical trigger signal applied to the light receiving unit, and then the load current of the auxiliary thyristor unit is It acts as a gate current of the main thyristor, and operates so that the entire surface of the element shifts to the conductive state. Such a thyristor having a structure in which the main thyristor portion is turned on by the current of the auxiliary thyristor portion is generally called an amplification type thyristor. Such a power thyristor according to the related art fails to turn off when a forward voltage is applied to the device at a time shorter than the device turn-off time as described with reference to FIG. 3, that is, when the device is turned off. And fire again. In this case, the location of the element inner region for re-ignition is indefinite, for example, the positions shown as A, B, and C in FIG. 5, and all are inside the main thyristor. Since the initial conduction region during re-ignition is very narrow, the above-described light-ignition thyristor is thermally destroyed due to the concentration of current.

[Problems to be Solved by the Invention] The conventional technology having the above-mentioned protection circuit has a problem that the reliability of protection is lacking, and an element having a protection function in the element itself must be present. However, the thyristor according to the related art has a problem that it is destroyed when a forward voltage is applied to the element in the forward recovery process of the thyristor.

The object of the present invention is to solve the above-mentioned problems of the prior art, and in the forward recovery process of the thyristor, even when a forward voltage is applied to the element, the element itself is safely turned on to prevent the element from being destroyed. An object of the present invention is to provide a self-protection type thyristor which has an element structure capable of preventing and does not require a protection circuit.

[Means for Solving the Problems] According to the present invention, the object is to provide a first conductivity type emitter layer, a second conductivity type base layer, between a pair of main surfaces of a semiconductor substrate.
A main thyristor portion including a first conductivity type base layer and a second conductivity type emitter layer, a first conductivity type emitter layer of the main thyristor portion, a second conductivity type base layer, a first conductivity type base layer, and at least one first In a thyristor including an auxiliary thyristor composed of a two-conductivity-type auxiliary emitter layer, a second-conductivity-type impurity layer is provided in the first-conductivity-type emitter layer of the auxiliary thyristor portion, and the first-conductivity-type emitter layer. This is achieved by partially providing the anode electrode in contact with the main surface of and also in contact with the anode electrode in contact with the main surface.

[Function] The n-type impurity region provided in the p-type emitter layer of the first conductivity type in the auxiliary thyristor region injects a carrier into the n-base layer in a transient state in which the element is turned off from the conductive state by application of a reverse voltage. Have a function. For this reason,
The excess carrier concentration in the base layer of the auxiliary thyristor region becomes higher than the excess carrier concentration of the main thyristor region, and when a forward voltage is applied during the turn-off process of the device, the auxiliary thyristor region always re-ignites first. , The device can be safely turned on.

Embodiments Embodiments of the self-protection type thyristor according to the present invention will be described in detail below with reference to the drawings.

1 (a) and 1 (b) are a sectional view and a plan view showing the configuration of the first embodiment of the present invention, and FIGS. 6 (a) to 6 (g) are views for explaining the manufacturing method thereof. In FIGS. 1 and 6, 10 is an n-type impurity layer, and other reference numerals are the same as those in FIG.

In the embodiment of the present invention shown in FIG. 1, as in the case of the prior art described with reference to FIG. 5, a light receiving portion by an auxiliary emitter layer 9 is provided in the central portion of the element, and the light receiving portion forms an auxiliary thyristor. Then, in the amplification type thyristor including the n-emitter layer 8 in the main thyristor region and the cathode electrode 3 surrounding the ring-shaped auxiliary cathode electrode 4 of the auxiliary thyristor, the p-emitter layer 5 in the auxiliary thyristor region is included. A region having a conductivity type opposite to that of the emitter layer 5, that is, an n-type impurity layer having an impurity concentration higher than that of the p-emitter layer 5 is provided inside.

 Next, the manufacturing method will be described with reference to FIG.

(1) First, an n-type substrate wafer having a thickness of 1200 μm and a resistivity of 300 Ωcm is prepared, and As, which is a p-type impurity, is diffused from both sides of the wafer to form a p-type impurity layer. The surface impurity concentration of this p-type impurity layer is approximately 8 × 10 ¹⁵ /
The cm ³ and the diffusion depth are about 150 μm [Fig. 6 (a)].

(2) Next, the p-type impurity layer on the cathode side is removed by about 50 μm, and the sheet resistance of the p-type impurity layer is adjusted to 500 Ω / port [FIG. 6 (b)].

(3) Subsequently, an n-type impurity layer is formed in the p-type impurity layer on the anode side. This n-type impurity layer uses P (phosphorus) as an impurity, and is formed by a known technique such as a selective diffusion method using a participating film as masking. In this case, it is appropriate that the surface impurity concentration of the n-type impurity layer is 10 ¹⁸ to 10 ¹⁹ / cm ³ and the depth is about 10 to ²⁰ μm [FIG. 6 (c)].

(4) Next, P (phosphorus) is diffused over the entire surface of the p-type impurity layer on the cathode side to form an n emitter layer. In this case, the surface impurity concentration is 1 to 3 × 10 ²⁰ / cm ³ , and the diffusion depth is about 10 μm [FIG. 6 (d)].

(5) Next, the n emitter layer is selectively removed by an etch-down method to form a short-circuit hole to form a cathode pattern. At this time, the diameter of the n emitter layer serving as the auxiliary thyristor region is about 3 mm. The main thyristor area is
This is a so-called n-emitter short-circuit structure, in which the diameter of the short-circuit holes is 0.2 mm and the distance between the short-circuit holes is 1 mm. [FIG. 6 (e)].

(6) In this way, the silicon wafer on which the bonding is completed is vapor-deposited with a metal film to be an electrode, for example, Al on the anode and cathode surfaces thereof, and then processed into a predetermined shape by a known photolithography technique. Then, the device is completed [FIG. 6 (e), (f)].

The characteristic feature of the device structure according to the first embodiment of the present invention completed as described above is that when a reverse voltage is applied from the state where a forward current is flowing through the device,
It means that the parasitic thyristor composed of the p-emitter layer 5, the n-base layer 6 and the p-base layer 7 operates to inject electrons from the n-type impurity layer 10 without causing so-called latch-up. To this end, the current amplification factor α _npn1 of the npn transistor formed by the n-type impurity layer 10, the p-emitter layer 5, and the n-base layer 6 and the p-base layer 7, the n-base layer 6, and the p-emitter layer 5 are used. The current amplification factor α _pnp2 of the formed pnp transistor needs to satisfy the relation of α _npn1 + α _{pnp2 <<} 1. In addition, the current amplification factor α _npn1 of the npn transistor formed by the n-type impurity layer 10, the p emitter layer 5, and the n base layer 6 and the npn formed by the n emitter layer 8, the p base layer 7, and the n base layer 6 When compared with the current amplification factor α _{npn3 of the} transistor, α _npn1 <α _npn3 must be _satisfied .

In order to satisfy the above-mentioned conditions, the embodiment of the present invention reduces the surface impurity concentration of the n-type impurity layer 10 as compared with the n-emitter layer 8 and the n-type impurity as compared with the p-base layer 7. It is necessary to increase the thickness of the p-emitter layer 5 in contact with the layer 10. In the example described with reference to FIG. 6, the surface impurity concentration of the n emitter layer 8 is on the order of 10 ²⁰ / cm ³ , whereas
The surface impurity concentration of the n-type impurity layer 10 is on the order of 10 ¹⁸ / cm ³ and is two orders of magnitude lower, and the thickness of the p base layer 7 is 90 μm.
On the other hand, the thickness of the p emitter layer 5 sandwiched by the n-type impurity layer 10 and the n base layer 6 is 110 μm, which is about 20 μm thicker.

7 (a) to 7 (d) are current distributions and carriers in the steady ON state near the gate region and when a reverse voltage is applied in the embodiment of the power optical thyristor according to the present invention configured as described above. It is a figure explaining distribution.

The operation of the thyristor according to the present invention will be described below with reference to this figure.

FIG. 6A shows the current distribution inside the element in the vicinity of the gate region in the steady ON state. In this figure, 10% of the total current flows between the current lines indicating the current flow. From this figure, it can be understood that a large current flows in the main thyristor region and a current of 10 to 20% also flows in the auxiliary thyristor region.

FIG. 6B shows the carrier (hole) concentration distribution inside the element near the gate region in the steady ON state. From this figure, it can be understood that about 20% of the carriers in the n-base of the main thyristor exist in the n-base of the auxiliary thyristor region according to the current distribution of FIG.

Next, when a reverse voltage is applied to the device, the J ₁ junction (p
The emitter junction) is reverse biased, and excess carriers in the n-base layer 6 pass through the p-emitter layer 5 to the anode electrode 3
Is swept up to. At this time, in the n-type impurity layer 10 formed in the p emitter layer 5 in the auxiliary thyristor region,
The holes of the excess carrier run laterally in the n-type impurity layer 10 and flow into the anode electrode 3.
The lateral resistance R _{s of} causes a voltage drop. When this voltage drop exceeds the built-in voltage due to the junction between the n-type impurity layer 10 and the p emission layer 5, injection of electrons from the n-type impurity layer 10 into the p emission layer 5 occurs.

FIG. 11C shows the current distribution in this case, that is, when the reverse voltage is applied. The electron current injected from the n-type impurity layer 10 spreads slightly in the n-base layer 6, but most of the current flows in the auxiliary thyristor region and enters the p-base layer 7 toward the cathode electrode 3 of the main thyristor. And suddenly change its direction and flow into the cathode electrode 3.

FIG. 6D shows the carrier (electron) concentration distribution in this case. From this figure, it can be understood that the carrier concentration in the auxiliary thyristor region is higher than the carrier concentration in the other regions corresponding to the current distribution described in FIG. However, in this case, the reverse parasitic thyristor formed by the n-type impurity layer 10, the p-emitter layer 5, the n-base layer 6, and the p-base layer 7 does not reach what is called a ratchet.

Then, when a reverse voltage is continuously applied to the device, the injection of electrons from the n-type impurity layer 10 is no longer present, and the excess carriers in the n-base layer 6 are gradually reduced, but compared with other regions. The carrier distribution state where the carrier distribution concentration in the auxiliary thyristor region is high does not change.

In the above-described embodiment according to the present invention, when a forward voltage is applied to the device in such a state, the region where the device is re-ignited becomes the auxiliary thyristor region with the largest excess carrier. That is, in the above-described embodiment according to the present invention, by re-igniting from the auxiliary thyristor region, the conduction region can be quickly expanded to the entire device, and thus the device is self-protected from destruction, so-called forward recovery protection. It is possible to

8 and 9 are cross-sectional views showing the configurations of the second and third embodiments of the present invention. In FIGS. 8 and 9, 13 is an etching region, 15 is a gate electrode, and other reference numerals are the same as those in FIG.

The second embodiment of the present invention shown in FIG. 8 is an application of the present invention to an optical thyristor having an overvoltage self-protection function by providing an etching region 13 in the gate region from the cathode side.

In this embodiment, according to the invention, the p emitter layer 5 is
The n-type impurity layer 10 formed inside is arranged at the center of the etched region 13.

The second embodiment of the present invention having such a structure has a forward recovery protection function in addition to the overvoltage self-protection function, so that the forward voltage or the forward overvoltage is applied to the device at any time. Has the effect that it can be safely turned on.

The third embodiment of the present invention shown in FIG. 9 is an application of the present invention to an amplification type thyristor having an electrical gate electrode.

In this embodiment, according to the invention, the p emitter layer 5 is
The n-type impurity layer 10 formed inside is provided not directly below the auxiliary n emitter layer 9 but directly below the gate electrode. As described above, the n-type impurity layer 10 does not necessarily have to be provided immediately below the auxiliary n-emitter layer 9, but it is possible to give the element a forward recovery protection function. This means that the operation shown in FIG. It will be clear from the explanation.

10 (a) and 10 (b) are a sectional view and a plan view showing the configuration of the fourth embodiment of the present invention. In FIG. 10, 17 is a second auxiliary n-emitter, 19 is a second auxiliary cathode electrode, and other symbols are the same as those in FIG.

The fourth embodiment of the present invention shown in FIG. 10 is one in which the present invention is applied to a two-stage amplification type optical thyristor, and another embodiment is also applied to such a multi-stage amplification type thyristor. The same effect as the example can be obtained.

In the above-described first to fourth embodiments of the present invention, the carrier lifetime τ _B1 in the n-base layer 6 in the auxiliary thyristor region is the carrier lifetime τ in the main thyristor region.
It is configured to be longer than _B2 (τ _B1 > τ _B2 ). As described above, in the first to fourth embodiments of the present invention, the carrier lifetime of the auxiliary thyristor region is made longer than the carrier lifetime of the main thyristor.
Disappearance of accumulated carriers in the auxiliary thyristor area can be made slower than in the main thyristor area, re-ignition from the auxiliary thyristor during forward recovery can be further facilitated, and protection performance can be further improved. .

[Effects of the Invention] As described above, according to the present invention, even when a forward voltage is applied during the turn-off process of the thyristor, the element itself can be safely turned on, and thus the protection conventionally used. A circuit can be eliminated, the number of parts of the device using the thyristor can be reduced, the cost of the device can be reduced, and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view and a plan view showing the configuration of a first embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a self-protection type thyristor according to the prior art, and FIG. 3 is a view for explaining its operation. ,
FIG. 4 is a diagram showing an example of a protection circuit for a light ignition thyristor,
FIG. 5 is a plan view and a cross-sectional view showing the structure of an optical thyristor for electric power according to the prior art having no self-protection function, FIG. 6 is a diagram for explaining a method of manufacturing the thyristor according to the present invention, and FIG. And FIG. 8 and FIG. 9 are views for explaining the current distribution and the carrier distribution in the steady ON state near the gate region and when a reverse voltage is applied in the embodiment of the thyristor according to the present invention. Sectional view showing the configuration of the embodiment, the tenth
The drawings are a sectional view and a plan view showing the configuration of a fourth embodiment of the present invention. 1 ... Semiconductor substrate, 2 ... Anode electrode, 3 ... Cathode electrode, 4 ... Auxiliary cathode electrode, 5 ... P emitter layer, 6 ... N base layer, 7 ... P base layer, 8 ... N Emitter layer, 9 ... Auxiliary n emitter layer, 10 ... N-type impurity layer, 12 ... Light guide, 13 ... Etching area, 15 ... Gate electrode, 17 ... Second auxiliary n emitter layer, 19 ... ... Second auxiliary cathode electrode.

Claims (3)

(57) [Claims] 1. A main thyristor portion comprising a first conductivity type emitter layer, a second conductivity type base layer, a first conductivity type base layer and a second conductivity type emitter layer between a pair of main surfaces of a semiconductor substrate. A thyristor including a first conductivity type emitter layer of the main thyristor portion, a second conductivity type base layer, an auxiliary thyristor including a first conductivity type base layer and at least one second conductivity type auxiliary emitter layer, A second conductive type impurity layer in the first conductive type emitter layer of the auxiliary thyristor portion is in contact with the main surface of the first conductive type emitter layer;
A self-protection type thyristor, which is partially provided so as to come into contact with the anode electrode which comes into contact with the main surface. 2. The self-protection type thyristor according to claim 1, wherein the auxiliary thyristor part is provided with an etching region reaching from the second conductivity type emitter layer side to the first conductivity type base layer. . 3. The second conductivity type impurity layer has a second conductivity type layer when a forward voltage is applied during a turn-off process of the thyristor.
The self-protection thyristor according to claim 1 or 2, wherein the auxiliary thyristor portion is re-ignited by injecting a carrier into the conductivity type base layer.