JPH04111358A - Overvoltage self-protection type thyristor - Google Patents

Abstract

PURPOSE:To control a breakdown voltage characteristic with high accuracy by a method wherein a part where an ion distribution density displays a peak value is formed by using a proton irradiation means and a part where a forward breakdown voltage is dropped is formed. CONSTITUTION:At a thyristor element in which electrodes 6, 7 have been formed, a shielding plate 15 is used so that only a region constituting a pilot thyristor part 8 is irradiated selectively with protons; the protons are irradiated from the cathode side of the element. After this irradiation has been finished, a short-time annealing operation is repeated until a prescribed breakdown voltage is obtained. Thereby, a peak region 12 appears in a prescribed position in an n-base layer 3 as shown on the right side in the figure as a damage distribution; a crystal defect production region 13 can be formed. An interaction between ion particles and semiconductor atoms appears strongly inside the region 13; the interaction becomes more strongly and a crystal defect density in a semiconductor becomes maximum in the region 12. An ion distribution and the damage distribution are set to a peak state in nearly the same position and the lifetime of carriers in the semiconductor becomes minimum at this part.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an overvoltage self-protection type device that prevents destruction of the device by safely turning on itself when an overvoltage exceeding the forward breakdown voltage is applied. The present invention relates to a thyristor, and particularly to an overvoltage self-protection type thyristor suitable for a large capacity thyristor equipped with a pilot thyristor section or an auxiliary thyristor section.

[Conventional technology]

If a voltage exceeding its breakdown voltage is applied to a thyristor element and it is forcibly turned on, there is a risk that the element will be destroyed, and this is particularly noticeable in the case of a large capacity thyristor element.

By the way, protection of the thyristor element against such overvoltage has conventionally been dealt with by installing a separate protection circuit.

However, installing such a protection circuit causes problems such as increased cost and reduced reliability due to an increase in the number of components.In recent years, the thyristor element itself, called an overvoltage self-protection type thyristor, has been developed. Various types of thyristors with protective functions have been proposed and are now being used.

Therefore, these conventional techniques will be explained below.

First, FIG. 8 is disclosed in Japanese Unexamined Patent Publication No. 126181/1981. In the figure, 1 represents a semiconductor substrate, and includes an n-emitter layer 2, an n-base layer 3, a p-base layer 4.
, and an n emitter layer 5. and,
An anode electrode 6 is connected to the n-emitter layer 2, and a cathode electrode 7 is connected to the n-emitter layer 5 with low resistance.

Furthermore, on the cathode side, an etched region E is provided extending from the n emitter layer 5 to the p base layer 4.
It is provided in low resistance contact with the base layer 4.

In this thyristor element, the p base layer 4 is configured to penetrate the n emitter layer 5 at some places and come into low resistance contact with the cathode electrode 7, thereby creating a so-called emitter short circuit structure. It is being

In the thyristor element shown in FIG. 8, the depth of the etched region E determines the overvoltage to be protected, that is, the self-protection voltage. That is, in this device, when a reverse bias is applied to the central junction Jc formed by the n-base layer 3 and the p-base layer 4, and it is in a forward blocking state by bearing withstand voltage, the p-base layer 4
A depletion layer is created within the depletion layer, and an etched region E is formed within this depletion layer.
This method takes advantage of the fact that the electric field strength between the bottom surface of the etched region E and the central junction Jc is larger than that in other parts due to the existence of this depletion layer. When a voltage higher than the self-protection voltage is applied, the electric field strength increases.

First, by generating a breakover, a self-protection function can be obtained.

Next, FIG. 9 is disclosed in Japanese Patent Application Laid-Open No. 53-80981, in which an etched region E is first formed in the n base layer 3, and then the p base layer 4 is formed. .

FIG. 1O is disclosed in Japanese Unexamined Patent Publication No. 59-158560, in which after forming the p base layer 4, an etched region E is formed thereon until it reaches the central junction Jc. The acceptor is diffused from the etched region E, thereby forming a curved portion at the central junction Jc.

In both of the thyristor elements shown in FIGS. 9 and 10, by forming a curved portion at the central junction Jc directly below the etched region E, the electric field strength of the depletion layer at this curved portion is increased, thereby It is designed to provide a protective function.

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into account the accuracy of setting the voltage at which the self-protection function is activated, resulting in a decrease in the manufacturing yield of thyristor elements having predetermined and accurate breakover voltage characteristics. , there was a problem of increased costs.

To explain specifically, first, in the prior art shown in FIG. 8, the breakover voltage characteristic largely depends on the flatness of the bottom surface of the etched region E, and similarly, in the prior art shown in FIGS. 9 and 10, Since the shape and curvature of the curved portion in the etched region E determines the breakover voltage characteristics, in the end, in these conventional techniques, in order to control the breakover voltage characteristics with high precision, it is necessary to It is necessary to control the shape with high precision, but it is extremely difficult to control the shape with high precision using techniques such as wet etching that have been conventionally used to form such etched areas.
Therefore, with the conventional technology, problems have arisen in improving yield and reducing costs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overvoltage self-protection type thyristor whose breakover voltage characteristics can be easily controlled with high accuracy and which can easily achieve high yield and low cost.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses proton irradiation means to form a portion in which the ion distribution density shows a peak value in a semiconductor layer constituting a thyristor, and to A portion where the forward breakdown voltage is lowered due to the presence of the portion exhibiting .

[Effect]

The properties of the portion in the semiconductor layer where the ion distribution density shows a peak value can be easily controlled by the proton irradiation conditions and the annealing treatment conditions performed as necessary after the proton irradiation.

Since both proton irradiation and annealing can be easily controlled with high precision, it is possible to easily obtain breakover voltage characteristics with high precision.

〔Example〕

Hereinafter, the overvoltage self-protection type thyristor according to the present invention will be explained in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment in which the present invention is applied to an overvoltage self-protection type thyristor having a pilot thyristor region. The n-emitter layer 5, anode electrode 6, and cathode electrode 7 are the same as in the prior art described above.

8 is a pilot thyristor portion, 1o is a pilot thyristor electrode, 12 is a peak region of ion distribution due to proton irradiation, and 13 is a crystal defect generation region due to proton irradiation.

First, to explain the function of the pilot thyristor region, in general, in such a relatively large capacity overvoltage self-protection thyristor, regions called pilot thyristor or auxiliary thyristor are set, and the break in these regions is set. The overvoltage is set slightly lower than the breakover voltage of the region that functions as the main thyristor.

Then, when an overvoltage is applied to the thyristor, the pilot thyristor region or the auxiliary thyristor region always starts to turn on. In this way, once the pilot thyristor region or the auxiliary thyristor region is turned on, conduction is transferred from these regions to the main thyristor region, thereby safely turning on the entire device and preventing destruction due to current concentration. It is possible to escape.

Returning to FIG. 1, regions 12 and 13 represent regions generated in the n-base layer 4 and the n-base layer 3 by selectively irradiating the pilot thyristor section 8 with protons, as will be described later. ing.

In this proton irradiation technique, for example, I.E.J., Proceedings on 1988
・International Symposium on Power Semiconductor Devices, p p , l 4
7-152 (IEEJ, Proceedings of
1988 International Sympo
sium on Power Semiconductor
r Devices, pp, 147-152)
, 1, by changing the irradiation energy, the peak position of the ion distribution within the semiconductor can be changed depending on the energy.

It is also well known that at this time, the peak intensity at the peak position of the ion distribution described above can be changed depending on the dose.

Therefore, as in the embodiment shown in FIG. 1, proton irradiation is performed perpendicularly to the pilot thyristor section 8, that is, from the cathode side, and by appropriately selecting the irradiation energy and dose, the n-base layer 3 is As shown as the damage distribution on the right side of the figure, the peak area 1
2 appears, the crystal defect generation region 13 can be formed.

In this crystal defect generation region 13, the interaction between ion particles and semiconductor atoms appears strongly, but in the peak region 12, this interaction becomes even stronger, and the crystal defect density in the semiconductor becomes maximum.

As shown in FIG. 2, the ion distribution and the damage distribution reach a peak state at approximately the same position, and the lifetime of carriers in the semiconductor at this portion becomes the minimum.

Therefore, by utilizing these properties, it is possible to arbitrarily adjust the lifetime distribution of carriers in the semiconductor. Therefore, by controlling the proton irradiation energy and dose, the on-characteristics of the semiconductor can be adjusted. In recent years, techniques for improving the trade-off between proton irradiation and switching characteristics have been widely adopted. This was made with attention to the point that the overvoltage can be arbitrarily defined, and this point will be explained in more detail below with reference to examples.

First, Fig. 3 shows a thyristor element with the same structure and the same dimensions, that is, the substrate resistivity is 400Ω, and the emitter thickness is 1.
0μm, p base thickness 100μm 1n base thickness 120
Using a thyristor element with an n emitter thickness of 0 μm and a thickness of 120 μm, protons of 9 M e V are emitted from the cathode side.
This shows the forward voltage-current characteristics when irradiating with varying doses.As the irradiation dose increases, the breakover voltage changes as shown by the characteristics ■, ■, and ■, with respect to the characteristic (■) before irradiation. It can be seen that the is decreasing. Note that the annealing conditions at this time were all the same: 400° C., 60 minutes.

The characteristic diagram in Figure 4 summarizes the relationship between the dose of irradiated protons and the breakover voltage at this time based on the characteristics in Figure 3.As shown in this characteristic,
The following may be the cause of the change (decrease) in the breakover voltage of the thyristor depending on the proton dose.

That is, first, when protons are irradiated onto silicon,
Although it is said that a shallow donor level is created, the formation of this donor becomes more noticeable when annealing is performed at a temperature of 300 to 400°C.

In this way, when silicon becomes a donor, its resistivity decreases. This is the resistivity ρ of n-type silicon. is expressed by the following formula, and the electron concentration n increases as donorization progresses.

ρ・″q・μ.・n Here, q: Elementary charge μfi: Electron mobility n: Electron concentration Also, the relationship between silicon avalanche breakdown voltage ■ヮ and substrate resistivity ρ is generally determined by the following experiment. The formula holds true, and as the substrate resistivity ρ becomes smaller, the avalanche breakdown voltage .

V-K・ρ, K: constant As shown above, as the proton dose increases, the substrate resistivity ρ, which is a condition for facilitating the formation of donors, decreases, so the breakdown voltage also decreases. Since the breakover voltage of the thyristor is determined by the breakdown voltage of the substrate wafer, it is thought that the breakover voltage can be controlled by the dose amount.

On the other hand, the way donors are formed also differs depending on the annealing after proton irradiation.

FIG. 5 shows the same thyristor element as in FIG.
P base thickness 100μm, N base thickness 1200μm
When a thyristor element with an emitter thickness of 120 μm is irradiated with protons of 6 Me V, 5 x 10 cm from the anode side, the voltage-current characteristics at breakover are shown as the characteristics immediately after proton irradiation. The characteristics after annealing (■) and (■) are shown separately. First, according to the characteristics immediately after proton irradiation, in this case, the voltage is approximately 8.5 kV.
There is a breakover at 320, as shown by the characteristic ■.
After annealing at 350° C. for 30 minutes, it drops to about 7.2 kV, and after annealing at 350° C. for 30 minutes, as shown by characteristic (2), it further drops to about 5.4 kV.

This is because donor formation was promoted by annealing after proton irradiation. As shown in 2, immediately after irradiation with radiation such as protons or electron beams, many crystal defects generated by this irradiation remain in the silicon, resulting in an increase in leakage current at high temperatures. Because it is stored away, it is common to anneal it before use.

From the results shown in FIG. 5, it can be seen that the breakover voltage due to proton irradiation can be controlled not only by the dose described above but also by the annealing conditions.

Therefore, according to the embodiment shown in FIG. 1, the breakover voltage characteristic by the peak region 12 can be arbitrarily set with high precision, and an overvoltage self-protection type thyristor having a predetermined and accurate breakover voltage characteristic can be easily obtained. be able to.

Next, a method of manufacturing the overvoltage self-protection type thyristor according to the embodiment shown in FIG. 1 will be explained with reference to FIG. 6.

First, as the semiconductor substrate 1, the substrate resistivity is 380Ω・mark,
An n-type silicon wafer with a thickness of 1500 μm is prepared, and AΩ (aluminum), which is an n-type impurity, is added to it approximately as follows.
Surface concentration is 7 x IO "low" diffusion source 145μm
The p-emitter layer 2 and the p-base layer 4 are formed by diffusing from both sides so that the p-type emitter layer 2 and the p-base layer 4 are formed (FIG. 6(a)).

Next, the diffusion surface that will become the cathode side, that is, the surface on the p-bar layer 2 layer 4 side, is etched to a depth of about 35 μm from the surface, and P (phosphorus), which is an n-type impurity, is etched there at 120 μm at 1100° C.
Due to the diffusion of
An n-type high concentration impurity layer n4 is formed (FIG. 6(b)).
, at this time, the sheet resistance under the J junction formed between these layers will be 600-1000Ω10. Note that the n" diffusion layer that is also formed on the anode side is about 20
Removed by micrometer chemical etching.

Next, the emitter pattern on the cathode side is transferred to the cathode surface using photolithography and formed using an etch-down method to create all the bonding structures required for the thyristor. Then, electrodes are placed on the anode and cathode sides respectively. After depositing Aα to a thickness of about 15 μm, it is selectively removed according to a predetermined pattern using the same photolithography technique to form an electrode (see Fig. 6 (C).
)).

In this way, the thyristor element with the bonding structure and electrodes formed is finally irradiated with protons.

In order to selectively irradiate protons only to the region constituting the pilot thyristor section, as shown in FIG. 6(d),
Using a shielding plate (mask) 15 made of a metal plate such as aluminum that has a shielding effect against protons, a dose of 5×10''' is applied from the cathode side (or the anode side) of the device at an energy of 9 MeV. Proton irradiation is performed under the conditions of -'.

After the irradiation is completed, the end face of the element is processed and a passivation material is applied to stabilize the surface, followed by an annealing treatment. The annealing temperature is in the range of 300 to 400° C. At this time, while observing the characteristics of the element with a curve tracer, short annealing of about 10 to 20 minutes is repeated until a predetermined breakover voltage is obtained.

Therefore, according to this embodiment, without changing the conventional manufacturing process of thyristor elements, proton irradiation is performed after the joining structure of the element is completed, and the subsequent annealing treatment is performed while monitoring the characteristics. By simply doing this, it is possible to easily obtain an overvoltage self-protection type thyristor having a predetermined breakover voltage.

Next, FIG. 7 shows another embodiment of the present invention, in which (a) is a cross-sectional view and (b) is a plan view, in which the present invention is applied to a thyristor having both a pilot thyristor and an auxiliary thyristor. In the figure, 9 is an auxiliary thyristor section, 11 is an auxiliary thyristor electrode, and the other configurations are the same as the embodiment shown in FIG.

Therefore, in this embodiment, there is a pilot thyristor region in the center of the device, an auxiliary thyristor region adjacent to the pilot thyristor region surrounding it, and a main thyristor region.
This is an overvoltage self-protection type thyristor constructed using a stage amplification method. In this embodiment, proton irradiation for forming the peak region 12 is performed from the side where the anode electrode 6 is present to the pilot thyristor region. This was carried out selectively in accordance with the

In this way, when protons are irradiated from the anode side, the crystal defect generation region 13 is applied to the J1 junction for blocking the reverse voltage of the thyristor. Leakage current in blocking conditions tends to be somewhat higher. Therefore, depending on the specifications of the element, it is only necessary to select whether proton irradiation is performed from the cathode side or from the anode side.

The embodiment shown in FIG. 7 also allows the breakover voltage in the pilot thyristor section 8 to be easily set with high precision, and similarly to the embodiment shown in FIG. The effect is that it can be easily obtained.

In the above description, an example in which the present invention is applied to an electric gate type thyristor has been described, but the present invention can also be applied to an optical trigger thyristor, a gate turn-off thyristor, etc.
Needless to say, the present invention can also be applied to thyristors other than electric gate type.

[Effects of the Invention] According to the present invention, the breakover voltage can be increased by adjusting the proton irradiation conditions after forming the junction necessary for the thyristor element and the subsequent annealing treatment conditions, without changing the conventional thyristor manufacturing process. Since it can be adjusted freely and easily with high precision, it is possible to easily provide a high-performance overvoltage self-protection type thyristor at low cost while improving yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an overvoltage self-protection type thyristor according to the present invention, FIG. 2 is a view showing the ion distribution and damage distribution in the depth direction, and FIG. 3 is a diagram showing the voltage - Current characteristic diagram, Figure 4 is a breakover voltage characteristic diagram with respect to dose amount, Figure 5 is a voltage-current characteristic diagram with annealing conditions as parameters, Figure 6 is a manufacturing process diagram,
FIG. 7 is a sectional view and a plan view showing another embodiment of the present invention,
FIG. 8, FIG. 9, and FIG. 10 are explanatory diagrams of the prior art, respectively. 1... Semiconductor substrate, 2... N emitter layer, 3... N base layer, 4... P base layer, 5... Old... n emitter layer. layer, 6... anode electrode, 7... cathode electrode, 8...
Pilot thyristor section, 9... Auxiliary thyristor section, 10... Pilot thyristor electrode, 1
1... Auxiliary thyristor electrode, 12...
Peak area of ion distribution due to proton irradiation, 13...
...This is a region where crystal defects are generated due to proton irradiation. 11\ Fig. 1 Fig. 2 Distance of the surface O Fig. 3 Voltage (kV) w & Fig. 5 Voltage (kV) O Fig. 4 Dose IL (cm-) Fig. 6 Fig. 7 Fig. 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. In a thyristor of a type that provides an overvoltage protection function by forming a portion where the forward breakdown voltage is lowered in a part of the junction surface, one of the semiconductors forming the junction surface. A feature is that a portion in which the ion distribution density exhibits a peak value is formed in the layer by proton irradiation, and the presence of the portion exhibiting this peak value forms a portion where the forward breakdown voltage is lowered. Overvoltage self-protection type thyristor. 2. In the invention of claim 1, the thyristor includes at least one of a pilot thyristor section or an auxiliary thyristor section, and the portion exhibiting the peak value is a section where at least one of the pilot thyristor section or the auxiliary thyristor section is formed. An overvoltage self-protection type thyristor characterized in that the overvoltage self-protection type thyristor is configured to exist in the thyristor. 3. In the invention of claim 1 or 2, the forward breakdown voltage characteristics of the portion where the forward breakdown voltage is decreased are determined by the irradiation conditions during the proton irradiation and the annealing treatment conditions after the proton irradiation. An overvoltage self-protection thyristor characterized by: