JPS61202465A - Thyristor with overvoltage protecting function - Google Patents

Abstract

PURPOSE:To accurately control a breakdown voltage by composing a high resistance base layer of layers having high and low impurity density, and partly removing the high density layer so that the region takes a voltage breakdown by punch-through. CONSTITUTION:A P-type emitter layer 11, an N-type base layer 12 and a P-type base layer 13 are commonly provided in the inner periphery of a main thyristor MT, and an auxiliary N-type emitter layer 17 and an auxiliary electrode 18 are provided to form a pilot thyristor PT. Further, a photoreceptor 23 is formed in the inner periphery of the thyristor PT, and a high impurity density base layer 21 directly under the thyristor PT is removed to form a voltage breakdown region 22 lower at a blocking voltage from the other region. The layer 17 of the thyristor PT is formed to be deeply diffused from an N-type emitter layer 14 of the thyristor MT to increase lateral resistance of the P-type base layer of the thyristor PT.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an overvoltage protection function that can safely trigger a voltage when an overvoltage that crosses the breakdown voltage (hereinafter abbreviated as VBO) is applied between an anode and a cathode. One thyristor is involved.

[Technical background of the invention and its problems]

When an overvoltage that crosses the breakdown voltage is applied between the anode and cathode of the thyristor, the thyristor is destroyed by a minute breakdown current of several mA to several tens of mA, resulting in -CL. In order to prevent the element from being destroyed due to erroneous firing due to the application of overvoltage, a thyristor with a rated voltage two to three times the power supply voltage is generally used. However, in devices that use a large number of thyristors connected in series, such as thyristor pulp for DC power transmission, if one of the thyristors fails to turn on, a small number of thyristors may receive an overvoltage several times the rated voltage. Overvoltage breakdown cannot be prevented by applying a margin t to the rated voltage described above. Therefore, an external protection circuit was required to prevent overvoltage from occurring. Under these circumstances, there has been a strong desire for a thyristor with an overvoltage protection function that will not destroy the thyristor when overvoltage is applied.

FIG. 3 is a schematic cross-sectional view of a conventional thyristor with an overvoltage protection function proposed to solve such problems. In the figure, an anode polarization 15 is provided on one surface of the P emitter layer 11 having a four-layer structure consisting of a CXP emitter layer 11, an N base layer 12, a P base layer 13, and an N emitter layer 14.
A cathode electrode 16t- is provided on the surface of the short-circuited N emitter layer 14.
A thyristor MTi is arranged and a thyristor MTi is arranged. In the inner peripheral part of the main thyristor MT, a P emitter layer 11 and an N emitter layer 11 are formed.
The base layer 12 and the P base layer 13t are commonly used, and an auxiliary N emitter layer 17 and an auxiliary electrode 18 are provided to form a C pilot thyristor PT. Further, on the inner circumference of the Vζ pilot thyristor PT, there is a P base layer 2 with a curved portion 19fc.
0 is the arrangement. This structure is, for example, a P base layer 13t.
- It is possible to realize "C" by etching away in a well shape and then thermally diffusing the Pfi impurity again to form a P base layer 20.Alternatively, by etching the NW wafer into a well shape and then applying Pfi from both sides of the Pfi impurity. A similar structure can also be obtained by diffusing type impurities.Also, in this structure, the auxiliary N emitter layer 17 of the pilot thyristor PT is diffused deeper than the N emitter layer 14 of the main thyristor MT, and the pilot thyristor FTOF base The layer lateral resistance is increased.

When an overvoltage is applied in the forward direction between the anode and cathode electrodes of 2C1 to such a structure, the electric field concentrates on the curved part 19, and the breakdown current generated near the curved part 19 causes the C pilot Thyristor FT and main thyristor MT are turned on in sequence.

However, such thyristors with overvoltage protection have encountered the following problems. VaO value is mainly curved 1!1s1
9 curvature and P base layer 13 and P base layer 200 step difference ΔX
is determined by ゛C. Since the curvature of the curved portion 19 is determined by etching conditions, it is not practical to control the cvno value by the curvature of the curved portion. Therefore, the 'c vB value is controlled by ΔX, but since the vno value sensitively affects ΔX, it is necessary to control ΔX with high precision. Figure 4 shows vao/vo and Δ
Indicates the relationship between X. However, Vo is the breakdown voltage when no curved portion is provided. The breakdown voltage is smaller when the junction temperature is lower, so for example, taking a thyristor with a rating of 4KV,
The value of Vo is selected to be 4 KV at the minimum guaranteed junction temperature (usually -40°C). V at -40℃
It is common to set the voltage to t-4 to 4.5 KV, so at '-400 Vo = 4.5 KV, vno =
Assuming that it is designed for 4 KV, VBo/Vo≦
It becomes 0.89.

As is clear from FIG. 4, in order to satisfy the condition of Yao/yo > 0.89, it is necessary to set Δx to 10 μm. From Fig. 3, ΔX is Δ”:′:Xoff −wPB+ 11)pr,
, , , , , , Moan - Song , , Song (1). however,
In formula (1), X. ff is the depth of the well-etched groove portion+'PB is the thickness of the P base layer 13+wp7 is the thickness of the P base layer 20C. ΔX is Xo f f・”
C is determined by three factors, PR and WPT.For example, when Δx<loμm, X is required to control minute ΔX with high precision. ff + WPBr 'PT
It became necessary to control VaO with even higher precision.
It is very difficult and rare to control the VC value to a predetermined value. [Object of the Invention] The present invention has been made with these circumstances in mind.
The purpose is to provide a thyristor with an overvoltage protection function that has a structure that allows the vBo value to be easily controlled.

[Summary of the invention]

The present invention consists of a high-resistance base layer of a thyristor consisting of a layer with a relatively high impurity concentration and a layer with a relatively low impurity concentration, and a part of the former is removed to cause voltage breakdown due to punch-through in this region. C1 is a thyristor with overvoltage protection function that can safely turn on when an overvoltage is applied between the anode and cathode.

〔Effect of the invention〕

According to the present invention, the VBG value is determined only by the thickness W of the layer with a relatively low impurity concentration of the high resistance base layer and the thickness Δω of the layer with a relatively high impurity concentration, so the etching depth and high precision can be determined. vBofLt with higher accuracy in a simple process compared to the conventional structure that controls the VBO value.
"It becomes possible to control the bending part 1.
Compared to the conventional structure in which voltage breakdown occurs at point 9, the area where voltage breakdown occurs can be made larger, so the thyristor can be safely turned on even if the gate sensitivity of pilot thyristor PT is low.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a thyristor according to an embodiment of the present invention. P emitter layer 11. N+ base layer 21°N- base layer 12. P base layer 13. An anode electrode 15 is provided on the surface of the P emitter layer 11 of the PNPN structure, which is made up of semiconductor layers laminated in this order.
A canned electrode 16 is arranged on the surface of the emitter layer 14.
C constitutes the main thyristor MT. The main thyristor MT has a P emitter layer 11. N base layer 12°P base layer 13 is shared, auxiliary N emitter layer 17
The pilot thyristor PT is completely formed by providing the auxiliary electrode 1st. Furthermore, a light receiving section 23 is formed in the inner peripheral part of the pilot thyristor PT, and the pilot thyristor PT
The N 2 base layer 21 immediately below is removed to provide a voltage breakdown region 22 having a lower blocking voltage than other regions.

In addition, in this structure, the auxiliary N emitter layer 17 of the pilot thyristor PT is formed by diffusion deeper than the N emitter layer 14 of the main thyristor MT, and the pilot thyristor PT
The lateral resistance of the P base layer is increased.

When an overvoltage is applied in the forward direction between the anode and cathode electrodes of the thyristor with overvoltage protection function having such a structure, a depletion layer grows in the N-base layer 12, and depletion occurs in the region where the N-base layer 21 is located. Either the layer is stopped at the N+ base layer, or the depletion layer continues to grow without being stopped in the region 22 where the N base layer is removed, and finally the depletion layer reaches the P emitter layer 11, causing a voltage breakdown due to punch-through. happen. The breakdown current that flows at this time flows laterally to the P base layer 13t of the pilot thyristor PT region, and flows from the C cathode electrode 16 to the external circuit via the short circuit t of the N emitter layer 14. As a result, the breakdown current causes a lateral voltage drop in the P base layer 13 of the pilot thyristor FT region and the auxiliary N emitter layer 1 of the pilot thyristor PT.
7 and the P base layer 13 are forward biased. When this forward bias value exceeds the built-in potential of the junction, electron injection occurs from the auxiliary N emitter layer 17, and the pilot thyristor PT is turned on with an overvoltage.

The on-current of the cono-pilot thyristor PT is auxiliary to pole 1.
8t-d P base layer 1 of C main thyristor MT
3 as a gate current, and the main thyristor MT is turned on.

Consider the conditions under which voltage breakdown occurs due to punch-through in the region 22 where the N+N base layer 1 is removed at the time of death due to the application of overpressure.

FIG. 2 shows the electric field strength in a region with and without an N+ base layer. N-base layer thickness 11: w, N+N base layer thickness is Δω, N+
The breakdown voltage value VPT due to punch-through in the dead area after removing the N base layer is 1 VPT: pressure (W + Δω) 2...
・・・・・・・・・・・・−・・・−(2) Given by 2ε. Here, e is the dielectric constant of the semiconductor, ? is the charge of one child, and N is the impurity concentration of the N-base layer. -Also, the forward blocking voltage in a certain region of the N+N base layer is V = Er, w -j! -! ! −w ”−・・−
・−・・−・−・−・・・・==−・−= (3) Given by g. Here, E is the value of the electric field at the central junction of the region around the N base layer. Therefore, the value of 6 when punch-through occurs in the region where the base layer is removed is E・=iN “1”122 from equation (2), f3).
・・・－・・・・・・・・・－・・・・－・・・(4) 2g
It becomes W. If E2 is smaller than the breakdown electric field gc of the semiconductor, then
Avalanche breakdown does not occur, but voltage breakdown occurs due to punch-through. The condition can be found from equation (4). For example, the impurity concentration of the N-base layer N = 4X
1013 crs-”, N-base layer thickness!1l=
When the thickness is 310 μm, the avalanche breakdown solder pressure value Vo is 4.5 KV. At this time, the maximum value of Δω is 73 μm according to equation (5), and by selecting a value of 73 μm less than Δω, an arbitrary Vpr less than or equal to vO can be selected.

For example, if VPT=4KV, ΔI#=51 μm.

The change in VPT when Δω shifts by 1 μm is 22V,
It is possible to set Vpt with sufficient accuracy.

Further, according to the structure of the present invention, the region 2 without the N+ base layer
Since the breakdown current flows throughout the curved portion 19, the area over which the breakdown current flows is larger than in the conventional structure in which voltage breakdown occurs at the curved portion 19, and breakdown is less likely to occur.

Furthermore, since there is no N+ base layer 21 directly under the pilot thyristor FT, the injection efficiency of holes from the P emitter layer 11 is high, and the trigger sensitivity of the pilot thyristor FTI is increased, so a □ thyristor with a large withstand capacity can be obtained. Go away.

Various methods can be considered to realize the structure of the present invention.

For example, a method of forming the N base layer by a selective diffusion method (9) and a method of combining a selective diffusion method and an epitaxial method can be considered.

However, when manufactured by the above method, it is necessary to carry out the entire diffusion to a depth of 70 to 100 μm, which is the sum of the thickness of the P emitter layer and the thickness of the N base layer, resulting in a long diffusion time. As a manufacturing method that can solve all of these problems, a technology for directly bonding silicone to each other has recently been proposed and is attracting attention. The outline of this technology is as follows. First, in the case of this structure, the N base layer 21 is selectively diffused in advance in one silicon wafer, the P emitter layer 11 is diffused over the entire surface from the opposite side, and the other silicon wafer is
has a P base layer 13. The N emitter layer 14 and the like are diffused, and then the surface to be bonded is mirror polished to a surface roughness of 500λ or less. At this time, the surface state of the silicon wafer is HlOl-4H,SO from ζ.

→) (F → Following the pre-treatment step with dilute HF, perform “C” to degrease and remove the stain film adhering to the surface of the silicon wafer. Next, the mirror surface of the silicon wafer is washed with clean water for several minutes, A greasy water treatment such as a spinner treatment is carried out at room temperature.In this treatment process, the moisture that is assumed to have been adsorbed on the mirror surface of the silicone wafer is left as is, and excess moisture is removed. Avoid heating and drying at temperatures above 100°C, where most of the gas is dissipated.

For example, silicon quaver that has undergone these treatments is classified as class 1.
The mirrors are installed in the following clean atmospheric environment and bonded in close contact with each other with substantially no foreign matter intervening between the mirror surfaces.

Note that the silicon wafers bonded in this way were
The bonding strength can be increased by heat treatment at 0°C or higher, preferably 1000°C to 1200°C.

By using the above manufacturing method, the structure of the present invention can be realized with a short diffusion process. For example, when the boundary between the N+ base layer 21 and the N- base layer 12 is used as the adhesive surface, the N base layer 21 can be diffused from the adhesive surface side, so the portion corresponding to the P emitter layer 11 is There is no need to perform diffusion, and the diffusion time can be significantly shortened.

Further, when an adhesive surface is set in the middle of the N base layer 21, selective diffusion can be performed to both sea urchins IJ-, and the diffusion time can be further shortened.

In the above embodiment, the light receiving section 23t is a light firing thyristor that can be triggered by an optical trigger signal, but it may be a normal electrically triggered thyristor. Moreover, it does not have to be an amplification gate structure.

Since the structure of the present invention has a low reverse blocking voltage, it is particularly effective for overvoltage protection of thyristors with a structure that inherently has a small reverse blocking voltage or with a structure that allows a droplet flow to actively flow in the reverse direction. . For example, the structure of the present invention is particularly effective when the main thyristor MT is a reverse conduction thyristor in which a reverse diode is combined, a gate turn-off thyristor (GTO) with an anode seat structure, a reverse conduction GTO, or the like.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the thyristor with overvoltage protection function of the present invention, Figure 2 is a diagram showing the electric field strength when a forward voltage is applied to the thyristor of the present invention, and Figure 3 is a diagram of the thyristor with overvoltage protection function of the prior art. FIG. 4 is a diagram showing the relationship between ΔX and Vao/Vo. MT...Main thyristor PT...Pilot thyristor 11...P emitter layer 12...N-base layer 13...P base layer 14...N emitter layer 15...Anode electrode 16...・Cathode electrode 17...Auxiliary N emitter layer 18...Auxiliary electrode 21...N base layer 22...Overvoltage breakdown region 23...Representative of light receiving section Patent attorney Noriyuki Chika (and 1 other person) Fig. 2 11-N+ base force abe1' t fist □N+ to one person tJ''no dougonggi E?'' Fig. 4 ΔX (μm)

Claims (7)

[Claims] (1) A first emitter layer of the first conductivity type, a first base layer of the second conductivity type with a relatively high impurity concentration, a first base layer with a second conductivity and a relatively low impurity concentration, a first base layer of the first conductivity type with a relatively low impurity concentration; In a thyristor in which a second base layer and a second emitter layer of a second conductivity type are laminated in this order, a portion of the first base layer having a relatively high impurity concentration is removed, and the forward blocking voltage value is reduced to another region. A thyristor with an overvoltage protection function that is characterized by having a breakdown voltage region lower than that of the thyristor. (2) When the thickness of the first base layer with a relatively high impurity concentration is W, the thickness Δω of the first base layer with a relatively low impurity concentration is ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ε: The overvoltage protection function according to claim 1, characterized in that dielectric constant of the semiconductor, g: electron charge Ec: breakdown electric field, N: lower than the impurity concentration of the first base layer, which has a relatively low impurity concentration. Thyristor. (3) The low breakdown voltage region is provided in a pilot thyristor region that shares three semiconductor layers other than the second emitter layer of the thyristor. Thyristor with overvoltage protection function. (4) The thyristor with an overvoltage protection function according to claim 1, wherein the pilot thyristor is fired by an optical trigger signal. (5) The thyristor with an overvoltage protection function according to claim 1, wherein the region with a low breakdown voltage has a longer N-based carrier lifetime than other regions. (6) The thyristor is manufactured by directly bonding semiconductors between a first base layer with a relatively low impurity concentration and a first base layer with a relatively high impurity concentration. Thyristor with overvoltage protection function as described in Range 1. (7) The thyristor with an overvoltage protection function according to claim 1, wherein the thyristor is manufactured by directly bonding semiconductors to each other in a first base layer having a relatively high impurity concentration.