JPS6154667A - Thyristor unit and method of producing same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thyristor device (including a gate turn-off device) and a method for manufacturing the same.

The invention particularly relates to a cyrisk device manufactured by a diffusion process. If an impurity is diffused into the semiconductor material from one major surface of the elementary element, the impurity concentration is greatest adjacent to said major surface and gradually decreases with increasing depth, substantially following the error function curve. go.

The dynamic switching characteristics of semiconductor silice devices are greatly influenced by a single common factor in the form of control base layer resistivity or conductivity, which affects both the turn-on and turn-off capabilities of the device.

When the conductive regions of a semiconductor device are formed by a diffusion process, the resistivity is maximum at the bottom and gradually decreases toward the surface.

Ideally, in an emitter shorted silicon risk, the lateral resistance of the base layer should be low, and the effective resistance between any part of the base layer and the emitter contact should be relatively high. This is the opposite of the result when applying a conventional diffusion process to the fabrication of silice, so the actual attempt is to have the base layer have the highest resistance value and the desired dv/dt material to achieve the desired turn-off/turn-on performance. This is a compromise solution to achieve the following.

In gate turn-off thyristors, the maximum load current that can be turned off is directly related to the gate injection current, which is limited by the resistance of the control base layer and the maximum available gate voltage. Therefore, the resistivity of the base layer is preferably low, while the mate voltage limit is determined by the reverse breakdown voltage of the emitter-base junction, which is improved if the resistivity of the base layer is high. This, in turn, requires a conductive profile that is the opposite of that created by conventional diffusion processes.

The basic concept of this invention is to use out-diffusion to reduce the concentration of impurity levels adjacent to the main surface.
n) process by which the lateral or sheet resistance of the desired layer can be controlled to an extent (F-) that advantageously influences the properties of the finished device.
British Patent No. 972, which discloses limited source diffusion in the manufacture of germanium transistors;
It is known from the specification of No. 653.

Germanium semiconductor technology has generally not been directly applicable to silicon device fabrication processes due to the inherent differences in the two materials, the differences in doping agents used, and their behavior.

British Patent No. 1,351.867 also discloses the fundamental problem of a "normally graded" diffused semiconductor layer in the base region of the silice, and proposes the production of a single "reversely graded" layer by Evita quintal vapor deposition. are doing.

Epitaxial methods are inherently more costly than diffusion methods and tend to form laterally non-uniform layers, which are particularly evident in the relatively large surface area element characteristic π of the thyristor.

According to the invention, in a method for manufacturing a thyristor device having a multiplicity of superimposed semiconductor layers of alternating conductivity type, the control base region diffuses at least a p-doping agent, such as Ilicum, from a source of pl'-pigment agent. After a period of time during this diffusion step, the dopant source is removed and the diffusion step continues to outdiffuse the surface region to form a graded dopant concentration profile with a maximum at a depth midway through the control base region. Provided is a method for manufacturing a thyristor device characterized by forming a thyristor device.

In the emitter-shorted thyristor device manufactured according to the method of the invention, the doping Di profile has a maximum in the base layer and decreases towards the emitter surface,
Forming an emitter short with relatively high resistivity.

In gate turn-off silicones produced by the method of the present invention, the dopant concentration profile has a maximum in the control base layer.

In order to better understand the invention and to show how it may be carried out, reference will now be made, by way of example only, to the accompanying drawings, in which: FIG.

In the emitter short-circuit type sirisk, in order to short-circuit the emitter, the p-
The lateral resistance in the base layer must have a sufficiently low value. On the other hand, the effective resistance between the emitter contact and any point on the base via the short-circuit path should have a relatively high value in order that the conduction properties are not unduly compromised. Furthermore, the effective resistance of the lateral ballistic resistance should ideally be the same for all points (sections) of the emitter layer.

Therefore, in theory, an effective emitter short thyristor structure would have a p-base resistance of zero (neglecting the effect of this on the emitter injection efficiency) and an electrical short path between the p-base and the emitter electrode. is expected to have a series resistance of .

In practice, this type of structure is approximately achieved if the distributed p-base resistance is as small as possible, but a relatively large resistance is included within the structure of the emitter short itself.

The present invention alters the diffusion process to form a p-type thermoelectric base layer and grade the resistivity of portions of the region that are later masked during n-type emitter diffusion to create an emitter with desired characteristics. Form a short circuit. After forming the p-doped layer by a normal diffusion process, subsequent steps such as oxide! , there is a slight tendency for the surface layer of p-based diffusion to "out-diffuse" during the skinning and emitter diffusion steps. The p-doping agent evaporates from the surface of the silicon flake, so that the thin surface layer is free of p-doping agent and has essentially no depth.

In this invention, a very strong out-diffusion penetrates to a considerable depth within the silicon flake and a significant reverse concentration profile compared to that originally given for normal in-diffusion is obtained. can get. By adjusting the time intervals of the presence and absence of the p-doping agent source during this step and appropriate adjustment of other parameters affecting the diffusion process, the out-diffusion is fully depleted to substantially the same depth as the subsequent n-emitter diffusion. strictly controlled to form a defined area.

Next, referring to the drawings, FIG. 1 shows a cross section of a thyristor 1 having an emitter short circuit structure. The short circuit 2 consists of a column 3 of p21 semiconductor material which extends upwardly from the p-type base layer 4 through a hole 5 in the upper n emitter layer 6. The shorts 2 have a circular cross-section with a diameter d and are arranged equilaterally triangularly on the entire surface of the device at mutual intervals.

For the illustrated type of device with the illustrated short configuration, the effective distributed lateral base resistance is approximately expressed as:

where Ra = distributed lateral base resistance at maximum mutual distance, D = mutual spacing of the shorts, d = diameter of the shorts,
7:1. = pm, average resistivity of the base layer.

W, = the depth of the p-type base layer, or the series resistance of the short-circuit is given by where Rs = the series resistance of the emitter short, pS = the average resistance of the p-type material in the column of the short-circuit. Wn=depth of n-type emitter layer.

The total resistance of the short circuit is therefore the sum of these two equations. That is, R (short circuit) = Ra -1-R.

The purpose of this invention is to increase the ratio RS /Ra. The proposed method consists in increasing the value of Rs without significantly affecting the value of Ra for one conventional device. Although there is no absolute theoretical limit on the value of R3, it is well noted that a thyrisk device where Rs << Ra does not provide a significant improvement over existing thyristor structures. On the other hand, performance improvement generally means that Rs is at least Ra/10
and preferably when R8>>Ra/lo.

In the thyristor constructed by the method proposed in this invention.

The lateral resistance ga of the base layer has properties that are substantially distinguishable from those obtained by conventional methods in similar devices. For comparison, FIG. 2 (ω) shows the doping agent profile obtained by the conventional or existing method (solid a) and that obtained by the proposed method (dotted line).

In Figure 2 (al), the p-doping agent concentration contour obtained with the existing conventional diffusion process is shown as a solid line, and the modified p-doping contour obtained by out-diffusion of the proposed diffusion process is shown with a dotted line. Indicated by

The outdiffusion effect is due to the fact that the p-doping agent source is introduced early enough in the process to provide enhanced surface removal of the p-type dopant in the p-type region formed by continuing out-diffusion for -periods. produced by removal. The increase in the initial p-dopant surface concentration forms a p-base region (see Figure 2(b)) below the emitter diffusion region, which has properties very similar to the contours obtained with conventional methods, especially in terms of injection efficiency and delivery rate. can be used to compensate for the initial removal of the p-doping agent.

Gallium has been found to be a particularly suitable doping agent since the diffusion of lanogallium atoms into and out of the silicon surface is substantially unhindered by surface oxides. A typical final profile of dopant concentration, including emitter diffusion, as can be seen in cross section X--X of the device of FIGS. 1 and 4 is shown in FIGS. 2 et al. As can be seen in particular from the drawings, the control base layer is located above and below the depth limit, e.g., about 3 below the emitter surface of the device.
The doping agent concentration reaches its peak at 0μ. However, the emitter diffusion extends to a relatively shallow depth of approximately 15 microns, forming an emitter junction within its lower limit region.

Therefore, the effective resistivity fs of the surface area used to form the emitter short with resistance Rs can be increased by a factor of ten. For a given value of the short-circuit resistance Rs, the short-circuit cross-section (-j, -d) can be increased by a corresponding factor, increasing the short-circuit diameter d by a factor of l"17, or 3.16
Increase twice. This allows the invention to achieve the desired short resistance while increasing the short diameter to a more advantageous dimension, thereby eliminating the problems that may arise due to the short diameter being too small for easy actuation. It will be resolved. For example, in a typical device where the total emitter short surface area is 2% of the total emitter area, the present invention can increase this area up to about 20%. However, such high values are an exception; in general, the emitter short area ranges from 5% to 5% of the total area of the cathode emitter.
As an example, for a typical device of the type referred to in the above equations with a high density of small shorts, the usual design calculations assume that the mutual spacing of the shorts D = 300 μm. In this case, the total short circuit area is 2.5% of the total emitter area.

Let the depth of the n-type layer be Wn =: 20 μm, and the depth of the n-type layer be wp = 40 μm.

It is. Therefore, the ratio Rs/Raz 2/)S//'1)
It is.

In conventional devices, the typical value of the resistivity ratio, Ps/Pp, is approximately 0. + and thus Rs/Ra = 0.2 O In a corresponding device constructed using the invention, the diffusion profile reduces the resistivity ratio to 7' s/J) p = 0.5
and therefore Rs/Ra=I.

It is found that the above-described diffusion profile is generally satisfactory if the aluminum surface contact is attached to the anode surface by vapor deposition and sintering or especially by alloying with aluminum or an aluminum alloy. If other types of contacts, such as nickel plating, are desired, one surface concentration of a conventional p-doping agent (typically gallium) may be initially enhanced with, for example, boron to obtain reliable low resistance contact properties. Boron is particularly suitable because it has a low diffusion constant and is highly soluble in silicon. This is inconsistent with the invention if the penetration depth of the enhancing dopant is small compared to the depth of the out-diffusion effect.

In gate turn-off thyristors, the current that can be turned on is directly related to the gate injection current, which is jointly determined by two factors. That is,
The first is the conductance of the p base region from which most of the carriers must be extracted to the extraction terminal, that is, the gate terminal.

Also second is the maximum voltage Vt that can be used to perform such injection.

As shown in Figure 3.4, the maximum voltage v2 is actually the reverse breakdown voltage of the emitter-base junction 53', which is
This can be improved if the resistivity of the p-base layer is relatively high. On the other hand, for a given emitter size, the conductance of the p-base layer is improved by keeping its resistivity to a minimum.

As previously described, the normal gradation of the p-base resistivity as formed by the normal diffusion process is the junction J2.
The junction J3 is generally at an intermediate resistivity; in the device shown in FIG. 4 this junction J3 rises to the surface of the edge of the emitter and therefore the breakdown voltage is at a minimum.

The breakdown voltage of junction J3 in the device mode according to the invention is increased compared to the breakdown voltage of prior art devices with the same average p-base resistivity below junction J3, so that the breakdown voltage and the lower p-base conductivity The product with the rate is increased. This also eliminates the defect of the junction J3 appearing at the surface of the device as in the case of FIG. 2, ie the resistivity increases towards the surface so that the breakdown voltage does not drop.

Preferably, the depth of the emitter diffusion to form junction J3 does not exceed the depth of the maximum diffusion concentration of the p base region. The lateral base resistance is determined by the harmonic average value of the base resistivities, while the p-base resistivity, which acts on the voltage breakdown of junction J3, is determined by the minimum resistivity approaching the junction. Therefore, additional benefits may be obtained in forming the emitter-base junction J3 at a shallower depth than the surface in gate turn-off thyristors compared to emitter-shorted thyristors, as shown in the relative contours of FIG. 5.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the cross-section of a short-circuited emitter thyristor, Figure 2 (ω is a comparison diagram of doping agent profiles in short-circuited emitter thyristors made by the existing method and the proposed method, and Figure 2 (C) 1 and 4 in a final device formed in accordance with the invention.
Figure 3 is a schematic cross-sectional perspective view of a gate turn-off thyristor with a mesa cathode structure, Figure 4 is a schematic cross-sectional perspective view of a gate turn-off thyristor with a planar structure, and Figure 5 is a schematic cross-sectional perspective view of a gate turn-off thyristor with a planar structure. and FIG. 6 shows the relative position of the junction with respect to the base layer dopant concentration profile of the gate turn-off thyristor. In the figure, 1: thyristor, 2: short circuit, 4: p-type base layer, 5: hole, 6: n-type emitter layer, Jl,
J2. J3: Joining. Engraving of drawings (no internal changes) Fta, 2 7-node procedural amendment (method) % formula % 1. Indication of the case 1982 Patent application No. 172544 3. Person making the amendment Relationship with the case Patent applicant address Great Britain, Wild Dodger, Chitsubenno 1
View Hill (no address or other information) Name Unirochiingtu Coffin φ Blake Book and Signal Come Honey Limited 4, Agent Drawing

Claims (1)

Claims: 1. A method of manufacturing a thyristor device having a plurality of stacked semiconductor layers of alternating conductivity type, wherein the control base region diffuses a p-doping agent, such as gallium, from at least a source of p-doping agent. After a period of time during this diffusion step, the dopant source is removed and a subsequent diffusion step is performed to outdiffuse the surface region to produce a graded dopant with a maximum at a depth midway through the control base region. A method for manufacturing a thyristor device, characterized in that it forms a concentration contour. 2. Out-diffusion of the surface region to form a depletion region of approximately the same depth as the subsequent n-emitter diffusion.
The method described in section. 3. Initial p for the concentration level used in the conventional method
3. A method as claimed in claim 1 or claim 2, in which the dopant surface concentration is enhanced to compensate for relatively early removal of the dopant source. 4. The method according to claim 3, wherein the normal p-doping agent is enhanced by an additional doping agent. 5. The method according to claim 4, wherein the addition enhancing doping agent is boron. 6. A thyristor device manufactured by the method according to any one of claims 1 to 5. 7. Thyristor device according to claim 6, in which the concentration profile of the base layer dopant has a maximum value in the base layer and a value in the emitter short that decreases towards the emitter surface. 8. Thyristor device according to claim 6 or 7, wherein the base layer doping agent has a maximum value in the control base layer. 9. Thyristor device according to any one of claims 6 to 8, wherein the series resistance of the emitter short is at least 10 times greater than the effectively distributed lateral base resistance.