DE1229651B - Process for the production of a power rectifier with a single crystal semiconductor body and four layers of alternating conductivity type - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

HOIl

German class: 21g -11/02

Number: 1229 651

File number: S 91516 VIII c / 21 g

Filing date: June 13, 1964

Opening day:! December 1966

The subject of patent application S 81478 VIIIc / 21 g, German Auslegeschrift 1214 790 is a power rectifier with a monocrystalline semiconductor body, containing four successive layers of alternately opposite conductivity types, of which the first, second and third layers have a first transistor and the second, third and fourth layers Form a second transistor and the second layer has a higher doping concentration than the third layer, in which the current gain factor of the first transistor in the current density range below 10 mA / cm ^{2 is} very small compared to one and in the current density range between 10 and 100 mA / cm ² steeply opposite One increases and the current amplification factor of the second transistor is practically independent in the last-mentioned current density range. Such a controllable semiconductor rectifier, also called a thyristor, can, according to the main patent, be designed, among other things, in such a way that at least the second layer additionally contains recombination centers. Those defects are favorable as recombination centers whose energy level is closer to the middle of the forbidden energy band of the semiconductor material between its valence and conduction band than the nearest edge of the forbidden energy band and which have a significantly larger capture cross-section compared to the minority carriers of the second inner layer than compared to their majority carriers. Such recombination centers can, for. B. consist of gold.

Processes of recombination and pair generation take place at the recombination centers. They therefore determine the service life of the charge carriers or their diffusion length in the rectifier, especially in its two inner layers or base areas. In particular, they bring about a highly current-dependent service life of the charge carriers in the low-resistance of the two inner layers. Only at relatively high current densities of more than 10 mA / cm ² does the life of the current carrier become very long. Therefore, the current gain in the low-resistance inner layer is initially very low with small currents, but increases sharply towards the value one ^{at higher current densities between 10 and 100 mA / cm 2.} With a sufficiently high doping of the low-resistance inner layer, for example a sufficiently high excess of acceptors if the low-resistance layer is p-conductive, this characteristic curve of the current gain factor remains unchanged up to relatively very high temperatures.

Method for manufacturing a power rectifier with a single-crystal semiconductor body and four layers alternating
Conductivity type

Addition to registration: S 81478 VIII c / 21 g ■
Interpretation document 1214 790

Applicant:

Siemens-Schuckertwerke Aktiengesellschaft,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Named as inventor:

Dr. rer. nat. Adolf Herlet, Pretzfeld;

Dr. rer. nat. Kurt Raithel, Uttenreuth

Claimed priority:

Switzerland of June 25, 1963 (7883)

Recombination centers with an energy level roughly in the middle of the forbidden band, which are for the minority carriers in the low-resistance inner layer have a much larger capture cross-section than for the majority carriers and those in the low-resistance inner layer have the lifespan Make the charge carriers current-dependent, if they are also in the second, higher-resistance inner layer of the opposite conductivity type are present, there a practically current-independent one Service life and thus a largely current-independent value of the current gain in this Layer. The total current gain factor, i.e. H. the sum of the current gain factors of the two Inner layers, at high currents, can be caused by the number of recombination centers that have diffused in and the choice of the thickness of the inner layers can be adjusted.

As is well known, thyristors only block in the forward direction as long as the total current gain factor of the two inner layers or base regions is less than the value one. The value becomes one reached, the thyristors flip; so they become leading. When enriching the inner layers with However, this danger exists in recombination centers

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not as long as the current density in the forward direction is not at least 10 mA / cm ² and more, provided that the current amplification factor of the higher-resistance inner layer is a reasonable value less than Ems. The latter, however, is also possible by introducing the special recombination centers into the higher-resistance inner layer and by appropriately dimensioning the thickness of this layer. Such high current densities (leakage currents) of more than 10 mA / cm ^{2 are} now reached by the pnpn- ίο rectifier in the blocked state only at the maximum blocking voltage determined by the punch-through voltage or the break-down voltage At very high temperatures, such leakage currents are already reached at lower voltages. However, since the specified curve for the service life of the charge carriers, as already mentioned, remains largely independent of temperature if the low-resistance inner layer is sufficiently highly doped, the breakover voltage also remains temperature-independent, namely, it is equal to the breakdown voltage or breakdown voltage up to very high temperatures of about 150 ° C. and more. By incorporating recombination centers, with a sufficiently high doping of the low-resistance inner layer, the breakover voltage has a sufficiently high value and is independent of temperature However, the low resistance is allowed The inner layer must not be doped too heavily, as otherwise the rectifier's ignition current will be unacceptably high.

With these measures, however, one also achieves good transmission properties at the same time. This is what it is for namely required that in the range of high forward currents, the diffusion lengths of the charge carriers in both inner layers are sufficiently large compared to the width of these layers. That means but that the sum of the current amplification factors of the two inner layers is in the range of high forward currents clearly greater than the value one must be. Since the current gain factor in the low resistance Inner layer is very small up to relatively high reverse currents, the current gain factor can be chosen to be relatively high in the higher-resistance inner layer. Since now the current gain factor in the low-resistance inner layer becomes very large and approximate at higher currents reaches the value one, is therefore the sum of both current amplification factors at high forward currents significantly larger than one. With a sufficiently high doping, the low-resistance inner layer is thus obtained through the installation of recombination centers also low forward voltages and therefore good transmission properties of the thyristor.

Although it is sufficient to place the recombination centers of the required type alone in the more highly doped inner layer to introduce, it will generally be easier to use the recombination centers described to be distributed approximately evenly over the entire semiconductor crystal.

With the invention, the power rectifier is further improved according to the main patent application. While maintaining good transmission properties and the temperature stability of the breakover voltage If the quenching speed is increased, the switching time of the rectifier and the ignition current are reduced. The latter is known not to be very large, d. H. not be greater than a few hundred milliamperes. Simultaneously the time of the operations in the manufacture of the rectifier is reduced, since also on two-stage diffusion processes are dispensed with when doping the low-resistance inner or base layer can be. In addition, the recombination centers are created at the same time as the emitter contacts are alloyed built into the low-resistance inner layer of the rectifier.

The invention accordingly relates to a method for producing a power rectifier with a monocrystalline semiconductor body, containing four successive layers of alternately opposite conductivity types, of which the first, second and third layers form a first transistor and the second, third and fourth layers form a second transistor and its second Layer has a higher doping concentration than the third layer, in which the current gain factor of the first transistor in the current density range below 10 mA / cm ^{2 is} very small compared to one and in the current density range between 10 and 100 mA / cm ² rises steeply to one and the current gain factor of the second Transistor in the last-mentioned current density range is practically independent of current, according to patent application S 81478 VIII c / 21g. According to the invention, acceptor material is diffused into an excess conductive flat silicon single crystal, which has a donor excess of at most 10 ¹⁵ cm ^-3 , and then the η emitter is formed by placing an antimony-containing gold foil in the diffusion zone created in this way by an alloying process at which temperature values in the range be held between 800 and 900 ° C for at least 5 minutes, is alloyed.

The invention and its advantages are explained in more detail with reference to the drawing.

The drawing shows the cross-sectional profile of a thyristor which has been produced by the method according to the invention. The rectifier consists of a semiconductor body 2, which is made, for example, from a single-crystal plate or disk made of weakly doped silicon as a raw crystal. The raw crystal is η-conductive and has at most a donor excess of 10 ¹⁵ cm ^-3 . A donor excess of 1 to 3 · 10 ¹⁴ cm ^-3 , preferably 2 · 10 ¹⁴ cm ^-3 , has proven to be useful The silicon wafers used were 18 mm in diameter and 0.3 mm thick. By diffusing in acceptor material such as gallium, boron or preferably aluminum, for example from the gas phase, a diffusion zone 4 surrounding the raw crystal on all sides is produced surrounds a region 3 of the raw crystal that has remained unchanged η-conductive and ultimately acts as the η-base and from which the p-base Aa of the rectifier finally emerges, thereby becomes p-conductive.

Subsequently, according to the invention, on one flat side of the semiconductor body 2, creating a contact 5 and an n-type emitter 6 consisting of the recrystallization zone is an annular one Gold foil containing antimony is alloyed into the diffusion zone 4. In this alloying process, according to the invention Maintained temperature values in the range between 800 and 900 ° C for at least 5 minutes. It has proven to be particularly beneficial to alloy at 840 ° C for 20 minutes. This will achieved that the recombination centers forming

Gold in sufficient concentration in those adjacent to the emitter 6, acting as p-base 4 α Part of the diffusion layer 4 and diffused into the effective n-base area 3.

To create the p-emitter 10 and the contact 9, the other On the flat side of the semiconductor body 2, an aluminum foil covering approximately the entire surface is alloyed. The recrystallization zone acts as a p-emitter 10. It is approximately uniform and higher with acceptor defects doped as the part of the diffusion zone 4 originally located in its place. In the center of the annular contact 5 is a control contact 8, for example made of aluminum, in the as p-base 4 a acting part of the diffusion zone 4 alloyed. So that the p-base 4 a with the p-emitter 10 has no low-resistance connection, the edge layer 4 is interrupted by an annular trench 7, which can be produced by mechanical or chemical processing. so

In a according to the method according to the invention rectifier made to the Akzeptorenüberschuß in the boundary layer between the p-type base 4a and the n-Emitter6 less than 10 ¹⁷ cm ^-3, but at least 10 ¹⁶ cm ~ ^s amount and in the boundary layer between the p-base 4 a and the area 3 effective as η-base lower by several powers of ten. The resulting mean acceptor concentration in the p-base 4 a is on the one hand high enough, in cooperation with the recombination centers built in by the alloy process according to the invention, a low forward voltage, good temperature stability of the breakover voltage and a short switching time or high quenching speed of the rectifier to ensure. On the other hand, the edge concentration of the acceptors in the region of the p-base 4a adjacent to the n-emitter 6 is not so high that the ignition current is too large, ie greater than a few hundred milliamperes.

Claims (5)

Patent claims: 1. A method for producing a power rectifier with a monocrystalline semiconductor body, containing four successive layers of alternately opposite conductivity types, of which the first, second and third layers form a first transistor and the second, third and fourth layers form a second transistor and the second layer forms a higher one Has doping concentration as the third layer, in which the current amplification factor of the first transistor in the current density range below 10 mA / cm ^{2 is} very small towards one and in the current density range between 10 and 100 mA / cm ² rises steeply towards one and the current amplification factor of the second transistor in the last-mentioned current density range is practically independent of current, according to patent application S 81478 VIIIc / 21g, characterized in that ^{acceptor material diffuses into an excess-conductive flat silicon single crystal, which has a donor excess of at most 10 15} cm ^-3 , and then the η- Emitter is formed by an antimony-containing gold foil are held by an alloying process in which temperature values in the range between 800 and 900 ⁰ C for at least 5 minutes in the thus formed diffusion zone, is alloyed. 2. The method according to claim 1, characterized in that the antimony-containing gold foil is alloyed into the diffusion zone at an alloy temperature of 840 ° C. 3. The method according to claim 2, characterized in that the alloy temperature of 840 ° C is maintained for 20 minutes. 4. The method according to claim 1, characterized in that an acceptor material, such as. B. gallium, boron or preferably aluminum, is diffused into the silicon single crystal in such a concentration that the excess acceptor in the boundary layer between the diffusion zone ^{and the η emitter formed by alloying the antimony-containing gold foil is at most 10 17 cm -3} and at least 10 ¹⁶ cm ~ ³ is. 5. The method according to claim 1, characterized in that a flat, monocrystalline silicon plate ^{or silicon wafer with a donor excess of 1 to 3 · 10 14 cm 3} , preferably 2 · 10 ¹⁴ cm "" ³ , is used as the starting body. Considered publications:
German interpretative document No. 1113 520. 1 sheet of drawings 60S 729/329 11.66 Bundesdruckerei Berlin