DE1275208B - Controllable semiconductor rectifier - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

HOIl

German KL: 21g-11/02

Number: 1275 208

File number: P 12 75 208.8-33 (N 20596)

Filing date: September 26, 1961

Opening day: August 14, 1968

The invention relates to a controllable semiconductor rectifier with a semiconductor wafer, which has two electrodes of unequal size and on one surface side of the semiconductor wafer the other surface side has a third electrode.

Such known controllable semiconductor rectifiers have a round or rectangular semiconductor wafer.

The invention is based on the knowledge that a round or rectangular semiconductor wafer is not necessary and also not expedient and that a different shape of the semiconductor wafers is possible is, the controllable semiconductor rectifier in a simple, time and material-saving process can be produced.

The invention consists in that the semiconductor wafer, controllable semiconductor rectifier, is sector-shaped and that of the two electrodes on one surface side, the larger one becomes one greater distance from the sector center than the other.

In the drawings, FIG. 18 readily shows that given electrodes 18 and 19 Unequal size, a sector-shaped semiconductor wafer can be smaller than a round or rectangular one Semiconductor wafer and that the volume of the sector-shaped semiconductor wafer is optimally used can be.

To manufacture the semiconductor wafers for controllable semiconductor rectifiers, it is known that the procedure is as follows: that a rod of semiconducting material transversely to its longitudinal direction in plates with two flat and parallel surface sides is divided, and these plates by cuts approximately perpendicular to them both surface sides of the plates are divided into smaller semiconductor wafers.

In known methods, the cuts are made through the plates so that the semiconductor wafers become rectangular or square. It is also known to make circular cuts in the panels to make so that round wafers are formed. In neither of these two cases is it possible to take full advantage of the panels, which are usually round or elliptical in shape. When cutting out rectangular or square semiconductor wafers occur in particular at the edge of the disks losses; These losses also occur when round semiconductor wafers are cut out between the semiconductor wafers themselves. These losses are greater, the smaller the number of from a plate to be cut semiconductor wafers.

Controllable semiconductor rectifier

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. E. E. Walther, patent attorney,

2000 Hamburg 1, Mönckebergstr. 7th

Named as inventor:

Willem Baas, Nijmegen (Netherlands)

Claimed priority:

Netherlands of September 29, 1960 (256 387)

It would also be possible to make rods of semiconductor material so thin that the resulting Plates are sized appropriately for a single semiconductor device. Step into this procedure only losses when sawing the rod into panels. It should be noted, however, that the price of semiconductor rods is determined essentially by the time during which the manufacturing equipment is stressed will. In the usual manufacturing processes, such as. B. in the case of the crucible-free or non-crucible Zone cleaning and crystal pulling, this time is only slightly dependent on the strength of the rods, so that a thin rod is significantly more expensive in relation to its weight than a thick rod.

When manufacturing controllable semiconductor rectifiers according to the invention, however, the plates can through Cuts are divided in such a way that the least amount of semiconductor material is lost.

According to the development of the invention, the manufacture of controllable semiconductor rectifiers proceed according to the invention in such a way that the cuts are made from the edge to the center of each plate, that sector-shaped semiconductor wafers arise and that on one surface side a sector-shaped one Semiconductor wafer two electrodes of different sizes at different distances from the center of the sector, namely the larger of the two electrodes at a greater distance from the center than the smaller one.

The term "sector-shaped" is not to be understood in a strictly geometric sense, it is rather

809 590/348

in the case of approximately circular or elliptical plates, understood in the same way as in the case of circular plates.

The plates can expediently first with redoped zones and with electrodes for several controllable semiconductor rectifiers are provided and then divided into sector-shaped semiconductor wafers. Also recesses or other specially designed parts that z. B. by etching or grinding the Panels obtained can be attached prior to dicing. The electrodes are preferably mounted symmetrically on the two surface sides of the panels.

It should be noted that in the manufacture of semiconductor devices it is known to use a plate or to provide a strip of semiconductor material with electrodes and then to divide it into semiconductor wafers. Usually the electrodes are placed in rows and the plates or strips are made cut through perpendicular to the rows, with the ao described material losses occur. These material losses also occur in the same way in another known method of manufacture of diodes, in which a large number of cylindrical supports for the diode semiconductor body be soldered regularly with certain gaps on a larger plate made of semiconductor material and the plate is separated by cuts along the spaces.

The division of a semiconductor plate into four sector-shaped semiconductor wafers is also known. This known method, in which zones of opposite conductivity in the semiconductor plate through out diffusion of impurity-forming substances produced, however, relates to the manufacture of transistors in which an electrode is located each surface side of the semiconductor wafer is located and the third electrode, the base electrode, so attached is that they have a portion of the disc rim and a rim area on each surface side covered.

The invention and its further development are explained in more detail on the basis of some exemplary embodiments, illustrated in the drawings.

F i g. 1 and 2 show a perspective view of two rods made of semiconductor material, which form the starting product the manufacturing process of the semiconductor wafer for controllable semiconductor rectifiers form;

Figures 3 through 8 illustrate the manner in which sectors are cut from a disk can;

F i g. 9 to 14 and 16 show different stages of manufacture of a controllable semiconductor rectifier on average;

F i g. 15 shows a plan view of the semiconductor plate provided with redoped zones and electrodes according to FIG. 16, and

F i g. 17 shows a view from below of these zones which have been redoped and which are provided with electrodes Semiconductor plate;

18 shows a controllable semiconductor rectifier in perspective view.

As a starting material for the production of a controllable semiconductor rectifier are generally Semiconductor rods 1 with an approximately round cross-section according to FIG. 1 are used, which by drawing can be obtained from a melt or by zone melting without a crucible. Such bars exist z. B. of germanium or silicon; they can already contain impurities that reduce their conductivity and their conductivity type. A rod 2 with a more or less elliptical shape Cross section that can be obtained by zone cleaning in a boat is shown in FIG. 2 shown.

From such rods plates 3 and 4 are made by sawing in a direction perpendicular to their longitudinal direction Direction established. These plates 3 are processed into smaller semiconductor wafers by adding radial Sections 5 (F i g. 3 to 5) are attached, so that sector-shaped semiconductor wafers 6 arise, which in the order of the F i g. 3, 4 and 5 have central angles of 120, 90 and 60 °, respectively. '

For comparison, FIGS. 3, 4 and 5, the material losses indicated by hatching, the when cutting out the same number of dashed round or square ones Semiconductor wafers of comparable size would occur.

The radial cuts are z. B. by sawing or grinding or by notching and breaking appropriate.

Let elliptical plates that can be cut from the rod shown in FIG on the in the F i g. 6 to 8 in the manner illustrated in sectors. Also in these figures are comparatively indicated the material losses that would occur if these plates were round or square semiconductor wafers are cut.

The production of sector-shaped semiconductor wafers not only saves material; in the construction of controllable semiconductor rectifiers with sector-shaped semiconductor wafers namely, other advantages are also achieved.

As a starting material z. B. a silicon rod 1 (Fig. 1) of the n-conductivity type with a diameter of 18 mm and a specific resistance of 20 ohm · cm. From this rod 1 plates 11 (Fig. 9) with a thickness of 300 μ are sawn, which _{are heated in an oven for 5 hours at 1200 ° C in powdered aluminum oxide (Al 2} O ₃ ), whereby a surface layer 12 of the p-conduction type with a thickness of 40 μ arises, which is shown in FIG. 9 is indicated schematically. This treatment is carried out in an oxygen-free environment, e.g. B. in hydrogen performed. A brief heating is then carried out in the presence of a small amount of oxygen, as a result of which a thin silicon oxide layer 13 is produced on the layer 12 (FIG. 10).

Parts of the plate surface are then coated with a layer of Apiezon wax, i.e. H. a round one central part 14 on the upper surface side and a part along the plate edge and the lower surface side, so that only an annular edge strip 16 remains uncovered on the upper surface side (Fig. 11).

The plate 11 is then etched in concentrated hydrofluoric acid, creating the silicon oxide layer 13 in the edge strip 16 is removed. The Apiezon wax is then removed (see Fig. 12).

The plate 11 is heated for one hour in a phosphorus-containing atmosphere, whereby only at the location of the annular edge strip 16

forms a semiconductor layer 17, which has n-conductivity, since those parts of the plate 11, which with the silicon oxide layer 13 are coated, are protected against the action of phosphorus (Fig. 13).

The plate 11 is again etched in a bath of concentrated hydrofluoric acid, whereby the remaining parts of the silicon oxide layer 13 are removed (Fig. 14).

The plate 11 is then introduced into a form gauge, not shown, and with three rings of each six electrodes provided. Six electrodes 18 are placed on the part 17 which has η conductivity melted. A second ring of six electrodes 19 becomes the electrodes 18 - see the F i g. 15, 16 and 17 - concentrically on that central part of the upper surface side of the plate 11 melted, which has p-conductivity. Eventually be on the lower surface side the plate 11 six electrodes 20 melted. These electrodes 18, 19 and 20 are all made of a lead alloy with 1% nickel which provides a neutral contact, d. H. a contact that neither rectifying effect on the p-conducting semiconductor material and on the η-conducting semiconductor material generated.

The electrodes are melted, for. B. in a hydrogen atmosphere at a temperature of 1000 ° C and for a period of 5 minutes. The semiconductor plate and the quantities of alloy material are first heated separately and then brought into contact with one another.

The electrodes 20 are made with sector-shaped plates 21 made of initially copper-plated and then with Gold plated molybdenum covered. This material has approximately the same coefficient of expansion like silicon and has a high thermal conductivity. At the electrodes 18 and 19 feed conductors 22 and 23 are attached.

The six controllable semiconductor rectifiers formed on the plate 11 are now separated. this happens z. B. in that by means of a diamond notches along three center lines between the Electrodes 18 and 19 are attached and then the plate 11 is broken. The plate 11 can can also be sawed through or cut through using an ultrasonic method.

A controllable semiconductor rectifier obtained in this way is shown in perspective in FIG. He can do it in the usual way in a Sheath can be accommodated.

In the manufacture of controllable semiconductor rectifiers with sector-shaped semiconductor wafers Not only is the material of the plate 11 used with little loss, but also for mounting of the semiconductor layers 12 and 17 and the melting of the electrodes 18, 19 and 20 for six controllable semiconductor rectifier only takes a little longer than the production of a single one Semiconductor rectifier is required for the corresponding work steps.

Claims (4)

Patent claims: 1. Controllable semiconductor rectifier with a semiconductor wafer on one surface side The semiconductor wafer has two electrodes of unequal size and on the other surface side has a third electrode, characterized in that the semiconductor wafer is sector-shaped and that of the two electrodes on one side of the surface the larger one is at a greater distance from the sector center ao point than the other is located. 2. A method for producing controllable semiconductor rectifiers according to claim 1, at which an approximately round rod made of semiconducting material transversely to its longitudinal direction in plates with as two planes and parallel surface sides is divided and in which these plates are cut approximately perpendicular to both surface sides are divided into smaller semiconductor wafers, characterized in that the cuts are guided from the edge to the center of each plate so that sector-shaped semiconductor wafers are formed and that on one surface side of a sector-shaped semiconductor wafer two different large electrodes at various distances from the sector center, namely the larger of the two electrodes at a greater distance from the center of the sector than the smaller one, be attached. 3. The method according to claim 2, characterized in that the plates are first redoped with Zones and provided with electrodes for several controllable semiconductor rectifiers and then are divided into sector-shaped semiconductor wafers. 4. The method according to claim 3, characterized in that the electrodes are symmetrical be attached to the two surface sides of the panels. Considered publications: German Auslegeschrift No. 1018 558;
Swiss Patent No. 335 766;
U.S. Patent Nos. 2,840,770, 2,930,107. 1 sheet of drawings