GB2090060A

GB2090060A - A Method of Producing Semiconductor Components

Info

Publication number: GB2090060A
Application number: GB8137685A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Current assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Priority date: 1980-12-19
Filing date: 1981-12-14
Publication date: 1982-06-30
Also published as: DE3048019A1; FR2496985A1; JPS57126142A

Abstract

A method of producing semiconductor components comprises applying a silicon disc (1) with a plurality of successive layers (2, 3, 4) of different types of conductivity to a carrier disc (6) of highly doped silicon through an intermediate layer (5) of aluminium/silicon. The structure is then subdivided (e.g. ultrasonically) to produce individual devices, the silicon carrier disc (6) forming part of the finished device. <IMAGE>

Description

SPECIFICATION A Method of Producing Semiconductor Components The invention relates to a method of producing semiconductor components comprising a silicon disc having a plurality of successive layers of different types of conductivity. In one such component, the layers may be produced by doping with elements forming impurities after masking has been carried out. The surfaces may then be provided with an alloyed, (diffused or coated metal) layer to which collector electrodes are applied in accordance with the existing arrangement of layers and regions of different conductivity and different type of conduction. The semiconductor disc may then be subdivided into a plurality of individual elements.

In accordance with known methods of production semiconductor components such as diodes, transistors, thyristors or triacs, for example, are produced in the following manner The surface of a homogeneously doped semiconductor disc is changed in terms of its electrical characteristics either completely or in some regions to a predetermined depth by incorporating elements which form impurities with the aid of methods of alloying and/or different such that an arrangement of layers and regions of a different type of conductivity and a diffusion degree of conductivity are formed. The different regions on the surface are then provided with metal contacts, say by soldering or alloying these on. The semiconductor components are finally connected to conductors by means of the metal contacts.

For financial reasons, small and medium sized elements are not produced individually if a rational method of manufacturing may be achieved, rather the conventional operations such as masking, doping and metallisation are carried out on relatively large semiconductor discs and are then subdivided into smaller individual elements of the prescribed size by means of etching, sawing, sandblasting, scoring and breaking or by means of ultrasonics and these individual elements are then connected up to the current carrying conductors by conventional methods.

Normally, molybdenum is used as the contact and carrier material for a semiconductor element comprising silicon or-less frequently-Tungsten, because the coefficient of thermal expansion of silicon and molybdenum or tungsten are similar and therefore there is only relatively little thermal stress during fluctuating operating temperatures and manufacturing operations, at soldering temperatures, for example, which are not too high.

If the requirements for resistance to fluctuations in temperature are high-particularly in power semiconductor components-then it is necessary to use alloyed contacts instead of soldered contacts. Since temperatures in the range of approximately 7000C occur during the alloying process the differences in the coefficient of expansion of silicon and of molybdenum or tungsten are very pronounced so that it is no longer possible to use large-area silicon and molybdenum discs. If in fact relatively thin molybdenum discs are used as carrier discs for the silicon, then these thin discs bend under the action of the different expansions of the materials and this bend can be noticed at high temperatures. In addition the semiconductor discs can be removed from the carrier discs.The crystal structure of the thin semiconductor disc may be damaged by bending or may even crack and this produces disadvantages with respect to the barrier capability of the finished component.

On the other hand the thickness of the carrier disc is increased to such an extent-for example to between 1 and 1.5 mm that it has sufficient mechanical strength but a molybdenum disc of this thickness is exceptionally difficult to separate into small disc parts and can only be effected at a high cost. This is why, when manufacturing power semiconductor components, which require a process whereby the contacts are alloyed, there is no subdivision of a large-area semiconductor disc complete with contacts into smaller parts.

Instead it was necessary to carry out the separation first of all after doping and, only after separation, to carry out the alloying process given the resultant large number of individual elements.

This in turn means that, when providing the contacts, an increase in labour costs is unavoidable-by the mere fact of having to adjust the individual elements-and the advantages of masking and doping the large semiconductor disc in one go are lost again to a large extent.

A semiconductor arrangement and device is known from German Offenlegungsschrift No. 28 28 044 in which a silicon disc serving as an active semiconductor member is applied to a carrier disc comprising highly doped silicon. This measure does of course relate exclusively to an arrangement and not to a method as well as exclusively to a large individual element which is not provided for subdivision into smaller individual elements.

The invention seeks to provide a method of producing power semiconductor components with alloyed contacts in which all of the conventional method steps, including providing the contacts are carried out on a large-area silicon disc and the silicon disc is only broken down into a large number of individual parts thereafter, the advantage of simultaneous masking, doping and contacting being fully utilised. The semiconductor disc is not separated from the carrier disc nor is there any danger of damage to the semiconductor element or to its crystal structure nor is any special cost necessary when subdividing the carrier disc combined with the semiconductor disc into parts during the contacting step at an alloying temperature of approximately 7000C.

According to the invention, there is provided a method of producing semiconductor components comprising a silicon disc having a plurality of successive layers of different types of conductivity wherein the silicon disc is applied over an intermediate layer of aluminium/silicon to a carrier disc of highly doped silicon.

It is advisable for the carrier disc to have a specific resistance of b < 1.5 m Ohms/cm and a disc thickness of approximately 1 mm. Both monocrystalline and polycrystalline silicon crucible pulled according to the conventional method are suitable.

The material for the semiconductor body and for the carrier disc may have the same coefficients of expansion so that, even with a large range of fluctuating temperatures and large areas, there is no thermal stress. Therefore it is possible to undertake alloying at fairly high temperatures during manufacture to the as yet undivided largearea silicon disc without there being any danger of the semiconductor disc lifting off from the carrier disc and without any danger of damage to the semiconductor disc. Therefore, besides masking and doping, the alloyed contact of power semiconductor components can be provided on the as yet undivided large disc and this makes it possible to provide contacts in a single operation for a large number of individual elements.

It is relatively easy to divide up the large carrier disc combined with the silicon disc into individual elements-by means of an ultrasonics process because a carrier disc comprising silicon can be divided up more easily than if the carrier disc was molybdenum, especially so if the carrier disc was of molybdenum with a fairly large layer thickness.

In addition, in the method in accordance with the invention there is the further economic advantage which arises from the fact that a carrier disc comprising silicon-which does not have to meet any excessively high requirements in terms of purity-is cheaper than an equivalent disc comprising molybdenum.

Since the thermal conductivity of molybdenum and silicon in accordance with the invention are effectively the same the loss of heat in a carrier disc made of silicon can be dissipated just as easily as a carrier disc comprising molybdenum.

The slightly poorer electrical conductivity of silicon as compared to molybdenum is compensated by its lower junction impedance.

The volumetric impedance and the voltage drop within the semiconductor disc play a smaller part than the junction impedances.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which.~ Figure 1 is a sectional view of a silicon disc in a first stage of a method in accordance with the invention.

Figures 2 to 6 are views similar to Figure 1 showing various further stages in the method.

Figure 1 shows a silicon disc 1 comprising nconductive starting material, the diameter of which is approximately 7.6 cm and the disc thickness of which is approximately 280 ym.

Using a conventional diffusion process, the nconductive layer 3 at the surfaces has been converted into an n+ conductive layer 2 and p+ conductive layer 4.

As can be seen from Fig. 2, a 10 to 30 ym thick intermediate layer 5 comprising an aluminium/silicon eutectic is initially applied to the p+ conductive layer 4. The disc 1 is then alloyed over the intermediate layer 5 to a carrier disc 6 comprising very highly doped silicon. The thickness of the carrier disc 6 is approximately 1 mm and its specific resistance is 8 < 1.5 m Ohm/cn According to Figure 3, aluminium layers 7 and 8 with a layer thickness of 10 to 30 ym are vapour deposited onto the surfaces of both layers 2 and 6. These layers 7 and 8 produced with the desired or prescribed shape and are then tempered.

The layer sequence produced in this way is subsequently adhered to a steel or glass plate 9 as Figure 4 shows and is subdivided into individual elements by means of an ultrasonics drill 10~for example. This type of individual element is shown in Figure 5. As Figure 6 shows in some cases the edges are worked in conventional manner and are provided with passivating layers 1 1 and a copper contact 12.

Claims

1. A method of producing semiconductor components comprising a silicon disc having a plurality of successive layers of different types of conductivity wherein the silicon disc is applied over an intermediate layer of aluminium/silicon to a carrier disc of highly doped silicon.

2. A method according to claim 1, wherein the carrier disc has a specific resistance of 8 < 1.5 m Ohms/cm.

3. A method according to claim 1 or 2, wherein the carrier disc has a thickness of approximately 1 mm.

4. A method according to any one of claim 1 to 3, wherein an aluminium layer is vapour deposited on to the surfaces of the layered silicon disc with a thickness of 10 to 30 ym.

5. A method according to any one of claims 1 to 4, wherein the layered silicon disc and the carrier disc are adhered to a steel or glass plate and is broken down into individual elements using an ultrasonics drill.

6. A method according to claim 5, wherein the individual elements are worked at their edges and are provided with edge passivating layers and a copper contact.

7. A method of producing semiconductor components substantially as described herein with reference to the drawings.