CH671653A5 - - Google Patents

Description

DESCRIPTION

field of use

The invention relates to a method for producing electrical conductor tracks in semiconductor elements of the type mentioned in the preamble of claim 1. It is mainly applicable in microelectronics. Semiconductor elements used there consist of different doped semiconductor regions which are carried by an insulating body and in which the semiconductor regions are connected to one another or to the outside in a current-conducting manner by primarily metallic conductor tracks.

State of the art

Semiconductor elements used in microelectronics consist of semiconductor layers that are doped or undoped in different regions in different ways. Inlets and outlets for currents and voltages lead to these regions. However, conductive connections between different regions of the semiconductor can also be provided, and conductive connections which enclose the entire component in the manner of a Faraday cage.

Aluminum was initially used for such conductor tracks, which was applied, for example, to the relevant areas by vapor deposition or sputtering, and which could optionally be partially removed again by etching. Sputtering is understood to mean the transfer of metal from a metal surface, from which it is removed by an impinging stream of ions, to another surface. Since the metal source can be flat during sputtering, in contrast to vapor deposition, where the metal surface is often a wire, it is easier to produce uniform layers on the surface on which the metal is deposited. Since there is no noticeable temperature effect associated with the transfer of the material during sputtering, mixtures with noticeably different boiling points can also be transferred in the correct composition. Connection processes of high conductivity are obtained with such processes. At the same time, it must be accepted that when aluminum is transferred, due to the high corrosion resistance of this metal, corrosive substances can penetrate along the connection surfaces. Elements constructed in this way therefore require separate, hermetically sealed housings in which they must be enclosed. In addition, the electrical supply or discharge from or to the outside presents difficulties, since the connection of such supply lines to the thin aluminum layer requires special techniques. Furthermore, it has not yet been possible to securely connect an aluminum layer applied to the base by vapor deposition or sputtering on its surface with a further insulating layer or a semiconductor layer.

An improvement for silicon semiconductor elements was the replacement of aluminum with metal silicide as a conductive layer. Their electrical conductivity is close to that of metals. They can be manufactured hermetically sealed on the silicon and have a high chemical resistance. A description of the properties of metal silicides in relation to their use in microelectronics can be found at S.P. Mura

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ka, Refractory silicides for integrated circuits, J. Vac. Sci. Technol. Vol. 17, No. 4, pp. 775-792, 1980. Table 1 below shows the most important data for microelectronics for the most frequently used metal silicides and, for comparison, for silicon. The sintering temperature is the temperature range at which the silicide can be produced at the interface between the two separate components by simple sintering. For silicon, the highest electrical resistance is that of pure silicon, the lowest resistance that of doped silicon. The silicides mentioned have a metallic conductivity, the temperature coefficient of the resistance is positive.

TABLE 1 Metal silicide and silicon data.

Connection Melt-Tem- Sinter-Tem- Resistance temperature

TiSi 1540 ° C 900 ° C 13-16 nQcm

TaSi 2200 ° C 1000 ° C 35-45 nfìcm

WSi 2165 ° C 1000 ° C 70 (xQcm

MoSi 1880 ° C 1000 ° C 100 jxßcm

PtSi 1229 ° C 400-800 ° C 30-35 nQcm

Si 1410 ° C 102 bislon £ 2cm

Metal silicides are produced by vapor deposition or sputtering of the metal onto silicon, the latter being available both as a single crystal and in polycrystalline form. The metal layers are then bonded to the silicon at the sintering temperatures given in Table 1 to form silicides. During the sintering process, the silicon penetrates into the metal. If the silicon is present in excess, a compact metal silicide layer is formed on pure silicon after sufficient sintering time, which cannot be separated mechanically.

Platinum silicide is particularly important because it can be formed well at temperatures which are lower than the temperatures used for doping silicon. The silicon can therefore be doped first, then a platinum silicide layer can be applied. The platinum silicide is chemically resistant, can not be etched in aqua regia like pure platinum, but only in a solution of HF and HNO3 in water, while pure silicon can be etched with KOH. In addition, the platinum silicide has a low resistance. If the silicon with which the platinum is to be siliconized has an oxidized surface, the platinum silicide cannot be produced by sintering at these points; the applied platinum can be dissolved by aqua regia. It is possible to solder or weld platinum silicide to other metals after it has been electroplated.

U.S. Patent 3,397,278 and G. Wallis and D.I. Pome-rantz, Field assisted glass-metal sealing, J. appi. Physics, Vol. 40, No. 10, pp. 3946-3949, anodic bonding, i.e. describes the production of mechanically non-destructible connections from an electrically conductive part and an inorganic insulating part. The insulating part must have a certain conductivity due to ions of one polarity at elevated temperature, the ions of the other polarity must remain stationary at this temperature. Such conditions are found in a number of inorganic insulators, e.g. for glasses, quartz and certain ceramics. The surfaces to be connected must also be machined so well in parallel that their spacing is smaller than about 1 | xm everywhere. The two parts are placed next to each other with the surfaces to be connected, heated to a temperature of a few hundred degrees Celsius, so that a certain conductivity in the sense mentioned above is created in the insulator. A DC voltage of 200 to 2000 V is applied to both parts to be connected in such a way that the insulating part lies on the pole that sucks the ions that have become mobile from it. The stationary ions then form a space charge in the area of the surface to be connected, an electrostatic force arises between the surfaces of the conductor and the insulator, the two surfaces are pulled together and combine to form a firm mechanical connection. A connection between an insulator and a conductive part formed in this way by anodic bonding is also hermetic in the sense that it prevents any penetration into the materials involved in the bonding by attacking substances in the connection layer.

The preamble of claim 1 relates to the prior art known from US Pat. No. 3,397,278.

Task and solution

It is the object of the invention to show a way in which, in the construction of a semiconductor element, conductor tracks can be produced which are completely protected against interfering influences from the outside, that is to say are hermetically sealed, give a high bond strength between the layers and can be used in microelectronics. This object is achieved by the features specified in the characterizing part of claim 1. Although anodic bonding has long been known, it has never been applied to thin metal silicide layers obtained by sintering on a semiconductor body. The other claims provide details of this method and describe devices that can be manufactured using this method.

drawings

The method is explained by way of example in the drawings and some exemplary embodiments are given for devices to be produced using the method. Show:

1 shows a silicon body with a metal or metal silicide layer,

2 shows a device for anodic bonding,

3 shows a component obtained by sintering and anodic bonding,

4 shows a semiconductor element in various production stages,

5 shows a semiconductor body with electrical leads that go through holes in the glass,

6 shows a semiconductor component and FIG. 7 shows a thermal pressure element.

In all figures, parts of the same type are designated with the same reference symbols.

Execution of the method, examples of devices that can be produced with it:

The basics of the method are explained by way of example in FIGS. 1 to 3. Fig. 1 shows in principle the structure of a conductive part which is used for anodic bonding with an insulator. A metal layer 2 is applied as uniformly as possible on a silicon body 1 on the surface provided for bonding, which can be done by applying a thin film by vapor deposition or sputtering. The silicon body 1 is now heated to the sintering temperature given in Table 1 and the metal is thus converted into the corresponding metal silicide. If the metal is to be completely converted into the metal silicide, then silicon must be present in excess compared to the stoichiometric ratio of the intermetallic compound in question.

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A compact metal silicide layer 3 then forms over the remaining silicon, which can no longer be separated mechanically from it, that is to say is hermetically sealed. The duration of the necessary action of the sintering temperature essentially depends on the thickness of the metal layer 2 and is between a few minutes and a few hours, the latter in the case of thick metal layers 2. The sintering process is complete when the electrical resistance of the metal silicide layer 2 no longer changes.

If the silicon body 1 is a single crystal and the metal silicide to be produced thereon has similar crystal shapes, the metal silicide layer produced by this method likewise has a single crystal structure, which is desirable in certain cases.

In order to anodically bond the silicon body 1 with the metal silicide layer to an inorganic insulator, for example to a glass body 4, the surfaces to be bonded must first be processed using the methods known in microelectronics in such a way that the smallest distance between the surfaces placed against one another for bonding is less than 1 µm.

FIG. 2 shows the diagram of a system for anodic bonding. The silicon body 1 with the metal silicide layer 3 is an inorganic insulator, e.g. a vitreous body 4 opposite. The distance between the underside of the glass body 4 to be bonded and the metal silicide layer 3 is drawn on an enlarged scale. It can be seen that the glass body 4 only touches the metal silicide layer 3 at a few points. A flat electrode 5 lies on the glass body 4 and is connected to a high-voltage source 6, the other pole of which leads to the silicon body 1. The entire arrangement can be heated, for example with an oven 7 which is connected to a power source 8.

If the temperature in the furnace 8 is low, no current flows from the high voltage source 6 via the silicon body 1, the metal silicide layer 3 after the glass body 4 and via the electrode 5 back to the high voltage source 6, since the glass body 4 insulates. Only when the temperature in the vitreous body 4 has risen to such an extent that the ions of one polarity have a certain mobility (in the cases that have become known these are always the positive ions), does a current form and through the remaining of the stationary ones Ions of the other polarity are a space charge which results in an electrostatic attraction between the underside of the glass body 4 and the top of the metal silicide layer 3. As a result of the very small distance between the surfaces to be bonded, this force is very large and, starting from the contact points 9, connects the surface of the metal silicide layer 3 with the underside of the glass body 4 in an intimate manner, so that mechanical separation is not possible. Since metal silicide layers 3 are very chemically resistant, a connection is created between the silicon body 1 and the glass body 4, between which a layer with high conductivity, namely the metal silicide layer 3, is hermetically sealed to them.

FIG. 3 shows a product produced according to the specified method, in which a silicon body 1 is connected to an inorganic insulator, here a glass body 4, by anodic bonding, a surface applied to the silicon body 1 being sintered on its surface intended for bonding Metal layer 2 produced hermetically sealed, highly conductive metal silicide layer 3 was applied.

If the affinity of the silicon for the metal is smaller than that for oxygen, then no metal silicide is formed by sintering when the silicon body 1 is covered with an SiO 2 skin. If the sintering of such a metal is also carried out in an oxygen-containing atmosphere, the silicon which has arrived at the free surface of the metal silicide layer 3 combines with the oxygen to form an SiO 2 skin which prevents the subsequent anodic bonding. Even when anodically bonding such a metal silicide in an oxygen-containing environment, there is a great risk that an SiO 2 skin forms between the metal silicide layer 3 and the glass body 4, which prevents the bonding. There are therefore metals in which the sintering and / or the bonding must be carried out in an oxygen-free atmosphere.

In semiconductor elements of microelectronics, the semiconductor bodies have regions which are doped in different ways, that is to say which have foreign atoms of different types in different spatial arrangements and different concentrations. The spatial arrangement and the concentration of the foreign atoms can be influenced by increased temperature. In many cases, the doping of the semiconductor body has already been carried out before the semiconductor element is built up in detail. It is therefore advantageous to select the metal silicides used so that the sintering and bonding can take place at temperatures at which the concentration and spatial shape of the doping is retained in the silicon body 1.

It is therefore of great advantage if a platinum silicide layer is used as the metal silicide layer 3, since platinum silicide

relatively low sintering and bonding temperatures are required, so that the doping state of the silicon body 1 does not change,

- has a high conductivity,

- is resistant to all chemical reagents except the solution of HF with HNO3 in water,

- Sintering only forms on the silicon, not on SÌO2,

- is not attacked by the etchant aqua regia used for pure platinum.

With platinum silicide, sintering can be carried out at temperatures around 400 ° C, and bonding at temperatures well below 500 ° C.

FIGS. 4a to 4f show a typical way of producing a semiconductor element using the described method. 4a shows a silicon body 1, in which doped regions are diffused into a first depression 14. In this case, it must therefore be noted that the sintering and the anodic bonding are carried out at temperatures which do not disturb the doping state of the silicon body 1. In Fig. 4b there are shallow recesses in the silicon body, e.g. by etching, which have been filled in with metal layers 2, for example by sputtering while covering the surroundings with a mask. The silicon body 1 is now held for a sufficient time at the sintering temperature, if appropriate in an oxygen-free environment. As a result, the metal layer 2 is converted into a metal silicide layer 3 in FIG. 4c. The surface of the silicon body 1 facing forward in FIG. 4d and the surface of the glass body 4 facing upward, which has a second recess 15, are processed by known means in such a way that they obtain a surface quality suitable for anodic bonding. According to FIG. 4f, parts of the metal silicide layer can now be exposed, which can be done by removing, for example, etching away part of the silicon. These exposed parts of the metal silicide layer can be reinforced by applying metal, for example by electroplating, in such a way that, for example, wire-shaped electrical connections can be attached to them. In this way, a hermetically sealed semiconductor element has been produced which contains a conductor track made of metal silicide with a low resistance, which supplies the doped regions with current or voltage.

In many cases, in the production of semiconductor elements for microelectronics, it is necessary to apply the conductive layers in patterns in order to make electrical connections

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to produce different doped regions. This can be achieved, for example, by masks, with the aid of which the metal layer 2 is only deposited on predetermined parts of the surface of the silicon body 1. This has long been used in microelectronics. However, the surface corresponding to the pattern can also be covered by a mask, which oxidizes the remaining surface and then metal can be applied to the entire surface after the mask has been removed. If sintering is then carried out, the metal is only converted into the metal silicide at the unoxidized points. The other part of the metal layer 2 is not converted because of the underlying SiO 2 skin. This non-siliconized metal portion can then be removed by etching with an agent which attacks the pure metal but not the associated metal silicide. In the case of the use of platinum silicide, the most suitable means of removing the non-siliconized platinum is aqua regia. FIG. 5 shows a semiconductor element in which a pattern of metal silicide layers 3 is applied to a silicon body 1, which layers 20 are intended to provide various doped regions (not shown) with electrical leads. For this purpose, 4 holes 10 are made in the bonded glass body, which end at the metal silicide layers 3. If the bores 10 are filled with metal after bonding or metal is applied to their lateral surfaces, then solderable or weldable electrically conductive leads to the metal silicide layers 3 and thus to the doped regions of the silicon body 1 are obtained in a simple manner.

6 shows a cross section through a semiconductor body. It consists of a silicon body 1 which is n-doped and into which a p-doped region is diffused. On top of it 30 there is an SiO 2 layer 11 with a window 12 which is just releasing the p-doped region of the silicon body 1. A metal silicide layer 3 is applied to it, a glass body 4 lies above it and bears a bore 10 which extends down to the metal silicide layer 3. By successively applying the method described, the vitreous body 4 with the metal silicide layer 3

bonded. In order to create a feed line to the metal silicide layer 3, the bore 10 is finally provided with contact metal 13. In this way, a reliable and hermetically sealed conductor path is created from the outside to the p-doped region.

According to the method described, it is also possible to produce thermal printing elements such as those used according to Swiss patent application 02 222 / 85-2 for solving value markings on credit cards used as a means of payment. Fig. 7 shows a printing block with two such printing elements after completion. They each consist of a silicon body 1 which contains no doping and therefore has low conductivity. A metal silicide layer 3 is sintered onto it. The dimensions of the metal silicide layer 3 are such that it brings the silicon body 1 serving as a thermal pressure element in its final form to the desired temperature by means of resistance heating at a predetermined electrical voltage. The silicon bodies 1 are then bonded to a glass body 4, in pairs in FIG. 7. The silicon body 1 is then brought into its final shape by etching. For each bonded metal silicon layer 3, the glass body 4 has two bores 10 at its ends, with which the bushings for the heating current are produced in the manner shown in FIG. 5.

The method described has the advantage that when anodically bonding a semiconductor body to an inorganic insulator, a highly conductive metal silicide layer 3 is interposed and at the same time a hermetically sealed connection of the silicon body 1 to the insulator is created. These highly conductive layers can be produced in patterns, so that differently doped regions of the silicon are provided with separate conductor tracks. If the sintering and bonding temperature is low enough, the spatial shape and concentration of the doped regions are not affected. The use of platinum silicide for such compounds is therefore particularly recommended.

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Claims (15)

671 653 2nd PATENT CLAIMS 1. A method for producing hermetically sealed electrical conductor tracks in semiconductor elements, in which a silicon body is connected to an inorganic insulator by anodic bonding, characterized in that on the silicon body (1) on its surface intended for bonding, by sintering, one of an applied metal layer ( 2) produced, hermetically tightly connected to the silicon body, electrically conductive metal silicide layer (3) applied and then the surface of the metal silicide layer (3) is connected to the insulator by bonding. 2. The method according to claim 1, characterized in that the sintering and / or the bonding is carried out in an oxygen-free environment. 3. The method according to claim 1, characterized in that the sintering and / or the bonding takes place at temperatures at which doping of the silicon body (1) in spatial shape and concentration are retained. 4. The method according to any one of claims 1 to 3, characterized in that platinum silicide is applied as the metal silicide. 5. The method according to claim 1, characterized in that a single crystal body is used as the silicon body (1), so that the sintered metal silicide layer (3) is also formed as a single crystal layer. 6. The method according to any one of the preceding claims, characterized in that recessed tracks are incorporated in the silicon body (1), in which the metal layers (2) are filled. 7. The method according to any one of the preceding claims, characterized in that after sintering, the surface of the silicon body (I) to be bonded is reworked in such a way that it receives a surface quality suitable for anodic bonding. 8. The method according to any one of the preceding claims, characterized in that after the bonding part of the metal silicide layer (3) is exposed by removing a corresponding part of the silicon body (1). 9. The method according to claim 7, characterized in that the exposed part of the metal silicide layer (3) is reinforced by applying metal. 10. The method according to any one of the preceding claims, characterized in that for the production of metal silicide layers (3) arranged in patterns, the surface corresponding to the pattern is covered by a mask which oxidizes the remaining surface, then after removal of the mask, metal is applied to the entire surface and is sintered, metal silicide forming only on the non-oxidized surface parts. 11. The method according to claim 9, characterized in that the non-siliconized metal is removed by etching with an agent which only attacks the non-siliconized metal. 12. The method according to claims 4, 9 and 10, characterized in that aqua regia is used as an etchant for the non-siliconized platinum. 13. The method according to any one of the preceding claims, characterized in that holes (10) are made in the inorganic insulator, which lead to the metal silicide layers (3) after the anodic bonding and these holes (10) are provided with a metal application on their outer surfaces , which creates an electrically conductive connection to the metal silicide layers (3). 14. The method according to claim 1, characterized in that for the production of a thermal pressure element on a silicon body (1) by applying a metal layer (2) and sintering to a metal silicide layer (3) an electrical resistance is generated, the given the electrical voltage the final shaped silicon body (1) heated to a predetermined temperature that at least one Body is bonded to an inorganic insulator and that devices are attached to supply the metal silicide layers (3) with the appropriate heating current. 15. A semiconductor element with a silicon body (1), an insulator and electrical conductor tracks made of metal silicide, produced by the method according to one of claims 1 to 12.