DE19531158A1 - Diffusion soldering method esp. for semiconductor components - Google Patents

Abstract

A method of producing a temp.-stable bond between two bodies involves interposing high melting (Hi) and low melting (Lo) metal layers, contacting the layers and heating to the bonding temp. (TB) under a predetermined temp. and pressure cycle such that the initially melted component (Lo) wets the joint surfaces and diffuses into the high melting component (Hi) to form an intermetallic phase which, after consumption of the low melting component (Lo), forms a stable bonding layer of melting point (TR) higher than that of the low melting component (Lo). The novelty is that (a) the high melting component (Hi) is selected from IV to VIII subgroup metals and is applied onto a first body comprising a semiconductor wafer; and (b) the low melting component (Lo) is selected from III or IV main group elements, is applied onto a second substrate body and, after contacting the high melting metal (Hi) on the semiconductor wafer, is melted.

Description

The invention relates to a method for generating a temperature stable connection of two bodies according to the generic term of claim 1.

The method is used in particular for mounting semiconductor chips on Substrates, for connecting "wafers" during the semiconductor process tion, as well as for contacting electronic components and Circuits.

A generic method is from the German application P 42 41 439 A1 known. In this application a procedure for Generation of a positive connection between metallic Ver binders and metallic contacts of semiconductor surfaces ben. The connectors are used in particular for the parallel connection of Solar cells with the help of solar cell contacts. Between a connector and a contact becomes an intermediate layer from one to the other Connector and metallic contact low melting metal attached arranges and warms up to or above the melting temperature. It is to ensure that the liquid intermediate layer the joining surfaces wetted by connector and contact. The liquid intermediate layer dif founded in the connector and the contact and forms one intermetallic phase with the material of the intermediate layer and the Materials of the connector and contact to be joined. Doing so by solidification during a given temperature and Contact pressure course the positive connection between Connector and contact made, the melting temperature of which is higher, than that of the original intermediate layer.  

In this publication, only In-Au and Sn-Ag are concrete combinations specified that as intermetallic compounds melting points below have half of 500 ° C.

It is also known to semiconductor devices by soldering or gluing procedure to assemble or contact. While it is at suchi gene, connections made by soldering is disadvantageous that these do not have a high temperature load and only relatively few Can be exposed to temperature changes, it is with glued Connections disadvantageous that they have only a limited heat conduction ability and have a relatively low moisture resistance.

Silicon is known from British patent application GB 235 642 A. discs on a base made of Mo or W or Fe-Ni by diffusion solder with Hi = Ag and Lo = In or Sn and a possible addition of To connect Ga.

From the German patent application DE 43 03 790 A1 for Diffusion soldering as a high-melting component (Hi) Ag, Au, Cu, Co, Fe, Mn, Ni, Pd, Pt, Ir, Os, Re, Rh or Ru and for the low-melting Component (Lo) Bi, Cd, Ga, In, Pb, Sn or Zn and especially Hi = Ag or Au and Lo = Sn or In selected. The lateral structuring of the Lo layer was provided and also a thin diffusion barrier between Hi and Lo to increase the lifespan during storage achieve.

From the European Patent application EP 0 365 807 is the electronic bonding components on printed circuit boards by diffusion hard soldering ten in the Pb-Sn system below the melting point of Sn at 183.5- 210 ° C known. In addition, from the publication by G. Izuta et al: "Development of Transient Liquid Phase Soldering Process for LSI Die-Bonding "Proc. 43rd Electronic Components and Technology Conf., IEEE, June 1993, Orlando, 1012-1016 (1993) known, power engineering connect elements with circuit boards. The connection at the nied temperature of 187 ° C reduces the mechanical bean spells by more than half compared to conventional ones Connection method. The reflow temperature of the connection grows to over 247 ° C after heat treating the compound for 12  Hours at 187 ° C, which is an added benefit of isothermal Represents torpor.

Isothermal solidification involves connection processes, some of which Distribute the conventional soldering or brazing processes using the process have diffusion bonding in common. The Diffusion bonding is described in the D.M. Jacob son and G. Humpston in: Diffusion Soldering ′ ′, Soldering Surface Mount Technol. 10 (2), 27-32 (1992).

One possible application is amalgam soldering. The various where application examples such as fastening, hermetic sealing, Flip chip mounting, mounting chips on glass, etc. are off the publication of C.A. Mac Cay: "Amalgams for Improved Elec tronics Interconection ", IEEE Micro, (4), 46-58 (1993). Experi mental data for amalgam soldered connections with Hi = Ag, Cu, Ni and Lo = Ga are listed there. These material combinations he do not in any way exhaust the thermal stability limits of other hi Ga combinations as seen in Table 1. The previously stated The material combinations mentioned are, however, flexible The selection of higher remelting temperatures is still incomplete.

The invention is therefore based on the object, a method for Er Generation of a reliable positive connection for metallic To create surfaces of semiconductor contacts, which at high re melting temperatures has a long life and a large one Number of temperature changes survives, as well as a high thermal Has conductivity.

According to the invention, the object is characterized by the characteristics of the An Proceed 1 contained procedural features solved. Further training and Embodiments of the invention are contained in the subclaims.

Isothermal solidification can be used to form very solid compounds at a relatively low temperature, these compounds being able to withstand much higher temperatures. The underlying principle of this connection process is that an intermediate layer of a low-melting metal Lo as a film or thin coating between the high-melting components Hi is angeord net. This arrangement is heated under low pressure to the connec tion temperature T _B , a liquid intermediate layer being formed. Either the melting point of the layer Lo can be exceeded or there is a eutectic reaction between the components Lo and Hi. The melted intermediate layer leads to rapid interdiffusion or reaction diffusion between Lo and Hi. The following approximation to the equilibrium state results in an isothermal solidification.

The solid phases that form at T _B in the connection area, with appropriate selection of materials for Lo and Hi, show a melting temperature above T _B , whereby certain additional advantages can be achieved by the material combinations listed in the invention.

Isothermal solidification is a process with the following advantages: It enables a high thermal stability of the connection with a much higher melting temperature T _{R of} the connection than the original connection temperature T _B it tolerates some surface roughness due to the temporary appearance of a liquid phase, it only requires a relatively small pressure to connect the surfaces (0.2 to 5 MPa), and the connection times are relatively short and of the order of minutes, the very thin connection layer, typically less than 10 μm, having very good mechanical properties. However, the surfaces must be reasonably flat beforehand. However, the connection generally cannot be melted again after solidification, for example in order to carry out repairs. This connection method will therefore be used wherever high ambient temperatures prevent the use of conventional connection technologies.

The temporary appearance of a liquid phase at relatively deep Temperatures are important for a good flat connection and can at the same time avoid thermal stresses that would otherwise occur High temperatures can be introduced into the connection could. In addition, the high thermal stability of the connector new opportunities for the following manufacturing steps  Result, which no longer gradually decrease in temperature ought to.

The underlying metallurgical facts and the invention are explained below with reference to the drawing.

It shows:

Fig. 1 is a schematic binary phase diagram demonstrating the principle of the diffusion brazing by means of diffusion reaction,

Fig. 2 is a schematic binary phase diagram demonstrating the principle of the diffusion brazing by interdiffusion,

Fig. 3, the Au-In phase diagram and the minimum reflow temperature T _R,

Fig. 4 shows the Ag-In phase diagram and the minimum melting temperature T _R and

Fig. 5 is a schematic diagram of a layer structure before and after the diffusion soldering.

The various connection processes that make up the isothermal Using solidification can be divided into three basic categories are: diffusion soldering, diffusion brazing and amalgam soldering.

The underlying metallurgical principles are best with Using a schematic binary phase diagram of the elementary Understand components Hi and Lo.

The basis of diffusion soldering is the existence of at least one in term metallic component, which is shown as the congruently melting phase HiLo in FIG. 1.

The composition in the area of the system which is affected by the diffusion processes during heating is given by the relative proportions of the components Hi and Lo. This average composition must be chosen within the range of the solid state at T _B , which represents the two-phase field Hi + HiLo in Fig. 1. If one assumes the original non-equilibrium state of the solid H + liquid Lo at T _B , the equilibrium state becomes due to reaction diffusion and growth of the intermetallic phase HiLo at the interface between solid phase H and the liquid alloy L. The isothermal solidification is achieved by consuming the liquid phase completed. The melting temperature T _{R of} the overall system is represented by the eutectic melting temperature of the phases Hi + HiLo, which is above T _B.

The equilibrium concentration of the overall system becomes an example through the black filled circle in the middle of the diagram shown.

Diffusion brazing requires that the composition of the entire system be within the range of the solid solution of the high-melting component Hi, as shown in FIG. 2. An intermetallic phase is not required. The connection is reintroduced at the temperature T _B in that Lo melts and some of the high-temperature phase Hi dissolves in the liquid alloy, the so-called filler. The isothermal solidification then necessarily only occurs when the component Lo is diffused into the solid solution H. In this case, the remelting temperature T _R depends very much on the degree of homogenization of the compound within the solidified intermediate layer. The maximum value of T _R is given by the solidus temperature of the overall system, as indicated in FIG. 2. This is achieved after prolonged heat treatment and diffusion in the solid state. It is also possible to achieve the binding below the melting point of Lo but above the eutectic temperature of approx. 550 ° C., as in FIG. 2. In this case, the liquid begins to form on the interface between Hi and Lo due to the eutectic reaction. After complete dissolution of Lo and widening of the liquid intermediate layer up to a maximum, the isothermal solidification process continues, as shown in FIG. 2.

In the third variant, amalgam soldering, several isothermal solidification processes will also play a role. The metallurgical principle of amalgam soldering is exactly the same as that explained for diffusion soldering in FIG. 1, however the geometry is not a layer structure but a powder (Hi) - liquid (Lo) mixture. This amalgam must be distributed between the components to be combined, which precludes a real thin-film process. The term amalgam soldering seems appropriate here because the process includes typical properties of soldering such as wetting and the formation of intermetallic phases. The terms diffusion soldering and diffusion brazing are also due to similarities with the metallurgical principles of soldering and brazing. The boundaries between diffusion soldering and diffusion brazing are fluid, as can be seen from the diffusion "brazing" in the Pb-Sn system at unusually low temperatures of 183.5 to 210 ° C or 187 ° C. After two hours of heat treatment at 187 ° C, the melting temperature rises to over 247 ° C.

The properties of diffusion soldering appear particularly for users attractive in the area of electronic components because the combi nation of typical low temperatures for soldering with the Mög possibilities of a thin-layer preparation of the connection system comb nable. The following table gives a summarized list of published experimental work.

Although amalgam soldering is not a thin film process, it was made for electronic connections in the material systems (Ni, Cu) -Ga, (Ag, Cu) -Ga and (Ag, Ni) -Ga used. An overview of the be Known material systems for diffusion brazing shows that this Studies are not intended for electronic applications.

Using Table 1, some special points regarding the Reaction rates, mechanical properties and pressure which the connection takes place, as well as the details of the production discussed thin layers.

The reaction rates with the liquid phase subsequently increase Au-In, Ag-In and Cu-In from. The Ni-Sn reaction is 1.5 to 2 times slower than the Cu-Sn reaction, as can be seen from the measurement of the consumption of the Melt and the growth rate of the intermetallic compounds has highlighted. The Cu-Sn connections are after 30 seconds still partially liquid and completely after 4 minutes at 280 ° C Reaction solidified.  

Table 1

Material combinations for diffusion soldering.

The low-melting components are Sn layers from 0.5 to 2 µm Thick, soft with electron beam evaporation on both sides of the Copper substrates were applied. The tensile strength ("Tensile strength") grows from 16 to 36 MPa in such samples. The The tensile strength of the Ni-Sn connection reaches a constant value of 38 MPa after one minute or a slightly longer setting time.

The shear strength of the Ag-In compound is after the formation of the Ag2n phase 62 MPa, which is much higher than the strength of one conventional Ag-In solder connection of approx. 8 MPa. The measured Shear stresses of diffusion soldered compounds in Ag-Sn System containing the ductile Ag3Sn phase is close to 23 MPa, which corresponds to the value for normally soldered Ag-Sn connections. With longer heating, however, the microstructure approaches diffusion soldered connection of a solid solution of silver and the shear strength is expected to increase up to one Maximum value of 75 MPa. In conclusion it can be stated that the mechanical properties of diffusion soldered connections, the far surpass the conventionally soldered and also the Exceed requirements in the electronics industry, yet another Reserve towards high temperature stability is available.

The determined contact pressures between the joining partners are nor sometimes low and in the range of 0.2 to 3 MPa. The be expected volume shrinkage during the formation of the intermetallic phases is 12% for Ni-Sn and only 0.7% for Cu Sn, with pores occasionally observed in the Ni-Sn compound were. The pores could not be applied by applying higher pressures can be avoided, since the liquid tin from the above 0.3 MPa Connection region is pushed away. The connections will preferably carried out in a reducing gas atmosphere. Man also uses vacuum, inert gases or air. The oxidation of the applied layers of the connection components can during storage problems. An additional oxidation during the connection can be bonded through an air layer between insufficiently planed connecting surfaces are created. A Oxide skin on the low-melting component or an oxide layer on the free surface of the high-melting component  finally prevent wetting, which does not connect came.

It has been found that the preparation of thin layers of the Lo component is a crucial step. Sputtered tin forms Islands on the copper layer, which are not particularly good for that Diffusion soldering is suitable.

Electroplated (electroplated) Sn layers 3 µm thick can be used, although they grow porous in places. At the the best seem to be electron beam vaporized Sn layers of 0.5 to be up to 2 µm layer thickness. It involves a more complicated structure a gold protective layer on the in-layer. This oxidation protection layer enables handling and storage in air.

To make Table 1 short, it can be said that the material combinations Ag, Au, Cu or Ni as Hi component with In or Sn as a Lo component has already been studied extensively and are therefore state of the art, whereby Fe and Hg are only special cases represent. Mechanical strength and thermal stability of the connector dung can be extremely high. The systems in the literature favored are Ag-Sn, Au-In, Cu-Sn and Ni-Sn.

The following is a summary overview of the selection criteria for the known material combinations (Ag, Au) -In given, with gold and silver as high-melting and indium as low-melting metal. These materials are for illustration purposes only the basic idea. It is a key property of diffusion solder and generally the isothermal solidification that the Lo component is chosen almost independently of the Hi component. It lies that the binding temperature is usually determined by the melting point the Lo component is limited and not like the ordinary one Soldering through a eutectic reaction with another component. That is why it is very easy to close all low melting metals for one specify the joining temperature.

Indium, tin and bismuth are suitable candidates for diffusion soldering, with gallium being the most prominent candidate for almalgam soldering, while it is difficult to handle in the form of thin films. Mercury, thallium, cadmium or lead are excluded due to their toxicity. The decisive criterion for a first selection of material combinations Hi-Lo is the minimum melting temperature T _{R of} the connection. It is defined here from the Hi-Lo phase diagram as the minimum solidus-eutectic or peritectic temperature that occurs in the connection area between pure Hi and the first intermetallic phase, which is formed during diffusion soldering. This is explained using practical examples, such as Au-In and Ag-In using FIGS. 3 and 4. The first intermetallic phase in the Au-In system is the AuIn₂ connection, as can be seen from FIG. 3. Immediately after the connection and the complete consumption of the indi-rich liquid phase, practically only the phases AuIn₂ and remaining gold are detected in the metallographic micrograph of the connection. Nevertheless, the minimum melting temperature of this structure is not the melting point of AuIn₂ at 540.7 ° C. This is because after slow heating all other intermetallic phases form a non-equilibrium zone between Au and AuIn₂. These phases can be present in ultra-thin layers that are not detected. These phases may form the lowest eutectic composition and become fluid at first and therefore cause the compound to melt. These are gamma and psi at T _R = 454 ° C, as shown in Fig. 3. This observation is confirmed experimentally by the measured temperature of the resolution of the mechanical connection at 459 ± 5 ° C.

The second important example is the Ag-In system according to Fig. 4. The first intermetallic phase, which is formed after diffusion soldering somewhat above the indium melting point, is AgIn₂. This phase breaks down in a peritectic reaction at only 166 ° C into L + gamma, which represents the theoretical value of T _R. However, due to diffusion soldering above 166 ° C, around 175 ° C, the gamma phase (Ag-In) forms directly from the melt as a homogeneous layer, which is stable even after extended storage times at 200 ° C. This phase transforms at 281 ° C in the zeta phase (Ag₃ In).

Although the melting of this stage of FIG. 4 is expected at 660 ° C, the connection remains stable up to 900 ° C. This is probably due to the accelerated solid-state diffusion of indium during the heating of the sample and during the transformation of the intermetallic phases into the solid solution (from Ag). The Ag-In system is another example of the fluid boundaries between diffusion soldering (formation of intermetallic compounds) and diffusion brazing (forming a solid solution), as shown in FIGS. 1 and 2. The basic difference between eutectic reactions such as in Au-In and systems characterized by peritectic reactions such as Ag-In is that the latter enables the melting temperature to be easily increased by bonding at a higher temperature. This fundamental difference is important for the interpretation of the calculation of the minimum melting temperature, which is shown in Table 2. This list is comprehensive in that, in addition to the high-melting metals (Cu, Ag, Au, Ni) previously used for soldering, the transition metals according to the invention from group IV b (Ti, Zr, Hf) to group VIII b and additionally the rele vanten elements Al, Si and Ge detected. These can be combined with suitable Lo components.

For a large number of combinations with the term are marked eutectically, there are no intermetallic phases. They are therefore unusable for diffusion or amalgam soldering. they are also useless for diffusion soldering in relation to the very narrow width of the solid solution area of the mostly degenerate eutectic system. The hi-elements, which are definitely not Isothermal solidification connections for any combination nation are aluminum, silicon and germanium.

Very promising and preferred combinations according to the invention are highlighted in Table 2. Not only is T _R significantly higher than the possible binding temperature for these combinations, the solubility and miscibility at higher temperatures are particularly favored. It appears that gallium and tin are the most versatile Lo elements with the highest number of highlighted entries in Table 2.

Table 2

Minimum re-melting temperature T _R in ° C of Hi-Lo material combinations (Lo = Ga, In, Sn and Bi). Preferred combinations are highlighted.

Indium has its special advantages for selected Hi elements such as Au, Mn, Pd and Pt. Bismuth often doesn't fit, it has the highest number of entries labeled eutectic. In addition, there is no highlighted combination in which bismuth cannot advantageously be replaced by Ga, In or Sn. It can be concluded that further applications will be called gallium as an amalgam soldering agent, and indium and tin for diffusion soldering. If you look at the Hi elements, all metals of the first subgroup (Cu, Ag, Au) are bondable, as are the metals of the last row of the eighth subgroup (Ni, Pd, Pt) with even higher values of T _R. Extremely high values of T _R can be achieved with the transition metals of the fourth subgroup (Ti, Zr, Hf). Peak values are 1530 ° C (Hf-Sn) and 1475 ° C (Ti-Sn). Very promising systems for electronic applications include these metals in terms of oxidation or corrosion resistance: Ag-Sn, Au-In, Cu-Sn, Ni-Sn, Ni-In, Pd-In, Pt-In, Pt-Sn. Only systems with Ag, Au, Cu and Ni are dealt with in the literature.

The following are some general principles of the invention explained. The systems with are very interesting for new applications Considering titanium and molybdenum (possibly also Zr and Hf) their use in high temperature process steps in the Manufacture of semiconductor devices, namely Ti-Sn and Mo-Sn.

The addition of a third element to the diffusion soldering systems opened a new degree of freedom that can be used, additional To gain benefits. Such additional advantages are protective layers, Adhesive layers, microstructural influences, etc. The influence of a third element can, however, by interacting with a undesirable element, for example aluminum from a metallic layer.

The additional effort, a multi-layer system for diffusion Creating soldering can only be justified by special advantages the. In addition to the base metals there are generally a number of Auxiliary layers are added that act as a diffusion barrier or corrosion protection or serve better liability.  

Corrosion protection layers consist of a precious metal (preferably Gold) and can be above the Lo component (and of course the Hi component) can be attached to the oxidation of the active To prevent surfaces. Oxidized surfaces prevent that Wetting if they are not mechanically destroyed. By a customized coverage can protect the sensitive layers before Bonding can be stored for a long time.

In many applications, these components are connected to the end parts such as semiconductor chip and substrate applied. To do this are often Adhesive layers are necessary and can be used in the bonding process related.

Diffusion barriers are also used to prevent the Interdiffusion of the active ingredients needed. Without this, they would React components early before use. You can also these barriers are used to diffuse disruptive elements from the connection zone into active semiconductor regions. Reducing the setting time - that is the minimum setting time - can be an important goal to improve lead time in Procedure. This can of course be achieved by Lo combination is chosen so that the intermetallic phase has a higher growth rate or by changing the setting temperature elevated. However, this is not always applicable and a practical way is the reduction in the active layer thickness. Because the growth rates often follow a parabolic growth law in these systems, results in the reduction in the layer thickness of the active Lo component the factor 1/2 a reduction of the solidification time by the factor 1/4. Because a lower limit for the active layer thickness by the Surface roughness or the curvature of the parts to be joined is given, you can help yourself over the active layer to distribute adjacent or repetitive layers.

One of the important applications of isothermal solidification concerns Attachment of power semiconductors to substrates that are used as Heat sink are provided. There are difficulties with this large components above 75 mm in diameter. It could already shown that a most successful solution by  Diffusion soldering can be achieved with systems such as Ag-Sn or Ag-In the re-melting temperature of these solders is still too low and above all limits the maximum possible Process temperatures in the further processing of the chips.

In the following the invention will be explained with the aid of examples.

example 1

A very innovative application of the above-mentioned results together with new considerations is the fastening of unmetallized semiconductors made of Si or SiC with special diffusion soldering systems, which can withstand extremely high temperatures. This makes it possible to completely redesign the subsequent manufacturing processes for the combined parts. In Fig. 5 such an example is shown with an active Ti-Sn system, which is applied directly to the silicon wafer. After diffusion soldering at 250-300 ° C, the Ti / Ti₆ Sn₅ connection forms, which remains completely solid up to 1475 ° C. This temperature is above the melting point of silicon. In fact, the thermal stability of this compound is limited by the Si / Ti interface that occurs in many semiconductor manufacturing processes.

At about 800 ° C, the formation of Ti silicides is expected at the Ti / Si interface as a solid-state reaction. The eutectic in the Ti-Si System produces a liquid phase at 1330 ° C. The existence of a Titanium layer after diffusion soldering is for thermal stability of the overall system is important so that there is direct contact between Ti₆Sn₅ and Si is avoided.

Additional advantages of diffusion soldering of silicon with the Ti-Sn-Sy stem are that tin has a very low diffusion coefficient in the Owns silicon. It is lower than that of indium and gallium and Sn is also electrically neutral, even when diffused into the silicon. The chemical activity of tin is due to the formation of the Ti₆ / Sn₅- Connection greatly reduced and thus the driving force for the Diffusion in the silicon. Titanium is the standard element for semiconductors processes known. These properties show that the Ti-Sn / Si system is very interesting for subsequent high-temperature semiconductor processes.  

FIG. 5 shows a schematic cross-section through the layer structure of two before and after the diffusion soldering semiconductor wafers. The connection is formed at 250-300 ° C and is stable up to 1475 ° C. One or both sides of one of the silicon wafers can also be replaced by SiC. This results from the well-known good adhesion of titanium to SiC, for the connection of SiC to Si or to SiC with the Ti-Sn system. An intermediate layer of SiO₂ can be introduced on one or both sides of the silicon wafers in FIG. 5 in order to form a sequence Si / SiO₂ / Ti / Sn. Based on the good adhesion of titanium to SiO₂, this forms an electrically insulating connection. Other insulation layers such as Si₃ N₄ are also possible.

The connection so described can be repeated to a Sta build up of several semiconductor wafers. The Ti-Sn connection between two semiconductor wafers in a single step or be made one after the other. This gives you a new free degree of manufacturing process. The low connection temperature of 250 ° C and the following high thermal stability are for everyone because subsequent formation of additional connections is of great advantage.

Example 2

A buried electrically conductive layer can be made using this method can also be manufactured. After diffusion soldering of Si / Ti / Sn (top) on Sn / Ti / SiO₂ / Si (bottom) the structure Si / Ti / Ti₆ is created Sn₅Ti / SiO2 / Si (below). The upper Si wafer can then on the required thickness can be thinned.

The layer thickness from FIG. 5 can be modified for both examples, it being necessary to note that a residual layer of unreacted titanium must be present after the complete isothermal solidification. The layers are preferably deposited by PVD (by evaporation or sputtering) without interrupting the vacuum. The titanium layer is therefore not exposed to atmospheric oxygen. The connection is carried out at the lowest possible pressure of 0.2-5 MPa in a vacuum oven. This will avoid gas inclusions and oxidation at the Sn / Sn interface. The heating rate up to the melting point of tin is chosen so high that a rapid melting and wetting of the interfaces is ensured and a premature Ti / Sn reaction during heating is avoided. The holding time for the isothermal solidification is 250-300 ° C and should be in the order of 1-10 min. lie, which depends somewhat on the total thickness of the tin layers.

Example 3

Other materials are also possible. In addition to Ti, Mo W and Ta attractive hi-components. Of these, W and Ta are not suitable for diffusion soldering, as shown in Table 2. Therefore In addition to the Mo-Sn system, the Ti-In system with the relative low remelting temperature of about 800 ° C left. Higher Remelting temperatures are achieved with Hf-Sn (1530 ° C) and Zr- Sn (1142 ° C), however, Hf and Zr are not in semiconductor manufacturing Standard metals and are relatively difficult to handle. Compared they have a higher affinity for oxygen with Ti. This comparison shows the outstanding properties of the Ti-Sn system.

Carrying out the diffusion soldering with the according to the invention preferred materials generally take place in a vacuum oven instead of. Metallized semiconductors (preferably Si or SiC) are used other metallized semiconductors (preferably Si or SiC) or with a metallized substrate (ceramics such as Al O₃ AlN, SiC or Metals such as Mo, W, Cu, Fe-Ni). The metallizations included one or more hi-components and one or more lo- Components and additional possible adhesion promoters and Protective layers. The connection by means of diffusion soldering proves to be along with good thermal and electrical conductivity as thermally very stable and mechanically very reliable.

To carry out the procedure, it should be noted that the Hi component and the Lo component can be found in Table 2 are on a careful and complete metallurgical Investigation based.

The so-called flip-chip connection of semiconductors for the Fastening and the local electrical connection in one step is created by a given arrangement of connections. The above suggestions also apply to this technology, though  the corresponding lateral structures of the metallization beforehand were carried out. For the self-adjusting connection, in Dome-like structures are commonly used. For this, the hi Component or the underlying metallization, which does not participate in the diffusion soldering process, with a greater layer thickness produced.

Amalgam soldering relates to the mechanical and / or electrical connection that of a semiconductor to a metallic or ceramic disk or a semiconductor pad. One applied in a relatively thick layer Amalgam filler is applied in its semi-liquid form. Prefers the metals of the first (Ag, Au, Cu) or the eighth Subgroup (Ni, Pd, Pt) amalgamated with Ga. For a connection with much higher thermal stability is suggested, Ga-based To use amalgams with Hi = Co, Cr, Fe, Mo and V. The Remelting temperatures are above 700 ° C with one exception of vanadium (500 ° C) as shown in Table 2. The highest Melting temperatures which are above 1120 ° C. achieved with the low transition metals Hf, Nb and Zr; however must one be very careful to prevent this metal powder from oxidizing and to prevent while mixing with liquid gallium.

Claims (11)

1. A method for producing a temperature-stable connection of two bodies, between which a layer of a higher-melting (Hi) and another of the low-melting metal (Lo) is arranged, the higher-melting metal (Hi) and the low-melting metal component (Lo) are brought into contact and heated by heating to the connection temperature (T _B ) under a predetermined temperature and contact pressure curve in such a way that the component (Lo) which first becomes liquid wets the joint surfaces, and whereby by diffusion of the liquid (Lo) in the higher melting component (Hi) an intermetallic phase is formed from the material of the lower melting intermediate layer (Lo) and the higher melting component, the lower melting component (Lo) being consumed by diffusion and formation of a new component (Hi-Lo), and after consumption of the melted portions this one layer with we sentli ch higher melting point (T _R ) than the low-melting component (Lo) and thereby a stable positive connection is formed, characterized in that one of the metals of the fourth to eighth subgroup of the periodic table is selected for the Hi component and on a Semiconductor wafer is applied as the first body and a low-melting metal (Lo) of the third or fourth main group of the periodic table is applied to a substrate as a second body and, after it has been brought into contact with the metal (Hi) on the semiconductor wafer, is melted. 2. The method according to claim 1, characterized, that as a low-melting component (Lo) metals with a Melting point below 450 ° C such as Bi, Ga, In, Pb or Sn used will.   3. The method according to claim 1, characterized, that on a body, d. H. Substrate or semiconductor, first an adhesive layer is deposited for the subsequent layer. 4. The method according to claim 1, characterized, that both on the substrate, as well as on the semiconductor first the higher melting layer (Hi) and then the low rig melting layer (Lo) is deposited. 5. The method according to any one of claims 1 to 4, characterized, that a low-melting layer (Lo) consists of Sn and with a layer (Hi) of one of the metals Co, Fe, Hf, Mn, Mo, Nb, Pt, Rh, Ru, V or Zr is combined. 6. The method according to any one of claims 1 to 4, characterized, that the low melting layer (Lo) consists of indium and with a high melting layer (Hi) made of Mn, Pd, Pt, Ti or Zr is combined. 7. The method according to any one of claims 1 to 6, characterized, that to protect the layer (Lo) against oxidation on this one Layer of a nobler metal is deposited. 8. The method according to any one of claims 1 to 7, characterized, that on the substrate and / or the semiconductor wafer Diffusion protection layer is deposited. 9. The method according to any one of claims 1 to 8, characterized, that the protective or diffusion barrier layer from the same Like the layer, material consists of the high melting point Material (hi).   10. The method according to any one of claims 1 to 5 or 7 to 9, characterized, that as a higher melting semiconductor or substrate metallization (Hi) Ti combined with the low melting component (Lo) Sn is used. 11. The method according to any one of claims 1 to 10, characterized, that the higher melting semiconductor metallization (Hi) in two Layers above and below the low-melting Layer (Lo) is applied.