DE19532250A1 - Diffusion soldering of a multi-layered structure - Google Patents

Abstract

The arrangement serves for diffusion soldering of one body to another. One of the bodies is coated with a metal layer (Hi) with a high melting point, while an intermediate metal layer (Lo) with a low melting point is placed between the two bodies. The layers (Hi, Lo) can be joined at certain temperatures by application of pressure, with intermetallic compounds being formed in the process. The bodies are a substrate (1) and a semiconductor disk (2), while the layer (Hi) takes the form of protective layers (Hi1, Hi2) on these bodies. Also claimed is a method for producing this arrangement.

Description

The invention relates to an arrangement for producing a temperature stable connection by means of diffusion soldering according to the generic term of Claim 1 and a method for diffusion soldering a multilayer construction.

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. There is a method for generating a positive connection between metallic connectors and me described metallic contacts of semiconductor surfaces. The verb which are used in particular to connect solar cells in parallel of solar cell contacts. Between a connector and a contact becomes an intermediate layer of one opposite the connector and Metallic contact low-melting metal arranged and on or warmed above the melting temperature. It is important to ensure that the liquid intermediate layer the joining surfaces of connectors and contact wetted. The liquid intermediate layer diffuses into the Connector and the contact and forms an intermetallic phase with the material of the intermediate layer and the materials of the to be joined Connector and contact. This is due to the solidification during a given temperature and contact pressure curve the form coherent connection between connector and contact established, de ren melting temperature 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 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 involves connection processes, some of which Distribute the conventional soldering or brazing processes using the process of diffusion bonding (diffusion bonding) have 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).

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 requires only 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 below 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 invention is therefore based on the object of a combination of Materials to produce a reliable positive Connection for metallic surfaces of semiconductor contacts specify that need the shortest possible joining time. Before the When connected, the components should survive a long storage period.

According to the invention, the object is characterized by the characteristics of the An claim 1 contained features solved. Developments of the invention and a method of making a solder joint are in there Subclaims included.

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, the Ag-In phase diagram and the minimum reflow temperature T _R,

Fig. 5 is a schematic diagram of a prior to the reaction and b after the diffusion soldering of Au-In-Ti-system, and

Fig. 6 is a schematic view of the multilayer structure to increase the rate of solidification a without and b with diffusion barrier.

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 a congruent 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 starts from the original non-equilibrium state of the solid Hi + liquid Lo at T _B , the equilibrium state becomes due to reaction diffusion and growth of the intermetallic phase HiLo at the interface between the solid phase Hi 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 Hi. 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.

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. An overview of the previously known material systems for diffusion brazing shows that these 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.

The low-melting components are Sn layers from 0.5 to 2 µm Thickness, which 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 Ag₂In 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 Systems 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.  

Table 1: Material combinations for diffusion soldering

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 intermetalli phases is 12% for Ni-Sn and only 0.7% for Cu-Sn, whereby Pores have occasionally been observed with the Ni-Sn compound. The Pores could not be avoided by using higher pressures as the liquid tin from the connec region is pushed away. The compounds are preferred carried out in a reducing gas atmosphere. One also uses Vacuum, inert gases or air. The oxidation of the applied layers the connection components can cause problems during storage cause. Additional oxidation during connection can occur when bonding through an air layer between insufficiently planned ver binding surfaces are created. An oxide skin on the low melting component or an oxide layer on the free top Finally, the surface of the high-melting component can be wetted prevent what the connection does not come about.

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 used here to illustrate the Basic ideas. It is a key property of diffusion soldering and generally isothermal solidification that the Lo component can be selected almost independently of the Hi component. The is because the binding temperature is usually determined by the Melting point of the Lo component is limited and not as with ge ordinary soldering by one eutectic reaction with another Component. Therefore it is very easy to use all low melting metals to indicate which are possible for a desired 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, diffusion soldering above 166 ° C, around 175 ° C, forms the gamma phase (Ag₂In) 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 into the zeta phase (Ag₃In).

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.

Table 2

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

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. Indium has its special advantages for selected Hi elements such as Au, Mn, Pd and Pt. Bismuth often does not fit, it has the highest number of entries labeled eutectic.

In addition, there is no highlighted combination in which bismuth cannot be advantageously replaced by Ga, In or Sn. It can be concluded that further applications will relate to gallium as an amalgam soldering agent, as well as 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. An important advantage is the reduction the joining time. Other benefits include the inclusion of protection layers and bond layers. The influence of a third Ele However, by interacting with an un desired element, for example aluminum from a metal layer.

The phase diagram is a key tool for understanding the aspects and the development of every isothermal solidification process ses. While the binary phase diagram is relevant for all Combinations are known, this is not the case for the ternary diagrams the case. The ternary systems are one exception with gold and on the other hand with silver.

Particular attention is paid here to selected Au-In metal systems because experimental data indicate that the binary Au-In system a promising basis for the connection represents sensitive electronic components.

The most interesting ternary alloy elements for the Au-In-M-Sy stem are the metals M = Ag, Cu, Ni, Pd, Pt and Ti. This selection is already through the combinations in the list of the most promising binary systems indicated. The third element acts as an additional one Hi component. Due to the phase diagrams one can consider do in how the knowledge of binary phases modified diagrams can be transferred into ternary systems, to be able to make appropriate predictions. Because they match the ternary phase diagrams are not sufficiently well known, one often has to focus on one when selecting suitable combinations leave happy grip.  

A three-substance system is implemented by a three-layer system arrangement represents. The additional effort, a multi-layered Diffusion soldering system can only be created by special Advantages such as shortening the joining time are justified. To the three base metals generally comes 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) are attached to the oxidation of the active upper to prevent areas. Oxidized surfaces prevent wetting if they are not mechanically destroyed. By an adapted Be The sensitive layers can last longer before bonding Time to be stored.

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 to prevent inter diffusion 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 a high growth rate or by setting the setting temperature increases. However, this is not always applicable and is a practical way the reduction in the active layer thickness. As the growth rates in these systems often follow a parabolic growth law reducing the layer thickness of the active Lo component by Factor 1/2 a reduction in the setting time by a factor of 1/4. There a lower limit for the active layer thickness by the upper given surface roughness or the curvature of the parts to be joined  you can help yourself by moving the active layer over neighboring ones or spreading repetitive layers.

example 1

An instructive and realistic example of the combination of a protective layer with an adhesive layer is shown in FIG. 5 using the tertiary Au-In-Ti system. The goal is to bond a silicon chip 2 to a silicon substrate 1 . Substrates such as AlN can also be used in the following examples. The active indium layer is deposited on the surface of the silicon chip 2 and not also on the substrate 1 . One would like to simplify the layer structure and avoid free residual indium on the substrate surface after the bonding. A titanium layer serves as an adhesive layer and is used on both sides. However, chrome or other adhesion enhancement layers and thinner layers can also be used. The protective gold covering of approximately 0.1 μm is intended to prevent the oxidation of indium, as shown in FIG. 5a. This gold covering reacts immediately (and even at room temperature) with the indium layer to AuIn₂. It is important to know that 0.3 µm of the original indium layer is consumed by this reaction and only 1.7 µm of the active indium layer remains, as shown in Fig. 5b. Since the AuIn₂ formed is a very stable phase, it is assumed that it also serves as an oxidation protection layer.

This AuIn₂ layer is destroyed by slight pressure during bonding and allows the gold-covered substrate 1 to be wetted after the active indium has melted. During the bonding, indium reacts with the gold covering of the substrate, for example 2 µm, to form 2.5 µm AuIn₂. This includes the 0.4 µm thick layer of distributed AuIn₂ created by isothermal solidification (see Fig. 5c). Lateral diffusion plays no role in the relatively short reaction time. Since the liquid indium is quite reactive, the formation of Ti₃In₄ is expected. 0.2 µm of the indium layer is completely used up. The formation of AuIn₂ from solid indium and gold is associated with a calculated volume increase of 2.6%. If you start with liquid indium, there is a small expansion of 0.7%, and therefore no voids are created during the solidification process.

The diffusion reaction ends abruptly when the liquid is used up. After a long time, solid state diffusion gives rise to a state as shown in FIG. 5d. Additional phases rich in gold, which contain indium, grow between AuIn₂ and Au due to the partial consumption of these end phases. The average composition of this region corresponds to 24.5% by weight indium and 75.5% by weight gold. Lateral diffusion and the Ti-Au reaction are not taken into account. The lateral diffusion provides a large gold reservoir and this shows the impossibility of developing a binary Au-In layer system in this configuration with a defined composition, for example in the range 37-53% by weight indium, in order to achieve the remelting temperature T _R after reaching equilibrium to 495.4 ° C (see Fig. 3).

The reaction zone in Fig. 5d is not yet completely in equilibrium, but the layer sequence Ti₃In₄ / AuIn₂ / Au-rich phases / Au is in a local equilibrium. The additional formation of TiAu in the compound is expected in consequences such as Ti₃In₄ / TiAu / AuIn₂ / Au-reich / Au or Ti₃In₄ / AuIn₂ / TiAu-reich / Au, but this depends on the movable components, gold in the former and titanium in the latter case. It is therefore important to accelerate the solidification rate and to set up diffusion barriers. The easiest way to divide the active layer into multiple, albeit thin, repeating layers is not possible for the Au-In system. Such layer structures suffer from the premature reaction to AuIn₂ during the storage period, with the active indium layer being consumed. This premature reaction can even be complete since the individual In / Au ratios should be set so that there is an excess of gold in order to ensure complete local solidification of each individual indium layer.

One way to solve this problem is to physically separate the components with low-temperature reactivity, i.e. In / Au or generally Hi1 on the one hand, and direct Hi2 / In contact with a high-melting component Hi2, which enables the early reaction with indium is not significantly exposed, as shown in Fig. 6a. An optional antioxidant Au covering is also shown in Fig. 6a. Further possible layers of adhesion are omitted. During bonding, the response from at Hi1 and Hi2 progresses. The indium layer is distributed over both reactions and disappears in the solidification phase. Gold is an obvious choice for Hi1, but other elements such as Pd or Pt, which form very stable compounds with indium, are also possible. For Hi2, any of the preferred elements of the In column in Table 2, except Au, can be selected as a preliminary candidate. The extent of the premature reaction with indium in the solid state must be determined experimentally. The data for the reaction rates are not known, except for liquid indium in the Ag-In reaction, which, however, proceeds more slowly than the corresponding Au-In reaction. Hi2 candidates are Ag, Ni, Pd or Pt.

Example 2

Another way to prevent the premature reaction is to place a diffusion barrier X between indium and Hi2, as shown in Fig. 6b. In this case, both Hi1 and Hi2 can be gold. Other possibilities for elements, which are listed in Table 1, are quite conceivable. A limited reaction in the solid state between indium X or Hi2 and X is tolerable. An important requirement for the diffusion barrier X is that it must sacrifice itself during bonding in order to allow the reaction between liquid indium and Hi2. That is certainly the case for X = Sn. The advantages of this technique result from the fact that the mass ratio Sn to In is limited to the value 23:77 or that the layer thickness is limited below a ratio of 0.6 µm Sn to 2 µm In. This is consistent with the processes shown in Figure 6b. The ability of tin (Sn) to act as an effective diffusion barrier against premature reaction between gold and indium has been experimentally verified. One embodiment of the invention uses high melting diffusion barriers such as X = Ti or Ni, which are even more efficient. A system with X = Sn and Hi1 = Hi2 = Au is very promising. This technique can of course also be carried out with the other elements from Table 2.

In the following, the invention is explained on the basis of applications.  

One of the few applications of isothermal solidification concerns Attachment of power semiconductors to substrates used as heat mesenke are provided. Here there are difficulties with large areas components above 75 mm in diameter. It could be already shown that a most successful solution through diffusion Soldering can be achieved with systems like Ag-Sn or Ag-In that The re-melting temperature of these solders is still too low and above all limits the maximum possible process temperatures forwarding the chips.

Carrying out the diffusion soldering with the be according to the invention preferred materials generally take place in a vacuum oven. Metallized semiconductors (preferably Si or SiC) are used with others metallized semiconductors (preferably Si or SiC) or with a metallized substrate (ceramics such as Al₂O₃, AlN, SiC or metals such as Mo, W, Cu, Fe-Ni) connected. The metallizations contain one or several Hi components and one or more Lo components and additional possible adhesion promoters and protective layers. The Ver Binding by means of diffusion soldering proves together with a good one thermal and electrical conductivity as thermally very stable and mechanically very reliable.

The following must be observed to carry out the procedure:

• - Physically, the main bodies of the Hi and Lo layers are separated, as shown in Figs. 5 and 6.
  This prevents premature reaction of the active Lo layers, even without a diffusion barrier. The specified layer thicknesses can be varied and the protective gold covering can be replaced by a protective layer made of silver.
• - The Hi components and the Lo components are shown in Table 2 refer to which on a careful and complete metallurgical investigation based.
• - In order to accelerate the solidification rate, multilayer structures are proposed, as shown in FIG. 6. The layer thicknesses given are only examples and silver protective layers can also be used.

The so-called flip-chip connection of semiconductors for mounting supply and the local electrical connection in one step made by a given arrangement of connections. The The aforementioned suggestions also apply to this technology if the corresponding lateral structures of the metallization beforehand were performed. For the self-adjusting connection are common Way used dome-like structures. This is the hi component or the underlying metallization, which is not on the Diffusion soldering process takes part, made with a larger layer thickness.

Claims (14)

1. Arrangement for producing a temperature-stable connection by means of diffusion soldering of a first to a second body, where a body is coated with a high-melting metal (Hi) and an intermediate layer of low-melting metal (Lo) is arranged between the first and second body, wherein the higher-melting layer (Hi) and the lower-melting intermediate layer (Lo) have surfaces that can be joined under a predetermined temperature and contact pressure, the liquid intermediate layer (Lo) wetting the joining surfaces, and thereby an intermetallic phase from the material of the low-melting intermediate layer ( Lo) and the higher-melting layer (Hi), which enables a positive connection between the two surfaces, characterized in that the first and second body is a substrate ( 1 ) or semi-conductor plate ( 2 ) that as a high-melting component a layer (Hi1) is applied to the substrate ( 1 ) eight and that a second high-melting layer (Hi2) is applied to the semiconductor wafer ( 2 ) as a protective layer. 2. Arrangement according to claim 1, characterized, that the protective layer under the low-melting layer (Lo) is arranged. 3. Arrangement according to claim 1, characterized, that the protective layer over the low-melting layer (Lo) is arranged.   4. A method for producing a temperature-stable connection by means of diffusion soldering of a first to a second body, wherein a body is coated with a high-melting metal (Hi) and an intermediate layer of low-melting metal (Lo) is arranged between the first and second body and then the higher-melting one Layer (Hi) and the low-melting intermediate layer (Lo) are brought into contact and heated under a predetermined temperature and contact pressure curve in such a way that the intermediate layer (Lo) becomes liquid and wets the joint surfaces, and thereby by diffusion of the liquid intermediate layer into the higher-melting layer (Hi) an intermetallic phase is formed from the material of the low-melting intermediate layer (Lo) and the higher-melting layer (Hi), the low-melting component being consumed by diffusion and the formation of a new component (Hi-Lo) and a fo A positive connection is formed between the two surfaces, and wherein after the molten layer has solidified, the newly formed phase has a significantly higher melting point (T _R ) than the low-melting component, by means of an arrangement according to claim 1, characterized in that the two bodies have substrate ( 1 ) or semiconductor wafers ( 2 ) are that a layer (Hi1) is applied as a layer as the high-melting component on the substrate ( 1 ) and that a second high-melting layer (Hi2) and a low-melting component (Lo) are applied to the semiconductor wafer ( 2 ) are applied and that the high-melting layers are chosen so thick that the low-melting layer (Lo) is completely converted during the joining process. 5. The method according to claim 4, characterized, that as low melting components (Lo) metals with a Melting point below 450 ° C such as Bi, Ga, In, Pb or Sn used will.   6. The method according to claim 4 or 5, characterized, that used as low-melting component (Lo) indium becomes. 7. The method according to claim 4 or 5, characterized, that tin is used as the low-melting component (Lo). 8. The method according to any one of claims 4 to 7, characterized, that on a body first an adhesive layer for the subsequent layer is deposited. 9. The method according to any one of claims 4 to 8, characterized, that both on the substrate, as well as on the semiconductor first a high-melting layer (Hi1, Hi2) is deposited becomes. 10. The method according to any one of claims 4 to 9, characterized, that a low-melting layer (Lo) consists of Sn and on a layer (Hi2) of one of the high-melting metals Co, Fe, Hf, Mn, Mo, Nb, Ni, Pt, Rh, Ru, V or Zr is deposited. 11. The method according to any one of claims 4 to 9, characterized, that the low melting layer (Lo) consists of indium and on a high melting layer (Hi) made of Mn, Pd, Pt, Ti or Zr is deposited. 12. The method according to any one of claims 4 to 11, characterized, that to protect the layer (Lo) against oxidation on this one Layer (Hi1) deposited from a high-melting precious metal becomes.   13. The method according to any one of claims 4 to 12, characterized, that on the substrate and / or the semiconductor wafer Diffusion protection layer (Hi2) is deposited. 14. The method according to any one of claims 4 to 13, characterized, that the protective layer is made of a high-melting material (Hi1) exists, which already with the low-melting layer (Lo) a stable intermetallic bond is established before joining, which does not oxidize appreciably.