DE3107857C2 - Process for the production of thin-film circuits with very easily solderable interconnect layer systems - Google Patents

Abstract

Compared to the conductive layer metals gold, silver, copper and palladium, nickel has the lowest dissolution in the solder. Nickel oxidizes in the air and intensifies on the surface when subjected to temperature treatment. This nickel oxide layer prevents complete wetting of the nickel surface during the soldering process and thus prevents a good soldered connection. According to the invention, therefore, either an aluminum, aluminum-silicon, copper or copper / aluminum layer is applied to a soldered layer made of nickel or a nickel alloy in the same vacuum.

Description

The invention relates to a method for producing thin-film circuits with precious metal-free and very easily solderable interconnect layer systems.

The field of thin film technology includes integrated hybrid circuits, resistor networks, RC networks and wiring for semiconductor chips, liquid crystal displays, plasma displays, solar cells, etc. For these applications usually consist of layer systems made up of resistor and / or capacitor layers and adhesive, solder and conductive layers together.

Thin layers are applied to an insulating substrate in a vacuum by means of vapor deposition or sputtering applied and, depending on the requirements, reinforced or refined by electrochemical deposition. The structure generation takes place either by steaming or sputtering through mechanical masks or by photo and etching processes.

When equipping layer circuits with z. B. coils, capacitors, transistors, micropacks and Connection elements are particularly demanding in terms of the solderability of the solder layer. Inadequate solderability (e.g. poor wettability, dewetting or rapid dissolving) makes it difficult or impossible. prevents the insertion and / or replacement of components. Made of copper and / or gold Due to their good solubility in the solder bath, conductive layers alloy relatively quickly. Layer circuits are thus unusable.

Solderable conductor track systems are made from combinations of precious metal layers using previously known methods, such as NiAu, TiPdAu, TiCuNiAu. In the case of non-precious metal-free layer combinations Pure copper is used as a conductive and soldering layer (DE-AS 17 90 013). Oxidize conductive layers made of copper at higher temperatures (> 250 ° C), for example when stabilizing resistance layers occur over time and can no longer be soldered.

In DE-AS 17 90 013 a thin-film circuit is specified in which the components and conductor tracks can be formed in the desired configuration using a selective etching process. There is the resistance layer made of a CrNi layer, the conductor track layers made of gold or copper and the protective separating layer made of iron, nickel, cobalt or aluminum.

With regard to the soldering properties, the conductor track systems already mentioned have the following disadvantages:

Ni-Au layer:

ίο Insufficient wetting of the oil layer by tin solder (for example 60 Sn / 40 Pb) after the tempering process
TiPdAu layer:

As a consequence of the rapid solubility of Pd / Au in tin solder, these layers alloy off after relatively short soldering times.
TiCuNiAu layer:

Perfect solderability is only guaranteed when tempered in air up to 250 ^{° C}
TiCu layer:

The rapid solubility of copper in solder requires relatively thick layers on the solder contacts.

The soldering properties of the conductor track systems described are not sufficient for many requirements. Compared to the conductive layer gold, Silver, copper and palladium have the lowest dissolution of nickel in the solder. Nickel oxidizes in the air and reinforced with temperature treatment on the surface.

This nickel oxide layer prevents complete wetting of the nickel surface during the soldering process and thus a good solder connection. To the oxide layer too relatively sharp fluxes are necessary to remove them, which experience has shown with thin-film construction elements and resistance layers are not compatible.

The invention is based on the object of implementing the method described at the outset, wherein a Nickel or nickel alloy layer during the tempering process against oxidation through a protective layer is protected. This object is achieved in that in a vacuum on an insulating substrate carrier an approx. 50 nm thick adhesive or resistance layer (titanium, chromium, molybdenum, tungsten, titanium tungsten, aluminum, Nickel, nickel chromium, tantalum nitride, tantalum aluminum, tin indium oxide and the like), a 50 to 2000 nm thick solder layer made of nickel or a nickel alloy and then a 10 to 2500 nm thick protective layer made of aluminum, an aluminum alloy, copper or copper / aluminum is applied.

Thus, in the method according to the invention, aluminum and / or copper layers protect the underlying Nickel layer against oxidation in the air. For Nikke layers that are annealed in air at higher temperatures oxidation protection from an aluminum or copper / aluminum layer is required. Layer thicknesses of 0.5 μίτι for copper / aluminum layer or approx. 20 nm for the aluminum layer are sufficient to prevent nickel, for example After tempering in air at 350 ° C., it diffuses to the surface for one hour and is oxidized. Before the appointment the aluminum protective layer must be removed from the soldering points. When in a vacuum or in a protective gas atmosphere Annealed nickel layers, a thin copper layer is sufficient to create a subsequent one Avoid oxidation of nickel in air. The advantage of the invention is in particular that the nickel-copper, nickel-aluminum or nickel-copper-aluminum layers are highly temperable and very

are easy to solder. A nickel alloy can also be used instead of nickel can be used. The nickel layer is given by the high solubility of nickel in tin solder Excellent for longer soldering times and multiple soldering

The solderability of the presented layer combinations was checked on structured layers that were tempered in air at 350 ° C. for one hour. The layer thicknesses for the NiCuAl variant: Ni soldering sheet 100 nm, Cu conductive layer 1000 nm and Al protective layer ίο 40 nm. The soldering took place in a 60 Sn / 40 Pb solder bath heated to 220 ° C. with an immersion time of 8 see. This soldering process could be done with the NiCu layer 6 χ can be repeated without traces of alloys being discernible.

The sheet resistance of the NiCu or NiCuAI layers is relatively low. If you take z. B. for a NiCuAl layer structure a Ni layer of 100 nm, a With a Cu layer of 500 nm and an Al protective layer of 40 nm, the conductor track resistance for a Total layer thickness of 640 nm approx. 0.04 Ω / D. This value increases after the heat treatment of 350 ° C, 1 hour in air to 0.05 Ω / G.

The method according to the invention is possible both by dispensing with expensive precious metals such as gold or palladium and especially because of the relatively small layer thicknesses for the Ni solder layer and the Cu conductive layer inexpensive.

The process can be implemented with the following layer thicknesses:

layer or copper / aluminum not applied. About the thickness of the protective layer 5 can simultaneously the track resistance can be influenced. The soldering points 8 are located on the conductor track 6.

The F i g. 2 differs in this respect from FIG. 1, that a conductive and protective layer 7 made of copper is provided over the solder layer 4

After construction, as shown in FIG. 3 is shown. absent in comparison to FIGS. 1 and 2 the resistance layer 2.

1 sheet of drawings

1. Adhesive layer approx. 50 nm Nickel alloy 2. Solder layer: Nickel 50-5000 nm or 50-5000 η m. 10-2500 nm 3. Conductive and / or protective layer: 50-2500 nm aluminum 50-2500 nm Copper / aluminum copper

} 5

40

Adhesive layers are the resistance layers nickel chrome, tantalum nitride, tin indium oxide and tantalum aluminum as well as chromium, titanium, molybdenum, tungsten, titanium tungsten, aluminum and the like.

For certain applications it is conceivable that the nickel layer is used as an adhesive and solder layer at the same time can be (see Fig. 1.3).

The manufacturing process for DF circuits becomes special Inexpensive if the resistance layer and one of the presented conductor track-layer combinations ^ nen be applied one after the other in a vacuum.

Advantageous embodiments of this method and features relating to the use of base material in such a procedure emerge from the subclaims.

The invention is illustrated by the figures, the three different variants of a layer structure in section / own, explained.

The layer structure according to FIG. 1 consists of a mi Substrate 1 on which a resistor b / w. Wider-hand capacitor layer or ln2Oj / SnO2- (ITO-) Layer 2 is applied. On it is as needed an adhesive layer Λ the z. B. made of titanium, chrome, aluminum and the like can exist. Above the sticky b5 The layer is a soldering pad 4 made of nickel or a nickel alloy intended. The protective layer 5 is either an aluminum PV. Aluminum-silicon. Copper-

Claims (1)

Patent claims: I. Process for the production of temperable thin-film circuits with precious metal-free and very well-solderable interconnect layer systems, characterized in that in a vacuum an insulating substrate carrier (1) an approx. 50 nm thick adhesive or resistance layer (titanium, chromium, Molybdenum, tungsten, titanium tungsten, aluminum, nikkei, nickel chrome, tantalum nitride, tantalum aluminum, Tin indium oxide and the like) (2, 3), a 50 to 2000 nm thick solder layer (4) made of Nicke! or one Nickel alloy and on top of it a 10 to 2500 nm thick protective layer (5) made of aluminum, an aluminum alloy, Copper or Kuofer / aluminum is applied. Z method according to claim 1, characterized in that that the soldering layer (4) made of nickel or a nickel alloy is at the same time an adhesive layer (3) 3. The method according to claim 1, characterized in that after the temperature processes Protective layer (5) is removed by etching before soldering.