JPS6032311B2 - Electric conductor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thin film and hybrid integrated circuits, and in particular to conductive systems for wiring in such circuits.

Thin film and hybrid integrated circuits are commonly used today in a wide range of applications such as filter circuits and memories for switching and transmission systems.

The most commonly used metal wiring system for these applications employs a titanium-palladium-gold multilayer structure. In this case, the gold layer is the main part that carries charges, and at the same time it also functions well as a bonding layer. Although such systems serve their purpose well, they require large amounts of money. Typically, the gold layer is approximately 500 mm thick.
00A and must be formed on almost all parts of the wiring pattern. As the price of gold increases, the cost of manufacturing such circuits becomes excessive. It is very difficult to find an alternative to such a system.

Such a system not only has good conductivity and strong adhesion to the substrate, but also processes required for circuit production such as thermocompression bonding and soldering, processing processes necessary for resistor and capacitor production, and processes such as stabilization and annealing. This is because it is important to balance both. The various elements in the system are also required to be mutually compatible, ie non-reactive. The objectives of the present invention are therefore primarily to provide a metal interconnect system that is less expensive than systems currently in use, while at the same time being compatible with the myriad process requirements of thin film and hybrid circuits.

This object, among other objects, can be achieved in accordance with the present invention, which provides a metal combination comprising a titanium-copper-nickel-gold layer for wiring. The required thickness of gold can be greatly reduced since the copper functions as the primary conductor and the gold only needs to function primarily as a bonding layer. The titanium provides sufficient adhesion to the insulating substrate and the nickel acts as a diffusion barrier between the copper and gold layers. Additionally, a layer of palladium can be added to further strengthen the adhesion between the titanium and copper layers. According to embodiments of the method of the present invention, thin layers of titanium and copper can be formed continuously over substantially the entire surface of the substrate by vapor deposition or sputtering. Additional copper is then electroplated onto the copper in the area encompassing the vaporized or sputtered interconnect pattern. A layer of nickel is then electroplated onto the surface of the plated copper. Gold is then electroplated over the entire nickel surface or only on the nickel in areas such as those containing bond pads. The parts of the titanium and copper not covered by the plated metal are removed by corrosion, creating the wiring pattern. To strengthen the bond, the present invention considers a new heat treatment method after layer formation. This is 200
This process includes heat treatment at 00 to 400°C for 3 to 1 time. These and other features will become clearer in the following description.
Now, the embodiment shown in FIG. 1 will be described.

Board 1 Kawama, American Love Company (theAm
ericanLava Company) with the product name “A-
76246" and Coor Company (C.
A ceramic material sold under the trade name "2" may be used. The titanium layer 12 is preferably initially deposited on the substrate 10 using known vapor deposition techniques. To increase the adhesion of the subsequently deposited layers, the thickness is approximately 1700 to 2500 nm. A layer 14 of palladium is then placed on the titanium by vapor deposition, at approximately 3000 Å.
It is desirable to have a thickness of .

Finally, a layer of gold 16 is deposited on the palladium 14 at a thickness of about 20,000
After electroplating to a thickness of A, a composite conductive thin film 17 is formed on the substrate I0.

If you want to reduce the amount of gold, most of the gold can be replaced with copper. In other words, the gold layer can be replaced with gold-plated copper. The gold must provide a good bonding surface that is not oxidized, but copper easily diffuses through the gold and oxidizes, destroying the bonding surface.

For this purpose, nickel is placed as a barrier layer between the copper and gold.
The copper-containing conductor layer thus includes titanium and palladium sequentially deposited on the substrate, and then copper, nickel, and gold plated sequentially on the palladium. Next, we will discuss Figure 2. Chitashi 12, Palladium 14
A composite conductive metal layer, in other words a thin film 17, consisting of a metal layer of gold 16 and gold 16 is formed on the substrate 10 in the form of a pattern 22 of individual conductors 18 and contact pads 20. The process flow diagram shown in FIG. 3 is preferably begun after placing resistors and capacitors, usually comprising tantalum or tantalum nitride, on an insulating material, most commonly using alumina.

The wiring began by placing a layer of titanium over virtually the entire area of the board. Specifically, the method employed was electron gun evaporation, but other known techniques such as sputtering may also be employed. The thickness of the titanium layer is preferably in the range of 1,500 to 3,000 Å in order to function well as a pig layer and avoid bonding problems.
Problems with bonding (like increasing y) typically occur at a thickness of about 1500A.
Occurs when: A thickness of approximately 2500A appears to be optimal. A thin (approximately 500 Å) layer of palladium is then deposited over the titanium, preferably by the same technique used to deposit the titanium. This layer contributes to improving the adhesion between the titanium and the copper layer described below. The palladium layer is not essential, but optional, since the degree of adhesion between titanium and copper is sufficient if the proper deposition method is followed. A suitable thickness for this layer appears to be 200 to 3000A. It is noteworthy that the insertion of a palladium layer increases the adhesion between copper and titanium, which is quite surprising since precious metals do not normally form strong bonds with non-noble metals. Probably. The reason for this effect is unknown, and research is currently ongoing. A thin layer of copper was then deposited over the palladium layer, again by electron gun evaporation in this example. This copper layer primarily acts as a highly conductive layer for subsequent plating steps. Typically the thickness of this layer is approximately 5
000A, but anything between about 3000A and 7000A would be appropriate. It is desirable to coat the copper surface with a thin layer of chromium to improve the adhesion of the photoresist before continuing with the photoresist step.

This process is well known in the art. photolithography method
cprocess), also well known in the art, essentially covers the entire copper surface with a layer of photoresist, exposes the desired areas through a mask, and
It involves developing the resist and removing the exposed areas to reveal a pattern representing the proper circuit. A copper layer was then electroplated selectively over the areas of the deposited copper layer not covered by the photoresist, as shown in FIG.

This was done by using the substrate as an anode during an electrolysis experiment, in which the electrolyte contained approximately 68% of the CuS04 and 180% of the H2SO4 solution. This particular electrolyte has been found to be most suitable for complete copper coating, but its composition ratios will be adjusted according to the needs of each case. It should be noted that although other electrolytes may be used for copper plating, copper sulfate electrolytes currently appear to be the most suitable. The plating was done under a current density of about 20 A/current, but again this parameter will be adjusted according to the amount of electrolyte and the shape of the circuit being formed. The thickness of this copper layer is very important and requires careful consideration. In this particular example, the deposited and plated copper thickness was approximately 35,000 Å. Suitable ranges for this thickness will be discussed later in connection with the thicknesses of the nickel and gold layers that follow. An important point to remember is the fact that exposing a copper surface to air for a long period of time will oxidize the surface and weaken the adhesion. Therefore, the copper plating operation must be performed following the copper evaporation and the subsequent nickel plating must be performed following the copper plating while the copper is still wet. In the next step nickel was plated onto the exposed areas of the plated copper surface.

The electrolyte specifically used for this plating operation is sold by Allied-Kelite Co. under the trade name Banett type SN and consists essentially of nickel sulfate and boric acid. The thickness of the nickel layer was approximately 10000A. However, as will be discussed later, in order for the nickel layer to act adequately as a diffusion barrier between the plated copper layer and the subsequently deposited gold layer while maintaining the inherent sheet resistance value, it is necessary to Well, it seems to be effective. Layers thinner than about 8000 amps will create pores in the film that will not impede the diffusion of copper and gold at the high temperatures required in subsequent thin film processing. Thus, the thickness of this layer has become an important parameter. The current density employed here was still about 20 skin A/cm, which makes it possible to form a sufficiently dense film. As before, current density should be adjusted according to specific needs. The minimum current density required to form a sufficiently dense nickel film (on the order of 9 taps) appears to be about 10 amperes per minute. It has also been discovered that one of the most suitable barrier layers is essentially pure nickel without any additives.

As seen in Figure 3, at this point in the process there are essentially two ways to form the top gold layer.
In the first step, a layer of photoresist previously formed on the substrate was utilized as a mask for electroplating a layer of gold over all exposed areas of the previously formed nickel layer. In the second pass, this photoresist layer is stripped, a second photoresist is applied, exposed, and developed.
Only the areas of metal that are to be utilized as bond pads for connection to elements outside the integrated circuit's chip or substrate are exposed. No matter which process is adopted, during electroplating, 20 μm of potassium cyanide, 50 μm of ammonium citrate,
ammonium sulfate (ammo
Gold cyanide (gol) containing nlumsulfa)
dcyanide) solution was used under a current density of approximately 2 mA/s. As previously mentioned, the solution composition and current density will be adjusted as necessary. The thickness of the gold layer was approximately 20,000 Å, but a thickness in the range of 15,000 to 25,000 Å would be desirable to obtain a surface with good adhesion. It is noteworthy that the required gold thickness in this conductive system could be greatly reduced compared to approximately 50,000 amps in previous Ti-Pd-Au systems. Thus, cost savings will be evident with this embodiment of the invention. In addition, in this embodiment, which includes a step of selectively plating only the adhesive area, although an extra photoresist layer is required, a relatively small amount of gold is required, which further reduces costs. It should be noted. The next steps include etching the bare gold and titanium deposits of the plated metal layer to finalize the wiring diagram pattern. In this way, the photoresist used during electroplating was removed for the first time. In either embodiment, ammonium persulfate (ammonium persulfate) is used to remove the evaporated copper.
For subsequent removal of the titanium layer, hydrofluoric acid (hydrofluoric acid) was used to remove the titanium layer.
id), each solution is known in the art. When removing deposited copper, it is important to be careful not to corrode the nickel or gouge out the area beneath the plated copper.
Typically 5000A in ammonium persulfate solution
The time required to remove 100 ml of copper is approximately 6 ml of sand. As a precaution, once all visible signs of copper had disappeared, the circuit was removed from the corrosive solution and immediately cleaned to prevent further corrosion. The use of other etchants for removal of titanium and copper layers may be possible in the future. As suggested earlier, Cu
, Ni and Au thicknesses are important to obtain proper sheet resistance values when used in place of the Tj-Pd-Au system. In particular, the desired sheet resistance value (Rs) is determined from the following formula:
can be calculated. Rs= where t is the specified metal thickness and p is its volumetric resistance.

For most cases the effective resistance of the sheet is approximately 0.005
It is desirable that it be within ohm/mouth. In this way, Ni
It is optimal to meet the sheet resistance requirements when the layer is between 8000 and 20000Δ, the Au is between 15000 and 25000A, and the Cu thickness is between 25000 and 40000A. It seems that. After forming the wiring pattern as described above, conventional circuit processes such as resistor patterning, thermocompression bonding, and soldering are performed according to the prior art.

FIG. 4 shows that wiring has just been formed according to the present invention,
1 is a perspective view of a simple thin film circuit before proceeding with the steps described above; FIG. Since this circuit is presented for illustrative purposes, it should be appreciated that this wiring diagram can be used with all types of circuits. Also note that this circuit is not to scale. Each element is formed on a ceramic plate shown at 10. Internally formed bond pads, such as 41, define an area 42 of the board in which an integrated circuit chip (not shown) is to be placed.

Pond pads formed near the edges, such as 43, allow the circuit to be connected to elements outside the board.

In this circuit, the first resistor 52 and the second resistor 44 are simply shown connected to the capacitor 45, but the resistors are usually made of tantalum nitride.
The capacitor has a tantalum monoxide conductor multilayer structure, which is well known in the art.

The connections between the pound pads and the circuit elements are made in accordance with the present invention. An enlarged cross-sectional view taken along line 3--3 is shown in FIG. The evaporated titanium layer is 46 and the palladium layer is 4.
It is 7. The copper layer, first formed in a thin layer by vapor deposition and then by electroplating, is shown at 49, and the nickel layer formed thereover is shown at 50. It will be readily seen that in accordance with the second alternative embodiment previously described, the Au layer 51 is formed only where connections are desired. During the subsequent heat treatment, one would be concerned that some alloying of Cu, Ni and Au would occur first near the Ni layer boundaries, but the basic Cu-Ni-Au multilayer structure is believed to be maintained during this period. In this regard, an important and surprising feature of this metal interconnect is that even though the configuration of the interconnect structure changes slightly due to subsequent processing, the thin film steps required for the circuit to be fully operational are This means that the functionality will not be damaged. In order to prove that this Ti-Cu-Ni-
The A-Kametsu electric system was heated for various times at various temperatures associated with normal circuit processing.

As an example, a thin film was heated with approximately 10,000 Å thick nickel at 250° C. for 5 hours, which is the temperature and time commonly employed to stabilize T to N resistance. It is Auger analysis (Augeranal pine is
), it was found that Cu and Au passed through the Ni layer.
Although some diffusion was observed, it was at a level that did not cause any problems. Also, the sheet resistance changed by 4%. On the other hand, 150q
When heat treated for 100 hours at 100 ℃, no diffusion through the Ni layer was observed and the sheet resistance changed by only 1.5%. The upper limit of heat treatment for this system is 350q
estimated to be 4 hours at o. This is because in this case, considerable diffusion was observed and the change in sheet resistance reached approximately 17%. These tests show that this Ti-Cu-Ni-Au system is superior to the Ti-Cu-Ni-Au system in terms of resistance to functional damage caused by the high temperatures required in the circuit formation process.
It was found that the system was comparable to the Pd-Au system. The present Ti-Cu-Ni-Au system was further exposed to air plus dry and wet HCI and further N0
2 and S02.

Under dry HCI, the system
It showed corrosion resistance comparable to that of the system. Humid environment (HC
1, S02 or N02), which is one of the most severe corrosion tests, showed only the same change in contact resistance as in a dry HCI environment. Thermocompression bonding to the thin film circuit is usually done after all high temperature steps have been completed.

Thus, in order to test whether the system was compatible with respect to adhesion, it was necessary to subject the metal layer to higher temperatures for a longer period of time. This system was applied to various thicknesses of nickel from 2000 to 10000A and 150, 25
After being heat treated at various temperatures of 0, 300 and 350°C, they were bonded and subjected to a tension test. Approximately maximum tension was obtained between the nickel layer of 10000Δ.

In addition, 15000 is up to 100 field hours, 250 qo is up to 1 field life, 300 pm is up to 4 hours, and 35
At 0oo, sufficient tension was observed for up to 2 hours. It appears that the minimum time is 30 minutes. Generally speaking, the tension of the present conductive system is similar to that of T tested under similar conditions.
The tensile strength was proven to be similar to that of the i-Pd-Au system. As a result of these tests, Ti-Cu-Nj-A
It has been found that it is possible to perform thermocompression bonding after heating the u at 300 qo for 4 hours, which conditions are used today to straighten insulation layers used in plated intersections. It has also been found that heating at 350°C for 2 hours is possible, and this condition is recommended for stabilizing the resistor prior to laser trimming. At that time, the thickness of the Ni layer was approximately 10,000Δ. An additional surprising advantage of the present conductive system was its good compatibility with the soldering process.

When soldering Ti-Pd-Au systems with conventional Sn-Pb solder, brittle scum-like Sn-Au intermetallic compounds are produced. However, in this system, the gold layer is thin enough that brittle scum-like intermetallic compounds do not form. Additionally, since gold prevents the nickel surface from arranging, the rate of leaching of the Ni surface into solder is slow enough to allow sufficient time to solder and unsolder for repairs. This will give you some leeway. Some embodiments of the invention are shown below.

'1} The same method as described in the claims.

'21 A method according to the claims, characterized in that the fabricated structure is heated to 200°C to 40,000°C for about 3 minutes to 1 time. {3}
A circuit having thin film elements and electrical connection means on a main surface of an insulating substrate, wherein a first metal layer containing titanium is placed on the substrate, and then a second metal layer containing copper is placed on the substrate. a third metal layer comprising nickel over the second metal layer, and a fourth metal layer comprising gold over at least a portion of the third metal layer. circuit.

(4) A method according to Embodiment 1, characterized in that the fourth metal layer is formed on substantially the entire surface of the third layer.

{5} A method according to embodiment 1, characterized in that the fourth metal layer is formed only on a portion of the third metal layer that includes bond pads for the circuit.'6'
A method according to embodiment 1, further comprising forming a fifth layer of palladium on the first layer prior to forming the second layer.

[71] A method according to Embodiment 1, characterized in that the first and second layers are formed by a vapor deposition method.

{8} A method according to Embodiment 1, characterized in that the first and second layers are formed by sputtering. '91 A method according to embodiment 1, wherein the first layer of Ti is formed to have a thickness in the range of 1,500 to 3,000 Å, and the second layer of copper is formed to have a thickness of 25,000 Å to 40 Å.
000A, the third layer of Ni is 8,000A thick, and the fourth layer of gold is 150A thick.
A method characterized in that it is formed so as to fall within a range of 00 to 25000A.

00 A method according to embodiment 1, characterized in that the applied copper is electroplated in a solution comprising CuS04 and S04.

(11) A method according to embodiment 1, wherein the second layer of Cu is removed by soaking in a solution containing ammonium persulfate, and the first layer of Ti is subsequently removed by soaking in a solution containing hydrofluoric acid. A method characterized by removal by infiltration.

(12) A method according to embodiment 1, further comprising the step of heating the residual structure at about 250 qo for 30 minutes to 10 hours.

13. A method according to embodiment 10, further comprising the step of heating the residual structure at about 30,030 degrees Celsius for 30 minutes to 4 hours.

(10) A method according to embodiment 10, further comprising the step of heating the residual structure at about 35,000 ℃ for 30 minutes to 2 hours.

(15) A method of forming a circuit including thin film elements and electrical connections on a major surface of an insulating substrate, the method comprising: forming a first metal layer consisting essentially of titanium on substantially the entire major surface;
depositing a second metal layer consisting essentially of palladium on substantially the entire surface of the first metal layer to a thickness of between 200 and 1000A; a third metal layer consisting essentially of copper on substantially the entire surface of the second metal layer;
Copper is deposited and added onto selected portions of the deposited copper layer to within the thickness range of A to form the desired wiring pattern.
C by electroplating in a solution containing S04 and ratio S04
a fourth metal layer consisting essentially of nickel on substantially the entire surface of the electroplated steel layer while the electroplated steel layer is still wet, Nickel sulfur mate (nic
electroplating a fifth metal layer consisting essentially of gold on at least a portion of the fourth metal layer using a plating solution containing metal cyanide; , to a thickness of between 25,000 A, and the portions of the deposited copper not covered by any of the electroplated layers are removed by soaking in an etchant containing ammonium persulfate; 1. A method comprising steps of removing uncoated portions of titanium by soaking them in a corrosive solution containing hydrofluoric acid.

(16) A method according to embodiment 13, characterized in that a fifth metal layer is formed substantially on the surface of the fourth layer.

(17) A method according to embodiment 13, characterized in that a fifth metal layer is formed only on that portion of the fourth layer that includes bond pads for the circuit.

(18) A method according to embodiment 13, further comprising the step of heating the residual structure to about 25,000 for about 30 minutes to 10 hours.

(190) A method according to Embodiment 16, further comprising the step of heating the structure to about 3000C for about 30 minutes to 4 hours. (20) Embodiment 1
6, further comprising heating the structure to about 350 oo for about 30 minutes to 2 hours.

(21) A circuit including a thin film element and electrical wiring on the main surface of an insulating substrate, the circuit including a first metal layer made of titanium formed on the substrate, and a first metal layer formed on the first metal layer. a second metal layer made of copper formed; a third metal layer made of nickel formed on the second layer; and a fourth metal layer made of gold formed on at least a portion of the third metal layer. A circuit characterized in that it includes.

(22) A circuit according to embodiment 19, wherein the first metal layer has a thickness of between 1500 and 3000 A, the second metal layer has a thickness of between 25000 and 40000 A, and the first metal layer has a thickness of between 25000 and 40000 A; The third metal layer has a thickness between 8000 and 20000A, and the fourth metal layer has a thickness between 15000A and 20000A.
A circuit characterized in that it has a thickness between 25,000 and 25,000.

(23) A method for strengthening the bond between an insulating substrate and a thin film conductor formed thereon, in which at least two metal layers are deposited on the substrate, the first metal layer being titanium. forming a thin layer of an electrically conductive material on the material, forming at least one thin film conductor from the material, and heating the substrate and the conductor for a given period of time after forming the conductor to form a thin layer between the conductor and the substrate. A method characterized by comprising a series of steps for increasing the adhesive strength of.

(Two cores) A method according to Embodiment 1, wherein the step of depositing the metal layer includes depositing a titanium layer on the ceramic substrate, depositing a palladium layer on the titanium, and depositing a gold layer on the palladium. A method characterized by including a series of plating steps.

(25) The method according to Embodiment 1, wherein the step of depositing the metal layer comprises depositing a titanium layer on the ceramic substrate, depositing a palladium layer on the titanium, and plating a copper layer on the palladium. , plating a layer of nickel on the copper and plating a layer of gold on the nickel.

(26) A method according to embodiment 2, characterized in that the heating step is carried out in air at a temperature of 200 to 400 qo for 1 to 8 hours.

(27) The method according to embodiment 4, wherein the titanium layer has a thickness of 1700 mm to 2500 mm, the palladium layer has a thickness of about 3000 mm, and the gold layer has a thickness of about 2000 mm.
A method characterized by being 0A.

(28) A method of increasing the bonding strength of the leads to the thin film conductor, first depositing titanium on the substrate and then depositing layers of palladium and gold to form the thin film from which the conductor is made. Thereafter, the conductor is first formed from the film to expose the end face of the conductor, and then the substrate is heated in air at about 25,000 °C for about 5 hours to heat the conductor against the substrate. A method comprising a series of steps for increasing the bonding strength of the lead to the conductor by increasing the adhesive strength. (29D) A method for increasing the bonding strength between a thin film conductor on a substrate and the substrate, in which a titanium layer with a thickness of 1,700 to 2,500 A is deposited on a ceramic substrate, and a palladium layer of about 3,000 A is layered on the titanium. forming a conductive thin film with other layers by plating a gold layer approximately 20,000 Å thick on the palladium, forming at least one electrical conductor from the thin film, and forming an electrical conductor thereon; 25 along with the board on which it is placed.
000 for about 5 hours in air to increase the adhesion of the conductor to the substrate, thereby increasing the bonding force to the conductor. How to do it.

[Brief explanation of the drawing]

FIG. 1 is an isometric view of a ceramic substrate with a thin film of metal layers on top. The thickness of the metal layers is exaggerated here for clarity. FIG. 2 is an isometric view of the ceramic substrate of FIG. 1 with conductors and contact pads formed from the thin film described above attached thereto. FIG. 3 is a flowchart illustrating two fabrication steps according to two alternative embodiments of the invention. Fourth
The figure is a perspective view of a thin film circuit made in accordance with one embodiment of the invention. FIG. 5 is an enlarged cross-sectional view taken along line 3--3 of FIG. [Explanation of symbols of main parts], 10...
...Substrate, 12...Titanium layer, 14...Regular radium layer, 16...Gold layer, 17...Thin film, 1
8...Individual conductive parts, 20...Contact pads, 41...Bond pads formed inside, 42...Part of the substrate on which the integrated circuit chip is to be placed, 43...Pound pad at the end of the board, 44...
...Second resistor, 45...Capacitor,
46"""Titanium, 47.../Radium, 49...Copper, 50...Nickel, 51...Gold, 52...First resistor. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Figure 5

Claims (1)

[Claims] 1. A step of forming a metal layer made of titanium in a desired pattern on an insulating substrate, a step of forming a metal layer made of copper on the metal layer made of titanium,
electrodepositing additional copper in selected areas of the metal layer of copper; electrodepositing a metal layer of nickel on the metal layer of copper; at least a portion of the metal layer of nickel; an insulating substrate comprising: electrodepositing a metal layer of gold thereon; and removing portions of the metal layer of titanium and copper that are not covered by the electrodeposited metal layer. A method for forming a conductor on an insulating substrate, comprising the step of forming a layer made of palladium on the metal layer made of titanium before the step of forming the metal layer made of copper. A method of forming a conductor on top. 2. The method according to claim 1, wherein the layer consisting of palladium is formed on substantially the entire surface of the metal layer consisting of titanium, and the layer consisting essentially of palladium is applied within a range of 200 Å to 3000 Å. A method for forming a conductor on an insulating substrate, the method comprising forming a conductor by vapor deposition to a thickness of . 3. In the method according to any one of the above claims, the structure formed by the step is
A method for forming a conductor on an insulating substrate, the method comprising the step of heating at a temperature of 00° C. to 400° C. for about 30 minutes to 10 hours. 4. A conductor on an insulating substrate used in a circuit including thin film elements and electrical interconnections on the main surface of the insulating substrate, a metal layer made of titanium on the insulating substrate, and a metal layer made of titanium on the insulating substrate. a metal layer of nickel on the metal layer of copper; and a metal layer of gold on at least a portion of the metal layer of nickel. . A conductor on an insulating substrate, characterized in that a layer made of palladium is provided between the metal layer made of titanium and the metal layer made of copper.