DE2402720A1 - Forming electric connections on electric circuits - by depositing a metal layer, anodically oxidising esp. its edges to cover any protrusions, and applying an outer insulating coating - Google Patents

Abstract

Layer of an anodically oxidisable metal (pref. Al, Ta, Ti or Mg) is formed on a substrate (pref. by deposition from the vapour phase or by cathodic sputtering) partly etched if necessary using a photomask; anodically oxidised esp. to cover with the oxide film protrusions (esp. on edges) which might cause short-circuiting, and then coated with an insulating film (pref. SiO, SiO2, Si3N4 or glass). Another electric connection can be formed on top of the insulating film by the same method.

Description

Isolation method for electrical circuit conductors The invention relates to an insulation method for electrical circuit line runs, in particular for several stacked or one on top of the other circuits with cable runs.

When on a substrate such as an alumina plate or a silicon wafer If a cable run is to be formed, a metal is applied to the entire conductor as a conductor Surface of the substrate or the disc applied by vapor deposition in a vacuum, Sputtering, chemical vapor deposition or galvanic Knock down; the deposited metal layer is covered with a photoresist, this becomes exposed to form an etch-resistant photo stencil or light mask of the zu forming circuit conductors, and then the exposed is deposited Metal removed with a suitable etchant. In this etching process it is inevitable that irregularities occur in the edge surfaces of the cable runs due to the tristallstruktur or the state of precipitation on the lines. Because of these irregularities the applied insulating layer is often penetrated by protrusions, or the insulating layer. is only applied to the bottom of wells and prevents the formation of an insulating film of uniform thickness. If therefore on further line cells are formed in the insulating film sometimes occurs between an electrical short circuit on the upper and lower cable runs. In particular It is the case with an integrated S # holding, with the, line branches lying on top of each other are provided, inevitably to use the edge surfaces of the lower cable runs. The defects of the insulating film in the edge surfaces are therefore serious ones Problem.

When the insulating film is deposited by vacuum vapor deposition or sputtering becomes, it is difficult to deposit the insulating film on the peripheral surfaces because these are inclined relative to the trajectories of the atoms or molecules of the insulating film run or are protected from it, so that the thickness of the insulating film is hardly any assumes the specified value. It is therefore necessary to adjust the evaporation or atomization time to lengthen, thereby increasing the manufacturing cost of the electric circuit wiring raise.

The task of the invention is to create an isolation method for electrical circuit lines through which even a thin insulating film has a sufficiently high breakdown voltage receives; the insulating film should have very good insulating properties, and the occurrence of defects in the insulating film as a result of irregularities in the edge surfaces of the cable runs should be prevented.

According to the invention is at least on edge surfaces on one Substrate formed conductor runs formed by anodic oxidation an oxide film, to which an insulating film is applied to insulate the line run.

The invention thus provides an insulation method for electrical Circuit cable runs specified, in which certain cable runs from anodic oxidizable metal being molded on a substrate; Edge surfaces of the cable runs are anodized to form an insulating oxide film; and on the oxide film an insulating film is formed, thereby smoothing the edge surfaces and making defects like z. B. pinholes in the insulating film can be eliminated.

The invention is explained in more detail below with reference to the drawing. The figures show: FIG. 1 a cross section through a circuit line that has already been developed; FIG. 2 shows a cross section through a circuit line according to the invention; FIG. Fig. 3 shows a cross section through a further circuit line according to the invention; 4 is an enlarged perspective view of an end portion of an already developed circuit wiring harness; Fig. 5 is a perspective View of a cable run with which the method according to the invention is tested; Fig. 6 shows a cross section along the line VI-VI of Fig. 5; Fig. 7 Leakage current-voltage characteristic curves of circuit lines already developed and manufactured according to the invention; 8 shows leakage current density versus supply voltage characteristic curves of various line runs; Fig. 9 performance curves of already developed and manufactured according to the invention Circuit cables.

As already mentioned, the invention is characterized in that the edge portions of a cable run on which an insulating film is formed, can be obtained by anodic oxidation. For this anodic precipitate according to Metals useful in the invention are aluminum, titanium, tantalum and magnesium, where Aluminum and tantalum are preferably used, as anodic oxidation films with them with good insulating properties can be obtained.

As an insulating material, each material has a specific 10 11 Resistance of 1010-1011 # cm or more suitable of sputtering, vapor deposition be subjected to vacuum, galvanic sputtering or chemical vapor deposition can. For example, silicon dioxide, silicon monoxide, aluminum oxide, Glass and silicon nitride.

As a substrate for the circuit lines to be formed, known Materials such as aluminum oxide, ceramic, ferrite and glass plates as well as a silicon wafer to be used.

Known vacuum vapor deposition or sputtering processes are used to shape the lines applicable. At this time, the pressure of the surrounding atmosphere is as follows; Aluminum: vapor deposition in vacuum at 1 ~ 10 5 to 1 ~ 10 -7 Torr; Titanium: vacuum evaporation at 1. 10 5 to 1 ~ 10 -7 Torr; Atomization at 1 ~ 10-2 to 1 ~ 10-3 torr; Magnesium: vapor deposition in vacuum at 1 ~ 10 5 to 1 µ 10-7 torr; Tantalum: atomization at 1 ~ 10-2 to 1 ~ 10-3 torr.

The thickness of the conductor forming the subsequent line run is arbitrary selectable depending on the current carrying capacity, the specific resistance or the like, preferably it is essentially 1-100 µm. With known etching processes A suitable etch-resistant cover template in the form of the cable run is required for the cable run is formed on the metal layer, and the exposed part of the metal layer becomes removed by treatment in a suitable etching bath. For shaping the etch-proof cover template For reasons of accuracy, it is advisable to use a photoresist method. Light-sensitive printing inks such as KPR (TM), KMER are suitable as photoresist (Wz) and KTFR (Wz).

The film of the cable run can be made by immersion etching, electrolytic Etching od. The like. Be formed. The following etching solutions are suitable for the metals: for Aluminum: 1% by volume (20% by weight) NaOH, 4% by volume conc. HCl and 1% by volume (15% by weight) FeC13-6H20; for tantalum: 10 vol .-% conc. HN03 and 1% by volume of 49% aqueous HF solution (25 ° C).

The electrolytic etching solutions are as follows: for aluminum: 10-20 % By weight - aqueous solution of NaOH or KOH (solution voltage 1-6 V) or 8 cm3 conc. H3P04, 2 cm3 concentrated H2S04 and 50 g K2CrO4 (solution voltage 5-15 V) or 10-15% by weight aqueous HC104 solution (solution voltage 5-15 V); for titanium: aqueous solution, containing 10% each of HF, HC1 and HN03 (solution voltage 40 V); for tantalum: 20% by volume conc. HN03 and 1% by volume HF (25 OC); for magnesium: aqueous solution containing 100 g / # K2Cr207 and 50 g / # NaH2P04 ~ H20 (50-55 C, current density 2 1.5-2 A / dm).

The etching time is such that the substrate is exposed to the solution is that the lines are clearly separated from each other and a certain pattern form. This etching time varies depending on the metal and its thickness, they is preferably 10 seconds to 10 minutes for the thicknesses discussed above.

For the formation of an anodic film on edge surfaces or on edge and surfaces of the lines formed by etching becomes a known treatment carried out with anodic precipitation. At this point lie when the-etch-resistant Covering layer is not removed, only the edge areas are exposed.

As a result, the anodic oxidation film only becomes formed on the edge surfaces. It goes without saying that if the etch-resistant cover layer is removed, the film formed by anodic oxidation is also on the surfaces dejected.

An example of the typical conditions for applying a Anodic deposition is as follows: For aluminum: 1) Chromic acid method: 3-5 % aqueous solution, 30-40 ° C, voltage rise to 40 V at one rate from 40 V / 15 min, hold at 40 V for 35 min, voltage rise to 50 V with a Speed of 50 V / 5 min, hold at this value for 5 min; 2) oxalic acid process: 2% aqueous solution, 80 V, 30 min; 3) sulfuric acid process: 20 ° Bé aqueous solution, 20-30 Or, 12V (1.5 A / dm2), 60 min; 4) Sulphamic acid process: 7.5 wt% solution, 25 oC, A / dm2, 60 min.

For tantalum: citric acid, 2-3% by weight 0/0 solution1 20-30 OC, 0.1 A / dm2.

For titanium: 1) mixture of boric acid and tartaric acid 2) 1% citric acid 3) Mixture of sulfuric acid, phosphoric acid and acetic acid.

For magnesium: mixture of ammonium sulphate, sodium dichromate and ammonia, 50-60 OC, 0.2 A / dm2.

Sufficient for the thickness of the anodic oxidation film it that he made at least one dense cast down movie and one on it located porous deposited film is used to protect the dense Film is required. A thickness of 0.1 µm or more is inclined substantially. Since with anodic oxidation treatment, the electric field on projections concentrated, such are electrolytically smoothed. Smoothing the edge surfaces that is, it can be carried out simultaneously with the formation of the anodic deposited film will.

As an anodically deposited film alone is not for isolation sufficient even if the entire free surface is covered with it, becomes a suitable insulating film on the line run formed by the anodic deposit upset.

The method of applying this insulating film depends on the one used Material. Some examples are given below: For SiO:: Evaporation in a vacuum at 1250-1400 0C and 10 4 to 10 Torr For SiO2:: chemical Vapor deposition: CH3SiCl3 or SiH4 0.5 # / min, 02 0.15 # / min and N2 5 / / min galvanic Sputtering: Ar-02 atmosphere, 10 2 to 10 -3 Torr for Si 3N4 High frequency sputtering: Ar partial pressure 10 to 10 -3 Torr for Al203: atomization: 10 to 10 3 torr for glass: atomization: Ar 10 2 to 10 3 torr.

By anodically oxidizing the end faces of the cable runs, the thereon applied insulating film of substantially uniform thickness and has no defects. As a result, even with a thin insulating film adequate isolation can be expected.

The insulating layer is so thick that the leakage or residual current is at least at the voltage used is lower than the specified value. For example For a simple thin film magnetic head, the leakage current at 20 V must be lower than be about 100 / uA. When the thickness of the insulating film is 0.5 µm or more the leakage current at 20 V O / uA or less.

Fig. 1 shows a thin film magnetic head with a wire drawing member from a ferrite substrate 1, a z. B. made of aluminum cable run 2 and a z. B. made of silicon monoxide insulating film 4.

Fig. 4 is a 3000 times enlargement of an edge surface of the line run, viewed through a scanning electron microscope at an angle of 300. The Figure shows a ferrite substrate 6, etch pits formed in the edge surface of the aluminum 7 and an aluminum layer 9. If an insulating film is placed directly on this edge surface is evaporated, a hole is formed in the insulating layer over each etching pit 7. If, as a result, another cable run is applied to the insulating layer, if conductor material for the cable run fills the hole in the insulating layer, see above that the lines are short-circuited.

2, films 3 formed by anodic oxidation are only formed on edge portions of the cable run 2. To the by anodic oxidation to apply formed film 3 only on the edge surfaces of the cable run, the with an etch-resistant cover provided surface of the line run of the anodic Exposed to oxidation. According to the invention, this can be anodic oxidation process can be easily performed without removing the etch-resistant cover.

3, the anodic oxidation film 3 is up of the total surface of the cable run provided in contrast to Fig. 2, wherein the etch-resistant cover on top of the cable run from the anodic Oxidation has been removed so that its entire surface is exposed to the treatment was.

5 and 6 show a first line run 11, a second line run 12, an insulating layer 13, a substrate 14 and one on the edge surfaces of the line run 11 film 15 formed by anodic oxidation.

In Fig. 7, curves A1, A2 and A3 represent the leakage current density, based on the supply voltage characteristics of an anodic oxidation on the Edge surface and the surface of the line run film formed. Here is the insulation layer 4 of FIG. 3 is not provided. The curve A1 refers to a through anodic Oxidation formed a film with a thickness of 0.5 / µm, while curves A2 and A3 refer to such films with a thickness of 1.0 and 1.5 µm, respectively. In all cases the leakage current increases with increasing supply voltage.

The curves B1 and B2 represent the leakage current density, based on the Supply voltage characteristics are for FIGS. 2 and 3 corresponding combination of the film formed by anodic oxidation with the insulating film. The curve B1 relates insists that a silicon dioxide film with a thickness of 1 / µm on one applied to the entire surface of the cable run by anodic oxidation Film with a thickness of 1 / µm is atomized, while at curve B2 a through anodic Oxidation formed film only on the edge sections of the cable run with a 1 / µm thick and a silicon dioxide film 1 / µm thick is applied to the entire surface of the cable run. In the latter two In cases where the supply voltage is 10 V, the leakage current is less than 5 ~ 10 9 A.

In Fig. 8, curve C1 illustrates the characteristic of the leakage current, based on the supply voltage if the cable run is made of tantalum and on a tantalum oxide film 0.35 µm thick was deposited thereon by anodic oxidation is. 7 and 8, the insulating properties of tantalum oxide are better than that of alumina. Curve C2 refers to that on the tantalum oxide film a silicon dioxide film having a thickness of 0.5 µm is formed by sputtering. In In this case, the leakage current at a supply voltage of 100 V becomes about 1/100 reduced over the leakage current in the case of tantalum pentoxide alone. The leakage current is even lower than that of the silicon dioxide film deposited on alumina a thickness of 1 µm. The curve C3 refers to the fact that the line run is titanium is deposited thereon by anodic oxidation titanium oxide to a thickness of 0.35 µm and then a silicon dioxide film 0.5 µm thick by sputtering is applied. The curve C4 relates to the fact that the line length is magnesium is, magnesium oxide by anodic oxidation with a thickness of 0.35 µm thereon is deposited and thereon a silicon dioxide film of a thickness by sputtering of 0.5 / µm is applied.

Fig. 9 shows the change in the failure rate of the anodic oxidation deposited film relative to the structure of the insulating layer and the thicknesses the insulating layer and the deposited oxide film. The curve D1 relates only on the anodic oxidation deposited film (aluminum oxide); Curve D2 only refers to the silicon dioxide film excluding that by anodic oxidation dejected film; Curve D relates to the case that both films 3 are formed are. In curves D1 and D3, the films formed by anodic oxidation became (i.e. A1203) applied to the entire surface of the aluminum cable run, however, at curve D3 (last line), anodically deposited oxide films were only formed on the edge surfaces of the cable run. The presence of Errors are determined depending on whether when applying a voltage of 10 V a short circuit occurs or not. This investigation occurred when shorted Even at supply voltages of around 1 V, quite large leakage currents occur while in the case of non-short-circuited films, even with supply voltages of 10 V, only one Leakage current of about 10 9 A occurred. As a result, a cable run that has both has a film formed by anodic oxidation and an insulating film, a very high resilience.

Claims (8)

Patent claims 1. Insulation method for for electrical circuit cable runs, characterized by the following steps: applying at least one line of cables made of anodically depositable metal on a substrate; anodic deposition an insulating oxide film on at least certain edge surfaces of the line run; Depositing an insulating film on at least a part of the oxide film and the wiring; and applying at least one further line of conductors to a specific part of the insulating film. 2. The method according to claim 1, characterized in that the application of the cable run by forming a film of anodically precipitable metal on the substrate and by removing unwanted parts of the metal film by means of Etching takes place; and that simultaneously with the deposition of the oxide insulating film on the certain edge surfaces of the cable run reducing projections and The edge surfaces are smoothed. 3. Isolation method according to claim 1 or 2, characterized in that that the anodically precipitable metal is aluminum, tantalum, titanium or magnesium is. 4. Isolation method according to claim 1 or 2, characterized in that that the insulating film is made of silicon monoxide, silicon dioxide, silicon nitride, aluminum oxide or glass. 5. Isolation method according to claim 1 or 2, characterized by vacuum evaporation of the anodically precipitable metal. 6. Isolation method according to claim 1 or 2, characterized by atomization of the anodically precipitable metal. 7. Isolation method according to claim 1 or 2, characterized by application of the further line run by vacuum evaporation. 8. Isolation method according to claim 1 or 2, characterized by application of the further cable run by sputtering.