DE1489019A1 - Process for the production of thin film capacitors - Google Patents

Description

Applicant: International Business Machines Corporation,

new York

Official File number: New registration File the applicant Dooket 14 029

Process for the production of thin-tube capacitors

For some time now, as part of the microminiaturization of electrical circuits Area capacitors manufactured with thin metal films that are difficult to melt · In the process of manufacturing single capacitors, a thin metal film is placed on a substrate Film applied to a part of the 3chioht by anodizing to one dielectric Oxydaohioht and then applied a second metal film · Daduroh are reduced current losses, a low resonance factor «a high dielectric efficiency and high capacities per unit area can be achieved.

The limits for improving single elements are based on the type of substrate used which is used for these circuits. In particular, it has hitherto not been possible to "form difficult-to-melt metal as a dielectric layer on a substrate" if the substrate did not have an extremely smooth surface with a roughness degree of 0.15 M or less, which is such a low roughness but only ^; achievable with glass substrates, for example, glazed substrates. On the other hand, capacitors applied to substrates with a higher degree of roughness, eg aluminum, steatite, magnesium I or beryl, always showed>. Short soles and were therefore not applicable in practice. To research and deal with this intolerance

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numerous attempts have been made.

The invention has now found a method by means of A thin-film capacitor shares a thin-film capacitor even with a relatively fine surface roughness of the substrate while completely avoiding short-circuits can be produced with the required parameters. The / experienced is characterized in that a metal with a high melting point on a ceramic substrate with a relatively high surface roughness is applied, then the substrate with the metal layer as the anode is immersed in an electrolyte bath that on the metal layer an oxide layer is applied by increasing the anode voltage, that after reaching a fixed value of the electrolyte current for a certain time the polarity of the anode current is reversed and finally on the anodized part of the hard applied fusible metal, an electrically conductive metal film is evaporated · '■ · ■■. V-I.

The reversal of the polarity of the anode current in an electrolyte bath is known, but only as a continuous reversal during the action of the bath. From a polarity shift of this kind but does not make use of the invention

The method according to the invention makes it possible to manufacture thin-film capacitors with improved reliability and performance. The possibility of using substrates with a relatively small surface has a favorable effect on manufacturing costs .

The method according to the invention is explained in the drawings described in more detail below.

Pig · 1 aseigt a thin capacitor in section and

ι Pig · 2 dlftgrammatically the course of voltage and current during the anodizing process in the electrolyte bath.

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The thin-film capacitor according to FIG. 1 is applied to a ceramic plate 2, the surface 5 of which has a roughness between 1.0 and 2.5 η . Difficult-to-melt metal 4 is applied to the ceramic surface J in a thickness between 0.25 and 1.2 η by means of one of the known Metallbesohiohtungsverfahrenl, for example by cathode sputtering, vapor deposition in a vacuum or electroplating. When producing layer 4, preference is given to a metal with a particularly high melting point, such as tantalum, niobium, titanium or bismuth, for example. %

After the layer 4 has been applied to the plate 2, the dielectric Layer 6 applied by the metal layer 4 is immersed as an anode in an anodization electrolyte bath, wherein a positive bias voltage is applied to the metal layer with respect to another electrode immersed in the electrolyte. This bias is maintained when the anodization forming voltage is maintained approaches a constant value. As shown in FIG. 2, this occurs when the anodizing current (dashed line in Fig. 2) flattens out in its curve, which occurs about ten to twenty minutes after the start of the process. To this Time, the polarity of the voltage is briefly reversed for a period of about thirty seconds to a value that is about Half of the voltage initially applied, whereby the metal layer becomes the cathode. The amount of reverse voltage applied and the duration of their effectiveness may exceed the specified values, however, adverse effects are possible if the reverse voltage is the original value of the applied voltage approaches and is effective for more than two minutes.

Then the polarity of the voltage is reversed again and the normal positive bias applied and the process continued until the oxide layer 6 reaches a thickness in the range of about 200 fi. To Completion of the anodization is a counter electrode 8 from a

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suitable metal, such as gold, tin, zinc or aluminum, Applied in a thickness of several thousand S to the Oxydechioht 6 by vapor deposition in a vacuum.

When reversing the polarity in the anodizing process is it is advisable to use a ceramic substrate with a rough surface, i.e. with a roughness of between 1.0 and 2.5 μm In contrast to the previously used substrates with a surface roughness of about 0.15 Ii. In the following table X is the Performance of capacitors built on ceramic substrates, with different voltages with and without application of the described reversedohnik compared. This compilation shows that the performance using polarity inversion is essential is increased, but the effect achieved below a voltage of 15 volts decreases at higher voltages

TABEL I. power tension with polarity reversal volt 80 % 8th 80 % 12th 45 % 16 20 % 20th 20 % 25th 10 % 30th

Performance without polarity reversal

. 30 % 25 * 12 %

15 % 0 % 0 %

In the following, a hypothesis is given for the causes that can be achieved by the method, especially for thin-film capacitors Results developed. When converting difficult-to-melt metal into an oxide, a certain lattice mismatch occurs, as shown in Table II.

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Density molecular mole degree of weight volume mismatch

Tantalum 16.6 18O, 9 11.4 _oo

Tantalum oxide 8.7 441.8 50.8 ^A *

Niobium 8.6 92.9 10.8 _o ^

Niobium oxide 4.8 265.8 55.3 ^{> v}

Bismuth 9 # 8 209.0 21.2 _{o n}

Bismuth Oxide 5.6 * 466.0 83.2 * ' ^υ

Titanium 4.5 47.9 10.6 ₁ «

Titanium oxide 4.26 79.9 18.8 ^! * °

This lattice mismatch is of no concern as long as one is complete smooth metal layer is oxidized as the oxide grows uniformly both in and out of the metal, namely so that the ratio of the oxide strength to the strength of the metal which has been consumed by the oxidation is equal to the ratio of the molar volume. However, this does not apply to a point on the rough surface more to. As a result of the greater electrical field strength in the vicinity of the rough area, this area anodizes faster than the others smooth surface area. The oxide therefore tends to increase smooth instead of following the original roughness profile. Complete smoothing occurs at about 60 volts of the forming voltage. As a result, wherever there is in the ur- ™ cracked layer was a rough place, more material than was there before, pressed into a given volume. This has a considerable tension in the oxydsohioht this only duroh cancels cracking · The tendency to crack is a function of the macroscopic structure of the ceramic surface and identified as the source of the short circuits.

The tension in the oxide layer is greatly reduced when the Layer thickness is limited to a depth of about 200 8 or less, which at room temperature of a formation stress of about 15 volts. When anodizing solids at low The achievement is very tense to achieve the desired strength low as a result of passivation at various points on the

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Surface of the refractory metal. Paesivated on these There is no oxidation, which then leads to the in the finished capacitor leads to short circuits.

Duron brief polarity reversal of the applied voltage, when the formation voltage approaches a constant value, the passivated areas can be activated so that the growth of the cb ydschioht is possible there. With the reversal of Polarity thus arise outgoing shafts that are free of P are short circuits,

To manufacture the capacitor, a ceramic substrate, e.g. aluminum oxide, is first cleaned by placing it in a solution Immersed in a cohesive cleaning agent, rinsed in water, reached in a 15 # ig®n solution of hydrogen peroxide gekoo!% rinsed in water again, washed in isopropyl alcohol and then steam degreased in isopropyl alcohol.

Then a so-meltable metal, e.g. tantalum, is applied to the Substrate surface applied, for example by cathode sputtering. The thin sleeves are in an argon glow discharge, * e.g. 2000 volts at 1 mA / om with one speed of about 10 Å / s for a period of about 15 minutes. Solo layers have specific sheet resistances of about 4 ohms / cm.

Then the substrate is immersed in an anodizing bath in such a way that that the schioht serves as the anode of the circuit. The anodization takes place in a corresponding electrolyte, which does not dissolve the metal oxide when it is formed. For this purpose there is one i £ ige aqueous solution of ammonium tetraborate particularly suitable, however, another 1 # solution can also be used, such as e.g. sodium sulphate, sulfuric acid, phosphoric acid, sodium citrate or citric acid. During the anodization, the temperature

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of the electrolyte is kept at about room temperature, the current density is between 0.1 and 1 voltage is reached «

is between 0.1 and 1 mA / cm of the anode area until the formation

The Oxydsohioht is anodisoh on the tantalum layer with a constant current density forms, while the voltage on the growing oxide increases to the desired formation voltage will. Gentle Fig. 2, with an initial forming current of about 1 mA / cm of the anode surface, the forming current flattens down to a value of about 1yuA / om of the anode surface, while the Formation voltage to your desired value of about 15 volts increases. At this constant voltage the formation process continues as the current loss decreases down in the uA-Bereloh made clear. When the formation voltage approaches or reaches this constant value and when the Formation current sloh begins to flatten out asymptotically «becomes the polarity of the applied voltage for a period of about 30 seconds vice versa, so that the metal layer is now the cathode. Here you go the Berelohe, which are resistant to oxide formation, are activated. The polarity is then reversed again at a voltage of about 7 * 5 volts, and the process is continued until the oxide layer is about 200 8 amounts to.

Then a counter electrode is made of electrically conductive metal in a strength of oa. 1000 St applied by using aluminum duroh a corresponding mask is vapor-deposited on the surface of the dielectric tantalum oxide

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Claims (5)

Claims Process for the production of capacitors with thin layers on ceramic substrates, characterized in that a metal with a high melting point is applied to a ceramic substrate of relatively high surface roughness, then the substrate with the metal layer as anode is immersed in an electrolyte bath, ae & on the metal layer by increasing the anode voltage an oxide layer is applied, after reaching a fixed value of the electrolyte current, the polarity of the anode current is reversed for a certain time and finally an electrically conductive metal film is vapor-deposited onto the anodized part of the hard-to-melt metal applied, 2. The method according to claim 1, characterized in that the difficult-to-melt metal is tantalum, niobium, titanium or bismuth is used. 3. The method according to claims 1 and 2, characterized in that the application of the difficult-to-melt metal by cathode sputtering, Vapor deposition takes place in a vacuum or electroplating. 4. The method according to claim 1, characterized in that the electrolyte bath is a 1 # solution of ammonium tetraborate, Sodium sulphate, sulfuric acid, phosphoric acid, sodium citrate or citric acid is used. 909825/0568 5. V * rf »hrtn ntoh An» pruoh 1, daduroh fttonnstlohnet, daft 111 » dta xtiuadtn MluUfii »(told, gin *,» ink odtr Y # rw «nd ·! will· , ■, 909825/0568 BATH ORIGINAL a rsei fβ