JPS5887884A - Forming method for electrode of oxide superconductor circuit - Google Patents

Abstract

PURPOSE:To enable the increase in the bonding strength of a gold electrode without deteriorating the superconductive characteristics of an oxide superconductor BaPb1-xBixO3, by forming a resist pattern after evaporation of gold, and by patterning an evaporated-gold film by etching by using the above pattern as an ethcing mask so as to form a desired electrode. CONSTITUTION:A superconducting thin film 2 made of BaPb0.75Bi0.25O3 and being 4,000Angstrom thick is formed on a substrate 1 (Figure a). Next, under the condition that the substrate is heated to a temperature of 200 deg.C, gold 6 is evaporated on the above superconducting thin film 2. Then, coating is made thereon with a positive type resist 3, and exposure is made to a light 5 through the intermediary of a mask 4 having a desired electrode pattern (Figure b). Thereafter, the resist 6 in the exposed part is removed by development (Figure c). The substrate thus prepared is immersed in the mixture solution of H2O, KI and I2 in the weight ratio of 100:20:10 for etching, and thereby the exposed gold 6 is removed (Figure d). Then, the remaining resist 3 is removed by acetone, and thereby an electrode formed of gold 6 and having a desired pattern on the superconducting thin film 2 can be formed.

Description

Detailed Description of the Invention The present invention provides an oxide superconductor BaPb 1- from i, O,
The present invention relates to a method for forming a gold electrode of a thin film circuit using e.

The superconductor BaPb has a low carrier concentration and is an oxide.
Gold is most commonly used as the electrode material for thin film circuits using Yo-1B1108.

FIG. 1 shows a conventionally used method for forming this type of electrode. That is, a superconducting thin film 2 consisting of a substrate 1 (-), KBapbl-1B1-8 (0,05≦X≦0,3) is formed (Fig. 1(a)), and a positive resist 3 is applied thereon. do. Next, a mask 4 with the desired circuit pattern drawn on it
(FIG. 1(b)). Thereafter, this substrate is immersed in a developing solution to remove unnecessary portions of the resist 3, that is, exposed portions (FIG. 1(C)). Next, after depositing gold 6 on this substrate (FIG. 1(d)), the remaining resist is removed using acetone, and at the same time, the gold 6 located on top of the resist 3 is also removed by so-called lift-off. By doing so, a gold electrode having a desired pattern can be formed (FIG. 1(e)).

However, in such a method, since the positive resist 3 generally hardens when the substrate temperature reaches 120 to 140° C. or higher, it is only possible to raise the substrate temperature to a high temperature when depositing the gold 6.

For this reason, it is possible to obtain a sufficiently strong adhesive force between the superconducting thin film 2 and the electrode made of gold 6, but it had drawbacks such as resistance to temperature cycles between room temperature and cryogenic temperature and contact resistance. 6. The present invention was developed in view of the above circumstances, and its purpose is to develop a 1g compound superconductor l3aPbl-.

To provide a method for forming an electrode of an oxide superconductor circuit, which allows a gold electrode having a desired pattern to be firmly and closely formed on a B1-08 thin film without impairing the superconductivity of the thin film. Particularly 1. To achieve the above objectives, the present invention
b1-, Bi, 恕, gold was deposited on the thin film at high temperature, and the -
After forming a resist film having a desired electrode pattern, the gold vapor deposited film is etched using this resist film as a mask and using a mixed aqueous solution of I and I2 as an etchant.

That is, as mentioned above, in order to obtain a high-quality electrode film with high adhesion and low contact resistance, it is necessary to raise the temperature of the substrate sufficiently during gold deposition, but at that time, if a resist film is present, it will harden. It's not very promising.

The present invention is characterized by depositing gold/? - This disadvantage is overcome by forming a resist pattern later, and using this as an etching mask, the gold vapor deposited film is patterned by etching to form a desired electrode. In this case, the etchant is BaPb1-, Bi, .
It was confirmed that the mixed aqueous solution of KI and I2 satisfies this requirement.

That is, as a result of immersing an oxide thin film made of the above BaPb 1-E13i-08 in a mixed aqueous solution of KI, O, and TOME, and measuring the transition temperature Tc and critical current IC of the oxide thin film over time, it was +1% or less. Due to experimental errors of , no decrease in these values was observed. , this situation is shown in FIG.

In Figure I, the values of the transition temperature T ((marked 0) and the critical current IC (marked X) are both normalized by the values before immersion in the etchant consisting of the mixed aqueous solution of KI and 12.

By raising the substrate temperature during gold deposition, we were able to obtain a high-quality electrode film with an order of magnitude lower contact resistance than when using the conventional lift-off method, and which is stable against temperature cycles. Hereinafter, the present invention will be explained in detail using Examples.

FIG. 3 is a cross-sectional view of a substrate during each process showing an embodiment of the present invention. First, BaPb1.7 was deposited on the substrate 1.
A superconducting thin film 2 having a thickness of 400X and having a thickness of 5B10.2508 is formed (FIG. 3(a)). Next, add this board to 2
Gold 6 is deposited on the superconducting thin film 2 while heated to 00°C.
Deposit. Next, a positive resist 3 is applied thereon, exposed to light 5 through a mask 4 having a desired electrode pattern (FIG. 3(b)), and then developed to remove the exposed portion of the resist 3 ( FIG. 3 (C>) After forming the electrode pattern with the resist 3 in this way, this substrate was coated with I20.KI and Iii in a ratio of 1 (10:20:1).
Etching is carried out by immersing the resist 3 in an eratint made of a mixed solution mixed at a weight ratio of 0:0 to remove the luminescent gold 6 from the resist 3 (FIG. 3(d)). By removing the resist 3 with acetone, an electrode made of gold 6 having a desired pattern was formed on the superconducting thin film 2.5 The oxide superconductor circuit with the electrode formed in this way was
As mentioned above, the adhesive strength between the electrode and the superconducting thin film 2 was high, it was stable against temperature cycles, and the superconducting properties were also good.

In addition, in the above-mentioned embodiment, only the case where the resist 3 was exposed to the light 5 was explained, but instead of the light, an electron beam,
Of course, X-rays or the like may also be used.

In addition, in the above-described embodiment, the substrate temperature during the deposition of gold 6 was set to 2.
It's 00℃. This value txt is practically sufficient to obtain good results as described above, but the processing temperature (70 (1'c or more)) when annealing the finally formed circuit to generate superconductivity is Similarly good results can be obtained by heating to a higher temperature, but not exceeding .

In addition, in the above-mentioned embodiment, KI 20? and l1llOf
Although we have explained the case where a mixture of KI and I2 is used, the mixing ratio of KI and I2 is not limited to this. Good results are obtained in all mixing ranges.In this case, the ratio of KI and I2 is almost constant, that is, when a large amount of KI is mixed, I2 also increases accordingly. If the mixing ratio of KI and T2 is too small than the above-mentioned range f21, a sufficient etching effect cannot be obtained for practical use, and on the other hand, if it is too large, the characteristics of the ultra-conducting thin film 2 may be affected. 1. As explained above, the present invention has the advantage of being able to produce oxide superconductors) Pl) 1-, . ．． ÷Consistency can be increased, contact resistance can be reduced, and oxide superconductor circuits of good quality can be obtained stably even under temperature cycles.

It has some excellent effects, such as making the work easier and without using the lift-off process.

[Brief explanation of drawings]

Figure 1C is a cross-sectional view of a substrate showing a method for forming electrodes of a conventional oxide superconductor circuit; Figure 2 is a diagram showing BaPb1-, Bi, j
) 8 is immersed in a mixed aqueous solution of KI and 12, and FIG. 3 is a graph showing changes in superconducting properties with respect to immersion time. 1...Substrate, 2...Superconducting thin film, 3...Resist, 4...Mask, 5...Light, 6...
·Money. Patent applicant Masaki Yamakawa, agent of Nippon Telegraph and Telephone Public Corporation Figure 1 Figure 2 ↑ Time (min)

Claims (1)

[Claims] A step of vacuum-depositing gold at high temperature on a thin film pattern made of BaPb1- to iJc○8 formed on a substrate, a step of forming a resist film having a desired electrode pattern on this gold vapor-deposited film, and a step of forming a resist film having a desired electrode pattern on this gold vapor-deposited film. An oxide superconductor circuit comprising the step of etching the gold evaporated film using the film as a mask and using a mixed aqueous solution of etching and etching as an etchant to remove unnecessary parts of the gold evaporation. Electrode formation method.