JPS6265487A - Resistor for cryogenic circuit and manufacture of the same - Google Patents

Abstract

PURPOSE:To obtain a resistor which has excellent durability and heat resistant properties, is free from characteristics degradation caused by aging and provides required resistance value by a method wherein crystalline (single-crystalline or polycrystalline) insulating material or semiconductor such as Al2O3, SiO2 or MgO, whose thermal conductivity at the temperature of liquid helium is 1W/cm.K, which is equal to that of metallic material, is employed to improve heat conduction properties by lattice vibration at a low temperature. CONSTITUTION:An Nb film 2 for magnetic shield is formed on a silicon wafer 1, which is not subjected to heat oxidization, and patterned by etching with CF4 gas to form a magnetic shielding film. Then an Si film 3 for layer insulation is formed by heat vaporization by an electron beam gun under the vacuum degree of higher than 10<-5>Pa and an MoNX film 4 is formed on it by sputtering and a resist pattern as a resistance film is formed by exposure. After the part of the MoNX film which is not coated with the resist is removed by ion etching with an Ar beam, the resist on the MoNX film is removed by acetone. If the sheet resistance formed like this is measured under the temperature of liquid helium, the deviation of the sheet resistance of the MoNX film with the width wider than 3mum is within 5% and, if the length is changed with the same width, contact resistance between the MoNX film and the Nb wiring film is 0.1OMEGA or less so that this film can be employed as a thin film for resistance of a superconductor integrated circuit.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a resistor for low-temperature circuits, and is particularly applicable to highly integrated superconducting switching circuits that operate at liquid helium temperature (4,2 K) or at a low temperature near the liquid helium temperature. The present invention relates to a suitable resistor for low temperature circuits and a method for manufacturing the same.

[Background of the invention]

Conventional Josephson integrated circuits have used Josephson junctions with pb gold alloy wiring electrodes.

Therefore, a material compatible with this was also used for the resistive film.

In particular, the literature [Properties of Au1n2 resistive film for Josephson integrated circuits] CJ Kircher, IBM Journal of Research and Development 8, 24
Volume 235 pages.

1980 ("Properties of Au
I n 2Resistors for Josep
hgon Integrated Circuits”
C., J. Kircher and S.,
Lahiri.

IBM, J, Res, Develop, Vol, 2
4, p. 2351980), Au1n2 alloy has been studied as a resistive film, and p.
b Used in Josephson integrated circuits with gold alloy wiring electrodes. However, the resistance film of the Josephson integrated circuit uses Nb as the wiring electrode, which has excellent durability and reliability.
As with the Josephson junction using wire electrodes, it is desirable to use a material with a high melting point and whose characteristics do not change over time.

On the other hand, a technical problem to be solved regarding the resistive film used in Josephson integrated circuits is the problem of heat generation. That is, the main portion of heat generated in the Josephson integrated circuit comes from the resistive film.

When a Josephson switching element or the like is placed in contact with a resistive film, heat generated from the resistor increases the temperature around the resistive film and the Josephson junction. A Josephson junction is a superconducting film whose critical temperature (klOK
), the operating temperature limit is defined by
An increase in temperature of IK from K reduces the Josephson current by about 10%. Changes in the characteristics of switching elements due to temperature fluctuations lead to a decrease in the operating margin of the entire circuit, which in turn causes a decrease in switching speed or calculation speed. Place it at a sufficient distance, or
Another possible method is to use a resistor structure with excellent heat dissipation efficiency to prevent temperature rise. When considering higher integration density, it is not appropriate to arrange the resistive film and the switching element in a swollen position.

[Purpose of the invention]

The purpose of the present invention is to provide a resistor structure with excellent heat dissipation efficiency regarding a resistor used in an integrated circuit operated at low temperature, and to provide a resistor structure suitable for use in a Josephson integrated circuit with Nb wiring electrodes, which has durability and heat resistance. The object of the present invention is to provide a resistor for a low-temperature circuit and a method for manufacturing the same, which can obtain a resistive film with excellent properties, no change in characteristics over time, and a desired value.

[Summary of the invention]

To achieve the above object, in the present invention, a single crystal or polycrystalline semiconductor or insulator is used as a base material or a protective film for a resistive film instead of a conventional amorphous insulating film. As such a material, An20. Si crystal, SiOg crystal, or MgO crystal having thermal conductivity equivalent to Si crystal is suitable. The reason for using these crystalline (single crystal or polycrystalline) insulators or semiconductors is to improve thermal conductivity due to lattice vibration at low temperatures.

As the resistive film, an MO film having a body-centered cubic crystal structure containing nitrogen as an impurity is used as the resistive film.

In order to obtain a desired sheet resistance, the concentration of nitrogen contained in the MO film is assumed to be 1 at.% or more and within 30 at.%. Furthermore, the film thickness is 50 nm or more and 500 nm.
Suppose that it is less than or equal to m. In order to use the resistive film as a resistor of a Josephson integrated circuit using Nb as a wiring electrode, the present invention includes a manufacturing process in which the nitrogen-containing MO film is formed on the semiconductor or insulator which is an insulating film. process,
A step of forming a resist pattern as a resistive film on the MO film, M not covered by the resist pattern.

a step of removing the film, a step of forming a protective film selected from the semiconductor or insulator at the center of the Mo film by a lift-off method after removing the resist pattern for the resistive film, and a step of forming wiring electrodes on both ends of the Mo film. It consists of a step of forming a certain Nb film.

[Embodiments of the invention]

The present invention will be described below based on examples. The Mo resistance film containing nitrogen as an impurity was formed by sputtering.

That is, on a thermally oxidized silicon wafer with a diameter of 2 inches,
A Mo film containing nitrogen as an impurity was deposited by direct current magnetron sputtering. Hereinafter, the Mo film containing nitrogen as an impurity will be referred to as the MoNX film, and the sputtering was performed using Ar.
The test was carried out in a mixed gas of nitrogen and nitrogen, and the total pressure was set to 0.5 Pa.

The deposition rate of the MoNx film was 1.7 nm/s, and the substrate temperature was room temperature. MON! When we investigated the resistivity of the M o N
% composition range, O9lμΩ at liquid helium temperature
Resistivities ranging from m to 0.22 μΩm were obtained (see FIG. 1); however, MoNz films containing nitrogen higher than this value exhibited superconductivity at liquid helium temperatures. According to the results of electron diffraction measurements, the nitrogen concentration was 30
The MONX film up to at% exhibited a body-centered cubic crystal structure, similar to pure Mo. The MoNX film that showed superconductivity at liquid helium temperature showed a face-centered cubic crystal structure, and the Mo2
It corresponded to the phase known as N.

As mentioned above, the resistivity of the MoNX film with a film thickness of 1100 nm changes from 0.1 μΩm to 0.22 μΩm in the composition range from 1 at% to 30 at% nitrogen concentration, so the resistivity changes from 1Ω/hole to 2.2Ω/hole. Sheet resistance was obtained. Therefore, by adjusting the film thickness in the range of 50 nm to 500 nm, the sheet resistance was made variable from 4.5 Ω/hole to 0.2 Ω/hole, that is, in a range of about 20 times.

Next, a resistor structure in an integrated circuit and an example of resistor fabrication will be described based on FIG. An Nb film 2 for magnetic shielding was formed to a thickness of 200 nm on a silicon wafer 1 that was not subjected to thermal oxidation. This Nb film was patterned by reactive ion etching using CF4 gas to form a magnetic shielding film. Next, a Si film 3 for insulation between the eyebrows was formed to a thickness of 300 nm. This Si film was formed by thermal evaporation using an electron beam gun in a high vacuum of 10-'Pa or higher.++ In order to improve the crystallinity of the Si film, the substrate temperature when the Si film was not deposited was 200°C. ~300℃
Patterning of the m Si film maintained at 100 nm was performed by reactive ion etching using CF4 gas. In addition, CF
When using 4 gases, there may be side etching of the Si film, but this does not cause any particular problem because dimensional accuracy is not required for this interlayer insulating film.
Although the i film is originally a semiconductor, the thickness direction resistance value of the Si film formed here showed a resistivity of 10901 or more at liquid helium temperature. Therefore, there is no problem of leakage current. MoNx with a thickness of 1100n on the Si interlayer insulating film
Film 4 was formed by sputtering. A resist pattern as a resistive film was formed using an optical exposure method. Next, using an ion etching method using an Ar beam, Mo
The portion of the NX film not covered by the resist was removed. After that, in order to define the length of the IIMONX film, which is obtained by removing the resist on the MoNX with acetone, as a resistive film, a Si film 3' with a thickness of 180 nm is formed in the center of the MoNz film, and both ends of the MONX film are It was exposed for connection with the wiring film.

The Si film 3' was formed by vacuum evaporation using an electron beam gun. When no Si film was deposited, the substrate temperature was 200 to 300°C, and the degree of vacuum was 10-'Pa or higher. The Si film formed under these conditions was polycrystalline. Ion etching using an Ar beam was used to pattern the Si film.

Further, an Nb film 2' having a thickness of 200 nm was formed by sputtering. The formed Nb film was patterned by reactive ion etching using CF4 gas to form a wiring film.

The sheet resistance of the resistor shown in FIG. 2 formed by the above method was measured at liquid helium temperature. According to this result, in the M o N X film having a width of 3 μm or more, the distribution of the sheet resistance film was within 5%. According to the results of measuring resistive films of M o N The contact resistance with the wire film was 0.1Ω or less. From these results, the MoNx of the present invention could be used as a resistive thin film of a superconducting integrated circuit using Nb as a wiring electrode.

Note that the reproducibility of the resistance value of the MONX film with a film thickness of 50 nm or less decreased from the viewpoint of film thickness control accuracy. In the case of a MoNX film with a film thickness of 500 nm or more, processing difficulties occurred in terms of etching selectivity. MON allows processing without affecting the underlying film! The film thickness was within 500 nm. In other words, when processing a MoNX film with an Ar ion beam, the etching rate of the MoNX film is approximately equal to the etching rate of the underlying Si.Therefore, since the etching uniformity within the wafer is 10%, the etching rate of the underlying Si is approximately equal to the etching rate of the underlying Si. In order to keep the overetching within 50 nm, the thickness of the MoNz film had to be within 500 rhm.

The heat dissipation characteristics of the resistor with this structure were as follows. Changes in characteristics such as the gap voltage of a Josephson junction in which the lower electrode is a NbN film and the upper electrode is a PB alloy film are correlated with temperature changes at arbitrary points on the substrate. A Josephson junction for temperature change detection was placed at a distance of 20 μm from the resistor.

When applying a power of 50 W/aJ to a resistor with this structure, the temperature rise detected at the Josephson junction was 0.2
was below. In addition, when the base interlayer insulating film and the resistive protection film of the conventional structure were both made of Si films, the temperature increase under the same conditions was 0.4. Therefore, the resistor structure according to this embodiment has a sufficient heat dissipation effect compared to the conventional structure. Note that crystalline S102 is used as the underlying interlayer insulating film and the resistance protective film.
+AQ2o or MgO had a similar heat dissipation effect.

The effects obtained by this example are shown below.

(1) The resistance distribution within the chip of the MoNX film with a width of 3 μm and a length of 18 times was within 5%.

(2) The prepared MoNz resistive film was exposed to air at 200°C for 5
Although heat treatment was performed for several hours, the change in the resistance film was within 3%. Furthermore, the MoN X resistive film was subjected to 10 thermal cycles between room temperature and liquid helium temperature, but there was no change in the resistive film.

(3) In the case of a resistance structure using a Si film as a base film and a resistance protection film, the rate of temperature rise around the resistance film was less than 1/2 of that in the case of using amorphous 5j Si O19.

Note that in order for the resistive film base material or protective film such as the Si film used in this example to be effective, it is necessary to use a high melting point material such as a MoN)c film as the resistive film. This is due to the following reason. In other words, in order to improve the crystallinity of a Si film, etc., it is necessary to raise the substrate temperature during film formation, and the MON
This is because the K film exhibits negligible changes in crystal structure or resistance characteristics when subjected to heat treatment at 200 to 300°C, and there is no diffusion reaction with the Si film, 5i02 film, etc.

〔Effect of the invention〕

As described above in the embodiments, the present invention has the following effects.

(1) In a resistor structure using crystalline Si or AI2Al22O31, etc. as the base material or protective film for the resistor film, the temperature around the resistor is higher than that in the case of using a conventional Si film for the same amount of heat generation. The rise is 1/2
It became the following. As a result, the density that can be integrated on a chip has become more than twice that of the conventional technology.

(2) MoN
It has sheet resistance characteristics in a wide range up to 2Ω/hole, and includes sheet resistances around 1Ω/hole, which are necessary as thin film resistors in superconducting switching circuits.

(3) The MONX resistive film can be applied to Josephson integrated circuits using Nb as wiring electrodes and integrated circuit processes, and can be miniaturized. - Also, the contact resistance with the wiring film is 0.1Ω or less, and the resistance value distribution for the same dimensions is within 5%.

(4) The properties of the MoNx film change within 3% when heated up to 200° C. and thermal cycled between room temperature and liquid helium temperature.

[Brief explanation of drawings]

Figure 1 is MON! A diagram showing the dependence of resistivity on nitrogen concentration at room temperature and liquid helium temperature of a film, FIG. 2(a) is a top view of the resistor according to the present invention, and FIG. 2(b) is its A-A
FIG. l...Si wafer, 2.2'...Nb
Film, 3.3'...Si film, 4...Mo
Nx film.

Claims (1)

[Scope of Claims] 1. Consisting of a base film made of a semiconductor or an insulator, a resistive film, and a resistive protective film made of a semiconductor or an insulator, and at least one of the base film and the resistive protective film is a single film. A resistor for low temperature circuits characterized by having crystalline or polycrystalline crystallinity. 2. In the low temperature circuit resistor according to claim 1, the semiconductor or insulator is Si crystal, Al_2O
A resistor for low-temperature circuits characterized by being made of a material selected from _3 crystal, SiO_2 crystal, or MgO crystal. 3. The resistor for a low temperature circuit according to claim 1, wherein the resistive film is mainly composed of Mo having a body-centered cubic crystal structure containing nitrogen as a component in the film in a range of 1 at% to 30 at%. A resistor for a low temperature circuit, characterized in that the film thickness is 50 nm or more and 500 nm or less. 4. A Mo film with a body-centered cubic crystal structure containing nitrogen in the range of 1 at% to 30 at% as a component in the film is coated with single crystal or polycrystalline crystal so that the film thickness is 50 nm to 500 nm. a step of forming a resist pattern as a resistive film on the Mo film, a step of removing the Mo film not covered by the resist pattern, a resist pattern for the resistive film. forming a protective film made of the semiconductor or insulator at the center of the Mo film by a lift-off method after removal;
A method for manufacturing a resistor for a low temperature circuit, comprising the step of forming a Nb film serving as a wiring electrode on both ends of the Mo film.