JPS62131588A - Manufacture of superconductive transistor - Google Patents

Abstract

PURPOSE:To improve the gain of a circuit and to implement high integration density, by providing a diffused layer, which has impurity concentration higher than that of a substrate, by an ion implantation, with an insulating film provided on a semiconductor layer as a mask, and a part, in which impurities are not diffused, between superconductive electrodes. CONSTITUTION:An SiO2 film 10 is formed on the surface of an Si substrate 1 with impurities. Then a resist pattern is formed on the surface. With the pattern as a mask, a protruded SiO2 part 10 is formed by plasma etching. Then with the SiO2 part as a mask, impurities are introduced from the surface by ion implantation, and a diffused layer 5 is formed. The surface of the Si substrate is etched, and a protruded part 9 is formed. After an insulating film 6 is formed, the insulating film 10 is removed. Then an Nb film is deposited. With this film as a mask, machining is performed by plasma etching and superconductive electrodes 2 and 3 are obtained. Thereafter, SiO2 insulating films 7 and 8 are formed. Then a control electrode 4 is formed. Thus, an element having a large circuit element can be obtained, dispersion in characteristics is reduced and the yield rate is improved.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to switching devices that operate at extremely low temperatures, and in particular to a method for manufacturing a superconducting transistor that increases circuit gain and reduces variation in characteristics and is suitable for high integration. Regarding.

[Background of the invention]

As a superconducting device that uses semiconductors and has electrodes for controlling the characteristics of the device, T.D. Clark (T.D.
, D, C1ark) proposed by JOF
ET (Hybrid Josephson Field Effect Transistor)
hsonField Effect Transist
ons) is reported in Journal of Applied Physics (J, ^pp1.phys, ), page 2736, volume 51 (1980), and is well known. J.O.
In an FET, an electrode made of a superconductor is formed on a semiconductor substrate into which impurities are introduced at a high concentration. In this case, the device is controlled by applying a voltage to the control electrode and expanding the inversion layer from the control electrode side to the semiconductor side.

Therefore, since the impurity concentration of the semiconductor layer directly under the control electrode is high, the voltage to be applied to the control electrode is several hundred millivolts or more. -The voltage obtained between the lease and drain electrodes as a force output is small, less than a few hundred millivolts. In other words, the gain of the circuit is less than 1, and high gain cannot be expected. Therefore, it was not possible to use circuits similar to those used in conventional semiconductor technology.

[Purpose of the invention]

An object of the present invention is to provide a superconducting transistor, which is a switching device whose characteristics can be controlled by voltage, which improves the gain of the circuit, enables high integration, has good controllability in the manufacturing process, and has small variations in characteristics. It is in.

[Summary of the invention]

In order to achieve the high gain of the circuit in the above purpose, a higher impurity concentration than the substrate is introduced into the part of the semiconductor layer in contact with the superconducting electrode in order to reduce the Schottky barrier, and a low impurity Provide a concentration section. That is, the above object is achieved by varying the concentration distribution of impurities contained in the semiconductor layer. Compared to the case where impurities are uniformly contained at a high concentration, the state of charge accumulation or inversion is different, and the voltage applied to the control electrode becomes smaller. Here, the distance between the superconducting electrodes needs to be about 10 times or less the coherent length in order to maintain a weak coupling state. The value varies depending on the material of the semiconductor or superconductor, but it is usually on the order of several hundred nanometers. Therefore, this several hundred n
It is difficult to bring about a change in the concentration distribution in a semiconductor with a length of m.

Therefore, by utilizing the lateral diffusion layer when impurity ions are implanted, the part where the semiconductor and superconducting electrode are in contact is formed with a high concentration, and the central part is formed with a low concentration.

[Embodiments of the invention]

Hereinafter, the first embodiment of the present invention will be explained as follows. This will be explained with reference to FIG.

Figure 1 shows a part of the cross section of a superconducting transistor.
11 on both sides of the protrusion 9 of the semiconductor substrate 1 consisting of
00n impurity diffusion layer 5 is formed, and the central portion is kept at the substrate concentration. At the top of this protrusion, a 50 nm thick S
Insulating film 7 made of J, Oz and 5i with a thickness of 1100n
C) A control electrode 4 is installed via an interlayer insulating film 8 made of z. On the other hand, on both sides of the protrusion, the thickness is 1100n.
Superconducting electrodes 2 and 3 made of Nb and having the same thickness as the protrusion are formed through an insulating film made of SiOz.

Next, the manufacturing process of the superconducting transistor shown in FIG. 1 will be explained using FIG. 2.

A 5iOz film 10 with a thickness of 300 nm is formed by CVD on the surface of a Si substrate 1 containing boron as an impurity with an impurity concentration of I x 10 "cm-" or less (see Fig. 2).
a)) - Thereafter, a resist pattern is formed on the surface using an electron beam lithography system, and using this as a mask, plasma etching is performed using CF4 gas to form protruding 33. Oz is formed (Fig. 2(b)). Next, using this protruding insulating film 10 as a mask, boron with an impurity concentration of 1×10 19 CIl-6 is introduced from the surface by ion implantation (FIG. 2(c)). In this case, the implanted depth is 400 nm. The range of diffusion under the mask 5 is 11
It is desirable that it is 00n. Next, using the insulating film 10 as a mask, the surface of the Si substrate was etched by plasma etching using CF4 gas to a height of 400 nm.
m, and a protrusion 9 with a width of 300 nm was formed (Fig. 2(d)
). Subsequently, 1
After oxidizing for 2 hours to form an insulating film 6 made of 5iOz and having a thickness of 1100 nm, the insulating film 10 used as a mask was oxidized with carbon.
It is removed by plasma etching using F4 gas. (Second
Figure (C)).

Next, Nb was evaporated by electron beam heating in a high vacuum of less than I to obtain superconducting electrodes 2 and 3 (Question 21 (f)).

The protrusion 9 and the superconducting m-poles 5 and 6 are present at almost the same height, and flattening can be achieved. Next, a thickness of 50 mm was obtained using the vapor phase growth method.
After forming the insulating films 7 and 8 of 5iOz nm, the control electrode 4 was formed by forming a Nb film by magnetron sputtering and processing by plasma etching, and the superconducting transistor of the present invention was completed (see Fig. 2 (g). ), (h)).

This superconducting transistor is heated at liquid helium temperature (4.2K).
), superconducting electrons easily seep into the semiconductor, and by applying a voltage of several mV to the control electrode, the gain can be changed significantly between the superconducting electrodes and the superconducting current flowing. We were able to obtain a large element.

Furthermore, since the spatial distribution of the impurity concentration can be realized with high accuracy, it is possible to obtain a circuit with small variations in characteristics and a high yield.

Next, a second embodiment of the present invention will be described with reference to FIG.

A superconducting electrode 2 is placed on a Si semiconductor substrate via an insulator.
.
In this structure, the control electrode 4 is installed via an insulator 7 made of 530z.

The central portion of the semiconductor layer 5 having a width of 1100n has an impurity concentration of I.times.10"am-", and both sides thereof have a high impurity concentration of I.times.10"cm-8. A manufacturing method that provides such an impurity distribution can be realized by the method described in the first embodiment. In other words, 5iO with a width of 300 nm
By implanting boron ions into the Z film as a mask, the lateral diffusion layer under the mask could be controlled to 1100 nm. In this way, the impurity distribution between the superconducting electrodes 2 and 3 with a distance of 300 nm or less can be controlled.

This superconducting transistor is heated at liquid helium temperature (4.2K).
), we were able to obtain a device with a large circuit gain.

Furthermore, when an integrated circuit was constructed using this, the impurity concentration distribution could be controlled with high accuracy, resulting in a circuit with small variations in characteristics and high yield.

Next, an embodiment of the tube 3 of the present invention will be described with reference to FIG. Superconducting electrodes 2 and 3 and interlayer insulating films 6 are alternately stacked, and a control electrode 4 is installed at the end of the superconducting electrodes 2 and 3 with a semiconductor 5 and an insulator 7 interposed therebetween. The impurity concentration in the semiconductor is low over 1100n between the superconducting electrodes 2 and 3 (L x 10 ”
cm”'δ), the area where the semiconductor and superconductor are in contact is high (
I x 1019 cm-').

A manufacturing method that provides such a concentration distribution can be realized by the method described in the first example. In other words, by implanting boron ions in an oblique direction using a SiOx film with a width of 300 nm as a mask, a low concentration region with a width of about 1100 nm can be left.

This superconducting transistor is heated at liquid helium temperature (4.2K).
), we were able to obtain a device with large circuit gain.

Furthermore, when we constructed an integrated circuit, we were able to control the distribution of impurity concentrations with high precision, making it possible to create a circuit with small variations in characteristics and high yield.

In this example, Si was used as the semiconductor material, but materials such as GaAs, InP, InSb, and InAs may be used instead. Nb was used as the superconducting material, but instead of this, pb, pb gold alloy NbN.

MoN, NbaSj, etc. may also be used. Moreover, phosphorus arsenic, antimony, etc. may be used instead of boron as an impurity.

〔Effect of the invention〕

According to the present invention, the impurity concentration distribution in the semiconductor layer in contact with the superconducting electrode can be created in minute portions with spatial precision and controlled with good reproducibility. Therefore, it is possible to realize a structure that can increase the gain when controlling the coupling state between the superconducting electrodes using an applied voltage, and has the effect of reducing variation in characteristics and achieving a high yield.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a part of a superconducting transistor according to a first embodiment of the present invention, FIG. 2 is a sectional view showing a manufacturing process of a superconducting transistor according to a first embodiment of the present invention, and FIG. The figure is a sectional view showing a part of a superconducting transistor according to an embodiment of the tube 2 of the present invention, and FIG. 4 is a sectional view showing a part of a superconducting transistor according to an embodiment of the tube 3 of the present invention.

Claims (1)

[Claims] 1. In a superconducting transistor having at least a pair of superconducting electrodes, a semiconductor layer connected to and extending to both superconducting electrodes, and a control electrode, the semiconductor layer is formed on the semiconductor layer. A superconducting transistor characterized in that a region in which impurities are not diffused is provided between a diffusion layer having a higher impurity concentration than the substrate and the superconducting electrode by ion implantation using an insulating film provided on the substrate as a mask. Manufacturing method. 2. A method for manufacturing a superconducting transistor, characterized in that the length of the portion in which impurities are not diffused as set forth in claim 1 is 300 nm or less.