JP2917933B2 - Method for manufacturing minute tunnel junction and method for manufacturing minute tunnel junction element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a single electron tunnel device.

[0002]

2. Description of the Related Art A lithography technique is indispensable for forming a minute tunnel junction which is a component of a single electron tunnel element. The most simplified lithography for forming a metal-based small tunnel junction is a double vapor deposition method using a mask 3 suspended in the air as shown in FIGS. 9, 10 and 11.

In this conventional method, first, as shown in FIG. 9, a suspension mask 3 which is lifted above a substrate 1 by a spacer 2 and partially floats in a hollow state is prepared. Next, FIG.
As shown in (1), after the deposition 5 of the first metal film is performed from the direction of a certain angle through the suspension mask 3, the surface of the first metal film is oxidized to form an oxide film barrier on the first metal film. Form. Next, vapor deposition 6 is performed through the same suspension mask 3 from a direction at an angle different from that of the first vapor deposition 5. The second vapor deposition is performed so as to partially overlap the first metal film at two places via the oxide film barrier.

As described above, the deposition 5 and the deposition 6 of the metal film are sequentially performed using the same mask from different directions from the above, and the metal film is oxidized between the two deposition steps to form a film on the first metal film. By forming the oxide film barrier, the minute tunnel junction 4 is formed at two places where the first and second deposited films overlap.

[0005] The mask pattern and each step will be described with reference to FIGS. 10 and 11 taking a single electron transistor consisting of two junctions, which is the simplest single electron element, as an example.

FIG. 10A shows a mask pattern. The bright areas are the holes in the mask. A first metal film 7 as shown in FIG. 10B is formed through such a mask.

After that, the surface of the first metal film 7 is oxidized to form an oxide film barrier on the first metal film. Next, the film forming angle is shifted in the “vertical direction” through the same suspension mask 3,
When the second metal film 8 is formed so as to partially overlap at two places with the first metal film and the oxide film interposed therebetween, two junctions as shown in FIG. A single-electron transistor composed of an island having a size of d 'and a region where the first and second metal films overlap (gate electrode is omitted) is obtained.

Further, a first metal film 7 as shown in FIG. 11B is formed through a mask as shown in FIG. 11A, and then the surface of the first metal film 7 is oxidized to An oxidation barrier is formed on the metal film. Next, through the same suspension mask 3,
When the film forming angle is shifted in the “lateral direction” and the second metal film 8 is formed so as to partially overlap at two places with the first metal film and the oxide film interposed therebetween, FIG. Thus, a single-electron transistor comprising two junctions (regions where the first and second metal films are in contact) and an island 7 having a size of d can be obtained (the gate electrode is omitted).

In this specification, an island refers to an isolated electrode region connected to an external electrode (lead electrode 12) by a tunnel junction.

[0010]

The operating temperature of a single electronic device depends on the magnitude of its electrostatic energy. The magnitude of the electrostatic energy is inversely proportional to the total capacitance of the device.
The total capacitance of the device is ultimately limited by the island's self capacitance.

The self-capacitance of the island is proportional to the size of the island (the size of the island in this case is the largest dimension among the thickness, length and width of the island). Therefore, in order to obtain a single electronic device having a high operating temperature, as small an island as possible must be formed.

In the conventional double vapor deposition method, the size of the island is d '.
However, in the manufacturing method in which the deposition angle is changed in the vertical direction as shown in FIG. 10, a region having a length of j 'which is unnecessary for the tunnel junction is formed at the center of the island. In order to prevent the influence of this region from being reflected on the transport characteristics, a condition of j ′ >> j is required, where j is the length of the joint.

Although j is determined by the deposition angle, it is affected by controllability, and usually j ≒ w. If d ′>d> j ′ and the resolution of lithography is δ, then at its limit, δ ≒ w ≒ j
Becomes Therefore, d '>> d, and the size of the island is much larger than the lithography resolution.

In the manufacturing method in which the deposition angle is changed in the horizontal direction as shown in FIG. 11, the size d of the island 11 is equal to the distance D between the electrodes.
(D = D + 2j). However, if a narrow bridge-shaped mask called D as shown in FIG. 11A is formed by electron beam lithography, d>D> δ ≒ w due to the influence of excessive exposure due to the proximity effect at the time of exposure. Would.

Accordingly, in the conventional method, the size of the island cannot be reduced to the limit resolution δ of lithography in any way, and the operating temperature cannot be increased.

An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing a single electronic device having a high operating temperature by reducing the size of an island to about the limit resolution δ of lithography.

[0017]

According to the present invention, there is provided a method for manufacturing a micro-tunnel junction, comprising the steps of:
By changing the deposition angle three times or more, a metal deposition film is sequentially formed on the substrate to form an overlapping portion in which the plurality of deposition films partially overlap, and the same portion is formed between the plurality of deposition film formation steps. A tunnel junction is formed in the overlapping portion by growing a tunnel barrier in a region where the overlapping portion of the deposited film is formed in the deposition apparatus.

The present invention also relates to a method of manufacturing a micro tunnel junction comprising a step of sequentially performing metal deposition at least three times on a substrate through holes of the same mask suspended in the air, wherein the holes of the mask are provided. Forming a first metal deposition film on a substrate through a process and forming a tunnel barrier by oxidizing at least a region of the surface of the first metal deposition film where a tunnel junction is to be formed in the same deposition apparatus And the second through the mask from a direction different from the first deposition direction.
A second deposition step of partially depositing a metal film through the oxide film and the first deposition film, and a third deposition process through the mask from a direction different from the first and second deposition directions. A third vapor deposition step of performing metal film vapor deposition in a region different from the overlapping portion where the first and second vapor deposited films are in contact with each other via the first vapor deposited film and the oxide film; The third and subsequent metal depositions are performed sequentially through the mask from a direction different from the previous deposition direction, through the mask, and in a region different from the previous overlapping portion through the first deposited film and the oxide film. And a third or later deposition step in which a tunnel junction is formed at the overlapping portion.

It is preferable to use a suspension mask in which the distance between the holes provided on the mask is larger than the size of the holes themselves.

According to a method of manufacturing a micro tunnel junction device of the present invention, the micro tunnel junction described above is formed, and the micro tunnel junction is formed between the plurality of overlapping portions formed by the plurality of vapor deposition steps. An electrode (hereinafter, this electrode is referred to as an island electrode) is formed on an island-like region, and a plurality of lead electrodes connected to the island electrode via a tunnel junction are formed.

Further, a gate insulating film is grown on the island electrode and the gate electrode is formed on the gate insulating film in the same vapor deposition device during the plurality of vapor deposition processes. This is a method for manufacturing a tunnel junction element.

[0022]

One embodiment of the manufacturing method according to the present invention will be described with reference to FIG. FIG. 8 is a sectional view of a tunnel junction manufactured according to the present invention.

First, the first vapor deposition 5 is performed from a certain angle through the suspension mask 3 to form a first vapor deposition film 7. Next, after oxidizing the surface of the first vapor-deposited metal film 7, vapor deposition 6 is performed through the same mask 3 from a direction different from that of the first vapor deposition, and at one place via the first vapor-deposited film 7 and the oxide film. The second deposited film 8 is formed so as to be partially in contact.

Subsequently, vapor deposition 5 is performed through the same mask 3,
The third vapor deposition 10 is performed from a direction different from the vapor deposition 6,
A third deposited film 9 is formed at a location different from the overlapping portion of the first and second deposited films so as to be in contact with the first deposited film via an oxide film.

In this manner, an island having a size of d and two tunnel junctions (a portion where the first and second deposited films are in contact and a portion where the first and third deposited films are in contact) are formed. Is done.

The size d of the island produced according to the present invention is
It is about the same as w of the hole formed in the mask, so that the size of the island can be reduced to the limit δ of lithography.

[0027]

【Example】

(Embodiment 1) FIG. 1 shows a first embodiment of the present invention. FIG. 1A shows a suspension mask 3 used in this embodiment (top view). The bright areas are the holes in the mask.
A first metal film 7 as shown in FIG. 1B is formed through this mask. FIG. 1 (b ′) is a cross-sectional view of FIG. 1 (b).

As a film forming method, a thermal evaporation method in which the direction components of atoms during film formation are relatively aligned is suitable. The material of the metal film to be deposited is not particularly limited, but a material capable of forming a stable native oxide film on the surface is desirable. For example, aluminum is a suitable metal material.

After the first metal film is formed, oxygen is introduced into the same vacuum apparatus to oxidize the film surface and to form a tunnel barrier (oxide film 1).
4) is prepared.

Next, the film forming angle is changed to the "vertical direction" and the second
When the metal film 8 is formed, an overlapping structure as shown in FIG. 1C is obtained. FIG. 1 (c ') is a cross-sectional view of FIG. 1 (c). Thereafter, the film forming angle is changed to the “vertical direction” again, and the third
When the metal film 9 is formed, a single electron transistor including two junctions 4 and islands 11 as shown in FIG. FIG. 1D is a cross-sectional view of FIG. Gate electrode 1
3 can be manufactured simultaneously with the tunnel junction as shown in FIGS. 1 (d) and (d ').

If D> d in the size of the mask, FIG.
It is possible to prevent an extra junction having the size of j ', which is a conventional problem as shown in FIG. According to the present embodiment, the size of the island is the size d and w of the hole formed in the mask.
, Which can be reduced to a size comparable to the resolution of lithography.

When a PMMA electron beam resist is used, the resolution of lithography is about 20 nm. According to this example, when D was set to 50 nm and d and w were each set to 20 nm, a single electronic device having an island of 20 nm was obtained, and the operating temperature was 100K or more. In the conventional method, it is difficult to increase the operating temperature to 4K or more, and according to the present invention, a single electronic device having a high operating temperature can be manufactured.

(Embodiment 2) FIG. 2 shows a second embodiment of the present invention. FIG. 2A shows a suspension mask used in this embodiment (top view). The bright areas are the holes in the mask. Through this mask, a first metal film 7 as shown in FIG. 2B is formed. FIG. 2 (b ′) is a point A in FIG. 2 (b).
FIG. 4 is a cross-sectional view taken along a dotted line between a point AA and a point AA.

After the film formation, oxygen is introduced into the same vacuum device,
The surface of the first deposited film is oxidized to form a tunnel barrier (oxide film 1).
4) is prepared.

Next, when the second metal film 8 is formed by changing the film forming angle to the “lateral direction”, an overlapping structure as shown in FIG. 2C is obtained. FIG. 2C is a cross-sectional view taken along a dotted line between points A and AA in FIG.

After that, the third metal film 8 is formed by changing the film forming angle to the “lateral direction” again, and a single electron transistor comprising two junctions 4 and islands 11 as shown in FIG. (The gate electrode is omitted). FIG. 2D is a cross-sectional view taken along a dotted line between points A and AA in FIG.

Since the size D of the mask can be relatively large irrespective of the size of the island, overexposure due to the proximity effect at the time of exposure, which has been a conventional problem, can be avoided. Therefore, the size of the island is equal to the sizes d and w of the holes formed in the mask, which can be reduced to a size equivalent to the resolution of lithography.

If D> w in the dimensions of the mask, no matter what the size of the overlapping portion is selected, an extra junction having the size of j ', which is a conventional problem as shown in FIG. Can be done on the island.

(Embodiment 3) FIGS. 3 and 4 show a third embodiment of the present invention. 3 and 4 show a series of steps (a
FIGS. 7A to 7E are diagrams which are divided for the purpose of drawing.

In the first and second embodiments, a single-electron transistor composed of two junctions and an island has been described as an example. However, a more complicated circuit can be manufactured by this multi-angle evaporation method. In this embodiment, a circuit having three junctions on one island can be realized by preparing an appropriate mask pattern and depositing the film four times at different angles, and the size of the island is equivalent to the resolution of lithography. Size can be maintained.

FIG. 3A shows a suspension mask 3 used in this embodiment (top view). The bright areas are the holes in the mask. A first metal film 7 as shown in FIG. 3B is formed through this mask. After the film is formed, oxygen is introduced into the same vacuum apparatus to oxidize the film surface to form a tunnel barrier.

Next, the film forming angle is changed to the “lateral direction” and the second
When the metal film 8 is formed, an overlapping structure as shown in FIG. 4C is obtained. Thereafter, when the third metal film 9 is formed by changing the film formation angle to the “lateral direction” again, two junctions as shown in FIG. 4D can be formed. Thereafter, when the film forming angle is changed to the “lateral direction” again and the fourth metal film 16 is formed, a circuit having three junctions on one island can be realized.

As in the first and second embodiments, overexposure due to the proximity effect at the time of exposure, which is a conventional problem, can be avoided. Thus, the size of the island is equal to the size of the hole in the mask, which can be reduced to a size equivalent to the resolution of lithography.

(Embodiment 4) FIGS. 5 to 7 show a fourth embodiment of the present invention. FIG. 5, FIG. 6, and FIG. 7 are views showing a series of steps (a to f).

In the single transistors of the first and second embodiments, the gate electrode is arranged beside the element. In order to increase the voltage gain, the capacitance of the gate must be increased. In this embodiment, a vertical gate electrode can be arranged on the island of the two-junction single-electron transistor via the insulating film 15, and the size of the island at that time can be maintained at a size corresponding to the resolution of lithography.

FIG. 4A shows a suspension mask used in this embodiment (top view). The bright areas are the holes in the mask. A first metal film 7 as shown in FIG. 5B is formed through this mask. After the film is formed, oxygen is introduced into the same vacuum apparatus to oxidize the film surface to form a tunnel barrier.

Next, the film forming angle is changed to the “horizontal direction” and the second
When the metal film 8 is formed, an overlapping structure as shown in FIG. 6C is obtained. Then, when the third metal film 9 is formed by changing the film forming angle to the “lateral direction” again, two junctions as shown in FIG. 6D can be formed. Thereafter, the film forming angle is changed to the “lateral direction” again, and the insulating film 15 is formed so as to cover the upper part of the island as shown in FIG. Finally, as shown in FIG. 7F, the deposition angle is further changed, and the gate electrode 13 is formed.

As described above, according to this embodiment, a single-electron transistor having a vertical gate electrode can be realized. At the same time, similarly to the first and second embodiments, the overexposure due to the proximity effect at the time of exposure, which is a conventional problem, can be avoided. Therefore, the size of the island is equal to the size of the hole in the mask,
This can be reduced to a size equivalent to the resolution of lithography.

[0049]

As described above, according to the present invention, it is possible to realize a single electronic device suitable for high-temperature operation having islands having a size equal to the resolution of electron beam lithography.
At the same time, it is possible to prevent the formation of an extra junction on the island, which has been a problem in the past.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a small tunnel junction device according to a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a small tunnel junction device according to a second embodiment of the present invention.

FIG. 3A is a top view showing a pattern of a suspension mask used in a third embodiment of the present invention. FIG. 3 (b) is a view (partly) of a process for manufacturing a small tunnel junction device according to the third embodiment of the present invention.

FIG. 4 is a manufacturing process diagram of the small tunnel junction device following FIG. 3B according to the third embodiment of the present invention.

FIG. 5A is a top view showing a pattern of a suspension mask used in a fourth embodiment of the present invention. FIG. 5 (b) is a view (partly) of a process for manufacturing a small tunnel junction device according to a fourth embodiment of the present invention.

FIG. 6 is a view showing a manufacturing process of the minute tunnel junction device following FIG. 5B according to the fourth embodiment of the present invention.

FIG. 7 is a manufacturing process diagram of the minute tunnel junction device following FIG. 6E according to the fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of a small tunnel junction device according to the present invention.

FIG. 9 is a configuration diagram of a minute tunnel junction device according to a conventional manufacturing method.

FIG. 10 is a manufacturing process diagram of a conventional minute tunnel junction device.

FIG. 11 is a manufacturing process diagram of a conventional minute tunnel junction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Spacer 3 Suspension mask 4 Joining 5 Deposition 6 Deposition 7 First deposition film 8 Second deposition film 9 Third deposition film 10 Deposition 11 Island 12 Lead electrode 13 Gate electrode 14 Oxide film 15 Insulating film 16 Fourth Evaporated film 17 Fifth evaporated film

Claims (4)

(57) [Claims] 1. The distance between holes of a mask suspended in the air.
Through a hole in the mask that is larger than the size of the hole itself , 3
The metallized film is sequentially formed on the substrate by changing the vapor deposition angle more than once to form an overlapping portion in which the plurality of vapor-deposited films partially overlap, and the same vapor deposition apparatus is used during the plurality of vapor-deposition processes. Forming a tunnel junction in the overlapping portion by growing a tunnel barrier in a region of the deposition film where the overlapping portion is formed. 2. The distance between the holes of a hollow suspended mask.
Is a method of manufacturing a micro tunnel junction having a step of sequentially performing at least three or more metal depositions on a substrate through a hole of the mask larger than the size of the hole itself, Forming a tunnel barrier by oxidizing at least a region of the surface of the first metal deposition film where a tunnel junction is to be formed in the same vapor deposition apparatus; A second vapor deposition step of performing a second metal film vapor deposition from a direction different from the first vapor deposition direction so as to be in partial contact with the first vapor deposited film via the oxide film; and a first and a second vapor deposition A third metal film is deposited from the direction different from the direction through the mask in a region different from the overlapping portion where the first and second deposited films are in contact with each other via the first deposited film and the oxide film. The third to do so The vapor deposition step and the third and subsequent metal vapor depositions are performed sequentially through the mask from a direction different from the previous vapor deposition direction, and the first vapor deposited film and the metal vapor deposited in a region different from the overlapping portion until the previous time. A method for manufacturing a minute tunnel junction, comprising: a third or later deposition step performed so as to be partially in contact with an oxide film, wherein a tunnel junction is formed in the overlapping portion. 3. A micro-tunnel junction according to claim 1, wherein said micro-tunnel junction is formed on a fine island-like region between said plurality of overlapping portions formed by said plurality of vapor deposition steps. An electrode (hereinafter, this electrode is referred to as an island electrode) is formed, and a plurality of lead electrodes connected to the island electrode via the tunnel junction are formed. 4. The method according to claim 1, wherein a gate insulating film is grown on the island electrode in the same vapor deposition apparatus and a gate electrode is formed on the gate insulating film during the plurality of vapor deposition processes. A method for manufacturing a small tunnel junction device according to claim 3.