JP2007250904A - Field effect transistor and manufacturing method thereof - Google Patents

Abstract

A high-frequency characteristic of a field effect transistor using carbon nanotubes is improved and can be manufactured at low cost.
A metallic carbon nanotube 8 or 9 includes a channel 4 formed parallel to the surface of a substrate 1 and one of a source electrode and a drain electrode crosses the channel 4 parallel to the surface of the substrate 1. Alternatively, both the source electrode and the drain electrode are formed of metallic carbon nanotubes 8 and 9 formed so as to intersect the channel 4 at different angles.
[Selection] Figure 1

Description

  The present invention relates to a field effect transistor and a method for manufacturing the same, and more particularly to a field effect transistor that has excellent high frequency characteristics using carbon nanotubes and can be manufactured at low cost, and a method for manufacturing the same.

  In recent years, with the progress of miniaturization and speedup of electronic equipment, there is a demand for further miniaturization and speedup of transistors used in electronic equipment. Device structures using these materials are being studied. A field effect transistor using carbon nanotubes is one of them, and by taking advantage of the fine structure of carbon nanotubes and the high speed of carriers, higher frequency characteristics than those of conventional field effect transistors are expected.

  FIG. 8 is a perspective view showing an example of a conventional field effect transistor using carbon nanotubes (Patent Document 1). In the field effect transistor shown in FIG. 1, a semiconductor carbon nanotube 38 is formed between a source electrode 36 and a drain electrode 37 formed on an insulating substrate 35 and used as a channel. It has a so-called back gate structure using the conductive film 39 formed in the above as a gate electrode.

  A top gate structure may be used instead of the back gate structure (Patent Document 2). In the top gate structure, a gate electrode is provided on the surface of the substrate 35 so as to cross the semiconductor carbon nanotube 38 via an insulating film, and carbon nanotubes can be used as a gate electrode material.

  Carbon nanotubes can be formed by means such as CVD or laser ablation. The diameter of the carbon nanotube is very small on the order of sub-nm, and when a normal growth method is used, a large number of carbon nanotubes are formed between the source electrode 36 and the drain electrode 37 in the horizontal and vertical directions in FIG. However, in the figure, for the sake of simplicity, the two carbon nanotubes 38 arranged in the horizontal direction are representatively shown. The same applies to the drawings referred to below.

In carbon nanotubes, impurity scattering and lattice scattering are suppressed, so the saturation rate of electrons is larger than that of commonly used crystalline Si and GaAs. Therefore, field effect transistors using carbon nanotubes as channels as described above are crystalline. High-speed operation is expected compared to the case of using Si or GaAs.
JP 2003-17508 A JP 2002-118248 A

  As described above, the diameter of the carbon nanotube is very small, and it is difficult to increase the density of the carbon nanotube that can be disposed between the source electrode and the drain electrode by a normal forming method. Therefore, a conventional field effect transistor using carbon nanotubes as a channel cannot increase the channel gain and increase the power gain, which limits the high frequency characteristics.

  In the back gate structure shown in FIG. 8, the channel length of the transistor is determined by the length of the semiconducting carbon nanotube 38, and therefore the distance between the source electrode 36 and the drain electrode 37 is set narrow in order to improve the high frequency characteristics. Thus, the semiconducting carbon nanotubes 38 formed between them must be shortened. However, when the normal visible light photolithography technique is used, the distance between the source electrode 36 and the drain electrode 37 is limited to about 1 μm. To further shorten the distance, an electron beam exposure apparatus is used. There is a problem that an expensive apparatus such as the above is required and the manufacturing cost is increased.

  On the other hand, in a field effect transistor having a top gate structure using a carbon nanotube as a gate electrode, the channel length can be easily reduced because the channel length is determined by the diameter of the carbon nanotube. However, in this configuration, as shown in FIG. 8, most of the carbon nanotubes 38 formed between the source electrode 36 and the drain electrode 37 contribute to the channel resistance, so that the power gain cannot be increased. The problem remains.

  Accordingly, an object of the present invention is to improve the high-frequency characteristics of a field effect transistor using carbon nanotubes, and to enable manufacture at a low cost.

    The problem is that a channel is formed in parallel with the substrate surface, and at least one of the source electrode and the drain electrode is made of metallic carbon nanotubes formed to cross the channel in parallel with the substrate surface. This is solved by a field effect transistor which is characterized.

  Alternatively, the above problem is solved by the field effect transistor, wherein the source electrode and the drain electrode are made of metallic carbon nanotubes formed so as to cross the channel at different angles.

  Alternatively, the problem is that the electric field is characterized in that the gate electrode is composed of metallic carbon nanotubes formed so as to cross the channel and the metallic carbon nanotubes through an insulating film parallel to the substrate surface. Solved by effect transistors.

  Or the said subject is solved by the said field effect transistor, wherein the said channel consists of a semiconducting carbon nanotube.

  Alternatively, the above-described problem is characterized in that a channel is formed in parallel to the substrate surface, and metallic carbon nanotubes are formed so as to cross the channel in parallel to the substrate surface to form a source electrode and / or a drain electrode. This is solved by the manufacturing method of the field effect transistor.

  FIG. 1 is a perspective view showing the configuration of a field effect transistor according to the present invention, and a channel 4 made of semiconducting carbon nanotubes is formed between a temporary source electrode 2 and a temporary drain electrode 3 on a substrate 1. Metallic carbon nanotubes 8 and 9 are formed from the electrode 6 and the electrode 7 so as to cross the channel 4, respectively. The field effect transistor shown here has a back gate structure in which the conductive film 5 formed on the back surface of the substrate 1 is used as a gate electrode.

  As can be seen from FIG. 1, in the field effect transistor according to the present invention, the channel length is determined by the distance L between two points where the metallic carbon nanotubes 8 and 9 intersect the channel 4. The distance L is determined by controlling the relative position of the electrodes 6 and 7 with respect to the channel 4 and the direction in which the metallic carbon nanotubes 8 and 9 formed from the electrodes 6 and 7 are formed. The length of the channel 4 disposed between the temporary drain electrodes 3 can be made sufficiently shorter. That is, the pattern accuracy required to set the distance L to a value on the order of submicron by controlling the relative arrangement position of the electrodes 6 and 7 and the formation direction of the metallic carbon nanotubes 8 and 9 is directly subtracted from the distance L. Compared to the pattern accuracy required when setting the value to the micron order, it is easy to use with ordinary visible light photolithography equipment without using expensive equipment such as an electron beam lithography system. The distance L that becomes the channel length can be set to a value on the order of submicrons.

  Also, the resistance of metallic carbon nanotubes is sufficiently small compared to semiconducting carbon nanotubes, and therefore the channel resistance is increased when metallic carbon nanotubes 8 and 9 are used as source / drain electrodes in the field effect transistor of FIG. And a large power gain can be obtained.

  The effects of the present invention as described above are not limited to the case where semiconducting carbon nanotubes are used in the channel, but can be obtained in the same manner when a normal semiconductor layer is used as the channel. Further, metallic carbon nanotubes are formed from only one of the electrode 6 and the electrode 7 to be a source electrode or a drain electrode, and either the temporary source electrode 2 or the temporary drain electrode 3 is a corresponding drain electrode or source electrode. Sometimes, the effects of the present invention can be obtained as well.

  By using metallic carbon nanotubes as a source electrode or a drain electrode, a field effect transistor having a channel length on the order of submicron was realized using an ordinary visible light photolithography apparatus.

  First, a method for forming a carbon nanotube used as a channel in the field effect transistor according to the present invention will be described with reference to FIGS. First, as shown in FIG. 2A, a silicon oxide film 11 having a thickness of 200 nm is formed on a silicon substrate 10 by a thermal oxidation method. Then, a temporary source electrode 14 made of an Al film 12 having a thickness of 5 nm and an Fe film 13 having a thickness of 1 nm is formed on the silicon oxide film 11 using a known lift-off method. The Fe film 13 has a catalytic action for the growth of carbon nanotubes.

  Next, as shown in FIG. 1B, an Al film having a film thickness of 6 nm is formed at a position away from the temporary source electrode 14 by a predetermined distance, for example, 5 μm, by the lift-off method described above, thereby forming the temporary drain electrode 15.

  Next, as shown in FIG. 2C, a semiconductor carbon nanotube 16 is grown from the temporary source electrode 14 toward the temporary drain electrode 15 to form a channel. The semiconductor carbon nanotubes 16 were grown by a CVD method using acetylene gas as a process gas and Ar gas as a carrier gas. Here, when the pressure is set to 100 Pa and the substrate temperature is set to 600 ° C. and a DC voltage is applied between the temporary source electrode 14 and the temporary drain electrode 15, the Fe film 13 formed on the surface of the temporary source electrode 14 is The carbon nanotubes start to grow, continue to grow parallel to the surface of the silicon substrate 10 along the electric field direction, and stop after reaching the temporary drain electrode 15.

  During the growth of the carbon nanotubes described above, when the substrate temperature is raised, the Fe film 13 is finely separated into particles on the surface of the temporary source electrode 14 by being affected by the wettability with respect to the Al film 12 as a base. Then, a large number of carbon nanotubes grow from the temporary source electrode 14 toward the temporary drain electrode 15 using each separated Fe particle as a growth base point. The diameter of the Fe particles on the surface of the temporary source electrode 14 depends on factors such as the film thickness of the Fe film 13 and the substrate temperature in addition to the wettability to the Al film 12. In general, when the diameter of Fe particles as a catalyst is small, the grown carbon nanotubes have semiconducting properties, and when the particle size becomes large, they become metallic. Here, since the carbon nanotube is used as a channel, the film thickness of the Fe film 13 is set to be as thin as 1 nm, thereby reducing the diameter of the Fe particles and forming the semiconducting carbon nanotube 16.

  As shown in FIG. 2 (c), the carbon nanotubes that have started growing on the surface of the temporary source electrode 14 are actually grown in the downward direction as shown by the dotted line in the figure. After growing along the oxide film 11 and reaching the temporary drain electrode 19, the growth is stopped. Here, for simplicity, the carbon nanotubes 16 grow linearly between the temporary source electrode 14 and the temporary drain electrode 15. It draws like so. The same applies to the drawings referred to below.

  Next, a method for manufacturing a field effect transistor using the formed carbon nanotube 16 as a channel will be described. FIG. 3A is a perspective view showing a semiconducting carbon nanotube formed as a channel on a silicon substrate using the method described in FIG. 2, and the same components as those in FIG.

  Following the process described in FIG. 2, as shown in FIG. 3B, the electric field applying electrodes 17, 18, and 19 made of a Ta film with a thickness of 10 nm are formed using a known lift-off method, A catalyst electrode 20 composed of an Al film with a thickness of 5 nm and an Fe film with a thickness of 3 nm is formed using a similar lift-off method. As seen in the figure, the electric field application electrode 17 is arranged on one side with the formation direction of the carbon nanotubes 16 serving as the channels in between, and the electric field application electrodes 18 and 19 are arranged on the opposite side. Further, the catalyst electrode 20 is on the same side as the electric field application electrode 17 across the formation direction of the carbon nanotubes 16 and includes the electric field application electrode 17 and the electric field application electrode 18, and the electric field application electrode 17 and the electric field application electrode 19. Place on the connecting line.

  Next, as shown in FIG. 4A, carbon nanotubes are grown from the catalyst electrode 20 using the CVD method. Here, acetylene gas is used as the process gas, Ar gas is used as the carrier gas, the pressure is set to 100 Pa, and the growth temperature is set to 600 ° C. Then, when the electric field application electrode 17 is grounded and a DC voltage is applied to the electric field application electrodes 18 and 19, the carbon nanotubes 21 and 22 that have started to grow on the catalyst electrode 20 are connected between the electric field application electrodes 17 and 18, respectively. It grows along the electric field generated between the application electrodes 17 and 19 and intersects with the carbon nanotubes 16 that become channels, and further grows and stops when it reaches the electric field application electrodes 18 and 19.

  As described above, when the carbon nanotube used as the channel is formed, the Fe film serving as the catalyst has a semiconducting property by reducing the film thickness to 1 nm, but here it is formed on the surface of the catalyst electrode 20. The metallic carbon nanotubes 21 and 22 were grown by increasing the film thickness of the Fe film to 3 nm and increasing the diameter of the Fe particles.

  Next, as shown in FIG. 4B, the catalyst electrode 20, a part of the carbon nanotubes 21 and 22 thereon, and the electric field applying electrode 17 are removed by ion milling. As a result, the metallic carbon nanotubes 21 and 22 are separated to form a source electrode and a drain electrode, respectively. In order to actually use the metallic carbon nanotubes 21 and 22 as a source electrode and a drain electrode, a conductive film pattern is formed at each end portion to be connected to an internal circuit, which is omitted in the figure.

  Next, a Ti film having a thickness of 10 nm and an Au film having a thickness of 100 nm are deposited on the back surface of the silicon substrate 10 by vapor deposition to form a gate electrode 23.

  FIG. 5 is a plan view of the field effect transistor shown in FIG. 4A, in which the metallic carbon nanotubes 21 and 22 are arranged in the direction of the electric field generated between the electric field applying electrode 17 and the electric field applying electrodes 18 and 19, respectively. It shows a state of being formed along. Here, the channel length of the field effect transistor is determined by the distance L between two points where the metallic carbon nanotubes 21 and 22 intersect with the semiconducting carbon nanotube 16, and the distance L is determined by the electric field applying electrodes 18 and 19. The distance L1 is controlled by the distance L1 between the semiconductor carbon nanotube 16 and the electric field applying electrode 17, and the distance L3 between the semiconductor carbon nanotube 16 and the electric field applying electrode 19.

  For example, if L1, L2, and L3 are each set to 2 μm, L = 1 μm, and if L1 and L2 are each set to 2 μm and L3 is set to 18 μm, L = 0.2 μm. That is, even when L1, L2, and L3 are set to values that can be set by a photolithography apparatus that uses visible light as a light source, the source-drain distance L can be easily controlled to a value on the order of submicrons.

  In the above embodiment, the case where both the source electrode and the drain electrode are composed of metallic carbon nanotubes has been described. However, only one of the source electrode and the drain electrode is composed of metallic carbon nanotubes 21 or 22, and the provisional source electrode 14 or provisional electrode is constructed. The drain electrode 15 may be used as the other electrode.

  In the above embodiment, the case where the semiconductor carbon nanotube is used as the channel has been described. However, a normal semiconductor layer can also be used as the channel.

  Since the field effect transistor described in the first embodiment has a structure in which the back surface of the silicon substrate 10 is the entire gate electrode, the manufacturing process is simplified, but the gate parasitic capacitance is increased and the high frequency characteristics may be deteriorated. . In order to avoid this, a top gate structure in which a gate electrode is formed on the surface of the silicon substrate 10 as described below can be adopted.

  In this embodiment, the same steps as those in Embodiment 1 are used until the gate electrode 23 is formed on the back surface of the silicon substrate 10 in FIG. Thereafter, as shown in FIG. 6A, an insulating film 24 having a film thickness of 50 nm is formed on the surface of the silicon substrate 10 on which the semiconductor carbon nanotubes 16 serving as channels are formed by the SOG method. Then, electric field applying electrodes 25 and 26 made of a Ta film having a thickness of 10 nm are formed on the insulating film 24 by a lift-off method. Here, the electric field applying electrodes 25 and 26 are arranged on both sides of the semiconductor carbon nanotube 16 formed under the insulating film 24. A catalyst electrode 27 made of a laminate of an Al film having a thickness of 5 nm and an Fe film having a thickness of 3 nm is disposed on the side on which the electric field application electrode 25 is formed on the insulating film 24 with the semiconducting carbon nanotubes 16 interposed therebetween. Form.

  Next, as shown in FIG. 6B, metallic carbon nanotubes 28 are formed by the CVD method similar to the above in the state where a voltage is applied between the electric field applying electrodes 25 and 26 to form a gate electrode.

  In the above configuration, although the higher pattern accuracy is required for setting the formation position of the metallic carbon nanotube 28 to be the gate electrode than in the first embodiment, the channel length is determined by the diameter of the metallic carbon nanotube 28. Compared to Example 1, the channel length can be shortened and the gate parasitic capacitance can be reduced.

  Next, a method for forming a field effect transistor according to another embodiment of the present invention will be described with reference to FIGS.

  The process until the formation of the semiconducting carbon nanotube to be the channel is the same as the process shown in FIG. In this example, the arrangement of the electric field application electrode and the catalyst electrode is different from that in Example 1, and after forming the semiconducting carbon nanotubes 16 as shown in FIG. Electric field applying electrodes 29 and 30 are formed on both sides of the sandwiched electrode, and two catalyst electrodes 31 and 32 are formed on one side of the semiconducting carbon nanotube 16. Here, the same materials as those used in Example 1 are used for the voltage application electrodes 29 and 30 and the catalyst electrodes 31 and 32.

  Next, as shown in FIG. 7 (b), when a voltage is applied between the electric field applying electrodes 29 and 30, and the same CVD method as described above is used, the metallic properties that have started to grow on the catalyst electrodes 31 and 32, respectively. The carbon nanotubes 33 and 34 grow along the direction of the electric field generated between the electric field applying electrodes 29 and 30 and stop growing when reaching the electric field applying electrode 29. Thereafter, the electric field applying electrodes 29 and 30 are removed by ion milling, and further, the metallic carbon nanotubes 33 and 34 in the vicinity of the electrode 29 are partially removed, so that the metallic carbon nanotubes 33 and 34 are separated to form source electrodes, respectively. Can be used as a drain electrode.

As in the first embodiment, a conductive film formed on the back surface of the silicon substrate 10 can be used as the gate electrode, or a top gate structure can be formed through the same manufacturing process as in the second embodiment.
(Supplementary note 1) It is provided with a channel formed parallel to the substrate surface, and at least one of the source electrode and the drain electrode is made of metallic carbon nanotubes formed so as to cross the channel parallel to the substrate surface. A characteristic field effect transistor.
(Supplementary Note 2) The field effect transistor according to claim 2, wherein the source electrode and the drain electrode are made of metallic carbon nanotubes formed so as to cross the channel at different angles.
(Supplementary Note 3) The field effect transistor according to claim 1, wherein the gate electrode is formed of metallic carbon nanotubes formed so as to cross the channel and the metallic carbon nanotubes through an insulating film parallel to the substrate surface. .
(Supplementary Note 4) The field effect transistor according to claim 1, wherein the channel is made of semiconducting carbon nanotubes.
(Supplementary Note 5) A step of forming a channel parallel to the substrate surface, and forming a metallic carbon nanotube so as to cross the channel parallel to the substrate surface to form a source electrode and / or a drain electrode A method of manufacturing a field effect transistor.
(Additional remark 6) The said metallic carbon nanotube which forms two metallic carbon nanotubes which cross | intersect at a mutually different angle from the said channel is used as a source electrode, and the other metallic carbon nanotube is used as the drain electrode characterized by the above-mentioned A method of manufacturing a field effect transistor.
(Supplementary Note 7) The manufacture of the field effect transistor according to claim 1, wherein a metallic carbon nanotube is formed so as to cross the channel and the metallic carbon nanotube through an insulating film in parallel with the substrate surface to form a gate electrode. Method.
(Additional remark 8) The manufacturing method of the said field effect transistor characterized by forming a semiconducting carbon nanotube in parallel with a substrate surface, and making it a channel.

The perspective view which shows the structure of the field effect transistor which concerns on this invention. (A)-(c) Process sectional drawing which shows the formation method of a carbon nanotube. (A), (b) The perspective view which shows the manufacturing method of the field effect transistor which concerns on Example 1 (the 1). (A), (b) The perspective view which shows the manufacturing method of the field effect transistor which concerns on Example 1 (the 2). 1 is a plan view of a field effect transistor according to Example 1. FIG. (A), (b) The perspective view which shows the manufacturing method of the field effect transistor which concerns on Example 2. FIG. (A), (b) The perspective view which shows the manufacturing method of the field effect transistor which concerns on Example 3. FIG. The perspective view which shows the conventional field effect transistor using a carbon nanotube.

Explanation of symbols

1, 35 Substrate 2, 14 Temporary source electrode 3, 15 Temporary drain electrode 4 Channel 5, 23, 39 Conductive film 6, 7 Electrode 8, 9, 21, 22, 28, 33, 34 Metallic carbon nanotube 10 Silicon substrate 11 Silicon oxide film 12 Al film 13 Fe film 16, 38 Semiconducting carbon nanotubes 17, 18, 19, 25, 26, 29, 30 Electric field application electrode 20, 27, 31, 32 Catalyst electrode 24 Insulating film 36 Source electrode 37 Drain electrode

Claims (5)

  An electric field comprising a channel formed in parallel with the substrate surface, wherein at least one of the source electrode and the drain electrode is composed of metallic carbon nanotubes formed so as to cross the channel in parallel with the substrate surface. Effect transistor.   2. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are made of metallic carbon nanotubes formed to cross the channel at different angles.   3. The electric field according to claim 1, wherein the gate electrode is composed of metallic carbon nanotubes formed so as to cross the channel and the metallic carbon nanotubes through an insulating film parallel to the substrate surface. Effect transistor.   4. The field effect transistor according to claim 1, wherein the channel is made of a semiconducting carbon nanotube. Forming a channel parallel to the substrate surface;
A method of manufacturing a field effect transistor, characterized in that metallic carbon nanotubes are formed so as to cross the channel in parallel with the substrate surface to form a source electrode and / or a drain electrode.

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