JPH0585899A - Preparation of needlelike single crystal - Google Patents

Abstract

PURPOSE:To epitaxially grow a needlelike single crystal of a kind the same or different from that of a substrate crystal by applying a voltage to an electroconductive needle in the vicinity of the substrate crystal, ionizing atoms in a gas and embedding the ionized atoms in a prescribed position of the substrate crystal. CONSTITUTION:A chamber 6 is evacuated to about 10<-8>Torr and a substrate [e.g. n type (111) GaAs] 1 is heated to about 600 deg.C. The temperature is then lowered to about 100 deg.C. Tetraethyltin gas is injected from a nozzle 4 and kept at about 10<-6>Torr. An electrically conductive needle 2 is approached to a position at a distance of tens of nm from the surface of the substrate 1 and a positive voltage of 10V is applied for 1 ms to embed tin atoms in the surface of the substrate 1, which is then transferred to a chamber 7. A gate valve 8 is closed to regulate the temperature of the substrate 1 to about 350 deg.C The objective raw material gas (e.g. a mixed gas of trimethylgallium and arsine) for the objective needlelike single crystal is injected from a nozzle 10 and a valve of a vent hole 11 is regulated to adjust the internal pressure to about 50Torr. Thereby, the needlelike single crystal (e.g. GaAs) is grown from the above-mentioned tin atoms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a needle-shaped single crystal, and more particularly to a method for producing a needle-shaped single crystal that can be used in electronic devices.

[0002]

2. Description of the Related Art It can be said that there is no technique for growing a needle-shaped single crystal (whisker) at an intended position, but its growth mechanism has been studied for a long time. For an overview, see, for example, Toshio Kuroda: "Crystals are alive" Science Company
pp. 247-250, 1. Preferential spiral growth by screw dislocation, 2. VLS (va) that grows while always depositing droplets on the tips of whiskers
pour phase-liquid phase-s
The solid phase mechanism and the like. In each of these, we investigated the cause of accidental needle-shaped crystal formation,
It cannot be said that the mechanism is clarified, and for the purpose of engineering, it does not describe a technique for producing a needle-shaped single crystal at a predetermined position in a designed size. Keiichi Haraguchi et al. 3 attempted to positively utilize needle-shaped single crystals for electronic devices.
Name: "pn junction characteristics of GaAs quantum wire crystals" Proceedings of the Joint Lecture on Applied Physics Autumn 1990, 28p
-M-1, page 1117 has a report example. For the growth method of these crystals, see Applied Physics Letters. 59, No. 4, 22, pp. 431-433 (H
iruma, T .; Katsyuyama, K .; Ogaw
a, M. Koguchi, H .; Kakibayashi
and G.D. P. Morgan: Quantum s
size microcrystals grow u
sing organometallic vapor
phase epitaxy, Appl. Phys.
Lett. 59 (4), 22 July 1991. )
However, regarding the growth mechanism, only speculative results with the VLS mechanism are described, and growing a fine wire crystal (acicular single crystal) at a specific position is not described.

[0003]

As described above, there is no technique for precisely determining the position of each needle-shaped single crystal in advance and growing the needle-shaped single crystal, and it has not been possible to control the generation of the needle-shaped single crystal. Therefore, there is a drawback that the designability of the element is lacking.

An object of the present invention is to eliminate these drawbacks and to provide a technique for growing a needle-shaped single crystal at a predetermined position.

[0005]

According to the present invention, a voltage is applied to a conductive needle that is brought close to the surface of a substrate crystal, and a gas or liquid existing between the tip of the needle and the surface of the substrate crystal is applied. A needle that is the same as or different from the substrate crystal by ionizing the contained atoms and embedding the ionized atoms in the surface of the substrate crystal by the repulsive force by the electric field at the tip of the needle, and then using the embedded atoms as nuclei -Shaped single crystal is epitaxially grown on the surface of the substrate crystal.

Further, according to the present invention, a focused ion beam is formed to inject ions into the surface of a substrate crystal, and needle-like single crystals of the same kind or different kinds as the substrate crystal are epitaxially grown on the surface of the substrate crystal by using the injected atoms as nuclei. It is characterized in that

[0007]

According to the present invention, an extremely thin single crystal having a diameter of 100 nm or less can be produced in an intended place, and a semiconductor thin wire structure for which a quantum effect can be expected, or a mechanism part of a micromachine, a sensor part, an electron emission. Since it can be used for filaments, etc., it has a large application field centered on the electronics industry.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 The production of a needle-shaped single crystal according to the present invention is divided into two processes.

First, there is a process of embedding an atom or molecule serving as a nucleus for acicular crystals in an intended position of a substrate crystal, and second, a needle-like single crystal is grown on the basis of the nucleus. Is a process. FIG. 1 shows the principle of an apparatus for carrying out these processes, and a mechanism portion 3 for bringing a conductive needle 2 close to the substrate 1 serves as a nucleus in the gap between the needle tip and the substrate. It is installed in a chamber 6 having a nozzle 4 and an exhaust hole 5 for flowing a source gas for supplying atoms. A voltage can be applied to the needle 2 from the electric terminal 2A.

The chamber 6 is vertically connected to the chamber 7 for performing the second growth process via the gate valve 8, and the above-mentioned structure is obtained by vertically moving the substrate support 9 having a heating mechanism 9A such as a heater. The two processes can be performed sequentially. In this embodiment, tin (Sn) is used as a nucleus atom, and the substrate 1 is made of n-type (111) Ga.
The case of As will be described. Set chamber 6 to 10 ^-8 T
After evacuating to a high vacuum of about orr, the substrate 1 is about 600
Heat to ℃. By this heating, the natural oxide film formed on the substrate surface is removed, and an atomically clean substrate surface is obtained.

Next, the temperature of the substrate 1 is lowered to 100 ° C., and tetraethyltin (TEn) gas is injected from the nozzle 4 to 1
The atmospheric pressure is maintained at about 0 ^-6 Torr. When the tungsten needle 2 is brought close to the position of several tens nm from the surface of the substrate 1 and a positive voltage of 10 V is applied to the substrate surface for 1 ms, T
ESn is decomposed into molecules mainly composed of tin atoms and ethyl groups, and several positively ionized tin atoms are electrically repelled from the tip of the needle 2 and embedded in the lattice of surface GaAs atoms of the substrate 1. Needle 2 for nucleation at another location
The substrate 1 is two-dimensionally moved while the position of is fixed and the same process is performed.

Next, the substrate 1 is transferred to the chamber 7, the gate valve 8 is closed, and then the temperature of the substrate 1 is set to 350.degree.
From the nozzle 10, trimethylgallium (TMG: room temperature suction type container) 5 cc, which is a raw material of GaAs, and arsine (As
(H ₃ : Suction from a 100% container) By injecting 15 cc of mixed gas and adjusting the valve of the exhaust hole 11 to set the internal pressure of the chamber 7 to 50 Torr, the tin atom was embedded in the first process. , The diameter of the root is about 150Å
When the needle-shaped single crystal of No. 1 grows and the growth height becomes about 1 μm, the diameter becomes 10 nm, and the diameter hardly changes even if it is grown further.

The voltage applied to the needle when forming the nucleus is 15 to
When the voltage is set to 20 V and the time is set to about 500 ms, the tin atoms form a cluster having a diameter of about 80 nm and form a kind of island in the substrate crystal. When acicular single crystals are grown with these islands as nuclei, crystals with a diameter of several tens nm grow. Considering these crystal growth mechanisms, when tin is a nucleus of several atomic layers, the volume is not enough to form droplets of tin and gallium, and the surface of the substrate crystal is laminated between 1 and 2 atomic layers. Forming a defect. In cubic crystals of diamond structure, such as gallium arsenide and silicon, half dislocations are formed around stacking faults. Usually, since half dislocations have a screw dislocation component in their Burgers vector, the stacking faults are the source of screw dislocations. It is thought that spiral growth occurred. On the other hand, the growth of a needle-shaped single crystal having nuclei of atoms gathered in a cluster form is judged from the cluster diameter to Sn.
-The size is such that Ga droplets can be formed. When this droplet is formed, when arsenic in the growth atmosphere is dissolved into the droplet and becomes supersaturated, epitaxial growth occurs on the substrate crystal.
This growth mechanism is due to the VLS mechanism. Therefore, it was shown that this method can control the mechanism of the needle-shaped single crystal itself by the voltage applied to the needle tip and the application time. Further, in this embodiment, the shape of the conductive needle tip is extremely important, and the tip was electrolytically polished and then sharpened by ion milling, and the radius of curvature was about 10 nm. When the radius of curvature is larger than this, clusters can be formed, but controlling the applied voltage is not always easy to control the generation of screw dislocations.

Example 2 As shown in Example 1, by embedding tin atoms into the crystal layer on the surface of the GaAs substrate, nuclei of needle-like single crystals can be formed, but a focused (focused) ion beam is used as the embedding method. Can be used. FIG. 2 shows a focused ion implantation apparatus using tin as an ion source, which includes an ion source 12, a focusing magnet 13 of the ion source, an ion beam scanning electromagnet 14,
And the substrate stage 15. The chamber 16 in which the substrate stage 15 is housed is a gate valve 1
7 is connected to the growth chamber 18 in the horizontal direction via 7, and after injecting tin ions into a predetermined position of the substrate crystal 1 in the chamber 16, the substrate crystal is moved to the growth chamber 18 and the gate valve is closed. It has a structure for growing GaAs.

First, a focused ion beam 12A is formed by the ion source 12 and the magnet 13, and the scanning electromagnet 14 is used to implant ions at a predetermined position in the substrate crystal. The minimum convergent diameter of an ordinary ion beam is about 20 nm.
40kV due to substrate crystal damage due to ion implantation
Even if it is injected at a low speed for about 30 seconds, the surrounding area 2
The atomic arrangement of 0 to 30 nm gallium and arsenic is disordered. Therefore, it is necessary to move the substrate crystal 1 to the growth chamber 18 and then perform annealing in arsine at 600 ° C. for several minutes by the heating mechanism 16A to restore the atomic arrangement of the crystal on the surface to the original state. In this way, after forming a nucleus portion at a predetermined position by ion implantation, and then performing GaAs crystal growth under the same conditions as in Example 1, needle-like crystals having a root diameter of 50 to 100 nm grow. .. In this case, the growth mechanism is as follows:
It is about 50 nm because it spreads by annealing, and it is due to the VLS mechanism because it is a size enough to form Sn-Ga droplets. However, in this ion implantation method, since the diameter of the focused ions is as large as 20 nm, it is not possible to distinguish the spiral growth mechanism due to the screw dislocation and the VLS mechanism as shown in Example 1 to grow needle crystals. .. In the future, if a technique capable of converging the beam diameter to about 1 nm can be developed, it is possible to artificially introduce the screw dislocation by the ion implantation method in principle.

As can be seen from the above explanation, the two main growth mechanisms of needle-like crystals are spiral growth with screw dislocations as nuclei, and VL.
It is clear that the present invention can be applied to either of the cases of the S mechanism, but the atomic species as the nucleus are atoms that make steps on the atomic plane when the screw dislocation is the nucleus. Since it is good, it may be an atom constituting the substrate crystal and does not specify the atomic species. On the other hand, VL
The S mechanism is based on the assumption that it forms an alloy with at least one element of the crystal composition that grows as needle crystals, and its melting point is lower than the melting point of the single crystal to be grown. Therefore, it is necessary to select an atomic species (a plurality of atoms can be simultaneously used) that satisfy these conditions. Further, the needle-like single crystal to be grown has been shown in the above as an example of homoepitaxial growth of the same kind as the substrate, but GaAs or I on silicon is used.
It is also possible to grow a needle-shaped single crystal by heteroepitaxial growth such as a compound semiconductor such as nP.

In the first embodiment, the gas is used to supply the atom serving as the nucleus, but a liquid may be used. It is possible to hang a diluted electrolytic solution of tin oxalate and water on the substrate and embed tin atoms in the substrate crystal with a needle as in Example 1. Also in the second process of growing needle crystals,
In addition to the organometallic raw material and the hydride shown in this embodiment as the raw materials, the hydride VPE method, the halide VPE method, the liquid phase method, and the electrolytic deposition method may be used.

[0019]

As described above, according to the present invention, a needle-shaped single crystal having a diameter of about 10 to 100 nm can be formed at an arbitrary position of a substrate crystal. Therefore, if this crystal is made of a conductive semiconductor, It can be used as a quantum wire device. Also, since a needle with a tip shape with an extremely small radius of curvature can be formed,
It can be used as a probe for a scanning tunneling microscope (STM) or as a filament for a field ion microscope (FIM). Furthermore, since the needle-shaped crystal is epitaxially grown on the substrate crystal, the mechanical coupling is extremely strong, so that the cantilever of the micromachine or the cantilever itself can be used as a pressure sensor. Alternatively, it is effective as a pin that captures bacteria, viruses and the like floating in the solvent by passing an electric current through the needle tip of the needle crystal.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configurations of a chamber for forming nuclei of needle crystals and a growth chamber.

FIG. 2 is a cross-sectional view showing the configurations of a chamber for forming nuclei of needle-like crystals by focused ion implantation and a growth chamber.

[Explanation of symbols]

1 Substrate Crystal 2 Conductive Needle 3 Vertical Driving Mechanism of Needle 4 Nozzle for Supplying Atoms to Be the Core of Needle Crystal with Raw Material on Gas 5 Exhaust Hole of Chamber 6 6 Core of Needle Crystal Chamber for growing 7 Chamber for growing needle-like crystals 8 Gate valve 9 Substrate heating stage 10 Supply nozzle for growth raw material 11 Exhaust hole for growth raw material 12 Ion source of atoms to be nuclei of needle-like crystals 13 Electromagnet for focusing ions 14 Electromagnet for scanning focused ion beam 15 Substrate stage 16 Focused ion implantation chamber 17 Gate valve 18 Growth chamber attached to focused ion beam implantation chamber

Claims (2)

[Claims] 1. A voltage is applied to a conductive needle placed close to the surface of a substrate crystal to ionize atoms contained in a gas or liquid existing between the tip of the needle and the surface of the substrate crystal. The ionized atoms are embedded in the surface of the substrate crystal by the repulsive force due to the electric field at the tip of the needle, and the acicular single crystal of the same type or different species as the substrate crystal is then used as the nucleus of the embedded atoms as the substrate crystal. A method for producing a needle-shaped single crystal, which comprises epitaxially growing the surface. 2. A focused ion beam is formed to inject ions into the surface of a substrate crystal, and acicular single crystals of the same kind or different kinds as the substrate crystal are epitaxially grown on the surface of the substrate crystal by using the injected atoms as nuclei. A method for producing a needle-shaped single crystal characterized by: