JP2007331953A - Atom-involved silicon cluster and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that the synthesis of an atomic metal-involved silicon cluster is reported up to now as a silicon cluster to be anticipated as a new electronics material but since the efficiency is extremely low when an ionized metal is produced, the silicon cluster can not be mass-produced. <P>SOLUTION: An atomic gas-involved silicon cluster is synthesized by reacting an atomic gas with silicon. An ionized gas is produced more easily in higher efficiency in comparison with the ionized metal. As a result, the silicon cluster can be mass-produced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a silicon cluster material containing gas atoms and a method for manufacturing the same.

Japanese Patent Laid-Open No. 2004-99349 S.M.Beck, J.Chem.Phys. 87 (1987) 4233 M. Ohara et al., Chem. Phys. Lett. 371 (2003) 490 K. Jackson et al., Chem. Phys. Lett. 254 (1996) 249

  In recent years, nanoclusters composed of carbon atoms, such as carbon fullerenes and carbon nanotubes, have been actively studied as new materials exhibiting excellent physical properties. Silicon, the same group IV element as carbon, is the most important device material for the current semiconductor industry, and many research assets have been accumulated for bulk silicon. On the other hand, nanoclusters consisting of silicon atoms, that is, silicon clusters, are expected to have excellent physical properties not found in bulk silicon and high consistency with silicon processes. Research is progressing as a material to realize.

1987, SMBeck et al, introduced a SiH ₄ / the He gas into the reaction chamber, by using a laser ablation method of irradiating a laser beam to the metal target, a silicon cluster _{MSi n (M = W, Co} , Cr, Mo , Cu, n = 15, 16) (Non-patent Document 1).
After that, Kanayama et al. Introduced SiH ₄ / He gas and metal vapor into the reaction chamber, radiated an electron beam to generate Si ions and metal ions, and used a quadrupole ion trap method to encapsulate metal atoms. silicon cluster MSi _n was synthesized (M = W, Nb, Ta , Re, Ir, Mo, Hf, n = 10, 12, 14, 16) and (Patent Document 1).
Furthermore, in 2003, Sakai et al. Vaporized metal and Si using a laser ablation method in which a metal rod and a Si rod were irradiated with laser light, and the generated vapor was cooled in high-pressure He gas to produce metal atoms. An embedded silicon cluster MSi _n (M = Ti, Hf, Mo, W, n = 15, 16) was synthesized (Non-patent Document 2).

According to the simulation, it is said that silicon clusters can exist stably by including atoms other than Si (Non-patent Document 3). On the other hand, all the silicon clusters containing atoms that have been reported in simulations and synthesis experiments so far were silicon clusters containing metal atoms. In other words, the metal atoms were the only atoms that succeeded in the synthesis of silicon clusters and proved that silicon clusters could be generated stably.
The reported metal atom-containing silicon clusters were synthesized by a special trap device (Patent Document 1) or a laser ablation method (Non-Patent Documents 1 and 2), and the device configuration was complicated. In addition, metal atoms have poor ionization efficiency, and there is a problem that a large amount of silicon clusters cannot be synthesized. In order to mass-produce silicon clusters, which are expected to be excellent new materials in the electronics field, at a level that can be industrially used, it is desired to develop a production method that can be synthesized with high production efficiency using a device with a simpler configuration. It was.

  The present invention (1) is an atom-containing silicon cluster that contains an inert gas atom.

The present invention (2) is the atomically encapsulated silicon cluster of the invention (1) whose chemical formula is represented by X @ Si _n (X = He, Ne, Ar, n = 12 to 18).

  The present invention (3) is a method for producing an atomically encapsulated silicon cluster that generates a silicon cluster that encapsulates inert gas atoms by reacting inert gas ions with silicon ions in plasma.

  The present invention (4) introduces an inert gas into a vacuum vessel, excites the inert gas by high frequency induction to generate an inert gas plasma, and simultaneously generates silicon ions in the vacuum vessel. The method for producing an atomically encapsulated silicon cluster according to the invention (3), wherein the inert gas ions and the silicon ions are reacted by being introduced into an inert gas plasma.

  The present invention (5) provides at least a vacuum vessel, a gas introduction pipe for introducing an inert gas into the vacuum vessel, a plasma generating means for ionizing the inert gas, and supplying silicon plasma into the vacuum vessel This is an apparatus for producing an atomically-encapsulated silicon cluster comprising silicon plasma generating means.

1. It has been demonstrated that silicon clusters can be stably generated as atomic-encapsulated silicon clusters not only when encapsulating metal atoms but also when encapsulating gas atoms.
2. Gas atoms are easier to ionize and have higher ion generation efficiency than metal atoms. By including gas atoms, silicon clusters can be manufactured with a simple configuration, enabling mass production.
3. By using an inert gas as the gas atoms contained in the silicon cluster, the safety of the synthesis work has increased.

  The best mode of the present invention will be described below.

(Gas atom inclusion silicon cluster)
The atomically encapsulated silicon cluster of the present invention is characterized in that it is a cluster encapsulating gas atoms. There are some reports of successful synthesis of gas atom inclusion clusters in carbon clusters. However, no papers mentioning gas-encapsulated silicon clusters have been submitted so far, and there have been no reports of successful synthesis.
The inventors have succeeded in synthesizing an Ar-containing silicon cluster for the first time by generating Si plasma by an electron beam and simultaneously generating inductively coupled Ar plasma to react Si ions with Ar ions. It is said that silicon clusters can be generated stably by including atoms. However, not only metal atoms that have been reported in the past but also silicon clusters can be generated stably even when gas atoms are used. It could be confirmed.
The use of gas atoms rather than metal atoms as the encapsulated atoms has a simpler device configuration and higher ion generation efficiency. Since general metal atoms are solid at room temperature, in order to be ionized, it is necessary to vaporize them by heating, electron beam irradiation, or ion beam irradiation. Therefore, the ion generation apparatus is complicated and the ion generation efficiency is low. In contrast, gas atoms are easily ionized and have high ion generation efficiency.
As the gas element to be included, it is particularly preferable to use an inert gas because it is safe, easy to handle, and easily ionized. In addition, in the inert gas plasma, the lifetime of Si ions and Si radicals is increased, and the amount of silicon clusters generated is also increased. The inventors tried to synthesize silicon clusters using He, Ne, Ar, and Kr. For He, Ne, and Ar, generation of atomic inclusion silicon clusters was confirmed, but for Kr, inclusion was not confirmed. It is considered that Kr could not be included in the cluster due to the relatively large atomic particle size.

Here, the “cluster” means an aggregate formed by combining a plurality of atoms and molecules of about 100 at most. Since the size of one aggregate is on the order of nanometers, it is also called a nanocluster. Clusters in which atoms and molecules are bonded in a spherical shape are called “fullerenes”, and clusters that are gathered in a cylindrical shape are called “nanotubes”.
The effects of inclusion of gas atoms on the physical properties of clusters have been reported for carbon fullerenes. In particular, the inert gas He, Ar, Kr, and Xe also reported that the physical properties of fullerenes can be changed. Has been. Accordingly, it can be sufficiently predicted that a silicon cluster material having excellent physical properties can be obtained by changing the physical properties of the silicon cluster even in the silicon cluster containing the inert gas.

(Production equipment for silicon clusters containing gas atoms)
FIG. 1 (a) is a schematic view of a specific example of the apparatus for producing a gas atom-containing silicon cluster according to the present invention. The manufacturing apparatus shown in FIG. 1 (a) includes a vacuum vessel 1, a vacuum pump 2, a Si plasma source 3, an inert gas introduction tube 4, a grid electrode plate 5, a high-frequency induction coil 6, and a deposition substrate 7.
Plasma generation and silicon cluster synthesis are performed according to the following procedure. First, the vacuum vessel 1 is depressurized by the vacuum pump 2. BACKGROUND vacuum is preferably not more than about 10 ^-3 Pa. Next, an inert gas, for example, Ar gas is introduced into the vacuum vessel 1 from the inert gas introduction tube 4, a high-frequency current is passed through the high-frequency induction coil 6, and the Ar gas is excited to generate Ar ions and positive ions. A plasma 8 is generated. A power source that supplies power to the high-frequency induction coil 7 includes a high-frequency power source 10, a matching box 11, and a blocking capacitor 12. The high-frequency power supply 10 is a power supply that supplies high-frequency power with a frequency of 13.56 MHz, and the high-frequency power can be controlled in the range of 0 to 300 W. Next, the Si plasma source 3 is operated to introduce Si positive ions into the plasma. Between the high frequency induction coil 6 and the Si plasma source 3, a grid electrode plate 5 is disposed. The potential of the grid electrode plate 5 is a ground potential. Thereby, the potential of the plasma 8 can be controlled, and at the same time, the plasma 8 can be prevented from flowing into the Si plasma source 3.
FIG. 1 (b) is a detailed view of the Si plasma source 3 shown in FIG. 1 (a) and is an explanatory view of the principle of generating Si plasma. The Si plasma source 3 includes a magnetic field applying means such as a crucible 15, an electron beam acceleration power source 17, a filament heating power source 18, an electron beam generating filament 19, and an electromagnetic coil. The Si solid raw material 16 is put into the crucible 15. First, a current is supplied to the electron beam generating filament 19 from the filament heating power source 18 to generate electrons from the filament 19. In the figure, an AC power source is used as the filament heating power source 18, but a DC power source can also be used. An acceleration voltage of about 4 kV is applied between the electron beam generating filament 19 and the crucible 15 by the electron beam acceleration power source 17. At the same time, the magnetic field B _EB is applied. Electrons generated from the filament 19 are accelerated by an acceleration voltage, bent in a traveling direction by a magnetic field, and irradiated onto the Si solid material 16 in the crucible 15. The Si solid raw material 16 is heated and evaporated by the collision of electrons, and is ionized to become plasma composed of Si ions 20 and electrons 21. The generation of Si ions was controlled by measuring the electron emission current I _EB .
In FIG. 1A, a stainless steel deposition substrate 7 is supported by a stainless steel rod at a position surrounded by the high frequency induction coil 6. Si ions 20 flow into the plasma 8, and Ar ions and Si ions in the plasma 8 react to deposit reaction products on the deposition substrate 7. In order to measure the state of the plasma 8, a plasma measurement probe 9 is disposed in the vicinity of the high frequency induction coil 6.
As described in the examples, the presence of Ar-encapsulated silicon clusters was confirmed in the reaction product on the deposition substrate. In addition to Ar, cluster synthesis experiments were also conducted for He and Ne in addition to Ar. In each case, formation of gas atom-containing silicon clusters was confirmed.

(Other configuration examples of manufacturing equipment)
In the schematic diagram shown in FIG. 1 (a), the gas plasma is generated by high frequency induction. However, the plasma generation is not limited to the high frequency induction, and the generation of the gas plasma or silicon cluster is also possible using direct current discharge, electron beam irradiation, or microwave discharge. Can be synthesized.
The generation of Si ions is not limited to the electron beam irradiation described with reference to FIG. 1B. For example, inert gas ions may be accelerated by an electrostatic field and collided with a Si raw material to be ionized. Furthermore, the silane gas may be introduced into the vacuum vessel simultaneously with the inert gas and ionized by, for example, high frequency induction.

(Metal atom inclusion silicon cluster production equipment)
By performing a simple modification to attach a metal target electrode to the gas atom-containing silicon cluster manufacturing apparatus shown in FIG. 1A, a silicon cluster including metal atoms can be manufactured. FIG. 2A is a schematic diagram of a specific example of a device for producing metal atom-containing silicon clusters. A target electrode plate 13 made of tungsten (W) is newly attached to the apparatus shown in FIG. 1A, and a negative voltage is applied by a bias voltage application power source 14. For example, the bias voltage is -500V.
FIG. 2B is an explanatory diagram of the principle of generating W plasma in the manufacturing apparatus shown in FIG. Ar positive ions 22 in the plasma 8 generated by high frequency induction are accelerated by a bias voltage applied to the target electrode plate 13 and collide with the target electrode plate 13. The W atoms constituting the target electrode plate 13 are ionized to become W ions 23 by the collision of Ar ions 22. The generated W ions 23 and Si ions 20 in the plasma 8 react to form W-containing silicon clusters, which are deposited on the deposition substrate 7. Mass analysis of the deposited product confirmed the presence of W-containing silicon clusters.
By using a target electrode plate produced using a metal material other than W, it is possible to synthesize different types of metal-containing silicon clusters. For example, it is possible to synthesize a metal-encapsulated silicon cluster that includes Nb, Ta, Re, Ir, Mo, Hf, Co, Cr, Cu, and Ti.
Since metal atoms are ionized in an inert gas plasma, the lifetime of metal ions and metal radicals is prolonged. Therefore, the generation efficiency of the silicon cluster is higher than that of the conventional method for producing a metal-encapsulating silicon cluster.

(Measurement of plasma parameters)
Generation of Si plasma, generation of Si-Ar plasma, and synthesis of the cluster were performed using the apparatus for manufacturing silicon clusters containing gas atoms shown in FIG. As process conditions, high-frequency power P _RF , Ar gas pressure P _Ar , and emission current I _EB of the Si plasma source were controlled. As plasma parameters, the electron density _ne and the electron temperature _Te were measured with a plasma measurement probe.
3 (a) it is not high-frequency power, also without introducing Ar gas, the electron density of the Si plasma generated by operating only Si plasma source n _e and the electron temperature T _e emission current I _EB of It is a dependency graph. It was confirmed that Si plasma with an electron density of the order of 10 ⁸ (cm ^-3 ) can be generated by setting the emission current I _EB to 50 mA or more.
FIG. 3 (b), actuates the Si plasma source, set the emission current I _EB to 100 mA, at the same time, Ar gas is introduced, and the electron density n _e of the Si-Ar plasma generated by high-frequency power it is a high-frequency power P _RF dependency graph of electron temperature T _e. The Ar gas pressure P _Ar was set to 0.1 Pa. The electron density when the high frequency power P _RF is 0 W is due to Si plasma. Increasing the high-frequency power P _RF increases the electron density, but this is due to the generation of Ar plasma. For example, by applying 400 W of high-frequency power, the electron density is about an order of magnitude higher than that of Si-only plasma. An increase in was observed.

(Mass spectrum)
FIGS. 4A and 4B are mass spectrometry data of products synthesized by Si plasma and Si-Ar plasma, respectively. Mass spectrometry was performed in a negative mode using a laser desorption time-of-flight mass spectrometer (LDTOF-MS).
FIG. 4 (a) is a mass analysis result of a product synthesized with a plasma containing only Si. The process conditions were I _EB = 100 mA, P _Ar = 0 Pa, P _RF = 0 W, synthesis time = 10 minutes. The peaks indicated by black circles are mass peaks corresponding to Si and Si clusters. Mass peak until Si ₁₀ gradually decrease, but the mass peaks exceeds Si ₁₀ drops sharply, it can be seen that the peak to Si ₁₇ can be observed. This means that a large silicon cluster that does not contain atoms cannot exist stably.
FIG. 4 (b) shows the mass analysis result of the product synthesized by Si-Ar plasma. The process conditions were I _EB = 100 mA, P _Ar = 0.1 Pa, P _RF = 300 W, synthesis time = 10 minutes. In the region where the mass number is 0 to 300, the same peak as the mass peak in the spectrum shown in FIG. Further, in the region of mass number 300 to 600, a new peak indicated by a black square is observed at a position shifted by 40 corresponding to the mass number of Ar with respect to a peak that is an integral multiple of the mass number 28 of Si. These peaks are observed only when Ar plasma is superimposed on Si plasma, and it is considered that a new substance with Ar acting on the Si cluster was generated. A prominent peak was observed in the mass number corresponding to ArSi _n (n = 12 to 18), and in particular, a large peak was observed in the mass number corresponding to ArSi _n (n = 15, 16). In addition, when Ar gas pressure was set in the range of 0.05 Pa-0.3 Pa, mass peaks corresponding to these new substances were observed.

(Composition analysis by XPS)
FIGS. 5A and 5B are XPS analysis data of products synthesized by Si plasma and Si-Ar plasma, respectively.
FIG. 5A shows XPS analysis data of a product synthesized with a plasma containing only Si. The process conditions were I _EB = 100 mA, P _Ar = 0 Pa, P _RF = 0 W, synthesis time = 10 minutes. In the data shown in FIG. 5 (a), a peak indicating the presence of Si is observed. In addition, peaks indicating the presence of C and O are also observed, but these are thought to be due to impurities mixed in from the air.
FIG. 5 (b) is XPS analysis data of the product synthesized with Si-Ar plasma. The process conditions were I _EB = 100 mA, P _Ar = 0.1 Pa, P _RF = 300 W, synthesis time = 10 minutes. In the data shown in FIG. 5 (b), a new peak indicating the presence of Ar was confirmed.
In the compositional analysis data by XPS, the presence of Ar in addition to the Si clusters was confirmed, indicating that a new substance consisting of Ar and Si clusters was generated. In addition, in the laser desorption time-of-flight mass spectrometry, Ar was not dissociated, but the substance incorporated into the Si cluster was observed. Therefore, it is considered that Ar in the new substance exists outside the Si cluster. Hateful. These indicate that the generated new substance is an Ar-containing silicon cluster.

(a) And (b) is the schematic of the specific example of the manufacturing apparatus of the gas atom inclusion silicon cluster which concerns on this invention, respectively, and explanatory drawing of the Si plasma production | generation principle. (a) And (b) is the schematic of the specific example of the manufacturing apparatus of a metal atom inclusion silicon cluster, respectively, and explanatory drawing of the W plasma production | generation principle. (a) and (b) are data of electron density and electron temperature in Si plasma and Si-Ar plasma, respectively. (a) and (b) are mass spectrometric data of the products synthesized by Si plasma and Si-Ar plasma, respectively. (a) and (b) are XPS analysis data of products synthesized by Si plasma and Si-Ar plasma, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Vacuum pump 3 Si plasma source 4 Inert gas introduction tube 5 Grid electrode plate 6 High frequency induction coil 7 Deposition substrate 8 Plasma 9 Probe for plasma measurement 10 High frequency power supply 11 Matching box 12 Blocking capacitor 13 W Target electrode plate 14 Bias Voltage application power source 15 Crucible 16 Si solid material 17 Electron beam acceleration power source 18 Filament heating power source 19 Electron beam generating filament 20 Si ion 21 Electron 22 Ar ion 23 W ion

Claims (5)

Atomic silicon clusters that contain inert gas atoms. The atomic inclusion silicon cluster according to claim 1, wherein the chemical formula is represented by X @ Si _n (X = He, Ne, Ar, n = 12 to 18). A method for producing an atomically encapsulated silicon cluster, wherein a silicon cluster enclosing an inert gas atom is generated by reacting an inert gas ion and a silicon ion in plasma. An inert gas is introduced into a vacuum vessel, and the inert gas is excited by high frequency induction to generate an inert gas plasma. At the same time, silicon ions are generated in the vacuum vessel and introduced into the inert gas plasma. 4. The method for producing an atomically encapsulated silicon cluster according to claim 3, wherein the inert gas ions and the silicon ions are reacted. At least a vacuum vessel, a gas introduction pipe for introducing an inert gas into the vacuum vessel, a plasma generation means for ionizing the inert gas, and a silicon plasma generation means for supplying silicon plasma into the vacuum vessel An atomic inclusion silicon cluster manufacturing device.

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