JP2008037716A - Method for producing semiconductor fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing semiconductor fine particles for producing fine particles with uniform particle sizes. <P>SOLUTION: Semiconductor fine particle raw materials are beforehand mixed at a low temperature in a glass capillary 4 with the inside diameter of 1 μm to 1 mm so as to control the polymerization degree of a precursor, thus the precursor having a uniform and selective molecular weight is produced. By continuously introducing the precursor into a flask 8 of a higher temperature (reaction temperature), semiconductor fine particles with uniform particle sizes are produced. By heating the flow passage directly after the mixing of the raw material solutions to a temperature lower than a fine particle producing temperature, higher size selectivity can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing semiconductor fine particles. Specifically, the present invention relates to a method for producing nanometer-scale semiconductor fine particles (nanoparticles) having a uniform particle size.

The production of fine particles and nanoparticles has been conventionally performed by the following method.
(Method by classification after synthesis)
A method is known in which fine particles are synthesized and sorted according to size by a method such as a precipitation method (hereinafter referred to as a first method). For example, when producing InP fine particles, InP fine particles are synthesized by a synthesis method with low size selectivity, and then sorted according to size by a method such as a precipitation method (see, for example, Non-Patent Documents 1 and 2). In other words, this is a technique for obtaining InP fine particles having a uniform size by synthesizing InP fine particles without synthesizing the fine particles with size selectivity.

  By heating indium chloride or indium oxalate and tristrimethylsilylphosphine (P (TMS) 3) in trioctylphosphine (TOP) or trioctylphosphine oxide (TOPO) at a temperature of about 300 ° C. for several days, InP fine particles with an extremely wide size distribution are synthesized. After the heat treatment, the reaction solvent is removed, and a poor solvent such as methanol is gradually added to the toluene dispersion of the produced InP fine particles. Thereby, the generated precipitate is separated by centrifugation. At this time, the particles having a large particle size are aggregated and precipitated. By repeating the addition of a poor solvent and the separation by centrifugation, fine particles classified for each particle size are obtained.

(Methods based on reaction system)
A technique is known in which the P raw material solution is added to the In raw material solution heated to the reaction temperature in a short time and the growth process of the fine particles is made as uniform as possible to narrow the size distribution of the generated fine particles (hereinafter referred to as “second”). Method). Heat an octadecene (OED) solution of indium long-chain fatty acid salt (10 to 18 carbon atoms) to a temperature of 250 to 300 ° C. and add the ODE solution of P (TMS) 3 in as short a time as possible while stirring rapidly. Have reported the synthesis of InP fine particles with a narrow particle size distribution (see Non-Patent Documents 3 and 4).

  This second approach is an effort to align the precursor that occurs in the initial stage of the reaction and the reaction stage in which the precursor is grown to produce fine particles. Therefore, although InP fine particles having a narrow particle size distribution are generated, fine particles having an arbitrary desired size have not been obtained. In Non-Patent Document 3, InP fine particles are grown using a multi-stage reaction in which an In raw material solution and a P (TMS) 3 solution are added to a reaction system alternately. However, the width of the controllable particle size is narrow, and it is only in the wavelength range of 550 to 580 nm when converted to the wavelength absorbed by the fine particles.

  Non-Patent Document 4 reports that the size of the generated fine particles can be controlled by changing the alkyl chain length of the fatty acid or by heating at a temperature of 200 to 250 ° C. immediately after mixing the solution. Again, the controllable particle size range is narrow and similar to Non-Patent Document 3. In addition, when the heating time is lengthened, the particle size distribution width is widened, and the particle size is not selective.

(Example of compound semiconductor synthesis using a narrow channel)
As a method for producing nanoparticles, the material is rapidly heated to the reaction start temperature while continuously supplying the raw material into a fine channel having an inner diameter of 1 μm to 1 mm arranged in the heating zone, and after the reaction is performed, the particle size is decreased by rapid cooling. A method for producing nanoparticles of 1 nm to 1 μm (hereinafter referred to as a third technique) is known (see, for example, Patent Document 1). The synthesis of compound semiconductors using this narrow channel is a technique that has been successful in size-selective synthesis of II-VI compound semiconductor fine particles such as CdSe.

  In Non-Patent Document 5 using this third method, CdSe fine particles having a uniform size can be obtained by mixing raw materials, filling a syringe, and flowing it at a constant speed in a glass capillary heated to an arbitrary particle synthesis temperature. Synthesizing. In Non-Patent Document 6, the Cd raw material solution and the Se raw material solution are filled in separate syringes, and these raw material solutions are mixed in a mixer. The mixed raw material solution is passed through a glass capillary heated to the reaction temperature to obtain CdSe fine particles in a size-selective manner. In the case of using the third method, precipitation of the raw material or the reaction product is observed on the reactor wall, and therefore, the particle size distribution may be changed, expanded, and further clogged. This is avoided by surface modification (coding) on the inner wall of the capillary.

JP 2003-225900 A JP 2005-125280 A A. A. Guzelian et al., J. Phys. Chem. 1996, 100, 7212. O. I. Micic et al., J. Phys. Chem. B, 1997, 101, 4904. D. Battaglia and X. Peng, Nano Lett. 2002, 2, 1027. D. W. Lucey et al., Chem. Matter. 2005, 17, 3754. H. Nakamura et al., Chem. Comm. 2002, 2844. B. K. H. Yen et al., Adv. Mater. 2003, 15, 1858.

  The first method requires a complicated process of adding a poor solvent at the post-treatment stage and repeatedly collecting the precipitate by centrifugation. In addition, the synthesis method itself is not size-selective and involves a large amount of fine particles that are not of the desired size, so the efficiency is extremely low.

  In the second method, precise temperature control of the reaction system is necessary, but it is expected that the difficulty rapidly increases with the scale-up, and the size selectivity is rapidly lost. In addition, in order to obtain fine particles of a specific size, a complicated multi-stage particle growth reaction is often required. Furthermore, it is highly likely that accidents such as fires will occur if a large amount of P raw material having a very high activity is poured into a high-temperature reaction solution at a time, which is problematic in terms of safety.

  It has been confirmed by the inventors that the third method has a problem in synthesis depending on the reaction system used. Specifically, when trying to produce InP nanoparticles, it was found that the phenomenon of clogging in the flow path frequently occurred at the reaction temperature (270 ° C.), and synthesis according to the flow path inner diameter was impossible. . Although it can be mitigated by modifying the surface of the inner wall of the capillary, a separate process is required for modifying the inner wall, so it is desirable to reduce deposition on the wall surface by controlling the reaction. Further, even when the flow path is boring, bubbles are often generated in the flow path due to boiling of the by-product at the reaction temperature. Due to the generation of the bubbles, the flow rate of the solution in the flow path varies remarkably, so that it is very difficult to keep the heating time uniform.

The present invention has been made based on the technical background as described above, and achieves the following objects.
The objective of this invention is providing the manufacturing method of the semiconductor fine particle which produces | generates the microparticles | fine-particles with uniform particle size.
Another object of the present invention is to provide a method for producing semiconductor fine particles in which, when producing fine particles, the reaction flow channel is not clogged or bubbles are not generated in the flow channel due to boiling of the by-product at the reaction temperature. Is to provide.
Still another object of the present invention is to provide a safe method for producing semiconductor fine particles which is less likely to cause an accident such as a fire in the reaction for producing fine particles.

In order to achieve the above object, the present invention employs the following means.
The degree of polymerization of the precursor is controlled by mixing semiconductor fine particle raw materials (for example, In raw material solution and P raw material solution) at a low temperature in a channel having an inner diameter of 1 μm to 1 mm in advance, and has a uniform and selective molecular weight. By forming a precursor (first heating reaction) and continuously introducing the precursor into a reaction vessel at a higher temperature (second heating reaction), semiconductor fine particles having a uniform particle size are produced. The molecular weight of the precursor is controlled by appropriately selecting the flow rate of the raw material solution and the inner diameter of the flow path. As a result, semiconductor fine particles having an arbitrary size can be generated.

  Furthermore, a higher size selectivity can be obtained by heating the flow path immediately after mixing the raw material solution to a temperature lower than the fine particle generation temperature. That is, by generating an amorphous or bulky precursor from a chain-like precursor, the spread of the size distribution due to the growth of the generated semiconductor fine particles in the fine particle generation container can be suppressed. If there is no problem of clogging in the fine channel at the temperature of the second heating reaction (hereinafter referred to as reaction temperature), both the first heating reaction and the second heating reaction are performed in the fine channel. Also good.

  Here, “reaction temperature” means a temperature in the second heating reaction, and indicates a temperature at which semiconductor fine particles are formed. When the semiconductor fine particles are semiconductor microcrystals (nanocrystals), it refers to the temperature at which crystallization occurs. The “temperature in the first heating reaction” refers to a temperature at which the raw material mixed solution can pass without clogging the flow path, although it varies depending on the raw material used. If the channel is not clogged, crystallization may occur at the “temperature in the first heating reaction”.

  Possible causes of clogging in the flow path include generation of gas, bubbles, and gas, and a decrease in solubility of the raw material in the solvent due to crystallization. The “temperature in the first heating reaction” may be room temperature. However, since the reaction rate becomes low at low temperatures, it is necessary to take measures such as lengthening the flow path and slowing the flow rate in order to form a precursor having a desired molecular weight (or degree of polymerization). As a result, the generation efficiency is lowered.

As an embodiment of the present invention, a method for producing InP fine particles will be described. However, the present invention is not limited to this.
A TOP solution ([In] = 0.05 mol / l) of a mixture of indium chloride and indium isopropoxide is used as the In raw material, and a 0.0375 mol / l TOP solution of P (TMS) 3 is used as the P raw material. These raw materials are filled into separate syringes. Each raw material solution is mixed in a glass capillary (corresponding to the “first fine channel” of the present invention) through a junction. A glass capillary having an inner diameter of 320 μm was used.

  Until the raw materials were mixed in the glass capillary, everything was performed at room temperature. After mixing, the mixture was dropped into the flask via a glass capillary heated to a temperature of 150 ° C. (corresponding to “temperature in the first heating reaction” of the present invention). The flask was replaced with an inert gas and heated to a temperature of 270 ° C. (“reaction temperature” corresponding to “temperature higher than the temperature in the first heating reaction” of the present invention). A precursor of InP fine particles is generated by mixing raw materials and passing through a glass capillary at a temperature of 150 ° C., and this precursor is heated to a reaction temperature in the flask to generate InP fine particles.

  As a result of considering the generation process of InP fine particles, a synthesis apparatus having such a configuration was selected. That is, in this embodiment, it is considered that the In raw material and the P raw material are rapidly polymerized even at room temperature after mixing to produce a chain precursor (see Equation 1).

  Also, heating the first microchannel, which is the mixed region, to about 150 ° C. increases the order of In—P bonds inside the precursor, and changes from a chain precursor to a bulky precursor or amorphous InP. This is for generating. This is to suppress the growth of the produced InP fine particles due to the fusion between the precursors in the InP fine particle production reaction flask or between the precursor and the InP fine particles, and to avoid a decrease in size selectivity.

  Further, by heating the precursor at a temperature of 270 ° C., the functional group bonded to In (in this case Cl or isopropoxyl group) and the functional group bonded to P (trimethylsilyl group) are β-eliminated, InP fine particles (nanocrystals) are generated. Therefore, if the InP precursor is generated with the molecular weight selectively and uniformly, the particle size selective synthesis of InP fine particles becomes possible. In this way, the space in which the two raw material solutions are mixed is limited within the first fine channel, the flow rate is appropriately selected, and the reaction time of the precursor generation is controlled, thereby controlling the molecular weight of the precursor. Is what you do.

  When the conventional method 3 is used for the synthesis of InP nanoparticles, insoluble substances generated by the reaction of impurities such as water adhering to the flow path inner wall and the raw material are deposited on the flow path wall, and the amount of precipitation is large. It is considered that the flow in the channel is hindered by the reaction temperature. In order to suppress such precipitation, according to the present invention, it is possible to synthesize semiconductor nanoparticles of any size without hindering the flow in the flow path. Further, since the conventional method 3 is reacted in the flow path, in the case of a reaction in which a gas is generated, it becomes difficult to control the flow rate of the reaction solution due to the generated gas. According to the present invention, the heating temperature of the first fine channel (corresponding to “temperature in the first heating reaction”) is sufficiently low that no gas is generated in the channel. Control is possible.

  Furthermore, the generation process of II-VI compound semiconductor nanoparticles is considered to be two processes of crystal nucleation and particle growth, and the size of the generated particles greatly depends on the reaction time and reaction temperature. On the other hand, in a III-V compound semiconductor, it is considered that there are two processes of polymer precursor formation and crystallization by intramolecular reaction of the precursor. In other words, in the production of III-V compound semiconductors including InP nanoparticles, the size of the produced nanoparticles can be controlled by controlling the size in the precursor formation process, so that subsequent crystallization Therefore, it is considered that the present invention is particularly suitable for the production of III-V compound semiconductors.

According to the present invention, the following effects can be obtained.
In the present invention, the flow in the flow channel is not hindered by the precipitation due to the impurities adhering to the inner wall of the flow channel.
According to the present invention, it is possible to synthesize semiconductor nanoparticles of any size by controlling the size in the process of forming a precursor and controlling the size of the generated nanoparticles.
In the present invention, since the heating temperature of the flow path is sufficiently low so that no gas (bubbles) is generated in the flow path, the flow rate of the reaction solution can be controlled.

The present invention performs precursor formation and crystallization by intramolecular reaction of the precursor, and is suitable for manufacturing a III-V compound semiconductor.
In the present invention, by controlling the size in the process of forming a precursor and controlling the size of the generated nanoparticles, it is possible to selectively generate InP fine particles of any size.
In the present invention, since the fine particles are selectively generated in size, classification after synthesis and multistage particle growth reaction, which are conventionally required, are unnecessary, and the synthesis efficiency of the fine particles is dramatically improved.

In the present invention, it is possible to easily scale up by increasing the number of flow paths.
In the present invention, since the raw material solution is mixed at a low temperature such as room temperature to be converted into a lower activity precursor and then introduced into a high temperature reaction vessel, the risk of an accident such as a fire is compared with the conventional method. As a result, it has become possible to significantly suppress it.

In Example 1, as indium (In) raw materials, indium isopropoxide (In (OiPr) ₃ ) (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and anhydrous indium chloride (InCl ₃ ) (manufactured by Kojundo Chemical Research Co., Ltd.) Used). As the phosphorus (P) raw material, tris (trimethylsilyl) phosphine (P (TMS) ₃ ) (manufactured by Acros Organics) was used. As the solvent, trioctylphosphine (TOP) (manufactured by Tokyo Chemical Industry Co., Ltd.) distilled under reduced pressure was used.

All mixing of the raw materials and the solvent was performed under a nitrogen atmosphere. Unless otherwise specified, it means that the raw materials and the solvent were used as they were without being treated. 73.0 mg (0.25 mmol) of In (OiPr) ₃ and 55.3 mg (0.25 mmol) of InCl ₃ were mixed and dissolved in 10 ml of TOP to obtain an In raw material solution. The In concentration was 0.05 mol / L. 109 μl (0.375 mmol) of P (TMS) ₃ was dissolved in 10 ml of TOP to obtain a P raw material solution.

  FIG. 1 shows an outline of the reaction apparatus used in Example 1. The Y-shaped connector 1 is attached with three glass capillaries (manufactured by GL Science, whose inner wall is modified with an octadecyl group) 2, 3, and 4. The inner diameters of the three glass capillaries 2, 3 and 4 are 320 μm. The lengths of the capillaries 2 and 3 are both 40 cm, and the length of the capillary 4 is 120 cm.

  The In raw material solution was put in the first syringe 5 for injecting the raw material solution. The P raw material solution was put in the second syringe 6 for injecting the raw material solution. The tips of the capillary 2 and the capillary 3 were attached to the first syringe 5 and the second syringe 6, respectively. An intermediate portion of the capillary 4 (corresponding to the “first fine channel” of the present invention) was immersed in an oil bath 7 heated to a temperature of 150 ° C. (corresponding to “temperature in the first heating reaction” of the present invention). The length of this intermediate part immersed in the oil bath 7 was 80 cm. The other end of the capillary 4 was inserted into a round flask 8 through a three-way cock 9. The flask 8 was previously immersed in nitrogen gas and immersed in an oil bath 10 having a temperature of 270 ° C. (corresponding to “temperature higher than the temperature in the first heating reaction” of the present invention). The volume of the flask 8 was 50 ml.

(Synthesis of InP fine particles)
InP fine particles were synthesized by the following procedure. 10 ml of the In raw material solution and 10 ml of the P raw material solution were filled in the syringes 5 and 6, respectively, under a nitrogen atmosphere. Using the syringe pumps 11 and 12, the In raw material solution and the P raw material solution were respectively flowed into the reaction apparatus at a rate of 30 μl per minute. In order to wash the insides of the capillaries 2, 3 and 4 with the raw material solution, about 0.5 ml of the initial effluent was discarded, and the subsequent effluent was collected in the flask 8.

  About 50 ml of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the solution obtained by collecting in the flask 8 by the synthesis of InP fine particles to generate a precipitate of InP fine particles. The produced precipitate was collected by a centrifuge (not shown), and about 1 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.) was added thereto to obtain a toluene solution of InP fine particles. Further, the process of adding ethanol, fractionating with a centrifuge, and obtaining a toluene solution of InP fine particles of toluene was repeated several times. This repeated process removed free TOP remaining in the solution.

  The absorption spectrum of the diluted toluene solution of the obtained InP fine particles was measured. The result of this measurement is shown in FIG. In addition, an absorption spectrum of a diluted toluene solution of InP fine particles synthesized by processing at a temperature of 300 ° C. for 10 minutes using a normal batch method is also shown in FIG. 2 as a comparative example. As shown in the graph of FIG. 2, the absorption spectrum of the InP fine particles synthesized using the batch method does not show a clear structure (absorption edge), whereas the absorption of the InP fine particles generated by the reactor of Example 1 is shown. In the spectrum, an absorption edge due to interband transition was clearly observed at 550 nm. This indicates that InP fine particles synthesized by the batch method have a wide size distribution, whereas InP fine particles generated by the reaction apparatus of Example 1 have a uniform size. In other words, it shows that InP fine particles having a uniform particle diameter are selectively generated by the reactor of the first embodiment.

(Generation of ZnS-coated InP fine particles)
Since InP fine particles are deep trap levels formed from surface levels, the efficiency of fluorescence alone is extremely low. Therefore, the influence of the trap level was suppressed by constructing a shell made of ZnS, and the fluorescence efficiency was improved. The ZnS shell was constructed as follows. To 20 mg of the synthesized InP microcrystals, 36.2 mg (0.1 mmol) of zinc diethyldithiocarbamate (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and dissolved in 5 ml of TOP. This was heated at a temperature of 240 ° C. for 3 hours, and then naturally cooled to room temperature, thereby synthesizing ZnS-coated InP fine particles dispersed in a TOP solvent.

  An excessive amount of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the resulting solution to generate precipitates of ZnS-coated InP fine particles. The produced precipitate was separated by centrifugation and dissolved in toluene. ZnS-coated InP fine particles showed high solubility in toluene. Each of the obtained ZnS-coated InP fine particles and InP fine particles was excited with 420 nm excitation light, and the emission spectrum was measured. The result of this measurement is shown in FIG. From the graph of FIG. 3, it can be seen that the emission intensity of the ZnS-coated InP fine particles is improved as compared with the InP fine particles not coated with ZnS. The half width of the emission spectrum of the obtained ZnS-coated InP fine particles was 70 nm.

  The present invention is preferably used in the field of new material development, the field of light emitting devices, the field of biotechnology, and the field of medicine.

FIG. 1 is a view schematically showing a reaction apparatus of Example 1. FIG. 2 is a graph showing the results of measuring the absorption spectrum of a diluted toluene solution of InP fine particles obtained by the reaction of Example 1. FIG. 3 is a graph showing emission spectra of ZnS-coated InP fine particles and InP fine particles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Y-shaped connector 2, 3, 4 ... Glass capillary 5 ... 1st syringe 6 ... 2nd syringe 7, 10 ... Oil bath 8 ... Flask 9 ... Three-way cock

Claims (6)

In a method for producing semiconductor fine particles by heating and reacting two or more raw materials,
The two or more raw materials are subjected to a first heating reaction while passing the two or more raw materials through a first fine channel having an inner diameter of 1 μm to 1 mm, and then the temperature is higher than the temperature in the first heating reaction. A method for producing semiconductor fine particles, comprising producing the semiconductor fine particles by subjecting two or more raw materials to a second heating reaction. In the semiconductor fine particle manufacturing method according to claim 1,
The second heating reaction is carried out by passing through a second fine channel having an inner diameter of 1 μm to 1 mm. In the semiconductor fine particle manufacturing method according to claim 1 or 2,
The two or more raw materials are mixed immediately before passing through the first fine flow path. In the semiconductor fine particle manufacturing method according to one selected from claims 1 to 3,
The method for producing semiconductor fine particles, wherein the semiconductor fine particles generate crystalline fine particles. In the semiconductor fine particle manufacturing method according to claim 1 selected from claims 1 to 4,
The method for producing semiconductor fine particles, wherein the semiconductor fine particles are III-V group compound semiconductors. In the semiconductor fine particle manufacturing method according to claim 5,
The two or more raw materials include an indium (In) raw material and a phosphorus (P) raw material.

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