KR100526828B1 - Method of forming quantum dots - Google Patents

Abstract

The present invention relates to a method for forming a quantum dot, a magnetic film and a semiconductor film manufactured using the same, comprising the steps of: forming a magnetic film or a semiconductor film on a substrate, and from about 30 mJ / cm 2 to about 300 mJ / in at least a portion of the film It provides a method for forming a quantum dot comprising the step of irradiating a laser so that the energy of the cm2.

According to the quantum dot forming method of the present invention, a quantum dot having a uniform distribution can be formed by irradiating a laser on a magnetic film or a semiconductor film. According to the method of the present invention, the process is not only simple and excellent in reproducibility, but also the size and arrangement of the quantum dots can be easily controlled by adjusting the irradiation conditions such as the laser power and the number of laser scans in consideration of the film thickness. It works.

Description

Quantum dot formation method {METHOD OF FORMING QUANTUM DOTS}

The present invention relates to a technique for forming a nanometer-sized quantum dot (quantum dot) on a substrate, and more particularly, to a method for forming a magnetic or semiconductor quantum dot by irradiating a laser to a magnetic film or a semiconductor film and manufactured using the same It relates to a magnetic film or a semiconductor film.

Quantum dots are several nanometers in size and exhibit excellent optical, magnetic, and electrical properties that are different from bulk conditions. These properties are applied in microelectronics and magnetic recording devices to reduce the size of devices. It is known to be highly functional.

In recent years, research has been actively conducted to apply quantum dots to quantum dot laser devices, high-density magnetic recording media, semiconductor devices, and the like. In particular, ferromagnetic quantum dots (FMQD) are means for realizing a next generation high density magnetic recording medium of 1 TB / in ² or more. I am in the spotlight.

Conventional quantum dot formation methods include a quantum dot spontaneous formation method using lattice phase difference of a thin film, a selective growth method using photolithography, and a chemical treatment method.

Spontaneous quantum dots are formed using strains generated during the growth of lattice mismatched material systems. A representative example is the Stranski-Krastanow method. This method is a technique that spontaneously generates quantum dots about 10nm in size by alternately growing materials with different lattice constants. However, since the S-K method uses expensive equipment such as a molecular beam epitaxy device or a pulsed laser deposition device, it is difficult to apply industrially and is currently limited to experimental implementation. In addition, there is a problem that it is difficult to control the uniformity and arrangement of the quantum dot size.

In addition, a method using general photolithography and selective growth uses a method of forming after quantum dot positions are patterned using photolithography. This is because the process is simple and accurate arrangement is possible by using a conventional semiconductor process, and since the spacing between quantum dots is determined by photolithography technology (pattern width that can be currently implemented: about 0.1 μm), the density of quantum dots Is very low. It is disadvantageous in that it is difficult to secure desired performance in device application.

Alternatively, there is a quantum dot forming method using a chemical treatment such as a colloidal solution. In general, since colloidal solutions exist in a state where particles of several tens of nanometers (nm) to micrometers (μm) are uniformly spread without aggregation in a solvent, quantum dots can be generated relatively uniformly through chemical action. It can be used to form However, such a chemical treatment method requires a post-treatment process for evaporating colloidal solution located in a quantum dot and removing impurities, which results in a complicated process.

On the other hand, in the quantum dot forming method, a means for easily controlling the quantum dot arrangement state such as the size of the quantum dots and the spacing of the quantum dots (quantum dot density) is strongly required in order to obtain desired characteristics depending on the application field when forming the quantum dots. However, in the conventional quantum dot forming method, it is difficult to adjust the arrangement state of the quantum dots as described above. For example, even in a method using photolithography having an advantage in uniform formation, there is a process troublesome in that a pattern for quantum dot formation has to be adjusted.

Therefore, in the art, there is a need for a method of forming a quantum dot, which is simple and has high reproducibility and can easily control the size and spacing of quantum dots formed on a substrate so that they can be put to practical use in various applications. come.

The present invention has been made to solve the above problems, the object of which is to easily form a quantum dot in the magnetic film or the semiconductor film using a laser, and furthermore, the size and spacing of the quantum dots can be precisely controlled The present invention provides a method for forming a new quantum dot.

Another object of the present invention is to provide a semiconductor film or a magnetic film in which quantum dots are formed according to the above method.

The present invention provides a method of preparing a substrate, comprising: forming a substrate, forming a magnetic film on the substrate, and irradiating a laser such that energy of about 30 mJ / cm 2 to about 300 mJ / cm 2 is applied to at least a portion of the magnetic film. It provides a quantum dot forming method comprising a.

Here, the magnetic film may be made of a magnetic material selected from the group consisting of Co, Ni, Fe, and alloys thereof, and the magnetic film is preferably greater than about 5 GPa and having a thickness of about 50 GPa or less.

In a preferred embodiment of the present invention, in order to prevent demagnetization of the magnetic film on which the quantum dots are to be formed, the method may further include applying a magnetic field to the magnetic film while irradiating the laser.

The irradiating the laser may be implemented by scanning the laser at a predetermined speed in the area where the quantum dot is to be formed. At this time, the laser scanning speed may be determined differently according to conditions such as laser power, but may be preferably set in the range of about 1 μm / s to about 1000 μm / s.

In the present invention, the laser power irradiated to form the quantum dots is preferably adjusted in the range of about 0.08 W to about 1 W, and such a laser may use a conventional Nd: YAG laser. In particular, the wavelength band of the laser used in the present invention is an ultraviolet wavelength band, preferably in the range of about 100 nm to about 360 nm.

Magnetic quantum dot forming method according to the present invention, by controlling the output of the laser, the thickness of the thin film and the number of irradiation can easily control the quantum dot size and distribution, that is, the quantum dot spacing.

Furthermore, the present invention also provides a method of forming quantum dots in a semiconductor film such as silicon. The method includes providing a substrate, forming a semiconductor film on the substrate, and irradiating a laser such that energy of about 30 mJ / cm 2 to about 300 mJ / cm 2 is applied to at least a portion of the semiconductor film. Include.

In addition, the present invention can provide a semiconductor film and a magnetic film produced according to the quantum dot forming method.

Conventional quantum dot forming method has been mainly dependent on the strain effect due to lattice mismatch between the substrate and the film to be formed quantum dot, the present invention is the strain effect generated when the instant melting by irradiating a laser to the film to be formed quantum dot It can be said to be based on.

A general laser has been used as a means for forming a fine pattern by vaporizing a portion irradiated with a high output energy of several W or more. Such high power lasers include Nd: YAG laser, Er: YAG laser, and excimer laser. have. However, in the present invention, such a laser is used in the output range in which the irradiated object is not evaporated, thereby forming quantum dots by the strain effect generated during the instant melting and reconstitution.

The quantum dot forming method may be used to form quantum dots on the magnetic film and the semiconductor film, wherein the energy range applied to the magnetic film or the semiconductor film by a laser is about 30 mJ / cm 2 to about 300 mJ / cm 2. When the energy applied by the laser is less than about 30 mJ / cm 2, the magnetic film or the semiconductor film is not enough to melt, and when larger than about 300 mJ / cm 2, the irradiated area is etched, which is not appropriate.

As the laser used in the present invention, it is preferable to use an ultraviolet wavelength band of about 100 nm to 380 nm in order to induce strain by melting the magnetic film and the semiconductor film in an instant.

One embodiment of the present invention provides a method of forming a magnetic quantum dot, that is, a method of forming a quantum dot in a magnetic body film. The magnetic film applied to the present invention may be made of a material selected from the group consisting of Co, Ni, Fe, and alloys thereof. Further, preferably, by applying a predetermined magnetic field to the magnetic film along the easy direction while the laser is being irradiated, excellent magnetic properties can be maintained even if heat is generated in the irradiated area.

In the present invention, the step of irradiating a laser, it is preferable to use a scanning method so that the laser is uniformly irradiated over the entire area to be formed quantum dot. Since the size of a laser beam that is commonly used is only 1 mm or less, a scanning method is used to uniformly apply the laser to the entire area to be irradiated.

This laser scanning process can be easily implemented using a galvanometer system. The influence on the irradiated area by the laser depends on the scanning speed. Therefore, in order to form a quantum dot, the scan speed of the laser is preferably set in the range of 1 µm / s to about 1000 µm / s, but is not limited thereto.

On the other hand, the magnetic quantum dot forming method according to the present invention provides an additional advantage that the quantum dot diameter and density, that is, the quantum dot spacing can be easily adjusted in various ways.

Factors that can adjust the quantum dot arrangement state in the present invention may be the output of the laser, the thickness of the magnetic film and the number of scanning times of the laser.

That is, in the present invention, as the laser power is increased, the diameter and the spacing of the quantum dots are generally increased, while the quantum dot density can be reduced. In addition, as the thickness of the magnetic film or the semiconductor film increases, the diameter of the quantum dots and their spacing increases, while the density of the quantum dots can decrease, and as the number of irradiation times of the laser increases, the diameter and the spacing of the quantum dots decreases. Can be.

As described above, in the method of forming a magnetic quantum dot according to the present invention, the size and arrangement of the quantum dots can be easily adjusted by adjusting the laser irradiation conditions in consideration of the deposition thickness of the thin film.

Example 1

In this experiment, while sputtering and depositing cobalt (Co) on a silicon substrate under a pressure condition of about 10 ^-8 torr, in the process, a magnetic field of about 300 Oe was applied along the easy direction of the magnetization axis, and a Co magnetic material of about 1 nm was used. Four membranes were prepared.

Subsequently, each of the magnetic films was moved to a laser irradiation chamber to irradiate a laser to the magnetic film region where the quantum dots are to be formed, and the laser beam outputs were differently applied to 0.06W, 0.08W, 0.1W, and 0.2W, respectively.

The laser used in this experiment was a Nd: YAG laser with a beam diameter of 0.5 mm and a 355 nm wavelength band capable of 2W output, and a galvanometer to apply the laser uniformly to the entire area where the magnetic film was to be formed. Laser irradiation at a scanning speed of 1 μm / s. The scanning frequency for each Co magnetic film was twice.

1A to 1D are photographs of four magnetic membranes to which a laser is applied, using a scanning electron microscope. It can be seen that the quantum dots are formed in the magnetic film shown in FIGS. 1B to 1D, that is, the magnetic film to which a laser of 0.08W or more is applied.

In order to investigate the properties of the quantum dots formed on the magnetic body films, the quantum dot diameter (nm), the quantum dot density (number / cm 2), and the interval (nm) were examined, and the results are shown in FIGS. 2A to 2C.

As shown in Figs. 2A to 2C, when the laser is irradiated at 0.06W, no quantum dots are formed. When the laser is irradiated at 0.08W, the quantum dots having a diameter of about 8 nm are spaced at an average interval of about 15 nm. The average density was found to be 3.7 × 10 ¹¹ / cm 2. In particular, it can be seen that the spacing of the quantum dots is fairly uniformly distributed at 11.3 to 14.8 nm.

In addition, when the laser power was increased to 0.1 W and 0.2 W, the average diameters of the quantum dots increased to 11.4 nm and 12.3 nm, respectively, and the average spacing increased to 22 nm and 23 nm. It was shown to decrease to 2.5 × 10 ¹¹ / ㎠ and 2.2 × 10 ¹¹ / ㎠, respectively.

Example 2

In this experiment, while sputtering depositing a cobalt iron (CoFe) alloy on a silicon substrate under a pressure condition of about 10 ^-8 torr, in the process, by applying a magnetic field of 300 Oe along the easy direction of the magnetization axis, CoFe of about 1 nm Four magnetic body films were prepared.

Subsequently, each of the magnetic body films is moved to a laser irradiation chamber, and the laser is irradiated to a magnetic body film area in which the quantum dots are to be formed under the same conditions as in Example 1, but the output of the laser beam is 0.04W, 0.06W, 0.8W, 0.1. Each W was applied differently.

The resulting four magnetic body films were taken by SEM. 3A to 3D are SEM photographs of four magnetic films to which a laser is applied. In addition, quantum dot diameter (nm), quantum dot density (number / cm 2), and spacing (nm) were examined in the same manner as in Example 1, and the results are shown in FIGS. 4A to 4C.

As shown in Figs. 4A to 4C, when the laser is irradiated at 0.04 W, no quantum dots are formed. When the laser is irradiated at 0.06 W, the quantum dots having a diameter of about 10.2 nm are at an average interval of about 18 nm. It was found to be distributed with an average density of about 3.9 × 10 ¹¹ / cm 2.

In addition, when the laser power was increased to 0.08 W and 0.1 W, the average diameter of the quantum dots increased to about 10.5 nm and 11.3 nm, respectively, and the average spacing increased to about 20 nm and about 24 nm, respectively. The average density of was decreased to about 3.7 × 10 ¹¹ / ㎠ and about 3.3 × 10 ¹¹ / ㎠, respectively.

Example 3

In this experiment, a sputtered deposition of cobalt (Co) on a silicon substrate under a pressure condition of about 10 ^-8 torr while applying a 300 Oe magnetic field along the easy direction of the magnetization axis during deposition, a Co magnetic film of about 1 nm was prepared. It was.

Subsequently, the magnetic film was moved to a laser irradiation chamber, and a laser was irradiated to a magnetic film region where a quantum dot is to be formed. In this embodiment, a 355 nm wavelength band Nd: YAG laser capable of 2W output was used. Since the diameter of the laser beam is 0.5 mm, a scanning method using a galvanometer system was used so that the laser is uniformly applied to the entire region where the magnetic film is to be formed.

At this time, under the same conditions as in Example 1, the scanning speed was irradiated twice at about 1 μm / s, but the output of the laser beam was 0.1W.

In addition, while irradiating the Co magnetic film with a laser, the magnetic field was applied in the same direction as the magnetic field applied during the magnetic film deposition process. Subsequently, after depositing a Ta cap layer of about 10 nm on the Co magnetic body film having the quantum dots formed thereon, the magnetic properties were examined with a superconducting quantum interference device (SQUID) at 5K.

5 is a result of measuring the magnetism of the Co magnetic body film of this embodiment.

Referring to the graph of FIG. 5, it was confirmed that the Co magnetic film retained ferromagneticity through a clear hysteresis curve and magnetization value. That is, even when the laser is irradiated, when a constant magnetic field is applied in the laser irradiation process, excellent ferromagnetic quantum dots (FMQD) could be formed.

Example 4

In the present embodiment, in order to observe the effect on the quantum dot arrangement state according to the thickness of the magnetic body film, seven magnetic bodies having a Co magnetic body film formed on the silicon substrate under the same conditions as in Example 3, but having a different thickness in the range of 5 kHz to 40 kHz Films (5 ', 10', 15 ', 20', 25 ', 30' and 40 'magnetic films) were prepared.

Subsequently, the magnetic film was moved to a laser irradiation chamber under the same conditions as in Example 3, and the laser was irradiated to the magnetic film region where the quantum dots are to be formed.

Whether or not quantum dots were formed in each of the seven magnetic films thus obtained and the arrangement state of the formed quantum dots, that is, the diameter, spacing, and density of the quantum dots were examined.

The measurement results of diameters, spacings and densities of the quantum dots are shown in the graphs of FIGS. 6A to 6C, respectively.

Referring to Fig. 6A, when the Co magnetic film has a thickness of 5 GPa, the magnetic film is not sufficiently grown and magnetic quantum dots are not formed. However, in the six Co magnetic films having a thickness of 10 GPa to 40 GPa larger than 5 GPa, about Quantum dots with diameters between 10 nm and about 100 nm were formed.

In addition, as shown in the graph of FIG. 6B, as the thickness of the film increases from about 10 ms to about 40 ms, the average spacing of the quantum dots formed in the six magnetic films increases from about 10 nm to about 115 nm. As shown, the average density was also shown to decrease from about 2.4 × 10 ¹¹ / cm 2 to about 0.075 × 10 ¹¹ / cm 2 in inverse proportion to the average interval.

Example 5

In this experiment, in order to observe the effect on the quantum dot arrangement state according to the number of laser scanning, a Co magnetic film was formed on the silicon substrate under the same conditions as in Example 3, but four Co magnetic films having a thickness of about 1 nm were prepared. .

Then, after moving the magnetic film to the laser irradiation chamber, under the same conditions as in Example 3 (Nd: YAG laser of 0.1W), the laser is irradiated to the magnetic film region where the quantum dots are to be formed, but the laser scanning for each magnetic film The number of times was applied differently from 1 to 4 times.

The arrangement state of the quantum dots, that is, the diameter, the spacing and the density of the quantum dots, formed on each of the four magnetic body films thus obtained were examined, and the results are shown in the graphs of FIGS. 6A to 6C, respectively.

Referring to FIG. 7A, the average diameter of the quantum dots formed in the four magnetic body films generally decreased from about 12 nm to about 8 nm as the number of laser scanning times increased.

In addition, as shown in the graph of FIG. 7B, the average spacing of the quantum dots formed in the four magnetic body films was generally reduced from about 28 nm to about 16 nm as the number of laser scanning times increased, as shown in FIG. 7C. Likewise, the average density was also inversely increased from about 1.4 × 10 ¹¹ / cm 2 to about 3.7 × 10 ¹¹ / cm 2.

Example 6

In this experiment, silicon (Si) was sputter deposited on a predetermined substrate to form an amorphous silicon film having a thickness of about 1 nm.

Subsequently, each of the silicon films was moved to a laser irradiation chamber, and the laser was irradiated with an output of about 0.1 W to form a quantum dot. In this embodiment, as in Example 1, a Nd: YAG laser having a 355 nm wavelength band of 0.5 mm in diameter and capable of 2W output was used. In addition, laser irradiation was performed at a scanning speed of 1 μm / s using a galvanometer system so that the laser was uniformly applied to the entire region where the magnetic film was to be formed, and the entire region was scanned twice.

8 is a photograph of a laser applied silicon film with an atomic force microscope. As shown in the AFM photograph of FIG. 8, it can be seen that silicon quantum dots of about 40 nm to 50 nm are formed in the silicon film.

As described above, the quantum dot forming method using the laser according to the present invention can be applied not only to a magnetic film but also to a film made of a semiconductor material.

The present invention described above is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims.

As described above, according to the present invention, a quantum dot having a uniform distribution can be formed by irradiating a laser on a magnetic film or a semiconductor film. According to the method of the present invention, the process is not only simple and excellent in reproducibility, but also the size and arrangement of the quantum dots can be easily controlled by adjusting the irradiation conditions such as the laser power and the number of laser scans in consideration of the film thickness. It works.

1A to 1D are SEM photographs showing a Co magnetic film prepared according to the quantum dot forming method of the present invention.

2A to 2C are graphs showing the relationship between the arrangement state of the quantum dots formed on the Co magnetic film and the output of the laser beam.

3A to 3D are SEM photographs showing a CoFe magnetic film prepared according to the quantum dot forming method of the present invention.

4A to 4C are graphs for showing the relationship between the arrangement state of the quantum dots formed on the CoFe magnetic film and the output of the laser beam.

5 is a graph showing magnetization according to an external magnetic field of a Co magnetic body film manufactured according to the quantum dot forming method of the present invention.

6A to 6C are graphs for illustrating the relationship between the arrangement state of quantum dots formed in the Co magnetic film and the thickness of the magnetic film.

7A to 7C are graphs showing the relationship between the arrangement state of the quantum dots formed on the Co magnetic film and the number of scanning times of the laser.

8 is an AFM photograph of an amorphous silicon substrate prepared according to the quantum dot forming method of the present invention.

Claims (15)

Forming a magnetic film on the substrate; And, And forming a quantum dot in the magnetic body film by irradiating a laser such that energy of 30 mJ / cm 2 to 300 mJ / cm 2 is applied to at least a portion of the magnetic body film. The method of claim 1, The magnetic film is a quantum dot forming method characterized in that the thickness of more than 5 kHz and 50 kHz or less. The method of claim 1, The magnetic film is formed of a magnetic material selected from the group consisting of Co, Ni, Fe and alloys thereof. The method of claim 1, The irradiating of the laser may include applying a magnetic field to the magnetic film while the laser is irradiated. The method of claim 1, The laser is a quantum dot forming method, characterized in that the laser in the ultraviolet wavelength band of 100nm to 380nm. The method of claim 1, The irradiating the laser is a step of irradiating an Nd: YAG laser with an output in the range of 0.05W to 0.2W. The method of claim 1, A method of forming a quantum dot, characterized in that the size and spacing of the quantum dot is adjusted by varying the thickness of the magnetic body film. The method of claim 1, A method for forming a quantum dot, characterized in that for adjusting the output of the laser to adjust the size and spacing of the quantum dot. The method of claim 1, The irradiating of the laser is a step of irradiating a laser by scanning a laser at a predetermined speed on a region where the quantum dot is to be formed. The method of claim 9, The laser scanning speed is a quantum dot forming method, characterized in that in the range of 1㎛ / s to 1000㎛ / s. The method of claim 9, The irradiating the laser is a step of repeating the laser irradiation at least twice or more times. The method of claim 11, A method of forming a quantum dot, characterized in that for adjusting the size and spacing of the quantum dot according to the repeated number of irradiation of the laser. delete Forming a semiconductor film on the substrate; And, And forming a quantum dot in the semiconductor film by irradiating a laser such that energy of 30 mJ / cm 2 to 300 mJ / cm 2 is applied to at least a portion of the semiconductor film. delete