JP2008019126A - Vacuum ultraviolet light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new vacuum ultraviolet light-emitting element material which emits light with high brightness, for example, in the vacuum ultraviolet region of emission wavelengths of ≤200 nm, and is suitably used for photolithography, sterilization, a large-capacity optical disk for next generation and medical treatment (ophthalmological treatment or DNA incision) or the like. <P>SOLUTION: This vacuum ultraviolet light-emitting element is characterized by comprising a barium lithium fluoride single crystal containing neodymium of about 0.001 to 1 mol% with respect to the above fluoride as an activator. The element emits the vacuum ultraviolet light by combining with a proper excitation source such as an electron beam or F2 laser. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a novel vacuum ultraviolet light emitting element material that can be suitably used for photolithography, semiconductor or liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical disks, medical treatment (ophthalmic treatment, DNA cutting), and the like.

  High-intensity ultraviolet light-emitting devices are materials that support advanced technologies in the semiconductor field, information field, medical field, etc. In recent years, in order to respond to many demands such as an increase in recording density on recording media, a shorter wavelength is required. Development of ultraviolet light-emitting elements that emit light at room temperature is underway. As an ultraviolet light-emitting element that emits light at a short wavelength, a light-emitting element having a light emission wavelength in the range of 300 nm using a material such as gallium nitride has been proposed (see Non-Patent Document 1). In recent years, a high-purity hexagonal boron nitride single crystal has been proposed. Has been proposed (see Patent Document 1).

  A vacuum ultraviolet light emitting device having an emission wavelength of 200 nm or less can be suitably used for photolithography, semiconductor or liquid crystal substrate cleaning, sterilization, etc., and thus development is desired. However, it is easy to obtain such a vacuum ultraviolet light emitting device. Instead, only a few examples are known (see Non-Patent Document 2).

  A factor that makes it difficult to develop a vacuum ultraviolet light emitting element is that vacuum ultraviolet rays are absorbed by many substances, so that materials that do not cause self-absorption are limited.

  Furthermore, the emission characteristics in the vacuum ultraviolet region are easily affected by impurities in the material, and even a material having an energy level of light emission in the vacuum ultraviolet region has a long wavelength based on a lower energy level. There are many cases in which the desired vacuum ultraviolet light emission cannot be obtained due to the fact that the light emission is dominant or the loss due to non-radiative transition is significant.

  Therefore, it is extremely difficult to predict the light emission characteristics in the vacuum ultraviolet region in advance, and this is a big barrier in the development of vacuum ultraviolet light emitting elements.

  Since the barium lithium fluoride single crystal is transparent to vacuum ultraviolet rays having a wavelength of about 130 nm or more, it is promising as a material that can overcome the above self-absorption problem. However, since lithium barium fluoride needs to grow crystals from an incongruent melt, it is difficult to obtain high-quality crystals.

  As a method for growing crystals from an incongruent melt, a method has been proposed in which the melt is leached from a hole provided in the bottom of the crucible and the leached melt is pulled down (see Patent Document 2). This method is now known as a micro-pulling method, and not only can crystals be grown from incongruent melts, but also has the advantage of being able to dope higher concentrations of impurities when doping. It is.

  However, since barium lithium fluoride has poor wettability to the crucible and the melt does not exude from the hole at the bottom of the crucible, it has been difficult to apply the above-described micro-pulling-down method.

JP 2005-228886 A JP-A-6-345588 Iwaya. M et al, “High-power UV-light-emitting diode on sapphire” Japan Journal of Applied Physics Part1-Regular Papers Shorts & Re: 400 & Res. A. C. Cefalas et al, "Intense vacuum ultraviolet emission at 172 nm from LaF3: Nd3 + crystals" Microelectronic Engineering 57, 93 (2001)

  The present invention is a new vacuum ultraviolet light that emits high brightness in the vacuum ultraviolet region and can be suitably used for photolithography, semiconductor and liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical disks, and medical treatment (ophthalmic treatment, DNA cutting). An object is to provide a light-emitting element.

  As a result of various studies on materials that emit light in the vacuum ultraviolet region and do not absorb the emitted vacuum ultraviolet light, the present inventors have excited a barium lithium fluoride single crystal containing neodymium as an activator by appropriate means. As a result, it was found that vacuum ultraviolet emission can be obtained, and the present invention has been completed.

  That is, the present invention is a vacuum ultraviolet light emitting element characterized by comprising a barium lithium fluoride single crystal containing neodymium as an activator.

  According to the vacuum ultraviolet light-emitting element comprising a barium lithium fluoride single crystal containing neodymium obtained by the present invention, it is possible to obtain light emission with high brightness in the vacuum ultraviolet region. Such a vacuum ultraviolet light-emitting device can be suitably used for photolithography, semiconductor and liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical disks, medical treatment (ophthalmic treatment, DNA cutting), and the like.

  Hereinafter, the barium lithium fluoride single crystal containing neodymium according to the present invention and its vacuum ultraviolet emission characteristics will be described.

  The vacuum ultraviolet light emitting device of the present invention contains neodymium (hereinafter also referred to as Nd) as an activator in a crystal of barium lithium fluoride (hereinafter also referred to as BaLiF3) generally represented by the chemical formula BaLiF3 (hereinafter referred to as Nd). It is made of a single crystal (also referred to as a dope) (hereinafter also referred to as an Nd-doped BaLiF3 single crystal).

  In the single crystal of the present invention, the higher the Nd content relative to BaLiF3, the higher the luminance can be obtained. However, if the content is too high, the transparency of the single crystal in the vacuum ultraviolet region is reduced, and the emitted vacuum ultraviolet light is absorbed by the single crystal itself, resulting in a decrease in luminance of light emission. . Therefore, the content of neodymium Nd with respect to BaLiF3 is preferably 0.001 to 1 mol% based on BaLiF3. By setting the content to 0.001 mol% or more, it is possible to obtain light emission with high luminance, and by setting the content to 1 mol% or less, an Nd-doped BaLiF 3 single crystal having high transparency in the vacuum ultraviolet region is obtained. be able to. In a single crystal, it is considered that doped Nd exists between crystal lattices or is replaced with Ba atoms, but the exact existence state is not clear.

  The Nd-doped BaLiF3 single crystal of the present invention is a colorless or light purple transparent crystal and belongs to a cubic crystal. It has good chemical stability, and in normal use there is no degradation of performance in a short period of time. Moreover, mechanical strength and workability are also good, and it is easy to process and use it in a desired shape.

  The production method of the Nd-doped BaLiF3 single crystal is not particularly limited, and can be produced by a known crystal production method, but can be preferably produced by a micro pull-down method.

  By producing by the micro pull-down method, it becomes possible to grow an Nd-doped BaLiF 3 single crystal having excellent quality such as transparency in the vacuum ultraviolet region from an incongruent melt. Moreover, higher concentration neodymium can be doped and high-luminance light emission can be realized.

  The micro pull-down method is a method for producing a crystal by drawing a raw material melt from a hole provided in the bottom of the crucible 5 using an apparatus as shown in FIG.

  Hereinafter, a general method for producing an Nd-doped BaLiF3 single crystal by the micro pulling method will be described.

First, a predetermined amount of raw material is filled into a crucible 5 having a hole at the bottom. The shape of the hole provided at the bottom of the crucible is not particularly limited, but is preferably a cylindrical shape having a diameter of 0.5 to 4 mm and a length of 0 to 2 mm. In the present invention, the raw material is not particularly limited, but the purity is 99. It is preferable to use a mixed raw material in which 99% or more of barium fluoride, lithium fluoride, and neodymium fluoride are mixed. By using such a mixed raw material, the purity of the Nd-doped BaLiF3 single crystal can be increased, and characteristics such as luminance of light emission are improved. The mixed raw material may be used after being sintered or melted and solidified after mixing.

  The molar ratio of lithium fluoride to barium fluoride in the mixed raw material is preferably 1 to 1.5, and by making such a molar ratio, crystal turbidity due to phase separation of barium fluoride or lithium fluoride can be prevented. Can be suppressed.

  Next, the crucible 5 filled with the raw material, the after heater 1, the heater 2, the heat insulating material 3, and the stage 4 are set as shown in FIG. After evacuating the inside of the chamber 6 to 1.0 × 10 −3 Pa or less using a vacuum evacuating apparatus, an inert gas such as high-purity argon is introduced into the chamber 6 to perform gas replacement. The pressure in the chamber after gas replacement is not particularly limited, but atmospheric pressure is common.

  By the gas replacement operation, moisture attached to the raw material or the chamber can be removed, and deterioration of the single crystal derived from the moisture can be prevented. In order to avoid the influence of moisture that cannot be removed by the gas replacement operation, it is preferable to use a solid scavenger such as zinc fluoride or a gas scavenger such as tetrafluoromethane. When using a solid scavenger, a method of mixing in the raw material in advance is preferable, and when using a gas scavenger, a method of mixing with the above inert gas and introducing it into the chamber is preferable.

  After performing the gas replacement operation, the raw material is heated and melted by the high-frequency coil 7, and the melted raw material melt is drawn out from the hole at the bottom of the crucible to start crystal growth.

  Here, when the Nd-doped BaLiF3 single crystal is manufactured by the micro pull-down method, the wettability of the raw material melt with respect to the crucible is poor and the melt does not exude from the hole at the bottom of the crucible, so special measures must be taken. The present inventors provided a metal wire at the tip of the pull-down rod, inserted the metal wire into the crucible through the hole at the bottom of the crucible, attached the raw material melt to the metal wire, and then supplied the raw material melt to the metal wire. The crystal can be grown by pulling it down together.

  That is, the high frequency output is adjusted, and the metal wire is inserted into the hole at the bottom of the crucible while the temperature of the raw material is gradually increased from 860 ° C., which is the melting point of BaLiF 3, and the drawing is performed. This operation is repeated until the raw material melt is drawn together with the metal wire, and crystal growth is started. The material of the metal wire can be used without limitation as long as it is a material that does not substantially react with the raw material melt, but a material excellent in corrosion resistance at high temperatures such as a W-Re alloy is preferable.

After pulling out the raw material melt with the metal wire, a single crystal can be obtained by continuously pulling it down at a constant pulling rate.
The pulling speed is not particularly limited, but is preferably in the range of 0.5 to 10 mm / hr.

  In the production of the Nd-doped BaLiF3 single crystal of the present invention, an annealing operation may be performed after the production of the single crystal for the purpose of removing crystal defects of the single crystal caused by thermal strain.

  The obtained Nd-doped BaLiF3 single crystal has good workability and can be easily processed into a desired shape. For processing, a known cutting machine such as a blade saw or wire saw, a grinding machine, or a polishing machine can be used without any limitation.

  The Nd-doped BaLiF3 single crystal can be processed into a desired shape to obtain a vacuum ultraviolet light emitting device. This vacuum ultraviolet light emitting element can be made into a vacuum ultraviolet light generator by combining with an appropriate excitation source such as an electron beam or F2 laser. Such a vacuum ultraviolet light generator is suitably used in fields such as photolithography, sterilization, next-generation large-capacity optical disks, and medicine (ophthalmic treatment, DNA cutting).

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1
A barium lithium fluoride single crystal doped with neodymium was manufactured using the crystal manufacturing apparatus shown in FIG. As raw materials, barium fluoride, lithium fluoride, and neodymium fluoride having a purity of 99.99% were used. The after heater 1, the heater 2, the heat insulating material 3, the stage 4, and the crucible 5 are made of high-purity carbon, and the shape of the hole provided at the bottom of the crucible is a circle having a diameter of 2.2 mm and a length of 0.5 mm. It was columnar.

  First, 2 g of barium fluoride, 0.4 g of lithium fluoride, and 0.01 g of neodymium fluoride were weighed, mixed well, and then charged in the crucible 5. The neodymium content relative to barium lithium fluoride was 0.5 mol%.

  The crucible 5 filled with the raw material was set on the upper part of the after heater 1, and the heater 2 and the heat insulating material 3 were sequentially set around the crucible. Next, the inside of the chamber 6 is evacuated to 1.0 × 10 −4 Pa using an evacuation apparatus including an oil rotary pump and an oil diffusion pump, and then an argon-tetrafluoromethane mixed gas is introduced into the chamber 6. Gas replacement was performed.

  After the pressure in the chamber 6 after gas replacement was changed to atmospheric pressure, the raw material was heated to the melting point of BaLiF 3 with the high-frequency coil 7 and melted, but no leaching of the raw material melt from the bottom of the crucible 5 was observed. It was. Then, while adjusting the high frequency output and gradually raising the temperature of the raw material melt, the W-Re wire provided at the tip of the pull-down rod 8 was inserted into the hole and pulled down repeatedly. The liquid could be drawn out from the hole.

  The high frequency output was fixed so that the temperature at this time was maintained, the raw material melt was lowered, and crystallization was started. It was continuously pulled down at a speed of 3 mm / hr for 20 hours, and finally a single crystal having a diameter of 2.2 mm and a length of 60 mm was obtained.

  The obtained single crystal was cut into a length of about 20 mm by a blade saw equipped with a diamond cutting grindstone, and the side surface was ground to be processed into a shape having a length of 20 mm, a width of 2 mm, and a thickness of 1 mm. The vacuum ultraviolet light emitting device of the present invention was obtained by mirror polishing.

  The vacuum ultraviolet light emission characteristics of the obtained vacuum ultraviolet light emitting element composed of the Nd-doped BaLiF3 single crystal were measured as follows using the measuring apparatus shown in FIG. The measurement was performed at room temperature.

  The vacuum ultraviolet light emitting element 9 of the present invention was set at a predetermined position in the measuring apparatus, and the entire interior of the apparatus was replaced with nitrogen gas. Excitation light from a deuterium lamp 10 as an excitation light source was dispersed with an excitation spectrometer 11 (manufactured by Spectrometer Co., Ltd., KV201 type extreme ultraviolet spectrometer) to obtain a monochromatic light of 152 nm. The 152 nm excitation light was irradiated to the vacuum ultraviolet light emitting element 9, and the light emitted from the vacuum ultraviolet light emitting element 9 was dispersed with an emission spectrometer 12 (KV201 type extreme ultraviolet spectrometer manufactured by Spectrometer Co., Ltd.). The wavelength of the spectrum by the emission spectrometer 12 was swept in the range of 170 to 250 nm, and the emission intensity at each emission wavelength was recorded by the photomultiplier tube 13.

  As a result of the above measurement, the emission spectrum shown in FIG. 1 was obtained, and it was confirmed that the vacuum ultraviolet light emitting device of the present invention emitted light with sufficient luminance at a wavelength of 183 nm.

This figure is an emission spectrum of the vacuum ultraviolet light emitting device of the present invention. This figure is a schematic view of an apparatus for producing a crystal by the micro pull-down method. This figure is a schematic view of an emission spectrum measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 After heater 2 Heater 3 Heat insulating material 4 Stage 5 Crucible 6 Chamber 7 High frequency coil 8 Pulling rod 9 Vacuum ultraviolet light emitting element 10 Deuterium lamp 11 Excitation spectrometer 12 Emission spectrometer 13 Photomultiplier tube

Claims (2)

A vacuum ultraviolet light emitting element comprising a barium lithium fluoride single crystal containing neodymium as an activator. The vacuum ultraviolet light-emitting device according to claim 1, wherein the content of neodymium is 0.001 to 1 mol% with respect to barium lithium fluoride.

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