JP2009186613A - Method of manufacturing wavelength conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a wavelength conversion element capable of stably manufacturing periodic polarity inversion structure at a desired pitch. <P>SOLUTION: The method of manufacturing the wavelength conversion element has a process for forming a stripe-like pattern 2 comprising an insulator having ultraviolet ray absorptivity, on one face of a substrate 1 comprising a nonlinear optical crystal, and a process for applying a voltage between liquid electrodes 6, 7 while irradiating the one face of the substrate 1 with an ultraviolet ray, under the condition where the liquid electrodes 6, 7 serving as positive and negative electrodes contact respectively with both faces of the substrate 1 formed with the stripe-like pattern 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a wavelength conversion element.

  In recent years, as the demand for miniaturization of projectors has increased, projectors using laser light sources have been developed along with the increase in output of semiconductor lasers and the appearance of blue semiconductor lasers. This type of projector has a great potential as a next-generation display device because the color reproduction range can be sufficiently widened, and the size and the number of components can be reduced. As the light source, laser light sources of three colors of red (R), green (G), and blue (B) are necessary. For example, the source light for the R light and the light source for the B light are present in the semiconductor laser, but the source light for the G light is not present, so the infrared light from the infrared laser is incident on the nonlinear optical element. A technique is adopted in which G light is obtained by wavelength conversion using second harmonic generation (hereinafter abbreviated as SHG) generated at the time of generation.

In wavelength conversion of light using the nonlinear optical effect, a phase matching condition needs to be established between the fundamental wave before conversion and the harmonic wave after conversion, and a pseudo phase that periodically reverses the polarization direction in the crystal A matching method is used. As an example, a structure in which the polarization direction is periodically reversed at a fine pitch (hereinafter referred to as a periodic polarization reversal structure in this specification) is formed in a LiNbO ₃ crystal, and this is used as a wavelength conversion element. As a method of forming this type of periodic domain-inverted structure, a periodic striped mask pattern made of a photoresist is formed on a LiNbO ₃ crystal substrate, and then a liquid electrode is brought into contact with both surfaces of the substrate. A method has been proposed in which a voltage is applied between the electrodes to periodically reverse the polarization direction of the crystal (see Patent Document 1). Alternatively, a method is also proposed in which a substrate on which no mask pattern is formed is applied and a voltage is applied between the liquid electrodes, and simultaneously, a photomask is used to irradiate ultraviolet rays in a stripe pattern to periodically reverse the polarization direction of the crystal. (See Patent Document 2).
JP 2000-29086 A JP 2004-279601 A

  However, in either method of Patent Documents 1 and 2, it is difficult to stably manufacture the periodically poled structure at a desired pitch. Since the wavelength conversion element has a narrow allowable wavelength range that satisfies the phase matching condition, there is a problem in that the output (conversion efficiency) decreases when the pitch of the periodically poled structure deviates from a desired value.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a wavelength conversion element that can stably manufacture a periodically poled structure at a desired pitch. .

  In order to achieve the above object, a method for manufacturing a wavelength conversion element according to the present invention includes a step of forming a striped pattern made of an insulator having ultraviolet absorptivity on one surface of a substrate made of a nonlinear optical crystal, and the substrate. Applying a voltage between the liquid electrodes while irradiating ultraviolet light onto one surface of the substrate on which the striped pattern is formed in a state where the liquid electrodes serving as the positive electrode and the negative electrode are in contact with both surfaces of the substrate, respectively. It is characterized by.

  According to the inventor's consideration, when the method described in Patent Document 1 is used, the resist pattern swells in the liquid electrode and changes its dimensions, or the resist pattern is slightly conductive. This is the reason why the periodically poled structure having a desired pitch cannot be obtained stably. On the other hand, when the method described in Patent Document 2 is used, even if there is a slight difference in the likelihood of polarization reversal between the region irradiated with ultraviolet rays and the region not irradiated, the voltage is applied across the entire surface of the substrate in contact with the liquid electrode. Therefore, there is a problem that the periodically poled structure cannot be formed with good contrast.

  On the other hand, according to the method for manufacturing a wavelength conversion element of the present invention, after forming a striped pattern made of an insulator having ultraviolet absorptivity on one surface of the substrate, the liquid electrodes are brought into contact with both surfaces of the substrate, respectively. In this state, in order to apply a voltage between the liquid electrodes while irradiating one surface of the substrate on which the striped pattern is formed with the ultraviolet light, the region of the substrate on which the striped pattern exists and the region where the striped pattern does not exist There will be a difference in both applied voltages. At this time, in a region where the striped pattern does not exist, polarization inversion is further promoted by a synergistic effect of applying a high voltage effectively and irradiation with strong ultraviolet light compared to a region where the striped pattern exists. The Therefore, according to the method of the present invention, the polarization inversion occurs at a lower voltage and in a shorter time than the method of Patent Document 1, and the problems such as the fluctuation of the polarization inversion pitch due to the swelling of the resist pattern can be solved. Further, according to the method of the present invention, the difference between the ultraviolet intensity and the applied voltage becomes clear between the region where the striped pattern is present and the region where the striped pattern is not present, as compared with the method of Patent Document 2. As described above, according to the method for manufacturing a wavelength conversion element of the present invention, the periodically poled structure can be stably manufactured at a desired pitch.

  Further, in the step of forming a striped pattern, a striped pattern made of a photoresist may be formed by applying a photoresist to one surface of the substrate and then exposing and developing the photoresist.

  When a photoresist is used, the photoresist can be used as it is as the striped pattern of the present invention by patterning by exposing and developing the photoresist, so that the manufacturing process can be simplified.

  Further, when forming a striped pattern made of a photoresist, after applying a photoresist having ultraviolet sensitivity on one surface of the substrate, a sealing member having a striped mask pattern is arranged on the one surface side of the substrate, In a state where a developer is filled in a space surrounded by a sealing member, the photoresist is exposed by irradiating ultraviolet rays through the sealing member, and a striped pattern is formed by developing the exposed photoresist with the developer. Then, after replacing the developer in the space with the liquid electrode, a step of applying a voltage between the liquid electrodes while irradiating one surface of the substrate with ultraviolet rays may be performed.

  When forming a striped pattern made of a photoresist, an apparatus separate from the apparatus used in the ultraviolet irradiation / voltage application process may be used for pattern formation, but if a photoresist having ultraviolet sensitivity is used, ultraviolet irradiation / It can also be shared with the device used in the voltage application step. That is, after applying an ultraviolet-sensitive photoresist on one surface of the substrate, a sealing member having a striped mask pattern is disposed on the one surface side of the substrate, and development is performed in a space surrounded by the substrate and the sealing member. Stripe pattern can be formed by exposing and developing the photoresist by irradiating ultraviolet rays through the sealing member in a state filled with the liquid, and then developing, and then replacing the developer in the space with the liquid electrode. A voltage application process can be performed. Thereby, the manufacturing process can be simplified, shortened, and the manufacturing apparatus can be shared. In addition, since the region where the striped pattern exists on the substrate is masked doubly by the mask pattern of the sealing member and the resist pattern, the contrast of the ultraviolet intensity between the region where the striped pattern exists and the region where the striped pattern does not exist Can be further enhanced.

  Alternatively, in the step of forming a striped pattern, an inorganic insulating film is formed on one surface of the substrate, a photoresist is coated on the inorganic insulating film, and the photoresist is exposed and developed to form a resist pattern. A striped pattern made of an inorganic insulating film can be formed by etching the inorganic insulating film using as a mask.

  As the material for forming the striped pattern, an inorganic insulating film can be used instead of the photoresist. In that case, since it is necessary to once form a resist pattern on the inorganic insulating film and to etch the inorganic insulating film using this resist pattern as a mask, the manufacturing process becomes complicated compared to the case of using a photoresist. However, since the inorganic insulating film has lower permeability of the liquid electrode than the photoresist, problems such as variations in the polarization inversion pitch due to the swelling of the photoresist are more easily solved.

[First Embodiment]
The first embodiment of the present invention will be described below with reference to FIG.
FIG. 1 is a process cross-sectional view sequentially showing the method for manufacturing the wavelength conversion element of this embodiment.

In the present embodiment, the substrate 1 made of lithium niobate (LiNbO ₃ ) is used as the nonlinear optical crystal. First, a photoresist is applied to one surface of the substrate 1, and the photoresist is exposed and developed using a photomask provided with a periodic striped pattern, so that the photoresist as shown in FIG. A striped pattern 2 is formed. For example, the width of one pattern 2 is several μm, and the interval between adjacent patterns 2 is also about several μm. Here, a photoresist having photosensitivity (absorption) to i-line (wavelength: 365 nm, ultraviolet ray) is used.

  Next, as shown in FIG. 1B, the sealing substrates 3 and 4 (sealing members) having ultraviolet transparency are set so as to face the upper and lower surfaces of the substrate 1 on which the striped pattern 2 is formed. Are arranged with an interval of (for example, about several μm). Here, the sealing substrate facing the surface on which the striped pattern 2 is formed is the first sealing substrate 3, and the sealing substrate facing the surface on which the striped pattern is not formed is the second sealing substrate. This is called a stop substrate 4. O-rings 5 are arranged at positions corresponding to the peripheral portions of the substrate 1 and the respective sealing substrates 3 and 4, and the space between the substrate 1 and the respective sealing substrates 3 and 4 is a sealed space. Each space is filled with an electrolytic solution such as an aqueous lithium chloride solution, which is used as liquid electrodes 6 and 7. As a result, the liquid electrodes 6 and 7 are in contact with both the surface of the substrate 1 on which the striped pattern 2 is formed and the surface on which the striped pattern 2 is not formed. In this embodiment, a quartz substrate is used as the sealing substrates 3 and 4, but other substrates such as a glass substrate can also be used. Of the two sealing substrates 3 and 4, at least the first sealing substrate 3 needs to use a substrate having ultraviolet transparency, but the second sealing substrate 4 does not necessarily have ultraviolet transparency. The substrate may not be included.

A voltage is applied between the liquid electrodes 6 and 7 while irradiating ultraviolet rays from an ultrahigh pressure mercury lamp or the like toward the substrate 1 (the surface on which the striped pattern 2 is formed) from the outside of the first sealing substrate 3. Apply. In the present embodiment, the liquid electrode 6 that contacts the surface on which the striped pattern 2 of the substrate 1 is formed is the positive electrode, and the liquid electrode 7 that contacts the surface on which the striped pattern 2 is not formed is the negative electrode. Further, the liquid electrodes 6 and 7 may be used at room temperature or heated. As a result, the region of the substrate 1 where the liquid electrode 6 is in contact between adjacent striped patterns 2 is inverted from the polarization state of the original LiNbO ₃ crystal, while the region where the liquid electrode 6 is not in contact is the original LiNbO. The polarization state of the _three crystals remains. In this way, a periodically poled structure is formed. The wavelength conversion element is manufactured through the above steps. Note that the striped pattern 2 made of a photoresist may or may not be removed after the polarization inversion process is completed.

  In addition, the above description has been made on the assumption that the wavelength conversion element is manufactured independently. However, when a plurality of chip-shaped wavelength conversion elements are manufactured simultaneously from the wafer state, formation of a striped pattern in the wafer state, What is necessary is just to perform each process of the polarization inversion process by ultraviolet irradiation and voltage application, and cutting out several chips from a wafer. Further, each step of polishing the light incident surface and the light exit surface corresponding to the end face of the wavelength conversion element, and the non-reflective coating on the light entrance surface and the light exit surface may be added.

  According to the method for manufacturing a wavelength conversion element of this embodiment, a voltage is applied between the liquid electrodes 6 and 7 while irradiating ultraviolet light onto one surface of the substrate 1 on which the striped pattern 2 is formed. A difference occurs in the ultraviolet intensity and the applied voltage between the region where the pattern 2 is present and the region where the pattern 2 is not present. At this time, in the region where the striped pattern 2 does not exist, the polarization inversion is more due to the synergistic effect of applying a higher voltage effectively and irradiation with strong ultraviolet light compared to the region where the striped pattern 2 exists. Promoted. Therefore, polarization reversal occurs in a short time with a low voltage, which can solve problems such as fluctuations in the polarization reversal pitch due to the swelling of the resist pattern. In addition, the region where the striped pattern 2 exists and the region where it does not exist The difference between UV intensity and applied voltage becomes clearer. Thereby, according to the manufacturing method of the wavelength conversion element of this embodiment, a periodic polarization inversion structure can be manufactured stably with a desired pitch.

  Further, in the case of the present embodiment, the photoresist can be used as it is as the striped pattern 2 by patterning by exposing, developing and patterning the photoresist by a normal photolithography technique, so that the manufacturing process can be simplified. .

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a process cross-sectional view illustrating the manufacturing method of the wavelength conversion element of this embodiment in order.
Since the same thing as 1st Embodiment can be used for the crystal substrate of this embodiment, a photoresist, a liquid electrode, etc., detailed description is abbreviate | omitted.

First, as shown in FIG. 2A, a photoresist 9 is applied to one surface of the substrate 1.
Here, in this embodiment, as shown in FIG. 2B, before patterning the photoresist 9, the first sealing substrate 13 and the second sealing substrate 4 are placed on the upper and lower surfaces of the substrate 1, respectively. Are arranged at predetermined intervals (for example, about several μm) so as to face each other. At this time, the first sealing substrate 13 is not a mere substrate, but a sealing substrate 13 provided with a periodic striped mask pattern 14 (that is, the photomask of the first embodiment). Use. Then, ultraviolet light is irradiated through the first sealing substrate 13 in a state where the space surrounded by the substrate 1 and the first sealing substrate 13 is filled with the developer 15. Then, it becomes equivalent to exposing the photoresist through the photomask, and the exposed photoresist 9 is developed with the developer 15 in direct contact, and the striped pattern 2 is formed.

  Next, as shown in FIG. 2C, the developer 15 in the space on the first sealing substrate 13 side is replaced with the liquid electrode 6, and the liquid electrode 7 is also in the space on the second sealing substrate 4 side. Then, a voltage is applied between the liquid electrodes 6 and 7 while irradiating ultraviolet rays from the outside of the first sealing substrate 13 toward the substrate 1 (the surface on which the striped pattern 2 is formed). Thereby, the area | region where the liquid electrode 6 between the adjacent striped patterns 2 contacted in the board | substrate 1 reverses a polarization, and a periodic polarization inversion structure is formed. The wavelength conversion element is manufactured through the above steps.

  Also in this embodiment, it is possible to obtain the same effect as in the first embodiment that the periodic polarization inversion structure of the wavelength conversion element can be stably manufactured at a desired pitch. Furthermore, in the case of the present embodiment, the stripe pattern forming step and the ultraviolet irradiation / voltage applying step can be performed by a single device by simply replacing the liquid filled in the space on the first sealing substrate 13 side. . Thereby, the manufacturing process can be simplified, shortened, and the manufacturing apparatus can be shared. Further, since the region where the striped pattern 2 exists on the substrate 1 is double masked by the mask pattern 14 of the first sealing substrate 13 and the striped pattern 2 of the resist, the striped pattern 2 exists. The contrast of the ultraviolet intensity can be further increased between the region that does and does not exist.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, an inorganic insulating film can be used as a material for forming the striped pattern instead of the photoresist. As an inorganic insulating film, a thin film can be formed on a LiNbO ₃ substrate by a method such as sputtering, patterning is possible, it has insulating properties, UV absorption, and electrolyte does not penetrate inside. For example, silicon nitride (SiN), boron nitride (BN), or the like can be used. In this case, it is necessary to once form a resist pattern on the inorganic insulating film and then etch the inorganic insulating film using this resist pattern as a mask, but problems such as fluctuations in the polarization inversion pitch due to the swelling of the photoresist are more solved. It becomes easy to do.

  In addition, specific descriptions regarding materials, dimensions, and the like of the constituent elements exemplified in the above embodiment can be appropriately changed.

It is process sectional drawing which shows the manufacturing method of the wavelength conversion element of 1st Embodiment of this invention. It is process sectional drawing which shows the manufacturing method of the wavelength conversion element of 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Striped pattern, 3, 13 ... First sealing substrate, 4 ... Second sealing substrate, 5 ... O-ring, 6, 7 ... Liquid electrode, 9 ... Photoresist, 14 ... Mask Pattern, 15 ... developer.

Claims (4)

Forming a striped pattern made of an insulator having ultraviolet absorptivity on one surface of a substrate made of a nonlinear optical crystal;
Applying a voltage between the liquid electrodes while irradiating one surface of the substrate with ultraviolet rays in a state where the liquid electrodes to be a positive electrode and a negative electrode are in contact with both surfaces of the substrate on which the striped pattern is formed, respectively. A method for manufacturing a wavelength conversion element, comprising:   The step of forming the striped pattern is characterized in that after the photoresist is applied to one surface of the substrate, the striped pattern made of the photoresist is formed by exposing and developing the photoresist. Item 2. A method for manufacturing a wavelength conversion element according to Item 1.   After coating the photoresist having ultraviolet sensitivity on one surface of the substrate, a sealing member having a striped mask pattern is disposed on the one surface side of the substrate, and is surrounded by the substrate and the sealing member In the state where the developer is filled in the space, the photoresist is exposed by irradiating ultraviolet rays through the sealing member, and the striped pattern is formed by developing the exposed photoresist with the developer. The manufacturing method of the wavelength conversion element according to claim 2, wherein a step of applying a voltage between the liquid electrodes is performed while irradiating one surface of the substrate with ultraviolet rays after replacing the developer in the liquid electrode. Method.   In the step of forming the striped pattern, after forming an inorganic insulating film on one surface of the substrate, applying a photoresist on the inorganic insulating film, exposing and developing the photoresist, forming a resist pattern; 2. The method of manufacturing a wavelength conversion element according to claim 1, wherein the striped pattern made of the inorganic insulating film is formed by etching the inorganic insulating film using the resist pattern as a mask.

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