JP2008300634A - Bonding method of optical crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonding method of an optical crystal capable of optical bonding even when bonding the optical crystals different in composition to each other. <P>SOLUTION: In the bonding method of the optical crystal 1 for bonding the first optical crystal 2 and second optical crystal 3 which are each different in the composition, on mutual bonding surfaces 2a and 3a, reactive ion etching is applied to the bonding surface 2b of the first optical crystal using a gas containing halogen which is allowed to chemically react with the first optical crystal, the reactive ion etching is applied to the bonding surface 3b of the second optical crystal using the gas containing the halogen which is allowed to chemically react with the second optical crystal, and the bonding surfaces 2a and 3a are optically bonded to each other thereafter. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for joining optical crystal bodies, and more particularly, to a method for joining optical crystal bodies in which optical crystal bodies having different compositions are optically joined (optical contact) to each other at their joint surfaces.

High-power solid-state lasers used for processing / evaluation and as light sources for various video display devices destroy the coating film formed on the crystal surface due to the heat generated in the crystal when exciting the laser light. In some cases, the laser output is reduced or the operation life is shortened.
As a means for solving the above problems, for example, as described in Patent Document 1, a high-power type solid-state laser is obtained by optically bonding a laser crystal body containing an optically active substance and an optical crystal body not containing an optically active substance. There is a method for joining optical crystals.
JP 2004-54170 A

However, the optical crystal bonding method described in Patent Document 1 is effective when optically bonding optical crystal bodies having the same composition to each other. In particular, a high-power solid-state laser for processing is used. When optical crystal bodies having different compositions are optically bonded, the crystal body that has been finished with high surface accuracy by mechanical polishing in advance due to the difference in the etching rate of ion beam etching with respect to the crystal orientation of the optical crystal body. The surface is etched with anisotropy by the ion beam etching.
Therefore, since the surface accuracy of the bonding surface, which is the crystal surface after ion beam etching, is worse than that before etching, it is difficult to optically bond optical crystal bodies having different compositions.

  Therefore, the problem to be solved by the present invention is to provide a method for bonding optical crystals that enables optical bonding even when optical crystals having different compositions are bonded together.

In order to solve the above problems, the present invention has the following means.
A bonding method of an optical crystal body (1) in which a first optical crystal body (2) and a second optical crystal body (3) having different compositions are bonded to each other at their bonding surfaces (2a, 3a), A first reactive ion etching step of performing reactive ion etching on the bonding surface (2b) of the first optical crystal using a gas containing a halogen element that chemically reacts with the first optical crystal; A second reactive ion etching step of performing reactive ion etching on the bonding surface (3b) of the second optical crystal using a gas containing a halogen element that chemically reacts with the second optical crystal; An optical bonding step of optically bonding the bonding surfaces (2a, 3a) after the first reactive ion etching step and the second reactive ion etching step.

  According to the present invention, in the method for bonding optical crystals, there is an effect that optical bonding becomes possible even when optical crystals having different compositions are bonded.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a perspective view for explaining a joined body produced by an embodiment of the optical crystal joining method of the present invention.
FIG. 2 is a process flow diagram for explaining an embodiment of the optical crystal bonding method of the present invention, and FIG. 3 shows a reactive ion etching apparatus and a reactive ion etching processing method using the same in the embodiment. It is a typical sectional view for explaining.

<Example>
In the embodiment, an optical crystal bonding method in a solid-state laser used as a light source for an image display device, for example, a green light source having a peak wavelength of 532 nm will be described as an example.

  First, the solid-state laser 1 that is an optical bonded body manufactured by the optical crystal bonding method of the present invention will be described.

As shown in FIG. 1, the solid-state laser 1 includes a YVO ₄ (Yttrium Orthovanadate) laser crystal body 2 containing Nd (neodymium) which is an optically active substance, and a KTiOPO ₄ (Potassium Titanyl Phosphate, KTP) which is a nonlinear optical crystal body. The crystal body 3 is an optically bonded body formed by optical bonding (optical contact).
In addition, since the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 are optically bonded, each of the bonding surfaces 2a and 3a of the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 has a surface accuracy of 150 nm. This is a flat surface having a surface roughness (centerline average roughness: Ra) of 1 nm or less.
Then, by exciting the YVO ₄ laser crystal body 2, an infrared laser beam having a peak wavelength of 1064 nm is oscillated, and when this infrared laser light passes through the KTiOPO ₄ crystal body 3, the second harmonic, Green laser light having a peak wavelength of 532 nm is emitted from the opposite side of the KTiOPO ₄ crystal 3 to the YVO ₄ laser crystal 2.

In the embodiment, the shape of the YVO ₄ laser crystal body 2 is a plate shape having a length L2 and a width W2 of 10 mm and a thickness t2 of 1 mm, and the shape of the KTiOPO ₄ crystal body 3 is 12 mm in length L3 and width W3. The plate was formed with a thickness t3 of 1 mm.

  Next, an example of a method for joining optical crystals for producing the above-described solid-state laser 1 will be described with reference to FIGS.

First, the surface to be the bonding surface 2a of the YVO ₄ laser crystal body 2 and the surface to be the bonding surface 3a of the KTiOPO ₄ crystal body 3 are polished by using a well-known polishing method. A flat surface having a surface roughness (centerline average roughness: Ra) of 1 nm or less is set to 150 nm or less (P1).

Next, if the polishing liquid or polishing agent used in the polishing is sufficiently removed by ultrasonic cleaning, and dust or foreign matter adheres to each surface after the removal, the dust or foreign matter is filtered. Blow off with nitrogen gas (nitrogen blow) to remove.
In addition, when the dust and foreign matter cannot be completely removed by nitrogen blowing, the dust and foreign matter are completely removed using a cotton swab or the like soaked with a volatile solvent such as isopropyl alcohol after nitrogen blowing ( P2).

  Thereafter, using an optical microscope or the like, it is confirmed that there is no dust or foreign matter adhering or cracking on each surface (P3).

  It is desirable to perform the above-described nitrogen blow or optical microscope confirmation in a clean room of class 100 or lower.

  Next, a reactive ion etching process using a halogen-based gas that exhibits a chemical reaction with respect to each of the crystals 2 and 3 is performed on each of the surfaces 2b and 3b (P4).

  Here, a specific processing method by reactive ion etching will be described with reference to FIG.

  First, the reactive ion etching apparatus 10 for performing reactive ion etching is demonstrated.

  As shown in FIG. 3, the reactive ion etching apparatus 10 mainly includes a cathode electrode 11 having a flat electrode surface 11a, a plate-like insulating member 12 provided on the electrode surface 11a, and an upper portion of the insulating member 12. And an anode electrode 13 having a flat electrode surface 13a that is opposed to the electrode surface 11a of the cathode electrode 11 with a predetermined gap, and accommodates the cathode electrode 11, the insulating member 12, and the anode electrode 13. A vacuum chamber 14 for reducing the pressure in the vacuum chamber 14, and a high-frequency power source 16 for applying a predetermined high-frequency electric field between the cathode electrode 11 and the anode electrode 13.

  The vacuum chamber 14 can freely open and close the gas introduction port 18 for introducing the gas such as the halogen-based gas and the inert gas into the vacuum chamber 14 and the introduction and blocking of the gas into the vacuum chamber 14. There is provided a universal open / close valve 19 to be controlled, an exhaust port 20 to which the above-described pressure reducing means 15 is connected, and a universal open / close valve 21 for controlling the pressure reduction and blocking in the vacuum chamber 14 by the pressure reducing means 15 so as to be openable and closable. .

The cathode electrode 11 is electrically connected to the anode side of the high-frequency power source 16 via the wiring capacitor 23 via the blocking capacitor 25.
The anode electrode 13 is electrically connected to the cathode side of the high-frequency power source 16 via the wiring portion 23, and the anode electrode 13 and the cathode side of the high-frequency power source 16 are grounded.
As the decompression means 15, a commercially available vacuum pump or the like can be used.

Next, using the reactive ion etching apparatus 10, first, a method of performing reactive ion etching on the surface of the YVO ₄ laser crystal 2 that has been subjected to the above-described processes of the P1 to P3 processes and the vicinity thereof. This will be described with reference to FIG.
Here, the surface that has been subjected to the processes in the above-described P1 to P3 steps is referred to as a surface 2b.

First, the YVO ₄ laser crystal body 2 is placed on the insulating member 12 so that the surface 2 b faces the anode electrode 13.
In an embodiment, an insulating plate 26 having a housing capable of opening 26a of the YVO ₄ laser crystal 2 and having substantially the same thickness as the YVO ₄ thickness t2 of the laser crystal 2, the insulating plate 26 insulating member Then, the YVO ₄ laser crystal body 2 was placed on the insulating member 12 so as to be accommodated in the opening 26a.
By using this insulating plate 26, when reactive ion etching is performed in a state where the YVO ₄ laser crystal 2 is accommodated in the opening 26a of the insulating plate 26, an electric field is generated at the edge of the YVO ₄ laser crystal 2. Since concentration can be prevented, in-plane variation in the etching rate can be reduced.

Next, the open / close valve 21 is opened, and the pressure in the vacuum chamber 14 is reduced by the pressure reducing means 15 through the exhaust port 20.
Then, after the pressure in the vacuum chamber 14 is reduced to, for example, 0.1 Pa or less, the open / close valve 19 is opened, and a halogen-based gas that exhibits a chemical reaction with respect to the YVO ₄ laser crystal 2 is vacuumed from the gas inlet 18. The pressure is introduced into the chamber 14 and the pressure in the vacuum chamber 14 is adjusted to 4 Pa.
In the examples, CHF ₃ (trifluoromethane) gas was used as the halogen-based gas. Further, instead of this CHF ₃ gas, a fluorine-based gas such as CF ₄ (tetrafluoromethane) gas or C ₂ F ₆ (hexafluoroethane) gas may be used.

Next, a high frequency electric field having a power of 100 W and a frequency of 13.56 MHz, for example, is generated between the cathode electrode 11 and the anode electrode 13 by the high frequency power supply 16 to generate plasma discharge.
By this plasma discharge, the CHF ₃ gas in the vacuum chamber 14 is ionized, and the ionized fluorine ions are attracted by the negative potential generated on the electrode surface 11a of the cathode electrode 11, and the surface 2b of the YVO ₄ laser crystal 2 The surface 2b and its vicinity are etched by a chemical reaction at that time. Such etching is generally referred to as reactive ion etching.
In the example, the reactive ion etching was performed for about 10 minutes, so that the YVO ₄ laser crystal body 2 was etched by about 50 nm from the surface 2b in the thickness direction.

Thereafter, the generation of the high-frequency electric field by the high-frequency power source 16 is terminated, the free opening / closing valve 19 is closed, and the introduction of the halogen-based gas into the vacuum chamber 14 is stopped.
Further, after the halogen-based gas in the vacuum chamber 14 is sufficiently exhausted by the decompression means 15, the atmosphere is introduced into the vacuum chamber 14 from, for example, the gas inlet 18 to bring the inside of the vacuum chamber 14 to an atmospheric pressure state.

Next, the YVO ₄ laser crystal body 2 and the insulating plate 26 that have undergone the above-described procedure are taken out from the vacuum chamber 14, and the KTiOPO ₄ crystal body 3 is processed on the insulating member 12 by the above-described P1 to P3 processes. It is placed so that the opposite surface faces the anode electrode 13.
Here, the surface that has been subjected to the processes in the above-described P1 to P3 steps is referred to as a surface 3b.

In an embodiment, an insulating plate 27 having a housing capable of opening 27a of KTiOPO ₄ crystal 3 which has substantially the same thickness as the thickness t3 of KTiOPO ₄ crystal 3, the insulating plate 27 insulating member 12 on Then, the KTiOPO ₄ crystal 3 was placed on the insulating member 12 so as to be accommodated in the opening 27a.
By using this insulating plate 27, when reactive ion etching is performed in a state where the KTiOPO ₄ crystal 3 is accommodated in the opening 27 a of the insulating plate 27, the electric field is concentrated on the edge of the KTiOPO ₄ crystal 3. Therefore, the in-plane variation in the etching rate can be reduced.

Next, the vacuum chamber 14 is depressurized through the exhaust port 20 by the depressurizing means 15 in a state where the openable on-off valve 21 is opened.
Then, after the pressure in the vacuum chamber 14 is reduced to, for example, 0.1 Pa or less, the openable valve 19 is opened, and a halogen-based gas that exhibits a chemical reaction with respect to the KTiOPO ₄ crystal 3 is vacuumed from the gas inlet 18. The pressure in the vacuum chamber 14 is set to 4 Pa by introducing into the chamber 14.
In the examples, CHF ₃ gas was used as the halogen-based gas. Further, instead of this CHF ₃ gas, a fluorine-based gas such as CF ₄ gas or C ₂ F ₆ gas can be used.

Next, a high frequency electric field having a power of 100 W and a frequency of 13.56 MHz, for example, is generated between the cathode electrode 11 and the anode electrode 13 by the high frequency power supply 16 to generate plasma discharge.
By this plasma discharge, the CHF ₃ gas in the vacuum chamber 14 is ionized, and the ionized fluorine ions are attracted by the negative potential generated on the electrode surface 11 a of the cathode electrode 11 and are attracted to the surface 3 b of the KTiOPO ₄ crystal 3. Colliding while accelerating, the surface 3b and its vicinity are etched by a chemical reaction. Such etching is generally referred to as reactive ion etching.
In the example, the reactive ion etching was performed for about 10 minutes, so that the KTiOPO ₄ crystal 3 was etched from the surface 3b in the thickness direction by about 50 nm.

Thereafter, the generation of the high-frequency electric field by the high-frequency power source 16 is terminated, the free opening / closing valve 19 is closed, and the introduction of the halogen-based gas into the vacuum chamber 14 is stopped.
After the halogen-based gas in the vacuum chamber 14 is sufficiently exhausted by the decompression means 15, for example, air is introduced into the vacuum chamber 14 from the gas inlet 18 to bring the inside of the vacuum chamber 14 into an atmospheric pressure state.

Next, the KTiOPO ₄ crystal 3 is taken out from the vacuum chamber 14, and the surface accuracy and surface roughness of the etched surfaces 2 a and 3 a after the reactive ion etching in the YVO ₄ laser crystal 2 and the KTiOPO ₄ crystal 3 are obtained. Is measured (P5 in FIG. 2).
As a result, it was confirmed that each of the etched surfaces 2a and 3a was a substantially flat surface having a surface accuracy of 150 nm or less and a surface roughness (centerline average roughness: Ra) of 1 nm or less.
These etched surfaces 2a and 3a become bonding surfaces 2a and 3a on which the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 that have undergone the above-described steps are optically bonded to each other.

Thereafter, the interference fringes generated between the joint surfaces 2a and 3a are observed using, for example, an interferometer while the joint surface 2a of the YVO ₄ laser crystal body 2 and the joint surface 3a of the KTiOPO ₄ crystal body 3 are pressed against each other. .
Then, after the interference fringes cannot be confirmed, the press contact is finished.
By this pressure welding, the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 are optically joined (referred to as optical contact) at the joint surfaces 2a and 3a (P6).

Further, the bonded body of the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 that has undergone the above-described process is subjected to a heat treatment, for example, at 550 ° C. for 48 hours in a vacuum or in an inert gas atmosphere such as Ar gas. Thus, the bonding strength in the optical bonding can be improved (P7).

Through the above-described steps, the solid laser 1 is obtained which is a bonded body in which the YVO ₄ laser crystal body 2 and the KTiOPO ₄ crystal body 3 shown in FIG.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

  For example, in the embodiments, a solid laser is described as an example of a joined body of optical crystal bodies having different compositions, but the present invention is not limited to this.

In the examples, the YVO ₄ laser crystal and the KTiOPO ₄ crystal have been described as examples of the optical crystal having different compositions. However, the present invention is not limited to this, and an optical crystal other than the above optical crystal. Also in the body, the same effect as in the embodiment can be obtained by performing the reactive ion etching process using the halogen-based gas that exhibits a chemical reaction on the optical crystal body on the surface to be the bonding surface. .

Further, after the reactive ion etching process in the embodiment, a reverse sputtering process using, for example, Ar (argon) gas may be performed on the etching process surface.
In this case, it is desirable that the etching amount by the reverse sputtering treatment be 10 nm or less in the thickness direction from the etching treatment surface. If the thickness exceeds 10 nm, the influence of anisotropic etching due to the reverse sputtering treatment increases, and the surface accuracy may deteriorate.

In the reactive ion etching process of the embodiment, aluminum oxide (for example, Al ₂ O ₃ ) or silicon oxide (for example, SiO ₂ ) can be used as the material for the insulating member 12 and the insulating plates 26 and 27. Further, as the other material, the same material as that of the optical crystal to be subjected to reactive ion etching can be used.

It is a perspective view for demonstrating the joined_body | zygote produced by the Example of the joining method of the optical crystal body of this invention. It is a process flow figure for explaining the example of the joining method of the optical crystal of the present invention. It is typical sectional drawing for demonstrating the reactive ion etching apparatus and reactive ion etching processing method using the same in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid state laser, 2 YVO ₄ laser crystal body, 2a, 2b, 3a, 3b surface, 3 KTiOPO ₄ crystal body, 10 Reactive ion etching apparatus, 11 Cathode electrode, 11a, 13a electrode surface, 12 Insulating member, 13 Anode electrode , 14 Vacuum chamber, 15 Depressurization means, 16 High frequency power supply, 18 Gas inlet, 19, 21 Free open / close valve, 20 Exhaust port, 23 Wiring section, 24 Insulating member, 25 Blocking capacitor, 26, 27 Insulating plate, 26a, 27a Opening, L2, L3 length, W2, W3 width, t2, t3 thickness

Claims (1)

A method of bonding optical crystals, in which a first optical crystal and a second optical crystal having different compositions are bonded to each other at their bonding surfaces,
A first reactive ion etching step of performing reactive ion etching on a bonding surface of the first optical crystal using a gas containing a halogen element that chemically reacts with the first optical crystal;
A second reactive ion etching step of performing reactive ion etching on the bonding surface of the second optical crystal using a gas containing a halogen element that chemically reacts with the second optical crystal;
An optical bonding step of optically bonding the bonding surfaces after the first reactive ion etching step and the second reactive ion etching step;
Bonding method of optical crystal body having

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