JPH05270988A - Formation of titanium-sapphire single crystal film - Google Patents

Abstract

PURPOSE:To provide a process for forming a titanium-sapphire single crystal film useful for the relatively low-cost production of a device such as waveguide- type solid laser or waveguide-type light-amplifier which uses exclusively one surface of the substrate. CONSTITUTION:The objective process is composed of a step for forming a Ti thin film 11 on a surface of a sapphire (Al2O3) substrate 10 and a step to partially heating and melting the surface of the substrate 10 having the Ti thin film 11 in a reducing atmosphere and recrystallizing the molten part while moving the heating position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a titanium-sapphire single crystal film, and more particularly to a method for forming a single crystal film suitable for use in an optical waveguide device.

[0002]

2. Description of the Related Art A titanium-sapphire single crystal has a broad fluorescence spectrum (λ = 700 to 1100 nm) and is therefore used as a basic element of an optical IC or an optical sensor. FIG. 3 shows an apparatus for producing a titanium-sapphire single crystal described in Journal of TOSOH Research Vol.33 No.2 (1989). In the figure, 1 is a sapphire (Al ₂ O ₃ ) seed crystal, 2 is a xenon arc lamp, and 3 is a polycrystalline titanium-sapphire (Ti: Al ₂ O ₃ ) raw material rod.

Reference numeral 4 is a molten portion of the raw material rod, 5 is a converging mirror house, 7 is a quartz tube, 8 is a monitor lens, and 9 is a monitor lens.
Is a monitor screen. In the figure, the seed crystal 1 attached to the tip of the raw material rod 3 is melted in a band shape by a condenser lamp, and the molten portion is moved in the axial direction of the raw material rod to obtain an Al ₂ O ₃ single crystal rod. be able to. In this case, the Ti in the polycrystal is Al when the quartz tube is made into a reducing atmosphere such as Ar + H _2.
Incorporated as Ti ³⁺ ions in ₂ O ₃ , 650-1
A laser crystal for variable wavelength having a broad fluorescence spectrum of 100 nm can be obtained.

[0004]

With the above-mentioned conventional manufacturing method, it is possible to obtain a large single crystal. However, the equipment is large and the melting point of Al ₂ O ₃ is 206
Since it is as high as 0 ° C., there is a problem that a large amount of power is required for heating. The present invention has been made to solve the above-mentioned problems of the prior art. For example, a device such as a waveguide type solid-state laser or a waveguide type optical amplifier that uses only the substrate surface can be manufactured at a relatively low cost. An object of the present invention is to provide a method for forming a titanium / sapphire single crystal film.

[0005]

In order to solve the above problems, the present invention provides a step of forming a Ti thin film on the surface of a sapphire (Al ₂ O ₃ ) substrate, and a step of forming the Ti thin film on the surface of the substrate. The method is characterized by including a step of partially heating and melting in a reducing atmosphere and recrystallizing the molten part while moving the heating position.

[0006]

[Function] When a Ti thin film is formed on an Al ₂ O ₃ substrate and the substrate is heated in a reducing atmosphere, the Ti thin film on the surface becomes Al.
_It is taken into the ₂ O ₃ substrate as Ti ³⁺ ions.

[0007]

1 (a) and 1 (b) are sectional views showing a schematic manufacturing process of a titanium / sapphire single crystal film of the present invention. It demonstrates according to a process. Step (a) A Ti thin film 1 having a thickness of about 0.03 μm is formed on the surface of the single crystal Al ₂ O ₃ substrate 10 by using a sputtering or vacuum deposition apparatus.
1 (the thickness of the Ti thin film 11 is determined by the doping concentration and the melting depth).

Step (b) The substrate 10 is placed in a reducing atmosphere in which Ar gas 98%: H ₂ gas 2% to Ar gas 96%: H ₂ gas 4% is mixed, and a substrate containing a Ti thin film 11 is placed. Partially heat the surface. FIG. 3 is a perspective view of the above step (b) performed by the present inventors. The substrate 10 has a width (a) of 2.5 m.
m, length (b) 25 mm, thickness 0.2 to 0.5 mm, a commercially available one, with a spot diameter of 3 m as a heating source
A CO ₂ laser beam with a wavelength of about m was used (the oscillation wavelength of the CO ₂ laser is well absorbed by Al ₂ O ₃ around 10 μm).

Then, a laser was applied to the vicinity of the edge of the substrate 10 to gradually increase the power from about 7 W to about 20 W in about 4 minutes (when the temperature is rapidly increased, a difference in thermal expansion occurs in the substrate and the substrate is destroyed. To). When the surface was melted, it was moved to the other end of the substrate at a speed of about 15 μm per minute. By gradually moving the heating part in this way, the melting part moves, and the passed part is cooled and recrystallized. In this case, the Ti thin film is oxidized during recrystallization in an oxidizing atmosphere and
Al ₂ O ₃ is doped as ⁴⁺ ions, but oxidation does not proceed sufficiently in a reducing atmosphere and Ti ³⁺ ions are ^added as A
A Ti: Al ₂ O ₃ single crystal film 20 doped in 1 ₂ O ₃ is formed.

Further, during recrystallization, epitaxial growth follows the surface orientation of the substrate 10, so that T
It is possible to obtain Al ₂ O ₃ single crystals doped with i ³⁺ ions (here a substrate with a C-axis in the surface is used). The thickness of the Ti: Al ₂ O ₃ single crystal produced as described above is about 50 to 100 μm, and this thin film has the same fluorescence spectrum characteristics as the bulk Ti: Al ₂ O ₃ single crystal produced by the conventional method. Met. Next, with reference to FIGS. 3 and 4, a method of forming an optical waveguide using the titanium-sapphire single crystal film produced according to the present invention will be described according to schematic steps.

Step 1 (see FIG. 1A) An Al ₂ O ₃ single crystal substrate 12 having a C axis on the surface is prepared separately, and the titanium sapphire thin film portion 20 produced as described above is joined by direct joining. At the time of joining, each joining surface is processed smoothly by optical polishing, washed with sulfuric acid / hydrogen peroxide to sufficiently remove stains, and then the C axes of the surfaces are made orthogonal to each other for close contact. The adhered substrates are heat-treated for 60 minutes in an electric furnace at 1300 ° C. while applying pressure of about 5000 Pa (0.5 kgf / cm ² ). In this case, if the heating temperature is low (about 1100 ° C.), the bonding is incomplete. Next, high (16
There is a risk of damage due to the difference in expansion coefficient depending on the plane orientation).

Step 2 (see FIG. 2B) Of the two bonded plates, the substrate 10 side is polished to form a thickness (t) of about 5 μm, and a thin film portion 2 of titanium sapphire is formed.
Expose 0. For this polishing, for example, rough grinding is performed with a lapping machine using diamond abrasive grains of about 6 μm, and then 1 μm
Mirror-finishing is performed to a desired thickness using diamond abrasive grains of about m, but since the final wall surface of the optical waveguide is used, it is processed sufficiently smoothly so as not to cause scattering loss.

Step 3 (see FIG. 3c) Next, after patterning a mask on the thin film portion 20 by photolithography, etching is performed by RIE (reactive ion etching). Mask width is 5μ
It is about m. As a mask material, Ti is initially 0.03
Then, Pt having a thickness of about 0.5 μm is formed thereon. Next, the power of the RIE device is 0.48 W / cm ² ,
CCl ₄ (carbon tetrachloride) is used as a reaction gas, and the pressure in the apparatus is set to about 120 mtorr, and etching is performed to about 3 μm (t ₁ ) (under these conditions, etching is about 0.03 μm / min). Step 4 (see FIG. D) Next, the SiO ₂ film 13 is formed on the thin film portion 20 to have a thickness of about 2 μm by sputtering, and the entrance surface and the exit surface are mirror-coated by a known method.

FIG. 4 is a perspective view of an optical waveguide manufactured by the above method. As shown in the figure, the Al ₂ O ₃ single crystal substrate 12 and the SiO ₂ film 13 function as a clad layer,
The titanium sapphire thin film portion 20 functions as an optical waveguide. Then, when pumping light is incident on the optical waveguide from the incident end face, oscillation light is generated in the waveguide functioning as a laser medium, and the oscillation light is amplified and emitted from the emission end face. It should be noted that in the present embodiment, the substrate dimensions, the laser beam diameter, and other specific numerical values have been described, but the present invention is not limited to the above embodiments. Further, as the heating means, it is possible to use lamp heating using a xenon lamp or the like, resistance heating, high frequency induction heating, and combined heating thereof.

[0015]

As described above in detail, according to the present invention, the step of forming a Ti thin film on the surface of a sapphire (Al ₂ O ₃ ) substrate and the surface of the substrate are partially exposed in a reducing atmosphere. It is heated and melted, and the molten part is recrystallized while moving the heating position. 1) Commercially available sapphire can be used as the substrate, and the heating power is small because it is a partial heating method. It can be manufactured at low cost. 2) Since a container such as a crucible is not used, impurities that are harmful to the laser medium other than Ti are not mixed, so that a crystal having excellent performance as a laser medium can be manufactured. 3) Essentially not doped as tetravalent ions, all become trivalent Ti ions useful as a laser medium. 4) High-concentration Ti doping, which was difficult in the past, can be performed relatively easily by controlling the thickness of the Ti thin film. There are features such as.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic manufacturing process (a) and (b) of a method for forming a titanium-sapphire single crystal film of the present invention.

FIG. 2 is a perspective view showing a heating process of the present invention.

FIG. 3 is a schematic process diagram showing a method for forming an optical waveguide using a titanium / sapphire single crystal film produced by the present invention.

FIG. 4 is a perspective view of an optical waveguide.

FIG. 5 is a diagram showing a conventional example.

[Explanation of symbols]

10 Al ₂ O ₃ substrate 11 Ti thin film 20 TiAl ₂ O ₃ single crystal

Claims (1)

[Claims] 1. A step of forming a Ti thin film on the surface of a sapphire (Al ₂ O ₃ ) substrate, and partially heating and melting the surface of the substrate on which the Ti thin film is formed in a reducing atmosphere, and the heating position. A method for forming a titanium-sapphire single crystal film, comprising the step of recrystallizing the molten portion while moving the film.