JP2010156996A - Method of manufacturing substrate for optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a substrate for an optical element where there is no risk of breakage or the like even when stress is applied and the shape of a side surface of a groove is controlled accurately. <P>SOLUTION: In the method of manufacturing the substrate for the optical element, a mask 14 is formed on a surface 11a of an LN substrate 11, then a groove where the corner between the bottom surface 12a and a side surface 12b is a recessed surface 13 with a radius of curvature of 0.5 μm or more is formed on the surface 11a of the LN substrate 11 using the mask 14 by a sandblasting method, and then the mask 14 is removed using fluoro-nitric acid or the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is suitable for use in an optical integrated circuit (OIC), an opto-electronic integrated circuit (OEIC) or the like in which optical elements such as an optical modulation element capable of high-speed optical modulation are integrated. The present invention relates to a method for manufacturing a device substrate.

In recent years, with the development of optical communication networks with large transmission capacity and low loss, optical integrated circuits in which optical elements such as optical modulation elements capable of high-speed optical modulation are integrated on a substrate, or optical elements and electronic components (elements) In optoelectronic integrated circuits and the like integrated on a substrate, there is a demand for further miniaturization and higher performance.
For example, in an optical integrated circuit in which an optical element such as an optical modulation element is integrated on a substrate, an LiNbO3 substrate (hereinafter abbreviated as an LN substrate) is used to manufacture an optical modulator that can operate in a wide band and is driven at a low voltage. In addition, a ridge-shaped optical waveguide having a width of several to several tens of μm and an interval of several tens to several tens of μm is formed.

As a processing method of this optical waveguide, there are mainly wet etching using a liquid chemical and dry etching using a reactive gas or the like.
Since wet etching uses a chemical reaction, it has a feature of high selectivity by an etching material.
FIG. 16 is a cross-sectional view showing a substrate on which grooves have been formed by wet etching. In the case of isotropic etching, a mask 2 patterned on the main surface 1a of the substrate 1 as shown in FIG. The groove 3 is formed using In the case of selective etching, a groove 3 is formed on the main surface 1a of the substrate 1 using a mask 2 as shown in FIG.

By the way, in recent years, since the whole process tends to be dry, processing by dry etching is generally performed. This dry etching has advantages such as control of the selection ratio, anisotropic etching, high processing accuracy, good processing efficiency, and excellent safety.
There are two types of dry etching: plasma etching using active radicals generated in plasma discharge and reactive ion etching (also called reactive sputter etching) that adds a sputtering effect to plasma etching. Plasma etching having features such as isotropic etching and fine pattern etching is used.

FIG. 17 is a cross-sectional view showing a substrate that has been grooved by plasma etching, and FIG. 17A is an etching cross-section in which the shape of the corner 4 between the side surface 3a and the bottom surface 3b of the groove 3 is sharp, FIG. 2B is an etching cross section in which the corner 4 between the side surface 3a and the bottom surface 3b of the groove 3 has a notch shape.
By forming an integrated circuit such as a modulator circuit on the substrate 1 thus obtained, an integrated circuit having desired electrical characteristics can be obtained.
In addition, in order to improve the characteristics of the integrated circuit integrated on the substrate, a shape in which a groove is formed at a position corresponding to the integrated circuit on the back surface of the substrate and the thickness of the substrate is partially reduced is proposed. It is used for practical use.
The groove is processed by, for example, irradiating the back surface of the substrate with laser light emitted from a high-power laser such as an excimer laser.

By the way, the above-described conventional wet etching has a problem that the side surface 3a of the groove 3 is easily over-etched (side-etched) because it is easily undercut in the case of isotropic etching. In the case of selective etching, unevenness in the etching depth is likely to occur due to the crystal structure. For example, when the side surface 3a is a hard-to-etch crystal surface, the side surface 3a is inclined with respect to the bottom surface 3b of the easy-to-etch crystal surface. There was a problem that the surface was not vertical.
Thus, in the conventional wet etching, it is difficult to control the shape of the side surface 3a.

Further, in the conventional plasma etching, the corner 4 has a sharp etching cross section or a notched etching cross section, so that the ridge is damaged by the stress of the substrate 1 during or after the processing of the groove 3. There is a risk that the substrate 1 may be damaged. Therefore, in order to prevent breakage, attempts have been made to make the cross section of the corner 4 a curved surface. However, since the curvature radius of the curved surface is about 0.2 μm at most, the breakage has not been eliminated. .
In addition, when an integrated circuit such as a modulator circuit is formed on the substrate 1 that has been subjected to groove processing by plasma etching, there is a problem that the drift becomes too large and the circuit characteristics may be adversely affected. This is because plasma etching etches the substrate mainly by a chemical reaction, so that reaction products are deposited on the substrate surface during the etching.
In addition, in the case of a substrate in which a groove is formed on the back surface in order to partially reduce the thickness of the substrate, there is a problem that the substrate is greatly damaged by irradiating laser light, and shape control is difficult. .

  Generally, in a processing process such as a plasma display, a method called a sand blast method using abrasive grains, which is a kind of dry etching, is used. In this method, a rubber negative resist having excellent durability against blasting is mainly used as a processing mask. However, since this negative resist is generally subjected to a heat treatment for baking and solidifying the resist after exposure and development, it tends to expand during this heat treatment, and therefore a fine pattern can be formed. It was difficult and it was difficult to fine-blast sandblasting.

  Note that a metal mask often used in plasma etching has high malleability, and thus is easily deformed during processing and cannot be used for etching a fine structure. Therefore, it is said that this metal mask is not suitable for the sandblasting method, and an example used for processing an LN substrate has not been reported.

  The present invention has been made in view of the above circumstances, and there is no fear of damage or the like even when stress is applied, and a method for manufacturing an optical element substrate in which the shape of the side surface of the groove is controlled with high accuracy The purpose is to provide.

In order to solve the above problems, the present invention provides the following method for manufacturing an optical element substrate.
That is, the method for manufacturing a substrate for optical elements according to the present invention is a method for manufacturing a substrate used for an optical element, and is made of a metal having a Young's modulus of 1.0 × 10 ¹¹ Pa or more on one principal surface of a plate-like body. Forming a fine pattern mask, and then by sandblasting, the mask is used to form a concave surface with a radius of curvature of 0.5 μm or more at the corner of the bottom surface and the side surface on the one main surface. A groove or a recess is formed, and then the mask is removed from the one main surface.

In the sandblast method, it is preferable to use abrasive grains having a radius of 0.5 μm to 20 μm.
The mask is preferably made of any one of chromium, nickel, and nickel-chromium alloy.
The plate-like body is preferably made of any one of lithium niobate, gallium arsenide, and indium phosphide.

According to the method for manufacturing an optical element substrate of the present invention, a fine pattern mask made of a metal having a Young's modulus of 1.0 × 10 ¹¹ Pa or more is formed on one main surface of a plate-like body, and then a sandblast method By using the mask, a groove or a concave portion having a substantially rectangular cross section in which the radius of curvature of the corner portion between the bottom surface and the side surface is a concave surface of 0.5 μm or more is formed on the one main surface, Since it is removed from the one main surface, breakage due to stress concentration or the like hardly occurs, and the processing yield of the substrate can be improved.
In addition, since damage due to stress concentration or the like is less likely to occur, the mechanical strength of the substrate can be increased, and the reliability of the substrate can be improved.

It is sectional drawing which shows the board | substrate of the 1st Embodiment of this invention. It is sectional drawing which shows the processing method of the board | substrate of the 1st Embodiment of this invention. It is a figure which shows the profile which measured the shape of the groove | channel of the LN board | substrate from which a processing method differs by the stylus method. It is a figure which shows the profile of the groove | channel of the LN board | substrate by the sandblasting method at the time of using an abrasive grain with a particle size of 10-20 micrometers. It is a figure which shows the profile of the groove | channel of the LN board | substrate by the sandblasting method at the time of using the abrasive grain whose particle diameter is 2 micrometers. It is a perspective view which shows the optical waveguide board | substrate of the 2nd Embodiment of this invention. It is process drawing which shows the processing method of the optical waveguide board | substrate of the 2nd Embodiment of this invention. It is process drawing which shows the processing method of the optical waveguide board | substrate of the 3rd Embodiment of this invention. It is a perspective view which shows the optical waveguide board | substrate of the 4th Embodiment of this invention. It is sectional drawing which shows the modification of the optical waveguide board | substrate of the 4th Embodiment of this invention. It is sectional drawing which shows the other modification of the optical waveguide board | substrate of the 4th Embodiment of this invention. It is sectional drawing which shows the other modification of the optical waveguide board | substrate of the 4th Embodiment of this invention. It is a perspective view which shows the optical waveguide board | substrate of the 5th Embodiment of this invention. It is a top view which shows the board | substrate of the 6th Embodiment of this invention. It is a principal part expanded sectional view of the board | substrate of the 6th Embodiment of this invention. It is sectional drawing which shows the board | substrate by which the groove process was given by the conventional wet etching. It is sectional drawing which shows the board | substrate by which the groove process was given by the conventional plasma etching.

  Embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a sectional view showing a substrate according to a first embodiment of the present invention. In the figure, reference numeral 11 denotes an LN substrate which is a plate-like body, and 12 denotes a surface (one main surface) 11a of the LN substrate 11. The groove has a substantially rectangular cross section.
The corners of the bottom surface 12a and the side surface 12b of the groove 12 are concave surfaces 13 having a radius of curvature of 0.5 μm or more.
The shape of the concave surface 13 is uniquely determined by the radius and shape of the abrasive grains used in the sandblast method. For example, the radius of curvature of the concave surface 13 can be arbitrarily changed within a range of 0.5 μm to 20 μm by setting the radius of the abrasive grains to an arbitrary value within a range of 0.5 μm to 20 μm.

  In this LN substrate 11, the corners of the bottom surface 12 a and the side surface 12 b of the groove 12 are the concave surfaces 13 having a radius of curvature of 0.5 μm or more, so that even when stress is applied to the LN substrate 11, stress concentration is caused. There is no possibility of causing damage. Thereby, the mechanical strength of the LN substrate 11 is improved, and the reliability of the LN substrate 11 is improved.

Next, a method for forming the groove 12 on the surface 11a of the LN substrate 11 by the sandblast method will be described with reference to FIG.
First, a mask 14 having a fine pattern is formed on the surface 11a of the LN substrate 11 using a lift-off method or a plating method.

The mask 14 is made of a metal having a Young's modulus of 1.0 × 10 ¹¹ Pa or more. As this metal, for example, Cr, Ni, Ni—Cr alloy or the like is preferably used. Here, when Cr is used as a mask material, the selection ratio with respect to the LN substrate 11 is 1: 4, so that Cr is less likely to be cut four times. Therefore, Cr is very preferable as a mask material.

Next, fine groove processing is performed on the surface 11a of the LN substrate 11 by the sand blasting method using the mask 14. The abrasive grains 15 used here are selected in radius and shape in accordance with the radius of curvature of the concave surface 13 to be formed. For example, in order to set the radius of curvature of the concave surface 13 to a desired value in the range of 0.5 μm to 20 μm, the radius of the abrasive grains may be determined corresponding to this desired value.
Since the etching rate of the LN substrate 11 by this sandblasting method is 150 nm / min or more, it is 10 times or more of the etching rate of conventional plasma etching (about 12 nm / min).

In this manner, the groove 12 in which the corners of the bottom surface 12a and the side surface 12b are concave surfaces 13 having a radius of curvature of 0.5 μm or more can be formed on the surface 11a of the LN substrate 11.
Next, the mask 14 is removed using hydrofluoric acid or the like.

Next, the groove 12 is subjected to an acid treatment using hydrofluoric acid, nitric acid, hydrochloric acid, or the like, and the processing strain layer 16 formed on the inner surface of the groove 12 is removed.
The thus obtained LN substrate 11 is not damaged even during substrate processing, and the yield in the processing step is markedly improved as compared with a substrate that is damaged by 70% or more during processing in conventional plasma etching. Yes. As a result, the reliability of the LN substrate 11 is greatly improved.

FIG. 3 is a diagram showing profiles obtained by measuring the groove shapes of LN substrates with different processing methods by the stylus method, and FIG. 3 (a) shows a groove having a sharp cross-sectional shape usually obtained by conventional plasma etching. FIG. 4B shows a notch-shaped groove that occurs when the input power of conventional plasma etching is strong, and FIG. 4C shows a groove that has been made concave by the sandblasting method obtained by the processing method of this embodiment. It is.
According to the above, the groove | channel 12 whose corner | angular part of the bottom face 12a and the side surface 12b is the concave surface 13 of a curvature radius of 0.5 micrometer or more can be formed in the surface 11a of the LN board | substrate 11 by the sandblasting method.

4 and 5 are diagrams showing profiles obtained by measuring the shape of the groove of the LN substrate, which has been grooved by sandblasting using abrasive grains having different radii, using the stylus method. FIG. FIG. 5 shows the groove shape when an abrasive grain having a radius of 1 μm is used, and FIG. 5 shows the groove shape when an abrasive grain having a diameter of 10 μm is used.
According to these figures, by using abrasive grains having a radius of 1 μm, grooves 12 such that the corners of the bottom surface 12 a and the side surface 12 b are concave surfaces 13 having a curvature radius of 1 μm are formed on the surface 11 a of the LN substrate 11. It became clear that it could be formed.

  According to the LN substrate 11 of the present embodiment, the corners of the bottom surface 12a and the side surface 12b of the groove 12 formed on the surface 11a of the LN substrate 11 are the concave surfaces 13 having a radius of curvature of 0.5 μm or more. Even when stress is applied to the substrate 11, there is no risk of breakage due to stress concentration or the like, and the mechanical strength of the LN substrate 11 can be increased. As a result, the reliability of the LN substrate 11 can be improved.

  According to the LN substrate processing method of the present embodiment, the sandblast method is used so that the corners of the bottom surface 12a and the side surface 12b become the concave surface 13 having a radius of curvature of 0.5 μm or more on the surface 11a of the LN substrate 11. Since the groove 12 is formed, breakage due to stress concentration or the like is less likely to occur during groove processing, and the processing yield of the LN substrate can be improved.

In addition, since damage due to stress concentration or the like is less likely to occur even after the groove processing, the mechanical strength of the LN substrate can be increased, and the reliability of the LN substrate can be improved.
Further, by selecting the radius and shape of the abrasive grains 15 corresponding to the radius of curvature of the concave surface 13, the radius of curvature of the concave surface 13 can be set to an arbitrary value in the range of 0.5 μm to 20 μm.

Further, since the processing strain layer 16 formed on the inner surface of the groove 12 is removed by subjecting the groove 12 to an acid treatment, the processing strain layer 16 that could not be removed by processing by dry etching is removed from the groove 12. Therefore, it is possible to manufacture a substrate that is not easily damaged due to stress concentration or the like.
In addition, since any one of Cr, Ni, and Ni—Cr alloy is used as the material of the mask 14, a fine mask pattern having high accuracy and a desired thickness can be formed. Therefore, it is possible to prevent deformation of the mask being processed.

[Second Embodiment]
FIG. 6 is a perspective view showing an optical waveguide substrate according to the second embodiment of the present invention. In the figure, reference numeral 21 denotes a ridge-shaped optical waveguide formed on the surface 11a of the LN substrate 11 which is a plate-like body. On both sides of the optical waveguide 21, grooves 12 are formed in which the corners of the bottom surface 12a and the side surface 12b are concave surfaces 13 having a radius of curvature of 0.5 μm or more.

  In this optical waveguide substrate, since the groove 12 having the concave surface 13 with the radius of curvature of 0.5 μm or more is formed on both sides of the optical waveguide 21, stress is applied to the LN substrate 11. Even in this case, there is no possibility that the optical waveguide 21 is damaged due to stress concentration or the like. Therefore, the reliability of the optical waveguide substrate is improved.

Next, a method for forming the grooves 12 on both sides of the optical waveguide 21 by the sandblasting method using a metal mask produced by the lift-off method will be described with reference to FIG.
First, as shown in FIG. 7A, a photoresist 22 is applied to the entire surface of the LN substrate 11 on which the optical waveguide 21 is formed by using a spin coating method.

Next, as shown in FIG. 7B, the portion of the photoresist 22a corresponding to the ridge-shaped optical waveguide is removed by photolithography.
Next, as shown in FIG. 7C, a Cr film 23 as a mask material is deposited on the entire surface of the LN substrate 11.

  Next, as shown in FIG. 7D, a mask 24 is formed on the LN substrate 11 by patterning the Cr film 23 by a lift-off method. Since the thickness of the mask that can be formed by the lift-off method is about 0.5 μm, the mask is suitable for short-time etching.

Next, as shown in FIG. 7E, the portions on both sides of the optical waveguide 21 of the LN substrate 11 are etched by the sandblast method using the mask 24, and the bottom surface 12a and the side surface 12b are formed on both sides of the optical waveguide 21. A groove 12 is formed such that the corner is a concave surface 13 having a radius of curvature of 0.5 μm or more.
Next, as shown in FIG. 7 (f), the mask 24 is removed using acid to obtain an optical waveguide substrate having a ridge-shaped optical waveguide 21.

  The optical waveguide substrate thus obtained is not damaged even during groove processing, and the yield in the processing step is markedly improved as compared with the conventional optical waveguide substrate using plasma etching. As a result, the reliability of the optical waveguide substrate is greatly improved.

According to the optical waveguide substrate of the present embodiment, the grooves 12 having the corners of the bottom surface 12a and the side surface 12b and the concave surfaces 13 having a radius of curvature of 0.5 μm or more are formed on both sides of the optical waveguide 21. Even when stress is applied to the waveguide substrate, there is no possibility of damage due to stress concentration or the like, and the mechanical strength of the optical waveguide substrate can be increased. As a result, the reliability of the optical waveguide substrate can be improved.
Also in the optical waveguide substrate processing method of the present embodiment, the same effects as the optical waveguide substrate processing method of the first embodiment described above can be obtained.

[Third Embodiment]
FIG. 8 is a process diagram showing a processing method of the optical waveguide substrate according to the third embodiment of the present invention. Grooves 12 are formed on both sides of the optical waveguide 21 by sandblasting using a metal mask manufactured by plating. The method is shown. The groove 12 is a concave surface having a radius of curvature of 0.5 μm or more at the corner between the bottom surface and the side surface.
In this optical waveguide substrate processing method, first, as shown in FIG. 8A, a Cr film 31 is deposited on the entire surface of the LN substrate 11 on which the optical waveguide 21 is formed.
Next, as shown in FIG. 8B, a photoresist 32 is applied to the entire surface of the Cr film 31 by using a spin coating method.

Next, as shown in FIG. 8C, the portion of the photoresist 32a corresponding to the ridge-shaped optical waveguide is removed by photolithography.
Next, as shown in FIG. 8D, a mask 33 made of Cr is formed by plating on the portion of the LN substrate 11 where the photoresist 32a has been removed.
Next, as shown in FIG. 8E, the remaining photoresist 32 is removed, and then the Cr film 31 other than the Cr film 31a under the mask 33 is removed by wet etching.

In this way, a mask pattern can be formed on the optical waveguide 21.
Since the thickness of the mask that can be formed by the plating method is about several μm to several tens of μm, long-time etching is possible.
Next, as shown in FIG. 8 (f), the portions on both sides of the optical waveguide 21 of the LN substrate 11 are etched by the sandblast method using the mask 33, and the corner portions of the bottom surface and the side surfaces are formed on both sides of the optical waveguide 21. Is formed as a concave surface 13 having a radius of curvature of 0.5 μm or more.

Next, the mask 33 and the Cr film 31a are removed using acid to obtain an optical waveguide substrate having a ridge-shaped optical waveguide shown in FIG.
Also in the processing method of the optical waveguide substrate of this embodiment, the same effect as the processing method of the optical waveguide substrate of the second embodiment described above can be obtained.

[Fourth Embodiment]
FIG. 9 is a perspective view showing an optical waveguide substrate according to the fourth embodiment of the present invention. A groove 41 is formed at a position corresponding to the optical waveguide 21 on the back surface (other main surface) 11b of the LN substrate 11. The corners of the bottom surface 41a and the side surface 41b of the groove 41 are the concave surface 13 having a radius of curvature of 0.5 μm or more.
In the LN substrate 11, the groove 41 is formed on the back surface 11b, so that the optical transmission loss characteristic of the optical waveguide 21 is improved, and as a result, the reliability of the optical waveguide 21 is improved.

The groove 41 is formed using a sand blast method. That is, a mask having a fine pattern is formed on the back surface 11b of the LN substrate 11 by using a lift-off method or a plating method, and then fine groove processing is performed on the back surface 11a of the LN substrate 11 by using this mask by a sandblast method. By applying, the groove | channel 41 by which the corner | angular part of the bottom face 41a and the side surface 41b became the concave surface 13 of the curvature radius of 0.5 micrometer or more can be formed in the back surface 11b of the LN board | substrate 11.
The diameter and shape of the abrasive grains used here, the etching rate of the LN substrate 11, the removal of the mask and the processing strain layer on the inner surface of the groove 41 by acid treatment, etc. are exactly the same as in the first embodiment described above.

FIG. 10 is a cross-sectional view showing a modification of the optical waveguide substrate of the present embodiment, and a groove 41 having a length that is only half of the optical waveguide 21 is formed at a position corresponding to the optical waveguide 21 on the back surface 11 b of the LN substrate 11. It is the structure which was made.
FIG. 11 is a cross-sectional view showing another modification of the optical waveguide substrate of the present embodiment, in which a groove 41 having substantially the length of the optical waveguide 21 is formed.
FIG. 12 is a cross-sectional view showing still another modified example of the optical waveguide substrate of the present embodiment, in which a groove 41 is formed only in the central portion of the optical waveguide 21.

  As described above, according to the optical waveguide substrate of the present embodiment, no breakage occurs during the processing of the substrate, and the yield in the processing step is significantly improved as compared with those processed by conventional plasma etching, As a result, the reliability of the LN substrate 11 is greatly improved.

[Fifth Embodiment]
FIG. 13 is a perspective view showing an optical waveguide substrate according to a fifth embodiment of the present invention. A plurality of ridge-shaped optical waveguides 21 are formed on the surface 11a of the LN substrate 11 so as to be parallel to each other. The groove 12 is formed on both sides of the waveguide 21.
The groove 12 is a concave surface 13 having a radius of curvature of 0.5 μm or more at the corner between the bottom surface 12a and the side surface 12b.
These ridge-shaped optical waveguides 21, 21,..., In addition to the above-mentioned shape, when the optical waveguides 21 and 21 cross each other in the middle, the interval between the adjacent optical waveguides 21 may be narrowed or widened. .

  Also in this optical waveguide substrate, since the grooves 12 having the concave surfaces 13 with the curvature radius of 0.5 μm or more are formed on both sides of each optical waveguide 21, stress is applied to the LN substrate 11. Even when is added, there is no possibility that the optical waveguide 21 is damaged due to stress concentration or the like, and the reliability of the optical waveguide substrate can be improved.

[Sixth Embodiment]
FIG. 14 is a plan view showing a substrate according to a sixth embodiment of the present invention, and FIG. 15 is an enlarged cross-sectional view of the main part of the substrate. A plurality of concave portions 52 having a rectangular cross section are formed on the back surface 51a of the substrate 51. It is the structure formed in the shape (random form). These concave portions 52, 52,... Are concave surfaces having a radius of curvature of 0.5 μm or more at the corners of the bottom surface 52a and the side surface 52b.

  According to this substrate, on the back surface 51a of the substrate 51, a plurality of concave portions 52 in which the corner portions of the bottom surface 52a and the side surface 52b are concave surfaces having a radius of curvature of 0.5 μm or more are formed in a spot shape (random shape). Therefore, signal reflection from the back surface 51a can be removed.

As mentioned above, although each embodiment of the present invention has been described with reference to the drawings, the specific configuration is not limited to each of the above-described embodiments, and the design can be changed without departing from the gist of the present invention. It is.
For example, the groove 12 only needs to be a concave surface 13 having a radius of curvature of 0.5 μm or more at the corners of the bottom surface 12a and the side surface 12b. It can be changed appropriately according to.

  In the optical waveguide substrate of the fourth embodiment, the groove 41 is formed at a position corresponding to the optical waveguide 21 on the back surface 11b of the LN substrate 11, but it corresponds to the integrated circuit on the back surface of the integrated circuit substrate. A groove may be formed at the position. With such a configuration, noise can be prevented from entering the integrated circuit, and thus the reliability of the integrated circuit can be improved.

  Further, in the substrate of the sixth embodiment, the plurality of recesses 52 may be formed in a spot shape (random shape) so that signal reflection from the back surface 51a can be sufficiently removed. It is not limited.

[effect]
According to the substrate described above, a groove having a substantially rectangular cross section is formed on one main surface or both surfaces of the plate-like body, and the corner portion between the bottom surface and the side surface of the groove is a concave surface having a curvature radius of 0.5 μm or more. Therefore, even when a stress is applied to the substrate from the outside, it is possible to prevent damage due to stress concentration and the like, and thus the reliability of the substrate can be improved.

  According to the substrate described above, an optical waveguide is formed on one main surface of the plate-like body, and the grooves are formed on both sides of the optical waveguide to form a ridge-shaped optical waveguide. Even when is added, damage due to stress concentration or the like can be prevented, and therefore the reliability of the optical waveguide substrate can be improved.

  According to the substrate described above, an optical waveguide is formed on one main surface of the plate-like body, and the groove is formed at a position corresponding to the optical waveguide on the other main surface of the plate-like body. The optical transmission loss characteristics of the optical waveguide can be improved, and therefore the reliability of the optical waveguide can be improved.

  According to the substrate described above, an integrated circuit is formed on one main surface of the plate-like body, and the groove is formed at a position corresponding to the integrated circuit on the other main surface of the plate-like body. Noise can be prevented from entering the semiconductor device, and thus the reliability of the integrated circuit can be improved.

  According to the substrate described above, a plurality of recesses having a substantially rectangular cross section are formed on one main surface of the plate-like body, and the corners between the bottom surface and the side surfaces of these recesses are concave surfaces having a curvature radius of 0.5 μm or more. Therefore, the reflection from this one main surface can be removed.

According to the substrate described above, the groove or the recess is formed by a sandblast method, and the radius of curvature of the concave surface is substantially equal to the radius of the abrasive grains used in the sandblast method. Damage due to stress concentration or the like can be prevented, and the reliability of the substrate can be improved.
This sandblasting method does not involve selective etching, and does not use an etching solution such as hydrofluoric acid, so there is no danger of wet etching.

  According to the substrate described above, since the radius of the abrasive grains is set to 0.5 μm to 20 μm, the radius of curvature of the concave surface can be arbitrarily changed within a range of 0.5 μm to 20 μm.

  According to the substrate described above, since the Young's modulus of the mask used in the sandblasting method is 1.0 × 10 11 Pa or more, a fine mask pattern having a desired thickness is formed with high accuracy by a lift-off method or a plating method. And deformation of the mask during processing caused by metal malleability can be avoided.

  According to the optical element described above, since the substrate described above is used, even when stress is applied to the substrate, damage due to stress concentration or the like can be prevented, and the reliability of the optical element is improved. be able to.

11 LN substrate 11a Surface (one main surface)
11b Back side (other main side)
12 groove 12a bottom surface 12b side surface 13 concave surface 14 mask 15 abrasive grains 16 processing strain layer 21 optical waveguide 22, 22a photoresist 23 Cr film
24 Mask 31 Cr film 32, 32a Photoresist 33 Mask 41 Groove 41a Bottom surface 41b Side surface 51 Substrate 51a Back surface 52 Recessed portion 52a Bottom surface 52b Side surface

Claims (4)

A method of manufacturing a substrate used in an optical element,
A mask having a fine pattern made of a metal having a Young's modulus of 1.0 × 10 ¹¹ Pa or more is formed on one main surface of the plate-like body, and then the bottom surface is formed on the one main surface using the mask by sandblasting. Forming a groove or recess having a substantially rectangular cross-section with a radius of curvature of 0.5 μm or more between the corner and the side surface, and then removing the mask from the one main surface Manufacturing method for industrial use.   2. The method for manufacturing an optical element substrate according to claim 1, wherein the sand blasting method uses abrasive grains having a radius of 0.5 to 20 [mu] m.   The method for manufacturing a substrate for an optical element according to claim 1, wherein the mask is made of any one of chromium, nickel, and nickel-chromium alloy.   4. The method for manufacturing a substrate for an optical element according to claim 1, wherein the plate-like body is made of any one of lithium niobate, gallium arsenide, and indium phosphide.

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