CN106948005A - The manufacture method of monocrystalline lithium tantalate substrate - Google Patents

Abstract

The present invention provides a method for manufacturing a lithium tantalate single crystal substrate with high homogeneity and a volume resistivity of more than 1×10 ¹⁰ Ω·cm and less than 1×10 ¹² Ω·cm without a decompression process. The present invention includes heat-treating a lithium tantalate single crystal substrate with a volume resistivity of 1×10 ¹² Ω·cm or more and a single-domain structure under normal pressure and in a hydrogen atmosphere at a temperature above 400°C and below the Curie temperature The first step and the second step of heat-treating the lithium tantalate single crystal substrate processed in the first step together with lithium carbonate under normal pressure in a hydrogen or nitrogen atmosphere at a temperature above 400°C and below the Curie temperature process.

Description

Manufacturing method of lithium tantalate single crystal substrate

technical field

The present invention relates to a method of manufacturing a lithium tantalate single crystal substrate used in a surface acoustic wave device.

Background technique

Lithium tantalate (LiTaO ₃ ; LT) single crystal has piezoelectricity and is used as a piezoelectric substrate of surface acoustic wave devices. On the other hand, lithium tantalate single crystal also has pyroelectricity, and the temperature changes, and the surface charge occurs. Such pyroelectricity exists when it is used as a sensor, but when a lithium tantalate crystal is used as a piezoelectric substrate of a surface acoustic wave element, this pyroelectricity becomes a problem.

For example, when the piezoelectric substrate is charged due to a temperature change, electrostatic discharge occurs in the piezoelectric substrate, causing cracks and fractures. In addition, electrodes formed on the surface of the piezoelectric substrate may be short-circuited by static electricity.

Therefore, for the purpose of suppressing the electrification of the lithium tantalate substrate, it is considered that the lithium tantalate substrate should be reduced at a temperature below the Curie temperature, and this method is widely used (Patent Documents 1 to 5 and Non-Patent Document 1 refer to ).

For example, Patent Document 1 describes a method of heat-treating together with metal vapor in a reducing atmosphere, and Patent Document 2 describes performing a heat treatment by contacting a reducing-treated substance at a Curie temperature or higher in a reducing atmosphere. The method of heat treatment. In addition, in Patent Documents 3 and 4, a method of embedding a mixed powder of Al and Al ₂ O ₃ and performing heat treatment is used. As a result, the volume resistivity of such a reduction-treated lithium tantalate substrate is less than 1×10 ¹² Ω·cm, making it possible to effectively suppress pyroelectricity.

In addition, it is known that a lithium tantalate substrate subjected to a reduction treatment is blackened. A normal lithium tantalate single crystal substrate has a light transmittance of about 70 to 80% at a wavelength of 365nm, and a lithium tantalate single crystal substrate subjected to reduction treatment has a light transmittance of about 50 to 60% at a wavelength of 365nm. Such suppression of light transmittance is advantageous in the photolithography process in the manufacture of surface acoustic wave devices.

On the other hand, in this lithium tantalate single crystal substrate, for example, as described in Patent Documents 6 and 7, iron element may be added. Then, when the reduction treatment is performed on the lithium tantalate single crystal substrate to which the iron element is added, the light transmittance is further suppressed compared with the case where the normal lithium tantalate single crystal substrate is subjected to the original treatment. The light transmittance at a wavelength of 365nm of a lithium tantalate single crystal substrate to which iron is added is about 50%, but if it is reduced, the light transmittance at a wavelength of 365nm becomes about 30%.

prior art literature

patent documents

Patent Document 1 Japanese Unexamined Publication No. 2004-035396

Patent document 2WO 2004/079061

Patent Document 3 JP-A-2005-119906

Patent Document 4 JP-A-2005-119908

Patent Document 5 JP-A-2005-314137

Patent Document 6 JP-A-2004-254114

Patent Document 7 WO 2007/046176

non-patent literature

Non-Patent Document 1 Yan Tao et al. "Formation mechanism of black LiTaO3 singlecrystals through chemical reduction." J.Appl.Cryst.44(2011), 158-162

However, a method using an alkali metal compound is known as a reduction treatment method for a lithium tantalate single crystal substrate. For example, Patent Document 5 describes a method of heat-treating an alkali metal compound under reduced pressure. Non-Patent Document 1 describes a method of heat-treating a mixed powder of Fe and Li ₂ CO ₃ in a nitrogen atmosphere.

However, such a reduction treatment method of a lithium tantalate single crystal substrate using an alkali metal compound has been found to be problematic. The inventors of the present invention carried out a reproduction experiment with the method described in Patent Document 5, but the reduction treatment of the lithium tantalate single crystal substrate could not be performed satisfactorily, and the pyroelectricity could not be suppressed. In addition, even if the reduction treatment is performed by the method described in Patent Document 5, the productivity is poor because a depressurization step is necessary.

In addition, the present inventors also carried out reproduction experiments on the method described in Non-Patent Document 1, and the reduction treatment of lithium tantalate single crystal substrates can be performed, but the degree of progress of the reduction is not sufficient, and there are stains on the surface of the substrate, and the in-plane direction of the substrate of poor homogeneity.

Therefore, one object of the present invention is to provide a product that does not require a depressurization process, can obtain high homogeneity, and has a volume resistivity of 1×10 ¹⁰ Ω·cm or more, and 1×10 ¹² Ω·cm or less. A new reduction-processed fabrication method for full LiTaO single crystal substrates.

In the photolithography process when producing a surface acoustic wave device, it is preferable that the transmittance of the exposure light of the lithium tantalate substrate is low so that a fine and accurate pattern can be formed. Generally, in photolithography, g-line (436 nm), i-line (365 nm) of a mercury lamp, KrF excimer laser (248 nm), and ArF excimer laser (193 nm) are used as exposure light. In particular, miniaturization is progressing in recent years, and exposure light with a wavelength shorter than the i-line is often used.

Therefore, if the lithium tantalate single crystal substrate with iron added is subjected to reduction treatment, the light transmittance at a wavelength of 365 nm is about 30%, which is lower than the light transmittance at a wavelength of 365 nm of a lithium tantalate single crystal substrate without iron added. , which is beneficial in the photolithography process. Generally, the light transmittance of the lithium tantalate single crystal substrate tends to decrease toward the shorter wavelength side and increase toward the longer wavelength side.

On the other hand, in the lithium tantalate single crystal substrate whose light transmittance on the short-wavelength side becomes low due to addition of iron element or reduction treatment, the light transmittance on the long-wavelength side also becomes low. It was confirmed that the light transmittance at a wavelength of 485 nm became less than 50% in the lithium tantalate single crystal substrate in which the light transmittance at a wavelength of 365 nm became 30% or less due to the addition of iron element and the reduction treatment.

The inventors of the present invention tested the reduction treatment of lithium tantalate single crystal substrates to which iron was added by the method described in Patent Document 2, and confirmed that the light transmittance at a wavelength of 365 nm is 30% or less, and the light transmittance at a wavelength of 485 nm is less than 30%. The pass rate is less than 50%.

However, in recent years, in surface acoustic wave devices, comb-shaped electrodes and the like are formed, and the functional substrate having the function of the device and the packaging substrate provided for protecting the electrode part are made of the same material. Similarly, surface acoustic wave device substrates and packaging substrates are well integrated, processability, and stability are excellent, and materials used as functional substrates are increasingly used as packaging materials.

However, in such a case, the light transmittance on the long wavelength side is low, and the manufacturing workability of the surface acoustic wave device may be deteriorated. When the functional substrate and the package substrate are integrated, an adjustment operation using a laser becomes necessary, and in this case, if the light transmittance at the adjustment laser wavelength of the package substrate is low, the adjustment operation is difficult.

Therefore, the light transmittance of the lithium tantalate single crystal substrate should be lower on the shorter wavelength side than the exposure light used in the photolithography process, and in the range of longer wavelengths than the exposure light used in the photolithography process. As high as possible is preferred.

Therefore, a second object of the present invention is to provide a light with a wavelength of 485 nm and a light transmittance of 30% or less at a wavelength of 365 nm that can be used well as a functional substrate of a surface acoustic wave device and also as a packaging substrate. A method for manufacturing a lithium tantalate substrate having a transmittance of 50% or more.

Contents of the invention

The present invention is a method for manufacturing a lithium tantalate single crystal substrate. The volume resistivity of the lithium tantalate single crystal substrate is more than 1×10 ¹⁰ Ω·cm and less than 1×10 ¹² Ω·cm, characterized in that , having a lithium tantalate single crystal substrate with a volume resistivity of 1×10 ¹² Ω·cm or more and a single-domain structure, under normal pressure, in a hydrogen atmosphere, for heat treatment at a temperature above 400°C and below the Curie temperature The first process and the lithium tantalate single crystal substrate processed in the first process, together with lithium carbonate, are carried out under normal pressure, in a hydrogen or nitrogen atmosphere, at a temperature above 400°C and below the Curie temperature. The second process of heat treatment.

In addition, in the first step of the heat treatment of the present invention, the volume resistivity is 1×10 ¹² Ω·cm or more, and the lithium tantalate single crystal substrate with a single-domain structure has the same Curie temperature in a reducing atmosphere. The above temperature is preferably heat-treated to contact the lithium tantalate single crystal substrate of the multi-domain structure that is heat-treated.

Furthermore, in the second step of the heat treatment of the present invention, it is preferable to embed the lithium tantalate single crystal substrate processed in the first step into lithium carbonate powder, and it is more preferable to perform the heat treatment in a nitrogen atmosphere.

The lithium tantalate single crystal substrate of the present invention preferably contains iron as an additive element, and in this case, the iron content is preferably 50 ppm to 200 ppm.

In the production method of the present invention, in addition to having a volume resistivity of 1×10 ¹⁰ Ω·cm or more and 1×10 ¹² Ω·cm or less, the light transmittance at a wavelength of 365 nm is 30%. Hereinafter, a lithium tantalate single crystal substrate having a light transmittance of 50% or more at a wavelength of 485 nm.

Invention effect

According to the present invention, a lithium tantalate single crystal substrate having a homogeneous high volume resistivity of not less than 1×10 ¹⁰ Ω·cm and less than 1×10 ¹² Ω·cm can be obtained without a decompression step. Since the volume resistivity of the substrate is less than 1×10 ¹² Ω·cm, it is possible to avoid electrification due to temperature changes, generation of cracks and fractures, and short-circuiting of electrodes.

Further, if the reduction treatment method of the present invention is implemented on a lithium tantalate single crystal substrate containing iron as an additive element, the light transmittance at a wavelength of 365 nm is 30% or less, and the light transmittance at a wavelength of 485 nm is 50% or more. Lithium tantalate substrate. This substrate can be used well not only as a functional substrate of a surface acoustic wave device but also as a packaging substrate, and has the advantage of easy adjustment work when used as a packaging material.

detailed description

Hereinafter, an embodiment of the present invention will be described in detail, but the present invention is not limited thereto.

The present invention is a production that has a volume resistivity of 1×10 ¹⁰ Ω·cm or more and 1×10 ¹² Ω·cm or less, and a light transmittance of 30% or less at a wavelength of 365 nm, A method of manufacturing a lithium tantalate substrate having a light transmittance of 50% or more at a wavelength of 485 nm. In this production, first, a lithium tantalate single crystal substrate having a volume resistivity of 1×10 ¹² Ω·cm or more and a single domain structure is prepared. Such a lithium tantalate single crystal substrate is obtained, for example, by growing a lithium tantalate single crystal by the Czochralski single crystal growth method, and processing the shape of the substrate while performing polarization treatment on the obtained bulk. of.

In the first step of heat treatment, the prepared lithium tantalate single crystal substrate is subjected to heat treatment at a temperature above 400° C. and below the Curie temperature under normal pressure and in a hydrogen atmosphere. This is because, if the heat treatment is performed at a temperature lower than 400°C, the reduction will not proceed sufficiently, and on the other hand, if the heat treatment is performed at a temperature higher than the Curie temperature, a multi-domain structure will be formed. At this time, the flow rate of hydrogen is preferably 3 l/min or more, more preferably 6 l/min or more, in order to always have fresh hydrogen.

In addition, in the first step, the lithium tantalate single crystal substrate with the multi-domain structure heat-treated at a temperature above the Curie temperature and the prepared lithium tantalate single crystal It is preferable to heat-treat the substrates in contact with each other.

At this time, it is preferable to alternately overlap and arrange the multi-domain lithium tantalate single crystal substrates heat-treated at a temperature above the Curie temperature in a reducing atmosphere to contact the front and back of the prepared lithium tantalate single crystal substrates. two sides. In this way, the uniformity in the thickness direction of the substrate is improved.

Furthermore, as the second step of heat treatment, the substrate after the first step is heat-treated together with lithium carbonate at a temperature above 400° C. and below the Curie temperature under normal pressure in a hydrogen or nitrogen atmosphere. For the same reason as in the case of the first step, it is not preferable to perform the second step at a temperature lower than 400° C. or higher than the Curie temperature. At this time, the flow rate of hydrogen or nitrogen is preferably more than 3l/min, more preferably more than 6l/min, so that there can always be fresh gas to exist,

In this second step, either hydrogen gas or nitrogen gas can be used. The cost of nitrogen, safety, equipment, etc. can be kept down, preferably. On the other hand, the reducing action of hydrogen gas is strong, and the transmittance and volume resistivity of the processed substrate tend to be lowered.

Here, the role of lithium carbonate used as the second step is to partially decompose at a temperature below 948K to generate lithium oxide, carbon dioxide, and carbon monoxide, and this carbon monoxide is considered to reduce Ta ⁵⁺ to Ta ⁴⁺ . Here, as a catalyst, a small amount of iron or the like may be present in addition to lithium carbonate. Iron decomposes the generated carbon dioxide into carbon monoxide, so it can promote the reduction of lithium tantalate. If iron is mixed in lithium carbonate, although it can promote the reduction compared with the reduction of lithium carbonate alone, when lithium carbonate and iron are heat treated together, stains will appear on the surface of the substrate, so it is best to use only lithium carbonate. is preferred.

In addition, in the second step, it is preferable to embed the substrate processed in the first step in the lithium carbonate powder, and it is preferable to make the lithium carbonate powder contact the front and back surfaces of the substrate by embedding. When processing a plurality of substrates at the same time, lithium carbonate powder may be present between the substrates.

The substrates after the first and second steps are polished as necessary to obtain homogeneous lithium tantalate with a volume resistivity of 1×10 ¹⁰ Ω·cm or more and 1×10 ¹² Ω·cm or less. single crystal substrate. If the volume resistivity is lower than 1×10 ¹⁰ Ω·cm, piezoelectric characteristics may deteriorate and dielectric breakdown may occur. On the other hand, if the volume resistivity is not less than 1×10 ¹² Ω·cm, it is easy to be charged and short-circuiting of the electrodes is caused. Therefore, it is necessary to control within this numerical range. By controlling the volume resistivity in this way, charging due to pyroelectricity can be suppressed, thereby preventing cracking and breaking of the substrate and short circuiting of the electrodes.

The method for manufacturing a lithium tantalate single crystal substrate of the present invention is suitable for a lithium tantalate single crystal substrate containing additive elements, especially suitable for a lithium tantalate single crystal substrate with an added iron element. Adding iron to the lithium tantalate single crystal can keep the light transmittance at a wavelength of 485nm above 50% while suppressing the light transmittance at a wavelength of 365nm to 30% or less. At this time, if the content of iron is 50ppm to 200ppm by weight, the light transmittance at a wavelength of 365nm can be effectively suppressed, but if it is outside the range of 50ppm to 200ppm, it cannot transmit light at a wavelength of 365nm. If the transmissivity is sufficiently suppressed, it is difficult to maintain the light transmittance at a wavelength of 485 nm at 50% or more, and various characteristics such as piezoelectric characteristics will deteriorate, which is not preferable.

Although it is not limited to the method of adding iron to lithium tantalate single crystals, generally speaking, when growing lithium tantalate single crystals by the Czochralski single crystal growth method, if iron oxide ( Fe ₂ O ₃ ) etc. can be used. For a lithium tantalate single crystal substrate containing iron as an additive element, when the reduction treatment method of the present invention is implemented, a volume resistivity of 1×10 ¹⁰ Ω·cm or more and 1×10 ¹² Ω·cm can be obtained. Homogeneous lithium tantalate single crystal substrate.

In addition, when the reduction treatment method of the present invention is carried out on a lithium tantalate single crystal substrate whose additive element is iron, the light transmittance at a wavelength of 365 nm can be reduced to 30% or less. This is advantageous for a photolithography process using a light source with a shorter wavelength than the i-line (wavelength: 365 nm), and the light transmittance at a wavelength of 365 nm is more preferably 25% or less.

Furthermore, when the reduction treatment method of the present invention is carried out on a lithium tantalate single crystal substrate whose additive element is iron, the light transmittance at a wavelength of 485 nm can be made 50% or more. In this way, when the lithium tantalate single crystal substrate is used as a packaging material, adjustment work with the functional substrate becomes easy.

Example

Example 1

In Example 1, at first, lithium tantalate single crystals were grown by the Czochralski single crystal growth method, and the obtained block was subjected to polarization treatment, and after single-regionalization, it was sliced to obtain a plurality of substrates (raw material substrate). In addition, a general lithium tantalate single crystal substrate was exposed to hydrogen gas at 1050°C to prepare a multi-domain substrate.

Then, as the first step of heat treatment, the single-domain lithium tantalate single crystal substrate with a volume resistivity of 4.5×10 ¹⁴ Ω·cm was brought into contact with the multi-domain lithium tantalate single crystal substrate, and carried out under normal pressure. Heat treatment at 570°C for 8 hours in a 100% hydrogen atmosphere.

Furthermore, as the second step of heat treatment, the raw material substrate after the first step was taken out, and the substrate was embedded in lithium carbonate powder. Thereafter, the substrate embedded in the lithium carbonate powder was heat-treated at 530° C. for 8 hours under normal pressure in an atmosphere of 100% hydrogen.

In addition, after polishing both sides of the substrate that completed the first and second steps to obtain a lithium tantalate single crystal substrate with a thickness of 0.2 mm, the volume resistivity was measured for the lithium tantalate single crystal substrate, and the value was 2.0×10 ¹¹ Ω·cm. In addition, the light transmittance at the wavelength of 365 nm and the wavelength of 485 nm was measured, and it was found that the light transmittance at the wavelength of 365 nm was 60%, and the light transmittance at the wavelength of 485 nm was 65%.

Example 2

In Example 2, at first, use the Czochralski single crystal growth method to make a lithium tantalate single crystal with an iron element of 100 ppm in weight ratio, and after the obtained block is subjected to polarization treatment, it is sliced to obtain a plurality of piece of substrate.

Then, these substrates with a volume resistivity of 4.5×10 ¹⁴ Ω·cm were subjected to heat treatment at 570° C. for 8 hours under normal pressure and in an atmosphere of 100% hydrogen as the first step of heat treatment.

Furthermore, as the second step of heat treatment, the substrate after the first step was taken out, and the substrate was embedded in lithium carbonate powder. Thereafter, the substrate embedded in the lithium carbonate powder was heat-treated at 530° C. for 8 hours under normal pressure in an atmosphere of 100% hydrogen.

In addition, after polishing both sides of the substrate after the first and second steps to obtain a lithium tantalate single crystal substrate with a thickness of 0.2mm, the iron element-containing lithium tantalate single crystal substrate was subjected to a wavelength of 365nm and a wavelength of 485nm. As a result of measuring the light transmittance, the light transmittance at a wavelength of 365 nm was 25%, and the light transmittance at a wavelength of 485 nm was 58%. Furthermore, the volume resistivity of the obtained substrate was measured and found to be 1.0×10 ¹¹ Ω·cm.

Example 3

In Example 3, first, a single crystal of lithium tantalate containing 100 ppm of iron by weight was grown by the Czochralski single crystal growth method, and the obtained block was subjected to a single-region polarization treatment (Polling), and then By slicing, a plurality of substrates (raw substrates) are obtained. In addition, a general lithium tantalate single crystal substrate was exposed to hydrogen gas at 1050° C. to prepare a multi-domain substrate.

Then, as the first step of heat treatment, a single-domain lithium tantalate single crystal substrate with an iron element of 100 ppm and a volume resistivity of 4.5×10 ¹⁴ Ω·cm was brought into contact with a multi-domain lithium tantalate single crystal substrate, Heat treatment was performed at 570° C. for 8 hours in an atmosphere of 100% hydrogen under normal pressure.

Furthermore, the second step of heat treatment and the grinding step were carried out under the same conditions as in Example 1. After the lithium tantalate single crystal substrate with a thickness of 0.2 mm was obtained, the iron element-containing lithium tantalate single crystal substrate was used at a wavelength of 365 nm and The light transmittance at a wavelength of 485 nm was measured, and it was found that the light transmittance at a wavelength of 365 nm was 20%, and that at a wavelength of 485 nm was 55%. Furthermore, the volume resistivity of the obtained substrate was measured and found to be 5.5×10 ¹⁰ Ω·cm.

comparative example

Comparative example 1

In Comparative Example 1, at first, a lithium tantalate single crystal was grown by the Czochralski single crystal growth method, and the obtained block was subjected to polarization treatment, and after being single-regionalized, it was sliced to obtain a plurality of substrates (raw substrates). ).

Furthermore, after embedding the substrate having a volume resistivity of 4.5×10 ¹⁴ Ω·cm in mixed powder of iron and lithium carbonate (Fe:Li ₂ CO ₃ =5:100bymass), the substrate embedded in the mixed powder is often Heat treatment was performed at a temperature of 540° C. for 6 hours in an atmosphere of 100% nitrogen under pressure.

In addition, both sides of the heat-treated substrate were polished to obtain a lithium tantalate single crystal substrate with a thickness of 0.2 mm. The volume resistivity of the lithium tantalate single crystal substrate was measured and found to be 7.3×10 ¹¹ Ω ·cm～2.3×10 ¹² Ω·cm. On the surface of the substrate, there were stains, and the homogeneity in the in-plane direction of the substrate was poor.

In Comparative Example 1, the reduction treatment of the lithium tantalate single crystal substrate was performed only once. In order to fully perform the reduction, the maximum value of the volume resistivity was 2.3×10 ¹² Ω·cm, which was as high as the in-plane direction of the substrate. The homogeneity is also poor. In addition, lithium carbonate and iron are heat-treated together in the mixed powder, and stains occur on the surface of the substrate.

Comparative example 2

In Comparative Example 2, first, a single crystal of lithium tantalate was grown by the Czochralski single crystal growth method, and the resulting block was polarized and then sliced into a plurality of substrates.

Then, both sides of the substrate with a volume resistivity of 4.5×10 ¹⁴ Ω·cm were polished to obtain a lithium tantalate single crystal substrate with a thickness of 0.2 mm. The lithium tantalate single crystal substrate was measured at a wavelength of 365 nm and a wavelength of 485 nm. According to the light transmittance, the light transmittance of wavelength 365nm is 72%, and the light transmittance of wavelength 485nm is 75%. Furthermore, the volume resistivity of the obtained substrate was measured and found to be 4.5×10 ¹⁴ Ω·cm.

In Comparative Example 2, since the reduction treatment of the lithium tantalate single crystal substrate was not performed, the light transmittance at a wavelength of 365 nm was as high as 72%, and the volume resistivity was also as high as 4.5×10 ¹⁴ Ω·cm, which were not satisfactory.

Comparative example 3

In Comparative Example 3, first, a single crystal of lithium tantalate containing 100 ppm by weight of iron was grown by the Czochralski single crystal growth method, and the obtained bulk was subjected to polarization treatment, and then sliced to obtain a plurality of substrates.

Then, both sides of the substrate with a volume resistivity of 5.0×10 ¹³ Ω·cm are ground to obtain a lithium tantalate single crystal substrate with a thickness of 0.2 mm. According to the measurement of the light transmittance at a wavelength of 485 nm, the light transmittance at a wavelength of 365 nm is 50%, and the light transmittance at a wavelength of 485 nm is 65%. Furthermore, the volume resistivity of the obtained substrate was measured and found to be 5.0×10 ¹³ Ω·cm.

In Comparative Example 3, since no reduction treatment was performed on the iron-containing lithium tantalate single crystal substrate, the light transmittance at a wavelength of 365 nm was as high as 50%, and the volume resistivity was also 5.0×10 ¹³ Ω·cm, High, nothing to satisfy.

Comparative example 4

In Comparative Example 4, at first, a lithium tantalate single crystal containing 100 ppm of iron element was grown by the Czochralski single crystal growth method, and the obtained block was subjected to polarization treatment, and sliced to obtain multiple pieces. substrate. In addition, a general lithium tantalate single crystal substrate was exposed to hydrogen gas at 1050° C. to prepare a multi-region substrate.

Then, as the first step of heat treatment, a polarized lithium tantalate single crystal substrate with a volume resistivity of 5.0×10 ¹³ Ω·cm containing 100 ppm of iron is contacted with a multi-domain lithium tantalate single crystal substrate , under normal pressure, in an atmosphere of 100% hydrogen, heat treatment at a temperature of 570° C. for 8 hours.

Furthermore, as the second step of heat treatment, heat treatment was performed under the same treatment conditions as in the first step.

In addition, after the first and second processes are finished, both sides of the substrate are polished to obtain a lithium tantalate single crystal substrate with a thickness of 0.2 mm, and the light with a wavelength of 365 nm and a wavelength of 485 nm is measured for the iron element-containing lithium tantalate single crystal substrate. As for the transmittance, it is known that the light transmittance at a wavelength of 365 nm is 25%, and that at a wavelength of 485 nm is 45%. Furthermore, the volume resistivity of the obtained substrate was measured and found to be 1.0×10 ¹¹ Ω·cm.

In this comparative example 4, the iron element-containing lithium tantalate single crystal substrate was subjected to reduction treatment, but in the second step, the raw material substrate after the first step was not heat-treated together with lithium carbonate, and the light with a wavelength of 485 nm was transmitted. The rate is 45%, which is less than 50%, and there is no satisfaction.

Claims (7)

1. a kind of manufacture method of monocrystalline lithium tantalate substrate, the specific insulation of the monocrystalline lithium tantalate substrate is 1 × 10¹⁰Ω· More than cm, 1 × 10¹²Ω cm less than, it is characterised in that including specific insulation be 1 × 10¹²More than Ω cm, and will be single At ambient pressure, in hydrogen atmosphere, more than 400 DEG C, the temperature below Curie temperature carries out heat to tectonic monocrystalline lithium tantalate substrate Processing the first process and, the monocrystalline lithium tantalate substrate that will be handled in first process, together with lithium carbonate, under normal pressure, hydrogen or In nitrogen atmosphere, more than 400 DEG C, the second process that the temperature below Curie temperature is heat-treated.

2. the manufacture method of monocrystalline lithium tantalate substrate according to claim 1, it is characterised in that in first process, make The specific insulation is 1 × 10¹²More than Ω cm, and single tectonic monocrystalline lithium tantalate substrate, and in reproducibility gas In atmosphere, the monocrystalline lithium tantalate substrate contact of the multi-region domain construction of temperature heat treatment more than Curie temperature is carried out at the heat Reason.

3. according to the manufacture method of the monocrystalline lithium tantalate substrate of claim 1 or 2, it is characterised in that in second process, The heat treatment is carried out in nitrogen atmosphere.

4. according to the manufacture method of the monocrystalline lithium tantalate substrate of any one of claims 1 to 3, it is characterised in that described In two processes, the monocrystalline lithium tantalate substrate of first process processing is embedded in lithium carbonate powder.

5. according to the manufacture method of the monocrystalline lithium tantalate substrate of any one of Claims 1-4, it is characterised in that the tantalic acid Lithium monocrystal substrate, is used as addition element iron content.

6. the manufacture method of monocrystalline lithium tantalate substrate according to claim 5, it is characterised in that the amount of above-mentioned iron is, 50ppm~200ppm.

7. according to the manufacture method of the monocrystalline lithium tantalate substrate of claim 5 or 6, it is characterised in that the specific insulation is 1 ×10¹⁰More than Ω cm, 1 × 10¹²Ω cm less than monocrystalline lithium tantalate substrate, wavelength 365nm light transmission rate be 30% Hereinafter, it is more than 50% in wavelength 485nm light transmission rate.