JP2012017218A - Substrate, substrate production method, nd filter, and optical characteristic measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for an ND filter, made from a material wherein breaks caused by thermal stress during use are unlikely to occur.SOLUTION: There is provided the substrate 10 for the ND filter 16 made from a spinel sintered material. It is desirable that the substrate 10 has a Young's modulus of 150 to 350 MPa, that the composition of the spinel sintered material composing the substrate 10 is MgO.nAlO(1.05≤n≤1.30), and that the Si content is 20 ppm or less.

Description

  The present invention relates to a substrate, a substrate manufacturing method, an ND filter, and an optical characteristic measuring apparatus, and more specifically, a substrate for an ND filter and a manufacturing method thereof, an ND filter using the substrate, and the ND The present invention relates to an optical characteristic measuring apparatus using a filter.

  For example, a filter called an ND (Neutral Density) filter may be used in a device using a blue-violet semiconductor laser, such as a dedicated device (optical information recording device) for reproducing a Blu-ray disc. The ND filter is a filter having a role of reducing the amount of light input to a lens, a reflecting mirror, or the like. The ND filter is used in an optical information recording apparatus, for example, to attenuate laser light output from a semiconductor laser supply apparatus to a light quantity that can be received by a light receiving element. The ND filter is disclosed in, for example, Japanese Patent Laid-Open No. 10-90114 (Patent Document 1). In this document, an ND filter is used in the lens evaluation apparatus.

JP 10-90114 A

  When an ND filter is arranged in a system that constitutes an evaluation device such as Patent Document 1 or a device that measures the characteristics of light transmitted through the ND filter, the ND filter generates heat when light passes through the ND filter. . The substrate constituting the ND filter in Patent Document 1 is made of a transparent member such as glass. For this reason, the ND filter has a problem that it easily breaks due to thermal stress applied during use.

  The present invention has been made in view of the above problems. The purpose is to provide a substrate for an ND filter made of a material that is less susceptible to cracking due to thermal stress during use than an ND filter made of glass. Moreover, it is providing the manufacturing method of the said board | substrate, the ND filter using the said board | substrate, and also the optical characteristic measuring apparatus using the said ND filter.

  The board | substrate which concerns on this invention is a board | substrate for ND filters which consists of a spinel sintered compact. As a result of earnest research, the inventors of the present invention have found that, for example, a spinel mainly used in the field of optical elements can be used instead of glass as a substrate used in the above-described ND filter. . A physical property value such as the strength of spinel is higher than a physical property value such as the strength of glass. It has been found that a substrate for an ND filter formed using spinel can withstand practical use in the same manner as a substrate for an ND filter made of glass. For example, a spinel ND filter substrate exhibits higher strength (Young's modulus) than a glass ND filter substrate.

  If an ND filter substrate is formed using spinel instead of glass, the occurrence of cracks due to the thermal stress of the substrate during use of the ND filter can be suppressed, and the ND filter can have a longer life. can do.

  The Young's modulus indicating the rigidity of the ND filter is preferably 150 GPa or more and 350 GPa or less. If a spinel having a Young's modulus in the above range is used, a substrate having a strength capable of suppressing cracking can be easily processed.

The spinel substrate is preferably a spinel sintered body having a composition of MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and a Si element content of 20 ppm or less. The sintered body preferably has a linear transmittance of 80% or more with a light beam having a thickness of 1 mm and a wavelength of 350 nm to 450 nm. If it does in this way, the transmittance | permeability of the light in the board | substrate which consists of spinels can be made equivalent to a glass substrate. Therefore, it is possible to provide an ND filter having a higher strength than a glass substrate and a function of attenuating light equivalent to that of the glass substrate.

The substrate manufacturing method according to the present invention comprises a spinel sintered body having a composition of MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and a Si element content of 20 ppm or less. It is a manufacturing method of the board | substrate for ND filters. The method for producing the substrate includes a step of forming a compact from a spinel powder having a Si element content of 50 ppm or less and a purity of 99.5% by mass or more, and the compact in a vacuum of 1500 ° C. to 1700 ° C. A first sintering step for forming a sintered body having a density of 95% or more by sintering at a following, and a second sintering step for pressure-sintering the sintered body at 1600 ° C. or higher and 1800 ° C. or lower, Is provided.

By the above method, a substrate as a spinel sintered body having a composition of MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and a Si element content of 20 ppm can be formed. . The said board | substrate is equipped with intensity | strength and light transmittance required as a board | substrate for ND filters. Therefore, by forming the spinel substrate instead of the glass substrate, it is possible to provide an ND filter having a higher strength than the glass substrate and a function of attenuating light equivalent to that of the glass substrate.

The first sintering step is performed at a pressure of 50 Pa or less, and the shortest thickness from the center of the sintered body to the outside of the sintered body is D (mm), and the temperature reaches from 1000 ° C. to the maximum temperature. When the heating time of t is t minutes,
D = a × t ^1/2
1 ≦ a ≦ 3
It is preferable to have the following relationship.

  If the temperature of the first sintering step is increased under the above conditions, the content of the Si element can be reduced to 20 ppm or less after the sintering step is finished, and as a result, light equivalent to that of the glass substrate can be obtained. A spinel sintered body having a transmittance can be obtained. Therefore, in an ND filter using a spinel substrate, an optical attenuation function equivalent to that of a glass substrate ND filter can be obtained.

  An ND filter according to the present invention includes the above-mentioned spinel substrate and a thin film formed on one main surface of the substrate. As described above, when a spinel substrate is used, an ND filter having higher strength than a glass substrate and having a transmittance for light in a specific wavelength region is equivalent to an ND filter using a glass substrate is provided. can do. Furthermore, an optical characteristic measuring device including the ND filter can be provided.

  According to the present invention, it is possible to provide an ND filter that is more difficult to break than an ND filter using a glass substrate and has an equivalent transmittance.

It is a general-view figure which shows the aspect of an example of the optical characteristic measuring apparatus containing the ND filter which concerns on this Embodiment. It is the schematic which shows the aspect of the ND filter in FIG. It is the schematic which shows the aspect of the ND filter by which the thin film was formed on the main surface of the board | substrate of FIG. It is a flowchart for demonstrating the manufacturing method of the board | substrate which concerns on this Embodiment. It is a flowchart for demonstrating the process included in the process (S30) in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
An optical characteristic measuring apparatus for inspecting optical characteristics of an ND filter included in an optical information recording apparatus, which includes the ND filter according to the present invention shown in FIG. 1, includes a semiconductor laser 11, a reflecting mirror 12, and a half mirror 13. A lens 14, a lens 15, an ND filter 16, and a light receiving element 17. The semiconductor laser 11 is a device that supplies laser light. The reflecting mirror 12 is a device that reflects incident light. The light receiving element 17 is a device that receives the light reflected by the half mirror 13.

  Here, the operation principle of the optical characteristic measuring apparatus will be described. Laser light emitted from the semiconductor laser 11 is collimated by the lens 14 and branched by the half mirror 13 into two beams of transmitted light and reflected light. The transmitted light is light that passes through the half mirror 13 and travels toward the ND filter 16, and the reflected light is light that reflects from the half mirror 13 and travels toward the light receiving element 17.

  The transmitted light passes through the ND filter 16 and the lens 15 and is collected on the reflecting mirror 12. The reflecting mirror 12 is equivalent to an optical disk or the like, and the amount of light reflected by the reflecting mirror 12 can be set to a desired value by adjusting the ND filter 16. That is, by adjusting the amount of light reaching the reflecting mirror 12 by attenuating the amount of light transmitted through the ND filter 16, the amount of light reflected by the reflecting mirror 12 can be set to a desired value.

  The reflected light from the reflecting mirror 12 returns along the optical path, and a part of the reflected light is transmitted through the half mirror 13. The transmitted light travels toward the semiconductor laser 11 and is focused on the semiconductor laser 11. The light output is observed by the light receiving element 17 reflected from the half mirror 13.

  Referring to FIG. 2, ND filter 16 includes substrate 10 of the present embodiment and edge member 19. The edge member 19 is a member fitted to the outer peripheral portion (circular arc on the outer periphery) in the direction along the main surface 10 a of the substrate 10.

  In FIG. 2, the main surface of the ND filter 16 (substrate 10) is circular. However, the main surface is not limited to this, and the main surface can take any shape such as an elliptical shape or a rectangular shape.

The substrate 10 of the present embodiment is a wafer made of a spinel sintered body. An example of the composition of the spinel constituting the substrate 10 is MgO.nAl ₂ O ₃ .

Here, the effect of the ND filter 16 of this Embodiment is demonstrated.
If the substrate 10 made of a spinel sintered body is used as in the ND filter 16 of the present embodiment, the substrate 10 generates heat when the ND filter 16 is used and the thermal stress is higher than that of an ND filter using a glass substrate. The crack of the board | substrate 10 resulting from generating can be suppressed. This is because spinel has higher strength and rigidity than glass.

  The light emitted from the semiconductor laser 11 of the optical characteristic measuring apparatus can pass through the substrate 10. This is because the spinel sintered body constituting the substrate 10 can transmit the light emitted from the semiconductor laser 11.

  As light passes through the substrate 10, the ND filter 16 including the substrate 10 generates heat. For this reason, considerable stress is applied to the substrate 10. That is, when the optical characteristic measuring apparatus is operated, the substrate 10 of the ND filter 16 generates heat, and thermal stress is generated on the substrate 10. For this reason, in order to suppress the crack of the board | substrate 10, it is preferable that the board | substrate 10 has a suitable intensity | strength.

  In general, a structure has high strength when the Young's modulus is high, and low strength when the Young's modulus is low. Therefore, the substrate 10 preferably has a Young's modulus of 150 GPa or more and 350 GPa or less in order to have strength that can withstand use under the above-described conditions. When the Young's modulus of the substrate 10 is 150 GPa or more, the substrate 10 has a strength that can withstand use under the above conditions. In general, the structure has a high hardness when the Young's modulus is high, and the hardness is low when the Young's modulus is low. For this reason, for example, when the Young's modulus of the substrate 10 exceeds 350 GPa, the hardness of the substrate 10 becomes excessively high, so that the possibility of causing chipping increases. Further, since the hardness of the substrate 10 becomes excessively high, processing becomes difficult. Therefore, the Young's modulus of the substrate 10 is preferably within the above range from the viewpoint of having appropriate strength and suppressing problems such as chipping, and the most preferable range is 180 GPa or more and 300 GPa or less. It can be said.

Next, the spinel sintered body constituting the substrate 10 has a composition of MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and a Si element content of 20 ppm or less. . This spinel sintered body has a linear transmittance of visible light having a wavelength of 350 nm or more and 450 nm or less at a thickness of 1 mm, preferably 80% or more, more preferably 82% or more, and particularly preferably 84% or more. Yes, the linear transmittance is sufficiently high. In addition, high light transmittance can be stably obtained, and variation is small. Further, even with a thick material, a stable and high transmittance for visible light can be obtained.

The spinel sintered body has a composition of MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and includes an oxide composed of MgO (magnesia) and Al ₂ O ₃ (alumina). . Since the spinel sintered body which is a polycrystalline body has a cubic crystal form, light scattering at the crystal grain boundary hardly occurs, and good light transmission can be obtained when sintered at a high density. By setting 1.05 ≦ n ≦ 1.30, the solid solution amount of MgO can be reduced, the variation and distortion of the microscopic crystal lattice can be reduced, and the translucency can be improved. From this viewpoint, 1.06 ≦ n ≦ 1.125 is preferable.

  In general, as a factor for reducing the light transmittance of the spinel sintered body, metal impurities are mixed. Examples of the metal impurities include Si, Ti, Na, K, Ca, Fe, and C. These metal impurities are derived from the raw material powder and mixed in the sintered body. Among these metal impurities, when the content of the Si element is 20 ppm or less, high light transmittance can be stably obtained. From this viewpoint, the content of Si element is more preferably 10 ppm or less, and particularly preferably 5 ppm or less. By controlling the content of the Si element in this way, uniform light transmission can be obtained even in a spinel sintered body having a thickness of 10 mm or more. The Si element reacts with the spinel powder during sintering to generate a liquid phase. This liquid phase has the effect of accelerating the sinterability of the spinel powder, but if this liquid phase remains at the grain boundary, it becomes a different phase and reduces the light transmittance.

Due to the inclusion of impurities including metal impurities other than Si element, such as Na, K, Ca or Fe, the light transmittance, variation and manufacturing stability of the spinel sintered body are adversely affected. For this reason, the purity of MgO.nAl ₂ O ₃ in the spinel powder is 99.5% by mass or more, preferably 99.9% by mass or more, and more preferably 99.99% by mass or more.

The high transmittance of the spinel sintered body described above is equivalent to the transmittance when the substrate constituting the ND filter 16 is made of glass. Therefore, by setting the value of n in the spinel composition formula MgO · nAl ₂ O ₃ to 1.05 ≦ n ≦ 1.30, the light of the wavelength emitted by the semiconductor laser 11 of the optical characteristic measuring device is reduced. Thus, the light transmittance is equivalent to that of an ND filter using a glass substrate. That is, the spinel substrate can have a function of attenuating light equivalent to that of a glass substrate.

  As described above, the ND filter 16 using the substrate 10 made of spinel according to the present embodiment has higher strength than the ND filter using the glass substrate, and therefore is less likely to crack and uses the glass substrate. It can have an optical attenuation function equivalent to that of the ND filter. Therefore, by using the substrate 10 made of spinel, a long-life and high-quality ND filter can be provided.

  As a modification of the ND filter 16 shown in FIG. 2, a thin film 18 may be provided so as to cover at least a part on one main surface 10a of the substrate 10 as in the ND filter 26 shown in FIG. The thin film 18 is a thin film formed so as to cover at least a part of one main surface 10 a of the substrate 10.

  In FIG. 3, the thin film 18 is formed so as to cover only the central portion of the main surface 10a. However, this is to make it easy to understand that the thin film 18 is formed, and the thin film 18 may be formed so as to cover the entire main surface 10a.

  Since the main surface 10a of the substrate 10 is covered with the thin film 18, the transmittance of the spinel substrate 10 with respect to the wavelength of light used in the optical characteristic measuring device is greatly different from the transmittance of the glass substrate. Even if it is a thing, the said transmittance | permeability can be adjusted and it can approach the transmittance | permeability of a glass-made board | substrate. Therefore, the ND filter 26 using the thin film 18 can achieve a desired light transmittance with higher accuracy than the ND filter 16.

Next, the manufacturing method of the board | substrate 10 of this invention is demonstrated.
With reference to FIG. 4, the manufacturing method of the board | substrate 10 which is a spinel sintered compact of this invention is a high purity spinel powder preparation process (S10), a formation process (S20), a sintering process (S30), and a process process ( S40).

In the high purity spinel powder process (S10), for example, the Si element content is 50 ppm or less, the average particle size is 0.1 μm or more and 0.3 μm or less, the purity is 99.5 mass% or more, and the composition is MgO · nAl. _A spinel powder that is ₂ O ₃ (1.05 ≦ n ≦ 1.30) is prepared.

  Here, the particle size of the powder particles is obtained by integrating the volume of the powder from the small particle size side toward the large particle size side when measured using a particle size distribution measurement method by a laser diffraction / scattering method. It means the value of the diameter of the powder cross section at the location where the cumulative volume is 50%. Specifically, the particle size distribution measuring method described above is a method of measuring the diameter of the powder particles by analyzing the scattering intensity distribution of the scattered light of the laser light irradiated onto the powder particles. The average value of the particle diameters of the plurality of powder particles contained in the prepared spinel powder is the average particle diameter described above.

In the molding step (S20), a molded body is formed from the spinel powder prepared in step (S10). Specifically, this is formed by press molding or CIP (Cold Isostatic Pressing). More specifically, for example, it is preferable that the powder of MgO · nAl ₂ O ₃ prepared in step (S10) is first preformed by press molding and then CIP is performed to obtain a compact. However, only one of press molding and CIP may be performed here, or both CIP may be performed after press molding, for example.

  Here, in press molding, for example, a pressure of 10 MPa to 300 MPa, particularly 20 MPa is preferably used, and in CIP, for example, a pressure of 160 MPa to 250 MPa, particularly 180 MPa to 230 MPa is preferably used.

  Next, the sintering step (S30) shown in FIG. 4 is performed. Specifically, it is preferable that the sintering step (S30) has two steps of a first sintering step (S31) and a second sintering step (S32) with reference to FIG.

  In the first sintering step (S31), the molded body is sintered at 1500 ° C. or higher and 1700 ° C. or lower in vacuum to form a sintered body having a density of 95% or higher. By sintering in a vacuum atmosphere, the liquid phase generated from the Si element as an impurity can be evaporated and removed in vacuum. From this viewpoint, the degree of vacuum is preferably 50 Pa or less, and more preferably 20 Pa or less.

The conditions of the first sintering step vary depending on the amount of Si element and the thickness of the sintered body, but the shortest thickness from the center of the sintered body to the outside of the sintered body is D (mm), When the temperature rise time from 1000 ° C. to the maximum temperature is t minutes,
D = a × t ^1/2
1 ≦ a ≦ 3
It is preferable to have the following relationship.

  When the Si element content in the spinel powder is 50 ppm or less by raising the temperature within such a range, the Si element content is reduced to 20 ppm or less after the end of the first sintering step. Therefore, a spinel sintered body having a high light transmittance can be obtained. In view of further reducing the Si element content in the sintered body and increasing the light transmittance of the spinel sintered body, the Si element content in the spinel powder is preferably 30 ppm or less. When the Si element content in the spinel powder is 50 ppm or more, the Si element content in the sintered body is reduced by further increasing the temperature raising time in the vacuum atmosphere in the first sintering step. It is possible to do.

Further, the temperature in the first sintering step is preferably 1500 ° C. or higher in terms of obtaining a high-density sintered body having a density of 95% or higher. The density of the sintered body is more preferably 95% or more in terms of increasing the light transmittance of the sintered body. In the present specification, the density refers to a relative density calculated by the Archimedes method. On the other hand, the sintering temperature is preferably 1700 ° C. or lower in terms of suppressing evaporation of MgO in a vacuum, preventing precipitation of Al ₂ O ₃ as a second phase during cooling, and maintaining high light transmittance. 1650 ° C. or lower is more preferable.

After completion of the first sintering step, the sintered body is subjected to pressure firing at 1600 ° C. or higher and 1800 ° C. or lower by HIP (Hot Isostatic Pressing) or the like in the second sintering step (S32). Conclude. When HIP is performed at a temperature of 1600 ° C. or higher and 1800 ° C. or lower and a pressure of about 100 MPa, removal of vacancies is promoted by the composition deformation and diffusion mechanism, so that the density can be further increased and the light transmittance is further improved. The gas used for the HIP is preferably an inert gas such as Ar gas or N ₂ gas, O ₂ gas, or a mixed gas thereof. If O ₂ gas is mixed, a decrease in translucency due to deoxygenation can be prevented. it can.

  As shown in FIG. 4, a processing step (S40) is performed on the sintered body sintered as described above. Specifically, the sintered body is first cut (cut) by dicing so as to have a desired thickness (of the substrate 10). Thereby, the foundation | substrate of the board | substrate 10 which has desired thickness is completed. Here, the desired thickness is preferably determined in consideration of the thickness of the substrate 10 to be finally formed, the polishing margin of the main surface 10a of the substrate 10 in a later step, and the like.

  Next, the underlying main surface of the substrate 10 is polished. Specifically, this is a step of polishing the main surface 10a of the substrate 10 finally formed as described above so that the average roughness Ra becomes a desired value. In particular, as described above, the substrate 10 as the substrate for the ND filter is preferably polished so that the Ra of the main surface 10a is, for example, not less than 0.01 nm and not more than 3.0 nm.

  When the main surface 10a of the substrate 10 is polished to achieve excellent flatness, it is preferable to sequentially perform three stages of polishing, rough polishing, normal polishing, and polishing using diamond abrasive grains. Specifically, in the first step of rough polishing and the second step of normal polishing, the main surface 10a is mirror-finished using a polishing machine (for example, NF-300 manufactured by Nano Factor). Here, the count of abrasive grains used for polishing differs between rough polishing and normal polishing. Specifically, it is preferable to use a GC grindstone whose abrasive grain number is # 800 to # 2000 for rough polishing, and a diamond grindstone whose grain size is 3 to 5 μm for normal polishing.

  Next, the polishing as the finishing process, which is the third stage, is preferably performed using diamond abrasive grains as described above. Diamond abrasive grains are very high in hardness, and the average grain diameter of the abrasive grains is as small as about 0.5 μm to 1.0 μm, so that they are suitable for use as abrasive grains for high-precision mirror finishing. For example, polishing is performed for 10 minutes using the abrasive grains. In this way, it is possible to realize the main surface 10a having high flatness in which the average roughness Ra of the main surface 10a described above is 0.01 nm or more and 3.0 nm or less.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  The present invention is particularly excellent as a technique for manufacturing an ND filter having a higher strength than an ND filter made of a glass substrate and having a light attenuation function equivalent to that of a glass substrate.

  DESCRIPTION OF SYMBOLS 10 Substrate, 10a Main surface, 11 Semiconductor laser, 12 Reflective mirror, 13 Half mirror, 14, 15 Lens, 16, 26 ND filter, 17 Light receiving element, 18 Thin film, 19 Edge member

Claims (9)

  A substrate for an ND filter made of a spinel sintered body.   The board | substrate of Claim 1 whose Young's modulus is 150 GPa or more and 350 GPa or less. _3. The substrate according to claim 1, wherein the composition of the spinel sintered body is MgO · nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30), and the content of Si element is 20 ppm or less.   4. The substrate according to claim 3, wherein the spinel sintered body has a linear transmittance of 80% or more with a light beam having a thickness of 1 mm and a wavelength of 350 nm or more and 450 nm or less. A method for producing a substrate for an ND filter comprising a spinel sintered body, the composition of which is MgO.nAl ₂ O ₃ (1.05 ≦ n ≦ 1.30) and the content of Si element is 20 ppm or less. And
Forming a molded body from spinel powder having a Si element content of 50 ppm or less and a purity of 99.5% by mass or more;
A first sintering step of forming a sintered body having a density of 95% or more by sintering the molded body in a vacuum at 1500 ° C. or higher and 1700 ° C. or lower;
And a second sintering step of pressure-sintering the sintered body at 1600 ° C. or higher and 1800 ° C. or lower.   The said sintered compact formed by a said 1st sintering process is a manufacturing method of the board | substrate of Claim 5 whose content of Si element is 20 ppm or less. The first sintering step includes
Performed at a pressure of 50 Pa or less,
When the shortest thickness from the center of the sintered body to the outside of the sintered body is D (mm), and the heating time until reaching the maximum temperature from 1000 ° C. is t minutes,
D = a × t ^1/2
1 ≦ a ≦ 3
The manufacturing method of the board | substrate of Claim 5 or 6 which has the relationship of these. A substrate according to claim 1;
An ND filter comprising: a thin film formed on one main surface of the substrate.   An optical characteristic measuring device comprising the ND filter according to claim 8.

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