JP5548997B2 - Silicon carbide mold having fine periodic structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a silicon carbide mold having a fine periodic structure and a method for manufacturing the same.

In recent years, optical elements having functions such as light diffraction, phase control, and antireflection have been proposed. For example, regarding the use of the diffraction function, it has been reported that aberrations of the lens can be corrected by forming a blazed diffraction grating on the lens surface (see, for example, Patent Document 1 below). As for phase control, it has been reported that structural birefringence can be generated by a one-dimensional rectangular periodic structure and a function as a wave plate can be expressed (for example, see Non-Patent Document 1 below).

  Furthermore, as an antireflection treatment, by forming minute irregularities regularly on the surface of the optical substrate with a pitch equal to or less than the wavelength of incident light, an antireflection effect having a relatively small incident angle dependency and wavelength dependency can be obtained. (For example, see Non-Patent Document 2 below). By performing this process, a rapid change in refractive index at the element interface is suppressed, and the refractive index gradually changes at the element interface. For this reason, reflection on the surface of the optical element is reduced, and a high light incidence rate into the optical element can be realized.

  Glass is a material with high heat resistance, chemical stability, wide refractive index, dispersion selection range and low temperature dependence thereof, compared with resin, and has a fine cycle for developing the various functions described above. It is considered promising as a base material that forms the structure.

A mold method is known as a method for forming a periodic structure on the surface of glass. The molding method is a method in which a glass and a mold are heated to a high temperature and pressed to form a desired shape. In this case, in order to form a fine shape on the glass surface having high heat resistance and chemical stability, it is necessary to select a mold material that does not deteriorate even when repeatedly used at a temperature of at least 300 ° C. As a typical material, tungsten carbide (WC) is known, but since such a material is sintered by mixing WC powder and a binder such as nickel (Ni), it is finely processed. However, the micro-processed surface is not smooth due to the influence of the interface between WC and binder.

On the other hand, silicon carbide produced by chemical vapor deposition (CVD) does not have grain boundaries, so a smooth micromachined surface can be obtained, but the hardness is too high to allow micromachining with a diamond tool, etc. . For this reason, a technique capable of finely processing the surface of silicon carbide is required.

As a technique for surface micromachining of silicon carbide, dry etching that is often used in silicon micromachining is known. For example, NTT-ATN has published a silicon carbide mold subjected to fine processing (for example, Non-Patent Document 3 below). However, the cross-section of the fine periodic structure of the silicon carbide mold that has been published so far is almost perpendicular to the substrate surface, and when glass is molded with such a mold, a large force is required when releasing the two. It is necessary and there is a high possibility that the glass or mold is broken.
JP2005-257867 T. Yoshikawa, T. Konichi, M. Nakajima, H. Kikuta, H. Kawata and Y. Hirai: Fabrication of 1/4 wave plate by nanocasting lithography, J. Vac. Sci. Technol. B 23, 2939-2943 ( 2005). H. Toyota, K. Takahara, M. Okano, T. Yotsuya and H. Kikuta: Fabrication of microcone array for antireflection structured surface using metal dotted pattern, Jpn. J. Appl. Phys. 40, L747-749 (2001). http://nanoimprint.jp/ntt_atn.pdf

The present invention has been made in view of the problems of the prior art described above, and its main purpose is to use glass molding in a mold having a fine periodic structure based on silicon carbide (SiC). The present invention provides a method capable of forming a mold having a fine periodic structure having an inclined cross-sectional shape suitable for the above with a relatively simple method with good reproducibility.

The inventor has conducted extensive research to achieve the above-described object. As a result, a dry etching mask made of tungsten silicite (WSi) having a predetermined opening is formed on silicon carbide used as a substrate, and then etching is performed with fluorine-containing gas or a mixed gas of fluorine-containing gas and oxygen gas. It has been found that by performing reactive ion etching using a gas, the inclination angle of the fine structure portion to be etched can be controlled to produce a mold having a fine periodic structure with an inclined cross-sectional shape, and the present invention is completed here. It came to do.

That is, the present invention provides the following silicon carbide mold, a method for producing the same, and a method for producing an optical material using the mold.
1. A mold having a concave periodic structure formed on a surface of silicon carbide, wherein the concave side wall has an inclination with respect to the substrate surface.
2. Item 2. The silicon carbide mold according to item 1, wherein the silicon carbide is polycrystalline silicon carbide or single crystal silicon carbide having a crystal grain size smaller than the period of the concave periodic structure.
3. Item 3. The silicon carbide mold according to Item 1 or 2, wherein the concave sidewall has an inclination angle of 45 to 88 degrees with respect to the silicon carbide substrate surface.
4). Furthermore, the mold in any one of said claim | item 1-3 by which the release film is formed in the surface. 5. Item 5. The mold according to Item 4, wherein the release film is a film containing at least one element selected from the group consisting of carbon, platinum, rhodium, iridium, ruthenium, osmium, rhenium, tungsten, palladium, and tantalum.
6). After forming a dry etching mask made of tungsten silicide having an opening on a silicon carbide substrate, a reactive ion etching method using a fluorine-containing gas alone or a mixed gas of fluorine-containing gas and oxygen gas as an etching gas. 4. The method for producing a silicon carbide mold according to any one of Items 1 to 3, wherein the silicon carbide substrate is dry-etched by:
7). A dry etching mask made of tungsten silicide is formed by reactive ion etching using sulfur fluoride as an etching gas after forming an etching resist film on a tungsten silicide film formed on a silicon carbide substrate. Item 7. The method for producing a silicon carbide mold according to Item 6, wherein the opening is formed by etching the tungsten silicide film.
8). The thickness of the dry etching mask made of tungsten silicide is 50 to 400 nm, and the volume ratio of fluorine-containing gas to oxygen gas in the etching gas used for etching the silicon carbide substrate is fluorine-containing gas: oxygen gas = 30: 0. Item 8. The method for producing a silicon carbide mold according to Item 6 or 7, which is in the range of 30: 7.
9. The resulting silicon mold is a mold having a two-dimensional pyramidal periodic structure in which conical recesses are two-dimensionally formed with a period of 100 to 500 nm,
Item 9. The method for producing a silicon carbide mold according to any one of Items 6 to 8, wherein the diameter of the opening of the mask material made of tungsten silicide is 1/6 to 2/5 of the period of the formed recess.
10. 6. A method for producing an optical material, comprising pressing a glass material using the silicon carbide mold described in any one of items 1 to 5.
11. An optical material produced by the method according to Item 11.

  Hereinafter, first, the manufacturing method of the mold of this invention is demonstrated one by one.

Substrate Material In the mold of the present invention, a silicon carbide (SiC) substrate is used as the substrate. In particular, it is preferable to use polycrystalline silicon carbide or single-crystal silicon carbide having a crystal grain size smaller than the intended concave period. Such silicon carbide has a dense and homogeneous composition, and can be produced by, for example, a chemical vapor deposition (CVD) method, a sputtering method, a vapor deposition method, or the like.
In particular, single crystal or polycrystalline silicon carbide formed by a CVD method is preferable in that it has good denseness, homogeneity, and the like, and can form a smooth finely processed surface.

The thickness of the silicon carbide substrate is not particularly limited, but is preferably 1 mm or more in consideration of the strength as a mold during glass molding. However, it is preferable that the thickness of the silicon carbide when silicon carbide is formed on another high-strength substrate is about twice or more the depth of the groove to be formed.

Mask material for dry etching In the present invention, tungsten silicide (WSi) is used as a mask material for dry etching.
Is used. By using a dry etching mask made of tungsten silicide, the rate at which the opening of tungsten silicide, which is a mask material, is expanded by plasma can be adjusted when dry etching is performed by a method described later. As a result, the inclination angle of the side wall of the concave portion with respect to the substrate can be adjusted by arbitrarily setting the ratio between the etching rate of tungsten silicide and the etching rate of silicon carbide. In addition, when tungsten silicide is used as a mask material, the surface of the sidewall of the concave portion formed by dry etching can be smoothed.

  The mask made of tungsten silicide can be formed by, for example, a sputtering method or a vapor deposition method. In particular, it is preferably formed by a sputtering method such as a DC sputtering method or an RF sputtering method because the composition is uniform and stable. At that time, if the substrate is heated to about 200 to 280 ° C., the etching rate of tungsten silicide in the silicon carbide etching process becomes slower than that at room temperature, which may be advantageous for etching silicon carbide. . As the tungsten silicide, one having a W content in the range of about 10 to 80 at% can be used.

  The shape of the opening formed in the tungsten silicide mask can be determined according to the fine periodic structure of the target mold. For example, when forming a one-dimensional groove-shaped periodic structure on a silicon carbide substrate, the portion enlarged by dry etching with the same shape as the periodic structure formed on the silicon carbide substrate with the shape of the tungsten silicide opening. In consideration of the above, the area of the opening as the mask material may be determined.

  When a two-dimensional conical periodic structure is formed on the silicon carbide substrate, the tungsten silicide film may be formed with a circular opening having the same period as the conical periodic structure. The area may be determined in consideration of a portion enlarged by dry etching.

  A method of forming the opening in the dry etching mask made of tungsten silicide is not particularly limited. For example, after forming an etching resist film having an opening that matches the shape of the opening of tungsten silicide, for example, A method of forming a predetermined opening in the tungsten silicide film by performing dry etching can be employed.

  The type of the etching resist film is not particularly limited, and any resist that can sufficiently protect the non-etched portion and can pattern the desired fine periodic structure when tungsten silicide is etched by the method described later. That's fine. For example, an electron beam drawing resist or a photoresist can be used.

As a method for etching the tungsten silicide film, it is preferable to perform reactive ion etching using sulfur fluoride such as SF ₆ as an etching gas. According to this method, since the tungsten silicide film can be etched under relatively mild conditions, the resist film formed on the tungsten silicide film can be maintained while the tungsten silicide film is being etched. In addition, after the tungsten silicide film is etched, the etching of the silicon carbide film does not proceed.

  The reactive ion etching method using sulfur fluoride as an etching gas is not particularly limited and may be a known method. In particular, by adding argon in addition to sulfur fluoride, the plasma can be stabilized. Can be made. The amount of argon added is not particularly limited, but the amount of argon is preferably about 1 to 50% by volume based on the total amount of sulfur fluoride and argon introduced into the etching chamber.

  The specific conditions for reactive ion etching may be determined as appropriate so that stable plasma is generated according to the flow rate of the etching gas used, the internal pressure in the chamber, etc., and the substrate is appropriately biased. Etching of tungsten silicide can be progressed by performing reactive ion etching.

  Regarding the temperature of the substrate at the time of etching, the plasma resistance of the resist is improved when the temperature is lowered, and therefore, for example, the substrate temperature is preferably about 5 to 25 ° C. In addition, if the etching is continued for a long time, the resist is heated and the etching selectivity between the resist and tungsten silicide cannot be sufficiently obtained. For example, the etching and cooling cycles are repeated to suppress the progress of the etching of the resist. Thus, it is preferable to etch the tungsten silicide film to a necessary depth. Etching conditions are preferably, for example, a chamber pressure of about 0.5 to 1.5 Pa, a total introduction amount of argon and sulfur fluoride of about 30 to 100 cc / min, a plasma power of about 50 to 800 W, and a bias power of about 20 to 100 W. Optimization is necessary as appropriate depending on the state and temperature of the chamber and the method of fixing the mold.

  The thickness of the tungsten silicide film is not particularly limited. For example, when the etching resist is formed on the tungsten silicide film using the above-described electron beam drawing resist, photoresist, etc., the thickness of the etching resist is not limited. The thickness is usually in the range of about 100 nm to 1 μm. After forming an etching resist in this range, when an opening is formed in tungsten silicide by a reactive ion etching method using sulfur fluoride, it is necessary for the tungsten silicide film before the etching resist completely disappears. In order to form the opening, it is appropriate that the tungsten silicide film has a thickness of about 50 nm to 400 nm.

  The specific thickness of the tungsten silicide mask is the target groove structure depth and target sidewall inclination angle depending on the silicon carbide / tungsten silicide selection ratio in the reactive ion etching method described later. What is necessary is just to determine suitably.

Etching method of silicon carbide substrate In the present invention, after a dry etching mask made of tungsten silicide is formed on a silicon carbide substrate by the above-described method, a fluorine-containing gas or a mixed gas of fluorine-containing gas and oxygen gas is used as an etching gas. Then, the silicon carbide substrate is etched by the reactive ion etching method. As the fluorine-containing gas, CHF ₃ , C ₃ F ₈ , C ₄ F ₈ , sulfur fluoride, or the like can be used.

  According to this method, by changing the ratio of the fluorine-containing gas used as the reactive gas and the oxygen gas, the etching rate of the silicon carbide substrate and the rate at which the opening of the tungsten silicide, which is the mask material, is expanded by the plasma. The ratio can be adjusted, and as a result, the inclination angle of the side wall of the recess to be formed can be adjusted.

  For example, when only a fluorine-containing gas is used without using oxygen gas, the etching rate ratio of silicon carbide / tungsten silicide, so-called selectivity, increases, the etching rate of the silicon carbide substrate increases, and the opening of the tungsten silicide mask increases. Since the enlargement speed of the portion becomes slow, as a result, the inclination angle of the side wall becomes nearly vertical with respect to the substrate plane. On the other hand, when oxygen gas is added to the fluorine-containing gas, the etching rate of both silicon carbide and tungsten silicide increases, but the etching rate of silicon carbide decreases when the oxygen gas content exceeds a certain level. Tend. Therefore, when an amount of oxygen exceeding this amount is added, the silicon carbide / tungsten silicide selection ratio decreases, the etching speed of tungsten silicide as a mask material increases, and the opening of the tungsten silicide mask gradually expands. The inclination angle of the sidewall of the recess, that is, the angle between the sidewall of the recess and the surface of the silicon carbide substrate can be reduced.

The mixing ratio of the fluorine-containing gas and the oxygen gas may be determined so that the concave portion having the target microperiodic structure is formed in consideration of the above points. For example, when a tungsten silicide mask having a thickness of about 50 to 400 nm is formed, the mixture ratio of fluorine-based gas and oxygen gas is fluorine-containing gas: oxygen gas = 30: 0-30: A range of about 7 is preferable. When the ratio of oxygen gas exceeds the above range, the etching rate of the entire mask increases, and it may be difficult to secure the depth of the groove structure with respect to the substrate surface of 50 nm or more.

  Regarding the size of the opening of the tungsten silicide mask, since the opening is gradually enlarged as the etching progresses, the period of the periodic structure, the area of the finally obtained recess, the inclination angle of the sidewall, the depth of the groove, etc. You may decide according to. For example, in the case where a concave periodic structure whose cross-sectional side walls are not perpendicular to the substrate surface is formed two-dimensionally on the silicon carbide surface, the fact that the opening of the tungsten silicide mask gradually widens with the etching time is used. By doing so, a periodic structure having a desired shape can be formed.

When forming a silicon carbide mold with a two-dimensional pyramidal periodic structure in which conical recesses are two-dimensionally formed with a period of about 100 to 500 nm, which is often used as a mold for optical elements. The diameter of the opening of the tungsten silicide mask is preferably in the range of about 1/6 to 2/5 of the period of the recess to be formed. If the opening before etching is larger than 2/5, it becomes difficult to form a spindle with a sharp tip, and if it is smaller than 1/6, the etching gas hardly reaches the silicon carbide surface. When it becomes difficult to form a deep pyramid, or when the etching gas reaches the silicon carbide surface, the tilt angle of the pyramidal side wall becomes steeper than 88 degrees, and it is separated during glass molding. Neither is preferred because the mold becomes difficult.

  Regarding the conditions of reactive ion etching performed on the silicon carbide substrate, the target fine cycle is performed in accordance with a conventional method except that a fluorine-containing gas alone or a mixed gas of fluorine-containing gas and oxygen gas is used as an etching gas. What is necessary is just to determine suitably so that the concave-shaped part of a structure may be formed.

Specifically, each operation condition may be determined so that stable plasma is generated according to the flow rate of the etching gas used, the internal pressure in the chamber, and the like. Further, by performing reactive ion etching with an appropriate bias applied to the substrate, silicon carbide etching can be preferentially advanced in the depth direction.

Etching conditions include, for example, a substrate temperature of 5-40 ° C., a chamber pressure of 0.5-1.5 Pa,
Argon: 10 to 70 cc / min, CHF ₃ : 5 to ₃₀ cc / min, plasma power 50 to 800 W, bias power 20 to 300 W are preferred, but optimization may be made as appropriate depending on the chamber conditions, temperature, mold fixing method, etc. is necessary.

Silicon Carbide Mold By performing reactive ion etching by the method described above, a concave fine periodic structure can be formed on the surface of the silicon carbide substrate. When a tungsten silicide film as a mask material remains on the surface of the obtained silicon carbide mold having a fine periodic structure, for example, by performing reactive ion etching using sulfur fluoride as an etching gas, silicon carbide Only the tungsten silicide film can be selectively removed with almost no roughening of the mold surface.

  The silicon carbide mold obtained by the above-described method has a concave portion etched by a reactive ion etching method, and the side wall of the concave portion is not perpendicular to the silicon carbide substrate surface but is inclined. It will have. As for the inclination angle of the side wall, when the glass is formed using the silicon carbide mold, it is appropriate that the inclination angle is 88 degrees or less with respect to the silicon carbide substrate surface so that the mold can be easily released with a small force. It is. In particular, when the inclination angle is about 60 degrees or less, it has a very good release property. In consideration of the optical characteristics of the glass to be molded, it is appropriate that the inclination angle of the side wall of the concave portion is 45 degrees or more.

  The silicon carbide mold has a fine periodic structure in which concave portions formed by etching are periodically formed. The periodic structure of the concave portion is not particularly limited, and may be a shape corresponding to the purpose of the glass to be formed. For example, a one-dimensional groove-shaped periodic structure in which groove-shaped recesses as shown in FIG. 7 are periodically and continuously formed on the surface of a silicon carbide substrate in a certain direction, and a spindle shape as shown in FIGS. Can be exemplified by a two-dimensional pyramidal periodic structure in which the recesses are periodically formed two-dimensionally on the surface of the silicon carbide substrate.

In the silicon carbide mold, the period in which the recesses are formed is not particularly limited, and the recesses having a period corresponding to the purpose of use of the glass to be molded may be formed. For example, when used for the purpose of a polarizer, a wavelength plate, an antireflection plate or the like used in a wavelength range of 400 nm to 800 nm, the period of the concave portion can be set to about 50 nm to 300 nm, for example. Moreover, in order to form a diffraction grating, the period of a recessed part can be about 300 nm-15 micrometers, for example.

The depth of the recess formed by etching is not particularly limited. For example, when used for the purpose of a polarizer, a wavelength plate, an antireflection plate, etc., it can be about 10 nm to 1000 nm. Further, in order to form the diffraction grating, for example, the depth of the concave portion can be set to about 100 nm to 20 μm.

  Moreover, as shown in FIG. 7, this silicon carbide mold may protect only the part in which the periodic concave-shaped part was formed with a mask, and may etch the peripheral part. In this case, as an etching method for the peripheral portion, in addition to reactive ion etching, a method such as ion milling can be adopted, and as a mask material, in addition to a metal mask such as Cr, Ni, tungsten silicide, etc., a resist But it is possible.

  In the mold of the present invention, the concave portion only needs to be concave with respect to the substrate surface of the silicon carbide substrate before starting the etching of the silicon carbide substrate, for example, a portion where the concave portion is formed. When the peripheral portion is etched, the entire periodic structure portion has a convex shape. This case is also included in the mold in which the concave periodic structure is formed on the surface of the silicon carbide substrate of the present invention.

Release Film A release film can be further formed on the surface of the silicon carbide mold described above in order to prevent the glass and silicon carbide from fusing at the time of molding. The release film can be formed by, for example, a vacuum film forming method such as a sputtering method or a vapor deposition method. Release films include carbon (C), platinum (Pt), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os),
A film containing at least one element selected from the group consisting of rhenium (Re), tungsten (W), palladium (Pd), and tantalum (Ta) is preferable. These materials are suitable for a vacuum film-forming method and are excellent in the effect of avoiding fusion with glass.

The thickness of the release film is usually about 10 nm to 1 μm, although it depends on the uneven shape of the periodic structure.

Manufacturing Method of Glass Material In order to form glass using the silicon carbide mold obtained by the above-described method, it is usually sufficient to adopt a press molding method and transfer the microstructure of the mold to the glass. For example, the shape of the mold can be transferred to the glass by pressing the glass heated to a temperature equal to or higher than the softening point of the glass to be molded and the mold.

  Usually, in optical applications, a high softening point glass having a softening point of 300 ° C. or higher is often used. The mold of the present invention uses silicon carbide having a high heat resistance as a substrate material and has a structure in which the side surface of the concave portion is inclined, so that even when repeatedly used at a processing temperature of 300 ° C. or higher, the mold is damaged. Without causing deterioration, the fine periodic structure formed on the surface of the silicon carbide mold can be transferred to the glass, and the glass having the fine periodic structure can be repeatedly and stably manufactured.

  According to the method for producing a silicon carbide mold of the present invention, a concave portion having a fine periodic structure can be easily formed on the surface of silicon carbide, which is a material having excellent heat resistance. The concave portion to be formed has a smooth surface and the side wall of the concave portion has an inclination, and when used as a glass molding mold, a fine shape can be easily formed on the glass surface. Moreover, since the said silicon carbide mold is favorable in heat resistance, intensity | strength, mold release property, etc., even if it shape | molds repeatedly at high temperature, it is hard to produce deterioration of a mold.

  Therefore, by forming a fine periodic structure in glass using the mold of the present invention, it becomes possible to stably and repeatedly manufacture an optical element having optical functions such as diffraction, structural birefringence, and antireflection. The formed optical element is useful for various optical devices such as antireflection, a wave plate, and a diffraction grating.

BRIEF DESCRIPTION OF THE DRAWINGS Drawing which shows typically the silicon carbide mold in which the two-dimensional and periodic concave spindle shape obtained by Example 1 was formed. In Example 1, the microscope picture which shows the surface state of the etched tungsten silicide. FIG. 3 is a micrograph showing a surface state of a silicon carbide mold on which a two-dimensional concave spindle-shaped periodic structure obtained in Example 1 is formed, and a schematic diagram showing a cross-sectional shape of the recess. The graph which shows the relationship between the etching rate of tungsten silicide and silicon carbide, and oxygen addition amount. 2 is a photomicrograph showing the surface state of the phosphate glass obtained in Example 1. FIG. The microscope picture which shows the surface state of the mold which has a two-dimensional concave spindle shape of inclination-angle 50 degree | times, and the glass molded product shape | molded using the mold. FIG. 4 is a schematic diagram showing a one-dimensional and periodic concave groove obtained in Example 2. FIG. 3 is a schematic diagram showing a micrograph showing a surface state of the one-dimensional periodic structure obtained in Example 2 and a cross-sectional shape of a recess.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the following examples, specific examples of silicon carbide molds manufactured according to the present invention will be described by taking the application to an antireflection structure or a structural birefringent wave plate as an example. The mold and the manufacturing method thereof according to the present invention are not limited to the following forms, and can be applied to, for example, high-hardness materials such as WC, diamond, and quartz whose binder does not affect the etching rate.

Example 1
Example 1 shows an example of manufacturing a silicon carbide mold in which concave pyramids are two-dimensionally and periodically formed on the surface of a planar silicon carbide substrate. The periodic structure obtained in Example 1 is transferred to the surface of an optical lens or the like, for example, and light reflection on the lens surface (such as generation of stray light due to multiple reflection) can be suppressed.

FIG. 1 is a drawing schematically showing a silicon carbide mold in which a two-dimensional and periodic concave pyramid shape obtained in Example 1 is formed. The concave weight in the mold has a period of 300 nm,
The cone depth is 300 nm. In this case, the conical sidewall is inclined 63.4 degrees with respect to the silicon carbide substrate surface. Such a shape can be manufactured with good reproducibility through the following process. Note that the manufacturing conditions described below are typical examples of the apparatus used in the present invention, and do not limit the present invention.
(1) A tungsten silicide film having a thickness of 120 nm was formed on the surface of an optically polished silicon carbide substrate by sputtering. At that time, if the substrate is heated to about 250 ° C., the plasma resistance at the time of subsequent etching is improved, and a deeper cone shape can be formed.
(2) Next, a positive resist for electron beam lithography (ZEP-520A, Zeon Co., Ltd.) is spin-coated on the tungsten silicide surface at a rotation speed of 1000 revolutions / minute so as to have a film thickness of 800 nm.
Heated for minutes.
(3) A circular hole having a diameter of 100 nm and an accelerating voltage of 50 kV and a current value of 500 pA was drawn two-dimensionally with a period of 300 nm on the resist surface, and then developed in an orthoxylene solution for 5 minutes.
(4) Next, the tungsten silicide layer was dry-etched through a resist mask. High frequency induction plasma power 110W, bias high frequency power 100W, chamber pressure 1Pa
As the etching gas, SF ₆ of 30 cc / min and argon gas of 5 cc / min were introduced. The substrate temperature during etching was set to 25 ° C., and a cycle of 1 minute etching and 30 second cooling was repeated a plurality of times to completely etch tungsten silicide exposed at the resist opening. FIG. 2 is a scanning electron micrograph showing the surface state of the etched tungsten silicide.
(5) Next, the underlying silicon carbide was etched through the opening formed in the tungsten silicide mask. High-frequency induction plasma power 200W, bias high-frequency power 150W, chamber pressure 1Pa, substrate temperature 25 ° C, CHF ₃ as an etching gas flows 30cc / min, oxygen (O ₂ ) 5cc / min on the surface of silicon carbide substrate A concave pyramidal periodic structure could be formed. FIG. 3 shows a micrograph showing a surface state of a silicon carbide mold in which a two-dimensional concave spindle-shaped periodic structure is formed, and a schematic diagram showing a cross-sectional shape of the formed recess.

Note that the remaining tungsten silicide mask could be selectively removed by etching using sulfur fluoride (SF ₆ ) gas as an etching gas.

  Using the obtained two-dimensional concave spindle mold, the periodic structure was transferred to phosphate glass, and a shape in which the fine shape of the mold was almost faithfully inverted was formed on the glass surface, and the mold release property It was confirmed that there was no problem.

Here, the result of quantitatively examining the etching rate of tungsten silicide and silicon carbide with respect to the amount of oxygen added is shown in FIG. As shown in FIG. 4, the CHF ₃ introduction rate was fixed at 30 cc / min, the O ₂ introduction rate was varied in the range of 0-7 cc / min, and the etching rates of tungsten silicide and silicon carbide were compared. The etching rate of silicide varies linearly with the amount of O ₂ introduced, but the etching rate of silicon carbide varies in a curved manner. That is, when a certain amount of O ₂ is added, tungsten silicide as a mask material is etched relatively quickly. Therefore, the opening portion of tungsten silicide formed by electron beam drawing and etching with sulfur fluoride gas is retreated faster (opening portion is expanded faster) by introducing O ₂ as an etching gas. Specifically, the etching rate ratio (selection ratio, silicon carbide etching rate / tungsten silicide etching rate) of both in the case of CHF ₃ alone (without oxygen) was 3.7, and oxygen was introduced thereto at 7 cc / min. The case is 2.05. By combining this phenomenon with other conditions such as plasma power and substrate temperature, the speed at which the tungsten silicide opening spreads can be controlled. As a result, the inclination of the sidewalls of each structural unit of the concave periodic structure with respect to the substrate surface is controlled. The corner can be controlled.

  In addition, a carbon film having a thickness of 0.05 μm was formed on the two-dimensional concave spindle mold obtained by the above method using a sputtering method. Using this as a glass molding mold, a commercially available phosphate glass was molded at 430 ° C. by a press molding method. A micrograph showing the surface state of the obtained phosphate glass is shown in FIG. The obtained glass is a glass element having an antireflection structure with an aspect ratio of 1.6 and an inclination angle of 63.4 degrees, a reflectance at a wavelength of 462 nm of 0.2%, and reflection when a fine structure is not formed. It was confirmed that reflection could be suppressed to about 1/25 of a rate of 5.2%.

FIG. 6 is a scanning electron micrograph showing the surface state of a mold having a two-dimensional concave spindle shape with a tilt angle of 50 degrees formed by dry etching on the surface of a silicon carbide substrate and a glass molded product formed using the mold. It is. Compared with the mold shown in FIG. 3, this mold has a better releasability, and it was confirmed that the obtained glass molded product was able to reduce the reflectance to about 0.6%.

Example 2
A silicon carbide mold in which concave grooves were formed one-dimensionally and periodically on the surface of the same flat silicon carbide as in Example 1 was produced. The obtained periodic structure is applied to, for example, a diffraction grating that separates light for each wavelength, a structural birefringent wavelength plate, and the like.

A schematic view of the one-dimensional and periodic concave groove obtained in Example 2 is shown in FIG. Such a shape can be manufactured with good reproducibility through the following processes. Note that the manufacturing conditions described below are typical examples of the apparatus used in the present invention, and do not limit the present invention.
(1) A tungsten silicide film having a thickness of 120 nm was formed on the optically polished silicon carbide substrate surface by the same method as in Example 1 of the invention.
(2) Next, a positive resist for electron beam lithography (ZEP-520A, Zeon Co., Ltd.) is spin-coated on the tungsten silicide surface at a rotational speed of 2000 revolutions / minute so as to have a film thickness of 500 nm.
Heated for minutes.
(3) A straight line having an acceleration voltage of 50 kV, a current value of 500 pA and a thickness of 250 nm was drawn one-dimensionally at a cycle of 500 nm on the resist surface, and then developed in an orthoxylene solution for 1 minute.
(4) The tungsten silicide exposed in the resist opening was completely etched under the same conditions as in Example 1.
(5) Under the same conditions as in Example 1, the underlying silicon carbide can be etched through the opening formed in the tungsten silicide mask to form a concave one-dimensional periodic structure on the surface. It was. FIG. 8 is a schematic diagram showing a micrograph showing the surface state of the obtained one-dimensional periodic structure and the cross-sectional shape of the formed recess.

  The concave portion formed by etching had a groove width of 250 nm and a groove depth of 540 nm, and the inclination angle of the side wall was 83 degrees with respect to the substrate plane.

When the periodic structure was transferred to phosphate glass using the obtained one-dimensional concave spindle mold, a shape in which the fine shape of the mold was almost faithfully inverted was formed on the glass surface, and the mold release property It was confirmed that there was no problem.

Comparative Example 1
For electron beam drawing, a chromium (Cr) film having a thickness of 20 nm was formed by sputtering on the surface of an optically polished silicon carbide substrate similar to that in Example 1, and then spin-coated and heat-treated to a thickness of 800 nm. A circular hole having a diameter of 100 nm was drawn and developed two-dimensionally with a period of 300 nm on the positive resist under the same conditions as in Example 1.

  The Cr layer was dry-etched through the resist mask under the same conditions as in Example 1. However, the resist disappeared before the Cr film was removed, and a desired opening could not be formed.

  Therefore, it was confirmed that Cr is not preferable as a mask material when a dry etching mask is formed by a dry etching method.

Claims (6)

A mold having a concave periodic structure formed on the surface of silicon carbide, wherein the concave side wall has an inclination with respect to the substrate surface.
Carbide on a silicon carbide substrate, forming a mask for dry etching of tungsten silicide having an opening, using a mixed gas of full Tsu-containing gas and oxygen gas as an etching gas, the reactive ion etching method A method for producing a silicon carbide mold, comprising dry etching a silicon substrate. The fluorine-containing gas is CHF ₃ The method for producing a silicon carbide mold according to claim 1, wherein A dry etching mask made of tungsten silicide is formed by reactive ion etching using sulfur fluoride as an etching gas after forming an etching resist film on a tungsten silicide film formed on a silicon carbide substrate. The method for producing a silicon carbide mold according to claim 1 or 2 , wherein the opening is formed by etching the tungsten silicide film. The thickness of the dry etching mask made of tungsten silicide is 50 to 400 nm, and the volume ratio of fluorine-containing gas to oxygen gas in the etching gas used for etching the silicon carbide substrate is fluorine-containing gas: oxygen gas = 30: 0. The method for producing a silicon carbide mold according to any one of claims 1 to 3, which is in a range of -30: 7. The resulting silicon mold is a mold having a two-dimensional pyramidal periodic structure in which conical recesses are two-dimensionally formed with a period of 100 to 500 nm,
The method for producing a silicon carbide mold according to any one of claims 1 to 4 , wherein the diameter of the opening of the mask material made of tungsten silicide is 1/6 to 2/5 of the period of the formed recess. A silicon carbide mold is manufactured by the method for manufacturing a silicon carbide mold according to any one of claims 1 to 5 , and then the glass material is press-molded using the obtained silicon carbide mold. A method for manufacturing an optical material.

Images