JP2851818B2 - Optical element components for high energy beams - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention constitutes an optical element such as a reflector or a diffraction grating used in an optical instrument for handling a high energy beam such as synchrotron radiation (SOR light), laser light and X-rays. Particularly, the present invention relates to a composite material in which a silicon carbide film is formed by coating a surface of a substrate made of silicon carbide or carbon by chemical vapor deposition.

[0002]

2. Description of the Related Art For example, as a conventional general laser reflecting mirror, a base material made of copper or the like is mirror-polished and gold is deposited thereon, or a base material is calculated and designed from the wavelength used. There are well-known ones in which a multilayer film having a predetermined thickness is coated to utilize the interference effect. However, such a reflecting mirror has a relatively small energy density and is not used in a long wavelength region (for example, visible light or infrared light). , Heat loss, etc., and it is extremely difficult to deal with it.

Therefore, recently, as an optical element such as a reflecting mirror which does not cause such inconvenience, a composite material obtained by chemically vapor-depositing silicon carbide on the surface of a silicon carbide sintered body or a substrate made of carbon sintered body is used as a constituent material. The one used as is promising. For example, a reflector made of such a constituent material is manufactured by polishing the surface of a silicon carbide film to a smooth surface (usually, the surface roughness is not more than RMS 10 °).
Since C has excellent physical properties such as heat resistance, thermal conductivity, and robustness, and has excellent optical properties such as high reflectivity in a short wavelength range, it is necessary to handle a high energy beam in a short wavelength range. Also, the inconvenience described above does not occur.

[0004]

However, an optical element such as a reflector made of a composite material formed by forming a chemical vapor deposition film of silicon carbide on the surface of a substrate has a high energy beam (SOR).
(E.g., light, laser light, X-rays, etc.), and is susceptible to damage due to the supply of high energy due to irradiation or the like, and there is a problem that the beam reflectance is also likely to decrease.

[0005] That is, when such a high energy beam is irradiated, the irradiated portion on the surface of the silicon carbide film becomes cloudy (cloudy).
May occur, but when such cloudiness occurs,
Not only does the beam reflectivity decrease, but the absorptivity of the high-energy beam increases, and the reflecting mirror and the like may be damaged. In addition, even when such white turbidity does not occur on the film surface, the reflecting mirror and the like may be damaged. Such damage to the reflector or the like is not limited to damage to itself, but may also cause damage to other optical elements constituting the optical device or damage to the entire optical device, leading to a major accident. Absent.

The present inventor has conducted a number of experiments and studies, and has determined that the cause of generation or breakage of such white turbidity is silicon deposition. That is, when the turbidity generated on the film surface is observed finely, it is confirmed that silicon is deposited in the form of fine droplets at the turbid portion, and that the deposition of silicon is a cause of the turbidity. Do you get it. In the case where the film surface was damaged in spite of not having noticeable cloudiness, silicon was remarkably precipitated in fine recesses such as polishing scratches and diffraction grating grooves existing in the irradiated area. When silicon is not deposited on the film surface to such an extent as to be visible, but silicon is deposited in a concave portion which is a part of the irradiated portion, a high energy beam is selectively applied to the silicon deposited portion. Therefore, there is a portion where the beam is absorbed and a portion where the beam is not absorbed at the irradiated portion, and a rapid thermal expansion difference is generated between the two portions due to the irradiation of the high-energy beam. Etc. were found to be damaged.

Further, the present inventor has conducted experiments and researches to find out that the cause of silicon deposition is mainly due to the purity of the silicon carbide film. That is, when the purity of the silicon carbide film is low, the content of silicon out of the chemical equivalence ratio increases, and such excess silicon is deposited by irradiation with a high energy beam. For example, as described above, in the laser reflecting mirror, the film surface is polished to an ultra-smooth surface with a surface roughness RMS of 10 ° or less. In the polishing step, crystals having irregularities on the surface are mechanically scraped off. Due to the physical impact, the conformity of the atomic arrangement is lost on the crystal surface or directly below the crystal surface, particularly in a concave portion where the crystal surface is cut off by a large external force. The atomic arrangement is remarkably disrupted. Therefore, when a high-energy beam is applied to a portion where the conformity of the atomic arrangement is broken, that is, if a high energy enough to promote the rearrangement of the atoms is supplied, the rearrangement of the atoms is performed. During the process, excess silicon is deposited outside the lattice of silicon carbide. At present, it is technically and economically impossible to remove atoms forming the surface layer of the silicon carbide film without disturbing the arrangement.

[0008] From these findings, in order to prevent damage to the reflecting mirror and the like and decrease in the beam reflectivity, deposition of silicon by supplying high energy, that is, the chemical equivalent ratio of the silicon carbide film of the optical element constituting material must be reduced. It was concluded that it was necessary to keep the lacking state as nonexistent as possible.

The present invention has been made on the basis of these findings and the conclusions obtained therefrom.
Even when high energy is directly supplied to the surface of the silicon carbide film due to irradiation of a high energy beam such as light, laser light, X-ray, or the like, silicon does not deposit at the energy supply location, and the above-described problem occurs. High energy such as laser reflectors that do not cause
It is an object of the present invention to provide a giant beam optical element component.

[0010]

SUMMARY OF THE INVENTION The high energy beam of the present invention is provided.
The optical element constituting material is a composite material in which a silicon carbide film is formed by coating a surface of a substrate made of silicon carbide or carbon by chemical vapor deposition. A high-density body of 93% or more and a silicon carbide film having a spectral absorption edge of 550 nm or less. The substrate may be a sintered body as long as it has a high density of 93% or more. The silicon carbide film is chemically vapor-deposited on the surface of the substrate by supplying a predetermined reaction gas into a CVD furnace in which a porous substrate, which is a silicon carbide sintered body, is disposed. Differently from the method, it is preferable to constantly exhaust gas from the CVD furnace to keep the inside of the CVD furnace in a reduced pressure atmosphere and to generate an exhaust gas flow on the surface of the substrate or its peripheral region.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A high energy beam optical element constituting material of the present invention is used for an optical device such as a reflecting mirror or a diffraction grating used in an optical device for handling high energy beams such as SOR light, laser light and X-rays. The composite material is suitable as a constituent element, and is a composite material in which a silicon carbide film is formed on a surface of a substrate made of silicon carbide or carbon by chemical vapor deposition.

The base is made of a sintered body of silicon carbide or carbon, for example, and its density needs to be 93% or more. The reason why such high density is set is mainly to secure the static strength, the thermal strength, and the like of the optical element such as the laser reflector obtained by using the constituent material, and to secure the durability. That is, if the substrate density is less than 93%, the mechanical strength and the like generally required for an optical element such as a laser reflecting mirror cannot be sufficiently secured.
In particular, when the substrate is a porous sintered body, there is a possibility that the air in the space of the substrate expands due to a temperature rise due to beam irradiation or the like, causing cracks or thermal distortion. In addition, when cooling the optical element, there is a possibility that a cooling liquid such as cooling water may enter the base body and crack or the like may occur due to evaporation and expansion of the entering water. Therefore, in order to sufficiently secure the strength of the base and the strength of the optical element, it is necessary to set the base density to at least 93%, and more preferably to set the density to 95% or more. .
The substrate density also has a relationship with the bonding strength of the silicon carbide film,
Generally, the higher the better, the better, and there is no particular upper limit. In addition,
As the base material, it depends on the method of depositing the silicon carbide film.
In consideration of the influence of impurities evaporating from the substrate during the deposition on the purity of the silicon carbide film, it is preferable to use silicon carbide or carbon with as high a purity as possible.

The silicon carbide film has a spectral absorption edge of 5
Β-SiC (3
It is a chemical vapor deposition film of C). Spectral absorption edge is 550n
m, that is, a silicon carbide film capable of absorbing light having a wavelength of 550 nm or less has a wide band gap (about 2.3 eV) and a small amount of impurities in solid solution. That is, the content of the heavy metal element in the film is extremely small (for example, Fe: 30 ppb or less, Cu: 50 ppb or less, Cr: 40 ppb or less), and the excess silicon content outside the chemical equivalent ratio is extremely large. Few. Therefore, the purity of the silicon carbide film becomes higher as the spectral absorption edge shifts to the shorter wavelength side, and the inconvenience caused by silicon deposition described above does not occur. On the other hand, the shift of the spectrum absorption edge to the longer wavelength side means that the band gap becomes narrower. In a silicon carbide film having a spectrum absorption edge exceeding 550 nm, the solid solution amount of impurities including excess silicon is large. As a result, remarkable silicon deposition occurs on the film surface or in fine concave portions such as polishing scratches due to irradiation of a high energy beam or the like. Such silicon deposition becomes more remarkable as the wavelength shifts to the longer wavelength side with a spectral absorption edge of 550 nm as a boundary.

By the way, in order to achieve the object of the present invention, it goes without saying that more favorable results are obtained as the spectral absorption edge of the silicon carbide film shifts to the shorter wavelength side with the longest limit being 550 nm. That is, it is preferable to make the spectrum absorption edge as short as possible in the range of 550 nm or less. However, there is a limit (about 520 nm) depending on the film formation conditions (mainly, the purity of raw materials, equipment conditions, and the like) for shortening the spectral absorption edge. If the edge is in the range of 520 to 550 nm, the intended purpose can be sufficiently achieved.

The silicon carbide film is formed by the CVD method. An example of the specific method is as follows.

That is, first, the substrate is placed in an appropriate CVD furnace, and the inside of the CVD furnace is kept in a reduced pressure atmosphere by evacuating from the exhaust port of the CVD furnace by a vacuum pump.

Then, the substrate is heated and maintained at a predetermined temperature while being kept in the reduced-pressure atmosphere, and then a predetermined reaction gas is continuously supplied into the CVD furnace. At this time, the exhaust is continuously performed without stopping, and the inside of the CVD furnace is kept at a predetermined reduced pressure atmosphere. Normally 200 Torr
It is preferable to keep it at r or less. However, for economic reasons considering the vacuum pump capacity, etc., 0.1 to 200 T
Preferably, it is set to orr. Also, the substrate is 140
It is preferable to heat and maintain the temperature at 0 to 1500 ° C. As the reaction gas, for example, a mixed gas of monomethyltrichlorosilane and hydrogen at a predetermined equivalent ratio (generally, about 20 equivalent ratio) is used.

When a reaction gas is supplied, CH ₃ SiCl ₃
By the reaction of + H ₂ → SiC + 3HCl, a silicon carbide film is formed on the substrate surface, that is, on the inner and outer peripheral surfaces of the substrate or on one of them.

Incidentally, the formation of the silicon carbide film is generally performed by
This is performed by a normal pressure CVD method in which a reaction gas is supplied while keeping the inside of the CVD furnace at normal pressure. However, this normal pressure C
The VD method cannot form a high-purity silicon carbide film having a spectral absorption edge of 550 nm or less.
That is, in the normal pressure CVD method, when the purity of the substrate is low, diffusion of impurities contained in the substrate cannot be prevented, or when the purity of the substrate is high, contaminant particles are scattered from the wall of the CVD furnace. Is contaminated on the surface of the substrate on which the silicon carbide film is to be formed or a peripheral region thereof, and is mixed into the silicon carbide film. As a film forming method, there is an intermittent CVD method in which exhaust and supply of a reactive gas are alternately repeated in a constant cycle, in addition to the normal pressure CVD method.
According to this intermittent CVD method, the above-mentioned contaminant particles and the like are exhausted to some extent during exhaustion, and it is expected that the purity of the silicon carbide film is improved. However, contaminant particles and the like are not completely exhausted in the exhaust process, but may remain at the beginning of the supply process of the reaction gas. It is impossible to form a silicon film. As described above, in any of the conventionally adopted CVD methods, impurities remain on the surface of the substrate or the peripheral region and are not removed. Therefore, a high-purity silicon carbide film having a spectral absorption edge of 550 nm or less cannot be formed.

However, as described above, if the inside of the CVD furnace is maintained in a reduced pressure atmosphere and the exhaust is continuously performed even during the supply of the reaction gas, the exhaust is performed on the surface of the substrate on which the silicon carbide film is to be formed or a peripheral region thereof. The exhaust flow in the mouth direction occurs,
Together with the migration of the impurities to the surface, the surface of the substrate or its peripheral region is kept clean. That is, impurities such as contaminant particles and reaction gas residues adhering to the wall surface of the CVD furnace are quickly discharged to the outside of the CVD furnace by the exhaust gas, and the inside of the CVD furnace is kept clean. As a result, a high-purity silicon carbide film having a spectral absorption edge of 550 nm or less is favorably formed on the substrate surface. The supply of the reaction gas may be performed intermittently instead of continuously, but the exhaust must be continuously performed regardless of the supply and stop of the reaction gas.

By the way, the thickness of the silicon carbide film is appropriately determined according to the conditions of use of the optical element such as a laser reflecting mirror made of the constituent material, provided that the adhesive strength to the substrate or the like is sufficient. Can be set to 50 to 15
Preferably, it is set to 0 μm. When the film thickness is less than 50 μm, there is a concern that defects due to through holes may be considered in consideration of the film thickness variation (± 20 μm). Conversely, when the film thickness exceeds 150 μm, the crystal becomes coarse and the surface becomes coarse. This is because the film lacks smoothness and requires time for film formation, resulting in high cost. Of course, when the surface needs to be polished like a laser reflecting mirror, it is necessary to consider the polishing allowance. Further, in consideration of easiness of polishing and the like, the crystal plane of the silicon carbide film is strongly oriented to a certain plane such as the (111) plane in Miller index display (especially the (220) plane is preferable). It is preferable that the ratio of the X-ray diffraction intensity of the plane to the other crystal plane be equal to or more than a certain value (99 or more) at the peak intensity.

[0022]

EXAMPLE A high-purity silicon carbide powder (particle diameter: less than 1 μm) was molded and fired without using a binder to obtain a diameter of 100 μm.
A substrate as a silicon carbide sintered body having a thickness of 10 mm, a thickness of 10 mm, and a density of 95% was manufactured. Then, while the substrate was placed in a CVD furnace and heated and maintained at 1500 ° C., monomethyltrichlorosilane and hydrogen at a 20 equivalent ratio were continuously supplied into the CVD furnace. During this time, the evacuation was continued by a vacuum pump connected to the exhaust port of the CVD furnace, and the inside of the furnace was kept at a reduced pressure atmosphere of 50 Torr. Thus,
Silicon carbide film (β-Si) having a thickness of 120 μm, a spectral absorption edge of 520 nm, and an absorbance of 0.246 / 600 nm
C (3C)) formed laser reflecting mirror constituent material (hereinafter referred to as “Example material”). In this silicon carbide film, there is almost no surplus Si deviating from the chemical equivalent ratio, and a very small amount of heavy metal elements (Fe: 30 pp) contained in the film.
b, Cu: 50 ppb or less, Cr: 40 ppb or less). The crystal plane of the silicon carbide film is strongly oriented to the (220) plane, and the other crystal plane ((11)
The peak intensity of the X-ray diffraction intensity ratio with respect to 1) plane) was 1000 or more.

As a comparative example, a laser reflecting mirror component (hereinafter referred to as "comparative example material") in which the same substrate as in the example material was manufactured and a silicon carbide film was formed by a normal method (normal pressure CVD method). I got CV used for forming silicon carbide film
The heating temperature of the furnace D, the reaction gas, and the substrate was the same as in the example materials. The thickness of the silicon carbide film in the comparative example material was 250 μm, but the spectral absorption edge was 620 n.
m.

The surface of the film of the example material and the material of the comparative example were polished to an RMS of 10 ° or less to obtain a laser reflecting mirror. Then, each laser reflector has an in-cavity intensity of 2 MW.
Then, an argon excimer laser having a pulse width of 5 ns was irradiated (one pulse), and the presence or absence of white turbidity or silicon deposition at the irradiated portion was examined. As a result, with respect to the laser reflecting mirror composed of the comparative example material, remarkable white turbidity or silicon precipitation was observed on the film surface and the polishing scratch, but the laser reflecting mirror composed of the example material was opaque. No silicon deposition was present. Thereafter, the irradiation with the argon excimer laser was repeated 10 times. As a result, the material of the comparative example was broken, but no change was observed in the material of the example.

[0025]

As can be easily understood from the above description , the optical element constituting material for a high energy beam of the present invention has 9 components.
Since a high-purity film having a spectral absorption edge of 550 nm or less is coated on a high-density substrate of 3% or more, high-energy
The static strength and thermal strength required as components of the optical element for lugi beam can be sufficiently secured, and even when high energy is supplied to the film surface, polishing scratches, diffraction grating grooves, etc. Irrespective of the presence or absence of the fine recess, the precipitation of silicon can be prevented as much as possible. Therefore, according to the optical element constituent material of the present invention, S
OR light, no any inconvenience such damaged or reflectance by irradiation or the like of a high energy beam such as a laser beam is lowered, an extremely durable, high energy beam of laser reflectors and the like having excellent optical performance it can provide use optical elements.

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI G02B 5/08 G02B 5/08 A G21K 1/06 G21K 1/06 C (56) References JP-A-6-281795 (JP, A) JP-A-5-339080 (JP, A) JP-A-6-239609 (JP, A) JP-A-5-246764 (JP, A) JP-A-4-358068 (JP, A) JP-A-5-87991 ( JP, A) JP-A-59-99401 (JP, A) JP-A-6-345568 (JP, A) JP-A-3-126667 (JP, A) JP-A-4-6157 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) G02B 1/10-1/12 G02B 5/00-5/136 C04B 41/80-41/91 C04B 35/56-35/58 C23C 16/00 -16/56 G21K 1/00-1/16

Claims (1)

(57) [Claims] 1. A composite material in which a silicon carbide film is coated and formed on a surface of a substrate made of silicon carbide or carbon by chemical vapor deposition, wherein the substrate is a high-density body of 93% or more,
An optical element constituent material for a high energy beam, wherein the silicon carbide film has a spectral absorption edge of 550 nm or less.