JPH1031096A - Half mirror type filter for x-ray and wave length selecting method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a half mirror type filter which is excellent in wave length selectivity by making light obliquely incident on a film surface of an extremely thin film, transmitting soft X-rays, and totally reflecting them by setting the incident angle as an angle not more than a total reflection critical angle of the light of an ultraviolet ray area from a vacuum ultraviolet rays. SOLUTION: An extremely thin film 1 is independently supported on a base board 2, and a half mirror type filter is formed. The extremely thin film 1 is formed of alight element such as silicon, aluminum and carbon or its nitride, carbide, an oxide or the like, and the base board 2 is formed of silicon or the like. When an incident angle 6 of the incident light 3 on the extremely thin film 1 is set as an angle not less than a total reflection critical angle to soft X-rays 4 transmitting the extremely thin film 1 and is set as an angle not more the total reflection critical angle to the light 5 of an ultraviolet ray area from reflecting vacuum ultraviolet rays, the light 5 is totally reflected by the extremely thin film 1. That is, when the incident angle 6 of the incident light 3 is changed, the light 5 of an ultraviolet ray area from vacuum ultraviolet rays of specific wave length or more is totally reflected. Therefore, the incident light 2 having a continuous spectrum can be separated into soft X-rays 4 and the light 5 of an ultraviolet ray area from vacuum ultraviolet rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a half-mirror type filter for light in a vacuum ultraviolet to soft X-ray region having a wavelength of 200 nm or less, and a wavelength selecting method using the same. This half-mirror type filter separates light in the soft X-ray region and light in the ultraviolet region from vacuum ultraviolet from light having a continuous spectrum obtained from synchrotron radiation light or a laser plasma X-ray source. . Soft X
Since it can separate light in the ultraviolet region from vacuum ultraviolet, which adversely affects the characteristics of the optical system in the line region, it can be applied as a filter for high-order light cut such as soft X-ray reduction projection exposure or diffraction grating spectroscope. It has a wide field of application in the field of soft X-ray optics.

[0002]

2. Description of the Related Art Light in the range from vacuum ultraviolet to soft X-rays having a wavelength of 200 nm or less is expected to be applied to industrial applications due to the emergence of high-intensity light sources such as synchrotron radiation and laser plasma X-ray sources. Have been. The light obtained from these light sources has a continuous spectrum, but in most applications it is performed using a specific wavelength region within it, and various methods are used to extract the specific wavelength region. I have. For example, as a simple method, there is a method of transmitting or absorbing light in a specific wavelength region using a filter using an absorption edge of an element. Also, Bragg (Br
agg) There is a method of reflecting a specific wavelength by a multilayer reflector using reflection, or a method of selecting a wavelength by using a diffraction grating spectroscope. Although a method using a filter is simple, its transmission characteristics are specific to the element, and the selectable wavelength range is limited. Furthermore, light in the soft X-ray region has a very large absorption, and an ultra-thin filter with a thickness of about 100 nm is required to increase the transmittance. As a method for producing an ultra-thin filter, a method has been employed in which a thin film is formed on a crystal of a metal salt by vapor deposition, the underlying metal salt is dissolved with water, and the multilayer film is scooped with a support. However, in this method, when the thin film is peeled from the base, there is a problem that cracks occur in the peeled thin film due to internal stress of the thin film, and the yield is low. Furthermore, when a mesh is used for the support, there is a problem that transmittance decreases due to the mesh, and when a ring opening is used for the support, the opening area is limited. In the method of reflecting a specific wavelength by using a multilayer reflector using Bragg reflection, long-wavelength light in the vacuum ultraviolet or ultraviolet region where the incident angle of the reflector satisfies the critical angle for total reflection may be mixed. There is a problem that short-wavelength light that satisfies the condition of high-order Bragg reflection is mixed. Further, the method using the diffraction grating spectroscope has problems that although the wavelength selectivity is high, the intensity is remarkably reduced, and high-order diffracted light having an integral multiple of the wavelength to be extracted is mixed. Even in these cases without filters, long-wavelength light in the vacuum ultraviolet or ultraviolet region has an adverse effect on the imaging characteristics of the imaging optical system, and long-wavelength higher-order diffracted light has an adverse effect on the wavelength selectivity of the spectroscope. Therefore, it was necessary to remove the filter together.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art.
The half-mirror type filter reflects light in the ultraviolet region from unnecessary long-wavelength vacuum ultraviolet light and transmits only light in the required soft X-ray region, thereby eliminating imperfect wavelength selectivity in the conventional method. An object of the present invention is to provide a half-mirror type filter having high transmittance and good wavelength selectivity.

[0004]

Means for Solving the Problems In order to achieve the object of the present invention, the present invention is configured as described in the claims. That is, according to the present invention, as described in claim 1, the incident angle of light in the vacuum ultraviolet to ultraviolet region from soft X-ray obliquely incident on the film surface of the ultra-thin film, and the specific wavelength λ included in the incident light X at least constituted by an ultrathin film made of a material for equalizing the critical angle of total reflection of light of _c
This is a line half mirror type filter. By adopting a filter having such a configuration, it is possible to obtain from a synchrotron radiation beam, a laser plasma X-ray source, etc. by utilizing the difference in the critical angle of total reflection by the independently supported flat and smooth ultra-thin reflective surface. From light having a given continuous spectrum, light in the soft X-ray region and light in the vacuum ultraviolet or ultraviolet region can be efficiently separated. Therefore, light in the vacuum ultraviolet or ultraviolet region that adversely affects the characteristics of the optical system in the soft X-ray region can be cut off, so that it can be used as a filter for soft X-ray reduction projection exposure or high-order light cut of a diffraction grating spectroscope. There is an effect that can be widely used in the field of soft X-ray optics. According to a second aspect of the present invention, in the X-ray half-mirror filter according to the first aspect, the ultra-thin film is selected from silicon, aluminum, carbon, diamond, boron, and beryllium. At least one light element, or at least one compound selected from nitrides, carbides, and oxides of the light elements, or at least one substance selected from the light elements and the compounds; This is a half mirror type filter for X-rays configured. in this way,
By using the above light element or a compound of the light element as a constituent material of the filter, an extremely smooth reflecting surface with small surface roughness can be obtained, and the absorption of transmitted soft X-rays is small. Light loss due to light transmission can be suppressed, and a large transmitted light intensity can be obtained. Also,
According to a third aspect of the present invention, there is provided an X-ray half mirror type filter according to the first or second aspect,
On the ultra-thin film constituting the filter, at least one selected from a high melting point metal (for example, platinum, iridium, chromium, molybdenum, tungsten, etc.) and a nitride, carbide, or oxide of the high melting point metal This is an X-ray half mirror type filter having a structure in which a single-layer film made of a substance or a multilayer film is laminated. As described above, by laminating the metal thin film or the metal compound thin film, the critical angle of total reflection of light can be further increased, the reflectance can be increased at a larger incident angle, and the wavelength selectivity can be improved. . Further, the present invention provides, as set forth in claim 4,
A method for selecting a wavelength using the half-mirror filter for X-rays according to any one of claims 1 to 3, wherein a surface of the filter in a vacuum ultraviolet to ultraviolet region from soft X-rays is provided. and the light incident obliquely at a predetermined incident angle, and the angle of incidence, and adjusted so that the total reflection critical angle of the light of a particular wavelength lambda _c contained in the incident light becomes equal to the specific wavelength lambda
It reflects light of wavelength longer than _c, and it is an method for selecting a wavelength by transmitting light of wavelength less than a specific wavelength lambda _c. As described above, since light having a specific wavelength or more is reflected and separated, unlike wavelength cut using the absorption edge of an element, there is no re-transmission in a long wavelength region due to a plurality of absorption edges, and a completely long wavelength. There is an effect that can be cut.

The half mirror type filter for X-rays according to the present invention is for realizing a filter that transmits light in a soft X-ray region and cuts light in a vacuum ultraviolet to ultraviolet region. Therefore, the most main feature of the filter is to make the filter material as an extremely smooth reflecting surface and reflect it as an oblique incident angle that satisfies the critical angle for total reflection of light cut in the vacuum ultraviolet to ultraviolet region. . That is,
The difference from the prior art is that the light to be cut is separated by reflecting the light instead of absorbing the constituent material of the filter. To select the wavelength by reflection,
In order to obtain an extremely smooth reflective surface, the filter is made of a material with a small surface roughness and a film forming method,
It is characterized by adding ultra-smooth polishing as required. Further, in order to use an oblique incident angle that satisfies the critical angle for total reflection, an ultra-thin membrane technology for forming a large opening with a high yield is used. Further, a metal thin film or a metal compound thin film having a smooth reflection surface made of a high melting point metal is laminated on an ultra-thin membrane so that a critical angle of total reflection can be obtained. . The present invention provides an ultra-thin membrane having an extremely smooth reflective surface.
It is used at an oblique angle of incidence that satisfies the critical angle for total reflection, reflects light in the ultraviolet region from vacuum ultraviolet, and transmits light in the soft X-ray region. Completely cut out the light in the area,
It functions as a filter that transmits light in a soft X-ray region in a specific wavelength region. Since light having a specific wavelength or more is reflected and separated, unlike a wavelength cut by absorption of an element, there is no re-transmission in a long wavelength region due to a plurality of absorption edges, and a complete long wavelength can be cut. In order to obtain an extremely smooth reflective surface, a filter is made of an element having a small surface roughness and a film forming method as a constituent material of the filter, and in some cases, the reflectance of reflected light is increased by adding ultra-smooth polishing, thereby increasing the reflectivity. Increase wavelength selectivity. Furthermore, on an ultra-thin membrane,
By laminating the metal thin films, the critical angle of total reflection is further increased, the reflectance is increased at a larger incident angle, and the wavelength selectivity is enhanced. Also, by using the ultra-thin membrane technology as a filter manufacturing method, a filter having a large opening that can be used at an oblique incident angle that satisfies the critical angle for total reflection can be manufactured with a high yield. it can.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> FIG. 1 is a schematic diagram showing a configuration of an X-ray half-mirror type filter exemplified in this embodiment.
In the drawing, reference numeral 1 denotes an independently supported ultrathin film structure (also referred to as an ultrathin film), and 2 denotes a substrate. 3 is incident light having a continuous spectrum such as synchrotron radiation or laser plasma X-ray source, 4 is soft X-ray transmitted through the filter, 5 is light in the vacuum ultraviolet to ultraviolet region reflected by the filter,
Reference numeral 6 denotes an incident angle of the incident light to the filter. The incident angle 6 of the incident light to the filter is set to be equal to or greater than the total reflection critical angle with respect to the soft X-rays 4 passing through the filter out of the incident light 3, and the light 5 in the vacuum ultraviolet to ultraviolet region reflected by the filter is reflected. On the other hand, when the angle is equal to or less than the total reflection critical angle, the light 5 in the vacuum ultraviolet to ultraviolet region can be transmitted to the independently supported ultrathin film 1
Is totally reflected. That is, by changing the incident angle 6 of the incident light to the filter, light having a specific wavelength or more, that is, light 5 in a vacuum ultraviolet to ultraviolet region can be totally reflected. Note that equation (1) below is satisfied with respect to the total reflection critical angle theta _c substances.

[0007]

(Equation 1)

Where 1-δ: real part of complex refractive index, r
_e : classical electron radius, λ: wavelength, ρ: density, N ₀ : Avogadro number, Α: atomic weight, f ₁ : atomic scattering factor. In the equation (Equation 1), the amount specific to the element is
By substituting the following (Equation 2),

[0009]

(Equation 2)

[0010] The total reflection critical angle Θ _c as ξ is large increases. This is because, as explained in the third embodiment to be described later, leading to stacking the metal thin film to increase the ultra-thin 1, the total reflection critical angle theta _c. As for the wavelength lambda, the total reflection critical angle theta _c the larger lambda is the greater. Therefore, by appropriately selecting the incident angle 6 of the incident light to the filter, the condition of total reflection can be satisfied for light having a specific wavelength or more. The constituent material of the ultra-thin film 1 is at least one selected from light elements such as silicon, aluminum, carbon, diamond, boron and beryllium, or compounds such as nitrides, carbides and oxides of these light elements. The above can be used. As the substrate 2, a substrate such as silicon can be used. FIG.
(A) to (f) show a manufacturing process of the X-ray half-mirror filter exemplified in the present embodiment. The substrate 2 made of Si (FIG. 2A) is coated with SiC by ECR (electron cyclotron resonance) plasma CVD (chemical vapor deposition).
An ultra-thin film 1 is laminated [FIG. 2 (b)]. On this occasion,
After the substrate 2 is back-etched, the stress of the thin film to be laminated is adjusted to a low tensile stress so that the reflection surface maintains flatness. Next, a resist 7 is applied to the back surface [FIG.
(C)], the window corresponding to the transmission portion is exposed to ultraviolet light or the like,
Exposure and development [FIG. 2 (d)]. Thereafter, the ultra-thin film 1 is etched using the resist 7 as a mask by dry etching such as reactive ion etching using a halogen gas such as CF ₄ or SF ₆ (FIG. 2E). further,
The substrate 2 is removed by wet etching using an etchant such as KOH or an amine [FIG.
(F)]. Through such a process, the independently supported ultrathin film structure 1 is manufactured. Further, since this manufacturing process can use the semiconductor manufacturing process as it is and has no special steps, it can be easily manufactured at low cost and is suitable for mass production. The ultra-thin film 1 can be formed by low pressure CVD or sputtering in addition to ECR plasma CVD. In particular, ECR plasma CVD can be formed at a low temperature and has low surface roughness and smoothness. , A thin film having a high refractive index can be formed, and the reflectance can be improved.

<Embodiment 2> FIGS. 3A to 3G show:
A manufacturing process of a half mirror type filter for X-rays exemplified in this embodiment will be described. In the present embodiment, an object is to obtain a high reflectance by improving the surface roughness generated at the time of forming the ultrathin film 1 by performing ultra-smooth polishing. An ultra-thin film 1 made of SiN is laminated on a substrate 2 made of Si by low pressure CVD (FIG. 3B). At this time, after the substrate 2 is back-etched, the stress of the thin film to be laminated is adjusted to a low tensile stress so that the reflection surface maintains flatness. Next, the surface of the laminated ultrathin film 1 is polished by an ultra-smooth polishing process [FIG. 3 (c)]. Next, a resist 7 is applied to the back surface (FIG. 3D), and the window corresponding to the transmitting portion is exposed and developed by ultraviolet exposure or the like (FIG. 3E). Then, C
By dry etching such as reactive ion etching using halogen gas such as F ₄ or SF _6, the resist 7
Is used as a mask to etch the very thin film 1 [FIG.
(F)]. Further, the substrate 2 is removed by wet etching using an etchant such as KOH or an amine system (FIG. 3G). Through these processes, the independently supported ultrathin film structure 1 can be obtained. In addition,
In this manufacturing process, the semiconductor manufacturing process can be used as it is, and since there is no special process, it can be easily manufactured at low cost and is suitable for mass production.

<Embodiment 3> FIG. 4 shows the configuration of an X-ray half-mirror filter exemplified in this embodiment.
In the present embodiment, as described in the first embodiment, the case where the metal thin film 8 is stacked on the ultrathin film 1 to increase the critical angle for total reflection is shown. 5 (a) to 5 (g) are process diagrams showing a manufacturing process of an X-ray half mirror type filter exemplified in the present embodiment. Substrate 2 made of Si [FIG. 5 (a)]
Next, an ultra-thin film 1 made of SiC is laminated by ECR plasma CVD (FIG. 5B). At this time, after the substrate 2 is back-etched, the stress of the thin film to be laminated is adjusted to a low tensile stress so that the reflection surface maintains flatness.
Next, a resist 7 is applied on the back surface (FIG. 5C), and the window corresponding to the transmitting portion is exposed and developed by ultraviolet exposure or the like (FIG. 5D). Thereafter, the ultra-thin film 1 is formed by dry etching such as reactive ion etching using a halogen gas such as CF ₄ or SF ₆ using the resist 7 as a mask.
Is etched [FIG. 5 (e)]. Further, the substrate 2 is removed by wet etching using an etchant such as KOH or an amine-based etchant (FIG. 5F). Finally, a high melting point metal, for example, Pt (platinum), Ir, is formed on the independently supported ultrathin film structure 1 produced by these processes by using a sputtering method, a vapor deposition method, a CVD method or the like.
A metal thin film 8 made of at least one metal selected from the group consisting of (iridium), Cr (chromium), Mo (molybdenum), W (tungsten), etc. is produced (FIG. 5 (g)). Here, the process conditions of the metal thin film 8 are optimized to reduce the surface roughness, and the stress is adjusted to a low tensile stress in order to maintain independent support. In this manufacturing process, the semiconductor manufacturing process can be used as it is, and since no special process is used, it can be easily manufactured at low cost and is suitable for mass production. In addition, the metal thin film 8 may be made of nitride, carbide, oxide, or the like of the high melting point metal. Further, as the metal thin film in the step of FIG. 5G, not only a single layer but also a multilayer film can be used. Further, the effects of the present invention are not impaired at all even if the step of FIG. 5G is replaced with the step of the back etch of FIG. 5F.

[0013]

The half-mirror type filter of the present invention utilizes synchrotron radiation light,
Light in the soft X-ray region and light in the vacuum ultraviolet or ultraviolet region can be separated from light having a continuous spectrum obtained from a laser plasma X-ray source or the like. Therefore, soft X
Since it is possible to separate light in the vacuum ultraviolet or ultraviolet region that adversely affects the characteristics of the optical system in the line region, the soft X
There is an effect that it can be widely used in the field of soft X-ray optics as a filter for line reduction projection exposure or a high-order light cut of a diffraction grating spectroscope. Further, the manufacturing process of the half-mirror filter of the present invention is suitable for mass production since the semiconductor manufacturing process can be applied as it is.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an X-ray half-mirror type filter exemplified in Embodiment 1 of the present invention.

FIG. 2 is a process chart showing a manufacturing process of the X-ray half-mirror filter exemplified in Embodiment 1 of the present invention.

FIG. 3 is a process chart showing a manufacturing process of the X-ray half mirror type filter exemplified in Embodiment 2 of the present invention.

FIG. 4 is a schematic diagram showing a configuration of an X-ray half-mirror filter exemplified in Embodiment 3 of the present invention.

FIG. 5 is a process chart showing a manufacturing process of the X-ray half-mirror filter exemplified in Embodiment 3 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Independently supported ultra-thin film structure (ultra-thin film) 2 ... Substrate 3 ... Incident light 4 ... Soft X-ray transmitted through a filter 5 ... Vacuum ultraviolet to ultraviolet light reflected by the filter 6 ... Filter of incident light Angle of incidence 7 ... Resist 8 ... Metal thin film

Claims (4)

[Claims] The incident angle of light in the vacuum ultraviolet to ultraviolet region from 1. A soft X-rays incident obliquely to the electrode film surfaces of the thin film, and the total reflection critical angle of light of a particular wavelength lambda _c contained in the incident light A half-mirror type filter for X-rays, characterized in that the filter is at least constituted by an extremely thin film made of a material which makes the same. 2. The X-ray half-mirror type filter according to claim 1, wherein the ultra-thin film is at least one kind of light element selected from silicon, aluminum, carbon, diamond, boron and beryllium. At least one selected from nitrides, carbides and oxides of light elements
A half-mirror type filter for X-rays, comprising a kind of compound or at least one kind of substance selected from the above light elements and the above compounds. 3. The X-ray half-mirror filter according to claim 1, wherein a refractory metal and a nitride of the refractory metal are formed on an extremely thin film constituting the filter.
A half-mirror filter for X-rays, comprising a single-layer film or a multilayer film made of at least one substance selected from carbides and oxides. 4. A method for selecting a wavelength using the X-ray half-mirror filter according to claim 1, wherein a soft X-ray is applied to the surface of the filter from a soft X-ray. the light in the ultraviolet to the ultraviolet region incident obliquely at a predetermined incident angle, and the angle of incidence, and adjusted so that the total reflection critical angle of the light of a particular wavelength lambda _c contained in the incident light becomes equal, wavelength selection method characterized by the selection of wavelengths by causing to reflect light of wavelength longer than a particular wavelength lambda _c, and transmits light of wavelength less than a specific wavelength lambda _c.