KR20100099208A - Optical member for euvl and surface treatment method thereof - Google Patents

Abstract

INDUSTRIAL APPLICABILITY The present invention is used for a reflective mask for an ultra-ultraviolet lithography (EUVL), a mirror, and the like, and has an excellent optical surface flatness and surface roughness, and an optical member for EUVL in which chamfering is suppressed from chipping. To provide. The present invention relates to an EUVL optical method comprising etching a gas cluster ion beam using a source gas containing at least one of fluorine and chlorine on an optical surface of an optical member for EUVL. A method for surface treatment of a member, wherein the optical member is made of a silica glass material having an OH concentration of 100 ppm or more, containing TiO ₂ and containing SiO ₂ as a main component.

Description

Optical member for EL and its surface treatment method {OPTICAL MEMBER FOR EUVL AND SURFACE TREATMENT METHOD THEREOF}

TECHNICAL FIELD This invention relates to the optical member for EUV lithography, and the surface treatment method of the optical surface thereof.

Background Art Lithographic techniques have conventionally used exposure apparatus for fabricating integrated circuits by transferring fine circuit patterns onto wafers. BACKGROUND OF THE INVENTION Due to the trend toward higher integration, higher speed, and higher functionality of integrated circuits, integrated circuits have become smaller. Therefore, an exposure apparatus for forming a high resolution circuit pattern on a wafer surface at a deep depth of focus has been demanded, and shortening the wavelength of exposure light has been advanced. The exposure light source goes further from the conventional g-ray (wavelength: 436 nm), i-ray (wavelength: 365 nm) and KrF excimer laser (wavelength: 248 nm), in which an ArF excimer laser (wavelength: 193 nm) is employed. Getting started. In addition, in order to cope with next-generation integrated circuits having a circuit line width of 70 nm or less, immersion exposure techniques and double exposure techniques using ArF excimer lasers are prominent, but even these technologies cover only generations having line widths of 45 nm or less. It seems that you can't.

In this technology trend, attention has been drawn from the fact that lithography techniques using EUV light as next generation exposure light are applicable for generations after 32 nm. EUV light referred to herein refers to light in the wavelength band of a soft X-ray region or vacuum ultraviolet region, specifically light having a wavelength of about 0.2 to 100 nm. Currently, the use of 13.5 nm lithographic light sources is under consideration. The exposure principle of this EUV lithography (hereinafter abbreviated as "EUVL") is similar to conventional lithography in that it uses a projection optical system to transfer the mask pattern. However, since there is no material transmitting light in the EUV light energy region, the refractive optical system cannot be used. Therefore, a reflection optical system is necessarily used (see Patent Document 1 below).

Examples of reflective optical systems used in EUVL include reflective masks and mirrors such as condensing optical mirrors, contrast optical mirrors, and projection optical mirrors.

The reflective mask basically consists of (1) an EUVL optical member (for example, a glass substrate), (2) a reflective multilayer film formed on the optical surface of the EUVL optical member, and (3) an absorber layer formed on the reflective multilayer film. On the other hand, the mirror is basically composed of (1) an EUVL optical member (for example, a glass substrate) and (2) an reflective multilayer film formed on the optical surface of the EUVL optical member.

As the reflective multilayer film, one having a structure in which a plurality of materials having different refractive indices with respect to the wavelength of exposure light is periodically laminated in units of nm is used. As examples of representative materials, Mo and Si are known. In addition, Ta and Cr are examined as an absorber layer.

As an optical member for EUVL, a material having a low thermal expansion coefficient is required so that deformation does not occur even during EUV light irradiation, and the use of glass having a low thermal expansion coefficient or glass-ceramic having a low thermal expansion coefficient is under consideration. Hereinafter, in this specification, the glass having a low thermal expansion coefficient and the glass-ceramic having a low thermal expansion coefficient are collectively referred to as "low expansion glass" or "ultra low expansion glass".

As such low-expansion glass and ultra-low-expansion glass, silica glass to which dopants are added to reduce the coefficient of thermal expansion of glass is most widely used. In addition, a representative example of the dopant added to reduce the coefficient of thermal expansion of glass is TiO ₂ . Specific examples of the silica glass to which TiO ₂ is added as a dopant include ULE (Code) Code 7972 (manufactured by Corning Incorporated).

At the time of manufacturing the optical member for EUVL, the raw material of such low expansion glass or ultra low expansion glass is cut | disconnected to predetermined shape and predetermined dimension. Next, the optical surface thereof is processed to have a predetermined flatness and a predetermined surface roughness.

The optical member for EUVL is required to be very excellent in the smoothness of an optical surface. Specifically, it is necessary to surface-treat so that the flatness of the produced surface is 50 nm or less and the surface roughness Ra is 5 nm or less.

When manufacturing a reflective mask or mirror or performing EUVL, a problem arises in that the edge of the optical member for EUVL is chipped. For this reason, the edge of the optical member for EUVL is chamfered normally.

However, even when the edges are chamfered, a problem arises in that the chamfered portions are chipped when the EUVL optical member is fixed to the processing apparatus or the exposure apparatus, and more specifically, when the optical member is gripped by a clamp or the like.

JP-T-2003-505891

In order to solve the above-mentioned problems associated with the prior art, the object of the present invention is that the flatness and surface roughness of the optical surface are very good and the strength near the surface layer is very good. It is to provide an optical member for EUVL in which chipping of the chamfered portion is suppressed. Still another object of the present invention is to provide a method for surface treatment of an optical surface of an optical member for EUVL.

In order to achieve the above object, the present invention provides fluorine and chlorine on the optical surface of an optical member for EUV lithography (EUVL) made of a silica glass material having an OH concentration of 100 ppm or more and containing TiO ₂ and containing SiO ₂ as a main component. Provided is a method for surface treatment of an optical member for EUVL comprising performing a gas cluster ion beam (GCIB) etching using a source gas containing one or more of them.

In the method for surface treatment of the optical member for EUVL of the present invention, TiO ₂ concentration in the optical member for EUVL preferably has from 3 to 10% by weight.

In the surface treatment method of the optical member for EUVL of this invention, it is preferable that the thermal expansion coefficient in 20 degreeC of the optical member for EUVL is 0 + 30 ppb / degreeC.

When increasing the energy of EUV light used for exposure to increase the throughput of the EUVL exposure apparatus, the temperature of the optical member increases more than usually estimated. Specifically, the temperature of the optical member may increase to a temperature of 40 to 110 ℃. In this case, in order to prevent the pitch of the pattern from changing when used as a photomask and the like, and to prevent the shape change when used as a stepper mirror or the like, at a temperature of 40 to 110 ° C of the optical member of the present invention. The thermal expansion coefficient is preferably 0 ± 30 ppb / ° C.

In the surface treatment method of the optical member for EUVL of this invention, it is preferable that surface roughness Ra before GCIB etching of the optical member for EUVL is 5 nm or less.

In the method for surface treatment of an optical member for EUVL of the present invention, the source gas used is a mixed gas of SF ₆ and O ₂ ; Mixed gas of SF ₆ , Ar and O ₂ ; Mixed gas of NF ₃ and O ₂ ; Mixed gas of NF ₃ , Ar, and O ₂ ; Mixed gas of NF ₃ and N ₂ ; Mixed gas of NF ₃ , Ar, and N ₂ ; Mixed gas of Cl ₂ and O ₂ ; Mixed gas of Cl ₂ , Ar, and O ₂ ; Mixed gas of Cl ₂ and N ₂ ; Mixed gas of Cl ₂ , Ar, and N ₂ ; Mixed gas of CF ₄ and O ₂ ; Mixed gas of CF ₄ , Ar, and O ₂ ; Mixed gas of CF ₄ and N ₂ ; Mixed gas of CF ₄ , Ar, and N ₂ ; Mixed gas of CH ₂ F ₂ and O ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and O ₂ ; Mixed gas of CH ₂ F ₂ and N ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and N ₂ ; Mixed gas of CHF ₃ and O ₂ ; Mixed gas of CHF ₃ , Ar and O ₂ ; Mixed gas of CHF ₃ and N ₂ ; And a mixed gas selected from the group consisting of CHF ₃ , Ar, and N ₂ .

Moreover, this invention provides the optical member for EUVL surface-treated by the surface treatment method of the optical member for EUVL of this invention.

Furthermore, the present invention is an optical member for EUV lithography (EUVL) made of a silica glass material having an OH concentration of 100 ppm or more, a TiO ₂ concentration of 3 to 10 mass%, and containing SiO ₂ as a main component, and the surface roughness of the optical surface. The optical member for EUVL which (Ra) is 5 nm or less and satisfy | fills a following formula is provided.

(log C _200nm -log C _20nm ) / (200-20) <-3.0 × 10 ^-3

The formula, C _200nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of 200 nm depth from the optical surface; C _20nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of the 20 nm depth from the optical surface.

Furthermore, the present invention is an optical member for EUV lithography (EUVL) made of a silica glass material having an OH concentration of 100 ppm or more, a TiO ₂ concentration of 3 to 10 mass%, and containing SiO ₂ as a main component, and the surface roughness of the optical surface. (Ra) is 5 or less and provides the optical member for EUVL which satisfy | fills a following formula.

C _20nm -C _200nm ≥ 5 ppm

In the formula, C _20nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the 20 nm where the depth from the optical surface, C _200nm is the fluorine concentration and the chlorine concentration at the location of the depth of 200 nm from the optical surface The total concentration (ppm) is shown.

In the optical member for EUVL, it is preferable that the chamfer is provided along the outer edge of the optical surface.

The optical member for EUVL of this invention is very excellent in the flatness and surface roughness of the optical surface, and is used suitably as a reflective mask, mirror, etc. for EUVL. Further, the optical member for EUVL of the present invention has improved strength near the surface layer on the optical surface side. Therefore, when manufacturing a reflective mask or mirror or when performing EUVL, the occurrence of edge chipping in the optical member for EUVL or when chamfering at the edge is suppressed.

The optical member for EUVL of this invention is obtained preferably by using the processing method of the optical member for EUVL of this invention.

1 is a graph showing the fluorine concentration in the depth direction from the substrate surface.

In the surface treatment method of the optical member for EUVL of the present invention, fluorine and chlorine are contained in the optical surface of the optical member for EUVL made of silica glass material containing OH concentration of 100 ppm or more and containing TiO ₂ and SiO ₂ as a main component. GCIB etching using the source gas containing 1 or more types is performed.

The optical surface of the optical member for EUVL mentioned herein refers to the surface on which the reflective multilayer film is formed when manufacturing a reflective mask, mirror, etc. using the optical member for EUVL. In order to suppress the occurrence of chipping at the time of manufacturing a reflective mask or mirror or performing EUVL, the edge of the outer edge of the optical surface of the optical member for EUVL is usually chamfered.

The silica glass material constituting the optical member for EUVL contains TiO ₂ as a dopant to reduce the coefficient of thermal expansion.

The TiO ₂ concentration in the silica glass material is not particularly limited as long as the coefficient of thermal expansion of the silica glass material can be sufficiently low for use as an optical member for EUVL, but 3 to 10 mass% is preferred. When the TiO ₂ concentration is within the above range, the coefficient of thermal expansion of the silica glass material is sufficiently low. Specifically, the resulting glass is a low expansion glass having a coefficient of thermal expansion at 0 ° C. of 0 ± 30 ppb / ° C., preferably an ultra low expansion glass having a coefficient of thermal expansion at 20 ° C. of 0 ± 10 ppb / ° C.

Specific examples of the low expansion glass and the ultra low expansion glass in which TiO ₂ is added as the dopant at the above concentration include ULE (registered trademark) code 7972 (manufactured by Corning Incorporated).

Silica glass material of the optical member for EUVL will contain more than 100 ppm in addition to the OH SiO ₂ and TiO _2. The addition of OH facilitates the structural relaxation of the glass and facilitates the realization of glass structures with low hypothetical temperatures. By lowering the virtual temperature of the glass, the temperature dependence of the coefficient of thermal expansion can be minimized, and such a silica glass material is preferable as the optical member for EUVL.

In addition, when the silica glass material contains OH, when performing GCIB etching using a source gas containing at least one of fluorine and chlorine on the optical surface of the optical member for EUVL, the optical member may be In the deeper portion near the surface layer fluorine and chlorine are incorporated. Therefore, in the surface treatment method of the optical member for EUVL of this invention, the effect produced by giving GCIB etching using the source gas containing 1 or more of fluorine and chlorine to the optical surface of the optical member for EUVL appears preferably. .

In the surface treatment method of the optical member for EUVL of this invention, the effect produced by giving GCIB etching using the source gas containing 1 or more of fluorine and chlorine to the optical surface of the optical member for EUVL is as follows.

The GCIB etching referred to herein is produced by injecting a reactive substance (source gas), which is gaseous at room temperature and atmospheric pressure, under pressurization into a vacuum apparatus through an expandable nozzle to form a gas cluster, and electronizing the gas cluster to ionize it. The object is etched by irradiating the ionized GCIB with the object. Gas clusters typically consist of a mass of atomic or molecular groups of thousands of atoms or molecules. In the surface treatment method of the optical member for EUVL of the present invention, when GCIB etching is performed on the optical surface of the optical member for EUVL, colliding a gas cluster on the optical surface causes a multibody collision effect due to interaction with a solid. Occurs and the optical surface is polished to improve flatness (first effect).

In the surface treatment method of the optical member for EUVL of this invention, when GCIB etching using the source gas containing 1 or more of fluorine and chlorine is performed to the optical surface of the optical member for EUVL, the optical surface of the optical member for EUVL Fluorine or chlorine is incorporated in the silica glass material near the surface layer on the side, specifically up to a depth of about 100 nm from the optical surface of the optical member for EUVL. In the vicinity of the surface layer on the optical surface side into which fluorine or chlorine is incorporated, a compressive stress layer can be formed. Thereby, the intensity | strength of the surface layer vicinity of the optical member for EUVL improves. As a result, the occurrence of chipping at the chamfer of the optical member for EUVL at the time of manufacturing the reflective mask or mirror or performing EUVL is suppressed (second effect).

In order to exhibit the second effect more effectively, it is preferable to perform GCIB etching on the entire optical surface including the chamfer provided at the edge or corner of the outer edge of the optical surface.

In order to more effectively exhibit the effect caused by GCIB etching, specifically the above-described second effect, the silica glass material constituting the optical member for EUVL preferably has an OH of at least 200 ppm, more preferably at least 500 ppm. It is contained in an amount.

In the surface treatment method of the optical member for EUVL of this invention, it is preferable that the optical surface by which GCIB etching is given is pre-polished so that predetermined flatness and surface roughness may be carried out.

The preliminary polishing method is not particularly limited and may be widely selected from known polishing methods used for polishing the surface of the silica glass material. However, the use of a polishing pad having a high polishing rate and a large surface area can polish a large area at a time, and therefore a mechanical polishing method is usually employed. The mechanical polishing method mentioned here includes a method using a polishing slurry that uses a combination of the polishing action of the polishing grains and the chemical polishing action of a chemical substance, in addition to the polishing processing made only by the polishing action of the polishing grains. Mechanical polishing can be one of lapping polishing and polishing polishing. The abrasive tool (s) and abrasive (s) used may be appropriately selected from known materials. When employing a mechanical polishing method, lapping is preferably performed at a surface pressure of 30 to 70 gf / cm 2, more preferably 40 to 60 gf / cm 2 to increase the processing rate; Polishing is preferably performed at a surface pressure of 60 to 140 gf / cm 2, more preferably at 80 to 120 gf / cm 2. As the polishing amount, lapping is preferably performed with an polishing amount of 100 to 300 mu m; Polishing is preferably performed with a polishing amount of 1 to 60 mu m.

When preliminary polishing is performed, the surface roughness Ra of the optical surface after the preliminary polishing is preferably 5 nm or less, more preferably 3 nm or less, even more preferably 1 nm or less. Surface roughness (Ra) referred to herein means surface roughness measured by atomic force microscope for an area of 1 to 10 μm ² . If the surface roughness of the optical surface after preliminary polishing exceeds 5 nm, the GCIB etching is carried out in the surface treatment method of the optical member for EUVL of the present invention, which is considerable to adjust the optical surface to provide a predetermined flatness and surface roughness. It takes time, which increases the cost.

As a source gas containing at least one of fluorine and chlorine used for GCIB etching, a mixed gas of SF ₆ and O ₂ ; Mixed gas of SF ₆ , Ar and O ₂ ; Mixed gas of NF ₃ and O ₂ ; Mixed gas of NF ₃ , Ar, and O ₂ ; Mixed gas of NF ₃ and N ₂ ; Mixed gas of NF ₃ , Ar, and N ₂ ; Mixed gas of Cl ₂ and O ₂ ; Mixed gas of Cl ₂ , Ar, and O ₂ ; Mixed gas of Cl ₂ and N ₂ ; Mixed gas of Cl ₂ , Ar, and N ₂ ; Mixed gas of CF ₄ and O ₂ ; Mixed gas of CF ₄ , Ar, and O ₂ ; Mixed gas of CF ₄ and N ₂ ; Mixed gas of CF ₄ , Ar, and N ₂ ; Mixed gas of CH ₂ F ₂ and O ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and O ₂ ; Mixed gas of CH ₂ F ₂ and N ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and N ₂ ; Mixed gas of CHF ₃ and O ₂ ; Mixed gas of CHF ₃ , Ar and O ₂ ; Mixed gas of CHF ₃ and N ₂ ; And any gas mixture selected from a gas mixture of CHF ₃ , Ar, and N ₂ .

In the mixed gas, an appropriate mixing ratio of each component varies depending on irradiation conditions and the like, but the following is preferable.

SF ₆ : O ₂ = (0.1 to 5%): (95 to 99.9%) (mixed gas of SF ₆ and O ₂ )

SF ₆ : Ar: O ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of SF ₆ , Ar and O ₂ )

NF ₃ : O ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of NF ₃ and O ₂ )

NF ₃ : Ar: 0 ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of NF ₃ , Ar, and O ₂ )

NF ₃ : N ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of NF ₃ and N ₂ )

NF ₃ : Ar: N ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of NF ₃ , Ar, and N ₂ )

Cl ₂ : O ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of Cl ₂ and O ₂ )

Cl ₂ : Ar: 0 ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of Cl ₂ , Ar and O ₂ )

Cl ₂ : N ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of Cl ₂ and N ₂ )

Cl ₂ : Ar: N ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of Cl ₂ , Ar and N ₂ )

CF ₄ : O ₂ = (0.1 to 5%): (95 to 99.9%) (mixed gas of CF ₄ and O ₂ )

CF ₄ : Ar: O ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CF ₄ , Ar and O ₂ )

CF ₄ : N ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of CF ₄ and N ₂ )

CF ₄ : Ar: N ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CF ₄ , Ar and N ₂ )

CH ₂ F ₂ : 0 ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of CH ₂ F ₂ and O ₂ )

CH ₂ F ₂ : Ar: O ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CH ₂ F ₂ , Ar and O ₂ )

CH ₂ F ₂ : N ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of CH ₂ F ₂ and N ₂ )

CH ₂ F ₂ : Ar: N ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CH ₂ F ₂ , Ar and N ₂ )

CHF ₃ : 0 ₂ = (0.1 to 5%): (95 to 99.9%) (mixed gas of CHF ₃ and O ₂ )

CHF ₃ : Ar: O ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CHF ₃ , Ar and O ₂ )

CHF ₃ : N ₂ = (0.1 to 5%) :( 95 to 99.9%) (mixed gas of CHF ₃ and N ₂ )

CHF ₃ : Ar: N ₂ = (0.1 to 5%) :( 9.9 to 49.9%) :( 50 to 90%) (mixed gas of CHF ₃ , Ar and N ₂ )

Irradiation conditions, including the cluster size, the ionization current applied to the ionization electrode of the GCIB etching apparatus to ionize the cluster, the acceleration voltage applied to the acceleration electrode of the GCIB etching apparatus, and the GCIB dosage, are characterized by the type of source gas and the surface characteristics of the optical surface. It may be appropriately selected according to. For example, in order to improve the flatness without excessively deteriorating the surface roughness of the optical surface, the acceleration voltage applied to the acceleration electrode is preferably 15 to 30 kV.

When performing GCIB etching, it is necessary to scan the optical surface with GCIB. As a method for GCIB injection, raster scanning and spiral scanning are known, and one of the above methods can be employed.

In the optical member for EUVL (hereinafter referred to as "the optical member for EUVL of the present invention") surface treated by the surface treatment method of the optical member for EUVL of the present invention, fluorine or chlorine is added to the optical surface treated by GCIB etching. Because of the incorporation, the fluorine concentration or chlorine concentration near the surface layer of the optical member for EUVL is higher as compared with the deeper portion of the optical member for EUVL.

It is preferable that the optical member for EUVL of this invention satisfy | fills following formula.

(log C _200nm -log C _20nm ) / (200-20) <-3.0 × 10 ^-3

Here, C _200nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration in the 200 nm where the depth from the optical surface, C _20nm is the total concentration of the fluorine concentration and the chlorine concentration at the position of depth of 20 nm from the optical surface (ppm).

The value of (log C _{200 nm} -log C _{20 nm} ) / ( _200-20 ) corresponds to the slope of the total concentration of fluorine concentration and chlorine concentration from near the surface layer of the optical member to the deeper portion of the optical member. The value is more preferably less than -8.0 x 10 ^-3 , still more preferably less than -10.0 x 10 ^-3 .

It is preferable that the optical member for EUVL of this invention satisfy | fills following formula.

C _20nm -C _200nm ≥ 5 ppm

The value of (C _{20 nm} -C _{200 nm} ) corresponds to the slope of the total concentration of fluorine concentration and chlorine concentration from the vicinity of the surface layer of the optical member to the deeper portion of the optical member. The value is more preferably at least 10 ppm, even more preferably at least 15 ppm.

The optical member for EUVL of this invention is very excellent in the flatness and surface roughness of an optical surface. Specifically, the flatness of the optical surface is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 30 nm or less. The surface roughness Ra of the optical surface is preferably 5 nm or less, more preferably 3 nm or less, and still more preferably 1 nm or less.

In the optical member for EUVL of the present invention, since the compressive stress layer is formed near the surface layer, the strength near the surface layer is improved. The crack initiation load of the optical surface is preferably 50 g or more, more preferably 100 g or more, and still more preferably 200 g or more.

The crack initiation load is measured in the following manner. That is, after injecting the Vickers indenter for 15 seconds in a Vickers hardness tester, the Vickers indenter is removed and the vicinity of the indent is observed. The probability of crack occurrence is evaluated by dividing the area into four areas with the line connecting the center and the edge of the indenter and examining whether cracks occur in each area. If cracks are found in only one of the four regions, mark 25%; If cracks are found only in two areas, mark 50%; If cracks are found only in three areas, 75%; If cracks are found in all four areas, 100% is indicated. By measuring a plurality of samples, the crack occurrence probability was determined. The lowest load at which the crack occurrence probability is 100% was taken as the crack initiation load.

<Examples>

The invention will be described in more detail with reference to the following examples, but the invention should not be considered as being limited thereto. Example 1 is an example of this invention, and Example 2 is a comparative example.

Example 1

A substrate made of a silica glass material (OH concentration: 880 ppm, TiO ₂ concentration: 7.0 mass%, dimension: 20 mm x 20 mm x 1.5 mm thickness) was preliminarily polished, and then GCIB etching was performed on the surface of the substrate. Prepolishing and GCIB etching conditions are as follows.

<Preliminary Polishing Conditions>

Polishing Type: Mechanical Polishing

Surface pressure: 100 g / ㎠

<GCIB etching condition>

Source gas: mixed gas of SF ₆ and N ₂ (SF ₆ : N ₂ = 5%: 95%)

Acceleration Voltage: 24 kV

Cluster size: 3,000

Beam current: 100 um

Example 2

Only preliminary polishing was performed on the substrate made of the same silica glass material as in Example 1.

Examples 1 and 2 The fluorine concentration in the depth direction from the substrate surface of the substrate made of each quartz glass material was measured using a secondary ionization mass spectrometer (SIMS). The results are shown in FIG.

As clearly shown in FIG. 1, in the substrate of Example 1 subjected to GCIB etching, it was confirmed that the fluorine concentration in the vicinity of the surface layer from the surface to the depth of 100 nm increased due to the incorporation of fluorine. Even in the substrate of Example 2, which was not subjected to GCIB etching, the reason for the high fluorine concentration in the surface region was that the substrate surface was washed with hydrofluoric acid before the fluorine concentration measurement.

Examples 1 and 2 Ten substrates made of the silica glass material were prepared and 100 g of Vickers indenters were pressed over the substrate surface for 15 seconds to evaluate the crack resistance.

In the case of the glass of Example 1, all 10 sheets did not generate a crack, but in the case of the glass of Example 2, all 10 sheets confirmed that a crack occurred. From this, it was confirmed that the chipping generation suppression effect due to the GCIB etching.

Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

This application is based on Japanese Patent Application No. 2007-336167, filed December 27, 2007, the content of which is incorporated herein by reference.

Claims (9)

A source gas containing at least one of fluorine and chlorine in the optical surface of an optical member for EUV lithography (EUVL) made of a silica glass material containing an OH concentration of 100 ppm or more and containing TiO ₂ and SiO ₂ as a main component ( A surface treatment method of an optical member for EUVL, comprising performing a gas cluster ion beam (GCIB) etching using a source gas. The method of claim 1 wherein the method for surface treatment of the optical members of the TiO ₂ concentration in the optical member for EUVL 3 to 10 mass% EUVL. The surface treatment method of the optical member for EUVL of Claim 1 or 2 whose thermal expansion coefficient in 20 degreeC of the optical member for EUVL is 0 +/- 30 ppb / degreeC. The surface treatment method of the optical member for EUVL as described in any one of Claims 1-3 whose surface roughness Ra before EUGL etching of the optical member for EUVL is 5 nm or less. The process of claim 1, further comprising: a mixed gas of SF ₆ and O ₂ as a source gas; Mixed gas of SF ₆ , Ar and O ₂ ; Mixed gas of NF ₃ and O ₂ ; Mixed gas of NF ₃ , Ar, and O ₂ ; Mixed gas of NF ₃ and N ₂ ; Mixed gas of NF ₃ , Ar, and N ₂ ; Mixed gas of Cl ₂ and O ₂ ; Mixed gas of Cl ₂ , Ar, and O ₂ ; Mixed gas of Cl ₂ and N ₂ ; Mixed gas of Cl ₂ , Ar, and N ₂ ; Mixed gas of CF ₄ and O ₂ ; Mixed gas of CF ₄ , Ar, and O ₂ ; Mixed gas of CF ₄ and N ₂ ; Mixed gas of CF ₄ , Ar, and N ₂ ; Mixed gas of CH ₂ F ₂ and O ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and O ₂ ; Mixed gas of CH ₂ F ₂ and N ₂ ; Mixed gas of CH ₂ F ₂ , Ar, and N ₂ ; Mixed gas of CHF ₃ and O ₂ ; Mixed gas of CHF ₃ , Ar and O ₂ ; Mixed gas of CHF ₃ and N ₂ ; And a mixed gas selected from the group consisting of a mixed gas of CHF ₃ , Ar, and N ₂ . The optical member for EUVL surface-treated by the method of any one of Claims 1-5. An optical member for EUV lithography (EUVL) made of a silica glass material having an OH concentration of 100 ppm or more, a TiO ₂ concentration of 3 to 10 mass%, and containing SiO ₂ as a main component,
The surface roughness Ra of an optical surface is 5 nm or less, and the EUVL optical member which satisfy | fills a following formula.
(log C _200nm -log C _20nm ) / (200-20) <-3.0 x 10 ^-3
Wherein, C _200nm indicates the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of 200 nm depth from the optical surface; C _20nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of the 20 nm depth from the optical surface. An optical member for EUV lithography (EUVL) made of a silica glass material having an OH concentration of 100 ppm or more, a TiO ₂ concentration of 3 to 10 mass%, and containing SiO ₂ as a main component,
The surface roughness Ra of an optical surface is 5 nm or less, and the EUVL optical member which satisfy | fills a following formula.
C _20nm -C _200nm ≥ 5 ppm
Wherein, C _20nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of the 20 nm depth from the optical surface; C _200nm represents the total concentration (ppm) in the fluorine concentration and the chlorine concentration at the position of 200 nm depth from the optical surface. The optical member for EUVL according to claim 7 or 8, wherein a chamfer is provided along the outer edge of the optical surface.

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