TWI435855B - Optical member for euvl and surface treatment method thereof - Google Patents

Description

Optical element for EUVL and surface treatment method thereof

The present invention relates to an optical element for extreme ultraviolet (EUV) lithography and a surface treatment method thereof.

In the lithography technology, an exposure tool for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used so far. With the trend toward higher integration, higher speed, and higher functionality of integrated circuits, improvements in integrated circuits are being made. Therefore, the exposure tool is required to form a circuit pattern image having a high resolution on the surface of the wafer with a long focal depth, and the wavelength of the light for exposure is being shortened. The exposure light source is further improved by conventional g-ray (wavelength: 436 nm), i-ray (wavelength: 365 nm), and KrF excimer laser (wavelength: 248 nm), and ArF excimer laser (wavelength: 193 nm) is about to be put into use. use. In addition, in order to cope with a next-generation integrated circuit in which the circuit line width will become not more than 70 nm, an immersion exposure technique and a double exposure technique using ArF excimer lasers are regarded as dominant. However, it is believed that even these technologies will only be able to cover a generation with a line width of up to 45 nm.

Under the aforementioned technical trend, it is considered that the use of EUV light as a lithography technique for next-generation exposure light is applied to 32 nm and beyond and is attracting attention. EUV light as referred to herein refers to light having a wavelength in a soft X-ray region or a vacuum ultraviolet region, especially having a wavelength of about 0.2 to 100 nm. Currently, a 13.5 nm lithography source is being studied. The exposure principle of this EUV lithography (hereinafter abbreviated as "EUVL") is equivalent to the exposure principle of conventional lithography using a projection optical system to transfer a reticle pattern. However, since there is no material that transmits light in the EUV light energy region, a refractive optical system cannot be used. Therefore, it is inevitable to use a reflection optical system (see Patent Document 1).

Examples of reflective optical systems for EUVL include reflective reticle and mirrors, such as concentrating optics mirrors, illumination optics mirrors, and projection optics mirrors.

The reflective mask mainly includes (1) an optical element for EUVL (for example, a glass substrate), (2) a reflective multilayer film formed on an optical surface of an optical element for EUVL, and (3) a reflective multilayer film. The absorption layer. On the other hand, the mirror surface mainly includes (1) an optical element for EUVL (for example, a glass substrate) and (2) a reflective multilayer film formed on the optical surface of the optical element for EUVL.

As the reflective multilayer film, a structure having a structure in which a plurality of materials having different refractive indices for wavelengths of exposure light are cyclically laminated to each other in a nanometer size are used. Representative examples of materials known from the Mo and Si systems. In addition, Ta and Cr have been studied as absorption layers.

As the optical element for EUVL, a material having a low coefficient of thermal expansion is required in order to generate no strain even after irradiation with EUV light, and it has been studied to use a glass having a low coefficient of thermal expansion or a glass-ceramic having a low coefficient of thermal expansion. In the present specification, a glass having a low coefficient of thermal expansion and a glass-ceramic having a low coefficient of thermal expansion are collectively referred to hereinafter as "low expansion glass" or "very low expansion glass".

As such a low-expansion glass and a very low-expansion glass, a vermiculite glass to which a dopant is added for the purpose of lowering the coefficient of thermal expansion of the glass is most widely used. A representative example of a dopant added for the purpose of lowering the coefficient of thermal expansion of the glass is TiO ₂ . Specific examples of the vermiculite glass to which TiO _{2 is} added as a dopant include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated).

In the preparation of the optical element for EUVL, first, the raw material of the low-expansion glass or the extremely low-expansion glass is cut into a predetermined shape and a predetermined size. The optical surface is then processed to achieve a predetermined flatness and a predetermined surface roughness.

The optical element for EUVL needs to have an optical surface with excellent smoothness. Specifically, surface treatment must be performed so that the surface to be fabricated has a flatness of not more than 50 nm and a surface roughness (Ra) of not more than 5 nm.

The problem of cutting the corners of the optical element for EUVL occurs when manufacturing a reflective mask or mirror or when EUVL is performed. For this purpose, the EUVL is usually subjected to chamfering with the corners of the optical elements.

However, even in the case where the corner is subjected to chamfering, cutting occurs after the EUVL optical element is fixed to the manufacturing apparatus or the exposure tool, more specifically, when it is clamped by a jig or the like. The problem of the chamfered part.

Patent Document 1: JP-T-2003-505891

In order to solve the problems of the above-mentioned background art, an object of the present invention is to provide an optical element for EUVL, which is used for a reflective mask of the EUVL, a mirror surface, etc., and has an optical surface excellent in flatness and surface roughness. And has excellent strength near the surface layer, and in which the cutting chamfer is prevented from being generated. Another object of the present invention is to provide a surface treatment method for an optical surface of an optical element for EUVL.

In order to achieve the above object, the present invention provides a surface treatment method for an optical element for EUVL, comprising: using an optical surface of an optical element for EUV lithography (EUVL) with a source gas containing at least one of fluorine and chlorine; Applying a gas cluster ion beam (GCIB) etching to the chamfer of the outer edge of the optical surface, wherein the optical element comprises an OH concentration of 100 ppm or more, containing TiO ₂ , and containing SiO ₂ as a main The component of the vermiculite glass material.

In the surface treatment method for the optical element for EUVL of the present invention, it is preferred that the optical element for EUVL has a concentration of TiO _{2 of} 3 to 10% by mass.

In the surface treatment method for the optical element for EUVL of the present invention, it is preferred that the optical element for EUVL has a thermal expansion coefficient of 0 ± 30 ppb / ° C at 20 °C.

In the case where the energy of the EUV light for exposure is raised to increase the throughput of the EUVL exposure tool, the temperature of the optical element increases beyond the general assumption. In particular, the temperature of the optical element may increase to a temperature of 40 to 110 °C. In this case, it is preferred that the optical element of the present invention has a thermal expansion coefficient of 0 ± 30 ppb / ° C at a temperature of 40 to 110 ° C to prevent a pitch change of the pattern when used as a mask or the like, And it is prevented from being changed in shape when used as a stepper mirror or the like.

In the surface treatment method for the optical element for EUVL of the present invention, it is preferred that the optical element for EUVL has a surface roughness (Ra) of not more than 5 nm before the application of the GCIB etching.

In the surface treatment method for the optical element for EUVL of the present invention, it is preferred that the source gas used is any mixed gas selected from the group consisting of the following mixed gases: a mixed gas of SF ₆ and O ₂ ; SF ₆ , Ar Mixed gas with O ₂ ; mixed gas of NF ₃ and O ₂ ; NF ₃ , mixed gas of Ar and O ₂ ; mixed gas of NF ₃ and N ₂ ; NF ₃ , mixed gas of Ar and N ₂ ; Cl ₂ and a mixed gas of O ₂ ; a mixed gas of Cl ₂ , Ar and O ₂ ; a mixed gas of Cl ₂ and N ₂ ; a mixed gas of Cl ₂ , Ar and N ₂ ; a mixed gas of CF ₄ and O ₂ ; CF ₄ , Ar Mixed gas with O ₂ ; mixed gas of CF ₄ and N ₂ ; CF ₄ , mixed gas of 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 a mixed gas of CH ₂ F ₂ and N ₂ ; a mixed gas of CH ₂ F ₂ , Ar and N ₂ ; a mixed gas of CHF ₃ and O ₂ ; a mixed gas of CHF ₃ , Ar and O ₂ ; CHF ₃ and N _{2 ;} a mixed gas; and a mixed gas of CHF ₃ , Ar and N ₂ .

The present invention also provides an optical element for EUVL which has been surface-treated by the surface treatment method of the optical element for EUVL of the present invention.

The present invention also provides an optical element for EUV lithography (EUVL), which comprises a fluorite glass material having an OH concentration of 100 ppm or more and a TiO ₂ concentration of 3 to 10% by mass, and containing SiO ₂ as a main component. And chamfering is provided along the outer edge of the optical surface; the optical element for EUVL has an optical surface having a surface roughness (Ra) of not more than 5 nm and satisfying the following expression: (log C _{200 nm} -log C _{20 nm} ) / (200- 20) <-3.0×10 ^-3 where C _200nm represents the total concentration (ppm) of fluorine concentration and chlorine concentration at a depth of 200 nm from the surface of the optical surface and chamfer; and C _{20 nm} indicates the surface at the optical surface and chamfer The total concentration (ppm) of the fluorine concentration and the chlorine concentration at a depth of 20 nm.

The present invention also provides an optical element for EUV lithography (EUVL), which comprises a fluorite glass material having an OH concentration of 100 ppm or more and a TiO ₂ concentration of 3 to 10% by mass and containing SiO ₂ as a main component. And chamfering is provided along the outer edge of the optical surface; the optical element for EUVL has an optical surface having a surface roughness (Ra) of not more than 5 nm and satisfying the following expression: C _{20 nm} - C _{200 nm} 5 ppm, where C _{20 nm} represents the total concentration (ppm) of fluorine concentration and chlorine concentration at a depth of 20 nm from the surface of the optical surface and the chamfer; and C _{200 nm} represents the fluorine concentration and the chlorine concentration at a depth of 200 nm from the surface of the optical surface and the chamfered surface. Total concentration (ppm).

The optical element for EUVL of the present invention has excellent flatness and surface roughness on its optical surface, and is suitably used as a reflective mask, a mirror surface, and the like for EUVL. Further, the optical element for EUVL of the present invention has an enhanced strength in the vicinity of the surface layer on the optical surface side. Therefore, it is prevented that the cutting angle of the optical element for EUVL is generated when the reflective reticle or mirror is manufactured or when EUVL is performed, or the cutting chamfer is prevented from being generated when the corner has been subjected to chamfering.

The optical element for EUVL of the present invention is suitably obtained by using the treatment method of the optical element for EUVL of the present invention.

In the surface treatment method for an optical element for EUVL of the present invention, a GCIB etching is applied to an optical surface of an optical element for EUVL using a source gas containing at least one of fluorine and chlorine, and the optical element comprises 100 ppm or more. An OH concentration, a vermiculite glass material containing TiO ₂ and containing SiO ₂ as a main component.

The optical surface of the optical element for EUVL referred to herein means a surface on which a reflective multilayer film is formed by using an optical element for EUVL to manufacture a reflective mask, a mirror surface or the like. In order to achieve the purpose of preventing the occurrence of cutting when manufacturing a reflective mask or mirror or when performing EUVL, the corners of the outer edge of the optical surface of the optical element for EUVL are usually subjected to chamfering.

In order to achieve a reduction in thermal expansion coefficient, the vermiculite glass material constituting the optical element for EUVL contains TiO ₂ as a dopant.

Although the concentration of TiO _{2 in the} vermiculite glass material is not particularly limited as long as the coefficient of thermal expansion of the vermiculite glass material is sufficiently low to be used as the optical element for EUVL, it is preferably from 3 to 10% by mass. When the TiO ₂ concentration is within the above range, the thermal expansion coefficient of the vermiculite glass material becomes sufficiently low. Specifically, the obtained glass is a low expansion glass having a thermal expansion coefficient of 0 ± 30 ppb / ° C at 20 ° C, and is preferably a very low expansion glass having a thermal expansion coefficient of 0 ± 10 ppb / ° C at 20 ° C.

Specific examples of the low-expansion glass and the extremely low-expansion glass to which TiO ₂ is added as a dopant at the above concentration include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated).

The vermiculite glass material constituting the optical element for EUVL contains 100 ppm or more of OH in addition to SiO ₂ and TiO ₂ . The addition of OH accelerates the structural relaxation of the glass and facilitates the realization of a glass structure having a low fictive temperature. Reducing the hypothetical temperature of the glass minimizes the temperature dependence of the coefficient of thermal expansion, and the vermiculite glass material is suitable as an optical element for EUVL.

Further, when the vermiculite glass material contains OH, when the GCIB etching is applied to the optical surface of the optical element for EUVL by using a source gas containing at least one of fluorine and chlorine, compared with the case where OH is not present, Fluorine or chlorine is incorporated into the deeper portion of the surface of the optical element. Therefore, in the surface treatment method for the optical element for EUVL of the present invention, the effect produced by applying the GCIB etching to the optical surface of the optical element for EUVL with a source gas containing at least one of fluorine and chlorine is advantageously exhibited.

In the surface treatment method for an optical element for EUVL of the present invention, the effect of applying GCIB etching to the optical surface of the optical element for EUVL by using a source gas containing at least one of fluorine and chlorine is as follows.

The GCIB etching as referred to herein is a method comprising the steps of: injecting a reactive substance (source gas) in a pressurized state (which is gaseous at normal temperature and normal pressure) into a vacuum device via an expansion nozzle A gas cluster is formed, the gas cluster is subjected to electronic irradiation to supply power, and the target is irradiated with the resulting ionized GCIB, thereby etching the target. Gas clusters are composed of a large number of atomic groups or molecular groups that typically contain thousands of atoms or molecules. In the surface treatment method for the optical element for EUVL of the present invention, when GCIB etching is applied to the optical surface of the optical element for EUVL, the collision of the optical surface with the gas cluster causes a multibody impact effect due to interaction with the solid (multibody) Impact effect), thereby polishing the optical surface and improving the flatness (first effect).

In the surface treatment method for the optical element for EUVL of the present invention, when a GCIB etching is applied to the optical surface of the optical element for EUVL using a source gas containing at least one fluorine and chlorine, fluorine or chlorine is incorporated into the optical element for the optical element for EUVL. The vicinity of the surface layer on the front side is specifically incorporated into the vermiculite glass material to a depth of about 100 nm from the optical surface of the optical element for EUVL. A compression stress layer may be formed in the vicinity of the surface layer on the side of the optical surface incorporating fluorine or chlorine. Thereby, the strength in the vicinity of the surface layer of the optical element for FUVL is enhanced. Therefore, it is prevented that the chamfering (second effect) of the optical element for FUVL is generated when the reflective mask or mirror is manufactured or when EUVL is performed.

In order to more effectively exhibit the second effect, the GCIB etch is preferably applied to the entire optical surface, including the chamfered portion at the corner or corner of the outer edge of the optical surface.

In order to more effectively exhibit the effect produced by the GCIB etching, particularly the second effect described above, the vermiculite glass material constituting the optical element for EUVL preferably contains OH in an amount of 200 ppm or more and more preferably 500 ppm or more.

In the surface treatment method for the optical element for EUVL of the present invention, it is preferred to initially polish the optical surface to which the GCIB etching is applied so as to have a predetermined flatness and a predetermined surface roughness.

The preliminary polishing method is not particularly limited and can be widely selected from known polishing methods for polishing the surface of a vermiculite glass material. However, since a large surface can be polished at a time using a polishing pad having a high polishing rate and a large surface area, a mechanical polishing method is usually used. In addition to the polishing process by the polishing function of the abrasive particles, the mechanical polishing method referred to herein also includes a method of using a polishing slurry to combine the polishing function of the abrasive particles with the chemical polishing function of the chemical. Mechanical polishing can be either polishing or polishing. The polishing tool and the abrasive material to be used can be appropriately selected among known materials. In the case of using a mechanical polishing method, in order to make the processing rate high, the polishing is preferably carried out at a surface pressure of 30 to 70 gf/cm ² and more preferably at a surface pressure of 40 to 60 gf/cm ² ; 60 to the lower surface pressure of 140gf / cm ² and more preferably of at surface 80 to a pressure of 120gf / cm ² was committed. Regarding the amount of polishing, the polishing is preferably carried out at a polishing amount of from 100 to 300 μm; and the polishing is preferably carried out at a polishing amount of from 1 to 60 μm.

In the case of preliminary polishing, the surface roughness (Ra) of the optical surface after the preliminary polishing is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm. The surface roughness (Ra) mentioned in the present specification means the surface roughness measured by an atomic force microscope for an area of 1 to 10 μm ² . When the surface roughness of the optical surface exceeds 5 nm after the preliminary polishing, it takes a lot of time in the surface treatment method for the optical element for EUVL of the present invention to adjust the optical surface by applying GCIB etching to obtain a predetermined flatness and a predetermined surface roughness. Degree, thus increasing costs.

When a source gas containing at least fluorine and chlorine is used for the GCIB etching, it is preferred to use any mixed gas selected from the group consisting of a mixed gas of SF ₆ and O ₂ , a mixed gas of SF ₆ , Ar and O ₂ , and NF _{3 .} Mixed gas with O ₂ ; NF ₃ , a mixed gas of Ar and O ₂ ; a mixed gas of NF ₃ and N ₂ ; NF ₃ , a mixed gas of Ar and N ₂ ; a mixed gas of Cl ₂ and O ₂ ; Cl ₂ , a mixed gas of Ar and O ₂ ; a mixed gas of Cl ₂ and N ₂ ; a mixed gas of Cl ₂ , Ar and N ₂ ; a mixed gas of CF ₄ and O ₂ ; a mixed gas of CF ₄ , Ar and O ₂ ; CF ₄ Mixed gas with N ₂ ; CF ₄ , mixed gas of Ar and N ₂ ; mixed gas of CH ₂ F ₂ and O ₂ ; CH ₂ F ₂ , mixed gas of Ar and O ₂ ; CH ₂ F ₂ and N ₂ Mixed gas; CH ₂ F ₂ , a mixed gas of Ar and N ₂ ; a mixed gas of CHF ₃ and O ₂ ; CHF ₃ , a mixed gas of Ar and O ₂ ; a mixed gas of CHF ₃ and N ₂ ; and CHF ₃ , Ar Mixed gas with N ₂ .

Among the mixed gases, although the appropriate mixing ratio of the individual components varies depending on the irradiation conditions and the like, the following is preferred.

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

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

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

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

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

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

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

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

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

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

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

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

CH ₂ F ₂ : O ₂ = (0.1 to 5%): (95 to 99.9%) (mixture 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%) (CH ₂ F ₂ , a mixed gas of Ar and O ₂ )

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

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

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

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

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

The irradiation conditions are appropriately selected depending on the type of the source gas and the surface characteristics of the optical surface, including the cluster size, the ionization current applied to the ionizing electrode of the ionizing cluster by the GCIB etching apparatus, and the acceleration of the accelerating electrode applied to the GCIB etching apparatus. Voltage and GCIB dosage. For example, in order to improve the flatness without excessively deteriorating the surface roughness of the optical surface, the acceleration voltage applied to the accelerating electrode is preferably 15 to 30 kV.

When performing a GCIB etch, the optical surface must be scanned with GCIB. As the GCIB scanning method, raster scanning and spiral scanning are known, and any of these methods can be used.

In the optical element for EUVL which has been surface-treated by the surface treatment method of the optical element for EUVL of the present invention (hereinafter referred to as "the optical element for EUVL of the present invention"), since fluorine or chlorine is incorporated by GCIB etching Since the optical surface is processed, the fluorine concentration or the chlorine concentration in the vicinity of the surface layer of the optical element for EUVL becomes higher than the deep portion of the optical element for EUVL.

The optical element for EUVL of the present invention preferably satisfies the following expression.

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

Here, C _{200 nm} represents the total concentration (ppm) of the fluorine concentration and the chlorine concentration at a depth of 200 nm from the optical surface; and C _{20 nm} represents the total concentration (ppm) of the fluorine concentration and the chlorine concentration at a depth of 20 nm from the optical surface.

The value of (log C _200nm -log C _20nm ) / (200-20) corresponds to the total concentration gradient of the fluorine concentration and the chlorine concentration from the vicinity of the surface layer of the optical element to the deep portion of the optical element in the optical element. value. This value is more preferably less than -8.0 × 10 ^-3 and further preferably less than -10.0 × 10 ^-3 .

The optical element for EUVL of the present invention preferably satisfies the following expression.

C _20nm -C _200nm 5ppm

The value of (C _{20 nm} - C _{200 nm} ) corresponds to the value of the total concentration gradient of the fluorine concentration and the chlorine concentration from the vicinity of the surface layer of the optical element to the deep portion of the optical element in the optical element. This value is more preferably 10 ppm or more and further preferably 15 ppm or more.

The optical element for EUVL of the present invention has excellent flatness and surface roughness on an optical surface. Specifically, the flatness of the optical surface is preferably not more than 100 nm, more preferably not more than 50 nm, and further preferably not more than 30 nm. Further, the surface roughness Ra of the optical surface is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm.

In the optical element for EUVL of the present invention, since a compressive stress layer is formed in the vicinity of the surface layer, the strength in the vicinity of the surface layer is enhanced. The optical surface preferably has a crack initiation load of 50 g or more, more preferably 100 g or more, and further preferably 200 g or more.

The crack initiation load is measured in the following manner. That is, after imprinting with a Vickers indenter for 15 seconds by a Vickers hardness-measurement apparatus, the Vickers indenter was removed and the vicinity of the indentation was observed. The area is divided into four regions, a line connecting the center of the indentation and the corner is used as a boundary, and the probability of crack generation is evaluated by detecting whether or not cracks are generated in the individual regions. The case where the crack was found only in one of the four regions was expressed as 25%; the case where the crack was found only in the two regions was expressed as 50%; the case where the crack was found only in the three regions was expressed as 75%; The case where cracks were found in all four regions was expressed as 100%. The probability of crack generation is determined by measuring a plurality of samples. The minimum load at which the probability of crack generation is 100% is regarded as the crack initiation load.

Instance

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

Example 1

After preliminary polishing of the vermiculite glass substrate (OH concentration: 880 ppm, TiO ₂ concentration: 7.0% by mass, size: 20 mm × 20 mm × 1.5 mm - thickness), GCIB etching was applied to the surface of the substrate. The conditions for preliminary polishing and GCIB etching are as follows.

<Preliminary polishing conditions>

Polishing type: mechanical polishing

Surface pressure: 100 g/cm ² .

<GCIB Etching Conditions>

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

Acceleration voltage: 24kV

Cluster size: 3,000

Beam current: 100um

Example 2

The same vermiculite glass material substrate as in Example 1 was subjected to only preliminary polishing.

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

As is apparent from Fig. 1, it was confirmed that in the substrate of Example 1 which had been subjected to GCIB etching, the fluorine concentration in the vicinity of the surface layer at a depth of up to 100 nm from the surface became high by incorporation of fluorine. The reason why the fluorine concentration in the surface region of the substrate of Example 2 which was not etched by GCIB was higher was that the surface of the substrate was washed with hydrofluoric acid before measuring the fluorine concentration.

Ten flake glass substrate sheets of each of Examples 1 and 2 were prepared, and a 100 g Vickers indenter was imprinted on the surface of the substrate for 15 seconds to evaluate crack resistance.

It was confirmed that for the glass of Example 1, no crack was generated in all of the 10 sheets, and for the glass of Example 2, cracks were generated in all of the 10 sheets. Thereby, the effect of cutting by the GCIB etching can be confirmed.

Although the present invention has been described in detail and by reference to the specific embodiments thereof, it will be understood that

The present application is based on Japanese Patent Application No. 2007-336167, filed on Dec. 27, 2007, the content of

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

(no component symbol description)

Claims (8)

A surface treatment method for optical components for extreme ultraviolet lithography (EUVL), comprising an optical element for extreme ultraviolet (EUV) lithography (EUVL) using a source gas containing at least one of fluorine and chlorine An optical surface and a chamfered gas cluster ion beam (GCIB) etching disposed along an outer edge of the optical surface, wherein the optical element comprises an OH concentration of 100 ppm or more, containing TiO ₂ and containing SiO ₂ as a main group Part of the meteorite glass material. The surface treatment method for an optical element for EUVL of claim 1, wherein the optical element for EUVL has a concentration of TiO _{2 of} 3 to 10% by mass. The surface treatment method for an optical element for EUVL of claim 1, wherein the optical element for EUVL has a thermal expansion coefficient of 0 ± 30 ppb / ° C at 20 °C. The surface treatment method for an optical element for EUVL of claim 1, wherein the optical element for EUVL has a surface roughness (Ra) of not more than 5 nm before the application of the GCIB etching. The surface treatment method for an optical element for EUVL according to claim 1, wherein a mixed gas selected from the group consisting of the following mixed gases is used as a source gas: a mixed gas of SF ₆ and O ₂ ; SF ₆ , Ar and Mixed gas of 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 ; Cl ₂ and O _a mixed gas of ₂ ; a mixed gas of Cl ₂ , Ar and O ₂ ; a mixed gas of Cl ₂ and N ₂ ; a mixed gas of Cl ₂ , Ar and N ₂ ; a mixed gas of CF ₄ and O ₂ ; CF ₄ , Ar and a mixed gas of O ₂ ; a mixed gas of CF ₄ and N ₂ ; a mixed gas of CF ₄ , Ar and N ₂ ; a mixed gas of CH ₂ F ₂ and O ₂ ; a mixed gas of CH ₂ F ₂ , Ar and O ₂ ; a mixed gas of CH ₂ F ₂ and N ₂ ; a mixed gas of CH ₂ F ₂ , Ar and N ₂ ; a mixed gas of CHF ₃ and O ₂ ; a mixed gas of CHF ₃ , Ar and O _{2 ;} and a mixture of CHF ₃ and N ₂ a mixed gas; and a mixed gas of CHF ₃ , Ar and N ₂ . An optical element for EUVL which has been surface-treated by the method of any one of claims 1 to 5. An optical element for EUV lithography (EUVL) comprising an OH concentration of 100 ppm or more and an TiO ₂ concentration of 3 to 10% by mass, a vermiculite glass material containing SiO ₂ as a main component, and optical The outer edge of the face is provided with a chamfer; the optical element for EUVL has an optical surface having a surface roughness (Ra) of not more than 5 nm and satisfying the following expression: (log C _{200 nm -} log C _{20 nm} ) / (200-20) <- 3.0×10 ^-3 wherein C _200nm represents the total concentration (ppm) of fluorine concentration and chlorine concentration at a depth of 200 nm from the surface of the optical surface and chamfer; and C _{20 nm} represents a depth of 20 nm from the surface of the optical surface and the chamfer The total concentration (ppm) of the fluorine concentration and the chlorine concentration. An optical element for EUV lithography (EUVL) comprising an OH concentration of 100 ppm or more and an TiO ₂ concentration of 3 to 10% by mass, a vermiculite glass material containing SiO ₂ as a main component, and optical The outer edge of the face is provided with a chamfer; the optical element for EUVL has an optical surface having a surface roughness (Ra) of not more than 5 nm and satisfying the following expression: C _{20 nm} - C _{200 nm} 5 ppm, where C _{20 nm} represents the total concentration (ppm) of fluorine concentration and chlorine concentration at a depth of 20 nm from the surface of the optical surface and chamfer, and C _{200 nm} represents a fluorine concentration at a depth of 200 nm from the surface of the optical surface and the chamfered surface The total concentration of chlorine concentration (ppm).