JP5042121B2 - EUVL optical member and smoothing method thereof - Google Patents

Description

  The present invention relates to a method for smoothing an optical member for EUV lithography (hereinafter abbreviated as “EUVL”). More specifically, the present invention relates to a method of smoothing an optical surface having concave defects such as pits and scratches of an optical member for EUVL (hereinafter referred to as “smoothing method of the present invention”).

  Moreover, this invention relates to the optical member for EUVL obtained by the smoothing method of this invention.

  Conventionally, in lithography technology, an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used. As integrated circuits become highly integrated, faster, and more functional, miniaturization of integrated circuits advances, and the exposure apparatus is required to image a high-resolution circuit pattern on the wafer surface with a deep focal depth. The wavelength of the exposure light source is being shortened. As an exposure light source, an ArF excimer laser (wavelength 193 nm) has started to be used further from the conventional g-line (wavelength 436 nm), i-line (wavelength 365 nm), and KrF excimer laser (wavelength 248 nm). In order to cope with next-generation integrated circuits whose circuit line width is 70 nm or less, immersion exposure technology and double exposure technology using an ArF excimer laser are considered promising, but this also has a line width of 45 nm. It is thought that it can cover only generations.

  In such a technical trend, lithography (EUVL) technology using EUV light as an exposure light source for the next generation is considered to be applicable over the generations of 32 nm and later, and has attracted attention. EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, specifically, light having a wavelength of about 0.2 to 100 nm. At present, the use of 13.5 nm as a lithography light source is being studied. The exposure principle of EUV lithography is the same as that of conventional lithography in that the mask pattern is transferred using a projection optical system. However, since there is no material that transmits light in the energy region of EUV light, a refractive optical system is used. It cannot be used, and a reflection optical system is used.

  Examples of the reflective optical system used for EUVL include a reflective mask (hereinafter referred to as “EUVL mask” in the present specification), a condensing optical system mirror, an illumination optical system mirror, a projection optical system mirror, and the like. Mirrors (hereinafter referred to as “EUVL mirrors” in this specification).

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

  As an EUVL optical member, a material having a low thermal expansion coefficient is required so that distortion does not occur even under EUV light irradiation, and the use of glass having a low thermal expansion coefficient or crystallized glass having a low thermal expansion coefficient has been studied. Yes. Hereinafter, in the present specification, a glass having a low thermal expansion coefficient and a crystallized glass 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, quartz glass to which a dopant is added in order to lower the thermal expansion coefficient of the glass is most widely used. The dopant added for the purpose of lowering the thermal expansion coefficient of glass is typically TiO ₂ . Specific examples of quartz glass to which TiO ₂ is added as a dopant include ULE (registered trademark) code 7972 (manufactured by Corning), Asahi Glass Co., Ltd. product number AZ6025, and the like.

The reflective multilayer film has a structure in which a plurality of materials having different refractive indexes in the wavelength region of EUV light that is exposure light are periodically stacked in the nm order, and has a high refractive index in the wavelength region of EUV light. By alternately laminating a molybdenum (Mo) layer that is a layer (high refractive index layer) and a silicon (Si) layer that is a layer having a low refractive index (low refractive index layer) in the wavelength region of EUV light, EUV light The most common is a reflective multilayer film having an improved light reflectivity when irradiating the surface of the layer.
For the absorber layer, a material having a high absorption coefficient for EUV light, specifically, a material mainly composed of, for example, Cr or Ta is used.

  When minute irregularities exist on the optical surface of the EUVL optical member, the reflective multilayer film and the absorber layer formed on the optical surface are adversely affected. For example, if minute irregularities exist on the optical surface, the periodic structure of the reflective multilayer film formed on the optical surface is disturbed, and an EUVL mask or EUVL mirror manufactured using the EUVL optical member is used. When EUVL is performed, a part of a desired pattern may be lost or an extra pattern may be formed in addition to the desired pattern. Disturbances in the periodic structure of the reflective multilayer film caused by irregularities present on the optical surface are called phase defects and are a serious problem, and it is desirable that the optical surface has no irregularities of a predetermined size or more.

  Non-Patent Documents 1 and 2 describe requirements regarding defects in EUVL masks and EUVL mask blanks, and the requirements regarding these defects are very severe. Non-Patent Document 1 is acceptable because if a defect exceeding 50 nm exists on the substrate, the structure of the reflective multilayer film is disturbed and an unexpected shape is generated in the pattern projected onto the resist on the Si wafer. It is stated that it is not possible. Further, Non-Patent Document 1 discloses that the surface roughness of the substrate is RMS (root mean square roughness) in order to prevent the line edge roughness from increasing in the pattern projected onto the resist on the Si wafer. It is described that it is necessary to be less than 0.15 nm. Non-Patent Document 2 describes that a mask blank coated with a reflective multilayer film used in EUV lithography cannot have a defect exceeding 25 nm.

  Non-Patent Document 3 describes how large a defect on a substrate can be transferred. Non-Patent Document 3 describes that there is a possibility of changing the line width of an image printed with phase defects. A phase defect having a surface bump having a height of 2 nm and a FWHM (full width at half maximum) of 60 nm is a boundary that determines whether or not the defect may be transferred. It is described as causing an unacceptable line width change of 20% (140 nm on the mask) for a 35 nm line.

  Patent Document 1 describes a method of correcting a concavo-convex portion by condensing a laser beam on the front or back surface of the concavo-convex portion of the EUVL mask substrate.

JP 2008-027992 A SEMI, P37-1102 (2002), “Specification for extreme ultraviolet lithography mask substrate” SEMI, P38-1102 (2002), “Specification for absorbing film stacks and multilayers on extreme ultraviolet lithography mask blanks” SPIE, vol. 4889, Alan Stivers., Et. Al., P.408-417 (2002), “Evaluation of the Capability of a Multibeam”. Confocal Inspection System for Inspection of EUVL Mask Blanks)

  Convex defects such as foreign particles and fibers, and bumps on the substrate itself, among the minute irregularities present on the optical surface, can be removed by conventional wet cleaning methods using hydrofluoric acid or aqueous ammonia, brush cleaning, or precision polishing. Etc. can be removed.

  However, concave defects such as pits and scratches cannot be removed by these methods. In addition, when a wet cleaning method using hydrofluoric acid or ammonia water is used to remove the convex defects, it is necessary to slightly etch the optical surface in order to lift off the convex defects. There is a possibility that a new concave defect is generated on the optical surface. Even when brush cleaning is used to remove the convex defect, there is a possibility that a new concave defect is generated on the optical surface.

  Further, in the method described in Patent Document 1, it is necessary to specify the position of the unevenness and change the position where the laser light is focused to the vicinity of the substrate surface or the vicinity of the back surface of the substrate depending on whether it is a concave portion or a convex portion. In addition, there is a problem that it is difficult to cope with a fine uneven defect.

  An object of the present invention is to provide a method for smoothing an optical surface having concave defects such as pits and scratches of an optical member for EUVL in order to solve the above-described problems in the prior art.

  In order to achieve the above object, the present inventors have intensively studied. As a result, by irradiating the optical surface with a carbon dioxide gas laser having a specific wavelength range and a specific peak intensity, the flatness is deteriorated and the surface roughness is reduced. The present inventors have found that an optical surface having a concave defect can be smoothed while suppressing adverse effects caused by the irradiation of the carbon dioxide laser such as deterioration of the above.

The present invention has been made based on the finding by the present inventors as described above, containing TiO _2, optical surface having a concave defect of the quartz glass material made of an optical component for EUVL composed mainly of SiO ₂ In contrast, a method of smoothing the optical surface of the optical member for EUVL by irradiating a carbon dioxide laser with a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ² (smoothing method of the present invention) I will provide a.

In the smoothing method of the present invention, the optical surface having the concave defect of the EUVL optical member is irradiated with a carbon dioxide gas laser having a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ^2. The concave defect depth repair rate of the optical surface of the optical member for EUVL defined by the following formula is preferably 50% or more.
Concave defect depth repair rate (%) = ((depth of concave defect before carbon dioxide laser irradiation (PV value)) − (depth of concave defect after carbon dioxide laser irradiation (PV value)) / (before carbon dioxide laser irradiation) Depth of concave defects (PV value)) × 100.

In the smoothing method of the present invention, a carbon dioxide gas laser having a wavelength of 10.6 μm is applied to an optical surface of an EUVL optical member having a concave defect with a depth of more than 2 nm and not more than 10 nm, with a peak intensity of 0.5 to 1.5 kW / cm ^2. It is preferable to make an optical member that satisfies (1) to (3).
(1) There is no concave defect with a depth of more than 2 nm on the optical surface after the carbon dioxide laser irradiation.
(2) Flatness of the optical member after carbon dioxide laser irradiation is 50 nm or less.
(3) Surface roughness (RMS) of the optical surface after carbon dioxide laser irradiation is 0.15 nm or less.

  In the smoothing method of the present invention, it is preferable to irradiate the carbon dioxide laser to the entire optical surface of the EUVL optical member.

In the smoothing method of the present invention, the TiO ₂ concentration of the EUVL optical member is preferably 3 to 10% by mass.

  In the smoothing method of the present invention, the pulse width of the carbon dioxide laser is preferably 1 msec or less.

  In the smoothing method of the present invention, it is preferable that the optical surface is irradiated with the carbon dioxide laser so that the number of shots at each irradiation site is 1000 to 100,000 or more.

  Here, the number of shots means the number of times the carbon dioxide laser is irradiated to the same location, and the optical surface is irradiated with the carbon dioxide laser as a pulse laser, and the carbon dioxide laser is scanned on the optical surface, or the carbon dioxide laser beam On the other hand, the number of shots in the case of scanning the optical surface is defined by the repetition frequency of the pulse laser × beam width in the scanning direction ÷ scanning speed.

  In the smoothing method of the present invention, the carbon dioxide laser is irradiated onto the optical surface as a line beam, and the line beam is scanned on the optical surface, or the optical surface is scanned with respect to the line beam. preferable.

In the smoothing method of the present invention, a carbon dioxide laser having a wavelength of 10.6 μm may be further irradiated to the back surface with respect to the optical surface at a peak intensity of 0.5 to 1.5 kW / cm ² .

  In this case, it is preferable to irradiate the carbon dioxide laser to the entire back surface.

In the smoothing method of the present invention, it is preferable that the peak intensity I ₁ of the carbon dioxide laser irradiated on the optical surface and the peak intensity I ₂ of the carbon dioxide laser irradiated on the back surface satisfy the relationship of the following formula.
0.5 ≦ I ₁ / I ₂ ≦ 1.5.

  In the smoothing method of the present invention, it is preferable that a pulse width of the carbon dioxide laser irradiated on the back surface is 1 msec or less. In the smoothing method of the present invention, it is preferable to irradiate the carbon dioxide laser on the back surface so that the number of shots at each irradiation site is 1000 to 100,000 or more.

  In the smoothing method of the present invention, it is preferable that the carbon dioxide laser is irradiated on the back surface as a line beam and the line beam is scanned on the back surface, or the back surface is scanned with respect to the line beam.

  In the smoothing method of the present invention, it is preferable that the optical surface is irradiated with a carbon dioxide laser in a state where the glass substrate is heated to 100 to 1050 ° C.

  The present invention also provides that the virtual temperature of the surface layer including the optical surface obtained by the smoothing method of the present invention in which only the optical surface is irradiated with a carbon dioxide laser is 30 ° C. higher than the virtual temperature of the remaining part. A featured optical member for EUVL is provided.

  Further, the present invention provides an optical member in which the virtual temperature of the surface layer including the optical surface and the virtual temperature of the surface layer including the back surface, which are obtained by the smoothing method of the present invention in which the optical surface and the back surface are irradiated with a carbon dioxide laser. The EUVL optical member is characterized by being 30 ° C. or more higher than the fictive temperature inside.

According to the smoothing method of the present invention, the optical surface having a concave defect of the EUVL optical member is flattened by irradiating a carbon dioxide gas laser having a wavelength of 10.6 μm with a peak intensity of 0.5 to 1.5 kW / cm ^2. The optical surface can be smoothed while minimizing the adverse effects caused by the irradiation of the carbon dioxide laser, such as deterioration of the degree and surface roughness.

  Hereinafter, the smoothing method of the present invention will be described.

According to the smoothing method of the present invention, an optical surface having a concave defect of an optical member for EUVL is irradiated with a carbon dioxide gas laser having a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ^2. This is a method of smoothing the surface.

The optical member for EUVL targeted by the smoothing method of the present invention is made of a quartz glass material containing SiO ₂ as a main component, and TiO ₂ is added as a dopant for reducing the thermal expansion coefficient.

The TiO ₂ concentration in the quartz glass material is not particularly limited as long as the thermal expansion coefficient of the quartz glass material can be made sufficiently low to be used as an EUVL optical member, but it is preferably 3 to 10% by mass. When the TiO ₂ concentration is in the above range, the thermal expansion coefficient of the quartz glass material is sufficiently low, specifically, low expansion glass having a thermal expansion coefficient of 0 ± 30 ppb / ° C. at 20 ° C., preferably at 20 ° C. It becomes an ultra-low expansion glass having a thermal expansion coefficient of 0 ± 10 ppb / ° C.

To the quartz glass material, a dopant other than TiO ₂ may be added as a dopant for lowering the thermal expansion coefficient. An example of such a dopant is SnO ₂ . When adding SnO ₂ as a dopant, SnO ₂ concentration in the silica glass material is not particularly limited as long as it can be low enough to use the thermal expansion coefficient of the quartz glass material as an optical member for EUVL, 0.1 It is preferable that it is -10 mass%. When adding SnO ₂ as a dopant, the SnO ₂ concentration is more preferably 0.3% by mass or more, and further preferably 0.5% by mass or more. The SnO ₂ concentration is more preferably 5% by mass or less, and further preferably 3% by mass or less.

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

The optical member for EUVL is required to have high smoothness and flatness on its optical surface. Specifically, the optical surface is required to have a smooth surface having a surface roughness expressed by RMS (root mean square roughness) of 0.15 nm or less and a flatness of 50 nm or less.
Even if these required values are satisfied, localized concave defects called pits and scratches may still exist on the optical surface.

  Further, the EUVL optical member is excellent in resistance to a cleaning liquid used for cleaning the EUVL mask blank or EUVL mirror, or cleaning the EUVL mask after patterning the EUVL mask blank. Preferably there is.

In addition, the EUVL optical member preferably has high rigidity in order to prevent deformation due to the film stress of the reflective multilayer film and the absorber layer formed on the optical surface. In particular, those having a high specific rigidity of 3 × 10 ⁷ m ² / s ² or more are preferable.

The size, thickness, and the like of the EUVL optical member vary depending on the application, but when the application is an EUVL mask blank, the EUVL optical member is appropriately determined depending on the design value of the EUVL mask.
As a specific example, for example, there is an external shape of about 6 inches (152.4 mm) square and a thickness of about 0.25 inches (6.3 mm).

  When carrying out the smoothing method of the present invention, first, the optical surface of the EUVL optical member prepared in advance is polished with polishing abrasive grains such as cerium oxide, zirconium oxide, colloidal silica, etc., and then hydrofluoric acid, silica fluoride is used. The optical surface is washed with an acid solution such as acid or sulfuric acid, an alkali solution such as ammonia water, or pure water, and dried. When foreign particles or particles such as fibers are present on the optical surface, or when convex defects such as bumps are present on the optical member itself, these are removed by these procedures.

  The smoothing method of the present invention is preferably used for an optical surface from which convex defects have been removed by performing surface polishing and cleaning in the above-described procedure.

  When the size of the concave defect existing on the optical surface is very small, there is no possibility that the EUVL mask blank or EUVL mirror manufactured using the EUVL optical member is adversely affected. However, if there is a concave defect larger than a certain size on the optical surface, a concave defect appears on the surface of the reflective multilayer film or absorber layer formed on the optical surface, and the EUVL mask manufactured using the optical member It may become a defect of a blank or a mirror for EUVL.

  How large a concave defect exists on the optical surface is a defect of the EUVL mask blank or EUVL mirror, because it is affected by the diameter, depth and shape of the concave defect and the use of the optical member. However, in the case of an optical member used for manufacturing an EUVL mask blank, if a concave defect with a depth of more than 2 nm exists on the optical surface, the concave surface is formed on the surface of the reflective multilayer film or absorber layer formed on the optical surface. Even if a defect appears and becomes a defect of the EUVL mask blank, and a concave defect is not expressed on the surface of the reflective multilayer film or the absorber layer, the phase is disturbed by the structure being disturbed in the film. In some cases, it becomes a defect, and when it is 2 nm or less, it is not resolved and becomes a practical defect. Therefore, it is preferable to smooth the optical surface using the substrate smoothing method of the present invention.

  On the other hand, a large concave defect having a depth of 10 nm or more is more appropriate from the viewpoint of processing time, cost, etc., to be eliminated by polishing performed for the purpose of removing foreign matters existing on the optical surface and convex defects such as bumps. It is.

  Therefore, the smoothing method of the present invention is preferably used for an EUVL optical member having a concave defect with a depth of more than 2 nm and not more than 10 nm on the optical surface.

In the smoothing method of the present invention, the optical surface is smoothed by irradiating an optical surface having a concave defect with a carbon dioxide gas laser having a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ^2. The mechanism is not clear, but it is assumed that the optical surface is smoothed by reflowing the quartz glass around the concave defect heated by the irradiation of the carbon dioxide laser to fill the concave defect.

  The reason why the present inventors presume in this way is that the virtual temperature of the surface layer including the optical surface irradiated with the carbon dioxide laser increases, and the other part of the optical member, that is, the inside of the optical member (with the surface layer) In comparison with the optical surface, the virtual temperature is higher than that on the back surface side. Here, the depth of the surface layer where the fictive temperature rises due to the carbon dioxide laser irradiation depends on the thermal diffusion distance from the irradiation site and the penetration length of the laser beam, but a carbon dioxide laser with a wavelength of 10.6 μm and a pulse width of 1 msec or less is used The depth is 20 μm or less.

  In addition, in terms of reflow of quartz glass around the concave defect, the virtual temperature of the surface layer including the optical surface irradiated with the carbon dioxide laser is different from other parts of the optical member, that is, the inside of the optical member and the optical surface. It is preferably 30 ° C. or higher than the fictive temperature on the back side, more preferably 50 ° C. or higher, more preferably 100 ° C. or higher, and particularly preferably 150 ° C. or higher.

  Further, in terms of reflow of quartz glass around the concave defect, the fictive temperature of the surface layer including the optical surface irradiated with the carbon dioxide laser is preferably 1180 ° C. or higher, more preferably increased to 1200 ° C. or higher, It is more preferable that the temperature is increased to 1250 ° C. or higher, and it is particularly preferable that the temperature is increased to 1300 ° C. or higher.

In the smoothing method of the present invention, it is necessary to use a laser having a wavelength region having a high absorption coefficient for the material used for the EUVL optical member. A carbon dioxide laser with a wavelength of 10.6 μm has high absorption and high intensity with respect to SiO ₂ that forms a skeleton structure of a quartz glass material (3 to 10 wt%) to which TiO ₂ is added as a dopant. It is suitable as a laser used in the smoothing method of the present invention. Further, since the carbon dioxide laser can oscillate a pulse having a pulse width of 1 msec or less using an external modulator or the like, the thermal diffusion distance at the irradiation site is short, only the surface layer including the optical surface is heated, and the inside of the optical member is heated. Therefore, it is preferable in that the problem of deterioration of the flatness of the substrate, deformation, birefringence, and the like due to stress is very small.

When the peak intensity of the carbon dioxide laser is less than 0.5 kW / cm ² , the surface layer including the optical surface is not sufficiently heated, and the glass around the concave defect does not reflow and the optical surface cannot be smoothed. On the other hand, if the peak intensity of the carbon dioxide gas laser exceeds 1.5 kW / cm ² , ablation is induced, so that the surface roughness of the optical surface is remarkably deteriorated and the flatness of the optical member is unacceptably deteriorated. Problem arises. For the following reasons, the peak intensity of the carbon dioxide laser is more preferably 0.5 to 1.5 kW / cm ² .

When an optical surface having concave defects is irradiated with a carbon dioxide laser with a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ² , the concave defect depth repair rate of the optical surface defined by the following formula is obtained. It is particularly preferable because it is 50% or more.
Concave defect depth repair rate (%) = ((depth of concave defect before carbon dioxide laser irradiation (PV value)) − (depth of concave defect after carbon dioxide laser irradiation (PV value)) / (before carbon dioxide laser irradiation) Depth of concave defects (PV value)) × 100.

In the smoothing method of the present invention, the preferred range of peak intensity of a carbon dioxide laser for irradiating the optical surface is preferably 0.6~1.2W / cm ^2, at 0.65~1.0kW / cm ² More preferably, it is 0.7 to 0.9 kW / cm ² . As the carbon dioxide laser for irradiating the optical surface, it is preferable to use a laser having a short pulse width because the thermal diffusion distance at the irradiated portion is shortened. In this respect, a carbon dioxide laser with a pulse width of 1 msec or less is preferably used, a carbon dioxide laser with a pulse width of 0.7 msec or less is more preferred, and a carbon dioxide laser with a pulse width of 0.5 msec or less is further used. preferable.

  In the smoothing method of the present invention, the optical surface can be smoothed even when the carbon dioxide laser is irradiated as a pulse laser so that the number of shots at each irradiation site is 1. However, in order to increase the effect of smoothing the optical surface by reflowing quartz glass around the concave defect, it is preferable to irradiate the carbon dioxide laser so that the number of shots at each irradiation site is 1000 or more, more preferably The number of shots is 30000 or more, and more preferably the number of shots is 70000 or more. However, it should be noted that the time required to irradiate the optical surface with the carbon dioxide laser increases as the number of shots at each irradiation site increases. Although depending on the pulse width of the carbon dioxide laser, the number of shots at each irradiation site is preferably 100000 or less, more preferably 95000 or less, and further preferably 90000 or less. Note that the number of shots at each irradiation site can be adjusted by the repetition frequency of the carbon dioxide laser and the scanning speed of the carbon dioxide laser on the optical surface or the scanning speed of the optical surface with respect to the carbon dioxide laser.

  The smoothing of the optical surface by the carbon dioxide laser irradiation can also be achieved by irradiating only the portion of the optical surface where the concave defect exists with the carbon dioxide laser. However, it is very time-consuming and impractical to specify the position of the concave defect existing on the optical surface and irradiate the carbon dioxide laser toward the site where the concave defect exists. In this regard, since there are usually a plurality of concave defects on the optical surface, and a different apparatus is usually used for the identification of the position of the concave defect and the carbon dioxide laser irradiation, a carbon dioxide laser is used for the identified concave defect. This is particularly true in view of the possibility of misalignment during irradiation.

  On the other hand, when a carbon dioxide laser is irradiated on the entire optical surface, it is not necessary to specify the position of the concave defect existing on the optical surface, and even if there are multiple concave defects on the optical surface, the operation is performed once. Thus, the optical surface can be smoothed, so that the optical surface can be smoothed in a short time.

  In addition, in the case where a concave defect having a very small size that cannot be detected because its size is less than the detection limit of the defect inspection machine is present on the optical surface, it may cause inconvenience in manufacturing a mask blank for EUVL. However, by irradiating the entire optical surface with a carbon dioxide laser, it is possible to eliminate a small concave defect that cannot be detected by inspection of the optical surface.

For the reasons described above, in the smoothing method of the present invention, it is preferable to irradiate the entire optical surface with a carbon dioxide laser. In the smoothing method of the present invention, since a carbon dioxide laser with a wavelength of 10.6 μm is irradiated at a peak intensity of 0.5 to 1.5 kW / cm ² , even if the entire optical surface is irradiated with a carbon dioxide laser, the surface roughness of the optical surface is reduced. It does not cause problems such as a significant deterioration in roughness and an unacceptable deterioration in flatness.

  It should be noted that even if a concave defect exists on the optical surface of the EUVL optical member, there may be no problem in use. For example, in the case of an optical member used for an EUVL mask blank, even if the optical surface of the optical member is used, even if there is a concave defect in the EUVL mask blank other than a portion that becomes an exposure region for patterning, It doesn't matter. For example, the outer edge of the optical surface corresponds to this.

  Even if the optical surface of the EUVL optical member is fixed to a film forming apparatus or an exposure apparatus, there is no problem in use even if there is a concave defect in a portion held by a clamp or the like.

  Even on the optical surface of such an optical member for EUVL, it is not necessary to irradiate a carbon dioxide gas laser on a portion where the presence of a concave defect does not cause a problem in use of the optical member.

  However, in consideration of the small proportion of these parts in the optical surface and the advantages of irradiating the entire optical surface with a carbon dioxide laser, at least 88% (area ratio) of the optical surface is carbonic acid. It is preferable to irradiate the gas laser, more preferably 92% or more (area ratio) to irradiate the carbon dioxide laser, and more preferably 95% or more (area ratio) to irradiate the carbon dioxide laser.

  As described above, in the smoothing method of the present invention, it is preferable to irradiate the entire optical surface with a carbon dioxide laser, but the entire optical surface of the EUVL optical member is irradiated with the carbon dioxide laser having the above peak intensity with a single irradiation. It is impossible in reality. This is apparent from the fact that the EUVL mask blank has an outer shape of about 6 inches (152.4 mm) square. Therefore, in order to irradiate the carbon dioxide laser on the entire optical surface of the EUVL optical member, it is necessary to scan the carbon dioxide laser on the optical surface or to scan the optical surface with respect to the carbon dioxide laser light.

  A method of scanning the carbon dioxide laser on the optical surface or a method of scanning the optical surface with respect to the carbon dioxide laser light is not particularly limited. As shown in FIG. 1, a line beam is applied to the optical surface 11 of the EUVL optical member 10. It is possible to irradiate a carbon dioxide laser as 21 and scan the line beam 21 on the optical surface 11 of the EUVL optical member 10, or to scan the optical surface 11 with respect to the line beam 21. This is preferable because it is easy to uniformly irradiate the entire surface with a carbon dioxide laser and the entire optical surface 11 can be irradiated with the carbon dioxide laser in a short time. Scanning the optical surface 11 with respect to the line beam 21 is more preferable because the optical system is not driven.

  In FIG. 1, a line beam 21 having the same length as the long side of the optical surface 11 of the EUVL optical member 10 is scanned in the vertical direction in the drawing. This is preferable because the entire optical surface 11 of the EUVL optical member 10 can be irradiated with a carbon dioxide laser by scanning the line beam 21 once in the vertical direction in the drawing. However, the present invention is not limited to this, and a line beam having a shorter length than the long side of the optical surface 11 may be used. In this case, the optical surface 11 of the EUVL optical member 10 is divided into a plurality of regions according to the length of the line beam, and the line beam is scanned for each region. In this case, the carbon dioxide laser is irradiated twice at the boundary between adjacent regions. However, the influence on the optical surface due to the overlap irradiation of the carbon dioxide laser is slight and is particularly problematic. Will not cause. Rather, there is a problem that the time required to irradiate the entire optical surface increases due to the overlapping irradiation of the carbon dioxide laser, but especially if the width of the overlapping irradiation portion is suppressed to about 3 mm. It doesn't matter. These points are the same when scanning the optical surface 11 with respect to the line beam 21.

  In FIG. 1, a cylindrical lens 21 is used as an optical system for irradiating the line beam 21. However, the optical system to be used is not limited to this as long as the line beam 21 can be irradiated. For example, a diffractive optical element (DOE) or the like may be used.

  In the smoothing method of the present invention, the optical surface may be irradiated with a carbon dioxide laser while the EUVL optical member is heated. As described above, in the smoothing method of the present invention, it is considered that the optical surface is smoothed by reflowing the glass around the concave defect heated by the carbon dioxide laser irradiation to fill the concave defect. When the optical surface is irradiated with a carbon dioxide laser while the optical member is heated, it is expected that the peak intensity of the carbon dioxide laser necessary for reflowing the glass around the concave defect is reduced.

In the smoothing method of the present invention, since the optical surface is irradiated with a carbon dioxide laser, the surface roughness of the optical surface may be deteriorated, and the flatness of the optical member may be deteriorated. However, in the smoothing method of the present invention, since the carbon dioxide laser is irradiated at a peak intensity of 0.5 to 1.5 kW / cm ² , the surface roughness of the optical surface deteriorates and the flatness of the optical member occurs. But it is a minor one.

  When the optical surface is irradiated with a carbon dioxide laser while the EUVL optical member is heated, the peak intensity of the carbon dioxide laser necessary for reflowing the quartz glass around the concave defect is reduced, thereby reducing the surface roughness of the optical surface. It is expected that the deterioration of the roughness and the deterioration of the flatness of the optical member are further reduced, and further the deterioration of the surface roughness of the optical surface and the deterioration of the flatness of the optical member are prevented.

  For the purpose of obtaining the above effects, when the optical surface is irradiated with a carbon dioxide laser with the EUVL optical member heated, the optical member is preferably heated to 100 ° C. or higher, more preferably 300 ° C. or higher. It is more preferable to heat to 500 ° C. or higher. However, if the heating temperature of the optical member is too high, problems such as the deformation of the substrate, the influence of stress, and the increase of the processing time due to cooling occur, so the heating temperature is preferably 1050 ° C. or less, and 900 ° C. or less. It is more preferable that the temperature is 800 ° C. or lower.

  As described above, in the smoothing method of the present invention, the optical member may be slightly deteriorated in flatness by irradiating the optical surface with a carbon dioxide laser. In the case of an EUVL optical member, the flatness tolerance is extremely narrow, so it is preferable to keep the flatness generated in the optical member as low as possible.

  By adjusting the irradiation conditions of the carbon dioxide laser, the deterioration of flatness that occurs in the optical member can be suppressed to a low level, but the cause of the deterioration of flatness is that the optical surface is irradiated with a high energy carbon dioxide laser. In view of this, after irradiating the optical surface with a carbon dioxide laser, the back surface of the optical surface (hereinafter referred to as “back surface”) is irradiated with the carbon dioxide laser, and the optical surface is irradiated with the carbon dioxide laser. By increasing the flatness in the direction opposite to the deterioration direction, the deterioration of the flatness of the optical member can be reduced, and further, the deterioration of the flatness of the optical member can be eliminated.

  As described above, in the smoothing method of the present invention, it is preferable to irradiate the entire optical surface with a carbon dioxide laser. Therefore, when irradiating the rear surface with a carbon dioxide laser, it is preferable to irradiate the entire rear surface with a carbon dioxide laser. However, even on the optical surface, for the reason described above, the back surface of the portion not irradiated with the carbon dioxide laser does not need to be irradiated with the carbon dioxide laser.

  In addition, when the magnitude of deterioration of flatness generated when the optical surface is irradiated with a carbon dioxide laser can be predicted, the flatness generated when the optical surface is irradiated with the carbon dioxide laser in advance and the optical surface is irradiated with the carbon dioxide laser. The flatness may be increased in the direction opposite to the direction of deterioration. Even if it does in this way, the deterioration of the flatness of an optical member can be reduced, and also the deterioration of the flatness of an optical member can be eliminated.

For the purpose of reducing or eliminating the deterioration of the flatness of the optical member, it is preferable that the irradiation conditions are the same as those on the optical surface when the back surface is irradiated with a carbon dioxide laser. When looking at the peak intensity of the carbon dioxide laser, it is preferable that the peak intensity I ₁ of the carbon dioxide laser irradiated on the optical surface and the peak intensity I ₂ of the carbon dioxide laser irradiated on the back surface satisfy the following formula (1). It is more preferable to satisfy (2), and it is preferable that I ₁ and I ₂ are substantially the same.
0.5 ≦ I ₁ / I ₂ ≦ 1.5 (1)
0.9 ≦ I ₁ / I ₂ ≦ 1.1 (2).

  When the back surface is irradiated with a carbon dioxide laser, the fictive temperature of the surface layer including the back surface irradiated with the carbon dioxide laser also rises. Here, the depth of the surface layer where the fictive temperature rises and the extent to which the fictive temperature rises are the same as described for the carbon dioxide laser irradiation on the optical surface. Therefore, when the back surface is irradiated with a carbon dioxide laser, the optical member after the carbon dioxide laser irradiation has a higher virtual temperature than the inside of the optical member in the surface layer including the optical surface and the surface layer including the back surface.

As described above, in the smoothing method of the present invention, it is more preferable to irradiate an optical surface having a concave defect with a carbon dioxide gas laser having a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ^2. Can smooth the optical surface with a peak intensity of 0.5 to 1.5 kW / cm ² . Specifically, it is preferable that a concave defect with a depth of more than 2 nm does not exist on the optical surface after the carbon dioxide laser irradiation.

  As described above, in the case of an optical member used for manufacturing an EUVL mask blank, if a concave defect with a depth of more than 2 nm exists on the optical surface, a concave defect is formed on the surface of the reflective multilayer film or the absorber layer formed on the optical surface. May appear as a defect of the EUVL mask blank, and even if no concave defect is expressed on the surface of the reflective multilayer film or the absorber layer, the phase defect is caused by the disorder of the structure in the film. It may become.

  According to the substrate smoothing method of the present invention, the optical surface of the EUVL optical member becomes an optical surface excellent in smoothness that does not have a concave defect that becomes a problem when manufacturing an EUVL mask blank or EUVL mirror. .

  It is more preferable that there is no concave defect with a depth of 1.5 nm or more on the optical surface after the carbon dioxide laser irradiation, and it is further more preferable that there is no concave defect with a depth of 1.0 nm or more.

  According to the smoothing method of the present invention, by irradiating the optical surface with a carbon dioxide laser, the optical member is significantly deteriorated in flatness, which becomes a problem when manufacturing an EUVL mask blank or EUVL mirror. I will not let you. Specifically, the flatness of the optical member after carbon dioxide laser irradiation is preferably 50 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less.

  According to the smoothing method of the present invention, by irradiating the optical surface with a carbon dioxide gas laser, the surface of the optical surface is deteriorated so as to cause a problem when manufacturing a mask blank for EUVL or a mirror for EUVL. The optical surface can be smoothed without any trouble. Specifically, the surface roughness (RMS) of the optical surface after carbon dioxide laser irradiation is preferably 0.15 nm or less, more preferably 0.12 nm or less, and further preferably 0.1 nm or less.

  If the surface roughness (RMS) of the optical surface is 0.15 nm or less, since the optical surface is sufficiently smooth, there is no possibility that the reflective multilayer film formed on the optical surface is disturbed. If the reflective multilayer film is disturbed, there is a risk of defects in the EUVL mask blank or EUVL mirror to be manufactured. Further, in the EUVL mask manufactured using the EUVL mask blank, the pattern edge roughness does not increase and the pattern dimensional accuracy is good. When the surface roughness of the optical surface is large, the surface roughness of the reflective multilayer film formed on the optical surface increases, and further, the surface roughness of the absorber layer formed on the reflective multilayer film increases. As a result, the edge roughness of the pattern formed on the absorber layer is increased, and the dimensional accuracy of the pattern is deteriorated.

  The surface roughness (RMS) of the optical surface after carbon dioxide laser irradiation is preferably 0.1 nm or less.

As described above, in the optical member whose optical surface has been smoothed by the smoothing method of the present invention, the fictive temperature of the surface layer including the optical surface irradiated with the carbon dioxide laser increases, and other parts of the optical member, that is, The fictive temperature is higher in the optical member and on the optical surface than on the back surface side.
On the other hand, when the carbon dioxide laser is also irradiated on the back surface, the fictive temperature of the surface layer including the optical surface and the surface layer including the back surface is higher than the inside of the optical member.

  By increasing the fictive temperature of the surface layer, it is expected that the mechanical strength of the surface layer, for example, Young's modulus, fracture toughness value, and fatigue characteristics are improved.

In the smoothing method of the present invention, since a carbon dioxide laser with a wavelength of 10.6 μm is irradiated at a peak intensity of 0.5 to 1.5 kW / cm ² , a surface layer including an optical surface and a surface layer including a back surface (a carbon dioxide laser is applied to the back surface). When irradiated, local structural defects are formed.

  When manufacturing an EUVL mask blank or EUVL mirror, the EUVL optical member of the present invention forms a reflective multilayer film or absorber layer on the optical surface, so that local structural defects are formed on the optical surface. However, there is no particular problem. Further, even if a structural defect is formed on the back surface, there is no problem when used as a EUVL mask blank or EUVL mirror.

A quartz glass substrate containing TiO ₂ as a dopant (TiO ₂ concentration 7.0 mass%) (manufactured by Asahi Glass Co., Ltd., product number AZ6025, 150 mm square) was prepared. The depth of the concave defects scattered on the surface of the quartz glass substrate was measured with an atomic force microscope.

A carbon dioxide laser was irradiated under the conditions shown in Table 1 to the region where the concave defect on the substrate surface was generated. The carbon dioxide laser was applied to the substrate as a focused beam (1.5 mm diameter) using a ZnSe plano-convex lens as an irradiation optical system. The PV value (depth of the concave defect) of the concave defect on the substrate surface after irradiation was measured using an atomic force microscope. The results are shown in Table 1. In Table 1, the concave defect depth repair rate was determined by the following formula.
Concave defect depth repair rate (%) = ((depth of concave defect before carbon dioxide laser irradiation (PV value)) − (depth of concave defect after carbon dioxide laser irradiation (PV value)) / (before carbon dioxide laser irradiation) Depth of concave defect (PV value)) × 100

In Example 1, since the irradiation peak intensity was 0.4 kW / cm ² and the irradiation conditions were not appropriate, the concave defect was not repaired. Particularly, in Example 2 in which the irradiation peak intensity of the carbon dioxide laser was 0.7 kW / cm ² , the concave defect repair rate was particularly excellent at 100%. In Example 3, the irradiation peak intensity exceeded 1.5 kW / cm ² , and the ablation occurred because the irradiation conditions were not appropriate.

  A quartz glass substrate similar to the above was prepared. The carbon dioxide laser was applied to the substrate as a focused beam (1.5 mm diameter) using a ZnSe plano-convex lens as an irradiation optical system. The fictive temperature of the carbon dioxide laser irradiation region and the fictive temperature of the back surface with respect to the irradiated surface were determined by performing respective FTIR spectrum measurements.

It is known that the peak of the FTIR spectrum of the quartz glass material, for example, the peak showing Si—O—Si stretching varies depending on the fictive temperature of the quartz glass material. Using a quartz glass material having the same composition as that of the glass substrate, a plurality of samples having different fictive temperatures were prepared, and FTIR spectrum measurement of the sample surface was performed. The wave number (cm ⁻¹ ) of the peak indicating the obtained Si—O—Si stretching was plotted in relation to the fictive temperature (° C.), and it was confirmed that there was a linear correlation between the two. Using this plot as a calibration curve, from the wave number (cm ⁻¹ ) of the peak indicating the Si—O—Si stretching obtained from the FTIR spectrum measurement of the carbon dioxide laser irradiated surface and the back surface of the glass substrate, The fictive temperatures of the carbon dioxide laser irradiated surface and the back surface were determined. The results are shown in FIGS.

FIG. 1 is a schematic diagram showing a state in which a carbonic acid laser is irradiated as a line beam on the optical surface of an EUVL optical member. FIG. 2 is a graph showing the dependence of the fictive temperature of the carbonic acid laser irradiation surface on the irradiation peak intensity. FIG. 3 is a graph showing the irradiation peak intensity dependence of the fictive temperature of the back surface with respect to the carbon dioxide laser irradiation surface.

Explanation of symbols

10: Optical member for EUVL 11: Optical surface 20: Cylindrical lens 21: Line beam (carbonic acid laser)

Claims (17)

Contains TiO _2, with respect to the optical surface having a concave defect of the quartz glass material made of EUV lithography (EUVL) for optical members as a main component SiO _2, the peak intensity carbon dioxide laser having a wavelength of 10.6 [mu] m 0.5 The method of smoothing the optical surface of the optical member for EUVL by irradiating at -1.5kW / cm < ² >. By irradiating the optical surface having concave defects of the EUVL optical member with a carbon dioxide laser having a wavelength of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ² , EUVL defined by the following formula: The method for smoothing the optical surface of an EUVL optical member according to claim 1, wherein the concave defect depth repair rate of the optical surface of the optical member for use is 50% or more.
Concave defect depth repair rate (%) = ((depth of concave defect before carbon dioxide laser irradiation (PV value)) − (depth of concave defect after carbon dioxide laser irradiation (PV value)) / (before carbon dioxide laser irradiation) Depth of concave defects (PV value) x 100 The optical surface of the EUVL optical member having a concave defect with a depth of more than 2 nm and not more than 10 nm is irradiated with a carbon dioxide gas laser of 10.6 μm at a peak intensity of 0.5 to 1.5 kW / cm ² , and (1) to The method of smoothing the optical surface of the EUVL optical member according to claim 1, wherein the optical member satisfies (3).
(1) There is no concave defect with a depth of more than 2 nm on the optical surface after the carbon dioxide laser irradiation.
(2) Flatness of the optical member after carbon dioxide laser irradiation is 50 nm or less.
(3) Surface roughness (RMS) of the optical surface after carbon dioxide laser irradiation is 0.15 nm or less.   4. The method of smoothing the optical surface of an EUVL optical member according to claim 1, wherein the carbon dioxide laser is irradiated to the entire optical surface of the EUVL optical member. 5. The method for smoothing the optical surface of an EUVL optical member according to claim 1, wherein the EUVL optical member has a TiO ₂ concentration of 3 to 10% by mass.   6. The method of smoothing an optical surface of an optical member for EUVL according to claim 1, wherein a pulse width of the carbon dioxide laser is 1 msec or less.   The optical surface of the EUVL optical member according to any one of claims 1 to 6, wherein the optical surface is irradiated with the carbon dioxide laser so that the number of shots at each irradiation site is 1000 to 100,000. How to turn.   8. The optical surface is irradiated with the carbon dioxide laser as a line beam, and the line beam is scanned on the optical surface, or the optical surface is scanned with respect to the line beam. The method of smoothing the optical surface of the optical member for EUVL in any one of. Furthermore, the carbon dioxide laser with a wavelength of 10.6 micrometers is irradiated with the peak intensity of 0.5-1.5 kW / cm < ² > with respect to the back surface with respect to the said optical surface. A method of smoothing the optical surface of an EUVL optical member.   The method of smoothing the optical surface of the optical member for EUVL according to claim 9, wherein the carbon dioxide laser is irradiated on the entire back surface. The EUVL according to claim 9 or 10, wherein the peak intensity I ₁ of the carbon dioxide laser irradiated to the optical surface and the peak intensity I ₂ of the carbon dioxide laser irradiated to the back surface satisfy the relationship of the following formula. Of smoothing the optical surface of the optical member for use.
0.5 ≦ I ₁ / I ₂ ≦ 1.5   The method for smoothing the optical surface of an EUVL optical member according to any one of claims 9 to 11, wherein a pulse width of the carbon dioxide laser irradiated to the back surface is 1 msec or less.   The optical surface of the optical member for EUVL according to any one of claims 9 to 12, wherein the back surface is irradiated with the carbon dioxide laser so that the number of shots at each irradiation site is 1000 to 100,000. how to.   14. The back surface is irradiated with the carbon dioxide laser as a line beam, and the line beam is scanned on the back surface, or the back surface is scanned with respect to the line beam. The method of smoothing the optical surface of the optical member for EUVL as described in 1 above.   The method of smoothing the optical surface of the optical member for EUVL according to any one of claims 1 to 14, wherein the optical surface is irradiated with a carbon dioxide laser while the optical member is heated to 100 to 1050 ° C.   9. An EUVL optical member obtained by the method according to claim 1, wherein the fictive temperature of the surface layer including the optical surface is 30 ° C. or more higher than the fictive temperature of the remaining part.   The virtual temperature of the surface layer including the optical surface and the virtual temperature of the surface layer including the back surface obtained by the method according to any one of claims 9 to 14 are 30 ° C or higher than the virtual temperature inside the optical member. EUVL optical member characterized by being high.

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