KR20100032865A - Method for removing foreign matter from glass substrate surface and method for processing glass substrate surface - Google Patents

Abstract

An object of the invention is to provide a method for removing foreign matter from a glass substrate surface to be finish-processed by a method accompanied with beam irradiation or laser light irradiation on the glass substrate surface. The present invention relates to a method for removing foreign matter from a glass substrate surface, which includes subjecting the glass substrate surface to gas cluster ion beam etching at an accelerating voltage of from 5 to 15 keV.

Description

METHODS FOR REMOVING FOREIGN MATTER FROM GLASS SUBSTRATE SURFACE AND METHOD FOR PROCESSING GLASS SUBSTRATE SURFACE}

The present invention provides a method for removing foreign matter from the surface of a glass substrate, particularly a glass substrate surface requiring high flatness, such as a glass substrate used for reflective masks for extreme ultraviolet (EUV) lithography in semiconductor manufacturing processes. The present invention relates to a method for removing foreign matter from the body. More specifically, it is processed by a method involving beam irradiation or laser light irradiation on the surface of a glass substrate, such as ion beam etching, gas cluster ion beam etching, plasma etching, and nano-abrasion by laser light irradiation. It relates to a method for removing foreign matter from the glass substrate surface.

In addition, the present invention involves removing the foreign matter from the glass substrate surface, followed by beam irradiation or laser light irradiation on the glass substrate surface, such as ion beam etching, gas cluster ion beam etching, plasma etching, nano-wear by laser light irradiation. It relates to a method of processing a glass substrate surface by a method.

BACKGROUND In lithographic techniques, exposure apparatuses for fabricating integrated circuits by transferring fine circuit patterns onto a wafer have been widely used. With the trend of higher integration, higher speed, and higher functionality of integrated circuits, integrated circuits have become smaller. For this reason, it is required for an exposure apparatus to form a circuit pattern on a wafer surface with a deep depth of focus and high resolution, and shortening of the exposure light source is progressing. The exposure light source is further advanced in the conventional g line (wavelength: 436 nm), i line (wavelength: 365 nm), KrF excimer laser (wavelength: 248 nm), and ArF excimer laser (wavelength: 193 nm) is used. Getting started. In addition, in order to cope with next-generation integrated circuits in which the line width of the circuit becomes 100 nm or less, it is promising to use an F ₂ laser (wavelength: 157 nm) as the exposure light source. However, this is also considered to be covered only by generations with line widths up to 70 nm.

Under these technical trends, lithography techniques using EUV light as the next generation exposure light sources are considered to be applicable for a plurality of generations having a line width of 45 nm or more and attract attention. EUV light refers to light in the wavelength range of the soft X-ray region or the vacuum ultraviolet region, and specifically refers to light having a wavelength of about 0.2 to 100 nm. At this point, the use of 13.5 nm as a lithographic light source is considered. The exposure principle of this EUV lithography (hereinafter abbreviated as "EUVL") is the same as conventional lithography in that the mask pattern is transferred using a projection optical system. However, since there is no material that can transmit light in the energy region of EUV light, the refractive optical system cannot be used, and the reflective optical system is inevitably used (see Patent Document 1 below).

The mask used for EUVL basically consists of (1) glass substrate, (2) reflective multilayer film formed on glass substrate, and (3) absorber layer formed on reflective multilayer film.

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 on a nanometer scale is used, and Mo and Si are known as representative materials. Moreover, Ta and Cr are examined as a material for an absorber layer. As a glass substrate, the material which has a low thermal expansion coefficient which does not generate distortion even if it puts on EUV light irradiation is needed, The use of the glass which has a low thermal expansion coefficient or the crystallized glass which has a low thermal expansion coefficient is examined. In the present specification, the glass having a low thermal expansion coefficient and the crystallized glass having a low thermal expansion coefficient are collectively referred to as "low expansion glass" or "ultra low expansion glass".

As the low expansion glass or the ultra low expansion glass used as a mask for EUVL, it is a quartz glass mainly composed of SiO ₂ , and TiO ₂ , SnO ₂ or ZrO ₂ is most widely added as a dopant to reduce the coefficient of thermal expansion of the glass. Used.

A glass substrate is manufactured by processing and washing the raw material of glass or crystallized glass with high precision. In the case of processing a glass substrate, the glass substrate surface is usually pre-polished at a relatively high processing speed until the desired flatness and surface roughness, and foreign matter such as polishing dust generated by preliminary polishing is removed by cleaning and After that, the glass substrate surface is finished to have the desired flatness and surface roughness by a method having higher processing accuracy. As a method of high processing accuracy used for finishing, a method involving beam irradiation or laser light irradiation on the surface of a glass substrate, such as ion beam etching, gas cluster ion beam etching, plasma etching, and nano wear by laser light irradiation. This is preferably used.

However, foreign matter not completely removed by washing may remain, or new foreign matter may adhere to the glass substrate surface after washing. The glass substrate surface in which such foreign matter exists is finished by the method which involves beam irradiation or laser beam irradiation on the glass substrate surface, such as ion beam etching, gas cluster ion beam etching, plasma etching, and nano wear by laser beam irradiation. If so, the portion where the foreign matter is present on the glass substrate surface is not processed, and subsequent cleaning to remove the foreign matter from the glass substrate surface has a problem of creating convex glass defects.

Patent Document 1: JP-T-2003-505891

In order to solve the above problems of the prior art, the present invention involves beam irradiation or laser light irradiation on the surface of a glass substrate, such as ion beam etching, gas cluster ion beam etching, plasma etching, nano wear by laser light irradiation. It is an object of the present invention to provide a method for removing foreign matter from a glass substrate surface to be finished by a method.

In addition, the present invention involves removing the foreign matter from the glass substrate surface, followed by beam irradiation or laser light irradiation on the glass substrate surface, such as nano-wear by ion beam etching, gas cluster ion beam etching, plasma etching and laser light irradiation. It is an object of the present invention to provide a method of processing the surface of the glass substrate by a method.

In order to achieve the above object, the present invention provides a method for removing foreign matter from the glass substrate surface, comprising performing a gas cluster ion beam etching with an acceleration voltage of 5 to 15 keV on the glass substrate surface.

In addition, the present invention performs a gas cluster ion beam etching on the glass substrate surface as a source gas of one or more gases selected from the group consisting of O ₂ , Ar, B, CO ₂ , N ₂ , N ₂ O and boron hydride. It provides a method for removing foreign matter from the glass substrate surface comprising the step of.

Hereinafter, each method described in the two paragraphs described above in the present invention is referred to as "the foreign material removing method of the present invention".

In the foreign matter removing method of the present invention, it is preferable to perform gas cluster ion beam etching under the condition that the etching amount is 20 nm or less.

In the foreign material removal method of the present invention, it is preferable that the glass substrate is made of low expansion glass having a coefficient of thermal expansion of 20 ° C or 50 ° C to 80 ° C of 0 ± 30 ppb / ° C.

In the foreign matter removal method of the present invention, it is preferable that the surface of the glass substrate before performing the gas cluster ion beam etching has a surface roughness (Rms) of 5 nm or less.

In the foreign matter removing method of the present invention, it is preferable to perform gas cluster ion beam etching under a condition that the cluster size is 2000 or more.

In the foreign matter removing method of the present invention, it is preferable to perform gas cluster ion beam etching while maintaining the angle formed by the normal of the glass substrate and the gas cluster ion beam incident on the glass substrate surface at 3 to 60 °.

Here, it is preferable to perform gas cluster ion beam etching, maintaining the said glass substrate surface in 3 to 60 degrees downward state with respect to a horizontal direction.

In addition, the present invention is the step of removing the foreign matter on the surface of the glass substrate by the foreign matter removal method of the present invention, and

A method of processing a glass substrate surface, comprising processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching, and nano wear (hereinafter, " Processing method (1) ".

In the processing method (1) of this invention, it is preferable that the said processing method is gas cluster ion beam etching.

Here, as a source gas, 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 ; And gas cluster ion beam etching of the processing step with an acceleration voltage exceeding 15 keV using a mixed gas selected from the group consisting of a mixed gas of NF ₃ , Ar and N ₂ .

The source gas may be 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 ; And a mixed gas selected from the group consisting of a mixed gas of NF ₃ , Ar, and O ₂ .

In addition, the present invention comprises the steps of measuring the flatness of the glass substrate surface,

Removing foreign substances on the surface of the glass substrate by the foreign substance removing method of the present invention, and

Processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching and nano wear,

In processing the glass substrate surface, setting processing conditions of the glass substrate surface for each portion of the glass substrate based on the result obtained from measuring the flatness of the glass substrate surface. A method of processing the surface (hereinafter referred to as "processing method (2) of the present invention") is provided.

In the processing method (2) of the present invention, the processing method is ion beam etching, gas cluster ion beam etching, or plasma etching, and the glass substrate surface is based on the result obtained from measuring the flatness of the glass substrate surface. It is preferable to specify the width of the wave pattern present in the surface of the glass substrate, and to process the surface of the glass substrate with a beam having a beam diameter of FWHM (full width of half maximum).

Here, the FWHM value of the beam diameter is preferably 1/2 or less of the width of the wave pattern.

In the processing method (2) of the present invention, the processing method is gas cluster ion beam etching, and 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 ; And gas cluster ion beam etching of the processing step at an acceleration voltage exceeding 15 keV using any one of the mixed gases selected from the group consisting of mixed gases of NF ₃ , Ar and N ₂ .

The source gas may be 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 ; NF _3, and more preferably any one of a mixed gas, selected from the group consisting of a gas mixture of Ar and O _2.

In the processing methods (1) and (2) of the present invention, it is preferable to perform the second processing step for improving the surface roughness of the glass substrate surface following the processing of the glass substrate surface.

As the second processing step, O ₂ gas alone, or a mixed gas of O ₂ and at least one gas selected from the group consisting of Ar, CO and CO ₂ as a source gas at an acceleration voltage of 3 keV or more and less than 30 keV It is preferable to perform gas cluster ion beam etching.

Also, as the second processing step, it is preferable to perform mechanical polishing at a surface pressure of 1 to 60 gf / cm 2 using the polishing slurry.

The present invention also provides a glass substrate obtained by the processing method of the present invention, wherein the substrate surface has a flatness of 50 nm or less and no convex glass defects having a height of more than 1.5 nm.

According to the present invention, the glass substrate surface is finished by a method involving beam irradiation or laser light irradiation on the glass substrate surface, such as ion beam etching, gas cluster ion beam etching, plasma etching, nano wear by laser light irradiation. If so, after processing, the formation of convex glass defects on the glass substrate surface can be prevented, and the glass substrate surface can be processed into a surface having excellent flatness and surface roughness.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows the relationship between the processing surface of a board | substrate and GCIB in the foreign material removal method of this invention.

Reference numerals used in the drawings are as described below, respectively.

1: substrate

10: machining surface

Best Mode for Carrying Out the Invention

The foreign material removal method of the present invention is a glass which is finished by a method involving beam irradiation or laser light irradiation on the glass substrate surface, such as ion beam etching, gas cluster ion beam etching, plasma etching and nano wear by laser light irradiation. It is a method of removing foreign matter from the substrate surface (hereinafter also referred to as "processing surface"), that is, the processing surface before finishing processing.

This machined surface is cleaned before performing the finishing process. In such a case, foreign matter that could not be completely removed by washing may remain or new foreign matter may adhere to the surface of the glass substrate after washing. The foreign material removal method of the present invention aims to remove such foreign matter.

The foreign substance targeted by the foreign substance removal method of the present invention refers to a substance which is adhered to the processed surface by van der Waals force, rather than a material that adheres to the processed surface by chemical bonding, and its size is usually about 1 to 2 mu m or less.

The glass substrate targeted by the foreign material removal method of the present invention is a glass substrate for a reflective mask for EUVL, which can mainly cope with high integration and high precision of an integrated circuit. Glass substrates used for this purpose are glass substrates having a small coefficient of thermal expansion and a small scattering. The glass substrate is preferably made of a low expansion glass having a coefficient of thermal expansion of 0 ± 30 ppb / ° C at 20 ° C. or 50 ° C. to 80 ° C., and an extremely low thermal expansion coefficient of 0 ± 10 ppb / ° C. at 20 ° C. or 50 ° C. to 80 ° C. It is more preferable that it is made of expanded glass.

The shape, size and thickness of the glass substrate are not particularly limited. In the case of the board | substrate for EUVL reflective masks, the shape is a plate-shaped object whose plane shape is rectangular.

It is preferable that the processing surface is preprocessed so that the glass substrate which the foreign material removal method of this invention makes object may have predetermined flatness and surface roughness.

Although ion beam etching, gas cluster ion beam etching, plasma etching and nano-abrasion used for the preliminary processing of the machining surface can process the glass substrate surface to a surface of good flatness and surface roughness, these processing methods are conventional Compared with mechanical polishing, the processing rate is poor, especially when processing a large area glass substrate surface. On the other hand, as will be described later in detail, the foreign matter removal method of the present invention is a method for removing foreign matter present on the processed surface without substantially processing the processed surface. For this reason, before performing the foreign material removal method of this invention, it is preferable to preprocess a process surface to predetermined flatness and surface roughness by the processing method which has a comparatively high processing rate.

The processing method used for preliminary processing is not specifically limited, It can be selected widely from the well-known processing methods used for the process of the glass surface. However, by using a polishing pad having a large processing rate and a large surface area, a large area can be polished at once, and therefore a mechanical polishing method is usually used. The mechanical polishing method referred to in the present specification includes not only polishing by abrasive action by abrasive grains, but also a method of using a polishing slurry in combination with abrasive action by chemicals and chemical polishing action by chemicals. The mechanical polishing method may be any of lapping and polishing, and the abrasives and abrasives used may also be appropriately selected from those known in the art. When using the mechanical polishing method, in order to increase the processing rate, lapping is preferably performed at a surface pressure of 30 to 70 gf / cm 2, more preferably at a surface pressure of 40 to 60 gf / cm 2, and polishing In the case of polishing, polishing is preferably performed at a surface pressure of 60 to 140 gf / cm 2, and more preferably at a surface pressure of 80 to 120 gf / cm 2. Lapping is preferably carried out to have a lapping amount of 100 to 300 µm, and polishing is preferably performed to have a polishing amount of 1 to 60 µm.

When performing preliminary processing, it is preferable that the surface roughness Rms of the processed surface after preprocessing is 5 nm or less, and it is more preferable that it is 1 nm or less. In this specification, the surface roughness means the surface roughness measured with the atomic force microscope about the area of 1-10 micrometer <^2> . When the surface roughness of the glass substrate after the preliminary processing exceeds 5 nm, it takes considerable time to finish the processed surface to have a predetermined flatness and surface roughness after implementing the foreign matter removing method of the present invention, which increases the cost. It becomes a factor.

The foreign matter removal method of the present invention is a processing surface by etching a gas cluster ion beam (hereinafter referred to as "GCIB") under specified conditions (hereinafter referred to as "low etching conditions") with a small etching amount with respect to the processing surface. It is characterized in that the foreign matter is removed from the processing surface while making the processing amount very small.

GCIB etching described herein forms a gas cluster by ejecting a reactive substance (source gas), which is gaseous at normal temperature and atmospheric pressure, into a vacuum apparatus under pressure through an expansion nozzle, and then irradiates electronized GCIB with electron irradiation. It is a method of irradiating and etching an object. Gas clusters are usually composed of agglomerate groups of atoms or molecules of thousands of atoms or molecules. In the foreign matter removal method of the present invention, when GCIB etching is performed on the processing surface, when a gas cluster collides with the processing surface, a multi-impact effect is generated by interaction with a solid, and foreign matter is removed from the processing surface. . And since GCIB etching is performed with respect to a process surface in low etching conditions, a process surface is not processed substantially.

In the foreign matter removal method of the present invention, a portion where foreign matter exists in the processed surface can be identified, and GCIB etching can be selectively performed on the portion. However, it is difficult to specify a portion where minute foreign matters having a size of about 1 to 2 mu m or less exist, and to selectively perform GCIB etching on the portion. Therefore, GCIB etching is usually performed at low etching conditions on the entire processed surface. In this case, GCIB needs to be scanned on the machined surface ���. As a method of injecting GCIB, although luster scanning and spiral scanning are known, any of these may be used.

In the first embodiment of the foreign matter removing method of the present invention, in order to perform GCIB etching on the processing surface at low etching conditions, the acceleration voltage applied to the acceleration electrode is controlled to 5 to 15 keV. In this case, the source gas used when performing GCIB etching for the finishing processing of the glass substrate surface may be a source gas used conventionally. Specific examples of such conventional source gases include, for example, SF ₆ , NF ₃ , CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₆ , SiF ₄ and COF ₂ alone Or it can mix and use.

By controlling the acceleration voltage applied to the accelerating electrode to 5 to 15 keV, even when a source gas used in the past is used when performing GCIB etching for the finishing of the processing surface, the etching amount of the processing surface is sufficiently low, It is possible to remove the foreign matter present on the processing surface without substantially processing. If the acceleration voltage is less than 5 keV, since the kinetic energy is small when the gas cluster collides with the processing surface, foreign matter existing on the processing surface cannot be removed depending on the size of the foreign matter. Specifically, foreign matters having a size of about 1 to 2 μm cannot be removed. If the acceleration voltage exceeds 15 keV, the kinetic energy is large when the gas cluster collides with the machining surface. Therefore, the action of etching the processed surface becomes more prominent than the action of removing the fine foreign matter present on the processed surface, and when foreign matter is present on the processed surface, only the part of the processed surface where the foreign matter is left without being etched is etched. This results in the problem of generating convex defects on the finished surface by finishing processing by means of cleaning and removing foreign matters.

As for the acceleration voltage, it is more preferable that it is 5-10 keV.

In a second embodiment of the foreign material removal method of the present invention, in order to perform GCIB etching on the processed surface at low etching conditions, O ₂ , Ar, B, CO ₂ , N ₂ , N ₂ O and boron hydride (for example, , BH ₃ , B ₄ H ₁₀ ) is subjected to GCIB etching using one or more gases selected from the group as the source gas. This kind of gas hardly causes a chemical reaction when it collides with the working surface, so that the action of etching the working surface is extremely weak. When GCIB etching is performed using such a gas type using a source gas, it is possible to remove foreign substances present on the processed surface without substantially processing the processed surface.

In the second embodiment of the foreign matter removing method of the present invention, the acceleration voltage for applying the kind of gas whose etching action is extremely weak to the acceleration electrode is not particularly limited. However, an acceleration voltage of 15 keV or more is preferable in that it removes foreign matter present in the processing surface without substantially processing the processing surface. As for an acceleration voltage, 20 keV or more is more preferable, and 30 keV or more is more preferable. If the acceleration voltage is less than 15 keV, since the kinetic energy is small when the gas cluster collides with the processing surface, there is a concern that foreign matter existing on the processing surface cannot be removed depending on the size of the foreign matter. However, even if the acceleration voltage is less than 15 keV, it is possible to remove foreign substances present on the processed surface by adjusting the cluster size, dose amount, irradiation time and the like.

According to the first embodiment and the second embodiment of the foreign matter removing method of the present invention described above, since the GCIB etching is performed on the processed surface at low etching conditions, the processing surface does not substantially process the processing surface, Foreign material can be removed. In the present specification, the low etching conditions are preferably conditions in which the etching amount is 20 nm or less, and more preferably conditions in which the etching amount is 10 nm or less.

In the first and second embodiments of the foreign material removal method of the present invention, irradiation conditions such as the cluster size, the ionization current applied to the ionizing electrode of the GCIB etching apparatus to ionize the cluster, and the dose of the GCIB are determined by the source gas. It may be appropriately selected depending on the type of the, the acceleration voltage applied to the acceleration electrode and the like. It is preferable to perform GCIB etching under the condition that the cluster size is 2000 or more. When the cluster size is 2000 or more, a relatively large gas cluster collides with the working surface, and therefore, the effect of removing foreign matter present on the working surface by the multiple collision effect is expected to be improved. The cluster size is more preferably 3000 or more, particularly preferably 5000 or more.

In 1st Embodiment and 2nd Embodiment of the foreign material removal method of this invention, it is preferable to irradiate GCIB with respect to a process surface from the diagonal direction. When the GCIB is irradiated to the machined surface from the inclined direction, the effect of removing foreign matter present on the machined surface by the multiple collision effect is expected to be improved. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the state which irradiates GCIB with respect to a process surface from the diagonal direction. In FIG. 1, the angle θ formed by the normal line N of the glass substrate 1 (thus, the normal line N of the machined surface 10) and the GCIB incident on the machined surface 10 are 3 to 60 degrees. It is preferable to keep it at °. By maintaining the angle θ at 3 ° or more, the improvement of the effect of removing foreign matters from the processing surface by the multiple collision effect is expected. On the other hand, if angle (theta) is kept over 60 degrees, the spot shape of GCIB in a process surface will become remarkably ellipse shape. Therefore, when the gas cluster collides with the machined surface, the kinetic energy is dispersed, and the effect of removing foreign matter present on the machined surface is lowered. In addition, since the spot shape of the GCIB on the processed surface becomes remarkably elliptical, there is a fear that the flatness of the processed surface after the GCIB etching is deteriorated.

It is more preferable to maintain the angle θ at 10 to 60 °, and more preferably to maintain the angle θ at 30 to 60 °.

When irradiating GCIB with respect to a process surface from the inclination direction, as shown in FIG. 1, GCIB is irradiated to a horizontal direction with the process surface 10 maintained 3 to 60 degrees downward with respect to the horizontal direction. It is desirable to. By doing so, the effect of removing foreign matters from the machined surface by the multi-impact effect can be improved and at the same time, the foreign matters removed can be prevented from reattaching to the machined surface. It is preferable to keep the process surface 10 in 10-60 degree downward state with respect to a horizontal direction, and it is more preferable to maintain at 30-60 degree.

The processing method (1) of the present invention comprises the steps of removing the foreign matter on the surface of the glass substrate by the foreign matter removing method of the present invention (hereinafter referred to as the "foreign matter removing step") and ion beam etching, GCIB etching, plasma etching and Processing the glass substrate surface by a processing method selected from the group consisting of nano-abrasion (hereinafter referred to as "processing step").

When the processed surface is preliminarily polished to a predetermined flatness and surface roughness, the foreign matter existing on the processed surface is removed by the above-described foreign material removing method of the present invention, followed by ion beam etching, GCIB etching, plasma etching and nano wear. The machining surface is finished by a machining method selected from the group consisting of.

In addition, in order to prevent new foreign matter from adhering to the processing surface after the foreign matter removing step, the foreign matter removing step and the processing step may be performed in the same chamber or arranged side by side in such a manner that the substrate can be transported without taking out the substrate from the apparatus. It is preferable to carry out in a preformed chamber. When GCIB etching is used in the machining step, it is preferable to use the same GCIB etching apparatus in the debris removing step and the machining step.

Of the above processing methods, it is preferable to use GCIB etching because the surface can be processed to have a small surface roughness and excellent smoothness.

When using GCIB etching, as the source gas, SF ₆ , Ar, O ₂ , N ₂ , NF ₃ , N ₂ O, CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₆ , SiF _4, COF ₂ may be used alone or in combination, such as a gas. Among these, SF ₆ , NF ₃ , CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₆ , SiF _4, and COF ₂ are characterized in terms of chemical reactions occurring when gas clusters collide with the machined surface. Excellent as a source gas. Among them, a mixed gas containing SF ₆ or NF ₃ , specifically, a mixed gas of SF ₆ and O ₂ , a mixed gas of SF ₆ , Ar and O ₂ , a mixed gas of NF ₃ and O ₂ , NF ₃ , Ar And a mixed gas of O ₂ , a mixed gas of NF ₃ and N ₂ , and a mixed gas of NF ₃ , Ar, and N ₂ are preferable for reasons of high etching rate and improvement in processing tact. In these mixed gases, although the suitable mixing ratio of each component changes with conditions, such as irradiation conditions, it is preferable that they are each below.

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 / O 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 )

Among these mixed gases, a mixed gas of SF ₆ and O ₂ , a mixed gas of SF ₆ , Ar and O ₂ , a mixed gas of NF ₃ and O ₂ , and a mixed gas of NF ₃ , Ar and O ₂ are preferable.

For example, irradiation conditions such as the cluster size, the ionization current applied to the ionization electrode of the GCIB etching apparatus to ionize the cluster, and the dose of the GCIB may be determined by the type of source gas, the surface properties of the processed surface, the purpose of finishing, and the like. Therefore, it can be appropriately selected. For example, when finishing finishing for the purpose of improving the flatness of the processed surface after preliminary processing, it is preferable that the acceleration voltage applied to the acceleration electrode is more than 15 keV, and the surface roughness of the processed surface is not excessively deteriorated. In order to improve the flatness, it is preferable that the acceleration voltage is more than 15 keV and 30 keV or less.

In the processing step, when GCIB etching is used, it is necessary to scan the GCIB onto the processing surface. As a method of injecting GCIB, gloss scanning and spiral scanning are known, and any of these may be used.

In the processing method (2) of the present invention, the flatness of the surface of the glass substrate is measured (hereinafter, referred to as the "flatness measuring step"), and the foreign matter on the processed surface is removed by the foreign matter removing method of the present invention described above. Removing the surface (hereinafter referred to as the "foreign material removal step") and machining the processed surface using a processing method selected from the group consisting of ion beam etching, GCIB etching, plasma etching and nano wear (hereinafter referred to as , This step is referred to as " machining step ", and in the above machining step, the machining conditions of the machining surface are set for each part of the machining surface based on the result obtained from the flatness measuring step.

For the purpose of processing the processed surface of the glass substrate, for example, the processed surface of the glass substrate for EUVL mask, when the finish processing is performed by preliminary processing, ion beam etching, GCIB etching, plasma etching or nano-wear, A partial wave pattern may exist in the processed surface after the preliminary processing. In the present specification, the wavy pattern means irregularities having a period of 5 to 30 mm among periodic irregularities existing on the processed surface.

It is difficult to remove such a wave pattern by finishing and to make a process surface into desired flatness. In addition, the wave pattern generated during the preliminary processing may grow into a larger wave pattern during the finishing process.

The processing method (2) of this invention is a method of removing this wave pattern which generate | occur | produced on the process surface after preprocessing, and finishing-processing a process surface to the surface of the outstanding flatness.

In the machining method (2) of the present invention, the flatness measuring step is preferably performed before the machining step in order to set the machining conditions of the machined surface for each part of the machined surface based on the result obtained from the flatness measuring step. The flatness measurement step may be performed after the foreign matter removal step. However, in order to prevent the adhesion of new foreign matter to the processed surface after the foreign matter removing step, the flatness measuring step is preferably performed before the foreign matter removing step.

In addition, in order to prevent the adhesion of new foreign matter to the processing surface after the foreign matter removing step, the foreign matter removing step and the processing step are arranged side by side in such a manner that the substrate can be transported without removing the substrate from the device. It is preferable to carry out in the chamber. When GCIB etching is used in the machining step, it is preferable to use the same GCIB etching apparatus in the debris removing step and the machining step.

In the flatness measurement step, the flatness in each part of the processing surface, that is, the height difference is measured. Therefore, the result obtained in the flatness measurement step is a flatness map (hereinafter referred to as "flatness map") showing the height difference of each part of the processed surface.

The flatness in each part of a process surface is measured, for example by a laser interference flatness measuring instrument. However, the present invention should not be construed as being limited thereto. A flatness map can be created using the measurement result obtained by measuring the height difference in each part of a process surface using a laser displacement meter, an ultrasonic displacement meter, or a contact displacement meter.

In the processing method (2) of this invention, after performing a flatness measurement and a foreign material removal step, based on the result obtained from the flatness measurement step, the processing conditions of a process surface are set for every part of the said process surface.

As described above, the result obtained in the flatness measurement step becomes a flatness map. When the coordinate of the processing surface which is a two-dimensional plane shape is (x, y), a flatness map is represented by S (x, y) (micrometer). The machining time is represented by T (x, y) (min). When the processing rate is Y (μm / min), these relationships are represented by the following formulas.

T (x, y) = S (x, y) / Y

Therefore, when setting the machining conditions of the machining surface for each part of the machining surface based on the result obtained in the flatness measuring step, machining conditions, specifically machining time are set for each machining part, according to the above formula.

In the machining step, when using a method involving beam irradiation to the machining surface, specifically when ion beam etching, GCIB etching or plasma etching is used, the machining conditions of the machining surface based on the result obtained in the flatness measuring step Can be set for each part of the processing surface. This setting procedure will be described in detail below.

When this setting procedure is performed, the width | variety of the wave pattern which exists in a process surface is specified using the result obtained by the flatness measurement step. As used herein, the width of the moire refers to the length of convex-concave or convex portions periodically present on the working surface. Therefore, the width of the wavy pattern is usually 1/2 of the period of the width of the wavy pattern. In the case where a plurality of wave patterns having different periods exist, the width of the wave pattern having the smallest period is the width of the wave pattern existing on the processed surface.

As mentioned above, the measurement result obtained in the flatness measurement step is a flatness map which shows the height difference of each part of a process surface. Therefore, the width of the wave pattern which exists in a process surface can be easily specified from the flatness map.

As specified in the above procedure, ion beam etching, GCIB etching or plasma etching is performed using a beam whose beam diameter is equal to or smaller than the width of the wavy pattern based on the width of the wavy pattern. In the present specification, the beam diameter is based on a full width of half maximum (FWHM) value. In the present specification, when referred to as the beam diameter, it means the FWHM value of the beam diameter. In the processing step, it is more preferable to use a beam whose beam diameter is 1/2 or less of the width of the wave pattern. By using a beam whose beam diameter is equal to or smaller than the width of the wave pattern, the beam can be focused on the wave pattern present on the processing surface, and the wave pattern can be effectively removed.

In the machining step, when using a method involving beam irradiation to the machining surface, that is, ion beam etching, GCIB etching or plasma etching, it is necessary to scan the beam onto the machining surface. This is because, in order to set the machining conditions of the machined surface for each part of the machined surface, it is necessary to make the range for irradiating the beam once as small as possible. In particular, when using a beam whose beam diameter is equal to or less than the width of the wave pattern, it is necessary to scan the beam onto the machined surface. Glossy irradiation and spiral irradiation are known as a method of scanning a beam, but any of these may be used.

Of the above processing methods, it is preferable to use GCIB etching in that the surface can be processed to have a small surface roughness and excellent smoothness.

When using GCIB etching, the source gas and the irradiation conditions are as described for the processing method (1) of the present invention.

When the processing step of the processing method (1) or (2) of this invention is performed, the surface roughness of a process surface may deteriorate to some extent according to the property of a process surface or the irradiation conditions of a beam. Moreover, even if desired flatness is achieved by the above-mentioned processing step, the surface may not be processed so that it may have desired surface roughness according to the specification of a glass substrate. For this reason, it is preferable to perform the 2nd processing step aiming at the improvement of the surface roughness of a process surface following the said processing step (henceforth "a 1st processing step").

In a second processing step, GCIB etching may be used. In this case, in the GCIB etching used for the foreign material removal step and the GCIB etching used in the first processing step, GCIB etching is performed by changing irradiation conditions such as source gas, ionization current, and acceleration voltage. Specifically, GCIB etching is performed under irradiation conditions in which the etching amount is lower than that of GCIB etching used in the first processing step. Compared to the GCIB etch used for the first processing step, the GCIB etch is performed under milder conditions using a lower ionization current, or a lower acceleration voltage. More specifically, the acceleration voltage is preferably 3 keV or more and less than 30 keV, and more preferably 3 to 20 keV. In addition, as a source gas, from a viewpoint that it is hard to produce a chemical reaction when a source gas collides with a process surface, O ₂ gas alone or O ₂ and one or more gases selected from the group consisting of Ar, CO and CO ₂ are used. It is preferable to use a mixed gas. Among these, it is preferable to use a mixed gas of O ₂ and Ar.

Further, in the second processing step, mechanical polishing using a polishing slurry can be performed at a low surface pressure of 1 to 60 gf / cm 2, called touch polishing. In touch polishing, a glass substrate is sandwiched between polishing plates provided with a polishing pad made of a nonwoven fabric or a woven fabric or the like, and the polishing plate is relatively rotated with respect to the glass substrate while supplying a slurry adjusted to a predetermined property. The machined surface is polished at a surface pressure of / cm 2.

As the polishing pad, BELLATRIX K7512 manufactured by Kanebo, for example, is useful. As the polishing slurry, it is preferable to use a polishing slurry containing colloidal silica, more preferably a polishing slurry containing colloidal silica having an average primary particle diameter of 50 nm or less and adjusted to have a pH range of 0.5 to 4. Do. The surface pressure of polishing is 1 to 60 gf / cm 2. When surface pressure exceeds 60 gf / cm <2>, a process surface cannot be processed to desired surface roughness by generation | occurrence | production of a scratch flaw etc. in a board | substrate surface. Moreover, there exists a possibility that the rotating load of an abrasive plate may become large. If the surface pressure is less than 1 gf / cm 2, it is not practical because the processing time becomes long. Moreover, when surface pressure is less than 30 gf / cm <2>, processing time will be long. Therefore, after processing to some extent with the surface pressure of 30-60 gf / cm <2>, it is preferable to finish-process with the surface pressure of 1-30 gf / cm <2>.

The average primary particle diameter of the colloidal silica is preferably less than 20 nm, more preferably less than 15 nm, particularly preferably less than 10 nm. If the average primary particle diameter of the colloidal silica is more than 50 nm, it is difficult to process the processed surface to the desired surface roughness. Moreover, as colloidal silica, it is preferable not to contain as much as possible the secondary particle formed through aggregation of a primary particle from a viewpoint of managing a particle size delicately. Even when a secondary particle is included, it is preferable that the average particle diameter is 70 nm or less. Incidentally, the particle size of the colloidal silica as used herein is a particle size obtained by measuring a 15 to 105 × 10 ³ times magnified image using a SEM (scanning electron microscope).

It is preferable that content of colloidal silica in a polishing slurry is 10-30 mass%. When the content of the colloidal silica in the polishing slurry is less than 10% by mass, the polishing efficiency may deteriorate, and economical polishing may not be achieved. On the other hand, when content of colloidal silica exceeds 30 mass%, since the usage-amount of colloidal silica increases, there exists a possibility that a problem may arise from a cost or washability viewpoint. The content of the colloidal silica in the polishing slurry is more preferably 18 to 25 mass%, particularly preferably 18 to 22 mass%.

When the pH of the polishing slurry is in the above-mentioned acidic range, that is, the pH is in the range of 0.5 to 4, the processed surface can be polished chemically and mechanically, and efficient polishing of the processed surface having excellent smoothness can be achieved. That is, the convex portion of the processed surface is softened by the acid of the polishing slurry, and the convex portion can be easily removed by mechanical polishing. As a result, not only the processing efficiency is improved but also the glass dust removed in the polishing process is softened, and the occurrence of new scratches by the glass dust or the like is prevented. When the pH of the polishing slurry is less than 0.5, corrosion may occur in the polishing apparatus used for touch polishing. From the viewpoint of the handleability of the polishing slurry, the pH is preferably 1 or more. In order to fully acquire the chemical polishing effect, it is preferable that the pH be? 4 or less, and particularly preferably the pH is in the range of 1.8 to 2.5.

PH adjustment of an abrasive slurry can be performed by adding an inorganic acid or an organic acid individually or in combination. Examples of inorganic acids that can be used include nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid. Among them, nitric acid is preferred from the viewpoint of ease of handling. Examples of organic acids also include oxalic acid and citric acid.

The water used for the polishing slurry is preferably pure water or ultrapure water from which foreign substances have been removed. That is, pure water or ultrapure water having a particle size of 0.1 µm or more and substantially 1 / mL or less is measured by a light scattering method using a laser light or the like. Regardless of material or shape, when more than 1 / mL of foreign matter is mixed, surface defects such as scratches and pits may be formed on the processed surface. The foreign matter in pure water or ultrapure water can be removed by, for example, filtration by a membrane filter or ultrafiltration, but the method of removing the foreign matter is not limited thereto.

In the glass substrate processed by the processing method (1) or (2) of this invention, a processed surface has the outstanding flatness and surface roughness, the flatness of the processed surface after processing is 50 nm or less, and is height to the said processing surface There are no convex glass defects greater than 1.5 nm. It is more preferable that the flatness of the processed surface after processing is 30 nm or less, and it is still more preferable that it is 20 nm or less.

Since the glass substrate processed by the processing method of this invention has the outstanding flatness and surface roughness, the optical element used for the optical system of the exposure apparatus for semiconductor manufacture, especially the exposure of the next-generation semiconductor manufacture whose line width is 45 nm or less. It is suitable as an optical element used for the optical system of the apparatus. Specific examples of such optical elements include lenses, diffraction gratings, optical films and composites thereof, such as lenses, multi lenses, lens arrays, lenticular lenses, fly-eye lenses, aspherical lenses, mirrors, Diffraction gratings, dual optics, photomasks and composites thereof.

Moreover, the glass substrate processed by the processing method of this invention is suitable as a mask blank for manufacturing a photomask and the said photomask, especially a reflective mask for EUVL, and a mask blank for manufacturing the said mask.

The light source of the exposure apparatus is not particularly limited, and may be a conventional laser capable of emitting g line (wavelength: 436 nm) or i line (wavelength: 365 nm). A shorter wavelength light source, specifically, a light source having a wavelength of 250 nm or less is preferable. Specific examples of such light sources include KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), F ₂ laser (wavelength: 157 nm), and EUV (wavelength: 13.5 nm).

Although the 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 can be made within the scope of the invention.

This application is based on Japanese Patent Application No. 2007-172274, filed June 29, 2007, the contents of which are incorporated herein by reference.

Claims (21)

And gas cluster ion beam etching the glass substrate surface at an accelerating voltage of 5 to 15 keV. Comprising gas cluster ion beam etching of the glass substrate surface using at least one gas selected from the group consisting of O ₂ , Ar, B, CO ₂ , N ₂ , N ₂ O and boron hydride as a source gas, Method of removing foreign matter from the glass substrate surface. The method according to claim 1 or 2, wherein the gas cluster ion beam etching is performed under the condition that the etching amount is 20 nm or less. The method according to any one of claims 1 to 3, wherein the glass substrate is made of low expansion glass having a coefficient of thermal expansion at 20 ° C of 0 ± 30 ppb / ° C. The method according to any one of claims 1 to 4, wherein the glass substrate surface before performing the gas cluster ion beam etching has a surface roughness (Rms) of 5 nm or less. . 6. The method of claim 1, wherein gas cluster ion beam etching is performed under conditions of a cluster size of at least 2000. 7. The gas cluster ion beam etching according to any one of claims 1 to 6, wherein the gas cluster ion beam etching is performed while maintaining the angle formed by the normal of the glass substrate and the gas cluster ion beam incident on the glass substrate surface at 3 to 60 °. Method of removing foreign matter from the glass substrate surface. 8. The method of claim 7, wherein gas cluster ion beam etching is performed while maintaining the glass substrate surface in a 3 to 60 ° downward direction with respect to the horizontal direction. Removing foreign matter on the surface of the glass substrate by the method according to any one of claims 1 to 8; And Processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching and nano-abrasion Comprising a glass substrate surface. The method of claim 9, wherein the processing method is gas cluster ion beam etching. The method of claim 10, 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 ; And performing a gas cluster ion beam etching of the processing step at an accelerating voltage exceeding 15 keV using a mixed gas selected from the group consisting of a mixed gas of NF ₃ , Ar, and N ₂ . The method of claim 11, wherein the source gas comprises: 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 ; And a mixed gas selected from the group consisting of a mixed gas of NF ₃ , Ar, and O ₂ . Measuring flatness of the glass substrate surface; Removing foreign matter on the surface of the glass substrate by the method according to any one of claims 1 to 8; And Processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching and nano wear. Including, In processing the glass substrate surface, the processing conditions of the glass substrate surface are set for each portion of the glass substrate based on the result obtained from the measuring flatness. The method of claim 13, wherein the processing method is ion beam etching, gas cluster ion beam etching, or plasma etching, The width of the wavy pattern present on the glass substrate surface is specified based on the result obtained from the step of measuring the flatness of the glass substrate surface, A method of processing a glass substrate surface, wherein the glass substrate surface is processed into a beam having a beam diameter less than or equal to the width of the wave pattern at a full width of half maximum (FWHM) value. 15. The method of claim 14, wherein the FWHM value of the beam diameter is no more than 1/2 of the width of the wave pattern. The method of claim 15, wherein the processing method is gas cluster beam etching, 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 ; And performing gas cluster ion beam etching of the processing step with an acceleration voltage exceeding 15 keV using any one of the mixed gases selected from the group consisting of mixed gases of NF ₃ , Ar and N ₂ . Way. The method of claim 16, wherein the source gas comprises: 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 ; And a mixed gas selected from the group consisting of a mixed gas of NF ₃ , Ar, and O ₂ . 18. The method according to any one of claims 9 to 17, further comprising the step of processing the glass substrate surface, followed by a second processing step for improving the surface roughness of the glass substrate surface. Way. 19. The method of claim 18, wherein the second processing step comprises at least 3 keV using O ₂ gas alone or a mixed gas of O ₂ and at least one gas selected from the group consisting of Ar, CO and CO ₂ as the source gas. A method of processing a glass substrate surface comprising gas cluster ion beam etching with an accelerating voltage of less than keV. The method of claim 18, wherein the second processing step comprises mechanical polishing with a surface pressure of 1 to 60 gf / cm ² using an abrasive slurry. A glass substrate obtained by the method according to any one of claims 9 to 20, wherein the substrate surface has a flatness of 50 nm or less and no convex glass defect having a height of more than 1.5 nm.

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