JP7491235B2 - Glass substrate for EUVL and its manufacturing method, and mask blank for EUVL and its manufacturing method - Google Patents

Description

This disclosure relates to a glass substrate for EUVL and a manufacturing method thereof, as well as a mask blank for EUVL and a manufacturing method thereof.

Traditionally, photolithography technology has been used to manufacture semiconductor devices. In photolithography technology, an exposure device irradiates light onto a photomask pattern, transferring the photomask pattern onto a resist film.

Recently, the use of short-wavelength exposure light, such as ArF excimer laser light or even EUV (Extreme Ultra-Violet) light, has been considered to enable the transfer of fine patterns.

Here, EUV light includes soft X-rays and vacuum ultraviolet light, and specifically refers to light with a wavelength of about 0.2 nm to 100 nm. At present, EUV light with a wavelength of about 13.5 nm is mainly being considered as exposure light.

Patent Document 1 describes a method for manufacturing a mask blank for EUVL (Extreme Ultra-Violet Lithography). The mask blank for EUVL includes a glass substrate, a reflective film formed on the glass substrate, and an absorbing film formed on the reflective film.

Mask blanks for EUVL require high flatness to improve the transfer accuracy of fine patterns. The flatness of EUVL mask blanks is determined primarily by the flatness of the glass substrate, which serves as the substrate, so the glass substrate must have high flatness.

Therefore, in order to improve the flatness of the glass substrate, an etching process is performed in which a beam of gas clusters is irradiated onto the main surface of the glass substrate. The main surface of the glass substrate is locally etched and flattened by the gas clusters.

Patent Document 1 discloses a technique for implanting fluorine or chlorine into the main surface of a glass substrate to a depth of about 100 nm by irradiating the substrate with gas clusters. This technique creates a compressive stress layer on the main surface of the glass substrate, improving the strength of the main surface of the glass substrate.

JP 2009-155170 A

After the etching process in which gas clusters are irradiated, glass substrates for EUVL are subjected to a polishing process, an inspection process, a film formation process, and the like. These processes are collectively called post-processing.

In a later process, the edge of the glass substrate is pressed against a holder or positioning tool. Therefore, the edge is easily scratched. Sometimes, instead of or in addition to the edge, the notch surface is pressed against the holder or positioning tool.

The notch surface is formed at an angle to the main surface so as to remove the corners of the two adjacent end faces and the main surface. The notch surface indicates the orientation of the glass substrate, and the glass substrate is placed in various devices and pressed against a holder or positioning tool so that the orientation of the glass substrate is the desired orientation.

The notch surface may be omitted.

It is unavoidable that scratches will occur on the edge or notch surface of the glass substrate. However, if the scratches spread and cause major defects, the glass substrate will be discarded as a defective product, which will result in a decrease in yield.

One aspect of the present disclosure provides a technology that can suppress the extension of scratches formed on the edge or notch surface of a glass substrate for EUVL.

A glass substrate for EUVL according to one aspect of the present disclosure has a rectangular first main surface, a rectangular second main surface facing opposite to the first main surface, four end surfaces perpendicular to the first main surface and the second main surface, four first chamfered surfaces formed at the boundaries between the first main surface and the end surfaces, and four second chamfered surfaces formed at the boundaries between the second main surface and the end surfaces. The glass substrate for EUVL is made of quartz glass containing _TiO2 . The end surfaces contain fluorine (F) and an element (A) other than fluorine that forms a gas cluster together with the fluorine, and satisfy the following formulas (1) and (2).

上記式（１）中、Ｄ１（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＦの強度であり、ｘは前記端面からの深さ（単位：ｎｍ）、ａ１ｘ+ｂ１はｘが２００以上４００以下の範囲におけるＤ１（ｘ）を最小二乗法で近似した直線である。上記式（２）中、Ｄ２（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＡの強度であり、ｘは前記端面からの深さ（単位：ｎｍ）、ａ２ｘ+ｂ２はｘが２００以上４００以下の範囲におけるＤ２（ｘ）を最小二乗法で近似した直線である。

In the above formula (1), D1(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the end face (unit: nm), and a1x+b1 is a straight line obtained by approximating D1(x) by the least squares method in the range of x from 200 to 400. In the above formula (2), D2(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the end face (unit: nm), and a2x+b2 is a straight line obtained by approximating D2(x) by the least squares method in the range of x from 200 to 400.

A glass substrate for EUVL according to another aspect of the present disclosure has a rectangular first main surface, a rectangular second main surface facing opposite to the first main surface, four end surfaces perpendicular to the first main surface and the second main surface, four first chamfered surfaces formed at the boundaries between the first main surface and the end surfaces, four second chamfered surfaces formed at the boundaries between the second main surface and the end surfaces, and one or more notch surfaces formed obliquely with respect to the first main surface so as to cut off corners of two adjacent end surfaces and the first main surface. The glass substrate for EUVL is formed of quartz glass containing _TiO2 . The notch surfaces contain fluorine (F) and an element (A) other than fluorine that forms a gas cluster together with the fluorine, and satisfy the following formulas (3) and (4).

上記式（３）中、Ｄ３（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＦの強度であり、ｘは前記ノッチ面からの深さ（単位：ｎｍ）、ａ３ｘ+ｂ３はｘが２００以上４００以下の範囲におけるＤ３（ｘ）を最小二乗法で近似した直線であり、上記式（４）中、Ｄ４（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＡの強度であり、ｘは前記ノッチ面からの深さ（単位：ｎｍ）、ａ４ｘ+ｂ４はｘが２００以上４００以下の範囲におけるＤ４（ｘ）を最小二乗法で近似した直線である。

In the above formula (3), D3(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the notch face (unit: nm), and a3x+b3 is a straight line obtained by approximating D3(x) using the least squares method when x is in the range of 200 to 400, and in the above formula (4), D4(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the notch face (unit: nm), and a4x+b4 is a straight line obtained by approximating D4(x) using the least squares method when x is in the range of 200 to 400.

According to one aspect of the present disclosure, it is possible to suppress the extension of scratches formed on the edge face or notch face of a glass substrate for EUVL.

FIG. 1 is a flowchart showing a method for manufacturing an EUVL mask blank according to one embodiment. FIG. 2 is a cross-sectional view showing an example of a glass substrate to be subjected to S101 in FIG. FIG. 3 is a plan view showing an example of the glass substrate of FIG. FIG. 4 is a cross-sectional view showing an EUVL mask blank according to an embodiment. FIG. 5 is a cross-sectional view showing an example of a photomask for EUVL. FIG. 6 is a cross-sectional view showing a processing device according to an embodiment. FIG. 7 is an enlarged cross-sectional view showing the glass substrate and its peripheral components in FIG. FIG. 8 is a diagram showing the glass substrate and its peripheral parts as viewed from the direction of irradiation of the gas clusters in FIG. FIG. 9 is a view of the clamp and spacer of FIG. 7 from another angle. FIG. 10 is a schematic diagram showing an example of collision of gas clusters with a glass substrate. FIG. 11 is a diagram showing irradiation of gas clusters onto the end face of the glass substrate of Example 1. In FIG. FIG. 12 is a diagram showing the F intensity/Si intensity distribution in the depth direction measured by TOF-SIMS on the end face of the glass substrate of Example 1. FIG. 13 is a diagram showing the depth direction distribution of C intensity/Si intensity measured by TOF-SIMS on the end face of the glass substrate of Example 1. FIG. 14 is a diagram comparing the hardness of the end face of the glass substrate of Example 1 before and after the gas cluster irradiation. FIG. 15 is a diagram showing the depth direction distribution of F intensity/Si intensity measured by TOF-SIMS on the notch surface of the glass substrate of Example 2. FIG. 16 is a diagram showing the depth direction distribution of C intensity/Si intensity measured by TOF-SIMS on the notch surface of the glass substrate of Example 2.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that the same or corresponding configurations in each drawing will be given the same reference numerals, and descriptions thereof may be omitted. In the specification, "~" indicating a numerical range means that the numerical values before and after it are included as the lower and upper limits.

As shown in FIG. 1, the method for manufacturing a mask blank for EUVL (Extreme Ultra-Violet Lithography) includes steps S101 to S107. A glass substrate is used for manufacturing the mask blank. The glass of the glass substrate is preferably quartz glass containing TiO _2. Quartz glass has a smaller linear expansion coefficient and a smaller dimensional change due to temperature change than general soda-lime glass. Quartz glass may contain 80% to 95% by mass of SiO ₂ and 4% to 17% by mass of TiO _2. When the TiO ₂ content is 4% to 17% by mass, the linear expansion coefficient is approximately zero near room temperature, and there is almost no dimensional change near room temperature. Quartz glass may contain a third component or impurities other than SiO ₂ and TiO _2. As such quartz glass, for example, Corning's ULE (registered trademark) 7973 series may be used.

2 and 3, the glass substrate 2 includes a first main surface 21, a second main surface 22, four end surfaces 23, four first chamfered surfaces 24, four second chamfered surfaces 25, and three notch surfaces 26. The first main surface 21 is rectangular. In this specification, a rectangular shape includes a shape with chamfered corners. A rectangle also includes a square. The second main surface 22 faces in the opposite direction to the first main surface 21. The second main surface 22 is also rectangular like the first main surface 21. The end surface 23 is perpendicular to the first main surface 21 and the second main surface 22. The first chamfered surface 24 is formed at the boundary between the first main surface 21 and the end surface 23. The second chamfered surface 25 is formed at the boundary between the second main surface 22 and the end surface 23. In this embodiment, the first chamfered surface 24 and the second chamfered surface 25 are so-called C-chamfered surfaces, but may be R-chamfered surfaces. The notch surface 26 is formed at an angle to the first main surface 21 so as to cut off the corners between the two adjacent end surfaces 23 and the first main surface 21. The notch surface 26 indicates the orientation of the glass substrate 2, and the glass substrate 2 is installed in various devices so that the orientation of the glass substrate 2 is a desired orientation. The number of notch surfaces 26 is three in this embodiment, but is not particularly limited as long as it is one or more. For example, even if the number of notch surfaces 26 is four, the orientation of the glass substrate 2 can be determined as long as the sizes of the notch surfaces 26 are different. It is to be noted that the notch surface 26 may not be present, and the number of notch surfaces 26 may be zero.

The first main surface 21 of the glass substrate 2 has a quality assurance region 27, which is shown by a dot pattern in FIG. 3. The quality assurance region 27 is an area that is processed to the desired flatness by steps S101 to S104. The quality assurance region 27 is an area excluding a peripheral region 28 that is within a distance L of 5 mm from the end face 23, for example, when viewed from a direction perpendicular to the first main surface 21. Although not shown, the second main surface 22 of the glass substrate 2 also has a quality assurance region and a peripheral region, similar to the first main surface 21.

First, in S101 of FIG. 1, the first main surface 21 and the second main surface 22 of the glass substrate 2 are polished. The first main surface 21 and the second main surface 22 may be polished simultaneously using a double-sided polisher, or may be polished sequentially using a single-sided polisher. In S101, the glass substrate 2 is polished while a polishing slurry is supplied between the polishing pad and the glass substrate 2. The polishing slurry contains an abrasive. The abrasive is, for example, cerium oxide particles. The first main surface 21 and the second main surface 22 may be polished multiple times with abrasives of different materials or grain sizes.

The abrasive used in S101 is not limited to cerium oxide particles. For example, the abrasive used in S101 may be silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, silicon carbide particles, etc.

Next, in S102 of FIG. 1, the surface shapes of the first main surface 21 and the second main surface 22 of the glass substrate 2 are measured. For example, a non-contact measuring device such as a laser interference type is used to measure the surface shape so as not to scratch the surface. The measuring device measures the surface shape of the quality assurance area 27 of the first main surface 21 and the quality assurance area of the second main surface 22.

Next, in S103 of FIG. 1, the measurement results of S102 are referenced, and the first main surface 21 and the second main surface 22 of the glass substrate 2 are processed with a beam-shaped gas cluster to improve flatness. The first main surface 21 and the second main surface 22 are etched in order with the gas cluster. The order in which they are etched may be either first or second, and is not particularly limited.

The gas clusters are ionized by the impact of the thermal electrons, then accelerated by the electric field, and after neutralization, are irradiated toward the first main surface 21 or the second main surface 22. The impact of the gas clusters locally etches and flattens the first main surface 21 or the second main surface 22. Details of S103 will be described later.

Next, in S104 of FIG. 1, the first main surface 21 and the second main surface 22 of the glass substrate 2 are subjected to finish polishing. The first main surface 21 and the second main surface 22 may be polished simultaneously using a double-sided polisher, or may be polished sequentially using a single-sided polisher. In S104, the glass substrate 2 is polished while a polishing slurry is supplied between the polishing pad and the glass substrate 2. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

Next, in S105 of FIG. 1, a reflective film 3 shown in FIG. 4 is formed in the quality assurance area 27 of the first main surface 21 of the glass substrate 2. The reflective film 3 reflects EUV light. The reflective film 3 may be, for example, a multilayer reflective film in which high-refractive index layers and low-refractive index layers are alternately stacked. The high-refractive index layers are formed of, for example, silicon (Si), and the low-refractive index layers are formed of, for example, molybdenum (Mo). The reflective film 3 is formed by a sputtering method such as ion beam sputtering or magnetron sputtering.

Next, in S106 of FIG. 1, an absorbing film 4 shown in FIG. 4 is formed on the reflective film 3 formed in S105. The absorbing film 4 absorbs EUV light. The absorbing film 4 is formed of a single metal, alloy, nitride, oxide, oxynitride, or the like containing at least one element selected from tantalum (Ta), chromium (Cr), and palladium (Pd), for example. The absorbing film 4 is formed, for example, by sputtering.

Finally, in S107 of FIG. 1, a conductive film 5 shown in FIG. 4 is formed in the quality assurance area of the second main surface 22 of the glass substrate 2. The conductive film 5 is used to electrostatically attract the photomask with an electrostatic chuck of an exposure device. The conductive film 5 is made of, for example, chromium nitride (CrN). The conductive film 5 is formed by, for example, sputtering. Note that, in this embodiment, S107 is performed after S105 and S106, but may be performed before S105 and S106.

The arrangement of the reflective film 3 and the conductive film 5 may be reversed. That is, the conductive film 5 may be formed in the quality assurance area 27 of the first main surface 21 of the glass substrate 2, and the reflective film 3 may be formed in the quality assurance area of the second main surface 22 of the glass substrate 2. The absorbing film 4 is formed on the reflective film 3.

By steps S101 to S107, the EUVL mask blank 1 shown in FIG. 4 is obtained. The EUVL mask blank 1 includes a glass substrate 2, a reflective film 3, an absorbing film 4, and a conductive film 5. Note that the EUVL mask blank 1 does not have to include the conductive film 5. Furthermore, the EUVL mask blank 1 may further include another film.

For example, the EUVL mask blank 1 may further include a low-reflection film. The low-reflection film is formed on the absorbing film 4. The low-reflection film is used to inspect the opening pattern 41 of the absorbing film 4 shown in FIG. 5, and has lower reflection characteristics with respect to the inspection light than the absorbing film 4. The low-reflection film is formed of, for example, TaON or TaO. The low-reflection film is formed, for example, by sputtering.

Moreover, the EUVL mask blank 1 may further include a protective film. The protective film is formed between the reflective film 3 and the absorbing film 4. The protective film protects the reflective film 3 so that the reflective film 3 is not etched when the absorbing film 4 is etched to form an opening pattern 41 in the absorbing film 4. The protective film is made of, for example, Ru, Si, or _TiO2 . The protective film is formed by, for example, sputtering.

As shown in FIG. 5, the EUVL photomask is obtained by forming an opening pattern 41 in the absorbing film 4. Photolithography and etching are used to form the opening pattern 41. Therefore, the resist film used to form the opening pattern 41 may be included in the EUVL mask blank 1.

Next, the processing device used in S103 in FIG. 1 will be described with reference to FIG. 6. The processing device 100 is a so-called GCIB (Gas Cluster Ion Beam) processing device.

The processing apparatus 100 includes a vacuum vessel 101. The vacuum vessel 101 has a nozzle chamber 102, an ionization/acceleration chamber 103, and a processing chamber 104. The three chambers 102, 103, and 104 are connected to each other and form a passage for the gas cluster. The three chambers 102, 103, and 104 are evacuated by three vacuum pumps 105, 106, and 107, and are maintained at a desired vacuum level. Note that the number of chambers and the number of vacuum pumps are not particularly limited.

The processing apparatus 100 includes a generation unit 110. The generation unit 110 generates gas clusters. The generation unit 110 includes, for example, a raw material tank 111, a pressure controller 113, a supply pipe 114, and a nozzle 116. The raw material tank 111 stores a raw material gas (for example, _CF4 gas). The pressure controller 113 controls the supply pressure of the raw material gas supplied from the raw material tank 111 to the nozzle 116 via the supply pipe 114. The nozzle 116 is provided in the nozzle chamber 102, and ejects the raw material gas into a vacuum to form a supersonic gas jet 118.

The source gas is cooled by adiabatic expansion in the gas jet 118. As a result, part of the gas jet 118 condenses into gas clusters, each of which is an aggregate of several to several thousand atoms or molecules. Many gas clusters are found near the center of the gas jet 118 flow. Therefore, the gas clusters can be efficiently delivered by passing only the center of the gas jet 118 flow using the schema 119.

The raw material gas is not limited to _CF4 gas, and may be _CHF3 gas, _CH2F2 gas, _C2F6 gas, _BF3 gas, _NF3 gas, _SF6 gas, _SeF6 gas, _TeF6 gas, or _WF6 gas. Of these gases, _CF4 gas, _CHF3 gas, or _CH2F2 gas is preferable, as described in detail below. A plurality of gases may be selected from these gases, _{or a mixed} gas may be used as the raw material gas.

The processing apparatus 100 includes an ionization section 120. The ionization section 120 ionizes at least a portion of the gas clusters in the gas jet 118. The ionization section 120 includes, for example, one or more thermal filaments 124 and a cylindrical electrode 126. The thermal filament 124 generates heat by power (voltage V _F ) from a power source 125 and emits thermoelectrons. The cylindrical electrode 126 accelerates the thermoelectrons emitted from the thermal filament 124 and causes the accelerated thermoelectrons to collide with the gas clusters. Electrons are emitted from some of the gas clusters due to the collision between the electrons and the gas clusters, and these gas clusters are positively ionized. Note that two or more electrons may be emitted and the gas clusters may be multiply ionized. A voltage V _A from a power source 127 is applied between the cylindrical electrode 126 and the thermal filament 124. The thermal electrons are accelerated by this voltage V _A (electric field) and collide with the gas clusters.

The processing apparatus 100 includes an acceleration section 130. The acceleration section 130 accelerates the gas clusters ionized in the ionization section 120 to form a GCIB 128. The acceleration section 130 includes, for example, a first electrode 132 and a second electrode 134. The second electrode 134 is grounded, and a positive voltage Vs is applied to the first electrode 132 from a power supply 135. The first electrode 132 and the second electrode 134 form an electric field that accelerates the positively ionized gas clusters. The accelerated gas clusters are extracted as a GCIB 128 from an opening of the second electrode 134. The power supply 136 supplies an acceleration voltage V _Acc that biases the ionization section 120 relative to the first electrode 132 and the second electrode 134, so that the total GCIB acceleration potential is equal to V _Acc . V _Acc is, for example, 1 kV to 200 kV, preferably 1 kV to 70 kV.

The processing apparatus 100 may include a neutralization section (not shown). The neutralization section neutralizes the GCIB 128 formed in the acceleration section 130 to form neutral gas clusters. Since the glass substrate 2 is irradiated with neutral gas clusters, charging of the glass substrate 2 can be prevented. Note that even if the glass substrate 2 is irradiated with positively ionized gas clusters, etching of the glass substrate 2 is possible.

The processing apparatus 100 includes an irradiation unit 150. The irradiation unit 150 irradiates the glass substrate 2 with a beam-shaped gas cluster 129 to locally etch the glass substrate 2. The half-width of the intensity distribution of the beam of the gas cluster 129 is, for example, 1 to 30 mm. The irradiation unit 150 includes, for example, a stage 151, a stage moving mechanism 152, and an aperture 153. The stage 151 is installed in the processing chamber 104 and holds the glass substrate 2. The stage moving mechanism 152 moves the stage 151 two-dimensionally in the Y-axis direction and the Z-axis direction to move the irradiation point of the gas cluster 129 on the glass substrate 2. By controlling the moving speed, the amount of etching can be controlled and the glass substrate 2 can be flattened. The stage moving mechanism 152 can also move the stage 151 in the X-axis direction. The stage moving mechanism 152 can also rotate the stage 151 around a rotation axis extending in the Y-axis direction. The aperture 153 is provided midway through the passage of the gas cluster 129 to increase the uniformity of the intensity of the gas cluster 129. The gas cluster 129 passes through the opening of the aperture 153 and is irradiated onto the glass substrate 2.

Next, the irradiation section 150 of the processing apparatus 100 will be described with reference to Figures 7 to 9. In this specification, the X-axis direction, the Y-axis direction, and the Z-axis direction are mutually perpendicular. The X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is vertical. In the following description, the positive X-axis direction is the forward direction, and the negative X-axis direction is the rearward direction. The irradiation direction of the gas cluster 129 indicated by the arrow in Figure 7 is the positive X-axis direction.

As shown in FIG. 7, the irradiation unit 150 irradiates the beam-shaped gas cluster 129 forward, and the irradiated gas cluster 129 locally etches the first main surface 21, the end surface 23, the first chamfered surface 24, and the notch surface 26 of the glass substrate 2. The first main surface 21 is arranged facing backward and tilted obliquely upward. The tilt angle is not particularly limited, but is, for example, 5°. By arranging the first main surface 21 tilted obliquely upward, it becomes possible to directly irradiate the beam-shaped gas cluster 129 to the lower end surface 23 of the four end surfaces 23. Note that if the orientation of the glass substrate 2 is reversed, it is naturally possible to locally etch the second main surface 22 and the second chamfered surface 25 of the glass substrate 2.

As shown in FIG. 9, the stage 151 is disposed opposite the second main surface 22 of the glass substrate 2. The stage 151 is disposed in front of the glass substrate 2. The stage 151 may hold the glass substrate 2 via a spacer 155, for example. The spacer 155 forms a gap between the stage 151 and the glass substrate 2. Compared to a case where the entire second main surface 22 of the glass substrate 2 is in contact with the stage 151, the occurrence of contact scratches on the second main surface 22 can be suppressed.

The spacer 155 may have a tapered surface. If the tapered surface of the spacer 155 holds the second chamfered surface 25 of the glass substrate 2, it will not come into contact with the second main surface 22 at all, so that the occurrence of contact scratches on the second main surface 22 can be reliably prevented. A part of the spacer 155 is positioned outside the glass substrate 2 when viewed from the irradiation direction of the gas cluster 129 as shown in FIG. 8.

In this embodiment, a part of the spacer 155 is disposed outside the glass substrate 2 when viewed from the irradiation direction of the gas cluster 129, but it is also possible to dispose the entire spacer 155 inside the glass substrate 2. In that case, the spacer 155 contacts the peripheral region excluding the quality assurance region of the second main surface 22, rather than the second chamfered surface 25 of the glass substrate 2.

The stage 151 may also hold the glass substrate 2 via a clamp 156. The glass substrate 2 can be stably held in a vacuum. The entire clamp 156 is disposed outside the glass substrate 2 when viewed from the direction of irradiation of the gas cluster 129. The clamp 156 holds down, for example, the end surface 23 of the glass substrate 2. A plurality of clamps 156 are provided at intervals along the periphery of the glass substrate 2.

In this embodiment, the clamp 156 presses against the edge surface 23 of the glass substrate 2, but it may also press against the peripheral region 28 of the first main surface 21 of the glass substrate 2. The clamp 156 may also press against the first chamfered surface 24 of the glass substrate 2. In these cases, too, a portion of the clamp 156 is positioned outside the glass substrate 2 when viewed from the irradiation direction of the gas cluster 129.

As shown in FIG. 1, after the etching process in which gas clusters 129 are irradiated, the glass substrate 2 is subjected to a polishing process, an inspection process, a film formation process, and the like. These processes are collectively called the post-process. In the post-process, the end surface 23 of the glass substrate 2 is pressed against a holder or a positioning tool. Therefore, the end surface 23 is easily scratched.

In this embodiment, fluorine (F) and elements other than fluorine (hereinafter also referred to as "A") are implanted into the end face 23 of the glass substrate 2 by irradiating the gas cluster 129, softening the vicinity of the end face 23. Because the hardness of the vicinity of the end face 23 is soft, the vicinity of the end face 23 can deform so as to absorb the stress that propagates the scratches. Therefore, the extension of the scratches can be suppressed, and a decrease in yield can be suppressed.

A is not particularly limited as long as it forms a gas cluster 129 together with F, but may be, for example, carbon (C), boron (B), hydrogen (H), nitrogen (N), sulfur (S), selenium (Se), tellurium (Te), or tungsten (W). As will be described in detail later, A is preferably an element with a small number of valence electrons and a small atomic radius. Specifically, A is preferably carbon (C), boron (B), or nitrogen (N), and more preferably carbon (C).

As shown in FIG. 10, when gas clusters 129 are implanted into the glass substrate 2, the highly reactive fluorine breaks the Si-O bonds near the glass surface. As a result, Si, O, F, and A bond randomly, making the density sparse, which is presumably why the hardness of the glass surface becomes softer.

If the density of the glass surface becomes low, no compressive stress occurs on the glass surface, so the hardness of the glass surface does not become high. In order to make the density of the glass surface low, A is preferably an element with a small number of valence electrons and an element with a small atomic radius. As described above, A is preferably carbon, boron, or nitrogen, and more preferably carbon. The gas cluster 129 formed by A and F is preferably CF ₄ , CHF ₃ , CH ₂ F ₂ , BF ₃ , or NF ₃ , and more preferably CF ₄ , CHF ₃ , or CH ₂ F _2. CF ₄ and the like are easier to handle than BF ₃ and NF ₃ .

In addition, if the density of the glass surface is low, compressive stress is not generated on the glass surface, and deformation of the glass substrate 2 due to compressive stress does not occur. Therefore, the flatness of the first main surface 21 and the second main surface 22 of the glass substrate 2 is good.

F and A are implanted into the end surface 23 of the glass substrate 2. In S103 of FIG. 1, the gas cluster 129 may be directly irradiated onto the end surface 23 of the glass substrate 2, or the gas cluster 129 that has been changed in direction due to collision with peripheral parts of the glass substrate 2 may be implanted into the end surface 23 of the glass substrate 2. In addition, in order to directly irradiate the four end surfaces 23 with the gas cluster 129, the glass substrate 2 may be rotated 90 degrees around a rotation axis parallel to the X-axis, and S103 may be performed multiple times. At this time, the amount of F and A implanted into the four end surfaces 23 can be controlled by controlling the irradiation time of the gas cluster 129 and the coordinates of the stage 151. Examples of peripheral parts of the glass substrate 2 include the stage 151, the spacer 155, and the clamp 156.

The end surface 23 includes F and A and satisfies the following formula (1) and formula (2).

上記式（１）中、Ｄ１（ｘ）は、ＴＯＦ－ＳＩＭＳ（Ｔｉｍｅ－ｏｆ－Ｆｌｉｇｈｔ Ｓｅｃｏｎｄａｒｙ Ｉｏｎ Ｍａｓｓ Ｓｐｅｃｔｒｏｍｅｔｒｙ）で測定される、Ｓｉの強度で規格化したＦの強度であり、ｘは端面２３からの深さ（単位：ｎｍ）、ａ１ｘ+ｂ１はｘが２００以上４００以下の範囲におけるＤ１（ｘ）を最小二乗法で近似した直線である。上記式（２）中、Ｄ２（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＡの強度であり、ｘは端面２３からの深さ（単位：ｎｍ）、ａ２ｘ+ｂ２はｘが２００以上４００以下の範囲におけるＤ２（ｘ）を最小二乗法で近似した直線である。上記式（１）の左辺の値Ｓ１は、好ましくは１０以下である。また、上記式（２）の左辺の値Ｓ２は、好ましくは１以下である。

In the above formula (1), D1(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), x is the depth (unit: nm) from the end face 23, and a1x+b1 is a straight line obtained by approximating D1(x) in the range of x from 200 to 400 using the least squares method. In the above formula (2), D2(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth (unit: nm) from the end face 23, and a2x+b2 is a straight line obtained by approximating D2(x) in the range of x from 200 to 400 using the least squares method. The value S1 on the left side of the above formula (1) is preferably 10 or less. The value S2 on the left side of the above formula (2) is preferably 1 or less.

As described above, the end face 23 includes F and A, and satisfies the above formula (1) and formula (2). This makes it possible to soften the hardness in the vicinity of the end face 23 that is brought into contact with a holder, positioning tool, or the like. Because the hardness in the vicinity of the end face 23 is soft, the vicinity of the end face 23 can deform so as to absorb the stress that causes the scratches to extend. Therefore, the extension of the scratches can be suppressed, and a decrease in yield can be suppressed.

In addition, instead of or in addition to the end face 23, the notch face 26 may be pressed against a holder or positioning tool. In this case, scratches on the notch face 26 are unavoidable. However, if the scratches extend and cause a major defect, the glass substrate will be discarded as a defective product. This will result in a decrease in yield.

Therefore, fluorine (F) and an element other than fluorine (A) may be implanted into the notch surface 26 of the glass substrate 2 by irradiating it with gas clusters 129, thereby softening the vicinity of the notch surface 26. Because the vicinity of the notch surface 26 is soft, the vicinity of the notch surface 26 can deform so as to absorb the stress that propagates the scratches. Therefore, the propagation of the scratches can be suppressed, and a decrease in yield can be suppressed.

In S103 of FIG. 1, the gas clusters 129 may be directly irradiated onto the notch surface 26 of the glass substrate 2, or the gas clusters 129 that have been changed in direction due to collision with peripheral components of the glass substrate 2 may be injected into the notch surface 26 of the glass substrate 2. Alternatively, S103 may be performed multiple times by rotating the glass substrate 2 by 90 degrees around a rotation axis parallel to the X-axis. At this time, the amount of F and A injected into all of the notch surfaces 26 can be controlled by controlling the irradiation time of the gas clusters 129 and the coordinates of the stage 151. The notch surface 26 is easier to directly irradiate with the gas clusters 129 than the end surface 23, and the content of F and A can be increased.

The notch surface 26 irradiated with the gas cluster 129 contains F and A, and satisfies the following formulas (3) and (4).

上記式（３）中、Ｄ３（ｘ）は、ＴＯＦ－ＳＩＭＳ（Ｔｉｍｅ－ｏｆ－Ｆｌｉｇｈｔ Ｓｅｃｏｎｄａｒｙ Ｉｏｎ Ｍａｓｓ Ｓｐｅｃｔｒｏｍｅｔｒｙ）で測定される、Ｓｉの強度で規格化したＦの強度であり、ｘはノッチ面２６からの深さ（単位：ｎｍ）、ａ３ｘ+ｂ３はｘが２００以上４００以下の範囲におけるＤ３（ｘ）を最小二乗法で近似した直線である。上記式（４）中、Ｄ４（ｘ）は、ＴＯＦ－ＳＩＭＳで測定される、Ｓｉの強度で規格化したＡの強度であり、ｘはノッチ面２６からの深さ（単位：ｎｍ）、ａ４ｘ+ｂ４はｘが２００以上４００以下の範囲におけるＤ４（ｘ）を最小二乗法で近似した直線である。上記式（３）の左辺の値Ｓ３は、好ましくは１０以下である。また、上記式（４）の左辺の値Ｓ４は、好ましくは１以下である。

In the above formula (3), D3(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), x is the depth (unit: nm) from the notch face 26, and a3x+b3 is a straight line obtained by approximating D3(x) by the least squares method in the range of x being 200 or more and 400 or less. In the above formula (4), D4(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth (unit: nm) from the notch face 26, and a4x+b4 is a straight line obtained by approximating D4(x) by the least squares method in the range of x being 200 or more and 400 or less. The value S3 on the left side of the above formula (3) is preferably 10 or less. Moreover, the value S4 on the left side of the above formula (4) is preferably 1 or less.

As described above, the notch surface 26 includes F and A, and satisfies the above formula (3) and formula (4). This makes it possible to soften the hardness of the vicinity of the notch surface 26 that is brought into contact with a holder, positioning tool, or the like. Because the hardness of the vicinity of the notch surface 26 is soft, the vicinity of the notch surface 26 can deform so as to absorb the stress that causes the scratches to extend. Therefore, the extension of the scratches can be suppressed, and a decrease in yield can be suppressed.

Next, the experimental data will be described with reference mainly to FIG. 12 to FIG. 14. In Example 1, the end surface 23 of the glass substrate 2 was directly irradiated with the gas cluster 129. Specifically, as shown in FIG. 11, the first main surface 21 was arranged facing backward and tilted obliquely upward so that the beam 129A of the gas cluster 129 was obliquely incident on the lower end surface 23 of the glass substrate 2. The tilt angle was 5°. As a result, the end surface 23 of the glass substrate 2 was directly irradiated with the gas cluster 129. This was performed by rotating the glass substrate 2 by 90 degrees each time around a rotation axis parallel to the X-axis, so that the gas cluster 129 was directly irradiated on four end surfaces 23. _CF4 gas was used as the raw material gas for the gas cluster 129. That is, the element (A) other than fluorine (F) was carbon (C). After irradiation with the gas cluster 129, the composition analysis of the end surface 23 of the glass substrate 2 was measured by TOF-SIMS. The sample for composition analysis was cut from the end surface 23 of the glass substrate 2 and fixed to a jig so that the end surface 23 was facing upward and approximately horizontal. A TOF.SIMS5 manufactured by ION-TOF was used for the composition analysis of the end surface 23. Quartz glass containing _TiO2 was used as the glass substrate 2.

Figure 12 shows the depth distribution of F intensity/Si intensity measured by TOF-SIMS on the end face 23 of the glass substrate 2 in Example 1. As is clear from Figure 12, F was implanted near the end face 23 of the glass substrate 2. The value S1 of the left side of the above formula (1) was 1.00. Note that when a composition analysis of the end face 23 was performed by TOF-SIMS before irradiation with the gas cluster 129, S1 was 0.139.

Figure 13 shows the depth distribution of C intensity/Si intensity measured by TOF-SIMS on the end face 23 of the glass substrate 2 in Example 1. As is clear from Figure 13, C was implanted near the end face 23 of the glass substrate 2. The value S2 of the left side of the above formula (2) was 0.07. Note that when a composition analysis of the end face 23 was performed by TOF-SIMS before irradiation with the gas cluster 129, S2 was 0.017.

FIG. 14 shows the hardness of the end surface 23 of the glass substrate 2 of Example 1 before and after the gas cluster irradiation. The hardness was measured by an ultra-microindentation hardness tester (product name: ENT-1100a) manufactured by Elionix. The indentation load was 60 mN, the holding time was 1000 ms, and the number of measurements was 100. In FIG. 14, H _min indicates the minimum value, H _25% indicates the 25th percentile, H _50% indicates the 50th percentile (median value), H _75% indicates the 75th percentile, and H _max indicates the maximum value. In general, when the measured values are arranged in ascending order, the value that is located at α% of the total, counting from the beginning, is called the α percentile. As is clear from FIG. 14, it can be seen that the hardness after the gas cluster irradiation is softer than the hardness before the gas cluster irradiation.

In Example 2, the notch surface 26 of the same glass substrate 2 as in Example 1 was directly irradiated with gas clusters 129. _CF4 gas was used as the raw material gas for the gas clusters 129. In other words, the element (A) other than fluorine (F) was carbon (C). After irradiation with the gas clusters 129, the composition of the notch surface 26 of the glass substrate 2 was analyzed by TOF-SIMS. The sample for composition analysis was cut from a corner including the notch surface 26 of the glass substrate 2, and was fixed horizontally to a jig with the notch surface 26 facing upward. A TOF.SIMS5 manufactured by ION-TOF was used for the composition analysis of the notch surface 26.

Figure 15 shows the depth distribution of F intensity/Si intensity measured by TOF-SIMS for the notch surface 26 of the glass substrate 2 in Example 2. As is clear from Figure 15, F was implanted near the notch surface 26 of the glass substrate 2. The value S3 of the left side of the above formula (3) was 4.83. Note that when a composition analysis of the notch surface 26 was performed by TOF-SIMS before irradiation with the gas cluster 129, S3 was 0.139.

Figure 16 shows the depth distribution of C intensity/Si intensity measured by TOF-SIMS on the notch surface 26 of the glass substrate 2 in Example 2. As is clear from Figure 16, C was implanted near the notch surface 26 of the glass substrate 2. The value S4 of the left side of the above formula (4) was 0.114. Note that when a composition analysis of the notch surface 26 was performed by TOF-SIMS before irradiation with the gas cluster 129, S4 was 0.017.

The above results show that the hardness of the notch surface 26 of the glass substrate 2 in Example 2 was softened by irradiation with the gas cluster 129, similar to that of the end surface 23 of the glass substrate 2 in Example 1.

The glass substrate for EUVL and its manufacturing method, as well as the mask blank for EUVL and its manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above-mentioned embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. Naturally, these also fall within the technical scope of the present disclosure.

1 EUVL mask blank 2 Glass substrate 21 First main surface 22 Second main surface 23 End surface 24 First chamfered surface 25 Second chamfered surface 26 Notch surface 3 Reflective film 4 Absorbing film 129 Gas cluster 129A Beam

Claims (13)

a rectangular first main surface, a rectangular second main surface facing opposite to the first main surface, four end surfaces perpendicular to the first main surface and the second main surface, four first chamfered surfaces formed at boundaries between the first main surface and the end surfaces, and four second chamfered surfaces formed at boundaries between the second main surface and the end surfaces;
It is made of quartz glass containing _TiO2 ,
The end surface of the glass substrate for EUVL contains fluorine (F) and an element (A) other than fluorine that forms a gas cluster together with the fluorine, and satisfies the following formulas (1) and (2):

In the above formula (1), D1(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the end face (unit: nm), and a1x+b1 is a straight line obtained by approximating D1(x) using the least squares method when x is in the range of 200 to 400, and in the above formula (2), D2(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the end face (unit: nm), and a2x+b2 is a straight line obtained by approximating D2(x) using the least squares method when x is in the range of 200 to 400. a rectangular first main surface, a rectangular second main surface facing away from the first main surface, four end surfaces perpendicular to the first main surface and the second main surface, four first chamfered surfaces formed at boundaries between the first main surface and the end surfaces, four second chamfered surfaces formed at boundaries between the second main surface and the end surfaces, and one or more notch surfaces formed obliquely with respect to the first main surface so as to cut off corners of two adjacent end surfaces and the first main surface,
It is made of quartz glass containing _TiO2 ,
The notch surface contains fluorine (F) and an element (A) other than fluorine that forms a gas cluster together with the fluorine, and satisfies the following formulas (3) and (4):

In the above formula (3), D3(x) is the intensity of F normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the notch face (unit: nm), and a3x+b3 is a straight line obtained by approximating D3(x) using the least squares method when x is in the range of 200 to 400, and in the above formula (4), D4(x) is the intensity of A normalized by the intensity of Si measured by TOF-SIMS, x is the depth from the notch face (unit: nm), and a4x+b4 is a straight line obtained by approximating D4(x) using the least squares method when x is in the range of 200 to 400. The glass substrate for EUVL according to claim 1 or 2, wherein the element (A) other than fluorine is carbon (C), boron (B), nitrogen (N), sulfur (S), selenium (Se), tellurium (Te), or tungsten (W). The glass substrate for EUVL according to claim 3, wherein the element (A) other than fluorine is carbon (C). A glass substrate for EUVL according to any one of claims 1 to 4,
a reflective film formed on a glass substrate for EUVL to reflect EUV light;
and an absorbing film that absorbs the EUV light and is formed on the reflective film. A method for producing the EUVL glass substrate according to claim 1, comprising the steps of:
A method for manufacturing a glass substrate for EUVL, comprising: irradiating the glass substrate for EUVL with gas clusters containing the fluorine and the element other than the fluorine, and implanting the fluorine and the element other than the fluorine into the end surface. A method for producing the EUVL glass substrate according to claim 2, comprising the steps of:
A method for manufacturing a glass substrate for EUVL, comprising: irradiating the glass substrate for EUVL with gas clusters containing the fluorine and the element other than the fluorine, and implanting the fluorine and the element other than the fluorine into the notch surface. 8. _{The method for producing a glass substrate for EUVL according to claim 6 or 7, wherein the gas clusters include CF4, CHF3, CH2F2, C2F6 , BF3 , NF3 , SF6 , SeF6 , TeF6} , or _WF6 . The method for producing a glass substrate for EUVL according to claim 8 , wherein the gas clusters include CF ₄ , CHF ₃ , or CH ₂ F ₂ . 2. A method for producing a mask blank for EUVL comprising: a glass substrate for EUVL according to claim 1; a reflective film that reflects EUV light and is formed on the glass substrate for EUVL; and an absorbing film that absorbs the EUV light and is formed on the reflective film, the method comprising the steps of:
A method for manufacturing an EUVL mask blank, comprising: irradiating the EUVL glass substrate with gas clusters containing the fluorine and the element other than the fluorine, and implanting the fluorine and the element other than the fluorine into the end surface. 3. A method for producing a mask blank for EUVL comprising: a glass substrate for EUVL according to claim 2; a reflective film that reflects EUV light and is formed on the glass substrate for EUVL; and an absorbing film that absorbs the EUV light and is formed on the reflective film, the method comprising the steps of:
A method for manufacturing a mask blank for EUVL, comprising: irradiating the glass substrate for EUVL with a gas cluster containing the fluorine and the element other than the fluorine, and implanting the fluorine and the element other than the fluorine into the notch surface. 12. _{The method for producing a mask blank for EUVL according to claim 10 or 11, wherein the gas clusters include CF4, CHF3, CH2F2, C2F6 , BF3 , NF3 , SF6 , SeF6 , TeF6} , or _WF6 . The method for producing a mask blank for EUVL according to claim 12 , wherein the gas cluster comprises CF ₄ , CHF ₃ , or CH ₂ F ₂ .

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