WO2023166961A1

WO2023166961A1 - Ultrasonic cleaning head, substrate cleaning method, substrate cleaning device, method for manufacturing substrate, and method for manufacturing mask blank for euvl

Info

Publication number: WO2023166961A1
Application number: PCT/JP2023/004703
Authority: WO
Inventors: 尚明宮本; 大介吉宗; 圭輔太田; 定達池田
Original assignee: Ａｇｃ株式会社
Priority date: 2022-03-03
Filing date: 2023-02-13
Publication date: 2023-09-07

Abstract

This ultrasonic cleaning head has a vibration surface that faces the upper surface of a substrate with a gap therebetween, and contacts a liquid film formed on the upper surface of the substrate. The vibration surface has a surface density of Ce element of 30×10¹⁰atoms/cm² as detected by a total reflection X-ray fluorescence analysis.

Description

Ultrasonic cleaning head, substrate cleaning method, substrate cleaning apparatus, substrate manufacturing method, and EUVL mask blank manufacturing method

The present disclosure relates to an ultrasonic cleaning head, a substrate cleaning method, a substrate cleaning apparatus, a substrate manufacturing method, and an EUVL mask blank manufacturing method.

In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), which is an exposure technology using Extreme Ultraviolet (EUV), has been developed. EUV includes soft X-rays and vacuum ultraviolet rays, and specifically refers to light with a wavelength of approximately 0.2 nm to 100 nm. At present, EUV with a wavelength of about 13.5 nm is mainly considered.

A reflective mask is used in EUVL. A reflective mask has, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV, and an absorbing film that absorbs EUV. An opening pattern is formed in the absorption film. In EUVL, a pattern of openings in an absorbing film is transferred to a target substrate, such as a semiconductor substrate. Transferring includes reducing and transferring.

In the middle of the EUVL mask blank manufacturing process, the glass substrate or the functional film formed on the glass substrate may be cleaned. Ultrasonic cleaning may be performed as one of the cleaning methods.

The cleaning method described in Patent Document 1 includes spraying a cleaning liquid to which ultrasonic waves have been applied in advance from a nozzle onto the upper surface of a rotating substrate. In the cleaning method described in Patent Document 2, a cleaning liquid is supplied between the upper surface of a rotating substrate and the lower surface of an ultrasonic cleaning head, and ultrasonic waves are applied to the cleaning liquid from the lower surface of the ultrasonic cleaning head. , cleaning the top surface of the substrate.

Japanese Patent Application Laid-Open No. 2013-158664 Japanese Patent Application Laid-Open No. 2001-87725

Even when using the cleaning method described in Patent Document 1, the number of particles adhering to the substrate could not be sufficiently reduced. The inventor of the present application investigated particles adhering to the substrate after ultrasonic cleaning, and found that cerium oxide particles were one of the causes of the particles. In addition, as a source of cerium oxide particles, it was found that cerium oxide particles adhering to the ultrasonic cleaning head detached during cleaning and adhered to the substrate. Since cerium oxide particles are generally used for mechanical polishing, they are considered to have adhered during the manufacturing process of the ultrasonic cleaning head. The manufacturing process of the ultrasonic cleaning head includes cutting and mechanical polishing, for example. Cutting processes the diaphragm into a desired shape. Mechanical polishing polishes the diaphragm with cerium oxide particles.

One aspect of the present disclosure provides a technique for reducing the number of particles adhering to a substrate by ultrasonic cleaning.

An ultrasonic cleaning head according to an aspect of the present disclosure has a vibrating surface that faces an upper surface of a substrate with a gap therebetween and contacts a liquid film formed on the upper surface of the substrate. The vibrating surface has a Ce element surface density of 30×10 ¹⁰ atoms/cm ² or less as detected by total reflection X-ray fluorescence analysis.

In the ultrasonic cleaning head of one aspect of the present disclosure, the surface density of Ce element on the vibration surface is 30×10 ¹⁰ atoms/cm ² or less, so the surface density of the cerium oxide particles adhering to the vibration surface is low. Therefore, the number of particles detached from the vibration surface of the ultrasonic cleaning head can be reduced, and the number of particles adhering to the substrate by ultrasonic cleaning can be reduced.

FIG. 1 is a side view showing a substrate cleaning apparatus according to one embodiment. FIG. 2 is a cross-sectional view showing an example of the internal structure of the cleaning head. FIG. 3 is a cross-sectional view showing another example of the internal structure of the cleaning head. FIG. 4 is a plan view showing an example of the movement locus of the cleaning head. FIG. 5 is a cross-sectional view showing an example of pretreatment of the cleaning head. FIG. 6 is a cross-sectional view showing another example of pretreatment of the cleaning head. FIG. 7 is a diagram showing an example of the relationship between the number of processed dummy substrates and the number of particles. 4 is a flow chart showing a method for manufacturing an EUVL mask blank according to one embodiment. FIG. 9 is a cross-sectional view showing an example of a substrate. 10 is a plan view of the substrate of FIG. 9. FIG. FIG. 11 is a cross-sectional view showing an example of an EUVL mask blank. FIG. 12 is a cross-sectional view showing an example of an EUVL mask.

Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same or corresponding configurations, and descriptions thereof may be omitted. In the specification, "-" indicating a numerical range means that the numerical values described before and after it are included as lower and upper limits.

A substrate cleaning apparatus 1 according to one embodiment will be described with reference to FIGS. The substrate cleaning apparatus 1 cleans the substrate W by applying ultrasonic vibrations to a liquid film F formed on the substrate W. As shown in FIG. Particles adhering to the substrate W can be removed. The substrate cleaning apparatus 1 includes a holding section 10 , a nozzle 20 , a cleaning head 30 , a rotating section 40 , a first moving section 50 , a second moving section 60 and a control section 90 . Cleaning head 30 is an example of an ultrasonic cleaning head.

The holding part 10 holds the substrate W horizontally. When viewed from above, the substrate W is rectangular (see FIG. 4), but may also be circular. Substrate W includes a glass substrate, a silicon wafer, or a compound semiconductor wafer. The substrate W may include a functional film formed on a glass substrate or the like. A functional film is, for example, a light reflecting film, a light absorbing film, a conductive film, an insulating film, or the like.

The holding part 10 includes a plurality of pins 11 arranged at intervals along the periphery of the substrate W, as shown in FIG. 1, for example. A plurality of pins 11 hold the peripheral edge of the substrate W. As shown in FIG. A substrate W is placed on a plurality of pins 11 . Since there is a space under the substrate W, it is also possible to install the sensor on the bottom surface of the substrate W. FIG. It should be noted that the holding unit 10 may hold the substrate W by suction.

The nozzle 20 forms a liquid film F by supplying cleaning liquid to the upper surface Wa of the substrate W held by the holding unit 10 . The top surface Wa of the substrate W is also referred to as the substrate top surface Wa. The nozzle 20 supplies the cleaning liquid, for example, near the center of the substrate upper surface Wa. The substrate W is rotating, and the cleaning liquid on the substrate W is wetted and spread from the center of the substrate W toward the periphery by centrifugal force. As a result, a liquid film F is formed on the entire substrate upper surface Wa. The nozzle 20 may be provided outside the cleaning head 30 as shown in FIG. 1, or may be provided inside the cleaning head 30 (not shown).

The nozzle 20 is connected to a cleaning liquid supply source 22 via a supply line 21 . A valve 23 is provided in the middle of the supply line 21 . The valve 23 opens and closes the channel of the supply line 21 . When the valve 23 opens the flow path of the supply line 21, the cleaning liquid is supplied from the supply source 22 to the nozzle 20, and the nozzle 20 discharges the cleaning liquid. When the valve 23 closes the flow path of the supply line 21, the nozzle 20 stops discharging the cleaning liquid.

The cleaning liquid is, for example, pure water (for example, deionized water), a mixture of pure water and X (at least one component selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, and acetic acid), pure water and Y (at least one component selected from the group consisting of ammonia, tetramethylammonium hydroxide, triethanolamine, choline, sodium hydroxide, potassium hydroxide, and cesium hydroxide) mixture, pure water and Z (hydrogen peroxide, at least one component selected from the group consisting of perchlorate ions and periodate ions), a mixture of pure water and X and Z, or a mixture of pure water and Y and Z.

The cleaning liquid may dissolve at least one gas selected from the group consisting of _H2 gas, _CO2 gas, _N2 gas, _O2 gas, _O3 gas, and Ar gas. By controlling the amount of dissolved gas, the cavitation generation efficiency can be improved, and the particle removal efficiency can be improved. The gas dissolved in the cleaning liquid is preferably _H2 gas, _CO2 gas or _N2 gas, more preferably _CO2 gas.

The cleaning head 30 includes, as shown in FIG. 2, a vibrating surface 31a that contacts the liquid film F, and an ultrasonic transducer 32 that vibrates the vibrating surface 31a. Cleaning head 30 includes diaphragm 31 . The vibration plate 31 has a downward vibration surface 31a that contacts the liquid film F, and an upward mounting surface 31b to which the ultrasonic transducer 32 is mounted.

The vibration surface 31a is installed parallel to the upper surface Wa of the substrate. The size of the vibration surface 31a is smaller than, for example, the size of the substrate upper surface Wa. The shape of the vibration surface 31a is, for example, circular. When the nozzle 20 is provided inside the cleaning head 30, the ejection port of the nozzle 20 is formed on the vibrating surface 31a.

The mounting surface 31b may be installed parallel to the vibration surface 31a as shown in FIG. 2, or may be installed obliquely to the vibration surface 31a as shown in FIG. In FIG. 3, θ is the angle between the normal to the vibration surface 31a and the normal to the mounting surface 31b. The normal direction of the mounting surface 31 b is the vibration direction of the ultrasonic transducer 32 .

The ultrasonic oscillator 32 applies ultrasonic vibration to the liquid film F and applies sound pressure to the substrate W by vibrating the vibration surface 31a. As a result, particles adhering to the upper surface Wa of the substrate can be peeled off. The output of the ultrasonic transducer 32 is controlled by the controller 90 . When the distance D between the cleaning head 30 and the substrate W is constant, the sound pressure acting on the substrate W increases as the output of the ultrasonic transducer 32 increases.

The rotating section 40 rotates the substrate W together with the holding section 10 . A rotation center line 10R of the holding part 10 is set vertically. The holding part 10 holds the substrate W so that the rotation center line 10R passes through the center of the substrate W. As shown in FIG. The rotating part 40 includes, for example, a servomotor 41 . The rotational driving force of the servomotor 41 may be transmitted to the holding portion 10 via pulleys and belts, or gears (not shown). The servomotor 41 transmits information about the rotational position of the holding section 10 to the control section 90 . The rotational position of the holding portion 10 is represented by a rotational angle. A stepping motor may be used instead of the servomotor 41 .

The first moving part 50 moves the cleaning head 30 in a horizontal direction orthogonal to the rotation center line 10R of the holding part 10. The cleaning head 30 is moved between a position directly above the center of the substrate W and a position directly above the periphery of the substrate W, for example. The 1st moving part 50 contains the servomotor 51, for example. The servo motor 51 transmits information regarding the horizontal position of the cleaning head 30 to the control section 90 . A stepping motor may be used instead of the servomotor 51 .

The first moving part 50 moves the cleaning head 30 in a horizontal direction orthogonal to the rotation center line 10R of the holding part 10 by rotating the pivot 52, for example. The swivel shaft 52 is fixed to one end of the swivel arm 53 , and the cleaning head 30 is fixed to the other end of the swivel arm 53 . A swivel centerline 30R of the cleaning head 30 is set vertically.

Although not shown, the first moving part 50 may move the cleaning head 30 in a horizontal direction orthogonal to the rotation center line 10R of the holding part 10 along a horizontal guide rail.

The second moving part 60 moves the cleaning head 30 in the vertical direction. For example, the second moving unit 60 moves the cleaning head 30 vertically by moving the turning shaft 52 vertically. The second moving section 60 includes a servomotor 61 . The second moving part 60 may include, for example, a ball screw that converts rotary motion of the servo motor 61 into linear motion. The servomotor 61 transmits information about the vertical position of the cleaning head 30 to the controller 90 . A stepping motor may be used instead of the servomotor 61 . The second moving part 60 may move the cleaning head 30 in the vertical direction by using an air cylinder instead of the motor.

Although not shown, the second moving part 60 may move the holding part 10 in the vertical direction instead of moving the cleaning head 30 in the vertical direction. In any case, the distance D between the substrate W and the cleaning head 30 can be changed.

The control section 90 controls the valve 23 , the ultrasonic transducer 32 , the rotating section 40 , the first moving section 50 and the second moving section 60 . The control unit 90 is, for example, a computer, and includes a CPU (Central Processing Unit) 91 and a storage medium 92 such as a memory. The storage medium 92 stores programs for controlling various processes executed in the substrate cleaning apparatus 1 . The control unit 90 controls the operation of the substrate cleaning apparatus 1 by causing the CPU 91 to execute programs stored in the storage medium 92 .

Next, the operation of the substrate cleaning apparatus 1, that is, the substrate cleaning method will be described. First, a transport robot (not shown) enters the interior of the substrate cleaning apparatus 1 and delivers the substrate W held by the transport robot to the holding unit 10 . After the holding unit 10 holds the substrate W horizontally, the transfer robot leaves the substrate cleaning apparatus 1 . The substrate W is carried in in this manner.

Next, the rotating part 40 rotates the substrate W together with the holding part 10, and the nozzle 20 supplies the cleaning liquid to the vicinity of the center of the substrate W. The cleaning liquid on the substrate W wets and spreads from the center of the substrate W toward the periphery due to centrifugal force. As a result, a liquid film F is formed on the entire substrate upper surface Wa. The supply rate of the cleaning liquid is, for example, 0.1 L/min to 5.0 L/min, preferably 0.8 L/min to 1.6 L/min.

Next, the first moving part 50 adjusts the horizontal position of the cleaning head 30 so that the vibration surface 31a of the cleaning head 30 contacts the liquid film F, and the second moving part 60 moves the cleaning head 30 vertically. Adjust position. A desired gap is formed between the cleaning head 30 and the substrate W. FIG. The interval is, for example, 0.1 mm to 5.0 mm, preferably 1.0 mm to 4.0 mm.

Next, the ultrasonic vibrator 32 vibrates the vibration surface 31a of the cleaning head 30 to apply ultrasonic vibration to the liquid film F and apply sound pressure to the upper surface Wa of the substrate.

Next, the first moving part 50 moves the cleaning head 30 in the horizontal direction orthogonal to the rotation center line 10R of the holding part 10. The cleaning head 30 is reciprocated between a position just above the center of the substrate W and a position just above the periphery of the substrate W. As shown in FIG. The substrate W is rotating, and the entire substrate upper surface Wa is cleaned.

Next, after the second moving part 60 raises the cleaning head 30, the first moving part 50 moves the horizontal position of the cleaning head 30 to the standby position. The standby position is a position outside the periphery of the substrate W when viewed from above. Further, the ultrasonic vibrator 32 stops vibrating the vibrating surface 31a, and the nozzle 20 stops supplying the cleaning liquid.

Next, with the nozzle 20 stopping the supply of the cleaning liquid, the rotating section 40 rotates the substrate W together with the holding section 10, so that the cleaning liquid on the substrate W is shaken off from the periphery of the substrate W by centrifugal force. The liquid film F is removed from the substrate W and the substrate W is dried.

Next, a transport robot (not shown) enters the interior of the substrate cleaning apparatus 1 and receives the substrate W from the holding section 10 . After the transport robot holds the substrate W, the transport robot leaves the substrate cleaning apparatus 1 . The substrate W is carried out in this manner.

Next, an example of pretreatment of the cleaning head 30 will be described with reference to FIGS. 5 and 6. FIG. The pretreatment of the cleaning head 30 is performed before the cleaning head 30 is incorporated into the substrate cleaning apparatus 1 . After the cleaning head 30 is installed in the substrate cleaning apparatus 1, the dummy substrate is cleaned by the substrate cleaning apparatus 1, and then the substrate W as a product is cleaned. The pretreatment of the cleaning head 30 may be performed before cleaning the dummy substrate, and may be performed after the cleaning head 30 is installed in the substrate cleaning apparatus 1 .

The dummy substrate is configured in the same manner as the substrate W, which is a product, and is cleaned in the same manner as the substrate W. Specifically, although not shown, ultrasonic vibration is applied to the liquid film F from the vibrating surface 31a while the liquid film F is formed between the vibrating surface 31a of the cleaning head 30 and the upper surface of the dummy substrate, which face each other. and wash the dummy substrate. Hereinafter, cleaning of the dummy substrate is also referred to as dummy cleaning. Dummy cleaning is performed for the purpose of suppressing dust generation from the cleaning head 30 .

As shown in FIGS. 5 and 6, particles P adhere to the vibration surface 31a of the cleaning head 30. As shown in FIGS. The distance between the vibration surface 31a of the cleaning head 30 and the upper surface of the dummy substrate is short, and the particles P separated from the vibration surface 31a of the cleaning head 30 easily adhere to the upper surface of the dummy substrate. It is practically difficult to reduce the number of attached particles P to zero.

Dummy cleaning is repeated while replacing the dummy substrate. As shown in FIG. 7, as the number of dummy substrates to be processed increases, that is, as the dummy cleaning time increases, dust generation from the cleaning head 30 is suppressed, and the number of particles P adhering to the dummy substrates due to ultrasonic cleaning decreases. decrease.

As shown in FIG. 7, when the dummy cleaning time is lengthened to some extent, the number of particles P adhering to the dummy substrate settles down to a constant value. After that, the substrate W, which is a product, is washed. The number of particles P adhering to the substrate W is approximately the same as the number of particles P adhering to the last dummy substrate.

By the way, the smaller the number of particles P adhering to the vibration surface 31a of the cleaning head 30 before dummy cleaning, the shorter the time required for the number of particles P adhering to the dummy substrate to settle down to a constant value. The constant value becomes smaller. Therefore, the smaller the number of particles P adhering to the vibration surface 31a of the cleaning head 30 before the dummy cleaning, the fewer the particles P adhering to the substrate W.

The inventor of the present application has investigated the cause of particles P adhering to the vibration surface 31 a of the cleaning head 30 . Particles P are considered to adhere during any one of the cleaning head 30 manufacturing process, packaging process, and transportation process. The inventor of the present application paid attention to the cerium oxide particles used in the manufacturing process of the cleaning head 30 .

The vibration surface 31a of the cleaning head 30 is formed on the vibration plate 31, as shown in FIGS. The material of the diaphragm 31 is quartz glass (SiO ₂ ), for example. The material of diaphragm 31 may be sapphire glass (Al ₂ O ₃ ). Further, the material of diaphragm 31 may be either crystalline or amorphous.

The manufacturing process of the cleaning head 30 includes cutting and mechanical polishing, for example. Cutting processes the diaphragm 31 into a desired shape. In the mechanical polishing, after cutting, the diaphragm 31 is polished with cerium oxide particles. It is believed that cerium oxide particles adhere to the diaphragm 31 during mechanical polishing. The manufacturing process of the cleaning head 30 may include, for example, flame polishing between cutting and mechanical polishing.

The inventors of the present application have found that cerium oxide particles adhering to the diaphragm 31 are removed by supplying at least one of a first chemical liquid L1 and a second chemical liquid L2, which will be described later, to the diaphragm 31 before dummy cleaning. investigated. By removing the cerium oxide particles, it is possible not only to shorten the time until the number of particles P adhering to the dummy substrate settles down to a constant value, but also to reduce the constant value.

The first chemical liquid L1 dissolves the cerium oxide particles adhering to the vibration plate 31, thereby removing the cerium oxide particles. _The first chemical liquid _L1 is not particularly limited as long as _it dissolves cerium oxide _. is an aqueous solution containing The first chemical liquid L1 may be heated to promote dissolution of the cerium oxide.

The first chemical liquid L1 is stored in the first chemical liquid tank 101, for example, as shown in FIG. By immersing diaphragm 31 in first chemical liquid L<b>1 stored in first chemical liquid tank 101 , first chemical liquid L<b>1 can be supplied to diaphragm 31 . A method of supplying the first chemical liquid L1 is not particularly limited. For example, the first chemical liquid L1 may be sprayed onto the diaphragm 31 using a spray.

The second chemical liquid L2 dissolves the surface of the diaphragm 31 to detach the cerium oxide particles from the diaphragm 31 . The second chemical liquid L2 is appropriately selected according to the material of the diaphragm 31, and is, for example, an aqueous solution containing hydrofluoric acid (HF) or an aqueous solution containing an alkaline detergent. An aqueous solution containing an alkaline detergent preferably has a pH of 9 or higher. If the pH is 9 or higher, Si—O bonds can be cut and SiO ₂ can be etched. Alkaline detergents include, for example, NaOH or KOH. The second chemical liquid L2 may be heated to promote dissolution of the cleaning head 30 .

The second chemical liquid L2 is stored in the second chemical liquid tank 102 as shown in FIG. 6, for example. By immersing the diaphragm 31 in the second chemical L2 stored in the second chemical tank 102, the second chemical L2 can be supplied to the diaphragm 31. As shown in FIG. In addition, the method of supplying the second chemical liquid L2 is not particularly limited. For example, the second chemical liquid L2 may be sprayed onto the vibration plate 31 using a spray.

The first chemical liquid L1 and the second chemical liquid L2 may be supplied not only to the vibration surface 31a of the diaphragm 31 but also to the side surface 31c. Moreover, although not shown, when the ejection port of the nozzle 20 is formed on the vibrating surface 31a of the diaphragm 31, it is preferable to supply the first chemical liquid L1 and the second chemical liquid L2 to the inside of the nozzle 20 as well. It is preferable to supply the first chemical liquid L1 and the second chemical liquid L2 to the portion of the vibration plate 31 that comes into contact with the cleaning liquid.

Only one of the first chemical liquid L1 and the second chemical liquid L2 may be used, but it is preferable to use both. When both the first chemical solution L1 and the second chemical solution L2 are used, it is preferable to supply the second chemical solution L2 to the diaphragm 31 after supplying the first chemical solution L1 to the diaphragm 31 .

If the second chemical liquid L2 is supplied to the diaphragm 31 after the first chemical liquid L1 is supplied to the diaphragm 31, surface roughness of the diaphragm 31 can be suppressed compared to the case where the order is reversed. This is because the surface of the diaphragm 31 can be uniformly dissolved by dissolving the surface of the diaphragm 31 after the particles P adhering to the surface of the diaphragm 31 are dissolved.

After supplying the acidic chemical liquid to the diaphragm 31 as the first chemical liquid L1 or the second chemical liquid L2, it is preferable to supply the alkaline chemical liquid to the diaphragm 31 . The alkaline chemical solution can adjust the zeta potentials of both the cleaning head 30 and the particles P to the same polarity (for example, negative), and can suppress the redeposition of the particles P. The alkaline chemical solution is, for example, an aqueous solution containing an alkaline detergent, or a mixed aqueous solution of ammonium hydroxide (NH ₄ OH) and hydrogen peroxide (H ₂ O ₂ ) (so-called SC-1).

After supplying the first chemical liquid L1 or the second chemical liquid L2 to the diaphragm 31, it is preferable to supply the rinse liquid to the diaphragm 31 to remove the residue of the chemical liquid. Pure water such as DIW (deionized water) is used as the rinse liquid.

It is also possible to detach the cerium oxide particles from the diaphragm 31 by dry etching the surface of the diaphragm 31 . Fluorine plasma, for example, is used for the dry etching of the vibration plate 31 .

The number of cerium oxide particles adhering to the vibrating surface 31a of the cleaning head 30 is expressed by the surface density of the Ce element detected by total reflection X-ray fluorescence (TXRF) of the vibrating surface 31a. can be done. The lower the areal density of the Ce element, the smaller the number of cerium oxide particles.

Although the details will be described in the section of Examples, the inventors of the present application used a chemical solution to reduce the surface density of the Ce element detected by the TXRF method on the vibration surface 31a of the cleaning head 30 to 30×10 ¹⁰ atoms/cm ² or less. It has been found that the number of particles P adhering to the substrate W can be reduced by ultrasonic cleaning.

If the surface density of the Ce element on the vibrating surface 31a of the cleaning head 30 is 30×10 ¹⁰ atoms/cm ² or less, the surface density of the cerium oxide particles adhering to the vibrating surface 31a is low. Therefore, the number of particles P detached from the vibration surface 31a of the cleaning head 30 can be reduced, and the number of particles P adhering to the substrate W by ultrasonic cleaning can be reduced.

Note that the method of making the surface density of Ce element on the vibration surface 31a of the cleaning head 30 to 30×10 ¹⁰ atoms/cm ² or less is to supply at least one of the first chemical liquid L1 and the second chemical liquid L2 to the vibration plate 31. The method is not limited. For example, the density of the cerium oxide particles may be brought to a predetermined range by scrubbing with a brush or sponge.

From the viewpoint of reducing the number of particles P adhering to the substrate W due to ultrasonic cleaning, the surface density of the Ce element on the vibration surface 31a of the cleaning head 30 is preferably 10×10 ¹⁰ atoms/cm ² or less, and more preferably. is 1×10 ¹⁰ atoms/cm ² or less. The surface density of the Ce element on the vibrating surface 31a of the cleaning head 30 should be 0 atoms/cm ² or more.

The vibration surface 31a of the cleaning head 30 is 100% for the surface density of the most abundant element among the elements with atomic numbers of 13 to 30 and 33 to 72 detected by the TXRF method. is preferably 1.0% or less. When the material of the vibrating surface 31a is _SiO2 , the most abundant element is Si. Further, when the material of the vibrating surface 31a is Al ₂ O ₃ , the most abundant element is Al. The atomic number of Ce is 58.

The element with atomic number 13 is Al. The element with atomic number 30 is Zn. The element with atomic number 33 is As. The element with atomic number 72 is Hf. Here, it is assumed that a W (tungsten) beam is used as an X-ray source for the TXRF method. When using a W beam, Ga with atomic number 31 and Ge with atomic number 32 are difficult to detect.

If the sum of the surface densities of all the remaining elements excluding the most abundant element is 1.0% or less, the number of particles P adhering to the vibrating surface 31a is small. Therefore, the number of particles P detached from the vibration surface 31a of the cleaning head 30 can be reduced, and the number of particles P adhering to the substrate W by ultrasonic cleaning can be reduced.

From the viewpoint of reducing the number of particles P adhering to the substrate W, the total surface density of all the remaining elements excluding the most abundant element is preferably 0.5% or less. The total areal density of all the remaining elements excluding the most abundant element may be 0.0% or more, but is preferably 0.1% or more from the viewpoint of productivity.

Next, a method of manufacturing the EUVL mask blank 200 shown in FIG. 11 will be described with reference to FIG. The manufacturing method of the EUVL mask blank 200 has steps S101 to S107. For example, a substrate 210 shown in FIGS. 9 and 10 is prepared in advance. Steps S101 to S104 are included in the substrate manufacturing method.

The substrate 210 includes a first major surface 211 and a second major surface 212 opposite to the first major surface 211 . The first major surface 211 is rectangular. In this specification, a rectangular shape includes a shape with chamfered corners. Rectangles also include squares. The second major surface 212 is opposite to the first major surface 211 . The second main surface 212 is also rectangular like the first main surface 211 .

The substrate 210 also includes four end surfaces 213 , four first chamfered surfaces 214 and four second chamfered surfaces 215 . The end surface 213 is perpendicular to the first major surface 211 and the second major surface 212 . A first chamfered surface 214 is formed at the boundary between the first major surface 211 and the end surface 213 . A second chamfered surface 215 is formed at the boundary between the second main surface 212 and the end surface 213 . The first chamfered surface 214 and the second chamfered surface 215 are so-called C-chamfered surfaces in this embodiment, but may be R-chamfered surfaces.

The substrate 210 is, for example, a glass substrate. The glass of substrate 210 is preferably quartz glass containing TiO ₂ . Silica glass has a smaller coefficient of linear expansion than general soda-lime glass, and its dimensional change due to temperature change is small. The quartz glass may contain 80% to 95% by weight of SiO ₂ and 4% to 17% by weight of TiO ₂ . When the TiO ₂ content is 4% by mass to 17% by mass, the coefficient of linear expansion near room temperature is approximately zero, and dimensional change hardly occurs near room temperature. Quartz glass may contain third components or impurities other than _SiO2 and _TiO2 .

The size of the substrate 210 in plan view is, for example, 152 mm long and 152 mm wide. The longitudinal and lateral dimensions may be 152 mm or greater.

The substrate 210 has a central region 211A and a peripheral region 211B on the first main surface 211. The central region 211A is a square region excluding a rectangular frame-shaped peripheral region 211B surrounding the central region 211A, is processed to a desired flatness in steps S101 to S104, and is a quality assurance region. The quality assurance area has a size of, for example, 142 mm long and 142 mm wide. The four sides of the central region 211A are parallel to the four end faces 213. As shown in FIG. The center of central region 211A coincides with the center of first main surface 211 .

Although not shown, the second principal surface 212 of the substrate 210 also has a central region and a peripheral region, similar to the first principal surface 211 . The central region of the second principal surface 212 is a square region, similar to the central region of the first principal surface 211, which is processed to a desired flatness in steps S101 to S104 of FIG. Guaranteed area. The quality assurance area has a size of, for example, 142 mm long and 142 mm wide.

Step S101 includes polishing the first main surface 211 and the second main surface 212 of the substrate 210 . The first principal surface 211 and the second principal surface 212 are simultaneously polished by a double-sided polisher (not shown) in this embodiment, but may be polished sequentially by a single-sided polisher (not shown). In step S<b>101 , the substrate 210 is polished while supplying polishing slurry between the polishing pad and the substrate 210 .

As the polishing pad, for example, a urethane-based polishing pad, a non-woven fabric-based polishing pad, or a suede-based polishing pad is used. The polishing slurry contains an abrasive and a dispersion medium. The abrasive is, for example, cerium oxide particles. The dispersion medium is, for example, water or an organic solvent. The first main surface 211 and the second main surface 212 may be polished multiple times with abrasives of different materials or grain sizes.

The abrasive used in step S101 is not limited to cerium oxide particles, and may be, for example, silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, or silicon carbide particles. good.

Step S102 includes measuring the surface shapes of the first main surface 211 and the second main surface 212 of the substrate 210 . For surface shape measurement, for example, a non-contact type measuring instrument such as a laser interference type is used so as not to damage the surface. The measuring machine measures the surface shape of the central region 211A of the first principal surface 211 and the central region of the second principal surface 212 .

Step S103 includes locally processing the first main surface 211 and the second main surface 212 of the substrate 210 with reference to the measurement result of step S102 in order to improve the flatness. The first main surface 211 and the second main surface 212 are locally machined in order. The order is not particularly limited and may be either one first.

For local processing, at least one selected from, for example, a GCIB (Gas Cluster Ion Beam) method, a PCVM (Plasma Chemical Vaporization Machining) method, a magnetic fluid polishing method, and polishing with a rotary polishing tool is used.

Step S104 includes final polishing of the first main surface 211 and the second main surface 212 of the substrate 210 . The first principal surface 211 and the second principal surface 212 are simultaneously polished by a double-sided polisher (not shown) in this embodiment, but may be polished sequentially by a single-sided polisher (not shown). In step S<b>104 , the substrate 210 is polished while supplying polishing slurry between the polishing pad and the substrate 210 . The polishing slurry contains an abrasive. Abrasives are, for example, colloidal silica particles.

Step S105 includes forming the conductive film 240 shown in FIG. The conductive film 240 is used to attract the EUVL mask to the electrostatic chuck of the exposure apparatus. The conductive film 240 is made of, for example, chromium nitride (CrN). As a method for forming the conductive film 240, for example, a sputtering method is used.

Step S106 includes forming the multilayer reflective film 220 shown in FIG. The multilayer reflective film 220 reflects EUV. The multilayer reflective film 220 is formed by alternately laminating high refractive index layers and low refractive index layers, for example. The high refractive index layer is made of silicon (Si), for example, and the low refractive index layer is made of molybdenum (Mo), for example. As a method for forming the multilayer reflective film 220, for example, a sputtering method such as an ion beam sputtering method or a magnetron sputtering method is used.

Step S107 includes forming the absorbing film 230 shown in FIG. 11 on the multilayer reflective film 220 formed in step S106. The absorbing film 230 absorbs EUV. The absorbing film 230 may be a phase shift film and may shift the phase of EUV. The absorption film 230 is formed of a single metal, alloy, nitride, oxide, oxynitride, etc. containing at least one element selected from tantalum (Ta), chromium (Cr), and palladium (Pd), for example. As a method for forming the absorption film 230, for example, a sputtering method is used.

Although steps S106 and S107 are performed after step S105 in this embodiment, they may be performed before step S105.

Through steps S101 to S107, the EUVL mask blank 200 shown in FIG. 11 is obtained. The EUVL mask blank 200 has a conductive film 240, a substrate 210, a multilayer reflective film 220, and an absorbing film 230 in this order. The EUVL mask blank 200 may include another film in addition to the conductive film 240, the substrate 210, the multilayer reflective film 220, and the absorption film 230. FIG.

For example, the EUVL mask blank 200 may further include a low-reflection film. A low-reflection film is formed on the absorbing film 230 . After that, an opening pattern 231 is formed in both the low reflection film and the absorption film 230 . The low-reflection film is used for inspection of the opening pattern 231 and has a lower reflection characteristic than the absorption film 230 with respect to inspection light. The low reflection film is made of TaON or TaO, for example. As a method for forming the low-reflection film, for example, a sputtering method is used.

Moreover, the EUVL mask blank 200 may further include a protective film. A protective film is formed between the multilayer reflective film 220 and the absorbing film 230 . The protective film protects the multilayer reflective film 220 from being etched when the absorbing film 230 is etched to form the opening pattern 231 in the absorbing film 230 . The protective film is made of, for example, Ru, Si, or _TiO2 . As a method for forming the protective film, for example, a sputtering method is used.

As shown in FIG. 12, the EUVL mask 201 is obtained by forming an opening pattern 231 in the absorbing film 230 of the EUVL mask blank 200 . A photolithography method and an etching method are used to form the opening pattern 231 . Therefore, the resist film used for forming the opening pattern 231 may be included in the EUVL mask blank 200 .

By the way, during the manufacturing process of the EUVL mask blank 200, the substrate 210 or various functional films formed on the substrate 210 may be cleaned. Cleaning using a chemical reaction with an acid or alkali, cleaning using a physical action, or a combination thereof is performed. Cleaning using physical action includes ultrasonic cleaning, scrub cleaning, or two-fluid cleaning. In the two-fluid cleaning, the cleaning liquid and the gas are mixed and sprayed.

Ultrasonic cleaning is performed using, for example, the substrate cleaning apparatus 1 shown in FIG. Ultrasonic cleaning is preferably performed at least one of between steps S104 and S105, between steps S105 and S106, between steps S106 and S107, and after step S107. In addition, although not shown, ultrasonic cleaning may be performed before and after the low-reflection film, hard mask film, or protective film.

The experimental data will be explained below. Example 1 below is a comparative example, and Examples 2 to 4 below are examples. Table 1 shows the experimental conditions and evaluation results of Examples 1 to 4.

In Examples 1 to 4, the various cleaning solutions listed in Table 1 were supplied to the vibration plate of the cleaning head in the order of the numbers listed in Table 1 to perform pretreatment of the cleaning head, and then dummy cleaning was performed. After that, the substrate was washed. The material of the vibration plate of the cleaning head was quartz glass. The diaphragm was previously subjected to cutting and mechanical polishing in this order. In the mechanical polishing, cerium oxide particles were used to polish the diaphragm.

In Table 1, "Area density of Ce" and "Area density of all elements except Si" were measured by the TXRF method after pretreatment of the cleaning head and before dummy cleaning. A W (tungsten) beam was used as the X-ray source for the TXRF method, and areal densities of elements with atomic numbers 13-30 and 33-72 were measured. The most abundant element was Si. "Area density of all elements other than Si" is the sum of surface densities of all elements except Si when the areal density of Si is 100%. The detection limit (detection lower limit) of the measuring device for measuring the surface density of various elements by the TXRF method was 0.8×10 ¹⁰ atoms/cm ² .

Note that measuring the areal density of various elements on the vibration surface of the cleaning head by the TXRF method would destroy the cleaning head, so a quartz glass plate was prepared separately from the cleaning head. Similar to the vibration plate of the cleaning head, the quartz glass plate was previously subjected to cutting and mechanical polishing in this order. In the mechanical polishing, cerium oxide particles were used to polish the quartz glass plate. After supplying various cleaning liquids shown in Table 1 to the quartz glass plate in the order of the numbers shown in Table 1, surface densities of various elements on the surface of the quartz glass plate were measured by the TXRF method.

In Table 1, "dummy cleaning time" is the time until the number of particles adhering to the dummy substrate by ultrasonic cleaning settles down to a constant value. The number of particles adhering to the dummy substrate due to ultrasonic cleaning was measured by measuring the number of particles on the dummy substrate before and after ultrasonic cleaning and calculating the difference.

In Table 1, "the number of particles on the substrate" is the average number of particles adhering to the substrate by ultrasonic cleaning after the dummy cleaning. The number of particles adhering to the substrate due to ultrasonic cleaning was measured by measuring the number of particles on the substrate before and after ultrasonic cleaning and calculating the difference.

The number of particles was measured by Lasertec's MAGICS series. The number of particles is the number of defects converted to SiO ₂ particles 40 nm size.

As shown in Table 1, in Example 1, both the first chemical solution (the chemical solution that dissolves cerium oxide) and the second chemical solution (the chemical solution that dissolves quartz glass) are supplied to the vibration plate of the cleaning head in the pretreatment of the cleaning head. Therefore, the "dummy cleaning time" was long and the "number of particles on the substrate" was large. The surface of the quartz glass plate, which was pretreated in the same way as the cleaning head, had a surface density of Ce exceeding 30×10 ¹⁰ atoms/cm ² and a surface density of all elements other than Si of 1. .0% was exceeded.

On the other hand, in Example 2, since "HF" was supplied to the vibration plate of the cleaning head in the pretreatment of the cleaning head, the "dummy cleaning time" was short and the "number of particles on the substrate" was small. "HF" corresponds to the second chemical (chemical that dissolves quartz glass). The surface of the quartz glass plate pretreated in the same manner as the cleaning head had a surface density of Ce of 30×10 ¹⁰ atoms/cm ² or less.

In Example 3, "SPM" and "HF" were supplied in this order to the vibration plate of the cleaning head in the cleaning head pretreatment, so the "dummy cleaning time" was short and the "substrate particle count" was small. . "SPM" corresponds to the first chemical solution (chemical solution that dissolves cerium oxide), and "HF" corresponds to the second chemical solution (chemical solution that dissolves quartz glass). The surface of the quartz glass plate, which was pretreated in the same manner as the cleaning head, had a surface density of Ce of 1×10 ¹⁰ atoms/cm ² or less and a surface density of all elements other than Si of 1. 0% or less.

In Example 4, "SPM" and "alkaline detergent" were supplied in this order to the vibration plate of the cleaning head in the pretreatment of the cleaning head. "SPM" corresponds to the first chemical solution (chemical solution that dissolves cerium oxide), and "alkaline detergent" corresponds to the second chemical solution (chemical solution that dissolves quartz glass). The surface of the quartz glass plate, which was pretreated in the same manner as the cleaning head, had a surface density of Ce of 10×10 ¹⁰ atoms/cm ² or less and a surface density of all elements other than Si of 1. 0% or less.

The following remarks are disclosed with respect to the above embodiments.
[Appendix 1]
An ultrasonic cleaning head having a vibrating surface facing an upper surface of a substrate with a gap therebetween and in contact with a liquid film formed on the upper surface of the substrate,
The ultrasonic cleaning head, wherein the vibrating surface has a Ce element surface density of 30×10 ¹⁰ atoms/cm ² or less as detected by total reflection X-ray fluorescence analysis.
[Appendix 2]
The ultrasonic cleaning head according to appendix 1, wherein the vibrating surface has a surface density of Ce element detected by total reflection X-ray fluorescence spectrometry of 10×10 ¹⁰ atoms/cm ² or less.
[Appendix 3]
The ultrasonic cleaning head according to appendix 2, wherein the vibrating surface has a surface density of Ce element detected by total reflection X-ray fluorescence analysis of 1×10 ¹⁰ atoms/cm ² or less.
[Appendix 4]
Of the elements with atomic numbers of 13 to 30 and 33 to 72 detected by total reflection X-ray fluorescence spectroscopy, the vibration surface is defined as 100% of the surface density of the most abundant element, and all the remaining elements excluding the most abundant element. 4. The ultrasonic cleaning head according to any one of Appendices 1 to 3, wherein the total areal density of the elements is 1.0% or less.
[Appendix 5]
The ultrasonic cleaning head according to appendix 4, wherein the most abundant element is Si.
[Appendix 6]
6. The ultrasonic cleaning head according to appendix 4 or 5, wherein the material of the vibration surface is _SiO2 .
[Appendix 7]
By supplying at least one of a first chemical solution for dissolving cerium oxide and a second chemical solution for dissolving the vibrating surface to the vibrating surface of the ultrasonic cleaning head, total reflection X-ray fluorescence analysis of the vibrating surface making the surface density of the detected Ce element 30×10 ¹⁰ atoms/cm ² or less;
After the surface density of the Ce element detected by total reflection X-ray fluorescence spectrometry on the vibration surface is set to 30×10 ¹⁰ atoms/cm ² or less, the vibration surface of the ultrasonic cleaning head and the substrate facing each other are separated. applying vibration from the vibrating surface to the liquid film while forming the liquid film between upper surfaces;
A substrate cleaning method comprising:
[Appendix 8]
The ultrasonic cleaning head according to any one of Appendices 1 to 6, a holding portion that horizontally holds the substrate, and a nozzle that forms the liquid film on the upper surface of the substrate held by the holding portion. A substrate cleaning apparatus comprising:
[Appendix 9]
A method for manufacturing a substrate, comprising cleaning the substrate using the substrate cleaning apparatus according to appendix 8.
[Appendix 10]
A method for manufacturing an EUVL mask blank, comprising cleaning a glass substrate or a functional film formed on the glass substrate using the substrate cleaning apparatus according to appendix 8.

The ultrasonic cleaning head, substrate cleaning method, substrate cleaning apparatus, substrate manufacturing method, and EUVL mask blank manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally belong to the technical scope of the present disclosure.

This application claims priority based on Japanese Patent Application No. 2022-032933 filed with the Japan Patent Office on March 3, 2022, and the entire contents of Japanese Patent Application No. 2022-032933 are incorporated into this application. .

30 cleaning head (ultrasonic cleaning head)
31a Vibration surface W Substrate Wa Substrate upper surface F Liquid film

Claims

An ultrasonic cleaning head having a vibrating surface facing an upper surface of a substrate with a gap therebetween and in contact with a liquid film formed on the upper surface of the substrate,
The ultrasonic cleaning head, wherein the vibrating surface has a Ce element surface density of 30×10 10 atoms/cm 2 or less as detected by total reflection X-ray fluorescence analysis.
2. The ultrasonic cleaning head according to claim 1, wherein the vibrating surface has a Ce element surface density of 10×10 10 atoms/cm 2 or less as detected by total reflection X-ray fluorescence analysis.
3. The ultrasonic cleaning head according to claim 2, wherein the vibrating surface has a Ce element surface density of 1×10 10 atoms/cm 2 or less as detected by total reflection X-ray fluorescence analysis.
Of the elements with atomic numbers of 13 to 30 and 33 to 72 detected by total reflection X-ray fluorescence spectroscopy, the vibration surface is defined as 100% of the surface density of the most abundant element, and all the remaining elements excluding the most abundant element. The ultrasonic cleaning head according to any one of claims 1 to 3, wherein the total areal density of the elements is 1.0% or less.
The ultrasonic cleaning head according to claim 4, wherein the most abundant element is Si.
5. The ultrasonic cleaning head according to claim 4, wherein the material of said vibration surface is SiO2 .
By supplying at least one of a first chemical solution for dissolving cerium oxide and a second chemical solution for dissolving the vibrating surface to the vibrating surface of the ultrasonic cleaning head, total reflection X-ray fluorescence analysis of the vibrating surface making the surface density of the detected Ce element 30×10 10 atoms/cm 2 or less;
After the surface density of the Ce element detected by total reflection X-ray fluorescence spectrometry on the vibration surface is set to 30×10 10 atoms/cm 2 or less, the vibration surface of the ultrasonic cleaning head and the substrate facing each other are separated. applying vibration from the vibrating surface to the liquid film while forming the liquid film between upper surfaces;
A substrate cleaning method comprising:
4. The ultrasonic cleaning head according to any one of claims 1 to 3, a holding portion for horizontally holding the substrate, and a nozzle for forming the liquid film on the upper surface of the substrate held by the holding portion. and a substrate cleaning apparatus.
A method for manufacturing a substrate, comprising cleaning the substrate using the substrate cleaning apparatus according to claim 8.
A method for manufacturing an EUVL mask blank, comprising cleaning a glass substrate or a functional film formed on the glass substrate using the substrate cleaning apparatus according to claim 8.