JP4219718B2 - Manufacturing method of glass substrate for EUV mask blanks and manufacturing method of EUV mask blanks - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for manufacturing a glass substrate for EUV mask blanks that uses light in an ultrashort wavelength region such as EUV (wavelength: 13 nm) as an exposure light source, and a method for manufacturing EUV mask blanks.
[0002]
[Prior art]
With recent increases in the density and accuracy of VLSI devices, the trend toward finer substrate surfaces required for mask blank glass substrates is becoming increasingly severe year by year. In particular, as the wavelength of the exposure light source becomes shorter, the requirements for the shape accuracy (flatness) and quality (defect size) of the substrate surface are becoming stricter. For mask blanks with extremely high flatness and no microdefects. There is a need for glass substrates.
[0003]
For example, when the exposure light source is F2, the required flatness of the glass substrate is 0.25 μm or less, the required defect size is 0.07 μm or less, and when EUV is used, the required flatness of the glass substrate is used. The degree is 0.05 μm or less, and the required defect size is 0.05 μm or less.
[0004]
2. Description of the Related Art Conventionally, a precision polishing method for reducing the surface roughness has been proposed in manufacturing a mask blank glass substrate (see, for example, Patent Document 1).
The precision polishing method disclosed in Patent Document 1 is a method in which a substrate surface is polished using an abrasive mainly composed of cerium oxide, and then finish-polished using colloidal silica. When a glass substrate is polished by such a polishing method, a batch type double-side polishing machine is generally used in which a plurality of glass substrates are set and both surfaces thereof are polished simultaneously.
[0005]
By the way, according to the precision polishing method described above, it is theoretically possible to achieve the required smoothness by reducing the average particle size of the abrasive grains. The flatness of a glass substrate that can be stably obtained is limited to about 0.5 μm because it is affected by mechanical precision such as a platen that sandwiches the substrate and a planetary gear mechanism that moves the carrier.
[0006]
Therefore, in recent years, a method for planarizing a glass substrate using plasma etching or local processing using a gas cluster ion beam has been proposed (see, for example, Patent Documents 2 and 3).
The flattening methods disclosed in Patent Documents 2 and 3 measure the uneven shape on the surface of the glass substrate and apply the processing conditions (plasma etching amount, gas cluster ion beam amount, etc.) according to the convexity of the convex portion to the convex portion. By applying local processing, the glass substrate surface is flattened.
[0007]
[Patent Document 1]
JP-A 64-40267 (2nd page)
[Patent Document 2]
JP 2002-316835 A (page 3)
[Patent Document 3]
JP-A-8-293383 (page 3, FIG. 1)
[0008]
[Problems to be solved by the invention]
By the way, when the flatness of the glass substrate surface is adjusted by plasma etching or local processing using a gas cluster ion beam, surface roughness occurs on the surface of the glass substrate after these local processing, or surface defects such as scratches and work-affected layers occur. Therefore, after the local processing, it is necessary to polish the glass substrate surface for the purpose of improving surface roughness and removing surface defects.
[0009]
However, in polishing after local processing, if a polishing tool surface such as a polishing pad directly contacts the glass substrate surface, the flatness of the glass substrate surface may be deteriorated, and the polishing time is limited to an extremely short time. For this reason, there has been a problem that surface roughness cannot be improved and surface defects cannot be sufficiently removed.
[0010]
  The present invention has been considered in view of the above circumstances, and when polishing the glass substrate surface subjected to local processing for the purpose of improving surface roughness and removing surface defects by local processing, in this polishing step, While maintaining the flatness of the glass substrate surface, the surface roughness of the glass substrate surface is improved, and by removing surface defects on the glass substrate surface, the flatness and smoothness are high and there are no surface defects.EUVGlass substrate for mask blanks, or using itEUVMask blanks are obtainedEUVManufacturing method of glass substrate for mask blanks, andEUVMask blanks manufacturing methodFor the purpose of provision.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, the present inventionEUVBased on the concavo-convex shape measuring step for measuring the concavo-convex shape on the glass substrate surface for mask blanks and the measurement result obtained in the concavo-convex shape measuring step, the degree of convexity of the convex portion existing on the glass substrate surface is specified, By subjecting the convex part to local processing under processing conditions according to this convexity, the flatness of the glass substrate surface is reduced.Required as a glass substrate for EUV mask blanksA flatness control step for controlling to a predetermined reference value or less; and after the flatness control step, the glass substrate surface that has been subjected to the local processing is brought into contact with the polishing tool surface without contacting the glass substrate surface. The method includes a non-contact polishing step of polishing by the action of a working fluid interposed between the polishing tool surface.
[0012]
  In this way,Local processing was appliedFor EUV mask blanksWhen polishing the glass substrate surface for the purpose of improving surface roughness by local processing and removing surface defects, in this polishing,For EUV mask blanksWithout bringing the glass substrate surface into contact with the polishing tool surface,For EUV mask blanksBy applying non-contact polishing that polishes by the action of a working fluid interposed between the glass substrate surface and the polishing tool surface,For EUV mask blanksWhile maintaining the flatness of the glass substrate surface,For EUV mask blanksWhile improving the surface roughness of the glass substrate surface,For EUV mask blanksIt becomes possible to remove surface defects on the surface of the glass substrate.
[0013]
  Moreover, in this invention, it is preferable that the said non-contact grinding | polishing process is a process of grind | polishing the surface defect of the said glass substrate below to the defect size requested | required as a glass substrate for EUV mask blanks.
[0014]
  In the present invention, the non-contact polishing step is performed by float polishing, EEM (Elastic). Emission Machining), hydroplane polishing, and the processing liquid is water, an acidic aqueous solution, an alkaline aqueous solution, or any one of the aqueous solutions and colloidal silica, cerium oxide, zirconium oxide, aluminum oxide. It is preferable to contain at least one selected fine powder particle.
  According to such a method, while the glass substrate for EUV mask blanks is levitated, the processing liquid is brought into contact with the surface of the glass substrate for EUV mask blanks, or fine powder particles are collided to make the surface of the glass substrate for EUV mask blanks extremely Since it can be polished with a very small force, not only can the surface roughness of the glass substrate surface for EUV mask blanks be maintained, but the surface roughness due to local processing can be improved to achieve an ultra-fine surface roughness, as well as fine surface defects. Can be removed.
  Further, when the processing liquid is as described above, the polishing force acting on the surface of the glass substrate for EUV mask blanks can be made minute, and deterioration of flatness due to polishing can be avoided reliably. here,By using a working fluid containing an alkaline aqueous solution, not only can the polishing rate be improved,EUVDefects such as scratches hidden on the surface of the mask blank glass substrate can be revealed.
[0015]
  Also,In the present invention, the local processing is preferably performed by plasma etching or a gas cluster ion beam.
  In this way, for EUV mask blanksBy controlling the moving speed of the ion beam and the moving speed of the plasma generation housing according to the convexity of the convex part on the glass substrate surface,For EUV mask blanksAppropriate local processing is performed on the convex portion of the glass substrate surface, and the flatness can be controlled to be equal to or less than a predetermined reference value.
  Also,For EUV mask blanksThe ion beam intensity and the plasma intensity may be controlled according to the convexity of the convex part on the glass substrate surface.
[0016]
  In the present invention, the reference value is 0.05 μm or less.
  In this way, by performing local processing with a flatness reference value of 0.05 μm, a glass substrate for EUV mask blanks requiring flatness of 0.05 μm or less is obtained.
[0017]
  In order to achieve the above object,EUV mask blanksThe manufacturing method of the aboveEUVIt was obtained by the manufacturing method of the glass substrate for mask blanks.EUVThis is a method for forming a thin film to be a transferred pattern on a glass substrate for mask blanks.
  EUVIf the manufacturing method of the mask blank is such a method, it has the required flatness and has high quality without surface defects.EUV mask blanks can be obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
[Manufacturing method of glass substrate for mask blanks]
First, the manufacturing method of the glass substrate for mask blanks in this invention is demonstrated with reference to drawings.
[0020]
FIG. 1 is a flowchart showing a manufacturing process of a glass substrate for mask blanks.
As shown in this figure, the manufacturing process of the glass substrate for mask blanks in the present invention includes a preparation step (P-1) for preparing a glass substrate whose surface is precisely polished, and an unevenness for measuring the uneven shape on the surface of the glass substrate. Shape measurement step (P-2), flatness control step (P-3) for controlling the flatness of the glass substrate surface by local processing, and non-contact polishing step (P-4) for polishing the glass substrate surface in a non-contact manner ).
[0021]
<Preparation process (P-1)>
A preparation process (P-1) is a process of preparing the glass substrate by which the single side | surface or both surfaces were precisely polished using the grinding | polishing apparatus mentioned later, for example.
The glass substrate is not particularly limited as long as it is used as mask blanks. Examples thereof include quartz glass, soda lime glass, aluminosilicate glass, borosilicate glass, and alkali-free glass.
In the case of an F2 mask blank glass substrate, in order to suppress the absorption of the exposure light source as much as possible, quartz glass doped with fluorine is used.
[0022]
In the case of a glass substrate for EUV mask blanks, 0 ± 1.0 × 10 × 10 is used in order to suppress distortion of the transferred pattern due to heat during exposure.^-7/ ° C., more preferably 0 ± 0.3 × 10^-7A glass material having a low coefficient of thermal expansion in the range of / ° C is used.
Moreover, since many films | membranes are formed on a glass substrate for EUV mask blanks, the glass material with high rigidity which can suppress the deformation | transformation by film | membrane stress is used. In particular, a glass material having a high Young's modulus of 65 GPa or more is preferable. For example, SiO₂-TiO₂Amorphous glass such as system glass and quartz glass, and crystallized glass on which β-quartz solid solution is deposited are used.
[0023]
FIG. 2 is a schematic sectional view of the polishing apparatus.
The polishing apparatus 10 shown in this figure includes a planetary gear type polishing processing unit including a lower surface plate 11, an upper surface plate 12, a sun gear 13, an internal gear 14, a carrier 15, and an abrasive supply unit 16. The polishing processing unit sandwiches the glass substrate set on the carrier 15 between the upper and lower surface plates 11 and 12 to which the polishing pads 11a and 12a are attached, and supplies an abrasive between the surface plates 11 and 12, By rotating and revolving the carrier 15, both surfaces of the glass substrate are polished. Hereinafter, the configuration of the polishing processing unit will be described.
[0024]
Each of the lower surface plate 11 and the upper surface plate 12 is a disk member having an annular horizontal surface, and polishing pads 11a and 12a are attached to the opposing surfaces thereof. The lower surface plate 11 and the upper surface plate 12 are supported so as to be rotatable about a vertical axis A (a vertical axis passing through the center of the polishing portion) and linked to a surface plate rotation drive unit (not shown). It is rotated by.
The upper surface plate 12 is supported so as to be movable up and down along the vertical axis A, and is moved up and down by driving an upper surface plate lifting and lowering drive unit (not shown).
[0025]
The sun gear 13 is rotatably provided at the center position of the polishing unit, and is rotated about the vertical axis A by driving a sun gear rotation driving unit (not shown).
The internal gear 14 is a ring-shaped gear having a tooth row on the inner peripheral side, and is arranged concentrically outside the sun gear 13. The internal gear 14 shown in FIG. 2 is fixed so as not to rotate, but may be rotated about the vertical axis A.
The carrier (planetary gear) 15 is a thin plate-shaped disk member having a tooth row on the outer peripheral portion, and one or a plurality of work holding holes for holding the glass substrate are formed.
[0026]
Usually, a plurality of carriers 15 are arranged in the polishing portion. These carriers 15 mesh with the sun gear 13 and the internal gear 14, and rotate while revolving around the sun gear 13 according to the rotation of the sun gear 13 (and / or the internal gear 14). Moreover, the outer diameters of the upper surface plate 12 and the lower surface plate 11 are smaller than the inner diameter of the internal gear 14, and between the sun gear 130 and the internal gear 140 and between the upper surface plate 12 and the lower surface plate 11. A donut-shaped region sandwiched between the two becomes an actual polishing region.
[0027]
The abrasive supply means 16 supplies a polishing agent reservoir 16a for storing the abrasive and a plurality of abrasives stored in the abrasive reservoir 16a to the polishing area between the upper surface plate 12 and the lower surface plate 11. Tube 16b.
As the abrasive, fine abrasive particles dispersed in a liquid are used. The abrasive particles are, for example, silicon carbide, aluminum oxide, cerium oxide, zirconium oxide, manganese oxide, colloidal silica, and the like, and are appropriately selected according to the material of the glass substrate, the processed surface roughness, and the like. These abrasive particles are dispersed in a liquid such as water, an acidic solution, or an alkaline solution to become an abrasive.
[0028]
The preparation step (P-1) includes at least a rough polishing step for rough polishing both surfaces of the glass substrate and a precision polishing step for precisely polishing both surfaces of the rough polished glass substrate, and performs stepwise polishing. .
For example, in the rough polishing process, an abrasive in which cerium oxide having relatively large abrasive grains is dispersed is used, and in the precision polishing process, an abrasive in which colloidal silica having relatively small abrasive grains is dispersed is used. .
[0029]
<Uneven shape measurement step (P-2)>
The uneven shape measuring step (P-2) is a step of measuring the uneven shape (flatness) of the glass substrate surface prepared in the previous step (P-1).
The measurement of the uneven shape is preferably performed with an optical interference type flatness measuring device from the viewpoint of measurement accuracy. This flatness measuring apparatus reflects coherent light on the surface of a glass substrate and reflects the difference in height of the surface of the glass substrate as a phase shift of reflected light.
In addition, the flatness in this invention means the difference of the maximum value and minimum value of a measurement surface with respect to the virtual absolute plane (focal plane) calculated by the least square method from the measurement surface of the glass substrate surface, for example.
[0030]
The measurement result of the uneven shape is stored in a recording medium such as a computer. Thereafter, it is compared with a predetermined reference value (desired flatness) set in advance, and the difference is calculated by a calculation means such as a computer. This difference is calculated for each predetermined region on the surface of the glass substrate, and the predetermined region is set to coincide with the processing region in the local processing. Thereby, said difference in each measurement area becomes a necessary removal amount of each processing area in local processing.
In addition, you may perform said arithmetic processing by any of an uneven | corrugated shape measurement process (P-2) and a flatness control process (P-3).
[0031]
<Flatness control step (P-3)>
The flatness control step (P-3) specifies the convexity of the convex portion existing on the glass substrate surface based on the measurement result obtained in the concave-convex shape measuring step (P-2), This is a step of controlling the flatness of the surface of the glass substrate to a predetermined reference value or less by locally processing the convex portion under the corresponding processing conditions.
[0032]
The local processing is performed according to processing conditions set for each predetermined region on the glass substrate surface. As described above, this processing condition is set based on the difference between the uneven shape of the glass substrate surface measured by the flatness measuring apparatus and a preset flatness reference value (necessary removal amount for local processing). The
The parameters of the processing conditions vary depending on the processing apparatus, but are set so that the removal amount increases as the convexity of the convex portion increases. For example, when the processing method of the local processing is ion beam or plasma etching, the ion beam moving speed or the plasma generating housing moving speed is controlled to be slower as the convexity of the convex portion is larger. Further, the ion beam intensity and plasma intensity may be controlled.
[0033]
As the local processing method used in the flatness control step (P-3), in addition to the ion beam and plasma etching, there are MRF (Magnetoological Finishing), CMP (Chemical-Mechanical Polishing) and the like.
MRF is a local processing method in which polishing abrasive grains contained in a magnetic fluid are brought into contact with a workpiece (glass substrate) at a high speed and the residence time of the contact portion is controlled to perform local polishing. is there.
[0034]
CMP is mainly performed by using a small-diameter polishing pad and an abrasive (containing abrasive grains such as colloidal silica) and controlling the residence time of the contact portion between the small-diameter polishing pad and the workpiece (glass substrate). This is a local processing method for polishing a convex portion on the surface of a workpiece.
Among these local processing methods, in particular, in local processing by ion beam, plasma etching, and CMP, surface roughness or a work-affected layer occurs on the surface of the glass substrate after local processing, so that the acid treatment described later is particularly effective. .
[0035]
Hereinafter, particularly preferable plasma etching and local processing using an ion beam in the flatness control step (P-3) will be described.
The local processing method by plasma etching is a local processing method in which a plasma generating housing is positioned above a surface portion to be removed and an etching gas is allowed to flow to etch the removed portion. That is, when an etching gas is flowed, neutral radical species generated in the plasma attack the glass substrate surface isotropically, and this portion is etched. On the other hand, since no plasma is generated in the portion where the plasma generating housing is not located, the plasma generation casing is not etched even when it hits the etching gas.
[0036]
When the plasma generating housing is moved on the glass substrate, the removal amount is adjusted by controlling the moving speed and the plasma intensity of the plasma generating housing according to the required removal amount on the surface of the glass substrate.
The plasma generation housing has a structure in which a glass substrate is sandwiched between electrode pairs. A plasma is generated between the substrate and the electrode by a high frequency, and radical species are generated by passing an etching gas therethrough, or an etching gas is guided. There is a system in which plasma is generated by oscillation of microwaves through a tube, and the generated radical species flow is applied to the glass substrate surface.
[0037]
The etching gas is appropriately selected according to the material of the glass substrate. For example, a halogen compound gas or a mixed gas containing a halogen compound is used. Specifically, tetrafluoromethane, trifluoride methane, hexafluoride ethane, octafluoride propane, decafluorobutane, hydrogen fluoride, sulfur hexafluoride, nitrogen trifluoride, carbon tetrachloride, tetrafluoro Examples thereof include silicon fluoride, trifluorochloromethane, and boron trichloride.
[0038]
The local processing method using ion beam (gas cluster ion beam irradiation) is a gas substance at normal temperature and normal pressure, for example, oxide, nitride, carbide, rare gas substance, or a mixed gas thereof (the above substances are appropriately used). A gas cluster of these substances is formed using a gas cluster ion beam that is ionized by irradiating electrons onto it and controlling the irradiation area as necessary. This is a local processing method for irradiating the surface (glass substrate surface).
[0039]
A cluster is usually composed of a group of several hundred atoms or molecules, and even if the acceleration voltage is 10 kV, each atom or molecule is irradiated as an ultra-slow ion beam of several tens eV or less, so that it is extremely low. The glass substrate surface can be treated with damage.
When this glass cluster ion beam is irradiated onto the glass substrate surface, the molecules or atoms that make up the cluster ions and the atoms on the glass substrate surface collide in multiple stages, generating reflected molecules or atoms with lateral motion components. . Thereby, selective sputtering occurs on the convex portion of the glass substrate surface, and the glass substrate surface can be flattened. This flattening phenomenon can also be obtained from the effect of preferentially sputtering atoms present on a surface or grain having a weak binding force by energy concentratedly applied to the glass substrate surface.
[0040]
In addition, about the production | generation of gas cluster itself, as already well-known, it can produce | generate by ejecting the gas of a pressurization state in a vacuum device through an expansion type nozzle. The gas cluster generated in this way can be ionized by irradiation with electrons.
Here, as the gaseous substance, for example, CO₂, CO, N₂Oxides such as O, NOx, CxHyOz, O₂, N₂And noble gases such as Ar and He.
[0041]
The flatness required for the mask blank glass substrate is determined according to the wavelength of the exposure light source used in the mask blank, and the flatness in the flatness control step (P-3) is determined according to the required flatness. A reference value for the degree control is determined.
For example, in the case of a glass substrate for F2 mask blanks, the reference value for flatness control is set to 0.25 μm or less, and in the case of a glass substrate for EUV mask blanks, the reference value for flatness control is set to 0.05 μm or less for local processing. Done.
[0042]
<Non-contact polishing process (P-4)>
In the non-contact polishing step (P-4), the glass substrate surface and the polishing tool surface are brought into contact with the polishing tool surface without bringing the glass substrate surface subjected to the local processing in the flatness control step (P-3) into contact with the polishing tool surface. Is a step of polishing by the action of a working fluid interposed between the two.
The non-contact polishing method used in this step is not particularly limited. For example, float polishing, EEM, hydroplane polishing and the like can be mentioned.
[0043]
As the fine powder particles contained in the processing liquid used for non-contact polishing, those having a small average particle diameter are selected in order to reduce the surface roughness of the glass substrate. The average particle diameter is preferably several tens of nm or less, more preferably several nm or less. As abrasive grains having a small average particle diameter, cerium oxide, silica (SiO₂), Colloidal silica, zirconium oxide, manganese dioxide, aluminum oxide and the like. Among them, in the case of a glass substrate, colloidal silica is preferable in terms of surface smoothness.
[0044]
In non-contact polishing, any one of water, an acidic aqueous solution, and an alkaline aqueous solution may be used as a processing liquid, or a processing liquid containing any one of the above aqueous solutions and the above-described fine powder particles may be used.
When water is used, pure water and ultrapure water are preferable.
Examples of the acidic aqueous solution include aqueous solutions of sulfuric acid, hydrochloric acid, hydrofluoric acid, silicic acid, and the like. By adding an acidic aqueous solution to the processing liquid in non-contact polishing, the polishing rate is improved. However, when the type and concentration of the acid are high, the glass substrate may be roughened. Therefore, an acid and a concentration that do not roughen the glass substrate are appropriately selected.
[0045]
Examples of the alkaline aqueous solution include aqueous solutions such as potassium hydroxide and sodium hydroxide. When an alkaline aqueous solution is included in the processing liquid in non-contact polishing, the polishing rate is improved. In addition, if there are potential extremely fine defects (cracks, scratches, etc.) on the surface of the glass substrate, they can be prominent, making it possible to detect minute defects reliably in the subsequent inspection process. Become. The alkaline aqueous solution is adjusted in a range in which the abrasive grains contained in the processing liquid do not dissolve, and is preferably adjusted so that the pH is 9 to 12 as the processing liquid.
[0046]
Hereinafter, processing principles of float polishing, EEM and hydroplane polishing will be described.
The polishing plate surface used in the float polishing has a shape that generates a dynamic pressure and a groove in which the machining liquid is lead. The machining fluid is a suspension of fine powder particles of several nm to several tens of nm in a solvent (pure water, alkaline aqueous solution, etc.), and the polishing plate axis (main axis) and workpiece to be processed in the machining liquid. The polishing plate and the workpiece are simultaneously rotated in the same direction with the rotation axis of the object (glass substrate) being eccentric by a certain distance.
[0047]
At this time, if the workpiece is allowed to float freely in the vertical direction and only the rotational torque is transmitted, a slight gap is created between the workpiece and the polishing plate due to the dynamic pressure effect. The work piece is lifted. Due to the collision of the fine powder particles passing through the gap with the processed surface, microfracture is repeated and processing of the workpiece proceeds. With such a processing principle, the workpiece can be processed to an ultrafine surface roughness, and the processing itself is performed with a small force, so that a processed surface without a work-affected layer can be finished.
When the workpiece is a glass substrate, the fine powder particles are CeO₂(Ultra high purity), colloidal silica and the like can be used.
[0048]
EEM brings fine powder particles of 0.1 μm or less into contact with the workpiece under almost no load, and at that time, an interaction (a kind of chemical bond) generated at the interface between the fine powder particles and the workpiece, This is a non-contact polishing method in which the surface atoms of the workpiece are removed in atomic units. In such processing principle, the processing characteristics greatly depend on the compatibility of the fine powder particles and the workpiece, and in order to efficiently process the workpiece, the fine powder particles are appropriately selected according to the material of the workpiece. Must be selected. For example, when the workpiece is a glass substrate, zirconium oxide, aluminum oxide, colloidal silica, or the like can be used as the fine powder particles. In order to improve the processing speed, fine powder particles may be suspended in a solvent that erodes the workpiece to obtain a processing liquid, which may be brought into contact with the workpiece.
[0049]
In hydroplane polishing, a work piece is fixed to a disc-like plate having a conical outer periphery so that the work piece faces the polishing pad, and the work piece and the polishing pad surface are separated from each other by about 100 μm. It is supported by a single rotating roller. When an abrasive layer is formed between the polishing pad and the workpiece and the space between the two is filled with the abrasive, the workpiece and the disk-shaped plate are driven by the rotation of the polishing pad, and the processing proceeds.
[0050]
Next, the float polishing apparatus and the EEM apparatus will be described.
FIG. 3 is a schematic cross-sectional view of the float polishing apparatus, and FIG. 4 is a main-part cross-sectional view of the float polishing apparatus.
As shown in these drawings, the float polishing apparatus 20 is provided with respect to a turntable 21, a cylindrical processing tank 22 for storing a processing liquid on the turntable 21, and a main shaft 23 (a rotation axis of the turntable 21). A polishing plate 24 provided on the turntable 21 so as to be decentered by a predetermined distance, a work holder 26 which is disposed opposite to the polishing plate 24 and rotates around a work holder shaft 25 concentric with the polishing plate 24, and a processing tank 22 is provided with a processing liquid supply means 27 for supplying a processing liquid containing fine powder particles.
[0051]
The turntable 21 is highly rigid and requires resistance to the machining fluid. Accordingly, the material of the turntable 21 may be any material having these conditions, but it is preferable to use stainless steel. Moreover, since the turntable 21 requires high rotational accuracy and high vibration absorption, it is preferable to support it with a high-performance bearing such as a hydrostatic oil bearing. Further, the turntable 21 is provided with a discharge port (not shown) for discharging the machining liquid supplied from the machining liquid supply means 27. At the tip of the discharge port, a recovery mechanism (not shown) for recovering the processing waste processed by float polishing is also provided. Although the discharge port is open during processing, the liquid level of the processing liquid in the processing tank 22 is maintained by controlling the supply amount of the processing liquid supply means 27.
The turntable 21 is rotated at several tens to several hundreds of rpm around the main shaft 23 by driving of a rotation driving means (not shown).
[0052]
The work holder 26 is rotated at a speed of several tens to several hundreds of rpm around a work holder shaft 25 by a rotation driving means (not shown). The work holder 26 is supported in a freely floating manner so that only the rotational driving torque is transmitted, and the ups and downs during machining are allowed. Note that the rotation direction of the work holder 26 is the same as the rotation direction of the turntable 21.
The method of holding the workpiece may be any method that does not damage the workpiece such as scratches. For example, the workpiece is fixed to the work holder 26 by vacuum suction or an adhesive.
[0053]
The shape of the polishing plate 24 is a donut shape with the main shaft 23 of the turntable 21 as the center, and its width is at least larger than the size of the workpiece. Since the workpiece rotates on the polishing plate 24 around the workpiece holder shaft 25, the workpiece has a square length when the workpiece is square, and when the workpiece is rectangular, the workpiece The width should be larger than the long diagonal length.
[0054]
The upper surface of the polishing plate 24 has an uneven shape, and a groove 24b that leads the machining liquid is formed between the convex portions 24a. The upper portion of the convex portion 24a is a tapered shape that generates dynamic pressure on the workpiece. It has become. The levitation force (the levitation distance) of the workpiece is controlled by this tapered inclination angle. The inclination angle of the tapered shape is the size of the workpiece so that the flying distance of the workpiece (distance between the convex portion 24a of the polishing plate 24 and the workpiece: the gap in which the machining fluid intervenes) is several μm. It adjusts suitably in the range of 1 degree-20 degrees according to etc. Further, the width, depth, and pitch of the groove 24b control the lead of the machining fluid. The width of the groove 24b is appropriately adjusted within a range of 1 to 5 mm, a depth of 1 to 10 mm, and a pitch of 0.5 to 30 mm.
In addition, the material of the polishing plate 24 should just have a tolerance with respect to a process liquid, For example, stainless steel, tin, ceramics etc. are mentioned.
[0055]
Depending on the liquid temperature of the processing liquid, the polishing plate 24, the turntable 21, the work holder 26, the workpiece, etc. may be thermally deformed, which may affect the processing accuracy. ing.
The processing liquid is, for example, pure water or ultrapure water, a solvent such as alkali or acid, or the above-mentioned solvent containing fine powder particles, and the concentration of the fine powder particles is 0.1 to 40 wt%. Use the one adjusted within the range.
[0056]
The machining liquid supply means 27 may circulate the machining waste contained in the machining liquid discharged from the discharge port so as to be supplied again into the machining tank 22 after being removed by the dust suction device, or discharged from the discharge port. A new machining fluid may be supplied into the machining tank 22 by the amount of the machining fluid. In the float polishing, since the thickness of the machining liquid layer interposed between the polishing plate 24 and the workpiece is an important factor, the machining liquid supply means 27 is used to strictly control the amount of the machining liquid in the machining tank 22. The machining fluid supply amount is controlled with high accuracy.
[0057]
FIG. 5 is a schematic sectional view of the EEM apparatus.
As shown in this figure, the EEM apparatus 30 includes a processing tank 31 for storing a processing liquid, a workpiece holding means 32 for holding the workpiece in the processing tank 31, and a processing liquid (fine powder particles) to be processed. A rotating body 34 that rotates about a rotating shaft 33 that faces the surface direction of the workpiece surface so as to preferentially contact a certain area of the workpiece surface; The moving means 35 which scans right and left, and the process liquid supply means 36 which supplies the process liquid containing a fine powder particle to the process tank 31 are provided.
[0058]
The material of the processing tank 31 should just have tolerance with respect to a processing liquid. Further, the processing tank 31 is provided with a discharge port 31 a for discharging the processing liquid supplied from the processing liquid supply means 36. A recovery mechanism (not shown) for recovering the processing waste processed by EEM is provided at the tip of the discharge port 31a. Although the discharge port 31a is open during processing, the liquid level of the processing liquid in the processing tank 31 is maintained by controlling the supply amount of the processing liquid supply means 36.
Note that the method of holding the workpiece may be any method that does not damage the workpiece such as a scratch.
[0059]
The shape of the rotating body 34 is appropriately selected according to the region on the surface of the workpiece to be preferentially contacted (reacted) with the processing liquid. When it is desired to contact the machining liquid locally, the shape is spherical or linear. When it is desired to contact the machining liquid preferentially in a relatively wide area, the shape is cylindrical.
The material of the rotating body 34 should be resistant to the machining fluid and have a low elasticity as much as possible. High elasticity (relatively soft) is not preferable because it may cause shape deformation during rotation or the shape may become unstable, which may deteriorate the processing accuracy. For example, polyurethane, glass, ceramics, etc. can be used.
[0060]
[Manufacturing method of mask blanks]
Next, an embodiment of a mask blank manufacturing method according to the present invention will be described.
The mask blank manufacturing method of the present invention includes a step of preparing a glass substrate obtained by the above-described mask blank glass substrate manufacturing method, and a step of forming a thin film to be a transferred pattern on the glass substrate. Have.
Mask blanks are classified into transmissive mask blanks and reflective mask blanks. In any mask blank, a thin film to be a transferred pattern is formed on a glass substrate. A resist film may be formed on the thin film.
[0061]
The thin film formed on the transmissive mask blank is a thin film that causes an optical change with respect to the exposure light (light emitted from the exposure light source) used when transferring to the transfer target. For example, the exposure light is blocked. It refers to a light-shielding film to be used, a phase shift film for changing the phase difference of exposure light, and the like.
As a light shielding film, in general, a Cr film, a Cr alloy film that selectively contains oxygen, nitrogen, carbon, and fluorine in Cr, a laminated film thereof, a MoSi film, and a MoSi alloy that selectively contains oxygen, nitrogen, and carbon in MoSi Examples thereof include films and laminated films thereof.
[0062]
As a phase shift film, SiO having only a phase shift function₂In addition to the film, a metal silicide oxide film having a phase shift function and a light shielding function, a metal silicide nitride film, a metal silicide oxynitride film, a metal silicide oxycarbide film, a metal silicide oxynitride carbide film (metal: Mo, Ti , Transition metals such as W and Ta), CrO films, CrF films, and halftone films such as SiON films.
[0063]
In the reflective mask blank, a laminated film including a reflective multilayer film (multilayer reflective film) and a light absorber film (absorber layer) to be a transferred pattern is formed on a glass substrate.
As the light reflecting multilayer film, Ru / Si periodic multilayer film, Mo / Be periodic multilayer film, Mo compound / Si compound periodic multilayer film, Si / Nb periodic multilayer film, Si / Mo / Ru periodic multilayer film, Si / Mo / Materials such as a Ru / Mo periodic multilayer film and a Si / Ru / Mo / Ru periodic multilayer film are used.
As the light absorber film, Ta or Ta alloy (for example, a material containing Ta and B, a material containing Ta, B and N), Cr or Cr alloy (for example, at least one of nitrogen, oxygen, carbon and fluorine in Cr) Material with two elements added).
[0064]
The transmissive mask blank uses g-line (wavelength: 436 nm), i-line (wavelength: 365 nm), KrF (wavelength: 246 nm), ArF (wavelength: 193 nm), F2 (wavelength: 157 nm) as an exposure light source. In the reflective mask blank, EUV (for example, wavelength: 13 nm) is used as an exposure light source.
Note that the above-described thin film can be formed by a sputtering method such as DC sputtering, RF sputtering, or ion beam sputtering.
[0065]
[Examples and Comparative Examples]
Hereinafter, examples of the present invention will be described using a method for manufacturing a glass substrate for EUV mask blanks (hereinafter referred to as a glass substrate) and a method for manufacturing EUV reflective mask blanks as examples. Needless to say, it is not limited to.
[0066]
<Example 1: Float polishing>
A glass substrate (size: 152.4 mm × 152.4 mm, thickness: 6.35 mm) polished in stages with cerium oxide abrasive grains or colloidal silica abrasive grains was prepared using the polishing apparatus 10 described above.
[0067]
The surface shape (flatness) of the glass substrate was measured with an optical interference type flatness measuring machine. The flatness of the glass substrate was 0.2 μm (convex shape), and the surface roughness was 0.15 nm in terms of root mean square roughness Rq (= RMS).
The shape measurement result of the glass substrate surface is stored in the computer, and compared with the flatness reference value 0.05μm (convex shape) required for the glass substrate for EUV mask blanks, and the difference (necessary removal amount) is calculated by the computer. did.
[0068]
Next, processing conditions for local plasma etching corresponding to the required removal amount were set for each predetermined region (5 mm □) in the glass substrate surface. According to the set processing conditions, the shape was adjusted by local plasma etching so that the flatness of the glass substrate was a reference value (flatness 0.05 μm) or less.
The etching gas for local plasma etching was methane tetrafluoride, and the plasma generation housing was a high-frequency type having a cylindrical electrode.
[0069]
After adjusting the shape by local plasma etching, the flatness of the glass substrate surface was measured and found to be as good as 0.05 μm. Further, the surface roughness of the glass substrate surface was about 1 nm in terms of Rq, and the surface was roughened by the plasma etching process.
[0070]
Therefore, a glass substrate was set in the above-described float polishing apparatus 20 and non-contact polishing was performed.
The polishing conditions in the float polishing were as follows.
Processing fluid: pure water + fine powder particles (concentration: 2 wt%)
Fine powder particles: Silica (SiO₂), Average particle size: about 70 nm
Turntable speed: 5 to 200 rpm
Work holder rotation speed: 10 to 300 rpm
Polishing time: 5-30min
[0071]
Thereafter, the glass substrate was washed with an alkaline aqueous solution to obtain a glass substrate for EUV mask blanks.
When the flatness and surface roughness of the obtained glass substrate were measured, the flatness was 0.05 μm, which was good, maintaining the state before float polishing. Moreover, the surface roughness was 0.09 nm in Rq, and the roughness of the glass substrate surface before float polishing could be improved.
[0072]
Further, surface defects on the surface of the glass substrate were inspected by a defect inspection apparatus described in Japanese Patent Application Laid-Open No. 11-24001. This inspection apparatus is a method for inspecting a defect by introducing laser light from a chamfered surface of a substrate, confining it in the substrate by total reflection, and detecting light scattered by the defect and leaking from the substrate. . As a result of this inspection, no scratch having a size exceeding 0.05 μm was found.
A glass substrate satisfying the specifications required for a glass substrate for EUV mask blanks could be obtained.
[0073]
<Example 2: Processing liquid for float polishing>
A glass substrate was produced in the same manner as in Example 1 except that the polishing conditions in the float polishing were as follows.
Processing liquid: alkaline aqueous solution (NaOH) + fine powder particles (concentration: 2 wt%), pH: 11
Fine powder particles: colloidal silica, average particle size: about 70 nm
Turntable speed: 5 to 200 rpm
Work holder rotation speed: 10 to 300 rpm
Polishing time: 3-25min
[0074]
Thereafter, the glass substrate was washed with an alkaline aqueous solution (NaOH) to obtain a glass substrate for EUV mask blanks.
When the flatness and surface roughness of the obtained glass substrate were measured, both the flatness and the surface roughness were almost the same as those of the glass substrate obtained in Example 1. Further, when a surface defect on the surface of the glass substrate was inspected by a defect inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 11-24201, no scratch having a size exceeding 0.05 μm was found. By using an alkaline aqueous solution as the solvent for the processing liquid, the polishing rate was improved and the polishing time could be shortened.
[0075]
<Example 3: Processing liquid 2 of float polishing>
A glass substrate was produced in the same manner as in Example 1 except that the polishing conditions in the float polishing were as follows.
Processing liquid: Alkaline aqueous solution (NaOH) 5 vol%
Fine powder particles: None
Turntable speed: 5 to 200 rpm
Work holder rotation speed: 10 to 300 rpm
Polishing time: 7 to 45 min
[0076]
Thereafter, the glass substrate was washed with pure water to obtain a glass substrate for EUV mask blanks.
When the flatness and surface roughness of the obtained glass substrate were measured, both the flatness and the surface roughness were almost the same as those of the glass substrate obtained in Example 1. Further, when a surface defect on the surface of the glass substrate was inspected by a defect inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 11-24201, no scratch having a size exceeding 0.05 μm was found. By using an alkaline aqueous solution as the solvent for the processing liquid, the polishing rate was improved and the polishing time could be shortened.
[0077]
<Example 4: EEM>
A glass substrate was produced in the same manner as in Example 1 except that EEM was performed as non-contact polishing after adjusting the flatness by local plasma etching. EEM processing conditions were as follows.
Processing fluid: pure water + fine powder particles (concentration: 3wt%)
Fine powder particles: Zirconium oxide (ZrO₂), Average particle size: about 60 nm
Rotating body: Polyurethane roll
Rotating body rotation speed: 10-300rpm
Work holder rotation speed: 10 to 100 rpm
Polishing time: 5-30min
[0078]
Thereafter, the glass substrate was washed with an alkaline aqueous solution to obtain a glass substrate for EUV mask blanks.
When the flatness and surface roughness of the obtained glass substrate were measured, the flatness was as good as 0.05 μm, maintaining the state before float polishing, the surface roughness was 0.11 nm in Rq, and EEM The state of the rough surface of the glass substrate before implementation could be improved. The reason why the surface roughness is slightly larger than in Examples 1 to 3 seems to be due to the influence of the hardness of the fine powder particles used.
[0079]
Further, when a surface defect on the surface of the glass substrate was inspected by a defect inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 11-24201, no scratch having a size exceeding 0.05 μm was found.
A glass substrate satisfying the specifications required for a glass substrate for EUV mask blanks could be obtained.
[0080]
<Comparative example>
For polishing after adjusting the flatness by local plasma etching, a glass substrate is set on the polishing plate facing the polishing platen, and the glass substrate is pressed from above onto the polishing pad area of the rotating polishing platen to rotate it. A glass substrate was produced in the same manner as in Example 1 except that the polishing method was performed. The polishing conditions for the single-side polishing method were as follows.
Processing liquid: alkaline aqueous solution (NaOH) + fine powder particles (concentration: 2 wt%), pH: 11
Fine powder particles: colloidal silica, average particle size: about 70 nm
Polishing platen rotation speed: 1-50rpm
Polishing plate rotation speed: 1-50rpm
Processing pressure: 0.1-10 kPa
Polishing time: 1-10min
[0081]
Thereafter, the glass substrate was washed with an alkaline aqueous solution (NaOH) to obtain a glass substrate for EUV mask blanks.
When the flatness and surface roughness of the obtained glass substrate were measured, the surface roughness was 0.15 nm in Rq, which was good, but the flatness was 0.25 μm and the state before single-side polishing, Became worse than before the flatness correction by local plasma etching.
[0082]
Further, when surface defects on the surface of the glass substrate were inspected by a defect inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 11-24201, many scratches having a size exceeding 0.05 μm were found. This is considered to be because the foreign substance or the like present in the polishing pad scratches the glass substrate during polishing because of the polishing in which the glass substrate and the polishing pad are in contact.
As a result, it was not possible to obtain a glass substrate that satisfies the specifications required for a glass substrate for EUV mask blanks.
[0083]
<Preparation of EUV reflective mask blanks and EUV reflective mask>
FIG. 6 is a cross-sectional view showing an EUV reflective mask blank and an EUV reflective mask.
An Si film (film thickness: 4.2 nm) and a Mo film (film thickness: 2.8 nm) are formed on the glass substrate 101 obtained by the above-described Examples 1 to 4 and the comparative example by a DC magnetron sputtering method for one cycle. As described above, after 40 cycles were stacked, a Si film (film thickness: 11 nm) was formed to form the multilayer reflective film 102. Next, a chromium nitride (CrN) film (film thickness: 30 nm) is formed as the buffer layer 103 and a TaBN film (film thickness: 60 nm) is formed as the absorber layer 104 on the multilayer reflective film 102 by the same DC magnetron sputtering method. As a result, EUV reflective mask blanks 100 were obtained.
[0084]
Next, using this EUV reflective mask blank 100, an EUV reflective mask 100a having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, a resist for electron beam irradiation was applied on the EUV reflective mask blank 100, and the resist pattern was formed by drawing and developing with an electron beam.
[0085]
Using this resist pattern as a mask, the absorber layer 104 was dry-etched with chlorine to form the absorber layer pattern 104 a on the EUV reflective mask blank 100.
Further, the resist pattern remaining on the absorber layer pattern 104a was removed with hot sulfuric acid. Thereafter, the buffer layer 103 was dry-etched with a mixed gas of chlorine and oxygen in accordance with the absorber layer pattern 104a to obtain an EUV reflective mask 100a as the patterned buffer layer 103a.
[0086]
Next, a method for transferring a pattern to the resist-coated semiconductor substrate 110 with EUV light using the EUV reflective mask 100a will be described.
FIG. 7 is an explanatory diagram showing a pattern transfer method using a reflective mask.
The pattern transfer apparatus 120 shown in this figure includes a laser plasma X-ray source 121, an EUV reflective mask 100a, a reduction optical system 122, and the like. The reduction optical system 122 is configured by using an X-ray reflection mirror, and the pattern reflected by the EUV reflection mask 100a is reduced to about ¼. Since the wavelength band of 13 to 14 nm is used as the exposure wavelength, it was set in advance so that the optical path was in vacuum.
[0087]
In this state, the EUV light obtained from the laser plasma X-ray source 121 is incident on the EUV reflective mask 100a, and the reflected light is reflected on the resist-coated semiconductor substrate 110 via the reduction optical system 122. Transcribed to.
That is, light incident on the EUV reflective mask 100a is absorbed and not reflected by the absorber layer 104 in a portion where the absorber layer pattern 104a is present, whereas light incident on a portion where the pattern of the absorber layer 104 is not present. Is reflected by the multilayer reflective film 102. In this way, the pattern formed by the reflected light from the EUV reflective mask 100 a is transferred to the resist layer on the semiconductor substrate 110 via the reduction optical system 122.
[0088]
When the EUV reflective mask 100a made of the glass substrate 101 obtained in Examples 1 to 4 and the comparative example was used and pattern transfer was performed on the semiconductor substrate 110 by the pattern transfer method described above, EUVs according to Examples 1 to 4 were performed. It was confirmed that the accuracy of the reflective mask 100a was 16 nm or less, which is the required accuracy of the 0.07 μm design rule. On the other hand, the accuracy of the EUV reflective mask 100a according to the comparative example could not satisfy the required accuracy of the 0.07 μm design rule of 16 nm or less.
[0089]
【The invention's effect】
As described above, according to the present invention, the surface of the glass substrate subjected to local processing is polished for the purpose of improving surface roughness and removing surface defects by local processing. While improving the surface roughness of the glass substrate surface while maintaining the flatness, by removing surface defects on the glass substrate surface, the glass substrate for mask blanks having high flatness and smoothness and no surface defects, Alternatively, mask blanks using the same can be obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart showing manufacturing steps of a mask blank glass substrate.
FIG. 2 is a schematic sectional view of a polishing apparatus.
FIG. 3 is a schematic sectional view of a float polishing apparatus.
FIG. 4 is a cross-sectional view of a main part of the float polishing apparatus.
FIG. 5 is a schematic cross-sectional view of an EEM apparatus.
FIG. 6 is a cross-sectional view showing an EUV reflective mask blank and an EUV reflective mask.
FIG. 7 is an explanatory diagram showing a pattern transfer method using a reflective mask.
[Explanation of symbols]
10 Polishing equipment
20 Float polishing equipment
30 EEM equipment
100 EUV reflective mask blanks
100a EUV reflective mask
101 glass substrate
102 multilayer reflective film
103 Buffer layer
104 Absorber layer

Claims (6)

An uneven shape measuring step for measuring the uneven shape of the glass substrate surface for EUV mask blanks,
Based on the measurement result obtained in the uneven shape measurement step, the convexity of the convex portion existing on the surface of the glass substrate is specified, and the convex portion is locally processed under the processing conditions corresponding to the convexity. By the flatness control step of controlling the flatness of the glass substrate surface below a predetermined reference value required as a glass substrate for EUV mask blanks ,
After the flatness control step, the surface of the glass substrate that has been subjected to the local processing is not brought into contact with the polishing tool surface, and the processing liquid interposed between the glass substrate surface and the polishing tool surface A non-contact polishing process for polishing by action;
The manufacturing method of the glass substrate for EUV mask blanks characterized by having. The non-contact polishing step
The surface defect of the glass substrate is a step of polishing to a defect size or less required as a glass substrate for EUV mask blanks. 1 The manufacturing method of the glass substrate for described EUV mask blanks. The non-contact polishing step
Performed by float polishing, EEM or hydroplane polishing,
And, the processing liquid is at least one kind of fine powder particles selected from water, acidic aqueous solution, alkaline aqueous solution, or any of the above aqueous solutions and colloidal silica, cerium oxide, zirconium oxide, aluminum oxide. The method for producing a glass substrate for EUV mask blanks according to claim 1 or 2, wherein the glass substrate for EUV mask blanks is contained. The method for producing a glass substrate for EUV mask blanks according to any one of claims 1 to 3, wherein the local processing is performed by plasma etching or a gas cluster ion beam. The said reference value is 0.05 micrometer or less, The manufacturing method of the glass substrate for EUV mask blanks in any one of Claims 1-4 characterized by the above-mentioned. The EUV mask blank glass substrate obtained by the method of manufacturing a glass substrate for an EUV mask blank as claimed in any of claims 1 to 5, EUV mask and forming a thin film to be the transfer target pattern Blanks manufacturing method.

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