JP4647967B2 - Mask blank glass substrate manufacturing method, mask blank manufacturing method, exposure mask manufacturing method, and semiconductor device manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for mask blanks, a method for manufacturing mask blanks, a method for manufacturing an exposure mask, and a method for manufacturing a semiconductor device, and in particular, an exposure light source used at 65 nm or 45 nm in a semiconductor design rule. For mask blanks that use ultrashort wavelength light such as ArF excimer laser (exposure wavelength: 193 nm), F2 excimer laser (exposure wavelength: 157 nm), EUV (Extreme Ultra Violet) light (exposure wavelength: 13 nm) as an exposure light source The present invention relates to a glass substrate manufacturing method, a mask blank manufacturing method, an exposure mask manufacturing method, and a semiconductor device manufacturing method.

In recent years, with the increase in density and accuracy of VLSI devices, the trend toward finer substrate surfaces required for mask blank glass substrates (referred to as glass substrates as appropriate) is becoming more severe year by year. In particular, as the wavelength of the exposure light source becomes shorter, the demand for the shape accuracy (flatness) of the substrate surface has become stricter, and a glass substrate for mask blanks with high flatness has been demanded.
For example, when the exposure light source is an F2 excimer laser, the required flatness of the glass substrate is 250 nm or less, and when the exposure light source is EUV light, it is 50 nm or less. That is, in a rectangular area of 142 mm long × 142 mm wide, a flatness of 50 nm or less is required with a PV value (difference between the maximum height and the minimum height with respect to the reference surface). The reason is that if the flatness of the glass substrate is poor, the dimensional accuracy of the pattern after exposure and transfer is deteriorated.

Conventionally, various precision polishing methods have been proposed for reducing the surface roughness of a mask blank glass substrate manufacturing method.
For example, Patent Document 1 discloses a technique of a precision polishing method in which a substrate surface is polished using a polishing agent mainly composed of cerium oxide and then finish-polished using colloidal silica. When polishing a glass substrate 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.

  By the way, according to the above-described precision polishing method, it is theoretically possible to achieve the required smoothness by reducing the average grain size of the abrasive grains. However, since it is affected by mechanical accuracy such as the carrier that holds the glass substrate, the surface plate that sandwiches the glass substrate, and the planetary gear mechanism that moves the carrier, the flatness of the glass substrate that can be stably obtained is limited to about 500 nm. there were.

In recent years, in order to overcome the above limitations, a method for planarizing a glass substrate that performs local processing using plasma etching, a gas cluster ion beam, or a magnetic fluid has been proposed.
For example, in Patent Documents 2, 3, and 4, the surface of a glass substrate surface is measured by measuring the uneven shape of the glass substrate surface and surface-treating the region including the convex portion under the processing conditions corresponding to the convexity of the convex portion. A technique of a flattening method for flattening is disclosed.
JP-A 64-40267 JP 2002-316835 A JP-A-8-293383 US2002 / 0081943A Publication

However, the flattening method measures the concavo-convex shape using a fringe observation interferometer or a mechanical shift interferometer (see Patent Document 4). The measurement results of these interferometers include errors due to striae of the glass substrate and reflection of the back surface. If the processing conditions are determined based on the measurement results with low accuracy, the measurement results are extremely high (for example, a level of 50 nm or less). ) Has a problem that the flatness cannot be controlled. In particular, in the case of SiO ₂ —TiO ₂ glass used as a glass substrate for EUV mask blanks, striae may occur inside the glass substrate as compared to synthetic quartz glass. There is a problem that the flatness cannot be controlled accurately.
Further, due to the above problem, there has been a problem that it is not possible to realize further higher density and higher accuracy of the ultimate LSI device.

  The present invention has been made in view of the above-mentioned problems, and when measuring the uneven shape of the surface to be measured of the glass substrate, the adverse effects due to the striae of the glass substrate and the reflection on the back surface are reduced or removed, and the processing conditions Is accurately determined, the flatness is controlled with extremely high accuracy, and a method for manufacturing a glass substrate for mask blanks having high flatness, a method for manufacturing mask blanks, a method for manufacturing an exposure mask, and a method for manufacturing a semiconductor device The purpose is to provide.

In order to achieve the above object, a method for producing a glass substrate for mask blanks according to the present invention irradiates a surface to be measured on a glass substrate for mask blanks with a wavelength modulation laser, minutely varies the wavelength of the wavelength modulation laser, The difference in frequency of interference fringes between the reflected light reflected from the measured surface and the back surface of the glass substrate and the front reference surface is detected, and interference due to the reflected light from the back surface of the glass substrate is eliminated. Based on the uneven shape measuring step of measuring the uneven shape of the measured surface in the glass substrate using the reflected light reflected from the measured surface of the substrate, and the uneven shape based on the measurement result obtained in the uneven shape measuring step Flatness control for controlling the flatness of the surface to be measured on the glass substrate to be equal to or lower than a predetermined reference value by performing surface processing on a region including The extent there as a method having.
In this way, the adverse effect of the reflected light on the back surface of the glass substrate can be reduced or eliminated, and the uneven shape of the surface to be measured can be accurately measured, so that the processing conditions can be accurately determined and flattened with extremely high accuracy. The glass substrate for mask blanks which can control a degree and has a high level flatness (for example, 50 nmPV or less) can be manufactured. Therefore, the dimensional accuracy of the pattern after exposure transfer can be greatly improved, and further higher density and higher accuracy of the ultimate LSI device can be realized.

Moreover, the manufacturing method of the glass substrate for mask blanks of this invention exists as the method by which the uneven | corrugated shape of the to-be-measured surface in the said glass substrate excluded and measured the interference by the striae of this glass substrate.
In this way, the adverse effect due to the striae of the glass substrate can be reduced or eliminated, and the uneven shape of the substrate surface can be measured with higher accuracy, and a glass substrate for mask blanks having a higher level of flatness is manufactured. be able to.

Moreover, the manufacturing method of the glass substrate for mask blanks of this invention measures the uneven | corrugated shape of the back surface in the said glass substrate using the back reference surface set to the back surface side of the said glass substrate in the said uneven | corrugated shape measurement process. Furthermore, it is a method for measuring variations in the thickness of the glass substrate.
In this way, the surface to be measured and the back surface of the glass substrate can be efficiently surface-treated based on the measurement results regarding the uneven shape of the surface to be measured and the back surface of the glass substrate and the variation in the thickness of the glass substrate. Can have a high flatness and a glass substrate for mask blanks having a high level of parallelism (for example, 50 nm PV or less).

Moreover, the manufacturing method of the glass substrate for mask blanks of this invention is a solvent containing the acid or alkali which has an erosion property with respect to the said glass substrate on the surface which performs the surface processing of the said glass substrate before giving the said surface processing. This is a method for performing surface treatment.
If there are minute cracks on the surface of the glass substrate before surface processing, there may be defects in the concave portions on the surface of the glass substrate after the cleaning step after surface processing. In this way, it is possible to remove fine cracks or the like present on the surface of the glass substrate, or to enlarge and reveal the minute cracks, and then to enlarge or reveal the cracks that have been enlarged or revealed. Since it removes by surface processing, the glass substrate for mask blanks without the defect of a fine recessed part can be obtained after the washing | cleaning process after surface processing.

Moreover, in order to achieve the said objective, the manufacturing method of the mask blank in this invention is as a method of forming the thin film used as a mask pattern on the glass substrate for mask blanks of the said Claim 1 or 2 .
In this way, it is possible to manufacture high-quality mask blanks that are excellent in flatness and capable of improving the dimensional accuracy of the pattern after exposure transfer.

Moreover, in order to achieve the said objective, the manufacturing method of the mask for exposure in this invention is a method of patterning the thin film of the said mask blank , and forming a thin film pattern on the said glass substrate.
In this way, it is possible to manufacture a high-quality exposure mask that has excellent flatness and can improve the dimensional accuracy of the pattern after exposure transfer.

In order to achieve the above object, a method for manufacturing a semiconductor device according to the present invention includes an exposure mask manufactured by the above-described exposure mask manufacturing method , and the exposure mask is formed by lithography using the exposure mask. This is a method for transferring a thin film pattern onto a semiconductor substrate.
In this way, it is possible to manufacture a semiconductor device such as a VLSI device that can realize higher density and higher accuracy than the current level.

  As described above, according to the present invention, when measuring the concavo-convex shape of the surface to be measured of the glass substrate, the processing conditions are accurately determined by reducing or eliminating the adverse effects caused by the striae of the glass substrate and the reflection of the back surface. By controlling the flatness with extremely high accuracy, a glass substrate for mask blanks, a mask blank, an exposure mask, and a semiconductor device having high flatness can be manufactured. As a result, the dimensional accuracy of the pattern after exposure transfer can be greatly improved, and further higher density and higher accuracy of the ultimate LSI device can be realized.

[Manufacturing method of glass substrate for mask blanks]
FIG. 1: has shown the schematic flowchart figure for demonstrating the manufacturing method of the glass substrate for mask blanks concerning embodiment of this invention.
In the same figure, the manufacturing method of the glass substrate for mask blanks of this embodiment includes a preparation step (P1) for preparing a glass substrate whose surface (measurement surface and back surface) is precisely polished, and a measurement surface of the glass substrate. It has the uneven | corrugated shape measurement process (P2) which measures an uneven | corrugated shape, and the flatness control process (P3) which controls the flatness of the to-be-measured surface of a glass substrate.

<Preparation process>
The preparation step is a step of preparing a glass substrate in which one side or both sides are precisely polished, and the surface roughness of the glass substrate is set to 0.4 nm or less by root mean square roughness RMS.
In general, the preparation step (P1) includes a rough polishing step for rough polishing both surfaces of a glass substrate, and a precision polishing step for precisely polishing one or both surfaces of the rough-polished glass substrate. Is done. At this time, 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. The

The glass substrate is not particularly limited as long as it is used as a mask blank. For example, synthetic quartz glass, soda lime glass, aluminosilicate glass, borosilicate glass, alkali-free glass and the like can be mentioned.
However, in the case of a glass substrate for mask blanks for F2 excimer laser exposure, synthetic quartz glass doped with fluorine is used in order to suppress the absorption of the exposure light source as much as possible.
In the case of a glass substrate for EUV mask blanks, in order to suppress distortion of the transferred pattern due to heat during exposure, it is within the range of about 0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably about 0 ± 0. A glass material having a low coefficient of thermal expansion in the range of 3 × 10 ⁻⁷ / ° C. is used.
Furthermore, since a large number of films are formed on a glass substrate, an EUV mask blank is made of a highly rigid glass material that can suppress deformation due to film stress. In particular, a glass material having a high Young's modulus of 65 GPa or more is preferable. For example, amorphous glass such as SiO ₂ —TiO ₂ glass or synthetic quartz glass, or crystallized glass on which β-quartz solid solution is deposited is used.

  Here, it is preferable that the acid or alkali that is erodible to the glass substrate is formed on the surface of the substrate to be surface-treated after the above-described precision polishing and before the surface treatment is performed on the glass substrate. The surface treatment may be performed with a solvent containing. In this way, it is possible to remove fine scratches and cracks existing on the surface of the glass substrate that are subjected to surface processing, or to enlarge and reveal minute cracks, and then enlarge and reveal them. Since the cracks are removed by surface processing, the glass substrate for mask blanks without defects of minute concave portions is obtained after the cleaning step after the surface processing. Moreover, this surface treatment may be performed after the uneven shape measuring step described later. In addition, by performing the surface treatment before the uneven shape measuring step, an effect of cleaning the substrate surface can be obtained, and measurement errors caused by dirt can be eliminated and measurement can be performed with high accuracy.

<Uneven shape measurement process>
The concavo-convex shape measuring step is a step of measuring the concavo-convex shape (flatness) of the surface to be measured of the glass substrate prepared in the preparation step.
An optical interferometer is usually used for measuring the uneven shape on the surface to be measured of the glass substrate. A typical optical interferometer irradiates and reflects coherent light on the surface to be measured of the glass substrate and interferes with the measuring machine reference surface (front reference surface) to measure the difference in height of the surface to be measured as interference fringes. Calculate and measure phase difference from (light intensity).

On the other hand, the features of the present invention will be described with reference to the drawings.
FIG. 2: has shown the schematic for demonstrating the measurement state in the uneven | corrugated shape measurement process of the manufacturing method of the glass substrate for mask blanks concerning embodiment of this invention.
In the figure, a surface shape measurement processing device 2 includes a surface shape measurement device including a wavelength modulation laser light source 21, a CCD camera 22, a front reference surface A, and a rear reference surface D (referred to as surfaces A and D as appropriate). It comprises means 20, a measurement data processing device 26 provided with data analysis means 23, machining amount calculation means 24 and machining condition determination means 25.

  In the surface shape measurement processing apparatus 2, a glass substrate 1 for mask blanks having a measured surface B and a back surface C (abbreviated as surfaces B and C as appropriate) between the surface A and the surface D is set. Is done. At this time, in order to identify each interference fringe, the distance between the surfaces A and B is L1, the plate thickness of the glass substrate 1 (the distance between the surfaces B and C) is T, and the distance between the surfaces C and D is When L2 is set and the distance between the surfaces A and D is L3, the glass substrate 1 is set so that each distance is different, that is, L1 ≠ T ≠ L2 ≠ L3.

  The surface shape measuring means 20 uses the wavelength modulation laser light source 2 as a light source, irradiates the glass substrate 1 for mask blanks with the wavelength modulation laser, and changes the wavelength of the wavelength modulation laser minutely. When the wavelength-modulated laser is irradiated, interference fringes on the surface (A + B) (interference fringes generated by interference between the reflected light from the surface A and the reflected light from the surface B), and the interference fringes on the surface (A + C) Group, surface (A + D) interference fringe group, surface (B + C) interference fringe group, surface (B + D) interference fringe group, surface (C + D) interference fringe group, and these interference fringe groups are CCD cameras. 22 is read.

  The data analysis means 23 receives the image data of each interference fringe group from the CCD camera 22, detects the difference in frequency of each interference fringe group by Fourier transform technology, and separates each interference fringe group. That is, it has a function of separating the interference fringe group on the surface (A + B) and the interference fringe group on the surface (C + D) from the plurality of interference fringe groups.

The data analysis means 23 can calculate the height difference of the surface to be measured B from the phase difference of the interference fringe group on the surface (A + B), and measure the uneven shape of the surface to be measured B. In this embodiment, since the rear reference plane D is provided, the data analysis unit 23 separates the interference fringe group on the surface (C + D), and determines the back surface from the phase difference of the interference fringe group on the surface (C + D). The difference in height of C can be calculated and the uneven shape of the back surface C can be measured. These measurement results do not include, for example, measurement errors due to reflected light from the back surface C of the glass substrate 1 or measurement errors due to striae inside the glass substrate 1, so that the flatness control process in the next process is processed. The conditions can be accurately determined. As a result, the flatness can be controlled with extremely high accuracy, and a glass substrate for mask blanks having high flatness can be manufactured.
In addition, the measured surface flatness can be calculated from the uneven shape measurement data of the measured surface B, and the back surface flatness can be calculated from the uneven shape measurement data of the back surface C.

  The data analysis means 23 can separate the interference fringe group of the surface (A + D) with the glass substrate 1 removed, and can calculate L3 from the phase difference of the interference fringe group of the surface (A + D). L1 and L2 can be calculated from the interference fringe group on the surface (A + B) and the interference fringe group on the surface (C + D), respectively. Here, since the distances L1, L2, and L3 are measured with extremely high accuracy, the thickness T (= L3-L1-L2) of the glass substrate 1 at an arbitrary measurement position can be easily and accurately calculated. Further, a variation in plate thickness (appropriately referred to as plate thickness variation (TTV) as appropriate) can be calculated from the plate thickness T at each measurement position. In addition, the uneven | corrugated shape and board thickness dispersion | variation of the to-be-measured surface B and the back surface C of the glass substrate 1 can be calculated | required substantially simultaneously.

  The measurement results of the uneven shape and the plate thickness variation of the glass substrate 1 are stored in a recording medium (not shown) such as a computer, and then the processing amount calculation means 24 uses the measurement results and a predetermined reference set in advance. It is compared with a value (required flatness, variation in plate thickness), and the difference is calculated for each predetermined region (for example, a region of 5 mm length × 5 mm width) of the measurement target surface B of the glass substrate 1. That is, the machining allowance is set according to the heights of the convex portions of the measured surface B and the back surface C of the glass substrate 1. This difference (machining allowance) is a necessary machining amount for each predetermined region in local surface machining.

The processing condition determination means 25 determines the processing conditions so that the required processing amount can be efficiently removed by the local processing machine 27. That is, by dividing the required processing amount by the processing amount per unit time by the spot of the local processing machine 27, the spot residence time is calculated, and subsequently the spot residence time at each position is calculated for the entire surface to be processed, Determine work feeding schedule efficiently.
Thus, according to the surface shape measurement processing apparatus 2, the measurement of the glass substrate 1 is performed based on the measurement results regarding the uneven shape of the measurement surface B and the back surface C of the glass substrate 1 and the variation in the thickness of the glass substrate 1. The surface B and the back surface C can be efficiently processed, and a glass substrate for mask blanks having both high flatness and a high level of parallelism (for example, 50 nm PV or less) can be manufactured. .
In addition, you may perform said arithmetic processing in any of an uneven | corrugated shape measurement process or a flatness control process.

<Flatness control process>
In the flatness control step, the flatness of the surface to be measured in the glass substrate is less than or equal to a predetermined reference value by performing surface processing on the region including the concavo-convex shape based on the measurement result obtained in the concavo-convex shape measuring step. It is a process to control.
The surface processing is performed according to processing conditions set for each predetermined region on the surface to be measured of the glass substrate. As described above, this processing condition is the difference between the uneven shape of the measured surface of the glass substrate measured by the optical interferometer and the preset flatness reference value (necessary processing amount for local surface processing). Set based on.

  The parameters of the processing conditions vary depending on the local processing machine 27, but are set so that the removal amount increases as the convexity of the convex portion increases. For example, when the processing method of local surface processing is ion beam or plasma etching, the higher the convexity of the convex portion, the slower the moving speed of the ion beam or plasma generating housing, or Control to increase the intensity of the beam or plasma.

  In addition, there is MRF (Magneto Rheological Finishing) as a processing method for local surface processing. MRF is a method in which polishing abrasive grains contained in a magnetic fluid are brought into contact with a workpiece (glass substrate) with the aid of a magnetic field, and the residence time of the contact portion is controlled to locally perform polishing. is there. In this polishing process, the longer the convexity of the convex part, the longer the residence time of the contact part by the abrasive grains. Further, the smaller the convexity of the convex part, the shorter the residence time of the contact part by the abrasive grains is controlled.

3A and 3B are schematic diagrams for explaining a processing state by the MRF processing method in the flatness control step of the present embodiment, where FIG. 3A is a front sectional view and FIG. 3B is a side sectional view.
In this figure, according to the MRF processing method, polishing abrasive grains (not shown) contained in a magnetic fluid 41 containing iron (not shown) are used for mask blanks which are workpieces with the aid of a magnetic field. The glass substrate 1 is brought into contact with the glass substrate 1 at high speed and the residence time of the contact portion is controlled to perform local polishing. That is, a mixed liquid (magnetic polishing slurry 4) of the magnetic fluid 41 and the polishing slurry 42 is put into the disc-shaped electromagnet 3 that is rotatably supported, and the tip thereof is used as a local processing polishing spot 5 to be removed. The convex portion 13 is in contact with the polishing spot 5. In this manner, the magnetic polishing slurry 4 is distributed along the magnetic field on the disk, the polishing slurry 42 is distributed on the glass substrate 1 side, and the magnetic fluid 41 is distributed on the magnet 3 side. Flowing. A part of this state is used as a polishing spot 5 for locally polishing, and is brought into contact with the surface of the glass substrate 1, whereby the convex portion 13 is locally polished and controlled to a flatness of several tens of nm.

In this MRF processing method, unlike the conventional polishing method, since the polishing spot 5 is always flowing, there is no deterioration in processing accuracy due to wear of the processing tool or shape change, and the glass substrate 1 is pressed with a high load. Since there is no need, there is an advantage that there are few latent scratches and scratches in the surface displacement layer.
In the MRF processing method, when the glass substrate 1 is moved while the polishing spot 5 is in contact, the moving speed of the glass substrate 1 is controlled according to the processing allowance (required processing amount) set for each predetermined region. Therefore, the removal amount can be easily adjusted.

  As the polishing slurry 42 mixed with the magnetic fluid 41, a slurry in which fine abrasive particles are dispersed in a liquid is used. The abrasive particles are, for example, silicon carbide, aluminum oxide, diamond, cerium oxide, zirconium oxide, manganese oxide, colloidal silica, and the like, and are appropriately selected according to the material of the workpiece, 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 form an abrasive slurry 42 and mixed with the magnetic fluid 41.

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 collide isotropically with the surface to be measured of the glass substrate, and this portion is etched. On the other hand, since no plasma is generated in the portion where the plasma generating casing is not located, the etching gas is not etched even if it contacts.
When the plasma generating casing is moved on the glass substrate, the removal amount is adjusted by controlling the moving speed and plasma intensity of the plasma generating casing in accordance with the required processing amount of the surface to be measured 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 a flow of generated radical species collides with a surface to be measured of a glass substrate.

  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 include silicon fluoride, trichlorochloromethane, and boron trichloride.

The local processing method by ion beam (gas cluster ion beam irradiation) is a gaseous 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). The gas cluster of these substances is formed using a gas cluster ion beam that is ionized by electron irradiation to the solid, while controlling the irradiation area as necessary. This is a local processing method for irradiating the surface (glass substrate surface).
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 measurement surface of a glass substrate is irradiated with this gas cluster ion beam, the molecules or atoms that make up the cluster ions and the atoms on the surface to be measured collide in multiple stages, and reflected molecules or atoms that have lateral motion components. Give rise to Thereby, selective sputtering occurs at the convex portion of the surface to be measured of the glass substrate, and the surface to be measured 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 surface to be measured of the glass substrate.
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.
Examples of the gaseous substance include oxides such as CO ₂ , CO, N ₂ O, NOx, and CxHyOz, and rare gases such as O ₂ , N ₂ , Ar, and He.

The flatness required for the glass substrate for the mask blank is determined according to the wavelength of the exposure light source used in the mask blank, and the flatness control standard in the flatness control process is determined according to the required flatness. The value is determined.
For example, in the case of a mask blank glass substrate for F2 excimer laser exposure, the flatness control reference value is 250 nm or less, and in the case of an EUV mask blank glass substrate, the flatness control reference value is 50 nm or less for local processing. Is called.

  In the above-described unevenness control step, if a rough surface or a work-affected layer occurs on the measured surface of the glass substrate, the measured surface may be polished for the purpose of removing the rough surface or the work-affected layer. Absent. In that case, any polishing method may be used as long as the surface roughness is improved while maintaining the flatness created by local surface processing. For example, polishing is performed by bringing a polishing tool surface such as a polishing pad into contact with the surface to be measured, or by the action of the machining liquid interposed between the surface to be measured and the polishing tool surface without direct contact. Non-contact polishing (for example, float polishing method, EEM (Elastic Emission Machining) method) method and the like.

  Thus, according to the manufacturing method of the glass substrate for mask blanks concerning this embodiment, the bad influence by the reflected light in the back surface of a glass substrate can be reduced or removed, and the uneven | corrugated shape of a to-be-measured surface can be measured accurately. Therefore, it is possible to accurately determine the processing conditions, control the flatness with extremely high accuracy, and manufacture a glass substrate for mask blanks having a high level of flatness.

[Manufacturing method of mask blanks]
Next, an embodiment of a method for manufacturing a mask blank according to the present invention will be described.
This mask blank manufacturing method includes the steps of manufacturing the glass substrate 1 by the above-described mask blank glass substrate manufacturing method, and a thin film that becomes a mask pattern (transfer pattern) on the main surface of the manufactured glass substrate 1. Forming the step.
By the way, mask blanks are classified into transmissive mask blanks and reflective mask blanks. The mask blank of this embodiment can be applied to any mask blank, and a thin film to be a transferred pattern is accurately formed on the glass substrate 1. A resist film may be formed on the thin film.

Mask blanks are classified into transmissive mask blanks and reflective mask blanks. In any mask blanks, a thin film to be a transferred pattern is formed on the glass substrate 1. A resist film may be formed on the thin film.
In addition, 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 And a phase shift film that changes the phase difference of exposure light.

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.
As the phase shift film, in addition to the SiO ₂ film having only the phase shift function, a metal silicide oxide film, a metal silicide nitride film, a metal silicide oxynitride film, and a metal silicide oxycarbide having a phase shift function and a light shielding function Examples thereof include a film, a metal silicide oxynitride carbide film (metal: transition metal such as Mo, Ti, W, and Ta), a halftone film such as a CrO film, a CrF film, and a SiON film.

In the reflective mask blank, a laminated film including a light reflective multilayer film (multilayer reflective film) and a light absorber film (absorber layer) to be a transferred pattern is formed on the glass substrate 1.
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).
The transmission type 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.
In addition, the above-mentioned thin film can be formed by sputtering methods, such as DC sputtering, RF sputtering, and ion beam sputtering, for example.

  Thus, according to the mask blank manufacturing method according to the present embodiment, the flatness is excellent, and the dimensional accuracy of the pattern after exposure transfer can be improved.

[Exposure Mask Manufacturing Method]
Next, an embodiment of a transfer mask manufacturing method according to the present invention will be described.
The transfer mask manufacturing method includes a step of manufacturing a mask blank with a resist film by the above-described mask blank manufacturing method, and a resist pattern forming step of forming a desired resist pattern on the resist film through drawing / development processing, etc. And a thin film pattern forming step of forming a thin film pattern on a glass substrate for mask blanks by masking the resist pattern and etching away the thin film.

  In a photomask which is a transmission type transfer mask, a desired resist pattern is formed on the resist film of the photomask blank in which a light-shielding film and a resist film are formed on a mask blank glass substrate through drawing / development processing, etc. Thereafter, the light shielding film is removed by etching using this resist pattern as a mask, and finally the resist film is removed to obtain a photomask in which the light shielding film pattern is formed on the glass substrate for mask blanks.

  In addition, in the halftone phase shift mask that is a transmissive transfer mask, the resist film of the halftone phase shift mask blank in which a halftone film, a light-shielding film, and a resist film are formed on a mask blank glass substrate is used. After forming a desired resist pattern through drawing / development processing, etc., this resist pattern is used as a mask to remove the light-shielding film, and a light-shielding film pattern is formed. Using this light-shielding film pattern as a mask, halftone film is etched By removing the resist film and the light-shielding film at the end, a halftone phase shift mask in which a halftone film pattern is formed on the glass substrate for mask blanks is obtained.

  In addition, in a reflective mask that is a reflective transfer mask, drawing and developing on the resist film of the reflective mask blank in which a light reflective multilayer film, a light absorber film, and a resist film are formed on a mask blank glass substrate. After forming a desired resist pattern through processing, etc., the light absorber film is etched away using this resist pattern as a mask, and finally the resist film is removed, whereby the light absorber film pattern is formed on the light reflecting multilayer film. A reflection type mask in which is formed is obtained.

  Thus, according to the method for manufacturing an exposure mask according to the present embodiment, the flatness is excellent, and the dimensional accuracy of the pattern after exposure transfer can be improved.

[Method for Manufacturing Semiconductor Device]
Next, an embodiment of a semiconductor device manufacturing method according to the present invention will be described.
In this semiconductor manufacturing apparatus manufacturing method, an exposure mask is manufactured by the above-described exposure mask manufacturing method, and a thin film pattern of the exposure mask is transferred onto a semiconductor substrate by lithography using the exposure mask. As a way to do. At this time, the semiconductor substrate has a conductive film to be a circuit pattern and a resist film, and the transfer mask is reduced and exposed to about 1/4 or 1/5 times so that a desired circuit pattern is formed into a resist film. And patterning the conductive film using the resist film as a mask, a semiconductor device having a desired circuit pattern formed on the semiconductor substrate can be obtained.
In this way, it is possible to manufacture a semiconductor device such as a VLSI device that can realize higher density and higher accuracy than the current level.

[Examples and Comparative Examples]
Hereinafter, embodiments of the present invention will be described with reference to a glass substrate for EUV mask blanks (hereinafter referred to as a glass substrate), an EUV reflective mask blank, and an EUV reflective mask manufacturing method as examples. It is not limited to.

Example 1
SiO ₂ having a double-side polishing apparatus and stepwise polishing with cerium oxide abrasive grains or colloidal silica abrasive grains, removing the abrasive with an aqueous solution containing silicic acid, and then treating the surface of the substrate with an aqueous solution of sodium hydroxide. A TiO ₂ -based glass substrate (size: about 152.4 mm × about 152.4 mm, thickness: about 6.35 mm) was prepared. The surface roughness of the obtained glass substrate was about 0.15 nm in terms of root mean square roughness (RMS) (measured with an atomic force microscope).

Irregular shapes (surface morphology, flatness) and TTV (plate thickness variation) on the front and back surfaces (measured surface and back surface) of this glass substrate were measured with a wavelength shift interferometer using a wavelength-modulated laser (measurement area of about 148 mm). X about 148 mm).
As described above, this wavelength shift interferometer has a difference in height of the measurement surface from the interference fringes between the reflected light reflected from the measurement surface and the back surface of the glass substrate and the measuring machine reference surface (front reference surface). Is calculated as a phase difference, the frequency difference of each interference fringe is detected, and the interference fringe with the measuring machine reference surface (front reference surface) by the reflected light reflected from the measured surface and the back surface of the glass substrate is separated. The uneven shape of the surface to be measured is measured. In this example, a measuring machine reference surface (rear reference surface) was further provided on the back surface side of the glass substrate, and the uneven shape on the back surface of the glass substrate and the thickness variation of the glass substrate were also measured. Note that the measurement result of the concavo-convex shape obtained by this measurement method does not include measurement errors due to striae inside the substrate, as described above.

As a result, the flatness of the measured surface and the back surface of the glass substrate was about 290 nm (convex shape). The flatness refers to a PV value calculated by defining a reference plane by the method of least squares with the measured surface as a reference.
The measurement results of the concavo-convex shape (surface morphology, flatness) of the measurement surface of the glass substrate by the wavelength shift interferometer are stored in a computer as height information with respect to the reference plane for each measurement point, and glass for EUV mask blanks. Compared to the reference value 50 nm (convex shape) of the measured surface flatness required for the substrate, the reference value 50 nm (convex shape) of the back surface flatness, and the reference value 50 nm of TTV (plate thickness variation), the difference (required processing amount) ) Was calculated on a computer.

Next, the processing conditions of the local surface processing according to the required processing amount were set for each processing spot shape region in the glass substrate surface.
Using a dummy substrate in advance, the dummy substrate is processed with spots without moving the substrate for a certain time in the same way as in actual processing, and the shape is the same as the apparatus for measuring the uneven shape of the measured surface and the back surface. It measured with the measuring machine and calculated the processing volume of the spot per time unit. Then, the scanning speed for raster scanning the glass substrate was determined according to the required processing amount obtained from the spot information and the uneven shape information of the glass substrate. For example, the processing amount is large in a portion where the scanning speed is slow, and the processing amount is small in a portion where the scanning speed is fast.

  According to the set processing conditions, the measured surface flatness, back surface flatness, and TTV (plate thickness variation) of the glass substrate by the MRF (magneto-rheological fluid) processing method using the substrate finishing device with magnetic fluid manufactured by QED. ) Was subjected to local surface processing so that the surface shape was adjusted to be equal to or less than the above reference value.

  When the uneven shape (surface form, flatness) of the measured surface and the back surface of the glass substrate after performing shape adjustment by local surface processing by MRF is measured, the flatness of the measured surface and the back surface is about 40 to 50 nm. TTV (plate thickness variation) was also 50 nm or less, which was good. Moreover, when the surface roughness of the to-be-measured surface and the back surface of the glass substrate was measured, the root-mean-square roughness RMS was about 0.37 nm, which was a state rougher than the surface roughness before local surface processing by MRF. became.

Next, double-side polishing was performed on the front and back surfaces of the glass substrate using a double-side polishing apparatus. Double-side polishing was performed under the following polishing conditions.
Processing liquid: alkaline aqueous solution (NaOH) + abrasive (concentration: 2 wt%),
pH: 11
Abrasive: colloidal silica, average particle size: about 70 nm
Polishing platen rotation speed: 1-50rpm
Processing pressure: 0.1-10 kPa
Polishing time: 1-10min
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 front and back surfaces of the obtained glass substrate were measured with the above-described measuring apparatus, the measured surface flatness was about 40 nm, the back surface flatness was about 50 nm, and the TTV (plate thickness variation) was about 50 nm. The state before processing by the double-sided processing machine was maintained and was good. Moreover, the surface roughness was about 0.13 nm in RMS, and the state of surface roughness of the glass substrate before double-side polishing could be improved. Further, when the surface of the glass substrate was inspected using a defect inspection apparatus, it was good without a convex or concave defect having a size larger than about 0.1 μm.

(Comparative example)
In the above-mentioned Example 1, the uneven shape of the measurement surface and the back surface of the glass substrate was measured with an optical interferometer (GPI-XP manufactured by Zygo) that performs interference measurement on the reference surface by piezo PZT scanning (measurement area about 148 mm). X about 148 mm). Since this optical interferometer cannot measure the concave and convex shapes on the surface to be measured and the back surface at the same time, it was measured separately. At that time, when measuring one surface, the other surface was subjected to an antireflection treatment such as oil to reduce the adverse effect from the opposite surface. As a result, the flatness of the measured surface and the back surface of the glass substrate was about 350 nm (convex shape).

Next, as in Example 1, the measured surface flatness reference value and the back surface flatness reference value necessary for the glass substrate for EUV mask blanks are compared, and the difference (required processing amount) is calculated by a computer. The processing conditions were set.
Subsequently, according to the set processing conditions, the surface shape was adjusted by local surface processing by the MRF processing method.

  When the unevenness (surface form, flatness) of the measured surface and back surface of the glass substrate after the shape adjustment by local surface processing by MRF is measured, the flatness of the measured surface and back surface is about 50 to 100 nm. , TTV (plate thickness variation) also exceeded about 50 nm, resulting in exceeding the flatness reference value and TTV reference value of the measured surface and the back surface.

  When the surface processed substrate surface was observed with an optical interferometer (New View manufactured by Zygo) that used white light as a light source and vertically scanned the reference mirror, undulations such as interference fringes were observed. This is because when the uneven shape (surface morphology) of the glass substrate was measured before processing, the surface shape of the surface to be measured could not be measured accurately due to interference fringes caused by reflected light on the back surface or inside of the substrate. It is considered that the processing conditions for obtaining the flatness reference value and the TTV reference value could not be set accurately.

  Moreover, when the surface roughness of the glass substrate surface after local surface processing was measured, the root mean square roughness RMS was about 0.37 nm, which was a state rougher than the surface roughness before local surface processing. became. Therefore, as in Example 1, double-side polishing was performed on the glass substrate surface using a double-side polishing apparatus.

  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 flatness of the measured surface and the back surface was about 100 nm, and the surface roughness was about 0.15 nm in RMS. Further, since there is no measuring instrument corresponding to the whole surface TTV measurement, the parallelism was measured with an optical interferometer, and the parallelism was about 2 to 3 μm. Moreover, when the thickness of several places of the glass substrate was measured with a micrometer, the variation was about 2 to 3 μm, and the measurement part was damaged due to contact measurement. 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.

(Example 2) Example of shape processing by DCP A glass substrate for mask blanks was produced in the same manner as in Example 1 except that the local surface processing method in Example 1 described above was changed to SpeedFam's DCP (Dry Chemical Planarization). did. In addition, as for the processing conditions by DCP, the processing conditions of local plasma etching corresponding to the required processing amount were set for each predetermined region (about 5 mm × about 5 mm) in the glass substrate surface. According to the set processing conditions, the flatness of the glass substrate becomes a reference value of 50 nm (convex shape) for the surface flatness, a reference value of 50 nm (convex shape) for the back surface flatness, and a reference value of 50 nm for TTV (plate thickness variation). I made it. Further, methane tetrafluoride was used as an etching gas for local plasma etching, and a high-frequency type having a cylindrical electrode was used as a plasma generating casing.

  When the unevenness (surface form, flatness) of the measured surface and back surface of the glass substrate after performing shape adjustment by local surface processing by DCP was measured, the flatness of the measured surface and back surface was about 50 nm, TTV (plate thickness variation) was also about 50 nm or less, which was good. Further, when the surface roughness of the glass substrate surface was measured, the root mean square roughness RMS was about 1.3 nm, which was a rougher state than the surface roughness before the local surface processing by DCP.

  As a result of performing double-side polishing similar to the above in order to improve the rough surface state, the flatness and surface roughness of the measured surface and the back surface of the obtained glass substrate are about 50 nm and the back surface is flat. The degree was about 50 nm, the TTV (plate thickness variation) was about 50 nm, and the state before processing by the double-sided processing machine was maintained, which was good. Further, the surface roughness was about 0.13 nm in RMS, and the rough state of the glass substrate surface could be improved. Further, when the surface of the glass substrate was inspected using a defect inspection apparatus, it was good without a convex or concave defect having a size larger than about 0.1 μm.

  Next, as shown in FIG. 4, a Si film (film thickness: about 4.2 nm) and a Mo film are formed on the glass substrate 201 obtained by the above-described Examples 1 and 2 and the comparative example by the DC magnetron sputtering method. After stacking about 40 cycles (film thickness: about 28 nm) as a cycle, a Si film (film thickness: about 11 nm) was formed to form a multilayer reflective film 202. Next, by the same DC magnetron sputtering method, a chromium nitride (CrN) film (film thickness: about 30 nm) is used as the buffer layer 203 on the multilayer reflective film 202, and a TaBN film (film thickness: about 60 nm) is used as the absorber layer 204. It formed and the EUV reflective mask blanks 200 were obtained.

  The obtained EUV reflective mask blanks were measured for flatness, surface roughness, and plate thickness variation (TTV). In Example 1, they were about 50 nm, about 0.13 to 0.17 nm, and about 50 nm, respectively. In Example 2, it was about 50 nm, about 0.13-0.17 nm, and about 50 nm, and it was about 100-150 nm, about 0.13 nm, and about 2-3 micrometers in the comparative example. In both Examples 1 and 2 and the comparative example, the surface roughness was not significantly changed before and after film formation. However, the flatness and thickness variation (TTV) were not significantly changed before and after film formation in Examples 1 and 2, but deteriorated in the comparative example.

Next, by using this EUV reflective mask blank 200, an EUV reflective mask 200a having a pattern for a 16 Gbit DRAM having a design rule of 0.0 μm was manufactured.
First, a resist for electron beam irradiation (not shown) was applied and formed on the EUV reflective mask blanks 200, developed by drawing with an electron beam, and a resist pattern (not shown) was formed.
Using this resist pattern as a mask, the absorber layer 204 was dry-etched with chlorine to form an absorber layer pattern 204a on the buffer layer 203.

Further, the resist pattern remaining on the absorber layer pattern 204a was removed with hot sulfuric acid.
Thereafter, the buffer layer 203 was dry-etched with a mixed gas of chlorine and oxygen according to the absorber layer pattern 204 a to form the buffer layer pattern 203 a on the multilayer reflective film 202. Thus, the buffer layer pattern 203a / absorber layer 204a was formed on the multilayer reflective film 202 to obtain an EUV reflective mask 200a.

Next, a method for transferring a pattern by EUV light to a semiconductor substrate with a resist using the EUV reflective mask 200a will be described.
FIG. 5 is a schematic diagram for explaining a pattern transfer method using a reflective mask according to an embodiment of the present invention and a comparative example.
In the figure, a pattern transfer apparatus 100 includes a laser plasma X-ray source 101, an EUV reflective mask 101, a reduction optical system 102, and the like. The reduction optical system 102 is configured by using the X-ray reflection mirror 103, and the pattern reflected by the EUV reflection mask 200a 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.

In this state, EUV light obtained from the laser plasma X-ray source 101 is incident on the EUV reflective mask 200a, and the light reflected here is incident on the resist-coated semiconductor substrate via the reduction optical system 102. Transcribed.
That is, the light incident on the EUV reflective mask 200a is absorbed and not reflected by the absorber layer in a portion having the absorber layer pattern, while the light incident on the portion without the pattern of the absorber layer is multi-layered. Reflected by the reflective film. In this way, the pattern formed by the reflected light from the EUV reflective mask 200 a is transferred to the resist layer on the semiconductor substrate 110 via the reduction optical system 102.

  Using the EUV reflective mask 200a made of the glass substrate obtained in Examples 1 and 2 and the comparative example, pattern transfer was performed on the semiconductor substrate 110 by the pattern transfer method described above. As a result, EUV reflection according to Examples 1 and 2 was performed. It was confirmed that the accuracy of the mold mask 200a 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 200a according to the comparative example could not satisfy the required accuracy of the 0.07 μm design rule of 16 nm or less.

  As mentioned above, although the manufacturing method of the glass substrate for mask blanks of this invention, the manufacturing method of mask blanks, the manufacturing method of the mask for exposure, and the manufacturing method of a semiconductor device were shown and demonstrated, preferable embodiment is concerned, The manufacturing method of the glass substrate for mask blanks, the manufacturing method of the mask blanks, the manufacturing method of the mask for exposure, and the manufacturing method of the semiconductor device are not limited to the above-described embodiments, and various in the scope of the present invention. Needless to say, it is possible to implement this change.

  As described above, the mask blank glass substrate manufacturing method, the mask blank manufacturing method, the exposure mask manufacturing method, and the semiconductor device manufacturing method according to the present invention include a mask blank glass substrate and a mask. Although it is as a blank, an exposure mask, and a semiconductor device, it is not limited to this. For example, it can be suitably used for a plate material that requires extremely excellent flatness and smoothness.

The schematic flowchart figure for demonstrating the manufacturing method of the glass substrate for mask blanks concerning embodiment of this invention is shown. The schematic for demonstrating the measurement state in the uneven | corrugated shape measurement process of the manufacturing method of the glass substrate for mask blanks concerning embodiment of this invention is shown. It is the schematic explaining the processing state by the MRF processing method in the flatness control process of this embodiment, (a) is front direction sectional drawing, (b) has shown side surface sectional drawing. It is the schematic explaining the manufacturing method of the reflective mask concerning the Example and comparative example of this invention, (a) is an expanded sectional view of a reflective mask blank, (b) is an expanded sectional view of a reflective mask. Show. The schematic diagram explaining the pattern transfer method by the reflective mask concerning the Example and comparative example of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for mask blanks 2 Surface shape measurement processing apparatus 3 Electromagnet 4 Magnetic polishing slurry 5 Polishing spot 13 Convex part 20 Surface shape measurement means 21 Wavelength modulation laser light source 22 CCD camera 23 Data analysis means 24 Processing amount calculation means 25 Processing conditions Determination means 26 Measurement data processing device 41 Magnetic fluid 42 Polishing slurry 100 Pattern transfer device 101 Laser plasma X-ray source 102 Reduction optical system 103 X-ray reflection mirror 110 Semiconductor substrate 200 EUV reflection type mask blanks 200a EUV reflection type mask 201 Glass substrate 202 Multilayer reflective film 203 Buffer layer 203a Buffer layer pattern 204 Absorber layer 204a Absorber layer pattern A Front reference surface B Surface to be measured C Back surface D Back reference surface

Claims (5)

A surface to be measured in a glass substrate for mask blanks is irradiated with a wavelength modulation laser, the wavelength of the wavelength modulation laser is minutely changed, and reflected light and a front reference surface reflected from the surface to be measured and the back surface of the glass substrate, respectively. The frequency difference of the interference fringes of the glass substrate is detected, interference due to the reflected light from the back surface of the glass substrate is eliminated, and the measured light on the glass substrate is measured using the reflected light reflected from the measured surface of the glass substrate. An uneven shape measuring step for measuring the uneven shape of the surface;
Based on the measurement result obtained in the concavo-convex shape measurement step, the flatness of the surface to be measured on the glass substrate is controlled to be equal to or lower than a predetermined reference value by performing surface processing on the region including the concavo-convex shape. A flatness control step ,
And in the said uneven | corrugated shape measurement process, the uneven | corrugated shape of the back surface in the said glass substrate is measured using the back reference surface set to the back surface side of the said glass substrate, Furthermore, the dispersion | variation in the plate | board thickness of the said glass substrate is measured. A method for producing a glass substrate for mask blanks, comprising: Before applying the surface processing, the surface is subjected to surface processing of the glass substrate, according to claim 1, characterized in that the surface treatment with a solvent containing an acid or alkali with erosive with respect to the glass substrate Manufacturing method of glass substrate for mask blanks. A method for producing a mask blank, comprising: forming a thin film to be a mask pattern on the glass substrate for a mask blank according to claim 1 or 2 . A method for producing an exposure mask, comprising: patterning a thin film of the mask blank according to claim 3 to form a thin film pattern on the glass substrate. An exposure mask is manufactured by the exposure mask manufacturing method according to claim 4, and a thin film pattern of the exposure mask is pattern-transferred onto a semiconductor substrate by lithography using the exposure mask. A method for manufacturing a semiconductor device.

Images