KR20110033997A - Optical member for photomask and method for manufacturing the optical member - Google Patents

Abstract

The optical member for photomasks is an optical member formed by adding TiO ₂ to synthetic quartz glass. TiO ₂ is contained 3.0 to 6.5% by weight. The manufacturing method of the optical member for photomasks synthesize | combines a quartz glass ingot, shape | molds to predetermined shape of flat form, and then anneals in an oxidizing atmosphere. By annealing by changing the Ti ^{+ 3} in the quartz glass ingot by Ti ^{4 +} it is possible to reduce the light absorption by the Ti ^{3 +.} Since the transmittance | permeability with respect to the light of wavelength 365nm is 90% or more, it has a practically sufficient transmittance also in the vicinity of wavelength 365nm, and does not thermally expand better than quartz glass.

Description

Optical member for photomask and its manufacturing method {OPTICAL MEMBER FOR PHOTOMASK AND METHOD FOR MANUFACTURING THE OPTICAL MEMBER}

TECHNICAL FIELD This invention relates to the photomask substrate used when manufacturing flat panel displays (henceforth FPD), such as a liquid crystal panel, and its manufacturing method.

FPD is manufactured through the process of forming the element of FPD with high precision on the surface of a glass substrate. Photolithography technology is used in this process. That is, the photomask in which the mask pattern was formed with high precision on the surface of the flat-shaped transparent substrate excellent in planarity is illuminated with exposure light, and the image of the mask pattern is image-formed on the glass substrate to which photoresist was apply | coated previously, and is developed by A resist pattern is formed on the glass substrate surface.

By the way, in order to enlarge the size of the screen of FPD and to make production more efficient, the glass substrate for FPD advances year by year, and with this, the size of the photomask for using for the production is also progressing. In the near future, glass substrates become very large sizes, such as 2200 mm x 2500 mm, and with this, the photomask used for exposing a mask pattern to this glass substrate is a size whose diagonal length exceeds 1470 mm. Thing, for example, 1220 mm x 1400 mm, and thickness becomes very large like 13 mm. However, the increase in size is not limited to this, and larger glass substrates and photomasks are required.

When exposing the pattern formed on a photomask to a board | substrate, exposure is performed in the state which hold | maintained the photomask horizontally. As a material used for such a photomask, quartz glass is known. The coefficient of linear thermal expansion of quartz glass is 5 × 10 ^-7 / ° C, but the deformation by heat is relatively small. Since it falls, it is preferable to use the material with very little thermal expansion. Further, for example, an ultraviolet ray having a wavelength of about 365 nm is used during exposure, but it is desired to have a high transmittance at such a short wavelength.

As a material for the thermal expansion is very small at around room temperature, a degree of added titania (TiO ₂₎ 7.5% by weight of the silica glass material is known. The coefficient of linear thermal expansion depends on the amount of titania added, and the coefficient of linear thermal expansion becomes almost zero by setting it to 7.5% by weight. However, in the composition around 7.5% by weight, the transmittance near the wavelength of 365 nm is less than 90%, which is not a sufficient transmittance. It is proposed to use such a material as the material of the reflective photomask for EUV which utilizes the property of low expansion and requires high precision.

Japanese Unexamined Patent Publication 2007-182367

An object of the present invention is to provide a photomask substrate and a method for producing the same, which have a practically sufficient transmittance even in the vicinity of a wavelength of 365 nm and are not thermally expanded better than quartz glass.

According to the first aspect of the present invention, there is provided an optical member in which TiO ₂ is added to synthetic quartz glass, wherein the optical member for photomask containing 3.0 to 6.5% by weight of TiO _{2 and} having a transmittance of 90% or more at a wavelength of 365 nm is provided. do.

According to the second aspect of the present invention, there is provided a method for producing an optical member for photomask, comprising: a synthesis step of synthesizing a quartz glass ingot containing TiO ₂ by mixing a source gas, and maintaining the quartz glass ingot at a predetermined temperature. Production of an optical member for photomask, comprising a molding step of molding into a predetermined shape of a flat plate shape by pressing in a state and an oxidation treatment step of oxidizing titanium contained in the quartz glass by heating in an oxidizing atmosphere after the molding step. A method is provided.

According to the present invention, by adding 3.0 to 6.5% by weight of titania to the quartz glass, a photomask substrate material having a practically sufficient transmittance such as a transmittance at a wavelength of 365 nm of 90% or more is realized.

1 is a view showing the relationship between the transmittance and the linear thermal expansion coefficient and the TiO ₂ concentration in the first preferred embodiment.
2 is a flowchart illustrating a process of manufacturing the photomask of Embodiment 2. FIG.

Carrying out the invention  Form for

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

Embodiment 1

Embodiment of the optical member of this invention is described. The optical member of this embodiment is, as an optical member made of the TiO ₂ is 3.0 to 6.5% by weight addition of a synthetic silica glass (SiO _2), it may take any shape. The optical member, the side it is preferred but not containing a substance other than TiO ₂ and SiO _2. For example, even when an element such as Al, Cu, Fe, Na, K, etc. is contained as an impurity, for example, Al is 0.1 wt · ppm or less, Cu is 0.05 wt · ppm or less, Fe is 0.1 wt · ppm Hereinafter, it is preferable that Na is 0.05 wt.ppm or less, and K is 0.05 wt.ppm or less.

The manufacturing method of the optical member of this embodiment is demonstrated. First, a deposition intermediate (suit body) composed of a mixture of SiO ₂ fine particles and TiO ₂ fine particles is prepared in a synthesis furnace. A chute body is an aggregate of microparticles | fine-particles, The method of making this aggregate transparent by heating more than vitrification temperature in an electric heating furnace etc. can be used.

In order to obtain the deposition intermediate of the present embodiment, it is possible to synthesize a chute body of a mixture by simultaneously synthesizing and mixing SiO ₂ fine particles and TiO ₂ fine particles in one synthesis furnace, and to synthesize the chute body by making it transparent. In this case, in one synthesis furnace, a synthesis furnace equipped with a first burner for synthesizing SiO ₂ fine particles and a second burner for synthesizing Ti0 ₂ fine particles can be used. The first burner for synthesizing the SiO ₂ fine particles includes a source gas containing a silicon compound such as silicon tetrachloride (SiCl ₄ ), silicon tetrafluoride (SiF ₄ ), silane (SiH ₄ ), and a retardant property. gas and combustion gas, such as (oxygen gas) and the combustible gas (hydrogen gas), by ejecting the inert gas, to produce a SiO ₂ glass particles by hydrolyzing a silicon compound in a flame. In addition, the second burner ejects a source gas containing a titanium compound such as titanium tetrachloride (TiCl ₄ ), combustion gases such as a delayed gas (oxygen gas) and a combustible gas (hydrogen gas), and an inert gas, Hydrolysis of the titanium compound in the flame produces TiO ₂ glass fine particles.

SiO ₂ glass fine particles produced by the first burner and TiO ₂ glass fine particles produced by the second burner are deposited on the deposition target formed on the inclined upper side of the two burners. By simultaneously burning the first burner and the second burner, a mixture of SiO ₂ glass fine particles and TiO ₂ glass fine particles is deposited on the target. The amount of TiO _{2 in} the composition is SiO ₂ produced by the first burner. And a it can be changed by changing the amount ratio of the resulting TiO ₂ by the second burner. For example, it can change by controlling the flow volume of the source gas introduce | transduced into a burner.

Since the chute body of the mixture thus prepared is opaque, it is made transparent by heating to 1300 degreeC or more. A sample for measurement was prepared by cutting the cleared sample to a size of about 16 mm in diameter and 10 mm in thickness, by polishing the surface of the sample and then washing it. The transmittance | permeability measured the transmittance | permeability in 365 nm (i-ray) using the ultraviolet, visible, near-infrared spectrophotometer Cary5 by a Varian company.

The relationship between the transmittance of the density of the TiO ₂ and the wavelength 365 ㎚ is shown in FIG. 1 shows the relationship between the transmittance and the concentration of the composite relationship with the wavelength of 365 ㎚ TiO ₂ concentration and the coefficient of linear thermal expansion of the TiO ₂ was added to the silica glass. Further, the composition of each sample was set to the horizontal axis of Figure 1, the concentration of TiO ₂ of the irradiation, the composition using a fluorescent X-ray analyzer. The concentration of TiO ₂ is in the range of 0.5 to 9.5% by weight, and the transmittance of the synthetic quartz glass without adding TiO ₂ is also described as a reference example. Synthesized transmittance of the silica glass is not added to the TiO ₂ was 92.9%. With the increase of the TiO ₂ concentration, the transmittance was lowered and, at 7.5% by weight, was lowered to 89.0%. The value of the transmittance | permeability shown in FIG. 1 becomes the value containing the reflectance of the sample of thickness 10mm. As a board | substrate used for the transmissive photomask which uses i line | wire (wavelength 365nm) as exposure light, it is preferable that 90% or more transmittance | permeability is ensured in order to expose the pattern of high definition and high contrast. In the relationship between the TiO ₂ concentration and the transmittance shown in Figure 1, the TiO ₂ concentration in the transmittance can be secured more than 90% is preferably in the range of not more than 6.5% by weight.

를 구하였다.Moreover, in the photomask used for pattern exposure of FPD, since the size of a mask is also enlarged, the influence of the position shift of the exposed pattern by thermal expansion of a photomask cannot be ignored. For this reason, the material with a small thermal expansion coefficient in the temperature environment to be used is preferable. In addition, measurement of the coefficient of linear thermal expansion is defined from the sample length L ₀ and the temperature change amount ΔL of the room temperature, the rate of change in length ΔL / L ₀ (referred to as coefficient of thermal expansion). This linear expansion coefficient (ΔL / L ₀ ) temperature curve is measured by the laser interference method, and the linear thermal expansion coefficient is expressed by the following equation (1).

Was obtained.

=(1/L₀)·(dL/dT) … (1)

= (1 / L ₀ ) · (dL / dT)... (One)

The coefficient of linear thermal expansion at 3.0 wt% of TiO ₂ is 2.5 × 10 ⁻⁷ / ° C., which is one half of that of quartz glass without TiO ₂ added, so that the alignment accuracy when used in the same temperature environment Can be expected to improve twice. In addition, the size (length) can be doubled while maintaining the same positioning accuracy.

In this way, it can be seen that the transmittance is not less than 90%, TiO ₂ concentration is linear thermal expansion coefficient is less than 2.5 × 10 ^-7 / ℃ is, 3.0 ~ 6.5% by weight. Even within this range, the transmittance is higher when TiO ₂ is 3.0 to 5.0% by weight, and the linear thermal expansion coefficient is further lowered when TiO ₂ is 5.0 to 6.5% by weight. Conventionally, it was considered that the quartz glass containing TiO ₂ was not usable at a wavelength of 365 nm or less because the transmittance could not be secured by the optical member used as transmission, but as described above, the TiO ₂ was 3.0 to 6.5 wt%. It has been found through experiments that thermal expansion can be suppressed to 1/2 or less of conventional quartz glass while ensuring a sufficient transmittance in the concentration range.

Further, by the inner quartz glass was added to TiO _2, the configuration The more the content of Ti ³⁺ in titanium element it is known that the number of absorption, reducing the content of Ti ^{+ 3,} even the composition of the TiO ₂ concentration close to 6.5% by weight By reducing the absorption, it is expected to improve the transmittance. However, it is known that the wavelength of the absorption edge tends to shift toward the longer wavelength side with increasing TiO ₂ concentration. For example, when used at a wavelength of 300 nm to 400 nm, the concentration of TiO ₂ or Ti ^{3 is increased.} There exists a possibility that the transmittance | permeability may fall rapidly by the variation of content of ⁺ . Thus even in the same token, in order to provide a photomask for an optical member having a stable and sufficient transmittance at a wavelength of 365 ㎚, preferably not more than 6.5% by weight of the TiO ₂ concentration.

Embodiment 2

In this embodiment, the method which improved the manufacturing method of the optical member for photomasks demonstrated in Embodiment 1 is demonstrated. As described above, when using the quartz glass binary expansion coefficient smaller by containing TiO ₂ as an optical member for a photomask, it is desirable that the internal absorption by the TiO ₂ less. When a material having a lot of internal absorption is used as the optical member for the photomask, in order to prevent the occurrence of the temperature rise of the photomask due to the absorbed exposure light or the decrease of the exposure light irradiated onto the wafer due to the decrease in the transmittance of the photomask, the light source. side exposure, since the measures such as increasing the light power is need, than in the silica glass which does not contain TiO _2, is a less increase in the inner absorbent material as possible is preferred. As described in the first embodiment, the present inventors were able to suppress thermal expansion while ensuring sufficient transmittance by setting the content of TiO ₂ in the range of 3.0 to 6.5% by weight. The present inventors conducted further studies to find a method for producing an optical member for photomask having a high transmittance.

The silica glass containing TiO _2, the more the content of Ti ³⁺ in the titanium element constituting it known that a number of absorption, by changing the Ti ^{+ 3} to Ti ^{+ 4} by oxidation can be reduced absorption. Such oxidation can be oxidized, for example, by annealing at a temperature of about 1000 ° C. in an oxidizing atmosphere such as air. In addition, absorption by Ti3 ⁺ can be calculated | required with high precision by measuring the transmittance | permeability in wavelength 420 nm vicinity.

The low-expansion optical member produced in Embodiment 1 tends to exhibit the effect of low expansion by using it for the large size photomask in which the diagonal dimension exceeds 1470 mm. This is because the larger the photomask, the larger the stretching length (expansion amount) due to thermal expansion. In the photomask used for the projection of the pattern for FPD, for example, a large photomask having a size of 1220 mm x 1400 mm, a thickness of 13 mm and a weight exceeding several tens of kilograms has been put into practical use. By using it, the effect of low expansion is easy to be exhibited.

Usually, the photomask substrate of such a size is manufactured by the following process. First, quartz glass containing TiO ₂ is produced by synthesis. For example, a mixture of SiO ₂ fine particles and TiO ₂ fine particles is produced in a synthesis furnace, and the obtained mixture is heated in an electric heating furnace above the vitrification temperature to obtain an ingot of a photomask substrate. The ingot obtained in this synthesis step is obtained while blowing from a burner that blows raw materials onto a deposition target. In order to make this a flat photomask substrate, it cuts so that the upper surface of an ingot may become flat, it is accommodated in a carbon mold, it deforms by pressurizing while heating in an inert gas atmosphere, and a flat quartz glass is shape | molded. The thus-formed quartz glass is ground to a predetermined shape after cooling to polish the surface, thereby obtaining a quartz glass substrate for a photomask. In order to use it as a photomask, the light shielding film which consists of Cr is formed into one surface used as a mask, and the pattern to be projected is formed by partially removing this light shielding film, and a photomask is completed.

The manufacturing method of the optical member for photomasks of Embodiment 2 is demonstrated referring FIG. First, a quartz glass containing TiO ₂ at a predetermined concentration is synthesized (S1: synthesis step). TiO ₂ is, from the results of the first embodiment preferably contains 3.0 ~ 6.5% by weight of the silica glass. In this synthesis process, any method of chute method or direct method can be used. For example, from a multi-pipe burner, the gas containing the source gas of a silicon compound, the source gas of a titanium compound, the retardant gas, and the combustion gas is blown out, reaction is performed in flame, and glass fine particles are made to rotate on the target. It is also possible to use a synthetic method for depositing and melting. SiCl ₄ , SiF ₄ , SiH _4, etc. may be used as the source gas of the silicon oxide, TiCl _4, etc. may be used as the source gas of the titanium compound, oxygen may be used as the retardant gas, and hydrogen may be used as the combustion gas, respectively. The TiO ₂ concentration can be adjusted by adjusting the mixing ratio of the source gas (SiCl ₄ , SiF ₄ , SiH _4, etc.) of the silicon oxide and the source gas (TiCl _4, etc.) of the titanium compound. In addition, the synthesis method disclosed in Unexamined-Japanese-Patent No. 10-279319 and Unexamined-Japanese-Patent No. 11-292551 can also be employ | adopted. In the case of using the chute method, the ingot of the quartz glass is further obtained by making it transparent (S2: transparent process), and from this ingot, the amount of quartz glass necessary for producing one photomask substrate is cut out.

Next, the cut out quartz glass is made into flat plate shape by heat press molding (S3: shaping | molding process). In the molding step, a rectangular carbon-shaped mold is prepared, the quartz glass is accommodated in a space in the mold, heated to around 1600 ° C. in a nitrogen gas atmosphere, and given a predetermined pressure while maintaining this temperature to form a flat plate. It is molded and cooled to room temperature. Since the surface of the quartz glass after shaping | molding may generate | occur | produce the part, bubble, etc. which reacted at a high temperature with a deposit, after each shaping | molding process, each surface is ground by the magnitude | size used as a photomask (S4: grinding process). In a grinding process, it is preferable to make thickness of quartz glass into 20 mm or less.

Subsequent to the grinding step, the transmittance of the flat quartz glass is measured (S5: transmittance inspection step). In order to accurately measure the transmittance, it is necessary to make the surface of the part to be measured a polishing surface. For example, only the vicinity of the corners of the flat plate may be polished to measure the transmittance of this part. Moreover, you may produce the test piece cut out from the same quartz glass mass after shaping | molding, and may substitute for the measurement of the transmittance | permeability of this test piece. The transmittance can be measured by Cary5, etc., of Varian Corporation. As for the wavelength to measure, 365 nm or 420 nm vicinity which is a wavelength of exposure light when a photomask is used by an exposure apparatus is preferable. Since the absorption by Ti ³⁺ is remarkable in the vicinity of the wavelength of 420 nm, a high precision measurement reflecting the influence of the absorption by Ti ³⁺ can be expected.

The conditions (temperature, oxidizing gas pressure, annealing time, etc.) of an annealing process which is the next process are selected based on the value of the transmittance | permeability measured in this way. In particular, from a viewpoint of management of a manufacturing process and productivity, it is preferable that an annealing time can fully oxidize in the shortest time possible. About the conditions of a transmittance | permeability and an annealing process, by performing preliminary experiment, the annealing conditions necessary for oxidation can be calculated | required, and conditions can be selected from the measured transmittance | permeability. In preliminary experiments, for example, a plurality of samples having TiO ₂ concentration as a variable are prepared (for example, a plurality of samples selected from a range of 3.0 to 6.5 wt% in quartz glass), and annealing conditions (temperature, time It is preferable to perform annealing experiment using the oxidizing gas pressure) as a variable and to measure the transmittance, the Ti ³⁺ concentration and the like before and after annealing. In addition, Ti ³⁺ concentration can be measured by ESR (Electron Spin Resonance).

In the said method, although the conditions of the annealing process were determined after performing the transmittance | permeability test process, when the annealing conditions of a prescribed | prescribed setting were set and the measured transmittance | permeability is a predetermined range, you may process by the prescribed annealing conditions. In addition, when the characteristic of the quartz glass ingot obtained by a synthesis | combination process is stable, annealing of a next process can also be performed on a prescribed annealing condition, without performing a transmittance | permeability test.

Next, by oxidizing the Ti ^{3 +} subjected to oxidation treatment in order to reduce the internal absorption (S6: annealing step). The quartz glass of plate shape is accommodated in a heat resistant furnace, and it heats, introducing an oxidizing gas (for example, air | atmosphere). In an annealing process, in order to fully oxidize to ^{Ti3 +} in the inside of flat quartz glass, it is preferable that the whole is oxidized efficiently. In Embodiment 2, since the grinding process of processing into the flat form of thickness same as the thickness used as a photomask is performed before an annealing process, oxidation can be performed efficiently in a short time. Moreover, in order that all the 2 surfaces through which the exposure light of flat plate quartz glass may permeate | transmit efficiently, it is preferable to heat in the state arrange | positioned so that both surfaces may fully contact an oxidizing gas. For this reason, in the annealing process, it is preferable that the support member which supports flat quartz glass does not contact as much as possible. For example, you may arrange | position so that the surface of a flat plate may become a perpendicular direction, and you may support the surrounding end surface by contacting with a support member. In addition, in an annealing process, in order to prevent distortion of quartz glass, it is preferable to set it as the temperature of 1200 degrees C or less. After cooling to room temperature after completion of the annealing process, the transmittance measurement may be performed again to confirm the effect of oxidation.

After the annealing step is completed, a polishing step is performed using an abrasive such as colloidal silica (S7) to complete the quartz glass substrate for the photomask. In the conventional manufacturing process of quartz glass, the annealing process for removing the distortion may be performed between the synthesis process and the grinding process, but in the shape of the ingot, since there is a thickness of several hundred mm or more, it is oxidized by heating in an oxidizing atmosphere. Even if it is made, in order to fully oxidize up to ^{Ti3 +} inside, further longer oxidation is required. If oxidation is insufficient, there is a fear that a sufficient transmittance may not be obtained by absorption by Ti ³⁺ . In Embodiment 2, since the annealing process of an oxidation process is performed after a shaping | molding process, since it can be oxidized to the inside efficiently in a comparatively short time, the optical member for photomasks of light transmittance can be manufactured in a comparatively short time. Moreover, it is more preferable to perform the annealing process for oxidation treatment after the grinding process which removes the unnecessary part of a surface after a shaping | molding process.

Industrial availability

Industrial Applicability The present invention is useful for optical members for transmissive photomasks that transmit ultraviolet rays with a wavelength of 300 nm or more, in particular for optical members for large-sized photomasks whose diagonal dimension exceeds 1470 mm.

Claims (10)

As an optical member in which TiO ₂ is added to synthetic quartz glass,
The composition of the TiO ₂ is 3.0 to 6.5% by weight,
The optical member for photomasks whose transmittance in wavelength 365nm is 90% or more. The method of claim 1,
The optical member for photomasks whose coefficient of linear thermal expansion in 20 degreeC-80 degreeC is 2.5 * 10 <^-7> / degreeC or less. The method according to claim 1 or 2,
As an impurity, a photomask containing 0.1 wt.ppm or less of Al, 0.05 wt.ppm or less of Cu, 0.1 wt.ppm or less of Fe, 0.05 wt.ppm or less of Na, and 0.05 wt.ppm or less of K. Optical member. A synthesis step of synthesizing the quartz glass ingot containing TiO ₂ by mixing the source gas;
A molding step of molding the quartz glass ingot into a predetermined shape of a flat plate shape by pressing the quartz glass ingot in a state of being kept at a predetermined temperature;
And a oxidation treatment step of oxidizing titanium contained in the quartz glass by heating in an oxidizing atmosphere after the molding step. The method of claim 4, wherein
The method for producing a quartz glass ingot, optical members, a photomask containing a TiO ₂ 3.0 ~ 6.5% by weight. The method according to claim 4 or 5,
The said oxidation treatment process is a manufacturing method of the optical member for photomasks which anneals flat quartz glass of thickness less than 20 mm. The method according to any one of claims 4 to 6,
Between the synthesis process and the oxidation treatment process, further comprising a transmittance inspection process, based on the transmittance measured by the transmittance inspection process, any of the temperature, time and gas pressure of the oxidation atmosphere of the oxidation treatment process The manufacturing method of the optical member for photomasks to determine. 8. The method according to any one of claims 4 to 7,
The manufacturing method of the optical member for photomasks which further includes the grinding process which removes the surface of flat quartz glass after the said molding process, and performs the said oxidation process process after the said grinding process. The method according to any one of claims 4 to 8,
The manufacturing method of the optical member for photomasks after the said oxidation process process further includes the grinding | polishing process of grind | polishing the surface to which light passes when used as a photomask. The method according to any one of claims 4 to 9,
The manufacturing method of the optical member for photomasks whose optical member for photomasks is rectangular shape, and the diagonal length is 1470 mm or more.

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