KR101606225B1 - Optical member for photomask and method for manufacturing the optical member - Google Patents

Abstract

The optical member for photomask is an optical member formed by adding TiO ₂ to synthetic quartz glass. TiO ₂ is contained in an amount of 3.0 to 6.5% by weight. The optical member for a photomask is produced by synthesizing a quartz glass ingot, molding it into a flat plate-shaped predetermined shape, and thereafter annealing in an oxidizing atmosphere. By the annealing, Ti ^{3 +} in the quartz glass ingot can be changed to Ti ^{4 +} , so that absorption of light by Ti ^{3 +} can be reduced. Since the transmittance with respect to light having a wavelength of 365 nm is 90% or more, even at a wavelength of 365 nm, it has a practically sufficient transmittance and is not thermally expanded better than quartz glass.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical member for a photomask, and an optical member for a photomask,

The present invention relates to a photomask substrate used for manufacturing a flat panel display (hereinafter referred to as FPD) such as a liquid crystal panel and a manufacturing method thereof.

The FPD is manufactured through a process of forming an FPD element on the surface of a glass substrate with high precision. In this process, a photolithography technique is used. That is, a photomask having a highly precise mask pattern formed on the surface of a flat plate-shaped transparent substrate having excellent planarity is illuminated with exposure light, an image of the mask pattern is formed on a glass substrate coated with a photoresist in advance, , And a resist pattern is formed on the surface of the glass substrate.

However, in order to increase the screen size of the FPD and to increase the production efficiency, the size of the FPD glass substrate is increasing year by year, and along with this, the photomask used for the production is also being enlarged. In the near future, the glass substrate has a very large size such as 2200 mm x 2500 mm, and accordingly, the photomask used for exposing the mask pattern to the glass substrate has a size with a diagonal length exceeding 1470 mm For example, 1220 mm x 1400 mm, and the thickness is very large, such as 13 mm. However, enlargement is not limited to this, and a larger glass substrate and a photomask are required.

When the pattern formed on the photomask is exposed to the substrate, exposure is performed in a state in which the photomask is held horizontally. As a material used for such a photomask, quartz glass is known. The coefficient of linear thermal expansion of the quartz glass is 5 x 10 < ^-7 > / DEG C, and the material is relatively less deformed by heat. However, when the volume change occurs due to the influence of ultraviolet rays or the like irradiated at the time of exposure, It is preferable to use a material having a very small thermal expansion. Further, for example, there is a case where ultraviolet rays having a wavelength of about 365 nm are used at the time of exposure, and it is desired to have a high transmittance at such a short wavelength.

As a material having a very small thermal expansion near room temperature, a material containing about 7.5% by weight of titania (TiO ₂ ) is known as quartz glass. The coefficient of linear thermal expansion is dependent on the amount of titania added, and when it is 7.5 wt%, the linear thermal expansion coefficient becomes almost zero. However, at a composition of about 7.5 wt%, the transmittance at a wavelength of about 365 nm is less than 90%, which is not a sufficient transmittance. It has been proposed to use such a material as a material for a reflection type photomask for EUV which requires high accuracy by taking advantage of the characteristic of low expansion.

Japanese Patent Application Laid-Open No. 2007-182367

An object of the present invention is to provide a substrate for a photomask which has a practically sufficient transmittance even in the vicinity of a wavelength of 365 nm and is not thermally expanded more than quartz glass, and a manufacturing method thereof.

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

According to a second aspect of the present invention, there is provided a method of manufacturing an optical member for a photomask, comprising the steps of: synthesizing a quartz glass ingot containing TiO ₂ by mixing a raw material gas; Forming a flat plate-like predetermined shape by pressurizing the quartz glass in one state, and an oxidation treatment step of oxidizing titanium contained in the quartz glass by heating in an oxidizing atmosphere after the forming step Method is provided.

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

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

Carrying out the invention  Form for

Hereinafter, embodiments of the present invention will be described.

[Embodiment 1]

An embodiment of the optical member of the present invention will be described. The optical member of this embodiment is an optical member formed by adding 3.0 to 6.5% by weight of TiO ₂ to synthetic quartz glass (SiO ₂ ), and may have any arbitrary shape. It is preferable that the optical member does not contain a substance other than TiO ₂ and SiO ₂ . For example, even when an element such as Al, Cu, Fe, Na, K 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 , Na of 0.05 wt ppm or less, and K of 0.05 wt ppm or less.

A method of manufacturing the optical member of the present embodiment will be described. First, a sedimentation intermediate (chute) comprising a mixture of SiO ₂ fine particles and TiO ₂ fine particles is prepared in a synthesis furnace. A chitosan is a collection of fine particles, and a method of making the aggregate transparent by heating it to an vitrification temperature or higher in an electric heating furnace or the like can be used.

In order to obtain the sedimented intermediate of the present embodiment, it is possible to synthesize SiO ₂ fine particles and TiO ₂ fine particles at the same time in a single synthesis furnace, and mix them to prepare a mixture body, and to make the body transparent. In this case, as a single synthesis furnace, a synthesis furnace having a first burner for synthesizing SiO ₂ fine particles and a second burner for synthesizing TiO ₂ fine particles can be used. The first burner for synthesizing the SiO ₂ fine particles is formed by mixing a source gas containing a silicon compound such as silicon tetrachloride (SiCl ₄ ), silicon tetrafluoride (SiF ₄ ), silane (SiH ₄ ) A combustion gas such as a gas (oxygen gas) and a combustible gas (hydrogen gas) and an inert gas are blown out to hydrolyze the silicon compound in the flame to produce SiO ₂ glass microparticles. The second burner is formed by ejecting a raw material gas containing a titanium compound such as titanium tetrachloride (TiCl ₄ ), a combustion gas such as a retarding gas (oxygen gas), a combustible gas (hydrogen gas), and an inert gas, TiO ₂ glass microparticles are produced by hydrolyzing the titanium compound in the flame.

The SiO ₂ glass microparticles produced by the first burner and the TiO ₂ glass microparticles produced by the second burner are deposited on the deposition target formed above the slopes of the two burners. By burning the first burner and the second burner at the same time, 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 such that the SiO ₂ produced by the first burner And TiO ₂ produced by the second burner. For example, by controlling the flow rate of the raw material gas introduced into the burner.

Since the chit of the thus prepared mixture is opaque, it is made transparent by heating to 1300 DEG C or higher. A sample for measurement was prepared by cutting the clarified sample into a size of about 16 mm in diameter and 10 mm in thickness, polishing the surface of the sample and then rinsing. The transmittance was measured by measuring the transmittance at 365 nm (i-line) using an ultraviolet / visible / near infrared spectrophotometer Cary5 manufactured by Varian.

The relationship between the concentration of TiO ₂ and the transmittance at a wavelength of 365 nm is shown in Fig. Fig. 1 shows the relationship between the concentration of TiO ₂ added to synthetic quartz glass and the coefficient of linear thermal expansion, and the relationship between the concentration of TiO ₂ and the transmittance at a wavelength of 365 nm. The composition of each sample was examined using a fluorescent X-ray analyzer, and the concentration of TiO _{2 in} the composition was taken as the horizontal axis in FIG. The concentration of TiO ₂ is from 0.5 to 9.5% by weight, and the transmittance of synthetic quartz glass without addition of TiO ₂ is also described as a reference example. The transmittance of the synthetic quartz glass without addition of TiO ₂ was 92.9%. As the TiO ₂ concentration was increased, the transmittance was lowered to 89.0% at 7.5 wt%. The value of the transmittance shown in Fig. 1 is a value including the reflectance of a sample having a thickness of 10 mm. As a substrate used for a transmission type photomask using an i-line (wavelength 365 nm) as exposure light, it is preferable that a transmittance of 90% or more is ensured in order to expose a pattern with high contrast and high contrast. From the relationship between the TiO ₂ concentration and the transmittance shown in FIG. 1, it is preferable that the TiO ₂ concentration is at most 6.5% by weight, which can ensure a transmittance of 90% or more.

를 구하였다.In addition, since the size of the mask is also increased in the photomask used for the pattern exposure of the FPD, the influence of the positional deviation of the exposed pattern due to thermal expansion of the photomask can not be ignored. Therefore, a material having a small thermal expansion coefficient in the temperature environment to be used is preferable. In addition, the coefficient of linear thermal expansion was defined by the change rate? L / L ₀ (referred to as linear expansion rate) of the length from the sample length L ₀ at room temperature and the temperature change amount? L thereof. The linear expansion coefficient (? L / L ₀ ) temperature curve was measured by laser interferometry, and the linear thermal expansion coefficient

Respectively.

=(1/L₀)·(dL/dT) … (1)

= (1 / L ₀ ) - (dL / dT) ... (One)

Since TiO ₂ has a coefficient of linear thermal expansion of from 3.0% by weight is a 2.5 × 10 ^-7 / ℃, this value of 1/2 of the silica glass is not added to the TiO _2, the alignment precision in the case of using the same temperature environment Can be expected to be improved by a factor of two. In addition, the size (length) may be doubled while maintaining the same alignment accuracy.

Thus, it can be seen that the TiO ₂ concentration at which the transmittance is 90% or more and the coefficient of linear thermal expansion is 2.5 × 10 ^-7 / ° C or less is 3.0 to 6.5% by weight. Even within this range, the transmittance is higher when the content of TiO ₂ is 3.0 to 5.0 wt%, and the coefficient of linear thermal expansion is further lowered when the content of TiO ₂ is 5.0 to 6.5 wt%. Conventional, TiO ₂ that below a quartz glass added with TiO _2, the wavelength 365 ㎚, as the optical member to be used as the transmission is eotneunde thought not available because it is not possible to ensure the transmission, as described above, 3.0 ~ 6.5% by weight It was found through experiments that the thermal expansion can be suppressed to 1/2 or less of that of the conventional quartz glass while securing a sufficient transmittance for practical use 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 Absorption can be reduced, and the transmittance can be expected to be improved. However, it is known that the wavelength of the absorption edge tends to shift toward the longer wavelength side with an increase in the TiO ₂ concentration. For example, when the wavelength is used in the wavelength range of 300 to 400 nm, the TiO ₂ concentration or the Ti ³ There is a possibility that the transmittance is rapidly lowered due to a variation in the content of ⁺ . For this reason, in order to provide an optical member for a photomask having a sufficient transmittance stably at a wavelength of 365 nm, it is preferable that the TiO ₂ concentration is 6.5 wt% or less.

[Embodiment 2]

In this embodiment, a method of improving the manufacturing method of the optical member for a photomask described in Embodiment 1 will be described. As described above, when quartz glass whose expansion coefficient is reduced by containing TiO ₂ is used as an optical member for a photomask, it is preferable that the internal absorption by TiO ₂ is small. When a material having a large internal absorption is used as an optical member for a photomask, in order to prevent the temperature rise of the photomask due to the absorbed exposure light and the decrease of the exposure light irradiated to the wafer due to the decrease of the transmittance of the photomask, A countermeasure such as increasing the power of the side exposure light is required. Therefore, a material having as little increase in internal absorption as possible is preferable to quartz glass not containing TiO ₂ . As described in the first embodiment, the present inventors have been able to suppress the thermal expansion while ensuring a sufficient transmittance by setting the content of TiO ₂ within the range of 3.0 to 6.5 wt%. The inventors of the present invention have conducted further research and have found a method for manufacturing an optical member for a 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 by, for example, annealing at a temperature of about 1000 캜 in an oxidizing atmosphere such as the atmosphere. The absorption by Ti ³⁺ can be obtained with high accuracy by measuring the transmittance in the vicinity of 420 nm.

The low expansion optical member manufactured in the first embodiment is liable to exhibit the effect of low expansion when used in a large-size photomask having a diagonal dimension exceeding 1470 mm. This is because a larger photomask has a larger expansion length (expansion amount) due to thermal expansion. In a photomask used for projecting a pattern for FPD, for example, a large photomask having a size of 1220 mm x 1400 mm and a thickness of 13 mm and a weight of more than several tens kilograms has been put to practical use, and a photomask substrate of such a size The effect of low expansion is likely to be exhibited.

Usually, a substrate for a photomask of such a size is manufactured by the following process. First, a 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 synthetic furnace, and the obtained mixture is heated in an electric heating furnace to a vitrification temperature or higher to obtain a photomask substrate ingot. The ingot obtained in this synthesis step is obtained while being ejected from the burner for ejecting the raw material onto the deposition application target. In order to make the plate-shaped photomask substrate, it is cut so that the upper surface of the ingot is flattened. The mold is accommodated in a mold made of carbon and deformed by heating while heating in an inert gas atmosphere to mold flat plate quartz glass. The thus-formed quartz glass is cooled and ground to a predetermined shape after cooling to obtain a quartz glass substrate for a photomask. For use as a photomask, a light shielding film made of Cr is formed on one surface to be used as a mask, and the light shielding film is partially removed to form a pattern to be projected, thereby completing the photomask.

A manufacturing method of the optical member for photomask of Embodiment 2 will be described with reference to Fig. First, a quartz glass containing TiO ₂ of a predetermined concentration is synthesized (S1: synthesis step). From the results of the first embodiment, TiO ₂ is preferably contained in the quartz glass in an amount of 3.0 to 6.5% by weight. In this synthesis step, any of a chute method and a direct method can be used. For example, a gas containing a raw material gas of a silicon compound, a raw material gas of a titanium compound, a gas containing a retardation gas and a combustion gas is ejected from a multi-tube burner to perform reaction in a flame, May be used for the deposition and melting. SiCl ₄ , SiF ₄ , SiH ₄ and the like can be used as the source gas of the silicon oxide, TiCl ₄ can be used as the source gas of the titanium compound, oxygen can be used as the delayed gas, and hydrogen can be used as the combustion gas. 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 Japanese Unexamined Patent Application Publication No. 10-279319 or Japanese Unexamined Patent Application Publication No. 11-292551 may be employed. In the case of using the Schmitt method, an ingot of quartz glass is obtained by further making it transparent (S2: vitrification step), and a quartz glass in an amount necessary for manufacturing one photomask substrate from this ingot is cut out.

Next, the cut quartz glass is flattened by heating and pressing (S3: molding step). In the molding step, a rectangular mold made of carbon is prepared, quartz glass is housed in a space in the mold, heated to about 1600 DEG C in a nitrogen gas atmosphere, and a predetermined pressure is applied while maintaining this temperature, Molded, and cooled to room temperature. Since the surface of the quartz glass after molding has a portion reacted with the adherend at high temperature or bubbles, etc., the respective surfaces are ground to a size used as a photomask after the molding step (S4: grinding step). In the grinding step, the thickness of the quartz glass is preferably 20 mm or less.

Following the grinding step, the transmittance of the flat quartz glass is measured (S5: transmittance inspection step). In order to accurately measure the transmittance, the surface of the portion to be measured needs to be a polished surface. For example, only the vicinity of the edge portion of the flat plate may be polished and the transmittance of this portion may be measured. Further, a test piece cut out from the same quartz glass block after molding may be prepared and used for measuring the transmittance of the test piece. The transmittance can be measured by using Cary 5 from Varian. The wavelength to be measured is preferably around 365 nm or 420 nm, which is the wavelength of the exposure light when the photomask is used in an exposure apparatus. Since the absorption by Ti ³⁺ is remarkable in the vicinity of the wavelength of 420 nm, high-precision measurement reflecting the influence of absorption by Ti ³⁺ can be expected.

Based on the value of the transmittance thus measured, the conditions (temperature, oxidizing gas pressure, annealing time, etc.) of the subsequent annealing process are selected. Particularly, from the viewpoints of management of the production process and productivity, it is preferable that sufficient annealing can be performed in a short time as long as possible. With respect to the transmittance and the condition of the annealing process, a preliminary experiment is carried out to obtain annealing conditions necessary for the oxidation, and conditions can be selected from the measured transmittance. In the preliminary experiment, for example, a plurality of samples having the TiO ₂ concentration as a variable are prepared (for example, a plurality of samples selected from the range of 3.0 to 6.5 wt% in quartz glass), annealing conditions (temperature, time , And the oxidizing gas pressure), it is preferable to measure the transmittance and the Ti ³⁺ concentration before and after the annealing. In addition, the Ti ³⁺ concentration can be measured by ESR (Electron Spin Resonance).

In the above method, the conditions of the annealing process are determined after the transmissivity inspection process is performed. However, when the measured annealing conditions are set and the measured transmittance is within the predetermined range, the process may be performed under the specified annealing conditions. When the characteristics of the quartz glass ingot obtained in the synthesis step are stable, the annealing of the next step may be carried out under the prescribed annealing conditions without conducting the transmittance inspection.

Next, by oxidizing the Ti ^{3 +} subjected to oxidation treatment in order to reduce the internal absorption (S6: annealing step). The flat quartz glass is accommodated in the heat-resistant furnace, and heated while introducing an oxidizing gas (for example, atmospheric air). In the annealing step, it is preferable that the whole is efficiently oxidized so as to sufficiently oxidize Ti ^{3+ present} in the flat quartz glass. In the second embodiment, since the grinding step is performed before the annealing step to form a flat plate shape having the same thickness as that used as the photomask, the oxidation can be efficiently performed in a short time. Further, in order to efficiently oxidize both of the two surfaces through which the exposure light of the flat plate-shaped quartz glass is transmitted, it is preferable to heat the two surfaces in a state in which they are arranged so as to sufficiently contact with the oxidizing gas. For this reason, it is preferable that the supporting member for supporting the flat quartz glass in the annealing process is not contacted as much as possible. For example, the surface of the flat plate may be arranged so as to be in the vertical direction, and the circumferential section may be supported in contact with the support member. In addition, in order to prevent deformation of the quartz glass in the annealing step, it is preferable to set the temperature to 1200 캜 or lower. After the end of the annealing process, after cooling to room temperature, the transmittance may be measured again to confirm the effect of oxidation.

When the annealing process is completed, a polishing process is performed using an abrasive such as colloidal silica (S7) to complete the quartz glass substrate for a photomask. In the conventional quartz glass manufacturing process, there is a case where an annealing process is performed between the synthesis process and the grinding process to remove distortion. Since the ingot has a thickness of several hundreds mm or more in the ingot, It is necessary to oxidize Ti ³⁺ to a longer time in order to sufficiently oxidize the Ti ³⁺ . If the oxidation is insufficient, there is a ^possibility that a sufficient transmittance can not be obtained due to the absorption by Ti ³⁺ . In the second embodiment, since the annealing process of the oxidation process is performed after the forming process, the optical member can be efficiently oxidized to the inside in a comparatively short time, so that the optical member for the photomask having the light transmittance can be manufactured in a comparatively short time. Further, it is more preferable to perform an annealing process for the oxidation process after the grinding process for removing unnecessary portions of the surface after the forming process.

Industrial availability

INDUSTRIAL APPLICABILITY The present invention is useful for an optical member for a transmissive photomask that transmits ultraviolet rays having a wavelength of 300 nm or more, particularly, for an optical member for a large-size photomask having a diagonal dimension exceeding 1470 mm.

Claims (10)

delete delete An optical member to which TiO ₂ is added to synthetic quartz glass,
The composition of the TiO ₂ is 3.0 to 6.5% by weight,
The transmittance at a wavelength of 365 nm is 90% or more,
A coefficient of linear thermal expansion at 20 占 폚 to 80 占 폚 is 2.5 占^10-7 / 占 폚 or less,
Wherein the impurity is Al in an amount of 0.1 wt ppm or less, Cu in an amount of 0.05 wt ppm or less, Fe in an amount of 0.1 wt ppm or less, Na in an amount of 0.05 wt ppm or less, and K in an amount of 0.05 wt ppm or less. A synthesis step of synthesizing a quartz glass ingot containing TiO ₂ by mixing the raw material gas,
A molding step of molding the quartz glass ingot into a predetermined flat plate shape by pressing the quartz glass ingot while keeping it at a predetermined temperature;
And an oxidation treatment step of oxidizing titanium contained in the quartz glass by heating in an oxidizing atmosphere after the molding step. 5. The method of claim 4,
Wherein the quartz glass ingot contains 3.0 to 6.5% by weight of TiO ₂ . The method according to claim 4 or 5,
Wherein the oxidation treatment step is a step of annealing a flat quartz glass having a thickness of 20 mm or less. The method according to claim 4 or 5,
Further comprising a permeability inspecting step between the synthesizing step and the oxidizing treatment step, wherein, based on the transmittance measured by the transmittance inspecting step, any of the temperature, the time, and the gas pressure of the oxidizing atmosphere Of the optical member for a photomask. The method according to claim 4 or 5,
Further comprising a grinding step of removing the surface of the flat quartz glass after the forming step, wherein the oxidizing treatment step is performed after the grinding step. The method according to claim 4 or 5,
Further comprising a polishing step of polishing the surface through which the light is transmitted when used as a photomask after the oxidation treatment step. The method according to claim 4 or 5,
Wherein the optical member for a photomask has a rectangular shape and the length of the diagonal line is 1470 mm or more.

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