JP2007230860A - Method for manufacturing material of objective projection lens for liquid immersion lithography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a material for an objective projection lens for liquid immersion lithography which contacts with a liquid immersion medium. <P>SOLUTION: A phosphate glass containing an alkaline earth oxide is formed by preparing a reaction zone on a deposition burner, supplying a synthetic phosphorus compound to be oxidized and an alkaline earth compound, forming amorphous oxide particles under the existence of an oxygen-containing gas, and depositing the particles on a carrier. The refractive index of the phosphate glass is at least 1.6 at a wave length of 193 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a material for a projection objective for immersion lithography.

  A large scale integrated circuit is fabricated on a substrate using a microlithographic projection system. The general requirement is that the light distribution in the target surface area of the illumination system be as homogeneous as possible, and kept at an angle, with the image plane of the projection objective lens conjugate to the target plane on the substrate to be exposed. The resolution is as high as possible.

  The achievable resolution of the projection objective varies with the operating wavelength. Modern microlithographic devices operate with excimer lasers that emit UV radiation at a wavelength of 248 nm (KrF laser) or 193 nm (ArF laser). To date, the operating wavelength has been continually shortening and has reached its physical and technical limits. That is why recently experiments with projection systems employing a technique called “immersion lithography” have been conducted. In this technique, the gap between the substrate to be exposed at the image plane and the last optical element of the lens system is filled with an immersion medium having a higher refractive index than air. The high refractive index of the immersion medium compared to air increases the overall numerical aperture of the objective lens, thereby increasing its resolution.

  The numerical aperture of the objective lens increases with the refractive index of the immersion liquid. Therefore, it is desirable to use an immersion liquid with a high refractive index. Adding salt can increase the refractive index of water. However, it should always be noted that, just like the optical element of a projection objective, the immersion liquid is high for optical radiation at its operating wavelength and, if possible, constant and constant transmission over time. Is to show the rate. For this purpose, sufficient radiation resistance to high energy UV radiation is required.

  Regarding the last optical element of the projection objective adjacent to the immersion liquid, there is an additional requirement that the refractive index of this material be as high as possible and that the material be chemically resistant to the immersion liquid. .

  Quartz glass is a preferred material for making high quality optical lenses because it is mechanically and chemically resistant, has low birefringence, and is easy to mold. Quartz glass is transparent to radiation with a wavelength of 193 nm, but the refractive index at this wavelength is only 1.56. The refractive index of quartz glass can be increased by adding dopants, and such a doping process increases the refractive index for operating wavelengths in the UV range, but usually reduces the transmission in the ultraviolet spectral range unacceptably. I will let you.

In the article “High Refractive Index Materials for 193 nm Immersion Lithography” by Joan H. Barnett published in SPIE Bulletin 5754, Optical Microlithography XVIII, various materials with high refractive index It is listed as suitable for the application. They are crystalline alkaline earth oxides, especially MgO, and single crystal and polycrystalline spinel (MgAl ₂ O ₄ ).

  However, it is known that even a crystal having a cubic lattice structure (for example, MgO) exhibits strong intrinsic birefringence. Moreover, it is very complicated to make lenses one by one from synthetic crystals. An additional difficulty arises from standard fabrication using the crucible melting method because impurities from the crucible material enter the optical material, thereby creating an absorption band in the operating wavelength range.

  The object of the present invention is therefore to provide a method for producing a projection objective material for immersion lithography, which has a high refractive index and at the same time a high transmission in the operating wavelength range around 193 nm. It is a prominent and therefore particularly suitable method for producing the last optical element of the projection objective in contact with the immersion medium.

  This object originates from the method described above, and is provided in accordance with the present invention by providing a reaction zone in a deposition burner, to which the oxidizable, synthesized phosphorus compound and alkaline earth compound are fed, where oxygen containing Amorphous oxide particles are formed in the presence of a gas, and the particles are deposited on a carrier to form a phosphate glass containing alkaline earth oxide, the refractive index of the phosphate glass being 193 nm And at least 1.6 at the wavelength.

  In accordance with the present invention, amorphous particles of phosphate glass containing alkaline earth oxides are produced by one or several deposition burners and deposited on a carrier to comprise phosphate glasses containing alkaline earth oxides Form a layer. For this reason, a reaction zone is created in the deposition burner by plasma or burner gas, and a starting material is supplied to the reaction zone and converted into glass particles.

The starting materials are at least one oxidizable phosphorus compound and at least one alkaline earth compound. These substances are supplied to the reaction zone in the form of gas, liquid or fine particles. In this process, they each enter the reaction zone via a deposition burner or they are fed from the outside of the deposition burner into the reaction zone, for example by spraying, by injection or by spraying.
The component element that supplies at least the phosphorus component of the phosphate glass is present here as a synthetically produced oxidizable phosphorus compound. Being oxidizable enhances the reactivity of the component elements for forming phosphorus particles. The method of synthesizing the phosphorus compound ensures a sufficiently high purity.

It should be noted here that the phosphorous oxide occupies the maximum weight part of the phosphate glass. In this respect, the method of the present invention is the same as the known method for producing synthetic SiO ₂ .

  In contrast to single component glasses such as quartz glass, what is important in the process of the present invention is the reaction zone at a molar ratio that can form a phosphate glass containing several components of an alkaline earth oxide. Is that there is a reaction partner.

The refractive index of phosphate glass is 1.6 or more for UV radiation with an operating wavelength of 193 nm, and the amount of alkaline earth oxide that causes inconvenience to the transmission characteristics in the short operating wavelength range is not obtained. It has been found that the refractive index of pure phosphate glass can be increased by adding alkaline earth oxides. Furthermore, the relatively low chemical resistance of pure phosphate glass is improved by that amount of alkaline earth oxide. Phosphate glass containing 75 mol% or more of P ₂ O ₅ is chemically low in stability.

  It may include some other material that contributes to increasing the refractive index or increasing the chemical resistance, but such doping operation makes the intrinsic absorption unacceptable at the 193 nm operating wavelength. There must not be a thing.

  The alkaline earth metal-containing phosphate glass produced in this way is suitable for the production of optical elements for immersion lithography because of its high refractive index and high chemical resistance.

  The process of the invention is particularly advantageous when using phosphorus compounds that vaporize at temperatures up to 500 ° C.

  Since the phosphorus compound is vaporized at a temperature of 500 ° C. or less which is easy to handle, the phosphorus compound can be prepared relatively easily in an ultrapure state. This is particularly advantageous for the purity of the phosphate glass because the phosphorous oxide occupies the largest molar part.

  In this respect, it is advantageous to use phosphorus compounds selected from the group consisting of phosphines, phosphanes, phosphites, phosphides and organic and inorganic derivatives of these compounds.

Phosphine is an inorganic derivative of monophosphane (PH ₃ ), also known as “phosphine”. From an official point of view, phosphine can be formed by exchanging one to three hydrogen atoms with organic molecules.

  Phosphan represents a three-bond phosphorus compound of phosphorus and hydrogen and / or an organic residue, and the organic residue is bonded to a phosphorus atom via a carbon atom (bonding unit: PC). .

Phosphite represents a three-bond phosphorus compound of phosphorus and hydrogen and / or organic residue, and the organic residue is bonded to the phosphorus atom through an oxygen atom (bonding unit: P -OC; Formula P (OR) ₃ ).

  In the phosphide, all or part of the three water atoms of monophosphane are replaced with one or more metal atoms. The metal atom may be an alkaline earth atom. In this respect, alkaline earth phosphides can also be used as alkaline earth compounds within the spirit of the invention.

  All of the above phosphorus compounds can be synthesized with high purity, and they exist partially in the liquid or gaseous state at temperatures below 500 ° C.

  In this respect, phosphorus derivatives in the form of phosphorus halogen compounds are used as phosphorus compounds in a particularly preferred manner.

  It has been found that it is particularly useful to use one or more compounds selected from the group consisting of phosphorus trichloride, diphosphorus tetrachloride or phosphorus pentachloride as the phosphorus halogen compound.

  These phosphorus chloride compounds have the special advantage that chlorine performs an additional purification action in the reaction zone by forming impurities and volatile chlorides. The disadvantage is the corrosive action of phosphorus chloride compounds.

  This disadvantage is eliminated by a chlorine-free phosphorus compound. That is why phosphines and their chlorine-free derivatives are used alternatively and equally favorably.

  Preference is given to a variant process in which alkaline earth compounds are used in the form of halogen compounds including magnesium, potassium, strontium and / or barium.

  The alkaline earth metal oxide increases the refractive index of the phosphate glass. The order of increasing the refractive index is Mg, Ca, Sr, Ba. Here, the phosphate glass contains one or several alkaline earth oxides in an amount giving a refractive index of at least 1.6 at an operating wavelength of 193 nm. The intrinsic absorption edge in the UV range moves in the order of Mg, Ca, Sr, and Ba toward longer wavelengths.

  The alkaline earth metal halogen compounds or acetate compounds described above can also be synthesized with high purity, are usually readily soluble, and can be easily introduced into the reaction zone in their dissolved form. Purity is increased by reprecipitation.

  It is preferred to use barium halogen or acetate compounds as alkaline earth compounds.

  Barium oxide is particularly effective in obtaining the desired high refractive index. Accordingly, the total alkaline earth content of the phosphate glass is preferably BaO, and at least the maximum portion. Furthermore, the barium oxide content improves the chemical resistance of the phosphate glass.

  It has been found advantageous to use barium halide oxide in the form of barium chloride.

  Barium chloride is water soluble and can therefore be easily introduced into the reaction zone in dissolved form. Barium chloride is particularly preferably used when the phosphorus compound contains chlorine.

In a particularly preferred variant of the invention, the phosphorus compound and alkaline earth are in a molar ratio such that phosphate glass particles are formed with a P ₂ O ₅ content between 40 mol% and 75 mol%. The compound is fed to the reaction zone.

The phosphate glass having a high content of P ₂ O _{5 in} the above range of 75 mol% as the upper limit is stable when Al ₂ O ₃ is present at the same time. Otherwise, the upper limit of P ₂ O ₅ is about 55 mol%. If the content of P ₂ O ₅ is less than the lower limit, it becomes difficult to form glass.

  Furthermore, it may be advantageous to supply the phosphorus compound and the barium compound to the reaction zone in a molar ratio such that phosphate glass particles with a barium oxide content between 30 mol% and 60 mol% are formed. I understand.

  A phosphate glass doped with barium oxide is formed in the reaction zone. As mentioned above, barium oxide is particularly effective for the desired high refractive index of phosphate glasses and helps to improve chemical resistance.

  Furthermore, it has been found useful to supply the reaction zone with an amount of aluminum oxide (based on phosphate glass) that forms up to 25 mole percent aluminum oxide.

  Aluminum oxide acts to some extent as a glass former, thereby enhancing the network of the glass structure and improving the chemical resistance of the phosphate glass. On the other hand, it is preferable that the content of aluminum oxide is not more than 25 mol% because high concentration aluminum oxide reduces the refractive index of the phosphate glass.

  Furthermore, it has been found useful to supply the reaction zone with an amount of boron compound (based on phosphate glass) that forms no more than 10 mole percent boron oxide.

Boron oxide is effective for forming a glass of phosphate glass, but also reduces the refractive index, so the content of B ₂ O ₃ is 10 mol% at the maximum.

  Phosphate glasses made in this way and containing alkaline earth oxides are notable for sufficient optical transparency and radiation resistance at operating wavelengths near 193 nm, and in particular 1. The group has a high refractive index of 6 or more. It is therefore particularly suitable as an optical element of an immersion lithography projection system in which linearly polarized UV laser radiation with a wavelength around 193 nm propagates through the immersion medium to the substrate.

  It has proved advantageous to premix the phosphorus compound and the alkaline earth compound and feed them as a mixture to the deposition burner.

  In this process, the deposition burner is already supplied with a mixture having a fixed mixing ratio of glass starting material, and a mixture that is uniform in time and place is adjusted in the reaction zone, so that a particularly homogeneous phosphoric acid is obtained. This produces salt glass.

  Another way of separately supplying the phosphorus compound and alkaline earth compound to the reaction zone is likewise preferred and is particularly simple.

  The invention will now be described in detail by way of example with reference to the accompanying drawings.

The deposition burner shown in FIG. 1 is a known one that has been conventionally used in the production of quartz glass. However, in this example, this known deposition burner is used as a modified embodiment in which phosphate glass particles doped with barium oxide are deposited in plasma on the cylindrical surface of the carrier 9 rotating about the longitudinal axis 20. . Reference numeral 1 denotes the entire plasma support burner. The plasma support burner includes a burner tube 2 made of quartz glass, and a plasma 4 is ignited by a high-frequency coil 3 in the burner tube. Furthermore, the plasma support burner 1 comprises an inner tube 5 of quartz glass, through which the plasma 4 is supplied to the plasma 4 in the form of phosphorus-containing glass starting material in the form of PCl ₃ (boiling point 76.10 ° C.) and oxygen. The inner tube 5 is in the form of a medium nozzle 7 which tapers towards the plasma 4.

  The inner tube 5 is concentrically surrounded by two quartz glass tubes 11; 12. Barium chloride dissolved in ultrapure water is placed in an annular gap 13 between the inner quartz glass tube 11 and the inner tube 5 together with a carrier gas in the form of oxygen. The annular gap 13 extends to the upper nozzle opening area facing the plasma 4 to form a diffuser 14. The gap “A” between the nozzle opening of the inner stainless steel tube 11 (diffuser 14) and the medium nozzle 7 is 23 mm. In the cylindrical portion, the gap width of the annular gap 13 is about 6 mm.

  A cooling gas in the form of oxygen is introduced into the annular gap 16 between the inner tube 11 and the outer tube 12. This cooling gas mainly serves to cool and protect the plasma support burner 1 against high temperature plasma. The gap width of the annular gap 16 is about 3 mm. The opening of the annular gap 16 oriented towards the plasma 4 forms an outer nozzle 17 that opens towards the plasma 4 and the outer tube 12 projects towards the plasma from the inner tube 11 about 13 mm. Yes. The interior of the burner tube 2 is sealed against the outside air as indicated by a sealing ring 18.

  An example of the method of the present invention will be described with reference to the plasma support burner shown in FIG.

Feed 4 grams of PCl ₃ per minute and 7 liters of oxygen per minute into the inner tube 5. In addition, 1.3 grams of dissolved BaCl ₂ per minute is injected into the annular gap 13 with 40 liters of carrier oxygen per minute. 70 liters of cooling gas / oxygen are injected into the annular gap 16 per minute.

In the region of the plasma 4, PCl ₃ is oxidized to phosphorus oxide, and BaCl ₂ becomes barium oxide in the form of nanoparticles on the cylindrical surface of the aluminum oxide rod 9 rotating about the longitudinal axis 20. And directly vitrified in this process to form a body 8 consisting of phosphate glass doped with barium oxide, wherein the molar ratio of BaO to P ₂ O ₅ is 1: 1. A phosphate glass blank (its composition and properties are shown in Table 1) is formed in layers along the cylindrical surface of the aluminum oxide rod 9 by periodically reversing the motion of the plasma support burner.

The fifth column of the table shows the measured values of the refractive index n _e at a measurement wavelength 546.04Nm, and column 6 of the table shows the refractive index at a wavelength 193nm determined empirically.

  As a result of making phosphate glass agglomerates without the use of tools other than plasma support burners, it is possible to use high-purity starting materials, ie high-purity phosphate glasses, and thereby in the wavelength range around 200 nm. Achieve low absorption. This in particular prevents contamination by multiply charged ions. This multiply charged ion usually exhibits a very strong and broad absorption band in the VUV and UV ranges and shifts the intrinsic VUV edge to the longer wavelength band side.

  A homogeneous glass block is formed from the tubular glass body 8 by molding and homogenization processing, for example, three-dimensional twisting, and the lens of the projection objective 21 (FIG. 2) is formed from the glass block by further processing, for example, annealing and machining. A blank is obtained.

A transmittance of 85% was measured in a wavelength range between 120 and 350 nm with a barium phosphate glass disk having a thickness of 0.2 mm and a composition (in molar ratio) of 50BaO and 50P ₂ O ₅ . This value is close to the theoretically calculated transmittance and is sufficient for the intended use with phosphate glass. Intrinsic UV absorption only begins at a wavelength of about 170 nm.

  In the part shown in FIG. 2 of the immersion lithography microlithographic projection system at an operating wavelength of 193 nm, the last lens 21 consists of a phosphate glass made according to the invention. The lens 21 is in direct contact with the immersion liquid 22 that completely fills the gap between the photosensitive film 23 on the substrate 24 and the lens 21.

  The optical path of radiation at the operating wavelength varies with the refractive index of the individual elements 21, 22, 23. The left side of FIG. 2 shows the optical path 25 b when the lens 21 has a higher refractive index than the immersion liquid 22 and the immersion liquid 22 has a lower refractive index than the photosensitive film 23.

  The right side shows the ideal optical path 25a for a large numerical aperture of the projection system and the smallest possible lens size. The lens 21, the immersion liquid 22, and the photosensitive film 23 each have the same refractive index.

1 is a schematic illustration of a deposition burner for plasma depositing phosphate glass on a carrier. 1 schematically illustrates a combination of a substrate to be exposed and a portion of a microlithographic projection system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Deposition burner 2 Burner tube 3 High frequency coil 4 Plasma 5 Inner tube 7 Medium nozzle 8 Body or tube-shaped glass 9 Aluminum oxide rod 11 Inner tube 12 Outer tube 13 Annular gap 14 Diffuser 16 Annular gap 17 Outer nozzle 18 Sealing ring 20 Longitudinal axis 21 Projection objective lens 22 Immersion liquid 23 Photosensitive film 24 Substrate 25 Optical path

Claims (15)

  The deposition burner (1) is provided with a reaction zone (4) to which an oxidizable, synthesized phosphorus compound and an alkaline earth compound are supplied, where it is amorphous in the presence of an oxygen-containing gas. Oxide particles are formed, and the particles are deposited on a carrier (9) to form a phosphate glass containing an alkaline earth oxide, the refractive index of the phosphate glass being at least 1 at a wavelength of 193 nm. A method for producing a material for a projection objective (21) of immersion lithography, characterized in that .6.   The production method according to claim 1, wherein a phosphorus compound that vaporizes at a temperature up to 500 ° C. is used.   The production method according to claim 1 or 2, wherein a phosphorous compound selected from the group consisting of phosphine, phosphane, phosphite, phosphide and organic and inorganic derivatives of these compounds is used.   4. The process according to claim 3, wherein a phosphorus derivative in the form of a phosphorus halogen compound is used.   The production method according to claim 4, wherein the phosphorus halogen compound used is one or a plurality of compounds selected from the group consisting of phosphorus trichloride, diphosphorus tetrachloride and phosphorus pentachloride.   The production method according to claim 3, wherein a chlorine-free phosphorus compound is used.   The production method according to any one of claims 1 to 6, wherein the alkaline earth compound is used in the form of a halogen compound or an acetate compound containing magnesium, potassium, strontium and / or barium.   8. The process according to claim 7, wherein the alkaline earth compound used is a barium halogen compound or an acetate compound.   9. The production method according to claim 8, wherein the barium halogen compound used is barium chloride. The phosphorus compound and the alkaline earth compound are supplied to the reaction zone at a molar ratio such that phosphate glass particles having a P ₂ O ₅ content between 40 mol% and 75 mol% are formed. The manufacturing method in any one of -9.   The production according to claim 10, wherein the phosphorus compound and the barium compound are fed to the reaction zone in a molar ratio such that phosphate glass particles having a barium oxide content between 30 mol% and 60 mol% are formed. Method.   12. A process as claimed in any one of the preceding claims wherein an amount of aluminum compound which forms no more than 25 mol% aluminum oxide (based on phosphate glass) is added to the reaction zone.   13. A method according to any of claims 1 to 12, wherein an amount of boron compound (based on phosphate glass) that forms no more than 10 mol% boron oxide is added to the reaction zone.   The manufacturing method according to any one of claims 1 to 13, wherein a phosphorus compound and an alkaline earth compound are mixed in advance and supplied to the deposition burner as a mixture. The production method according to claim 1, wherein the phosphorus compound and the alkaline earth compound are separately supplied to the reaction zone.

Images