DE112005003341T5 - Synthetic silica with low polarization-induced birefringence, process for producing the same and lithographic apparatus comprising the same - Google Patents

Abstract

Synthetic silica glass material suitable to be used in the beam path of lithographic radiation below about 300 nm in lithography apparatus and having less than 1 nm / cm of polarization-induced birefringence measured at about 633 nm after having 5 × 10 ⁹ pulses of a linear polarized pulsed laser beam has been exposed at about 193 nm, which has a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns.

Description

Field of the invention

The The present invention relates to synthetic silica material, the process of producing the same material and optical systems which optical members made of such material. In particular, the present invention relates to synthetic silica material, which has a low polarization-induced birefringence, when exposed to elliptical or linearly polarized UV radiation is, and the process for producing selbigen material as well optical systems, which are optical members made of such material are made, included. The present invention is, for example in the production of synthetic glass material of silicon dioxide for the Use in UV lithography systems, in particular the immersion lithography systems, in which linearly polarized radiation is used, of use.

General state of the technology

As it for commercial concerns is common practice, become optical links of fused silica such as lenses, prisms, Filters, photomasks, reflectors, etalon plates and optical windows from unmounted blanks of molten silica made in big ones production furnaces getting produced.

such Non-specific shaped blanks produced in large production furnaces are known in the art as preforms or blanks. From these preforms or blanks moldings are cut, and from such glass moldings are the optical finished parts produced using manufacturing steps apply to cutting, polishing and / or coating of glass parts belonging to a molding, without limitation to be. Many of these optical members are made in many forms Appliances used in environments where used they are exposed to ultraviolet light having a wavelength of approximately 360 nm or less, for example, an excimer laser beam or another ultraviolet laser beam. The optical links are incorporated into a variety of instruments, including lithographic ones Laser exposure equipment for Production of highly integrated circuits, laser manufacturing equipment, medical equipment, equipment for the Nuclear fusion or some other apparatus, where an ultraviolet laser beam high power is used.

There the photon energy, the pulse energy and the pulse rate of laser increase, the optical links associated with such Lasers used increased Exposed to energy levels. Melted silica has due its excellent optical properties and durability across from laser-induced damage Widely used as the material of choice for optical applications Limbs in those laser-based optical systems work.

The Laser technology is short in the ultraviolet spectral range wavelength and high energy penetrated, the impact of which in one increase the frequency (shortening the wavelength) consists of the light generated by the laser. Of special interest are shortwave lasers that are in the wavelength ranges of the UV, the deep UV (DUV) and vacuum UV work, which includes lasers that at about 248 nm, 193 nm, 157 nm and even shorter wavelengths work, without limited to these to be. Excimer laser systems are in microlithographic applications popular, and the ever shorter wavelength enable an increased resolution features and, consequently, line densities in manufacture of integrated circuits and microchips, leading the production of circuits, have the greatly reduced feature dimensions. A direct one physical sequence of shorter ones wavelength (higher Frequencies) are higher Photon energies. In such optical systems, the optical Molten silica fused over longer periods of high radiation levels exposed, and this may lead to a loss of quality of optical properties lead these optical elements.

generally known influences such a laser-induced loss of quality adversely affects the optical properties of the optical members fused silica by decreasing the values of light transmission, by the discoloration of the Glass, through the change the refractive index, the change in density and the increase the absorption values of the glass. There are many over the years Process for improving the resistance of molten Silica glass opposite optical damage been proposed. It is well known that molten High purity silica produced by such processes as flame hydrolysis, CVD soot reflow, Plasma CVD method, electric melting of quartz crystal powder and other methods has been made to a different one Degree of laser damage is subject.

A general proposal is to raise the OH content of such glass to a high level. For example, confirmed Escher, GC, KrF Laser Induced Color Centers in Commercial Molten Silica Materials, SPIE Vol. 998, Ex Cimerstrahlanwendungen, pp. 30-37 (1988) In particular, they find that high OH content silicon dioxide is more resistant to damage than low OH silicon dioxide -Salary.

in the U.S. Patent 5,086,352 and in the relatives U.S. Patent 5,325,230 It is also disclosed that the ability to resist the optical damage caused when the material is exposed to a short wavelength laser beam depends on the content of OH groups in the presence of hydrogen. In particular, these references show that for high purity silica glass having a low OH content, the resistance to KrF excimer laser is low. Therefore, an OH content of at least 50 ppm is proposed in them. Similarly disclosed Yamagata, S., Improving the Resistance of Silica Glass to Excimer Lasers, Transactions of the Materials Research Society of Japan, Vol. 8, pp. 82-96 (1992) , the effect of dissolved oxygen on the fluorescence emission behavior and the deterioration of transmission upon irradiation with a KrF excimer laser beam for high purity silica glass containing OH groups up to 750 ppm by weight, such as that obtained by the oxygen flame hydrolysis method Silicon tetrachloride of high purity has been produced synthetically.

Others have also suggested methods for increasing the optical stability of molten silica. For example Faile, SP, and Roy, DM, Mechanism of Destruction of Color Centers in Hydrogen-Impregnated Radiation Resistant Glasses, Materials Research Bull., Vol. 5, pp. 385-390 (1970). discloses that hydrogen-impregnated glasses tend to resist radiation damage induced by gamma rays. In the summary of the Japanese Patent 40-10228 discloses a method by which an article of quartz glass prepared by melting is heated in a hydrogen-containing atmosphere to about 400 to 1000 ° C to prevent the discoloration due to the influence of ionizing radiation (solarization). Similar in the summary of the Japanese Patent 39-23850 discloses that the transmittance of silica glass for UV light can be improved by heat-treating the glass in a hydrogen atmosphere at 950 to 1400 ° C, followed by heat treatment in an oxygen atmosphere in the same temperature range.

Shelby, JE, Effects Radiation Effects in Hydrogen Impregnated Glassy Silica, J. Applied Physics, Vol. 50, No. 5, pp. 3702-06 (1979) indicates that the irradiation of hydrogen impregnated vitreous silica suppresses the formation of optical defects, but that hydrogen impregnation also leads to the formation of large amounts of bound hydroxyl and hydride and also results in a change in the density of the glass.

Recently was in the U.S. Patent 5,410,428 discloses a method for preventing the induced optical quality loss by a complicated combination of treatment processes and measures regarding the material composition of the fused silica parts, such that a particular hydrogen concentration and refractive index are obtained with the aim of resistance to deterioration To improve UV laser light. It is believed that under such UV irradiation, some chemical bonds between silicon and oxygen in the network structure of the molten silica are generally broken and reconnected to other structures resulting in increased local density and increased refractive index of the molten silica Silicon dioxide in the impingement of the radiation leads.

Recently, in the Araujo et al. other members U.S. Patent 5,616,159 discloses a high purity fused silica having high resistance to optical damage up to 10 ⁷ pulses (350 mJ / cm ² per pulse) at the laser wavelength of 248 nm, and a method of producing such a glass. The composition described by Araujo et al. comprises at least 50 ppm OH and has an H2 concentration of more than 1 × 10 ¹⁸ molecules / cm ³ .

It is reported that when silica glass is exposed to an unpolarized or circularly polarized UV laser beam, additional birefringence (induced edge birefringence) due to deformation phenomena caused by the laser damage is usually generated around the periphery of the exposure light beam but in the central region of the light beam there is usually negligible induced birefringence. Recently, a new phenomenon of laser damage to silica material has been observed: when the silica glass is exposed to a linearly polarized laser beam in deep UV, additional birefringence is induced in the middle of the exposed portion of the glass in addition to the induced edge birefringence ("polarization indi This induced birefringence, particularly polarization-induced birefringence, is of particular importance for those immersion lithography systems where a liquid fills the gap between the last lens element and the wafer to increase the numerical aperture of the lens system The induced birefringence in the glass alters the polarization state of the UV radiation, causing a reduction in the phase contrast and resolution of the system, thus making it suitable for immersion lithography systems in deep UV and UV Vacuum UV is very desirable in that the glass material used to fabricate the lens elements, in addition to low laser induced wavefront interference (" LIWFD ") and high transmission, has low damage Induced birefringence, in particular low birefringence-induced birefringence, when exposed to linear or elliptically polarized UV radiation

CK Van Peski et al. Report in the Journal of Non-Crystalline Solids, 265, 286 (2000) on experimental observations on the effect of polarization-induced birefringence in a SEMATECH study in which molten silica was exposed by several suppliers and subjected to measurements. The publication does not disclose any details about the samples other than the damage measured. NF Borelli et al. Report in Applied Physics Letters 80 (2) 219 (2002) on observations of this effect in various types of fused silica produced by the so-called direct-to-glass process. Here it is shown that polarization-induced birefringence occurs in samples showing a delayed wavefront in the damaged area (called compaction at that time), as well as in samples showing an anticipated wavefront in the damaged area (called expansion at that time). An explanation of the polarization-induced birefringence on the anisotropic density change is presented. The application for a European patent EP 1,340,722A1 mentions the polarization-induced birefringence in silica glass. However, it is not clear whether the examples in this cited patent for the glasses of different composition made using the carbon black-to-glass process disclose polarization-induced birefringence. It is apparent from the description of this document that the samples have birefringence induced by circularly polarized radiation or by unpolarized radiation. Those glasses were charged with molecular hydrogen during solidification of the carbon black. These references do not teach the high purity silica material having a low degree of polarization-induced birefringence, nor does it teach a method for making the same.

consequently There is a need for a synthetic silica material which a low degree of polarization-induced birefringence and to a method for producing such. The present invention provides a remedy for this.

Presentation of the invention

According to a first aspect of the present invention, there is provided a synthetic silica glass material which is suitable for use in photolithography below about 300 nm and which has a polarization-induced birefringence of less than about 1 nm / cm, advantageously less, measured at about 633 nm as 0.4 nm / cm, more preferably less than about 0.1 nm / cm, after being 5 x 10 ⁹ , preferably 1 x 10 ^10, and more preferably 2 x 10 ^10, and even more preferably 5 x 10 ¹⁰ and Most preferably, 1 × 10 ¹¹ pulses of a linearly polarized pulsed laser beam have been exposed at approximately 193 nm with a fluence of approximately 40 μJ cm ^-2 per pulse and a pulse length of approximately 25 ns. In certain embodiments, the synthetic silica glass material of the present invention has less than 0.04 nm / cm of polarization-induced birefringence, measured at about 633 nm, after having 2 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm with a fluence of approximately 40 μJ · cm ^-1 per pulse and a pulse length of about 25 ns has been exposed. In some other embodiments, the synthetic silica glass material of the present invention has a polarization-induced birefringence value measured at 633 nm, which is less than 1 nm / cm, advantageously less than 0.4 nm / cm, more preferably less than 0.1 nm / cm after being exposed to 5 × 10 ⁹ pulses of a linearly polarized pulsed laser beam at about 193 nm with one having a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns, but higher than about zero , 01 nm / cm (in some embodiments, higher than about 0.04 nm / cm) after having 2 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm with a fluence of about 40 μJ cm ^-2 per pulse and has been exposed to a pulse length of about 25 ns. When the silica glass material of the present invention is exposed to a linearly polarized pulsed UV laser irradiation, this material advantageously has a polarization induced birefringence (PIB) approaching linearly of the number (N) and fluence (F). the pulse depends on a given pulse length before saturation of the polarization-induced birefringence occurs.

Thus, according to a second aspect of the present invention, there is provided a synthetic silica material having a polarization-induced birefringence (PIB) which is approximately linear in number (N) and fluence (F) for a given pulse length before saturation of the polarization-induced birefringence where PIB (M) is the polarization-induced birefringence measured at approximately 633 nm, N is the number of pulses per million, and F is the fluence of the laser light beam, and α is a constant. When the laser pulse has a wavelength of approximately 193 nm and a pulse length of approximately 25 ns, the constant α of the silica glass material of the present invention, measured at approximately 633 nm, is preferably less than approximately 5 × 10 ^-7 cm ² · μJ ^-1 , more preferable less than about 2.5 x 10 ^-7 cm ² · microjoules ^-1, even more preferable less than about 1.25 x 10 ^-7 cm ² · microjoules ^-1, and most preferable less than about 5 x 10 ^{- 8} cm ² · μJ ^-1 .

According to one Another aspect of the present invention is a silica glass which, when exposed to an excimer laser at about 193 nm At about 633 nm, a normalized PIB is exposed ("PIB (N)" - see later definition) less than 10, advantageously less than 8, is more preferable less than 5 and strongest preferable to have less than 2.

Preferably includes the silica glass material of the present invention an OH concentration of less than about 500 ppm by weight, preferably less than 300 ppm by weight, more preferable less than 100 ppm by weight, more preferably less than 50 ppm by weight and the strongest preferably less than 20 ppm by weight.

Preferably comprises the silica glass material of the present invention, before being exposed to linearly polarized UV radiation, a initial measured at about 633 nm Birefringence of less than 5 nm / cm, more preferable of less than 1 nm / cm, even stronger preferably less than about 0.5 nm / cm, and most preferably less than about 0.1 nm / cm.

Preferably, the silica glass material of the present invention has an induced edge birefringence measured at about 633 nm of less than about 0.5 nm / cm, preferably less than 0.1 nm / cm, after being 5 x 10 ¹⁰ , preferably 1 x 10 ¹¹ , more preferably 2 × 10 ¹¹ pulses of a linearly polarized pulsed laser beam at about 193 nm with a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns has been exposed

Preferably contains the synthetic silica glass of the present invention less than 50 ppm of Cl.

• (i) Bereitstellung eines verfestigten synthetischen Siliziumdioxidglasmaterials hoher Reinheit, welches eine OH-Konzentration von weniger als etwa 500 Gew.-ppm, vorzugsweise von weniger als 300 Gew.-ppm, stärker vorzuziehen von weniger als 100 Gew.-ppm, noch stärker vorzuziehen von weniger als 50 Gew.-ppm und am stärksten vorzuziehen von weniger als 20 Gew.-ppm aufweist, und
• (ii) Behandlung des verfestigten synthetischen Siliziumdioxidglases in Gegenwart von H₂ bei einer Temperatur unter 800 °C, vorzugsweise über etwa 300 °C, stärker vorzuziehen bei etwa 500 °C wenigstens dann, wenn das unmittelbar nach Schritt (i) erhaltene verfestigte Glas eine H₂-Konzentration von weniger als 1 × 10¹⁶ Molekülen/cm³ aufweist.

According to another aspect of the present invention, there is provided a method of making a synthetic silica glass material which is suitable for use in photolithography below about 300 nm and which has a low degree of polarization-induced birefringence after being approximately linearly polarized 193 nm, this method comprising the following steps:

• (i) providing a consolidated high purity synthetic silica glass material which is even more preferable to have an OH concentration of less than about 500 ppm by weight, preferably less than 300 ppm by weight, more preferably less than 100 ppm by weight of less than 50 ppm by weight, and most preferably less than 20 ppm by weight, and
• (ii) treating the consolidated synthetic silica glass in the presence of H ₂ at a temperature below 800 ° C, preferably above about 300 ° C, more preferably at about 500 ° C at least when the solidified glass obtained immediately after step (i) has a solidified glass H ₂ concentration of less than 1 × 10 ¹⁶ molecules / cm ³ .

According to one preferred embodiment of Process of the present invention is solidified in step (i) High purity synthetic silica glass material by application a soot-to-glass process educated

• (A) Bildung einer Vorform aus Siliziumdioxidruß;
• (B) Trocknen der Vorform aus Siliziumdioxidruß mit einem Trocknungsmittel; und
• (C) Verfestigung der Vorform aus Siliziumdioxidruß in Gegenwart einer Atmosphäre, welche H2O mit einem gesteuerten Partialdruck enthält.

In a preferred embodiment of the process of the present invention, step (i) comprises the following steps:

• (A) formation of a silica soot preform;
• (B) drying the silica soot preform with a desiccant; and
• (C) solidification of the silica soot preform in the presence of an atmosphere containing H2O at a controlled partial pressure.

In step (B), the desiccant is preferably selected from F ₂ , Cl ₂ , Br ₂ , halogen-containing compounds, CO, CO ₂ and compatible mixtures thereof. Preferably, immediately after drying in step (B), the OH concentration in the carbon black preform is less than about 0.1 ppm by weight. Preferably, immediately after step (C), the OH concentration in the solidified glass is less than or equal to 150 ppm by weight. In one embodiment of this process, in step (C), the atmosphere in which the carbon black preform is solidified also contains O ₂ . In another embodiment of this process, in step (C), the atmosphere in which the carbon black preform is solidified also includes H ₂ .

• (A1) Bildung einer Vorform aus Siliziumdioxidruß; und
• (B1) Trocknen der Vorform aus Siliziumdioxidruß mit einem trockenen Inertgas bei erhöhter Temperatur bis zu einer OH-Konzentration von über etwa 20 Gew.-ppm.

In a further preferred embodiment of the process of the present invention, step (i) comprises the following steps:

• (A1) formation of a silica soot preform; and
• (B1) drying the silica soot preform with a dry inert gas at elevated temperature to an OH concentration of greater than about 20 ppm by weight.

According to another preferred embodiment of the process of the present invention, prior to step (ii), the solidified glass has an H ₂ concentration of less than or equal to about 1 x 10 ¹⁶ molecules per cm ³ .

According to one third aspect of the present invention, an immersion lithography system is presented, which at least one of the UV radiation exposed lens part which consists of the silica glass material of the present Invention, as has been generally described above is, has been manufactured. The one used in the lithography system Lithographic radiation is preferably elliptical or linear polarized, more preferable is linearly polarized radiation. The lithographic radiation preferably has a wavelength of about 248 nm or 193 nm.

Further Features and advantages of the invention will be found in the detailed Description that follows, and the professionals on In this area, these are taken from the description or by the practical execution of the invention as described in the specification and the appended claims is, as well as the attached Recognize drawings quickly

This is to be understood that the preceding general description and the following detailed Description is merely an exemplary illustration of the invention and are intended to provide an overview or framework for understanding Nature and the character of the invention to convey, on whose Protection claim is made.

Of the accompanying drawing set, which is incorporated in this description and forms part of the same, the understanding of the invention should be further facilitate. Brief description of the drawings

in the accompanying drawing set are:

1 Figure 3 is a two-dimensional image of the birefringence of a sample of synthetic silica glass exposed to a circularly polarized excimer laser beam at about 193 nm measured at about 633 nm.

2 Figure 3 is a two-dimensional image of the birefringence of a sample of synthetic silica glass exposed to a linearly polarized excimer laser beam at about 193 nm measured at about 633 nm.

3 Figure 3 is a two-dimensional image of the birefringence of another sample of synthetic silica glass exposed to a linearly polarized excimer laser beam at about 193 nm measured at about 633 nm.

4 is a diagram showing the vertical section (x = 15.5 mm) and the horizontal section (y = 13 mm) through the birefringence image of 3 shows, wherein the vertical section is shifted by 0.4 nm / cm from the actual curve upwards.

5 Figure 4 is a graph showing the measured center birefringence as a function of the number of pulses at 193 nm for a given number of synthetic silica glass samples having different OH concentrations, H ₂ concentrations, and H ₂ impingement temperatures after they have been exposed to linearly polarized excimer laser beams with a pulse length of 25 ns and different fluences. Each line represents the behavior of a sample.

6 Fig. 12 is a graph showing the measured center birefringence as a function of the fluence of a laser beam for a certain number of synthetic silica glass samples after exposure to linearly polarized excimer laser beams having a pulse length of 25 ns and different fluence values. For each curve, the OH concentration, the temperature of H ₂ impingement, and the number of pulses are essentially the same.

7 Fig. 4 is a graph showing the effect of H ₂ impingement temperature and OH concentration on polarization-induced birefringence for a certain number of synthetic silica glass samples after having linearly polarized excimer laser beams with a pulse length of 25 ns and different fluence values have been suspended. The factor α for the polarization-induced birefringence in PIB = α · F · N is shown in this figure as a symbolic size of circles.

8th Figure 4 is a graph showing normalized polarization-induced birefringence as a function of OH concentration in the glasses of a certain number of synthetic silica glass samples.

9 is a calculated two-dimensional image of birefringence, where the stress-optical model and finite element analysis are based on the same set of data as in FIG 3 have been applied.

10 is a diagram showing a horizontal section and a vertical section through the two-dimensional image of the birefringence of 9 shows.

11 is a calculated two-dimensional image of birefringence, where the stress-optical model and the finite-element analysis are based on the same set of data as in FIG 2 have been applied.

Detailed description of the invention

Of the Expression "polarization-induced Birefringence " as used in this document means the peak the level of the in the middle region of the uniformly exposed surface of the Glass's measured birefringence after a certain time interval or laser pulses, if a pulsed laser beam is used, minus the initial Birefringence of the glass before exposure. In the present Registration will, when the glass is exposed, increase the value of polarization-induced Birefringence of the silica glass to quantify a linear polarized pulsed laser beam at approximately 193 nm at approximately 3 mm Diameter and a given fluence and pulse length a fixed area directed to the glass plate. The birefringence in the middle of the exposed area becomes measured after a certain number of pulses. The value of polarization-induced birefringence is calculated by the measured center birefringence the initial birefringence of the Glass is subtracted.

Of the Expression "induced Edge birefringence " as used in this document means the peak the level of measured birefringence in the periphery outside the exposed area of the glass, but adjoining it (ie the area directly at the opening, where the light intensity falls from the nominal value to zero), after a certain time interval or a certain number of laser pulses, if a pulsed laser beam is used minus the initial Birefringence of the glass before exposure. In the present application is the induced edge birefringence of the silica glass measured after a linearly polarized pulsed laser beam at nearly 193 nm with approximately 3 mm diameter and a given fluence and a given pulse length on a fixed surface the glass plate over a certain amount of time or a given number of pulses has been addressed. The value of induced edge birefringence is calculated by taking the peak value of the measured in the peripheral area Birefringence the initial one Birefringence of the glass is subtracted.

The term "low polarization-induced birefringence" as used in this document means polarization-induced birefringence less than or equal to 0.1 nm / cm measured at about 633 nm after the material has 5 × 10 ⁹ pulses of a linearly polarized pulsed laser beam at about 193 nm with a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns.

wobei PIB(N) die normierte polarisationsinduzierte Doppelbrechung und PIB(M) die gemessene polarisationsinduzierte Doppelbrechung in nm/cm, gemessen bei etwa 633 nm, sind; N ist die Anzahl der Impulse in Milliarden Impulsen, F ist die Fluenz des ArF-Lasers, welchem das Glas ausgesetzt wird, in mJ·cm^–2 pro Impuls. Beispielsweise für eine Glasprobe, die 5 × 10¹⁰ Impulsen eines ArF-Lasers mit einer Fluenz von 40 μJ·cm^–2 pro Impuls ausgesetzt worden ist, berechnet sich mit einer sich ergebenden gemessenen PIB(M) von 0,2 nm/cm ihre PIB(N) wie folgt:

The "normalized polarization-induced birefringence" as used herein is calculated from the measured polarization-induced birefringence as follows:

wherein PIB (N) is the normalized polarization-induced birefringence and PIB (M) is the measured polarization-induced birefringence in nm / cm measured at about 633 nm; N is the number of pulses in billions of pulses, F is the fluence of the ArF laser to which the glass is exposed in mJ · cm ^-2 per pulse. For example, for a glass sample exposed to 5 × 10 ¹⁰ pulses of an ArF laser with a fluence of 40 μJ cm ^-2 per pulse, its resulting PIB (M) is 0.2 nm / cm PIB (N) as follows:

A single sample may have a different PIB (N) if the Measurement with different N and F takes place. Therefore, values are the PIB (N), over which is reported in the present application or in this means of which are described.

The inventors of the present invention have found that the level of polarization-induced birefringence of silica glass depends on the composition of the glass and the process conditions. In light of such findings, the present inventors have shown silicon dioxide materials having a low level of polarization-induced birefringence and invented the processes for producing low-level polarization-induced birefringence silica glass.

What relates to the composition of the silica glass, so have the inventors of the present invention found that Another important factor is the OH concentration in the glass which is the polarization-induced birefringence of the glass adversely affected. Therefore, the general statement can be made be that if all other conditions remain the same polarization-induced birefringence of the glass is higher, The higher the OH content is. To a low level of polari sationsinduzierten To achieve birefringence in silica glass, therefore, have this Inventors found that it is desirable that the OH concentration in the glass is lower than 500 ppm by weight, preferably lower than 300 ppm, stronger preferable lower than 100 ppm, even more preferable lower than 50 ppm and the strongest preferably lower than 20 ppm.

To a lesser extent, the H ₂ content of the silica glass also adversely affects the level of polarization-induced birefringence. For a silica glass with low polarization-induced birefringence, it is desirable to contain H ₂ of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ molecules per cm ³ , preferably less than about 5.0 × 10 ¹⁷ molecules / cm ^3, and even more preferably less as about 2.0 x 10 ¹⁷ molecules per cm ³ .

Around a low level of polarization-induced birefringence it is desirable to achieve that the silica glass has a low content of contaminants, in particular metals such as alkali metals, alkaline earth metals and transition metals having. If the glass is to be used in lithography systems, especially in those that are in the areas of deep UV and of Working vacuum UV, it is highly desirable that the glass is less than 10 ppb of alkali metals, alkaline earth metals or transition metals contains. Stronger It is preferable that the synthetic silica glass material of the present invention less than 1 ppb of alkaline earth or transition metals contains. It is also desirable that the synthetic silica glass is less than about 50 weight ppm Contains Cl.

As has been found in experiments and described below is, the synthetic silica glass of the present Invention a very low damage by polarization-induced birefringence when exposed to radiation is exposed at 193 nm. It is expected to be a very low one polarization-induced birefringence even at longer wavelengths such as 248 nm has. Therefore, the silica glass of the present application advantageously used in the production of optical members which are used in immersion lithography equipment, which in the areas of deep UV and vacuum UV work such as at about 248 nm and 193 nm where the lithographic radiation is usually elliptical or is linearly polarized.

The However, silica glass of the present invention is not on limited use in such applications. The glass of the present Invention can, for example, for optical members of dry lithography apparatuses are used work in areas of deep UV or vacuum UV and at even longer wavelengths. The silica glass of the present application may also be used in others devices Find application where synthetic glass of molten silica find typical application.

The Process of the present invention for the production of synthetic Silica glass of high purity and with a low level polarization-induced birefringence comprises a step (i) providing a solidified synthetic silica glass with a relatively low level of OH concentration. The term "low Level of "OH concentration" as used here means that the measured OH concentration of the glass is lower more preferable than 500 ppm by weight, preferably lower than 300 ppm lower than 200 ppm, even more preferable lower than 100 ppm, even stronger preferable lower than 50 ppm, and most preferably lower than 20 ppm.

For this purpose, the synthetic silica glass can be made using the carbon black-to-glass process which first forms a preform of porous silica soot, for example by external vapor deposition ("OVD"), internal vapor deposition ("IVD") or axial Alternatively, the glass can be made by the direct process of forming the silica soot particles directly into transparent glass without the intermediate step of forming a porous preform therefrom. Various silicon precursor compounds, such as silicon halides, organosilicon compounds, can be used to prepare the to produce desired glass in these processes. These processes can be plasma assisted.

In a preferred embodiment of the process of the present invention, a solidified silica glass having a low level of OH concentration is formed by the carbon black-to-glass process. This process is preferred because of the ease of controlling the composition and property of the glass such as impurities, OH concentration, H ₂ concentration, fictitious temperature, and the like.

The co-pending and co-authored U.S. Patent Application No. 11 / 064,341 . 11 / 148,504 and 11 / 148,764 describe soot-to-glass processes for the production of synthetic silica material which has a particular composition and transmission and has certain laser damage and refractive index properties, with reference to relevant parts herein.

In a soot-to-glass process, when the carbon black preform is formed in an atmosphere having a high water partial pressure, the promptly formed carbon black preform usually contains a high level of OH concentration. To lower the OH concentration of the final consolidated glass, the carbon black preform must be dried before solidification. It has been found that to produce glass with an OH concentration above about 50 ppm, the carbon black preform must be easily brought into helium or other inert gas such as nitrogen, argon and the like at elevated temperatures to increase the OH content in the gas phase To reduce soot before it is sintered into dense glass. However, to achieve a low OH concentration, such as below 50 ppm by weight, it is preferred to use a desiccant. Preferred drying agents include, but are not limited to, CO ₂ , CO, chlorine (Cl ₂ ), bromine (Br ₂ ), and halogen-containing compounds such as, but not limited to, CF _x Cl _y Br _z where x, y and z are nonnegative integers with x ≤ 4, y ≤ 4, z ≤ 4, and x + y + z = 4, as well as compatible mixtures thereof. For example, for applications in lithography in deep UV and in vacuum UV, it is preferred that because of the problems with UV damage and transmission, the final consolidated silica glass has little to no Cl (<50 ppm by weight). Thus, in this preferred embodiment, when Cl ₂ or Cl-containing compounds are used to dry the silica soot preform, it is important that the residual Cl be removed from the SiO ₂ soot prior to solidification to the dense glass. The desiccant is capable of lowering the OH concentration in the carbon black to <0.001 to 0.1 ppm by weight (verified by sintering the carbon black to dense glass in the dry heat and then analyzing the glass). In order to obtain the desired value of OH in the solidified silica glass and to remove the residual Cl if necessary, the thus-dried silica soot preform may be solidified in an atmosphere containing H ₂ O. By controlling the partial pressure of H ₂ O in this solidification atmosphere and the thermal history of the solidification process, the OH concentration and the distribution thereof in the final solidified glass can be maintained at the desired level. Regardless of whether the carbon black preform is solidified in the presence of H ₂ O or not, oxygen may be used in the solidification atmosphere to remove or oxidize any oxygen-deficient silicon species that may have formed. The carbon black preform may also be solidified in the presence of H ₂ .

It is preferred that the consolidated glass is further subjected to a heat treatment in the presence of H ₂ for an effective period of time such that the H ₂ concentration in the finished glass reaches a desired level. The H ₂ concentration in the finished glass and the temperature at which the H ₂ treatment is carried out also adversely affect the level of polarization-induced birefringence and the behavior of the finished glass. It has been found that H ₂ treatment at a temperature below 800 ° C is preferable to achieve a low level of polarization-induced birefringence, particularly for glasses having an OH content of less than about 100 ppm by weight. However, in order to accelerate the process of H ₂ treatment, it is desirable that the treatment temperature be at least 300 ° C.

The following examples, which do not limit the scope of protection for the Purpose of illustrating the present invention, on which the Scope of protection is claimed, and may not be interpreted in the sense become as if the invention to which the scope is claimed restrict in any way.

EXAMPLES

Experimental procedure and dates

sample presentation

Glass of molten silica was produced using the so-called direct-to-glass process as well as the soot-to-glass process. For the latter, silica particles are deposited on a substrate, which leads to a soot molding. In a second step, this molding is solidified into a solid glass molding.

Of the OH content (or water content) of the glass is controlled during solidification. In a third step, copies of the glass molding, the have nearly the final shape, with molecular hydrogen at elevated temperatures up to applied to the different target concentrations.

Exposure and measurements

The rod-shaped Samples of molten silica were exposed, with Light was used by an ArF excimer laser at a Repetition frequency of 4000 Hz. The pulse length was about 25 ns. Of the Beam diameter was 3 mm, imposed by an aperture, and his form was approximate the top hat. The light beam was polarized where this required, depending on the individual case, a commercial linear or circular polarizer was used. The typical Sample size was 20 × 25 × 100 mm, and the beam used for exposure, polarized as desired or not, was through the center of the sample parallel to the longitudinal axis directed. The samples were taken after about 4 billion pulses of the structure for the Exposure decreased, and the birefringence was at a wavelength of 633 mm using a commercially available birefringence measurement system added. In addition was the wave front disturbance measured with interferometers at 633 nm and 193 nm.

Experimental data

1 shows the two-dimensional image of birefringence of a glass sample exposed to a circularly polarized light beam. As with the other two-dimensional images of birefringence in this application, the magnitude of the birefringence is gray-wedge-coded, as shown on the right-hand side of the image. The white lines indicate the direction of the slow axis of the glass at this particular point. Their length also encodes the magnitude. This image shows a high induced edge birefringence, but the polarization-induced birefringence in the center region of the exposed surface is nearly zero.

2 Figure 11 shows an extreme example of a sample exposed to a linearly polarized light beam which is extreme in that this sample has almost no birefringence outside the exposed area (at the scale chosen there). It has been chosen to show the effect as clearly as possible. More common, however, such as in 3 linear exposure patterns like the one in 2 pictured, where the birefringence outside the exposure area similar to that of 1 is, with some mid-birefringence added. These two examples of 2 and 3 show that the ratio between the polarization-induced birefringence in the middle of the exposure spot and the induced edge birefringence - observed in the unexposed glass surrounding the exposure area - can vary considerably. It has also been observed that the level of polarization-induced birefringence decreases with continued exposure as the polarization is switched to orthogonal polarization in between. This agrees with the expectation of the stress-optical response from anisotropic deformation associated with the direction of linear polarization, as will be described below.

3 shows a two-dimensional image of birefringence from another sample exposed to a linearly polarized light beam. 4 shows the vertical section (x = 15.5 mm) and the horizontal section (y = 13 mm) through the image of birefringence of 3 , For better clarity, the values of the birefringence of the vertical section have been shifted up by 0.4 nm / cm. For reasons of symmetry, the direction of the slow axis on the vertical section does not change its direction at all. Therefore, the only obvious difference to the circular exposure is the non-vanishing value in the middle of the exposure spot. In the horizontal direction, the slow axis of birefringence changes its direction from the vertical inside the exposure spot to the horizontal outside it. This change in direction forces the magnitude of the birefringence close to the edge of the exposure spot to zero. This shows up as two separate ditches in horizontal section (positions at about 11 and 13 mm, respectively). The expected abrupt drop to zero is somewhat masked by the smoothing resulting from the beamwidth of the birefringence measurement instrument.

A number of samples of different composition (for example, OH concentration, H ₂ concentration) and different process conditions (for example temperature of H ₂ impingement) were examined for polarization-induced birefringence when exposed to a linearly polarized laser beam with different fluence and pulse numbers were. In the diagram of 5 is their behavior in terms of polarization-induced birefringence reproduced. From this figure it is clear that for the great majority of the samples tested and for the conditions and the limited number of pulses reproduced here, their polarization indices Double birefringence develops linearly with the number of impulses used for exposure. This is in sharp contrast to the behavior of the laser-induced wavefront perturbation, which is non-linear and may even show a sign change for certain types of silica.

5 also suggests that the value of polarization-induced birefringence depends linearly on the fluence of the light beam exposed to exposure for a given length of laser pulse. 5 does not directly show the saturation of polarization-induced birefringence with exposure, but saturation has been observed at higher dose levels. 6 Figure 12 shows the value of the polarization-induced birefringence of certain samples having substantially the same composition and process condition for a given number of pulses as a function of the fluence of the light beam. Therefore, the relationship between the polarization-induced birefringence, the number of pulses and the fluence can be represented by PIB = α · N · F, where α is a sample-dependent texture, N is the number of pulses, F is the fluence, and PIB is the level the polarization-induced birefringence. In 7 For various samples, this factor (coded as the size of the symbol) is shown above the temperature of the H ₂ treatment after solidification and the OH concentration in the glass. In 8th are the data from certain samples 5 plotted again in a graph of the normalized PIB above the OH concentration (ppm). Out 7 and 8th it is clear that the main driving force of the polarization-induced birefringence seems to be the OH concentration, while the temperature of the H ₂ treatment is less influential. The area of best performance is where both the OH concentration and the exposure temperature are low at the scales shown in the figure. The behavior of some samples in linear extrapolation would result in a birefringence at end of life (200 billion pulses) of 1 nm / cm at a fluence of 40 μJ cm ^-2 per pulse. This is at least a factor of 8 lower than for the glasses reported in the prior art and a factor of 10 better than commercially available direct-to-glass silica glass.

Tension-optic interpretation

und A ≡ (εxx + εyy – 2εzz) (2)wobei ε_ij eine Komponente der Verformung ist (Gradient der Verschiebung) und die Koordinatenachsen so gewählt sind, dass z längs des Weges des der Exposition dienenden Lichtes durch die Probe liegt und x und y längs der Ellipsenachsen für die elliptische Polarisation liegen. (Die lineare Polarisation ist ein Spezialfall der elliptischen Polarisation; wenn die elliptische Polarisation in Betracht gezogen wird, dann sind die individuellen Verformungskomponenten unterschiedliche Linearkombinationen von D und A je nach der Form der Ellipse.) Mit gegebenen Werten für D und A, die typischerweise in der Größenordnung von 10^–6 für die Studien zu den Laserschädigungen liegen, wurde eine Untersuchung nach der Finite-Element-Methode für den elastischen Fall durchgeführt, um die endgültigen elastischen Verformungen (und Spannungen) zu berechnen, die sich aus den anfänglichen Verformungswerten, die durch D und A festgelegt sind, ergeben. D. h. die Untersuchung des elastischen Falls ist erforderlich, um die Probengeometrie und die Randbedingungen zu berücksichtigen. Bei diesem Schritt wird das tatsächliche Beleuchtungsprofil eingearbeitet. Wenn die anfängliche (uneingeschränkte) und die elastische Verformung bekannt sind, dann wird die spannungsoptische Formulierung benutzt, um Änderungen im „Impermeabilitätstensor" ΔB zu berechnen, der gegeben ist durch ΔBij = pijklΔεkl + rijklε0kl (3) wobei p_ijkl der spannungsoptische Tensor ist, Δε_kl sind die Verformungswerte der elastischen Reaktion sind, die von den anfänglichen Verformungswerten, der Probengeometrie und dem Beleuchtungsprofil abhängen, r_ijkl ist ein separater spannungsoptischer Tensor, der mit den permanenten Verformungen verknüpft ist, und ε 0 / kl sind die anfänglichen oder uneingeschränkten Verformungen sind, die in den Gl. (1) und (2) aufgetreten sind. Die Summation über wiederholt auftretende Indizes ist inbegriffen. Die Verwendung eines speziellen spannungsoptischen Tensors für die permanenten Verformung im Gegensatz zu den elastischen Verformungen ist auf der Grundlage in der optischen Reaktion erforderlich, die für permanente Verformungen gegenüber elastischen Verformungen beobachtet wird. Während der spannungsoptische Tensor p_ijkl im Schrifttum wohlbekannt ist und für einen Bereich von Wellenlängen für Siliziumdioxid kennzeichnend ist, ist der die permanenten Verformungen darstellende spannungsoptische Tensor r_ijkl weniger etabliert und ist Gegenstand einer Studie. Der Impermeabilitätstensor B_ij ist das Inverse des dielektrischen Tensors. Nach der Projizierung von ΔB in die Ebene rechtwinklig zum Pfad der Lichtmessung liefern seine Eigenwerte die spannungsoptischen Änderungen im Brechungsindex und in der Doppelbrechung, und seine Eigenvektoren liefern die langsame Achse der Doppelbrechung. Weil die Elastizitätstheorie und die Theorie der Spannungsoptik beide linear sind, tritt eine große Vereinfachung ein, und für eine gegebene Probengeometrie und ein gegebenes Beleuchtungsprofil läuft die gesamte oben angegebene Analyse auf zwei einfache Beziehungen hinaus:

und R = cD + dA (5)wobei a, b, c und d Konstanten sind, die von der Geometrie – und der Beleuchtungabhängen,

ist die Änderung des optischen Wegs pro Längeneinheit (die weiter vorn erwähnte Wellenfrontstörung LIWFD), und R ist die Magnitude der Doppelbrechung. Die Konstanten a, b, c und d ändern sich von Punkt zu Punkt auf der Probenfläche und hängen von der Polarisation ab, welcher die Probe exponiert ist. Beispielsweise für den Fall der linearen Polarisation und in der Mitte des exponierten Bereichs ist die Magnitude der Doppelbrechung (der polarisationsinduzierten Doppelbrechung oder PIB) gegeben durch PIB = d'A (6)wobei d' benutzt wird, um die Proportionalitätskonstante von d zu unterscheiden. Dies liefert das sehr nützliche Ergebnis, dass die PIB zur uneingeschränkten Anisotropie A direkt proportional ist und von der uneingeschränkten Dichte D völlig unabhängig ist. Die Konstanten a, b, c und d hängen von den elastischen Eigenschaften (E-Modul und Poisson-Zahl) und von den spannungsoptischen Konstanten p_ijkl und dem Tensor r_ijkl ab. Nur die beiden letztgenannten Tensoren haben je zwei unabhängige Konstanten im isotropen Glas; diese werden mit p₁₁ und mit p₁₂ und analog mit r₁₁ und r₁₂ bezeichnet. Das Vorhandensein dieser spannungsoptischen Konstanten macht die linearen Koeffizienten a, b, c und d auch von der Wellenlänge des zur Messung dienenden Lichtes abhängig.We now want to interpret the permanent changes in the optical properties caused by the excimer laser exposure with the aid of the glass deformation and the stress-optical effect. Direct proof of the strain is provided by the far-reaching strain field observed in the birefringence outside the aperture (in the unexposed glass), and for example 1 is apparent. This is in accordance with the 1 / r ² deformation field predicted by a plane deformation model (or by the finite element analysis for the elastic case) as the exposed area shrinks. If the strain were isotropic, then the exposed area would be in a state of "tympanic nerve entrapment" with equal strain values (and equal stress values) perpendicular to the sample length, in which case the birefringence would disappear within the exposed area as determined by the experiment in FIG 1 will be shown. The linearly polarized exposure produces a very high birefringence within the exposed region ( 2 However, it seems reasonable to conclude that the anisotropy of the linearly polarized radiation field causes a permanent anisotropic strain in the glass. This anisotropic strain occurs in spite of the initial isotropy of the glass and entirely as a result of the anisotropy of the light field. This is reasonable from a physical point of view because, for reasons of symmetry, only two types of deformations can occur in response to linearly polarized light: one is simply isotropic, referred to herein as isotropic density change, and the second has a distortion component only along the direction of the electrical field. Previously, a deformation theory with only one "unrestricted" fractional density change δp / p (to be called D for the sake of simplicity) was considered, and because of the linearity of both the elastic response and the stress-optical response, all results were ranked by this single value The unrestricted density change D was previously used to represent laser damage of silica in a shape independent of the sample geometry Now, both D and "unrestrained anisotropic deformation" A are needed to fully characterize the deformation and optical changes of an exposed sample , These two quantities can be related to the usual components of deformation by the following relationships:

and A ≡ (ε xx + ε yy - 2ε zz ) (2) where ε _{ij is} a component of the deformation (gradient of the displacement) and the coordinate axes are chosen so that z lies along the path of the light serving for the exposure through the sample and x and y are along the ellipse axes for elliptical polarization. (Linear polarization is a special case of elliptical polarization, and if elliptical polarization is taken into account, then the individual deformation components are different linear combinations of D and A depending on the shape of the ellipse.) Given values for D and A, which are typically in In the order of magnitude of 10 ^-6 for the laser damage studies, a finite element method study was performed for the elastic case to calculate the final elastic deformations (and stresses) resulting from the initial deformation values, the are determined by D and A, result. Ie. the investigation of the elastic case is necessary to consider the sample geometry and the boundary conditions. In this step, the actual lighting profile is incorporated. If the initial (unrestrained) and elastic deformation are known, then the stress-optic formulation is used to calculate changes in the "Impermeability Tensor" ΔB given by .DELTA.B ij = p ijkl Δε kl + r ijkl ε 0 kl (3) where p _{ijkl is} the stress- _optical tensor, Δε _kl are the strain values of the elastic response that depend on the initial _{strain values} , the sample geometry, and the illumination _profile , r _ijkl is a separate stress- _optical tensor associated with the permanent _strain , and ε 0 / kl are the initial or unrestricted deformations that appear in Eqs. (1) and (2) have occurred. The summation over recurring indices is included. The use of a special stress-optical tensor for permanent deformation as opposed to elastic deformation is required on the basis of the optical response observed for permanent deformations against elastic deformations. While the stress- _optical tensor p _{ijkl is} well-known in the literature and is _indicative of a range of wavelengths for silicon dioxide, the _strain-optic tensor r _ijkl that is the permanent _{strain is} less well established and is the subject of a study. The impermeability tensor B _ij is the inverse of the dielectric tensor. After projecting ΔB in the plane perpendicular to the light measurement path, its eigenvalues provide the stress optical changes in refractive index and birefringence, and its eigenvectors provide the slow axis of birefringence. Because the theory of elasticity and the theory of stress optics are both linear, there is a great deal of simplification, and for a given sample geometry and lighting profile, the whole analysis given above is based on two simple relationships:

and R = cD + dA (5) where a, b, c, and d are constants that depend on the geometry and lighting,

is the optical path change per unit length (the wavefront interference LIWFD mentioned earlier), and R is the magnitude of the birefringence. The constants a, b, c and d vary from point to point on the sample surface and depend on the polarization to which the sample is exposed. For example, in the case of linear polarization and in the middle of the exposed region, the magnitude of birefringence (of polarization-induced birefringence or PIB) is given by PIB = d'A (6) where d 'is used to distinguish the proportionality constant of d. This provides the very useful result that the PIB is directly proportional to the unrestrained anisotropy A and is completely independent of the unrestricted density D. The constants a, b, c and d depend on the elastic properties (modulus of elasticity and Poisson's number) and on the stress- _optical constants p _ijkl and the tensor r _ijkl . Only the last two tensors have two independent constants in the isotropic glass; these are denoted by p ₁₁ and by p ₁₂ and analogously by r ₁₁ and r ₁₂ . The presence of these voltage-optical constants also makes the linear coefficients a, b, c and d dependent on the wavelength of the light used for the measurement.

If one uses literature values for p ₁₁ and p ₁₂ and makes a rational approach to r ₁₁ and r ₁₂ with respect to our sample geometry, then the value of A, which is given in Eq. (2) is always negative in the experimental measurements. This follows from our definition of A from Eq. (2), from the assumed values for the stress-optical constants and from the experimental observation that the slow axis of PIB is always perpendicular to the linear polarization of the exposure laser. We consider this as given for example for both contracting and expanding samples, ie for each sign of D.

It is appropriate to repeat that the use of circularly polarized light for the Exposure yields the result PIB = 0. The elliptical polarization yields slightly more PIB, and of course the linear polarization produces the largest PIB. Any averaging over polarizations which tends to randomize the accumulated values for polarization exposure will proportionally lower the PIB.

Comparison of experimental Data with the model

Here becomes the formalism described in the previous section ("Tension-Optical Interpretation") used to adjust the experimental birefringence data. Therefor become the density change D and the anisotropy A varies until the sum of the least squares between experimental and calculated images of birefringence reached the minimum value. This procedure identifies the induced Birefringence at a certain level of exposure and shows that the assumption of anisotropic deformation is correct. It should be noted be that the entire two-dimensional image of the magnitudes of birefringence and the directions of the slow axis is shown with a single pair of values (D, A). It should not be tried here be a modeling of the evolution of injury over the Course of exposure.

9 shows calculated values in the form of a two-dimensional image of birefringence, such as this from an adaptation to the experimental data from earlier in FIG 3 has been obtained. All the main features observed in the experimental data are well reported: the circular maximum of birefringence, the radial pattern outside the exposure spot, and the non-zero birefringence in the middle of the exposed area. A horizontal and a vertical section of 9 are in 10 shown. The in 10 illustrated horizontal section 5 shows the two Einsattelungen near the edge of the spot. Both the experimental and the calculated image suffer from the coarse grid, which leads to underestimation of the large gradients in the birefringence distributions, and from the smoothness associated with the beamwidth of the laser used for the measurement. This model grid was chosen to match the limited spatial resolution of the measurement system (approximately 0.5 mm), and the results calculated with the model included the smoothing in proportion to the profile of the measurement beam.

11 contains an adaptation to the experimental data 2 , It is a sample with predominant anisotropy and relatively low density change. As in the previous example, the experimental features are reproduced: the substantial absence of birefringence outside the exposed area and the strong center birefringence with all the slow axes aligned vertically.

It It is important to note here that when the polarization status the lithographic radiation such as that of an immersion lithography apparatus of the present invention is changed periodically, for example from the parallel to the orthogonal position, the cumulative effect should decrease in the form of polarization-induced birefringence, since the polarization-induced birefringence actually decrease starts as soon as after an initial one Exposure switched polarization to orthogonal polarization becomes.

The It will be apparent to those skilled in the art that various Modifications and modifications can be made to the present invention, without that the scope and spirit of the invention are abandoned. Therefore It is intended that the present invention all the modifications and changes covered by this invention provided they are within the scope of protection the attached claims and their equivalents.

Summary

There are disclosed a synthetic silica glass having a low polarization-induced birefringence, a process for producing this glass, and a lithography system containing optical members made of this glass. The silica glass has a polarization-induced birefringence measured at 633 nm, which is less than about 0.2 nm / cm when exposed to excimer laser pulses at about 193 nm with a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns for 5 × 10 ⁹ pulses is exposed.

Claims (31)

Synthetic silica glass material suitable to be used in the beam path of lithographic radiation below about 300 nm in lithography apparatus and having less than 1 nm / cm of polarization-induced birefringence measured at about 633 nm after having 5 × 10 ⁹ pulses of a linear polarized pulsed laser beam has been exposed at about 193 nm, which has a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns. A synthetic silica glass material according to claim 1, which has less than about 0.1 nm / cm of polarization-induced birefringence, measured at about 633 nm, after being 5 × 10 ⁹ pulses of a linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns. The synthetic silica glass material of claim 1, having less than about 0.1 nm / cm of polarization-induced birefringence measured at about 633 nm after being exposed to 1 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm, comprising a Fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns. The synthetic silica glass material of claim 1, having less than about 0.1 nm / cm of polarization-induced birefringence measured at about 633 nm after being exposed to 2 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm, comprising a Fluence of about 40 μJ · cm ² per pulse and a pulse length of about 25 ns. The synthetic silica glass material of claim 4, having less than about 0.04 nm / cm of polarization-induced birefringence, measured at about 633 nm, after being exposed to 2 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm, comprising a Fluence of about 40 μJ cm ² per pulse and a pulse length of about 25 ns. The synthetic silica glass material of any one of claims 1 to 4, which has greater than about 0.01 nm / cm of polarization-induced birefringence measured at about 633 nm after being exposed to 2 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm which has a fluence of about 40 μJ cm ^-2 per pulse and a pulse length of about 25 ns. Synthetic silica glass material according to a of the preceding claims, at which the glass, when it is a linearly polarized pulsed Laser radiation is exposed, a polarization-induced birefringence which approximates linearly of the number and fluence of the pulses given a pulse length before saturation the polarization-induced birefringence in the exposed area depends. Synthetic silica glass material according to a of the preceding claims, that is an OH concentration less than about 500 ppm by weight, preferably less than about 300 ppm by weight, more preferably less than about 100 ppm by weight. Synthetic silica glass material according to a of the preceding claims, which is less than about 5 nm / cm at the initial polarization-induced Birefringence, measured at about 633 nm, preferably less than 0.5 nm / cm, before it is a linearly polarized pulsed laser beam is suspended. A synthetic silica glass material according to any one of the preceding claims which has an induced edge birefringence of less than 0.5 nm / cm after being exposed to 5 x 10 ¹⁰ pulses of a linearly polarized pulsed laser beam at about 193 nm having a fluence of approximately 40 μJ cm ^-2 per pulse and has a pulse length of about 25 ns. The synthetic silica glass material of claim 10 having an induced edge birefringence of less than 0.5 nm / cm after being exposed to 1 x 10 ¹¹ pulses of a linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 μJ · Cm ^-2 per pulse and has a pulse length of about 25 ns. A synthetic silica glass material according to claim 10 which has an induced edge birefringence of less than 0.5 nm / cm after being exposed to 2 x 10 ¹¹ pulses of a linearly polarized pulsed laser beam at about 193 having a fluence of about 40 μJ · cm ^-2 per pulse and has a pulse length of about 25 ns. Synthetic silica glass material according to a of the preceding claims with less than 50 ppm of Cl. A synthetic silica glass material according to any one of the preceding claims, wherein the glass, when exposed to linearly polarized pulsed laser radiation of about 193 nm, has a polarization-induced birefringence that approximately satisfies the equation: PIB = α * F * N, where PIB is the polarization-induced birefringence measured at about 633 nm, F is the fluence of the laser radiation of 193, N is the number of pulses in millions, and α <5.0 × 10 ^-7 cm ² .μJ ^-1 . Synthetic silica glass material according to a of the preceding claims, which is a normalized polarization-induced measured at 633 nm Has birefringence of less than 10, if it is a linear one exposed to polarized pulsed laser irradiation at about 193 nm becomes. Process for producing a syntheti and a low level of polarization-induced birefringence after exposure to linearly polarized radiation at about 193 nm, which method is known in the art comprising the steps of: (i) providing a solidified high purity synthetic silica glass material having an OH concentration of less than about 500 ppm by weight, and (ii) treating the consolidated synthetic silica glass in the presence of H ₂ at a temperature below 800 ° C, at least when the solidified glass obtained immediately after step (i) has an H ₂ concentration of less than 1 x 10 ¹⁶ molecules / cm ³ . Method according to claim 16, wherein in step (i) the consolidated synthetic silica glass material by using the soot-to-glass process is formed. The method of claim 17, wherein in step (i) the steps comprises: (A) forming a silica soot preform; (B) drying the silica soot preform with a desiccant; and (C) solidifying the silica soot preform in the presence of an atmosphere containing H ₂ O at a controlled partial pressure. The method of claim 18, wherein in step (B) the desiccant is selected from Cl ₂ , Br ₂ , halogen containing compounds, CO, CO ₂ and compatible mixtures thereof. Method according to claim 18, wherein immediately after drying in step (B) the OH concentration in the soot preform less than about 0.1 ppm by weight. Method according to claim 18, in which immediately after step (C) the OH concentration in the solidified glass is less than or equal to 50 ppm by weight. The method of claim 18, wherein in step (C) the atmosphere in which the carbon black preform is solidified further comprises O ₂ . The method of claim 18, wherein in step (C) the atmosphere in which the carbon black preform is solidified further comprises H ₂ . Method according to claim 18, wherein in step (i) comprises the following steps: (A1) Forming a silica soot preform; and (B1) drying the Siliceous silica preform with a dry inert gas at an elevated Temperature to an OH concentration above about 40 ppm by weight. A process according to claim 16 wherein in step (ii) the solidified silica synthetic glass is in the presence of H ₂ at a temperature above 300 ° C. The method of claim 16, wherein in step (ii) the solidified synthetic silica glass has an H ₂ concentration below about 1 x 10 ¹⁶ molecules / cm ³ . Immersionslithografiegerät, which at least one optical Contains member in the beam path of the lithographic radiation, the of the silica glass material according to any one of claims 1 to 15 has been produced. An immersion lithography apparatus according to claim 27, wherein the lithographic Radiation is linear or elliptically polarized. An immersion lithography apparatus according to claim 27, wherein the lithographic Radiation is linearly polarized. An immersion lithography apparatus according to claim 27, wherein the lithographic Radiation a wavelength of about 248 nm. An immersion lithography apparatus according to claim 27, wherein the lithographic Radiation a wavelength of about 193 nm.