WO2006074083A1 - Synthetic silica having low polarization-induced birefringence, method of making same and lithographic device comprising same - Google Patents
Synthetic silica having low polarization-induced birefringence, method of making same and lithographic device comprising same Download PDFInfo
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- WO2006074083A1 WO2006074083A1 PCT/US2005/047452 US2005047452W WO2006074083A1 WO 2006074083 A1 WO2006074083 A1 WO 2006074083A1 US 2005047452 W US2005047452 W US 2005047452W WO 2006074083 A1 WO2006074083 A1 WO 2006074083A1
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B19/00—Other methods of shaping glass
- C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
- C03B19/1453—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/07—Impurity concentration specified
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/07—Impurity concentration specified
- C03B2201/075—Hydroxyl ion (OH)
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
- C03B2201/21—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with molecular hydrogen
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
- C03B2201/23—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with hydroxyl groups
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2201/00—Glass compositions
- C03C2201/06—Doped silica-based glasses
- C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
- C03C2201/21—Doped silica-based glasses containing non-metals other than boron or halide containing molecular hydrogen
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2201/00—Glass compositions
- C03C2201/06—Doped silica-based glasses
- C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
- C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2203/00—Production processes
- C03C2203/50—After-treatment
- C03C2203/52—Heat-treatment
- C03C2203/54—Heat-treatment in a dopant containing atmosphere
Definitions
- the present invention relates to synthetic silica material, process for making the same and optical systems comprising optical elements made from such material.
- the present invention relates to synthetic silica material having low polarization-induced birefringence when exposed to elliptically or linearly polarized UV irradiation and method of making the same, as well as optical systems comprising optical elements made from such silica material.
- the present invention is useful, for example, in the production of synthetic silica glass material for use in UV lithography systems, especially immersion lithography systems in which linearly polarized irradiation is employed. ' BACKGROUND OF THE INVENTION
- fused silica optical members such as lenses, prisms, filters, photomasks, reflectors, etalon plates and windows, have been manufactured from bulk pieces of fused silica made in large production furnaces.
- Bulk pieces of fused silica manufactured in large production furnaces are known in the art as boules or ingots.
- Blanks are cut from boules or ingots, and finished optical members are manufactured from glass blanks, utilizing manufacturing steps that may include, but are not limited to, cutting, polishing, and/or coating pieces of glass from a blank.
- optical members are used in various apparatus employed in environments where they are exposed to ultraviolet light having a wavelength of about 360 nm or less, for example, an excimer laser beam or some other ultraviolet laser beam.
- the optical members are incorporated into a variety of instruments, including lithographic laser exposure equipment for producing highly integrated circuits, laser fabrication equipment, medical equipment, nuclear fusion equipment, or some other apparatus which uses a high- power ultraviolet laser beam.
- lithographic laser exposure equipment for producing highly integrated circuits
- laser fabrication equipment laser fabrication equipment
- medical equipment nuclear fusion equipment
- nuclear fusion equipment nuclear fusion equipment
- Fused silica has become widely used as the material of choice for optical members in such laser-based optical systems due to their excellent optical properties and resistance to laser induced damage.
- Laser technology has advanced into the short wavelength, high energy ultraviolet spectral region, the effect of which is an increase in the frequency (decrease in wavelength) of light produced by lasers.
- short wavelength lasers operating in the UV and deep UV (DUV) and vacuum UV wavelength ranges, which include, but are not limited to, lasers operating at about 248 nm, 193 nm, 157 nm and even shorter wavelengths.
- Excimer laser systems are popular in microlithography applications, and the shortened wavelengths allow for increased feature resolution and thus line densities in the manufacturing of integrated circuits and microchips, which enables the manufacture of circuits having decreased feature sizes.
- a direct physical consequence of shorter wavelengths (higher frequencies) is higher photon energies.
- fused silica optics are exposed to high irradiation levels for prolonged periods of time, and this may result in the degradation of the optical properties of the optical members.
- 5,410,428 has disclosed a method of preventing induced optical degradation by a complicated combination of treatment processes and compositional manipulations of the fused silica members to achieve a particular hydrogen concentration and refractive index, in order to improve resistance to UV laser light degradation. It is suggested that under such UV irradiation some chemical bonds between silicon and oxygen in the network structure of the fused silica is generally broken and then rejoins with other structures resulting in an increased local density and an increased local refractive index of the fused silica at the target area.
- U.S. Pat. No. 5,616,159 to Araujo et al disclosed a high purity fused silica having high resistance to optical damage up to 10 7 pulses (350 mJ/cm 2 /pulse) at the laser wavelength of 248 nm and a method for making such glass.
- the composition disclosed in Araujo et al. comprises at least 50 ppm OH and has a concentration of H 2 greater than 1 x 10 18 molecules/cm 3 .
- the induced birefringence is of particular concern to immersion lithography systems where a liquid fills the gap between the last lens element and the wafer in order to enlarge the numerical aperture of the lens system.
- the polarization state of the UV radiation needs to be controlled, desirably linearly polarized.
- the induced birefringence in the glass alters the polarization state of the UV radiation, causing reduction of phase contrast and system resolution.
- the glass material used in making the lens elements has low induced birefringence damage, especially a low polarization-induced birefringence, when exposed to linearly or elliptically polarized UV radiation, in addition to low laser-induced wave-front distortion ("LIWFD") and high transmission.
- LIWFD laser-induced wave-front distortion
- a synthetic silica glass material capable of being used in photolithography below about 300 nm having less than about 1 nm/cm, advantageously less than about 0.4 nm/cm, more advantageously less than about 0.1 nm/cm of polarization-induced birefringence measured at about 633 nm after being subjected to 5 x 10 9 , preferably 1 x 10 10 , more preferably 2 x 10 10 , still more preferably 5 x 10 10 pulses, most preferably 1 x 10 11 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 /d-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
- the synthetic silica glass material of the present invention has less than about 0.04 nm/cm of polarization-induced birefringence measured at about 633 nm after being subjected to 2x10 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ j-cm "1 -pulse "1 and a pulse length of about 25 ns.
- the synthetic silica glass material of the present invention has a polarization-induced birefringence value measured at 633 nm, lower than 1 nm/cm, advantageously lower than 0.4 nm/cm, more advantageously lower than 0.1 nm/cm after being subjected to 5 x 10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 /J-cm ⁇ -pulse '1 and a pulse length of about 25 ns, but higher than about 0.01 nm/cm (in certain embodiments higher than about 0.04 nm/cm) after being subjected to 2 x 10 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 /J-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
- the silica glass material of the present invention when exposed to linearly polarized UV pulsed laser irradiation, has a polarization-induced birefringence (PIB) approximately linearly dependent on the number (N) and fluence (F) of the pulses at a given pulse length before saturation of polarization-induced birefringence.
- PIB polarization-induced birefringence
- PIB(M) a NF
- the constant a of the silica glass material of the present invention is less than about 5 x 10 "7 cm 2 - ⁇ J ⁇ , more preferably less than about 2.5 x 10 '7 Cm 2 YJ "1 , still more preferably less than about 1.25 x 10 "7 cm 2 - ⁇ T ⁇ , and most preferably less than about 5 x 10 "8 cm 2 -/*! "1 .
- a silica glass having a normalized PIB (PIB(N)", see later definition) when subjected to excimer laser at about 193 nm, measured at about 633 nm, of less than 10, advantageously less than 8, more advantageously less than 5, most advantageously less than 2.
- the silica glass material of the present invention has 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, still more preferably less than 50 ppm, most preferably less than 20 ppm by weight.
- the silica glass material of the present invention has an initial birefringence before being exposed to linearly polarized UV irradiation of less than 5 nm/cm measured at about 633 nm, more preferably less than 1 nm/cm, still more preferably less than about 0.5 nm/cm, most preferably less than about 0.1 nm/cm.
- the silica glass material of the present invention has an induced edge birefringence of less than about 0.5 nm/cm measured at about 633 nm, preferably less than 0.1 nm/cm, after being subjected to 5 x 10 10 , preferably 1 x 10 n , more preferably 2 x 10 n pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm "2 -pulse "1 and a pulse length of about 25 ns.
- the synthetic silica glass of the present invention comprises less than 50 ppm of Cl.
- a method for producing a synthetic silica glass material capable of being used in photolithography below about 300 nm having a low level of polarization-induced birefringence upon exposure to linearly polarized irradiation at about 193 nm comprising the following steps: (i) providing a high purity consolidated synthetic silica glass material having OH concentration of less than about 500 ppm by weight, preferably less than 300 ppm by weight, more preferably less than 100 ppm, still more preferably less than 50 ppm, 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 0 C, preferably over about 300 0 C, more preferably at about 500°C, at least if the consolidated glass obtained immediately after step (i) has an H 2 concentration of less than 1 x 10 16 molecules/cm 3 .
- step (i) the high purity consolidated synthetic silica glass material is formed by using a soot-to-glass process.
- step (i) comprises the following steps:
- step (B) the drying agent is selected from F 2 , Cl 2 , Br 2 , halogen- containing compounds, CO, CO 2 and compatible mixtures thereof.
- the OH concentration in the soot preform is less than about 0.1 ppm by weight.
- the OH concentration in the consolidated glass is less than or equal to 150 ppm by weight.
- the atmosphere in which the soot preform is consolidated further comprises O 2 .
- the atmosphere in which the soot preform is consolidated further comprises H 2 .
- step (i) comprises the following steps:
- the consolidated glass prior to step (ii), has a H 2 concentration of less than or equal to about 1 x 10 16 molecules/cm 3 .
- an immersion lithographic system comprising at least one lens element exposed to UV irradiation made of the silica glass material of the present invention generally described above.
- the lithographic irradiation employed in the lithographic system is preferably elliptically or linearly polarized, more preferably linearly polarized.
- the lithographic irradiation has a wavelength of about 248 nm or 193 nm.
- FIG. 1 is a two-dimensional birefringence map of a synthetic silica glass sample exposed to a circularly polarized excimer laser beam at about 193 nm, measured at about 633 nm.
- FIG. 2 is a two-dimensional birefringence map of a synthetic silica glass sample exposed to a linearly polarized excimer laser beam at about 193 nm, measured at about 633 nm.
- FIG. 3 is a two-dimensional birefringence map of another synthetic silica glass sample exposed to a linearly polarized excimer laser beam at about 193 nm, measured at about 633 nm.
- FIG. 5 is a diagram showing the measured center birefringence as a function of number of pulses at 193 nm of a plurality of synthetic silica glass samples having various OH concentrations, H 2 concentrations and H 2 loading temperature upon being exposed to linearly polarized excimer laser beams having pulse length of 25 ns and various fluences. Each line represents the behavior of a sample.
- FIG. 6 is a diagram showing measured center birefringence as a function of fluence of laser beam of a plurality of synthetic silica glass samples upon being exposed to linearly polarized excimer laser beams having pulse length of 25 ns and various fluences.
- FIG. 7 is a diagram showing the impact on polarization-induced birefringence of H 2 loading temperature and OH concentration of a plurality of synthetic silica glass samples upon being exposed to linearly polarized excimer laser beams having pulse length of 25 ns and various fluences.
- FIG. 8 is a diagram showing normalized polarization-induced birefringence as a function of OH concentration in the glasses of a plurality of synthetic silica glass samples.
- FIG. 9 is a calculated two-dimensional birefringence map by using the Strain-Optical Model and finite element analysis based on the same set of data in FIG. 3.
- FIG. 10 is a diagram showing a horizontal cross-section and a vertical cross- section of the two-dimensional birefringence map of FIG. 9.
- FIG. 11 is a calculated two-dimensional birefringence map by using the Strain-Optical Model and finite element analysis based on the set of data in FIG. 2.
- polarization-induced birefringence means the peak measured birefringence level in the center portion of the uniformly exposed area of the glass after a certain time interval or laser pulses, if a pulsed laser beam is used, less the initial birefringence of the glass before the exposure.
- a linearly polarized pulsed laser beam at approximately 193 nm having about 3 mm diameter with a given fluence and pulse length is directed to a fixed area of the glass sample.
- the birefringence at the center portion of the exposed area is measured after a certain number of pulses.
- the polarization-induced birefringence value is calculated by subtracting the initial birefringence of the glass from the measured center birefringence.
- induced edge birefringence means the measured peak birefringence level in the peripheral portion outside of but abutting the exposed area (i.e., the area right at the aperture where the light intensity changes from nominal value to zero) of the glass after a certain time interval or laser pulses, if a pulsed laser beam is used, less the initial birefringence of the glass before the exposure.
- the induced edge birefringence of the silica glass is measured after a linearly polarized pulsed laser beam at approximately 193 nm having about 3 mm diameter with a given fluence and pulse length has been directed to a fixed area of the glass sample for a certain period of time or a given number of pulses.
- the induced edge birefringence value is calculated by subtracting the initial birefringence of the glass from the peak measured birefringence at the peripheral portion.
- low polarization-induced birefringence means a polarization-induced birefringence of less than or equal to 0.1 nm/cm measured at about 633 nm after being subjected to 5 x 10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
- normalized polarization-induced birefringence is calculated from the measured polarization-induced birefringence as follows:
- PIB(N) TMWl ⁇ U ,
- PIB(N) normalized polarization-induced birefringence
- PIB(M) measured polarization-induced birefringence in nm/cm measured at about 633 nm
- N number of pulses in billion pulses
- F fluence of the ArF laser to which the glass is exposed to in mJ-cm ⁇ -pulse "1 .
- PIB(N) is calculated as follows:
- a single sample may have differing PIB(N) when measured at differing N and
- the present inventors have found that the polarization-induced birefringence level of silica glass is dependent on the composition of the glass and the processing conditions thereof. In light of such findings, the inventors have prepared silica materials having low polarization-induced birefringence level and invented the processes for making silica glass with a low level of polarization-induced birefringence. [0050] As regards the composition of the silica glass, the present inventors have found that, among others, OH concentration in the glass is a major factor affecting the polarization-induced birefringence of the glass. Generally, all other conditions remaining equal, the higher the OH level, the higher the polarization-induced birefringence of the glass.
- the present inventors have found that, to achieve a low level of polarization- induced birefringence in the silica glass, it is desired that the OH concentration in the glass is less than 500 ppm by weight, preferably less than 300 ppm, more preferably less than 100 ppm, still more preferably less than 50 ppm, most preferably less than 20 ppm.
- the H 2 level of the silica glass affects the polarization- induced birefringence level as well.
- the silica glass comprises H 2 from 1 x 10 16 to 1 x 10 19 molecules/cm 3 , preferably less than about 5.O x 10 17 molecules/cm 3 , and more preferably less than about 2.0 x 10 17 molecules/cm 3 .
- the silica glass comprises a low level of contaminants, especially metals, such as alkali, alkaline earth and transition metals. If the glass is to be used in lithography systems, especially those operating in deep and vacuum UV regions, it is highly desirable that the glass comprises less than 10 ppb alkali, alkaline earth, or transition metal elements. More preferably, the synthetic silica glass material of the present invention comprises less than 1 ppb alkaline earth or transition metal elements. It is also desired that the synthetic silica glass comprises less than about 50 ppm by weight of Cl.
- the synthetic silica glass of the present invention has a very low polarization-induced birefringence damage when exposed to irradiation at 193 nm. It is expected that it should have a very low polarization-induced birefringence at longer wavelength, such as 248 nm as well. Therefore, the silica glass of the present application can be advantageously used in making optical elements used in immersion lithography devices operating in deep and vacuum UV regions, such as at about 248 nm and 193 nm, where the lithographic irradiation is usually elliptically polarized or linearly polarized. [0054] However, the silica glass of the present invention is not limited for use in those applications.
- the glass of the present invention may be used, for example, for optical elements of dry lithography devices operating in deep or vacuum UV region and longer wavelength.
- the silica glass of the present application may find applications in other devices where high purity synthetic fused silica glass typically finds use.
- the process of the present invention for making high purity synthetic silica glass with a low polarization-induced birefringence level comprises a step (i) of providing a consolidated synthetic silica glass having a relatively low level of OH concentration.
- low level of OH concentration means the measured OH concentration by weight of the glass is less than 500 ppm by weight, preferably less than 300 ppm, more preferably less than 200 ppm, still more preferably less than 100 ppm, still more preferably less than 50 ppm, most preferably less than 20 ppm.
- the synthetic silica glass may be produced by using soot-to-glass processes, wherein a porous silica soot preform is first formed by, for example, outside vapor deposition ("OVD"), inside vapor deposition (“IVD”) or vapor axial deposition (“VAD”), and the like, and subsequently consolidated to transparent silica glass.
- the glass may be produced by the direct process, wherein silica soot particles are directly formed into transparent glass without the intermediate step of forming a porous preform thereof.
- Various silicon precursor compounds, such as silicon halides, organosilicon compounds may be employed to produce the desired glass in these processes. These processes may be plasma-assisted.
- the consolidated silica glass with a low level of OH concentration is formed by the soot-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, fictive temperature, and the like.
- the soot preform may be simply placed in helium or other inert gas, such as nitrogen, argon and the like, at elevated temperatures in order to reduce the OH in the soot before sintering it to dense glass.
- a drying agent is used to achieve a low OH concentration, such as below 50 ppm by weight.
- the drying agent is capable of reducing the OH concentration in the soot to ⁇ 0.001 to 0.1 ppm by weight (seen after by sintering the soot to dense glass in dry He then analyzing the glass).
- the thus-dried silica soot preform may be consolidated in an atmosphere containing H 2 O.
- OH concentration and distribution thereof in the final, consolidated glass may be controlled at the desired level.
- oxygen may be used in the consolidation atmosphere to remove or re-oxidize any oxygen deficient silica species that may have been created.
- the soot preform may be consolidated in the presence of H 2 as well.
- the consolidated glass is further subject to a heat treatment in the presence of H 2 for an effective period of time so that the H 2 concentration in the final glass reaches a desired level.
- the H 2 concentration in the final glass as well as the temperature at which the H 2 treatment is undergone affect the polarization-induced birefringence level and behavior of the final glass as well. It has been found that H 2 treatment at a temperature below 800 0 C is preferred for a low polarization-induced birefringence value especially for glasses having OH less than about 100 ppm by weight. However, to expedite the H 2 treatment process, it is desired that the treatment temperature is at least 300 0 C.
- Fused silica glass was made using both the so-called direct-to-glass as well as the soot-to-glass processes. For the latter, silica particles are deposited on a substrate which results in a soot blank. In a second step, this blank is consolidated to a solid glass blank. The OH (or water) content of the glass is controlled during consolidation. In a third step, near-net-shape pieces of the glass blank are loaded with molecular hydrogen at elevated temperatures to various target concentrations. [0065] Exposure and Measurements [0066] The bar-shaped fused silica samples were exposed using light from an ArF excimer laser running at a repetition rate of 4000 Hz. The pulse length was about 25 ns.
- the beam diameter was 3 mm, imposed by an aperture, and its shape was approximately top-hat.
- the light beam was rendered polarized where necessary by using commercially available linear polarizer or circular polarizer where applicable.
- Typical sample size was 20x25x100 mm 3 and the exposing beam, polarized or not as desired, was directed through the center of the sample parallel to the long axis.
- the samples were taken off the exposure setup about every 4 billion pulses and birefringence was mapped at a wavelength of 633 nm using a commercial birefringence measurement system.
- wavefront distortion was measured in 633 nm and 193 nm interferometers.
- FIG. 1 shows the two-dimensional birefringence map of a sample glass exposed to a circularly polarized light beam.
- the birefringence magnitude is grey-scale coded as shown on the right hand side of the map.
- the white lines indicate the direction of the slow axis of the glass in that particular location. Their length also codes the magnitude.
- This map shows high induced edge birefringence, yet the polarization-induced birefringence in the center portion of the exposed area is near zero.
- FIG. 2 shows an extreme example of linearly-polarized light beam exposed sample insofar as it barely has (on the scale chosen there) any birefringence outside of the exposed area.
- FIG. 3 shows that the ratio between the polarization-induced birefringence in the center of the exposure spot and the induced edge birefringence - observed in the unexposed glass surrounding the exposure area - can vary substantially. It has also been observed that the level of polarization-induced birefringence decreases with continued exposure if the polarization is switched midway to the orthogonal polarization. This is consistent with expectation for strain-optical response from anisotropic strain correlated with the direction of linear polarization, described below.
- FIG. 3 shows a two-dimensional birefringence map of another sample exposed to linearly polarized light beam.
- the birefringence values of the vertical cross-section are shifted upward by 0.4 nm/cm. Due to the symmetry, the direction of the slow axis on the vertical cross-section does not change direction at all. So the only obvious difference from a circular exposure is the non-zero value at the center of the exposure spot. In the horizontal direction the slow birefringence axis changes direction from being vertical inside the exposure spot to horizontal outside of it.
- FIG. 5 also suggests the polarization-induced birefringence value is linearly dependent on the fluence of the exposing light beam at a given laser pulse length.
- FIG. 5 does not directly show saturation of polarization-induced birefringence with exposure, but saturation has been observed at higher doses.
- FIG. 6 shows the polarization-induced birefringence value of certain samples having essentially the same composition and processing condition at a given number of pulse count as a function of the fluence of the light beam.
- PIB a-N-F with a being a sample- dependent factor, N being the number of pulses, F being the fluence and PIB ⁇ being the level of polarization-induced birefringence.
- this factor is shown (coded as symbol size) vs. H 2 treatment temperature after consolidation and OH concentration in the glass for different samples.
- FIG. 8 the data of certain samples in FIG. 5 are re- plotted in a normalized PIB - OH Concentration (ppm) diagram. From FIGS.
- ⁇ tJ is a component of strain (gradient of displacement) and the coordinate axes are chosen to place z along the path of exposing light through the sample and x and y are along the ellipse axes for elliptical polarization.
- Linear polarization is a special case of elliptical polarization; when elliptical polarization is being considered, then the individual strain components are different linear combinations of D and A depending on the ellipse shape.
- D and A hold for arbitrary elliptical polarization.
- D and A which are typically of order 10 '6 for laser damage studies.
- a finite element elastic analysis was performed to calculate the final elastic strains (and stresses) that result from the initial strains defined by D and A That is, elastic analysis is needed in order to account for sample geometry and boundary conditions. In this step the actual illumination profile is incorporated.
- the strain-optical formulation is used to calculate changes in the "impermeability tensor" AB given by
- p ljU is the strain-optical tensor
- a ⁇ k are the elastic response strains that depend on the initial strains and the sample geometry and illumination profile
- r ljkl is a separate strain-optical tensor associated with permanent strains
- ⁇ k ° l are the initial or unconstrained strains that appeared in Eqs. (1) and (2). Summation over repeated indices is implied.
- the use of a special strain-optical tensor for permanent strains, as opposed to elastic strains, is needed based on the difference in optical response observed for permanent strains vs. elastic strains.
- strain-optical tensor p ljkl is well known in the literature and characterized for a range of wavelengths for silica
- the permanent-strain strain-optical tensor r u is less well established and is a subject of study.
- R cD + dA (5) [0077] where a, b, c, and d are geometry - and illumination - dependent constants, ⁇ inL) — - is the change in optical path per unit length (the LIWFD mentioned above), and R
- birefringence magnitude polarization-induced birefringence or PIB
- d' is used to distinguish the constant of proportionality from d .
- PIB is directly proportional to unconstrained anisotropy A and completely independent of unconstrained density D.
- a, b, c, and d depend on the elastic properties (Young's modulus and Poisson ratio) and on the strain-optical constants p a and the tensor r ⁇ 1 .
- the latter two tensors only have two independent constants each in isotropic glass; these are denoted p n and p l2 , and analogously r n and r n .
- the presence of these strain-optical constants makes the linear coefficients a, b, c, and d also dependent on the wavelength of the measurement light.
- FIG. 9 shows calculated results in the form of a two-dimensional birefringence map as obtained from a fit to the experimental data from above in FIG. 3. All main features observed in the experimental data are well reproduced: the ring-shaped birefringence maximum, the radial pattern outside of the exposure spot, and the non-zero birefringence in the center of exposed region. Horizontal and vertical cross-sections of FIG. 9 are shown in FIG. 10. The horizontal cross-section shown in FIG. 10 exhibits the two dips close to the edge of the spot.
- model grid was chosen to agree with the limited spatial resolution of the measurement system (about 0.5 mm), and model calculated results include smoothing in proportion to the measured beam profile.
- FIG. 11 contains a fit to the experimental data from FIG. 2. This is a sample with dominant anisotropy and relatively small density change. As in the previous example, the experimental features are reproduced: the virtual absence of birefringence outside of the exposed area and the strong center birefringence with all the slow axes aligned vertically.
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Abstract
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Priority Applications (2)
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DE112005003341.4T DE112005003341B4 (en) | 2004-12-30 | 2005-12-29 | Synthetic silica with low polarization-induced birefringence, process for producing the same and lithographic apparatus comprising the same |
JP2007549650A JP5538679B2 (en) | 2004-12-30 | 2005-12-29 | Synthetic silica having low polarization-induced birefringence, method for producing the silica, and lithographic device comprising the silica |
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US64069604P | 2004-12-30 | 2004-12-30 | |
US60/640,696 | 2004-12-30 | ||
US64986005P | 2005-02-02 | 2005-02-02 | |
US60/649,860 | 2005-02-02 | ||
US69610605P | 2005-06-30 | 2005-06-30 | |
US60/696,106 | 2005-06-30 | ||
US11/241,075 | 2005-09-30 | ||
US11/241,075 US7589039B2 (en) | 2004-12-29 | 2005-09-30 | Synthetic silica having low polarization-induced birefringence, method of making same and lithographic device comprising same |
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DE (1) | DE112005003341B4 (en) |
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US7635658B2 (en) * | 2005-11-07 | 2009-12-22 | Corning Inc | Deuteroxyl-doped silica glass, optical member and lithographic system comprising same and method of making same |
JP2013075827A (en) * | 2005-11-07 | 2013-04-25 | Corning Inc | Deuteroxyl-doped silica glass, optical member and lithographic system comprising the glass and method for making the glass |
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- 2005-12-29 WO PCT/US2005/047452 patent/WO2006074083A1/en active Application Filing
- 2005-12-29 TW TW094147460A patent/TWI312768B/en active
- 2005-12-29 JP JP2007549650A patent/JP5538679B2/en active Active
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DE112005003341T5 (en) | 2008-02-28 |
TW200704604A (en) | 2007-02-01 |
JP2008526672A (en) | 2008-07-24 |
TWI312768B (en) | 2009-08-01 |
DE112005003341B4 (en) | 2019-01-31 |
JP5538679B2 (en) | 2014-07-02 |
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