JP5349721B2 - Optical glass with small refractive index change by light irradiation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical glass excellent in beam resistant, suppressing refraction gradient generated by a laser irradiation of 300-400 nm or a high-power ultraviolet ray. SOLUTION: After a pulsed laser at a wavelength of 351 nm (an average output power is 0.43 W, a pulse repetition rate is 5 kHz, a pulse width is 400 ns) is irradiated to glass for an hour, a variation of an index of refraction (Δn is a difference of the index of refraction between before and after irradiation) is below 5 ppm.

Description

  The present invention relates to an optical glass that is less deteriorated by light irradiation in an optical glass used in the near-ultraviolet light region, and in particular, changes in the refractive index due to irradiation with a strong light beam having a light wavelength of 300 to 400 nm (for example, an ultrahigh pressure mercury lamp or an ultraviolet laser). Of small optical glass.

As one of optical systems using near-ultraviolet rays, an optical lithography technique for exposing and transferring a fine pattern of an integrated circuit onto a wafer such as silicon, that is, an exposure apparatus (i) using i-line (365 nm) of an ultra-high pressure mercury lamp. Line stepper) is known. In recent years, the exposure area of this exposure apparatus has been increased with the high integration of LSI, and in general, a lens having a diameter of 200 mm or more is used for the optical system of the i-line stepper, and the lens is used for the lens. The optical glass for i-line has very high refractive index homogeneity, and the internal transmittance of i-line at the glass thickness = 10 mm is 99% or more and the deterioration of the transmittance due to ultraviolet irradiation (solarization). It is necessary that there is no.
Therefore, the optical glass for i-line is manufactured in the establishment of technologies such as adoption of high-purity raw materials with less impurities, preparation of raw materials and cleaning of the melting process, high-homogeneous melting, and strain removal by precision annealing.
However, the i-line stepper is required to have higher integration, exposure / transfer processing capability and long-term durability, and the optical glass lens used for it has high homogeneity, high transmittance, and solar resistance. It has been demanded that resistance to high-power i-ray light irradiation, that is, a change in refractive index due to i-ray irradiation is small, along with the characterization.

The so-called compaction phenomenon in which the refractive index changes due to light irradiation is a synthetic quartz glass that is irradiated with high-power ultraviolet excimer laser light for a long period of time, causing a change in density along with a change in transmittance, resulting in a change in refractive index and glass surface shape. It has been known.
Synthetic quartz glass is produced by burning silicon tetrachloride with an oxyhydrogen flame to synthesize silicon oxide fine powder, and heating and solidifying the silicon oxide fine powder at a high temperature.
That is,
SiCl ₄ + 2O ₂ + 4H ₂ → SiO ₂ + 4HCl + 2H ₂ O
It is synthesized by the reaction of
The compaction phenomenon in synthetic quartz glass is caused by moisture-induced ions (ions such as OH ^- and H ⁺ ) remaining in the synthetic quartz glass during synthesis and the breakage of Si-O bonds due to incomplete reaction. ing.

Further, it has not been specifically known that the compaction phenomenon occurs in the optical glass for i-line used for i-line irradiation.
However, surprisingly, in the optical glass for i-line as well as conventionally known for synthetic quartz glass, the refractive index changes in the portion irradiated with high-power ultraviolet light or laser light in the wavelength region of 300 to 400 nm. It has been found that the homogeneity is deteriorated due to the above, the distortion is increased, and the glass surface shape is deformed, and the optical glass for i-line does not have sufficient light resistance. Therefore, such an optical system using glass causes deterioration in imaging performance, and may cause problems in higher integration of LSI and improvement in processing capability of exposure / transfer than in the past.

Problems to be solved by the invention

  Accordingly, an object of the present invention is to provide an optical glass excellent in light resistance, in which a change in refractive index caused by irradiation with high-power ultraviolet light or laser light in the wavelength region of 300 to 400 nm is suppressed.

Means for solving the problem

As a result of intensive studies and research to achieve the above object, the present inventors have unexpectedly caused light irradiation by containing a fluorine component and / or a titanium oxide component and / or an arsenic oxide component as a glass component. It has been found that the refractive index change is reduced. Specifically, in (1) SiO ₂ -PbO-alkali metal oxide glass, a relatively small amount of fluorine component and / or Sb is used as a glass refining agent. containing the As ₂ O ₃ component in place of the ₂ O ₃ component and / or the content of TiO ₂ component of very small amounts of negligible influence on the _{transmission, (2) SiO 2 -B 2} O 3 - alkali metal In oxide and / or alkaline earth metal oxide glass, As ₂ O ₃ component is used instead of Sb ₂ O ₃ component as a fluorine component and / or glass refining agent. Containing and / or containing a very small amount of TiO ₂ component with negligible influence on transmittance, (3) In P ₂ O ₅ -Al ₂ O ₃ -alkaline earth fluoride glass, a refining agent and It has been found that a glass having a small refractive index change by ultraviolet light irradiation can be obtained by containing no TiO ₂ component or adding a very small amount of at least one of these components.

That is, the optical glass of the present invention according to claim 1 for achieving the above object is characterized in that a pulse laser beam having a wavelength = 351 nm (average output power = 0.43 W, pulse repetition number ( Pulse Repetition Rate) = 5 kHz, pulse width (Pulse Width = 400 ns) after irradiation for 1 hour, the amount of change in refractive index (Δn: difference in refractive index before and after irradiation) is 5 ppm or less, in terms of mass%, SiO 2 ₂ 40-70%, PbO 14-50%, Na ₂ O 0-14%, K ₂ O 0-15%, provided that the total amount of Na ₂ O and / or K ₂ O is 8-17%, B ₂ O _{3 to} 5%, Sb ₂ O ₃ 0 to 1%, TiO ₂ 0 to 0.2%, and the total amount of F of one or more fluorides as the fluorine component 0.1 to 2 % and oxidation as ₂ O ₃ 0.001~1% as arsenic component, there is to contain l ₂ O ₃ 0~0.4%.

The optical glass of the present invention according to claim 1 is characterized in that, in the optical glass according to claim 4, Li ₂ O 0-2%, CaO 0-2%, SrO 0-2%, BaO 0 to 5%, Al ₂ O ₃ 0 to 0.4 %, provided that the total amount of one or more of the above components is 5% or less.

  First, in the optical glass of the present invention, a pulse laser beam having a wavelength = 351 nm (Average Output Power = 0.43 W, Pulse Repetition Rate = 5 kHz, Pulse Width = Pulse Width = 400ns) is the reason why the amount of change in refractive index after irradiation for 1 hour (Δn: difference in refractive index before and after irradiation) is set to 5 ppm or less. For glass that satisfies the conditions, even when irradiated with high-power ultraviolet light or continuous laser light in the wavelength region of 300 to 400 nm, there is no deterioration in homogeneity due to changes in refractive index, distortion, or deformation of the glass surface shape. Have sufficient light resistance as an optical glass for i-line, and an optical system using such glass does not deteriorate the imaging performance as described above. In high integration and exposure and transfer, it has been found, which may correspond to the processing capabilities improve.

Next, the reason why each component is limited to the composition range is as follows. That is, in the SiO ₂ -PbO-alkali metal oxide glass, the SiO ₂ component is an indispensable component for glass formation, and the unique characteristics of the SiO ₂ -PbO glass can be derived in combination with the PbO component. it can. However, if the amount is less than 40%, the refractive index becomes too high and the light transmittance is not sufficient in a short wavelength region, which makes it unsuitable for an optical system using i-line such as an i-line exposure apparatus. Moreover, when it exceeds 70%, the viscosity of glass will become high too much and it will become difficult to obtain homogeneous glass.

  The PbO component is an effective component for making the glass highly refracted and highly dispersed and appropriately reducing the viscosity of the glass. However, if the amount is less than 14%, the glass is hard and it is difficult to obtain a homogeneous glass, and if it exceeds 50%, the refractive index becomes too high and it is difficult to obtain a sufficiently high light transmittance in the short wavelength region. .

The Na ₂ O component and the K ₂ O component are effective for promoting the melting of the SiO ₂ component and the PbO component in the glass raw material and adjusting the viscosity of the glass. However, if the amount of Na ₂ O component exceeds 14% and that of K ₂ O component exceeds 15%, chemical properties such as weather resistance and acid resistance of the glass are liable to deteriorate, which is not preferable. Further, if the total amount of both components is less than 8%, the above effect is insufficient, so that the viscosity of the glass becomes too high to obtain a homogeneous glass, and the total amount of both components exceeds 17%. Then, chemical properties such as weather resistance and acid resistance of the glass easily deteriorate.

The B ₂ O ₃ component can be added to the glass as an optional component and works as a glass forming component in the same manner as the SiO ₂ component. However, when it is contained in a large amount in the SiO ₂ -PbO-alkali metal oxide glass, the chemical properties Therefore, the amount is preferably 5% or less.

The As ₂ O ₃ component and the Sb ₂ O ₃ component have an effect as a glass refining aid, and further, the As ₂ O ₃ component has an effect of suppressing the compaction phenomenon of the glass, and can be arbitrarily added respectively. However, in order to obtain the above effects, each up to 1% or less is sufficient. Further, when the fluorine component and the TiO ₂ component are not present in the SiO ₂ -PbO-alkali metal oxide glass, the As ₂ O ₃ component is added in an amount of 0.001 to 1 in order to reduce the refractive index change due to the compaction phenomenon. % Should be added.

The TiO ₂ component is effective in adjusting the refractive index and Abbe number of the glass, and suppressing the compaction phenomenon and solarization of the glass due to the irradiation of high-power ultraviolet light and laser light. Since the light transmittance is deteriorated, the amount is preferably 0.2% or less. Further, when the fluorine component and the As ₂ O ₃ component are not present in the SiO ₂ -PbO-alkali metal oxide glass, the TiO ₂ component is added in an amount of 0.001 to 0 in order to reduce the refractive index change due to the compaction phenomenon. .2% should be added.

The fluorine component can be optionally added as a fluoride substituted with one or two or more of the above oxides, suppressing the compaction phenomenon of glass due to irradiation with high-power ultraviolet light or laser light, Effective for adjusting refractive index and viscosity. However, if the total amount of the fluoride exceeds 2%, the volatilization of the fluorine component becomes too large and it becomes difficult to obtain a homogeneous glass. Further, when the As ₂ O ₃ component and the TiO ₂ component are not present in the SiO ₂ —PbO—alkali metal oxide glass, the total amount of the fluorides is set to 0.00% in order to reduce the refractive index change due to the compaction phenomenon. It should be 1-2%.

Further, the SiO ₂ —PbO-alkali metal oxide glass of the present invention includes Li ₂ O component, CaO component as optional components for adjusting the viscosity, refractive index, chemical properties, stability, etc. of the glass. Each of the SrO component and the Al ₂ O ₃ component can be contained up to 2%, and the BaO component can be contained up to 5%. However, the total amount of one or more of the Li ₂ O component, CaO component, SrO component, Al ₂ O ₃ component and BaO component should be 5% or less.

Next, in the SiO ₂ -B ₂ O ₃ -alkali metal oxide and / or alkaline earth metal oxide glass, the SiO ₂ component is formed in the same manner as the SiO ₂ -PbO-alkali metal oxide glass. It is an essential ingredient. However, if the amount is less than 30%, a relatively large amount of components such as B ₂ O ₃ and BaO are required, and the refractive index becomes too high or the chemical properties are deteriorated, which is not preferable. Moreover, when it exceeds 70%, the viscosity of glass will become high too much and it will become difficult to obtain homogeneous glass.
The B ₂ O ₃ component is a glass-forming oxide like the SiO ₂ component, and is effective for reducing the dispersion of the glass and adjusting the viscosity of the glass. However, if the amount is less than 3%, the effect is insufficient, and if it exceeds 20%, the chemical properties deteriorate, which is not preferable. The Al ₂ O ₃ component is effective in improving the chemical durability of the glass and adjusting the viscosity and refractive index. However, if the amount exceeds 6%, the viscosity of the glass becomes too high.

The Li ₂ O component is effective because it has an effect of accelerating melting of the glass raw material, and is less likely to cause a decrease in refractive index and chemical properties as compared with other alkali metal oxides. However, if the amount exceeds 5%, the devitrification of the glass increases, which is not preferable.

The Na ₂ O component and the K ₂ O component are effective for accelerating melting of the glass raw material, and even if a large amount is contained in the glass, a stable glass is produced. However, if the amount of Na ₂ O component and K ₂ O component exceeds 13% and 12%, respectively, the chemical properties are deteriorated, which is not preferable.

  The BaO component can improve the refractive index without significantly increasing the dispersion of the glass (without reducing the Abbe number too much), and can provide a stable glass having high devitrification resistance in a wide composition range. However, when the amount exceeds 42%, the chemical durability of the glass is extremely deteriorated.

  The ZnO component is an effective component for improving the refractive index, adjusting the viscosity, and improving the devitrification resistance. However, if the amount exceeds 7%, the light transmittance in the short wavelength region may be lowered. Because there is, it is not preferable.

In addition, in order to obtain a glass that is stable and excellent in chemical properties and has good light transmittance up to a short wavelength region, one or more of Na ₂ O component, K ₂ O component, BaO component and ZnO component are used. The total amount of is preferably 10% to 45%.

The PbO component and the TiO ₂ component are effective in preventing glass solarization in SiO ₂ —B ₂ O ₃ —alkali metal oxide and / or alkaline earth metal oxide glass. Furthermore, the TiO ₂ component is effective in suppressing the so-called compaction phenomenon. However, if these components are contained in an excessive amount, the light transmittance in the short wavelength region is deteriorated. Therefore, the amount of these components is preferably up to 2% and 0.5%, respectively. In addition, when the fluorine component and the As ₂ O ₃ component are not present in the SiO ₂ —B ₂ O ₃ —alkali metal oxide and / or alkaline earth metal oxide glass, the refractive index change due to the compaction phenomenon is reduced. Therefore, 0.001 to 0.5% of TiO ₂ component should be added.

As ₂ O ₃ component and S component have an effect as a glass refining aid,
Further, the As ₂ O ₃ component has an effect of suppressing the compaction phenomenon of glass and can be arbitrarily added. However, up to 1% or less is sufficient for obtaining the above effect. In addition, when the fluorine component and the TiO ₂ component are not present in the SiO ₂ -B ₂ O ₃ -alkali metal oxide and / or alkaline earth metal oxide glass, in order to reduce the refractive index change due to the compaction phenomenon 0.001 to 1% of the As ₂ O ₃ component should be added.

The fluorine component can be optionally added as a fluoride substituted with one or two or more of the above oxides, suppressing the compaction phenomenon of glass due to irradiation with high-power ultraviolet light or laser light, Effective for adjusting refractive index and viscosity. However, if the total amount of the fluoride exceeds 11%, the glass becomes milky, the refractive index becomes too small, or the volatilization of the fluorine component becomes too large at the time of melting, so that it is difficult to obtain a homogeneous glass. It is not preferable because it becomes. Further, when the As ₂ O ₃ component and the TiO ₂ component do not exist in the SiO ₂ -B ₂ O ₃ -alkali metal oxide and / or alkaline earth metal oxide glass, the refractive index change due to the compaction phenomenon is reduced. Therefore, the total amount of the fluoride should be 0.1 to 11%.

In addition to the above components, one or two selected from a CaO component, a SrO component and a ZrO ₂ component are optionally used for the purpose of adjusting the refractive index and improving the chemical properties of the glass. The above may be added up to 2% in total.

Next, in the P ₂ O ₅ —Al ₂ O ₃ —alkaline earth fluoride glass, the P ₂ O ₅ component is a glass forming component, and if the amount is less than 4%, the devitrification resistance is excellent. It is difficult to obtain a stable glass, and if it exceeds 39%, the Abbe number of the glass becomes too small and it becomes difficult to obtain the merit (low dispersibility) of the present composition system.

The Al ₂ O ₃ component is a component that forms a glass structure when present together with the P ₂ O ₅ component, and is effective in improving the chemical properties of the glass. However, if the amount exceeds 9%, devitrification increases.

  Each component of MgO, CaO, SrO and BaO is usually contained in the glass as a phosphate, which is useful for improving the stability and chemical durability of the glass, adjusting the refractive index and the Abbe number, and the like. However, if the amount of each of these components exceeds 5%, 6%, 9% and 10%, respectively, the glass tends to be devitrified, which is not preferable. Moreover, in order to make glass which does not easily cause devitrification, the total amount of one or more of these components is more preferably 20% or less.

Each component of Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ increases the refractive index without lowering the Abbe number, prevents the glass from devitrifying, and further improves the chemical durability of the glass. Has the effect of improving the performance. However, if the amount of each of these components exceeds 10%, 10%, 20% and 10%, respectively, devitrification resistance is deteriorated. Further, if the total amount of one or more of these components exceeds 20%, the devitrification resistance of the glass deteriorates, which is not preferable.

The TiO ₂ component has the effect of improving the refractive index of the glass, preventing solarization, and reducing the refractive index change due to the compaction phenomenon. Therefore, the TiO ₂ component can be optionally added as necessary. An amount of 0.1% or less is sufficient, and if it exceeds 0.1%, the light transmittance in the short wavelength region of the glass deteriorates, which is not preferable.

The SnO ₂ component is effective for improving the refractive index of glass and preventing devitrification. However, an amount of 1% or less is sufficient.

The As ₂ O ₃ and Sb ₂ O ₃ components have an effect as a glass refining aid, and further, the As ₂ O ₃ component has an effect of suppressing the compaction phenomenon of the glass. The amount of each is 0.5% or less.

The AlF ₃ component reduces the dispersion of the glass and is effective in preventing devitrification. However, if the amount exceeds 29%, the glass becomes unstable and crystals tend to be formed in the glass.

Each component of MgF ₂ , CaF ₂ , SrF ₂ and BaF ₂ is effective for suppressing devitrification of the glass. If the amount of BaF ₂ is less than 10%, it becomes difficult to obtain a chemically stable glass. If MgF ₂ exceeds 8%, CaF ₂ exceeds 27%, SrF ₂ exceeds 27% and BaF ₂ exceeds 47%, devitrification tends to occur. Further, the total amount of one or more of MgF ₂ , CaF ₂ , SrF ₂ and BaF ₂ components is suitably 30 to 70%.

Each component of YF ₃ , LaF ₃ and GdF ₃ is effective in increasing the refractive index of the glass and improving the devitrification resistance, but these amounts are each suitably 10% or less.

  Each component of LiF, NaF and KF has the effect of improving the devitrification resistance of the glass, but when these amounts exceed 3%, 1% and 1%, respectively, they tend to devitrify and are not suitable. .

Furthermore, in P ₂ O ₅ —Al ₂ O ₃ —alkaline earth fluoride glass, the total of F contained in one or more of the above fluorides is used to reduce the refractive index change of the glass due to the compaction phenomenon. Suitably the amount is in the range of 10-45%. In addition, the oxide and fluoride may be appropriately replaced with oxide and fluoride within a range that maintains the ratio of the respective metal ions, oxygen ions, and fluorine ions.

Next, the Example concerning the optical glass of this invention is described. Example composition examples No. 1 to Table 4 1-No. 24 is an implementation composition example of the SiO ₂ —PbO—alkali metal oxide glass according to the present invention. Moreover, the implementation composition example No. shown in Table 5-Table 6 is shown. 25-No. 38 is an example of the practical composition of the SiO ₂ —B ₂ O ₃ —alkali metal oxide and / or alkaline earth metal oxide glass according to the present invention. In addition, Examples Nos. 7 to 9 shown in Tables 7 to 9 were used. 39-No. 59 is an implementation composition example of the P ₂ O ₅ —Al ₂ O ₃ —alkaline earth fluoride glass according to the present invention.
Further, Table 10 shows an example of composition No. of the SiO ₂ —PbO—alkali metal oxide glass according to the present invention. 60-No. 64 and comparative glass composition example No. A and No. Comparison with B (Comparison I and Comparison II)
Table 11 shows practical composition Nos. Of SiO ₂ —B ₂ O ₃ —alkali metal oxide and / or alkaline earth metal oxide glass according to the present invention. 65 and no. No. 66 and conventional glass composition No. C and No. Comparison with D (Comparison III and Comparison IV) is shown.

In addition, Δn (ppm) shown in Tables 1 to 11 is a pulse laser beam having a beam diameter = 2.0 mm and a wavelength = 351 nm (Average Output Power = 0.43 W, pulse repetition rate (Pulse Repetition Rate). ) = 5 kHz, pulse width (Pulse Width = 400 ns) under irradiation conditions of irradiation time = 1 hour, the amount of change in refractive index before and after irradiation of the portion irradiated onto the glass is shown.
Table 12 shows the composition example No. of the SiO ₂ —PbO—alkali metal oxide glass according to the present invention. 67-No. No. 70 and examples of composition No. of SiO ₂ —B ₂ O ₃ —alkali metal oxide and / or alkaline earth metal oxide glass according to the present invention. 71-No. 73, Table 13 shows the portion of the glass shown in Table 12 irradiated with the output of the laser (wavelength 351 nm, beam diameter = 2.0 mm) and the irradiation time with the irradiation conditions being different from those in Tables 1 to 11. The amount of change in refractive index before and after irradiation: Δn (ppm) is shown.

As seen in Tables 1 to 12, Example Composition Nos. 1-No. In each of the glasses No. 73, the amount of change in refractive index (Δn) before and after laser irradiation was 5 ppm or less. 60-No. No. 66 is a comparative composition example No. 66 in which the contents of SiO ₂ , PbO, B ₂ O ₃ , alkali metal oxides, BaO, etc., and nd and νd are similar to those of these example compositions. A-No. Compared with the conventional glass of D, the refractive index change amount (Δn) before and after laser irradiation is small, indicating the effect of containing a fluorine component and / or a titanium oxide component and / or an arsenic oxide component.

  In addition, the glasses of the above-mentioned embodiment examples of the present invention are all prepared by weighing and mixing raw materials for optical glass such as oxides, carbonates, nitrates, hydroxides, phosphates, fluorides, and the like. It is easily manufactured by melting, clarifying, stirring and homogenizing at 900-1500 ° C. for about 3-10 hours using a quartz container, etc., cooling to a predetermined temperature, casting into a preheated mold, and slow cooling. be able to.

Effect of the invention

As described above, the optical glass according to the present invention has a pulse laser beam having a wavelength of 351 nm (Average Output Power = 0.43 W, pulse repetition rate = 5 kHz, pulse width = Pulse Width = 400 ns) is an optical glass having a refractive index change amount (Δn: difference in refractive index before and after irradiation) of 5 ppm or less after irradiation for 1 hour, and also a fluorine component and / or a titanium oxide component and / or an arsenic oxide SiO ₂ —PbO-alkali metal oxide glass containing a fluorine component and / or a titanium oxide component and / or an arsenic oxide component in a specific composition range, or a specific composition range containing a fluorine component and / or titanium oxide component and / or arsenic oxide ingredient SiO ₂ -B ₂ O ₃ - alkali metal P ₂ O ₅ -Al ₂ O ₃ containing a fluorine component and / or titanium oxide component and / or arsenic oxide ingredient compound and / or alkaline earth metal oxide glass or a specific composition range, - an alkaline earth fluoride Since it is a compound glass, the amount of change (Δn) in the refractive index of the portion of the glass irradiated with high-power ultraviolet light or laser light in the wavelength region of 300 to 400 nm is small. Therefore, when the optical glass of the present invention is used in a high-precision optical system that uses light beams with a high energy density such as high-power ultraviolet light and laser light in the wavelength region of 300 to 400 nm, the glass homogeneity deteriorates, the glass The distortion of the image and the deformation of the glass surface shape hardly occur, so that the image is not distorted or blurred. As described above, the glass of the present invention is very useful. For example, when the optical glass of the present invention is used as an i-line stepper optical system or illumination system lens, high-resolution LSI pattern exposure / transfer can be performed at a high resolution. Can be done.

Claims (2)

After irradiating the glass with pulse laser light having a wavelength = 351 nm (Average Output Power = 0.43 W, Pulse Repetition Rate = 5 kHz, Pulse Width = 400 ns) for 1 hour The amount of change in refractive index (Δn: difference in refractive index before and after irradiation) is 5 ppm or less, and in mass%, SiO ₂ 40 to 70%, PbO 14 to 50%, Na ₂ O 0 to 14%, K ₂ O 0-15%, provided that the total amount of Na ₂ O and / or K ₂ O is 8-17%, B ₂ O ₃ 0-5%, Sb ₂ O ₃ 0-1%, TiO ₂ 0-0.2% and, the total amount from 0.1 to 2% of F in one or more of fluoride as a fluorine component and _as 2 _O 3 _0.001~1% as arsenic oxide component, _Al 2 O 3 0 to 0.4 % Optical glass.
By mass%, Li ₂ O 0-2%, CaO 0-2%, SrO 0-2%, BaO 0-5%, Al ₂ O ₃ 0-0.4%, provided that one or two of the above components are used. The optical glass according to claim 1, comprising a total amount of 5% or less of seeds or more.