Precision component

Abstract

The present invention relates to a precision component and also to a glass-ceramic which can be used for producing the precision component.

Claims

1. A precision component comprising at least one inorganic material whose differential CTE in a temperature interval T.sub.P having a width of at least 40 K is less than 00.015 ppm/K and/or in a temperature interval T.sub.p having a width of at least 50 K is less than 00.025 ppm/K, wherein the inorganic material is a LAS-glass-ceramic comprising a main crystal phase comprising a high-quartz solid solution, wherein the LAS-glass-ceramic comprises Li.sub.2O in a range from 7 to 12 mol %, and wherein if Al.sub.2O.sub.3<17.0 mol %, then SiO.sub.264.0-65.6 mol %, and 30.7(molar amount of SiO.sub.2-(2 times molar amount of Al.sub.2O.sub.3))<34.0; or if Al.sub.2O.sub.317.0 mol %, then SiO.sub.2 62.0-66.0 mol %, and 142.5(molar amount of SiO.sub.2+(4.6 times molar amount of Al.sub.2O.sub.3)) 149.0.

2. The precision component according to claim 1, where the temperature interval T.sub.P is in a range from 10 to +100 C.

3. The precision component according to claim 1, where a CTE-T curve of the precision component in a temperature interval T.sub.P having a width of at least 30 K has a gradient of at most 10 x 10.sup.-4 ppm/K.sup.2.

4. The precision component according to claim 1, having an edge length or a diameter of at least 100 mm and/or less than 500 mm and/or a thickness of less than 50 mm and/or at least 1 mm.

5. The precision component according to claim 1, where the precision component is selected from the group consisting of astronomic mirrors, mirrors for EUV lithography, reticle masks for EUV lithography, reference frames or grid plates for microlithography, mirrors or prisms for LCD lithography, and components for metrology or spectroscopy.

6. A method of using of a precision component in astronomy, in precision measurement technology, in LCD lithography or in microlithography, comprising making precision measurements with the precision component of claim 1.

7. An astronomic mirror comprising the precision component of claim 1.

8. A stepper for LCD lithography or for microlithography comprising the precision component of claim 1.

9. The precision component according to claim 1, wherein the precision component comprises a glass-ceramic comprising the following composition (in mol % based on oxide): TABLE-US-00005 SiO.sub.2 62.0-66.0 Al.sub.2O.sub.3 10-25 P.sub.2O.sub.5 1-10 TiO.sub.2 >0.sup. ZrO.sub.2 0-5 TiO.sub.2 + ZrO.sub.2 2.0 Li.sub.2O 7-12 Na.sub.2O 0-2 K.sub.2O 0-2 MgO 0.1-5.sup. CaO 0-5 BaO 0-5 SrO 0-5 ZnO >0-5.

10. The precision component according to claim 9, where the sum of the molar amounts of ZnO and MgO is at least 2.0 mol %.

11. The precision component according to claim 1, for which applies if molar amount of Al.sub.2O.sub.3<17.0 mol %, then Al.sub.2O.sub.315.8 mol %.

12. The precision component according to claim 9, where the sum of the molar amounts of ZnO+MgO +Li.sub.2O is at least 10.0 mol %.

13. The precision component according to claim 9, where the sum of the molar amounts of SiO.sub.2+Al.sub.2O.sub.3+P.sub.2O.sub.5 is 80 to 90 mol %.

14. The precision component according to claim 9, wherein the glass-ceramic comprises at least one of Na.sub.2O and K.sub.2O in an amount of at least 0.05 mol %.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows CTE-T curves of state-of-the-art materials with low linear thermal expansion for precision components.

(2) FIG. 2 shows schematically a preferred compositional range for a glass-ceramic composition, and also the position of inventive examples and comparative examples within this range.

(3) FIG. 3 shows a I/I.sub.0-T curve of a glass-ceramic which can be used for producing a precision component according to the invention, while FIG. 4 shows the associated CTE-T curve.

(4) FIGS. 4 to 6 show CTE-T curves with CTE plateau for glass-ceramics which can be used to produce precision components of the invention.

(5) FIGS. 7 and 8 show CTE-T curves of glass-ceramics without a broad CTE plateau, although the glass-ceramic in FIG. 7 has a zero crossing of the CTE-T curve at more than 40 C.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(6) The precision components of the invention have a CTE plateau; that is, in a temperature interval T.sub.P with a width of at least 40 K or 40 C., the differential CTE lies or is in a range of 00.015 ppm/K, and/or in a temperature interval T.sub.P having a width of at least 50 K it is less than 00.025 ppm/K.

(7) According to further embodiments, it is also possible to select a different or more stringent range for the differential CTE, of, for example, 00.020 ppm/K, 00.010 ppm/K or 00.005 ppm/K. For the 00.010 ppm/K or 00.005 ppm/K case, a temperature interval T.sub.P of at least 30 K, preferably at least 35 K, is already in accordance with the invention.

(8) A restriction on the maximum width of the temperature interval T.sub.P is not desirable in accordance with the invention; it is expected that for a deviation of 00.025 ppm/K plateaus with a width of up to 100 K, possibly up to 150 K or else up to 200 K, are achievable.

(9) The determination of plateaus of the CTE-T curve is generally carried out by first determining the differential CTE(T). The differential CTE(T) is determined as a function of the temperature. The CTE is then defined according to the following formula (1):
CTE(T)=(1/I.sub.0)(I/T)(1)

(10) To produce a I/I.sub.0-T curve or an expansion curve, or to plot the change in length, I/I.sub.0, of a test specimen against the temperature, it is possible to measure the temperature-dependent change in the length of a test specimen from the original length I.sub.0 at the initial temperature t.sub.0 to the length I.sub.t at the temperature t. In this case preferably small temperature intervals of, for example, 5 C. or 3 C. are selected for determining a measurement point. Such measurements may be carried out, for example, by dilatometric methods, interferometric methods, for example the method of Fabry-Perot, i.e. the evaluation of the shift in the resonance peak of a laser beam coupled into the material, or by other suitable methods. The method selected for determining the I/I.sub.0-T measurement points preferably has an accuracy of preferably at least 0.10 ppm, more preferably of at least 0.05 ppm, most preferably of at least 0.01 ppm, and according to certain embodiments even 0.005 ppm. FIG. 3 shows a I/I.sub.0-T curve for a precision component of the invention.

(11) A CTE-T curve is obtained by the derivation of the I/I.sub.0-T curve. From the CTE-T curve it is possible to determine the zero crossing, the gradient of the CTE-T curve, and also the average thermal expansion within a temperature interval.

(12) Surprisingly it was found that precision components having a CTE plateau can be produced. A CTE plateau refers to a range, extending over a section of the CTE-T curve, within which the differential CTE does not exceed a value of 00.015 ppm/K, more preferably 00.010 ppm/K, most preferably 00.005 ppm/K, i.e. a CTE of close to 0 ppb/K. The temperature interval of the CTE plateau is identified as T.sub.P.

(13) It may be advantageous if the temperature interval T.sub.P is in a range from 10 to +100 C., preferably 0 to 80 C.

(14) The position of the CTE plateau is preferably adapted to the application temperature of the precision component. Preferred application temperatures lie in the 60 C. to +100 C. range, more preferably from 40 C. to +80 C. Particular variants of the present invention relate to precision components for application temperatures T.sub.A of 22 C., 40 C., 60 C., 80 C. and 100 C. The CTE plateau, i.e. the curve region with the small deviation in the differential CTE in the temperature interval T.sub.P, may also be situated in the temperature range of [10; 100 C.]; [0; 80 C.], [0; 30 C.], [10; 40 C.], [20; 50 C.], [30; 60 C.], [40; 70 C.] and/or [50; 80 C.].

(15) According to one variant of the invention, the CTE-T curve additionally has at least one curve section with a low gradient in a temperature interval having at least a width of 30 K, preferably 40 K, more preferably 50 K, more particularly a gradient of at most 1010.sup.4 ppm/K.sup.2, i.e. 1 ppb/K.sup.2, preferably at most 810.sup.4 ppm/K.sup.2, and even, according to specific variants, only at most 510.sup.4 ppm/K.sup.2.

(16) According to a further variant, a precision component is provided whose CTE-T curve at a temperature of at least 40 C., preferably at least 45 C., more preferably at least 50 C., and according to one variant at least 60 C., has at least a value of the CTE of at most 00.020 ppm/K, preferably at most 00.010 ppm/K, more preferably at most 00.005 ppm/K. In accordance with this variant of the invention, furthermore, the CTE-T curve may also have one or more zero crossings.

(17) The precision component of the invention preferably has a high total spatial variation of CTE. The value of the total spatial variation of CTE (also referred to as CTE homogeneity, German: CTE Homogenitaet) refers to the peak-to-valley value, i.e. the difference between, respectively, the highest and lowest CTE values of the samples taken. In accordance with the invention, the figure is reported in ppb/K, where 1 ppb/K=0.00110.sup.6/K. The total spatial variation of CTE over the precision component as a whole is at most 5 ppb/K, preferably at most 4 ppb/K, most preferably at most 3 ppb/K.

(18) The precision component preferably comprises an inorganic material selected from the group consisting of doped fused silica, glass-ceramic and ceramic, preferably Ti-doped fused silica, LAS glass-ceramic and cordierite.

(19) One embodiment relates to precision components having relatively small dimensions, more particularly edge lengths (width and/or depth) in the case of (rect)angular forms or diameters, in the case of circular areas, of at least 100 mm and/or less than 500 mm and/or a thickness of less than 50 mm, preferably less than 10 mm and/or at least 1 mm, more preferably at least 2 mm. Precision components of this kind may be employed, for example, in microlithography.

(20) It is also possible, however, to produce very large precision components. One embodiment of the invention therefore relates to components of high volume. For the purposes of this specification, this is intended to refer to a component having a mass of at least 500 kg, preferably at least 1 t, more preferably at least 2 t, and according to one variant of the invention at least 5 t, and/or having edge lengths (width and/or depth), in the case of (rect)angular forms, of at least 0.5 m, more preferably at least 1 m, and a thickness (height) of at least 50 mm, preferably 100 mm, or, in the case of circular forms, having a diameter of at least 0.5 m, more preferably at least 1 m, more preferably at least 1.5 m, and/or having a thickness (height) of at least 50 mm, preferably 100 mm. In the case of specific embodiments of the invention, the components may be even larger, having, for example, a diameter of at least 3 m or at least 4 m or greater. According to one variant, the invention also relates to rectangular components, where preferably at least one surface has an area of at least 1 m.sup.2, preferably at least 1.2 m.sup.2, more preferably at least 1.4 m.sup.2. Produced in general are high-volume components which have a significantly larger base area than height. The process of the invention is also suitable, however, for producing high-volume components having a form approximate to a cube or to a sphere. Such a component may be described not only by the volume and the weight but also by a form factor R=h/d. Here, h corresponds to the height of the component, and d to the diameter. The form factor R=h/d here is defined as the ratio of height h to transverse extent d, with the transverse extent d being the diameter of a cylindrical form and the diagonal of a cuboidal form. Whereas, in the production of certain large-volume components, such as lenses or telescope mirrors, for instance, the form factors are generally below 0.1, there is also a requirement for large-volume components whose form factors are above 0.1, in the range between 0.1 and 0.3, for instance, an example being prisms. A further embodiment of the present invention therefore relates to large-volume components having high form factors, which may be between about 0.1 and 0.3, up to a maximum of about 0.5.

(21) The precision components of the invention are very advantageous, since now a component not only can be optimized for the subsequent application temperature, but also has a low thermal expansion when subject, for example, to higher temperature loads, such as during production, for example. Precision components for microlithography and metrology are customarily used under standard clean-room conditions, more particularly at an ambient temperature of 22 C. The CTE may be adapted to this application temperature. However, such components are subjected to various process steps, such as to coating with metallic layers, for example, and to cleaning, patterning and/or exposure operations, in which the temperatures present may be higher than those prevailing during subsequent use in the clean room. The precision components of the invention, which have a CTE plateau and hence an optimized zero expansion not only at application temperature but also at possibly higher temperatures during production, are therefore very advantageous.

(22) Precision components may be, for example, optical components, and specifically a normal incidence mirror, i.e. a mirror which is operated close to perpendicular radiation incidence, or a grazing incidence mirror, i.e. a mirror which is operated with grazing radiation incidence. Such a mirror comprises the substrate and also a coating which reflects the incident radiation. In the case of a mirror for X-radiation, in particular, the reflective coating is for example a multi-layer system or multilayer having a multiplicity of layers of high reflectivity for non-grazing incidence in the X-ray range. A multi-layer system of this kind for a normal incidence mirror preferably comprises 40 to 200 layer pairs, consisting of alternate layers of one of the material pairings Mo/Si, Mo/Bi and/or MoRu/Be.

(23) The optical elements of the invention may in particular be X-ray-optical elements, i.e. optical elements which are used in conjunction with X-radiation, more particularly soft X-radiation or EUV radiation, and more particularly may be photomasks or reticle masks operated in reflection, especially for EUV (extreme UV) microlithography. With further advantage the precision component can be used as a mirror for EUV lithography.

(24) Furthermore, the precision component of the invention may be a component, more particularly a mirror, for astronomical applications. In that case such components for astronomical application may be used both terrestrially and in space.

(25) The component according to the invention may be a lightweight structure. The component according to the invention may further comprise a lightweight structure. This means that in certain regions of the component, cavities are provided for weight reduction. The weight of a component is preferably reduced, by processing for light weight, by at least 80%, more preferably at least 90%, by comparison with the unprocessed component.

(26) The invention also relates, furthermore, to the use and a method of using of the precision component according to the invention for metrology, spectroscopy and in astronomy, for example as mirror supports for segmented or monolithic astronomic telescopes or else lightweight or ultralight mirror substrates for, for example, space-based telescopes or optics for observation of the Earth, as precision components, such as standards for precision measurement technology, mechanical precision parts, e.g. for ring laser gyroscopes, spiral springs for the horological industry, in LCD lithography, for example as mirrors and prisms, and also in microlithography, for example as mask holders, wafer tables and reference plates, grid plates.

(27) The invention relates further to a glass-ceramic which can be used for producing the precision component according to the invention or to a corresponding method of using.

(28) The invention further relates to an astronomic mirror comprising a precision component according to the invention.

(29) The invention also relates to a stepper for LCD lithography or for microlithography comprising a precision component according to the invention.

(30) The invention also relates to a ring laser gyroscope comprising a precision component according to the invention.

(31) A glass-ceramic in accordance with the invention refers to inorganic, non-porous materials having a crystalline phase and a vitreous phase, with the matrixi.e. the continuous phasegenerally being a glass phase. To produce the glass-ceramic, the components of the glass-ceramic are first of all mixed, melted and refined, and a so-called green glass is cast. The green glass, after cooling, is subjected to control crystallization by reheating. The chemical composition (analysis) of the green glass is the same as that of the glass-ceramic produced from it; ceramization alters only the internal structure of the material. Consequently, in any reference below to the composition of the glass-ceramic, the statement made is equally valid for the precursor of the glass-ceramic, i.e. for the green glass.

(32) The glass-ceramic is an LAS (Lithium-Aluminium-Silicate) glass-ceramic which comprises at least the components SiO.sub.2, Al.sub.2O.sub.3, P.sub.2O.sub.5, ZnO, MgO, Li.sub.2O and TiO.sub.2.

(33) The glass-ceramic comprises the following composition (in mol % based on oxide):

(34) TABLE-US-00002 SiO.sub.2 55-75 Al.sub.2O.sub.3 10-25 P.sub.2O.sub.5 1-10 TiO.sub.2 >0.sup. ZrO.sub.2 0-5 TiO.sub.2 + ZrO.sub.2 2.0 Li.sub.2O 1-15 Na.sub.2O 0-2 K.sub.2O 0-2 MgO 0.1-5.sup. CaO 0-5 BaO 0-5 SrO 0-5 ZnO >0-5

(35) It was surprisingly found that in the vicinity of compositions that are already customary, there are specific new composition ranges for LAS glass-ceramics in which, in contrast to the glass-ceramics already known, it is possible to form a CTE plateau.

(36) The glass-ceramic preferably comprises a fraction of silicon dioxide (SiO.sub.2) of at least 55 mol %, more preferably at least 60 mol %, also preferably at least 61 mol %, also preferably at least 61.75 mol %, further preferably at least 62.0 mol %. The fraction of SiO.sub.2 is preferably at most 75 mol %, more preferably at most 70 mol %, with further preference at most 66.0 mol %. At higher fractions of SiO.sub.2 the batch is more difficult to melt; smaller amounts may be preferred for this reason. In the case of variants with an Al.sub.2O.sub.3 content of less than 17.0 mol %, a fraction of at most 65.5 mol %, preferably 65.25 mol %, possibly even at most 65.0 mol %, may be preferred as an upper limit for SiO.sub.2, and/or, as a more preferred lower limit, at least 63.5 mol %, also preferably at least 63.75 mol %, with further preference at least 64.0 mol % may be appropriate. In the case of variants with an Al.sub.2O.sub.3 content of at least 17.0 mol %, a preferred lower limit for SiO.sub.2 may be at least 62.0 mol %, preferably more than 62.0 mol %. Some advantageous variants may also include at least 62.25 mol %. In the case of variants with an Al.sub.2O.sub.3 content of at least 17.0 mol %, a preferred upper limit for SiO.sub.2 may be 65.75 mol %.

(37) The fraction of Al.sub.2O.sub.3 is preferably at least 10 mol %, more preferably at least 15 mol %, also preferably at least 15.8 mol %, also preferably at least 16.0 mol %, with further preference at least 16.1 mol %, and also preferably more than 16.1 mol %. The fraction of Al.sub.2O.sub.3 is preferably at most 25 mol %, more preferably at most 20 mol %, with further preference at most 19.0 mol %.

(38) In accordance with the invention it was found that a particular ratio of SiO.sub.2 to Al.sub.2O.sub.3, i.e. of the components which form the high-quartz solid solution, may be beneficial to the formation of a CTE plateau. Preferred compositional ranges may be defined by the equation (molar amount of SiO.sub.2(mmolar amount of Al.sub.2O.sub.3))=d, where m describes the gradient of a straight line and d describes a constant term. According to a variant A, based on compositions having an Al.sub.2O.sub.3 fraction of at least 17.0 mol %, limits of a preferred range may be described by straight lines having a gradient m.sub.1=4.6 and a term d.sub.1 of at least 142.5 and/or preferably at most 149.0. A limit of a preferred range may be described according to variant B by a straight line having a gradient m.sub.3=2.0 and a term d.sub.3 of preferably less than 101.0, more preferably at most 100.5. According to a variant C with an Al.sub.2O.sub.3 fraction of less than 17.0 mol %, limits of a preferred compositional range may be described by straight lines having a gradient m.sub.2=2.0 and a term d.sub.2 of preferably at most 34.0 and/or preferably at least 30.7. In the case of variant C, d.sub.2 could also be at most 32.0.

(39) Glass-ceramics which fall into variant A are particularly suitable if a plateau at relatively high temperatures is desired. Depending on application, however, a glass-ceramic with differently formed CTE plateaus may also be preferred.

(40) Variants A to C may be combined arbitrarily with the aforementioned upper and lower limits for SiO.sub.2 and Al.sub.2O.sub.3, unless otherwise defined in the case of the particular variant.

(41) Specifically, a first variant of the invention relates to glass-ceramics having an Al.sub.2O.sub.3 content of less than 17.0 mol %, in which one or more of the following conditions are met:

(42) the Al.sub.2O.sub.3 content is preferably at least 15.0 mol %, more preferably at least 15.8 mol %, more preferably at least 16.0 mol %, preferably at least 16.1 mol %, more preferably more than 16.1 mol %, and

(43) the SiO.sub.2 content is preferably at least 63.5 mol %, more preferably at least 63.75 mol %, more preferably at least 64.0 mol %, and/or preferably at most 65.6 mol %, more preferably at most 65.0 mol % and

(44) the condition applies that 30.7(molar amount of SiO.sub.2(2.0 molar amount of Al.sub.2O.sub.3)), advantageously 30.9(molar amount of SiO.sub.2(2.0 molar amount of Al.sub.2O.sub.3)), preferably 31.0(molar amount of SiO.sub.2(2.0 molar amount of Al.sub.2O.sub.3)).

(45) Advantageously the condition that (molar amount of SiO.sub.2(2.0 molar amount of Al.sub.2O.sub.3))34.0 may apply.

(46) Further variants of the invention relate to glass-ceramics having an Al.sub.2O.sub.317.0 mol %, in which one or more of the following conditions are met:

(47) the Al.sub.2O.sub.3 content is preferably at most 19.5 mol %, more preferably at most 19.0 mol % and

(48) the SiO.sub.2 content is preferably at least 62.0 mol %, preferably more than 62.0 mol %, and/or preferably at most 66.0 mol %, and

(49) it is the case that 142.5(molar amount of SiO.sub.2+(4.6 molar amount of Al.sub.2O.sub.3)), advantageously 143.0(molar amount of SiO.sub.2+(4.6 molar amount of Al.sub.2O.sub.3)), preferably 143.0<(molar amount of SiO.sub.2+(4.6 molar amount of Al.sub.2O.sub.3)), and one of the following conditions applies: (molar amount of SiO.sub.2+(4.6 molar amount of Al.sub.2O.sub.3))149.0, or (molar amount of SiO.sub.2+(2.0 molar amount of Al.sub.2O.sub.3))101.0, preferably100.5.

(50) The glass-ceramic always contains P.sub.2O.sub.5. The phosphate content P.sub.2O.sub.5 of the glass-ceramic is preferably at least 1 mol %, more preferably at least 2 mol %, and/or at most 10 mol %, more preferably at most 8 mol %, according to one variant at most 5 mol %, with further preference at most 4 mol %.

(51) The sum total fraction in mol % of the basic constituents of the LAS glass-ceramic, SiO.sub.2 and Al.sub.2O.sub.3, is preferably at least 75 mol %, more preferably at least 78 mol % and/or preferably at most 85 mol %.

(52) The sum total fraction in mol % of the basic constituents of the LAS glass-ceramic, SiO.sub.2, Al.sub.2O.sub.3 and P.sub.2O.sub.5, is preferably at least 70 mol %, advantageously at least 75 mol %, more preferably at least 78 mol %, also preferably at least 80 mol %, and/or preferably at most 95 mol %, more preferably at most 90 mol %, according to one variant at most 89 mol %.

(53) The glass-ceramic further comprises titanium oxide (TiO.sub.2). It contains TiO.sub.2 in a fraction of preferably at least 0.5 mol %, preferably at least 1.0 mol % and/or preferably at most 5 mol %, more preferably at most 3 mol %, with further preference at most 2.0 mol %.

(54) The glass-ceramic may further comprise zirconium oxide (ZrO.sub.2) in a fraction of at most 5 mol %, preferably at most 3 mol %, more preferably at most 2 mol %. ZrO.sub.2 is included preferably in a fraction of at least 0.1 mol %, more preferably at least 0.5 mol %, at least 0.6 mol %. ZrO.sub.2-free variants are possible.

(55) The sum total of the fractions of the nucleating agents TiO.sub.2 and ZrO.sub.2 is preferably at least 2 mol %, more preferably more than 2 mol %, more preferably at least 2.5 mol %, according to certain variants at least 3.0 mol %. An advantageous upper limit may be 10 mol %, preferably 8 mol %, more preferably 5 mol % or 4 mol %.

(56) As a further constituent the glass-ceramic comprises lithium oxide (Li.sub.2O), preferably in a fraction of at least 1 mol %, preferably at least 5 mol %, very preferably at least 7 mol %. The fraction of Li.sub.2O is limited to preferably at most 15 mol %, more preferably at most 12 mol %, with further preference at most 10 mol %.

(57) Sodium oxide (Na.sub.2O) and/or potassium oxide (K.sub.2O) are present optionally in the glass-ceramic, i.e. Na.sub.2O-free and/or K.sub.2O-free variants are possible. The fraction of Na.sub.2O and/or K.sub.2O, in each case and independently of one another, may be at most 2 mol %, preferably at most 1 mol %, most preferably at most 0.5 mol %. Na.sub.2O and K.sub.2O may each be included, independently of one another, in a fraction of at least 0.01 mol %, preferably at least 0.02 mol %, more preferably at least 0.05 mol %, in the glass-ceramic.

(58) The glass-ceramic further comprise magnesium oxide (MgO). It contains MgO preferably in a fraction of preferably at least 0.1 mol %, more preferably at least 0.5 mol %, according to one variant at least 1.0 wt %, and/or at most 5 mol %, preferably at most 3 mol %, according to one variant at most 2 mol %.

(59) As a further component the glass-ceramic comprises zinc oxide (ZnO). This component is included in a fraction of preferably at least 0.1 mol %, more preferably at least 0.5 mol % and according to one variant of the invention in a fraction of at least 1.0 mol %. The fraction of ZnO is preferably limited to at most 5 mol %, more advantageously to at most 4 mol %, according to one variant to at most 3 mol %. Some variants may have at most 2 mol % of ZnO.

(60) The sum total fraction in mol % of the components MgO and ZnO is preferably at least 1.8 mol %, more preferably at least 2.0 mol % and/or preferably at most 10 mol %, more preferably at most 5 mol %.

(61) According to some variants of the invention, the sum total fraction in mol % of the components MgO and ZnO and Li.sub.2O is preferably at least 10.0 mol %, according to certain variants advantageously at least 11.0 mol %, more preferably at least 11.2 mol %, with further preference at least 11.5 mol %. In the case of a glass-ceramic with an Al.sub.2O.sub.3<17.0 mol % it may be advantageous if the sum total fraction in mol % of the components MgO and ZnO and Li.sub.2O is at least 10.0 mol %, preferably at least 10.4 mol %. In the case of a glass-ceramic with an Al.sub.2O.sub.317.0 mol % it may be advantageous if the sum total fraction in mol % of the components MgO and ZnO and Li.sub.2O is at least 11.0 mol %, preferably more than 11.0 mol %, more preferably at least 11.2 mol %, also preferably at least 11.5 mol %. Both for a glass-ceramic having an Al.sub.2O.sub.3<17.0 mol % and for a glass-ceramic having an Al.sub.2O.sub.317.0 mol %, an advantageous upper limit may be 25 mol %, preferably 20 mol %, more preferably 15 mol %. In the case of particular variants, 13 mol % as well may be a favourable upper limit.

(62) The glass-ceramic may comprise further alkaline earth metal oxides, such as CaO, BaO and/or SrO. The fraction of CaO is preferably at most 5 mol %, more preferably at most 3 mol %, more preferably at most 2 mol %. The glass-ceramic may contain at least 0.1 mol %, preferably at least 0.5 mol %, of CaO. The glass-ceramic may contain BaO in a fraction of at least 0.1 mol %, preferably at least 0.5 mol %, and/or at most 5 mol %, preferably at most 3 mol %, more preferably at most 2 mol %. The glass-ceramics may contain SrO in a fraction of at most 5 mol %, preferably at most 4 mol %, more preferably at most 3 mol % and/or preferably at least 0.1 mol %. According to individual embodiments, the glass-ceramics are free of CaO, BaO and/or SrO.

(63) The glass-ceramic may further comprise one or more customary refining agents, selected from the group consisting of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO, SO.sub.4.sup.2, F.sup., Cl.sup., Br.sup., or a mixture thereof, in a fraction of at least 0.1 mol % and/or at most 1 mol %.

(64) The main crystal phase of the glass-ceramics of the invention comprises high-quartz solid solution. These glass-ceramics typically comprise, as main crystal phase, about 50% to 80% of solid solutions containing high-quartz, which are also called -eucryptite solid solutions. This crystallization product is a metastable phase which, depending on the crystallization conditions, changes its composition and/or structure, or is transformed into a different crystal phase. The solid solutions containing high-quartz have a very low thermal expansion or even a thermal expansions which falls as the temperature goes up.

(65) In accordance with the invention, the expression X-free or free from a component X means that the glass-ceramic essentially does not contain this component X, in other words that such a component is present at most as an impurity in the glass, but is not added as an individual component to the composition. X here stands for any component, such as SrO, for example.

(66) According to one embodiment of the present invention, a transparent glass-ceramic is used. Because of the transparency it is possible to make a better assessment of many properties of such a glass-ceramic, and in particular, of course, its internal quality. The glass-ceramics of the invention are transparent, meaning that they have an internal transmission of at least 70% in the wavelength range from 350 to 650 nm.

(67) It will be appreciated that the features of the invention identified above, and those still to be elucidated below, can be used not only in the particular combination indicated but also in other combinations, without departing from the scope of the invention.

(68) The entire disclosures of all applications, patents and publications, cited above and below, and of corresponding German application 10 2017 208 907.5 filed May 26, 2017, are hereby incorporated by reference.

(69) The present invention will be illustrated below by a series of examples. However, the present invention is not limited to the examples mentioned.

EXAMPLES

(70) Production of the glass-ceramic is described in WO 2015/124710 A1, for example. Tables 1 and 2 show compositions of inventive glass-ceramics and comparative examples, and also their properties.

(71) TABLE-US-00003 TABLE 1 Compositions, ceramization and properties (mol %) Example number Al.sub.2O.sub.3 <17 mol % 1 2 3 4 5 Li.sub.2O 8.5 8.3 8.5 7.9 8.2 Na.sub.2O 0.2 0.1 0.2 0.5 0.6 K.sub.2O 0.4 0.4 0.2 0.2 MgO 1.9 1.2 1.7 1.1 0.9 ZnO 1.3 1.3 1.4 1.5 1.3 CaO 1.8 0.8 1.3 BaO 0.6 0.5 Al.sub.2O.sub.3 16.4 16.6 16.9 16.5 16.4 SiO.sub.2 64.3 64.1 64.9 64.8 64.7 P.sub.2O.sub.5 3.9 3.5 2.8 3.1 2.9 TiO.sub.2 1.9 2.0 1.9 2.0 1.8 ZrO.sub.2 1.1 1.1 1.0 1.0 1.0 As.sub.2O.sub.3 0.2 0.1 0.2 0.2 0.2 Total 100.1 100.1 99.9 100.2 100.0 SiO.sub.2 + Al.sub.2O.sub.3 + P.sub.2O.sub.5 84.6 84.2 84.6 84.4 84.0 SiO.sub.2 (2 Al.sub.2O.sub.3) 31.5 30.9 31.1 31.8 31.9 Temperature [ C.] 790 795 810 800 770 Duration [days] 5 5 10 5 5 CTE(0; +50 C.) [ppm/K] 0.003 0.008 0.005 0.002 0.006 Zero crossing CTE [ C.] 5 4 6 7 Zero crossing CTE [ C.] 48 18 53 26 Plateau position [ C.] 0 0.015 ppm/K [4; +57] [11; 37] [1; +60] [2; +55] [+2; +55] 0 0.01 ppm/K [1; +54] [9; 31] [+1; 58] [0; +50] [+5; +51] 0 0.005 ppm/K [1; 52] [+3; 13] [+3; +40] [+11; +45] 0 0.005 ppm/K [48; 56] 15 ppb plateau width 61K 48K 61K 57K 53K 10 ppb plateau width 55K 40K 57K 50K 46K 5 ppb plateau width 51K 10/6K 37K 34K Comparative Example No. Al.sub.2O.sub.3 <17 mol % 1 2 3 4 5 6 Li.sub.2O 9.2 8.3 8.9 8.7 8.7 8.5 Na.sub.2O 0.1 0.1 0.1 0.2 0.2 K.sub.2O 0.4 0.4 0.4 MgO 1.6 1.8 1.3 2.2 1.8 1.9 ZnO 0.6 1.4 0.5 0.9 1.4 1.2 CaO 1.2 1.3 1.5 BaO 0.4 0.3 0.5 Al.sub.2O.sub.3 16.2 15.7 16.1 16.2 17.0 16.9 SiO.sub.2 63.3 65.4 64.6 62.7 63.5 64.4 P.sub.2O.sub.5 3.8 3.7 3.8 4.0 3.9 3.5 TiO.sub.2 2.2 1.9 2.0 1.8 2.0 1.9 ZrO.sub.2 1.1 1.0 1.1 1.1 1.1 1.1 As.sub.2O.sub.3 0.2 0.2 0.2 0.1 0.2 0.2 Total 99.9 99.9 100.2 99.9 100.2 100.0 SiO.sub.2 + Al.sub.2O.sub.3 + P.sub.2O.sub.5 83.3 84.8 84.5 82.9 84.4 84.8 SiO.sub.2 (2 Al.sub.2O.sub.3) 30.9 34.0 32.4 30.3 29.5 30.6 Temperature [ C.] 770 780 760 770 810 810 Duration [days] 5 5 5 5 7.5 4.5 CTE(0; +50 C.) [ppm/K] 0.060 0.010 0.040 0.070 0.030 0.02 Zero crossing CTE [ C.] Zero crossing CTE [ C.] Plateau position [ C.] 0 0.015 ppm/K 0 0.01 ppm/K 0 0.005 ppm/K 0 0.005 ppm/K 15 ppb plateau width 10 ppb plateau width

(72) TABLE-US-00004 TABLE 2 Compositions, ceramization and properties (mol %) Example No. Al.sub.2O.sub.3 17 mol % 6 7 8 9 10 11 Li.sub.2O 8.6 8.6 8.7 8.5 9.0 8.7 Na.sub.2O 0.1 0.2 0.1 0.2 0.2 0.2 K.sub.2O 0.4 0.4 0.4 0.4 0.5 0.4 MgO 1.8 1.8 1.8 1.8 1.9 1.8 ZnO 1.1 1.3 1.3 1.4 1.4 1.2 Al.sub.2O.sub.3 18.3 18.1 17.2 17.6 18.0 18.5 SiO.sub.2 63.7 64.1 63.5 62.4 62.5 62.7 P.sub.2O.sub.5 2.9 2.5 3.8 4.4 3.4 3.3 TiO.sub.2 2.0 1.9 2.0 2.0 1.9 2.0 ZrO.sub.2 1.1 1.1 1.1 1.1 1.1 1.1 As.sub.2O.sub.3 0.1 0.1 0.2 0.1 0.2 0.1 Total 100.1 100.1 100.1 99.9 100.1 100.0 SiO.sub.2 + Al.sub.2O.sub.3 + P.sub.2O.sub.5 84.9 84.7 84.5 84.4 83.9 84.5 SiO.sub.2 + (4.6 Al.sub.2O.sub.3) 147.9 147.4 142.6 143.4 145.3 147.8 Temperature [ C.] 800 800 805 790 805 800 Duration [days] 5 5 5 5 5 5 CTE(0; +50 C.) 0.000 0.020 0.006 0.003 0.010 0.005 [ppm/K] Zero crossing 18 12 24 CTE [ C.] Zero crossing 71 29 56 CTE [ C.] Zero crossing 94 89 95 80 CTE [ C.] Plateau position [ C.] 0 0.015 ppm/K [>10] [21; 96] [+2; 49] [1; +49] [14; >100] [64; >100] 0 0.01 ppm/K [>55] [26; 95] [+5; 47] [2; 46] [+17; 69] 0 0.005 ppm/K [>64] [72; 92] [5; 41] 15 ppb plateau >85K 75K 47K 50K >90K width 10 ppb plateau >45K 70K 42K 44K 52K width 5 ppb plateau >36K 20K 36K width Example No. Al.sub.2O.sub.3 17 mol % 12 13 14 15 16 17 18 Li.sub.2O 8.7 8.6 8.0 8.4 8.6 8.5 8.7 Na.sub.2O 0.2 0.2 0.2 0.2 0.1 0.2 0.2 K.sub.2O 0.5 0.4 0.4 0.4 0.4 0.4 0.4 MgO 1.9 1.9 2.2 1.8 1.9 1.8 1.9 ZnO 1.1 1.0 1.4 1.2 1.2 1.3 1.3 Al.sub.2O.sub.3 17.5 18.8 17.1 17.2 17.6 17.6 18.1 SiO.sub.2 63.5 62.3 64.2 65.7 64.1 65.1 62.4 P.sub.2O.sub.5 3.5 3.5 3.4 2.0 3.0 2.0 3.8 TiO.sub.2 2.0 2.0 2.0 1.9 1.9 1.9 2.0 ZrO.sub.2 1.1 1.1 1.0 1.1 1.1 1.1 1.1 As.sub.2O.sub.3 0.2 0.2 0.1 0.1 0.1 0.1 0.2 Total 100.2 100.0 100.0 100.0 100.0 100.0 100.1 SiO.sub.2 + Al.sub.2O.sub.3 + P.sub.2O.sub.5 84.5 84.6 84.7 84.9 84.7 84.7 84.3 SiO.sub.2 + (4.6 Al.sub.2O.sub.3) 144.0 148.8 142.9 144.8 145.1 146.1 145.7 Temperature [ C.] 800 785 765 830 810 810 800 Duration [days] 10 5 5 6.5 5 8.5 5 CTE(0; +50 C.) 0.000 0.02 0.004 0.014 0.010 0.016 0.000 [ppm/K] Zero crossing 22 12 75 15 CTE [ C.] Zero crossing 66 57 CTE [ C.] Zero crossing 85 CTE [ C.] Plateau position [ C.] 0 0.015 ppm/K [3; 86] [18; 61] [15; 63] [57; 97] [18; 90] [7; 71] 0 0.01 ppm/K [53; 65] [21; 55] ab [18; 52] [71; 92] [21; 84] [11; 67] 54 C. 0 0.005 ppm/K [8; 62] [26; 48] [79; 89] [45; 63] 15 ppb plateau 43K 48K 40K 72K 64K width 10 ppb plateau 62K 34K >55K 34K 63K 56K width 5 ppb plateau 54K 22K width Comparative Example No. Al.sub.2O.sub.3 17 mol % 7 8 9 10 11 Li.sub.2O 8.6 8.5 9.4 8.9 8.4 Na.sub.2O 0.2 0.2 0.2 0.7 0.2 K.sub.2O 0.6 0.4 0.4 MgO 1.9 1.8 1.2 2.0 1.7 ZnO 1.5 1.2 0.6 1.9 1.3 CaO 0 0 1.0 0 0 BaO 0 0 0.3 0 0 Al.sub.2O.sub.3 18.1 18.6 19.0 17.9 18.5 SiO.sub.2 61.9 63.8 61.4 61.5 61.5 P.sub.2O.sub.5 3.9 2.4 3.9 3.8 4.7 TiO.sub.2 2.1 1.9 1.9 2.0 2.0 ZrO.sub.2 1.1 1.1 1.1 1.0 1.1 As.sub.2O.sub.3 0.2 0.1 0.2 0.2 0.1 Total 100.1 100.0 100.2 99.9 99.9 SiO.sub.2 + Al.sub.2O.sub.3 + P.sub.2O.sub.5 83.9 84.8 84.3 83.2 84.7 SiO.sub.2 + (4.6 Al.sub.2O.sub.3) 145.2 149.4 148.8 143.8 146.6 Temperature [ C.] 810 810 780 Duration [days] 8 5 5 CTE(0; +50 C.) [ppm/K] 0.050 0.031 0.02 Zero crossing CTE [ C.] 42 56 Plateau position [ C.] 0 0.015 ppm/K [35; 64] 0 0.01 ppm/K [43; 62] 0 0.005 ppm/K 15 ppb plateau width 29K 10 ppb plateau width 19K

(73) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(74) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.