Method for producing an MAS glass body, powder mixture, MAS glass body, and use of a MAS glass body

Abstract

The invention relates to a method for producing an X-ray-amorphous MAS glass body, having - a mass of ≥ 3 kg and - a surface area / volume ratio of ≤ 1.5 cm-1. The method has the steps of: a) preparing a powder mixture comprising 10 to 40 mol.% of MgO, 5 to 30 mol.% of Al2O3, and 40 to 70 mol.% of SiO2 or precursors of said raw materials, auxiliary elements, and foreign elements, wherein the auxiliary elements are the elements of main group I and / or main group II and / or main group IV and / or Fe, and a total content of auxiliary elements and foreign elements of at least 10 ppm - 300 ppm is set, in particular at least 30 ppm - 150 ppm, preferably at least 50 ppm - 100 ppm; b) melting the powder mixture provided in step a); c) cooling the melt produced in step b) and comminuting the cooled melt in order to form particles with a diameter of ≤ 10 mm; d) heating and melting the particles obtained in step c); and e) cooling the melt obtained in step d).

Description

[0001] QSIL GmbH Quartz Smelter Ilmenau

[0002] Method for producing a MAS glass body, powder mixture, MAS glass body and use of a MAS glass body

[0003] Description

[0004] The present invention relates to a method for producing an MAS glass body, a powder mixture for producing an MAS glass body, an MAS glass body and the use of an MAS glass body according to the invention.

[0005] Plasma-assisted dry etching – also referred to as "plasma etching" for short – is an indispensable technology for producing ultrafine structures in semiconductor devices, high-resolution displays, and in solar cell production.

[0006] EP 3 708 547 A1 describes plasma etching in a vacuum reactor at a relatively high temperature and in a highly corrosive atmosphere. The vacuum reactor is purged with an etching gas at low pressure. A highly reactive, etch-active plasma is generated by high-frequency discharge between electrodes or by electrodeless microwave discharge.

[0007] During plasma etching, not only is the desired layer removed from the processed wafer, but as an undesirable side effect, also from the components of the etching chamber, which are typically made of quartz glass.

[0008] Quartz glass is particularly suitable because it is relatively etch-resistant to the fluorine-containing plasmas used. In addition, quartz glass can be produced with very high purity. This is particularly important for the use of components in plasma etching chambers, as possible impurities in the quartz glass can reach the wafer during the etching process. The purer the etched quartz glass, the lower the risk of contamination to the wafer during the plasma etching process. Therefore, quartz glass components made of synthetically produced material with a nearly 100% purity level are used for demanding etching steps. The lower the impurities in the components of the plasma etching chamber, the better suited the materials are for this demanding application.This general finding also applies to high-quality ceramics, which are sometimes used as a replacement for quartz glass in plasma etching chambers due to their high etch resistance.

[0009] With regard to applications in etching processes, it is well known that all foreign substances should be avoided, as they could contaminate the wafer during the plasma process. Therefore, it is known from the state of the art to always strive for maximum purity of the manufactured glass components and thus of the raw materials used, which corresponds to minimizing all foreign substances.

[0010] A low etch rate of the materials or components used can also be advantageous, as the risk of contamination is reduced with less material removed. Furthermore, a low etch rate of the components in the etching chamber also has advantages with regard to the very precise geometries, which are extremely important for feature widths of less than 10 nm. A lower etch rate leads to fewer changes in the component geometry during the component's life cycle.

[0011] For example, it is known from US Pat. Nos. 7,015,163 B2 and 7,084,084 B2 that MAS glass is highly resistant to plasma etching processes using a fluorine-containing gas atmosphere. During the etching process, the fluorine in the etching atmosphere reacts with the magnesium in the MAS glass, forming a low-volatility MgF2 layer on the component's surface, which significantly reduces further etching loss.

[0012] WO 2022 / 075687 A1 further discloses the additional doping of a MAS glass with MgF2. However, it has been shown that such doping only marginally improves etch resistance.

[0013] MgO-Al2O3-SiO2 glasses (MAS glasses) have very different physical and chemical properties depending on their chemical composition. The different compositions are referred to in the literature under different names, as illustrated in Fig. 1. When using MAS glass for etching applications, it is important that the glass is completely X-ray amorphous, as crystalline regions lead to local variations in the etch removal. These effects, also known as etch inhomogeneity, easily lead to "under-etching" and thus to particle release.

[0014] Despite the known advantages of MAS glass, no industrially attractive products have been identified to date. MAS glass is known in the form of fibers, which are primarily used to reinforce mechanical strength. Attempts to produce lightweight (weight < 1 kg) thin-walled ring components are also known. However, attractive industrial applications require compact, heavy semi-finished products, such as cylinders or rods, from which rings or plates of the desired dimensions can be cut.

[0015] It is known from the geometry of any body that as the volume increases, the surface area-to-volume ratio (S / V) decreases, since the surface area grows quadratically while the volume grows cubically (square-cube law). This is crucial for the cooling rate of masses of different sizes. The cooling rate is proportional to the surface area, which, however, grows more slowly than the volume as the body grows, so larger masses cool more slowly than smaller ones.

[0016] MAS glass must be cooled rapidly from its melting temperature of approximately 1,300 °C to 1,000 °C because of its chemical nature, which makes it highly prone to crystallization and segregation. Both effects have a severe negative impact on the material's further processing and use in plasma etching.

[0017] Therefore, the production of large, heavy and compact MAS components while avoiding crystallization and demixing seems to be impossible due to the increasingly slow cooling rate.

[0018] To further investigate the properties of the MAS glasses, glasses with different chemical compositions were prepared and their influence on the tendency to demixing and crystallization was investigated. The chemical glass compositions of 13 of these MAS samples are summarized in Table 1 and arranged in a phase diagram in Fig. 2.

[0019] Table 1: Glass composition [mol%] of manufactured MAS glass samples The size of the laboratory samples was 300g each.

[0020] For samples 0-12 shown in Fig. 2, an evaluation of the glass quality was carried out, whereby the glasses were rated as follows: grey (samples 2, 4, 7, 8, 9, 10): clear glass hatched (samples 3, 5, 6, 11, 12): blistered glass white (samples 0, 1): glasses with segregations

[0021] It turns out that there is a preferred range of MAS compositions that produce attractive glasses without increased bubble content and without spontaneous demixing. This range lies in the region of SiO2: 50–65 mol%.

[0022] • MgO: 25-35 mol%

[0023] • AI2O3: 10-25 mol%

[0024] If the SiO2 content is too high (> 70%), the glasses cannot be refined well and therefore contain many bubbles.

[0025] If the Al2O3 content is too low (< 10%), the MgO no longer dissolves well in the glass and spontaneous demixing occurs.

[0026] In terms of etch resistance, glass composition 2 has proven advantageous: SiO2 60 mol%, MgO 30 mol%, Al2O3 10 mol%. However, this glass is close to the spontaneous demixing range, making the production of heavy and compact components particularly difficult.

[0027] The critical temperature range for demixing was determined by heat-treating samples of glass composition 2. For this purpose, samples were placed in a furnace at a preset temperature and held there for 60 minutes. These samples are shown in Fig. 3.

[0028] When examining the samples shown in Fig. 3, it becomes clear that the temperature range between 1,300 °C and 1,000 °C is critical for the formation of segregations. Therefore, rapid traversal of this temperature range is particularly important in the technological production of MAS glass components.

[0029] The fact that large and compact components are particularly susceptible to segregation was experimentally confirmed during the production of a ring-shaped component as follows:

[0030] In order to achieve a glass of particularly high purity, as is generally desired for applications in the etching process of semiconductor production, starting materials of synthetic purity were used:

[0031] SiO2: synthetic, impurity < 1 ppm AI2O3: synthetic, impurity < 10 ppm

[0032] • MgO: synthetic, impurity < 30 ppm

[0033] By weighting the impurities with the mass fractions of the individual components of the glass composition, the total contamination of the glass, i.e. the proportion of all chemical elements that are not Si, Al, Mg or O, is 10 < ppm.

[0034] The inner diameter of the annular component was 300 mm, the outer diameter of the annular component was 400 mm and the height of the annular component was 25 mm.

[0035] With these dimensions, the density of the glass is 2.6 g / cm 3 a component weight of 3.57 kg and a surface-to-volume ratio of 1.2 cm -1 .

[0036] Surprisingly, it turns out that a heavy, compact component manufactured according to this recipe exhibits significant segregation after cooling from the melt. This manufactured component, namely a heavy, compact component made of MAS glass using synthetic-purity raw materials, and the resulting segregation is shown in Fig. 4. The segregation shown in Fig. 4 is particularly surprising because, in laboratory tests, a clear glass can be produced with this glass composition using a sample size of 300 g (see Fig. 2, Sample 2).

[0037] The demixings are not as pronounced as shown in Fig. 3 and also show a slightly different appearance, but it was proven by electron microscopy that the phenomenon is droplet-shaped demixing.

[0038] The experiments clearly demonstrate how critical the effect of segregation is for the production of MAS components. It is therefore obvious that segregation must be largely avoided during the production of MAS components. In addition to good homogenization of the MAS glass during the melting process, the time during which the sample cools from over 1,300 °C to 1,000 °C is critical. Considerable segregation can occur during this phase, and it is therefore important to minimize this time.

[0039] When manufacturing heavy, compact bodies, the increasingly unfavorable surface-to-volume ratio (square-cube law) with increasing weight represents a physical limitation. Due to the cubically increasing volume and only quadratically increasing surface area, it becomes increasingly difficult to dissipate heat energy from the central regions of the MAS component. As a result, the central portion of the material remains in the critical temperature zone between 1,000 °C and 1,300 °C for longer.

[0040] Fig. 5 clearly illustrates this effect of temperature distribution during the cooling of a heavy, compact sample. It shows a cooling, heavy, compact MAS body with sustained high temperatures in the core region. This illustrates the high heat capacity and poor heat dissipation in glass bodies with a mass of > 3 kg.

[0041] However, due to these physical boundary conditions, the cooling time in the critical temperature range between over 1,300 °C and 1,000 °C can only be shortened to a limited extent.

[0042] It is therefore an object of the present invention to overcome the disadvantages of the aforementioned prior art. In particular, a compact and large MAS glass body is to be provided in a simple manner, which is homogeneous and in which crystallization and demixing during curing are minimized. Furthermore, the MAS glass body is to be X-ray amorphous. In this case, the MAS glass body should have a weight of more than 3 kg and a surface-to-volume ratio of <1.5 cm -1 have.

[0043] These objects were surprisingly achieved by a method for producing an MAS glass body according to claim 1, by a powder mixture for producing an MAS glass body according to claim 8, by an MAS glass body according to claim 11, and by the use of an MAS glass body according to claim 15. Advantageous further developments are described in the subclaims.

[0044] Numerous specific details are discussed below to provide a thorough understanding of the subject matter. However, it will be apparent to one skilled in the art that the subject matter can be practiced and recreated without these specific details.

[0045] All features of one embodiment may be combined with features of another embodiment if the features of the different embodiments are compatible.

[0046] The terminology used in the description of the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the subject matter. As used in this description and the claims, the singular forms "a," "an," and "the" are intended to include the plural forms, unless the context clearly dictates otherwise. The reverse is also true, meaning that the plural forms are intended to include the singular forms. It is also understood that the term "and / or," as used herein, refers to and includes all possible combinations of one or more of the related listed elements.It is further understood that the terms "includes," "including," "comprises," and / or "comprising," when used in the present description and claims, specify the presence of the stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0047] In the present description and claims, the terms "includes", "comprises" and / or "comprising" may also mean "consisting of", ie the presence or addition of one or more other features, steps, operations, elements, components and / or groups is excluded. The present invention relates to a method for producing an X-ray amorphous MAS glass body with

[0048] - a mass > 3 kg and

[0049] - a surface / volume ratio <1.5 cm -1 comprising the process steps: a) preparing a powder mixture with 10 to 40 mol% MgO, 5 to 30 mol% AI2O3 and 40 to 70 mol% SiC or precursors of these raw materials, as well as with auxiliary elements and foreign elements, wherein the auxiliary elements are elements of the I. main group and / or II. main group and / or IV. main group and / or Fe, wherein a

[0050] The total content of auxiliary elements and foreign elements is set at at least 10 ppm - 300 ppm, in particular at least 30 ppm - 150 ppm, particularly preferably at least 50 ppm - 100 ppm; b) melting the powder mixture provided in step a); c) cooling the melt produced in step b) and comminuting the cooled melt to particles with a diameter of < 10 mm; d) heating and melting the particles obtained in step c); and e) cooling the melt obtained in step d).

[0051] Precursors of these raw materials are preferably understood to be the corresponding hydroxides and / or carbonates of MgO and AI2O3.

[0052] The proportions of the individual elements, as specified in step a), are preferably determined using the LA-ICP-MS (laser ablation - inductively coupled plasma - mass spectrometry) method. This method is also preferably used for all other specified content or proportion data in a powder mixture and / or an MAS glass body. Surprisingly, it is possible to produce heavy and compact MAS glass bodies with significantly better results in terms of crystallization and demixing by adding auxiliary elements to a powder mixture.

[0053] The addition of auxiliary elements, among others, advantageously increases the entropy of the melt. This increase in entropy significantly reduces the melt's tendency to segregate.

[0054] Here the entropy of mixing is assumed:

[0055] Due to the addition of auxiliary elements, a large increase in entropy is achieved and thus dominates the Gibbs free energy:

[0056] The entropy is positive, meaning the contribution to free enthalpy is negative, which means that the mixed state is energetically more favorable at high entropy. Therefore, the melt remains in the mixed state instead of demixing when auxiliary elements are present according to the invention.

[0057] According to the invention, the auxiliary elements are alkalis and / or alkaline earths and / or Fe. These auxiliary elements can be used to produce particularly good, compact and large MAS glass bodies that exhibit no or virtually no segregation. At the same time, the MAS glass bodies produced in this way are suitable for use in semiconductor manufacturing processes, as tests have shown.

[0058] Auxiliary elements are, in particular, those elements whose proportion in the powder mixture to be prepared prevents demixing during the production of the MAS glass body.

[0059] The auxiliary elements are preferably added during the preparation of the powder mixture during the preparation of the MgO-Al2O3-SiC mixture. Regarding the alkalis and / or alkaline earths, Na and / or K and / or Ca and / or Li are particularly preferred as auxiliary elements.

[0060] Preferably, mixtures of at least two of the elements Na, K, Ca, Li and Fe are used.

[0061] In the context of the process according to the invention, MgO - AI2O3

[0062] - SiO2 mixtures containing auxiliary elements are prepared. Thus, the invention represents a departure from the standard procedure of using powder mixtures that are as pure as possible without additional elements.

[0063] Particularly preferred is a powder mixture containing auxiliary elements as follows:

[0064] - a Na content of at least 2 ppm - 50 ppm and / or

[0065] - a K content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or

[0066] - a Ca content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or

[0067] - a Li content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or

[0068] - an Fe content of at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm.

[0069] The foreign elements contained in the prepared powder mixture are preferably elements of main group III and / or main group V and / or transition metals with the exception of Fe.

[0070] The content of the foreign elements is preferably adjusted such that the content of the elements Cr, Mn, Co, Ni, Ti, Zn and Zr is each < 2 ppm and / or the content of the elements B, P and Cu is each < 1 ppm.

[0071] Preferably, in step a), a powder mixture is prepared which comprises 25 to 35 mol% MgO, 10 to 25 mol% Al2O3, and 50 to 65 mol% SiO2, particularly preferably 30 mol% MgO, 10 mol% Al2O3, and 60 mol% SiO2. In a preferred embodiment, the process according to the invention is characterized in that less than 0.01 mol% of material additives comprising fluorine and / or yttrium compounds are added during the preparation of the powder mixture and / or the production of the MAS glass body.

[0072] Preferably, step b) and / or c) is / are carried out with a temperature exposure of 1200 °C to 2000 °C, preferably of 1500 °C to 1750 °C.

[0073] In a preferred embodiment, the process according to the invention is characterized in that steps c), d), and e) are performed multiple times, with the melt in step c) being the melt previously produced by step e). Multiple times means 2, 3, 4, 5, etc. times. Homogeneity can be further improved by performing steps c), d), and e) multiple times.

[0074] In a preferred embodiment, the process according to the invention is characterized in that the duration of step b) is 0.1 to 10 hours, preferably 0.1 to 7 hours.

[0075] In a preferred embodiment, the process according to the invention is characterized in that the duration of step d) is 0.1 to 10 hours, preferably 0.1 to 7 hours.

[0076] In a preferred embodiment, the process according to the invention is characterized in that the mixture from step d) is cooled in step e) to a temperature of below 25 °C.

[0077] In a further preferred embodiment, the process according to the invention is characterized in that the melt from step d) is cooled in step e) first rapidly to a temperature of 600 to 900 °C and then significantly more slowly to a temperature of below 25 °C.

[0078] For example, "rapid" means cooling of more than 75 K per minute, preferably more than 90 K per minute and less than 120 K per minute. "Slow" means cooling of less than 5 K per minute, preferably less than 2.5 K per minute and greater than 0.5 K per minute.

[0079] Rapid cooling to the temperature range of 600 to 900 °C has the advantage of minimizing the risk of crystallization, further preventing the formation of inhomogeneities. Subsequent slow cooling to room temperature prevents the formation of stresses or cracks.

[0080] In a preferred embodiment, the process according to the invention is characterized in that the heating of the mixture in steps b) and / or d) takes place in Pt and / or Pt / Rh crucibles.

[0081] In a preferred embodiment, the process according to the invention is characterized in that the cooling of the melt in step e) is carried out first in a steel mold coated with a release agent and then, after demolding, in a cooling furnace.

[0082] A further, in particular subordinate, aspect of the invention relates to a powder mixture for producing an X-ray amorphous MAS glass body, in particular for use in a method according to the invention.

[0083] The powder mixture comprises 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiO2 or precursors of these raw materials, preferably 25 to 35 mol% MgO, 10 to 25 mol% Al2O3 and 50 to 65 mol% SiO2 or precursors of these raw materials, particularly preferably 30 mol% MgO, 10 mol% Al2O3 and 60 mol% SiO2 or precursors of these raw materials, wherein the powder mixture further comprises auxiliary elements and foreign elements, and the auxiliary elements are elements of the I main group and / or II main group and / or IV main group and / or Fe, and the total content of the auxiliary elements and foreign elements is 10 ppm - 300 ppm, in particular 30 ppm - 150 ppm, particularly preferably 50 ppm - 100 ppm.

[0084] Similar advantages arise as already mentioned in connection with the process according to the invention. The auxiliary elements are preferably alkalis and / or alkaline earths, in particular Na and / or K and / or Ca and / or Li, and / or Fe, preferably mixtures of at least two of the elements Na, K, Ca, Li, and Fe.

[0085] Particularly preferred is / are

[0086] - the Na content is at least 2 ppm - 50 ppm and / or

[0087] - the K content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or

[0088] - the Ca content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm

[0089] - 20 ppm, and / or

[0090] - the Li content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm

[0091] - 20 ppm, and / or

[0092] - the Fe content is at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm.

[0093] The powder mixture preferably contains less than 0.01 mol% of material additives comprising fluorine and / or yttrium compounds.

[0094] The foreign elements of the powder mixture according to the invention are preferably elements of main group III and / or main group V and / or transition metals with the exception of Fe.

[0095] Preferably, the content of the elements Cr, Mn, Co, Ni, Ti, Zn, and Zr is each < 2 ppm. Furthermore, the content of the elements B, P, and Cu is each < 1 ppm.

[0096] A further, in particular subordinate, aspect of the invention relates to a MAS glass body which can be produced in particular by carrying out the method according to the invention.

[0097] The MAS vitreous body according to the invention has a mass > 3 kg and a surface / volume ratio <1.5 cm-1, wherein the MAS vitreous body is X-ray amorphous.

[0098] The MAS glass body comprises 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiO2, preferably 25 to 35 mol% MgO, 10 to 25 mol% Al2O3 and 50 to 65 mol% SiO2, particularly preferably 30 mol% MgO, 10 mol% Al2O3 and 60 mol% SiO2, wherein the MAS glass body further comprises auxiliary elements and foreign elements, and the auxiliary elements are elements of the I main group and / or II main group and / or IV main group and / or Fe, wherein the total content of the auxiliary elements and foreign elements is 10 ppm - 300 ppm, in particular 30 ppm - 150 ppm, particularly preferably 50 ppm - 100 ppm.

[0099] The same or similar advantages arise as those already stated in connection with the method according to the invention.

[0100] An X-ray amorphous MAS vitreous body is a glass without extensive regions of long-range crystalline order, so that in a corresponding examination it only produces very widespread X-ray reflections (the so-called glass hillock).

[0101] X-ray amorphous in the context of the present invention means that there are no crystalline regions larger than 10 nm in the MAS glass body, which can be determined, for example, with a diffractometer.

[0102] Preferably, the auxiliary elements are alkalis and / or alkaline earths and / or Fe.

[0103] With regard to the alkalis and / or alkaline earths, the auxiliary elements are particularly preferably Na and / or K and / or Ca and / or Li.

[0104] Preferably, the MAS glass body comprises mixtures of at least two of the elements Na, K, Ca, Li and Fe.

[0105] Particularly preferred is / are

[0106] - the Na content is at least 2 ppm - 50 ppm and / or

[0107] - the K content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or

[0108] - the Ca content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm

[0109] - 20 ppm, and / or

[0110] - the Li content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm

[0111] - 20 ppm, and / or - the Fe content is at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm.

[0112] The MAS glass body preferably has less than 0.01 mol% of material additives comprising fluorine and / or yttrium compounds.

[0113] The foreign elements of the MAS glass body according to the invention are preferably elements of the III main group and / or the V main group and / or transition metals with the exception of Fe.

[0114] Preferably, the content of the elements Cr, Mn, Co, Ni, Ti, Zn, and Zr is each < 2 ppm. Furthermore, the content of the elements B, P, and Cu is each < 1 ppm.

[0115] Due to the specified content of the foreign elements mentioned, elements that can promote crystallization, such as Ti and Zr, are kept to a minimum or preferably avoided. Furthermore, the MAS glass bodies according to the invention have a composition that is not harmful to semiconductor manufacturing processes.

[0116] The MAS glass body can be ring-shaped, cylindrical, or rod-shaped. The cylindrical shape enables, for example, the subsequent production of ring-shaped MAS glass components.

[0117] The present invention also relates to a component comprising the MAS glass body described above.

[0118] All definitions and preferred embodiments listed above for the method according to the invention and the MAS glass body according to the invention apply analogously to the component.

[0119] In a preferred embodiment, the MAS glass body according to the invention or a component produced from an MAS glass body according to the invention is used in semiconductor production, preferably in an etching chamber. This use of an MAS glass body according to the invention also relates to MAS glass bodies produced by the method according to the invention.

[0120] All definitions and preferred embodiments listed above for the method according to the invention and the MAS glass body according to the invention apply analogously to the use of the MAS glass body and / or the component.

[0121] The invention is explained in more detail below using non-limiting examples.

[0122] To produce a MAS glass body, a powder mixture was prepared, using the oxides of the elements Si, Al and Mg as starting materials, which were weighed and mixed in the following composition:

[0123] - MgO: 30 mol%

[0124] - AI2O3: 10 mol%

[0125] - SiO2: 60 mol%

[0126] The proportion of auxiliary elements and foreign elements in the mixture was set at 60 ppm, with a

[0127] - Ca content of: 10 ppm,

[0128] - Fe content of: 1.5 ppm,

[0129] - Na content of: 35 ppm,

[0130] - K content of: 6 ppm,

[0131] - Content of foreign elements, namely Mn, Cr and Zr, was set at < 1 ppm.

[0132] A 300 g sample was melted in a Pt / Rh crucible at 1,650 °C for 3 hours. The melt was then poured into cold, deionized water.

[0133] The resulting frits were ground and remelted for 6 hours and 40 seconds at 1,650 °C. To determine the second melting time, the melt was observed and melted until a clear and bubble-free melt was formed.

[0134] After the second melting process, the glass was poured into a metal mold.

[0135] A clear MAS glass body without any segregation was obtained. Example 2:

[0136] In another embodiment, the powder mixture was prepared according to Example 1, and a 3 kg sample was produced. The ground frit was melted in a large Pt / Rh crucible and then poured into a metallic ring mold. A clear, demixed ring was obtained with an outer diameter of 400 mm, an inner diameter of 300 mm, and a height of 21 mm. This ring-shaped MAS glass body is shown in Fig. 6 and shows no signs of demixing.

Claims

Claims 1. Method for producing an X-ray amorphous MAS vitreous body with - a mass > 3 kg and - a surface / volume ratio <1.5 cm -1 comprising the process steps: a) preparing a powder mixture with 10 to 40 mol% MgO, 5 to 30 mol% AI2O3 and 40 to 70 mol% SiCh or precursors of these raw materials, as well as with auxiliary elements and foreign elements, wherein the auxiliary elements are elements of the I. main group and / or II. main group and / or IV. main group and / or Fe, wherein a The total content of auxiliary elements and foreign elements is set at at least 10 ppm - 300 ppm, in particular at least 30 ppm - 150 ppm, particularly preferably at least 50 ppm - 100 ppm; b) melting the powder mixture provided in step a); c) cooling the melt produced in step b) and comminuting the cooled melt to particles with a diameter of < 10 mm; d) heating and melting the particles obtained in step c); and e) cooling the melt obtained in step d).

2. Process according to claim 1, characterized in that alkalis and / or alkaline earths, in particular elements Na and / or K and / or Ca and / or Li, and / or Fe, preferably mixtures of at least two of the elements Na, K, Ca, Li and Fe, are used as auxiliary elements.

3. Method according to claim 2, characterized in that - a Na content of at least 2 ppm - 50 ppm and / or - a K content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - a Ca content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - a Li content of at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - an Fe content of at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm, is set.

4. Process according to one of the preceding claims, characterized in that the foreign elements are elements of main group III and / or main group V and / or transition metals with the exception of Fe.

5. Process according to claim 4, characterized in that the content of the elements Cr, Mn, Co, Ni, Ti, Zn and Zr is each < 2 ppm and / or the content of the elements B, P and Cu is each < 1 ppm.

6. Process according to one of the preceding claims, characterized in that in step a) a powder mixture is prepared which comprises 25 to 35 mol% MgO, 10 to 25 mol% Al2O3 and 50 to 65 mol% SiO2, particularly preferably 30 mol% MgO, 10 mol% Al2O3 and 60 mol% SiO2.

7. Method according to one of the preceding claims, characterized in that step b) and / or c) is carried out with a temperature of 1200 °C to 2000 °C, preferably of 1500 °C to 1750 °C.

8. Powder mixture for producing an X-ray amorphous MAS glass body, in particular for use in a process according to one of claims 1 to 7, wherein the powder mixture contains 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiO2 or precursors of these raw materials, preferably 25 to 35 mol% MgO, 10 to 25 mol% Al2O3 and 50 to 65 mol% SiO2 or precursors of these raw materials, particularly preferably 30 mol% MgO, 10 mol% Al2O3 and 60 mol% SiO2 or precursors of these raw materials, wherein the powder mixture further comprises auxiliary elements and foreign elements, wherein the auxiliary elements are elements of the I. main group and / or II. main group and / or IV. main group and / or Fe, and the total content of the auxiliary elements and foreign elements 10 ppm - 300 ppm, in particular 30 ppm - 150 ppm, particularly preferably 50 ppm - 100 ppm.

9. Powder mixture according to claim 8, characterized in that the auxiliary elements are alkalis and / or alkaline earths, in particular Na and / or K and / or Ca and / or Li, and / or Fe, preferably mixtures of at least two of the elements Na, K, Ca, Li and Fe, wherein preferably - the Na content is at least 2 ppm - 50 ppm and / or - the K content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Ca content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Li content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Fe content is at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm, is / are.

10. Powder mixture according to one of claims 8 or 9, characterized in that the foreign elements are elements of the III. main group and / or the V. main group and / or transition metals with the exception of Fe, wherein preferably the content of the elements Cr, Mn, Co, Ni, Ti, Zn and Zr each < 2 ppm and / or the content of the elements B, P, and Cu is each < 1 ppm.

11. MAS glass body, in particular produced by a process according to one of claims 1 to 7, having a mass > 3 kg and a surface-to-volume ratio < 1.5 cm -1 , where the MAS vitreous body is X-ray amorphous and 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiO2, preferably 25 to 35 mol% MgO, 10 to 25 mol% Al2O3 and 50 to 65 mol% SiO2, particularly preferably 30 mol% MgO, 10 mol% Al2O3 and 60 mol% SiO2, wherein the MAS glass body further comprises auxiliary elements and foreign elements, wherein the auxiliary elements are elements of the I main group and / or II main group and / or IV main group and / or Fe, and the total content of the auxiliary elements and foreign elements is 10 ppm - 300 ppm, in particular 30 ppm - 150 ppm, particularly preferably 50 ppm - 100 ppm.

12. MAS glass body according to claim 11, characterized in that the auxiliary elements are alkalis and / or alkaline earths, in particular Na and / or K and / or Ca and / or Li, and / or Fe, preferably mixtures of at least two of the elements Na, K, Ca, Li and Fe, wherein preferably - the Na content is at least 2 ppm - 50 ppm and / or - the K content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Ca content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Li content is at least 0.5 ppm - 50 ppm, in particular at least 0.5 ppm - 20 ppm, and / or - the Fe content is at least 0.5 ppm - 10 ppm, in particular at least 1 ppm - 5 ppm, is / are .

13. MAS glass body according to claim 11 or 12, characterized in that the foreign elements are elements of main group III and / or main group V and / or transition metals with the exception of Fe, wherein preferably the content of the elements Cr, Mn, Co, Ni, Ti, Zn and Zr is each < 2 ppm and / or the content of the elements B, P and Cu is each < 1 ppm.

14. MAS glass body according to one of claims 11 to 13, characterized in that the MAS glass body has a ring shape or a cylindrical shape or a rod shape.

15. Use of a MAS glass body according to one of claims 11 to 14 or of a component made from a MAS glass body according to one of claims 11 to 14 in an etching chamber.

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