Process for producing an mas glass with high etch homogenieity

Abstract

What is described is a process for producing an MAS glass which is characterized in that 10 to 40 mol% of MgO, 5 to 30 mol% of Al2O3 and 40 to 70 mol% of SiO2 or precursors of these raw materials are mixed, the mixture is melted, the melt is cooled and comminuted to afford particles of less than 10 mm, preferably less than mm and particularly preferably less than 2 mm in diameter, the particles are heated and melted and the melt is cooled, as well as an MAS glass obtainable by this process, a component comprising the MAS glass and the use of such a component.

Description

[0001] Process for producing a MAS glass with high etching homogeneity

[0002] Description

[0003] The present invention relates to a method for producing a MAS glass, a MAS glass obtainable according to this method, a component comprising this MAS glass and the use of such a component.

[0004] 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.

[0005] 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.

[0006] US Pat. No. 7,084,084 B2 discloses the use of a halogenated gas, such as a fluorine-containing or chlorine-containing gas, in plasma etching. The halogenated gas and its plasma are highly reactive and are therefore used in various steps, for example, as an etching gas in an etching process or cleaning process in the semiconductor industry. The halogenated gases and plasmas used include fluorine-containing gases such as F2, HF, CF4, C2F6, C3F8, C4F8, CHF3, SF6, and NF3; chlorine-containing gases such as Cl2, HCl, BCl3, and CCl4; and bromine-containing gases such as Br2 and HBr.

[0007] Elemental fluorine, fluorine ions, and radicals not only exhibit the desired etching effect but also react with the other components exposed to the plasma. The resulting corrosive wear can lead to the generation of particles and severe deterioration of the components used, which then require replacement. Due to its high chemical resistance to many substances used in the manufacturing process and its relatively high temperature resistance, quartz glass is often used for components subject to particularly high stress. This particularly applies to the etching chamber. However, when fluorine-containing etching gas is used, the SiO2 in the quartz glass reacts with reactive fluorine to form SiF4. The boiling point of SiF4 is -86 °C, so this compound easily enters the gas phase, which is accompanied by severe corrosion of the quartz glass surface and the formation of particles.

[0008] A well-known attempt to counteract quartz corrosion through fluoridation is doping. The aim is to ensure that the element added to the quartz glass forms a compound with the halogenated gas used that has a higher sublimation temperature or boiling point than the silicon halide present in the quartz glass. The resulting glass network exhibits a reduced etch rate.

[0009] For doping, oxides of Sm, Eu, Yb, Pm, Nd, Ce, Tb, Gd, Ba, Mg, Y, Tm, Dy, Ho, Er, Cd, Co, Cr, Cs and / or Zr can be added, but these can lead to destruction of the quartz glass network.

[0010] Specifically, the SiO2 network of which quartz glass is composed is disrupted by the incorporation of secondary elements, and non-crosslinking oxygen with weak binding force is often formed locally. This undesirable phenomenon is particularly detrimental under etching conditions. It is therefore possible that the addition of secondary elements locally increases the etching rate of glass and reduces its durability.

[0011] In order to maintain the stability of the glass despite doping, additional Al, In, Cu, Fe, Bi, Ga and / or Ti can be added as oxides.

[0012] A known doped glass mixture consists of 20 wt.% MgO, 20 wt.% Al2O3, and 60 wt.% SiO2 and is referred to as MAS glass. During etching processes with fluorine-containing etching gas, the glass mixture reacts with reactive fluorine to form MgF2. The boiling point of MgF2 is >2200 °C, so it hardly enters the gas phase, which is associated with reduced corrosion on the surface of the glass mixture and leads to a minimization of the etching rate. Other dopings, such as with MgF2, to further reduce the etching rate are also known from the prior art (WO2022075687A1).

[0013] A disadvantage of the production of conventional MAS glasses is that material inhomogeneities often arise during the melting of the magnesium, aluminum, and silicon oxide components to produce the glass. These inhomogeneities can arise from insufficient mixing of the raw materials, as well as from demixing or local crystallization during the production process. These material inhomogeneities also lead to locally varying etch rates and thus to inhomogeneous etch removal. They therefore pose a high risk of particle formation during the plasma etching process. Obvious qualitative indicators of inhomogeneities are streaks or cloudy glass areas. A very good quantitative detection of material inhomogeneities with different etch rates is the measurement of the surface roughness of the glass after an etching process.The surface topology reflects the spatial distribution of the inhomogeneities and the associated inhomogeneity in the etching rate very precisely.

[0014] Plasma etching with fluorine-containing plasma requires a material that combines a low etch rate with high etch homogeneity, thus resulting in low particle release during the etching process. While materials of the XO-ALOs-SiOz type (X = alkaline earth metals, particularly Mg, Ca, and Ba) are known from the prior art, which exhibit relatively low etch rates, these often have the disadvantage of low etch homogeneity, which can lead to particle release during the etching process.

[0015] The object of the present invention is therefore to overcome the disadvantages of the prior art. In particular, it is to provide a simple, homogeneous MAS glass in which crystallization and demixing during curing are minimized. Furthermore, the MAS glass should have a reduced etch rate and high etch homogeneity.

[0016] These objects were surprisingly achieved by a method for producing a MAS glass according to claim 1 and by a MAS glass according to claim 10.

[0017] Advantageous further developments are described in the subclaims. The MAS glasses produced using the inventive method have the advantage of being extremely homogeneous, thus avoiding crystallization and demixing. Furthermore, the MAS glasses according to the invention exhibit a reduced etching rate and high etching homogeneity. These advantageous properties can also be reliably achieved for larger dimensions of the MAS glasses or components.

[0018] 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.

[0019] All features of one embodiment may be combined with features of another embodiment if the features of the different embodiments are compatible.

[0020] 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.

[0021] In the present description and claims, the terms "includes," "comprises," and / or "comprising" may also mean "consisting of," i.e., 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 process for producing a MAS glass, characterized in that a) 10 to 40 mol% MgO, 5 to 30 mol% Al2O3, and 40 to 70 mol% SiC or precursors of these raw materials are mixed, b) the mixture from step a) is melted, c) the melt from step b) is cooled and comminuted into particles with a diameter of less than 10 mm, preferably less than 5 mm, and particularly preferably less than 2 mm, d) the particles from step c) are heated and melted, and e) the melt from step d) is cooled.

[0022] Precursors of these raw materials are preferably understood to be the corresponding hydroxides and / or carbonates of MgO and AI2O3.

[0023] 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.

[0024] In a preferred embodiment, the process according to the invention is characterized in that the mixture in steps b) and / or d) is heated to a temperature of 1200 to 2000 °C, preferably to a temperature of 1500 to 1750 °C and particularly preferably 1550 to 1700 °C.

[0025] 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.

[0026] 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. In a preferred embodiment, the process according to the invention is characterized in that the mixture from step d) is cooled to a temperature below 25°C in step e).

[0027] In a preferred embodiment, the process according to the invention is characterized in that the mixture 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In a preferred embodiment, the process according to the invention is characterized in that the cooling of the mixture in step e) takes place in a steel mold coated with a release agent in a cooling furnace.

[0032] 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 production of the MAS glass. The present invention further relates to a MAS glass obtainable by the process described above.

[0033] All definitions and preferred embodiments listed above for the process according to the invention apply analogously to the MAS glass obtainable by the process described above.

[0034] In a preferred embodiment, the MAS glass is obtainable by the above-described process according to the invention, characterized in that the MAS glass comprises 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiO2, is X-ray amorphous and that the surface of the glass, after the etching process described below, has a mean roughness (R a ) of less than 50 nm, preferably less than 30 nm, particularly preferably less than 10 nm and most preferably less than 5 nm, wherein the mean roughness (R a ) according to ISO 4287-1: 1984.

[0035] In a preferred embodiment, the MAS glass is obtainable by the above-described method according to the invention, characterized in that the surface of the glass, after the etching process described below, has an average roughness depth (R z) of less than 100 nm, preferably of less than 70 nm, particularly preferably of less than 50 nm and most preferably of less than 35 nm, wherein the average roughness (R z ) according to ISO 4287-1: 1984.

[0036] For the purposes of the present invention, etch homogeneity refers to the local variations in etching behavior. The smaller the local variations in etching behavior, the higher the etch homogeneity of the MAS glass.

[0037] The etching homogeneity can be determined quantitatively using a standardized measurement of the surface roughness (Ra and Rz values) of the MAS glass after a defined etching process.

[0038] The etching homogeneity is described by the unevenness of the surface after the etching process and can be measured by parameters such as the mean roughness (R a ) and the average roughness depth (R z ) can be represented quantitatively. A low value for R a and Rz expresses a high etching homogeneity. R a is defined by the mean distance of a measuring point on the surface to the center line. R z is defined by the mean value of individual roughness depths of five consecutive individual measurement sections in the roughness profile. The determination of the roughness values ​​R a and R z is carried out in accordance with ISO 4287-1: 1984.

[0039] The determination of the etching homogeneity of the MAS glasses can be achieved by the following steps (specific etching process): 1. cleaning the MAS glass, 2. masking certain glass areas with Kapton tape and 3. an etching process.

[0040] The MAS glasses are cleaned using the following wet chemical steps:

[0041] 1. Ultrasound 100% at 10min with Tickopur R33 (5%),

[0042] 2. Solvent cleaning with acetone and isopropanol and

[0043] 3. Rinse with DI water and dry.

[0044] Tickopur R33 (5%) is a universal cleaner for ultrasound that contains 5 to 15% anionic surfactants, 5 to 15% phosphate, less than 5% non-ionic surfactants, less than 5% silicate and complexing agents.

[0045] The masking of certain glass areas with Kapton tape is done by partially masking certain areas of the substrate with plasma-stable Kapton foil.

[0046] The etching process for smoothing the surface of the MAS glasses according to the invention is carried out in the Sentech Si-500 apparatus. The following parameters are set in the associated execution software:

[0047] 1. ICP 500 W,

[0048] 2. RF bias 200 W, 3. Choke 100% (0.25 Pa),

[0049] 4. CHF330 sccm,

[0050] 5. Etching time (cyclic, 2 min etching, 3 min cooling),

[0051] 6. He back cooling 1000 Pa,

[0052] 7. Heating power 0% and

[0053] 8. Al sampling.

[0054] The roughness of the glass surfaces was determined according to ISO 4287-1: 1984. The etch depths were determined by measuring the etch profile (i.e., a section through the etching step) under a light microscope. The etch rates were determined as a function of time to the etch profile.

[0055] Compared to undoped quartz glass, the MAS glass according to the invention exhibits an approximately eight-fold lower etch rate (nm / min) with comparably good etch homogeneity (Ra and Rz values). Compared to known MAS glass, the MAS glass according to the invention exhibits better etch homogeneity (Ra and Rz values). These advantageous properties are surprisingly achieved through the use of the process according to the invention.

[0056] In a preferred embodiment, the MAS glass is obtainable by the process according to the invention described above, characterized in that it is X-ray amorphous.

[0057] An X-ray amorphous MAS glass is a glass without extensive regions of long-range crystalline order, so that it yields only very diffuse X-ray reflections (the so-called glass hillock) when examined accordingly. X-ray amorphous in the context of the present invention means that the MAS glass contains no crystalline regions larger than 10 nm, which can be determined, for example, using a diffractometer.

[0058] In a preferred embodiment, the MAS glass according to the invention is obtainable by the process according to the invention described above, characterized in that it comprises 20 to 40 mol% MgO, 5 to 30 mol% AI2O3 and 40 to 70 mol% SiCh, preferably 25 to 35 mol% MgO, 10 to 25 mol% AI2O3 and 50 to 65 mol% SiO2.

[0059] In a preferred embodiment, the MAS glass is obtainable by the above-described inventive process, characterized in that the MAS glass contains less than 0.01 mol% of material additives comprising fluorine and / or yttrium compounds. This has the advantage of further minimizing the risk of local inhomogeneities forming during the material manufacturing process.

[0060] The homogeneity of an optical substrate characterizes changes in the refractive index, which lead to a deformation of the transmitted wavefront and polarizing transmission effects. A high degree of homogeneity or a small change is particularly important for applications with high-power lasers. Homogeneity fluctuations arise from the melting processes during material production. Inaccuracies in mixing and thermodynamic imbalances lead to density fluctuations. In addition, deformations can occur due to cooling and annealing processes. Inhomogeneities occur in the form of global inhomogeneity (deviation of the refractive index across the entire piece of glass) or in the form of striae (localized deviations from homogeneity in a glass with a length of 0.1 mm to 2 mm).Inclusions are foreign bodies present in optical glass and can arise, for example, from contamination during melting, incomplete melting of substrate batches, and wall materials with low solubility. Furthermore, bubbles can form as a result of reactions during glass melting. The bubbles are almost completely eliminated in the finishing step during glass melting. In a preferred embodiment, the MAS glass according to the invention is obtainable by the above-described inventive process, characterized in that it contains less than 100 ppm of crystallization-promoting elements.

[0061] In a preferred embodiment, the MAS glass according to the invention is obtainable by the process according to the invention described above, characterized in that the Al atoms contained therein are more than 80%, preferably more than 90%, particularly preferably more than 95% in fourfold coordination to oxygen.

[0062] This has the advantage that it simplifies homogeneous curing and the formation of an X-ray amorphous glass and makes crystallization more difficult.

[0063] The glass structure and the incorporation of the individual cations change depending on the MgO / AlCh ratio. A high proportion of Mg(II) leads to the formation of non-bridging oxygens (NBOs), which reduce the viscosity. The proportion of non-bridging oxygens depends on the MgO / AlCh ratio. As long as the ratio is < 1, magnesium is incorporated as a glass former, i.e., one Mg(II) ion stabilizes two [AlC] p-tetrahedra (tetravalent aluminum). If the Mg(II) proportion is further increased, Mg(II) is incorporated as a glass converter, which leads to the formation of NBOs and correspondingly reduces the viscosity.

[0064] The proportion of Al atoms present in four-fold coordination is determined using the MQMAS-NMR (multiple quantum magic angle spinning nuclear magnetic resonance spectroscopy) measurement method.

[0065] For example, NMR spectra are recorded on a Varian VNMRs 11.7 T NMR spectrometer using a Varian 1.6 mm T3-MAS-NMR probe head at rotation frequencies of 35 kHz. To support the results, the 27 AI-MAS NMR spectra were also generated in a field of 7 T (Bruker Avance III spectrometer; 4 mm triple resonance probe head; rotation frequency 10 kHz).

[0066] In a preferred embodiment, the MAS glass according to the invention is obtainable by the above-described process according to the invention, characterized in that the coefficient of linear expansion (CTE) of the MAS glass is greater than 3.0x l0' 6 K' 1 (300 to 600 °C), preferably greater than 4.0x l0' 6 K' 1 (300 to 600 °C) and more preferably greater than 4.5x l0' 6 K' 1 (300 to 600 °C).

[0067] The coefficient of linear expansion (CTE) is a material property that describes the behavior of a material with respect to changes in its dimensions when exposed to temperature changes. The effect responsible for this is thermal expansion. Since thermal expansion does not occur uniformly across all temperature ranges for many materials, the coefficient of thermal expansion itself is also temperature-dependent and is therefore specified for a reference temperature or temperature range.

[0068] The coefficient of linear expansion (CTE) is determined according to ISO 7991-1998.

[0069] In a preferred embodiment, the MAS glass according to the invention is obtainable by the process according to the invention described above, characterized in that it has a glass transition temperature (T g ) of less than 900 °C, preferably less than 850 °C and particularly preferably less than 800 °C.

[0070] The glass transition temperature (T g ) is a material property at which a glass exhibits the greatest change in deformability. The glass transition temperature separates the brittle, energy-elastic region below, where the material exists as a glass, from the soft, entropy-elastic region above.

[0071] The determination of the glass transition temperature (T g ) is carried out in accordance with ISO 7884-8: 1998.

[0072] A lower glass transition temperature has the advantage that the oxides used to produce the glass become miscible at lower temperatures and the produced glass can be formed at lower temperatures.

[0073] In a preferred embodiment, the MAS glass according to the invention is obtainable by the process according to the invention described above, characterized in that it is not fire polished.

[0074] Fire polishing is costly and can lead to deformation of the component geometry, which is why it is considered disadvantageous. After grinding a glass part, the glass surface is usually rough and matte, which is why fire polishing is used to achieve a smooth surface by heating and leveling the surface. In this one preferred embodiment of the invention, no fire polishing is necessary.

[0075] In a preferred embodiment, the MAS glass according to the invention is obtainable by the above-described method according to the invention, characterized in that the plasma etching rate of the MAS glass is lower than that of a quartz glass by more than 50%, preferably by more than 70% and particularly preferably by more than 85%.

[0076] In a preferred embodiment, the MAS glass according to the invention is obtainable by the above-described method according to the invention, characterized in that the plasma etching rate of the MAS glass is less than 50 nm / min, preferably 40 nm / min and particularly preferably 30 nm / min.

[0077] The plasma etch depth is determined by measuring the etch profile (i.e., a cross-section through the etching step) under a light microscope. The plasma etch rate is defined as the etch rate resulting from the etching of a material using plasma. The etch rate is defined as the thickness of the material to be etched removed per unit of time. Relative etch rates result from the ratio of the etch rates of the materials being compared. The etch rate is determined by measuring the etch profile over a specific time period.

[0078] The present invention also relates to a component comprising the MAS glass described above.

[0079] All definitions and preferred embodiments listed above for the process according to the invention and the MAS glass according to the invention apply analogously to the component.

[0080] In a preferred embodiment, the component according to the invention is used in semiconductor production, preferably in an etching chamber.

[0081] All definitions and preferred embodiments listed above for the method according to the invention and the MAS glass according to the invention apply analogously to the use of the component.

[0082] The invention is explained in more detail below using non-limiting examples. It will be understood by those skilled in the art that the use of CaO and its precursors instead of MgO and its precursors also leads to comparable results.

[0083] Examples

[0084] Glasses were produced at temperatures between approximately 1600 and 1700 °C. 300 g each of the mixtures listed in Table 1 were melted in Pt and Pt / Rh crucibles. A summary of the production conditions can be found in Tables 1 and 2. The glasses were first melted at temperature Ti for time ti. The cooled melt was then ground and melted again at temperature T2 and time tz. After the second melting process, the melt was poured into a metal mold. The melting time primarily depends on the time required to form a clear and bubble-free melt. Correspondingly longer times (and higher temperatures) were required for high-melting compositions. For some compositions, the amount of glass was also varied, as special geometries were required, some of which necessitated a very high crucible fill level.Accordingly, the melting process for these compositions also took a longer time.

[0085] It has been shown that glass No. 1 (Tables 1 & 2) can also be melted at a temperature of 1560 °C. However, it takes a comparatively long time for the laboratory melt to become bubble-free. To ensure better homogeneity and facilitate pouring, a temperature of 1650 °C was chosen for production. The glass was then poured into a steel mold coated with a release agent and transferred to a lehr. The lehr was preheated to 810 °C and then turned off to ensure slow cooling (1-2 K / min) to room temperature. Table 1: Composition of the MAS glasses

[0086] Table 2: Melting temperature and melting time of MAS glasses

[0087] A summary of the properties determined by dilatometry (heating rate 5 K / min) can be found in Table 3. It is known that glasses with a low CTE often have high glass transition temperatures. This is usually a problem in joining applications in the field of fuel cells. Here, high CTEs and high glass transition temperatures are equally required. In the MAS system, it is shown that T gHowever, CTE and CTE do not follow exactly the same composition trends. The higher the SiO2 content, the lower the CTE. A high MgO content increases the CTE. The glass transition temperature increases with increasing SiO2 concentrations. However, this dependence is not as strong as the dependence on the MgO / Al2O3 ratio, so the highest glass transition temperature is not found at the highest SiO2 content. This is also due to the fact that the glass structure and the incorporation of the individual cations change depending on the MgO / Al2O3 ratio. A high proportion of Mg(II) leads to the formation of non-bridging oxygens (NBO), which reduce the viscosity. However, Mg(II) can be incorporated into the glass not only as a network modifier, but also as a network former. The proportion depends on the MgO / Al2O3 ratio. As long as the ratio is < 1, magnesium is incorporated as a network former, i.e.One Mg(II) ion stabilizes two [AlC]' tetrahedra. If the Mg(II) content is further increased, Mg(II) is incorporated as a network modifier, leading to the formation of NBOs and correspondingly reducing the viscosity.

[0088] Table 3: Glass transition temperature, linear thermal expansion coefficient and dilatometric softening point of the MAS glasses

[0089] To determine the tendency to crystallize, glass fragments were melted in a corundum crucible. The crucibles were filled with glass at room temperature and then transferred to a furnace preheated to 1700 °C. After a few minutes, the furnace was cooled at 5 K / min. This cooling rate can be maintained up to approximately 1000 °C. At lower temperatures, the furnace cools correspondingly more slowly. The resulting MAS glasses are clear and X-ray amorphous.

[0090] A determination of the etching homogeneity of the MAS glasses will be achieved by the following steps: 1. cleaning the MAS glass, 2. masking certain glass areas with Kapton tape and 3. an etching process.

[0091] The MAS glasses are cleaned using the following wet chemical steps:

[0092] 1. Ultrasound 100% at 10min with Tickopur R33 (5%), 2. Solvent cleaning with acetone and isopropanol and

[0093] 3. Rinse with DI water and dry.

[0094] Tickopur R33 (5%) is a universal cleaner for ultrasound that contains 5 to 15% anionic surfactants, 5 to 15% phosphate, less than 5% non-ionic surfactants, less than 5% silicate and complexing agents.

[0095] The masking of certain glass areas with Kapton tape is done by partially masking certain areas of the substrate with plasma-stable Kapton foil.

[0096] The etching process for smoothing the surface of the MAS glasses according to the invention is carried out in the Sentech Si-500 apparatus. The following parameters are set in the associated execution software:

[0097] 1. ICP 500 W,

[0098] 2. RF bias 200 W,

[0099] 3. Throttle 100% (0.25 Pa),

[0100] 4. CHF3 30 sccm, 5. Etching time (cyclic, 2 min etching, 3 min cooling),

[0101] 6. He back cooling 1000 Pa,

[0102] 7. Heating power 0% and

[0103] 8. Al sampling.

[0104] The total etching process took 40 minutes. The surface roughness of the glasses was determined according to ISO 4287-1: 1984. The etch depths were determined by measuring the etch profile (i.e., a section through the etching step) with a light microscope. The etch rates were determined as a function of time to the etch depth. Table 4: Etch rates, etch depths, and surface roughness of the MAS glasses

[0105] Table 4 shows that the MAS glasses according to the invention have a significantly improved etching rate and comparable etching homogeneity compared to the undoped quartz reference sample.

Claims

Claims 1. A process for producing an MAS glass, characterized in that a) 10 to 40 mol% MgO, 5 to 30 mol% AI2O3 and 40 to 70 mol% SiC or precursors of these raw materials are mixed, b) the mixture from step a) is melted, c) the melt from step b) is cooled and comminuted to particles with a diameter of less than 10 mm, preferably less than 5 mm and particularly preferably less than 2 mm, d) the particles from step c) are heated and melted and e) the melt from step d) is cooled.

2. The method according to claim 1, characterized in that steps c), d) and e) are carried out several times, the cooled melt in step c) being the melt previously produced by step e).

3. Process according to one of the preceding claims, characterized in that the mixture in steps b) and / or d) is heated to a temperature of 1200 to 2000 °C, preferably to a temperature of 1500 to 1750 °C.

4. Process according to one of the preceding claims, characterized in that the duration of step b) is 0.1 to 10 hours, preferably 0.1 to 7 hours.

5. Process according to one of the preceding claims, characterized in that the duration of step d) is 0.1 to 10 hours, preferably 0.1 to 7 hours.

6. Method according to one of the preceding claims, characterized in that the mixture from step d) is cooled in step e) to a temperature below 25 °C.

7. Process according to one of the preceding claims, characterized in that the mixture from step d) is cooled in step e) first rapidly to a temperature of 600 to 900 °C and then more slowly to a temperature of below 25 °C.

8. Process according to one of the preceding claims, characterized in that the heating of the mixture in steps b) and / or d) takes place in Pt and / or Pt / Rh crucibles.

9. Process according to one of the preceding claims, characterized in that the cooling of the mixture in step e) takes place in a steel mold coated with a release agent in a cooling furnace.

10. MAS glass obtainable by the process according to any one of claims 1 to 9.

11. MAS glass according to claim 10, comprising 10 to 40 mol% MgO, 5 to 30 mol% Al2O3 and 40 to 70 mol% SiCh, characterized in that the MAS glass is X-ray amorphous and that the surface of the MAS glass has a mean roughness (R a ) of less than 50 nm, preferably less than 30 nm, particularly preferably less than 10 nm and most preferably less than 5 nm, wherein the mean roughness (R a ) according to ISO 4287-1:1984.

12. MAS glass according to one of claims 10 or 11, comprising 20 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. MAS glass according to one of claims 10 to 12, characterized in that the MAS glass contains less than 0.01 mol% of material additives comprising fluorine and / or yttrium compounds. MAS glass according to one of claims 10 to 13, characterized in that more than 80%, preferably more than 90%, of the Al atoms contained in the MAS glass are in four-fold coordination with oxygen. MAS glass according to one of claims 10 to 14, characterized in that the coefficient of linear expansion (CTE) of the MAS glass is greater than 3.0×10' 6 K' 1(300 to 600 °C). MAS glass according to one of claims 10 to 15, characterized in that the MAS glass has a glass transition temperature of less than 900 °C. MAS glass according to one of claims 10 to 16, characterized in that the relative plasma etching rate of the MAS glass is more than 50%, preferably more than 70%, and particularly preferably more than 85% lower than that of quartz glass. Component comprising a MAS glass according to one of claims 10 to 17. Component according to claim 18, characterized in that the component is not fire-polished. Use of the component according to claim 19 in semiconductor production. Use according to claim 20 in an etching chamber.

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