TUBE-SHAPED COMPOSITE BODY MADE OF QUARTZ GLASS AND METHOD FOR MANUFACTURING AND USING THE SAME

Description

Technical background

[0001] The present invention relates to a composite body made of quartz glass, in particular a tubular composite body made of quartz glass with a length of at least 1000 mm, a raw wall and an inner diameter of at least 250 mm.

[0002] Furthermore, the invention relates to the production of a tubular quartz glass composite body, in particular to a method for producing a tubular quartz glass composite body in an external deposition process comprising the following process steps: (a) Providing a substrate tube which has a continuous through-opening running coaxially to a substrate tube longitudinal axis, a substrate tube outer diameter, a substrate tube inner diameter, a substrate tube outer surface, a substrate tube inner surface and a substrate tube wall with a wall thickness, (b) Rotating the substrate tube about an axis of rotation running coaxially or parallel to the substrate tube longitudinal axis, (c) Deposition of SiO 2 particles on the outer surface of the substrate tube by means of at least one deposition burner to form a composite of the substrate tube and an SiO 2 soot body, (d) Sintering the composite body by heating at a sintering temperature in a heating zone to form the tubular quartz glass composite body and using a holding device which is suitable for holding the composite body at least temporarily in the heating zone with the substrate tube longitudinal axis oriented vertically.

[0003] Quartz glass components in the form of preforms, tubes, rods, flanges, plates, rings, reactors, crucibles, and the like are used in semiconductor manufacturing and for the production of optical fibers. Such components are often produced from tubular semi-finished quartz glass by thermally forming and / or mechanically processing them. As productivity increases, larger dimensions of such components are increasingly sought, which, especially for tubular semi-finished products, requires larger wall thicknesses and inner diameters.

[0004] For the production of tubular semi-finished products made of synthetically produced silicon dioxide, CVD (chemical vapor deposition) processes are known, in which SiO2 particles are deposited from the gas phase onto a substrate. The CVD external deposition process, known by the abbreviation "OVD" (outside vapor deposition), is generally suitable for the production of large-volume semi-finished products. A silicon-containing starting material is converted into SiO2 particles in a reaction zone by means of flame hydrolysis or pyrolysis, and these particles are deposited layer by layer onto the outer surface of a cylindrical substrate rotating about its longitudinal axis. The reaction zone is created using a heat source, with the substrate's longitudinal axis and the heat source reciprocating back and forth relative to each other. The substrate can be tubular and is also referred to here and below as the "substrate tube."The substrate tube consists, for example, of quartz glass, SiC, SiSiC (reaction-bonded silicon-infiltrated silicon carbide), Al 2 O 3 or another ceramic material or of graphite and is held and rotated around its longitudinal axis by means of a lathe-like device, which is also referred to here as "substrate tube holder".

[0005] Depending on the temperature during the deposition process, the layer of synthetic SiO2 deposited on the substrate tube is either still porous and is referred to below as a "soot layer" or "soot body," or it forms a dense layer of more or less transparent quartz glass. In the case of a porous soot layer, this is sintered in a separate process step to form more or less transparent quartz glass (the sintering process is also referred to as "vitrification"). The resulting tubular quartz glass semi-finished product is subjected to mechanical, chemical, and / or thermal post-processing to produce a component made of synthetic quartz glass, such as a solid cylinder, a hollow cylinder, or parts of these components, which can themselves also serve as semi-finished products for the production of other components. State of the art

[0006] US Pat. No. 8,316,671B2 describes an OVD external deposition process for producing a hollow cylinder made of quartz glass. A quartz glass substrate tube is provided, and a porous SiO2 soot layer is deposited on its outer surface. The composite of substrate tube and SiO2 soot layer is vitrified in such a way that the inside of the substrate tube remains below the deformation temperature. For this purpose, the inner bore of the substrate tube can be cooled by a gas or liquid during the vitrification process. The inner wall of the resulting tubular quartz glass composite body is formed by the substrate tube; it is smooth and no longer requires mechanical processing.

[0007] US 2013 / 115391 A1 discloses a process for producing hollow quartz glass cylinders with a large outer diameter. A porous soot body made of silicon dioxide soot is deposited on a substrate using an OVD external deposition process. After removing the substrate, the soot body is sintered to form a hollow cylinder. Rings made of quartz glass with a low chlorine content and a low hydroxyl group content, thus exhibiting high viscosity, are sawn from this. The quartz glass rings are used as so-called "plasma etching rings" for holding semiconductor wafers in plasma etching systems.

[0008] To vitrify the soot body, it is held in a sintering furnace in a vertical orientation or in a horizontal orientation along its longitudinal axis. With a vertical orientation along the longitudinal axis, the soot body can be vitrified while standing on a pedestal. However, there is a risk that the soot body will deform and collapse due to its weight. This can result in a caterpillar-like structure of circumferential folds, which can prevent dimensional accuracy requirements from being met, and in particular, the specified minimum inner diameter may be exceeded.

[0009] The method known from EP 701 975 A2 avoids some of these disadvantages. In this method, the tubular soot body is introduced into a vitrification furnace and held therein in a vertical orientation by means of a holding device comprising a holding rod which extends from above through the inner bore of the soot body and which is connected to a holding foot on which the soot body initially rests with its lower end. The holding rod is made of carbon fiber reinforced graphite (CFC) and is tightly enclosed by a gas-permeable, thin-walled cladding tube made of pure graphite. In a position above the upper end of the cladding tube, a graphite support ring is embedded in the inner bore of the soot body and projects inward from the soot body wall into the soot body's inner bore.

[0010] During vitrification, the soot body is moved zone by zone, beginning with its upper end, through an annular heating element. The soot body gradually collapses onto the graphite cladding tube and also shrinks in length, resting on the support base during a first sintering phase. The position of the graphite support ring embedded in the soot body is selected so that, as a result of the increasing longitudinal shrinkage, it rests on the graphite cladding tube during a second sintering phase, so that the soot body is then held suspended at the upper end. This method is also referred to below as "suspended vitrification." After vitrification, the cladding tube is removed, and the internal bore of the resulting quartz glass tube is reworked by drilling, grinding, honing, or etching.

[0011] To reduce the graphite contact surfaces, a modification of this process according to DE 103 03 290 B3 provides a sleeve made of synthetic quartz glass between the support rod and the soot body to be vitrified. The production of this sleeve is time-consuming and costly, and it is or becomes part of the quartz glass tube.

[0012] In the process known from DE 100 64 730 A, SiO 2 particles are deposited on an elongated substrate tube which rotates about its longitudinal axis and which has a stepped outer diameter along its length. After removal of the stepped substrate tube, a porous, hollow-cylindrical soot body is obtained whose inner bore has a complementary shape corresponding to the outer diameter profile of the substrate tube, i.e. it has a stepped shoulder. The soot body thus obtained is vitrified while suspended vertically in a furnace, with the narrowed region of the inner bore being arranged at the top and a holding rod projecting into the inner bore from above engaging below the stepped shoulder. The reliable holding of a heavy soot body requires a relatively wide shoulder in the inner bore. Technical task

[0013] With increasingly larger quartz glass cylinders, the weight of the soot bodies to be sintered and the increasing temperature differences between the interior and exterior complicate the manufacturing process. With the processes described above, reliable support of heavy soot bodies during vitrification and the reproducible production of quartz glass tubes are problematic. In particular, rejects at late process stages, such as during vitrification of the soot body, must be avoided.

[0014] Similar problems also arise when vitrifying other bodies made of porous SiO 2 that have not been produced via the SiO 2 soot route, such as porous SiO 2 bodies that have been obtained via the well-known sol-gel route or by pressing processes.

[0015] The invention is therefore based on the object of specifying a method for producing such large-volume, tubular composite bodies made of quartz glass using an external deposition method, in particular using an OVD build-up welding method.

[0016] In particular, the invention is based on the object of specifying a method for the reproducible production of a tubular composite body made of quartz glass with a large inner diameter by the external deposition process, in particular with an inner diameter of more than 200 mm and with a wall thickness of more than 25 mm, which avoids the above-mentioned disadvantages and in which in particular the risk of rejects is reduced.

[0017] Furthermore, the invention is based on the object of providing a tubular quartz glass composite body which is characterized on the one hand by large dimensions, in particular by an inner diameter of more than 200 mm, a wall thickness of more than 25 mm and a length of at least 1000 mm, and at the same time by high dimensional accuracy. General description of the invention

[0018] With regard to the method for producing the tubular composite body made of quartz glass, this object is achieved according to the invention, starting from a method of the type mentioned at the outset, in that a holding device is used which comprises a holding element which is produced in a forming step in a holding region of the substrate tube.

[0019] The method comprises a process step in which a porous SiO2 soot body made of synthetic silicon dioxide is produced using an external deposition process, in particular an OVD external deposition process. This soot body is also referred to below as "soot body." The porous SiO2 soot body can optionally be subjected to a dehydration treatment in an inert gas, a chlorine-containing gas, or under vacuum to reduce the hydroxyl group content of the quartz glass before it is sintered to form a more or less transparent quartz glass. Sintering (or vitrification) takes place, for example, under vacuum or in an atmosphere containing helium, hydrogen, and / or nitrogen.

[0020] The substrate tube is designed to produce the SiO2 soot body with a large inner diameter on its outer surface using the external deposition process. The substrate tube, for example, has a length of up to 4 m and is cylindrical, conical, or stepped over its entire length or over part of its length. The inner contour is either constant or variable over the entire length of the substrate tube.

[0021] After the deposition process is complete, the substrate tube remains in the composite of substrate tube and soot body and becomes part of the tubular quartz glass composite body to be produced (hereinafter also referred to as "quartz glass composite body" or "composite body"). It is made of quartz glass and preferably has an inner diameter of at least 250 mm. Its wall thickness is preferably in the range of 4 mm to 10 mm and is thus small relative to its outer diameter. The wall thickness is usually less than 20% of the substrate tube's outer diameter. This makes the substrate tube lightweight, which reduces the dynamics of the rotational movement and facilitates handling and alignment, and also has a low thermal mass, which minimizes heat dissipation and the formation of thermal stresses within the wall.

[0022] On the other hand, the wall thickness of the substrate tube is large enough to support a large-volume SiO2 soot body. Therefore, the wall thickness of the substrate tube is preferably at least 1% of the substrate tube outer diameter. The wall thickness "WS" (in mm) can also depend on the substrate tube length. It is advantageous if the wall thickness also increases with increasing substrate tube length. Therefore, WS can alternatively be set as a function of the substrate tube outer diameter DS (in mm) and also taking into account the substrate tube length "LS" (in mm) as follows: WS <0.2*(LS / 2000mm)*DS .

[0023] After completion of the external deposition process and the optional dehydration treatment of the soot body, the soot body is sintered (vitrified) according to process step (d), specifically in the form of a composite consisting of the substrate tube and the SiO2 soot body, i.e., in conjunction with the substrate tube. The substrate tube used for this purpose is characterized by having a holding element that is produced in a holding area of ​​the substrate tube during a forming step.

[0024] The holding element forms part of the holding device during sintering of the composite body. It is designed, for example, as a local constriction of the through-holes or the substrate tube inner diameter, or as a local expansion of the substrate tube outer diameter. During sintering, it serves to suspend the composite body and interacts with a support element of the holding device. The support element is, for example, a cladding tube that is arranged within the substrate tube during sintering and onto which the composite body collapses during sintering. The holding element rests on the support element at least temporarily during sintering, thus enabling suspended glazing of the composite body.

[0025] In contrast to the prior art, the invention eliminates the need to connect a separate body to the inner bore of the soot body, which can serve as a suspension. During the connection process, damage and contamination of the soot body can occur. This is avoided in the invention by vitrifying the substrate tube, which is required anyway in the external deposition process, together with the soot body in the form of a composite body, and using the substrate tube as a component of the suspension.

[0026] For this purpose, the holding element is created in a holding area of ​​the substrate tube in a forming step.

[0027] The holding area is usually located near one of the front ends of the substrate tube. These front end areas may be essentially free of SiO2 soot particles after the soot deposition process. However, they may also be covered by the ends of the SiO2 soot body being formed.

[0028] The forming step for producing the holding element can be carried out before sintering (vitrification) according to process step (d).

[0029] With regard to a previously produced holding element, a first preferred method variant provides that the holding element is produced before the deposition of the SiO 2 particles according to method step (c), wherein the deposition of the SiO 2 particles according to method step (c) is preferably carried out such that the SiO 2 soot body covers the holding region.

[0030] In this process variant, the holding element is created by forming an existing substrate tube. The substrate tube wall is, for example, locally heated and softened and collapsed, forming an indentation in the wall, or inflated, forming an expansion, such as a local bulge. Alternatively, the holding element is formed, for example, by the molding process during the production of the substrate tube, such as by creating a constriction in the substrate tube's inner bore during a drawing process in which the substrate tube is drawn from a melt or in which a mother tube is elongated to form the substrate tube.

[0031] This manufacturing step is easy to carry out and the retaining element obtained afterwards can be checked for completeness and dimensional accuracy.

[0032] During the subsequent deposition process, the pre-created support element is covered by the forming soot body. This protects the support element from thermal and mechanical influences. It is sufficient if the cover is only applied to one of the front ends of the soot body. The soot body ends usually form tapered areas that cannot be used for the production of the final quartz glass body. However, this measure is not mandatory; the pre-created support element can also be located entirely outside the soot body.

[0033] Alternatively or additionally, and equally preferably, the forming step for producing the holding element takes place in a sintering phase during sintering according to process step (d); the holding element is thereby generated virtually "in situ" during vitrification.

[0034] With regard to a holding element produced during sintering, a second preferred method variant provides that the holding element is produced after the deposition of the SiO 2 particles according to method step (c) and before or during sintering according to method step (d).

[0035] The formation of the retaining element can be carried out in the sintering furnace in a single operation with the sintering of the composite body. This avoids a separate manufacturing and hot-forming step and the associated costs.

[0036] In both the first and the second process variants, it has proven advantageous if the holding element is designed as a constriction of the substrate tube inner diameter.

[0037] This narrowing of the substrate tube inner diameter is created during the forming step and is formed, for example, as a local circumferential indentation in the area of ​​the inner surface of the substrate tube wall or as a gradual, for example conical, taper of the substrate tube inner diameter.

[0038] The constriction in the substrate tube's inner diameter serves as a holding element during sintering to suspend the composite body. It is preferably designed to be as small as possible to minimize the degree of deformation of the substrate tube, and as large as necessary to ensure reliable support of the composite body's weight. The constriction advantageously has a length in the direction of the substrate tube's longitudinal axis in the range of 20 to 200 mm, preferably in the range of 30 to 100 mm.

[0039] Over this length of the constriction, the substrate tube's inner diameter can remain constant or it can vary. In this context, it has proven effective if the constriction results in a maximum reduction in the substrate tube's inner diameter in the range of 4 mm to 80 mm, preferably in the range of 6 mm to 50 mm.

[0040] In a particularly preferred procedure, the constriction is designed as a local indentation of the substrate tube inner surface and / or as a taper of the substrate tube through-opening in the holding area.

[0041] It has proven to be advantageous if the tapering of the substrate tube passage opening is produced during sintering after process step (d) by softening an upper substrate tube end together with a molded body placed thereon, against which the upper substrate tube end rests, and in the process the upper substrate tube end is bent inwards under the influence of the weight of the molded body.

[0042] The tapering of the substrate tube passage opening in the holding area takes place gradually, continuously and preferably conically by softening the upper substrate tube end and bending it inwards under the influence of the weight of a shaped body.

[0043] In a further, also preferred case, a molded body having an inner cone against which the upper substrate tube end rests is placed on the upper substrate tube end. The molded body and the adjacent upper substrate tube end are heated in a zone sintering furnace, thereby softening the upper substrate tube end. Under the weight of the molded body, the outer surface of the substrate tube in the region of the upper end is formed into an outer cone, and the inner surface of the substrate tube is formed into an inner cone.

[0044] In both the first and the second process variant, it has proven advantageous if the holding element is designed as an extension of the substrate tube outer diameter.

[0045] The expansion of the outer diameter, for example, forms a circumferential bulge in the holding area of ​​the substrate tube.

[0046] This widening of the substrate tube outer diameter is generated during the forming step and is formed, for example, as a local circumferential bulge in the area of ​​the outer surface of the substrate tube wall or as a gradual, for example conical, widening of the substrate tube outer diameter.

[0047] The extension of the substrate tube's outer diameter serves as a holding element during sintering to suspend the composite body. It is preferably designed as small as possible to minimize the degree of deformation of the substrate tube and as large as necessary to ensure reliable support of the composite body's weight. Over this length of the extension, the substrate tube's outer diameter can be constant or it can vary.

[0048] Advantageously, the extension has a length extension in the direction of the substrate tube longitudinal axis in the range of 20 to 200 mm, preferably in the range of 30 to 100 mm.

[0049] In this context, it has proven useful if the extension results in a maximum increase in the substrate tube outer diameter in the range of 4 mm to 80 mm, preferably in the range of 6 mm to 50 mm.

[0050] The expansion is preferably produced during sintering after process step (d) by softening an upper substrate tube end together with a spreading device which has a radially outwardly movable spreading body which rests against the inner wall in the region of the upper substrate tube end, and in the process the spreading body is moved radially outwards under the influence of the weight of the spreading device and in the process the substrate tube wall is deformed in the region of the upper substrate tube end to form the bulge.

[0051] In a particularly preferred procedure, a substrate tube is provided which consists at least partially of quartz glass of a first quartz glass quality, wherein the soot body consists of quartz glass of a second quartz glass quality, and wherein the first quartz glass quality has a material-specific viscosity at the sintering temperature which is higher than the material-specific viscosity of the second quartz glass quality.

[0052] The substrate tube used is characterized by high thermal stability, so that it softens less than the soot body during sintering. The thermally more stable substrate tube not only provides a certain degree of support for the softening soot body, allowing it to achieve and maintain the desired cylindrical shape, but also forms a particularly thermally stable support element.

[0053] The comparatively higher viscosity of the substrate tube is achieved, for example, by the fact that it consists of a quartz glass over at least part of its length and / or at least over a thickness range of its wall, which has a higher viscosity at the sintering temperature than the synthetic quartz glass of the soot body. In the simplest and preferred case, the substrate tube consists entirely of quartz glass of the first quartz glass quality, i.e., the higher-viscosity quartz glass. In another, equally preferred embodiment, the quartz glass of the substrate tube consists of a higher-viscosity quartz glass only over part of its length, for example, in the part of its length that is used as a holding element during sintering of the soot body.

[0054] During sintering, the composite body is softened zone by zone, starting with its upper end. During a first sintering phase, it preferably rests on a pedestal. The position of the holding element is selected such that, during a second sintering phase, as a result of the increasing longitudinal shrinkage, it rests on a support element of the holding device, such as a cladding tube arranged in the through-bore of the substrate tube. During the second sintering phase, the composite body is held suspended at its upper end. The holding element is no longer located in the hottest area of ​​the heating zone and has therefore already cooled down sufficiently that it can take over the suspended support of the composite body. This is achieved if the substrate tube is made entirely, or at least in the area of ​​the holding element, of first-class quartz glass, which is characterized by a comparatively high viscosity.

[0055] The sintering temperature typically ranges from 1200°C to 1450°C. It has proven effective if, at a measurement temperature of 1350°C, the decimal logarithm of the viscosity of the first quartz glass grade is at least 0.25 µg(dPa·s), preferably at least 0.4 µg(dPa·s), particularly preferably at least 0.6 µg(dPa·s) higher than that of the second quartz glass grade. Viscosity differences are expressed here as the difference in the decimal logarithm µg(dPa·s) of the respective viscosity values. Viscosity differences greater than 1 µg(dPa·s) at the measurement temperature are generally not necessary.

[0056] The viscosity of quartz glass can be modified by stiffening its glass network structure, particularly through dopants. Stiffening of the glass network structure can be achieved through oxygen defect centers (also known as "ODC centers" - Oxygen Deficiency Centers). Nitrogen, titanium oxide, and aluminum oxide are dopants suitable for increasing the viscosity of quartz glass. In this regard, a preferred method provides that the quartz glass of the first quartz glass grade has an aluminum oxide content that is at least 5 ppm by weight, preferably at least 10 ppm by weight, higher than the aluminum oxide content in the quartz glass of the second quartz glass grade. Therefore, aluminum oxide can be added to quartz glass designed for components used at high temperatures and that are required to exhibit a certain temperature stability in order to increase its viscosity.The viscosity of synthetically produced quartz glass can also be increased in this way.

[0057] Naturally occurring raw materials for quartz glass often contain a certain amount of aluminum oxide. For this reason, top-quality quartz glass is preferably melted from a naturally occurring raw material. The costs for producing substrate tubes from natural quartz glass are comparatively low. For example, such substrate tubes can be manufactured cost-effectively using well-known crucible-pulling processes.

[0058] The quartz glass of the second quartz glass quality is, for example, high-purity, synthetically produced quartz glass without a significant proportion of aluminum oxide or with a small proportion of aluminum oxide of less than 1 ppm by weight, preferably less than 0.5 ppm by weight.

[0059] In contrast, the quartz glass of the first quartz glass grade preferably contains at least 5 ppm by weight, preferably at least 10 ppm by weight. However, an aluminum oxide content of more than 100 ppm by weight is generally not preferred.

[0060] The viscosity of quartz glass can also be modified by hydroxyl groups. Hydroxyl groups can reduce the viscosity of quartz glass. In this regard, a preferred method provides that the quartz glass of the first quartz glass grade has a hydroxyl group content of less than 30 ppm by weight, and preferably a hydroxyl group content of less than 20 ppm by weight.

[0061] Hydroxyl group contents of less than 30 ppm by weight can be achieved in quartz glass produced from natural raw materials, for example, by melting the raw material in an electrically heated furnace or using a hydrogen-free plasma. The hydroxyl group content of synthetically produced quartz glass via the SiO2 soot route can be adjusted to a large extent by drying the soot body before vitrification. This drying treatment also makes it possible to achieve low hydroxyl group contents in the range of a few ppm by weight in synthetically produced quartz glass, which are characterized by a comparatively low viscosity. Synthetic quartz glass with a low hydroxyl group content may be suitable as a substrate tube material, provided the quartz glass of the soot body applied to it has a comparatively low viscosity.

[0062] In a preferred procedure, a substrate tube is used which has a wall thickness in the range of 1.5 mm to 10 mm, preferably in the range of 4 to 8 mm.

[0063] The wall thickness is as large as necessary to ensure the desired thermal stability. On the other hand, the wall thickness is as small as possible, since the substrate tube material is usually removed during further processing of the quartz glass composite body.

[0064] The tubular quartz glass composite body obtained after vitrification of this composite of substrate tube and SiO2 soot layer has an inner wall region made of first-quality quartz glass, which originates from the former substrate tube. It also has an outer wall region made of second-quality quartz glass, which results from the former soot body. The thickness of the outer wall region scales with the wall thickness of the soot body and the soot density.

[0065] The soot density typically ranges from 25 to 33% of the density of quartz glass. In view of this, the soot body obtained by the external deposition process is advantageously substantially cylindrical and preferably has a wall thickness that, after sintering of the composite body, results in a glass layer with a layer thickness in the range of 25 mm to 100 mm, preferably in the range of 30 mm to 60 mm.

[0066] With regard to the tubular quartz glass composite body, the above-mentioned technical problem is solved according to the invention starting from a composite body of the type mentioned at the outset in that the tube wall has an inner wall region and an outer wall region, wherein the inner wall region comprises a holding element which is designed as a constriction of the substrate tube inner diameter or as an extension of the substrate tube outer diameter.

[0067] The tubular quartz glass composite body can be produced according to the invention using the method described above. The outer wall region of the quartz glass composite body is optionally formed from quartz glass obtained by sintering a former soot body, and the inner wall region is formed from the quartz glass of the former substrate tube.

[0068] The inner wall region comprises a holding element that enables suspended glazing during the sintering process, forming the quartz glass composite body. This suspended glazing ensures high dimensional stability in the resulting quartz glass composite body according to the invention.

[0069] The constriction of the retaining element is designed, for example, as a circumferential indentation or as a partially conical taper of the substrate tube's inner diameter. The widening is designed, for example, as a circumferential bulge or as a partially conical widening of the substrate tube's outer diameter.

[0070] The holding element is characterized by particularly high dimensional stability during the sintering process if the inner wall area consists at least partially of quartz glass of a first quartz glass quality, and the outer wall area consists of quartz glass of a second quartz glass quality, wherein at a measuring temperature of 1350°C the viscosity of the first quartz glass quality is higher than the viscosity of the second quartz glass quality.

[0071] A hollow quartz glass cylinder is manufactured from the quartz glass composite body by removing the inner wall area, for example, by drilling, milling, or etching. The resulting hollow quartz glass cylinder is used to manufacture etching rings for single-wafer plasma etching chambers or pressure vessels for use in chemical process engineering.

[0072] The etching rings or pressure vessels have a specified nominal inner diameter. For the production of the etching rings or pressure vessels, a composite body with an outer wall area with an inner diameter that is at least 1 mm smaller than the nominal inner diameter is preferably used. The nominal inner diameter is adjusted by removing the entire inner wall area and an excess of the outer wall area, with the excess being 1 mm or more. Definitions and measurement methods

[0073] Individual terms from the above description are defined below for additional information. These definitions are part of the description of the invention. For terms and measurement methods not specifically defined in the description, the interpretation according to the International Telecommunication Union (ITU) applies. In the event of a contradiction between one of the following definitions and the rest of the description, the remainder of the description prevails. Tubular composite body made of quartz glass

[0074] The result of the deposition process is a tubular composite consisting of a quartz glass substrate tube and an SiO2 soot body. The substrate tube defines the inner bore of the composite. Sintering (vitrification) of the soot body produces a tubular quartz glass composite body. Subsequent removal of the substrate tube from the quartz glass composite body produces a hollow quartz glass cylinder. The substrate tube can be removed, for example, by drilling out. Mechanical, thermal, or chemical processing is used to create quartz glass components from the hollow quartz glass cylinder. Mechanical processing includes drilling, sawing, cutting, milling, grinding, and polishing the inner and outer contours. Thermal processing includes thermal drying, sintering, vitrification, melting, forming, and tempering. Chemical processing includes doping and etching.The quartz glass component is a ready-to-use quartz glass product or a semi-finished product therefor, for example a quartz glass hollow cylinder for the production of a pressure vessel or a quartz glass ring or a quartz glass ring for the production of a retaining ring for wafers. Quartz glass / synthetic quartz glass

[0075] Quartz glass is defined here as glass with a SiO 2 content of at least 87 wt.%. It is doped (SiO 2 content = 100%) or contains dopants such as fluorine, chlorine, nitrogen, carbon, or oxides of boron, germanium, rare earth metals, aluminum, or titanium.

[0076] For example, quartz glass is melted from naturally occurring SiO 2 raw material (natural quartz glass), or it is synthetically produced (synthetic quartz glass) or it consists of mixtures of these types of quartz glass. Sintering / Glazing

[0077] "Sintering" or "vitrification" refers to a process step in which a soot body made of porous silicon dioxide is treated in a furnace at high temperatures. Sintering / vitrification takes place in an inert gas, a hydrogen and / or helium-containing atmosphere, or under vacuum. vacuum

[0078] The vitrification of the composite body can be carried out under a vacuum. The negative pressure is specified as the absolute gas pressure. A vacuum is defined as an absolute gas pressure of less than 50 mbar. Substrate tube outer diameter / Substrate tube inner diameter

[0079] The substrate tube cross-section has a circular outer contour or an outer contour that deviates from a circular shape. If the outer contour deviates from a circular shape, the local "outer diameter value" is determined from the diameter of the (smallest) circumscribed circle.

[0080] The substrate tube cross-section has a circular inner contour or an inner contour that deviates from a circular shape. If the inner contour deviates from a circular shape, the local "inner diameter value" is determined from the diameter of the (largest) inscribed circle.

[0081] In the longitudinal section of a substrate tube, the local outer diameter values ​​are either constant or non-constant over the entire length of the substrate tube. With constant outer diameter values, the substrate tube has a cylindrical shape when viewed from the outside. The non-constant outer diameter values ​​can vary over the entire length or over a partial length. The outer contour can, for example, change continuously or in steps. In this case, the outer diameter is determined from the local outer diameter values ​​averaged over the entire length.

[0082] In the longitudinal section of a substrate tube, the local values ​​for the inner diameter are either constant over the entire length of the substrate tube or they are not constant. With constant inner diameter values, the through-hole of the substrate tube is cylindrical. The non-constant inner diameter values ​​can vary over the entire length or over a partial length. The inner contour can, for example, change continuously or in steps. In this case, the inner diameter is determined from the local inner diameter values ​​averaged over the entire length. viscosity

[0083] The viscosity of the quartz glass is measured using a beam bending viscometer. Beam bending viscometry covers a viscosity range from 10 8 < to 10 15 < dPa s. The measurement setup includes a heatable three-point bending device with a measuring beam made of the quartz glass to be measured (beam / strip: 50 mm long, 3 mm high, 5 mm wide). The measured variable is the bending rate at the respective temperature.

[0084] Instead of using exponential notation, viscosity values ​​are often given using the decimal logarithm in the form Ig(dPa·s). Softening temperature

[0085] Glasses cannot be assigned a specific softening temperature, but rather a softening temperature range. For the purpose of determining a temperature value, the determination according to DINReference is made to ISO 7884 (1998), which defines the softening temperature as the temperature at which the glass has a viscosity of 10 7.6 < dPas. Temperature values ​​in the range of 1600°C to 1730°C are cited in the literature for the softening temperature of undoped quartz glass. Example

[0086] The invention is explained in more detail below using exemplary embodiments and a patent drawing. In detail, a schematic representation Figure 1 a device for producing a composite body from substrate tube and soot body in a first embodiment of a substrate tube holder in a longitudinal section, Figure 2 a device for producing a composite body from substrate tube and soot body in a second embodiment of a substrate tube holder in a longitudinal section, partly as a cutout, Figure 3 a section of the substrate tube holder from Figure 2in enlarged view, Figure 4 Components of a zone sintering furnace, as used for vitrifying a composite body, Figure 5 the vitrification of a standing composite body using the zone sintering furnace, Figure 6 a method step for producing a first embodiment of a holding edge on the substrate tube, Figure 7 a further process step for producing the holding edge on the substrate tube, Figure 8 the vitrification of a partially hanging composite body by means of the first embodiment of the holding edge on the substrate tube in the zone sintering furnace, Figure 9 a method step for producing a second embodiment of a holding edge on the substrate tube, Figure 10 a further process step for producing the holding edge on the substrate tube, Figure 11 an embodiment of a substrate tube with a retaining edge produced before the external deposition process in the form of a taper of its inner diameter, Figure 12the substrate tube of Figure 11 after completion of the external deposition process during vitrification of the composite body in the zone sintering furnace of Figure 4 , Figure 13 a first embodiment of a tubular quartz glass composite body according to the invention in a longitudinal section, and Figure 14 a second embodiment of a tubular quartz glass composite body according to the invention in a longitudinal section.

[0087] In the following examples, different substrate tubes are used, some of whose properties are summarized in Table 1. Table 1 - Substrate tubes Nr material Viscosity [lg(dPa·s) at 1350°C] Outer diameter [mm] Inner diameter [mm] Length [mm] form 1 Natural quartz glass (electro-fused) 11,28 280 270 2000 cylinder 2 Natural quartz glass (electro-fused) 11,28 280 270 1500 Cylinder with constriction 3 Synthetic quartz glass (thermally dried) 10,77 280 270 1500 Cylinder with constriction 4 Synthetic quartz glass (dried with chlorine) 10,64 280 270 1500 Cylinder with constriction

[0088] "Natural quartz glass" is melted from naturally occurring SiO2 raw material, preferably in an electrically heated melting furnace. A particularly cost-effective production of the substrate tube from natural quartz glass is achieved using a vertical crucible drawing process. This quartz glass typically contains aluminum oxide in a concentration range between 6 and 18 ppm by weight and hydroxyl groups in a concentration of less than 50 ppm by weight.

[0089] "Synthetic quartz glass" is obtained, for example, by flame hydrolysis or oxidation of synthetically produced silicon compounds, by polycondensation of organic silicon compounds using the so-called sol-gel process, or by hydrolysis and precipitation of inorganic silicon compounds in a liquid. The viscosity of synthetic quartz glass depends on its composition, which can vary widely. In general, however, it can be said that synthetic quartz glass typically has a significantly lower viscosity than natural quartz glass.

[0090] The Figure 1The schematically illustrated device is used to produce a large-volume composite of a substrate tube 1 and a SiO 2 soot body 9. It comprises a glass lathe 2 for holding and rotating the substrate tube 1 according to number 1 in Table 1. The substrate tube 1 has a left end face 1a, a right end face 1b, an outer surface 1c, an inner surface 1d, a horizontally oriented longitudinal axis 1e and a cylindrical through-bore 1f. Adjacent to the end face 1a is a free substrate tube section 1g, on which a reduced deposition of SiO 2 soot particles takes place during the soot deposition process. The free substrate tube section 1g can be formed into a holding edge during vitrification, which will be explained further below with reference to the Figures 4 and 6 to 10 will be explained in more detail.

[0091] The glass lathe 2 is indicated by two opposing chucks 2a, 2b, of which chuck 2a is spring-loaded, as indicated by the compression spring 2c. The compression spring 2c generates a compressive force F that presses the two chucks 2a, 2b against each other, as indicated by the directional arrows 2d.

[0092] A hollow stainless steel spindle 3a, 3b is clamped at its proximal end in each of the chucks 2a, 2b. The rotation axes of the hollow spindles 3a, 3b ideally run coaxially with the substrate tube's longitudinal axis 1e. The hollow spindles 3a, 3b have an outer diameter of 90 mm and an inner diameter of 82 mm.

[0093] The distal ends of the hollow spindles 3a, 3b are pivotally connected to an annular pressure plate 4a, 4b made of stainless steel. For this purpose, the distal ends of the hollow spindles 3a, 3b taper conically and, due to the force of the spring 2c, press against the respective pressure plate 4a, 4b. The conical end protrudes into a central bore of the respective annular pressure plate 4a, 4b and rests against the inner edge of the central bore.

[0094] The pressure plates 4a, 4b each rest against graphite buffer disks 5a, 5b, which in turn rest against the substrate tube end faces 1a and 1b, respectively. The buffer disks 5a, 5b have a central bore whose diameter corresponds to that of the pressure plates and which runs coaxially with them. The pressure plates 4a, 4b have an outer diameter that is 10 mm smaller than the outer diameter of the substrate tube 1. The buffer disks 5a, 5b have an outer diameter that exceeds the outer diameter of the substrate tube 1 by 40 mm.

[0095] A tubular centering support 6 made of SiSiC with a total length L z and an outer diameter of 80 mm extends through the substrate tube through-bore 1f as well as through the center bores of pressure plates 4a, 4b and buffer disks 5a, 5b. One end 6a of the centering support 6 projects a length L a of 500 mm into the hollow spindle 3a and terminates within it, leaving a variable range of motion B a of approximately 6 mm. The other end 6b projects a length L b of 600 mm into the hollow spindle 3b and terminates within it, leaving a variable range of motion B b of also approximately 6 mm. The total range of motion B z = B a + B b for the centering support 6 within the hollow spindles 3a, 3b is thus 12 mm. The outer diameter of the centering carrier 6 is constant over its length and is adapted with a clearance fit to the inner diameter of the hollow spindles 3a, 3b and can be moved telescopically therein.

[0096] Three graphite centering rings 7a, 7b, and 7c are mounted on the centering support 6. The centering ring 7a is located in the area of ​​the left substrate tube end face 1a, the centering ring 7b is located in the area of ​​the right substrate tube end face 1b, and the centering ring 7c is located approximately in the center of the substrate tube through-bore 1f. All centering rings 7a, 7b, and 7c have an outer diameter that is adapted with a clearance fit to the substrate tube inner diameter, and they have an inner diameter that is adapted with a clearance fit to the centering support outer diameter.

[0097] The terminal centering ring 7a, the buffer disk 5a, and the thrust disk 4a are loosely connected to each other by screws 4c. The screws 4c have a thread that borders a cylindrical section 4d. The screw threads each engage an internal thread in the thrust disk 4a, so that the cylindrical section 4d rests firmly against the thrust disk 4a when tightened. The length of the cylindrical section 4d is greater than the total thickness of the component stack consisting of the centering ring 7a and the buffer disk 5a, so that the heads of the screws 4c do not rest against the centering ring 7a, but rather a gap remains between the centering ring 7a and the screw heads. In addition, the through holes for the passage of the cylinder section 4d in the buffer disc 5a and in the centering ring 7a are larger than the diameter of the cylinder section 4d, so that the screws 4c can also be slightly inclined in the through holes.This loose connection is therefore suitable for both allowing thermally induced length changes between components of the substrate tube holder and compensating for deviations in the target dimensions, positioning, and alignment of the components. Furthermore, the screws 4c provide a certain torsional rigidity between the buffer disk 5a and the thrust disk 4a during the rotational movement of the substrate tube 1 and thus serve as driver elements for this rotational movement. The same applies to the connection of the centering ring 7b, the buffer disk 5b, and the thrust disk 4b. A gap is provided between the centering ring 7a, 7b and the buffer disk 5a, 5b for the purpose of thermal decoupling (not visible in the figure).

[0098] Several deposition burners 8 for generating SiO 2 particles are mounted on a common carriage 8a, by means of which they can be moved reversibly and transversely along the outer surface 1c of the substrate tube 1 or along a forming SiO 2 soot body 9 and can be displaced perpendicularly thereto, as indicated by the directional arrows 8b.

[0099] If in Figure 2 and in Figure 3 the same reference numbers as in Figure 1 are used, these designate identical or equivalent components or parts of the device.

[0100] The Figure 2 The device shown schematically differs from that of Figure 1 essentially in the manner of the substrate tube holder and the substrate tube 21. If the same reference numerals are used as in Figure 1 , these designate identical or equivalent components or parts of the Figure 1explained device.

[0101] The substrate tube 21 corresponds to number 2 in Table 1. In one end region 21a, it has a circumferential constriction 26 of its inner diameter. The constriction 26 is created before the start of the external deposition process, for example, by locally softening the substrate tube 21 after it has been clamped into the glass lathe 2. The constriction 26 is located approximately 80 mm in front of the substrate tube end face. The inner diameter is 270 mm, except in the area of ​​the constriction 26, where it is 250 mm.

[0102] The hollow spindles 23a, 23b, each clamped at their proximal end in chucks, are made of stainless steel. The rotation axes of the hollow spindles 23a, 23b ideally run coaxially with the substrate tube's longitudinal axis 1e. The hollow spindles 23a, 23b have an outer diameter of 100 mm. A circumferential extension arm 2c is welded to the distal ends of each of the hollow spindles 23a, 23b.

[0103] The pivotable connection between the hollow spindles 23a, 23b and the respective pressure plates 24a, 24 is designed here as a floating bearing and preferably comprises a cardanic ball-cone seat. The distal ends of the hollow spindles 23a, 23b each form a convexly curved seat having a spherical or radial section on which the pressure plate 24a or the pressure plate 24b is movably mounted by having a concavely curved spherical or radial section that interacts with the convexly curved seat.

[0104] Figure 3shows the pivoting connection between the hollow spindles 23a, 23b and the respective pressure plates 24a, 24b in an enlarged view. The terminal centering ring 7a, the buffer disc 5a, and the pressure disc 24a form a component stack that is loosely connected to one another by means of threaded screws 24c, each of which engages a thread in the extension arm 23c. The cylinder section 24d has a length that is greater than the total thickness of the component stack comprising the centering ring 7a, buffer disc 5a, and pressure disc 24a. In addition, the width of the bore for accommodating the threaded screws 24c in the component stack is significantly larger than the diameter of the cylinder section 24d. This results in several gaps 25 remaining between the screw head 24e and the centering ring 7a, as well as between the pressure plate 24 and the boom 23c, and along the cylinder section 24d, even when the threaded screw 24c is firmly tightened.The gaps 25 ensure that the connection between the hollow spindles 23a, 23b and the respective pressure plates 24a, 24b remains pivotally movable. At the same time, the screws 24c serve as driver elements for the rotational movement of the substrate tube 1.

[0105] The following are based on the Figures 1 and 4 to 10 Examples of manufacturing a quartz glass composite body are explained. Soot separation process

[0106] Oxygen and hydrogen are supplied to the deposition burners 8 as burner gases, and a gas stream containing SiCl 4 or another silicon-containing starting material is supplied as feedstock for the formation of SiO 2 particles. These components are converted into SiO 2 particles in the respective burner flame, and these SiO 2 particles are deposited on the substrate tube 1 rotating about the longitudinal axis 1e, forming the soot body 9 made of porous SiO 2 soot.

[0107] To rotate the substrate tube 1, the glass lathe 2 transmits a torque to the hollow spindles 2a, 2b. At the same time, the compression spring 2c generates a compressive force F acting in the axial direction, which presses the two hollow spindles 3a, 3b against each other and which, depending on the deflection of the spring from the spring's rest length, lies in the range between 0.5 kN and 10 kN. The initially set compressive force is 1 kN and is applied to the pressure plates 4a, 4b, the buffer disks 5a, 5b, and thus also to the substrate tube end faces 1a, 1b. This compressive force F creates a frictional connection between the buffer disks 5a, 5b, which is sufficient to hold the dead weight of the substrate tube 1 and the weight of the soot body 9. The centering rings 7a, 7b, 7c serve only to protect against unforeseen slipping or bending of the substrate tube 1.A certain axial guidance is achieved by the interaction of hollow spindles 3a, 3b and centering carrier 6, which, due to the existing mechanical play, compensates for any radial offsets and angular differences between the rotation axes of the hollow spindles 3a, 3b and avoids mechanical stresses.

[0108] The deposition process is terminated as soon as the soot body 9 has reached a predetermined outer diameter, which, depending on the density of the soot layer, results in the predetermined outer diameter of the hollow cylindrical quartz glass composite body, plus an oversize of at least 1 mm. For example, with a soot density of approximately 30% (relative to the density of quartz glass) and a target outer diameter of the quartz glass composite body of 362 mm, the soot body outer diameter is approximately 520 mm.

[0109] After the deposition process, the soot body 9 has a substantially barrel-shaped form and extends to just before both ends of the substrate tube 1. The substrate tube section 1g protruding from the soot body 9 and only slightly covered by SiO 2 soot has a length of approximately 100 mm. Drying and vitrification process

[0110] The substrate tube 1 remains in the soot body 9. The composite (1; 9) of the substrate tube 1 and the soot body 9 is subjected to a dehydration treatment in a drying oven in an inert gas atmosphere, a halogen-containing atmosphere, or under vacuum. The soot body 9 is dried thermally by heating it to a temperature of around 1100°C in a nitrogen atmosphere. By vitrifying the resulting dried SiO 2 soot body under vacuum, a synthetic quartz glass with the following properties is obtained: Hydroxyl group content: about 200 ppm by weight, chlorine content: < 0.2 ppm by weight Viscosity at 1350°C: 10.77 Ig(dPa·s). Glazing

[0111] The subsequent vitrification of the soot body 9 takes place in a zone sintering furnace with a vertically oriented substrate tube longitudinal axis 1e under vacuum or in an atmosphere of gases that diffuse quickly in quartz glass, such as helium and hydrogen, and thus do not cause bubbles. Figure 4shows a schematic view of a section of such a zone sintering furnace 40. The furnace chamber 41 encloses a furnace interior 42 in which an annular heating element 43 and a holding device 44 are located. This comprises a support rod 45 made of fiber-reinforced carbon, the lower end of which is connected to a graphite pedestal 46. The upper end of the support rod 45 is held by a movable gripper (not shown in the figure) and can be moved up and down by means of this. The support rod 45 extends through the annular opening of the heating element 43 and through a graphite cladding tube 47, which rests on the pedestal 46. Apart from the openings for the support rod 45, the end faces of the cladding tube are closed. Compared to a cladding tube that is open on both sides, the largely closed top and bottom sides 47a give the cladding tube 47 greater dimensional stability against external pressure.

[0112] During vitrification, the substrate tube 1 remained in the soot body 9. The holding device 44 serves to hold the assembly (1; 9) of substrate tube 1 and soot body 9, the weight of which is taken up by the support rod 45 via the pedestal 46. As in Figure 5 As shown schematically, the substrate tube 1 surrounds the cladding tube 47. The outer diameter of the cladding tube is adapted to the inner diameter of the substrate tube 1 in such a way that the annular gap remaining during sintering is as small as possible, taking into account the higher thermal expansion coefficient of the graphite cladding tube 47 compared to the quartz glass substrate tube, and is, for example, in the range of 1 mm to 10 mm, preferably less than 5 mm.

[0113] During vitrification, the heating element 43 is heated to a temperature of approximately 1400°C, and the support rod 45 is continuously pulled upward, so that the soot body 9 is vitrified from top to bottom. In the process, the composite (1; 9) shrinks onto the cladding tube 47, so that its outer diameter defines a lower limit for the inner diameter of the vitrified, tubular quartz glass composite body. The substrate tube 1 is made of natural quartz glass, which has a higher viscosity at the sintering temperature than the synthetic quartz glass of the soot body 9. At a measurement temperature of 1350°C, according to Table 1, the viscosity difference, corresponding to the difference between the decimal logarithms of the respective viscosity values, is approximately 0.51 Ig(dPa s) [11.28 Ig(dPa s) - 10.77 Ig(dPa s)].

[0114] The substrate tube 1 is thus comparatively thermally stable and deforms little or not at all. This stabilizes the soot body 9 during vitrification. In particular, this counteracts the risk of the soot body 9 collapsing during vitrification, causing circumferential wrinkles to form, or of the inner diameter expanding, which would lead to rejects.

[0115] After cooling, a tubular composite body is obtained from the substrate tube 1 and a glass layer with a thickness of approximately 41 mm, which was obtained by vitrifying the soot body 9. Despite the shrinking of the synthetic quartz glass onto the inner graphite cladding tube 47, the latter can be easily removed after vitrification because graphite has a significantly higher thermal expansion coefficient than quartz glass and contracts more strongly upon cooling.

[0116] The quartz glass of substrate tube 1 can then be removed by mechanical processing, for example, by drilling. After grinding and smoothing the outer wall, a hollow quartz glass cylinder with an outer diameter of 360 mm and an inner diameter of 290 mm is obtained. Comparison example

[0117] As explained above, the substrate tube 1 contributes to the shape stabilization of the soot body 9 during vitrification due to its comparatively high viscosity.

[0118] To investigate the effect of the substrate tube 1 on the shape stabilization of the soot body 9, in a first comparative test, the substrate tube was removed before vitrification, and only the soot body 9 was vitrified in the zone sintering furnace 40, starting from the top downwards. In the process, the soot body 9 collapsed under its own weight, and the partially vitrified area detached from the cladding tube 47, resulting in a local expansion of the inner diameter. The resulting quartz glass tube was unusable.

[0119] In another comparative test, a substrate tube made of synthetic quartz glass with the same dimensions as substrate tube 1 was used, as specified in number 3 of Table 1. The viscosity of this quartz glass is lower than that of the quartz glass obtained by vitrifying the soot body 9. It was found that when this composite body was used, the cladding tube provided better adhesion to the vitrified soot body 9, preventing large-scale detachment of the vitrified material. However, the continuously increasing weight of the vitrified upper region of the composite body led to compression towards the end of the process, rendering the quartz glass tube thus produced ultimately unusable.

[0120] In a further comparative test, a substrate tube made of synthetic quartz glass with the same dimensions as substrate tube 1 was used, as specified under number 4 of Table 1. The viscosity of this quartz glass corresponds to the viscosity of the quartz glass obtained by vitrifying the soot body 9. However, it is also evident here that during sintering of the composite (1; 9), compression occurs towards the end of the process, so that the quartz glass tube produced in this way was ultimately unusable. Hanging glazing

[0121] To counteract the effect of compression due to its own weight, a glazing method is often used in which the composite (1; 9) is not permanently supported on the platform 46 during glazing, but is suspended at least temporarily. This procedure, which is known, for example, from EP 0 701 975 B1, is referred to here as "suspended glazing."

[0122] This ensures that the composite (1; 9) is either suspended in the vitrification furnace from the outset, or that the support of the composite (1; 9) can change from a standing position at the beginning of vitrification to a suspended support during the vitrification process as soon as the unavoidable axial sintering shrinkage becomes noticeable. To achieve the suspended support, measures can be taken on the substrate tube even before the external deposition process is carried out. This can be achieved, for example, by reshaping a substrate tube or by the forming process during the production of the substrate tube, such as by creating a constriction of the substrate tube's inner bore during a drawing process in which the substrate tube is drawn from a melt or in which a mother tube is elongated to form the substrate tube. Alternatively or additionally, and equally preferably, these measures are generated "in situ" during vitrification.

[0123] A suitable measure for implementing suspended glazing is the formation of a retaining edge on the substrate tube, which serves to ensure that the composite (1; 9) is glazed at least temporarily in a vertically suspended position (and not exclusively in an upright position). In addition to the above-mentioned effect of the thermally stable substrate tube 1, the at least temporarily suspended support counteracts compression of the soot body 9 during glazing, so that it retains its desired geometry and rejects are avoided.

[0124] For the suspension of the composite (1; 9), the substrate tube section 1g can, for example, be formed into a holding edge during the vitrification of the soot body 9. Suitable methods for producing the holding edge "in situ" are described below using the Figures 6 to 10 explained in more detail.

[0125] Figure 6schematically shows a first method and a device for producing the suspension "in situ." The composite (1; 9) consisting of substrate tube 1 and soot body 9 is introduced into the vitrification furnace 40 and mounted on the pedestal 46 with the soot body's longitudinal axis 1e oriented vertically by means of a support rod 45 and cladding tube 47. An annular spacer 61 is placed on the upper end face 47a of the cladding tube 47, and a conical body 62 in the form of an inverted cup is placed on the upper end face of the substrate tube 9. The spacer 61 and the conical body 62 are made of graphite. The conical body 62 has an inner cone 62a, which merges into a flat support surface 62b, in which a through-opening 62c is located. In the initial state, the inner cone 62 rests against the outside of the upper substrate tube section 1g. The support rod 45 extends through the through-opening 62c and through the annular spacer 61.

[0126] The upper substrate tube section 1g is formed into a suspension during the vitrification process. The forming process is shown schematically in Figure 7 shown. By means of the support rod 45, the upper substrate tube section 1g is moved far enough into the heating element 43, which is heated to vitrification temperature, that it softens. Due to its weight, the conical body 62 presses the soft upper substrate tube section 1g inward toward the substrate tube's longitudinal axis 1e. In doing so, the substrate tube section 1g rests against the inner cone 62a and is thus formed into an outer cone. The forming process is completed as soon as the spacer 61 comes into contact with the support surface 62b of the conical body 62.

[0127] During further vitrification, the composite body (1; 9) is heated zone by zone, starting with its upper end. In the process, the composite body (1; 9) gradually collapses onto the graphite cladding tube 47 and also shrinks in length. The sintering shrinkage forces are so strong that a shortening of the length of the substrate tube 1 also occurs. However, the shortening is slight.

[0128] In a first glazing phase, the composite (1; 9) stands on the pedestal 46. Figure 8shows a schematic of a second vitrification phase. During this phase, the former substrate tube section 1g, which has been reshaped into an outer cone, emerges from the heating area of ​​the heating element 43, cools, and solidifies. It rests with its inner side on the cladding tube top 47a and then acts as a suspension 63 for the composite (1; 9). As a result of the longitudinal shrinkage, the composite lifts off the pedestal 46, forming a narrow gap 48, which then enables further "hanging vitrification." This counteracts the collapse of the soot body 9, with the substrate tube 47 additionally stabilizing the shape of the resulting tubular quartz glass composite body due to its higher viscosity.

[0129] Figure 9shows schematically a second method and a device for producing the suspension in situ, i.e. in a single operation with the vitrification of the composite (1; 9) comprising substrate tube 1 and soot body 9. This is introduced into the vitrification furnace 40 and mounted on the pedestal 46 with the soot tube longitudinal axis 1e oriented vertically by means of a support rod 45 and cladding tube 47. A circular ring 91 is placed on the upper end face 47a of the cladding tube 47. This circular ring is composed of two or more separate circular sector plates 91a, 91b that border on a circular ring central opening 91b and are mounted so as to be movable in the radial direction. A conical body 92 made of graphite projects from above into the central opening 91b and has a conical shaft 92a and a conical head 92b with a flat underside. Circular ring 91 and conical body 92 are made of graphite.The outer diameter of the circular ring 91 corresponds approximately to the inner diameter of the substrate tube 1; it rests against the inner wall of the upper substrate tube section 1g. The diameter profile of the conical shaft 92a is designed such that, in the initial state, it extends approximately halfway into the central opening 91b.

[0130] During further vitrification of the composite body (1; 9), the bulge 93 reaches the area above the heating element 43, cools down, and solidifies. The composite body (1, 9) is heated zone by zone, starting with its upper end, as described above for the first method. In a first vitrification phase, the composite (1; 9) rests on the pedestal 46, and during the second vitrification phase, the bulge 93 serves as a support for the "hanging glazing." The circular sector plates 91a protrude from the inside into the bulge 93 and are fixed therein vertically together with the substrate tube 1.

[0131] The length and inner diameter of the resulting quartz glass composite body are determined by the substrate tube 1. The former soot body forms a layer of transparent synthetic quartz glass with a thickness of approximately 41 mm. After removing the quartz glass material from the substrate tube 1 and grinding and smoothing the outer wall, a quartz glass tube with an outer diameter of 360 mm and an inner diameter of 290 mm is obtained. Etching rings for single-wafer plasma etching chambers and pressure vessels for use in chemical process engineering can be cut from this.

[0132] To manufacture the etching ring or pressure vessel, a composite body with an outer wall area with an inner diameter that is at least 1 mm smaller than the target inner diameter is preferably used. The target inner diameter can be adjusted by mechanical or chemical machining of the composite body's inner bore.

[0133] In the following, a further embodiment for the realization of a retaining edge for the hanging glazing of the composite body (21, 9) is described on the basis of the Figures 2 and 3 and the Figures 11 to 13 explained. Soot separation process

[0134] The soot separation process is carried out as described above using Figure 1 explained. Figure 11 shows the substrate tube 21 used in this process in a longitudinal section. The previously created constriction 26 is provided in the end region 21a. As can be seen from Figure 2 As can be seen, the soot body 9 is created in such a way that it completely covers the constriction 26. However, this measure is not absolutely necessary; the constriction can also be located completely outside the soot body 9.

[0135] The deposition process is terminated as soon as the soot body 9 has reached a predetermined outer diameter: With a soot density of 30% (relative to the density of quartz glass) and a target outer diameter of the quartz glass composite body of 362 mm, the soot body outer diameter is approximately 520 mm.

[0136] The composite (21; 9) obtained after the soot deposition process is subjected to a dehydration treatment in a chlorine-containing atmosphere at a temperature of 1200°C. By vitrifying the subsequently obtained, dried SiO 2 soot body under vacuum, a synthetic quartz glass with the following properties is obtained: Hydroxyl group content: <0.2 ppm by weight Chlorine content: about 1,000 ppm by weight Viscosity at 1350°C: 10.64 Ig(dPa·s)

[0137] The composite (21; 9) is then vitrified in the zone sintering furnace 40 under vacuum. Figure 12shows the composite (21; 9) used in the zone sintering furnace 40. During vitrification, the heating element 43 is heated to a vitrification temperature of approximately 1400°C, and the support rod 45 is continuously pulled upward, so that the soot body 9 is vitrified from top to bottom. In the process, the composite (21; 9) shrinks onto the graphite cladding tube 47, so that its outer diameter defines a lower limit for the inner diameter of the vitrified quartz glass composite body. Since the substrate tube 21 is made of a quartz glass that has a higher viscosity at the vitrification temperature than the quartz glass of the soot body 9, it deforms only slightly or not at all, thus stabilizing the soot body 9 during vitrification. In particular, this counteracts the risk of the soot body 9 being compressed during vitrification, resulting in circumferential wrinkles forming, or of the inner diameter expanding.

[0138] In the process stage shown, the vitrification process is already advanced, and a certain shrinkage of the soot body 9 has already occurred. Thus, the transition from the initial vitrification phase with a standing composite (21; 9) to the "hanging vitrification" phase has already been completed. Due to the shrinkage of the soot body 9, the length of the substrate tube 21 has also shortened slightly, and it has already lifted off a portion of the platform 46, forming the gap 98.

[0139] In an alternative procedure, the composite (21; 9) is held suspended in the zone sintering furnace from the beginning by the constriction 26 resting on the upper edge of the graphite cladding tube 47.

[0140] After cooling, a composite body 100 ( Figure 13 ) from the substrate tube 21 and a glass layer 9a with a thickness of about 41mm, which was obtained by vitrifying the soot body 9.

[0141] In a comparative test, a substrate tube made of synthetic quartz glass with the same dimensions as the substrate tube 21, as specified in number 3 of Table 1, was used. The viscosity of this quartz glass is higher than the viscosity of the quartz glass obtained by vitrifying the soot body 9. More specifically, the decimal logarithm of the viscosity of this quartz glass at a measurement temperature of 1350°C is 0.13 1g(dPa*s) higher than the decimal logarithm of the viscosity of the quartz glass obtained by vitrifying the soot body 9.

[0142] However, it turns out that this viscosity difference is too small to provide sufficient stability to the large-volume and heavy substrate tube during sintering of the composite body.

[0143] Figure 13 shows a cross-section of the composite body 100 obtained after vitrification in a view along the Figure 2drawn line A'-A". The substrate tube 1 with the through-holes 1f, the diameter constriction 26 and the layer 9a of synthetic quartz glass obtained after vitrification can be seen.

[0144] After removing the quartz glass material from the substrate tube 21 and grinding and smoothing the outer wall, a hollow quartz glass cylinder with an outer diameter of 360 mm and an inner diameter of 290 mm is obtained. From this, etching rings with the appropriate inner and outer diameters can be sawn for use in holding semiconductor wafers in single-wafer plasma etching chambers or pressure vessels for industrial applications.

[0145] Figure 14shows schematically a further tubular composite body 110 obtained after cooling in longitudinal section. This has an inner wall layer 111 consisting of the former substrate tube (1), and it has a glass layer 112 with a thickness of approximately 41 mm, which was obtained by vitrifying the former soot body 9. The inner wall layer 111 shows a holding element 113, which in the exemplary embodiment is designed as a taper of the substrate tube ( Figure 8 , reference number 1).

[0146] After removing the quartz glass material from the substrate tube (1) and grinding and smoothing the outer wall, a fully synthetic quartz glass hollow cylinder with an outer diameter of 360 mm and an inner diameter of 290 mm is obtained. From this, etching rings with the corresponding inner and outer diameters—or with larger inner and smaller outer diameters—can be sawn for use in holding semiconductor wafers in single-wafer plasma etching chambers and quartz glass pressure vessels for use in chemical process engineering.

Claims

1. A method for producing a tubular quartz glass composite body in an external deposition method, comprising the following method steps: (a) providing a substrate tube which comprises a continuous through-opening running coaxially to a substrate tube longitudinal axis, a substrate tube outer diameter, a substrate tube inner diameter, a substrate tube outer lateral surface, a substrate tube inner lateral surface, and a substrate tube wall having a wall thickness, (b) rotating the substrate tube about an axis of rotation running coaxially with or parallel to the substrate tube longitudinal axis, (c) depositing SiO2 particles on the substrate tube outer lateral surface by means of at least one deposition burner to form a composite (1 / 9; 21 / 9) consisting of the substrate tube and an SiO2 soot body, (d) sintering the composite (1 / 9; 21 / 9) by heating at a sintering temperature in a heating zone to form the tubular quartz glass composite body (100; 110) and using a holding device which is suitable for holding the composite body at least temporarily with a vertically oriented substrate tube longitudinal axis in the heating zone, characterized in that a holding device is used which comprises a holding element which is produced in a forming step in a holding region of the substrate tube.

2. The method according to claim 1, characterized in that the holding element is produced prior to the deposition of the SiO2 particles according to method step (c), wherein the deposition of the SiO2 particles according to method step (c) is preferably carried out in such a way that the SiO2 soot body covers the holding region.

3. The method according to claim 1, characterized in that the holding element is produced after the deposition of the SiO2 particles according to method step (c) and before or during the sintering according to method step (d).

4. The method according to one or more of the preceding claims, characterized in that the holding element is designed as a constriction of the substrate tube inner diameter or as an expansion of the substrate tube outer diameter.

5. The method according to claim 4, characterized in that the constriction of the substrate tube inner diameter has a longitudinal extension in the direction of the substrate tube longitudinal axis in the range from 20 to 200 mm, preferably in the range from 30 to 100 mm, wherein the constriction preferably brings about a maximum reduction in the substrate tube inner diameter in the range from 4 mm to 80 mm, preferably in the range from 6 mm to 50 mm.

6. The method according to one of claims 4 or 5, characterized in that the constriction is designed as a local indentation of the substrate tube inner lateral surface and / or as a taper of the substrate tube through-opening in the holding region.

7. The method according to claim 6, characterized in that the taper of the substrate tube through-opening is produced during the sintering according to method step (d) by softening an upper substrate tube end together with a shaped body placed thereon, against which the upper substrate tube end rests, and bending the upper substrate tube end inward under the effect of the weight of the shaped body.

8. The method according to claim 4, characterized in that the expansion of the substrate tube outer diameter has a longitudinal extension in the direction of the substrate tube longitudinal axis in the range from 20 to 200 mm, preferably in the range from 30 to 100 mm.

9. The method according to claim 4 or 8, characterized in that the expansion brings about a maximum enlargement of the substrate tube outer diameter in the range from 4 mm to 80 mm, preferably in the range from 6 mm to 50 mm.

10. The method according to one or more of claims 4, 8 or 9, characterized in that the expansion is produced during the sintering according to method step (d) by softening an upper substrate tube end together with an expansion device, which comprises an expansion body that can move radially outward and rests against the inner wall in the region of the upper substrate tube end, and moving the expansion body radially outward under the effect of the weight of the expansion device, and deforming the substrate tube wall in the region of the upper substrate tube end while forming the bulge.

11. The method according to one or more of the preceding claims, characterized in that a substrate tube is provided that consists at least partly of quartz glass of a first quartz glass quality, and in that the soot body consists of quartz glass of a second quartz glass quality, wherein the first quartz glass quality has a material-specific viscosity at the sintering temperature which is higher than the material-specific viscosity of the second quartz glass quality.

12. The method according to claim 11, characterized in that at a measurement temperature of 1350°C, the common logarithm of the viscosity of the first quartz glass quality is at least 0.25 Ig(dPa·s), preferably at least 0.4 Ig(dPa·s) and particularly preferably at least 0.6 Ig(dPa·s) higher than that of the quartz glass of the second quartz glass quality.

13. A tubular composite body consisting of quartz glass, having a length of at least 1000 mm, a tube wall with a wall thickness of at least 25 mm and with an inner diameter of at least 250 mm, characterized in that the tube wall comprises an inner wall region and an outer wall region, wherein the inner wall region comprises a holding element which is designed as a constriction of the substrate tube inner diameter or as an expansion of the substrate tube outer diameter.

14. The composite body consisting of quartz glass according to claim 13, characterized in that the inner wall region consists at least partly of quartz glass of a first quartz glass quality, and the outer wall region consists of quartz glass of a second quartz glass quality, wherein at a measurement temperature of 1350°C, the viscosity of the first quartz glass quality is higher than the viscosity of the second quartz glass quality.

15. A use of the tubular composite body according to claim 13 or 14 for producing etching rings for semiconductor manufacturing or a pressure vessel, wherein a quartz glass hollow cylinder is produced by removing the inner wall region, and this cylinder is processed to form the etching rings or the pressure vessel.