Tubular composites made of quartz glass and methods for producing and using same

Abstract

A known method for producing a tubular quartz glass composite in an external deposition process comprises the following method steps: providing a substrate tube; rotating the base tube about an axis of rotation; depositing SiO2 particles on the outer jacket surface of the base tube to form a composite material consisting of the base tube and a SiO2 soot body; and sintering the composite material by heating at a sintering temperature to form the tubular quartz glass composite, and using holding means adapted to at least temporarily hold the composite together with the vertically oriented longitudinal axis of the base tube in a heating zone. In order to be able to produce a tubular composite made of quartz glass having a particularly large inner diameter of more than 200 mm and a wall thickness of more than 25 mm on the basis thereof, while reducing waste, it is proposed to use a holding device comprising a holding element which is produced in a holding region of the base tube in a shaping step.

Description

Background Art

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

[0002] The invention further relates to the production of a tubular quartz glass composite body, in particular to a method for producing a tubular quartz glass composite body by an external deposition method, the method comprising the following method steps:

[0003] (a) providing a substrate tube having a continuous through hole, a substrate tube outer diameter, a substrate tube inner diameter, a substrate tube outer jacket surface, a substrate tube inner jacket surface, and a substrate tube wall having a wall thickness,

[0004] The continuous through hole extends coaxially with the longitudinal axis of the substrate tube,

[0005] (b) rotating the base tube about a rotation axis extending coaxially or parallel to the longitudinal axis of the base tube,

[0006] (c) depositing SiO2 particles on the outer jacket surface of the substrate tube by at least one deposition burner to form a composite material from the substrate tube and the SiO2 soot body,

[0007] (d) sintering the composite material by heating at a sintering temperature in a heating zone to form the tubular quartz glass composite body, and using a holding device suitable for at least temporarily holding the composite body with the vertically oriented longitudinal axis of the substrate tube in the heating zone.

[0008] Components made of quartz glass in the form of preforms, tubes, rods, flanges, plates, rings, reactors, crucibles, etc. are used in semiconductor production and optical fiber production. Such components are usually produced from tubular semi-finished products made of quartz glass by hot forming and / or mechanical treatment. Due to the increase in production rates, larger dimensions of such components are increasingly sought, especially in tubular semi-finished products, which are associated with larger wall thicknesses and inner diameters.

[0009] In order to produce semi-finished products from synthetically produced silicon dioxide, a CVD process (chemical vapor deposition) is known, in which SiO particles are deposited on a substrate from the gas phase. The CVD external deposition process, abbreviated as "OVD" (external vapor deposition), is generally suitable for producing large-volume semi-finished products. In this process, the silicon-containing starting material is converted into SiO particles by flame hydrolysis or pyrolysis in a reaction zone, and these particles are deposited in layers on the outer jacket of a cylindrical substrate rotating around its longitudinal axis. The reaction zone is generated by a heat source, in which the substrate longitudinal axis and the heating source move back and forth relative to each other. The substrate can be tubular, and is also referred to as "substrate tube" here and below. The substrate tube is, for example, composed of quartz glass, SiC, SiSiC (reaction bonded silicon infiltrated silicon carbide), AlO or other ceramic materials or graphite, and is fixed and rotated around its longitudinal axis by a lathe-shaped device (also referred to as "substrate tube holder" here).

[0010] Depending on the temperature during the deposition process, the synthetic SiO2 layer deposited on the substrate tube is still porous and is also 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 layer is sintered in a separate method step to form more or less transparent quartz glass (the sintering process is also referred to as "vitrification"). From the tubular quartz glass semi-finished product produced in this way, synthetic quartz glass components such as solid cylinders, hollow cylinders or parts of these components are obtained by mechanical, chemical and / or thermal aftertreatment, which components themselves can also be used as semi-finished products for producing other components.

[0011] Prior art

[0012] US Patent No. 8,316,671 B2 describes an OVD external deposition method for producing hollow cylindrical bodies made of quartz glass. A substrate tube made of quartz glass is provided and a porous SiO2 soot layer is deposited on its outer surface. The composite material consisting of substrate tube and SiO2 soot layer is vitrified in such a way that the interior of the substrate tube remains below the deformation temperature. For this purpose, the inner bore of the substrate tube can be cooled by gas or liquid during the vitrification process. The inner wall of the tubular composite body of quartz glass produced in this way is formed by the substrate tube; it is smooth and no longer requires mechanical treatment.

[0013] US2013 / 115391 A1 discloses a method for producing a quartz glass hollow cylinder with a large outer diameter, wherein a porous soot body made of silicon dioxide carbon black is deposited on a substrate by an OVD external deposition process. After the substrate is removed, the soot body is sintered to form a hollow cylinder. Rings are thereby sawn, which are made of quartz glass with a low chlorine content and at the same time a low hydroxyl content and therefore have a high viscosity. The quartz glass rings are used as so-called "plasma etching rings" for holding semiconductor wafers in plasma etching systems.

[0014] For vitrification of the soot body, the soot body is held in a sintering furnace with its longitudinal axis oriented vertically or horizontally. If the longitudinal axis is oriented vertically, the soot body can be vitrified standing on a support. However, there is a risk that the soot body will deform due to its weight and collapse. This can result in a circumferentially corrugated caterpillar-like structure, which makes it impossible to meet the dimensional accuracy requirements; in particular, the specified minimum inner diameter can be exceeded.

[0015] The method known from EP 701 975 A2 avoids some of these disadvantages. In the method, a tubular soot body is inserted into a vitrification furnace and held in a vertical orientation therein by a holding device, which comprises a holding rod extending from above through the inner bore of the soot body and connected to a holding foot, on which the soot body initially rests with its lower end. The holding rod consists of carbon fiber reinforced graphite (CFC; carbon fiber reinforced carbon) and is tightly surrounded by a gas-permeable, thin-walled jacket tube made of pure graphite. In a position above the upper end of the jacket tube, a graphite support ring is embedded in the inner bore of the soot body, which graphite support ring protrudes from the soot body wall inwardly into the soot body inner bore.

[0016] During vitrification, the soot body is moved in sections starting from its upper end through the annular heating element. In the process, the soot body collapses successively onto the graphite jacket tube and also shrinks in length, wherein in the first sintering stage the soot body stands upright on the retaining feet. The position of the graphite support ring embedded in the soot body is selected so that the graphite support ring is supported on the graphite jacket tube in the second sintering stage due to the increased length shrinkage, so that the soot body is then kept suspended at the upper end. This method is also referred to below as "suspended vitrification". After vitrification, the jacket tube is removed and the inner bore of the resulting quartz glass tube is reprocessed by drilling, grinding, honing or etching.

[0017] In order to reduce the graphite contact surface, in a modification of the method according to DE 103 03 290 B3, a sleeve of synthetic quartz glass is arranged between the holding rod and the soot body to be vitrified. Such a sleeve is very time-consuming and expensive to produce and is or forms part of the quartz glass tube.

[0018] In the method known from DE 100 64 730 A, SiO2 particles are deposited on an elongated substrate tube which is rotated about its longitudinal axis and whose outer diameter has a gradient over its length. After the stepped substrate tube is removed, a porous hollow cylindrical soot body is obtained, the inner bore of which 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 suspended in a furnace for vitrification in a vertical orientation, wherein the narrowing region of the inner bore is arranged at the top and the retaining rods which protrude from above into the inner bore engage below the stepped shoulder. Reliable retention of heavy soot bodies requires a relatively wide shoulder on the inner bore.

[0019] Technical issues

[0020] As quartz glass cylinders become larger, the weight of the soot body to be sintered and the increasing temperature difference between the inside and outside make the manufacturing process more difficult. With the above-described method, it is difficult to reliably hold the heavy soot body during vitrification and to reproducibly manufacture tubes from quartz glass. In particular, the generation of waste in the later stages of the method, such as when vitrifying the soot body, should be avoided.

[0021] Similar problems also arise when vitrifying other bodies made of porous SiO 2 which were not produced via the SiO 2 soot route, such as porous SiO 2 bodies obtained via the known sol-gel route or by pressing.

[0022] It is therefore an object of the present invention to specify a method for producing such a massive tubular composite body from quartz glass by means of an external deposition process, in particular by means of an OVD deposition welding process.

[0023] Furthermore, the object of the present invention is to specify a method for the reproducible production of a tubular composite body made of quartz glass with a large inner diameter, in particular with an inner diameter of more than 200 mm and a wall thickness of more than 25 mm, according to an external deposition process, which method avoids the above-mentioned disadvantages and, in particular, reduces the risk of waste.

[0024] Furthermore, the object of the present invention is to provide a tubular quartz glass composite body which is characterized on the one hand by large dimensions, in particular an inner diameter of more than 200 mm, a wall thickness of more than 25 mm and a length of at least 1000 mm, while at the same time having a high dimensional stability. DETAILED DESCRIPTION

[0025] With regard to a method for producing a tubular composite body made of quartz glass, this object is achieved according to the invention based on a method of the type mentioned at the outset, wherein a holding device is used which comprises a holding element which is produced in a forming step in the holding region of the substrate tube.

[0026] The method comprises a method step in which a porous SiO2 soot body, also referred to hereinafter as "soot body", is produced from synthetic silicon dioxide by an external deposition method, in particular by an OVD external deposition method. 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 content of the quartz glass and is then sintered to form more or less transparent quartz glass. Sintering (or vitrification) takes place, for example, under vacuum or in an atmosphere containing helium and / or hydrogen and / or nitrogen.

[0027] The substrate tube is designed to produce SiO2 bodies on its outer jacket surface with a large inner diameter based on an external deposition method. For example, the substrate tube has a substrate tube length of up to 4 m and is cylindrical, conical or stepped over its entire length or part of its length. The inner profile is constant over the length of the substrate tube or it varies.

[0028] After the deposition process is complete, the substrate tube remains in the composite material consisting 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 simply "composite body"). The substrate tube consists of quartz glass and preferably has an inner diameter of at least 250 mm. The wall thickness of the substrate tube is preferably in the range of 4 mm to 10 mm and is therefore small relative to its outer diameter. The wall thickness is typically less than 20% of the outer diameter of the substrate tube. Thus, on the one hand, the substrate tube has a low weight, which reduces the dynamics of the rotational movement and facilitates handling and alignment, and on the other hand, the substrate tube has a low thermal mass, which keeps the heat dissipation and the formation of thermal stresses in the wall at a low level.

[0029] On the other hand, the wall thickness of the substrate tube is large enough to support a large volume of SiO2 soot body. Therefore, the wall thickness of the substrate tube is preferably at least 1% of the outer diameter of the substrate tube. The wall thickness "W S "(in mm) may also depend on the length of the substrate tube. Advantageously, the wall thickness also increases with increasing length of the substrate tube. Thus, WS may alternatively be set to the outer diameter D of the substrate tube. S function (in mm), taking into account the length of the substrate tube "L S ” (in mm), as follows: W S <0.2*(L S / 2,000mm)*D S .

[0030] After the external deposition method and the optional dehydration of the soot body, according to process step (d), the soot body is sintered (vitrified) in the form of a composite material consisting of substrate tube and SiO2 soot body, i.e. in a form connected to the substrate tube. The substrate tube used for this purpose is characterized by the fact that it has a retaining element produced in the retaining region of the substrate tube in the shaping step.

[0031] The holding element forms part of the holding device during the sintering of the composite body. For example, the holding element is designed as a local constriction of the through hole, or as a local constriction of the inner diameter of the substrate tube, or as a local widening of the outer diameter of the substrate tube. During the sintering, the holding element serves to achieve the suspension of the composite body and in the process interacts with the support element of the holding device. The support element is, for example, a jacket tube, which is arranged inside the substrate tube during the sintering and onto which the composite body collapses during the sintering. During the sintering, the holding element rests at least temporarily on the support element, so that a suspended vitrification of the composite body can be achieved.

[0032] Compared to the prior art, the invention does not require a separate body to be connected to the inner bore of the soot body which can be used as a suspension. During the production of the connection, damage and contamination of the soot body can occur. This is avoided in the invention because the substrate tube, which is required anyway in the external deposition method, is vitrified together with the soot body in the form of a composite and, during this, is used as part of the suspension.

[0033] For this purpose, in a shaping step, a retaining element is produced in the retaining region of the substrate tube.

[0034] The holding area is usually located in the region of one of the end faces of the substrate tube. After the soot deposition process, these end face regions can be substantially free of SiO2 soot particles. However, they can also be covered by the end portions forming the SiO2 soot body.

[0035] The shaping step for producing the retaining element can be carried out before the sintering (vitrification) according to method step (d).

[0036] With regard to the previously generated retaining element, a first preferred method variant provides that the retaining element is generated before the deposition of SiO 2 particles according to method step (c), wherein the deposition of SiO 2 particles according to method step (c) is preferably carried out in such a way that the SiO 2 soot body covers the retaining region.

[0037] In this method variant, the retaining element is produced by shaping an already existing substrate tube. In doing so, for example, the substrate tube wall is locally heated and softened and collapsed to form a depression in the wall or expanded to form an expansion, such as a local bulge. Or the retaining element is formed, for example, by a forming process during the manufacture of the substrate tube, such as by forming a constriction of the inner bore of the substrate tube during a drawing process of drawing the substrate tube from a melt or elongating a mother tube to form the substrate tube.

[0038] This production step can be carried out easily and the retaining element thus obtained can be checked for integrity and dimensional accuracy.

[0039] During the subsequent deposition process, the previously produced holding elements are covered by the formed soot body. The holding elements are thereby protected from thermal and mechanical effects. It is sufficient if the overlap occurs only in the region of one of the end faces of the soot body. The ends of the soot body usually form conical regions which cannot be used for the production of the finished quartz glass body. However, this measure is not absolutely necessary; the previously produced holding elements can also be located completely outside the soot body.

[0040] Alternatively or additionally and likewise preferably, the shaping step for producing the retaining element is carried out during the sintering according to method step (d) in a sintering phase; the retaining element is produced more or less “in situ” during the vitrification.

[0041] With regard to the retaining element produced during sintering, in a second preferred method variant, the retaining element is produced after the deposition of the SiO 2 particles according to method step (c) and before or during the sintering according to method step (d).

[0042] The retaining element can be formed by a single operation of sintering the composite body in a sintering furnace. Separate manufacturing and hot forming steps and the associated costs can thus be avoided.

[0043] In both the first method variant and the second method variant, it has proven to be advantageous if the retaining element is designed as a constriction of the inner diameter of the substrate tube.

[0044] This constriction of the substrate inner diameter is produced during the shaping step and is designed, for example, as a local circumferential depression in the inner jacket region of the substrate tube wall or as a gradual (eg conical) taper of the inner diameter of the substrate tube.

[0045] The constriction of the inner diameter of the substrate tube serves as a holding element during sintering for holding the composite body in suspension. It is preferred to make the constriction as small as possible to minimize deformation of the substrate tube and as large as possible to ensure that the weight of the composite body is reliably accommodated. Advantageously, the constriction has a longitudinal extension in the direction of the longitudinal axis of the substrate tube in the range of 20 mm to 200 mm, preferably in the range of 30 mm to 100 mm.

[0046] The substrate tube inner diameter can be constant or can vary over the length of the constriction. In this case, it has proven useful that the constriction causes a maximum reduction in the inner diameter of the substrate in the range of 4 mm to 80 mm, preferably in the range of 6 mm to 50 mm.

[0047] In a particularly preferred method, the constriction is designed as a local depression of the inner jacket surface of the substrate tube and / or as a taper of the substrate tube through-bore in the holding region.

[0048] It has proven useful here to produce the tapering of the substrate tube through-bore during the sintering according to method step (d) by softening the upper substrate tube end together with the shaped body placed thereon and bending the upper substrate tube end inwards under the effect of the weight of the shaped body on which the upper substrate tube end rests.

[0049] The tapering of the substrate tube through-opening in the holding region occurs stepwise, continuously and preferably conically, since the upper substrate tube end softens and bends inwards under the weight of the shaped body.

[0050] In another equally preferred case, a shaped body having an inner cone is placed on the upper substrate tube end, which rests on the inner cone. The shaped body and the upper substrate tube end resting thereon are heated in a zoned sintering furnace, thereby softening the upper substrate tube end. Under the weight of the shaped body, the outer jacket surface of the substrate tube in the upper end region is shaped to form an outer cone, and the inner jacket surface of the substrate tube is shaped to form an inner cone.

[0051] In both the first method variant and the second method variant, it has proven to be advantageous if the retaining element is designed as an expansion of the outer diameter of the substrate tube.

[0052] The expansion of the outer diameter forms, for example, a circumferential bulge in the holding region of the substrate tube.

[0053] This expansion of the outer diameter of the substrate tube is produced during the shaping step and is designed, for example, as a local circumferential bulge in the region of the outer jacket surface of the substrate tube wall or as a gradual, conical expansion of the outer diameter of the substrate tube.

[0054] The expansion of the outer diameter of the substrate tube serves as a holding element during sintering to hold the composite in suspension. It is preferred to make the expansion as small as possible to minimize deformation of the substrate tube and as large as possible to ensure reliable acceptance of the weight of the composite. The substrate tube outer diameter may be constant or may vary over the length of the expansion.

[0055] Advantageously, the expansion has a longitudinal extension in the direction of the longitudinal axis of the substrate tube in the range of 20 mm to 200 mm, preferably in the range of 30 mm to 100 mm.

[0056] In this case, it has proven useful if the expansion brings about a maximum enlargement of the outer diameter of the substrate tube in the range from 4 mm to 80 mm, preferably in the range from 6 mm to 50 mm.

[0057] During sintering according to method step (d), the expansion portion is preferably produced in the following manner: the upper substrate tube end is softened together with an expansion device, the expansion device having an expansion body that can be moved radially outward and abuts against the inner wall in the area of ​​the upper substrate tube end; and the expansion body is moved radially outward under the action of the weight of the expansion device; and the substrate tube wall is formed into a bulge in the area of ​​the upper substrate tube end while being deformed.

[0058] In a particularly preferred method, a substrate tube is provided which is at least partially made 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 material-specific viscosity of the first quartz glass quality at the sintering temperature is higher than the material-specific viscosity of the second quartz glass quality.

[0059] The substrate tube used is characterized by a high thermal stability, so that when the soot body is sintered, it becomes less soft than the soot body. The substrate tube with higher thermal stability not only provides the softened soot body with a certain holding force, so that it can achieve or maintain the desired cylindrical shape, but also forms a particularly thermally stable holding element.

[0060] The relatively high viscosity of the substrate tube is achieved, for example, by the fact that over at least a portion of its length and / or over at least the thickness region of its wall, the substrate tube consists of quartz glass 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 completely of quartz glass of the first quartz glass quality, i.e. quartz glass of higher viscosity. In a further, likewise preferred embodiment, the quartz glass of the substrate tube consists of quartz glass of higher viscosity only over a portion of its length, e.g. in the portion of its length which serves as a retaining element during sintering of the soot body.

[0061] During sintering, the composite body softens zone by zone, starting from its upper end, wherein the composite body preferably stands upright on a base in a first sintering stage. The position of the holding element is selected such that it is supported on a supporting element of a holding device, such as a jacket tube arranged in a through-hole of the substrate tube, in the second sintering stage due to the increased length contraction. In the second sintering stage, the upper end of the composite body remains suspended. In this case, the holding element is no longer in the hottest region of the heating zone and has therefore cooled sufficiently to assume the suspended holding of the composite body. This is advantageous if the substrate tube consists completely or at least in the region of the holding element of a first quality quartz glass, which is characterized by a relatively high viscosity.

[0062] The sintering temperature is generally in the range of 1200° C. to 1450° C. It has proven useful if, at a measuring temperature of 1350° C., the common logarithm of the viscosity of the first quartz glass quality is at least 0.25 log (dPa·s), preferably at least 0.4 log (dPa·s), particularly preferably at least 0.6 log (dPa·s) higher than the common logarithm of the viscosity of the quartz glass of the second quartz glass quality. The viscosity difference is expressed here as the difference between the common logarithms log (dPa·s) of the corresponding viscosity values. At the measuring temperature, the viscosity difference generally does not need to be greater than 1 log (dPa·s).

[0063] The viscosity of quartz glass can be altered by hardening its glass network, in particular by dopants. The hardening of the glass network can be achieved by oxygen-deficient centers (also called ODC centers). Nitrogen, titanium oxide and aluminum oxide are suitable dopants for increasing the viscosity of quartz glass. In view of this, a preferred method provides that the aluminum oxide content of the quartz glass of the first quartz glass quality is at least 5 weight ppm, preferably at least 10 weight ppm higher than the aluminum oxide content in the quartz glass of the second quartz glass quality. Therefore, aluminum oxide can be added to quartz glass for the purpose of increasing the viscosity, which quartz glass is designed for use at high temperatures and is intended to have a certain temperature stability. The viscosity of synthetically produced quartz glass can also be increased in this way.

[0064] Naturally occurring quartz glass raw materials usually contain a certain proportion of aluminum oxide. In view of this, quartz glass of the first quartz glass quality is preferably melted from naturally occurring raw materials. The production of substrate tubes from natural quartz glass is relatively inexpensive. For example, such substrate tubes can be produced economically and efficiently using the known crucible drawing method.

[0065] Quartz glass of the second quartz glass quality is, for example, high-purity, synthetically produced quartz glass which has no significant proportion of aluminum oxide or has a low proportion of aluminum oxide of less than 1 ppm by weight, preferably less than 0.5 ppm by weight.

[0066] In contrast, quartz glass of the first quartz glass quality preferably contains at least 5 wt. ppm, preferably at least 10 wt. ppm. However, aluminum oxide contents of more than 100 wt. ppm are generally not preferred.

[0067] The viscosity of the quartz glass can also be changed by hydroxyl groups. Hydroxyl groups can reduce the viscosity of the quartz glass. In view of this, a preferred method provides that the quartz glass of the first quartz glass quality has a hydroxyl content of less than 30 wt ppm and preferably less than 20 wt ppm.

[0068] In quartz glass qualities produced from natural raw materials, for example by melting the raw materials in an electrically heated furnace or by using a hydrogen-free plasma, hydroxyl contents of less than 30 ppm by weight can be achieved. The hydroxyl content of quartz glass produced synthetically via the SiO2 soot route can be adjusted within a wide range by drying the soot body before vitrification. As a result of this drying process, low hydroxyl contents in the range of a few ppm by weight, characterized by a relatively low viscosity, can also be achieved in synthetically produced quartz glass. Optionally, synthetic quartz glass with a low hydroxyl content is suitable as a substrate tube material, provided that the quartz glass of the soot body applied thereto has a relatively low viscosity.

[0069] In a preferred method, a substrate tube is used having a wall thickness in the range of 1.5 mm to 10 mm, preferably in the range of 4 mm to 8 mm.

[0070] The wall thickness is as large as possible in order to ensure the desired thermal stability. On the other hand, the wall thickness is as small as possible since material of the substrate tube is usually removed during further processing of the quartz glass composite.

[0071] The tubular quartz glass composite body obtained after vitrification of such a composite material consisting of substrate tube and SiO2 soot layer has an inner wall region consisting of quartz glass of a first quality originating from the preceding substrate tube. And the tubular quartz glass composite body has an outer wall region consisting of quartz glass of a second quality originating from the preceding soot body. The thickness of the outer wall region is proportional to the wall thickness of the soot body and the soot density.

[0072] The soot density is typically 25% to 33% of the density of quartz glass. In view of this, the soot body obtained according to the external deposition method is advantageously essentially cylindrical and preferably has a wall thickness which, after sintering of the composite body, produces 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.

[0073] With regard to a tubular quartz glass composite body, the technical object is achieved according to the invention starting from a composite body of the type mentioned at the outset, in which the tube wall has an inner wall region and an outer wall region, wherein the inner wall region comprises a retaining element which is designed as a constriction of the inner diameter of the substrate tube or as an expansion of the outer diameter of the substrate tube.

[0074] A tubular quartz glass composite body can be produced using the method according to the invention described above. The outer wall region of the quartz glass composite body is optionally formed from quartz glass obtained by sintering a preceding soot body, and the inner wall region is formed from quartz glass of a preceding substrate tube.

[0075] The inner wall region comprises a holding element which enables suspension vitrification during the sintering process to form the quartz glass composite body. This suspension vitrification ensures a high dimensional stability of the quartz glass composite body obtained according to the invention.

[0076] The constriction of the retaining element is realized, for example, as a circumferential depression or a partially conical taper of the inner diameter of the substrate tube. The expansion is designed, for example, as a circumferential bulge or a partially conical expansion of the outer diameter of the substrate tube.

[0077] If the inner wall region at least partially consists 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 measuring temperature of 1350° C. the viscosity of the first quartz glass quality is higher than the viscosity of the second quartz glass quality, the holding element is characterized by a particularly high dimensional stability during the sintering process.

[0078] A quartz glass hollow cylinder is produced from the quartz glass composite by removing the inner wall region, for example by drilling, milling or etching. The quartz glass hollow cylinder obtained in this way is used to produce etching rings for single-wafer plasma etching chambers or pressure vessels used in chemical engineering.

[0079] The etched ring or pressure vessel has a specified target inner diameter. For producing the etched ring or pressure vessel, preferably a composite body is used which has an outer wall region whose inner diameter is at least 1 mm smaller than the target inner diameter. Here, the target inner diameter is set by removing the margin over the entire inner wall region and the outer wall region, wherein the margin is 1 mm or more.

[0080] Definition and measurement methods

[0081] The various terms described above are further defined below. These definitions are part of the specification of the present invention. For terms and measurement methods that are not specifically defined in the specification, the interpretation according to the International Telecommunication Union (ITU) is relevant. In the event that one of the following definitions is inconsistent with the rest of the specification, the statement in this specification shall prevail.

[0082] Tubular composite made of quartz glass

[0083] The deposition process produces a tubular composite material consisting of a quartz glass substrate tube and a SiO2 soot body. The substrate tube defines the inner pores of the composite material. By sintering (vitrification) the soot body, a tubular composite body made of quartz glass is obtained. By subsequently removing the substrate tube from the quartz glass composite body, a quartz glass hollow cylinder is obtained. The substrate tube is removed, for example, by drilling out. Mechanical, thermal or chemical treatments are used to produce quartz glass components from the quartz glass hollow cylinder. Further mechanical treatments include drilling, sawing, cutting, milling, grinding, and polishing of inner and outer contours. Thermal further treatments include thermal drying, sintering, vitrification, melting, shaping, and tempering. Further chemical treatments include doping and etching. The components consisting of quartz glass are ready-to-use quartz glass products or semi-finished products thereof, for example quartz glass hollow cylinders for producing pressure vessels or quartz glass rings for producing retaining rings for wafers.

[0084] Quartz glass / synthetic quartz glass

[0085] Quartz glass is understood here to mean glass with a SiO2 content of at least 87% by weight. Quartz glass is doped (SiO2 content = 100%) or contains dopants such as fluorine, chlorine, nitrogen, carbon, or oxides of boron, germanium, rare earth metals, aluminum, or titanium.

[0086] Quartz glass is, for example, a fusion product from a naturally occurring SiO 2 raw material (natural quartz glass), or it is produced synthetically (synthetic quartz glass), or consists of a mixture of these quartz glass types.

[0087] Sintering / vitrification

[0088] "Sintering" or "vitrification" here means a method step in which a porous silicon dioxide soot body is treated at high temperature in a furnace. Sintering / vitrification takes place in an inert gas, in an atmosphere containing hydrogen and / or helium or in a vacuum.

[0089] vacuum

[0090] The vitrification of the composite can be carried out under vacuum. Negative pressure refers to absolute gas pressure. Vacuum refers to an absolute gas pressure below 50 mbar.

[0091] Base tube outer diameter / base tube inner diameter

[0092] 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 given by the diameter of the (smallest) circumference.

[0093] 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 given by the diameter of the (largest) inscribed circle.

[0094] In a longitudinal section of the substrate tube, the local value of the outer diameter may be constant or not constant over the entire length of the substrate tube. In the case of a constant outer diameter value, the substrate tube has a cylindrical shape when viewed from the outside. Non-constant outer diameter values ​​may vary over the entire length or over a portion of the length. The outer contour may vary, for example, continuously or gradually. In this case, the outer diameter results from the local outer diameter values ​​averaged over the entire length.

[0095] In a longitudinal section of the substrate tube, the local value of the outer diameter may be constant or not constant over the entire length of the substrate tube. In the case of a constant inner diameter value, the through-opening of the substrate tube is cylindrical. Non-constant inner diameter values ​​may vary over the entire length or over a portion of the length. The inner contour may vary, for example, continuously or gradually. In this case, the inner diameter results from the local inner diameter values ​​averaged over the entire length.

[0096] Viscosity

[0097] The viscosity of quartz glass is measured using a beam bending viscometer. The beam bending viscosity measurement covers 10 8 dPa·s to 10 15 The viscosity range is 20 dPa·s. The measuring device comprises a heatable three-point bending device with a measuring beam consisting of the quartz glass to be measured (beam / strip: 50 mm long, 3 mm high, 5 mm wide). The variable measured is the bending speed at a given temperature.

[0098] Viscosity values ​​are also usually specified using the common logarithm in the form log(dPa·s) rather than exponential notation.

[0099] Softening temperature

[0100] Glasses cannot be assigned a specific softening temperature, but rather a softening temperature range. To determine the temperature values, reference is made here to the determination according to DIN ISO 7884 (1998), according to which the softening temperature is defined as the temperature at which the glass viscosity is 10 7.6 dPa·s. For the softening temperature of undoped quartz glass, the literature mentions temperature values ​​in the range of 1600°C to 1730°C.

[0101] Exemplary embodiments

[0102] The present invention is explained in more detail below with reference to exemplary embodiments and patent drawings. In detail, in the schematic diagram,

[0103] Figure 1 shows a longitudinal section through a device for producing a composite body consisting of a substrate tube and a soot body in a first embodiment of a substrate tube holder,

[0104] Figure 2 shows a longitudinal section through a device for producing a composite body consisting of a substrate tube and a soot body in a second embodiment of a substrate tube holder, partly in detail, and

[0105] Figure 3 Shows Figure 2 A magnified view of the detail of the substrate tube holder,

[0106] Figure 4 shows the components of a zoned sintering furnace for vitrification of a composite body,

[0107] Figure 5 shows the vitrification of a vertical composite using a zoned sintering furnace,

[0108] Figure 6 The method steps for producing a first embodiment of a retaining edge on a substrate tube are shown.

[0109] Figure 7 A further method step for producing a retaining edge on a substrate tube is shown.

[0110] Figure 8 shows the vitrification of a partially suspended composite by means of a first embodiment of a holding edge on a substrate tube in a zoned sintering furnace,

[0111] Fig. 9 The method steps of a second embodiment for producing a retaining edge on a substrate tube are shown.

[0112] Fig.10 A further method step for producing a retaining edge on a substrate tube is shown.

[0113] Fig.11 shows an embodiment of a substrate tube having a retaining edge produced in a tapered form with its inner diameter prior to the external deposition process,

[0114] Fig.12 Shown in Figure 4 After the external deposition process is completed during the vitrification of the composite body in the partitioned sintering furnace Fig.11 The base tube,

[0115] Fig.13 shows a longitudinal section through a first embodiment of a tubular quartz glass composite body according to the invention, and

[0116] Fig.14A longitudinal section through a second embodiment of a tubular quartz glass composite body according to the invention is shown.

[0117] In the embodiments explained below, different substrate tubes are used, some characteristics of which are summarized in Table 1.

[0118] Table 1 - Base tube

[0119]

[0120] "Natural quartz glass" is produced by melting a naturally occurring SiO2 raw material (preferably in an electrically heated furnace). Substrate tubes consisting of natural quartz glass are particularly economical and efficient to produce using the vertical crucible pulling method. Such quartz glass generally contains aluminum oxide in a concentration in the range of 6 to 18 ppm by weight and hydroxyl groups in a concentration of less than 50 ppm by weight.

[0121] "Synthetic quartz glass" is obtained, for example, by flame hydrolysis or oxidation of synthetically produced silicon compounds, by polycondensation of organic silicon compounds according to 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 within wide ranges. However, it can be said very generally that synthetic quartz glass generally has a significantly lower viscosity than natural quartz glass.

[0122] Figure 1 The apparatus schematically shown in is used for producing a large-volume composite material consisting of a substrate tube 1 and a SiO2 soot body 9. The apparatus comprises a glass lathe 2 for holding and rotating a substrate tube 1 corresponding to number 1 in Table 1. The substrate tube 1 has a left end face 1a, a right end face 1b, an outer jacket surface 1c, an inner jacket surface 1d, a horizontally oriented longitudinal axis 1e, and a cylindrical through hole 1f. Adjacent to the end face 1a is a free substrate tube section 1g, on which reduced SiO2 soot particle deposition occurs during the soot deposition process. The free substrate tube section 1g can be formed as a holding edge during vitrification, which will be referred to below. Figure 4 and Figures 6 to 10 Explain in more detail.

[0123] The glass lathe 2 is represented by two oppositely disposed chucks 2a, 2b, wherein the chuck 2a is spring loaded, as indicated by the compression spring 2c. The compression spring 2c generates a pressure F which presses the two chucks 2a, 2b against each other, as indicated by the directional arrow 2d.

[0124] A hollow spindle 3a, 3b made of stainless steel is clamped in each of these chucks at the proximal end of the chucks 2a, 2b. Ideally, the axis of rotation of the hollow spindle 3a, 3b extends coaxially with the substrate tube longitudinal axis 1e. The hollow spindle 3a, 3b has an outer diameter of 90 mm and an inner diameter of 82 mm.

[0125] The distal ends of the hollow spindles 3a, 3b are pivotably connected to annular pressure plates 4a, 4b made of stainless steel. To this end, the distal ends of the hollow spindles 3a, 3b taper conically and are pressed against the corresponding pressure plates 4a, 4b due to the force of the spring 2c. Here, the conical ends protrude into the central holes of the corresponding annular pressure plates 4a, 4b and abut against the inner edges of the central holes.

[0126] The pressure plates 4a, 4b each adjoin a buffer disk 5a, 5b made of graphite, which in turn adjoin the substrate tube end faces 1a and 1b, respectively. The buffer disks 5a, 5b have a central hole, the diameter of which corresponds to the diameter of the pressure plates and extends coaxially therewith. The outer diameter of the pressure plates 4a, 4b is 10 mm smaller than the outer diameter of the substrate tube 1. The outer diameter of the buffer disks 5a, 5b extends beyond the outer diameter of the substrate tube 1 by 40 mm.

[0127] Made of SiSiC, total length L z A tubular centering support 6 having an outer diameter of 80 mm extends through the base tube through hole 1f and through the center holes of the pressure plates 4a, 4b and the buffer plates 5a, 5b. One end 6a of the centering support 6 is 500 mm long. a It extends into the hollow spindle 3a and ends inside the hollow spindle, leaving a variable movement gap Ba of about 6 mm. The other end 6b has a length L of 600 mm. b It protrudes into the hollow spindle 3b and ends inside the hollow spindle, leaving a variable movement gap Bb of about 6 mm. Therefore, the total movement gap B of the centering support 6 in the hollow spindle 3a, 3b is z =B a +B b The outer diameter of the centering support 6 is constant over its length and is adapted to the inner diameter of the hollow spindles 3a, 3b in a clearance fit and can be displaced telescopically therein.

[0128] Three centering rings 7a, 7b, 7c made of graphite are placed 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 middle of the substrate tube through hole 1f. All centering rings 7a, 7b, 7c have an outer diameter that matches the inner diameter of the substrate tube in a clearance fit, and they have an inner diameter that matches the outer diameter of the centering support in a clearance fit.

[0129] The end centering ring 7a, the buffer disk 5a and the pressure disk 4a are loosely connected to each other by means of screws 4c. The screws 4c have threads that abut against the cylindrical portion 4d. The threads are in each case engaged in the internal threads in the pressure disk 4a, so that the cylindrical portion 4d rests firmly against the pressure disk 4a in the tightened state. The length of the cylindrical portion 4d is greater than the total thickness of the component stack of the centering ring 7a and the buffer disk 5a, so that the head of the screw 4c does not rest against the centering ring 7a, but a gap is left between the centering ring 7a and the screw head. In addition, the through hole in the buffer disk 5a and the centering ring 7a through which the cylindrical segment 4d passes is greater than the diameter of the cylindrical segment 4d, so that the screw 4c can also be slightly tilted in the through hole. Therefore, this loose connection is suitable for both allowing thermally induced length changes between the components of the substrate tube holder and compensating for deviations in the target size, positioning and alignment of the components. Furthermore, the screw 4c provides a certain torsional strength between the buffer disk 5a and the pressure disk 4a during the rotational movement of the substrate tube 1 and in this respect serves as a drive element for this rotational movement. The same applies to the connection of the centering ring 7b, the buffer disk 5b and the pressure disk 4b. For the purpose of thermal decoupling, a gap (not visible in the figure) is provided between the centering ring 7a, 7b and the buffer disk 5a, 5b.

[0130] Several deposition burners 8 for producing SiO2 particles are mounted on a common slide 8a, by means of which they can be moved reversibly and laterally along the outer jacket surface 1c of the substrate tube 1 or along the formed SiO2 soot body 9, and can be moved perpendicularly to the outer jacket surface, as indicated by the direction arrow 8b.

[0131] When Figure 2 and Figure 3 Use with Figure 1 When the same reference numerals are used throughout the text, these reference numerals represent the same or equivalent components or parts of the device.

[0132] Figure 2 The device schematically shown in Figure 1 The difference between the devices is mainly in the substrate tube holder and the substrate tube 21. Figure 1 When the same reference numerals are used in the Figure 1 The same or equivalent components or parts of the device explained.

[0133] Substrate tube 21 corresponds to number 2 in Table 1. In the end region 21a, the inner diameter of the substrate tube has a circumferential constriction 26. The constriction 26 is produced before the start of the external deposition process, for example by local softening of the substrate tube 21 after clamping in the glass lathe 2. The constriction 26 is located at a distance of about 80 mm in front of the substrate tube end face. The inner diameter is 270 mm, except in the region of the constriction 26, where the inner diameter is 250 mm.

[0134] The hollow spindles 23a, 23b are made of stainless steel and are each clamped with their proximal ends in a clamping chuck. Ideally, the axis of rotation of the hollow spindles 23a, 23b extends coaxially with the substrate tube longitudinal axis 1e. The hollow spindles 23a, 23b have an outer diameter of 100 mm. In the region of the distal ends of the hollow spindles 23a, 23b, a circumferential extension arm 2c is respectively welded.

[0135] The pivot connection between the hollow spindles 23a, 23b and the corresponding pressure plates 24a, 24 is designed here as a floating bearing and preferably comprises a universal ball-cone seat. Here, the distal ends of the hollow spindles 23a, 23b each form a convexly curved seat with a spherical or radius section, on which the pressure plate 24a or pressure plate 24b is movably mounted by having a concavely curved spherical or radius section that cooperates with the convexly curved seat.

[0136] Figure 3 An enlarged view of the pivotal connection between the hollow spindle 23a, 23b and the corresponding pressure plate 24a, 24b is shown. The end centering ring 7a, the buffer washer 5a and the pressure plate 24a form a stack of components that are loosely connected to each other by threaded screws 24c, which are each engaged in a thread in the extension arm 23c. The length of the cylindrical portion 24d is greater than the total thickness of the component stack consisting of the centering ring 7a, the buffer plate 5a and the pressure plate 24a. In addition, the width of the hole for receiving the screw 24c in the component stack is significantly greater than the diameter of the cylindrical portion 24d. This results in a number of gaps 25 being retained between the screw head 24e and the centering ring 7a and between the pressure plate 24 and the extension arm 23c, even in the case of a fixedly tightened threaded screw 24c, and along the cylindrical portion 24d. The gaps 25 ensure that the connection between the hollow spindle 23a, 23b and the corresponding pressure plate 24a, 24b remains pivotable. At the same time, the screw 24 c serves as a driving element for the rotational movement of the substrate tube 1 .

[0137] Reference below Figure 1 and Figures 4 to 10 An example for producing a quartz glass composite body is explained.

[0138] Soot deposition process

[0139] Oxygen and hydrogen are supplied as burner gases to the deposition burner 8, and a gas stream containing SiCl4 or another silicon-containing starting material is used as feed material for forming SiO2 particles. These components are converted into SiO2 particles in the associated burner flame, and these SiO2 particles are deposited on the substrate tube 1 rotating about the longitudinal axis 1e, thereby forming a soot body 9 from porous SiO2 soot.

[0140] In order to rotate the substrate tube 1, the glass lathe 2 transmits a torque to the hollow spindles 2a, 2b. At the same time, a pressure F acting in the axial direction is generated by the compression spring 2c, which presses the two hollow spindles 3a, 3b against each other and, depending on the offset of the spring relative to the spring rest length, is in the range between 0.5 kN and 10 kN. The pressure F is initially set to 1 kN and is applied to the pressure plates 4a, 4b, the buffer disks 5a, 5b and therefore also to the substrate tube end faces 1a, 1b. This pressure F produces a friction connection between the buffer disks 5a, 5b, which is sufficient to hold the inherent weight of the substrate tube 1 and the weight of the soot body 9. The centering rings 7a, 7b, 7c serve only to prevent the substrate tube 1 from accidentally sliding or bending. The interaction of the hollow spindles 3a, 3b and the centering support 6 provides a certain amount of axial guidance which compensates for any radial offset and angular differences between the axes of rotation of the hollow spindles 3a, 3b and avoids mechanical stresses due to the presence of mechanical play.

[0141] 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 a predetermined outer diameter of the hollow cylindrical quartz glass composite body plus a margin of 1 mm. At a soot density of about 30% (relative to the density of quartz glass) and a target outer diameter of the quartz glass composite body of 362 mm, the outer diameter of the soot body is, for example, about 520 mm.

[0142] After the deposition process, the soot body 9 is substantially barrel-shaped and extends just in front of the two side ends of the substrate tube 1. The substrate tube section 1g protruding from the soot body 9 and only lightly covered with SiO2 soot has a length of approximately 100 mm.

[0143] Drying and vitrification process

[0144] The substrate tube 1 remains in the soot body 9. The composite material (1; 9) consisting of the substrate tube 1 and the soot body 9 is dehydrated in a drying furnace in an inert gas atmosphere, a halogen-containing atmosphere or in a vacuum. The soot body 9 is dried thermally by heating to a temperature of about 1100° C. in a nitrogen atmosphere. By vitrifying the resulting dried SiO2 soot body in a vacuum, a synthetic quartz glass having the following properties is obtained:

[0145] Hydroxyl content: about 200 ppm by weight,

[0146] Chlorine content: <0.2 ppm by weight

[0147] Viscosity at 1350°C: 10.77 log (dPa·s).

[0148] Vitrification

[0149] The subsequent vitrification of the soot body 9 is carried out in a zoned sintering furnace with a vertically oriented substrate tube longitudinal axis 1 e under vacuum or in an atmosphere of gases that diffuse rapidly in quartz glass, such as helium and hydrogen, and therefore without the formation of bubbles. Figure 4 The details of such a partitioned sintering furnace 40 are schematically shown. A furnace chamber 41 surrounds a furnace interior 42, in which an annular heating element 43 and a holding device 44 are located. The device includes a support rod 45 made of fiber-reinforced carbon, which is connected to a base 46 of graphite by its lower end. The upper end of the support rod 45 is held by a movable clamp (not shown in the figure) and can be moved up and down thereby. The support rod 45 extends through the annular opening of the heating element 43 and through a graphite sheath tube 47 standing upright on the base 46. Except for the passage for the support rod 45 to pass through, the end face of the sheath tube is closed. Compared with a sheath tube with openings on both sides, the largely closed upper and lower sides 47a give the sheath tube 47 a higher dimensional rigidity relative to the pressure acting from the outside.

[0150] During vitrification, the substrate tube 1 remains in the soot body 9. The holding device 44 is used to hold the composite material (1; 9) consisting of the substrate tube 1 and the soot body 9, the weight of which is supported by the support rods 45 on the base 46. Figure 5 As schematically shown in FIG, the substrate tube 1 surrounds a jacket tube 47. Taking into account the higher thermal expansion coefficient of the graphite jacket tube 47 compared to the quartz glass substrate tube, the outer diameter of the jacket tube is adapted to the inner diameter of the substrate tube 1 so that the annular gap remaining during sintering is as small as possible and, for example, in the range of 1 mm to 10 mm, preferably less than 5 mm.

[0151] During vitrification, the heating element 43 is heated to a temperature of about 1400° C. and the support rod 45 is continuously pulled upwards, so that the soot body 9 is vitrified from top to bottom. During this period, the composite material (1; 9) shrinks onto the jacket tube 47 so that its outer diameter defines the lower limit of the inner diameter of the vitrified tubular quartz glass composite body. The substrate tube 1 consists 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 measuring temperature of 1350° C., according to Table 1, the viscosity difference corresponding to the difference between the common logarithms of the corresponding viscosity values ​​is about 0.51 log (dPa·s) [11.28 log (dPa·s)-10.77 log (dPa·s)].

[0152] The substrate tube 1 is therefore relatively thermally stable and does not deform or deforms slightly. In this way, it creates stability for the soot body 9 during vitrification. Specifically, the risk of the soot body 9 collapsing and forming circumferential folds during vitrification, or the risk of an expansion of the inner diameter leading to waste, is counteracted.

[0153] After cooling, a tubular composite body consisting of substrate tube 1 and glass layer with a thickness of about 41 mm is obtained, which is obtained by vitrification of soot body 9. Although synthetic quartz glass shrinks onto inner graphite sheath tube 47, since graphite has a significantly higher thermal expansion coefficient than quartz glass and shrinks more during cooling, the glass can be easily removed after vitrification.

[0154] The quartz glass of the substrate tube 1 can then be removed by mechanical treatment, for example by drilling. After grinding off and smoothing the outer wall, a quartz glass hollow cylinder with an outer diameter of 360 mm and an inner diameter of 290 mm is obtained.

[0155] Comparative Example

[0156] As already mentioned above, due to its relatively high viscosity, the substrate tube 1 contributes to the stabilization of the shape of the soot body 9 during vitrification.

[0157] In order to investigate the influence of the substrate tube 1 on the shape stabilization of the soot body 9, in a first comparative experiment, the substrate tube was removed before vitrification and only the soot body 9 was vitrified from top to bottom in the zoned sintering furnace 40. In doing so, the soot body 9 collapsed due to its own weight and the vitrified region detached from the jacket tube 47, resulting in a local widening of the inner diameter. The quartz glass tube produced in this way is unusable.

[0158] In a further comparative experiment, a synthetic quartz glass substrate tube with the same dimensions as the substrate tube 1 was used, as designated by number 3 in Table 1. The viscosity of this quartz glass is lower than the viscosity of the quartz glass obtained by vitrification of the soot body 9. It was found that when using this composite, the sheath tube provides better adhesion of the vitrified soot body 9, so that detachment does not occur over large areas of the vitrified material. However, the weight of the vitrified upper region of the composite increases continuously, resulting in compression towards the end of the process, so that the quartz glass tube produced in this way is ultimately unusable.

[0159] In a further comparative experiment, a substrate tube consisting of synthetic quartz glass was used, the dimensions of which were identical to those of substrate tube 1, as specified by number 4 in Table 1. The viscosity of this quartz glass corresponds to the viscosity of the quartz glass obtained by vitrification of the soot body 9. However, it was also shown here that during the sintering of the composite material (1; 9), there is compression towards the end of the process, so that the quartz glass tube produced in this way is ultimately also unusable.

[0160] Suspension vitrification

[0161] In order to counteract the compression effect of the inherent weight, a vitrification method is usually used, in which the composite material (1; 9) does not stand permanently on the base 46 during vitrification, but at least temporarily remains suspended. This method, for example, known from EP 0 701 975 B1, is referred to here as "suspension vitrification".

[0162] It is thereby ensured that the composite material (1; 9) remains suspended in the vitrification furnace from the outset, or that the retention of the composite material (1; 9) during the vitrification process can be switched from being upright at the start of vitrification to being suspended once the inevitable axial sintering shrinkage becomes apparent. To achieve suspended retention, measures can be taken on the substrate tube even before the external deposition method is carried out. This can be done, for example, by shaping the substrate tube or by a shaping process during the manufacture of the substrate tube, such as by producing a constriction in the inner bore of the substrate tube during the drawing process of the substrate tube from the melt or of the mother tube to form the substrate tube. Alternatively or in addition and likewise preferably, these measures are generated "in situ" during vitrification.

[0163] A suitable measure for achieving suspended vitrification is to form a retaining edge on the substrate tube, which serves to ensure that the composite material (1; 9) is vitrified at least for some time while suspended vertically (rather than just standing upright). As a result of at least temporary suspended retention, in addition to the above-mentioned effect of thermally stabilizing the substrate tube 1, compression of the soot body 9 during vitrification is counteracted, so that the soot body retains its desired geometry and waste is avoided.

[0164] For the suspension of the composite material (1; 9), for example, the substrate tube section 1g can be reshaped during the vitrification of the soot body 9 to form a retaining edge. Figures 6 to 10 Suitable methods for producing the holding edge "in situ" are explained in more detail.

[0165] Figure 6A first method and device for the "in situ" production of a suspension are schematically shown. A composite material (1; 9) consisting of a substrate tube 1 and a soot body 9 is placed in a vitrification furnace 40 and supported on a platform 46 by support rods 45 and a jacket tube 47, wherein the longitudinal axis 1e of the soot body is oriented vertically. An annular spacer 61 is placed on the upper end face 47a of the jacket tube 47, and a cone 62 in the form of an inverted cup is placed on the upper end of the substrate tube 9. The spacer 61 and the cone 62 consist of graphite. The cone 62 has an inner cone 62a, which merges into a flat support surface 62b, in which a through hole 62c is present. In the initial state, the inner cone 62 rests against the outer side of the upper substrate tube section 1g. The support rod 45 extends through the through hole 62c and through the annular spacer 61.

[0166] The upper substrate tube section 1g is shaped to form a suspension during the vitrification process. Figure 7 The shaping process is schematically shown in FIG. 4 . By means of the support rods 45, the upper substrate tube segment 1 g is moved into the heating element 43, which is heated to the glass transition temperature, to a temperature sufficient to soften it. Due to its weight, the cone 62 presses the soft upper substrate tube segment 1 g inwardly in the direction of the longitudinal axis 1 e of the substrate tube. In doing so, the substrate tube segment 1 g abuts against the inner cone 62 a and is thereby reshaped to form an outer cone. The reshaping process is terminated as soon as the spacer 61 abuts against the support surface 62 b of the cone 62.

[0167] During the further vitrification, the composite body (1; 9) is heated zone by zone starting from its upper end. In doing so, the composite body (1; 9) collapses continuously onto the graphite jacket tube 47 and also shrinks in length. Here, the sintering shrinkage forces are strong enough that the length of the substrate tube 1 is also shortened. However, the length shortening is very small.

[0168] In the first vitrification stage, the composite material ( 1 ; 9 ) stands upright on the platform 46 . Figure 8 The second vitrification stage is schematically shown. During this period, the previous substrate tube section 1g, which has been formed into an outer cone, moves out of the heating area of ​​the heating element 43, cools and solidifies. The inner side of this section rests on the upper side of the jacket tube 47a and then acts as a suspension 63 of the composite material (1; 9). Due to the length contraction, the composite material is lifted from the platform 46, forming a narrow gap 48, which can then undergo further "suspension vitrification". This counteracts the collapse of the soot body 9, wherein the substrate tube 47 additionally stabilizes the shape of the resulting tubular quartz glass composite due to its higher viscosity.

[0169] Fig. 9A second method and device for in-situ production of a suspension, i.e. vitrification of a composite material (1; 9) consisting of a substrate tube 1 and a soot body 9 in one operation, is schematically shown. The composite material is placed in a vitrification furnace 40 and supported on a platform 46 by support rods 45 and a jacket tube 47, wherein the longitudinal axis 1e of the soot body is oriented vertically. A ring 91 is placed on the upper end face 47a of the jacket tube 47 and consists of two or more individual sector plates 91a, 91b, which adjoin the central opening 91b of the ring and are mounted so as to be movable in the radial direction. A cone 92 consisting of graphite protrudes from above into the central opening 91b, the cone having a conical rod 92a and a conical head 92b with a flat lower side. The ring 91 and the cone 92 consist of graphite. The outer diameter of the ring 91 corresponds approximately to the inner diameter of the substrate tube 1; the ring rests against the inner wall of the upper substrate tube section 1g. The diameter profile of the tapered shaft 92a is designed so that in the initial state, the tapered shaft is inserted approximately halfway into the central opening 91b.

[0170] During the further vitrification of the composite (1; 9), the ridge 93 moves into the area above the heating element 43, cools and solidifies. The composite (1, 9) is heated zone by zone starting from its upper end, as described above for the first method. In the first vitrification stage, the composite (1; 9) stands upright on the base 46, and during the second vitrification stage, the ridge 93 acts as a holder for "suspended vitrification". The circular sector plate 91a protrudes from the inside into the ridge 93 and is fixed in the ridge in the vertical direction together with the substrate tube 1.

[0171] The length and inner diameter of the quartz glass composite body thus obtained are predetermined by the substrate tube 1. The preceding soot body forms a transparent synthetic quartz glass layer with a layer thickness of 41 mm. After removing the quartz glass material of the substrate tube 1 and grinding off 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. Thus, etching rings can be cut for single-wafer plasma etching chambers and pressure vessels used in chemical engineering.

[0172] For the production of etched rings or pressure vessels, preferably a composite body is used which has an outer wall region whose inner diameter is at least 1 mm smaller than the target inner diameter. The target inner diameter can be set by mechanical or chemical treatment of the pores in the composite body.

[0173] Reference below Figure 2 and Figure 3 as well as Figures 11 to 13 Another embodiment of a retaining edge for achieving suspended vitrification of the composite (21, 9) is explained.

[0174] Soot deposition process

[0175] The soot deposition process is as described above. Figure 1 Carry out as explained. Fig.11 2 shows a longitudinal section of a substrate tube 21 used in the process. A previously produced constriction 26 is provided in the end region 21a. Figure 2 It can be seen that the soot body 9 is produced 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 .

[0176] The deposition process is terminated as soon as the soot body 9 has reached a defined outer diameter: at a soot density of 30% (based on 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.

[0177] The composite material (21; 9) present 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 resulting dried SiO2 soot body under vacuum, a synthetic quartz glass having the following properties is obtained:

[0178] Hydroxyl content: <0.2 ppm by weight

[0179] Chlorine content: about 1,000 ppm by weight

[0180] Viscosity at 1350°C: 10.64Iog (dPa·s)

[0181] The composite material (21; 9) is then vitrified in a zoned sintering furnace 40 under vacuum. Fig.12 The composite material (21; 9) placed in a zoned sintering furnace 40 is shown. During vitrification, the heating element 43 is heated to a vitrification temperature of approximately 1400° C. and the support rods 45 are continuously pulled upwards so that the soot body 9 is vitrified from top to bottom. During this period, the composite material (21; 9) shrinks onto the graphite sheath tube 47 so that its outer diameter defines the lower limit of the inner diameter of the vitrified quartz glass composite body. Since the substrate tube 21 consists of quartz glass, which has a higher viscosity at the vitrification temperature than the quartz glass of the soot body 9, the substrate tube does not deform or deforms only slightly and stabilizes the soot body 9 during vitrification. In particular, this counteracts the risk of the soot body 9 collapsing during vitrification and forming circumferential wrinkles, or the risk of the inner diameter expanding.

[0182] At the stage shown in the method, the vitrification process has progressed and a certain shrinkage of the soot body 9 has occurred. This means that the transition from the initial vitrification stage with upright composite material (21; 9) to "suspended vitrification" has been completed. Due to the shrinkage of the soot body 9, the length of the substrate tube 21 has also shortened a little and the substrate tube has lifted slightly from the base 46, forming a gap 98.

[0183] In an alternative method, the composite material ( 21 ; 9 ) is kept suspended in the zoned sintering furnace from the outset by the constriction 26 resting on the upper edge of the graphite jacket tube 47 .

[0184] After cooling, a composite body 100 ( 200 mm in thickness) consisting of the substrate tube 21 and the glass layer 9a is obtained. Fig.13 ), which composite is obtained by vitrification of the soot body 9.

[0185] In the comparative experiment, a substrate tube composed of synthetic quartz glass was used, which had the same dimensions as the substrate tube 21, as designated by No. 3 in Table 1. The viscosity of this quartz glass was higher than the viscosity of the quartz glass obtained by vitrification of the soot body 9. More precisely, the common logarithm of the viscosity of this quartz glass at a measuring temperature of 1350° C. was 0.13 log (dPa·s) higher than the common logarithm of the viscosity of the quartz glass obtained by vitrification of the soot body 9.

[0186] However, this viscosity difference proved to be too small to provide sufficient stability for the bulky and heavy substrate tube when sintering the composite body.

[0187] Fig.13 Shown along Figure 2 1 . A cross section of the composite body 100 obtained after vitrification in a view along the line A′-A″ drawn in FIG. The substrate tube 1 with the through-opening 1 f , the diameter constriction 26 and the synthetic quartz glass layer 9 a obtained after vitrification is shown.

[0188] After removing the quartz glass material of the substrate tube 21 and grinding off and smoothing the outer wall, a quartz glass hollow cylinder having an outer diameter of 360 mm and an inner diameter of 290 mm was obtained.

[0189] From the hollow cylinder, an etching ring having corresponding inner and outer diameter values ​​can be sawn for use in fixing semiconductor wafers in industrial single wafer plasma etching chambers or pressure vessels.

[0190] Fig.14 A longitudinal section of another tubular composite body 110 obtained after cooling is schematically shown. The other tubular composite body has an inner wall layer 111 consisting of the previous substrate tube 1 and a glass layer 112 having a thickness of about 41 mm obtained by vitrifying the previous soot body 9. The inner wall layer 111 shows a retaining element 113, which in the exemplary embodiment is realized as a substrate tube ( Figure 8 , the tapered portion of figure 1).

[0191] After removing the quartz glass material of the substrate tube 1 and grinding off 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. Etching rings with corresponding inner and outer diameter values, or with larger inner diameter values ​​and smaller outer diameter values, can be sawed out of the hollow cylinder for holding semiconductor wafers in single-wafer plasma etching chambers and pressure vessels composed of quartz glass used in chemical 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 pipe having a continuous through hole, a substrate pipe outer diameter, a substrate pipe inner diameter, a substrate pipe outer jacket surface, a substrate pipe inner jacket surface, and a substrate pipe wall having a wall thickness, wherein the continuous through hole extends coaxially with a longitudinal axis of the substrate pipe, (b) rotating the base tube about a rotation axis extending coaxially or parallel to the longitudinal axis of the base tube, (c) depositing SiO2 particles on the outer jacket surface of the substrate tube by at least one deposition burner, and forming a composite material (1 / 9; 21 / 9)， (d) sintering the composite material (1 / 9; 21 / 9) to form the tubular quartz glass composite body (100; 110), and using a holding device suitable for at least temporarily holding the composite body together with the vertically oriented longitudinal axis of the substrate tube in the heating zone, It is characterized in that A holding device is used which comprises a holding element which is produced in the holding region of the substrate tube during a forming step.

2. The method according to claim 1, characterized in that: The holding element is produced prior to 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 in such a way that the SiO 2 soot body covers the holding region.

3. The method according to claim 1, characterized in that The retaining element is produced after the deposition of the SiO 2 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 retaining element is realized as a constriction of the inner diameter of the substrate tube or as an expansion of the outer diameter of the substrate tube.

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

6. The method according to claim 4 , wherein: The constriction is designed as a local depression of the inner jacket surface of the substrate pipe and / or as a taper of the substrate pipe through-bore in the holding region.

7. The method according to claim 6, characterized in that During sintering according to method step (d), the tapering of the substrate tube through-bore is produced by softening the upper substrate tube end together with a shaped body placed thereon and bending the upper substrate tube end inwards under the weight of the shaped body, on which the upper substrate tube end rests.

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

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

10. The method according to one or more of claims 4, 8 or 9, characterized in that During sintering according to method step (d), the expansion portion is preferably produced in the following manner: the upper substrate tube end is softened together with an expansion device, the expansion device having an expansion body that can be moved radially outward and abuts against the inner wall in the area of ​​the upper substrate tube end; and the expansion body is moved radially outward under the action of the weight of the expansion device; and the substrate tube wall is formed into a bulge in the area of ​​the upper substrate tube end while being deformed.

11. Method according to one or more of the preceding claims, characterized in that A substrate tube is provided which at least partially consists of quartz glass of a first quartz glass quality, and the soot body consists of quartz glass of a second quartz glass quality, wherein the material-specific viscosity of the first quartz glass quality at the sintering temperature 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 measuring temperature of 1350° C., the common logarithm of the viscosity of the first quartz glass quality is at least 0.25 log (dPa·s), preferably at least 0.4 log (dPa·s) and particularly preferably at least 0.6 log (dPa·s) higher than the common logarithm of the viscosity of the quartz glass of the second quartz glass quality.

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

14. The composite body composed of quartz glass according to claim 13, characterized in that The inner wall region at least partially consists 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 measuring temperature of 1350° C. the viscosity of the first quartz glass quality is higher than the viscosity of the second quartz glass quality.

15. Use of the tubular composite body according to claim 13 or 14 for producing a pressure vessel or an etching ring for semiconductor production, wherein a quartz glass hollow cylinder is produced by removing the inner wall area and the cylinder is processed to form the etching ring or the pressure vessel.

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