Method for manufacturing a workpiece from quartz glass for use in a plasma-assisted manufacturing process and use of the workpiece

Abstract

Method for producing a workpiece (64) made of quartz glass, which has at least one melt-polished workpiece surface (113) for use in a plasma-assisted manufacturing process, comprising the process steps: a) Providing a workpiece (64) made of quartz glass which has at least one raw surface (111) produced by cutting or machining, and b) Polishing the raw surface (111) to the polished workpiece surface (113) by laser polishing using at least one laser beam (81) moving relative to the raw surface (111), wherein the relative movement is generated by superimposing a translational-oscillating movement and a feed movement, wherein, as a result of the translational-oscillating movement, a quasi-line (87) is generated by a relative velocity between the raw surface (111) and the laser beam (81) above 500 mm / s, and wherein the feed movement has a relative velocity between the raw surface (111) and the laser beam (81) between 1 mm / s and 50 mm / s, c) and wherein a polished workpiece surface (113) is produced which has a micro-roughness and waviness, wherein the white light interferometry at a spatial wavelength λ OMicroroughness measured in the range of 1 µm to 10 µm has a surface roughness Sa of less than 0.5 nm, characterized in that the measurement is taken by means of a white light interferometer at a spatial wavelength in the range λ O Surface roughness (waviness) measured from 100 µm to 1000 µm has a value Sa of more than 5 nm, where the quasi-line (87) has a radiation intensity within the quasi-line (87) on the workpiece (64) between 10 W / cm² 2 and 1000 W / cm² 2 is produced wherein, for laser polishing of an annular end face (80) of a hollow cylindrical workpiece (64), the feed movement comprises rotation of the end face (80) about the longitudinal axis (84), and the translational-oscillating movement comprises a reversing movement of the laser beam (81) between an inner workpiece surface (85) and an outer workpiece surface (86), and wherein the speed of the translational-oscillating movement is set higher in the region of the inner surface (85) than in the region of the outer surface (86).

Description

Technical field

[0001] The invention relates to a method for producing a workpiece made of quartz glass, which has at least one polished workpiece surface for use in a plasma-assisted manufacturing process, in particular in semiconductor manufacturing, comprising the process steps: • Providing a workpiece made of quartz glass that has at least one raw surface produced by cutting or machining, and • Polishing the raw surface to a polished workpiece surface by laser polishing using at least one laser beam moving relative to the raw surface, wherein the relative movement is generated by superimposing a translational-oscillating movement and a feed movement, wherein, as a result of the translational-oscillating movement, a quasi-line is generated by a relative velocity between the raw surface and the laser beam above 500 mm / s. • and wherein a polished workpiece surface is produced which exhibits micro-roughness and waviness, wherein the white light interferometry at a spatial wavelength λ O The microroughness measured in the range of 1 µm to 10 µm exhibits a surface roughness Sa of less than 0.5 nm.

[0002] Furthermore, the invention relates to the use of a workpiece made of quartz glass, which has a melt-polished workpiece surface exhibiting micro-roughness and waviness.

[0003] Plasma-assisted manufacturing processes, such as plasma-assisted dry etching - also known as "plasma etching" - are an indispensable technology for producing ultra-fine structures of semiconductor devices, high-resolution displays and in solar cell manufacturing.

[0004] Plasma etching is performed in a plasma chamber purged with etching gas at low pressure and at a relatively high temperature. A reactive, etching plasma is generated in the plasma chamber by a high-frequency discharge between electrodes or by an electrodeless microwave discharge. The walls of chamber internals near the object being processed—usually a wafer—that are exposed to the plasma are often made of fused silica. Fusing silica is characterized by its inertness, chemical resistance to many substances used in the manufacturing process, and relatively high temperature resistance. Chamber internals include wafer holders, heating elements, pedestals, gas injectors, and support or clamping elements.

[0005] Halogen-containing etching gases, such as CF4, CHF3, C2F6, C3F8, NF3, or SF6, are typically used for etching silicon-based structures. However, the dry etching process relies not only on chemical etching but also on physical ablation through bombardment of the surface with ionized atoms (sputtering). This process attacks the object being processed as well as other chamber internals exposed to the plasma. Of particular concern is the generation of particles, which can form from the corrosive wear of the chamber internals or from the flaking of coatings, such as polymer or ceramic layers, which inevitably also form on the surfaces of the chamber internals during the plasma process. Particle formation is highly critical for the etching process because particles can end up on the wafer.This leads to the failure of the affected structures and thus to the loss of the corresponding chip. Therefore, the formation of particles reduces the yield of the process.

[0006] The functional properties of a wall are significantly influenced by its surface finish. For example, smoothness or surface roughness affects the adhesion of coatings and thus particle formation. Furthermore, the surface finish also directly impacts particle formation, as plasma attack and the associated erosion of the quartz glass can generate additional particles. State of the art

[0007] Quartz glass workpieces intended for use in plasma-assisted manufacturing processes are typically manufactured from semi-finished products. Typical rough machining steps include cutting, sawing, milling, drilling, turning, or grinding, which essentially give the workpiece its desired external shape. However, the resulting surfaces are usually still too rough and require post-processing to achieve the required smoothness.

[0008] The present invention relates in particular to this post-processing. A large number of methods for this are already known from the prior art.

[0009] US Patent 6,805,952 B2 proposes reducing the formation of polymer particles, such as fluorocarbons, on the surfaces of fused silica workpieces by increasing polymer adsorption through surface roughening. For this purpose, the surface is coated by plasma spraying with a finish that achieves a specific surface roughness (Ra = 3.8 µm - 4.8 µm).

[0010] US patent 7,250,114 B2 proposes that, to reduce particle formation during plasma chamber use, quartz glass workpieces should first be mechanically polished after rough machining to achieve an arithmetic mean roughness (Ra) in the range of 0.125 µm to 0.75 µm. Any remaining polishing compound or surface defects created by the polishing process are then removed by acid etching. The surface obtained after etching exhibits an arithmetic mean roughness (Ra) in the range of 0.025 µm to 2.5 µm. The surface topography of the plasma-exposed surface differs from the polishing-produced surface topography of another surface used for vacuum sealing.

[0011] In JP 2004-296 753 A, it is proposed to reduce the problem of particle release during plasma etching by sandblasting quartz glass workpieces exposed to the plasma and then etching them in hydrofluoric acid. This eliminates microcracks and improves adhesion to polymer films.

[0012] Mechanical processing of glass workpieces in general, and mechanical polishing in particular, are suitable for producing flat surfaces with a micro-roughness that varies depending on the method used and can be quite low. When surfaces with very low roughness are required, multi-stage mechanical polishing processes are typically employed. However, this method is correspondingly time-consuming and expensive.

[0013] A certain acceleration in this respect is achieved through thermal polishing processes such as flame or laser polishing. In laser polishing, a laser beam is typically scanned across the surface to be polished. The smoothing of the surface is achieved by locally melting a thin surface layer.

[0014] For example, Christian Weingarten, Andreas Schmickler, Edgar Willenborg, Konrad Wissenbach, and Reinhart Poprawe describe the laser polishing of optical quartz glass surfaces in "Laser polishing and laser shape correction of optical glass"; Journal of Laser Applications 29, 011702 (2017); https: / / doi.org / 10.2351 / 1.4974905; supplemented by a further laser-assisted process step (laser beam figuring, LBF) by which quartz glass material can be removed or compacted for shape correction. Laser polishing generates a relative movement between the workpiece surface and the laser beam, based on a superposition of a translational-oscillating motion and a feed motion. A high-speed translational-oscillating motion creates a "quasi-line" that is moved across the workpiece surface at a feed rate.

[0015] US patent 7,749,930 B2 describes a positive effect on the dry etch resistance of quartz glass workpieces when plasma etched after laser processing of the surface.

[0016] JP 2002-150 548 A deals with the polishing of storage platters made from a substrate that, in the area of ​​the surface to be polished, consists of a crystalline phase and an amorphous phase, for example, quartz glass. The polishing is carried out using a polishing fluid containing a first polishing agent that acts mechanically and chemically on the amorphous phase, and a second polishing agent that exerts a predominantly mechanical polishing effect on the crystalline phase. After polishing, the substrate is cleaned in a hydrofluoric acid solution. The average surface roughness R is then measured using AFM (atomic force microscopy). a is 0.38 nm with a maximum structure height R maxof 3.9 nm. The ripple (95% of the PV value) is specified as 1.8 nm.

[0017] German patent DE 10 2011 103 793 A1 describes a method for polishing high-precision optical elements made of quartz glass for optics manufacturing. In this process, material is vaporized from the surface of a blank to be polished by means of coarse laser ablation, thus roughly structuring the surface in the direction of the desired surface contour. The surface is then polished by laser-induced melting, whereby a "quasi-line" of a defocused laser beam is passed over the surface. This creates waviness with wavelengths of less than 100 µm, which is subsequently eliminated by fine ablation using locally applied laser radiation with a focused laser beam.

[0018] CN 1 09 590 603 A also describes a method for polishing optical elements made of quartz glass using a laser. In this process, a blank is pre-structured by mechanical grinding, then cleaned, and subsequently scanned using a continuous CO2 laser at a scan speed of 1 mm / s to 1 m / s. The laser energy of the CO2 laser is adjusted so that the process temperature of the polished optical quartz glass element remains within a predetermined temperature range, limited at the upper end by the evaporation temperature of quartz glass. After laser polishing, the surface roughness (RMS value) is 0.18 nm.

[0019] DE 44 40 104 C2 describes a method for producing a shaped body comprising a base body made of opaque quartz glass and a surface layer of transparent quartz glass that is smooth and has a micro-roughness of less than 8 µm. The transparent surface layer is produced on a base body in the form of a flange by clamping the flange in a rotary device and rotating it about its central axis. The top surface of the flange is heated by the flame of a hydrogen-oxygen burner. In addition to rotating the flange about its central axis, the burner is moved back and forth radially. A CO2 laser can also be used instead of the hydrogen-oxygen burner.

[0020] JP 2008-81 375 A describes a method for polishing a quartz glass disc mounted on a rotary table using two independently movable hydrogen-oxygen burners. With the rotary table rotating, the first burner is moved from the outer circumference of the quartz glass disc towards the center, heating the surface to a temperature in the range of 1900°C to 2000°C. During this process, the rotational speed of the rotary table is increased to maintain a constant relative velocity between the surface and the first burner, ensuring uniform fire polishing. After a predetermined time, the second burner is moved from the outer circumference of the quartz glass disc towards the center at a higher relative velocity than that of the first burner, but chosen so that the second burner reaches the center of the quartz glass disc after the first burner.The surface of the quartz glass disc is reheated by the second burner to a temperature in the range of 1600°C to 1800°C. This reheating process removes SiO2 soot particles from the surface.

[0021] From WO 2013 / 117 754 A1 a method for processing the outside or inside of a tube is known, wherein a laser is moved in an axial direction along the longitudinal axis of the tube and a ring-shaped intensity distribution of the laser light is generated. Technical task

[0022] In general, high demands are placed on the suitability of the surfaces exposed to the plasma for components made of quartz glass that are to be used in a plasma etching chamber in semiconductor technology, particularly with regard to dry etching resistance and the avoidance of particle formation.

[0023] Laser polishing of the surface of a quartz glass workpiece can achieve a low micro-roughness (hereinafter also referred to as "micro-smoothness") at a comparatively high area rate. The surface is smoothed by heating the quartz glass surface with laser radiation, which softens it, thus reducing the viscosity at the surface layer and consequently decreasing the roughness due to surface tension. This process results in little to no ablation of the quartz glass. However, this leaves behind streaks, waviness, and shape defects present on the original raw surface. Correcting or reducing these defects requires further time-consuming and costly measures, or alternatively, laser polishing must be performed as a final polishing step on a surface that has already undergone extensive mechanical polishing.

[0024] It is an object of the invention to avoid the disadvantages of the known methods and in particular to provide a method for producing a workpiece which exhibits low particle formation with comparatively little effort for surface treatment when the workpiece is used in the plasma-assisted manufacturing of a semiconductor component.

[0025] Furthermore, the invention is based on the objective of specifying a use for a specifically designed workpiece that has at least one polished workpiece surface. General description of the invention

[0026] With regard to the method, this problem is solved by the method of claim 1, starting from a method of the aforementioned type.

[0027] The polishing of the raw surface of the workpiece is carried out by laser polishing using at least one laser beam moving relative to the raw surface, whereby a polished workpiece surface is produced which has a micro-roughness and a waviness, wherein the by means of white light interferometry at a spatial wavelength λ O The microroughness measured in the range of 1 µm to 10 µm exhibits a surface roughness Sa of less than 0.5 nm, and is measured by white light interferometer at a spatial wavelength λ O The waviness measured in the range of 100 µm to 1000 µm exhibits a surface roughness Sa of more than 5 nm. The measurement conditions are described in more detail in Tables 1 and 2.

[0028] The following aspects are particularly characteristic of the process and the workpiece surface produced by laser polishing. (a) The workpiece surface to be smoothed by laser polishing is a rough, raw surface of the quartz glass workpiece that has only been roughly machined beforehand. The raw surface is produced by a rough mechanical manufacturing step such as cutting, sawing, milling, drilling, turning, or grinding, which gives the workpiece the desired external shape. The otherwise usual mechanical polishing is omitted in the inventive method, thus eliminating the associated machining effort. (b) The raw surface, which has only undergone rough mechanical processing beforehand, is rough and inevitably bears traces of the processing tool. These traces cannot be completely removed by laser polishing, and remnants of them appear as waviness on the final polished workpiece surface. During laser polishing, locally molten glass material is only displaced in small areas of the surface, so that existing streaks, grooves, and shape defects on the original raw surface are not completely eliminated. Therefore, a certain degree of waviness remains on the polished workpiece surface, influenced by the nature of the raw surface. Here, "waviness" refers to a surface texture or roughness with a more or less regular longitudinal structuring by waves or grooves. When measured at a spatial wavelength λ o In the range of 100 to 1000 µm, the invention results in a surface roughness Sa of more than 5 nm, preferably more than 10 nm and preferably less than 40 nm. A certain degree of waviness on the polished workpiece surface can reduce particle formation during plasma etching. This surprising effect, which can be attributed to the larger effective surface area compared to a flat surface, will be explained in more detail below. (c) During laser polishing, the polished workpiece surface acquires a low micro-roughness on a micrometer scale. With a view to achieving the smoothest possible surface, the micro-roughness is as low as possible. Its measurement at a spatial wavelength λ O In the range of 1 to 10 µm, the invention results in a surface roughness Sa of less than 0.5 nm, preferably less than 0.1 nm. The local melting of the surface layer during laser polishing minimizes the surface area due to the reduced viscosity and high surface tension of the molten quartz, resulting in a smoothing of the raw surface on a micrometer scale. Even when considered on the scale of plasma species, the roughness of the laser-polished surface is small, thus offering a minimal surface area for plasma molecules, radicals, and ions to attack. It is assumed that minimal microroughness is advantageous for preventing particle formation during plasma etching.

[0029] The inventive method thus aims for the lowest possible microroughness while maintaining surface waviness, with a view to minimizing particle formation during plasma etching. Furthermore, the fact that these properties can be achieved by laser polishing a roughly machined raw surface results in a short processing time for the production of the quartz glass workpiece.

[0030] The measurement procedures for determining waviness and micro-roughness as well as for characterizing workpiece surfaces based on the "local wavelength λ" o “ and the “surface roughness Sa” are explained in the section “Definitions”.

[0031] The laser beam is scanned across the surface to be smoothed, which heats up to a temperature between 1700°C and a temperature at which quartz glass does not yet evaporate significantly, for example, up to 2100°C. A high area coverage rate is generally desired, but this also depends on the speed of the laser beam's scanning movement (hereinafter also referred to as "scan speed"). With this in mind, the lower limit of the radiation intensity specified above is designed so that sufficient micro-smoothness of the surface is still achieved at a medium scan speed, and the upper limit is determined taking into account the evaporation of quartz glass and a reasonable ablation volume per stroke (pass).

[0032] The scanning movement of the laser beam over the raw surface is generated by a relative movement resulting from the superposition of a translational-oscillating movement and a feed movement, wherein, as a result of the translational-oscillating movement, a quasi-line with a radiation intensity within the quasi-line on the workpiece of between 10 W / cm² is generated by a relative velocity between the raw surface and the laser beam of at least 500 mm / s, preferably at least 3000 nm / s. 2 and 1000 W / cm² 2 preferably between 100 W / cm² 2 and 500 W / cm² 2 , is generated. The feed motion depends on the radiation intensity and, for example, is in the range between 1 mm / s and 50 mm / s when the relative speed between the raw surface and the laser beam is between 1 mm / s and 50 mm / s.

[0033] As a result of the high speed of the translational-oscillating movement, the laser beam, which preferably strikes the surface in a defocused manner, creates a "quasi-line" under which the surface to be smoothed is pushed with a feed movement that is at least one order of magnitude slower.

[0034] The principle of this polishing process is explained below with reference to Fig. 7 explained in more detail. A defocused CO2 laser beam 110 is accelerated to the velocities v s (Scan speed) and v v (Feed rate) over the workpiece surface 111 to be polished. Since v s is significantly larger than v vThe line described by laser beam 110 can be considered a "quasi-line" QL with a radiation intensity that is almost constant over the line width d and the line length L. The polishing process then proceeds approximately as if only a line-shaped laser beam (and not a single spot) with v v The laser beam would be guided over the workpiece surface. Absorption of the laser radiation in the material heats the surface, leading to a softening of the material. This results in a material flow driven by surface tension, thus smoothing the glass surface, although a certain waviness in the polished surface area, caused by the previous mechanical processing, remains.

[0035] The radiation intensity generated on the workpiece in the area of ​​the quasi-line is between 10 W / cm². 2 and 1000 W / cm² 2 preferably between 100 W / cm² 2 and 500 W / cm² 2, and is lower, due to the movement of the laser beam, than the radiation intensity of the stationary laser beam hitting the workpiece, which is, for example, between 100 W / cm² 2 and 10000 W / cm² 2 may lie.

[0036] The higher the relative speed of the translational-oscillating motion, the more homogeneous the polish. The higher the radiation intensity, the greater the suitable relative speed of the feed motion within the speed range defined above.

[0037] In this respect, the laser radiation is shaped into a quasi-line by a translational-oscillating movement of the laser beam at a speed of at least 500 mm / s, which is then guided over the raw surface with a feed motion.

[0038] The quasi-line is created by a high-speed translational-oscillating movement of the light beam striking the workpiece surface at a relative speed of at least 500 mm / s with respect to the workpiece surface. This quasi-line is then guided across the surface to be smoothed with a feed rate at least ten times slower.

[0039] For laser polishing of an annular end face of a hollow cylindrical workpiece having a longitudinal axis, the feed movement is effected by rotating the end face around the longitudinal axis, and the translational-oscillating movement is carried out by reversing movement of the laser beam between an inner surface of the workpiece and an outer surface of the workpiece, whereby the speed of the translational-oscillating movement is set higher in the area of ​​the inner surface than in the area of ​​the outer surface.

[0040] The laser beam can also sweep across the inner surface and / or the outer surface if the reversing points of the reversing movement are located outside the workpiece ends.

[0041] By aligning the laser beam appropriately with the workpiece, it can also sweep across the inner and / or outer surfaces of the workpiece. This achieves not only polishing of the end face but also of the inner and / or outer surfaces.

[0042] With constant rotational motion, the circumferential speed is greater in the region of the outer surface than in the region of the inner surface. This can lead to a longer interaction time between the surface and the laser beam in the inner surface, and thus to a higher process temperature. This effect is partially or completely compensated for by modulating the translational-oscillating motion. Ideally, this speed is modulated so that processing takes place at a higher scan speed in the inner surface, thus resulting in the same process temperature in both the inner and outer surfaces.

[0043] The term "interaction duration" refers to the length of time a point on the quartz glass surface remains within the "quasi-line" of the scanning laser beam. To ensure sufficient smoothing of the raw surface while retaining waviness on the workpiece surface, the relative movement between the quasi-line and the raw surface is adjusted to achieve an interaction duration between 1 s and 10 s.

[0044] The CO2 laser beam source is operated in continuous or pulsed mode. A laser beam defocused with respect to the raw surface is preferably used.

[0045] By defocusing the laser beam, a leveled radiation intensity is distributed over a certain height range during surface treatment, so that even with uneven surfaces, such as grooves or steps, surface sections at different height levels can be smoothed. This effect is particularly helpful for smoothing the coarsely structured, wavy raw surface according to the invention.

[0046] Good results regarding surface smoothing are achieved when a laser power in the range of 1 kW to 10 kW is used to generate the laser beam. The laser beam on the raw surface then has a beam diameter of, for example, between 4 mm and 25 mm, preferably between 8 mm and 20 mm. With higher laser power, the laser beam can be larger; with lower laser power, it can be correspondingly smaller.

[0047] In another, equally preferred method variant, the laser radiation is shaped into a line using beam shaping optics, which is projected onto the workpiece with a radiation intensity between 10 W / cm². 2 and 1000 W / cm² 2 preferably between 100 W / cm² 2 and 500 W / cm² 2 , which preferably has a width between 4 mm and 25 mm in the feed direction, is then guided over the raw surface with a feed movement

[0048] As already mentioned, the inventive method targets a quartz glass workpiece with a polished surface characterized by the lowest possible microroughness while simultaneously exhibiting surface waviness. White light interferometry (WLI) is one of the methods suitable for quantitatively determining these properties.

[0049] With regard to the use of the workpiece made of quartz glass, the above-mentioned problem is solved by a use with the features of claim 13.

[0050] The quartz glass workpiece has at least one melt-polished surface characterized by a small micro-roughness combined with surface waviness, which can be obtained, for example, by laser polishing. The quartz glass workpiece can be manufactured using the above-described method of the invention and is designed and suitable for exposure to plasma in a plasma-assisted manufacturing process. The workpiece is, for example, a plasma chamber or a part thereof, or it forms chamber internals such as wafer holders, heating elements, pedestals, gas injectors, and support or clamping elements.

[0051] The micro-roughness and waviness of the melt-polished workpiece surface are optimized with regard to low particle formation when used in a plasma-assisted manufacturing process.

[0052] The white light interferometer at a spatial wavelength λ O The microroughness of the melt-polished workpiece surface, measured in the range of 1 µm to 10 µm, exhibits a surface roughness Sa of less than 0.5 nm, and the surface roughness measured by white light interferometer at a spatial wavelength λ O The waviness measured in the range of 100 µm to 1000 µm exhibits a surface roughness Sa of more than 5 nm.

[0053] When measuring the melt-polished workpiece surface using white light interferometry, the micro-roughness is less than 0.5 nm, preferably less than 0.1 nm. The waviness is at least 5 nm, preferably at least 10 nm, and preferably less than 40 nm.

[0054] The waviness of the melt-polished workpiece surface is evident in a more or less regular longitudinal structuring by waves or grooves, which are defined by a spatial wavelength λ. o The surface texture is defined as being in the range of 100 to 1000 µm. A certain degree of waviness on the melt-polished workpiece surface can reduce particle formation during plasma etching. This surprising effect can be attributed to the larger effective surface area compared to a flat surface.

[0055] The melt-polished workpiece surface is smooth and exhibits a micro-roughness – defined by a spatial wavelength λ. oin the range of 1 to 10 µm. The roughness is small, even when considered on the size scale of plasma species, and offers a small surface area for attack by plasma molecules, radicals, and ions. This surface is advantageous both in terms of high dry etch resistance—resulting in a low removal rate during plasma etching—and in terms of low particle formation. Definitions and measurement methods

[0056] Individual terms from the above description are further defined below. In case of a discrepancy between one of the following definitions and the rest of the description, the definition in the rest of the description shall prevail. Quartz glass

[0057] In this context, quartz glass refers to high-silica glass with a SiO₂ content of at least 90 mol%. The quartz glass is either doped or undoped. The doping may consist of one or more dopants. A "doper" is a substance intentionally added to the glass to achieve desired properties. Raw surface of the workpiece to be machined

[0058] The workpiece is typically obtained through rough machining of a semi-finished product. This machining gives the workpiece a near-final contour shape that largely corresponds to the specified contour of the final quartz glass workpiece. Rough machining includes cutting operations without chip formation as well as machining operations such as sawing, drilling, turning, milling, and grinding. The machining tool used in rough machining leaves more or less periodic grooved or striped structures on the raw surface, which can be removed or reduced by mechanical polishing. Melt-polished workpiece surface

[0059] The workpiece surface is achieved through laser polishing. This process softens a near-surface layer of quartz glass, resulting in a smoothing effect caused by molten glass flow due to the reduced viscosity and surface tension. The resulting smoothed surface is also referred to as "melt-polished". Surface roughness Sa

[0060] The surface roughness Sa is determined in accordance with EN ISO 25178-2. Sa is calculated as the magnitude of the height difference at each point compared to the arithmetic mean of the surface. A white light interferometer is used to determine the surface roughness Sa. White light interferometry (WLI) allows 3D profile measurements of structures with lateral dimensions ranging from a few centimeters down to approximately 0.5 µm and vertical dimensions from a few hundred µm down to 0.1 nm. For the values ​​presented in this application, a Zygo NexView™ NX2 measuring instrument with a height resolution of < 1 nm was used. spatial wavelength λ O

[0061] The spatial wavelength λ ODescribes the length of a spatial period; here, the period of a spatial surface structure. The local melting of the quartz glass surface during laser polishing, compared to the initial state (raw surface), results in a surface smoothing, especially of structures with spatial wavelengths λ. O of less than 10 µm. The largest spatial wavelength whose roughness is smoothed compared to the initial state is also referred to as the "critical spatial wavelength".

[0062] Based on Fig. 6 becomes the spatial wavelength λ O This is explained in more detail below. The roughness profile (surface profile) measured on the raw surface can be decomposed into a multitude of (local) wavelengths and associated amplitudes by means of filtering. Fig. Figure 6 schematically shows a surface profile 100 of the raw surface. By applying a low-pass filter 101 with a long spatial wavelength of, for example, 100 µm (λ), O100) the waviness 103 of the surface profile is determined. By applying a high-pass filter 102 with a short spatial wavelength of, for example, 10 µm (λ) O The microroughness 104 of the surface profile is determined (=10). The amplitude A1; A2 of the respective profile represents a measure of the waviness or a measure of the microroughness. Measurement procedure for characterizing workpiece surfaces

[0063] To determine the surface roughness Sa using a white light interferometer (as described above), areas of the surface with an area dependent on the magnification used, in the range of a few µm, are measured. 2 to a few mm 2 Recorded by a white-light interferometer (examples are given below in Table 1). Measurement of the surface roughness Sa as a function of the spatial wavelength λ. OThis is achieved by filtering the measurement data with a bandpass filter, where the lower bandpass limit is defined as λ. Oa and the upper bandpass limit as λ Ob is denoted. The defined bandwidth thus corresponds to: λ Ob -λ Oa .

[0064] For each surface roughness data point Sa(λ Ox The measurement data filtered by the bandpass filter are used and the mean wavelength λ is calculated. Ox assigned to the corresponding spatial wavelength interval. In this way, the diagram is successively created in Fig. 2. Table 1: Characterization of microroughness as a measure of surface roughness. Determination of four data points with the following parameters: Measurement field size Bandwidth l Ob - l Oa Mean spatial wavelength λ Ox 88 µm x 88 µm 0,625 µm 0,9375 µm 220 µm x 220 µm 1,25 µm 1,875 µm 436 µm x 436 µm 2,5 µm 3,75 µm 875 µm x 875 µm 5 µm 7,5 µm λ Ob represents the upper range limit and λ Oa represents the lower limit value of the wavelength range under consideration. Table 2: Characterization of waviness as a measure of surface roughness. Determination of four data points with the following parameters: Measurement field size Bandwidth l Ob -l Oa Mean spatial wavelength λ Ox 12678 µm x 12678 µm 80 µm 120 µm 160 µm 240 µm 320 µm 480 µm 640 µm 960 µm λ Ob represents the upper range limit and λ Oa represents the lower limit value of the wavelength range under consideration. Example of implementation

[0065] The invention is explained in more detail below with reference to an exemplary embodiment and a drawing. Specifically, it shows Fig. 1. A sketch comparing the topographic profiles of a surface smoothed by abrasive-mechanical polishing and a surface smoothed by laser polishing. Fig. 2 a roughness spectrum of a surface smoothed by abrasive-mechanical polishing and a surface smoothed by laser polishing, Fig.3 a sketch showing the processing steps for producing a quartz glass workpiece using the inventive method in comparison to two other manufacturing techniques known from the prior art, Fig. 4. A sketch illustrating the adhesion of a polymer film to the quartz glass surfaces produced using the different manufacturing techniques. Fig. 5. An embodiment of a reactor for carrying out a plasma-assisted manufacturing process and in particular for carrying out dry etching procedures in a schematic representation. Fig. 6. A diagram to explain the spatial wavelength λ O , Fig. 7. A diagram to explain the laser polishing process and Fig. 8 A sketch to illustrate the laser polishing of the end face of a ring-shaped raw surface on a hollow cylindrical workpiece.

[0066] The sketch of Fig.Figure 1 on the left schematically shows the profile of a raw surface of a quartz glass workpiece after mechanical grinding. The figures on the right show surface profiles obtained from the raw surface after various finishing methods. The top figure shows a flat surface with a certain roughness in the nanometer range, symbolized by the magnifying glass. This surface is typical of one produced by mechanical grinding. The bottom figure schematically shows a surface profile produced by laser polishing. Compared to mechanical polishing, this profile exhibits lower flatness and some waviness. However, the microroughness is significantly lower.

[0067] In contrast to conventional quartz glass workpieces for use in plasma etching chambers with a flat and micro-rough surface, the workpiece surface smoothed by laser polishing is wavy and smooth.

[0068] In the double-logarithmic diagram of the Fig. 2 is the surface roughness Sa (in nm) of a mechanically polished and a laser-polished quartz glass surface as a function of the spatial wavelength λ. O (in µm). The measured values ​​were determined using a WLI measurement.

[0069] Depending on the magnitude of the spatial wavelength λ O The diagram area is divided into micro-roughness, meso-roughness, and waviness. "Micro-roughness" encompasses the surface roughness, which is determined by filtering down to a spatial wavelength λ. O measured from 1 µm to 10 µm, and under "ripple" the surface roughness when filtered from a spatial wavelength λ Ofrom 100 µm to 1000 µm. At spatial wavelengths around 1 µm, the surface roughness (microroughness) of the laser-polished surface is an order of magnitude lower than that of the mechanically polished surface. At spatial wavelengths around 1000 µm, the surface roughness (waviness) of the laser-polished surface is an order of magnitude higher.

[0070] In Fig. Figure 3 outlines the processing steps of the inventive method for the production of ring-shaped quartz glass workpieces in comparison to two other manufacturing techniques known from the prior art. All three methods have in common that a semi-finished product in the form of a hollow quartz glass cylinder 61 is cut into rings 62 (process step S1) and subsequently the workpiece 64 with the specified geometry is produced by mechanical shaping using a processing tool, such as a grinding machine 63 (process step S2).

[0071] The simplest and most widespread process chain is shown in process A. After mechanical shaping (process steps S1 and S2), the workpiece 64 is successively subjected to a multi-stage mechanical polishing procedure with increasingly finer polishing media (process steps S3, S4, and S5). The result is a quartz glass workpiece with flat surfaces, which, however, still exhibits a certain degree of micro-roughness.

[0072] This can be significantly reduced by additional hot polishing using a flame or a laser beam, as shown in process chain B. The resulting surfaces of the quartz glass workpiece are flat and microscopically smooth.

[0073] The production of the quartz glass workpiece using process chain B is complex. Process chain C avoids this disadvantage by smoothing one or more surfaces of the workpiece 64 immediately after mechanical shaping (process steps S1 and S2) using the processing tool 63 by laser polishing with at least one laser beam 65. The multi-stage mechanical polishing procedure with successively finer polishing media (process steps S3, S4, and S5) is thus omitted. The resulting quartz glass surface has a micro-roughness similar to that achieved in process chain B, but exhibits a certain waviness due to the surface defects resulting from the mechanical shaping using the processing tool 63.

[0074] The waviness and micro-roughness of the treated surfaces are summarized in Table 3 and Table 4: Table 3: Microroughness • Measurement field size: 88×88µm 2 • Filter type for bandpass: FFT Fixed Bandwidth l Ob_ -l Oa Mean local wavelength λ Ox microroughness Process chain A Process chain C 9 µm 5,5 µm 2.09 nm 0.09 nm Table 4: Ripple • Measurement field size: 6.307×6.307mm 2 • Filter type for bandpass: FFT Fixed Bandwidth l Ob_ -l Oa Mean local wavelength λ Ox ripple Process chain A Process chain C 900 µm 550 µm 3.1 nm 23.4 nm

[0075] This surface waviness of the workpiece 64 processed according to process chain C contributes to low particle formation during the plasma-assisted dry etching process and thus has a favorable effect on the intended use of the quartz glass workpiece.

[0076] One possible explanation for this effect is given below. Fig. Figure 4 illustrates this. During a typical semiconductor process in a plasma etching chamber, polymerized material is deposited on the quartz glass ring (for example, workpiece 64). Fig.Figure 4(a) schematically shows a quartz glass ring 64a produced according to process chain A with a quartz glass surface 70 completely smoothed and flat by mechanical polishing and a polymer film 71 deposited on it. Fig. 4(b) schematically shows the process chain C ( Fig. 3) achieved a wavy quartz glass surface 72 and also a polymer film 71 deposited on it.

[0077] In the (very likely) case of a difference in the coefficients of thermal expansion between the quartz glass ring 64 and the polymer layer 71, temperature fluctuations during the subsequent manufacturing process cause mechanical stresses in the polymer layer 71. These stresses can lead to parts of the polymer layer 71 detaching, thus resulting in particle formation. Due to the continuous changes in the direction of the acting forces, the wavy surface of Fig.4(b) lower stresses than on the smooth surface of Fig. 4(a). This is shown by the different lengths of the block arrows σ. e and σ w symbolizes.

[0078] The wavy and smooth surface 72 according to process chain C ( Fig. 3) exhibits little microroughness and low-frequency waviness, allowing the polymer film to conform to the wavy surface and resulting in better adhesion compared to the ideally flat quartz glass surface 70.

[0079] The smooth yet low-frequency wavy surface, as produced in process chain C, exhibits comparable plasma resistance and is characterized by lower particle generation, even without the need for the time-consuming, step-by-step mechanical polishing process according to process chains A and B.

[0080] The inventive method for producing ring-shaped quartz glass workpieces is described below. Fig. 8 in conjunction with Fig. 3 explained in more detail: How based Fig. As explained in section 3, a cylindrical semi-finished product 61 made of quartz glass is cut into rings 62 (process step S1), and these rings are then mechanically shaped using a grinding machine 63 to produce ring-shaped workpieces 64 made of quartz glass (process step S2). The quartz glass ring 62 has the specified final dimensions of the quartz glass workpiece to be produced, namely, for example, an outer diameter of 370 mm, an inner diameter of 300 mm, and a thickness of 20 mm. Subsequently, at least one of the surfaces mechanically processed by sawing or grinding 63 is smoothed by laser polishing.

[0081] CO2 laser radiation is used to smooth the annular end face 80 (raw surface) of the workpiece 64. This generates a laser beam 81 with a radiation intensity of approximately 400 W / cm². 2 and with a beam diameter of approximately 8 mm, widened by defocusing, strikes the front face 80 and scans it in a raster pattern.

[0082] The scanning is performed by superimposing a translational-oscillating scan movement of the laser beam 81, indicated by the block arrow 82, and a feed movement by rotating (83) the end face 80 around the ring's central axis 84. The translational-oscillating movement occurs at a speed in the range of 7000 mm / s to 9000 mm / s, and the feed movement at a rotational speed of 0.07 rpm. Due to the high speed of the translational-oscillating movement, a "quasi-line" 87 is created, under which the ring to be polished is rotated.

[0083] The speed of the translational-oscillating motion is modulated so that it is higher in the region of the inner surface 85 than in the region of the outer surface 86. This compensates for the lower circumferential speed of the inner surface 85, resulting in an approximately equal interaction duration of about 5 s between the laser beam 81 and the surface across the width of the end face 80, and the laser beam 81 generates a process temperature of around 2090 °C on the raw surface.

[0084] Fig.Figure 5 schematically shows a plasma reactor 1 for the dry etching of a wafer 13. The reactor 1 has a wall 2 that encloses a plasma reactor chamber 3. The wall 2 is provided with a gas inlet 4, which is connected to a gas source (not shown) from which gases can be supplied to the reactor chamber 3. The interior of the chamber 3 is evacuated via a gas outlet 5, which is connected to a high-vacuum pump (not shown), in order to establish a low chamber pressure between 0.5 Pa and 10 Pa suitable for dry etching. An RF power source 8 for 13.56 MHz, which is connected to an upper electrode 9, inductively couples energy into a plasma 10 ignited within the reactor chamber 3.A further RF power source 11 for 13.56 MHz is connected to a lower electrode 12, which is positioned below the wafer 13 and by means of which an independent electrical bias voltage can be applied to the measurement sample 13. The wafer 13 is fixed on a holding device, which is assigned the reference numeral 15. This includes an outer retaining ring 14 made of quartz glass, the outer surfaces of which, as well as the top and bottom surfaces, are smoothed by laser polishing. The upper termination of the reactor wall 2 is formed by a dielectric window 18.

Claims

[1] Method for producing a workpiece (64) made of quartz glass, which has at least one melt-polished workpiece surface (113) for use in a plasma-assisted manufacturing process, comprising the process steps: a) Providing a workpiece (64) made of quartz glass which has at least one raw surface (111) produced by cutting or machining, and b) Polishing the raw surface (111) to the polished workpiece surface (113) by laser polishing using at least one laser beam (81) moving relative to the raw surface (111), wherein the relative movement is generated by superimposing a translational-oscillating movement and a feed movement, wherein, as a result of the translational-oscillating movement, a quasi-line (87) is generated by a relative velocity between the raw surface (111) and the laser beam (81) above 500 mm / s, and wherein the feed movement has a relative velocity between the raw surface (111) and the laser beam (81) between 1 mm / s and 50 mm / s, c) and wherein a polished workpiece surface (113) is produced which has a micro-roughness and waviness, wherein the white light interferometry at a spatial wavelength λ O The microroughness measured in the range of 1 µm to 10 µm exhibits a surface roughness Sa of less than 0.5 nm,characterized by that the measurements were taken using a white light interferometer at a spatial wavelength in the range λ O Surface roughness (waviness) measured from 100 µm to 1000 µm has a value Sa of more than 5 nm, where the quasi-line (87) has a radiation intensity within the quasi-line (87) on the workpiece (64) between 10 W / cm² 2 and 1000 W / cm² 2 is produced wherein, for laser polishing of an annular end face (80) of a hollow cylindrical workpiece (64), the feed movement comprises rotation of the end face (80) about the longitudinal axis (84), and the translational-oscillating movement comprises a reversing movement of the laser beam (81) between an inner workpiece surface (85) and an outer workpiece surface (86), and wherein the speed of the translational-oscillating movement is set higher in the region of the inner surface (85) than in the region of the outer surface (86). [2] Method according to claim 1, characterized by , that the microroughness has a surface roughness Sa of less than 0.1 nm and the waviness has a surface roughness Sa of more than 10 nm. [3] Method according to claim 1 or 2, characterized by , that the laser beam (81) is generated by means of a CO2 laser, and that the radiation intensity of the stationary laser beam incident on the workpiece (64) is between 100 W / cm 2 and 10000 W / cm² 2 lies. [4] Method according to any one of the preceding claims, characterized by , that a laser power in the range of 1 kW to 10 kW is used to generate the laser beam (81). [5] Method according to any one of the preceding claims, characterized by , that a laser beam (81) defocused with respect to the raw surface (111) is used. [6] Method according to any one of the preceding claims 3 to 5, characterized by, that the laser beam (81) on the raw surface (111) has a beam diameter between 4 mm and 25 mm. [7] Method according to any one of the preceding claims, characterized by , that as a result of the translational-oscillating movement due to the relative velocity between raw surface (111) and laser beam (81) above 3000 mm / s, the quasi-line (87) with a radiation intensity within the quasi-line (87) on the workpiece (64) between 100 W / cm 2 and 500 W / cm² 2 is generated. [8] Method according to claim 1, characterized by , that the laser beam (81) as a result of the reversing movement sweeps over the inner surface of the workpiece (85) and the outer surface of the workpiece (86). [9] Method according to claim 1, characterized by , that in process step 1 (b) the laser radiation is shaped into a line by means of beam shaping optics with a radiation intensity on the workpiece (64) between 10 W / cm 2and 1000 W / cm² 2 preferably between 100 W / cm² 2 and 500 W / cm² 2 , and which has a dimension between 4 mm and 25 mm in the feed direction, and this line is then guided over the raw surface (111) with the feed movement. [10] Method according to any one of the preceding claims, characterized by , that the relative motion between laser beam (81) and raw surface (111) is adjusted so that an interaction duration between 1 s and 10 s results. [11] Method according to any one of the preceding claims, characterized by , that the laser beam (81) on the raw surface (111) generates a maximum temperature between 1700 °C and 2100 °C. [12] Method according to any one of the preceding claims, characterized by , that different positions of the raw surface (111) are polished using at least two laser beams simultaneously. [13] Use of a workpiece (64) made of quartz glass having a melt-polished workpiece surface (113) which has a micro-roughness and waviness wherein the by means of a white light interferometer at a spatial wavelength λ O The microroughness measured in the range of 1 µm to 10 µm exhibits a surface roughness Sa of less than 0.5 nm, and which is measured by white light interferometer at a spatial wavelength λ O waviness measured in the range of 100 µm to 1000 µm exhibits a surface roughness Sa of more than 5 nm, for use in a plasma-assisted manufacturing process, for the purpose of low particle formation. [14] Use according to claim 13, characterized by , that the microroughness has a surface roughness Sa of less than 0.1 nm, and the waviness has a surface roughness Sa of more than 10 nm and less than 40 nm.

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