Electrostatic holding device with studded electrodes and method for their manufacture

Abstract

Holding device (100) which is designed for the electrostatic holding of a component (1), in particular a silicon wafer, comprising: - a base body (10) composed of a first plate (11A) and a second plate (12), wherein the first plate is arranged on a top surface (10A) of the base body (10) and the second plate (12) supports the first plate (11A) and wherein the second plate (12) is made of an electrically insulating material, - a plurality of projecting, upper studs (13A) arranged on the top (10A) of the base body (10) and forming a bearing surface for the component (1), and - a first electrode arrangement (20A) with a plurality of first electrodes (21A) arranged on the top (10A) of the base body (10) for applying an electrical holding voltage, wherein - the first plate (11A) is made of an electrically conductive, Si-based ceramic and carries an upper plate insulating layer (14A) which covers the top (10A) of the base body (10) with the upper studs (13A), and - the first electrodes (21A) comprise electrode layers arranged on the upper studs (13A) and each carrying an upper electrode insulation layer (15A).

Description

[0001] The invention relates to a holding device configured for the electrostatic holding of a component, in particular a silicon wafer. The invention also relates to a method for producing the holding device. Applications of the invention include the provision of devices or tools for holding components using electrostatic forces, in particular for holding semiconductor components, for example, silicon wafers.

[0002] Holding devices for the electrostatic holding of components, also known as electrostatic chucks, electrostatic clamps, electrostatic clamps, ESCs, or electrostatic chucks, are well known. An important application of electrostatic holding devices is the holding of silicon wafers in lithographic semiconductor processing, for example, in chip production. This utilizes the special advantages of electrostatic holding, such as the simple switching of electrostatic holding or clamping forces, high positioning accuracy, and reliable fixation of silicon wafers.

[0003] Typically, an electrostatic chuck comprises a structure with multiple plate- or layer-shaped elements that fulfill different functions (see, e.g., US Pat. No. 4,502,094 A or US Pat. No. 8,476,167 B2). At least one plate-shaped element is equipped with an electrode device with which the electrostatic holding forces are generated. According to US Pat. No. 8,476,167 B2, the electrode device comprises a plurality of electrodes embedded between the plate-shaped elements. Furthermore, an electrostatic chuck typically comprises, at least on its upper side, a plurality of protruding upper nubs that form a support surface for the silicon wafer.

[0004] A conventional electrostatic chuck with embedded electrodes, e.g., according to US Pat. No. 8,476,167 B2, has the following disadvantages. Since the electrostatic chucking force depends on the distance between the silicon wafer and the electrodes, studs with the smallest possible height (e.g., < 10 µm) are used to generate a high chucking force. However, this increases the sensitivity to unwanted particles, which may not find sufficient space between the studs and can impair the flatness of the silicon wafer support. Alternatively, the chucking force can be increased by increasing the electrode voltage, but this is associated with risks of electrical breakdowns or other malfunctions. Furthermore, since the electrodes are arranged in the spaces between the studs, the held silicon wafer can be subjected to undesirable deformation between the support points.Further disadvantages may exist with regard to the thermal and mechanical coupling of the held silicon wafer. For example, the silicon wafer may tend to slip laterally along the support surface despite high holding force.

[0005] The above-mentioned disadvantages occur not only in electrostatic chucks for silicon wafers, but also in chucks with embedded electrodes for other components, such as glass plates with transparent electrode (ITO) that form AMLCD substrates.

[0006] The object of the invention is to provide an improved electrostatic holding device that avoids the disadvantages of conventional techniques. In particular, the holding device should enable a reduction in the holding voltage without impairing the electrostatic holding forces, reduced sensitivity to unwanted particles, less deformation of the held component, improved mechanical coupling of the component, and / or improved thermal coupling of the component. A further object of the invention is to provide an improved method for producing the electrostatic holding device that avoids the disadvantages of conventional techniques and is characterized, in particular, by simplified process control.

[0007] These objects are achieved by a holding device and a method having the features of the independent claims. Advantageous embodiments and applications of the invention are set forth in the dependent claims.

[0008] According to a first general aspect of the invention, a holding device for electrostatically holding a component, in particular a silicon wafer, is provided. The holding device comprises a base body composed of a first plate and a second plate, wherein the first plate is arranged on an upper side of the base body and the second plate supports the first plate, and wherein the second plate is made of an electrically insulating material. Upper nubs protruding from the upper side of the base body are provided on the first plate, the upper end faces of which define a support surface for the component. Furthermore, the holding device comprises a first electrode device having a plurality of first electrodes arranged on the upper side of the base body for application of an electrical holding voltage.According to the invention, the first plate is made of an electrically conductive, Si-based ceramic and provided with an upper plate insulation layer covering the upper side of the base body, including the upper studs. Furthermore, the first electrodes comprise electrode layers arranged on the upper studs, in particular on their end faces, and each carrying an upper electrode insulation layer.

[0009] Advantageously, according to the invention, the distance between the electrodes and the component to be held is minimized, whereby the height of the studs can be increased compared to conventional techniques without compromising the holding force. At the same time, the use of the upper plate of the base body, which comprises Si-based ceramic, and the relatively thin electrode insulation layer on the electrodes improves the thermal coupling with the component to be held. The combination of these features enables the component to be held with high thermal and mechanical stability and flatness. A further advantage of the invention is the possibility of reducing the time required to manufacture the holding device, since the holding device can be manufactured from a relatively smaller number of parts.

[0010] According to a second general aspect of the invention, the holding device according to the above first general aspect of the invention is manufactured by prefabricating the first plate with the upper studs and the second plate, depositing the upper plate insulation layer on the first plate, depositing the first electrodes and the upper electrode insulation layers on the upper studs of the first plate, and assembling the first plate to the second plate.

[0011] According to a preferred embodiment of the invention, the holding device is designed for electrostatic fixation on a carrier platform. For this purpose, the holding device has a third plate, which is arranged on the underside of the base body opposite the first plate on the second plate and is also made of an electrically conductive, Si-based ceramic. The third plate is preferably made of the same ceramic as the first plate. Furthermore, a plurality of protruding, lower knobs are provided on the third plate, which protrude from the underside of the base body and whose lower end faces span a support surface for the holding device on the carrier platform.A second electrode device with a plurality of second electrodes is arranged on the underside of the base body, wherein the second electrodes comprise electrode layers that are arranged on the lower studs, in particular on their end faces, are electrically insulated from the underside of the base body and the lower studs by a lower plate insulation layer, and each carry a lower electrode insulation layer. To produce the holding device according to the embodiment with the third plate, the third plate with the lower studs is also prefabricated, provided with the lower plate insulation layer, the second electrodes, and the lower electrode insulation layers, and joined to the second plate.

[0012] Preferably, the first and / or second electrodes are arranged exclusively on the upper and / or lower studs, in particular their flattened end faces, while the spaces between the upper and / or lower studs are free of electrodes for applying the electrical holding voltage. This advantageously prevents deformation of the component to be held between the studs.

[0013] Advantageously, there are various possibilities for designing the upper and / or lower studs depending on the requirements of a specific application. According to a first, particularly preferred variant, the upper and / or lower studs have a surface roughness Ra > 200 nm, in particular Ra > 250 nm. The inventor has determined that the unintentional lateral displacement of components along the extent of the support surface is caused by the low roughness of the studs provided in conventional techniques (Ra < 40 nm). In contrast, the risk of lateral displacement is reduced by the roughness provided according to the invention. The roughness is produced, for example, by etching the studs and remains effective even after deposition of the electrode insulation layer, the electrodes, and the optionally provided wear protection layer on the free surface of the studs.

[0014] According to a further variant, the upper and / or lower studs are electrically conductively connected to the first and / or third plate. This advantageously improves the thermal coupling of the component to be held. Particularly preferably, the upper and / or lower studs are made of the same electrically conductive, Si-based ceramic as the first and / or third plate. For example, the upper and / or lower studs can be integrally connected to the first and / or third plate. The studs can be produced by structuring the associated plate, e.g., by etching, thus further simplifying the manufacture of the holding device.

[0015] According to further preferred embodiments of the invention, the upper and / or lower studs are each provided with upper and / or lower wear-resistant layers. The wear-resistant layers are arranged correspondingly on the upper and / or lower electrode insulation layers. Advantageously, the wear-resistant layers, which are preferably made of silicon nitride or electrically insulating amorphous carbon, provide mechanical protection for the electrode insulation layers and the electrodes, extending the service life of the holding device.

[0016] To contact the electrodes, the first and / or second electrode devices preferably each have first and / or second conductor tracks, which are arranged accordingly on the top and / or bottom of the base body, in particular on the associated plate insulation layer. The conductor tracks are configured to connect the first and / or second electrodes to a voltage source for generating an electrostatic holding voltage.

[0017] The electrostatic holding voltage is generated between the electrodes and the component to be held, which is connected to ground potential via a separate voltage connection or, if the studs also carry a layer of electrically conductive material connected to ground potential, by contacting the studs. It is therefore advantageous if each electrode is equipped with exactly one conductor track.

[0018] Advantageously, there are various ways of connecting the electrodes to the voltage source via the conductor tracks. For example, all electrodes can be connected in parallel. This variant of the invention offers the advantage that the arrangement of the conductor tracks is simplified. Alternatively, at least one of the electrodes can be connected to the voltage source via a conductor track that is electrically separated from the other conductor tracks and is designed to apply a specific holding voltage to the associated electrode. Advantageously, this allows the holding voltage to be varied along the surface of the holding device, for example to compensate for local fluctuations in the electrostatic holding force. For example, each of the electrodes can be connected to the voltage source via an associated conductor track that is separate from all other conductor tracks and can be applied with a specific holding voltage.Alternatively, groups of electrodes can be equipped with electrically connected conductors, allowing the electrodes of a group to be subjected to a common, specific holding voltage. This advantageously allows for the electrostatic holding force to be optimized along the surface of the holding device and the flatness of the held component to be improved, for example, at the outer edge of the holding device. Furthermore, applying specific holding voltages to electrodes individually or in groups offers the possibility of specifically controlling the clamping process, for example, when setting down a held component.

[0019] According to further variants of the invention, the first and / or third plate can have at least one electrical contact area for connection to ground potential. This contact area allows the plates to be connected directly to ground potential, thus further improving the robustness of the holding device.

[0020] Preferably, the first plate consists of the electrically conductive, Si-based ceramic, i.e., the first plate consists of a ceramic containing Si. SiC-containing ceramics, such as SiSiC or SSiC ceramics, have proven particularly advantageous. Preferably, the second plate consists of an electrically insulating solid, particularly preferably Si3N4 or SiC ceramics or borosilicate glass (e.g., glass with the product name Borofloat 33®). The first and / or second electrodes are preferably made of Al, TiN, or WC.

[0021] Further details and advantages of the invention are described below with reference to the accompanying drawings. They show: Fig. 1: a schematic sectional view of a first embodiment of the electrostatic holding device according to the invention; and Fig. 2: a schematic illustration of an upper protruding nub with an electrode.

[0022] Features of preferred embodiments of the electrostatic holding device according to the invention and the method for its production are described below with exemplary reference to features of an electrostatic holding device for silicon wafers. It is emphasized that the implementation of the invention is not limited to holding devices for silicon wafers. Rather, other applications of the holding device are also conceivable, such as for holding glass plates with transparent electrodes for the production of display screens. In these cases, the shape of the bearing and / or support surfaces of the first and / or third plates, their structuring, the materials, and the dimensions are adapted to the specific requirements.Furthermore, it is emphasized that the implementation of the invention is not limited to the exemplary variants of the holding device with a first, second, and third plate, each of which is manufactured in one piece. Alternatively, at least one of the plates can be manufactured in multiple layers from several sub-plates. Finally, the figures do not show scaled illustrations of holding devices, but rather illustrate in particular the provision of electrodes on the upper and lower studs.

[0023] The structure of the base body of the holding device can be selected as is known per se from conventional holding devices. Further details of the specific design of the holding device, for example, as a monopolar or bipolar holding device, the arrangement of the nubs and electrodes, e.g., with a so-called Manhattan pattern, the temperature control, and the application of electrical voltages to generate the electrostatic holding forces will not be described, as far as these are known from conventional holding devices.

[0024] Fig. 1 shows a first embodiment of the electrostatic chuck 100 according to the invention for use in semiconductor processing in a schematic sectional view. The chuck 100 comprises a base body 10 with a stacked structure comprising a first plate 11A, a second plate 12, and a third plate 11B. The first and third plates 11A, 11B are made, for example, of SiSiC. For a monopolar chuck, the first and third plates 11A, 11B have, for example, a circular shape with a diameter of 30 cm and a thickness of 5 mm each. Alternatively, larger dimensions are feasible, e.g., a diameter of up to 2 m for holding glass panes with transparent electrodes.

[0025] The second plate 12 is made, for example, of Si3N4. The first and third plates 11A, 11B are connected to the second plate 12 on both sides. The second plate 12 has recesses on its top and bottom sides into which the first and third plates 11A, 11B are embedded. The recesses on both sides of the second plate 12 have the advantage that all outer surfaces of the holding device 100 are electrically insulated. Furthermore, the edges of the second plate 12 provide lateral shielding of the environment against electrostatic effects.

[0026] The first and third plates 11A, 11B each have protruding upper or lower nubs 13A, 13B, which form a support surface for a component 1, e.g., a silicon wafer, or a support surface for placing the holding device 100 on a carrier platform 30. The nubs 13A, 13B have, for example, the shape of cuboids, cylinders, pyramids, cones, truncated pyramids, and / or truncated cones, preferably with a height in the range of 5 µm to 25 µm, a diameter of 20 µm to 100 µm, and a mutual spacing of 1 mm.

[0027] On the surfaces of the first and third plates 11A, 11B, upper and lower plate insulation layers 14A, 14B are arranged, respectively, which electrically insulate the upper and lower surfaces of the base body 10. The plate insulation layers 14A, 14B are made, for example, of silicon nitride and / or silicon oxide with a thickness of 2 µm. Furthermore, each of the upper studs 13A carries a layer sequence comprising an upper plate insulation layer 14A, a first electrode 21A, an upper electrode insulation layer 15A, and an upper wear protection layer 16A, which are described in detail in Fig. 2. Each of the lower nubs 13B carries a layer sequence of a lower plate insulation layer 14B, a second electrode 21B, a lower electrode insulation layer 15B and a lower wear protection layer 16B, which are arranged on the underside of the base body 10 as shown in Fig. 2 with reference to the top side.

[0028] The first and third plates 11A, 11B are electrically conductive. For connection to ground potential, the first and third plates 11A, 11B are each equipped with a contact area. By way of example, the contact area 17 is shown on the first plate 11A, which is configured for electrical connection to a ground contact of a voltage source 40. The contact areas (e.g., 17) each comprise, for example, a blind hole in the first and third plates 11A, 11B, respectively, which has a diameter of, for example, 0.5 mm and is designed as a fit. A metal sleeve, for example made of gold, is pressed into the hole and accommodates an electrical line for connection to the voltage source (e.g., 40).

[0029] Temperature control lines 18 are embedded in the second plate 12 and are coupled to a temperature control device (not shown). The temperature control device forms a temperature control circuit with which the temperature of the holding device 100 can be adjusted.

[0030] Fig. Figure 2 illustrates an enlarged sectional view of a section of the first plate 11A with the upper nub 13A. The plate insulation layer 14A is arranged on the surface of the first plate 11A. The layered electrode 21A is arranged limited to the surface of the upper nub 13A. The electrode 21A can cover the entire nub 13A or only its upper end face, as shown, and is produced, for example, by depositing a TiN layer with a thickness of 50 nm. The advantage of TiN is its good passivation to protect the underlying insulation layer. The electrode 21A is connected to the substrate via a separate conductor track 22A (see Fig. 1), which runs on the surface of the plate insulation layer 14A, is connected to a voltage source 40. The upper electrode insulation layer 15A, e.g., made of aluminum nitride and / or silicon nitride, and the upper wear protection layer 16A, e.g., made of amorphous carbon (DLN or DLC, diamond-like nanocomposite / carbon) with thicknesses of up to 1 µm, are arranged on the electrode 21A.

[0031] With the structure according to Fig. 2, the electrostatic holding force F acts on the end faces of the protruding studs 13A (see double arrow), while no electrostatic holding force is generated between the studs 13A. The holding force F can, for example, correspond to a clamping pressure of 1 bar at a holding voltage of 400 V.

[0032] The holding device 100 is manufactured by first individually prefabricating the plates 11A, 12, and 11B. The plate insulation layers, the electrodes, and the electrode insulation layers are deposited on the surfaces of the first and third plates 11A, 11B, e.g., by vapor deposition or sputtering. Subsequently, the first plate 11A and the third plate 11B are each connected to the second plate 12 by high-temperature soldering. Afterward, the electrical and hydraulic connections are coupled to the contact areas 17 and the temperature control lines 18, respectively.

Claims

[1] Holding device (100) which is designed for the electrostatic holding of a component (1), in particular a silicon wafer, comprising: - a base body (10) composed of a first plate (11A) and a second plate (12), wherein the first plate is arranged on an upper side (10A) of the base body (10) and the second plate (12) supports the first plate (11A), and wherein the second plate (12) is made of an electrically insulating material, - a plurality of projecting upper knobs (13A) arranged on the upper side (10A) of the base body (10) and forming a support surface for the component (1), and - a first electrode device (20A) with a plurality of first electrodes (21A) arranged on the upper side (10A) of the base body (10) for applying an electrical holding voltage, wherein - the first plate (11A) is made of an electrically conductive, Si-based ceramic and carries an upper plate insulation layer (14A) which covers the upper side (10A) of the base body (10) with the upper studs (13A), and - the first electrodes (21A) comprise electrode layers arranged on the upper nubs (13A) and each carrying an upper electrode insulation layer (15A). [2] Holding device according to claim 1, comprising - a third plate (11B) arranged on a bottom side (10B) of the base body (10), supporting the second plate (12) and made of an electrically conductive, Si-based ceramic, - a plurality of projecting lower knobs (13B) arranged on the underside (10B) of the base body (10) and forming a support surface for the holding device (100) on a support platform (30), - a second electrode device (20B) with a plurality of second electrodes (21B) arranged on the underside (10B) of the base body (10) for applying an electrical holding voltage, wherein - the second plate (11B) carries a lower plate insulation layer (14B) which covers the underside (10B) of the base body (10) with the lower studs (13B), and - the second electrodes (21B) comprise electrode layers arranged on the lower studs (13B) and each carrying a lower electrode insulation layer (15B). [3] Holding device according to one of the preceding claims, in which - the first and / or second electrodes (21A, 21B) are each limited to the upper and / or lower knobs (13A, 13B) and distances between the upper and / or lower knobs (13A, 13B) are free of electrodes for applying the electrical holding voltage. [4] Holding device according to one of the preceding claims, in which the upper and / or lower knobs (13A, 13B) have at least one of the following features: - the upper and / or lower knobs (13A, 13B) have a surface roughness Ra > 200 nm, - the upper and / or lower studs (13A, 13B) are electrically connected to the first and / or second plate (11A, 11B), - the upper and / or lower knobs (13A, 13B) are made of the electrically conductive, Si-based ceramic, and - the upper and / or lower studs (13A, 13B) are each integrally connected to the first and / or second plate (11A, 11B). [5] Holding device according to one of the preceding claims, in which - the upper and / or lower electrode insulation layers (15A, 15B) on the upper and / or lower studs (13A, 13B) each carry an upper and / or lower wear protection layer (16A, 16B). [6] Holding device according to claim 5, in which - the upper and / or lower wear protection layer (16A, 16B) is made of silicon nitride or electrically insulating amorphous carbon. [7] Holding device according to one of the preceding claims, in which - the first and / or second electrode devices (20A, 20B) each comprise first and / or second conductor tracks (22A, 22B) arranged to connect the first and / or second electrodes (21A, 21B) to a voltage source (40). [8] Holding device according to claim 7, in which - the first and / or second conductor tracks (22A, 22B) and the voltage source (40) are configured such that at least one of the first and / or second electrodes (21A, 21B) can be selectively subjected to a specific holding voltage. [9] Holding device according to one of the preceding claims, in which - the first and / or third plate (11A, 11B) has at least one electrical contact area (17) for connection to ground potential. [10] Holding device according to one of the preceding claims, with at least one of the features - the first and / or third plate (11A, 11B) is made of SiSiC or SSiC ceramic, - the second plate (12) is made of Si3N4 or SiC ceramic or borosilicate glass, and - the first and / or second electrodes (21A, 21B) are made of Al, TiN or WC. [11] Method for producing a holding device according to one of the preceding claims, comprising the steps - Prefabrication of the first and second panels (11A, 12), - deposition of the upper plate insulation layer (14A) on the first plate (11A), - deposition of the first electrodes (21A) and the upper electrode insulation layers (16A) on the upper studs (13A), and - Joining the first plate (11A) with the second plate (12).

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