Patent Application
20110005923
The present disclosure relates to a sputtering system. More specifically, the present disclose relates to a sputtering system including a rotatable cylindrical target assembly including a target backing tube and at least one target element, and a least one cooling shield. Further, the present disclosure relates to a rotatable cylindrical target assembly. More specifically, the present disclosure relates to a rotatable cylindrical target assembly including a backing tube and at least one target element disposed around the backing tube. According to some embodiments, the present disclosure relates to cooling shield, in particular for a sputtering system including a rotatable target. Additionally, the present disclosure relates to a target element, in particular for a rotatable cylindrical target assembly of a sputtering system. Further, the present disclosure relates to target backing tube for a rotatable cylindrical target assembly.
In many applications, it is necessary to deposit thin layers on a substrate. The term “substrate” as used herein shall embrace both inflexible substrates, e.g. a wafer or a glass plate, and flexible substrates such as webs and foils. Known techniques for depositing layers are in particular evaporating, sputtering and chemical vapor deposition.
Representative examples include (but are not limited to) applications involving: semiconductor and dielectric materials and devices, silicon-based wafers, flat panel displays (such as TFTs), masks and filters, energy conversion and storage (such as photovoltaic cells, fuel cells, and batteries), solid-state lighting (such as LEDs and OLEDs), magnetic and optical storage, micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS), micro-optic and opto-elecro-mechanical systems (NEMS), micro-optic and optoelectronic devices, transparent substrates, architectural and automotive glasses, metallization systems for metal and polymer foils and packaging, and micro- and nano-molding.
In an evaporation process, the material to be deposited is heated so that it evaporates and condenses on the substrate. Sputtering is a vacuum coating process used to deposit thin films of various materials onto the surface of a substrate. For example, sputtering can be used to deposit a metal layer such as a thin layer of aluminum or ceramics. During the sputtering process, the coating material is transported from a target consisting of that material to the substrate to be coated by bombarding the surface of the target with ions of an inert gas that are accelerated by a high voltage. When the gas ions hit the outer surface of the target, their momentum is transferred to the atoms of the material so that some of them can gain sufficient energy to overcome their bonding energy in order to escape from the target surface and to deposit on the substrate. Thereon, they form a film of the desired material. The thickness of the deposited film is, inter alia, dependent on the duration of exposing the substrate to the sputtering process.
In light of the above, a target backing tube for a rotatable target according to independent claim 1, a target cylinder for a rotatable cylindrical target assembly of a sputtering system according to independent claim 6, a cooling shield for a sputtering system comprising a rotatable target according to independent claim 12, a rotatable cylindrical target assembly according to claim 19 and a sputtering system according to claim 23 are provided.
According to one embodiment, target backing tube for a rotatable cylindrical target assembly is provided including: a tube for at least one target element to be disposed there around, wherein the tube has an exterior surface adapted to face the at least one target element, wherein a portion of the exterior surface of the backing tube has a mean emissivity of 0.7 to 1, wherein the portion is at least 50% of the exterior surface of the backing tube.
According to a further embodiment, a target element for a rotatable cylindrical target assembly of a sputtering system is provided, wherein the target element an interior surface adapted to face a target backing tube onto which the target cylinder is adapted to be disposed and exterior surface, wherein a portion of the interior surface of the target element has a mean emissivity of 0.7 to 1, wherein the portion is at least 50% of the interior surface of the target element.
According to yet another embodiment, a cooling shield for a sputtering system is provided including a rotatable target, the cooling shield has an interior surface adapted to face a target element of a sputtering system and an exterior surface; wherein a portion of the interior surface of the target element has a mean emissivity of 0.7 to 1, wherein the portion is at least 50% of the interior surface of the target element.
Further aspects, advantages and features of the present invention are apparent from the dependent claims, the description and the accompanying drawings.
A full and enabling disclosure including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:
Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations.
The process of coating a substrate as a material at the scraping refers typically to thin film applications. The term “coating” and the term “depositing” are used synonymously herein.
In a typical embodiment, which may be combined with other embodiments disclosed herein, the target elements 126 are not bonded to the backing tube 122. For example, spacers or springs or other elements may be used for centering the target elements on the backing tube 122. Typically, in an embodiment, a plurality of target elements, for example two or more, is arranged side by side around the backing tube 122. The number and the kind of target elements may depend on the material to be sputtered and the length or form of the backing tube.
The temperature of the material of the target elements 126 may be controlled in a typical embodiment in order to avoid nodules or pickles on the substrate to be coated.
Typically, heat is generated during deposition operations. For example plasma has to be generated and, in some embodiments the substrate to be coated may be heated. However, the magnetrons 124 have to be cooled such that they do not loss their magnetic characteristics due to high temperatures. Thus, in typical embodiments, which may be combined with other embodiments disclosed herein, the backing tube 122 is cooled inside. For example, the cooling may be performed with a water circuit within the backing tube 122.
As already explained here above, the control of the temperature of the target elements 126 may be important. Typically, the backing tube 122 is cooled, such that a cooling of the target elements 126 relates to the heat transfer between the backing tube 122 and the target elements 126. Thereby, an important factor to be considered for the disclosed embodiments is the fact that the target elements and the backing tube are located in a vacuum environment, for example in the vacuum chamber 100. According to typical embodiments, which can be combined with other embodiments described herein, the pressure in the plasma area can be 10−4 to 10−2 mbar, typically about 10−3 mbar.
Thus, in a typical embodiment, there are substantially no particles or atoms between the outer surface of the backing tube 122 facing the target elements and the inner surface of the target elements 126 facing the backing tube 122. Even, if a heat conductive layer having a high thermal conductivity, for example a metal layer, would be used, the heat conductivity of the metal layer, e.g. a copper layer would only cool the target elements 126 if the target elements 126 and the intermediate layer would be press fitted on the backing tube. Typically, when ITO (Indium Titan Oxide) targets elements are used, such a pressure is difficult to provide. Further, the target elements may expand and retract due to high temperature differences before and during the sputtering process. Thus, as there is no contact pressure, a metal layer between the target element 126 and the backing tube 122 would act rather as a shield, such that the heat transfer between the target elements 126 and the backing tube 122 is reduced.
Typically, under vacuum a heat transfer contact cannot be established well without a contact pressure. The contact pressure depends on the contact with respect on a scale of the surface roughness of the contacting surfaces.
Typically, a gap 128 is provided between the target elements 126 and the backing tube 122. Such a gap 128 may be provided for assembling and disassembling the target elements 126 from the backing tube 122, for example for exchanging the target elements 126 after the target elements are used up or another deposition material has to be used. According to some embodiments, which may be combined with other embodiments herein, the gap may have a width in radial direction between 0.1 mm and about 3 mm, typically between 0.2 mm and 2 mm.
According to Stefan-Boltzmann law the total energy radiated per unit surface area of a black body is proportional to the fourth power of the black body's temperature T (absolute temperature). In a case of a gray body, that is a body that does not absorb or emit the full amount of radiative flux, the gray body radiates only a portion of the radiative flux that is characterized by its emissivity ε. Typically, the absorbed irradiance is also proportional to the fourth power of the temperature of the surrounding.
Commonly, a backing tube is formed by a stainless steel which has typically an ε-value of about 0.2.
According to embodiments describe herein, which may be combined with other embodiments disclosed herein, a portion of at least 50%, in particular more than 70%, of the exterior surface of the backing tube facing the inner surface of the target elements and/or a portion of at least 50%, in particular more than 70%, of the interior surface of the target elements facing the backing tube has a mean ε-value that is greater than 0.7, for example between 0.8 and 1.
According to yet further embodiments, which may be combined with other embodiments disclosed herein, the backing tube has on its outer or exterior surface a coating for improving the emissivity and the target elements have a coating on their inner or interior surface to improve the emissivity. Thus, the heat transfer from the target element to the backing tube is further improved.
According to yet further embodiments, which may be combined with other embodiments herein, the surfaces one or more of the following group: the backing tube, the target element, a coating on the backing tube; and a coating on the target element, can be provided or configured to have a roughness to improve the heat transfer between the target element and the backing tube. For example, the roughness (Rz) may be greater than 50, in particular greater than Rz 100.
According to some embodiments, which can be combined with other embodiments described herein, a heat transfer gas can be provided through a heat transfer gas inlet 136, e.g., arranged in the stop 134. The heat transfer gas at an increased pressure of, for example, 0.1 to 10 mbar may improve the heat transfer between the target element 126c and the backing tube 120c in addition to the heat radiation improved based on emissivity. The heat transfer gas inlet is arranged such that the gas enters the gap 128c between the target elements 126 and the backing tube 120c. For example, the heat transfer gas may be argon, helium or another gas that does not disturb the deposition procedure of the substrate in the vacuum chamber. For example, the pressure between the backing tube and the target elements could be, in an embodiment which may be combined with other embodiments disclosed herein at about 1 mbar. The pressure in the vacuum chamber is typically less than about 1×10−2 mbar, typically about 1×10−3 mbar.
In a further embodiment, the gap 128c between the target elements and the backing tube is sealed with respect to the vacuum chamber such that the heat transfer gas does substantially not enter the vacuum chamber. However, some loss of gas might be acceptable, for example between two of the target elements 126c, if the heat transfer gas may be used as a process gas for creating the plasma in the vacuum chamber 100. For example, argon may be used as a heat transfer gas and as a carrier gas for creating the plasma between the cylindrical target assembly and the substrate.
According to the embodiment shown in
The tube(s) 146f, 146g may be connected, in a typical embodiment, which may be combined with other embodiments disclosed herein, to a cooling circuit used for cooling the magnetrons in the backing tube.
According to some embodiments, which may be combined with other embodiments disclosed herein, a cooling shield may be provided, such that it surrounds the cylindrical target assembly at a radial position for which no sputtering is conducted.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the described subject-matter, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, those skilled in the art will recognize that the spirit and scope of the claims allows for equally effective modifications. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope is defined by the claims, and may include such modifications and other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09165334 | Jul 2009 | EP | regional |
