Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-11-09
2002-06-11
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298190
Reexamination Certificate
active
06402912
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a thin integral cooling and pressure relieving sputtering cathode target assembly for a sputtering apparatus.
BACKGROUND OF THE INVENTION
One of the most important commercial processes for depositing thin films of a desired material onto a substrate is sputter deposition, also known as sputter coating or sputtering. Sputter deposition is used extensively in many industries including the microelectronics, data storage and display industries to name but a few.
Generally, the term sputtering refers to an “atomistic” process in which neutral, or charged, particles (atoms or molecules) are ejected from the surface of a target material through bombardment with energetic particles. A portion of the sputtered particles condenses onto a substrate to form a thin film. The science and technology of sputtering is well known and described for example in Vossen, J. L., Kern, W., Thin Film Processes, Academic Press (1978). Sputtering can be achieved through several techniques. Generally, in “cathodic” (“diode”) sputtering the target is at a high negative potential relative to other components, usually through application of a negative bias from a power supply, in a vacuum chamber system, typically containing an inert gas or mixture of gases at low pressure. A plasma containing ionized gas particles is established close to the target surface and ionized gas particles are accelerated by the action of the electric field towards the target surface. The bombarding particles lose kinetic energy through momentum exchange processes with the target atoms, some of the latter particles gain sufficient “reverse” momentum to escape the body of the target, to become sputtered target particles. Note a sputtered particle may be an atom, atom cluster or molecule either in an electrically neutral or charged state. A flux of sputtered particles may contain any one or any mixture of such entities.
Coating high aspect ratio structures is of critical importance, e.g., in emerging submicron semiconductor interconnect metalization and high density data storage media applications. In such cases the bounds of application of magnetron sputter deposition is approaching its limit. For example, in coating via type structures in microelectronics interconnect applications, it is well known that sputter deposition suffers from film buildout at the upper edges of the via resulting in a trapped void, “keyhole” type film defect as well as other film defects. See, for example, Rossnagel, S., J.Vac. Sci. Tech.B., Vol.16, No.5, p. 2585 (1998). This effect is exasperated with reducing dimensionality and increased aspect ratio. Proponents of current commercial PVD processes assert they can conformally cover relatively high aspect ratio features, or fill relatively high aspect ratio channels or vias, having a critical dimension of at least 0.18 micron, or perhaps greater than 0.13 micron.
Several sputter PVD techniques, many of them developed commercially relatively recently, attempt to control the directionality of the incident sputtered particle flux at a substrate e.g., physical collimation techniques, hollow cathode sputtering, arc sputtering, self ionized sputtering, ionized physical vapor deposition (IPVD) and long throw methods. The latter two techniques probably represent state of the art commercial technologies. The scope, scalability, efficiency and cost considerations of directional sputter technologies have been reviewed by Rossnagel, S., J.Vac. Sci. Tech.B., Vol.16, No.5, p. 2585 (1998). The best techniques utilize tooling and/or process attributes to achieve a degree of control over the angular distribution of incident sputtered particles. These methods are in fact expressly designed to overcome what are believed to be inherent deficiencies in basic magnetron cathode sputter deposition characteristics and target materials design which limit control of the substrate incident angular sputtered flux distribution.
U.S. Pat. Nos. 5,948,215; 5,178,739; and Patent Cooperation Treaty published application No. WO 98/48444 disclose ionized plasma vapor deposition processes, and are incorporated herein by reference.
Long throw methods utilize ballistic (i.e., collisionless) transport and a long throw path to the substrate to “optically” filter the magnetron cathode emitted flux such that only relatively low angle components of the emitted flux (i.e., those close to the target normal) are incident at the substrate. The long throw process is clearly inefficient through flux dilution and suffers from inherent asymmetries in the incident flux. See Rossnagel, S., J. Vac. Sci. Tech. B., Vol.16, No.5, p. 2585 (1998).
Planar Magnetron Sputtering apparatuses are well known Physical Vapor Deposition (PVD) tools commonly used in, for example, the semiconductor industry for the deposition of thin films of metals such as aluminum and its alloys, refractory metals, and ceramics onto a substrate; for example, a silicon wafer or glass sheet being processed. In general, the process of Planar Magnetron Sputtering involves creating and confining a plasma of ionized inert gas over the consumable surface of an energized Cathode Assembly in order to dislodge, by momentum transfer, atoms or molecules from the consumable surface. The consumable surface of a cathode assembly consists of the material to be sputtered and is commonly called a sputter “target” in Industry. The target is placed a relatively short distance from the substrate in order to improve collection of the ejected target atoms onto the substrate.
Initially, a discharge caused by primarily electrons emitted from the surface of the target, produced by gas ion bombardment of the target resulting from ionization of the gas by natural background ionizing radiation, strike or ignite the plasma. The target is energized by an applied electric field (DC, RF, or both) in an evacuated chamber that is backfilled with an inert gas to typically the 10
−4
-10
−1
millitorr pressure range. Then, both electrons emitted by the target surface and electrons created by ionizing impacts with the inert gas will be confined near the target surface by means of the magnetron's magnetic field; which is applied crosswise to the electric field. The created ions accelerate towards the surface of the target and dislodge atoms or molecules from it; many of these atoms or molecules will be directed towards the substrate creating a thin film onto the substrate.
It is well known, that maximum erosion of a target occurs where lines of magnetic flux are parallel to the consumable surface of the target. To increase the sputter-deposition rate for a given applied electric field to the cathode, the magnetron should also ride as close as possible to the side opposite to the consumable surface of the target such that the intensity of the parallel component of magnetic field lines above the target is maximized. Therefore, a design goal is to design a target assembly with as thin a cross-section as possible.
In addition, film-properties, for example uniformity on the substrate, depend greatly on the uniformity of erosion of the target; therefore, other design goals are to design a magnetron that can produce a uniform plasma intensity, and design a drive mechanism that can sweep the magnetron uniformly over the entire target surface.
As the magnetron is swept over the target, considerable energy is dissipated in the form of heat by the ions striking the surface of the target; therefore, the target must be cooled in order to avoid melting the cathode assembly or damaging the equipment. The target in the cathode assembly is normally mounted over a backing plate and cooling means provided to it.
The target assembly in a magnetron sputtering device is generally placed over a sputtering opening of a process chamber to seal the process chamber such that it can be evacuated and then maintained at the low pressures required for the sputter process. The large forces acting on the target assembly due to the pressure differential between ambient atmospheric pressure and the va
Herrera Manuel J.
Pitcher Philip G.
Cantelmo Gregg
Honeywell International , Inc.
Nguyen Nam
Wells St. John P.S.
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