Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-09-28
2003-07-01
Ryan, Patrick (Department: 1745)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298120
Reexamination Certificate
active
06585870
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the preparation of thin films by magnetron sputter deposition in which the angular distribution of sputtered particles emitted from the target and arriving (depositing) at the substrate is directional. Directional emission and arrival mean that the angular distribution of flux intensity of sputtered particles emitted from the target, and incident at the substrate are each characterized by a narrow peak or peaks on a low level background angular distribution. In other words, the majority of particles emit and arrive at about the same one or few narrow ranges of angles. The directional emission is preserved by ballistic transport to result in the directional arrival.
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 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.
One category of sputtering processes is known as magnetron sputtering. Magnetron sputtering is the most widely used form of sputtering and is the mainstay of commercial sputter deposition processes. In magnetron sputtering, crossed electric and magnetic fields generated by a magnetron assist in the sputtering by concentrating sputtering action.
According to the known art, the sputtered particles from a typical magnetron sputter cathode source emit with a cosine distribution or some variant based upon it. See Wasa, K., Hayakawa, S., Handbook of Sputter Deposition Technology, Noyes Publications, 1992. Film thickness distributions generally reflect that of calculations based upon a cosine emission model. See Vossen, J. L., Kern, W., Thin Film Processes, Academic Press (1978); see also U.S. Pat. No. 5,417,833 to Harra et al. Typically in many commercial sputter processes, sputtered particles are incident at the substrate at angles far from normal incidence even under ballistic transport conditions. See Rossnagel, S., J. Vac. Sci. Tech. B., Vol.16, No.5, p. 2585 (1998). This effect is desirable if the substrate features to be coated have low aspect ratios. However, many leading edge technological applications involve, for example, filling deep, sub-micron high aspect ratio trench or via structures or coating high aspect ratio features with a high degree of conformality. However, there are limits on the smallness of the critical dimension of such features that can be conformally covered or filled by PVD.
A directional sputter deposition technology based upon magnetron sputtering (further described below), in which the angular distribution of sputtered particles incident at a substrate/thin film growth surface could be “tailored” to the particular requirements of the thin film application, would be of significant technical and commercial value with a wide scope of technological application. Such a technique may allow the following to be improved: film coverage, engineering and control of thin film microstructure and therefore related functional characteristics of the film. For example, directional deposition would greatly ease step coverage of high aspect ratio features, e.g., channels on patterned surfaces. However, methods proposed to improve directionality, while providing some benefits, need further improvement.
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.
For example, in IPVD techniques a coil is located in the vacuum chamber between the sputtering cathode and substrate on which the film is to be deposited. The coil is configured to form a secondary plasma in the region above the substrate. The magnetron sputtered particles pass through a relatively high pressure ambient for creating the desired secondary plasma to undergo significant gas phase scattering, ionization (partial) in the secondary plasma followed by electrostatic deflection towards the substrate surface, generally provided by electrically biasing the substrate. At the substrate, partial resputtering of the growing film by the electrostatically accelerated particles is used to control film characteristics. For example bottom and sidewall coverage in semiconductor interconnect applications. Clearly complex post sputter emission processes are central to the directionality and the degree of conformal coverage achieved by the IPVD technique.
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) tr
Pitcher Philip George
Yan Zhihua
Cantelmo Gregg
Honeywell International , Inc.
Ryan Patrick
Wells St. John P.S.
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