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`Surface and Coatings Technology 93 ( i998 ) 12454250
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`Asymmetric bipolar pulsed DC: the enabling technology for reactive PVD
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`J. Sellers *
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`EN], 4150 Freidrich Ln., Suite J, Austin. TX 78744, USA
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`Abstract
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`The use of reactive DC sputtering for the deposition of insulators from conductive targets has been limited by the intrinsic
`problem of target poisoning and the consequent arcing and process instabilities. The need to deposit high quality dielectric films
`rapidly is becoming more important as technology pushes forward. Asymmetric bipolar pulsed DC eliminates target poisoning
`through preferential sputtering, enabling existing PVD tools to produce the high—quality, low-defect dielectric films needed for
`next generation processes. Typical films being produced with asymmetric bipolar pulsed,DC from metallic targets include A1203,
`AIN, Si02, SiN, Ta2O,, DLC. TaN, TiN and ITO. The mechanisms of target poisoning and dielectric arcing are explained in this
`paper, and solutions are given. © 1998 Published by Elsevier Science S.A.
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`Keywords: Sputter; Reactive; Magnetron; Thin film; PVD
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`1. Introduction
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`Asymmetric bipolar pulsed DC technology has been
`quickly proving its effectiveness
`in a wide variety
`of standard and reactive
`sputtering applications.
`Acceptance of this technology has been extremely rapid
`due to its elimination of many long-standing process
`limitations. Asymmetric bipolar pulsed DC was specifi-
`cally developed to optimize the deposition of insulating
`films from conductive targets with reactive sputtering.
`Further, it is important to understand that this technol-
`ogy did not evolve as an afterthought to control arcing:
`rather, it was conceived with a definite understanding
`of the electrical and physical process requirements. This
`understanding led to a unique solution in which the
`power source is given the dual properties of a current
`source and a voltage source, depending on which plasma
`constituent is being driven. Thus, both ions and electrons
`are driven in their optimal manner, and the plasma’s
`asymmetry of masses (ions versus electrons) is matched
`by the supply’s source dual characteristics (current
`source (forward sputter) versus voltage source (reverse
`bias). Films successfully reactively sputtered with this
`technology include A1203, Ta2O5, BST, PZT, Ta,O5,
`TaN, TiO2, TiN and ITO. Additional applications for
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`the technique include etching/cleaning, CVD bias, and
`substrate bias for sputtered films.
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`2. Target poisoning
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`The key to the successful production of insulating
`films from metallic targets is the elimination of target
`poisoning. Poisoning is the build-up of insulating layers
`on the target surface. In simple metallic sputtering, the
`target (or cathode) is driven by the sputtering supply to
`a specific DC voltage based on the power, chamber
`pressure, magnetron design. etc. This voltage accelerates
`the argon ions into the target with sufficient kinetic
`energy to cause them to knock atoms from the target.
`The freed target atoms then condense on the substrate
`to form the desired film. The free atoms also deposit on
`the walls of the chamber and back on the target. In
`pure metallic sputtering, this redeposition on the target
`does not represent a problem, since the target and the
`redeposited atoms are the same material. But in reactive
`sputtering, the deposited film is a compound, and there-
`fore a different material
`to the target. For example,
`aluminium oxide, a ceramic, has properties which are
`quite dilferent from metallic aluminum. If the reactive
`film is an insulator, such as aluminum oxide, then the
`situation becomes intolerable.
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`“ Corresponding author. Tel: +1 512 4622191; Fax: + I 512 2462941 I.
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`When an insulator is deposited on the surface of the
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`0257-8972/98/$19.00 © 1998 Published by Elsevier Science S.A. All rights reserved.
`Pl! S0257-8972(97)00403-9
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`TSMC et al. v. Zond, Inc.
`GILLETTE-1022
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`TSMC et al. v. Zond, Inc.
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