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Directed Evaporation for Step Coverage

IP.com Disclosure Number: IPCOM000039053D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Smith, DA: AUTHOR [+2]

Abstract

Step coverage is a generic problem in physical vapor deposition which is ordinarily a line-of-sight process. Integrated circuits are becoming increasingly 3-dimensional as their complexity increases and there is a practical need to coat surfaces uniformly even when they have complicated topography. In the absence of other influence the thickness of a deposit depends on the cosine of the angle between the surface normal and the line joining the source and the substrate, as shown in Fig. 1. This geometrical feature imposes a limitation on the slope of steps which may be covered by evaporation onto a multilayer device and thus limits the density of components and the speed of the circuit as a whole. A portion of the atoms electron beam evaporated from a source are ionized.

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Directed Evaporation for Step Coverage

Step coverage is a generic problem in physical vapor deposition which is ordinarily a line-of-sight process. Integrated circuits are becoming increasingly 3- dimensional as their complexity increases and there is a practical need to coat surfaces uniformly even when they have complicated topography. In the absence of other influence the thickness of a deposit depends on the cosine of the angle between the surface normal and the line joining the source and the substrate, as shown in Fig. 1. This geometrical feature imposes a limitation on the slope of steps which may be covered by evaporation onto a multilayer device and thus limits the density of components and the speed of the circuit as a whole. A portion of the atoms electron beam evaporated from a source are ionized. This proportion is increased as the evaporation rate is increased by raising the bias on the filament of the electron gun. Ions can be deflected by electric and magnetic fields. Since the ions in this case have low energies (less than 1 eV), they can be deflected through large angles by small fields (a few tens of volts/meter for the case of an electric field). This effect can be exploited to mitigate the geometrical limitations on step coverage. Deflector plates are placed between the source and the substrate, as shown in Fig. 2. An alternating or static field is set up between the plates according to what kind of step orientation is to be covered. Ionized...