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SELECTIVE DEPOSITION OF POLYCRYSTALLINE SILICON

IP.com Disclosure Number: IPCOM000005730D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-31
Document File: 2 page(s) / 205K

Publishing Venue

Motorola

Related People

H. Ming Liaw: AUTHOR [+2]

Abstract

Continued reduction of feature size into the submicron regime in IC devices has caused severe difficulty in multilayered metallization. For example, electrical contact to the substrate can no longer be simply done by direct deposition of a metal film such as Al into the contact holes. This is due to the fact that conformal deposition of the metal film is very difficult to obtain at the sidewalls of the contact holes because of the sharp steps. This problem can be solved if the contact holes are prefilled with a material to plug the contact holes and form a planar surface. An ideal material to plug the contact holes should be a highly electrical conductive and refractive metal such as W. However, filling with heavily doped silicon is also very promising since it eliminates the material incompatibility between the filler and substrate silicon.

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MOTOROLA Technical Developments Volume 8 October 1988

SELECTIVE DEPOSITION OF POLYCRYSTALLINE SILICON

by H. Ming Liaw, and Chris Seelbach

   Continued reduction of feature size into the submicron regime in IC devices has caused severe difficulty in multilayered metallization. For example, electrical contact to the substrate can no longer be simply done by direct deposition of a metal film such as Al into the contact holes. This is due to the fact that conformal deposition of the metal film is very difficult to obtain at the sidewalls of the contact holes because of the sharp steps. This problem can be solved if the contact holes are prefilled with a material to plug the contact holes and form a planar surface. An ideal material to plug the contact holes should be a highly electrical conductive and refractive metal such as W. However, filling with heavily doped silicon is also very promising since it eliminates the material incompatibility between the filler and substrate silicon.

   A selective polysilicon deposition technique has been reported by Furumura et al' to fill the contact holes. Polycrystal growth rather than epitaxial growth was forced by the introduction of a large amount of impurity such as trichloroethylene into the epitaxial reactor during silicon deposition. The deposited polycrystalline silicon therefore contained carbon of a concentration of 1 x E(20) atoms/cc or higher. The majority of the carbon piled up at the substrate and polysilicon interface and increased the contact resistance.

   We have developed a selective polysilicon deposition technique without the use of any impurity to force polysilicon nucleation. The technique involves a seeding step which uses silicon tetrachloride to purge through the substrate surface at a low temperature. Hydrogen is used as a carrying gas which bubbles through silicon tetrachloride at room temperature. A flow rate of hydrogen in the range of 15 to 32 literslmin was found to be optimum since the polycrystalline silicon seeds were deposited only on the exposed silicon surface but not on the masking oxide. A typical p...