Browse Prior Art Database

BOROPHOSPHOSILICATE GLASS INTERLEVEL DIELECTRIC PLANARIZATION

IP.com Disclosure Number: IPCOM000006077D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2001-Nov-30
Document File: 6 page(s) / 277K

Publishing Venue

Motorola

Related People

F. J. Robinson: AUTHOR

Abstract

Planarization of interlevel dielectrics is required for process flows which utilize anisotropic etching of the various layers of conductors. The vertical step formed by the anisotropic etch of an underlying layer and conformal coating of that layer with dielectric, can cause shorting bars in a subsequent conductor layer, if it is also etched anisotropically. This is because the thickness of the conductor at the steps is thicker, by the thickness of the vertical step in the underlying layer, than that on the horizontal surfaces and will take longer to etch. Figure-l demonstrates the increased thickness over steps and post-etch shorting bars.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 40% of the total text.

Page 1 of 6

0 M

MOTOROLA INC. Technical Developments Volume 12 April 1991

BOROPHOSPHOSILICATE GLASS INTERLEVEL DIELECTRIC PLANARIZATION

by F. J. Robinson

INTRODUCTION

  Planarization of interlevel dielectrics is required for process flows which utilize anisotropic etching of the various layers of conductors. The vertical step formed by the anisotropic etch of an underlying layer and conformal coating of that layer with dielectric, can cause shorting bars in a subsequent conductor layer, if it is also etched anisotropically. This is because the thickness of the conductor at the steps is thicker, by the thickness of the vertical step in the underlying layer, than that on the horizontal surfaces and will take longer to etch. Figure-l demonstrates the increased thickness over steps and post-etch shorting bars.

  The preferred method of planarization has been "Etch-back Planarization". This method deposits a dielectric thicker than the layer to be planarized, if the final surface is to be entirely within that layer, or thinner, if some of the planarizing layer is to be left on top. Figure-2 shows a thick planarizing film, of organic resist or spin-on-glass, deposited then reactive ion etched (RIE) back to or into the first layer at a one-to-one selectivity between the hvo layers. "Etch- back Planarization" is very difficult to control. The selectivity of the films can change due to variations in pattern density, deposition parameters, ambient, and the etch process itself. Another problem, in addition to control, is the incomplete planarization or fill of the wide spaces. A reasonably thick planarizing layer will not fully~ planarize these spaces.

  A better method is to etch away the high points of a conformal borophosphosilicate coating, to the same level as the low points, and reflow it to remove any sharp transitions in the resulting topography.

EXPERIMENTAL

Figure-3 is a drawing of the main steps involved in the planarization of Borophosphosilicate glass
(B.P.S.G.) over a patterned polysilicon layer. A

lO,OOOA thick Plasma Enhanced B.P.S.G. (3S%B and
3.5%P) is deposited over 4,OOOA of patterned polysilicon. An image reversal process is used to form a reverse density mask over the conformal
B.P.S.G. film; masking the low points and leaving the high points exposed to any etchant. A Buffered Oxide Etch (B.O.E.) is then used to etch -4OOOA of the
B.P.S.G., undercutting the resist mask as it does. The mask is removed, by ashing or wet strip, and the film is furnace annealed at 9OO'C - lOOO"C, in nitrogen ambient, for 30 minutes to reflow and smooth any abrupt changes in topography.

  S.E.M. samples are prepared by depositing silicon nitride on the planarized surface then cleaving the wafer to produce a cross-section. The nitride allows a
B.O.E. delineation of the oxides only, so the limits of the sectioned films could be seen.

  The amount of planarization is calculated by dividing the final step height by the step height of the underlying pattern to be plan...