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IN SITU GENERATION OF SiC14 FOR TRENCH PROFILE CONTROL DURING R.I.E

IP.com Disclosure Number: IPCOM000005959D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-20
Document File: 2 page(s) / 118K

Publishing Venue

Motorola

Related People

Frederick J. Robinson: AUTHOR [+2]

Abstract

Trenches etched in silicon, for use in isolation, capacitors, or as device locations, require a profile with smooth, straight (non-bowed) sidewalls and rounded bottoms. The smooth walls are necessary to ensure oxide integrity, straight walls allow refilling without voids, and rounded bottoms prevent slipplane dislocations in the device active area caused by trench sidewall oxidation.

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0 M MO-ROLA

Technical Developments Volume 11 October 1990

IN SITU GENERATION OF SiC14 FOR TRENCH PROFILE CONTROL DURING R.I.E.

by Frederick J. Robinson and Francine Y. Robb

INTRODUCTION:

   Trenches etched in silicon, for use in isolation, capacitors, or as device locations, require a profile with smooth, straight (non-bowed) sidewalls and rounded bottoms. The smooth walls are necessary to ensure oxide integrity, straight walls allow refilling without voids, and rounded bottoms prevent slipplane dislocations in the device active area caused by trench sidewall oxidation.

   The preferred method for achieving the proper trench profile is the redeposition of a silicon containing material on the trench sidewall, during the reactive ion etch (R.I.E.) process. Silicon containing material, for redeposition on the trench sidewall, is normally supplied as a reactant gas in the R.I.E. chamber. Two of the favorite sources are the liquid SiC14 and the gas SiF,, which require gas supply cabinets, welded stainless steel tubing, and mass flow controllers. The reactant supplies an excess of silicon in the chamber, which deposits on all available surfaces. The directional com- ponent of R.I.E. removes the deposition from the horizontal surfaces, allowing further vertical etching, and leaves it on the trench sidewalls, preventing additional horizontal etch. As the trench etch proceeds, the deposition gets thicker; protecting slightly more of the trench bottom near the sidewall. The net effect is to cause a rounding of the corner be tween the wall and the bottom of the trench.

EXPERIMENTAL:

An alternate source of silicon for sidewall redeposition is one which is internal to the etch chamber. This method would eliminate the need for the equipment mentioned above.

   Since SiC14 addition to the R.I.E. can cause redeposition of a silicon containing material, the generation of an ex- cess of SiC14 in the plasma should have the same effect. SiCl., is the normal product of the etch reaction when using chlorine based chemistry to etch trenches in silicon, so the addition of more silicon surface area to be etched should give the needed excess of SiCl.,. The following equation allows calculation of the silicon surface area needed.

& = (Si E.R.) tsicl 1Flw) W Density) Csi MiI, wt.) (Molar Vol.),

4

where "Si E.R." = etch rate of silicon @/min.) in the process of choice and "SiC14 Flow" is the amount of excess SiCla (seem) desired for sidewall redeposition.

   This method of sidewall redeposition was tested in a non-load-locked, hexode configured reactor, using 4" wafers. An SIC& flow of 15 seem was chosen, because 15 _ 20 seem had been reported in the literature for this type of reactor.' Using the calculation shown above, it was determined that 10, 4" wafers would supply the requisite 15 seem of SiCL. A standard BCl&lz trench etch process (Table-l) was run; with and wit...