Process including silo-chloro passivation for etching tungsten silicide overlying polysilicon

Abstract

A method of plasma etching tungsten silicide over polysilicon particularly useful in fabricating flash memory having both a densely packed area and an open (iso) area requiring a long over etch due to microloading. Wafer biasing is decreased in the over etch. The principal etchant include NF₃ and Cl₂. Argon is added to prevent undercutting at the dense/iso interface. Oxygen and nitrogen oxidize any exposed silicon to increase etch selectivity and straightens the etch profile. SiCl₄ as an example of a silicon and chlorine containing passivating gas may be added for additional selectivity.

Description

RELATED APPLICATION[0001]This application is a division of Ser. No. 11 / 445,709 filed Jun. 2, 2006.FIELD OF THE INVENTION[0002]The invention relates generally to plasma etching. In particular, the invention relates to etching tungsten and other tungsten-containing materials over silicon.BACKGROUND ART[0003]Flash memory has assumed an increasingly important position in semiconductor memory technology. It provides relatively fast non-volatile rewritable memory, which is particularly attractive in mobile applications such as cell phones, portable music players, and other devices which rely upon battery power but are often turned off for extended periods. Nonetheless, flash memory chips are being economically fabricated which have a capacity of greater than a gigabit.[0004]However, large-capacity flash memories of the desired characteristics have been accomplished by aggressively reducing the area of the memory cells, by reducing the thickness of many of the important layers, and by rely...

AI Technical Summary

Benefits of technology

[0013]The principal etchant for the tungsten is gas containing both chlorine and fluorine, for example, NF3 and Cl2. Low wafer biasing, for example, less than one-third that of the source power, reduces depth microloading.

[0014]Addition of an oxidizing gas, for example, both oxygen and nitrogen, increases selectivity to silicon.

[0015]Addition of argon or helium, particularly in the main etch, reduces the residence time for etch byproducts and prevents undercutting of the tungsten material.

[0016]Decreasing the NF3 / Cl2 ratio in the over etch improves selectivity and reduces undercutting.

[0017]Silicon tetrachloride may be added for a further increase in selectivity.

Problems solved by technology

The shrinkage has introduced severe requirements upon the etching process used to form the memory cell, especially the etching of the tungsten-based contact on the polysilicon control gate.

The etching of the tungsten-based contact layer 54, particularly when it is composed of WSi, has presented increasing difficulties as the lateral and vertical dimension shrink with increasingly large flash memories.

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