Oxide-nitride-oxide stack having multiple oxynitride layers

Abstract

A semiconductor device including an oxide-nitride-oxide (ONO) structure having a multi-layer charge storing layer and methods of forming the same are provided. Generally, the method involves: (i) forming a first oxide layer of the ONO structure; (ii) forming a multi-layer charge storing layer comprising nitride on a surface of the first oxide layer; and (iii) forming a second oxide layer of the ONO structure on a surface of the multi-layer charge storing layer. Preferably, the charge storing layer comprises at least two silicon oxynitride layers having differing stoichiometric compositions of Oxygen, Nitrogen and / or Silicon. More preferably, the ONO structure is part of a silicon-oxide-nitride-oxide-silicon (SONOS) structure and the semiconductor device is a SONOS memory transistor. Other embodiments are also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 60 / 931,947, entitled Oxide-Nitride-Oxide Stack Having Multiple Oxynitride Layers; which application is hereby incorporated by reference.TECHNICAL FIELD[0002]This invention relates to semiconductor processing and, more particularly to an oxide-nitride-oxide stack having an improved oxide-nitride or oxynitride layer and methods of forming the same.BACKGROUND OF THE INVENTION[0003]Non-volatile semiconductor memories, such as a split gate flash memory, typically use a stacked floating gate type field effect transistors, in which electrons are induced into a floating gate of a memory cell to be programmed by biasing a control gate and grounding a body region of a substrate on which the memory cell is formed.[0004]An oxide-nitride-oxide (ONO) stack is used as either a charge storing layer, as in silicon-oxide-nitride-oxi...

AI Technical Summary

Benefits of technology

The present invention provides an improved ONO structure and method for making it, which includes a multi-layer charge storing layer. The ONO structure and method can improve data retention, programming and erase speed, and stochiometry of the oxynitride layer. This is useful for improving the performance and reliability of non-volatile semiconductor memories, such as split gate flash memories.

Problems solved by technology

One problem with conventional SONOS structures 102 and methods of forming the same is the poor data retention of the nitride or oxynitride layer 118 that limits the device 100 lifetime and / or its use in several applications due to leakage current through the layer.

Another problem with conventional SONOS structures 102 and methods of forming the same is the stochiometry of the oxynitride layer 118 is neither uniform nor optimized across the thickness of the layer.

Consequently, the charge storage characteristics, and in particular programming and erase speed and data retention of a memory device 100 made with the ONO stack 104, are adversely effected.

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