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STRUCTURE AND METHOD OF USING OXIDIZED SILICON NITRIDE AS AN ETCH-STOP LAYER FOR WET CHEMISTRY ETCHING OF SILICON NITRIDE

IP.com Disclosure Number: IPCOM000019209D
Publication Date: 2003-Sep-04
Document File: 6 page(s) / 274K

Publishing Venue

The IP.com Prior Art Database

Abstract

Stacked silicon nitride layers are commonly used to produce various semiconductor devices and electrical components. When stacking a first layer of silicon nitride upon a second layer of silicon nitride, an intermediary layer of deposited polysilicon has been used as a means for providing an etch stop for dry etch chemistries. The intermediary deposited polysilicon layer provides a means to stop dry etch chemistry removal of the overlying silicon nitride without continuing through the etch stop layer (polysilicon) into the underlying silicon nitride. While deposited polysilicon provides adequate etch selectivity for common dry etch chemistries to function as a dry etch chemistry etch stop layer, dry etch chemistry processing is more expensive and complicated in comparison to wet etch processing. Additionally, deposition of polysilicon is slow and expensive. Moreover, deposited polysilicon cannot be selectively deposited on silicon nitride; therefore additional masking steps are required to restrict deposition to the underlying silicon nitride layer as is common when forming devices or components. Thus, it would be advantageous to form an etch stop layer between silicon nitride layers that would enable the use of low cost wet etch, wherein the etch stop layer material is inexpensive to form, has high etch selectivity to silicon nitride and can be selectively formed on underlying silicon nitride.

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STRUCTURE AND METHOD OF USING OXIDIZED SILICON NITRIDE AS AN ETCH-STOP LAYER FOR WET CHEMISTRY ETCHING OF SILICON NITRIDE

Background

Stacked silicon nitride layers are commonly used to produce various semiconductor devices and electrical components. When stacking a first layer of silicon nitride upon a second layer of silicon nitride, an intermediary layer of deposited polysilicon has been used as a means for providing an etch stop for dry etch chemistries. The intermediary deposited polysilicon layer provides a means to stop dry etch chemistry removal of the overlying silicon nitride without continuing through the etch stop layer (polysilicon) into the underlying silicon nitride.

While deposited polysilicon provides adequate etch selectivity for common dry etch chemistries to function as a dry etch chemistry etch stop layer, dry etch chemistry processing is more expensive and complicated in comparison to wet etch processing. Additionally, deposition of polysilicon is slow and expensive. Moreover, deposited polysilicon cannot be selectively deposited on silicon nitride; therefore additional masking steps are required to restrict deposition to the underlying silicon nitride layer as is common when forming devices or components.

Thus, it would be advantageous to form an etch stop layer between silicon nitride layers that would enable the use of low cost wet etch, wherein the etch stop layer material is inexpensive to form, has high etch selectivity to silicon nitride and can be selectively formed on underlying silicon nitride.

Detailed Description of The Drawings

Fig. 1a shows a structure or portion of a device or component comprising a silicon substrate having a material stack formed on the surface. A semiconductor device has been formed encapsulated with a first layer of silicon nitride (e.g., “nitride #1”). Other regions of the substrate can be free of silicon nitride.

Fig. 1b shows the structure after forming an etch-stop layer of oxidized nitride or “oxynitride” selectively on the underlying silicon nitride. In one embodiment, the oxynitride is formed by thermal growth at a temperature of approximately nine-hundred degrees centigrade for approximately twenty minutes in an ambient mixture of steam including about four percent hydrochloric acid (HCL) gas. As is well known in the art, oxynitride is selectively formed on exposed silicon nitride, thus the oxynitride is not formed elsewhere on the substrate. Furthermore, oxynitride has been established in this work, as being an excellent wet chemistry etch stop layer having high selectivity with respect to silicon nitride (e.g., greater than one-thousand to one).

A blanket deposition of a second layer of silicon nitride (e.g., “nitride #2”) is then formed on the oxynitride and all exposed regions of the substrate. This is shown in Fig. 1c. The above described oxynitride layer provides a robust etch-stop layer that can act as an etch-stop for a phosphoric acid wet-nitride etch in orde...