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Method Useful in Failure Analysis Which Provides Excellent Visibility on Trench Sidewalls

IP.com Disclosure Number: IPCOM000034753D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Merlot, F: AUTHOR

Abstract

This failure analysis technique allows examination of the silicon lying on trench sidewall edges without etching the silicon in order to reveal potential defects. This technique could be applied to any semiconductor products embedding trench isolated transistors. The layer opposite silicon should be made of an oxide. The transistors isolated by polysilicon filled trenches are commonly used today. The transistors are isolated by a 2 m wide and 4.5 m deep trench. The trench is filled up with polysilicon, the polysilicon/silicon interface being comprised of 3000 Ao of silion oxide and silicon nitride. The sample is prepared as follows: - Deoxidize the sample by etching in a hydrogen fluoride solution (for 30 minutes). During this step, oxide and nitride layers on the trench sidewalls are selectively etched.

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Method Useful in Failure Analysis Which Provides Excellent Visibility on Trench Sidewalls

This failure analysis technique allows examination of the silicon lying on trench sidewall edges without etching the silicon in order to reveal potential defects. This technique could be applied to any semiconductor products embedding trench isolated transistors. The layer opposite silicon should be made of an oxide. The transistors isolated by polysilicon filled trenches are commonly used today. The transistors are isolated by a 2 m wide and 4.5 m deep trench. The trench is filled up with polysilicon, the polysilicon/silicon interface being comprised of 3000 Ao of silion oxide and silicon nitride. The sample is prepared as follows:

- Deoxidize the sample by etching in a hydrogen fluoride solution (for 30 minutes). During this step, oxide and nitride layers on the trench sidewalls are selectively etched. - Clean the sample with acetone and make one or several replicas in order to remove polysilicon from the trench. A replica is prepared by applying a sheet of an acetylcellulose replicating film previously dipped in acetone. After drying, the sheet is removed with the polysilicon stuck to it. - Using a scanning electron microscope, visualize silicon on the trench sidewalls as well as in the trench bottom. The advantages of this technique are that it allows the shape of the trench to be visualized without performing slicing of the chip and it allows the trench sidewalls, the t...