An advanced reactive ion etching process for very high aspect-ratio sub-micron wide trenches in silicon

This paper reports on a practical modification of the two-step time-multiplexed plasma etching recipe (also known as the Bosch process) to chieve high aspect-ratio sub-micron wide trenches in silicon. Mixed argon and oxygen plasma depassivation steps are introduced in between the assivation and etching phases to promote the anisotropic removal of the passivation layer at the base of the trench. Argon does not chemically eact with polymers and silicon and removes the passivation layer only by physical sputtering. Therefore, it results in a highly anisotropic polymer tching process. This recipe can be easily integrated on conventional ICP equipment and the scalloping on the trench sidewall can potentially e reduced in size to less than 50 nm. To clean up all the passivation residues, a short oxygen plasma step is also added at the end of the cycle hat effectively improves the uniformity of the etching profile over various opening sizes. Excellent anisotropy of the inserted argon depassivation tep facilitates narrow trenches down to 130 nm wide and gap aspect-ratios as high as 40:1, extending the application of deep reactive ion etching DRIE) processes into a new broad regime. 2008 Elsevier B.V. All rights reserved.