Optimization of Reactive Ion Etching to Fabricate Silicon Nitride Stencil Masks in SF6 Plasma

Stencil masks are used to print ultra-high resolution patterns using helium ion/atom beam lithography and are often manufactured from thin, free-standing silicon nitride membranes. The masks have sub-200nm openings etched through the thickness of the membrane using a reactive ion etch (RIE) process that determine the printed pattern. This project deals with the optimization of a sulfur hexafluoride and oxygen RIE. In this process, 0.5µm thick silicon nitride membranes are coated with 20nm of copper (hard mask) and 200nm of poly (methyl methacrylate) (resist). The desired patterns are then formed in the resist by electron beam lithography, and the patterns are transferred through copper by argon milling. A mixture of 0.8 millitorr of sulfur hexafluoride and 0.2 millitorr of oxygen is used in an RIE step at a power of 15 watts to transfer them through the thickness of the membrane. The process allows for the patterning of extremely straight features (anisotropic etch), has excellent selectivity (200) between silicon nitride and copper, suffers from minimal RIE lag, and is generally very robust. The challenges associated with this process lie in etch non-uniformity due to membrane heating and pattern fidelity in the milling step. Solutions to these problems have been explored and stencil masks with sub-200 nm etched openings have been successfully fabricated.

Name thesis:degree_name

Master of Science in Electrical Engineering

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Electrical Engineering

Grantor

University of Houston

Year dc:date.issued

2013

Author dc:creator

• Basu, Prithvi

Advisor dc:contributor.advisor

• Ruchhoeft, Paul

Committee members dc:contributor.committeemember

• Litvinov, Dmitri
• Willson, Richard C.

• Optimization
• Ion beam lithography
• Stencil Masks
• Reactive Ion Etching
• Sulfur hexafluoride

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10657/1083

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/1083