Latest revision as of 13:51, 9 May 2020

Technology Development of Silicon Plasma Etching Process at Nanoscale

Project type: Ph.d. project
Project responsible: Vy Thi Hoang Nguyen
Supervisors:Henri Jansen, Flemming Jensen, Jörg Hübner
Partners involved: DTU Danchip
Project start: November 2017

Project Description

Plasma processes are important for silicon-based micro electromechanical systems (MEMS) with critical dimensions around a few microns. Although widely utilized and largely understood, silicon plasma etching fails to reproduce at the nanoscale. Transport effects ‘down the etched cavity’ limit rate and selectivity while high aspect ratios, profile and passivation control are more challenging. The so-called Bosch etch process is probably the most popular technique in MEMS production facilities today. However, the high roughness with finite sidewall scallop size and hard to remove fluorocarbon (FC) residue on the sidewalls of etched structures make the process less favorable for nanoscale engineering. In this project, the usability of SF6 and O2 plasma will be studied as a replacement for Bosch process to avoid FC residue and facilitate the nanoscale silicon etching with profile control and sufficient mask selectivity preferably at room temperature. The focus will be on the development of a fundamental understanding of the special challenges in SF6-O2 plasma etching at the nanoscale including the physics and chemistry involved. The aim is to establish a generic knowledge platform for future applications such as injection molding. For this, modern lithography tools (MLA, DUV stepper, e-beam) will be utilized to define the structure down to 10nm critical dimension on top of a silicon wafer. Subsequently, the pattern will be transferred into the silicon layer using a modern plasma tool (SPTS, DRIE-Pegasus). During the process, various etching parameters (flow, pressure, power, etc.) are varied to discover performance-affecting factors. Finally, etching results are characterized under scanning electron microscopy (Carl Zeiss AG, SEM Supra 60VP).

Publications

Name of publication 1 made in this project

Reference and link to the publication

Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share

Name of publication2 made in this project

Reference and link to the publication

Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share

Name of publication3 made in this project

Reference and link to the publication

Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share

@@ Line 1: / Line 1: @@
-=Smoothed advanced silicon NEMS devices=
+=Technology Development of Silicon Plasma Etching Process at Nanoscale=
 *'''Project type:''' Ph.d. project
 *'''Project responsible:''' Vy Thi Hoang Nguyen
 *'''Supervisors:'''Henri Jansen, Flemming Jensen, Jörg Hübner
 *'''Partners involved:''' DTU Danchip
+*'''Project start:''' November 2017
 ==Project Description==
-Plasma processes are important for micro electro-mechanical systems (MEMS) with critical dimensions of a few microns. The so-called Bosch etch process is probably the most popular technique in MEMS production facilities today. It uses a repeating sequence of plasma enhanced deposition to passivate silicon features, a physical etch for directional removal of this layer at the base of the features, and an isotropic etch for silicon removal at the cleared surfaces. However, it is not well suited to the nanoscale due to finite sidewall scallop size and undercut unless rate and selectivity are severely compromised.
+Plasma processes are important for silicon-based micro electromechanical systems (MEMS) with critical dimensions around a few microns. Although widely utilized and largely understood, silicon plasma etching fails to reproduce at the nanoscale. Transport effects ‘down the etched cavity’ limit rate and selectivity while high aspect ratios, profile and passivation control are more challenging. The so-called Bosch etch process is probably the most popular technique in MEMS production facilities today. However, the high roughness with finite sidewall scallop size and hard to remove fluorocarbon (FC) residue on the sidewalls of etched structures make the process less favorable for nanoscale engineering.
+In this project, the usability of SF6 and O2 plasma will be studied as a replacement for Bosch process to avoid FC residue and facilitate the nanoscale silicon etching with profile control and sufficient mask selectivity preferably at room temperature. The focus will be on the development of a fundamental understanding of the special challenges in SF6-O2 plasma etching at the nanoscale including the physics and chemistry involved. The aim is to establish a generic knowledge platform for future applications such as injection molding.
+For this, modern lithography tools (MLA, DUV stepper, e-beam) will be utilized to define the structure down to 10nm critical dimension on top of a silicon wafer. Subsequently, the pattern will be transferred into the silicon layer using a modern plasma tool (SPTS, DRIE-Pegasus). During the process, various etching parameters (flow, pressure, power, etc.) are varied to discover performance-affecting factors. Finally, etching results are characterized under scanning electron microscopy (Carl Zeiss AG, SEM Supra 60VP).
-Anisotropic wet etching such as potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) can form smooth sidewalls, but the geometry is limited by crystal planes. Another solution is to develop post-dry etching processes to remove the sidewall scallops. Sacrificial thermal oxidation has been utilized to improve sidewall quality. However, the process consumes too much silicon and builds up residual stress. By employing hydrogen annealing, it was reported that sidewall scallops can be dramatically reduced. The surface mobility of silicon atoms is enhanced by heated hydrogen at temperatures much lower than the melting point (1414oC). Based on this phenomenon, migrating atoms smooth out the surface roughness to minimize the total surface energy without losing volume.
+==Publications==
+===Name of publication 1 made in this project===
+Reference and link to the publication
-Hydrogen-induced surface migration not only changes the surface morphology but also affects the global profile if the surface migration length is comparable to or larger than structural dimensions. This effect is similar to the reflow process in glasses or polymers, but unlike the reflow process, this mechanism only depends on surface-atom movement and the crystalline structure is preserved. Thermal annealing in hydrogen ambient has also been reported to produce round corners and various voids in bulk silicon.
+*[[/Process flow form|Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share]]
-This project aims to facilitate a reliable creation of smooth and slender nanostructures to demonstrate the ability in some state-of-the-art and novel NEMS applications include 1) resonators and sensors for physical and bio-chemical sensing down to the molecular level both because of the much reduced mass, 2) nanowires for novel transistors and photovoltaics increasingly exploring quantum effects starting at the sub-50nm level, 3) nanostructures for photonics (around the wavelength of the guided photons) and next generation storage (10nm and below), 4) black silicon for high area catalyzed reaction chambers and photovoltaics, 5) through wafer vias for packaging applications, and 6) nano imprint lithography (NIL) masters. The approach is to first create nanoscale silicon patterns using the modern high density plasma tool (SPTS DRIE-Pegasus). This structure is then annealed in pure hydrogen at high temperature (1100oC) and high vacuum (10E-6 mbar) using an annealling tool (Annealsys RTP-150-HV). The quantitative analysis on the sidewall roughness reduction will be measured using scanning electron microscopes (SEM) and atomic force microscope (AFM).
+===Name of publication2 made in this project===
+Reference and link to the publication
+*[[/Process flow form|Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share]]
+===Name of publication3 made in this project===
+Reference and link to the publication
+*[[/Process flow form|Process flow(s) relevant to this publication including links to Process development made in connection to this publication this is describes in either LabAdviser or Process2Share]]