Plasma-Assisted Etching and Reactive Ion Etching Using High and Low Density Plasmas

Preliminary course date in 2013: October 7-8, in Dresden (Germany).

In 2012 a shorter version of this course will be integrated with course #88 "Plasma Etching for CMOS Technology and ULSI Applications". Click here to read more.

TECHNOLOGY FOCUS
Plasma-assisted etching is used in many technologies. It is most critical in ultra large scale integrated (ULSI) circuit fabrication and is used many times during the processing of a single wafer. Other areas that rely heavily on plasma-assisted etching include micro-electrical-mechanical (MEMS) structure fabrication, many so-called nano-science processes, micro-optical and photonic activities and numerous other material processing where near room temperature chemical reactions are required.

COURSE OBJECTIVES 
The objective of this course is to describe the extent to which the fundamental processes in plasma-assisted etching are understood and to relate this understanding to the practical applications of the technology. The reactive gas plasma environment is very complex and depends strongly on the type of plasma source that is used. 
Atoms, molecular radicals and energetic positive ions dominate the etching surface chemistry. The fundamental aspects of the reactions of these species with solid surfaces have been studied extensively and a qualitative understanding of this complex surface chemistry has been developed. 

WHO SHOULD ATTEND 
Any person with a technical background wishing to obtain a better understanding of the mechanistic aspects of plasma-assisted etching, or of reactive gas plasma-surface interactions in general, should benefit from taking this course. 

Although the emphasis of the course is on the ULSI circuit fabrication applications, much of the information presented should be of value in the implementation of other processes involving reactive gas plasmas. A familiarity with the basic concepts of plasma-assisted etching would be helpful but is not essential as the course includes a short summary of the basics. 

Monday
Plasma Sources and Etching Mechanisms 
An introductory discussion of reactive gas plasmas will be given, emphasizing phenomena that are known to be important in reactive gas plasmas such as electron impact induced dissociation and ionization and the electron energy 
distribution in the plasma. The significance of the vapor pressure of etch product molecules will be discussed.

The operation of the various types of plasma sources (e.g., capacitive, dual and triple frequency capacitive, inductive and wave generated) that are used in this technology will be covered in detail. The importance of the self-bias voltage and the plasma potential, including the reasons for the existence of these voltages, will be described. A global model of high density discharges will be described, which allows calculating the ion flux and ion energy impinging on the wafer. A short summary of the evolution of plasma etching equipment will be presented along with the rationale for the equipment changes that were made.

The surface science aspects of this complex chemical environment will be discussed in detail both on the wafer and on the reactor walls. The importance of energetic positive ion bombardment of the surface being etched in obtaining anisotropic etching will be highlighted. Other factors that determine the degree of anisotropy (neutral radical/ ion flux ratio, degree of spontaneous etching, sidewall passivation layers, temperature) will be included.

• Introductory Concepts
• Physics of Plasma Sources
• High Density vs. Low Density Plasma Etching
• Surface Science Aspects of Etching Reactions
• The Role of Energetic Positive Ions in Etching
• Etching Anisotropy

Tuesday
Etching Chemistries, Plasma Diagnostics
The mechanisms that control the densities of radicals in the plasma will be discussed. Examples of the importance of wall reactions (deposition, radical-radical recombination, ion neutralizations) will be presented, including a discussion on process drifts issues. The etching of silicon and its compounds (SiO₂,Si₃N₄, SiC), as practiced in present-day ULSI device fabrication will be summarized. Included in this discussion are such topics as selectivity, loading effects, aspect ratio dependent etching, sidewall charging and other feature-scale phenomena such as notching and trenching. The etching of other materials (Al, organics solids, silicides, tungsten, titanium, III-V compounds, Cr)  will be described but in less detail.

Etching uniformity (including critical dimension control) and equipment related issues are discussed in some detail. Plasma and surface diagnostic methods (optical emission spectroscopy, mass spectrometry, and reflectometry) are described briefly including their application to process control and process development.

• Wall Effects
• Loading Effects
• Feature Scale Phenomena
• Fluorine-to-Carbon Ratio Concept in Fluorocarbon Plasma
• Etching of Si and Its Compounds
• Selectivity (SiO2/Si and Si/SiO2)
• Etching of Other Materials
• Etching Non-Uniformity
• Contamination and Damage
• Plasma Diagnostics

Said about the course from previous participants:
"The course notes are very elaborate, this will help me when I want to look something up."
"Good overview of what is possible, and it gave another view on some aspects of my project."
"Huge amount of information given in that short period of time."
" Good and easy to understand presentation of complex information."
"I gained much insight in plasma fundamentals. Examples of calculating plasma properties. Solutions for common problems were suggested."