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Process simulation of plasma etching processes

Plasma etching of silicon and silicon compounds is a key technology of semiconductor industry and micro mechanics. A key feature of plasma etching is the ability to etch silicon isotropic or anisotropic independent of the crystal orientation.

In plasma etching, the gas entering the reactor will be ionized and fragmented by electric of magnetic excitation,  generating electrons, ions radicals and molecule fragments.  By diffusion or drift they reach the sample surface, where they undergo chemical (radicals, molecule fragments) or physical (energetic ions) interactions with the sample. In this way, the sample surface can be etched, or thin films can be deposited.

It is the goal and the dream of plasma process engineers to precisely predict the outcome of a process. Numerical simulations of the different phenomena during plasma etching seem to be a promising approach.  In practice, however, simplification and approximations are necessary, because exact calculations would take too long, or because exact values of parameters (e.g. rate constants, cross sections) are not known.

 

The perfect profile simulator

 

Figure 1: The perfect profile simulator. From [1] (c) B.E. Volland 2004

Figure 1: The perfect profile simulator Taken from ››Burkhard E. Volland, "Profile simulation of gas chopping etching processes - Model development and comparison with experiments - ", Dissertation Universität Kassel, URN: urn:nbn:de:hebis:34-1167 (2004) ‹‹.  (c) B.E. Volland 2004

A perfect profile simulator is schematically depicted in figure 1. It consists of 3 modules, namely the plasma module, the transport module, and the surface module. The plasma module calculates, based on boundary and initial conditions (such as reactor geometry, excitation, operating pressure) the concentrations and temperatures of the plasma species (e.g. ions, radicals, electrons).

The transport module deals with effects concerning the transport of species from the plasma bulk onto the sample surface, including shadowing, diffusion or charging effects.

The surface module finally deals with the interactions of the species which reached the surface. By menas of chemical or physical interaction the surface is either eroded (etching) or thin films (e.g. polymer films) are deposited on the surface.

The various effects influence each other b y means of feedback. A realistic process simulation therefore needs to consider these interactions and feedbacks, which makes the numerical simulation more challenging. Suitable numerical methods or adequate approximations are crucial for the simulation of feedback and interactions.

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Profile simulator "WinSimEtch"

The self made profile simulator “WinSimEtch” (fig. 2) calculates profiles generated by time-multiplexed or “gas chopping” etching recipes (DRIE). It employs some approximations and simplifications.

Figure 2: Profile simulator “WinSimEtch”. The corresponding experimental profile is superimposed. Taken from ››Burkhard E. Volland and Ivo W. Rangelow: The influence of reactant transport on the profiles of gas chopping etching processes: a simulation approach, Microelectron. Eng. 67-68, pp. 338-348 (2003).‹‹

The profile simulator was evaluated by comparing experiments with simulated profiles (fig. 3). In particular, profiles with different timings between the etching and deposition cycles were simulated and compared with the experiments. The profile simulator “WinSimEtch” produces simulation results which agree with corresponding experiments.

Figure 3: Comparison of simulated profiles and corresponding experiments for different aspect ratios. Taken from ››Burkhard E. Volland and Ivo W. Rangelow: The influence of reactant transport on the profiles of gas chopping etching processes: a simulation approach, Microelectron. Eng. 67-68, pp. 338-348 (2003).‹‹

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European research project "NanoPlasma"

Profile simulator "ViPER"

ViPER (Virtual Plasma Etch Reactor) is a port/further development of the original WinSimEtch program.

An evaluation version will be available here for download in the near future.

This profile simulator is currently under further development and enhancement within the scope of the research project “NanoPlasma” funded by the European Union.

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Publications and conference contributions

 

EIPBN ("3beam") 2002 conference
"Profile simulation of gas chopping based etching processes"

Poster (113 kB, PDF)Pre-Print (310 kB, PDF)

Publication:
B.E. Volland, Tzv. Ivanov and I.W. Rangelow:
"Profile simulation of gas chopping based etching processes", J. Vac. Sci. Technol. B 20(6), pp. 3111-3117 (2002).
(http://scitation.aip.org/)

Micro and nano engineering (MNE 2002) conference

Presentation (908 kB, PDF)
Pre-Print (210 kB, PDF)

Publication:
B.E. Volland and I.W. Rangelow
 "The influence of reactant transport on the profiles of gas chopping etching processes: a simulation approach"
 Microelectron. Eng. 67-68, pp. 338-348 (2003).
 (
www.sciencedirect.com)

Micro and nano engineering (MNE 2005) conference

Poster (431 kB, PDF)
Pre-Print (681 kB, PDF)

Publication:
B.E. Volland and I.W. Rangelow
"Aspect ratio dependent plasma polymer deposition of fluorocarbons"
Microelectronic Engineering Volume 83, pp. 1174-1177 (2006).
(www.sciencedirect.com)

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Literature

[1] Burkhard E. Volland, "Profile simulation of gas chopping etching processes - Model development and comparison with experiments - ", Dissertation Universität Kassel, URN: urn:nbn:de:hebis:34-1167 (2004). [PDF, 9.7 MB]


[2] Burkhard E. Volland and Ivo W. Rangelow: The influence of reactant transport on the profiles of gas chopping etching processes: a simulation approach, Microelectron. Eng. 67-68, pp. 338-348 (2003).

Translation: B. Volland
Please report mistakes to: Burkhard.Volland@Tu-Ilmenau.de