S-O2-1
Plasma Simulation of Si3N4 CVD Process
Si3N4膜のCVDシミュレーション	 Song-Yun Kang
康	  松潤Technology Development Center, Tokyo Electron Ltd.
650 Mitsuzawa, Hosaka-cho, Nirasaki City, Yamanashi 407-0192, Japan
東京エレクトロン	  技術開発センター 〒407-0192	  山梨県韮崎市穂坂町三ツ沢650
The plasma produced by a microwave source is discussed based on a simulation using a multiphysics
coupled 2 dimensional fluid model. The technological aspects in a silicon nitride chemical vapor
deposition (CVD) process using a disilane and ammonia mixture are addressed. The model includes theincompressible Navier–Stokes, the multiple convection and diffusion transport modules, the convection
and conduction heat transport for gas and electron temperature, and the transverse electromagnetic wave
propagation for a planar microwave source structure coupled to the plasma. The chemical reactions usedin this simulation were prepared based on quantum chemical calculation. The dominant precursors,deposition rate and mechanisms, and performance of the CVD process in terms of the film properties areinvestigated. Distributions of the ionic and radical species are calculated and the simulation results arecorrelated with experimental data. The significant impact of the surface reactions with the involvement of
H, NH, and NxHy radicals and ions were established.

1. Introduction
Microwave plasma sources (MWPS) are
widely used in thin film technology andunderstanding the phenomena involved inmaterials processing by MWPS is important inorder to provide full control of the source
performance and its design. Recently, the plasma
processing, configurations, and characteristics ofvarious plasma reactors were studied[1–2] and inparticular an MWPS has been shown to achieve
good process performance. For this type ofsystem the gas mixture composition is one of thecritical factors in controlling the deposition rateand film properties. In this work, theinvestigation of a disilane (Si2H 6) with ammonia(NH 3) plasma produced by MWPS is done bysimulation means. The 2D plasma fluid within
multiphysics coupling (FEM framework) model
was formulated for a 300mm wafer reactor.
Extensive studies were done in previous works on
numerical modeling and silane chemistry by
several authors.[3–5] Although, disilane andhigher silanes are produced in a silane plasma, toour knowledge similar work has not beenreported for disilane as a working gas or in
mixture with other gases.
In this paper, we will describe a model
consisting of the coupled modules forcalculations of the wave propagations, reactive
gas and plasma transports, and energybalances.[6]2. ModelThe investigated CVD system consisted of acylindrical reactor (φ 45 cm x 20 cm, see Figure 1)
equipped with a planar MWPS, annular gas feeders,and a φ 300 mm heated wafer stage. The MWPS is
composed of a coaxial waveguide (CWG) and aplanar slot antenna separated by a dielectricwindow from the plasma zone.

Fig.1. Configuration of microwave plasma reactor

The TEM mode which is excited by a 2.45 GHz
generator propagates from the CWG through theplanar radial waveguide and penetrates into thereactor through slots in antenna. The details on slot
arrangements and their structure is not discussed inthis work. We formulated a plasma fluid modelwith mutual coupling between individual variables
associated with the reactor physics and chemistry.
The reaction chemistry and film growth model are
shown in Figure 2.
We examined the mixture of Si2H6/NH3(N2)/Arby the developed model. In the simulation theindividual gas components were fed from the upper(NH3) and lower (Ar with Si2H6) gas feeders
located in an annular fashion on the side wall
(Figure 1) and the gas was evacuated through thepumping port located at the lower side of theplasma reactor.

Fig.2. Reaction chemistry and film growth model

3. Results and Discussion
The actual modeling results generated a robust
dataset, which had explicit and valuable impact on
the tool development. The computed raw data wereused to create the simulative diagnostics sheets(SDS) in order to perform cumulative and statisticalanalysis for each particular conditions. The SDS
consisted of the comprehensive characterization andspecification about the particular process, including
fluxes, deposition rate, film composition, etc. andthey were found very useful and practical forprocess engineers to validate computed results. In
respect to experimental processing results, webelieve that the simulation results represented
reasonable values of plasma parameters andcomposition.
We observed that a significant amount of themolecular hydrogen and nitrogen were produced inthe Si2H6/NH3/Ar plasma. N and H radicals weregenerated in the whole volume of the plasma
reactor via various gas phase chemical reactions.
Despite the differences in plasma sources between
MWPS and RF CCP[4] for both cases it wasobserved that most of the hydrogen was located inthe center. The disilane was shown to be an
efficient source of the radicals as the chamber
volume was filled with species such as Si2H4, Si2H2,SiH3, NH2 and NH. On the other hand, the species

Si2H6, SiH4, SiH, NH3, N2 or H2 have increased
concentration closer to the gas inlets and dissociate
when propagating into the bulk plasma.
The idea on the competing processes ofvolatilization of H(s) versus successive insertion
into Si–Si(g) bonds by hydrogen flux toward thesurface still needs further investigation for disilane
plasma. More comprehensive understanding ofthese surface processes can be gained bysophisticated surface models or from molecular
dynamics simulations.
Nevertheless, many diverse modeling aspects
were tested within the computation process. We canconclude that the approach based on multiphysics
coupling under FEM framework gave us anopportunity to study complex chemistry in a modelwith mutually coupled variables within reasonable
computation times, characterize the complexity of
the involved chemistry, and investigate the role ofthe numerous species such as NxHym and SixHym (m= 0 or +) in film growth.
4. Conclusion
From the industrial and engineering aspects, we
see an advantage of using a modular and flexible
model with integrated multiphysics coupling thatallows one to generate results within reasonable
time to sustain either hardware or processdevelopment. The technologically rich and valuable
information was obtained by a simulation using thedescribed model with mutually coupled variables
that are associated with various aspects of theinvestigated configurations and chemistry.
5. Acknowledgements
The authors thank Nakanishi Toshio, Minoru
Honda, and Masayuki Kohno for deposition ratemeasurements.
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Ishibashi: Thin Solid Films 506–507 (2006) 503.
[2] A. Tsuji, Y. Yasaka, S.-Y. Kang, T. Morimoto, I.
Sawada: Thin Solid Films 516 (2008) 4368.
[3] M. J. Kushner: J. Appl. Phys. 71 (1992) 4173.
[4] G. J. Nienhuis and W. Goedheer: Plasma Sources
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[5] A. Salabas, G. Gousset, L. L. Alves: Plasma Sources
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[6] J. Brcka and S.-Y. Kang: Plasma Sources andPolymers 6 (2009) S776.