20
DEPOSITION
Keep your chamber clean
The manufacturing processes within the semiconductor industry are becoming
increasingly fast and complex. The equipment used needs to be maintained and
cleaned on a regular bases to ensure precise operation. The materials used for these
cleaning processes are gases. This article describes the use of Ar/N
2
/F
2
for chamber
cleaning in the CVD and ALD processes. By Marcello Riva, Michael Pittroff,
Thomas Schwarze, John Oshinowo, Robert Wieland (Solvay Fluor GmbH,
FraunhoferIZM).
F
2
gas mixtures offer ideal properties to be employed meets the above mentioned requirements and is considered to be
as chamber cleaning gas: low dissociation energy easily integrated into the fab, gas supply is relatively expensive.
and high reactivity, which leads to superior The work presented here investigates argon/nitrogen diluted
efficiency and ease of abatement. In this work, a new F
2
gas fluorine (Ar/N
2
/F
2
), delivered from conventional cylinder gas
mixture was used with a combination ratio of 10% Ar, 20% F
2
bottles. 20% F
2
mixtures are easily available on the market and
and 70% N
2
in order to obtain a maximum of 20% fluorine in are already delivered in bulk quantities to the automotive
inert gases. This novel Ar/N
2
/F
2
gas mixture has been evaluated industry for the fluorination process of plastic gasoline tanks and
as a candidate to replace conventional cleaning gases, like NF
3
, to the semiconductor industry for the so-called ‘thermal
C
2
F
6
and CF
4
in an industrial AMAT P5000 CVD chamber tool. cleaning’[7].
Standard equipment has been used, showing complete Our approach, to use the classical stainless steel gas bottles,
compatibility with the new gas. The tested Ar/N
2
/F
2
mixture differs from the on site fluorine generation, that utilises hydrogen
shows improvements in both parameters, cleaning at a faster fluoride (HF) as feed material [8, 9, 10]. Since the deposition,
rate (up to 27%), even requiring a lower amount of gas (minus etching and selective removal of silicon based dielectric
96% versus NF
3
). The higher etching rate and the lower gas materials [11] are very important process applications, we have
consumption assure a sensible CoO (Cost of Ownership) used SiO
2
and Si
3
N
4
layers on Si for tests.
advantage to any potential user. The superior etch rate It is important to underline the good environmental properties
performance of the Ar/N
2
/F
2
gas mixture was combined with of Ar/N
2
/F
2
, due to the fact that the global warming potential
excellent etch non uniformities values, of ±3% (1sigma) on SiO
2
(GWP) is zero, unlike all other chamber clean gases.
and of ±8% (1sigma) on Si
3
N
4
, respectively. Also amorphous
Silicon (a-Si) was etched completely and uniformly. The particle Experimental
performance data showing in average just 14 particle adders Two gas mixtures in stainless steel bottles containing 20% F
2
(0.25µm), indicating that no significant particle contamination were used; this F
2
concentration conforms to the standard used
was induced by the process and Ar/N
2
/F
2
can be used as a highly in the automotive and the semiconductor industry, so that all
clean and efficient etching gas as well as an ideal drop in necessary system parts can be easily procured on the market.
replacement for the conventional cleaning gases.
Introduction
Deposition steps in the CVD and ALD applications usually not
only cover the surface of the substrate but also the walls of the
chamber inside. Regular removal of those residuals has to be
done to obtain stable and repeatable deposition results with
uniform surfaces at acceptable particle levels[1]. Since long
time, chamber cleaning gases like Tetrafluoromethane (CF
4
) and
Hexafluoroethane (C
2
F
6
) are used[2, 3, 4]. The high
requirements to sustain stable processes has lead to more
frequent chamber cleans. Nitrogentrifluoride (NF
3
) has emerged Figure 1a/b: Taguchi-L9 matrix of experiment of SiO2 etch
as the main clean gas for 300mm tools equipped with Remote rate [nm/min] (square6) and etch non uniformity (triangleup) [% 1sigma]
Plasma Source (RPS) systems, which show significantly shorter of N2/F2 gas as a function of flow rate (left) and pressure
clean times compared to CxFy based cleans[5, 6]. While NF
3
(right). The SiO
2
layer thickness is 1 µm
www.euroasiasemiconductor.com August 2008
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