24
DEPOSITION
average (mean) 1522 nm/min with a corresponding within wafer
oxide etch non uniformity of ±8.0% (1sigma). This demonstrates
for all wafer runs, a very repeatable and stable oxide etching
rate of the Ar/N
2
/F
2
gas mixture.
In order to get information about the particle performance
behaviour of the Ar/N
2
/F
2
etching gas mixture on the wafer
surface, the three the particle monitor wafer (located in slot 1,
12 and 25) have been measured before (reference) and after the Table 4: comparison of the required F
2
gas consumption
wafer run. With a Tencor Surfscan 6400, the minimal particle [%] for Ar/N
2
/F
2
, CF
4
and NF
3
on SiO
2
and Si
3
N
4
,
size measured was 0.25µm. The virgin reference wafer showed a respectively
particle contamination of about 20 particles (0.25µm).
The results of the particle measurements are shown in table 2.
After the SiO
2
deposition and oxide etching process the average select the best working parameters for NF
3
in the oxide/nitride
particle adders on the wafer surface was in average 22 particles chamber. NF
3
flow rates higher than 150 sccm and a chamber
for run 1, 14 particles (run 2) and 6 particles (run 3). In pressure higher than 0,6 Torr cause non uniformity > 20%,
average (mean) just 14 particle adders were generated from run which is not acceptable for a proper chamber cleaning. The
to run. The data indicating, that no significant particle maximum achievable etching rate with a non uniformity below
contamination was induced by the process and Ar/N
2
/F
2
can be 20% (1sigma) was 1200nm/min. Table 3 summarises all
used a highly clean etching gas. obtained etch rates for SiO
2
and Si
3
N
4
with different cleaning
It has to be pointed out, that all the obtained oxide etch rates chemistries and the process parameters used. In order to confirm
and oxide etch non uniformities of the Ar/N2/F2 cleaning gas the reliability of the obtained data on the oxide/nitride chamber,
mixture on SiO
2
, are equal or better than the standard CF
4
the etch rate on SiO
2
and Si
3
N
4
has been measured also in a
based BKM chamber clean of Applied Materials. The achieved Tungsten Chamber, where NF
3
is installed as a standard. For this
cleaning time with Ar/N
2
/F
2
gas mixture was approximately chamber type, AMAT suggests a BKM chamber cleaning recipe.
30% shorter than the CF
4
based BKM Applied Material clean Its etching performance does not differ sensibly from the best
time. The particle values were < 50 adders, which is well within parameter we set on the reference Oxide/Nitride chamber. In
specification for the AMAT P5000 process based on CF
4
analogy, it can be supposed that the F
2
mixture can improve
cleaning chemistry. cleaning performance also in TEOS chamber which normally use
The chamber was opened after processing the first 25 wafer a C
2
F
6
/O
2
/NF
3
cleaning mixture, even though no direct tests
run as well as after the final run (run 3) and visually inspected have been performed.
(see fig. 5). For both inspections, the surface of the shower head, The total cost of chamber cleaning process is determined
shadow ring, pumping plate and chamber lid O-rings, were clean from the wafer throughput of the CVD equipment and the cost of
and showed no signs of wear or residues. Si-pieces with a thin the consumables. Owing to the high cost of the equipments,
SiO
2
layer have been placed on the pumping ring, in order to which require high investments, the throughput is considered to
check the cleaning efficiency outside the susceptor area. The have the highest impact. Through the etching rates of the
complete oxide layer on the Si pieces has been removed different gas recipes in table 4, it is possible to estimate the
throughout the three repeatability runs. This verifies that the required time and the required amount of gas to etch, as an
Ar/N
2
/F
2
gas mixture cleaned all important CVD chamber areas example, 1µm of SiO
2
and Si
3
N
4
. The required cleaning time is
very well. directly correlated to the throughput of the equipment, while the
With the aim to achieve a direct performance comparison amount of required gas directly influences the cost of the
between the selected F
2
mixture and NF
3
, a new L9 Taguchi necessary consumables.
matrix has been calculated on SiO
2
deposited layers in order to The tested mixture Ar/N
2
/F
2
shows improvements in both
parameters, cleaning at a faster rate, even requiring a lower
amount of gas. Particularly, the NF
3
cleaning method requires,
It has to be pointed out, that all
for SiO
2
processes, a longer cleaning time (+27%) and almost
the double amount of process gas (+196%).
the obtained oxide etch rates
Last but not least, the etch performance of Ar/N
2
/F
2
plasma
and oxide etch non uniformities
on amorphous Silicon (a-Si) has been measured. A layer of
300nm of a-Si has been deposited on a layer of 100nm of SiO
2
.
of the Ar/N
Our standard Ar/N
2
/F
2
cleaning gas
2
/F
2
mixture has been applied for 15 sec,
setting the plasma parameters at the optimum conditions we
mixture on SiO
2
, are equal or fixed in this work.
better than the standard CF
The F
2
cleaning recipe allowed to etch completely and
4 uniformly both the a-Si layer and the SiO
2
substrate, indicating
based BKM chamber clean of
an etching rate > 1200nm/min.
The test was repeated with the NF
Applied Materials
3
best cleaning recipe,
which has been defined in this work. The a-Si layer was not
completely and not uniformly etched.
www.euroasiasemiconductor.com August 2008
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