DEPOSITION
23
respectively. Immediately after SiO2 deposition, the wafers left
the CVD reaction chamber.
The cleaning recipe was chosen as follows: a gas flow rate of
900 sccm Ar/N
2
/F
2
and a chamber pressure of 2.1 Torr. The RF
power was 800 W and the susceptor temperature 400
O
C with
540 mils spacing (maximum spacing value on the silane based
oxide/nitride CVD chamber). The total cleaning time of 60 sec,
included an over cleaning of about 30% in order to make sure,
Table 1: Summary of the three repeatability runs of 1µm- that any previously deposited oxide at the chamber walls,
SiO
2
deposition for 35 sec, followed by an Ar/N
2
/F
2
pumping plates, susceptor edges and on the shower head will be
chamber clean etching for about 60 sec. The data showing completely removed.
the average values of SiO
2
layer deposition thickness [nm], The deposition recipe to deposit 1 µm of SiO
2
was the
oxide deposition non uniformity (within wafer/ wafer to standard BKM recipe of Applied Materials with SiH
4
and N
2
O
wafer) in [%1sigma] and Ar/N
2
/F
2
oxide etching rate as the main process gas.
[nm/min] non uniformity (within wafer) in [%1sigma] for Figure 3 shows the results of a repeatability runs of 1µm-
three wafer runs (total 75 wafers). The average (mean) SiO
2
deposition followed by an Ar/N
2
/F
2
chamber clean etch
values of the batch to batch uniformity are shown as well. (run 2). The graphs display the oxide deposition thickness as well
For the first run, the etch rate was not measured (n/m). as the oxide deposition non uniformity as a function of wafer
position.
A SiO
2
deposition of about 1034 nm was achieved for all 25
uniformity, is the limiting factor to improve etching wafers. The oxide deposition non uniformity was measured within
performance. the wafer as well as wafer to wafer. The within wafer oxide
The cleaning gas behaviour on Si
3
N
4
with the addition of Ar deposition non uniformity was about ±1.4% (1sigma) and wafer
at the N
2
/F
2
mixture has been studied next (see fig.2). A to wafer non uniformity was ±0.8% (1sigma), demonstrating a
preliminary Taguchi matrix study evidenced a reduced very stable oxide deposition. In order to verify the repeatability
dependency of the etching performance on the RF power applied. of the SiO
2
oxide etching rate for 25 wafers, the previously
It has been found that a small addition of Ar notably increases deposited wafers were run again and partially etched by
the uniformity of the etching, which is generally one of the Ar/N
2
/F
2
for 30 sec. After measuring the remaining oxide
limiting conditions for industrial processes. thickness, the cleaning rate was calculated.
It has been possible to achieve etching rates > 1300 nm/min
even maintaining non-uniformity values < 5%, far below from
the value of 20% which is generally considered the highest
acceptable. These results are more encouraging in consideration
of the fact that the addition of Ar to the F
2
/N
2
mixture dilutes
the concentration of the active specie F
2
, which is a not
desirable; Figure 2a shows the slight decrease in etch rate with
increasing Ar flow. As a consequence of the described test
results, the mixture 10% Ar / 70% N
2
/ 20% F
2
, has been Table 3: amount of cleaning gas and cleaning time
chosen for the following parts of this study. The mixture was needed for three different cleaning gas chemistries
premixed by Solvay Fluor and delivered in a cylinder, so to avoid (Ar/N
2
/F
2
, CF
4
,C
2
F
6
/O
2
and NF
3
) normalised to 1µm
any F
2
dilution effect by adding Ar during operation. dielectric film (SiO
2
and Si
3
N
4
) thickness (20% over
In order to test the repeatability within wafer, wafer to wafer cleaning time included)
and batch to batch of the Ar/N
2
/F
2
etching and particle
performance, three runs with 25 wafers each have been
performed. Processing the wafer batch has been done in full Fig. 4 shows the results of SiO
2
etching rate of Ar/N
2
/F
2
as a
automatic mode, by the deposition of a 1µm SiO
2
film for 35 sec function of wafer position (run 2). For the first wafer, the etching
and a subsequent 60 sec plasma chamber clean in Ar/N
2
/F
2
gas. rate was about 1280nm/min and significant lower compared to
The particle monitor wafers were placed in slot 1, 12 and 25, the rest of the 24 wafer batch, indicating the “first wafer
effect”. From the second wafer on, the oxide etching rate was in
average about 1525 nm/min for all wafer with a corresponding
within wafer oxide etch non uniformity of ±7.1% (1sigma). This
shows, within the wafer as well as wafer to wafer, a very
repeatable and stable oxide etching rate.
In order to verify Ar/N
2
/F
2
etch rate non uniformity on SiO
2
from batch to batch, three wafer runs (75 wafers) were carried
out. Table 1 displays the result of all three runs. An average
SiO
2
deposition thickness of 1036 nm was achieved for all three
wafer batches. For all three runs, the within wafer oxide
Table 2: The number of particle adders with a particle size deposition non uniformity was in average ±1.3% (1sigma) and
?= 0.25µm on 200mm (slot 1, 12 and 25). The SiO
2
the wafer to wafer non uniformity was in average ±0.7%
deposition (1036 nm for 35sec.) was followed by a (1sigma), demonstrating a very constant oxide deposition across
subsequent Ar/N
2
/F
2
oxide etch (> 1500nm for 60 sec.) for all three batches.
three wafer runs (total 75 wafer) The Ar/N
2
/F
2
etching rate on SiO
2
was batch to batch in
August 2008 www.euroasiasemiconductor.com
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