Chemistry Reference
In-Depth Information
discussed in Chapter 6. Plasma diagnostics is in particular informative near the
wafer surface.
For high density, low pressure etching in different plasma sources it could be
shown that the etch rate (e.g., of SiO
2
in a CF
4
plasma) depends only on the plasma
parameters in front of the wafer [93]. The etch process occurs by ions and neutrals,
e.g., F atoms. Also, the deposition of polymers (by CF
2
) has to be taken into account.
Theetchrate
R
using the experimental values of ion current density
J
i
and its energy
E
i
as well as the neutral fluxes of the etching
J
e
and depositing
J
d
species (which are
proportional to the particle densities) are given by
K
es
J
i
E
i
1
−
C
sp
(
J
d
/
J
e
)
2
R
=
,
(8.51)
1
+
A
s
(
J
i
E
i
/
J
e
)
K
es
,
C
sp
, and
A
s
being constants. The etch rates of SiO
2
in CF
4
plasmas determined in
different tools (electron cyclotron reactor [ECR], helicon reactor [HRF], magnetically
confined inductively coupled plasma [MCICP], and RIE) are presented in Figure 8.24
according to Equation 8.51 using experimental values of the plasma parameters.
Equation 8.51 fits the data of the different tools very well [93].
3500
ECR
HRF
RIE
MCICP
3000
2500
2000
1500
1000
500
0
0
50 100
J
i
E
i
[1 - 0.13(
n
CF
2
/
n
F
)
2
]/(1+3.3 × 10
-3
150
200
250
300
J
i
E
i
/
n
F
)
FIGURE 8.24
Etching rates of SiO
2
in CF
4
plasmas in ECR, RIE, MCICP, and HRF reactors,
experimental and calculated data (8.51). (From Hershkowitz, N. et al.,
Phys. Plasmas
, 3(5),
2197, 1996.)
