Cl2 Manifold
Regulator
Manual Isolating
Valve
MFC 1
PT
Pressure Transducer
ROR system
Regulator
MFC 2
N2 Manifold
Sonic flow
ROR device
Vacuum
Pump
Manual Isolating
Valve
Figure 1. Test setup
The lack of actual flow characterization for MFCs in the real gas application creates several areas of unknown
for the process engineer responsible
for developing process recipes. In previous generations of semiconductor
processes, MFC repeatability over
specific flow regimes was sufficient.
However with ever decreasing critical dimensions and incorporation of
new materials for oxide layers, inter-layer dielectric films and larger wafer
sizes stretching the requirements for
uniformity, the accuracy of process
flows becomes critical. As process
flow decreases, the flow errors and
impact of contamination on process
gas flow increases.
In this paper, the discrepancy
between gas calibration factors (
gas cal factor) used for approximating live or real gas flows in MFCs is
highlighted as an example of the discrepancy that arise between real or
live chemistry characterization and
N2 or surrogate gas characterization
of a critical component.
Figure 2. MFC flow rate error for 500 sccm Cl2 MFC
Test Program
Figure 1 shows the schematic of the
test setup used in the characterization
study. A well characterized, commercially available rate of rise system (ROR)
(Lucas Labs/ Florizel) was modified and
used to conduct the flow testing.
Figure 3. Flow error range for 200 sccm and 500 sccm Cl2 MFC
Test Procedure
The MFCs were calibrated for Cl2
by the manufacturer and were tested
in both N2 and Cl2. Two MFCs of 200
sccm and 500 sccm flow ranges were
used for the study. In order to mini-
mize extraneous factors and to ensure
that test system conditions remained
the same, all tests were conducted
consecutive to one another. MFCs
were tested at 10 set points rang-
ing from 2% to 100% of full scale of
the device. Each test was conducted
at least 3 times at each set point to
derive standard deviation values. The
test system reliability at all set points
was also measured. The results of this
test are shown in Figures 2 and 3.
