TECHNICAL NOTEDC Power Fault Detectedby FabGuard®
FabGuard Sensor Integration and Analysis System is a fully
automated, real-time early fault detection and analysis system
for improving semiconductor equipment and process productivity
and various INFICON in situ diagnostic sensors. The powerful analysis techniques of FabGuard are capable of "smart
diagnostics" by combining sensor and tool data for fault
detection and classification. FabGuard puts in situ sensors
to work to:• Baseline normal process and tool behavior• Analyze process data in real-time to detect problems andpinpoint problem sources• Issue warnings and alarms
One benefit of FabGuard is continuous real time monitoring of
how close variables measured by the process tool are to their
setpoints.
Figure 1 shows a screen captureof the data collected by a Tool
Data Sensor (TDS) for one wafer
during a PVD process. SECS wasused to collect five variables fromthe tool for this chamber. The fivevariables are: DC power setpoint,pressure manometer, pressure iongauge, DC power actual, andArgon AFC.

Figure 1 - Data collected by a Tool
Data Sensor for one wafer during aPVD process.

The lower left section of the screen contains a plot of data
versus time for one or more variables. The vertical line at 16
seconds indicates the user-selected time used in the upperplot. The upper plot is a snapshot of all five variables at one
specific time during the process. In the lower plot, two variables
are selected for display: DC power setpoint (red) and DC
power actual (green). Notice that the DC power took about 10
seconds to reach its setpoint. This 10 second delay is quite
significant since the DC power should only be turned on for a
total of 20 seconds. For this wafer, the deposited film thickness
would have been only about half of what it was supposed tobe. The cause of this fault was traced to a DC generator thatwas beginning to fail. FabGuard detected this fault long before
the tool itself would have.

HOW FABGUARD WORKS
Figures 2 and 3 show how FabGuard automatically detected
this fault. Figure 2 is the same as Figure 1, except thatdifferent information is selected for plotting in the lower left.
Figure 2 plots a calculated value: the DC power divided by its
setpoint. In FabGuard, time series values calculated from raw
data are called Signal Bins. The DC power/setpoint Signal
Bin should be nearly equal to 1.0 whenever the DC power issupposed to be turned on. It is only 0.0225 at the timeshown, which is 6 seconds after the DC power was turnedon.

Figure 2. Signal Bin showing DC power divided by its setpoint.

(red alarm) because wafers are in immediate danger if thisfault occurs. This analysis automatically detected a fault 14
seconds into the process. An alarm was generated inside
FabGuard and an alarm message was sent to the tool. As aresult, the tool was stopped and it was determined that theDC power generator needed to be replaced.
Without intervention from FabGuard, hundreds of wafers
would have been misprocessed before the DC power
generator problem became bad enough for the tool to detect
the problem itself.

Figure 3. Analysis logic used to detect the DC power fault.

Figure 3 shows the settings for the Math Logic Analysis thatFabGuard used to detect this fault. The logic is defined sothat a fault is generated if the DC power is less than 0.95 of
setpoint or greater than 1.05 of setpoint for 3 seconds orlonger. A persistence of 3 seconds was chosen to allow forvariability in the turn-on time of the power supply andstabilization of the plasma. This is marked as a critical fault

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