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Introduction
The Mattson Aspen asher
runs a dual-wafer photoresist removal process. A customer indicated that they are running
a series of ashers where the process end-point is based on time only, due to mismatch
between their specific process and the machine that does not allow for efficient use of
the built-in end-point. The main issues were use of mixed processes and type of wafers.
The asher, as most other machines, could not determine the wafers' quality (resist exists,
removed or rework), as a result of which it could not indicate true completion of the
process (End-point) at sufficiently high probability. The customer believed Tadin can help
to increase yields, speed and capacity, and cut the intensive operation and engineering
intervention that was required.
The customer asked for
Tadin's help to improve the overall performance. The TadiGuard Connection
One of TadiGuard's many
features, namely the Combined Alarm system is an optimal solution to the end-point
problem. It can be set to sense the slope of the signals and the true end of the resist
removal, enabling accurate and reliable detection of the end point. In addition, TadiGuard
enables to distinguish between processed, unprocessed and rework wafers, enabling
continuos operation with high-yields, high capacity and minimal operator / engineering
intervention.
The TadiGuard enables
also real-time graphics display of the machine’s operation and full history analysis
of the machine and its process, with SPC functions, correlation to lot and wafer numbers
and many additional built-in 'goodies'.
TadiGuard
Application
The TadiGuard was set to
monitor and test two end point signals simultaneously. The process sequence is as
follows:
Step 1 When the TadiGuard detects
wafers in the process chamber(s), it starts testing the end point signal (for the specific
wafers). At first the TadiGuard verifies that the end-point signal crosses the
“Analog Start Point”, moving in the right direction.
- An end-point signal
that does not cross the “Analog start point” at the right time and direction
indicates that the wafer in the chamber is faulty.
- If end-point signal
does cross the “Analog Start point” in the right direction, then the TadiGuard
will continue the test.
Step 2 The TadiGuard evaluates the
signal’s stability during this stage. The process reaches a successful end when the
end-point signal is stable for at least a given period of time which in turn depends on
the actually measured process time. When the right stability has been detected, all
photoresist was removed and the wafer can proceed to the next step with optimal
timing.
If the end-point signal
is not stable for the given time, it indicates that photoresist removal was incomplete or
the wafer is defective.
In the case that TadiGuard
detects a wafer that didn’t complete the process in the expected time, the TadiGuard
would stop machine operation only at the completion of the lot processing. The operator
would then check the reason for the alarm and would decide how to proceed. Thus, a bad
wafer can not pass the machine.
TadiGuard
Benefits
- Identifies good and
bad wafers.
- Prevents wafers with
photoresist residues or faulty wafers from continuing to the next step.
- Shortens process time
and total wafer time.
- Provides real-time
monitoring of the ashing machine.
- Provides real-time
supervision and alarm to deviations.
- Provides full
historical analysis of machine and process.
Mattson asher Analog and
Binary TadiGuard Channels Examples
| Number |
Analog Channels |
Binary Channels |
| 1 |
RF Power Forward |
RF On |
| 2 |
RF Power Reflected |
Gas #1 Valve |
| 3 |
RF DC-Bias |
Gas #2 Valve |
| 4 |
MFC #1 |
Gas #3 Valve |
| 5 |
MFC #2 |
Gas #4 Valve |
| 6 |
MFC #3 |
Isolation Valve |
| 7 |
MFC #4 |
Vacuum Valve |
| 8 |
Pressure |
Vent Valve |
| 9 |
Control Valve |
Ballast On |
| 10 |
End-Point |
Pins Up |
| 11 |
A-Cell |
Pins Down |
| 12 |
B-Cell |
Shuttle in Position |
| 13 |
DAC Volts |
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TadiGuard's
contribution to the asher operation
| Subject |
TadiGuard Solutions |
| Detection of wafer
condition |
The TadiGuard uses
its combined stability alarm for two purposes:
- To sense the end-point
signal slope thereby determining the quality of the wafer and of the process.
- To determine the
stability of the end point signal. A signal that is stable for a preset time indicates
that all photoresist material was removed from the wafer.
TadiGuard gives a
comprehensive solution to the end-point monitoring of ashers and etchers. |
| Historical data
storage and analysis |
TadiGuard provides
process history going more than one year back. It enables historical analysis such as SPC,
trends, etc., enabling process optimization and process problems detection and analysis. |
| Machine performance
optimization |
TadiGuard enables
easy and accurate measuring of machine performance and allows immediate performance
enhancements. It can measure net process time, net wafers/hour, total wafer run per
process, etc. thus enabling comparison and long-term machine analysis. Analyzing the
machine and the process can increase capacity by up to 20%. Return on investment is within
weeks. |
| Real-time process
and machine supervision |
TadiGuard monitors
all “suspect” parameters in real-time and alarms to any deviation from normal
conditions, thereby eliminating damage to wafers and lost production time. |
| Maintenance and
diagnostics, Intermittent problem detection |
TadiGuard monitors
the machine parameters in real-time, and enables history analysis of various machine
intermittent and lasting malfunctions. This efficiently results in more up-time and
capacity with lower maintenance cost. |
1) Mattson and Aspen are trademarks of Mattson Technology,
www.mattson.com
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