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’.
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.
- 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|
|9||Control Valve||Ballast On|
|12||B-Cell||Shuttle in Position|
TadiGuard’s contribution to the asher operation
|Detection of wafer condition||The TadiGuard uses its combined stability alarm for two purposes:
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