STRASBAUGH CONFIDENTIAL INFORMATION
2
Special Options for Special Processes
Two additional options have been added to accommodate special needs. Choosing them carelessly may damage
wafers, but they are useful in certain applications. Both are set in Machine Variable 19, Special Options.
In some applications, prealigner errors may occur frequently. The symptom is that the prealigner centers the
wafer correctly but fails to find the notch or flat. This may result from ragged tape on a taped wafer or from a
coating on the wafer. You want the benefit of centering, so you do not want to use the Prealigner Bypass, and
you are willing to accept the inability to find the notch or flat. This is useful for round wafers only.
If you set variable 19 to the value 1 the prealigner will try up to three times to align the wafer. If it still cannot
succeed, it will pretend that it has succeeded. The Prealigner Error fault will not appear.
Other applications may need to allow very low vacuum at the work chuck. This may be useful for wafers with
wavy surfaces, where poor surface contact allows the chuck vacuum to leak. Ordinarily this would produce a
Left/Right Chuck Vac fault or a grind abort. If you set variable 19 to 10 this condition will be tolerated.
For both options, set variable 19 to 11.
As a precaution against setting these options carelessly, they will be tied to the Left-Off and Right-Off options
in machine variable 18, since their known uses require those as well. The rule is:
Variable 19 will be ignored unless you select Left-Off or Right-Off or both.
Tracking Wafers Through GEM
Several new GEM variables are introduced to help with wafer tracking. There is a new Collection Event,
number 77, called Wafer Moved to New Station (Grind Cycle Only). During the grind cycle, this event will be
triggered whenever a wafer has moved to a new station. VID’s 155 and 156, called SourceStationOfGet and
DestinationStationOfPut, will report the source and destination of that move. Station ID’s are A and B for the
send cassettes, C for the prealigner, D and E for the work chucks, F for the spin station, G and H for the receive
cassettes. In addition, the destination in VID 156 can be used to find out which slot of which send cassette
originally held the wafer that was just moved.
If VID 156 is: Then these VID’s hold the originating send cassette ID and slot number:
C (prealigner) 143,144 called PrealignerSourceCassette and PrealignerSourceSlot
D (left chuck) 145,146 called LeftChuckSourceCassette and LeftChuckSourceSlot
E (right chuck) 147,148 called RightChuckSourceCassette and RightChuckSourceSlot
F (spin station) 149,150 called SpinStationSourceCassette and SpinStationSourceSlot
G (receive 1) 151,152 called ReceiveCassette1SourceCassette and ReceiveCassette1SourceSlot
H (receive 2) 153,154 called ReceiveCassette2SourceCassette and ReceiveCassette2SourceSlot
Note that Send Cassette 1 is B while Send Cassette 2 is A. This results from the letter ID’s following a circular
path around the 7AF in their normal ordering of ABCDEFGH. Also note that slot numbers range from 1 to 25.
More Information in the Grind Data
The grind data on the C: drive will now include the originating send cassette ID and slot number just described.
This will be true whether or not the GEM option is installed. Several additional data items are also added.
These include the chuck on which the wafer was ground, the wheel wear, the wheel and chuck speeds, the chuck
vacuum level, the chuck D.I. coolant flow rate, the water temperature, and the motor current. Although these
items appear on disk and can be processed externally by a program such as Microsoft Excel, they do not appear
on the Grind Data screen, and are not passed through to GEM. However, GEM is able to obtain this
information in other ways, such as reading real-time data.
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