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Polycrystalline silicon (also called "poly-Si" or "poly") is deposited at a low pressure (~500 mtorr) using silane (SiH4). The tube has a sloping temperature profile. Deposition temperature is ~620C for polysilicon and ~560C for amorphous silicon. The deposition rate for poly silicon is ~125A/minute for 3 inch wafers and ~137A/minute for 4 inch wafers.

Tylan LPCVD Furnace Operation (short)


Clean substrates

Diffusion clean with HF last


Enable the furnace


Verify Pump program running

Go to the furnace and use the STATUS button to verify that the system is in 'RUN' mode and running the “PUMP program”. 

End Pump program 



Verify the Tube is vented

Ten minutes after the pump program has ended you must manually test that the tube is vented. Push MANUAL on the boat puller, push FAST, then LOOK AT THE TUBE while you hold down OUT. You should immediately see the boat start to come out.  If it does not, stop and wait 10 more minutes and test it again.


Load your program (only after verifying manually that tube is vented)

From TYCOM type "LO  <program name>  <furnace#>" <RET>.  You will be asked to enter the deposit time.


Run program


Load your wafers


Send in tube



Monitor furnace

Take pressure readings during the gross leak check, leak check and the deposition steps of the program and write the values in the logbook.


Unload wafers


End program



Load pump program


Run Pump program


Measure wafers and log results


Disable the furnace.


Process Monitoring and Machine Qualification


To provide a standard procedure to monitor Poly thickness and uniformity both wafer-to-wafer and within-a-wafer.



To be completed after major maintenance such as a tube change or on a set schedule to be determined or as needed based on user feedback.



Test results are recorded on Coral.



  1.  Use four wafers with 1000A of SiO2.
  2.  Clean at wbdiff in the following sequence; 5:1:1 H2O:H2O2:NH4OH ten minutes, rinse, 5:1:1 DI;HCl:H2O2 ten minutes, rinse, spin dry.
  3.  Load program POLYEMIT into Tylanpoly furnace.  Time variable is 00:15:00.
  4.  Load wafers into boats using very clean tweezers or vacuum wand.  Load wafers with the major flat up into the boats in the following positions:

1st boat: (Front), 20 empty slots,

1st  two dummies,

1st boat:  two test wafers(slot 23 & 24),

1st boat: one dummy.

2nd boat: one dummy,

2nd boat: two test wafers (slot 2 &3),

2nd boat one dummy,  21 empty slots. 

LPCVD Test wafers

Test wafer location


Use Nanospec to measure poly thickness at the flat, center, bottom, left and right on each wafer.  Test sites should be no more than about 15mm from the edge of the wafer.

locations on wafer




Record results on the on coral. If test’s values aren’t not within 10% of plotted test average, contact the Diffusion Process/Maintenance team.


TylanPoly Qual Data


Save wafers in a box with the date, furnace number, program name and growth time.  They may be re-tested sometime in the future.



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