Hong Kong University of Science & Technology
Department of Electrical & Electronic Engineering
Spring 2006
ELEC 300Q: Integrated Circuit Fabrication Technology
Lab 6: March 22nd , 2006
Step 10: Buffer Oxide Removal
10.0: Standard clean all run wafers plus 2 test wafers with field oxide and a new silicon wafer
10.1 During the Standard Clean, etch the buffer oxide with HF (or BOE)
Method: ____________
Expected Etch Rate: _______________
Time: _____________
End-point detection method: ________________
Remark (if any): __________________________________________________
10.2 Take out one of the test wafers with field oxide and measure oxide thickness :
wafer used: ___________
Equipment used: ____________
Program: _____________
Flat
Average =
Standard deviation =
Flat
Average =
Standard deviation =
Remark: _____________________________________________________________
Step 11: Gate Oxidation
11.0: TCA furnace clean performed? Yes/No: ____________________
11.1 Dry oxidation: (Run wafer, 1 test wafer with field oxide, plus the new silicon wafer)
Furnace: ____________
Initial Furnace Temperature = _____________
Wafer loading speed = _______________
Ramp time = ___________
Final temperate = _____________
Dry oxidation time: _________
O2 flow rate = ____________
Post oxidation anneal time = _____________
N2 flow rate: _________
Ramp down time: _________
Wafer pulling speed: _____________
Observed color change: _____________
Remark (if any): __________________________________________________
Note: While doing the gate oxidation, pre-clean a control wafer with 100nm of oxide to be ready for next step
11.2 Measure gate oxide thickness with the new silicon wafer :
Wafer used: ___________
Equipment used: ____________
Program: _____________
Flat
Average =
Standard deviation =
Flat
Average =
Standard deviation =
Remark: _____________________________________________________________
11.3 Measure field oxide thickness with the test wafer :
Wafer used: ___________
Equipment used: ____________
Program: _____________
Flat
Average =
Standard deviation =
Flat
Average =
Standard deviation =
Remark: _____________________________________________________________
Step 12: Polysilicon deposition: (Target = 400nm)
12.0: Transfer all run wafers plus one control wafer with 100nm of oxide to the LPCVD polysilicon tube
12.1: Polysilicon deposition
Equipment: ____________________
Expected deposition rate: __________________
Initial tube temperature while loading wafers: _______________________
Wafer loading speed: ____________________
Ramp time = ___________
Final processing temperature = _____________
Deposition time: _________
SiH4 flow rate = ____________
Pressure: _______________
Ramp down time: _________
Wafer pulling speed: _____________
Observed color change: _____________
Remark (if any): __________________________________________________
12.2: Polysilicon thickness measurement:
Wafer used: ___________
Equipment used: ____________
Program: _____________
Flat
Average =
Standard deviation =
Flat
Average =
Standard deviation =
Remark: _____________________________________________________________
Report to be submitted:
(1) Fill in data for standard cleaning in the lab description for those that are relevant
(2) Sketch the cross-section of the entire wafer
(a) after step 10
(b) after step 11
(c) after step 12
(3) Answer the following questions:
Step 10:
1) You are using the HF dip in the standard clean process to remove the buffer oxide. How would you monitor the
end-point?
2) It is better to over-etch a bit to ensure complete removal of the buffer oxide. However, what problem it might
cause if you do too much (say 100%) over-etch?
Step 11:
3) The gate oxide thickness of MOSFETs is critical. What problem it may cause if the oxide thickness differ from
the targeted value?
4) What would you do if the gate oxide thickness is too thin?
5) What would you do if the gate oxide thickness is too thick?
Step 12:
6)
7)
8)
9)
10)
In picking the polysilicon thickness, what factors have you considered?
What problem it may cause if the polysilicon is too thin?
What would you do if you found the polysilicon you deposited is too thin?
What problem it may cause if the polysilicon is too thick?
What would you do if the polysilicon thickness you deposited is really too thick?