Specific Process Knowledge/Thermal Process/Dope with Phosphorus
The furnace A4 phosphorus predep(N-predep) can be used to predeposit silicon wafers with phosphor. The silicon wafers are positioned in a quarts boat. Phosphor is predeposited in the silicon wafers.
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Test of Phosphorus Predep furnace
Purpose
To study the coherence between the temperature of the Predep and dive-in for doping with phosphorus in DTU-Danchip Phosphorus Predep furnace (A4).
Experiment setup
There was used 20 boron doped wafers (p-type). There was used four wafer to the five different temperature. There was five dummy wafers on each side of the test wafers. The dummy wafer nearest to the test wafers was changed in between the runes so doping from a dummy wafer was minimized.
| Run # | Temperature | Process time with POCl3 | Anneal time in N2 | Wafer # |
| 1 | 850 oC | 15 minutes | 20 miuntes | 1, 2, 3, 4 |
| 2 | 900 oC | 15 minutes | 20 miuntes | 5, 6, 7, 8 |
| 3 | 950 oC | 15 minutes | 20 miuntes | 9, 10, 11, 12 |
| 4 | 1000 oC | 15 minutes | 20 miuntes | 13, 14, 15, 16 |
| 5 | 1050 oC | 15 minutes | 20 miuntes | 17, 18, 19, 20 |
After the Predep was two wafer from each run taken out to be further processed. The wafers was 1, 2, 5, 6, 9, 10, 13, 14, 17, 18.
These wafers was dipped in BHF to get the phosphorus glass layer of before the Drive-in process. The Drive-in process was made in Danchip Phosphorus Drive-in furnace (A3). There was a dummy wafer in between the wafers from different temperatures so doping from wafer to wafer was minimized. The Drive-in was done with the process "DRY1050" with is a dry oxidation at 1050 oC for 100 minutes and 20 minutes annealing. At the oxdation was the O2 flow was 5 SLM and N2 flow for annealing was 3 SLM.
Test measurement
There was made several measurement on the different wafer in the process. After the Predep was the Phosphorus glass layer thickness measured and the sheet resistance and slice resistivity measured on the same after a BHF etch.
| Elipsometer | Four Point Probe | |||
|---|---|---|---|---|
| Wafer # | Thinkness [nm] | Refrative index | Sheet resistance [Ωsq] | Slice Resistivity [Ωcm] |
| 3 | 27,4 | 1,4623 | 311 | 17,32 |
| 7 | 45,27 | 1,4622 | 138,5 | 7,61 |
| 11 | 61,36 | 1,4625 | 16,12 | 0,859 |
| 15 | 80,45 | 1,4624 | 7,4 | 0,392 |
| 19 | 119,37 | 1,4623 | 6,6 | 0,246 |