Specific Process Knowledge/Thermal Process/Dope with Phosphorus
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The Phosphorus Predep furnace (A4) can be used for predeposition of silicon wafers with phosphorus doping (N-type). In the furnace, the silicon wafers are positioned in a quarts boat.
Test of the Phosphorus Predep furnace
Purpose
To study the coherence between the temperature for the predeposition process and drive-in of the doping with phosphorus in the Phosphorus Predep furnace (A4) at DTU Danchip.
Experimental setup
20 boron doped wafers (p-type) was used. Four wafer to each of the five different predeposition temperatures. In the furnace was there five dummy wafers on each side of the processed 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.
Result
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 wafer after a BHF etch.
| Ellipsometer (center point only) | Four Point Probe | ||||
|---|---|---|---|---|---|
| Wafer # | Temperature [C] | Thinkness [nm] | Refrative index | Sheet resistance [Ωsq] | Slice Resistivity [Ωcm] |
| 3 | 850 | 27,4 | 1,4623 | 311 | 17,32 |
| 7 | 900 | 45,27 | 1,4622 | 138,5 | 7,61 |
| 11 | 950 | 61,36 | 1,4625 | 16,12 | 0,859 |
| 15 | 1000 | 80,45 | 1,4624 | 7,4 | 0,392 |
| 19 | 1050 | 119,37 | 1,4623 | 6,6 | 0,246 |
| Avg. five point on Filmtek | Four Point Probe | ||||
|---|---|---|---|---|---|
| Wafer # | Temperature [C] | Thinkness [nm] | Refrative index | Sheet resistance [Ωsq] | Slice Resistivity [Ωcm] |
| 2 | 850 | 110,44 | 1,4654 | 189,7 | 13,06 |
| 6 | 900 | 116,28 | 1,4629 | 101,6 | 5,32 |
| 9 | 950 | 137,06 | 1,4604 | 10,05 | 0,527 |
| 14 | 1000 | 141,46 | 1,4651 | 4,72 | 0,216 |
| 18 | 1050 | 139,87 | 1,4659 | 3,23 | 0,165 |
| Test | 110,71 | 1,46286 | - | - | |
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Looking at the 'SIMS Measurement after Drive-in Process at 1050 C' it can be seen that 'Pre-dep at 950 C' and 'Pre-dep at 1000 C' are crossing each other but they should not do that. There have only been meassured on one wafer so there is not that mush statistical data to verify it with.