Specific Process Knowledge/Thermal Process/Dope with Phosphorus

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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.

Test of Phosphorus Predep furnace

Purpose

To study the coherence between the temperature for the predeposition process and dive-in of the doping with phosphorus in DTU-Danchip Phosphorus Predep furnace (A4).

Experiment 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.

Measurement after Predeposition

		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

Measurement after Drive-in

		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	-	-

Resistivity	Sheet resistance
SIMS Measurement After Pre-dep	SIMS Measurement After Drive-in Process at 1050 C

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.