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, resulting in N-type doping. 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) were used - Four wafers for each of the five different predeposition temperatures. In the furnace five dummy wafers were placed on each side of the processed wafers. The dummy wafer nearest to the test wafers were changed in-between the runs to miniminze doping from this dummy wafer.

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 predeposition two wafers from each run were taken out to be further processed. These wafers were: 1, 2, 5, 6, 9, 10, 13, 14, 17, 18.

These wafers were dipped in BHF to remove the phosphorus glass layer before the drive-in process. The drive-in process was made in the Phosphorus Drive-in furnace (A3). At the drive-in process a dummy wafer was placed 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 oxidation was the O₂ flow was 5 SLM, and the N₂ flow for annealing was 3 SLM.

Result

Several measurements were done for the different wafers in the process. After the pre-deposition thickness of the Phosphorus glass layer was 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.