Specific Process Knowledge/Thermal Process/Dope with Phosphorus: Difference between revisions
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{{cc-nanolab}} | |||
'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/Specific_Process_Knowledge/Thermal_Process/Dope_with_Phosphorus click here]''' | |||
The Phosphorus Predep furnace (A4) can be used for phosphorus pre-deposition of silicon wafers, resulting in n-type doping. In the furnace, the silicon wafers are positioned vertically in a quarts boat. | |||
''' | ''' | ||
==Test of the Phosphorus Predep furnace== | ==Test of the Phosphorus Predep furnace== | ||
====Purpose==== | ====Purpose==== | ||
''' | ''' | ||
To study the correlation between the temperature for the predeposition process and drive-in of the phosphorus doping in the Phosphorus Predep furnace (A4) at DTU | To study the correlation between the temperature for the predeposition process and drive-in of the phosphorus doping in the Phosphorus Predep furnace (A4) at DTU Nanolab. | ||
''' | ''' | ||
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====Experimental setup==== | ====Experimental setup==== | ||
''' | ''' | ||
20 boron doped device wafers (p-type) were used - Four wafers for each of the five different predeposition temperatures (see table below). In the furnace five dummy wafers were placed on each side of the device wafers. The dummy wafers nearest to the device wafers were changed in-between the runs to | 20 boron doped device wafers (p-type) were used - Four wafers for each of the five different predeposition temperatures (see table below). In the furnace five dummy wafers were placed on each side of the device wafers. The dummy wafers nearest to the device wafers were changed in-between the runs to minimize doping from these dummy wafers. | ||
{| border="1" cellspacing="1" cellpadding="2" style="text-align:center;" width="690" ||3||4||5 | {| border="1" cellspacing="1" cellpadding="2" style="text-align:center;" width="690" ||3||4||5 | ||
!| Run #||Temperature||Process time with POCl<sub>3</sub>||Annealing time in | !| Run #||Temperature||Process time with POCl<sub>3</sub>||Annealing time in O<sub>2</sub>||Wafer # | ||
|- | |- | ||
|1||850 <sup>o</sup>C||15 minutes||20 | |1||850 <sup>o</sup>C||15 minutes||20 minutes||1, 2, 3, 4 | ||
|- | |- | ||
|2||900 <sup>o</sup>C||15 minutes||20 | |2||900 <sup>o</sup>C||15 minutes||20 minutes||5, 6, 7, 8 | ||
|- | |- | ||
|3||950 <sup>o</sup>C||15 minutes||20 | |3||950 <sup>o</sup>C||15 minutes||20 minutes||9, 10, 11, 12 | ||
|- | |- | ||
|4||1000 <sup>o</sup>C||15 minutes||20 | |4||1000 <sup>o</sup>C||15 minutes||20 minuntes||13, 14, 15, 16 | ||
|- | |- | ||
|5||1050 <sup>o</sup>C||15 minutes||20 | |5||1050 <sup>o</sup>C||15 minutes||20 minutes||17, 18, 19, 20 | ||
|} | |} | ||
''' | ''' | ||
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! width="130" | Temperature [C] | ! width="130" | Temperature [C] | ||
! width="130" | Oxide thickness [nm] | ! width="130" | Oxide thickness [nm] | ||
! width="130" | | ! width="130" | Refractive index | ||
! width="150" | Sheet resistance [Ω<sub>sq</sub>] | ! width="150" | Sheet resistance [Ω<sub>sq</sub>] | ||
! width="150" | Slice Resistivity [Ωcm] | ! width="150" | Slice Resistivity [Ωcm] | ||
| Line 106: | Line 108: | ||
! width="130" | Temperature [<sup>o</sup>C] | ! width="130" | Temperature [<sup>o</sup>C] | ||
! width="130" | Oxide thickness [nm] | ! width="130" | Oxide thickness [nm] | ||
! width="130" | | ! width="130" | Refractive index | ||
! width="150" | Sheet resistance [Ω<sub>sq</sub>] | ! width="150" | Sheet resistance [Ω<sub>sq</sub>] | ||
! width="150" | Slice Resistivity [Ωcm] | ! width="150" | Slice Resistivity [Ωcm] | ||
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|} | |} | ||
Looking at the "SIMS Measurement After Drive-in Process at 1050 <sup>o</sup>C" graph, it can be seen that the two curves "Pre-dep at 950 <sup>o</sup>C" and "Pre-dep at 1000 <sup>o</sup>C" are crossing each other, but according to the theory they should not do that. Only one wafer has been | <br clear="all" /> | ||
Looking at the "SIMS Measurement After Drive-in Process at 1050 <sup>o</sup>C" graph, it can be seen that the two curves "Pre-dep at 950 <sup>o</sup>C" and "Pre-dep at 1000 <sup>o</sup>C" are crossing each other, but according to the theory they should not do that. Only one wafer has been measured so there is not that much statistical data to verify it with. | |||
<br clear="all" /> | |||
==Test of the Phosphorus Predep furnace== | ==Test of the Phosphorus Predep furnace== | ||
====Purpose==== | ====Purpose==== | ||
To find the result of a specific process using the Phosphorus Predep furnace (A4) followed by a drive in and oxidating the substrate in the | To find the result of a specific process using the Phosphorus Predep furnace (A4) followed by a drive in and oxidating the substrate in the Phosphorus drive in furnace (A3). | ||
''' | ''' | ||
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After removing the oxide in BHF the wafers were oxidized in Phosphor Drive in Furnace (A3) using DRY1050 at 1050°C for 70 min without further annealing in N<sub>2</sub>. Results are listed in the table below: | After removing the oxide in BHF the wafers were oxidized in Phosphor Drive in Furnace (A3) using DRY1050 at 1050°C for 70 min without further annealing in N<sub>2</sub>. Results are listed in the table below: | ||
====Results==== | |||
{| border="2" cellpadding="2" cellspacing="1" style="text-align:center;" | {| border="2" cellpadding="2" cellspacing="1" style="text-align:center;" | ||
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<br clear="all" /> | <br clear="all" /> | ||
''Result from GreenBelt, @nanolab,Jan 2015'' | |||
<br clear="all" /> | |||
==Test of the Phosphorus Predep furnace== | ==Test of the Phosphorus Predep furnace== | ||
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'''Wet oxidation in Furnace (C1):''' WET1050, 30 min, no further anneal | '''Wet oxidation in Furnace (C1):''' WET1050, 30 min, no further anneal | ||
====Results==== | |||
The wafer was analyzed with SIMS and the profile is shown on the graph below: | The wafer was analyzed with SIMS and the profile is shown on the graph below: | ||
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<br clear="all" /> | <br clear="all" /> | ||
==Phosphorous doping test after hardware and software upgrades== | |||
In 2022, the POCl<sub>3</sub> line on the furnace was modified to make the setup more safe. At the same time some software changes were also made, and the recipes on the furnace were updated. | |||
Afterwards, a phosphorus doping test was made to see, if the modification had affected the phosphorus doping process. The test was done with a test wafer and four dummy wafers (two dummy wafers on each side of the test wafers) in the furnace. | |||
====Process:==== | |||
* RCA cleaning of the test wafer (p-type, 1-20 Ωcm) and the dummy wafers | |||
* Phosphorus pre-deposition in the Phosphorus Pre-dep furnace (A4). | |||
** Recipe: "POCL900" | |||
** Temperature: 900 °C | |||
** Time: 15 min phosphorus pre-dep and 20 min annealing/N<sub>2</sub> post purge | |||
* BHF dip in the RCA cleaning bench to remove phosphorus glass from the test wafer | |||
* Measure sheet resistance using the 4-point proble | |||
====Results:==== | |||
After the process describe above, the sheet resistance on the test wafer was measured. | |||
The sheet resistance was 54 Ωsq in the center of the wafer and 45-48 Ωsq in the edge of the wafer. This correspond quite good to the results that previously had been obtained for the furnace as can be seen on this LabAdviser page. | |||
====Notes about the POCL recipes==== | |||
A new recipe for POCL doping called was made, after the POCl<sub>3</sub> line was modified. The N<sub>2</sub> high flow (3 SLM) is on all the time through the recipe. There is a 2 min pre-purge with first N2 low (150 sccm) through the POCl3 bubbler, i.e. with the valves v4a and v4b closed, and then with O2 (0.50 SLM), before the pre-deposition time starts. After the pre-deposition, an N2 low post-purge (500 sccm) is done for 2 minutes with v4a and v4b closed. | |||
For safety reasons it is important that the POCl<sub>3</sub> is completely removed from the furnace, before it is opened to load or unload wafers. | |||
With 150 sccm N2 low through 25°C POCl<sub>3</sub> liquid + 3 slm N<sub>2</sub> high + 0.5 slm O<sub>2</sub>, 3300 ppm Cl<sub>2</sub> is created in the tube. These 3300 ppm Cl<sub>2</sub> must be diluted to less than 0.5 ppm (the TLV value). | |||
The tube diameter is 16 cm and the length without ball valve is about 125 cm, and thus the volume is about 25 L. After the phosphorus pre-deposition step, the N<sub>2</sub> high flow (3 SLM) is on during the annealing/N<sub>2</sub> post purge, the cooling and a waiting step. The time for the waiting step is 30 minutes, so even if the annealing time is set to 0 minutes, and the furnace does not have to cool down, there will still be an N<sub>2</sub> high flow for 30 minutes to remove the POCl<sub>3</sub> from the furnace. The waiting time is the same in the abort recipe that is activated, if the POCL doping recipe is aborted. | |||
The recipe can be modified with other temperatures and names. | |||