More test with CF4/H2 - SiO2 etch
Tests performed by Maria Farinha @DTU Nanolab
The gas flows were combined and the following results were achieved. It´s visible that with higher CF4 the selectivity is not good, so by adding H2, until 1:1, the selectivity improves. Additionally, the uniformity gets slightly worse while going for 1:1 of gas chemistry.
The recipe CF4lowCP 22.5/22.5 seems to be the only one good enough to use. It is a slow etch recipe, with good selectivity with AZ5214E resist.
CF4ICP
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SiO2 ER (nm/min)
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Uniformity (SiO2 etch)
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Selectivity (SiO2:resist)
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Si3N4 ER (nm/min)
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SixN ER (nm/min)
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45 CF4 + 0 H2
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71.4
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11.7%
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0.74
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-
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-
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35 CF4 + 10 H2
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69
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12.6%
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0.89
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-
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-
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22.5 CF4 + 22.5 H2
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58.6
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13.3%
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1.43
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84.4
|
42.9
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- The uniformity considers a 100mm wafer, calculated with 5 points.
CF4lowCP
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SiO2 ER (nm/min)
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Uniformity (SiO2 etch)
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Selectivity (SiO2:resist)
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Si3N4 ER (nm/min)
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SixN ER (nm/min)
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45 CF4 + 0 H2
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24.9
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11.5%
|
0.47
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-
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-
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35 CF4 + 10 H2
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22.6
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11.6%
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0.64
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-
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-
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22.5 CF4 + 22.5 H2
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17.8
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13.7%
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1.85
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28
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22.5
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Profile pictures of some tests - April 2023
Even in the cases with the resist strip (plasma asher 2 processing for 10/15min), there are some traces of resist left on the edges of the features.
Also, it´s noticeable that the feature profile is trenching, being more evident with faster etch rates.
CF4ICP 45 CF4 + resist strip
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CF4ICP 45 CF4 / 10 H2 + resist strip
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CF4ICP 35 CF4/ 10 H2
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CF4lowCP 45 CF4/ 10 H2
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CF4lowCP 45 CF4/ 0 H2 + resist strip
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CF4lowCP 35 CF4/ 10 H2 + resist strip
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CF4lowCP 22.5 CF4/ 22.5 H2 + resist strip
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Recipes and results - CF4 / H2 tests
Recipe
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Recipe parameters
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Process time
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Date
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SEM picture
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Etch rate in SiO2
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Etch rate in resist (AZ5214E inverse)
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Selectivity (SiO2:resist)
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CF4ICP 22.5/22.5
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CF4= 22.5 sccm H2= 22.5 sccm Coil= 800W Platen= 15W Press= 2.5mTorr Temp= 20°C
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11:00 min
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11/09/2023
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68 nm/min +/- 8.5%
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60,2 nm/min +/- 9%
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1.13
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CF4ICP 35/10
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CF4= 35 sccm H2= 10 sccm Coil= 800W Platen= 15W Press= 2.5mTorr Temp= 20°C
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08:00 min
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March 2023
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69 nm/min +/- 11.1%
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77,1 nm/min +/- 9.4%
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0.9
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CF4ICP 45/0
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CF4= 45 sccm H2= 0 sccm Coil= 800W Platen= 15W Press= 2.5mTorr Temp= 20°C
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08:00 min
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March 2023
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71.4 nm/min +/- 10.3%
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96,5 nm/min +/- 6.0%
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0.74
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CF4ICP 45/10
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CF4= 45 sccm H2= 10 sccm Coil= 800W Platen= 15W Press= 2.5mTorr Temp= 20°C
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08:00 min
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March 2023
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67.8 nm/min +/- 14.9%
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88,86 nm/min +/- 4.8%
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0.76
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CF4lowCP 22.5/22.5
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CF4= 22.5 sccm H2= 22.5 sccm Coil= 150W Platen= 25W Press= 2.5mTorr Temp= 20°C
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20:00 min
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Sept 2023
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23.8 nm/min +/- 11%
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20,6 nm/min +/- 19.4%
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1.16
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CF4lowCP 35/10
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CF4= 35 sccm H2= 10 sccm Coil= 150W Platen= 25W Press= 2.5mTorr Temp= 20°C
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10:00 min
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Feb 2023
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22.65 nm/min +/- 10.2%
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35.9 nm/min +/- 10.1%
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0.63
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CF4lowCP 45/0
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CF4= 45 sccm H2= 0 sccm Coil= 150W Platen= 25W Press= 2.5mTorr Temp= 20°C
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10:00 min
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Feb 2023
|
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24.9 nm/min +/- 10.1%
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52,3 nm/min +/- 7.1%
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0.47
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CF4lowCP 45/10
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CF4= 45 sccm H2= 10 sccm Coil= 150W Platen= 25W Press= 2.5mTorr Temp= 20°C
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10:00 min
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Feb 2023
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29,4 nm/min +/- 13.7%
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100,6 nm/min +/- 16.5%
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0.29
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Recipes and results - CF4 / H2 tests
The following results were processed on chips bonded to a 100mm wafer. They were patterned with 915 UVN resist (DUV negative) and 65nm of BARC. The SiO2 layer was 2um (deposited on the C1 furnace).
CF4ICP @ 30W platen, 8min
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Values
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SEM pictures
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Comments
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Structure size (nm)
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structure pitch (nm)
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SiO2 ER (nm/min)
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Resist ER (nm/min)
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Selectivity SiO2/resist
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|
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250
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500
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69.36
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114.38
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0.61
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Across the sample, the resist was fully etched away
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500
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1000
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87.04
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114.38
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0.76
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|
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1000
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2000
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98.83
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114.38
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0.86
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2000
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4000
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100.03
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114.38
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0.87
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CF4lowCP @ 45W platen, 15min
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Values
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SEM pictures
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Comments
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Structure size (nm)
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structure pitch (nm)
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SiO2 ER (nm/min)
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Resist ER (nm/min)
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Selectivity SiO2/resist
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|
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250
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500
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33.54
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33.45
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1.0
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there was visible redeposition across smaller structures
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500
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1000
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35.94
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30.45
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1.18
|
|
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1000
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2000
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36.54
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29.85
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1.22
|
|
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2000
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4000
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38.09
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28.65
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1.33
|
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