Specific Process Knowledge/Etch/ICP Metal Etcher/silicon oxide

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This page is written by Berit Herstrøm @ DTU Nanolab (BGHE) if nothing else is stated

SiO2 etching in the ICP metal

It is possible to etch SiO2 in the ICP metal etcher but it is not designed for it and we prefer that you do it elsewhere. It is a challenge to get a good selectivity to resist (typically in the range of 1:1 or worse) and it is probably not possible to get a profile angle of 90 degrees. More likely about 75-85 degrees. Different chemistries can be applied either based on CF4 or C4F8. If seems that C4F8 can give the best selectivity to resist (best case I have seem was 1:11 but it depends a lot on the process parameters)). If low coil power is needed CF4 chemistry is used because C4F8 needs a higher power to generate a plasma. /bghe 2016-04-25

Slow etch of SiO2 with resist as masking material - using a 6" carrier wafer with recess

This recipe can be used for slow etching of SiO2 with resist as masking material. Here are some test results presented.

Parameter Resist mask
Coil Power [W] 200
Platen Power [W] 25
Platen temperature [oC] 0
CF4 flow [sccm] 20
H2 flow [sccm] 10
Pressure [mTorr] 3


Results Test on wafer with 50% load (Travka 50), by BGHE @nanolab 100% load on 100mm wafers with Barc and KRF (no mask)
Etch rate of thermal oxide 44.1 nm/min (50% etch load) (01-02-2014)
Selectivity to resist [:1] ~0.9 (SiO2:resist) ~1.25:1 (Barc:KRF)
Etch rate in silicon

bghe@Nanolab 20190117

  • 33.8 nm/min (middle of wafer with 80% load) bghe@Nanolab 20190117
  • 34.3 nm/min (edge of wafer with 80% load)
Wafer uniformity (100mm) ±1.6% (01-02-2014)
Profile [o] Take a look at the images but be aware that the resist profile was not good to begin with.
Wafer uniformity map (click on the image to view a larger image)
Contour plot of the etch rate over the wafer, 9 points measured
SEM profile images
Etch rate in barc 50 nm/min (2014-09-09)
Etch rate in KRF resist 40 nm/min (2014-09-09)


SiO2 etch using DUV mask

Two chemistry regimes has been explored: One using CF4 and one using C4F8

  • CF4: bad selectivity to the resist mask.
  • C4F8: Better selectivity to the resist mask can be achieved


Parameter Recipe on ICP metal: A SiO2 etch with C4F8 with resist mask
Coil Power [W] 1000
Platen Power [W] 200
Platen temperature [oC] 0
C4F8 flow [sccm] 10
H2 flow [sccm] 28
Pressure [mTorr] 2.5


Results Test
Etch rate of thermal oxide
  • 145-172 nm/min by bghe@nanolab (2015-06-02)
  • 145 nm/min by Martin Lind Ommen (fall 2016)
Selectivity to resist [:1] 4-5:1 (SiO2:resist) by bghe@nanolab (2015-06-02)
Cr etch rate 1.6 nm/min (1:90 to SiO2) by Martin Lind Ommen (fall 2016)
Profile [o] 86-87 dg by bghe@nanolab (2015-06-02)
Wafer uniformity map (click on the image to view a larger image)
SEM profile images
by bghe@nanolab (2015-06-02)
Etch rate in barc
Etch rate in KRF resist 34 nm/min by bghe@nanolab (2015-06-02)
Comments
  • Sample: s007592 by bghe@nanolab (2015-06-02)
  • See Martin Lind Ommen's results with hard masks: [1]
    There were problems with polymer on the surface after etching.


SiO2 etch nLOF

Parameter Resist mask
Coil Power [W] 800
Platen Power [W] 100
Platen temperature [oC] 0
CF4 flow [sccm] 30
H2 flow [sccm] 10
Pressure [mTorr] 4


Results Test on wafer with 50% load (Travka 50), by BGHE @nanolab
Etch rate of thermal oxide >110 nm/min (50% etch load) (09-03-2015)
Selectivity to resist [:1] <0.7:1 (SiO2:resist)
Wafer uniformity (100mm) Not known
Profile [o] Not known
Wafer uniformity map (click on the image to view a larger image) Not known
SEM profile images NONE
Etch rate in nLOF resist 1.6µm was removed after 10min
Comment After 10min etch the resist was gone and the etch depth as 1.145µm in the oxide


SiO2 etch with e-beam resist


Parameter Resist mask
Coil Power [W] 800
Platen Power [W] 150
Platen temperature [oC] -10
C4F8 flow [sccm] 8
H2 flow [sccm] 30
Pressure [mTorr] 2.5


Results Test on 6" wafer, by Peixiong Shi@nanolab
Etch rate of thermal oxide 131 nm/min (15-01-2014)
Selectivity to resist [:1] ~1.8:1 (SiO2:resist)
Profile [o] Not measured
Wafer uniformity map (click on the image to view a larger image) Not known
SEM images