2014-01

2014-01Edit

mardi 14/01

BPCD7_3, second half of the chip
Check the hypothesis of PMGI development issue
in 'vieux canon':

ion mill 500V, 3mA, 2x10" @ +/- 22°
vertical evaporation of 30nm gold @1nm/s

lift-off remover PG 60°C 20' and 2 x 1 second US and rinse in H2O, N2 blow dry.

Taking SEM pictures of the Au lines, see BPCD7-3 all photos.pdf

observation XL40:

Conclusions:
-3 line is wider than the 70 nm line.
-none of the 1 line existed.
-designed 70 nm line with relative dose 1.1 was not visible.
-comparing this to result of BPCD7-3 first part shows that it is unlikely that the gold grains are blocking the opening of the line in the PMMA.
-measured linewidth (i.e. Au linewidth) is only around 30 percent larger than the designed linewidth.
 

BPCD7_4 (change developper)
Expo XL30 300µC/cm2 - 1200pC/cm
dev @19°C:

MIBK+IPA (1+3) 1'30
rinse IPA 30"
no dry
rinse ODI 15"
MIF726 1'
rinse ODI 1'
dry N2

optical obs:
No big difference than with MFCD26: the single line seems to have residues whatever the dose; all other patterns seem OK, except for smallest dose. Usual observations remain the same.

No clear conclusion as long as we have not observed in SEM under angle, but MIF726 seems similar to CD26 on first approach.

BPCD7_5 (dose tests true pattern)
New pattern for dose test of true design

(add drawings)
Expo XL30 300µC/cm2 - 1200pC/cm
dev @19°C: same as previously

mercredi 15/01

in 'vieux canon':

ion mill 500V, 3mA, 2x10" @ +/- 22°
double angle evaporation of 30nm gold @1nm/s +/- 22°

lift-off remover PG 60°C 20' and several seconds US (rinse ODI)

obs XL30:
- the long PMMA strip between the gates and the island is deformed during development, and sticks to the PMMA wall next to it. As a consequence, one pattern is widened and deformed, the next pattern is closed.
- otherwise most single line (vertical) are here for all doses, comforting the previous interpretation of mask blocking by PMGI residues. (Now the PMGI is evacuated on large openings close to the small designs)
- single vertical lines are in the range 30 - 55nm
- the second evaporation is absent on most designs, and first evaporation in the range 25 - 60nm (for 3 lines design as well as for 70nm polygon design). Very convenient!

BPCD7_6 (dose test true pattern)
Slightly modify the design:
- increase the gap between island and gate (the PMMA strip width)
- add a new design which has strips of PMMA lateraly to decrease the long strips aspect ratio

(add drawings)

Change exposure sequence of polygons from 'meander' to 'line'. Supposed to have better resolution, but longer settling time.
Expo XL30 300µC/cm2 - 1200pC/cm (20.5pA)
dev @19°C:

MIBK+IPA (1+3) 1'30
rinse IPA 30"
no dry
rinse ODI 15"
MIF726 1'
rinse ODI 1'
rinse ethanol 15"
very very gently dry N2

in 'vieux canon':

ion mill 500V, 3mA, 2x10" @ +/- 22°
double angle evaporation of 30nm gold @1nm/s +/- 22°

jeudi 16/01

lift-off remover PG 60°C 30' and barely 1 second US (rinse ODI)

obs XL40:
- still the same problem of strip deformation (exact same statistics), although additional care was taken during development.
- 1 pattern has resisted this issue: the dose 11 pattern l2,c2 (polygons of 70nm wide and a gap of XXnm between the gates and the island). This is reproducible for the 2 exposure done on this sample, so maybe this design is more robust to development than others.
- Some junctions appear with typical sizes 40x40, 50x50
- There is, as previous tests on 07/2013, a strong asymetry between left arm and right arm of the design, the right end of the island thinned by 10-20nm as comapred to the left end, same for the upper part of the loop but inverted.
don't really understand why looking at the design (constraints on PMMA mask? way the exposure sweep is done?) but pragmatically, we have to change dose and or design on these parts to account for it.
- vertical part of the island is more reproducible in polygon than in single wire
- the dashed strips have functionned (the patterns have the correct shape) however, the PMMA mask is too thick, and there is a huge shadowing effect -> no overlapping between the 2 evaporations, and result in multiple islands, not wanted even for the gates (coulomb blockade)
-

- to complete, images to put

BPCD7_7 (dose test true pattern)
Slightly modify the design:
- hybrid design: vertical part of the island is more reproducible

- images of designs to put

Expo XL30 300µC/cm2 - 1200pC/cm (20.5pA)
dev @19°C: same as previous

in 'vieux canon':

ion mill 500V, 3mA, 2x10" @ +/- 22°
double angle evaporation of 30nm gold @1nm/s +/- 22°

vendredi 17/01

lift-off remover PG 60°C 20' and barely 1 second US (rinse ODI)

obs -> BPCD7_7.zip

- to complete, images to put

lundi 20/01

BPCD7_8 (oxidation)
Arrange design according to previous observations.
/!\ No order /!\
polygon exposure type: "meander"
see file for designs and SEM observations

30keV, 300µC/cm2, 1200pC/cm
x2000 (Small patterns, layer 2) : spot 1, 20.6pA, 
    line dwell (1nm, ~2.3µs), area dwell (4nm, ~5.8µs)
x1000 (mid connections, layer 3) : spot 4, 0.375nA, 
    area dwell (18nm, ~2.6µs) (dose factor x1.2 on playlist)
x32 (large pads, layer 1) : spot 7, 49.2nA (41.6nA on sample, no drift during expo), 
    area dwell (188nm, ~2.2µs)  (dose factor x1.6 on playlist)

dev : same as previous

evap: Pumping over night

mardi 21/01

In vieux canon (Pch = 1.7e-7mb)

ion mill 500V, 3mA, 2x10" @ +/- 22°
Al 30nm @ 1nm/s (Pchamber = 4.3e-7mb, Psas = 8e-7mb) @ +22°
Dynamic oxidation, 100µb (8e-2 Torr), 5' 
Al 60nm @ 1nm/s (Pchamber = 4.3e-7mb, Psas = 9e-7mb) @ -22°

lift-off: same as previous

obs XL30 UHR, 20keV spot 3:
- All PMMA strips have performed very well: the widening of the gates was a good idea. Gap ~100nm as designed -> can try to get pads closer (try 70nm)
- Problem with the second evaporation of the island edge box: makes an isolated island (unwanted)

Measurement in probe station:
- bottom junction (47*62 nm): 31kΩ -> 90 Ω.µm²
- middle squid (left junction: 48*36nm ; right junction: 48*73nm): 11kΩ -> 57 Ω.µm²

Note: according to Simon S. and Denis V. the resistance of the junctions are modified by SEM observation. Either they get shorted or they increase, within 10% of their initial value.

mercredi 22/01

BPCD7_9 (test oxidation)
expo XL30
Arrange design according to previous observations.
ORDER gds avant expo
polygon exposure type: "line" pour champ x200, "meander" pour le reste (fait un HALT dans la position list)

sap
spot 1, 20.5pA
spot 4, 0.370nA
spot 7, 48nA (40.5nA on sample, 39.9nA at end of expo)

see file for designs and SEM observations

dev : same as previous ("sap")
evap: sap. Less pumping (over lunch time) -> Psas ~ 1e-6mb during both evap

Dynamic oxidation, 150µb (1.15 e-1 Torr), 5'

lift-off sap

Measurement in probe station:
(before SEM observation)
- top junction (42x65nm) 30kΩ -> 82 Ω.µm²
- bottom junction (47x59nm) 29.2kΩ -> 81 Ω.µm²
(after SEM observation)
- top junction 29.6kΩ (-1.5%)
- bottom junction 27.9kΩ (-4.5%)

Observation UHR XL30, 20keV, spot 3

Conclusions
- designs are not completely satisfying yet, several modifications to do:
    strenghten the link between the horizontal and vertical part of the island
    improve the asymetry of the junctions (remove the second line on the right arm and increase the dose of the remaining -> at least 1.5, from previous test BPCD7_7)
    find a trick to evacuate PMGI from the end of the wire without having to add a pad (undesired island on second evap) -> develop more?? increasing the arm's length could help (tested on 1,2 but this design is missing)
- Can achieve a gap of 50nm over 1.5µm !!

- the oxidation level is perfect

jeudi 23/01

I'm convinced we will get the expected results with PMGI / PMMA, so I'll process the BPC1 wafer, and cut the 2 wafers (BPCT1) together on diamond saw (LPN)

Bilayer spin

spin PMGI SF8 (batch 1206047, exp. 7/1/2013) @ 3000rpm 60"
bake hot plate 170°C (measured: 159.6°C, same at different places), 5'
spin PMMA A6 (batch 11060394, exp. 7/1/2012) @ 6000rpm 60"
bake hot plate 170°C, 15'
spin UV III (bouteille vivien) @ 4000rpm 60"
bake hot plate 140°C, 90"

NB: temperature fluctuations (left hot plate on 'lithographie 2') can be important, excursions down to 156°C have been seen. Not during the bake though, fortunately.

vendredi 24/01

Cleave some samples out of wafer BPCT1 (the left edge, 5 chips in total, designed for CSNSM RF holder)

Arrange design and position list to expose a true chip (with 4 test junctions in each corner of the chip and a x1000 field to do some design tests)

lundi 27/01

BPCT1_1
Trying to expose mouton (wafer BPCT1) using design step2_CPB1_CS (designed for CSNSM RF holder).

Expo XL30 sap (20.5pA)
dev: sap

Observation: The whole write field (either 48x48 or 96*96 um^2) seems to be exposed as the resist collapsed in this area and cracks can be seen in the PMMA-layer.

BPCT1_2
repeat the same thing, same behavior.

see file for scans of the optical pictures

Could be due to :
- during the alignement procedure, the field is exposed entirely which provokes solubility of the PMGI layer. (but strange! has to be linked to a spin issue as well)
- the wafer was not baked properly.
- the thickness are very different from wafer BPCD7 (since we took chips from the edges)

mardi 28/01

Test if alignment procedure is causing the problem of overexposure:
BPCD7_10
Exposing design "singleJJ" on a BPCD7 using the exact same alignement procedure to check for overexposure problem.

Expo XL30 sap
dev sap

MIF726 1'

Observation: only alignment marks and the design itself were exposed and not the whole writefield. This is what we expected.

In a next step it is necessary to check if the thicknesses of the resists are correct on BPCT1. So we used the failed sample from 27/01 and cleaved it and sputtered Au for 30" before taking SEM images -->  BPCT1_2.zip

BPCT1_2
Cleave it and observe it under angle in XL40
Observation: PMMA is around 250nm and PMGI around 620nm thick. The thickness of the Nb layer is around 140nm. That seems alright keeping in mind that resists shrinks a bit during the time we took pictures.

mercredi 29/01

BPCT1_3
Test if there was something wrong on the position list -> Do a completely new position list (same orders)
expo sap 
dev now we also test the evolution, so we stop first at 15" MIF726.
The working area still shows interference patterns (indicating a non uniform PMMA thickness), but the undercut is quite small (<1µm) indicating a decrease in PMMA thickness only. There are cracks on the edges of the PMMA.

Then we add 15" MIF726. Now the undercut is huge, and the interferences are even more pronouced. The cracks have extended.

Everything indicates that the layer has not been baked properly

BPCT1_4 & 5
Bake the last 2 samples 170°C for 15'
expose BPCT1_4 sap
dev sap, only 15" MIF726
-> NO cracks in PMMA, no interference patterns
Add 45" : catastrophe, again (but cracks are not as present as before, looks better than previous tests 1 and 2)

jeudi 30/01

BPCT1_5
expose sap
dev sap 30" MIF
see optical observations below

evap

Heat Al source 1h @ 160mA during pumping to desorb it
Pi_ch = 1.1e-7mb, Pi_sas = 6e-7mb
ion mill 500V, 3mA, 2x10" @ +/- 22°
Flash Ti (~150nm @ 0.5nm/s) Pi_ch = 1.3e-7, Pi_sas = 6e-7; Pf_ch = 3.8e-8, Pf_sas = 4e-7
Al 30nm @ 1nm/s (Pchamber = 1.4e-7mb, Psas = 5e-7mb) @ +22°
Dynamic oxidation, 150µb (1.1e-1 Torr), 5'
Flash Ti (~75nm @ 0.5nm/s) Pi_ch = 1e-7, Pi_sas = 6e-7; Pf_ch = 3.6e-8, Pf_sas = 4.5e-7
Al 60nm @ 1nm/s (Pchamber = 1.5e-7mb, Psas = 6e-7mb) @ -22°

lift ~30' @ 80°C
obs Patterns are not correctly issued

New dicing of the BPCT1 (whole wafer re-baked 15' @ 170°C) and of BPC1 wafers.
Several samples cut from BPCT1: 5 single BPC with no ground plane, and 3 single BPC on top of the wafer (designed for quantro RF holders)

BPCT1_6
expose sap(increase the dose 1.3 -> 1.4 on the arms and on one line out of 3 of the island, also, try the new symmetric design for the island)
dev sap 45" MIF

observation: Most patterns went well,but on the DC part the PMMA Mask collapsed and cracked, as before bake !!!
below comparison between 15, 30 and 45" on re-baked wafer, and the "error" on DC part 45" (NB: pads of resonator are 10µm, gap where CPB is located also 10µm)

vendredi 31/01

evap

Pump over night
Heat Al source 30min @ 160mA during pumping to desorb it
Pi_ch = 1.1e-7mb, Pi_sas = 6e-7mb
ion mill 500V, 3mA, 2x10" @ +/- 22°
Flash Ti (~200nm @ 0.5nm/s) Pi_ch = e-7, Pi_sas = e-7; Pf_ch = 3.6e-8, Pf_sas = 3e-7
Al 30nm @ 1nm/s (Pchamber = 1.7e-7mb, Psas = e-7mb) @ +22°
Dynamic oxidation, 150µb (1.1e-1 Torr), 5'
no Flash Ti
Al 60nm @ 1nm/s (Pchamber = 2.2e-7mb, Psas = 8e-7mb) @ -22°
(to complete)

lift sap
obs patterns went wrong, many filaments (look like a skeleton)