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Center of MicroNanoTechnology CMi

PLADE wetbench user manual

chapelle chimique PLADE

Attention Preliminary and fundamental remark:

Contents: CMI

  1. Introduction
  2. Standards at CMi
  3. Modus operandi
  4. Pictures

I. Introduction CMI

The baths of the PLADE wetbench in zone 2 are arranged as depicted in figure 1. A rinsing/drying system from Semitool separates the two parts of this wetbench. The left side is dedicated to HF filled baths (silicon oxide, pyrex and float glass etching) and the right side is dedicated to metals etching and miscellaneous SiO2 (Aluminum, phosphorus contaminated SiO2 after POCl3 doping and SiO2 selective over Aluminum). Each bath is fitted with a timer to control etching times, with a temperature adjusting system (but bath 5) and with a circulating pumping system to activate etching (but bath 5). All three functions are activated by large pneumatic buttons so they are accessible with the chemistry equipment. Swithcing on/off of rinsing baths is possible with the same type of buttons. Dedicated Teflon carriers are at disposal for 4 and 6 inches wafers.

Disposition des bains
FFR: Fast Fill Rinse (rough rinsing)
TT: Trickle Tank (fine rinsing)
Figure 1: Schematic of the UltraFab wetbench in zone 2

Bath N° 1 2 3 4 5 6 7
ANP HF(49%):H2O

(Pad etch)

Poly Etch
Application   Pyrex
Float glass
SiO2 Pyrex
Float glass
Aluminum Titanium SiO2 etching
selective over Al
* NH4F(40%):CH3COOH(97.7%):H2O 

II. Standards at CMi CMI

Table 1 briefly shows accessible wet etching properties of PLADE wetbench in zone 2.
Important remarks linked to the Silox bath: SiO2 etching in Silox (Padetch) must absolutely be done with the circulating system switched on. If not, it's mostly probable that etching stops during the process (creation of stopping layer due to the nature of the bath and the presence of the photoresist mask). Also, it is highly recommended not to do multiple partial etchings in this bath at the risk of stopping the etching due to the creation of the layer previously mentionned. Therefore, etching is to be done in one single shot.

Material to etch
Bath number
Chemicals used
Masks Etch rate (nm/min) T (°C)
Glass materials1BHF 7:1Cr/PR » 33 (Pyrex)
» 68 (Pyrex)
3HF(49%):H2O 1:4Cr/PR 380 (Pyrex) 25
SiO22BHF 7:1PR

27 (Borofloat)
77 (WetOx)
86 (DryOx)
80 (Fused Silica)
250-300 (LAB HRI)
225 (LTO no densification)
120 (LTO with densification)
262 (TEOS no densification)
470 (PSG)

70 Al2O3 (ALD)

6SiloxPR40 (WetOx)
240 (LTO)
aSi, polySi7HNO3(70%):HF(49%):H2O 50:3:20PR73020
PR: Photosensitive Resist

Table 1: wet etching properties of PLADE wetbench in zone 2

Remark: etch rate of WetOx in BOE (25:1) is 24 nm/mn.

III. Modus operandi CMI

  1. Login on the PLADE wetbench (Piranha part) using zone 2 computer (either Plade oxide or Plade metal)
  2. Activate the circulating system and the heating system after having checked/changed the set point. If working at room temperature, there is no need to activate the heating system
  3. Adjust the timer according to the etch rate and the wanted result
  4. Load the wafers in one of the dedicated Teflon carrier and put the handle on
  5. Full protection is now required (apron, face shield, chemical gloves) before going further
  6. Once the wanted temperature is reached, open the lid of the bath and gently plunge the carrier into it
  7. Start the timer (with clean hand)
  8. Rinse the gloves and gently clean the bath's surroundings with a moist paper (several cleanings/rinsings are necessary)
  9. Wait the end of the etching. Eventually, take the chemistry equipment if waiting time is long. Please fill-in a chemical label to inform other users about your running process
  10. If needed, get ready with the chemistry equipment a few minutes before etching is supposed to finish
  11. A buzzer indicates the end; press once on the timer button to stop the buzzer
  12. Open the FFR lid and gently transfer the Teflon carrier from the etching bath to FFR
  13. Activate the FFR button
  14. Stop the heating system and the circulating system of etching bath
  15. During FFR, rinse the gloves and gently clean the etching bath's surroundings with a moist paper (several cleanings/rinsings are necessary)
  16. When FFR is finished, switch the Teflon carrier to the Trickle Tank TT
  17. Once resistivity is reached (~12, put the carrier in the spin rinser and dryer SRD (the carrier's handle must be removed)
  18. A recipe is already selected. Just press STOP and the START
  19. When the SRD is finished, get the wafers back and put the carrier where it belongs
  20. Carefully check the cleanliness of the wetbench before taking off the chemical protection (apron, face shield, chemical gloves)
  21. Perform wetbench logout on zone 2 computer
Any droplets of any kind MUST be removed from the wetbench before leaving it. Suspicious droplets must be cleared using a moist paper (2 to 3 cleanings/rinsings are necessary) and remaining water droplets must be removed with absorbent paper.

IV. Pictures CMI

Gravure profonde du Pyrex dans le bain N°3
Figure 2: deep etching of Pyrex in bath N°3

Gravure de 1 µm d'oxyde thermique dans le BOE
Figure 3: 1 µm etching of thermal oxide in BOE