Reservation  -     

Center of MicroNanoTechnology CMi

Manual for Arias Acid Wetbench

Acid Wet bench

Attention Preliminary and fundamental remarks:

Contents: CMI

  1. Introduction
  2. Standards at CMi
  3. Modus Operandi

I. Introduction CMI

Zone 14 offers three wetbenches for use of acids, bases and solvents chemistries. They are all dedicated to a given type of chemicals so they give the opportunity to use standard and/or new wet etching recipes. The bath preparation is done by the user, which allows nicely adapting the chemistry (i.e. mixtures, concentrations and temperatures) to the needed applications.
Safety rules must be strictly observed at any time.

  • HNO3 Nitric Acid (69.5%)
  • HCl Chlorhydric Acid (37%)
  • H2SO4 Sulfuric Acid (96%)
  • Diluted HF Hydrofluoric Acid (5%)
  • Concentrated HF Hydrofluoric Acid (49%)
  • BOE Buffered Oxide Etch (7:1)
  • H3PO4 Phosphoric Acid (85%)
  • H2O2 Hydrogen Peroxyde (30%)
  • Gold etch
  • Copper etch
  • CR7 Chromium Etch CR7 MOS
  • Chromium Etch selective over Cu
  • ANP Aluminun Etch VLSI
  • Nickel etch

  • List 1: Available acids

    Top view of the Wet bench acid

    Figure 1: Top view of the Wet bench acid

    II. Standards at CMi CMI

    Material to etch
    Chemicals used
    Masks Etch rate (nm/min) T (°C)
    PyrexBHF (7:1)Cr/PR» 33
    » 68
    Room temp.
    HF(49%):H2O (1:4)Cr/PR198
    Room temp.
    SiO2BHF (7:1)PR

    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)
    250 (SiO2 Spider)
    70 Al2O3 (ALD)

    Room temp.
    SiloxPR40 (WetOx)
    240 (LTO)
    Room temp.
    AlTechniEtch Al80PR30035

    H3PO4 (85%)

    BHF (7:1)


    72 (ALD), 120 (Spider)

    70 (ALD)


    Room temp.

    aSi, polySiHNO3(70%):HF(49%):H2O (50:3:20)PR730Room temp.
    Pt HCl(37%):HNO3(70% ):H2O, (3:1:2) (Diluated Aqua Regia)PR2Room temp.
    AuTechniEtch ACI2
    KI + I2 = 25 g/l and 12 g/l
    PR40 - 80Room temp.
    CrTechniEtch Cr01
    (NH4)2Ce(NO3)6 + HClO4
    PR65Room temp.
    Cr (selective over Cu)KMnO4 + Na3PO4
    60 g/l and 200 g/l
    PR24Room temp.
    Ni(NH4)2S2O8 + FeCl3
    91 g/l and 7.3 g/l
    Remark: etches Au ~15nm/min
    Room temp.
    Cu(NH4)2S2O8 + H2SO4 (96%)
    60 g/l and 10 ml/l
    PR200Room temp.
    Mo H3PO4(85% ):CH3COOH(100%):HNO3(69,5%), (80:16:4)PR 125Room temp.
    SixNyHF 49%PR4
    12 (Si3N4)
    Room temp.
    PR: Photosensitive Resist

    Table 1: wet etching properties of Arias Acid wetbench in zone 14

    III. Modus Operandi CMI

  • Login on the Wet bench acid zone 14.(It controls the protection window)
  • Lift the window using the switch on the board below the wet bench.
  • Attention Be careful with optical sensors: to act on the window, nothing must be on its path.
  • Get a timer, plastic tweezers, springs and the wafers ready.
  • Install the Heating Magnetic Stirrer. (Arec X+ Digital Thermoregular) (If you need it).(fig.3)

  • Chemicals Available
    Figure 2: Aqua regia Solution Setup

    Schematic Top view of the Wet bench acid
    Figure 3: Setup using a Heating Magnetic Stirrer

    Full protection is now required before going further:
    (1 ⇒ apron, 2⇒face shield, 3⇒chemical gloves)
  • Fill a beaker with the required chemicals.
    AttentionRespect the AAA rule (Always Add Acid) if you had to mix chemicals (aqua regia, RCA…)

  • Place it on the Heating Magnetic Stirrer and add a magnet. The left potentiometer controls the temperature heating rate. The right one controls the rotation velocity of the magnet. This stiring is needed to have a uniform temperature.
  • Set the temperature using Digital thermoregular by clicking on SET, then by adjusting the value with the arrows Cursors. When it is done click on SET. Adjust the height; the thermic sensor must not touch the bottom.

  • Chemicals Available
    Figure 4: Wet etching at room temperature

    Schematic Top view of the Wet bench acid
    Figure 5: Wet etching with heater

  • Put the wafer in the chemicals using a plastic tweezers. Start the timer.(fig.4)
  • In the case of a long process, add a cover, and label the setup (templates available on the window of the wetbench).

  • Chemicals Available
    Figure 6: the wafer is rinsed in the 2nd bath

    Schematic Top view of the Wet bench acid
    Figure 7: The wafer is rinsed with the DI Gun

  • When the process is done, take the wafer out (with plastic tweezers) and rinse it with 2 different beakers filled with DI water.(fig.6)
  • Finish by pouring DI water on the wafer in the DI rinser. Dry it.(fig.7)
  • Clean three times and Dry the bottle used before replacing it into the cabinet.
  • If the bottle is empty, it has to be washed inside AND outside (in this order!) three times and place into the dressing room (dedicated container available)
  • Put the chemicals into the corresponding waste bottle (located below the wetbench) and rinse all glasswares and tools as necessary.
  • Perform wet bench logout on zone 14 computer

  • Attention Any droplets of any kind MUST be removed from the wetbench before leaving it.
    Suspicious droplets must be diluted in DI water using a tissue (2 to 3 cleanings/rinsings are necessary) and remaining water droplets must be removed with absorbent paper.