Specific Process Knowledge/Lithography/Pretreatment

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Pretreatment

All surfaces can be divided to hydrophilic or hydrophobic surfaces. Oxidized surfaces such as SiO2 or surfaces with native oxide (e.g. Si or Al substrates) are considered to be hydrophilic and have very bad wetting with hydrophobic resist. The adhesion of most resists on hydrophilic surfaces is deteriorated if moisture is present on the surface.

Therefore it is very important to do the pretreatment step before the spinning. Here we will give an overview of treatments available at DTU Nanolab to promote photoresist adhesion.

Comparing pretreatment methods

HMDS Buffered HF-Clean Oven 250C
Generel description

Vapor priming

Native oxide strip

Dehydration

Chemical

hexamethyldisilazane (HMDS)

12%HF with Ammoniumflouride

none

Substrate size
  • Chips
  • 50 mm wafers
  • 100 mm wafers
  • 150 mm wafers
  • 100 mm wafers
  • 100 mm wafers
  • 150 mm wafers
Allowed materials

Silicon, glass, and polymer substrates (Tg > 150°C)

Film or pattern of all types, except type IV and resist/polymer

  • Silicon
  • Poly Silicon
  • Silicon Oxide
  • Silicon Nitride
  • Silicon Oxynitride
  • Photoresist
  • Blue film
  • Silicon
  • Silicon Oxide
  • Silicon Nitride
  • Glass
Restrictions Type IV and resist/polymer on polymer substrate

i.e. no resist coated wafers or crystalbonded chips!

Wafers with metal is not allowed Resist is not allowed


Pretreatment of substrates other than Si

This section is under construction

HMDS

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The chemical treatment with hexamethyldisilazane (HMDS) before the spin coating can be used to promote the adhesion for photoresist. Vapor priming with HMDS leaves a mono-layer of TMS (trimethylsilyl) on the Si or SiO2 surface. The process dehydrates the substrate surface, and lowers the surface tension.

The molecular formula for hexamethyldisilazane, or bis(trimethylsilyl)amine, is C6H19NSi2. Here is a schematic overview of HMDS treatment of silicon-oxide surface.

Priming of oxide-forming substrates by HMDS treatment.


Comparing HMDS priming

Equipment Oven: HMDS 2 Gamma UV/ Gamma e-beam and UV
Purpose
  • HMDS priming only
  • HMDS priming only
  • HMDS priming and spin coating
Priming chemical

hexamethyldisilazane (HMDS)

Performance Contact angle


  • Si (native oxide): 77.8°
  • SiO2 (110 nm): 81.7°
  • Boron Glass: 97.6°

Fast recipe [standard recipe]:

  • Si (native oxide): 72.9° [81.0°]
  • SiO2 (110 nm): 71.0° [79.7°]
  • Boron Glass: 90.7° [96.2°]
Process parameters Process temperature

150°C

120°C

Process time

25 minutes

1 min / wafer

Substrates Substrate size
  • Chips (using holder or silicon carrier)
  • 50 mm wafers
  • 100 mm wafers
  • 150 mm wafers
  • 50 mm wafers (tool change required)
  • 100 mm wafers
  • 150 mm wafers
  • 200 mm wafers (tool change required)
Allowed materials

Silicon, glass, and polymer substrates

III-V materials on silicon carrier

Film or pattern of all but types, except type IV and resist/polymer (incl. Crystalbond)

Silicon and glass wafers

Film or pattern of all but types, except type IV and resist/polymer (incl. Crystalbond)

Batch

1 - 25, multiple batches possible

1 - 25


Oven: HMDS 2

The Oven: HMDS 2 oven is located in E-5.

The user manual, user APV, and contact information can be found in LabManager:

Oven: HMDS 2 in LabManager

Process information

  • Recipe 1: baseline prime process with 5 min HMDS priming time


Spin Coater: Gamma UV

HMDS module in Spin Coater: Gamma UV in E-5.

The user manual, user APV, and contact information can be found in LabManager:

Spincoater: Gamma UV labmanager page


Additional information about the spin coater and processes can be found in Labadviser:

Spincoater: Gamma UV labadviser page


Spin Coater: Gamma e-beam & UV

Spin Coater: Gamma e-beam & UV in E-5.

The user manual, user APV, and contact information can be found in LabManager:

Spin Coater: Gamma e-beam & UV labmanager page


Additional information about the spin coater and processes can be found in Labadviser:

Spin Coater: Gamma e-beam & UV labadviser page


Buffered HF-Clean

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BHF clean wetbench 04 in D-3.

Another commonly used method to render the surface of silicon wafers hydrophobic is the dilute HF dip.

BHF is mostly used to do pretreatment step for new Si wafers. The native dioxide layer will be removed during 30 sec etching and in this way we will promote the resist adhesion on the Si substrates. We recommend to spin resist asap after the procedure.

The user manual, user APV, and contact information can be found in LabManager:

Buffered HF-Clean in LabManager

Process information

For more information on this BHF bath take a look here: Wet Silicon Oxide Etch (BHF)


Oven 250C

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Oven 250C for pretreatment in C-1

The oven is typically used for pretreatment (dehydration) of Si and glass substrates to promote the resist adhesion. We recommend to place the wafers in metal carrier in the oven at least for 4 hours, better during the night, and spin the resist on them asap.

The user manual, and contact information can be found in LabManager: Oven 250C