Lithography

Micro Structuring Based on Resists and Polymers

Micro lithography is used as a basic technique for patterning. Wafers and other substrates are coated with thin films of energy-sensitive resist materials. Then the resist is locally modified by the appropriate exposure system. After development a resist mask suitable for further pattern transfer is formed. Patterning is accomplished by using UV-sensitive resists for photo lithography and e-beam resists for e-beam lithography. Both types of resists are processed in positive or negative characteristics. Other polymers e.g. BCB (Cyclotene), epoxy resins (SU-8), and polyimides are used for special patterning techniques and for planarization respectively.

All resists applied and developed make use of automatic processing tools (Süss MicroTec ACS 200, IOS Cube 5) to provide high precision and reproducibility. These tools are distinguished by process flexibility and high productivity. In addition, manual techniques of lithography are carried out. Parts of wafers and special substrates are processed as well. After appropriate patterning processes resist masks are removed by means of lift-off processing tools (Steag Hamatech and SSEC). All lithography processes are carried out in particularly air-conditioned clean room facilities with minimum clean room class ISO 5 standard.

Photolithography

Wafer stepper
Wafer stepper NIKON NSR-2205i12D

Photolithography at 365 nm wavelength (i-line) using optical masks is performed by:

  • Projection lithography (5:1) with step-and-repeat system
    • NIKON NSR-2205i12D
    • Demagnification 5x
    • Automatic processing of wafers and reticles
    • Equipped for 2", 3" and 100 mm wafers
    • Automatic alignment
    • Flexible covering of wafer area by step-and-repeat technology
  • Contact lithography with contact printing tools
    • Süss MicroTec MA 100
    • EVGroup EVG 420

According to lithography techniques pattern sizes down to 0.35 µm can be achieved.

Electron beam lithography

Electron beam exposure system
Electron beam exposure system Vistec SB 251

The e-beam exposure system Vistec SB251 is a production type variable-shaped beam system with a resolution minimum of 50 nm. It is used for the fabrication of of Cr masks and reticles and for direct writing of sub µm structures such as gate structures in GaN power HFET technology and optical gratings for diode lasers:

  • Direct write applications on wafer size 2"-, 3"- and 100 mm
  • Photomask writing on 4", 5" und 6"

Technical data of electron beam exposure system Vistec SB251:

  • Variable-shaped beam system
  • Vector-scan writing for high productivity
  • Acceleration voltage: 50 kV
  • Current density: max. 20 A/cm2
  • Address grid: 1 nm
  • Minimum feature size: ≤ 50 nm (isolated line in resist)
  • Direct write overlay accuracy: (3 σ) ≤ 30 nm
  • Stitching accuracy: 30 nm max. dev.