Processes and Processing

FIRST offers for general use a wide variety of generic technology processes, such as epitaxial growth, thin-film technologies and micro- and nano-structuring. These have been derived from more complex device technology developments of the different research groups working in FIRST, and are combined, to the benefit of all projects in FIRST, into a wide variety of new processes for optical and electronic devices.

Epitaxial crystal growth
In FIRST, we offer MBE and MOVPE technology for the growth of binary, ternary and quaternary III-V compound semiconductor materials such as GaAs, InP, AlxGa1-xAs, InxGa1-xAsyP1-y, InxGa1-xNyAs1-y and AlxGa1-xAsySb1-y, with different composition, doping and lattice matched to InP or GaAs. Processes include simple and complex layer structures, as well as overgrowth and selective area growth of structured substrates. Layer structures are grown for diode lasers, HBT- and HEMT-transistors, waveguide structures, SESAMs, wideband optical mirrors, and complete VCSEL and VECSEL structures, etc.

Thin films for optics and electronics
SiOx, SiOxNy and SiNx are deposited using PECVD for surface passivation, for electrical insulation, or for thin film MIM-capacitors. PECVD SiNx can be used as a hard mask for ICP etching or as a mask for MOVPE re-growth of III-V layers on structured substrates. Metals, such as Ge, Ni, Au, Ti, Cr and Pt for ohmic and Schottky-contacts or interconnect metallization are evaporated. For instance, these metals produce very low resistance contacts to electronic devices. Layer thicknesses between a few nm and several µm can be achieved with reproducible homogeneities of approximately 1% over a 2-inch substrate.

Micro- and nanolithography
Micro- and nanolithography using optical printing and electron-beam methods are used to define structures with feature sizes down to 30 nm. FIRST offers various positive- and negative-tone photo resists and developer systems for UV- and for electron beam lithography. With electron-beam lithography, we define e.g. 100 nm T-gates, or 250 nm holes on a 500 nm grid. Atomic force microscope (AFM) lithography is used to define extremely narrow line widths of approximately 10 nm in thin Titanium films on top of semiconductor materials. This uses the humidity of the air in a bias-dependent local oxidation process. This technology is used to define quantum Coulomb blockade devices and single-electron transistors.

Structuring of layers and devices
Wet-chemical etching or plasma etching can be used to transfer structures into dielectric or polymer materials. RIE and ICP plasma etching are also available to etch semiconductors. Deep sub-µm holes with diameters down to 300 nm and etch depths up to 1.5 µm have been etched successfully in InP. This kind of structuring is important for optical devices such as photonic crystals, etched mirrors, optical waveguides and gratings, electronic devices such as bipolar and field-effect transistors, are plasma etched too.

Combining technologies into processes
All of these processes are available to the users. However, FIRST staff does not provide complete device technology as a service. But specific training on the equipment enables a user to design, develop and apply a process on various materials. When combined in the proper sequence, these processes can be concatenated to produce new devices, ranging from quantum spin devices, transistors, photo-detectors, wide-band optical mirrors or lasers to light emitting diodes, photo-diodes and integrated circuits.