Development of new Proton Beam Writing techniques and creation of 3-dimensional microstructures in III-V semiconductors

Dr. Frank Menzel

The work with the new method of grayscale lithography by proton beam writing (PBW) was developed further leading among other things to the creation of a Fresnel lens in negative resist (Fig. 1(a)). However, detailed investigations concerning the improvement of the structure quality produced by this technique, especially the surface roughness, has to be to carried out.

Figure 1: REM images of microstructures in different materials created by PBW followed by a chemical or electrochemical etch
procedure: (a) Fresnel lens in the negative ma-N resist, (b) micro pillars in p-type GaAs, (c) self-supporting structure in p-type InP, and (d) 3-dimensional and partly underetched microstructure in SI GaAs.

Furthermore a new approach for the creation of 3-dimensional resist structures using masks and homogeneous ion irradiation was developed. Thereby the mask absorbs part of the primary ion energy leading to a lateral distribution of ions with different energies and penetration depths in the irradiated negative resist layer beneath the mask. Due to the different exposure depths 3-dimensional freestanding resist structures result.

Experiments dealing with the creation of microstructures in GaAs and InP by PBW and electrochemical etching were continued. In p-type GaAs an increase of the etch current density leads to high aspect microstructures with vertical side walls and with heights of some tens of micrometers as well as with lateral dimensions down to ~1 µm (Fig. 1(b)). In p-type InP similar microstructures as well as self-supporting microstructures (Fig. 1(c)) already shown for p-type Si and GaAs were created successfully. Furthermore, the irradiation of SI GaAs with 1.125 MeV H₂⁺-molecules and different fluences leads to partly underetched multilevel microstructures due to the influence of the irradiation fluence on the electrochemical etch rate (Fig. 1(d)).