The clean room includes all equipment and processes technologies (chemistry, photolithography, deposits, engravings, ...) intended the preparation of substrates and the manufacture of micro-components and optoelectronic. The realization of objects or devices of small size (micro- or nanometric) requires conditions essential cleanliness. In order to carry out these processes, it is therefore necessary to work in a controlled atmosphere area (particle rate, temperature, humidity and pressure). Upstream of epitaxy, optical lithography is used to structure substrates 1 to reduce stress in the realized structures and thus to limit the appearance of dislocations and cracks. After epitaxy, the clean room can be used to make 3D objects such as micro-drives 2 on which growth can be achieved again. Else motives with resolutions of the order of a few nanometers can be drawn with 3 electronic lithography, allowing in particular the realization of meta-surfaces. Finally, downstream of epitaxy, the clean room allows the realization of 4 devices micro- and optoelectronic devices such as high mobility transistors electronic and light-emitting diodes.

1) Structuring of substrates

Examples of structuring of the substrate by optical lithography, before epitaxial growth.
GaN or ZnO waveguides for integrated photonics are made on strips (26 / 4µm) 1.7µm depth of ZnO substrate (figure. 1) or 7µm strips of Si substrate (figure. 2).
Figure 3: A Si substrate patterned in mesas 200µm * 200µm, spaced from trenches of 10µm wide and 5µm deep.

Lithographie optique Lithographie optique Lithographie optique
Figure 1: ©S. Chenot - figures 2 and 3: ©S. Chenot, M. Gromovyi

2) Realization of semiconductor micro-disks

The selective etching of hetero-epitaxial semiconductor thin films allows the realization of micro-disks found in advanced micro- and opto-electronic devices (MEMS and MOEMS).
Figure 1: SiC Micro-Disks on Si.
Figure 2: GaN epitaxy on AlN micro-disks, with the aim of developing GaN facets semi-polar on silicon to produce LEDs emitting at a long wavelength. The plans semi-polar GaN allow to incorporate more indium than the polar planes and the structuration 3D of GaN eliminates extensive stresses responsible for cracking epitaxial GaN layers on silicon.

Micro-disques Micro-disques
Figure 1 : ©S. Chenot, M. Portail - figure 2: ©S. Chenot, F. Semond

3) Electronic lithography

Electron beam lithography is a technique for drawing patterns with resolutions of the order of a few nanometers, and to achieve objects such as grids for high frequency transistors, nanoscale wires (better crystalline quality as films), or meta-surfaces.
Figure 1: Grid from 100nm to 200nm of a GaN / AlGaN HEMT transistor.
Figure 2: Growth of GaN nanowires with a patterned SiO 2 dielectric mask holes 100nm in diameter, spaced 500nm apart.
Convergent meta-lens of 200 .mu.m in diameter (figure. 3) based on GaN piers from 50 nm to 100 nm in diameter (figure. 4).

Lithographie électronique Lithographie électronique Lithographie électronique Lithographie électronique
Figure 1 : ©S. Chenot, V. Brändli - figure 2: ©V. Brändli, B. Alloing - figures 3 and 4: ©G. Brière

4) Realization of devices

The manufacture of devices, such as light emitting diodes (LEDs) or HEMT transistors (High Electron Mobility Transistor), combines steps of chemistry and photolithography (with alignment of several levels of masks, physical-chemical plasma etching of mesas, deposition of contacts by evaporation with electron gun, and heat treatments).
Figure 1: LEDs based on gallium nitride.
Figure 2: GaN / AlGaN HEMT.

Dispositif Dispositif
Figure 1 : ©S. Chenot, Y. Cordier - figure 2: ©S. Chenot, B. Damilano

The devices used are described in the page technology platform of CRHEA.

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