GAAs High-Speed Devices: Physics, Technology, and Circuit Applications

4

PROCESS TECHNIQUES

4.1 INTRODUCTION TO PROCESS TECHNIQUES

The demands of modern commercial and military industries have stimulated the research and development in process techniques. In this chapter we will describe the cleaning of GaAs wafers for IC applications, wet and dry etching methods, plasmaenhanced chemical vapor deposition (PECVD), and rapid thermal processing for GaAs ICs.

Wet chemical etching has been the technique most widely employed in device fabrication. Wet etching processes include pattern formation, polishing, and defect or damaging visualization. However, the need to interconnect a number of separate elements to form a circuit and to shrink this down to the dimensions of a device has led to dry processing techniques.

Reactive plasma-etching techniques have rapidly been developed to manufacture silicon-based integrated circuits, gallium arsenide MESFETs, and heterostructure high-speed circuits. Dry etching offers substantial directionality and etch anisotropy. In this chapter we will discuss the reactive ion etching techniques and laser-assisted dry etching techniques.

Plasma-assisted techniques are especially important to GaAs and other 111-V compound processing because they can be accomplished at relatively low temperatures. Deposition of thin film materials is an excellent example of this low-temperature advantage. In the case of GaAs processing, PECVD can grow thin films at a lower substrate temperature (300°C) than CVD. An electron-cyclotron-resonance ...