Etch process, plasma-assisted

Dry etching techniques permit etch processes to be carried out in various modes. These can be described as purely chemical, purely physical, and a mixture of chemical and physical. With plasma etching and RIE, we have concentrated on chemical and ion assisted processes. In this section, etching methods that depend either solely or primarily on physical processes (momentum transfer) will be discussed briefly. 

Like the literature of plasma-assisted etching, the literature on the PECVD of specific materials is considerable. Because film properties are ultimately determined by chemical reaction mechanisms, reactor design, and film structure (Figure 5), the determination of the exact relationships between properties and processing is difficult. At present, the fundamental understanding of such relationships is limited, and thus, empirical efforts have been the norm. In this chapter, the more widely studied film materials deposited by PECVD will be briefly discussed. More extensive information on these and other films can be found in a number of review articles (9-14, 32, 50, 200-203) and references therein. 

In this Chapter, we will review the chemical, ion sputtering, plasma-assisted and reactive ion etching techniques for SiC. These processes can be used in fabricating SiC devices. 

Chemical reactions initiated in gas discharges and plasmas, in particular in low-temperature, nonequilibrium plasmas, have become indispensable for the advancement of many key technologies in the past 10-15 years (see, e.g Becker et al., 1992 Garscadden, 1992). The plasma-assisted etching of microstructures and the deposition of high-quality thin films with well-defined properties have become crucial steps in the fabrication of microelectronic devices with typical feature sizes of less than 0.5 /rm. The manufacture of state-of-the-art microchips now involves hundreds of process steps, most of them serial, to yield circuits with millions of discrete elements and interconnections in an area of a single square centimeter (Garscadden, 1992). Each step is a physical-chemical interaction that must be controlled. More than one-third of the process steps rely on plasma... 

The plasma-assisted shrink techniques (e.g., MOTIF ) use plasma to deposit a thin film that conformally coats contact holes and spaces printed in resists, which on dry etching result in smaller contact holes and spaces. In the remainder of this section, we provide a more detailed treatment of the postexposure-hased singlelayer exposure techniques employed in advanced resist processing. 

Dry etching processes can be based on purely mechanical removal of material by ion impact (physical or sputter etching (PE) and ion beam etching (IBE)) or on the removal of material by very reactive gases or plasmas (plasma etching) or by combinations of both process types (reactive ion etching (RIE), reactive ion beam etching (RIBE), or chemical-assisted ion beam... 

As with many new processes, the goal of plasma etching was to find a more cost effective, environmentally sound, safer alternative to a chemically intensive procedure, in this case wet resist stripping. However, as with many new processes, new or subtle hazards may be introduced. Plasma-assisted etching was welcomed by the safety community since early plasma systems used nonhazardous gases such as oxygen and freons to perform operations that were traditionally performed in open tanks of corrosives and solvents. 

Matsumoto et al. [233] tried a bias assisted plasma jet with the reactive gas mixture Ar-N2-BF3-H2 for selective etching of h-BN [234]. Using a d.c. bias voltage, the nano-cBN grain size in the layers could be increased from 7 nm (-150 V) to 12 nm (-80 V) [235], By optimizing the process, nano-cBN coatings thicker than 20 pm with c-BN grain size up to 100 nm could be deposited [230],... 

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