0018-8646/99/$5.00  (C)  1999 IBM

Preface

Plasma etching and deposition processes play a critical role in the 
production of high-density, high-performance  microelectronic 
products. Generally, their underlying mechanisms consist of 
plasma-phase chemical reactions, particle transport, and surface 
reactions. Either one can dominate, depending on whether conditions 
are chosen to favor etching, deposition, or a combination of both. 
Each is a nonequilibrium process, making characterization quite 
complex. Nevertheless, considerable progress has been achieved in 
the development of plasma etching and deposition--and in the 
development of the reactor systems in which they are carried out. 
This issue contains papers that discuss relevant mechanisms; 
processing, system, and materials aspects; and potential advances. 

Many of the dielectric layers of ULSI (ultralarge-scale integrated) 
semiconductor circuits (containing structures having minimum pattern 
widths of 0.25 [muon]m and less) are patterned using plasma-assisted 
CVD (chemical vapor deposition). In the paper by D. R. Cote et al., 
the following relevant aspects are discussed: materials, processing, 
and device-related issues; deposition mechanisms; reactor design and 
process optimization; and considerations regarding extendibility to 
a wafer diameter of 300 mm. 

Plasma etching is used to pattern many of the layers of ULSI 
circuits. M. Armacost et al. cover etching selectivity, masking 
material, multilayer structures, aspect ratio, self-aligned contact 
structures,  microloading effects, device damage, and the use of 
high-density plasma sources. 

Active-matrix liquid crystal displays make use of large-area arrays 
of thin-film transistors (TFTs) fabricated using amorphous silicon 
containing hydrogen (a-Si:H). Plasma deposition and etching play 
important roles in the fabrication of the arrays. The paper by Y. 
Kuo et al. covers the influence of plasma deposition and etching 
phenomena on the TFTs and associated films, factors affecting 
relevant etching rates and selectivity, control of the edge profiles 
of the various films used, and control of plasma-etching-induced 
damage to the TFTs. 

The rapidly increasing area density of disk drives will probably 
soon make it necessary to employ plasma etching in the fabrication 
of magnetic recording heads. However, the thin-film materials used 
in the heads, such as Al[SUB]2O3, NiFe, Cu, Ta, and Au, differ from 
those used in silicon-based microelectronics applications. R. Hsiao 
discusses relevant broad-beam ion etching processes and the plasma 
etching of magnetic recording head materials. 

With the introduction of new thin-film materials to consistently 
shrinking  microelectronic devices and circuits, plasma-based process 
damage has become a serious concern. In addition to process flow, 
device and circuit layout can be a causal factor. These issues are 
discussed in the paper by S. J. Fonash. 

High-density plasma chemical vapor deposition (HDP CVD) appears to 
be a promising alternative for the deposition of dielectric layers. 
Although in many respects layers deposited in that manner are 
superior to those deposited using conventional low-density plasma 
processes, metal contamination concerns remain to be satisfactorily 
addressed. Because of concurrent etching and deposition, the process 
can be an effective local planarization method for high-aspect-ratio 
structures. In S. V. Nguyen's paper, the following are discussed: 
HDP CVD processing and equipment aspects; the characterization of HDP 
CVD fluorinated and nonfluorinated SiO[SUB]2 films and carbon 
films; and applications in  interlevel insulation, gap filling, and 
planarization. 

Layer-formation processes having a low ``thermal budget'' are 
required for the manufacture of advanced semiconductor devices. Thin 
dielectrics, such as  SiO[SUB]2 and Si[SUB]3N[SUB]4, can be grown 
from a silicon substrate at low temperatures using plasma-based 
methods. D. W. Hess discusses the oxidation and anodization of 
silicon and silicon-germanium, including the influence of film 
crystallinity and the plasma source used; the mechanisms and 
processes of nitridation and  oxynitridation; and nano-oxidation 
possibilities using an approach based on scanning tunneling 
microscopy or atomic force microscopy. 

Because of their wide range of physical and chemical properties, 
diamondlike carbon (DLC) films prepared from PECVD are useful in a 
number of electrical, optical, and mechanical areas. They also 
appear to have potential for achieving low-dielectric-constant 
insulation in ULSI circuits. A. Grill discusses plasma-based DLC 
deposition; the structural, electrical, optical, mechanical, and 
tribological properties of DLC films; and associated applications. 

Film deposition by sputtering in a plasma is a process that has seen 
extensive use for film deposition. As the aperture ratio of an 
integrated-circuit structure increases, conformal step coverage 
becomes increasingly difficult to achieve using conventional 
sputtering. S. M.  Rossnagel covers this subject, including recent 
work on I-PVD (ionized physical vapor deposition), which, for 
high-aperture-ratio structures, appears to have many advantages over 
existing methods. 

Surface reactions in plasma etching play an important role in 
determining the outcome of the etching. Although the reactions are 
difficult to delineate, many surface- characterization tools and 
techniques can be used to probe the etched surfaces for indications 
of possible reactions. The paper by G. S.  Oehrlein et al. covers 
aspects pertaining to integrated circuits, with emphasis on the 
formation of self-aligned contacts to a polysilicon layer through a 
SiO[SUB]2 layer and a Si[SUB]3N[SUB]4 etch-stop layer. 

Modeling and numerical simulation of plasma processes are important 
in the development of the processes and the reactors in which they 
are implemented. S.  Hamaguchi discusses the continuum and kinetic 
modeling and simulation of plasma sources as well as the modeling 
and simulation of the evolution of surface topography during plasma 
etching and deposition. 

There is no doubt that plasma processing will continue to play a 
critical role in the fabrication of microelectronic products, but 
advances in the processes will likely become increasingly dependent 
on improved understanding of their underlying mechanisms. 

                               Yue Kuo 
                                                                    Dow Professor 
                               Texas A&M University 

                               Guest Editor 

                               Previous affiliation: 
                               IBM Thomas J. Watson 
                                 Research Center