Metal deposits etching

During the fabrication process the surface of the semiconductor is etched and metal contacts are deposited. These features can represent a topographical challenge to subsequent metal wiring levels. For this reason it is important that the dielectric film used tends to smooth out such discontinuities as metal and etched edges (150,217). Additional appHcations for spin-on dielectrics include forming integrated microlenses for optoelectronics (218). 

Plating T anks. An electroless plating line consists of a series of lead-lined (for plastics etching) or plastic-lined tanks equipped with filters and heaters, separated by rinse tanks (24). Most metal tanks, except for passivated stainless steel used for electroless nickel, cannot be used to hold electroless plating baths because the metal initiates electroless plating onto itself. Tank linings must be stripped of metal deposits using acid at periodic intervals. 

There has been extensive recent use of track-etched membranes as templates. As will be discussed in detail below, these membranes are ideal for producing parallel arrays of metal nanowires or nanotubules. This is usually done via electroless metal deposition [25], but many metals have also been deposited electrochemically [26]. For example, several groups have used track-etched templates for deposition of nanowires and segmented nanowires, which they then examined for giant magnetoresistance [27-29]. Other materials templated in the pores of track etch membranes include conducting polymers [30] and polymer-metal composites [31]. 

It is always interesting to know the fate of the Fe species remaining on the surface. For the W plug application, after W CMP, the subsequent relevant processes are the deposition, patterning and etch of the Ti-Al (aluminum)-TiN stack. The Fe residuals on the surface will not cause any problem for the metal deposition because the entire surface is covered by metals. However, a problem may occur in the metal etch process because the BCI3 plasma chemistry can not etch away Fe. The reaction products between Fe and BCI3 are FeCl complexes, which are nonvolatile [22]. They... 

Figure 6.12 Cross-sectional view of the 4H-SiC power BJT fabrication, (a) Starting epilayer structure. (b) Dry etching of emitter and base epilayers. (c) p implantation for guard rings and contacts to p-base. (d) Formation of ohmic contacts, (e) Over layer metal deposition, (f) Double metal process.

It has been known for a long time that the presence of specifically adsorbed anions affects the electrochemical reactivity of a metal electrode in deposition, etching, corrosion and electrocatalysis. For example, blocking of reaction sites through specific adsorption may result in a reduced reaction rate. 

Figure 15. Simplified process sequence for the fabrication of an NMOS transistor (a) substrate preparation, (b) selective exposure of substrate, (c) mask formation by differential solubility, (d) etching, (e) stripping of resist, (/) doping, (g) reoxidation of silicon surface, (h) formation of gate oxide, and (i) metal deposition and patterning. Abbreviations are defined as follows p-Si, p-type silicon PR, photoresist S, source G, gate and D, drain.

Substrate Treatment. When the desired image is developed in the resist, the pattern created provides a template for substrate modification. The various chemical and physical modifications currently used can be classified into additive and subtractive treatments. Examples of additive treatments include the insertion of dopants (by either diffusion or ion implantation) to alter the semiconductor characteristics and metal deposition (followed by lift-off or electroplating) to complete a conduction network. In most cases, however, the substrate material is etched by a subtractive process. 

A developer solution is utilized to remove the excess photoresist and obtain the desired pattern. Once the pattern is obtained, the next step can be an etching or a metal deposition step, depending on the process chosen, and the remaining photoresist can be removed through etching or lift-off procedures.44,48... 

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