CVD plasma enhanced

One approach which can be taken for PECVD is the parallel plate reactor (see figure 8.4). The plasma can be created by either an RF or a DC discharge. When pure WF6 is used only etching of tungsten will occur according to the gas phase reaction  

It may still be desirable to have a moderately high wafer temperature for other reasons. For example, at very low temperatures, film density may be low, or temperature may play an important role in determining film structure. Nonetheless, it is possible to operate at lower wafer temperatures than would be allowed by a strictly thermal process. 

In the present chapter, we will review the nature of plasma-enhanced CVD (PECVD) films for a variety of applications. We will look at dielectrics (silicon nitride, silicon dioxide), semiconductors (polysilicon, epi silicon) and metals (refractory metals, refractory metal silicides, aluminum). There are many other important films (i.e., amorphous silicon for solar cells and TiN for tool harden- 

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Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

There are two types of deposited films known as siUcon nitride. One is deposited via plasma-enhanced CVD at temperatures <350° C (18). In this process silane and ammonia react in an argon plasma to form siUcon imide [14515-04-9] SiNH. 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH, and nitrous oxide, N2O, for deposition of siUcon nitride. The most common CVD films used are siUcon dioxide, siUcon nitride, and siUcon oxynitrides. 

Plasmas can be used in CVD reactors to activate and partially decompose the precursor species and perhaps form new chemical species. This allows deposition at a temperature lower than thermal CVD. The process is called plasma-enhanced CVD (PECVD) (12). The plasmas are generated by direct-current, radio-frequency (r-f), or electron-cyclotron-resonance (ECR) techniques. Eigure 15 shows a parallel-plate CVD reactor that uses r-f power to generate the plasma. This type of PECVD reactor is in common use in the semiconductor industry to deposit siUcon nitride, Si N and glass (PSG) encapsulating layers a few micrometers-thick at deposition rates of 5—100 nm /min. 

In PECVD, the plasma generation region may be in the deposition chamber or precede the deposition chamber in the gas flow system. The latter configuration is called remote plasma-enhanced CVD (RPECVD). In either case, the purpose of the plasma is to give activation and partial reaction/reduction of the chemical precursor vapors so that the substrate temperature can be lowered and still obtain deposit of the same quaUty. 

Hoffman, D. M., et al., Plasma-Enhanced CVD of Silicon Nitride Films from a Metallo-Organic Precursor, J. Mater. Res., 9(12) 3019-3021 (1994)... 

Thermal CVD, reviewed above, relies on thermal energy to activate the reaction, and deposition temperatures are usually high. In plasma CVD, also known as plasma-enhanced CVD (PECV) or plasma-assisted CVD (PACVD), the reaction is activated by a plasma and the deposition temperature is substantially lower. Plasma CVD combines a chemical and a physical process and may be said to bridge the gap between CVD andPVD. In this respect, itis similar to PVD processes operating in a chemical environment, such as reactive sputtering (see Appendix). 

Kember, P. N., and Astell-Burt, P. J., Plasma-Enhanced CVD of Tungsten and Tungsten Silicide, Vide, Couche Minces, 42(236) 167-173 (Mar.-Apr., 1987)... 

Reif, R., Low Temperature Silicon Epitaxy by Plasma Enhanced CVD, Proc. 5th European Conf. on CVD, (J. Carlsson and J. Lindstrom, eds.), pp. 13-19, Univ. ofUppsala, Sweden (1985)... 

The compound truw-perfluoro-l-methyl-1-propenylsilver has been shown to be tetrameric, [CF3CF=C(CF3)Ag]4, and it is a suitable precursor to prepare pure silver films by plasma-enhanced CVD, or to deposit silver films under MOCVD conditions. 

The growth direction of nanotubes can be controlled by the gas flow or by applying electric fields (plasma-enhanced CVD) [67]. Controlling CNTgrowth with CVD yields more organized CNT that can be readily integrated into addressable structures for fundamental characterization and potential applications. 

Figure 3.14 Different configurations of vertically aligned CNTs either by m-situ growth of CNTs from plasma enhanced CVD or CNT self-assembly through surface reactions on gold or silicon substrates.

A thick (> 1 jum) field oxide layer is formed after the implant activation. The field oxide is generally deposited nsing low-pressnre CVD (LPCVD) or plasma-enhanced CVD (PECVD) process becanse the Si-face of SiC has very low oxidation rate and becanse consumption of the implanted layer must be minimized. The field oxide layer is then patterned by selectively etching to remove all oxide from the... 

There are numerous materials, both metallic and ceramic, that are produced via CVD processes, including some exciting new applications such as CVD diamond, but they all involve deposition on some substrate, making them fundamentally composite materials. There are equally numerous modifications to the basic CVD processes, leading to such exotic-sounding processes as vapor-phase epitaxy (VPE), atomic-layer epitaxy (ALE), chemical-beam epitaxy (CBE), plasma-enhanced CVD (PECVD), laser-assisted CVD (LACVD), and metal-organic compound CVD (MOCVD). We will discuss the specifics of CVD processing equipment and more CVD materials in Chapter 7. 

Additional growth considerations, as well as process modeling and plasma diagnostics underlying plasma-enhanced CVD are further discussed by Hess and Graves in Chapter 8, which is specifically devoted to plasma processing. 

The balance over the ith species (equation IV. 5) consists of contributions from diffusion, convection, and loss or production of the species in ng gas-phase reactions. The diffusion flux combines ordinary (concentration) and thermal diffusions according to the multicomponent diffusion equation (IV. 6) for an isobaric, ideal gas. Variations in the pressure induced by fluid mechanical forces are negligible in most CVD reactors therefore, pressure diffusion effects need not be considered. Forced diffusion of ions in an electrical field is important in plasma-enhanced CVD, as discussed by Hess and Graves (Chapter 8). 

The determination of specific phosphorus compounds in thin films is important. Only through wet chemical analysis was it possible to first discover the presence and then to accurately measure the quantities of P2Os, P203, and phosphine found in plasma, plasma-enhanced, LPO-LTO (low-pressure oxide-low-temperature oxide), and CVD (chemical vapor deposition) processes (3). Methods such as X-ray or FTIR spectroscopy would have seen all phosphorus atoms and would have characterized them as totally useful phosphorus. In plasma and plasma-enhanced CVD films, phosphine is totally useless in doping processes. 

A brief review of the literature concerning the several materials employed in the fabrication of both TIR and ARROW structures is given in Table 2. The processes employed are completely different, ranging from molecular beam epitaxy to several chemical vapor deposition (CVD) systems, such as low-pressure CVD (LPCVD) or plasma-enhanced CVD (PECVD). As a rule, all suitable materials for ARROWS (and in general for IOCs) should have homogeneous refractive indexes, high mechanical and chemical stability, few... 

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