Plasma Enhanced CVD PECVD

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). 

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. 

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. 

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... 

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-... 

In addition to thermally-created CVD films, much work has been done using glow discharges to modify the deposition. Therefore, Chapter 2 reviews the fundamentals of plasma-enhanced CVD (PECVD). Initially, the basic character of a plasma is covered. Then we discuss the influence of the reactor configuration on the plasma behavior and PECVD deposition. The two major PECVD reactor systems are reviewed, and then several new concepts are considered. 

There are some reports [7,8] about preparing a-SiC and p-SiC films at low temperature by Cat-CVD and other methods, such as magnetron sputtering and plasma enhanced CVD (PECVD). In order too get high quality p-SiC films, the substrate temperatures are still high (400 600°C). Furthermore, the growth mechanism of P-SiC films by Cat-CVD is not well understood. In this work, by using Cat-CVD with precarbonization process, nanocrystalline p-SiC films were successfully synthesized on Si substrate at the low substrate temperature of 300 C. 

Figure 1.3 clearly demonstrates the luminous gas phase created under the influence of microwave energy coupled to the acetylene (gas) contained in the bottle. This luminous gas phase has been traditionally described in terms such as low-pressure plasma, low-temperature plasma, nonequilibrium plasma, glow discharge plasma, and so forth. The process that utilizes such a luminous vapor phase has been described as plasma polymerization, plasma-assisted CVD (PACVD), plasma-enhanced CVD (PECVD), plasma CVD (PCVD), and so forth. 

In order to find the domain of LCVD, it is necessary to compare various vacuum deposition processes chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma chemical vapor deposition (PCVD), plasma-assisted CVD (PACVD), plasma-enhanced CVD (PECVD), and plasma polymerization (PP). All of these terms refer to methods or processes that yield the deposition of materials in a thin-film form in vacuum. There is no clear definition for these terms that can be used to separate processes that are represented by these terminologies. All involve the starting material in vapor phase and the product in the solid state. 

PP is a CVD process in which the chemically reactive species are created by plasma. Terms such as plasma-assisted CVD (PACVD) and plasma-enhanced CVD (PECVD) are inadequate to describe PP. Unless the substrate temperature is raised... 

A variety of CVD methods and CVD reactors have been developed, depending on the types of precursors used, the deposition conditions applied, and the forms of energy introduced to the system to activate the chemical reactions desired for the deposition of solid fihns on snbstrates. For example, when metalorganic compounds are used as precursors, the process is generally referred to as MOCVD (metalorganic CVD), and when plasma is nsed to promote chemical reactions, this is called plasma-enhanced CVD (PECVD). There are many other modified CVD methods, such as LPCVD (low-pressure CVD), laser-enhanced or assisted CVD, and aerosol-assisted CVD (AACVD). 

Akitmoto and Watanabe219, have reported the deposition of V Si mixtures by plasma enhanced CVD (PECVD). Depending on the flow ratio of WF6/SiH4, x can be varied from 0.04 to 0.99. The deposition was carried out at a substrate temperature of 230°C. It is interesting that both the as-deposited and annealed (1100°C, 60 min., N2) films, with x values of 0.45 or less, did not exhibit any X-ray diffraction pattern due to a WSi2 phase. From their data it can be estimated that a near stoichiometric disilicide film would have a resistivity of about 200 ptflcm after anneal. The authors claimed that specular films were obtained. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

Chemical vapor deposition includes various systems, and they are low-pressure CVD (LPCVD), atmospheric pressure CVD (APCVD), plasma enhanced CVD (PECVD), and others. Each type of CVD system has its own advantages and limitations. For instance, in LPCVD, the reactor is usually operated at 1 torr. Under this condition, the diffusivity of the gaseous species increases significantly compared to that under atmospheric pressure. Consequently, this increase in transport of the gaseous species to the reaction sites and the by-products from the reaction sites in LPCVD will not become the rate-limiting steps. This leads to the surface reaction step to be the rate limiting one. 

Thin film dielectrics are usually deposited using chemical vapor deposition (CVD). A variation of CVD utilizing a plasma discharge is called plasma-enhanced CVD (PECVD) and is the standard in IC fabrication for the deposition of dielectric films. Plasma-enhanced CVD involves the formation of a solid film in a substrate surface from volatile precursors (vapor or gas) in a plasma discharge. The precursors are chosen to contain the constituent elements of the final film and chemical reactions in the gas phase are encouraged. They are condensed in a substrate that is heated or cooled. It will be shown later that porosity can be introduced in the PECVD films. Spin coating is another preparation technique and a popular choice... 

In the Chemical Vapor Deposition (CVD) methods, the starting material undergoes specific chemical reactions at the hot surface of the substrate to form thin layers of the desired material. The reaction can be stimulated by various energy sources, e.g. plasma, giving plasma enhanced CVD (PECVD), or a laser, giving laser CVD. 

One method which has been investigated extensively and applied widely over the last decade is plasma-enhanced CVD (PECVD). Many CVD processes employing plasmas still require substrate heating, since plasma temperatures typically are several hundred degrees lower than those demanded for conventional CVD. Thus, the technique often is known as plasma-enhanced CVD (PECVD) or plasma-assisted CVD (PACVD). 

In the first chapter of this book, an overview of CVD techniques has been given, and more detailed descriptions can be found in several textbooks [9, 10]. Many different CVD reactors have been used for the deposition of conducting films, i.e., thermal, UV-enhanced CVD (UVCVD), laser-assisted CVD (LACVD), plasma-enhanced CVD (PECVD) and metal-organic CVD (MOCVD). In addition, two techniques were included, which are not typically part of CVD, chemical transport and spray pyrolysis. 

A wide variety of deposition methods are available, and several systems of each type are produced commercially. A review of typical systems has been published [10]. In regard to the CVD of insulating films, four general reactors are presently used atmospheric pressure CVD (APCVD), low and medium temperature low pressure CVD (LPCVD), and plasma-enhanced CVD (PECVD). 

Plasma-enhanced CVD (PECVD) has been successfully applied to silicate glasses [57]. PECVD of PSG and BPSG is typically performed at substrate temperature of 300°C, although deposition has been reported at as low as 165°C [58]. 

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