CVD atmospheric pressure

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). 

The CVD reactions used to produce epitaxial silicon are described in Ch. 8. Originally, atmospheric-pressure CVD was used, but it is gradually being replaced by low-pressure CVD in spite of higher equipment cost and complexity. Low-pressure CVD appears to yield a better film with less autodoping and pattern shift. 

Figure 15.5. Atmospheric-pressure CVD production system for the deposition of photovoltaic coating. (Source Watkins-Johnson, Palo Alto, CA)...

Modeling of Cold-Wall, Atmospheric-Pressure CVD Reactors. 

LPCVD reactor modeling involves many of the same issues of multi-component diffusion reactions that have been studied in the past decade in connection with heterogeneous catalysis. Complex fluid-flow phenomena strongly affect the performance of atmospheric-pressure CVD reactors. Two-dimensional and some three-dimensional flow structures in the classical horizontal and vertical CVD reactors have been explored through flow visual-... 

Figure 6 Atmospheric pressure CVD system with gas injector.2...

Aerosol delivery of the precursors was chosen because it was expected that although the species were monomeric, their volatility was likely to be low based on the TGA results described earlier, and that the crown ether might dissociate on heating for extended periods. The compound Ca(SOCMe)2(15-crown-5) was dissolved in ethanol and delivered in a nitrogen gas stream to a cold-wall atmospheric pressure CVD reactor where the substrate temperature was varied between 300 and 400°C. Analysis of films deposited at 310°C revealed that crystalline CaS was deposited, approximately 100 nm thick, with a deposition rate of 10 nm/min. The X-ray powder pattern indicates that CaS was formed with preferential (200) orientation (see Fig. 63). The SEM data showed that the films comprised cubic crystallites with dimensions consistent with the linewidth of the peaks observed by X-ray diffraction. The bulk composition corresponded to CaS as determined by AES. 

Atmospheric pressure CVD can be employed to prepare arrays and networks of PbS nanowires.222 Monodisperse PbTe nanorods of sub-10 nm diameter are obtained by sonoelectrochemicai means by starting with a lead salt and TeO, along with nitriiotriacetic... 

Evans, P., Pemble, M. E. and Sheel, D. W. (2006). Precursor-directed control of crystalline type in atmospheric pressure CVD growth of Ti02 on stainless steel. Chem. Mater. 18(24), 5750-5755. 

Fig. 10 Schematic diagram of a continuous flow, atmospheric-pressure CVD reactor.

When pressure is used to control the deposition process, CVD can be classified into three categories, namely atmospheric-pressure CVD, low-pressure CVD (i.e. <1 Torr) or ultra-high vacuum CVD (i.e. 10 3 Torr) [10], Pressure has a considerable effect on the deposition rate and quality of the finished products, in terms of coating thickness uniformity. Detailed impacts of the pressure control are discussed in Chapter 4. 

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. 

Atmospheric pressure CVD was first used for CVD in the microelectronics industry. The reactor for APCVD is, in general, relatively simple. However, as compared to LPCVD, APCVD can be mass-transport rate limited. Most of the APCVD used are for low-temperature oxide deposition and epitaxy. 

Atmospheric pressure CVD of NbCi-yN, using NbCl, NH3, and CH4 has been employed in three separate approaches toward the optimization of reaction characteristics [69]. These were (i) simultaneous deposition of niobium, carbon, and nitrogen by hydrogen reduction of NbCls with decomposition of methane and ammonia at a temperature of 900-1000°C (ii) deposition of a niobium amide complex derived from NbCl.s/NHi in nitrogen as a carrier gas at 250-350 °C, and subsequent conversion in ammonia/methane at 1 000-1 100 °C (iii) separate deposition of elemental niobium or NbCl.3 by hydrogen reduction at 500-1000°C and subsequent conversion to NbCi yNy in an ammonia/methane atmosphere at 1000-1 100°C. The results of these three approaches are given below. 

The superconducting properties of Ta films on alumina substrates prepared by atmospheric pressure CVD have recently been reported [55]. Hydrogen reduction of tantalum pentachloride at an unreported temperature gives superconducting a-7a films with r, = 3.3 K and 77, = 11.2 kOe. 

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). 

Atmospheric pressure CVD Low temperature LPCVD Medium temperature LPCVD Plasma-enhanced CVD... 

The reactor in which the chemical coating processes actually take place is the essential part of the system and must be designed according to the specific physical and chemical process parameters. To coat glass by atmospheric-pressure CVD, generally low temperature reactors are used which can be classified according to their gas flow characteristics and operation principles into four basic types [69] ... 

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