Deposition systems

The widely used Parylene C owes its popularity ptincipaHy to the room temperature volatiUty of its monomer. The Parylene C monomer, chloro-A-xylylene, has become the de facto performance standard. By comparison, the Parylene N monomer, A"xylylene itself, is too volatile and would perform better ia a sub-ambient temperature deposition system. The Parylene D monomer, dichloro-A-xyljlene [85586-88-5] is too heavy, and causes distribution problems ia larger deposition systems. 

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. 

Fig. 1. Vacuum deposition system having a plasma processing capabiHty, where the dashed lines represent optional additions to a system.

In appHcatioa, the automobile or other article to be coated is made the cathode ia an electro deposition system. A current differential on the order of 250 to 400 V is appHed, which attracts the positively charged coating aggregates to the cathode. At the cathode, hydroxide ions from the electrolysis of water precipitate the aggregates on the surface of the metal. As the conveyor removes the coated product from the bath, residual Hquid is tinsed off with water and the article is conveyed iato a bakiag ovea for a high temperature bake. 

The deposition system or reactor (the term reactor is universally used in CVD parlance to describe the vessel in which the reaction takes place and has nothing to do with a nuclear reactor). 

HfC is produced by CVD mostly on an experimental basis. The most common deposition system is the reaction of the metal chloride with a hydrocarbon, which can be propane (C3H8), propene (C3H6), toluene (C7Hg), or methane (CH4) as follows b H l... 

Most SiC deposition systems involve the Si-C-H-Cl chemical combination. Avery commonly used reaction is the decomposition of methyl trichlorosilane (MTS) P CP" ]... 

Another common deposition system is based on the reaction of silane with a hydrocarbon such as propane or benzene in the following simplified reactions ... 

The most common deposition system is the reaction of the metal chloride with a hydrocarbon as follows ... 

More so than the carbides, the interstitial nitrides are susceptible to the presence of even minute amounts of impurities such as hydrogen and particularly oxygen which tend to distort the structure. To avoid such harmful contamination, it is necessary to maintain a deposition system that is completely free of oxygen and hydrogen. 

Tungsten disilicide (WSi2) is refractory and stable with low resistivity. As with other silicides, a common deposition system uses silane as the silicon source with tungsten hexafluoride as follows ... 

Deposition has been carried out on architectural glass yielding single-junction amorphous silicon with an efficiency of 13% in the laboratory, but with lower efficiency in production devices. An atmospheric-pressure deposition system in shown in Fig. 15.5. The gas injection device is shown in Fig. 15.6. 

A similar deposition system uses a plasma which is produced by a traveling microwave cavity. No other source of heat is required. The deposition system is shown schematically in Fig. 16.12. The reactants are the same as in the thermal CVD process. Pressure is maintained at approximately 1 Torr. In this case, the deposition occurs at lower temperature, no soot is formed and a compact glass is produced directly. A main advantage of this method is the more accurate grading of the refractive index of the cladding material. 

In developing and applying the erosional-depositional system, careful consideration was given to the environmental factors which influence the potential for erosion, transport and deposition climate, topography, geology and soils, as well as human activity. 

The PTFE/Si3N4 multilayers were prepared by Ar+ ion beam alternatively sputtering pure PTFE and Si3N4 ceramic target in a polyfunctional beam assisted deposition system. Si (100) wafer is the substrate. The mutlilayer film has eleven layers with alternatively PTFE and Si3N4 layers, the inmost and... 

In a similar way, electrochemistry may provide an atomic level control over the deposit, using electric potential (rather than temperature) to restrict deposition of elements. A surface electrochemical reaction limited in this manner is merely underpotential deposition (UPD see Sect. 4.3 for a detailed discussion). In ECALE, thin films of chemical compounds are formed, an atomic layer at a time, by using UPD, in a cycle thus, the formation of a binary compound involves the oxidative UPD of one element and the reductive UPD of another. The potential for the former should be negative of that used for the latter in order for the deposit to remain stable while the other component elements are being deposited. Practically, this sequential deposition is implemented by using a dual bath system or a flow cell, so as to alternately expose an electrode surface to different electrolytes. When conditions are well defined, the electrolytic layers are prone to grow two dimensionally rather than three dimensionally. ECALE requires the definition of precise experimental conditions, such as potentials, reactants, concentration, pH, charge-time, which are strictly dependent on the particular compound one wants to form, and the substrate as well. The problems with this technique are that the electrode is required to be rinsed after each UPD deposition, which may result in loss of potential control, deposit reproducibility problems, and waste of time and solution. Automated deposition systems have been developed as an attempt to overcome these problems. 

Significant improvements in ECALE deposit morphology and quality were reported as achieved by switching from a thin layer cell to a thick layer H-form cell, integrated in an automated deposition system [46]. Thin epitaxial films of zinc blende CdTe, CdSe, and CdS with predominate (111) orientations were grown. 

Figure 16.1 Schematic of the UHV deposition system. TA, transfer arm TC, Transfer...

The deposition setup as shown in Figure 4a is the central part of the most commonly used planar diode deposition system. The power to the reactor system is delivered by means of a power supply connected to the reactor via appropriate dc or RF circuitry (matchboxes). Power supplies can consist of generator and amplifier combined in one apparatus, with a fixed RF frequency. More flexible is to have an RF generator coupled to a broadband amplifier [119, 120]. 

FIG. 5. Schematic representation of the ASTER deposition system. Indicated are (I) load lock. (2) plasma reactor for intrinsic layers. (3) plasma reactor for />-type layers. (4) plasma reactor for t -type layers, (5) metal-evaporation chamber (see text). (6) central transport chamber. (7) robot arm. (8) reaction chamber, (9) gate valve, (10) gas supply. (11) bypass. (12) measuring devices, and (13) tur-bomolecular pump. 

The ID fluid discharge model has been applied to the ASTER deposition system (see Section 1.2.4). The deposition reactor has an inner volume of 10 1 and an inner diameter of 20 cm. The upper electrode is grounded (see Fig. 4a), and the powered electrode is located 2.7 cm lower. Other typical silane-hydrogen discharge parameters are summarized in Table IV. 

The SiHa H2 ratio was 20% 80% in all simulations. As most experiments in the ASTER deposition system are performed at a constant total power, the... 

Luft and Tsuo have presented a qualitative summary of the effects of various plasma parameters on the properties of the deposited a-Si H [6]. These generalized trends are very useful in designing deposition systems. It should be borne in mind, however, that for each individual deposition system the optimum conditions for obtaining device quality material have to be determined by empirical fine tuning. The most important external controls that are available for tuning the deposition processs are the power (or power density), the total pressure, the gas flow(s), and the substrate temperature. In the following the effects of each parameter on material properties will be discussed. 

FIG. 40. The influence of deposition temperature on (a) the hydrogen concentration, (b) the microstructure parameter, and (c) the Raman half width P/2. The labels A and P refer to the ASTER and the PASTA deposition system. Series A1 was prepared from a SiH4 H2 mixture at 0.12 mbar. Series A2 and A3 were deposited from undiluted SiHa at 0.08 and 0.12 mbar. respectively. Series PI was deposited from undiluted SiHa. (From A. J. M. Bemtsen. Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands, 1998, with permission.)... 

A systematic study of the role of the ions in the deposition process and their influence on the quality of the layers has been performed by Hamers et al. [163, 301, 332] in the ASTER deposition system. More specifically, a study has been made on the relation between the plasma parameters and the material properties in both the a- and the y -regime at typical deposition conditions. Here, the... 

In the ASTER deposition system, experiments have been carried out in which the excitation frequency was varied between 13.56 and 65 MHz [169]. The other process conditions were kept constant at a power of 10 W, a pressure of 0.16 mbar, gas flows of 30 seem SiHa and 30 seem H2, and a substrate temperature of 250°C. As in Section 1.6.2.3, plasma properties that are deduced from lED measurements are compared with material properties in Figure 63. The lEDs of SiH at four frequencies are shown in Figure 64. 

The plasma potential is about 25 V (Figure 63a). This value of the plasma potential is typical for the silane plasmas in the asymmetric capacitively coupled RF reactors as used in the ASTER deposition system, and is also commonly found in argon or hydrogen plasmas [170, 280, 327]. From the considerable decrease of the dc self-bias with increasing frequency (Figure 63a) it is inferred that the... 

Prototype electrostatic loudspeakers where the graphite is replaced by a-Si H have been made, where a Mylar foil (area 10 x 10 cm-, thickness 6 /im) is used [657]. Deposition of the a-Si H layer was carried out in the ASTER deposition system. Uniform deposition (standard deviation of thickness, 1.5%) was achieved by diluting the SiHa with Ht with SiHa Hi = 1 2 [370]. The deposition was at room temperature. The hydrogen content amounted to 18 at.%, and the bandgap was 1.81 eV. The dark conductivity and AM 1.5 photoconductivity were 7.5 X 10 and 1.8 x 10 cm" , respectively. In practice the film would not... 

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