Chlorine plasma

Fig. 5. Molybdenum sheet recrystallizcd in nitrogen/chlorine plasma. Electron scanning microscope, 480x...

Fig. 6. Mechanism of recrystallization of molybdenum in nitrogen/chlorine plasma. A cross-sectional view of the sheet with the growing crystals...

Low energy electron-enhanced etching (LE4) uses a DC plasma in which electrons with energies <15 eV and reactive species at thermal velocities are incident on a sample. The sample is also heated at temperatures ranging from 50 to 250°C. Gillis et al [26,27] used hydrogen and chlorine plasmas to produce highly anisotropic etch profiles and smooth etch surfaces, at etch rates of 50 - 70 nm/min. 

One of the most important aspects of plasma-surface processing is that the plasma itself often strongly modifies the near-surface region. An example of this is shown schematically in Figs. 3a and b, in the case of etching. Figure 3a is a depth profile of an originally crystalline silicon surface that has been exposed to a chlorine plasma. (Chlorine plasma is commonly used to etch silicon and other materials.) The plasma has created various silicon... 

Fig. 3. (a) Steady-state depth composition profile of an originally crystalline silicon surface that has been exposed to a chlorine plasma, obtained from angle-resolved X-ray photoelectron spectroscopy, (b) Corresponding side-view schematics of near-surface atomic coordination left, 280-eV ions right, 40-eV ions. (From Layadi et al., 1997.)... 

Plasma etchants are available for most of the films commonly used in micromachining. Etching of oxide, nitride, and silicon is usually done with fluorine-containing compounds such as SiF4, CF4, and SF6. Aluminum and other metals can be etched in chlorine plasmas such as SiC l4 and BC13. In certain conditions, better results can be obtained by combining several gases. 

Poly(2,3-norbornene) has an etch rate that is 15% slower than that of a novolac resin in an aggressive chlorine plasma and is another primary 193 nm resist platform [241], Vinyl addition polymerization of norbornenes resulting in... 

Neutral species do not have any directionality. They can etch equally well in all directions undercutting the mask (e.g., etching of silicon by fluorine atoms). When ion bombardment is necessary for etching to occur (e.g., etching of undoped silicon in chlorine plasma), anisotropic (vertical) wall profiles can result (Fig. 2, left). The mask pattern can then be faithfully reproduced into the film. There is a host of gases [9-12] that have been used for plasma etching materials encountered in microelectronics. Table 2 provides only a small sample. 

Table 4. Representative reactions in argon and chlorine plasmas.

The MPRES simulator has been validated by comparing predictions to experimental data taken in a Gaseous Electronics Conference (GEC) reference cell [155]. Predicted [101] (lines) and measured [156] (points) radial profiles of electron density, electron temperature, and plasma potential for a chlorine plasma are shown in... 

Wafer temperature affects the rate of spontaneous etching and also polymerization reactions. Wafer temperature control is important in semiconductor manufacturing. The temperature is typically controlled by relatively high pressure (several torr) He cooling from the backside of the wafer. The model below refers to silicon etching in a chlorine plasma as a typical example [98]. 

Fig. 30. Mechanisms of heat gain and loss of a silicon wafer during etching in a chlorine plasma. After [98).

Fig. 32. (top) Spatiotemporal profiles of etch rate of silicon in a chlorine plasma measured by laser interferometry. The measured Cl atom concentration is also shown (bottom) Etch rate of silicon (at the wafer center) in a chlorine plasma as a function of lime predicted by a mathematical model (solid lines) and measured under the same conditions (points). Curves a and b correspond to accommodation coefficient values of 0.50 and 0.75, respectively. After [98],... 

This is a long essay question which can be answered using any of the major modification techniques listed in the chapter on polyethylene modification. All information needed to compare and contrast two modification techniques, the changes in polyethylene physical and chemical properties, and an example of real world applications for that modified polyethylene are to be found for each ofthe techniques Sulphochlorination, Chlorination, Plasma Modification, Crosslinking - Chemical and E-Beam, and Graft Modification with Maleic Anhydride. 

Heavily anodized aluminum is used in plasma systems exposed to chlorine plasmas, which corrode staiidess steel. After anodization, the anodized layer is densified by seating using hot water contaiiung itickel acetate or, if heavy metal contamination is a concern, steam sealing can be used. The Hastalloy C-22 alloy is also used for chlorine environments. Monel and polymer-coated surfaces are used in some applications. 

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