Planetary reactors

Aixtron has manufactured both a cold-wall planetary reactor and a hot-wall planetary reactor for 7 x 2-inch wafer capacity or 5 x 3-inch. The cold-wall reactor has provided very good uniformities and its performance has been described in... 

Figure 4-13. (a) Schematic of horizontal tube (b) schematic of cylindrically symmetric vertical barrel reactor tube (c) schematic of circularly symmetric Planetary Reactor (d) schematic of vertical pedestal reactor (pedestal may be rotated or entire reactor may be inverted) and e) schematic of cluster tool type reactor systems. (Courtesy of EMCORE Corp.). 

A more recent and significant, improvement to the horizontal tube is the wrapping of it into circularly symmetric space, resulting in what Aixtron has termed a Planetary Reactor, Figure 4-13b. To counter depletion effects, the wafer platter and wafers are all rotated. Further a graded temperature scheme also is typically used. While this is complex, it has proven effective in production as described below. This system uses a radial flow scheme inside and, thus, provides a controlled depletion in flow direction, producing uniform films over large areas and multiple wafers. 

One strategy for the increase of the wafer area has been to increase the number of wafers in the reactor. Modem reactors today can carry 30x2 inch and 42x2 inch wafers for the CRIUS Close-Coupled-Showerhead (CCS) and Planetary Reactor types, respectively (see Fig. 1). 

Fig. 3. Schematic of three commonly used types of MOCVD reactors where the arrows indicate gas flow (a) vertical rotating disk where (— represents an inlet to promote a laterally uniform gas flow, (b) planetary rotation, and (c) hori2ontal.

Planck s constant, 23 33 Planck spectrum, 23 2 Plan-Do-Check-Act (PDCA) model, 21 174 Plane-polarized light (PPL), 16 470, 476 Planetary rotation reactor, 22 154, 155 Planetary type mixers, 16 720 Plane wall, heat-transfer rate through,... 

There are other advantages of employing magnetic ball mills besides the control of mechanical milling modes. Since the centrifugal force becomes a secondary factor in milling, and the reactor shell rotates at low RPM, contamination from balls and shell wear is lower than in a vibrational or a planetary mill there is less ball wear involved and contaminations with Fe from steel become less of the problem. Also lower rotations and uniaxial movement of reactors paced on horizontal axle allow... 

Curtis, D., Benjamin, T. et al. 1989. The Oklo nuclear reactors cumulative fission yields and nuclear characteristic of reactor 9. Earth and Planetary Science Letters, 89, 193-206. 

Hidaka, H., Sugiyama, T., Ebihara, M. Holliger, P. 1994. Isotopic evidence for the retention of 90Sr inferred from excess 90Zr in the Oklo natural fission reactors implication for geochemical behaviour of fissiogenic Rb, Sr, Cs and Ba. Earth and Planetary Science Letters. 122, 173-182. 

All scientists agree that chemistry is the basis of life and with that preamble it seems almost certain that the first cells one sees in the Hadean stones are the first ones on earth their ancestors were the heat- and light-driven bio-reactors. The Darwinians see the same cells but because the (in principle unprovable) single origin is a creed of the model, they postulate that a single ancestor must have lived much earlier and mutated into all of the cells that are visible at this horizon. At this point the old hypothesis is defeated by the researchers in planetary sciences who do not see any biology-time before the time of the first massive invasion of the earth crust by cells. The hell fire of global accretion was too close for descent with variation . 

FIGURE 5 Schematic diagram of a typical large-scale horizontal gas foil Planetary MOCVD reactor chamber. The precursor gases are injected in the center of the rotating wafer carrier and the gas flows horizontally over the individually rotating wafers. 

Mechanical activation was performed in a high energy (acceleration up to 70 g) planetary ball mill with stainless steel reactor and balls under an argon atmosphere during 1 h. All the sample handling has been operated in Ar-filled glow box (MBraun), in which the water/oxygen levels were below 1 ppm. 

An oxide reactor featuring two planetary systems arranged concentrically was described by Wollam (1971). In this complex reactor, the driver element is a cylinder rotating within an annular spacing between a circular inner resistance-heated block and an outer heat ring. The gases are dispensed in a... 

True compound semiconductor production, in the Si sense of production, has only recently begun to come about with the introduction of large planetary systems and cluster tool compatible reactors [18]. Si equipment manufacturers have been reluctant to enter this niche market in force, and are generally unlikely to do so in the near future because of the small market size (—35-50 million dollars compared to the multi-billion dollar Si equipment markets, for example see Applied Materials sales). 

Figure 10.7 shows an example from the hazard log created during the PHA effort. The example hazard shown is nuclear reactor overheating. Nuclear power generation and use, particularly during planetary surface operations, was considered to be an important option in the architectural tradeoffs. The potential accident and its effects are described in the hazard log as ... 

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