Accelerating tube

The insulated core transformer is another direct electron beam machine. It is similar to a three-phase power transformer in that a core and coils are used. One insulated core transformer will drive three accelerator tubes, which allows great flexibility and good power utilization. The Linac (linear accelerator) is an indirect electron beam ma-... 

Typically, a source gas such as boron trifluoride [7637-07-2], BF3, is exposed to an ion source that causes the gas to ionize. An analyzer discriminates between all the ionic particles using a magnetic field that can select particles having the correct mass-to-charge ratio to pass through the analyzer to an acceleration tube. The ions are accelerated in the tube and collimated into a beam that is scanned over the substrate wafer. The three primary parameters of any implantation process are the type of dopant species, the accelerating energy used for implantation, and the dose of the source gas. The dose is the total number of ions that enter the wafer. Dose, ( ), can be calculated... 

Fig. 7.2. Diagram of the PDS-1000/He, a stationary particle bombardment machine that is connected to a helium gas container. Controlled by adjustable valves, the gas stream (He) terminates in an acceleration tube, which is mounted on the top of a target chamber. This chamber is closed by a door and set under vacuum shortly before bombardment. When gas flows into the acceleration tube, the rupture disc bursts releasing the shock wave into the lower part of the tube. The gas pressure then accelerates the macrocarrier sheet containing the microprojectiles on its lower surface. The net-like stopping screen holds the macrocarrier sheet back and serves to block the shock wave, while the microprojectiles slip through the pores of the grid and continue on towards their final target.

Referring to Fig. 2.1. assume the particle enters the accelerating tube at a zero velocity. From Points 1 to 2. the particle is accelerated by its interaction with the gas stream and moves in the same direction as that of the gas stream. Thus we have... 

Separating variables and integrating them in the integral of [0, np0], the distance that the particle has to travel in the accelerating tube, or, in other words, the effective length of the accelerating tube needed, L.K, can be obtained as... 

Figure 2.6 shows the relationship between the residence time of a single particle in the impingement zone, tf, and the length of the accelerating tube, /ac. As can be seen, in the range of /ac smaller than 1.0, t increases quickly as /ac increases while after /ac = 1.0, the increase in /, with /ac is smoothed. 

Consider the impingement between two opposed particles-gas suspension streams from accelerating tubes of the same diameter. The assumptions made in the establishment of the model are (1) The streams are symmetrical with respect to both the jet axis and the impingement plane (2) The gas flow velocity and all the physical properties of gas and solid are kept constant and (3) The particles beyond collision penetrate into the opposing stream up to. rlllas, while any particle will be drawn out of the system immediately once it collides with another particle. 

Inside the accelerating tube the particles are accelerated by the air flow from zero to a certain velocity, usually 60-70% of the gas flow velocity. During acceleration, the relative velocity between the particles and the gas flow is very high. On the other hand, the concentration of particles in the solid-gas suspension to be processed with impinging streams is generally very small, as mentioned above, so that the interaction between particles can be neglected. Therefore the movement of particles can be described approximately with Newton s motion equations for a single particle, as follows ... 

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