Doping chamber:
In order to ensure that only boron ions are used for doping, just before the beam enters the doping chamber, a magnetic field is used to change the direction of the ion beam. The magnetic field will change the direction of only the ions. The neutral atoms will not be affected by the magnetic field. Thus only the ions will fall on the wafer. The next section is called wafer chamber (Figure 7.6)..  The beam size is approximately 1 cm2. The wafer size can be 200 mm or 300 mm. So the beam has to be scanned over the entire wafer. There are two ways of scanning: one is called electrical scanning and the other is mechanical scanning. In the electrical scanning, using electrodes, the beam is moved by applying suitable positive and negative voltages. In the mechanical scanning the wafer is moved, while the beam is held stationary. Sometimes, a combination of beam scan and rotation of wafer is also used to ensure uniformity.

Figure 7.6. Doping chamber

When the boron ion is added to the wafer, the positive charge has to be neutralized. This is done by supplying electrons from the back of the wafer. We can measure the total current used for this and from this calculate the amount of boron deposited. By this method, the exact quantity of boron added can be measured very precisely.