Process steps of thermal diffusion method

Process steps of thermal diffusion method.

1, the radius of donor or acceptor impurity atoms is generally large, so it is difficult for them to directly enter the gap of semiconductor lattice. Only when there are lattice vacancies in the crystal can impurity atoms enter and occupy these vacancies, thus entering the crystal.

2. In order to produce a large number of lattice vacancies in the crystal, it is necessary to heat the crystal to intensify the thermal motion of the crystal atoms, so that some atoms can get high enough energy to leave the lattice position, leaving vacancies (at the same time, the same amount of interstitial atoms are produced, and vacancies and interstitial atoms are collectively referred to as thermal defects), so the diffusion coefficient of atoms increases exponentially with the increase of temperature.

3. For Si crystal, to form a large number of vacancies in it, the required temperature is about 1000 degrees [C], which is the temperature of thermal diffusion.