Doping of Epitaxial Films

In the case of in-situ doping during epitaxy, a small amount of dopant gas is introduced into the reactor at the same time as the silicon precursor. The 

At high temperature, the molecules of dopant are dissociated into different volatile species. The equilibrium partial pressures of these species can be calculated thermodynamically. In the case of diborane, equilibrium partial pressures of gaseous species in the system Si-H-Cl-B have been calculated by Bloem and Giling [8]. The data can provide information on dominant dopant species for a given partial pressure. For example, for low partial pressure of PH3, the dominant species in the gas phase are PH3 and PH2. For high partial pressure PH3, P2 becomes the dominant species. 

The actual incorporation of dopants in silicon is determined by a factor of segregation Keg. It is given by the concentration of dopants in silicon divided by the ratio of partial pressure of dopant gas (Pgopant) and silicon precursor 

On the one hand, when Keg is less than 1, part of the incorporated dopant atoms are rejected from the silicon layer. On the other hand, when Keg is equal to 1, the atoms of the dopant gas are completely incorporated in the silicon. 

In the regime limited by the surface kinetics, adding a dopant gas to induce n-type or p-type doping causes an increase in the growth rate. On the contrary, in the regime limited by mass transfer, adding dopants in the reactive gas does not affect the silicon growth rate [16-18]. 

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