Diffusion Engineering by Carbon in Silicon

Abstract

The possibility to suppress undesirable diffusion of the base dopant boron in siliconbased bipolar transistor structures by the incorporation of a high concentration of carbon has lead to renewed interest in the behavior of carbon in crystalline silicon. The present paper will review essential features of carbon in silicon including solubility, diffusion mechanisms and precipitation behavior. Based on this information the possibilities to use carbon to influence diffusion of dopants in silicon by the introduction of non-equilibrium concentrations of intrinsic point defects will be discussed as well as the reason for the relatively high resilience against carbon precipitation. Interactions between carbon and oxygen will be mentioned, especially in the context of an as yet unexplained fast out-diffusion of carbon close to the surface.

Doping of silicon by carbon during laser ablation process

“…Hydrocarbon molecules are always present in the air as pollutants and have good ability to be adsorbed on surfaces. An equilibrium solubility of carbon substitutionally dissolved in Si is 10 18 cm -3 at 1300 o C [7]. Solubility of interstitial carbon is less by more orders of magnitude.…”

“…Even at later dissolution in silicon, the CO 2 molecules remained in the bulk due to their large size. Complexes corresponding to CO and CO 2 molecules may be fast diffusing entities in silicon [7].…”

“…Further, the plasma actively reacts with the ambient air creating ions that can be adsorbed onto the surface. Therefore, the surface features formed in air are likely to be influenced by such ablation products as well as by dopants that become mobile during the high temperature laser heating cycle [7].…”

IR studies of the oxygen and carbon precipitation processes in electron irradiated tin-doped silicon

“…Considering co-doping pairs (C, Sn) in Si will help us gain a more complete understanding of mechanisms that govern O and C precipitation processes as well as the ways that Sn isovalent dopants affect these processes. Importantly, since V and Si I play [61][62][63][64][65][66][67] a key role in the O and C precipitation processes we can reversibly deepen our understanding on the mechanisms through which these primary defects affect the agglomeration of O and C impurities in Si treated at elevated temperatures. Also it could enhance the opportunities for technological improvements of Si providing an engineering strategy for thermal defects that could be employable to analogous systems.…”

Comparative study of defect evolution in carbon implanted strained SiGe and SiSn layers

“…It is well known that carbon atoms effectively influence the diffusion of the main dopant atoms in Si and SiGe strained layers due to the capture of excess self-interstitials in Si resulting in migration suppression of interstitial-type diffusing dopants such as B and P atoms in Si and SiGe [8][9][10][11]. This is because carbon atoms in silicon may occupy substitutional lattice sites (C S ) in concentration up to ~ 3x10 17 cm -3 and these C S atoms are effective trap for selfinterstitials (I) [8].…”