2.2.1 Dopant Species

In modern semiconductor technology several impurity species with different applications are used. The most important ones are atoms of the third and the fifth group of the periodic table. They are used to generate positively (p-type) or negatively (n-type) doped regions in the semiconductor. For p-type doping mainly boron and indium are used while the preferred species for n-type doping are phosphorus, arsenic and antimony. The implantation of nitrogen is used to influence the diffusion behavior of boron in silicon dioxide and polysilicon. Sometimes also silicon, germanium and carbon are implanted to destroy the crystalline structure of the substrate (pre-amorphization) before the implantation of a dopant species. Thereby shallower dopant profiles can be generated because the channeling effect is suppressed (Sec. 5.2). Recently there are also investigations on the implantation of oxygen to form buried silicon dioxide layers, for the generation of silicon-on-insulator (SOI) devices. This technique is called: Separation by IMplanted OXygen (SIMOX) [91].

The impurities are implanted by single atomic ion beams or by molecular ion beams, which facilitate shallower doping profiles. The disadvantage of the molecular ion implantation is that additional impurities are introduced. The most widely used molecular species are BF$_2$ and recently also B$_{10}$H$_{14}$ for the implantation of boron and N$_2$ for the implantation of nitrogen. Tab. 2.1 summarizes some properties of the most important dopant species.

Table 2.1: Physical properties of some impurity species.

Species	Atomic number	Mass (amu)
Antimony$_{121}$	51	120.903820
Antimony$_{123}$	51	122.904210
Argon$_{40}$	18	39.962383
Arsenic$_{75}$	33	74.921596
Beryllium$_{9}$	4	9.0121822
Boron$_{10}$	5	10.012937
Boron$_{11}$	5	11.009305
Carbon$_{12}$	6	12.000000
Carbon$_{13}$	6	13.003354
Fluorine$_{19}$	9	18.998403
Gallium$_{69}$	31	68.925580
Gallium$_{71}$	31	70.924707
Germanium$_{70}$	32	69.924249
Germanium$_{72}$	32	71.922076
Germanium$_{74}$	32	73.921178
Hydrogen$_{1}$	1	1.0078250
Indium$_{113}$	49	112.904060
Indium$_{115}$	49	114.903870
Nitrogen$_{14}$	7	14.003073
Oxygen$_{16}$	8	15.994914
Phosphorus$_{31}$	15	30.973761
Silicon$_{28}$	14	27.976926
Silicon$_{29}$	14	28.976494
Silicon$_{30}$	14	29.973770