Electron-Beam Doping at Room Temperature
By Dr. Takao Wada, Nagoya, Japan
In 1980, an electron–beam doping (EBD) method at room temperature was proposed by one of the authors (Wada). This study was also concerned with general problems of semiconductor physics. In this method the surface of semiconductor substrates is covered with an overlayer of impurity sheet on the substrate is bombarded with high-energy electrons. The electron energy is 750 KeV and 3-9 MeV, and the electron fluence is (1-10)×1017e cm-2. More effective EBD is obtained in another case of a two-layer system in which the impurity layers were deposited on the substrates. Alloying layers are also formed at the interface of such samples. If water is used instead of an impurity sheet, EB oxide layers are grown on the substrates.
Experiments involving 750 keV electron beam doping (EBD) of Si and Zn into GaAs were performed for systems of GaAs (layer 3)/Si(Zn)//Si(Zn)/GaAs(layer 1). Si(Zn)/GaAs consists of Si(Zn) evaporation deposited layers on GaAs wafers. The overlying layer is in contact only with another Si(Zn) layer. The electron beam source of the Van de Graaff accelerator is used for EBD. After EBD, Si and Zn atoms were detected by secondary-ion mass spectrometry (SIMS). The photoluminescence (PL) spectra for layer 1 show two peaks that can be attributed to the band-to-acceptor transitions and neutral acceptor-bound exciton peaks.
Very thin diffusion layers (some 10 ～ some 100 Å) can be produced by electron beam doping (EBD). In this method, either an impurity layer or a film deposited on the substrate is used as an impurity source. The EBD method was developed further by coworkers. Using EBD, many kinds of impurity atoms can be introduced into substrates such as Si, GaAs, SiC and diamond. Here, we report the EBD methods of boron (B) and phosphorous (P) atoms into Si and diamond substrate to produce a pn homojunction on Si.
The authors report their attempt to develop an algorithm for animation of electron beam doping (superdiffusion). The algorithm system is capable of presenting a continuous display of superdiffusion using computer graphics to simultaneously present several continuous processes of impurity doping in semiconductors. The overall migrations of impurity atoms in the animation is in good qualitative agreement with the experimental results.
EBD (superdiffusion) processes would be useful with advantages over alternative doping technique, because even in the damageless region and at room temperature doping processes may be possible in very thin diffusion layers.
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