epdf.pub_nanotechnology-and-nanoelectronics-materials-devic

3.3 Applications of Nanodefects in Crystals 31
Fig. 3.20 Formation of a three-layered structure in exposed silicon [31]
(left). Very high penetration rates are achieved: after four hours the 380 µm thick
wafer is completely converted into n-type. A conversion depth of 80 µm for instance,
is received after 16 min. The same depth is obtained for a classical diffusion
after 16 h (Ga, 1300 °C).
If the penetration depth vs. the annealing time is plotted, the diffusion constant
D = 2.9·10 6 cm 2 / s can be derived. This number is comparable with the prediction
of van Wieringen and Warmholz [29] for the diffusion constant of atomic hydrogen.
The limited thermal budget of these p-n junctions and the devices made from
them can be clearly extended if a procedure is used which leads to the so-called
new thermal donors.
Another variant is obtained if denuded silicon is used. This is the fundamental
material for electronic devices: a thin layer is denuded from oxygen (by simple
outdiffusion), while in two subsequent steps of nucleation and precipitation, the
inside of the silicon is prepared as gettering zone for impurities. Thus a high-grade
cleaned surface zone remains for the manufacturing of electronic circuits.
After the application of hydrogen plasma and the subsequent annealing for the
formation of thermal donors in this material, a double peak appears upon measurement
of the spreading resistance (Fig. 3.20). As an explanation, it should be remembered
that the transformation to n-type requires the use of both oxygen (the
later thermal donors) and hydrogen (as catalyst). On the right of the second maximum,
a p-type behavior of the raw material is observed. The hydrogen could not
reach this region. The zone between the two maxima is converted; oxygen and
hydrogen are available. Before the first maximum no oxygen is available for the
transformation in the exposed zone. Some types of devices can be expected on the
basis of this structure.
3.3.3 Smart and Soft Cut
One of the fundamental problems of the production of integrated circuits lies in
the mutual isolation of passive and active devices which are built on the surface of