Implanted layers

Diffusion. Another technique for modifying the electrical properties of siUcon and siUcon-based films involves introducing small amounts of elements having differing electrical compositions, dopants, into substrate layers. Diffusion is commonly used. There are three ways dopants can be diffused into a substrate film (/) the surface can be exposed to a chemical vapor of the dopant at high temperatures, or (2) a doped-oxide, or (J) an ion-implanted layer can be used. Ion implantation is increasingly becoming the method of choice as the miniaturization of ICs advances. However, diffusion is used in... 

NTD wafers were produced by irradiating natural ultra pure Ge crystals by means of a flux of thermal neutrons (see Section 15.2.2). To realize the electrical contacts, both sides of the wafers (disks, 3 cm in diameter, 3 mm thick) were doped by implantation with B ions to a depth of 200nm. The implanted layers are doped to such a high concentration that the semiconductor becomes metallic. Then a layer of Pd (about 20 nm) and Au (about 400 nm) was sputtered onto the both sides of the wafers. Finally, the wafers were annealed at 200°C for 1 h. The wafers are cut to produce thermistors of length 3 mm between the metallized ends (3x3x1 mm3 typical size) the electrical contacts are made by ball bonding with Au wires. 

Another effect of lattice contraction of a boron-implanted layer might be to cause reorientation of the B—H complexes in the layer. Calculations (Denteneer et al., 1989) and measurements (Stavola et al., 1988) show that the B—H complex can readily reorient itself in response to an applied stress at room temperature. Thus, reorientation might occur in a boron-implanted layer and vitiate the analysis of the channeling experiment. In a (100) sample, however, all the (111) directions lie at the same angle to the stress axis if relaxation in the plane of the sample is isotropic, and all orientations of the B—H complex are energetically equivalent. This would not be true in (111) material. 

Burggraaf, A. J., K. Keizer and B. A. van Hassel. 1989a. Nanophase ceramics, membranes and ion implanted layers. Paper read at S.I.C. Mat. 88-Nato ASl, Surfaces and interfaces of ceramic materials, 4-16 September 1988, lie d 01eron. 

A thick (> 1 jum) field oxide layer is formed after the implant activation. The field oxide is generally deposited nsing low-pressnre CVD (LPCVD) or plasma-enhanced CVD (PECVD) process becanse the Si-face of SiC has very low oxidation rate and becanse consumption of the implanted layer must be minimized. The field oxide layer is then patterned by selectively etching to remove all oxide from the... 

Reverse Time Effect of Diffusion. Michel (51) observed two new effects associated with the low-temperature annealing of B-implanted layers (1) an... 

D removal from hydrogenated films was also studied under exposure to other atmospheric gases. Nitrogen exposure and heating in vacuum at or below 570 K was found to have no effect on the release of deuterium from D-implanted layers [63]. On the other hand, exposure of D-implanted layers [63], as well as TFTR co-deposits [61], to water vapor did result in D removal, but with no evidence of C erosion. It is suggested that D is removed via isotope... 

R.A. Causey, W.R. Wampler, D. Walsh, Comparison of the thermal stability of the codeposited carbon/hydrogen layer to that of the saturated implant layer, J. Nucl. Mater. 176-177 (1990) 987... 

Si02 layers pre-implanted with 140keV Si ions, and those with embedded Si nanociystals (Si-ncs) have been irradiated with 130 MeV Xe ions, HREM and photoluminescence spectroscopy wo e used for the characterizations. In the Si-implanted layers HREM revealed the 3-4 nm-size dark spots, whose number and size grew with increase in Xe ion dose. Photoluminescenoe showed the presence of two bands - at 780 nm and at 670 nm. The intensity and position of the bands depended on the dose. Changes of the spectra and the results of passivation were interpreted as transformation of Si-ncs (-780 nm) into damaged Si-ncs (-670 nm) and vice versa. It is concluded, that electronic losses are responsible for the formation of new Si-ncs, whereas elastic losses introduce the defects. 

This friction behaviour has been related to the three-dimensionally cross-linked structure of the ion-irradiated polymer material, since, with increasing fluence, the polymer surface becomes harder and less elastic due to a greater extent of cross-linking. The stick-slip behaviour is thus caused by the adhesion of the two surfaces, and the periodic elastic extension and sudden release of the cross-linked structure of the implanted layer. The microfriction results have been correlated with nanoindentation hardness measurements, which are an indirect measure of the extent of cross-linking (Rao etal, 1995). 

The doping concentration is often confused with the carrier concentration. In uniformly and moderately doped substrates the two are virtually identical at room temperature. This is no longer true when the substrate is heavily doped or when a diffused or ion-implanted layer is measured. Even if all the dopant atoms are electrically active, the carrier concentration in heavily-doped material is lower than the doping concentration, as described by Fermi-Dirac statistics if). This is further aggravated if, for example, the ion-implanted layer is not wholly activated or if there is a steep doping gradient. It is important that one is aware of these difficulties. 

Fig. 10.3. Solid-phase epitaxial regrowth versus anneal time for an amorphous-implanted layer on (100) oriented single crystalline Si...

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