Crystal growth of silicon is discussed on the basis of in situ X-ray topographic observation in order to obtain a general view of interface structure in melt growth. The effect of dislocations on the faceted growth indicates that Si crystals (Jackson's parameter = 2.7) grow with singular sharp interfaces. However, the in situ observation of the growth interfaces and the dependence of impurity incorporation on the interface orientation lead to the conclusion that a supercooled layer with an intermediary structure between the crystal and melt exists on the melt-side of the interface in growth processes. This layer seems to play an important role in formation of growth bandings and propagation of dislocations. The in situ observation shows that dislocations generally cannot intersect with growth interfaces. This fact is probably due to the presence of the supercooled layer. Dislocations propagate into newly grown dislocation-free regions after the interface proceeds. On the other hand, melting interfaces have a superheated layer on their crystal-side where crystal perfection is degraded : An example is the formation of liquid droplets in the layer which results in microdefects, i.e., swirl defects in dislocation-free crystals are considered to be formed during remelt periods of the growth.
Recently, perfect crystals are desired to fabricate semiconductor devices because of a good performance and a high yield rate. In this review, it is mentioned on growth mechanisms and defects in the epitaxial growth of silicon, which lead successfully to obtain perfect crystals. Growth mechanisms in the chemical vapor deposition methods are devided into the volume reaction dominatingly occuring in the pyrolysis of SiH_4 and the surface reaction in the hydrogen reduction of chlorosilane such as SiCl_4, SiHCl_3, etc.. The volume reaction has been suggested by the fact that silicon fine particles are nucleated above a critical SiH_4 concentration. The surface reaction mechanism has been investigated by the light-irradiated growth, the infrared-absorption spectroscopy of products and the observation of surface morphologies. Important products from a chlorosilane have been considered to be SiCl_2 and SiH_2Cl_2, which contribute both of the growth and the etching reaction. The observation of surfaces of grown layers has resulted in the conclusion that the surface migration of adsorbed clusters may limit the growth rate and cause the rapid layer growth combined with the Kossel's mechanism. The purity of epitaxial layers is interfered by the redistribution of back-etched impurities as well as the generation of defects. The significant defect is dislocations generated mainly by the lattice misfit. However, this is relieved by the lattice-strain compensation using another impurities additional to the usual doped impurity. We have pointed out the point defects and their influences in the last section of this review.
Economically viable means of producing silicon solar cells for the conversion of solar energy into electric power are discussed. Emphasis is given to the discussion of crystal growth techniques capable of growing single crystal silicon ribbons directly and inexpensively from molten silicon. The recently developed capillary action shaping technique has this potential and is discussed in detail. The successful application of this technique to ribbon growth is demonstrated and problems which must be overcome to achieve the goal of low cost silicon are pointed out.
X-ray diffraction topography is one of the powerful non-destructive methods to characterise crystal perfections. The method is complementary to "goniometry" ; for example, the measurement of the rocking curve due to single crystals. The present article is divided into four sections. I. Traverse and Section Topographs II. The Section Topograph of Perfect Crystals III. Comparison between Theory and Experiment IV. Discussion In the first two sections, the experimental and theoretical backgrounds about the observation of Pendellosung fringes are briefly reviewed. Emphasis is put on explaining the wave-optical nature of the fringes. In the last two sections, the work of Wada and Kato (Acta Cryst. A33 (1977) 161) on the intensity distribution of the section topograph is reviewed. The fringe profile could be represented well by the sum of two terms: The dynamical term and the kinematical term. The ratio, however, was very small and an order of 10^<-3> in magnitude, evaluated at the depth zero, in the case of available perfect crystals. The diffraction represented by the kinematical term is infered to be created along the incident beam by slightly distorted lattice. For this reason the magnitude of the kinematical term can be used for a measure to characterise the perfection of very perfect crystals.
For the characterization of single crystals, X-ray diffraction technique has widely been used. To meet the requirement to obtain accurate and detailed information about crystal defects or imperfections, it is important to controll the angular and wavelength spreads of the X-ray beam according to objectives of the study. For this purpose the multiple crystal arrangement has fruitfully been utilized. Firstly, the principle of the multiple crystal arrangement is explained using DuMond diagram which shows the angular and wavelength spreads of the X-ray beam diffracted by crystals, and next its topographic and goniometric applications are discussed. In topography, where the diffracted X-ray beam is recorded on a photographic plate or by TV system as a function of position in the crystal, some applications using collimated X-ray beam obtained by plane crystals as well as monochromatic divergent beam obtained by curved crystal are given. Special emphasis is put on the plane wave topographic study of silicon. In goniometry, where the intensity is measured as a function of angular position of the crystal, various characteristics of rocking curve available for characterization of crystals are discussed, and some examples using highly collimated X-ray beam are shown.
A soft X-ray diffraction technique using asymmetric diffraction is developed as a method of evaluating both thin crystalline films and bulk crystals. It is confirmed that an asymmetric diffraction technique using soft X-ray beams (TiKα_1 and CrKα_1) enables the sampling of only a surface layer within 0.1〜0.3μm contrary to conventional techniques. The improved technique is successfully applied to SOS wafers. As a result, the half-width is found to correlate with both a fault density and a Hall mobility. At the same time, the X-ray anomalous transmission phenomenon in "Bragg case" diffraction is applied in bulk crystal evaluation. Anomalously transmitted peak intensity in the Bragg case is 2〜3 times that of anomalously transmitted intensity in conventional Laue case diffraction at the same μ_0t value. Therefore, high sensitivity to lattice defects is obtained. The technique has been tentatively applied in the evaluation of micro-defects both in Si and GaP crystals.
Lattice strain of dislocation-free epitaxial silicon crystal doped with phosphor (4.5×10^1fcm^<-3>) was measured by X-ray double crystal diffraction. In a middle part of this crystal, where stress is balanced because of the symmetry of crystal shape, strain of the direction perpendicular to the deposited plane (111) is larger in thinner epitaxial layer. On the contrary, strain (expansion) of the direction in this plane is nearly equal to each other and substrate crystal without depending on thickness of deposited layer. These lattice expansion are contradictory to Poisson rule, but can be explained by supposing an anisotropic distortion angle between lattice plane of substrate and epitaxial crystal. These angles are not necessarily related to bending radius of the crystal, but depend thickness of epitaxial layer, and are estimated to be an order of 10^<-3> degree of arc from the relative lattice constant in epitaxial layer, d^e_<333>, d^e_<422>, d^e_<511>. Against this middle part, in an edge part of this crystal, lattice is considered to be hardly strained becuse of the asymmetry of crystal shape.
From the view point of silicon device technology, recent advances in application of ion backscattering to the silicon device processes are reviewed and systematized. Important progresses in silicon materials, diffusion and ion implantation, passivation and metallization are discussed in relationship with the targets for high performance semiconductor devices. The backscattering and channeling technology is briefly explained. Then, as an example of its contributions to the studies of silicon materials, gettering mechanism investigations of heavy metals, such as gold and cupper, are described, comparing "diffusion gettering" with "ion-damage gettering." Next, the backscattering studies of impurity doping are summarized. Particularly, keeping in mind arsenic-emitter high speed devices, the backscattering investigation results of the arsenic diffusion and implantation are discussed. Several examples of the backscattering and channeling analyses on the passivation materials, such as SiO_2, Si_3N_4, and Al_2O_3, are described. Especially, the spectra are discussed to determine depth dependence of the composition, density, total thickness, interface change and reaction, and moving species in such films. From the metallization view point, interdiffusions observed by backscattering and channeling technique are summarized for metal-metal and silicon-metal reactions. Especially, metal silicide reaction mechanisms are systematized, for reliable ohmic contact formation. Epitaxial growth of silicon layer obtained by solid-phase transport through PdSi layer has been studied by channeling measurement. Polycrystalline silicon-metal reactions also have been analyzed by backscattering spectra. It is concluded that the backscattering and channeling analysis technique can be used as a universal tool to investigate the silicon device manufacturing processes.
Silicon is most abndant metalic element of the lithosphere constituent elements in the forms of compounds with oxygen. Today, dislocation-free silicon crystals are basic material in the electronics devices because of resource and its properties. Growth and process induced defects in silicon crystals are mutually related defects. Both defects are connected by oxygen, carbon and other heavy metalic impurities through the solid-liquid interface at growing time. Geometrical stabilities of wafers, required from micro-lithography for Large Scale Integration fabrication, are also connected to solid-liquid interface of crystal growth. New problems are occurred in an interface of silicon-oxide, oxide-metal, poly-silicon-metal and/or silicon-metal by decreasing of the thickness with microminiaturization of device and those problems will solved by view point of crystal growth in solid.