Method of forming spatial regions of a second material in a first material

#The present invention relates to solid state materials and, in particular, to a novel method of forming spatial regions having various geometries in such solid state materials.

#Crystalline solid state materials, such as single-crystal semiconductors, are the basis of the current microelectronics industry. Each single crystalline solid is a periodic structure in space, with a basic repeating unit called the unit cell. Crystalline solids are characterized by a variety of properties, for example, electrical properties such as electrical conductivity or charge mobility, optical properties such as refractive index or speed of photons, thermal properties such as thermal conductivity or thermal expansion, mechanical properties such as stress or strain curves, and chemical properties such as resistance to corrosion or reaction consistency, among others.

#Over the past years, theoretical and experimental interests have focussed on controlling various properties of the solid state materials, for example, their optical and/or physical properties. As such, numerous photonic lattice experiments have been carried out to realize photonic bandgap effects at optical wavelength in periodic crystalline solids as a way of obtaining novel photonic properties in such solids. In one photonic lattice experiment, for example, Yablonovitch et al. (E. Yablonovitch. Phys. Rev. Lett., 58, 2059 (1987)) have suggested that the electromagnetic radiation propagating in periodic dielectric structures is similar to the electron waves propagating in a crystal. Yablonovitch et al. realized that setting up a periodic index of refraction pattern in a material can produce a band structure for electromagnetic waves where certain wavelengths can or cannot propagate, producing therefore the electromagnetic wave equivalent of a metal, semiconductor or insulator. If the wavelength is in the order of the dimensions of the crystal lattice, a photonic bandgap (a frequency range where photons are not allowed to propagate) can open up in two or three dimensions and lead to interesting phenomena, such as inhibition of spontaneous emission from an atom that radiates inside the photonic gap or frequency selective transmission and reflection. This way, for example, if a photonic crystal can be constructed to posses a full photonic bandgap, then a photonic insulator is created by artificially controlling the optical properties of the solid.

#FIG. 1 illustrates a portion of a silicon substrate undergoing a sequence of steps for empty-spaced sphere formation.

#FIG. 2 illustrates a portion of a silicon substrate undergoing a sequence of steps for empty-spaced pipe formation.

#FIG. 3 illustrates a portion of a silicon substrate undergoing a sequence of steps for empty-spaced plate formation.

#In the following detailed description, reference is made to various exemplary embodiments for carrying out the invention. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be employed, and that structural, electrical and process changes may be made, and equivalents substituted, without departing from the invention. Accordingly, the following detailed description is exemplary and the scope of the present invention is not limited by the detailed description but is defined solely by the appended claims.

#In the exemplary embodiments described in detail below, reference will be made to a first solid material which is employed to form various spatial patterns and regions embedded in such first solid material for interacting with optical wavelengths. These various spatial regions and/or patterns are formed by an analogous method to that employed in the formation of empty-spaced void patterns in a silicon substrate. Accordingly, reference is made first to FIGS 1-3 which illustrate the formation of empty-spaced void patterns 50, 23, 33 in a silicon substrate 10 of <100> crystal orientation. Techniques for the formation of empty-spaced (void) patterns of different geometries in silicon are described by Sato et al., in Substrate Engineering for the Formation of Empty Space in Silicon (ESS) Induced by Silicon Surface Migration, 1999 IEDM Digest, Paper 20.6.1, the disclosure of which is incorporated by reference herein.

#Empty spaces which are formed in silicon substrates and have various shapes, such as plates, spheres or pipes, may be formed as a result of the self-organizing migration properties on the silicon surface. As such, when deeply-etched silicon substrates are annealed in an ambient atmosphere, such as a hydrogen ambient, for example, the silicon atoms on the surface migrate so that their surface energy is minimized. Based on these findings, Sato et al. have demonstrated that the geometry of empty spaces, such as sphere, plate and pipe, formed under the surface of a silicon substrate depends on the size, number and spacing of a plurality of cylindrical holes that are initially formed at temperatures lower than the melting temperature of silicon.