Control of solid state dimensional features

#This invention relates to fabrication of solid state structures, and more particularly relates to dimensional control of solid state structural features.

#Precise dimensional control of solid state structural features is essential for many applications in fields ranging from biology and chemistry to physics, optics, and microelectronics. The term “solid state” is here meant to refer to non-biological materials generally. Frequently the successful fabrication of a solid state system critically depends on an ability to articulate specific structural features, often of miniature dimensions, within very tight tolerances. Accordingly, as solid state systems evolve to the micro-regime and further to the nano-regime, nanometric dimensional feature control is increasingly a primary concern for system feasibility.

#There have been established a wide range of microfabrication techniques for producing and controlling structural feature dimensions in micromechanical and microelectromechanical systems. For example, high resolution lithographic techniques and high-precision additive and subtractive material processing techniques have been proposed to enable small-scale feature fabrication. But in the fabrication of many nano-regime systems, in which structural feature dimensions of a few nanometers are of importance, it is generally found that conventionally-proposed techniques often cannot form the requisite nano-scale features reproducibly or predictably, and often cannot be controlled on a time scale commensurate with production of such nano-scale features. As a result, volume manufacture of many systems that include nanometric feature dimensions and/or tolerances is not practical or economical.

#FIGS. 1A-1D are schematic cross-sectional views of fabrication sequence steps for the production of an aperture in accordance with the invention;

#FIGS. 2A-2G are schematic cross-sectional views of an example fabrication sequence of steps for the production of the cavity of FIG. 1A in a membrane;

#FIGS. 3A-3B are schematic diagrams of an ion beam sputtering system configured in accordance with the invention to implement precision feedback control;

#The processes for dimensional feature control provided by the invention can be directed to a wide range of materials and structural configurations. The example processes here described are meant to be illustrative but not to represent specific limitations in materials or configurations. The processes of the invention are particularly well-suited for precisely controlling structural feature dimensions, and for enabling such control on the scale of nanometers. This control can be especially advantageous for the precise formation and definition of nanometric-sized features and spaces, such as gaps existing as an aperture, e.g., pores, slits, orifices, vents, and holes, as well as trenches, channels, troughs, and in general, the spacing between two or more distinct feature edges.

#Referring to FIG. 1, in one example implementation of a method provided by the invention for precisely and reproducibly defining the spacing of features, there is carried out a process for forming an aperture of a prespecified extent, e.g., diameter, in a structural layer. In a first process step, referring to FIG. 1A, a starting structure 10 is provided, shown in cross-section in the figure. Such starting structure 10 can be supplied as, e.g., a substrate, a thick or thin layer provided on a support such as a substrate, a membrane, or suitable structure. A cavity 12 is formed in the structure 10 on a selected surface 14 of the structure and in a region at which an aperture is desired.

#The cavity 12 extends into the bulk of the structure 10 for only a fraction of the structure's thickness, rather than through the entire thickness of the structure, to an opposing surface 18. As a result, the deepest level, i.e., the bottom 16, of the formed cavity lies at some midpoint in the structure's bulk. As explained in more detail below, the geometry of the cavity bottom 16 and the cavity sidewalls 20 are preferably selected to enable controlled formation of a limiting aperture of controlled transverse and longitudinal dimensions in later processing steps. In the example illustrated, a bowl-shaped cavity is employed.