Single-crystal silicon is being increasingly employed in a variety of new commercial products not because of its well-established electronic properties, but rather because of its excellent mechanical properties. In addition, recent trends in the engineering literature indicate a growing interest in the use of silicon as a mechanical material with the ultimate goal of developing a broad range of inexpensive, batch-fabricated, high-performance sensors and transducers which are easily interfaced with the rapidly proliferating microprocessor. This review describes the advantages of employing silicon as a mechanical material, the relevant mechanical characteristics of silicon, and the processing techniques which are specific to micromechanical structures. Finally, the potentials of this new technology are illustrated by numerous detailed examples from the literature. It is clear that silicon will continue to be aggressively exploited in a wide variety of mechanical applications complementary to its traditional role as an electronic material. Furthermore, these multidisciplinary uses of silicon will significantly alter the way we think about all types of miniature mechanical devices and components.

Silicon as a mechanical material

The anisotropic etching of single crystal silicon oil ((loo) and (110) orientation in a solution of pyrocatechol, ethylene di:nnine, and water is reviewed and the fabrication of three novel types of nicro- structures is described in detail. Controlled etching of Si, whicpi is re- quired to fabricate devices with a predictable geometry depends on : an accurately oriented, defect-free substrate, a well-defined and ali.ped pattern geometry, and rigorously clean etching conditions. Chnven- tional IC processing methods were used to fabricate: 1) a high-precision circular orifice in a thin pfSi membrane for use as an ink jet ncmle, 2) a multisocket miniature electrical connector with octahedral 'c wities suitable for cryogenic applications, and 3) multichannel anri;ys in (100) and (110) Si useful in various applications, eg., charge elecdttodes, physical masks, and optical devices. To make some of these strcwlures, a novel bonding technique to fuse silicon wafers with phosphalsilicate glass films was developed.

Fabrication of novel three-dimensional microstructures by the anisotropic etching of

Anisotropic etching of silicon in hydrazine

Silicon diodes with large aspect ratio trenched microstructures, backfilled with 6LiF, show a dramatic increase in thermal neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill 6LiF into the silicon microstructures. The highest detection efficiency realized thus far is over 42% intrinsic thermal neutron detection efficiency by device-stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1 cm2 area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device was operated at 3 V and utilized simple signal amplification and counting electronic components that have been adjusted from previous work for slow charge integration time. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a 3He proportional counter.

Improved High Efficiency Stacked Microstructured Neutron Detectors Backfilled With Nanoparticle $^{6}$ LiF

Advantageous use of the silicon, diamond cubic crystal structure is described from the aspect of orientation-dependent etching. The use of this technology can affect device characteristics, device and circuit isolation, circuit element densities, and process control. Several laboratories have reported advantageous use of }100{ oriented silicon. This paper discusses the advantageous use of both {100} and {110} silicon orientations. In particular, the {110} technology is discussed from a high packing density aspect as applied to the processing and characteristics of silicon diode array targets with improved television blooming control.

K.E. Bean

Papers

Application of silicon crystal orientation and anisotropic effects to the control of charge spreading in devices