Julius J. Muray

The physics of microfabrication

1 Preliminary Survey.- 2 Particle Beams: Sources, Optics, and Interactions.- 3 Thin Films.- 4 Pattern Generation.- 5 Special Processes Developed for Microcircuit Technology.- 6 Submicron Microscopy and Microprobes.- 7 Future Directions.- Appendices.- A. The Error Function and Some of Its Properties.- B. Properties of Silicon.- C. Useful Physical Constants in Microscience.- References.

Intense Plasma Source For X-Ray Microscopy

A pulsed soft x-ray source for use in contact microscopy would provide high-resolution, high-contrast images with minimal radiation damage to the biological specimen involved. An x-ray plasma source offers some advantages over synchrotron radiation in terms of smaller physical size, lower cost, larger beam size, and higher flux per pulse. The operation of a pulsed plasma focus device is described and this system is compared to other plasma sources. Results of a radiation model calculation predict that the use of neon gas would produce 1.2- to 1.4-nm radiation in 50- to 100-J pulses (emitted into 47 sterradians) with an efficiency of 1%. The actual source is about 2 mm in diameter and the x-ray pulse lasts about 15 to 20 ns. By choosing the proper gas or electrode material, one can generate a combination of emission lines that cover the region between the carbon edge (300 eV) to 2 keV. The system operates in the pressure range of a few torr. With the x-ray resists being developed for submicron x-ray lithography, microradiographs can be produced that have resolutions of 0.1 pm. The intense pulsed output can provide enough flux to make possible the micrography of wet or alive specimens.

Characteristics and applications of multiple beam machines

Abstract Several multiple electron- and ion-beam machines have been developed at SRI in the last decade. These microfabrication tools use multiple focused electron or ion beams that are deflected, blanked in synchrony, and used to lithograph or etch a whole wafer instead of a single chip. Such machines can reduce the processing time for a wafer and thus increase the throughput. This class of machine has several interesting characteristics. The depth of focus is of the order of 1 cm, the beams are focused on the target in first order and the magnification can be changed easily. These characteristics make these machines quite useful for different microfabrication processes such as lithography, mask making, etching, and micromechanics.

Particle Beams: Sources, Optics, and Interactions

A key element in our ability to view, fabricate, and in some cases operate microdevices has been the availability of tightly focused particle beams, particularly of photons, electrons, and ions. Consideration of diffraction effects leads to the general rule that if one wishes to focus a beam of particles into a spot of a given size, the wavelength associated with the particles must be less than the required spot diameter. In Table 1 are listed the wavelengths (in μm) of three particles (photons, electrons, and protons) at various energies.

Radiation-Supported Space Mirror: Overview of Concept

A high-altitude communications reflector can be supported by radiation pressure beamed at it from below. Potential applications of such a communications device are reviewed. The supporting radiation can balance the weight of the mirror as well as inertial effects, including mirror drift toward the equator. Approximately polarized supporting radiation can rotate the mirror. The reflected signal may serve to monitor mirror orientation. Questions of stability are investigated when the mirror is made of fibers that can support only tension (not compression, shear, or bending.) If the supporting radiation beam is appropriately configured, the mirror can be stabilized with respect to vertical and horizontal displacements, libration, and distortion.

Limits to Nanofabrication

Devices can be made with decreasing linear dimensions until one of two limitations is reached, namely Limitations imposed by the physical principles by which the device operates Limitations imposed by our ability to fabricate the device to the required dimensions and tolerances

Ground Radiation Pattern Generated by High-Altitude Reflectors

A method is given to calculate the shape a high-altitude reflector must have to produce any intensity distribution inside the illuminated ground area. The method consists of setting up and solving a differential equation appropriate to the required ground intensity distribution. Cylindrical and spherical mirrors are discussed in detail, and mirror shapes for producing a particular type of uniform ground illumination are derived. These shapes approach paraboloids in the limit when the mirror altitude is much greater than the diameter of the illuminated area.

Special Processes Developed for Microcircuit Technology

Since we are illustrating the principles of microfabrication with application to microelectronics, we devote this chapter to discussing in some detail those special processes that have been developed for planar silicon technology, namely, epitaxy, oxidation, doping, and annealing. This is not to imply that analogous or similar processes could not or have not been applied to other materials and devices, but it reflects the fact that the major thrust in the microdevice area over the past two decades has been associated with silicon, and hence more work has been done in this area. We have included some special epitaxial processes developed for devices utilizing III–V compound semiconductors, since these are of emerging importance for high-speed microcircuits.

Submicron Microscopy and Microprobes

Having built a device consisting of elements made to submicron tolerances, it is often necessary to examine it to see whether the device was built as specified and whether the components are of the required materials with the desired physical properties.