Radiant energy – Electrically neutral molecular or atomic beam devices and...
Reexamination Certificate
2001-02-06
2002-10-08
Anderson, Bruce (Department: 2881)
Radiant energy
Electrically neutral molecular or atomic beam devices and...
C250S492200, C250S492220, C427S595000
Reexamination Certificate
active
06462333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the fabrication of nano-devices and semiconductor devices. More specifically, the present invention relates to direct write fabrication and lithography techniques and systems employing the Lorenz force interactions of light fields with the dipole moment of atoms to build stable nanostructures of matter via the direct deposition of atoms upon substrates.
2. Description of the Prior Art
The nano-device and semiconductor device manufacturing communities consistently strive to develop fabrication techniques and equipment that enable the precise definition of ever smaller structural components of functional devices. These device manufacturers expend extensive financial and technological resources in the exploration and development of improved photolithography process tools and methods on a continual basis.
The potential rewards for achieving significant reduction in minimal dimension manufacturable structures, features or spot sizes, are tremendous. Smaller structural components can be used to create smaller devices. Semiconductor devices constructed with smaller feature and structure dimensions operate at faster speeds, consume less power and embody higher functional complexities. Smaller nano-devices function within finer scales of precision. The economic motivation of manufacturers to improve over the capabilities of conventional photolithography has therefore led to the funding of much intensive work in the field of x-ray level photolithography.
Yet the fundamentals of prior art photolithography are self-limiting to enhancements in several ways. Conventional photolithography,is a multi-step process. Each step typically contributes an error factor to a finished structure. An example of a photolithography process might include a deposition of a specific material onto a substrate, the application of a layer of photoresist over the substrate, a soft bake of the photoresist, an exposure of the photoresist layer to a pattern-masked light source, the development of the photoresist, a hard bake of the photoresist and finally an etching step.
Each step in this example photolithography process has limitations in accuracy and result. The validity of the deposition action is dependent upon the uniformity of the layer of material actually deposited. The resolution of the component structures of the device defined in the photoresist development steps is limited by the wavelength of light used, the geometric accuracy of the pattern-mask, the effects of unintended under or over exposure to the light source, and the equally unintended effects of under development or over development of the photoresist after exposure to the light source. The soft baking and/or the hard baking of the photoresist can also be over or under done. The precision of the etch step is affected by the degree of selectivity of the etching agent and the degree of anisotropy achieved in the delivery of the wet or dry etching agent across the entire surface of the substrate.
The errors introduced by each step of the photolithography process are further compounded by the fact that the fabrication of most semiconductor devices requires the repeated application of entire cycles of photolithography processes which employ widely varying deposition materials, photoresist compounds, etching chemicals, pressure and temperature requirements. The net result is often an increasing limitation in the smallest achievable individual structure size, as well as reduction in the control of precision in device feature fabrication.
The sheer number of individual process steps of a typical device fabricated with conventional photolithography techniques raises the statistical occurrence of contaminating events during the manufacturing process. The elimination of process steps in itself typically results in yield improvement.
The dominant trend in the art is to attempt to increase the accuracy of each step of the photolithography process. Accuracy in etching may be increased by reducing the thickness of the deposited film. However, this increases the requirements for uniformity in the deposition phase. In addition, these thin deposition layers are, in some cases, thin enough to experience and exhibit quantum phenomenon and behavior. However, for the most part, these layers have bulk material properties. This can lead to many uncontrolled parameters during the fabrication stage. For example, a convex surface profile of the deposited layer may lead to strained and mismatched lattices, thus creating devices susceptible to failure through numerous mechanisms.
The pursuit of better photolithography through the application of higher frequency light waves, such as hard ultraviolet and x-rays, is based upon a relationship expressed in the Rayleigh Criterion between the wavelength of a light wave and its corresponding achievable diffraction limit.
The Rayleigh Criterion is given by:
d
=0.61
&lgr;N.A.
where &lgr;=operational wavelength of the emitted light;
N.A.=Numerical Aperture of the imaging optic; and
d=diameter of the minimal achievable spot size.
Replacing &lgr; in the equation of the Rayleigh Criterion with the wavelength &lgr; of a particular light wave will yield the diffraction limit of the light wave emitted at that frequency. Higher frequencies obviously exhibit lower diffraction limits.
The employment of shorter illumination wavelengths does theoretically allow for the definition of significantly smaller device feature sizes. Unfortunately, however, the greater photon energies of higher frequency light waves often create other obstacles to the process of manufacturing smaller geometric features. Higher frequency light waves are more likely to damage lithographic mask optics very quickly because of their high levels of material interaction reactivity. Light waves of wavelengths below 200 nm are more prone to uncontrolled scatter and absorption by the substrate and other deposited materials. Higher energy photons are also more prone to damage the material that they are bombarding.
Conventional photolithography techniques, including those employing x-rays, still typically include an etching step and require the provision of a substrate composed of a pure single crystal, such as silicon or gallium arsenide. Device structures are currently fabricated with atoms in higher energy states, which result in an increased incidence of lattice mismatch and attendant structural fragility.
Furthermore, most conventional photolithography applications entail the production of environmentally hazardous solutions, reagents and by-products. Manufacturing techniques that reduce the generation of biohazardous material by the nano-device industry, and especially the semiconductor device industry, are of significant benefit to the both manufacturers and the world community.
Creative and meaningful work has been done in the area of controlling the deposition of atoms through the Lorenz force effect created by the interactions between an atomic dipole and a standing light wave. Much of this work exploits the generation of a Lorenz force caused by the interaction of an atom, behaving like an oscillating dipole, with the oscillating electric field of a laser. The atom behaves like an oscillating dipole acted on by a Lorenz force, where the Lorenz force is proportional to the intensity gradient of the oscillating electric field of the laser.
J. J. McClelland and M. R. Scheinfein, for a first example, proposed the use of a laser beam as a means of focusing an atomic beam to create nanometer, or nm, scale spots. (J. J. McClelland and M. R. Scheinfein, “Laser focusing of atoms: a particle-optics approach”, J. Opt. Soc. Am. B/Vol. 8, No. 9/September 1991, pp. 1974-1986, which is hereby incorporated by reference) McClelland and Scheinfein envisioned the employment of a TEM
01
laser as an atomic lens whereby the direction of an atomic beam is purposely directed with a focal spot size on the order of one nanometer.
T. Sleater et al. have reported on the su
Anderson Bruce
Leary James J.
Titus Carol D.
Wells Nikita
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