Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
1996-07-31
2003-04-08
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S383100, C427S397700
Reexamination Certificate
active
06544599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and apparatus for applying particles to a substrate, to a process for forming a layer on a substrate, to substrates having particles, and to substrates having thin layers. In another aspect, the present invention relates to a process and apparatus for applying charged particles to a substrate, to a process for forming the charged particles into a layer, to substrates having charged particles, and to substrates having a thin layer. In even another aspect, the present invention relates to a process and apparatus for applying charged particles to a substrate at a density greater than 10
11
paricles per cm
2
, to a process of forming the particles into a layer, to a substrate coated with greater than 10
11
charged particles per cm
2
, to a substrate having a layer having a nucleation density greater than 10
11
paricles per cm
2
. In still another aspect, the present invention relates to a process and apparatus for applying charged diamond particles to a silicon substrate, to a process of forming the diamond particles into a layer on the silicon substrate, to silcon substrates having charged diamond particles, and to a silcon substrate having a thin diamond layer. In yet another aspect, the present invention relates to a process and apparatus for applying charged diamond particles to a silicon substrate at greater than 10
11
particles per cm
2
, to a process of forming the particles into a diamond layer on the silicon substrate, to silcon substrates having charged diamond particles at a density of greater than 10
11
diamond particles per cm
2
, and to a silcon substrate having a thin diamond layer with nucleation density greater than 10
11
particles per cm
2
.
2. Description of the Related Art
A. Diamond Film Nucleation
Due to a unique combination of its mechanical, physical, chemical, and electrical properties, diamond is an excellent material for a variety of applications. A wide range of applications which will utilize the exceptional mechanical, thermal, optical, and electronic properties of diamond are anticipated for thin diamond films. Examples include coating of mechanical tools and optical windows, protective layers on intergrated circuits, heat spreaders for high power electronic devices, microsensors, cold emitters, and high temperature semiconductor devices. The diamond films for these applications need to be prepared with specific desired microstructure, thickness, and reproducibility within the practical limits of time and expense.
The nucleation of diamond growth on a substrate depends on the substrate material on which the diamond is to be grown. The initiation of diamond growth is also affected by the surface conditions of the substrate. Unfortunately, formation of diamond films on non-diamond substrates has proved extremely difficult. It has long been understood that the low-nucleation density behavior of diamond is one of the key factors responsible for poor microstructure and morphology of films on non-diamond substrates. Lower nucleation densities require longer deposition times for continuous films and, consequently, result in large surface roughness due to large grain sizes, with problems being more pronounced for highly oriented films and low temperature growth.
From a technological point of view, silicon, as the basic material for present electronics, is strongly favored as a substrate material for thin film diamond devices. Consequently, diamond growth on silicon has received substantial attention in the prior art. However, owing to the high surface energy of diamond and the relatively low sticking probability of the precurser for diamond nucleation, diamond nuclei grow very poorly on a mirror-polished silicon substrate.
In general, the diamond films produced consist of polycrystalline, highly defective, randomly-oriented diamond crystals containing varying amounts of non-diamond carbon and hydrogen. Furthermore, a large number of microvoids (or microcavities) is present in CVD diamond films due to the large grain size of the crystallites (columnar growth) in combination with a low density of grains. The control of the microstructure of diamond films depends, to a great extent, on the nucleation density, and consequently, it requires control of the nucleation process. The deposition of diamond is enhanced by increasing the number of nucleation sites on the substrate, increasing the carbon content in the hydrogen plasma, or reinforcing the bonds between nuclei and the substrate. Failure to provide a high nucleation density results in polycrystalline diamond films with very rough surfaces and/or a porous core.
Diamond-nucleation density on a polished silicon surface is generally on the order of 10
4
per cm
2
. The ability to create an extremely high nucleation density for the growth of diamond films is a key problem for the realization of electrical and optical quality synthetic diamond.
Prior art methods exist to enhance diamond nucleation several orders of magnitude into the range of 10
7
to 10
11
per
2
cm. These prior art methods for enhancing diamond nucleation density on such a mirror-polished silicon substrate generally include (1) scratching or abrading the surface of the substrate; (2) creating submicrometer-craters by focused ion beams; (3) electrophoretic deposition of diamond monolayers (4) sputtering; (5) preferentially etching with a chemical solution to create micrometer-scale V-grooves; (6) coating with a low vapor pressure and high thermal stability hydrocarbon oil; (7) coating with a thin layer of evaporated carbon; (8) applying a substrate bias voltage; (9) spin-coating of photoresist containing seed particles, and (10) Si+ion beam implantation.
B. Machine Tools
The coating of machine tools (substrates) with diamond for enhanced cutting and operating life has been pursued for several years. The conventional approach to coating of substrates is by microwave chemical vapor deposition or hot filament chemical vapor deposition. Although these methods work to grow nearly pure diamond, they are expensive and/or slow. The initiation of chemical vapor diamond growth (i.e., nucleation) is affected by the surface conditions of the substrate. In general, diamond growth nucleates very poorly (i.e., slowly) on a substrate because of the high surface energy of diamond and the relatively low sticking probability of the precursor(s) for diamond nucleation.
C. References
Examples of prior art references dealing with diamond nucleation densities include the following.
U.S. Pat. No. 5,075,257, issued Dec. 24, 1991 to Hawk et al., discloses a method for the deposition of silicon and the formation of silicon films. Silicon powder of optimum particle size is aerosolized, charged, and then electrostatically deposited onto high melting point substrates, which may include semiconducting, insulating, and conducting materials such as silicon, sapphire, and molybdenum, respectively.
“Focused ion-beam crater arrays for induced nucleation of diamond film”, A. R. Kirkpatrick et al., J. Vac. Sci. Technol. B 7 (6), November/December 1989, discloses the use of focused ion-beam (FIB) systems to ion-beam mill (sputter) shallow, small craters in precisely defined, reproducible patterns and spacings, and site densities of 1 per &mgr;m
2
or greater, with these craters causing nucleation.
“Early formation of chemical vapor deposition diamond films”, S. Iijima et al., Appl. Phys. Lett. 57 (25) Dec. 17, 1990, discloses pretreatment of sonication of a silicon wafer in a water suspension of 10 micron-sized diamond powder, resulting in deposition of diamond powder in the range of 10
10
to 10
11
per cm
2
on the wafer.
“Surface And Interface Effects In The Nucleation And Growth Of Diamond”, K.V. Ravi et al., New Diamond Science and Technology, 1991 MRS Int. Conf. Proc., discloses deposition of thin diamond like carbon (DLC) films on non-diamond surfaces is shown to substantially increase the nucleation density as well as facilitate the control of the microstructure of th
Beera Rajan A.
Brown William D.
Malshe Ajay P.
Naseem Hameed A.
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