Synthetic diamond having alternating layers with different concentrations of impurities

Abstract

Synthetic monocrystalline diamond compositions having one or more monocrystalline diamond layers formed by chemical vapor deposition, the layers including one or more layers having an increased concentration of one or more impurities (such as boron and / or isotopes of carbon), as compared to other layers or comparable layers without such impurities. Such compositions provide an improved combination of properties, including color, strength, velocity of sound, electrical conductivity, and control of defects. A related method for preparing such a composition is also described., as well as a system for use in performing such a method, and articles incorporating such a composition.

Description

TECHNICAL FIELD The present invention relates to synthetic diamonds and to methods for preparing and using synthetic monocrystalline diamonds. In particular, the invention relates to monocrystalline diamonds produced by the method of chemical vapor deposition. BACKGROUND OF THE INVENTION Monocrystalline diamonds, as found in nature, can be classified according to color, chemical purity and end use. The majority of monocrystalline diamonds are colored, and contain nitrogen as an impurity, and are thereby used primarily for industrial purposes; these would be classified as type Ia and Ib. The majority of gem diamonds (which are all considered “monocrystalline” diamonds) are colorless or various light colors and contain little or no nitrogen impurities; and would be classified as type IIa. Types Ia, Ib and IIa are electrical insulators. A rare form of monocrystalline diamond (classified as type IIb) contains boron as an impurity, is blue in color and is a semiconductor. In nature the...

AI Technical Summary

Problems solved by technology

In nature these characteristics are uncontrolled and therefore the color, impurity level and electrical characteristics are unpredictable and cannot be utilized to produce large volumes of specialized articles in a predictable manner.

The engineering and industrial uses of diamonds have been hampered only by the comparative scarcity of natural monocrystalline diamond.

However, on a practical level, in order to manufacture useful objects by the “high pressure method”, there are limitations imposed by the presence or absence of impurities.

As an example, it has been suggested that the addition of nitrogen might assist in the growth of large crystals, although the elimination of nitrogen, or the addition of boron, can make it more difficult to grow large crystals.

In addition, it appears that it is not possible to make monocrystalline structures having layers of varied composition without having to remove the seed crystal from the reactor after each layer is grown, and then replacing the seed crystal in the reactor in order to grow a subsequent layer having a different composition.

Moreover, large seeds cannot be accommodated in the “high pressure method”.

It is actually difficult and expensive to produce high quality pure monocrystalline diamond by the high pressure method.

Today, however, the production of monocrystalline diamond by the CVD process is considerably less mature than high pressure, and the resultant materials tend to have higher defect levels and smaller sizes.

Growth rates for the various deposition processes vary considerably, and it is usually found that higher growth rates can be achieved only at the expense of a corresponding loss of film quality.

In general, combustion methods deposit diamond at high rates (typically 100 μm / hr to 250 μm / hr), but often only over very small, localized areas and with poor process control, thereby leading to poor quality films.

One of the great challenges facing researchers in CVD diamond technology is to increase the growth rates to economically viable rates, (to the level of 100+μm / h, or even one or more mm / hr) without compromising film quality.

One major problem receiving a lot of attention is the mechanism of heteroepitaxial growth, that is, the initial stages by which diamond nucleates upon a non-diamond substrate.

Regardless of the abrasion method, however, the need to damage the surface in such a poorly defined manner, prior to deposition, may severely inhibit the use of CVD diamond for applications in areas such as the electronics industry, where circuit geometries are frequently on a submicron scale.

Several problems need to be addressed and over come before this technology begins to make a significant impact however.

If that heat is not removed the temperature of the cutting tool increases to the point that it degrades by oxidation, corrosion or fracturing and the tool becomes unusable.

Furthermore, as the tool is degrading, the quality and precision of the part being fabricated degrades significantly.

Since the heat generated by the laser beam must be dissipated to the outer surfaces of the sense there will be a gradient in the index of refraction of the material and that will cause the laser beam to be distorted or to focus or defocus in an uncontrolled manner.

Such uncontrolled distortion will result in uncontrolled cutting or welding in high power laser fabrication equipment and limit the useful power and thereby the number of applications to which such lasers can be used.

The same problems arise in the use of high power lasers for communications, fusion power or other applications well known to those who are engaged in the art.

This heat must be removed or the device temperature will rapidly rise to the level that the device will cease to operate properly or fail catastrophically.

However, the thermal conductivity (TC) of diamond is dramatically effected by impurities, crystal defects and by polycrystallinity.

Since no natural diamond or synthetic diamond has been found which has a thermal conductivity higher than 2200 W / mK it was concluded by those skilled in the art that either, the theory was wrong or there is some yet unaccounted factor which degrades the thermal conductivity of natural isotope concentration diamond.

The advantages of enhanced thermal conductivity diamond have, to date however, not been applicable to any commercial application because the cost of producing 12C enhanced precursor gasses (typically methane gas) is prohibitively high compared to the cost of natural isotope gasses.

Since only 1 to 2% of the methane is converted to diamond this would result in a cost of materials for enhance thermal conductivity of $7,500 to $20,000 per gram of diamond crystal produced and the cost for natural isotope raw materials at less than $1 per gram of diamond produced.

This high cost far overshadows the advantages in tool, wire die, window or device performance obtained and would permit such enhanced thermal conductivity diamond to be used in only the most demanding and cost tolerant and low volume specialty applications.