BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a chemical vapor deposition reactor and, more particularly, to a ring structure that focuses microwaves in the reactor to facilitate growth of a diamond film on a growth substrate. The present invention is also directed to a method of using the chemical vapor deposition reactor.

Description of Related Art

Polycrystalline diamond films have long been recognized for their unique combination of optical properties. Its low absorption of 10.6 um and 1 um wavelengths makes it an ideal material for use in windows transparent to a range of wavelengths with applications such as advanced photolithographic patterning techniques. In addition to near IR and mm wave transparency, polycrystalline diamond films have extraordinarily high thermal conductivity (sometimes exceeding 2000 W/mK), low thermal expansion coefficient, microwave transparency, and extreme hardness. These properties and more make it a valuable material for a variety of applications.

Presently, polycrystalline diamond films are grown on the industrial scale using a technique called Chemical Vapor Deposition (CVD). Examples of CVD reactors for diamond include: hot filament, DC arc jet, flame, and microwave plasma.

To achieve the highest quality diamond in terms of optical, microwave and nuclear detector performance, microwave plasma CVD (MPCVD) is commonly employed. For MPCVD growth, a growth substrate (typically made of W, Mo or Si) is loaded into the bottom of MPCVD growth chamber. A microwave plasma is generated within the growth chamber flowing a reactive gas mixture of H2with ˜0.1-5% CH4. The substrate is heated to a temperature generally ranging from ˜700-1200 C at a reactive gas pressure of ˜10-250 Torr. Within this range of conditions, diamond is a metastable material that, due to differences in density, is preferentially deposited on the growth substrate. The microwave plasma generates chemical precursors necessary for diamond deposition reactions to take place on the growth substrate surface.

One major drawback of MPCVD is the dimensional limitations of the growth chamber. Common chamber designs are limited as a function of one-half of one wavelength of the excitation microwave frequency. One option to expand the size of the resonant chamber is to reduce the frequency of the incoming microwaves. However, there are significant regulatory barriers associated with frequency selection. Another option to expand the substrate size available for diamond growth would be to introduce specialized features inside the growth chamber.

There are diamond growth chambers known in the art that employ plasma control techniques including, for example, a focusing ring protruding from the sidewall (US 2014/0308461), and freestanding rings surrounding the growth substrate and control of growth substrate sidewalls. (US 2014/0339684).

To date, no MPCVD growth chamber design allows for substrate diameters that are significantly larger than one-half of one wavelength of the excitation microwave frequency. In addition, these MPCVD growth chamber designs are limited in versatility. Due to the nature of their construction, typical MPCVD growth chambers accommodate a limited number of growth substrates. This limits the size and shape of growth substrates in any given growth chamber and modification requires significant monetary and design cost.

SUMMARY OF THE INVENTION

Disclosed herein is a variety of ring structures, having interchangeable features, and growth substrates that can be used within the same MPCVD growth chamber. This dramatically expands the versatility of the MPCVD growth chamber.

More specifically, disclosed herein are a number of focusing ring-structures, including a number of interchangeable features, that can be fixed to a bottom of an MPCVD chamber. The focusing ring-structures can include internal cooling channels and/or gas flow channels which mate with corresponding channels on the MPCVD chamber bottom providing customizability of the MPCVD chamber design. The cooling channels of the focusing ring structures can be independent of cooling channels at the bottom of the MPCVD chamber and gas channels that can be used to provide processes gasses into both the reaction space (typically H2, CH4and Ar) and purge (typically Ar) allowing control of the reaction zone.

Given the modular nature of the focusing ring-structures disclosed herein, a variety of designs can be used, each addressing specific design problems (e.g. varying diameter sizes, center-to-edge stress differences, and curved surfaces).

