Patent Application
20100027273
Embodiments of the present invention relate to the field of optics. More specifically, embodiments of the present invention relate to systems and methods of coatings for reflective surfaces.
Numerous industries and technologies utilize reflective surfaces. For example, the semiconductor industry widely utilizes reflective surfaces, or reflectors, to uniformly convey heat and/or light energy from a lamp to a semiconductor wafer, e.g., as used in the formation of epitaxial layers for semiconductors. For example,
Another application of reflective surfaces is illustrated in
The materials used in forming reflective surfaces 130 and 240 as well as other applications of reflective surfaces may be subject to high temperatures, corrosive chemical environments, mechanical wear due to forced air cooling, cleaning, polishing and handling, as well as other detrimental effects. Consequently, improvements in temperature and chemical resistance, improvements in mechanical wear characteristics as well as improvements in reflectivity are highly desired.
Therefore, systems and methods of coatings for reflective surfaces are needed. In addition, systems and methods of coatings for reflective surfaces that provide increased hardness, improved scratch resistance and/or increased chemical inertness are needed. A further need exists for systems and methods of coatings for reflective surfaces with reduced maintenance requirements are needed. A still further need exists for systems and methods of coatings for reflective surfaces that are compatible and complimentary with existing systems and methods of semiconductor manufacturing are needed. Embodiments of the present invention provide these advantages and others as evident from the below description.
Accordingly, systems and methods of coatings for reflective surfaces are disclosed. An optical system includes a reflective surface for reflecting optical energy and a transparent coating disposed upon the reflective surface. The coating may be characterized as more chemically inert than the reflective surface in an operating environment of the reflector. The coating may be characterized as harder than the reflective surface. The coating may be characterized as more refractory than the reflective surface. The coating may include diamond like carbon and/or other tetrahedrally bonded stable material, e.g., silicon carbide and/or boron nitride.
In accordance with a method embodiment of the present invention, a method of processing a semiconductor substrate includes positioning a semiconductor substrate in an optical path with a light source and conveying energy from the light source to the semiconductor substrate via a direct optical path. Energy from the light source emitted in a non-direct path is reflected to the semiconductor substrate. The reflector includes a reflective surface and a transparent coating disposed thereon. The processing may further include growing an epitaxial layer on the substrate, wafer cleaning, etching, chemical vapor deposition, chemical mechanical polishing, sputtering, ion implantation, photo lithography, stripping and/or diffusion.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. Unless otherwise noted, the drawings are not drawn to scale.
Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it is understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be recognized by one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the invention.
The terms “diamond-like” and “diamond-like carbon” are used by those of skill in the art and herein to refer to at least seven forms of amorphous carbon materials that display some of the unique properties of natural diamond.
While exemplary embodiments of the present invention may be illustrated with respect to the formation of epitaxial layer(s) on silicon wafers or substrates, it is appreciated that embodiments in accordance with the present invention are not limited to such exemplary devices and applications, and are well suited to many semiconductor manufacturing processes and semiconductor processing equipment types in addition to a variety of other optical reflecting applications. For example, embodiments in accordance with the present invention are well suited to a variety of optical and optical-like applications, including lasers, photo diode-based sensing devices, photomultiplier tubes, particle detectors, stepper imaging systems for use in photolithographic manufacturing, extreme ultraviolet (EUV) light sources and the like.
A reflector system, similar to reflector system 100 (
In a semiconductor processing system, a heating lamp and reflector are generally not intentionally exposed to the highly corrosive gaseous environment of a CVD) processing chamber. However, high degrees of chemical inertness and hardness are desired of the reflector due to the presence of cooling water and/or forced air cooling, including debris and/or impurities in a cooling stream. For example, water leaks from system cooling water may spread spray or splatter on critical reflective surfaces, thus leaving deposits, foreign material or simply dirt on an otherwise highly polished reflective surface.
In addition, there exists a possibility of inadvertent exposure to processing chemicals, e.g., due to accidents and/or maintenance activities. Exemplary environments may comprise, for example, gas phase silicon sources, such as silicon tetrachloride (SiCl4), trichlorosilane (SiHCl3), dichlorosilane (SiH2Cl2) and/or silane (SiH4) in a hydrogen carrier gas. In addition, reaction byproducts may be highly corrosive.
Further, agents utilized for periodic maintenance and cleaning of such processing chambers, e.g., nitric acid (HNO3) and/or hydrofluoric acid (HF), and their byproducts, may be corrosive as well. Such cleaning or cleaning byproduct chemicals are likely to form detrimental contaminants as well. Still further, periodic maintenance, cleaning and polishing generally expose the processing equipment, including lamps and/or reflectors, to “normal” atmospheric air, water, dust and other agents, which alone or in concert with other agents may produce additional contaminants and/or may damage reflective surfaces.
The semiconductor industry widely utilizes a reflective surface, e.g., reflective surface 130 (
Coating 330 may comprise diamond-like carbon, e.g., tetrahedral amorphous carbon, in accordance with embodiments of the present invention. Coating 330 may have a thickness in the range of about 5-50,000 angstroms. Coating 330 may be highly transparent, highly refractory (heat resistant), and highly resistant to chemicals. In addition, coating 330 should be highly resistant to mechanical wear.
In accordance with alternative embodiments of the present invention, coating 450 may be deposited over a reflective surface 430 comprising materials) other than the conventional gold.
For example, silver has many attributes that are desirable for use as a reflective surface. Silver can be highly reflective, and is far less expensive than gold. However, silver is chemically reactive, and for this reason has generally not been suitable for use in many reflective applications, e.g., for heating wafer processing chambers.
However, in accordance with embodiments of the present invention, coating 330 (
In addition to silver, coating 330 may enable use of a variety of other materials as a reflective surface 320. For example, aluminum is highly chemically reactive, e.g., forming aluminum oxide almost instantaneously in the presence of air. Such an oxide layer is generally deleterious to reflectivity. Consequently, under the conventional art, aluminum, while generally well suited for use as a base structure 310, is generally deemed unacceptable for use as a reflective surface 320.
In accordance with embodiments of the present invention, aluminum may be highly polished and coated with coating 330, e.g., in vacuo, producing a useful reflective surface 320. It is to be appreciated that coating 330 both passivates the aluminum reflective surface 320 as well as providing mechanical abrasion resistance. In this novel manner, aluminum, which is well suited to base structure 310, may also form reflective surface 320. For example, reflective surface 320 can be formed as a surface of base structure 310, without plating of another material. Accordingly, materials and production steps are advantageously eliminated in formation of a reflective structure 300.
In addition to the aforementioned materials, other materials generally considered undesirable for use as a reflective surface under the conventional art may be made desirable as reflective surfaces 320 by the addition of coating 330, in accordance with embodiments of the present invention. For example, many reflective materials may be too chemically active for various reflector applications. As previously discussed, silver and aluminum may be included in this category. In addition, reflective materials may be undesirably soft for various reflector applications, e.g., gold. Coating 320 beneficially improves both chemical inertness as well as hardness. Other materials that may form beneficial reflective surfaces 320 in combination with coating 330 include nickel, nickel chrome, nickel iron, rhodium, platinum rhodium, inconel (Ni, Fe, Cr) and the like.
In accordance with alternative embodiments of the present invention, coating 330 may comprise silicon carbide. Silicon carbide more readily forms a single stable crystalline phase, in contrast to carbon, which can form multiple structures, e.g., “diamond like” or “graphite like.” For mechanical and chemical durability, a “diamond like” crystal form may generally be preferred. However, the diamond like structure of carbon is not assured, but rather depends on a variety of deposition conditions, including, for example, source gas impurities, vacuum integrity, temperature and the like. It may be desirable to form a coating 320 comprising a stable compound of great durability, e.g., silicon carbide.
In 520, energy from the light source is conveyed to the semiconductor substrate via a direct optical path. In 530, energy from the light source emitted in a non-direct path to the semiconductor substrate is reflected by a reflector to the semiconductor substrate. The reflector comprises a reflective surface, e.g., reflective surface 320, 430, and a coating, e.g., coating 330, 450, disposed thereon, e.g., as shown in
In optional 540, a processing operation is performed on the semiconductor substrate. The processing may include growing an epitaxial layer, wafer cleaning, etching, chemical vapor deposition, rapid thermal processing, chemical mechanical polishing, sputtering, ion implantation, photo lithography, stripping and/or diffusion.
In accordance with embodiments of the present invention, the coating may comprise diamond like carbon. In accordance with alternative embodiments of the present invention, the coating may comprise silicon carbide. In another embodiment, the coating substantially comprises amorphous silicon carbide, e.g., silicon carbide characterized as having short range order in the solid film comprising a few molecular dimensions. It is further appreciated that embodiments in accordance with the present invention are well suited to coatings comprising other forms of silicon carbide.
In one embodiment, the thickness of the coating may range from about 5 to 50,000 angstroms. It is appreciated that embodiments in accordance with the present invention are well suited to other thickness of coatings as well.
In accordance with alternative embodiments of the present invention, coating 330 (
In addition, in accordance with alternative embodiments of the present invention, a multi-layer coating may have multiple indexes of refraction and multiple optical interfaces, which may be utilized to create or prevent internal reflections, e.g., reflections with the multiple layers. Further, a multi-layer coating may be utilized to filter selected wavelengths of light energy, for example, passing desirable wavelengths and rejecting unwanted wavelengths.
Embodiments in accordance with the present invention provide systems and methods of coatings for reflective surfaces. Embodiments in accordance with the present invention also provide for systems and methods of coatings for reflective surfaces that provide increased hardness, improved scratch resistance and/or increased chemical inertness. In addition, systems and methods of coatings for reflective surfaces with reduced maintenance requirements are provided. Further, embodiments in accordance with the present invention provide for systems and methods of coatings for reflective surfaces that are compatible and complimentary with existing systems and methods of semiconductor manufacturing.
Various embodiments of the invention are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the invention should not be construed as limited by such embodiments, but rather construed according to the below claims.
