METHOD FOR FORMING COMPOUND EPITAXIAL LAYER BY CHEMICAL BONDING AND EPITAXY PRODUCT MADE BY THE SAME METHOD

The present invention is to provide a method for forming a compound epitaxial layer by chemical bonding, which comprises the steps of forming a contact layer on a substrate; chemically reacting atoms on a surface of the contact layer with non-metal atoms, such that the non-metal atoms form non-metal ions for chemically bonding to the atoms on the surface of the contact layer; exciting the non-metal ions by energy excitation, such that unpaired electrons of the non-metal ions not yet bound to the atoms on the surface of the contact layer become dangling bonds; and conducting chemical vapor deposition by introducing an organic metal compound and a reactant gas, wherein metal ions of the organic metal compound are bound to the dangling bonds by electric dipole attraction, and anions of the reactant gas are bound to the metal ions by ionic bonding, such that the compound epitaxial layer is formed.

DETAILED DESCRIPTION OF THE INVENTION

The inventor of the present invention has long been engaged in research, development and designing in epitaxy-related fields. In the process, the inventor has found that so far mirror-like planar crystals cannot be made epitaxially without using MBE. However, not only is MBE costly, but also the epitaxial layers formed by MBE are bound together by physical contact, whose binding strength is low; as a result, delamination may occur, and low product yield follows, which is highly undesirable. Although attempts have been made in search for improvement, an ideal solution has yet to be found. In consideration of this, the inventor came up with taking advantage of the properties of dangling bonds and using an unsaturated ionic bond layer to realize chemical bonding between a contact layer and a compound epitaxial layer. Thus, by increasing the binding strength between the layers, delamination can be effectively prevented.

The present invention discloses a method for forming a compound epitaxial layer by chemical bonding and an epitaxy product made by the method. To describe the method and the epitaxy product in detail, a preferred embodiment of the present invention is presented as follows. Referring toFIG. 1, the method begins by forming a contact layer11on a substrate10. In this preferred embodiment, the substrate10is a silicon wafer, and yet the material of the substrate10is not limited to silicon. The substrate10may also be made of fused quartz, copper-molybdenum alloy, tungsten, titanium or like materials capable of standing the temperature of the manufacturing process. The contact layer11, on the other hand, can be a metal layer made of titanium, tantalum, aluminum, zinc, scandium, zirconium or magnesium, or an amphoteric-element layer made of boron or silicon. In this preferred embodiment, the contact layer11is formed of titanium, and the titanium is in ohmic contact with the silicon wafer. The term “ohmic contact” refers to the contact between a metal and a semiconductor, wherein the resistance at the contact surface is far lower than the resistance of the semiconductor such that the voltage drop during operation typically takes place in an active region rather than at the contact surface. It should be understood that the materials of the substrate10and of the contact layer11are not limited to those disclosed herein. All variations easily conceivable by a person skilled in the art should fall within the scope of the present invention.

After the formation of the contact layer11, referring toFIG. 2, the atoms (i.e., titanium atoms110) on the surface of the contact layer11are chemically reacted with non-metal atoms at a temperature of, as in this preferred embodiment, 200° C. or above. Consequently, the non-metal atoms form non-metal ions120, which are bound to the atoms on the surface of the contact layer11by chemical bonding. As such, the non-metal ions120form an unsaturated ionic bond layer12on the surface of the contact layer11. The non-metal atoms can be atoms of nitrogen, phosphoms, oxygen or sulfur and are nitrogen atoms in this preferred embodiment. After chemical reaction with the atoms (i.e., titanium atoms110) on the surface of the contact layer11, the nitrogen atoms become nitrogen ions (i.e., non-metal ions120) and form the unsaturated ionic bond layer12.

In the present invention, referring toFIG. 3, the non-metal ions120are excited by energy excitation such that the unpaired electrons of the non-metal ions120that have not been bound to the atoms on the surface of the contact layer11become dangling bonds121. A “dangling bond” refers to a free radical consisting of an electron that is not part of a chemical bond (i.e., an unpaired electron). In the present invention, the dangling bonds121generated by energy excitation exhibit extremely high activity and have electric dipole attraction. The inventor has found that, once the dangling bonds121are generated by excitation, epitaxial barriers are effectively lowered, and this is helpful in forming the subsequent epitaxial layer. In practice, laser can be used as the means of energy excitation, and the present invention imposes no limitations on the excitation means. When performing an epitaxial manufacturing process based on the technical features of the present invention, a manufacturer may change the means of energy excitation according to product requirements and process conditions. For instance, thermal excitation or excitation by other means is equally applicable. All changes conceivable by a person skilled in the art should be viewed as equivalent variations of the present invention and as not departing from the scope of the present invention.

Referring toFIG. 4, upon completion of the foregoing step, chemical vapor deposition is carried out by, as in this embodiment, introducing a titanium compound (i.e., an organic metal compound) and ammonia (i.e., a reactant gas). The titanium ions130of the titanium compound are guided in the directions of the electric dipoles of the dangling bonds121and are uniformly bound to the dangling bonds121. In addition, referring toFIG. 5, the nitrogen ions131of the ammonia (NH3) are bound to the titanium ions130by ionic bonding. Thus, a titanium nitride epitaxial layer13(i.e., a compound epitaxial layer) is formed. In this preferred embodiment, tetrakis(dimethylamido)titanium (TDMAT) is used as the organic metal compound, and ammonia (NH3) as the reactant gas. With TDMAT being only one example of organic metal compounds, applicable organic metal compounds are by no means limited thereto. A manufacturer may change the composition of the organic metal compound according to the manufacturing process used and product design requirements. Apart from that, phosphine (PH3), water (H2O), hydrogen sulfide (H2S) or arsine (AsH3) may also be used as the reactant gas in order to produce a compound epitaxial layer containing the element phosphorus, oxygen, sulfur or arsenic. All changes in materials readily conceivable by a person skilled in the art should fall within the scope of the present invention.

Referring toFIG. 5, the technical features of the present invention are such that, owing to the strong polarity of the dangling bonds121and the specific directions of the electric dipole attraction of the dangling bonds121, not only are epitaxial barriers lowered, but also the titanium ions130of the titanium compound are guided in the correct directions to be uniformly bound to the dangling bonds121, with a strong bonding force between the titanium ions130and the dangling bonds121. Moreover, the binding between, and the arrangement of, the nitrogen ions131and the titanium ions130are rendered uniform, thanks to the electric dipoles that enable automatic adjustment of the direction of contact between the nitrogen ions131and the titanium ions130. Therefore, the titanium nitride epitaxial layer13formed according to the present invention has high quality, high hardness and excellent spectrum absorption features. Further, as the titanium nitride epitaxial layer13, the unsaturated ionic bond layer12and the contact layer11are bound together by chemical bonding, with a bond strength far greater than the binding strength conventionally achieved by physical contact, delamination of the different layers is effectively prevented. Not only that, since the present invention does not need the complicated buffer structure conventionally required, the reduced complexity of the manufacturing process lowers production costs while the reduced use of chemicals contributes to environmental protection.

Using KLA-Tenor's testing machine RS75, the inventor conducted a four-point probe test on a product made by the method of the preferred embodiment, and the product under test could not be pierced. Given that the probe is made of tungsten carbide, whose Mohs hardness ranges from 8.5 to 9.0, the epitaxy product of the present invention possesses the characteristic of a superhard material. Also, a thickness test was performed with THERMA WAVE's measuring machine OP2600 in the DUV (deep ultraviolet) mode, and yet the correct thickness could not be obtained. This means that the reflectivity of the product is less than 13% and that the product is highly absorptive in the DUV range. An additional SEM (scanning electron microscope) thickness check shows that the thickness of the titanium nitride epitaxial layer13is 30±0.1 nm, wherein the thickness uniformity (0.1+30) is less than 0.35% and complies with the thickness uniformity requirement for epitaxy, i.e., less than 1.0%.

To sum up, with the electric dipole attraction of the dangling bonds121serving to guide and arrange the titanium ions130(i.e., the metal ions) and the nitrogen ions131(i.e., the anions of the reactant gas) in the correct directions during the formation of the titanium nitride epitaxial layer13(i.e., the compound epitaxial layer), mirror-like planar crystals can be successfully formed without island-type nucleation or cluster growth, which are two structural characteristics of columnar crystals. A manufacturer can therefore produce mirror-like planar crystals without using the expensive MBE manufacturing process, and product yield can be significantly increased while production costs are lowered.

While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.