SURFACE MODIFICATION METHOD OF ALUMINUM NITRIDE CERAMIC SUBSTRATE

Abstract

A surface modification method of an aluminum nitride ceramic substrate uses a sputtering deposition and a metal organic chemical vapor deposition (MOCVD) to perform a surface modification of the polycrystalline aluminum nitride ceramic substrate. Accordingly, an aluminum nitride layer is epitaxially grown in two stages of temperature by MOCVD, such that a crystallization phase of monocrystalline aluminum nitride material may be formed on the surface of the polycrystalline aluminum nitride ceramic substrate, so as to decrease a surface roughness of the polycrystalline aluminum nitride ceramic substrate.

Claims

1. A surface modification method of an aluminum nitride ceramic substrate, wherein steps of the surface modification method comprise: (A) providing a polycrystalline aluminum nitride substrate, and forming a titanium metal layer on the polycrystalline aluminum nitride substrate by a sputtering deposition; (B) forming an aluminum nitride buffer layer on the titanium metal layer by another sputtering deposition; (C) forming an aluminum nitride thin film epitaxial layer on the aluminum nitride buffer layer by a metal organic chemical vapor deposition (MOCVD), wherein a thickness of the aluminum nitride thin film epitaxial layer is less than 1 μm; and (D) continuing the metal organic chemical vapor deposition and increasing a process temperature of the metal organic chemical vapor deposition to form an aluminum nitride thick film epitaxial layer on the aluminum nitride thin film epitaxial layer, wherein a thickness of the aluminum nitride thick film epitaxial layer is greater than 1 μm.

2. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein a thickness of the titanium metal layer in the step (A) ranges from 100 nm to 500 nm.

3. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein the sputtering deposition in the step (A) is performed with a titanium target, and a sputtering gas of the sputtering deposition in the step (A) is argon.

4. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein a thickness of the aluminum nitride buffer layer in the step (B) ranges from 100 nm to 500 nm.

5. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein the sputtering deposition in the step (B) is performed with an aluminum target, and a sputtering gas of the sputtering deposition in the step (B) is a combination of argon and nitrogen.

6. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein in the step (C), reactants are trimethyl aluminum (Al.sub.2(CH.sub.3).sub.6) and ammonia (NH.sub.3), and an epitaxial growth temperature ranges from 950° C. to 1030° C.

7. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein in the step (D), reactants are trimethyl aluminum (Al.sub.2(CH.sub.3).sub.6) and ammonia (NH.sub.3), and an epitaxial growth temperature ranges from 1030° C. to 1160° C.

8. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein the thickness of the aluminum nitride thin film epitaxial layer ranges from 100 nm to 500 nm.

9. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein the thickness of the aluminum nitride thick film epitaxial layer ranges from 1 μm to 5 μm.

10. The surface modification method of the aluminum nitride ceramic substrate of claim 1, wherein the aluminum nitride thin film epitaxial layer and the aluminum nitride thick film epitaxial layer have a monocrystalline aluminum nitride with a crystal face which is (101).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a flowchart of a surface modification method of an aluminum nitride ceramic substrate according to the present invention.

[0021] FIG. 2 is a schematic diagram showing a cross-sectional view of a polycrystalline aluminum nitride ceramic substrate after processing surface modification according to an embodiment of the present invention.

[0022] FIG. 3 shows X-ray diffraction spectrums of a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention.

[0023] FIG. 4 shows SEM pictures of a surface and a cross-sectional view of an epitaxial layer of a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention.

[0024] FIG. 5 shows AFM pictures of a polycrystalline aluminum nitride ceramic substrate and a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0025] Specific examples will be detailed in the follow description to explain an implementation of the present invention. Those skilled in the art can easily understand an advantage and an effect of the present invention from contents disclosed in this specification.

[0026] Referring to FIG. 1, FIG. 1 is a flowchart of a surface modification method of an aluminum nitride ceramic substrate according to the present invention. As shown in FIG. 1, steps of the surface modification method of the aluminum nitride ceramic substrate of the present invention include: (A) providing a polycrystalline aluminum nitride substrate, and forming a titanium metal layer on the polycrystalline aluminum nitride substrate by a sputtering deposition (step S101); (B) forming an aluminum nitride buffer layer on the titanium metal layer by another sputtering deposition (step S102); (C) forming an aluminum nitride thin film epitaxial layer on the aluminum nitride buffer layer by a metal organic chemical vapor deposition (MOCVD), wherein a thickness of the aluminum nitride thin film epitaxial layer is less than 1 μm (step S103); and (D) continuing the metal organic chemical vapor deposition and increasing a process temperature of the metal organic chemical vapor deposition to form an aluminum nitride thick film epitaxial layer on the aluminum nitride thin film epitaxial layer, wherein a thickness of the aluminum nitride thick film epitaxial layer is greater than 1 μm (step S104).

Embodiment

[0027] In this embodiment, the polycrystalline aluminum nitride substrate is provided first. A titanium metal layer is formed on the polycrystalline aluminum nitride substrate by a sputtering deposition (using a titanium target, and sputtering parameters: 100 W of power, 30-150 minutes of time, 8 sccm of flow rate of argon, and 5×10.sup.−3 torr of pressure) to serve as an adhesive layer. Then, an aluminum nitride thin film is formed by another sputtering deposition (using an aluminum target, and sputtering parameters: 100 W of power, 30-150 minutes of time, 8 sccm of flow rate of argon/nitrogen, and 5×10.sup.−3 torr of pressure) to serve as a buffer layer between an epitaxial layer and the substrate. Next, by using the metal organic chemical vapor deposition (MOCVD) and using trimethyl aluminum (TMAl) and ammonia (NH.sub.3) to be raw materials, an aluminum nitride thin film epitaxial layer and an aluminum nitride thick film epitaxial layer are epitaxially grown in two stages (first stage MOCVD parameters: 950-1030° C. of temperature, 30 minutes of time, 10 sccm of flow rate of TMAl/500 sccm of flow rate of NH.sub.3, and 200 mbar of pressure; second stage MOCVD parameters: 1030-1160° C. of temperature, 60 minute of time, 20 sccm of flow rate of TMAl/1000 sccm of flow rate of NH.sub.3, and 200 mbar of pressure), so as to complete the surface modification of the polycrystalline aluminum nitride ceramic substrate of the present invention. Referring to FIG. 2, FIG. 2 is a schematic diagram showing a cross-sectional view of a polycrystalline aluminum nitride ceramic substrate after processing surface modification according to an embodiment of the present invention. As shown in FIG. 2, the structure includes a polycrystalline aluminum nitride ceramic substrate, a titanium metal thin film, an aluminum nitride thin film and an aluminum nitride epitaxial layer.

[0028] Referring to FIG. 3, FIG. 3 shows X-ray diffraction spectrums of a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention. The crystallization phase identification is performed by using X-ray diffractometer. First, the crystallization phase identification for the polycrystalline aluminum nitride ceramic substrate is performed. As shown in (a) of FIG. 3, it shows that the polycrystalline aluminum nitride ceramic substrate has diffraction peaks of the polycrystalline aluminum nitride material at 20=23.4°, 25.4°, 29.6°, 30.7°, 33.2°, 34.3°, 36.0°, 37.9°, 49.8°, 59.4°, 66.1°, 69.7°, 71.5° and 72.7°. One titanium metal thin film is formed on the polycrystalline aluminum nitride ceramic substrate by the sputtering deposition to serve as the adhesive layer, and then, the aluminum nitride buffer layer and the aluminum nitride epitaxial layer are formed on the titanium metal thin film/the polycrystalline aluminum nitride ceramic substrate by the sputtering deposition and the metal organic chemical vapor deposition (MOCVD). After that, as shown in (b) of FIG. 3, it shows that a diffraction peak of the titanium metal thin film appears at 2θ=38.2°. Finally, the crystallization phase identification for the surface of the aluminum nitride epitaxial layer/the aluminum nitride buffer layer/the titanium metal thin film (the adhesive layer)/the polycrystalline aluminum nitride ceramic substrate is performed by using the X-ray diffractometer with grazing incident diffraction. As shown in (c) of FIG. 3, single diffraction peak of the aluminum nitride thin film appears at 2θ=35.9°. It means that the surface of the polycrystalline aluminum nitride ceramic substrate may be indeed converted from polycrystalline phase to monocrystalline phase after the substrate surface modification technique is applied on the polycrystalline aluminum nitride ceramic substrate.

[0029] Referring to FIG. 4, FIG. 4 shows SEM pictures of a surface and a cross-sectional view of an epitaxial layer of a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention. The result shows that the aluminum nitride epitaxial layer prepared by the present invention has aluminum nitride crystal grains with more regular shape and uniform distribution of the epi facets, which are pyramids, wherein the side of the pyramid is 62° to the c-plane (i.e., the surface parallel to the substrate surface), which is a crystal face of (101). The distribution of the crystal face of AlN shown in SEM picture is consistent with the measuring result of XRD (X-ray diffraction). Generally, the quantum well grown on the c-plane is a polar quantum well which has the largest polarized electric field. The crystal face of (101) is very helpful to the luminous efficiency of UV LED, wherein the surface of this pyramid may greatly reduce the probability of total reflection of the light beam inside the component, so as to effectively improve the light extraction efficiency of the LED. The surface modification method proposed by the present invention may use a low cost to produce a larger and more uniform aluminum nitride substrate, which may serve as a high-quality GaN epitaxial substrate, thereby opening up the application market of UV LED.

[0030] Referring to FIG. 5, FIG. 5 shows AFM pictures of a polycrystalline aluminum nitride ceramic substrate and a polycrystalline aluminum nitride ceramic substrate after processing a surface modification according to an embodiment of the present invention, wherein surface roughness measured by AFM is shown in table 1. Picture (a) of FIG. 5 is a surface picture of the polycrystalline aluminum nitride ceramic substrate of the present invention, and a combination of picture (a) and table 1 shows that a surface roughness of the polycrystalline aluminum nitride ceramic substrate is 25.5 nm; picture (b) of FIG. 5 is a surface picture of the polycrystalline aluminum nitride ceramic substrate after processing the surface modification according to the present invention, and a combination of picture (b) and table 1 shows that a surface roughness of the polycrystalline aluminum nitride ceramic substrate after processing surface modification according to the present invention is 7.8 nm. They show that the surface roughness of the polycrystalline aluminum nitride ceramic substrate may be effectively decreased from 25.5 nm to 7.8 nm when the surface modification method is applied on the polycrystalline aluminum nitride ceramic substrate.

TABLE-US-00001 TABLE 1 Polycrystalline aluminum nitride ceramic substrate Polycrystalline aluminum after processing surface nitride substrate modification Surface roughness 25.5 nm 7.8 nm (Ra)

[0031] The surface modification method of the aluminum nitride ceramic substrate of the present invention uses the sputtering deposition and MOCVD to perform the surface modification of the aluminum nitride ceramic substrate. This surface modification method may make the crystallization phase of the monocrystalline aluminum nitride material be formed on the surface of the polycrystalline aluminum nitride ceramic substrate, such that the surface roughness of the polycrystalline aluminum nitride ceramic substrate may be decreased, and the epi facets are distributed uniformly and are pyramids. Thus, the polycrystalline aluminum nitride ceramic substrate may serve as a high-quality GaN epitaxial substrate, which is very helpful to the luminous efficiency of UV LED when it is applied to UV LED, wherein it may make the probability of total reflection of the light beam inside the component be greatly reduced to effectively improve the light extraction efficiency of the LED. The surface modification method of the aluminum nitride ceramic substrate according to the present invention may make the subsequent process be performed on components such as light-emitting diodes, stacked memories and stacked integrated circuits, so as to make these components be used in more fields in the future.

[0032] The above examples are merely to explain the features and effects of the present invention and not to limit the scope of the present invention. Those skilled in the art may make numerous modifications and alterations of the above embodiments without departing from the spirit and scope of the invention. Accordingly, the present invention should be construed as limited only by the metes and bounds of the appended claims.