Method of fabricating double sided Si(Ge)/Sapphire/III-nitride hybrid structure

Abstract

One aspect of the present invention is a double sided hybrid crystal structure including a trigonal Sapphire wafer containing a (0001) C-plane and having front and rear sides. The Sapphire wafer is substantially transparent to light in the visible and infrared spectra, and also provides insulation with respect to electromagnetic radio frequency noise. A layer of crystalline Si material having a cubic diamond structure aligned with the cubic <111> direction on the (0001) C-plane and strained as rhombohedron to thereby enable continuous integration of a selected (SiGe) device onto the rear side of the Sapphire wafer. The double sided hybrid crystal structure further includes an integrated III-Nitride crystalline layer on the front side of the Sapphire wafer that enables continuous integration of a selected III-Nitride device on the front side of the Sapphire wafer.

Claims

1. A method of fabricating a hybrid structure, the method comprising: providing a C-plane Sapphire wafer having first and second opposite sides; forming a plurality of first layers on the first side of the Sapphire wafer, wherein each of the first layers comprise a material selected from the group consisting of III-Nitride and ZnO materials; forming a plurality of Si/SiGe(C) layers on the second side of the Sapphire wafer utilizing an epitaxial growth process.

2. The method of claim 1, including depositing a heat absorption layer on the first side of the Sapphire wafer before forming the Si/SiGe(C) layers and before forming the first layers.

3. The method of claim 2, including raising the temperature of the Sapphire wafer to an optimum growth temperature of rhombohedrally aligned Si/SiGe(C) on C-plane Sapphire utilizing a substrate heater that applies heat to the heat absorption layer coated on the first side of the Sapphire wafer.

4. The method of claim 3, including removing the heat absorption layer prior to forming a plurality of III-Nitride layers on the first side of the Sapphire wafer.

5. The method of claim 1, wherein at least one III-Nitride layer is formed on the first side of the Sapphire wafer before the Si/SiGe(C) layers are formed on the second side of the Sapphire wafer.

6. The method of claim 1, wherein at least one layer of Si/SiGe(C) is formed on the second side of the Sapphire wafer before the first layers are formed on the first side of the Sapphire wafer.

7. The method of claim 1, wherein at least one of the first layers comprises a III-Nitride material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a fragmentary isometric/schematic view of a hybrid double sided epitaxy with rhombohedral super hetero epitaxy;

(2) FIG. 2 is a schematic view of a device having a III-Nitride LED/LD structure on a front side of a Sapphire wafer and a Si/SiGe device layer on the back side;

(3) FIG. 3 is a schematic cross-sectional view of a structure including an Si/SiGe layer on the backside of a Sapphire wafer that functions as a solar cell, with a front side (GaN-side) illumination in combination with back-side (silicon-side) illumination;

(4) FIG. 4 is a schematic cross-sectional view of a structure/device wherein front-side illumination through transparent Sapphire is utilized in connection with dense metal electrodes;

(5) FIG. 5 is a flow chart showing a process that may be utilized to fabricate a double sided Si(Ge)/Sapphire/III-Nitride hybrid structure.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) For purposes of description herein, the terms upper, lower, right, left, rear, front, vertical, horizontal, and derivatives thereof shall relate to the invention as oriented in FIG. 2. However, it is to be understood that the invention can assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

(7) Technologies that have recently been developed allow the growth of single crystalline Si and SiGe on C-plane Sapphire. It is described as Rhombohedral super hetero epitaxy because Si and SiGe of cubic diamond structure is aligned with cubic <111> direction on trigonal Sapphire's (0001) C-plane and Si/SiGe can be strained as Rhombohedron in this atomic alignment. C-plane Sapphire is the most common substrate for the growth of III-Nitride semiconductor devices such as Gallium Nitrides (GaN) Blue, Green, and ultra violet (UV) Light Emitting Diodes (LEDs) and Laser Diodes (LDs).

(8) A hybrid crystal growth technology utilized in the present invention includes use of Rhombohedral super-hetero epitaxy which provides for the growth of Si/SiGe devices 10 (FIGS. 1 and 2) on the back side 16 of a Sapphire wafer 15. Also, III-Nitride devices 20 such as GaN, InGaN, and AlGaN devices are grown on the front side 18 of a Sapphire wafer 15. This hybrid epitaxy creates a device/structure 30 having continuously integrated single crystalline layers 10, 20 with different crystal structures on the front and back sides of a Sapphire wafer 15. The hybrid layer structure 30 provides for integration of III-Nitride devices 20 (such as LEDs and LDs) on the front side 18 of a Sapphire wafer 15, and Si/SiGe devices 10 (such as solar cell, logic devices, or RF devices) on the back side 16 of a Sapphire wafer 15 as shown in FIGS. 1 and 2.

(9) The two layers 10 and 20 are electrically separated by Sapphire layer or wafer 15. Sapphire is a good insulator, but it is optically transmittable since Sapphire is transparent in visible and IR spectra. Unlike prior GaN on SiC technologies in which a GaN layer is electrically connected to a SiC substrate, a hybrid double sided epitaxy according to the present invention allows electric separation of the GaN layer 20 and the Si/SiGe layer 10 so that the Si/SiGe layer 10 can operate at extremely high frequencies above several hundred gigahertz. This is possible because it is based on Si/SiGe material on a Sapphire insulator (i.e. Silicon-On-Insulator (SOI) and Silicon-On-Sapphire (SOS) technologies). Because Sapphire is a good insulator, it does not produce substrate capacitance related parasitic RF noises and leaks at high frequencies. In contrast, known Si/SiGe on Si wafer or SiC wafer technologies can have problems (e.g. parasitic noises and leaks) that are associated with substrate capacitance.

(10) A transparent Sapphire substrate 15 utilized with a wide bandgap III-nitride device layer according to the present invention does not block the sunlight 26 (FIG. 2) from the front side 24 of the device/structure 30. Therefore, the Si/SiGe layer 10 on the back side 16 of the Sapphire 15 can work as a solar cell 35 with the front-side 18 (GaN-side) providing LED/light illumination 28 as well as the backside illumination 32A and 32B as shown in FIG. 3. With reference to FIG. 4, front side illumination of solar cell 35A through the transparent Sapphire 15 allows dense (closely spaced) metal electrodes 32A and 32B that do not block the sun light 26 and shorter carrier travel distance, thereby delivering more photo-voltaic currents.

(11) With reference to FIG. 5, a process of fabricating a multi layer hybrid structure 30 includes providing a C-plane Sapphire wafer 15 at step 50. Processes for fabricating C-plane Sapphire wafers are known, such that step 50 will not be described in detail. An optional heat absorption layer 52 such as Carbon (C) or Titanium (Ti) can be disposed (for example, by deposition) on one side of the Sapphire wafer 15 at step 55 utilizing a suitable known process. A substrate heater 54 is utilized to apply IR heat 53 to raise the temperature of the Sapphire layer 15 to the optimum growth temperature for rhombohedrally aligned Si/SiGe on C-plane Sapphire. The optional heat absorbing layer 52 absorbs more IR heat 53 and assists in maintaining a uniform high substrate temperature. It will be understood that other heating methods and processes may also be utilized.

(12) At step 60, Si/SiGe layers 10 are grown on the back side of the Sapphire wafer 15 utilizing a known epitaxial growth method. Examples of such processes include sputtering, molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), physical vapor epitaxy (PVE), hydride vapor phase epitaxy (HVPE), e-Beam deposit, liquid phase epitaxy (LPE), low pressure chemical vapor deposit (LPCVD), etc. The fabrication process can further include optional Si/SiGe device pre-fabrication processes such as chemical-mechanical polishing (CMP), dopant drive-in, ion-implantation, and other such processes, which can optionally be performed at step 65. The deposition or growth of a protection layer 72 is performed at step 70. The protection layer 72 protects the Si/SiGe layer 10 during formation of the III-Nitride structures.

(13) In step 75, the optional heat absorbing layer 52 is removed (if necessary) utilizing a suitable known etching process such as, for example, wet etching, dry etching, plasma etching, reactive ion etching, or the like to form an exposed Sapphire surface 76. Then, at step 80, heat 82 is applied and III-Nitride layers 20 such as, for example, GaN, AlN, aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and InN are grown on the exposed surface 76 of the front side 18 of C-plane Sapphire (opposite side from Si/SiGe layers). III-Nitride processes are known in the art, and this step in the process will not therefore be described in detail. Known III-Nitride pre-device fabrication processes such as, for example, chemical-mechanical polishing (CMP), dopant drive-in, ion-implantation, and the like can be performed in step 85. In step 90, a second protection layer 92 (such as, for example, silicon oxide or silicon nitride) is deposited or grown utilizing known processes. The second protection layer 92 protects the III-Nitride layers 20. After step 90, the hybrid wafer 30 with Si/SiGe layers 10 and III-Nitride layers 20 can be used as a wafer product.

(14) It will be understood that steps 65 and 85 are optional, and may or may not be included in a process for manufacturing a hybrid wafer product according to the present invention.

(15) After step 90, the hybrid wafer product can be further processed by removing and depositing each protection layer at a time and performing further post-wafer device fabrications as steps 95 and 100 in order make full hybrid circuit with Si/SiGe 10 on one side and III-Nitride 20 on the other side. A double sided hybrid wafer product 30 can be commercialized after stop 90 and full hybrid devices/products can be commercialized after step 100. It will be understood that it is possible to exchange the order of growth and device fabrication sequences of Si/SiGe and III-Nitrides such that III-Nitrides are grown first and Si/SiGe layers are grown later. The double sided hybrid crystal growth technology described above also applies to Si(Ge)/Sapphire/ZnO hybrid structure as well since ZnO has the same Wurtzite crystal structure as III-Nitride on C-plane Sapphire.

(16) Growth of the Si/SiGe and III-Nitrides during the process illustrated in FIG. 5 can be adjusted utilizing x-ray diffraction methods as described in U.S. Pat. Nos. 7,769,135 and 7,558,371. Use of these x-ray diffraction methods provides quality control and permits the optimum growth parameters for forming hybrid crystals with more than 99% single crystallinity. These x-ray diffraction methods permit measuring the single crystal versus twin defect ratio in full wafer scale.

(17) It will be understood that the principles and processes described above can also be utilized with SiGeC alloy in addition to SiGe alloy on C-plane sapphire. Si, Ge, and C are group IV semiconductor materials that can readily build the rhombohedral double side structure with GaN in a substantially similar epitaxy.

(18) All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

(19) All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range.

(20) The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Or means and/or. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. As also used herein, the term combinations thereof includes combinations having at least one of the associated listed items, wherein the combination can further include additional, like non-listed items. Further, the terms first, second, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity).

(21) Reference throughout the specification to another embodiment, an embodiment, exemplary embodiments, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and can or cannot be present in other embodiments. In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments and are not limited to the specific combination in which they are discussed.

(22) This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.