Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Total dielectric isolation
Reexamination Certificate
2002-02-28
2004-03-02
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Total dielectric isolation
C438S455000
Reexamination Certificate
active
06699770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of semiconductor substrate manufacture; i.e., a substrate on which semiconductor materials or devices can be formed.
2. Description of the Related Art
The present invention makes use of a separation by implantation of oxygen (SIMOX) process.
In accordance with this invention, a SIMOX process provides that oxygen implanter apparatus is used to create a very thin silicon dioxide (SiO
2
, SiO
x
) layer that is buried within a relatively thick silicon carbide (SiC) wafer, thereby leaving a thin membrane layer of SiC on top of the SiC wafer. For example, such oxygen implantation equipment is manufactured by Ibis Technology Corporation.
The present invention uses a step of etching SiO
2
(SiO
x
) in hydrofluoric acid.
The present invention uses a wafer-bonding step. Wafer bonding of a variety of materials is known.
U.S. Pat. No. 5,798,293, incorporated herein by reference, is cited for its teaching of the production of a semiconductor layer of SiC of the 3C polytype on top of a semiconductor substrate layer using a wafer-bonding technique.
U.S. Pat. No. 5,877,070, incorporated herein by reference, is cited for its teaching of transferring an upper portion of a first mono-crystalline substrate to a second substrate using hydrogen trap-induced implantation of the first substrate, forming micro-cracks in the hydrogen traps, direct wafer bonding the first substrate to the second substrate, and growing the micro-cracks such that the upper portion of the first substrate separates from the first substrate.
U.S. Pat. No. 5,966,620, incorporated herein by reference, is cited for its teaching of the use of the implantation of helium ions or hydrogen ions into a single crystal silicon substrate in order to form micro-cavities in the implantation region. Separation is achieved due to the fragility of the implantation region, and by the application of an external force, by oxidation of the implantation layer, or by laser heating of the implantation layer.
U.S. Pat. No. 6,054,370, incorporated herein by reference, is cited for its teaching of the formation of first damaged regions in a substrate underneath areas wherein active devices are formed forming second damaged areas in the substrate at locations between the first damaged regions, causing a film to detach from the substrate at locations where the first and second damaged regions are formed, and transferring the film to a wafer.
U.S. Pat. No. 6,120,597, incorporated herein by reference, is cited for its teaching of the detaching of a single crystal film from an epilayer/substrate or bulk crystal structure wherein ions are implanted into the crystal structure to form a damaged layer within the crystal structure at an implantation depth below a top surface of the crystal structure, and wherein chemical etching effects detachment of the single crystal film from the crystal structure.
SUMMARY OF THE INVENTION
This invention provides for the fabrication of hybrid substrates wherein a thin membrane of SiC is lifted off or sliced from a relatively thick SiC wafer, and wherein the thin SiC membrane is wafer bonded to the surface of a substrate-of-choice, to thereby form a hybrid substrate that is made up of the thin membrane of SiC and the substrate-of-choice.
While the invention will be described relative to the use of a relatively thick SiC wafer within the spirit and scope of the invention such a semiconductor wafer can be selected from SiC polytypes, non-limiting examples being 6H—SiC, 4H—SiC, 3C—SiC and 15R—SiC.
Use of the relatively thick and expensive SiC wafer is maximized since many thin SiC membranes can be produced from one thick SiC wafer. That is, the thick and expensive SiC wafer can be re-used to form a number of thin SiC membranes wherein the now-exposed surface of the relatively thick SiC wafer is polished before the next thin SiC membrane is removed from the thick SiC wafer.
Wafer bonding of the SiC membrane to the substrate-of-choice is performed using commercially-available substrates-of-choice. In this manner, the invention provides relatively inexpensive hybrid SiC substrates.
An embodiment of the invention includes a three-step process. In this three-step process, a buried SiO
2
layer, or more generally a SiO
x
layer, is first formed in a relatively thick SiC wafer by oxygen implantation at an elevated temperature thereby forming a thin SiC membrane on top of the buried SiO
2
layer.
Secondly, the exposed surface of the thin SiC membrane is wafer bonded to the surface of a substrate-of-choice; for example, to a silicon (Si), or a polycrystalline SiC substrate. Optionally, a wetting/bonding layer can be provided between the two wafer-bonding surfaces. Non-limiting examples of such a wetting/bonding layer are layers that contain silicon, such as silicon nitride (Si
3
N
4
).
Thirdly, the thin SiC membrane is separated from the relatively thick SiC wafer; for example, by using a hydrofluoric acid etching step to remove the buried SiO
2
(SiO
x
) layer.
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Blum David S
Sheridan & Ross P.C.
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