This disclosure relates generally to the field of semiconductor device fabrication.
Tunnel field effect transistors (TFETs) offer improved sub-threshold slope over other complementary metal-oxide-semiconductor (CMOS) devices. A TFET comprises a tunnel barrier, which may comprise a PiN junction. A PiN junction is a semiconductor device having three contiguous regions: p-type doped, intrinsic, and n-type doped. The height of the tunnel barrier may be modulated by the TFET gate potential, controlling the transport current of the TFET. This mechanism of TFET transport current control may give a relatively steep sub-threshold slope. However, the ability of the gate potential of a TFET to modulate the TFET tunnel barrier height may lessen over time, as an inversion layer may form in the TFET due to screening.
In one aspect, a structure for use in fabrication of a PiN heterojunction tunnel field effect transistor (TFET) includes a silicon wafer, the silicon wafer comprising an alignment trench and a p-type silicon germanium (SiGe) region, wherein the silicon wafer further comprises a hydrogen implantation region in the silicon wafer underneath the p-type SiGe region and the alignment trench, the hydrogen implantation region dividing the silicon wafer into a upper silicon region and a lower silicon region, and wherein the upper silicon region comprises the alignment trench and the p-type SiGe region; and a first oxide layer located over the alignment trench and the p-type SiGe region in the silicon wafer, wherein the oxide layer fills the alignment trench, and wherein the first oxide layer is bonded to a second oxide layer located on a handle wafer, wherein the first oxide layer and the second oxide layer comprise a bonded oxide layer; wherein the alignment trench is configured to align a wiring level of the device comprising the PiN heterojunction TFET to the p-type SiGe region during formation of the device comprising the PiN heterojunction TFET.
Additional features are realized through the techniques of the present exemplary embodiment. Other embodiments are described in detail herein and are considered a part of what is claimed. For a better understanding of the features of the exemplary embodiment, refer to the description and to the drawings.
Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:
Embodiments of systems and methods for fabricating a structure for use in fabrication of a TFET having a tunnel barrier comprising a PiN heterojunction are provided, with exemplary embodiments being discussed below in detail. In a PiN heterojunction, at least one of the three regions comprising the heterojunction is made from a different material from the other regions. A PiN heterojunction TFET may operate at its quantum capacitance limit, at which the total gate capacitance is dominated by the semiconductor, or quantum, capacitance as opposed to the geometrical oxide capacitance. At the quantum capacitance limit, substantial scaling benefits are obtained. Screening is reduced, and the TFET gate potential may have relatively strong control of the tunnel barrier height. Control of the tunnel barrier height may be independent of the applied gate bias. A linear change in the TFET gate bias may cause a linear change in the tunnel barrier height, and an exponential change in the TFET transport current. The structure also comprises a zero level trench, or alignment trench, for aligning additional wiring layers that may be formed in subsequent processing steps.
In block 102, as shown in
In block 103, as shown in
In block 104, as shown in
In block 105, wafer 1200 is bonded to a handle wafer comprising bulk silicon 1201 and a top thermal oxide 1202, as shown in
In block 106, wafer 1300 is annealed, releasing silicon 1102 from silicon 1103 at the cleaving plane comprising implantation region 1101. Annealing may comprise spike annealing or flash annealing. The resulting structure 1400, shown in
Structure 1400 comprises a top-down silicon nanowire structure for use in fabrication of a PiN heterojunction TFET device. P-type SiGe region 901 comprises a nanowire, and may comprise the p-type region of a PiN heterojunction that may comprise a TFET tunnel barrier. Structure 1400 also comprises an alignment layer (i.e., zero level trench 202) that may be used to align wiring levels that are formed in subsequent fabrication steps, including the gate polysilicon conductor layer (PC) and active silicon conductor layer (RX), to the p-type SiGe nanowire layer. A PiN heterojunction may be formed on structure 1400 using top-down nanowire fabrication methods. The n-type region of the PiN heterojunction may be formed by n-type diffusion implant, which may be performed using either non-self aligned masking (as in lateral TFET devices) or through a high angle asymmetric implantation. The n-doped portion of the PiN heterojunction structure may comprise self-aligned doped n-type material.
The technical effects and benefits of exemplary embodiments include fabrication of a PiN heterojunction TFET that may operate at its quantum capacitance limit.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
This application is a divisional of U.S. application Ser. No. 12/684,331, filed on Jan. 8, 2010, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | 12684331 | Jan 2010 | US |
Child | 13571392 | US |