The present invention generally relates to MOS structures and methods for fabricating MOS structures, and more particularly relates to nonplanar, multi-gate MOSFET structures known as FinFETs.
In contrast to traditional planar metal-oxide-semiconductor field-effect transistors (MOSFETs), which are fabricated using conventional lithographic fabrication methods, nonplanar FETs incorporate various vertical transistor structures, and typically include two or more gate structures formed in parallel. One such semiconductor structure is the “FinFET,” which takes its name from the multiple thin silicon “fins” that are used to form the respective gate channels, and which are typically on the order of tens of nanometers in width. In general, the FinFET is one of a class of nonplanar, multi-gate transistors typically built on a silicon-on-insulator (SOI) substrate.
More particularly, referring to the exemplary prior art nonplanar FET structure shown in
As conventional MOSFET gate lengths are scaled below 100 nm, the resulting FET may be subject to excessive leakage and other short-channel effects. FinFETs, by virtue of their non-planar gate channel structure, do not exhibit these short-channel effects. Nevertheless, while FinFETs are advantageous with respect to scalability and electrical characteristics, there is a continuing need to improve their performance. For example, it is desirable to provide FinFET structures that can accommodate increased drive current (i.e., the drain-source current that can flow through the parallel fins). Furthermore, it is desirable to reduce the effective contact resistance of the structure. These and other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
FinFET structures and methods are provided. In one embodiment, a fabrication method includes patterning a semiconductor substrate to form a nonplanar semiconductor structure comprising a first fin, a second fin substantially parallel to the first fin, and an inter-fin semiconductor strip coupled therebetween. The first fin, the second fin, and the inter-fin semiconductor strip each extend from a drain region to a source region. A gate dielectric layer is formed on the first and second fins and the inter-fin semiconductor strip in a gate region substantially orthogonal to the first and second fins and between the drain and source region. A gate electrode layer is then formed on the gate dielectric layer. In one embodiment, the semiconductor substrate is a silicon-on-insulator (SOI) material comprising a buried oxide layer (BOX) having a silicon layer formed thereon.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
In general, the present invention relates to a fin field-effect transistor (“FinFET”) structure that incorporates a thin, inter-fin semiconductor strip between two or more parallel, non-planar fin structures, thereby increasing drive current and reducing effective contact resistance. In this regard, the following detailed description is merely exemplary in nature and is not intended to limit the range of possible embodiments and applications. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
For simplicity and clarity of illustration, the drawing figures depict the general structure and/or manner of construction of the various FinFET embodiments. Elements in the drawings figures are not necessarily drawn to scale: the dimensions of some features may be exaggerated relative to other elements to assist improve understanding of the example embodiments.
Terms of enumeration such as “first,” “second,” and the like may be used for distinguishing between similar elements and not necessarily for describing a particular spatial or chronological order. These terms, so used, are interchangeable under appropriate circumstances. The embodiments of the invention described herein are, for example, capable of use in sequences other than those illustrated or otherwise described herein. Unless expressly stated otherwise, “connected” means that one element/node/feature is directly joined to (or directly communicates with) another element/node/feature, and not necessarily mechanically. The terms “comprise,” “include,” “have” and any variations thereof are used synonymously to denote non-exclusive inclusion. The term “exemplary” is used in the sense of “example,” rather than “ideal.”
In the interest of conciseness, conventional techniques, structures, and principles known by those skilled in the art may not be described herein, including, for example, standard semiconductor processing techniques, fundamental principles of semiconductor devices, and basic operational principles of FETs. For the purposes of clarity, some commonly-used layers may not be illustrated in the drawings, including various protective cap layers, seed layers, substrates, or the like.
Referring now to the conceptual isometric overview depicted in
Inter-fin strip 202 is preferably contiguous with (i.e., electrically and physically connected to) both fins 104 and 106, and has a doping profile along its length (i.e., along the y-axis) that is equivalent to that of fins 104 and 106. That is, various portions of fins 104, 106, and 202, may be doped with P-type conductivity-determining impurities or N-type conductivity-determining impurities using, for example, implantation and subsequent thermal annealing of dopant ions such as boron or arsenic. The selection of dopant species depends upon, inter alia, the desired polarity and type of FET structure, as is known in the art.
In accordance with one embodiment, and as described in further detail below, fins 104 and 106 are non-planar structures formed using a SOI substrate—i.e., by selectively patterning the silicon layer to form fins that extend in the z direction from the underlying buried oxide layer 204 such that an inter-fin strip 202 remains.
A conductive gate structure 102 (e.g., a polysilicon or metal gate) “wraps around” three sides of both fins 104 and 106 and overlies strip 202 in a gate region orthogonal to the fins, and is separated from the fins by a suitable gate dielectric layer 103 (e.g., a conventional oxide layer). Fins 104 and 106 are doped to produce the desired FET polarity, as is known in the art, such that the gate channel is formed within the near surface of the fins adjacent to gate oxide 103. The dimensions of the fin (i.e., its height along the z-axis, its width along the x-axis) as well as the width along the x-axis of the inter-fin strip 202 together determine the effective channel width of the FET device. Comparing the illustrated embodiment of
The various dimensions of fins 104, 106, and inter-fin strip 202 may be selected to achieve particular device performance. In one embodiment, for example, the gate length as determined by the length in y direction of gate 102 is on the order of 10-100 nm, and the thickness of inter-fin strip 202 is between approximately 5-20 nm. The fins preferably have a height of about 10-100 nm, a width of about 10-100 nm, and a length that is significantly greater than 10 nm. In various embodiments inter-fin semiconductor strip has a first thickness that is less than the fin height by approximately a factor of 2 to 5.
Having thus given an overview of an exemplary FinFET structure 200, a method of fabricating such a structure will now be described in conjunction with
Initially, a silicon-on-insulator (SOI) substrate 304 is provided, including a silicon layer 304 and a buried oxide layer 302. Buried oxide layer 302 is typically incorporated into a further structural silicon layer, which for clarity is not shown in the figures. A variety of methods may be used to produce such an SOI substrate, including, for example, SIMOX (Separation by IMplantation of OXygen), wafer bonding, and various seed methods. Note that while the illustrated invention is described in the context of a silicon substrate, other semiconductor materials or combinations thereof may be used, including Ge, Si—Ge, and the like.
Next, as depicted in
Next, as shown in
As shown in
Next, the dielectric layer 306 is etched away to leave an opening 802 bordered by layer 304 and sidewall spacers 312. This etching process may be performed using a selected wet or dry etch technique.
Next, the silicon layer 304 is selectively etched such that the thinner, outer regions (defined by surface 310) are substantially etched away to leave fins 104, 106, and the central region underlying area 802 (formerly region 308) between spacers 312 is partially etched away such that the aforementioned thin inter-fin strip 202 remains. The thickness of inter-fin strip 202 is determined by, among other things, the difference in thicknesses of silicon layer 304 between spacers 312 and external to spacers 312, as well as the etching process used. The etch process is chosen such that the silicon layer 304 as well as central region 308 are etched uniformly while the spacer layer 312 is not etched.
The spacers 312 are then removed using a suitable etching process, leaving the desired fin structures 104 and 106 and inter-fin strip 202 (
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.