CN113228300A - FINFET including source and drain regions and dopant diffusion barrier superlattice layers to reduce contact resistance and related methods - Google Patents

FINFET including source and drain regions and dopant diffusion barrier superlattice layers to reduce contact resistance and related methods Download PDF

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CN113228300A
CN113228300A CN201980085367.9A CN201980085367A CN113228300A CN 113228300 A CN113228300 A CN 113228300A CN 201980085367 A CN201980085367 A CN 201980085367A CN 113228300 A CN113228300 A CN 113228300A
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semiconductor
region
finfet
source
drain regions
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武内英树
D·康奈利
M·海塔
R·伯顿
R·J·米尔斯
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Atomera Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/785—Field effect transistors with field effect produced by an insulated gate having a channel with a horizontal current flow in a vertical sidewall of a semiconductor body, e.g. FinFET, MuGFET
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
    • H01L29/66787—Unipolar field-effect transistors with an insulated gate, i.e. MISFET with a gate at the side of the channel
    • H01L29/66795—Unipolar field-effect transistors with an insulated gate, i.e. MISFET with a gate at the side of the channel with a horizontal current flow in a vertical sidewall of a semiconductor body, e.g. FinFET, MuGFET
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/7842—Field effect transistors with field effect produced by an insulated gate means for exerting mechanical stress on the crystal lattice of the channel region, e.g. using a flexible substrate
    • H01L29/7848—Field effect transistors with field effect produced by an insulated gate means for exerting mechanical stress on the crystal lattice of the channel region, e.g. using a flexible substrate the means being located in the source/drain region, e.g. SiGe source and drain

Abstract

The FINFET may include a semiconductor fin, spaced apart source and drain regions in the semiconductor fin with a channel region extending therebetween, and at least one dopant diffusion barrier superlattice dividing at least one of the source and drain regions into a lower region and an upper region, wherein the upper region has the same conductivity as the lower region and a higher dopant concentration than the lower region. The dopant diffusion barrier superlattice may include a plurality of stacked groups of layers, with each group of layers including a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The FINFET may also include a gate over the channel region.

Description

FINFET including source and drain regions and dopant diffusion barrier superlattice layers to reduce contact resistance and related methods
Technical Field
The present disclosure relates generally to semiconductor devices and, more particularly, to semiconductor devices having enhanced contact configurations and related methods.
Background
Structures and techniques are presented to enhance the performance of semiconductor devices, such as by enhancing carrier mobility. For example, U.S. patent application No. 2003/0057416 to Currie et al discloses strained material layers of silicon, silicon-germanium, and relaxed silicon and further including impurity-free regions that would otherwise cause performance degradation. The resulting biaxial strain in the upper silicon layer alters carrier mobility, enabling higher speed and/or lower power devices. U.S. patent application No. 2003/0034529, published by Fitzgerald et al, discloses a CMOS inverter that is also based on similar strained silicon technology.
U.S. patent No. 6,472,685B 2 to Takagi discloses a semiconductor device that includes a layer of silicon and carbon sandwiched between layers of silicon such that the conduction and valence bands of the second silicon layer receive a tensile strain. Electrons having a smaller effective mass and caused by an electric field applied to the gate are confined in the second silicon layer, thus claiming that the n-channel MOSFET has a higher mobility.
U.S. patent No. 4,937,204 to Ishibashi et al discloses a superlattice in which a plurality of layers (less than eight monolayers) are alternately and epitaxially grown and which contains fractional (fractional) or binary compound semiconductor layers. The direction of the main current is perpendicular to the layers of the superlattice.
U.S. Pat. No. 5,357,119 to Wang et al discloses a Si-Ge short period superlattice with higher mobility achieved by reducing alloy scattering in the superlattice. In accordance with these approaches, U.S. patent No. 5,683,934 to Candelaria discloses an enhanced mobility MOSFET including a channel layer comprising an alloy of silicon and a second material substitutional present in the silicon lattice at a percentage that places the channel layer under tensile stress.
U.S. patent No. 5,216,262 to Tsu discloses a quantum well structure comprising two barrier regions and a thin epitaxially grown semiconductor layer sandwiched between the barriers. Each barrier region consists of alternating layers of SiO2/Si, having a thickness typically in the range of 2 to 6 monolayers. A much thicker portion of silicon is sandwiched between the spacers.
An article also known as Tsu entitled "Phenomena in silicon nanostructured devices" and published online at 9/6/2000 by Applied Physics and Materials Science & Processing, page 391-. Si/O superlattices are disclosed as being useful in silicon quantum and light emitting devices. In particular, a green electroluminescent diode structure was constructed and tested. The current in the diode structure is vertical, i.e. perpendicular to the layers of the SAS. The disclosed SAS may include semiconductor layers separated by adsorbed species such as oxygen atoms and CO molecules. Silicon growth beyond the adsorbed oxygen monolayer is described as epitaxial with a fairly low defect density. One SAS structure included a 1.1nm thick silicon portion (which was about eight atomic layers of silicon), and another structure had twice this silicon thickness. An article entitled "Chemical Design of Direct-Gap Light-Emitting Silicon" by Luo et al, published in Physical Review Letters, Vol.89, No. 7 (8/12 2002) also discusses the Light Emitting SAS structure of Tsu.
U.S. patent No. 7,105,895 to Wang et al discloses barrier structural units of thin silicon and oxygen, carbon, nitrogen, phosphorus, antimony, arsenic or hydrogen, thereby reducing current flow vertically through the lattice by more than four orders of magnitude. The insulating layer/barrier layer allows for low defect epitaxial silicon to be deposited next to the insulating layer.
United kingdom patent application 2,347,520, published by Mears et al, discloses that the principles of Aperiodic Photonic Band Gap (APBG) structures are applicable to electronic band gap engineering. In particular, this application discloses that material parameters such as band minimum location, effective mass, etc. can be adjusted to produce new aperiodic materials with desirable band structure characteristics. It is disclosed that other parameters such as electrical conductivity, thermal conductivity and dielectric constant or magnetic permeability can also be designed into the material.
Furthermore, Wang et al, U.S. patent No. 6,376,337, discloses a method for producing an insulating or barrier layer for a semiconductor device, which includes depositing layers of silicon and at least one additional element on a silicon substrate, whereby the deposited layer is substantially defect-free such that epitaxial silicon substantially defect-free can be deposited on the deposited layer. Alternatively, a monolayer (preferably comprising oxygen) of one or more elements is adsorbed on the silicon substrate. A plurality of insulating layers sandwiched between the epitaxial silicon form a barrier composite.
Despite such approaches, further enhancements may be desirable to achieve improved performance using advanced semiconductor materials and processing techniques in semiconductor devices.
SUMMARY
A FINFET may include a semiconductor fin, spaced apart source and drain regions in the semiconductor fin with a channel region extending therebetween, and at least one dopant diffusion blocking superlattice dividing at least one of the source and drain regions into a lower region and an upper region, wherein the upper region has the same conductivity as the lower region and a higher dopant concentration than the lower region. The dopant diffusion barrier superlattice may include a plurality of stacked groups of layers, with each group of layers including a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The semiconductor device may further include a gate electrode on the channel region.
More particularly, the at least one dopant diffusion barrier superlattice may comprise a respective dopant diffusion barrier superlattice for each of the source and drain regions. In example embodiments, the upper region may be elevated above an upper surface of the semiconductor layer. In addition, the lower region may comprise a different material than the upper region. By way of example, the lower region may comprise silicon and the upper region may comprise silicon germanium. According to another example, the lower region may comprise silicon germanium and the upper region may comprise silicon.
The FINFET may also include a metal contact on the upper region. By way of example, the metal contact may comprise at least one of titanium, cobalt, nickel, and platinum. In addition, the FINFET may also include a semiconductor substrate (from which the semiconductor fin extends vertically upward) and insulators on the semiconductor substrate and on opposite sides of the semiconductor fin. Also by way of example, the base semiconductor monolayer may comprise silicon, and the at least one non-semiconductor monolayer may comprise oxygen.
A method of fabricating a FINFET may include forming spaced apart source and drain regions in a semiconductor fin with an extended channel region therebetween. At least one of the source and drain regions may be separated into a lower region and an upper region by a dopant diffusion barrier superlattice, wherein the upper region has the same conductivity as the lower region and a higher dopant concentration than the lower region. The dopant diffusion barrier superlattice may include a plurality of stacked groups of layers, with each group of layers including a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The method may also include forming a gate over the channel region.
More particularly, each of the source and drain regions may be divided into a lower region and an upper region with a respective dopant diffusion barrier superlattice. In example embodiments, the upper region may be raised above an upper surface of the semiconductor layer. In addition, the lower region may comprise a different material than the upper region. By way of example, the lower region may comprise silicon and the upper region may comprise silicon germanium. According to another example, the lower region may comprise silicon germanium and the upper region may comprise silicon.
The method may also include forming a metal contact on the upper region. By way of example, the metal contact may comprise at least one of titanium, cobalt, nickel, and platinum. The method may also include forming a semiconductor fin extending vertically upward from a semiconductor substrate, and forming insulators on the semiconductor substrate and on opposite sides of the semiconductor fin. Also by way of example, the base semiconductor monolayer may comprise silicon, and the at least one non-semiconductor monolayer may comprise oxygen.
Brief description of the drawings
Fig. 1 is a greatly enlarged schematic cross-sectional view of a superlattice for use in a semiconductor device in accordance with an example embodiment.
Fig. 2 is a perspective schematic atomic diagram of a portion of the superlattice shown in fig. 1.
Fig. 3 is a greatly enlarged schematic cross-sectional view of another embodiment of a superlattice in accordance with an example embodiment.
Fig. 4A is a calculated band structure plot from the gamma point (G) of a prior art bulk silicon and 4/1 Si/O superlattice as shown in fig. 1-2.
Fig. 4B is a ribbon structure diagram calculated from the Z point of a prior art bulk silicon and 4/1 Si/O superlattice as shown in fig. 1-2.
Fig. 4C is a ribbon structure diagram calculated from the gamma and Z points of a prior art bulk silicon and 5/1/3/1 Si/O superlattice as shown in fig. 3.
Fig. 5 is a schematic cross-sectional view of a semiconductor device including a dopant diffusion barrier superlattice that separates source and drain regions to provide reduced source and drain contact resistance.
Fig. 6 is a schematic cross-sectional view of a semiconductor device including source and drain regions separated by respective dopant diffusion barrier superlattices and providing reduced source and drain contact resistance.
Fig. 7A-7C are a series of schematic cross-sectional views illustrating a method of fabricating a semiconductor device having transitional (inter) source and drain superlattice layers to provide schottky barrier height modulation by controlling interfacial insulator formation.
Fig. 8-9 are schematic cross-sectional views of example semiconductor devices including source and drain regions separated by respective superlattices and having different upper and lower semiconductor source/drain materials and metal contact regions.
Fig. 10 is a perspective view of a FINFET that includes source and drain regions separated by respective superlattices and that provides reduced source and drain contact resistance.
Fig. 11 is a cross-sectional view of the FINFET of fig. 10 taken along line a-a.
Fig. 12 is a cross-sectional view, taken along line a-a, of an alternative implementation of the FINFET of fig. 10 formed using a similar process as shown in fig. 7A-7C.
Fig. 13 and 14 are cross-sectional views, taken along line a-a, of alternative embodiments of the FINFET of fig. 10 including similar source and drain configurations as the devices of fig. 8 and 9, respectively.
Fig. 15 is a series of schematic atomic scale diagrams illustrating a way in which a non-semiconductor insertion layer from the MST film shown in fig. 1-4C may be used to provide a reduced schottky barrier height to a metal-semiconductor contact having a proximate dopant in the embodiments of fig. 5-14.
Fig. 16 is a schematic cross-sectional view of a semiconductor device including a body contact with a dopant diffusion barrier superlattice to provide reduced contact resistance in accordance with an example embodiment.
Fig. 17 is a schematic cross-sectional view of a semiconductor device including a backside body contact with a dopant diffusion barrier superlattice to provide reduced contact resistance in accordance with an example embodiment.
Fig. 18 is a cross-sectional view of an alternative contact structure that may be used to provide reduced contact resistance according to an example embodiment.
Detailed Description
Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments are shown. Embodiments may, however, be embodied in many different forms and should not be construed as limited to the specific examples set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. Like numbers refer to like elements throughout, and prime and multiple prime notation are used to indicate similar elements in different embodiments.
In general, the present disclosure relates to the use of enhanced superlattice materials in the source and drain regions to reduce schottky barrier height and thereby reduce source and drain contact resistance. The enhanced semiconductor superlattice is also referred to in this disclosure and the figures as a "MST" layer or "MST technique".
More particularly, MST technology relates to advanced semiconductor materials such as the superlattice 25 as further described below. The applicant has theorized (without wishing to be bound thereto): some superlattices as described herein reduce the effective mass of carriers and this thereby leads to higher carrier mobility. Various definitions in the literature are used to describe effective masses. As a measure of the improvement in effective mass, applicants used the "conductivity reciprocal effective mass tensor" for electrons and holes, respectively "
Figure BDA0003125782590000061
And
Figure BDA0003125782590000062
the definition is as follows:
Figure BDA0003125782590000063
for electrons and:
Figure BDA0003125782590000064
for holes, where f is the Fermi-Dirac distribution, EFIs the fermi energy, T is the temperature, E (k, n) is the energy of the electrons in the states corresponding to the wave vector k and the nth band, the indices i and j refer to the cartesianThe x, y and z, molar coordinates are integrated within the brillouin zone (B.Z.) and summed within energy bands having energies greater and less than the fermi energies of the electrons and holes, respectively.
Applicants' definition of the conductivity reciprocal effective mass tensor is such that the greater the tensor component of the conductivity of the material, the greater the value of the corresponding component of the conductivity reciprocal effective mass tensor. Again, the applicant has theorized (without wishing to be bound thereto): the superlattices described herein establish the values of the conductivity reciprocal effective mass tensor so as to enhance the conductive properties of the material, such as the preferred direction for charge carrier transport generally. The inverse of the appropriate tensor element is referred to as the conductivity effective mass. In other words, to characterize the semiconductor material structure, the conductivity effective mass of electrons/holes as described above and calculated in the direction of intended carrier transport is used to distinguish improved materials.
Applicants have identified improved materials or structures for use in semiconductor devices. More particularly, applicants have identified materials or structures having band structures for which the appropriate conductivity effective mass for electrons and/or holes is significantly less than the corresponding value for silicon. In addition to the enhanced mobility characteristics of these structures, they may also be formed or used in such a way that: such that they provide piezoelectric, pyroelectric, and/or ferroelectric properties that are advantageous for use in a variety of different types of devices, as will be discussed further below.
Referring now to fig. 1 and 2, the material or structure is in the form of a superlattice 25 whose structure is controlled at the atomic or molecular level and which may be formed using known techniques for atomic or molecular layer deposition. The superlattice 25 includes a plurality of layer groups 45a-45n arranged in stacked relation, as perhaps best understood with specific reference to the schematic cross-sectional view of fig. 1.
Each group of layers 45a-45n of the superlattice 25 illustratively includes a plurality of stacked base semiconductor monolayers 46 defining a respective base semiconductor portion 46a-46n and an energy band-modifying layer 50 thereon. For clarity of illustration, the energy band-modifying layers 50 are indicated by stippling in fig. 1.
The energy band-modifying layer 50 illustratively comprises a non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. By "constrained within the crystal lattice of adjacent base semiconductor portions" it is meant that at least some of the semiconductor atoms from the opposing base semiconductor portions 46a-46n are chemically bound together by the non-semiconductor monolayer 50 therebetween, as shown in fig. 2. In general, this configuration is made possible by: the amount of non-semiconductor material deposited on the semiconductor portions 46a-46n by atomic layer deposition techniques is controlled such that not all (i.e., less than full or 100% coverage) of the available semiconductor binding sites are filled with non-semiconductor atoms (polulanes), as will be discussed further below. Thus, as additional monolayers 46 of semiconductor material are deposited on or over non-semiconductor monolayer 50, the newly deposited semiconductor atoms will fill the remaining vacant binding sites for semiconductor atoms under the non-semiconductor monolayer.
In other embodiments, more than one such non-semiconductor monolayer may be possible. It should be noted that reference herein to a non-semiconductor or semiconductor monolayer means that the material used for the monolayer is non-semiconductor or semiconductor if formed in bulk. That is, a single monolayer of a material, such as silicon, may not necessarily exhibit the same properties as it would if it were formed in bulk or relatively thick layers, as will be understood by those skilled in the art.
The applicant has theorized (without wishing to be bound thereto): the energy band-modifying layers 50 and the adjacent base semiconductor portions 46a-46n cause the superlattice 25 to have a lower conductivity effective mass for the charge carriers in the parallel layer direction than would otherwise be present. Considered another way, such parallel direction is orthogonal to the stacking direction. The band modifying layers 50 may also cause the superlattice 25 to have a common energy band structure that also advantageously acts as an insulator between regions or layers that are vertical above and below the superlattice.
In addition, such a superlattice structure may also advantageously act as a barrier to dopant and/or material diffusion between layers that are vertical above and below the superlattice 25. These properties may thus advantageously enable the superlattice 25 to provide an interface for the high-K dielectric that not only reduces diffusion of the high-K material into the channel region, but may also advantageously reduce unwanted scattering effects and improve device mobility, as will be appreciated by those skilled in the art.
It is also explained theoretically: semiconductor devices including the superlattice 25 may enjoy higher carrier mobility based on a lower conductivity effective mass than would otherwise be present. In some embodiments, and as a result of the band engineering achieved by the present invention, the superlattice 25 may also have a substantially direct energy bandgap that may be particularly advantageous for optoelectronic devices, for example.
The superlattice 25 also illustratively includes a cap layer 52 on an upper layer group 45 n. The cap layer 52 may comprise a plurality of base semiconductor monolayers 46. The cap layer 52 may have between 2 and 100 monolayers of the base semiconductor, and more preferably between 10 and 50 monolayers.
Each base semiconductor portion 46a-46n may comprise a base semiconductor selected from the group consisting of: group IV semiconductors, group III-V semiconductors, and group II-VI semiconductors. Of course, the term group IV semiconductor also includes group IV-IV semiconductors, as will be understood by those skilled in the art. More particularly, the base semiconductor may comprise, for example, at least one of silicon and germanium.
Each energy band-modifying layer 50 may, for example, comprise a non-semiconductor selected from the group consisting of: oxygen, nitrogen, fluorine, carbon and carbon-oxygen. The deposition of the non-semiconductor through the next layer is also desirably thermally stable to facilitate fabrication. In other embodiments, the non-semiconductor may be another inorganic or organic element or compound that is compatible with the given semiconductor processing, as will be understood by those skilled in the art. More particularly, the base semiconductor may comprise, for example, at least one of silicon and germanium.
It is noted that the term monolayer is meant to include a single atomic layer and also a single molecular layer. Note also that the energy band-modifying layer 50 provided by a single monolayer is also meant to include a monolayer in which not all of the possible sites are occupied (i.e., there is less than full or 100% coverage). For example, referring specifically to the atomic diagram of FIG. 2, an 4/1 repeating structure is illustrated for silicon as the base semiconductor material and oxygen as the band-change material. In the illustrated example only half of the possible sites for oxygen are occupied.
In other embodiments and/or using different materials, as will be appreciated by those skilled in the art, this half occupation need not be so. Indeed, it can even be seen in this schematic diagram that the individual atoms of oxygen in a given monolayer are not precisely aligned along a flat plane, as will also be understood by those skilled in the art of atomic deposition. By way of example, a preferred occupation range is from about one-eighth to one-half of all possible oxygen sites, although other numbers may be used in some embodiments.
Silicon and oxygen are currently widely used in conventional semiconductor processing, and thus manufacturers will be readily able to use these materials as described herein. Atomic or monolayer deposition is also now widely used. Accordingly, semiconductor devices incorporating the superlattice 25 in accordance with the invention may be readily adopted and implemented, as will be appreciated by those skilled in the art.
Theoretically, it is stated (applicant does not wish to be bound thereto): for superlattices such as Si/O superlattices, the number of silicon monolayers should desirably be seven or less so that the energy band of the superlattice is relatively uniform or common throughout to achieve the desired advantages. The 4/1 repeat structure shown in fig. 1 and 2 for Si/O has been modeled to indicate enhanced mobility of electrons and holes in the X direction. For example, the conductivity effective mass calculated for electrons (isotropic for bulk silicon) is 0.26 and for the 4/1 SiO superlattice it is 0.12 in the X direction, resulting in a ratio of 0.46. Similarly, the calculation for holes yields a value of 0.36 for bulk silicon and 0.16 for the 4/1 Si/O superlattice, resulting in a ratio of 0.44.
While such a directionally preferential feature may be desirable in some semiconductor devices, other devices may benefit from a more uniform increase in mobility in any direction parallel to the groups of layers. It may also be beneficial to have an increased mobility for both electrons and holes or only one of these types of carriers, as will be understood by those skilled in the art.
The lower conductivity effective mass for the 4/1 Si/O embodiment of the superlattice 25 may be less than two-thirds of the conductivity effective mass that would otherwise occur, and this applies to both electrons and holes. Of course, the superlattice 25 may further comprise at least one type of conductivity dopant therein as will also be appreciated by those skilled in the art.
In fact, referring now additionally to fig. 3, another embodiment of a superlattice 25' in accordance with the invention having different properties is now described. In this embodiment, a repeating pattern of 3/1/5/1 is illustrated. More particularly, the lowermost base semiconductor portion 46a 'has three monolayers and the second lowermost base semiconductor portion 46 b' has five monolayers. This pattern repeats throughout the superlattice 25'. The energy band-modifying layers 50' may each comprise a single monolayer. For such superlattices 25' including Si/O, the enhancement of carrier mobility is independent of orientation in the plane of the layers. Those other elements of fig. 3 not specifically mentioned are similar to those discussed above with reference to fig. 1 and need not be discussed further herein.
In some device embodiments, all of the base semiconductor portions of the superlattice may be a same number of monolayers thick. In other implementations, at least some of the base semiconductor portions may be a different number of monolayers thick. In still other implementations, all of the base semiconductor portions may be a different number of monolayers thick.
In FIGS. 4A-4C, the band structure calculated using Density Functional Theory (DFT) is presented. It is well known in the art that DFT underestimates the absolute value of the bandgap. All bands larger than the band gap can thus be shifted by a suitable "scissors correction". The shape of the known belt is however much more reliable. The vertical energy axis should be explained in this respect.
Fig. 4A shows the band structure calculated from the 4/1 Si/O superlattice 25 (represented by the dotted line) and the gamma point (G) of the bulk silicon (represented by the continuous line) shown in fig. 1. The directions refer to the unit cell of the 4/1 Si/O structure and not to the conventional unit cell of Si, but the (001) direction in the figure does correspond to the (001) direction of the conventional unit cell of Si and thus shows the expected position of the Si conduction band minimum. The (100) and (010) directions in the figure correspond to the (110) and (-110) directions of a conventional Si unit cell. Those skilled in the art will appreciate that the Si ribbons in the figures are folded to indicate that they are in the appropriate reciprocal lattice orientation for the 4/1 Si/O structure.
It can be seen that the conduction band minimum for the 4/1 Si/O structure is located at the gamma point compared to bulk silicon (Si), whereas the valence band minimum occurs at the edge of the brillouin zone in the (001) direction, we refer to as the Z point. It may also be noted that the curvature of the conduction band minimum of the 4/1 Si/O structure is greater compared to the curvature of the conduction band minimum of Si due to band splitting caused by perturbations introduced by the additional oxygen layer.
Fig. 4B shows the band structure calculated from the Z-points of the bulk silicon (continuous lines) and the 4/1 Si/O superlattice 25 (dotted lines). This figure illustrates the increase in curvature of the valence band in the (100) direction.
Fig. 4C shows the band structure calculated from both the 5/1/3/1 Si/O structure (dotted lines) and the gamma and Z points of the bulk silicon (continuous lines) of the superlattice 25' of fig. 3. Due to the symmetry of the 5/1/3/1 Si/O structure, the calculated band structures in the (100) and (010) directions are equivalent. The conductivity effective mass and mobility are therefore expected to be isotropic in the plane parallel to the layers, i.e. perpendicular to the (001) stacking direction. Note that in the 5/1/3/1 Si/O example, both the conduction band minimum and the valence band maximum are at or near the Z point.
Although the increased curvature is indicative of reduced effective mass, appropriate comparison and discrimination can be made by conductivity reciprocal effective mass tensor calculations. This has led applicants to further theorize 5/1/3/1 that the superlattice 25' should be substantially direct bandgap. As will be appreciated by those skilled in the art, a suitable matrix element for optical transition is another indicator of the distinction between direct and indirect bandgap behavior.
Having now described the structure and formation of example MST materials, various embodiments of semiconductor devices and their methods of fabrication will now be described, which advantageously provide metal-silicon contacts with immediately adjacent dopants using the MST materials described above. By way of background, in semiconductor devices, electrons are typically transferred between a semiconductor (e.g., silicon) and a conductive metal "interconnect" that transfers charge between semiconductor devices. The resistance between the semiconductor and the metal increases the required energy and reduces the maximum speed of computation and other functions performed by the circuit using the device. It is therefore advantageous to minimize this resistance.
When electrons are transferred between a metal and a semiconductor, such as silicon, there is a potential barrier that the electrons encounter. Such barriers are commonly referred to as "schottky barriers". Electrons may have sufficient kinetic energy to directly overcome the schottky barrier, or electrons with lower kinetic energy may be transported between the metal and the semiconductor through quantum mechanical tunneling. The thinner the schottky barrier is spatially, the more likely such tunneling is. A common way to achieve a reduced potential barrier is to increase the electric field. Higher levels of ionized impurities ("dopants") generally produce higher electric fields and thus increase the tunneling probability, thereby increasing the electron flux between the metal and the semiconductor, thus reducing the effective resistance. But in addition to increasing the electric field, the high impurity levels may additionally reduce the schottky barrier itself by reducing the effective bandgap of the semiconductor immediately adjacent to the metal-semiconductor interface (and via other chemical effects). This effect is evident from the density functional theory calculations.
An Oxygen Insertion (OI) layer (or other non-semiconductor layer) provided in, for example, an MST film, may result in a lower schottky and/or thinner barrier by trapping dopants. Density functional theory calculations show that the OI layer provides a favorable replacement of silicon atoms by specific dopant atoms within one or both atomic layers of the OI layer. By trapping the dopant in direct close proximity to the metal-semiconductor interface, e.g., separated from the metal-semiconductor interface by one or two atomic layers, the OI layer may thus result in a relatively high concentration of dopant in direct proximity to the metal-semiconductor interface, thereby increasing the electric field and additionally reducing the schottky barrier.
In addition to trapping dopants, the OI layer may immobilize the dopants by trapping point defects that would otherwise aid in dopant diffusion. Thus, while the OI layer immediately adjacent the metal-semiconductor layer may trap the dopants immediately adjacent the interface, the additional OI layer, which is further from the interface but still immediately adjacent the interface, may trap point defects that would otherwise help the dopants diffuse away from the interface. Thus, it may be beneficial to have more than one, e.g., two, three, or four, OI layers immediately adjacent to the interface.
In general, the embodiments described herein use one or more oxygen insertion ("OI" or "MST") layers in close proximity to the metal-semiconductor interface, along with a high (e.g., more than 10 nm) close (e.g., shorter than 1nm) to the metal-silicon interface21/cm3Or 2% of the crystalline sites in the silicon lattice) of ionized impurities such as boron, phosphorus, arsenic, antimony, indium, or gallium. Examples of metals include aluminum, tungsten, nickel, titanium, copper, cobalt, indium, gold, platinum, erbium, ytterbium, and compounds of any of these metals with silicon or germanium.
Because the OI layer may provide an advantageous replacement of the doping atoms of the silicon atoms far from one or two atomic layers, the OI layer is most advantageously spaced from the metal-semiconductor interface by one or two atomic layers, allowing the trapping of high concentrations of dopants up to and directly adjacent to the metal-semiconductor interface. Other separations, such as three or four atomic layers, may provide benefits. Additionally, it may be beneficial to include an additional oxygen insertion layer in addition to this first oxygen insertion layer.
An example of such an approach is shown in the graph 500 of fig. 15, in which: si ═ silicon atom, M ═ metal atom (e.g., titanium), O ═ oxygen atom, and D ═ dopant atom (e.g., boron). The oxygen atoms depicted are part of an oxygen insertion layer, where oxygen bonds to adjacent silicon atoms. Although oxygen atoms are necessarily present in the OI layer, nitrogen atoms not represented in the figure may additionally be present. The presence of nitrogen may be beneficial, for example, for the trapping of dopants or for the thermal stability of the OI layer.
Similarly, the dopants shown replace silicon atoms in the crystalline lattice, rather than occupying "interstitial" positions or clusters of dopants (so they will not contribute to free carriers in the semiconductor). However, although alternative dopants are shown, the high concentration of dopants trapped near the metal-semiconductor interface may reduce the schottky barrier with an alternating atomic configuration. The position of the dopants in the figures is a schematic representation for illustrative purposes. The actual distribution of dopant atoms will be partially random, influenced by the specific atomic configuration of the oxygen atoms and the local incorporation of the atoms. The illustrated configuration represents the distance of an atom from the metal-semiconductor interface, rather than the specific location of the atom within the layer. The illustrated construction is as follows:
(a) the OI layer is in contact with the metal and captures the dopant below the OI layer;
(b) an OI layer separated from the metal by one atomic layer of silicon, capturing dopants above and below the OI layer;
(c) an OI layer separated from the metal by two atomic layers, capturing dopants above and below the OI layer;
(d) an OI layer separated from the metal by three atomic layers, trapping dopants above and below the OI layer, but not reaching the metal interface itself in this example;
(e) the OI layer, separated from the metal by four atomic layers, captures the dopants above and below the OI layer, but in this example does not reach the metal interface itself.
In addition to these configurations, additional configurations with multiple OI layers are also possible, such as one layer separated from the metal-semiconductor interface by two silicon layers, and an additional layer separated by an additional four atomic layers. These multilayers can provide dopant trapping at the metal-semiconductor interface, which contributes to chemical schottky barrier lowering and higher electric fields, and also below the metal-semiconductor interface, which contributes primarily to higher electric fields. The embodiments listed herein are generally defined by the presence of a layer immediately adjacent to the metal-semiconductor interface, along with a high concentration of dopants, but do not exclude additional layers or dopant atoms not immediately adjacent to the OI layer(s). A particular advantage of the additional OI layers is that these additional layers may improve structural stability, such as blocking the loss of oxygen from the layer closest to the metal-semiconductor interface, or trapping point defects that would otherwise result in the loss of dopant atoms from the region immediately adjacent to the metal-semiconductor interface.
Referring now to fig. 5, the superlattice structure described above may be advantageously used in semiconductor devices to provide reduced source/drain contact resistance by applying the principles described above. In typical semiconductor processingIn (e.g., p), a reduction in the metal-to-semiconductor contact area requires a lower contact resistivity (e.g., p)c<1E-8ohm.cm2). The contact resistivity is determined by two parameters, which are:
ND: active dopant concentration at the metal/semiconductor interface; and
ΦFBo: schottky barrier height at the metal/semiconductor interface.
Furthermore, the metal-semiconductor schottky barrier height is "pinned" for different metals. In addition, the interface insulator can "depin" the fermi level depending on thickness, bandgap, and dielectric constant.
In the semiconductor device 100(FET) shown in fig. 5, a dopant diffusion barrier superlattice 125 (such as those described above in fig. 1-4C) is used to advantageously increase the surface dopant concentration to allow higher N during in-situ doped epitaxial processing by preventing diffusion into the channel region 130 of the deviceD. More particularly, the device 100 illustratively includes a semiconductor layer or substrate 101, and spaced apart source and drain regions 102, 103 formed in the semiconductor layer with a channel region 130 extending therebetween. The dopant diffusion barrier superlattice 125 illustratively extends through the source region 102 to divide the source region into a lower source region 104 and an upper source region 105, and also extends through the drain region 103 to divide the drain region into a lower drain region 106 and an upper drain region 107.
The dopant diffusion barrier superlattice 125 may also be conceptually considered as a source dopant barrier superlattice within the source region 102, a drain dopant barrier superlattice within the drain region 103, and a bulk dopant barrier superlattice below the channel 130, although all three are provided in this configuration by a single blanket deposition of MST material as a continuous film across the substrate 101. Semiconductor material above the dopant blocking superlattice 125, in which the upper source/ drain regions 105, 107 and the channel region 130 are defined, may be epitaxially grown on the dopant blocking superlattice 125 in the form of a thick superlattice cap layer or bulk semiconductor layer, as discussed further above. In the illustrated example, the upper source/ drain regions 105, 107 may each be level with the upper surface of this semiconductor layer (i.e., they are implanted into this layer).
As such, the upper source/ drain regions 105, 107 may advantageously have the same conductivity as the lower source/ drain regions 104, 106, yet have a higher dopant concentration. In the illustrated example, the upper source/ drain regions 105, 107 and lower source/ drain regions 104, 106 are N-type for N-channel devices, but these regions may also be P-type for P-channel devices (this also applies to the other configurations described herein). The surface dopant may be introduced by, for example, ion implantation. However, the MST film material through the diffusion barrier superlattice 125 reduces dopant diffusion because it traps point defects/gaps caused by ion implantation that affect (mediate) dopant diffusion.
Semiconductor device 100 also illustratively includes a gate 108 over channel region 130. The gate illustratively includes a gate insulation layer 109 and a gate electrode 110. Sidewall spacers 111 are also provided in the illustrated example.
Referring now to fig. 6, a semiconductor device 200(FET) according to another example embodiment illustratively includes a semiconductor layer or substrate 201, and spaced apart source and drain regions 202, 203 with a channel region 230 extending therebetween. In the illustrated embodiment, the source diffusion barrier superlattice 225s illustratively extends through the source region 202 to divide the source region into the lower source region 204 and the upper source region 205. Similarly, the drain diffusion barrier superlattice 225d extends through the drain region 203 to divide the drain region into a lower drain region 206 and an upper drain region 207. Alternatively, it is contemplated that the upper source and drain regions 205, 207 are each raised above the upper surface of the semiconductor layer 201 and there is no superlattice extending between the source and drain regions 202, 203 (i.e., below the gate 208) as in the example of fig. 5. The gate 208 illustratively includes a gate insulator 209 and a gate electrode 210, and gate sidewall spacers 211 may also be provided.
In this embodiment, the surface dopants in the upper source/ drain regions 205, 207 may be introduced by selectively growing an MST film followed by an in-situ doped epi film formation. Here again, the MST material of the source/drain dopant diffusion barrier superlattice 225s, 225b advantageously helps prevent dopant diffusion into the channel region 230 and thus allows for higher surface dopant concentrations as noted above.
In accordance with another exemplary embodiment now described with reference to fig. 7A-7C, the semiconductor device 100 shown in fig. 5 may be subjected to further processing steps to perform schottky barrier height modulation by controlling the thickness and composition of the interfacial insulator. With conventional metal contacts, an overly thick source/drain insulator results in high contact resistivity due to high tunneling resistance. However, the superlattice 125' advantageously provides the desired non-semiconductor (e.g., oxygen) dose control for fermi level de-pinning and tunneling resistance. After forming the gate 108 'over the channel region 130', the co-implantation of N, C or F may further modulate the insulator composition to a lower dielectric constant (e.g., using C and F for low-k ILD films to modulate SiO)2Composition) as illustrated in fig. 7A. The MST film of the superlattice 125' effectively accumulates these elements into the surface region. It should be noted that in some embodiments N and C may be passed through a gaseous form (e.g., N2Annealing or CO, CH4Annealed) instead of co-implantation into the silicon surface.
Heat treatment and metal deposition may then be performed (fig. 7B-7C). The thermal treatment moves up the non-semiconductor atoms (oxygen in this example) from the non-semiconductor monolayer of the dopant diffusion barrier superlattice 125 ' which react with the metal to form respective source and drain contact insulating interfaces 140 ', 141 ' between the upper source and drain regions and adjacent portions of the metal layers 142 ', 143 ' formed by the metal deposition. In other words, because oxygen atoms are detached from the superlattice 125 ' in the source and drain regions and move upward to form the contact insulating interfaces 140 ', 141 ', there is no longer a defined superlattice layer separating the lower/upper source regions 104 ', 105 ' and lower/upper drain regions 106 ', 107 ' (see fig. 7B).
According to an exemplary embodiment, Co/Co may be performed at a temperature in the range of about +200 to 400C0.75Ti0.25(2nm) metal deposition for about 10min to form source and drain contact insulating interfaces 140 ', 141' and metal layers 142 ', 143'. Furthermore, in some embodiments, additional metal deposition (e.g., Co) may be performed to form upper source/drain metal contact layers 144 ', 145 ' in the semiconductor device 100 '.
Another example embodiment similar to semiconductor device 200 is now described with reference to fig. 8. In this illustrated example, the source and drain dopant diffusion barrier superlattices 225s ', 225 d' advantageously provide schottky barrier height modulation via heteroepitaxial film integration. More particularly, the lower source and drain regions 204 ', 206' comprise a different material than the upper source and drain regions 205 ', 207'. In this example, the lower source and drain regions 204 ', 206' are silicon and the upper source and drain regions 205 ', 207' are SiGeC, although different materials may be used in different embodiments.
C (1-2%) incorporation into Si or SiGe on Si can cause a positive conduction band offset because MST materials effectively integrate heteroepitaxial semiconductor materials. More particularly, this is a SiGeC/MST/n + Si structure that is effective for reducing the Schottky barrier height.
Referring additionally to fig. 9, another similar semiconductor device 200 "advantageously provides schottky barrier height modulation via heteroepitaxial film integration. In the illustrated example, the semiconductor layer/substrate 201 "is silicon germanium and the lower source/drain regions 204", 206 "are P + SiGe. However, the upper source/drain regions 205 ", 207" are also silicon, and respective platinum contact layers 242 ", 243" are formed on each upper source/drain region. The upper source/drain regions 205 ", 207" may be formed in a relatively thin epitaxial silicon layer (e.g., 2-5 nm). Here again, the MST material effectively integrates a heteroepitaxial semiconductor material, and the strained Si on SiGe (or Ge) may advantageously cause negative valence band deviation. As a result, the illustrated s-Si/MST/p + SiGe structure also effectively reduces the Schottky barrier height.
Turning now additionally to fig. 10, some of the planar FET structures described above may also be advantageously implemented in vertical semiconductor devicesAnd (5) manufacturing. The example FINFET300 illustratively includes a semiconductor layer or substrate 301 (e.g., silicon), an insulating layer 350 (e.g., SiO) on the substrate2) And one or more semiconductor fins 351 extending vertically from the substrate up through the insulating layer.
Spaced apart source and drain regions 302, 303 and a channel region 330 extending therebetween are formed in each semiconductor fin 351. The source dopant diffusion barrier superlattice 325s extends through the source region 302 to divide the source region into a lower source region 304 and an upper source region 305, and the drain dopant diffusion barrier superlattice 325d extends through the drain region 303 to divide the drain region into a lower drain region 306 and an upper drain region 307. Similar to the embodiment of fig. 6, the upper source/ drain regions 305, 307 have the same conductivity and higher dopant concentration (N + +) than the lower source/drain regions 304, 306(N +). Furthermore, upper source/ drain regions 305, 307 extend above the upper surface of the semiconductor fin 351. That is, the superlattices 325s, 325d may be formed on top of the semiconductor fin 351 and the upper source/ drain regions 305, 307 may be epitaxially grown on the respective superlattices. In this regard, the upper source/ drain regions 305, 307 may be implanted with dopants, or they may be in-situ doped epitaxial layers as described above.
FINFET300 also illustratively includes a gate 308 overlying the channel region 330 of fin 351. The gate 308 illustratively includes a gate insulator 309 and a gate electrode 310 on the gate insulator.
According to another example embodiment, the FINFET300 ' may be fabricated using a similar process as described above with reference to fig. 7A-7C, i.e., including heat treatment and metal deposition to define the upper source/drain regions 305 ', 307 ' and metal layers 342 ', 343 ', respectively (e.g., CoTi)x) Source/drain insulating layers 340 ', 341' between. Upper metal layers 344 ', 345' (e.g., Co) may also be formed on the lower metal layers 342 ', 343' in some implementations. Here again, the heat treatment causes the source/drain dopants to block upward movement of the non-semiconductor atoms in the superlattice layer, resulting in upper source/drain regions 305 ', 307' and lower source ≧ H in the final FINFET300No superlattice is left between the drain regions 304 ', 306'. Here again, this approach advantageously provides schottky barrier height modulation by controlling the thickness and composition of the interface insulators 340 ', 341'.
Referring additionally to fig. 13, a FINFET300 "similar to the embodiment of fig. 8 above is provided in which the source and drain dopant blocking superlattices 325 s", 325d "advantageously provide schottky barrier height modulation via heteroepitaxial film integration. More particularly, the lower source and drain regions 304 ", 306" comprise a different material than the upper source and drain regions 305 ", 307". In this example, the lower source and drain regions 304 ", 306" are silicon and the upper source and drain regions 305 ", 307" are SiGeC, although different materials may be used in different embodiments. Also, in the illustrated example, the lower metal layers 342 ", 342" are titanium, and the upper metal layers 344 ", 345" are cobalt.
In yet another example shown in fig. 14, like the embodiment of fig. 9, the FINFET300 "' may also provide schottky barrier height modulation via heteroepitaxial film integration. In the illustrated example, the semiconductor fin 351' is silicon germanium and the lower source/drain regions 304 ", 306" are P + SiGe. However, the upper source/drain regions 305 ", 307" are silicon, and a respective platinum contact layer 342 ", 343" is formed on each upper source/drain region. Here again, the upper source/drain regions 305 ", 307" may be formed from a relatively thin epitaxial silicon layer (e.g., 2-5 nm).
In the examples described above, the dopant blocking superlattice is shown in both the source and drain regions of the illustrated device. It should be noted, however, that in some implementations not both the source and drain regions need to have a dopant blocking superlattice. That is, the dopant blocking superlattice may be in only one of the source or drain regions in some implementations.
Further, turning now to fig. 16, in some implementations a dopant blocking superlattice may be introduced into the body contact in addition to or instead of in the source/drain regions to provide reduced body contact resistance. In the illustrated example, a semiconductor device 400 (here a planar FET) includes a semiconductor layer or substrate 401, spaced apart source and drain regions 402, 403 (which in this example have respective lightly doped source/drain extensions 404, 405) in the semiconductor layer 401 and a channel region 430 extending therebetween, and a gate 408 having sidewall spacers 411 over the channel region. As similarly described above, gate 408 illustratively includes gate insulator 409 and gate electrode 410. The semiconductor device 400 further illustratively includes a body contact 420 in the semiconductor layer 401, and the body contact 420 includes a body contact dopant diffusion barrier superlattice 425 extending through the body contact to divide the body contact into a first body contact region 421 and a second body contact region 422. As similarly described above, the second body contact region 422 has the same conductivity and a higher dopant concentration as the first body contact region 421. Here again, the body contact dopant diffusion barrier superlattice 425 may be similar to those superlattice structures described above, and the materials used for the first and second body contact regions 421, 422 and the dopant concentrations within the first and second body contact regions 421, 422 may also be similar to those described above to provide a desired reduction in contact resistance.
In another example device 400 'shown in fig. 17, a similar configuration is provided having a backside body contact 420' instead of the top side or front side body contact 420 shown in fig. 16. The remaining components are similar to those discussed with reference to fig. 16 and therefore need not be discussed further herein. It should be noted that the first and second regions 421 ', 422 ' are vertically flipped in the backside embodiment relative to the first and second regions 421, 422 in the device 400, as they are on opposite sides of the device 400 '.
Turning now to fig. 18, another example contact structure 500 is now described that may also be used in some embodiments of source/drain, body, or other contacts to provide a reduced schottky barrier height and thus reduced contact resistance. A contact 500 is formed in the semiconductor layer 501. The contacts illustratively include one or more oxygen monolayers 550 constrained within the crystal lattice of adjacent semiconductor portions 546a, 546b of the semiconductor layer 501. The oxygen monolayer(s) 550 are spaced apart from the surface of the semiconductor layer 501 by one to four monolayers (the spacing of the four monolayers is shown in the semiconductor portion 546b in the illustrated example). Further, a metal layer 531 (which may include the same metals discussed above) is formed on the surface of the semiconductor layer 501 over the oxygen monolayer(s) 550. The contact 500 may be formed on a semiconductor layer or substrate 521.
By way of example, the dopant concentration within the portion 546b (i.e., between the oxygen monolayer(s) 550 and the metal layer 531) may be 1 × 1021Atom/cm3Or greater (although lower concentrations may also be used in different embodiments). Alternatively, it is contemplated that in an example configuration the dopant atoms may advantageously occupy a dopant concentration equivalent to about 2% of the crystallization sites in the silicon lattice. This is based on an estimate of the maximum distance range over which the oxygen monolayer can directly capture a dopant (e.g., boron) close enough to the metal to directly reduce the schottky barrier of the contact, rather than reducing diffusion, while otherwise maintaining the conventional doped metal-semiconductor interface in the case of a body-line environment for the dopant atoms, and the minimum concentration of dopant where benefit would be realized.
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and embodiments are intended to be included within the scope of the appended claims.

Claims (22)

  1. A FINFET, comprising:
    a semiconductor fin;
    spaced apart source and drain regions in the semiconductor fin with a channel region extending therebetween;
    at least one dopant diffusion barrier superlattice dividing at least one of the source and drain regions into a lower region and an upper region, wherein the upper region has the same conductivity as the lower region and a higher dopant concentration than the lower region;
    the dopant diffusion barrier superlattice comprises a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions; and
    a gate over the channel region.
  2. 2. The FINFET of claim 1, wherein at least one dopant diffusion barrier superlattice comprises a respective dopant diffusion barrier superlattice for each of the source and drain regions.
  3. 3. The FINFET of claim 1, wherein the upper region is raised above an upper surface of the semiconductor layer.
  4. 4. The FINFET of claim 1, wherein the lower region comprises a different material than the upper region.
  5. 5. The FINFET of claim 4, wherein the lower region comprises silicon; and wherein the upper region comprises silicon germanium.
  6. 6. The FINFET of claim 4, wherein the lower region comprises silicon germanium; and wherein the upper region comprises silicon.
  7. 7. The FINFET of claim 1, further comprising a metal contact on the upper region.
  8. 8. The FINFET of claim 7, wherein the metal contact comprises at least one of titanium, cobalt, nickel and platinum.
  9. 9. The FINFET of claim 1, further comprising a semiconductor substrate and insulators on the semiconductor substrate and on opposite sides of the semiconductor fin, the semiconductor fin extending vertically upward from the semiconductor substrate.
  10. 10. The FINFET of claim 1, wherein the base semiconductor monolayer comprises silicon.
  11. 11. The FINFET of claim 1, wherein at least one non-semiconductor monolayer comprises oxygen.
  12. 12. A method for fabricating a FINFET, comprising:
    forming spaced apart source and drain regions in the semiconductor fin with an extended channel region therebetween, at least one of the source and drain regions being divided into a lower region and an upper region by a dopant diffusion barrier superlattice, wherein the upper region has the same conductivity as the lower region and a higher dopant concentration than the lower region;
    the dopant diffusion barrier superlattice comprises a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions; and
    a gate is formed over the channel region.
  13. 13. The method of claim 12, wherein each of the source and drain regions is divided into a lower region and an upper region by a respective dopant diffusion barrier superlattice.
  14. 14. The method of claim 12, wherein the upper region is raised above an upper surface of the semiconductor layer.
  15. 15. The method of claim 12, wherein the lower region comprises a different material than the upper region.
  16. 16. The method of claim 15, wherein the lower region comprises silicon; and wherein the upper region comprises silicon germanium.
  17. 17. The method of claim 15, wherein the lower region comprises silicon germanium; and wherein the upper region comprises silicon.
  18. 18. The method of claim 12, further comprising forming a metal contact on the upper region.
  19. 19. The method of claim 18, wherein the metal contact comprises at least one of titanium, cobalt, nickel, and platinum.
  20. 20. The method of claim 12, further comprising forming a semiconductor fin extending vertically upward from a semiconductor substrate, and forming insulators on the semiconductor substrate and on opposite sides of the semiconductor fin.
  21. 21. The method of claim 12, wherein the base semiconductor monolayer comprises silicon.
  22. 22. The method of claim 12, wherein the at least one non-semiconductor monolayer comprises oxygen.
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