N-TYPE OF TRANSITION METAL DICHALCOGENIDE CHANNELS VIA SURFACE CHARGE TRANSFER FROM A DOPANT LAYER

Abstract

A structure includes a dopant layer at or close to a channel to n-dope TMDs, wherein the dopant layer includes at least one of: at least one of halides (MX.sub.2; M=(Ti, Zr, or Hf), X=at least one of {Cl, Br, or I}); at least one of hydroxides (M(OH).sub.2; M=(Ru, Os, or Ni)); Ca.sub.4As.sub.4; or Zn.sub.2H.sub.8N.sub.4Te.sub.2. A method for fabricating a channel includes depositing a delta-doped layer having a low dielectric constant and a band gap>0.1 eV onto a high-k layer, and n-doping a TMD layer, wherein an absolute value of ionization energy of the delta-doped layer is less than an absolute value of the electron affinity of the TMD layer, the delta-doped layer includes one of a halide, hydroxide, chalcogenide, oxide, arsenide, or multi-anion compound, and a fractional ratio of the delta-doped layer to the high-k layer is 0 to 0.3.

Claims

1. A structure comprising a dopant layer at or within 3 nm from a channel comprising at least one transition metal dichalcogenide to n-dope the at least one transition metal dichalcogenide, wherein the dopant layer comprises at least one of: (i) at least one of halides represented by MX.sub.2, wherein M is Ti, Zr, or Hf, and X is at least one of Cl, Br, or I; (ii) at least one of hydroxides represented by (M(OH).sub.2, wherein M is Ru, Os, or Ni; (iii) Ca.sub.4As.sub.4; or (iv) Zn.sub.2H.sub.8N.sub.4Te.sub.2.

2. The structure according to claim 1, wherein the dopant layer is at the channel to n-dope the at least one transition metal dichalcogenide.

3. The structure according to claim 1, wherein the dopant layer comprises at least one of halides represented by MX.sub.2, wherein M is Ti, Zr, or Hf, and X is at least one of Cl, Br, or I.

4. The structure according to claim 1, wherein the dopant layer comprises at least one of hydroxides represented by M(OH).sub.2, wherein M is Ru, Os, or Ni.

5. The structure according to claim 1, wherein the dopant layer comprises Ca.sub.4As.sub.4.

6. The structure according to claim 1, wherein the dopant layer comprises Zn.sub.2H.sub.8N.sub.4Te.sub.2.

7. The structure according to claim 2, wherein the dopant layer comprises at least one of halides represented by MX.sub.2, wherein M is Ti, Zr, or Hf, and X is at least one of Cl, Br, or I.

8. The structure according to claim 2, wherein the dopant layer comprises at least one of hydroxides represented by M(OH).sub.2, wherein M is Ru, Os, or Ni.

9. The structure according to claim 2, wherein the dopant layer comprises Ca.sub.4As.sub.4.

10. The structure according to claim 2, wherein the dopant layer comprises Zn.sub.2H.sub.8N.sub.4Te.sub.2.

11. A method for fabricating a channel, comprising: depositing a delta-doped layer onto a high-k layer, and n-doping a transition metal dichalcogenide layer, wherein the delta-doped layer has a dielectric constant below the dielectric constant of silicon nitride, wherein a band gap of the delta-doped layer is >0.1 eV, wherein an absolute value of ionization energy of the delta-doped layer is less than an absolute value of the electron affinity of the transition metal dichalcogenide layer, wherein the delta-doped layer includes one of a halide, hydroxide, chalcogenide, oxide, arsenide, or multi-anion compound, and wherein a fractional ratio of the delta-doped layer to the high-k layer is between 0 and 0.3.

12. The method according to claim 11, wherein the delta-doped layer has a dielectric constant below the dielectric constant of silicon dioxide.

13. The method according to claim 11, wherein the delta-doped layer has a dielectric constant below 3.5.

14. The method according to claim 11, wherein the delta-doped layer has a dielectric constant below 3.0.

15. The method according to claim 11, wherein the delta-doped layer has a dielectric constant below 2.5.

16. The method according to claim 11, wherein the high-k layer has a dielectric constant greater than 15.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0050] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0051] Example embodiments of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:

[0052] FIG. 1 is a graph showing the metronomic progress in CMOS transistor density and switching energy over time,

[0053] FIG. 2 shows a representative transistor structure,

[0054] FIG. 3 is a graph showing the mobility (u) of electrons as a function of channel thickness (t.sub.CH), and illustrates that for Si on insulators (SOI), the mobility degrades when t.sub.CH is below 4 nm, while transition metal dichalcogenides (MoS.sub.2, WSe.sub.2, etc.) show robust mobility for thinner channels,

[0055] FIG. 4 is a schematic energy level diagram of surface charge transfer doping (SCTD) between organic molecules and MoS.sub.2, and illustrates depletion and a p-doping process via SCTD of organic molecules with higher electron affinity (EA) than the ionization energy (IE) of TMDs,

[0056] FIG. 5 is a diagram showing energy relative to vacuum for various compounds,

[0057] FIG. 6 is a schematic diagram for n-doping TMDs via a neighboring dopant layer,

[0058] FIG. 7 are graphs showing the electronic structure of (left) MoS.sub.2 monolayer and (right) monolayer Ni(OH).sub.2,

[0059] FIG. 8 is a graph showing the electronic structure of monolayer MoS.sub.2 interfaced with monolayer Ni(OH).sub.2, wherein the Fermi level (green) is set to zero,

[0060] FIG. 9 are graphs showing the electronic structure of (left) MoS.sub.2 monolayer and (right) monolayer ZrI.sub.2,

[0061] FIG. 10 is a graph showing the electronic structure of monolayer MoS.sub.2 interfaced with monolayer ZrI.sub.2, wherein the Fermi level (green) is set to zero,

[0062] FIG. 11 is a graph showing reaction energy as a function of mixing ratio between MoS.sub.2 and Ni(OH).sub.2,

[0063] FIG. 12 is a graph showing reaction energy as a function of mixing ratio between MoS.sub.2 and ZrI.sub.2,

[0064] FIG. 13 is a schematic diagram of the top view of the different regions in a typical FET (e.g., a slice of a Gate All Around (GAA) FET), and

[0065] FIG. 14 is a schematic diagram of the side view of the different regions in a typical FET.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0066] The embodiments of the disclosure described herein are example embodiments, and thus, the disclosure is not limited thereto, and may be realized in various other forms. Each of the embodiments provided in the following description is not excluded from being associated with one or more features of another example or another embodiment also provided herein or not provided herein but consistent with the disclosure. For example, even if matters described in a specific example or embodiment are not described in a different example or embodiment thereto, the matters may be understood as being related to or combined with the different example or embodiment, unless otherwise mentioned in descriptions thereof. In addition, it should be understood that all descriptions of principles, aspects, examples, and embodiments of the disclosure are intended to encompass structural and functional equivalents thereof. In addition, these equivalents should be understood as including not only currently well-known equivalents but also equivalents to be developed in the future.

[0067] As used herein, expressions such as at least one of, when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, the expression, at least one of a, b and c, should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b and c.

[0068] The present disclosure provides a structure including a dopant layer near (at or close to) the channel which can n-dope a TMD channel. In this regard, the term close to means a distance within 3 nm. The distance is preferably within 2 nm, and more preferably within 1 nm.

[0069] 20 candidates were identified for dopant layers that can n-dope TMDs with the correct ionization energy and thermodynamic stability with respect to TMDs. The chemistries include: [0070] halides (MX.sub.2; M=(Ti, Zr, Hf), X=combination of {Cl, Br, I}); [0071] hydroxides (M(OH).sub.2; M=(Ru, Os, Ni)); [0072] Ca.sub.4As.sub.4; [0073] Zn.sub.2H.sub.8N.sub.4Te.sub.2.

[0074] Such a dopant layer can effectively dope the gate-region, the extension region and the contact region. In the gate-region, the original high-k dielectric properties are expected to be present when the fractional ratio of dopant layer to the high-k layer is 0<x<0.3. The low-k behavior typically exhibited by these dopant candidates make higher doping concentration (0<x<1) possible in the extension and contact regions.

[0075] The C2DB database was screened for materials with band gap>0.5 eV (semiconductors with minimal leakage current), absolute value of computed ionization energy of dopant layer<absolute value of experimentally reported electron affinity (EA) of MoS.sub.2 (see Table 1 below for the experimentally reported EA of MoS.sub.2 and other suitable TMDs for the present disclosure).

TABLE-US-00001 TABLE 1 Monolayer Electron Affinity (eV) Reported MoS.sub.2 3.9* MoSe.sub.2 3.5* WS.sub.2 3.8* WSe.sub.2 3.6* *K. Keyshar et al., ACS Nano, 11, 8, 8223 (2017) + Y. Yang et al., Nano Lett. 20, 12, 8846 (2020)

[0076] The results are shown in FIG. 5. Removing false positives (shown in yellow boxes in FIG. 5), 20 candidates were found: [0077] Halides: TiI.sub.2, TiBrI, TiBr.sub.2, ZrI.sub.2, ZrBrI, ZrBr.sub.2, ZrClI, ZrClBr, HfI.sub.2, Hf.sub.2Br.sub.3I, HfBrI, HfBr.sub.2, HfClI, HfClBr, HfCl.sub.2 [0078] 3 hydroxides with 3 cations (Ru, Os, Ni). [0079] Ca.sub.4As.sub.4 and Zn.sub.2H.sub.8N.sub.4Te.sub.2

[0080] FIG. 6 is a schematic diagram for n-doping TMDs via a neighboring dopant layer, by which embodiments of the present disclosure can be obtained.

[0081] In one embodiment of the present disclosure, FIG. 7 shows the electronic structure of (left) MoS.sub.2 monolayer and (right) monolayer Ni(OH).sub.2, and in view of the scheme shown in FIG. 6, the electronic structure of monolayer MoS.sub.2 is interfaced with monolayer Ni(OH).sub.2 as shown in FIG. 8, with the Fermi level (green) being set to zero. The conduction band minima (CBM) of MoS.sub.2 crosses the Fermi level leading to a net n-doping in the TMD layer via surface charge transfer from the Ni(OH).sub.2 layer.

[0082] The band alignment between MoS.sub.2 and Ni(OH).sub.2 is such that a surface charge transfer induced n-doping can occur in MoS.sub.2.

[0083] In another embodiment of the present disclosure, FIG. 9 shows the electronic structure of (left) MoS.sub.2 monolayer and (right) monolayer ZrI.sub.2, and in view of the scheme shown in FIG. 6, the electronic structure of monolayer MoS.sub.2 is interfaced with monolayer ZrI.sub.2 as shown in FIG. 10, with the Fermi level (green) being set to zero. The conduction band minima (CBM) of MoS.sub.2 crosses the Fermi level leading to a net n-doping in the TMD layer via surface charge transfer from the ZrI.sub.2 layer.

[0084] The band alignment between MoS.sub.2 and ZrI.sub.2 is such that a surface charge transfer induced n-doping can occur in MoS.sub.2.

[0085] Reaction energy as a function of mixing ratio between MoS.sub.2 and Ni(OH).sub.2 is shown in FIG. 11, and reaction energy as a function of mixing ratio between MoS.sub.2 and ZrI.sub.2 is shown in FIG. 12. With respect to the thermodynamic stability of the MoS.sub.2 surface with the dopant layer, while there is a nominal energy gain of 0.2 eV/f.Math.u. for Ni(OH).sub.2 and 0.4 eV/f.Math.u. for ZrI.sub.2 the surfaces are essentially non-reactive from thermodynamics as the energy gain is so small that it is unlikely to overcome the kinetic barrier of bond breakage.

[0086] Thus, an embodiment of the present disclosure can be a structure including a dopant layer as shown in FIGS. 13 and 14.

[0087] In particular, FIG. 13 shows a schematic diagram of the top view of the different regions in a typical FET (e.g., a slice of a Gate All Around (GAA) FET). A dopant layer (in green) surrounds the channel layer (in red). The dopant layer need not be directly interfacing the channel layer (i.e., it need not be at the channel layer), but can be a few layers away (e.g., three layers away). Fractional dopant concentration relative to the surrounding layer (x) of 1 is shown in the schematic diagram. If one whole layer is not fully doped, then 0<x<1.

[0088] FIG. 14 shows a schematic diagram of the side-view of the different regions in a typical FET. The dopant layer (in green) surrounds the channel layer (in red). The dopant layer need not be directly interfacing the channel layer (as in L1) and can be a few layers away (as in L2).

[0089] An embodiment of the present disclosure includes a method for fabricating a channel, comprising: [0090] depositing a delta-doped layer onto a high-k layer, and [0091] n-doping a transition metal dichalcogenide layer, [0092] wherein the delta-doped layer has a low dielectric constant, [0093] wherein a band gap of the delta-doped layer is >0.1 eV, [0094] wherein an absolute value of ionization energy of the delta-doped layer is less than an absolute value of the electron affinity of the transition metal dichalcogenide layer, [0095] wherein the delta-doped layer includes one of a halide, hydroxide, chalcogenide, oxide, arsenide, or multi-anion compound, and [0096] wherein a fractional ratio of the delta-doped layer to the high-k layer is between 0 and 0.3.

[0097] In this regard, the delta-doped layer has a low dielectric constant (i.e., below the dielectric constant of silicon nitride). The dielectric constant of the delta-doped layer is preferably below the dielectric constant of silicon dioxide, more preferably below 3.5, still more preferably below 3, and particularly preferably below 2.5. The delta-doped layer can comprise, e.g., amorphous boron nitride, SiO.sub.xF.sub.y, or amorphous SiCOH.

[0098] The delta-doped layer is deposited on the high-k layer, e.g., by chemical vapor deposition.

[0099] The high-k layer can be a layer with a dielectric constant which is higher than that of silicon dioxide, preferably higher than that of silicon nitride. In particular, the high-k layer can be a layer with a dielectric constant which is greater than 3.9, preferably greater than 7, more preferably greater than 8, still more preferably greater than 15. The high-k layer can comprise, e.g., HfO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, or Zr.sub.xHf.sub.1-xO.sub.2.

[0100] By carrying out such a method, a structure of the present disclosure can be obtained.

[0101] The foregoing is illustrative of exemplary embodiments and is not to be construed as limiting the disclosure. Although a few exemplary embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the above embodiments without materially departing from the disclosure.