FINFET WITH BACKGATE, WITHOUT PUNCHTHROUGH, AND WITH REDUCED FIN HEIGHT VARIATION

• US 20150228795A1
• Filed: 02/12/2014
• Published: 08/13/2015
• Est. Priority Date: 02/12/2014
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: YANG, Bin, LI, Xia, YEAP, Choh Fei, CHIDAMBARAM, Chidi
• Granted Patent: US 9,236,483 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H01L 29/0607 for preventing surface leakage or controlling electric field concentration
• CPC Class Codes: H01L 29/267 in different semiconductor regions , e.g. heterojunctions H01L29/263 takes precedence
• CPC Class Codes: H01L 29/66795 with a horizontal current flow in a vertical sidewall of a semiconductor body, e.g. FinFET, MuGFET
• CPC Class Codes: H01L 29/7842 means for exerting mechanical stress on the crystal lattice of the channel region, e.g. using a flexible substrate variation of the composition of the channel H01L29/1054
• CPC Class Codes: H01L 29/7848 the means being located in the source/drain region, e.g. SiGe source and drain
• CPC Class Codes: H01L 29/7851 with the body tied to the substrate
• CPC Class Codes: H01L 29/7855 with at least two independent gates
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors
• CPC Class Codes: H03K 2017/6878 using multi-gate field-effect transistors
• CPC Class Codes: H03K 2217/0018 Special modifications or use of the back gate voltage of a FET
• CPC Class Codes: H03K 2217/0054 Gating switches, e.g. pass gates

Abstract

A FinFET having a backgate and a barrier layer beneath the fin channel of the FinFET, where the barrier layer has a bandgap greater than that of the backgate. The barrier layer serves as an etch stop layer under the fin channel, resulting in reduced fin channel height variation. The backgate provides improved current control. There is less punchthrough due to the higher bandgap barrier layer. The FinFET may also include deeply embedded stressors adjacent to the source/drain diffusions through the high bandgap barrier layer.

Claims

1. A FinFET comprising:

a substrate;

a backgate comprising a first layer formed in the substrate, the first layer comprising a first semiconductor;

a second layer formed over the first layer, the second layer comprising a second semiconductor;

a fin channel formed over the second layer, the fin channel comprising a third semiconductor;

a backgate contact through the second layer and in electrical contact with the first layer;

a deep trench isolation region formed down into the substrate; and

wherein the first semiconductor has a first bandgap and the third semiconductor has a third bandgap, wherein the second semiconductor has a second bandgap greater than the first bandgap and the second bandgap.

2. The FinFET of claim 1, wherein the first, second, and third semiconductors are each selected form a group consisting of III-V semiconductor compounds, II-VI semiconductor compounds, group IV semiconductor elements or compounds, graphine, and carbon nanotubes.

3. The FinFET of claim 2, wherein the first and third semiconductors each comprise GaAs, and the second semiconductor comprises AlAs.

4. The FinFET of claim 1, wherein the first bandgap equals the third bandgap.

5. The FinFET of claim 1, further comprising:

a dielectric layer formed over the fin channel; and

a gate formed over the dielectric layer.

6. The FinFET of claim 5, further comprising:

a first rail coupled to the gate to provide a first voltage to turn ON the FinFET; and

a second rail coupled to the backgate contact to provide a second voltage to turn ON the FinFET.

7. The FinFET of claim 6, wherein the first and second rail are at a same voltage.

8. The FinFET of claim 1, further comprising:

a first stressor and a second stressor epitaxially grown in the second layer to provide a stress to the fin channel.

9. The FinFET of claim 8, further comprising:

a first source/drain diffusion adjacent to the fin channel and adjacent to the first stressor; and

a second source/drain diffusion adjacent to the fin channel and adjacent to the second stressor.

10. The FinFET of claim 9, further comprising:

a first rail coupled to the gate to provide a first voltage to turn ON the FinFET; and

a second rail coupled to the backgate contact to provide a second voltage to turn ON the FinFET.

11. The FinFET of claim 1, wherein if the FinFET is n-type the first layer is heavily p-type doped with a doping concentration in a range of 1·

10¹⁹ cm<sup>−

3</sup> to 1·

10²² cm<sup>−

3</sup>, and if the FinFET is p-type the first layer is heavily n-type doped with a doping concentration in the range of 1·

10¹⁹ cm<sup>−

3</sup> to 1·

10²² cm<sup>−

3</sup>.

12. The FinFET of claim 11, wherein if the FinFET is n-type the second layer is lightly p-type doped with a doping concentration in the range of 1·

10¹³ cm<sup>−

3</sup> to 1·

10¹⁷ cm<sup>−

3</sup>; and

if the FinFET is p-type the second layer is lightly n-type doped with a doping concentration in the range of 1·

10¹³ cm<sup>−

3</sup> to 1·

10¹⁷ cm<sup>−

3</sup>.

13. The FinFET of claim 11, wherein the second layer is un-doped.

14. The FinFET of claim 1, wherein the FinFET is used in a device selected from the group consisting of a cellular phone, a tablet, a computer system, and a base station.

15. A method to fabricate a FinFET, the method comprising:

forming a first semiconductor layer in a substrate;

forming a second semiconductor layer over the first semiconductor layer;

forming a third semiconductor layer over the second semiconductor layer;

etching the third semiconductor layer to form a FinFET fin channel;

etching through the second semiconductor layer to the first semiconductor layer and forming an electrical backgate contact to the first semiconductor layer; and

forming a deep trench isolation region to the substrate;

wherein the first, second, and third semiconductor layers each have, respectively, a first bandgap, a second bandgap, and a third bandgap, wherein the second bandgap is greater than the first bandgap and the second bandgap.

16. The method of claim 15, further comprising:

forming a dielectric layer over the FinFET fin channel; and

forming a gate over the dielectric layer.

17. The method of claim 15, wherein the first bandgap equals the third bandgap.

18. The method of claim 15, further comprising:

forming a first trench in the second layer;

epitaxially growing a first stressor in the first trench to provide stress to the FinFET fin channel;

forming a second trench in the second layer; and

epitaxially growing a second stressor in the second trench to provide stress to the FinFET fin channel.

19. The method of claim 18, wherein the first and second stressors are selected from a group consisting of a silicon germanium alloy (SiGe), a silicon carbide alloy (SiC), III-V semiconductor compounds, II-V semiconductor compounds, and group IV semiconductor elements or compounds.

20. The method of claim 18, further comprising:

epitaxially growing the first stressor adjacent to a first source/drain diffusion; and

epitaxially growing the second stressor adjacent to a second source/drain diffusion.

21. The method of claim 20, further comprising:

forming a dielectric layer over the FinFET fin channel; and

forming a gate over the dielectric layer.

22. The method of claim 18, further comprising:

forming the first trench in the first layer; and

forming the second trench in the first layer.

23. The method of claim 15, wherein the first, second, and third semiconductors layers are each selected form a group consisting of III-V semiconductor compounds, II-VI semiconductor compounds, group IV semiconductor elements or compounds, graphine, and carbon nanotubes.

24. The method of claim 23, wherein the first and third semiconductor layers each comprise GaAs, and the second semiconductor layer comprises AlAs.

25. The method of claim 15, wherein

if the FinFET is n-type, p-type doping the first layer with a doping concentration in a range of 1·

10¹⁹ cm<sup>−

3</sup> to 1·

10²² cm<sup>−

3</sup>; and

if the FinFET is p-type, n-type doping the first layer with a doping concentration in the range of 1·

10¹⁹ cm<sup>−

3</sup> to 1·

10²² cm<sup>−

3</sup>.

26. The method of claim 25, wherein

if the FinFET is n-type, p-type doping the second layer with a doping concentration in the range of 1·

10¹³ cm<sup>−

3</sup> to 1·

10¹⁷ cm<sup>−

3</sup>; and

if the FinFET is p-type, n-type doping the second layer with a doping concentration in the range of 1·

10¹³ cm<sup>−

3</sup> to 1·

10¹⁷ cm<sup>−

3</sup>.

27. The method of claim 25, wherein the second layer is un-doped.

28. A method to turn ON a FinFET, the FinFET comprising a gate, a backgate, and a substrate, the method comprising:

coupling the gate of the FinFET to a first rail; and

coupling the backgate of the FinFET to a second rail, wherein the backgate comprises a first layer formed in the substrate and comprises a first semiconductor;

wherein the gate is formed over a fin channel formed over a second layer, the second layer formed over the first layer and comprising a second semiconductor, the fin channel comprising a third semiconductor;

wherein the first semiconductor has a first bandgap and the third semiconductor has a third bandgap, wherein the second semiconductor has a second bandgap greater than the first bandgap and the second bandgap.

29. The method of claim 28, wherein the first and second rails are at a same voltage.

30. The method of claim 28, wherein the first bandgap and the third bandgap are equal to each other.