Method of forming spacers for a gate of a transistor

Patent metadata

Field	Value
Publication number	US-2016197160-A1
Application number	US-201614997347-A
Country	US
Kind code	A1
Filing date	Jan 15, 2016
Priority date	Jul 18, 2014
Publication date	Jul 7, 2016
Grant date	—

Abstract

The invention describes a method for forming spacers ( 152 a, 152 b ) of a field effect transistor gate, comprising a step of forming a protection layer ( 152 ) covering the gate of said transistor, at least a step of modifying the protection layer, executed after the step of forming the protection layer, by contacting the protection layer ( 152 ) with plasma comprising ions heavier than hydrogen and CxHy where x is the proportion of carbon and y is the proportion of hydrogen to form a modified protection layer ( 158 ) and a carbon film ( 271 ). The protection layer being nitride (N)-based and/or silicon (Si)-based and/or carbon (C)-based and shows a dielectric constant equal or less than 8.

First claim

1 . A method for forming spacers of a field effect transistor gate, with the gate comprising a top and flanks and being located above an active layer made of a semiconductor material, characterized in that it comprises:
at least a step of forming a protection layer covering the gate, the protection layer being a layer based on nitride (N) and/or based on silicon (Si) and/or based on carbon (C) with a dielectric constant equal to or less than 8; at least a step of modifying the protection layer by contacting the protection layer with a plasma wherein CxHy is introduced, where x is the proportion of carbon (C) and y is the proportion of hydrogen ions (H), and comprising ions heavier than hydrogen; with the conditions of plasma, more particularly the concentration of CxHy, the energy of ions of the plasma and the main implantation direction being so chosen that:
plasma creates an anisotropic bombardment with hydrogen-based ions (H, H + , H 2 + , H 3 + etc.), resulting from the CxHy, with the bombardment being anisotropic in the main implantation direction which is parallel to the flanks of the gate so as to form a modified protection layer by modifying portions of the protection layer located on the top of the gate and both sides of the gate and so as to keep non-modified portions of the protection layer covering the flanks of the gate.
carbon-containing plasma chemical species from the CxHy, form a carbon-containing film in particular on surfaces parallel to the main direction of implantation;
the plasma creates a bombardment with ions heavier than hydrogen which prevents said carbon-containing plasma chemical species from the CxHy from forming a carbon-containing film, more particularly on the surfaces of the protection layer which are perpendicular to the main direction.
at least a step of removing the modified protection layer using a selective etching of the modified protection layer relative to non-modified portions of the protection layer.

2 . The method according to claim 1 , wherein a dielectric constant of the protection layer is less than 4 and preferably less than 3.1 and preferably less than or equal to 2.

3 . The method according to claim 1 wherein the protection layer is a nitride (N)-based layer and preferably a silicon nitride (SiN) layer.

4 . The method according to claim 1 wherein the protection layer is silicon (Si)-based layer.

5 . The method according to claim 1 wherein the protection layer is a carbon (C)-based layer.

6 . The method according to claim 1 wherein the protection layer is made of a material selected among: the SiCO, the SiC, the SiCN, the SiOCN, the SiCBN, the SiOCH, the CBN, the BN, Si—CBO and the SiO2.

7 . The method according to claim 1 wherein the protection layer is a porous layer.

8 . The method according to claim 1 wherein the protection layer is a non-porous layer.

9 . The method according to claim 1 wherein the step of forming the protection layer comprises a step of depositing the protection layer and wherein a step of reducing the dielectric constant of the protection layer is performed during the step of depositing the protection layer.

10 . The method according to claim 9 wherein the step of reducing the dielectric constant of the protection layer comprises introducing a porosity in the protection layer.

11 . The method according to claim 9 wherein the step of forming the protection layer comprises introducing precursors in the protection layer which is being deposited.

12 . The method according to claim 1 wherein the step of forming the protection layer comprises a step of depositing the protection layer, wherein a step of reducing the dielectric constant of the protection layer is performed during the step of depositing the protection layer, wherein the step of forming the protection layer comprises introducing precursors in the protection layer which is being deposited, wherein the protection layer is a silicon nitride-based layer and wherein the precursors are so selected as to form bindings that are less polar than the silicon nitride.

13 . The method according to claim 1 wherein the precursors are selected among: the Si—F, the SiOF, the Si—O, the C—C, the C—H, and the Si—CH3.

14 . The method according to claim 1 wherein during said step of modifying the protection layer, the concentration of CxHy ranges from 2% to 50% and preferably from 8% to 40%.

15 . The method according to claim 1 wherein during said step of modifying the protection layer, the concentration of ions heavier than the hydrogen in the plasma ranges from 50% to 98%.

16 . The method according to claim 1 comprising, prior to the step of modifying, a step of depositing a layer comprising carbon, with such layer comprising carbon being different from said transistor, and wherein said etching is selective of the modified protection layer relative to carbon and relative to non-modified portions of the protection layer.

17 . The method according to claim 16 , wherein the layer comprising carbon is a layer of photo-sensitive or thermo-sensitive resin.

18 . The method according to claim 16 , wherein the layer comprising carbon is a hard mask.

19 . The method according to claim 18 , wherein the layer comprising carbon is a hard mask formed with carbon.

20 . The method according to claim 17 , wherein the layer comprising carbon is so configured as to cover a structure different from said transistor.

21 . The method according to claim 20 , wherein said transistor is a NMOS transistor and said structure is a PMOS transistor, or wherein said transistor is a PMOS transistor and said structure is a NMOS transistor.

22 . The method according to claim 17 , wherein, during the step of modifying executed by contacting the protection layer with plasma comprising CxHy, the carbon-containing film covers the walls of the layer comprising carbon, with the thickness e2 of the carbon-containing film covering the walls of the layer comprising carbon being higher than the thickness e1 of the carbon-containing film at the level of the flanks of the gate.

23 . The method according to claim 1 , wherein CxHy is CH4.

24 . The method according to claim 1 , wherein the ions heavier than hydrogen are selected among argon (Ar), helium (HE), nitrogen (N2), xenon (Xe) and oxygen (O2).

25 . The method according to claim 1 , wherein the step of modifying is so executed that the plasma generates an anisotropic bombardment with ions heavier than hydrogen according to the main implantation direction parallel to the flanks of the gate, so as to prevent said carbon-containing plasma chemical species from CxHy from forming a carbon-containing film on the surfaces perpendicular to the flanks of the gate.

26 . The method according to claim 1 , wherein the step of modifying is so executed that the ions heavier than hydrogen of plasma dissociate the CxHy molecule so as to enable the hydrogen ions (H) from CxHy to form hydrogen-based ions and to implant into said portion of the protection layer.

27 . The method according to claim 1 , wherein the step of modifying is executed so as to modify only an upper portion of the thicknesses of the protection layer at the level of the flanks of the gate by keeping a non-modified thicknesses of the protection layer at the level of the flanks of the gate.

28 . The method according to claim 1 , wherein the

Assignees

• Commissariat Energie Atomique

Inventors

• Posseme Nicolas

Classifications

• H10P14/6902

  composed of carbon, e.g. alpha-C, diamond or hydrogen doped carbon · CPC title

• H10P14/6336

  in the presence of a plasma [PECVD] · CPC title

• H10P50/287

  by chemical means · CPC title

• H10P50/283

  by chemical means · CPC title

• H10P50/244

  comprising alternated and repeated etching and passivation steps · CPC title