# Patent

## Title
Method for forming a semiconductor device having a metal gate recess

## Abstract

Provided are approaches of forming a semiconductor device (e.g., transistor such as a FinFET or planar device) having a gate metal recess. In one approach, a liner layer and a metal layer (e.g., W) are applied in a trench (e.g., via CVD and/or ALD). Then, a single chamber (e.g., an extreme fill chamber) will be utilized to separately etch back the liner layer and the metal layer. In general, the liner layer may be etched back further than the metal layer to provide for larger contact and lower resistance. After etching is complete, a bottom-up fill/growth of metal (e.g., W) will be performed (e.g., via CVD in a W chamber or the like) to increase the presence of gate metal in the trench.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of, and claims the benefit of, co-pending and co-owned U.S. patent application Ser. No. 13/688,259, filed Nov. 29, 2012, the entire contents of which are herein incorporated by reference.


BACKGROUND
1. Technical Field
This invention relates generally to the field of semiconductors and, more particularly, to approaches for using a low resistivity metal (e.g., tungsten (W)) in a recessed gate structure for semiconductor devices such as planar or FinFET devices.
2. Related Art
Along with other metals, Tungsten (W) is actively being explored as a possibly gate metal. In general, replacement metal gates (RMGs) are attractive due to superior T(inv)-V(t) performance. One approach is to attempt to provide a recessed gate structure. However, forming a W recess is currently an expensive process, as the process typically involves chemical mechanical polishing (CMP) and a reaction ion etch (RIE) chamber for W etching. For example, a typical approach may include a series of expensive and/or time-consuming deposition processes, CMP processes, and RIE processes. Moreover, existing techniques typically recess liner layers and gate metals evenly, which results in reduced metal contact and increased resistance. Still yet, the current approaches result gate lengths and contact sizes being of such a nature so as to increase resistance. Specifically, existing approaches rely on additional layers such as TiN and nucleation layers, which increase resistance.
SUMMARY
Embodiments of the present invention generally relate to approaches of forming a semiconductor device having a metal gate recess. In a typical embodiment, a liner layer and a metal layer (e.g., W) will be applied in a trench (e.g., via CVD). Then, a single chamber (e.g., an extreme fill chamber) will be utilized to separately etch back the liner layer and the metal layer. In general, the liner layer may be etched back further than the metal layer to provide for larger contact and lower resistance. After etching is complete, a bottom-up fill/growth of metal (e.g., W) will be performed (e.g., via CVD in a W chamber or the like) to increase the presence of gate metal in the trench.
A first aspect of the present invention provides a method of forming a semiconductor device having a metal gate recess, comprising: forming a liner layer over a work function metal layer within a trench of the semiconductor device, the work function metal layer being formed over a high k-layer that is formed over a substrate; forming a metal layer over the liner layer; performing a first etch to etch at least a portion of the metal layer in the trench; performing a second etch to etch at least a portion of the liner layer; and performing a bottom-up fill of metal within the trench after the second etch to form the metal gate recess.
A second aspect of the present invention provides a method of forming a semiconductor device having a metal gate recess, comprising: depositing a liner layer over a work function metal layer within a trench of the semiconductor device, the work function metal layer being formed over a high k-layer that is formed over a substrate; depositing a tungsten (W) layer over the liner layer; performing a first etch to etch at least a portion of the metal layer in the trench; performing a second etch to etch at least a portion of the liner layer; and performing a bottom-up growth of W within the trench after the second etch to form the metal gate recess.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
FIG. 1 shows a liner layer and metal layer being applied within a set of trenches of a semiconductor device according to an embodiment of the present invention.
FIG. 2 shows an etching back of the metal layer shown in FIG. 1 according to an embodiment of the present invention.
FIG. 3 shows an etching back of the liner layer of FIG. 1 according to an embodiment of the present invention.
FIG. 4 shows bottom-up fill/growth of W to yield a semiconductor device having a W interconnect/gate recess according to an embodiment of the present invention.
FIG. 5 shows a graph of etch rates versus temperature for various materials according to an embodiment of the present invention



The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting in scope. In the drawings, like numbering represents like elements.
DETAILED DESCRIPTION
Illustrative embodiments will now be described more fully herein with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms “a”, “an”, etc., do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “set” is intended to mean a quantity of at least one. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Reference throughout this specification to “one embodiment,” “an embodiment,” “embodiments,” “exemplary embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “in embodiments” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms “overlying” or “atop”, “positioned on” or “positioned atop”, “underlying”, “beneath” or “below” mean that a first element, such as a first structure (e.g., a first layer) is present on a second element, such as a second structure (e.g. a second layer) wherein intervening elements, such as an interface structure (e.g. interface layer) may be present between the first element and the second element.
As indicated above, embodiments of the present invention generally relate to approaches of forming a semiconductor device (e.g., transistor such as a FinFET or planar device) having metal gate recess. In a typical embodiment, a liner layer and a metal layer (e.g., W) will be applied in a trench (e.g., via CVD and/or ALD). Then, a single chamber (e.g., an extreme fill chamber) will be utilized to separately etch back the liner layer and the metal layer. In general, the liner layer may be etched back further than the metal layer to provide for contact grains and lower resistance. After etching is complete, a bottom-up fill/growth of metal (e.g., W) will be performed (e.g., via CVD in a W chamber or the like) to increase the presence of gate metal in the trench. It is understood that although an illustrative embodiment described herein pertains to a metal gate recess, this need not be the case. Rather, the teachings described herein could be applied to other types of elements such as contacts, interconnects, etc. Moreover, although W is described herein as a typical metal of which the metal gate/interconnect recess is formed, this need not be the case. Rather, other metals such as Co, Cu, etc. may be utilized as well.
Under previous approaches, W gate metals were polished using processes such as CMP and RIE. Not only were such processes expensive and time consuming, but the previous approaches resulted in uniform polishing of liner layer and metal layers within the trenches. Such a result increased device resistivity and reduced overall performance.
Referring now to FIG. 1, an initial formation stage of a semiconductor device 10 is shown. As depicted, device 10 generally comprises a set of trenches 12A-B formed over substrate 14. Each trench 12A-B generally comprises a high-k layer 16 formed (e.g., deposited via CVD) over substrate 14, a work function metal layer 18 formed (e.g., deposited via CVD) over high-k layer 16, a liner layer 20 formed (e.g., TiN, TaN, WN, WCN, etc. deposited via ALD) over work function layer 18, and a metal layer 22 formed (e.g., W deposited via CVD) over liner layer 20. It is understood that although not specifically described, device 10 may comprise additional materials/layers such as a silicon germanium (SiGe), an oxide layer, a high density plasma (HDP) layer, etc.
Regardless, the process is continued in FIG. 2, which shows an etching back of the metal layer 22 within trenches 12A-B. In general, the etching will be performed in an etch chamber such as an extreme fill chamber (EFx®). “EFx” is a trademark of Lam Research in the United States and/or other countries). This approximately results in a ratio of 100:1 of liner layer 20 to metal layer 22. In FIG. 3, the same etch chamber (e.g., an EFx® chamber) may be used to then provide a second etch step, namely, an etching back of liner layer 20 to be approximately uniform with metal layer 22. As then shown in FIG. 4, a bottom-up fill (e.g., W growth) process is then performed (after the second etch process) to yield a metal gate recess. In a typical embodiment, the growth step is performed using W in a CVD chamber or the like. This will result in a semiconductor device having a W gate recess 24A-B in trenches 12A-B as shown in FIG. 4.
It is understood that although not specifically described, semiconductor device 10 may have additional layers and/or components such as a Silicon Germanium (SiGe) layer, a buried oxide layer, high density plasma layer, etc. In any event, among other things, the approach shown in FIGS. 1-4 allow for W fill and the recess process to occur via one tool. Moreover, W has more space for larger grains and lower resistance than previous approaches. In addition, the approach of the present invention is less costly and improves the WIP turn due to the elimination of the need to use W CMP and an RIE chamber.
Referring now to FIG. 5, a graph 100 of etch rates versus temperature is shown. Specifically, graph 100 shows etch rates at various temperatures for TiN 102A, Ti 102B, and W 102C. As shown, W etches at the highest rate in an EFx® chamber at a temperature of approximately 50° (C.), which makes it highly useable in the processes described herein. Specifically, this allows W to be selectively etched (as compared to Ti and TiN (e.g., the liner layer)) at temperatures of about 50° (C.) and lower.
In various embodiments, design tools can be provided and configured to create the data sets used to pattern the semiconductor layers as described herein. For example data sets can be created to generate photomasks used during lithography operations to pattern the layers for structures as described herein. Such design tools can include a collection of one or more modules and can also include hardware, software, or a combination thereof. Thus, for example, a tool can be a collection of one or more software modules, hardware modules, software/hardware modules, or any combination or permutation thereof. As another example, a tool can be a computing device or other appliance on which software runs or in which hardware is implemented. As used herein, a module might be implemented utilizing any form of hardware, software, or a combination thereof. For example, one or more processors, controllers, application-specific integrated circuits (ASIC), programmable logic arrays (PLA)s, logical components, software routines, or other mechanisms might be implemented to make up a module. In implementation, the various modules described herein might be implemented as discrete modules or the functions and features described can be shared in part or in total among one or more modules. In other words, as would be apparent to one of ordinary skill in the art after reading this description, the various features and functionality described herein may be implemented in any given application and can be implemented in one or more separate or shared modules in various combinations and permutations. Even though various features or elements of functionality may be individually described or claimed as separate modules, one of ordinary skill in the art will understand that these features and functionality can be shared among one or more common software and hardware elements, and such description shall not require or imply that separate hardware or software components are used to implement such features or functionality.
While the invention has been particularly shown and described in conjunction with exemplary embodiments, it will be appreciated that variations and modifications will occur to those skilled in the art. For example, although the illustrative embodiments are described herein as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events unless specifically stated. Some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the invention.

## Claims

1. A method of forming a semiconductor device having a metal gate recess, comprising:
forming a liner layer over a work function metal layer within a trench of the semiconductor device, the work function metal layer being formed over a high k-layer that is formed over a substrate;
forming a metal layer over the liner layer;
performing a first etch to etch at least a portion of the metal layer in the trench;
performing a second etch to etch at least a portion of the liner layer; and
performing a bottom-up fill of metal within the trench after the second etch to form the metal gate recess;
wherein the first etch and the second etch are performed in a single etch chamber.

2. The method of claim 1, the liner layer comprising titanium nitride (TiN).

3. The method of claim 1, the metal layer comprising tungsten (W).

4. The method of claim 1, the bottom-up fill of metal comprising a bottom-up growth of W.

5. The method of claim 1, the bottom-up fill of metal being performed using a chemical vapor deposition (CVD) W chamber.

6. The method of claim 1, the liner layer being formed over a work function metal layer, and the work function metal layer being formed over a high-k layer.

7. The method of claim 1, further comprising a semiconductor device formed by the method of claim 1.

8. A method of forming a semiconductor device having a metal gate recess, comprising:
depositing a liner layer over a work function metal layer within a trench of the semiconductor device, the work function metal layer being formed over a high k-layer that is formed over a substrate;
depositing a tungsten (W) layer over the liner layer;
performing a first etch to etch at least a portion of the metal layer in the trench;
performing a second etch to etch at least a portion of the liner layer; and
performing a bottom-up growth of W within the trench after the second etch to form the metal gate recess;
wherein the first etch and the second etch are performed in a single etch chamber.

9. The method of claim 8, the liner layer comprising titanium nitride (TiN).

10. The method of claim 8, the metal layer comprising tungsten (W).

11. The method of claim 8, the bottom-up growth of W being performed using a chemical vapor deposition (CVD) W chamber.

12. The method of claim 8, the work function metal layer being deposited over a high-k layer.

13. The method of claim 8, further comprising a semiconductor device formed by the method of claim 1.