# Patent

## Title
Process for manufacturing stress-providing structure and semiconductor device with such stress-providing structure

## Abstract

A process for manufacturing a stress-providing structure is applied to the fabrication of a semiconductor device. Firstly, a substrate with a channel structure is provided. A silicon nitride layer is formed over the substrate by chemical vapor deposition in a halogen-containing environment. An etching process is performed to partially remove the silicon nitride layer to expose a portion of a surface of the substrate beside the channel structure. The exposed surface of the substrate is etched to form a recess in the substrate. Then, the substrate is thermally treated at a temperature between 750° C. and 820° C. After the substrate is thermally treated, a stress-providing material is filled in the recess to form a stress-providing structure within the recess. The semiconductor device includes a substrate, a recess and a stress-providing structure. The recess has a round inner surface. The stress-providing structure has a round outer surface.

## Background
FIELD OF THE INVENTION
The present invention relates to a process for manufacturing a stress-providing structure, and more particularly to a process for manufacturing a stress-providing structure in fabrication of a semiconductor device. The present invention also relates to a semiconductor device with such a stress-providing structure.
BACKGROUND OF THE INVENTION
Generally, in the fabrication of a complementary metal-oxide-semiconductor (CMOS) transistor, a selective area epitaxial (SAE) process is widely used to form source/drain regions. By using the selective area epitaxial process to provide stress, the channel mobility of the transistor is improved and the performance of the transistor is enhanced.
However, the efficacy of using the conventional selective area epitaxial process to increase the performance of the transistor is still unsatisfied.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a process for manufacturing a stress-providing structure and a semiconductor device with such a stress-providing structure.
In accordance with an aspect, the present invention provides a process for manufacturing a stress-providing structure in fabrication of a semiconductor device. Firstly, a substrate with a channel structure is provided. Then, a silicon nitride layer is formed over the substrate by chemical vapor deposition in a halogen-containing environment. Then, an etching process is performed to partially remove the silicon nitride layer to expose a portion of a surface of the substrate beside the channel structure. Then, the exposed surface of the substrate is etched to form a recess in the substrate. After the recess is formed in the substrate, the substrate is thermally treated at a temperature between 750° C. and 820° C. After the substrate is thermally treated, a stress-providing material is filled in the recess to form a stress-providing structure within the recess.
In an embodiment, the process further includes a step of forming a gate structure over the channel structure.
In an embodiment, the halogen-containing environment is a chlorine-containing environment, and the chlorine-containing environment includes a chlorine-containing species.
In an embodiment, the chlorine-containing species is hexachlorodisilane (Si2Cl6) or dichlorosilane (SiH2Cl2).
In an embodiment, after the etching process is performed, the recess has a sigma-shaped inner surface.
In an embodiment, the step of thermally treating the substrate is performed by baking the substrate under a hydrogen gas atmosphere.
In an embodiment, after the step of thermally treating the substrate is performed, the recess has a round inner surface.
In an embodiment, after the substrate is thermally treated, the recess has a depth from 550 to 700 angstroms, and preferably from 600 to 650 angstroms.
In an embodiment, the substrate is a silicon substrate.
In an embodiment, the channel structure is a p-type channel structure, and the stress-providing material is silicon germanium (SiGe) or germanium.
In an embodiment, the channel structure is an n-type channel structure, and the stress-providing material is silicon carbide (SiC).
In accordance with another aspect, the present invention provides a semiconductor device. The semiconductor device includes a substrate, a recess and a stress-providing structure. A channel structure is formed in the substrate. The recess is formed in the substrate and arranged beside the channel structure. The recess has a round inner surface. The stress-providing structure is formed within the recess. Corresponding to the round inner surface, the stress-providing structure has a round outer surface.
In an embodiment, the semiconductor device further includes a gate structure, which is formed over the channel structure.
In an embodiment, the recess has a depth from 550 to 700 angstroms, and preferably from 600 to 650 angstroms.
In an embodiment, the substrate is a silicon substrate.
In an embodiment, the channel structure is a p-type channel structure, and the stress-providing structure is made of silicon germanium (SiGe) or germanium.
In an embodiment, the channel structure is an n-type channel structure, and the stress-providing structure is made of silicon carbide (SiC).



BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
FIGS. 1A ̃1E schematically illustrate a process for fabricating a stress-providing structure according to an embodiment of the present invention.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
FIGS. 1A ̃1E schematically illustrate a process for fabricating a stress-providing structure according to an embodiment of the present invention. The process for fabricating the stress-providing structure may be applied to the fabrication of a semiconductor device such as a complementary metal-oxide-semiconductor (CMOS) transistor.
Firstly, as shown in FIG. 1A, a substrate 1 is provided. An example of the substrate 1 includes but is not limited to a silicon substrate. In addition, a channel structure 10 is formed in the substrate 1, and a gate structure 11 is formed over the channel structure 10. In this embodiment, the gate structure 11 comprises a gate insulator layer 110 and a gate conductor layer 111.
Then, as shown in FIG. 1B, a silicon nitride layer 12 is formed over the substrate 20 by chemical vapor deposition in a halogen-containing environment. In an embodiment, the chemical vapor deposition is performed in a chlorine-containing environment. The chlorine-containing environment includes a chlorine-containing species such as hexachlorodisilane (Si2Cl6, also referred as HCD) or dichlorosilane (SiH2Cl2, also referred as DCS). In such way, the silicon nitride layer 12 is chlorine-rich.
Then, as shown in FIG. 1C, a series of photolithography and etching processes are performed to partially remove the silicon nitride layer 12 so as to partially expose the surface of the substrate 1 beside the channel structure 10. Then, an etching process is performed to remove the exposed surface of the substrate 1 to produce a recess 13. The depth of the recess 13 is from 550 to 700 angstroms, and preferably from 600 to 650 angstroms. As shown in FIG. 1C, the recess 13 has a sigma-shaped inner surface 130. The profile of the sigma-shaped inner surface 130 is similar to the sidewall of the conventional embedded source/drain structure. By utilizing the lattice property of the silicon substrate and performing dry/wet etching processes, the sigma-shaped inner surface 130 will be produced.
Then, the substrate 1 with the recess 13 is subject to a thermal treatment process. For example, the thermal treatment process is performed by baking the substrate 1 under a hydrogen gas atmosphere at a temperature between 750° C. and 820° C. for a time period from 10 to 10000 seconds. Prior to the thermal treatment process, the halogen-rich atoms (e.g. chlorine-rich atoms) of the silicon nitride layer 12 are released to the inner surface of the recess 13, and the halogen-rich atoms and the silicon atoms interact with each other at the inner surface of the recess 13. Moreover, during the thermal treatment process is performed, the elevated temperature between 750° C. and 820° C. causes migration and recombination of the silicon atoms at the inner wall of the recess 13. Consequently, a recess 20 with a round inner surface 20 is produced (see FIG. 1D). The depth of the recess 20 is from 550 to 700 angstroms, and preferably from 600 to 650 angstroms.
Then, a stress-providing material is filled into the recess 20 to form a stress-providing structure 21 within the recess 20. Corresponding to the round inner surface of the recess 20, the stress-providing structure 21 has a round outer surface. In a case that the channel structure 10 is a p-type channel structure, the stress-providing material is silicon germanium (SiGe) or germanium (Ge). Whereas, in a case that the channel structure 10 is an n-type channel structure, the stress-providing material is silicon carbide (SiC).
From the above description, the process for manufacturing a stress-providing structure according to the present invention may be applied to the fabrication of a semiconductor device. The inner surface of the recess 20 has enhanced cleanliness and is chlorine-free. Moreover, the round inner surface of the recess is helpful for providing increased channel stress. Experiments demonstrate that if the stress-providing material is unchanged, the round inner surface of the recess may provide better channel mobility than the conventional sigma-shaped inner surface.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

## Claims

1. A process for manufacturing a stress-providing structure in fabrication of a semiconductor device, the process comprising steps of:
providing a substrate with a channel structure;
forming a silicon nitride layer over the substrate by chemical vapor deposition in a halogen-containing environment;
performing an etching process to partially remove the silicon nitride layer to expose a portion of a surface of the substrate beside the channel structure;
etching the exposed surface of the substrate to form a recess in the substrate;
thermally treating the substrate at a temperature between 750° C. and 820° C. after the recess is formed in the substrate; and
filling a stress-providing material in the recess to form a stress-providing structure within the recess after the substrate is thermally treated.

2. The process according to claim 1, further comprising a step of forming a gate structure over the channel structure.

3. The process according to claim 1, wherein the halogen-containing environment is a chlorine-containing environment, and the chlorine-containing environment comprises a chlorine-containing species.

4. The process according to claim 3, wherein the chlorine-containing species is hexachlorodisilane (Si2Cl6) or dichlorosilane (SiH2Cl2).

5. The process according to claim 1, wherein after the etching process is performed, the recess has a sigma-shaped inner surface.

6. The process according to claim 1, wherein the step of thermally treating the substrate is performed by baking the substrate under a hydrogen gas atmosphere.

7. The process according to claim 1, wherein after the step of thermally treating the substrate is performed, the recess has a round inner surface.

8. The process according to claim 1, wherein after the substrate is thermally treated, the recess has a depth from 600 to 650 angstroms.

9. The process according to claim 1, wherein the substrate is a silicon substrate.

10. The process according to claim 1, wherein the channel structure is a p-type channel structure, and the stress-providing material is silicon germanium (SiGe) or germanium.

11. The process according to claim 1, wherein the channel structure is an n-type channel structure, and the stress-providing material is silicon carbide (SiC).