# Patent

## Title
Semiconductor devices and fabrication methods thereof

## Abstract

Semiconductor devices and methods of fabricating semiconductor devices are disclosed. A disclosed semiconductor device includes a silicon substrate, a source region and a drain region. A gate electrode is formed on the silicon substrate. Also, a metal silicide layer is formed on each of the gate electrode, the source region, and the drain region. The metal silicide layer has a thickness uniformity of about 1 ̃20%. A disclosed fabrication method includes forming a metal layer on a silicon substrate having a gate electrode, a source region, and a drain region; performing a plasma treatment on the metal layer; forming a protective layer on the metal layer; and heat treating the silicon substrate on which the protective layer is formed to thereby form a metal silicide layer. A gas that includes nitrogen is used as a plasma gas during the plasma treatment.

## Background
RELATED APPLICATIONS
This application is a divisional of application Ser. No. 10/852,823, filed on May 25, 2004 now U.S. Pat. No. 7,307,017, incorporated herein by reference in its entirety.


FIELD OF THE DISCLOSURE
The present disclosure relates generally to semiconductor devices, and, more particularly, to semiconductor devices that include nickel silicide on select areas, and to methods of fabricating such semiconductor devices.
BACKGROUND
The performance of a transistor forming a semiconductor device is dependant on its speed, driving current, and leakage current. In an effort to improve the performance of the transistor, (that is, to increase its speed and to reduce its driving and leakage currents), much effort has been made to reduce the resistance of the source/drain regions and the resistance of the gate electrode. For example, a common method used in recent times to reduce these resistances is to form a metal silicide layer on an interfacial surface of the source/drain region and/or on an upper interfacial surface of the gate electrode.
Among the different types of metal suicides, nickel silicide is often used because of its particular advantages with respect to leakage current and level of resistance.
Conventional techniques using a nickel salicidation process are described in U.S. Pat. Nos. 6,383,880 and 6,586,333.
In a conventional method of forming a gate electrode using nickel silicide, nickel (Ni) is first deposited on a silicon substrate having a predetermined gate electrode and source/drain region. As a result, a nickel layer is formed on the interfacial surface of the source/drain region and on an upper interfacial surface of the gate electrode.
Next, a protective metal layer (e.g., a titanium layer or a titanium nitride layer) is formed on the nickel layer. These elements are then heat treated to induce a reaction between the nickel and the silicon, and to thereby form a nickel silicide layer.
However the above described conventional method has a serious flaw. In particular, as a result of the large reaction between the nickel and the silicon, the nickel silicide layer grows abnormally on part of the interfacial surface of the gate electrode and/or on part of the source/drain regions. That is, heat treating is performed at a high temperature of 300-600° C. At this high temperature, the nickel and silicon react too quickly on part of the interfacial surface and/or on part of the source/drain regions. This excessively quick reaction results in abnormal growth of the nickel silicide layer.
As a result of this abnormal growth, the nickel silicide layer has an uneven thickness. This uneven thickness ultimately causes an increase in the leakage current such that the characteristics and driving of the semiconductor device become unstable.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of an example semiconductor device constructed in accordance with the teachings of the present invention.
FIGS. 2a-2d are cross-sectional views sequentially illustrating an example method of fabricating a semiconductor device in accordance with the teachings of the present invention.



DETAILED DESCRIPTION
In the drawings, thicknesses of the various layers and regions have been enlarged for better illustration of their shapes and interrelations. Thus, the drawings are not to be taken as dimensionally accurate. Further, like reference numerals will be used for identical elements in all of the following description and drawings. Finally, when it is stated that an element is “above”, “on”, etc. another element, the two referenced elements may be directly adjacent to one another (i.e., without an element interposed therebetween), or the two referenced elements may have one or more element(s) interposed therebetween. However, if it is stated that an element is present “directly above”, “directly on”, etc. another element, there is no element interposed between these two elements.
FIG. 1 is a cross-sectional view of an example semiconductor device. The illustrated device includes a silicon substrate 10. A device isolation region 12 is formed in the silicon substrate 10. The device isolation region 12 defines an active region. A gate oxidation layer 14 is formed on a portion of the active region. A gate electrode layer 16 (for example, polycrystalline silicon) is formed on the gate oxidation layer 14, thereby completing a gate 17.
A spacer 18 made of an insulation material is formed along the side walls of the gate electrode layer 16 and the gate oxidation layer 14. Source and drain regions 19 are formed on opposite sides of the gate electrode layer 16 and the spacer 18. The source and drain regions 19 are doped at a high concentration with n-type or p-type impurities.
One or more silicide layers 30 are formed on the gate electrode layer 16, and on the source and drain regions 19. In the illustrated example, the silicide layers 30 include nitrogen to decrease the rate at which they grow. Therefore, the silicide layers 30 are prevented from undergoing abnormal growth. In particular, the nitrogen in the silicide layers 30 acts such that a thickness of the silicide layers 30 is within a range of about 100 ̃400 Å, and the thickness uniformity of the silicide layers 30 is about 1 ̃20%.
Further, the nitrogen prevents the silicide layers 30 from excessively permeating the elements of the silicon substrate 10. In an example, a lower surface of the silicide layers 30 contacting the silicon substrate 10 permeates the silicon substrate 10 to a depth of less than about 400 Å. The silicide layers 30 may be made of nickel (Ni). The thickness of the nickel silicide layers 30 may be about 100 ̃400 Å.
When the silicide layers 30 as described above are contacted to wiring made of metal or polysilicon, the contact resistance of the interfacial surfaces is reduced.
A method of fabricating the semiconductor device described above will now be described. In particular, FIGS. 2a-2d are cross-sectional views illustrating sequential processes of an example fabrication method.
In the illustrated example, a nickel layer is used as an example of a metal layer.
Referring first to FIG. 2a, a device isolation region 12 is formed in a silicon substrate 10 to define an active region. Next, an oxidation layer and a polysilicon layer are sequentially formed on the silicon substrate 10. The polysilicon layer and the oxidation layer then undergo photolithography by using a mask to sequentially pattern the polysilicon layer and the oxidation layer. As a result, a gate 17 comprising a gate electrode layer 16 and a gate oxidation layer 14 is formed on an exposed surface of the active region.
Next, silicon nitride (SiNx) is deposited on the silicon substrate 10. The silicon nitride covers the gate 17 to thereby form a nitride layer. An etch back process is then performed on the nitride layer such that spacers 18 are formed on the side walls of the gate 17.
Subsequently, an oxidation layer is formed over the entire surface of the silicon substrate 10. The oxidation layer is then patterned to form a cap oxidation layer (not shown) to protect the gate 17. While using the cap oxidation layer as a mask, conductive impurity ions are doped into the active region to thereby form a source region 19 and a drain region 19. The injected ions may be n-type or p-type impurities such as phosphorus (P) or boron (B).
Although in the above, only the source region 19 and the drain region 19 were formed, an LDD region (not shown) may also be formed prior to the formation of the spacer 18.
Next, with reference to FIG. 2b, nickel (Ni), for example, is deposited over the entire surface of the silicon substrate 10 to thereby form a nickel layer 20 for silicide use. The nickel layer 20 is typically formed using PVD (physical vapor deposition) or CVD (chemical vapor deposition).
Referring to FIG. 2c, a plasma treatment is then performed on the nickel layer 20 using a gas that contains nitrogen. In an example, N2 gas or NH3 gas is used as the gas that contains nitrogen. Further, in the illustrated example, the plasma treatment is performed in-situ in the same chamber used to form the nickel layer 20.
Nitrogen is injected into the nickel layer 20 through the plasma treatment. The nitrogen reduces the speed at which a metal silicide layer (described below) is grown. Therefore, the gas that contains nitrogen slows the reaction rate between the nickel and the silicon when the nickel layer 20 and the silicon are reacted in a subsequent silicide process used to form a nickel silicide layer.
Subsequently, with reference to FIG. 2d, a protective layer 25 for protecting the nickel layer 20 is formed on the nickel layer 20. The protective layer 25 is formed by performing a PVD or CVD process with Ti, TiN, or a compound such as Ti/TiN.
Next, a first heat treatment process is performed to form a nickel silicide layer 30 on the gate electrode layer 16, the source region 19, and the drain region 19. In an example, the first heat treatment process is performed in a gas atmosphere (i.e., an N2 or NH3 gas atmosphere).
During the formation of the nickel silicide layer 30, nickel atoms are sufficiently accumulated on the upper interfacial surfaces of the source/drain regions 19 and the gate electrode layer 16 even if a natural oxidation layer is present on these elements. Therefore, such a natural oxidation layer does not impede the formation of the nickel silicide layer 30.
The first heat treatment process may be performed using an RTP method or the more common method that utilizes an electric furnace. In an example when the RTP method is used, a temperature of about 300-600° C. is maintained for about 10-60 seconds. In another example when an electric furnace is used, the process is performed at a temperature of about 300-600° C. for about 20-60 seconds.
Through the use of the above method, a metal silicide layer 30 is formed having a thickness uniformity of about 1 ̃20%, to a thickness of about 100 ̃400 Å, and to a depth of less than about 400 Å within the silicon substrate 10.
Forming the nickel layer 20, performing the plasma treatment, forming the protective layer 25, and performing the heat treatment process may be performed in situ in the same vacuum chamber. This reduces the manufacturing time.
Next, the nickel layer 20 and the protection layer 25 are removed. This removal is accomplished by etching the silicon substrate 10 using an SPM solution at about 50-150° C. for about 5-15 minutes. Also, cleaning is performed for about 3-10 minutes in an SCl solution to remove impurities generated during etching. An example SPM solution may be realized by using hydrogen peroxide and sulfuric acid at a ratio of 1:6.
A second heat treatment process is performed following the above processes to stabilize the nickel silicide layer 30. In an example when the RTP method is used, a temperature of about 800-950° C. is maintained for about 10-60 seconds. In another example, when an electric furnace is used, the process is performed at a temperature of about 500-900° C. for about 20-60 seconds.
In the examples described above, the reaction rate between the nickel and the silicon is slowed to thereby prevent abnormal growth of nickel silicide. Therefore, the interfacial contact resistance and the leakage current of the source/drain regions 19 and of the gate electrode 17 of a transistor may be reduced, thereby stabilizing the semiconductor device characteristics and the driving of the same.
From the foregoing, persons of ordinary skill in the art will appreciate that a semiconductor device that does not exhibit abnormal growth of nickel silicide and, thus, has a nickel silicide layer of a uniform thickness has been disclosed.
In an illustrated example, the semiconductor device includes a silicon substrate 10 having a source region 19 and a drain region 19; a gate electrode 17 formed on the silicon substrate 10; and a metal silicide layer 30 formed on each of the gate electrode 17, the source region 19, and the drain region 19, and having a thickness uniformity of about 1 ̃20%.
In an example, each of the metal silicide layers 30 is a nickel silicide layer having a thickness of about 100 ̃400 Å. Each of the metal silicide layers 30 includes nitrogen to reduce the speed at which the metal silicide layers 30 grow. The metal silicide layers 30 are formed to a depth of less than about 400 Å within the silicon substrate 10.
An example fabrication method disclosed herein includes: (a) forming a metal layer on a silicon substrate 10 having a gate electrode 17, a source region 19, and a drain region 19; (b) performing a plasma treatment on the metal layer; (c) forming a protective layer on the metal layer that has undergone the plasma treatment; and (d) heat treating the silicon substrate on which the protection layer is formed to thereby form a metal silicide layer 30. A gas that includes nitrogen is used as a plasma gas during the plasma treatment.
In an example, the metal layer 30 is formed using nickel and one of PVD and CVD.
In an example, the plasma treatment is performed in-situ in the same chamber used to form the metal layer.
The nitrogen, which reduces the speed at which the metal silicide layer 30 grows, is injected into the metal layer through the plasma treatment.
In an example, forming a metal layer 20, performing a plasma treatment, forming a protective layer 25, and heat treating the silicon substrate 10 are all performed in the same chamber.
One of titanium, titanium nitride, and a titanium/titanium nitride compound is used to form the protective layer.
One of PVD and CVD is used to form the protective layer.
In forming a metal layer, the thickness uniformity is about 1 ̃20%, the thickness is about 100 ̃400 Å, and the metal layer enters a surface of the silicon substrate 10 to a depth of less than about 400 Å.
In heat treating the silicon substrate 10, one of an RTP method and an electric furnace is used. In the RTP method, a temperature of about 300-600° C. is maintained for about 10-60 seconds. In the electric method, a temperature of about 300-600° C. is maintained for about 20-60 seconds.
The illustrated example further includes removing the protective layer 25 and the metal layer that has not been formed into the silicide layer 30 following the formation of the metal silicide layer 30.
In the illustrated example, a second heat treating process following the removing of the metal layer is employed. In the second heat treating process, one of an RTP method and an electric furnace is used. A temperature of about 900-950° C. is maintained for about 10-60 seconds in the RTP method, and a temperature of about 500-900° C. is maintained for about 20-60 seconds in the method utilizing an electric furnace.
Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.

## Claims

1. A semiconductor device comprising:
a silicon substrate having a source region and a drain region;
a gate on the silicon substrate; and
a nickel silicide layer on the gate electrode, the source region, and the drain region, and having a thickness of about 100 to 400 Å and a thickness uniformity of about 1 ̃20%.

2. A semiconductor device as defined in claim 1, wherein the nickel silicide layer includes nitrogen to reduce a speed at which the nickel silicide layer grows.

3. A semiconductor device as defined in claim 1, wherein the nickel silicide layer is formed to a depth of less than about 400 Å within the silicon substrate.

4. A semiconductor device as defined in claim 1, further comprising a protective layer on the nickel silicide layer.

5. A semiconductor device as defined in claim 4, wherein the protective layer comprises titanium, titanium nitride, or titanium/titanium nitride.

6. A semiconductor device as defined in claim 1, further comprising nitride spacers on sidewalls of the gate.

7. A semiconductor device as defined in claim 6, wherein the source and drain regions are on opposite sides of the gate and the spacers.

8. A semiconductor device as defined in claim 1, further comprising an oxidation layer on the silicon substrate.

9. A semiconductor device as defined in claim 1, further comprising a cap oxidation layer on the gate electrode.

10. A semiconductor device as defined in claim 1, wherein the source and drain regions comprise a high concentration of n-type or p-type impurity ions.

11. A semiconductor device as defined in claim 10, wherein the impurity ions comprise phosphorus (P) or boron (B).

12. A semiconductor device as defined in claim 1, further comprising an LDD region in the substrate adjacent to the gate.

13. A semiconductor device as defined in claim 1, wherein the gate comprises a gate electrode layer and a gate oxidation layer.

14. A semiconductor device as defined in claim 13, wherein the gate electrode layer comprises polycrystalline silicon.

15. A semiconductor device as defined in claim 13, wherein the gate oxidation layer is on the silicon substrate and is between the source and drain regions.

16. A semiconductor device as defined in claim 1, wherein the source and drain regions are on opposite sides of the gate.

17. A semiconductor device as defined in claim 1, wherein the silicon substrate comprises a device isolation region defining an active area.

18. A semiconductor device as defined in claim 1, further comprising wirings in electrical contact with the nickel silicide layer.

19. A semiconductor device as defined in claim 18, wherein the wirings comprise metal or polysilicon.

20. A semiconductor device as defined in claim 1, wherein the nickel silicide is formed at a temperature of about 300 to 600° C.