METAL-OXIDE SEMICONDUCTOR TRANSISTOR
A metal-oxide semiconductor (MOS) transistor includes a gate structure positioned in an active area defined in a substrate, a recessed source/drain, and an asymmetric shallow trench isolation (STI) for electrically isolating the active areas. A surface of the asymmetric STI and the substrate is coplanar.
This continuation application claims the benefits of U.S. application Ser. No. 11/669,164, filed on Jan. 31, 2007 and incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a metal-oxide semiconductor (MOS) transistor and manufacturing methods thereof, and more particularly, to a MOS transistor and manufacturing methods thereof utilizing selective epitaxial growth (SEG) method.
2. Description of the Prior Art
Selective epitaxial growth (SEG) technology is used to form an epitaxial silicon layer on a single-crystalline substrate, in which the crystalline orientation of the epitaxial silicon layer is almost identical to that of the substrate. SEG technology is widely applied in manufacturing numerous kinds of semiconductor devices, such as MOS transistors having raised source/drain regions which benefits from good short channel character and low parasitical resistance and a MOS transistor having recessed source/drain which improves drain induced barrier lowering (DIBL) and punchthrough effect and reduces off-state current leakage and power consumption.
Generally, SEG technology includes performing a cleaning process to remove native oxides and other impurities from a surface of a substrate, and then depositing an epitaxial silicon layer on the substrate and making the epitaxial silicon layer grow along with the silicon lattice of the substrate. Please refer to
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Therefore the present invention provides a MOS transistor and manufacturing methods thereof to prevent the current leakage around the STI.
According to the claimed invention, a method for manufacturing a MOS transistor is provided. The method comprises steps of providing a substrate having at least a gate structure and a shallow trench isolation (STI) formed thereon, performing a first etching process to form recesses in the substrate respectively on two sides of the gate structure, performing a selective epitaxial growth (SEG) process to form epitaxial silicon layers in the recesses respectively, a seam being accordingly formed between the epitaxial silicon layer and the STI, forming a dielectric layer in the seam, and performing a self-aligned silicidation (salicide) process.
According to the claimed invention, another method for manufacturing a MOS transistor is provided. The method comprises steps of providing a substrate having at least a gate structure comprising a hard mask layer and a cap layer formed thereon and an STI, performing a first etching process to form recesses in the substrate respectively on two sides of the gate structure, performing an SEG process to form epitaxial silicon layers in the recesses respectively, a seam being accordingly formed between the epitaxial silicon layer and the STI, performing a deposition process to deposit a dielectric layer on the substrate, the dielectric layer filling the seams, performing a second etching process to remove the dielectric layer except the seams, the hard mask layer, and the cap layer, and performing a salicide process.
According to the claimed invention, a MOS transistor is further provided. The MOS transistor comprises a gate structure positioned in an active area defined in a substrate, a recessed source/drain, and an asymmetric shallow trench isolation (STI) for electrically isolating the active areas.
Accordingly, because a deposition process is performed after the SEG process, the deposited dielectric layer thus fills the seam formed in between the epitaxial silicon layer and the STI. Therefore the seams are prevented from enlarging and deepening in the following etching or cleaning processes, and thus the epitaxial silicon layer and the substrate is prevented from being excessively consumed in the salicide process. Consequently the current leaking caused by the existence of the seam is effectively improved.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
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It is noteworthy that the epitaxial silicon layer 252 grows along the silicon lattice of the substrate 200 in the recess 250. As shown in
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In the first preferred embodiment, the seams 254 caused by the abovementioned growth characters of the epitaxial silicon layer are filled with the dielectric layers 262, therefore damages to the substrate 200 through the seams 254 during the following etching or cleaning processes are prevented by the filled dielectric layers 262. The dielectric layers 262 also prevent the epitaxial silicon layers 252 and the substrate 200 from excessive consumption through the seams 254 in the salicide process. Consequently, current leakage caused by the salicide which is formed under the STI 230 is prevented.
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Next, the substrate 300 undergoes a salicide process. Because the process is similar to the process in the first preferred embodiment, further description of the process is omitted in the interest of brevity in the second embodiment.
In the second preferred embodiment, the seams 354 caused by the abovementioned growth characters of the epitaxial silicon layer 352 are filled with the dielectric layers 362, therefore damages to the substrate 300 through the seams 354 during the following etching or cleaning processes are prevented by the filled dielectric layer 362. The dielectric layers 362 also prevent the epitaxial silicon layers 352 and the substrate 300 from excessive consumption through the seams 354 in the salicide process. Consequently, current leakage caused by the salicide which is formed under the STI 330 is prevented. Furthermore, because the dielectric layer 360 except the seams 354, the hard mask layer 316, and the cap layer 340 are removed simultaneously, the processes are simplified and damages to the substrate 300 in the etching or cleaning processes are accordingly reduced.
The present invention herein also provides a MOS transistor. Please refer to
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It is noteworthy that the STI 370 provided by the present invention is an asymmetric and multiple STI. As shown in
As abovementioned, because seams are formed in between epitaxial silicon layers and STIs after a SEG process, a deposition is performed to fill the seams with a dielectric layer after the SEG process. In other words, the contiguous point of the epitaxial silicon layer, the substrate, and the STI is filled with the dielectric layer, therefore the contiguous point is prevented from downward etching in the following etching or cleaning processes. The problems of excessive consumption to the substrate through the seams in the salicide process and current leakage caused from the salicide formed under the STI are also prevented.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A metal-oxide semiconductor (MOS) transistor comprising:
- a gate structure positioned in an active area defined in a substrate;
- a recessed source/drain; and
- an asymmetric shallow trench isolation (STI) for electrically isolating the active areas, a surface of the asymmetric STI and the substrate being coplanar.
2. The MOS transistor of claim 1 wherein the gate structure further comprises:
- a gate dielectric layer;
- a gate conductive layer positioned on the gate dielectric layer;
- a spacer positioned on sidewalls of the gate conductive layer; and
- lightly doped drains (LDDs) respectively positioned in the substrate on two sides of the gate conductive layer.
3. The MOS transistor of claim 1 wherein the asymmetric STI is a multiple STI.
4. The MOS transistor of claim 3 wherein the multiple STI comprises a main STI and a sub-STI positioned on at least one side of the main STI.
5. The MOS transistor of claim 4, wherein a surface of the main STI and a surface of the sub-STI are coplanar.
6. The MOS transistor of claim 4 wherein the sub-STI comprises silicon dioxide, silicon oxynitride, or silicon nitride.
7. The MOS transistor of claim 1 wherein the gate structure is a gate structure of a PMOS transistor.
8. The MOS transistor of claim 7, wherein the recessed source/drain comprises silicon germanium (SiGe).
9. The MOS transistor of claim 1, wherein the gate structure is a gate structure of an NMOS transistor.
10. The MOS transistor of claim 9, wherein the recessed source/drain comprises silicon carbide (SiC).
Type: Application
Filed: Nov 23, 2008
Publication Date: Mar 19, 2009
Inventors: Chih-Chiang Wu (Taichung County), Shih-Fang Tzou (Hsinchu City), Shih-Chieh Hsu (Hsinchu City), Jen-Hong Huang (Tao-Yuan City)
Application Number: 12/276,397
International Classification: H01L 29/78 (20060101);