Method of fabricating semiconductor device and semiconductor device fabricated thereby

Abstract

A method of fabricating a semiconductor device is disclosed. The method includes the steps of forming recesses in a semiconductor substrate; epitaxial growing a first SiGe seed layer with constant Ge content in the recesses; epitaxial growing a second SiGe layer with a constant Ge content higher than the Ge content of first SiGe seed layer on the first SiGe seed layer; epitaxial growing a third SiGe layer with a constant Ge content lower than the Ge content of the second SiGe layer; and forming a cap layer on the third SiGe layer.

Claims

1. A method of fabricating a semiconductor device comprising the steps of: Step 1: providing a semiconductor substrate, forming shallow trench isolations in SRAM regions in the semiconductor substrate, and forming a mask layer on the semiconductor substrate; Step 2: patterning the mask layer and etching the semiconductor substrate to form at least one recess in the semiconductor substrate; Step 3: epitaxial growing a first SiGe seed layer with a constant Ge content in the at least one recess; Step 4: epitaxial growing a second SiGe layer with a constant Ge content on the first SiGe seed layer, wherein the Ge content of the second SiGe layer is higher than that of the first SiGe seed layer; Step 5: epitaxial growing a third SiGe layer with a constant Ge content on the second SiGe layer, wherein the Ge content of the third SiGe layer is lower than that of the second SiGe layer; Step 6: forming a cap layer on the third SiGe layer, wherein the cap layer is a Si epitaxial cap layer.

2. The method according to claim 1, wherein the semiconductor device is a PMOS device.

3. The method according to claim 1, wherein each of the at least one recess is U-shaped or -shaped.

4. The method according to claim 1, wherein the Ge content of the first SiGe seed layer is in a range of 1% to 25%.

5. The method according to claim 1, wherein the Ge content of the second SiGe layer is in a range of 25% to 45%.

6. The method according to claim 1, wherein the Ge content of the third SiGe layer is in a range of 1% to 40%.

7. The method according to claim 1, wherein the thickness of the first SiGe seed layer is in a range of 10 to 300 ; the thickness of the second SiGe layer is in a range of 100 to 800 ; the thickness of the third SiGe layer is in a range of 10 to 300 .

8. The method according to claim 1, wherein the thickness of the cap layer is in a range of 10 to 300 .

9. The method according to claim 1, wherein the second SiGe layer, the third SiGe layer, and the cap layer contain in-situ doped boron, wherein the concentration of the boron is less than 210.sup.21 cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a semiconductor structure at the first stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

(2) FIG. 2 is a cross-sectional view of a semiconductor structure at the second stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

(3) FIG. 3 is a cross-sectional view of a semiconductor structure at the third stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

(4) FIG. 4 is a cross-sectional view of a semiconductor structure at the fourth stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

(5) FIG. 5 is a cross-sectional view of a semiconductor structure at the fifth stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

(6) FIG. 6 is a cross-sectional view of a semiconductor structure at the sixth stage of the fabricating method of a semiconductor device according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The figures referred to are not necessarily drawn to scale, should be understood to provide a representation of particular embodiments of the invention, and are merely conceptual in nature and illustrative of the principle involved. In the figures, each identical, or substantially similar component that is illustrated in various figures is typically represented by a single numeral or notation.

(8) The present invention provides an improved SiGe epitaxial growth technology, which reduces or eliminates dislocations in the SiGe layer, increases the content of Ge in the SiGe layer, improves the profile of the cap layer, and facilitates the formation of the subsequent metal silicide (NiSi).

(9) FIGS. 1-6 show processing steps of the fabricating method of a semiconductor device in a preferred embodiment of the present invention. The method is particularly suitable to fabricate a PMOS device.

(10) As shown in FIGS. 1-6, in a preferred embodiment of the present invention, the fabricating method includes the following steps.

(11) Step 1: as shown in FIG. 1, a semiconductor substrate 10 is provided, shallow trench isolations 20 are formed in SRAM regions in the semiconductor substrate 10, and a mask layer 30 is formed on the semiconductor substrate 10.

(12) The semiconductor substrate can be a single crystal silicon substrate, or other semiconductor substrate such as a SOI substrate.

(13) Step 2: as shown in FIG. 2, the mask layer 30 is patterned and the semiconductor substrate 10 is etched by using the patterned mask layer 30 as a mask to form at least one recess 40. Preferably, each recess 40 is U-shaped or -shaped.

(14) Step 3: as shown in FIG. 3, a first SiGe seed layer 50 with a constant Ge content is epitaxial grown in the at least one recess 40;

(15) Step 4: as shown in FIG. 4, a second SiGe layer 60 with a constant Ge content is epitaxial grown on the first SiGe seed layer 50; wherein the Ge content of the second SiGe layer 60 is higher than that of the first SiGe seed layer 50;

(16) Step 5: as shown in FIG. 5, a third SiGe layer 70 with a constant Ge content is epitaxial grown on the second SiGe layer 60; wherein the Ge content of the third SiGe layer 70 is lower than that of the second SiGe layer 60.

(17) Step 6: as shown in FIG. 6, a cap layer 80 is formed on the third SiGe layer 70. Preferably, the cap layer 80 is a Si epitaxial cap layer.

(18) By the fabricating method of the present invention, since the second SiGe layer has a higher Ge content than the first SiGe layer and the third SiGe layer, the stress applied to the channel region can be increased while an occurrence of dislocations due to the crystal mismatches at the interface between the substrate and the first SiGe layer, the interface between the first and second SiGe layers, the interface between the second and third SiGe layer, or the interface between the third SiGe layer and the cap layer is decreased. Furthermore, since the third SiGe layer with lower Ge content is formed between the second SiGe layer with high Ge content and the cap layer, the profile of the second SiGe layer as well as the cap layer in the SRAM regions can be improved, which facilitates the formation of the subsequent metal silicide (NiSi).

(19) In a preferred embodiment, the Ge content of the first SiGe seed layer 50 is in a range of 1% to 25% (mass-content). In a preferred embodiment, the Ge content of the second SiGe layer 60 is in a range of 25% to 45% (mass-content). In a preferred embodiment, the Ge content of the third SiGe layer 70 is in a range of 1% to 40% (mass-content).

(20) In a preferred embodiment, a thickness of the first SiGe seed layer 50 is in a range of 10 to 300 , the thickness of the second SiGe layer 60 is in a range of 100 to 800 (the top surface of the second SiGe layer 60 can either below, at same level with, or above the surface of the substrate); a thickness of the third SiGe layer 70 is in a range of 10 to 300 ; a thickness of the cap layer 80 is in a range of 10 to 300 .

(21) In a preferred embodiment, the second SiGe layer 60, the third SiGe layer 70, and the cap layer 80 contains in-situ doped B, wherein the concentration of B is less than 210.sup.21 cm.sup.3.

(22) In a preferred embodiment, during the epitaxial growth, the processing temperature is in a range of 590 to 1200 C., the pressure in a reaction chamber is a the range of 5 to 800 Torr.

(23) In a preferred embodiment, during the epitaxial growth, the reactant gases includes SiH.sub.4, SiH.sub.2Cl.sub.2, HCL, H.sub.2, GeH.sub.4, and B.sub.2H.sub.6. Wherein a flow rate of Hz is in a range of 1000 to 60000 sccm; a flow rate ratio between GeH.sub.4 and SiH.sub.4 or a flow rate ratio between GeH.sub.4 and SiH.sub.2Cl.sub.2 is in a range of 1:0.01 to 1:100; a flow rate ratio between GeH.sub.4 and HCL is in a range of 1:0.05 to 1:50.

(24) It will be understood that, the terms such as first, second and third recited in the present application are merely identifiers, but do not have any other meanings, for example, a particular order and the like.

(25) The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspect of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.