Isolation structure for strained channel transistors
A method and system is disclosed for forming an improved isolation structure for strained channel transistors. In one example, an isolation structure is formed comprising a trench filled with a nitrogen-containing liner and a gap filler. The nitrogen-containing liner enables the isolation structure to reduce compressive strain contribution to the channel region.
This application is a divisional of co-pending U.S. patent application Ser. No. 10/875,141, filed Jun. 23, 2004, which is a continuation in part of co-pending U.S. patent application Ser. No. 10/423,513, filed Apr. 25, 2003, now U.S. Pat. No. 6,882,025 to Yeo, the entirety of which are incorporated by reference.
TECHNICAL FIELDThe present disclosure relates generally to the field of semiconductor devices, and more particularly to strained channel transistors with enhanced performance using improved isolation regions and the method for making same.
BACKGROUNDSize reduction of the metal-oxide-semiconductor field-effect transistor (MOSFET), including reduction of the gate length and gate oxide thickness, has enabled the continued improvement in speed performance, density, and cost per unit function of integrated circuits over the past few decades. To enhance transistor performance further, strain may be introduced in the transistor channel for improving carrier mobility. Therefore, strain-induced mobility enhancement is another way to improve transistor performance in addition to device scaling. Several existing approaches of introducing strain in the transistor channel region have been proposed.
There are several existing approaches of introducing strain in the transistor channel region to enhance further transistor performance. In one conventional approach, a relaxed silicon germanium (SiGe) buffer layer 102 is provided beneath the channel region, as shown in
In a conventional shallow trench isolation structure, as shown in
What is needed is an improved isolation structure for strained channel transistors and the method for making same.
SUMMARY OF INVENTIONIn view of the foregoing, the present disclosure provides a system and method for forming an improved isolation structure for strained channel transistors.
In one example, an isolation structure is formed comprising a trench filled with a silicon oxide liner, a nitrogen-containing liner, and a gap filler. In another example, an isolation structure is formed comprising a trench filled with a nitrogen-containing liner and a gap filler. The nitrogen-containing liner enables the isolation structure to reduce compressive strain contribution to the channel region. The nitrogen-containing liner minimizes confined volume expansion and reduces compressive stress in the surrounding active region.
The present disclosure provide isolation structures with reduced compressive strain contribution and reduced thermal budget in a tensile strained silicon substrate. Another object of the present disclosure is to teach a method of engineering the strain in the channel of the tensile strained transistor by engineering the isolation structure to improve transistor performance.
These and other aspects and advantages will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure.
BRIEF DESCRIPTION OF DRAWINGSThe present disclosure will be more clearly understood after reference to the following detailed description of preferred embodiments read in conjunction with the drawings, wherein:
FIGS. 1(a)-(b) illustrate the cross-section of a conventional strained silicon transistor with a relaxed SiGe and the illustration of the origin of strain in the Si/SiGe hetero-structure, respectively.
FIGS. 3(a)-(b) illustrate a novel low-stress isolation structure for the strained silicon transistor according to one example of the present disclosure.
FIGS. 4(a)-(e) illustrate a first method of manufacturing a novel low-stress isolation structure for the strained silicon transistor according to another example of the present disclosure.
FIGS. 5(a)-(e) illustrate a second method of manufacturing a novel low-stress isolation structure for the strained silicon transistor according to another example of the present disclosure.
FIGS. 6(a)-(e) illustrate a third method of manufacturing a novel low-stress isolation structure for the strained silicon transistor according to another example of the present disclosure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSAs illustrated below, the structure of and methods are disclosed below for the manufacture of an improved isolation structure with reduced compression strain contribution to the channel region and/or reduced thermal budget. Several embodiments are shown as illustrated examples.
First Embodiment
FIGS. 4(a)-(e) illustrate a first method embodiment of the present disclosure, describing a process flow for forming strained silicon transistors with reduced thermal budget and reduced compressive strain contribution by the isolation structure to the channel region. The isolation structure 400 preferably comprises a nitrogen-containing liner 440 in direct contact with the trench sidewall surface 445. The nitrogen-containing liner 440 can be a single silicon nitride layer or a silicon oxynitride layer. The nitrogen content of the nitrogen-containing liner 440 may be in the range of 5 to 60 percent (%) by atomic percentage. A substrate comprising a strained silicon layer 405 (
The cross-section in
The cross-section in
FIGS. 5(a)-(e) illustrate a second method embodiment of the present disclosure, describing a process flow for forming strained silicon transistors with reduced thermal budget and compressive strain contribution by the isolation structure to the channel region. The isolation structure 500 preferably comprises a nitrogen-containing liner 550 overlying a silicon oxide liner 555. In this method embodiment, the silicon oxide liner 555 is formed by chemical vapor deposition, preferably plasma-enhanced chemical vapor deposition (PECVD). The silicon oxide liner 555 is in direct contact with the trench sidewall surface 565. A substrate comprising a strained silicon layer 505 overlying a relaxed silicon-germanium (SiGe) layer 510 is used as the starting material. The starting substrate may further comprise a silicon substrate 520 underlying a graded SiGe buffer layer 515. A first patterned mask is formed on the substrate, and trenches 525 are etched into the substrate, as illustrated in
The cross-section illustrated in
A planarization step, preferably using a chemical mechanical polishing process, is performed. The resulting cross-section is illustrated in
FIGS. 6(a)-(e) illustrate a third method embodiment of the present disclosure, describing a process flow for forming strained silicon transistors with reduced thermal budget and compressive strain contribution by the isolation structure to the channel region. The isolation structure 600 comprises a nitrogen-containing liner 650 overlying a silicon oxide liner 645. The third method embodiment differs from the second method embodiment of the present disclosure in that the silicon oxide liner 645 of the third method embodiment is formed by a thermal oxidation process. The thermally grown silicon oxide liner 645 is in direct contact with the trench sidewall surface 660. Since the growth of the thermal oxide results in rounded corners, the corner rounding process is optional. A substrate comprising a strained silicon layer 605 overlying a relaxed silicon-germanium (SiGe) layer 610 is used as the starting material. A first patterned mask is formed on the substrate, and trenches 625 are etched into the substrate, as illustrated in
The cross-section illustrated in
A planarization step, preferably using a chemical mechanical polishing process, is performed. The resulting cross-section is illustrated in
The above disclosure provides many different embodiments, or examples, for implementing different features of the present disclosure. Specific examples of components, and processes are described to help clarify the present disclosure. These are, of course, merely examples and are not intended to limit the present disclosure from that described in the claims. For example, while a shallow trench isolation is illustrated, it is understood that the present disclosure may be extended to other isolation structures, which are improvements of the shallow trench isolation structure. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense.
While the present disclosure has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure, as set forth in the following claims.
Claims
1. A method for forming an isolation structure for strained channel transistors comprising:
- forming a pattern mask over a semiconductor substrate;
- forming a trench in the semiconductor substrate through the pattern mask;
- forming a nitrogen-containing liner in the trench; and
- filling the trench with a gap filler material,
- wherein the nitrogen-containing liner reduces a compressive strain caused by the isolation structure.
2. The method according to claim 1, wherein the trench is formed by an anisotropic plasma etching with fluorine chemistry.
3. The method according to claim 1, wherein the nitrogen-containing liner is comprised of silicon nitride or silicon oxynitride.
4. The method according to claim 1, wherein the nitrogen-containing liner has a nitrogen content of 5 to 60 percent (%).
5. The method according to claim 1, wherein the nitrogen-containing liner has a thickness in the range of 10 to 500 angstroms.
6. The method according to claim 1, wherein the nitrogen-containing liner is formed by a low-pressure chemical vapor deposition (LPCVD).
7. The method according to claim 6, wherein the low-pressure chemical vapor deposition (LPCVD) uses precursor gases such as ammonia or silane.
8. The method according to claim 6, wherein the low-pressure chemical vapor deposition (LPCVD) operates at a temperature between 500 and 900 degrees Celsius.
9. The method according to claim 1, wherein the nitrogen-containing liner is a high tensile stress conformal nitride liner.
10. The method according to claim 1, wherein the gap filler material is at least one of silicon oxide, CVD silicon oxide, or CVD poly-crystalline silicon.
11. The method according to claim 1, further comprising, after filling the trench with the gap filler material, densifying the gap filler material by either a pyrogenic oxidation anneal or a conventional anneal process.
12. The method according to claim 1, wherein the pyrogenic oxidation anneal process is conducted at a temperature of 800 degrees Celsius.
13. The method according to claim 1, further comprising, after forming the trench, forming an oxide liner underlying the nitrogen-containing liner.
14. The method according to claim 13, wherein the oxide liner is a silicon oxide liner.
15. The method according to claim 14, wherein the step of forming the oxide liner is a chemical vapor deposition step or a thermal oxidation step.
16. The method according to claim 1, further comprising the step, after the step of forming the trench:
- widening the pattern mask by a predetermined pull-back portion; and
- performing a corner rounding of the trench.
17. The method according to claim 16, wherein the corner rounding step is an anneal at a temperature in the range of 700 to 950 degrees Celsius in a gaseous ambient.
18. The method according to claim 16, further comprising a step, after the step of corner rounding, of forming a silicon oxide liner.
19. The method according to claim 16, wherein the pull back portion is in the range of 50 to 1000 angstroms.
20. The method according to claim 16, wherein the pull back portion is formed by a chemical treatment with a wet etch process.
21. The method according to claim 2, wherein the patterned mask comprises a silicon nitride layer overlying a pad oxide layer.
22. The method according to claim 2, further comprising, after filling the trench with the gap filler material, planarizing trench with the gap filler material and the pattern mask.
23. The method according to claim 12, further comprising removing the pattern mask.
24. The method according to claim 2, wherein a surface of the gap filler material is higher than two ends of the liner in the trench.
25. A method for forming an isolation structure for strained channel transistors, the method comprising:
- forming a pattern mask over a semiconductor substrate;
- forming a trench in the semiconductor substrate through the pattern mask;
- widening the pattern mask by a predetermined pull-back portion;
- forming an oxide liner in the trench;
- forming a nitrogen-containing liner on the oxide liner; and
- filling the trench with a gap filler material,
- wherein the nitrogen-containing liner reduces a compressive strain asserted by the gap filler material contained therein.
26. The method according to claim 25, wherein the nitrogen-containing liner is comprised of silicon nitride or silicon oxynitride.
27. The method according to claim 25, wherein the nitrogen-containing liner has a nitrogen content of 5 to 60 percent (%).
28. The method according to claim 25, wherein the nitrogen-containing liner has a thickness in the range of 10 to 500 angstroms.
29. The method according to claim 25, wherein forming the nitrogen-containing liner uses a low-pressure chemical vapor deposition (LPCVD).
30. The method according to claim 25, further comprising, after filling the trench with the gap filler material, densifying the gap filler material by either a pyrogenic oxidation anneal or a conventional anneal process.
31. The method according to claim 25, further comprising, wherein the oxide liner is a silicon oxide liner.
32. The method according to claim 25, further comprising performing a corner rounding of the trench.
33. The method according to claim 25, wherein the pull back portion is in the range of 50 to 1000 angstroms.
34. The method according to claim 25, wherein the patterned mask comprises a silicon nitride layer overlying a pad oxide layer.
35. The method according to claim 25, further comprising, after filling the trench with the gap filler material, planarizing the trench with the gap filler material and the pattern mask.
36. The method according to claim 35, further comprising removing the pattern mask.
37. The method according to claim 25, wherein a surface of the gap filler material is higher than two ends of the liner in the trench
Type: Application
Filed: Oct 26, 2006
Publication Date: Jul 12, 2007
Inventors: Chih-Hsin Ko (Fongshang City), Yee-Chia Yeo (Singapore), Wen-Chin Lee (Hsinchu), Chung-Hu Ge (Taiwei)
Application Number: 11/586,936
International Classification: H01L 21/76 (20060101);