Damascene interconnect structure having air gaps between metal lines and method for fabricating the same
An exemplary damascene interconnect structure includes a substrate (20), a first dielectric layer (21) on the substrate, a plurality of trenches (27) formed in the first dielectric layer, and a plurality of metal lines (24) filled in the trenches. The first dielectric layer includes multi sub-dielectric layers (211, 212, 213). Wherein a plurality of air gaps (28) are maintained between the metal lines and at least one of the sub-dielectric layers. A method for fabricating the damascene interconnect structure is also provided.
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The present invention relates to damascene interconnect structures and methods for fabricating the same, and particularly to a damascene interconnect structure having air gaps between metal lines and a method for fabricating the same.
BACKGROUNDIn semiconductor devices, such as large scale integrated circuits (LSI) and ultra-large scale integration (ULSI) integrated circuits, the damascene process has been commonly used to form interconnect lines. A typical damascene process involves etching trenches or canals in a planar dielectric layer, and then filling the trenches or canals with metal, such as aluminum or copper. After filling, the excess metal outside the trenches is planarized and polished by chemical polishing so that metal is only left within the trenches.
A method for fabricating the damascene interconnect structure is as follows. In step 1, referring to
In step 2, referring to
In step 3, referring to
In step 4, referring to
In order that the damascene interconnect structure 1 has good electrical properties, a resistance R in the metal lines 17 and a capacitance C between the metal lines 17 must both be as low as possible. This is so that the resistance-capacitance (RC) delay and leakage current caused by the resistance R and the capacitance C can be minimal.
With recent developments in semiconductor technology, millions and even billions of electronic elements can be integrated in one chip. Current flows and electrical processing occurring in a single chip are massive. Therefore leakage current and RC delay can be prevalent, and may significantly impair the performance of the chip.
What is needed is a damascene interconnect structure and a method for fabricating the same which can help ensure that performance of a corresponding integrated circuit is satisfactory.
SUMMARYAn exemplary damascene interconnect structure includes a substrate, a first dielectric layer on the substrate, a plurality of trenches formed in the first dielectric layer, and a plurality of metal lines filled in the trenches. The first dielectric layer includes multi sub-dielectric layers. Wherein a plurality of air gaps are maintained between the metal lines and at least one of the sub-dielectric layers.
An exemplary method for fabricating a damascene interconnect structure is provided as below. A substrate is provided. A multilayer dielectric film is formed on the substrate. A patterned photoresist is formed on the multilayer dielectric film. Etching the multilayer dielectric film to form a plurality of trenches, a portion of each of the trenches having an enlarged width at each of sidewalls thereof. Filling the trenches with conductive metal to form conductive lines such that air is trapped in extremities of the enlarged width portions of the trenches.
Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.
The first dielectric layer 21 is a multilayer structure, which includes a first sub-dielectric layer 211, a second sub-dielectric layer 212, and a third sub-dielectric layer 213 arranged in that order from bottom to top. The first and the third sub-dielectric layers 211 and 213 reach side edges of the metal lines 24. The second sub-dielectric layer 212 maintains a distance from the metal lines 24, so that a plurality of air gaps 28 are maintained between the metal lines 24 and the second sub-dielectric layer 212.
The first dielectric layer 21 is a multilayer structure with a plurality of air gaps 28 between the metal lines 24 and the second sub-dielectric layer 212. Because each air gap 28 has the lowest dielectric constant (k=1), the capacitance C between adjacent metal lines 24 is significantly reduced. Accordingly, RC delay of electrical signals and leakage current are reduced. Therefore the speed of an integrated circuit incorporating the damascene interconnect structure 2 is significantly improved, and power consumption of the integrated circuit is reduced.
An exemplary method for fabricating the damascene interconnect structure 2 is as follows. In step 11, referring to
In step 12, referring to
In step 13, referring to
In step 14, referring to
In step 15, referring to
In step 16, referring to
In the above-described method for fabricating the damascene interconnect structure 2, the first dielectric layer 21 is formed by depositing three sub-dielectric layers 211, 212, 213 with different materials, and by etching the first dielectric layer 21 to form the trenches 27 having the enlarged width portions at the sidewalls thereof. Therefore when the metal lines 24 are formed in the trenches 27, air gaps 28 are also formed in the extremities of the enlarged width portions of the trenches 27. Because the air gaps 28 have the lowest dielectric constant of air, a capacitance C between adjacent metal lines 24 can be significantly reduced. Thus in a corresponding integrated circuit chip, RC delay in electrical signals and leakage current are reduced. Accordingly, the speed and power consumption characteristics of the integrated circuit chip can be significantly improved.
Various alternative embodiments can be practiced. For example, the first, the second, and the third sub-dielectric layers 211, 212, 213 can be made of the same material. Such material can be silicon oxide or silicon nitride. During the deposition process, a deposition rate of the second sub-dielectric layer 212 is lower than that of the first sub-dielectric layer 211, and a deposition rate of the third sub-dielectric layer 213 is higher than that of the second sub-dielectric layer 212. Therefore the densities of the first and the third sub-dielectric layers 211 and 213 are greater than that of the second sub-dielectric layer 212. Accordingly, etching rates of the first and the third sub-dielectric layers 211 and 213 are lower than that of the second sub-dielectric layer 212. During the etching process, portions of the trenches 27 at the second sub-dielectric layer 212 are wider than portions of the trenches 27 at the first and the third sub-dielectric layer 211, 213. As a result, air gaps 28 are subsequently formed between the metal lines 24.
The metal lines 24 can be made of another suitable material, such as aluminum, silver, or an alloy including any one or more of copper, aluminum and silver.
The first dielectric layer 21 can be a multilayer structure having two, four or more sub-dielectric layers, so long as air gaps 28 are maintained between the metal lines 24 and at least one of the sub-dielectric layers.
The trenches 27 can be etched by dry etching method. In such method, the etchant can be a mixture of sulfur hexafluoride (SF6) gas and carbon tetrafluoride (CF4) gas.
It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Claims
1. A damascene interconnect structure, comprising:
- a substrate;
- a first dielectric layer on the substrate, the first dielectric layer comprising a plurality of sub-dielectric layers;
- a plurality of trenches formed in the first dielectric layer; and
- a plurality of metal lines filled in the trenches;
- wherein a plurality of air gaps are maintained between the metal lines and at least one of the sub-dielectric layers.
2. The damascene interconnect structure as claimed in claim 1, wherein the plurality of sub-dielectric layers comprises a first, a second, and a third sub-dielectric layers arranged in that order from bottom to top, and the air gaps are maintained between the metal lines and the second sub-dielectric layer.
3. The damascene interconnect structure as claimed in claim 2, wherein the first and the third sub-dielectric layers are silicon nitride layers, and the second sub-dielectric layer is a silicon oxide layer.
4. The damascene interconnect structure as claimed in claim 2, wherein the first, the second, and the third sub-dielectric layers are silicon nitride layers, and a density of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer.
5. The damascene interconnect structure as claimed in claim 2, wherein the first, the second, and the third sub-dielectric layers are silicon oxide layers, and a density of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer.
6. The damascene interconnect structure as claimed in claim 1, further comprising a capping layer and a second dielectric layer, the capping layer covering the first dielectric layer and the metal lines, and the second dielectric layer covering the capping layer.
7. The damascene interconnect structure as claimed in claim 2, wherein material of the metal lines is at least one of copper, silver, aluminum, and an alloy comprising any one or more of copper, aluminum and silver.
8. A method for fabricating a damascene interconnect structure, the method comprising:
- providing a substrate;
- depositing a multilayer dielectric film on the substrate;
- forming a patterned photoresist on the multilayer dielectric film;
- etching the multilayer dielectric film to form a plurality of trenches, a portion of each of the trenches having an enlarged width at each of sidewalls thereof;
- filling the trenches with conductive metal to form conductive lines such that air is trapped in extremities of the enlarged width portions of the trenches.
9. The method for fabricating a damascene interconnect structure as claimed in claim 8, wherein the conductive metal filled in the trenches is formed by means of physical vapor deposition.
10. The method for fabricating a damascene interconnect structure as claimed in claim 8, wherein the multilayer dielectric film comprises a first, a second, and a third sub-dielectric layer, and the air is trapped between the second sub-dielectric layer and the conductive lines.
11. The method for fabricating a damascene interconnect structure as claimed in claim 10, wherein the first and the third sub-dielectric layer are silicon nitride layers, and the second sub-dielectric layer is a silicon oxide layer.
12. The method for fabricating a damascene interconnect structure as claimed in claim 10, wherein all three sub-dielectric layers are silicon nitride layers or silicon oxide layers, and a deposition rate of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer.
13. The method for fabricating a damascene interconnect structure as claimed in claim 8, wherein the multilayer dielectric layer is etched by a wet etching method.
14. The method for fabricating a damascene interconnect structure as claimed in claim 13, wherein an etchant of the wet etching method is a mixture of hydrogen fluoride and ammonium fluoride.
15. The method for fabricating a damascene interconnect structure as claimed in claim 8, wherein the multilayer dielectric layer is etched by a dry etching method.
16. The method for fabricating a damascene interconnect structure as claimed in claim 15, wherein an etchant of the dry etching method is a mixture of sulfur hexafluoride and carbon tetrafluoride.
17. The method for fabricating a damascene interconnect structure as claimed in claim 8, further comprising forming a capping layer covering the multilayer dielectric layer and the conductive lines, and forming a dielectric layer on the capping layer.
18. The method for fabricating a damascene interconnect structure as claimed in claim 8, wherein material of the conductive lines is at least one of copper, aluminum, silver, and an alloy comprising any one or more of copper, aluminum and silver.
Type: Application
Filed: Nov 27, 2007
Publication Date: May 29, 2008
Applicant:
Inventor: Shuo-Ting Yan (Miao-Li)
Application Number: 11/998,030
International Classification: H01L 23/52 (20060101); H01L 21/4763 (20060101);