Low dielectric constant materials and their production and use

Details Low dielectric constant materials and their production and use Low dielectric constant materials and their production and use

2002-04-12

2004-05-18

Metzmaier, Daniel S. (Department: 1712)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S245000, C427S380000, C427S387000, C106S287160, C524S858000, C556S465000, C556S466000, C556S482000, C556S484000, C528S010000

Reexamination Certificate

active

06737118

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to low dielectric constant materials such as insulating films (dielectrics) used between LSI element layers, etc., and to their production and use.
2. Description of the Related Art
With higher speeds and higher integration of LSI elements, signal delays are becoming an ever more serious problem. Signal delays are related to the product of the wiring resistance R and the capacity C between the wirings and between layers, and an effective means of minimizing delays involves lowering the wiring resistance while also reducing the relative dielectric constant of the interlayer dielectrics. By the year 2001, it is said that higher integration will result in wiring spacings of about 0.18 &mgr;m, thus requiring materials with a relative dielectric constant of less than 2.5.
Previously known methods form films as interlayer dielectrics by a spin-on-glass (SOG) process using sols prepared by hydrolyzing tetraalkoxysilanes. However, the molecular structures of materials fabricated in this fashion have absolutely no voids in their three-dimensional network structures of ≡Si—O—Si≡, and their relative dielectric constants have been as high as 4.0. Some methods proposed for lowering the relative dielectric constant involve CVD for formation of SiOF films, formation of organic material films, and porous film formation. The relative dielectric constant of SiOF reduces to about 3.3 as the F content increases, but higher moisture absorption with greater F content has been a problem. Organic materials are low dielectric constant materials with relative dielectric constants of down to about 2.2, but their problems include poor heat resistance and low adhesion to substrates. In organic SOG systems, introduction of organic groups into SiO
2
has been investigated to achieve lower density and lower the relative dielectric constant, but the limit is said to be about 2.7. On the other hand, porous materials have variable relative dielectric constants depending on the amount of pores, and they are therefore promising as materials offering relative dielectric constants lower than 2.5.
One example of a porous material has been reported where inorganic SOG is reacted with a silylating agent to form a film and then the silylating agent is heat treated to decomposition to introduce approximately 80-nm pores, by which the relative dielectric constant has been lowered to 2.3 [N. Aoi, Jpn. J. Appl. Phys. 36(1997) 1355]. This film, however, has an increase of about 13% in the dielectric constant due to moisture absorption in air, while the introduced pores are also large so that only an average of 2 pores are present in a gap of 0.18 &mgr;m between wiring, and thus film strength is therefore a problem.
Another example of a porous film is a fine porous xerogel film obtained by forming a film of a solution made from tetraethoxysilane as the starting material, aging it under a controlled atmosphere, performing solvent substitution with a low surface tension solvent, drying it in such a manner that the film does not contract upon evaporation of the solvent, and treating the surface with a silylating agent [Mat. Res. Soc. Symp. Proc. 443, 99(1997)]. However, the xerogel not only has a complicated fabrication process but strict control is necessary for each step in the process, and therefore lack of reproducibility for actual device fabrication is thought to be one of its drawbacks. The basic backbone of the film is composed of a SiO
4
tetrahedron. The backbone interior is composed of only the SiO
4
tetrahedron, but because of the organic groups introduced by the silylating agent, organic groups substitute for some of the oxygens of the SiO
4
tetrahedrons only around the pores and on the surface.
Films formed from hydrogenated silica fine particles with surface Si—H bonds and modified with hydrogen silsesquioxane (HSQ) have been reported as materials with relative dielectric constants of less than 2.5 [Muraguchi et al., 58th Symposium of the Association of Applied Physics, Lecture Summary No.2, 4p-K-7]. However, the heat resistance of Si—H is not very high, as escape of hydrogen begins from 400° C. and is marked at 450° C. and above. Once hydrogen is released, the moisture absorption of the film begins to increase. Since the annealing temperature for metal wiring in LSI processes is said to be 450° C., this film would be expected to pose a problem when applied to such processes.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide silica-based materials with low moisture absorption and a low dielectric constant, which can be applied for semiconductor elements and electrical circuit parts.
This object is achieved by the invention as described below.
1. A silica-based porous film having a three-dimensional network structure containing a siloxane skeleton comprising a SiO
4
tetrahedron structural unit, the silica-based porous film including on the surface and in the interior a backbone wherein at least one of the crosslinked oxygens of some or all of the SiO
4
tetrahedron structural units are replaced with organic groups, and having fine voids with an average size of no greater than 10 nm, preferably no greater than 5 nm, more preferably no greater than 2 nm, especially no greater than 1 nm the direct perimeters of which are surrounded with the backbone containing organic group-substituted tetrahedron structural units.
2. A silica-based porous film according to 1. above which includes in the three-dimensional network structure at least one element selected from the group consisting of B, Al, Ge, Ti, Y, Zr, Nb and Ta as an inorganic component in addition to Si and O.
3. A silica-based porous film according to 1. or 2. above, which contains at least a methyl group and/or phenyl group as the organic group.
4. A silica-based porous film according to any one of 1. to 3. above, which includes in the three-dimensional network structure at least one element selected from the group consisting of B, Al, Ge, Ti, Y, Zr, Nb and Ta as an inorganic component in addition to Si and O and which contains at least a methyl group and/or phenyl group as the organic group, wherein the molar ratio of the inorganic component element other than Si and O with respect to Si is from 0.005 to 0.15, and the molar ratio of the methyl group and/or phenyl group with respect to Si is from 0.6 to 1.5.
5. A silica-based porous film according to any one of 1. to 4. above, wherein the specific surface area according to BET is at least 100 m
2
/g and the contact angle of water is at least 90°.
6. A silica-based porous film according to 2. above, wherein the molecular structure of the main chain in the three-dimensional network structure includes at least one selected from among molecular structure (
1
): a ring structure, molecular structure (
2
): a structure wherein ring structure units including ladder-like structures and polyhedral structures are linked in two or three dimensions, and molecular structure (
3
): a linked chain structure which is crosslinked with at least two of the aforementioned structures and has no uncrosslinked ends.
7. A silica-based porous film according to 2. above, wherein the chemical structure of the terminal portion of the main chain in the three-dimensional network structure is —O—M′R′
1
R′
2
. . . R′
n−1
(where R′
1
, R′
2
. . . R′
n−1
are terminal groups and n is the valency of element M′), and the difference in electronegativity for all the bonded atom pairs of the M′R′
1
. . . R′
n−1
portion is no greater than 0.7.
8. A semiconductor device including a silica-based porous film according to any one of 1. to 7. above as an interlayer dielectric.
9. A process for production of a silica-based porous film, which comprises heat treating a silica-based film with at least two different organic groups bonded to Si having at least two different pyrolytic temperatures (T
1
, T
2
: T
1
>T
2

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