Organosilicon precursors for interlayer dielectric films...

Details Organosilicon precursors for interlayer dielectric films... Organosilicon precursors for interlayer dielectric films...

2001-08-31

2003-06-24

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

Reexamination Certificate

active

06583048

ABSTRACT:

BACKGROUND OF THE INVENTION
The electronics industry utilizes dielectric materials as insulating layers between circuits and components of integrated circuits (IC) and associated electronic devices. Line dimensions are being reduced in order to increase the speed and storage capability of microelectronic devices (e.g. computer chips). Microchip dimensions have undergone a significant decrease in the past decade such that line widths previously about 1 micron are being decreased to 0.18 micron with forecasts for as low as 0.10-0.05 in the next 5-10 years. As the line dimensions decrease, the requirements for preventing signal crossover (crosstalk) between chip components become much more rigorous. These requirements can be summarized by the expression RC, where R is the resistance of the conductive line and C is the capacitance of the insulating dielectric interlayer. C is inversely proportional to spacing and proportional to the dielectric constant (k) of the interlayer dielectric (ILD). Thus, shrinking the spacing requires a lower k to maintain an acceptable RC.
Historically, silica (SiO
2
) with a dielectric constant of 4.2-4.5 has been employed as the ILD. However, at line dimensions less than 0.18 microns, silica is no longer acceptable and an ILD with a k of 2.4-3.3 and below is needed.
Two general approaches to making a low k ILD are spin-on and chemical vapor deposition (CVD). Although both methods are capable of generating a low k ILD, CVD processes have the advantage of being able to utilize existing toolsets. Another advantage to CVD is simpler integration due to the silica-like structure of CVD-produced films compared to organic polymer films produced by some spin-on processes. CVD is also thought to have better conformality and gap filling capability than the spin-on method.
The current method of choice for dissociating or activating the reactive gases in a CVD chamber is by using a RF coupled plasma in a reaction zone above the substrate, such as that described in WO9941423. In plasma enhanced chemical vapor deposition (PECVD) the temperature required for the dissociation and deposition is typically between 100 and 400° C., which is generally lower than temperatures required for thermal CVD.
Conventional silica (SiO
2
) CVD dielectric films produced from SiH
4
or TEOS (Si(OCH
2
CH
3
)
4
, tetraethylorthosilicate) and O
2
have a dielectric constant k greater than 4.0. There are several ways in which industry has attempted to produce silica-based CVD films with lower dielectric constants, the most successful being the doping of the insulating film with carbon atoms, fluorine atoms, or organic groups containing carbon and fluorine. Carbon doped silica, having the general formula, Si
a
O
b
C
c
H
d
, (in which the atomic % of a+b+c+d=100%; a=10-35%, b=1-66%, c=1-35%, d=0-60%) will be referred to herein as organosilicate glass or OSG. Fluorine and carbon doped silica, having the general formula, Si
a
O
b
C
c
H
d
F
e
(wherein the atomic % of a+b+c+d+e=100% and a=10-35%, b=1-66%, c=1-35%, d=0-60%, and e=0.1-25%) will be referred to as F-OSG. The ratio and structural arrangement of carbon, silicon, oxygen, fluorine, and hydrogen atoms in the final ILD is dependent on the precursors chosen, the oxidant, and the CVD process conditions, such as RF power, gas flow, residence time, and temperature.
Doping the silica with carbon atoms or organic groups lowers the k of the resulting dielectric film for several reasons. Organic groups, such as methyl, are hydrophobic; thus, adding methyl or other organic groups to the composition can act to protect the resulting CVD deposited film from contamination with moisture. The incorporation of organic groups such as methyl or phenyl can also serve to “open up” the structure of the silica, possibly leading to lower density through space-filling with bulky CH
x
bonds. Organic groups are also useful because some functionalities can be incorporated into the OSG, and then later “burned out” or oxidized to produce a more porous material which will inherently have a lower k. The incorporation of voids or pores in a low dielectric constant material will result in reductions in the dielectric constant proportional to the amount of porosity. While this is beneficial, the amount of porosity incorporated into the film must be balanced with the deleterious effects that the introduction of pores will have on the mechanical properties of the film. Thus the optimum amount of porosity will be material dependant.
Doping the ILD with fluorine provides low polarizability, thus leading to lower k. Fluorine-containing organic groups such as CF
3
are very hydrophobic, so their presence will also serve to protect the silica from contamination with moisture.
While fluorinated silica materials have the requisite thermal and mechanical stability to withstand very high temperatures (up to 500° C.), the materials' properties (e.g., low water sorption, mechanical properties) are susceptible to being compromised when large amounts of fluorine are incorporated into the material. Fluorinated organic materials, such as poly(tetrafluoroethylene) despite having very low k values down to 2.0 or less, have not shown sufficient stability to the temperatures experienced during subsequent processing steps involved in the manufacture of an integrated circuit. Organic polymers in general do not possess sufficient mechanical strength for processing under current conditions. Also, fluorocarbon polymers can have other drawbacks such as poor adhesion, potential reaction with metals at high temperature, and poor rigidity at high temperature in some cases.
One way to incorporate carbon into an ILD is by using an organosilane such as methylsilanes (CH
3
)
x
SiH
4-x
as a silicon source in the PECVD reaction. WO9941423 and U.S. Pat. No. 6,054,379 describe the reaction of a silicon compound containing methyl groups and Si—H bonds with nitrous oxide (N
2
O) oxidant to give an SiOC film with a carbon content of 1-50% by atomic weight and a low dielectric constant.
U.S. Pat. No. 6,159,871 disclose methylsilanes (CH
3
)
x
SiH
4-x
(x is 1-4) as suitable CVD organosilane precursors to OSG low k films. Materials with 10-33% carbon content, by weight, and k less than 3.6 are reported.
An article by M. J. Loboda, et al., entitled “Deposition of Low-K Dielectric films using Trimethylsilane,” in
Electrochemical Soc. Proc.,
Vol. 98-6, pages 145 to 152, describes the use of trimethylsilane in a PECVD process to provide films with a k of 2.6 to 3.0.
Other patents describe the use of phenyl or vinyl containing organosilane precursors in producing dielectric films. For example, U.S. Pat. No. 5,989,998 discloses the preparation of PECVD low k films from, for example, (C
6
H
5
)
x
SiH
4-x
or (CH
2
═CH)
x
SiH
4-x
) (x is 1,2 or 3), and an oxidizing gas. WO 9938202 discloses dielectric films deposited from phenyl or methylsilanes with hydrogen peroxide as the oxidant and the addition of oxygen to aid in the association between the silicon compound and the oxidant.
WO 9941423 and EP 0935283 A2 disclose siloxanes such as H(CH
3
)
2
SiOSi(CH
3
)
2
H, (CH
3
)
3
SiOSi(CH
3
)
3
, and cyclic (—OSiH(CH
3
)—)
4
as precursors for PECVD produced OSG films.
Silyl ethers (alkoxysilanes) have also been disclosed as precursors for dielectric films. EP 0935283 A2 discloses methoxy and ethoxysilanes, such as (CH
3
)
2
Si(OCH
3
)
2
and (CH
3
)(C
6
H
5
)Si(OCH
3
)
2
. U.S. Pat. No. 6,086,952 discloses a method of forming thin polymer layers by blending reactive p-xylylene monomers with one or more comonomers having silicon-oxygen bonds and at least two pendent carbon-carbon double bonds, such as tetraallyloxysilane.
U.S. Pat. No. 6,171,945 discloses a process in which organosilanes with “labile” ligands, such as formyl or glyoxyl groups, are reacted with a peroxide compound at the surface of the substrate, and are subsequently removed by annealing to provide a porous ILD.
U.S. Pat. No. 6,054,206 d

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