Fluorine-containing materials and processes

Details Fluorine-containing materials and processes Fluorine-containing materials and processes

2001-04-24

2002-10-01

Sherry, Michael (Department: 2829)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

Reexamination Certificate

active

06458718

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods for making fluorine-containing materials, and more particularly to methods for depositing such materials onto substrates using chemicals that contain carbon atoms and fluorine atoms.
2. Description of the Related Art
As the dimensions of microelectronic devices become smaller, the importance of the physical properties of the materials used in their manufacture becomes more important. This is particularly true of the dielectric materials that are used to insulate metal lines and vias from one another because of the contributions to parasitic capacitance across insulators between closely spaced conductors. Silicon dioxide has been employed within the industry as a dielectric material for the manufacture of devices for nearly three decades, but may become less suitable in the future because of its relatively high dielectric constant (k~4.1).
A number of fluorinated materials have been studied as possible replacements for silicon dioxide. U.S. Pat. No. 5,563,105 discloses a chemical vapor deposition (CVD) process employing SiF
4
and tetraethoxysilane (TEOS) to form a fluorosilicate glass, which is stated to have lower water absorption than a sample formed from C
2
F
6
. U.S. Pat. No. 5,703,404 discloses silicon oxide films containing Si-F bonds through the use of fluorosilanes. U.S. Pat. No. 5,876,798 discloses the use of fluorotriethoxysilane (FTES). U.S. Pat. No. 5,244,698 discloses PECVD deposition using organosilanes and organohalogenosilanes. The use of fluorinated compounds containing carbon-carbon double bonds is disclosed in U.S. Pat. Nos. 5,989,998. 6,051,321 discloses the use of fluorinated aromatic compounds. U.S. Pat. No. 5,900,290 discloses the use of octafluorocyclobutane, as does T. Shirafuji et al., “PE-CVD of Fluorocarbon/SiO Composite Thin Films Using C
4
F
8
and HMDSO,” Plasmas and Polymers, Vol. 4, No. 1, p. 57 (1999). Other references in this regard are Indrajit Banerjee, et. al., “Characterization of Chemical Vapor Deposited Amorphous Fluorocarbons for Low Dielectric Constant Interlayer Dielectrics.” J. Electrochem. Soc., Vol. 146(6), p. 2219 (1999); C. B. Labelle, et. al., DUMIC, pg. 1998 (1997); Sang-Soo Han, et. al., “Deposition of Fluorinated Amorphous Carbon Thin Films as a Low-Dielectric Constant Material.” J. Electrochem. Soc., Vol. 146(9), p. 3383 (1999); and Scott J. Limb, “Growth of fluorocarbon polymer thin films with high CF
2
fractions and low dangling bond concentrations by thermal chemical vapor deposition,” Appl. Phys. Lett., Vol. 68(20), p. 2810 (1996).
Spin-on processes are also known for making low-k films. These processes generally involve dissolving or dispersing a low-k polymer in a solvent to form a liquid coating mixture, depositing the coating mixture onto a substrate, spinning the substrate to create a uniform coating, then drying the coating to remove the solvent. Another known method for reducing the dielectric constant of a film is to introduce porosity into the film.
A wide variety of fluorinated polymers such as polytetrafluoroethylene (PTFE) are known. PTFE materials generally have low dielectric constants but are structurally based upon long, uncrosslinked chains. The uncrosslinked structure of these materials is likely the source of the mechanical instabilities that have been observed during attempts to integrate them into microelectronic devices. Current spin-on processes face a serious challenge in attempting to crosslink PTFE because they are typically produced using nanoemulsions of PTFE particles that are delivered to the substrate in solution. These particles are typically five to twenty nanometers in size and thus represent relatively large building blocks for the deposition of thin film materials, resulting in problems with step coverage. Furthermore, because these films are formed from particles, they often require adhesion promoters to obtain adherent films. Current CVD PTFE materials are typically deposited using plasma-enhanced chemical vapor deposition (PECVD) of mixtures of CF
4
and CH
4
. It is believed that the deposited materials result from reactive C-F species derived from partially ionized source gas molecules. Typical C-F species are believed to be CF
4
+
, CF
3
+
, CF
2
2+
and very limited amounts of CF
3+
, and thus represent a broad range of source species for the deposition of the film. Coupled with ion bombardment of the depositing film, this can lead to non-homogeneous film composition and properties, including dangling bonds, as well as to the incorporation of undesirable impurities within the depositing film. Furthermore, because of the charged nature of the species being used to deposit these materials, gap-filling of dimensionally small, high aspect ratio structures can be poor and loading effects between large and small open areas on the wafer surface can be problematic.
There remains a need for fluorinated materials such as low-k films having better properties more suitable for use in microelectronics manufacturing, and for processes for producing such films that can be readily integrated into fabrication process flows.
SUMMARY OF THE INVENTION
The inventor has discovered better ways to make fluorinated materials. In preferred embodiments, these fluorinated materials have a low dielectric constant suitable for use in microelectronics manufacturing. In one aspect, chemical precursors that contain one or more —CF
3
(trifluoromethyl) groups are disclosed, and processes for using these precursors to deposit fluorine-containing materials onto substrates are taught. In another aspect, mixtures of chemical precursors with sources of various elements are used to deposit fluorine-containing materials onto substrates. In yet another aspect, processes for making porous fluorinated materials are taught.
In one embodiment, a process is provided for depositing a material onto a surface, comprising providing a substrate; providing a chemical precursor of the formula (F
3
C)
4−m−n
MX
m
R
n
, wherein M is Si or Ge; X is halogen; R is H or D; m is 0, 1, 2 or 3; and n is 0, 1, 2, or 3; with the proviso that (m+n)≦3; and activating the chemical precursor to thereby deposit a fluorine-containing material onto the substrate.
In another embodiment, a chemical vapor deposition process is provided for depositing a dielectric film onto a surface, comprising providing a chemical vapor deposition chamber having disposed therein a substrate; introducing a gas to the chamber, wherein the gas comprises a chemical precursor selected from the group consisting of (F
3
C)SiH
3
, (F
3
C)
2
SiH
2
, (F
3
C)SiD
3
, (F
3
C)
2
SiD
2
, (F
3
C)SiF
2
H, (F
3
C)SiF
3
, (F
3
C)SiFD
2
, and (F
3
C)SiF
2
D; and reacting the chemical precursor to deposit onto the substrate a film having a dielectric constant of about 2.7 or lower.
In yet another embodiment, a process for making a porous material is provided, comprising providing an oxygen source; providing a compound of the formula (F
3
C)
4−m−n
MX
m
R
n
, wherein M is Si or Ge; X is halogen; R is H or D; m is 0, 1, 2 or 3; and n is 0, 1, 2, or 3; with the proviso that (m+n)≦3; providing a substrate; activating the oxygen source and the compound at a temperature of about 300° C. or less to thereby deposit an oxygen-containing film onto the substrate; and heating the oxygen-containing film to a temperature in the range of about 150° C. to about 400° C. to form a porous film.
These and other embodiments are described in greater detail below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A wide variety of fluorine-containing materials can be prepared by practicing the processes described herein. “Fluorine-containing material” is used in its usual sense to include materials that contain the element fluorine as part of their chemical structure. The fluorine atoms can be incorporated into the material in various ways, preferably by ionic or covalent bonds, and can be dispersed homogeneously or non-homogeneously. Preferably, fluor

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