Method for producing hydrogenated silicon oxycarbide films having low dielectric constant

This invention pertains to a method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant. The method comprises reacting an methyl-containing silane in a controlled oxygen environment using plasma enhanced or ozone assisted chemical vapor deposition to produce the films. The resulting films are useful in the formation of semiconductor devices and have a dielectric constant of 3.6 or less.

FIELD OF THE INVENTION 
This invention pertains to a method for producing hydrogenated silicon 
oxycarbide (H:SiOC) films having low dielectric constant. The method 
comprises reacting a methyl-containing silane in a controlled oxygen 
environment using plasma enhanced or ozone assisted chemical vapor 
deposition to produce the films. The resulting films are useful in the 
formation of semiconductor devices. 
BACKGROUND OF THE INVENTION 
The use of chemical vapor deposition (CVD) to produce SiO.sub.2, SiNC or 
SiC thin films on semiconductor devices from silicon-containing materials 
is well known in the art. Chemical vapor deposition processes typically 
comprise introducing the gaseous silicon-containing material and a 
reactive gas into a reaction chamber containing the semiconductor 
substrate. An energy source such as thermal or plasma induces the reaction 
between the silicon-containing material and reactive gas thereby resulting 
in the deposition of the thin film of SiO.sub.2, SiNC or SiC on the 
semiconductor device. Plasma enhanced chemical vapor deposition (PECVD) is 
typically carried out at low temperatures (&lt;500.degree. C.) thereby making 
PECVD a suitable means for producing dielectric and passivation films on 
semiconductor devices. Silicon-containing materials include silane 
(SiH.sub.4), tetraethyl orthosilicate (TEOS), silacyclobutanes, and 
alkylsilanes such as trimethylsilane. 
The use of methyl-containing silanes to produce silicon dioxide 
(SiO.sub.2), amorphous SiNC and silicon carbide (SiC) films by chemical 
vapor deposition is known in the art. For example, U.S. Pat. No. 5,465,680 
to Loboda discloses a method for making crystalline SiC films. The method 
comprises heating the substrate 600.degree. C. to 1000.degree. C. and 
thereafter exposing the substrate to trimethylsilane in a standard 
chemical vapor deposition process. EP Patent Application No. 0 774 533 to 
Loboda discloses a method of making SiO.sub.2 coatings from the CVD of a 
reactive gas mixture comprising an organosilicon material and an oxygen 
source. EP Patent Application No. 0771 886 to Loboda discloses a method of 
making SiNC coating from the CVD of a reactive gas mixture comprising an 
organosilicon material and a nitrogen source. 
As semiconductor device structures become increasingly smaller the 
dielectric constant as well as the integrity of the film become important. 
Films produced by known CVD processes have high dielectric constants (i.e. 
3.8 or greater). Therefore there is a need for processes and materials 
that result in low dielectric constant films. A new deposition processes 
known as Low-k Flowfill.RTM., produces films having a dielectric constant 
of &lt;3.0. This method uses a chemical vapor deposition reaction between 
methylsilane and hydrogen peroxide to produce a methyl doped silicon oxide 
film (See S. McClatchie, K. Beekmann, A. Kiermasz; Low Dielectric Constant 
Oxide Films Deposited Using CYD Techniques, 1988 DUMIC Conference 
Proceedings, 2/98, p. 311-318). However, this process requires a non 
standard CVD system, the use of a lower stability oxygen source (hydrogen 
peroxide) and generates water as a by-product which can be undesirable in 
semiconductor devices. 
It is therefore an object of this invention to provide a method for 
producing low dielectric constant thin films of hydrogenated silicon 
oxycarbide by chemical vapor deposition. 
SUMMARY OF THE INVENTION 
This invention pertains to a method of producing thin films of hydrogenated 
silicon oxycarbide (H:SiOC) having low dielectric constants on substrates, 
preferably semiconductor devices. The method comprises the plasma enhanced 
or ozone enhanced chemical vapor deposition of a reaction mixture 
comprising an methyl-containing silane and an oxygen providing gas. By 
controlling the amount of oxygen available during the reaction/deposition 
process a film comprising hydrogen, silicon, carbon and oxygen is 
produced. These films typically have a dielectric constant of 3.6 or less 
and are particularly suited as interlayer dielectrics. 
DETAILED DESCRIPTION OF THE INVENTION 
This invention pertains to a method for producing hydrogenated silicon 
oxycarbide films on substrate, preferably semiconductor substrates. The 
method for producing the films comprises the chemical vapor deposition 
reaction of a reactive gas mixture comprising an alkysilane and an oxygen 
providing gas wherein the amount of oxygen present during the reaction is 
controlled. By "semiconductor substrate" it is meant it is meant to 
include silicon based devices and gallium arsenide based devices intended 
for use in the manufacture of a semiconductor components including focal 
plane arrays, opto-electronic devices, photovoltaic cells, optical 
devices, transistor-like devices, 3-D devices, silicon-on-insulator 
devices, super lattice devices and the like. Semiconductor substrates 
include integrated circuits preferably in the wafer stage having one or 
more layers of wiring or integrated circuits before the application of any 
metal wiring. 
The hydrogenated silicon oxycarbide films produced herein may be 
represented by the general formula Si.sub.w O.sub.x C.sub.y H.sub.z where 
w has a value of 10 to 33, preferably 18 to 20 atomic %, x has a value of 
I to 66, preferably 18 to 21 atomic percent, y has a value of 1 to 66, 
preferably 3 1 to 38 atomic % and z has a value of 0.1 to 60, preferably 
25 to 32 atomic %; and w+x+y+z=100 atomic %. 
The hydrogenated silicon oxycarbide films are produced from a reactive gas 
mixture comprising an methyl-containing silane and an oxygen providing 
gas. Methyl-containing silanes useful herein include methylsilane 
(CH.sub.3 SiH.sub.3), dimethylsilane ((CH.sub.3).sub.2 SiH.sub.2), 
trimethylsilane ((CH.sub.3).sub.3 SiH) and tetramethylsilane 
((CH.sub.3).sub.4 Si), preferably trimethylsilane. 
A controlled amount of oxygen is present in the deposition chamber. The 
oxygen may be controlled by the type of oxygen providing gas used, or by 
the amount of oxygen providing gas that is used. If too much oxygen is 
present in the deposition chamber a silicon oxide film with a 
stoichiometry close to SiO.sub.2 will be produced and the dielectric 
constant will be higher than desired. Oxygen providing gases include, but 
are not limited to air, ozone, oxygen, nitrous oxide and nitric oxide, 
preferably nitrous oxide. The amount of oxygen providing gas is typically 
less than 5 volume parts oxygen providing gas per volume part of 
methyl-containing silane, more preferably from 0.1 to 4.5 volume parts of 
oxygen providing gas per volume part of methyl-containing silane. One 
skilled in the art will be able to readily determine the amount of oxygen 
providing gas based on the type of oxygen providing gas and the deposition 
conditions. 
Other materials may be present in the reactive gas mixture. For example, 
carrier gases such as helium or argon, dopants such as phosphine or 
diborane, halogens such as fluorine or any other material that provides 
additional desirable properties to the film may be present. 
The reactive gas mixture is introduced into a deposition chamber containing 
a substrate, preferably an semiconductor substrate, wherein the reaction 
between the methyl-containing silane and oxygen providing gas is induced 
resulting in the deposition of a film on the substrate wherein the film 
comprises hydrogen, silicon, carbon and oxygen and has a dielectric 
constant of 3.6 or less on the substrate. Any chemical vapor deposition 
(CVD) method which has a substrate temperature of less than 500.degree. C. 
may be used herein. Temperatures greater than 500.degree. C. are typically 
not suitable for semiconductor substrates, in particular semiconductor 
substrates having aluminum wiring. Plasma enhanced chemical vapor 
deposition (PECVD) is preferred due to the low temperatures that can be 
used and wide use in the industry. Ozone enhanced CVD may be also be used 
herein. 
In PECVD the gas mixture is reacted by passing it through a plasma field. 
The plasmas used in such processes comprise energy derived from a variety 
of sources such as electric discharges, electromagnetic fields in the 
radio-frequency or microwave range, lasers or particle beams. Generally 
preferred in the plasma deposition processes is the use of radio frequency 
(10 kHz to 10.sup.2 MHz) or microwave (1.0 to 10 GHz) energy at moderate 
power densities (0.1 to 5 watts/cm.sup.2). The specific frequency, power 
and pressure, however are generally tailored to the equipment. Preferably 
the films are produced using PECVD at a power of 20 to 1000 W; a pressure 
of 1 to 10,000 mTorr; and a temperature of 25 to 500.degree. C. Confined, 
low pressure (1-5 mTorr) microwave frequency plasmas, often referred to as 
high density plasmas, can be combined with a RF frequency excitation in a 
process which helps planarize a varying surface topography during CVD 
growth. This process is useful in the formation of interlayer dielectrics. 
The films produced herein may be of varying thicknesses. Films having 
thicknesses of 0.01 to 10 .mu.m may be produced by the method of this 
invention. Preferably the films have a thickness of 0.5 to 3.0 .mu.m. 
One advantage to the instant method is that when nitrous oxide is used as 
the oxygen providing gas, the film composition and properties remain 
essentially the same even when the amount of nitrous oxide in the reactive 
gas mixture is significantly varied (1.2:1 to 4.5:1 volume parts N.sub.2 O 
to methyl-containing silane) 
Another advantage to the method of this invention is the ability to link 
successive growth processes to produce multilayer structures for example 
of SiO.sub.2 /H:SiOC/SiO.sub.2 or SiC:H/H:SiOC/SiC:H by increasing or 
deleting the oxygen providing gas at the appropriate time during the CVD 
process. It is preferred to produce discreet layers by stopping the 
reactive gas flow, adjusting the amount of oxygen providing gas and 
thereafter resuming the reactive gas flow to produce the next layer. 
The films produced herein, due to the low dielectric constant, are 
particularly suited as interlayer dielectrics in semiconductor integrated 
circuit manufacturing including, but not limited to, gate dielectrics, 
premetal and intermetal dielectrics and passivation coatings. The films 
produced herein have a dielectric constant of 3.6 or less, preferably, 3.2 
or less, more preferably 3.0 or less. 
EXAMPLES 
So that those skilled in the art can understand and appreciate the 
invention taught herein, the following examples are presented, it being 
understood that these examples should not be used to limit the scope of 
this invention found in the claims. 
In Examples 1-9 and Comparative Examples 1-2, dielectric properties were 
measured using metal-insulator-semiconductor (Examples 4-9) and 
metal-insulator-metal capacitors (Examples 1-3, Comparative Examples 1-2). 
Measurements were performed immediately after the metal gate deposition 
(top electrode) and again after one or more anneal cycles in N.sub.2 in 
the temperature range of 350 to 400.degree. C. Relative permittivity, K, 
was calculated from the capacitor geometry and the film thickness.