Process gas distribution for forming stable fluorine-doped...

Details Process gas distribution for forming stable fluorine-doped... Process gas distribution for forming stable fluorine-doped...

1999-07-27

2002-05-07

Ghyka, Alexander G. (Department: 2812)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S787000, C438S788000

Reexamination Certificate

active

06383954

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for substrate processing. More particularly, the present invention relates to an apparatus and a method for improved process gas distribution forming a variety of films including fluorosilicate glass (FSG) films.
One of the primary steps in the fabrication of modem semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. Plasma enhanced CVD processes promote the excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive species. The high reactivity of the released species makes the process condition window for deposition larger than in thermal processes.
In one design of plasma CVD chambers, a vacuum chamber is generally defined by a planar substrate support, acting as a cathode, along the bottom, a planar anode along the top, a relatively short sidewall extending upwardly from the bottom, and a dielectric dome connecting the sidewall with the top. Inductive coils are mounted about the dome and are connected to a source radio frequency (SRF) generator. The anode and the cathode are typically coupled to bias radio frequency (BRF) generators. Energy applied from the SRF generator to the inductive coils forms a plasma within the chamber. Such a chamber is referred to as a high density plasma CVD (HDP-CVD) chamber.
In some HDP-CVD chambers and in other types of chambers, it is typical to mount two or more sets of equally spaced gas distributors, such as nozzles, to the sidewall such that the nozzles extend into the region above the edge of the substrate support surface. The gas nozzles for each set are coupled to a common manifold for that set; the manifolds provide the gas nozzles with process gases.
In one substrate processing chamber of this type, the nozzles have different lengths depending on the type of gas injected into the chamber through the nozzle. For example in this chamber, in some undoped silicate glass (USG) deposition processes using a process gas including silane (SiH
4
) and molecular oxygen (O
2
), precise amounts of silane are injected into the chamber with large amounts of oxygen so that enough oxygen exists to react with all the silane. Because so much oxygen exists, and often fills the chamber, it is commonly believed that the oxygen nozzle lengths do not affect the USG process significantly. In fact, for such a process, some chambers do not use nozzles at all to introduce oxygen but instead leak the oxygen into the chamber through holes in the chamber wall or walls.
In another type of substrate deposition chamber, it has been proposed to include multiple gas injection nozzles with some nozzles being on different levels from (e.g., above or below) other nozzles. It has also been proposed in these chambers that nozzles on higher levels extend further into the deposition chamber to aid in deposition uniformity.
In both the above described chambers and in other chambers, some gases may be injected together through common nozzles. Typically, gases that are injected together through common nozzles include gases that are not likely to react, or that react slowly enough during the delivery, with each other. For example, in deposition of the USG layer referred to above it is common to mix an inert gas such as helium or argon with either oxygen or silane prior to introducing those gases into the chamber.
Halogen-doped silicon oxide layers, and fluorine-doped silicate glass (FSG) layers in particular, are becoming increasingly popular in a variety of applications due to the low dielectric constants achievable for these films which are lower than the dielectric constants of USG films and their excellent gap-fill properties, especially for high speed semiconductor devices with increasingly smaller features sizes. In the deposition of FSG layers, it is common to use SiF
4
as the fluorine source since SiF
4
provides both Si and F species for fluorine-doped silicon oxide (SiOF). Other suitable gases include SiH
2
F
2
and NF
3
. SiF
4
can be introduced in the chamber separately from the other source gases, such as O
2
and SiH
4
, but it would increase the complexity and cost of the system by requiring separate gas distribution apparatus. The need for additional gas injection nozzles inside the chamber would render the chamber less robust and make it more difficult to obtain process repeatability. Thus, it is common to mix the fluorine source with other gases that are chemically comparable (e.g., with the oxygen source) prior to introducing the gases into the chamber.
The fluorine source can also be mixed with a separate silicon source gas (e.g., SiH
4
, SiCl
4
, SiCH
6
, or SiC
3
H
10
) and injected from the same nozzle, but it will generate a relatively nonuniform film due to a more localized concentration of silicon source feeding. Fluorine is known to have a relatively long residence time. Thus, like oxygen, it is commonly believed that the length of the nozzle used to introduce a fluorine source into the chamber is not particularly important. It is commonly believed that the introduced fluorine will be distributed throughout the chamber because of its relatively long residence time.
Thus, for reasons discussed above, known deposition techniques currently used that employ separate silicon, oxygen and fluorine sources combine the fluorine source and oxygen source and flow the combination into the CVD chamber through relatively short nozzles while the separate silicon source (e.g., SiH
4
) is introduced (flowed) through longer nozzles. FSG films deposited in such a manner have physical properties acceptable for many applications. For some applications, however, improved deposition techniques are desirable.
SUMMARY OF THE INVENTION
The present invention is directed toward an improved substrate processing chamber having an improved process gas delivery system. The improved system is particularly applicable to the deposition of FSG films using SiF
4
as a source of fluorine, but can also be used with many other processes. In part, the improvement is achieved by varying the length of the gas injection nozzles in a manner not previously known.
As described above, it was commonly thought that the length of the nozzles used to introduce a fluorine source into a substrate processing chamber for the formation of an FSG film was not particularly important because fluorine has a relatively long residence time in most chemical deposition chambers. The present inventors, however, discovered that this conventional thinking may result in the deposition of FSG layers having less than optimal properties in some instances. Specifically, the present inventors discovered that nozzle length affects the stability of FSG layers deposited from fluorine sources such as SiF
4
in some processes. The inventors discovered that in addition to the uniform distribution of fluorine species across the substrate surface, that the uniform distribution of SiF
x
species (e.g., SiF, SiF
2
, SiF
3
) across the substrate surface helps create a stable FSG layer. When relatively short nozzles for the fluorine source are used, SiF
x
species are not distributed uniformly across the entire substrate surface. It is believed that the uneven distribution of SiF
x
species may result across the substrate surface. Thus, when SiF
x
species are formed near the orifices of the short nozzles, it is harder for the SiF
x
species to reach all areas of the wafer (e.g., the center). Instead, it is believed that the exhaust system pumps many of the SiF
x
species out of the chamber before they reach certain areas of the wafer, creating an uneven distribution of SiF
x
across the wafer with the center of the

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