Coating processes – Direct application of electrical – magnetic – wave – or... – Chemical vapor deposition
Reexamination Certificate
1999-11-03
2001-09-25
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Chemical vapor deposition
C427S140000, C427S255395, C427S374100, C427S398100, C427S402000
Reexamination Certificate
active
06294228
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for forming a thin film on a substrate, and more particularly to a method and apparatus for forming a desired thin film on a substrate by using a chemical vapor deposition (i.e., CVD) process.
2. Description of the Related Art
In manufacturing a semiconductor device typified by LSI devices (i.e., Large Scale Integrated circuits), memories, microprocessors and like devices, it is necessary to form various types of thin films on the same substrate of a semiconductor. In general, these thin films comprise various types of insulation films and conductive films. The insulation films comprise: a silicon nitride (i.e., Si
3
N
4
) film serving as an oxidation-resistant mask film used in forming a dielectric isolation film in an LSI device of MOS (i.e., Metal Oxide Semiconductor) type; and, an insulation film formed of a silicon oxide film, which serves as a surface protection film or the like. On the other hand, as for the above-mentioned conductive films, they comprise: a polysilicon film serving as gate wirings, or the like ; and, a tungsten film serving as contact plugs or the like in realizing a so-called multilevel interconnection or metallization.
As a method for forming the above-mentioned thin films, heretofore widely used is an LPCVD (i.e., Low Pressure Chemical Vapor Deposition) process. In this LPCVD process, a reactor furnace having received a semiconductor substrate (which is a workpiece) is reduced in pressure in its atmosphere. Under such a reduced pressure in the atmosphere of the reactor furnace, a reactant gas is introduced into the reactor furnace to form a desired thin film on the workpiece or semiconductor substrate. In comparison with an NPCVD (i.e., Normal Pressure Chemical Vapor Deposition) process, the LPCVD process is superior to the NPCVD process in that: the former process is less in consumption of the reactant gas than the latter process; the former process may form the thin film at a relatively low temperature, which is lower than that used in the latter process; and, the former process is superior to the latter process in uniformity of film thickness of its product (i.e., thin film) or in covering properties of the thus formed thin film.
Further, as for an LPCVD unit used in the LPCVD process, though a horizontal type of the LPCVD unit was employed during the early stages, recently a vertical type of the LPCVD unit has been widely employed since the vertical type is improved: in easiness in control of the reactant gas in flow; in uniformity of heating the reactant gas; and, efficiency in chemical reaction of the reactant gas, in comparison with the horizontal type.
Now, a conventional method for forming a thin film will be described with reference to an example, in which a thin film is formed of a silicon nitride film serving as a major insulation film in the semiconductor device.
First, the LPCVD unit provided with a vertical type of a reactor furnace is arranged, wherein its reactor tube is made of quartz (i.e., SiO
2
). In the LPCVD process, the interior of this reactor tube is heated, and kept at a temperature of approximately 760° C., which is equal to a film-forming temperature of the silicon nitride film. Then, a jig carrying thereon a set of semiconductor substrates (which are workpieces) on each of which a thin film should be formed is loaded into the reactor furnace. After that, a plurality of reactant gases, for example such as dichlorosilane (i.e., SiH
2
Cl
2
) gas and ammonia (i.e., NH
3
) gas are introduced into the reactor tube to react with each other, so that a thin film, i.e., silicon nitride film is formed on each of the semiconductor substrates. Such film-forming process for forming the silicon nitride film on each of the semiconductor substrates is performed for a predetermined period of time, so that a desired silicon nitride film with a necessary film thickness is formed on each of the semiconductor substrates. After completion of formation of the desired silicon nitride film on each of the semiconductor substrates, the supply of the reactant gases is stopped to take out the jig from the reactor furnace. After the jig is taken out of the reactor furnace, then, the whole cycle in the above film-forming process is repeated with respect to a next new set of semiconductor substrates, which are carried out on another jig or the jig previously used and are loaded into the reactor tube together with the jig.
On the other hand, in the film-forming process described above, the silicon nitride film is formed not only on the surface of each of the semiconductor substrates but also on the surfaces of other members disposed inside the reactor furnace, for example such as an inner wall of the reactor tube, jig, and like members all disposed inside the reactor tube. The silicon nitride film formed on each of these members other than the semiconductor substrates forms an unnecessary thin film, formation of which is inevitable in any reactor furnace. Further, such unnecessary thin film or unnecessary silicon nitride film is accumulated to increase its film thickness particularly in the inner wall of the reactor tube when a plurality of the film-forming processes are performed in the same reactor tube. The unnecessary silicon nitride film thus accumulated on the reactor tube made of quartz differs in coefficient of thermal expansion from its substrate made of quartz, and is therefore subjected to stress due to the presence of a difference in thermal expansion coefficient, wherein the stress gradually increases as the film thickness of the unnecessary silicon nitride film increases due to its accumulation through the plurality of the film-forming processes.
FIG. 17
shows a longitudinal sectional view of an essential part of the reactor furnace, illustrating the above phenomenon. In
FIG. 17
, for example, when the accumulated film thickness of the unnecessary silicon nitride film
53
formed on each of an outer tube
51
, inner tube
52
and like members disposed inside the reactor furnace exceeds a predetermined value, the unnecessary silicon nitride film
53
cracks of its self due to its own stress to produce a crack
54
together with contaminant particles
55
(i.e., fragments of the unnecessary silicon nitride film
53
itself), as shown in FIG.
18
. These contaminant particles
55
thus produced are naturally scattered, and fall on the surface of each of the semiconductor substrates to cause each of the semiconductor substrates to suffer from contamination (i.e., fall-on defects deposited on each of the semiconductor substrates).
FIG. 19
is a plan view of the surface of the semiconductor substrate
56
formed by the conventional method for forming the thin film, illustrating the contaminant particles
55
which are scattered from the unnecessary silicon nitride film
53
and now deposited on the surface of the semiconductor substrate. Each of the contaminant particles
55
shown in
FIG. 19
has a diameter of equal to or more than 200 nm. As is clear from
FIG. 19
, the contaminant particles
55
thus scattered and deposited on the surface of the semiconductor substrate
56
are concentrated in a peripheral area of the semiconductor substrate
56
. This is because the peripheral area of the semiconductor substrate
56
is disposed in the vicinity of the inner tube
52
of the reactor furnace.
FIG. 20
is a graph showing the relationship between: the batch process numbers (in the x-axis, i.e., abscissa); and, each of the number of contaminant particles (in the left-hand y-axis, i.e., ordinate) and the accumulated film thickness of the unnecessary thin film (in the right-hand y-axis, i.e., ordinate), according to the conventional method for forming the thin films.
In FIG.
20
: the reference letter “A” denotes the accumulated film thickness of the unnecessary thin film; “B” denotes the number of the contaminant particles; and, the reference letters “a”, “b” and “c” denote an upper (i.e., top), an intermediate (i.e., center) and a lo
McGinn & Gibb PLLC
NEC Corporation
Pianalto Bernard
LandOfFree
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