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FIELD OF THE INVENTION
This invention relates to a reaction chamber design and a method for
minimizing particle generation in a plasma-enhanced chemical vapor
deposition (CVD) reactor.
BACKGROUND OF THE INVENTION
CVD apparatus is conventionally used to form various thin films in a
semiconductor integrated circuit. Such CVD apparatus can form thin films
such as SiO.sub.2, Si.sub.3 N.sub.4, Si or the like with high purity and
high quality. In the reaction process of forming a thin film, a reaction
vessel in which semiconductor substrates are arranged can be heated to a
high temperature condition of 500.degree.-1000.degree. C. Raw material to
be deposited can be supplied to the vessel in the form of gaseous
constituents so that gaseous molecules are thermally dissociated and
combined in the gas and on the surface of the specimen so as to form a
thin film.
For instance, U.S. Pat. No. 4,962,727 ("the '727 patent") discloses a CVD
apparatus in which a silicon oxide film is formed. The '727 patent points
out, however, that silicon oxide molecules adhere to the inner wall
surface of the vessel and that the deposit may peel off and even adhere to
a wafer surface, thus causing defects in the SiO.sub.2 film being formed.
A plasma-enhanced CVD apparatus utilizes a plasma reaction to create a
reaction similar to that of the above-described CVD apparatus but at a
relatively low temperature in order to form a thin film. The plasma CVD
apparatus includes a specimen chamber, a gas introducing system, and an
exhausting system. For instance, such a plasma-enhanced CVD apparatus is
disclosed in U.S. Pat. No. 4,401,054, the disclosure of which is hereby
incorporated by reference. Plasma is generated in such an apparatus by a
microwave discharge through electron cyclotron resonance (ECR). A specimen
table is provided in the specimen chamber, and plasma generated in the
plasma formation chamber passes through a plasma extracting orifice so as
to form a plasma stream in the specimen chamber. The specimen table may
have a cooling mechanism in order to prevent a rise in temperature of the
specimen due to the plasma action.
A plasma apparatus using ECR for a CVD apparatus, an etching apparatus, a
sputtering apparatus or the like for manufacturing semiconductor
components is disclosed in U.S. Pat. No. 4,902,934, the disclosure of
which is hereby incorporated by reference. Such a plasma apparatus
includes a specimen mount in a reaction chamber with electrostatic chuck
means for holding a specimen (such as a silicon wafer) in good thermal
contact and in a vertical orientation. The specimen mount can also be
provided with cooling and heating means. In general, such reaction
chambers can be operated under vacuum conditions, and the plasma
generation chamber can be formed by walls which are water cooled.
Electrostatic chucking devices are disclosed in U.S. Pat. Nos. 3,993,509;
4,184,188; and 4,384,918, the disclosures of which are hereby incorporated
by reference. With such systems, a specimen or wafer is typically located
on a dielectric layer, and the wafer supporting surface of such
electrostatic chucking arrangements can be larger or smaller than the
specimen or wafer supported thereon.
The background of U.S. Pat. No. 4,709,655 ("the '655 patent") discloses
that reaction chambers employed for chemical vapor deposition are
generally classified as cold-wall or as hot-wall systems. The '655 patent
further discloses that in the cold-wall systems, the substrate (wafer) can
be heated by inductive coupling, radiant heating, or direct electrical
resistance heating of internal support elements. The '655 patent states
that when the wafers are mounted on a susceptible material adapted for
heating by RF energy, heat is localized to the immediate semiconductor
wafer area so that 1) chemical vapor deposition is limited to the heated
areas, and 2) the unheated walls are below CVD temperatures thereby
reducing depositions on the walls. In plasma-enhanced CVD reactors,
however, deposition of a film will occur even on cold walls since heat in
the plasma will cause a reaction no matter what the temperature of the
reaction surface.
A problem with plasma-enhanced CVD apparatus is that deposits are formed on
the wafer and all other surfaces inside the reaction chamber. The
deposited film can crack and flake off, resulting in particles on the
wafer. Oxide films have inherent stresses as deposited. The energy in the
film increases as the film thickness increases. Differential thermal
expansion between the deposited film and base material adds additional
stress. Although it is known in the art to dry etch deposition surfaces in
a reaction chamber, as disclosed by U.S. Pat. No. 4,910,042, there exists
a need in the art for improving integrity and adhesion of deposited films
to surfaces in the reaction chamber, especially line-of-sight surfaces and
specimen surrounding surfaces. The term "line-of-sight surfaces" as used
herein means surfaces from which a straight line can be drawn directly to
a specimen mounted in the reaction chamber. The term "specimen surrounding
surfaces" as used herein means surfaces surrounding the specimen mounted
in the reaction chamber and which are directly contacted by a plasma
stream. The term "specimen" as used herein means any semiconductor
substrate, such as a wafer of silicon or other material, having a flat or
uneven surface onto which a film is formed by a plasma reaction.
SUMMARY OF THE INVENTION
The invention provides a method and apparatus for minimizing particle
generation in CVD reactors to thereby improve the quality of a film
deposited on a specimen. In particular, the invention allows the
deposition quality of line-of-sight and specimen surrounding surfaces to
be controlled. By controlling the deposition quality of line-of-sight and
specimen surrounding surfaces, the adhesion of a film formed thereon
during a depositing step and the integrity of the film can be improved.
According to one aspect of the invention, the line-of-sight and specimen
surrounding surfaces are maintained at a substantially constant
temperature during the depositing step, thereby minimizing stresses in the
deposited film caused by differential thermal expansion. For instance, the
line-of-sight and specimen surrounding surfaces can be maintained at
substantially ambient temperature whereby thermal expansion of a deposited
film can be avoided even when the equipment is not in use or is being
serviced. According to another aspect of the invention, the geometry of
the line-of-sight and specimen surrounding surfaces is controlled so the
surfaces are substantially smooth, continuous surfaces which are free of
edges which generate stress in the deposited film. A further feature of
the invention is the use of a material for the line-of-sight and specimen
surrounding surfaces which enhances adhesion of the deposited film.
The apparatus of the invention includes a plasma shield and a specimen
surrounding surface. The plasma shield comprises a member having a
line-of-sight surface thereon. The member includes means for controlling
the deposition quality of the line-of-sight surface to improve the
adhesion of a film formed thereon when the plasma shield is mounted in a
reaction chamber of a plasma-enhanced CVD apparatus and a film is
deposited on a specimen in the reaction chamber as a result of a reaction
with plasma gas. The member further includes means for mounting the member
in a plasma-enhanced CVD apparatus so that a plasma reaction region is
located between the line-of-sight surface and a specimen mounted for
treatment in the reaction chamber.
In a preferred embodiment, the plasma shield comprises a member having a
plasma extracting bore extending therethrough, the bore being defined by a
line-of-sight surface on the member. Regulating means is provided for
maintaining the line-of-sight surface at a substantially constant
temperature. The member also includes means for mounting the member in a
chemical vapor deposition apparatus so that plasma passes from a plasma
chamber, through the bore and into a reaction chamber of the apparatus.
The member can include a horn extending from an outlet end of the bore.
The member can also include gas ejection means for ejecting gas into the
bore, the gas ejection means comprising a plurality of orifices spaced
apart in a circumferential direction around the member. The orifices can
be oriented such that the gas is ejected in a downstream direction with
respect to the direction of movement of plasma through the bore. The horn
can also include cut-out means extending radially through an outer
periphery of the horn for allowing a specimen to be moved therethrough.
The specimen surrounding surface comprises a member having a specimen
surrounding surface which comes into contact with a plasma gas when the
specimen surrounding surface is mounted in a reaction chamber of a
plasma-enhanced CVD apparatus. The member includes means for controlling
deposition quality of the specimen surrounding surface to improve adhesion
of a film formed thereon when the specimen surrounding surface is mounted
in the reaction chamber and a film is deposited on a specimen mounted on a
specimen-supporting surface in the reaction chamber as a result of a
reaction with plasma gas. The member further includes means for mounting
the member in the reaction chamber so that the specimen surrounding
surface surrounds the specimen-supporting surface and so that the member
does not thermally affect a temperature of the specimen-supporting surface
when the plasma gas contacts the specimen surrounding surface and the
specimen-supporting surface.
In a preferred embodiment, the specimen surrounding surface comprises a
member having a specimen surrounding surface which comes in direct contact
with a plasma stream. Regulating means is provided for maintaining the
specimen surrounding surface at a substantially constant temperature. The
member includes means for mounting the member in a reaction chamber of a
CVD apparatus so that the specimen surrounding surface surrounds a
specimen-supporting surface in the reaction chamber and so that the member
does not thermally affect a temperature of the specimen-supporting surface
when a plasma stream simultaneously contacts the specimen surrounding
surface and the specimen-supporting surface.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described with reference to the accompanying
drawing, in which:
FIG. 1a shows one embodiment of a plasma-enhanced CVD apparatus in
accordance with the invention;
FIG. 1b shows another embodiment of a plasma-enhanced CVD apparatus in
accordance with the invention;
FIG. 2 shows a plasma shield in accordance with the invention;
FIG. 3 shows a modification of the plasma shield shown in FIG. 2;
FIG. 4 shows a front view of a gas ejection ring in accordance with the
invention;
FIG. 5 shows a cross-section taken along line V--V in FIG. 4;
FIG. 6 shows a cross-section taken along line VI--VI in FIG. 4;
FIG. 7 shows a front view of a specimen surrounding surface in accordance
with the invention;
FIG. 8 shows a side view of the specimen surrounding surface shown in FIG.
7;
FIG. 9 is a bottom view of the specimen surrounding surface shown in FIG.
7;
FIG. 10 is a cross-section of part of the specimen surrounding surface
shown in FIG. 8;
FIG. 11 is a front view of part of a specimen surrounding surface according
to another embodiment of the invention;
FIG. 12 is a side view of the part shown in FIG. 11;
FIG. 13 is a front view of the second part of the specimen surrounding
surface shown in FIG. 11; and
FIG. 14 is a side view of the part shown in FIG. 13.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a method and apparatus for improving the adhesion
and the integrity of a deposited film on line-of-sight and specimen
surrounding surfaces in a plasma-enhanced CVD apparatus. In particular,
deposition quality of line-of-sight and specimen surrounding surfaces can
be controlled in accordance with the invention.
According to one aspect of the invention, the line-of-sight and specimen
surrounding surfaces are maintained at a substantially constant
temperature during a step of depositing a film on a specimen such as a
silicon specimen. As a result, differential thermal expansion between the
deposited film and the base material is avoided, thereby minimizing
stresses in the deposited film. By improving the adhesion of the film, the
deposited film is less likely to crack and flake off, thereby minimizing
particle generation and reducing the amount of particles on the specimen.
According to another aspect of the invention, the geometry of the
line-of-sight and specimen surrounding surfaces is controlled to eliminate
edges which would generate stress in the deposited film. According to a
further aspect of the invention, the line-of-sight and specimen
surrounding surfaces are formed of a material which provides strong
adhesion to the deposited film.
The line-of-sight and specimen surrounding surfaces can be maintained at
any substantially constant temperature. According to a preferred
embodiment, however, these surfaces are maintained at ambient temperature.
As a result, when the apparatus is not in use or being serviced, such that
the surfaces in the reaction chamber are at ambient temperature,
differential thermal expansion of the film and of the line-of-sight and
specimen surrounding surfaces is minimized. Alternatively, the
line-of-sight and specimen surrounding surfaces can be maintained at an
elevated temperature, such as at least 300.degree. C. However, these
surfaces could also be maintained at a temperature below ambient
temperature.
According to a further aspect of the invention, the line-of-sight and
specimen surrounding surfaces can be conditioned prior to the depositing
step. The conditioning step comprises eliminating adsorbed layers on the
line-of-sight and specimen surrounding surfaces which tend to reduce
adhesion of the film thereon. For instance, the conditioning step can
comprise contacting these surfaces with oxygen plasma, argon plasma, or a
combination of oxygen and argon plasma.
According to the invention, it has been determined that SiO.sub.2 film has
good adhesion to bare aluminum. Accordingly, the line-of-sight and
specimen surrounding surfaces can comprise exposed aluminum surfaces in
order to obtain good adhesion of the first deposited film. In addition,
before each deposition, oxygen or argon or a combination of oxygen and
argon plasma can be used to condition the line-of-sight and specimen
surrounding surfaces. It is believed that such a conditioning treatment
eliminates adsorbed layers which tend to reduce film adhesion.
According to another aspect of the invention, specially designed components
are provided for improving the quality of a film deposited on a specimen.
According to one feature of the invention, such components include
regulating means for maintaining the line-of-sight and specimen
surrounding surfaces at a substantially constant temperature. According to
a second feature of the invention, sharp edges and corners are avoided in
the line-of-sight and specimen surrounding surfaces. According to a third
feature of the invention, these surfaces can be made of a material, such
as exposed aluminum, which provides strong adhesion of the deposited film.
By combining two or all three of these features, it is possible to
maximize film integrity and adhesion to the line-of-sight and specimen
surrounding surfaces.
The regulating means can be used to limit thermal cycling of the
line-of-sight and specimen surrounding surfaces to .+-.5.degree. C. during
thermal cycling of the CVD apparatus due to plasma on/off cycles. For
instance, the regulating means can comprise fluid passages in components
having line-of-sight and specimen surrounding surfaces to maintain such
surfaces at room temperature, thereby limiting thermal cycling to ambient
temperature when removing parts from the apparatus. Alternatively, these
surfaces can be maintained at a high temperature of
300.degree.-400.degree. C. Furthermore, such surfaces can comprise exposed
surfaces of aluminum or aluminum alloys, nickel or nickel alloys,
stainless steel or molybdenum. Such surfaces can also be provided with
different surface treatments, such as a sandblasted surface finish.
FIG. 1a shows plasma-enhanced ECR CVD apparatus 1 in accordance with one
embodiment of the invention. As shown, treated surface S of a
semiconductor specimen is held in a vertical orientation on
specimen-supporting surface 5 located in reaction chamber 3.
Specimen-supporting surface 5 is movable in a horizontal direction toward
and away from plasma chamber 2. Plasma generated in plasma chamber 2
passes through aperture 4 in a plasma aperture ring and forms a plasma
reaction region adjacent specimen-supporting surface 5.
According to one aspect of the invention, plasma shield 6 is provided which
includes at least one line-of-sight surface located inwardly from the
inner walls of reaction chamber 3 such that the plasma reaction region is
between the line-of-sight surface on plasma shield 6 and a specimen
mounted for treatment in the reaction chamber. If the plasma shield is
omitted, the inner walls of reaction chamber 3 include line-of-sight
surfaces 3a from which a straight line can be drawn directly to the
treated surface of the semiconductor specimen.
Plasma shield 6 shown in FIG. 1a has a bore therethrough. However, the
line-of-sight surface could be provided on a plasma shield which does not
include such a bore. Also, plasma chamber 2 could be omitted, and the
plasma could be generated in another manner. For instance, the specimen
holder could include means for generating the plasma. In such a case, the
line-of-sight surface could be located closely adjacent the plasma
reaction region. It would be advantageous, however, to minimize the area
of the line-of-sight surface to facilitate cleaning thereof by sputtering
treatment.
FIG. 1b shows another embodiment of a plasma-enhanced ECR CVD apparatus 1a
in accordance with the invention. In this case, treated surface S of a
semiconductor specimen is held in a horizontal orientation on
specimen-supporting surface 5. The specimen-supporting surface is movable
in a vertical direction toward and away from plasma chamber 2. As in the
embodiment shown in FIG. la, plasma generated in plasma chamber 2 passes
through aperture 4 of a plasma aperture ring and forms a plasma reaction
region adjacent specimen-supporting surface 5. Also, the inner walls of
reaction chamber 3 include line-of-sight surfaces 3a.
Plasma shield 6a shown in FIG. 1b differs from plasma shield 6 shown in
FIG. 1a in that it forms a removable inner liner at the top of reaction
chamber 3. However, plasma shield 6 of FIG. 1a can be used in place of
plasma shield 6a, if so desired. In either case, specimen-supporting
surface 5 can be located slightly beyond the outer end of the plasma
shield (as shown in FIG. 1a), or specimen-supporting surface 5 can be
moved such that the specimen is located within the bore of the plasma
shield during treatment of the specimen.
The embodiments shown in FIGS. 1a and 1b also include specimen surrounding
surface 7. Plasma specimen surrounding 7 includes a specimen surrounding
surface which comes into direct contact with a plasma stream during
treatment of the specimen.
FIGS. 2-6 show features of plasma shield 6, and FIGS. 7-14 show features of
plasma specimen surrounding 7.
Plasma shield 6 comprises member 8 which preferably comprises metal such as
aluminum or an aluminum alloy. The member includes bore 9 extending
therethrough in an axial direction A, and bore 9 is defined by
line-of-sight surface 10 on member 8. The line-of-sight surface can be
located closely adjacent the plasma stream passing through bore 9 to
minimize area of the line-of-sight surface. However, the line-of-sight
surface should not intercept the plasma stream. According to a preferred
embodiment of the invention, the line-of-sight surface completely
surrounds the plasma stream and diverges from a center of the plasma
stream so as to become wider in a direction toward the surface of the
specimen.
Plasma shield 6 also includes regulating means for maintaining
line-of-sight surface 10 at a substantially constant temperature. Plasma
shield 6 also includes means 12 for mounting member 8 in a CVD apparatus
so that plasma passes from plasma chamber 2, through bore 9, and into
reaction chamber 3 of the apparatus, as shown in FIG. 1a. Plasma shield 6
can include gas ejection means 13 for ejecting gas into or from an outlet
end of bore 9.
Plasma shield 6 can include horn 14, as shown in FIG. 3. Bore 9 can be
conical with inlet end 15 smaller than outlet end 16 of bore 9. Horn 14
extends from outlet end 16 of the bore. Horn 14 can include conical
opening 17 therethrough, opening 17 being tapered such that inlet end 18
thereof is smaller than outlet end 19 thereof. Opening 17 is defined by a
line-of-sight surface on the horn 14. That is, the surfaces forming bore 9
and opening 17 directly face a specimen mounted on specimen-supporting
surface 5 shown in FIG. 1a when plasma shield 6 is mounted in CVD
apparatus 1. Opening 17 can have a greater tapered angle than bore 9 or
opening 17, and bore 9 can be formed by one smooth, continuous rectilinear
surface. Alternatively, the line-of-sight surface could be arcuate.
As shown in FIG. 3, horn 14 can include cut-out 20 extending radially
between opening 17 and an outer periphery of horn 14 for allowing a
specimen to be moved therethrough when the specimen is placed on the
specimen-supporting surface. However, cut-out 20 can be omitted, as shown
in FIG. 2.
Recess 21 can be provided between member 8 and horn 14, as shown in FIG. 3.
Gas ejection means 13 can include ring 24 (as shown in FIG. 4) which can
be removably mounted in recess 21. Gas ejection means 13 can also include
a plurality of orifices 22 spaced apart in a circumferential direction
around ring 24. A cross-section taken along the line VI--VI in FIG. 4 of
one of the orifices 22 is shown in FIG. 6. Ring 24 can also include
temperature probe means 23 (as shown in FIG. 5) comprising a bore for
supporting a thermo-couple. A cross-section taken along the line V--V in
FIG. 4 of the temperature probe means 23 is shown in FIG. 5.
As shown in FIG. 3, horn 14 can include conical opening 17 which is tapered
to a greater extent than conical bore 9. Gas ring 24 can include a first
surface 27 which is tapered to the same extent as bore 9, and ring 24 can
include a second surface 28 which is tapered to the same extent as opening
17. First surface 27 can be coterminous with the line-of-sight surface
defining bore 9, and second surface 28 can be coterminous with the
line-of-sight surface defining opening 17. Thus, a smooth surface free of
edges which would cause stress in the deposited film is provided through
plasma shield 6.
The regulating means comprises a fluid passage 11 in member 8, and a
suitable fluid medium, such as water, can be circulated in fluid passage
11 for maintaining the line-of-sight surfaces at a substantially constant
temperature. As shown in FIG. 3, fluid passage 11 extends
circumferentially around member 8 at a location between the inner and
outer peripheries of member 8. The regulating means also includes inlet
and outlet means 25 for circulating the fluid medium in fluid passage 11.
Member 8 can include circumferentially extending groove 26 which is spaced
radially outwardly from bore 9. Ring 24 can be removably mounted to member
8 such that orifices 22 are in fluid communication with groove 26. Gas
ejection means 13 can include a gas supply, as shown in FIG. 2.
Accordingly, if oxygen plasma is used in the apparatus, gas ejection means
13 can supply SiH.sub.4 in order to deposit an SiO.sub.2 film.
As shown in FIG. 6, each of the orifices 22 for ejecting gas can have a
central axis B at an outlet end thereof, central axis B being oriented
such that gas is ejected from the orifices 22 toward a center axis of bore
9. Central axis B can be inclined with respect to axial direction A such
that an end of the orifice 22 facing bore 9 is located further downstream
with respect to the direction of movement of plasma through bore 9 than
other portions of the orifice. Central axis B can form an angle, such as
about 15.degree., with a plane perpendicular to axial direction A. Central
axis B could also be oriented such that the gas is ejected from the
orifices 22 in a helical pattern about a center axis of bore 9.
Plasma specimen surrounding surface 7 comprises member 29 having specimen
surrounding surface 30, as shown in FIGS. 7-12. Plasma specimen
surrounding surface 7 includes regulating means for maintaining specimen
surrounding surface 30 at a substantially constant temperature. In
addition, specimen surrounding surface 7 includes means 32 for mounting
member 29 in a reaction chamber of a CVD apparatus so that specimen
surrounding surface 30 surrounds a specimen-supporting surface in the
reaction chamber and so that member 29 does not thermally affect a
temperature of the specimen-supporting surface when a plasma stream
simultaneously contacts specimen surrounding surface 30 and the specimen
surface and/or the specimen-supporting surface. Accordingly, specimen
surrounding surface 7 can be mounted in the arrangements shown in FIGS. 1a
and 1b such that the specimen surrounding surface surrounds
specimen-supporting surface 5. In the arrangement shown in FIG. 1a,
specimen-supporting surface 5 is oriented vertically. Thus, specimen
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