Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1997-10-20
2001-09-18
Kalafut, Stephen (Department: 1745)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298110, C204S298230, C204S298260
Reexamination Certificate
active
06290826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the art of sputtering, and more particularly to a composite sputtering cathode assembly having a plurality of targets and a sputtering apparatus having such a composite sputtering cathode assembly. More specifically, the present invention is concerned with the sputtering technology which is capable of forming a thin film in minute holes (hereafter the words “minute holes” include narrow slits) of a high aspect ratio with a good coverage using a composite sputtering cathode assembly.
2. Description of the Prior Art
Sputtering apparatus are widely used in the fabrication of electronic devices such as semiconductor devices and liquid crystal display units.
As shown in
FIG. 10
of the accompanying drawings, a conventional sputtering apparatus
108
has a target
105
mounted on a cathode electrode
104
disposed in a vacuum housing
110
, and a substrate
112
placed on a substrate holder
111
disposed in the vacuum housing
110
in confronting relation to the target
105
. A plasma is generated on the surface of the target
105
to expel the material of the target
105
as sputtering particles which are deposited as a thin film on the surface of the substrate
112
.
The substrate
112
and the target
105
are closely spaced from each other by a distance of about 6 cm. Therefore, the sputtering particles are applied to the surface of the substrate
112
at various angles as indicated by the arrow
120
. Therefore, the minimum angle &thgr; at which the sputtering particles are applied to the surface of the substrate
112
is very small at ends of the substrate
112
.
Recent years have seen an increase in the degree of integration of electronic devices such as semiconductor devices. Because of such an increased degree of integration, minute holes defined in substrate surfaces of such electronic devices have increased aspect ratios (depth-to-diameter ratios).
When a thin film is deposited on a substrate having minute holes with a high aspect ratio by the conventional sputtering apparatus, a thin-film overhang is developed at the open ends of the minute holes, and no sufficient thin film is produced at the bottom ends of the minute holes.
One solution which has heretofore been proposed is shown in
FIGS. 11 and 11
a
of the accompanying drawings. As shown in
FIG. 11
, the distance “d” between a target
205
and a substrate
212
is increased, and a high vacuum is developed to increase the mean free path of sputtering particles, for thereby increasing the minimum angle &thgr; at which the sputtering particles are applied to the surface of the substrate
212
.
However, the increased distance “d” between the target
205
and the substrate
212
is not sufficient to deposit a thin film on the bottom of a minute hole
215
at an end of the substrate
212
with a uniform coverage.
Specifically, sputtering particles expelled from a large surface area of the target
205
, ranging from the right end to the left end as shown in
FIG. 11
, reach the substrate
212
as indicated by the arrows
221
. As shown in
FIG. 11
a,
on the right end of the substrate
212
, more sputtering particles arrive at the right-hand side of the minute hole
215
as indicated by the arrows
221
1
, and less sputtering particles arrive at the left-hand side of the minute hole
215
as indicated by the arrow
221
2
. Therefore, a thin film
218
deposited on the bottom of the minute hole
215
is thicker at the right-hand side and thinner at the left-hand side, and hence the coverage by the thin film
218
of the bottom of the minute hole
215
is asymmetric (known as a step coverage).
The asymmetry of the coverage by the thin film
218
of the bottom of the minute hole
215
can be eliminated if the distance “d” between the target
205
and the substrate
212
is further increased to allow the sputtering particles to be applied perpendicularly to the substrate
212
. However, the further increase in the distance “d” reduces the number of sputtering particles that reach the substrate
212
, resulting in a reduction in the film growth rate.
FIG. 12
of the accompanying drawings shows another conventional sputtering apparatus
302
. The conventional sputtering apparatus
302
has a target
305
mounted on a cathode electrode
304
disposed in a vacuum housing
310
, and a collimator
307
disposed between the target
305
and a substrate holder
311
disposed in the vacuum housing
310
in confronting relation to the target
305
. Sputtering particles expelled in various directions indicated by the arrow
320
from the target
305
are applied to the collimator
307
. The collimator
307
passes only those sputtering particles that are directed perpendicularly as indicated by the arrow
327
to a substrate
312
supported on the substrate holder
311
, and entraps those sputtering particles that are directed in other directions toward the substrate
312
, for thereby depositing a thin film in minute holes in the substrate
312
with a uniform coverage at their bottom ends.
However, as the number of sputtering particles entrapped by the collimator
307
increases, the openings of the collimator
307
are constricted and progressively limit the number of sputtering particles that can travel through the collimator
307
, resulting in a reduction in the film growth rate.
If the target
305
is increased in diameter, then the plasma developed on the surface of the target
305
suffers large density irregularities, and hence the sputtering rate on the surface of the target
305
differs greatly depending on the position on the surface of the target
305
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a composite sputtering cathode assembly capable of forming a thin film in minute holes in a substrate with a symmetric coverage at bottom ends of the minute holes.
Another object of the present invention is to provide a sputtering apparatus which employs such a composite sputtering cathode assembly.
According to the present invention, a composite sputtering cathode assembly includes a plurality of targets and a plurality of shields each disposed between adjacent ones of the targets.
Those sputtering particles expelled from the targets which are directed obliquely to the substrate hit the shields and do not reach the substrate. Therefore, sputtering particles that are applied to the substrate strike the substrate at a large minimum angle, i.e., substantially perpendicularly to the substrate.
The shields have tip ends spaced from a surface of the targets by a distance which is at least the diameter of the targets.
It is thus possible to form a thin film with a highly symmetric bottom coverage of 50% in minute holes in the substrate which have an aspect ratio of 2, for example.
The shields may comprise tubular sleeves, respectively, the targets being surrounded by the tubular sleeves, respectively.
The targets may include a target of different materials.
If targets of different materials are sputtered simultaneously, then a thin film of alloy can be deposited on the substrate. If targets of different materials are sputtered separately, then a multilayer thin film can be deposited on the substrate. If targets of different materials are switched for sputtering, then a thin film of different materials transversely across the thin film can be deposited on the substrate.
According to the present invention, a sputtering apparatus includes a vacuum housing, a substrate holder disposed in the vacuum housing for holding a substrate thereon, and a composite sputtering cathode assembly disposed in the vacuum housing, the composite sputtering cathode assembly comprising a plurality of targets and a plurality of shields each disposed between adjacent ones of the targets, the targets being disposed in confronting relation to the substrate held on the substrate holder.
The substrate holder and the composite sputtering cathode assembly may lie parallel each other and may be rotatable relatively to each other.
Minute h
Higuchi Yasushi
Komatsu Takashi
Obinata Hisaharu
Tamura Morohisa
Armstrong Westerman Hattori McLeland & Naughton LLP
Kalafut Stephen
Mercado Julian A.
Nihon Shinku Gijutsu Kabushiki Kaisha
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