U.S. patent application number 10/043103 was filed with the patent office on 2002-05-16 for dry etching method and apparatus.
Invention is credited to Shimizu, Masao, Yasutake, Kiyoshi, Yoshii, Kumayasu.
Application Number | 20020058419 10/043103 |
Document ID | / |
Family ID | 17224773 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058419 |
Kind Code |
A1 |
Shimizu, Masao ; et
al. |
May 16, 2002 |
Dry etching method and apparatus
Abstract
An accurate dry etching technique is described that employs a
flow of neutral radicals and a light beam. A dry etching apparatus
50 employs a neutral radical flow source 20 and a light beam 40 to
irradiate a flow of neutral radicals 32, so that the velocity
component of the neutral radicals parallel to the surface of an
object to be etched 12 is reduced, and etches anisotropically the
object to be etched, while the object 12 is exposed to the radical
flow 32 whose parallel velocity component is decreased. The
invention reduces the problem of etching parallel to the substrate
while etching perpendicular to the substrate to improve anisotropic
dry etching without any adverse or damage producing effect to
dielectric or semiconductor layers due to ions.
Inventors: |
Shimizu, Masao;
(Moriyama-shi, JP) ; Yoshii, Kumayasu; (Osaka-shi,
JP) ; Yasutake, Kiyoshi; (Minou-shi, JP) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Family ID: |
17224773 |
Appl. No.: |
10/043103 |
Filed: |
January 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10043103 |
Jan 14, 2002 |
|
|
|
09154763 |
Sep 17, 1998 |
|
|
|
Current U.S.
Class: |
438/690 ;
257/E21.252; 438/706 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01J 37/32339 20130101 |
Class at
Publication: |
438/690 ;
438/706 |
International
Class: |
H01L 021/302; H01L
021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 1997 |
JP |
9-251569 |
Claims
Having thus described our invention, what we claim as new and
desire to secure by letters patent is:
1. A method for dry etching comprising the steps of: preparing an
object to be etched; preparing a flow of neutral radicals;
irradiating said flow of neutral radicals with a light beam so that
their velocity component parallel to a surface of said object is
reduced; and exposing said flow of neutral radicals whose parallel
velocity component is decreased to said object and etching said
object.
2. The dry etching method according to claim 1, wherein said step
of reducing said parallel velocity component of said neutral
radicals includes a step of exchanging kinetic momentum between the
photons of said light beam and said neutral radicals (Doppler
cooling effect) to reduce said velocity component of said neutral
radicals parallel to said surface of said object to be etched.
3. The dry etching method according to claim 2, wherein said step
of preparing said object to be etched includes a step of mounting
said object to be etched on a table provided in a vacuum
container.
4. The dry etching method according to claim 3, wherein said step
of preparing said neutral radicals includes a step of emitting a
neutral radical beam toward said object to be etched from a source
of the neutral radical flow provided at a position opposite to an
etching surface of said object to be etched mounted on said
table.
5. The dry etching method according to claim 4, wherein said step
of irradiation with said light beam includes irradiation with a
light beam traveling in a direction that is substantially
perpendicular to a direction in which said radical beam is
projected.
6. The dry etching method according to claim 4, wherein said step
of irradiation with said light beam includes irradiation with a
light beam traveling along paths leading in at least two different
directions that are substantially perpendicular to a direction in
which said radical beam is projected.
7. The dry etching method according to claim 6, wherein said two
different directions diverge at an angle of 90 degrees.
8. The dry etching method according to claim 2, wherein said light
beam has a wavelength of "W+.DELTA., " which is slightly greater
than a wavelength of "W" that resonates when said neutral radicals
have a predetermined transition level.
9. The dry etching method according to claim 1, wherein said
neutral radicals include radical fluorine atoms.
10. The dry etching method according to claim 1, wherein said light
beam is a laser beam.
11. The dry etching method according to claim 1, wherein said
object to be etched includes a semiconductor substrate.
12. The dry etching method according to claim 9, wherein said laser
beam has a light wavelength of 685.6+.DELTA. [nm], when radical
fluorine atoms are used.
13. A dry etching apparatus comprising: a vacuum container; an
object table provided in said vacuum container on which to mount
thereon an object to be etched; a radical flow source, located at a
position opposite the surface of said object table on which said
object to be etched is mounted, for emitting a flow of neutral
radicals toward said object to be etched mounted on said object
table; and a light beam source, located between said object table
and said radical flow source, for irradiating a light beam toward
said flow of said neutral radicals emitted by said radical flow
source, so that velocity component of said neutral radicals
parallel to the surface of said object to be etched is negligible
compared to the velocity component perpendicular to said
surface.
14. The dry etching apparatus according to claim 13, wherein a
source of said radical flow is connected to said vacuum container
so that a beam-shaped flow of neutral radicals is introduced to
said vacuum container through an opening that is formed in said
vacuum container.
15. The dry etching apparatus according to claim 14, wherein said
light beam source is connected to said vacuum container so that a
light beam is introduced into said vacuum container through a
transparent window that is formed in a side wall of said vacuum
container.
16. The dry etching apparatus according to claim 15, wherein said
light beam source is so located that said light beam source emits a
light beam traveling along a path in a direction that is
substantially perpendicular to a direction in which said radical
beam flow is projected.
17. The dry etching apparatus according to claim 15, wherein said
light beam source is so located that said light beam source emits a
light beam traveling along paths leading in at least two different
directions that are substantially perpendicular to a direction in
which said radical beam flow is projected.
18. The dry etching apparatus according to claim 17, wherein said
two different directions are away from each other almost at 90
degrees.
19. The dry etching apparatus according to claim 15, further
comprising a mirror, provided inside or outside of a side wall of
said vacuum container opposite to said side wall whereat said
transparent window is formed, for reflecting a light beam from said
light beam source to again irradiate said flow of radicals.
20. The dry etching apparatus according to claim 13, wherein said
velocity component of said radicals parallel to said surface of
said object to be etched is reduced as a result of a kinetic
momentum exchange between the photons of said irradiated light beam
and said neutral radicals (Doppler cooling effect).
21. The dry etching apparatus according to claim 20, wherein said
light beam has a wavelength of "W+.DELTA., " which is slightly
greater than a wavelength of "W" that resonates when said neutral
radicals have a predetermined transition level.
22. The dry etching apparatus according to claim 21, wherein said
neutral radicals include radical fluorine atoms or other halogen
radicals.
23. The dry etching apparatus according to one of claims 13 to 22,
wherein said light beam source is a laser beam source.
24. The dry etching apparatus according to claim 22, wherein said
laser beam has an emission wavelength of 685.6+.DELTA. [nm], when
radical fluorine atoms are used.
25. A dry etching method comprising the steps of: preparing an
object to be etched; preparing a flow of neutral radicals;
irradiating said flow of neutral radicals with a light beam to
impart a change in the velocity component of said neutral radicals
parallel to the surface of said object to be etched; and etching
said object to be etched while said object to be etched is exposed
to said flow of said neutral radicals whose parallel velocity
component has been altered.
26. A dry etching apparatus comprising: a vacuum container; an
object table provided in said vacuum container to hold thereon an
object to be etched; a neutral radical flow source, located at a
position opposite the surface of said object table on which said
object to be etched is mounted, for emitting a flow of neutral
radicals directed toward said object to be etched mounted on said
object table; and a light beam source, located between said object
table and said neutral radicals flow source, for emitting a light
beam to irradiate said flow of said neutral radicals emitted by
said neutral radical flow source to impart a change in the velocity
component of said neutral radicals parallel to the surface of said
object to be etched.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a dry etching technique,
and in particular to an anisotropic dry etching method that is
employed in the semiconductor field for the delicate processing of
thin film layers, and an apparatus therefor.
[0002] BACKGROUND OF THE INVENTION
[0003] In accordance with increases in the storage densities
provided for semiconductor memories, such as DRAMs, the widths of
lines in thin film layers deposited on semiconductor substrates
have become narrower, and at present, methods are being pursued by
which to provide lines having widths of 0.1 micron or less.
[0004] Concomitanly, there is a demand for an improvement in the
preciseness available with anisotropic dry etching, which is used
for the delicate fabrication of a thin film layer, i.e., an
improvement on the accuracy provided by etching performed
perpendicular to the substrate, while the occurrence of etching
parallel to the substrate is reduced to the minimum possible.
[0005] In response to this demand, for improved etching properties,
a conventional anisotropic dry etching technique now employs the
force of an electric field or of a magnetic field to increase the
velocity of charged particles traveling perpendicular to a
substrate containing reactive ions, such as fluorine ions.
[0006] However, with this method, damage incurred to a
semiconductor layer due to the reactive ions is increased in
accordance with the increase in the kinetic energy of the reactive
ions, and either a defect will occur in the layer, or the quality
of the layer will be altered.
[0007] To resolve the conventional problems, it is one object of
the present invention to provide an accurate dry etching technique
having no adverse or damage producing effect.
[0008] It is another object of the present invention to provide a
new dry etching technique that employs a particle flow and a light
beam, especially a flow of neutral radicals and a light beam.
SUMMARY OF THE INVENTION
[0009] To achieve the above objects, according to the present
invention, a dry etching method comprises the steps of: preparing
an object to be etched; preparing a flow of neutral radicals;
irradiating the flow of neutral radicals with the light beam to
impart a change in the velocity component of the neutral radicals
parallel to the surface of the object to be etched; and etching the
object to be etched while the object to be etched is exposed to the
flow of the neutral radicals whose parallel velocity component has
been altered.
[0010] Further, according to the present invention, a dry etching
apparatus comprises: a vacuum container; an object table provided
in the vacuum container to hold thereon an object to be etched; a
neutral radical flow source, located at a position opposite the
surface of the object table on which the object to be etched is
mounted, for emitting a flow of neutral radicals directed toward
the object to be etched mounted on the object table; and a light
beam source, located between the object table and the neutral
radical flow source, for emitting a light beam to irradiate the
flow of the neutral radicals emitted by the neutral radical flow
source to impart a change in the velocity component of the neutral
radicals parallel to the surface of the object to be etched.
[0011] More specifically, a dry etching method comprises the steps
of: preparing an object to be etched; preparing a flow of neutral
radicals; irradiating the flow of neutral radicals with a light
beam so that their velocity component parallel to a surface of the
object is reduced; and exposing the flow of neutral radicals whose
parallel velocity component is decreased as it approaches the
object and upon impact, etching the object.
[0012] In addition, according to the present invention, a dry
etching apparatus more specifically comprises: a vacuum container;
an object table provided in the vacuum container on which to mount
thereon an object to be etched; a radical flow source, located at a
position opposite the surface of the object table on which the
object to be etched is mounted, for emitting a flow of neutral
radicals toward the object to be etched mounted on the object
table; and a light beam source, located between the object table
and the radical flow source, for irradiating a light beam toward
the flow of the neutral radicals emitted by the radical flow
source, so that velocity component of the neutral radicals parallel
to the surface of the object to be etched is negligible compared to
the velocity component perpendicular to the surface.
DESCRIPTION OF THE DRAWINGS
[0013] These and other features, objects, and advantages of the
present invention will become apparent upon consideration of the
following detailed description of the invention when read in
conjunction with the drawing in which:
[0014] FIG. 1 is a side view of a cross-section of a dry etching
apparatus according to one embodiment of the present invention.
[0015] FIG. 2 is a top view of a cross-section of the dry etching
apparatus according to the embodiment of the present invention.
[0016] FIG. 3 is a flowchart for a dry etching method according to
the present invention.
[0017] FIG. 4 is a graph showing the relationship between an atomic
resonance absorption curve and emission spectra for laser
beams.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] FIG. 1 is a side view of a cross-section of a dry etching
apparatus 50 according to one embodiment of the present
invention.
[0019] An object table 14 for mounting thereon an object to be
etched 12, and an evacuation opening 16 are formed in the lower
portion of a vacuum container (chamber) 10. An evacuating pipe 18
communicates with the opening 16, and the end of the pipe 18 is
connected to a vacuum pump 19, such as a turbo molecular pump.
[0020] A radical flow source (also called a"radical gun") 20 is
located at a position above the vacuum container 10 and opposite to
the object table 14, and emits a flow of neutral radicals toward an
object to be etched. An opening 22 is formed for the introduction
by the radical flow source 20 of F.sub.2, SF.sub.6, NF.sub.3,
CF.sub.4 or other halogenated chemicals, which are gases for the
production of neutral halogen radicals which may be a single
halogen atom, a free radical containing a halogen atom or one or
more atoms forming a molecule or molecular fragment containing at
least one atom of a halogen. A free radical may be a group of atoms
bonded together that is considered an entity in various kinds of
reactions. In addition, electrodes 23 are provided in the radical
flow source 20. An RF/DC power source 24 is connected to the
electrodes 23 to perform decomposition of the gas and separation of
ions and radicals between the electrodes 23. A microwave source may
be employed instead of the RF/DC power source 24 to decompose the
gas. The radical flow source 20 has an opening 26 and a guide 28,
which is so connected to the vacuum container 10 that it covers an
opening 30 formed in the vacuum container 10.
[0021] A transparent window 34 is formed in a side wall of the
vacuum container 10, and a light beam source 36 is located at a
position opposite the window 34. A laser beam source is used as the
light beam source 36. A mirror 38 is provided on the side wall of
the vacuum container 10 opposite the window 34.
[0022] FIG. 2 is a cross-sectional top view of the center portion
of the dry etching apparatus 50. Two light beam sources are
provided: the light beam source 36 in the X axial direction and the
light beam source 36' in the Y axial direction. The window 34 and
the mirror 38 are provided for the light beam source 36, while the
window 34' and the mirror 38' are provided for the light beam
source 36'.
[0023] FIG. 3 is a flowchart showing a dry etching method according
to the present invention. Step (A) Preparation of object to be
etched is shown in box 39 in FIG. 3. An object to be etched is
mounted on the object table 14 of the vacuum container 10, and then
air in the vacuum container 10 is evacuated by a vacuum pump 19,
such as a diffusion pump or a turbo molecular pump, until a vacuum
is attained in the container 10. The object to be etched is an Si
substrate on which is deposited SiO.sub.2, for which, for example,
a pattern photoresist layer is formed.
[0024] Step (B), Preparation of radical flow is shown in box 40 in
FIG. 3. Gas for a radical flow, such as F.sub.2, SF.sub.6, NF.sub.3
or CF.sub.4, is introduced into the neutral radical flow source 20
through the opening 22. The gas is decomposed between the
electrodes 23 by the RF power supplied from the RF/DC power source
24. Ions and fluorine radicals are separated by the electric field
generated by a DC voltage, and only the fluorine radicals are
introduced through the opening 26. The flow of radicals, after
being passed through the opening 26, is transmitted along the guide
28 and enters the vacuum container 10 through the opening 30.
[0025] At this time, because of a difference in pressure between
the radical flow source 20 (the guide 28) and the vacuum container
10, the fluorine radical flow is linearly directed as a beam toward
the object to be etched. It should be noted, however, that as is
represented by 32 in FIG. 1, the fluorine radical beam spreads as
it approaches the object to be etched. The internal (excitation)
energy and the velocity of the fluorine radicals are controlled by
gas pressure, RF power, a DC voltage and the distance between the
electrodes.
[0026] Step (C), Adjustment of velocity of radical flow is shown in
box 41 in FIG. 3. The fluorine radical flow, which linearly
transits the vacuum container 10 toward the object to be etched, is
irradiated by light beams 40 in the X and the Y axial directions
that respectively are emitted by the light beam sources 36 and 36'.
The light beams 40 are emitted in directions perpendicular to the
direction in which the fluorine radical beam is projected. The
light beams 40, after irradiating the fluorine radical beam, are
reflected by the mirrors 38 and 38', and again irradiate the
fluorine radical beam.
[0027] A laser beam source is used as the light beam source 36 for
irradiating the fluorine radicals. The laser that is employed
has
[0028] a central emission wavelength of "685.6+.DELTA." nm, which
is slightly longer than the 685.6 nm that is a resonance wavelength
for transient energy between the 3 s.sup.4P(5/2) level and the 3
p.sup.4D.sup.0(7/2) level of fluorine atoms. This is because the
Doppler cooling effect, which will be described later, is employed.
".DELTA." indicates an appropriate wavelength width that is smaller
than 1 nm.
[0029] When a laser beam irradiates the flow of radicals, the
velocity component of the radicals parallel to the surface of the
object to be etched is reduced due to the Doppler cooling effect.
That is, since kinetic momentum is exchanged by the photons of the
laser beam emitted by the laser beam source 36 and fluorine atoms,
the velocity component of the fluorine atoms in the X axial
direction (FIG. 2) is reduced. Similarly, since kinetic momentum is
exchanged between the photons of the laser beam emitted by the
laser beam source 36' and fluorine atoms, the velocity of the
fluorine atoms in the Y axial direction (FIG. 2) is reduced. As a
result, the velocity component perpendicular to the surface of the
object to be etched (in the Z direction) is relatively increased.
It is possible to reduce the velocity components of the fluorine
atoms in the X and Y axial directions almost to zero, and as a
result, the fluorine radicals will enter or impact the surface of
the object to be etched perpendicularly. Therefore, the control of
the locus of neutral radicals, which is difficult conventionally,
is implemented.
[0030] The Doppler cooling effect will be further explained. The
Doppler cooling effect is attained by the employment of the optical
Doppler effect to reduce the velocity of moving neutral atoms. A
detailed explanation on will be given below.
[0031] FIG. 4 is a graph showing a relationship between an atomic
resonance absorption curve 42 and the emission spectra of laser
beams. A resonance absorption curve 42 in FIG. 4 peaks at central
frequency f.sub.0, and represents the relationship between the
resonance absorption rate for fluorine atoms and the frequency of
light. Lines 43, 44 and 45 represent emission spectra for laser
beams having their central emission frequencies f.sub.1, f.sub.2
and f.sub.3 as seen by a fluorine atom. Specifically, the central
frequency f.sub.0 corresponds to 685.6 nm, which is the resonance
wavelength for transition energy between the 3s.sup.4P(5/2) level
and the 3p.sup.4D.sup.0(7/2) level for fluorine atoms. In addition,
this frequency is lower than the frequency f.sub.0 of the laser
beam the equivalent of the above described wavelength width
.DELTA..
[0032] Assume that the fluorine atoms are moving at velocity v
toward the laser beam (toward the laser beam source 36 in FIG. 2)
that is emitted by the laser beam source 36 and that along the X
axis has a frequency of f.sub.1. In this case, when the light
velocity is c, the frequency f.sub.2 for the laser beam viewed from
the fluorine atoms is
f.sub.2=f.sub.1/(1-v/c).
[0033] That is, the emission spectrum for the laser beam viewed
from the fluorine atoms shows a curve 44, as in FIG. 4, not a curve
43, in FIG. 4.
[0034] Assume that the fluorine atoms are moving at velocity v in
the same direction as the laser beam (in the direction toward the
mirror 38 along the X axis). The frequency f.sub.3 of the laser
beam viewed from the fluorine atoms is
f.sub.3=f.sub.1/(1+v/c).
[0035] Then, the emission spectrum shows a curve 45, as in FIG. 4,
not the curve 43.
[0036] Let us discuss the relationship between the resonance
absorption curve and the change in the frequency of the light,
relative to the fluorine atoms, that is due to the Doppler effect.
As is apparent from FIG. 4, since the frequency is nearer the peak
resonance absorption frequency when it is changed to the frequency
f.sub.2 (spectrum 44), more light resonance absorption occurs than
when the frequency is changed to the frequency f.sub.3 (spectrum
45). That is, light resonance absorption for the fluorine atoms
that are moving toward the laser beam source 36 along the X axis in
FIG. 2 is greater than that for the fluorine atoms that are moving
toward the mirror 38 on the opposite side, and as a result, there
is a difference in the quantities of light they absorb.
[0037] The fluorine atoms, which are moving toward the light source
36 that has absorbed more light, are altered and enter an excited
state, i.e., their energy level is changed to the excitation level.
Then, the light is emitted and the fluorine atoms acquire a more
stable energy state, i.e., they are returned to the lower energy
level. Since the light emitted at this time is isotropically
radiated by the atoms, no force is applied to the fluorine atoms in
a specific direction due to the spontaneous emission of the
light.
[0038] Under a situation of momentum conservation, the fluorine
atoms moving toward the laser beam source 36 absorb not only the
light but also are influenced by the kinetic momentum held by
photons. The kinetic momentum influencing the fluorine atoms acts
as force to move the fluorine atoms in a direction opposite to that
in which they are traveling. That is, under the conditions
associated with moumentum conversation, an exchange of kinetic
momentum occurs between the atoms and the photons, and the fluorine
atoms are subjected to a driving force impelling them toward the
mirror 38, which is in the opposite direction to the direction in
which they are traveling along the X axis. As a result, the
velocity of the fluorine atoms, which are traveling along the X
axis toward the laser beam source 36, is reduced.
[0039] the fluorine atoms that are traveling toward the mirror 38
also acquire the kinetic momentum from the photons. However, since
these fluorine atoms do not absorb much light, the acquired
momentum is accordingly negligible. As a result, no force is
applied, in the direction of travel, to the fluorine atoms that are
traveling toward the mirror 38. The velocity increase is also
negligible.
[0040] The same conditions can be predicated for the fluorine
radical atoms that are traveling in concert with a laser beam that
is reflected by the mirror 38. More specifically, the velocity of
the fluorine radical atoms that are traveling toward the X axial
laser beam (toward the mirror 38) can be reduced by the Doppler
cooling effect. In addition to the previously described reduction
in the velocity when the fluorine atoms are traveling toward the X
axial laser beam 36, the velocity of the fluorine atoms is reduced
in the X axial direction.
[0041] The above explanation is given for a case wherein fluorine
atoms are traveling along the X axis. Actually, the X axial
component v.sub.x of the velocity vector v of the fluorine atoms is
reduced.
[0042] The same conditions can be predicated for the Y axis in FIG.
2. The velocity of the fluorine radical atoms traveling in the Y
axial direction can be reduced by the Doppler cooling effect
produced by a laser beam. As a result, the velocity component, of
the fluorine radical atoms that are irradiated by the laser beam,
that is perpendicular to the surface of the object to be etched (in
the Z axial direction) is relatively increased.
[0043] Step (D), Dry etching is shown in box 47 in FIG. 3.
[0044] The object to be etched is etched in a direction
perpendicular to the surface by reactions occurring between the
fluorine radicals, which are perpendicularly incident to the
surface of the object, and the atoms or molecules of the object. In
short, the object to be etched is anisotropically etched by the
fluorine radicals.
[0045] When a Si substrate is employed on which is deposited
SiO.sub.2, for which a patterned photoresist layer is provided, a
predetermined SiO.sub.2 pattern is formed by dry etching as
outlined in FIG. 3. No damage due to ions is introduced in a
pattern formed on the SiO.sub.2 or the Si substrate. Since the
fluorine radicals are perpendicularly incident to the surface of
the object to be etched without having any velocity components
parallel to the surface, a more delicate anisotropic pattern can be
formed.
[0046] The preferred embodiment has been described, but the present
invention is not limited to this embodiment and can be variously
modified or applied as within the scope of the subject of the
present invention. In the above embodiment, the light beam is used
to reduce the velocity component of the fluorine radicals traveling
parallel to the surface of the object to be etched; however, the
light beam may be used to increase the above velocity component and
to relatively reduce the velocity component perpendicular to the
surface of the object (in the Z axial direction), so that a flow of
fluorine radicals can be spread across the surface of the object to
be etched. For example, f.sub.1, may be above f.sub.0 instead of
below f.sub.0, by the same absolute amount to utilize curve 42
above f.sub.0 to increase the parallel velocity component.
* * * * *