U.S. patent application number 11/103604 was filed with the patent office on 2005-10-06 for system and method for etching a mask.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Yamashita, Asao, Yue, Hongyu.
Application Number | 20050221619 11/103604 |
Document ID | / |
Family ID | 34574882 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221619 |
Kind Code |
A1 |
Yue, Hongyu ; et
al. |
October 6, 2005 |
System and method for etching a mask
Abstract
A system and method for transferring a pattern from an overlying
layer into an underlying layer, while laterally trimming a feature
present within the pattern is described. The pattern transfer is
performed using an etch process according to a process recipe,
wherein at least one variable parameter within the process recipe
is adjusted given a target trim amount. The adjustment of the
variable parameter is achieved using a process model established
for relating trim amount data with the variable parameter.
Inventors: |
Yue, Hongyu; (Plano, TX)
; Yamashita, Asao; (Wappingers Falls, NY) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
34574882 |
Appl. No.: |
11/103604 |
Filed: |
April 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11103604 |
Apr 12, 2005 |
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10813570 |
Mar 31, 2004 |
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6893975 |
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Current U.S.
Class: |
438/714 ;
257/E21.257; 257/E21.525 |
Current CPC
Class: |
H01L 21/31144 20130101;
H01L 22/20 20130101 |
Class at
Publication: |
438/714 |
International
Class: |
H01L 021/302 |
Claims
What is claimed is:
1. A method of preparing a process model comprising: defining a
nominal process recipe for transferring a pattern having a first
feature size from an overlying layer to an underlying layer on a
substrate, wherein said nominal process recipe comprises at least
one variable parameter and at least one constant parameter;
accumulating trim amount data as a function of said at least one
variable parameter by measuring the trim amount for one or more
values of said at least one variable parameter; and curve-fitting
said trim amount data as a function of said at least one variable
parameter.
2. The method of claim 1, wherein said curve-fitting includes
fitting said trim amount data as a function of said variable
parameter with an expression of the form y=(x+a)/(bx+c), where a,
b, and c are constants, and where x is the at least one variable
parameter and y is the trim amount.
3. An etching system comprising: a process chamber; a substrate
holder coupled to said process chamber, and configured to support a
substrate; a plasma source coupled to said process chamber, and
configured to form plasma in said process chamber; a gas injection
system coupled to said process chamber, and configured to introduce
a process gas to said process chamber; and a controller coupled to
said process chamber, said substrate holder, said plasma source, or
said gas injection system, or any combination of two or more
thereof, and configured to execute a process recipe in order to
transfer a pattern having a feature with a first critical dimension
in an overlying layer to an underlying layer on said substrate,
while reducing said first critical dimension to a second critical
dimension by a target trim amount set by a process model.
4. The etching system of claim 3, wherein said target trim amount
is set by determining a difference between said first critical
dimension and said second critical dimension.
5. The etching system of claim 3, wherein said process model
relates said target trim amount to a variable parameter in a
process recipe.
6. The etching system of claim 5, wherein said variable parameter
includes a flow rate of CF.sub.4, a flow rate of O.sub.2, a chamber
pressure, a RF power to an upper electrode, or a RF power to a
lower electrode, or any combination of two or more thereof.
7. The etching system of claim 5, wherein said process gas
comprises a first process gas and a second process gas, and said
variable parameter includes an amount of said first process gas, an
amount of said second process gas, a total amount of said first
process gas and said second process gas, a chamber pressure, or at
least one RF power, or any combination of two or more thereof.
8. The etching system of claim 7, wherein determining said variable
parameter includes determining said amount of said first process
gas from said process model, and determining said amount of said
second process gas from said amount of said first process gas and
said total amount of said first process gas and said second process
gas.
9. The etching system of claim 3, wherein said process model
relates said target trim amount (y) to a variable parameter (x) in
a process recipe according to a relationship of the form
y=(x+a)/(bx+c), where a, b, and c are constants.
10. The etching system of claim 3, wherein said underlying layer
includes a film formed by spin-on deposition and/or vapor
deposition.
11. The etching system of claim 3, wherein said underlying layer
includes an organic layer.
12. The etching system of claim 3, wherein said overlying layer
includes a film formed by spin-on deposition and/or vapor
deposition.
13. The etching system of claim 3, wherein said overlying layer
includes a layer of light-sensitive material.
14. The etching system of claim 3, wherein said pattern in said
overlying layer is formed by micro-lithography.
15. The etching system of claim 3, wherein said substrate holder
comprises an electrostatic clamping system.
16. The etching system of claim 3, wherein said plasma source
comprises an electrode configured to capacitively couple power to
said process gas.
17. The etching system of claim 3, wherein said plasma source
comprises a coil configured to inductively couple power to said
process gas.
18. The etching system of claim 3, wherein said substrate holder is
configured to control a temperature of said substrate.
19. The etching system of claim 3, wherein said process gas
comprises a C.sub.xF.sub.y containing gas (wherein x, y are
integers greater than or equal to unity), and an oxygen containing
gas.
20. The etching system of claim 19, wherein said C.sub.xF.sub.y
containing gas includes CF.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6,
C.sub.4F.sub.6, C.sub.4F.sub.8, or C.sub.5F.sub.8 or any
combination of two or more thereof, and said oxygen containing gas
includes O.sub.2, CO, CO.sub.2, NO, NO.sub.2, or N.sub.2O, or any
combination of two or more thereof.
Description
[0001] This is a continuation of U.S. patent application Ser. No.
10/813,520, filed Mar. 31, 2004, Issue Fee Paid, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a system and method for
etching a mask and, in particular, to a system and method for
transferring a pattern from an overlying layer into the mask layer
while laterally trimming the pattern in the mask by means of
etching.
BACKGROUND OF THE INVENTION
[0003] During semiconductor processing, a (dry) plasma etch process
can be utilized to remove or etch material along fine lines or
within vias or contacts patterned on a silicon substrate. The
plasma etch process generally involves positioning a semiconductor
substrate with an overlying patterned, protective layer, for
example a photoresist layer, in a processing chamber. Once the
substrate is positioned within the chamber, an ionizable,
dissociative gas mixture is introduced within the chamber at a
pre-specified flow rate, while a vacuum pump is throttled to
achieve an ambient process pressure. Thereafter, a plasma is formed
when a fraction of the gas species present are ionized by electrons
heated via the transfer of radio frequency (RF) power either
inductively or capacitively, or microwave power using, for example,
electron cyclotron resonance (ECR). Moreover, the heated electrons
serve to dissociate some species of the ambient gas species and
create reactant specie(s) suitable for the exposed surface etch
chemistry.
[0004] Once the plasma is formed, selected surfaces of the
substrate are etched by the plasma. The process is adjusted to
achieve appropriate conditions, including an appropriate
concentration of desirable reactant and ion populations to etch
various features (e.g., trenches, vias, contacts, gates, etc.) in
the selected regions of the substrate. Such substrate materials
where etching is required include silicon dioxide (SiO.sub.2),
low-k dielectric materials, poly-silicon, and silicon nitride.
[0005] During material processing, etching such features generally
comprises the transfer of a pattern formed within an overlying
layer to the underlying layer within which the respective features
are formed. The overlying layer can, for example, comprise a
light-sensitive material such as (negative or positive)
photo-resist. Once the pattern is transferred from the overlying
layer into the underlying layer, the underlying, either by itself
or with the overlying layer, can serve as a mask for etching
underlying films.
SUMMARY OF THE INVENTION
[0006] In one aspect of the invention, a method for performing a
one-step mask open process comprises: forming a first layer on a
substrate; forming a second layer on the first layer; forming a
pattern in the second layer, wherein the pattern includes a feature
in the second layer having a first critical dimension; setting a
target trim amount for reducing the first critical dimension to a
second critical dimension; determining a variable parameter for a
process recipe using the target trim amount and a process model
relating trim amount data to the variable parameter; and
transferring the pattern from the second layer to the first layer
using the process recipe, while achieving the second critical
dimension of the feature in the first layer.
[0007] In another aspect of the invention, a method of preparing a
process model comprises: defining a nominal process recipe for
transferring a pattern having a first feature size from an
overlying layer to an underlying layer on a substrate, wherein the
nominal process recipe comprises a variable process parameter and
at least one constant process parameter; accumulating trim amount
data as a function of the variable parameter by measuring the trim
amount for one or more values of the variable parameter; and
curve-fitting the trim amount data as a function of the variable
parameter.
[0008] In yet another aspect of the invention, an etching system
comprises: a process chamber; a substrate holder coupled to the
process chamber, and configured to support a substrate; a plasma
source coupled to the process chamber, and configured to form
plasma in the process chamber; a gas injection system coupled to
the process chamber, and configured to introduce a process gas to
the process chamber; and a controller coupled to at least one of
the process chamber, the substrate holder, the plasma source, and
the gas injection system, and configured to execute a process
recipe in order to transfer a pattern having a feature with a first
critical dimension in an overlying layer to an underlying layer on
the substrate, while reducing the first critical dimension to a
second critical dimension by a target trim amount set by a process
model.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the accompanying drawings:
[0010] FIGS. 1A and 1B illustrate a schematic representation of a
film stack;
[0011] FIG. 2 shows a simplified schematic diagram of a plasma
processing system according to an embodiment of the invention;
[0012] FIG. 3 shows a schematic diagram of a plasma processing
system according to another embodiment of the invention;
[0013] FIG. 4 shows a schematic diagram of a plasma processing
system according to another embodiment of the invention;
[0014] FIG. 5 shows a schematic diagram of a plasma processing
system according to another embodiment of the invention;
[0015] FIG. 6 shows a schematic diagram of a plasma processing
system according to another embodiment of the invention;
[0016] FIG. 7 shows etch rate data as a function of a gas
ratio;
[0017] FIG. 8 shows additional etch rate data as a function of the
gas ratio;
[0018] FIG. 9 shows a ratio of the etch rate data presented in
FIGS. 7 and 8 as a function of the gas ratio;
[0019] FIG. 10 presents the ratio of etch rate and two process
models as a function of the gas ratio;
[0020] FIG. 11 presents trim amount data as a function of the gas
ratio;
[0021] FIG. 12 presents a process model for relating the trim
amount data to the gas ratio;
[0022] FIG. 13 compares the process model of FIG. 12 with a second
order polynomial fit and a third order polynomial fit of the trim
amount data;
[0023] FIG. 14 illustrates a method of performing a one-step mask
open process according to an embodiment of the invention; and
[0024] FIG. 15 illustrates a method of preparing a process model
according to an embodiment of the invention.
DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS
[0025] In material processing methodologies, pattern etching
comprises the application of a thin layer of light-sensitive
material, such as photoresist, to an upper surface of a substrate,
that is subsequently patterned in order to provide a mask for
transferring this pattern to the underlying thin film during
etching. The patterning of the light-sensitive material generally
involves exposure by a radiation source through a reticle (and
associated optics) of the light-sensitive material using, for
example, a micro-lithography system, followed by the removal of the
irradiated regions of the light-sensitive material (as in the case
of positive photoresist), or non-irradiated regions (as in the case
of negative resist) using a developing solvent.
[0026] Additionally, multi-layer masks can be implemented for
etching features in a thin film. For example, when etching features
in a thin film using a bilayer mask, the mask pattern in the
overlying mask layer, such as the layer of light-sensitive
material, is transferred to the underlying mask layer using a
separate etch step preceding the main etch step for the thin film.
For example, the underlying mask layer can include an organic thin
film, such as an organic anti-reflective coating (ARC, or bottom
ARC (BARC)), an inorganic thin film, or a hybrid organic-inorganic
thin film.
[0027] In order to reduce the feature size formed in the thin film,
the underlying mask layer can be trimmed laterally, while the mask
pattern formed in the overlying mask layer is transferred into the
underlying mask layer. For instance, FIG. 1A illustrates a film
stack 11 comprising a substrate 10 having a thin film 12 deposited
thereon. The film stack 11 further includes a first layer 14 formed
on the thin film 12, followed by a second layer 16 formed on the
first layer 14. The first layer 14 and the second layer 16 can be
formed using spin-on deposition (SOD) techniques, and/or vapor
deposition techniques, such as chemical vapor deposition (CVD).
Both techniques are well known to those skilled in the art of
material deposition.
[0028] The second layer 16 can include a layer of light-sensitive
material, such as photoresist. The second layer 16 can be formed
using a track system. The track system can be configured for
processing 248 nm resists, 193 nm resists, 157 nm resists, EUV
resists, (top/bottom) anti-reflective coatings (TARC/BARC), and top
coats. For example, the track system can comprise a Clean Track ACT
8, or ACT 12 resist coating and developing system commercially
available from Tokyo Electron Limited (TEL). Other systems and
methods for forming a photoresist film on a substrate are well
known to those skilled in the art of spin-on resist technology.
Once the second layer 16 is formed, a pattern 20 can be formed in
the second layer 16 using micro-lithography. After developing the
irradiated (exposed) second layer 16, a feature 21 remains having a
first critical dimension (CD) 22, as indicated in FIG. 1A.
[0029] Referring now to FIG. 1B, the pattern 20 is transferred to
the first layer 14 by etching, such as dry plasma etching. During
the etching process, longitudinal etching (as indicated by
reference numeral 24) completes the pattern transfer, and lateral
etching (as indicated by reference numeral 26) trims the feature 21
in the lateral dimension such that the first critical dimension 22
becomes a second critical dimension 28.
[0030] The etch process for performing both the longitudinal and
lateral etching comprises a one-step process. The process chemistry
for the one-step chemistry includes a C.sub.xF.sub.y containing gas
(wherein x, y are integers greater than or equal to unity), and an
oxygen containing gas. For example, the C.sub.xF.sub.y containing
gas can include CF.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6,
C.sub.4F.sub.6, C.sub.4F.sub.8, or C.sub.5F.sub.8 or any
combination of two or more thereof. Additionally, for example, the
oxygen containing gas can include O.sub.2, CO, CO.sub.2, NO,
NO.sub.2, or N.sub.2O, or any combination of two or more thereof.
Optionally, the one-step process chemistry can further include an
inert gas, such as a Noble gas (e.g., He, Ar, Kr, Xe, or Ne, or any
combination of two or more thereof), and/or N.sub.2.
[0031] According to one embodiment, a plasma processing system 1
for performing the one-step etch process is depicted in FIG. 2
comprising a plasma processing chamber 10, a diagnostic system 12
coupled to the plasma processing chamber 10, and a controller 14
coupled to the diagnostic system 12 and the plasma processing
chamber 10. The controller 14 is configured to execute a process
recipe comprising at least one of the above-identified chemistries
(i.e. C.sub.xF.sub.y containing gas, and oxygen containing gas,
etc.) to etch the first mask layer. Additionally, controller 14 is
configured to receive at least one endpoint signal from the
diagnostic system 12 and to post-process the at least one endpoint
signal in order to accurately determine an endpoint for the
process. In the illustrated embodiment, plasma processing system 1,
depicted in FIG. 2, utilizes a plasma for material processing.
Plasma processing system 1 includes an etch chamber.
[0032] According to the embodiment depicted in FIG. 3, plasma
processing system 1a can comprise plasma processing chamber 10,
substrate holder 20, upon which a substrate 25 to be processed is
affixed, and vacuum pumping system 30. Substrate 25 can be, for
example, a semiconductor substrate, a wafer or a liquid crystal
display. Plasma processing chamber 10 can be, for example,
configured to facilitate the generation of plasma in processing
region 15 adjacent a surface of substrate 25. An ionizable gas or
mixture of gases is introduced via a gas injection system (not
shown) and the process pressure is adjusted. For example, a control
mechanism (not shown) can be used to throttle the vacuum pumping
system 30. Plasma can be utilized to create materials specific to a
pre-determined materials process, and/or to aid the removal of
material from the exposed surfaces of substrate 25. The plasma
processing system 1a can be configured to process 200 mm
substrates, 300 mm substrates, or substrates of any size.
[0033] Substrate 25 can be, for example, affixed to the substrate
holder 20 via an electrostatic clamping system. Furthermore,
substrate holder 20 can, for example, further include a cooling
system including a re-circulating coolant flow that receives heat
from substrate holder 20 and transfers heat to a heat exchanger
system (not shown), or when heating, transfers heat from the heat
exchanger system. Moreover, gas can, for example, be delivered to
the back-side of substrate 25 via a backside gas system to improve
the gas-gap thermal conductance between substrate 25 and substrate
holder 20. Such a system can be utilized when temperature control
of the substrate is required at elevated or reduced temperatures.
For example, the backside gas system can comprise a two-zone gas
distribution system, wherein the helium gas gap pressure can be
independently varied between the center and the edge of substrate
25. In other embodiments, heating/cooling elements, such as
resistive heating elements, or thermoelectric heaters/coolers can
be included in the substrate holder 20, as well as the chamber wall
of the plasma processing chamber 10 and any other component within
the plasma processing system 1a.
[0034] In the embodiment shown in FIG. 3, substrate holder 20 can
comprise an electrode through which RF power is coupled to the
processing plasma in process space 15. For example, substrate
holder 20 can be electrically biased at a RF voltage via the
transmission of RF power from a RF generator 40 through an
impedance match network 50 to substrate holder 20. The RF bias can
serve to heat electrons to form and maintain plasma. In this
configuration, the system can operate as a reactive ion etch (RIE)
reactor, wherein the chamber and an upper gas injection electrode
serve as ground surfaces. A frequency for the RF bias can range
from about 0.1 MHz to about 100 MHz. RF systems for plasma
processing are well known to those skilled in the art.
[0035] Alternately, RF power is applied to the substrate holder
electrode at multiple frequencies. Furthermore, impedance match
network 50 serves to improve the transfer of RF power to plasma in
plasma processing chamber 10 by reducing the reflected power. Match
network topologies (e.g. L-type, .pi.-type, T-type, etc.) and
automatic control methods are well known to those skilled in the
art.
[0036] Vacuum pump system 30 can, for example, include a
turbo-molecular vacuum pump (TMP) capable of a pumping speed up to
about 5000 liters per second (and greater) and a gate valve for
throttling the chamber pressure. In conventional plasma processing
devices utilized for dry plasma etch, about 1000 to about 3000
liter per second TMP is generally employed. TMPs are useful for low
pressure processing, typically less than about 50 mTorr. For high
pressure processing (i.e., greater than about 100 mTorr), a
mechanical booster pump and dry roughing pump can be used.
Furthermore, a device for monitoring chamber pressure (not shown)
can be coupled to the plasma processing chamber 10. The pressure
measuring device can be, for example, a Type 628B Baratron absolute
capacitance manometer commercially available from MKS Instruments,
Inc. (Andover, Mass.).
[0037] Controller 14 comprises a microprocessor, memory, and a
digital I/O port capable of generating control voltages sufficient
to communicate and activate inputs to plasma processing system 1a
as well as monitor outputs from plasma processing system 1a.
Moreover, controller 14 can be coupled to and can exchange
information with RF generator 40, impedance match network 50, the
gas injection system (not shown), vacuum pump system 30, as well as
the backside gas delivery system (not shown), the
substrate/substrate holder temperature measurement system (not
shown), and/or the electrostatic clamping system (not shown). For
example, a program stored in the memory can be utilized to activate
the inputs to the aforementioned components of plasma processing
system 1a according to a process recipe in order to perform the
method of etching a mask layer. One example of controller 14 is a
DELL PRECISION WORKSTATION610.TM., available from Dell Corporation,
Austin, Tex.
[0038] The diagnostic system 12 can include an optical diagnostic
subsystem (not shown). The optical diagnostic subsystem can
comprise a detector such as a (silicon) photodiode or a
photomultiplier tube (PMT) for measuring the light intensity
emitted from the plasma. The diagnostic system 12 can further
include an optical filter such as a narrow-band interference
filter. In an alternate embodiment, the diagnostic system 12 can
include at least one of a line CCD (charge coupled device), a CID
(charge injection device) array, and a light dispersing device such
as a grating or a prism. Additionally, diagnostic system 12 can
include a monochromator (e.g., grating/detector system) for
measuring light at a given wavelength, or a spectrometer (e.g.,
with a rotating grating) for measuring the light spectrum such as,
for example, the device described in U.S. Pat. No. 5,888,337.
[0039] The diagnostic system 12 can include a high resolution
Optical Emission Spectroscopy (OES) sensor such as from Peak Sensor
Systems, or Verity Instruments, Inc. Such an OES sensor has a broad
spectrum that spans the ultraviolet (UV), visible (VIS), and near
infrared (NIR) light spectrums. The resolution is approximately 1.4
Angstroms, that is, the sensor is capable of collecting 5550
wavelengths from 240 to 1000 nm. For example, the OES sensor can be
equipped with high sensitivity miniature fiber optic UV-VIS-NIR
spectrometers which are, in turn, integrated with 2048 pixel linear
CCD arrays.
[0040] The spectrometers receive light transmitted through single
and bundled optical fibers, where the light output from the optical
fibers is dispersed across the line CCD array using a fixed
grating. Similar to the configuration described above, light
emitting through an optical vacuum window is focused onto the input
end of the optical fibers via a convex spherical lens. Three
spectrometers, each specifically tuned for a given spectral range
(UV, VIS and NI R), form a sensor for a process chamber. Each
spectrometer includes an independent A/D converter. And lastly,
depending upon the sensor utilization, a full emission spectrum can
be recorded every 0.1 to 1.0 seconds.
[0041] In the embodiment shown in FIG. 4, the plasma processing
system 1b can, for example, be similar to the embodiment of FIG. 2
or 3 and further comprise either a stationary, or mechanically or
electrically rotating magnetic field system 60, in order to
potentially increase plasma density and/or improve plasma
processing uniformity, in addition to those components described
with reference to FIG. 2 and FIG. 3. Moreover, controller 14 can be
coupled to magnetic field system 60 in order to regulate the speed
of rotation and field strength. The design and implementation of a
rotating magnetic field is well known to those skilled in the
art.
[0042] In the embodiment shown in FIG. 5, the plasma processing
system 1c can, for example, be similar to the embodiment of FIG. 2
or FIG. 3, and can further comprise an upper electrode 70 to which
RF power can be coupled from RF generator 72 through impedance
match network 74. A frequency for the application of RF power to
the upper electrode can range from about 0.1 MHz to about 200 MHz.
Additionally, a frequency for the application of power to the lower
electrode can range from about 0.1 MHz to about 100 MHz. Moreover,
controller 14 is coupled to RF generator 72 and impedance match
network 74 in order to control the application of RF power to upper
electrode 70. The design and implementation of an upper electrode
is well known to those skilled in the art.
[0043] In the embodiment shown in FIG. 6, the plasma processing
system 1d can, for example, be similar to the embodiments of FIGS.
2 and 3, and can further comprise an inductive coil 80 to which RF
power is coupled via RF generator 82 through impedance match
network 84. RF power is inductively coupled from inductive coil 80
through dielectric window (not shown) to plasma processing region
45. A frequency for the application of RF power to the inductive
coil 80 can range from about 10 MHz to about 100 MHz. Similarly, a
frequency for the application of power to the chuck electrode can
range from about 0.1 MHz to about 100 MHz. In addition, a slotted
Faraday shield (not shown) can be employed to reduce capacitive
coupling between the inductive coil 80 and plasma. Moreover,
controller 14 is coupled to RF generator 82 and impedance match
network 84 in order to control the application of power to
inductive coil 80. In an alternate embodiment, inductive coil 80
can be a "spiral" coil or "pancake" coil in communication with the
plasma processing region 15 from above as in a transformer coupled
plasma (TCP) reactor. The design and implementation of an
inductively coupled plasma (ICP) source, or transformer coupled
plasma (TCP) source, is well known to those skilled in the art.
[0044] Alternately, the plasma can be formed using electron
cyclotron resonance (ECR). In yet another embodiment, the plasma is
formed from the launching of a Helicon wave. In yet another
embodiment, the plasma is formed from a propagating surface wave.
Each plasma source described above is well known to those skilled
in the art.
[0045] In one embodiment, a one-step etch process is performed,
whereby longitudinal etching completes the transfer of a pattern
from a second layer to a first layer, and lateral etching achieves
a target critical dimension (CD) for the feature formed following
the etch process. For example, the plasma processing device can
comprise various elements, such as described in any of FIGS. 2
through 6, or combinations thereof.
[0046] In the one embodiment, the method of etching comprises a
process chemistry having a C.sub.xF.sub.y containing gas, and an
oxygen containing gas. For example, the process chemistry can
include CF.sub.4 and O.sub.2. The process parameter space can
comprise a chamber pressure of about 1 to about 1000 mTorr, a
CF.sub.4 process gas flow rate ranging from about 5 to about 1000
sccm, an O.sub.2 process gas flow rate ranging from about 5 to
about 1000 sccm, an upper electrode (e.g., element 70 in FIG. 5) RF
bias ranging from about 200 to about 2500 W, and a lower electrode
(e.g., element 20 in FIG. 5) RF bias ranging from about 10 to about
2500 W. Also, the upper electrode bias frequency can range from
about 0.1 MHz to about 200 MHz, e.g., 60 MHz. In addition, the
lower electrode bias frequency can range from about 0.1 MHz to
about 100 MHz, e.g., 2 MHz.
[0047] In a first example, a process model is prepared in order to
form a relationship between a trim amount (e.g., the difference
between the first CD 22 and the second CD 28; see FIGS. 1A and 1B),
and an amount of gas. For instance, a process recipe is defined,
whereby the total process gas flow rate (i.e., CF.sub.4 and
O.sub.2), the chamber pressure, the RF bias on the upper electrode,
the RF bias on the lower electrode, the temperature of the
substrate holder, and the temperature of the chamber is maintained
constant while the O.sub.2 ratio is varied. The O.sub.2 ratio is
the ratio of the amount of O.sub.2 (e.g., molar flow rate of
O.sub.2), to the total amount of process gas (e.g., molar flow rate
of O.sub.2 and molar flow rate of CF.sub.4).
[0048] FIG. 7 presents the longitudinal (or vertical) etch rate as
a function of the O.sub.2 ratio. The longitudinal etch rate can be
determined by taking the ratio of the known thickness of the first
layer 14, and the time to reach endpoint when etching the first
layer 14. The asterisks (*) represent the data, the solid line
represents a curve fit (such as a polynomial fit, a power law fit,
or an exponential fit) of the data, and the dashed lines indicate
the predicted 95% confidence limits. The curve fit for the data of
FIG. 7 is given by ER1 (etch rate)=3.328 x+0.976 (where x
represents the abscissa data).
[0049] FIG. 8 presents the lateral etch rate as a function of the
O.sub.2 ratio. The longitudinal etch rate can be determined by
taking the ratio of the measured trim amount, and the time to reach
endpoint when etching the first layer 14. The asterisks (*)
represent the data, the solid line represent a curve fit (such as a
polynomial fit, a power law fit, or an exponential fit) of the
data, and the dashed lines indicate the predicted 95% confidence
limits. The curve fit for the data of FIG. 8 is given by ER2 (etch
rate)=1.233x+0.056.
[0050] FIG. 9 presents a ratio of the lateral etch rate to the
longitudinal etch rate. The asterisks (*) represent the data (i.e.,
from raw data), the solid line represents a curve fit (such as a
polynomial fit, a power law fit, or an exponential fit) of the
data, and the dashed lines indicate the predicted 95% confidence
limits. The curve fit for the data of FIG. 9 is given by ERR (etch
rate ratio)=(x+0.035)/(2.999 x+0.685). The expression for the etch
rate ratio from the curve fit of the longitudinal etch rate data
(FIG. 7), and the lateral etch rate data (FIG. 8) is
(x+0.044)/(2.699 x+0.791) (i.e., ERR.about.ER2/ER1).
[0051] FIG. 10 presents the data of FIG. 9, including the raw data,
the curve fit of the etch rate ratio (i.e., data model), and the
ratio of the longitudinal and lateral etch rate curve fits (i.e.,
ER model).
[0052] The trim amount (TA) during the one-step etch process (i.e.,
the difference between the first CD 22 and the second CD 28) can be
given by the following expression
TA=2OE ER.sub.lateral(.tau./ER.sub.longitudinal), (1)
[0053] where OE represents the amount of overetch (e.g., OE=1.1 for
a 10% overetch), ER.sub.lateral represents the lateral etch rate,
ER.sub.longitudinal represents the longitudinal etch rate, and
.tau. represents the thickness of the first layer 14. By inspection
of equation (1), the trim amount (TA) is directly proportional to
the etch rate ratio (ERR). Now referring to FIG. 11, the trim
amount data is presented as a function of the O.sub.2 ratio. The
asterisks (*) represent the data (i.e., from raw data), the solid
line represents a curve fit of the data, and the dashed lines
indicate the predicted 95% confidence limits. The curve fit is of
the form
TA=(x+a)/(bx+c), (2)
[0054] where a, b, and c are constants. As shown in FIG. 12,
extrapolation of the process model outside of the original bounds
of the model (e.g., 0.25<O.sub.2 ratio<0.4) exhibits an
improvement over polynomial fitting, for example. For instance,
Table 1 illustrates the curve-fitting statistics for a second order
polynomial expression, a third order polynomial expression, and an
expression of the form in equation (2) (i.e., ER-based model). The
curve-fitting statistics include the prediction R.sup.2, the root
mean square of the error (RSME), the maximum predicted error, the
average predicted error, and the predicted RMSE.
[0055] As depicted in Table 1 and FIG. 13, the ER-based model
compares well with the third order polynomial expression; however,
it does not exhibit over-fitting as exhibited by the third order
polynomial expression.
[0056] FIG. 14 illustrates the method for performing a one-step
etch process using a flow chart 100. Flow chart 100 begins in 110
with forming a first layer on a substrate. The first layer can, for
example, include an organic layer.
1 TABLE 1 Second- Third-order ER-based order model model model R2
0.9802 0.9953 0.9888 RMSE 1.1641 0.6331 0.8752 Max Pred. Err 1.0988
0.7455 0.8987 Avg. Pred. Err 0.4972 0.4439 0.4023 Pred. RMSE 0.3812
0.2468 0.2369
[0057] In 120, a second layer is formed on the first layer. The
second layer can, for example, include a layer of light-sensitive
material. In 130, a pattern is formed in the second layer, wherein
the pattern includes a feature in the second layer having a first
critical dimension. The pattern can, for example, be formed using
micro-lithography.
[0058] In 140, a target trim amount is set for trimming the first
critical dimension to a second critical dimension. In 150, a
variable parameter for a process recipe is determined using the
target trim amount and a process model relating trim amount data
with the variable parameter. For example, the variable parameter
can include an amount of process gas, a chamber pressure, a RF
power, a temperature, etc. Additionally, for example, the amount of
gas can include a mass, a number of moles, a mass flow rate, a
molar flow rate, a mass fraction, a mole fraction, a partial
pressure, or a concentration. Additionally, for example, the
process model can relate the trim amount with a mole fraction, as
shown in FIGS. 11 through 13.
[0059] In 160, the pattern is transferred from the second layer (or
overlying layer) into the first layer (or underlying layer) using
an etch process according to the process recipe. While transferring
the pattern into and through the first layer, the first critical
dimension of the feature formed in the second layer is reduced to
the second critical dimension as the feature is formed in the first
layer.
[0060] In an alternate embodiment, following the transfer of the
pattern into the first layer, the second critical dimension is
measured, and a difference between the first critical dimension and
the second critical dimension is determined. The difference is
compared with the target trim amount, and an offset (or error) is
determined from this comparison. Thereafter, when selecting a new
target trim amount for another substrate, following the previously
executed substrate, the new target trim amount is adjusted using
the offset. For instance, the adjustment can utilize a filter, such
as
x.sub.new,a=(1-.lambda.)x.sub.new+.lambda.y, (3)
[0061] where x.sub.new,a is the adjusted new target trim amount,
x.sub.new is the new target trim amount, y is the offset, and
.lambda. is the filter constant (0<.lambda.<1).
[0062] Now referring to FIG. 15, a method for preparing a process
model is described. The method includes a flow chart 200 beginning
in 210 with defining a nominal process recipe for transferring a
pattern having a first feature size from an overlying layer to an
underlying layer on a substrate, wherein the nominal process recipe
comprises at least one variable parameter and at least one constant
parameter.
[0063] In 220, trim amount data is accumulated as a function of the
at least one variable parameter by measuring the trim amount for
one or more values of the variable parameter. In 230, the trim
amount data as a function of the variable parameter is curve-fit.
For example, the curve-fit can include an expression of the form
y=(x+a)/(bx+c), where a, b, and c are constants, x is the at least
one variable parameter and y is the trim amount.
[0064] Although only certain embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
embodiments without materially departing from the novel teachings
and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention.
* * * * *