U.S. patent application number 13/227404 was filed with the patent office on 2013-03-07 for pulsed plasma chamber in dual chamber configuration.
This patent application is currently assigned to Lam Research Corporation. The applicant listed for this patent is Andrew D. Bailey, III, Rajinder Dhindsa, Eric Hudson, Alexei Marakhtanov. Invention is credited to Andrew D. Bailey, III, Rajinder Dhindsa, Eric Hudson, Alexei Marakhtanov.
Application Number | 20130059448 13/227404 |
Document ID | / |
Family ID | 47753486 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130059448 |
Kind Code |
A1 |
Marakhtanov; Alexei ; et
al. |
March 7, 2013 |
Pulsed Plasma Chamber in Dual Chamber Configuration
Abstract
Embodiments for processing a substrate in a pulsed plasma
chamber are provided. A processing apparatus with two chambers,
separated by a plate fluidly connecting the chambers, includes a
continuous wave (CW) controller, a pulse controller, and a system
controller. The CW controller sets the voltage and the frequency
for a first radio frequency (RF) power source coupled to a top
electrode. The pulse controller is operable to set voltage,
frequency, ON-period duration, and OFF-period duration for a pulsed
RF signal generated by a second RF power source coupled to the
bottom electrode. The system controller is operable to set
parameters to regulate the flow of species between the chambers to
assist in the negative-ion etching, to neutralize excessive
positive charge on the wafer surface during afterglow in the OFF
period, and to assist in the re-striking of the bottom plasma
during the ON period.
Inventors: |
Marakhtanov; Alexei;
(Albany, CA) ; Dhindsa; Rajinder; (San Jose,
CA) ; Hudson; Eric; (Berkeley, CA) ; Bailey,
III; Andrew D.; (Pleasanton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Marakhtanov; Alexei
Dhindsa; Rajinder
Hudson; Eric
Bailey, III; Andrew D. |
Albany
San Jose
Berkeley
Pleasanton |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
47753486 |
Appl. No.: |
13/227404 |
Filed: |
September 7, 2011 |
Current U.S.
Class: |
438/711 ;
156/345.26; 156/345.28; 257/E21.218 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01J 37/32146 20130101; H01J 37/32091 20130101; H01J 37/32825
20130101; H01L 21/67069 20130101; H01J 2237/3341 20130101 |
Class at
Publication: |
438/711 ;
156/345.28; 156/345.26; 257/E21.218 |
International
Class: |
H01L 21/3065 20060101
H01L021/3065; H01L 21/306 20060101 H01L021/306; C23F 1/08 20060101
C23F001/08 |
Claims
1. A wafer processing apparatus with a top chamber and a bottom
chamber separated by a plate that fluidly connects the top chamber
to the bottom chamber, comprising: a continuous wave (CW)
controller operable to set a voltage and a frequency for a first
radio frequency (RF) power source coupled to a top electrode in the
top chamber; a pulse controller operable to set voltage, frequency,
ON-period duration, and OFF-period duration for a pulsed RF signal
generated by a second RF power source coupled to a bottom electrode
in the bottom chamber; and a system controller operable to set
parameters for the CW controller and the pulse controller to
regulate a flow of species from the top chamber to the bottom
chamber through the plate during operation of the chamber, wherein
the flow of species assists in a negative-ion etching and in
neutralizing excessive positive charge on the wafer surface during
afterglow in the OFF period, and assists in re-striking a plasma in
the bottom chamber during the ON period.
2. The wafer processing apparatus as recited in claim 1, wherein
the system controller is further operable to set a first pressure
in the top chamber and a second pressure in the bottom chamber, and
wherein the first pressure is higher than the second pressure.
3. The wafer processing apparatus as recited in claim 2, wherein a
duration of the ON period is different from a duration of the OFF
period.
4. The wafer processing apparatus as recited in claim 2, wherein a
duration of the ON period is equal to a duration of the OFF
period.
5. The wafer processing apparatus as recited in claim 1, wherein a
frequency of the first RF power source has a value between 27 MHz
and 100 MHz.
6. The wafer processing apparatus as recited in claim 1, wherein a
frequency of the second RF power source has a value between 0.4 MHz
and 25 MHz.
7. The wafer processing apparatus as recited in claim 1, wherein a
voltage of the first RF power source has a value between 100 V and
600 V.
8. The wafer processing apparatus as recited in claim 1, wherein a
voltage of the second RF power source has a value between 1000 V
and 6000 V.
9. The wafer processing apparatus as recited in claim 1, wherein
the top chamber is operable to form a top plasma in the top chamber
while processing the wafer.
10. The wafer processing apparatus as recited in claim 1, wherein
the top chamber is operable to have a first pressure between 20
mTorr and 60 mTorr during processing, and wherein the bottom
chamber is operable to have a second pressure between 10 mTorr and
19 mTorr during processing.
11. A method for processing a wafer in a wafer processing apparatus
with a top chamber and a bottom chamber separated by a plate that
fluidly connects the top chamber to the bottom chamber, the method
comprising: setting first parameters for a continuous radio
frequency (RF) signal generated by a first RF power source coupled
to a top electrode in the top chamber, wherein the first parameters
include a first voltage and a first frequency; setting second
parameters for a pulsed RF signal generated by a second RF power
source coupled to a bottom electrode in the bottom chamber, wherein
the second parameters include a second voltage, a second frequency,
ON-period duration, and OFF-period duration; applying the
continuous RF signal to the top electrode; and applying the pulsed
RF signal to the bottom electrode, wherein setting the first
parameters and the second parameters regulates a flow of species
from the top chamber to the bottom chamber during operation of the
chamber, wherein the flow of species assists in a negative-ion
etching and in neutralizing excessive positive charge on the wafer
surface during afterglow in the OFF-period, and assists in
re-striking a plasma in the bottom chamber during the ON
period.
12. The method as recited in claim 11 further including: setting a
first pressure in the top chamber; and setting a second pressure in
the bottom chamber.
13. The method as recited in claim 12, further including:
increasing the first pressure to increase the flow of species from
the top chamber to the bottom chamber.
14. The method as recited in claim 11 further including: adjusting
a length of through-holes in the plate separating the top chamber
and the bottom chamber, wherein decreasing the length of the
through-holes increases the flow of species from the top chamber to
the bottom chamber.
15. The method as recited in claim 14 further including: reducing a
number of the through-holes in the plate to decrease the flow of
species between the top chamber and bottom chamber.
16. The method as recited in claim 11, wherein setting the first
parameters includes: increasing the first voltage to increase the
flow of species.
17. The method as recited in claim 11, wherein operations of the
method are performed by a computer program when executed by one or
more processors, the computer program being embedded in a
non-transitory computer-readable storage medium.
18. A wafer processing apparatus with a top chamber and a bottom
chamber separated by a plate that fluidly connects the top chamber
to the bottom chamber, comprising: a continuous wave (CW)
controller operable to set first parameters for a first radio
frequency (RF) power source coupled to a top electrode in the top
chamber; a pulse controller operable to set second parameters for a
second pulsed RF signal generated by a second RF power source
coupled to a bottom electrode in the bottom chamber, and to set
third parameters for a third pulsed RF signal generated by a third
RF power source coupled to the bottom electrode; and a system
controller operable to transfer the first, second, and third
parameters to regulate a flow of species from the top chamber to
the bottom chamber through the plate during operation of the
chamber, wherein the flow of species assists in a negative-ion
etching and in neutralizing excessive positive charge on the wafer
surface during afterglow in the OFF period, and assists in
re-striking a plasma in the bottom chamber during the ON
period.
19. The wafer processing apparatus as recited in claim 18, wherein
the first RF power source has a frequency between 30 MHz and 100
MHz, the second RF power source has a frequency between 0.4 MHz and
4 MHz, and the third RF power source has a frequency between 20 MHz
and 100 MHz.
20. The wafer processing apparatus as recited in claim 18, wherein
the top chamber is operable to have a first pressure between 20
mTorr and 60 mTorr during processing, and wherein the bottom
chamber is operable to have a second pressure between 10 mTorr and
19 mTorr during processing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. patent application Ser.
No. 12/850,552, filed on Aug. 4, 2010, entitled "Plasma Processing
Chamber with Dual Axial Gas Injection and Exhaust"; U.S. patent
application Ser. No. 12/850,559, filed on Aug. 4, 2010, entitled
"Dual Plasma Volume Processing Apparatus for Neutral/Ion Flux
Control"; U.S. patent application Ser. No. 13/188,421, filed Jul.
21, 2011, and entitled "Negative Ion Control For Dielectric Etch",
all of which are incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to methods, systems, and
computer programs for dielectric etching of a semiconductor device,
and more particularly, methods, systems, and computer programs for
dielectric etching of a semiconductor device in a dual-module
capacitively-coupled plasma (CCP) chamber.
[0004] 2. Description of the Related Art
[0005] The manufacturing of integrated circuits includes immersing
silicon substrates (wafers) containing regions of doped silicon
into chemically-reactive plasmas, where the submicron device
features (e.g., transistors, capacitors, etc.) are etched onto the
surface. Once the first layer is manufactured, several insulating
(dielectric) layers are built on top of the first layer, where
holes, also referred to as vias, and trenches are etched into the
material for placement of the conducting interconnectors.
[0006] SiO.sub.2 is a common dielectric used in semiconductor
manufacturing. The plasmas used for SiO.sub.2 etching often include
fluorocarbon gases such as carbon tetrafluoride CF.sub.4 and
octafluorocyclobutane (C--C4F.sub.8), along with argon (Ar) and
oxygen (O.sub.2) gases. The word plasma is used to refer to those
gases in which the constituent atoms and molecules have been
partially or wholly ionized. Capacitive radio frequency (RF) power
coupling is often used for striking and sustaining the plasma
because of the low dissociation rates obtained, favoring larger
passivating molecules and high ion energies at the surface. To
obtain independent control of the ion energy and the ion flux to
the silicon substrate, dual frequency capacitive discharges
(DF-CCP) are sometimes used.
[0007] Current plasma processing systems used in semiconductor
wafer fabrication rely on highly interdependent control parameters
to control radical separation, radical flux, ion energy, and ion
flux delivered to the wafer. For example, current plasma processing
systems attempt to achieve necessary radical separation, radical
flux, ion energy, and ion flux by controlling a single plasma
generated in the presence of the wafer. Unfortunately, chemistry
dissociation and radical formation are coupled to ion production
and plasma density and often do not work in concert to achieve the
desired plasma processing conditions.
[0008] Some semiconductor processing equipment uses pulsed RF power
sources. The current pulsed RF plasma technology does not provide
control of the afterglow plasma during the RF OFF period when the
plasma shuts off. Typically, during the RF OFF period, the plasma
potential collapses and electrons escape to the walls of the
chamber. In the afterglow, the electron density drops and the
negative ion density increases. Then ions to escape to the walls as
well. The charged species dynamics determines the distribution of
charges inside the chamber and, therefore, its etching properties,
but unfortunately these dynamics and fluxes of charged species are
mostly uncontrolled. The only controls available for the afterglow
period are the frequency of the modulation and the duty cycle.
[0009] Another problem with pulsed plasma technology is plasma
re-ignition when the RF power turns on. If the plasma and the
afterglow are extinguished completely during the RF OFF period,
re-striking the plasma requires high RF voltage levels. Further,
there can be trouble with RF issues, especially when operating at
low gas pressures.
[0010] It is in this context that embodiments arise.
SUMMARY
[0011] Embodiments of the present invention provide systems,
methods, and computer programs for processing a semiconductor
substrate in a pulsed plasma chamber in a dual chamber
configuration.
[0012] It should be appreciated that the present invention can be
implemented in numerous ways, such as a process, an apparatus, a
system, a device or a method on a computer readable medium. Several
inventive embodiments of the present invention are described
below.
[0013] In one embodiment, a wafer processing apparatus with a top
chamber and a bottom chamber separated by a plate that fluidly
connects the top chamber to the bottom chamber includes a
continuous wave (CW) controller, a pulse controller, and a system
controller. The CW controller is operable to set the voltage and
the frequency for a first radio frequency (RF) power source coupled
to a top electrode in the top chamber. The pulse controller is
operable to set voltage, frequency, ON-period duration, and
OFF-period duration for a pulsed RF signal generated by a second RF
power source coupled to the bottom electrode in the bottom chamber.
Further, the system controller is operable to set parameters for
the CW controller and the pulse controller to regulate the flow of
species from the top chamber to the bottom chamber through the
plate during operation of the chamber. The flow of species assists
in the negative ion density control during afterglow in the OFF
period, and assists in the re-striking of the plasma in the bottom
chamber during the ON period.
[0014] In another embodiment, a method, for processing a wafer in a
wafer processing apparatus with a top chamber and a bottom chamber
separated by a plate that fluidly connects the top chamber to the
bottom chamber, includes an operation for setting first parameters
for a continuous radio frequency (RF) signal generated by a first
RF power source coupled to a top electrode in the top chamber. The
first parameters include a first voltage and a first frequency.
Further, the method includes an operation for setting second
parameters for a pulsed RF signal generated by a second RF power
source coupled to a bottom electrode in the bottom chamber. The
second parameters include a second voltage, a second frequency,
ON-period duration, and OFF-period duration. The continuous RF
signal is applied to the top electrode, and the pulsed RF signal is
applied to the bottom electrode. Setting the first parameters and
the second parameters regulates the flow of species from the top
chamber to the bottom chamber during operation of the chamber. The
flow of species assists in a negative ion density control during
afterglow in the OFF period, and assists in re-striking a plasma in
the bottom chamber during the ON period.
[0015] In yet another embodiment, a wafer processing apparatus,
with a top chamber and a bottom chamber separated by a plate that
fluidly connects the top chamber to the bottom chamber, comprises a
CW controller, a pulse controller, and a system controller. The CW
controller is operable to set first parameters for a first radio
frequency (RF) power source coupled to a top electrode in the top
chamber, and the pulse controller is operable to set second
parameters for a second pulsed RF signal generated by a second RF
power source coupled to a bottom electrode in the bottom chamber.
The pulse controller is further operable to set third parameters
for a third pulsed RF signal generated by a third RF power source
coupled to the bottom electrode. Additionally, the system
controller is operable to transfer the first, second, and third
parameters to regulate a flow of species from the top chamber to
the bottom chamber through the plate during operation of the
chamber. The flow of species assists in the negative ion density
control during afterglow in the OFF period, and assists in
re-striking the plasma in the bottom chamber during the ON
period.
[0016] Other aspects will become apparent from the following
detailed description, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention may best be understood by reference to the
following description taken in conjunction with the accompanying
drawings.
[0018] FIG. 1 shows an etching chamber, according to one
embodiment.
[0019] FIG. 2 illustrates the behavior of a pulsed plasma chamber,
according to one embodiment.
[0020] FIG. 3 illustrates the effect of RF power frequency and
chamber pressure on the plasma density, according to one
embodiment.
[0021] FIG. 4 shows a semiconductor wafer processing apparatus with
two chambers, according to one embodiment of the invention.
[0022] FIG. 5 shows a semiconductor wafer processing apparatus, in
accordance with one embodiment of the present invention.
[0023] FIG. 6 shows the chamber of FIG. 5 with an upper plasma and
a lower plasma, in accordance with one embodiment of the present
invention.
[0024] FIG. 7 illustrates the normalized ion flux as a function of
the plate thickness, according to one embodiment.
[0025] FIG. 8 shows the flow of an algorithm for operating a
semiconductor wafer processing apparatus, in accordance with one
embodiment of the invention.
[0026] FIG. 9 shows the flow of an algorithm for processing a
wafer, in accordance with one embodiment of the invention.
[0027] FIG. 10 is a simplified schematic diagram of a computer
system for implementing embodiments of the present invention.
DETAILED DESCRIPTION
[0028] The following embodiments provide systems, methods, and
computer programs for processing a semiconductor substrate in a
pulsed plasma chamber in a dual chamber configuration. It will be
apparent, that the present embodiments may be practiced without
some or all of these specific details. In other instances, well
known process operations have not been described in detail in order
not to unnecessarily obscure the present embodiments.
[0029] FIG. 1 shows an etching chamber, according to one
embodiment. Exciting an electric field between two electrodes is
one of the methods to obtain RF gas discharge in an etching
chamber. When an oscillating voltage is applied between the
electrodes, the discharge obtained is referred to as a capacitive
coupled plasma (CCP) discharge.
[0030] Plasma can be created utilizing stable feedstock gases to
obtain a wide variety of chemically reactive by-products created by
the dissociation of the various molecules caused by
electron-neutral collisions. The chemical aspect of etching
involves the reaction of the neutral gas molecules and their
dissociated by-products with the molecules of the to-be-etched
surface, and producing volatile molecules, which can be pumped
away. When plasma is created, the positive ions are accelerated
from the plasma across a space-charge sheath separating the plasma
from the walls, to strike the wafer surface with enough energy to
remove material from the surface of the wafer. This is known as ion
bombardment or ion sputtering. Some industrial plasmas, however, do
not produce ions with enough energy to efficiently etch a surface
by purely physical means. It has been proven that that the combined
actions of both neutral-gas etching and ion bombardment produces a
faster etch rate than simply adding the effects of each method.
[0031] In one embodiment, Fluorocarbon gases, such as CF.sub.4 and
C--C.sub.4F.sub.8, are used in the dielectric etch process for
their anisotropic and selective etching capabilities, but the
principles of the invention can be applied to other plasma-creating
gases. The Fluorocarbon gases are readily dissociated into smaller
molecular and atomic radicals. These chemically reactive
by-products etch away the dielectric material, which in one
embodiment can be SiO.sub.2 or SiOCH for low-k devices.
[0032] The chamber of FIG. 1 includes a top electrode 104 connected
to ground, and a bottom electrode 108 powered by low-frequency RF
generator 118 and high-frequency RF generator 116. The bottom
electrode 108 is connected, via matching network 114, to the
low-frequency RF generator 118 and to the high-frequency RF
generator 116. In one embodiment, low-frequency RF generator 118
has an RF frequency of 2 MHz, and high-frequency RF generator 116
has an RF frequency of 27 MHz.
[0033] The chamber of FIG. 1 includes a gas showerhead on the top
electrode 104 to input gas in the chamber, and a perforated
confinement ring 112 that allows the gas to be pumped out of the
chamber. When substrate 106 is present in the chamber, silicon
focus ring 110 is situated next to the substrate such that there is
a uniform RF field at the bottom surface of the plasma 102 for
uniform etching on the surface of the wafer.
[0034] In one embodiment, low-frequency RF generator 118 is pulsing
while high-frequency RF generator 116 is not pulsing. In another
embodiment, both RF generators are pulsing, and, in yet another
embodiment, the high-frequency RF generator 116 is pulsing while
low-frequency RF generator 118 is not pulsing, i.e., low-frequency
RF generator 118 is always turned on while processing the
wafer.
[0035] FIG. 2 illustrates the behavior of a pulsed plasma chamber,
according to one embodiment. The pulsed plasma chamber associated
with FIG. 1 includes one pulsing RF power source. Graph 202
illustrates the voltage of the RF power source, that includes an ON
period, when the RF power source is turned on, and an OFF period,
when the RF power source is turned off. The graph 204 illustrates
that the power of the RF power source has two levels, one level
during the ON period, which is greater than zero, and a second
level during the OFF period, which is equal to 0, i.e., the RF
power is turned off.
[0036] The ON period has two phases: a first phase when the plasma
is being ignited (i.e., turned on), and a second phase
corresponding to a steady-state when the plasma is present in the
chamber. In the turn-on phase, the plasma sheaths are forming and
changing as the plasma ignites. There is a larger electron average
energy, and a low ion flux density. In addition, the power is not
well matched in the turn-on phase due to the varying plasma
impedance while igniting the plasma. In the steady state phase, the
electron density is nearly constant, and there is a large positive
ion flux density. The power is well matched with an almost constant
plasma impedance, and the plasma sheets oscillate in steady
fashion.
[0037] The OFF period has two phases: a first phase when the plasma
is being turned off, and a second phase named "late afterglow." In
the turn-off phase, there is a rapidly decreasing electron average
energy, a rapidly falling ion flux density, and a decreasing plasma
potential. The plasma sheaths disintegrate as the electron density
decay. In the late-afterglow phase, the power level is zero with a
small electron average energy. There is also a small ion flux
density, and the negative ions can reach the surfaces of the
chamber. The plasma sheaths disintegrate as the electron density
decays.
[0038] Graph 206 shows the electron energy changing during the ON
and OFF periods. In the ON period, the electron energy is high, and
in the OFF period, the electron energy decreases to zero. Graph 208
shows the density of electrons 220, and the positive ion density
222. The positive ion density 222 is high during the ON period, and
decreases in the OFF period. Therefore, etching with positive ions
takes place mainly during the ON period.
[0039] Graph 210 shows the evolution of the plasma potential over
time. As discussed above, the plasma potential spikes at the
beginning of the turn on phase and then reaches a stable value. In
the turned off phase, the plasma potential decays until the plasma
potential reaches a value of zero. Graph 212 shows the value of the
positive ion flux, which is almost constant during the ON period,
and quickly decays to 0 in the OFF period.
[0040] In addition, graph 214 shows the value of the negative ion
flux over time. The negative ion flux is substantially 0 during the
ON period, but the negative ion flux has a positive spike in the
OFF period, which causes etching in the wafer with negative ions
and neutralizing excessive positive charge on the wafer surface
during the OFF period.
[0041] Pulsing the RF power source helps etching performance
because trenching, notching and charging damages can be reduced,
when compared to a non-pulsing RF power source. Charges can build
up between the top and the bottom of a well during continues
discharge, which can cause the deflection of ions. The charge
buildup can be reduced in pulsed discharges because the low
electron density in the afterglow regime allows more negative ions
and electrons to be pulled to the well bottom, to neutralize the
positive charges that might have accumulated at the bottom of the
well.
[0042] FIG. 3 illustrates the effect of RF power frequency and
chamber pressure on the plasma density, according to one
embodiment. FIG. 3 illustrates some measurements taken on a
non-pulsing plasma chamber under different conditions of RF power
frequency and pressure in the chamber. The measurements were taken
with a single RF power source at 400 W, in a chamber with oxygen
and 5% Argon.
[0043] Line 302 charts the values for the positive ion flux at
different levels of pressure and with an RF frequency of 2 MHz. As
the pressure in the chamber increases, the negative ion flux
increases to about a maximum positive ion flux at about 300 mTorr.
Therefore, for a low RF frequency (2 MHz), the chamber is more
efficient at high pressure. Line 306 charts the volumes when the RF
frequency is 27 MHz. In this case, the flux gradually increases
until the pressure is about 100 mTorr, and then remains
substantially constant. Line 304 charts the values for the flux
when using an RF frequency of 60 MHz. At this high frequency, the
chamber is more efficient at low pressure, and less efficient as
the pressure increases.
[0044] In general, when using a pulsed RF power, it is more
desirable to run the chamber at low pressure, so the ions can
penetrate deep in the holes. However, it is relatively hard to
strike plasma in a low pressure plasma chamber, because there are
fewer electrons when operating at low pressure than when operating
at high pressure.
[0045] Embodiments of the invention utilize a dual chamber
configuration, where the bottom chamber is pulsed on the top
chamber is not pulsed. As discussed in more detail below with
reference to FIGS. 4-6, the two chambers are separated by a
perforated grid that provides flow of species from the top chamber
to the bottom chamber. Electrons escape the top plasma and flow to
the bottom chamber to assist in the re-striking of the plasma.
Since there are have more electrons in the bottom chamber, it is
easier to re-strike the plasma. Therefore, the use of the dual
chamber facilitates having a low pressure chamber and a pulsed RF
power source at the same time.
[0046] FIG. 4 shows a semiconductor wafer processing apparatus with
two chambers, according to one embodiment of the invention. The
semiconductor wafer processing apparatus includes a dual volume
plasma source. Top chamber 414 is a Continuous Wave (CW) Radical
Control Plasma (RCP), separated from lower pulsed RF capacitive
plasma chamber 420 by perforated grounded electrode 424, also
referred to herein as plate or grid. The lower volume is a pulsing
CCP plasma chamber, and the upper volume acts as a source of
radicals, electrons, and ions that are injected into the lower
volume.
[0047] During the afterglow in the OFF period of the pulsed
lower-chamber RF, the flux of neutral and charged species in the
lower chamber can be controlled by adjusting the parameters in the
top chamber. Having charged species from the RCP top chamber
flowing to the lower chamber also helps with re-striking the bottom
plasma 418 during the RF ON period. In one embodiment, the
afterglow and re-striking is controlled by using different plasma
sources in the upper chamber. For example, using an inductively
coupled or helicon plasma in the top chamber.
[0048] This configuration improves performance of the chamber,
because the upper plasma 416 source provides control of the plasma
afterglow in the bottom chamber, and provides control of the
charged species dynamics for etching substrate 422. Furthermore,
the RCP in the top chamber helps to re-ignite the plasma 418 in CCP
bottom chamber by providing initial charged species to strike the
CCP plasma.
[0049] In a single volume pulsing chamber, the only control for
negative ion etching is the ON and OFF period cycles. In a
dual-volume chamber, since the upper chamber is always on, there is
a constant flow of species coming from the top chamber, even in the
bottom chamber OFF period. Therefore, it is possible to control the
etching process both in the ON and OFF periods. The electrons from
the top plasma 416 go through the through-holes 426 that connect
the top chamber to the bottom chamber. The electrons carry energy,
so the through-holes 426 form electron beams into the bottom
chamber.
[0050] In one embodiment, bottom chamber 420 is powered by a first
pulsed RF power source 406 and by a second pulsed RF power source
410. The RF power sources are connected to the bottom electrode in
chamber 420 via respective RF Matches 408 and 412. The top
electrode in top chamber 414 is connected to a third RF power
source 402 via matching network 404. In one embodiment, the third
RF power source 402 provides a continuous wave RF power to top
chamber 414.
[0051] A pulse controller 430 controls the parameters for the RF
power generated by the first pulsed RF power source 406 and by the
second pulsed RF power source 410. The parameters that control the
first and the second RF power sources include the pulsing cycle
(i.e., the duration of the ON and OFF periods) of the RF power
sources, the frequency, the voltages, and the power levels for the
first and second RF power sources. By controlling the parameters of
the RF power sources, the system controls, for example, the RF OFF
period and the plasma afterglow in the bottom chamber. This control
of the RF parameters also enables the system to control the flux of
neutral and charged species from the top chamber. Having charged
species from the top chamber traveling to the lower chamber also
assists with the re-striking of the plasma at the beginning of the
RF ON period, which means that plasma re-strikes faster than in the
case of a single chamber device with the same RF power.
[0052] A continuous wave controller 428 controls the RF power
generated by third RF power source 402. Thus, the continuous wave
controller 428 controls the parameters of the RF power on the top
chamber, which include frequency, voltage, and power. System
controller 432 is in communication with pulse controller 430 and
continuous wave controller 428, and system controller 432 sets the
control parameters for the RF power in the top and bottom chambers.
By controlling the parameters for the CW controller and the pulse
controller, the system controller 432 is operable to regulate the
flow of species from the top chamber to the bottom chamber through
the plate during operation of the chamber, where the flow of
species assists in the negative-ion etching and in neutralizing
excessive positive charge on the wafer surface during afterglow in
the OFF period, and assists in the re-striking of the plasma in the
bottom chamber during the ON period. System controller 432 has
plasma recipe setting 434 as an input. The plasma recipe setting
434 includes the parameters for the three RF power sources,
including frequency, voltage, power, and ON/OFF cycles, and other
parameters for the operation of the chamber. Other values in the
plasma recipe setting may include the configuration of the plate
separating the chambers (e.g., the number of through-holes, the
thickness of the plate, the distribution of the through-holes,
etc.), the pressure in the top chamber, the pressure in the bottom
chamber, duration of the etching cycle, gas flow into the chambers,
etc.
[0053] Besides controlling the RF power sources, system controller
432 is also operable to control other parameters of the chamber,
such as the pressure in the top chamber, the pressure in the bottom
chamber, and the configuration of the plate 424 situated between
the top and bottom chambers.
[0054] The top and bottom chambers have independent controls for
the gas flow into the respective chambers. There is a separate
source of gas intake in the top chamber. The grid 424 also includes
gas outlets that form a gas showerhead into the bottom chamber.
Grid 424 has an outside surface which is an insulator dielectric,
such as aluminum oxide. In one embodiment, grid 424 is made of
aluminum and coated with aluminum oxide. In another embodiment, the
grid is made of silicon. Grid 424 is connected to ground. In one
embodiment, grid is 27 mm thick, (i.e., the through-holes have the
length of 27 mm), and the through-holes have a diameter of 2 mm,
although other values are also possible.
[0055] Having dual volumes increases the amount of negative ions in
the bottom chamber during the OFF period, which improves the
etching with negative ions. As electrons from the top chamber
arrive at the bottom chamber, the electrons attach to ions and
create more negative ions in the chamber during the OFF period.
[0056] There are several parameters of the top chamber that affect
the performance of the bottom chamber. First, the electron density
in the top chamber. The higher the density, the higher the number
of electrons traveling to the bottom chamber. Second, the voltage
on the sheath of the top chamber, which defines the energy of some
electrons, such as the secondary electrons. Third, the pressure in
the chamber. The higher the pressure in the top chamber, the more
particles (electrons, ions) that will travel to the bottom chamber.
Fourth, the thickness of the plate 424 and the density of
through-holes 426. The bigger the thickness of the plate, the less
number of species that will travel to the bottom chamber. In
addition, the higher the density of the through-holes 426, the more
species that will travel to the bottom.
[0057] The embodiment of FIG. 4 includes a first pulsed RF power
source 406 at 2 MHz and a second pulsed RF power source 410 at 27
MHz. The RF power sources are connected to the bottom electrode in
chamber 420 via respective RF Matches 408 and 412. The top
electrode in top chamber 414 is connected to a third RF power
source 402 via matching network 404. The third RF power source 402
is not pulsing.
[0058] It is noted that the embodiment illustrated in FIG. 4 is
exemplary. Other embodiments may utilize different types of
chambers, different frequencies, only one RF power source in the
bottom chamber, different size separation plates, different
pressures in top and bottom chambers, etc. For example, in one
embodiment, top chamber is a CCP plasma chamber. Furthermore, some
of the modules described above in the semiconductor wafer
processing apparatus may be combined into a single module, or the
functionality of a single module may be performed by a plurality of
modules. For example, in one embodiment, continuous wave controller
428 and pulse controller 430 are integrated within system
controller 432, although other configurations are also possible.
The embodiment illustrated in FIG. 5 should therefore not be
interpreted to be exclusive or limiting, but rather exemplary or
illustrative.
[0059] In one embodiment, the top electrode is connected to a RF
power source at 27 MHz, and the bottom electrode in the bottom
chamber is connected to an RF power source at 2 MHz. In another
embodiment, the pressure in the top chamber has a value between 20
mTorr and 60 mTorr, and the pressure in the bottom chamber has a
value between 10 mTorr and 19 mTorr.
[0060] In yet another embodiment, the top chamber has a single RF
power source with a frequency between 27 MHz and 100 MHz, and the
bottom chamber has a single RF power source with a frequency
between 0.4 MHz and 25 MHz. The voltage in the top power source can
be in the range of hundreds of volts (e.g., 100 V to 2000 V or
more). The bottom RF power source can have a voltage up to 6000 V
or more. In one embodiment, the voltage is 1000 V. In another
embodiment, the voltage of the top RF power source has a value
between 100 V and 600 V, and the voltage of the bottom RF power
source has a value between 1000 V and 6000V.
[0061] The pressure in the top chamber and the bottom chamber can
have a value between 10 mTorr to 500 mTorr. In one embodiment, the
top chamber operates at a pressure of 20 mTorr and the bottom
chamber operates at 15 mTorr.
[0062] FIG. 5 shows a semiconductor wafer processing apparatus, in
accordance with one embodiment of the present invention. The
apparatus includes a chamber 500 formed by a top plate 500A, a
bottom plate 500B, and walls 500C. In one embodiment, the walls
500C form a contiguous cylindrical shaped wall 500C. In other
embodiments, the walls 500C can have other configurations, so long
as an interior cavity 500D of the chamber 500 can be isolated from
an external environment outside the chamber 500. In various
embodiments, the top plate 500A, bottom plate 500B, and walls 500C
of the chamber 500 can be formed of a metal that is a good
conductor of electricity and heat, and that is chemically
compatible with the process gases to which the interior cavity 500D
is to be exposed during wafer processing. For example, in various
embodiments, metals such as aluminum, stainless steel, or the like,
maybe used to form the chamber 500 components.
[0063] The chamber 500 structure, including the top plate 500A,
bottom plate 500B and walls 500C, is formed of an electrically
conducting material and is electrically connected to a reference
ground potential. The chamber 500 includes an exhaust port 535
which provides for fluid connection of the interior cavity 500D to
an external exhaust pump 537, such that a negative pressure can be
applied through the exhaust port 535 to remove gases and
particulates from within the interior cavity 500D. In various
embodiments, the exhaust pump 537 can be implemented in different
ways, so long as the exhaust pump 537 is capable of applying a
suction at the exhaust port 535 to draw a fluid flow from the
interior cavity 500D of the chamber 500.
[0064] A dual plasma processing apparatus is disposed within the
interior cavity 500D of the chamber 500. The dual plasma processing
apparatus includes an upper plasma chamber 512 that includes an
upper plasma generation volume 503. The dual plasma processing
apparatus also includes a lower plasma chamber 514 that includes a
lower plasma generation volume 509. The upper and lower plasma
chambers 512 and 514 are physically and fluidly connected by a gas
distribution unit 515, which is disposed to separate the upper and
lower plasma generation volumes 503 and 509.
[0065] The upper plasma chamber 512 is formed in part by an outer
structural member 504 defined around a periphery of the upper
plasma chamber 512 and connected to the top plate 500A. The upper
plasma chamber 512 also includes a showerhead electrode 501
disposed above the upper plasma generation volume 503 within the
outer structural member 504.
[0066] During operation, radiofrequency (RF) power is transmitted
from an RF power source 505 to the showerhead electrode 501. In one
embodiment, the RF power source 505 is defined to provide RF power
at multiple frequencies. In one embodiment, frequencies of the RF
power source 505 are set within a range extending from 5 kHz to 500
MHz. In another embodiment, frequencies of the RF power source 505
are set within a range extending from 400 kHz to 60 MHz.
[0067] Additionally, in one embodiment, the showerhead electrode
501 is connected to a DC bias source 520 to enable control of
plasma potential within the upper plasma generation volume 503
independent of the plasma density. The DC bias source 520 is
defined to control a bias of the showerhead electrode 501 at
various voltage settings extending upward from ground. In one
embodiment, the DC bias source 520 of the showerhead electrode 501
can be defined to operate in a pulsed manner to synchronize the
plasma in the upper plasma generation volume 503 with the plasma in
the lower plasma generation volume 509. More specifically, this
pulsed control of the DC bias source 520 can be used to control a
time-dependent voltage differential between the plasmas in the
upper and lower plasma generation volumes 503 and 509.
[0068] Each of the through-holes 517 is defined in open fluid
communication through the upper surface of the gas distribution
unit 515. However, the gas supply ports 519 are not fluidly exposed
through the upper surface of the gas distribution unit 515.
Therefore, the gas supply ports 519 are defined to flow plasma
process gas into only the lower plasma generation volume 509. In
contrast, the through-holes 517 are defined to enable fluid
communication between the upper and lower plasma generation volumes
503 and 509. Fluid flow through the through-holes 517 of the gas
distribution unit 515 may be controlled by a pressure differential
between the upper plasma generation volume 503 and the lower plasma
generation volume 509.
[0069] It should be understood that the gas distribution unit 515
serves as a RF return path electrode, plasma process gas manifold,
fluid flow baffle plate, and ion filter. In various embodiments the
gas distribution unit 515 can be formed of metal that is a good
conductor of electricity and heat, and that is chemically
compatible with the processes to be conducted in the upper and
lower plasma generation volumes 503 and 509, such as aluminum,
stainless steel, silicon, silicon carbide, silicon oxide, yttrium
oxide, or essentially any other material that provides adequate
plasma resistance, electrical conduction, and thermal conduction
for the plasma processes to which it is exposed.
[0070] In various embodiments, the gas distribution unit 515 is
connected to its own DC bias source 524 and RF power source 522 to
enable the gas distribution unit 515 to provide an appropriate
ground return path for the RF power sources 505 and 511, while also
providing appropriate bias to affect ions generated in the upper
plasma generation volume 503. The RF power source 522 can also be
defined to provide RF power at multiple frequencies. Additionally,
in one embodiment, electrodes 530 are embedded within the gas
distribution unit 515 and are connected to the DC bias source 524
to provide bias voltage for influencing ions generated in the upper
plasma generation volume 503. In one embodiment, the embedded
electrodes 530 within the gas distribution unit 515 are defined
around the through-holes 517, such that bias voltage applied to the
embedded electrodes 530 can be used to either accelerate or
decelerate ions passing through the through-holes 517. Also, in one
embodiment, the embedded electrodes 530 within the gas distribution
unit 515 are defined in multiple separately controllable zones,
with each zone connected to its own DC bias source 524. This
embodiment enables independent regional biasing across the gas
distribution unit 515, to provide for independent regional ion
control across the gas distribution unit 515.
[0071] In one embodiment, portions of the gas distribution unit 515
that are exposed to plasma in either the upper or lower plasma
generation volumes 503 and 509 are protected by a covering of
plasma resistant material. In one embodiment, the plasma resistant
material is formed as a coating. In another embodiment, the plasma
resistant material is formed as a protective structure, e.g.,
plate, that conformally covers the gas distribution unit 515. In
either of these embodiments, the plasma resistant material is
secured to the gas distribution unit 515 to ensure adequate
electrical and thermal conduction between the plasma resistant
material and the gas distribution unit 515. In the embodiment of
the plasma resistant protective structure, the protective
structure, may be secured to the gas distribution unit 515 by a
pressure differential between the upper and lower plasma generation
volumes 503 and 509, by a number of fasteners, or by a combination
thereof. In various embodiments, the plasma resistant coating, the
protective structure, used to protect the gas distribution unit 515
can be formed of silicon, silicon carbide, silicon oxide, yttrium
oxide, or essentially any other material that provides adequate
plasma resistance, electrical conduction, and thermal conduction
for the plasma processes to which it is exposed.
[0072] Each of the gas supply ports 519 and through-holes 517 is
defined to optimize fluid flow through it, while simultaneously
preventing adverse intrusion of plasma into it. Fluid flow and
plasma intrusion through each of the gas supply ports 519 and
though-holes 517 is directly proportional to its size. Therefore,
it is necessary to define each of the gas supply ports 519 and
though-holes 517 such that its size is small enough to prevent
adverse plasma intrusion into it, while remaining large enough to
provide adequate fluid flow through it. In various embodiments, the
diameter of the gas supply ports 519 is sized within a range
extending from about 0.1 mm to about 3 mm. In various embodiments,
the diameter of the through-holes 517 is sized within a range
extending from about 0.5 mm to about 5 mm. It should be understood,
however, that in various embodiments the gas supply ports 519 and
through-holes 517 can be respectively defined with essentially any
diameter size, so long as the diameter size provides for adequate
fluid flow there through while simultaneously providing for
adequate suppression of plasma intrusion therein.
[0073] A chuck 507 is disposed within the interior cavity 500D of
the chamber 500 below the lower plasma generation volume 509. In
one embodiment, the chuck 507 is cantilevered from the wall 500C of
the chamber 500. In one embodiment, the chuck 507 is an
electrostatic chuck and provides an electrode for transmitting RF
power to the lower plasma generation volume 509. The chuck 507 is
defined to hold a substrate 513, i.e., wafer 513, in exposure to
the lower plasma generation volume 509. In one embodiment, a wafer
edge ring 549 is disposed on the chuck 507 about the periphery of a
substrate 513 holding area on the chuck 507. In various
embodiments, the wafer edge ring is formed of quartz or silicon.
Also, in one embodiment, a conductor 548 is disposed below the
wafer edge ring 549, and is connected to drive DC bias through the
wafer edge ring 549.
[0074] A vertical distance across the lower plasma generation
volume 509, as measured perpendicular to both the chuck 507 and the
gas distribution unit 515, can be set and controlled by controlling
the vertical position of the chuck 507. The vertical distance
across the lower plasma generation volume 509 can be set to achieve
a sufficient center-to-edge plasma uniformity and density, and can
also be set to avoid printing on the wafer 513 by jets of gas
flowing from the gas supply ports 519 and through-holes 517. In
various embodiments, the vertical distance across the lower plasma
generation volume 509 can be set within a range extending from
about 1 cm to about 5 cm, or from about 2 cm to about 3.6 cm.
[0075] The chuck 507 is further defined to supply RF power from an
RF power source 511 to the lower plasma generation volume 509, such
that chuck 507 serves as an electrode for the lower plasma
generation volume 509. It should be understood that the RF power
source 511 of the lower plasma chamber is separate and independent
from the RF power source 505 of the upper plasma chamber.
Therefore, the RF power supplied to the upper and lower plasma
generation volumes 503 and 509 can be separately and independently
controlled.
[0076] In one embodiment, the RF power source 511 provides a
pulsing RF power, with an ON cycle and an OFF cycle. In another
embodiment, the RF power source 511 provides RF power at two
different frequencies, where the RF power for both frequencies is
pulsing. In another embodiment, one RF power at a first frequency
is pulsing and the other RF power at a second frequency is not
pulsing. Pulse controller 430 is coupled to RF power source 511,
and pulse controller 430 sets the parameters for the RF power
provided by RF power source 511. These parameters include the
frequency, power, and ON/OFF duty cycle of the RF power generated
by the power source 511. In addition, continuous wave controller
428 is coupled to the RF power source 505, and continuous wave
controller 428 sets the parameters for the RF power generated by RF
power source 505, including frequency and power of the RF power
generated in the top chamber.
[0077] In one embodiment, the RF power source 511 is defined to
provide RF power and multiple frequencies. For example, the RF
power source 511 can be defined to provide RF power at frequencies
of 2 MHz, 27 MHz, and 60 MHz. It should be understood that each of
the RF power sources 505 and 511 for the upper and lower plasma
chambers 512 and 514, respectively, are connected through their own
matching networks to enable transmission of the RF power to the
showerhead electrode 501 and the chuck 507, respectively. As
previously discussed, in one embodiment, the gas distribution unit
515 serves as a reference ground electrode in the RF power return
path for both the upper and lower plasma generation volumes 503 and
509.
[0078] The upper plasma chamber is defined to include an exhaust
channel 525 through which gases within the upper plasma generation
volume 503 are exhausted into the interior cavity 500D of the
chamber 500. A pressure throttle ring 527 is defined to move within
the exhaust channel 525 to throttle a fluid flow, i.e., flow of
gases, from the upper plasma generation volume 503 through the
exhaust channel 525 to the interior cavity 500D of the chamber 500.
In one embodiment, the pressure throttle ring 527 is defined to
move vertically within a conformally defined recessed region within
the outer structural member 504 of the upper plasma chamber 512. In
this embodiment, the pressure throttle ring 527 can be moved in a
controlled manner down into the exhaust channel 525 to reduce a
flow area through the exhaust channel 525 and thereby throttle the
fluid flow from the upper plasma generation volume 503. In one
embodiment, the pressure throttle ring 527 is defined to enable a
complete shutoff of flow from the upper plasma generation volume
503 through the exhaust channel 525 into the interior cavity 500D
of the chamber 500.
[0079] It should be understood that the pressure throttle ring 527
configuration depicted in FIG. 5 is one example embodiment of its
implementation. In other embodiments, the pressure throttle ring
527 can be implemented in different ways, so long as the pressure
throttle ring 527 provides for control of fluid flow through the
exhaust channel 525. The lower plasma chamber is defined to include
a set of slotted exhaust channels 529 through which gases within
the lower plasma generation volume 509 are exhausted into the
interior cavity 500D of the chamber 500.
[0080] A pressure control ring 531 is defined to move toward and
away from the set of slotted exhaust channels 529 to throttle a
fluid flow, i.e., flow of gases, from the lower plasma generation
volume 509 through the set of slotted exhaust channels 529 into the
interior cavity 500D of the chamber 500. In one embodiment, the
pressure control ring 531 is defined as a horizontally oriented
annular-shaped disc which is movable in a vertical direction toward
and away from the set of slotted exhaust channels 529. The pressure
control ring 531 is defined to cover the set of slotted exhaust
channels 529 (on the interior cavity 500D side) when placed against
the set of slotted exhaust channels 529, i.e., when placed against
a lower surface of the horizontally oriented portion of the outer
structural member 506 within which the set of slotted exhaust
channels 529 is formed.
[0081] Fluid flow from the lower plasma generation volume 509
through the set of slotted exhaust channels 529 to the interior
cavity 500D of the chamber 500 can be throttled, i.e., controlled,
through vertical movement of the pressure control ring 531 toward
and away from the set of slotted exhaust channels 529. In one
embodiment, the pressure control ring 531 is defined to enable a
complete shutoff of flow from the lower plasma generation volume
509 through the set of slotted exhaust channels 529 into the
interior cavity 500D of the chamber 500. Also, in one embodiment, a
pressure manometer is disposed to measure the pressure within the
lower plasma generation volume 509. In this embodiment, this
measured pressure within the lower plasma generation volume 509 is
used to generate feedback signals for controlling the position of
the pressure control ring 531, which in turn provides active
control of the pressure within the lower plasma generation volume
509.
[0082] It should be understood that both the upper plasma chamber
512 and the lower plasma chamber 514 enclose respective confined
plasmas. A confined plasma is beneficial in that its residence time
can be controlled by controlling volume, pressure, and flow within
the plasma region, i.e., within the upper and lower plasma
generation volumes 503 and 509. The plasma residence time affects
the dissociation process, which is a factor in radical and neutron
formation.
[0083] As previously discussed, the upper and lower plasma chambers
512 and 514 have respective RF power source controls, pressure
controls, temperature controls, plasma process gas source controls,
and gas flow controls. In various embodiments, a pressure within
the upper plasma processing volume 503 can be controlled within a
range extending from about 100 mTorr to about 1 Torr, or from about
200 mTorr to about 600 mTorr. In various embodiments, a pressure
within the lower plasma processing volume 509 can be controlled
within a range extending from about 5 mTorr to about 100 mTorr, or
from about 10 mTorr to about 30 mTorr.
[0084] In the embodiment of FIG. 5 with the showerhead electrode
501, the upper plasma chamber 512 is a capacitively coupled plasma
chamber. In this embodiment, a vertical distance across the upper
plasma generation volume 503, as measured perpendicularly between
the lower surface of the showerhead electrode 501 and the upper
surface of the gas distribution unit 515, is set within a range
extending from about 1 cm to about 5 cm. In one embodiment, this
vertical distance across the upper plasma generation volume 503 is
about 2 cm. In another embodiment, the showerhead electrode 501 can
be functionally replaced by an induction coil, such that the upper
plasma chamber 512 is an inductively coupled plasma chamber. In
this embodiment, the vertical distance across the upper plasma
generation volume 503 can be up to about 12 cm.
[0085] The gas distribution unit 515 is disposed between the upper
plasma generation volume 503 and the lower plasma generation volume
509. The gas distribution unit 515 is defined as a plate formed to
separate the upper plasma generation volume 503 from the lower
plasma generation volume 509, such that an upper surface of the gas
distribution unit 515 plate provides a lower boundary of the upper
plasma generation volume 503, and such that a lower surface of the
gas distribution unit 515 plate provides an upper boundary of the
lower plasma generation volume 509.
[0086] The gas distribution unit 515 is held in a fixed position by
the outer structural member 506 of the lower plasma chamber 514.
The gas distribution unit 515 is defined to defined to supply a
plasma process gas to the lower plasma generation volume 509
through an arrangement of gas supply ports 519. The gas
distribution unit 515 is further defined to include an arrangement
of through-holes 517 to provide controlled fluid communication
between the upper plasma generation volume 503 and the lower plasma
generation volume 509. Each of the through-holes 517 extends
through the gas distribution unit 515 plate from its upper surface
to its lower surface.
[0087] FIG. 6 shows the chamber 500 of FIG. 5 with an upper plasma
501 and a lower plasma 503, in accordance with one embodiment of
the present invention. It should be understood that the independent
control of the upper and lower plasma chambers 512 and 514 provides
for extensive possibilities with regard to wafer processing
recipes, particularly concerning the independent control of radical
and neutral flux relative to ion flux. A couple of example wafer
processes are provided below. However, it should be understood that
the example wafer processes disclosed herein are provided as
examples only and in no way represent any limitation on use of the
dual plasma processing chamber 500 disclosed herein.
[0088] In one example embodiment, the chamber 500 is used to
perform a wafer process that utilizes high fluorine radical and
neutral flux with low dissociation of CxFy (C4F8, C4F6, etc.) in
the wafer processing plasma. In this example embodiment, a mixture
of Ar and NF3 is supplied as the plasma process gas to the upper
plasma generation volume 503. The upper plasma generation volume
503 is operated at high pressure and high RF frequency (60 MHz).
The high fluorine radical and neutral flux is generated in the
upper plasma chamber 503 and is flowed through the through-holes
517 of the gas distribution unit 515. The ions generated in the
upper plasma processing volume 503 are filtered by the gas
distribution unit 515.
[0089] Also, in this example embodiment, a mixture Ar and CxFy gas
is supplied as the plasma process gas to the lower plasma
generation volume 509. The lower plasma generation volume 509 is
operated at low pressure and low to medium RF frequency (2 MHz and
27 MHz) with pulsing RF power. The low RF frequency of the lower
plasma generation volume 509 corresponds to low dissociation of
CxFy in the plasma exposed to the wafer 513. It should be
appreciated that the high power required in the upper plasma
generation volume 503 to generate the necessary fluorine radical
and neutral flux would cause high dissociation of CxFy if applied
to the lower plasma generation volume 509. Therefore, the dual
plasma chamber 500 enables performance of the above described
process.
[0090] In another example embodiment, the chamber 500 is used to
perform a wafer process that utilizes high dissociation of CxFy
(C4F8, C4F6, etc.) in a high pressure volume with a high density Ar
plasma in a low pressure volume. In this example embodiment, a
mixture of CxFy and Ar is supplied as the plasma process gas to the
upper plasma generation volume 503. The upper plasma generation
volume 503 is operated at high pressure and high RF frequency (60
MHz) to cause high dissociation of CxFy. The highly dissociated
CxFy generated in the upper plasma chamber 503 flows through the
through-holes 517 of the gas distribution unit 515. The ions
generated in the upper plasma processing volume 503 are filtered by
the gas distribution unit 515. Also, in this example embodiment, Ar
gas is supplied as the plasma process gas to the lower plasma
generation volume 509. The lower plasma generation volume 509 is
operated at low pressure and low to medium RF frequency (2 MHz and
27 MHz) to generate a high density Ar plasma with high ion
flux.
[0091] It should be appreciated that the dual plasma chamber 500 is
defined to decouple radical and neutral flux generation from ionic
plasma generation. Also, in one embodiment, the lower plasma
chamber 514 can be inactive, i.e., exhaust only, such that radical
and neutral flux from the upper plasma chamber 512 can be applied
to the wafer 513 without exposing the wafer 513 to a plasma.
[0092] FIG. 7 illustrates the normalized ion flux as a function of
the plate thickness, according to one embodiment. One of the
parameters that affect the interaction between the upper chamber on
the lower chamber is the configuration of the plate between the
chambers. The thickness defines the length of the through-holes,
and the longer the through-holes are, the bigger the obstacle for
the ions and electrons to travel from the upper chamber to the
lower chamber.
[0093] The chart in FIG. 7 shows the measurements taken in a dual
chamber for the normalized ion flux at different pressures in the
lower chamber, with an RF frequency of 27 MHz at 300 W in argon
chamber. As expected, the ion flux decreases as the length (depth)
of the through-holes increases. In addition, the higher the
pressure in the lower chamber, the lower the ion flux is because
the higher pressure in the lower chamber increases the resistance
for fluids and species to travel to the bottom chamber.
[0094] A second factor affecting the flow between the upper chamber
and the lower chamber, is the diameter of the through-holes. As
expected, the bigger the diameter of the through-holes is, the
bigger the flux of particles to the lower chamber. Another factors
affecting the interaction between the upper chamber on the lower
chamber are the number and distribution of through-holes in the
plate. The greater the number of through-holes is, the more
electrons will travel from the upper chamber to the lower chamber,
as there are more paths between the upper and lower chambers.
[0095] In one embodiment, grid is 27 mm thick, (i.e., the
through-holes have a length of 27 mm), and the through-holes have a
diameter of 2 mm, although other values are also possible. In one
embodiment, the thickness of the grid is between 10 mm and 30 mm.
In various embodiments, the diameter of the through-holes is sized
within a range extending from about 0.5 mm to about 5 mm. It should
be understood, however, that in various embodiments the
through-holes can be respectively defined with essentially any
diameter size, so long as the diameter size provides for adequate
fluid flow there through while simultaneously providing for
adequate suppression of plasma intrusion therein.
[0096] FIG. 8 shows the flow of an algorithm for operating a
semiconductor wafer processing apparatus, in accordance with one
embodiment of the invention. The embodiment of FIG. 8 illustrates
the different operations that can be performed to control the flow
of species between the upper chamber and the lower chamber.
[0097] In operation 802, the parameters for the top plasma chamber
are set. These parameters include the operating frequency of the RF
power source, the voltage and wattage of the RF power source, the
pressure in the upper chamber, the gases injected in the upper
chamber, etc. In operation 804, the parameters for the bottom
plasma chamber are set. The same parameters described above for the
upper chamber may also be adjusted for the bottom chamber. In
addition, the parameters for the plate separating the upper chamber
and the lower chamber are also defined. The parameters for the
plate include the thickness of the plate, the number and
distribution of through-holes in the plate, the diameter of the
through-holes, etc.
[0098] In operation 806, a wafer is processed in the lower chamber
with the parameters set in operations 802 and 804. After the wafer
is processed, the operator may decide to adjust some of the
parameters of the chamber to improve wafer processing. To determine
the quality of etching in the chamber, probes can be used to
measure the performance of the chamber. For example, a probe can be
used to measure the ion flux from the top chamber to the bottom
chamber.
[0099] In operation 810, a check is made to determine if the power
is to be adjusted, and if the result of the check in operation 810
is that an adjustment is required, the method continues to
operation 812. In operation 812, the wattage for the top or bottom
chambers, or for both top and bottom chambers, are set. As the
power is increased in the chambers, the number of particles in the
plasma will also increase.
[0100] In operation 814, a check is performed to determine if the
voltage of the RF power sources is to be adjusted, and if the
voltage is to be adjusted, new voltage levels for the top and/or
bottom chambers are set, in operation 816. As previously discussed,
the bottom chamber includes a pulsing RF power source. A check is
performed to determine if the pulsing cycle of the RF power source
is to be adjusted, in operation 820. In operation 826, the
durations of the ON and OFF periods (i.e., the cycle of the RF
signal) are set. For example, if negative ion etching needs to be
increased, the OFF period may be increased to allow for a higher
afterglow etching.
[0101] In operation 822, a check is made to determine if the
pressure in the first chamber of the second chamber is to be
adjusted. If the pressure in either chamber is to be changed, in
operation 828, the pressure from the top chamber, or the bottom
chamber, or both chambers are adjusted. As described above with
reference to FIG. 7, the higher the pressure difference between the
top chamber and the bottom chamber, the higher the flow of
particles between the chambers.
[0102] Further, in operation 824, a check is made to determine if
the parameters of the plate need to be changed. As previously
discussed, several parameters of the plate can be changed, such as
thickness of the plate, the number, distribution, and size of the
through-holes, etc. If the parameters of the plate are to be
adjusted, in operation 830, any of the aforementioned parameters of
the plate can be adjusted.
[0103] After all the parameters of the chamber are adjusted, if
any, the method flows back to operation 806 and continues with the
processing of wafers. It is noted that the embodiments illustrated
in FIG. 8 are exemplary. Other embodiments may utilize different
adjustments, or perform adjustments in a different order, or
perform checks periodically, etc. The embodiments illustrated in
FIG. 8 should therefore not be interpreted to be exclusive or
limiting, but rather exemplary or illustrative.
[0104] FIG. 9 shows the flow of an algorithm for processing a
wafer, in accordance with one embodiment of the invention. In
operation 902, first parameters are set for a continuous radio
frequency (RF) signal generated by a first RF power source coupled
to a top electrode in the top chamber. The first parameters include
a first voltage and a first frequency. Further, in operation 904,
second parameters are set for a pulsed RF signal generated by a
second RF power source coupled to a bottom electrode in the bottom
chamber, where the second parameters include a second voltage, a
second frequency, an ON-period duration, and an OFF-period
duration.
[0105] In operation 906, the continuous RF signal is applied to the
top electrode, and in operation 908, the pulsed RF signal is
applied to the bottom electrode. Setting the first parameters and
the second parameters regulates the flow of species from the top
chamber to the bottom chamber during operation of the chamber. The
flow of species assists in the negative-ion etching and in
neutralizing excessive positive charge on the wafer surface during
afterglow in the OFF period, and assists in re-striking the plasma
in the bottom chamber during the ON period.
[0106] FIG. 10 is a simplified schematic diagram of a computer
system for implementing embodiments of the present invention. It
should be appreciated that the methods described herein may be
performed with a digital processing system, such as a conventional,
general-purpose computer system. Special purpose computers, which
are designed or programmed to perform only one function, may be
used in the alternative. The computer system includes a central
processing unit (CPU) 1004, which is coupled through bus 1010 to
random access memory (RAM) 1028, read-only memory (ROM) 1012, and
mass storage device 1014. Phase control program 1008 resides in
random access memory (RAM) 1028, but can also reside in mass
storage 1014 or ROM 1012.
[0107] Mass storage device 1014 represents a persistent data
storage device such as a floppy disc drive or a fixed disc drive,
which may be local or remote. Network interface 1030 provides
connections via network 1032, allowing communications with other
devices. It should be appreciated that CPU 1004 may be embodied in
a general-purpose processor, a special purpose processor, or a
specially programmed logic device. Input/Output (I/O) interface
provides communication with different peripherals and is connected
with CPU 1004, RAM 1028, ROM 1012, and mass storage device 1014,
through bus 1010. Sample peripherals include display 1018, keyboard
1022, cursor control 1024, removable media device 1034, etc.
[0108] Display 1018 is configured to display the user interfaces
described herein. Keyboard 1022, cursor control 1024, removable
media device 1034, and other peripherals are coupled to I/O
interface 1020 in order to communicate information in command
selections to CPU 1004. It should be appreciated that data to and
from external devices may be communicated through I/O interface
1020. The invention can also be practiced in distributed computing
environments where tasks are performed by remote processing devices
that are linked through a wire-based or wireless network.
[0109] Embodiments of the present invention may be practiced with
various computer system configurations including hand-held devices,
microprocessor systems, microprocessor-based or programmable
consumer electronics, minicomputers, mainframe computers and the
like. The invention can also be practiced in distributed computing
environments where tasks are performed by remote processing devices
that are linked through a network.
[0110] With the above embodiments in mind, it should be understood
that the invention can employ various computer-implemented
operations involving data stored in computer systems. These
operations are those requiring physical manipulation of physical
quantities. Any of the operations described herein that form part
of the invention are useful machine operations. The invention also
relates to a device or an apparatus for performing these
operations. The apparatus may be specially constructed for the
required purpose, such as a special purpose computer. When defined
as a special purpose computer, the computer can also perform other
processing, program execution or routines that are not part of the
special purpose, while still being capable of operating for the
special purpose. Alternatively, the operations may be processed by
a general purpose computer selectively activated or configured by
one or more computer programs stored in the computer memory, cache,
or obtained over a network. When data is obtained over a network
the data maybe processed by other computers on the network, e.g., a
cloud of computing resources.
[0111] One or more embodiments of the present invention can also be
fabricated as computer readable code on a computer readable medium.
The computer readable medium is any data storage device that can
store data, which can be thereafter be read by a computer system.
Examples of the computer readable medium include hard drives,
network attached storage (NAS), read-only memory, random-access
memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes and other optical
and non-optical data storage devices. The computer readable medium
can include computer readable tangible medium distributed over a
network-coupled computer system so that the computer readable code
is stored and executed in a distributed fashion.
[0112] Although the method operations were described in a specific
order, it should be understood that other housekeeping operations
may be performed in between operations, or operations may be
adjusted so that they occur at slightly different times, or may be
distributed in a system which allows the occurrence of the
processing operations at various intervals associated with the
processing, as long as the processing of the overlay operations are
performed in the desired way.
[0113] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications can be practiced
within the scope of the appended claims. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein, but may be modified within the scope and equivalents
of the appended claims.
* * * * *