U.S. patent application number 10/200499 was filed with the patent office on 2003-01-23 for particle counting method and particle counter.
Invention is credited to Makino, Toshiharu, Suzuki, Nobuyasu, Yamada, Yuka, Yoshida, Takehito.
Application Number | 20030015045 10/200499 |
Document ID | / |
Family ID | 26619079 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030015045 |
Kind Code |
A1 |
Yoshida, Takehito ; et
al. |
January 23, 2003 |
Particle counting method and particle counter
Abstract
The object of the present invention is to provide a particle
counter that can count particles in aerosol having a particle size
of from 2 nm to 50 nm in an operating pressure range from an
atmospheric pressure through a reduced pressure to a low vacuum and
calculate a particle size distribution. The present invention
provides a particle counter that charges particles existing in the
aerosol and then applies an electrostatic field to the particles,
and a particle counter that charges the particles existing in the
aerosol and then mixes the aerosol with a non-charged sheath gas
flow shaped like a laminar flow and applies an electrostatic field
to the particles. This can get the respective particles into traces
depending on their particle size. Thus, it is possible to count the
number of particles having specific traces. Further, by using an
electron multiplier for exciting cluster ions to detect the charged
particles and operating it as a high-pass filter, even if the
number density of the particles is small, it is possible to
effectively count the particles.
Inventors: |
Yoshida, Takehito;
(Kawasaki-shi, JP) ; Suzuki, Nobuyasu;
(Kawasaki-shi, JP) ; Makino, Toshiharu;
(Kawasaki-shi, JP) ; Yamada, Yuka; (Kawasaki-shi,
JP) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Family ID: |
26619079 |
Appl. No.: |
10/200499 |
Filed: |
July 23, 2002 |
Current U.S.
Class: |
73/865.5 |
Current CPC
Class: |
G01N 15/0656
20130101 |
Class at
Publication: |
73/865.5 |
International
Class: |
G01N 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2001 |
JP |
2001-221008 |
Dec 28, 2001 |
JP |
2001-400001 |
Claims
What is claimed is:
1. A particle counting method, comprising the steps of: taking in
as aerosol a process gas in a process apparatus for conducting a
physical or chemical reaction in a reduced vapor phase including a
vacuum; charging particles existing in the aerosol; then applying
an electrostatic field to the particles to get the respective
particles into traces depending on their particle sizes; and
measuring the number of particles having specific traces to thereby
calculate the particle size distribution of the particles floating
in the process apparatus.
2. A particle counting method according to claim 1, wherein an
electron amplifier tube for exciting cluster ions is used for
detecting the charged particles.
3. A particle counting method according to claim 1, wherein the
step of measuring the number of particles having specific traces to
thereby calculate the particle size distribution of the particles
floating in the process apparatus is replaced with the step of
measuring the number of particles having particle sizes larger than
a specific particle size to thereby perform a high-pass
filtering.
4. A particle counting method according to claim 1, wherein the
step of measuring the number of particles having specific traces to
thereby calculate the particle size distribution of the floating
particles in the process apparatus is replaced with the step of
measuring a spatial number density of particles having particle
sizes larger than a specific particle size on the basis of three or
more specific particle sizes by the use of a high-pass filtering
operation to thereby predict a particle size distribution in a
range covering all particle sizes.
5. A particle counting method, comprising the steps of: taking in
as aerosol a process gas in a process apparatus for conducting a
physical or chemical reaction in a vapor phase; charging particles
existing in the aerosol; then mixing the aerosol with a non-charged
sheath gas flow shaped like a laminar flow and applying an
electrostatic field to the particles existing in the aerosol to
thereby get the respective particles into traces depending or their
particle sizes; and detecting particles having specific traces and
measuring the number of particles to thereby calculate the particle
size distribution of the particles floating in the process
apparatus.
6. A particle counting method according to clam 5, further
comprising the step of taking in atmosphere in a clean zone, in
which the process apparatus to be measured is disposed, as a
non-charged sheath gas.
7. A particle counting method according to clam 5, in the step of
detecting the charged particles, further comprising the step of
modulating an electrostatic field intensity applied to a
classifying region at low frequency and amplifying the electric
signal of detecting the charged particles tuned to the low
frequency in a narrow band.
8. A particle counting method according to clam 5, further
comprising the step of applying voltage to a conductive plate,
which is disposed after the taken-in aerosol is subjected to a
charging process and can apply voltage to the aerosol flow, to
thereby electrostatically attract and remove floating ions included
in the aerosol.
9. A particle counting method according to claim 5, wherein the
step of mixing the aerosol with a non-charged sheath gas flow
shaped like a laminar flow and applying an electrostatic field to
the particles existing in the aerosol to thereby get the respective
particles into traces depending on their particle sizes is replaced
with the step of applying the electrostatic field to the particles
in the aerosol to thereby get the respective particles-into traces,
and wherein the step of detecting particles having specific traces
and measuring the number of particles to thereby calculate the
particle size distribution of the particles floating in the process
apparatus is replaced with the step of calculating the number of
particles having particle sizes close to a specific particle size
to thereby perform a band-pass filtering.
10. A particle counting method according to clam 5, wherein the
step of detecting particles having specific traces and measuring
the number of particles to thereby calculate the particle size
distribution of the particles floating in the process apparatus is
replaced with the step of measuring a spatial number density of
particles having particle sizes larger than a specific particle
size on the basis of three or more specific particle sizes by the
use of a band-pass filtering operation to thereby predict a
particle size distribution in a range covering all particle
sizes.
11. A particle counter comprising: aerosol introducing means
connected to an aerosol supply source provided on an object to be
measured; charging means for charging the aerosol introduced by the
aerosol introducing means arid a group of particles existing in the
aerosol; floating ion attracting and removing means for attracting
and removing floating ions that interfere with the measurement of
the charged particles charged by the charging means; particle
classifying means for classifying the group of charged particles
from which the floating ions are attracted and removed; and sheath
gas carrying line for making a sheath gas into a laminar flow and
supplying the sheath gas to the particle classifying means, wherein
the particle classifying means mixes the aerosol with the
non-charged sheath gas flow shaped like a laminar flow and then
applies an electrostatic field to the non-charged sheath gas to get
the respective particles existing in the aerosol into traces
depending on their particle sizes to thereby classify the
particles.
12. A particle counter according to claim 11, further comprising
measuring means for detecting the particles having specific traces
and counting the number of particles.
13. A particle counter according to claim 11, further comprising
sheath gas taking-in means for taking in atmosphere in a clean zone
where the object to be measured is disposed.
14. A particle counter according to claim 11, wherein the particle
classifying means has amplifying means that modulates an
electrostatic field intensity applied to a classifying region at a
low frequency and amplifies the electric signal of detecting the
charged particles tuned to the low frequency in a narrow band to
detect the charged particles.
15. A particle counter according to claim 11, wherein the particle
classifying means has a conductive member capable of applying
voltage to the aerosol flow and applies voltage to conductive
member to thereby electrostatically attract and remove floating
ions in the aerosol.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to measuring and evaluating
the particle size distribution of particles in aerosol and, in
particular, can quickly and easily measure and evaluate particles
having a particle size not more than 100 nm and thus is suitable
for in-situmeasuring particles in a reduced pressure vapor phase
process apparatus and a clean room used for manufacturing a
semiconductor integrated device and a liquid crystal display device
and contributes to the improvement of the manufacturing yield of
these devices.
[0003] 2. Description of the Related Art
[0004] As an example in the related art, a particle size measuring
unit using a laser scattering method, which is a mainstream at
present. This is a method of measuring the particle sizes of
particles in aerosol and utilizes the phenomenon that when laser
light is applied to the aerosol, the spatial intensity distribution
of diffracted light of the laser is varied by the distribution of
particle size. The constitution and operation to be described below
with reference to FIG. 1 are now widely used in the industry
concerned, and is disclosed in a literature, for example, "Particle
Size Measuring Technology" compiled by Society of Powder
Technology, Japan, published by Daily Industry Newspaper Co. Ltd.,
(1994), Item 145 to Item 148.
[0005] A helium-neon (He--Ne) or semiconductor probe laser 1 having
an output power of several mW is used as a light source. It's
luminous flux is expanded into a parallel luminous flux having a
diameter of several mm by a beam expander 2 and is applied to a
group of particles 3 in aerosol introduced into a measuring
section. In this beam expander 2 is built a spatial filter so as to
produce irradiating luminous flux having high parallelism. The
laser light scattered by the group of particles in the aerosol is
refracted by a receiving lens 4 and is entered into a detector 6 on
a focal plane 5. A f.theta. lens is used as the light receiving
lens 4 and the laser luminous flux scattered is collected on the
same circumference on the focal plane for each scattering angle.
The detector 6 is constituted by semiconductor photoelectric
devices arranged on concentric circles the center of which is on
the surface of the focal plane to which front scattering
(non-scattering) light of the laser luminous flux is applied. This
constitution makes it possible to measure the dependence of
intensity of the laser light scattered by the particles in the
aerosol on the scattering angles. Here, by utilizing that the
dependence of intensity of the scattered laser light on the
scattering angles depends on the particle distribution of the group
of particles, the particle distribution of the group of particles
is calculated by a signal processing device 7.
[0006] However, since a visible laser is used as the probe light in
the related art, a minimum measurable particle size is about 100
nm. This is because if particles to be measured become smaller in
size with respect to a probe light wavelength, in particular,
smaller than one tenth of the wavelength, they produce Rayleigh
scattering in which the dependence of scattering phenomenon on the
particle size is hard to observe and thus the particle size
distribution can not be calculated by a scattered light intensity
distribution. The use of the fourth harmonic of a Nd:YAG laser can
produce ultraviolet coherent light (wavelength: 266 nm) by a
comparatively small sized apparatus but, even by this light, a
minimum measurable particle size is about 40 nm. In order to
produce the ultraviolet light having a smaller wavelength, an
excimer laser needs to be used, which in turn increases the size of
a light source unit and further limits the use of a transmission
type lens in an optical system. To realize the ultraviolet light
having a smaller wavelength, it is thought to use ultraviolet light
having a wavelength of 126 nm, produced by an Ar.sub.2 excimer
laser, but even if this ultraviolet coherent light is used, a
minimum measurable particle size is about 20 nm. On the other hand,
a practical design rule in the semiconductor integrated circuit
manufacturing technology is 130 nm at present and will be 70 nm in
the year of 2008. Further, generally, it is said that a particle
size needs to be controlled within a range of one fifth to the
design rule. Therefore, it is impossible to control the particles
in the semiconductor integrated circuit manufacturing system to
keep and improve a manufacturing yield by using the Rayleigh
scattering method described above.
SUMMARY OF THE INVENTION
[0007] One aspect of a particle counting method in accordance with
the present invention is to provide means that charges particles
existing in aerosol and then applies an electrostatic field to the
aerosol without using light scattering for measurement to thereby
get the respective particles into traces depending on their
particle sizes and then counts the particles having specific
traces.
[0008] Further, the method has means that uses an electron
multiplier for exciting cluster ions to detect the charged
particles and further performs a high-pass filtering, that is,
counts particles having particle sizes larger than a specific
particle size.
[0009] In addition, the method has means that measures the number
density of particles having particle sizes larger than a specific
particle size on the basis of three or more specific particle sizes
by the use of a high-pass filtering operation to thereby predict a
particle size distribution in a range covering all particle
sizes.
[0010] These means can constitute a particle counter capable of
quickly and easily measuring and evaluating the particles having
particle sizes, in particular, not larger than 50 nm to obtain the
particle size distribution of particles in a process aerosol in a
reduced pressure vapor phase apparatus.
[0011] Further, the particle counting method in accordance with the
present invention has means that charges particles existing in the
aerosol and then mixes the aerosol with a non-charged sheath gas
flow shaped like a laminar flow, applies an electrostatic field to
the particles without using light scattering for measurement to
thereby get the respective particles into traces depending on their
particle sizes, and counts the number of particles having specific
traces. Here, without using a bomb gas as a non-charged sheath gas,
the atmosphere in a clean zone in which a process apparatus to be
measured is disposed is taken in and effectively utilized.
[0012] Still further, the method has means that modulates an
electrostatic field intensity applied to a classifying tube at a
low frequency and amplifies the electric signal of detecting the
charged particles tuned to the low frequency in a narrow band in
the detection of the charged particles.
[0013] In addition, the method has means that applies voltage to a
conductive plate, which is disposed after the taken-in aerosol is
subjected to a charging process and can apply voltage to the flow
of aerosol, to electrostatically attract and remove ions floating
in the aerosol to thereby improve the accuracy of detecting the
charged particles.
[0014] These means can constitute a particle counter capable of
quickly and easily measuring and evaluating the particles having
particle sizes, in particular, not larger than 50 nm to obtain the
particle size distribution of particles in a process aerosol in a
reduced pressure vapor phase apparatus.
[0015] Then, another aspect of the present invention is to provide
a particle counting method including the steps of taking in as
aerosol a process gas in a process apparatus for conducting a
physical or chemical reaction in a reduced vapor phase including a
vacuum, and charging particles existing in the aerosol; then
applying an electrostatic field to the particles to get the
respective particles into traces depending on their particle sizes.
By measuring the number of particles having specific traces, it is
possible to calculate the particle size distribution of the
particles floating in the process device described above.
[0016] Further, the present invention is characterized in that an
electron amplifier tube for exciting cluster ions is used for
detecting the charged particles. This makes it possible to
effectively measure particles even if the number density of
particles in the sampling aerosol is small.
[0017] Still further, the present invention is characterized in
that the particles existing in the aerosol are charged and that an
electrostatic field is then applied to the charged particles to get
the respective particles into traces depending on their particle
sizes and that the number of particles having particle sizes larger
than a specific particle size is calculated, that is, a high-pass
filtering is performed. This can achieve a more effective
measurement even if the number density of particles in the sampling
aerosol is small.
[0018] Still further, the present invention is characterized in
that the number density of particles having particle sizes larger
than a specific particle size on the basis of three or more
specific particle sizes by the use of a high-pass filtering
operation. This makes it possible to exert a function of predicting
a particle size distribution in a range covering all particle
sizes.
[0019] In addition, the present invention is characterized in that
it includes the steps of: taking in as aerosol a process gas in a
process apparatus for conducting a physical or chemical reaction in
a vapor phase; charging particles existing in the aerosol; then
mixing the aerosol with a non-charged sheath gas flow shaped like a
laminar flow and applying an electrostatic field to the particles
existing in the aerosol to thereby get the respective particles
into traces depending on their particle sizes; and detecting
particles having specific traces and measuring the number of
particles. This makes it possible to calculate the particle size
distribution of the particles floating in the process
apparatus.
[0020] Here, the present invention is characterized in that
atmosphere in a clean zone, in which the process apparatus to be
measured is disposed, is taken in as a non-charged sheath gas to
reduce a bomb gas accompanying the present apparatus. This makes it
possible to simplify the constitution of the preset apparatus.
[0021] Further, the present invention is characterized in that, in
the detection of the charged particles, an electrostatic field
intensity applied to a classifying tube is modulated at a low
frequency and the electric signal of detecting the charged
particles tuned to the low frequency is amplified in a narrow band.
This makes it possible to effectively measure the particle size
even if the concentration of particles is low.
[0022] Still further, the present invention is characterized in
that after taken-in aerosol is charged, a conductive plate capable
of applying voltage to the flow of the aerosol is disposed and that
voltage is applied to the conductive plate to thereby
electrostatically attract and remove floating ions included in the
aerosol. This makes it possible to improve the accuracy of
detecting the charged particles existing in the aerosol described
above.
[0023] In addition, the present invention is characterized in that
the particles in the aerosol is charged and that the electrostatic
field is then applied to the particles to get the particles into
traces depending on their particle sizes and that the number of
particles having particle sizes close to a specific particle size
is calculated. That is, this makes it possible to perform a
function of high-pass filtering.
[0024] As described above, according to the present invention,
there is provided means that charges particles existing in the
aerosol and then applies an electrostatic field to the particles to
get the respective particles into traces depending on their
particle sizes without using light scattering for measurement in a
particle counter, to thereby measure the number of particles having
specific traces.
[0025] Further, there is provided means that uses an electron
amplifier tube for exciting cluster ions to detect the charged
particles and operates as a high-pass filter to thereby effectively
count particles even if the number density of particles is
small.
[0026] In addition, there is provided means that measures the
number density of particles having particle sizes not smaller than
a specific particle size by the use of a high-pass filtering
operation on the basis of three or more specific particle sizes to
predict a particle size distribution in a range covering all
particle sizes.
[0027] These means can constitute a particle counter capable of
quickly and easily in-situ measuring the particles having particle
sizes, in particular, not larger than 50 nm to obtain the particle
size distribution of particles in a process aerosol in a reduced
pressure vapor phase apparatus.
[0028] According to the present invention, there is provided means
that charges particles existing in the aerosol are charged and then
mixes the aerosol with a non-charged sheath gas flow shaped like a
laminar flow and applies an electrostatic field to the particles
existing in the aerosol without using light scattering for the
particle counter to thereby get the respective particles into
traces depending on their particle sizes, and counts the number of
particles getting the specific traces. Further, there is provided
means that modulates an electrostatic field intensity applied to a
classifying tube at a low frequency and amplifies the electric
signal of detecting the charged particles tuned to the low
frequency in a narrow band in the detection of the charged
particles, to thereby effectively measure the particles even if the
concentration of particles is small. In addition, there is provided
means that charges voltage to a conductive plate, which is disposed
after taken-in aerosol is subjected to a charging process and can
apply voltage to the flow of aerosol, to electrostatically attract
and remove floating ions included in the aerosol to thereby improve
the accuracy of detecting the charged particles existing in the
aerosol described above.
[0029] These means can constitute a particle counter that can
quickly and easily in-situ measure the particles having particle
sizes, in particular, not larger than 50 nm and calculate the
particle size distribution.
[0030] Therefore, it is the object of the present invention to
provide a particle counter capable of counting particles having a
particle size ranging from 2 nm to 50 nm in the aerosol in an
operating pressure range from the atmospheric pressure through the
reduced pressure atmosphere to a low vacuum and calculating a
particle size distribution.
[0031] The object and advantages of the present invention will be
made clearer by the preferred embodiments to be described below
with reference to accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a block diagram to show the configuration of a
particle counter in the related art.
[0033] FIG. 2 is a block diagram to show the configuration in
accordance with the first embodiment of the present invention.
[0034] FIG. 3 is a characteristic curve of the result of
measurement and evaluation using a particle counter in accordance
with one embodiment of the present invention:
[0035] (a) characteristic curve of anode current-electric potential
of electric potential applying plate of inner shell cylinder;
[0036] (b) characteristic curve of particle number density
distribution-electric potential of electric potential applying
plate of inner shell cylinder; and
[0037] (c) a characteristic curve of particle number density
distribution-particle size.
[0038] FIG. 4 is a block diagram to show the general configuration
of a particle counter in accordance with one embodiment of the
present invention.
[0039] FIG. 5 is a cross-sectional configurational view of a
floating ion attracting and removing chamber that is a constituent
part of a particle counter in accordance with one embodiment of the
present invention.
[0040] FIG. 6 is a block diagram to show the configuration of a
particle classifying system that is a constituent part of a
particle counter in accordance with one embodiment of the present
invention.
[0041] FIG. 7 is a cross-sectional configurational view of a
classifying tube of a particle classifying system that is a
constituent part of a particle counter in accordance with one
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] (First Embodiment)
[0043] Next, the preferred embodiment in accordance with the
present invention will be described in detail. FIG. 2 is a block
diagram to schematically show the general configuration of a
particle counter in accordance with the present embodiment. In FIG.
2, a reference numeral 101 denotes a reduced pressure process
apparatus process chamber; a reference numeral 102 denotes an
aerosol intake valve that is connected to the reduced pressure
process apparatus process chamber 101 and takes in aerosol from the
reduced pressure apparatus process chamber 101; a reference numeral
103 denotes a intake conductance adjusting valve that adjusts the
intake of the aerosol in the aerosol intake valve 102; a reference
numeral 104 denotes a charging device that charges the aerosol
introduced and a group of particles existing therein; a reference
numeral 105 denotes an Ar.sub.2 excimer light source that conducts
vacuum ultraviolet ray irradiation in a charging process by the
charging device 104 described above; a reference numeral 106
denotes a mass flow meter that measures the mass flow of the
aerosol; a reference numeral 107 denotes a capacitance manometer
that measures an operating pressure in a particle classifying tube
(to be described later); a reference numeral 108 denotes the
particle classifying tube into which the aerosol whose mass flow is
measured by the mass flow meter 106 is introduced and which
classifies particles in the aerosol.
[0044] The particle classifying tube 108 usually has a cylindrical
structure, that is, a double cylindrical structure including an
outer shell cylinder 109 constituting its outer shape and an inner
shell cylinder 110 forming the inside of the outer shell cylinder
109 in a nearly annular shape. The outer shell cylinder 109 is
electrically insulated from the inner shell cylinder 110. Near the
inlet or the uppermost stream portion of the particle classifying
tube 108 is provided a sheet mesh 111. Near the outlet of the
particle classifying tube 108 is provided an orifice 112. Further,
an electric potential applying plate 109a is mounted on the outside
wall of the outer shell cylinder 109, whereas an electric potential
applying plate 110a is mounted on the outside wall (outside wall on
the inner diameter side with respect to the aerosol passage) of the
inner shell cylinder 110.
[0045] A reference numeral 114 denotes an exhaust system
conductance adjusting valve that adjusts the exhaust of the
aerosol. A reference numeral 115 denotes a high-pressure-operated
helical pump that is the main body of a large-capacity exhaust
system. A reference numeral 116 denotes a thermocouple gage. A
reference numeral 117 denotes a leak valve that discharges the
exhausted aerosol . A reference numeral 118 denotes a scroll pump.
The constituent parts of the exhaust system conductance adjusting
valve 114, the high-pressure-operated helical pump 115, the
thermocouple gage 116, the leak valve 117, and the scroll pump 118
constitute the large-capacity exhaust system that exhausts the
aerosol.
[0046] Further, a reference numeral 119 denotes a multiplier ion
measuring pipe. The multiplier ion measuring pipe 119 has an ion
cathode 120 that discharges electrons by the collision impact of a
group of particles (that are called also charged cluster ions)
jetted out of the orifice 112 and introduced into the multiplier
ion measuring pipe 119, an electron producing dynode 121 that is
provided next to the ion cathode 120 and produces many electrons by
the group of electrons discharged by the impact caused by the
cluster ions, an electron multiplying dynode 122 at the last stage,
and an anode 123 that is provided next to the electron multiplying
dynode 122 and is set at an electric potential higher than the
electron multiplying dynode 122. At the inlet of the multiplier ion
measuring pipe 119, a skimmer 113 is provided opposite to the
downstream side of the orifice 112.
[0047] Further, a reference numeral 125 denotes an ammeter that
measures the micro current of the anode 123. A reference numeral
126 denotes a signal processing system that collects and processes
various kinds of numerical values necessary for classifying and
measuring the particles. A reference numeral 127 denotes a personal
computer that performs a computation necessary for processing the
signal of the signal processing system 126. The operation of the
particle counter having the configuration described above will be
described. The particle counter of the present embodiment is
connected in a vapor phase to the process chamber 101, in
particular, in a chemical vapor deposition (CVD) or a physical
vapor deposition (PVD), which is conducted in a reduced pressure
gaseous phase, or a dry etching in a semiconductor integrated
circuit manufacturing process system in conformity with an
ultra-fine design rule (130 nm or less). The particle counter has,
as a whole, a function of reducing pressure or exhausting to a
vacuum.
[0048] The aerosol that is introduced into the particle counter via
the aerosol intake valve 102 to constitute a process atmosphere has
its mass flow adjusted by the intake conductance adjusting valve
103. This is because while the particle classifying tube 108
requires as large an aerosol mass flow as possible, the multiplier
ion measuring pipe 119 mounted next to the particle classifying
tube 108 needs to be operated under as high a vacuum as
possible.
[0049] Next, the introduced aerosol and the group of particles
existing therein are charged by the charging device 104. While
vacuum ultraviolet rays irradiated from the Ar.sub.2 excimer laser
light source 105 operated under a wide range of aerosol gas
pressure is used in this charging process in the present
embodiment, it is also recommended that a radioisotope, a
direct-current corona discharge, an ion beam, an electron beam be
used (in the decreasing order of operating gas pressure), depending
on the operating gas pressure. In particular, in a high vacuum of
10.sup.-3 Pa or less, it is effective to use the ion beam or the
electron beam that can charge the particles into a single
polarity.
[0050] The aerosol has its mass flow measured by the mass flow
meter 106 and then is introduced into the particle classifying tube
108. Here, since the capacitance manometer 107 is provided just
before the particle classifying tube 108 and thus a pressure drop
between them is extremely small the operating gas pressure in the
particle classifying tube 108 can be measured.
[0051] Although the particle classifying tube 108 is shown as a
cross-sectional schematic view in FIG. 2, it has the
double-cylindrical structure that is basically constituted by the
outer shell cylinder 109 and the inner shell cylinder 110. The
introduced aerosol goes to the downstream side, in a laminar state,
in the gap between the outer shell cylinder 109 and the inner shell
cylinder 110, which are electrically insulated from each other. The
sheet mesh 111 is provided at the uppermost stream side to help the
flow of the aerosol in the particle classifying tube 108 to become
a laminar flow.
[0052] The aerosol becomes a laminar flow in the particle
classifying tube 108 and flows in the gap between the outer shell
cylinder 109 and the inner shell cylinder 110 from the upstream
side to the downstream side (in FIG. 2, from the left side to the
right side in the horizontal direction) at a constant speed. Here,
since the mass flow of the aerosol is monitored by the mass flow
meter 106 and the cross-sectional area of the flow passage is
already known, the average speed in the horizontal direction of the
aerosol and the particles therein can be easily obtained. On the
other hand, the outer shell cylinder 109 and the inner shell
cylinder 110 are independent of (electrically insulated from) each
other and further are provided with the electric potential applying
plates 109a, 110a (portions longitudinally hatched in FIG. 2),
respectively.
[0053] If the electric potential applying plate 109a of the outer
shell cylinder 109 is made a ground potential and the electric
potential applying plate 110a of the inner shell cylinder 110 is
fixed at a negative electrostatic potential, an electrostatic field
is generated concentrically from the outer side to the inner side
(in the vertical direction in FIG. 2) in the double-cylindrical
cross section. If the aerosol is in a viscous fluid range, the
particles existing in the aerosol is drifted in the direction of
the concentric center at a speed corresponding to the product of a
mobility Z and an electric field intensity E. Thus, the group of
particles move at the resultant speed of the speed in the same
horizontal direction, caused by the flow of the aerosol, and the
speed in the direction of the concentric center, caused by the
electric field drift vertical to the flow of the aerosol. Since the
mobility Z of the particle in the viscous fluid is approximately
determined by the cross-sectional area of the particle, the group
of particles moves in different traces in accordance with the
respective particle sizes. Naturally, as the particle is smaller in
size, it tends to be polarized from the horizontal direction speed,
and as the particle becomes larger in size, it tends to keep the
original horizontal direction on speed.
[0054] As a result, the particles larger than a certain particle
size pass through the particle classifying tube 108, the orifice
112, and the skimmer 113 and reach the multiplier ion measuring
tube 119, whereas the particles smaller than the certain particle
size are attached to the electric potential applying plate 110a of
the inner shell cylinder 110 side, if the particles are charged
positively, or the electric potential applying plate 109a of the
outer shell cylinder 109 side, if the particles are charged
negatively. In general, once the particles in the range of
nanometer are collided with the wall of the device, they remain
being attracted at the portions. The certain particle size
described above means the boundary size of a particle that passes
through or is attracted by the particle classifying tube 108 and is
determined by the geometrical shape of the particle classifying
tube 108, the flow rate of the aerosol, and the electrostatic field
intensity. In practice, the boundary size of a particle passing or
being attracted is adjusted by varying the electrostatic field
intensity having the largest range of variability. It is said that
the particle classifying tube 108 shows an operation as a high pass
filter because it can measure the particles while shutting off all
the particles smaller than the set particle size.
[0055] The downstream side of the orifice 112 is set at a pressure
of the order of 10.sup.-4 Torr, or a range of molecule rays by a
pressure loss caused by the orifice 112 of low conductance and the
large-capacity exhaust system having the high-pressure-operated
helical pump 115 as a main body. The group of particles jetted out
of the orifice 112 (that can be called also charged cluster ions)
pass through the skimmer 113 and collide with the ion cathode 120
that is the first stage of the multiplier ion measuring tube 119.
In the ion cathode 120, electrons are discharged by the collision
impact of the cluster ions. Since the ion cathode 120 is fixed at a
negative electric potential of several V to several tens V, the
cluster ions charged positively are accelerated by the
electrostatic field even after they pass through the skimmer 113,
thereby being supplied with collision energy large enough to ionize
atoms on the surface of the ion cathode 120 and to discharge
electrons.
[0056] The group of electrons discharged by the collision impact of
the cluster ions charged positively fly to and collide with the
electron producing dynode 121, which is disposed at the next stage
and is fixed at the higher electric potential, to produce many
electrons there. Usually, the number of produced electrons is
larger than that of collided electrons, that is, a multiplier
effect can be realized. This operation is repeated several times (4
times in FIG. 2) between the electron multiplier dynodes in the
multiplier ion measuring tube 119, which finally achieves a
multiplier factor of about 10.sup.6. The many groups of multiplied
electrons are recovered by the anode 123 fixed at a higher
potential than the electron multiplier dynode 122 at the last stage
and are measured by the ammeter 125 for measuring the micro
current.
[0057] In setting the electric potential between the ion cathode
120, the electron producing dynode 121, the electron multiplying
dynode 122 and the anode 123 in the multiplier ion measuring tube
199, assuming that the entering cluster ions are positively
charged, the ion cathode 120 is set at minus several V to minus
several tens V and the anode 123 is set at a high electric
potential of plus 1000 V to plus 3000 V, wherein the high electric
potential described above are equally distributed among the
electron producing dynode 121 and three stages of electron
multiplying dynodes 122. The electric potential in the multiplier
ion measuring tube 119 is set by an ion measuring tube power supply
system 124. Here, in order to easily discharge electrons, the alloy
of alkaline and alkaline-earth metal having a small work function
is vapor deposited on the surfaces of the ion cathode 120, the
electron producing dynode 121, and the electron multiplying dynode
122.
[0058] The various kinds of numerical data necessary for
classifying and measuring the particles, that is, the mass flow of
the aerosol measured by the mass flow meter 106, the pressure of
the aerosol measured by the capacitance manometer gage 107, the
electric potential of the electric potential applying plate 110a of
the inner shell cylinder 110 of the particle classifying tube 108,
the micro current measured by the ammeter 125 (anode current) are
collected by the signal processing system 126 and are converted
into digital signals that can be easily processed by the personal
computer 127. In a usual method of displaying data, the electric
potential of the electric potential applying plate 110a of the
inner shell cylinder is scanned with the mass flow and the pressure
of the aerosol kept at fixed vales and the current value of the
ammeter 125, which increases or decreases in accordance with the
scanning, is displayed. A typical measurement example is shown in
FIG. 3(a) where the potential V.sub.in of the potential applying
plate 110a of the inner shell cylinder is plotted on a horizontal
axis in an absolute value and where an anode current I.sub.a is
plotted on a vertical axis. The particle classifying tube 108 acts
as a high pass filter as a whole. As the absolute value V.sub.in
increases, the maximum particle size of all the particles which can
not pass (are shut off by) the particle classifying tube 108
increases and thus the characteristic curve in FIG. (a)
monotonously decreases.
[0059] Next, assume that when the voltage V.sub.in is applied to
the particle classifying tube 108, the maximum particle size of all
the particles which are shut off by the particle classifying tube
108 is d.sub.p and its number density distribution is f. Taking
into account a function of V.sub.in in accordance wit the FIG.
3(a), and I.sub.a and f are combined with each other by the
following relationship (Equation 1). 1 I a Q c V in .infin. f ( V
in ) V in ( Equation 1 )
[0060] Where Q.sub.c is the flow rate of a carrier gas. That is, by
standardizing and differentiating the characteristic curve (FIG.
3(a)) of I.sub.a measured while sweeping V.sub.in by and with
respect to the flow rate of carrier gas, the number density
distribution f can be obtained as a function of V.sub.in. This will
be shown in FIG. 3(b). Further, the following relationship
(equation 2) holds between V.sub.in and d.sub.p. 2 d p ( V in ) = 2
e C c L 3 Q c In ( R 2 / R 1 ) V in ( Equation 2 )
[0061] Where e is a charge elementary quantity; C.sub.c is
Cunningham's correction factor; .mu. is the viscosity of the
carrier gas; Q.sub.c is the flow rate of the carrier gas; L is the
classifying length of the particle classifying tube (length of the
electric potential applying plate); R.sub.1 is the radius of the
inner shell cylinder of the particle classifying tube; and R.sub.2
is the radius of the outer shell cylinder of the particle
classifying tube. The use of the relationship of the equation 2
makes it possible to convert the number density distribution f into
a function of the particle size d.sub.p, that is, a particle size
distribution function. The result of conversion will be shown in
FIG. 3(c). This corresponds to the particle spatial number density
of the reduced pressure apparatus process chamber 101 that is the
object to be measured. In the present preferred embodiment, the
mathematical transformation described above is processed by the
computer 127, so that the particle size distribution function
f(d.sub.p) of the space to be measured can be calculated from the
data of V.sub.in and I.sub.a which are directly measured. This
measurement and evaluation method fundamentally makes it possible
to conduct measurement during the process operation, that is, an
in-situ measurement.
[0062] Further, in the present preferred embodiment, even when a
helium gas is used as the carrier gas, if the pressure of the
carrier gas in the particle classifying tube 108 is 5 Torr or more,
the particle having a size of 2 nm or more can be sufficiently
classified. As the flow rate of the carrier gas, the pressure of
the gas to be classified, and the molecular size of the carrier gas
become larger, the accuracy of classification tends to be
improved.
[0063] Still further, if the characteristics of the particle size
distribution function f(d.sub.p) (which becomes a logarithmic
normal distribution in many cases) for each reduced pressure
apparatus process chamber 101 are stored by repeating the
continuous sweeping of V.sub.in several times, thereafter, it is
also possible to more quickly estimate and evaluate the particle
size distribution function f(d.sub.p) from about three measurement
results of V.sub.in.
[0064] (Second Embodiment)
[0065] Next, the second embodiment in accordance with the present
invention will be described in detail. FIG. 4 is a block diagram to
show the general configuration of a particle counter in accordance
with the present embodiment. The particle counter of the present
embodiment is connected in a vapor phase to a process chamber 301,
in particular, in a chemical vapor deposition (CVD) or a physical
vapor deposition (PVD) that is conducted in a reduced pressure
vapor phase or a dry etching in a semiconductor integrated circuit
manufacturing process system in conformity with an ultra-fine
design rule (130 nm or less). In the present embodiment, the
process chamber 301 is a process apparatus conducting a physical or
chemical reaction in the vapor phase, and has a function as an
aerosol supply source.
[0066] This particle counter is provided with an aerosol intake
valve 302 connected to the process chamber 301, a charging device
303 for charging the aerosol introduced from the aerosol intake
valve 302 and a group of particles existing in the aerosol, a
floating ion attracting and removing system 304 for attracting and
removing floating ions that interfere with the measurement of the
charged particles charged by the charging device 303, a particle
classifying system 305 for classifying the group of charged
particles from which the floating ions are attracted and removed,
and an exhaust system 306 that is provided at the last stage of the
particle counter and differentially exhausts the whole particle
counter.
[0067] Further, the particle counter has a sheath gas carrying line
309 in parallel to the configuration connected in the vapor phase
to the process chamber 301, as described above. The sheath gas
carrying line 309 is connected to a sheath gas intake port 308 made
separately from the process chamber 301 and cleans air is
introduced as a sheath gas from the sheath gas intake port 308. The
sheath gas is introduced into the sheath gas carrying line 309 into
the particle classifying system 305.
[0068] This configuration provides the particle counter as a whole
with a function of reducing pressure thereof or exhausting itself
to a vacuum. That is, during the operation of the particle counter,
exhausting the particle counter differentially by the exhaust
system 306 provided at the last stage forms the forward flow of the
aerosol to be measured from the process chamber 301 at the first
stage to the exhaust system at the last stage.
[0069] The process atmosphere aerosol introduced into the particle
counter via the aerosol intake valve 302, firstly, has its mass
flow adjusted by the flow-rate adjusting function of the aerosol
intake valve 302. This is because in the particle classifying
system 305, a large mass flow is required to improve a particle
classifying ability but too big mass flow increases the
electrostatic field intensity necessary for classification to a
value exceeding a practical range.
[0070] Next, the aerosol introduced and the group of particles
existing in the aerosol are charged by a charging device 303. In
the present embodiment, an Ar.sub.2 excimer light source to be
operated during the charging process under a wide range of the
aerosol gas pressure is provided in the charging device 303 and
vacuum ultraviolet rays irradiated from the Ar.sub.2 excimer laser
light source is used. It is also recommended that, depending on the
operating gas pressure, an radioisotope, a direct-current corona
discharge, an ion beam, or an electron beam be used appropriately
(in the decreasing order of the operating gas pressure). In
particular, in a high vacuum of 10.sup.-3 Pa or less, it is
effective to use the ion beam or the electron beam that can charge
particles into a unipolar state.
[0071] The aerosol subjected to the charging process is introduced
into the floating ion attracting and removing system 304 and the
floating ions that interfere with the measurement of the charged
particles to be measured are attracted and removed there. Needless
to say, the floating ions are extremely smaller than the particles
to be measured (particle size range: 2 nm to 50 nm) and thus their
electric mobilities in a viscous gas are extremely small. The
floating ions are produced by a plasma process in the reduced
process apparatus chamber 301 and the charging process in the
charging device 303.
[0072] FIG. 5 is a cross-sectional configurational view of a
floating ion attracting and removing chamber constituting the
floating ion attracting and removing system 304 of the particle
counter in the present embodiment. This floating ion attracting and
removing chamber 401 is provided with a chamber body 401a having a
hollow cylindrical structure, an aerosol introduction port 402 for
introducing the charged particles charged by the charging device
303, an aerosol discharge port 403 for discharging the group of
charged particles from which the floating ions are attracted and
removed, a floating ion attracting cylinder 404 that is disposed in
the hollow space of the chamber body 401a and attracts and removes
the floating ions, an attracting cylinder suspending bar 405 for
suspending the floating ion attracting cylinder 404 to dispose the
floating ion attracting cylinder 404 in the hollow space of the
chamber body 401a, and an electric potential applying device 406
that is connected to the attracting cylinder suspending bar 405 and
applies an electrostatic potential to the floating ion attracting
cylinder 404 via the attracting cylinder suspending bar 405. The
chamber body 401a and the floating ion attracting cylinder 404 are
coaxially arranged.
[0073] The operation of the floating ion attracting and removing
chamber 401 having such a constitution will be described. The
floating ion attracting and removing chamber 401 has a constitution
in which the aerosol flow supplied from the charging device 303
passes through the inside thereof along the rotational central
axis. The aerosol flowing into the chamber 401 through the aerosol
introduction port 402 passes through the inside of the floating ion
attracting cylinder 404 that has a hollow cylindrical shape and has
the same rotational central axis as the chamber body 401a and flows
out from the aerosol discharge port 403. Here, the floating ion
attracting cylinder 404 is made of good conductive metal
(oxygen-free copper or SUS304) and is held by an attracting
cylinder suspending bar 405 that is insulated from the wall of the
chamber body 401 itself. The attracting cylinder suspending bar 405
is made of the same good conductive metal as the floating ion
attracting cylinder 404 and is connected to an electric potential
applying device 406, whereby a negative electric potential is
electrostatically applied to the floating ion attracting cylinder
404. The magnitude of the negative electric potential of the
floating ion attracting cylinder 404 is set, in view of the flow
rate (residence time in the floating ion attracting and removing
chamber 401) of the aerosol and the gas pressure (that determines
the electric mobilities of the ions and particles existing in the
aerosol), such that the floating ions are electrostatically
deflected from the starting direction of velocity of flow and
attracted by the ion attracting cylinder 404 and that the charged
particles (2 nm to 50 nm) are not attracted by but can pass through
the ion attracting cylinder 404.
[0074] In the floating ion attracting and removing chamber 401, the
aerosol passing the floating ion removing process is introduced
into the particle classifying system 305 shown in FIG. 4 where the
group of charged particles existing in the aerosol are classified
according to the values of electric mobilities depending on the
particle sizes. The principle of classification of the charged
particles will be described in more detail with reference to FIG.
7.
[0075] FIG. 7 is a cross-sectional configurational view of the
classifying tube 501 (see FIG. 6) constituting the particle
classifying system 305 of the particle counter in the present
embodiment. The classifying tube 501 is provided with a carrier gas
introducing line 601 for introducing the aerosol from which the
floating ions are removed in the floating ion attracting and
removing chamber 401, a sheath gas introducing line 602 connected
to the sheath gas carrying line 309, a classified aerosol discharge
port 603 for discharging the classified aerosol containing the
charged particles, and a sheath gas discharge port 604 for
discharging the sheath gas introduced from the sheath gas
introducing line 602 through the exhaust system 306.
[0076] Further, the classifying pipe 501 is provided with an
aerosol jetting-out slit 605 for introducing the aerosol to be
measured, which is introduced into the carrier gas introducing line
601, into a classifying region (shown by a reference character L in
FIG. 7); an aerosol introducing slit 606 for introducing the
aerosol classified in the classifying region L from the classifying
region L into the classified aerosol discharge port 603; a filter
mesh 607 for filtering the sheath gas introduced from the sheath
gas introducing line 602 to make the sheath gas into a laminar
flow; an inner shell cylinder 608 that becomes an inside shell for
forming the classifying region L; and an outer shell cylinder 609
that is arranged so as to cover the outside of the inner shell
cylinder 608 and becomes an outside shell for forming the
classifying region L along with the inner shell cylinder 608.
[0077] Still further, the classifying tube 501 is provided with a
positive high-voltage electrode 610 placed on the outside wall of
the inner shell cylinder 608 and a ground electrode 611 that is
placed on the inside wall of the outer shell cylinder 609 and
produces an electrostatic electric field when voltage is applied
across itself and the above-mentioned positive high-voltage
electrode 610. The inner shell cylinder 608 and the outer shell
cylinder 609 are arranged such that they have the same central
axis.
[0078] The operation of the classifying tube 501 having the
configuration like this will be described. In the present,
embodiment, first, clean air is introduced as a sheath gas at a
flow rate of 2.5 l/min through the sheath gas introducing line 602.
This clean air is taken from a clean zone (class 1 or less) in
which a reduced pressure process apparatus is disposed through the
sheath gas taking-inport 308 in the general configurational view of
the particle counter shown in FIG. 4 and is introduced through the
sheath gas carrying line 309. The sheath gas is introduced into the
space formed between the inner shell cylinder 608 and the outer
shell cylinder 609 (which becomes the classifying region L in a
limited meaning) through the filter mesh 607, thereby being
effectively made a laminar flow in the classifying region L. Here,
the inner shell cylinder 608 and the outer shell cylinder 609 are
arranged such that their rotational central axes are parallel and
concentric to the sheath gas flow. The sheath gas having the same
flow rate as the introduced sheath gas is discharged, from the
sheath gas discharge port 604 by the exhaust system 306. The
exhaust system 306 is constituted by a dry mechanical pump or a
combination of the dry mechanical pump and a high-pressure-operated
turbo-molecular pump arranged at its preceding side. On the other
hand, the aerosol to be measured is introduced into the classifying
region L at a flow rate of 0.5 l/min through the carrier gas
introducing line 601 from the aerosol jetting-out slit 605.
[0079] In the classifying region L, a radial electrostatic electric
field is applied to the common central axis by the positive
high-voltage electrode 610 placed on the outside wall of the inner
shell cylinder 608 and the ground electrode 611 placed on the
inside wall of the outer shell cylinder 609. The particles existing
in the aerosol, which are introduced from the aerosol jetting-out
slit 605 into the classifying region L and are not charged
(charging efficiency of the charging device 303 is smaller than 1),
are carried with the sheath gas flow shaped like a laminar flow
from the aerosol jetting-out slit 605 to the direction of the
sheath gas discharge port 604 (from the left to the right in FIG.
7) and are discharged from the sheath gas discharge port 604. The
particles existing in the aerosol, which are charged by the
charging device 303, are deflected by the electrostatic field
formed in the classifying region L. In particular, the particles
negatively charged are attracted to the side of the inner shell
cylinder 608 side and part of them can be discharged from the
classified aerosol discharge port 603 through the aerosol
introducing slit 606.
[0080] The trace of the charged particle in the classifying region
L, in principle, is determined by the mobility (particle size) of
the charged particle in the sheath gas, a lateral carrying speed by
the sheath gas, an electrostatic field intensity distribution, a
geographical shape (length of the classifying region L, diameter of
the inner shell cylinder R.sub.1, diameter of the outer shell
cylinder R.sub.2). By setting these parameters appropriately,
particles of a special particle size can be extracted from the
classified aerosol discharge port 403, that is, can be classified.
Usually, the central value of the particle size after
classification is determined by setting the lateral carrying speed
and the geographical shape and finally by adjusting the
electrostatic field intensity (as a soft parameter), the particle
size after classification can be arbitrarily selected. Measuring
the number of charged particles after classification (spatial
number density) by the use of the ammeter measuring a micro current
while scanning the electrostatic field intensity makes it possible
to calculate and evaluate the particle size distribution of the
particles existing in the aerosol to be measured.
[0081] Next, the constitution of a signal detecting section and the
operation of detecting a signal in the particle classifying system
305 will be described with reference to FIG. 6. The detection of
the signal in the embodiment of the particle counter in accordance
with the present invention is based on measuring the number of
charged particles existing in the aerosol flow after
classification, that is, the spatial number density by the use of
the ammeter. Here, it is the case where the number density of the
floating ions can not neglected as compared with the number density
of charged particles to be measured that presents a problem. As
described already also in the present embodiment, the floating ions
are removed by the use of the floating ion attracting and removing
chamber 401 but can not be sufficiently removed in many cases. In
other words, even if the floating ions are removed and classified
from the charged particles of specific particle size by the
electrostatic attraction or deflection, the effect (flowing into
the ammeter) of the floating ions scattered in the whole aerosol
flow passage of the particle counter by a vapor phase diffusion
phenomenon presents a problem.
[0082] In the present embodiment, therefore, by modulating the
electrostatic field intensity applied to the classifying operation
in the classifying tube 501 at low frequency (several Hz to several
tens Hz), the charged particles reaching the ammeter for detection
are shut off by the modulation frequency. By amplifying only this
modulation frequency component in a narrow band, it is intended to
remove the effect of the floating (diffused) ions constantly
flowing into the ammeter.
[0083] FIG. 6 is a block diagram to show the constitution of the
signal detecting section of the particle counter classifying system
305. The signal detecting section is provided with a detector 502
disposed at the downstream of the classified aerosol discharge port
603, a voltage function generator 503 for generating the
electrostatic field for the classification operation of the
classifying tube 501, a preamplifier 504 for converting a current
signal representing the number of charged particles after
classification measured by the detector 502 into a voltage signal,
and a lock-in amplifier 505 for amplifying the signal converted
into the voltage signal by the preamplifier 504 in a narrow band by
the modulation frequency described above.
[0084] In the signal detecting section having the constitution like
this, an electrostatic field of a rectangular waveform is applied
to the classifying tube 501 for its classifying operation by the
voltage function generator 503. This electrostatic field has a
frequency of several Hz, a duty ratio of 1/2, a maximum application
voltage by which all particles of the particle size to be measured
(50 nm or less) are deflected and attracted to the wall of the
inner shell cylinder 608 on the upstream side of the aerosol
taking-in slit 606, and a minimum application voltage by which
particles of a specific particle size to be measured are made to
reach the aerosol jetting-out slit 606. The number of charged
particles after classification is measured as a current signal by
the detector 502 whose main part is the ammeter disposed on the
down stream side of the classified aerosol discharge port 603. This
current signal is converted into a voltage signal by the
preamplifier 504 and then is amplified in a narrow band by the
modulation frequency described above. Here, as a reference
frequency signal, the same waveform that generates the
electrostatic filed for classifying operation is applied by the
voltage function generator 503.
[0085] While the present invention has been described based on the
preferred embodiments shown in the drawings, it is clear to the
person skilled in the art that the present invention can be easily
changed or modified and those changes and modifications will be
included within the spirit and scope of the present invention.
* * * * *