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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dry etching apparatus and method, and
more particularly to a dry etching apparatus and method which are suitable
to implement high-selectivity high-anisotropy etching at high speed and
with high throughput.
2. Description of the Related Art
Conventional dry etching techniques have used low gas pressure of 1-10
mTorr or so in order to improve anisotropy. Discharging gas with such a
low gas pressure requires adoption of effective discharging techniques.
One of them is microwave discharging. Examples of microwave gas
discharging are disclosed in "Journal of Electrochemical Society" 1982,
page 2764, "Journal of Vacuum Science Technology" A7, 1989, page 899 and
"Proceeding of Dry Process Symposium" 1990, page 99.
Generally, reducing pressure lowers etching speed, so the conventional dry
etching at low gas pressure uses high density plasma with the degree of
ionization being high. The higher the plasma density, the higher the
etching speed because the ion current incident to a sample to be treated
increases. In microwave discharging, the plasma density can be made high
by boosting the power of the microwave.
As an alternative way of improving the anisotropy, the conventional dry
etching adopts an exchange of gas. For example, the process disclosed in
JP-A-61-61423 and JP-A-63-65628 uses different gases in different steps in
such a manner that the first step performs an anisotropic etching, the
second step forms a side wall protection film and the third step performs
an isotropic etching. The process disclosed in JP-A-60-50923 and
JP-A-2-105413 realizes anisotropic treatment by making "time modulation
etching" of exchanging etching gas for deposition gas at intervals of a
few seconds. The process disclosed in JP-A-2-270320, in order to improve
the temperature controllability in lower temperature etching to thereby
increase the anisotropy, fixes a wafer by electrostatic adsorption,
requires a plasma which (as does the wafer removal). Discharging gas
exchanged into inert gas assures more accurate etching. Thus, the
efficient method of improving the anisotropy has been to exchange gas.
A dry etching apparatus with the short gas residence time of 25 ms is
disclosed in "Journal of Vacuum Science Technology" B8 (1990) p. 1185. The
apparatus has a volume of about 2 liters between electrodes and an
effective exhaust speed of 80 liter/sec.
The prior art described above has the following problems to be solved. The
conventional dry etching techniques show a phenomenon that even when the
incident ion current density is enhanced with the density plasma made
high, the etching speed of a sample ceases to increase. This causes a
problem that the necessary etching speed cannot be obtained solely by
making the plasma density high. The etching speed can also be increased by
applying an RF bias to a sample or body to be treated to thereby enhance
the energy of incident ions. Enhancing the incident ion energy, however,
deteriorates the etching selectivity ratio of the sample and a mask or
underlying layer.
For example, the Si gate treatment process in which a resist is used as a
mask, a poly-Si (polycrystalline silicon) sample having an underlying
SiO.sub.2 is to be treated and, requires a poly-Si/resist selectivity
ratio of 5 or more and a poly-Si/SiO.sub.2 selectivity ratio of 50 or
more. This treatment process uses Cl.sub.2 gas plasma for etching. In
order to provide the above selectivity ratios, the plasma etching was
performed at the poly-Si etching speed of 300 nm/min or so. Since the
poly-Si film is about 300 nm thick, the treatment time including 50%
over-etching was 1.5 minutes. But the treatment time is desired to be one
minute or less for good throughput. Therefore, the first problem to be
solved is:
(1) to realize a poly-Si etching speed of 450 nm/min or more with a
poly-Si/resist selectivity ratio of 5 or more and a poly-Si/SiO.sub.2
selectivity ratio of 50 or more.
With development of miniaturization of semiconductor devices, the resist
mask and the underlying SiO.sub.2 is expected to become about half as
thick as at the present time. On the other hand, since the thickness of
the poly-Si gate is expected to remain fixed, selectivity ratios which are
twice as large as before are required. Therefore, the second problem to be
solved is:
(2) to realize a poly-Si etching speed of 450 nm/min or more with a
poly-Si/resist selectivity ratio of 10 or more and a poly-Si/SiO.sub.2
selectivity ratio of 100 or more.
The conventional dry etching technique has a disadvantage that if the
sample to be treated contains plural kinds of atoms like AlCuSi, a
material with a low gas pressure such as a reaction product of Cu is
likely to be left as residue. Therefore, the third problem to be solved
is:
(3) to make the etching without leaving, a material with a low gas pressure
as residue.
Uniformity in etching depends on the uniformity in the density of the ion
current supplied to the sample. But the conventional dry etching has no
means of examining the uniformity in the ion current density. Thus, the
uniformity in etching cannot be known until the etching is completed. The
fourth problem to be solved is:
(4) to estimate and control etching uniformity before the etching.
The conventional dry etching apparatus, in which the gas residence time
within a chamber was 0.4-3 sec or so, could not introduce gas in a pulse
shape into the chamber at time intervals shorter than the residence time
which is the time that the gas resides within the chamber from when it is
supplied into the chamber to when it is exhausted. The gas residence time
can be calculated by
gas residence time=(volume within the apparatus)/(effective exhaust speed)
(1)
In order to implement "atomic layer etching" in which a sample is etched at
a sufficient etching speed (100 nm/min or more) for each atomic layer, at
a pressure of 0.1 mTorr, it is necessary to control gas adsorption with
the accuracy of at least 10 atomic layers, preferably 0.01 atomic layers,
for the surface of the sample. In order to control the gas adsorption with
the accuracy of 10 atomic layers, it is necessary to introduce the gas
with a pulse width of 100 ms, and in order to control the gas adsorption
with the accuracy of 0.01 atomic layers, it is necessary to the gas with a
pulse width of 0.1 ms. The fifth problem to be solve is:
(5) to introduce gas in a pulse shape with a pulse width of 0.1 ms to 100
ms into a treatment chamber.
The conventional dry etching apparatus, in which the gas residence time in
the treatment chamber is 0.4-3 sec or so, took one second or more to
exchange gas. The etching accompanied by gas exchange has a problem that
it takes relatively longer time to exchange the gas to thereby reduce the
throughput. In order to observe or examine the shape of the sample during
the etching by an observing means attached to the etching apparatus, the
gas supply must be stopped to reduce the gas pressure. It took a few
seconds to exhaust gas so that the etching with observation of the sample
shape reduces the throughput. Therefore, the sixth problem to be solved
is:
(6) to improve throughput in the etching accompanied by gas exchange.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a dry etching
technique which can realize a poly-Si etching speed of 450 nm/min or more
with a poly-Si/resist selectivity ratio of 5 or more and a
poly-Si/SiO.sub.2 selectivity ratio of 50 or more.
The second object of the present invention is to provide a dry etching
technique which can realize a poly-Si etching speed of 450 nm/min or more
with a poly-Si/resist selectivity ratio of 10 or more and a
poly-Si/SiO.sub.2 selectivity ratio of 100 or more.
The third object of the present invention is to provide a dry etching
technique which can etch without leaving the material with a low gas
pressure as residue.
The fourth object of the present invention is to provide a dry etching
technique which can estimate and control etching uniformity before the
etching.
The fifth object of the present invention is to provide a dry etching
technique which can introduce gas in a pulse shape with a pulse width of
0.1 ms to 100 ms into a treatment chamber.
The sixth object of the present invention is to provide a dry etching
technique which can improve throughput in the etching accompanied by gas
exchange.
In order to attain the above objects, in accordance with the present
invention, the following means for solving the problems described above
are proposed.
(1) Means for solving the first problem
In the conventional dry etching, when the poly-Si/resist selectivity ratio
was 5 and the poly-Si/SiO.sub.2 selectivity ratio was 10, with an ion
current density of 8 mA/cm.sup.2, the etching speed of poly-Si was 300
nm/min. In order to enhance the etching speed with the selectivity ratios
fixed, first, it is necessary to increase the ion current density to 12
mA/cm.sup.2 which is 1.5 times as large as 8 mA/cm.sup.2 without changing
the ion energy. To this end, it is necessary to boost high frequency
application power to thereby make the plasma density high. Generally, the
ion density can be increased to 1.5 times by increasing the high frequency
application power to 1.5 times. The necessary application power depends on
the area of a sample and the size of a treatment chamber. In order to
obtain the same ion current density, a large sample, and this a large
treatment chamber, requires large application power. Even with the size of
the sample and treatment chamber changed, the same power surface density
(high density power per unit area of radiation) results in the same ion
current density. The reason why the ion current density depends on the
power surface density will be explained below.
The applied high frequency is not absorbed in all parts of a plasma. For
example, in microwave discharging, microwave energy is absorbed in the
plasma by electron cyclotron resonance (ECR) which occurs at a face
portion called an ECR face. Thus, the ion current density depends on the
microwave energy (power surface density) radiated for a unit area of the
ECR face. In a parallel plate type dry etching apparatus, the ion current
density depends on the power surface density of the high frequency energy
supplied for a unit area of an electrode. Namely, in the etching apparatus
in which the high frequency is absorbed in a face area, the ion current
density depends on the power surface density. Generally, the area of the
portion where the high frequency is absorbed is almost equal to that of
the section of a treatment chamber and also equal to that of a sample to
be treated. In other words, the power surface density can be approximated
as (applied high frequency power)/(the surface area of the sample).
Also where the high frequency is absorbed in the entire plasma like a
helicon wave plasma, the power surface density can be assumed. For
example, in the helicon wave plasma, the length of a discharge part
depends on the wavelength of the high frequency power, but does not depend
on the size of the sample. On the other hand, the sectional area of the
discharge part depends on the size of the sample. In order to provide the
same ion current density, the applied high frequency power must be
increased in proportion to the sectional area of the discharge part. Thus,
assuming that (the application high frequency power)/(the sectional area
of the discharge part) represents the power surface density, the ion
density depends on the power surface density.
Now, the power surface density necessary to raise the etching speed of
poly-Si to 450 nm/min will be investigated below. In the conventional dry
etching apparatus, with the ion current density of 8 mA/cm.sup.2, the
etching speed of poly-Si was 300 nm/min. Then, where the sample was an
8-inch wafer, the high frequency power of 1 kW was required. Thus, the
power surface density was 3 W/cm.sup.2. In order to increase the etching
speed of poly-Si to 450 nm/min, the ion current density must be increased
to 12 mA/cm.sup.2 which is 1.5 times as large as before, and the power
surface density of 4.5 W/cm.sup.2 is required. In order to obtain this
power surface density, where the 8-inch wafer is used, the high frequency
application power of 1.5 kW or more is required.
As described in connection with the problem to be solved, the conventional
dry etching which only increases the ion density to 1.5 times cannot
increase the etching speed. This is ascribed to the influence of the
etching reaction product. For example, when the 8 inch Si wafer is etched
at 450 nm, the reaction product of Si is made at the rate of
1.3.times.10.sup.19 /s. This rate corresponds to a gas flow of 27 sccm.
The conventional dry etching, in which the gas exhaust rate is as low as
760 liter/s or so, permits a gas flow of only 60 sccm at a pressure of 1
mTorr. Thus, half of the gas results in a reaction product. When the
plasma density is made high, re-dissociation/re-deposition as well as the
ion current density increases. As a result, the etching speed does not
increase.
If the reaction product is exhausted outside the treatment chamber by
increasing the exhaust speed, the influence by the reaction product is
restrained so that the etching speed as well as the ion current density
can be increased. Concretely, if the ratio of the reaction product in the
gas is reduced to 30% or less, its influence can be restrained. This
circumstance corresponds to a gas flow which is three times as much as the
amount of the reaction product. In order to realize this, with the gas
pressure of 1 mTorr, the Cl.sub.2 gas flow must be 90 scmm and the exhaust
speed must be 1200 liter/s or more.
In the present invention in which the power surface density is set for 4.5
W/cm.sup.2 or more and the effective exhaust speed is set for 1200 liter/s
or more, with the selectivity ratios of poly-Si/resist and
poly-Si/SiO.sub.2 being as high as 5 and 50, respectively, the poly-Si can
be etched at the high speed of 450 nm/min.
If the power surface density is raised, the ion current density can be
increased to thereby further enhance the etching speed. But if the plasma
is ionized completely, further power is not required so that the power may
be up to 1000 W/cm.sup.2. The exhaust speed is also desired to be higher
because the reaction product can be exhausted more swiftly. But, the
effective exhaust speed should not exceed 1,000,000 liter/s in view of the
size of the apparatus.
(2) Means of solving the second problem
In the feature, with the selectivity ratios of poly-Si/resist and
poly-Si/SiO.sub.2 being 10 and 100 or more, respectively, which are twice
or more as large as before, the etching speed of poly-Si of 450 nm/min or
more will be required. In order to enhance the selectivity ratio, the ion
energy must be reduced as compared with the condition described in
connection with the above item.
(1). If the ion energy is reduced to make the selectivity ratio twice, the
etching speed of poly-Si becomes 200 nm/min. Thus, in order to make the
etching speed 2.3 times as high as 200 nm/min to provide 450 nm/min, the
ion current density must be raised to 27 mA/cm.sup.2 which is 2.3 times as
high as that in the item (1). This can be realized with a power surface
density of applied high frequency of 10 W/cm.sup.2 or more to provide an
high density plasma.
Even when the ion current density as large as 27 mA/cm.sup.2 is given in
the conventional dry etching, the etching speed could not be increased
because of great influence by the reaction product. In the present
invention, since the reaction product is exhausted at the exhaust speed of
1200 liter/s or more, the etching speed of poly-Si can be increased to 450
nm/s. In this case, the sample which is an 8-inch wafer having a surface
area of 320 cm.sup.2, requires high frequency power of 3.2 kW or more. The
sample, which is an 6-inch wafer having a surface area of 180 cm.sup.2,
requires high frequency power of 1.8 kW or more. The sample which is an
5-inch wafer having a surface area of 130 cm.sup.2 requires high frequency
power of 1.3 kW or more.
In this way, the present invention can solve the above problem in such a
way that the high frequency power of 1.3 kW is applied and also the
effective exhaust speed of the treatment chamber is 1200 liter/s.
Additionally, when the high frequency power is applied to generate high
density plasma, temperature becomes very high at the wall of the chamber
and the sample. To obviate this, the wall of the chamber is made of metal
so that it can be cooled by a coolant, and the back surface of the sample
is directly touched with the coolant. Thus, the wall of the chamber and
the sample can be effectively cooled.
(3) Means of solving the third problem
Also in the material providing the reaction product with low vapor
pressure, the reaction creating a reaction product advances even if the
incident ion energy is little. For example, in the reaction of Cl.sub.2
gas plasma with Cu, chlorination of the Cu surface advances relatively
swiftly. If the incident ion energy is little, its reaction product will
be left as residue because its vapor pressure is low.
In order to remove the residue of the reaction product, the incident ion
energy must be increased. In the prior art technique, the incident ion
energy was increased while etching gas was being discharged. This also
promotes the etching reaction of the mask, thus providing a small
selectivity ratio.
In order to remove the residue of a reaction product, only the incident ion
energy has to be high, and a reaction activation species such as Cl.sub.2
is not required. In other words, when an inert gas plasma such as Xe is
discharged so that ions of the inert gas are incident, it is possible to
remove the residue of a reaction product. Then, if an RF bias is applied,
the residue can be effectively removed. Further, if the plasma is made
more dense to increase the incident ion current, the residue of a reaction
product can be removed more effectively.
Thus, since the reaction activation species is not supplied while the inert
gas is being discharged, the etching reaction on the mask does not
significantly occur, and only the residue of a reaction product can be
removed.
In the present invention, since etching is carried out in such a way that
the reactive gas and inert gas are alternately discharged, high
selectivity is enabled even if the reaction product contains a material
with a low vapor pressure.
(4) Means of solving the fourth problem
In accordance with the present invention, plural temperature detection
units are located on a sample stage, and discharging conditions are
adjusted so that the temperatures at the respective temperature detection
units are equal. Since a temperature increase during discharging is
proportional to the ion current density at the position at issue, the
above adjustment can make the ion current density uniform. Since the
etching speed depends on the ion current density, the adjustment can
improve etching uniformity. In the prior art technique, in order to adjust
the etching uniformity, the etching was actually carried out to
investigate the in-plane distribution of the etching speed of the sample.
On the contrary, in accordance with the present invention, the conditions
which can provide good etching uniformity can be easily obtained for a
short time.
(5) Means of solving the fifth problem
If the gas residence time in a treatment chamber is longer than 100 ms as
in the conventional dry etching, even if the response speed of a gas flow
rate controller is set for 100 ms or less, the gas in a pulse shape with
the pulse width of 100 ms cannot be supplied into the treatment chamber
because it takes a time approximately equal to the gas residence time from
when gas supply is stopped by the gas flow rate controller to when the gas
within the chamber is exhausted. In accordance with the present invention,
the effective exhaust speed of the chamber which generally has a volume of
100 liters is set for 1000 liter/s or more so that the gas residence time
in the chamber is 100 ms or less, and the response time of the gas flow
rate controller is set for 100 ms or less so that the gas pulse shape with
the pulse width of 100 ms or less can be supplied into the treatment
chamber. If the exhaust speed is increased to 1,000,000 liter/s, the pulse
width can be shortened to 0.1 ms. But if the exhaust speed is further
increased to shorten the pulse width, the control precision of gas
adsorption will become as excessively small as a 0.001 atomic layer, which
requires a very bulky apparatus.
So, in the present invention, the effective exhaust speed of the treatment
chamber is set for a value ranging from 1000 liter/s to 1,000,000 liter/s
inclusive so that the gas residence time in the treatment chamber ranges
from 0.1 ms to 100 ms inclusive. At least one gas introduction system is
provided and the gas flow rate controller having a response time ranging
from 0.1 ms to 100 ms inclusive is attached to the gas introduction
system. Further, in order to implement high speed pulse control, the gas
flow rate controller, discharging means and exhaust speed control means is
controlled by a batch controller.
(6) Means of solving the sixth problem
In order to improve throughput in the etching accompanied by gas exchange,
it is necessary to shorten the time taken for the gas exchange. Where the
used gas is exchanged from gas A to gas B during the etching, the etching
using gas B must be performed after gas A is sufficiently exhausted. If
not, in the gas exchange, the gases A and B mix with each other,
deteriorating the etching characteristic. If the exhaust is carried out
for a sufficiently long time, the pressure reduces to the base pressure in
the apparatus. But this deteriorates the throughput extremely so that
actually, the next gas is introduced when the gas exhaust of about 95% is
completed. The pressure changes as shown in FIG. 4 during the time from
when gas A is stopped to when gas B is introduced.
The change in the pressure from the stopping of gas A to completion of its
exhaustion accords with the differentiation equation expressed by
dP/dt=-SP/V (3)
where P represents pressure, S represents an effective exhaust speed in the
treatment chamber and V represents the volume of the chamber. With the
stopping time of gas A at t=0, solving the above equation provides the
time until the gas pressure becomes the pressure after exhaust in FIG. 4
(exhaust time) expressed by
exhaust time=(V/S) in (pressure before exhaust/pressure after exhaust) (4)
Since (V/S) represents the gas residence time, the exhaust time can be
expressed by
exhaust time=residence time.times.1 n (pressure before exhaust/pressure
after exhaust) (5)
FIG. 6 is a graph showing the relationship of the rate of gas exhausted
outside the chamber and in (pressure before exhaust/pressure after
exhaust). When gas is exhausted for the residence time after gas supply is
stopped, only 60% of the gas remaining in the chamber is exhausted. As
seen from the graph of FIG. 6, the gas exhaust of 95% corresponds to 1 n
(pressure before exhaust/pressure after exhaust) of 4. Thus, unless the
gas exhaust is carried out for four times as long as the gas residence
time, 95% of the remaining gas cannot be exhausted.
In the conventional dry etching apparatus, in which the residence time was
1 second or so, an exhaust time of several seconds was required. On the
other hand, in the present invention, since the effective exhaust speed is
set for 1000 liter/s so that the residence time is 100 ms or less, the
exhaust time can be shortened to about one-tenth as long as before. As a
result, the gas exchange time can be shortened to improve throughput.
By using the respective means described above, the present invention
permits high-anisotropic etching to be performed with high selectivity and
at high speed. Because of provision of the batch controller for
controlling the discharging means and exhaust speed control means as well
as the gas flow rate controller, the present invention permits high
precision etching to be performed with high throughput.
Further, in accordance with the present invention, means for recovering gas
after the etching is completed is provided to separate and recover unused
gas so that costs necessary to remove harmful components can be reduced.
The present invention, in which means for observing a sample is provided,
permits high precision etching to be performed with high throughput.
The present invention, in which means for observing a sample is provided,
permits high precision etching to be performed while monitoring an etched
shape. In this case, since the time taken for gas stopping and pressure
reduction can be decreased to 100 ms or less, the etching can be carried
out while monitoring the etched shape without reducing the throughput.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the arrangement of a dry etching
apparatus according to one embodiment of the present invention;
FIG. 2 is a plan view showing the arrangement of plural temperature
detection units on the sample stage in one embodiment of the present
invention;
FIG. 3 is a sectional view of the dry etching apparatus according to
another embodiment of the present invention;
FIG. 4 is a timing chart for gas exchange;
FIG. 5 is a timing chart for gas exchange;
FIG. 6 is a graph showing the relationship of the rate of exhausted gas and
the natural logarithm of pressure ratio;
FIGS. 7 and 8 (a)-(b), are timing charts for gas exchange;
FIG. 9 is a timing chart of the time modulation etching according to the
prior art;
FIG. 10 is a timing chart of the time modulation etching according to the
present invention;
FIG. 11 is a graph showing the relationship of the pressure ratio before
and after exhaust and its natural logarithm; and
FIGS. 12(a)-(d) are flow charts showing one embodiment of very high speed
pulse time modulation etching.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
An explanation will be given of one embodiment of the dry etching apparatus
according to the present invention. FIG. 1 shows the arrangement of one
embodiment of the dry etching apparatus according to the present
invention. In this apparatus, microwave energy is generated by a microwave
generator 1. The microwave energy is radiated into a discharging part 25
located in a vacuum treatment chamber 10 through a waveguide 4 and a
microwave introduction window 5. The wafer to be etched is an 8-inch wafer
having a surface area of 320 cm.sup.2. In accordance with the present
invention, the microwave generator 1 is activated so that the power
surface density of the microwave energy for the 8-inch wafer becomes 4.5
W/cm.sup.2. For this purpose, a microwave generator having maximum
activation power of 1.5 W or more is used to discharge high density
plasma. Thus, the walls of the microwave generator 1, waveguide 4 and
discharging part 25 generate more heat than in the conventional dry
etching apparatus. In order to absorb the heat, a cooling mechanism 2
through which coolant flows is provided to cool the apparatus. In order to
radiate the activated microwave power effectively to the discharging part
25, sticks 3 for tuning are provided on the way of the waveguide 4.
Etching treatment gas, the flow rate of which is controlled by a gas flow
rate controller 7, is introduced from a gas conduit 6 via a gas inlet 8
into the discharging part 25. In order to lower the gas flow rate to
thereby introduce the gas into the discharging part 25 uniformly, a buffer
chamber 9 is provided between the gas introduction inlet 8 and the
discharging part 25. The gas is introduced into the discharging part 25
through a large number of mesh-like pores made in the wall of the buffer
chamber 9.
In order that the introduced etching gas is effectively discharged by the
microwave energy, a magnetic field is produced by solenoid coils 24 so
that because of ECR (electron cyclotron resonance) the microwave energy is
effectively absorbed in the plasma.
The gas after the etching treatment is completed is exhausted from the
vacuum treatment chamber 10 by a turbo molecular pump 18 via a conductance
valve 17. In the dry etching apparatus according to this embodiment, the
gas is supplied with a large flow rate so that only 30% or less of the
entire gas flow is consumed in an etching reaction, and 70% or more
thereof is exhausted as unused treatment gas by the turbo molecular pump
18. So, a means for recovering the unused treatment gas of the exhausted
gas is provided. The treatment gas is liquefied by a liquefaction machine
19, and the liquefied gas is purified by a purifier 20. The unused
treatment gas thus separated is recovered by a recovering reservoir 21.
The liquefier 19 liquefies the unused treatment gas by adjusting pressure
and temperature. The purifier 20 separates the unused treatment gas from
the other gas by distillation. The used gas (reaction product) separated
by the liquefier 19 and purifier 20 is passed through a detoxication
machine 22 and a scrubber 23 and released in the atmosphere. As described
above, the unused gas is recovered so that little harmful etching gas will
pass through the detoxication machine 22. The frequency of exchanging the
adsorbent in the detoxication machine 22 can thus be reduced from
12-times/year to once/year or less. Since the recovered gas can be used
again, cost for the gas and detoxication can be restricted.
The wafer 14 to be etched is placed on a sample stage 11. The sample stage
11 is provided with a cooling line 12 for the sample to be treated. The
cooling line 12 is opened at the upper portion of the stage 11 so that
coolant directly contacts with the back surface of the wafer 14. The
coolant is cooled by a circulator 13 to circulate in the cooling line 12.
The coolant directly contacts with the back surface of the wafer 14, but
the coolant must not leak into the vacuum treatment chamber 10. So in this
embodiment, using a dielectric 15 and a DC power source, the sample stage
11 and the wafer 14 are brought into intimate contact with each other by
electrostatic adsorption.
An RF power source 16 can be connected with the sample stage 11 so that an
RF bias can be applied to the wafer 14.
Also using high density plasma, this embodiment can carry out the etching
with the influence by the reaction product being restrained. For example,
under the conditions of the Cl.sub.2 gas pressure of 1 mTorr, gas flow
rate of 90 sccm, microwave power of 1.5 kW and power surface density of
4.5 W/cm.sup.2, the etching can be carried out at the poly-Si etching
speed of 450 nm/min to provide a poly-Si/resist selectivity ratio of 5 and
a poly-Si/SiO.sub.2 selectivity ratio of 50.
The above meritorious effect is true of etching other materials as well as
the resist mask and Si. The conditions which make side etch for the metal
or semiconductor such as Al, W, Cu and GaAs does not make the side etch
for the insulating material such as SiO.sub.2. In other words, an etching
reaction occurs with the lower incident ion energy for the metal or
semiconductor than for the insulating material. Where the metal or
semiconductor is etched using the insulating material as a mask, the same
effect as in this embodiment can be obtained.
Embodiment 2
In the apparatus according to Embodiment 1, the high ion current density
permits etching with improved uniformity. The uniformity of the ion
current density can be regulated using an etching parameter such as an
exterior magnetic field condition. This embodiment proposes the means and
method for regulation.
Since ions accelerated by plasma potential are incident, an incident
portion is heated by Joule heating so that its temperature is increased.
The degree of temperature increase depends on the ion current density.
Thus if the exterior magnetic field condition is regulated so that the
temperatures in the plural temperature detection units previously provided
on the stage 11 are equal, the uniformity of the ion current density can
be increased.
FIG. 2 shows the layout of the temperature detection units on the stage. As
seen from the figure, plural temperature detection units 27 are placed on
the stage 11. In this embodiment, the temperature detection units 27
detect the temperature of SiO.sub.2 serving as covers from its back face
by means of contact-type fluorescent thermometers. The temperatures at the
respective positions are detected during the discharging, and the exterior
magnetic field is regulated so that these temperatures are equal. The
exterior magnetic field condition can be regulated by regulating the
current which is caused to flow through a solenoid coil 24 (FIG. 1) and
the position of the coil. By means of the above regulating means and
method, the uniformity of the ion current density can be improved, which
leads to etching with improved uniformity.
In order that the conventional dry etching can enhance etching uniformity,
the sample must be actually etched to acquire the in-plane distribution of
the etching speed. For this reason, it took time and labor to optimize the
exterior magnetic condition. By the method according to this embodiment,
the exterior magnetic field condition can be optimized for a short time
for each process so that the time and cost necessary for regulation can be
reduced.
In addition to the exterior magnetic field condition, the regulation
parameter may be the position where tuning sticks for matching the
microwave energy are located, the propagation mode of the microwave
energy, the position where the dielectric is placed in the discharging
chamber, microwave input power and the kind of energy to be radiated. The
method according to this embodiment can also be applied to regulation of
these parameters.
Embodiment 3
As described in connection with Embodiment 1, the present invention can
carry out the high-speed high-selectivity etching by increasing the amount
of incident ions without changing the ion energy. But it has a problem
that when the sample to be etched contains plural kinds of atoms, a
reaction product with a low gas pressure remains as residue. For example,
in the etching of the AlCuSi, the reaction product of Cu is likely to
remain as a residue. So in the conventional dry etching technique, a high
RF bias was applied to prevent the reaction product with low vapor
pressure from remaining as a residue. But, this gave rise to a problem
that the selectivity ratio with the mask becomes small because the
incident ion energy is high.
In order to desorb the reaction product with low vapor pressure, the amount
of incident ions may be increased instead of increasing the incident ion
energy. But in this case, the reaction product with high vapor pressure is
likely to be further desorbed so that the reaction product with low vapor
pressure still remains as a residue.
To obviate this, in accordance with this embodiment, the steps of supplying
low incident ion energy and high incident ion energy are repeated
alternately. Then, the step of low incident ion energy discharges reactive
gas whereas the step of high incident ion energy discharges inert gas.
Such a technique realizes the high-speed high-selectivity etching without
substantially leaving a residue. This etching technique will be explained
for an example of etching of AlCuSi using a resist mask.
The step of supplying low incident ion energy discharges Cl.sub.2 gases.
The same process condition as in Embodiment 1 is adopted. Making the
plasma dense restrains the etching reaction of the resist mask so that the
etching reacti | | |
