U.S. patent application number 11/288105 was filed with the patent office on 2007-04-12 for etching method and etching equipment.
Invention is credited to Yutaka Kudou, Kazuo Takata, Satoshi Tani.
Application Number | 20070080136 11/288105 |
Document ID | / |
Family ID | 37910257 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070080136 |
Kind Code |
A1 |
Takata; Kazuo ; et
al. |
April 12, 2007 |
Etching method and etching equipment
Abstract
The invention provides an etching method for realizing trench
etching without causing any damages to the side walls of the trench
while maintaining a high-etching rate. The plasma etching method
relates to forming a groove or a hole by forming a silicon trench
to a silicon substrate or a silicon substrate having a silicon
oxide dielectric layer via a mixed gas plasma containing a mixed
gas of SF6 and O2 or a mixed gas of SF6, O2 and SiF4 and having
added thereto a gas containing hydrogen within the range of 5 to
16% (percent concentration) of the total gas flow rate of the mixed
gas.
Inventors: |
Takata; Kazuo;
(Kudamatsu-shi, JP) ; Kudou; Yutaka;
(Kudamatsu-shi, JP) ; Tani; Satoshi;
(Kudamatsu-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
37910257 |
Appl. No.: |
11/288105 |
Filed: |
November 29, 2005 |
Current U.S.
Class: |
216/58 ;
156/345.29; 156/345.33; 216/17; 257/E21.218; 257/E21.597;
438/706 |
Current CPC
Class: |
H01L 21/3065 20130101;
H01L 21/76898 20130101 |
Class at
Publication: |
216/058 ;
438/706; 216/017; 156/345.29; 156/345.33 |
International
Class: |
H01B 13/00 20060101
H01B013/00; H01L 21/306 20060101 H01L021/306; H01L 21/461 20060101
H01L021/461; B44C 1/22 20060101 B44C001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 2005 |
JP |
2005-295462 |
Claims
1. An etching method for forming a trench (a groove or a hole) to a
silicon substrate or a silicon substrate having a silicon oxide
dielectric layer, the etching performed via a plasma generated by a
mixed gas formed by adding a gas containing hydrogen to a mixed gas
composed of SF6 and O2 or a mixed gas composed of SF6, O2 and SiF4,
wherein the amount of added gas containing hydrogen is within a
range of 5 to 16% (percent concentration) of the total gas flow
rate of said mixed gas composed of SF6 and O2 or said mixed gas
composed of SF6, O2 and SiF4.
2. The etching method according to claim 1, wherein said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3.
3. The etching method according to claim 1, wherein said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3 being diluted
by Ar, He or N2 when being added to the mixed gas, or said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3 being diluted
in advance by said gases.
4. The etching method according to claim 1, wherein said gas
containing hydrogen does not contain carbon or fluorine.
5. The etching method according to claim 1, wherein a temperature
of a sample stage for holding the silicon substrate or the silicon
substrate having the silicon oxide dielectric layer is controlled
to 0 deg. C. or lower.
6. An etching equipment for forming a trench (a groove or a hole)
to a silicon substrate or a silicon substrate having a silicon
oxide dielectric layer via a plasma generated by a mixed gas, the
etching equipment comprising: a gas feeding unit for feeding the
mixed gas formed by adding a gas containing hydrogen to a mixed gas
composed of SF6 and O2 or a mixed gas composed of SF6, O2 and SiF4,
wherein the amount of added gas containing hydrogen is within a
range of 5 to 16% (percent concentration) of the total gas flow
rate of said mixed gas composed of SF6 and O2 or said mixed gas
composed of SF6, O2 and SiF4; and a sample stage for holding the
silicon substrate or the silicon substrate having a silicon oxide
dielectric layer.
7. The etching equipment according to claim 6, wherein said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3.
8. The etching equipment according to claim 6, wherein said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3 being diluted
by Ar, He or N2 when being added to the mixed gas, or said gas
containing hydrogen is HBr, HI, HCl, H2, H2O or NH3 being diluted
in advance by said gases.
9. The etching equipment according to claim 6, wherein said gas
containing hydrogen does not contain carbon or fluorine.
10. The etching equipment according to claim 6, wherein a
temperature of the sample stage for holding the silicon substrate
or the silicon substrate having the silicon oxide dielectric layer
is controlled to 0 deg. C. or lower.
Description
[0001] The present application is based on and claims priority of
Japanese patent application No. 2005-295462 filed on Oct. 7, 2005,
the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and equipment for
etching a semiconductor device. More specifically, the present
invention relates to a method and equipment capable of preventing
the side walls of a trench (groove or hole) from being damaged.
[0004] 2. Description of the Related Art
[0005] Recently, silicon (Si) trench etching is applied as a device
isolation technique to devices such as in-vehicle
pressure-resistant IGBT (insulated gate bipolar transistor) devices
corresponding to hybrid vehicles, which is drawing keen attentions
in the motor vehicle industry. This method relates to electrically
isolating devices by forming a deep trench via dry etching to the
device isolation region of the semiconductor device, and embedding
an insulating film to the formed trench via CVD (chemical vapor
deposition) method or the like.
[0006] Moreover, there are active attempts to apply this Si trench
to a three-dimensional mount technology, which also requires a deep
trench to be formed via etching as described above.
[0007] In forming the above-mentioned trench, the depth of the hole
(or groove) of the trench profile is required to be as deep as
several tens of micrometers, so in order to ensure sufficient
throughput, the etching must be performed at high etching rate.
Fluoride-based gases having higher reactivity with Si is dominant
over chlorine-based gases in the method for realizing high-rate
plasma etching.
[0008] Japanese Patent Application Laid-Open Publication No.
11-135489 (patent document 1) discloses, for example, a dry etching
method carried out by adding approximately 80 to 150 mL/min of HBr
(hydrogen bromide) gas to a mixed gas (total flow rate being 24
mL/min) consisting of SF6/O2/SiF4 (sulfur
hexafluoride/oxygen/silicon tetrafluoride) to enhance the ion
etching performance and to control the trench angle profile to
around 90 degrees.
[0009] Japanese Patent Application Laid-Open Publication No.
2004-87738 (patent document 2) discloses a dry etching method for
processing a trench via a mixed gas plasma using a mixed gas
consisting of SF6, O2 and SiF4 to process trenches with an opening
diameter or opening width of 3 micrometers or smaller and a depth
of 15 micrometers or smaller, or an opening diameter or opening
width of 3 micrometers or larger and a depth of 20 micrometers or
deeper.
[0010] However, according to the above-mentioned prior art
performing high-rate etching using mainly fluorine-based gases, the
effect of protecting the side walls of the trench is insufficient,
and especially when forming a deep trench, the protection of the
upper portion of the side walls of the etched trench becomes
insufficient while the etching is progressed in the depth
direction, causing damages such as recess and roughness to be
generated on the surface of the side walls.
[0011] That is, considering the embedding process that follows the
forming of the trench, the trench must be somewhat tapered, and in
that case, the tapered portion of the trench is subjected to damage
by the ion bombardment if the ionicity is high. However, there is
no consideration on the above problem according to the prior art
method disclosed in patent document 1, and since the method carries
out etching with high ionicity, the ion bombardment on the inner
wall surfaces of the trench may damage the protective layer and
generate recesses and surface roughness on the side walls.
[0012] Further, according to the prior art method disclosed in
patent document 2, there is no disclosure on an etching method
related to processing a trench with a small opening (under 3
micrometers) and a deep hole (over 20 micrometers) with a high
aspect ratio. Since the etching method for a trench having a high
aspect ratio is not established according to patent document 2, the
protections on the upper portion of the side walls of the trench
having completed etching becomes insufficient, and the side walls
are damaged at the end of the etching process.
SUMMARY OF THE INVENTION
[0013] The object of the present invention is to provide an etching
method and an etching apparatus capable of etching a trench without
causing any damages, such as recess and surface roughness, on the
side wall surface of the trench while maintaining a high-etching
rate.
[0014] The object of the present invention is realized by carrying
out plasma etching for forming a silicon trench to create a groove
or a hole to a silicon substrate or a silicon substrate having a
silicon oxide dielectric layer, the etching performed via a plasma
generated by a mixed gas containing hydrogen formed by adding a gas
containing hydrogen to a mixed gas composed of SF6 and O2 or a
mixed gas composed of SF6, O2 and SiF4, wherein the amount of added
gas containing hydrogen is within a range of 5 to 16% (percent
concentration) of the total gas flow rate of said mixed gas.
[0015] According to the present invention, a trench profile having
no side wall damage can be formed while maintaining a high-etching
rate, that is, while maintaining throughput. Furthermore, since the
protection of the side walls of the trench is realized by adding
gas containing a small amount of H (hydrogen), the rapid increase
of reaction byproducts attaching to the inner walls of the chamber
can be disregarded, and the inside of the chamber can maintain a
clean condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a microwave plasma etching equipment according
to the present invention;
[0017] FIG. 2(a), FIG. 2(b) and FIG. 2(c) illustrate a damage
generated to the surface of side walls of a Si substrate according
to the prior art;
[0018] FIG. 3(a), FIG. 3(b) and FIG. 3(c) show dependencies of
adding HBr according to the present invention; and
[0019] FIG. 4(a) and FIG. 4(b) show etching profiles obtained by
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The preferred embodiments for carrying out the present
invention will be described in detail with reference to the
drawings.
Embodiment 1
[0021] FIG. 1 shows a microwave plasma etching equipment according
to embodiment 1 of the present invention utilizing microwaves and
magnetic fields as means for generating plasma.
[0022] In the present equipment, etching gas is supplied to an
etching processing chamber 101 from a gas supply means 104 via a
permeation window 105 having a porous structure made of quartz, for
example.
[0023] Further, microwaves generated from a microwave generator
(not shown) are transmitted via a matching box 106 and a wave guide
107 and through a microwave introduction window 108 into the
etching processing chamber 101 to turn the above-mentioned etching
gas into plasma.
[0024] In order to enhance the radiation efficiency, a solenoid
coil 109 for generating magnetic fields is disposed around the
etching chamber, a magnetic field of 0.0875 T is generated, and
high-density plasma is generated by the magnetic field utilizing
electron cyclotron resonance. A sample stage 103 is disposed in the
etching chamber 101, on which a substrate to be processed 102 is
placed, which is subjected to etching by gas plasma generated via
microwaves. A high-frequency power source 113 is connected to the
sample stage 103 for placing the object to be processed, which is
designed to apply a high frequency bias in the range of 400 kHz to
13.56 MHz. A static adsorption force is generated on the surface of
the sample stage 103 by applying DC voltage through a static
adsorption power source 110, and the substrate 102 to be processed
is attracted to the sample stage 103 via static chuck.
[0025] Further, grooves are formed on the surface of the sample
stage 103, so that by feeding cooling gas such as He, Ar and O2
from a cooling gas inlet 112 to a flow channel (not shown) defined
by the grooves and the back surface of the substrate 102 to be
processed fixed thereto, the channel can be maintained at
predetermined pressure. The rise of temperature of the surface of
the substrate 102 to be processed is transmitted via thermal
conduction between the gas in the channel and the contact surface
to the surface of the sample stage 103, by which the substrate is
maintained at a constant temperature. In order to cool the
substrate 102 to be processed to 0 degrees or lower, a coolant
having a temperature cooled to a predetermined temperature by a
chiller unit 111 is circulated in a coolant circulation channel
embedded in the sample stage 103.
[0026] An insulating cover 114 made of ceramics or quartz is
disposed around the substrate 102 to be processed. The etching gas
introduced into the etching chamber 101 is discharged to the
exterior of the etching chamber 101 after the etching is completed
via an exhaust pump and exhaust pipe not shown.
[0027] Next, the actual embodiment of the Si etching method
according to the present invention will be described.
[0028] In the present embodiment, an example of a process is
illustrated by using the above-described plasma etching equipment
to carry out a plasma process primarily using a mixed gas composed
of SF6, O2 and SiF4. The detailed structure of the substrate 102 to
be processed and the status after the etching is illustrated in
FIG. 2.
[0029] As shown in FIG. 2(a), the substrate 202 to be processed is
an Si substrate patterned by a mask material 201 consisting of SiO2
or the like, and as shown in FIG. 2(b), the substrate is etched
through a trench opening 203. In this etching process, the SF6 and
O2 gases introduced to the etching chamber 101 are dissociated into
ions and radicals of Si, S, F and O, respectively, and SiF and SiO
are generated by the reaction with the surface of the substrate
202. The SiF generated during this reaction process and the SiF
generated by the dissociation of SiF4 gas lead the etching
performed within the trench opening 203.
[0030] On the other hand, simultaneously with the progress of the
etching within the trench opening 203, an appropriate amount of SiO
is formed as a side wall protecting film, by which the isotropic
etching by F radicals is suppressed and an anisotropic high-rate
etching is enabled. Moreover, since the SiO generated by the
reaction of mixed gas composed of SF6 and O2 gases with the silicon
in the substrate is deposited as a relatively thin layer on the
inner wall of the chamber, only very little contaminants are
generated by detached attachments, so the wetting cycle of the
chamber can be advantageously elongated.
[0031] Furthermore, according to the above explanation, it was
necessary that SiF4 was contained in the mixed gas. However, gases
such as SF6 and O2 can be used to achieve the objects of the
present invention as long as an appropriate amount of SiO is
deposited as a side wall protection layer.
[0032] As shown in FIG. 2(b), if the trench depth is relatively
shallow (or when the etching time is short), the side walls of the
trench are not damaged, and the etching can be carried out by the
present process without any problem. However, if the etching is
carried out to a further depth as shown in FIG. 2(c), the progress
of the etching in the depth direction causes the protection of the
side walls to be insufficient, and as a result, a damaged side wall
204 is generated.
[0033] According to the present process, it is possible to to
suppress such damage 204 to the Si surface by reducing the amount
of fluorine radicals acting as the etchant, but in that case, the
etching in the depth direction is also suppressed, according to
which the etch rate is deteriorated or the etching is stopped.
[0034] Thus, one example of a process according to the plasma
etching method of the present invention will be described with
reference to FIG. 3.
[0035] FIG. 3 illustrates the results of trench etching carried out
by adding HBr (hydrogen bromide) to the aforementioned etching
conditions. As an example, by adding 30 mL/min of HBr to a mixed
gas composed of 150 mL/min of SF6, 30 mL/min of O2 and 200 mL/min
of SiF4, the surface damage 204 generated to the Si trench was
suppressed. In the example, the amount of HBr gas being added is
approximately 8% (percent concentration) of the total gas flow
rate.
[0036] FIG. 3(a) illustrates the Si trench etching quantity
dependency showing the quantity of etched Si (m) with respect to
the added flow rate of HBr (mL/min). When the added flow rate of
HBr is relatively small (0 to 50 mL/min), the influence of adding
HBr is small and the Si etching quantity is substantially constant
(approximately 100 .mu.m), and the etching rate can be maintained.
However, when the added flow rate of HBr exceeds 50 mL/min, the Si
etching quantity is reduced as the added flow rate of HBr
increases, and when the added flow rate of HBr exceeds 60 mL/min,
the etching rate is reduced by more than 20% (percent
concentration). In this state, the object of the present invention
to suppress the damage to the side walls of the Si trench while
maintaining a constant etch rate cannot be achieved.
[0037] As for the Si trench etching quantity dependency
representing the Si etching quantity (.mu.m) with respect to the
added flow rate of HBr, similar tendencies are shown when gases
containing hydrogen other than HBr, such as HI, HCl, H2, H2O and
NH3, are used, and also when gases having a gas containing hydrogen
diluted by Ar, He or N2 as added gas are used, or when gases
diluted in advance by the above-mentioned gases are used. In the
case of diluted gas, the quantity of gas containing hydrogen prior
to dilution is considered as the added quantity.
[0038] The amount of HBr being added, or 60 mL/min, according to
which the damage to the side walls of the Si trench cannot be
suppressed while maintaining the above-mentioned etch rate,
corresponds to approximately 16% (percent concentration) of the 380
mL/min of mixed gas composed of 150 mL/min of SF6, 30 mL/min of O2
and 200 mL/min of SiF4.
[0039] FIG. 3(b) illustrates an Si trench side wall damage quantity
dependency, which represents the amount of damage caused to the
side walls of the Si with respect to the added flow rate of HBr
(mL/min).
[0040] When the added flow rate of HBr is small (about 0 mL/min),
approximately 140 nm of damage is caused to the Si side walls.
However, the amount of damage is reduced by adding HBr, and when
the added flow rate of HBr reaches 20 mL/min, the damage is reduced
to approximately 15 nm, by which the amount of damage to the side
walls of the Si trench is greatly reduced compared to the case
where no HBr is added. The added flow rate of HBr, which is 20
mL/min, corresponds to approximately 5% (percent concentration) of
the amount of mixed gas, which is 380 mL/min.
[0041] When the added flow rate of HBr is increased to exceed 5%
(percent concentration) and further gradually increased, the damage
to the side walls of the Si trench is reduced, and substantially no
damage is caused to the side walls of the Si trench for a
while.
[0042] When the added flow rate of HBr is even further increased,
the damage to the sidewalls of the Si trench is gradually
increased. When the added flow rate of HBr is approximately 60
mL/min (approximately 16% (percent concentration) of the mixed
gas), a slight damage occurs to the side walls of the Si trench,
but the level of the damage is practically acceptable.
[0043] When the added flow rate of HBr exceeds approximately 60
mL/min, a considerable amount of damage is caused to the side walls
of the Si trench, which becomes a problem. Further, when the added
flow rate of HBr reaches approximately 80 mL/min (21% (percent
concentration) of the mixed gas), a considerable amount of damage
exceeding the acceptable level occurs to the side walls of the Si
trench, by which the object of suppressing damage to the side walls
of the Si trench while maintaining the etch rate is no longer
realized. This increase of damage to the side walls of the Si
trench is considered to be caused by the radical species
contributing to the etching (in this case, fluoride) becoming
excessive and reacting with the side walls of the Si trench,
resulting in the damage to the side walls.
[0044] The Si trench side wall damage dependency, which is the
amount of damage (nm) caused to the side walls of the Si trench
with respect to the added flow rate of HBr, shows a similar
tendency when gases containing hydrogen other than HBr, such as HI,
HCl, H2, H2O or NH3, are used, and also when gases having the
listed gases containing hydrogen diluted with Ar, He or N2 are
used, or when gases being diluted by the aforementioned gases in
advance are used. In the case of diluted gas, the quantity of gas
containing hydrogen prior to dilution is considered as the added
quantity.
[0045] FIG. 3(c) shows a selectivity dependency against mask, which
is the mask selectivity with respect to the added flow rate of HBr.
Here, mask selectivity refers to the ratio of the etching rates
between the material to be etched (which is silicon in the present
example) and the material of the mask (which is SiO2 in the present
example). Regarding etching, it is important to carry out etching
of the material to be etched without etching the mask material as
much as possible. In an extreme case, if the mask selectivity is
not good, the mask is removed even before the target etch quantity
of the material to be etched is achieved, and the etching cannot be
completed. Therefore, it is necessary to retain a high mask
selectivity.
[0046] With reference to FIG. 3(c), the mask selectivity is
gradually decreased in correspondence to the added flow rate of
HBr. With respect to the mixed gas, the mask selectivity ratio is
sufficiently high when the added flow rate of HBr is within the
range of approximately 5% (percent concentration) to 16% (percent
concentration).
[0047] As for the selectivity dependency against mask which is the
mask selectivity with respect to the added flow rate of HBr, a
similar result is achieved when gases containing hydrogen other
than HBr, such as HI, HCl, H2, H2O or NH3, are used, and also when
gases having the above-mentioned gases diluted with Ar, He or Ne
are used, or when gases being diluted with the above-mentioned
gases in advance are used.
[0048] As described, it is recognized from FIG. 3 that when the
added ratio of HBr is 5% (percent concentration) or less, the
effect of suppressing damage to the side walls of the Si cannot be
achieved. This is considered to be because there is not enough
supply of depositing reaction products having side wall protecting
effects. Moreover, if the added amount of HBr is 16% (percent
concentration) or greater, then the generation of reaction products
having side wall protecting effects becomes excessive,
deteriorating the etching carried out in the depth direction. As a
result, the etching ratio of Si is gradually deteriorated, which is
simultaneously accompanied by the deterioration of the selectivity
ratio against mask. Moreover, when the etching rate in the depth
direction is deteriorated, the Br-based etchants also become
excessive and the side walls having been protected is subjected to
reaction again, and further damage to the side walls of the Si is
caused. From these results, it can be concluded that the ratio of
addition of HBr should approximately be in the range of 5to 16%
(percent concentration).
[0049] FIG. 4 shows examples of the aforementioned etching profile.
In a structure with a relatively small aspect ratio (the aspect
ratio, which is the ratio between the diameter of the trench
opening 203 formed to the substrate 202 to be processed and the
depth, being about 5), as shown in FIG. 4(a), an etching profile
having no damage caused to the side walls of the trench was
achieved. Further, as shown in FIG. 4(b), also in a structure with
a large aspect ratio (the aspect ratio, which is the ratio between
the diameter of the trench opening 203 formed to the substrate 202
to be processed and the depth, being about 7), an etching profile
having no damage caused to the sidewalls of the trench was
achieved, and no problems such as etch stops occurred.
[0050] Further according to the plasma etching method of the
present invention, the deposition probability of the generated
deposition components can be improved by reducing the electrode
temperature in combination with the above arrangement. This is
considered to be the reason why in comparison to the etching
process performed in a temperature region equal to or above normal
temperature, the present method is capable of carrying out the
etching process without causing side wall damages, since the
protective layer is formed even under conditions where the amount
of reaction byproducts that form the protective layer to the side
walls of the trench is small.
[0051] The processing conditions shown in Table 1 are typical
etching conditions used in the microwave plasma etching equipment
with a magnetic field illustrated in FIG. 1. The processing
conditions shown here are adjusted for the present invention, and
the optimum values of the process factors may somewhat vary in
other etching equipments, such as a helicon wave etching equipment,
an inductively-coupled plasma etching equipment, a
capacitively-coupled plasma etching equipment, or a magnetic field
RIE equipment. TABLE-US-00001 TABLE 1 Typical Etching Conditions of
the Present Invention Items Main Etch SF6 flow rate (ml/min) 150 O2
flow rate 30 SiF4 flow rate 200 Microwave (W) 800 Processing
Pressure (Pa) 4.0 RF bias (W) 20 Temperature of sample stage (deg.
C.) -45 Coil current (A) 14/14/4
[0052] The present method for suppressing the damage to the side
walls in trench etching is not only applicable to the present
equipment, but also applicable to other etching equipments. Based
on the processing conditions disclosed above, those familiar to the
etching process can easily adjust and optimize the conditions for
other equipments.
* * * * *