U.S. patent application number 10/449596 was filed with the patent office on 2003-12-04 for method of removing germanium contamination on semiconductor substrate.
This patent application is currently assigned to NEC ELECTRONICS CORPORATION. Invention is credited to Oguro, Shizuo.
Application Number | 20030221703 10/449596 |
Document ID | / |
Family ID | 29561635 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030221703 |
Kind Code |
A1 |
Oguro, Shizuo |
December 4, 2003 |
Method of removing germanium contamination on semiconductor
substrate
Abstract
A method of removing Ge contamination existing on a
semiconductor substrate is provided. A surface of a semiconductor
substrate is oxidized to convert a germanium (Ge) contamination
existing on the surface of the substrate to an oxide of Ge.
Thereafter, the surface of the substrate is contacted with an
aqueous solution containing fluorine (F) ions. The oxide of
germanium existing on the surface of the substrate is dissolved in
the solution, thereby removing the Ge contamination from the
substrate. Possible performance degradation of a semiconductor
device to be fabricated with the substrate having the Ge
contamination is prevented.
Inventors: |
Oguro, Shizuo; (Kanagawa,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037
US
|
Assignee: |
NEC ELECTRONICS CORPORATION
|
Family ID: |
29561635 |
Appl. No.: |
10/449596 |
Filed: |
June 2, 2003 |
Current U.S.
Class: |
134/1.2 ; 134/2;
257/E21.228 |
Current CPC
Class: |
H01L 21/02052
20130101 |
Class at
Publication: |
134/1.2 ;
134/2 |
International
Class: |
C25F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2002 |
JP |
161290/2002 |
Claims
What is claimed is:
1. A method of removing germanium (Ge) contamination on a
semiconductor substrate, comprising the steps of: oxidizing a
surface of a semiconductor substrate to convert a germanium
contamination existing on the surface of the substrate to an oxide
of germanium; and contacting the surface of the substrate with an
aqueous solution containing fluorine (F) ions.
2. The method according to claim 1, wherein the oxide of germanium
existing on the surface of the substrate is dissolved in the
solution.
3. The method according to claim 1, wherein at least one selected
from the group consisting of DHF, FPM, and BHF is used as the
aqueous solution containing fluorine (F) ions.
4. The method according to claim 1, wherein at least one selected
from the group consisting of APM, HPM, SPM, and aqua regia is used
in the oxidation step.
5. The method according to claim 1, wherein an oxygen (O.sub.2)
plasma is used for oxidizing the Ge contamination existing on the
surface of the substrate.
6. The method according to claim 1, wherein an oxygen (O.sub.2)
plasma is used for oxidizing the Ge contamination existing on the
surface of the substrate and thereafter, at least one selected from
the group consisting of APM, HPM, SPM, and aqua regia is used for
further oxidizing the Ge contamination.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of removing
Germanium (Ge) contamination. More particularly, the invention
relates to a method of removing Ge contamination existing on a
semiconductor substrate, where the Ge contamination is usually
adhered onto the substrate during a fabrication process sequence of
semiconductor devices. This method makes it possible to remove
effectively Ge contamination existing on a semiconductor substrate
to thereby prevent the performance degradation of semiconductor
devices due to the Ge contamination.
[0003] 2. Description of the Related Art
[0004] Conventionally, various cleaning processes or methods have
been developed and used actually to remove metal contamination
adhered onto a semiconductor substrate during a fabrication process
sequence of semiconductor devices. With the prior-art cleaning
methods, a solution of a sulfuric peroxide mixture (SPM) or a
hydrochloric peroxide mixture (HPM) is used as a cleaning solution.
A "SPM" means a mixture of sulfuric acid (H.sub.2SO.sub.4) and
hydrogen peroxide (H.sub.2O.sub.2), which may be expressed as a
H.sub.2SO.sub.4--H.sub.2O.sub.2 mixture. A "HPM" means a mixture of
hydrochloric acid (HCl) and hydrogen peroxide (H.sub.2O.sub.2),
which may be expressed as a HC.sub.1--H.sub.2O.sub.2 mixture.
[0005] FIG. 1 is a flowchart showing the prior-art methods of
removing metal contamination existing on a semiconductor
substrate.
[0006] As seen from FIG. 1, a semiconductor substrate (e.g., a
single-crystal silicon (Si) substrate) on which metal contamination
exists is rinsed with a SPM or HPM (step S111). Thus, the metal
contamination existing on the substrate is removed and as a result,
the substrate is cleaned.
[0007] Although not shown in FIG. 1, a cleaning process using an
ammonium peroxide mixture (APM) may be carried out prior to the
step S111. An "APM" means a mixture of ammonium hydroxide
(NH.sub.4OH) and hydrogen peroxide (H.sub.2O.sub.2), which may be
expressed as a NH.sub.4OH--H.sub.2O.sub.2 mixture. However, this
process using a APM is to remove "particles" existing on the
substrate, not metal contamination existing thereon. In this
process using an APM, there is a possibility that metal
contamination to be introduced during the fabrication process
sequence, such as aluminum (Al) and iron (Fe), is likely to adhere
onto the substrate again.
[0008] On the other hand, with the conventional fabrication
processes of semiconductor devices, there is the following
problem.
[0009] In recent years, it has become popular to use SiGe layers in
the fabrication processes of semiconductor devices. Usually, a
silicon dioxide (SiO.sub.2) or silicon nitride (SiN.sub.x) layer is
formed on or over a single-crystal Si substrate and then, necessary
openings are selectively formed in the SiO.sub.2 or SiN.sub.x layer
thus formed, selectively exposing the surface of the Si substrate.
Thereafter, SiGe layers are epitaxially and selectively grown on
the exposed surface of the substrate in the respective openings of
the SiO.sub.2 or SiN.sub.x layer.
[0010] In this case, it is said that no SiGe layer is grown on the
exposed areas of the SiO.sub.2 or SiN.sub.x layer if the epitaxial
growth condition for the SiGe layer is well selected or controlled.
Actually, the inventor did not observe SiGe in the form of
micro-particles on the said exposed areas with the use of a
scanning electron microscope (SEM).
[0011] However, by way of research, the inventor found that
unwanted Ge atoms existed on the exposed areas of the SiO.sub.2 or
SiN.sub.x layer even if the epitaxial growth condition for the SiGe
layer was well selected, and that the level of the existing Ge
atoms as contamination was in the order of 10.sup.11 to 10.sup.12
atoms/cm.sup.2. Ge contamination existing at this level seems to
affect badly the performance of semiconductor devices fabricated by
using the said substrate.
[0012] In this specification, the word "contamination (including Ge
contamination)" means that contamination (including Ge
contamination) exists on a semiconductor substrate at a specific
level or higher in such a way as to badly affect the performance of
a semiconductor device.
[0013] If a Si substrate including Ge contamination is used to
fabricate semiconductor devices, the Ge contamination will be
transferred to other Si substrates used in the same lot and as a
result, the other substrates will be contaminated as well.
According to the inventor's research, it was found that if Ge
contamination occurs at a high level on a Si substrate, the
junction leakage current will increase and/or the reliability of
the gate dielectric will deteriorate due to the Ge contamination,
thereby degrading the performance of semiconductor devices.
Accordingly, to prevent the performance degradation of
semiconductor devices fabricated by using a Ge contaminated Si
substrate and to avoid the contamination of other Si substrates due
to the Ge-contaminated one, it is essential to remove the Ce
contamination.
[0014] Recently, SiGe layers have been popularly introduced into
the semiconductor device fabrication and therefore, to remove Ge
contamination on a semiconductor substrate is now an important
problem which cannot be bypassed.
SUMMARY OF THE INVENTION
[0015] Accordingly, an object of the present invention is to
provide a method of removing Ge contamination existing on a
semiconductor substrate.
[0016] Another object of the present invention is to provide a
method of removing Ge contamination existing on a semiconductor
substrate that is carried out easily.
[0017] The above objects together with others not specifically
mentioned will become clear to those skilled in the art from the
following description.
[0018] A method of removing germanium (Ge) contamination on a
semiconductor substrate according to the present invention
comprises the steps of:
[0019] oxidizing a surface of a semiconductor substrate to convert
a germanium contaminant existing on the surface of the substrate to
an oxide of germanium; and
[0020] removing the oxide of germanium from the surface of the
substrate with an aqueous solution containing fluorine ions.
[0021] With the method of removing Ge contamination on a
semiconductor substrate according to the present invention, a
surface of a semiconductor substrate is oxidized to convert a Ge
contaminant existing on the surface of the substrate to an oxide of
Ge and thereafter, the oxide of Ge is removed from the surface of
the substrate with an aqueous solution containing fluorine ions.
Since the oxide of Ge is soluble in an aqueous solution containing
fluorine ions, the oxide of Ge existing on the surface of the
substrate will dissolve into the solution and finally, it will be
removed from the substrate. As a result, the Ge contamination
existing on the surface of the substrate is removed and thus,
possible performance degradation of a semiconductor device to be
fabricated with the substrate is prevented.
[0022] In the present invention, the word "semiconductor substrate"
means not only a semiconductor substrate per se but also a
semiconductor substrate having at least one dielectric, conductive,
or semiconductive layer formed thereon. This is because Ge
contamination is typically caused in a selective growth process of
an epitaxial SiGe layer in openings of a dielectric layer formed on
a semiconductor substrate, where a Ge contaminant or contaminants
exist(s) on the exposed areas of the dielectric layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order that the present invention may be readily carried
into effect, it will now be described with reference to the
accompanying drawings.
[0024] FIG. 1 is a flowchart showing the process steps of prior-art
methods of removing metal contamination on a semiconductor
substrate.
[0025] FIG. 2 is a flowchart showing the process steps of a method
of removing Ge contamination on a semiconductor substrate according
to an embodiment of the invention.
[0026] FIG. 3 is a flowchart showing the process steps of a method
of removing Ge contamination on a semiconductor substrate according
to another embodiment of the invention.
[0027] FIG. 4 is a flowchart showing the process steps of a method
of removing. Ge contamination on a semiconductor substrate
according to a still another embodiment of the invention.
[0028] FIG. 5 is a flowchart showing the process steps of a method
of removing Ge contamination on a semiconductor substrate according
to a further embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention will be described in detail below
while referring to the drawings attached.
[0030] According to the inventor's test, the inventor obtained the
following technical results.
[0031] (i) A SPM (i.e., H.sub.2SO.sub.4--H.sub.2O.sub.2 mixture)
and a HPM (i.e., HCl--H.sub.2O.sub.2 mixture), which have ever been
used for removing metal contamination, scarcely have an effect or
action to remove a Ge contaminant adhered onto a semiconductor
substrate. This is because a Ge contaminant does not dissolve into
a SPM and a HPM.
[0032] (ii) If a Ge contaminant on the substrate is in the form of
oxide of Ge, the Ge contaminant will dissolve into one of HF-system
solutions.
[0033] (iii) A Ge contaminant generated just after the epitaxial
growth of a SiGe layer is not in the form of oxide of Ge.
Therefore, even if the Ge contaminant is cleaned with one of
HF-system solutions, the said contaminant is unable to be
removed.
[0034] Based on the knowledge (i), (ii), and (iii), the inventor
created the present invention.
[0035] As described above, with the method of removing Ge
contamination on a semiconductor substrate according to the present
invention, a surface of a semiconductor substrate is oxidized to
convert a Ge contaminant existing on the surface of the substrate
to an oxide of Ge. This step is termed the oxidation step.
Subsequently, the oxide of Ge is removed from the surface of the
substrate with an aqueous solution containing fluorine (F) ions.
This step is termed the removal step.
[0036] In the removal step, the oxide of Ge existing on the surface
of the substrate is dissolved in the said aqueous solution. This
means that the Ge contaminant existing on the surface of the
substrate is removed, and that possible performance degradation of
a semiconductor device to be fabricated with the substrate is
prevented.
[0037] On the other hand, with a known cleaning method of removing
"native oxide" existing on a surface of a semiconductor substrate,
a cleaning process using a diluted hydrofluoric acid (HF), i.e.,
DHF, is carried out. This cleaning process is conducted after the
well-known RCA cleaning process is carried out. A contamination
removal process for removing metal contamination is carried out
during the RCA cleaning process, which is prior to the process of
forming a gate oxide.
[0038] The above-described cleaning process using a DHF exhibits
some effect of removing metal contamination. However, if the
substrate has exposed areas of Si, this process has no effect to
remove copper (Cu) contamination. Instead, if the solution of DHF
is contaminated by Cu, the Cu contaminant in the solution is likely
to adhere to the exposed areas of the Si substrate. Alternately, if
the substrate has a contaminated area by Cu, the Cu contaminant on
the substrate will dissolve into the solution of DHF and as a
result, the Cu contaminant in the solution is likely to adhere to
the exposed areas of the Si substrate. Therefore, a cleaning
process for removing metal contamination with a strong cleaning
effect is usually carried out before the cleaning process using a
DHF. After the metal contamination is removed from the substrate,
an etching process for selectively removing an oxide layer formed
on the substrate is carried out. If a thin chemical oxide layer,
which is likely to be formed in the said metal contamination
removing process, causes no problem relating to the semiconductor
device performance, the metal contamination removing process may be
conducted after the etching process for selectively removing an
oxide layer formed on the substrate is carried out.
[0039] The method of the present invention is to remove Ge
contamination, not native oxide. Therefore, the method of the
invention is unlike the prior-art cleaning processes explained
here.
[0040] In a preferred embodiment of the method of the invention, as
shown in FIG. 2, a surface of a semiconductor substrate is oxidized
with an APM (NH.sub.4OH--H.sub.2O.sub.2), to convert a Ge
contaminant existing on the surface of the substrate to an oxide of
Ge (step S1). Subsequently, to remove the oxide of the Ge
contaminant, the surface of the substrate is contacted with a DHF
as an aqueous solution containing fluorine (F) ions (step S2).
Thus, the oxide (i.e., the Ge contaminant) is removed.
[0041] In this embodiment of the invention, a process for removing
"metal" contamination may be additionally carried out after the
removal step (step S2) of contacting the surface of the substrate
with a DHF. In the process for removing metal contamination, a HPM
(HCl--H.sub.2O.sub.2) or SPM (H.sub.2SO.sub.4--H.sub.2O.sub.2) is
preferably used as the cleaning solution.
[0042] Moreover, it is possible to conduct a process for removing
"metal" contamination between the oxidation step of oxidizing the
Ge contamination and the removal step of removing the oxide of Ge.
In this case, the effect of the invention to remove the Ge
contaminant is not lost. However, taking the danger of metal
contamination (e.g., Cu contamination) occurring after the removal
step using a DHF into consideration, it is preferred that the
process (step S33) for removing "metal" contamination is carried
out after the removal step (step S32) using an aqueous solution
containing F ions (e.g., DHF), as shown in FIG. 5. The step S31 in
FIG. 5 is to oxidize the Ge contaminant on the surface of the
substrate.
[0043] Furthermore, a fluorine peroxide mixture (FPM) may be used
instead of DHF. A "FPM" means a mixture of hydrofluoric acid (HF)
and hydrogen peroxide (H.sub.2O.sub.2), which may be expressed as a
HF--H.sub.2O.sub.2 mixture. A mixture of DHF and HCl or HNO.sub.3
may be used instead of DHF. In these two cases, there is an
additional advantage that the danger of Cu contamination can be
eliminated.
[0044] In a preferred embodiment of the method of the invention, at
least one selected from the group consisting of DHF, FPM, and BHF
is used as the aqueous solution containing F ions. In this
embodiment, there is an additional advantage that the oxide of the
Ge contamination is soluble more easily.
[0045] In a preferred embodiment of the method of the invention, at
least one selected from the group consisting of APM, HPM, SPM, and
aqua regia is used in the oxidation step. In this embodiment, there
is an additional advantage that the Ge contamination is oxidized
more easily.
[0046] In a preferred embodiment of the method of the invention, an
oxygen (O.sub.2) plasma is used for oxidizing the Ge contamination
existing on the surface of the substrate (step S11), as shown in
FIG. 3. The step S12 in FIG. 3 is the same as the step S2 in FIG.
2. In this embodiment, there is an additional advantage that the Ge
contamination is oxidized more easily.
[0047] In a preferred embodiment of the method of the invention, an
oxygen (O.sub.2) plasma is used for oxidizing the Ge contamination
existing on the surface of the substrate (step S21) and thereafter,
at least one selected from the group consisting of APM, HPM, SPM,
and aqua regia is used for further oxidizing the Ge contamination
(step S22), as shown in FIG. 4. In this embodiment, there is an
additional advantage that the Ge contamination is oxidized while
removing the metal contamination and particles induced by the
O.sub.2 plasma.
EXAMPLES
[0048] Concrete examples of the present invention are explained in
detail below.
Example 1
[0049] A silicon nitride (SiN.sub.x) layer was formed on a
single-crystal Si substrate and then, necessary openings were
selectively formed in the SiN.sub.x layer thus formed. A SiGe layer
was epitaxially and selectively grown in the openings of the
SiN.sub.x layer.
[0050] Thereafter, the Si substrate with the SiGe layer in the
SiN.sub.x layer was immersed into an APM solution. This process was
carried out to oxidize a Ge contamination existing on the surface
of the SiN.sub.x layer, generating an oxide of Ge. At this time,
the composition of the APM solution used was adjusted to
NH.sub.4OH:H.sub.2O.sub.2:H.sub.2O=1:4:- 20. The temperature of the
APM solution was set at 65.degree. C. while the immersion period
was set at about 10 minutes.
[0051] Subsequently, the substrate thus oxidized was rinsed with a
diluted HF (DHF) solution, thereby dissolving the oxide of Ge in
the DHF solution. At this time, the composition of the DHF solution
used was adjusted to HF:H.sub.2O=1:100. The temperature of the APM
solution was set at room temperature while the immersion period was
set at about 10 minutes.
[0052] Before the above-described cleaning processes were
conducted, the density of a Ge contamination existing on the
surface of the SiN.sub.x layer was approximately 2.times.10.sup.12
atoms/cm.sup.2. By way of the above-described cleaning processes,
the density of the Ge contamination was decreased to approximately
5.times.10.sup.9 atoms/cm.sup.2. Thus, it was confirmed that the
above-described cleaning processes exhibited a conspicuous cleaning
effect.
[0053] On the other hand, when only the immersion process into the
APM solution was carried out, the density of the Ge contamination
was approximately 6.times.10.sup.11 atoms/cm.sup.2. When only the
immersion process into the DHF solution was carried out, the
density of the Ge contamination was approximately 1.times.10.sup.12
atoms/cm.sup.2. This means that almost no cleaning effect was
observed in these two cases. As a result, it was seen that the Ge
contamination existing on the surface of the SiN.sub.x layer was
scarcely removed, even if only one of the immersion process into
the APM solution and that into the HF solution was carried out. It
was seen that a sufficient cleaning effect to remove the Ge
contamination existing on the surface of the SiN.sub.x layer was
obtainable by the combination of these two processes in this
order.
[0054] In the above-described immersion process into the APM
solution for oxidizing the Ge contamination, the composition (i.e.,
the ratio of NH.sub.4OH:H.sub.2O.sub.2:H.sub.2O) of the APM
solution, and the temperature of the said solution, and the
immersion period were not limited to the above-described values,
respectively. These values may be changed or adjusted in such a way
that a desired oxidizing operation of the Ge contamination was
obtainable.
[0055] Similarly, in the above-described immersion process into the
DHF solution for dissolving the oxide of the Ge contamination, the
composition (i.e., the ratio of HF:H.sub.2O) of the DHF solution,
and the temperature of the said solution, and the immersion period
were not limited to the above-described values, respectively. These
values may be changed or adjusted in such a way that a desired
dissolution operation of the oxide of the Ge contamination was
obtainable.
[0056] Moreover, instead of the immersion process into the DHF
solution, any other aqueous solution such as a FPM solution, a BHF
solution, a HF solution containing a surfactant or surface-active
agent, may be used if it is capable or dissolution of an oxide of
Ge contamination.
Example 2
[0057] A SiN.sub.x layer was formed on a single-crystal Si
substrate and then necessary openings were selectively formed in
the SiN.sub.x layer thus formed. A SiGe layer was epitaxially and
selectively grown in the openings of the SiN.sub.x layer.
[0058] On the other hand, oxygen (O.sub.2) gas was passed through a
plasma region formed in a plasma chamber. The plasma region was
surrounded by an RF (radio frequency) coil for RF plasma
excitation. In the plasma region, O.sub.2 gas was excited to ionize
the O.sub.2 molecules, resulting in an O.sub.2 plasma in the
chamber.
[0059] Thereafter, the Si substrate with the SiGe layer in the.
SiN.sub.x layer was placed in the plasma chamber to contact the
surface of the SiN.sub.x layer at room temperature. This process
was carried out to oxidize a Ge contamination existing on the
surface of the SiN.sub.x layer, generating an oxide of Ge.
[0060] Subsequently, the substrate thus oxidized was rinsed with a
DHF solution, thereby dissolving the oxide of Ge in the DHF
solution. The composition of the DHF solution used was adjusted to
HF:H.sub.2O=1:100. The temperature of the DHF solution was set at
room temperature while the immersion period was set at about 10
minutes. These values were the same as those used in Example 1.
[0061] Before the above-described cleaning processes were
conducted, the density of a Ge contamination existing on the
surface of the SiN.sub.x layer was approximately 2.times.10.sup.12
atoms/cm.sup.2. By way of the above-described cleaning processes,
the density of the Ge contamination was decreased to the level of
1.times.10.sup.9 atoms/cm.sup.2 or lower. Thus, it was confirmed
that the above-described cleaning processes exhibited a conspicuous
cleaning effect.
[0062] In the above-described immersion process into the OHF
solution for dissolving the oxide of the Ge contamination, the
composition (i.e., the ratio of HF:H.sub.2O) of the DHF solution,
and the temperature of the said solution, and the immersion period
were not limited to the above-described values, respectively. These
values may be changed or adjusted in such a way that a desired
dissolution operation of the oxide of the Ge contamination was
obtainable.
[0063] Moreover, instead of the immersion process into the DHF
solution, any other aqueous solution such as a FPM solution, a BHF
solution, a HF solution containing a surfactant or surface-active
agent, may be used if it is capable of dissolution of an oxide of
Ge contamination.
[0064] A cleaning process may be additionally carried out between
the contact process with a O.sub.2 plasma and the immersion process
into a DHF solution. This is to remove contamination such as metal
contamination and/or particles, to be adhered onto the exposed
areas of the Si substrate in the plasma chamber. In this case, it
was found that the cleaning effect to remove the Ge contamination
existing on the surface of the SiN.sub.x layer was not lost.
Other Examples
[0065] It is needless to say that the invention is not limited to
the above-described embodiments and examples. Any modification is
applicable to them.
[0066] While the preferred forms of the present invention have been
described, it is to be understood that modifications will be
apparent to those skilled in the art without departing from the
spirit of the invention. The scope of the present invention,
therefore, is to be determined solely by the following claims.
* * * * *