U.S. patent application number 09/887098 was filed with the patent office on 2001-12-27 for semiconductor device and method of fabricating the same.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Fujii, Osamu, Yamada, Hiroaki.
Application Number | 20010055859 09/887098 |
Document ID | / |
Family ID | 18690640 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055859 |
Kind Code |
A1 |
Yamada, Hiroaki ; et
al. |
December 27, 2001 |
Semiconductor device and method of fabricating the same
Abstract
A high-resistance substrate with good RF characteristics, which
has an interstitial oxygen concentration ([Oi]) of 8E17 cm.sup.-3
or less, an oxygen precipitate density ([BMD]) of 1E8 cm.sup.-3 or
more, and a substrate resistivity of 500 .OMEGA..multidot.cm or
more is used. A heat-treating step of the device process is
performed for 25 hrs or less as a value calculated assuming that
the temperature is 1,000.degree. C. This suppresses a decrease in
the resistance of the substrate, prevents crystal defects such as
slip, and improves the yield.
Inventors: |
Yamada, Hiroaki;
(Yokohama-Shi, JP) ; Fujii, Osamu; (Yokohama-Shi,
JP) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Assignee: |
Kabushiki Kaisha Toshiba
|
Family ID: |
18690640 |
Appl. No.: |
09/887098 |
Filed: |
June 25, 2001 |
Current U.S.
Class: |
438/479 ;
257/E21.321; 257/E29.107 |
Current CPC
Class: |
H01L 21/3225 20130101;
H01L 29/32 20130101 |
Class at
Publication: |
438/479 |
International
Class: |
C30B 001/00; H01L
021/20; H01L 021/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2000 |
JP |
2000-191323 |
Claims
What is claimed is:
1. A semiconductor device obtained by forming a circuit in a
surface portion of a semiconductor substrate, wherein said
semiconductor substrate has an interstitial oxygen concentration
(to be referred to as [Oi] hereinafter) of not more than 8E17
cm.sup.-3, an oxygen precipitate density (to be referred to as
[BMD] hereinafter) of not less than 1E8 cm.sup.-3, and a
resistivity of not less than 500 .OMEGA..multidot.cm.
2. A device according to claim 1, wherein said circuit is formed in
the surface portion of said semiconductor substrate by a device
process including a heat-treating step of not more than 25 hrs as a
value calculated assuming that the temperature is 1,000.degree.
C.
3. A device according to claim 1, wherein said semiconductor
substrate is obtained by performing heat-treating at 500 to
700.degree. C. for not more than 5 hrs for a semiconductor
substrate having an [Oi] of not more than 8E17 cm.sup.-3, and a
resistivity of not less than 500 .OMEGA..multidot.cm, thereby
setting a [BMD] of not less than 1E8 cm.sup.-3, and said circuit is
formed in the surface portion of said semiconductor substrate by a
device process including a heat-treating step of not more than 25
hrs as a value calculated assuming that the temperature is
1,000.degree. C.
4. A device according to claim 1, wherein said semiconductor
substrate has a [BMD] of not less than 1E8 cm.sup.-3, which is
obtained by doping not less than 1E13 cm.sup.-3 of [N] during
crystal pulling, and also has an [Oi] of not more than 8E17
cm.sup.-3 and a resistivity of not less than 500
.OMEGA..multidot.cm, and said circuit is formed in the surface
portion of said semiconductor substrate by a device process
including a heat-treating step of not more than 25 hrs as a value
calculated assuming that the temperature is 1,000.degree. C.
5. A method of fabricating a semiconductor device by forming a
circuit by using a semiconductor substrate, comprising the step of
performing a heat-treating step of a device process for forming
said circuit for not more than 25 hrs as a value calculated
assuming that the temperature is 1,000.degree. C., by using a
semiconductor substrate having an [Oi] of not more than 8E17
cm.sup.-3, a [BMD] of not less than 1E8 cm.sup.-3, and a
resistivity of not less than 500 .OMEGA..multidot.cm.
6. A method according to claim 5, further comprising the step of
obtaining said semiconductor substrate by performing heat-treating
at 500 to 700.degree. C. for not more than 5 hrs for a
semiconductor substrate having an [Oi] of not more than 8E17
cm.sup.-3, and a resistivity of not less than 500
.OMEGA..multidot.cm, thereby setting a [BMD] of not less than 1E8
cm.sup.-3.
7. A method according to claim 5, further comprising the step of
obtaining said semiconductor substrate having a [BMD] of not less
than 1E8 cm.sup.-3, which is obtained by doping not less than 1E13
cm.sup.-3 of [N] during crystal pulling, and also having an [Oi] of
not more than 8E17 cm.sup.-3 and a resistivity of not less than 500
.OMEGA..multidot.cm.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit of priority under 35 USC 119
to Japanese Patent Application No. 2000-191323, filed on Jun. 26,
2000, the entire contents of which are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a semiconductor device and
a method of fabricating the same and, more particularly, to a
device using radio-frequency signals and a method of fabricating
the same.
[0003] RF (Radio Frequency) communication devices using RF signals
are often fabricated by using an SOI (Silicon On Insulator) wafer
which uses, as a support substrate, a high-resistance substrate
(resistivity .rho..gtoreq.1,000 .phi..multidot.cm) formed by
crystal pulling by the CZ method, in order to suppress energy loss
of an RF signal and form a spiral inductance having a high Q value
even in the GHz band. This fabrication method improves the RF
characteristics.
[0004] Unfortunately, if the interstitial oxygen concentration (to
be referred to as [Oi] hereinafter) in the semiconductor substrate
is high, heat-treating performed during the device process for
forming a circuit in the substrate generates oxygen donors and
lowers the resistivity of the substrate. Hence, a substrate having
a low [Oi] ([Oi].ltoreq.8E17 cm.sup.-3) must be used.
[0005] The oxygen concentration can be decreased by
[0006] (1) crystal pulling by the MCZ method, or
[0007] (2) heat-treating a substrate having a high [Oi]
([Oi].gtoreq.13E17 cm.sup.-3) to form bulk micro defect (to be
referred to as BMD hereinafter) by oxygen precipitation, thereby
reducing the concentration of a solid solution of oxygen.
[0008] When an RF device is formed using a substrate obtained by
method (1) above, however, slip occurs in heat-treating during the
device process because the pinning effect of dislocation by a solid
solution of oxygen lowers. This is a phenomenon in which, when
heat-treating is performed by supporting a semiconductor substrate
by a 4-point-supporting boat, cracks and the like occur in portions
where the substrate contacts the boat.
[0009] When an RF device is formed using a substrate obtained by
method (2) above, it is possible to prevent the occurrence of slip
in the boat contact portions during heat-treating by the pinning
effect of dislocation by oxygen redissolving from BMD. However,
thermal stress during the device process forms slip on the entire
surface of the substrate.
[0010] As described above, it is conventionally impossible to
effectively prevent slip in a high-resistance substrate having a
low [Oi]. This lowers the yield by defects caused by slip.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an object of the present invention to
provide a semiconductor device capable of preventing defects caused
by slip and improving the yield by using a high-resistance
substrate having excellent RF characteristics, and provide a method
of fabricating the same.
[0012] A semiconductor device of the present invention is a
semiconductor device obtained by forming a circuit in a surface
portion of a semiconductor substrate, wherein the semiconductor
substrate has an interstitial oxygen concentration (to be referred
to as [Oi] hereinafter) of 8E17 cm.sup.-3 or less, an oxygen
precipitate density (to be referred to as [BMD] hereinafter) of 1E8
cm.sup.-3 or more, and a resistivity of 500 .OMEGA..multidot.cm or
more.
[0013] The circuit can be formed in the surface portion of the
semiconductor substrate by a device process including a
heat-treating step of 25 hrs or less as a value calculated assuming
that the temperature is 1,000.degree. C.
[0014] The semiconductor substrate is obtained by performing
heat-treating at 500 to 700.degree. C. for 5 hrs or less for a
semiconductor substrate having an [Oi] of 8E17 cm.sup.-3 or less,
and a resistivity of 500 .OMEGA..multidot.cm or more, thereby
setting [BMD] of 1E8 cm.sup.-3 or more, and the circuit can be
formed in the surface portion of the semiconductor substrate by a
device process including a heat-treating step of 25 hrs or less as
a value calculated that assuming that the temperature is
1,000.degree. C.
[0015] The semiconductor substrate has a [BMD] of 1E8 cm.sup.-3 or
more, which is obtained by doping 1E13 cm.sup.-3 or more of [N]
during crystal pulling, and also has an [Oi] of 8E17 cm.sup.-3 or
less and a resistivity of 500 .OMEGA..multidot.cm or more, and the
circuit can be formed in the surface portion of the semiconductor
substrate by a device process including a heat-treating step of 25
hrs or less as a value calculated assuming that the temperature is
1,000.degree. C.
[0016] A method of fabricating a semiconductor device by forming a
circuit by using a semiconductor substrate according to the present
invention comprises the step of performing a heat-treating step of
a device process for forming the circuit for 25 hrs or less as a
value calculated assuming that the temperature is 1,000.degree. C.,
by using a semiconductor substrate having an [Oi] of 8E7 cm.sup.-3
or less, a [BMD] of 1E8 cm.sup.-3 or more, and a resistivity of 500
.OMEGA..multidot.cm or more.
[0017] The method can further comprise the step of obtaining the
semiconductor substrate by performing heat-treating at 500 to
700.degree. C. for 5 hrs or less for a semiconductor substrate
having an [Oi] of 8E17 cm.sup.-3 or less, and a resistivity of 500
.OMEGA..multidot.cm or more, thereby setting a [BMD] of 1E8
cm.sup.-3 or more.
[0018] The method can further comprise the step of obtaining the
semiconductor substrate having a [BMD] of 1E8 cm.sup.-3 or more,
which is obtained by doping 1E13 cm.sup.-3 or more of [N] during
crystal pulling, and also having an [Oi] of 8E17 cm.sup.-3 or less
and a resistivity of 500 .OMEGA..multidot.cm or more.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a flow chart showing the procedure of a method of
fabricating a semiconductor device according to an embodiment of
the present invention;
[0020] FIG. 2 is a graph showing the relationship between the [BMD]
and the slip length;
[0021] FIG. 3 is a graph showing the relationship between the [BMD]
and the mechanical strength;
[0022] FIG. 4 is a graph showing the relationship between the
heat-treating time and the mechanical strength; and
[0023] FIG. 5 is a view for explaining the RF characteristics, the
yield ratio, and the presence/absence of crystal defects in each of
Examples 1 and 2 and Comparative Examples 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] As described above, when the [Oi] of a high-resistance
substrate is lowered while the substrate resistivity is kept high,
slip occurs in boat contact portions during heat-treating, or slip
caused by thermal stress occurs on the entire substrate
surface.
[0025] One countermeasure is a method of forming a predetermined
number of BMD or more. FIG. 2 shows the relationship between the
density of BMD (to be referred to as [BMD] hereinafter) and the
slip length. As shown in FIG. 2, slip can be effectively prevented
by a [BMD] of 1E8 cm.sup.-3 or more.
[0026] Oxygen precipitation hardly occurs in a low-[Oi] substrate
having an [Oi] of 8E17 cm.sup.-3 or less. However, BMD can be
formed by accelerating oxygen precipitation by, e.g.,
low-temperature heat-treating at 500 to 700.degree. C. or by
introducing N.sub.2.
[0027] When BMD are formed at high density, the mechanical strength
(upper yield stress; .sigma.) sometimes deteriorates to cause slip
to frequently occur during the device process.
[0028] FIG. 3 shows the dependence of the mechanical strength on
the [BMD]. Curves indicated by an alternate long and short dashed
line L1, a dotted line L2, and a solid line L3 represent the
relationships between the [BMD] and the mechanical strength when
the [Oi] is 14E17, 10E17, and 8E17 cm.sup.-3, respectively.
[0029] As is apparent from FIG. 3, the mechanical strength
decreases as the [BMD] increases. The higher the [Oi], the more
conspicuous the decrease; no large mechanical strength decrease
occurs when the [Oi] is low.
[0030] FIG. 4 shows the dependence of the mechanical strength on
the heat-treating time. Curves indicated by a dotted line L11 and a
solid line L12 represent the relationships between the
heat-treating time and the mechanical strength when the [Oi] is
14E17 and 8E17 cm.sup.-3, respectively.
[0031] It is evident from FIG. 4 that the mechanical strength
decreases as the heat-treating time increases. Also, the higher the
[Oi], the more conspicuous the decrease; the mechanical strength
does not decrease much when the [Oi] is low. On the basis of FIG.
4, deterioration of the mechanical strength can be prevented by
setting the heat-treating time to 25 hrs or less, as a value
calculated assuming that the temperature is 1,000.degree. C.,
during the device process.
[0032] On the basis of the above consideration, in an embodiment of
the present invention as shown in FIG. 1, a substrate having a low
[Oi] ([Oi].ltoreq.8E17 cm.sup.-3 ) and a high resistivity
(.rho..gtoreq.500 .OMEGA..multidot.cm) is prepared (step S100).
This substrate is subjected to low-temperature heat-treating (500
to 700.degree. C.) for 5 hrs or less to form a predetermined number
of BMD or more ([BMD].gtoreq.1E8 cm.sup.-3) (step S102).
[0033] To prevent a decrease in the mechanical strength caused by
excess growth of BMD in the heat-treating step during the device
process, the heat-treating time during the device process is set to
25 hrs or less as a value calculated assuming that the temperature
is 1,000.degree. C. (step S104).
[0034] BMD can also be formed by introduction of N.sub.2 or C, as
well as by low-temperature heat-treating.
[0035] To perform conversion into the heat-treating time (t) at
1,000.degree. C., the relation ([Oi]-[oi]E)*(D.multidot.t)=constant
is used.
[0036] In this equation, [Oi] is the concentration of oxygen
contained in a substrate before heat-treating, [Oi]E is the
supersaturation degree of oxygen, and D is the diffusion
constant.
[0037] Examples 1 and 2 formed on the basis of the above embodiment
and Comparative Examples 1 and 2 corresponding to the conventional
techniques will be described below.
(1) EXAMPLE 1
[0038] A mirror wafer having a substrate resistivity .rho. of 5 k
.OMEGA..multidot.cm and an [Oi] of 6E17 atoms.multidot.cm.sup.-3
was fabricated by using the MCZ method. This wafer was subjected to
low-temperature heat-treating at 600.degree. C. for 6 hrs to obtain
5E8 cm.sup.-3 of BMD.
[0039] This mirror wafer was used as a support substrate to form a
thin-film SOI wafer having a silicon thickness (tsi) of 0.2
.lambda.m and a buried oxide film thickness (tBOX) of 0.2 .mu.m by
using a bonding method.
[0040] RF communication devices were formed on this SOI wafer by
using an RF BiCOMS process. The heat-treating time of the RF
communication devices during the BiCMOS process was set to 15 hrs
as a value calculated assuming that the temperature was
1,000.degree. C.
[0041] The mechanical strength of the wafer on which these RF
devices were formed was evaluated by three-point bending, and found
to be 11 MPa at 1,000.degree. C.
(2) EXAMPLE 2
[0042] The BMD formation method was different from Example 1
described above; BMD were formed by doping 1E14 cm.sup.-3 of
N.sub.2 during crystal pulling. The rest of the fabrication was the
same as Example 1, so a detailed description thereof will be
omitted.
(3) COMPARATIVE EXAMPLE 1
[0043] Unlike Examples 1 and 2 described above, no low-temperature
heat-treating for BMD formation was performed. The rest of the
fabrication was the same as Examples 1 and 2, so a detailed
description thereof will be omitted.
(4) COMPARATIVE EXAMPLE 2
[0044] In Example 1 described above, RF communication devices were
annealed for 40 hrs, as a value calculated assuming that the
temperature was 1,000.degree. C., during the BiCMOS process. The
rest of the fabrication was the same as Examples 1 and 2, so a
detailed description thereof will be omitted. The mechanical
strength of a wafer on which RF communication devices were formed
in accordance with Comparative Example 2 was measured and found to
be 8 MPa.
[0045] The RF characteristics, the yield ratio, and the occurrence
of crystal defects (slip) of each of Examples 1 and 2 and
Comparative Examples 1 and 2 were examined. The results were as
shown in FIG. 5.
[0046] All of Examples 1 and 2 and Comparative Examples 1 and 2 had
good RF characteristics.
[0047] No crystal defects occurred in Examples 1 and 2, and the
yield ratios of Examples 1 and 2 were higher by 20% than that of
Comparative Example 1.
[0048] In Comparative Example 1, crystal defects occurred in the
boat contact portions. In Comparative Example 2, crystal defects
occurred on the entire surface to make device formation impossible.
So, no semiconductor device was completed.
[0049] As described above, the results of Examples 1 and 2 show
that the above-mentioned embodiment can prevent crystal defects
even in the boat contact portions and improve the yield ratio.
[0050] That is, it was possible by precipitating 1E8 cm.sup.-3 or
more of BMD to suppress the occurrence of slip even in the boat
contact portions, thereby preventing defective devices and
improving the yield. As a method of precipitating BMD in a low-[Oi]
substrate, it is possible to use the method of performing
low-temperature heat-treating for 5 hrs or more as in Example 1,
the method of doping N.sub.2 as in Example 2, or a method of doping
C.
[0051] The above embodiment is merely an example and hence does not
restrict the present invention. For example, an SOI wafer is used
in the above embodiment. However, a bulk wafer having a high
resistivity of 500 .OMEGA..multidot.cm or more can also be
used.
[0052] As has been described above, a semiconductor device of the
present invention can maintain good RF characteristics, prevent
crystal defects, and improve the fabrication yield by forming a
circuit in a substrate having an [Oi] of 8E17 cm.sup.-3 or less, a
[BMD] of 1E8 cm.sup.-3 or more, and a resistivity of 500
.OMEGA..multidot.cm or more. This semiconductor device can be
obtained by the fabrication method of the present invention.
* * * * *