U.S. patent application number 09/203816 was filed with the patent office on 2001-05-31 for apparatus and method for manufacturing semiconductor device.
Invention is credited to URABE, KOJI.
Application Number | 20010001954 09/203816 |
Document ID | / |
Family ID | 18250588 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010001954 |
Kind Code |
A1 |
URABE, KOJI |
May 31, 2001 |
APPARATUS AND METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE
Abstract
In a semiconductor device manufacturing apparatus comprising at
least a reaction chamber and a substrate holder located within the
reaction chamber, a silicon nitride film is deposited on the
substrate holder within the reaction chamber, and then, a
semiconductor substrate is put on the silicon nitride film of the
substrate holder within the reaction chamber. A titanium film or a
titanium nitride film is deposited on the semiconductor substrate
within the reaction chamber, by a chemical vapor deposition process
using a titanium halide as a raw material gas.
Inventors: |
URABE, KOJI; (TOKYO,
JP) |
Correspondence
Address: |
NORMAN P SOLOWAY
HAYES SOLOWAY HENNESSEY GROSSMAN & HAGE
175 CANAL STREET
MANCHESTER
NH
03101
|
Family ID: |
18250588 |
Appl. No.: |
09/203816 |
Filed: |
December 2, 1998 |
Current U.S.
Class: |
118/728 ;
257/E21.168; 257/E21.17 |
Current CPC
Class: |
H01L 21/28556 20130101;
H01L 21/28568 20130101; C23C 16/4581 20130101 |
Class at
Publication: |
118/728 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 2, 1997 |
JP |
9-332050 |
Claims
1. A semiconductor device manufacturing apparatus for forming a
titanium film or a titanium nitride film on a principal surface of
a semiconductor substrate by a chemical vapor deposition process
using a titanium halide as a raw material gas, the apparatus
comprising at least a reaction chamber and a substrate supporting
member located within said reaction chamber for supporting said
semiconductor substrate thereon, said substrate supporting member
being coated with a silicon nitride film.
2. A semiconductor device manufacturing apparatus claimed in claim
1 wherein said silicon nitride film is a silicon nitride film
deposited within said reaction chamber.
3. A semiconductor device manufacturing apparatus claimed in claim
2 wherein said silicon nitride film is further coated with a
titanium nitride film.
4. A semiconductor device manufacturing apparatus claimed in claim
3 wherein said titanium nitride film is a titanium nitride film
deposited within said reaction chamber.
5. A semiconductor device manufacturing apparatus claimed in claim
1 wherein said silicon nitride film is further coated with a
titanium nitride film.
6. A semiconductor device manufacturing apparatus claimed in claim
5 wherein said titanium nitride film is a titanium nitride film
deposited within said reaction chamber.
7. A semiconductor device manufacturing method for forming a
titanium film or a titanium nitride film on a principal surface of
a semiconductor substrate by a chemical vapor deposition process
using a titanium halide as a raw material gas, the method using a
semiconductor device manufacturing apparatus comprising at least a
reaction chamber and a substrate supporting member located within
said reaction chamber and coated with a silicon nitride film,
locating a semiconductor substrate on said silicon nitride film of
said substrate supporting member within said reaction chamber, and
depositing a titanium film or a titanium nitride film on an upper
surface of said semiconductor substrate held on said substrate
supporting member within said reaction chamber, by a chemical vapor
deposition process using a titanium halide as a raw material
gas.
8. A semiconductor device manufacturing method claimed in claim 7
wherein said silicon nitride film is further coated with a titanium
nitride film, and said semiconductor substrate is located on said
titanium nitride film of said substrate supporting member.
9. A semiconductor device manufacturing method for forming a
titanium film or a titanium nitride film on a principal surface of
a semiconductor substrate by a chemical vapor deposition process
using a titanium halide as a raw material gas, the method using a
semiconductor device manufacturing apparatus comprising at least a
reaction chamber and a substrate supporting member located within
said reaction chamber, depositing a silicon nitride film on a
surface of said substrate supporting member within said reaction
chamber, locating a semiconductor substrate on said silicon nitride
film of said substrate supporting member within said reaction
chamber, and depositing a titanium film or a titanium nitride film
on said semiconductor substrate held on said substrate supporting
member within said reaction chamber, by a chemical vapor deposition
process using a titanium halide as a raw material gas.
10. A semiconductor device manufacturing method claimed in claim 9
wherein after said silicon nitride film is deposited on said
substrate supporting member within said reaction chamber, a
titanium nitride film is deposited on said silicon nitride film of
said substrate supporting member within said reaction chamber, and
thereafter, said semiconductor substrate is located on said
titanium nitride film of said substrate supporting member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus and a method
for manufacturing a semiconductor device, and more specifically to
a semiconductor device manufacturing apparatus and method for
forming a titanium film or a titanium nitride film by use of a
chemical vapor deposition process using a titanium halide as a raw
material gas.
[0003] 2. Description of Related Art
[0004] Now, a prior art semiconductor device manufacturing method
for forming a titanium film and a titanium nitride film in a
contact hole of a semiconductor device, by use of a chemical vapor
deposition process using a titanium halide as a raw material gas,
will be described with reference to FIG. 4, which is a diagrammatic
view of a reaction chamber of a chemical vapor deposition apparatus
for depositing a titanium film and a titanium nitride film by using
a titanium halide as a raw material.
[0005] In a reaction chamber 300, a substrate holder 10 for holding
a semiconductor substrate thereon, is formed of a nickel-based
alloy having an excellent corrosion resistant property against
chlorine. The substrate holder 10 is coated with a titanium nitride
film (called a "pre-coated titanium nitride film" hereinafter) 13
in order to prevent the metal of the substrate holder 10 from
reacting with a silicon of a bottom surface of a semiconductor
substrate such a silicon substrate 1.
[0006] Here, the pre-coated titanium nitride film 13 is formed by a
chemical vapor deposition process (called a "CVD process"
hereinafter) performed in the reaction chamber 300 using titanium
tetrachloride, ammonia and nitrogen as a raw material gas, before
the process for depositing a film on the silicon substrate 1 is
carried out.
[0007] A resistor heater 14 is incorporated in the substrate holder
10 to control the temperature of the substrate holder 10 in a film
deposition process. An evacuating line 15 is provided for
exhausting from the reaction chamber 300, a reaction gas generated
in the course the film deposition process and an unreacted gas. An
upper electrode 16 is provided at an upper portion of the reaction
chamber 300.
[0008] Next, the prior art semiconductor device manufacturing
method will be described with reference to FIGS. 5A to 5D, which
are diagrammatic sectional views for illustrating various steps in
the semiconductor device manufacturing process.
[0009] As shown in FIG. 5A, a device isolation oxide film 2 having
a thickness of 200 nm is formed on a principal surface of a silicon
substrate 1 by a conventional method, and a predetermined impurity
is doped into the principal surface of the silicon substrate 1, so
that a diffused layer 3 is formed.
[0010] Furthermore, an insulating film 4 having a thickness of 1500
nm is formed on the principal surface of the silicon substrate 1,
and a portion of the insulating film 4 positioned on the diffused
layer 3 is selectively removed so that a contact hole 5 is formed
through the insulating film 4.
[0011] Thereafter, as shown in FIG. 5B, a titanium film 6 having a
thickness of 10 nm is deposited on an upper surface of the
insulating film 4 and an inner surface of the contact hole 5, by
the CVD process using titanium tetrachloride, hydrogen and argon as
a raw material gas. In the same process, a titanium silicide film 7
having a thickness of 20 nm is formed on the upper surface of the
diffused layer 3.
[0012] Then, as shown in FIG. 5C, the titanium film 6 on the
surface of the insulating film 4 is nitrided by ammonia in the
reaction chamber 300 (FIG. 4), so that a titanium nitride film 8 is
formed.
[0013] Furthermore, as shown in FIG. 5D, a titanium nitride film 9
having a thickness of 500 nm is deposited on a surface of the
titanium nitride film 8 and the titanium silicide film 7, by the
CVD process using titanium tetrachloride, ammonia and nitrogen as a
raw material gas.
[0014] In the above mentioned process for forming the titanium film
and the titanium nitride film by using the titanium tetrachloride,
since the substrate holder is exposed to an active chlorine
atmosphere at a temperature of 500.degree. C. to 600.degree. C.,
the substrate holder is required to have the nature that a thermal
deformation such as a thermal expansion and a plastic deformation
is low, a high electric conductivity, a high heat conductivity and
a high-temperature corrosion resistant property.
[0015] The vapor pressure of nickel chloride is the least within
chlorides of refractory metals, and a nickel-based alloy is widely
known as a heat resistant material for a structural member. In
addition, the nickel-based alloy has some degree of electric
conductivity and some degree of heat conductivity. Therefore, the
nickel-based alloy has been used as a material of the prior art
substrate holder. In addition, when a metal substrate holder is
used, the pre-coated titanium nitride film is formed as mentioned
above in order to prevent a reaction with the silicon of the bottom
surface of the substrate.
[0016] If the substrate holder is formed of a ceramic material,
since the ceramic material is low in heat conductivity, a long time
is required to heat the substrate, and since the electric
conductivity is low, the substrate potential varies in a high
frequency discharge. These are problems.
[0017] A method for coating the metal substrate-holder with an
insulating film by use of the CVD process is disclosed in Japanese
Patent Application Pre-examination Publication No. JP-A-03-183151,
(the content of which is incorporated by reference in its entirety
into this application, and also an English abstract of
JP-A-03-183151 is available from the Japanese Patent Office and the
content of the English abstract of JP-A-03-183151 is also
incorporated by reference in its entirety into this application).
In the method disclosed in JP-A-03-183151, the coating of the metal
substrate-holder upper surface by the insulating film is previously
carried out in a predetermined reaction chamber which is different
from the reaction chamber in which the metal substrate-holder is to
be installed. Therefore, the insulating film formed in the
predetermined reaction chamber is required to resist to a heat
stress caused by a heat history from an ordinary room temperature
to a process temperature. Accordingly, the combination of the metal
material used to form the substrate holder with the insulating film
formed on the upper surface of the metal substrate-holder is
restricted to ones which have a thermal characteristics near to
each other.
[0018] However, the following problem has been encountered in the
prior art semiconductor device manufacturing apparatus and method
mentioned above.
[0019] Since the substrate holder is coated with the precoated
titanium nitride film, it is possible to prevent the reaction
between the silicon of the substrate bottom surface and the metal
of the substrate holder. However, the nickel and the other metal(s)
of the substrate holder are corroded through the precoated titanium
nitride film by active chlorine generated in the process of
depositing the titanium film and the titanium nitride film by using
the titanium tetrachloride.
[0020] As the result of the corrosion, a vapor of nickel chloride
and chloride of the other metal(s) is generated in the reaction
chamber, with the result that nickel and the other metal(s) are
deposited on the surface of the silicon substrate because of a
silicon reduction reaction of the chloride of the nickel and the
other metal(s) at the surface of the silicon substrate.
[0021] The nickel and the other metal(s) deposited on the substrate
surface diffuse into the interior of the substrate when the
substrate holder temperature is high. As a result, impurity energy
level(s) caused by the contaminating metals are formed in a
junction near to the contact hole in the semiconductor device, so
that a junction leakage current is apt to occur, and therefore, a
stable electric characteristics of the contact electrode cannot be
obtained.
SUMMARY OF THE INVENTION
[0022] Accordingly, it is an object of the present invention to
provide a semiconductor device manufacturing apparatus and method
which have overcome the above mentioned defect of the conventional
one.
[0023] Another object of the present invention is to provide a
semiconductor device manufacturing apparatus and method, capable of
preventing generation of a metal contaminating the semiconductor
device, in a reaction chamber.
[0024] The above and other objects of the present invention are
achieved in accordance with the present invention by a
semiconductor device manufacturing apparatus for forming a titanium
film or a titanium nitride film on a principal surface of a
semiconductor substrate by a chemical vapor deposition process
using a titanium halide as a raw material gas, the apparatus
comprising at least a reaction chamber and a substrate supporting
member located within the reaction chamber for supporting the
semiconductor substrate thereon, the substrate supporting member
being coated with a silicon nitride film.
[0025] Preferably, the silicon nitride film is a silicon nitride
film deposited within the reaction chamber. In one embodiment, the
silicon nitride film is further coated with a titanium nitride
film. This titanium nitride film is preferably a titanium nitride
film deposited within the reaction chamber.
[0026] According to another aspect of the present invention, there
is provided a semiconductor device manufacturing method for forming
a titanium film or a titanium nitride film on a principal surface
of a semiconductor substrate by a chemical vapor deposition process
using a titanium halide as a raw material gas, the method using a
semiconductor device manufacturing apparatus comprising at least a
reaction chamber and a substrate supporting member located within
the reaction chamber and coated with a silicon nitride film,
locating a semiconductor substrate on the silicon nitride film of
the substrate supporting member within the reaction chamber, and
depositing a titanium film or a titanium nitride film on the
semiconductor substrate held on the substrate supporting member
within the reaction chamber, by a chemical vapor deposition process
using a titanium halide as a raw material gas.
[0027] In one embodiment, the silicon nitride film is further
coated with a titanium nitride film, and the semiconductor
substrate is located on the titanium nitride film of the substrate
supporting member.
[0028] According to still another aspect of the present invention,
there is provided a semiconductor device manufacturing method for
forming a titanium film or a titanium nitride film on a principal
surface of a semiconductor substrate by a chemical vapor deposition
process using a titanium halide as a raw material gas, the method
using a semiconductor device manufacturing apparatus comprising at
least a reaction chamber and a substrate supporting member located
within the reaction chamber, depositing a silicon nitride film on
the substrate supporting member within the reaction chamber,
locating a semiconductor substrate on the silicon nitride film of
the substrate supporting member within the reaction chamber, and
depositing a titanium film or a titanium nitride film on the
semiconductor substrate held on the substrate supporting member
within the reaction chamber, by a chemical vapor deposition process
using a titanium halide as a raw material gas.
[0029] In one embodiment, the silicon nitride film is further
coated with a titanium nitride film, and the semiconductor
substrate is located on the titanium nitride film of the substrate
supporting member.
[0030] The above and other objects, features and advantages of the
present invention will be apparent from the following description
of preferred embodiments of the invention with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagrammatic view of a first embodiment of the
semiconductor device manufacturing apparatus in accordance with the
present invention;
[0032] FIGS. 2A to 2D are diagrammatic sectional views for
illustrating various steps in a first embodiment of the
semiconductor device manufacturing process in accordance with the
present invention;
[0033] FIG. 3 is a diagrammatic view of a second embodiment of the
semiconductor device manufacturing apparatus in accordance with the
present invention;
[0034] FIG. 4 is a diagrammatic view of the prior art semiconductor
device manufacturing apparatus; and
[0035] FIGS. 5A to 5D are diagrammatic sectional views for
illustrating various steps in the prior art semiconductor device
manufacturing process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Now, a first embodiment of the semiconductor device
manufacturing apparatus in accordance with the present invention
will be described with reference to FIG. 1, which is a diagrammatic
view of the first embodiment of the semiconductor device
manufacturing apparatus in accordance with the present
invention.
[0037] Referring to FIG. 1, the semiconductor device manufacturing
apparatus includes a reaction chamber 100 in which a titanium film
and a titanium nitride film are deposited. Within the reaction
chamber 100, a substrate holder 10 is provided, which is formed of
a nickel-based alloy having an excellent corrosion resistant
property against chlorine. A resistor heater 14 is incorporated in
the substrate holder 10 to control the temperature of the substrate
holder 10 in a film deposition process. An evacuating line 15 is
provided for exhausting from the reaction chamber 100, a reaction
gas generated in the course the film deposition process and an
unreacted gas. An upper electrode 16 is provided at an upper
portion of the reaction chamber 100.
[0038] The substrate holder 10 is coated with a silicon nitride
film 11 having a thickness of about 500 nm. This silicon nitride
film 11 is formed by a thermal CVD process in the reaction chamber
100, before the titanium film and the titanium nitride film are
deposited on a principal surface of a semiconductor substrate such
as a silicon substrate 1 in the same reaction chamber 100. For
example, the silicon nitride film 11 is formed under the condition
in which the temperature of the substrate holder 10 is 650.degree.
C., the pressure of the reaction chamber 100 is 1 Torr, a flow rate
of silane (SiH.sub.4) gas is 50 sccm, a flow rate of ammonia gas is
150 sccm, and a flow rate of argon (Ar) gas is 100 sccm. The
temperature of the substrate holder 10 is controlled by the heater
14.
[0039] In the case that a high frequency electrode is provided in
the reaction chamber, the silicon nitride film 11 can be formed by
a plasma CVD process.
[0040] Next, a first embodiment of the semiconductor device
manufacturing method which uses the first embodiment of the
semiconductor device manufacturing apparatus mentioned above, will
be described with reference to FIGS. 2A to 2D, which are
diagrammatic sectional views for illustrating various steps in the
semiconductor device manufacturing process.
[0041] As shown in FIG. 2A, a device isolation oxide film 2 having
a thickness of 200 nm is formed on a principal surface of a silicon
substrate 1 by a conventional method, and a predetermined impurity
is doped into the principal surface of the silicon substrate 1, so
that a diffused layer 3 is formed.
[0042] Furthermore, an insulating film 4 having a thickness of 1500
nm is formed on the principal surface of the silicon substrate 1,
and a portion of the insulating film 4 positioned on the diffused
layer 3 is selectively removed so that a contact hole 5 penetrating
through the insulating film 4 is formed on the diffused layer
3.
[0043] Thereafter, as shown in FIG. 2B, a titanium film 6 having a
thickness of 10 nm is deposited on an upper surface of the
insulating film 4 and an inner surface of the contact hole 5, by
the CVD process under the condition in which for example, the
temperature of the substrate holder 10 is 500.degree. C., the
pressure of the reaction chamber 100 is 5 Torr, and a high
frequency discharge power is 500 kW, and using as a raw material
gas, a mixed gas composed of titanium tetrachloride of 2 sccm in
flow rate, hydrogen of 1000 sccm in flow rate, and argon of 500
sccm in flow rate. In the same process, a titanium silicide film 7
having a thickness of 20 nm is formed on the upper surface of the
diffused layer 3.
[0044] Then, as shown in FIG. 2C, the titanium film 6 on the
surface of the insulating film 4 is nitrided by ammonia of 100 sccm
in flow rate, in the reaction chamber 100 (FIG. 1) under the
condition in which for example, the temperature of the substrate
holder 10 is 600.degree.C., the pressure of the reaction chamber
100 is 20 Torr, a high frequency discharge power is 500 kW, so that
a titanium nitride film 8 is formed.
[0045] Furthermore, as shown in FIG. 2D, a titanium nitride film 9
having a thickness of 500 nm is deposited on a surface of the
titanium nitride film 8 and the titanium silicide film 7, by the
CVD process under the condition in which for example, the
temperature of the substrate holder 10 is 600.degree.C. and the
pressure of the reaction chamber 100 is 20 Torr, and using as a raw
material gas, a mixed gas composed of titanium tetrachloride of 40
sccm in flow rate, ammonia of 100 sccm in flow rate, and nitrogen
of 3000 sccm in flow rate.
[0046] In the above mentioned first embodiment, since the substrate
holder 10 provided in the reaction chamber 100, in which the
titanium film and the titanium nitride film are deposited, is
coated with the silicon nitride film 11, the substrate holder 10 is
not corroded by the titanium tetrachloride which is the raw
material gas, and by hydrogen chloride which is the reaction
product. Therefore, since the nickel-base alloy forming the
substrate holder 10 is not corroded, a vapor of nickel chloride is
not generated in the reaction chamber 100. As a result, the metal
contamination of the semiconductor substrate 1 is minimized, so
that the stability of the electric characteristics of the contact
electrode in the semiconductor device is elevated.
[0047] Furthermore, since the nitride film is formed in the
reaction chamber 100, there does not occur a crack which would
otherwise occur in the silicon nitride film because of a thermal
stress generated in the course of moving between a process
temperature and an ordinary room temperature when the nitride film
is formed in another apparatus. Therefore, the silicon nitride film
can prevent the substrate holder 10 from being influenced by active
chlorine.
[0048] Now, a second embodiment of the semiconductor device
manufacturing apparatus in accordance with the present invention
will be described with reference to FIG. 3, which is a diagrammatic
view of the second embodiment of the semiconductor device
manufacturing apparatus in accordance with the present invention.
In FIG. 3, element corresponding to those shown in FIG. 1 are given
the same Reference Numerals, and explanation will be omitted.
[0049] Referring to FIG. 3, the semiconductor device manufacturing
apparatus includes a reaction chamber 200 in which a titanium film
and a titanium nitride film are deposited. Within the reaction
chamber 100, a substrate holder 10 is provided, which is formed of
a nickel-based alloy having an excellent corrosion resistant
property against chlorine. A resistor heater 14 is incorporated in
the substrate holder 10 to control the temperature of the substrate
holder 10 in a film deposition process.
[0050] A surface of the substrate holder 10 is coated with a
silicon nitride film 11 having a thickness of about 500 nm. This
silicon nitride film 1 is formed by a thermal CVD process in the
reaction chamber 200, before the titanium film and the titanium
nitride film are deposited on an upper surface of a semiconductor
substrate such as a silicon substrate 1 in the same reaction
chamber 200. For example, the silicon nitride film 11 is formed
under the condition in which the temperature of the substrate
holder 10 is 650.degree.C., the pressure of the reaction chamber
100 is 1 Torr, a flow rate of silane (SiH.sub.4) gas is 50 sccm, a
flow rate of ammonia gas is 150 sccm, and a flow rate of argon (Ar)
gas is 100 sccm. The temperature of the substrate holder 10 is
controlled by the heater 14.
[0051] In the case that a high frequency electrode is provided in
the reaction chamber, the silicon nitride film 11 can be formed by
a plasma CVD process.
[0052] Furthermore, the silicon nitride film 11 is coated with a
titanium nitride film 13 having a thickness of for example 500 nm.
This titanium nitride film 13 is formed by the thermal CVD process
or the plasma CVD process under condition in which for example the
temperature of the substrate holder 10 is 600.degree.C and the
pressure is 20 Torr, and using as a raw material gas, a mixed gas
composed of titanium tetrachloride of 40 sccm in flow rate, ammonia
of 100 sccm in flow rate, and nitrogen of 3000 sccm in flow rate.
The temperature of the substrate holder 10 is controlled by the
heater 14.
[0053] With provision of the titanium nitride film 13, the electric
conductivity between the semiconductor substrate and the substrate
holder is improved.
[0054] A semiconductor device manufacturing method using the second
embodiment of the semiconductor device manufacturing apparatus as
mentioned above is the same as the semiconductor device
manufacturing method explained with reference to FIGS. 2A to 2D,
using the first embodiment of the semiconductor device
manufacturing apparatus. Therefore, explanation will be
omitted.
[0055] In this second embodiment, since the substrate holder 10
provided in the reaction chamber 200, in which the titanium film
and the titanium nitride film are deposited, is coated with the
silicon nitride film 11, the substrate holder 10 is not corroded by
the titanium tetrachloride which is the raw material gas, and by
hydrogen chloride which is the reaction product. Therefore, since
the nickel-base alloy forming the substrate holder 10 is not
corroded, a vapor of nickel chloride is not generated in the
reaction chamber 100. As a result, the metal contamination of the
semiconductor substrate 1 is minimized, so that the stability of
the electric characteristics of the contact electrode in the
semiconductor device is elevated. In addition, since the silicon
nitride film is coated with the titanium nitride film, it is
possible to stabilize the potential of the substrate holder.
[0056] As mentioned above, according to the present invention,
since the substrate holder provided in the reaction chamber for
depositing the titanium film and in the reaction chamber for
depositing the titanium nitride film, is coated with the silicon
nitride film, the substrate holder is not corroded by the titanium
tetrachloride which is the raw material gas, and by hydrogen
chloride which is the reaction product. Therefore, since the
nickel-base alloy forming the substrate holder is not corroded, a
vapor of nickel chloride is not generated in the reaction chamber.
As a result, the metal contamination of the semiconductor substrate
is minimized, so that the stability of the electric characteristics
of the contact electrode in the semiconductor device is elevated.
In addition, if the silicon nitride film is coated with the
titanium nitride film, it is possible to stabilize the potential of
the substrate holder.
[0057] The invention has thus been shown and described with
reference to the specific embodiments. However, it should be noted
that the present invention is in no way limited to the details of
the illustrated structures but changes and modifications may be
made within the scope of the appended claims.
* * * * *