U.S. patent application number 12/860981 was filed with the patent office on 2011-03-03 for polishing apparatus.
Invention is credited to Norihiko MORIYA, Kazutaka Shibuya.
Application Number | 20110053474 12/860981 |
Document ID | / |
Family ID | 43034190 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110053474 |
Kind Code |
A1 |
MORIYA; Norihiko ; et
al. |
March 3, 2011 |
POLISHING APPARATUS
Abstract
The polishing apparatus is capable of improving accuracy of
polishing a work. The work is pressed onto a polishing cloth, with
an elastic sheet, by a pressing force generated by second pressing
means and applied to a carrier and inner pressure of a first fluid
chamber generated by a fluid supplied thereto, so as to polish the
work. The fluid, which has been downwardly supplied into the first
fluid chamber, horizontally flows outward in the first fluid
chamber, collides with a side wall of a concave part of a
board-shaped member and flows upward, and then the fluid is
discharged outside from a fluid outlet, thereby a fluid feeding
member follows movement of the elastic sheet and maintains parallel
to the elastic sheet, and the fluid feeding member is centered in
the first fluid chamber.
Inventors: |
MORIYA; Norihiko;
(Nagano-shi, JP) ; Shibuya; Kazutaka; (Nagano-shi,
JP) |
Family ID: |
43034190 |
Appl. No.: |
12/860981 |
Filed: |
August 23, 2010 |
Current U.S.
Class: |
451/288 |
Current CPC
Class: |
B24B 37/30 20130101 |
Class at
Publication: |
451/288 |
International
Class: |
B24B 7/22 20060101
B24B007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2009 |
JP |
2009-200690 |
Claims
1. A polishing apparatus for polishing a surface of a work,
comprising: a polishing plate having a surface on which a polishing
cloth is adhered; a polishing head for pressing the work onto the
polishing cloth; and a driving mechanism for relatively moving the
polishing head with respect to the polishing plate, wherein the
polishing head includes: a main body section; a board-shaped member
having a concave part whose open end is aimed downward, the
board-shaped member being suspended from the main body section and
movable in the vertical direction; a carrier being located in the
concave part of the board-shaped member, being supported by the
board-shaped member and being capable of inclining, in a state
where a prescribed gap is formed between an outer circumferential
face of the carrier and a side wall of the concave part, with
respect to the horizontal plane, the carrier having a fluid feeding
member which has a plurality of spraying ports from which a fluid
is sprayed downward; fluid supplying means for supplying the fluid
to the carrier so as to spray the fluid downward from the fluid
feeding member; an elastic sheet being provided to the board-shaped
member and covering a lower side of the fluid feeding member so as
to form a first fluid chamber, the elastic sheet being capable of
holding the work on a lower surface thereof; a ring-shaped member
being provided to an outer edge part of the lower surface of the
elastic sheet, the ring-shaped member being capable of enclosing
the work held on the lower surface of the elastic sheet; first
pressing means for pressing the board-shaped member downward so as
to press the ring-shaped member onto the polishing cloth with the
elastic sheet; second pressing means for pressing the carrier
downward; and a fluid outlet for discharging the fluid from the
first fluid chamber, the fluid outlet being formed, in the
board-shaped member, at a position higher than a lower surface of
the fluid feeding member, and wherein the work is pressed onto the
polishing cloth, with the elastic sheet, by a pressing force
generated by the second pressing means and applied to the carrier
and inner pressure of the first fluid chamber generated by the
fluid supplied to the first fluid chamber, so as to polish the
work, and the fluid, which has been downwardly supplied into the
first fluid chamber, horizontally flows outward in the first fluid
chamber, collides with the side wall of the concave part and flows
upward, and then the fluid is discharged outside from the fluid
outlet, thereby the fluid feeding member follows movement of the
elastic sheet and maintains parallel to the elastic sheet, and the
fluid feeding member is centered in the first fluid chamber.
2. The polishing apparatus according to claim 1, wherein the
carrier is supported by the board-shaped member with a diaphragm
and capable of inclining in the state where the prescribed gap is
formed between the outer circumferential face of the carrier and
the side wall of the concave part, and the second pressing means
includes: a second fluid chamber being formed, by the diaphragm,
between the carrier and the board-shaped member; and second fluid
supplying means for supplying the fluid to the second fluid
chamber.
3. The polishing apparatus according to claim 1, wherein the
board-shaped member is suspended, by a diaphragm, from the main
body section and movable in the vertical direction, and the first
pressing means includes: a third fluid chamber being formed, by the
diaphragm, between the board-shaped member and the main body
section; and third fluid supplying means for supplying the fluid to
the third fluid chamber.
4. The polishing apparatus according to claim 2, wherein the
board-shaped member is suspended, by a diaphragm, from the main
body section and movable in the vertical direction, and the first
pressing means includes: a third fluid chamber being formed, by the
diaphragm, between the board-shaped member and the main body
section; and third fluid supplying means for supplying the fluid to
the third fluid chamber.
5. The polishing apparatus according to claim 1, wherein a
discharge pipe is connected to the fluid outlet, a relief valve is
provided to the discharge pipe, and inner pressure of the first
fluid chamber is maintained, at prescribed pressure, by the relief
valve.
6. The polishing apparatus according to claim 2, wherein a
discharge pipe is connected to the fluid outlet, a relief valve is
provided to the discharge pipe, and inner pressure of the first
fluid chamber is maintained, at prescribed pressure, by the relief
valve.
7. The polishing apparatus according to claim 3, wherein a
discharge pipe is connected to the fluid outlet, a relief valve is
provided to the discharge pipe, and inner pressure of the first
fluid chamber is maintained, at prescribed pressure, by the relief
valve.
8. The polishing apparatus according to claim 5, wherein the fluid
discharged from the discharge pipe is collected and reused.
9. The polishing apparatus according to claim 1, wherein the
pressing force, which is applied to the work via the elastic sheet,
is different in a plurality of coaxial zones of the work, and flow
volume of the fluid toward the first fluid chamber is set for each
of the coaxial zones.
10. The polishing apparatus according to claim 1, wherein the fluid
fed into the first fluid chamber is air.
11. The polishing apparatus according to claim 1, wherein the
elastic sheet is a two-layered sheet constituted by a sheet-shaped
member and a holding member provided under the sheet-shaped member.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. P2009-200690,
filed on Aug. 31, 2009, and the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The present invention relates to a polishing apparatus for
polishing a work, e.g., wafer.
BACKGROUND
[0003] A single-side polishing apparatus for polishing a work,
e.g., semiconductor wafer, is known. In the single-side polishing
apparatus, the work held by a polishing head is pressed onto a
polishing surface of a polishing plate, on which a polishing cloth
is adhered, and the polishing plate is relatively moved with
respect to the polishing head so as to polish the surface of the
work.
A conventional single-side polishing apparatus is disclosed in
Japanese Laid-open Patent Publication No. P2000-317819A. The
single-side polishing apparatus has a polishing head for holding a
wafer, the wafer is pressed onto a polishing pad (polishing cloth)
adhered on a rotary polishing plate so as to polish the surface of
the wafer. The polishing head comprises: a main body section facing
the polishing plate and being capable of rotating; a carrier being
loosely fitted in the polishing head and being capable of moving in
the vertical direction; and a retainer ring enclosing the wafer and
being brought into contact with the polishing pad with the wafer.
The retainer ring is attached to the carrier by an O-ring, an air
spraying member is provided on a lower face of the carrier, a
protection sheet covers an outer face of the air spraying member,
and the wafer is pressed onto the polishing pad, together with the
protection sheet, by air (air layer) sprayed from the air spraying
member.
[0004] In the polishing apparatus disclosed in Japanese Laid-open
Patent Publication No. P2000-317819A, the air layer is formed
between the air spraying member and the protection sheet, and the
wafer is pressed onto the polishing pad (polishing cloth), together
with the protection sheet, by the air layer. With this structure,
even if concavities and convexities exist in a surface of the
polishing cloth, the wafer is pressed, together with the protection
sheet, by the air layer. Therefore, the wafer can move to follow
the concavities and convexities, so that the wafer can be polished
with high polishing accuracy and damaging the wafer can be
prevented by the protection sheet.
[0005] However, in the polishing apparatus disclosed in Japanese
Laid-open Patent Publication No. P2000-317819A, the O-ring is
provided between the retainer ring and the carrier, so the carrier
and the air spraying member fixed to the carrier hardly move in the
horizontal direction. Namely, the carrier and the air spraying
member can move only in the vertical direction with maintaining the
horizontal state. When the wafer moves to follow the concavities
and convexities of the polishing cloth, the wafer sometimes
inclines with respect to the air spraying member which always
maintains the horizontal state. Air is downwardly sprayed from the
air spraying member. If the wafer inclines with respect to the
horizontal plane, a distance between the wafer and the air spraying
member is vary from place to place, so pressure applied to the
wafer must be uneven and the wafer cannot be polished evenly.
[0006] These days, sizes of wafers are getting larger and larger.
So, even if such unevenness is minute, it will highly affect the
polishing accuracy.
SUMMARY
[0007] Accordingly, it is an object in one aspect of the invention
to provide a polishing apparatus, which is capable of highly
improving polishing accuracy.
[0008] To achieve the object, the polishing apparatus of the
present invention, which polishes a surface of a work,
comprises:
[0009] a polishing plate having a surface on which a polishing
cloth is adhered;
[0010] a polishing head for pressing the work onto the polishing
cloth; and
[0011] a driving mechanism for relatively moving the polishing head
with respect to the polishing plate,
[0012] the polishing apparatus is characterized in,
[0013] that the polishing head includes: [0014] a main body
section; [0015] a board-shaped member having a concave part whose
open end is aimed downward, the board-shaped member being suspended
from the main body section and movable in the vertical direction;
[0016] a carrier being located in the concave part of the
board-shaped member, being supported by the board-shaped member and
being capable of inclining, in a state where a prescribed gap is
formed between an outer circumferential face of the carrier and a
side wall of the concave part, with respect to the horizontal
plane, the carrier having a fluid feeding member which has a
plurality of spraying ports from which a fluid is sprayed downward;
[0017] fluid supplying means for supplying the fluid to the carrier
so as to spray the fluid downward from the fluid feeding member;
[0018] an elastic sheet being provided to the board-shaped member
and covering a lower side of the fluid feeding member so as to form
a first fluid chamber, the elastic sheet being capable of holding
the work on a lower surface thereof; [0019] a ring-shaped member
being provided to an outer edge part of the lower surface of the
elastic sheet, the ring-shaped member being capable of enclosing
the work held on the lower surface of the elastic sheet; [0020]
first pressing means for pressing the board-shaped member downward
so as to press the ring-shaped member onto the polishing cloth with
the elastic sheet; [0021] second pressing means for pressing the
carrier downward; and [0022] a fluid outlet for discharging the
fluid from the first fluid chamber, the fluid outlet being formed
in the board-shaped member, at a position higher than a lower
surface of the fluid feeding member, and
[0023] that the work is pressed onto the polishing cloth, with the
elastic sheet, by a pressing force generated by the second pressing
means and applied to the carrier and inner pressure of the first
fluid chamber generated by the fluid supplied to the first fluid
chamber, so as to polish the work, and [0024] the fluid, which has
been downwardly supplied into the first fluid chamber, horizontally
flows outward in the first fluid chamber, collides with the side
wall of the concave part and flows upward, and then the fluid is
discharged outside from the fluid outlet, thereby the fluid feeding
member follows movement of the elastic sheet and maintains parallel
to the elastic sheet, and the fluid feeding member is centered in
the first fluid chamber.
[0025] By employing the polishing apparatus of the present
invention, the work can be uniformly polished with high polishing
accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Embodiments of the present invention will now be described
by way of examples and with reference to the accompanying drawings,
in which:
[0027] FIG. 1 is a schematic explanation view of an embodiment of a
polishing apparatus;
[0028] FIG. 2 is a schematic sectional view of a polishing
head;
[0029] FIG. 3 is an explanation view showing inclination of a work;
and
[0030] FIG. 4 is a schematic sectional view of another polishing
head.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0031] Preferred embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0032] FIG. 1 is a schematic explanation view of a polishing
apparatus of the present embodiment.
[0033] The polishing apparatus 10 comprises: a polishing plate 12
having an upper surface on which a polishing cloth 11 for polishing
a work W (see FIG. 2) is adhered; a polishing head 14 for holding
the work W on a lower surface and pressing the work W onto the
polishing cloth 11; and a driving mechanism for relatively moving
the polishing head 14 with respect to the polishing plate 12.
[0034] The driving mechanism is constituted by a first rotary
driving unit (not shown) for rotating the polishing plate 12 about
a rotary shaft 15 and a second rotary driving unit (not shown) for
rotating the polishing head 14 about a rotary shaft 16. Further,
the polishing head 14 has a vertical driving unit (not shown) and a
horizontal driving unit (not shown), holds the work W on the lower
surface, and presses the work W onto the polishing cloth 11. While
pressing the work W onto the polishing cloth 11, the driving
mechanism relatively rotates the polishing plate 12 and the
polishing head 14 so as to polish the lower surface of the work W.
A slurry supply nozzle 18 supplies slurry to the polishing cloth 11
adhered on the polishing plate 12.
[0035] FIG. 2 is a schematic sectional view of the polishing head
14.
[0036] A main body section 20 has a side wall 20a and a concave
part whose open end is aimed downward.
[0037] A board-shaped member 22 has a side wall 22a and a concave
part 23 whose open end is aimed downward. The board-shaped member
22 is suspended, in the main body section 20, by a ring-shaped
rubber diaphragm 24 having enough elasticity, and capable of moving
in the vertical direction. The side wall 20a acts as a guide for
the vertical movement of the board-shaped member 22.
[0038] A third fluid chamber 25 is formed, between the board-shaped
member 22 and the main body section 20, by the diaphragm 24. Air is
supplied from a compressed air source (not shown), e.g., air
compressor, to the third fluid chamber 25 via a fluid path 26
formed in the rotary shaft 16 (not shown in FIG. 2) of the
polishing head 14. The fluid path 26 is connected to the compressed
air source by a rotary joint (not shown). The fluid path 26, the
compressed air source, etc. constitute third fluid supplying
means.
[0039] Further, the third fluid chamber 25, the third fluid
supplying means, etc. constitute first pressing means.
[0040] A carrier 28 is located in the concave part 23 of the
board-shaped member 22, supported by a diaphragm 29 and capable of
inclining, in a state where a prescribed gap is formed between an
outer circumferential face of the carrier 28 and an inner face of
the side wall 22a of the concave part 23, with respect to the
horizontal plane.
[0041] A second fluid chamber 34 is formed, between the carrier 28
and the board-shaped member 22, by the diaphragm 29. Air is
supplied from the compressed air source (not shown) to the second
fluid chamber 24 via a fluid path 35 formed in the rotary shaft 16
(not shown in FIG. 2) of the polishing head 14. The fluid path 35
is connected to the compressed air source by a rotary joint (not
shown). The fluid path 35, the compressed air source, etc.
constitute second fluid supplying means.
[0042] Further, the third second chamber 34, the second fluid
supplying means, etc. constitute second pressing means.
[0043] An air reservoir 30 is formed in the carrier 28. A fluid
feeding member 31 is fixed to the carrier 28 and covers the lower
side of the air reservoir 30. A plurality of spraying ports, which
are capable of spraying air downward, are formed in the fluid
feeding member 31. Air is supplied from the compressed air source
(not shown) to the air reservoir 30 via a fluid path 37 formed in
the rotary shaft 16 (not shown in FIG. 2) of the polishing head 14.
The fluid path 37 is connected to the compressed air source by a
rotary joint (not shown). The fluid path 37, the compressed air
source, etc. constitute first fluid supplying means.
[0044] An elastic sheet 36 covers the lower side of the fluid
feeding member 31, and an outer edge of the elastic sheet 36 is
air-tightly fixed to a lower end of the side wall 22a of the
board-shaped member 22 by suitable means (not shown). With this
structure, a first fluid chamber 38 is formed under the fluid
feeding member 31.
[0045] The elastic sheet 36 is a two-layered sheet constituted by a
sheet-shaped member 39, which is composed of rubber and has enough
elasticity, and a holding member 40, which is provided under the
sheet-shaped member 39 and has many holes for holding the work W by
surface tension of water.
[0046] A ring-shaped member 42 composed of plastic, which encloses
the work W held on a lower surface of the elastic sheet 36, is
attached to a lower edge of the elastic sheet 36.
[0047] While polishing the work W, air is supplied to the third
fluid chamber 25 so as to press the board-shaped member 22
downward, and the ring-shaped member 42 is pressed onto the
polishing cloth 11 with the elastic sheet 36. By downwardly
pressing the polishing cloth 11 near an outer edge of the work W
until reaching a level with the lower surface of the work W,
excessive polishing of the outer edge of the work W can be
prevented.
[0048] A plurality of fluid outlets 44 for discharging the fluid
from the first fluid chamber 38 are formed, in the board-shaped
member 22, at positions higher than the lower surface of the fluid
feeding member 31. The fluid outlets 44 are equiangularly
arranged.
[0049] In the present embodiment, discharge pipes 45 are
respectively connected to the fluid outlets 44, and the discharge
pipes 45 are connected to a collecting pipe 46. A relief valve 47
is provided to the collecting pipe 46. The relief valve 47
maintains inner pressure of the first fluid chamber 38 at
prescribed pressure. When the inner pressure of the first fluid
chamber 38 is higher than the prescribed pressure, the relief valve
47 discharges air from the first fluid chamber 38.
[0050] Note that, number of the fluid outlet 44 may be one.
[0051] The discharge pipes 45 are extended outside of the main body
section 20 via large through-holes formed in the side wall 20a.
[0052] Air discharged by the relief valve 47 may be collected and
introduced to the compressed air source (not shown) to reuse. With
this structure, running cost of the apparatus can be reduced and
the apparatus is better for the environment.
[0053] Note that, the discharge pipes 45 and the relief valve 47
may be omitted. Further, the fluid may be directly discharged from
the fluid outlets 44.
[0054] The polishing apparatus of the present embodiment has the
above described structure. Next, a polishing method in the
polishing apparatus will be explained.
[0055] As described above, air is supplied into the third fluid
chamber 25 to press the board-shaped member 22 (the press action is
performed by the first pressing means) and the ring-shaped member
42 is pressed onto the polishing cloth 11 with the side wall 22a of
the board-shaped member 22 and the elastic sheet 36 while polishing
the work W, so that excessive polishing of the outer edge of the
work W can be prevented.
[0056] Air is supplied into the second fluid chamber 34 so as to
press the carrier 28 downward. Further, air is supplied into the
first fluid chamber 38 so as to press the elastic sheet 36.
[0057] Therefore, a pressing force for pressing the carrier 28,
which is applied by the second fluid chamber 34 (the second
pressing means), and the inner pressure of the air supplied into
the first fluid chamber 38 are applied to the work W via the
elastic sheet 36, so that the work W is pressed onto the polishing
cloth 11 and polished thereon.
[0058] Note that, air supplied into the first fluid chamber 38 is
always discharged outward from the fluid outlets 44. A prescribed
air layer must be always formed in the first fluid chamber 38.
Thus, the inner pressures of the first fluid chamber 38 and the
second fluid chamber 34 are suitably set so as not to break the air
layer in the first fluid chamber 38 by the inner pressure of the
second fluid chamber 34. By providing the relief valve 47, the
inner pressure of the first fluid chamber 38 can be easily
controlled.
[0059] While polishing the work W, the air, which has been
downwardly supplied into the first fluid chamber 38, horizontally
flows outward in the first fluid chamber 38, collides with the
inner face of the side wall 22a of the concave part 23 of the
board-shaped member 22 and flows upward, and then the air is
discharged outside from the fluid outlets 44. The fluid outlets 44
are located at positions sufficiently-higher than a lower surface
of the fluid feeding member 31. Since the air horizontally flows
outward in the first fluid chamber 38, collides with the inner face
of the side wall 22a of the concave part 23 of the board-shaped
member 22 and flows upward, the carrier 28 (the fluid feeding
member 31) is centered by a reactive force generated by colliding
the air with the ring-shaped side wall 22a.
[0060] As described above, the carrier 28 (the fluid feeding member
31) is floated and the carrier 28 does not directly act on the work
W. Therefore, even if concavities and convexities exist on the
surface of the polishing cloth 11 like gurge, the wafer can move to
follow the concavities and convexities thereon.
[0061] In the present embodiment, the carrier 28 (the fluid feeding
member 31) is supported by the board-shaped member 22 and capable
of inclining, with respect to the horizontal plane, in a state
where a prescribed gap is formed between an outer circumferential
face of the carrier 28 and the inner face of the side wall 22a of
the concave part 23.
[0062] In a state where the surface of the polishing cloth 11 is
horizontal, the carrier 28 (the fluid feeding member 31) is also
horizontal. If concavities and convexities exist in the surface of
the polishing cloth 11, the work W is inclined, with respect to the
horizontal carrier 28 (the fluid feeding member 31), as shown in
FIG. 3. Note that, the inclination of the work W is exaggerated in
FIG. 3. In the conventional polishing apparatus disclosed in
Japanese Laid-open Patent Publication No. P2000-317819A, the
horizontal state of the carrier is maintained, so a distance
between the carrier (the fluid feeding member) and the work is
varied, so the work cannot be uniformly pressed and cannot be
evenly polished.
[0063] On the other hand, in the present embodiment, the carrier 28
(the fluid feeding member 31) is inclinable with respect to the
board-shaped member 22. As shown in FIG. 3, when the work W is
inclined and a distance between the carrier 28 (the fluid feeding
member 31) and the work W is varied, pressure (a reactive force)
applied to the carrier 28 (the fluid feeding member 31) from a part
X of the work W, at which the distance is short, is higher; on the
other hand, pressure (a reactive force) applied to the carrier 28
(the fluid feeding member 31) from a part Y of the work W, at which
the distance is longer, is lower. Since the work W contacts the
polishing cloth 11, one part of the carrier 28 (the fluid feeding
member 31), which corresponds to the part X of the work W and to
which the higher pressure (the reactive force) is applied, is moved
away from the work W; the other part of the carrier 28 (the fluid
feeding member 31), which corresponds to the part Y of the work W
and to which the lower pressure (the reactive force) is applied, is
moved close to the work W. With this action, the carrier 28 (the
fluid feeding member 31) is inclined and made parallel to the work
W. Therefore, the distance between the carrier 28 (the fluid
feeding member 31) and the work W is made constant, so that the
pressing force can be uniformly applied to the work W and the work
W can be evenly polished.
[0064] As described above, the air pressure is applied to the
carrier 28 (the fluid feeding member 31) so as to center the
carrier 28 (the fluid feeding member 31). Even if the carrier 28
(the fluid feeding member 31) is inclined and shifted from the
center of the board-shaped member 22, the carrier 28 (the fluid
feeding member 31) is always biased toward the center of the
board-shaped member 22.
[0065] In the present embodiment, the carrier 28 has the above
described floating structure, and no load is applied from the work
W while the polishing operation. Therefore, the diaphragm 29, which
suspends the carrier 28, need not have high rigidity, so the
carrier 28 can be easily inclinably suspended.
[0066] FIG. 4 is a schematic sectional view of another polishing
head 14. Note that, the structural elements shown in FIG. 2 are
assigned the same symbols and explanation will be omitted.
[0067] In the present embodiment, an air reservoir of the carrier
28 is divided into a plurality of reservoirs, e.g., a central air
reservoir 30a and an outer air reservoir 30b. Fluid supplying means
50a and 50b respectively supply air to the air reservoirs 30a and
30b. A flow volume controller 52 is provided to the fluid supplying
means 50a so as to control flow volume of the air supplied to the
air reservoir 30a. Another flow volume controller (not shown) may
be provided to the fluid supplying means 50b. Note that, a pressure
controller or controllers may be employed instead of the flow
volume controller or controllers.
[0068] In the present embodiment, the pressing force applied to a
center zone and an outer zone of the work W can be controlled.
Namely, polishing conditions can be precisely controlled.
[0069] Note that, the work W may be coaxially divided into three
zones or more, and the pressing force can be controlled in the
zones respectively.
[0070] In each of the above described embodiments, the fluid is
air. The fluid may be a liquid. Further, the first pressing means
(the third fluid chamber 25, etc.) and the second pressing means
(the second fluid chamber 34, etc.) may be mechanical means, e.g.,
spring, screw mechanism.
[0071] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority and
inferiority of the invention. Although the embodiments of the
present invention has been described in detail, it should be
understood that the various changes, substitutions, and
alternations could be made hereto without departing from the spirit
and scope of the invention.
* * * * *