U.S. patent application number 13/573148 was filed with the patent office on 2014-02-27 for method for grinding wafers by shaping resilient chuck covering.
This patent application is currently assigned to Strasbaugh, Inc.. The applicant listed for this patent is Salman M. Kassir. Invention is credited to Salman M. Kassir.
Application Number | 20140057531 13/573148 |
Document ID | / |
Family ID | 50148400 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140057531 |
Kind Code |
A1 |
Kassir; Salman M. |
February 27, 2014 |
Method for grinding wafers by shaping resilient chuck covering
Abstract
This method facilitates and improves the production of quality
thin wafers by adhering traditional resilient back-grind tape that
has been perforated over the area that will contact the wafer on
the ceramic porous grind chuck, so as to allow vacuum to be applied
to the wafer back surface to hold the wafer for processing. The
tape adhering to the chuck is ground with a abrasive grind wheel,
bringing the surface of the tape parallel to the chuck surface
which was previously ground by the same grinding device. Grinding
the tape while it is mounted on the chuck establishes the plane
perpendicular to the grind wheel spindle, removes the bumpiness
from the perforation holes and evens out the non-uniformity of the
tape, resulting in improved wafer back side grinding and thus good
site flatness.
Inventors: |
Kassir; Salman M.; (Paso
Robles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kassir; Salman M. |
Paso Robles |
CA |
US |
|
|
Assignee: |
Strasbaugh, Inc.
|
Family ID: |
50148400 |
Appl. No.: |
13/573148 |
Filed: |
August 27, 2012 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 53/017 20130101;
B24B 7/228 20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 7/22 20060101
B24B007/22 |
Claims
1. A method of grinding a first wafer having first and second
surfaces comprising the steps of: providing a grind chuck having
first and second surfaces; providing a first resilient member
having top and bottom surfaces; cutting the resilient member to a
size and shape that conforms to said first surface of said chuck;
placing said bottom surface of said resilient member on the first
surface of said chuck; grinding the top surface of the resilient
member to remove debris therefrom and shape the top surface thereof
utilizing a first grinding apparatus; placing said first wafer on
said top surface of said resilient member; securing said first
wafer to said grind chuck; and grinding the first surface of said
first wafer to the desired shape using said first grinding
apparatus.
2. The method of claim 1 wherein openings are formed in said
resilient member.
3. The method of claim 1 wherein said grinding chuck is porous.
4. The method of claim 1 wherein openings are formed in said grind
chuck.
5. The method of claim 1 further including the step of removing
said first wafer from said grinding chuck and inverting said first
wafer such that said second surface thereof faces said first chuck
surface.
6. The method of claim 5 wherein a vacuum is provided to secure
said wafer to said grind chuck.
7. The method of claim 5 wherein the second surface of said first
wafer is removably positioned on said first chuck surface.
8. The method of claim 3 wherein said second surface of said wafer
is ground by said first grinding apparatus.
9. The method of claim 5 further including the step of removing
said first wafer from said chuck.
10. The ground method of claim 1 further including the step of
replacing said fist wafer with a second wafer.
11. The method of claim 1 wherein said first resilient member is
removed from said ground chuck and replaced with a second resilient
member.
12. The method of claim 11 wherein said second resilient member is
processed in the same manner as said first resilient member.
13. The method of claim 1 wherein said resilient member comprises a
tape.
14. The method of claim 1 wherein said resilient member comprises
material selected from the group comprising Ultron 1034R-9.8 or
Ultron 1044R-9.8.
15. The method of claim 14 wherein the selected material is Ultron
1034R-9.8.
16. The method of claim 14 wherein the selected material is Ultron
1044R-9.8.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is utilized in the manufacture of
semiconductor material wafers without components on the front side
and in particular, a method and apparatus for preventing the wafer
from distorting during the planarization steps by attaching a
grindable resilient tape to a porous grind chuck or hard chuck with
discrete vacuum holes, grinding the tape and then placing a wafer
on the chuck for processing.
[0003] 2. Description of the Prior Art
[0004] The semiconductor industry has, and is, interested in
producing material wafers with very low total thickness variation
(TTV) from wafers that are uneven in thickness, post wire sawing
for example. Most wafers are cut from their growth boule using a
high production wire-sawing method that inherently produce waviness
and high TTV due to the irregular motion of the wire position as
the boule is turned. This waviness and sometime highly irregular
wafer shape after sawing presents subsequent difficulties
especially for batch processes.
[0005] U.S. Pat. No. 6,866,564 to Strasbaugh et al, assigned to the
assignee of the present invention, discloses a method of
back-grinding device-mounted wafers wherein a resilient back
grinding component, such as a tape or pad, is applied to the
surface of a solid chuck. The component is held to the chuck
surface as each wafer is sequentially placed on the component and
after grinding the backside of the wafer, each wafer is removed
from the chuck. This patent applies to thinning wafers, such as
those made from silicon, for final packaging to facilitate the
process by eliminating the taping and de-taping of thin device
wafers, and to save the cost associated with this step.
[0006] U.S. Pat. No. 5,964,646, assigned to the assignee of the
present discloses a method and apparatus for planarizing silicon
wafers initially having wavy surfaces. A vacuum is applied to one
side of a porous ceramic plate, and a perforated resilient pad is
affixed to the opposite side of the porous ceramic plate. A vacuum
extends through the perforations on the resilient pad to permit a
wafer to be mounted on the exposed side of the resilient pad. The
wafer is not deformed while being held in place for grinding and
thus the wafer has no tendency to spring back to its original wavy
shape. Once one side of the wafer has been planarized, the second
wafer surface is planarized on a flat chuck to provide a wafer that
has uniform thickness.
[0007] U.S. Pat. No. 8,025,533 to Seklya discloses a method for
back grinding a wafer wherein the face-side surface of the wafer is
covered with a resin film, the surface of the resin film being cut
to form a flat surface parallel to the face-side surface of the
wafer. The wafer is held with the surface of the resin film in
contact with a suction surface of a chuck table in a grinding
apparatus, and the exposed backside surface of the wafer is ground.
Unevenness in thickness of the resin film is suppressed, the
thickness of the wafer subjected to back grinding as a result being
made uniform.
[0008] Although the above-noted patents disclose various techniques
for maintaining a uniform wafer thickness, the total thickness
(TTV) variation is too high to meet the requirements of new chip
technology.
[0009] What is desired is to provide a method for treating wafers
wherein the TTV is reduced to the point that it meets the
requirements of thin semiconductor manufacturers for producing
semiconductor chips that can be used in various devices, such as
MP3 players, televisions, etc.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method of producing
semiconductor material wafers with very low TTV from wafers that
are uneven in thickness.
[0011] Specifically, a soft chuck surface is prepared with the soft
chuck being of semiconductor production compatible clean-room
material whose surface characteristics can be altered with holes
for facilitating vacuum and via grinding and/or polishing to form a
planar surface parallel to the cutting plane of either grinding
(grind wheel plane) or polishing (pad plane).
[0012] This method facilitates and improves the first side
planarization of a substrate of any shape by adhering traditional
resilient back-grind tape (such as Ultron 1034R-9.8 or Ultron
1044R-9.8) that has been perforated for example, by a laser
punching over the area that will contact the wafer on to the
ceramic porous grind chuck, so as to allow vacuum to be applied to
the wafer back surface (i.e., surface facing the chuck) to hold the
wafer for processing. The tape adhering to the chuck is ground with
an abrasive grind wheel, bringing the surface of the tape parallel
to the chuck surface which was previously ground by the same
grinding wheel. The act of grinding the tape while it is mounted on
the chuck establishes the plane perpendicular to the grind spindle,
removes the bumpiness from the perforation holes and evens out the
non-uniformity of the tape application onto the chuck, which
attachment normally being highly operator dependent, resulting in
improved wafer first side grinding and thus good site flatness.
DESCRIPTION OF THE DRAWINGS
[0013] For a better understanding of the present invention as well
as other objects and further features thereof, reference is made to
the following description which is to be read in conjunction with
the accompanying drawing therein:
[0014] FIGS. 1(a)-1(f) illustrate the steps of backgrinding wafers
in accordance with the teachings of the present invention; and
[0015] FIGS. 2(A)-2(B) are illustrative of how non-uniformities in
a tape surface are corrected after grinding.
DESCRIPTION OF THE INVENTION
[0016] Referring to FIGS. 1(a)-(f), the steps of grinding the wafer
in accordance with the teachings of the present invention is
illustrated.
[0017] A porous ceramic chuck 20 is first ground to the desired
shape (FIG. 1A) and then a flexible tape 22 with holes 24 formed
therein is placed on the top surface 26 of chuck 20 (FIG. 1B). The
area of the tape that interfaces with surface 26 is referred to as
the "soft" chuck surface. FIG. 2A illustrates, in simplified form,
when tape 22 is first applied to chuck 20.
[0018] The upper surface 28 of tape 22 is then ground by grinder 21
parallel to surface 26 (FIG. 1C). The bottom surface 30 of wafer 32
(shown to have a wavy shape) is then positioned in contact with the
upper surface 36 of tape 22 and a vacuum is applied through holes
24 to secure wafer 32 to tape 22 (FIG. 1d). Surface 38 of wafer 32
is then ground (FIGS. 1d and 1e) producing a wafer with a surface
parallel to the chuck top surface 26. The wafer is then removed
from the tape and then turned over and the ground surface 38 of
wafer 32 placed on the upper chuck surface (FIG. 1f), the second
surface of wafer 32 then also being ground.
[0019] The purpose of grinding tape 22 is to correct any anomaly
that might be associated with applying the tape to the chuck
surface since this is usually a manual step depending on the skill
of the operator performing the grinding step. In addition, the tape
itself typically has some degree of non-uniformity that is
corrected by the grinding step.
[0020] A more detailed description of the process set forth
hereinabove follows: The grind chuck 20, porous as illustrated, is
prepared by pre-grinding a small amount from the surface using the
abrasive grind wheel 37 (FIG. 2A) thus cleaning the chuck 20 and
shaping the chuck as desired to produce a flat wafer surface. A
suitable resilient plastic background tape of predetermined
thickness (the hardness of the tape is dependent on the tape
selected) 22 is selected such that unwanted bumps or ridges on the
wafer back can be "absorbed" by the soft tape rather than
protruding from the top surface upwards (the preferred thickness
range of the tape is 130 um to about 300 um). The tape sheet is cut
into a size and shape to fit exactly onto the grind chuck surface
and then perforated with small holes (a laser punch may be
utilized). The holes cover the chuck contact area and are about one
millimeter apart in a uniform pattern.
[0021] The film that protects the adhesive on the back of the tape
(not shown) is then removed and the perforated tape 22 is then
attached to the entire surface of grind chuck 20 with the
perforated area aligned where the wafer 32 will be attached by
vacuum for surface grinding or polishing. Alternatively, perforated
tape holes can be aligned with holes in the top surface of a hard
chuck so as to facilitate vacuum attachment onto a solid chuck
rather than a porous ceramic chuck. The top tape surface is then
ground with a light down force (typically less than 4 pounds) to
remove bits of debris caused by perforation holes generated by the
laser and to shape the top surface of the tape. The wafer 32 to be
ground is then placed on the perforated portion of the tape and
attached by applying vacuum from below the chuck. With the wafer
held firmly, a predetermined amount of wafer material from the top
side of the wafer is ground so that the wafer achieves its desired
shape. The wafer 32 is then removed from the chuck, turned over and
then placed on the upper surface of the chuck. The exposed surface
of the wafer is then ground to a predetermined thickness.
[0022] The grinding platform utilized in the Strasbaugh 7AF grinder
may be utilized to grind the tape. Using the same grinder to shape
the tape that was used to shape the grind chuck enables a precise
tape surface parallel to the contacting chuck surface to be
fabricated which meets the stringent dimensional requirements of
wafer manufacturers.
[0023] FIGS. 2A and 2B are simplified representations of how the
surface of tape 22 is ground by grinder 21. Tape 22 is first
applied to chuck 20 where a first surface 23 of tape 22 is placed
in contact with surface 25 of chuck 20. Surface 27 of tape 22 is
shown as being uneven (FIG. 2A).
[0024] FIG. 2B illustrates top surface 27 of tape 22 after it
ground with wheel 37.
[0025] Typical resilient back-grind tape that has been successfully
utilized is Ultron.RTM. tape 1034R-9.8 and Ultron.RTM. tape
1044R-9.8, distributed by Ascend Performance Materials Operations
LLC, Houston, Tex.
[0026] The process of the present invention thus enables
semiconductor wafers to be produced of superior uniform thickness
from various materials.
[0027] It should be noted that this planarization concept also
applies to polishing whereby the carrier film that is currently
used for wafer backing during polish, such as the Strasbaugh DF200,
can be replaced with a malleable tape that can be polished to
remove the non-uniformity associated with material and operator
applications.
[0028] While the invention has been described with reference to its
preferred embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the true
spirit and scope of the invention. In addition, many modifications
may be made to adapt a particular situation or material to the
teachings of the invention without departing from its essential
teachings.
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