U.S. patent application number 11/757522 was filed with the patent office on 2007-12-13 for apparatus for grinding a wafer.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Bernhard P. Lange.
Application Number | 20070287363 11/757522 |
Document ID | / |
Family ID | 38663666 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070287363 |
Kind Code |
A1 |
Lange; Bernhard P. |
December 13, 2007 |
Apparatus for Grinding a Wafer
Abstract
An apparatus for grinding a wafer comprises a grinding member.
The grinding member has a grinding element for grinding a first
section of a wafer surface and a wafer contact element planar with
and adjacent the grinding element. The wafer contact element is
configured to contact a second section of the said wafer surface
when the grinding element is grinding the first section.
Inventors: |
Lange; Bernhard P.;
(Freising, DE) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
Dallas
TX
|
Family ID: |
38663666 |
Appl. No.: |
11/757522 |
Filed: |
June 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60882438 |
Dec 28, 2006 |
|
|
|
Current U.S.
Class: |
451/41 ;
257/E21.237; 451/285 |
Current CPC
Class: |
B24B 7/228 20130101;
H01L 21/304 20130101; B24B 37/245 20130101; B24B 37/042
20130101 |
Class at
Publication: |
451/41 ;
451/285 |
International
Class: |
B24B 7/30 20060101
B24B007/30; B24B 29/00 20060101 B24B029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2006 |
DE |
10 2006 026 467.3 |
Claims
1. An apparatus for grinding a wafer on a wafer surface generally
opposing a chip active surface, the apparatus comprising: a
grinding member, the grinding member having a grinding element for
grinding a first section of a said wafer surface and a wafer
contact element planar with and adjacent the grinding element, the
wafer contact element being configured to contact a second section
of the said wafer surface when the grinding element is grinding the
first section.
2. The apparatus according to claim 1, wherein the wafer contact
element is peripheral to and surrounding the grinding element.
3. The apparatus according to claim 1, wherein the grinding member
is generally disk-shaped.
4. The apparatus according to claim 1, wherein the grinding member
is operable to rotate about a central axis of rotation.
5. The apparatus according to claim 1, wherein the grinding member
is operable to move relative to the wafer surface in the same plane
as the wafer surface.
6. The apparatus according to claim 1, wherein a minimum diameter
of the grinding member is equal to twice the wafer diameter.
7. The apparatus according to claim 1, wherein the grinding element
and the wafer contact element are integrally formed.
8. The apparatus according to claim 1, wherein the wafer contact
element is provided as a substrate on the grinding member and the
grinding element is formed on the substrate.
9. The apparatus according to claim 1, further comprising a control
means for controlling movement of the grinding member against the
wafer surface.
10. A method of separating a semiconductor chip from a wafer, the
method comprising the steps of: cutting the wafer on a chip-active
surface to form a plurality of blind apertures defining chip
boundaries; grinding the wafer on a wafer surface generally
opposing the chip-active surface in a first section by means of a
grinding member, which includes a grinding element and a contact
element, whereby the wafer contact element is contacting a second
section of the wafer surface, which is not contacted by the
grinding element when the grinding of the first section is taking
place; and applying pressure to the first section of the wafer
surface thereby breaking the wafer between the wafer surface and a
blind end of each of said apertures.
Description
[0001] The present invention generally relates to an apparatus for
grinding a wafer. More particularly, the present invention relates
to an apparatus for back grinding a wafer with half precut.
BACKGROUND
[0002] Wafers need to be back ground (ground on the side opposite
the active chip side) in order to achieve the small thicknesses
currently required for semiconductor device packages. A schematic
diagram of a known back grinding technique is shown in FIG. 1. A
wafer 10 having a chip active side 11 is ground down from its back
side 12 to make it thinner using a grinding wheel 1. The grinding
wheel 1 has a grinding surface 2 which is entirely covered with
grinding material. The wheel 1 partially overlaps the wafer 10 and
rotates eccentrically about the wafer 10 so as to grind down the
whole wafer surface.
[0003] However, special copper metallization layers on the wafer,
which are used in today's chip designs, cause the wafer to warp
after back grinding has taken place. For this reason, the wafer is
partially cut on the chip active side prior to the back grinding
process to release some of the stress generated by the
metallization, This cutting process causes the formation of some
partial singulated chips.
[0004] A problem with current back grinding techniques is that, as
the wafer becomes thinner during the back grind operation, such
partial singulated chips can become loose and stand up above the
wafer surface. The loose chips can be pulled away from the wafer
surface by the edge of the grinding wheel, which can cause the
remaining wafer to be damaged by being shattered or scratched.
SUMMARY
[0005] The present invention has been devised with the foregoing in
mind.
[0006] Thus, the present invention provides an apparatus for
grinding a wafer on a wafer surface generally opposing a chip
active surface, the apparatus comprising: a grinding member, the
grinding member having a grinding element for grinding a first
section of a said wafer surface and a wafer contact element planar
with and adjacent the grinding element so as to contact a second
section of the said wafer surface when the grinding element is
grinding the first section. Thus, the wafer contact element
supports the wafer surface while grinding of the wafer is taking
place.
[0007] Preferably, the wafer contact element should be peripheral
to and surrounding the grinding element and the grinding member
should be generally disk-shaped and operable to rotate about a
central axis of rotation as a grinding wheel. The grinding member
should also be capable of moving in the same plane as the wafer
surface so that the entire wafer surface can be background. For
example, the grinding member can be configured to rotate
eccentrically about its central axis of rotation. This can be
achieved by having an actuation means, such as a shaft, to
establish a driveable connection between the grinding member and a
drive means, for example an electric motor. Control means, such as
a microprocessor, can also be provided to control the movement of
the apparatus with respect to a wafer surface, and control the
amount of grinding to achieve the desired wafer thickness.
[0008] The minimum diameter of the grinding member should
preferably be equal to twice the diameter of the wafer so that the
grinding member completely covers the surface of the wafer. The
grinding element and the wafer contact element can be integrally
formed or the wafer contact element can be provided as a substrate
on the grinding member such that the grinding element is formed on
the substrate, In this way the outer area of the grinding member
will be covered with the same substrate as used for keeping the
grinding material in the grinding element. This means that the
surface of the grinding member is flatter overall; therefore the
whole surface of the grinding member is able to get close to the
wafer surface being ground.
[0009] The present invention also provides a method of separating a
semiconductor chip from a wafer, the method comprising cutting the
wafer on a chip active surface to form a plurality of blind slit
apertures defining chip boundaries, grinding the wafer on a wafer
surface generally opposing the chip active surface in a first
section and providing a contact means to contact a second section
of the wafer surface when grinding of the first section is taking
place, and applying stress to the first section of the wafer
surface so as to break the wafer between the wafer surface and a
blind end of each of said apertures. Stress can be applied to the
wafer surface by tape laminating the newly ground wafer surface and
stretching the tape in a direction parallel to the wafer surface.
The stress on the wafer breaks up the small pieces of wafer between
the wafer surface and the blind end of the apertures or cuts. This
causes chip singulation and individual chips can then be removed
from the wafer. After stretching, stress can also be applied to the
ground wafer surface perpendicular to the surface so as to further
assist in bending the surface and breaking the chip boundaries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Further characteristics and advantages of the invention
ensue from the description below of a preferred embodiment and from
the accompanying drawings, in which:
[0011] FIG. 1 is a schematic diagram of a known back grinding
technique;
[0012] FIG. 2 is a side view of a section of an apparatus for
grinding a wafer according to the invention;
[0013] FIG. 3 is a schematic view of a grinding surface of an
apparatus for grinding a wafer according to the invention.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0014] Referring now to FIG. 2, a wafer 10 having a chip active
side 11 and a back side 12 has undergone metallization with a metal
layer 13, for example copper, and has been partially cut through
from the active chip side 11 to form cuts 14 defining blind slit
apertures at chip boundaries in the chip active side 11 of the
wafer 10. A protective film 15 has been attached to the active chip
side 11 after the formation of cuts 14 so as to prepare the wafer
10 for back grinding.
[0015] A grinding wheel 20 (only the half of the grinding wheel
covering the chip surface is shown in FIG. 2) has a grinding
element 21 and a wafer contact element 22 provided on a grinding
surface 23. The wafer contact element 22 can form a substrate upon
which the grinding element 21 can be formed. Alternatively, the
wafer contact element 22 can itself be formed on a substrate
separately from the grinding element 21. The grinding element 21 is
formed by depositing grinding material in the substrate so that the
grinding element 21 is provided in the centre of the grinding
surface 23 and is surrounded by the wafer contact element 22. This
is shown more clearly in FIG. 3. The grinding wheel 20 is generally
disk-shaped, such that its thickness is small in comparison with
its diameter, and its central axis of rotation is perpendicular to
the grinding surface 23. A shaft 24 connects the grinding wheel 20
with a drive means (not shown). The central vertical axis of the
shaft 24 is coincident with the central axis of rotation of the
grinding wheel 20. The shaft 24 is driven so as to allow the
grinding wheel 20 to simultaneously rotate about its central axis
of rotation and move in the same plane as the grinding surface
23.
[0016] To grind down the wafer 10 from its back side 12, the
grinding wheel 20 is held against the surface of the back side 12
of the wafer 10 and rotated by the shaft 24 about its central axis
of rotation, perpendicular to the surface of the wafer 10, such
that it rotates over the surface of the wafer 10. The grinding
wheel 20 can be made to rotate by any suitable drive means (not
shown), for example an electric motor.
[0017] As the grinding wheel 20 rotates over the surface of the
wafer 10, the grinding element 21 grinds down the section of the
surface of the wafer 10 that is in contact with the grinding
element 21, while the wafer contact element 22 provided in the
outer section of the wheel 20 contacts the part of the surface of
the wafer 10 that is not undergoing grinding and supports it.
Therefore, as the wafer 10 is ground down and becomes thinner,
loose chips are prevented from sticking up above the surface of the
back side 12 of the wafer 10. Ideally, the grinding surface 23
should be in contact with the wafer 10 at all times as it is moved
across the surface of the backside 12 of the wafer 10.
[0018] At the same time as the grinding wheel 20 is rotated about
its central axis of rotation against the wafer 10, it is also moved
over surface of the wafer 10 (by moving the shaft so that the wheel
20 rotates eccentrically about its central axis of rotation, or
otherwise) so that the outer edge of the grinding element 21 is
coincident with the centre of the wafer 10 and the grinding element
21 is eventually brought into contact with the entire surface of
the back side 12 of the wafer 10, while the section of the wafer 10
that is not being background is supported by the wafer contact
element 22. In this way the whole of the wafer 10 can be ground
down to the same desired thickness.
[0019] Provision of the wafer contact element 22 on the grinding
surface 23 for supporting the wafer 10 during grinding provides the
advantage that the wafer 10 can be ground down to a smaller
thickness without damage. This enables chips to be separated from
the wafer 10 after back grinding without a further cutting
operation. To separate chips from the wafer 10 after back grinding,
the surface of the wafer 10 is simply stretched on the back side 12
in a direction parallel with the wafer surface, and/or bent by
applying stress to the back side 12 in a direction perpendicular to
the wafer surface, so that the wafer 10 breaks between the blind
ends of the cuts 14 and the back side 12 to form individual
chips.
[0020] Although the present invention has been described
hereinabove with reference to specific embodiments, it is not
limited to these embodiments and no doubt further alternatives will
occur to the skilled person which lie within the scope of the
invention as claimed.
[0021] For example, the grinding member is not limited to being
disk-shaped and rotatably moveable relative to the wafer surface.
The grinding member could be rectangular, for example, and be
configured to move across the surface of the wafer in a straight
line backwards and forwards relative to the surface of the
wafer.
* * * * *