U.S. patent application number 10/040019 was filed with the patent office on 2003-07-03 for semiconductor wafer singulation method.
Invention is credited to Maiz, Jose A..
Application Number | 20030124771 10/040019 |
Document ID | / |
Family ID | 21908629 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030124771 |
Kind Code |
A1 |
Maiz, Jose A. |
July 3, 2003 |
SEMICONDUCTOR WAFER SINGULATION METHOD
Abstract
Layers of a processed semiconductor wafer are ablated with laser
light from a laser gun. A CO.sub.2 laser gun is used, which creates
laser light in a wavelength in the 9 to 11 .mu.m range. The layers
all have absorption coefficients that are relatively high when
radiated by laser light having such a wavelength. Silicon of the
wafer is, however, relatively transparent to laser light having
such a wavelength. A trench is thereby formed in the layers, which
prevents damage to the layers when the silicon is subsequently
sawed.
Inventors: |
Maiz, Jose A.; (Portland,
OR) |
Correspondence
Address: |
Stephen M. De Klerk
BLAKELY, SOKOLOFF, TAYLOR & ZAFMAN LLP
Seventh Floor
12400 Wilshire Boulevard
Los Angeles
CA
90025-1026
US
|
Family ID: |
21908629 |
Appl. No.: |
10/040019 |
Filed: |
January 3, 2002 |
Current U.S.
Class: |
438/113 ;
257/E21.238; 257/E21.599 |
Current CPC
Class: |
H01L 21/3043 20130101;
H01L 21/78 20130101 |
Class at
Publication: |
438/113 |
International
Class: |
H01L 021/44 |
Claims
What is claimed:
1. A semiconductor wafer singulation method comprising: generating
a beam of laser light having a wavelength of at least 4.5 .mu.m;
and forming a trench into a scribe street between adjacent
integrated circuits of a processed semiconductor wafer by directing
the beam onto the scribe street.
2. The method of claim 1 wherein the wafer includes a substrate of
semiconductor material and a plurality of layers formed on the
semiconductor material, and all the layers up to the substrate have
absorption coefficients of at least 1E+03 cm.sup.-1 at the
wavelength of the laser light.
3. The method of claim 2 wherein the semiconductor material has an
absorption coefficient of less than 1E+02 cm.sup.-1 at the
wavelength of the laser light.
4. The method of claim 3 wherein the semiconductor material is
silicon.
5. The method of claim 3 wherein the semiconductor material has an
absorption coefficient of at least 1E+05 cm.sup.-1 of laser light
having a wavelength of 355 nm.
6. The method of claim 2 wherein one of the layers is SiO.sub.2 or
fluorinated silica glass.
7. The method of claim 2 wherein one of the layers has an
absorption coefficient of less than 1E+01 cm.sup.-1 of laser light
having a wavelength of 355 nm.
8. The method of claim 1 wherein the wavelength of the laser light
is between 9 and 11 .mu.m.
9. The method of claim 2, further comprising: separating the
substrate between the integrated circuits.
10. The method of claim 9 wherein the substrate is separated by
sawing the substrate.
11. The method of claim 1, further comprising: forming three
additional trenches on different sides of one of the integrated
circuits.
12. The method of claim 1 wherein the beam is generated using a
CO.sub.2 laser gun.
13. A semiconductor wafer singulation method, comprising:
generating a beam of laser light using a CO.sub.2 laser gun; and
forming a trench into a scribe street between adjacent integrated
circuits of a processed semiconductor wafer by directing the beam
onto the scribe street.
14. The method of claim 13 wherein the wafer includes a substrate
of semiconductor material and a plurality of layers formed on the
semiconductor material, and all the layers up to the substrate have
absorption coefficients of at least 1E+03 cm.sup.-1 at a wavelength
of the laser light.
15. The method of claim 14, further comprising: separating the
substrate between the integrated circuits.
16. A semiconductor wafer singulation method, comprising:
generating a beam of laser light; and forming a trench into a
scribe street between adjacent integrated circuits of a processed
semiconductor wafer by directing the beam onto the scribe street,
the wafer including a substrate of a semiconductor material having
a relatively low absorption coefficient at a wavelength of the
laser light, and a plurality of layers on the substrate, all of
which having absorption coefficients that are relatively high at
the wavelength of the laser light.
17. The method of claim 16 wherein the semiconductor material has
an absorption coefficient of less than 1E+02 cm.sup.-1 at the
wavelength of the laser light.
18. The method of claim 17 wherein the semiconductor material is
silicon.
19. The method of claim 16 wherein one of the layers is SiO.sub.2
or fluorinated silica glass.
20. The method of claim 16 wherein the semiconductor material is
silicon and one of the layers is SiO.sub.2.
Description
BACKGROUND OF THE INVENTION
[0001] 1). Field of the Invention
[0002] This invention relates to a method whereby a semiconductor
wafer is singulated into individual dies.
[0003] 2). Discussion of Related Art
[0004] Integrated circuits are usually formed in and on silicon and
other semiconductor wafer substrates. One substrate typically
carries an array of integrated circuits. Each integrated circuit
may include millions of electronic semiconductor components, such
as transistors, capacitors, diodes, etc. The integrated circuits
further include alternating metal lines and dielectric layers
formed on the silicon substrate. The metal lines interconnect the
electronic components with one another, and provide communication
between the electronic components and terminals on the layers. The
dielectric layers isolate the metal lines electrically from one
another.
[0005] A wafer which is processed to include such integrated
circuits is subsequently "singulated" or "diced" into individual
dies, each die carrying a respective one of the integrated
circuits. A saw is typically used to cut in x- and y-directions
through scribe streets between the integrated circuits.
[0006] The layers of the integrated circuits overlap the scribe
street, so that the saw has to be directed through the layers.
Previously, the layers were made of mechanically strong dielectric
materials such as SiO.sub.2 and fluorinated silica glass. These
materials were sufficiently strong to prevent cracking into the
integrated circuits when being sawed. More recently, the dielectric
layers have been made of low K-value (low electric permitivity)
dielectric materials. These low K-value dielectric materials are
much weaker, and cracks propagate easily from the saw through these
materials into the integrated circuits.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention is described by way of examples with reference
to the accompanying drawings, wherein:
[0008] FIG. 1 is a cross-sectional side view illustrating a
CO.sub.2 laser gun, which is used to ablate the layers of a
processed semiconductor wafer;
[0009] FIG. 2 is a view similar to FIG. 1, after the laser gun
forms a trench in the layers;
[0010] FIG. 3 is a plan view of the wafer, further illustrating
additional trenches formed therein;
[0011] FIG. 4 is a view similar to FIG. 2, illustrating sawing of a
silicon substrate of the wafer; and
[0012] FIG. 5 is a cross-sectional side view of a wafer in which
trenches are formed according to another method of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Throughout the following description, specific details are
set forth in order to provide a more thorough understanding of the
invention. However, the invention may be practiced without these
particulars. In other instances, well-known elements have not been
shown or described in detail to avoid unnecessarily obscuring the
present invention.
[0014] FIG. 1 of the accompanying drawings illustrates a CO.sub.2
laser gun 10 which, together with beam-shaping optics 12, is used
to ablate layers of a processed semiconductor wafer 14, to
singulate the wafer 14 into individual dies according to the
invention. The CO.sub.2 laser gun creates laser light 16 at a
wavelength in the range of 9 to 11 .mu.m. For purposes of further
discussion, the wavelength of the CO.sub.2 laser gun is assumed to
be 10 .mu.m. As will be discussed hereinafter, the wavelength of
the laser light 16 is ideally suited to ablate the layers, but not
silicon, of the wafer 14. A trench is thereby created in the layers
which prevents damage to the layers when the wafer 14 is
subsequently sawed.
[0015] The wafer 14 includes a silicon (semiconductor material)
substrate 18 in which semiconductor electric elements (not shown),
such as transistors, capacitors, etc., are formed. A number of
layers 20 are then formed on the silicon substrate 18. The layers
20 include alternating metal and dielectric layers. A top layer 22
of SiO.sub.2 is formed on the layers 20 for purposes relating to
mechanical strength. In another embodiment, the layer 22 may be
fluorinated silica glass. Some of the layers 20 are low K-value
dielectric layers that are relatively weak mechanically, but
desirable because of their electrical properties. Other ones of the
layers 20 are layers of metal lines between the dielectric layers.
Guard rings 24 are formed in the layers 20 and 22. Each guard ring
24 surrounds a respective integrated circuit 26 formed by the
electric components and the layers 20 and 22. A scribe street 28 is
defined between the guard rings 24.
[0016] The beam-shaping optics 12 shape the laser light 16, and
direct the laser light 16 as a beam 30 onto on an upper surface of
the scribe street 28. The light from the beam 30 is absorbed by
each one of the layers 22 and 20. The respective layer 22 or 20 is
ablated after absorbing the light. A respective layer 22 or 20 is
more easily ablated, the more absorbent it is to the light.
[0017] The following table lists absorption coefficients of the
layers 22 and 20 and of the silicon substrate 18 when radiated by
laser light having a wavelength of 355 nm and 10 .mu.m,
respectively.
1 355 nm 10 .mu.m Absorption Absorption Material coefficient
(cm.sup.-1) coefficient (cm.sup.-1) Notes Silicon 1.07E+06 1.00E+00
Key layer SiO.sub.2 0.00E+00 .about.1E4 Key layer SiO.sub.xF.sub.y
Expect high Key layer Cardon doped Silica 1.06E+03 Expect high Key
layer Si.sub.3N.sub.4 (passivation) 2.48E+03 Polyimide
(passiviation) Si.sub.xN.sub.y (Etch stop layer) 1.72E+04 SiC (Etch
stop layer) 4.60E+03 6.00E+03 Cu
[0018] A higher absorption coefficient indicates that the light is
more easily absorbed and the particular material is then more
easily ablated. It can be seen from the table that SiO.sub.2 (layer
22) has a relatively high absorption coefficient when radiated by
laser light having a reference of 10 .mu.m, and is relatively
transparent when radiated with laser light at a wavelength of 355
nm. Specific absorption coefficients at 10 .mu.m laser light are
not available for all the layers 20. It has been found that they
are easily ablated with 10 .mu.m laser light, and for that reason
it is believed that their absorption coefficients of 10 .mu.m laser
are all at least 1E+03 cm.sup.-1.
[0019] What should also be noted is that silicon is relatively
transparent at 10 .mu.m laser light. Relatively little damage will
occur to the silicon substrate 18. In comparison, it can also be
noted that silicon is relatively absorptive, and SiO.sub.2 is
relatively transparent at laser light of 355 mn.
[0020] Laser light at 10 .mu.m will thus ablate all the layers 22
and 20 without causing ablation or damage to the silicon substrate
18. The wavelength of the laser light is preferably between 9 and
11 .mu.m, the wavelengths of a CO.sub.2 laser gun, although it is
believed that a laser with a wavelength of at least 4.5 .mu.m and
larger will ablate all the layers in the table above, without
significant damage to the silicon substrate 18.
[0021] FIG. 2 illustrates the wafer 14 of FIG. 1 after portions of
the layers 20 and 22 have been ablated. A trench 32 is thereby
formed in the scribe street 28. The trench 32 has a vertical depth
in a z-direction of between 5 and 20 .mu.m, and a width in an
x-direction of between 10 and 150 .mu.m. The trench 32 extends all
the way down through the layers 22 and 20, and terminates against
the silicon substrate 18.
[0022] As can be seen in FIG. 3, an x-y array of integrated
circuits 26 is formed as part of the wafer 14. The wafer 14 is
moved relative to the beam-shaping optics 12 of FIG. 1 to form a
plurality of trenches 32, and more trenches 42. The trenches 32
extend in a y-direction and are spaced in an x-direction direction
relative to one another, and the trenches 42 extend in an
x-direction and are spaced in a y-direction relative to one
another. Four trenches are so formed on different sides of each
integrated circuit 26.
[0023] As illustrated in FIG. 4, a saw 44 is then used to cut
through the silicon substrate 18 in a region below the trench 32.
The saw 44 does not cut through the layers 20 and 22, so that no
damage occurs to the layers 20 or 22. The saw 44 is repeatedly used
to cut through the silicon below each one of the trenches 32 and 42
in FIG. 3. The wafer 14 is so singulated into individual dies, each
die carrying a respective one of the integrated circuits 26.
[0024] Damage to the layers 20 and 22 may also be avoided as
illustrated in FIG. 5. A CO.sub.2 laser gun is used to form two
trenches 50 between the guard rings 24. A saw is then used to cut a
groove 52 through the layers 20 and 22 between the trenches 50 and
through the silicon substrate 18. The trenches 50 isolate the saw
from the integrated circuits 26. The trenches 50 do not have to be
as wide as shown as FIG. 2, which allows for the use of a more
concentrated beam of laser light.
[0025] While certain exemplary embodiments have been described and
shown in the accompanying drawings, it is to be understood that
such embodiments are merely illustrative and not restrictive of the
current invention, and that this invention is not restricted to the
specific constructions and arrangements shown and described since
modifications may occur to those ordinarily skilled in the art.
* * * * *