U.S. patent application number 10/323839 was filed with the patent office on 2003-05-15 for method for producing wafer notches with rounded corners and a tool therefor.
Invention is credited to Garvin, James F. JR., Guldi, Richard L., Mukerjee-Roy, Moitreyee.
Application Number | 20030089931 10/323839 |
Document ID | / |
Family ID | 26766214 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030089931 |
Kind Code |
A1 |
Guldi, Richard L. ; et
al. |
May 15, 2003 |
Method for producing wafer notches with rounded corners and a tool
therefor
Abstract
A semiconductor wafer for use in the fabrication of
semiconductor devices which includes a circular wafer (13) of
semiconductor material having a perimeter and a notch (11) having a
wall disposed in the wafer and extending to the perimeter which
includes a preferably rounded apex (5) interior of the perimeter
and a pair of rounded intersections (7, 9) between the wall and the
perimeter. The notch is formed with a tool (23) for forming rounded
corners in the semiconductor wafer which includes a body of a
material having a hardness greater than the semiconductor wafer
which has a generally rounded or paraboloidally shaped front
portion having a forwardmost tip (25) portion and a wing portion
(27) extending outwardly from the body and having a taper narrowing
in the direction of the forwardmost tip portion. The wing portion
can be one or more spaced apart wing members or the wing portion
can be a single member which extends completely around the tool
axis. The notch is formed by rotating the tool and moving the tool
in a direction along a radius of the wafer until the wing portion
contacts the wafer and forms a rounded intersection between the
notch and the wafer perimeter in the shape of the intersection of
the rounded tip portion and the wing of the tool.
Inventors: |
Guldi, Richard L.; (Dallas,
TX) ; Garvin, James F. JR.; (Carrollton, TX) ;
Mukerjee-Roy, Moitreyee; (Dallas, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
26766214 |
Appl. No.: |
10/323839 |
Filed: |
December 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10323839 |
Dec 20, 2002 |
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09781446 |
Feb 13, 2001 |
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09781446 |
Feb 13, 2001 |
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09289499 |
Apr 9, 1999 |
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6448154 |
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60081986 |
Apr 16, 1998 |
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Current U.S.
Class: |
257/259 |
Current CPC
Class: |
H01L 21/67092 20130101;
H01L 29/0657 20130101; B24B 9/065 20130101; Y10S 438/975 20130101;
B24D 5/02 20130101 |
Class at
Publication: |
257/259 |
International
Class: |
H01L 029/80 |
Claims
1. A semiconductor wafer for use in the fabrication of
semiconductor devices which comprises: (a) a circular wafer of
semiconductor material having a perimeter; and (b) a notch having a
wall disposed in said wafer and extending to said perimeter, said
notch including: (i) an apex interior of said perimeter; and (ii) a
pair of rounded intersections between said wall and said
perimeter.
2. The wafer of claim 1 wherein said apex is rounded.
3. A tool for forming rounded corners in a semiconductor wafer for
use in the fabrication of semiconductor devices, which comprises:
(a) a body of a material having a hardness greater than said
semiconductor wafer, said body having: (i) a generally rounded
front portion having a forwardmost tip portion; and (ii) a wing
portion extending outwardly from said body and having a taper
narrowing in the direction of said forwardmost tip portion.
4. The tool of claim 3 wherein said body is formed of a material
taken from the class consisting of silicon carbide and diamond.
5. The tool of claim 3 wherein said rounded front portion is in the
shape of a paraboloid.
6. The tool of claim 4 wherein said rounded front portion is in the
shape of a paraboloid.
7. The tool of claim 3 wherein said wing portion includes a
plurality of spaced apart wing members.
8. The tool of claim 4 wherein said wing portion includes a
plurality of spaced apart wing members.
9. The tool of claim 5 wherein said wing portion includes a
plurality of spaced apart wing members.
10. The tool of claim 6 wherein said wing portion includes a
plurality of spaced apart wing members.
11. The tool of claim 3 wherein said body has a major axis and said
wing portion extends completely around said axis.
12. The tool of claim 4 wherein said body has a major axis and said
wing portion extends completely around said axis.
13. The tool of claim 5 wherein said body has a major axis and said
wing portion extends completely around said axis.
14. The tool of claim 6 wherein said body has a major axis and said
wing portion extends completely around said axis.
15. A method of providing a semiconductor wafer for use in the
fabrication of semiconductor devices, which comprises the steps of:
(a) providing a tool having body of a material having a hardness
greater than said semiconductor wafer, said body having: (i) a
generally rounded front portion having a forwardmost tip portion;
and (ii) a wing portion extending outwardly from said body and
having a taper narrowing in the direction of said forwardmost tip
portion; (b) providing a circular semiconductor wafer having a
perimeter; and (c) forming a notch in said perimeter of said
semiconductor wafer with said tool.
16. The method of claim 15 wherein said rounded front portion is in
the shape of a paraboloid.
17. The method of claim 15 wherein said wing portion includes a
plurality of spaced apart wing members.
18. The method of claim 16 wherein said wing portion includes a
plurality of spaced apart wing members.
19. The method of claim 15 wherein said body has a major axis and
said wing portion extends completely around said axis.
20. The method of claim 16 wherein said body has a major axis and
said wing portion extends completely around said axis.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method producing wafers with
rounded corners in the notch used for alignment for use in the
fabrication of semiconductor devices and a tool for producing such
wafers.
[0003] 2. Brief Description of the Prior Art
[0004] The fabrication of semiconductor devices generally starts
with a slice or wafer of semiconductor material on which the
semiconductor devices are fabricated. Such wafers are generally
thin in width and have a pair of surfaces with the corners at the
perimeter of the wafer generally being rounded.
[0005] In order to properly align the semiconductor wafers in
processing equipment during the fabrication of semiconductor
devices on the wafers, it has been necessary to provide a physical
indication on the wafer to assist in such wafer alignment. The
general such physical indication in the prior art has been
formation of a flat end portion on the otherwise circular wafer
with this indication more recently having been changed to a
triangularly-shaped or parabolically-shaped notch at the wafer
perimeter. A problem with these forms of wafer alignment is that
the flat or notch regions used for alignment generally have sharp
corners, particularly in the case where notches are used. These
sharp corners generate particles during handling which can have
deleterious effects during subsequent processing operations. In
addition, damage from sharp corners may propagate into the wafer
during device fabrication, causing eventual breakage and yield
diminution.
[0006] It has also been determined that there is often a thick
resist buildup at the sharp corner made between the notch and the
perimeter of the wafer which is difficult to remove by ashing and
chemical treatment. To date, it has not been appreciated that the
sharp edges or corners located in the notch contribute to the above
problems and it is not known that there has been any attempt in the
prior art to remove the sharp corners from the notch and the
regions connected to the notch.
SUMMARY OF THE INVENTION
[0007] In accordance with the present invention, the above
described problems of the prior art wafer and particularly such
wafer using a notch for alignment are minimized and there is
provided a method of fabricating semiconductor devices on a wafer
having a notch for alignment and tools for effecting such method
for minimization of the above described problem and rounding of the
junction of the notch and wafer perimeter as well as the notch apex
and edges of the notch running from the wafer perimeter to the
notch apex.
[0008] Briefly, there are provided one or more tools in the form of
a grinding wheel or belt which rounds all sharp edges or corners
existing in the notch either when forming the notch or when
altering the shape of an already existing notch to eliminate all
sharp corners both at the apex of the notch as well as along all
intersections of the walls of the notch with the planar wafer
surface and also with the perimeter of the wafer. Conventional
stress relief etching in hydrogen fluoride plus nitric acid plus
phosphoric acid or other suitable acidic solutions enhances notch
corner rounding. In such a solution, rounding occurs as a normal
consequence of etching both the top and side surfaces, the corners
etching faster by virtue of being exposed to a greater volume of
etchant. A wafer having a notch with rounded corners reduces the
likelihood of edge damage during wafer handling due to flat
finding, wafer centering, etc., prevents thick resist buildup at
corners of the notch during photolithography, eliminates particle
contamination from resist buildup at sharp notch corners and
reduces ash time required to remove thick resist buildup.
[0009] The grinding tool provided in accordance with the present
invention has a rounded front end somewhat in the shape of half of
a paraboloid. The tool is formed of a material which is harder than
the material of which the wafer is made. Generally, the grinding
surface of the tool is fabricated from diamond with an approximate
800 mesh grit. The tool also includes one or more wing portions
extending outwardly from the paraboloid surface and set back from
the tool front tip a distance generally equal to the ultimate depth
of the notch from the wafer perimeter. The wing is tapered in the
direction toward the tool front tip. In the case of a single wing,
such wing can extend completely around the entire tool or can
extend only partially around the tool. The tool is rotated it axis
which is the major axis of the paraboloid and moved against the
edge of the wafer in a direction along a radius of the wafer either
in a predetermined location on the wafer edge or into a previously
formed notch in the wafer perimeter. The tool will grind away the
wafer to form a notch until the wing or wings contact the perimeter
of the wafer. At that point, the tool will grind the corner made
between the notch and the wafer perimeter into the shape of the
round on the tool between the paraboloid portion of the tool and
the wing portion of the tool, this being rounded. A second grind
step is optionally provided at this time using an identically
shaped wheel with finer grit size to remove surface damage, if
desired. A third grind step may be provided in order to round the
top edge of the wafer along the intersection of the edge of Th.
notch with the top and/or bottom planar surfaces of the wafer.
Examples are grinding this surface using a cylindrical grinding
wheel rotating against the edge or using a long belt with diamond
grit on its interior surface that revolves about an axis parallel
to the top wafer surface. The tool is then removed with the wafer
now ready for processing in standard manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a top view of a typical prior art wafer having a
notch therein for alignment;
[0011] FIG. 2 is a view taken along the line 2-2 of FIG. 1;
[0012] FIG. 3 is a perspective view of a tool in accordance with
the present invention which has just ground a notch in accordance
with the present invention;
[0013] FIG. 4 is an enlarged view of the rounded corner formed by
use of the tool of FIG. 3;
[0014] FIG. 5 is a schematic diagram showing a second type of
grinding tool which can be used in accordance with the present
invention;
[0015] FIG. 6 is a schematic diagram showing a third type of
grinding tool which can be used in accordance with the present
invention;
[0016] FIG. 7 is a schematic diagram showing the trajectory along
the notch of the grinding wheel of FIG. 6; and
[0017] FIG. 8 is a schematic diagram of a fourth type of grinding
tool which can be used in accordance with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Referring to FIGS. 1 and 2, there is shown in typical prior
art wafer 1 having a notch 3 therein. While the perimeter of the
wafers in FIGS. 1 and 2 as well as in FIGS. 3 and 4 which are
described hereinbelow are shown to have sharp corners, it should be
understood that the wafers are generally purchased with the corners
along the perimeter away from the notch or flat rounded or these
corners are rounded before commencement of fabrication of
semiconductor device on the wafer. As can be seen, there are sharp
corners at the apex 5 of the notch, at the intersections 7, 9 of
the notch with the outer edge of the wafer and at the intersections
of the notch with the upper and lower surfaces or opposing major
surfaces of the wafer. These corners cause the problems enumerated
above and often result in resist buildup, especially on the surface
of the wafer on which device fabrication is taking place and where
a sharp corner exists, particularly at locations 7, 9.
[0019] Referring to FIGS. 3 and 4, there is shown a notch 11 formed
in a semiconductor wafer 13 in accordance with the present
invention. The apex 15 of the notch 11 as well as the junctions 17
and 19 of the side walls 21 of the notch are rounded. Accordingly,
there are no sharp edges with the wafer outer edge or perimeter 22
to break off or to cause damage to the wafer during handling.
[0020] The rounded corners are formed by use of a grinding tool 23
as shown in FIG. 3 which is formed of a mesh of diamond grit or
other hard material and which has a rounded or paraboloidally
shaped nose portion 25. Spaced backward from the front tip of the
nose portion 25 are one or more wings 27 having a tapered portion
29 in the direction of the front tip of the nose portion. The
distance between the front tip of the nose portion 25 and the
forwardmost portion of the wing or wings 27 is about the depth of
the notch 11 which is formed by the tool. The rounded corners 17,
19 are formed by and take the shape of the tapered portion 29 of
the wing or wings 27. Though two wings 27 are shown, it should be
understood that one or more wings can be used and that the width of
the wings in a direction around the tool axis can be anything from
a small fraction of the total circumference about the tool axis to
the entire circumference about the tool axis.
[0021] Referring to FIG. 5, there is shown a grinding tool 31 that
can be used in accordance with the present invention for grinding
the sharp corners 33 of a wafer 35. The grinding tool 31 is shown
in the form of a wheel and is translated toward the wafer surface
in the z-direction and then along an appropriate path in the x- and
y-directions to follow the complete wafer edge trajectory. The
z-position and wheel tilt can be adjusted as the wheel moves
farther from the notch edge (increase in y value) to produce a
gradual edge rounding instead of an abrupt rounding. The wheel
position is moved to follow the trajectory of the notch along its
entire extent. Both top and bottom notch corners can be smoothed in
this way. A second step grinding can be provided with a finer grit
wheel for reduction in mechanical damage.
[0022] Referring to FIG. 6, there is shown a further embodiment of
a grinding wheel 41 which rotates about the axis of rotation 43.
This grinding wheel allows the top edge rounding to be accomplished
by maintaining the wheel without tilt or z-motion by simply
translating the wheel around the notch perimeter 45 from the
starting position 47 in the direction of the arrow 49 as shown in
FIG. 7.
[0023] Referring to FIG. 8, there is shown a still further
embodiment of a system for rounding the sharp edges 51 of the notch
53. There is shown a belt 55 which extends above and below the
wafer 57 so that it contacts the two sharp edges in the notch 53.
The interior surface 63 of the belt 55 has a diamond grit embedded
therein. The belt 55 is moved around the notch in the direction of
the arrows 59 with the belt rotating about its axis 61. As the belt
55 is moved around the notch 53, the belt also rotates about the
axis 61 which is also moving with the belt. The belt interior
surface 63 impinges against the corners or sharp edges 51 with the
surface thereof which contains the grit, thereby grinding away and
rounding the sharp edge. As in the prior embodiment, a subsequent
stop can be a repeat of the grinding process with a belt having a
finer grit.
[0024] It can be seen that there has been provided a tool which
forms a notch in a semiconductor wafer having rounded corners for
purposes alignment during semiconductor fabrication. There is also
provided the notch which has the rounded corners.
[0025] Though the invention has been described with respect to
specific preferred embodiments thereof, many variations and
modifications will immediately become apparent to those skilled in
the art. It is therefore the intention that the appended claims be
interpreted as broadly as possible in view of the prior art to
include all such variations and modifications.
* * * * *