Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
1997-11-20
2001-02-06
Picardat, Kevin M. (Department: 2823)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C438S106000, C438S110000, C225S096000, C225S104000
Reexamination Certificate
active
06184063
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Cross reference is made to the following commonly assigned co-pending patent applications, each being incorporated into the present application by reference.
SERIAL NO.
TITLE
FILED
08/367,970
METHOD AND APPARATUS FOR
01/03/95
BREAKING AND SEPARATING DIES
FROM A WAFER
08/485,168
METHOD AND APPARATUS FOR
06/07/95
BREAKING AND SEPARATING DIES
FROM A WAFER
TI-23376
UV EXPOSURE OF STRETCHED
HEREWITH
(Attorney's
UV-TAPE ON WAFER FRAMES TO
Docket #)
ELIMINATE PREMATURE TAPE
DELAMINATION FROM THE FRAME
TI-24718
METHOD AND APPARATUS FOR
HEREWITH
(Attorney's
STRETCHING SAW FILM TAPE
Docket #)
AFTER BREAKING A PARTIALLY
SAWN WAFER
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the field of integrated circuits and wafer processing, and more particularly to methods and apparatus for breaking a semiconductor wafer into individual die including those having an exceptionally high aspect ratio.
BACKGROUND OF THE INVENTION
A cost effective way of fabricating integrated circuit die is to simultaneously form multiple circuits on a single semiconductor wafer and then break the wafer into die. This form of batch processing, or wafer processing, allows the cost of each step of the fabrication process to be spread among many devices and reduces the handling that would be required to process each device individually. A typical process flow includes many lithography, deposition, doping, etching, and testing steps. As the circuits are formed on the wafer, horizontally and vertically extending “streets” are defined in the wafer which extend between and separate the circuits from one another. These streets then may typically be scribed or partially sawn process to form kerfs. The wafer can then be broken along these kerfs to form the individual die which can then be packaged with leads.
When a micromechanical wafer is broken to form the individual die, care must be taken so as to minimize the generation of particles, and prevent the die edges from touching. Conventionally, the completed wafer is first placed on a flexible membrane or wafer stretch tape having an adhesive on one side to secure the wafer to the tape. This adhesive tape maintains the individual die in place as the dies are formed during the break process. Care must be taken to prevent the tape from shrinking back to the point where the die edges could touch one another and cause damage. This is especially critical for micromechanical devices having moving parts.
Conventionally, the die formed on a wafer are generally square, or slightly rectangular and thus have a low aspect ratio. That is, the length of the die sides are about equal and the aspect ratio approaches 1:1. These generally square die can thus be separated using many conventional techniques. One such technique is shown in commonly assigned U.S. Pat. No. 3,562,057. A spherical dome can be driven downward against the backside of the wafer to cause the wafer to break along the intersecting kerfs and form individual die. A spherical dome is appropriate when the dies are generally square, that is, having a low aspect ratio. Another similar device is shown in U.S. Pat. No. 5,104,023 whereby a hemispherical body presses a wafer against a resilient rubber mat. Such a device breaks the wafer along the kerfs in both directions from the wafer center outward, that is, such that cracking of the wafer is initiated from a center thereof towards the periphery thereof.
However, such hemispherically shaped domes are unsuitable for separating wafer die that have a high aspect ratio, such as rectangular spatial light modulators used in display systems, and exceptionally elongated die used in printer systems. Such systems incorporating elongated die are shown in commonly assigned U.S. Pat. No. 5,079,544 to DeMond, et al. entitled “Standard Independent Digitized Video System” and U.S. Pat. No. 5,105,369 to Nelson, entitled “Printing System Exposure Module Alignment Method and Apparatus of Manufacture”, the teachings of each incorporated herein by reference. The spatial light modulator die used in the display system typically has an aspect ratio of 9:16. The die used in the printer system is comprised of an integrated circuit formed as an exceptionally elongated array of micromirrors, having a length of about 5″ and an aspect ratio of 1:25. Due to the extreme length of this die, especially in view of the short width, this die can not be suitably separated from the other dies of a wafer using a spherically shaped dome as the die would fracture in the long direction. A plurality of elongated dies formed on a wafer for displays and printers is shown in FIG.
2
(
a
) and FIG.
2
(
b
), respectively, of the present application.
It is desired to provide a method and apparatus to be used for breaking die having a high aspect ratio, ie. those being rectangular rather than square, without fracturing the die in the long dimension during the breaking process. Such a method and apparatus should reduce the generation of silicon particles during wafer break while preventing the die edges from rubbing with one another during and after the break.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a wafer break method and apparatus using a multi-radii domed anvil having a first radii in the X-direction and a second radii in the Y-direction. The radius of curvature in the X-direction typically has a larger radii and is used to break the wafer and separate the die along the longer sides. The dome radius of curvature in the Y-direction is smaller than the radius of curvature in the X-direction, and is used to break the wafer into die along the short sides of the die. The two different radii of curvature evenly concentrate the breaking forces down the kerfs in 2 different directions, independently. In an alternative embodiment, the anvil is curved in the X-direction and flat in the Y-direction, and is thus a cylindrical dome.
The method of the invention comprises mounting the wafer having integrated circuits formed thereon onto a flexible membrane or wafer tape. The membrane supporting the wafer is inverted, and a multi-radii wafer dome is pressed against the membrane proximate the underside of the wafer such that the dome larger radii along the X-direction is aligned with the elongated sides of the circuits. The X-Y axis of the dome is precisely aligned with the X-Y axis of the wafer. By pressing the dome against the wafer in this orientation, the breaking forces are evenly directed down the kerfs to break the wafer along the streets in both the X and Y directions. The tape is stretched by the dome while applying a vacuum thus forcing the tape to conform to the surface of the dome, ensuring that all die are broken. This stretching insures that the die remain separated from one another while remaining on the tape after a wafer break. Subsequently, pick and place equipment is utilized to remove the die from the tape, and these die are packaged.
By using a break dome having different radii in the X and Y-direction, a single dome can be used to break a wafer into die having a moderately high aspect ratio, without accidentally fracturing the die in the long dimension. By controlling the direction and amount of the breaking force in the X and Y directions, independently, the break process reduces silicon particle generation, which is critical when manufacturing micromechanical devices. The wafer is broken in the inverted position, and any particles generated will fall downwardly and away from the die.
In an alternative embodiment, a cylindrical anvil that is flat (no curvature) in the X-direction and curved in the Y-direction is used to separate die having an exceptionally high aspect ratio, as shown in FIG.
2
(
b
). The wafer ends are first broken away along the short ends of the elongated circuits with a custom anvil. Then, the cylindrical anvil is aligned such that the X-direction having no curvature is aligned with the long sides of the circuits. The anvil is pressed against the wafer, and wafer wraps around th
Croff R. Scott
McKenna Robert G.
Tom Edwin L.
Brady III Wade James
Brill Charles A.
Collins D. Mark
Picardat Kevin M.
Telecky , Jr. Frederick J.
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