Semiconductor device manufacturing: process – Semiconductor substrate dicing – With attachment to temporary support or carrier
Reexamination Certificate
2000-07-20
2002-01-08
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Semiconductor substrate dicing
With attachment to temporary support or carrier
C436S169000, C436S169000, C436S169000
Reexamination Certificate
active
06337258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of dividing a wafer and a method of manufacturing a semiconductor device, and more particularly, to manufacturing steps of dicing semiconductor elements formed on a wafer into chips and sealing the chips in packages. These methods are suitably used in reducing semiconductor packages in size and thickness and adopted when a lager wafer is used.
The manufacturing steps for a semiconductor device are roughly classified into two: one is a step for forming patterns of various semiconductor elements on a wafer (semiconductor substrate) and the other is a step for dicing the semiconductor elements formed on the wafer into chips and sealing them in packages. Recently,, to reduce manufacturing cost of semiconductor devices, the diameters of wafers have been increased. At the same time, to enhance the packaging density, the packages are desired to be miniaturized (decreased in size and thickness).
Conventionally, in order to seal a semiconductor chip in the miniaturized package, a wafer is reduced in thickness prior to dicing the wafer into chips. More specifically, a bottom surface of a wafer (opposite to a pattern formation surface (major surface) of the wafer) is lapped by a grindstone and polished by free grind grains, and thereafter the wafer is diced. When the wafer is lapped, the pattern formation surface of the wafer is protected by attaching an adhesive sheet thereon or coated with a resist. Thereafter, grooves are formed along dicing lines formed on the major surface of the wafer. These grooves are formed by means of a diamond scriber, a diamond blade, a laser scriber, or the like. In the dicing step, a half-cut method in which the wafer itself is diced to ½ of the thickness of the wafer or diced until the wafer is about 30 &mgr;m thick; a half-cut method in which an adhesive sheet is attached to the bottom surface of the wafer, and thereafter, the wafer is diced in the same manner as above; or a full-cut method in which the wafer with the adhesive sheet attached thereto is completely diced until the adhesive sheet is cut into to a depth of 20 to 30 &mgr;m. The half-cut method requires a chip-separation step. When the wafer is used alone, the wafer is separated into chips by sandwiching it between soft films and applying an external force to the wafer by means of a roller or the like. When the adhesive sheet is attached to the wafer, the wafer is separated into chips by applying an external force to the wafer via the sheet. The chips thus separated are removed from the sheet in the following manner. The bottom surface of the sheet is pushed up by a pickup needle provided in a die bonding device. The needle penetrates the sheet and comes in direct contact with the bottom surface of each chip and further lifts up the chip to remove it from the sheet. The surface of the chip thus removed is adsorbed by means of a tool called a “collet” and mounted on an island of a lead frame. After each of the pads of the chip is electrically connected to an inner lead portion of the lead frame by means of wire bonding, the resultant chip is sealed in a package. The chip is mounted on the island by previously applying a conductive paste on the island, by using gold-silicon eutectic, or by a method in which a thin metal film is deposited on the bottom surface of the wafer and then the wafer is mounted by use of solder.
FIGS. 1
to
7
are used for explaining an example of the conventional wafer dividing method and semiconductor device manufacturing method mentioned above. More specifically,
FIG. 1
illustrates a step of attaching a surface protection tape on a wafer;
FIG. 2
is a step of lapping and polishing the bottom surface of the wafer;
FIG. 3
is a step of removing the surface protection tape;
FIGS. 4A and 4B
are steps of fixing the wafer on a fixing sheet;
FIG. 5
is a step of dicing the wafer;
FIG. 6
is a step of picking up separated chips; and
FIG. 7
is a die bonding step.
As is shown in
FIG. 1
, after an element formation step is completed, the bottom surface of a wafer
1
is fixed on a porous chuck table
2
. A protection tape
3
is attached to a pattern formation surface
1
′ of the wafer
1
by moving an attachment roller
4
in the direction indicated by an arrow in the figure while rotating it. Subsequently, as shown in
FIG. 2
, the wafer
1
is fixed on a chuck table
5
with the pattern formation surface
1
′ thereof (having the protection tape
3
attached thereto) faced down. The bottom surface of the wafer
1
is lapped and polished to a predetermined depth (i.e. a predetermined thickness of a finished chip) by means of a grindstone
6
. Thereafter, as shown in
FIG. 3
, a tape
7
(for use in removing the protection tape
3
) is attached to the protection tape
3
and then the protection tape
3
is removed from the pattern formation surface
1
′. Subsequently, a flat ring
8
is fixed on a wafer fixing sheet
9
, as shown in
FIG. 4A
, to prevent the sheet
9
from becoming slack or wrinkled. In this state, the wafer
1
is fixed on the sheet
9
within the opening of the flat ring
8
, as shown in FIG.
4
B. The sheet
9
having the wafer
1
fixed thereon and the flat ring
8
are fixed on a dicing chuck table
10
. The wafer
1
is diced (full-cut) by a dicing blade
11
into chips
12
(see FIG.
5
). Thereafter, as is shown in
FIG. 6
, a pickup needle
13
is allowed to pass through the sheet
9
from the bottom thereof and brought in contact with the bottom surface of each chip
12
. The chip
12
is pushed upward by the needle
13
to thereby remove it from the sheet
9
. The separated chip
12
is mounted on an island
14
of a lead frame, as shown in
FIG. 7
, by using a die bonding adhesive
15
such as a conductive paste. Thereafter, inner lead portions (not shown) of the lead frame are wire-bonded to pads of the chip
12
, and the resultant structure is sealed into a package formed of a resin or ceramic. In this way, the semiconductor device are completely fabricated.
However, the above-described wafer dividing method and semiconductor device manufacturing method have the following problems (a) to (c).
(a) The wafer is easily broken while it is reduced in thickness by lapping. Even if the wafer is lapped with the protection tape being attached thereto, the wafer may warp by distortion due to the lapping. As a result, the wafer may be caught and broken during transfer within the lapping apparatus. The wafer is reduced in strength as the wafer becomes thin or large in diameter. Therefore, in the transfer method presently employed of transferring the wafer after it is reduced in thickness in order to apply various treatments, there is a high possibility of breaking the wafer. For example, the durable stress of the wafer is up to about 1.6 Kgf/mm
2
in the case of a wafer having a thickness of 400 &mgr;m, whereas, when the thickness of the wafer is reduced to 200 &mgr;m, the durable stress decreases to ¼ as low as 0.4 Kgf/mm
2
.
(b) Since two sheets are used for protecting the pattern formation surface and for holding the wafer at the time of dicing, cost for materials increases. Extra steps are required for attaching and removing each of the two sheets, so that the number of manufacturing steps also increases.
(c) When the wafer is diced, the bottom surface of the wafer is chipped more than the upper surface side, with the result that the breaking-resistance of the chip decreases. In addition, recently transistors, resistors and capacitors for monitoring various characteristics (hereinafter referred to as “TEG” (Test Element Group)) have been arranged on dicing lines to integrate devices with a high density, although they are arranged within the chip in conventional devices. Since the TEG devices are formed of oxide films, aluminum, etc., when the TEG devices are diced by using a diamond blade, the clogging of the blade easily occurs. As a result, the cutting edge of the blade is made dull. Therefore, when the TEG is arranged on the dicing lines, the
Kurosawa Tetsuya
Nakayoshi Hideo
Takyu Shinya
Tokubuchi Keisuke
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Le Dung A
Nelms David
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