Semiconductor device manufacturing: process – Semiconductor substrate dicing – Having a perfecting coating
Reexamination Certificate
2000-11-28
2002-06-04
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Semiconductor substrate dicing
Having a perfecting coating
C438S459000
Reexamination Certificate
active
06399464
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to fabrication of semiconductor structures. More particularly, the present invention relates to chip packaging processes and pre-packaging wafer preparation including wafer thinning and die separation.
2. The Relevant Technology
In the microelectronics industry, a substrate refers to one or more semiconductor layers or structures which includes active or operable portions of semiconductor devices. In the context of this document, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term substrate refers to any supporting structure including but not limited to the semiconductive substrates described above. The term semiconductor substrate is contemplated to include such structures as silicon-on-insulator and silicon-on-sapphire.
In the microelectronics industry, the process of miniaturization entails the shrinking of individual semiconductor devices and crowding more semiconductor devices into a given unit area. Included in the process of miniaturization is the effort to shrink the size of chip or die packages in the fabrication sequence, chip packaging follows the fabrication of chips or dies upon a semiconductor substrate or wafer.
After a semiconductor wafer has been fabricated and the circuits thereon have been processed to completion, the die or chip packaging process begins. The purpose of the die or chip packaging process is to place individual die into a package which can then be inserted into a printed circuit board or other substrate so as to connect the die to a larger functional circuit.
Prior to chip packaging, other steps may be needed to be undertaken in order to prepare a wafer. One step is the reducing of the thickness of a wafer. It is desirable to reduce the thickness of a wafer because a greater amount of time and expense is required to saw through a thick wafer in order to separate the dies thereon. Typically, wafer sawing produces a precise die edge. Nevertheless, sawing adds expense and processing time, and requires expensive machinery.
It may also be desirable to thin the wafer if contaminants have entered into the backside of a wafer opposite its circuit side where the electrical circuitry has been formed. For instance, dopants may have entered the backside of the wafer during a fabrication process. These dopants will form electrical junctions that may interfere with the circuitry on the front side of the wafer. Thus, in order for the electrical circuits to properly operate, the thinning of the contaminated portion of the backside of the wafer may be required.
Conventionally, thing of the wafer is performed prior to separating the dies from the wafer. This thinning step typically reduces the wafers to a thickness between 0.762 millimeters to about 0.2 millimeters. Several processes are available to perform the thinning operation. Specifically, a mechanical or chemical-mechanical operation, such as planarization, can be used to thin the wafers. Also, the backside of the wafer can be chemically etched in order to reduce the thickness thereof
The wafer thinning operation can cause scratching of the top side of the wafer or the inducement of stress during the abrading operation which may cause the wafer to break. In order to perform the thinning operation, the circuit side of the wafer is placed face down upon a surface. Preferably, the circuit side of the wafer will be protected from scratching or other surface defect. A material removal operation then begins to remove material from the backside of the wafer.
Where material is moved from the backside of the wafer using a chemical etchant, it is also necessary to protect the circuit side of the wafer. Such a method includes the forming of a photoresist layer on the circuit side of the wafer. Sheets composed of a polymer material having an adhesive back can also be fitted over the circuit side of the wafer to protect the same.
It is desirable to thin wafers before packaging in order to reduce the cost of packaging the dies after separation. The separation process becomes expensive as the wafer thickness goes up. Particularly, a deeper die attach cavity is required if a wafer is thicker. As such, the combination of a deeper die attach cavity and the thicker die results in a more expensive chip package. Thus, wafer thinning is an important part of reducing the cost of chip packaging.
FIG. 1
depicts a grinding table
12
having an adhesive film
14
thereon. A semiconductor substrate
10
is on adhesive film
14
. Semiconductor substrate
10
includes a die side
16
and abase layer
18
. Base layer
18
has a back surface
20
thereon. Die side
16
has a plurality of die formed therein which are to be singulated by a division of semiconductor substrate
10
into a plurality of pieces. Back surface
20
is subjected to a back grinding process. The purpose of the back grinding process to be performed upon back surface
20
is to thin base layer
18
prior to singulating die side
16
. As seen in
FIG. 1
, a distance
25
indicates a distance between a center of semiconductor substrate
10
and a grinding force
26
applied to back surface
20
by a grinding wheel
24
via a grinding pad
22
thereon. With the increase in distance
25
and/or an increase in grinding force
26
, the torque product of distance
25
and grinding force
26
increases. With the increase in torque, the propensity of semiconductor substrate
10
to crack or break improperly also increases. As such, it would be desirable to reduce the propensity of semiconductor substrate
10
to break during a substrate thinning process.
After wafer thinning, the wafer is divided. Conventional techniques for die separation involve sawing and scribing processes. The sawing process uses a saw and a table to cut scribe or saw lines in the circuit side of the wafer. The wafer is placed upon the table and a rotating saw blade is brought down in contact with the circuit side of the wafer. As each scribe or saw line is cut into the wafer, a stress line forms along the crystalline interior of the wafer substantially perpendicular to the backside of the wafer. After the scribe or saw lines are cut into the wafer, a stress is applied to the scribe lines to separate the wafer and individual die. This stress may be applied via a roller or other pressure technique. Alternatively, the rotating saw blade can cut all the way through the wafer to separate the wafer and individual die.
An alternative technique to sawing the wafer into singulated dies is a scribing technique which cuts a scratch along scribe lines on the circuit side of the wafer by application of a force from a diamond-tip scribe. As in sawing, the dies are separated by applying a stress to the wafer, such as a roller applied to a surface of the wafer. Upon the application of the pressure from the roller, individual dies will be separated as they break away from the consolidated wafer along the scratched scribe lines. Due to the crystalline structure of the wafer, the separation of the die will follow the scribe line approximately perpendicular to the opposing surfaces of the wafer. As such, stress will cause the wafer to break along the scratched lines.
FIG. 2
depicts semiconductor substrate
10
including die side
16
and base layer
18
. Semiconductor substrate
10
has saw or scribe lines marked within die side
16
and above stress lines. Each scribe line is cut into die side
16
by a cutting tool
28
with a cutting force
30
. Cutting tool
28
can be a diamond tipped scribe or a rotating saw blade. Once the saw or scribe lines are cut within die side
16
, a roller
32
having a surface
34
applies a roller force
36
to die side
16
to separate a singulated die
19
along each stress line.
While it
Ball Michael B.
Heppler Steven W.
Muntifering Tom A.
Jr. Carl Whitehead
Micro)n Technology, Inc.
Vockrodt Jeff
Workman & Nydegger & Seeley
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