Severing by tearing or breaking – Methods – With preliminary weakening
Reexamination Certificate
1999-03-01
2001-02-13
Rachuba, M. (Department: 3724)
Severing by tearing or breaking
Methods
With preliminary weakening
C219S121610
Reexamination Certificate
active
06186384
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of cleaving a brittle material using a point heat source which is capable of providing a thermal stress to the brittle material.
As conventional methods of cutting a brittle material such as semiconductor wafers, ceramic wafers and glass substrates, a dicing method and a scribing method have generally been known. The dicing method is carried out by use of a diamond blade. The scribing method is carried out by forming a crack on a surface of the wafer and then applying a mechanical stress to the wafer to cut the wafer along the scribing lines.
The above conventional methods have disadvantages in cutting the material on which electric circuits are formed. The above conventional methods allow generation of micro-cracks or particles.
In order to solve the above problems with micro-cracks or particles, it was proposed to use a point heat source such as a laser beam for applying a thermal stress to the brittle material to cleave the same. This method is, for example, disclosed in Japanese laid-open patent publication No. 3-13040. This method will be described with reference to
FIG. 1. A
brittle material
21
is intended to be cleaved along a cleaving line
24
. A recess
22
is first formed by use of a mechanical tool at a cleaving starting point which is defined as a crossing point of the cleaving line
24
and one side edge of the brittle material
21
. A point heat source is used to locally apply a heat point
23
which is positioned on the cleaving line
24
and in the vicinity of the recess
22
so that a tensile stress is generated in a direction along tangential lines of virtual isothermal lines defined by the heat point
23
. For this reason, the tensile stress causes a crack from the recess
22
. The crack propagates from a tip of the recess
22
toward the point of the heat point
23
. The tip of the crack propagates from the recess
22
toward the point of the heat source
23
so that the crack extends to a position which is close to but distanced from the point of the heat source
23
. The crack, however, does not reach the point of the heat source
23
because no tensile stress appears on the point of the heat source
23
. The point of the heat source
23
is moved to a point which is distanced from the tip of the crack and also which is positioned on a tangential line of the cleaving line
24
at the tip of the crack, so that the tip of the crack further propagates along the cleaving line
24
. Namely, the heat source point
23
is positioned not just on the cleaving line but in the vicinity of the cleaving line
24
.
In the above conventional cleaving method using the point heat source, heating conditions such as the position of the heat source
23
and the heating time have been found by trial-and-error method, wherein a distance between the tip of the crack and the point of the heat source
23
as well as a heating time should be varied to determine an optimum heating point and an optimum heating time for effectively and efficiently adding the thermal stress to the crack of the brittle material strip. The optimum heating point and the optimum heating time depend upon the material of the brittle strip and the width thereof. This means that the optimum distance between the tip of the crack and the point of the heat source
23
as well as the optimum heating time depend upon the material of the brittle strip and the width thereof, for which reason the optimum distance between the tip of the crack and the point of the heat source
23
as well as the optimum heating time are required to be found for every different materials of the brittle strip and the different widths thereof. Even if the distance between the tip of the crack and the point of the heat source as well as the heating time are required by the trial-and-error method, then those distance and heating time might be slightly different from the actual optimum distance and heating time. The conventional cleaving work is time-consuming procedure. This makes it difficult to realize automation of the laser beam machining.
In the above circumstances, it had been required to develop a novel method of cleaving a strip of brittle material free from the above problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel method of cleaving a strip of brittle material free from the above problems.
It is a further object of the present invention to provide a novel method of cleaving a strip of brittle material which is capable of automatically deciding optimum conditions, for example, position and time of a point heat source to be applied onto the brittle materiel to realize automation of a laser beam machining for various strips of brittle material which are different in width of the strip and materials.
It is a still further object of the present invention to provide a novel method of cleaving a strip of brittle material which enables to shorten the necessary time for finding the optimum distance between a tip of a crack and a point of a heat source as well as the optimum heating time for suppressing an ultimate maximum temperature to prevent any thermal influence to devices formed or the strip of brittle material.
The first aspect of the present invention provides a method of determining optimum heating conditions for applying a pulse laser point heat source onto a strip of a brittle material at its position in the vicinity of a tip of a crack of the strip for cleaving the strip by a thermal stress, wherein at least one of a non-dimensional pulse time of the pulse laser point heat source, a non-dimensional distance of the pulse laser point heat source from the tip of the crack, and a non-dimensional heating area is decided so that a ratio of non-dimensional stress intensity factor to temperature takes just or approximately a maximum value.
The second aspect of the present invention provides a method of cleaving a strip of a brittle material along a predetermined cleaving line by applying a pulse laser point heat source onto the strip of the brittle material to locally apply a thermal stress in the vicinity of a tip of a crack of the strip, wherein the pulse laser point heat source is applied under optimum heating conditions decided by deciding at least one of a non-dimensional pulse time of the pulse laser point heat source, a non-dimensional distance of the pulse laser point heat source from the tip of the crack, and a non-dimensional heating area so that a ratio of non-dimensional stress intensity factor to temperature takes just or approximately a maximum value.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.
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patent: 3790744 (1974-02-01), Bowen
patent: 4615765 (1986-10-01), Levinson et al.
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patent: 5585018 (1996-12-01), Kanaoka et al.
patent: 5776220 (1998-06-01), Allaire et al.
patent: 5939010 (1999-08-01), Yuyama et al.
patent: 5968382 (1999-10-01), Matsumoto et al.
patent: 5984159 (1999-11-01), Ostendarp et al.
patent: 5998759 (1999-12-01), Smart
patent: 6023039 (2000-02-01), Sawada
Flores-Saánchez Omar
NEC Corporation
Rachuba M.
Young & Thompson
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