Electric heating – Metal heating – By arc
Reexamination Certificate
2001-08-29
2003-05-27
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121800
Reexamination Certificate
active
06570124
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser processing method for processing a surface of a processing target using laser light, and specifically to a laser processing method preferably usable for ablating a processing target including an organic substance so as to form a flat face which is parallel or inclining with respect to an optical axis of the laser light.
2. Description of the Related Art
One method for processing an organic substance on a substrate by etching uses an ablation function of a laser beam such as, for example, an excimer laser beam.
FIG. 14
shows a schematic view illustrating a structure of a laser processing apparatus
200
usable for performing laser processing. The laser processing apparatus
200
is used for, for example, forming a recessed portion in a processing target
15
. The processing target
15
includes an organic sheet formed of, for example, polycarbonate (PC) or polyethylene terephthalate (PET) which is degraded when irradiated with light such as a laser beam. The laser processing apparatus
200
includes an X-Y stage
16
on which the processing target
15
is placed, and a laser oscillator
11
for emitting an excimer laser beam
12
toward the processing target
15
. The excimer laser beam
12
emitted by the laser oscillator
11
is provided with a prescribed pattern through a projection mask
13
, then is reduced in cross-sectional area by an objective optical system
14
, and is directed toward the processing target
15
fixed on the X-Y stage
16
.
FIG. 6
is a plan view of the projection mask
13
. The projection mask
13
is formed of a glass plate and a metal film provided on the glass plate so as to form a light shielding area
13
b
. An area of the glass plate which is not covered with the metal film is a rectangular light transmitting area
13
a
through which the excimer laser beam
12
is allowed to be transmitted.
A spot
21
c
of the excimer laser beam
12
on the projection mask
13
is elliptical. The spot
21
c
on the projection mask
13
covers the light transmitting area
13
a
so that the entirety of the light transmitting area
13
a
is uniformly irradiated with the excimer laser beam
12
. In
FIGS. 6
,
7
and
8
, arrow X represents a direction of longer sides
21
a
of the rectangular light transmitting area
13
a
, and arrow Y represents a direction of shorter sides
21
b
of the rectangular light transmitting area
13
a
. In this specification, the direction indicated by arrow X will be described as the “X direction”, and the direction indicated by arrow Y will be described as the “Y direction”.
The excimer laser beam
12
which is transmitted through the light transmitting area
13
a
of the projection mask
13
is reduced in cross-sectional area by the objective optical system
14
and collected on the processing target
15
fixed on the X-Y stage
16
. Thus, an image of the rectangular light transmitting area
13
a
is projected on the processing target
15
. The image on the processing target
15
reflects the reduction ratio of the objective optical system
14
. A surface of the processing target
15
irradiated with the excimer laser beam
12
is ablated with the excimer laser beam
12
. As a result, a recessed portion defined by faces parallel to an optical axis of the excimer laser beam
12
is formed in the processing target
15
.
A face inclining with respect to the optical axis of the excimer laser beam
12
can be formed in the processing target
15
by moving the processing target
15
while being irradiated with the excimer laser beam
12
.
With respect to
FIG. 12
, a method for producing the inclining face will be described.
The processing target
15
includes a substrate
15
a
and an organic sheet
15
b
bonded to the substrate
15
a
. For irradiating the processing target
15
with the excimer laser beam
12
, conditions for ablating only the organic sheet
15
b
are used. The excimer laser beam
12
transmitted through the rectangular light transmitting area
13
a
of the projection mask
13
is directed toward the processing target
15
. In this state, the processing target
15
is moved in the direction of arrow C shown in
FIG. 12
at a constant speed. A surface of the substrate
15
a
is perpendicular to the optical axis.
While the processing target
15
is moved in this manner, the irradiation of the excimer laser beam
12
is stopped. Therefore, the total amount of the excimer laser beam
12
received by a front portion of the processing target
15
is different from the total amount of the excimer laser beam
12
received by a rear portion of the processing target
15
. The terms “front” and “rear” are defined with respect to the direction in which the processing target
15
is moved. As a result of the above-mentioned difference in the total amount of received excimer laser beam
2
, the processing target
15
is etched to a different degree in the front portion compared to the rear portion. Therefore, the inclining face which inclines downward from the rear portion toward the front portion of the processing target
15
is formed. A face inclining at any angle can be formed by adjusting the intensity of the excimer laser beam
12
and the moving speed of the processing target
15
.
FIG. 7
shows a profile
29
(solid line) of the recessed portion obtained by ablating the surface of the processing target
15
by the laser processing apparatus
200
. Since the entirety of the light transmitting area
13
a
is irradiated with the excimer laser beam
12
, the entirety of the profile
29
is wave-shaped, as opposed to an ideal profile
30
(dashed line) which is formed of four straight sides.
The reason why the profile
29
is wave-shaped is because the excimer laser beam
12
transmitted through the light transmitting area
13
a
of the projection mask
13
is diffracted by edges (i.e., both of the longer sides
21
a
and the shorter sides
21
b
; see
FIG. 6
) of the light transmitting area
13
a.
FIG. 8
shows a light intensity distribution of the excimer laser beam
12
irradiating the surface of the processing target
15
after being transmitted through the light transmitting area
13
a
. Since the excimer laser beam
12
is diffracted by the edges of the light transmitting area
13
a
, the light intensity received by the surface of the processing target
15
is not uniform, but portions having a higher light intensity than the rest of the surface appear in a lattice pattern as shown in FIG.
8
. Since these portions are ablated more strongly than the rest of the surface the entirety of the profile
29
is wave-shaped.
FIG. 9
is a graph illustrating light intensity distributions of the excimer laser beam
12
irradiating the surface of the processing target
15
along the X direction. A solid line
9
a
represents a light intensity distribution actually obtained by the laser processing apparatus
200
. A dashed line
9
b
represents a light intensity distribution obtained when the excimer laser beam
12
is not diffracted by the edges of the light transmitting area
13
a
. The solid line
9
a
in
FIG. 9
corresponds to the lattice shown in FIG.
8
. The solid line
9
a
has peaks having a light intensity level of higher than 1 (referred to as “overshoot”) at positions corresponding to the vicinity of the shorter sides
21
b
of the light transmitting area
13
a
(FIG.
6
). In addition, the solid line
9
a
fluctuates in a central portion thereof.
Since it is substantially unavoidable that the light is diffracted at the edges of the light transmitting area
13
a
, it is difficult to form a recessed portion defined by flat faces as shown by the dashed line
30
in FIG.
7
. The inclining face shown in
FIG. 12
is also wave-shaped, and it is difficult to form a flat inclining face for the same reason.
Japanese Laid-Open Publication No. 9-206974 discloses a method for improving a light intensity distribution characteristic of a laser beam irradiating a processing target after being transmitted through a light transmitting area of
Conlin David G.
Dike, Bronstein, Roberts & Cushman Intellectual Property Practic
Evans Geoffrey S.
Hartnell, III George W.
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