Method of forming groove by laser

Details Method of forming groove by laser Method of forming groove by laser

1998-08-28

2001-07-31

Evans, Geoffrey S. (Department: 1725)

Electric heating

Metal heating

By arc

C219S121730, C219S121800

Reexamination Certificate

active

06268585

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a groove with desired cross sections by irradiating a laser beam to a work, and more particularly to a method of easily forming the groove which has a constant depth in a scanning direction and an arbitrary depth distribution in the direction vertical to the scanning direction by relatively moving the irradiated area on the work.
2. Description of the Related Art
As a method of forming a groove having various figures of cross sections by a laser beam aberration, a method of irradiating a slit-shaped laser beam converted through a projection mask to the surface of a work, which is moved in the width direction synchronizing to the laser beam pulse oscillation (Japanese Patent Laid-open No. 8-19878) is known.
However, the prior method described above have several problems. In accordance with the method, a complicated and precise control of a scanning velocity is needed to form a desired cross section because a depth of the groove depends on the scanning velocity of the slit-shaped laser beam in the width direction. Furthermore, a period of controlling the scanning velocity, which is modulated in accordance with a desired cross sectional figure, is necessary to be repeated at each time when the laser beam on the work is moved little by little in the longitudinal direction of the groove. Accordingly, in conventional methods, a complicated control for displacement and velocity of the work is required and a large amount of manufacturing time is required because of scanning in two directions of the x-axis and the y-axis.
SUMMARY OF THE INVENTION
An object of the present invention is to form a groove having a desired cross section easily and rapidly, by making a laser beam scan only in a longitudinal direction of the groove to form.
To achieve the above object, the present invention provides a method of forming grooves by irradiating a laser beam to a work. The longitudinal direction of a groove is defined as the x-axis, the width direction of that is defined as the y-axis, and an intensity distribution of an irradiated region on the work is defined as f(x, y). The intensity distribution f(x, y) is formed by passing the laser beam through a mask pattern so that g(y), an integral of f(x, y) with respect to x, may be proportional to d(y), a depth distribution of the groove. And the irradiated region is moved in the x-axis direction.
In the invention described above, f(x, y) may be a constant. In that case, f(x, y) is a function which is 0 out of the irradiated region and a constant A within the region. Accordingly, the function g(y) is A·&Dgr;L(y), where &Dgr;L(y) denotes a length in the x-axis direction at y in the irradiated region. &Dgr;L(y) is determined so that A·&Dgr;L(y) may be proportional to a depth distribution of groove, d(y). The laser beam is irradiated to the work through the mask pattern having a figure similar to the irradiated region, and then the irradiated region having a desired figure &Dgr;L(y) is obtained.
When the irradiated region with the intensity distribution f(x, y) scans in the x-axis direction at an constant velocity v, an energy w(x, y) which the point (x, y) receives is given by the following equation: ∫f(x, y) dx/v=g(y)/v. The depth d(y) of the groove formed at the point (x, y) is proportional to the energy w(x, y). Accordingly, the groove having the desired depth distribution d(y) can be obtained when the irradiated region with the strength f(x, y) is formed so that g(y), i.e., the integral of f(x, y) with respect to x may be proportional to d(y), and is moved at the constant velocity v in the x-axis direction. The depth distribution d(y) and the intensity distribution f(x, y) satisfy the relation defined by:
∫
f
(
x, y
)
dx=k~d
(
y
)  (1),
where k=v/a, “a” represents a proportional constant of depth d(y) to the energy w(x, y).
f(x, y) is obtained by multiplying I(x, y), an intensity distribution of the laser beam without passing the mask pattern, and T(x, y), a transmission factor distribution of the mask pattern. Accordingly I(x, y) and T(x, y) are satisfied with:
I
(
x, y
)·
T
(
x, y
)=
f
(
x, y
)  (2),
∫
I
(
x, y
)·
T
(
x, y
)
dx=∫f
(
x, y
)
dx
  (3).
The following equation is obtained by substituting Eq. 1 into Eq. 3:
∫
I
(
x, y
)·
T
(
x, y
)
dx=k·d
(
y
)  (4).
Generally, T(x, y) is determined so as to satisfy the Eq. 4 and the irradiated region is moved at a constant velocity in the x-axis direction, to form the groove having the depth distribution of d(y).
When a mean value of T(x, y) with respect to x which is weighted with I(x, y) is defined as S(y), and a length in the x-axis direction at the coordinates y in the irradiated region is defined as L(y), the Eq. 4 is expressed by:
S
(
y
)·
L
(
y
)=
k·d
(
y
)  (5).
When a mean transmission factor of the mask pattern and a figure in the x-axis direction are determined so as to satisfy the relation represented by the Eq. 5, d(y) is obtained.
In a case where the transmission factor of the mask pattern is 1 in the irradiated region and 0 outside the region, the following equation is satisfied:
∫
I
(
x, y
)
dx=k·d
(
y
)  (6).
When a mean value of I(x, y) with respect to x is defined as b(y), the following equation is satisfied:
L
(
y
)=
k·d
(
y
)/
b
(
y
)  (7).
Because the irradiated region is equal to magnification of the mask pattern m times, a length distribution E(y) in the x-axis direction, in the area where the transmission factor of the mask pattern is 1, can be expressed with d(y) as follows:
E
(
y
)=
k·d
(
y
)/(
b
(
y
)·
m
)  (8).
And in case that b(y) can be approximated to be a constant b, E(y) is expressed by the following equation:
E
(
y
)=
k·d
(
y
)/(
b·m
)  (9).
Thus the length distribution of the mask pattern, E(y), can be determined by the depth distribution of the groove, d(y). By passing the laser beam through the thus-obtained mask pattern, forming the irradiated region on the work, and moving the region at a constant velocity in the x-axis direction, the groove having the desired depth distribution d(y) and a length in the x-axis can be obtained. Because a cross sectional figure of the groove is determined by the mask pattern, the groove having a complicated cross section can be easily obtained. Furthermore, the groove having a desired cross section can be obtained only by making laser beam scan one time, at a constant velocity in one axis direction. Thus, in the present invention, an operation of forming a groove having a desired cross section becomes simple and easy.


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patent: 7-9180 (1995-01-01), None
patent: 8-19878 (1996-01-01), None
patent: 8-148803 (1996-06-01), None

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