Electric heating – Metal heating – By arc
Reexamination Certificate
1999-02-18
2002-02-12
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121610, C219S121820
Reexamination Certificate
active
06346687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a processing method using an optical beam such as a laser beam and an energy beam such as of a charged particle, and a processing apparatus, utilizing the beam, more particularly, to a processing method for processing objects such as a resin, ceramic, metal and photolithographic photosensitive layer to drilling, half-etching, surface treatment and exposure to a photoresist using an energy beam such as a laser beam emitted from a CO
2
laser, YAG laser or excimer laser.
2. Description of the Related Art
The CO
2
laser (at infrared region of from 9 to 11 &mgr;m) and YAG laser (at near-infrared region of 1.064 &mgr;m) that are currently versatile for industrial application have been used mainly in cutting and welding of processing objects (workpiece or “work”) because of their heat-melt capability. The processing method using such long-wavelength lasers is known as a heat-processing method taking advantage of heating induced by the laser beam.
Processing of the work using the excimer laser having a very short wavelength (193, 248, 308 and 351 nm) is classified as a non-heating processing for processing the work by taking advantage of a photochemical effect through a photochemical reaction induced by the laser beam, enabling to process the work with a superior processing accuracy to the heat-processing.
In the processing method using the excimer laser having such short wavelength, ceramics such silicon nitride, alumina, SiC and TiC, and synthetic resins such as polyimide, polyester, epoxy resin and polycarbonate are processed without melting with heat. In this method, intermolecular bonds are cleaved by exciting respective molecules in the polymer successively from the surface during the irradiation with the laser beam, which allows the molecules in a solid state to be scatter directly. This processing method is usually called an ablation processing, and makes it possible to achieve a more precise processing compared with the processing method using the CO
2
laser and YAG laser.
As a work processing method taking advantage of characteristics of such an excimer laser is a half-etching processing by which the surface of a relatively thick resin plate is drilled to a given depth. The half-etching processing using the excimer laser is utilized as a processing method for thinning the work at the minute hole portion of the printing mask in order for a paste such as a cream solder, or an ink for use in minute holes formed on the printing mask, to be readily discharged.
The laser beam emitted from the laser mentioned above is usually focused to have a beam spot shape of about 2 mm square on the processing surface of the work after passing through an aperture or a condenser. Therefore, the work has to be processed by displacing relative to the laser beam when the length of an etching groove or the size of a hole to be formed on the work, or the length of a cutting or welding site of the work, is larger than the beam spot of the laser beam.
Accordingly, a table with an approximately horizontal mounting face for mounting the work is usually placed on a X-Y table which is capable of displacing of traveling the work mounting face along the X-Y directions. The X-Y table is provided so as to travel along the X-Y directions, to thereby for the work mounted on the mounting table to travel relative to the laser beam.
A driving motor such as a servomotor or a stepping motor is used for the driving source of the X-Y table equipped with the mounting table in the conventional processing apparatus using the aforementioned laser beam. It has been known that a rotational velocity of this driving motor is not immediately increased to a given speed Sm, but gradually accelerated for a period of time t
1
after a driving signal is outputted from the driving circuit at t
0
for initiating the rotation, as shown in FIG.
7
. For halting the X-Y table, on the other hand, rotation of the driving motor is not allowed to stop instantaneously but has to be decelerated starting at t
2
from the given speed Sm, to finally stop the rotation at t
3
.
Accordingly, the traveling velocity of the mounting table on the X-Y table driven with the driving motor is gradually accelerated, approximately by the same way as in the rotational velocity of the driving motor, during a time interval of from t
0
to t
1
after initiation of travel and is gradually decelerated during a time interval of from t
2
to t
3
before stopping in this processing apparatus.
However, as shown in
FIG. 8
, a pulse laser beam having an irradiation energy Em is immediately emitted from the laser by turning the laser driving circuit on to initiate the irradiation at to which is repeated in response to a trigger frequency given to the laser driving circuit. The laser beam having a constant pulse width, repeating frequency and irradiation energy Em is always emitted from the laser, without being increased or decreased in contrast to the driving motor described above, until the laser driving circuit is turned off at t
3
for ceasing the irradiation.
Accordingly, the laser beam irradiation density, per unit time and unit area on a beam irradiation surface of the work during the accelerating or decelerating travel period of the work, becomes larger than the beam irradiation density per unit time and unit area on the laser beam irradiation surface during the period at which the rotational velocity has reached to a given constant speed Sm in the processing method.
Consequently, the irradiation energy density per unit time and unit area of the laser beam irradiating at an initiation point
2
a
and a termination point
2
b
of the etching groove
2
(see
FIGS. 9A and 9B
) of the work
1
becomes larger than that irradiating the other portions. Therefore, when a half-etching processing with a given depth is to be applied on the work by using the excimer laser method, there is a drawback in that (1) the etching grooves at the processing initiation point
2
a
and processing termination point
2
b
of the etching groove
2
are formed deeper than the other portions, as shown in
FIG. 9A
, or (2) a hole is penetrated all through the depth of the work
1
at the processing initiation point
2
a
and termination point
2
b
of the etching groove
2
, as shown in FIG.
9
B.
When the work is to be cut off by the processing method using the CO
2
laser and YAG laser, the quantity to be melted of the work
1
at a cutting initiation point
3
a
or termination point
3
b
of the cut-off site
3
of the work
1
becomes larger than that of the other cutting portions as shown in
FIG. 9C
, thereby resulting an error in the dimension, as well as burning and sticking of the cut-off site
3
at the initiation point
3
a
and termination point
3
b.
In order to obviate the aforementioned difficulties in the conventional processing method, the laser beam has been irradiated on the work merely within the time interval when rotation of the driving motor is stabilized by simply extending the overall driving time of the driving motor. In this case, the processing is started by initiating laser irradiation to the work with a timing later than the time t, when the rotational velocity of the driving motor has reached to a given speed Sm, and processing is completed by ceasing laser irradiation to the work with a timing prior to the time t
2
when the rotational velocity of the driving motor initiates to reduce the speed from the given speed Sm as shown in FIG.
7
.
However, the overall driving time T
2
required for driving the driving motor largely exceed the maximum processing time T
1
required for stable processing of the work as shown in
FIG. 7
in the processing method as described above, causing a difficulty in that the substantial processing time of the work is unduely prolonged.
In addition, the difficulties such as the aforementioned dimensional error at the travel initiation point and termination point or non-uniform processing, or the substantially prolonged processing time may be c
Kinoshita Makoto
Kobayashi Takeshi
Evans Geoffrey S.
Ricoh Microelectronics Company, Ltd.
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