Laser machining apparatus using focusing lens-array

A laser beam machining apparatus for finely machining a semiconductor circuit or similar workpiece on a stage including a scanning mirror for directing the beam, scanning lens for converting the beam to a beam substantially perpendicular to the workpiece, lens array unit and mask for focusing the beam, driving means for X-Y movement of the lens array unit and control means for controlling the mirror driving means and stage.

BACKGROUND OF THE INVENTION 
The present invention relates to an improvement in a laser machining 
apparatus for finely machining a semiconductor circuit or similar 
workpiece by focusing a laser beam thereonto. 
A laser machining apparatus of the type described generally focuses a laser 
beam to a machining position by either one of two different laser 
positioning systems. One of the positioning systems uses a mirror which is 
rotatably driven by a galvanometer and steers an incident laser beam, and 
an f.theta. lens which focuses the steered laser beam onto a workpiece. 
The other system shifts an XY stage or table loaded with a workpiece while 
maintaining a laser beam fixed in position, until a predetermined 
machining position coincides with the focusing position of the laser beam, 
as disclosed in U.S. Pat. No. 4,543,464. 
The beam steering scheme mentioned above features an inherently high beam 
scanning rate. However, it has a drawback that the laser beam cannot be 
positioned with accuracy relative to a workpiece. Another drawback is that 
the beam spot cannot be reduced in radius while keeping the same scanning 
area because the focal length of the f.theta. lens has to be reduced for 
the decreased beam spot. While the stationary beam scheme is successful in 
determining an accurate machining position, it results in a bulky and 
expensive apparatus construction due to the need for a precision XY stage 
which is movable over a substantial distance and slow in movement. 
A beam positioning system which constitutes an improvement over the 
above-discussed two systems is disclosed in U.S. Pat. No. 4,532,402. 
Specifically, the improvement uses an XY stage which is made up of an X 
stage and a Y stage and loaded with a workpiece. A galvanometer and a 
focusing lens are rigidly mounted on one of the X and Y stages for 
steering a laser beam. The XY stage roughly adjusts the position of the 
laser beam over a broad area, while a mirror mounted on the galvanometer 
steers the laser beam at a high speed over a small area around a desired 
machining position. This kind of approach, however, requires the XY stage 
to move over a broad area and requires a substantial period of time for 
moving the XY stage, while increasing the overall dimensions of the 
assembly. Since the final positioning of the laser beam is effected by the 
galvanometer, the accuracy of machining position is not satisfactory. 
Further, complicated control is needed for the XY stage and galvanometer. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a laser 
machining apparatus which locates a laser beam at a desired machining 
position rapidly and, yet, with accuracy. 
In accordance with the present invention, a laser machining apparatus for 
machining a workpiece by focusing a laser beam to a desired position on a 
surface of the workpiece comprises a laser beam source for emitting the 
laser beam, a scanner for steering the laser beam from the laser beam 
source in a first direction, a scanning lens for converting the laser beam 
steered by the scanner into a beam which is substantially perpendicular to 
the surface of the workpiece, a lens array unit having a plurality of 
miniature focusing lenses which are arranged in an array in the first 
direction for focusing a part of the laser beam from the scanning lens to 
the desired position, a stage movable in a second direction perpendicular 
to the first direction while being loaded with the workpiece, a first 
driver for moving the lens array unit in the first direction by a small 
amount, a second driver for driving the stage, and a controller for 
controlling the scanner, first driver, and second driver. The controller 
controls the scanner such that the optical axis of the laser beam incident 
to the lens array unit is located in close proximity to the desired 
position on the workpiece. The controller controls the first driver such 
that the optical axis of one of the focusing lenses of the lens array unit 
coincides with the desired machining position. Further, the controller 
controls the second driver such that the stage is positioned in the second 
direction. 
Also, in accordance with the present invention, a laser machining apparatus 
for machining a desired position on a surface of a workpiece by focusing a 
laser beam to the desired position comprises a laser beam source for 
emitting the laser beam, a scanner for steering the laser beam from the 
laser beam source in a first and a second directions which are 
perpendicular to each other, a scanning lens for converting the laser beam 
steered by the scanner into a beam which is substantially perpendicular to 
the surface of the workpiece, a lens array unit having a plurality of 
miniature focusing lenses which are arranged in a two-dimensional array in 
the first and second directions for focusing a part of the laser beam from 
the scanning lens to the desired position, a stationary stage loaded with 
the workpiece, a driver for moving the lens array unit in the first and 
second directions by a small amount, and a controller for controlling the 
scanner and driving means. The controller controls the scanner such that 
the optical axis of the laser beam incident to the lens array unit is 
directed in close proximity to the desired position on the workpiece. 
Further, the controller controls the driver such that the optical axis of 
one of the focusing lenses of the lens array unit coincides with the 
desired machining position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 of the drawings, a laser machining apparatus embodying 
the present invention comprises a laser beam source 1, an X galvanometer 
2, scanning lens 3, and lens array unit 5. The laser beam source 1 emits a 
parallel laser beam having a uniform intensity distribution as measured on 
a plane perpendicular to the optical axis. The X galvanometer 2 steers the 
laser beam in the X direction by rotating a mirror 2a which is mounted 
thereon. The scanning lens implemented as an f.theta. lens 3 transforms 
the beam from the mirror 2a into a beam which is perpendicular to the 
surface of a workpiece 7. A lens array unit 5 has a plurality of miniature 
focusing lenses 4 arranged one-dimensionally in the X direction and 
focuses a part of the laser beam from the lens 3 onto the workpiece 7. 
There are also shown in the figure an X linear motor 6, a Y stage 8 which 
is loaded with the workpiece 7, a Y motor 11 for driving the Y stage 8 in 
a Y direction which is perpendicular to the X direction, and a main 
controlling and driving unit 10 for controllably driving the X 
galvanometer 2 and the motors 6 and 11. 
The laser beam emitted from the laser beam source 1 is reflected by the 
mirror 2a mounted on the galvanometer 2 to become incident to the scanning 
lens 3. Specifically, the beam is incident to a position on the reflecting 
surface of the mirror 2a which is on an extention of a rotation axis of 
the mirror and which is also a focal point of the scanning lens 3. Hence, 
while the mirror 2a is rotated about the axis which extends perpendicular 
to the sheet surface of FIG. 1, the beam steered thereby in the X 
direction is transformed by the lens 3 into a beam which is perpendicular 
to an X-Y plane. The lens array unit 5 which will be described in detail 
focuses a part of the beam coming out of the lens 3 onto the workpiece 7 
in the form of a small beam spot. 
Assume that the workpiece 7 is an IC (Integrated Circuit) wafer which is 
dimensioned 8 inches at maximum. Then, the scanning range in the 
X-direction defined by the galvanometer 2 and scanning lens 3 is about 200 
millimeters and, hence, the lens 3 needs to have a long focal length. On 
the other hand, each miniature focusing lens 4 has a focal length as short 
as possible in order to provide a small beam spot. If desired, the 
miniature lenses 4 may each be constituted by a GRIN (gradient index 
materials) lens having a generally parabolic refractive index distribution 
whose index of refraction is greatest on the optical axis and gradually 
decreases with the square of the distance from the optical axis. As shown 
in FIG. 4, the miniature lenses 4 are arranged in an array at the same 
distance l.sub.x, while a mask 9 screens the end surfaces of the lenses 4 
except for their portions around the optical axes. The individual lenses 4 
are arranged parallel with each other in their optical axes, and have the 
same physical properties and dimensions. Specifically, they have 
substantially the same length and refractive index distribution. The unit 
lens array 5 is disposed so that the laser beam from the scan lens strikes 
the end surfaces of the lenses 4 perpendicularly. In this configuration, 
only a part of the laser beam from the lens 3 which is incident to one of 
the lenses 4 is focused onto the workpiece 7 to form a beam spot. The 
position of the beam spot on the workpiece 7 is adjustable by moving the 
optical axis of the lens 4 in the X direction because the laser beam 
incident to the lens 4 is focused on the optical axis of the lens. 
To move the beam spot on the workpiece 7 in the X direction, the main 
controlling and driving unit 10 controls the galvanometer 2 to rotate the 
mirror 2a and thereby to shift the laser beam at high speed to the 
vicinity of a predetermined machining position P (FIG. 4). At the same 
time, the unit 10 controls the linear motor 6 to move the lens array unit 
5 finely in the X direction until an optical axis O of a particular 
focusing lens 4 which is located the closeset to the machining position P 
reaches the position P. As a result, a part of the laser beam incident to 
the lens array unit 5 is focused to the machining position by the lens 4 
with accuracy. In this instance, the lens array unit 5 has only to be 
moved by the distance between nearby miniature lenses 4. Specifically, 
assuming that the distance between the lenses 4 is 1 millimeter, then the 
required distance of movement is not more than about 1 millimeter at 
maximum, enhancing rapid movement of the lens 4. This, coupled with the 
fact that the galvanometer 2 steers the laser beam at high speed, promotes 
rapid positioning of the laser beam in the X direction and rapid 
positioning of the beam spot. The beam spot is manipulated in the Y 
direction by the Y stage 8 which is loaded with the workpiece 7. 
Referring to FIG. 2, the main controlling and driving unit 10 includes an 
inputting subunit 101 for entering X and Y coordinates data representative 
of a particular laser machining position of the workpiece 7 in the X and Y 
directions beforehand, a memory 102, and a control circuit 103. The memory 
102 is loaded with the entered X and Y coordinates data. A control circuit 
103 controls the unit 10 on the basis of the data stored in the memory 
102. A galvanometer controller 110 controls a driver 111 for driving the 
galvanometer 2, in response to the X coordinate data. A linear motor 
controller 120 controls a driver 121 for driving the X linear motor 6, 
also in response to the X coordinate data. A Y stage controller 130 
controls a motor driver 131 which drives the Y motor 11, in response to 
the Y coordinate data. 
In the illustrative embodiment, assume that the machining ranges of the 
workpiece 7 as measured in the X and Y directions are 200 millimeters 
each, and that the resolution of the focusing position in the X and Y 
directions is 0.01 micron (.mu.m). Then, the data length of X and Y 
coordinates data to be stored in the memory 102 has to be 25 bits at 
minimum. In FIG. 2, the 26-bit X and Y coordinates data are stored in the 
memory 102. 
The positioning with the Y stage 8 is implemented by an ordinary stage 
positioning method. Specifically, the 26-bit Y coordinate data stored in 
the memory 102 is transferred to the Y-stage controller 130 via a Y 
register 103b which is built in the control circuit 103. As shown in FIG. 
3, the Y stage controller 130 has a subtractor 130b for effecting 
subtraction with the Y coordinates data fed from the Y register 103b and 
the Y coordinate data representative of the previous position (data stored 
in the memory 130a), and a counter 130c in which the absolute value of the 
resulting difference is preset. The subtractor 130b determines a direction 
and a distance by which the Y stage 8 has to be moved relative to the 
current position. The absolute value of the resulting difference shows the 
distance, while the sign (positive or negative) of the same indicates the 
direction. When a signal representative of the sign of the difference is 
fed from the subtractor 130b to the motor driver 131, a direction for 
moving the Y stage 8 is determined. A Y position measuring instrument 132 
(commercially available laser interferometer) is responsive to the 
movement of the Y stage 8 and generates one pulse every time the latter 
moves 0.01 micron. The counter 130c of the Y stage controller 130 counts 
the output pulses of the instrument 132 and, on counting a preset number 
of pulses, stops its operation. While the counter 130c is in operation, 
the motor driver 131 drives the Y motor 11 to thereby move the Y stage 8 
in the Y direction. As soon as the counter 130 counts up the present 
number of pulses and thereby changes its output, the motor driver 131 
stops driving the Y motor 11 immediately. 
As stated above, the Y stage 8 is shifted to a particular position 
represented by the Y coordinate data while being measured by the 
instrument 132 on a 0.01 micron basis. 
The drive and control over the X galvanometer 2 and X linear motor 6 will 
be described in detail with reference to FIGS. 1 and 2. The X galvanometer 
2 positions the laser beam through the scanning lens (usually f.theta. 
lens) 3, as previously stated. Assuming that the focal length of the lens 
3 is f, and the length of the lous of the beam on the lens 3 is 
x.sub..theta. when the rotation angle of the mirror 2a mounted on the 
galvanometer 2 is .theta., then there holds a relationship: 
EQU x.sub..theta. =2f.theta. (1) 
Hence, the resolution .DELTA.x.sub..theta. of the beam position relative 
to the resolution .DELTA..theta. the rotation angle of the mirror 2a is 
expressed as: 
EQU .DELTA.x.sub..theta. =2f.DELTA..theta. (2) 
In order to position that laser beam over a broad area by a galvanometer 
whose rotation angle is limited, a lens is provided with a large focal 
length f. Then, the resolution .DELTA.x.sub..theta. of the beam position 
will increase and thereby eliminate the need for coordinate data 
associated with high resolution in effecting the positioning control over 
the galvanometer. 
In FIG. 2, among the 26 bits of X coordinate data transferred from the 
memory 102 to the X register 103a of the controller 103, upper 14 bits are 
used as position coordinate data X.sub.1 for controlling the X 
galvanometer 2. In this instance, resolution regarding the position in the 
X direction is 40.96 microns. Specifically, every time the data X.sub.1 
changes by one (LSB), the galvanometer 2 shifts the laser beam 40.96 
microns in the X direction; as the data X.sub.1 reaches the minimum or 
maximum value, the galvanometer 2 substantially locates the laser beam at 
either one of opposite ends of the X direction scanning area. On receiving 
data X.sub.1, the galvanometer controller 110 converts it into an analog 
signal associated with the rotation angle of the mirror 2a. This analog 
signal corresponds to a voltage which a rotation angle sensor 112 
generates to indicate a rotation angle of the mirror 2a. The driver 111 
generates a drive current proportional to a difference between the analog 
signal from the controller 110 and the output voltage of the rotation 
angle sensor 112, the drive current being applied to the galvanometer 2. 
In response, the galvanometer 2 rotates the mirror 2a. When the actual 
rotation angle of the mirror 2a equals the angle indicated by the data 
X.sub.1, the drive current from the driver 111 becomes zero to stop the 
rotation of the mirror 2a. In this manner, beam positioning by the 
galvanometer 2 is finished. 
In the illustrative embodiment, the beam positioning resolution available 
with the X galvanometer 2 is 40.96 microns, as previously stated. Further 
accurate positioning is, therefore, achieved by the linear motor 6 which 
drives the lens array unit 5. How the lens array unit 5 is positioned will 
be described with reference to FIGS. 2 and 4. 
In FIG. 4, the center axis of the laser beam S from the scanning lens 3 is 
located in the vicinity of the position P (within the range of 40.96 
microns as measured from the position P). A dashed circle represents the 
boundary of the illuminating area of the laser beam S coming out of the 
scanning lens 3. In the condition shown in FIG. 4, a part of the laser 
beam is incident to the miniature lens 4 which is located at the right of 
the position P, i.e., it is focused on the optical axis O of that lens 4. 
The lens array unit 5, therefore, has to be shifted by a distance x.sub.2 
to the left so that the optical axis O may coincide with the position P. 
Assuming that the X coordinate of the position P is x.sub.2, then it is 
produced by: 
EQU x.sub.2 =MOD (x, l.sub.x)-e.sub.x /2 (3) 
where MOD (x, l.sub.x) is a residual produced by dividing the coordinate x 
by the distance l.sub.x. 
The distance x.sub.2 lies between -l.sub.x /2 and +l.sub.x /2, and it is 
positive when the target position P is located at the right of the optical 
axis O of the lens 4 and is negative when the latter is located at the 
left. Since the laser beam can be accurately positioned only if the linear 
motor 6 shifts the lens array unit 5 by x.sub.2, the shifting range is 
only -l.sub.x /2 to +l.sub.x /2. 
In FIG. 2, the control circuit 103 calculates the equation (3) on the basis 
of the 26-bit X coordinate data having been stored in the memory 102. The 
resulting 26-bit data X.sub.2 representative of a distance x.sub.2 is fet 
to a linear motor controller 120. Let the data l.sub.x be assumed to be 
stored in the memory 102 beforehand. An X position measuring instrument 
122, like the Y position measuring instrument 132, generates one pulse 
every time the lens array unit 5 is moved by 0.01 micron and feeds it to 
the linear motor controller 120. 
The linear motor controller 120 counts the output pulses of the instrument 
122, drives the driver 121 until the count equals the absolute value of 
the data X.sub.2, and indicates the driver 121 a direction for moving the 
lens array unit 5 on the basis of the sign of the data X.sub.2. Hence, as 
the optical axis O of the lens shown in FIG. 4 approaches the target 
position P until the number of output pulses equals the data X.sub.2, the 
linear motor controller 120 commands the driver 121 the stop of drive of 
the linear motor 6. If desired, the linear motor 120 may use, in place of 
the data X.sub.2, data X.sub.3 produced by adding to the data X.sub.2 a 
correction value E(X) derived from positional errors which are dependent 
upon the optics. The positional errors mentioned mainly comes from the 
ununiformity in the focal length, interval and other factors of the lenses 
4 of the lens array unit 5, and the insufficient accuracy of the X 
galvanometer 2 (deviation of incidence angle and movement relative to the 
lens array unit 5). Various approaches are available for sensing such 
positional errors. One possible approach is to place a reference pattern 
on the Y stage 8, emit and focus a laser beam onto the reference pattern 
to sense a reflection (diffracted light), and then produce a correction 
value E(X). An alternative is to directly machine a test substrate, 
measure the position of the machined spot, and then produce a correction 
value E(X). The correction value E(X) is stored in the linear motor 
controller 120 and added to input data X.sub.2 to produce the data 
X.sub.3. 
Referring to FIG. 5, an alternative embodiment of the present invention is 
shown. The alternative embodiment comprises the laser beam source 1, a 
beam scanning unit 20 for steering a laser beam from the laser beam source 
1 in the X and Y directions, a scanning lens 30 for converting the steered 
laser beam into a beam which is perpendicular to the surface of the 
workpiece 7, a lens array unit 40 comprised of a plurality of miniature 
focusing lenses 4 arranged in the X and Y directions, an X linear motor 50 
and a Y linear motor 60 for moving the unit 40 in the X and Y directions, 
respectively, and a stationary table 70 to be loaded with the workpiece 7. 
While the apparatus shown in FIG. 1 controls the position in the Y 
direction by moving the Y stage 8 loaded with the workpiece 7, the 
apparatus of FIG. 5 holds the workpiece 7 stationary and controls the 
position in the X and Y directions by causing the beam scanning unit 20 to 
manipulate the laser beam in the X and Y directions and by finely 
adjusting the beam focusing position which is determined by the X linear 
motor 50 and the Y linear motor 60. 
The beam scanning unit 20 has an X galvanometer 21, a mirror 22 rigidly 
mounted on a drive shaft 23 of the galvanometer 21 and rotated thereby for 
steering the laser beam in the X direction, a block 24 rotatably mounted 
on the shaft 23, and a motor 26 for rotating the block 24 about a 
vertically extending shaft 25. The motor 26 is mounted on a support 27 of 
the apparatus and rotates the block 24 about the shaft 25, so that the 
mirror 22 (and galvanometer 21) is also rotated about the shaft 25 to 
manipulate the laser beam in the Y direction. The laser beam is incident 
to the reflecting surface of the mirror 22 at the center of rotation of 
the latter which is coincident with the focal point of the scanning lens 
30. The scanning lens 30 is implemented as an f.theta. lens and, hence, 
the laser beam manipulated in the X and Y directions by the mirror 22 will 
be incident to the lens array unit 40 perpendicularly to the X and Y axes. 
As shown in FIG. 6, the focusing lenses 4 of the lens array unit 40 are 
arranged regularly in the X and Y directions at equal distances, i.e., a 
distance l.sub.x in the X direction and at a distance l.sub.y in the Y 
direction. In this particular embodiment, the distances l.sub.x and 
l.sub.y are equal to each other. A mask 41 screens the lens array unit 40 
except for the portions around the optical axes of the individual lenses 
4. Sixteen lenses 4 are shown in FIG. 6 by way of example. 
The X linear motor 50 and Y linear motor 60 for moving the lens array unit 
40 and the X galvanometer 21 and motor 26 for manipulating the laser beam 
are controlled by a main controlling and driving unit 80 (FIG. 7). The 
positioning in the X direction on the workpiece 7 as effected by the X 
galvanometer 21 and X linear motor 26 is the same as the positioning 
effected by the X galvanometer 2 and X linear motor 6 of FIG. 1. The 
positioning in the Y direction on the workpiece 7 is implemented by the 
motor 26 and Y linear motor 60 in the same manner as the positioning in 
the X direction. Assume that the machining range is 200 millimeters both 
in the X direction and in the Y direction, the positioning resolution 
determined by the controllable drive of the galvanometer 21 and motor 26 
is 40.96 microns, and the positioning resolution determined by the X and Y 
linear motors 50 and 60 is 0.01 micron, as with the first embodiment. 
Then, the center axis of the laser beam is controlled by the galvanometer 
21 and motor 26 to a range of 40.96 microns as measured from a target 
position on the workpiece 7. It is further located at the target position 
with accuracy of 0.01 micron by the controllable drive of the X and Y 
linear motors 50 and 60. 
As shown in FIG. 6, when the optical axis O of the focusing lens 4 of the 
lens array unit 40 is not aligned with the target position P on the 
workpiece 7, the laser beam S from the scanning lens 30 is focused to the 
optical axis O of the lens and not to the position P. In order to focus 
the laser beam S to the position P, the optical axis O of the lens 4 is 
shifted by x.sub.2 and y.sub.2 in the directions X and Y, respectively, to 
the position P. While the distance x.sub.2 is produced by the equation (3) 
as indicated previously, the distance y.sub.2 is given by: 
EQU y.sub.2 =MOD (y,l.sub.y)-l.sub.y /2 (4) 
where y and MOD (y, l.sub.y) are respectively the Y coordinate of the 
position P and the residual produced by dividing y by l.sub.y. The unit 80 
drives the motors 50 and 60 in response to x.sub.2 and y.sub.2 derived 
from the equations (3) and (4) so as to bring the optical axis O of the 
lens 4 into coincidence with the position P. 
Referring to FIG. 7, the main controlling and driving unit 80 comprises an 
inputting subunit 201 accessible for entering X and Y coordinates data 
representative of the machining position (P, FIG. 6) of the workpiece 7 
beforehand, a memory 202, and a control circuit 203. The memory 202 stores 
the entered X and Y coordinates data. The control circuit 203 controls the 
unit 80 on the basis of the stored coordinates data. The X and Y 
coordinates data are each represented by 26 bits, as in the apparatus of 
FIG. 1. Upper 14 bits of the X and Y coordinates data are adapted to drive 
and control the X galvanometer 21 and motor 26. In the unit 80, an X 
galvanometer controller 210, a driver 211, a rotation angle sensor 212, an 
X linear motor controller 220, a motor driver 221 and an X position 
measuring instrument 222 are the same as the galvanometer controller 110, 
driver 111, rotation angle sensor 112 linear motor controller 120, linear 
motor driver 121, and X position measuring instrument 122 which are shown 
in FIG. 2. Specifically, the X galvanometer controller 210 and driver 211 
control the galvanometer 21 on the basis of data X.sub.1 constituted by 
upper 14 bits of X coordinate data which is stored in the memory 202. The 
X linear motor controller 220 and linear motor driver 221 control the X 
linear motor 50 on the basis of data X.sub.2 which corresponds to x.sub.2 
produced by the equation (3). 
The motor controller 230 and motor driver 231 drive the motor 26 in 
response to data Y.sub.1, which is upper 14 bits of Y coordinate data, in 
the same manner as the controllable driver over the X galvanometer 21. 
More specifically, the motor controller 230 transforms data Y.sub.1 into 
an analog signal associated with the rotation angle of the shaft 25 of the 
motor 26, while the motor driver 231 feeds to the motor 26 a drive current 
proportional to a difference between the analog signal from the motor 
controller 230 and the voltage from the rotation angle sensor 232 which is 
representative of the rotation angle of the shaft 25. The motor 26 rotates 
the block 24 about the shaft 25 in response to the drive current. When the 
block 24 is rotated by an angle associated with the data Y.sub.1, the 
drive current from the driver 231 becomes zero to stop the rotation of the 
motor 26. The motor 26 positions the optical axis of the laser beam from 
the laser beam source 1 within the range of 40.96 microns as measured from 
the target position P, while the Y linear motor 60 positions it with 
further accuracy by finely shifting the lens array unit 40 in the Y 
direction. 
More specifically, the control unit 203 calculates the equation (4) on the 
basis of the 26-bit Y coordinate data stored in the memory 202 and thereby 
delivers 26-bit data Y.sub.2 representative of a distance y.sub.2 to the Y 
linear motor controller 240. It is assumed that the data l.sub.y is stored 
in the memory 202 beforehand. A Y position measuring instrument 242, like 
the X position measuring instrument 222, generates one pulse every time 
the lens array unit 40 moves 0.01 micron and feeds it to the Y linear 
motor controller 240. The Y linear motor controller 240 counts the output 
pulses of the instrument 242, drives the driver 241 until the count equals 
the absolute value of the data Y.sub.2, and indicates the driver 241 a 
direction for moving the lens array unit 40 on the basis of the sign of 
the data Y.sub.2. Therefore, as the optical axis O of the lens 4 shown in 
FIG. 6 approaches the target position P until the count of the pulses 
equals the data Y.sub.2, the linear motor controller 240 commands the 
driver 241 the stop of operation of the linear drive 241. Again, the 
linear motor controller 240 may use, in place of the data Y.sub.2, a 
correction data which is the sum of the data Y.sub.2 and a correction 
value E(Y) associated with positional errors dependent upon optics. 
While the lens array units 5 and 40 have each been shown and described as 
being driven by a linear motor, they may of course be driven by any other 
suitable kind of motor. The miniature focusing lenses of the lens array 
unit may be replaced with Fresnel lenses, if desired. In the apparatus 
shown in FIG. 5, the laser beam from the laser beam source 1 is scanned by 
a single mirror 22 in the X and Y directions. Alternatively, it may be 
steered in the X and Y directions by independent mirrors which are driven 
by exclusive galvanometers. 
In summary, it will be seen that the present invention provides a laser 
machining apparatus which realizes rapid and accurate laser spot scanning, 
i.e., implements high speed by using a mirror which is rotated by a 
galvanometer, for example, and accuracy by moving a laser spot by a 
distance which is not longer than the distance between nearby lenses of a 
focusing lens array. Further, the present invention eliminates the need 
for a large X and Y stage assembly for positioning a broad area.