JPH11104873A - Laser beam machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining device which is capable of preventing the decrease in machining accuracy attending on the fluctuation of ambient temperature of the device. SOLUTION: This laser beam machining device is provided with a machining laser beam source I and stages 20 and 13 with which a wafer 11 to be machined is moved in optical axis direction (Z direction) and in perpendicular directions (X and Y directions) to the optical axes. A control circuit 2 of an autofocus mechanism of a machining laser beam is provided with an autofocus temperature correction part 31 which automatically corrects the fluctuation of focal point caused by the fluctuation of air temperature of the surroundings of the device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus for performing processing by applying a laser beam to a workpiece. In particular, the present invention relates to a laser processing apparatus improved so that a fuse in a semiconductor device can be accurately cut.

[0002]

2. Description of the Related Art An example of fuse processing in a semiconductor device will be described. In a semiconductor device, there is a case where a wiring portion called a fuse for cutting a laser beam is provided. For example, in DRAM,
A fuse is attached to each memory cell column at the time of manufacture, and a spare memory cell column is arranged. The fuse of the memory cell column found defective during inspection is cut off to isolate the cell column in the device. At the same time, a spare memory cell column is replaced with a spare column by cutting a fuse for designating an address of a defective column, thereby improving the yield of DRAM (see Japanese Patent Application Laid-Open No. 1-224189). Further, in a gate array, a specific program is built in a device by cutting a part of a fuse in a circuit called a program link and selectively leaving a part of the fuse. Laser repair for the former,
The latter is called laser trimming.

A fuse in such a semiconductor device is generally formed of a thin line made of polysilicon or aluminum (for example, a width of 0.8 to 1.5 μm and a thickness of 0.3 to 1.0 μm).
μm, cut length 3-10 μm). A laser beam from a processing laser light source such as a YAG laser is condensed and irradiated to the fuse, and the material constituting the fuse is heated and evaporated by light energy to remove the fuse, thereby cutting the fuse. The fuse is usually formed under a transparent SiO ₂ film (0.2 to 0.5 μm). As for the position data of the fuse to be blown, data from a tester, which is another device for inspecting a defective portion, is input to the laser repair device via a medium such as online communication or FD. In the laser repair apparatus, the wafer is placed on an XY table and positioned, and the fuses are sequentially cut while automatically aligning the position of the fuse to be cut with the focal point of the laser beam.

[0004] Such a laser processing apparatus is provided with an autofocus mechanism for adjusting the focus of the processing laser light (to reduce the beam diameter). A representative example of the autofocus mechanism is a so-called oblique incidence type optical autofocus apparatus which is widely used in an exposure apparatus for a semiconductor device. In this autofocus apparatus, sensing light such as LED light is applied to a surface of a workpiece from obliquely above, and the reflected light is detected by a detector arranged diagonally above and on the opposite side.

[0005]

However, in the above-described auto-focusing device, since the auto-focusing light passes through the air around the device, the position of optical components of the auto-focusing system shifts when the temperature of the air changes. This causes a focus shift. For example, if the air temperature is 1
When the temperature changes by ℃, it may change on the order of μm. This type of apparatus is located in a clean room of a semiconductor device manufacturing line, and the temperature of the room is controlled to be constant. However, in practice, a fluctuation of about ± 3 ° C. is inevitable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a laser processing apparatus capable of preventing a reduction in processing accuracy due to a change in ambient temperature of the laser processing apparatus. I do.

[0007]

Means for Solving the Problems In order to solve the above problems, a laser processing apparatus of the present invention is an apparatus for irradiating a workpiece with laser light for processing; an autofocus mechanism for processing laser light; And an autofocus temperature correction unit that automatically corrects a focus position change due to a temperature change around the device. That is, since the focus position shift caused by the temperature change is positively corrected, the focus position shift caused by the temperature change can be prevented.

[0008]

In the present invention, the correction section detects a Z-stage position at which a beam diameter of a processing laser beam on a workpiece is minimized, and indicates the Z-stage position and an auto-focus mechanism. It is preferable to calculate a difference from the focus position of the Z stage and give the difference as an offset to the autofocus mechanism. in this case,
Since the focus position deviation is detected and the autofocus is offset by using the beam diameter, which is the final control target, as the observation target, correction can be performed including other errors, and excellent laser processing can be performed.

Hereinafter, description will be made with reference to the drawings. FIG.
FIG. 1 is a diagram schematically illustrating an entire configuration of a laser processing apparatus according to one embodiment of the present invention. The laser processing apparatus according to the present embodiment includes a processing laser light source 1, an optical attenuator 3 for setting a beam diameter and / or an energy value of the processing laser light, and a process for moving a workpiece in an optical axis direction (Z direction) and perpendicular to the optical axis. Direction (X, Y direction)
, A position detecting unit 15 for monitoring the position of the stage, an auto-focus mechanism for processing laser light, a control circuit 2 for controlling the above-described units, and a focus position change due to a temperature change around the device. An automatic focus temperature correction unit 31 for performing automatic correction is provided.

The laser processing apparatus shown in FIG. 1 has a laser light source 1 for processing, and the laser light source 1 emits processing laser light under the control of a control circuit 2, and this laser light is incident on an optical attenuator 3. You. The optical attenuator 3 sets a beam diameter and an energy value of the processing laser light, and is controlled by the control circuit 2. The laser light emitted from the optical attenuator 3 passes through the lens 4 and is reflected by the reflecting mirror 5, passes through the slit 6, the half mirror 7 a, the half mirror 7 b, and the objective lens 9 in order, and the workpiece (semiconductor wafer). 11 is irradiated.
The workpiece 11 is located on the XY stage 13 in the Z direction.
It is fixed by a suction holder 12 provided on the stage 20. Thereby, the wafer 11 is processed.

The XY stage 13 and the Z stage 20
The semiconductor wafer 11 to be processed is moved to a predetermined position. The movement of both stages 13 and 20 is controlled by the drive unit 1
4, and the drive unit 14 is controlled by the control circuit 2. The position of the XY stage 13 is monitored by an optical interference type position detector 15, and the data is sent to the control circuit 2.

Further, the laser processing apparatus has an alignment laser 8, and a laser beam emitted from the alignment laser 8 is reflected by a half mirror 7a, then passes through a half mirror 7b and an objective lens 9 in this order, and is placed on the wafer 11. Is irradiated. The reflected light from the wafer 11 passes through the objective lens 9 again, is reflected by the half mirror 7b, and is incident on the alignment photodetector 10. Then, data obtained by the alignment photodetector 10 is sent to the control circuit 2.

An LED light source 19 for autofocus is disposed diagonally to the upper left of the wafer 11 and emits autofocus light (AF light) toward the vicinity of a processing point on the wafer 11. The emitted light is collected by the lens 18. The AF light strikes the surface of the wafer 11 and is reflected. The AF light passes through the AF offset mechanism 21 and the lens 17 which are sequentially arranged on the upper right of the wafer 11 and reaches the AF light detector 16. The AF light detector 16 detects the AF light, sends an AF signal to the control circuit 2, and the control circuit 2 analyzes the signal to detect focus or defocus. When the defocus is detected, the Z stage 20 is moved up and down via the driving unit 14 to adjust the surface of the wafer 11 to the focus position. An auto focus correction unit 31 is provided in the control circuit 2. This correction unit and AF offset mechanism 21
Will be described later.

Next, a specific method of autofocus temperature correction will be described with reference to FIGS.
FIG. 2 is a plan view showing a shape of a reference mark on a wafer used for measuring a beam diameter. FIG. 3 is a waveform of the intensity level of the reflected light from the mark when the reference mark in FIG. 2 is scanned with the processing laser light. The horizontal axis is the moving length of the XY stage. FIG. 4 is a graph in which the Z stage is moved around the focus position (Z ₀ ) and the beam diameter of the processing laser light is measured. The horizontal axis indicates the Z stage position, and the vertical axis indicates the beam diameter.

To measure the beam diameter of the processing laser light,
The XY stage 13 is driven to scan the reference laser beam 41 while the processing laser beam is continuously transmitted at a low output and applied to the wafer 11. Here, the reference mark 41 is, for example, a planar L-shaped film formed on the wafer 11 using a material having a high light reflectance such as Au.
The upper side 43 and the right side 45 of the reference mark are considerably thin lines with respect to the beam diameter of the processing laser light. However, the relationship between the width of the reference mark and the width of the processing laser does not necessarily have to be “reference mark <processing laser”. What is important is that the gradient of the waveform detected when the reference mark is scanned changes due to defocusing, and the point where this gradient stands most is the focal point.

The upper side 43 is scanned with the processing laser light beam in the X direction as indicated by the arrow in the figure (actually, the reference mark 41 is moved). Then, the intensity of the reflected light from the reference mark 41 is monitored by the alignment photodetector 10. Similarly, the right side 45 is scanned in the Y direction. As shown in FIG. 3, the waveform 51 monitoring the intensity of the reflected light rises upward when the beam and the side of the mark overlap. The width of the rising waveform 51 (the threshold is appropriately selected) represents the beam diameter.

Next, a change in the beam diameter is observed while moving the Z stage under a certain ambient temperature. The result is the graph shown in FIG. Z _{0 of the} Z stage position is a focus position indicated by the autofocus mechanism, and L 0
₀ is a position where the diameter of the light beam detected by the alignment detector 10 is smallest, and L 'is a general position. Normally, Z ₀ and L ₀ are adjusted so as to coincide with each other, but as described above, if the focus position shifts due to the temperature fluctuation of the air around the apparatus, a difference appears between Z ₀ and L ₀ .
Therefore, the measurement shown in FIG.
(Once for each processing lot) to measure the deviation between Z ₀ and L ₀ . Then, the deviation (Z ₀ −L ₀ ) is given as an offset to the AF offset mechanism (21 in FIG. 1).
Correct the misalignment.

FIG. 5 is a side view schematically showing a harbing mechanism as an example of the AF offset mechanism 21 of FIG. The harbing mechanism 61 includes a rotatable parallel prism 63. And the parallel prism 63
, The AF light 65 traverses from right to left. Here, when the parallel prism 63 is tilted by a slight angle θ, the AF light 6
Numeral 5 denotes refraction when the light passes through the parallel prism 63. The refraction light 5 'is shifted from the parallel prism 63 by the amount of OS, and goes out to the left. This deviation OS is the offset. Actually, the OS amount is adjusted by the inclination of the AF light 65 and given to the AF offset mechanism.

As described above, in this embodiment, the Z stage position at which the beam diameter of the processing laser beam on the workpiece is minimized is detected, and the Z stage position and the Z stage focus indicated by the autofocus mechanism are detected. The difference from the position is calculated, and this difference is given to the autofocus mechanism as an offset. Therefore, since the focus position deviation is detected and the autofocus is offset by using the beam diameter, which is the final control target, as the observation target, correction can be performed including other errors, and favorable laser processing can be performed.

[0020]

As is apparent from the above description, the laser processing apparatus according to the present invention includes the auto-focus temperature correction unit for automatically correcting the focus position fluctuation due to the temperature fluctuation around the apparatus. A focus position shift can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an overall configuration of a laser processing apparatus according to one embodiment of the present invention.

FIG. 2 is a plan view showing a shape of a reference mark on a wafer used for measuring a beam diameter.

FIG. 3 is a waveform of an intensity level of reflected light from a mark when the reference mark in FIG. 2 is scanned with a processing laser beam. The horizontal axis is the moving length of the XY stage.

FIG. 4 is a graph in which a Z stage is moved around a focus position (Z ₀ ) and a beam diameter of a processing laser beam is measured. The horizontal axis indicates the Z stage position, and the vertical axis indicates the beam diameter.

FIG. 5 is a side view schematically illustrating a harbing mechanism as an example of an AF offset mechanism of the laser processing apparatus in FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Control circuit 3 Optical attenuator 4 Lens 5 Reflecting mirror 6 Slit 7a, b Half mirror 8 Alignment laser 9 Objective lens 10 Alignment photodetector 11 Workpiece (semiconductor wafer) 12 Suction holder 13 XY stage 14 Drive Unit 15 Position detection unit 16 AF photodetector 17, 18 Lens 19 LE for AF
D 20 Z stage 21 AF offset mechanism 31 Auto focus correction unit 41 Reference mark 43 Upper side 45 Right side 51 Mark scanning waveform W Processing laser beam diameter 61 Harving mechanism 63 Parallel prism 65 AF light

Claims (3)

[Claims] 1. An apparatus for processing a workpiece by irradiating a workpiece with laser light; an autofocus mechanism for processing laser light; and an autofocus temperature correction unit for automatically correcting focus position fluctuation due to temperature fluctuation around the apparatus. A laser processing apparatus, comprising: 2. An apparatus for processing a workpiece by irradiating the workpiece with laser light; a processing laser light source; an optical attenuator for setting a beam diameter and / or an energy value of the processing laser light; Optical axis direction (Z direction) and optical axis vertical direction (X,
A stage to be moved in the Y direction), a position detector for monitoring the position of the stage, an auto-focus mechanism for the processing laser beam, a control circuit for controlling each of the above-described units, and automatic correction of focus position fluctuation due to temperature fluctuation around the apparatus. A laser processing apparatus, comprising: 3. The correction section detects a Z-stage position at which a beam diameter of a processing laser beam on a workpiece is minimized, and detects the Z-stage position and Z-position indicated by an autofocus mechanism.
3. The laser processing apparatus according to claim 1, wherein a difference from a focus position of the stage is calculated, and the difference is given to the autofocus mechanism as an offset.