JPH07124764A - Laser beam machining device - Google Patents

Abstract

PURPOSE:To effectively utilise laser energy and to realise stable machining by restraining change of reflectance caused by change of pressure, difference of number of layers and quality of a thin film and fixing the reflectance to machining laser beam in laser beam machining for an object to be machined which consists of thin film construction. CONSTITUTION:Machining is executed by projecting the image of a variable opening 14 on the film to be machined using a variable wavelength laser beam 11. Varying the laser wavelength, a reflected beam from the surface of film to be machined is monitored by a detector 12 to obtain the optimum wavelength and the film is machined. When the wavelength of laser beam 11 is fixed, actual reflectance of the thin film to the laser beam is optimized by using a means by which incident angle to the surface of substrate is changed. Thus, stable laser beam machining for an arbitrary thin film construction is realised.

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, and more particularly to a laser processing apparatus such as a laser trimmer and a laser repair, which is used for removing processing of a thin film constituting substrate.

[0002]

2. Description of the Related Art A wiring substrate or a photomask, which is a processing object such as a laser trimmer or a laser repairer, has a pattern of a multilayer thin film structure on a Si or glass substrate. The thin film forming the multilayer film is a nitride film such as Al / Ta / Cr or Si /
It is an oxide film and has a film thickness of 1 μm or less. When such a thin film is irradiated with laser light, the pattern itself exhibits the effect of a reflecting mirror having wavelength dependence. Therefore, thin film material / number of layers /
Depending on the film thickness, it has a high reflectance with respect to the wavelength of the processing laser light, and a high output laser is required for effective processing. In order to avoid such a situation, conventionally, in designing a pattern, a method has been taken so that the pattern does not have an unnecessarily high reflectance with respect to the processing laser light.

For example, as described in Japanese Patent Application Laid-Open No. 60-212822, during laser annealing of a polycrystal silicon film on an insulator substrate, the polycrystal silicon film thickness is different from that of a processing laser beam. And the film thickness is controlled so that the reflectance becomes the lowest. In the field of laser trimming, there is a memory repair technique for repairing a defective LSI to a good product by cutting a fuse forming a redundant circuit provided in an LSI memory with a laser. Polycrystalline silicon is deposited on the substrate as a fuse material, on which a glass material is applied as a protective layer. The fact that the thickness of this protective layer greatly affects the irradiation laser energy required for processing is described in, for example, J. Master. Res. , Vol. 1, N
o. 2 (1986) p. 368-p. 381. Also in this case, conventionally, the design of the protective layer has been optimized so that stable processing can be performed with the minimum required energy. The thin film structure under the layer to be processed is also affected by laser trimming or the like. When a thin film resistor is made of a metal film such as Ti on a film made of silicon nitride / oxide, and is cut by the laser trimming method, it is better to process the lower multilayer film as well for better trimming. . This is described, for example, in Reference J. Appl. Phys. , V
ol. 48, No. 6 (1977) p2323-p. Two
419 and the like.

On the other hand, the reflectance and absorption coefficient of the object to be processed such as metal, semiconductor and polymer material have wavelength dependence.
Generally, the shorter the laser wavelength, the higher the absorption coefficient of the substance, and the higher the processing efficiency. From this viewpoint, JP-A-58-86
As described in Japanese Patent No. 787, there is a method in which a plurality of lasers having different wavelengths are provided as processing laser light sources, and the lasers are switched or the outputs are mixed according to the absorption characteristics of the processing target. In addition, JP-A-1-192492
As described in the specification, there is a method in which a nonlinear optical element is used, a harmonic wave of laser output light is generated by a wavelength conversion technique, and this is used for processing by switching it as needed.

[0005]

The conventional laser processing apparatus has the following problems. In the method of optimizing the multilayer film structure according to the processing laser light wavelength, the nonuniformity of the film thickness becomes a problem. As an example, the document J. A
ppl. Phys. , Vol. 50, No. 7 (197
9) p. The film structure quoted from 5012 is shown in FIG. FIG. 6 shows the reflectance change when the thickness of the oxide film changes by ± 10% in the film structure of FIG. In FIG. 6, the center position of the X axis of the graph corresponds to the YAG laser beam having a wavelength of 1.064 μm.
Looking at the reflectance at 1.064 μm, the oxide film thickness is 0.6
When the thickness was 3 μm, the reflectance R was 1.6%, but when the film thickness increased 10%, R = 15.1%, and when the film thickness decreased 10%, R = 18.0. %. Since the reflectance of the film increases in accordance with the change in the film thickness in this way, the laser energy effective for processing the film decreases and the processing becomes unstable. In the processing of fine patterns such as LSIs and photomasks, in order to minimize the influence on the lower layer part and the processing peripheral part, the laser power close to the processing threshold is set, and laser light of unnecessarily high power is set. I try not to irradiate. For this reason, variations in the reflectance of the multilayer film structure have a great influence on the processing quality.

Further, the method of equipping a plurality of laser processing apparatuses has a problem from the viewpoint of increase in apparatus cost / maintenance, etc., and in the method of using harmonics, at most 2nd harmonic, 3rd harmonic, etc. can be selected. Therefore, it cannot always be processed at a wavelength suitable for the film structure. In general, the film thickness / material is not determined on the premise of laser processing such as the pattern of a photomask, so that the incompatibility between the processing laser light wavelength and the film structure is often more remarkable.

[0007]

In the laser processing apparatus of the present invention, in order to reduce the reflectance from the surface of the thin film substrate and increase the processing efficiency, the effective refractive index of the thin film material is changed to obtain a stable reflectance. Control to obtain. There are two types of configuration methods for this purpose. First, the processing laser to be installed is tunable in wavelength, and a wavelength suitable for the thin film structure is selected. The other one has a means for adjusting the incident angle of the laser with respect to the thin film substrate by changing the processing laser light to a fixed wavelength, and changes the effective refractive index of the material to the laser light.
In either configuration method, a means for detecting the intensity of reflected light or transmitted light from the surface of the thin film substrate is provided, and the optimum laser oscillation wavelength or incident angle to the substrate is controlled and set by the detection signal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. First Embodiment FIG. 1 is a configuration diagram of a first embodiment of the present invention. In this example,
It is a laser repair that uses a variable wavelength laser and projects a variable aperture image irradiated with the laser light onto a thin film substrate with an objective lens for processing. The output beam of the tunable laser 11 is
The output light detector 13 monitors the power, and the optical attenuator 15 controls so as to obtain a predetermined processing laser intensity. The variable opening 14 is processed by the control unit 17 according to a command,
The opening shape is adapted to the defects on the upper side. The aperture shape of the variable aperture 14 is transferred onto the thin film substrate 22 by the objective lens 18, and the defective portion is laser processed. The thin film substrate 22 is fixed on the XY stage, moved in the focal plane of the objective lens 18 by the X-axis motor 20 and the Y-axis motor 21, and positioned at a predetermined defect position. The reflected light from the processed surface is monitored by the reflected light detector 12, and the output light wavelength of the laser 11 is controlled so as to have a predetermined reflected light intensity. The reflected light is monitored by weakening the irradiation laser light by the optical attenuator 15 before the actual processing. Irradiate the weakened laser light to the processed part,
If the signal intensity when the wavelength is sequentially changed is taken, this intensity change corresponds to the reflectance change. As a matter of course, the output of the reflected light detector 12 is standardized by the signal intensity of the output light detector 13 to take measures to minimize the influence of laser power fluctuation. For example, when the output wavelength of the laser 11 is changed in the thin film structure of FIG. 5, the graph shown in FIG. 6 is the film thickness (0). In this case, the wavelength at which the reflectance is minimum is approximately Y
It is in the vicinity of the wavelength of the AG laser (1.064 μm). 1.
The wavelength of the laser 11 is set to around 064 μm, and
When the thin film substrate 22 having the above thin film structure is irradiated, the laser light efficiently reaches the lower silicon substrate.
Even if laser light absorption by the multilayer film is small, effective heating of the silicon substrate can be realized, and the multilayer film on the upper part can be removed by the heat generation / transpiration process.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the detector means is changed from the reflected light detector 12 to the transmitted light detector 23 in the structure of the first embodiment. The transmitted light that has passed through the thin film 22 to be processed is transmitted by the condensing lens 24 fixed to the XY stage base to the transmitted light detector 23.
Collected in. Here, the thin film 22 to be processed applied in this embodiment is a transparent conductive film or the like formed on a glass substrate used in a liquid crystal panel or the like. While the transmitted light intensity is monitored by the transmitted light detector 23, the wavelength of the laser 11 is changed and laser processing is performed at the wavelength that provides the optimum transmittance.

Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, instead of changing the wavelength of the processing laser light in the first embodiment, the wavelength of the processing laser light is fixed and the incident angle to the multilayer thin film substrate is changed, whereby the effective refraction of the thin film forming the multilayer film is changed. The rate is changed, and as a result, the reflectance for the incident laser light is reduced. In this embodiment, as a method of changing the incident angle θ with respect to the thin film substrate 22, laser light is applied to the objective lens 18.
The optical axis is made eccentric with respect to the optical axis and incident.
In addition to this, various methods can be considered in which the laser light is incident at an angle with respect to the processed surface. For example, there are a method of fixing the beam and rotating the substrate itself with respect to the optical axis, and a method of rotating the entire optical axis of the laser processing optical system with respect to the substrate surface normal. The laser light intensity is set below the processing threshold value, and the reflected light intensity is monitored by the detector 12 while moving the beam splitter 16 in the X-axis direction on the paper surface. When the beam splitter 16 moves, the incident angle θ of the laser light on the substrate changes. As an example, in the thin film configuration of FIG.
64 μm) and the thickness of the oxide film SiO2 is 0.693.
FIG. 7 shows how the reflectance changes depending on the incident angle in the case of μm. When the incident angle is other than 0 degree, the reflectance varies depending on the polarization direction of the laser light. As can be seen from FIG. 7, the reflectance, which was about 15% at normal incidence, decreases to about 2% at an incident angle of 30 degrees. Therefore, in such a thin film structure, it is more efficient to process at an incident angle of 30 degrees. This effect is that assuming that the refraction angle in each thin film layer is φ, the refractive index (effective refractive index) of each polarization of the thin film is ns = n × cosφ, np = n / cosφ, and the Fresnel reflection formula is applied as it is. Because you can.

Further, in the fourth embodiment, like the relationship between the first embodiment and the second embodiment, in the configuration of the third embodiment, the reflected light detector 12 is changed to the transmitted light detector 23 to perform the above operation. .

Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, the processing laser light has a fixed wavelength, and the beams divided into a plurality of beams are simultaneously irradiated to the processing locations on the multilayer thin film substrate by changing the incident angles. The effective refractive index of the multilayer thin film for each incident beam varies depending on the incident angle. As a result, the same effect as when the laser beams of multiple wavelengths are simultaneously incident on the thin film substrate is obtained, and the total amount of laser energy reflected by the thin film is changed even if the film thickness of the substrate varies depending on the substrate or the position within the substrate. Can be made uniform to some extent, and more stable thin film processing can be realized. In the embodiment of FIG. 4, the output light of the processing laser 11 is split by the four beam splitters 16, and the split beam intensity is set to be equal at each angle. Each split beam is focused by the objective lens group 18 at the same position on the thin film 22 to be processed. The total irradiation laser energy is monitored by the output photodetector 13, and the optical attenuator 1
5 is controlled to set the optimum laser power for processing. The intensity ratio of the split beams and the incident angle of each of the beams (θ1: minimum incident angle, θ2: maximum incident angle) can be set to predetermined values depending on the thin film structure, film thickness variation in manufacturing, and processing characteristics. Is. FIG. 8 shows the incident angle dependence of the reflectance when the oxide film thickness varies by 2.5%, 5.0%, and 10% in the thin film structure of FIG. Laser light is s-polarized. The incident angle θ is evenly divided into four types of 0 degree, 10 degrees, 20 degrees, and 30 degrees, and when the average reflectance Rs at that time is calculated, there is no change in the oxide film thickness (do = 0.6 μm). When Rs = 5.6%, d = do + 2.5% Rs =
When 3.4% and d = do + 5.0%, Rs = 3.3%,
When d = do + 10%, Rs = 9.3%. Considering that the reflectance R changes from 1.6% to 15.1% in the case of only vertical incidence, the average reflectance by the irradiation method of the present invention suppresses the reflectance fluctuation quite effectively. I understand. Therefore, the laser processing can be performed with such a stable power, and more stable laser processing that is less affected by the film thickness variation can be realized.

[0013]

As described above, in the laser processing apparatus according to the present invention, in the processing of a substrate having a multilayer thin film structure, when there is a variation in the thickness of the thin film, the wavelength of the laser for processing or the surface of the substrate is changed. By controlling the incident angle, the interference effect in the multilayer thin film material can be kept constant, and as a result, the laser light reflectance on the substrate surface can be kept constant. Therefore, even if the membrane pressure varies to some extent,
This has the effect of realizing stable laser processing. Further, even for multi-layered thin film substrates of different materials / structures, by selecting the wavelength or the incident angle, it is possible to optimize the laser processing conditions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a fifth embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of a substrate having a multi-layered thin film structure to be processed by the present invention.

6 is a graph showing a calculation result showing the wavelength dependence of the reflectance when the thickness of the oxide thin film is changed in the multilayer thin film substrate of FIG.

7 is a graph showing a calculation result showing the incident angle dependency of reflectance in the multilayer thin film substrate having the structure of FIG.

FIG. 8 is a graph showing a calculation result showing the incident angle dependence of the reflectance at each oxide film thickness in the multilayer thin film substrate having the structure of FIG.

[Explanation of symbols]

 11 Processing Laser 12 Reflected Light Detector 13 Output Light Detector 14 Variable Aperture 15 Optical Attenuator 16 Beam Splitter 17 Control Section 18 Objective Lens 19 Stage Drive Section 20 X-Axis Motor 21 Y-Axis Motor 22 Processing Target Thin Film 23 Transmitted Light Detector 24 Collection Optical lens 25 Detection lens

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 21/027 27/01 321 H01S 3/10 Z

Claims (3)

[Claims] 1. A laser oscillator whose oscillation wavelength is variable, means for condensing laser light on the surface of a workpiece, moving means for positioning the laser light at a specified position on the surface of the workpiece, and a workpiece. A laser processing apparatus comprising: a means for detecting the intensity of reflected light or transmitted light from the surface; and a means for controlling the oscillation wavelength and laser output of the laser oscillator according to the intensity of the detection signal by the detecting means. 2. A laser oscillator having a fixed oscillation wavelength, a means for condensing the laser light on the surface of the processing object, a moving means for positioning the laser light at a designated position on the surface of the processing object, and a laser light The means for controlling the incident angle to the surface of the object to be processed, the means for detecting the intensity of the reflected light or the transmitted light from the surface of the object to be processed, and the angle of incidence of the laser beam by the intensity of the detection signal by the detection means. And a means for controlling the laser processing apparatus. 3. A laser oscillator having a fixed oscillation wavelength, a means for condensing the laser light on the surface of the object to be processed, a moving means for positioning the laser light at a designated position on the surface of the object to be processed, and the laser light. Laser processing having means for splitting a plurality of beams into a plurality of beams at a predetermined intensity and means for simultaneously irradiating the plurality of beams at the same location on the surface of the object to be processed at independent incident angles. apparatus.