JPH04137744A - Laser marking apparatus - Google Patents

Abstract

PURPOSE:To apply an appropriate laser mark on various materials by employing second higher harmonic of laser beam in the marking operation. CONSTITUTION:A laser unit 1 comprises a continuous Q switch mode YAG laser and generates a continuous pulse laser beam L1 which is then impinged on a second higher harmonic generator 2. The second higher harmonic generator 2 generates a basic wave L1 and a second higher harmonic L2 which are impinged on a wavelength separator 3. Second higher harmonic outputted from the wavelength separator 3 is then subjected to optical axis adjustment through optical axis adjusting mirrors 41, 42 and then impinged on scanning mirrors 51, 52. The scanning mirrors 51, 52 are controlled by galvanometer scanners 51a, 52a to scan a character or a figure to be marked with the second higher harmonic wave L2. According to the constitution, appropriate laser marking can be applied on a marking object of various materials by means of limited types of laser unit.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to laser marking, which marks an object by scanning a continuous pulse laser beam corresponding to a marking pattern and irradiating the object with the laser beam. Regarding equipment.

[Background Art] For example, in a semiconductor manufacturing process, a marking such as a manufacturing lot number is performed on the surface of a silicon or other semiconductor wafer.

Conventionally, this marking work has been performed by an operator using a diamond pen or the like, but this work is complicated and the written characters are difficult to read. Furthermore, since marking involves scraping the wafer surface along the marking pattern, scraps are generated. In the semiconductor manufacturing process, the presence of dust is extremely undesirable because it directly affects the yield of products.

For this reason, scanning marking type laser marking equipment is now being used, which applies a marking by irradiating a laser beam onto the wafer surface and altering, evaporating, or melting the surface along a marking pattern. .

By the way, when marking a wafer with a high-density wiring pattern such as an LSI, the laser marking also prevents the scattering of silicon, etc. (splash, debris) generated during laser marking.
It has been found that this has a significant negative effect on the performance and yield of the resulting devices.

For this reason, a soft marking method has recently been proposed in which a marking free of flying particles can be obtained by melting the surface of silicon or the like without evaporating it. Basically, this soft marking can be done by setting the intensity of the irradiated laser beam to an appropriate value, but specifically, the pulse energy of the laser pulse, the intensity distribution and pulse width of the beam cross section, or the marking For example, Ga
Depending on the material of As or other materials, the actual situation is that the optimum conditions are currently being determined experimentally.

Currently, soft marking on wafers such as silicon for LSI is performed using a Q-switch YAG laser device (fundamental wave wavelength: 1.064 μm), which has a highly stable pulse peak value and can relatively easily control the pulse frequency. It has been successful using .

E Problem to be Solved by the Invention M] By the way, especially recently, with the demand for high-speed calculation, wafers such as GaAs have been used instead of wafers such as silicon. Of course, this G
It is also necessary to perform soft marking on aAs wafers.

However, this GaAs wafer has the above-mentioned Q switch Y.
When conducting an experiment to perform soft marking using an AG laser device, it was found that good soft marking could not be obtained. In other words, when trying to find the optimal intensity by gradually increasing the laser power, ablation (a phenomenon in which material on the irradiated surface evaporates or scatters) suddenly occurs at a certain intensity, resulting in melting suitable for soft marking. It was found that there were almost no When this ablation occurs, in addition to ions, atoms, and molecules, particulate flying objects are scattered, and these particulate flying objects cause circuit defects in later steps.

Therefore, we considered other laser devices and conducted various experiments by comprehensively considering factors such as power and stability, but in the end,
It has been found that there is nothing more advantageous than the Q-switched YAG laser device by extension of the conventional concept.

Such a situation also occurs when selecting a combination of a wafer made of another material and a laser device suitable for performing soft marking on the wafer.

The present invention was made against the above-mentioned background, and provides a laser marking device that makes it possible to perform appropriate laser marking on marking objects made of various materials using limited types of laser devices. It is intended to provide.

[Means for Solving the Problems] The present invention solves the above problems by having the following configurations.

(1) a laser beam generating means that generates a continuous pulse laser beam; a second harmonic generating means that receives the laser beam emitted from the laser beam generating means and generates a second harmonic of the laser beam; scanning means for scanning the second harmonic beam emitted from the second harmonic generation means in accordance with the marking pattern; and condensing lens means for condensing the second harmonic beam onto the marking target. Configuration with.

(2) In the configuration (1), the laser generating means is a Q-switch YAG laser device, and the marking target is a GaAs wafer.

[Operation] According to the above configuration (1), since the second harmonic of the laser beam emitted from the laser beam generating means is used as the light for marking, the wavelength of a limited type of laser device can be used. The selection range is doubled, and it becomes possible to apply appropriate laser marking to objects made of a wider variety of materials using a limited number of laser devices. Here, the reason why the laser generation means is limited to one that performs continuous pulse oscillation is that in the case of pulsed light, the pulse energy (including the peak value) of the second harmonic generated by the second harmonic generation means ) can be extracted as the strength necessary for marking. Furthermore, according to configuration (2), GaA
An apparatus is obtained that can apply appropriate markings to S wafers.

Note that the idea of using the second harmonic is difficult to conjure up by simply extending the conventional idea in the technical field of the present invention, so some explanation will be given regarding the circumstances in this regard.

This technical field involves vaporizing or melting the surface of the marking target, and the laser beam used is required to have the necessary power. Therefore, first, a laser device with sufficient oscillation power is selected as the laser device to be used. Usually, consideration is given to irradiating the target object with this laser power without attenuating it as much as possible.

On the other hand, a second harmonic generator can only obtain a second harmonic that is significantly weaker than the fundamental light (for example, about 115 points of the fundamental wave), so the second harmonic is used in this field. It is usually unthinkable to do so.

In contrast, the present inventor first focused on the minimum energy required to form the small molten dots that constitute the mark. According to this, it was found that if all the energy of the irradiated light is absorbed, a relatively small amount of energy is sufficient. Next, we investigated a laser device with a wavelength that has a high absorption rate for the marking target. As a result, it was found that some materials had extremely low absorption rates for the fundamental wave, but extremely high absorption rates for the second harmonics. Therefore, for such a combination, the second
The effect of attenuation by the harmonic generation means and the effect of increasing absorbed energy due to an increase in absorption rate were estimated. the result,
It has been found that there are certain combinations in which the use of the second harmonic would be much more advantageous in terms of melting than the use of the fundamental wave. Based on this consideration, an experiment was conducted and it was confirmed that there are combinations in which appropriate marking cannot be achieved with the fundamental wave, but appropriate marking can be achieved with the second harmonic.

[Embodiment] FIG. 1 is a diagram showing the configuration of a laser marking device according to an embodiment of the present invention. Hereinafter, one embodiment will be described in detail with reference to these drawings. Note that in this example, Ga
This is an example of applying soft marking to an As wafer.

In FIG. 1, numeral 1 is a laser device, numeral 2 is a second harmonic generator, numeral 3 is a wavelength separator, numeral 41.42 is an optical axis adjustment mirror, numeral 51.52 is a scanning mirror, numeral 6 is
is a condensing lens, and numeral 7 is an object to be marked.

The laser device 1 is composed of a continuous Q-switch mode YAG laser, and a continuous pulse laser beam L1 with a wavelength of 1.064 μm, a pulse width of 5 μs, and a pulse interval of 1 ms is emitted as a fundamental laser beam from this laser device 1. be done.

The laser beam L1 emitted from this laser device 1 is
It is designed to be input to a harmonic generator 2. This second harmonic generator 2 is composed of KTP (KTiOPO4>, C
DA (CsD2 As04), KD*P (K
A crystal such as D2 PO4) is housed in a temperature control device, etc., and the fundamental wave pulsed laser beam L1 is incident on it.
A second harmonic L2 of this fundamental wave L1 is generated and emitted together with Ll.

The fundamental wave L1 and the second harmonic L2 emitted from the second harmonic generator 2 are made to enter the wavelength separator 3. This wavelength separator 3 receives the fundamental wave L1 and the second harmonic L2 and extracts only the second harmonic L2 as light traveling on a predetermined optical path, and is composed of, for example, a prism or a dichroic mirror. be done.

The second harmonic emitted from the wavelength separator 3 has its optical axis adjusted through an optical axis adjustment mirror 41.42, and then enters a scanning mirror 51.52.

The scanning mirrors 51 and 52 are controlled by carbanometer scanners 51a and 52a, and scan the second harmonic L2 in accordance with the characters, figures, etc. to be marked.

This scanned second harmonic L2 is applied to GaA, which is the marking target, by an f-θ lens 7 constituting a condensing lens.
The light is focused on the surface of the S wafer 7.

As a result, a large number of molten dots (dots with a diameter of about 30 μm) are formed on the surface of the GaAs wafer 7 along a predetermined mark shape.
m, dot depth of about 0.5 to 1.5 μm) is formed,
Marking is done.

FIG. 2 is an enlarged view of one molten dot constituting a mark when a GaAs wafer is actually marked using the apparatus of the above embodiment. As shown in this figure, it can be seen that according to this example, the surface of GaAs was appropriately melted, a clean dot was formed, and no scattered matter was generated around it.

On the other hand, for comparison, Figure 3 shows an enlarged view of the dots forming the mark when the mark was formed on a GaAs wafer using the fundamental wave (wavelength, 1.064 μm) of a YAG laser. .

As shown in FIG. 3, in this case, ablation occurred and various types of dust including granular particles were generated in the surrounding area.

In the above embodiment, a GaAs wafer is marked using the second harmonic of a YAG laser, but in this embodiment, Se, As2 S3, It can also be applied to wafers made of CdS or the like.

It goes without saying that the present invention can also be applied to marking objects made of other materials using other lasers.

[Effects of the Invention] As detailed above, the present invention is capable of marking objects made of various materials using limited types of laser devices by performing marking using the second harmonic of laser light. The present invention provides a laser marking device that enables appropriate laser marking on objects.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a laser marking device according to an embodiment of the present invention, FIG. 2 is an enlarged view of one fused dot constituting a mark formed by the device of one embodiment, and FIG. 3 is a YAG FIG. 2 is an enlarged view of dots constituting marks formed on a GaAs wafer using the fundamental wave of a laser. 1... Laser device, 2... Second harmonic generator, 3...
・Wavelength separator, 41.42...Mirror for optical axis adjustment, 5
1°52... Galvano mirror 16... f-theta lens, 7... Marking target.

Claims (2)

[Claims] (1) a laser beam generating means that generates a continuous pulse laser beam; a second harmonic generating means that receives the laser beam emitted from the laser beam generating means and generates a second harmonic of the laser beam; scanning means for scanning the second harmonic beam emitted from the second harmonic generation means in accordance with the marking pattern; and condensing lens means for condensing the second harmonic beam onto the marking target. Laser marking device with. (2) The laser marking device according to claim (1), wherein the laser beam generating means is a Q-switched YAG laser device, and the marking target is a GaAs wafer.