JPH11287707A - Measuring apparatus for laser pulse energy, and control apparatus for providing working laser pulse and method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring apparatus for laser pulse energy that accurately measures laser pulse energy in an infrared region. SOLUTION: A measuring apparatus 20 for laser pulse energy has a semiconductor optical detector 6 which a laser pulse B2 for monitoring is made incident, a detector temperature control device 21 (7, 8, 9) that controls so that temperature C of the detector 6 is maintained at C1, an integrator 10 that time- integrates an output D0 (D) of the detector 6 corresponding to luminous energy of 1-shot laser pulse to determine energy E of the laser pulse B2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser pulse energy measuring apparatus, and more particularly, to measuring the energy of a laser pulse having a very high peak output and a relatively small pulse width, such as a laser pulse for laser processing. The present invention relates to a measuring device, and a processing laser pulse supply control device and method using the same.

[0002]

_2. Description of the Related Art BVH (blind via) is applied only to the surface resin layer of a high-density multilayer printed circuit board using an infrared laser pulse oscillator having a very high peak output and a relatively small pulse width such as a TEA-CO ₂ laser. Forming holes) is known. At this time, a single-shot pulse does not form a hole having a predetermined depth, and a pulse (a via hole) having a predetermined depth is formed by irradiating a plurality of shots with a pulse.
It is often necessary to open

[0003] In the case of a laser pulse having a very high peak output and a relatively small pulse width, such as a pulse from a TEA-CO ₂ laser, the energy of each pulse varies. For example, when at least one pulse energy of a plurality of shot pulses is excessively large and, for example, a via hole having a predetermined depth is formed without the pulse of the last one shot, a predetermined number of shot pulses are set in advance. If drilling is performed unconditionally, loss of processing energy and processing time is caused in connection with the input of excessive pulse energy. On the other hand, when the pulse energy of at least one of the pulses of the plurality of shots is excessively small, the holes do not penetrate the resin layer and the predetermined via holes are not formed with the predetermined number of shot pulses.

In order to avoid such a problem, when drilling with a plurality of shot pulses, the drilling is performed while monitoring the pulse energy to be irradiated. For example, it is determined whether each pulse energy has reached a predetermined level. (For example, irradiating an additional pulse when there is a pulse that does not reach a predetermined level) (Japanese Unexamined Patent Application Publication No. 9-253878), and a plurality of shot pulses while measuring each pulse energy. Irradiation is performed, and an additional pulse is irradiated when the integrated value of the measured pulse energy does not reach a predetermined level (Japanese Patent Laid-Open No. 9-308977).

By the way, in order to monitor the pulse energy, it is necessary to branch a processing laser pulse at a constant energy ratio and take it out for monitoring, and measure the energy of the monitoring laser pulse in real time as accurately as possible. .

In order to detect the energy of a laser pulse in the infrared region, a heat-sensitive detector for detecting the magnitude of the pulse energy in the form of thermal energy, or a semiconductor-type photodetector such as a photodiode or a phototransistor is usually used. Is used.

[0007]

However, the thermal detector is not suitable for measuring the energy of a pulse having a high repetition frequency because of its slow response speed. In addition, it takes time for the detector to stabilize, and a drift occurs in the output of the detector at the beginning of measurement, making it difficult to perform rapid processing control.

On the other hand, in a semiconductor-type photodetector such as a photodiode, the sensitivity of the detector is sensitive to temperature, so that the output of the detector is prevented from fluctuating due to a change in ambient temperature or the like. It was difficult.

Therefore, the conventional measurement of the energy of the processing laser pulse is somewhat inaccurate. Further, in a state where the pulse energy measurement is inaccurate, the above-described processing control is difficult to be performed as intended. The problem of measuring the pulse energy is not only a laser in the far infrared region such as a TEA-CO ₂ laser, but also a laser in the near infrared region such as an Nd: YAG laser or a visible region such as a harmonic YAG laser. It is believed that this also applies somewhat to laser pulse energy measurement.

The present invention has been made in view of the above points, and has as its object to provide a laser pulse energy measuring device capable of accurately measuring the energy of a laser pulse.
Another object of the present invention is to provide a processing laser pulse supply control device and method using the same.

[0011]

SUMMARY OF THE INVENTION According to the present invention, it is an object of the present invention to provide a semiconductor photodetector on which a laser pulse for monitoring is incident, and a detector for controlling the temperature of the detector to be constant. This is achieved by a laser pulse energy measurement device having a temperature control device and an integrator for integrating the output of a detector according to the light amount of a one-shot laser pulse to obtain the energy of the laser pulse.

[0012] In this specification, "laser for monitoring", TEA-CO ₂ laser or Nd for working: YA
It refers to a part of a laser beam of a laser pulse having a high peak output emitted from an infrared laser such as a G laser or a visible or ultraviolet laser such as a 2 or 3rd harmonic YAG laser for monitoring.

In this specification, a "semiconductor photodetector" is a quantum detector that utilizes the electronic excitation of electrons in a semiconductor by the absorption of photons, and depends on the light quantity or energy of a laser pulse. Any device that can provide an output may use a photovoltaic effect, such as a photodiode, or may use a photoconductive phenomenon. As a device utilizing the photovoltaic effect, a junction type or a photon drag type may be used. In any case, in the semiconductor type photodetector, the detection sensitivity (output) greatly depends on the temperature.

"The output of the detector according to the light quantity of the one-shot laser pulse" means that when the semiconductor photodetector receives the "one-shot laser pulse", the peak output and pulse width of the laser pulse are obtained. Means a time-dependent output given during a time sufficiently shorter than the pulse repetition period.

In order to measure the energy of a laser pulse having a very high peak output and a relatively small pulse width as accurately as possible, various studies were made on the energy measurement by a photodiode type semiconductor photodetector. When avoiding the occurrence (influence) of an error caused by the temperature of the semiconductor photodetector, the user has the following characteristics in the waveform of the time-dependent output of the semiconductor photodetector. (It can be effectively used for energy measurement for processing control and the like).

That is, although a very small portion is taken out for monitoring, the processing laser pulse has a very high peak output and a short rise time until the peak, so that the pulse form corresponding to the light amount of the laser pulse is detected. The output of the laser is almost saturated immediately after rising, and it is difficult to linearly respond to the peak output of the laser pulse. If the intensity or sensor sensitivity is adjusted so as not to saturate at the peak output, the dynamic range becomes too large to observe the pulse time shape. However, the increase in the peak power of the laser pulse affects the time waveform of the detector output, and by integrating the detector output over time, an amount that is approximately proportional to the laser pulse energy can be determined.

The "detector temperature control device" may be of any type as long as the temperature of the photodetector can be kept constant within a temperature range in which the photodetector has desired detection characteristics. In addition, the temperature set and controlled by the detector temperature controller is not affected unless the detection characteristics such as the sensitivity of the photodetector are significantly affected.
The temperature is preferably a temperature at which the photodetector is easy to handle, for example, a temperature that does not require cooling of the photodetector, that is, a temperature slightly higher than room temperature or room temperature. Further, it is preferable that the temperature of the photodetector set and controlled by the detector temperature control device is such that the temperature dependency of the detection sensitivity of the detector becomes as low as possible.

[0018]

The laser pulse energy measuring device of the present invention has a detector temperature control device for controlling the temperature of the semiconductor photodetector so as to keep the temperature constant. Therefore, the influence of the heat generated by the light reception can be minimized, and the detection accuracy of the light amount of the laser pulse by the semiconductor photodetector can be enhanced.
In the laser pulse energy measuring device of the present invention, 1
Since the output of the detector according to the light amount of the laser pulse of the shot is integrated over time to obtain the energy of the laser pulse, based on the relatively accurate output of the temperature-controlled photodetector, For a one-shot laser pulse, the energy of the pulse can be determined relatively accurately in the form of the output of the integrator. As a result, the integrated value obtained by integrating the measured values of the energy of the laser pulses of a plurality of shots can be used as a significant amount for the processing control.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The detector temperature control device may be of a type in which a constant temperature bath is used to forcibly keep the detector at a constant temperature, but preferably, a temperature at which the temperature of the photodetector is sensed. It has a sensor and a controller for thermally controlling the photodetector so that the temperature sensed by the temperature sensor becomes constant.

Here, the "temperature sensor" may be a thermocouple or another type of temperature detector. As the constant temperature, a temperature higher than room temperature is preferably selected. In this case, a resistance heating type heater or the like may be used as the “controller that thermally controls the photodetector”. Depending on the detector to be used, a temperature equal to or lower than room temperature is selected as the constant temperature. In this case, even if the cooling of the light detector is controlled by the refrigerant, the light detector is placed in a low-temperature bath lower than the certain temperature. In addition, the temperature of the photodetector may be controlled by a heater or the like.

When a processing laser pulse supply control device is formed using the above-described laser pulse energy measurement device, basically, the integrated output of the integrator for a plurality of shots of laser pulses is compared with a reference value. Then, when the integrated output reaches a reference value (predetermined predetermined value), a comparator for stopping the supply of the laser pulse from the laser oscillator and generating a signal for initializing the integrator may be provided.

In this case, since the laser pulses of a plurality of shots have a predetermined energy defined by the reference value as a whole, the workpiece can be processed reliably and quickly with the laser pulse of the predetermined energy without waste. become. In order to stop the pulse supply, the emission of the pulse itself from the laser oscillator may be stopped, or the emitted pulse may be deflected to a portion other than the irradiated portion of the workpiece. In addition, as the processing, a processing other than the drilling such as the drilling or the cutting may be used.

[0023]

Next, a preferred embodiment of the present invention will be described with reference to the drawings.

It is assumed that the processing by the laser pulse is a perforation on the printed wiring board 50 as shown in FIG. The printed wiring board 50 includes, for example, a resin layer 51 and a metal wiring layer 52 formed on a lower surface of the resin layer 51.
It is assumed that it is necessary to make a hole in the resin layer 51. Further, for example, the pulse energy is 150 mJ and the pulse width is 200 n
s, pulse repetition frequency 300 Hz, average output 45
When a laser pulse from a pulse oscillation laser such as a TEA-CO ₂ laser of about W is irradiated with a predetermined energy, the laser pulse is irradiated in a plurality of shots, for example, 5 shots, so that the wiring layer 52 is formed from the substrate surface 53.
A case in which a hole such as a hole 54 penetrating through the resin layer 51 can be made up to this point will be described as an example. Here, when the energy of the laser pulse of one shot or a plurality of shots is considerably smaller than the normal energy, the hole does not completely penetrate the resin layer 51 with the laser pulse of five shots. It is necessary to change the hole 55 to a hole 54 penetrating the resin layer 51 by additionally irradiating a pulse only for one shot (in some cases, two shots or more). is there. on the other hand,
When the energy of the laser pulse of one shot or a plurality of shots is considerably larger than the normal energy, for example, the hole 5 penetrating through the resin layer 51 by the laser pulse of four shots is used.
No. 4 is formed, and laser pulse irradiation for the fifth shot is unnecessary (excessive).

When the energy of a monitoring laser pulse is measured using a semiconductor photodetector such as a photodiode while the temperature of the semiconductor photodetector is kept constant, the peak output of the laser pulse is measured. The inventor has confirmed that an output as shown in FIG. 2 can be obtained according to the laser pulse energy depending on the pulse width and the pulse width.
In FIG. 2, the horizontal axis represents time, and the vertical axis represents the output of the photodetector.

That is, for example, when the peak output of the laser pulse is normal, assuming that the output waveform of the detector shown by the solid line 41 in FIG. 2 is obtained, the peak output of the laser pulse is relatively low. , An output waveform as shown by a two-dot chain line 42 in FIG. 2 is obtained. When the output waveform 42 and the output waveform 41 are compared, the output waveform 42
Then, the peak value of the detector output slightly decreases depending on the decrease in the peak output of the pulse (in some cases, the peak value does not actually change), and the tail becomes shorter due to the influence of the decrease in the peak output. (The pulse width of the detector output (waveform) is narrow). When the peak output of the laser pulse is considerably higher than usual and the pulse energy is high, the output waveform becomes as shown by a broken line 43 in FIG. When the output waveform 43 and the output waveform 41 are compared, in the output waveform 43, the peak value of the detector output is increased even though the peak output of the pulse is increased.
, But the tail is longer due to the increased peak power. In addition,
The longer the pulse width of the laser pulse, the longer the tail of the detector output in the form of a correspondingly distorted pulse.

FIG. 1 schematically shows a laser processing apparatus using a processing laser pulse supply control apparatus having a laser pulse energy measuring apparatus according to a preferred embodiment of the present invention.

Reference numeral 1 denotes a laser oscillator which emits an infrared laser pulse like a TEA-CO ₂ laser oscillator. A laser pulse B0 emitted from the laser oscillator 1 is a partial reflection mirror (partially transmitting mirror) for extracting monitor light. After being reflected by the surface 2, the surface 53 is transferred to a printed circuit board 50, which is a member to be processed, via a transmission optical system 5 having mirrors 3 and 4.
Irradiation is performed from the side as an irradiation laser pulse B1. In addition, as the mirror 4, or on the substrate 50 side of the mirror 4,
An optical scanner including one or more galvanometer mirrors may be provided to perform processing at different locations on the substrate 50.

In the partially reflecting mirror 2, only a small part, for example, 1% of the energy of the laser pulse B0 emitted from the oscillator passes through the mirror 2 and the amount or energy of the laser pulse B2 as a monitoring laser pulse B2 is changed to a semiconductor. The remaining 99% of the energy detected by the photodetector 6 is used for processing as an irradiation laser pulse B1. Therefore, by measuring the energy of the monitoring laser pulse B2, the energy of the irradiation laser pulse B1 can be measured.

When the temperature of the semiconductor photodetector 6 is kept constant, the semiconductor photodetector 6 has the characteristics shown in FIG. 2 with respect to the laser pulse B2. The temperature of the photodetector 6 is determined by a temperature sensor 7 such as a thermocouple and a temperature controller 9 for controlling heating by a resistance heater 8 so that a temperature signal C detected by the temperature sensor 7 coincides with a set temperature C1. And is controlled by Naturally, the heater 8 has a size sufficient to uniformly heat the entire detector 6 so that the temperature of the photodetector 6 becomes uniform over the entire light detecting portion of the detector 6. It is preferable that the detector 6 is in contact with the detector 6 with as low a thermal resistance as possible so that the detector 6 can be heated in a short time. Further, it is preferable that the temperature sensor 7 is in contact with the light detecting section of the detector 6 with a minimum thermal resistance so that the temperature of the light detecting section itself of the detector 6 can be detected. It is preferable that the heater 8 is located as far as possible from the heater 8 so as not to be directly affected by the heat.

Reference numeral 15 denotes an amplifier. The detection output D0 from the photodetector 6 is sent to the integrator 10 as a detection output D after being amplified by the amplifier 15. Usually, the amplifier 15 may be one that performs linear amplification, and will be described below on this assumption. However, in some cases, it is considered that the output of the photodetector 6 becomes sublinear and saturates with respect to the increase in the peak output due to the high peak output of the laser pulse B2, and the tail of the detector output D0 is taken into consideration. In consideration of the method of application, a suitable kind of function converter that amplifies nonlinearly is used as the amplifier 15, and the time integral value (of the conversion output D) of the laser pulse of one shot (or the processing power) The output may be converted to an output closer to an amount proportional to the actual effective energy value).

The integrator 10 has a detector output D (after amplification)
For example, when the output waveform 42 of FIG. 2 is input as the detector output D, the output waveform 42
After the output time t42, an output E corresponding to the area E42 of the hatched portion in FIG. 2 is given.

Reference numeral 11 denotes a laser pulse energy supply controller comprising, for example, a personal computer provided with an input / output control device, a display, and the like. Then, a trigger pulse F for controlling the emission of the laser pulse B0 from the laser oscillator 1 is given, and the integration / integration value (the integrated value of the integration value) E of the integrator 10 is given to the integrator 10. It is determined whether or not a predetermined energy E0 has been reached, and when the integrated / integrated value E of the integrator 10 reaches the predetermined energy E0, a trigger pulse G for initializing the integrator 10 is given to the integrator 10. It has a comparator.

In the above, the laser pulse energy measuring device 20 includes the semiconductor type photodetector 6 which receives the infrared laser pulse B2 for monitoring and gives an output corresponding to the light amount of the laser pulse, and the temperature C of the photodetector 6. , A temperature controller 9 for thermally controlling the photodetector 6 with a heater 8 so that the temperature C sensed by the temperature sensor 7 becomes constant C1, and a laser pulse B2 for one shot. An integrator 10 for integrating the output D0 (ie, D) of the detector 6 with time to obtain the energy of the laser pulse B2 (ie, B1 or B0). The detector temperature control device 21 includes a temperature sensor 7 and a temperature controller 9 for thermally controlling the photodetector 6 with the heater 8. The processing laser pulse supply control device 22 includes the laser oscillator 1 and the laser pulse supply control device 11 in addition to the laser pulse energy measurement device 20. Further, the laser processing device 23 includes a laser pulse transmission optical system 5 in addition to the laser pulse supply control device 11.

The laser processing apparatus 2 configured as described above
In 3, first, the detector temperature controller 21 sets and controls the temperature C of the semiconductor photodetector 6 to a predetermined temperature C1 which is somewhat higher than room temperature. Next, after the integrator 10 is initialized to an initial value (for example, zero) by the trigger pulse G or at the same time, the laser oscillator 1 is triggered by the trigger pulse F to cause the oscillator 1 to emit the laser pulse B0. Almost all parts B of the emitted laser pulse energy
1 (for example, 99%) is radiated via the optical system 5 to a perforated portion of the printed wiring board 50 to be processed disposed at a predetermined position. On the other hand, the energy of one shot of the emitted laser pulse is accurately controlled by the detector temperature control device 21 and is not affected by room temperature fluctuation or the like.
By integrating the detected output D0 (amplified value D) from the time with the integrator 10, the value can be obtained as an accurate value sufficiently significant for machining control. After a predetermined pulse repetition period H (not shown) from the transmission of the first trigger pulse F, a second trigger pulse F is given from the controller 11 to the laser oscillator 1 and the emission of the laser pulse B0 follows. On the one hand, the detection by the detector 6 and the integral integration by the integrator 10 are repeated, and on the other hand, further drilling by the pulse B1 is performed.

For example, at least one of the laser pulses from the first shot to the fourth shot has a relatively large energy, and after the emission of the fourth laser pulse B0, the integrator 10 (such as room temperature fluctuation). When the integrated integration output E reaches the predetermined value E0, the controller 11 generates a trigger pulse G for initializing the integrator 10 without activating the fifth laser oscillation. A control signal J is issued to a mirror device 4 including an optical scanner having a galvanomirror to change the irradiation position of 50. This makes it possible to avoid irradiating the substrate 50 with an excessive pulse while accurately measuring the energy of the laser pulse without being affected by fluctuations in room temperature or the like.

Conversely, for example, at least one of the laser pulses from the first shot to the fifth shot has a relatively small energy, and after the fifth laser pulse B0 is emitted, the integrator also remains. If the integrated output E of 10 (not affected by room temperature fluctuations, etc.) does not reach the predetermined value E0, the controller 11 provides the laser oscillator 1 with a signal F which activates the emission of the sixth additional pulse. In principle, this additional pulse emission control is continued until the integrated value E of the integrator 10 reaches the predetermined value E0. Thus, while the energy of the laser pulse is accurately measured without being affected by fluctuations in room temperature or the like, an additional pulse can be applied to the substrate 50 to make a predetermined hole 54 in the substrate 50.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a laser processing apparatus using a laser pulse supply control device having a laser pulse energy measuring device according to a preferred embodiment of the present invention.

FIG. 2 is a graph illustrating characteristics of a semiconductor photodetector used in the laser pulse energy measurement device of FIG.

FIG. 3 is an explanatory view of a substrate drilled by the laser processing apparatus of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Partial reflection mirror 5 Transmission optical system 6 Semiconductor type photodetector 7 Temperature sensor 8 Heater 9 Temperature controller 10 Integrator 11 Laser pulse supply controller 20 Laser pulse energy measurement device 21 Detector temperature control device 22 Processing Laser pulse supply control device 23 laser processing device 41, 42, 43 output waveform 50 workpiece (substrate) 54, 55 hole B0, B1, B2 laser pulse C sensing temperature C1 set temperature D0, D detector output E integral value (Integrated / integrated value) E0 Predetermined integrated energy value F, G Trigger pulse

Claims (6)

[Claims] 1. A semiconductor type photodetector into which a laser pulse for monitoring is incident, a detector temperature control device for controlling the temperature of the detector to be constant, and a detector corresponding to the light quantity of one shot laser pulse. A laser pulse energy measuring device, comprising: an integrator for obtaining the energy of the laser pulse by time-integrating the output of the detector. 2. A detector temperature control device comprising: a temperature sensor for sensing a temperature of a photodetector; and a controller for thermally controlling the photodetector so that the temperature sensed by the temperature sensor becomes constant. Item 2. A laser pulse energy measuring device according to item 1. 3. The laser pulse energy measuring device according to claim 1, wherein the laser light is a laser light in an infrared region or a visible region. 4. A processing laser pulse supply control device provided with the laser pulse energy measurement device according to claim 1, wherein the integrator for a plurality of shots of laser pulses is provided. A processing laser pulse supply control device having a comparator that compares an integrated output with a reference value and, when the integrated output reaches the reference value, stops the supply of pulses from the laser oscillator and generates a signal for initializing the integrator. 5. An output of the semiconductor detector according to the amount of one-shot laser pulse while controlling the temperature of the semiconductor photodetector to which a laser pulse for monitoring is incident so as to keep the temperature of the detector constant. The laser pulse energy is integrated by repeating the time integration to obtain the laser pulse energy for a plurality of shots of the laser pulse, and when the integrated value reaches the reference value, the supply of the laser pulse from the laser oscillator is stopped and the integration is performed. A method for controlling the supply of a processing laser pulse, comprising resetting a value to an initial value. 6. The method according to claim 5, wherein the laser light is infrared or visible laser light.