JPH06285654A - Method for predicting laser beam machining, manufacture of laser beam machined parts and laser beam machine - Google Patents

Abstract

PURPOSE:To realize an appropriate laser beam machining by detecting the removal by means of melting-evaporation or evaporation of small parts of a laser beam machined goods by the predicted result of the laser beam machining by the simulation method, and executing the feedback of the detected result. CONSTITUTION:A ports 2 to be machined is irradiated with the laser beam 3 and the removal machining by means of the melting-evaporation or the evaporation is predicted by the simulation. The energy density distribution and the radiation energy distribution of the laser beam irradiation within the parts to be machined are calculated. The heat generation at the small part of the parts 2 to be machined is calculated based on this result, and the removal by means of the melting-evaporation at the evaporation is detected. This detected result is incorporated in the calculating process of the energy density distribution and the radiation energy distribution to execute the simulation of the laser beam machining. The continuously detected result of the removal of the melting-evaporation or the evaporation of the small part is fed back to the computation, and the simulation which is well matched with the actual condition can be executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser machining predicting method, a laser machining product manufacturing method and a laser machining apparatus which are used when a workpiece is irradiated with a laser for machining.

[0002]

2. Description of the Related Art There is laser processing in which a semiconductor thin film is scribed by irradiating a laser (laser beam). The semiconductor thin film to be subjected to this laser processing is not limited to a single layer, but is a multi-layer (4 in the case of a solar cell, in which different materials are applied and laminated as in the case of a laminated compound semiconductor solar cell).
Sometimes).

In the case of laser processing for scribing a semiconductor thin film, there are special circumstances which are not found in bulk materials such as thin film properties of materials, selective removal processing, and a multi-layer laminated structure of different materials in addition to the solar cells.

When scribing a semiconductor thin film,
It is important that the target area be removed accurately, and that the peripheral area and lower layers are not physically or thermally damaged. For this purpose, the laser irradiation conditions must be set appropriately. is there.

However, it is not possible to easily know this appropriate laser irradiation condition. It may be possible to perform a cut-and-try experiment to know the appropriate laser irradiation conditions, but it takes a lot of time and
The results obtained are less effective against process changes,
Searching for laser irradiation conditions by cut-and-try is not realistic.

That is, conventionally, it is difficult to properly perform laser processing on a thin film because it is difficult to know the appropriate laser irradiation conditions.

[0007]

In view of the above circumstances, it is an object of the present invention to provide a method capable of easily knowing appropriate laser irradiation conditions for a workpiece to be laser processed. An object of the present invention is to provide a method and an apparatus capable of performing appropriate laser processing on a work piece.

[0008]

In order to solve the above-mentioned problem of simply knowing the appropriate laser irradiation conditions, the method for predicting laser processing according to the present invention irradiates a laser beam onto a workpiece to perform irradiation. In predicting the processing performed by evaporating and removing a part with or without melting, by simulation method, the energy density distribution by laser irradiation in the work piece and radiation in the work piece as necessary The energy distribution is calculated, and the calorific value in the microscopic portion of the workpiece is calculated based on the calculation result of the energy density distribution or the both calculation results, and the microscopic portion is melted using the calorific value calculation result. Alternatively, the evaporation removal is detected, and the detection result of the melting or evaporation removal of this minute portion is calculated according to the energy density distribution calculation process and the necessity. It has a configuration for simulating laser processing incorporated in the process of calculating the radiant energy distribution Te. As a specific form of this laser processing prediction method, there is a form in which the work piece is a work piece having a thin film, and the laser irradiation is performed on the thin film portion of the work piece, but not limited to this. The workpiece may be a non-thin film bulk material. Of course, the simulation in this invention utilizes computer calculation.

Although the simulation can be performed only by the calculation result of the energy density distribution, a highly accurate simulation can be expected by using the calculation result of the radiant energy distribution in addition to the calculation result of the energy density distribution.

In order to solve the latter problem of providing a method and an apparatus capable of performing appropriate laser processing on the above-mentioned workpiece, the laser processing method according to the present invention provides a laser processing method. In the method for obtaining a processed product, the condition of the laser processing is set on the basis of a prediction result of the laser processing by a simulation method, and the laser processing apparatus according to the present invention is applied to a workpiece. A laser irradiation means for performing laser processing and a processing condition setting means for setting the conditions of the laser processing are provided, and the processing condition setting means sets the laser processing conditions based on the prediction result of the laser processing by the simulation method. It features a configuration that can be done.

The present invention will be described in more detail below. First, the prediction of laser processing by the simulation method of the essential element in the present invention will be described first.

In the present invention, as shown in FIG. 1, the thin film 1
Laser (wavelength λ,
The processing performed by irradiating the output P) 3 and evaporating and removing the irradiated portion with or without melting is predicted by a simulation method using computer calculation before processing. In addition, in FIG.
Is a condenser lens system (numerical aperture NA), and 8 is an aperture.

For the simulation of laser processing, the energy density distribution EE (x,
y, z, t) and the radiant energy distribution Ef (x, y, z, t) per unit time and unit area in the thin film must be calculated.

The energy density distribution EE (x, y, z, t) can be calculated as follows.

In the case of the laser irradiation system shown in FIG. 1 (a),
The relative light intensity distribution I (x, y, t) on the surface of the thin film 1 is given by the following equations (1) and (2), and has a distribution as shown in FIG.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

Where J ₁ (Ur): Ur's one-order Bessel function, λ: laser wavelength, NA: optical system numerical aperture, x,
y: The distance from the center of the screen in the x and y directions.

Assuming that there is no energy loss due to the optical system and space, the light energy density distribution E on the thin film surface
Assuming that (x, y, t) follows the relative light intensity distribution I (x, y, t), ∫sE (x, y, t) ds = C ∫sI (x, y, t) ds = P (3) The following relationship holds.

Here, S is a laser spot area on the thin film, C is a constant having a unit of energy per unit area, and P is an output power.

IB = ∫sI (x, y, t) ds / S
Is defined, the output power P is represented by P = C · IB · S. Here, when C · IB = E ₀ is defined, from the above equation, E ₀ = P / S, and this E ₀ is defined as the average power density.

Then, the actual light energy density distribution E (x,
When y, t) and the average power density E ₀ are overlapped and illustrated, the result is as shown in FIG. The shaded area rising to the right shows the light energy density distribution, and the shaded area rising to the left shows the average power density. The size (area) of the oblique line rising to the right is ∫sI (x, y, t) ds, and the size (area) of the oblique line rising to the right is E ₀ · S = P.

On the other hand, in the case of the laser irradiation system having no aperture shown in FIG. 1B, if the light energy density distribution E (x, y, t) on the surface of the thin film 1 is assumed to be a single beam mode, It is given by the following formula (A), and when illustrated, it becomes as shown in FIG.

E (x, y, t) = I ₀ · exp (−2r ² / r ₀ ² ) ... (A) where I ₀ = 2P / (πr ₀ ² ), r = (x ² + y ² )
It is ^1/2 .

Here, I ₀ : maximum energy density, P:
The output power is r ₀ : E = I ₀ / e ² and the focused beam radius is set.

On the other hand, in the laser processing process of the thin film 1, the laser applied to the thin film 1 is first partially reflected on the surface of the thin film 1 and the rest is incident on the thin film 1 and passes through the thin film 1. While being absorbed and attenuated, part of it is transmitted.

When the reflectance of the laser on the surface of the thin film 1 is R and the transmittance of the thin film 1 is T, the laser energy EE (x, y, t) contributing to the processing is given by the following equation (4). .

EE (x, y, t) = E (x, y, t). (1-RT) .. (4) When the laser incident on the thin film 1 passes through the inside thereof, the thin film surface Absorption depth a
Then, the relative light intensity distribution I (x, y, z, t) at the position at the depth z from the surface of the thin film 1 is given by the following equation (5).

I (x, y, z, t) = I (x, y, t) e ^{-z / a} ... (5) Therefore, the energy density distribution EE (x, y, z, t) is as follows. It can be calculated by the equation (6).

EE (x, y, z, t) = EE (x, y, t) e ^{−z / a} ··· (6) Here, here, the laser Irregular reflection, temperature rise of thin film, change of laser light absorption rate by phase change, laser light scattering by plasma generation,
Negligible factors such as absorption, alteration due to heat absorption of thin film, and influence of laser beam divergence angle are not taken into consideration.

The radiant energy distribution Ef (x, y, z, t) per unit time and unit area in the thin film can be calculated as follows.

Energy transfer between the thin film 1 and the outside world is limited to energy injection by a laser and emission of energy due to radiation from the thin film 1, which are main factors, and neglectable convection of air in the outside world is not considered. Regarding radiation, only the coordinate directions (orthogonal system) used were dealt with. Radiation energy per unit time and unit area from one surface in one direction at an appropriate position in the thin film 1, that is, radiation energy distribution Ef
(x, y, z, t) can be calculated by the following equation (7).

Ef (x, y, z, t) = σεf (Tp ⁴ −To ⁴ )  (7) where σ: Stefan-Boltzmann constant (5.67032 × 10
^-8 W / (m ² · K ⁴ ), ε: emissivity, f: view factor, Tp:
Radiation source temperature, To: radiation destination temperature.

In this way, if the energy density distribution EE (x, y, z, t) due to laser irradiation in the thin film and the radiation energy distribution Ef (x, y, z, t) in the thin film can be calculated respectively. The heat generation amount (energy absorption amount) at an appropriate position in the thin film 1 is obtained. The heat generation amount per unit time at a proper position in the thin film 1 per unit volume (minute portion), that is, the heat generation distribution S (x, y, z, t) in the thin film 1 is calculated by the following equation (8). It can be calculated. That is, S (x, y, z, t) = EE (x, y, z, t)-(Efx + Efy + Efz) ... (8) The calculation is performed based on the equation.

Here, Efx = Efx (x, y, z, t), Efy = Efy
(x, y, z, t), Efz = Efz (x, y, z, t), and
It is the radiant energy per unit time in the x, y and z directions.

Along with the laser irradiation, heat is generated in the thin film 1 in an amount calculated by the heat generation distribution S (x, y, z, t). As a result, as shown in FIG. Temperature, melting, evaporation etc. occur. On the other hand, the temperature at an appropriate position (a minute portion) in the thin film 1 can be calculated by Fourier's three-dimensional unsteady heat conduction equation represented by the following formula (9).
The temperature at an appropriate position in the inside is calculated, and subsequently, the melting or evaporation of the material at that position is detected from the obtained temperature.

[0037]

[Chemical 3]

In this case, the melting point considering the latent heat of fusion is corrected to the melting point θmc, and the boiling point considering the latent heat of vaporization is corrected to the boiling point θvc.
As a result, the calculation can be facilitated by incorporating these virtual physical quantities (virtual temperature Tc). That is, as shown in FIG. 5, T is used for the heat conduction calculation and Tc is used for the fictive temperature used for the phase change. In the case of a substance that sublimes without undergoing melting, since it is the melting point, that is, the boiling point, the corrected melting point θmc, that is, the corrected boiling point θvc.

That is, θmc = θm + hm / C1,
.theta.vc = .theta.v + hv / C2. Where θm
: Melting point, hm: latent heat of fusion, C1: specific heat of solid phase, .theta.v: melting point, hv: latent heat of vaporization, C2: specific heat of liquid phase.

Fourier's three-dimensional unsteady heat conduction equation is
For example, the calculation can be easily performed by using the control volume method and discretizing in the form of the complete implicit method (implicit method) and using the line-by-line method as the calculation scheme.

As the laser processing progresses, the phase boundary shifts in the thin film 1. This phase boundary shift shows a two-dimensional example in which the thin film 1 is rectangular (including square).
It is also possible to divide it into cells (micro parts) and use a cell-limb model in which dissolution / evaporation is considered for each cell in a simplified manner. In the cell-limb model, energy transfer, that is, the calorific value is calculated on a cell-by-cell basis, and in the case of a substance that undergoes an evaporation phenomenon after melting, the cell that has reached the corrected melting point θmc is treated as vaporized as a liquid phase, and the corrected boiling point θvc is set. The reached cell is considered to have evaporated and the removal operation is performed. In the case of a sublimable substance that melts and evaporates at the same time, the cell that has reached the corrected melting point θmc is
Since mc has the corrected boiling point θvc, the removal operation is performed assuming that it has evaporated.

In the case of the complete implicit method, the equation (9) is set for each cell (that is, there are equations corresponding to the number of cells), and calculation is performed by matrix operation.
In this complete implicit method, an accurate result can be obtained even if Δt is roughened, so that the time required for calculation can be shortened.

The removal of the thin film 1 considers only evaporation due to heat absorption of the material, and regarding factors that can be excluded, such as the influence of thermal stress, the movement of particles ejected from the thin film, and the influence of gas generation from the thin film. Although not considered, other removal factors may be incorporated in the calculation process as in the case of using a liquid phase removal means such as gas spraying.

The liquid phase in the cell and the removal of the cell are
The energy density distribution EE (x, y, z, t) and the radiation energy distribution Ef (x, y, z, t) are fed back to the calculation results. Therefore, since accurate calculation is performed in accordance with the momentary change of the laser-irradiated portion, the simulation matches the actual machining result well. The change from the solid phase to the gas phase in the cell is performed, for example, by the EE of the formula (6).
(x, y, z, t) = EE (x, y, t) e ^{-z / a} changes a,
In Ef (x, y, z, t) = σf (Tp ⁴ -To ⁴ ) of the equation (7), ε is changed and fed back.

Since the change from the liquid phase to the gas phase in the cell is the change of the thin film surface position, for example, EE (x, y,
z, t) = EE (x, y, t) e ^{-z / a} , Ef (x, y, z, t) in equation (7)
= Σ · ε · f (Tp ⁴ -To ⁴ ) changes the depth (z) is fed back.

Also in the equation (9), the change from the solid phase to the liquid phase is incorporated as the changes in the density, specific heat and thermal conductivity of the equation (9).

Of course, instead of the cell-limb model, a large number of line segments extending from the surface of the thin film 1 to the inside are set in advance, specific points are set along each line segment, and temperatures are calculated at these points. Alternatively, it may be determined that the melting or evaporation removal has been performed, and the removal may be performed above the boundary connecting the phase boundary points. In this case, it is also possible to determine the line segments from the surface of the thin film 1 to the inside in a direction perpendicular to the boundary connecting the phase boundary points, without completely predetermining the line segments. Good.

Table 1 shows changes in the aluminum phase and changes in the physical properties.

[0049]

[Table 1]

In the case of aluminum, the density is about 2.
6. The liquid phase has a melting point of about 2.3, a melting point of 933.5K and a boiling point of 2723K.

The time-dependent temperature change, phase change, and evaporation of the thin film 1 calculated in this way are monitored by using a normal computer graphic technique as shown in FIG.
V) can be displayed above. For example, the monitor screen shows (a) → (b) →
The change from (c) can be visually observed, and it can be well understood in advance by simulation that the thin film 1 is scraped by laser processing. If you use the color change to show the difference in temperature and the difference in phase on the color monitor, the simulation becomes easier to understand.

Next, an example of the laser processing machine (laser processing apparatus) of the present invention will be described.

The laser processing machine 20 shown in FIG. 8 is provided with a laser irradiation means 21 for performing laser processing on a thin film portion of a workpiece and a processing condition setting means 22 for setting conditions for laser processing.

In the laser irradiation means 21, the excitation lamp 31
The laser 3 generated on the YAG rod 32 by the excitation of is reflected by the bend mirror 33 in the direction of 90 degrees, narrowed down by the condenser lens system 7, and then irradiated on the surface of the thin film 1. Further, the surface of the thin film 1 can be enlarged and displayed on the screen of the monitor 37 by the TV camera 36. The light emitting section is cooled by the cooling means 38 so as not to be overheated.

In the processing condition setting means 22 for setting the laser processing conditions, the processing conditions can be set with the operation keys or the like. With this setting, the excitation lamp 3
The power supply 39 for 1 and the like are appropriately controlled.

FIG. 9 shows an example of the flow from the simulation to the end of laser processing according to the present invention.

The preconditions for the simulation are determined, the simulation results are examined, and the laser processing apparatus to be used and the processing conditions are determined. Then, the thin film is processed according to the processing conditions determined using the laser processing apparatus selected according to this determination.

In some cases, a human may decide the preconditions for the simulation, examine the simulation result, and decide the laser processing apparatus and the processing conditions to be used, or install AI (artificial intelligence) or the like. In some cases, the processing is performed by a computer, and in the latter case, the control system including the computer or another computer controls the processing condition setting means 22 of the laser processing apparatus used for processing based on the simulation result.

The laser processing apparatus is determined in consideration of the type of laser, that is, the wavelength (YAG laser, CO ₂ laser), maximum output, pulse width, peak value, scanning speed, etc., from the simulation result. Once the laser processing equipment is decided,
Set the processing conditions such as irradiation power, frequency, and focus diameter. Of course, if the laser processing apparatus itself can also set one or more of the laser type, maximum output, pulse width, peak value, and scanning speed, these can also be used as the processing conditions.

The present invention is not limited to the above. The workpiece may be a bulk material instead of a thin film. The material of the workpiece may be, for example, a metal in addition to the semiconductor.

In the above case, a factor that can be ignored in the calculation process is removed. However, depending on the conditions, it may be incorporated as a correction factor in the calculation process to ensure accuracy.

[0062]

In the method for predicting laser processing according to the present invention, since the detection result of the melting or evaporation removal of the minute portion is fed back to the calculation every moment, it is possible to perform a simulation that matches the actual situation.

In the method for manufacturing a laser processed product and the laser processing machine according to the present invention, since the conditions for laser processing are set on the basis of the prediction result of laser processing by the simulation method, a product subjected to appropriate laser processing can be obtained. You can

[0064]

EXAMPLES Next, examples will be described.

In the simulation of the example, laser processing was performed on a CdS sintered film having a thickness of about 40 μm provided on the glass substrate. CdS becomes a gas directly from a solid,
In other words, it is a substance that sublimes without melting.

In the case of CdS, density: 4820 [kg / m
² ], thermal conductivity 15.9 (W · m ⁻¹ · K ⁻¹ ), true sublimation point: 1253.2 [K], latent heat of sublimation: 1487.9 [K
J · Kg ⁻¹ ], specific heat of solid phase: 0.337 [KJ · Kg ⁻¹ ·
K ⁻¹ ], modified melting point: 1487.9 ÷ 0.337 + 125
3.2 = 5668.3 [K].

The performance of the laser processing machine assumed in the simulation is as follows. Laser type: YAG laser (wavelength 1.06 μm), oscillation mode TEM ₀₀ , focusing lens focal length: 25 mm, Q switch repetition frequency average output pulse width peak output (kHz) (W) (ns) (KW) 1 3.5 120 29.1 3 7.5 160 15.6 5 9.0 190 9.4 Figure 1 shows the instantaneous temperature distribution in the CdS sintered film after laser irradiation.
It shows in 0. 10A shows the relationship between the depth and the temperature at a position at a predetermined distance from the irradiation center, and FIG. 10B shows the relationship between the distance from the irradiation center and the temperature at a certain depth.

FIG. 7 shows a monitor screen of the progress of processing by computer graphic. FIG. 7A shows a state 1 msec after the irradiation starts, FIG. 7B shows a state 3 msec after the irradiation starts, and FIG. (C) of 7 shows the state 5 msec after the start of irradiation.

In the case of the CdS sintered film, a temperature difference of about 600 K is recognized between the film front surface and the back surface of the beam spot center portion, and exhibits an exponential change in the depth direction. On the other hand, at a position with a radius of 30 μm from the beam spot center, the temperature difference is about several tens of K, and the temperature is almost uniform in the depth direction. Similarly, the temperature distribution in the radial direction from the center of the beam spot was similar to the light intensity distribution having an inflection point in the middle.

It was confirmed that the processed shape and the thermal damage area of the CdS sintered film were progressing momentarily with a strong correlation with the approximate light intensity distribution around the beam spot center.

Q switch repetition frequency is 5 Hz,
Laser processing was actually performed for a diameter of about 20 μm, a laser power of 0.5 W, and a laser scanning speed of 50 mm / S.

FIG. 11 shows the processing result by simulation, and FIG. 12 shows the actual processing result. The two are in good agreement, and it is clear that the simulation method of the present invention can accurately predict the machining result.

[0073]

In the method of predicting laser processing according to the present invention, since the detection result of melting or evaporation removal of the minute portion is fed back to the calculation every moment, a simulation that matches the actual situation can be performed. Based on
It can be said that the present invention is very useful because it is possible to obtain a product that has been subjected to very suitable laser processing.

In the method for manufacturing a laser processed product and the laser processing apparatus according to the present invention, since the conditions for laser processing are set on the basis of the prediction result of laser processing by the simulation method, a product subjected to appropriate laser processing can be obtained. It is very useful because it can

[Brief description of drawings]

FIG. 1 is an explanatory view showing a state of laser irradiation according to the present invention.

FIG. 2 is a graph showing a relative light intensity distribution I (x, y, t) and energy density on the surface of a workpiece.

FIG. 3 is a characteristic curve diagram showing a light energy density distribution and an average power density.

FIG. 4 is a characteristic curve diagram showing a schematic temperature change of a workpiece after laser irradiation.

FIG. 5 is a characteristic curve diagram showing a modified melting point and a modified boiling point used in the present invention.

FIG. 6 is an explanatory diagram showing a cell-limb model used in the present invention.

FIG. 7 is an explanatory diagram showing an example of a monitor screen showing a simulation result.

FIG. 8 is an explanatory view showing a configuration example of a main part of the laser processing machine of the present invention.

FIG. 9 is a flowchart showing the flow of processing progress by the laser processing method of the present invention.

FIG. 10 is a characteristic curve diagram showing a temperature state of a thin film in an example.

FIG. 11 is an explanatory diagram of a monitor screen showing a simulation result in the example.

FIG. 12 is a cross-sectional view of a thin film after laser processing in an example.

[Explanation of symbols]

 1 Thin Film 2 Workpiece 3 Laser (Laser Beam) 7 Focusing Lens System

Claims (6)

[Claims] 1. A method for predicting a processing, which is performed by irradiating a workpiece with a laser, and evaporating and removing an irradiated portion with or without melting, by a simulation method. Of the energy density distribution by laser irradiation in the inside and the radiant energy distribution in the work piece as necessary, and the calculation result of the energy density distribution or a minute portion of the work piece based on the both calculation results. The calorific value is calculated, and the melting or evaporation removal of the minute portion is detected using the calculated result of the calorific value, and the detection result of the melting or evaporation removal of the minute portion is necessary for the calculation process of the energy density distribution. A method of predicting laser processing, which is characterized by performing simulation of laser processing by incorporating it into the calculation process of the radiant energy distribution. 2. The method for predicting laser processing according to claim 1, wherein the workpiece is a workpiece having a thin film, and the laser irradiation is performed on a thin film portion of the workpiece. 3. A method for manufacturing a laser-processed product, comprising: setting a condition for the laser processing on the basis of a prediction result of the laser processing by a simulation method in a method for obtaining a laser-processed product. 4. The method for manufacturing a laser processed product according to claim 3, wherein the prediction result of the laser processing by the simulation method is obtained by the prediction method of the laser processing according to claim 1. 5. A laser processing apparatus comprising laser irradiation means for performing laser processing on a workpiece and processing condition setting means for setting conditions of the laser processing, wherein the processing condition setting means is a simulation method. The laser processing apparatus is characterized in that the laser processing conditions can be set based on the prediction result of the laser processing by. 6. The prediction result of laser processing by a simulation method is obtained by the prediction method of laser processing according to claim 1 or 2.
The laser processing device described.