RU2486628C1 - Method of processing nonmetallic materials - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: in compliance with this invention proposed method consists in irradiating material surface with pulse laser rays. Note here that laser pulse power density is generated on the basis of relationship that relates material sublimation specific energy, material absorption index in laser wave-length and material reflection factor.

EFFECT: electric power savings.

Description

The invention relates to the field of technological processes and can be used for scribing semiconductor, ceramic and glassy materials.

A known method of processing non-metallic materials used for amorphization of silicon and consisting in irradiating them with a laser pulse [1]. There is also a known method of processing non-metallic materials used for annealing of ion-doped silicon [2]. The disadvantage of these methods is that the thermoelastic stresses arising in the materials can lead to spallation from the irradiated surface.

There is also a method of processing non-metallic materials used for annealing, which consists in irradiating them with a single rectangular laser pulse [3].

The disadvantage of this method is that the thermoelastic stresses arising in the material can lead to destruction of the material due to spallation from the irradiated surface.

Also known is a method of processing non-metallic materials [4], in which processing is carried out by irradiating materials with a laser pulse. The temporal shape of the pulse is described by a certain ratio, depending on the laser energy flux density, the constants b ₁ and b ₂ characterizing the front and decay of the laser pulse, the duration of the laser pulse, the current time from the onset of exposure, the energy density and the maximum value of the laser radiation flux density in momentum. The effect is achieved by forming a laser pulse, the temporary shape of which is described by the relation

$$q\left(t\right)=\{\begin{array}{l}{b}_{\mathrm{one}}\cdot t\cdot e^{-b_{2}t};0\le t\le \tau ;\\ 0;t>\tau ,\end{array}$$

where q (t) is the energy density of the laser radiation, W / m ² ;

τ is the laser pulse duration, s;

b ₁ and b ₂ - constants characterizing the front and the decline of the laser pulse;

t is the current time from the onset of exposure, s.

A known method of laser processing of holes [5], in which the density of energy absorbed in the evaporated layer is equal to

$$W=z\cdot L_u\cdot \rho ,\text{(one)}$$

where z is the coordinate measured from the surface into the interior of the material;

ρ is the density of the material;

L _u - latent heat of evaporation of a unit mass.

Equation (1) characterizes the stationary process of material evaporation under the action of laser radiation when it is absorbed in a very thin layer of the material (much less than the thickness of the vaporized layer) and does not take into account the absorption in the vapor of the material and the increase in the internal energy of the vapor. It is valid for a small range of laser radiation power densities, when absorption in the vapor of the material can be neglected. In addition, equation (1) cannot be used when the absorption of laser radiation occurs in the bulk of the material, for example, in a layer several millimeters thick.

In expression (1) in [5], the latent heat of evaporation L _u characterizes the evaporation of the material from the surface of the light spot. The disadvantage of this method is the inability to determine the optimal value of the energy density of the laser radiation when processing materials having volumetric absorption of radiation with a wavelength at which the material is processed.

This method is selected as a prototype. The aim of the invention is to reduce energy costs in the processing of non-metallic materials by laser radiation. For example, glassy, ceramic, and semiconductor materials may exhibit volumetric absorption at the wavelength of the incident radiation. If the conditions are met:

и $$R_n>>\sqrt{a\tau }$$

, $$\chi >>\sqrt{a\tau }$$

and $$R_n>>\sqrt{a\tau }$$

,

where χ is the absorption coefficient of the material;

a is the coefficient of thermal diffusivity of the material;

τ is the laser pulse duration;

R _n is the radius of the spot of laser radiation,

then we can consider the problem of the evaporation of the material in a one-dimensional formulation and neglect the energy transfer in the material due to thermal conductivity. The power density of laser radiation in the material is determined by the equation [5]:

q (t, z) = (1-R) q ₀ (t) e ^-χz ,

where R is the reflection coefficient of the material;

q ₀ (t) is the power density of the laser radiation;

z is the coordinate measured from the surface into the interior of the material.

If the absorbed energy in the cross section z exceeds the specific sublimation energy of the material, that is, the condition

$$\left(\mathrm{one}-R\right)\chi W{e}^{-\chi z}\ge Q,\text{(2)}$$

where R is the reflection coefficient of the material;

- плотность энергии лазерного излучения; $$W={\displaystyle \underset{0}{\overset{\tau }{\int }}q\left(t\right)dt}$$

- energy density of laser radiation;

q (t) is the power density of the laser radiation;

z is the coordinate measured from the surface into the interior of the material;

Q is the specific energy of sublimation of the material,

This will evaporate the absorbing layer of material. From (2) we obtain the relation for the thickness of the evaporated layer

$$z=\frac{\mathrm{one}}{\chi }\ln \frac{\left(\mathrm{one}-R\right)\chi W}{Q}.$$

The mass of material vaporized per unit area is

$$m=z\rho \frac{\rho }{\chi }\ln \frac{\left(\mathrm{one}-R\right)\chi W}{Q},$$

where - ρ is the density of the material.

The specific (per unit of energy input) ablation of the mass of material will be

$$m_{\mathrm{At}D}=\frac{m}{\left(\mathrm{one}-R\right)W}=\frac{\rho }{\left(\mathrm{one}-R\right)\chi W}\ln \frac{\left(\mathrm{one}-R\right)\chi W}{Q}.\text{(3)}$$

(e - основание натурального логарифма), причем величина m_УД в точке максимума является постоянной для конкретного типа материала величиной и составляетA study of the extremum of equation (3) shows that the specific ablation of the mass has a maximum at $$\frac{\left(\mathrm{one}-R\right)\chi W}{Q}=e$$

(e is the base of the natural logarithm), and the value of m _UD at the maximum point is constant for a specific type of material, and is

(m _UD ) _max ≈0.368ρ / Q.

In order to save energy costs, it is advisable to process materials with a laser energy density

$$W=\frac{eQ}{\left(\mathrm{one}-R\right)\chi }.$$

The thickness of the evaporated layer will then be 1 / χ. An increase in groove depth during processing is obtained by the action of several pulses. Thus, the optimal processing regime of non-metallic materials with volumetric absorption at the wavelength of the laser is observed.

Literature

1. Boyazitov P.M. Amorphization and crystallization of silicon by subnanosecond laser pulses. Abstracts / TL of the All-Union Conference on the interaction of optical radiation with matter. Leningrad. March 11-18, 1988, from 24.

2. Kuzmenchenko T.A. et al. Laser annealing of ion-doped silicon by radiation with a wavelength of 2.94 microns. Leningrad. March 11-18, 1988, with. 29.

3. Bakeev A.A., Sobolev A.P., Yakovlev V.I. Studies of thermoelastic stresses arising in the absorbing layer of a substance under the action of a laser pulse. PMTF, - 1982. - No. 6. - p. 92-98.

4. Atamanyuk V.M., Kovalenko A.F., Levun I.V., Fedichev A.V. A method of processing non-metallic materials. RU 2211753 C2.

5. Laser equipment and technology. In 7 kn. Book 4. Laser processing of non-metallic materials: Textbook. manual for universities / A.G. Grigoryants, A.A. Sokolov; Ed. A.G. Gregorianets. - M .: Higher. school 1998 .-- 191 pp., Ill. ISBN 5-06-001453-3.

Claims (1)

A method of processing non-metallic materials, which consists in irradiating the surface with laser radiation, characterized in that they form a laser pulse, the energy density of which is determined by the ratio
$$W=\frac{eQ}{(\mathrm{one}-R)\chi },$$

where Q is the specific energy of the sublimation of the material;
e is the base of the natural logarithm;
χ is the absorption coefficient of the material at the wavelength of the incident laser radiation;
R is the reflection coefficient of the material.