Features of Controlled Laser Thermal Cleavage of Crystalline Silicon
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RY Dedicated to the memory of B.N. Grechushnikov
Features of Controlled Laser Thermal Cleavage of Crystalline Silicon A. N. Serdyukov, S. V. Shalupaev, and Yu. V. Nikityuk Gomel State University, Gomel, 246019 Belarus email: [email protected] Received June 9, 2010
Abstract—Controlled laser thermal cleavage of crystalline silicon has been numerically simulated. A 3D analysis of the thermoelastic fields formed in a singlecrystal silicon wafer as a result of successive laser heat ing and exposure to a coolant was performed for three different versions of anisotropy. The simulation was performed for laser irradiation with different wavelengths: 1.06 and 0.808 µm. The calculation results have been experimentally verified using a YAG laser. The results can be used in the electronics industry to optimize the precise separation of silicon wafers into crystals. DOI: 10.1134/S1063774510060064
Controlled laser thermal cleavage is one of the most effective methods to precisely separate brittle nonmetallic materials. One distinctive feature of this method is that the material separation occurs as a result of crack formation during successive laser heating and exposure to coolant [1]. The main advantages of controlled laser thermal cleavage are high separation accuracy, short process time, and wastelessness. The specific features of this method as applied to glasses and ceramics were investigated in [2–5].
more rapidly than the thermal equilibrium is obtained [10].
Recent publications devoted to the controlled laser thermal cleavage of different crystals (see, for exam ple, [6]) are of particular interest. However, in these studies thermoelastic fields were numerically simu lated in the 2D statement and the elastic properties of crystals were disregarded. At the same time, the dynamics of various physical processes even in cubic crystals may radically change in comparison with iso tropic media [7, 8]. In this context, it is expedient to perform a 3D simulation of the controlled laser ther mal cleavage of crystalline silicon (which belongs to the cubic system) taking into account its anisotropy.
The calculations were performed using the follow ing values of density, specific heat, thermal conductiv ity, and linear thermal expansion coefficient of silicon: ρ = 2330 kg/m3, С = 758 J/(kg K), λ = 109 W/(m K), and α = 2.33 × 10–6 K–1, respectively [12, 13].
The processes of laser thermal cleavage of Si wafers were simulated using the finiteelement method [9]. In the first stage we calculated the temperature fields and then found the thermoelastic stresses formed as a result of the laser irradiation of silicon and its subse quent exposure to coolant. Such a simulation sequence allows one to obtain results within the unbound problem of thermoelasticity in the quasi static statement. From the physical point of view, the quasistatic statement of the thermoelasticity problem is the assumption that the strained state is settled much
We chose the condition of maximum tensile stresses as the criterion determining the directi
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