Lateral Crystallization Velocity in Explosive Crystallization of Amorphous Silicon Films Induced by Flash Lamp Annealing

Abstract

We propose a new method to estimate the explosive crystallization (EC) velocity (v EC ) of amorphous silicon (a-Si) films using multi-pulse flash lamp annealing (FLA). This system produces discrete pulses at frequencies of 1-10 kHz to form a quasi-millisecond pulse. The multi-pulses leave behind macroscopic stripe patterns on the surfaces of polycrystalline Si (poly-Si) films, the widths of which are indications of v EC . We find that catalytic chemical-vapor-deposited (Cat-CVD) and sputtered a-Si films show v EC of $4 m/s, whereas the use of electron-beam-evaporated a-Si results in much higher v EC of $14 m/s, indicating the emergence of different EC mechanisms.Rapid annealing using sub-second pulse light is of great importance as the methods of crystallizing precursor amorphous silicon (a-Si) films to form device-quality polycrystalline Si (poly-Si) films because of the availability of low-cost glass or plastic substrates. [1][2][3][4][5][6][7][8] This non-thermal equilibrium sub-second annealing sometimes induces explosive crystallization (EC), high-speed lateral crystallization driven by the release of latent heat. 9-15 It has been know that the EC of a-Si occurs in liquid-phase and/or in solid-phase, which results in different EC velocity (v EC ). 9-13 In-situ observation of EC, however, is not easy because of enormously high v EC on the order of m/s. Although v EC of a-Si films has been experimentally estimated by some of in-situ or ex-situ methods, 9,14 they require complicated experimental system or expensive equipments.We have so far found that flash lamp annealing (FLA), millisecond-order annealing using Xe lamps, can induce EC of a few m-thick a-Si films and the EC observed is based on solid-phase nucleation (SPN) and partial liquid-phase epitaxy (LPE), 16 unlike previously reported results that have shown the clear evidences of EC through simple LPE. 9 The v EC of Si films in the case of FLA, however, has not been evaluated, because of the difficulty of using an additional measurement system in a FLA system that has a character of large-area pulse emission. The purpose of this study is to utilize a quasi-millisecond multi-pulse FLA system, instead of conventional single millisecond-pulse FLA, in order to estimate the v EC of Si films from signatures left on poly-Si films formed due to multi-pulse emission which induces temperature modulation of Si during millisecond treatment. The determination of v EC can contributes to understand the mechanism of EC.We first formed 60-nm-thick Cr films on 20 Â 20 Â 0.7 mm 3 -sized quartz substrates by sputtering in order to suppress Si film peeling during FLA. 17 We then prepared 2-4 m-thick a-Si films formed by catalytic chemical vapor deposition (Cat-CVD), sputtering, and electron-beam (EB) evaporation on Cr-coated quartz glass substrates, the detailed deposition conditions of which are summarized in Table I. FLA system used in this study, produced by Design System Co., Ltd., can supply a quasi-millisecond pulse consisting of discrete sub-pulses emitted at variabl...

Liquid-phase explosive crystallization of electron-beam-evaporated a-Si films induced by flash lamp annealing

“…We have confirmed that the quasi-millisecond pulse can induce the crystallization of a-Si films equivalent to conventional single-pulse FLA [15]. Furthermore, the cyclic temperature modulation of Si films induced by discrete pulses during quasi-millisecond pulse emission results in the formation of macroscopic stripe patterns on FLC poly-Si films, the interval of which yields the velocity of EC (v EC ) [15]. The crystallization of a-Si films was evaluated by Raman spectroscopy and X-ray diffraction (XRD).…”

“…We then performed FLA onto each a-Si film under stage pre-heating by a halogen lamp at 500 1C. The FLA system supplies a quasi-millisecond pulse consisting of discrete sub-pulses at emitted tunable frequencies of 1-10 kHz [15]. We have confirmed that the quasi-millisecond pulse can induce the crystallization of a-Si films equivalent to conventional single-pulse FLA [15].…”

“…The FLA system supplies a quasi-millisecond pulse consisting of discrete sub-pulses at emitted tunable frequencies of 1-10 kHz [15]. We have confirmed that the quasi-millisecond pulse can induce the crystallization of a-Si films equivalent to conventional single-pulse FLA [15]. Furthermore, the cyclic temperature modulation of Si films induced by discrete pulses during quasi-millisecond pulse emission results in the formation of macroscopic stripe patterns on FLC poly-Si films, the interval of which yields the velocity of EC (v EC ) [15].…”

Mechanism and control of crack generation in glass substrates during crystallization of a-Si Films by flash lamp annealing

“…We have confirmed the crystallization of Si films by Raman spectroscopy. The typical Raman spectrum of a flash-lamp-crystallized (FLC) poly-Si film is seen in a previous paper [25]. We observed no significant differences in Raman peak width, peak position (~520.5 cm − 1 ), and crystalline fraction for FLC poly-Si films formed on various glass substrates, meaning that the FLC poly-Si films have similar microstructures and stresses.…”

“…1. The details of the FLA system have been summarized elsewhere [25]. We have confirmed the crystallization of Si films by Raman spectroscopy.…”