CW laser crystallization of amorphous silicon; dependence of amorphous silicon thickness and pattern width on the grain size

In situ micro-Raman spectroscopic study of laser-induced crystallization of amorphous silicon thin films on aluminum-doped zinc oxide substrate

“…5a, b, it was observed that irrespective of the deposition substrate, the 330 nm Si films possessed higher crystalline volume fraction and larger average grain size than the 40 nm Si films did and, moreover, the crystalline volume fraction dependence on thickness is more obvious for Si films on AZO substrate. The decrease of crystalline Si average grain size with film thickness was accordance with previous reports [13,14]. The 330 nm thick Si films possess a large amount of heat, and the cooling rate is slow, so they can hold excess heat for a long time; on the other hand, the 40 nm thin Si films possess less heat, and the cooling rate is so fast that the excess heat can't last in the films.…”

“…The above mentioned contradiction is mainly caused by the difference in crystallization kinetics, arising from initial a-Si films property, surface structures of AZO substrate, as well as crystallization method. With the advantages of short time needed and no destructive effects exerted on the substrate, continuous wave (cw) laser crystallization is a widely used method to make high performance and low temperature crystalline Si films for solar cells [13,14]. Laser crystallization process is commonly described in terms of a thermal transport model [15], the a-Si films structure [14,16,17] and the substrate thermal property [18] are believed to have influence on laser crystallization process.…”

Temperature and hydrogen diffusion length in hydrogenated amorphous silicon films on glass while scanning with a continuous wave laser at 532 nm wavelength

“…Indeed, improvement of films and devices based on a-Si:H and related materials by annealing is well known: (i) light-induced defects in a-Si:H are known to anneal out near 150°C, 1 (ii) amorphous silicon based solar cells deposited at the rather low temperature of 120°C improved considerably when annealed at T = 120°C for up to 2 h, 2 (iii) silicon heterojunction solar cells with thin layers of a-Si:H on top of crystalline silicon have been reported to require an annealing step near 180°C to reach high carrier lifetime at the c-Si surface and high conversion efficiencies, 3 and (iv) hydrogenated silicon nitride films on multicrystalline silicon solar cells have been found to reduce the light-induced degradation in these solar cells when annealed near 700-800°C. 4 Annealing of a-Si:H is also of interest for driving out hydrogen for subsequent laser crystallization, [5][6][7][8][9] as in laser crystallization processes the presence of hydrogen in amounts of about 10 at. % can complicate the crystallization 9 and can cause bubble formation, 10 explosive hydrogen evolution, 11,12 and film ablation.…”

“…Although laser annealing without crystallization was applied to hydrogenated amorphous silicon as early as 1979 18 and there was intensive work on laser crystallization of amorphous silicon, [5][6][7][8][9][10][11][12][13][14][15][16][17]19 rapid thermal annealing (including laser annealing) without intentional crystallization is, to our knowledge, not widely applied in silicon technology so far. For dehydrogenation of a-Si:H films targeting subsequent crystallization, multistep laser treatments were proposed.…”

Laser processing for thin film crystalline silicon solar cells

“…This behaviour is attributed to the Gaussian profile of the laser spot, which induces a temperature distribution profile around the main part of the laser beam: the central region is submitted to higher thermal budget than the surrounding region. The grain sizes is therefore expected to be gradually decreasing from the central region towards the a-Si region in the side due to this thermal gradient as well as to higher cooling and solidification rate in the outer direction 3,16,17 . The a-Si samples, those deposited by MW-PECVD without being pre-annealed, showed bubbles in scanning electron microscopy imaging.…”