Selective Single-Crystalline-Silicon Growth at the Pre-defined Active Region of a Thin Film Transistor on Glass by Using Continuous Wave Laser Irradiation

Abstract

We have developed a new silicon (Si) crystallization method that makes it possible to form single-crystalline Si in the channel regions of thin-film transistors (TFTs) on non-alkali glass without introducing thermal damage. The method includes using a frequency-doubled (2!) diode-pumped solid-state (DPSS) Nd:YVO 4 continuous-wave (CW) laser ( ¼ 532 nm). The unique characteristics of this crystallization method are the introduction of a pre-defined thick capping-Si layer on a pre-patterned channel region and laser irradiation from the back surface through the glass substrate. We succeeded in forming 2-mm-wide and 20-mm-long single-crystalline Si in the channel region of a TFT. A high-performance n-channel TFT on a glass substrate was obtained using a 450 C fabrication process. The TFT had a field-effect mobility of 400 cm 2 /Vs, a subthreshold swing of 0.16 V/dec, and a threshold voltage of 0.24 V.

Low-Temperature Fabricated TFTs on Polysilicon Stripes

“…The interlayer oxide must be transparent at this wavelength to prevent its heating to avoid cracks, deformation, and other damage [17]. At the same time, the absorption coefficient for amorphous Si film must be high enough to provide complete melting of the irradiated film.…”

“…For this reason, we chose for an irradiation at 515-nm wavelength, which has much lower measured absorption coefficients. That ensures a larger penetration depth of ≈49 nm for a-Si and near 200 nm for crystallized poly-Si film [18], leading to a more homogeneous melting of silicon layer [17]. This widens the process window for recrystallization in terms of the laser power and pulse duration.…”

Improved Uniformity and Electrical Performance of Continuous-Wave Laser-Crystallized TFTs Using Metal-Induced Laterally Crystallized Si Film

“…2,3 Continuous-wave (CW) laser crystallization (CLC) of a-Si has also been recently employed to fabricate high-performance LTPS TFTs. [4][5][6][7] Compared with the excimer laser crystallization (ELC) process, the CLC process is simpler, easier, and relatively inexpensive. Unfortunately, the resulting uniformity was poor because the shape of the beam profiles was Gaussian.…”

Electronic devices fabricated at CMOS backend-compatible temperatures

“…The laser choice is dictated by certain conditions. In case of 3-D integration the interlayer oxide must be transparent at this wavelength to prevent its heating to avoid cracks, deformation and other damage [102]. At the same time, the absorption coefficient for the amorphous Si film must be high enough to provide complete melting of the irradiated film.…”

“…For this reason we chose for an irradiation at 515 nm wavelength, which has a much lower measured absorption coefficients. This ensures a larger penetration depth of ≈ 49 nm for a-Si and near 200 nm for the crystallized poly-Si film [103], leading to a more homogeneous melting of the silicon layer [102] [ 104,105]. This widens the process window for the re-crystallization in terms of the laser power and pulse duration [104][105][106].…”