Laser Crystallized Polysilicon TFT'S Using LPCVD, PECVD and PVD Silicon Channel Materials-A Comparative Study

1999 ◽  
Vol 557 ◽  
Author(s):  
R.T. Fulks ◽  
J. B. Boyce ◽  
J. Ho ◽  
G. A. Davis ◽  
V. Aebi
Keyword(s):  
Low Temperature ◽  
Field Effect ◽  
Room Temperature ◽  
Laser Energy ◽  
Laser Crystallization ◽  
Drain Bias ◽  
Excimer Laser Crystallization ◽  
Laser Anneal ◽  
Active Channel ◽  
Very Low Temperature

AbstractIn this work polysilicon TFI's were fabricated by excimer laser crystallization of active channel silicon which was deposited by three different methods: I) LPCVD at 550 °C; 2) PECVD at 225 °C; and 3) PVD at room temperature. CMOS devices were produced with the same low temperature (less than 600 °C) top gate process and the laser anneal condition was optimized for the material type and thickness. For PECVD material a pre-anneal step of 450 °C for 1 hour was required before crystallization to avoid bubbling and ablation due to hydrogen evolution, but no such anneal was required for either LPCVD or PVD material due to their low hydrogen and Ar content. For 50 nm films, laser energy densities were typically in the range of 300-400 miJ/cm2. Excellent device results were obtained for both LPCVD and PECVD material with n-channel field effect mobilities greater than 100 cm2/Vs and on/off ratios greater than 108 at 5 V drain bias. Good results were also obtained for PVD films that can be further improved by optimizing deposition and anneal conditions. In moving toward very low temperature polysilicon processing (less than 230 °C) both PECVD and PVD channel films appear to be viable candidates.

Single-Crystal Thin Film Transistor by Grain-Filter Location-Controlled Excimer-Laser Crystallization

2001 ◽  
Vol 685 ◽  
Author(s):  
Barry D. van Dijk ◽  
Paul Ch. Van der Wilt ◽  
G. J. Bertens ◽  
Lis.K. Nanver ◽  
Ryoichi Ishihara
Keyword(s):  
Thin Film ◽  
Chemical Mechanical Polishing ◽  
Field Effect ◽  
Thin Film Transistor ◽  
Subthreshold Swing ◽  
Filter Method ◽  
Field Effect Mobility ◽  
Laser Crystallization ◽  
Excimer Laser Crystallization ◽  
Grain Filters

AbstractThin film transistors (TFTs) are fabricated inside a large, location-controlled, silicon grain, fabricated with the grain-filter method. In a first experiment TFTs with high field-effect mobility for electrons of 430 cm2/Vs are fabricated. The off-current and subthreshold swing have high values of 60 pA and 1.2 V/dec, respectively. The grain-filter is improved by doping the channel and by planarizing the grain-filter by chemical mechanical polishing (CMP). TFTs fabricated in CMP-planarized grain-filters have mobility, off-current, and subthreshold swing of 430 cm2/Vs, 0.3 pA, and 0.29 V/dec, respectively, which compares well with the characteristics for SOI TFTs.

A Novel Two-Pass Excimer Laser Crystallization Process to Obtain Homogeneous Large Grain Polysilicon

1999 ◽  
Vol 558 ◽  
Author(s):  
L. Mariucci ◽  
R. Carluccio ◽  
A. Pecora ◽  
V. Foglietti ◽  
G. Fortunato ◽  
...  
Keyword(s):  
Excimer Laser ◽  
Crystallization Process ◽  
Laser Energy ◽  
Spatial Modulation ◽  
Lateral Growth ◽  
Laser Crystallization ◽  
First Pass ◽  
Wide Energy ◽  
Excimer Laser Crystallization ◽  
Polysilicon Tft

ABSTRACTNew approach to control the lateral growth mechanism through the opportune spatial modulation of the absorbed laser energy and with a two-pass excimer laser crystallization process is presented. In the first pass, spatial modulation of the light intensity has been obtained by irradiating the sample through a patterned mask in contact with the sample. Lateral growth is triggered when the irradiated regions are fully melted and a lateral extension of the grains in excess to 1 μm has been observed for samples irradiated at RT. In order to homogeneously crystallize the sample, the film can be re-irradiated (second pass) without the mask. By using opportune energy densities it can be induced a complete melting of the residual a-Si regions (masked areas during the first pass), while partially melting the polysilicon regions (unmasked areas during the first pass). Different mask geometries have been investigated and for optimized conditions, the sample area can be fully covered with laterally grown grains. The proposed novel technique can be rather attractive for polysilicon TFT fabrication, being characterized by only a two laser-shot process and wide energy density windows.

Low Temperature Characteristics of Hydrogenated Amorphous Silicon Field Effect Transistors

1989 ◽  
Vol 149 ◽  
Author(s):  
Byung-Seong Bae ◽  
Deok-Ho Cho ◽  
Jae-Hee Lee ◽  
Choochon Lee ◽  
Jin Jang
Keyword(s):  
Low Temperature ◽  
Amorphous Silicon ◽  
Threshold Voltage ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Hydrogenated Amorphous Silicon ◽  
Field Effect Mobility ◽  
Temperature Dependent ◽  
Hydrogenated Amorphous ◽  
Very Low Temperature

ABSTRACTWe investigated the temperature dependent characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT's) at temperatures down to 20 K. With decreasing temperature, the threshold voltage increased, the field effect mobility and the on-current decreased. The measured on-currents versus inverse temperature above 80 K are represented as the sum of two exponentially varied currents. It is concluded that on-current is nearest-neighbour hopping between 120 K and 80 K. Below this temperature, the temperature dependence of on-current is explained by variable range hopping and below about 30 K on-current becomes nearly independent of temperature. At very low temperature hopping probability may be governed not by temperature but by temperature independent tunneling, depending on the overlap of the wave function. The explanation of threshold voltage increase at low temperature is given.

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