Semiconductor Equipment Assessment Linking European Equipment Suppliers with Global Users

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Project LACRASIL

The SAELC System

Dedicated to low temperature polysilicon thin film transistors for AMLCDs, the SAELC unit combines a VEL 15J-XeCl laser (l:308 nm) and a motion stage with a high performance optical set-up to homogeneise the energy distribution.

Workstation unit

Typical laser pulse characteristics : t = 210 ns

The standard workstation unit consists of a built-in motion stage derived from proven state-of the-art technology developed by SOPRA since 1992, which has been designed to handle panels up to 650x750 mm2 in their spectroscopic ellipsometers.

Long, stable and reliable pulse

At optimal working conditions the pulse width is stable and is typically 210 ns ± 1.5%. Such a long pulse enables a "smooth" process which reduces the roughness and the residual stress in the treated material.

The shot-to-shot energy repeatability Spp= (Emax-Emin/Emax+Emin) of the laser pulse is typically 2.5% (3s).

Straightforward process

By virtue of the long laser-pulse duration, the SAELC unit enables silicon processing at room temperature in air at atmospheric pressure. Neither a heater or a vacuum chamber is required making the system far easier to maintain. This process has been developed for low temperature polysilicon-TFT AMLCDs with an n-mobility up to 200 cm2/V.s.

As an option, the combination of a heater and a vacuum chamber can be implemented to achieve even higher mobilities.

Stability of the 1 Hz laser system. (calculated over 100 shots – drift corrected). Spp over 17000 shots: 3.7%.

Large spot area - high quality optics

Particular attention has been focused on the implementation of the optical set-up to provide a large area ‘flat top-hat’ profile for the laser beam spot. The patented set-up minimises the number of optical components making it easy to adjust (typically less than 4 hours). It also raises the transmission of the laser energy to 85%. Furthermore, the long depth of field of the focusing system (±4 mm), ensures a long-term reliability for the optical adjustment. The laser light is transferred onto the sample through a "fly eyes" type beam homogeniser yielding a very flat energy distribution over a very large area. Typically, uniformity better than 2.5% is delivered over a spot of 17 cm2 and an energy density adjustable up to 820 mJ/cm2.

Process stability

In addition to the shot-to-shot energy repeatability, pulse duration stability and homogeneity of the laser beam, the SAELC unit exhibits long-term stability which assures reproducibility of the process in terms of crystallinity of annealed silicon over a very large laser spot area. Thus, processes with a narrow process window can be used.

The SAELC unit is designed to comply with the requirements of the high quality contamination-free environment of the semiconductor industry and meets international facility standards and safety guidelines.