CRYSTALAS. UV Optics System for Excimer Laser Based Crystallization of Thin Silicon Films

Transcription

1 L A S E R S Y S T E M G M B H CRYSTALAS UV Optics System for Excimer Laser Based Crystallization of Thin Silicon Films

2 CRYSTALAS The New Optical Crystallization System CRYSTALAS is an excimer laser-based optical system for the annealing and crystallization of thin silicon films. It is an ideal research tool for developing new production processes in the semiconductor industry. The flexible system design allows annealing processes on laboratory samples as well as on large size substrates. Thus, research results can be easily transferred to fabrication processes in industrial production lines. A well-established application of excimer laser- based annealing processes is the crystallization of thin amorphous silicon films on glass substrates by line beam exposure. This technique generates homogeneous polycrystalline films that provide the basis for the fabrication of thin-film-transistors (TFTs) for active-matrix liquid-crystal displays (AMLCDs). However, line beam exposure cannot produce single-crystal or near-single-crystal films that are required for the fabrication of complementary-metal-oxide-semiconductor (CMOS) devices for high-performance integrated circuits. The answer to this challenge is a new annealing process called Sequential Lateral Solidification (SLS). This low temperature process developed by Professor James Im at Columbia University (New York, NY) delivers a homogenous polycrystalline film with large, single crystals. Thus, it opens the door for semiconductor manufacturers to use ultra-high performance silicon films for the fabrication of systems-on-a-substrate such as silicon-on-insulator or silicon-on-glass. Even silicon on flexible plastic substrates can be considered. When considering flat panel display logic devices, like CPU and RAM, these devices could be integrated with the AMLCD. Furthermore, organic light emitting diode (OLED) displays that require high crystal quality to minimize leakage currents could profit from this technique. SLS employs a mask imaging technique instead of a line beam exposure. The amorphous silicon covered substrate is illuminated by a pattern of lines and spaces (typical widths 2 to 3 µm within a 4 x 15 mm 2 field). The projected pattern yields a melting zone of 2.5 µm wide with well-defined edges. Crystal growth at the solid/liquid interface appears and leads to a crystal length of µm. The second exposure, half of the grating period shifted, melts the unprocessed area and produces a closed, homogeneous polycrystalline film. Let Your Crystals Grow Large Microscope photo (left) and SEM image (right) show poly-silicon film created with the SLS process Speed Up Your Process The CRYSTALAS optical annealing system employs the mask imaging technique to generate polycrystalline thin films. Since only two laser pulses are needed to generate a poly-silicon film of 0.5 cm 2, a 15-inch display can be crystallized with only 3,000 laser pulses. Use Specific Mask Structures The SLS process can also produce controlled, single-crystal like silicon film segments. Specific mask structures like chevron shaped patterns can be used to illuminate the substrate. To obtain a homogeneous single-crystal segment, the pattern is scanned sequentially across the substrate. A scanned chevron pattern exposure yields a singlecrystal like region Masked exposure provides large direction- oriented silicon crystals Find More Literature J. S. Im et al., Controlled Super-Lateral Growth of Si Films for Microstructural Manipulation and Optimization, Phys. Stat. Sol. (a) 166, 1998, p H. J. Kahlert, Creating Crystals, OE magazine 11, 2001, p S. Uchikoga et al., Low Temperature Poly-Si TFT-LCD by Excimer Laser anneal, Thin Solid films 383, 2001, p

3 CRYSTALAS Optical System CrystaLas Optical Annealing System CrystaLas Mask Stage Wide System Applications Amorphous Silicon annealing for the fabrication of: - Thin film transistors (TFTs) for LCD and OLED-displays - CMOS elements (logic and memory devices) - High power electronic components (diodes etc.) Amorphous Silicon annealing on flexible plastic substrates Metal film annealing Superior System Benefits High energy density Homogeneous energy density profile Large area illumination Fast processing with high power lasers System versatility for the integration into other mechanical set-ups CrystaLas Homogenizer Optics Outstanding System Features Variable attenuator for precise control of energy density Energy measurement and feedback to attenuator for constant energy density CCD cameras for laser and mask beam profile measurement Homogenizer exchange capability for different mask beam profiles High precision XY-mask stage High resolution projection lenses with 18 mm and 30 mm field of view (FOV) Projection lens temperature stabilization Auto focus system for control of objective-substrate distance CCD cameras for mask and substrate observation Nitrogen purging of the entire beam path Pulse width enhancement by integration of pulse duration extender (option)

4 CRYSTALAS Optical Concept System Design The schematic drawing of the CRYSTALAS optical system shows the optical beam path and all optical components necessary to perform high precision laser annealing. The entire optical set-up is mounted on a granite table that ensures the required mechanical stability. The length of the granite table can be varied to meet customer requirements. System Beam Entrance The way the laser beam enters the optical system can be individually adapted to any beam height and beam orientation of Lambda Physik excimer lasers. Attenuator A variable attenuator with a dynamic range of 10 to 1 can adjust the energy density on the substrate. In case a pulse duration extender is employed, the attenuator also controls the amount of energy in the extender. Telescope An anamorphic telescope configuration efficiently adapts the beam profile to the aperture of the homogenizer. Homogenizer The homogenizer consists of two pairs of lens arrays two for each beam axis. The condenser lens generates the uniform illumination field on the mask. By exchanging the homogenizer elements, different field sizes on the mask can be adjusted. Field Lens Group The field lenses are used to project the light into the entrance aperture of the projection lens. Mask Stage The high precision 6 x 6 mask stage allows accurate positioning of the mask to the uniform beam profile. Different travel ranges and mask sizes are possible. Projection Lens The diffraction limited projection lens allows annealing processes to be performed with a resolution of 2 µm. Projection lenses with a field of view (FOV) of 18 mm or 30 mm are available.

5 CRYSTALAS System Specifications System wavelength (standard) 308 nm Optical system efficiency 1 up to 40 % Projection lens 5x/ x/ x/ Demagnification 5x 5x 5x - NA 0.13 diff. limited 0.13 diff. limited 0.10 diff. limited - Resolution 2.0 µm 2.0 µm 2.5 µm lines & spaces lines & spaces lines & spaces - Field of view (FOV) 10 mm 18 mm 30 mm - Depth of focus (DOF) 2 typical ± 15 µm typical ± 15 µm typical ± 25 µm Minimum uniform beam profile width on mask 5 mm x 5 mm Maximum length of mask profile 50 mm 80 mm 150 mm Homogeneity of beam profile at mask ± 2.5% (2σ) Substrate beam profile for full FOV in one axis 10 mm x 1 mm 16 mm x 1 mm 30 mm x 1mm Energy density 3 at 1100 mj/cm mj/cm mj/cm 2 substrate with LPX 210i with LS 670 with LS 1000 for 10 mm x 1 mm for 16 mm x 1 mm for 30 mm x 1 mm 1. Efficiency specification does not include pulse duration extender. 2. Stated DOF values derived from MicroLas SLS process data. 3. Higher energy density values can be easily achieved if the area of the substrate beam profile is decreased.

6 CRYSTALAS Laser Sources Lambda LPX 210i Medium to High Duty Excimer Lasers The LPX 210i is a medium to high duty cycle excimer laser, offering a high repetition rate for scientific and industrial applications. It combines proven design with state-of-the-art technology, setting new standards for reliability and performance. Features NovaTube technology for outstanding gas and tube lifetimes Magnetic Switch Control (MSC ) technology for extended thyratron lifetimes Electrostatic gas processor for extended gas lifetimes and window cleaning intervals Slide valves with an extra set of spare optics mounts for fast window exchange Easy access to optical components through the top panel of the laser Technical Data Model LPX 210i Multigas version Wavelength 308 nm Pulse energy 400 mj max. 1, 280 mj stabilized Max. repetition rate 100 Hz Average power 2 38 W Pulse duration 3 28 ns Pulse-to-pulse stability 4 ± 3.5 % Beam dimensions (v x h) x 23 mm 2 Beam divergence (v x h) 3 1 x 3 mrad Time jitter 5 ± 2 ns Electrical CEE 400 V, ±10 %, 32 A, 50 Hz, 3 Ph/N/PE, 7.5 kva. Optional 208 V, ±10 %, 50/60 Hz switchable, 3 phase Water cooling 4 l/min (1.1 gal/min), C, connection: 1/2 Dimensions (l x w x h) Laserhead: 1966 x 800 x (feet/range + 40 mm) mm x 31.5 x 18.6 (feet/range inches) inches Power supply: 460 x 185 x 750 mm 3 / 18.1 x 7.3 x 29.5 inches Vacuum pump: 230 x 240 x 530 mm 3 / 9.1 x 9.4 x 20.9 inches Weight Laserhead: 270 kg / 595 lbs Power supply: 50 kg /110 lbs Vacuum pump: 23 kg / 51 lbs 1. measured at low repetition rate 4. based on 90% of all pulses 2. measured at max. repetition rate 5. typical, 1s 3. typical, FWHM

7 CRYSTALAS Laser Sources Lambda STEEL Series Advanced Design for Better Performance Lambda STEEL (STable Energy Excimer Laser) lasers are designed for high throughput and high duty-cycle industrial production. The focus of the design was a high-power laser with excellent pulse stability that ensures superior accuracy of large area processing. Features Redesigned NovaTube technology for outstanding gas and tube lifetimes Super Magnetic Switch Control (SuperMSC ) technology for extended thyratron lifetimes Resonator optics separated from the laser tube for stable beam performance Pneumatic activated window slide valves mechanism for fast and safe window exchange Single-side access for maintenance and service minimizes clean room floor space requirements Technical Data Model Lambda STEEL 670 Lambda STEEL 1000 Wavelength 308 nm Pulse energy 670 mj stabilized 1000 mj stabilized Max. repetition rate 300 Hz Average power 200 W 300 W Pulse duration 22 ± 5 ns 29 ± 5 ns Pulse-to-pulse stability (6σ) 1 12 % 15 % Max. pulse energy deviation above average 2 7 % 8.5 % Beam dimensions (typical, FWHM) 3 (35 ± 3) x (12 ± 2) mm 2 (38 ± 3) x (13 ± 2) mm 2 Beam divergence (typical, FWHM) 4.5 mrad x 1.5 mrad Angular pointing stability (typical, FWHM) mrad x 0.15 mrad Gas lifetime > 30 x 10 6 pulses > 20 x 10 6 pulses Laser tube lifetime > 1 x 10 9 pulses Beam height 1200 ± 20 mm Electrical 5 25 kva 3-phase, 400 VAC ±10 %, 200 VAC ±10 % Water cooling l/min. T = (10 15) C at inlet for 100% duty cycle Cabinet size (l x w x h) 2500 x 850 x 1900 mm 3 / 98.5 x 33.5 x 75 inches 1. Full width of 6s, Interval ± 3s 4. at 1.0 m from beam exit, 10 pulses at 10 Hz 2. Max. energy minus average energy 5. LS 1000 delivered with external transformer 3. at 1.0 m from beam exit for 200 VAC version

8 CRYSTALAS Diagnostic Tools To ensure full annealing process control and stability, the CRYSTALAS annealing system is equipped with various diagnostic tools: CCD camera for laser beam profile analysis (including PC and beam analysis software). This allows checking the emitted laser beam profile in front the optical system. CCD camera for analysis of the homogenized mask beam (including PC and beam analysis software). This enables the examination of the homogeneity and the size of the beam profile on the mask. Online monitor for the measurement of the pulse energy incident on the mask. This provides pulse energy monitoring with feedback to the variable attenuator to precisely control the energy density. Mask structure observation by CCD camera. This permits a fast and an immediate check of mask patterns during the process. CCD camera for substrate monitoring during the laser operation. This enables accurate positioning of the substrate and immediate control of the annealing process. Energy measurement after the projection lens. This provides the means to monitor the overall optical efficiency between process intervals. System Integration The CRYSTALAS optical annealing system is designed for integration into a pure research tool for R&D process development as well as integration into a complete fabrication system for industrial production lines. MicroLas cooperates with specialized system integrators worldwide. Worldwide Sales Representatives Germany and Austria Lambda Physik AG Hans-Böckler-Str. 12 D Göttingen Tel.: Fax.: USA Lambda Physik Inc West Commercial Blvd. Fort Lauderdale, Fl 33308, USA Tel.: (954) (800) EXCIMER Fax.: (954) Asia Lambda Physik Japan Co.,Ltd. German Industry Center , Hakusan, Midoriku Yokohama 226, Japan Tel.: (045) Fax.: (045) Europe MicroLas Lasersystem GmbH Robert-Bosch-Breite Göttingen a subsidiary of TEL: 49 (0) FAX: 49 (0) info@microlas.de 01/02