|
|
|
|
|
BTU MERIDIAN In-Line Diffusion System
DESCRIPTION
The MERIDIAN™ In-line Diffusion System combines our latest second generation phosphorus coating technology with our flagship quartz lined diffusion furnaces. The system is comprised of a direct spray phosphorus coater integrated with a conveyor belt diffusion furnace for processing silicon solar cells. The coater now includes back-side, topside and drying capability which can translate into improved cell efficiency. The system can be configured to achieve up to 1500 wafers per hour (156 mm). The in-line process offers reduced wafer handling and greater through-put than traditional batch processing. Reduced handling translates into lower breakage rates and improved yield.
INNOVATION ASPECT
The new MERIDIAN™ In-Line Diffusion System includes the following improvements and changes:
- Phosphorus Coater
- Coating application is accomplished via a nozzle-less ultrasonic spray system. This unique approach eliminates clogging typically found in nozzle type spray designs.
- The addition of backside phosphorus coating capability. The Meridian coater is now capable of applying both topside and backside coating. The well known advantage of this capability is to promote impurity gettering from the wafer which can yield and efficiency improvement. Initial test results in our laboratory have shown a 60-65% averaged improvement of minority carrier lifetime depending on wafer type and quality. These numbers can vary widely.
- The transport system of the coater has been changed from a non-metallic mesh belt to non-metallic rollers. The roller transport enables backside coating without having to flip the wafers.
- Addition of an integrated wafer dryer is included within the coater to dry carrier liquid from the wafers prior to diffusion.
- Software features allow the coating to be independently applied to the top, bottom or both side of the wafer. This user selectable feature can be advantageous to in-line customers who wish to purchase the equipment and add backside coating to their process at later date. This is also very useful for process development trials.
- The ultrasonic spray heads have been changed to include proprietary features which improve spray coating uniformity. Spray pattern liquid distribution has been improved by an estimated 15-20% resulting in more uniform liquid distribution across the wafer.
- Other new features include automatic system cleaning, isolated spray chambers, overhead electrics and quick-change dopant reservoirs.
Diffusion Furnace Changes:
The diffusion furnace formerly known as the BTU TFQ series has experienced improvements as noted below.
- Software current limiting which reduces furnace startup power by as much as 30%.
- Heaters in ramping zones optimized for greater adjustability of thermal profile ramp rates.
- Integrated thermal profiling option added to aid the user in thermal profiling of the furnace.
BENEFITS
BTU’s Meridian Diffusion System increases cell efficiency through the use of backside doping and precision temperature controls while also providing high throughput and significantly reduced breakage rates through the use of in-line processing. The Meridian spray coater utilizes 3 methods of control to adjust the dopant application thickness and uniformity. Uniform, repeatable and controlled application of the dopant is required to insure consistent results. The Meridian diffusion furnace series includes temperature trim controls to maintain and adjust for temperature gradients across the width of the belt. Temperature uniformity across the belt is within +/- 2°C. This tight temperature uniformity is required to achieve uniform sheet resistance values. Tight atmosphere control is required to create a clean continuous flow of atmosphere. Atmosphere management is accomplished by injecting fresh process gas at specific inlets and utilizing controlled exhaust to direct atmosphere flow. This combined with our quartz-lined process chamber assures a clean processing atmosphere and safe removal of process effluent. Finally, the Meridian™ in-line process dramatically reduces total cost of ownership over traditional diffusion batch processing. Relative models show a 3x improvement in total cost of ownership.
