There are many thermal processes involved in the creation of solar cells from silicon wafers. It is SierraTherm's goal to supply quality in-line equipment for these processes, and we will continue to develop our capabilities in this regard. At present, we are able to provide many of the systems used in typical mono-crystalline and multi-crystalline solar cell processing. The table below outlines these processes and the in-line SierraTherm series used for each application:
| Process | Series | Description |
|---|---|---|
| 1) Phosphorus Diffusion | XR Or 7500 | In-line Metal-free Roller Hearth Furnace Infrared Conveyor Belt Furnace |
| 2) Metalization Drying | 7500 | Infrared Conveyor Dryer |
| 3) Metalization Firing | 7500 | Infrared Conveyor Furnace |
| 4) Anti-reflective Coating (TiO2) | 5500 | APCVD System |
| 5) Oxidation | 1500 | Fast Response Conveyor Furnace |
| 6) Hydrogen Annealing | 2500 | Controlled Atmosphere Conveyor Furnace |
1) Phosphorous Diffusion:
An efficient and cost effective alternative to batch methods of forming the P-N junction is the vapor deposition and diffusion of phosphorus from a liquid source in an in-line process. SierraTherm manufactures two types of furnaces for dopant drive-in: the 7500 Series IR Conveyor Belt Diffusion Furnace, and the XR Series Roller Hearth Diffusion Furnace. These furnaces use high temperatures to uniformly drive phosphorous into the silicon wafer. The XR Series furnace is sold together with the Schmid GmbH phosphorous doper. The Schmid phosphorous doper applies dopant by passing the wafer through an extremely uniform phosphorous/water mist. As both the furnace and the doper are available from a single source (Schmid GmbH), there are no interface or compatibility issues to worry about. Thus, what was an expensive cumbersome batch operation becomes an inexpensive continuous mass production process, improving diffusion uniformity, increasing throughput, and greatly reducing handling.
2,3) Paste Drying and Firing
SierraTherm infrared lamp conveyor firing furnaces and dryers use high quality tungsten filament quartz lamps as a short wavelength heat source. Thick films can be processed at an extremely high rate with unbeatable process consistency. Precision control of spike firing profiles is assured with SierraTherm's exclusive temperature and atmospheric control and monitoring systems. The highest quality construction and components are used in designs based on years of solar applications experience. See: SierraTherm 7500 Series Infrared Conveyor Furnaces
4) Anti-reflective Coating (TiO2)
Deposition of titanium dioxide in an atmospheric pressure CVD system is an effective and economical method for anti-reflective coating. The process is in-line, so handling is minimized at a throughput unmatched by alternative systems. Equipment and per-cell costs are much less than alternative coating methods. SierraTherm APCVD equipment is designed for low-maintenance dependability. See: SierraTherm 5500 Series APCVD Systems for Titanium Oxide and SiO2
5) Oxidation
Surface passivation by oxidation of wafers prior to application of the anti-reflective coating can improve open circuit voltage, Voc. SierraTherm manufactures a proven line of conveyor oxidation furnaces for this application. See: SierraTherm 1500 Series Conveyor Furnaces
6) Hydrogen Annealing
Hydrogen annealing can improve a cell's fill factor by as much as 1.5%. SierraTherm's controlled atmosphere conveyor systems are ideally suited for processing in a tightly controlled high temperature hydrogen environment. See: SierraTherm 2500 Series Conveyor Furnaces
Our ability to offer many pieces of the cell processing puzzle is sure to simplify equipment planning, selection, and integration. SierraTherm's extensive capabilities and experience are just a phone call way, and we look forward to discussing the possibilities with you.