Solar wafer production in horizontal furnace
Modern micro-electronics and photovoltaics “live“ on coated silicon chips. The most cost-effective way to produce them is to cut out individual transistors, CPU chips and solar cells from large units known as silicon wafers. This means that the highly sterile silicon wafer has to be accurately and reproducibly coated with a range of different substances. Special horizontal furnaces are used for this process, as they allow the conditions to be defined exactly for the relevant reaction. High-performance, extremely reliable modern microdrives are perfect for the furnace logistics, i.e. the loading and unloading of furnace pipes and the opening and closing of the furnace doors.
Virtually all modern electronic devices are based on silicon chips incorporating a range of components, such as transistors. They need to be produced quickly and in large volumes in order to offer cost-effective pricing for individual chips. The chips are therefore produced in large quantities on what are known as “wafers”, which are silicon sheets measuring between 100 and 300 mm, and are then separated. Specific surface treatment of the wafers is just as likely to involve the atmospheric absorption of phosphorus and boron compounds as chemical vapor deposition (CVD) at low pressure. Tempress Systems B.V. from Vaassen in the Netherlands have developed a highly flexible range of horizontal furnaces that offer chip manufacturers a high degree of flexibility. The furnaces are used for mass producing quality solar cells based on wafers. Robust microdrives developed by microdrive expert FAULHABER from Schönaich near Stuttgart are used to load the individual furnace pipes. They also automatically close the furnace doors, which is a crucial safety function as highly reactive chemicals are used in the furnaces.
Made-to-measure wafer treatment
Production methods change in the electronics industry quicker than virtually any other sector. So all the systems used need to have the capacity to adapt flexibly to a wide range of different production requirements. The horizontal furnaces put these industry requirements into practice with consummate perfection. The four reaction furnace chambers are arranged horizontally above one another and are loaded with 156 mm x 156 mm wafers for the production of solar cells. There are around 400 to 500 wafers per pipe, so it takes just a single process to coat up to 1500 wafers per hour. In solar panel production, the surface area of a wafer can later be used to generate an average of 4 W of energy. If you consider that an average house roof has around 50 panels producing around 200 W each, the production output of the Tempress furnace represents solar electrical performance of 30 to 35 MW per year. High throughput levels allow cost-effective mass produc-tion of solar cells. Depending on the procedure, the furnaces either work under normal pressure or in a vacuum, with temperatures ranging between 380 and 1380 °C. Because the wafer sheets are expensive, process reliability is crucial, and all the components need to satisfy exacting requirements. The Tempress Data Management System allows a wide range of parameters to be configured, from temperature management through precise gas measurement to pressure control. There is a special loading system which loads and unloads the individual furnace pipes. Microdrives are used as actuators. The main requirements of the drive are a high level of torque from a very compact drive, plus precision positioning. It is also imperative that the drives are extremely reliable. After all, errors can be very expensive because of the high cost levels and the use of corrosive chemicals. The robust design of the planetary gearheads was also a decisive factor here. Other benefits of the actuators selected by the company included the compact design of the complete drive, with the matching encoder, and its dynamism and intuitive controls.
Microdrives – robust and precise
Various drive solutions from the FAULHABER range are deployed in the different furnaces. The loading systems, for example, use a DC-Microdrive. The diameter-compliant planetary gearheads reduce the speed and at the same time increase the drive torque. Depending on the design (normal or heavy-loader), the drives used have a diameter of 32 or 38 mm and metal planetary gearheads with transformation ratios of 14:1 or 3.71:1. In both versions, there are plug-in encoders which allow precise positioning of the wafers in the system based on 256 pulses per revolution of the motor shaft. The gear transformation also increases the precision of the drive shaft. There are even more exacting requirements for the safety-critical function of closing the furnace door. A reliable locking system must be guaranteed in order to ensure that gas cannot escape from the furnace pipes. This is why, as well as a motor with encoder and planetary gearheads, some models also have electromagnetic brakes installed. These guarantee that the doors close safely even in the event of a power outage. The brake unit also plugs into the 32 mm motor, with the whole unit – including the motor – measuring just 72.5 mm. Modern microdrives offer all the functions of larger drives within a compact space. Whether it‘s encoders, gearheads or brakes, virtually all components are now available in miniaturized form. Their best-in-class design guarantees high levels of process reliability.