Spang Power Electronics is a manufacturer of custom power equipment installed for polysilicon manufacturing utilizing the widely applied SIEMENS process. Spang’s expertise in power control and conversion has helped them become a global leader for the following applications.
Internal preheat is used to reduce the starting / discharge voltage of the polysilicon rods (the voltage point at which the polysilicon rod begins to conduct current). A resistive load is added internal to the CVD reactor for the purpose of adding heat which increases the temperature of the polysilicon rods, reducing the point at which starting / discharge occurs. Internal preheat is not used in every reactor design and is dependent upon the reactor design and the process approach implemented by the customer.
Spang Power Electronics provides SCR Controllers, Transformers, and Power Systems to provide highly accurate controlled power to the preheat resistive heating elements.
Starting / Discharge
In many power supply and CVD reactor system designs a separate starting / discharge circuit is included to achieve the high voltage per pair necessary to achieve rod current flow through the polysilicon rods. This circuit provides high voltage at low current and manages the transition of no current flow to regulated current (cold to hot transition). In some cases the power supply provides more than a 10X reduction in controlled voltage from the initiation of the process to the point of a rod conducting current in stable control. Once stable current control is achieved the starting / discharge power system is disabled and the load is transitioned to the main power system for the actual deposition process (growth of the polysilicon rods). The use and ratings of the starting / discharge system relate to many factors including the use and magnitude of preheat, the length of rods, the number of rod pairs in series, and the voltage handling capability of the main power supply.
Spang Power Electronics provides SCR Controllers, Transformers, and Power Systems to provide highly accurate controlled power to the silicon rods during the starting / discharge process.
Chemical Vapor Deposition (CVD) Reactor
Once the main power supply phase is transitioned from starting / discharge, it maintains a predetermined current while all other phases of the reactor are started / discharged and transitioned to the main phase. After all phases of the reactor are running by the main power supply and regulating current, the actual deposition process begins. Based upon the customer’s desired operating profile, the main power supply delivers ever increasing current at ever reducing voltage as the polysilicon rods grow in diameter and resistance continues to drop. Because of the broad resistance range of the polysilicon rods from start to finish, a wide controllable voltage range is required. The power supply then must provide this wide voltage range and use the latest power control technology to maintain high power factor and low harmonic distortion.
Spang Power Electronics provides SCR Controllers, Transformers, and Power Systems to provide highly accurate controlled power to the silicon rods during deposition process.
Hydrogenation / Converter
During the CVD reactor process for the manufacturing of polysilicon in the SIEMENS process STC (silicon tetrachloride) is formed as a byproduct of the chemical reaction of converting purified TCS (trichlorosilane) feedstock into high quality polysilicon. The hydrogenation / converter is a method to take the STC exhaust stream and convert it back to TCS which is then recycled back into the polysilicon reactor for decomposition. This process allows the customer’s plant to operate in an environmentally friendly closed loop and maximize the utilization of the TCS feedstock.
Spang Power Electronics provides SCR Controllers, Transformers, and Power Systems to provide highly accurate controlled power to the heating elements within the hydrogenation / converter reactor. The process is a “thermal conversion” which requires the addition of heat to allow for the chemical conversion.
With the interrelationships between the different technologies required to successfully operate a CVD reactor a sophisticated automation control system is often required. The control system not only manages the transition from the preheat to starting / discharge to main growth process of the CVD reactor but also provides advanced alarm and fault monitoring as well as data collection and reporting.
Spang Power Electronics provides sophisticated automation solutions ranging from mid-tier PLCs (programmable logic controllers) and operator panels to redundant PLCs, redundant servers, and computer based HMI stations.