Deposition – reactor / Siemens reactor

Silver-plated Deposition Reactor / Siemens-Reactor

  • This part of the plant comprises the heart of the production system where on hot silicon slim rods solar-grade silicon is deposited from SiHCl3.
  • These reactors were designed according to our customers needs.
  • The electronics (thyristors) to heat and thermally control the silicon rods were produced by an experienced company.
  • In the D-reactors gaseous TCS and hydrogen is converted to polysilicon by chemical vapor deposition (CVD). The polysilicon deposits on the surface of hot silicon slim rods at temperatures of approx. 1,100 °C. The silicon rods grow continuously to a thickness of 150 mm – 180 mm rods. Electrical power is used to heat the rods. The deposition process takes about 3 to 5 days.
  • Physical and mechanical design parameters of the D-reactors were checked and tested with respect to safety by an independent testing institution (TÜV, Germany).

Process development (in-house)

  • Thermal and flow simulations to optimize and improve the deposition process.
  • Target power consumption of CVD-process: < 45 kWh/kg silicon.
  • Optimization of start procedure to avoid slim rod breakage.
  • Improvement of contact electrode-slim rod.
  • Highly automation of CVD-process control to reduce man power and gain reproducible results.

Advantages of our silver-plated bell jar

Cost advantages:

  • >50% electric power savings due to avoiding radiation heat losses of the reactor.
  • Thicker silicon rods (up to 180 mm) corresponding also with energy savings.
  • Easier and less intense cleaning of the bell jar.

Quality advantages:

  • Less pop-corn surface of the rods ➔ enhanced purity.
  • Less thermal stress ➔ less breakage before harvesting.
  • Less contamination from stainless steel in silicon.
  • Higher reflection ➔ better distribution of radiation ➔
    higher homogenization of rods.

Advantages of our silver-plated CVD-Reactor

Energy Efficiency/Energy recovery

  • Silver-plated bell jar.
  • Liebig pipe heat exchanger.
  • High temperature cooling water jacket.

Enhanced productivity

  • Up to 3,200 mm rod length.
  • Up to 180 mm rod diameter.
  • Up to 3,700 kg poly-silicon / run.

Enhanced poly-silicon quality

  • Less thermal stress of rods.
  • Less popcorn surface.
  • Homogeneous rod diameter.
  • Flat surface without cracks.

Main production figures for solar-grade silicon (example):

Silicon rod growing rate: up to 1.9 mm/h
Silicon deposition rate: 30 kg/h
Molar ratio H2/TCS: 3.5 mol/mol
Total silicon deposition per run: up to 3,700 kg
Specific energy consumption: 45 kWh/kg Si
Specific energy recuperation: 35 kWh/kg Si

In addition, it is enable to use for our CVD-reactors the energy recuperation of the high temperature cooling water. This high temperature cooling water is pumped through CVD-reactors as cooling water. This kind of energy can be used for example to produce steam for heating for example distillation columns. An additional reduction of energy consumption (approx. 35 kWh/kg Si) can be reached.