Method for producing polycrystalline silicon

A process for producing polycrystalline silicon, comprising:

• introducing a reaction gas comprising silane and/or at least one halosilane as well as hydrogen into a reaction space of a gas phase deposition reactor, wherein the reaction space comprises at least one heated support body upon which by deposition silicon is deposited to form the polycrystalline silicon, wherein for detection of dust at least one measuring apparatus is used to determine haze inside the reaction space during the deposition by measuring the attenuation of the electromagnetic radiation emitted from the heated support body and/or by measuring the attenuation of the electromagnetic radiation emitted from an external source of electromagnetic radiation, wherein the external source emits radiation having wavelengths or a wavelength distinct from the wavelengths of an emission spectrum of silicon, wherein the attenuation is caused by absorption and/or by scattering and wherein the gas phase deposition reactor is a Siemens Reactor or a fluidized bed reactor, wherein the deposition is interrupted or terminated upon exceeding a threshold value of the haze or upon exceeding or falling below a threshold value of the haze as determined by at least one parameter selected from the group consisting of reactor pressure, support body temperature, reaction gas composition and volume flow is varied, and wherein the haze determined is a measure of an amount of particles within a reaction gas atmosphere within the reaction space of the gas phase deposition reactor.