Process for producing polycrystalline silicon

Method for producing polycrystalline silicon, comprising:

• introducing a reaction gas, which in addition to hydrogen contains silane and/or at least one halosilane, into a reaction space of a vapour deposition reactor, wherein the reaction space comprises at least one filament rod which is heated by way of the passage of current and on which by means of deposition silicon is deposited to form a polycrystalline silicon rod, wherein for the determination of the morphology of the silicon rod during the deposition at a rod temperature TS
• wherein a first resistance value Ry of the silicon rod is determined according to
• R
• 1
• =
• U
• I
• where U is a voltage between two ends of the silicon rod and I is a current strength;
• wherein a second resistance value R2 of the silicon rod is determined according to
• R
• 2
• =
• ρ
• ⁢
• L
• A
• wherein ρ is a resistivity of silicon, L is a length of the silicon rod and A is a cross-sectional area of the silicon rod;
• and
• wherein a morphology index M is calculated from the ratio R1/R2, wherein the deposition is controlled by varying at least one parameter selected from the group comprising U, I, surface temperature TOF, reaction gas composition and standard volume flow rate in such a way that for the production of
• a polysilicon type B M has a value of 1.2 to 1.4, or
• a polysilicon type C M has a value of 1.4 to 1.7, or
• a polysilicon type D M has a value of greater than 1.7,
• wherein U is in a range from 50 to 500 V, I is in a range from 500 to 4500 A, TOF is in a range from 950 to 1200° C., the standard volume flow rate of the reaction gas is 1500 to 9000 m3/h and the reaction gas prior to entry into the reactor contains hydrogen in a proportion of 50% to 90%, and wherein TS is the surface temperature TOF of the silicon rod or the arithmetic mean of two or more surface temperatures TOF of the same or different silicon rods.