Flowable chips and methods for the preparation and use of same, and apparatus for use in the methods
A method for recharging a crucible with polycrystalline silicon comprises adding flowable chips to a crucible used in a Czochralski-type process. Flowable chips are polycrystalline silicon particles made from polycrystalline silicon prepared by a chemical vapor deposition process, and flowable chips have a controlled particle size distribution, generally nonspherical morphology, low levels of bulk impurities, and low levels of surface impurities. Flowable chips can be added to the crucible using conventional feeder equipment, such as vibration feeder systems and canister feeder systems.
1. Flowable chips comprising: polycrystalline silicon pieces prepared by a chemical vapor deposition process and having a controlled particle size distribution, where at least 75% of the particles have a particle size of 0.2 to 45 mm, generally nonspherical morphology, a level of bulk impurities not exceeding 0.03 ppma, and a level of surface impurities not exceeding 15 ppba.
2. The flowable chips of claim 1 , where the bulk impurities are boron in an amount less than or equal to 0.06 ppba, donor in an amount less than or equal to 0.30 ppba, phosphorous in an amount less than or equal to 0.02 ppba, carbon in an amount less than or equal to 0.024 ppma, and total bulk metal impurities in an amount less than or equal to 4.5 ppba.
3. The flowable chips of claim 2 , where the total bulk metal impurities are present in an amount less than or equal to 1 ppba.
4. The flowable chips of claim 3 , where the total bulk metal impurities comprise Cr in an amount less than or equal to 0.01 ppba, Cu in an amount less than or equal to 0.01 ppba, Fe in an amount less than or equal to 0.01 ppba, and Ni in an amount less than or equal to 0.01 ppba.
5. The flowable chips of claim 1 , where the surface impurities are Cr in an amount less than or equal to 0.06 ppba, Cu in an amount less than or equal to 0.15 ppba, Fe in an amount less than or equal to 10 ppba, Na in an amount less than or equal to 0.9 ppba, Ni in an amount less than or equal to 0.1 ppba, and Zn in an amount less than or equal to 0.6 ppba.