SEMI PV90 - Guide for Material Requirements of Internal Feeders Used in Monocrystal Silicon Growers
1.1 An internal feeder is a device that enables the loading of additional polycrystalline silicon into the crucible of a crystal grower for either top-up or recharge purposes, while still maintaining full furnace vacuum and temperature conditions.
1.2 Internal feeders are widely used in the photovoltaic industry for growing monocrystalline silicon. During the feeding process the high purity polycrystalline silicon is in close contact with parts of the feeder. Therefore, the materials used in the construction of the internal feeders may contaminate the polycrystalline silicon, thus adversely affecting the quality of the silicon crystal.
1.3 Internal feeders work in a high temperature environment. Its construction materials need to maintain adequate mechanical strength under such an environment.
1.4 Many material suppliers, semiconductor device manufacturers, equipment makers, and crystal producers are involved in the manufacturing and utilization of internal feeders. Thus, a guide for material requirements is needed to assure product quality.
1.5 The purpose of this technical guide is to make the best practice recommendations regarding materials used in the construction of internal feeders, so that the feeders can perform well in the challenging working environment, while minimizing contamination to the polycrystalline silicon material.
2.1 This Guide covers internal feeders that are used to grow single crystal silicon for the photovoltaic industry.
2.2 This Guide quantifies the impurity levels which are potentially transferred into the silicon melt from various construction materials used for internal feeders. It also provides guidance for selecting appropriate construction materials for internal feeders.
2.3 This Guide lists the impurities typically found in polycrystalline silicon, and describes shortly the effects these impurities may have on finished solar cells.
2.4 This Guide also describes the different temperature regions of an internal feeder and the temperature limits of the materials used in each region.
Referenced SEMI Standards:
SEMI PV17 — Specification for Virgin Silicon Feedstock Materials for Photovoltaic Applications