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New Method of Float Zone Crystal Growth Based on a Heated Load Coil With RF Power Supply

IP.com Disclosure Number: IPCOM000042169D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Kim, KM: AUTHOR [+3]

Abstract

The use of a heated load coil results in a uniform radial dopant distribution, and control of the float zone (FZ) crystal growth becomes rather easy. Conventional FZ silicon crystal growth uses a high frequency (usually 2.3 MHz) of RF power in conjunction with a water-cooled single turn coil. Due to the high frequency, only a shallow surface layer of approximately of 0.1 mm thickness of the polycrystal feed rod is melted. The solid-liquid interface shape of both the growing single crystal and the liquid polycrystal rod is convex toward the melt (Fig. 1a). This, in turn, causes a strong radial inhomogeneous dopant distribution in the crystal. This is one of the major disadvantages of the FZ technique as compared to the Czochralski technique.

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New Method of Float Zone Crystal Growth Based on a Heated Load Coil With RF Power Supply

The use of a heated load coil results in a uniform radial dopant distribution, and control of the float zone (FZ) crystal growth becomes rather easy. Conventional FZ silicon crystal growth uses a high frequency (usually 2.3 MHz) of RF power in conjunction with a water-cooled single turn coil. Due to the high frequency, only a shallow surface layer of approximately of 0.1 mm thickness of the polycrystal feed rod is melted. The solid-liquid interface shape of both the growing single crystal and the liquid polycrystal rod is convex toward the melt (Fig. 1a). This, in turn, causes a strong radial inhomogeneous dopant distribution in the crystal. This is one of the major disadvantages of the FZ technique as compared to the Czochralski technique. FZ silicon crystal growth using low frequency (200-400 KHz) in conjunction with a water-cooled load coil has been tried in the past, and has the potential to improve the radial dopant distribution of FZ crystals. So far this technique failed to achieve any meaningful FZ crystal growth results, because the outer surface of the feed polycrystal rod is difficult to melt. The major problem encountered is the development of so-called "dendrites" which prevents a continuous melting of the feed rod. The invention described in this article prevents this "dendrite" melting problem. Fig. 1b illustrates a new approach to FZ silicon crystal growth, where a heated load coil is used in conjunction with an RF power supply. The frequency of the RF generator is medium (200-400 KHz) or high (N 2 MHz). Note that in the conventional FZ technique the coil is cooled continuously. In the new FZ method the heated load coil acts as a radiational heat source in addition to the conventional induction heating of...