Effect of Heater Structure on Oxygen Impurities in Lightly Phosphorus-Doped Czochralski Monocrystalline Silicon with Ultra-Low Oxygen Content

doi:10.16553/j.cnki.issn1000-985x.2024.0319

Abstract

Abstract: Insulated gate bipolar transistor （IGBT） is a core device for energy conversion and transmission， which widely used in rail transportation， smart grid， aerospace， electric vehicles and other fields. As the substrate material for IGBT chips， the quality of lightly phosphorus-doped silicon wafers with ultra-low oxygen content plays a crucial role in the performance of IGBT chips. Due to the use of oxygen-containing quartz crucibles during the Czochralski （CZ） method for monocrystalline silicon growth， the oxygen content of the obtained silicon is typically 4×10¹⁷~9×10¹⁷ atoms/cm³， which is much higher than the oxygen content of less than 2.5×10¹⁷ atoms/cm³ required for IGBT silicon wafers. To solve the above problems， this article presents a numerical simulation of monocrystalline silicon growth using a 32 inch hot zone， and designs a new heater to produce ultra-low oxygen monocrystalline silicon ingots that meet the requirements of IGBT substrates. The simulation results show that the flow rate of silicon melt near the quartz crucible wall and solid-liquid interface decreases when using a split heater. This phenomenon is beneficial to reduce the oxygen content in the melt and the transport of oxygen impurities to the solid-liquid interface， thereby effectively reducing the overall oxygen content of the crystal rod. In addition， due to the use of a split heater， the axial temperature gradient of the crystal rod at solid-liquid interface is significantly reduced compared to conventional heaters， which is also beneficial to reduce the oxygen content in the silicon rod. The experimental results further confirmed the simulation results. The oxygen content of the monocrystalline silicon rod produced under the split heater is much lower and remains below 2.5×10¹⁷ atoms/cm³ throughout， fully meeting the requirements for IGBT substrates.

Key words: Cz method; monocrystalline silicon with ultra-low oxygen content; split heater; oxygen content

CLC Number:

SHANG Runlong, CHEN Ya, RUI Yang, WANG Liguang, MA Cheng, YI Ran, YANG Shaolin. Effect of Heater Structure on Oxygen Impurities in Lightly Phosphorus-Doped Czochralski Monocrystalline Silicon with Ultra-Low Oxygen Content[J]. Journal of Synthetic Crystals, 2025, 54(5): 801-808.

Figures/Tables 11

Fig.1 Process of oxygen production and transmission

Fig.2 Two-dimensional model and the corresponding grid division of the furnace structure composed of a conventional heater （a） and a split heater （b）

Fig.3 Schematic diagram of conventional heater （a） and split heater （b）

Fig.4 Schematic diagram of magnetic field location

Table 1 Physical properties of silicon melt

Physical property	Value
Density/（kg·m^-3）	2 520
Coefficient of thermal expansion/K^-1	1.4×10^-4
Melting temperature/K	1 685
Dynamic viscosity/（kg·m^-1·s^-1）	7.6×10^-4
Emissivity	0.33

Table 2 Simulation and experimental process conditions

Parameter	Value
Crystal rotation/（r·min^-1）	5
Crucible rotation/（r·min^-1）	0.5
Pulling rate/（mm·min^-1）	0.5
Argon flow rate/slm	120
Furnace pressure/kPa	8
Magnetic field intensity/T	0.25

Fig.5 Cloud （a） and vector （b） plot of the velocity of silicon melt when the rod length is 300 mm

Fig.6 Crystal rod temperature gradient diagram under different heaters when the rod length is 300 mm

Fig.7 Cloud （a） and vector （b） plot of the velocity of silicon melt at 600 mm rod length

Fig.8 Crystal rod temperature gradient diagram under different heaters when the rod length is 600 mm

Fig.9 Oxygen content at different positions of crystal rod

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