CN1003380B - Nonlinear magnetic field single crystal silicon drawing method and device - Google Patents

Abstract

A method for pulling single crystal in magnetic field and single crystal furnace, the spiral tube of the single crystal furnace is divided into two groups with different inner diameters, the armature of the spiral tube is made into the shape of furnace wall, and at the same time, it is used as the furnace wall of the whole furnace body, and forms a totally enclosed structure with the upper and lower end covers of the furnace body and magnetic ring, the spiral tube is supported by the lifter, and can move up and down relative to the crucible, when pulling crystal, the crucible is located in the upper end or lower end of the magnetic field generated by the spiral tube and has a horn-shaped nonlinear area, so as to obtain the maximum inhibition effect to the heat convection of the molten silicon, the furnace wall of the totally enclosed structure also serves as armature, making it possible to obtain.

Description

Method and device for drawing monocrystalline silicon by nonlinear magnetic field

The present invention belongs to a method for drawing monocrystalline silicon in magnetic field and its equipment.

Silicon crystal used in the microelectronics industry has not changed significantly in its basic production process since its production technology was pioneered three decades ago. However, in recent years, rapid advances in microelectronic technology, as typified by integrated circuits, have placed increasing demands on silicon crystals used in the fabrication of integrated circuits and other semiconductor devices. Crystal growth technology has become a focus of research for industrial applications and has constituted one of the major pillars of the modern microelectronics industry.

In the growth of Silicon crystals by the Czochralski method, there is often thermal convection (see J. R. Corruther. Scmiconductor, Silicon, 1977, P61) which is either natural or forced. Natural convection makes it difficult to control the variation of the solidification rate (see AF · Witt, at al, J · electric · Soc, Vol122, No. 2) which results in an uneven distribution of the thickness of the diffusion boundary layer near the crystal-melt interface, these variations leading to periodic disorder of the crystal and micro and macro inhomogeneities, and non-uniformity of convection leading to temperature oscillations in the silicon melt, the oscillation amplitude increasing with increasing temperature gradient. These temperature changes are associated with the pitch of the fringes formed due to the non-uniformity of the impurity concentration distribution in the crystal, as shown in fig. 1. Local growth and melt-back are induced at the crystal-melt interface due to the presence of temperature instability. This growth, solidification and meltback phenomenon is related to the formation of micro-defects in the crystal, and fig. 2 shows the vortex striations generated by the micro-defects of the material when Si is produced. In particular, the concentration and distribution of interstitial oxygen in silicon is responsible for thermally induced defects such as stacking faults, dislocation loops and precipitates. Therefore, to improve the quality and yield of semiconductor devices, precise control of the concentration and distribution of oxygen is required.

The proper application of the magnetic field allows for effective monitoring of thermal convection and stabilization of oxygen concentration and distribution.

In 1953, Thompson theoretically analyzed the interaction between the conductive fluid and the magnetic field (see W. B. Thompson phil, Mag, Ser7, Vol42, NO 335 (1951)) concluded that the use of a magnetic field to increase the viscosity of the effective movement of the conductive melt allows for convenient control of the strength of free convection. According to lenz's law: when the conductor cuts the magnetic force line to move, an induced current is generated in the conductor, and the magnetic field of the induced current resists the movement of the conductor. The same principle can be applied to the convective motion of the silicon melt in the magnetic field.

The magnetic field can change the convection action of silicon melt, and indirectly control the melting rate and the transport at the interface of quartz, and2 x 10 can be obtained by using a magnetic field single crystal furnace¹⁷Per centimeter³The crystal with low oxygen concentration can eliminate the phenomena related to vortex defect, fault, oxide precipitation and generation of thermal donor, thereby obviously improving the homogeneity of the material (see Baomuo, published Patent application (A) Sho 58-190891 (1983), Yize Youxing, published Patent application (A) Sho 56-104791 (1981), T, Suzuki, at al, UK Patent, application GB 21029267A (1983) and2059932 (A))

The number of the drawings is 11 in total. FIG. 1 shows impurity streaks in a Czochralski silicon single crystal. Fig. 2 shows a vortex pattern generated by micro defects in a material when Si is manufactured. FIG. 3 shows the relationship between the oxygen content in the silicon wafer and the magnetic field strength. FIG. 4 shows the improvement in the uniformity of a silicon single crystal after application of a magnetic field. FIG. 5 is a schematic diagram of a transverse magnetic field single crystal furnace composed of hollow saddle-shaped coils, in which 1 is a furnace body, 2 is an electromagnet, and 3 is a DC power source. FIG. 6 is a schematic diagram of a transverse magnetic field single crystal furnace composed of an iron core and an armature, wherein 1 is an Ar inlet, 2 is a silicon single crystal 3 which is a heat preservation cover, 4 is a magnetic pole, and 5 is molten silicon.

FIG. 7 is a schematic diagram of a vertical magnetic field single crystal furnace composed of two groups of fixed hollow coils, wherein 1 is a furnace body, 2 is a coil, and 3 is a direct current power source.

FIG. 8 is a schematic view of a vertical magnetic field single crystal furnace composed of a set of fixed hollow spiral tubes, in which 1 is a crystal, 2 is a spiral tube, 3 is a heater, 4 is a crucible, and 5 is molten silicon.

FIG. 9 is a schematic view showing thermal convection of molten silicon in the crucible.

FIG. 10 is a schematic view of a method for pulling single crystal silicon in a non-linear magnetic field, wherein 1 is silicon melt, 2 is a crucible, 3 is magnetic lines of force, 4 is an ingot, 5 is a crucible at the upper end of the magnetic field, and 6 is a crucible at the lower end of the magnetic field.

Fig. 11 is a schematic diagram of a spiral tube position-adjustable magnetic field single crystal furnace with a fully-closed outer wall, in the diagram, 1 and2 are hydraulic drivers, 3 is a magnetic ring, 4 and 5 are spiral tubes, 6 is a cooler, 7 is a cooling water outlet, 8 is a cooling water inlet, 9, 10 and 11 are observation ports for different purposes, 12 is a heat preservation cover, 13 is a heating body, 14 is a crucible support, 15 is silicon melt, 16 is a crucible, 17 is an inner furnace wall, 18 is a furnace body upper end cover, 19 is a furnace body lower end cover, and20 is an armature.

FIG. 3 is a graph showing the change in oxygen content in a CZ silicon single crystal pulled by a transverse magnetic field. FIG. 4 is one example of a microstructure in which uniformity is improved in a Silicon single crystal after application of a magnetic field (see T. Suzuki, at al, Semiconductor Silicon (1981)) from which it can be seen that the oxygen content in the single crystal after application of a magnetic field tends to be stable and the uniformity of the material is improved.

Currently, when a magnetic field is used for pulling a CZ silicon single crystal, two methods are mainly adopted, one method is to use a transverse magnetic field, and as shown in fig. 5 and 6, schematic diagrams of a transverse magnetic field single crystal furnace are shown, but the influence of the transverse magnetic field on a heating body is serious. Another way is to use a vertical magnetic field to pull a CZ silicon single crystal, using equipment such as that shown in FIGS. 7 and 8 (see Georg Fiegl, Solid State Teohnoiogy, Vol. 26, No.8 (1983) P.121, and Keigo Hoshikava Jap J. appl. Phys., VOL.21, 9, L545-547 (1982) or Interpretet: Zhang Jun's translation, J. Semicondum, 1983, 5, P52). The vertical magnetic field single crystal furnace solves the influence of a transverse magnetic field on a heating body, but the control capability of the vertical magnetic field single crystal furnace on temperature fluctuation is weakened. This is because the vertical magnetic field has a larger suppression effect on convection in section a of fig. 9 than in section B, and in addition, such vertical magnetic fields are formed by air-core coils without iron cores and armatures, so that a large power source (generally 60-7 QKW) is required to generate sufficient magnetic field strength, resulting in large energy consumption.

In order to overcome the defects of a transverse magnetic field single crystal furnace and a vertical magnetic field single crystal furnace, the invention uses the nonlinear region of the magnetic field generated by the spiral tube to draw the single crystal silicon so as to obtain the effect of inhibiting the thermal convection of the silicon melt as much as possible by the magnetic field, and simultaneously designs the single crystal furnace realized by using the method.

The gist of the present invention resides in that a magnetic field is generated by a group of spiral pipes having different inner diameters, and magnetic lines of force at the upper end and the lower end of the magnetic field have a flare shape which is flared outward, respectively, as shown in fig. 10. When the single crystal is pulled, the relative position of the spiral tube and the crucible is adjusted to enable the crucible to be in a bell-mouthed nonlinear area at the upper end or the lower end of the magnetic field. In this region, the direction of the magnetic force lines is nearly orthogonal to the movement locus of the thermal convection of the molten silicon, so that the effect of suppressing the thermal convection of the molten silicon as much as possible can be obtained.

In order to realize the method, the invention designs a spiral tube position-adjustable magnetic field single crystal furnace with a totally-enclosed outer wall, which comprises three hydraulic drivers, a magnetic ring, a spiral tube armature, upper and lower end covers of a furnace body, a crucible, a heat preservation cover, a heating body, a crucible support and the like, wherein the number of the spiral tubes is 11, the upper end group 5 has a larger inner diameter of 380 mm, the lower end group 6 has a smaller inner diameter of 350 mm, the 11 groups of spiral tubes are separated by a water cooler, the spiral tube group is carried by the magnetic ring, the magnetic ring is supported by the three synchronous hydraulic drivers, and the relative position of the spiral tube group and the crucible can be adjusted by the hydraulic drivers during crystal pulling, so that the crucible is positioned in a nonlinear area of a magnetic field generated by the spiral tubes, and the thermal convection of silicon melt is effectively inhibited. The single crystal furnace is characterized in that the armature serving as a spiral tube is made into the shape of a furnace wall, and simultaneously serves as an outer furnace wall of the whole furnace body, the upper end cover and the lower end cover of the furnace body are also made of ferromagnetic materials and form a closed magnetic loop together with the furnace wall and a magnetic ring so as to increase the magnetic field intensity and reduce the leakage flux to the maximum extent, and three observation holes are arranged at the upper end of the furnace body so as to facilitate the observation operation and the control of the equal-diameter growth process during seeding and shouldering. Meanwhile, the observation hole 9 is a furnace door for loading raw materials and loading and unloading equipment in the furnace, such as a heating body heat preservation system and the like, so that the operation is convenient.

As the spiral pipe is added with the armature and the furnace body is made into a totally-enclosed structure, the magnetic field of 1500-2000 Gauss can be generated only by using a 10KW direct current power source. The invention selects the optimum condition of crystal pulling by adjusting the relative position of the spiral tube and the crucible, thereby better controlling the introduction of oxygen into the single crystal and reducing the temperature fluctuation caused by heat convection in the pulling process. Conditions are created for the production of silicon crystals of higher integrity. Meanwhile, due to the reasonable design of the furnace body structure, energy can be greatly saved, and the production cost is reduced, so that great economic benefits are obtained.

Claims (2)

1. A method for pulling single crystal Si in a nonlinear magnetic field, characterized in that the nonlinear magnetic field is formed by superimposing the magnetic fields generated by two groups of spiral tube groups with different diameters, the two spiral tube groups are supported by a lifting system, and when pulling the crystal in this magnetic field, a crucible containing molten silicon is placed in the spiral tube group, and the lifting system is adjusted to make the spiral tube group move relative to the crucible, so that the crucible is respectively placed in the linear region and the nonlinear region of the superimposed magnetic field, and the adjustment procedure should ensure that the direction of the magnetic lines of force and the motion trajectory of the molten silicon thermal convection are always close to orthogonal. 2. A single crystal furnace for implementing the method of claim 1, comprising a lifting system magnetic ring, a spiral tube group, a cooler, a heat-insulating cover, a heating element, a crucible support, a crucible, an inner furnace wall, upper and lower end covers, and an armature, characterized in that the spiral tube group (4) and the spiral tube group (5) have different inner diameters, each spiral group is composed of separate windings, and the windings are separated by a cooler (6), the armature (20) is formed into the shape of a furnace wall, and the spiral tube groups (4, 5) are covered therein, the armature (20) and the upper and lower end covers (18, 19) and the magnetic ring (3) form a closed magnetic circuit, the armature (20) is provided with an observation hole (11), and the inner furnace wall (17) is provided with observation holes (9, 10).

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