DE2240301A1 - PROCESS FOR MANUFACTURING SEMICONDUCTOR SINGLE CRYSTAL BARS WITH SPECIFIC RESISTANCE DROPPING DOWN TO THE CENTER OF THE BAR - Google Patents

Description

72/1143

Process for the production of semiconductor single crystal rods with a specific resistance decreasing towards the center of the rod _

The present invention relates to a method of manufacture of semiconductor single crystal rods with a specific resistance decreasing towards the center of the rod due to crucible-free zones melt a semiconductor rod held vertically at its ends with an inductive heating device which surrounds the rod in the shape of a ring and generates the Sehajelzzone starting from a seed crystal, the melting zone in the direction of the rod axis of a supply rod part from below is moved above through the semiconductor crystal rod.

It is known to melt single crystal rods by means of crucible-free zone melting by using seed crystals to produce polycrystalline semiconductor rods, in particular silicon rods, be converted into single crystals by creating a melting zone from the end at which the seed crystal is attached is to the other end of the semiconductor rod (supply rod part) lets wander. The semiconductor rod is usually clamped in two holders in a vertical position, at least the a holder in rotation around during zone melting the rod axis is offset so that a symmetrical growth of the solidifying material is guaranteed.

In general, it is desirable to _{produce single crystal rods} for the production of semiconductor components which have very equal values with regard to their radial resistance curve, i.e. h »in the production of these Kriatallatab I strive for a very good mixture of durums of the thrown during the crucible-free zone melting? * so

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the dopant distribution as homogeneously as possible over the Cross section of the silicon crystal rod takes place.

For the production of semiconductor material for manufacturing of special semiconductor components, e.g. B. of overhead ignitable thyristors, a semiconductor base material is used, which consists of silicon crystal wafers, which in in the middle of the crystal disc show a targeted drop in the electrical specific resistance (P). For other power components it is z. B. advantageous, with a homogeneous λ-course in the center of the disc a targeted To have edge increase in resistivity.

Figures 1 and 2 of the drawing show resistance profiles as they are used for overhead ignitable thyristors (Fig. 1) and for high-power diodes (Fig. 2). The specific electrical Y / ideratand G in ohm * cm is plotted as the ordinate and the radius of the crystal disk is plotted as the abscissa. The dashed line running parallel to the ordinate is intended to indicate the center of the pane. The object of the present invention is to generate the resistance profiles shown in FIGS. 1 and 2 by means of crucible-free zone melting in semiconductor single crystal rods, in particular in silicon single crystals.

According to the method according to the invention, this object is achieved in that in the case of concentric or nearly concentric Pulling the single crystal rod at below the Schraelzzone lying seed crystal the formation of the in the lütte the melt compared to the edge areas of the melt occurring cooler area by turning the Seed crystal and / or by cooling the above the skin zone arranged supply rod part is supported. The flow in the melt is influenced in such a way that in the In the middle of the growing interface of the crystal an increased

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Dopant concentration occurs.

These relationships can be seen from FIG. 3 contained in the drawing. In this 1 represents the from polycrystalline silicon "existing stock rod part, 2 the single crystal rod which crystallizes on the seed crystal (not shown in the drawing) and 3 the melting zone located between the "two rod parts, which is produced by the flat coil 4 The dashed line 10 located in the melting zone 3 shows the course of the dopant without Influence of the flow, while the solid line 11 in the melting zone shows the dopant distribution reflects which. is received> when the training of the in the middle of the melting zone 3 compared to the edge areas the cooler area occurring in the melting zone is supported. This can be done, for example, by that either the seed crystal and thus the single crystal rod 2 to be produced is rotated very quickly or, and also at the same time the supply rod part 1 above the melting zone 3 by means of a rod part 1 enclosing the rod part 1 with ' Water-filled cooling coil 5 is cooled. The direction of single crystal growth is indicated by arrow 6; the rotary arrow 7 indicates that the seed crystal or the single crystal rod part 2 is set in rotation about its axis will. The arrows 8 drawn in the area of the melting zone .3 show the course of the natural convection flow at. ·

It is within the scope of the invention that the speed of rotation of the seed crystal or of the recrystallized rod part 2 is set as a function of the diameter of the single crystal to be produced. For example, for a rod diameter of 20 mm a rotation speed of 100 rpm., for a diameter of 25 ra a rotation speed

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speed of 60 rpm, for 35 mm 0 a rotation speed of 30 rpm. and a rotating speed of 15 rpm for a single crystal rod with a diameter of 40 mm. set.

According to a particularly favorable embodiment according to the teaching of the invention, the distance between the cooling coil is from the melting zone a maximum of 10 mm.

The method according to the teaching of the invention can be used when the semiconductor single crystal is drawn concentrically or almost concentrically and the axis offset of the rod axes is set to be less than 10 ^c ß> the diameter of the semiconductor single crystal rod to be produced.

With the method according to the teaching of the invention can with a silicon single crystal rod with a! Specific V / resistance of 60 to 70 Ohm. cm a P drop in the center of the bar of 20 ^c /> can be expected.

The method can be used for crystal rods with any Orientation. This is important because so far Crystal rods with a (, ^ - incursion ir. Otabraitte only by means of (111) -oriented single crystals in which facet formations expected, was possible.

Finished single crystal rods with locally limited strong fluctuations in resistance (line 3. by ο - spikes or striation ") can be made usable for thyristors that can be ignited overhead if, in a further development of the inventive concept, they are as close as possible to the melting point of the semiconductor material in a protective gas atmosphere or be terapert in air. A heat treatment in a range from 1300 to 1400 ⁰ C in the period from five hours a Siliciuna-ear this is sufficient for Siliciumeinkristallstäbe. A

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broad drop in resistance in the center of the bar is retained; a narrowly limited drop in resistance is leveled,

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Claims (1)

Claims 1. Method of manufacturing semiconductor single crystal rods with the specific resistance decreasing towards the center of the rod due to the crucible-free zone melting of a perpendicular its ends held semiconductor rod with a ring surrounding the rod, generating the melting zone inductive heating device in which, starting from a seed crystal, the melting zone in the direction of the rod axis a supply rod part is moved from bottom to top through the semiconductor crystal rod, thereby characterized that with concentric or nearly concentric ZJaien the single crystal rod in the case of the seed crystal lying below the Schraelzzone the * Formation of the cooler surface that occurs in the middle of the melt compared to the hand areas of the melt zone Area by rapidly rotating the seed crystal and / or by cooling the one above the Schraelzzone Stock rod part is supported. 2. The method of claim 1, marked thereby, for calibration et η, that the rotational speed of the Keirc-krictal ~ U? is set depending on the diameter of the single crystal rod to be produced 5. The method according to claim 1 and 2, characterized in that that in the manufacture of single-crystal rods with diameters of 25 mn a speed of rotation of the seed crystal of at least 60 rpm. is set. 4. The method according to claim 1 and 2, characterized in that that for the production of single crystal rods with diameters of 20 min a turning & e- YIVv 9/110/2 057c "- 7 - ■ 409809/1050 BATH ORIGINAL speed of 100 rpm. and a speed of rotation for bars with diameters greater than 35 m of a maximum of 30 rpm. is set. 5. The method according to claim 1 to 4, characterized in that the cooling of the The supply rod part is carried out by means of a cooling coil which surrounds the rod and is filled with water, 6. The method according to claim V to 5 »characterized in that the distance of the The cooling coil is adjusted from the melting zone so that it is a maximum of 10 mm. 7. The method according to claim 1'bi's "6, characterized in that during kon.zentr-isch.en pulling the axis offset of the rod axes is set to be less than 10 ^c / o of the diameter of the semiconductor crystal rod to be produced. 8. The method according to claim 1 to 7, characterized marked da3 following the Zonensehraelzprocess of the semiconductor single crystal rod of a tempering as close as possible to the melting point of the semiconductor material is subjected. 9. The method according to claim 8, characterized in that 'the tempering, in a protective gas atmosphere or air is made. 10. The method according to claim c u; ia ^, characterized characterized that the teraper time on is employed for at least five hours. 11. The method according to claim 8 to 10, d ad ur c h characterized 'that for production of a Siiiciuia single crystal rod with sloping towards the center of the rod specific resistance the tempering 1300 to 1400 ° G is carried out in a silicon tube, VPA 9/110 / 2057C 4 0 9 8 0 971050 ORKSINAL BATHROOM