A method of obtaining a uniformly doped silicon single crystals

 

(57) Abstract:

The invention relates to growing silicon single crystals by the Czochralski method with their subsequent use in the manufacture of semiconductor devices, in particular powerful and power transistors, power diodes, thyristors, etc. and allows to increase the output into useful products for growing monocrystalline silicon, and in the manufacture of semiconductor devices on the basis of such silicon. This is achieved by the fact that when growing the single crystal is conducted partial doping of silicon with phosphorus, and colagiovanni to the specified level of electrical resistivity (electrical resistivity) is carried thermodore by annealing silicon or 350 - 500oWith combining or combining it with temperature treatments containing these temperatures in the cycle of manufacture of the device, and the content and distribution of donors caused by doping phosphorus, as well as the content and distribution of termodonte chosen so that the total concentration of donors at each point of the single crystal silicon in the finished devices meet the specified level of resistivity. 5 Il.

The invention relates to a semiconductor metallurg ingots with their further use in the manufacture of semiconductor devices, in particular, the powerful and power transistors, power diodes and thyristors, etc.

Closest to ispitaniy is a method, in accordance with which the single crystal silicon grown by the Czochralski method, the doped donor impurity is carried out by introducing into the crucible with the molten silicon specified number fosforsoderzhashchie ligatures and annealed at 350 500oC.

The disadvantage of this method is the low yield in the annual production of the final design of single crystals by WES due to inhomogeneous (increase in concentration from the top to bottom end) of the distribution of phosphorus along the length of the crystal. This is due to significant deviation from unity of the ratio distribution of phosphorus in silicon.

The task of the invention is the selection conditions doping of silicon with phosphorus when grown by the Czochralski and conditions of use of such silicon in the manufacture of semiconductor devices so that the magnitude of the electrical resistivity in the fabricated semiconductor structures for all points of the crystal length and the cross section correspond to the specified denomination WES.

This is achieved by a method of doping silicon single crystal grown by the method of COHR is ultimate, including doping of phosphorus in the process of growing a single crystal from the concentration of donors increasing from the upper to the lower end face of the ingot, when growing the single crystal is conducted partial doping of silicon with phosphorus, and colagiovanni to the specified level WES carry thermodore by annealing the silicon at 350 500oWith combining or combining it with temperature treatments containing these temperatures in the cycle of manufacture of the device, and the content and distribution of donors caused by doping phosphorus (Np), as well as the content and distribution of termodonte (NTrchosen so that the total concentration of donors (NDin each point of the single crystal silicon in the finished semiconductor devices meet the specified level of resistivity.

Given the concentration and distribution of termodonte along the length of the crystal provide for adequate concentration of oxygen (No) and the distribution profile of oxygen in the cultivation of oxygen, as well as the choice of the duration of annealing (t) at 350 500oWith silicon wafers in the manufacture of a semiconductor device, since, as we know from the "model of the Kaiser" generated in the silicon termedia education termodonte.

In turn, the desired profile of the distribution of oxygen, decreasing from the upper to the lower face of the crystal, implement the use of appropriate magnitudes and directions of rotation of the crystal (kr) and the crucible (t).

Given the concentration of donors, due to the doping of phosphorus is achieved by using the necessary amount of fosforsoderzhashchie ligatures in the molten silicon, and the distribution of N along the length of the crystal (the increase in the concentration from the top to bottom end) the distribution coefficient of phosphorus in silicon ( 0,35) and application programs to change the speed of growing.

Example 1. For use in the production of power transistor with a breakdown voltage 1500 V (specified nominal KES 90 Ohms.cm) was grown dislocation single crystal silicon orientation III, with a diameter of 80 mm and a length of 700 mm in the "Subject-30" duct argon. For doping with phosphorus in the melt of polycrystalline silicon was placed phosphate ligature in the form of pieces of silicon doped with phosphorus to 0,0218 Ohms.cm. The speed of growing of the single crystal was changed from 1.0 mm/min 0.5 mm/min

The rotation frequency of the crystal remains constant and equal to 20 rpm, and the world Cup a pressure of 10 mm RT.article.

Electrical resistivity grown in such conditions monocrystal, rex.decreased from 250 Ohms.cm at the top to 105 Ohms.see at the bottom, which corresponded to the increase in the concentration of donors, caused by doping phosphorus, Np, from 1,51013cm-3to 3,31013cm-1(Fig. 1 and 2).

The oxygen concentration in the single crystal, measured by the IR absorption at the wavelength of 9.1 µm TO 2,451017c-2decreased from the top to bottom end from 7,61017cm-3to 5,51017cm-3(Fig. 1).

Next, the silicon wafer produced from this single crystal were used in the production of power transistor ANDKBsamples.1500 C. the total duration of stay plates in the temperature range of 350 500oWith the creation process of the transistor was 30 min (burn-AI, burn Nickel, soldering).

Concentration generated during this time of termodonte in the silicon wafers at the level indicated above, the oxygen content decreased from the upper to the lower section of the single crystal from the 313cm-3to 0,91013cm-3(Fig. 2). Thus, the total concentration of donor impurity caused legirovanie corresponded to the values of resistivity in the finished transistor structures 85 93 Ohm cm (Fig. 1). The relative deviation of the resistivity of the nominal value, the radial and axial variation of the resistivity along the length of the single crystal did not exceed 10%

Measured next breakdown voltage, ANDKBsamples.made from the single crystal transistor structures were in a fairly narrow range of values 1900oC 2100 C. other parameters of the transistors did not differ from commercially available products.

An example of the prototype. In the "Subject-30" (from example 1) was grown on the silicon single crystal with a diameter of 80 mm and a length of 600 mm in accordance with the prototype. In this case, the doping of the silicon donor impurity at a nominal resistivity of 90 Ohms. cm was only the phosphorus using fosforsoderzhashchie ligatures placed in a melt of polycrystalline silicon. Frequency of rotation of the crystal and crucible remained constant during the whole growth process and was, respectively, 15 and 5 rpm Speed of the single crystal growth was changed from 1.5 mm/min 0.5 mm/min for the sample program. Other growing conditions were similar to those described above. Data analysis the electrophysical parameters of this crystal is shown in Fig. 3.

The magnitude of the electrical resistivity is grown on the proto Ohms.cm) when cutting the crystal at WES entered only 270 mm, i.e. less than half of the total length of the crystal, which has significantly reduced the yield of products in comparison with the proposed solution.

The concentration of oxygen transferred to the fabrication of transistors part of the crystal was changed in range (6 to 8) 1017cm-3(Fig. 3).

In the process of manufacturing of the power transistor values of resistivity in the silicon wafers due to the generation of termodonte in the temperature range 350oC 500oWith decreased to values of the 37oC 48 Ohm cm (Fig. 3). This circumstance made it impossible to obtain the desired breakdown voltage transistors, ANDKBsamples.The range of values ANDKBsamples.that was 1000 1200 V, which is considerably lower than required for this class of devices.

Example 2. For use in the production of power diode (the specified denomination WES in the finished diode structure 50 Ω cm) was expressed dislocation single crystal silicon orientation with a diameter of 80 mm and a length of 500 mm in the "Subject-30". Growing conditions and methods of doping were similar to those described in example 1 with the exception of the initial doping with phosphorus, which was 2.5 1013cm-3in the upper part of the crystal and 6.0 1013see17cm-3to 5.2 1017cm-3(Fig. 4).

Silicon wafer, made of the grown single crystal, in the process of creating diode were subjected to a controlled heat treatment at T 350 - 500oC for 40 min at the stage of fusing and spraying. The concentration of termodonte generated in silicon under these conditions, was 5.3 1013cm-3in the upper part and 1.9 1013cm-3in the lower part of the single crystal (Fig. 5). Total concentration of termodonte generated in the process of creating diode, and donors caused by doping phosphorus in the process of growing the crystal was (7,8 7,9) 1013cm-3along the length of the crystal, which led to extremely high axial uniformity of the resistivity 48 50 Ohm cm (Fig. 4).

The breakdown voltages of the diodes were in the range 1900 to 2000, i.e. in a fairly narrow range and is fully consistent with this class of diodes.

Thus, the proposed method can significantly improve the output into useful products with the release of monocrystalline silicon as the final design by WES, there is no need tenderloin fit on the WES side of the crystal, and all without is grown on the proposed method, the silicon is considerably cheaper than the previously used materials.

In addition, the proposed solution allows to increase the yield and manufacturing devices on the basis of such silicon. Inherent in the silicon grown on Choralschola, the lack of high oxygen content in the solution plays a positive role: optimized level and the distribution profile of the oxygen used for the controlled introduction of additional impurities electronic conductivity type of termodonte in the process of creating semiconductor devices, which ensures the production of a given denomination and high axial uniformity of the distribution of resistivity.

In this regard, grown on the proposed method of silicon single crystals can be fabricated devices with high breakdown voltages, located in a fairly narrow range of values.

In addition, in the proposed method, when grown on Choralschola no inherent method, floating zone melting restrictions on the diameter of the grown crystal, and peculiar method of radiation doping environmental challenges (risk of radiation exposure).

A method of obtaining a uniformly doped silicon single crystal grown by the method Correctronic type conductivity, including doping of phosphorus in the process of growing a single crystal from the concentration of donors, increasing from the upper to the lower end face of the ingot, and subsequent heat treatment at 350 to 500oWith the formation of termodonte, characterized in that at the stage of growth of the single crystal is conducted controlled doping of silicon with oxygen concentration decreasing from the upper to the lower end of the ingot, doping of phosphorus perform partial and colagiovanni to the specified level of electrical resistivity carry thermodore, mixing or combining the above with the final heat treatment temperature treatments at the stage of manufacturing semiconductor devices.

 

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