The method of obtaining bulk single crystals of silicon p-type

 

(57) Abstract:

The invention relates to the production of silicon Zener diodes and substrates for epitaxy. Summary of the invention in the melt of silicon containing an impurity of boron substitution in concentration 3,610-4- 8,110-2wt.%, introducing a second impurity substitution of aluminum in a concentration of 310-4- 310-2wt.% with respect to silicon. Growing lead by the Czochralski method. table 2.

The invention relates to metallurgical and electronic industries, and more specifically to the production of silicon Zener diodes and substrates for epitaxy.

A method of obtaining silicon with a degree of doping above the limit of solubility (U.S. Pat. Germany CL d 11/02, N 01 Z, N 12922258 stated 21. 09. 62, posted 28. 01. 71). According to their technical solution it is closest to the claimed and was adopted for the prototype. The method consists in growing single crystals from a melt containing two impurities, giving the silicon of one conductivity type. One of them is a mixture of substitution and the other implementation. In silicon doped with phosphorus or arsenic, administered lithium. The method does not give the possibility to obtain single crystals with perfect structure and uniform distribution is shirouma impurity introduction (lithium) will avtalegiro epitaxial or diffusion layers, formed on silicon.

The present invention is directed to solution of the problem, providing bulk single crystals of silicon p-type with a high uniformity of resistivity in volume, mechanical strength with high perfection of the crystalline structure and high thermal stability. This technical result is achieved by growing single crystals from melts containing impurity substitution of boron in concentrations 3,610-58,110-2wt. and the second impurity substitution of aluminum in concentrations 810-3- 310-2wt.

Significant difference between the proposed method of producing silicon single crystals is the simultaneous introduction into the melt of the two impurity substitution, which provides one conductivity type in the silicon (acceptors) in a strictly predetermined intervals of concentration: boron 3,610-48,110-2wt. and aluminium 810-3310-2wt. The introduction of boron and aluminum to the melt in the indicated concentrations allows to achieve the technical result: obtaining a silicon single crystal p-type with a uniform distribution of electrical resistivity in volume, with high mechanical strength and heat stability, and also with a perfect crystal structure compared to monocrystaline boron, the second acceptor aluminum increases its uniformity, suppresses convection currents due to compaction of the melt, which indicate the results of measuring the density of the melt. What if this changes the interatomic interactions in the melt determine the corresponding changes of the properties of the coexisting in the silicon single crystal and crystallization kinetics. The resulting crystals have a perfect structure and high thermal stability.

The choice of the lower limit of the concentration of aluminum is due to the fact that at smaller values of the positive effect is absent. At concentrations of aluminum, exceeding its upper limit, the crystals appear microinclusions, and perfection of the structure of single crystals rapidly deteriorating (see tab. 1). When the concentration of boron in the melt is less 3,610-5wt. the impact of the introduction of aluminum disappears. Grown from this melt the silicon single crystals have properties are the same as those doped with only one element. At concentrations of boron in excess of 8,110-2wt. the goal is not achieved, as the deteriorating quality of the crystalline structure in single crystals of a large number of grown single crystals of silicon, obtained by the proposed method, we measured the electrical resistivity by four-probe method at nine points on the ends (silicon monocrystalline ingots GOST 19658-81), rocking curves on a double-crystal spectrometer brand TRS, the lifetime of minority charge carriers () on the installation of the microwave relaxometry.

Example 1. Grew single crystals of silicon with a diameter of 60 ml by the Czochralski method at the facility, the Subject-10. The mixture in a quartz crucible contained: silicon raw weight of 4 kg, the ligature boron in amounts that corresponded to the concentration of boron in the charge 3,110-2wt. and produces single crystals with WES 310-3MSM 10% When calculating the distribution coefficient of boron was taken equal to 0.9. In addition, the mixture was injected aluminum brand 99,996% concentrations: 0,008, and 0,019 0,003 wt. The speed of extrusion and rotation of the single crystals were respectively 1.6 mm/min and 12 rpm rotation Speed of the crucible was about 4/min For each concentration of aluminum in the charge raised five single crystals. WES on single crystals was measured by four-probe method, and the variation of resistivity at the ends was calculated by the formula

< / BR>
where the index "Mac" refers to its maximum value, and min - minimum measured among the nine values at the end of a 5% Yield was determined in relation to the weight of the charge as the average of five single crystals. The measurement results of the average values of resistivity in five single crystals, as for the other properties, are presented in table. 1, Washers cut from a single crystal at a distance of 70 to 80 mm from the exit of its diameter, polished chemically. On the polished surface of the washer to installing TRS measured the width of the swing curves R and . The measurement results are presented in table. 1. All crystals were without dislocations. As can be seen from the table, the values of the half-width curves swing in heavily doped silicon of the same as the undoped reference silicon 3,4.

Example 2. Growing single crystals of silicon, dimension t, K, WES and determination of the yield of material was performed as in example 1. The boron concentration in the charge was, as in example 1, and the aluminium concentration of 0.005 and 0.035 wt. The average measured properties in five single crystals are presented in table. 1. The single crystals were without dislocations. For comparison, grew three single crystal doped only with boron (analog). On single crystals was carried out the same measurements as obtained by the proposed method (table. 1).

Example 3. Grew single crystals of silicon and measured their properties (in addition), as in examples 1,2; the Concentration of boron in the mixture was 610-4

Example 4. Grew single crystals of silicon and measured their properties (except t), as in examples 1,2. The boron concentration in the charge and the electrical resistivity in three grown single crystals of each of the aluminum concentration was as in example 3. The concentration of aluminium in two variants was as in example 2. The average values of the measured properties for the three single crystals are presented in table. 1. All crystals were dislocation.

Example 5. Grew single crystals of silicon and measured their properties as in examples 1, 2. The weight of the mixture was as in example 1. The concentration of boron, which was introduced, as in examples 1 to 4 in the form ligatures, was in all processes 310-5wt. ie had a fantastic value. Varied the concentration of aluminum in the charge (see tab. 1). It was five grown single crystals, each of which is pulled from the melt with different concentrations of aluminum. On each single crystal was measured properties as in example 1. Not measured only. The results of the measurements are presented in table. 1. WES along the length of the single crystals was 0,415% of All single crystals were dislocation.

-2wt. Varied the concentration of aluminum in the charge (see tab. 1). It was five grown single crystals from melts with different concentrations of aluminum. On each single crystal was measured properties as in example 1. WES along the length of the single crystals was 110-310% MSM. The measurement results are presented in table. 1. It was two grown single crystal from the melt with a concentration of boron 910-2wt. with the concentration of aluminum 0,019 and 0.005 wt. In both crystals in the etching revealed concentric rings with fine inclusions, and the values of R was 10". Concentrations of boron 910-2wt. are marginal to obtain single crystals with perfect structure. Therefore there was no reason to vary the concentration of aluminum, because the goal is not implemented.

Example 7. Growing silicon single crystals, the calculations ligatures, growing conditions, dimensions, and the aluminum concentration is varied, as in examples 1 and 2 (table. 2). The concentration of boron in the mixture was 610-5wt. WES in the obtained single crystals were changed to 0.25 MSM 10% Of single crystals cut samples with dimensions 2,52,5 cm and 3 mm thick Samples after etching in poly after annealing the samples was measured resistivity and mobility of charge carriers by the method of Vander-PAH. The results of the measurements are presented in table. 2.

Example 8. The silicon single crystals, grown as in examples 1 and 2 was cut into wafers and polished and then subjected to polishing by conventional technology ET 035.206 THAT. The yield of wafers (without cracks and chips) from single crystals, grown as in example 1 was 82 90% and in the case of single crystals, grown as in example 2, 65 to 75% On polished wafers was measured mechanical stress on the deflection plates. Their values in the wafer cut from the single crystals obtained in example 2 had an average of 6.95 MPa, and the plates of the single crystals obtained in example 1 - 2.5 MPa.

As can be seen from the tables and other results obtained in examples 1 to 8, the silicon single crystals grown from melts containing boron at a concentration of 3,6103wt. and aluminum in the specified concentration range, has the following predominant in comparison with the known methods:

1. increased uniformity in the distribution of electrical resistivity up to 3% in the transverse cross section of the single crystals and the yield at a given value of resistance;

2. increases thermal stability of silicon; its electrical parameters practically n u undoped silicon;

4. increases the mechanical strength of the wafer cut from the single crystals: the reduced marriage through fractures by 20% and reduced mechanical stress.

The method of obtaining bulk single crystals of silicon of p-type, which includes the cultivation of the melt containing two impurities of one conductivity type, characterized in that the melt containing the impurity substitution of boron in a concentration of 3,610-48,110-2wt. introducing a second impurity substitution of aluminum in a concentration of 310-3- 310-2wt. with respect to silicon.

 

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