Method for growing silicon-germanium heterostructures

FIELD: electricity.

SUBSTANCE: in method for growing of silicon-germanium heterostructures by method of molecular-beam epitaxy of specified structures due to silicon and germanium evaporation from separate crucible molecular sources on the basis of electronic-beam evaporators, silicon evaporation is done in automatic crucible mode from silicon melt in solid silicon shell, and germanium is evaporated from germanium melt in silicon insert, which represents a previously spent hollow residue, produced as a result of silicon evaporation in automatic crucible mode, and arranged in crucible cavity of cooled case of crucible unit of electron-beam evaporator used to develop molecular flow of germanium. At the same time process of epitaxy is controlled with account of germanium deposition speed selection, determined from given dependence.

EFFECT: increased stability and expansion of assortment of generated high-quality silicon-germanium heterostructures as a result of improved control of molecular-beam epitaxy of heterostructures due to accurate control of silicon and germanium deposition mode in the optimal range of speed values, reduction of concentration of uncontrolled admixtures in heterostructures produced by proposed method, and reduction of resource expenditures for preparation of process equipment.

2 cl, 3 dwg

 

The invention relates to the technology of epitaxial deposition of semiconductor materials on a substrate and can be used to ensure accountability and controllability of the process of vacuum deposition of silicon and germanium from separate electron beam evaporators in the implementation of molecular-beam epitaxy silicon-germanium heterostructures.

Epitaxy of silicon and germanium to form their heterostructures popular modern solid-state micro - and nano-electronics to create microwave devices, optoelectronic devices and circuits, which play an important role layered (and mixed) patterns of submicron size with different chemical composition, in particular on the basis of silicon and germanium (see, for example, U.S. patent No. 4861393, H01L 29/165, H01L 31/06, H01L 21/203, 1989, as well as a book in English. lang. Herman M.A., Sitter H. Molecular Beam Epitaxy Fundamentals and Current Status. Berlin, Springer, 1996, p.286-287, fig.5.32).

Thus the controllability of the deposition processes for forming these structures largely depends on the method of obtaining molecular beams of silicon and germanium.

So when used for evaporation Germany is known of the molecular source based on the Knudsen cell with a crucible of boron nitride, equipped with a heater (see U.S. patent No. 4550411, NV 3/02, 1985), number Zagra the developments made in the grown film structural elements of the source increases dramatically when driven by the requirements of an acceptable deposition rate of the temperature increase of the molecular source (see Belousova T.V. and Sadofyev YG Features of growing germanium on gallium arsenide by the MBE method. Electronics, 1990, No. 10, p.78).

The closest to the technical essence is similar, selected by the applicant as a prototype and represents a method of growing silicon-germanium heterostructures by molecular beam epitaxy of these structures due to the evaporation of silicon and germanium from separate molecular sources based on electron-beam evaporators (see patent EP No. 0276914 A2, SW 23/02, 1988).

However, the drawback of the prototype method is applicable for Germany the so-called mode autothermal evaporation, providing a stable evaporation material. To implement this mode requires that adjacent to the walls of the cooled crucible portion of the evaporated material was in the unfused condition that creates the temperature gradient necessary for a stable evaporation material without splashing (see this article Belousova T.V. and Sadofyev YG, P80). In the case of Germany due to low pressure when the tempo is the atur melting its own vapor to achieve an acceptable rate of deposition of the melt Germany to be heated considerably above the melting temperature. In the result, the entire volume of Germany in the crucible, including the walls of the crucible becomes liquid, and that makes for Germany autothermal mode.

This automically mode of evaporation sell by electron-beam evaporation of silicon, because the pressure of vaporized silicon at the melting point to two orders of magnitude higher than that of Germany at its melting point. The result is an acceptable deposition rate of silicon is achieved when the transition in the molten state, only the Central part of the material in the crucible.

Additional stabilization measures the rate of evaporation Germany, such as the introduction of the graphite insert between germanium and water-cooled metal crucible walls of the unit to reduce the temperature drop of Germany in the center and on the periphery of its melt (see this article Belousova T.V. and Sadofyev YG, P80), did not allow the deposition of Germany with the concentration of electrically active impurities in the formed structure is less than 1016cm-3.

The technical result of the claimed invention - improved stability and expansion of the range to form a high quality silicon-germanium heterostructures as a result of improved control of molecular beam epitaxy these heterostructures due to ensure the ing accurate control of the mode of deposition of silicon and germanium in the optimal interval of values of the velocities of successive and simultaneous deposition, the reduction of the concentration of uncontrolled impurities in the received offer by way heterostructures, as well as reduced resource costs for preparation of process equipment to achieve the specified result due to the proposed modernization of the crucible block electron-beam evaporator.

To achieve the stated technical result in the method of growing silicon-germanium heterostructures by molecular-beam epitaxy of these structures due to the evaporation of silicon and germanium from separate molecular sources based on electron-beam evaporators evaporation of silicon are in autothermal mode from the silicon melt in the solid silicon membrane and evaporation Germany - of germanium in the silicon melt the liner, which represents a previously developed hollow residue resulting from evaporation of silicon autothermal mode, and located in the crucible cavity cooled crucible body unit electron beam evaporator is used to create molecular flux Germany.

The process of epitaxial silicon-germanium heterostructures regulate with regard to choice of baseline for accountability of this process within the provision of high quality heterostructures deposition rate ger the project in accordance with the value

where νGethe deposition rate of the Ge;

rcp- the average radius of curvature of evaporated surface of an ingot of germanium in silicon liner;

R is the distance between the evaporable surface of the ingot of germanium in silicon liner and substrate grown silicon-germanium heterostructures.

When forming the silicon-germanium heterostructures under high vacuum installation molecular-beam epitaxy "BALZERS" UMS 500P at an operating voltage of electron beam evaporators 10 kV and the electron emission current up to 100 mA using a silicon liner having a wall thickness of 5-10 mm to create a temperature gradient between the melt Germany and cooled crucible body unit, which determines the conditions of stable evaporation Germany at the maximum growth rate of the mixed heterostructure of 0.2 nm/sec.

Figure 1 shows the General scheme of the high-vacuum installation molecular beam epitaxy for the implementation of the proposed method of growing silicon-germanium heterostructures; figure 2 - electron-beam evaporator for evaporating Germany as part of the installation of figure 1; figure 3 - x-ray spectrum obtained in accordance with the inventive method, the silicon-germanium heterostructures, confirming precise control of the deposition of silicon and germaniae the formation of the layers of the heterostructure with a given distribution of composition.

The inventive method of growing silicon-germanium heterostructures is carried out using high-vacuum installation molecular beam epitaxy.

For evaporation of silicon and germanium specified installation (see figure 1) equipped with electron beam evaporators 1 and 2 (electron beam evaporator 1 is designed for evaporation of Germany, an electron-beam evaporator 2 for evaporation of silicon), which consists of water-cooled copper crucible blocks 3 and 4.

In crucible cavity block 3 (see figure 2), designed for evaporation of Germany, is a silicon liner 5 in contact with its internal walls with GE 6, placed in turn in the specified liner. Silicon liner 5 is a previously developed hollow residue resulting from evaporation of silicon autothermal mode and uncovered after that of the cavity of the crucible unit 3 electron beam evaporator is used to create molecular flux Germany.

For molecular beam epitaxy of silicon-germanium heterostructures high vacuum installation with moveable flaps 7, allowing you to independently control the molecular beams of silicon and germanium, falling on the substrate 8.

Molecular beam epitaxy silicon-germanium hetero is ructur in vacuum is carried out by evaporation of silicon from the silicon melt in the solid silicon membrane in the crucible unit 4 in autothermal mode and evaporation from Germany germanium melt in a hollow solid silicon the liner 5 in the crucible block 3 (see figure 2) subject to the choice of the value of the deposition rate of Germany in accordance with the proposed applicant for plants of various types (derived from technical installations and patterns of molecular process of evaporation and precipitation) ratio (1) and their deposition at the open flaps 7 on the substrate 8 (see Fig 1).

In the example implementation of the proposed method was used to install "BALZERS" UMS 500P - production firm "Balzers (Liechtenstein).

When forming in the specified installation silicon-germanium heterostructures at an operating voltage of electron beam evaporators 10 kV and the electron emission current up to 100 mA evaporation Germany led from its melt in silicon liner having a wall thickness of 5-10 mm, the wall thickness of the silicon liner needed to create a temperature gradient between the cooled walls of the crucible unit and evaporated germanium for stable evaporation Germany at the rate of deposition (when the distance between the surface of the evaporated Germany and the substrate forming the heterostructure ~ 510 mm), not exceeding 0.1 nm/s

As starting materials for evaporation in electron beam evaporators served as monocrystalline silicon and germanium (with the average radius of curvature of evaporated surface the ingot ~15 mm) with acceptor type conductivity, and boron concentration ≤1·10 15cm-3.

The use of silicon liner is possible to eliminate splashing and dripping Germany during the evaporation of Germany from its melt in such a liner with a volume of its cavity ~3-4 cm3when the volume of the crucible cavity 7.5 cm3.

The result is the ability to lower the level of uncontrolled impurities in the generated structures in comparison with the known method using graphite inserts and greatly improve the stability and controllability of evaporation Germany in the process of their formation in comparison with the method of the prototype. This allowed to significantly improve the stability of the quality of the formed silicon-germanium heterostructures and to obtain structures with the given parameters of the composition and thicknesses of the layers.

3 shows the experimentally measured (curve a) and calculated (curve b) x-ray diffraction spectra from the grating with five periods (Si0.7Ge0.3d=3 nm) / Si d=20 nm), obtained in the vicinity of the peak of Si (004) from the substrate, confirming the good agreement between experimental and calculated spectra, which means that the values match, the composition and thickness of layers in a heterostructure formed with predetermined before growing.

Layer-by-layer analysis of a wide class of grown silicon-germanium heterostructures by means of secondary ion mass-spectra the Mat showed the concentration of impurities of oxygen and carbon in them is at the level of 1·1016÷5·1017cm17that corresponds to the content of these impurities in pure raw materials. The level of electrically active uncontrolled impurities is less than 1015cm-3.

In addition, is provided to reduce the resource costs of preparing installation to achieve a specified result in the identification of additional technology to increase the efficiency of the equipment (silicon liner - residue resulting from evaporation of silicon autothermal mode and uncovered after that of the cavity of the crucible block electron-beam evaporator used in the proposed method to generate molecular flux Germany).

1. The method of growing silicon-germanium heterostructures by molecular-beam epitaxy of these structures due to the evaporation of silicon and germanium from separate molecular sources based on electron-beam evaporators, characterized in that the evaporation of silicon are in autothermal mode from the silicon melt in the solid silicon membrane and evaporation Germany - of germanium in the silicon melt the liner, which represents a previously developed hollow remnant, education is avisa as a result of evaporation of silicon autothermal mode, and located in the crucible cavity cooled crucible body unit electron beam evaporator is used to create molecular flux Germany, the process of epitaxial silicon-germanium heterostructures regulate with regard to choice of baseline for accountability of this process within the provision of high quality heterostructures deposition rate of Germany in accordance with the ratio:

where νGethe deposition rate of the Ge;
rcf- the average radius of curvature of evaporated surface of an ingot of germanium in silicon liner;
R is the distance between the evaporable surface of the ingot of germanium in silicon liner and substrate grown silicon-germanium heterostructures.

2. The method according to claim 1, characterized in that when forming the silicon-germanium heterostructures under high vacuum installation molecular-beam epitaxy "BALZERS" UMS 500P at an operating voltage of electron beam evaporators 10 kV and the electron emission current up to 100 mA using a silicon liner having a wall thickness of 5-10 mm to create a temperature gradient between the melt Germany and cooled crucible body unit, which determines the conditions of stable evaporation Germany at the maximum growth rate of the mixed heterostructures is 0.2 nm/sec.



 

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