RU2482228C1 - Method for production of indium ammonide large-size monocrystals - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: for production of coarse-grain indium ammonide monocrystals oriented in the crystallographic direction [100] one performs synthesis and production of a polycrystal coarse-grain ingot by way of a combined process according to the Czochralski method with addition of an amount of stibium in excess of the stoichiometric 3.0-3.5 at %; then one performs monocrystal growth (equally according to the Czochralski method) using a seed crystal oriented in a crystallographic direction [100], the axial temperature gradients maintained as equal to 35-40 grad/cm.

EFFECT: invention enables improvement of crystals structure with simultaneous increase of their diameter up to 70,2 mm, increase of mountain plates yield during ingot cutting due to the growth direction, reduction of the process material intensity due to reduction of the share of non-stoichiometric material and reduction of energy and labour costs due to usage of a combined process of polycrystal ingot synthesis, cleaning and growing.

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Description

The invention relates to the field of obtaining semiconductor materials, namely to the production of indium antimonide single crystals, which are widely used in various photodetectors operating in the infrared region of the spectrum.

A general trend in the development of technologies for manufacturing devices based on indium antimonide is the transition to a matrix version with a continuously increasing number of elements (more than 10 ⁶ ). As a result, there is a need to increase the diameter of the single crystals used while maintaining stringent requirements for the perfection of the structure. As a rule, when creating matrix photodetectors, indium antimonide plates with a working orientation (100) are used as the element base.

The technical problem solved by this invention is the creation of energy and resource-saving technology for producing dislocation large-sized indium antimonide single crystals grown in the crystallographic direction [100].

Traditionally, indium antimonide single crystals were grown in the crystallographic directions [211] and [111], the stability of single crystal growth in which is achieved with axial temperature gradients at the crystallization front of ~ 10-15 deg / cm. The production of indium antimonide single crystals in the crystallographic direction [100] using these gradients for a long time was considered practically impossible due to the extremely low twin energy characteristic of single crystal growth in this crystallographic direction [see M.G. Milvidsky, V. B. Oswensky. Structural defects in single crystals of semiconductors. M., Metallurgy, 1984, 255 pp.].

A known method of producing bulk single crystals of semiconductor compounds, in particular gallium arsenide, horizontal directional crystallization. The advantage of this method is the possibility of combining the cleaning process of a semiconductor with the subsequent growth of a single crystal. The application of this method in the technology of decaying semiconductor compounds allows you to combine three operations at once in one technological cycle: synthesis, purification of the synthesized material and growing a single crystal. In addition, the ability to control the composition of the crystallized melt by creating above it the required pressure of the volatile component allows to obtain single crystals of stoichiometric composition or with any desired deviation from it [see Nashelsky A.Ya. Technology of special materials for electronic equipment. M .: Metallurgy, 1993. - 365 p.].

The disadvantage of this method is that to obtain indium antimonide single crystals in the crystallographic direction [100], small temperature gradients (less than 10 deg / cm), typical for horizontal directional crystallization, are clearly insufficient and do not allow to grow a single crystal without twins.

In addition, since the growth by horizontal directional crystallization is carried out in boats, the resulting single crystals have a semicircular section, which is very undesirable when using the material as a substrate.

A known method of producing single crystals of indium antimonide by extrusion from a melt, in which a high-purity InSb crystal and an element of the compound of group A ^III B ^V are used as starting materials, which is an impurity that is electrically neutral for indium antimonide. The load is placed in a quartz crucible and installed in the furnace, the seed crystal is fixed in the seed holder and also placed in the furnace. The furnace is evacuated and filled with a gas mixture consisting of 90% nitrogen and 10% hydrogen. The initial indium antimonide is heated to its melting point (525 ° C), the seed crystal is brought to the melt, after which the melt temperature is raised to 550 ° C. With the continuous rotation of the seed crystal, the seeds are etched and the single crystal begins to grow, forming the conical part of the single crystal, maintaining a growth angle of ≤20 deg. Upon reaching the required diameter, a cylindrical part of the grown single crystal is formed [see Japanese application No. 8319197, IPC С30В 15/00, publ. December 3, 1996].

The disadvantage of this method is the high melt temperature at which a single crystal is grown. Despite the fact that the elasticity of Sb vapor over the indium antimonide melt at the melting point is ~ (3-5) · 10 ^-2 mm Hg, since the process of growing a single crystal is carried out over a long period of time ~ 8-10 hours, evaporation of Sb from the melt is very significant, which leads to a violation of the stoichiometry of the melt. The consequence of this is inevitably a failure of single crystal growth and a decrease in the yield of single crystals.

In addition, the angle of expansion of the cone of the obtained single crystal of ~ 20 deg indicates that the growth is carried out in the crystallographic direction [211] and [111], which are not competitive in the direction [100].

In addition, the described production method involves the growth of a single crystal from a load of ~ 700 g, which is insufficient for growing large-sized single crystals with a diameter of ~ 65 mm.

A known method of producing single crystals of indium antimonide in a three-stage process, in which at the first stage the synthesis is carried out by direct fusion of the starting components In and Sb (purity 6N) in a quartz ampoule, in an atmosphere of high-purity hydrogen. After synthesis, the compound is sometimes subjected to vacuum heat treatment to remove volatile acceptors (Zn, Cd) that are difficult to remove by zone melting. In the second stage, indium antimonide purified from volatile impurities is loaded into specially treated quartz boats and zone melting is carried out in an atmosphere of purified hydrogen. After 20-40 passes of the molten zone, the yield of the purified compound is about 60% of the length of the ingot. It is possible to carry out synthesis and purification in one technological cycle using special equipment. In the third stage, zone-purified indium antimonide with controlled parameters is loaded into a vacuum growth apparatus and the process of growing a single crystal by seed using the Czochralski method is carried out. In this case, the growth of single crystals is carried out in the crystallographic direction [211], in which the stable growth of single crystals is most easily realized [see book edited by member of the correspondent. USSR Academy of Sciences B. A. Sakharov “Metallurgy and technology of semiconductor materials”, Moscow, Metallurgy, 1972, pp. 427-432]. This method of obtaining adopted as a prototype.

The disadvantage of this method is the high material consumption, energy intensity and the complexity of the process. In addition, as already mentioned, to create photodetectors, substrates with a working orientation of (100) are used, which is relative to the direction of growing a single crystal [211] at an angle of ~ 35 degrees, which leads to large losses of material during cutting of the ingot and subsequent calibration of the plates.

The technical result of the invention is:

- obtaining single crystals in the crystallographic direction [100], which reduces material loss during cutting of the ingot and subsequent calibration of the plates;

- a decrease in the dislocation density in large-sized single crystals of indium antimonide, as a factor determining the parameters of photodetectors created on its basis;

- reduction of energy, material and labor costs.

The technical result is achieved by the fact that in the method for producing indium antimonide single crystals, including synthesis, obtaining polycrystalline indium antimonide and growing a single crystal by the Czochralski method, according to the invention, the synthesis and preparation of a polycrystalline ingot is carried out in a combined process according to the Czochralski method with the addition of excess antimony over stoichiometric 3.0 3.5 at.%, After which the single crystal is also grown by the Czochralski method using a seed crystal, oriented in the crystallographic direction [100], while maintaining the axial temperature gradients at the crystallization front equal to 35-40 deg / cm.

The essence of the proposed method consists in the fact that, instead of an extremely laborious and energy-intensive process of synthesis and purification of the obtained polycrystalline ingot by the zone melting method with the number of passes of the zone up to 40, the synthesis process and the preparation of the polycrystalline ingot are carried out in a single technological cycle by the Czochralski method. The stated conditions for the process of synthesis of indium antimonide and growing a polycrystalline ingot provide the source material with the required parameters and minimal losses. Deviation from the synthesis conditions in the direction of increasing or decreasing the excess of elemental antimony violates the conditions for obtaining a polycrystalline ingot of stoichiometric composition and increases the loss of the starting components.

During the process of growing a single crystal directly by the Czochralski method in the crystallographic direction [100], a change in the declared modes, namely a decrease or increase in axial temperature gradients at the crystallization front, violates the conditions of the process and does not allow to grow a large single crystal with high structural perfection.

An example of the method

To obtain a large-block polycrystal of indium antimonide, which is then used as a boot to obtain undoped indium antimonide single crystals, the initial indium and antimony components (6N purity) in a stoichiometric ratio, providing an excess of antimony in the range of 3-3.5 at.%, To prevent its evaporation during the synthesis process, they are loaded into a filter crucible installed in the working crucible of a crystal growth furnace by the Czochralski method. After evacuation of the furnace to 1 · 10 ^-3 mm RT.article Then, in a static vacuum, the starting components are melted in a filter crucible at a temperature of ~ 750 ° C and the melt is held for ~ 1 hour. Then the melt is filtered into the working crucible through an opening in the bottom of the filter crucible. By lowering the temperature of the melt in the working crucible to a temperature close to the crystallization temperature of indium antimonide (525 ° C), a large-block polycrystal is grown on a seed of any orientation with rotation of the crucible and the seed in opposite directions.

During the synthesis of indium antimonide from the starting components with the addition of an excess of Sb in an amount of less than 3 at.%, The fraction of non-stoichiometry in the obtained polycrystal was more than 35% of the total weight of the ingot. An increase in the excess of Sb in excess of 3.5 at.% Significantly impeded crystal growth due to an increase in supercooling at the crystallization front and also led to a significant fraction of non-stoichiometric material (~ 40%) of the total weight of the ingot.

Subject to an excess of elemental Sb in excess of stoichiometric amount in the range of 3-3.5 at.%, The share of non-stoichiometric material was minimal and amounted to no more than 10% of the total weight of the ingot.

After controlling the electrophysical parameters in the initial and final parts of the ingot, its lower small part is usually removed. If the electrophysical parameters of the grown polycrystal meet the requirements for the starting material for producing a single crystal, the ingot is subjected to appropriate chemical treatment and re-loaded into the apparatus for the subsequent production of a large-sized indium antimonide single crystal by the Czochralski method in the crystallographic direction [100].

As in the preparation of polycrystalline indium antimonide, to obtain a single crystal, the processed polycrystalline ingot is loaded into a filter crucible, which is installed in a working crucible, and placed in a plant for growing according to the Czochralski method. The single crystal is also grown in static vacuum ~ 1 · 10 ^-3 mm Hg. Since the vapor pressure of Sb over the InSb melt at a melting temperature is ~ (3-5) · 10 ^-2 mm Hg, ~ 1% of the mass is added to the filter crucible to maintain the stoichiometric composition of the melt. elemental Sb. The polycrystalline ingot is melted at a temperature of ~ 650 ° C and the melt is held at this temperature for ~ 35 min. Then the melt is filtered into the working crucible through an opening in the bottom of the filter crucible, and the melt is further cleaned from accidental mechanical impurities and oxide formations remaining on the walls of the filter crucible. Next, the melt temperature is reduced to a temperature close to the crystallization temperature of indium antimonide (525 ° C), after which a seed oriented in the crystallographic direction is applied to it [100], and the crystal is pulled out at a speed of 2-2.5 cm / hour during rotation crucible with a speed of 10-12 rpm and seed with a speed of 20-25 rpm and maintaining the axial temperature gradient at the crystallization front of 35-40 deg / cm.

An increase in axial temperature gradients over 40 deg / cm leads to a failure of single-crystal growth due to strong supercooling at the crystallization front. Growing a single crystal in the crystallographic direction [100] at temperature gradients at the crystallization front of less than 35 deg / cm also does not allow to obtain a perfect single crystal without twins and other structural defects such as lamellas, slip bands, etc.

According to the proposed method, under the claimed conditions for the growing process, namely: an excess of Sb in the range of 3-3.5 at.% And axial temperature gradients at the crystallization front of 35-40 deg / cm, 6 undoped indium antimonide single crystals with a diameter of 62-70 were grown , 2 mm with crystallographic orientation (100).

On plates with a (100) orientation, cut from the initial and final part of the ingots, perpendicular to the growth axis, the electrophysical parameters of the obtained single crystals were monitored: the concentration and mobility of the main charge carriers. The dislocation and defect structure of the obtained indium antimonide single crystals was detected on the same plates using selective etching in an etchant with the composition HCl: H ₂ O ₂ = 2: 1 for 1 min [see Bagel V.T., Smirnov V.M., Milvidskaya A.G. Crystallography, 37, 1992, No. 2]. The structural features of the obtained single crystals were investigated by optical microscopy. As samples for comparison, we used indium antimonide single crystals with a diameter of up to 40 mm grown by standard technology in the crystallographic direction [211].

Table 1 presents the electrophysical parameters and the values of the density of dislocations obtained by the above method of single crystals of indium antimonide.

Table 1 Electrophysical parameters and dislocation density in the obtained indium antimonide single crystals No. m / a Crystallographic orientation Diameter The concentration of the main charge carriers, n, cm ^-3 , 77K The mobility of the main charge carriers, µ, cm ² / V · s, 77K The density of dislocations, cm ^-2 one 2 3 four 5 6 551 top (one hundred) 60.3 8.510 ¹³ 5.610 ⁵ 1,0 · 10 ² bottom 63.5 5.010 ¹⁴ 4.0 · 10 ⁵ 1.2 · 10 ² 554 top (one hundred) 63.8 8.810 ¹³ 5.8 · 10 ⁵ 1,0 · 10 ² bottom 67.2 5.310 ¹⁴ 4.2 · 10 ⁵ 1,110 ² 557 top (one hundred) 65,2 1.5 · 10 ¹⁴ 5.0 · 10 ⁵ 1,110 ² bottom 68.5 1,0 · 10 ¹⁵ 3.2 · 10 ⁴ 1.2 · 10 ² 567 top (one hundred) 62.0 1.610 ¹⁴ 5.210 ⁵ 1,0 · 10 ² bottom 65.8 9.610 ¹⁴ 3,510 ⁵ 1.2 · 10 ² 569 top (one hundred) 68.5 1.5 · 10 ¹⁴ 5.8 · 10 ⁵ 1,0 · 10 ² bottom 70,2 1.2 · 10 ¹⁵ 3.0 · 10 ⁵ 2.0 · 10 ² 570 top (one hundred) 65,2 3.0 · 10 ¹⁴ 4.810 ⁵ 1,0 · 10 ² bottom 68.0 9.0 · 10 ¹⁴ 4.0 · 10 ⁵ 1.5 · 10 ²

The results obtained indicate that the electrophysical parameters of large-sized undoped indium antimonide single crystals grown in the crystallographic direction [100] are at the level of these parameters (n = 8 · 10 ¹³ -2 · 10 ¹⁵ cm ^-3 , µ = 6, 0 · 10 ⁵ -3.0 · 10 ⁵ cm ² / V · s, 77K) in indium antimonide single crystals obtained by standard technology in the crystallographic direction [211] with a diameter of up to 40 mm. As the results shown in Table 1 show, in their structural perfection, large-sized indium antimonide single crystals with a diameter of up to 70.2 mm grown in the crystallographic direction [100] significantly exceed indium antimonide single crystals obtained in the crystallographic direction [211], the diameter of which does not exceed 40 mm, and the density of dislocations in them is at least 5 · 10 ² cm ^-2 . It should also be noted that the distribution of dislocation density over the diameter of plates with (100) orientation is much more uniform than on plates with orientation (211), in which this distribution is W-shaped. The latter circumstance is extremely important for materials used as a substrate, since it to a large extent determines the perfection of stacked epitaxial layers.

Thus, the claimed invention allows:

1. At the stage of synthesis of polycrystalline indium antimonide, subject to the claimed process conditions, significantly reduce the material consumption of the process by reducing the proportion of non-stoichiometric material. Using the combined process of synthesis, purification and growing of a polycrystalline ingot instead of previously used synthesis in an ampoule and zone purification with the number of passes of the zone up to 40 significantly reduces the energy and labor costs characterizing this process.

2. To improve the structure of the obtained single crystals with a simultaneous increase in their diameter to 70.2 mm, namely, to reduce the average value of the dislocation density and improve the uniformity of their distribution over the crystal as a factor determining the parameters of photodetectors created on its basis;

3. To increase the yield of wafers when cutting ingots due to the fact that the direction of growing a single crystal [100] coincides with the working orientation of the wafers (100).

Claims (1)

A method for producing indium antimonide single crystals, including synthesis, preparation of polycrystalline indium antimonide and growing a single crystal by the Czochralski method, characterized in that the synthesis and preparation of a polycrystalline large block ingot is carried out in a combined process according to the Czochralski method with the addition of excess antimony over stoichiometric 3.0-3.5 %, after which the single crystal is also grown by the Czochralski method using a seed crystal oriented in crystallographic direction ION [100], while maintaining the axial temperature gradient at the crystallization front, equal to 35-40 deg / cm.