DD218638A1 - PROCESS FOR PREPARING CRYSTALS AND LAYERS FROM MELTING SOLUTIONS BY THERMODIFFUSION - Google Patents

Abstract

The invention relates to the field of growth of single crystals of fused solutions in closed containers and may find application in Kristallzuechtungseinrichtungen especially for the purposes of the semiconductor industry, micro and optoelectronics, optics, chemistry and Festkoerpergrundlagenforschung. The object of the invention is to cultivate single crystal bodies or layers at temperatures below the melting point without changing an initially set growth parameter during the growth process. In essence, the process consists in the thermodiffusive separation process between dissolved (crystallization material) and solvent component within a convection-free, quiescent and sealed melt solution with an imposed temperature gradient. The thermodiffuse segregation requires a local Übersaettigung the melt solution with the component to be crystallized and their deposition at the cold end of the container.

Description

; Process for the preparation of crystals and layers of melt solutions by means of! Thermodiffusion

Anwendungsgeriet, the invention

The invention relates to a process for the preparation of crystals or layers of melt solutions and is primarily designed for growing dissociating compound semiconductors (but also other mono- and multicomponent materials) at temperatures below the melting point, which results in a low dislocation density. lack of excess components (precipitates) and uncritical vapor pressure conditions, and is therefore geared towards the production of perfect analysis samples for the solid state research, substrate material and layers for microelectronics and optoelectronics, synthesis samples for chemical analysis purposes and optionally optical components ,

ν, - characteristic of the known technical solutions

From the previous experimental state of crystal growth and 'layer deposition, no solution is known that the thermal

Diffusion effect in multicomponent melt solutions for growing crystalline objects exploited (Wilke, K. Crystal Growing, Berlin, 1973, Sovremennaja kristallografi, yes, t 3, Moskva, 1979, all volumes of Journal of Crystal Growth, 1969-82) , The effect of thermodiffusion in inhomogeneously heated mixtures is known (C. Ludwig: SB Akad. Wiss., Vienna 20 (1856) 539; Ch. Soret: Arch. Sei. Phys. Nat., Geneva 2 (1879) ² ^ if- (1880) 209; Comptes Hendus'Acad. Sei., Paris j

0. KT. 19 3 2 * 0 41 λ η 3

    - 2 - ·

(1880) 2? 9), according to which ¹ , either the lighter component diffuses to the colder spot (negative thermal diffusion effect) or the heavier component diffuses to the colder spot (positive thermal diffusion coefficient). However, the technical application of this effect is known only the separation of gases for isotope separation (W. Einkeinburg: atomic physics, 11th / 12th edition, Berlin, 1967), but not for the deliberate separation of enamel solutions followed by phase transition for the purpose of crystal growth. Also known are various processes which exploit the diffusion of the component to be crystallized (dissolved or high-tem- perature component) in a concentration gradient imprinted from the outset in order to obtain an undercooling. place the supersaturation of the melt solution and thus initiate the crystallization or separation. The driving force of the progressive crystallization in these processes, which are described below, is the concentration gradient which causes the necessary transport of material (transport) and thus supersaturation at the coolest point of the melt solution or on a seed pad. None of these methods makes use of the thermodiffusive separation effect of two or more dissolved components in a temperature gradient as a driving force of the progressive crystallization.

In the crystal growth process by means of a migrating solution center Iz one in the negative temperature gradient (Traveling Solvent Method TSH; Wolff, G, A. Mlavsky, AI: Traveling SoIv Techniques, Crystal Growth, Vol 1 (Ed., CH, J. Goodman Plenum Press 1974-j Lozovskio, V.U.: Zonnajja plavka s gradientom temperatury, Moskva, 1972) there is a narrow solvent zone between a single crystal (seed crystal) and a polycrystal, wherein a temperature gradient imposed by this growth arrangement causes both phase boundaries of the liquid zone at different temperatures' and thus have different solution equilibria. The resulting concentration difference between the two phase boundaries

causes a diffusion of the dissolved component (substance to be crystallized) from the high-temperature solution equilibrium phase boundary (on the polycrystal) to the low-temperature

  Solution equilibrium phase boundary (on single crystal) and the

there supersaturation or deposition. As decisive '. Deficiencies for this method are a complex preliminary preparation of the three sections seed crystal, solvent slices and polycrystal, which must be brought to a uniform diameter in a presynthesis, as well as instabilities / the phase boundaries and concentration subcooling of the solution pitches (Seidensticker, R ₀ G .: I · GGG Conference Boston, 1966, Wolff, GA »Mlavsky, A. Ι.ί C ^: \ see above).

Another method (Traveling Heater Method = IHM, Wolff, G.A., Mlavsky, A.I .: see above), which uses the same arrangement of seed crystal, solution, polycrystal. is a concentration gradient in the solution zone by a moving Bingheizer with · Tempera turmasimum ini center of the solution zone. The high temperature solution equilibrium phase boundary adjusts itself to the polycrystal, since the temperature minimum moves toward it, the high temperature solution equilibrium phase boundary.

adjusts itself to the seed crystal, from which the tempera ture aziririum moves away. The consequent concentration

' Difference between the two phase boundaries leads to the diffusion W ,, of the material to be crystallized towards the low-temperature a

turphase boundary and here for separation. Basic shortcomings of this procedure also exist in; high Prapara-. in the production of the breed in order and

: in need of a precision translation mechanism

for the heater. "'.

'..;. In another method (Synthesis Solute Diffusion)

SSD; Eodot, H. et al.: J. Gryst. Growth ^ Λ (1968), 305-308). ".." .. A component of a compound ^{1 is} evaporated and at the

free surface of a melt reservoir of the second component with this brought to the chemical compound reaction.

- This creates a concentration in the surface area

Excess of the compound, The concentration gradient caused thereby causes a diffusion of the compound to a supercooled point of the melt solution reservoir and the crystallization there. The essential deficiency of this process consists in the exclusive application to compounds and in the difficult construction of the culture container (outer bulb with evaporation source). inner hinged unilaterally opened ampoule with melt reservoir).

Furthermore, known breeding methods are known from .Schmelzlösungen in which a "supersaturation initiated by lowering the melt solution in a supercooled area or a layer deposition by! Temperature reduction is achieved (Liquid Phase Epitaxy = LPS, Zschauer, KH in: solid state problems, VoI · 15 ( . · J. Queisser), Braunschweig, Germany, 1975) · These methods do not use thermal diffusion in melt solution volumes as crystallization driving force and require either mechanical helical movements between heaters, and cultivation arrangement or electronically complex temperature-cooling programs.

Object of the invention.

The object of the invention is to grow massive single crystal bodies or epitaxial layers of mono- or multicomponent materials from melt solutions with low equipment and economical expenditure.

Presentation of the invention · invention

The invention has for its object to develop a method that makes it possible, with little effort, without mechanical movement mechanisms and without tempera turabsenkprogramme crystals and layers of melt solutions to grow · According to the invention the object is achieved in that the thermal diffusion effect in a molten solution with a impressed temperature gradient is effective as a driving Eristallisations force.

The method consists of inducing a thermodiffusive component separation (segregation) within a melt solution in a closed on both sides vertical ^; Container and thereby caused at the cold end of the melt solution reservoir supersaturation with respect to the solution equilibrium and onset of crystallization, for which a temperature difference between the two container ends, set and maintained, to prevent thermal convection, the hotter end should be above. The onset of the temperature difference thermal diffusion causes a movement of the component to be crystallized for. This end of the container is designed as a capillary tip or a non-dissolving substrate (heterogeneous seed crystal) is introduced at this location. The crystallization is terminated when the remaining melt solution reservoir can no longer exceed the solution weight despite further thermodiffusive separation effect. The process steps are subdivided into the sub-operations: Weighing granulated crystallization and solvent in solid form and placing in the container evacuation and closing of the container placing the container in a preheated vertical tube furnace with temperature gradient holding the container in the temperature gradient over a period of the rate of thermal diffusion is determined - removal of the container from the oven - opening of the container and removal, take the crystallization product. The. The invention is given the abbreviation TDM (Thermo-Diffusion-On-Me- thode).

Embodiment. ,.

The invention will be explained below using an exemplary embodiment. In the accompanying drawing: FIG. 1: Axial temperature profile in the growth furnace

FIG. 2: Solubility diagram in the system of two components A and B (temperature concentration section in the binary phase diagram)

Figure '3i arrangement of the breeding container for massive' -. Single crystal growth during crystallization.

As a generalized example, serve the crystallization of a component A from a B-rich melt solution whose solubility diagram is shown in FIG. A and B are complete in the liquid phase and not solid in the solid state. The system must have a sufficiently large thermodiffusion effect, ie, a large quotient of the thermal diffusion coefficient D ♦ and. the diffusion coefficient D, which causes an accumulation of the component A at the colder end of the breeding container. In the specific case, for example, lead A (Fd) and component B tin (Sn) may be used if lead crystals below the melting point (327 ^° C.) are to be formed at the cold end of the ampoule. but in practice also represent a compound, for example, the optoelektronis.ch important semiconductor lead telluride (PbTe) and act as a solvent B, the hand koiaponente tellurium (Te). Also in this system, the Therinodif fusion force is large (D ^f / D> 1 Q ~ %). The first process step is the weighing in of the components A and B corresponding to the desired starting composition c in solid form. The most homogeneous mixture thus obtained is filled into the culture container 1, which can be designed as a quartz glass ampoule (FIG. According to the material properties of the components A and B, the selected temperatures and the Hunchensfed replies to the substance to be crystallized, evacuation and closing of the culture container will generally prove necessary. The thus-filled culture container is mounted in a vertical cultivation furnace characterized by a high upward temperature. The temperature increase along the axis of the culture container

(Figure 1) may be linear or deviate from the linearity for the purpose of influencing the time course of the crystallization. The arrangement of the cultivation ampoule in the oven is not changed at a constant oven temperature for a sufficiently long time. The solid homogenised batch, which consisted of the separate solid phases A and B when the container was placed in the growth furnace, is converted by the applied temperature into a liquid mixed phase of concentration c. The time required for the dissolution process is dependent on the original grain size of the granulated or pulverized starting material ¹ and shortly against the subsequent breeding time. '' ·

Due to the thermodiffusive separation effect, there is an accumulation of the component A at the bottom of the breeding container, which is designed for the purpose of seed selection as a tip /. The thermal conditions at the ampoule tip must be selected according to the material properties in the system A - B so that the separation effect causes an exceeding of the saturation curve and an associated crystallization of the solid component A. , The further crystallization proceeds without depending Possible external manipulation by the crystallization through the already made of the component A disturbed balance (The. Melting solution has become B-rich), resets, wherein the thermal diffusion causes a continuous extension of crystallization.

If the crystallization is finished, or should it be stopped prematurely, then the ampoule is removed from the cultivation furnace or the furnace is switched off. After removing the solid bar from the opened culture ampoule, the grown crystal must be separated from the best of the solidified melt solution. This as well as the further steps of the preparation take place according to conventional technologies (eg 3. wire saw, electroerosive separation). '.

If the thermodiffusive separation effect is to be used for the heteroepitaxial deposition of crystalline layers, then so

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to change the step of filling the homogenised starting mixture so that first the non-soluble substrate on the bottom of the correspondingly shaped. All other process steps are carried out in the manner described. The stripping off of the residual solution takes place according to the conventional technique: (ζV B. tilting technique :) β

Claims (1)

S p a c tio n s pr uc h Method of hexablation of crystals and layers of enamel solutions in closed containers with or without initial seed deposited at temperatures below the melting point of the component to be crystallized, in particular for the production of dissociating compounds and Ib-monocrystalline heteroepitaxial layers with low stoichiometric deviation and dislocation density, characterized a by that under. Utilization of thermal diffusion in a convection-free, inhomogeneously heated melt solution column with an impressed temperature gradient, a mixture of the components; and thus the supersaturation of the component to be crystallized at the cold end and its crystallization or deposition is carried out at this point. '' For this see 1 sketch drawings