DD285797A5 - METHOD OF CONJUNCING UDP GROUP CRYSTALS FROM WAESSRESS SOLUTIONS - Google Patents

Abstract

The invention relates to a method for culturing crystals of the KDP group from aqueous solutions, preferably by the temperature-lowering method. The aim of the invention is to reduce the time and technological manufacturing effort and the increase in the yield. The object is to provide a method in which the achievable Einkristallgroesze not limited by separately zuemchtende germ carriers and the risk of dissolution of the germ carriers is eliminated in the undersized solution of the crystal material. According to the invention, the object is achieved by introducing, as a germ carrier, a plate made of water-insoluble material which has a relief-like microstructure on the surface at any concentration of the aqueous solution before reaching the transfer point. This microstructure is such as to allow oriented growth of the seed material on the plate. Single crystals of the KDP type, in particular KDP, DKDP and ADP, are the starting material for the production of electro-optical and non-linear optical components of the optical precision device construction.

Description

Field of application of the invention

The invention relates to a method for growing single crystals of the KDP group from aqueous solutions, preferably by the temperature lowering method, in which dissolved crystal material grows as a result of a temperature reduction achieved by supersaturation of the aqueous solution of this monocrystalline on a seed carrier. According to the invention, the term KDP group is understood to mean, in addition to potassium dihydrogone phosphate (KDP) itself, all phosphates which are isomorphic to KDP by arsenates in which potassium is replaced by ammonium, rubidium or cesium or else hydrogen by deuterium. In particular, KDP, ADP (ammonium dihydrogen phosphate) and DKDP (potassium dideuterium phosphate) single crystals are of great importance in precision optical instrument manufacturing. They serve as starting material for the production of electro-optical and non-linear optical components, polarizing prisms and analyzer crystals.

Characteristic of the known state of the art It is known to grow single crystals of the KDP type from aqueous solutions of the respective crystal material, wherein drj to Crystallization required supersaturation of the solution, usually caused by lowering the temperature, we j, but

can also be achieved by solvent evaporation. In this case, the crystallizing material grows on crystals of seed crystal plates introduced into the solution, which are cut out of previously grown single crystals of the same material with a specific crystallographic orientation.

In the cultivation of these single crystals according to the known temperature lowering method z. B. is initially a Heißgosättigte

prepared aqueous solution of the desired crystal material, in which then the seed crystals are used.

Subsequently, the temperature of the solution is slowly lowered by defined amounts. The free-wording crystal material sets

starting at the germ plates. The determination and setting of the optimum cooling rate (typical value: 0.1 K / d) is today largely automatic.

In order to produce macroscopically large, homogeneous single crystals of the KDP type, it is due to the Growth mechanism of these crystals necessary, of seed crystals of quite definite crystallographic orientation

go out.

The single crystal 3 of the KDP group, whose crystallographic form of a tetragonal prism and a tetragonal Dipyramide is known to grow on a germ of any order always towards the c-axis. in the Case of using the pyramid surface as a germ or of so-called diagonal germ plates is obtained theoretically

flawless. '! Crystal growth without turbidity; in practice, however, it has been shown that even the smallest misorientations of the

Germination surfaces and other effects can lead to serious growth disorders, so that the use of so

bred single crystals as optical components is often no longer possible.

When germplates were used, which were cut perpendicular to the c-axis, that is, the (001 H netbeno originate from

Only the natural growth areas can develop. During this growth phase, microscopic pyrrrids are formed, which grow together much later to form a uniform, optically homogeneous body. The resulting inner caps, as well as the immediately adjacent to these caps crystal areas are for the

Production of components or seed crystals unsuitable. From the inner caps further entforni However, crystal areas usually have a higher optical quality than sio in the case of using pyramidal surfaces

or diagonal plates is achieved as a crystal nucleus.

For obtaining seed crystals of the corresponding crystallographic orientation for the production of further Single crystals must be cut again already grown single crystals. The resulting loss of the Total yield can be 10% or more. Added to this is the problem of producing germs of the required cross-section when crystals of a particular Substance and should be cultivated. A lengthy process of breeding, selecting the best samples for seed crystals,

renewed breeding and selection, etc. is required.

Generally, the size of the monocrystals to be grown has narrow limits since it depends on the particular seed crystal size

which, in turn, results from the realized cross-section of the respective underlying, likewise cultivated, single crystal.

Another problem is the process of inserting the seed crystals in the saturated solution. The solution must not,

or be supersaturated only slightly, since otherwise accumulate on the germ surface parasite crystals that are too significant

Growth disturbances of the crystal lead. It must not be undersaturated, because otherwise the crystals on or or

would dissolve. For this reason, an exact adjustment of the saturation temperature of the solution must be made.

Setting the saturation temperature is a tedious process. Usual z. B. Methods in which test germ crystals of

e.g. Weighed 10mm χ 10mm cross-section, subjected to the reading and weighed again. Only when the corrected temperature has settled in the solution, a new test germ experiment can be performed.

However, the real weakness in the production of large single crystals of the KDP type is the onset of the seed crystals in

the saturated solution. As is known, these crystals are very sensitive to sudden sudden temperature changes. They react with the formation of cracks and cracks, which render the germ unusable for further crystal growth.

Therefore, it is necessary to carefully heat the seed crystals before inserting them into the solution, using the ones already on one Bracket mounted germs are gradually brought to the temperature of the solution in a separate device. After that

transferred to the seed crystals together with the holder in the actual breeding vessel. It is unavoidable that the

Germs briefly the climate of the crystal growing space and thus a temperature drop of z. B. 30grd exposed, resulting in The consequence is that in spite of all caution it sometimes leads to mechanical leaps and thus to further losses of yield

can come.

Furthermore, from the semiconductor technology, the so-called graphite epitaxy is known, which is sometimes used when

thin semiconductor layers of the vapor phase, e.g. B. after the CVC (Chemical Vapor DepositionJ method) to be deposited on an amorphous substrate.

By graphite epitaxy is meant a process in which a crystalline layer is deposited on an amorphous substrate

is, wherein the substrate previously "artificial", i. B. photolithographically was patterned. It must the structure of the

Substrate surface in its geometry largely with the geometry of the growing network level of the layer

to match. The main technological difficulty in the realization of such layers is that at most precipitate very fine-grained polycrystalline or amorphous semiconductor films on amorphous substrates, which are then heated by a heat treatment z. B. between 500 ⁰ C and 1000 ° C, such as by laser scanning, must be recrystallized.

The graphite epitaxy serves only to assist the recrystallization process, e.g. with lower Proceed process temperatures and / or to obtain larger monocrystalline areas in the layer. In the crystal growth of aqueous solution, graphite epitaxy has been used only occasionally to date

to deposit microscopic crystallites with the aim of studying their nucleation mechanism.

Object of the invention

The object of the invention is to reduce the technological and time expenditure in the production of large, optically homogeneous crystals of KDP type while increasing the yield of good.

Explanation of the essence of the invention

The invention has for its object to provide a technologically easy to handle, simple method in which a macroscopic, homogeneous single crystal grows on a germ carrier, in which the size of the single crystal to be grown is not limited by separately grown seed crystals nor the risk of dissolution the germ consists in an undersaturated solution of the crystal material.

This object is achieved by an ancestor for growing single crystals of the KDP group from aqueous solutions, preferably after the Temperatursenkvorfahren in the dissolved crystal material as a result of a achieved by lowering the temperature supersaturation of the aqueous solution of this monocrystalline on a seed carrier, solved according to the invention that Germ carrier at any concentration of the aqueous solution, a plate is introduced, which consists of oinom wasserunlöslichen, different from the monocrystalline monocrystalline material and whose surface is a mikrolithographisch generated reliefartigcn structure with structure widths in the micrometer or submicromoter range versohen, the geometry of this structure coincides with the crystallographic geometry of the present in the growing zone level of the single crystal to be grown in such a way that an oriented growth of the crystal material on the stru Kturierton surfaces of the water-insoluble plate takes place. It is advantageous if a germ carrier is used, the microstructure of which represents an integral trench system consisting of trenches arranged parallel to one another and to two edges of the plate.

Furthermore, it is advantageous if a plate is used, the microstructure receives a second, perpendicular to the first trench system arranged trench system.

It is also advantageous if a germ carrier is used whose microstructured surface is additionally roughened over the entire surface as a result of further etching treatment, specifically with a relief depth which is small compared to the roughness depth of the microstructure

According to the invention derived from previously grown monocrystals germ plates in (001! Orientation by

water-soluble, preferably made of glass germplates replaced, the microlithographically generated

Surface structure causes a growth mechanism of the growing crystal material associated with the Growth mechanism of KDP grown on natural KDP plates with (OOD orientation largely

so that an oriented growth of the seed material on the structured surfaces of the water-insoluble

Plate done. As with the use of natural Koimen arises due to the specific for these single crystals Growth mechanism in the vicinity of the germplates first a crystallographically strongly disturbed growth zone in the form

a so-called cap, wherein the dislocations emerging from the caps but emerge from the single crystal in the course of further crystal growth, so that finally forms a perfect crystal.

The use of graphite epitaxy, with the help of which crystallites in the growing stage, the necessary pre-orientation

is given, thereby allowing to dispense with perfect seed crystals. This makes it possible to grow macroscopically large single crystals, the size of which only by the maximum editable format in each microlithography device used for

Structuring of the germ plates is limited and not by the size of previously grown single crystals. The inventive method substantially simplifies the immediate preparatory phase of the Crystal growth achieved. The use of water-insoluble germination plates allows the tedious procedure of the Setting the exact saturation temperature to be waived. Dio germination plates are simply introduced into a solution of the crystal material which is undersaturated by increasing the temperature,

after which the temperature of the solution is first lowered relatively rapidly to near the saturation point and then continuously reduced further after a conventional temperature reduction program. In this way, the critical step of transferring the annealed germs into the saturated solution is also bypassed.

The application of the method according to the invention can also be applied to the cultivation of single crystals with similar Growth mechanism such as that of KDP be extended from aqueous or non-aqueous solutions. Ausführungsbelsplel The invention will be explained in more detail with reference to a Ausführungsbetopieles. For the growth of KDP single crystals from aqueous solution by the temperature reduction method are previously germ carriers

manufactured. For this purpose, a glass plate, e.g. 100mm χ 100mm χ 5mm, coated on one side with a photoresist, which is now provided in a conventional manner by photolithographic means with a microstructure. By a suitable etching technology, this microstructure is transferred to the glass body, so that the surface of the glass plate receives a corresponding trench system. As a microstructure z. B. a grid can be selected, which consists of each other and two

Edges of the plate consists of parallel trenches. The lattice constant of this trench system may be 1.8mm,

wherein the width of the trenches 0.9 mm and the width of the webs between the trenches can also be 0.9μηι.

Of course, the glass plate can also be structured on both sides. In an intended for carrying out the temperature method crystal growing apparatus with appropriate Effective volume is first prepared a wäßn'ge KDP solution containing so much dissolved KDP material that they only at 5O ⁰ C.

reaches its saturation temperature. After heating the solution to about 57 ° C, the microstructured germ carrier is introduced into the now relatively undersaturated solution. The temperature of the KDP solution can now be set to a value that is about the above

Saturation temperature is relatively quickly cooled. The further reduction of the temperature takes place in defined

small steps after a conventional temperature reduction program. Upon reaching the saturation temperature at about 50 ° C, the crystallization process begins.

The exact determination of the saturation temperature, as for the introduction of water-soluble, from a KDP single crystal

cut germplates would be required, can be omitted according to the invention.

Of course, several water-insoluble microstructured germ carriers in one and the same crystal growing vessel

for the simultaneous production of several KDP-type crystals.

Claims (4)

1. A process for the growth of single crystals of the KDP group from aqueous solutions, preferably by the temperature lowering process, in which dissolved crystal material as a result of achieved by lowering the temperature supersaturation of the aqueous solution of this monocrystalline grows on a germ carrier, characterized in that as the germ carrier in any Concentration of the aqueous solution, a plate is introduced, which consists of a water-insoluble, different from the monocrystal to be grown material and whose surface is provided with a microlithographically generated relief-like structure with structure widths in the micrometer or Submikrometerbereich, the geometry of this structure with the crystallographic geometry the mesh plane of the single crystal to be grown in the growth zone coincides in such a way that an oriented growth of the crystal material on the structured surfaces of the water insoluble Ien plate takes place. 2. The method according to claim 1, characterized in that a germ carrier is used, the microstructure is a first trench system consisting of mutually parallel and to two edges of the plate arranged trenches. 3. The method according to claim 2, characterized in that a germ carrier is used, the microstructure in addition to the first trench system includes a second trench system, wherein the second trench system is arranged perpendicular to the first. 4. The method according to claims 1 to 3, characterized in that a seed carrier is used, the microstructured surface is roughened in addition over the entire surface, wherein the surface roughness is small compared to the ^r ielieftiefe the microstructure.