JPS5946917B2 - crystal growth furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal growth furnace used to produce single crystals.

The furnace according to the invention uses the so-called solution depletion method.
That is, it is particularly suitable for producing a single crystal based on a method of crystallizing a solute by displacing and cooling a solution consisting of a solute dissolved in a solvent.

This method of crystallization, in which the solute to be crystallized is present in the solvent, generally offers the main advantage of being able to crystallize at lower temperatures than when crystallizing the solute alone, as well as offering better It is possible to produce crystals with excellent crystal quality.

However, the crystal growth furnace according to the invention can also be applied to other single crystal production methods, in particular purification by liquefaction and recrystallization.

The crystal growth furnace according to the invention is housed in a substantially cylindrical vertical body which is displaced downwardly in the temperature distribution space such that in the lower part the solute slowly crystallizes from the bottom upwards. It is applicable to all crystallization methods starting from a mixture of (solute and solvent).

The properties of single crystals depend to a large extent on the accuracy and stability of the temperature distribution within the space through which the body containing the substance to be crystallized moves.

In such crystal growth reactors, the body generally moves in a vertical direction.

Conventionally used furnaces include means for generating an axial temperature distribution within the furnace and means for linearly displacing the body containing the substance to be crystallized and the furnace relative to each other. .

In this type of furnace, it is almost impossible to consistently obtain crystals of good quality by the solution depletion method.

As a practical matter, crystal manufacturing conditions vary over time, and at the beginning of crystallization, the operating conditions (heating to generate an axial temperature distribution and rate of displacement of the body) are such that the crystallization It is chosen to occur in the furnace region where the axial gradient is maximum and the lateral gradient is zero, creating a horizontal flat crystal interface.

During crystallization, the concentration of solvent relative to solute changes.

That is, the solute content of the solvent decreases as the solute crystallizes.

As a result, the quality temperature of the solute in the solvent changes, so that the crystal interfaces are displaced relative to the fixed axial temperature distribution generated in the furnace.

Crystallization thus occurs where the temperature distribution is relatively imprecisely controlled, in other words where the lateral gradient is no longer zero, resulting in a deformation of the crystal interfaces.

Furthermore, because the crystal interfaces are displaced in the temperature distribution space, the crystallization conditions cannot generally be controlled in an optimal manner.

In the most frequently used case in which the body containing the solute and solvent moves relative to the furnace, the crystal growth furnace according to the invention has the advantage that the rate of displacement of the body and the solid-liquid interface of the solution It allows continuous adaptation so that the interface remains in a fixed position relative to the crystallization furnace over a long period of time as a function of the properties of the solute at that position.

That is, according to the present invention, since the position of the interface is maintained unchanged with respect to the heating means of the crystallization furnace, the crystallization rate becomes equal to the displacement rate of the main body.

In contrast, in conventional devices of this kind, when the crystal interface is moved relative to the heating means of the furnace, the crystallization rate is not equal to the displacement rate of the body, but the displacement rate of the interface and the velocity of the body are Therefore, as mentioned above, it was not possible to precisely control the operating conditions.

The crystal growth furnace proposed by the present invention includes a main body filled with a solution consisting of a solute to be crystallized and a solvent and placed in a heating chamber, and a main body filled with a solution consisting of a solute to be crystallized and a solvent, and a main body that is heated to generate a temperature distribution along the axial direction in the heating chamber. and means for displacing the body along the axis, further comprising: means A for controlling the instantaneous displacement rate of the body; and means A for controlling the instantaneous displacement rate of the body;
max(t) as a function of time at a level position where said temperature is substantially above a maximum; means B coupled to said means A for calculating the solute concentration of the solvent as a function of the displacement rate of the body; and means C for calculating the crystallization temperature T(t) of the liquid corresponding to the concentration as a function of time t;
(t) and a constant temperature increment ΔT.

The means may be an amplifier arrangement controlling n stages, for example made up of cyrisks, followed by n autotransformers, so as to enable distribution of the total power to the various windings of the furnace. be able to.

By accurately knowing the concentration of the solute in the solvent, we can calculate the crystallization concentration of the solute in the solvent at any point in time, and thereby reduce the maximum temperature of the chamber above the crystal interface to the maximum temperature level (height position). It is possible to adjust so that the distance between the crystallization level and the crystallization level remains constant and the crystallization temperature is maintained at the same level in the chamber.

The chamber in which the body is arranged can be purged with an inert gas or a gas containing a gaseous dopant, in which case the gas can be circulated, for example, from the bottom of the chamber to the top.

Furthermore, fill the entire chamber with any gas, close the chamber,
It is also possible to start the crystal growth operation afterwards.

In both cases it is necessary to use an open body.

In a variant of the invention, an open chamber and a closed body can be used, to which a suitably neutral reducing oxidizing or doping gas can be added.

Other features and advantages of the invention will become clearer from the following description of non-limiting embodiments, with reference to the accompanying drawings, in which: FIG.

As shown in FIG. 1, the chamber 2 is provided with heating means consisting of a plurality of heating rings 4 which are resistance heated and arranged concentrically with respect to the axis of the chamber.

The main body 8 contains a solution 10 consisting of a solute dissolved in a liquid phase solvent.
It accommodates.

The main body 8 moves downward as shown by arrow 12 while being controlled by a motor 14 .

By means of the motor 14, it is also possible to rotate the arm 16, which is integral with the main body 8, in the direction of the arrow 18.

By supplying power from the power supply, the heating ring 4 can generate a temperature distribution in the room as shown in detail in FIG.

Note that each resistance heating ring 4 is provided with an independent power source.

In the apparatus shown in FIG. 1, a gas supply pipe 20 extends from a gas supply source 22, and the gas that has reached the bottom is discharged from the top at a point 23 by, for example, a pump 24.

This gas may be an inert gas, reducing or oxidizing gas, and includes a doping agent or dopant.

The crystallization furnace is also equipped with a thermocouple 26 connected to device B for measuring the room temperature Tmax(t) at level N2, ie at ordinate level z2, where the maximum temperature prevails in the room.

The crystallization interface 30 is located at level N1, ie at ordinate level z1.

Below the level N1, at the location indicated by the reference numeral 32, the solute of the solute-solvent mixture 10 crystallizes out.

According to the furnace of the invention, it is possible to maintain the crystal interface 30 at a constant level z1 with respect to the chamber, so that between the levels N1 and N2 (δj −22−Zl) corresponding to each ordinate z1 and z2 temperature difference can be maintained constant.

The chamber 2 is made of refractory alumina, for example, and the body 8 is made of quartz.

By using the temperature measuring device B in combination with the thermocouple 26, the value of the temperature T max (t) can be controlled by the power supply.

As a function of the rate of downward displacement of the body 8, the concentration of the solute in the solvent and thus also the crystallization temperature of the solute in the solvent 10 can be calculated in the device C.

The motor 14 that performs the linear displacement is controlled by device A.

Device A includes device C for the purpose of giving commands via conductor 40 regarding the temperature program of the furnace determined by the device.
is connected.

Device C may comprise any suitable device, such as, for example, a mini-computer, which is capable of performing the operations detailed in connection with FIG.

The crystal growth furnace according to the invention operates in the following manner.

The body 8 is filled with a solute-solvent mixture.

The linear displacement speed of the body 8 can be constant and this speed is chosen below the critical speed at which the phenomenon of systematic supercooling appears.

Alternatively, it may be decreased continuously if desired.

This velocity information is sent to device C, which integrates the displacement velocity to determine the solute concentration in the solvent 10 as a function of time.

The apparatus controlled by apparatus C determines the temperature at level N2 on the vertical axis z2 as a function of this concentration, such that the temperature change between levels N1 and N2 is constant and the temperature at N1 is equal to the solute in the solvent at a given concentration. Adjust to correspond to the crystallization temperature.

Device B in combination with thermocouple 26 is able to detect the maximum temperature at level N2.

The operation of the crystal growth furnace according to the invention can be more clearly understood from the explanation of the graph in FIG.

In FIG. 2, the body 8 is shown in a first position 50 representing the starting position of crystallization and in a second position 52 after a time t.

During this time, solute 32 is crystallizing.

Ordinate 2. The levels N1 and N2 of and z2 are chosen relative to the axis OZ of the furnace chamber.

Temperature is shown on the abscissa axis, and curves 54 and 56 represent the temperature gradient within the furnace chamber that occurs as a function of time.

Curve 54 corresponds to the initial temperature distribution and curve 56 corresponds to the temperature distribution at time t.

Difference between the temperatures of levels N2 and N1 at the initial time △
T determines the temperature gradient expressed by:

The maximum initial temperature is represented by T max (Q, which is ΔT higher than the interface temperature TΩ.

From the curves 54 and 56 representing the temperature distribution measured along O2 for two quantities of time t, the temperature Tmax(t
) and T(t) is kept constant.

The maximum humidity Tmax(t) in the furnace at level N2 is
It is calculated using a curve 58 representing the crystallization temperature T(t) of the solute in the solvent as a function of the solute concentration X in the solvent.

From the initial concentration X(0) at an initial point in time, which corresponds to the crystallization temperature T(0) of the solute, it can be seen that the concentration x(t), like the corresponding crystallization temperature T(t), decreases with time.

Curve 58 is a curve drawn as a function of the phase of the solute within the solvent.

Generally T(t)<T(0), T max(t)<T
max(0).

Referring to FIG. 1, since the rate of descent is determined by device A, this rate is integrated by device C, thereby the amount of solute crystallized and therefore also the solute concentration value of the solvent X(t
) can be determined.

Therefore, the programmer of device C can determine the crystallization temperature value T(t)
is determined, and the temperature value T max (t) - T is determined by the heating means.
(t)+△T is generated at level N2, and level N1
The temperature value T(t) can be set to .

The furnace according to the invention is suitable in particular for example for CdTe y ZnT
e.

HgTe, PbTe y Pb5e, 5nTe
y MgTe t CdHgTe .

Pb5nSe, Cd, ZnTe t ZnMgTe
p-CdMgTe-like n-IY and IV-Vl
type semiconductor single crystals can be manufactured.

Tellurium can be used as the solvent in that case.

The composition thus obtained has very excellent quality.

This is because the crystallization rate corresponds to the true displacement rate of the body 8 and it is possible to maintain the crystal interface in the region of optimum temperature gradient.

゛Example The following crystals were able to be produced using the crystal growth furnace according to the present invention.

ZnTe: rod length 250 dragons Diameter 451m Low impurity concentration Dislocation 1000/ffl or less Not suitable for electroluminescence.

ZnMgTe: Rod length 250mm Diameter 45mm Low impurity concentration Dislocation 1000/ffl or less Suitable for electroluminescence.

CdTe: Rod length 250mm CdMgTe: Diameter 45mm Example suitable for detecting nuclei with low impurity concentration dislocations below 1000/i 1 Constant crystallization rate body 8, 105 corresponding to tellurium molar fraction 0.6!
A mixture of 1 liter of tellurium and 620 g of cadmium was charged and the initial crystallization temperature was set at 967°C.

The selected constant displacement rate of the body 8 in this example was 300 microns/hour.

Under these conditions, the furnace adjustment temperature provided by the equipment was a parabolic function of time, as listed in column 6 of Table 1 below.

This function was incorporated as a program into the device C that controls the device.

From the above components, diameter 45mm and length 148mvt
CdTe crystals were made.

Crystal growth and conditions are summarized in Table I.

Example 2 Variable crystallization rate body 8 contains 1055, corresponding to a tellurium mole fraction of 0.6
．． A mixture of 9 g of tellurium and 620 g of cadmium was charged.

The initial crystallization temperature was 967°C.

In this example, the furnace temperature change is a linear function of time (Table ■
(see column 6), and the speed was changed continuously under the control of device A.

This rate decreased linearly as a function of crystallization length (see second column of Table 2).

The speed was programmed into device C which controlled device A.

From the above composition, Cd with a diameter of 45 mm and a length of 148 mm
A Te crystal was created.

Regarding crystal growth and conditions, please refer to Table 3.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general configuration of a crystal growth furnace according to the invention, and FIG. 2 is a graph illustrating the development of crystallization temperature as a function of concentration and time. 8... Displaceable main body, 32... Crystallized solute, 14... Morph, 4... Heating ring, 2... Furnace, 26... Thermocouple, A... Speed control device, C... Computer, D... Power supply, B... Temperature measurement. Device.

Claims (1)

[Scope of Claims] 1. A main body filled with a solution consisting of a solute to be crystallized and a solvent and placed in a heating chamber, a heating means for generating a temperature distribution along the axis of the chamber, and a heating means for generating a temperature distribution along the axis of the chamber; means for displacing the body along an axis, the means for controlling the instantaneous rate of displacement of the body, the temperature in the chamber (T max (t)) being adjusted so that the temperature is substantially means B for measuring the solute concentration of the solvent as a function of time at a maximum level position;
Crystallization temperature at the interface between a solution and a crystal growing in that solution (
means C for calculating T(t)) as a function of time (1); and for all time values (1) said maximum temperature (T max(t)
) is equal to the sum of the crystallization temperature (T(t), l and a constant temperature increment (ΔT), and T(t)<T( 0), T
A crystal growth furnace characterized in that max(t)<Tmax(0). 2. The crystal growth furnace according to claim 1, wherein the chamber is open and the main body is closed. 3. said chamber is open and said furnace is or comprises a supply pipe arranged in a lower region of said chamber and a discharge pipe arranged in an upper region and a gas source delivering gas to said supply pipe; A crystal growth furnace according to claim 1, characterized in that: 4. The crystal growth furnace according to claim 1, wherein the chamber is closed and filled with gas. 5. The crystal growth furnace according to claim 3, wherein the gas is an inert gas or a gas containing a vapor phase doping substance. 6. heating means for generating a temperature distribution within the furnace chamber comprises a series of resistance heating rings surrounding the chamber;
2. The crystal growth furnace according to claim 1, wherein the temperature near each ring is adjusted by a device.