CN1993503B - Method for growing monocrystals from melt - Google Patents

Abstract

The present invention relates to the technology of growing single crystals from melts on a seed crystal. The technical problem to be solved by the present invention is to provide a universal method ofgrowing single crystals of various chemical composition, for example, of A<SUB>2</SUB>B<SUB>6</SUB> and A<SUB>2</SUB>B<SUB>5</SUB> type, and also single crystals of refractory oxides, such as sapphire. The technical result of the claimed invention is its universality with regard to the material of the single crystal to be grown, enhanced performance, and improved structural finish of resulting single crystals by ruling out melt overcooling in the coursed of growing. The technical result is attained by that in the method of growing single crystals from melt, which comprises fusing the startingmaterial and pulling a single crystal by crystallization of the melt on a seed crystal with controlled removal of the crystallization heat and using independent heating sources constituting thermal zones, according to the invention, independent heating sources constitute two equalsized coaxially arranged thermal zones, which make up a united thermal area for the melt and the single crystal beinggrown and are separated by the melt starting material being carried out heating the upper thermal zone with heater 30-50% of power required for obtaining the melt, until in the upper thermal zone maximum temperature is reached, which secure stable state of the solid phase of the seed crystal; then the remaining power is supplied to the lower thermal zone to the lower heater with maintaining constant temperature of the upper thermal zone till complete melting of the charge; the process of the single crystal enlargement and growing is conducted with controlled lowering of temperature in the upper thermal zone, the amount of power supplied to the lower thermal zone being preserved constant.

Description

Method from the melt growing single-crystal

The present invention relates on crystal seed technology from the melt growing single-crystal.

The technical problem to be solved in the present invention provides the various chemical constitutions of growth (A for example ₂B ₆And A ₂B ₅Type) monocrystalline, the universal method of the monocrystalline of refractory oxide (for example sapphire) in addition.

A ₂B ₆And A ₂B ₅Type monocrystal material and those monocrystal materials based on oxide compound are used as optical material.Increased demand widely based on the exploitation of the instrument of these materials, and improved requirement quality, efficient and cost value to them.

As known in the art is from the grow method of colourless sapphire single-crystal of melt on crystal seed, it comprises the longitudinal temperature gradient deviation of the thermograde that exists in the 0.05-1.0 ℃/mm scope and＞1 and the ratio of radial symmetry gradient deviation, the charging that vacuum melting is initial, introduce crystal seed, and from refrigerative melt pull monocrystalline (referring to RU 2056463, C30B 29/20, publ.1996).

The main points of described method are to determine crystal seed introducing temperature from the appearance of the 1-3mm monocrystalline on positive refrigerative melt surface, and be under the withdrawing rate that the 0.1mm/hr when crystallization begins progressively changes to the 1.0mm/hr of this process final stage, simultaneously at the melt temperature of the 25-50 ℃/hr growing single-crystal down that underspeeds.Stop process of growth by the monocrystalline that cools off gained with the speed of 25-50 ℃/hr.The starting stage of this process medium and small speed ground pull can formation rule lattice, thereby eliminated the appearance of dislocation and slide block and the formation of bubble.Shortened the process time with the speed pull that improves 10 times in stage in the end.

This method is considered the melt growing crystal from " cold excessively " at place, crystallization forward position.Because the melt centre radial symmetry gradient at crystal seed place always equals zero, so both made slight reduction heater temperature, reduce the melt temperature then, will produce the zone that temperature is lower than Tc at place, crystallization forward position.For the heat of crystallization that produces in the process of removing growing crystal, in described method, reduce crystal growth rate, therefore reduced the heat that produces during the crystallization, and because the thermal conduction of the crystalline material of just growing provides the time of removing heat along crystal.

This method has inefficient shortcoming, and this causes it can't be used for the production of a large amount of monocrystalline.

Known on crystal seed from the method for melt growth arsenide gallium monocrystal, crystal seed is contacted with the melt that is placed in the smelting furnace under the liquid flux layer, (referring to RU 2054495, C30B 17/.00, publ.1996) then to make the crystallization of melt of whole volumes under with the flux liquid encapsulation.This method is intended for use to grow and makes the arsenide gallium monocrystal of unicircuit substrate.Therefore, the thickness of selection melt layer equals the thickness of substrate.This method can not be used to the bulk single crystals of gallium arsenide of growing.

Known Czochralski method by using three well heaters (ratio-frequency heating has the conical well heater of active pull-up of the control of the well heater of platinum smelting furnace, heating furnace bottom of melt and heating crystal seed, its clamper and rod) is from melt growing optics monocrystalline, it comprise the violent oxide compound that grinds of fusing and on the crystal seed of rotation from the melt growing single-crystal, wherein when having set up thermal equilibrium and having arrived melt-crystal interface planar or implemented growth during slight protrude surperficial.For this reason, extremely surpass the crystal growth temperature certain value at additional heating crystal seed, seed holder and rod, thereby IR radiation ratio, i.e. λ are provided in melt and solid phase _Melt/ λ _CrystalCarry out whole process=0.25 time.In the stage that the pull crystal increases, unreal apply heat (referring to DD 290226, A5, C03B 15/22, publ.1991).

The main points of this method are to produce the temperature field, at this temperature of crystal seed and clamper and rod crystalline temperature～T of equaling just growing after the match _FusingIntroduce crystal seed (seeding), crystalline increases and further growth based on from the crystallization forward position to crystal and to the IR radiating heat transfer difference of melt.Because the crystalline heat transfer coefficient is greater than melt, crystal has the temperature that is lower than melt naturally.As a result, crystal taking place grows on crystal seed.By additional heating crystal seed, seed holder and rod, during whole crystal growth, keep this thermodynamic equilibrium automatically.Adopted this method as maximally related prior art.

There is a large amount of substantial drawback in described method, and it can not be used for the material by the ten minutes broad range of Czochralski or the growth of Kiropulos method:

1. this method can not be used for decomposable material, for example A ₃B ₅, wherein at T _FusingDown a kind of vapour pressure of component reach 40atm and more than.

2. this method can not be used for volatilizable material, for example A ₂B ₆, wherein at the T of compound _FusingThe vapour pressure of following two kinds of components reach 3atm and more than.

3. this method can not be used in a large number at T _FusingViscous deformation (α-the Al for example of growing crystal because when having observed viscous deformation under 1600 ℃ temperature, takes place in the material that has high plasticity down under himself weight ₂O ₃).

When reach for a short time ± when the fluctuation of 0.5 ℃ heater temperature caused the spontaneous crystallization of the fusing of crystal seed or melt in furnace thing, this method can not be used for having in a large number little melt and cross the material of cold value (for example for CdTe, 1 ℃ of Δ T ≌).

5. this method can not be used for a large amount of following materials, and wherein the IR gamma absorption of melt and crystalline heat emissivity coefficient and well heater is approaching, for example in the situation of Ge, Si, InSb etc.

6. by the difference of melt and crystalline dark heat with less than the heat of crystallization that produces with measuring incommensurability.α-Al for example ₂O ₃Therefore=255cal/g only can realize this method under very little crystallization rate, promptly it is industrial inapplicable.

The technique effect of the invention that the application asks for protection has been to eliminate melt and has crossed cold and aspect the structure integrity (structural finish) that improve at material, enhanced performance and the gained monocrystalline of the monocrystalline that will grow, it has universality in process of growth.

The described technique effect of following acquisition: from the method for melt growing single-crystal, it comprise by make when removing heat of crystallization on control ground and using the independent thermal source that constitutes the high-temperature zone melt on crystal seed crystallization to melt starting material and pull monocrystalline, described method is characterised in that described independent thermal source constitutes the high-temperature zone of the coaxial arrangement of two equidimensions, it forms melt and the unified high-temperature area of the monocrystalline of growing, described high-temperature zone is separated by melt surface, in two stages, implement raw-material fusing: at first obtain the 30-50% of melt power demand (power) to heat upward high-temperature zone by the heater fed that makes progress, until reach maximum temperature in last high-temperature zone, this has just guaranteed the steady state of crystal seed solid phase; On keeping, in the homo(io)thermism of high-temperature zone, well heater is extremely descended in high-temperature zone under the remaining power supply, then until the fusing of finishing charging; In the temperature on reducing in the high-temperature zone, carry out the process that monocrystalline increases and grows with controlling, make the amount of the power of high-temperature zone under the supply keep constant.

In addition, under the monocrystalline crystallization rate of calculating by following formula, be implemented in the removal of the heat of crystallization in monocrystalline increase and the growth phase:

(1), g/ second, wherein

Δ m is a crystalline weight, g;

Δ τ is the time of weight gain (Δ m), second;

T _FusingBe raw-material temperature of fusion, ℃;

T _CrystalBe the maximum temperature of crystal seed solid phase steady state, ℃;

Δ T is the temperature variation on the upper heater during this process, ℃;

Δ H _FusingBe the specific heat of fusing, cal/g;

P is a pressure, and is constant;

R is a crystal radius, cm;

Be place, crystallization forward position radial symmetry gradient, ℃/cm;

Be initial axial-temperature gradient in the crystal growth district, ℃/cm;

C _PBe crystalline specific heat, cal/g ℃;

λ is the crystalline thermal conductivity, cal/cm second ℃

Main points of the present invention are as follows.In order to be grown in its configuration aspects " ideal " monocrystalline, in known method, need between by t ° in the thermograde of t ° of generation of melt and the growing crystal district, find " golden section " to remove heat of crystallization.

In RU 2056463, in order to remove heat of crystallization, reduce crystallization rate, thereby be that cost provides heat extraction along crystal with the heat transfer of seed crystal material.

Perhaps, reduce the power of supplying with the well heater in the smelting furnace district with melt, thereby reduce temperature of fusion (RU 2054495).

Use these technology to have negative effect.Reduce crystallization rate and significantly reduced process efficiency.To reduce heating power is that cost reduces the melt temperature and causes at crystallization forward position melt coldly excessively, and the result causes the generation (low angle grain boundary, polycrystalline structure) of textural defect.

In the present invention, by increase the axial-temperature gradient the growing crystal district from its minimum value, remove the heat of crystallization that is produced along crystal.

In the present invention, the technology that uses brand-new grain husk obtains described effect.

In the reaction zone of having arranged starting material and crystal seed and clamper and rod, by two well heater high-temperature zones of producing two equidimensions independently, these in districts are arranged in above another and constitute unified high-temperature zone.In order to melt initial charge, at first heat upward high-temperature zone by melting the required part of starting material (30-50%) power supply upper heater.The amount of described power makes it upper area to be heated to and can make crystal seed remain on the maximum temperature (T of in fact stable solid state shape _Crystal).Therefore, for example, for A ₃B ₅In fact compound does not exist dislocation; For A ₂B ₆There is not evaporation in compound; For refractory oxide α-Al ₂O ₃, do not have viscous deformation.Then, with well heater under the remaining power supply, heating is the high-temperature zone down.Keep and equal T _CrystalThe homo(io)thermism of upper heater, melt fully and between liquid phase (melt) and solid phase (crystal seed), obtain running balance until initial charge.

After reaching running balance, the stable power of well heater down.

By in the unified high-temperature area that constitutes of high-temperature zone and following high-temperature zone, the T of melt _{Molten Change}And T _CrystalBetween temperature head above melt and in the melt, produce minimum axial gradient.The power by reduce supplying with upper heater and thereby reduce on the temperature of high-temperature zone change under the axial-temperature gradient, implement the increase and the growth of monocrystalline.Under keeping supply, in the power of well heater, implement described cooling.

The thermograde that increases the melt top by the temperature that reduces upper heater is implemented the removal of heat of crystallization, to implement the crystalline growth.Calculate crystallization rate (g/ second) from formula (1).

When the temperature of upper heater reduced the temperature reduction of also therefore going up the high-temperature zone, axial-temperature gradient increased, and crystal growth.

Meanwhile, the quantity of power of well heater under in whole growth process, keeping supplying with, according to route: around following well heater → smelting furnace → melt → melt central authorities → crystal → upper heater, from of the reduction of hotter object to not too hot object generation crystal-melt temperature.

The melt at place, prevention crystallization forward position is cold excessively, and the temperature of melt reduces by the direct ratio ground that is lowered into of crystallizing field and upper heater temperature.Therefore, always only to hotter melt district growth, the removal of heat is the central authorities of process melt in the direction of growing crystal always for the crystal of just growing.

In all known methods, reduce crystal-melt temperature always in opposite direction.

Adopt the described method of technology implementation of the present invention to guarantee in the crystal of growth, not have low angle grain boundary and low dislocation desity.In addition, it is highly important that, so process efficiency increases with the temperature that reduces upper heater with being directly proportional because when closing upper heater, also there be not the cold excessively of melt.

The technology of asking for protection is characterised in that the single crystal growing technology of complete novelty, because hot-fluid always moves ahead along above-mentioned route, is not melt from " cold excessively " according to this technology, but obtains monocrystalline from " superheated " melt.

The unified high-temperature area that is made of the high-temperature zone of an equidimension that is positioned at above another and is separated by melt surface comprises the smelting furnace district and will form the crystalline zone.By supplying the fusing that whole power are realized charging, will cause melt crystallization in smelting furnace thereby reduce the power of supplying with a high-temperature zone to two high-temperature zones.The generation of unified high-temperature area has determined the generation of and radial symmetry gradient axial for the minimum unification of certain material possibility.Because crystal increase and the process of growth in, the variation of thermograde can not cause the cold excessively of melt, so described method can growing single-crystal, wherein the appropriate value of melt supercooling temperature can be in 70 ℃～0 ℃ scope.

In addition, producing the unified high-temperature area that is made of the equidimension high-temperature zone can equate by the temperature that makes the high-temperature zone, reduces the power of upper heater and following well heater simultaneously, the crystal of growing is cooled to room temperature waiting under the heat condition.

Because in implementing described method, do not have the cold excessively of melt at place, crystallization forward position, so use this method can be from following material growing single-crystal, wherein melt approaches zero to supercooled ability (faculty), and (CdTe, the α-Al of [0001] direction until now can't be grown by the Czochralski method ₂O ₃The GaAs of direction) or have definite textural difference [001].

Specific embodiments

To the resistance heater supply power that is arranged in smelting furnace top, and make temperature approach the critical temperature T of given crystalline material with charging.

The critical temperature of material is following temperature: under this temperature, irreversible and uncontrolled process takes place on the crystalline solid phase surface: processes such as disassociation, evaporation, viscous deformation, this moment, other practical application of crystallisation process was nonsensical.Therefore, work as T for instance _FusingIn the time of=1467 ℃, the remarkable dissociative temperature of GaP crystal of observing growth above flux is～1300 ℃; Work as T _FusingIn the time of=1092 ℃, the remarkable dissociative temperature of CdTe crystal of observing growth above flux is～700 ℃; Work as T _FusingIn the time of=1420 ℃, observe the α-Al of growth ₂O ₃The temperature of the remarkable viscous deformation of crystal is～temperature＞1100 of 1600 ℃ and the remarkable viscous deformation of Si crystal ℃; Or the like.

When the temperature of last resistance heater became near threshold value, the high-temperature zone temperature was stable in the enforcement.Temperature detecting unit is mounted in the thermopair in the upper heater top, thereby makes down the influence minimum of resistance heater to thermocouple readings.

After having heated whole inside furnace equipment, will be used for melting well heater under the power supply of smelting furnace charging.The temperature of upper heater remains unchanged, and equals≤T _CrystalAlong with charging is melted and the melt temperature-stable gradually, produce critical (minimum) axial-temperature gradient or given material automatically.Then, introduce crystal seed.When between solid phase (crystal seed) and liquid phase (melt), reaching stable running balance (around crystal seed, having constant bright haloing) gradually, in the power of stable well heater down, reduce the temperature of upper heater, thereby increased the axial-temperature gradient of crystal seed and melt respectively, and therefore increased the radial symmetry gradient of crystal seed and melt.

Generation condition like this, crystal is grown from the over hot melting thing under this condition.During whole crystalline process, there is not crystallization forward position superheated areas of melt.Because crystal continuous is from " superheated " melt, rather than from the melt of " cold excessively ", grow, this not only can eliminate and form textural defect inadvisablely on the crystallization forward position, and have an opportunity to obtain the material that can not therefrom produce or be difficult to produce by Czochralski, for example along CdTe, the GaAs monocrystalline of [100] direction orientation; Al along [0001] orientation ₂O ₃Or the like.

When whole melt goes out to be grown in crystalline form crystallization on the crystal seed, the temperature of following well heater is reduced to the temperature of upper heater, the performance number that reduces well heater then synchronously so produces isothermal condition until reaching room temperature, thereby removes the residual heat stress in the monoblock monocrystalline.

So, as the α-Al that grows from " superheated " melt ₂O ₃During monocrystalline, (load charging in the working chamber that is ready for described method, well heater circular or abnormity (profiled) is installed, suitable crystal seed is installed, according to the heater profile orientation, the degassing and the atmosphere that generation is determined in the working chamber, and other operation) after, open upper heater, and make the temperature that records according to thermopair at T _CrystalIn～1600 ℃ the scope.Work as T _CrystalWhen reaching, all equipment heating several hrs in the working chamber are become stable until heat exchange.Then, open down well heater, regulate its power, make heater temperature equal T _FusingAl ₂O ₃=2050 ℃, and be maintained until steady state, this determines from the behavior of melt surface by vision.By handling down the power of well heater, introduce crystal seed.Stable haloing from the liquid-solid interface around the crystal seed is determined the steady state of system.After reaching running balance, implement stablizing of heater power down, and in whole crystallisation process, keep stability.By reducing temperature for ± 0.5 ℃ thermocouple readings, implement crystalline and increase according to precision.The result who increases in time as thermograde is along the removal of crystal generation heat of crystallization.

Because following well heater is a power stability, therefore also will reduce so have the temperature of the smelting furnace of melt, but it will always be kept above T _Fusing, i.e. the melt at crystallization forward position place always " overheated ".According to the increment of its weight of time per unit, promptly, realize keeping and be downloaded in the program (program) of growing crystal diameter according to from relation (1) precalculated crystallization rate.When single crystal growth process is finished, reduce the power of well heater down, make that the temperature in the smelting furnace equates with the temperature in growing single-crystal district.Under isothermal condition, crystal is cooled to room temperature by the performance number that reduces by two well heaters simultaneously.

Embodiment

With reference to mentioned above, the meaning of formula Δ m/ Δ τ is to determine under the speed that maximum allows by the temperature condition of Amosov method from " superheated " melt growing single-crystal as.When using this formula, should consider that in the increase process, the crystal radius of just growing increases continuously in time: R1=Ro+ Δ T/A, R2=R1+ Δ T/A.

Along with crystal radius increases,, because in increase Δ T/A → 0 of furnace wall place radial gradient, and further reduce the increase that in fact temperature on the upper heater can not cause crystal radius near the radius (stage that increase is finished) of smelting furnace.Because along the increase of crystal axial-temperature gradient, crystal continued growth.

Initial parameters:

Material: corundum (α-Al ₂O ₃)

T _Fusing=2050 ℃;

T _Crystal～1600 ℃, at distance melt surface h=20cm point place;

λ～0.008cal/cm second ℃

R ₀=0.5cm (radius of crystal seed);

Δ H _Fusing=255cal/g;

C _p＝0.3cal/g·℃；

In our the formula (1) with these value substitution crystallization rates (Δ m/ Δ τ).Then, we are provided with the temperature reduction of upper heater, for example Δ T=-5 ℃.At increase stage (stage ofenlargement), the increment of crystal weight will be Δ m/ Δ τ=8.02g/hr.

Temperature by further reduction upper heater continues the process that crystal increases, until obtaining crystalline predetermined diameter, for example 120mm.

Keep time per unit crystal weight increment constant and reduce the temperature of upper heater, implement process of growth.When the diameter of growing crystal is 120mm, Δ m/ Δ τ=1149g/hr.

Growth 30kg crystalline process continues～26 hours.In the crystal of growth, there are not thermal stresses, low angle grain boundary and textural defect fully.

So, adopt the inventive method can grow bulky single crystal expeditiously and their chemical constitution is celebrated without limits and with perfect structure.

Claims (3)

1. one kind prepares the method for monocrystalline by growing from melt, it comprise by make when removing heat of crystallization on control ground and using the independent thermal source that constitutes the high-temperature zone melt on crystal seed crystallization to melt starting material and pull monocrystalline, described method is characterised in that described independent thermal source constitutes the high-temperature zone of the coaxial arrangement of two equidimensions, melt is formed and the unified high-temperature area of the monocrystalline of growing in this high-temperature zone, described high-temperature zone is separated by melt surface, in two stages, implement raw-material fusing: at first obtain the 30-50% of melt power demand to heat upward high-temperature zone by the heater fed that makes progress, until reach maximum temperature in last high-temperature zone, this has just guaranteed the steady state of crystal seed solid phase; On keeping, in the homo(io)thermism of high-temperature zone, well heater is extremely descended in high-temperature zone under the remaining power supply, then until the fusing of finishing charging; In the temperature on reducing in the high-temperature zone, carry out the process that monocrystalline increases and grows with controlling, make the amount of the power of high-temperature zone under the supply keep constant.

2. according to the method for claim 1, it is characterized in that in the removal of implementing described heat of crystallization monocrystalline increase and growth phase under the crystallization rate of calculating from following formula:

(1), g/ second, wherein

Δ m is a crystalline weight, g;

Δ τ is the time of weight gain (Δ m), second;

T _FusingBe raw-material temperature of fusion, ℃;

T _CrystalBe the maximum temperature of crystal seed solid phase steady state, ℃;

Δ T is the temperature variation on the upper heater during this process, ℃;

Δ H _FusingBe the specific heat of fusing, cal/g;

P is a pressure, and is constant;

R is a crystal radius, cm;

Be place, crystallization forward position radial symmetry gradient, ℃/cm;

Be initial axial-temperature gradient in the crystal growth district, ℃/cm;

C _PBe crystalline specific heat, cal/g ℃;

λ is the crystalline thermal conductivity, cal/cm second ℃.

3. according to the method for claim 1 or 2, it is characterized in that described method is the Amosov method.