RU2184803C2 - Technique controlling process of growth of monocrystals from melt and device for its realization - Google Patents

Abstract

FIELD: manufacture of semiconductors. SUBSTANCE: technique can be employed to produce monocrystalline ingots of germanium. Device for implementation of process ( Fig.1 ) presents microprocessor system based on microcomputer 7 which controls growth of monocrystalline ingot 13 having diameter d with elongation rate V₃ and crystal rotation velocity ω₃ in chamber 12 by the Czochralski process. Molten metal 14 placed in melting pot 15 ( with inner diameter D ) rotates with angular velocity ω₁ and simultaneously rises up with rate V_m.p ( as amount of melt in melting pot decreases ). Ingot 13 is extracted from additional intermediate melting pot 20 with diameter of replenishment hole d_dr which in addition to required purity of melt in intermediate melting pot and uniformity of doping of grown ingot makes it possible to position level gauge 3 in more overheated zone of melt and to utilize additional heater 19 fed from source 18 with setting of minimal heating current I_∂ by computer for automatic heating of lower part of gauge. This approach makes it feasible to guarantee temperature of lower part of gauge contacting melt above possible temperature of its crystallization and to secure absence of built-up of melt on gauge in process of operation. Given microprocessor control system determines refined difference control signal Y as function of deviation of present area from specified one on basis of immediate translations of crystal and melting pot measured by transducers in the course of evaluation cycle of control signal given that level of melt in melting pot is kept constant. In periods of open state of melt level gauge rate of upward rise of melting pot is set greater by advance value N than it is necessary for condition of constancy of level of melt with specified diameter d₃ of crystal, inner diameter D of melting pot and present elongation rate V₃ of crystal. In periods of closed state of melt level gauge rate of rise diminishes by factor of M as compared with rate of open state of gauge maintaining in this case conditions of stabilization of level of melt. Later more precise difference control signal Y is used in adjustment system to diminish misbalance of area of growing crystal and to send signals over four channels: T₃-temperature of side point of heater, V₃-elongation rate, ω₃-crystal rotation velocity, ω_т-rotation velocity of melting pot which secures stabilization of area or diameter, if form is round, of growing crystal in process of entire technological cycle of growth of crystal without use of any optical or other methods for stabilization of level of melt and determination of present diameter of ingot. Invention makes it possible to input systematic ( by chart ) changes into process of growth simultaneously with stabilization of area ( diameter ) of growing crystal under any present values of all four control channels (T₃,V₃,ω₃,ω_т), as well as to place whole crystal into closed cylindrical screen or closed heating equipment practically without any visual inspection of ingot. EFFECT: improved reliability of control over growth of monocrystals. 2 cl, 1 dwg

Description

 The invention relates to production for controlling the process of growing single crystals from a melt according to the Czochralski method and can be used in semiconductor production to produce single crystal germanium ingots.

 A device is known (1. USSR author's certificate 599403, class C 30 V 15/26, 1980), which is a system for automatically controlling the diameter of a crystal grown from a melt according to the Czochralski method, in it receiving a signal proportional to the diameter of the grown crystal ( from the forming unit), based on the projection of the light ring around the crystal onto the sensitive photodetector of the optical unit, provided that the system maintains a constant level of melt in the crucible. Further, after the regulator, a signal proportional to the diameter is fed to the regulator for moving the speed of drawing the crystal and the side point of the heater, in order to reduce the mismatch of the current diameter of the crystal from the specified one.

 The constancy of the level of the melt in this device (system) is achieved by controlling the regulator for moving the crucible upward from the output of the computer, the inputs of which receive signals proportional to the speed, drawing the crystal to a given diameter and inner diameter of the crucible.

The disadvantages of the proposed device include the following:
1. The use of an optical method for measuring the diameter of a crystal, for noise immunity, as a rule, requires the presence of an open melt in the crucible with sufficient brightness of the light ring around the crystal and its round shape, which does not allow single crystals to be grown under low-gradient conditions (with a large faceting completely enclosed thermal equipment).

 2. The method used in this device for maintaining the melt level, based on the calculation of the crystal drawing speed, the inner diameter of the crucible and the given crystal diameter, due to the summation of the errors across all three channels at the input of the calculator, inevitably affects the accuracy of stabilization of the melt level, leading to its displacement during the drawing process and an error in the signal for measuring the diameter of the crystal by the optical system.

The presence of a weak luminosity of the light ring (meniscus) around the germanium crystal (936 ^o C), as well as the need for many brands of germanium to grow in closed thermal equipment in low-gradient conditions, which is accompanied by large faceting (non-circular shape of the crystal), significantly complicates the use of the optical measurement method diameter (as in the device [1]).

 The presence of melt vibration when grown by the Czochralski method (with a rotating crucible) complicates the use of laser melt level meters for germanium.

 All this led to the search for a new method for determining the control signal by diameter and the creation on its basis of a device (systems) for the automatic growth of germanium single crystals.

 A device, prototype (2. Patent 2128250 Russia, priority 01.16.97) is known, which is a microprocessor control system, under the control of which single-crystal ingots of a given area or diameter are grown with a round crystal shape, with a constant level of melt in the crucible stabilized for an account for controlling the crucible lifting speed upward by issuing control pulses to the crucible stepper drive at the moments of opening of the contact sensor relative to the screen floating on the metal surface then, in turn, causes movement of the crucible when mikropriostanovki up into periods closed state of the contact sensor.

 This device employs a method for determining a difference control signal as a function of the deviation of the current area or diameter, in a round shape, from a given one, based on the measured movements of the crystal and crucible (from the issued total control pulses to the step drive), during the diameter estimation, provided control the issuance of the magnitude of the crucible lifting speed up (during periods of open state of the contact sensor), greater than that required based on the conditions of constant melt level (for a given diameter of the grown crystal, its pulling speed and the inner diameter of the crucible), which, as a result, leads to a stop in the rise of the crucible, at the moment of contact sensor closure.

The disadvantages of this method and device include the following:
1. Due to the micro-suspension of the crucible during the growing process, the smoothness of the stroke of the crucible rod and the accuracy of determining the control signal are deteriorated.

 2. Calculation of the total crucible movement based on the issued pulses to the crucible stepper drive (during the diameter estimation) also gives a significant (periodic) error in the control signal estimation, due to the lack of information about the real movement of the crucible and crystal, taking into account the errors of the mechanical motion transmission system on the stock of the crucible and the seed.

 3. Evaluation of the control signal based on the operation of the contact sensor, relative to the floating screen, puts forward difficult requirements for the accuracy of the geometric shape of the manufacturing of the floating screen, which also determines the accuracy of the evaluation of the control signal.

The essence of this invention is as follows:
1. A method of controlling the process of growing single crystals from a melt, including changing the temperature of the melt T _s by controlling the drawing speeds V _s and crystal rotation ω ₃ , the lifting speeds V _t and the rotation of the crucible ω _T , while measuring the height of the crystal X _zz and the crucible’s movement X _SCC , at a constant melt level, with the introduction of the melt level sensor of the crucible upward velocity V _N during the open periods of the melt, which is greater by the advance value N than is necessary for the condition of the melt level constancy, p For these parameters, the drawing speeds V _s , the given crystal diameter d _s and the inner diameter of the crucible D, characterized in that during periods of the closed state of the melt level sensor, the crucible's lifting speed decreases by a reduction coefficient M, compared to the speed when the level sensor is open of the melt and subject to the conditions of stabilization of the level of the melt in the crucible, which allows, when the crucible is moving, with an increase in V _N and a decrease in the speed of M M by a decrease coefficient _M during the evaluation cycle T _c , based on the measurement For direct direct movements of the crucible X of the _TCS and the crystal of X _zts , taking into account the errors of the mechanical transmission system, select the updated difference control signal Y proportional to the deviation of the current crystal diameter d from the given d _z , introducing it into the control system to stabilize the area or diameter of the drawn crystal, its round shape.

2. Apparatus for controlling the process of growing single crystals from a melt, comprising a sensor 5 and controller 6 side point T _of the heater, crystal displacement sensor 11, the melt level sensor 3 which is triggered relative to its surface, withdrawal speed of rotation and drives 2 of the crystal 1, movement speed drives 10 and the rotation of the crucible 8, connected to the control microcomputer 7, characterized in that the level sensor of the melt 3 is located between the inner 20 and the outer crucibles 15 with the melt and is made with additional heating 19, from races the heater laid on it, powered by a source 18 controlled by a microcomputer 7, and is triggered when the temperature of the lower part of the sensor in contact with the melt is higher than the crystallization temperature of the melt, the device contains a movement sensor for the crucible 4, and the movement sensors of the crystal 11 and crucible 4 are made photoelectric and connected through the control microcomputer 7, with the corresponding mechanical gears 16 and 9.

 The proposed device and method of growing single crystals can significantly improve the accuracy of the estimation of the control signal, create a smoother and more non-stop movement of the crucible rod up during the growing process and thereby increase the accuracy of stabilization of the diameter of the grown ingots.

The proposed device based on this method (Fig. 1) is a microprocessor-based control system for growing single-crystal germanium ingots according to the Czochralski method, based on microcomputer 7, under the control of which (in chamber 12) a single-crystal ingot 13 (diameter d is grown) ) with a pulling speed V and the rotation ω _of the crystal _3, the molten metal 14, 15 located in the crucible (internal diameter D) is rotated at an angular velocity ω _T and simultaneously rises upwards at a speed V _m (for m D decreasing the melt in the crucible).

The ingot 13 (diameter d) is drawn from an additional intermediate crucible 20 (with a feed hole d _p ), which, in addition to ensuring the necessary purity of the melt in the intermediate crucible and uniform alloying of the grown ingot, allows you to position the level 3 sensor in a more overheated melt zone and use it for automatic heating of the lower part of the sensor, an additional heater 19, located around the melt sensor and powered by the source 18, with the minimum heating current I _{∂ set} by the computer, which allows to guarantee the temperature of the lower part of the sensor in contact with the melt is higher than the possible temperature of its crystallization and to ensure that the melt does not freeze on the sensor during operation.

 The signal from the level sensor 3 is fed through a smoothing chain C1, R1, R2 and computer 7 to make a decision on controlling the rise of the crucible up.

Control from the computer 7 of the speed of pulling the crystal V _s , rotation of the crystal ω ₃ , rotation of the crucible ω _T and movement v _{t of the} crucible is carried out through analog drives 1, 2, 8, 10, and the temperature of the side point of the heater 17 is controlled by the temperature sensor 5 and the controller temperature 6 on the instructions of T _s computer.

The readings on the movement of the crystal X _z (with discreteness Δ ₃ ) and the movement of the crucible X _t (with discreteness Δ _T ) are taken from the photoelectric displacement sensors 11 and 4, respectively, which are connected through the control microcomputer with the corresponding mechanical reducers 16 and 9, which allows achieving high accuracy of measuring the movements of the crystal and the crucible, taking into account the error of the mechanical motion transmission system.

In this microprocessor control system, an updated differential control signal Y is determined as a function of the deviation of the current area or crystal diameter from the given one, based on measured sensors for reading the direct movements of the crystal and the crucible, during the control signal evaluation cycle, provided that the melt level in the crucible remains constant, due to the fact that during periods of open state of the melt level sensor, the crucible's ascent rate is set higher by an advance value (N) than is necessary o for the condition that the melt level is constant (for a given d _диамет diameter of the crystal, the inner diameter of the crucible D and the current speed of drawing the crystal V _s ), and during periods of a closed state of the sensor, the rate of rise of the crucible up decreases by a decrease (in M times), compared with the speed in the open state of the sensor, the melt, while maintaining the conditions for stabilizing the level of the melt in the crucible.

Further, the refined difference control signal Y is used in the control system to reduce the imbalance in the diameter of the growing crystal, along the channels _Tz is the temperature of the side of the heater, _Vz is the pulling speed, ω ₃ is the crystal rotation speed, ω ₁ is the crucible rotation speed (with the corresponding laws regulation), which ensures stabilization of the diameter of the growing crystal during the entire technological cycle of crystal growth, without the use of optical and other methods, to stabilize the level of the melt and dividing the current diameter ingot.

где Т_ц - время периодической оценки сигнала Y, мин;
V_з - текущая скорость вытягивания кристалла, мм/мин;
Δ₃ - дискрета (цена) одного импульса перемещения кристалла, мм;
Х_зц - величина перемещения кристалла за время Т_ц в импульсах отсчета системы (фиксированная величина).The main relationships for determining the imbalance signal by this method (with a conditionally round crystal) are as follows:
With a fixed (according to the program) value of the crystal moving up X _zts (with discreteness Δ ₃ ), the system determines the cycle time of measuring (evaluating) the diameter T _c , which depends only on the current speed of the crystal moving along f-le (1):

where T _c - the time of the periodic evaluation of the signal Y, min;
V _s - the current speed of drawing the crystal, mm / min;
Δ ₃ - discrete (price) of one pulse of movement of the crystal, mm;
X _zc - the amount of movement of the crystal during the time T _c in the impulses of the reference frame of the system (fixed value).

,
где К_у - уставка диаметра системы;
Δ_T, Δ₃ - дискрета (цена) одного импульса перемещения тигля и кристалла, мм;
q_ж, q_т - плотности жидкой и твердой фаз кристалла, г/см³;
D - внутренний диаметр тигля, мм;
d_з - заданный диаметр кристалла, мм;
V_N - скорость подъема тигля вверх с опережением, мм/мин;
N - величина опережения скорости тигля;
В - коэффициент умножения уставки;
С - коэффициент опережения скорости.The value of the crucible lifting speed up V _N (ahead of N), with the sensor 3 open, is set from the relations determined by the formulas (2-4):

,
where K _y - the setting of the diameter of the system;
Δ _T , Δ ₃ - discrete (price) of one impulse of movement of the crucible and crystal, mm;
q _W , q _t - the density of the liquid and solid phases of the crystal, g / cm ³ ;
D is the inner diameter of the crucible, mm;
d _s - the specified diameter of the crystal, mm;
V _N - crucible lifting speed upstream, mm / min;
N is the magnitude of the advance of the crucible speed;
B is the multiplication factor of the set point;
C is the coefficient of speed ahead.

где d_max - максимальный возможный диаметр разращивания, мм.With this control of raising the crucible up, the control system should ensure that the crystal diameter does not grow larger than a certain maximum value determined by formula (5), beyond which it is unacceptable because of the possible lag of the crucible from the level sensor 3:

where d _max - the maximum possible diameter of the expansion, mm

где V_М - минимальная скорость подъема тигля вверх с понижением в М раз, мм/мин;
М - коэффициент снижения скорости.During the closed state of the level 3 sensor, a lower crucible lifting speed V _M (with a decrease of M times) is introduced, which is determined by the formula (6):

where V _M - the minimum speed of the crucible upward with a decrease in M times, mm / min;
M - coefficient of speed reduction.

где d_min - минимальный диаметр выращиваемого кристалла, мм.Subject to condition (6), the control system must not allow a decrease in the crystal diameter to less than a certain minimum value, which is determined by the formula (7):

where d _min is the minimum diameter of the grown crystal, mm

C≥4. (9)
Суммарное время движения тигля Т_м с пониженной скоростью за время цикла замера Т_ц и уточненный разностный сигнал управления у определяются по формулам (10-11):

Т_M - время движения тигля вверх суммарное со сниженной скоростью за время Т_ц, мин;
d - текущий диаметр слитка, мм;
Y - уточненный разностный сигнал управления;
Х_ТЦС - суммарное перемещение тигля за время Т_ц в импульсах отсчета;
А - коэффициент деления импульсов перемещения.The ratio of the coefficients M and C must satisfy the conditions (8-9):

C≥4. (9)
The total time of movement of the crucible T _m with a reduced speed during the measurement cycle T _c and the updated difference control signal y are determined by the formulas (10-11):

T _M - when driving up the total crucible at a reduced speed in the time T _n, m;
d is the current diameter of the ingot, mm;
Y is the adjusted difference control signal;
X _TCS - the total movement of the crucible during the time T _c in the impulses of reference;
A is the division ratio of the movement pulses.

d_зу=L•d_з, (13)

где d_зу - уточненный заданный диаметр выращиваемого слитка, мм.Relation (11) can be represented in the form of formulas (12-15):

d _zu = L • d _z , (13)

where d _zu - specified specified diameter of the grown ingot, mm

 Relations (12-13) give a direct functional relationship of the updated differential control signal, as a function of the deviation of the current diameter from the given one.

This method allows, at the same time as stabilizing the area of the growing crystal or its diameter, with a round shape, at any current values of all four control channels T _s , V _s , ω ₃ , ω _t , to introduce them as systematic, that is, according to the schedule, changes in the growth process, as well as placing the entire crystal in a closed cylindrical screen or closed thermal equipment, without visual viewing of the ingot.

Claims (2)

 1. A method of controlling the process of growing single crystals from a melt, including changing the melt temperature by controlling the rates of extrusion and rotation of the crystal, the rates of rise and rotation of the crucible while measuring the height of the rise of the crystal and the movement of the crucible at a constant level of the melt with the introduction of a velocity melt level sensor during open periods the crucible rises upward by a greater advance value than is necessary for the condition of a constant melt level, for given velocity parameters in pulling, a given diameter of the crystal and the inner diameter of the crucible, characterized in that during periods of closed state of the melt level sensor, the rate of rise of the crucible up decreases by a reduction coefficient compared to the speed when the melt level sensor is open and the conditions for stabilizing the melt level in the crucible are met, which allows for the movement of the crucible with the speed increased and decreased by a reduction coefficient during the evaluation cycle based on the measured direct movements of the crucible and crystal with Chet errors mechanical transmission systems allocate proximate difference control signal proportional to the current deviation from a predetermined crystal diameter, having got it into the control system to stabilize the diameter of the pulled crystal.  2. A device for controlling the process of growing single crystals from a melt, comprising a sensor and a regulator of the side point of the heater, a crystal displacement sensor, a melt level sensor that is triggered relative to its surface, crystal speed and crystal speed drives, crucible speed and rotation speed drives connected to the control micro -Computer, characterized in that the melt level sensor is located between the inner and outer crucibles with the melt and is made with additional heating from located on it a heater powered from a source controlled by a microcomputer, and is triggered when the temperature of the lower part of the sensor in contact with the melt is higher than the crystallization temperature of the melt, the device contains a sensor for moving the crucible, the crystal and crucible movement sensors being made photoelectric and connected through the control microcomputer with the corresponding mechanical gearboxes.