DE2449275A1 - DEVICE FOR PULLING A CRYSTAL FROM A MELT - Google Patents

Description

PATENT LAWYERS

DIPL.-ING. LEO FLEUCHAUS. DR.-ING. HANS LEYH

DIPL.-ING. ERNST RATHMANN

Monks 7i, October 16

Melchloretr. 42

Our reference: M0165P-1212

Motorola, Inc. 5725 East River Road. Chicago , Illinois V.St.A.

Device for pulling a crystal see from. a S. ^ ircvlz.e

The invention relates to a device for pulling a Crystal from a melt, (Lerer. OoerflächeA-iiveau v / er Tnd of pulling is kept constant.

The Czochralski method of pulling,? Xnes Kris \ everything is e ^ ..- known in common, and they are different! Massive "ν.ειι"nekaiit; in order to keep the surface level of the melt essentially constant while the crystal is pulled from the melt. These measures, whether it is a control system or a simple control system, are unsatisfactory because, on the one hand, they require enormous technical effort in order to obtain a good crystal quality and, on the other hand, hardly any further improvement in the crystal quality make possible.

60-9817 / 1075

BATH ORIGIWAL

η Μ0163Ρ-1212

The object of the invention is therefore to provide a device and to provide a system for raising and lowering the surface of the melt from which the Crystal is pulled, "automatically adjust," taking this Surface can be kept at a constant level within very narrow limits. This is intended for this purpose facility used to work and be very simple to set up and further improve the crystal quality both regarding the thermal stability as well as the crystal diameter make possible.

This object is achieved according to the invention in that a Motor drive for raising and lowering the crucible is available is that a first and a second radiation source each emits a light beam to the surface of the melt, where the angle to the vertical for the two light beams is different that a radiation receiver is that of the surface receives reflected light rays and depending on the changed angles of incidence of the reflected Light rays deliver a signal to a melt level controller when the surface shifts in level, and that the The melt level controller controls the motor drive via a motor control unit in such a way that the crucible is set to a desired one Level raised or is lowered.

Further features and refinements of the invention are the subject matter of further claims.

With the device according to the invention, it is possible to advantageously Way by using two rays that hit the surface of the at a slightly different angle Hitting the melt, the changed in the radiation receiver Determine the position of the reflected beam and derive a signal therefrom, which immediately reflects the change in the level of the melt is proportional. This signal is after another

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Processing fed to the drive motor for raising and lowering the crucible to keep it at its height to change until the surface of the melt in the desired level. A red light with a wavelength of 6500 A ^ is used for the light rays. > Γ preferably used. The aux'tr-jifenden on the receiving system Depending on their position, red light rays cause larger or smaller charge or discharge pulses to be generated, applied to a capacitor change its charge level accordingly, in order to use it for the height adjustment of the crucible to derive the corresponding control signal.

The advantages and features of the invention will also give you aas the following description of an exemplary embodiment in Connection with the claims and the drawing. Show it:

Fig. 1 is a partially sectioned schematic representation the inventive device for automatic Adjustment of the melting level when growing a semiconductor crystal;

FIG. 2 shows a plan view of the device according to FIG. 1;

Fig. 3 shows the circuit diagram of the electrical system of the device according to FIG. 1;

4a to 4c are schematic representations of operating states in realizing the invention.

In Fig. 1, a device 10 is shown with which a Semiconductor crystal 11 from a melt 12 geaogeu wei-cc-r. can. The semiconductor crystal can be made of silicon, geriraniuji or another suitable material.

- 3 - The

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g M0163P-1212

The device 10 can comprise a more or less cylindrical reaction chamber of conventional shape and of one Master cylinder 14, a base part 15 and a cover dome

16 exist. The interior of the reaction chamber 13 can be filled with an atmosphere suitable for the reaction to take place. Furthermore, a crucible is inside the reaction chamber 13

17, which can for example consist of quartz and is fastened on a shaft 18 which extends from the base part 15 into the Reaction chamber 13 protrudes and is connected to a gear 19. A drive motor 21 is assigned to the transmission 19, with the aid of which the crucible 17 can be set in rotation via the shaft 18 and raised or lowered to the surface 22 to keep the melt constant during the entire drawing process.

The crucible 17 is more conventional of a heater 23 Kind of surround. A bearing 24 is arranged on the covering dome 16 , through which a shaft 25 is guided, which carries the seed crystal 26 at its lower end. Wave 25 is on upper end connected to a gearbox 27, to which a motor is assigned to the seed crystal via the gearbox from the Draw melt. In the process, the seed crystal 26 is pulled away from the surface 22 of the melt 12, with a Neck-like tapered in diameter part 29, a shoulder 31 and finally the crystal in its final diameter form.

In the covering dome 16, observation windows 32 and 33 are also attached.

Opposite one another in a plane lying outside of a diameter, two further windows 34 and 35 are provided, through which a red light radiation is introduced and tapped. The red light radiation is supplied by a red light transmitter 36 with two red light sources 37 and 38 and occurs in the form of two bundles of rays 39 and 41

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into the reaction chamber. The beams are on one Point 4-2 aligned on surface 22 of melt 12. ' Reflected bundles of rays 43 and 44 emerge through the window 35 and. are received in a receiver 45. It will be ■ one . visible red light radiation used to ■■ Red light from the infrared and other frequencies associated with the hot surface of the silicon To distinguish radiation. ■ ''

The bundles of rays 39 and 4-1 are introduced into the reaction chamber through a water-cooled infrared filter.46. The reflected beams 4J and 44 also exit through water-cooled infrared filters 47. The red light sources in the red light transmitter 36 are excited via lines 48 and 49 from a melting level controller 50 to which the sensors ic. Signals delivered to the receiver 45 are fed via a line 51. The melt level controller supplies, ufcer Vrine L · · ..- device 52 control signals to a motor control 53 » ¹ U- üvlresponding control signals via a line 54 ά *: ~ ΰ Λοζ r 21 '. - The control signals cause the motor'' : - "j 3ί? η _t -melting crucible raises or lowers, as can be seen in detail from atsr".iacni'ol · - ^{v the} following explanation.

In Fig. 2 is a plan view of the reaction chamber ¹ Darr. This illustration shows the main cylinder 14 of the reaction chamber 13, the red light transmitter 56 and the red light receiver 45. The bundles of rays 39 and 41 are directed at the point 42 and are thereby reflected as bundles of rays 43 and 44 in FIG Direction of the radiation receiver 45 reflected.

FIGS. 3, 4a to 4c give further details. and their mode of operation, the same reference numerals being provided for the same functions and parts.

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BATH

: .- M0163P-1212

The melt level controller 50 according to FIG. 1 comprises an oscillator 55 »a modulator 56, a tuned AC amplifier 57, a demodulator 58, an amplifier 59 and connecting lines 61, 62, 63, 64 and 65

The oscillator 55 generates a square wave with relatively high frequency, e.g. 1 kHz, which is fed to the modulator 56 via the conductor 61. This modulator 56 is essentially represents a high frequency switch which first has one red light source 37 and then the other red light source 38 excited. The two red light sources 37 and. 38 switched on and off alternately. For example, 3. the high Signal level of the square wave 66 of the excitation of the red light source 37 and the low signal level of this square wave be assigned to the excitation of the red light source 38. These red light sources 37 and 38 can, for example, from light-emitting diodes, as indicated in Fig. 4a, exist. According to FIG. 4a, the red light source 37 is a lens system 37A assigned, which directs the bundle of rays 39 to the point 42. Correspondingly, the red light source 38 is a lens system 38A assigned, which the beam 41 is also on point 42 is directed. These bundles of rays are reflected at point 42 and emerge as bundles of rays 43 and 44, respectively the reaction chamber from ..

As the red light receiver 45, conventional and known Sensor elements such as a photodiode or photocells 45 Find use. In the red light receiver, a lens system 45A is also provided, which has a sufficiently large diameter has to detect both reflected beams 43 and 44.

The through the lens system 45 on the photosensitive element Impinging bundles of rays 43 and 44 generate electrical energy, which is tuned in a downstream AC amplifier 57 is amplified. That

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The amplified signal is sent to the demodulator 58 via the conductor 63 which provides a voltage signal, for example on a capacitor 67, in a conventional manner. If that Level of the melt 22 lies in the correct intended level, a certain charge results on the capacitor 67, so that no signal is fed to the motor 21 via the conductor 54- and this remains in the standing state. As the melting level rises, the charge in capacitor 67, for example, is increased, whereby a signal is fed to the amplifier 59 via the conductor 64- which is sent via the conductor 65 to the motor control 53 acts and thus sets the motor in rotation, which a lowering of the crucible 17 and thus the melt level triggers. If, on the other hand, the melt level is below the the intended level drops, the "charge of the capacitor" 67 from, so that via the conductor 64 · and the amplifier 59 via the motor controller 53 driven the motor in the reverse direction and the crucible 17 raises until the surface of the melt is at the correct level.

In Fig. 4-a, the melt level 22 is in the desired position shown, it being indicated that the surface of the melt is not completely flat, but rather criss-crossed by waves is. It is known from practice that when crystals are pulled in devices such as the present invention lie, the surface of the liquid silicon, germanium od. The like. Always with a running over the surface Crimp is provided. This ripple corresponds to one relatively low frequency of, for example, five Vibrations per second and should not be ignored when controlling the melt level. The frequency of the oscillator 55 niit 1 kHz is high enough to avoid the influence of the Eliminate ripple 22A on the mode of operation of the control as far as possible. At a certain point on the undulating surface this causes a sufficiently high number of oscillations of the high-frequency red light radiation so that the the ripple caused level difference disregarded

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can stay. The level point to be taken into account for the control can e.g. in the upper or lower vertex the crimp or lie in a plane located in between, assumed for the explanation of the invention becomes that point 42 is at the apex of the crimp.

If the melt level 22 runs through the correct point, namely the point 42 according to FIG. 4a, the reflected one lies The bundle of rays 44 on one side and the reflected bundle of rays 43 on the other side of the lens system 45A, based on the optical axis. The distance of the hitting The bundle of rays from the optical axis is the same size in this case. In this respect, the one striking the receiver 45 is also Energy share for the two bundles of rays 43 and 44 is the same. The square wave generated by the oscillator 55 66 has the effect, through the transmission via the conductor 62 and the modulator 58), that the energy component e.g. from the received radiation bundle 39 increases the charge of the capacitor 67 during the one half-wave, on the other hand during the excitation of the beam 41 of the demodulator 57 triggers a reduction in the charge of the capacitor 67. In this way receives the capacitor depending on the half-waves of the square wave of the oscillator 55 pulses that the Charge or discharge the capacitor. When the melt level 22 is in the desired level, they alternate for the charging and discharging pulses received the same value, so that on the capacitor 67 the average charge remains unchanged. As a result, no control signal is supplied by the engine controller 53 either, so that the Crucible 17 remains in the same level.

It can be seen that the angle of the bundle of rays 44 with respect to the perpendicular is equal to the angle of the bundle of rays 41 is. Correspondingly, it applies to the bundle of rays 43 that its angle, based on the vertical, is equal to the bundle of rays 39 is. The angle between the two rays

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bundle 4-1 and 44 is approximately 4-5 °, whereas the angle between the bundle of rays 39 and the bundle of rays 4-3 is slightly larger, since the red light sources 37 and are arranged side by side. The difference angle is very small, so that it can be disregarded for all practical purposes and an angle of approximately 4-5 ° can also be assumed for the angle between the bundles of rays 39 and 4-3. This angle of reflection is chosen arbitrarily and can be changed as required to adapt to the local conditions. ^y ·

In Fig. 4-b a state is shown in which the Melt level 22B is below normal melt level 22. Under these conditions, this hits from the beam 4-1 originating reflected bundle of rays 44 onto the lens system 4-5A at a point outside the optical axis, and although opposite to the conditions according to FIG. 4a. The reflected beam emanating from the beam 39 4-3 meets the lens system 4-5A on the same side the optical axis at the edge of the lens system. Under these conditions it is found that the reflected energy component of the 'beam 43 with much lower energy is received by the red light receiver 45, compared to the proportion of energy due to the beam 44.

With these conditions according to FIG. Over a period of several periods. there is an accumulation of the charge. the capacitor 67 in a positive sense, d.fa _o the capacitor voltage rises, since the positive "charging pulses, the negative charge pulses. numerically exceed. Thus, generated by the demodulator 58, a positive signal after amplification in

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Amplifier 59 is fed to motor control 53 and ultimately acts on motor 21. This control signal acting on the motor 21 raises the crucible Y] until the melt level 22B coincides with the level 22.

4c shows the conditions that arise when the melting level 220 is above the desired Melt level 22 is located. The bundle of rays 39, the Hitting the surface of the melt is called a bundle of rays 4-3 reflects and hits the lens system 45A next to the optical axis. In a corresponding manner, the bundle of rays 41 is reflected by the melt and hits as a bundle of rays 44 on the same side of the optical axis of the lens system 45A and that in the edge area. Corresponding the conditions in the operating states shown in FIGS. 4a and 4b is determined by the red light receiver received a smaller amount of energy for the reflected beam 44, which means that smaller charging pulses for this energy component can be fed to the capacitor 67. The bundle of rays received immediately next to the optical axis 43, 'which originates from the bundle of rays 39, causes larger charge impulses acting as discharge impulses on the capacitor 67 work. This gives an average of the effect of the smaller charge pulses and the larger discharge pulses an average state of charge on capacitor 67, which corresponds to a reduced charge. This takes the on the charge dependent capacitor voltage, which via the conductor 64 and the amplifier 59 on the motor control 53 acts to send a control signal via line 54 to the motor 21 to feed, which drives the motor in one direction, .the ibsenken the crucible 17 and thus the melt level 22C triggers until the melt level is back at the desired level 22. Is this state of affairs in the Ir-rich? to have the charge pulses and discharge pulses acting on the capacitor 67

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impulses of the same size, so that their effect is alternating Half-waves of the oscillator oscillation keep the charge level constant. "

The control system described represents a closed loop system represents in which the melt level automatically from the motor 21 and the motor controller 53 depending on the location the melting level is set to a desired level when the melting level changes during operation.

The light-emitting diodes of the red light source 37 and 38 can emit red light in the range from about 5000% to about 10000 S. A preferred wavelength is 6500 S. The filters 46 are designed as narrow bandpass filters in order to transmit the radiation with a wavelength of 6500 Å with a bandwidth of ± 50 i. The filter 4-6 can comprise two relatively thin quartz plates, between which there is an approximately 1 cm thick layer of water. Such a quartz filter, which is sealed along the edges, reduces the proportion of infrared radiation in order to protect itself and the receiving device from heating up, which could not be avoided if the infrared radiation were to act. The infrared filter 47 is constructed in the same way as the filter 46. The photocells 45 can be designed in a conventional manner, it being possible for two photocells instead of one to be provided in the same circuit arrangement, which, however, results in a higher noise level. Better results have been achieved using a single photocell and higher quality electronic circuitry *.

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Claims (7)

2U9275 M0163P-1212 claims 1. Device for pulling a crystal from a melt, its surface level during pulling is kept constant, characterized in that a motor drive (12, 21) for lifting and Lowering of the crucible (17) is present that a first and a second radiation source (37, 38) each a light beam (39, 4-1) to the surface (22) of the Emits melt, the angle to the vertical for the two light rays being different, that one Radiation receiver (4-5) receives the light rays reflected from the surface (22) and as a function of the changed angles of incidence of the reflected light rays with a shift in level of the Surface supplies a signal to a melt level controller (50), and that the melt level controller (50) over a motor control (53) controls the motor drive in such a way that the crucible (17) is set to a desired Level is raised or lowered. 2. Device according to claim 1, characterized in that the radiation sources are red light radiation deliver. 3. Apparatus according to claim 2, characterized in that the red light radiation a Has a wavelength of about 6500 Å. 509817/1075 ju M0163P-1212 4-. Device according to one of Claims 1 to 3, characterized marked that the radiation source and the radiation receiver are each provided with a narrow-band bandpass filter (4-6, 4-7). 5. Device according to claim 4-, characterized in that g e k e η η, that the bandpass filter transmits radiation with a wavelength of about 6500 S ± 50 S. 6. Device according to one or more of claims 1 to 5, characterized in that the Melt level controller (50) on the sum of the reflected radiation from the first and second radiation source appeals to. 7. The device according to claim 1, characterized in that g e k e η η - ζ e i c hn e t that the angle of reflection of the radiation is about 4-5 °. 509817/1075