JPH08301689A - Detection of optimum melting liquid temperature in production process of semiconductor single crystal - Google Patents

Abstract

PURPOSE: To enable high-accuracy detection without using a radiation thermometer or a dichromatic thermometer by using a phenomenon as an index in which a seed crystal and a highly bright ring-like part of melted liquid face are observed as concentric circles. CONSTITUTION: A seed crystal in a crucible and the solid-liquid interface of a melted liquid face are observed by a television camera and a video signal corresponding to horizontal scanning line crossing a meniscus ring generated on the solid-liquid interface is obtained and peak number corresponding to brightness of meniscus formed to video signal every one of horizontal line corresponding to each position of the meniscus ring is counted, and a process of decreasing number of peaks from four peaks through three peaks to two peaks, accompanied with the movement of horizontal scanning line from the upper end to the lower end of one television screen and the presence of a process of decreasing the number of peaks from four peaks to three peaks or from three peaks to two peaks are detected. Thereby, optimum temperature of melted liquid in the crucible is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the temperature of a semiconductor melt by processing a video signal from a video image from a television camera in the process of manufacturing a semiconductor single crystal by the Czochralski method (CZ method). It is about.

[0002]

2. Description of the Related Art Conventionally, as one of methods for producing a silicon single crystal which is a basic material of a semiconductor integrated circuit, a Czochralski method (hereinafter referred to as CZ method) for pulling a cylindrical single crystal from a raw material melt in a crucible is used. Is used. In the CZ method, a crucible installed in the main chamber of a single crystal manufacturing apparatus is filled with high-purity polycrystalline silicon, the polycrystalline silicon is heated and melted by a heater provided on the outer periphery of the crucible, and then attached to a seed chuck. The seed crystal is immersed in the melt, and the seed chuck is pulled up while the seed chuck and the crucible are rotated in the same direction or in the opposite direction to grow a silicon single crystal.

FIG. 6 shows a schematic structure of a conventional general silicon single crystal manufacturing apparatus by the CZ method. 31
Is a wire winding motor, and 32 is a wire winding drum. 33 is the wire winding motor 3
1. A motor that gives rotary motion to a vacuum container in which the wire winding drum 32 is installed.
Finally, through the rotation of 4, the single crystal grown from the seed crystal is given a rotary motion. Reference numeral 35 is a television camera, 36 is a transparent quartz glass window, and 37 is a seed chuck for holding a seed crystal. Further, 38 is a melt surface, 39 is a graphite heater for heating and melting the polycrystalline silicon material in the crucible,
Reference numeral 40 is a graphite heat insulating material, 41 is a motor that gives a rotational motion to the crucible via a crucible pedestal, and 42 is a crucible shaft lifting device.

When pulling the silicon single crystal, the meniscus ring generated at the boundary between the melting surface 38 and the silicon single crystal is photographed by the television camera 35, and the obtained video signal is transmitted through the camera control unit 43 to the radiometer unit. Input to 44, the diameter of the single crystal crossing the meniscus ring is calculated. Then, the diameter control device 45 controls the pulling rate of the seed crystal and the melt temperature to bring the diameter of the pulled single crystal close to the set value.
Reference numeral 46 is a television monitor.

In the above-mentioned single crystal manufacturing apparatus, in order to make the single crystal dislocation-free, when growing the crystal from the seed crystal, first, the diameter is controlled to 3 to 4 mm and the diameter is set to 100 to 1
It is grown to a length of 50 mm, and then expanded and grown to a predetermined single crystal diameter. 3-4 mm diameter for this dislocation free
The process of growing a crystal in this state is called necking.

In this necking process, if the temperature at the start of the process is not appropriate, the crystals will suddenly thin during the necking and may be separated from the melt, or 3 to 4 mm.
However, there is a problem that it becomes difficult to make dislocation free. That is, when the temperature of the melt in the crucible is high, the crystal diameter of the necking portion is rapidly reduced, and the melt and the crystals are separated instantaneously. On the other hand, when the melt temperature is low, the diameter rapidly increases and it becomes difficult to eliminate dislocation. Therefore, various methods for accurately measuring the melt temperature during necking have been proposed. For example, in Japanese Unexamined Patent Publication (Kokai) No. 4-325488, the success rate of the necking step is increased by accurately controlling the surface temperature of the melt before immersing the seed crystals. in this case,
In order to accurately measure the temperature of the molten liquid surface, JP-A-4-25
The radiation thermometer must be arranged right above the surface of the molten liquid, as described in Japanese Patent No. 4488.
As described in 88, a two-color thermometer that measures the liquid surface temperature from the ratio of radiant energy of two wavelengths is required.

[0007]

However, according to these conventional techniques, since the position of the melt surface at which necking is actually performed is the center of the crucible made of quartz glass for containing the melt, the radiation temperature If the meter is set to measure vertically from the melt surface, the seed crystal holder 37
In addition, since it interferes with the seed crystal vertical movement drive device 32, the drive device 33 for rotating the seed crystal (see above, see FIG. 6), etc., it is necessary to observe a position at least 10 cm or more away from the center.

The temperature of the molten liquid surface usually has a large temperature gradient in the radial direction, and largely depends on the rotational speed of the crucible, the relative positional relationship with the heater, and the flow rate of argon gas introduced into the furnace. It is well known to those skilled in the art that the temperature distribution changes. Therefore, even if the temperature of the melt surface distant from the central portion can be controlled accurately, the temperature of the central portion where necking is actually carried out varies greatly depending on the conditions inside the furnace. Therefore, it was difficult to accurately control the central portion of the furnace to an appropriate temperature for necking. In addition, the two-color thermometer is more than twice as expensive as a normal radiation thermometer in the single wavelength region, and it can be installed so that it can be observed from the vertical direction with respect to the melt surface. Often structurally difficult.

Therefore, when the portion called a meniscus ring formed at the contact portion between the seed crystal and the melt surface has the optimum melt temperature for necking, the present inventors have found that a high brightness ring-shaped portion is Focusing on the overlap, we used this phenomenon as an index of the optimum melt temperature to stabilize necking. In view of the above problems, the present invention provides a method for accurately detecting the optimum melt temperature during necking of the central portion of the furnace without using a radiation thermometer or a two-color thermometer whose temperature measurement is unstable. That is the purpose.

[0010]

Therefore, according to the present invention, in the step of producing a semiconductor single crystal by the Czochralski method (CZ method), the solid-liquid interface in the crucible is observed by a television camera, and the solid-liquid interface is obtained. A video signal corresponding to a horizontal scanning line that crosses the meniscus ring is generated, and the luminance of the meniscus ring formed in each video signal of the horizontal scanning line corresponding to each position of the meniscus ring is obtained. The process of counting the number of peaks and decreasing the number of peaks from four to three with the movement of the horizontal scanning line from the upper end to the lower end of one television screen to two, or 4. The first feature is to detect the existence of the process of decreasing from three to three or from three to two and detect the optimum temperature of the molten liquid in the crucible, which corresponds to the brightness of the meniscus. Pee The number of the numbers increases from 4 to 3 after 2 to 3 with the movement of the horizontal scanning line from the upper end to the lower end of one TV screen, or from 3 to 4. The second characteristic is to detect the existence and detect the optimum temperature of the molten liquid in the crucible.
Furthermore, the temperature of the semiconductor melt is automatically adjusted to reduce the difference between the detection frequency of the number of peaks corresponding to the brightness of the meniscus and a preset threshold value in the manufacturing equipment. It is provided with a means for adjusting.

[0011]

In the present invention, the meniscus portion is observed by the television camera, it is determined that the high-luminance ring-shaped portion of the meniscus is double in the image, and the horizontal scanning line intersecting with the meniscus on the television screen is detected. It is detected that the number of peaks corresponding to the high luminance of the constituent video signals changes peculiarly as the scanning of one screen progresses.

As shown in FIG. 2, when the scanning is started from the upper part of the seed crystal, the number of peaks appearing on one scanning line is
It changes in the order of 0 to 2 to 4 to 3 to 2-1 to 0. However, in reality, the height of each peak changes individually due to the rotation of the seed crystal and the local change of the surface temperature of the melt, so that the change in the number of peaks as described above is not necessarily observed on all screens. It is not always detected.

Since the change of 0-2, 1-0 occurs not only in the double ring but also in the case of the single ring, actually, as a change pattern peculiar to the double ring, among the changes of 4-3-2, It is desirable and easy to detect either a 4-3 change or a 3-2 change.

When the change pattern is detected on one screen, the circuit is configured to output one pulse, and if it is detected stably for each screen, a normal television camera is used. 60 seconds per second for a video system
The frequency of the pulse output is 60 because the screen is updated.
It becomes Hz.

Since this frequency is considered to be roughly proportional to the clarity of the double ring, as described above,
By converting this frequency into an analog voltage and inputting it to the control computer, it is possible to automatically determine the optimum temperature and adjust the optimum temperature. Further, this detecting operation can be performed easily and inexpensively as a function addition to the television camera system used for controlling the necking diameter.

For example, FIG. 1 of JP-A-2-164789.
The pulse counter 12 described in 1 can count the number of pulses for each scanning line. By adding the function of the present invention to this counter portion, it is possible to detect a change of 4 to 3 in the count number. You can

As shown in FIG. 3, the threshold level (threshold value) for detecting the number of pulses may be set separately from the threshold level (threshold value) for measuring the diameter. For example, it is possible to detect the optimum necking temperature without affecting the conventional diameter measurement function.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a semiconductor single crystal growth apparatus according to the present invention will be described in detail below with reference to FIG. In this embodiment, a two-dimensional CCD camera is used and the focal length is 200 mm.
The image of the vicinity of the solid-liquid interface of the seed crystal and its video signal are obtained using the lens. For the video signal, a waveform-shaped pulse is obtained by the threshold level setting circuit 1 and the comparator 2 with respect to the waveform showing the luminance above the threshold level, and the pulse width discrimination circuit 3 obtains a pulse having a predetermined pulse width or more. Only pulses are passed. This makes it possible to prevent noise due to bit defects in the two-dimensional CCD sensor.

The counter 4 which is reset by the horizontal synchronizing pulse counts the pulse for each scanning line. The output of the counter 4 is compared with the code (n = 4) of the digital switch 6 set separately by the digital comparator 5 at the end of scanning, and then reset by the slightly delayed horizontal synchronizing pulse. At this time, if the count number of the counter 4 is 4, the output of A = B of the comparator 5 becomes “H level”, and the flip-flop 7 inputs this and transits to “state of outputting H level”. To do.

That is, in one screen, there are four peaks showing brightness above the threshold level on one scanning line.
When there are more than one, the flip-flop 7 maintains "H level" until the scanning of the screen is completed.

When the counter 4 once counts four pulses and then counts three pulses in the same screen, similarly, the output of A = B of the comparator 8 becomes "H".
This output is input to the gate circuit 10, but when four pulses have already been detected, the input 12 of the gate circuit 10 is at "H level", and therefore its output is also ""Hlevel", and the output of the flip-flop circuit 11 also becomes "H level".

At the end of scanning one screen, each flip-flop circuit 11 is reset by the pulse VDD slightly delayed from the vertical synchronizing pulse VD.
When the output of the flip-flop circuit 11 is “H level”, the gate circuit 13 outputs a pulse having the same pulse width in synchronization with VD. The output of the gate circuit 13 is F-
It is input to the V converter 14 and converted into an analog voltage proportional to the pulse frequency. Therefore, 1 in 1 screen
It is possible to reliably detect that there is a process in which the number of luminance peaks appearing on one scanning line decreases from four to three.

As described above, the above method is expanded to 4 to 3 to 2.
It is also easy to generate a single-shot pulse only when the number of pulses changes, but since the product of detection probabilities of 4 to 3 and 3 to 2, the single-shot pulse generation frequency decreases.

It is basically possible to turn the TV camera upside down and confirm that the number of pulses counted in the order of operation of the TV screen changes to 2 to 3 to 4 and use it as an index of the optimum temperature. This is possible with the device configuration shown in FIG. Also, F-V
It is also easy to output an analog voltage that is approximately proportional to the number of pulses by an integrating circuit without using a converter.

In this embodiment, the parts forming the circuit are
This can be realized by using ten or more ICs having the smallest scale called L, and the function can be added at an extremely low cost.

The diameter measurement required for controlling the diameter of the aperture is conventionally performed by measuring the pulse width of the pulse waveform-shaped by the threshold level set separately. Details of these are described in Japanese Patent Application Laid-Open No. 2-164789 filed by the present applicant.

The above detection output is input to the control computer to determine whether or not the temperature is appropriate for necking, and to correct the temperature if it is not appropriate. Further, after the necking is automatically started by the device of the present invention, the automatic diameter control of the necking can be performed by the diameter measurement output obtained at the same time.

In the silicon single crystal manufacturing apparatus shown in FIG. 6, the width measuring unit indicated by 44 was replaced with the apparatus having the structure of the present invention (see FIG. 1) to perform actual necking. 60 kg of polycrystalline silicon material was used. A quartz crucible holding a silicon melt has a diameter of about 460 mm.

In the present embodiment, in the configuration shown in FIG.
When a circuit adjusted to output a voltage of 10 Volt at a pulse frequency of 60 Hz using a converter was used and the meniscus looked like a complete double ring, 4.
A varying voltage around 5 Volt to 6.5 Volt was obtained. It is considered that this fluctuation is due to the local temperature fluctuation due to convection of the molten liquid, the shape of the meniscus changed, the fluctuation of the luminance peak height, and the unstable detection of individual peaks. Since these fluctuations are every few seconds, averaging for about 1 minute can reduce the fluctuations to a practically acceptable level.

After that, when the temperature was intentionally lowered and the double ring disappeared, the output voltage was 0.1 Volt or less. The relationship between the FV converter output voltage and the heater temperature at the start of necking was obtained as shown in FIG. Further, the relationship between the output of the FV converter and the heater temperature is shown in FIG. The heater temperature shows a deviation from the temperature when the temperature that gives the optimum value of the output of the FV converter (the voltage when the necking success rate is highest in FIG. 4) is 0 ° C.

From FIG. 5, it can be seen that if the initial heater temperature setting is within 15 ° C. above and below the optimum value, the FV converter output can be controlled to the optimum output by controlling the heater temperature.

In this embodiment, the optimum temperature for necking is obtained by a method commonly called cascade control in which the deviation between the output of the FV converter and its set value (optimal value) is integrated and fed back to the heater temperature set value. It was automatically controlled.

If the initial set temperature is higher than the optimum value by 15 ° C. or more, the tip of the seed crystal is completely melted and separated from the melt surface. Further, when the initial set temperature is lower than the optimum value by 15 ° C. or more, the seed crystal grows to spread to the melt surface. In any case, if the diameter measurement by the television camera is performed in parallel, it can be detected as a sharp decrease or increase in the diameter measurement value, and the operator can be automatically alerted accordingly. However, usually, if the initial setting temperature of the heater temperature is set to a value that can obtain the optimum temperature during the crystal growth of the previous batch, it is easy to control the temperature within approximately 7 ° C. above or below the optimum value.
After that, the optimum temperature may be automatically controlled by the above-mentioned cascade control.

[0034]

Since the present invention is constructed as described above, it is possible to accurately determine the optimum melt temperature at the time of necking in the center of the furnace without using a radiation thermometer or a two-color thermometer whose temperature measurement is unstable. It can be detected well. As a result, there is an excellent effect that the success rate of the necking process is significantly increased, the time required for rework due to failure and the temperature adjustment of the operator is reduced, the productivity of the single crystal is improved, and the manufacturing cost can be reduced. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a video signal processing circuit according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a television image of a meniscus and a waveform of a video signal at an optimum temperature.

FIG. 3 is an explanatory diagram showing setting of threshold levels (threshold values) for pulse number detection and diameter measurement.

FIG. 4 is a graph showing the relationship between the necking success rate and the FV converter output voltage.

FIG. 5 is a graph showing the relationship between FV converter output and heater set temperature.

FIG. 6 is a schematic configuration diagram of a general silicon single crystal manufacturing apparatus.

[Explanation of symbols]

 1 Threshold level setting circuit 2 Comparator 3 Pulse width discrimination circuit 4 Counter 5 Digital comparator 6 Digital switch 7 Philip flop circuit 8 Digital comparator 9 Digital switch 10 Gate circuit 11 Philip flop circuit 12 Gate signal 13 Gate circuit 14 F -V converter

Claims (3)

[Claims] 1. In a process of manufacturing a semiconductor single crystal by the Czochralski method (CZ method), a solid-liquid interface in a crucible is observed by a television camera, and horizontal scanning is performed across a meniscus ring generated at the solid-liquid interface. A video signal corresponding to a line is obtained, the number of peaks corresponding to the brightness of the meniscus formed in the video signal of each horizontal scanning line corresponding to each position of the meniscus ring is counted, and the number of peaks of this peak is counted. The number decreases from 4 to 3 with the movement of the horizontal scanning line from the upper end to the lower end of one TV screen, or decreases from 4 to 3 or from 3 to 2. A method for detecting an optimum melt temperature, which comprises detecting the existence of a process of decreasing to individual pieces and detecting the optimum temperature of the melt in the crucible. 2. The number of peaks corresponding to the luminance of the meniscus increases from 2 to 3 to 4 with the movement of the horizontal scanning line from the upper end to the lower end of one television screen. 2. The method for detecting a melt temperature according to claim 1, wherein the optimum temperature of the melt in the crucible is detected by detecting the existence of a process or a process of increasing from three to four. 3. The temperature of the semiconductor melt is automatically adjusted so as to reduce the difference between the detection frequency of the number of peaks corresponding to the brightness of the meniscus and a preset threshold value. An apparatus for producing a semiconductor single crystal, which has a means for adjusting.