JPS63281022A - Level measuring method for molten liquid of single crystal growing device - Google Patents

Abstract

PURPOSE:To detect a molten liquid level directly by capturing a reference point determined on a radiation screen and a reflection image of the reference surface for the molten liquid surface by a linear sensor, and finding the isolation dimension between the reference point and reflection image on the sensor. CONSTITUTION:A camera 11 is arranged outside facing the observation window 1b of a chamber 1. The linear sensor 2 of the camera 11 is directed crossing the tangent to the curved edge part of the lower edge 5c of the tapered part 5b of the radiation screen 5 and captures an image Na of the lower edge 5c and a reflection image Nb of the edge 5 for the molten liquid surface. Then electric signals corresponding to the images Na and Nb captured by respective photodetecting elements are outputted. An arithmetic control part 13 detects the positions of the images Na and Nb according to the signal level from the sensor 12 and computes the isolation dimension (h) between the lower edge 5c and reflection image from those positions. Therefore, the distance lfrom the lower edge 5c to the molten liquid surface is h/2. A control part 13 compares the distance l with a predetermined reference level value and outputs a control signal to a motor M2 for a crucible 2 so as to eliminate the difference, thereby adjusting the position of the crucible 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for measuring the level of the melt surface of a single crystal raw material in an apparatus for manufacturing single crystals, mainly semiconductors, by the Czochralski method (CZ method). Regarding.

[Prior art]

This type of single crystal growth apparatus is generally constructed as shown in FIG.

FIG. 4 is a schematic vertical cross-sectional view of a conventional device, and numeral 1 in the figure indicates a chamber. A double-structured crucible 2 in which a quartz container 2b is arranged inside a graphite container 2a is disposed in the center of the chamber 1, and a heater 3 and a heat-insulating wall 4 are arranged around the outer periphery of the crucible 2.
are disposed concentrically with gaps constituting exhaust passages between them, and a radiation screen 5 is further disposed from the heat insulating wall 4 to the peripheral edge of the melt surface of the crucible 2. be.

A pulling port 1a for the single crystal 6 is opened in the upper wall of the chamber 1, and a pulling shaft constituting a pulling device is introduced into the chamber 1 through the pulling port 1a, and a seed crystal fixed to the pulling shaft is introduced into the chamber 1. The single crystal 6 is grown on the lower end of the crystal 7 while being pulled up.

The radiation screen 5 consists of a flat annular rim 5a and a truncated conical tapered part 5b whose diameter decreases downward from its inner edge, and the outer edge of the annular rim 5a is placed on the peripheral edge of the heat retaining wall 4. to block radiant heat from the crucible 2, heater 3, melt surface, etc., increase the temperature gradient in the pulling direction of the single crystal 6, and at the same time prevent Ar, etc., from being fed from above the chamber 1 toward the crucible 2. A carrier gas is guided into the crucible 2, and SiO gas etc. generated from the crucible 2 are guided below the crucible 2 and discharged from there to the outside of the chamber.

By the way, in such a single crystal growth apparatus, the single crystal 6
Changes in the growth conditions of crucible 2 cause polycrystalization, so not only the temperature but also the level of the melt surface in the crucible 2 must be kept constant, and the level of the melt surface must also be constantly monitored. , the change in the level of the melt surface due to the pulling of the single crystal 6 is compensated for by adjusting the position of the crucible 2 itself.

That is, the single crystal diameter during pulling is φ. , the diameter of the melt surface is φ
, the crucible rising speed V for maintaining the melt surface at a constant height is determined by the following (Equation 11).

However, ρC: Specific gravity of crystal ρ; Specific gravity of melt [Problem to be solved by the invention] However, the quartz container 2b constituting the crucible 2 has variations in its inner diameter, and the quartz container 2b and graphite container 2a The inner diameter of both is eroded by the reaction with SiO and the inner diameter of each changes, resulting in variations of several cranes for each pulling batch, making it difficult to make accurate corrections, making it difficult to accurately control the rise of crucible 2, and causing polycrystalline formation. This phenomenon occurs frequently, and due to fluctuations in the melt surface level, the melt comes into contact with the lower edge of the radiant screen, contaminating the melt, and this also blocks the passage of exhaust gases such as SiO. There was a problem.

The present invention was made in view of the above circumstances, and its purpose is to directly detect the melt level by using a part of the existing equipment as is, without making any special modifications. The present invention provides a method for measuring a melt level.

[Means for solving problems]

In the method of the present invention, a reference point is set on a part of the radiation screen that is an immovable part above the melt surface, the reference point and the reflected image of the reference point on the melt surface are captured by a linear sensor, and the reference point is set on the linear sensor. The distance from the reference point to the melt surface is calculated based on the distance between the reference point and the reflected image.

[Effect]

This makes it possible for the method of the present invention to directly grasp changes in the level of the melt surface, regardless of the deformation or volume change of the crucible itself.

〔Example〕

Hereinafter, the method of the present invention will be specifically explained based on drawings showing examples thereof. Figure 1 is a schematic sectional view showing the implementation state of the method of the present invention, Figure 2 is an explanatory diagram of the measurement principle, and Figure 3 (A).
An explanatory diagram showing the positional relationship between the beam near sensor, the reference point captured by it, and its reflected image. Figure 3 (b) is a waveform diagram showing the signal level. In the diagram, 1 is the chamber, 2 is the crucible, and 3 is the heater. , 4 indicates a heat insulation wall. A heat retaining wall 4 is disposed inside the chamber 1 along its side periphery, and a crucible 2 is disposed in the central portion surrounded by the heat retaining wall 4.
A heater 3 is disposed between them with a gap forming an exhaust air passage between them, and a radiant screen 5 extends from the heat retaining wall 4 to the peripheral edge of the melt surface in the crucible 2. It is arranged.

The crucible 2 has a double structure in which a quartz container 2b is fitted inside a graphite container 2a, and the upper end of a shaft 2c passing through the bottom wall of the chamber 1 is connected to the center of the bottom. Motors M, , M, connected to the lower end of the shaft 2C
It can be rotated and raised and lowered.

A single-crystal pulling port 1a that also serves as a supply port for atmospheric gas in the chamber 1 is opened at the center of the upper wall of the chamber 1, and an observation window 1b is opened at one location around the single-crystal pulling port 1a. A protection tube 8 is provided upright at the pulling port 1a, and a camera 11 is provided facing outside the observation window 1b.

A pulling shaft 7a is suspended from the upper end of the protection tube 8, and a seed crystal 7 is suspended from the lower end of the shaft via a chuck.
Further, the upper end of the pulling shaft 7a is a motor M.

It is connected to the rotation and lifting functions equipped with M4, and after the seed crystal 7 is blended with the melt, the single crystal 6 is grown at the lower end of the seed crystal 7 by rotating and raising it. There is.

The radiation screen 5 is constructed by providing a tapered part 5b on the inner peripheral edge of a metal annular rim 5a, the diameter of which decreases downward from here and is inclined to form a hollow inverted truncated cone shape. It is held on the heat retaining wall 4 by suspending the outer peripheral edge thereof in contact with the heat retaining wall 4.

As shown in FIGS. 2 and 3, the camera 11 places a linear sensor 12 at the imaging position of the lens lla, and within its field of view, the lower edge 5C of the tapered portion 5b of the radiation screen 5 and the reflected image of the lower edge 5c with respect to the melt surface. The installation position and installation angle (approximately 30 degrees) are set so that the image can be captured.

The linear sensor 12 is oriented perpendicularly to the tangent to the curved edge of the lower edge 5c as shown in FIG. The length is set to capture both of the
It is designed to output an electrical signal according to the brightness of the images Na and Nb captured by each light receiving element, and the output is read into the arithmetic control section 13.

Among the images captured by the linear sensor 12, the image Na of the lower edge 5c is relatively dark, while the reflected image Nb from the melt surface shows that the melt surface itself is at a high temperature, and that the back surface of the lower edge 5c is exposed to heat from the heater 3, etc. The light is reflected and the melt surface is illuminated by the reflected light, making it extremely bright, and the signal level of the electrical signal output from the light receiving elements of each part of the linear sensor 12 is as shown in Figure 3 (b). become. That is, the signal level is highest at the image receiving position of image Nb, exhibits a substantially constant level from there to the image receiving position of image Na, and decreases rapidly after passing the image receiving position of image Na.

The calculation control unit 13 detects the positions of the images Na and Nb based on the signal levels from these linear sensors 12, and calculates the distance between the lower edge 5c of the tapered portion 5b and the source of the reflected image based on these positions. .

That is, if the distance from the lens lla of the camera 11 to the lower edge 5C is a, the distance from the lens lla to the linear sensor 2 is b, and the inclination angle of the optical axis of the lens lla is θ, the following relational expression holds true.

-a (Nb -Na) mΔd However, Δd: Size of a single light receiving element in the longitudinal direction of the linear sensor 2 Nb-Na: Image Na on the linear sensor.

The distance l from the lower edge 5C of the tapered portion 5b to the melt surface is given by the following equation (3).

1='/2h (3) The arithmetic control unit 13 compares the calculated l with a predetermined reference level value, and controls the motor M2 for the crucible 2 to eliminate the difference.
A control signal is output to the crucible 2 to adjust the position of the crucible 2.

In the above embodiment, a case has been described in which the level of the melt surface is detected using the lower edge 5c of the tapered portion 5b of the radiation screen 5 as a reference point, but the present invention is not limited to this, and instead of the radiation screen 5, It is also possible to use another immovable member as a reference point or to arrange a special reference member.

[Test example]

Using an 18-inch crucible, 60 kg of silicon polycrystalline grains as a raw material were put into it, and 1.5 kg of silicon single crystal with a diameter of 150 fl. During the pulling process at a speed of Owm/min, the melt surface level was measured by the method of the present invention as described above, and the position of the crucible was controlled based on this. The distance between the lower edge of the radiation screen and the melt surface was It was confirmed that the change could be kept within the range of ±0.3.

In the above embodiment, the tapered portion 5b in the radiation screen 5
Although we have explained the case where the melt surface level is detected by determining the distance between the image Na of the lower edge 5c and the image Nb of its reflected image, and the position of the crucible is controlled based on this, in reality, the radiation screen Since the position of the lower end edge 5C of 5 is immovable, it is sufficient to focus only on the position of the image Nb on the linear sensor 12.

Therefore, when the image Nb moves to the opposite side of the image Na on the linear sensor 12, it means a decrease in the melt level, and when it moves toward the image Na side, it means an increase in the melt level. , the position and movement speed of the crucible 2 may be controlled so that the position of the image Na does not change from the initially determined position.

〔effect〕

As described above, in the method of the present invention, a reference point is set above the melt surface and the distance from this reference point to the melt surface is determined. It has become possible to accurately detect changes in the liquid level,
It is possible to accurately and quickly adjust the height of the crucible in accordance with this, maintain stable single crystal growth conditions, and greatly suppress the frequency of occurrence of polycrystalline phenomena. The present invention has excellent effects, such as being able to prevent inconveniences such as contact between the melt and the radiation screen due to changes in the temperature, and closure of the exhaust gas passage due to this.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the implementation state of the method of the present invention, Figure 2 is a partially enlarged explanatory diagram, Figure 3 is an explanatory diagram showing the measurement principle, and Figure 4 is an explanatory diagram showing the measurement principle.
The figure is a schematic vertical cross-sectional view of a conventional device. 1... Chamber 2... Crucible 3... Heater 4.
...Heat insulation wall 5...Radiation screen 5b...Tapered portion 5c...Lower edge 6...Single crystal 7...Seed crystal 11...Camera 12...Linear sensor 13.
...Arithmetic control section Na, Nb... Image patent Applicant: Osaka Titanium Manufacturing Co., Ltd. (1 other person) Agent: No. 2 Noboru Kono, patent attorney
Figure 3

Claims (1)

[Claims] 1. In a method for measuring the level of the melt surface in a single crystal growth apparatus in which a radiation screen is provided above the melt surface in the crucible and around the single crystal pulling area, The reference point and the reflected image of the reference point with respect to the melt surface are captured by a linear sensor that emits a signal according to the light intensity, and the melting is performed based on the distance between the reference point and the reflected image on the linear sensor. A method for measuring the level of a melt surface in a single crystal growth apparatus, characterized by determining the level of the liquid surface.