JPH02102187A - Measurement of height of melt level in cz method - Google Patents

Abstract

PURPOSE:To accurately measure height of melt level without being influenced by waving of melt level by adding compensation based on distance between peaks to a peak position in the vertical direction at the central part of the peaks to obtain height of melt level. CONSTITUTION:Single crystal 4 of silicon, etc., is successively pulled up from melt 2 in a crucible 1 and a fusion ring 5 is produced at a position in contact with melt level at the lower part of the single crystal 4. For example, the fusion ring 5 is observed by an optical means 8 through an observing window 7. An ordinary optical measuring device can be used as the optical means 8 to measure the fusion ring by light or a CCD camera may be used. In the case of measurement by the CCD camera, diameter of the fusion ring can be measured by measuring the diameter of the fusion ring on a measuring line. A value corresponding to the height of melt level can be measured at a peak position in the vertical direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for measuring the height of a melt surface when a single crystal is pulled from a crucible by the CZ method (Chicklasky method).

[Conventional technology]

The C7 method is well known as a method for manufacturing single crystals such as silicon used in manufacturing ICs, LSIs, and the like. This method uses a rotating crucible as shown in the schematic diagram of Figure 1.
A crystal melt 2 of silicon or the like contained in a crucible is pulled up and solidified while being rotated with respect to a crucible 1 by a wire 3, thereby producing a columnar single crystal 4. The crucible 1 is heated from the outer circumferential side by an electric heater 12.

A difference in curvature due to the meniscus occurs at the boundary between the growing part of the single crystal 4 being pulled, that is, the solidified part, and the crystal melt 2, and by changing the apparent emissivity, a so-called fusion ring 5 appears.

This fusion ring 5 has an optical means 8 located diagonally above.
By observing through the measurement window 7 provided in the chamber 6, the shape is captured as a semi-ellipse.

By the way, in such a CZ method, the liquid level height of the melt 2 is an extremely important factor in controlling the pulling speed of the single crystal 4. As a melt level gauge, a liquid level gauge as shown in Fig. 7, which uses a laser and measures the laser reflection on the liquid surface by triangulation, has been introduced in literature.

[Problem to be solved by the invention]

However, in the liquid level measurement method using a laser, the liquid surface acts like a mirror surface, so a stationary liquid surface causes specular reflection as shown in 9, but normally the liquid surface is undulating, resulting in a two-dimensional reflection as shown in 10. It is difficult to capture the reflected light effectively.

Furthermore, even if one attempts to photometer the fusion ring without using a laser and determine the melt surface height from the position of the fusion ring, the diameter of the fusion ring 5 cannot be measured from the image projected on the optical means 8. However, it is not possible to directly determine the melt surface height.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for accurately measuring the height of a melt surface without being affected by ripples in the liquid surface using a fusion ring image received by an optical means.

(Means for Solving the Problems) The method of the present invention measures the diameter of the fusion ring by photometry from obliquely above the fusion ring that is generated in the growth area of a single crystal that is pulled into a cylindrical shape from the melt by the CZ method. The horizontal distance between the peaks and the vertical peak position at the center between the peaks are measured, and the measured vertical peak position is corrected based on the distance between the peaks to obtain the melt surface height. be.

(Function) Since the peak position in the vertical direction is corrected based on the distance between the peaks, the melt remains stable regardless of the ripples on the liquid surface and regardless of the position and size of the fusion ring image captured by optical means. Enables surface height measurement.

〔Example〕

The method of the present invention will be specifically explained below.

As shown in Figure 1, a single crystal 4 of silicon, etc. is placed in a crucible l.
The fusion ring 5 is sequentially pulled up from the melt 2 inside, and a fusion ring 5 is generated at a location in contact with the melt surface at the bottom of the single crystal 4. In the method of the invention, the fusion ring 5 is photometered through the observation window 7 by optical means 8 .

The optical means 8 for photometering the fusion ring includes:
It can be measured by a normal optical measuring device or by a CCD camera. When using a CCD camera, the light is measured as a peak at the fusion ring on the measurement line. The diameter of the fusion ring can then be measured by measuring the distance between the peaks in the horizontal direction. Furthermore, a value corresponding to the height of the melt surface can be measured based on the peak position in the vertical direction.

FIG. 2 shows an example of a device using a partial CCD camera. In the horizontal measuring section 16, the diameter of the fusion ring is measured with a first partial CCD camera, and in the vertical measuring section 17, the vertical position in the center of the fusion ring is measured with a second partial COD camera. is measured. FIG. 3 is an example of a two-dimensional field of view 18 captured using a two-dimensional CCD camera. According to this example, the horizontal direction and the vertical direction distribution at the center of the horizontal direction are determined as shown in FIG. 4, as in the case of FIG. 2.

Then, the diameter of the fusion ring is measured from the horizontal peak interval 19.19, and the vertical bead 92
The 0 position is taken as the detection point of the liquid level height.

By the way, as shown in Fig. 5, the image of the fusion ring projected in the field of view of the optical means has the minor axis,
In the horizontal direction, it is projected as an ellipse with a major axis. Only the front part of the oval is visible. Then, the melt surface height is estimated as follows based on the image of the field of view 11 of the optical means.

The detection point that serves as a reference for the melt surface height is point A on the short axis in the vertical direction. However, in reality, the liquid level height at the zero point at the center of the ring is the standard for measuring the liquid level.

If a liquid level scale 13 that can detect the horizontal line MN passing through the 0 point as the liquid level height is previously created within the field of view, then move the point A to the 0 point at the same melt level level. For example, the reading on the liquid level scale 13 at that position will indicate the melt level height. This will be explained with reference to FIG.

The optical means consists of a lens 14 and an image receptor 15, and the image of the fusion ring on the melt surface is focused on the field of view 11 on the image receptor 15. The angle between the center line of the ring and the center line in the photometric direction is θ. . If we consider the case where the detection point A' on the melt surface is moved to the center point 0', C' perpendicular to the photometric axis 0-0'
The interval 0' between and 0' is expressed as l = D, CO5θ/2. This distance ρ passes through the lens 14 to the image receptor 15 from the center 0 to l'=l/k=DocO5θ7
Connect images A-0 separated by 2K (where K is the reduction magnification) (
However, since it is a single lens, the image will be inverted).

Therefore, within the field of view 11 of the image receptor 15, if the detection point A on the image receiving screen is shifted toward the center of the screen by i', the 0 point, which is the display point of the melt surface height on the liquid level scale, can be set on the image receiving screen. can be specified. Based on this zero point, the melt level height is measured by the liquid level scale 13.

When the diameter is the nominal diameter D0 at the time of manufacture, it is only necessary to move it upward from the detection point A by ffi'=D, cOsθ/2. If the diameter is less than the nominal diameter, the error Δd (−〇, −D
, ), the detection point B' on the melt surface of the fusion ring is read as point B on the image receptor 15. l'+ΔN'=DOCOS above the detection point B
It is possible to reach the 0 point by moving only +Δd−COSθ/2 to θ/2.

The height of the melt surface was actually determined as described above and the height was kept constant, and the results are as follows. The specifications of the CCD camera used were as follows: Number of elements in the camera, ie, number of pixels: 2048 Viewing range: 100 na++ Viewing angle = 25°. According to this, the melt surface height can be measured with a measurement accuracy of ≦±0.2 m++.

By accurately determining the height of the melt surface and suppressing its fluctuations, we were able to obtain the following effects.

By controlling the liquid level based on the method of the present invention, it was possible to reduce the standard deviation σ1 of the liquid level change from ±10a++ to ±11a++.

A state in which the polycrystalline structure remains within the single crystal as it grows and breaks the arrangement of the single crystal is called DF breakage (DF is location free, that is, no dislocations).
It is said that This DF breakage can be reduced by keeping the melt surface height constant and optimizing the displacement between the melt surface and the heater position.

The oxygen concentration that is grown and incorporated into a single crystal is called Ol. The oxygen concentration changes as oxygen in one component of the crucible is taken into the silicon melt. The 0mm variation δ2 in the length direction of the pulled single crystal 4 is smaller when the liquid level is measured according to the present invention and the liquid level is kept constant, compared to when the melt level height is not measured. We were able to reduce it to 30%.

〔Effect of the invention〕

According to the present invention, by correcting the photometric position of the fusion ring, it is possible to immediately know the accurate melt surface height, thereby enabling highly accurate melt surface height management,
It is highly effective in improving product quality and product yield.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the CZ method, Figure 2 is a partial image reception range diagram of the fusion ring when using an original CCD camera, Figure 3 is a diagram of the reception range of the fusion ring when using a two-dimensional CCD camera, and Figure 4 is the CZ method.
A brightness distribution diagram of the fusion ring taken by a CD camera. Figure 5 is a re-examination diagram of the fusion ring projected in the field of view of the image receiver. Figure 6 is an optical path diagram showing the positional relationship between the fusion ring and the photometer. Figure 7 is the laser. 1 is a schematic diagram of a liquid level gauge using l: crucible, 2: crystal melt, 3: wire, 4: single crystal,
5: Fusion ring, 6: Chamber, 7: Observation window,
8: Optical means, 9: Specular reflection, 10: H dynamic reflection, 11
; Field of view, 12: Electric heater, 13: Liquid level scale, 14
: Lens, 15: Image receptor, 16j Horizontal direction measurement section, 17
: Vertical direction measurement unit, 18: Two-dimensional visual field, 19: Horizontal direction peak, 20: Vertical direction peak. Applicant: Osaka Titanium Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. By photometrically measuring the fusion ring that occurs in the growth area of a single crystal that is pulled into a cylindrical shape from the melt using the CZ method from obliquely above, we can determine the horizontal distance between the peaks corresponding to the diameter of the fusion ring and the central area between the peaks. Measurement of the melt surface height in the CZ method, which is characterized in that the peak position in the vertical direction is measured and the measured peak position in the vertical direction is corrected based on the distance between the peaks to obtain the melt surface height. Law.