JPS6321280A - Method for controlling diameter of single crystal - Google Patents

Abstract

PURPOSE:To precisely control the diameter of the tail part of a columnar product by deviating the optical axis of an optical means for a pulling-up axis in such a position that the observation of a fusion ring at the tail part of the columnar product is made possible. CONSTITUTION:A columnar single crystalline product 18 is pulled up by a CZ method and the position on a line A is monitored till the pulling thereof is finished, and the diameter of a fusion ring 20 is directly measured from the position enhanced in a brightness and the pulling velocity of single crystal is adjusted so that this diameter is regulated to the objective diameter. In a squeezing stage of a tail part, when the tail part 19 is positioned at the shadow of the product 18 and the ring 20 disappears from the range of a field of view for a camera, and the optical axis of the camera is deviated to a position B to make the ring 20 photometrical and the pulling up velocity of single crystal is adjusted while measuring the diameter of the tail part 19. In case the ring 20 is made small, the optical axis of the camera is deviated at a position C and furthermore the optical axis of the camera is returned on the line A in such a stage that the contraction of the tail part has progressed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method for controlling the diameter of a single crystal when pulling it from a crucible using the CZ method (Czochralski method), and in particular, relates to a method for controlling the diameter of a single crystal when pulling it from a crucible using the CZ method (Czochralski method). The present invention relates to a method for accurately controlling the diameter of a tail part in a tail drawing process after pulling up a product part.

[Conventional technology]

BACKGROUND ART The °ζ and CZ methods are well known as methods for manufacturing single crystals of silicon or the like used in the manufacture of ICs, LSIs, and the like. As shown in the schematic diagram in Fig. 5, this method involves rotating a crystalline melt (4) of silicon or the like contained in a rotating crucible (2) with respect to the crucible (2) using a wire (8). A columnar single crystal 00 is produced by pulling and solidifying it. The manufactured single crystal is finished into a cylindrical ingot, but in order to increase the yield at that time, it is required that the single crystal 0υ being pulled has the same diameter in each part.

Conventionally, as one method for controlling the diameter of this single crystal αυ, as shown in Fig. Measuring the diameter of the fusion ring (20) by optical means θ;
There is a method of estimating the diameter of the single crystal OD from that value and adjusting the temperature of the crystal melt (4) and the drawing speed of the single crystal 01) so that the estimated diameter matches the target value. It is taken.

In this case, the optical means 02) (e.g., RV, CCD camera, etc.) measures the fusion ring from diagonally above due to the relationship with the incidental equipment and the need to look close to the bottom of the crucible (2). The angle θ of the optical axis with respect to the vertical line is about 30'.

On the other hand, when finishing the pulling of the single crystal 00, it is necessary to prevent dislocation due to thermal strain as shown in Figure 6 (al~(C
As shown in Fig. 1, the tail part 091 is the product part when viewed from the optical means 02, which requires a step called tail drawing to gradually reduce the crystal diameter. 08), making photometry of the fusion ring impossible. For this reason, feed hack control cannot be used to control the diameter during tail drawing, so the operator usually performs the operation while visually monitoring the crystal diameter, or performs foot fort control using a program. There is.

[Problem that the invention seeks to solve]

By the way, in the above-mentioned tail squeezing step, the crucible (2) is required to be emptied when the tail squeezing is completed in order to increase the usage efficiency of the crystal melt (4) in the crucible (2). Furthermore, it is also necessary to avoid giving the tail portion an excessive volume. Therefore, strict diameter control is required for the tail portion 0ω.

FIG. 7 shows the shape of the tail portion when the diameter of the tail portion is controlled by the aforementioned visual operation.

The crystal diameter can be changed by changing the melt temperature or the pulling speed, but since the pulling speed has a large effect on product quality, when performing visual operations, the crystal diameter should be adjusted by changing the melt temperature. . In that case, increasing the melt temperature will reduce the crystal diameter, but over time an equilibrium will be reached between the temperature and the diameter, and the crystal will not become thinner than that. Therefore, in order to further reduce the crystal diameter, it is necessary to raise the melt temperature again. For this reason, the tail portion 09) is finished in a stepped shape as shown in the figure. This shape itself is not a particular problem, but
The work is extremely complex, requires a high degree of skill, and is inefficient.

On the other hand, program control τ11 is efficient, but if conditions such as remaining liquid amount and crucible position change, all (
There is a problem that cannot be solved, and furthermore, the tail part is 0 due to disturbance.
! ! There is also the problem that the shape of the material changes significantly. Figure 8 (
(a) and (b) show how the shape of the tail part 09) changes, and (a) shows that when the tail part (I'11) is too short,
(b) is a case where the length is too long.

If the tail portion 09) is too short, the crystal melt (4) remains in the crucible (2) even after the pulling is finished, reducing the efficiency of raw material use. On the other hand, if it is too long, excess material will be applied to the tail part 09), which will not only reduce the raw material usage efficiency as in the case where it is too short, but also cause the crucible (2
) is consumed, and the tail part (I'll
The lower end of the crucible (2) will adhere to the bottom of the crucible (2), and when it is removed there is a risk that a crack will enter the product part 0 (end).

Such a problem can naturally occur if a mistake is made in the visual operation described above.

In addition, recent research by the present inventors has revealed that the length of the tail portion aω affects the quality of the product portion 0ω. In other words, although the detailed reason is not clear, the longer the length of the tail part 09), the longer the product part 081
The quality defects that occur in the tail part are absorbed by the tail part, and the product part
The quality of 0 is improved.

However, if the tail portion Q91 is simply made longer, as fate would have it, the raw material usage efficiency will decrease and the risk of the tail portion 09) adhering to the bottom of the crucible (2) will increase. Therefore, for example, while considering the remaining amount of melt in the crucible (2), the crystal diameter is made as thin as possible and the tail part is 0ω.
Extremely sophisticated diameter control is required, such as increasing the length of the diameter.

[Means for solving problems]

The present invention provides a rational and highly accurate method for controlling the diameter of the tail portion by a simple means using existing equipment, which can fully meet such high-level demands.The present invention is characterized by the following: As illustrated in the schematic side view of Fig. 1, when performing tail aperture after pulling up the cylindrical product part α, the fusion ring of the tail part 09) allows light to be measured by optical means. The axis (0) is deviated from the pull axis (0゛), and the tail portion 09) is also determined on the diametrical side based on the photometric data of the fusion ring. 11
The point is to do 1.

Typical concrete means for deflecting the optical axis (0) include means for pivoting the optical means α2) outward around the fusion ring, as indicated by X in FIG. As shown by Y in FIG. 1, there are two means for moving the optical axis (0) in parallel by sliding the optical means (0) outward without changing its aiming angle.

In the former turning movement, the target position does not change, so there is an advantage that the crystal diameter can be determined directly from the fusion ring even after movement. In addition, in the latter case of parallel movement, although the target position changes and the crystal diameter cannot be determined directly from the photometric data, the distance to the target remains unchanged, making it relatively easy to calculate the crystal diameter, and the movement mechanism also It becomes simple.

〔Example〕

Examples regarding parallel movement will be described below.

In FIG. 2, (1) is a chamber, the interior of which is maintained in an inert gas atmosphere such as A. A crucible (2) is placed inside the chamber (1), and a heater (3) is placed around it.
) surrounds the crucible (2) to control the crystal melt (4) at a predetermined temperature. (5) is the crucible rotation motor, (6)
(7) is the lifting motor, and (7) is the radiation thermometer.

A pulling wire (8) is also suspended from above inside the chamber (1), and its rotation motor (9) and lifting motor 00) are provided outside the chamber +1. The crystal θυ is pulled out of the crystal melt (4) while rotating in the opposite direction with respect to the crucible (2).

CCD camera as an optical meansOld, chamber (
1) It is located diagonally above the chamber (1) so that the fusion ring can be monitored from the outside through the window (1), and is configured so that it can be moved in parallel to the outside and inside with respect to the pulling shaft by a motor. ing.

The output of the CCD camera Q2+ is manually input to the processing device Oa to calculate the diameter of the single crystal 0υ, and this and the output from the target diameter setting device α5) are manually input to the comparator Q61, and the difference between the two inputs is calculated by the calculation device. 07) to measure the pulling speed of the single crystal 01) at which the difference in force between the two men becomes 0, and command the motor 00) for pulling the single crystal 0υ.

Figures 3 (a) to (c) (al to (dl) shown in stages are concrete examples of the procedure for controlling the diameter of the tail section using the device in Figure 2. (b) is a perspective view showing the shape of the single crystal and its fusion ring as seen from the camera position, (c) is the output waveform diagram of the camera.Ta+ is the start point of the tail aperture, (bl is the tail (C) represents the 50% end point of the drawing process, (C) also represents the 75% end point, and (di also represents the 99% end point r), respectively.

Until the start of the tail aperture, that is, until the end of pulling the product part 08), the camera monitors the A line, directly captures the diameter of the fusion ring aO+ from the point of increase in brightness, and adjusts the diameter of the single crystal 01) so that this diameter becomes the target diameter. Adjust the pulling speed.

If the tail drawing process is carried out in this state, the tail part will be 0.
91 is in the shadow of the product department OI, and the fusion ring (2
Since Ql disappears from the field of view of the camera θ, at the start of tail aperture, move the fusion ring (2111) parallel to the outside to the position where it can measure light.

The changed aim position of camera Q2+ is shown by line B. When the Fusion Ring Q Shun is photometered at this position, the length of the Sony John Ring I2 Shun string is observed, so the diameter of the tail part 09 is calculated using the following formula, with the moving distance of the camera α as γ. I will do it.

φA: Crystal diameter φB: Measured string length γ: Camera horizontal movement path # (distance M from the crystal center to the string) In this way, while determining the diameter of the tail part 0!1, make sure that the diameter matches the target. Adjust the pulling speed of the single crystal 0υ so that it gradually decreases.

As the tail aperture advances and the fusion ring (t20) becomes smaller, the fusion ring (20) disappears from line B, so move the aiming position of camera 02 (as shown in C1) onto line C between line A and line B. At the stage when the tail aperture has further advanced, the aiming position of the camera (b) is returned to the A line as shown in (d+).

As described above, the diameter of the fusion ring can be actually measured over the entire period of the tail drawing process, and by controlling the diameter of the tail part using foot hack control based on this measured value, the tail part Q91 of any shape can be formed with high precision. Can be molded.

When the diameter of a silicon single crystal with a diameter of 6 inches was controlled using the above-described procedure, the dimensional error could be suppressed to ±0.5 in the product part 0ψ and to ±111 in the tail part α. FIG. 4 illustrates the shape of a single crystal tail obtained by the method of the present invention.

In this example, the aiming position of the camera is changed to three stages, A, B, and C, but the number of stages depends on the desired tail shape, the angle of the camera's optical axis with respect to the pulling axis, the required accuracy, etc. It will be changed as appropriate based on the above.

〔Effect of the invention〕

According to the diameter control method of the present invention, the tail diameter can be measured continuously from the fusion ring in the tail drawing process in the same way as in the product part pulling process, and feed hack control is possible based on the measured value, making it possible to This not only improves manufacturing efficiency by eliminating the need for human supervision, but also enables the required tail shape to be achieved accurately, thereby minimizing the amount of melt remaining in the crucible after pulling.
This has the effect of suppressing unnecessary enlargement of the tail and greatly increasing raw material usage efficiency.

Furthermore, since the tail part can be finished into the required shape, it is also possible to absorb defects in the product part into the tail part, and a great effect can be obtained in terms of product quality.

Furthermore, since the tail drawing process is stabilized, it is expected that variations in the time required for the process will be reduced and the furnace operating schedule will be stabilized.

Furthermore, the method of the present invention allows existing optical means to be used as is, and does not require the installation of additional optical means1 or other measuring means (such as a crystal weighing scale), resulting in an overall low cost. It also has the great advantage that it can be implemented on M,il.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the basic principle of the present invention, Fig. 2 is a diagram of a device configuration according to an embodiment of the present invention, and Figs. An explanatory diagram, FIG. 4 is an explanatory diagram of the tail shape obtained in the same example, and FIG. 5 is an explanatory diagram showing the CZ method and a general method of diameter control in the same method.
Figures 6(a) to (C) are explanatory diagrams of the tail drawing process;
The figure is an explanatory diagram of the tail shape obtained by conventional visual operation.
Figures (a) and (b) are explanatory diagrams of the tail shape obtained by conventional program control. 1: Chamber, 2 Nilpot, 3: Heater, 8: Wire, 10: Pulling motor, 11: Single crystal, 12: Optical means (CCD camera), 18: Product department, 19: Tail section, 20: Fusion ring . Figure 2 15 1! *. 17 Arithmetic Ratio Soft 16 IQ Straight 14 B 12 Nutoshizuku, I, 1' (a) CCO optical axis camera tilting Fig. 3 (O) (c) 1430 - Fig. 5 "・ 34," Bci, o. l,,) Jl Figure 6 I

Claims (2)

[Claims] (1) In a method in which the fusion ring that is generated in the growth area of a single crystal that is pulled into a cylindrical shape by the CZ method is photometered diagonally from above using optical means, and the diameter of the single crystal is managed and controlled based on the photometric data. When performing tail aperture after pulling up a columnar product part, the optical axis of the optical means is deviated from the pulling axis to a position where the fusion ring in the tail part can perform photometry, and the fusion ring is also applied to the tail part. A method for controlling the diameter of a single crystal, characterized by controlling the diameter based on photometric data. (2) The method for controlling the diameter of a single crystal according to claim 1, wherein the deviation of the optical axis is a parallel movement outward from the pulling axis.