JPS6021893A - Apparatus for preparing single crystal - Google Patents

Abstract

PURPOSE:To obtain single crystals having uniform diameter by compensating for the shift of focus due to variation of distance between the surface of melt and a diameter detector in accompany with displacement of crucible in the stage of growth of single crystal by Chokralsky method by the displacement of an objective lens and compensating for the change of the magnification. CONSTITUTION:A vertically movable crucible 3 is provided in a vessel 1 to maintain the melt 4 in the crucible 3. Single crystal is grown by Chokralsky method by changing the position of the surface of the melt by moving the crucible 3, and the diameter of the crystal 6 is detected by a TV camera 15 simultaneously to control the pulling speed to obtain a fixed diameter. In this stage, the displacement of the crucible 3 is calculated by integrating program signal from a program signal generator 13 for the displacement of the crucible 3, and the diameter of the single crystal is detected by controlling the position of an objective lens 17 of the TV camera 15 in accordance with the program signal. The gain is controlled in accordance with the displacement of the crucible 3 to amplify the diameter detection signal. Thus, the detection error of the diameter is compensated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a single crystal production apparatus using the Czochralski method (pulling a single crystal, for example, a silicon single crystal, from two strands).

[Prior art and its problems]

Most silicon single crystals are grown by the Czochralski method, but the grown single crystals must be of high quality and free of dislocations, and at the same time, the crystal must be controlled to a predetermined shape. In recent years, with the development of large-scale integrated circuits such as VLSI, it has become increasingly necessary to have an appropriate oxygen concentration and a good uniformity of oxygen concentration in the direction of the pulling axis. Therefore, a method has been used in which the crucible is moved in accordance with the temperature distribution of the heater and the crystal is grown while changing the position of the melt surface.

Conventionally used single-crystal manufacturing equipment that has automatic crystal diameter control features detect changes in diameter using a fixed optical sensor or TV camera, etc., and keep the diameter constant. The pulling speed is adjusted accordingly, and the crucible is also moved up and down in response to this, and control is performed so that the melt surface is always maintained constant relative to the optical sensor or TV camera. In other words, the pulling speed of the crystal is Let the speed be Vs and the moving speed ty of the crucible be Vc.

There is a relationship of vc = (psd2/plD2) ・Vs -=-song (1). Here, ρS and ρl are the densities of the silicon crystal and melt, and d and D are the diameters of the crystal and crucible.

Therefore, if crystals are grown while moving the crucible and changing the position of the melt surface in accordance with the temperature distribution of the heater, it will not be possible to maintain a constant distance between the optical sensor, TV camera, etc. and the melt surface. , an error in the detected diameter occurs due to the defocus of the optical system (2).

As a result, the diameter control accuracy decreases, and when the
The problem is that it becomes uncontrollable. In addition, the inability to control the shape of the crystal (-1) promotes striations in the crystal and changes in impurity concentration, leading to a decrease in crystal quality.Furthermore, material loss during peripheral grinding and diameter defects (secondary yield decreases). There are drawbacks such as a decrease in

On the other hand, it is possible to move the optical sensor to maintain a constant relative distance between the optical sensor and the melt surface in synchronization with the vertical movement of the crucible, or to move the optical sensor to maintain a constant relative distance between the optical sensor and the melt surface. A single crystal manufacturing device having a structure that changes the viewing angle has been proposed (Japanese Patent Laid-Open No. 54-82383).
reference). Normally, the optical cell detects the meniscus through a viewing window provided diagonally above the furnace body. If the moving distance of the optical sensor increases, there are problems such as the meniscus part moving out of the field of view of the peephole, and the optical sensor moving mechanism needs to be robust, increasing the cost of the device.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned drawbacks, and eliminates diameter ejection errors due to changes in the distance between the melt surface and the diameter detector when moving the crucible in accordance with the temperature distribution of the heater. i
To provide a simple and inexpensive device that can obtain a single crystal with a uniform diameter.

It is.

[1] Summary of the Invention The apparatus of the present invention corrects the out-of-focus of the optical system and the change in magnification based on the information on the movement of the crucible (2), and the change in the weight capacity of the melt surface and the diameter detector (2). In other words, in a single crystal production apparatus using the Chijochralski method, a program signal for crucible movement (from the second step, the program signal is divided to calculate the movement of the crucible @II), and the optical system is controlled according to the program signal. The diameter of the single crystal is detected by controlling the position of the crucible, and the gain is controlled according to the amount of movement of the crucible to amplify the detection signal, thereby correcting the diameter ejection error. .

〔Effect of the invention〕

As explained above, in the single crystal manufacturing apparatus of the present invention, the drive mechanism and circuit are smaller and simpler than the conventional apparatus in which the optical sensor itself is moved.

It requires less power consumption. Furthermore, by increasing the distance the crucible can move, it is less likely to fall out of the field of view of the viewing window, and the range of crucible movement is wide. It can be easily implemented without modifying ordinary single crystal production equipment, and equipment costs are reduced.This allows the crucible to be moved in accordance with the temperature distribution of the heater and the position of the fused surface to be changed. Single crystals with uniform diameters can be produced with high yield. Therefore, it is possible to improve crystal quality, such as by obtaining single crystals with good uniformity in oxygen concentration, and the quality can be improved by industrial use.
d. There are effects as described above.

[Embodiments of the invention]

Hereinafter, an example of the present invention will be explained in detail based on the drawings.

Figure 1 is an example of a single crystal manufacturing apparatus equipped with the functions (+i&) according to the invention. , 6 is crystal, 7 is pulling up (zasuke), 8 is crucible movement/sleeve.

9 is a pulling motor, IO is a crucible moving motor, 11 is a pulling speed controller, 12 is a crucible moving speed controller,
13 is a crucible movement program signal generator, 14 is an integral 1
, f;, 15 is a TV camera, 16 is an imaging plane, 17 is an objective lens, 18 is an objective lens movement motor, and 19 is an objective lens.

20 is an amplifier, 21 is a reference diameter setting device, and n is a diameter control device.

There is a crucible 3 in the container 1 that can be moved from crucible movement @bst 2 to the top, and a heater 2 is provided around it. The pulled crystal 6 is manufactured in a fast reaction time (two configurations).

Near the peephole 5 attached to the container l (2゛v ■ camera 1
5 is arranged, and the size of the meniscus ring of the crystal 6 is measured to detect the diameter of the crystal 11. Therefore, crystal 6 and TV
Depending on the distance of the camera 15, it is necessary to focus the optical system in advance and precisely adjust the distance between the objective lens 17 and the imaging plane 16 of the image pickup tube (not shown here). The detection signal of this TV camera 15 and the reference diameter setting device 2
] to obtain an error signal, IP+:
& the control device 22i drives the pulling motor 9 via the pulling speed controller 11 so that this difference becomes zero,
Change the pulling speed. Simultaneously (2) The crucible moving motor 10 is driven via the crucible moving speed controller 12 so that the position of the melt surface is kept constant at C', and the crucible moving speed is adjusted according to equation (1). Set.

The crucible movement program signal generator 13 generates a preset program signal to realize an optimal melt surface position corresponding to the temperature distribution of the heater 2. This program signal also applies to the crucible movement speed. Controller 12
added to. In other words, the crucible movement speed is set to the value determined by equation 11 plus the program signal.At this time, the distance between the crystal 6 and the TV camera 15 is increased by the crucible movement distance due to the program signal port. This causes a shift in focus.

Therefore, we decided to use program No. 4N for rapid production of objective lens movement.
1. Input to the integrator 19 to drive the objective lens moving motor 18 to correct the focal shift (2. Automatically set the distance between the objective lens 17 and the imaging plane 16. At the same time, the integrator 14 (
- is also input to calculate the time of crucible movement, and from this value (2) the gain on the amplifier side is set to compensate for changes in the magnification of the optical system.This allows the gain to be correct even if the position of the melt surface changes Since the diameter signal can be detected, highly accurate diameter i
l? IJ control can be realized.゛Here, it is sufficient to use the formula for a common lens of order ih to correct the shift of focus and the change in magnification.

However, 1. The focal length of the objective lens 17, a is the distance between the meniscus interface of the crystal 6 and the pair of the proboscis lenses 17, b is the distance between the imaging plane 16 and the objective lens J7, and M4; i indicates the magnification. If a changes by an amount Δa, the following equation holds true between the focus shift Δb and the change in magnification ΔM.

Next, as a specific example, using the single crystal manufacturing apparatus of the present invention,
For example, a case in which a silicon single crystal is manufactured while pushing up a crucible in order to equalize the oxygen concentration in the crystal will be explained in detail. In figure a1, a diameter of 8CrfL1 is obtained from a -15Ky melt 4 in a quartz crucible 3 with a diameter of 20mm.
A silicon single crystal with a length of 30 (m) is grown. First, the height of the crucible 3 and the heater 2 are equal, and -2 (!l2) is set with the height of the crucible 3 and the heater 2 being equal. uses a focal point with If% of 10 cm,
After setting the distance to the melt at 100 cm and focusing, pulling-E drawing was started.

When the crystal pulling rate is l FIIIL / ryh+ (second, the rising rate of the crucible is 0.145 from formula (1)
mw/'+. FIG. 2 shows the process of raising the crucible by the program signal generator 13.
In the diagram showing UitV, Lj) is shown. FIG. 3 is a diagram showing the change in the program signal (the moving speed Vt of the objective lens 17 which is interlocked with the two) and the gain G (relative value) on the amplifier side. 7M of heater
The reaction between the quartz crucible and the melt (according to the temperature distribution), the crucible movement speed is adjusted to ~1.
Acceleration was continued at I x 10-% m/ms2, and the position of the melt surface was moved by ζ2 to 50fl until the end of the pulling. Correspondingly, the moving speed of the objective lens 17 is set to ~1.1 x 10-' using equation (4) to correct the focal shift.
**/m2 Accelerate until the end of lifting (2~
Moved by 0.5. At the same time, the gain is raised to compensate for the change in magnification due to equation (5) (-) and the gain is ~0.94 by the end.
changed to twice that.

The gain can be easily adjusted by known methods such as rotating a gain 8I transformer on the amplifier side with a motor or changing the bias voltage. This (the deviation of the diameter from the second is ±0.5n
A silicon single crystal within

On the other hand, with the conventional apparatus, substantially tapered crystals were obtained with a diameter deviation of ±3H or more. FIG. 4 is a diagram showing the relationship between the assimilation rate and oxygen concentration of the grown crystal. In the figure, the change in oxygen concentration was ~0.11 x 1018 atoms/d, and the distribution was also flatter than the usual monotonically decreasing one.

As explained above (2) According to the single crystal manufacturing apparatus of the present invention, even if the position of the melt surface changes in response to the temperature distribution of the heater, can be obtained, and a high quality single crystal with good uniformity in oxygen dA degree can be produced.

In the embodiment, a TV camera is used as the diameter detection device, and an analog circuit is used as the control system.

For example, CCD
The single crystal manufacturing apparatus of the present invention can also be implemented using a camera or a computer algorithm.

[Brief explanation of drawings]

! 1°Sl is a diagram showing the configuration of an embodiment of the single crystal manufacturing apparatus of the present invention, FIG. 2 is a diagram showing an example of the program signal of the crucible 4 movement, and FIG. Figure 4 is a diagram showing the relationship between the solidification rate of the manufactured single crystal and oxygen (41 degrees). 1... Container, 2... Heater, 3... Crucible, 4... Melt, 5... Peephole, 6... Crystal, 7... Pulling (ura), 8... Crucible movement axis, 9...
・Lifting motor, 10... Crucible movement motor, 11・
... Pulling speed controller, 12... Crucible movement speed controller, 13... Crucible movement program signal generator, 14...
・Integrator, 15...TV camera,]6...Imaging surface, 17...pair of 4 lenses, 18...objective lens moving motor. 19...objective movement speed if control, (a)...
- Amplifier, 21... Reference diameter setting device, 22... Diameter control device. Agent Patent attorney Keisuke Norichika ((YokS1 person) Figure 1 Figure 4 I R4 Ihi Sen (=/, Ji

Claims (1)

[Claims] A program signal generator that generates a program signal for crucible movement set correspondingly to the τ attitude distribution of the heating element, and a crucible movement speed 1tilJ that controls the movement of the crucible according to the program signal. an integrator that refines the program signal to calculate the amount of crucible movement; a detector that controls the position of the optical system according to the program signal to detect the diameter of the single crystal; an amplifier for amplifying the detection signal with controlled gain; and the amplifier output signal 5 compared with a reference diameter setting signal.
and a pulling speed controller for controlling the pulling speed of the single crystal, which corrects a detection error in the diameter of the single crystal due to a change in the distance between the melt surface and the detector due to movement of the crucible. A single crystal manufacturing device characterized by the following.