JPH09208381A - Apparatus for pulling up single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically detect a change into a state of formed dislocations in a single crystal, thereby reduce a load on an operator and automate operations to remelt the single crystal at the time of the occurrence of the change into the state of the formed dislocations in the process of pulling up the single crystal by a Czochralski method (CZ method). SOLUTION: The shape of an outer peripheral surface of a single crystal B pulled up from a melt A or the shape of a fusion ring formed in the periphery of the interface between the melt A and the single crystal B is monitored with a camera 20. The disappearance of a seam part produced as the result of the crystal structure of the single crystal on the outer peripheral surface in the form of a vertical rib is detected by a change in the shape of the outer peripheral surface or the fusion ring. The occurrence of the change into the state of formed dislocations is detected by the disappearance of the seam and remelting operations of the single crystal are carried out on the basis of a prescribed program. The contact and separation of the single crystal B from the melt are detected from a change in voltage applied across the melt A and the single crystal B according to the remelting program to intermittently lower the single crystal B.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a single crystal pulling apparatus mainly used for manufacturing a silicon single crystal.

[0002]

2. Description of the Related Art A silicon wafer used for manufacturing a semiconductor device is often obtained from a rod-shaped silicon single crystal pulled by the CZ method. In the pulling of a silicon single crystal by the CZ method, as is well known, the single crystal is pulled from a silicon melt generated in a quartz crucible while being rotated by a wire. At this time, the temperature change of the melt or minute foreign matters such as oxides mixed in the melt,
So-called dislocations may occur in which the crystal structure of the single crystal collapses due to attachment to the single crystal. Further, vertical rib-shaped ridges called seam portions are formed on the outer peripheral surface of the single crystal. This seam portion occurs at a circumferential position specific to the crystal structure, and when dislocation occurs, the seam portion is interrupted at that time.

When dislocations occur in a single crystal, the portion pulled up after the occurrence becomes a defective product. Therefore, it is necessary to quickly detect the occurrence of dislocation.
From this point of view, conventionally, the seam portion is visually observed while pulling the single crystal, and the pulling of the single crystal is stopped when a break in the seam portion is found. Further, when the crystal length when the pulling is stopped is short, it is customary to redissolve the single crystal and pull up again from the beginning.

[0004]

In such a pulling operation, since the presence of dislocations is visually monitored over the entire period of pulling the single crystal, the burden on the operator is heavy. Also,
Occurrence of dislocation generation may be overlooked, and in that case, unnecessary pulling is performed, resulting in a decrease in operating efficiency.

In the re-melting of the single crystal, the lower end of the single crystal is dipped in the melt with the heater power raised to dissolve it, and after the lower end surface is separated from the melt, the lower end surface reaches the melt. The operation of lowering the single crystal is repeated. However, conventionally, single crystal syneresis / separation is visually determined. The syneresis / separation of a single crystal cannot be accurately determined by visual observation, and when the synergic state is left, the temperature of the melt rises, which adversely affects the crystal growth by re-pulling. If the liquid contact state is left, there arises a problem that the single crystal collides with the crucible.

It is an object of the present invention to provide a single crystal pulling apparatus for reducing the burden on the operator and improving the monitoring accuracy by automating the monitoring of dislocation generation.

Another object of the present invention is to monitor the occurrence of dislocations and to automate the single crystal remelting operation when dislocations occur so that the single crystal pulling operation can be performed with high accuracy and high efficiency. To provide a device.

[0008]

A single crystal pulling apparatus of the present invention is a pulling apparatus main body for pulling a single crystal from a raw material melt by a CZ method while rotating it, and a single crystal pulling apparatus for pulling a single crystal due to a crystal structure of the single crystal. An optical measurement unit that detects the presence or absence of a seam portion formed in a vertical rib shape on the outer peripheral surface, and an arithmetic control unit that determines the occurrence of dislocations in the single crystal based on the presence or absence of the seam portion detected by the optical measurement unit. It is characterized by doing.

Even if the optical measuring unit detects the presence or absence of a seam portion from the change in the outer peripheral surface of the single crystal pulled up from the melt, the seam portion is obtained from the change in the shape of the fusion ring around the interface between the melt and the single crystal. It may be one that detects the presence or absence of.

The arithmetic and control unit judges whether or not remelting is necessary from the crystal pulling length at the time when dislocation of the single crystal occurs.
When it is determined that remelting is necessary, the pulling stop of the single crystal is instructed to execute a predetermined remelting program.

The remelting program provided in the arithmetic control unit detects the step of lowering the single crystal and the liquid deposition of the single crystal from the change in the voltage applied between the single crystal and the melt. And the step of lowering the single crystal that has been deposited by a predetermined length, and the step of detecting the liquid separation from the melt of the single crystal from the change in the voltage and lowering the single crystal again. Including.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing an outline of the structure and function of an example of a single crystal pulling apparatus embodying the present invention, and FIG. 2 is a detailed explanatory view of a dislocation generation detection process,
FIG. 3 is a detailed explanatory diagram of the crystal remelting process.

The pulling device, as shown in FIG.
It is composed of a pulling device body 10 and an automatic system for detecting dislocation generation / crystal remelting combined with the pulling device body 10.

The pulling apparatus main body 10 is the same as the conventional pulling apparatus, and is configured to pull the single crystal B from the silicon melt A in the chamber. That is, the chamber is composed of a main chamber 11 and a pull chamber 12 connected to the center of the main chamber 11. A crucible 13 is arranged in the main chamber 11, and a heater 14 is arranged outside the crucible 13. There is. The crucible 13 is lifted and lowered by a support shaft 15 and is also rotated.

In pulling the single crystal B, the heater 14 is controlled to generate the melt A of silicon in the crucible 13 while the chamber is kept in a low-pressure inert gas atmosphere. Main chamber 1 through pull chamber 12
The seed crystal at the lower end of the wire 16 suspended in 1 is soaked in the melt A, and the wire 16 is raised while rotating from this state, so that the single crystal B is pulled from the melt A and pulled into the pull chamber 12. At this time, the crucible 13 rotates in the opposite direction.

In order to measure the diameter of the single crystal B pulled from the melt A and automatically control the wire driving unit so that the diameter becomes constant, in order to keep the surface level of the melt A constant, The automatic control of the crucible drive unit so that the crucible 13 rises as the liquid A is consumed is the same as in the conventional case. This pulling device is different from the conventional one in that it is equipped with an automatic system for detecting dislocation generation and crystal remelting.

The automatic system for detecting dislocation generation and re-dissolving a crystal includes a line sensor camera 20 arranged obliquely above the main chamber 11. This camera 20
As shown in FIG. 2 (A), the main chamber 1
The liquid surface near the crystal outer peripheral portion or the crystal outer peripheral position is scanned in the crystal radial direction through the window provided in No. 1.

When scanning the outer peripheral portion of the crystal in the radial direction of the crystal, since the brightness of the single crystal B is different from that of the other portion containing the melt A, the seam portion generated in the single crystal B can be detected. it can. When the liquid surface at the outer peripheral position of the crystal is scanned in the radial direction of the crystal, a bright and bright fusion ring corresponding to the outer peripheral shape of the single crystal B exists at the outer periphery of the interface between the melt A and the single crystal B. The seam portion can be detected by utilizing this.

In any case, the outer surface position of the single crystal B on the scanning line is detected by scanning with the camera 20 in the crystal radial direction. The output of the camera 20 is constant when the outer surface of the crystal other than the seam passes along the scanning line as the single crystal B rotates, but the output changes when the seam passes. Therefore, the seam portion is detected from the output change of the camera 20.

Here, when the single crystal B has a crystal orientation of <100>, the seam portion symmetrically occurs at four positions in the circumferential direction of the single crystal B, so that dislocation is not generated and sound crystal growth occurs. 4A continues, the output of the camera 20 increases at equal pitches with four peaks as one cycle, as shown in FIG. However, when dislocation occurs, the result shown in FIG.
As shown in (B), the occurrence is interrupted at one or more seam portions.

In this pulling device, as shown in FIG. 2B, the output of the camera 20 is captured and the period and number of peaks corresponding to the seam portion are counted. And n
When the number of peaks does not reach the reference value in the cycle count, it is judged that dislocation has occurred. As a result, dislocation generation is automatically detected quickly and with high accuracy.

When the outer peripheral portion of the crystal is scanned in the crystal radial direction by the line sensor camera 20, if a position far away from the surface of the melt is measured, even if dislocation is generated in the single crystal A, the dislocation portion is generated. Since it is not possible to determine the presence of dislocations until reaching the measurement position and the crystal part until reaching the measurement position is wasted, it is desirable to measure within a range of 50 mm or less above the liquid surface.

When the occurrence of dislocation formation is detected, it is determined whether the pulling should be stopped or the crystal should be redissolved based on the crystal pulling length at the time of detection. The criterion at this time can be changed. For example, 50% of the target length of the single crystal is used as the criterion, and if it is more than 50%, the pulling process is stopped and the single crystal is taken out. Move to redissolution process. If the amount of residual melt is small in the latter half of pulling when the generation of dislocation occurs, the pulling may be continued without being stopped in order to avoid a change in the thermal history of the single crystal.

In the crystal remelting process, as shown in FIG. 1, pulling OFF and rotation OFF commands are sent to the wire driving unit of the pulling apparatus body. At the same time, an instruction to turn off the crucible rise is sent to the crucible drive section.
With these, the pulling of the single crystal B is automatically stopped.

Next, a command for lowering the crucible 13 to the crystal remelting position and a command for lowering the rotation speed of the crucible 13 to a speed suitable for crystal remelting (for example, about 2 rpm) are sent to the crucible driving unit. As a result, the crucible 13 enters the crystal remelting state. Then, the single crystal B is automatically re-dissolved in accordance with the re-dissolution program shown in FIG.

According to this remelting program, the single crystal B first descends. At this time, a voltage is applied between the melt A and the single crystal B, and the voltage value is detected. Melt A
When the voltage value in the state where the single crystal B is separated from is the normal voltage, the voltage value drops from the normal voltage due to the single crystal B landing on the melt A. For example, when the normal voltage value is 24V, the voltage drops to 4V or less. The liquid drop of the single crystal B is determined by this voltage drop, and from this time point, the single crystal B is lowered by a predetermined length (for example, 30 mm) and the lowering is stopped. As a result, re-dissolution of the landing portion of the single crystal B starts.

When the re-dissolution of the landing portion is completed, the single crystal B separates from the melt A. Along with this, the voltage value rises to the normal value. It is judged that the single crystal B is synergic by this voltage increase,
Single crystal B descends again. Then, the single crystal B is redissolved until the designated length is reached by repeating the processes of descending the crystal, landing, stopping the descending, dissolving, separating, and descending again.

When the re-melting of the single crystal B is completed in this way,
A command to raise the crucible 3 to the raising start position, and the crucible 1
A command to increase the rotation speed of 3 to the growth speed is sent to the crucible driving unit. Then, after the temperature of the melt A is stabilized at the growth temperature, re-growth is started.

Using such a redissolution program,
Not only the operation is automatically performed, but the liquid deposition and the syneresis of the single crystal B are accurately detected automatically from the change of the voltage applied between the melt A and the single crystal B. Between the single crystal B and the crucible 13 due to excessive descent of the single crystal B
It is possible to avoid an increase in the liquid temperature and the like due to an insufficient decrease in

[0030]

As described above, the apparatus for pulling a single crystal of the present invention automatically and accurately detects the generation of dislocations in the single crystal during the pulling in a short time after the occurrence, so that the occurrence of dislocations is visually monitored. You don't have to. Therefore, it is possible to reduce the burden on the operator and avoid a decrease in operating efficiency due to continued pulling due to oversight.

The arithmetic and control unit judges whether or not remelting is necessary from the crystal pulling length at the time when dislocation of the single crystal occurs.
If you decide to stop pulling a single crystal and execute a predetermined remelting program when it is determined that remelting is necessary, the remelting operation after the single crystal has dislocations is automatically performed. The burden on the person is further reduced.

A remelting program provided in the arithmetic control section detects the step of lowering the single crystal and the change in voltage applied between the single crystal and the melt to detect the single crystal landing on the melt. And the step of lowering the single crystal that has been deposited by a predetermined length, and the step of detecting the liquid separation from the melt of the single crystal from the change in the voltage and lowering the single crystal again. In the case of containing, since the single crystal landing and syneresis which could not be detected accurately by visual inspection is automatically detected with high precision, excessive lowering and insufficient lowering of the single crystal in the re-dissolution process are avoided, The process is performed stably and with high accuracy.

[Brief description of drawings]

FIG. 1 is a system diagram showing an outline of the structure and function of an example of a single crystal pulling apparatus embodying the present invention.

FIG. 2 is a detailed explanatory diagram of a dislocation generation detection process.

FIG. 3 is a detailed explanatory diagram of a crystal remelting process.

FIG. 4 is a waveform diagram showing a change in output of the camera when dislocation does not occur and when dislocation occurs.

[Explanation of symbols]

 10 Pulling Device Main Body 13 Crucible 14 Heater 16 Wire 20 Line Sensor Camera A Melt B Single Crystal

Claims (3)

[Claims] 1. A pulling apparatus body for pulling a single crystal from a raw material melt while rotating by a CZ method, and a presence or absence of a seam portion formed in a vertical rib shape on the outer peripheral surface of the single crystal due to the crystal structure of the single crystal. An apparatus for pulling a single crystal, comprising: an optical measuring section for detecting; and an arithmetic control section for judging occurrence of dislocation of the single crystal based on the presence or absence of a seam section detected by the optical measuring section. 2. The arithmetic control unit determines whether remelting is necessary or not based on the crystal pulling length at the time when the dislocation of the single crystal occurs, and when the remelting is determined to be necessary, the pulling of the single crystal is stopped. And executing a predetermined re-dissolution program.
The single crystal pulling apparatus described in 1. 3. A remelting program provided in the arithmetic control unit, a step of lowering the single crystal, and a liquid deposition of the single crystal on the melt based on a change in voltage applied between the single crystal and the melt. A step of detecting the liquid crystal, a step of lowering the single crystal that has landed on it by a predetermined length, and a step of detecting the liquid separation from the melt of the single crystal from the change of the voltage and lowering the single crystal again. The single crystal pulling apparatus according to claim 2, which comprises repetition.