JPH07277879A - Apparatus for producing single crystal by cz method and melt level control method - Google Patents

Abstract

PURPOSE:To hold the melt surface and the radiation preventive cylinder always in prescribed positions in production of a single crystal by a CZ method. CONSTITUTION:A crucible shaft 3 is driven to install a crucible 4 in a prescribed position and the position of the crucible shaft 3 when melting of a raw material is completed is stored. The position of the melt surface is calculated in accordance with the data on the position of a seed shaft when a seed crystal fixed to the seed shaft 2 comes into contact with a melt 5. A shaft 8 for vertically moving the radiation preventive cylinder is so driven that the spacing between the bottom surface of the radiation preventive cylinder 7 and the melt surface attains a prescribed value in accordance with the position of the melt surface. The radiation preventive cylinder 7 is then fixed. The specific section of the projected image of the rear surface of the radiation preventive cylinder 7 reflected from the surface of the melt 5 is detected by a CCD camera 9. The position of the melt surface is adjusted by driving the crucible shaft 3 when the specific section changes. The control is executed by a command section 11 and a control arithmetic section 12. The melt surface and the radiation preventive cylinder 7 are held always in the prescribed positions by these operations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a single crystal by the CZ method, and more specifically, an apparatus for producing a single crystal provided with a position detection / control device for holding a melt surface at a predetermined position, and an apparatus for producing a melt. A liquid level control method.

[0002]

2. Description of the Related Art A high-purity single crystal silicon is mainly used for a substrate of a semiconductor element, and one of the methods for producing this single crystal silicon is the Czochralski method (hereinafter referred to as the CZ method). In the CZ method, a graphite crucible is placed on the upper end of a crucible shaft installed in a chamber of a semiconductor single crystal manufacturing apparatus via a crucible receiver, and a quartz crucible housed in the graphite crucible is filled with polycrystalline silicon. The polycrystalline silicon is heated and melted by a heater provided around the graphite crucible to form a melt. Then, the seed crystal attached to the seed chuck is immersed in the melt, and the seed chuck is pulled up while the seed chuck and the graphite crucible are rotated in the same direction or in the opposite direction to grow single crystal silicon.

When the single crystal silicon is manufactured by the CZ method, the melt in the crucible is decreased with the growth of the single crystal silicon and the melt level is lowered, but the crucible shaft is used to obtain high quality single crystal silicon. It is necessary to control the melt level so that the crucible is driven up to raise the crucible and the melt surface is always held at a constant position with respect to the heater. In controlling the melt level, the position of the melt surface must be grasped first, and the following means are known as such means. (1) As shown in Japanese Utility Model Laid-Open No. 3-18171, the detection light is projected obliquely from above toward the melt surface, the reflected light from the melt surface is detected by the light receiving element, and the melt surface position is detected. Is calculated. (2) JP-A-63-274687, JP-A-2-1021
As shown by 87, the position of the meniscus ring generated in the single crystal growth portion is measured by the CCD camera, and the melt surface position is calculated. (3) JP-A-5-194079 and JP-A-5-19408
As shown in 0, laser light is projected on the melt surface, and the spot diameter of the laser light on the melt surface or the scanning width of the laser light on the melt surface is measured to calculate the melt surface position. .

[0004]

The above-mentioned conventional melt level measuring devices have the following problems, respectively. (1) In the measuring method using the actual Kaihei 3-18171 or the like, since the reflected light of the light projected on the melt surface is scattered in each direction due to the fluctuation of the melt surface, the detection accuracy becomes low. Liquid level cannot be detected. Therefore, it is difficult to accurately control the melt level. (2) In the measuring method according to Japanese Patent Laid-Open No. 63-274687, the measurement accuracy decreases when the single crystal growth surface becomes unstable. Further, in the tail process, the meniscus ring cannot be seen through the viewing window provided in the chamber, so that the melt level cannot be controlled. (3) The measuring method according to JP-A-5-194079,
The laser projection optical system becomes complicated, and an expensive optical system is required to improve the measurement accuracy. (4) These melt level measuring devices are not provided with means for synchronously controlling the position of the radiation preventing cylinder with respect to the melt surface. Then, in order to synchronously control the position of the radiation prevention cylinder, the seed axis, the crucible axis, and the vertical axis of the radiation prevention cylinder must be controlled in an absolute coordinate system.

The present invention pays attention to such a conventional problem and keeps the melt surface at a predetermined position and prevents the radiation regardless of the volume of the quartz crucible and the thermal deformation of the quartz crucible which vary from batch to batch. By the CZ method, which keeps the flow of the inert gas for the single crystal to be grown, the pressure in the furnace, and the temperature environment at a constant state by holding the cylinder at a predetermined position with respect to the melt surface. It is an object of the present invention to provide a single crystal manufacturing apparatus and a melt level control method.

[0006]

In order to achieve the above object, in the single crystal manufacturing apparatus by the CZ method according to the present invention, the seed axis, the crucible axis, and the radiation prevention cylinder vertical axis are all absolute coordinates based on the same standard. A vertical displacement amount detecting means and a displacement amount correcting means in the system, and means for detecting the crucible axis position P ₃ when the crucible is installed at a predetermined position with respect to the heater, and the crucible. Means for detecting the position of the melt surface after the completion of the melting of the raw material charged in the inside as a seed axis position P ₁ when the lower end of the seed crystal comes into contact with the melt surface, and radiation based on the seed axis position P _1. Means for installing the prevention cylinder at a predetermined position P ₂ with respect to the melt surface,
A means for detecting a specific portion of the image of the lower surface of the radiation preventing cylinder on the melt surface and controlling the crucible shaft to move up and down in order to correct the crucible shaft position P ₃ when the specific portion is displaced. .

In the single crystal manufacturing apparatus equipped with each of the above means, the distance between the horizontal reference plane F ₁ provided above the crucible and the horizontal reference plane F ₂ provided below the crucible is H _T , the distance to the melt surface from the reference surface F ₁ P _1, the distance from the reference surface F ₂ to a crucible bottom P _3, the melt depth H _M, the lower surface of the melt surface and the radiation prevention tube Assuming that the distance is H ₀ and the distance from the reference plane F ₂ to the lower surface of the radiation prevention cylinder is P ₂ , the above H _T , P ₁ , P ₂ , and H ₀ are always constant, and H _T = P _{by 1 + H M + P 3 =} P 1 -H 0 + P 2 to control the P ₃ to stand, and shall keep the melt surface at a predetermined position.

Further, according to the method for controlling the melt level of the single crystal production apparatus by the CZ method according to the present invention, the crucible shaft is raised when the crucible shaft is raised with respect to the heater so that the melt surface comes to a predetermined position. after detecting the position P ₃ of the lowers the seed axis, detects the position P ₁ of the seed axis when the lower end of the seed crystal mounted on a seed chuck is brought into contact with the melt surface, the radiation relative to the P ₁ The vertical axis of the radiation preventing cylinder is lowered so that the gap between the lower surface of the preventing cylinder and the melt surface becomes a predetermined value H _0, and the position P _{2 of the} vertical axis of the radiation preventing cylinder at this time is detected. The displacement of the image of the specific portion of the lower surface of the radiation preventing cylinder reflected from the CCD camera is detected by the CCD camera, and the crucible axis is controlled in the vertical direction so that the displacement amount does not exceed the threshold value. It is configured to be held at.

[0009]

According to the above construction, the positions of the seed shaft, the crucible shaft, and the vertical axis of the radiation preventing cylinder have an absolute coordinate system based on the same standard. FIG. 2 is an explanatory view showing the positions of the melt surface and the lower surface of the radiation preventing cylinder in the absolute coordinate system. A horizontal reference plane F ₁ provided above the crucible 4 and a horizontal reference plane F provided below the crucible 4. The distance from ₂ is set as a constant length H _T , where H _T is a set value P ₁ indicating the position of the melt surface, a set value P ₃ indicating the position of the crucible shaft 3, and the melt depth. It _consists of the sum of H _M and H ₀ is a set value of the gap between the lower surface of the radiation prevention cylinder and the melt surface, and P ₃
+ H _M + H ₀ = P ₂ is a set value indicating the position of the lower surface of the radiation prevention cylinder 7. In controlling the melt level, first, the crucible shaft position P ₃ at the time of completion of melting of the raw materials is stored, and the seed shaft position data P ₁ when the seed crystal of a predetermined length fixed to the seed shaft comes into contact with the melt surface is obtained. Based on this, the melt surface position is calculated.
Next, based on the melt surface position data, the radiation preventing cylinder vertical axis is driven so that the gap H ₀ between the lower surface of the radiation preventing cylinder and the melt surface becomes a predetermined value, so that the radiation preventing cylinder has a predetermined value. Is set to the position. That is, the radiation preventing cylinder can be installed at a position having a predetermined gap with respect to the actual melt surface position at the start of single crystal growth.

The image of the lower surface of the radiation preventing cylinder on the melt surface is detected by a CCD camera attached to the chamber of the single crystal manufacturing apparatus. FIG. 3 is an explanatory diagram of a map detected by the CCD camera. A specific portion is set in the map 13.
The specific portion is, for example, the horizontal axis Y that contacts the inner circumference of the map 13.
₀ and the intersection of the vertical axis X ₀ through the center of the radiation prevention tube. The horizontal axis Y ₀ may be set at a position in contact with the outer circumference of the map 13. When the gap between the melt surface and the lower surface of the radiation preventing cylinder widens, the horizontal axis Y ₀ moves upward in FIG. 3, and when the gap becomes small, the horizontal axis Y ₀ moves downward in FIG. This allows
The vertical movement of the melt surface with respect to the radiation preventing cylinder can be detected. Since the lower surface of the radiation prevention cylinder is flat and has a large area, the specific portion can be detected regardless of the fluctuation of the melt surface by taking the center of gravity of the white pixel of the image. By controlling the crucible axis so that this detection data matches a predetermined value, it is possible to maintain the "melt level" and the "distance between the melt surface and the radiation prevention cylinder lower end" at predetermined values. it can.

As described above, in the apparatus for producing a single crystal and the melt level control method according to the present invention, the radiation preventing cylinder is set at a predetermined position with reference to the actual melt surface position when the seed crystal comes into contact. During the growth of the single crystal, it was decided to control the melt surface position based on the position of the radiation preventing cylinder lower surface, so that the melt surface was set at a predetermined position regardless of the volume fluctuation or thermal deformation of the quartz crucible. Can be held.

[0012]

EXAMPLES Examples of a single crystal production apparatus by the CZ method according to the present invention will be described below with reference to the drawings. Figure 1
FIG. 3 is an explanatory view showing a schematic configuration of a single crystal manufacturing apparatus equipped with a melt level measuring / controlling apparatus. A seed shaft 2 and a crucible shaft 3 are vertically movable and rotatable in a chamber 1 of the single crystal manufacturing apparatus. A seed crystal is attached to the lower end of the seed shaft 2 via a seed chuck, and a crucible 4 is placed on the upper end of the crucible shaft 3 via a crucible receiver. The single crystal 6 is grown by immersing the seed crystal in the melt 5 in the crucible 4 and pulling it up. The radiation prevention cylinder 7 surrounding the single crystal 6 is
The radiation prevention cylinder can be moved up and down by the vertical shaft 8.
Reference numeral 9 denotes a CCD camera that observes the surface of the melt 5 from the outside of the chamber 1 and outputs the image as an electric signal.

The seed shaft 2, the radiation preventing cylinder vertical shaft 8, and the crucible shaft 3 are moved up and down by driving servomotors M ₁ , M ₂ , and M ₃ , respectively. Reference numeral 11 is a command unit, 12 is a control calculation unit, and the command signal output from the command unit 11 is sent to the motor amplifiers A ₁ , A ₂ , and A ₃ via the control calculation unit 12, and the servo motors M ₁ , respectively. Drive M ₂ and M ₃ . The rotation angles of these servomotors are the encoder data P ₁ , from the motor encoders E ₁ , E ₂ , E ₃ attached to the servomotors M ₁ , M ₂ , M ₃ , respectively.
It is input to the control calculation unit 12 as P ₂ and P ₃ . Also,
The output signals (X ₀ , Y ₀ ) of the CCD camera 9 are also input to the control calculation unit 12.

A procedure for measuring and controlling a melt level in the case of growing a single crystal by using a single crystal manufacturing apparatus equipped with the above melt level measuring and controlling apparatus will be described with reference to FIGS. 1 and 2. (1) Raise the crucible 4 and fix the crucible shaft 3 at the position of the set value P ₃ . When the melting of the raw material filled in the crucible 4 is completed, the melt surface is at a predetermined position with respect to the heater (not shown). (2) The seed shaft 2 is lowered to immerse the seed crystal in the melt 5. The control calculation unit 12 stores the position P ₁ ′ at which the seed crystal comes into contact with the melt 5. (3) Next, the radiation prevention cylinder vertical axis 8 is driven so that the gap between the lower surface of the radiation prevention cylinder 7 and the surface of the melt 5 becomes a predetermined value H ₀ . Then, the control calculation unit 12 stores the position P ₂ ′ of the radiation prevention cylinder vertical axis 8 when the gap becomes H ₀ . (4) At the time of the above (3), coordinate data (X) of a specific portion of the image of the lower surface of the radiation preventing cylinder 7 reflected from the surface of the melt 5
₀ , Y ₀ ) is detected by the CCD camera 9 and input to the control calculation unit 12. By the above operations (1) to (4), the position of the radiation preventing cylinder 7 with respect to the melt 5, that is, the gap between the lower surface of the radiation preventing cylinder 7 and the surface of the melt 5 becomes a predetermined value H ₀ . After that, the melt level can be controlled with the lower surface position of the radiation prevention cylinder 7 as a reference.

Single crystal production apparatus by CZ method according to the present invention
1 and 2 for the melt level control method of
A description will be given based on FIG. Figure 4 shows the measurement of melt level
In the flowchart to execute the control, check the left shoulder of each step.
The numbers listed are step numbers. Step 1
Position command signal P₃From the control calculation unit to the motor amplifier A ₃
Servo motor M via₃Output to the ascending crucible shaft
Let As a result, the crucible 4 becomes a heater (not shown).
In contrast, it is installed at a predetermined position. Melting of raw materials in crucible 4
After the solution is completed, in step 2, the seed axis descending command signal P
₁From the control calculation unit to the motor amplifier A₁Through the servo
Data M₁Is output to lower the seed shaft 2. seed
The axis 2 stops descending when the seed crystal comes into contact with the melt 5,
The contact position P at step 3₁′ Is motor encoder E₁
Is input to the control calculation unit 12. Then in step 4 △
P₁= P₁-P₁′ Is calculated. P₁Seed crystals melt
The set value of the seed axis position when it comes into contact with liquid 5
P₁The difference from ′ is ΔP₁Is.

In step 5, a correction value P ₂ ′ based on the actual melt surface position is calculated with respect to the set value P _{2 at} the lower end position of the radiation preventing cylinder 7. This calculation is P ₂ ′ = P ₂ + k
_It is obtained by the formula of ₁ × ΔP ₁ . Here, k ₁ is a conversion coefficient. In step 6, since the vertical axis 8 of the radiation prevention cylinder is lowered, the control calculation unit 12 causes the motor amplifier A ₂
The radiation prevention cylinder vertical axis lowering command signal P ₂ ′ is output to the servomotor M ₂ via. As a result, the vertical axis 8 of the radiation prevention cylinder is lowered, and the distance between the lower end of the radiation prevention cylinder 7 and the melt surface is H.
_The radiation prevention cylinder 7 is fixed at a position where it becomes _zero . At this time, the mapping data (X ₀ , Y ₀ ) at the lower end of the radiation prevention cylinder 7 reflected from the melt surface is input from the CCD camera 9 to the control calculation unit 12 in step 7 and stored.

During the growth of the single crystal, the mapping data (X ₀ , Y ₀ ) at the lower end of the radiation prevention cylinder 7 is constantly input to the control calculation unit 12. When the mapping data changes to (X ₀ ′, Y ₀ ′), ΔY = Y ₀ −Y ₀ ′ is calculated in step 8 and the threshold value Y ₁ is read in step 9. In step 10, the ΔY and Y ₁ are compared. If ΔY is equal to or less than the threshold value Y ₁ , it is determined that the position of the melt surface is within the allowable range, and the process returns to step 7. If ΔY exceeds the threshold value Y ₁ , in step 11, ΔP ₃ = k ₂ × ΔY is calculated. Here, k ₂ is a conversion coefficient. Then, 'after performing operation = P ₃ + △ P _3, the crucible position from the P ₃ P ₃ in step 13' P ₃ at step 12 outputs an instruction signal P ₃ 'for correcting the step 7 Return to. The command signal P ₃ 'is output to the servo motor M ₃ via the motor amplifier A _3, raise or lower the crucible shaft 3. As a result, the melt surface position is corrected to a predetermined position, and the distance between the lower end of the radiation prevention cylinder 7 and the melt surface maintains the set value H ₀ .

The apparatus for producing a single crystal and the method for controlling the melt level according to this embodiment are arranged so that the melt surface at the time when the melting of the raw material is completed and the growth of the single crystal is started is at a predetermined position with respect to the heater. After controlling the crucible shaft and fixing the radiation prevention cylinder so that the lower surface of the radiation prevention cylinder is at a predetermined position with respect to the actual position of the melt surface positioned by this method, the radiation prevention reflected on the melt surface is prevented. The position of the melt surface is controlled with reference to a specific portion of the mapping on the lower surface of the cylinder. Therefore, although the control procedure is simple, the melt surface can always be held at a fixed position, and the gap between the melt surface and the radiation preventing cylinder lower surface can be maintained at a predetermined value. is there.

[0019]

As described above, according to the present invention, C
The single crystal manufacturing device by the Z method is equipped with a melt level detection / control device by an absolute coordinate system in which the positions of the seed axis, the crucible axis, and the vertical axis of the radiation prevention cylinder are controlled based on the same standard, and the seed crystal comes into contact After detecting the actual melt surface position when, the radiation prevention cylinder is installed at a predetermined position with respect to the melt surface position, and the image of the bottom surface of the radiation prevention cylinder reflected on the melt surface during single crystal growth Since it has been decided to control the melt surface position with reference to the specific portion of, the following effects can be obtained. (1) It is possible to easily control the position of the melt surface with respect to the heater and the position of the radiation preventing cylinder with respect to the melt surface at a preset position. (2) The radiation prevention cylinder affects the pressure in the furnace and the flow of the inert gas, and effectively acts on the quality of the single crystal, especially the heat history, but the position of the radiation prevention cylinder with respect to the melt surface is accurate. Control becomes easy. (3) Since the melt level can be maintained at a predetermined position without being affected by the volume of the quartz crucible that varies from batch to batch or the thermal deformation of the quartz crucible, stable and high quality single crystal growth is possible. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a single crystal manufacturing apparatus equipped with a melt level measuring / controlling apparatus.

FIG. 2 is an explanatory view showing positions of a melt surface and a radiation prevention cylinder lower surface in an absolute coordinate system.

FIG. 3 is an explanatory diagram of a map detected by a CCD camera.

FIG. 4 is a flowchart for measuring and controlling a melt level.

[Explanation of symbols]

 2 Seed Axis 3 Crucible Axis 4 Crucible 5 Melt 7 Radiation Prevention Tube 8 Radiation Prevention Tube Vertical Axis 9 CCD Camera 13 Mapping

Claims (4)

[Claims] 1. The seed axis, the crucible axis, and the radiation prevention cylinder vertical axis are each provided with a vertical displacement amount detecting means and an displacement amount correcting means in an absolute coordinate system based on the same reference. Single crystal manufacturing equipment by CZ method. 2. A means for detecting a crucible shaft position P ₃ when a crucible is installed at a predetermined position with respect to a heater, and a melt surface position after completion of melting of a raw material filled in the crucible are defined as seed crystal Seed axis position P ₁ when the lower end contacts the melt surface
And a means for setting the radiation prevention cylinder at a predetermined position P ₂ with respect to the melt surface based on the seed axis position P ₁ , and a specific portion of the mapping of the lower surface of the radiation prevention cylinder on the melt surface. And means for vertically moving the crucible shaft so as to correct the crucible shaft position P ₃ when the specific portion is displaced.
Single crystal manufacturing apparatus by the Z method. 3. A horizontal reference plane F ₁ provided above the crucible.
And the distance to a horizontal reference plane F ₂ provided below the crucible is H _T , the distance from the reference plane F ₁ to the melt surface is P ₁ , and the distance from the reference plane F ₂ to the bottom of the crucible is P _3, when the melt depth H _M, the distance between the lower surface of the melt surface with the radiation prevention tube H _0, the distance from the reference surface F ₂ to the lower surface of the radiation prevention tube was P _2, the H _T , P ₁ , P ₂ , H ₀
Is always constant, and single crystals by _{H T = P 1 + H M} + P 3 = P 1 -H 0 + CZ method according to claim 1, P _2, characterized in that the controlling the P ₃ to stand Manufacturing equipment. 4. The position P of the crucible shaft when the crucible shaft is raised so that the melt surface is at a predetermined position with respect to the heater.
_{After 3} detects the lowers the seed shaft, the lower end of the seed crystal mounted on a seed chuck detects the position P ₁ of the seed axis when in contact with the melt surface, the radiation prevention tube relative to the P ₁ The vertical axis of the radiation preventing cylinder is lowered so that the gap between the lower surface and the melt surface becomes a predetermined value H _0, and the position P _{2 of the} vertical axis of the radiation preventing cylinder at this time is detected and then reflected from the melt surface. The displacement of the image of a specific portion on the lower surface of the radiation prevention cylinder is detected by a CCD camera, and the crucible axis is controlled in the vertical direction so that the displacement amount does not exceed a threshold value, thereby holding the melt surface at a predetermined position. A melt level control method for a single crystal manufacturing apparatus by the CZ method, which is characterized in that