JPH0651598B2 - Semiconductor rod floating melting zone control method - Google Patents

Description

TECHNICAL FIELD The present invention is used in a semiconductor single crystal manufacturing apparatus by the FZ method, and indirectly controls the zone length of a melting zone and the crystallized crystal diameter of a semiconductor rod floating melt. The present invention relates to a band control method.

[Prior Art] Generally, in the semiconductor rod floating melting zone control method, a polycrystalline rod having a diameter close to the desired diameter of a single crystal rod is used as a raw material. For example, the tip of a round rod-shaped seed crystal of 4 mm is arranged, the lower end of the polycrystalline rod is heated and melted by high frequency induction heating, the upper end of the seed crystal is melted by this radiant heat, and the vicinity thereof is heated, and further fused, Further, the upper end of the seed crystal is gradually melted, and after reaching thermal equilibrium, crystal growth from the seed crystal starts. During the crystal growth process, the polycrystalline rod and the single crystal rod rotate about a coaxial or eccentric axis, descend at a controlled descending speed, and move relative to the heating coil. In the initial stage of crystal growth, the growth rate is relatively fast, and the diameter is narrowed down to, for example, 1 to 2 mm, and this state is continued up to, for example, 10 to 30 mm in length, and then the diameter is increased. From the time when the crystal growth from the seed crystal enters the thickening of the diameter until the desired diameter is reached, the single crystal has an inverted cone shape (hereinafter referred to as a cone).
However, after reaching the desired diameter, control to a constant diameter is started. After that, the polycrystalline rod and the seed crystal move relative to the heating coil until the melting of the effective length of the polycrystalline rod is completed. Normally, the polycrystalline rod and the seed crystal descend to the fixed heating coil, but the descending speed of the polycrystalline rod is faster in the inverted cone portion than that of the seed crystal, and becomes almost the same velocity after reaching a constant diameter. .

Conventionally, the crystallized crystal diameter or the angle formed between the semiconductor rod and the tangent to the vertical cross-section contour line of the melting zone is detected, and the crystallized crystal diameter is controlled to reach a set target value (see, for example, Japanese Patent Publication No. No. 52-33042, Japanese Patent Publication No. 56-7
No. 998, Japanese Patent Publication No. 60-49160, etc.).

However, the following problems occur even if only the crystallized crystal diameter is controlled.

As shown in FIG. 4, in the melting zone 20 formed by the induction heating coil 12 between the descending melting side semiconductor rod 16 and the crystallization side semiconductor rod 18, the lower surface of the melting side semiconductor rod 16 is There is an unmelted cone 21 that has protruded from the center and is not yet melted. When the zone length L becomes shorter and the lower end of the unmelted cone 21 approaches the crystallization interface 24, the crystallization interface 2
Since the temperature of the central portion of No. 4 becomes lower than that of the peripheral portion, the crystallization rate becomes faster, which causes the central portion to rise and cause dislocation.

Further, when the crystallization interface 24 is further cooled, the central part thereof rises, the lower end of the unmelted cone 21 and the top part of the crystallization interface 24 come into contact with each other, and the crystallization side semiconductor rod 18 which is a single crystal is separated. The melting side semiconductor rod 16 which is a crystal is fixed, and it becomes impossible to continue the floating melting zone method.

On the contrary, when the zone length L becomes too long, the diameter of the melt neck portion 35 becomes small and the surface tension causes the melt zone 2 to melt.
0 is cut at the melt neck portion 35, and under the melt droplet occurs.

Gaseous impurities from the surface of the melting zone 20 to the melting zone 20
When the gas is injected into the inside (gas doping) or when the atmosphere is evacuated to remove impurities in the melting zone 20 (vacuum method), the surface area of the melting zone 20 is changed when the zone length L is changed. The injection rate and the removal rate of Pd fluctuate, and the resistivity of the crystallization side semiconductor rod 18 becomes non-uniform in the axial direction.

Therefore, the zone length L and the crystallized crystal diameter D _S are detected, and the axial distance between the melting side semiconductor rod 16 and the crystallization side semiconductor rod 18 is adjusted so that the detected zone length L reaches a target value. ,
A method of adjusting the electric power P supplied to the induction heating coil 12 based on the empirical formula P = A (D _{s1 / 2} + BLD _s ) so that the detected crystallized crystal diameter D _s becomes a target value has been proposed. (JP-A-56-45888). Where A and B
Is a constant.

[Problems to be Solved by the Invention] However, the above empirical formula is a formula that holds in a steady state, and in practice, for example, when the supply power P is increased, the crystallized crystal diameter D _s temporarily increases. However, the zone length L then increases with a delay, and along with this, the crystallized crystal diameter D _si decreases and becomes approximately equal to the original value. That is, although the relationship between the power supply P, the crystallized crystal diameter D _s, and the zone length L changes with time, the above method ignores such time change and controls. However, the predictability is not sufficient, and the control response and stability are lacking.

Further, since the above method does not predict the change in the zone length L, the melt-side semiconductor rod is adjusted so that the zone length L reaches the target value after the change in the zone length L is detected to some extent (minimum detection amount). The axial distance between 16 and the crystallization side semiconductor rod 18 is directly adjusted. Therefore, the control response speed becomes too slow before the change of the zone length L is detected to some extent, and after the change of the zone length L is detected to some extent, the control response speed becomes too fast and hunting occurs. , The stability of control becomes poor.

If the control response is slow or if stable control cannot be performed, the zone length becomes too short or too long, causing crystal disorder or sticking as described above, or melting zone May cause quality deterioration or make it impossible to continue the floating zone method. In the cone portion at the initial stage of crystal growth, even if there is no quality problem, for example, if the zone length is too long, the cone length becomes long, resulting in product loss.

In view of the above problems, an object of the present invention is to provide a semiconductor rod floating melting zone control method capable of controlling the zone length L and the crystallized crystal diameter D _s with fast response and stability. .

[Means for Solving the Problems] In the present invention, a part of a vertically arranged semiconductor rod is melted by a heating device to form a melting zone, and a melting side semiconductor rod on the upper side of the heating device and the heating The melting zone is moved in the axial direction by moving the crystallization side semiconductor rod on the lower side of the apparatus in the axial direction relative to the heating apparatus, and the melting zone and its vicinity are imaged by an imaging device. Then, the image taken by the imaging device is processed by the image processing means to measure the geometrical amount, and the electric power supplied to the heating device and the relative moving speed of the semiconductor rod are adjusted according to the measured value. In the semiconductor rod floating melting zone control method, the geometric amount is a shoulder near the crystallization interface of the melting zone and a melt shoulder diameter at a certain distance upward from the crystallization interface,
The melt side semiconductor including a neck portion near the heating device in the melting zone and a diameter of the melt neck portion at a certain distance downward from the heating device, so that the diameter of the melt neck portion becomes a target value. It is characterized in that the moving speed of the rod is adjusted and the electric power supplied to the heating device is adjusted so that the diameter of the melt shoulder portion becomes a target value.

[Embodiment] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the overall configuration of a semiconductor rod floating melting zone control device to which the present invention is applied.

A high-frequency current is supplied from the oscillator 10 to the induction heating coil 12, a part of the semiconductor rod 14 is heated and melted, and the melting zone 20 is provided between the leaching side semiconductor rod 16 and the crystallization side semiconductor rod 18.
Is formed.

The crystallization side semiconductor rod 18 is arranged vertically and is moved downward at a speed V _s by a variable speed motor 22 for raising and lowering. Further, the crystallization side semiconductor rod 18 is rotated at a constant speed by a motor (not shown), and the temperature distribution near the crystallization interface 24 of the crystallization side semiconductor rod 18 and the melting zone 20 becomes rotationally symmetrical.

On the other hand, the smelting-side semiconductor rod 16 is also arranged vertically and is moved downward at a speed V _p by a variable speed motor 26 for raising and lowering. Further, the melting side semiconductor rod 16 is rotated at a constant speed by a motor (not shown), and the temperature distribution near the melting interface 28 between the melting side semiconductor rod 16 and the melting zone 20 is rotationally symmetrical.

The melting zone 20 and its surroundings are monitored by a fixed industrial television camera 30, and the composite video signal is supplied to the image processing circuit 32, and the diameter D _{s at} the crystallization interface 24 and the crystal of the melting zone 20 are supplied. The diameter D _n of the melt-side melt neck 36 and the diameter D _m of the melt-side melt shoulder 34 between the crystallize-side melt neck 36 and the crystallizing interface 24 are detected.

The melt neck portion diameter D _n is the diameter of the crystallization-side melt neck portion 36 at a position apart from the lower surface of the induction heating coil 12 by a predetermined distance h _n .

Further, the melt shoulder diameter D _m is the diameter of the crystallization-side melt shoulder portion 34 at a position apart from the crystallization interface 24 by a predetermined distance h _m .

The melt shoulder diameter D _m and the melt neck diameter D _n are measured by the length of the scanning line where the brightness amplitude is larger than the reference value. Further, the positions of the crystallization interface 24 and the lower surface of the induction heating coil 12 are detected as the positions where the luminance amplitude in the vertical direction of the scanning line suddenly changes. Further, the distances h _n and h _m correspond to the distances from the scanning lines corresponding to the lower surface of the induction heating coil 12 and the crystallization interface 24 to the scanning lines separated by a certain number.

<< Relationship Between Melt Shoulder Diameter D _m and Crystallized Crystal Diameter D _s >> The present inventor has found that the melt shoulder diameter D _m has a constant relationship with the crystallized crystal diameter D _s after a certain time. It was discovered that the correlation is large.

Therefore, rather than directly controlling the crystallized crystal diameter D _s ,
When the crystallized crystal diameter D _s is indirectly controlled by controlling the melt shoulder diameter D _m , the responsiveness becomes faster and stable control can be performed.

Further, the cross-section at the crystallization side melt shoulder 34 is closer to a perfect circle than the crystallization interface due to the surface tension of the melt. For this reason,
Using the melt shoulder diameter D _m rather than the crystallized crystal diameter D _s
More accurate control can be performed.

From the above, by controlling the melt shoulder diameter D _m , in the manufacture of the cone portion, the melt in the melting zone is dropped while the length of the cone portion which cannot be used as a product is shortened as much as possible. Can be prevented.

Here, as a result of experiments, it was found that the value of the above-mentioned distance h _m is preferably 3 to 5 mm, and values before and after that may be used.

"Relationship of the melt neck portion diameter D _n and the zone length L" The inventors have melt neck portion diameter D _n is in the fixed relationship between the zone length L after a certain time, that the correlation is greater discovered.

Therefore, rather than controlling the zone length L directly, controlling the zone length L indirectly by controlling the melt neck diameter D _n results in faster responsiveness and stable control. .

Therefore, when the straight body portion is manufactured, the surface area of the melting zone 20 can be made more constant by controlling the melt neck portion diameter D _n to be constant, so that the impurity injection rate and the vacuum in gas doping can be increased. The impurity removal rate in the method can be made more constant, and the crystallization side semiconductor rod 18
Can be made more uniform in the axial direction.

Here, the above-mentioned distance h _n is large under the condition that the change amount of the melt neck portion diameter D _n with respect to the change amount of the zone length L is large, that is, the sensitivity is high and the measured value is stable. It is determined. Specifically, it is preferable that it is closer to the constricted portion, which is the smallest diameter, and the number from the lower surface of the induction heating coil 12 is small.
Within mm is good.

<< Zone Length Control >> Next, the control of the zone length L of the melting zone will be described.

In FIG. 1, the neck diameter setting device 40 sets the melt neck target diameter D _no . This melt neck target diameter D _no is a crystallized crystal diameter D _s during the manufacture of the cone portion.
Of the crystallized crystal diameter D _si during the production of the straight body portion, and the value becomes a constant value just before the movement to the straight body portion.

Melt neck detection diameter D _ni , melt neck target diameter D _no
Are the image processing circuit 32 and the neck diameter setting device 4, respectively.
0 is supplied to the differential amplifier 42, compared and amplified, and P
It is supplied to the ID controller 43. The differential amplifier 44 compares and amplifies the detected value of the rotation speed of the lifting / lowering variable speed motor 26 by the speed detector 45 and the output value of the PID controller 43, and supplies it as an operation signal to the speed controller 46. As a result, the rotation speed of the variable speed motor 26 for raising and lowering is adjusted through the drive circuit 47, and the melt neck portion diameter D _ni is changed to the target diameter D _ni.
Controlled to be _no . Therefore, the zone length L is indirectly controlled to be constant at the time of manufacturing the straight body part.

Here, since the measurement lines of the melt shoulder diameter D _mi and the melt neck diameter D _ni are parallel to each other, the diameters can be measured by the both common methods.

Moreover, since the number of scanning lines is limited, the industrial TV camera 30 is arranged so that the scanning lines are horizontal, whereby the melt shoulder diameter D _mi and the melt neck diameter D _ni are measured. The accuracy is high.

<< Control of Crystallized Crystal Diameter in Cone >> Next, control of the crystallized crystal diameter D _{si in} the cone will be described.

The straight body part target diameter D _b is set by the straight body part diameter setting device 48 and is supplied to the diameter difference setting device 50. Diameter difference setter 50
Is designed to set the target diameter difference ΔD _o as a function of the crystallized crystal diameter D _s , an example of which is shown in FIG. The curve of this target diameter difference ΔD _o is the straight body diameter setter 4
It is determined by the straight body target diameter D _b as a parameter, which is supplied from No. 8. The diameter difference setter 50 includes the image processing circuit 3
This target diameter difference ΔD _o is output to the differential amplifier 52 in accordance with the crystallized crystal detection diameter D _si supplied from 2.

On the other hand, the melt shoulder detection diameter D _mi and the crystallized crystal detection diameter D _si are supplied from the image processing circuit 32 to the subtractor 54 and compared, and the difference is supplied to the differential amplifier 52 as the detection diameter difference ΔD _i. , The target diameter difference ΔD _o is compared.

Then, the deviation of the detected diameter difference ΔD _i with respect to the target diameter difference ΔD _o is supplied to the controller 56 as an operation signal, and then the controller 5
The output signal of 6 is supplied to the control terminal of the oscillator 10 via the switching contact 58, and the electric power P supplied from the oscillator 10 to the induction heating coil 12 is adjusted.

Here, by setting the target diameter difference ΔD _o as large as possible within the range where dislocation-free is maintained, it is possible to quickly shift to the straight body part which is the product part. However, the larger the target diameter difference ΔD _o , the more easily the melted liquid drops are generated.
The input / output characteristics of are especially important.

FIG. 3 shows the input signal of the regulator 56 and the induction heating coil 12.
An example of the relationship with the electric power P supplied to is shown. In this example, when ΔD _i = ΔD _o when ΔD _i > ΔD _{o is changed} to ΔD _i <ΔD _o , the supply power P increases by a constant value in a stepwise manner as shown in (a). Then ΔD _i =
Until ΔD _o , the supply power P increases at a constant slope as shown in (b). Such power adjustment (a),
By (b), the quick response of the detection diameter difference ΔD _i is expected.

Next, Δ when transitioning from ΔD _i <ΔD _o to ΔD _i > ΔD _o
At the time when D _i = ΔD _o , the supplied power P as shown in (c)
Decreases stepwise by a certain amount. Then, during the next fixed time, the supplied power P becomes constant as shown in (d), and if ΔD _i > ΔD _o after the fixed time elapses, the supplied power P is further stepped as shown in (e). Decrease by a certain amount. Next, as shown in (f), the state where the value of the supplied power P is kept constant for a certain period of time will be examined. If ΔD _i = ΔD _o within the fixed time, the supply power P increases by a constant value in a stepwise manner as in the case of (a). If ΔD _i = ΔD _o is not established within the fixed time, the value of the supplied power P is further reduced by one step in the same manner as in (d), (e), and (f). By adjusting the electric power (c) to (f) in this way, the rapid response is expected and the under-melting droplet is prevented.

Now, in FIG. 1, the values of the straight body target diameter D _b and the crystallized crystal detection diameter D _si are supplied to the switching circuit 62, and D _si = D
_When it becomes _b , the switching contact 58 operates to cut off the output terminal of the controller 56 and the input terminal of the oscillator 10 and the PID controller 6
The output terminal of 0 and the input terminal of the oscillator 10 are connected, and control is passed to control of the crystallized crystal detection diameter D _si in the straight body part.

<< Control of Crystallized Crystal Diameter in Straight Body >> Next, control of the crystallized crystal diameter D _{s in} the straight body will be described.

The melt shoulder diameter setting device 64 outputs a melt shoulder target diameter D _mo that is a constant value smaller than the value of the straight body target diameter D _b supplied from the straight body diameter setting device 48. The differential amplifier 66 includes a melt shoulder detection diameter D _mi and a melt shoulder target diameter D supplied from the image processing circuit 32 and the melt shoulder diameter setting device 64, respectively.
It compares and amplifies _mo and supplies it to the PID controller 60 as an operation signal. The output signal of the PID controller 60 is supplied to the oscillator 10 via the switching contact 58, the power P supplied to the induction heating coil 12 is adjusted, the melt shoulder diameter D _mi is controlled to a constant value, and indirectly. The crystallized crystal diameter D _si is controlled to a constant value.

By setting the melt shoulder target diameter D _mo as a function of the crystallized crystal diameter D _s or the length Y of the crystallized side semiconductor rod 18 with the program setting device, not only the straight body portion but also the cone portion is set. Can be controlled in the same manner.

In this case, the components 48 to 58, 62 in FIG.
And the output terminal of the PID regulator 60 is connected to the control terminal of the oscillator 10. Similarly to the diameter difference setter 50, the melt shoulder diameter setter 64 is a program setter for the crystallized crystal diameter D _s or the length Y of the crystallized side semiconductor rod, and the crystallized crystal diameter D _si or the crystallized crystal is set. The length Y of the side semiconductor rod 18 is supplied to the program setter so that the corresponding melt shoulder target diameter D _mo
Is supplied from the setter to the differential amplifier 66. The length Y of the crystallization side semiconductor rod is determined by the descending speed V of the crystallization side semiconductor rod 18.
Obtained by integrating _s .

<< Control Characteristics >> Next, the control characteristics of the crystallized crystal diameter D _s and the zone length L by adjusting the electric power P supplied to the induction heating coil 12 and the lowering speed V _p of the semiconductor rod (upper bar) on the melting side will be described. To do. It is assumed that the descending speed V _s of the crystallization side semiconductor rod 18 is constant.

When the upper bar descending speed V _p is kept constant and the supply power P is increased stepwise, the crystallized crystal diameter D _s temporarily increases, but the zone length L then increases with a delay, and accordingly. The crystallized crystal diameter D _si decreases and becomes approximately equal to the original value. That is, only increasing the supply power P does not substantially change D _si .

On the other hand, when the upper bar descending speed V _p is increased stepwise with the supply power P kept constant, the zone length L decreases relatively quickly. At the same time, the crystallized crystal diameter D _si increases. However, even if only the upper bar descending velocity V _p is increased, the crystallized crystal diameter D _si is increased, but there is a risk that the zone length L becomes too short and crystal disorder or the above-mentioned sticking occurs.

In the present embodiment, the crystallized crystal diameter D _s is controlled by the supply power P, and the zone length L is controlled by the upper bar descending speed V _{p, which} enables effective diameter control.

In addition, the melt crystal shoulder diameter D _m is used to indirectly control the crystallized crystal diameter D _s , and the melt neck diameter D _n is used to indirectly control the zone length L. In addition, the inaccuracy of the crystallized crystal diameter D _s can be eliminated, and accurate diameter control can be performed.

Therefore, the fluctuation range of the diameter D _m of the melt shoulder portion becomes small, and the response speed is fast, so that it is possible to prevent the generation of melt droplets.

Here, if the power supply P is increased and the crystallized crystal diameter D _si is increased, the zone length L is also increased. Therefore, it is necessary to increase the upper bar descending speed V _p to keep the zone length L constant. There is. If the upper bar descending speed V _p is increased, the crystallized crystal diameter D
_{Since si} increases, it is necessary to reduce the supplied power P. As described above, the control of the crystallized crystal diameter D _{si and} the control of the zone length L are interrelated and complicated.

However, when actually performing such control, mutual relation worked well, and the above reason was added, and the control with high response speed and good stability could be performed. For this reason, hunting can be reduced, and therefore, it is possible to prevent melted droplets from falling down and obtain a high-quality single crystal.

Although the relative position of the vertical rotation axis of the melting side semiconductor rod 16 and the crystallization side semiconductor rod 18 was not mentioned in the above-mentioned embodiment, the rotation axis may be coaxial or may be eccentric. The present invention is also effective.

Further, it is needless to say that an image sensor may be used as the optical sensor instead of the image pickup tube used in the industrial television camera 30.

EFFECTS OF THE INVENTION In the semiconductor rod floating melting zone control method according to the present invention, the neck portion near the heating device in the melting zone and the melt neck portion diameter at a certain distance downward from the heating device are set to a target value. The heating device is adjusted so that the moving speed of the semiconductor rod on the smelting side is adjusted so that the diameter of the shoulder of the smelting zone near the crystallization interface and the diameter of the melted shoulder at a certain distance upward from the crystallization interface reach the target value. The power supplied to the
Due to (3), the control response is faster than before,
Moreover, it has an excellent effect that stable control can be performed, and the semiconductor single crystal also largely contributes to the improvement of quality and the improvement of retention.

(1) The melt neck diameter has a fixed relationship with the zone length after a fixed time, and the correlation is large.

(2) The diameter of the melt shoulder has a fixed relationship with the crystallized crystal diameter after a fixed time, and the correlation is large.

(3) The cross-section at the melt shoulder on the crystallization side is closer to a perfect circle than the crystallization interface due to the surface tension of the melt.

[Brief description of drawings]

FIG. 1 is a block diagram of a semiconductor rod floating melting zone control device to which the present invention is applied, FIG. 2 is a diagram showing input / output characteristics of a diameter difference setting device 50, and FIG. 3 is input / output characteristics of a controller 56. FIG. FIG. 4 is a diagram for explaining the conventional example. 12: Induction heating coil 14: Semiconductor rod 16: Melting side semiconductor rod 18: Crystallizing side semiconductor rod 20: Melting zone 24: Crystallizing interface 28: Melting interface 34: Crystallizing side melt shoulder 36: Crystallizing GawaTorueki neck 38: crystal egress melt steep section V _p:熔出side semiconductor rod descending speed V _s: crystallisation side semiconductor rod lowering speed L: zone length D _ni: melt neck portion detects the diameter D _no : Melt neck target diameter D _mi : Melt shoulder detection diameter D _mo : Melt shoulder target diameter D _si : Crystallized crystal detection diameter ΔD _i : Detection diameter difference ΔD _o : Target diameter difference D _b : Straight body Part target diameter

Claims (3)

[Claims] 1. A vertically arranged semiconductor rod (14) is melted by a heating device (12) to form a melting zone (20), and a melting side semiconductor rod (16) above the heating device. And a crystallization side semiconductor rod (18) below the heating device,
By moving the melting zone in the axial direction relative to the heating device, the melting zone is moved in the axial direction and an image of the melting zone and its vicinity is picked up by an image pickup device (30), and an image picked up by the image pickup device is taken. Is processed by an image processing means (32) to measure a geometrical amount, and the electric power supplied to the heating device and the relative moving speed of the semiconductor rod are adjusted according to the measured value. In the above, the geometrical quantity is the shoulder (34) near the crystallization interface (24) of the melt zone and the melt shoulder diameter (D _m ) at a certain distance upward from the crystallization interface (24). , A neck portion (36) near the heating device in the melting zone and a melt neck portion diameter (D _n ) at a certain distance downward from the heating device, wherein the melt neck diameter reaches a target value. Adjust the moving speed of the melt side semiconductor rod so that Semiconductor rods floating melting zone control method characterized by adjusting the power supplied to the heating device so that the diameter becomes the target value. 2. The melt shoulder diameter (D _m ) is a melt diameter at a fixed distance of 3 to 5 mm upward from the crystallization interface (24). The method according to item 1. 3. The melt neck diameter (D _n ) is the melt diameter at a fixed distance of several mm downward from the heating device (12). Item or the method according to Item 2.