JPH05279174A - Method for lifting single crystal - Google Patents

Abstract

PURPOSE:To provide the subject method capable of lifting the single crystal having a preliminarily set shape/dimension and enabling to obtain the single crystal iof a high quality reduced in the defects caused by its heat distortion and having the stable deposition amount of impurities under an approximately constant lifting rate for the single crystal. CONSTITUTION:The single crystal having a preliminarily set shape dimension is lifted by operating a single crystal-lifting device at a lifting rate within a preliminarily set range and by adjusting the heat-generating amount and temperature of a heater. The single crystal-lifting device comprises a crucible for melting the polycrystals of a raw material for semiconductors, a heating means arranged around the crucible, a lifting means for growing the single crystal and lifting the single crystal from a melted liquid in the crucible, and a means for measuring the diameter of the lifted single crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pulling a single crystal, more specifically, a crucible for melting a polycrystal semiconductor material, a heating means arranged around the crucible, and a single crystal from the melt in the crucible. The present invention relates to a single crystal pulling method for controlling the diameter of a single crystal using a single crystal pulling apparatus including a pulling tool for pulling while growing the single crystal and a means for measuring the diameter of the pulled single crystal.

[0002]

2. Description of the Related Art A control system of a general single crystal pulling apparatus will be described with reference to FIG. Reference numeral 11 in the drawing denotes a crucible, a heater 12 is arranged around the crucible 11, and a pulling tool 14 for pulling up the single crystal 13 while growing the single crystal 13 is arranged above the crucible 11. And crucible 11
The computer 15 controls the rotation speed, the temperature of the heater 12, the diameter of the single crystal 13, and the pulling speed of the pulling tool 14.

Conventionally, in the single crystal pulling apparatus 10, the manipulated variables for controlling the diameter of the single crystal 13 include the single crystal pulling speed, the heater temperature, and the rotation speed of the crucible 11. Of these, the single crystal pulling rate is particularly suitable for the manipulated variable because the single crystal 13 has a quick response to the diameter of the single crystal 13.
On the other hand, the heater temperature has a slow response to the diameter of the single crystal 13,
Since there is a dead time in which the diameter does not change from the time when the heater temperature is changed to the time when the diameter starts to change, it has been considered difficult to set a single operation amount. Therefore, the diameter of the single crystal 13 is temporarily controlled by the single crystal pulling speed, and the single crystal pulling is performed by simple feedback control in which the heater temperature is corrected so as to eliminate the average deviation of the actual single crystal pulling speed from the reference pulling speed. The method was adopted (Japanese Patent Publication No. 51-5993).

[0004]

In the method of pulling the single crystal 13 using the above-mentioned pulling speed as the manipulated variable,
The response of the single crystal diameter to the manipulated variable of the single crystal pulling rate is fast, and the controllability of the single crystal diameter is good, but the distance between the solidification interface of the single crystal 13 and the surface of the melt varies because the single crystal pulling rate is changed. The amount of heat that flows into the interface fluctuates, thermal distortion occurs and defects easily occur,
By changing the single crystal pulling rate, the cooling temperature of the crystal in the cooling hood (16 in FIG. 3) fluctuates, and there are problems such as generation of defect seeds due to thermal strain.

Further, since the single crystal pulling rate is constantly changing, and promptly compensating for this with a heater temperature is a large disturbance, so generally, the average single crystal pulling rate for a certain period of time is also as described above. However, due to the delay in the response of the heater temperature, sufficient compensation cannot be performed, and the pulling speed may deviate from the target. Therefore, the heat treatment time of the portion of the single crystal 13 that has already been pulled and cooled fluctuates, and the precipitation amount of impurities (mainly oxygen in the case of silicon) fluctuates.
There was a problem that the quality of 3 causes a big problem.

Therefore, when this single crystal 13 is used as a substrate for a VLSI having a high degree of integration of megabits or more, L
There is also a problem that the product yield of SI is reduced.

On the other hand, when it is attempted to control only by the heater temperature, the response of the heater temperature is slow and there is a dead time, and a simple feedback for changing the manipulated variable based on the deviation between the conventional crystal diameter and the target diameter. In the worst case of control, crucible 1
There was a problem that the melt temperature of No. 1 was too low and the melt was solidified, and conversely the melt temperature was too high and the single crystal 13 was torn from the melt.

The present invention has been invented in view of the above problems, and provides a single crystal pulling method capable of producing a single crystal having few defects due to thermal strain and a stable precipitation amount of impurities such as oxygen. The purpose is to do.

[0009]

In order to achieve the above object, a method for pulling a single crystal according to the present invention comprises a crucible for melting a polycrystal of a semiconductor material, a heating means arranged around the crucible, and For the purpose of controlling the diameter of the single crystal, the pulling rate is controlled by using a single crystal pulling device including a pulling tool that pulls up the single crystal from the melt in the crucible while growing the single crystal, and a means for measuring the diameter of the pulled single crystal. A single crystal having a preset shape and size is pulled by operating the heater temperature and the number of rotations of the crucible in addition to operating within a preset range (1), and the above (1) In the single crystal pulling method, from the past and present values of the heater temperature, the rotation speed of the crucible and the single crystal pulling speed, and the past and present values of the single crystal diameter. Using a model to predict the future value of the crystal diameter, predict the deviation between the predicted value and the target value of the single crystal diameter under the condition that the rotation speed of the crucible is maintained as it is, the single crystal of a predetermined time ahead To eliminate the deviation between the predicted value and the target value of the diameter, the square sum of the deviation between the predicted value and the target value of the single crystal diameter up to a predetermined time, and the square sum of the heater temperature change amount calculated from the model, The heater temperature change amount and the pull speed change amount up to a predetermined time ahead so that the sum of the square of the pull speed change amount and the sum of the square of the deviation between the pull speed and the target pull speed multiplied by each coefficient is minimized. Is determined (2).

Further, in the single crystal pulling method described in (1) above, past and present values of heater temperature and single crystal pulling rate, past and present values and planned values of crucible rotation speed, and past single crystal diameter. Using the model that predicts the future value of the single crystal diameter from the current value and the current value, the deviation between the predicted value of the single crystal diameter and the target value is predicted, and the deviation between the predicted value and the target value of the single crystal diameter after a predetermined time So as to eliminate the square sum of the deviation between the predicted value and the target value of the single crystal diameter up to a predetermined time ahead, the square sum of the heater temperature change amount calculated from the model, the square sum of the pull rate change amount, and the pull rate. The heater temperature change amount and the pull speed change amount up to a predetermined time ahead are determined so that the sum of the squared sum of the deviations between the target temperature and the target pull speed is multiplied by a coefficient, and the heater temperature and the pull speed are changed. Prior to by operating by operating the rotational speed of the crucible is characterized by pulling a single crystal (3).

Alternatively, in the single crystal pulling method described in the above (1), the past actual values of the heater temperature, the crucible rotation speed, the single crystal pulling speed, and the single crystal diameter, and the target value and the actual value of the single crystal diameter. And the past total of the deviation, the past total of the deviation between the target value and the actual value of the single crystal pulling speed, the future target value of the single crystal diameter and the planned value of the single crystal pulling speed, respectively. , The heater temperature change amount and the pulling speed change amount are multiplied by a gain determined in advance so as to obtain the heater temperature change amount and the pulling speed change amount so that the single crystal diameter becomes the target value and the pulling speed does not deviate from the target. It is characterized by determining (4).

Alternatively, in the single crystal pulling method described in the above (1), past actual values of the heater temperature, the crucible rotation speed, the single crystal pulling speed, and the single crystal diameter, and the target value and the actual value of the single crystal diameter. And the past total of the deviation, the past total of the deviation between the target value and the actual value of the single crystal pulling speed, the future target value of the single crystal diameter, the planned value of the single crystal pulling speed, and the crucible. To each of the planned values of the rotation speed of the above, multiply the heater temperature change amount and the pulling speed change amount that are predetermined so that the single crystal diameter becomes the target value and the pulling speed does not deviate from the target, by multiplying by The heater temperature change amount and the pulling speed change amount are determined (5).

In the method for pulling a single crystal according to the above (3) or (5), a time pattern is given to the rotation speed of the crucible so that the oxygen concentration in the single crystal falls within a predetermined range, and the amount of influence on it is compensated. However, by determining the heater temperature change amount and the pulling speed change amount, the oxygen concentration in the single crystal is set within a predetermined range (6).

That is, the inventors of the present invention created a discretized single crystal diameter prediction formula for quantitatively predicting a dynamic change in the diameter of the single crystal due to fluctuations in the single crystal pulling rate and heater temperature. By determining the heater temperature change amount and the pulling speed change amount based on the relational expression, the deviation between the pulling speed change amount and the target pulling speed and the pulling speed can be reduced, and moreover, the single crystal with substantially the same dimensional accuracy as the conventional one. The present invention has been accomplished by discovering that the above can be raised.

The equation for predicting the diameter of a single crystal is shown in Equation 1.

[0016]

[Equation 1]

The order m of the equation shown in the equation 1 is determined by the accuracy required for the model, but here m = 3.

Mathematical formula 1 predicts the single crystal diameter which is one time after the discrete time Δt from the past and present values of the single crystal diameter, the heater temperature, the single crystal pulling speed, and the crucible rotation speed. An example is shown in FIG.

In FIG. 2, the amount of change in the diameter of the single crystal with respect to the passage of time calculated by Equation 1 is shown by the dotted line, and the amount of change in the actual diameter of the single crystal is shown by the solid line.

A method for controlling the heater temperature and the pulling rate will be described below. Using the model for predicting the single crystal diameter from the past and present values of single crystal diameter, heater temperature, single crystal pulling speed, and crucible rotation speed shown in Equation 1, the crucible rotation speed is maintained as it is. The sum of squares Σ (R _{n + i} −X _{n + i} ) ² of the difference between the predicted diameter and the target diameter after L hours and the sum of squares of the heater temperature change amount after K hours Σ. (U _{n + i + 1} −U _{n + i} ) ² , sum of squares of change in pulling speed Σ (V _{n + i + l} −V _{n + i} ) ² , sum of squares of deviation between target pulling speed and pulling speed Σ (S
_{n + i} −V _{n + i} ) ² and weighting factors Qu, Qv, Qs, respectively.
The sum of the value obtained by multiplying the determining heater temperature operating amount U _n ~U _n + _K and pulling speed manipulated variable V _n ~V _n + _k to minimize.

Alternatively, a model for predicting the single crystal diameter based on the past and present values of the single crystal diameter, the heater temperature, and the single crystal pulling speed and the past, present and planned values of the crucible rotation speed shown in Equation 1 is used. Then, the sum of squares Σ (R _{n + i} −X _{n + i} ) ² of the difference between the predicted diameter and the target diameter up to the L-th time is used, and K
Sum of squares of heater temperature change amount up to time Σ (U _{n + i + 1} −
U _{n + i} ) ² , the sum of squares of the pulling speed change amount Σ (V _{n + i + l}
−V _{n + i} ) ² and the sum of squared sum Σ (S _{n + i} −V _{n + i} ) ² of the deviation between the target pulling speed and the pulling speed, multiplied by the weighting factors Qu, Qv, and Qs, respectively. there is a method of determining heater temperature operating amount U _n ~U _n + _K and pulling speed manipulated variable V _n ~V _n + _k to a minimum.

Alternatively, as shown in the following equations 2 and 3, the past history of diameter (first term), the past history of heater temperature change (second term), and the past history of single crystal pulling rate. (Clause 3), Past history of crucible rotation speed (Claim 4),
The past integrated value of the deviation between the target diameter and the measured diameter prepared to eliminate the deviation from the target diameter (section 5), and the target pulling speed and pulling speed prepared to eliminate the deviation from the target pulling speed Heater operation amount and pulling speed considering the past accumulated value of deviation from (6th item), planned value of crucible rotation speed (7th item) and future target diameter of single crystal diameter (8th item) Determine the manipulated variable.

[0023]

[Equation 2]

[0024]

[Equation 3]

Further, in the equations shown in the equations 2 and 3,
There is also a method of determining the heater temperature change amount and the pulling speed change amount without considering the planned value of the rotation speed of the crucible (7th term).

The control gain in the above-mentioned control law is determined by a mathematical method so as to minimize the evaluation function shown in equation (4).

[0027]

[Equation 4]

Further, there is also a method of giving a time pattern to the rotational speed of the crucible in order to keep the oxygen concentration in the crystal constant, and determining the heater temperature change amount while compensating for the amount of influence on it.

[0029]

According to the above-mentioned method, the crucible for melting the polycrystal semiconductor material, the heating means arranged around the crucible, and the pulling tool for pulling the single crystal from the melt in the crucible while growing the single crystal. , Using a single crystal pulling apparatus consisting of a means for measuring the diameter of the pulled single crystal, the pulling speed is set within a preset range for diameter control, and the heater temperature is set in advance. Since the single crystal with the specified shape and dimensions is pulled up, there is little fluctuation in the distance between the solidification interface of the single crystal and the surface of the melt, the amount of heat flowing into the interface is stable, and there are few defects due to thermal strain. The heat treatment time of the single crystal portion therein is constant, and a single crystal in which the amount of impurities such as oxygen deposited is stable is manufactured.

Also, in the single crystal pulling method described in (2) above, the same effect as in (1) above can be obtained.

Alternatively, the future value of the single crystal diameter is calculated from the past and present values of the heater temperature and the pulling rate of the single crystal, the past, present and planned values of the rotation speed of the crucible, and the past and present values of the single crystal diameter. Using the model to predict, predict the deviation between the predicted value of the single crystal diameter and the target value, so as to eliminate the deviation between the predicted value and the target value of the single crystal diameter after a predetermined time, the single crystal up to the predetermined time Sum of squares of deviation between predicted value of diameter and target value, sum of squares of heater temperature change amount calculated from the model, sum of squares of change amount of pulling speed, sum of squares of difference between target pulling speed and pulling speed Rotation of the crucible is determined by determining the heater temperature change amount and the pull-up speed change amount up to a predetermined time so that the sum of the value multiplied by the coefficient is minimized and operating the heater temperature and the pull-up speed in advance. number Operation to when pulling a single crystal, the desired oxygen concentration in the single crystal in addition to the above effects is included, a single crystal amount impurity deposition is stabilized is manufactured.

Alternatively, also in the single crystal pulling method described in (4) above, the same action as in the single crystal pulling method described in (1) above can be obtained.

In the method for pulling a single crystal according to the above (3) or (5), a time pattern is given to the rotation speed of the crucible so that the oxygen concentration in the single crystal falls within a predetermined range, and the amount of influence on it is compensated. However, when determining the heater temperature change amount and the pulling speed change amount, the oxygen concentration in the single crystal falls within a predetermined range, and a single crystal is produced in which the amount of impurity precipitation is stable and the number of defects due to thermal strain is small. It

[0034]

EXAMPLES Examples of the single crystal pulling method according to the present invention will be described below. The configuration of the control system of the single crystal pulling apparatus according to the present embodiment is almost the same as that of the conventional one, and the description thereof will be omitted.

In the single crystal pulling method according to this embodiment, the target diameter is 154 mm and the target pulling speed is 1.1 m.
It was set at m / min.

From the equation shown in the equation 1, 30 minutes ahead (L = 3
0 min) the sum of squares of the deviation between the predicted diameter of the single crystal and the target diameter, the value obtained by multiplying the sum of squares of the heater temperature change amount up to 20 minutes (K = 20 min) by 1000, and the square of the pulling speed change amount. Obtain the heater temperature change amount and the pull speed change amount up to 20 minutes ahead that minimizes the sum of the value obtained by multiplying the sum by 10 and the value obtained by multiplying the sum of squares of the difference between the target pull speed and the pull speed by 100. FIG. 1 shows the diameter control result when the heater temperature change amount is determined.

As is apparent from FIG. 1, by operating the pulling rate within a preset range and controlling the heater temperature detected by the voltage change of the temperature sensor, the diameter variation is small and the desired diameter is obtained. It can be seen that the single crystal can be pulled.

Also, in the evaluation function J shown in the equation 4, Q
The gain was determined with u = 1000, Qv = 10, and Qs = 100, and the diameter control result when used was similar to that shown in FIG.

Further, a time pattern is given to the rotation speed of the crucible so that the oxygen concentration in the single crystal falls within a predetermined range.
Table 1 shows the single crystal quality when the influence amount on it is compensated by changing the heater temperature and changing the pulling rate.

[0040]

[Table 1]

As described above, in the single crystal pulling method according to the above-mentioned embodiment, the single crystal pulling speed is operated within the preset range, and the heater temperature is controlled to obtain the single crystal having the preset shape and dimension. The crystal can be pulled up, and there are few defects due to thermal strain,
It is possible to obtain a high-quality single crystal in which the amount of precipitated impurities is stable.

In the above embodiment, the case where the heater temperature amount is operated has been described, but the heater heat input amount may be operated instead of the heater temperature.

[0043]

As described above in detail, in the method for pulling a single crystal according to the present invention, a crucible for melting a polycrystalline semiconductor material, a heating means arranged around the crucible,
A pulling tool for pulling while growing a single crystal from the melt in the crucible, and a single crystal pulling device consisting of means for measuring the diameter of the pulled single crystal, the pulling speed is operated within a preset range In addition, by operating the heater temperature, the single crystal having a preset geometrical dimension is pulled up, so there is little fluctuation in the distance between the solidification interface of the single crystal and the surface of the melt, and the amount of heat flowing into the interface is stable. In addition, the occurrence of defects due to thermal strain can be reduced, and the heat treatment time of the single crystal portion during pulling and cooling can be made substantially constant, and a single crystal with a stable precipitation amount of impurities such as oxygen can be manufactured. ..

Also, in the single crystal pulling method described in (2) above, the same effect as in (1) above can be obtained.

Alternatively, the past and present values of the heat input to the heater and the pulling rate of the single crystal, the past and present values and the planned value of the rotation speed of the crucible, and the past and present values of the single crystal diameter are used to determine the future value of the single crystal diameter. Using a model that predicts the deviation of the predicted value of the single crystal diameter from the target value, and to eliminate the deviation of the predicted value of the single crystal diameter of the predetermined time from the target value, The square sum of the deviation between the predicted value and the target value of the crystal diameter, the square sum of the heater temperature change amount calculated from the model, the square sum of the pulling speed change amount, and the square sum of the deviation between the target pulling speed and the pulling speed. The heater temperature change amount and the pulling speed change amount up to a predetermined time are determined so that the sum of the values multiplied by the respective coefficients is minimized, and the heater temperature and the pulling speed are operated in advance to operate the crucible. Number of rotations Operation to when pulling a single crystal, in addition to the effect desired oxygen in the single crystal is included, the amount of impurity deposition can be produced a stable single crystal.

Alternatively, in the single crystal pulling method described in (4) above, the same effect as in the single crystal pulling method described in (1) above can be obtained.

In the method for pulling a single crystal according to the above (3) or (5), a time pattern is given to the rotational speed of the crucible so that the oxygen concentration in the single crystal falls within a predetermined range, and the amount of influence on it is compensated. However, when the heater temperature change amount is determined, the oxygen concentration in the single crystal falls within a predetermined range, the amount of impurity precipitation is stabilized, and a single crystal having few defects due to thermal strain can be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing the diameter controllability of an example of a single crystal pulling method according to the present invention.

FIG. 2 is a graph showing the estimation accuracy of the diameter of the model of the single crystal pulling method.

FIG. 3 is a schematic diagram showing a configuration of a diameter control system in a single crystal pulling method.

Front page continued (72) Inventor Matoba Yoshiyuki, 4-533 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Toshiyuki Yamamoto 4-53, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Issue Sumitomo Metal Industries Co., Ltd. (72) Inventor Eiji Kajita 2201 Kamioda, Kohoku-cho, Kishima-gun, Saga Prefecture Kyushu Electronic Metals Co., Ltd. Yasunori Maeda 2201 Kamioda, Kokuhoku-cho, Kijima-jima, Saga Prefecture Kyushu Electronic Metal Co., Ltd.

Claims (6)

[Claims] 1. A crucible for melting a polycrystal semiconductor material, a heating means arranged around the crucible, a pulling tool for pulling a single crystal from a melt in the crucible while growing the single crystal, and the pulled single crystal. Using a single crystal pulling device consisting of means for measuring the diameter of the crystal, operating the pulling speed within a preset range, and operating the heater heat value or heater temperature (hereinafter referred to as "heater temperature"). According to the method, a single crystal pulling method of pulling a single crystal having a preset shape and dimension. 2. A model for predicting a future value of a single crystal diameter from past and present values of a heater temperature, a rotation speed of a crucible and a pulling speed of a single crystal, and past and present values of a diameter of a single crystal is used, Predict the deviation between the predicted value and the target value of the single crystal diameter under the condition that the rotation speed is maintained as it is, so as to eliminate the deviation between the predicted value and the target value of the single crystal diameter after a predetermined time, Squared sum of deviations between the predicted value and the target value of the single crystal diameter up to a predetermined time ahead, the squared sum of the heater temperature change amount calculated from the model, the squared sum of the pulling speed change amount, the pulling speed and the target pulling speed, The method for pulling a single crystal according to claim 1, wherein the heater temperature change amount and the pulling speed change amount up to a predetermined time ahead are determined so that the sum of the squared sum of the deviations of the above ones and the value obtained by multiplying each coefficient is minimized. 3. The future value of the single crystal diameter is calculated from the past and present values of the heater temperature and the pulling speed of the single crystal, the past, present and planned values of the rotation speed of the crucible, and the past and present values of the single crystal diameter. Using the model to predict, predict the deviation between the predicted value of the single crystal diameter and the target value, so as to eliminate the deviation between the predicted value and the target value of the single crystal diameter after a predetermined time, the single crystal up to the predetermined time Sum of squares of deviation between predicted value of diameter and target value, sum of squares of heater temperature change amount calculated from the model, sum of squares of change amount of pulling speed, sum of squares of difference between pulling speed and target pulling speed, respectively. Rotation of the crucible is determined by determining the heater temperature change amount and the pull-up speed change amount up to a predetermined time so that the sum of the value multiplied by the coefficient is minimized and operating the heater temperature and the pull-up speed in advance. Manipulating numbers The method for pulling a single crystal according to claim 1, wherein the single crystal is pulled. 4. The past actual values of the heater temperature, the crucible rotation speed, the single crystal pulling speed, and the single crystal diameter, and the past total of deviations between the target value and the actual value of the single crystal diameter, and the single crystal. The past total of the deviation between the target value and the actual value of the pulling rate, and the future target value of the single crystal diameter and the planned value of the single crystal pulling rate, respectively, the single crystal diameter becomes the target value and the pulling rate 2. The method for pulling a single crystal according to claim 1, wherein the heater temperature change amount and the pulling speed change amount are determined by multiplying the heater temperature change amount and the pulling speed change amount by a predetermined gain so that the heater temperature change amount and the pulling speed change amount are obtained. .. 5. The past actual values of the heater temperature, the rotation speed of the crucible, the single crystal pulling speed, and the single crystal diameter, the past total of the deviations between the target value and the actual value of the single crystal diameter, and the single crystal pulling. The past total of the deviation between the target value of the speed and the actual value, the future target value of the single crystal diameter, the planned value of the single crystal pulling speed, and the planned value of the rotation speed of the crucible, respectively, Multiply the heater temperature change amount and the pulling speed change amount by multiplying the heater temperature change amount and the pulling speed change amount by a predetermined gain so that the single crystal diameter becomes the target value and the pulling speed does not deviate from the target. The single crystal pulling method according to claim 1, which is determined. 6. A heater temperature change amount and a pulling speed change amount are determined while giving a time pattern to the rotation speed of the crucible so that the oxygen concentration in the single crystal falls within a predetermined range, and compensating the influence amount thereof. 6. The method for pulling a single crystal according to claim 3, wherein the oxygen concentration in the single crystal is set within a predetermined range according to the above.