JP2001146496A - Single crystal pulling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the controlling accuracy of pulling speed in a single crystal pulling method. SOLUTION: This single crystal pulling method comprises the pulling of a semiconductor single crystal from molten semiconductor in a crucible. The method contains a step S6 of detecting the deviation ratio (d) of the real pulling speed to the preset pulling speed and temperature correction steps S81-S89 to correct the temperature of the molten semiconductor by a correction factor dependent upon the above speed deviation ratio. The temperature correction factor is changed by the temperature correction steps according to the growing condition varying according to the progress of the pulling of the semiconductor single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal pulling method for pulling a semiconductor single crystal from a semiconductor melt stored in a crucible using a CZ method (Czochralski method).

[0002]

2. Description of the Related Art In general, a single crystal pulling method using a CZ method is known as one of means for growing a semiconductor single crystal such as silicon (Si) or gallium arsenide (GaAs). In this single crystal pulling method, for example, a semiconductor melt is stored in a quartz crucible provided on a susceptor inside a chamber, and the semiconductor melt is brought to a predetermined temperature by a cylindrical heater arranged around the quartz crucible. This is a method of heating and pulling a semiconductor single crystal from the semiconductor melt.

In this pulling method, a method of controlling a heating amount by a heater and a method of controlling a pulling speed are generally used in order to control a diameter of a semiconductor single crystal to be pulled to a constant value. Since the response of the diameter change to the change in the heating amount is slow and it is difficult to perform high-precision control, the latter, which has a fast response to the diameter change, is used. Conventionally, the control of the pulling speed is performed by detecting a ratio of an actual pulling speed to a preset pulling speed as a speed deviation ratio, monitoring the speed deviation ratio at a constant time interval, and controlling a temperature by a heater. Feedback is performed so that the speed deviation rate is reduced by performing correction with a predetermined correction amount (a control method for correcting a deviation in the pulling speed by temperature: an AGC control method).

[0004]

However, the above-mentioned conventional single crystal pulling method has the following problems. That is, conventionally, in the control of the pulling speed,
The temperature correction amount and the correction time interval for the speed deviation rate are constant over the entire pulling length irrespective of the pulling length of the semiconductor single crystal C, but during pulling, according to the pulling length,
Since the pulling speed, the temperature, the number of rotations of the crucible, and the like change based on a preset program, the temperature correction amount and the correction interval may be too large or small, which may cause the speed fluctuation. Had become.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a single crystal pulling method capable of controlling the pulling speed with higher precision.

[0006]

The present invention has the following features to attain the object mentioned above. In other words, the single crystal pulling method of the present invention is a single crystal pulling method for pulling a semiconductor single crystal from a semiconductor melt in a crucible, wherein a ratio of an actual pulling speed to a set pulling speed is set to a speed. A speed deviation rate detection step of detecting as a deviation rate, and a temperature correction step of correcting a preset temperature of the semiconductor melt with a different temperature correction amount according to the speed deviation rate, the temperature correction step includes: A technique is employed in which the temperature correction amount is changed according to a growth condition that changes with the pulling length of the semiconductor single crystal.

Further, the single crystal pulling method of the present invention is a single crystal pulling method for pulling a semiconductor single crystal from a semiconductor melt in a crucible, wherein a set pulling speed and an actual pulling speed are compared. And a temperature correction step of correcting a preset temperature of the semiconductor melt with a different temperature correction amount according to the speed deviation amount. The correction step employs a technique of changing the temperature correction amount in accordance with a growth condition that changes with the pulling length of the semiconductor single crystal.

In these single crystal pulling methods, in the temperature correction step, the amount of temperature correction is changed according to the growth conditions that change with the pulling length of the semiconductor single crystal. Can be made to correspond to the temperature correction amount, and the speed fluctuation can be suppressed with higher accuracy. For example, the correction amount is appropriately adjusted by increasing the temperature correction amount in the portion of the pull-up portion where the change in the growth condition is large, and decreasing the temperature correction amount in the portion of the pull-up portion where the change in the growth condition is small. Speed fluctuation can be further suppressed.

In these single crystal pulling methods, it is preferable that the growth condition is at least one of the rate of change of the temperature, the rate of change of the pulling speed, and the number of rotations of the crucible. In other words, in this case, a correction can be made in consideration of these growth conditions that have a different program depending on the pulling length and that have a great influence on the speed fluctuation, and more appropriate feedback becomes possible.

In these single crystal pulling methods, in the temperature correction step, the pulling length is divided into a plurality of regions, and the temperature correction amount according to the growth condition is determined in advance for each of these regions. Preferably. That is, in this case,
Since the temperature correction value corresponding to each region is determined in advance, the temperature correction amount according to the growth condition can be easily determined by determining which region has the pulling length at the time of correction.

In these single crystal pulling methods, it is preferable that, in the temperature correction step, the correction is performed at every preset cycle time, and the cycle time is changed according to the pulling length of the semiconductor single crystal. . That is, in this case, the cycle time can be made to correspond to different growth conditions depending on the pulling length, and the speed fluctuation can be suppressed with higher accuracy. For example, the cycle time is shortened in the portion of the pulling length where the change of the growth condition is large, and the cycle time is lengthened in the portion of the pulling length where the change of the growth condition is small, so that the speed fluctuation is more effectively suppressed. be able to.

Further, in the single crystal pulling method, it is preferable that a plurality of different cycle times are simultaneously set in the temperature correction step. That is,
In this case, it is possible to cope with a shift in the pulling speed that changes in various ways, as compared with the case where the correction is performed only by one cycle time.

Further, in these single crystal pulling methods, it is preferable to use an average of the pulling speed repeatedly measured at a constant sampling time within the cycle time as the actual pulling speed. That is, in this case, since the averaged value is used as the actual pulling speed, appropriate correction can be performed even if the pulling speed varies within the cycle time or a large deviation occurs locally.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of a single crystal pulling method according to the present invention will be described with reference to FIGS. In these figures, reference numeral 1 denotes a chamber, 2 denotes a shaft, 3 denotes a susceptor, 4 denotes a crucible, 5 denotes a heater, 6
Indicates a heat retaining cylinder.

FIG. 1 shows a single crystal pulling apparatus for carrying out the single crystal pulling method of the present embodiment. The single crystal pulling apparatus is provided in a chamber 1 which is a hollow airtight container. A vertically movable shaft 2 erected vertically below the center of the chamber 1, a susceptor 3 mounted on the shaft 2, and a silicon melt mounted and supported on the susceptor 3 (SiO2) for storing the semiconductor melt L
A crucible 4 made of stainless steel, a heater 5 arranged on the outer periphery of the crucible 4 at a predetermined distance, and a heat retaining cylinder 6 arranged around the heater 5 are arranged.

The single crystal pulling apparatus has a flow tube 7 supported by an upper ring 8 above the crucible 4. The flow tube 7 cuts off radiant heat to the semiconductor single crystal C during growth, and blows onto the semiconductor melt L through an argon gas (inert gas) supplied from a gas inlet 1 a at the upper end of the chamber 1. , Which blows off SiO2 generated from the semiconductor melt L.

The crucible 4 rotates on a horizontal plane about the axis of the shaft 2. The heater 5 heats and melts the silicon raw material in the crucible 4 and keeps the temperature of the semiconductor melt L generated. Usually, resistance heating is used.

The heat insulating cylinder 6 is formed of a heat insulating material 6a made of carbon fiber (carbon fiber), and has a carbon plate 6b as a support plate on the inner surface thereof. A pull-up wire 9 is suspended from the upper part of the chamber 1 so as to be vertically movable and rotatable, and a silicon seed crystal is fixed to a lower end of the pull-up wire 9. The upper end of the pulling wire 9 is connected to a lifting / lowering rotating mechanism 11 composed of a motor or the like for raising / lowering and rotating the lifting wire 9, and the lifting / lowering rotating mechanism 11 is connected to a control unit 12. I have.

The control unit 12 controls each of the growth conditions such as the pulling speed by controlling the lifting / lowering rotating mechanism 11 and the like, and also measures the diameter measurement data of the semiconductor single crystal C by a diameter sensor (not shown) and the like. It has a function of calculating a temperature correction amount for stabilizing the pulling speed based on the speed sampling data and various set values and performing temperature correction control. Note that a transparent window 12 for observing the solid-liquid interface of the semiconductor single crystal C is provided in the upper part of the chamber 1.

Next, the single crystal pulling method according to the present embodiment will be described below.

First, an argon gas is supplied from the gas inlet 1a, and the heater 5 is energized to melt the silicon raw material in the crucible 4 to form a semiconductor melt L. Then, the power of the heater 5 is adjusted to adjust the semiconductor melt. The vicinity of the center liquid level of liquid L is kept at the single crystal growth temperature. Next, the seed crystal suspended by the pull-up wire 9 is lowered and immersed in the semiconductor melt L to be blended, so that dislocation is eliminated by so-called necking. Then, the crucible 5 and the pull-up wire 9 are opposite to each other. The semiconductor single crystal C is pulled up and grown while being rotated.

After growing the shoulder portion of the semiconductor single crystal C, a straight body portion having a constant diameter is grown. At this time, in order to keep the diameter of the semiconductor single crystal C to be pulled constant, the diameter is actually measured by a diameter sensor, and the elevating / lowering rotating mechanism 11 is controlled by the control unit 12, so that the actual pulling speed of the pulling wire 9 is reduced. For example, as shown in FIG. 2 (a), when deviation from a preset program pulling speed (set pulling speed) is performed, the heater 5 is controlled to perform temperature correction.

The control method for correcting the pulling speed with the temperature will be described with reference to the flowchart shown in FIG. 3. First, when the growth of the straight body portion is started, the current pulling length region is determined. (Step S1). That is, it is determined whether the pull-up length of the straight body portion is the area A of 0 mm or more and less than αmm, the area B of αmm or more and less than βmm, or the area C of βmm or more. Next, the temperature correction amount for each area is determined. Are determined (steps S21, S22,
S23).

The cycle time is different depending on the pulling length, that is, the number and numerical value set for each area are different. In areas A and B, two for X and Y are set at the same time, and area C is set for W. One of them is set. Immediately after the start of the growth, the region A is determined, and the parameters and the cycle time in the region A are determined.

The above parameters are set according to at least one of the rate of change of temperature, the rate of change of the pulling speed, and the number of rotations of the crucible 4, for example, as shown in Table 1 below. Is determined. The parameters also determine the speed deviation rate range in which it is not necessary to perform temperature correction, that is, the upper and lower limits of the dead zone. Therefore, the upper and lower limits of the dead zone are also set differently for each region. For example, in the region A, the lower limit of the dead zone is set to a speed deviation rate of 95%, and the upper limit is set to a speed deviation rate of 105%.

[0026]

[Table 1]

Further, during the growth of the straight body portion, the sampling time for measuring the pulling speed is set at 1 second intervals, and the measured pulling speed is sent to the control unit 12 (step S2).
Next, it is determined whether or not the determined cycle time has elapsed (step S4). If the cycle time has elapsed, the process proceeds to a temperature correction process. Do not do.

When the cycle time has elapsed, the control unit 12 calculates an average pulling speed (actual pulling speed) by averaging the pulling speeds detected during the cycle time (step S5). . Further, the ratio of the average pulling speed to the set pulling speed in which a profile is set in advance is calculated as the speed shift ratio d by the following equation (1) (step S6) (speed shift ratio detecting step). Speed deviation rate (d) =
((Average lifting speed-setting lifting speed) / setting lifting speed) x
100 ... (1)

Next, the determined speed deviation rate d is determined to fall within a range divided into nine, and the temperature of the semiconductor melt L set in advance is corrected according to the speed deviation rate d. The correction amount is calculated (Step S7). In the present embodiment, the speed deviation rate d is determined to be one of the following nine temperature corrections 1 to 8 and no temperature correction, and the temperature correction amount is determined based on parameters individually set for these.

Temperature correction 1: d ≧ 130% Temperature correction 2: 130%> d ≧ 120% Temperature correction 3: 120%> d ≧ 110% Temperature correction 4: 110%> d ≧ dead band upper limit Temperature correction pear: dead band upper limit > D> dead zone lower limit Temperature correction 5: dead zone lower limit ≧ d <90% temperature correction 6: 90% ≧ d> 80% temperature correction 7: 80% ≧ d> 70% temperature correction 8: 70% ≧ d

That is, the temperature correction amount is determined in accordance with the pulling length of the semiconductor single crystal C at the time of correction, and in this embodiment, which of the regions A and B the correction time belongs to Determines the above parameter for the speed deviation rate d, and further determines the temperature correction amount depending on whether the speed deviation rate d belongs to any of the temperature corrections 1 to 8. As shown in FIGS. 2A, 2B, and 2C, the temperature correction amount in each region is a predetermined rate of change in temperature, a rate of change in pulling speed, or the number of rotations of the crucible 4. Is calculated by multiplying a parameter determined according to at least one of the above by a temperature change factor, and is set in advance for each area by the following relational expression (2).

Temperature correction amount = Temperature change factor × (Slope of temperature program + Slope of pull-up speed + Crucible rotation speed) (2) (Temperature change factor: Fixing to temperature preset based on experience value) Feedback amount)

Thereafter, the temperature corrections 1 to 8 are performed based on the temperature correction amount obtained according to the speed deviation rate d and the inclination of the temperature program (steps S81 to S89).
(Temperature correction step). As described above, when the speed deviation rate d is within the range of the dead zone (step S85),
Does not perform temperature compensation.

After the temperature correction, the controller 12 determines whether or not the final pull-up length has been reached (step S9). If the final pull-up length has not been reached, the area of the pull-up length is determined (step S9).
The process from 1) is repeated to grow the straight body portion while controlling the pulling speed by temperature correction in the order of the regions A, B and C. When the final pulling length has been reached, the temperature correction control of the straight body by the control unit 12 ends.

In the present embodiment, in order to stabilize the pulling speed, the temperature correction amount is changed in accordance with the growth condition (the inclination of the temperature program, etc.) which changes together with the pulling length of the semiconductor single crystal C. , The temperature correction amount can be made to correspond to different growth conditions, and the speed fluctuation can be suppressed with higher accuracy. That is, the speed variation can be further suppressed by increasing the temperature correction amount in the area A of the pull-up length where the change of the temperature program inclination or the like is large, and decreasing the temperature correction amount in the area C where the change is small. .

Further, since the cycle time is changed in accordance with the pulling length of the semiconductor single crystal C at the time of correction, the correction interval can be made to correspond to different growth conditions in accordance with the pulling length, and the speed can be adjusted with higher accuracy. Fluctuations can be suppressed. That is, the cycle time is shortened in the pull-up areas A and B where the change such as the gradient of the temperature program is large, and the cycle time is lengthened in the area C where the change is small.
Speed fluctuation can be further suppressed.

Further, since a plurality of different cycle times are set in combination at the same time, it is possible to cope with a shift of the pulling speed which varies in a variety of ways as compared with a case where the correction is performed only by one cycle time. . In addition, since the average of the pulling speed repeatedly measured at a fixed sampling time within the cycle time is used for the calculation as the actual pulling speed, variation in the pulling speed and a large local deviation occur within the cycle time. This also enables proper correction.

Next, the second method of the single crystal pulling method according to the present invention will be described.
An embodiment will be described with reference to FIG.

The difference between the second embodiment and the first embodiment is that, in the first embodiment, the pull-up length is divided into three regions A to C, and parameters according to the growth conditions are set for each of these regions. In the second embodiment, the temperature correction amount is set according to the speed deviation rate d. On the other hand, in the second embodiment, as shown in FIG. The point is that the temperature correction amount is set according to the speed deviation amount D which is the difference between the upper speed and the average pulling speed.

That is, in the second embodiment, the growth is performed while sampling the pulling speed (step S10).
1) When a predetermined cycle time has elapsed (step S102), the pulling speeds within the cycle time are averaged to obtain an average pulling speed (step S103), and the average pulling speed is calculated as the actual pulling speed. Is calculated by the following equation (3) (step S1).
04) (Speed deviation detection step). Speed deviation (D) = Average pulling speed-Set pulling speed ... (3)

Next, at least one of the growth conditions (gradient of temperature program, gradient of pulling speed, number of rotations of the crucible) for changing the temperature correction amount together with the speed deviation (D), the temperature change factor and the pulling length. Is determined by multiplying by the parameter determined according to That is, the temperature correction amount is calculated by the following equation (4) (step S105). In addition,
The parameters of the growth condition used in the equation (4) are not determined for each region as in the first embodiment, but are directly obtained from the profile of the growth condition at the time of correction. Temperature correction amount = Speed deviation amount × Temperature change factor × (Slope of temperature program + Slope of pull-up speed + Number of crucible rotations) ... (4)

Further, the temperature is corrected based on the temperature correction amount (step S106), and thereafter, the pull-up growth is performed while repeatedly performing the temperature correction until the final pull-up length is reached (step S107).

Therefore, in the first embodiment, since the parameters are uniformly set in one area,
Although the correction is performed according to the speed deviation rate d, the finer correction cannot be performed according to the growth condition that changes in the area. On the other hand, in the second embodiment, the absolute deviation can be obtained by using the speed deviation amount D. In addition to considering the amount, the parameter and the correction amount according to the growth condition are sequentially determined based on the above equation (5), and the temperature is corrected, so that more precise control becomes possible and a stable pulling speed can be obtained. Can be.

[0044]

EXAMPLE A specific example in which a single crystal of silicon was actually grown by the first embodiment will be described with reference to FIGS.

FIGS. 5 and 6 are graphs showing actual measurements of the pulling speed with respect to the pulling length when the silicon single crystal is manufactured in the first embodiment and when the silicon single crystal is manufactured by the conventional method. It is. In this embodiment, as shown in FIG. 2 (b), based on a preset temperature program, a temperature correction amount is set according to the inclination (change rate: temperature / mm) of the set temperature program at the time of correction. Is calculated by the relational expression (2).

As can be seen from FIGS. 5 and 6, in the method of the above embodiment, it is understood that the variation in the pulling speed is suppressed as compared with the conventional method. In particular, in a region where the inclination of the set pulling speed is large, the pulling speed fluctuates greatly in the related art, whereas in the method according to the embodiment, a stable pulling speed near the set pulling speed is obtained. I have. As shown in FIGS. 2A and 2C, since the pulling speed and the crucible rotation speed are also set and changed in advance according to the pulling length, the inclination (change rate) of the temperature program is changed.
As described above, the temperature correction amount may be obtained in accordance with these parameters, including the inclination of the pulling speed and the number of rotations of the crucible, as described above.

[0047]

According to the single crystal pulling method of the present invention, in the temperature correcting step, the amount of temperature correction is changed in accordance with the growth conditions which change together with the pulling length of the semiconductor single crystal. The temperature correction amount can be made to correspond to different growth conditions, and the speed fluctuation can be suppressed with higher accuracy to obtain a stable pulling speed.

[Brief description of the drawings]

FIG. 1 is an overall sectional view showing a single crystal pulling apparatus for carrying out a first embodiment of a single crystal pulling method according to the present invention.

FIG. 2 is a graph showing a program for setting a pulling speed, a temperature, and a crucible rotation speed with respect to a pulling length in the single crystal pulling method according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing a temperature correction operation in the single crystal pulling method according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing an operation of temperature correction in a single crystal pulling method according to a second embodiment of the present invention.

FIG. 5 is a graph showing a measured pulling speed with respect to a pulling length in a conventional example of a single crystal pulling method according to the present invention.

FIG. 6 is a graph showing an actually measured pulling speed with respect to a pulling length in the first embodiment of the single crystal pulling method according to the present invention.

[Explanation of symbols]

 4 Crucible 12 Control part C Semiconductor single crystal d Speed deviation rate D Speed deviation L Semiconductor melt

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA02 BA04 CF00 EG02 EH07 EH09 HA12 PF34 PF35 5F053 AA12 AA13 BB04 BB08 DD01 DD03 FF04 GG01 HH04 RR01

Claims (7)

[Claims] 1. A single crystal pulling method for pulling a semiconductor single crystal from a semiconductor melt in a crucible, wherein a speed shift detecting a ratio of an actual pulling speed to a set pulling speed as a speed shift rate. A rate detecting step, and a temperature correcting step of correcting a preset temperature of the semiconductor melt with a different temperature correcting amount according to the speed deviation rate. The temperature correcting step includes: A method for pulling a single crystal, wherein the method is changed in accordance with a growth condition that changes with the pulling length of the single crystal. 2. A single crystal pulling method for pulling a semiconductor single crystal from a semiconductor melt in a crucible, wherein a speed between a set pulling speed and an actual pulling speed is detected as a speed shift amount. A shift amount detecting step, and a temperature correcting step of correcting a preset temperature of the semiconductor melt with a different temperature correcting amount according to the speed shift amount, wherein the temperature correcting step includes: A method for pulling a single crystal, wherein the method is changed in accordance with a growth condition that changes with the pulling length of a semiconductor single crystal. 3. The single crystal pulling method according to claim 1, wherein the growth condition is at least one of the rate of change of the temperature, the rate of change of the pulling speed, and the number of rotations of the crucible. A method for pulling a single crystal. 4. The single crystal pulling method according to claim 1, wherein the temperature correcting step divides the pulling length into a plurality of regions,
A single crystal pulling method, wherein the temperature correction amount according to the growth condition is determined in advance for each of these regions. 5. The single crystal pulling method according to claim 1, wherein the temperature correction step performs the correction at every preset cycle time, and the cycle time of the semiconductor single crystal is adjusted. A single crystal pulling method characterized by changing according to a pulling length. 6. The single crystal pulling method according to claim 5, wherein in the temperature correction step, a plurality of different cycle times are set at the same time. 7. The single crystal pulling method according to claim 5, wherein an average of pulling speeds repeatedly measured at a constant sampling time within the cycle time is used as the actual pulling speed. Single crystal pulling method.