JPH09208376A - Pulling up of single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for pulling up a single crystal without any tail squeezing step by cutting off a pulled up single crystal in a dislocation-free state from a melt in a Czochralski(CZ) process. SOLUTION: A body part of 6 prescribed length is pulled up and a pulled up single crystal 9 is then cut off in a dislocation-free state from a melt 8 without carrying out the tail squeezing when pulling up and growing the single crystal 9 from the melt 8 according to a Czochralski(CZ) process. At this time, the cutting off speed of the single crystal 9 is set at >=300mm/min and the cutting off distance of the single crystal 9 from the melt 8 is set at >=20mm. The resultant pulled up crystal 9 is cut off from the melt 8.

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 while growing a single crystal such as a silicon single crystal used as a semiconductor material.

[0002]

2. Description of the Related Art The CZ method (Czochralski method) is widely known as a method for growing a single crystal such as a silicon single crystal. In this CZ method, a single crystal raw material filled in a crucible is heated and melted by a heater, and then a seed crystal hung on a pulling shaft is dipped in this melt, and the seed crystal is pulled upward while being rotated to form a seed crystal. This is a method of growing a single crystal at the lower end.

FIG. 7 is a schematic view showing a pulling process of a single crystal in the CZ method. When a single crystal 9 is grown from the melt 8 of the single crystal raw material in the crucible 3, the neck part and the shoulder part are transferred, and then the body part is pulled up (FIG. 7).
(A), (b)). After pulling up the body part of a predetermined length,
In order to grow the single crystal 9 without dislocation, a tail drawing is performed from the end of the body to gradually reduce the diameter held by the body, and pulling is performed so that dislocation does not enter the body (FIG. 7). (C) to (f)).

The top of the single crystal pulled up in this way is the region where the shoulder portion is formed, and oxygen precipitation abnormalities occur due to the unstable pulling rate at several tens of mm at the tip of the body portion, and the oxygen concentration taken in is allowable. It becomes an unnecessary portion that is cut off during wafer processing because it is out of the range and the crystal diameter is not constant unlike the body portion. Further, the tail is also a tail forming region by tail drawing and abnormal oxygen precipitation occurs due to unstable pulling conditions such as pulling speed, and the oxygen concentration taken in and the dopant concentration are out of the allowable range, and However, because the diameter of the crystal is not constant, it becomes an unnecessary portion that is cut off during wafer processing.

[0005]

When dislocations occur in the body, the dislocations penetrate the body obliquely upward from the solid-liquid interface, and the body just above the melt, which is about the diameter of the crystal, has dislocations. Will turn into. In order to prevent this, the purpose of the tail drawing is to reduce the diameter of the crystal gradually from the bottom of the body portion so as to suppress dislocation invasion into the body portion as much as possible even if dislocations occur in the middle of the crystal.

Since the diameter of a single diaphragm is made smaller than that of pulling a single crystal with a constant diameter, it is necessary to gradually increase the pulling speed or increase the heater power. . However, if one of them is made too large, the other may be made smaller so that the reduction rate of the diameter of the single crystal does not change so much. In this case, the bite of the diameter may occur due to the excessive increase of the power of the heater. In that case, the bite should be suppressed.

In the usual control of the tail diaphragm, the diameter is gradually reduced by gradually raising the pulling speed and the heater power so as to reduce the diameter, and then gradually decreasing the diameter. After that, the pulling speed and the heater power are gradually raised again to reduce the diameter. At this time, if the diameter of the diameter is too small or too small, the tail is squeezed while coping manually, and finally the diameter becomes very small and the single crystal 9 is separated from the melt 8 (FIG. ), (F)). During this period, all are in a dislocation-free state, or even if dislocation occurs in the latter half of the tail, no dislocation penetrates into the body portion. FIG. 8 shows an X-ray topographic photograph showing the tail in the dislocation-free state. Further, FIG. 9 shows an X-ray topographic photograph showing a tail in a dislocation state.

By the way, the tail diaphragm in the latter half of pulling up is
The larger the diameter of the single crystal 9 to be pulled, the longer the processing time is required. Further, the tail squeezing is difficult to control, and often the temperature rise of the melt 8 is too large or the pulling speed is too high, so that the single crystal 9 is separated from the melt 8 without being sufficiently thin. It becomes dislocation. On the contrary, if the temperature of the melt 8 is too low, the crystallization on the surface of the melt 8 may start and the pulling of the single crystal 9 may not be continued. Further, in the tail drawing step, since the diameter variation of the single crystal 9 is remarkable, dislocation easily occurs. In the tail drawing step, the pulling speed, the power of the heater, the rotation of the crucible 3 and the like change intricately, so that the heat history during pulling is not constant and the uniformity of crystal defects in the pulling single crystal is deteriorated.

As described above, tail drawing is a necessary treatment for pulling up the body of the single crystal 9 without dislocations.
The control is difficult and the processing time is long. In particular, in the case of a large-diameter single crystal 9 having a diameter of 8 inches or more, when dislocations occur in the tail drawing, a very large amount of single crystals become dislocations, and a large-diameter tail drawing requires a very long time. As a result, the ratio to the time required for production is large. Further, the cost of the region of the body portion which has become dislocated and becomes unusable due to the dislocation in the first half of the tail and the raw material consumed for the tail to be cut off during wafer processing are also very high.

The present invention has been made in view of the above circumstances, and a single crystal pulled up in the CZ method is separated from a melt in a dislocation-free state, thereby eliminating a tail drawing step. The purpose is to provide a method.

Another object of the present invention is to provide a method for pulling a single crystal which eliminates wasteful consumption of raw materials and can reduce the cost as compared with the conventional example because a tail drawing step is unnecessary. It is in.

Still another object of the present invention is to provide a single crystal pulling method which can shorten the pulling time as compared with the conventional example because a tail drawing step is unnecessary.

[0013]

A method for pulling a single crystal according to claim 1 is a method for pulling a single crystal while growing a single crystal from a melt in which a single crystal raw material is melted. It is characterized by separating in a dislocation-free state.

According to a second aspect of the present invention, in the single crystal pulling method according to the first aspect, the separating speed of the single crystal is set to 300 mm / min or more, and the separating distance of the single crystal from the melt is set to 20 mm or more. It is characterized by

According to the present invention, when a single crystal such as single crystal silicon is pulled by the CZ method while growing, a body portion having a predetermined length is pulled and then the pulled single crystal is melted in a dislocation-free state. Do not squeeze the tail. Specifically, the pulling-off single crystal is separated from the melt at a speed of 300 mm / min or more, and the single crystal is separated from the melt at a distance of 20 mm or more.

When the single crystal is pulled up in a dislocation-free state at the time of pulling up the single crystal, the single crystal is cut off from the melt at a rapid cutting speed so that dislocations do not occur on the bottom side of the crystal. Therefore, the bottom side of the body portion is in a dislocation-free state, and the single crystal can be separated from the melt in a dislocation-free state without tail drawing.

Next, the conditions for disconnection will be described. Single crystal separation speed at the time of separation is 300 mm /
It should be more than a minute. This is because if the cutting speed is less than 300 mm / min, the cutting in the dislocation-free state cannot be performed. Immediately after the separation, the bottom side of the single crystal is separated from the melt by 20 mm or more from the melt. This is because a protruding tail is formed near the center on the bottom side of the separated single crystal when it is rapidly separated from the melt, and if it does not separate from the melt, dislocation occurs from that site. . Furthermore, when the single crystal separates from the melt due to abrupt detachment, if a splash from the melt attaches to the bottom of the detached single crystal, dislocations enter from that site and dislocation occurs. Therefore, in order to prevent splashes from the melt from returning to the single crystal, the separation speed should be increased (300 mm
/ Min) or more, and it is necessary to take a large separation distance (20 mm or more) immediately after the separation of the single crystal from the melt.

Next, the experimental data that supports the numerical limitation of the separation speed and the separation distance will be described. Figure 10 shows the pulling rate of single crystal at 1.2 mm / min.
3 is a graph showing the success rate of pulling in a dislocation-free state when the separation speed is 200 mm / min and the separation distance is 25 mm in each of the three cases of 0 mm / min and 0.8 mm / min. The pulling speed is 1.2 mm / min,
At 1.0 mm / min and 0.8 mm / min, the success rates are 40%, 60% and 80% respectively, and the cutting speed is 200%.
Satisfactory results have not been obtained at mm / min. On the other hand, in Fig. 11, the pulling rate of the single crystal is 1.2 mm / min.
6 is a graph showing the success rate of pulling in a dislocation-free state when the separation speed is 600 mm / min and the separation distance is 25 mm in each of the three cases of 0 mm / min and 0.8 mm / min. The success rate is 100% at any pulling speed, and the detaching speed is 600 mm.
/ Min, the pulling in the dislocation-free state was completely successful.

FIG. 12 shows that the pulling rate of the single crystal is 1.2 mm.
/ Min, 1.0 mm / min, 0.8 mm / min, each of the three types of graphs showing the success rate of pulling in the dislocation-free state when the cutting speed was 600 mm / min and the cutting distance was 10 mm Is. Lifting speed is 1.2 m
At m / min, 1.0 mm / min, and 0.8 mm / min, the success rates were 20%, 40%, and 60%, respectively, and sufficient results were obtained when the separation distance was 10 mm. Absent.
On the other hand, pulling speed of single crystal is 1.2 mm / min, 1.0 mm
/ Min and 0.8 mm / min for each of the three types, the separation speed is 600 mm / min and the separation distance is 25
The success rate of pulling in the dislocation-free state when mm is
The result is shown in the graph of FIG. 11 described above. The success rate was 100% at any pulling rate, and when the separation distance was 25 mm, the pulling in the dislocation-free state was completely successful.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

FIG. 1 is a schematic vertical sectional view of a single crystal pulling apparatus, in which 1 indicates a main chamber. The main chamber 1 is a cylindrical vacuum container, and a crucible 3 is arranged at the center of the main chamber 1. The crucible 3 comprises a bottomed cylindrical quartz inner layer holding container 3a and a bottomed cylindrical graphite outer layer holding container 3b fitted to the outside of the inner layer holding container 3a.

In this example, the diameter is 18 inches and the height is
A 12-inch inner layer holding container 3a is used. A shaft 10 for rotating and moving the crucible 3 up and down is provided at the bottom of the outer layer holding container 3b of the crucible 3, and the outer periphery of the crucible 3 has, for example, 30
A heater 4 having a heat generation length of about 0 mm is arranged in a concentric cylindrical shape. A heat insulating cylinder 5 is provided around the heater 4.

On the other hand, above the crucible 3 is the main chamber 1
A pulling shaft 11 is vertically rotatably and vertically movable through a small cylindrical pull chamber 2 continuously formed on the upper part of the seed crystal 6, and a seed crystal 6 can be attached to and detached from a seed chuck 7 at a lower end of the pulling shaft 11. It is installed. Then, after the lower end of the seed crystal 6 is immersed in the melt 8, the single crystal 9 is grown from the lower end of the seed crystal 6 by raising the seed crystal 6 and the crucible 3 while rotating them. ing.

When the single crystal 9 is grown by using the single crystal pulling apparatus thus configured, the crucible 3 is filled with 45 kg of silicon polycrystal as a raw material for crystal, and the electrical resistivity of the single crystal 9 is increased. Is added to the p-type dopant such that boron is about 10 Ωcm. Then, after making the inside of the main chamber 1 and the pull chamber 2 an Ar atmosphere of 10 Torr, the power of the heater 4 is set to about 65 kW to melt all the crystal raw materials.

Next, the power of the heater 4 is set to about 50 kW and the position of the heater 4 is adjusted. After that, the lower end of the seed crystal 6 is immersed in the solution 8, and the single crystal 9 is pulled while rotating the crucible 3 and the pulling shaft 11 at a ratio of rotation of the crucible 3 / rotation of the pulling shaft 11 = 12 rpm / 20 rpm. The pulling of the single crystal 9 moves to the neck portion and the shoulder portion, and after moving to the body portion, the power of the heater 4 and the pulling speed are adjusted,
The single crystal 9 having a predetermined crystal length is pulled at a constant pulling rate while adjusting the power of the heater 4 so that the diameter of the pulled crystal is maintained at 154 mm.

When the body reaches a predetermined length, the pulling speed of the pulling shaft 11 is set to 600 mm / min, the single crystal 9 is separated from the melt 8 by 25 mm, and then the separated single crystal is cut. The crystal 9 is raised and taken out of the pull chamber 2.

As the constant pulling speed, specifically, 1.
0 mm / min, 0.7 mm / min, 0.4 mm / min, 0.35 mm /
The above-mentioned pull-up growth was carried out for five cases of min. And 0.3 mm / min. 2 to 6 show the bottom side portion of the single crystal 9 obtained in each of the five cases.
It is an X-ray topographic photograph after heat-processing at 00 degreeC for 16 hours. The temperature in the photograph is the temperature of each part of the single crystal 9 when it was connected to the melt 8 immediately before separation. It can be confirmed that all the single crystals 9 were successfully separated from the melt 8 in the dislocation-free state.

[0028]

As described above, according to the present invention, in the pulling growth of a single crystal such as a silicon single crystal, the bottom side of the pulled single crystal is separated from the melt while keeping a dislocation-free state. In addition, pulling growth of a dislocation-free single crystal is possible.

According to the present invention, since the tail diaphragm is not necessary,
Can solve various problems associated with tail diaphragm. The tail drawing tends to cause dislocation from various viewpoints, but in the present invention, the body portion can be easily separated from the melt without dislocation. Further, in the present invention, the raw material cost can be reduced by the amount that the tail does not have to be formed. Further, the larger the diameter of the single crystal, the longer the processing time required for the tail drawing step, but if the separation of the present invention is performed, this tail drawing step can be omitted and the pulling time can be shortened.

Further, it is not necessary to control and manage the pulling condition related to the tail drawing step, and the program can be easily automated by forming a program in accordance with the separating procedure. Further, unlike a conical tail, the bottom side of the separated crystal is columnar and the bottom is flat, so that it is stable when the crystal is set up. Furthermore, when several short crystals are continuously pulled up, the dislocation-free separation technique of the present invention can shorten the pulling time and save the weight of the raw material, and eliminate the fear of the tail having dislocations. Is effective for.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a single crystal pulling apparatus.

FIG. 2 is an X-ray topographic photograph showing a dislocation-free state on the bottom side of a single crystal pulled by the method of the present invention (pulling rate: 1.0 mm / min).

FIG. 3 is an X-ray topographic photograph showing a dislocation-free state on the bottom side of a single crystal pulled by the method of the present invention (pulling rate: 0.7 mm / min).

FIG. 4 is an X-ray topographic photograph showing a dislocation-free state on the bottom side of a single crystal pulled by the method of the present invention (pulling rate: 0.4 mm / min).

FIG. 5 is an X-ray topographic photograph showing a dislocation-free state on the bottom side of a single crystal pulled by the method of the present invention (pulling rate: 0.35 mm / min).

FIG. 6 is an X-ray topographic photograph showing a dislocation-free state on the bottom side of a single crystal pulled by the method of the present invention (pulling rate: 0.3 mm / min).

FIG. 7 is a schematic diagram showing a single crystal pulling process in the CZ method.

FIG. 8 is an X-ray topographic photograph showing a tail of a single crystal in a dislocation-free state.

FIG. 9 is an X-ray topographic photograph showing a tail of a single crystal in a dislocation state.

FIG. 10 is a graph showing a success rate of pulling a single crystal in a dislocation-free state (separation speed: 200 mm / min, separation distance: 25 mm).

FIG. 11 is a graph showing a success rate of pulling a single crystal in a dislocation-free state (separation speed of 600 mm / min, separation distance of 25 mm).

FIG. 12 is a graph showing a success rate of pulling a single crystal in a dislocation-free state (separation speed of 600 mm / min, separation distance of 10 mm).

[Explanation of Codes] 1 Main chamber 2 Pull chamber 3 Crucible 4 Heater 5 Heat-insulating cylinder 6 Seed crystal 7 Seed chuck 8 Melt liquid 9 Single crystal 10 Axis 11 Pulling axis

Claims (2)

[Claims] 1. A method of pulling a single crystal while growing a single crystal from a melt obtained by melting a single crystal raw material, wherein the single crystal being pulled is separated from the melt in a dislocation-free state. 2. When separating, the separation speed of the single crystal is controlled.
The method for pulling a single crystal according to claim 1, wherein the separation distance from the melt of the single crystal is set to 300 mm / min or more and the separation distance from the melt is set to 20 mm or more.