JP2990661B2 - Single crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for growing a single crystal, and more particularly to a method for growing a semiconductor single crystal such as silicon.

[0002]

2. Description of the Related Art There are various methods for manufacturing a silicon single crystal used for a semiconductor substrate, and a CZ method (Czochralski method), which is a rotational pulling method, is widely used. FIG. 8 is a schematic cross-sectional view showing an embodiment of the CZ method, in which 1 indicates a crucible. The crucible 1 includes a bottomed cylindrical inner layer holding container 1a made of quartz and a bottomed cylindrical outer layer holding container 1b made of graphite fitted to hold the outside of the inner layer holding container 1a. , And is fixed to the upper end of a support shaft 4 that can rotate and move up and down. A resistance heating type heater 2 is arranged concentrically outside the crucible 1, and the crucible 1 is filled with a melt 9 obtained by melting a predetermined weight of a raw material by the heater 2. On the central axis of the crucible 1, a pulling shaft 3 made of a pulling rod or a wire, which is rotated at a predetermined speed in the opposite direction or the same direction with the same axis as the supporting shaft 4, is provided. The seed crystal 10 is suspended via the holder 3a.

According to the CZ method, a crystal raw material is charged into a crucible 1 and melted by a heater 2 disposed around the crucible 1 under a reduced pressure in an inert gas atmosphere.
Seed crystal 1 suspended on lifting shaft 3 in melt 9
0, while rotating the crucible 1 and the lifting shaft 3,
The pulling shaft 3 is pulled upward to grow the crystal 8 at the lower end of the seed crystal 10.

In the crystal growth step, generally, a method of controlling the crystal diameter by measuring the reflected light of the meniscus portion at the solid-liquid interface by an optical sensor is mainly employed. From the obtained crystal diameter position, the crucible lifting speed is controlled so that the melt surface position becomes constant.

When the semiconductor single crystal grown by the CZ method is cut off from the melt 9, the dislocation of the semiconductor single crystal due to the heat shock and the propagation to the crystal body 8 a serving as a product part are prevented. A method of gradually reducing the diameter to form an inverted conical crystal tail portion 8b and separating the melt from the molten liquid 9 when the diameter becomes sufficiently small so that even if dislocations are generated and dislocations do not propagate to the product portion, the crystal tails 8b are formed. Has been adopted.

[0006]

The wafer diameter (crystal diameter) used in the semiconductor device manufacturing process has been increasing year by year in order to make the device production more efficient and lower cost.
At present, those having a crystal diameter of 150 to 200 mm are mainly used. In the future, large-diameter crystals of 300 mm are considered to be the mainstream. In such a large-diameter crystal, when the crystal diameter is reduced, the meniscus is reduced to the straight body portion 8a.
It is difficult to measure the crystal diameter because it is hidden behind. Therefore, when forming the tail portion 8b, a pulling speed, a crucible raising speed, and a heater temperature are empirically determined, and a means for forming the tail portion 8b without measuring and controlling the crystal diameter is employed.

However, in such a conventional method, the single crystal growth rate does not coincide with the pulling rate because the crucible rising speed does not become a speed for keeping the melt surface position constant. Change. Such a change in the growth rate of the single crystal causes a change in the shape of the solid-liquid interface and the crystal diameter, which causes a problem of causing dislocation. Furthermore, since the surface position of the melt changes, the state of receiving heat from the heater also changes, so that there is a problem that dislocations easily occur.

In particular, the apparatus and method for lifting a high-purity semiconductor rod from a molten material disclosed in Japanese Patent Publication No. 57-40119 uses a cover device serving as a heat shield, and the surface position of the melt is limited. If it changes, the distance between the lower end of the heat shield and the melt surface changes. When the surface position of the melt rises, it comes into contact with the heat shield and cannot be lifted. Also,
When the melt surface position lowers, the heat shielding effect decreases,
There is a problem that dislocations are likely to occur.

In the case of large-diameter crystals, since the crystal diameter is large, even when the tail has dislocations, the dislocation propagates to the product part, and the yield (= product part weight / raw material weight) is greatly reduced. there were.

The present invention has been made in view of the above problems, and eliminates fluctuations in the growth rate of a single crystal, and furthermore, reduces fluctuations in the solid-liquid interface shape and crystal diameter by keeping the melt surface position constant. It is another object of the present invention to provide a single crystal growth method capable of preventing dislocation of the tail portion.

[0011]

In order to achieve the above object, a single crystal growth method (1) according to the present invention comprises:
In a single crystal growth method in which a semiconductor crystal raw material filled in a crucible is melted and a single crystal is pulled from the melt and grown, in order to separate the crystal from the melt, a crystal diameter is gradually reduced to form a tail. In this case, the crucible raising speed and the pulling speed are set so that the single crystal growth speed is constant.

According to the above single crystal growth method (1),
Since the single crystal growth rate becomes constant during the formation of the tail, fluctuations in the solid-liquid interface shape and crystal diameter can be reduced, and dislocation of the tail can be prevented.

The method for growing a single crystal according to the present invention (2)
In a single crystal growth method in which a semiconductor crystal raw material filled in a crucible is melted and a single crystal is pulled up from the melt and grown, in order to separate the crystal from the melt, the crystal diameter is gradually reduced and the tail is reduced. When forming, while the single crystal growth rate is constant, so that the melt surface position is constant,
It is characterized in that the crucible lifting speed and the lifting speed are set.

According to the above single crystal growth method (2),
During the formation of the tail, while the single crystal growth rate is constant,
Since the surface position of the melt is constant, the change in the state of the heat received from the heater is eliminated, the variation in the solid-liquid interface shape and the crystal diameter is reduced, the dislocation of the tail is further prevented, and the product yield is reduced. Can be improved.

Further, the method for growing a single crystal according to the present invention (3)
In the above single crystal growth method (1) or (2),
The crucible lifting speed and the pulling speed are set so that the length of the tail is a cone of 0.7 to 1.2 times the crystal diameter.

According to the above single crystal growth method (3),
Even if the set length differs from the actual length, a large difference in single crystal growth rate can be prevented. On the other hand, when the ratio is more than 1.2 times, the formation time of the tail becomes longer and the productivity is reduced. When the ratio is less than 0.7 times, it is difficult to actually form the tail.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A single crystal growing method according to the present invention comprises:
The length of the tail is 0.7 to 1.2 times the diameter of the crystal as a cone,
The crucible raising speed and the pulling speed are set so that the single crystal growth speed is constant. Further, the crucible lifting speed and the pulling speed are set so that the melt surface position is constant.

Hereinafter, the relationship between the single crystal growth rate, the pulling rate, and the crucible raising rate will be described in detail.

First, the crystal straight body analysis model shown in FIG. 1 will be described. However, for simplicity, it is assumed that the densities of the melt and the crystal are equal.

[0020] t time, crystal pulling length X _s, pulling rate melt surface position from a V _s changes by X _m.

At this time, equations (1) to (3) hold.

[0022]

X _s = V _s · t

[0023]

[Number 2] _{^{S = πr 2 (X s -X}} m)

[0024]

X _m = V _c · t-S / πR ² Equations 1 to 3 are rearranged into Equation 4.

[0025]

X _m = (R ² V _c −r ² V _s ) · t / (R ² −r ² ) Accordingly, the single crystal growth rate V _g is represented by the following equation (5).

[0026]

In Equation 5] _{V g = V s -dX m /} dt = (V s -V c) R 2 / (R 2 -r 2) Eq. 4, the melt surface position when X _m = 0 is a constant since the case of the crucible lifting speed V _c ^* at this time it becomes equation (6), and this time V _g = V _s.

[0027]

V _c ^* = V _s r ² / R ^{2 In} general, in the straight body portion, the rising speed of the crucible is controlled using Equation 6 so that the melt surface position is constant. In this case, the pulling speed matches the single crystal growth speed.

Next, the crystal tail analysis model shown in FIG. 2 will be described.

The minute volume dS raised during the minute time dt is expressed by the following equation (7).

[0030]

DS = πr ² (1-h / H) ² dh Therefore, the volume that can be raised during the time t is given by the following equation (8).

[0031]

(Equation 8)

[0032] For simplicity, the dh taking sufficiently small, the number 9 expression is approximated with ^{S = πr 2 (1-h} / H) 2 (X s -X m).

[0033]

(Equation 9)

Therefore, the single crystal growth rate V _g is given by the following equation (10).

[0035]

V _g = R ² (V _s −V _c ) / ｛R ² −r ²
(1-h / H) ² } Hereinafter, an embodiment of a single crystal growth method according to the present invention will be described with reference to the drawings.

FIG. 3 is a schematic sectional view of a crystal growth apparatus for performing the single crystal growth method according to the present invention. In the figure, reference numeral 1 denotes a crucible, and the crucible 1 is a bottomed cylindrical inner holding container 1a made of quartz and a bottomed cylindrical graphite made of graphite fitted to hold the outside of the inner holding container 1a. It is composed of an outer layer holding container 1b, and is fixed to the upper end of a support shaft 4 that can rotate and move up and down. A resistance heating type heater 2 is arranged concentrically outside the crucible 1, a heat insulation cylinder 6 a is arranged concentrically outside the heater 2, and a heat insulation plate 6 b is arranged at the bottom. .

In crucible 1, a predetermined weight of raw material is supplied to heater 2.
Is filled with the melt 9 melted by the method. On the central axis of the crucible 1, a pulling shaft 3 made of a pulling rod or a wire, which is rotated at a predetermined speed in the opposite direction or the same direction with the same axis as the supporting shaft 4, is provided. The seed crystal 10 is suspended via the holder 3a. By pulling up the pulling shaft 3, the crystal 8 is grown from the lower end of the seed crystal 10.
The crystal 8 has a crystal straight body 8a and a crystal tail 8b.
The hollow cylindrical chamber 5 is composed of a cylindrical main chamber 5a and a cylindrical pull chamber 5b connected and fixed to the main chamber 5a. 7 in the figure is C
Shows a CD camera.

Next, a single crystal growing method according to the embodiment (1) will be described.

In the state where the crucible is not lifted when the tail portion 8b is formed, the pulling speed is set so that the single crystal growth speed becomes constant. Since this is a case where the single crystal growth speed V _g is constant and the crucible raising speed V _c = 0 in the equation (10),
The pulling speed V _s ^* is expressed by Equation 11.

[0040]

V _s ^* = [{R ² −r ² (1-h / H) ² }
/ R ² ] V _g According to the single crystal growth method according to the above-mentioned embodiment (1),
Since the single crystal growth rate is constant and the rise of the crucible 1 is stopped, fluctuations in the solid-liquid interface shape and crystal diameter can be reduced, and dislocation of the tail 8b can be prevented.

Next, a single crystal growing method according to the embodiment (2) will be described.

The crucible lifting speed and the pulling speed are set so that the single crystal growth speed and the melt surface position are constant when the tail portion 8b is formed. This in equation (9), since it is the case of the melt surface moving amount X _m = 0, the crucible lifting speed V _c is represented by the equation (12). At this time, the pulling rate V _s = single crystal growth rate V _g.

[0043]

According to the single crystal growth method according to the number 12 ^{_{V c = (r 2 / R}} 2) (1-h / H) 2 V s above embodiment (2),
Since the single crystal rising speed and the melt surface position are constant, fluctuations in the solid-liquid interface shape and crystal diameter can be reduced, and dislocation in the tail 8b can be further prevented.

Next, in the single crystal growth method according to the embodiment (3), the length of the tail portion 8b is set to be a cone of 0.7 to 1.2 times the crystal diameter.

According to the method for growing a single crystal according to the above embodiment (3), even if the set length differs from the actual length, it is possible to prevent a large difference in single crystal growth rate from occurring. On the other hand, when the ratio exceeds 1.2 times, the formation time of the tail portion 8b becomes longer and the productivity decreases. When the ratio is less than 0.7 times, it is difficult to actually form the tail portion 8b.

[0046]

EXAMPLES Examples of the single crystal growth method will be described below.

Pulled crystal: silicon single crystal having a diameter of 300 mm Raw material charge amount: 150 kg of high-purity polycrystalline silicon Melting method: resistance heating furnace atmosphere: 10 Torr Ar (argon) 50 liter / min Size of quartz crucible: diameter 650 mm, high 400 mm Heater size: 700 mm inside diameter, 740 mm outside diameter Height: 500 mm Size of heat retaining cylinder: 800 mm inside diameter, 950 mm outside diameter Dimensions of main chamber 5 a: 1000 mm diameter, 1200 mm height Number of rotations of lifting shaft 3: 10 rpm Rotation of crucible 1 Number: 8 rpm Length of crystal straight body portion 8a: 650 mm This is carried out as described above. When the tail portion 8b is formed, the single crystal growth speed is constant, and when the single crystal growth speed and the melt surface position are constant. The lifting speed and the crucible lifting speed .

When the single crystal rising speed is constant (Example 1), the length H of the crystal tail 8b is 280 mm, the rising speed V _{c of the} crucible 1 is 0 mm / min, and the single crystal growing speed V _{g is} 0.41 mm / min pulling speed V _s : Equation (11) is used. FIG. 4 shows changes in single crystal growth speed, pulling speed, tail 8b length, and melt surface position in the case of performing in this manner.
Shown in

As is apparent from this figure, a crystal 8 having a smooth tail 8b with little variation in crystal diameter was obtained without dislocations throughout.

When the growth rate of the single crystal and the position of the melt surface are constant (Example 2), the length H of the crystal tail 8b: 280 mm The rising speed V _{c of the} crucible 1: Equation 12 is used. V _g : 0.4 mm / min Pulling speed V _s : 0.4 mm / min Changes in single crystal growth speed, pulling speed, crucible raising speed, length of tail portion 8 b and melt surface position in this case Is shown in FIG.

As is apparent from this figure, a crystal 8 having a smooth tail portion 8b with little variation in crystal diameter was obtained without dislocation throughout.

FIG. 6 shows changes in the single crystal growth rate, the pulling rate, the length of the tail 8b, and the melt surface position when the pulling rate is kept constant with the crucible being stopped during the formation of the tail 8b. (Conventional method 1).

FIG. 7 shows the single crystal growth speed, the pulling speed, the crucible lifting speed, and the length of the tail portion 8b when the crucible rising speed is set to be constant at the initial stage of the formation of the tail portion 8b and is set to be reduced at a constant rate from the middle. 2 shows changes in the melt position and the melt surface position (conventional method 2).

Table 1 compares the product yield (= product part weight / raw material weight) between the conventional method and the embodiment of the present invention. In the conventional method, the dislocation propagation in the tail part is large even in the dislocation at the tail due to the large diameter, and the yield is greatly reduced, but in the embodiment, the dislocation is prevented and the product yield is significantly reduced. Could be improved.

[0055]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a model diagram for explaining the relationship among a pulling speed, a crucible lifting speed, and a single crystal growth speed in a crystal straight body.

FIG. 2 is a model diagram for explaining a relationship among a pulling speed, a crucible lifting speed, and a single crystal growth speed at a crystal tail.

FIG. 3 is a schematic sectional view of a crystal growth apparatus for performing a single crystal growth method according to the present invention.

FIG. 4 is a diagram showing changes in a single crystal rising speed, a pulling speed, a tail length, and a melt surface position when a single crystal growth speed is set to be constant when a crystal tail is formed.

FIG. 5 shows changes in single crystal growth speed, pulling speed, tail length, and melt surface position when the single crystal growth speed and the melt surface position are set to be constant during the formation of the crystal tail. FIG.

FIG. 6 shows changes in the single crystal growth rate, the pulling rate, the length of the tail, and the melt surface position in the case of the conventional method 1 in which the pulling rate was kept constant while the crucible was not lifted when forming the crystal tail. FIG.

FIG. 7 shows a single crystal growth speed, a pulling speed, a tail length, and a melt surface in the case of the conventional method 2 in which the crucible ascending speed is set to be constant at the initial stage of the formation of the crystal tail, and is set to be reduced at a constant rate from the middle. It is a figure showing change of a position.

FIG. 8 is a schematic sectional view showing an embodiment of a conventional CZ method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 1a Quartz inner layer holding container 1b Graphite outer layer holding container 2 Resistance heating type heater 3 Pull-up shaft 3a Holder 4 Support shaft 5 Chamber 5a Main chamber 5b Pull chamber 6a Heat insulating cylinder 6b Heat insulating plate 7 CCD camera 8 Single crystal 8a Crystal body 8b Crystal tail 9 Melt 10 Seed crystal

Claims (3)

(57) [Claims] In a single crystal growth method for melting a semiconductor crystal raw material filled in a crucible and pulling a single crystal from the melt to grow the crystal, the crystal diameter is gradually reduced to separate the crystal from the melt. A method for growing a single crystal, comprising: setting a crucible lifting speed and a pulling speed such that a growth rate of a single crystal is constant when forming a tail portion. 2. A single crystal growth method for melting a semiconductor crystal raw material filled in a crucible and pulling a single crystal from the melt to grow the crystal, wherein the crystal diameter is gradually reduced to separate the crystal from the melt. A method for growing a single crystal, comprising: setting a crucible lifting speed and a pulling speed such that a single crystal growth speed is constant and a melt surface position is constant when forming a tail portion. 3. The length of the tail part is 0.7-1.
3. The method of growing a single crystal according to claim 1, wherein the crucible raising speed and the pulling speed are set so as to obtain a double cone.